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Research Notes: Creatine and MyopathyNote: This page contains abstracts and other materials primarily having to do with the use of creatine for the treatment of myopathy (muscle problems). Please see here for abstracts regarding creatine synthesis and transport disorders (which primarily affect the brain) and the use of creatine for those disorders. From Treatment of Mitochondrial Cytopathies (Medscape Pediatrics) Creatine is an amino acid produced endogenously in the liver from arginine and glycine, and it is also found in meat products. Creatine phosphate is synthesized from creatine and ATP, and it is catalyzed by creatine kinase (CK). Unlike ATP, which the body is unable to store, creatine phosphate can be stored to a limited degree in tissues, allowing for a supply of the high-energy phosphate bond, which can be utilized when needed. The hydration of phosphocreatine to creatine and ATP thereby allows the ATP to be utilized by the tissue. Creatine is found in highest concentrations in skeletal muscle and to lesser degrees in cardiac muscle, smooth muscle, brain, sperm, and kidney. Intramuscular phosphocreatine may be reduced in patients with mitochondrial cytopathies. Supplemental creatine seems to be most effective at increasing phosphocreatine and creatine in this setting. Harris et al demonstrated that administration of creatine to healthy subjects resulted in a greater effect for those patients whose initial total creatine concentration was low. There were no side effects from supplementation with doses ranging from 70 g to 330 g with maximum treatment time of 21 days.[48] The rationale for using creatine is to increase the tissue concentrations and possibly increase the ability of muscle (or other organs) to accumulate creatine phosphate. Tarnopolsky et al have shown that creatine monohydrate (at doses of 5 g twice per day for 2 weeks followed by 2 g twice per day for 1 week) improved strength for high-intensity anaerobic and aerobic activities and lean muscle mass in patients with neuromuscular diseases, including those with mitochondrial myopathy. Both trials were based on short-term results, and the long-term beneficial effects of creatine remain to be proven. Regardless, the use of creatine in critical situations seems to be reasonable.[49,50] In one study of nine healthy men provided with either oral creatine (as creatine monohydrate, 20 g dose) or placebo demonstrated no effect on performance for maximum exercise or on phosphocreatine levels. However, the supplement was only administered over a 3-day period and was in a setting of likely normal muscle creatine levels; therefore, its relevancy to those with mitochondrial disease is not known.[51] Br J Sports Med. 2007 Aug 23. Purpose: To study the effects of 8 wk creatine monohydrate (CrM) supplementation on blood and urinary clinical health markers in soccer players. METHODS: 14 soccer players were randomly assigned in a double-blinded fashion to Cre (N = 7) or Pla (N = 7) group. Cre group ingested 15 g/d of CrM during 7 d, and 3 g/d for the remaining 49 d, whereas the Pla group ingested maltodextrin following the same protocol. Soccer-specific training was performed during the study. Total body mass was determined and blood and urine samples were analized for metabolic, hepatic, renal and muscular function markers, before and after supplementation. RESULTS: A gain of total body mass was observed after CrM intake, not with placebo. Blood and urinary markers remained within normal reference values. There were no significant changes in renal and hepatic markers after CrM intake. However, total CK activity significantly increased, and uric acid level tended to decrease after CrM use. Likewise, serum glucose decreased in the Cre group following supplementation. No significant differences in urine parameters were found in either group after supplementation. CONCLUSIONS: 8 wk of CrM supplementation had no negative effect on blood and urinary clinical health markers in soccer players. Properties of CrM may, however, be associated with an increase in CK activity, improving the efficiency for ATP resynthesis, phenomenon indirectly confirmed by the decreasing tendency in uric acid concentration. Furthermore, CrM seems to slightly influence glucoregulation in trained subjects. Am J Physiol Cell Physiol. 2007 Jul 25. In myogenic C2C12 cells, 5mM creatine increased the incorporation of labelled [(35)S] methionine into sarcoplasmic (+20%, P<0.05) and myofibrillar (+50%, P<0.01) proteins. Creatine also promoted the fusion of myoblasts assessed by an increased number of nuclei incorporated within myotubes (+40%, P<0.001). Expression of myosin heavy chain type II (MHC II, +1300%, P<0.001), troponin T (+65%, P<0.01) and titin (+40%, P<0.05) was enhanced by creatine. Neither mannitol, taurine, nor beta-alanine mimicked the effect of creatine, ruling out an osmolarity-dependent mechanism. The addition of rapamycin, the inhibitor of mammalian target of rapamycin/70kDa ribosomal S6 protein kinase (mTOR/p70(s6k)) pathway, and SB202190, the inhibitor of p38, completely blocked differentiation in control cells, and creatine did not reverse this inhibition, suggesting that the mTOR/p70(s6k) and the p38 pathways could be potentially involved in the effect induced by creatine on the differentiation. Creatine upregulated phosphorylation of protein kinase B (Akt/PKB, +60%, P<0.001), glycogen synthase kinase-3 (GSK-3, +70%, P<0.001) and p70(s6k) (+50%, P<0.001). Creatine also affected the phosphorylation state of p38 (-50% at 24h and +70% at 96h, P<0.05) as well as the nuclear content of its downstream targets myocyte enhancer factor-2 (MEF-2, -55% at 48h and +170% at 96h, P<0.05) and MyoD (+60%, P<0.01). In conclusion, this study points out the involvement of the p38 and the Akt/PKB-p70(s6k) pathways in the enhanced differentiation induced by creatine in C2C12 cells. Med Sci Sports Exerc. 2007 May. INTRODUCTION: Creatine kinase, found in osteoblasts, is an enzyme that is upregulated in response to interventions that enhance bone mass accretion. Creatine monohydrate supplementation can increase fat-free mass in young healthy men and women and can reduce markers of bone breakdown in boys with Duchenne muscular dystrophy. PURPOSE: The objective of this study was to determine the influence of supplementation with creatine monohydrate on bone structure and function in growing rats, to establish a therapeutic model. MATERIALS AND METHODS: Creatine monohydrate (2% w.w.) (CR; N = 16) or standard rat chow (CON; N = 16) was fed to Sprague-Dawley rats beginning at 5 wk of age, for 8 wk. Bone mineral density (BMD) and content (BMC) were assessed using dual-energy x-ray absorptiometry at the beginning and end of the protocol. The rats were sacrificed, and one femur was removed for the determination of mechanical properties. RESULTS: The CR-treated rats showed greater lumbar BMD and femoral bending load at failure compared with the CON rats (P < 0.05). CONCLUSIONS: Together, these data suggest that creatine monohydrate potentially has a beneficial influence on bone function and structure; further investigation is warranted into its effect on bone functional properties and its effects in disorders associated with bone loss. Annu Rev Nutr. 2007 Apr 12. Creatine and phosphocreatine serve not only as an intracellular buffer for adenosine triphosphate, but also as an energy shuttle for the movement of high-energy phosphates from mitochondrial sites of production to cytoplasmic sites of utilization. The spontaneous loss of creatine and of phosphocreatine to creatinine requires that creatine be continuously replaced; this occurs by a combination of diet and endogenous synthesis. Vegetarians obtain almost no dietary creatine. Creatine synthesis makes major demands on the metabolism of glycine, arginine, and methionine. Large doses of creatine monohydrate are widely taken, particularly by athletes, as an ergogenic supplement; creatine supplements are also taken by patients suffering from gyrate atrophy, muscular dystrophy, and neurodegenerative diseases. Children with inborn errors of creatine synthesis or transport present with severe neurological symptoms and a profound depletion of brain creatine. It is evident that creatine plays a critical, though underappreciated, role in brain function. Neurobiol Aging. 2007 Apr 6. The supplementation of creatine (Cr) has a marked neuroprotective effect in mouse models of neurodegenerative diseases. This has been assigned to the known bioenergetic, anti-apoptotic, anti-excitotoxic, and anti-oxidant properties of Cr. As aging and neurodegeneration share pathophysiological pathways, we investigated the effect of oral Cr supplementation on aging in 162 aged C57Bl/6J mice. Outcome variables included "healthy" life span, neurobehavioral phenotyping, as well as morphology, biochemistry, and expression profiling from brain. The median healthy life span of Cr-fed mice was 9% higher than in control mice, and they performed significantly better in neurobehavioral tests. In brains of Cr-treated mice, there was a trend towards a reduction of reactive oxygen species and significantly lower accumulation of the "aging pigment" lipofuscin. Expression profiling showed an upregulation of genes implicated in neuronal growth, neuroprotection, and learning. These data show that Cr improves health and longevity in mice. Cr may be a promising food supplement to promote healthy human aging. Amino Acids. 2007 Mar 30. Recent findings have indicated that creatine supplementation may affect glucose metabolism. This study aimed to examine the effects of creatine supplementation, combined with aerobic training, on glucose tolerance in sedentary healthy male. Subjects (n = 22) were randomly divided in two groups and were allocated to receive treatment with either creatine (CT) ( approximately 10 g . day over three months) or placebo (PT) (dextrose). Administration of treatments was double blind. Both groups underwent moderate aerobic training. An oral glucose tolerance test (OGTT) was performed and both fasting plasma insulin and the homeostasis model assessment (HOMA) index were assessed at the start, and after four, eight and twelve weeks. CT demonstrated significant decrease in OGTT area under the curve compared to PT (P = 0.034). There were no differences between groups or over time in fasting insulin or HOMA. The results suggest that creatine supplementation, combined with aerobic training, can improve glucose tolerance but does not affect insulin sensitivity, and may warrant further investigation with diabetic subjects. Muscle Nerve. 2007 Feb. Mitochondrial disorders share common cellular consequences: (1) decreased ATP production; (2) increased reliance on alternative anaerobic energy sources; and (3) increased production of reactive oxygen species. The purpose of the present study was to determine the effect of a combination therapy (creatine monohydrate, coenzyme Q(10), and lipoic acid to target the above-mentioned cellular consequences) on several outcome variables using a randomized, double-blind, placebo-controlled, crossover study design in patients with mitochondrial cytopathies. Three patients had mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), four had mitochondrial DNA deletions (three patients with chronic progressive external ophthalmoplegia and one with Kearns-Sayre syndrome), and nine had a variety of other mitochondrial diseases not falling into the two former groups. The combination therapy resulted in lower resting plasma lactate and urinary 8-isoprostanes, as well as attenuation of the decline in peak ankle dorsiflexion strength in all patient groups, whereas higher fat-free mass was observed only in the MELAS group. Together, these results suggest that combination therapies targeting multiple final common pathways of mitochondrial dysfunction favorably influence surrogate markers of cellular energy dysfunction. Future studies with larger sample sizes in relatively homogeneous groups will be required to determine whether such combination therapies influence function and quality of life. Nutr Rev. 2006 Feb. In recent years, dietary supplementation with creatine has been shown to enhance neuromuscular function in several diseases. Recent studies have suggested that creatine can be beneficial in patients with muscular dystrophy and other mitochondrial cytopathies, and may attenuate sarcopenia and facilitate rehabilitation of disuse atrophy. Though the mechanisms are still unknown, creatine has been shown to decrease cytoplasmic Ca2+ levels and increase intramuscular and cerebral phosphocreatine stores, providing potential musculoskeletal and neuroprotective effects. Ann Neurol. 2005 Jul. We tested the efficacy and safety of glutamine (0.6 gm/kg/day) and creatine (5 gm/day) in 50 ambulant boys with Duchenne muscular dystrophy in a 6-month, double-blind, placebo-controlled clinical trial. Drug efficacy was tested by measuring muscle strength manually (34 muscle groups) and quantitatively (10 muscle groups). Timed functional tests, functional parameters, and pulmonary function tests were secondary outcome measures. Although there was no statistically significant effect of either therapy based on manual and quantitative measurements of muscle strength, a disease-modifying effect of creatine in older Duchenne muscular dystrophy and creatine and glutamine in younger Duchenne muscular dystrophy cannot be excluded. Creatine and glutamine were well tolerated. Ann Pharmacother. 2005 Jun. OBJECTIVE: To examine the effect of creatine supplementation on renal function and estimates of creatinine clearance. DATA SOURCES: A MEDLINE search was conducted (1966-September 2004) using the key terms creatine, creatinine, kidney function tests, drug toxicity, and exercise. Relevant articles were cross-referenced to screen for additional information. DATA SYNTHESIS: Supplementation with creatine, an unregulated dietary substance, is increasingly common in young athletes. To date, few studies have evaluated the impact of creatine on renal function and estimates of creatinine clearance. Because creatine is converted to creatinine in the body, supplementation with large doses of creatine may falsely elevate creatinine concentrations. Five studies have reported measures of renal function after acute creatine ingestion and 4 after chronic ingestion. All of these studies were completed in young healthy populations. Following acute ingestion (4-5 days) of large amounts of creatine, creatinine concentrations increased slightly, but not to a clinically significant concentration. Creatinine is also only minimally affected by longer creatine supplementation (up to 5.6 y). CONCLUSIONS: Creatine supplementation minimally impacts creatinine concentrations and renal function in young healthy adults. Although creatinine concentrations may increase after long periods of creatine supplementation, the increase is extremely limited and unlikely to affect estimates of creatinine clearance and subsequent dosage adjustments. Further studies are required in the elderly and patients with renal insufficiency. Int J Sports Med. 2005 May. Although oral creatine supplementation is very popular among athletes, no prospective placebo-controlled studies on the adverse effects of long-term supplementation have yet been conducted. We performed a double-blind, placebo-controlled trial of creatine monohydrate in patients with the neurodegenerative disease amyotrophic lateral sclerosis, because of the neuroprotective effects it was shown to have in animal experiments. The purpose of this paper is to compare the adverse effects, and to describe the effects on indirect markers of renal function of long-term creatine supplementation. 175 subjects (age = 57.7 +/- 11.1 y) were randomly assigned to receive creatine monohydrate 10 g daily or placebo during an average period of 310 days. After one month, two months and from then on every fourth month, adverse effects were scored using dichotomous questionnaires, plasma urea concentrations were measured, and urinary creatine and albumin concentrations were determined. No significant differences in the occurrence at any time of adverse effects due to creatine supplementation were found (23 % nausea in the creatine group, vs. 24 % in the placebo group, 19 % gastro-intestinal discomfort in the creatine group, vs. 18 % in the placebo group, 35 % diarrhoea in the creatine group, vs. 24 % in the placebo group). After two months of treatment, oedematous limbs were seen more often in subjects using creatine, probably due to water retention. Severe diarrhoea (n = 2) and severe nausea (n = 1) caused 3 subjects in the creatine group to stop intake of creatine, after which these adverse effects subsided. Long-term supplementation of creatine did not lead to an increase of plasma urea levels (5.69 +/- 1.47 before treatment vs. 5.26 +/- 1.44 at the end of treatment) or to a higher prevalence of micro-albuminuria (5.4 % before treatment vs. 1.8 % at the end of treatment). J Sports Med Phys Fitness. 2004 Dec. This review focuses on the potential side effects caused by oral creatine supplementation on gastrointestinal, cardiovascular, musculoskeletal, renal and liver functions. No strong evidence linking creatine supplementation to deterioration of these functions has been found. In fact, most reports on side effects, such as muscle cramping, gastrointestinal symptoms, changes in renal and hepatic laboratory values, remain anecdotal because the case studies do not represent well-controlled trials, so no causal relationship between creatine supplementation and these side-effects has yet been established. The only documented side effect is an increase in body mass. Furthermore, a possibly unexpected outcome related to creatine monohydrate ingestion is the amount of contaminants present that may be generated during the industrial production. Recently, controlled studies made to integrate the existing knowledge based on anecdotal reports on the side effects of creatine have indicated that, in healthy subjects, oral supplementation with creatine, even with long-term dosage, may be considered an effective and safe ergogenic aid. However, athletes should be educated as to proper dosing or to take creatine under medical supervision. Rinsho Shinkeigaku. 2004 Oct. To investigate the effects of creatine monohydrate on muscle performance and cognitive functions in muscular dystrophy patients, we made an open trial. Twenty-nine individuals, including 14 myotonic dystrophy (DM), seven facioscapurohumeral muscular dystrophy (FSHD), two limb-girdle muscular dystrophy and six healthy volunteers, were enrolled in this study and 27 participants completed it. All participants took creatine 20g/day for an initial week and 5g/day for successive eight weeks. Somatotonic measurements, global subjective assessment, muscle performance, cardiopulmonary function, cognitive function, laboratory studies and magnetic resonance spectroscopy (MRS) were evaluated at both pre and post examination. Subjective improvements were reported from twelve individuals. Contrary adverse effects were also complained from ten individuals, although all these problems were not serious. Quantitative muscle power was slightly but significantly increased in the patients and the number of the patients who failed to complete cycle ergometer test was decreased. Phosphocreatine concentrations of left calf muscle were not different between pre and post trial examination. No obvious changes were detected in cardiopulmonary assessment, cognitive function and laboratory date. Creatine has certain expectance for muscular dystrophy patients in motor performance. The effect may be achieved not only by increase of energy buffer, because clinical improvements were observed in our study nevertheless no increase was detected in phosphocreatine concentration. The usage of creatine should be managed under medical monitoring since ideal protocol has not yet been established and adverse effects can not be ignored. Neurology. 2004 May 25. OBJECTIVE: To determine whether creatine monohydrate (CrM) supplementation increases strength and fat-free mass (FFM) in boys with Duchenne muscular dystrophy (DD). METHODS: Thirty boys with DD (50% were taking corticosteroids) completed a double-blind, randomized, cross-over trial with 4 months of CrM (about 0.10 g/kg/day), 6-week wash-out, and 4 months of placebo. Measurements were completed of pulmonary function, compound manual muscle and handgrip strength, functional tasks, activity of daily living, body composition, serum creatine kinase and gamma-glutamyl transferase activity and creatinine, urinary markers of myofibrillar protein breakdown (3-methylhistidine), DNA oxidative stress (8-hydroxy-2-deoxyguanosine [8-OH-2-dG]), and bone degradation (N-telopeptides). RESULTS: During the CrM treatment phase, there was an increase in handgrip strength in the dominant hand and FFM (p < 0.05), with a trend toward a loss of global muscle strength (p = 0.056) only for the placebo phase, with no improvements in functional tasks or activities of daily living. Corticosteroid use, but not CrM treatment, was associated with a lower 8-OH-2-dG/creatinine (p < 0.05), and CrM treatment was associated with a reduction in N-telopeptides (p < 0.05). CONCLUSIONS: Four months of CrM supplementation led to increases in FFM and handgrip strength in the dominant hand and a reduction in a marker of bone breakdown and was well tolerated in children with DD. J Physiol. 2004 Mar 1. Recent observations have suggested that creatine supplementation might have a beneficial effect on glucoregulation in skeletal muscle. However, conclusive studies on the direct effects of creatine on glucose uptake and metabolism are lacking. The objective of this study was to investigate the effects of creatine supplementation on basal and insulin-stimulated glucose transporter (GLUT4) translocation, glucose uptake, glycogen content, glycogen synthesis, lactate production, glucose oxidation and AMP-activated protein kinase (AMPK) phosphorylation in L6 rat skeletal muscle cells. Four treatment groups were studied: control, insulin (100 nM), creatine (0.5 mM) and creatine + insulin. After 48 h of creatine supplementation the creatine and phosphocreatine contents of L6 myoblasts increased by approximately 9.3- and approximately 5.1-fold, respectively, but the ATP content of the cells was not affected. Insulin significantly increased 2-deoxyglucose uptake ( approximately 1.9-fold), GLUT4 translocation ( approximately 1.8-fold), the incorporation of D-[U-(14)C]glucose into glycogen ( approximately 2.3-fold), lactate production ( approximately 1.5-fold) and (14)CO(2) production ( approximately 1.5-fold). Creatine neither altered the glycogen and GLUT4 contents of the cells nor the insulin-stimulated rates of 2-DG uptake, GLUT4 translocation, glycogen synthesis and glucose oxidation. However, creatine significantly reduced by approximately 42% the basal rate of lactate production and increased by approximately 40% the basal rate of (14)CO(2) production. This is in agreement with the approximately 35% increase in citrate synthase activity and also with the approximately 2-fold increase in the phosphorylation of both alpha-1 and alpha-2 isoforms of AMPK after creatine supplementation. We conclude that 48 h of creatine supplementation does not alter insulin-stimulated glucose uptake and glucose metabolism; however, it activates AMPK, shifts basal glucose metabolism towards oxidation and reduces lactate production in L6 rat skeletal muscle cells. Excerpts from the full text article: The physiological roles of creatine in the human body have been extensively investigated. Its main biochemical effect in skeletal muscle, usually described as the 'energy shuttle', is to transfer chemical energy from mitochondria, where ATP is produced, to the myofibrils (Wallimann et al. 1992; Ruggeri, 2000). In humans, approximately 95% of the total body creatine is found in skeletal muscle. More than 60% is in the form of phosphocreatine (PCr) and the remainder is stored in the non-phosphorylated form (Walker, 1979; Mesa et al. 2002). After Harris et al. (1992) demonstrated the efficacy of oral creatine intake for increasing skeletal muscle creatine content in humans, interest in the effects of oral creatine supplementation on skeletal muscle contractile performance and metabolism rapidly increased. It is now well established that the ingestion of a high dose (20-25 g per day) of oral creatine can rapidly (3-5 days) raise muscle total creatine content (Mesa et al. 2002). This elevation in muscle creatine storage has been associated with increased muscle power output during repeated short high-intensity exercise tasks (Greenhaff et al. 1993; Balsom et al. 1995) and enhanced effects of weight training on muscle volume and strength (Vandenberghe et al. 1997; American College of Sports Medicine, 2000). Additionally, It has been shown that the combination of creatine and carbohydrate supplements results in a greater postexercise muscle glycogen accumulation than carbohydrate alone (Robinson et al. 1999), suggesting that creatine could also exert an effect on peripheral glucose metabolism. Additional evidence suggesting that creatine supplementation might be effective in regulating peripheral glucose metabolism comes from a recent study on transgenic Huntington mice, which are hyperglycaemic. The addition of creatine to the diet of these mice significantly reduced hyperglycaemia, while improving the glucose response to intravenous glucose injection (Ferrante et al. 2000). It has been suggested that the effects of creatine supplementation on glucose homeostasis may be due to an increase in insulin secretion (Gempel et al. 1996). Although some in vitro studies have indicated that creatine may increase insulin secretion modestly in the perfused rat pancreas (Alsever et al. 1970) and isolated mouse islets (Marco et al. 1976) or insulinoma cells (Gempel et al. 1996), evidence from in vivo human studies indicates that either one 5 g dose of creatine (Green et al. 1996a) or 3 days of creatine supplementation (Green et al. 1996b) does not alter insulin secretion. Therefore, we hypothesized that the glucoregulatory effect of creatine supplementation may be caused by a direct alteration in peripheral glucose metabolism independently of changes in insulin secretion. Recently, it was reported that oral creatine supplementation increased by ~40% the GLUT4 content in vastus lateralis muscle after rehabilitation training in subjects who had previously had one of their legs immobilized (Op't Eijnde et al. 2001a). It was also demonstrated that muscle glycogen and total creatine content were higher in creatine-supplemented subjects, but no data were presented regarding glucose uptake and other aspects of glucose metabolism in this study (Op't Eijnde et al. 2001a). In rats, it has also recently been reported that creatine supplementation reduces the PCr : TCr (total free creatine) ratio, suggesting an alteration in the energy state in muscle cells, but has no effect on glucose uptake in isolated plantaris muscles (Young & Young, 2002). Energy and metabolic sensing in muscle cells have been attributed to AMP-activated protein kinase (AMPK) (Hardie et al. 1998; Winder, 2001), which has been shown to regulate glucose uptake and metabolism in skeletal muscle. An alteration of the energy state of the cell is likely to alter the activity of AMPK and the demand for glucose. Investigation of GLUT4 translocation and glucose uptake, as well as the fate of glucose via the pathways of glycogen synthesis, oxidation and lactate production, is crucial to characterizing the implications of altering the energy state of muscle cells by creatine supplementation. However, the possible effects of creatine supplementation on AMPK activation and the implications for glucose uptake and metabolism have not been fully investigated. This study was designed to enhance our understanding of the metabolic response of skeletal muscle with respect to glucose uptake and metabolism in response to creatine supplementation. Accordingly, we investigated the in vitro effects of short-term (48 h) creatine supplementation on glucose uptake, GLUT4 translocation, lactate production, glycogen synthesis, glucose oxidation, citrate synthase activity and AMPK phosphorylation in L6 rat skeletal muscle cells. Results Creatine, phosphocreatine and ATP contents The creatine and PCr contents of the cells increased from 6.75 ± 0.73 and 4.5 ± 0.36 ug (mg protein)-1 before supplementation to 46.39 ± 1.23 and 22.10 ± 1.48 ug (mg protein)-1 after 24 h and 62.36 ± 2.04 and 23.0 ± 0.78 ug (mg protein)-1 after 48 h of creatine supplementation (Fig. 1A), respectively. The expansion of the creatine and PCr contents, however, was not accompanied by an increase in the total ATP concentration in L6 muscle cells after creatine supplementation (5.40 ± 0.67 versus 5.07 ± 0.28 nmol (mg protein)-1 in the control and creatine supplemented cells, respectively) (Fig. 1B). Glucose uptake, GLUT4 translocation, glycogen synthesis, and GLUT4 and glycogen contents In the present study, glucose uptake (Fig. 2A), GLUT4 translocation (Fig. 2B) and the incorporation of d-[U-14C]glucose into glycogen (Fig. 2C) increased by ~1.9-fold, ~1.8-fold and 2.3-fold, respectively, after insulin stimulation. AICAR (1 mm, 30 min) was used as a positive control and it significantly increased glucose uptake by ~1.7-fold (1.5 ± 0.19 and 2.53 ± 0.17 nmol (ug protein)-1 for the control and AICAR-treated cells, respectively) in L6 muscle cells. However, creatine supplementation neither altered the basal nor the insulin-stimulated rates of glucose uptake, GLUT4 translocation and glycogen synthesis. Furthermore, the GLUT4 protein content (Fig. 2D) was not altered by creatine supplementation in L6 rat skeletal muscle cells. The glycogen content of the cells increased from 3.38 ± 0.32 umol (mg protein)-1 before supplementation to 4.36 ± 0.22 and 4.63 ± 0.55 umol (mg protein)-1 after 24 and 48 h of creatine supplementation, respectively. However, there was no significant difference between the control and creatine-supplemented cells (Fig. 3). Lactate production, glucose oxidation and citrate synthase maximal activity In the presence of insulin, the L6 myoblasts elicited a significant ~1.5-fold increase in lactate production compared to control cells. Interestingly, creatine supplementation reduced the basal production of lactate by ~42%, but did not alter the insulin-stimulated lactate production by the cells (Fig. 4A). Concomitantly, creatine supplementation significantly increased (1.4-fold) the basal production of 14CO2 from d-[U-14C]glucose but did not alter the effect of insulin on this variable (Fig. 4B). These results are supported by a significant increase (~30%) in citrate synthase activity after creatine supplementation (Fig. 5). In fact, the maximal activity of citrate synthase increased from 21.22 ± 0.84 nmol min-1 (mg protein)-1 before supplementation to 23.40 ± 2.48 and 27.54 ± 1.4 nmol min-1 (mg protein)-1 after 24 and 48 h of creatine supplementation, respectively. Although there was a tendency towards an increase after 24 h, it only reached statistically significant values after 48 h of creatine supplementation (Fig. 5). AMPK phosphorylation Insulin did not alter AMPK phosphorylation in L6 skeletal muscle cells (Fig. 6A); however, AMPK phosphorylation was significantly increased (~1.8-fold) under basal or insulin stimulated conditions after creatine supplementation (Fig. 6A). The increase in AMPK activity in our experiments was confirmed by the ~2.2-fold increase in phosphorylation of a well-characterized substrate of AMPK, namely ACC (Fig. 6B), after creatine supplementation. Additionally, we used AICAR as a positive control for AMPK and ACC phosphorylation. The magnitude of ACC phosphorylation caused by creatine supplementation was similar to that obtained after the incubation of L6 muscle cells with AICAR (Fig. 6B). We also investigated if creatine regulated the phosphorylation of both alpha-1 and alpha-2 isoforms of AMPK. To do this, we immunoprecipitated alpha-1 and alpha-2 using isoform-specific antibody and then Western blotted the immunoprecipitates with phospho-AMPK(Thr172)-specific antibodies. Interestingly, phosphorylation of both isoforms was significantly increased by creatine supplementation. We detected a significant ~2-fold increase in the phosphorylation state of both AMPK alpha-1 and alpha-2 isoforms, with no alteration in total AMPK alpha-1 and alpha-2 protein contents (Figs 6C and 6D). Discussion Oral creatine supplementation in humans (Mesa et al. 2002) and rats (Young & Young, 2002) has been proven to increase the contents of creatine and phosphocreatine in skeletal muscle. In humans, creatine is usually administered as a dosage regimen consisting of a loading phase of 20 g day1 (four times 5 g) for 5-7 days and a maintenance dosage of 3-5 g day1 thereafter (Mesa et al. 2002). It has been reported that 1 h after a single oral dose (5 g) of creatine the serum concentration of this substance rises from 0.05 to 0.1 mmol l1 (fasting serum values) to 0.6-0.8 mmol l-1 (Perski et al. 2003). In response to a 20 g oral dose, plasma creatine concentration reaches peak values of 2.17 mmol l-1 (50-fold increase) after 2.5 h of ingestion (Mesa et al. 2002). The uptake of creatine by muscle cells presents Michaelis-Menten kinetics, with a maximum rate of creatine uptake (Vmax) obtained at concentrations higher than 0.3-0.4 mmol l-1 (Sora et al. 1994). Based on these data, we decided to supplement the incubation medium with 0.5 mm l-1 of creatine, which corresponds to the concentration achieved in humans after a single 5 g oral dose of creatine. This value is also within the range that seems to elicit the maximal rate of muscle creatine uptake (Sora et al. 1994). We incubated the L6 muscle cells in the presence of 0.5 mm creatine for 48 h, since it has been established that the majority of muscle creatine accumulation is maximal in the first 2 days of oral supplementation (Kamber et al. 1999). The effectiveness of our supplementation regimen was confirmed by the ~9.6- and ~5.4-fold increases in creatine and PCr contents of the cells after 48 h of creatine supplementation, respectively. In fact, these increases were significantly higher than those reported in humans (15-20% increase in muscle total creatine content) after supplementation (Febbraio et al. 1995; Hultman et al. 1996; Casey et al. 1996; Robinson et al. 1999). Therefore, although we have attempted to recreate the physiological milieu as closely as possible, care must be taken when extrapolating our data regarding the effects of increased intracellular creatine and PCr on glucose uptake and metabolism to intact muscle tissue. We did not find any significant alteration in GLUT4 content, basal or insulin-stimulated GLUT4 translocation or glucose uptake and glycogen content in these cells upon creatine supplementation. Additionally, contrary to what has been observed in humans (Robinson et al. 1999; Op't Eijnde et al. 2001a) and rats (Op't Eijnde et al. 2001b), we did not observe any alteration in either basal or insulin-stimulated glycogen synthesis after creatine supplementation. Interestingly, creatine supplementation has been reported to cause an increase in glycogen accumulation in humans only in muscles that are subject to exercise (Robinson et al. 1999; Op't Eijnde et al. 2001a). This suggests that some muscle contraction is necessary in order to observe any additive effect of creatine on glycogen synthesis in muscle. This could be one reason why creatine supplementation did not alter glycogen content and the basal or insulin-stimulated rates of glycogen synthesis in our in vitro model. In fact, our experiments were performed in non-contracting cells and the results obtained are in agreement with what has been reported in non-exercising rats in which creatine supplementation did not alter basal and insulin-stimulated glucose uptake (Young & Young, 2002), glycogen synthase activity (Op't Eijnde et al. 2001b; Rooney et al. 2002) and the incorporation of [14C]-glucose into glycogen (Op't Eijnde et al. 2001b) in skeletal muscle. The GLUT4 and glycogen contents of the cells were not altered by creatine supplementation, and although we did not observe any effect of creatine on basal and insulin-stimulated GLUT4 translocation and glucose uptake, L6 muscle cells supplemented with creatine significantly increased (~40%) their basal production of 14CO2 from d-[U-14C]glucose. This suggests that creatine supplementation shifted basal glucose metabolism towards oxidation, which is compatible with the significant reduction (~42%) in basal lactate production observed in the creatine-supplemented cells. These observations are also in agreement with data obtained from mitochondria isolated from muscles of creatine-supplemented human subjects (Walsh et al. 2001) and from mice cardiac skinned muscle fibres incubated with creatine (Saks et al. 2000). In both models, oxygraphic measurements point towards an increase in mitochondrial respiration in the presence of creatine (Saks et al. 2000; Walsh et al. 2001). It has been demonstrated that in the presence of creatine the mitochondrial isoform of creatine kinase (mi-CK) uses ATP to produce ADP, which is channelled directly to adenine nucleotide translocase for regulation of respiration (Saks et al. 2000). This means that creatine, by activating mi-CK, changes the energy state of the cell and directly controls the mitochondrial energy production (Saks et al. 2000). The increase in CO2 production that we observed in our creatine-supplemented L6 muscle cells could have resulted from the elevation of creatine concentration in the cell, leading to higher mi-CK activity and increased oxidative phosphorylation. It has been repeatedly reported that creatine supplementation increases total creatine concentration in muscle in both humans (Greenhaff et al. 1994; Green et al. 1996a,b; Hultman et al. 1996; Steenge et al. 1998; Robinson et al. 1999) and rats (Brannon et al. 1997; McMillen et al. 2001; Young & Young, 2002). Interestingly, the expansion of the total creatine (TCr) pool in muscle is due to an increase in both the free and phosphorylated (PCr) forms of creatine. However, PCr does not seem to increase in the same proportion as free creatine in the muscle cell, and hence the PCr : TCr ratio actually falls after supplementation (Greenhaff et al. 1994; Green et al. 1996a,b; Hultman et al. 1996; Steenge et al. 1998). This was also the case in our experiments, since the PCr : TCr ratios were 0.67 and 0.37 for control and 48 h creatine-supplemented cells, respectively. Considering that the PCr : TCr ratio reflects cellular energetics (Connet, 1988; Op't Eijnde et al. 2001a,b), a decrease in PCr : TCr might have been interpreted as an altered energy state in our resting muscle cells, which in turn might have increased their basal glucose oxidation rate. This is compatible with our data showing increases (~30%) in both glucose oxidation and maximal activity of citrate synthase after 48 h of creatine supplementation. The AMP-activated protein kinase (AMPK) has been established as a protein that monitors the metabolic and energetic states of the muscle cells (Hardie et al. 1998; Winder, 2001). Additionally, it has been shown that AMPK activity is modulated by the PCr : TCr ratio (Pontikos et al. 1998). A fall in the PCr : TCr ratio within the cell would be expected therefore to cause activation of AMPK as a result of the release of inhibition exerted by PCr (Pontikos et al. 1998). Interestingly, we found an ~1.8-fold increase in AMPK phosphorylation. Previous studies have reported specific induction of AMPK alpha-2 isoform activity in skeletal muscle by exercise (Wojtaszewski et al. 2000; Fuji et al. 2000; Stephens et al. 2002), suggesting that this isoform may be involved in the metabolic responses observed in contracting skeletal muscles. A more detailed analysis of changes in activity of the catalytic AMPK isoforms in our study revealed an ~2-fold increase in phosphorylation of both alpha-1 and alpha-2 isoforms in creatine-supplemented muscle cells. Additionally, we demonstrated that similar amounts of the alpha-1 and alpha-2 AMPK isoforms were present in L6 muscle cells. Therefore, the metabolic effects we observed in the present study with non-contracting L6 muscle cells are likely to be due to the activation of both alpha-1 and alpha-2 AMPK isoforms. This is again different from exercise conditions, which lead to the degradation of intracellular glycogen content (Fuji et al. 2000) and other energy substrates and may cause isoform-specific activation of the catalytic subunits of AMPK. In fact, the exercise-induced increase in the alpha-2-specific activity of AMPK has been reported to be intensity dependent (Wojtaszewski et al. 2000; Fuji et al. 2000) and inversely correlated with glycogen depletion in skeletal muscle (Fuji et al. 2000; Stephens et al. 2002), suggesting that the glycogen content of muscle cells may indeed play an important role in triggering the multiple cellular effects of AMPK. AMPK activation has been suggested to play a key role in increasing glucose uptake in contracting skeletal muscle (Zierath, 2002). Yet we do not observe an increase in glucose uptake following creatine supplementation, despite activation of AMPK. In order to demonstrate that L6 muscle cells have the ability to react to increased AMPK activity by elevating glucose transport, we treated cells with AICAR and observed a significant increase (~1.7-fold) in glucose uptake. However, it has been reported that AMPK activity and glucose uptake may be completely dissociated in contracting perfused slow-twitch rat muscle (Derave et al. 2000). It seems that the major factor that dissociates AMPK activation from an increase in glucose uptake in skeletal muscle is the glycogen content of the cells (Derave et al. 2000). In our experiments the glycogen content was similar in the control and creatine-supplemented conditions and this may be the reason why the increased phosphorylation of AMPK in our creatine-supplemented cells was not followed by an increment in glucose uptake. Furthermore, there are many instances where activation of a given mediator of glucose uptake does not lead to glucose uptake, e.g. PI3-kinase (Jiang et al. 1998). It may also be that creatine activates AMPK in a compartment-specific manner such that only a subset of AMPK not involved in stimulating glucose uptake is activated. One intriguing point in our results is the fact that creatine increased the basal glucose oxidation rate and this may have resulted from AMPK activation; however, when the glycolytic flux was acutely increased by insulin in the creatine-supplemented cells the rate of glucose oxidation was not affected at all by creatine, despite a similar increase in AMPK phosphorylation. At the present time we do not have a precise explanation for this finding. However, it is possible that the increase in glucose oxidation observed under basal conditions, which was compensated for by a proportional reduction in lactate production, was already sufficient to meet the new energetic demands of the cells in order to adjust for the reduction in the PCr : TCr ratio caused by creatine supplementation. Therefore, no additional increases in glucose oxidation were necessary, even though the glycolytic flux in the cells was acutely increased by insulin stimulation. In summary, our study demonstrates that 2-day treatment of L6 rat skeletal muscle cells with creatine increased the proportion of glucose being oxidized and caused a corresponding reduction in lactate production (Fig. 7) in L6 rat skeletal muscle cells. The ability of creatine to phosphorylate and activate AMPK may be responsible for this effect. Although creatine supplementation caused an increase in AMPK activity and GLUT4 and glycogen contents, the ability of insulin to stimulate GLUT4 translocation, glucose uptake and glycogen synthesis was not affected in these cells. Muscle Nerve. 2004 Jan. Creatine monohydrate (CrM) supplementation may increase strength in some types of muscular dystrophy. A recent study in myotonic muscular dystrophy type 1 (DM1) did not find a significant treatment effect, but measurements of muscle phosphocreatine (PCr) were not performed. We completed a randomized, double-blind, cross-over trial using 34 genetically confirmed adult DM1 patients without significant cognitive impairment. Participants received CrM (5 g, approximately 0.074 g/kg daily) and a placebo for each 4-month phase with a 6-week wash-out. Spirometry, manual muscle testing, quantitative isometric strength testing of handgrip, foot dorsiflexion, and knee extension, handgrip and foot dorsiflexion endurance, functional tasks, activity of daily living scales, body composition (total, bone, and fat-free mass), serum creatine kinase activity, serum creatinine concentration and clearance, and liver function tests were completed before and after each intervention, and muscle PCr/beta-adenosine triphosphate (ATP) ratios of the forearm flexor muscles were completed at the end of each phase. CrM supplementation did not increase any of the outcome measurements except for plasma creatinine concentration (but not creatinine clearance). Thus, CrM supplementation at 5 g daily does not have any effects on muscle strength, body composition, or activities of daily living in patients with DM1, perhaps because of a failure of the supplementation to increase muscle PCr/beta-ATP content. CNS Drugs. 2004. Creatine is consumed in the diet and endogenously synthesised in the body. Over the past decade, the ergogenic benefits of synthetic creatine monohydrate have made it a popular dietary supplement, particularly among athletes. The anabolic properties of creatine also offer hope for the treatment of diseases characterised by weakness and muscle atrophy. Moreover, because of its cellular mechanisms of action, creatine offers potential benefits for diseases involving mitochondrial dysfunction. Recent data also support the hypothesis that creatine may have a neuroprotective effect. Amyotrophic lateral sclerosis (ALS) is characterised by progressive degeneration of motor neurons, resulting in weakening and atrophy of skeletal muscles. In patients with this condition, creatine offers potential benefits in terms of facilitating residual muscle contractility as well as improving neuronal function. It may also help stabilise mitochondrial dysfunction, which plays a key role in the pathogenesis of ALS. Indeed, the likely multifactorial aetiology of ALS means the combined pharmacodynamic properties of creatine offer promise for the treatment of this condition. Evidence from available animal models of ALS supports the utility of treatment with creatine in this setting. Limited data available in other neuromuscular and neurodegenerative diseases further support the potential benefit of creatine monohydrate in ALS. However, few randomised, controlled trials have been conducted. To date, two clinical trials of creatine monohydrate in ALS have been completed without demonstration of significant improvements in overall survival or a composite measure of muscle strength. These trials have also posed unanswered questions about the optimal dosage of creatine and its beneficial effects on muscle fatigue, a measure distinct from muscle strength. A large, multicentre, clinical trial is currently underway to further investigate the efficacy of creatine monohydrate in ALS and address these unresolved issues. Evidence to date shows that creatine supplementation has a good safety profile and is well tolerated by ALS patients. The purpose of this article is to provide a short, balanced review of the literature concerning creatine monohydrate in the treatment of ALS and related neurodegenerative diseases. The pharmacokinetics and rationale for the use of creatine are described along with available evidence from animal models and clinical trials for ALS and related neurodegenerative or neuromuscular diseases. J Herb Pharmacother. 2004. Creatine is a popular supplement used by athletes in an effort to increase muscle performance. The purpose of this review was to assess the literature evaluating the effects of creatine supplementation on renal function. A PubMed search was conducted to identify relevant articles using the keywords, creatine, supplementation, supplements, renal dysfunction, ergogenic aid and renal function. Twelve pertinent articles and case reports were identified. According to the existing literature, creatine supplementation appears safe when used by healthy adults at the recommended loading (20 gm/day for five days) and maintenance doses (</=3 gm/day). In people with a history of renal disease or those taking nephrotoxic medications, creatine may be associated with an increased risk of renal dysfunction. One case report of acute renal failure was reported in a 20-year-old man taking 20 gm/day of creatine for a period of four weeks. There are few trials investigating the long-term use of creatine supplementation in doses exceeding 10 gm/day. Furthermore, the safety of creatine in children and adolescents has not been established. Since creatine supplementation may increase creatinine levels, it may act as a false indicator of renal dysfunction. Future studies should include renal function markers other than serum creatinine and creatinine clearance. J Am Diet Assoc. 2003 Aug. Mitochondrial disorders are degenerative diseases characterized by a decrease in the ability of mitochondria to supply cellular energy requirements. Substantial progress has been made in defining the specific biochemical defects and underlying molecular mechanisms, but limited information is available about the development and evaluation of effective treatment approaches. The goal of nutritional cofactor therapy is to increase mitochondrial adenosine 5'-triphosphate production and slow or arrest the progression of clinical symptoms. Accumulation of toxic metabolites and reduction of electron transfer activity have prompted the use of antioxidants, electron transfer mediators (which bypass the defective site), and enzyme cofactors. Metabolic therapies that have been reported to produce a positive effect include Coenzyme Q(10) (ubiquinone); other antioxidants such as ascorbic acid, vitamin E, and lipoic acid; riboflavin; thiamin; niacin; vitamin K (phylloquinone and menadione); creatine; and carnitine. A literature review of the use of these supplements in mitochondrial disorders is presented. Muscle Nerve. 2003 May. The effect of creatine (Cr) supplementation on muscle function and body composition of 12 boys with Duchenne muscular dystrophy and three with Becker dystrophy was evaluated by a randomized double-blind cross-over study (3 g Cr or maltodextrin daily for 3 months, with wash-out period of 2 months). After placebo, no change was observed in maximal voluntary contraction (MVC) and resistance to fatigue, whereas total joint stiffness (TJS) was increased by approximately 25% (P < 0.05). The patients receiving Cr did not show any change in TJS, improved MVC by 15% (P = 0.02), and almost doubled their resistance to fatigue (P < 0.001). In patients still independent of a wheelchair (n = 5), bone mineral density increased by 3% (P < 0.05), and urinary excretion of collagen type I cross-linking N-telopeptide declined to about one third (P < 0.001) after Cr. No adverse effect was observed. Thus, Cr may provide some symptomatic benefit in these patients. Neurology. 2003 Feb 11. The efficacy and safety of creatine monohydrate (Cr) in patients with myotonic dystrophy type 2/proximal myotonic myopathy were studied in a small placebo-controlled double-blind trial. Twenty patients received either Cr or placebo for 3 months. After 3 months, there were no significant differences of muscle strength as assessed by hand-held dynamometry, testing of maximum grip strength, Medical Research Council scoring, and the Neuromuscular Symptom Score between the two groups. Some measures indicated trends toward mild improvement with Cr. Myalgia improved in two patients. J Neurol. 2002 Dec. We assessed safety and efficacy of creatine monohydrate (Cr) in myotonic dystrophy (DM1) in a double-blind, cross-over trial. Thirty-four patients with defined DM1 were randomized to receive Cr and placebo for eight weeks (10.6 g day 1-10, 5.3 g day 11-56) in one of 2 treatment sequences. There was no significant improvement using manual and quantitative muscle strength, daily-life activities, and patients' own global assessment comparing verum with placebo administration. Cr supplementation was well tolerated without clinically relevant side effects, but did not result in significant improvement of muscle strength or daily-life activities. Arch Neurol. 2002 Jan. BACKGROUND: In a recent study, we showed that administration of low-dose creatine (Cr) (60 mg/kg daily) improved work capacity in patients with McArdle disease. OBJECTIVE: To assess the efficacy of high-dose Cr therapy in McArdle disease. DESIGN: Randomized, double-blind, placebo-controlled crossover study. PATIENTS: Nineteen patients with McArdle disease. INTERVENTION: Treatment with Cr, 150 mg/kg daily. Each treatment phase with Cr or placebo lasted 5 weeks. MAIN OUTCOME MEASURES: The patient's daily rating of symptoms of exercise intolerance. At the end of each treatment phase, serum creatine and serum creatine kinase levels, phosphorus 31 magnetic resonance spectroscopy, and surface electromyograms were assessed. RESULTS: Clinical end points revealed increases in the intensity of exercise-induced pain in working muscles (mean treatment-induced difference [d], 0.30 in log(score); 95% confidence interval [CI], 0.05-0.55; P =.02), the limitation of daily activities (d, 0.59; 95% CI, 0.22-0.97;P =.005), and body mass index (d, 0.33 kg/m2, 95% CI, 0.10-0.56 kg/m2; P =.008) with Cr use. Surface electromyograms revealed a smaller increase in the electromyographic amplitude over time during muscle contraction with Cr use (d, -13.52%/min; 95% CI, -23.71%/min to -3.34%/min; P =.01). There were no significant changes in phosphorus 31 magnetic resonance spectroscopy variables. CONCLUSIONS: Administration of high-dose Cr worsened the main clinical symptoms of exercise intolerance in McArdle disease. These neurologic adverse effects represent a major dose-limiting factor in Cr therapy for McArdle disease. Taken together with results of a previous study, the indication for symptomatic therapy with Cr needs to be clarified. An effective Cr dosage without adverse effects may be between 60 and 150 mg/kg daily. Pharmacol Rev. 2001 Jun. Creatine is a dietary supplement purported to improve exercise performance and increase fat-free mass. Recent research on creatine has demonstrated positive therapeutic results in various clinical applications. The purpose of this review is to focus on the clinical pharmacology and therapeutic application of creatine supplementation. Creatine is a naturally occurring compound obtained in humans from endogenous production and consumption through the diet. When supplemented with exogenous creatine, intramuscular and cerebral stores of creatine and its phosphorylated form, phosphocreatine, become elevated. The increase of these stores can offer therapeutic benefits by preventing ATP depletion, stimulating protein synthesis or reducing protein degradation, and stabilizing biological membranes. Evidence from the exercise literature has shown athletes benefit from supplementation by increasing muscular force and power, reducing fatigue in repeated bout activities, and increasing muscle mass. These benefits have been applied to disease models of Huntington's, Parkinson's, Duchenne muscular dystrophy, and applied clinically in patients with gyrate atrophy, various neuromuscular disorders, McArdle's disease, and congestive heart failure. This review covers the basics of creatine synthesis and transport, proposed mechanisms of action, pharmacokinetics of exogenous creatine administration, creatine use in disease models, side effects associated with use, and issues on product quality. From the full text article: A. Synthesis Creatine (-methyl guandino-acetic acid) is distributed throughout the body with 95% of Cr found in skeletal muscle (Walker, 1979). The remaining 5% of the creatine pool is located in the brain, liver, kidney, and testes (Walker, 1979). Cr is obtained through the diet (~1 g/day for an omnivorous diet) and synthesized in the liver, kidney, and pancreas (~1 g/day). The majority of synthesis in humans occurs in the liver and kidney (Walker, 1979; Wyss and Kaddurah-Daouk, 2000). The dietary intake and endogenous production of Cr matches the spontaneous degradation of phosphocreatine (PCr) and Cr to creatinine at a rate of 2.6% and 1.1% per day, respectively (Walker, 1979). Therefore, creatinine production from Cr and PCr sums to 2 g/day or 0.017/day of total body Cr (Cr + PCr) based on a 70-kg human and a total Cr (tCr) pool of 120 g (Walker, 1979). Once creatinine is formed it enters circulation by diffusion and is eliminated from the body through glomerular filtration. Supplementation of Cr has been shown to reduce endogenous production in humans; however, normal rates return upon termination of supplementation (Walker, 1979). Circulating levels of creatinine also increase with supplementation (Kamber et al., 1999; Schedel et al., 1999; Volek et al., 2000). Cr is derived from glycine and arginine by the formation of guanidinoacetate and ornithine in a reaction catalyzed by arginine:glycine amidino-transferase (AGAT) (Walker, 1979; Wyss and Kaddurah-Daouk, 2000). It is theorized that guanidinoacetate is formed in the kidney and transferred via the blood to the liver (Wyss and Kaddurah-Daouk, 2000). In the liver, the methyl group from methionine, found as S-adenosylmethionine, is donated to guanidinoacetate by S-adenosylmethionine:guanidinoacetate N-methyltransferase (GAMT) (Walker, 1979; Wyss and Kaddurah-Daouk, 2000). The rate-limiting step in Cr synthesis is the formation of guanidinoacetate by AGAT (Walker, 1979; Wyss and Kaddurah-Daouk, 2000). Cr is capable of feedback inhibition of AGAT possibly by inhibiting steps before translation of AGAT mRNA (Walker, 1979; Wyss and Kaddurah-Daouk, 2000). Other factors that have been shown to regulate Cr synthesis include thyroid hormone, growth hormone, testosterone, ornithine, and dietary deficiencies (e.g., fasting, vitamin E) (Walker, 1979; Wyss and Kaddurah-Daouk, 2000). Figure 1 is a simplistic representation of Cr synthesis and degradation. B. Transporters In the body, there is little Cr found at the site of production, and therefore Cr must be transported from areas of synthesis to areas of storage and utilization. Typically, organs that contain the highest levels of AGAT and/or GAMT have the lowest levels of creatine kinase, the enzyme responsible for the phosphorylation of Cr to PCr (Walker, 1979). Since Cr is only produced in certain organs and utilized in others, it must enter the blood to reach other tissue systems such as skeletal muscle. The cellular uptake of Cr by organs is critical due to the potential down-regulation of these systems with chronic exposure to Cr (Guerrero-Ontiveros and Wallimann, 1998). Once in the blood, Cr is transported into tissues against a concentration gradient through a sodium- and chloride-dependent transporter (CreaT). CreaT is similar to the transporters for dopamine, guanidino γ-aminobutyric acid, and taurine (Guerrero-Ontiveros and Wallimann, 1998). The location of expression of these transporters matches that of creatine kinase expression because the mRNA for CreaT has been found in kidney, heart, skeletal muscle, brain, testis, and colon, but not in the liver, pancreas, and intestine (Guimbal and Kilimann, 1993; Nash et al., 1994; Sora et al., 1994). The Km for CreaT ranges from 20 to 160 µM depending on species and location of transporter (i.e., red blood cell, macrophage, muscle fiber type) (Ku and Passow, 1980; Loike et al., 1986; Moller and Hamprecht, 1989; Guimbal and Kilimann, 1993; Schloss et al., 1994; Sora et al., 1994; Willott et al., 1999). Blood levels of Cr vary between species with rat > mouse > rabbit > human (Marescau et al., 1986). Table 1 summarizes the blood levels and Km of Cr transporters in various species. The content of tCr is dependent on the skeletal muscle fiber type. Type 2 fibers have higher levels of Cr and PCr (Meyer et al., 1985; Kushmerick et al., 1992; Casey et al., 1996). Rodent Type 2a and 2b fibers contain ~32 mM PCr and 7 mM Cr and the EDL, a Type 2 fiber-rich muscle, has a higher Km (160 µM) and higher Vmax (100 nmol h_1 g wet weight) compared with the Type 1 fiber-rich soleus. Type 1 fibers in rodents have ~16 mM PCr and 7 mM Cr and the Type 1 fiber-rich soleus has a Km = 73 µM and a Vmax = 77 nmol h_1 g wet weight (Kushmerick et al., 1992; Willott et al., 1999). Therefore, Cr uptake is muscle fiber-type dependent. In humans, intramuscular levels of Cr have been found to be ~125 mmol kg_1 dry muscle (DM) with ~60% of tCr in the form of PCr (Harris et al., 1992; Balsom et al., 1995; Casey et al., 1996; Hultman et al., 1996). For example, Hultman et al. found tCr levels in humans of 123 mmol kg_1 DM of which 80.36 mmol kg_1 DM was PCr (~65%) and 43.01 mmol kg_1 DM was Cr (~35%). In general, human muscle tCr levels can range from 110 to 160 mmol kg_1 DM (Harris et al., 1974). Catecholamines, insulin-like growth factor 1 (IGF-1), insulin, and exercise can influence the net uptake of Cr into skeletal muscle. Odoom et al. (1996) used a G8 mouse skeletal muscle cell line to study the effects of α- and β-agonists, IGF-1, and insulin on Cr uptake. Thyroid hormone (T3) increased tCr content up to 3-fold relative to controls, and IGF-1 increased tCr content by 40 to 60% relative to controls. Insulin at 3 nM stimulated tCr accumulation by 2.3-fold relative to control. Other studies have shown that both insulin and carbohydrate increase tCr accumulation in both humans and rodents (Haugland and Chang, 1975; Green et al., 1996a,b; Steenge et al., 1998, 2000). In the G8 cell line, the nonspecific β-agonist isoproterenol increased tCr content 40 to 60%, which is similar to that of the nonspecific α-,β-agonist norepinephrine. The α1-agonist methoxamine decreased tCr content by 30% whereas the β2-agonist clenbuterol increased tCr content by 30%. The β-antagonists (i.e., atenolol, butoxamine, and propranolol) caused a slight reduction (<10%) in tCr content. Exercise has also shown stimulatory effects on Cr uptake (Harris et al., 1992; Robinson et al., 1999). Harris supplemented human subjects with Cr (4 × 5 g for 3-5 days) followed by one-legged cycle ergometry (Harris et al., 1992). The tCr in the exercised leg increased from 118.1 mmol kg_1 DM to 162.2 mmol kg_1 DM (~37% increase) with 103.1 mmol kg_1 DM as PCr. The control leg increased from 118.1 mmol kg_1 DM to 148.5 mmol kg_1 DM (~25% increase) with 93.8 mmol kg_1 DM of PCr. It was hypothesized that increased uptake resulted from enhanced blood flow, but changes in transport kinetics were not ruled out. It is possible the exercise may increase the translocation of CreaT to the muscle membrane similar to effects seen between exercise and GLUT-4 translocation (Thorell et al., 1999). III. Mechanisms of Action Cr exerts various effects upon entering the muscle. It is these effects that elicit improvements in exercise performance and may be responsible for the improvements of muscle function and energy metabolism seen under certain disease conditions. Several mechanisms have been proposed to explain the increased exercise performance seen after acute and chronic Cr intake. A. Energy Metabolism Adenosine triphosphate (ATP) concentrations maintain physiological processes and protect tissue from hypoxia-induced damage. Cr is involved in ATP production through its involvement in PCr energy system. This system can serve as a temporal and spatial energy buffer as well as a pH buffer. As a spatial energy buffer, Cr and PCr are involved in the shuttling of ATP from the inner mitochondria into the cytosol (Meyer et al., 1984; Bessman and Carpenter, 1985). In the reversible reaction catalyzed by creatine kinase, Cr and ATP form PCr and adenosine diphosphate (ADP) (Fig. 2). It is this reaction that can serve as both a temporal energy buffer and pH buffer. The formation of the polar PCr "locks" Cr in the muscle and maintains the retention of Cr because the charge prevents partitioning through biological membranes (Greenhaff, 1997) (Fig. 2). At times during low pH (viz., during exercise when lactic acid accumulates), the reaction will favor the generation of ATP. Conversely, during recovery periods (e.g., periods of rest between exercise sets) where ATP is being generated aerobically, the reaction will proceed toward the right and increase PCr levels. This energy and pH buffer is one mechanism by which Cr works to increase exercise performance. Finally, Cr is also involved in regulating glycolysis. When humans and animals are depleted of tissue Cr, they adapt by increasing oxidative enzymes such as mitochondrial creatine kinase (O'Gorman et al., 1996), succinate dehydrogenase (Ren et al., 1993; O'Gorman et al., 1996), citrate synthase (Ren et al., 1993), and GLUT-4 glucose transporters (Ren et al., 1993). All of these proteins are involved in aerobic metabolism and can offset the lack of anaerobic energy supplied by the PCr system. Little information is available on whether enzyme activities are affected by increasing intracellular Cr stores. One study by Brannon et al. (1997) found citrate synthase activity increased in the soleus but not the plantaris in rodents supplemented with 3.3 mg of Cr per gram of diet. PCr and inorganic phosphate may also regulate energy processes by inhibiting the enzymes glycogen phosphorylase a, phosphofructokinase, pyruvate kinase, and lactate dehydrogenase (Wyss and Kaddurah-Daouk, 2000). However, the control of PCr on these enzymes has come under debate since the PCr used in these studies contained impurities like inorganic pyrophosphate (Wyss and Kaddurah-Daouk, 2000). B. Protein Synthesis One beneficial effect of Cr supplementation in young, healthy males is enhanced muscle fiber size and increased lean body mass. Typically, Cr loading of 20 g/day for 4 to 28 days in humans increases total body mass from 1 to 2 kg (Balsom et al., 1993; Greenhaff et al., 1994; Earnest et al., 1995; Green et al., 1996a; Vandenberghe et al., 1997; Kreider et al., 1998; Maganaris and Maughan, 1998; McNaughton et al., 1998; Snow et al., 1998) with increases coming from fat-free mass (Vandenberghe et al., 1997; Kreider et al., 1998; Volek et al., 1999; Becque et al., 2000; Mihic et al., 2000). Volek et al. (1999) found after 12 weeks of resistance training in men, Cr supplementation increased muscle fiber diameter in both Type 1 and Type 2 muscle fibers by 35% (Fig. 3). Resistance-trained subjects not supplemented with Cr had fiber-type increases of 6 to 15%. Subjects both trained and supplemented had fat-free mass increases of 1.5 kg after 1 week and 4.3 kg after 12 weeks compared with the trained-only group that had a fat-free mass increase of 2.1 kg after 12 weeks. Sipila et al. (1981) found a 42% increase in Type 2 muscle fibers after 1 year of supplementation of 1.5 g/day in patients with gyrate atrophy without resistance training. The increases in muscle mass may result from increased protein synthesis or reduced protein catabolism. Studies using cell culture by Ingwall and colleagues (Ingwall et al., 1972, 1974, 1975; Ingwall, 1976; Ingwall and Wildenthal, 1976) support the theory that exogenous Cr can increase protein synthesis both in vitro and in vivo. It was hypothesized by the authors that Cr, an end-product of contraction, may serve as a stimulus of protein synthesis and muscle hypertrophy. They found the rate of myosin and actin synthesis in chick embryo myoblasts increased in the presence of Cr, but the degradation rate of the muscle proteins remained unchanged. However, using a similar model to Ingwall, Fry and Morales (1980) did not find an effect of Cr on protein synthesis in cell culture. Recently, Tarnopolsky's group (Parise et al., 2000) reported measuring protein synthesis using whole body leucine kinetics and mixed muscle fractional protein synthetic rates during Cr supplementation in humans. They found no increase in protein synthesis, but a possible decrease in protein catabolism. The results from cell culture and the human study offer conflicting results as far as the role of Cr and regulation of protein metabolism. The equivocal results from cell culture may be the result of small changes in culture conditions or the method by which protein synthetic rates were determined. Future research should focus on humans especially with respect to changes in myosin and actin metabolism in Type 2 muscle fibers. The regulation of protein metabolism by an osmotic agent like Cr is supported by studies investigating the effect of cell swelling on protein synthesis. When Cr accumulates in cells, water drag occurs and increases cell hydration. Hyperhydration can act as an anabolic signal stimulating protein synthesis (Haussinger et al., 1994) or the hypo-osmolality can act as a protein-sparing signal and reduce protein degradation (Berneis et al., 1999). This theory of Cr-induced hydration affecting protein synthesis is still under debate because it has not been directly investigated. Another mechanism by which Cr may increase muscle mass is Cr may be involved in satellite cell activity (Dangott et al., 2000). Dangott and colleagues examined the effect of Cr on compensatory hypertrophy in the rodent. There was no difference between supplemented and unsupplemented groups with regard to muscle mass and fiber diameter for muscles that underwent compensatory hypertrophy. The combination of Cr and increased functional loading did increase satellite cell mitotic activity. C. Membrane Stabilization Cr can potentially prevent tissue damage by two possible mechanisms. The first mechanism involves stabilization of cellular membranes and the second involves maintenance of ATP. Cr, more specifically PCr, may stabilize membranes due to the zwitterion nature of PCr with negatively charged phosphate and positively charged guanidino groups. PCr binds to the phospholipid head groups and thus decreases membrane fluidity and decreases loss of cytoplasmic contents such as intracellular enzymes (e.g., creatine kinase). Sharov et al. (1987) administered PCr to attenuate ischemic damage to cardiomyocytes of rabbit. They found that PCr decreased the elevation in inulin diffusable space seen in untreated cardiomyocytes indicating maintenance of membrane integrity and reduced necrotic zone size (Fig. 4). Recently studies have examined whether Cr supplementation would reduce exercise-induced muscle damage. No difference was found in the indirect indicators of muscle damage in a double-blind placebo study in males between the Cr supplement groups and unsupplemented control (Rawson et al., 2001). However, oxidative damage markers were not measured, and it may be possible that Cr attenuated oxidative stress by maintaining mitochondrial energy homeostasis. The second mechanism of protection relates to ATP production. In cases of transient ischemia, the ability to generate ATP through oxidative pathways is reduced resulting in cell damage. Since Cr supplementation increases PCr, there is a higher reserve of ATP, thus providing the energy until eupoxic conditions are re-established. A. Dosing Currently, manufacturer's instructions and athletes' use of Cr follows a dosing regimen of a "loading" phase of 20 g/day (4 × 5 g) for 5 days and a maintenance dose of 3 to 5 g/day. Investigators have found that intramuscular tCr levels increase from 17 to >20% with a dosing regimen of 20 to 30 g for 2 or more days (Harris et al., 1992; Greenhaff et al., 1994; Balsom et al., 1995; Febbraio et al., 1995; Gordon et al., 1995; Hultman et al., 1996). It has also been reported that up to 20% of this increase is due to PCr (Harris et al., 1992; Gordon et al., 1995; Casey et al., 1996; Hultman et al., 1996; Vandenberghe et al., 1997, 1999). However, there does appear to be an upper limit of intramuscular tCr content at ~160 mmol kg_1 of DM (Harris et al., 1992; Casey et al., 1996). Similar intramuscular PCr levels from this dosing regiment can be accomplished by taking 3 g/day over 30 days (Hultman et al., 1996). After ~2 days of loading, maximal accumulation of intramuscular Cr occurs and therefore amounts of >20 g/day are unnecessary (Terjung et al., 2000). The maximal accumulation of intramuscular tCr in humans is reflected in the progressive increase in urinary Cr with continuous Cr ingestion (Harris et al., 1992; Vandenberghe et al., 1997; Bermon et al., 1998; Maganaris and Maughan, 1998). Cr levels in humans can remain elevated for up to 1 month post-supplementation (Febbraio et al., 1995; Hultman et al., 1996). Clinical studies have used different dosing regimens than those previously mentioned in the exercise literature. Table 2 describes some dosing regimens used in the literature in human subjects for exercise and treatment of disease. These differences in dosing amount and duration need to be addressed to better understand the regulation of endogenous synthesis of Cr and regulation of transporters.
B. Absorption and Distribution Cr is administered orally either as a solution or solid dosage form. Oral absorption of Cr is determined by physicochemical properties of the molecule as well as splanchnic blood flow. Drugs and nutrients can pass through the gastrointestinal tract epithelia into the blood by diffusion, active transport, facilitated transport, or through paracellular pathways. Because Cr is structurally similar to basic amino acids (e.g., arginine, lysine), Cr may enter systemic circulation through the amino acid transporter, peptide transporters, or specialized transporters (i.e., taurine). Cr may also enter systemic circulation through the paracellular pathway. Creatinine has a molecular weight of 113, a net positive charge at intestinal pH, and a partition coefficient of 1.8, which allows it to move paracellularly through Caco-2 monolayers and diffuse through biological membranes (Karlsson et al., 1999). Cr has a molecular weight of 131, a net positive charge, and an estimated partition coefficient of 2.7 and therefore should also cross through via the paracellular pathway. However, in a preliminary investigation, Cr was found to have very poor movement through the Caco-2 monolayer (Dash et al., 1999). This lack of movement could be caused by a lack of amino acid transporters specific for Cr or may indicate a lack of importance of paracellular transport in Cr absorption. Oral administration of low doses of Cr in humans (1-10 g) show a time of maximal plasma concentration (Tmax) of <2 h (Harris et al., 1992; Green et al., 1996b; Schedel et al., 1999). At doses above 10 g, Tmax increases to >3 h (Schedel et al., 1999). Once in the vasculature, Cr distributes into red blood cells, white blood cells, skeletal muscle, brain, cardiac muscle, spermatozoa, and the retina (Wyss and Kaddurah-Daouk, 2000). Because of low aqueous solubility (~13 mg ml1 water) and a low partition coefficient, the apparent volume of distribution should probably not exceed total body water. Protein and tissue binding also determine the volume of distribution; however, there currently is no data on the extent of protein binding. C. Clearance Cr can be eliminated from the blood via two parallel pathways. The first pathway is a saturable uptake into various organs and cells. The second pathway is renal elimination. As mentioned earlier, insulin, catecholamines, exercise, and IGF-1 can affect Cr uptake by the Na+-Cl-dependent transporter. Therefore, clearance of Cr from the blood is dependent on intramuscular tCr levels, hormone levels, muscle mass, and kidney function [glomerular filtration rate (GFR)]. Pitts (1934) found that Cr is excreted at rates equivalent to that of xylose in humans, indicating renal elimination of Cr may be equivalent to GFR. However, Sims and Seldin (1949) found that Cr is reabsorbed in the kidney, which may explain the lack of Cr found in urine under healthy, unsupplemented conditions. This finding supports evidence that CreaT is found in the kidney and may serve to reabsorb Cr from the urine (Wyss and Kaddurah-Daouk, 2000). D. Pharmacokinetic Studies To date, much of the work on Cr has focused on the pharmacological effects rather than on characterizing the pharmacokinetics. Of the studies that examined the behavior of Cr in blood, none have truly characterized the pharmacokinetics except for Cmax and Tmax thus leaving a gap in the research. Despite the lack of pharmacokinetic interpretation, these studies can serve as a basis for future work on Cr pharmacokinetics. To truly understand the pharmacokinetics of Cr, data are needed after an intravenous bolus dose. Although some studies have administered Cr as an intravenous infusion in humans (Crim et al., 1976) there is only one available intravenous bolus study from Fitch and Sinton (1964). Small amounts of 14C-Cr (2-60 µCi or 0.1-3 mg) were given as an intravenous bolus to five patients with various muscular disorders and followed over time. The half-life of 14C-Cr in plasma was calculated to be 20 to 70 min. It appears the Cr follows a one-compartment body model. However, two of the five patients exhibited a slight distribution phase of less than 40 min. Unfortunately, there is insufficient data at early time points to fully understand the profile after intravenous bolus administration. Clinically, the two patients that had a distribution phase were two of the oldest patients in the study (43 and 77 years of age) and also had two of the heavier body weights (63 and 100 kg). It is unknown how age or body weight would influence Cr pharmacokinetics. Harris et al. (1992) investigated blood concentrations over time after oral administration of Cr monohydrate in young and middle-aged humans (ages 28-62 years). After a single 5-g dose, plasma Cr reached a mean Cmax of approximately 100 mg l1 at a Tmax of 1 h. In another human study, Green et al. (1996b) investigated the effect of carbohydrate ingestion on plasma Cr levels at day 1 and day 3 of a 2-day, 20 g/day regimen. Following a 5-g dose on day 1, plasma Cr reached a Cmax of 170 mg l_1 at a Tmax of 50 min. When 5 g of Cr was ingested with 500 ml of an 18.5% w/v glucose simple sugar solution, the Cmax for plasma Cr was 80 mg l_1 and the Tmax was 90 min. The addition of carbohydrate during administration on day 1 caused over a 3-fold reduction in the AUC of plasma Cr. This reduction has been attributed to enhanced removal of Cr from blood caused by the stimulatory effect of insulin on Cr uptake by skeletal muscle. On day 3 after a 5-g dose, plasma Cr had a Cmax of 234 mg 1_1 at a Tmax of 50 min, a nonsignificant 37% increase in Cmax. Interestingly, Green found a nonsignificant ~7% difference in AUC between day 1 and day 3 in the Cr without carbohydrate group. This lack of difference was probably caused by incomplete elimination of Cr from the blood on day 3. On day 1, plasma Cr reached near baseline by 270 min; however, at day 3, plasma Cr was 7 times higher than baseline at 270 min. These data suggest reduced volume of distribution after 2 days of 20 g/day Cr administration. Steenge et al. (1998) also tested the effects of insulin on plasma Cr in humans. In their study, 100 mM Cr was administered as an enteral infusion at 2.5 ml min1 with an intravenous insulin infusion at varying rates. Peak Cr levels were reached 1 to 1.5 h after start of infusion. A decrease of 20% in plasma Cr AUC was shown to be dependent on insulin infusion rate. Based on the work of Odoom et al. (1996) on the stimulatory effects of -agonists on Cr uptake, Vanakoski et al. (1998) investigated the pharmacokinetics of Cr with and without caffeine ingestion. Following 3 days of 3 × 100 mg kg_1 (~15 g/day) Cr ingestion, a single dose of 100 mg kg_1 (6-7 g) was administered for pharmacokinetic analysis. Cr had a Cmax of 160 mg l_1 at a Tmax of 92 min and a terminal half-life of 172 min. The concomitant administration of caffeine had no statistically significant effect on Cr pharmacokinetics. Because the pharmacokinetics were calculated after 3 days of loading, this profile may be more indicative of steady-state rather than single-dose pharmacokinetics. Additionally, this was a double-blind, placebo-controlled crossover design study with 1 week washout between treatments. This would further conflict the pharmacokinetic data because elevated muscle tCr levels can last up to 28 days, and as such, accumulation could confound results by changing volume of distribution. Recently, Schedel et al. (1999) administered increasing doses and measured plasma Cr over time. They found larger doses lead to longer absorption times, as a single 20-g dose demonstrated an absorption phase even after 4 h. Dr. E. S. Rawson (personal communication) recently compared blood levels of Cr after a 5-g dose in young healthy males and elderly healthy males. They found no difference in pharmacokinetic parameters between groups but found that intramuscular PCr levels in elderly males did not increase with supplementation. The lack of an increase in intramuscular PCr levels seen in this study supports this group's work with supplementation in the elderly in that exercise performance in the elderly does not increase with Cr supplementation. It is very difficult to compare/contrast studies of Cr pharmacokinetics due to differences in the study design (dose, single versus after multiple doses or infusion), Cr products, and method of analysis (photometric, enzyme, high performance liquid chromatography). It is difficult to determine whether Cr pharmacokinetics is dose-dependent; however, the data by Schedel et al. (1999) indicate this possibility. The dose dependence can be caused by transporter-based uptake into muscle or transporter-based uptake from the gastrointestinal tract. As mentioned earlier, the reported studies are incomplete in the pharmacokinetic analysis, and further research is needed to establish standard pharmacokinetic parameters. V. Therapeutic Usage Although the majority of studies on Cr have been on exercise performance in healthy subjects, recent evidence indicates Cr may be useful in the treatment of certain diseases. Patients with diseases that result in atrophy or muscle fatigue secondary to impaired energy production may benefit from Cr supplementation. The true mechanisms by which Cr can be effective in these diseases are unclear but the theorized mechanisms of increased energy in the form of PCr, increased muscle accretion, and stabilization of membranes may be influential as discussed previously. Research has recently focused on the clinical application of Cr in rodents and humans, and therefore there is a limited amount of information available on the relationship between the rodent studies and human studies. Although studies involving rodents offer credence in the therapeutic use of Cr, the results may not fully explain the usefulness in humans. Rodents typically have a higher blood Cr level than humans (Marescau et al., 1986) and do not respond to supplementation in the same manner that humans respond. For example, rats fed a 3% Cr diet for 40 days showed little increase in skeletal muscle tCr levels with large increases in tCr in liver and kidney (Horn et al., 1998). Therefore, the distribution processes in the rodent may differ from humans and may cause some differences in Cr application. A. Exercise Performance The initial studies on Cr supplementation in the 1990s in humans focused on exercise performance, which served as a basis for subsequent clinical research and applications. As mentioned earlier, supplementation increases intramuscular tCr content. The increase in Cr in young healthy males has been shown to enhance anaerobic exercise performance by increasing power output (Earnest et al., 1995), muscular strength and work (Casey et al., 1996; Vandenberghe et al., 1997; Volek et al., 1999), and muscle fiber size (Volek et al., 1999). Studies have also been performed on young healthy females, middle-aged males (30-60 years of age), and the elderly (>60 years of age). Both females (Vandenberghe et al., 1997) and middle-aged males (Smith et al., 1998) benefited from Cr supplementation, but the elderly did not show an exercise performance enhancement (Bermon et al., 1998; Rawson et al., 1999; Rawson and Clarkson, 2000). The lack of an effect in the elderly may be explained by changes in transporter density associated with aging and decreased Cr uptake. The American College of Sports Medicine recently had a roundtable discussion on the physiological and health effects of Cr supplementation (Terjung et al., 2000). Performance has been enhanced in swimming, all-out cycling, sprinting, repeated jumping, and resistance training (Juhn and Tarnopolsky, 1998a). The greatest improvements in performance have been found in series, high-power output exercises and the latter exercise bouts of a series (Terjung et al., 2000). Those activities that are repetitive in nature and those of high-energy output, which would stress the PCr system, would likely benefit from Cr supplementation (Terjung et al., 2000). B. Gyrate Atrophy 1. Human Studies. Gyrate atrophy (GA) is an autosomal recessive error that causes hyperornithinaemia and leads to chorioretinal degeneration and atrophy of Type 2 muscle fibers (Heinanen et al., 1999b). GA patients have lower levels of skeletal muscle PCr since ornithine inhibits the rate-limiting step of Cr biosynthesis (Heinanen et al., 1999b). Current therapy for GA can include diet modification to reduce plasma ornithine (Sipila et al., 1981). Sipila et al. (1981) supplemented seven patients with 1.5 g of creatine daily for 1 year. The diameters of Type 2 muscle fibers increased from 34.1 to 49.9 µm (~ 45%) without a significant increase in the diameters of Type 1 fibers. Examination of the eyes revealed a slowing of impairment at an age normally associated with rapid progression of the disease. Another prospective study followed 13 GA patients for 5 years who were treated with 0.75 to 1.5 g (depending on age) of Cr per day (Vannas-Sulonen et al., 1985). The progression of the disease was unaffected by Cr but abnormalities in skeletal muscle such as tubular aggregates and Type 2 fiber atrophy disappeared. Discontinuation of Cr therapy in these patients caused reappearance of tubular aggregates. Patients supplemented with Cr (1.5-2.0 g/day) for 8 to 15 years were found to have a greater than 1.5-fold increase in PCr/Pi ratio than patients receiving no Cr (Heinanen et al., 1999a). The supplemented group had nearly equivalent PCr/Pi levels compared with healthy age- and sex-matched controls. The PCr/ATP ratio of Cr-treated patients was also similar to healthy controls. Additionally, patients supplemented with Cr precursors guanidinoacetate and methionine had increased muscle PCr although not as high as normal controls (Heinanen et al., 1999a). C. Diseases Affecting Mitochondria Because Cr is involved in energy production and acts as a shuttle of ATP from the inner mitochondria to the cytosol, Cr was theorized to be useful in diseases of mitochondria where energy production is altered. Cr supplementation has been shown to be beneficial in diseases in which there is mitochondrial dysfunction such as Parkinson's, Huntington's, and myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). 1. Parkinson's Disease. a. Animal Studies. Parkinson's disease is an idiopathic neurodegenerative disease characterized by depletion of dopamine levels in the brain. The loss of dopaminergic neurons may be caused by energy impairment resulting in cell death. MPTP neurotoxicity is used as a model for Parkinson's. MPTP is converted to MPP+, which inhibits complex I of the electron transport chain and impairs oxidative phosphorylation and subsequent ATP production. The administration of MPTP alone results in 70% depletion in brain dopamine levels in rodents (Matthews et al., 1999). Matthews et al. (1999) used this model and found that rats fed a 1% Cr diet (w/w diet) for 2 weeks showed less than a 10% brain dopamine loss when compared with nonsupplemented animals after exposure to MPTP/MPP+. There was a dose dependence from 0.25 to 1% Cr diet; however, this protection disappeared at 2 and 3% Cr diet. Interestingly, the Cr analog cyclocreatine was also neuroprotective at concentrations of 0.25 to 1% w/w diet. Histologically, there was no significant loss of nigral neurons in the Cr-treated group. There was no explanation for the inverted U-shaped response curve in dopamine protection or whether higher doses elicited additional beneficial or toxicological effects. Reasons for the inverted U-shape may be the result of changes in CreaT density, changes in intracellular osmotic pressure, or dysfunction in energy metabolism. Additionally, no intracellular Cr, tCr, PCr, or ATP levels were measured in this study. 2. Huntington's Disease. a. Animal Studies. Huntington's disease results in the formation of lesions in the brain from an alteration in energy production. Matthews et al. (1998) used 3-nitropropionic acid (3-NP) to mimic changes in energy metabolism seen in Huntington's. 3-NP irreversibly inhibits complex II of the electron transport system and produces lesions caused by energy depletion. They reported that 1% Cr (w/w diet) after 2 weeks showed an 83% reduction in lesion volume as compared with untreated animals. Animals treated with the Cr analog cyclocreatine showed no protection and appeared to have exacerbated toxicity. Malonate can also be used to induce Huntington's-like lesions. In the same study, Matthews et al. found similar protection against malonate-induced toxicity with a U-shaped dose-response curve using a 1 and 2% Cr w/w diet demonstrating the most protection. In these studies, Cr-fed animals had higher striatal levels of PCr than control animals and Cr-treated animals exposed to 3-NP had higher levels of Cr, PCr, AMP, GDP, NAD, ATP, and lower levels of lactate than control animals treated with 3-NP. These changes would correlate with improved energy production. Cr-fed animals also showed reduced markers of oxidative damage caused by malonate or 3-NP. Again, no reason was given for the U-shaped response curve of Cr against lesion size. Ferrante et al. (2000) used the transgenic R6/2 mouse model for Huntington's disease to examine the effect of Cr. There was a U-shaped dose-dependent increase of 9.4%, 17.4% for survival in mice fed a 1 and 2%, respectively. However, only a 4.4% increase in survival was found for a 3% w/w diet of Cr. Mice supplemented with Cr also showed increased rotarod performance when fed 1 and 2% Cr but not a 3% diet. Additionally, Cr maintained brain weight, reduced striatal atrophy, reduced striatal aggregates, and delayed the onset of diabetes. A recent study by Shear et al. (2000) supports the previous studies that Cr can attenuate anatomical abnormalities induced by 3-NP as well as improve motor performance variables. 3. Other Mitochondrial Pathologies. a. Animal Studies. Other mitochondrial-related diseases can be affected by Cr supplementation. In a model for amyotrophic lateral sclerosis, GP3A transgenic mice (SOD1 mutation) had a life-span increased by 13 and 26 days when fed 1% or 2% Cr (w/w diet), respectively (Klivenyi et al., 1999). These animals also had no increase in 3-nitrotyrosine and other indicators of oxidative damage and showed increased motor performance, and Cr protected against loss of motor neurons and substantia nigra neurons. However, no levels of cellular tCr, Cr, PCr, ATP, or ADP were assessed in this study. b. Human Studies. In a large study of 81 patients, Tarnopolsky and Martin (1999) investigated Cr supplementation in various neuromuscular diseases including mitochondrial cytopathies, neuropathic disorders, dystrophies, congenital myopathies, and inflammatory myopathies. They found increases in high-intensity strength measurements such as isometric dorsiflexion, handgrip strength, and isokinetic and isometric knee strength in these patients following supplementation of 10 g/day for 5 days with 5 g/day for 5 to 7 days of maintenance. These patients also showed small but significant increases in body weight with supplementation. In the same investigation, 21 patients were supplemented in a single-blind placebo-controlled study and found results similar to that of the 81-patient study. Tarnopolsky's group also performed a short-term, randomized, crossover trial of Cr supplementation in patients with mitochondrial cytopathies (MELAS) (Tarnopolsky et al., 1997). Patients treated with Cr (2 × 5 g/day for 2 weeks with 2 × 2 g/day for 1 week of maintenance) showed a 19% increase in hand-grip strength and a reduction in post-exercise cycle ergometry blood lactate. There were no differences in body composition, maximal voluntary contraction, resting energy expenditure, oxygen consumption, or rating of perceived exertion. It was concluded that Cr increased strength and high-intensity anaerobic and aerobic activities with no effect in lower intensity aerobic activity. Most of the patients in this study were already taking vitamin E and C and coenzyme Q10 for treatment of their mitochondrial cytopathy. D. Other Brain Pathologies 1. Animal Studies. Hypoxia and energy-related brain pathologies (e.g., stroke) might benefit from Cr supplementation. Cr has been shown to protect the brainstem and hippocampus from hypoxia and that this protection may be attributable to the prevention of ATP depletion (Balestrino et al., 1999; Dechent et al., 1999; Wilken et al., 2000). Rodents supplemented with Cr (~2 g kg1 of body weight per day) showed increased brain Cr:choline levels with a slight decrease in apparent diffusion coefficient (ADC) during an acute ischemic challenge (Wick et al., 1999). ADC is associated with cytotoxic cellular swelling, and therefore a reduction in ADC may offer protection. Michaelis et al. (1999) found that Cr supplementation (~2 g kg_1 of body weight per day) showed no differences in metabolic responses after global cerebral ischemia despite increased brain tCr. Due to increases in glucose and slight reductions in lactate found in the Cr-fed group, the authors concluded that neuroprotection may occur with more focal ischemia rather than global ischemia. Cr has been found to be neuroprotective against N-methyl-D-aspartate and malonate excitotoxicity following a 1% (w/w) diet for 1 week in rats (Malcon et al., 2000). These investigators did not find protection against α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid or kainic toxicity. In either case, no dose-response relationship was established. Cr has been shown to protect hippocampal neurons from glutamate toxicity and partially protect embryonic neurons from β-amyloid toxicity (Brewer and Wallimann, 2000). This protection against β-amyloid was also seen in adult and aged neurons and therefore may attenuate the formation of senile plaques seen in Alzheimer's disease. In both cases, intracellular Cr and PCr were elevated when compared with toxin-treated neurons not supplemented with Cr. 2. Human Studies. There are few clinical data on the effect of Cr in the human brain. Stockler et al. (1994, 1996) report a treatable inborn error in Cr metabolism that causes tCr depletion in the brain and results in extrapyramidal movement disorders. Treatment with Cr in these patients restores Cr levels and improves neurologic symptoms. Other studies have found supplementation (4 × 5 g/day) for 4 weeks in human volunteers caused an 8.7% increase in brain tCr. The largest increases were seen in gray matter (4.7%), white matter (11.5%), cerebellum (5.4%), and thalamus (14.6%). Although no human studies have been done on Cr supplementation and resistance to brain injury, the increase in brain Cr may be relevant in ischemic injury similar to that seen in the rodent models. E. Muscular Disease 1. Animal Studies. Since 95% of Cr in the body is found in skeletal muscle, supplementation may be useful in treating myopathies. Duchenne's muscular dystrophy is a degenerative disease that causes mechanical instability of the sarcolemma leading to increased calcium leakage during periods of stress. Using mdx mice as a model for Duchenne's muscular dystrophy, Pulido et al. (1998) prepared a primary cell culture from hind-limb muscles. During myotube formation, cells were incubated with 20 mM Cr. After 12 to 14 days, cells were exposed to hypo-osmotic shock. Cells treated with Cr showed significantly lower intracellular calcium levels that were nearly equivalent to baseline calcium levels of control myotubes. This effect of Cr could be due to decreased sarcolemmal leakage or enhanced uptake by the sarcoplasmic reticulum. Further evidence from the Pulido study supported more of an effect on calcium uptake by sarcoplasmic reticulum Ca2+ ATPase. Intracellular PCr increased in both mdx and control myotubes with the former having a more pronounced increase. 2. Human Studies. In a double-blind crossover clinical study, Felber et al. (2000) examined Cr supplementation (10 g/day for adults and 5 g/day for children) for 8 weeks in 32 patients with various muscular dystrophies. At the end of the treatment period, the Cr group had a 3% increase in strength and a 10% increase in neuromuscular symptom score. There were no differences in clinical chemistries between groups. The authors concluded that long-term Cr supplementation in this population is needed. In other studies related to muscle, patients with rheumatoid arthritis had strength improvements after supplementation with 20 g of Cr/day for 5 days and then 2 g/day for the remaining 16 days but no change in physical functional ability or disease activity (Willer et al., 2000). This was an open study examining arthritis pre- and post-supplementation, but after supplementation there was a small increase in muscle Cr (~7%) and a decrease in both PCr (~24%) and tCr (~14.3%). The lack of change in muscle tCr may reflect the lack of change in functional ability and raises a more important question of why these patients did show the more typical increase of 20% seen in young healthy males. Patients with myophosphorylase deficiency (McArdle's disease) showed mild improvements from supplementation of 150 mg kg1 for 1 week with maintenance doses of 60 mg kg1 day1 in a placebo-controlled crossover trial (Vorgerd et al., 2000). These improvements consisted of lower self-reported severity and lower frequency of muscle pain and increased exercise performance including increased strength. Cr-treated patients showed increase in muscle PCr and increases in exercise performance during ischemia. This was the first study to examine the effects of Cr supplementation in McArdle's disease. F. Heart Disease 1. Animal Studies. The effects of Cr on cardiac tissue have been investigated. A study by Sharov et al. (1987) showed a protective effect of PCr on cardiac tissue following ischemia. Using rabbit hearts, PCr was administered intravenously either before and during cardiac artery ligation or 30 min post-ligation. These investigators found a reduction in necrotic zone under both PCr treatments compared with controls (Fig. 4). Ruda et al. (1988) found that PCr administration reduced ventricular arrhythmia after acute myocardial infarctions, but the effects of Cr on cardiac tissue are still unclear. Other studies have also shown PCr to possess anti-arrhythmic activities (Rosenshtraukh et al., 1988). Feeding Cr to healthy rats or rats after a myocardial infarction failed to increase intramuscular Cr (Horn et al., 1998). The -blocker bispropolol has been shown to increase total cardiac Cr up to 40% (Laser et al., 1996). The ability to increase Cr and related energetics in heart tissue may be one beneficial mechanism of the action of β-blocker therapy (Laser et al., 1996). Ingwall et al. (1985) have also shown that diseased myocardium has lower Cr content. Supplementation with Cr has also provided protection to cardiac tissue from metabolic stress (Constantin-Teodosiu et al., 1995) 2. Human Studies. Gordon et al. (1995) investigated the effect on ingestion of Cr in patients with congestive heart failure in a double-blind, placebo-controlled study (20 g/day for 10 days). Ejection fraction at rest and at work did not change but increased exercise performance in regard to both strength and endurance. Another study in patients with congestive heart failure showed that Cr supplementation improved skeletal muscle metabolism with reductions in ammonia and lactate accumulation (Andrews et al., 1998). Recently, Neubauer et al. (1999) showed that hearts with dilated cardiomyopathy had 50% less tCr compared with healthy hearts as well as 30% less CreaT. Cr supplementation also has been shown to lower total plasma cholesterol and triglycerides (Earnest et al., 1996). These results were similar in humans and rodents and may suggest a therapeutic benefit of Cr supplementation. G. Use of Creatine Analogs Analogs of Cr were used initially to study Cr metabolism and uptake. These analogs are currently being investigated as a treatment for Huntington's disease, anti-tumor agents, and as antiviral agents. The most commonly used analogs are β-guanidinopropionic acid and cyclocreatine. This class of compounds has been shown to inhibit replication of several viruses including human and simian cytomegaloviruses and varicella zoster virus (Lillie et al., 1994), to protect neurons from 3-NP toxicity disease (Matthews et al., 1998), and reduce tumor size (Bergnes et al., 1996). A recent article by Wyss and Kaddurah-Daouk (2000) reviews the use and potential use of Cr analogs. VI. Side Effects Side effects from Cr supplementation have been reported both anecdotally and in the scientific literature. Possible side effects of Cr supplementation have been previously reviewed by Juhn and Tarnopolsky (1998b). Briefly, Cr supplementation has been documented as being associated with weight gain, gastrointestinal distress, and renal dysfunction and anecdotally reported to cause muscle cramps and hepatic dysfunction. Typically weight gain is between 1 and 2 kg and is initially brought on by water retention, but may be maintained by changes in amount of lean body mass. Athletes generally desire this effect. Gastrointestinal distress has been reported anecdotally but little to no studies have documented nausea, vomiting, or diarrhea. This may be a function of single large doses of Cr or subsequent ingestion of large amounts of carbohydrates. Muscle cramps have been reported anecdotally, but published studies have yet to find muscle cramps associated with supplementation. In a double-blind, crossover study, subjects were supplemented with Cr at 20 g/day (4 × 5 g/day) for 5 days with a 28-day washout between treatments (Kamber et al., 1999). Supplementation had no effect on hepatic function as indicated by no changes in blood liver enzymes (i.e., creatine kinase, urea, aspartate aminotransferase, alanine aminotransferase, -glutamyl transferase, lactate dehydrogenase). This study indicates that short-term supplementation may be safe, but the effect of long-term supplementation is still unknown. Cardiovascular function as assessed by changes in systolic and diastolic blood pressure was unaffected by Cr (Mihic et al., 2000). Finally, Cr has been implicated in renal dysfunction. In two isolated cases, one patient presented with interstitial nephritis that improved upon termination of Cr use (Koshy et al., 1999), and another patient with focal glomerular sclerosis showed a reduction in GFR with Cr supplementation that returned upon termination of supplementation (Pritchard and Kalra, 1998). Before the diagnosis of focal glomerular sclerosis, the patient had relapsing steroid-responsive nephrotic syndrome and was currently on cyclosporin. It was recently found that cyclosporin inhibits Cr uptake in vitro and may explain the nephropathy brought on by Cr (Tran et al., 2000). Although these pathologies are serious, these were isolated incidences including one patient that had a history of kidney disease. Studies have shown that renal function and glomerular filtration are not effected by supplementation despite slight increases in plasma creatinine (Poortmans et al., 1997; Poortmans and Francaux, 1999). In one of these studies (Poortmans et al., 1997), subjects were self-supplementing with 2 to 30 g of Cr for 10 months to 5 years, and no changes in renal responses to creatinine, urea, or albumin were observed. It was recently hypothesized that Cr supplementation could be cytotoxic (Yu and Deng, 2000). Cr can be ultimately converted to formaldehyde and hydrogen peroxide by the reaction illustrated in Fig. 1. Formaldehyde has the potential to cross-link proteins and DNA leading to cytotoxicity. The investigators did find increased urine formaldehyde after Cr administration; however, they did not measure markers of protein or DNA cross-linking or indicators of oxidative stress VII. Products Cr products may be purchased from supermarkets, nutrition stores, and via the Internet. Because Cr falls under the Dietary Supplement Health Education Act of 1994, the Food and Drug Administration does not regulate the quality of dietary supplements but does regulate structure/function claims. Therefore, there is some concern of the quality of products available. A recent review by Benzi (2000) discusses some product quality issues, some of which are discussed briefly here. Commercial Cr is produced from the reaction of sarcosine and cyanamide. This process can yield several possible contaminants such as creatinine, dicyandamide, dihydrotrianzines, and ions such as arsenic. The ion contaminants as well as dicyandamide could be a potential health hazard. Therefore, good manufacturing practices need to be employed to protect the consumer. The ultimate goal for product quality research is to establish a monograph for the United States Pharmacopoeia (USP). [...] J Sports Med Phys Fitness. 2001 Mar. Because of assumed ergogenic effects, the creatine administration has become popular practice among subjects participating in different sports. Appropriate creatine monohydrate dosage may be considered a medicinal product since, in accordance with the Council Directive 65/65/EEC, any substance which may be administered with a view to restoring, correcting or modifying physiological functions in humans beings is considered a medicinal product. Thus, quality, efficacy and safety must characterise the substance. In addition, the European Court of Justice has held that a product which is recommended or described as having preventive or curative properties is a medicinal product even if it is generally considered as a foodstuff and even if it has no known therapeutic effect in the present state of scientific knowledge. In biochemical terms, creatine administration increases creatine and phosphocreatine muscle concentration, allowing for an accelerated rate of ATP synthesis. In thermodynamics terms, creatine stimulates the creatine-creatine kinase-phosphocreatine circuit, which is related to the mitochondrial function as a highly organised system for the control of the subcellular adenylate pool. In pharmacokinetics terms, creatine entry into skeletal muscle is initially dependent on the extracellular concentration, but the creatine transport is subsequently downregulated. In pharmacodynamics terms, the creatine enhances the possibility to maintain power output during brief periods of high-intensity exercises. In spite of uncontrolled daily dosage and long-term administration, no researches on creatine monohydrate safety in humans were set up by standardised protocols of clinical pharmacology and toxicology, as currently occurs in phases I and II for products for human use. More or less documented side effects induced by creatine monohydrate are weight gain; influence on insulin production; feedback inhibition of endogenous creatine synthesis; long-term damages on renal function. A major point that related to the quality of creatine monohydrate products is the amount of creatine ingested in relation to the amount of contaminants present. During the industrial production of creatine monohydrate from sarcosine and cyanamide, variable amounts of contaminants (dicyandiamide, dihydrotriazines, creatinine, ions) are generated and, thus, their tolerable concentrations (ppm) must be defined and made consumers known. Furthermore, because sarcosine could originate from bovine tissues, the risk of contamination with prion of bovine spongiform encephalopathy (BSE or mad-cow disease) can't be excluded. Thus, French authorities forbade the sale of products containing creatine. Creatine, as other nutritional factors, can be used either at supplementary or therapeutic levels as a function of the dose. Supplementary doses of nutritional factors usually are of the order of the daily turnover, while therapeutic ones are three or more times higher. In a subject of 70 kg with a total creatine pool of 120 g, the daily turnover is approximately of 2 g. Thus, in healthy subjects nourished with fat-rich, carbohydrate, protein-poor diet and participating in a daily recreational sport, the oral creatine monohydrate supplementation should be of the order of the daily turnover, i.e., less than 2.5-3 g per day, bringing the gastrointestinal absorption to account. In healthy athletes submitted daily to high-intensity strength or sprint training, the maximal oral creatine monohydrate supplementation should be of the order of two times the daily turnover, i.e., less than 5-6 g per day for less than two weeks, and the creatine monohydrate supplementation should be taken under appropriate medical supervision. The oral administration of more that 6 g per day of creatine monohydrate should be considered as a therapeutic intervention and should be prescribed by physicians only in the cases of suspected or proven deficiency, or in conditions of severe stress and/or injury. The incorporation of creatine into the medicinal product class is supported also by the use in pathological conditions, e.g., some mitochondrial cytopathies, the guanidinoacetate methyltransferase deficiency, etc. Curr Opin Clin Nutr Metab Care. 2000 Nov. Creatine plays a role in cellular energy metabolism and potentially has a role in protein metabolism. Creatine monohydrate supplementation has been shown to result in an increase in skeletal muscle total and phosphocreatine concentration, increase fat-free mass, and enhance high-intensity exercise performance in young healthy men and women. Recent evidence has also demonstrated a neuroprotective effect of creatine monohydrate supplementation in animal models of Parkinson's disease, Alzheimer's disease, amyotrophic lateral sclerosis, and after ischemia. A low total and phosphocreatine concentration has been reported in human skeletal muscle from aged individuals and those with neuromuscular disorders. A few studies of creatine monohydrate supplementation in the elderly have not shown convincing evidence of a beneficial effect with respect to muscle mass and/or function. Future studies will be required to address the potential for creatine monohydrate supplementation to attenuate age-related muscle atrophy and strength loss, as well as to protect against age-dependent neurodegenerative disorders such as Parkinson's disease and Alzheimer's disease. Br J Sports Med. 2000 Aug. BACKGROUND: The use of creatine (Cr) as a nutritional supplement to aid athletic performance has gained widespread popularity among athletes. However, concerns have recently been expressed over potentially harmful effects of short and long term Cr supplementation on health. METHODS: Forty eight young healthy subjects were randomly allocated to three experimental protocols aimed at elucidating any potential health risks associated with five days (20 g/day) to nine weeks (3 g/day) of Cr supplementation. Venous blood samples were collected before and after periods of Cr supplementation and were analysed for some haematological indices, and for indices of hepatic, muscular, and renal dysfunction. FINDINGS: All measured indices were well within their respective normal range at all times. Serum creatinine concentration tended to be increased the day after Cr supplementation. However, values had returned to baseline six weeks after the cessation of supplementation. These increases were probably attributable to increased creatinine production rather than renal dysfunction. No indication of impairment to the haematological indices measured, hepatic function, or muscle damage was apparent after Cr supplementation. INTERPRETATION: These data provide evidence that there are no obvious adverse effects of acute or more chronic Cr supplementation on the haematological indices measured, nor on hepatic, muscle, and renal function. Therefore there is no apparent health risk associated with Cr supplementation to healthy people when it is ingested in quantities that have been scientifically proven to increase muscle Cr stores. Arch Neurol. 2000 Jul. OBJECTIVE: To determine whether treatment with creatine can improve exercise intolerance in myophosphorylase deficiency (McArdle disease). DESIGN: Double-blind, placebo-controlled crossover study with oral creatine monohydrate supplementation. PATIENTS: Nine patients with biochemically and genetically proven McArdle disease were treated. INTERVENTION: Five days of daily high-dose creatine intake (150 mg/kg body weight) were followed by daily low-dose creatine intake (60 mg/kg). Each treatment phase with creatine or placebo lasted 5 weeks. MAIN OUTCOME MEASURES: The effect of treatment was estimated at the end of each treatment phase by recording clinical scores, ergometer exercise test results, phosphorus 31 nuclear magnetic resonance spectroscopy, and surface electromyography. RESULTS: Of 9 patients, 5 reported improvement of muscle complaints with creatine. Force-time integrals (P =.03) and depletion of phosphocreatine (P =.04) increased significantly during ischemic exercise with creatine. Phosphocreatine depletion also increased significantly during aerobic exercise (P =.006). The decrease of median frequency in surface electromyograms during contraction was significantly larger (P =.03) with creatine. CONCLUSION: This is the first controlled study indicating that creatine supplementation improves skeletal muscle function in McArdle disease. Sports Med. 2000 Sep. The consumption of oral creatine monohydrate has become increasingly common among professional and amateur athletes. Despite numerous publications on the ergogenic effects of this naturally occurring substance, there is little information on the possible adverse effects of this supplement. The objectives of this review are to identify the scientific facts and contrast them with reports in the news media, which have repeatedly emphasised the health risks of creatine supplementation and do not hesitate to draw broad conclusions from individual case reports. Exogenous creatine supplements are often consumed by athletes in amounts of up to 20 g/day for a few days, followed by 1 to 10 g/day for weeks, months and even years. Usually, consumers do not report any adverse effects, but body mass increases. There are few reports that creatine supplementation has protective effects in heart, muscle and neurological diseases. Gastrointestinal disturbances and muscle cramps have been reported occasionally in healthy individuals, but the effects are anecdotal. Liver and kidney dysfunction have also been suggested on the basis of small changes in markers of organ function and of occasional case reports, but well controlled studies on the adverse effects of exogenous creatine supplementation are almost nonexistent. We have investigated liver changes during medium term (4 weeks) creatine supplementation in young athletes. None showed any evidence of dysfunction on the basis of serum enzymes and urea production. Short term (5 days), medium term (9 weeks) and long term (up to 5 years) oral creatine supplementation has been studied in small cohorts of athletes whose kidney function was monitored by clearance methods and urine protein excretion rate. We did not find any adverse effects on renal function. The present review is not intended to reach conclusions on the effect of creatine supplementation on sport performance, but we believe that there is no evidence for deleterious effects in healthy individuals. Nevertheless, idiosyncratic effects may occur when large amounts of an exogenous substance containing an amino group are consumed, with the consequent increased load on the liver and kidneys. Regular monitoring is compulsory to avoid any abnormal reactions during oral creatine supplementation. Neurology. 2000 May 9. The authors assessed the safety and efficacy of creatine monohydrate (Cr) in various types of muscular dystrophies in a double-blind, crossover trial. Thirty-six patients (12 patients with facioscapulohumeral dystrophy, 10 patients with Becker dystrophy, 8 patients with Duchenne dystrophy, and 6 patients with sarcoglycan-deficient limb girdle muscular dystrophy) were randomized to receive Cr or placebo for 8 weeks. There was mild but significant improvement in muscle strength and daily-life activities by Medical Research Council scales and the Neuromuscular Symptom Score. Cr was well tolerated throughout the study period. Neurol Res. 2000 Mar. The decrease in intracellular creatine concentration in Duchenne muscular dystrophy may contribute to the deterioration of intracellular energy homeostasis and may thus be one of the factors aggravating muscle weakness and degeneration. Oral creatine supplementation should have potential in alleviating the clinical symptoms. To test this hypothesis, creatine was orally administered over a period of 155 days to a 9-year-old patient with Duchenne muscular dystrophy. In accordance with previous investigations on normal subjects and trained athletes, the patient experienced improved muscle performance during creatine supplementation. Further evidence supporting this hypothesis derived from plasma creatine kinase and lactate dehydrogenase activities and repeated 31P magnetic resonance spectroscopy of the gastrocnemius muscle. These preliminary observations indicate a potential role for creatine supplementation in the symptomatic therapy of patients with muscle disease. J Am Pharm Assoc (Wash). 1999 Nov-Dec. OBJECTIVE: To provide an overview of the data on the efficacy and safety of the nutritional supplement creatine. DATA SOURCES: Human studies in English in MEDLINE, Current Contents, BIOSIS, Science Citation Index, and the popular media (including a LEXIS-NEXIS search and information from the World Wide Web and lay media) for 1966 to July 1999 using the search terms creatine, creatine supplement#, creatine monophosphate, and creatine NOT kinase. DATA SYNTHESIS: Creatine use is common among professional athletes. Its use has spread to college athletes, recreational athletes, and even children. Most creatine supplement regimens include a loading dose of 20 to 30 grams divided in 4 equal doses for 5 to 7 days, followed by a 2 gram per day maintenance dose. The increased creatine in the muscle may allow larger stores of phosphocreatine to build, and provide extra energy in the form of adenosine triphosphate. Despite the many clinical trials, high-quality research is lacking. Laboratory investigations of endurance isotonic exercises, strength and endurance during isotonic exercises, isokinetic torque, isometric force, and ergometer performance have yielded roughly an equal number of published studies showing a positive effect or lack of effect. Field studies (i.e., on subjects participating in sports activities) are less impressive than laboratory studies. Performance was more often improved for short-duration, high-intensity activities. Reports have linked creatine to weight gain, cramping, dehydration, diarrhea, and dizziness. Creatine may decrease renal function, but only two case reports of this effect have been published. Creatine appears to be well tolerated in short-term trials. CONCLUSION: While creatine may enhance the performance of high-intensity, short-duration exercise, it is not useful in endurance sports. Because commercially marketed creatine products do not meet the same quality control standards of pharmaceuticals, there is always a concern of impurities or doses higher or lower than those on the labeling. Consumers should balance the quality of information supporting the use of creatine with the known and theoretical risks of using the product, including possible renal dysfunction. Mol Cell Biochem. 1998 Jul. Interest in creatine (Cr) as a nutritional supplement and ergogenic aid for athletes has surged over recent years. After cellular uptake, Cr is phosphorylated to phosphocreatine (PCr) by the creatine kinase (CK) reaction using ATP. At subcellular sites with high energy requirements, e.g. at the myofibrillar apparatus during muscle contraction, CK catalyzes the transphosphorylation of PCr to ADP to regenerate ATP, thus preventing a depletion of ATP levels. PCr is thus available as an immediate energy source, serving not only as an energy buffer but also as an energy transport vehicle. Ingestion of creatine increases intramuscular Cr, as well as PCr concentrations, and leads to exercise enhancement, especially in sprint performance. Additional benefits of Cr supplementation have also been noticed for high-intensity long-endurance tasks, e.g. shortening of recovery periods after physical exercise. The present article summarizes recent findings on the influence of Cr supplementation on energy metabolism, and introduces the Cr transporter protein (CreaT), responsible for uptake of Cr into cells, as one of the key-players for the multi-faceted regulation of cellular Cr homeostasis. Furthermore, it is suggested that patients with disturbances in Cr metabolism or with different neuro-muscular diseases may benefit from Cr supplementation as an adjuvant therapy to relieve or delay the onset of symptoms. Although it is still unclear how Cr biosynthesis and transport are regulated in health and disease, so far there are no reports of harmful side effects of Cr loading in humans. However, in this study, we report that chronic Cr supplementation in rats down-regulates in vivo the expression of the CreaT. In addition, we describe the presence of CreaT isoforms most likely generated by alternative splicing. Muscle Nerve. 1997 Dec. Fatigue in patients with mitochondrial cytopathies is associated with decreased basal and postactivity muscle phosphocreatine (PCr). Creatine monohydrate supplementation has been shown to increase muscle PCr and high-intensity power output in healthy subjects. We studied the effects of creatine monohydrate administration (5 g PO b.i.d. x 14 days --> 2 g PO b.i.d. x 7 days) in 7 mitochondrial cytopathy patients using a randomized, crossover design. Measurements included: activities of daily living (visual analog scale); ischemic isometric handgrip strength (1 min); basal and postischemic exercise lactate; evoked and voluntary contraction strength of the dorsiflexors; nonischemic, isometric, dorsiflexion torque (NIDFT, 2 min); and aerobic cycle ergometry with pre- and post-lactate measurements. Creatine treatment resulted in significantly (P < 0.05) increased handgrip strength, NIDFT, and postexercise lactate, with no changes in the other measured variables. We concluded that creatine monohydrate increased the strength of high-intensity anaerobic and aerobic type activities in patients with mitochondrial cytopathies but had no apparent effects upon lower intensity aerobic activities. |
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