Research Notes: Mitochondria

From Medscape Pediatrics, Treatment of Mitochondrial Cytopathies

Understanding therapy for those with mitochondrial disease requires knowledge of the underlying pathogenesis. The term mitochondrial cytopathies refer to the human illnesses resulting from primary and secondary mitochondrial dysfunction. The mitochondria are responsible for energy production, which is generated in the form of adenosine triphosphate (ATP). A series of well-orchestrated chemical reactions culminate in the phosphorylation of adenosine diphosphate (ADP) by the process of oxidative phosphorylation (OXPHOS), which occurs in the five enzyme complexes imbedded in the inner mitochondrial membrane that comprise the electron transport chain (ETC). In addition to energy generation, the mitochondria also play pivotal roles in both the generation of free radicals and the process of apoptosis, or "programmed" cell death. Although therapy primarily focuses on improving energy production, the other functions of the mitochondria may be important in future consideration of treatment options.

Physicians caring for those with mitochondrial cytopathies are faced with a new challenge. The current practice of specialized medical care stratifies physicians and their patients by diseases of organs and organ systems. Although dysfunction of one organ can affect another adjacent organ, such as congestive heart failure causing pulmonary edema, it is usually observed that successful treatment of the primary disease will result in improvement of other organ dysfunction. Mitochondrial cytopathies are not diseases of particular organs, but a disease or disease state of an organelle. The consequences of faulty ATP production are more severe in those tissues with a high-energy requirement, which may impact on the function of only a few selected organs or cause widespread damage affecting most organ systems. Successful management of an ill person with a mitochondrial cytopathy requires the orchestrated efforts of a primary care physician, medical specialists, and a physician comfortable with the intricacies of mitochondrial disorders. Because of the diverse nature of affected organ systems, evaluation of any given therapy can be quite a challenge.

In spite of the multiplicity of clinical presentations and underlying pathophysiology, there are several well-described phenotypes that have been instrumental in the evolution of our knowledge of mitochondrial diseases. Kearns-Sayre syndrome (KSS), typically seen in conjunction with a defect in metabolism of coenzyme Q10, usually presents with ophthalmoplegia, retinopathy, cardiac conduction defects, ataxia, and short stature. Episodic vomiting, lactic acidosis, myopathy, seizures, strokelike events, and short stature tend to characterize mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (MELAS). Myoclonic epilepsy with ragged-red fibers (MERRF) is distinguished by the presence of severe myoclonus, epilepsy, ataxia, and myopathy with ragged-red fibers. Leber hereditary optic neuropathy (LHON) is characterized primarily by blindness in men. Respiratory irregularities, myopathy/weakness, and visual and auditory impairments comprise Leigh's syndrome. Despite these well-defined syndromes, their clinical expression often overlaps.

A number of factors make it difficult to assess whether a given treatment may be effective. These include:

1. Mitochondrial cytopathies represent literally hundreds of different disease states. They may be caused by genetic mutations that result in deficient quantity or function of an enzyme, assembly of multisubunit enzymes, disorders of mitochondrial membrane structure, defects in substrate transport, or vitamin and cofactor deficiencies. The mutations themselves may involve nuclear DNA (nDNA) or mitochondrial DNA (mtDNA); point mutations, deletions, or rearrangements. It is not reasonable to believe that any one treatment would have a similar effect on all mitochondrial diseases.
2. Mitochondrial diseases affect an unpredictable combination of a number of organs or organ systems. This is a result of the process known as segregative replication, in which the abnormal mitochondria may be "compartmentalized" within a given organ (i.e., muscle, brain) and not others. There may be a "threshold" effect in which a certain level of mutant mitochondrial genomes is required for disease to be evident clinically and/or biochemically.[1] Despite the existence of this critical threshold, the genetic burden or measured biochemical deficiency does not necessarily correlate with the severity or rapidity of progression of the disease. The variability of clinical features among affected family members is enormous, even if the underlying genetic or biochemical defect is the same. In addition, exacerbations and remissions are characteristic of these disorders, potentially clouding evaluation of the efficacy of a particular intervention.
3. Mitochondrial diseases can be classified on the basis of a genetic defect, biochemical defect, or pathologic finding. Based on this classification, there are no defined methods of defining severity of illness, nor is there any understanding or consistent ability to predict the natural history of any one patient's illness. Therefore, treatment trials that are not conducted over a sufficient time period could reject a potentially adequate treatment.
4. Given the potentially systemic nature of the mitochondrial cytopathies, developing a treatment trial looking at efficacy of a particular medication or supplement by evaluating the response of all possible affected organ systems would be quite cumbersome and expensive and would require an unacceptable number of patients. On the other hand, trials that look at the response of only one organ system to therapy may miss an existent benefit to other organ systems.
5. The commonly investigated biochemical parameters (i.e., serum or cerebrospinal fluid lactate, pyruvate, enzyme assays) in isolation may not be a full indicator of therapeutic efficacy for any given supplement or medication. Monitoring progress via neurophysiologic studies, magnetic resonance spectroscopy (MRS), and/or objective muscle strength testing will likely add to the overall assessment of patients maintained on specific treatment regimens.

For these reasons, it is very unlikely that there will be class 1 proof that any specific medication or supplement will be effective in the treatment of mitochondrial cytopathies. There is good reason for this skepticism. At this time mitochondrial cytopathies are still considered by most to be relatively rare disorders. There are limited patients with any one specific mutation, and the clinical variability of those with a specific mutation is tremendous. Even if mitochondrial disorders are ultimately shown to be common, the vast phenotypic variability in terms of distribution of organ dysfunction and severity even among family members with identical genotypic disorders makes it impossible to know the natural history of disease progression (and unexplained occasional temporary remissions). Trying to collect class 1 data in a group of diseases with varied molecular genetics and biochemical defects is not likely to be possible.

Although there may be one best treatment approach for one individual with mitochondrial disease, it is naïve to think that there can be a unified treatment strategy for groups of patients identified as having a mitochondrial cytopathy. As mitochondrial diseases are often considered to be degenerative in nature, familiarity with the underlying pathophysiology of these disease processes can aid the clinician in developing potentially effective treatment regimens that can result in an improved quality of life. Despite this knowledge, therapy/amelioration of these disorders continues to pose quite a challenge. In general, therapeutic approaches are principally based on the use of antioxidants, vitamins and supplements (Table 1), replacement of respiratory chain cofactors, dietary management, and medications aimed at reduction of a particular symptom (i.e., seizures, neuropathic pain, cardiac dysfunction).

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Evaluating the efficacy of treatments for mitochondrial cytopathies is influenced by the relative rarity of these conditions and their variable and unpredictable natural course, as well as their extensive clinical and biochemical heterogeneity. The lack of conclusive evidence in favor of any one treatment, or combinations of treatments, makes it impossible to determine conclusively which metabolic therapies might be effective. It is important to note that there is no evidence suggesting therapy alters the ultimate course of these otherwise potentially progressive diseases. There is evidence to suggest some patients may have an improvement in symptoms and an improved quality of life. The majority of data available with regards to specific therapies is anecdotal, though more recently there has been an emphasis on controlled trials. Unfortunately, even in this setting, the patient population varies significantly and statistical constraints make it impossible to evaluate all potential responses.

Because mitochondrial diseases have so many potential symptoms, identifying which symptom or sign to evaluate as part of any study is problematic. If a study relies on one endpoint, improvements in other functions may be ignored and miss a potential benefit of a treatment. Attempting to measure every symptom and sign of the disease would be so burdensome that a study would be prohibitively expensive. As an example, relying on serum or CSF measurements of lactate alone may not fully demonstrate the full therapeutic benefit of a particular medication. It has also been demonstrated in many of the studies discussed that even with diminishment of lactate levels, there is not necessarily concurrent symptomatic improvement. Therefore, the use of other objective measures and possibly many objective measurements (i.e., nuclear magnetic resonance spectroscopy of brain and/or muscle and bicycle ergometry) to evaluate the efficacy of these interventions remains crucial to proving or disproving their benefit. Determination of clinical improvements should also be included in an effort to prove a link between the biochemical and functional improvements.

Despite the lack of consistent data, providing supplements as part of an individual trial in which the patient serves as their own control seems to be a reasonable approach. The clinician and patient will need to use their best judgment as to the issues of efficacy and cost. The use of medications such as dichloroacetate is still under investigation and will likely remain reserved for those patients with life-threatening lactic acidosis that is not responsive to conventional treatment. Uridine remains under investigation with regards to its utility in the treatment of mitochondrial cytopathies.

Childs Nerv Syst. 2007 Jun 19.
Nonspecific mitochondrial disease with epilepsy in children: diagnostic approaches and epileptic phenotypes.
Kang HC, Kwon JW, Lee YM, Kim HD, Lee HJ, Hahn SH.
Department of Pediatrics, Epilepsy Center, Sanggye Paik Hospital, Inje University College of Medicine, Sang-gye 7 Dong 761-1, Nowon-gu, Seoul, South Korea.

OBJECTIVES: This study sought to characterize epileptic phenotypes in children with nonspecific mitochondrial disease (MD) and to evaluate MD diagnostic approaches. METHODS: A retrospective analysis of the medical, electroencephalogram, and laboratory records of 142 patients with epilepsy was performed. The patients were evaluated for MD, and 124 patients were included in the final cohort. The MD criteria used included an oral glucose lactate stimulation test (OGLST) and urine organic acid/plasma amino acid (UOA/PAA) assays as metabolic indicators of modified Walker criteria, as suggested by Bernier et al. (Neurology 59:1406-1411, 2002). RESULTS: Twenty-two patients were classified as having definite MD (9), probable MD (5), possible MD (6), or pyruvate dehydrogenase (PDH) deficiency (3), including one patient which showed a respiratory chain (RC) defect and PDH deficiency. Seven out of eight patients in whom significant RC defects were observed showed complex I defects. In 14 patients, epileptic seizures start at infantile ages. Of 17 patients who substantially presented generalized seizures, 4 patients started with partial seizures. Five patients consistently presented only partial seizures. The OGLST and UOA/PAA assays were useful for a more precise diagnosis of MD, although low positive predictive value of the OGLST was regrettable. No patient was classified as definite MD by Walker's original criteria, but the use of our revised MD criteria resulted in the classification of nine additional patients as definite MD. CONCLUSIONS: MD manifested considerable diverse epileptic phenotypes and should be considered in the differential diagnosis of epilepsy in children with unexplained encephalomyopathy and progressive and fluctuating clinical courses.

Biosci Rep. 2007 May 31.
Neuropathology of mitochondrial diseases.
Filosto M, Tomelleri G, Tonin P, Scarpelli M, Vattemi G, Rizzuto N, Padovani A, Simonati A.
Clinical Neurology, Section for Neuromuscular Diseases and Neuropathies, University Hospital “Spedali Civili”, P.le Spedali Civili 1, Brescia, Italy.

The term "mitochondrial diseases" (MD) refers to a group of disorders related to respiratory chain dysfunction. Clinical features are usually extremely heterogeneous because MD may involve several tissues with different degrees of severity. Muscle and brain are mostly affected, probably because of their high dependence on oxidative metabolism.Muscle can be the only affected tissue or involved as a part of a multi-system disease; ragged red fibers, accumulation of structurally altered mitochondria and cytochrome-c-oxidase (COX) negative fibers are the main pathological features.In mitochondrial encephalopathies, central nervous system (CNS) structures are affected according to different patterns of distribution and severity. Characteristic lesions are neuronal loss, vasculo-necrotic changes, gliosis, demyelination and spongy degeneration.In accordance with either grey matter or white matter involvement two main groups of diseases may be distinguished. Neuronal loss and vasculo-necrotic multifocal lesions are the common features of grey matter involvement; demyelination and spongy degeneration occur when white matter is affected, often associated with less severe lesions of the grey structures.Grey matter lesions are prevalent in MERRF, MELAS, Alpers and Leigh syndromes. White matter involvement is always seen in Kearns-Sayre syndrome and was recently described in mtDNA depletion syndrome linked to dGK mutations and in the rare conditions associated with complex I and II deficiency.In this review we describe the main histopathological features of muscle and CNS lesions in mitochondrial diseases.

Semin Reprod Med. 2007 May.
Actions of steroids in mitochondria.
Gavrilova-Jordan LP, Price TM.
Division of Reproductive Endocrinology and Fertility, Department of Obstetrics and Gynecology, Duke University Medical Center, Durham, North Carolina.

Investigations of indirect and direct actions of steroids on the mitochondria are relatively new areas of research. In this review we provide brief background information regarding mitochondrial structure and function and then focus upon interactions of glucocorticoid, estrogen, androgen, and progesterone receptors with mitochondria. We evaluate the current evidence for steroid receptor localization in the mitochondria based on techniques of Western blot analysis, immunocytochemistry, electron microscopy, and mass spectrometry. Steroid receptor-dependent interactions with mitochondria may include transcriptional regulation of nuclear DNA-encoded mitochondrial proteins, transcriptional regulation of mitochondrial DNA-encoded proteins, or indirect effects on mitochondria due to interactions with cytoplasmic signaling peptides and non-genomic control of cation fluxes. These interactions may play a role in mitochondrial-dependent processes of oxidative phosphorylation and apoptosis. Physiological examples of these interactions are discussed.

Chem Biol Interact. 2006 May 24.
Mitochondrial function and toxicity: Role of B vitamins on the one-carbon transfer pathways.
Depeint F, Bruce WR, Shangari N, Mehta R, O'brien PJ.
Department of Pharmaceutical Sciences, University of Toronto, Canada; Department of Nutritional Sciences, University of Toronto, Canada.

The B vitamins are water-soluble vitamins that are required as coenzymes for reactions essential for cellular function. This review focuses on the essential role of vitamins in maintaining the one-carbon transfer cycles. Folate and choline are believed to be central methyl donors required for mitochondrial protein and nucleic acid synthesis through their active forms, 5-methyltetrahydrofolate and betaine, respectively. Cobalamin (B12) may assist methyltetrahydrofolate in the synthesis of methionine, a cysteine source for glutathione biosynthesis. Pyridoxal, pyridoxine and pyridoxamine (B6) seem to be involved in the regeneration of tetrahydrofolate into the active methyl-bearing form and in glutathione biosynthesis from homocysteine. Other roles of these vitamins that are relevant to mitochondrial functions will also be discussed. However these roles for B vitamins in cell function are mostly theoretically based and still require verification at the cellular level. For instance it is still not known what B vitamins are depleted by xenobiotic toxins or which cellular targets, metabolic pathways or molecular toxic mechanisms are prevented by B vitamins. This review covers the current state of knowledge and suggests where this research field is heading so as to better understand the role vitamin Bs play in cellular function and intermediary metabolism as well as molecular, cellular and clinical consequences of vitamin deficiency. The current experimental and clinical evidence that supplementation alleviates deficiency symptoms as well as the effectiveness of vitamins as antioxidants will also be reviewed.

Nervenarzt. 2007 Apr 26.
Gene expression profiling of classic mitochondrial disorders : Its value in finding therapeutic strategies. [Article in German]
Mende S, Storch A, Reichmann H.
Klinik und Poliklinik fur Neurologie, Technische Universitat Dresden, Fetscherstrasse 74, Dresden, Deutschland.

Mitochondria are semiautonomous cell organelles which possess their own genome (mtDNA) but nonetheless depend on the import of nuclear-encoded proteins. In recent years, several mutations of mtDNA have been associated with specific diseases of the muscles and nervous system. In 1993, the A>G point mutation at position 3243 of the mtDNA, until then a prominent genetic marker for mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), was detected in patients with progressive external ophthalmoplegia (PEO). Due to the divergent clinical presentations of MELAS and PEO, the presence of potential nuclear secondary mutations or so-called modifier genes had been suspected. Now it is well known that a bidirectional information flow between the mitochondrion and the cell nucleus exists and that nuclear gene expression adapts to the functional status of the mitochondria. However it remains unclear when and how the nucleus responds to changes or mutations of the mtDNA and if there are indeed disease-specific biomarker genes whose expression changes in case of mtDNA aberrations. This review article focuses on the most recent gene expression profiling studies in the field of classic mitochondrial disorders.

Mol Biol Cell. 2007 Mar 1.
Diverse Cytopathologies in Mitochondrial Disease Are Caused by AMPK Signalling.
Bokko PB, Francione L, Bandala-Sanchez E, Ahmed AU, Annesley SJ, Huang X, Khurana T, Kimmel AR, Fisher PR.
Department of Microbiology, La Trobe University, Victoria 3086, Australia; National Institutes of Health, Bethesda, MD.

The complex cytopathology of mitochondrial diseases is usually attributed to insufficient ATP. AMP-activated protein kinase (AMPK) is a highly sensitive cellular energy sensor that is stimulated by ATP-depleting stresses. By antisense-inhibiting chaperonin 60 expression we produced mitochondrially diseased strains with gene dose-dependent defects in phototaxis, growth and multicellular morphogenesis. Mitochondrial disease was phenocopied in a gene dose-dependent manner by overexpressing a constitutively active AMPK alpha subunit (AMPKalphaT). The aberrant phenotypes in mitochondrially diseased strains were suppressed completely by antisense-inhibiting AMPKalpha expression. Phagocytosis and macropinocytosis, although energy-consuming, were unaffected by mitochondrial disease and AMPKalpha expression levels. Consistent with AMPK's role in energy homeostasis, mitochondrial "mass" and ATP levels were reduced by AMPKalpha antisense inhibition and increased by AMPKalphaT overexpression, but near normal in mitochondrially diseased cells. We also found that AICAR, a pharmacological AMPK activator in mammalian cells, mimics mitochondrial disease in impairing Dictyostelium phototaxis and that AMPKalpha antisense-inhibited cells were resistant to this effect. The results show that diverse cytopathologies in Dictyostelium mitochondrial disease are caused by chronic AMPK signaling not by insufficient ATP.

CNS Drugs. 2007.
Mitochondrial dysfunction as the molecular basis of bipolar disorder : therapeutic implications.
Kato T.
Laboratory for Molecular Dynamics of Mental Disorders, RIKEN Brain Science Institute, Wako-shi, Saitama, Japan.

Multiple lines of evidence, such as impaired energy metabolism in the brain detected by magnetic resonance spectroscopy, a possible role of maternal inheritance, co-morbidity with mitochondrial diseases, the effects of mood stabilisers on mitochondria, increased mitochondrial DNA (mtDNA) deletion in the brain, and association with mtDNA mutations/polymorphisms or nuclear-encoded mitochondrial genes, suggest that mitochondrial dysfunction is an important component of bipolar disorder. Global reduction of mitochondria-related gene expression in the postmortem brains of patients with bipolar disorder may also be an indicator, but such findings are affected by sample pH and thus need to be interpreted with caution. A recently developed animal model carrying mtDNA deletion in neurons suggested that accumulation of mtDNA deletions causes bipolar disorder-like phenotypes. The next step in the study of mitochondrial dysfunction in bipolar disorder should be clarification of how mitochondrial dysfunction, a nonspecific risk factor, can cause specific symptoms of bipolar disorder. Two hypothetical mechanisms are mtDNA neuroplasticity and nonvisual photoreception impairment.Further study of mitochondrial dysfunction in bipolar disorder is expected to be useful for the development of new mood stabilisers.

Diabetes. 2007 Jan.
Role for mitochondrial reactive oxygen species in brain lipid sensing: redox regulation of food intake.
Benani A, Troy S, Carmona MC, Fioramonti X, Lorsignol A, Leloup C, Casteilla L, Penicaud L.
Laboratoire de Neurobiologie, Plasticite Tissulaire et Metabolisme Energetique, UMR 5018 CNRS-UPS, Institut Louis Bugnard, IFR31, BP 84225, Hopital de Rangueil, Toulouse Cedex 4, France.

The ability for the brain to sense peripheral fuel availability is mainly accomplished within the hypothalamus, which detects ongoing systemic nutrients and adjusts food intake and peripheral metabolism as needed. Here, we hypothesized that mitochondrial reactive oxygen species (ROS) could trigger sensing of nutrients within the hypothalamus. For this purpose, we induced acute hypertriglyceridemia in rats and examined the function of mitochondria in the hypothalamus. Hypertriglyceridemia led to a rapid increase in the mitochondrial respiration in the ventral hypothalamus together with a transient production of ROS. Cerebral inhibition of fatty acids-CoA mitochondrial uptake prevented the hypertriglyceridemia-stimulated ROS production, indicating that ROS derived from mitochondrial metabolism. The hypertriglyceridemia-stimulated ROS production was associated with change in the intracellular redox state without any noxious cytotoxic effects, suggesting that ROS function acutely as signaling molecules. Moreover, cerebral inhibition of hypertriglyceridemia-stimulated ROS production fully abolished the satiety related to the hypertriglyceridemia, suggesting that hypothalamic ROS production was required to restrain food intake during hypertriglyceridemia. Finally, we found that fasting disrupted the hypertriglyceridemia-stimulated ROS production, indicating that the redox mechanism of brain nutrient sensing could be modulated under physiological conditions. Altogether, these findings support the role of mitochondrial ROS as molecular actors implied in brain nutrient sensing.

Brain. 2006 Dec.
Aerobic training is safe and improves exercise capacity in patients with mitochondrial myopathy.
Jeppesen TD, Schwartz M, Olsen DB, Wibrand F, Krag T, Duno M, Hauerslev S, Vissing J.
Department of Neurology, Neuromuscular Research Unit, The Copenhagen Muscle Research Centre, Rigshospitalet, Copenhagen, Denmark.

Exercise intolerance is a prominent symptom in patients with mitochondrial myopathy (MM), but it is still unsettled whether exercise training is safe and beneficial for patients with MM. To address this, we studied the effect of 12 weeks cycle training on exercise capacity, quality of life and underlying molecular and cellular events in five patients with single large-scale deletions, one with a microdeletion and 14 with point mutations of mitochondrial DNA (mtDNA), and 13 healthy subjects. Each training session lasted 30 min, and was performed at an intensity of 70% of VO2max (maximal oxygen uptake). Each subject performed 50 training sessions in 12 weeks. All subjects were evaluated before and after training, and 13 MM patients were studied after 8 weeks of deconditioning. Evaluation included VO2max and mutation load and mtDNA quantity, mitochondrial enzymatic activity, and number of centrally nucleated, apoptotic, ragged red and cytochrome oxidase (COX)-negative fibres in muscle biopsies from the quadriceps muscle. After 12 weeks of training, VO2max and muscle citrate synthase increased in MM (26 and 67%) and healthy (17 and 65%) subjects, while mtDNA quantity in muscle only increased in the MM patients (81%). In the MM patients, training did not change mtDNA mutation load in muscle, mitochondrial enzyme complex activities, muscle morphology and plasma creatine kinase. After deconditioning, VO2max and citrate synthase activity returned to values before training, while muscle mtDNA mutation load decreased. These findings show that aerobic training efficiently improves oxidative capacity in MM patients. Based on unchanged levels of mutant load in muscle, morphological findings on muscle biopsy and plasma creatine kinase levels during training, the treatment appears to be safe. Regular, supervised aerobic exercise is therefore recommended in MM patients with the studied mutations.

Anesthesiology. 2006 Oct.
Clinical implications of mitochondrial dysfunction.
Muravchick S, Levy RJ.
Department of Anesthesiology and Critical Care, Hospital of the University of Pennsylvania, and The Children's Hospital of Philadelphia, 3400 Spruce Street, Philadelphia, PA, USA.

Mitochondria produce metabolic energy, serve as biosensors for oxidative stress, and eventually become effector organelles for cell death through apoptosis. The extent to which these manifold mitochondrial functions are altered by previously unrecognized actions of anesthetic agents seems to explain and link a wide variety of perioperative phenomena that are currently of interest to anesthesiologists from both a clinical and a scientific perspective. In addition, many surgical patients may be at increased perioperative risk because of inherited or acquired mitochondrial dysfunction leading to increased oxidative stress. This review summarizes the essential aspects of the bioenergetic process, presents current knowledge regarding the effects of anesthetics on mitochondrial function and the extent to which mitochondrial state determines anesthetic requirement and potential anesthetic toxicity, and considers some of the many implications that our knowledge of mitochondrial dysfunction poses for anesthetic management and perioperative medicine.

Mol Cell Endocrinol. 2006 Feb 26.
The mitochondrion as a primary site of action of steroid and thyroid hormones: presence and action of steroid and thyroid hormone receptors in mitochondria of animal cells.
Psarra AM, Solakidi S, Sekeris CE.
Foundation for Biomedical Research of the Academy of Athens, Center for Basic Research, Athens, Greece.

Mitochondria are key cellular organelles that regulate events related to energy production and apoptosis. These processes are modulated, in turn, by steroid and thyroid hormones in the course of their actions on metabolism, growth and development. In this context, a direct effect of these hormones on the mitochondrial-linked processes, possibly by way of cognate mitochondrial receptors, has been proposed. In this paper we review data from the literature and present new findings supporting this concept. Receptors for steroid hormones, glucocorticoids and estrogens, and for T(3), have been detected in mitochondria by immunofluorescence labeling and confocal laser microscopy, by Western blotting of mitochondrial proteins and by immunogold electron microscopy. Furthermore, the mitochondrial genome contains nucleotide sequences with high similarity to known hormone-responsive elements, which interact with the appropriate receptors to confer hormone-dependent activation of reporter genes in transfection experiments. Thus, thyroid hormone stimulates mitochondrial transcription mediated by the cognate receptor when added to an in organello mitochondrial system, capable of faithful transcription.

Can J Neurol Sci. 2005 May.
Pathology of mitochondrial encephalomyopathies.
Sarnat HB, Marín-García J.
University of Calgary Faculty of Medicine, Alberta, Canada.

Muscle biopsy provides the best tissue to confirm a mitochondrial cytopathy. Histochemical features often correlate with specific syndromes and facilitate the selection of biochemical and genetic studies. Ragged-red fibres nearly always indicate a combination defect of respiratory complexes I and IV. Increased punctate lipid within myofibers is a regular feature of Kearns-Sayre and PEO, but not of MELAS and MERRF. Total deficiency of succinate dehydrogenase indicates a severe defect in Complex II; total absence of cytochrome-c-oxidase activity in all myofibres correlates with a severe deficiency of Complex IV or of coenzyme-Q10. The selective loss of cytochrome-c-oxidase activity in scattered myofibers, particularly if accompanied by strong succinate dehydrogenase staining in these same fibres, is good evidence of mitochondrial cytopathy and often of a significant mtDNA mutation, though not specific for Complex IV disorders. Glycogen may be excessive in ragged-red zones. Ultrastructure provides morphological evidence of mitochondrial cytopathy, in axons and endothelial cells as well as myocytes. Abnormal axonal mitochondria may contribute to neurogenic atrophy of muscle, a secondary chronic feature. Quantitative determinations of respiratory chain enzyme complexes, with citrate synthase as an internal control, confirm the histochemical impressions or may be the only evidence of mitochondrial disease. Biological and technical artifacts may yield falsely low enzymatic activities. Genetic studies screen common point mutations in mtDNA. The brain exhibits characteristic histopathological alterations in mitochondrial diseases. Skin biopsy is useful for mitochondrial ultrastructure in smooth erector pili muscles and axons; skin fibroblasts may be grown in culture. Mitochondrial alterations occur in many nonmitochondrial diseases and also may be induced by drugs and toxins.

J Inherit Metab Dis. 2005.
Glutathione deficiency in patients with mitochondrial disease: implications for pathogenesis and treatment.
Hargreaves IP, Sheena Y, Land JM, Heales SJ.
Neurometabolic Unit, National Hospital for Neurology and Neurosurgery, Queen Square, London, UK.

Glutathione (GSH) is a key intracellular antioxidant. With regard to mitochondrial function, loss of GSH is associated with impairment of the electron transport chain (ETC). Since GSH biosynthesis is an energy-dependent process, we postulated that in patients with ETC defects GSH status becomes compromised, leading to further loss of ETC activity. We performed electrochemical HPLC analysis to determine the GSH concentration of 24 skeletal muscle biopsies from patients with defined ETC defects compared to 15 age-matched disease controls. Comparison of these groups revealed a significant (p < 0.001) decrease in GSH concentration in the ETC-deficient group: 7.7 +/- 0.9 vs 12.3 +/- 0.6 nmol/mg protein in the control group. Further analysis of the data revealed that patients with multiple defects of the ETC had the most marked GSH deficiency: 4.1 +/- 0.9 nmol/mg protein (n = 4, p < 0.05) when compared to the control group. These findings suggest that a deficiency in skeletal muscle GSH concentration is associated with an ETC defect, possibly as a consequence of diminished ATP availability or increased oxidative stress. The decreased ability to combat oxidative stress could therefore cause further loss of ETC activity and hence be a contributing factor in the progressive nature of this group of disorders. Furthermore, restoration of cellular GSH status could prove to be of therapeutic benefit in patients with a GSH deficiency associated with their ETC defects.

Pediatrics. 2004 Oct.
Clinical spectrum, morbidity, and mortality in 113 pediatric patients with mitochondrial disease.
Scaglia F, Towbin JA, Craigen WJ, Belmont JW, Smith EO, Neish SR, Ware SM, Hunter JV, Fernbach SD, Vladutiu GD, Wong LJ, Vogel H.
Department of Molecular and Human Genetics, Baylor College of Medicine, One Baylor Plaza, Houston, TX, USA.
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OBJECTIVES: The aim of this study was to elucidate the frequency of major clinical manifestations in children with mitochondrial disease and establish their clinical course, prognosis, and rates of survival depending on their clinical features. METHODS: We performed a retrospective review of the medical records of 400 patients who were referred for evaluation of mitochondrial disease. By use of the modified Walker criteria, only patients who were assigned a definite diagnosis were included in the study. RESULTS: A total of 113 pediatric patients with mitochondrial disease were identified. A total of 102 (90%) patients underwent a muscle biopsy as part of the diagnostic workup. A significant respiratory chain (RC) defect, according to the diagnostic criteria, was found in 71% of the patients who were evaluated. In this cohort, complex I deficiency (32%) and combined complex I, III, and IV deficiencies (26%) were the most common causes of RC defects, followed by complex IV (19%), complex III (16%), and complex II deficiencies (7%). Pathogenic mitochondrial DNA abnormalities were found in 11.5% of the patients. A substantial fraction (40%) of patients with mitochondrial disorders exhibited cardiac disease, diagnosed by Doppler echocardiography; however, the majority (60%) of patients had predominant neuromuscular manifestations. No correlation between the type of RC defect and the clinical presentation was observed. Overall, the mean age at presentation was 40 months. However, the mean age at presentation was 33 months in the cardiac group and 44 months in the noncardiac group. Twenty-six (58%) patients in the cardiac group exhibited hypertrophic cardiomyopathy, 29% had dilated cardiomyopathy, and the remainder (13%) had left ventricular noncompaction. Patients with cardiomyopathy had an 18% survival rate at 16 years of age. Patients with neuromuscular features but no cardiomyopathy had a 95% survival at the same age. CONCLUSIONS: This study gives strong support to the view that in patients with RC defects, cardiomyopathy is more common than previously thought and tends to follow a different and more severe clinical course. Although with a greater frequency than previously reported, mitochondrial DNA mutations were found in a minority of patients, emphasizing that most mitochondrial disorders of childhood follow a Mendelian pattern of inheritance.

Exp Physiol. 2003 Jan.
The effects of steroid hormones on the transcription of genes encoding enzymes of oxidative phosphorylation.
Scheller K, Sekeris CE.
Department of Cell and Developmental Biology, Biocenter of the University, Wurzburg, Germany.
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Regulation of energy metabolism is one of the major functions of steroid hormones. In this process, mitochondria, by way of oxidative phosphorylation, play a central role. Depending on the energy needs of the cell, on the tissue, on the developmental stage and on the intensity of the hormonal stimulus, the response can be an activation of pre-existing respiratory chain components, an increased transcription of nuclear-encoded and/or mitochondrial-encoded respiratory chain enzyme (OXPHOS) genes and of biosynthesis of the respective enzyme subunits or, in extreme cases of high energy needs, an increase in the number of mitochondria and mitochondrial DNA content per cell. Some of the hormonally regulated systems involving effects on nuclear and mitochondrial OXPHOS genes are reviewed in this paper. The possible molecular mechanisms of steroid hormone action on nuclear and mitochondrial gene transcription and possible ways of coordination of transcription in these two separate cell compartments involving direct interaction of steroid receptors with hormone response elements in nuclear OXPHOS genes and in mitochondria and induction/activation of nuclear-encoded regulatory factors affecting mitochondrial gene transcription are presented.

Int Rev Cytol. 2003.
Glucocorticoid and thyroid hormone receptors in mitochondria of animal cells.
Scheller K, Seibel P, Sekeris CE.
Department of Cell and Developmental Biology, Biocenter of the University, Wurzburg, Germany.

This article concerns the localization of glucocorticoid and thyroid hormone receptors in mitochondria of animal cells. The receptors are discussed in terms of their potential role in the regulation of mitochondrial transcription and energy production by the oxidative phosphorylation pathway, realized both by nuclear-encoded and mitochondrially encoded enzymes. A brief survey of the role of glucocorticoid and thyroid hormones on energy metabolism is presented, followed by a description of the molecular mode of action of these hormones and of the central role of the receptors in regulation of transcription. Subsequently, the structure and characteristics of glucocorticoid and thyroid hormone receptors are described, followed by a section on the effects of glucocorticoid and thyroid hormones on the transcription of mitochondrial and nuclear genes encoding subunits of OXPHOS and by an introduction to the mitochondrial genome and its transcription. A comprehensive description of the data demonstrates the localization of glucocorticoid and thyroid hormone receptors in mitochondria as well as the detection of potential hormone response elements that bind to these receptors. This leads to the conclusion that the receptors potentially play a role in the regulation of transcription of mitochondrial genes. The in organello mitochondrial system, which is capable of sustaining transcription in the absence of nuclear participation, is presented, responding to T3 with increased transcription rates, and the central role of a thyroid receptor isoform in the transcription effect is emphasized. Lastly, possible ways of coordinating nuclear and mitochondrial gene transcription in response to glucocorticoid and thyroid hormones are discussed, the hormones acting directly on the genes of the two compartments by way of common hormone response elements and indirectly on mitochondrial genes by stimulation of nuclear-encoded transcription factors.

J Neurol. 2001 Sep.
Retrospective study of a large population of patients affected with mitochondrial disorders: clinical, morphological and molecular genetic evaluation.
Sciacco M, Prelle A, Comi GP, Napoli L, Battistel A, Bresolin N, Tancredi L, Lamperti C, Bordoni A, Fagiolari G, Ciscato P, Chiveri L, Perini MP, Fortunato F, Adobbati L, Messina S, Toscano A, Martinelli-Boneschi F, Papadimitriou A, Scarlato G, Moggio M.
Centro Dino Ferrari, Istituto di Clinica Neurologica, University of Milan, Italy.

Mitochondrial disorders are human genetic diseases with extremely variable clinical and genetic features. To better define them, we made a genotype-phenotype correlation in a series of 207 affected patients, and we examined most of them with six laboratory examinations (serum CK and basal lactate levels, EMG, cardiac and EEG studies, neuroradiology). We found that, depending on the genetic abnormality, hyperckemia occurs most often with either chronic progressive external ophthalmoplegia (CPEO) and ptosis or with limb weakness. Myopathic EMGs are more common than limb weakness, except in patients with A8344G mutations. Peripheral neuropathy, when present, is always axonal. About 80% of patients with A3243G and A8344G mutations have high basal lactate levels, whereas pure CPEO is never associated with increased lactate levels. Cardiac abnormalities mostly consist of conduction defects. Abnormalities on CT or MRI of the brain are relatively common in A3243G mutations independently of the clinical phenotype. Patients with multiple mtDNA deletions are somehow "protected" against the development of abnormalities with any of the tests. We conclude that, despite the phenotypic heterogeneity of mitochondrial disorders, correlation of clinical features and laboratory findings may give the clinician important clues to the genetic defect, allowing earlier diagnosis and counselling.

Arch Dis Child. 1999 Sep.
Multiple presentation of mitochondrial disorders.
Nissenkorn A, Zeharia A, Lev D, Fatal-Valevski A, Barash V, Gutman A, Harel S, Lerman-Sagie T.
Pediatric Neurology Unit and Metabolism Clinic, Wolfson Medical Center, Holon, Israel.

The aim of this study was to assess the heterogeneous clinical presentations of children with mitochondrial disorders evaluated at a metabolic neurogenetic clinic. The charts of 36 children with highly suspected mitochondrial disorders were reviewed. Thirty one children were diagnosed as having a mitochondrial disorder, based on a suggestive clinical presentation and at least one of the accepted laboratory criteria; however, in five children with no laboratory criteria the diagnosis remained probable. All of the patients had nervous system involvement. Twenty seven patients also had dysfunction of other systems: sensory organs in 15 patients, cardiovascular system in five, gastrointestinal system in 20, urinary system in four, haematopoietic system in four, and endocrine system in nine. The clinical presentation was compatible with an established syndrome in only 15 children. Severe lactic acidosis or ragged red muscle fibres were encountered in very few patients. These results suggest that mitochondrial disorders should be evaluated in children presenting with a complex neurological picture or multisystem involvement.

Mol Cell Biochem. 1997 Sep.
Clinical, morphological, biochemical, and neuroradiological features of mitochondrial encephalomyopathies. Presentation of 19 patients.
Lindner A, Hofmann E, Naumann M, Becker G, Reichmann H.
Division of Neuroradiology, University of Wurzburg, Germany.

Nineteen patients (9 females, 10 males) with mitochondrial encephalomyopathies (ME) were studied. The diagnosis was established according to clinical and histopathological criteria. Leading clinical features were chronic progressive external ophthalmoplegia (CPEO) and muscle weakness in 95% of the patients. Pigmentary retinopathy was seen in 63%, and was always associated with CPEO. Hypacusis was present in 47% and cerebellar ataxia in 63% of patients. Clinical or electrophysiological signs of involvement of the central nervous system (CNS) were found in 21% of the patients. In muscle biopsy ragged red fibers were the predominant histopathological findings (100% of the patients), while COX-negative fibers were seen in 74%, deletions of the mitochondrial DNA in 42%, and defects of the respiratory chain in 32% of the patients. Increased blood lactate levels were found in 79% of the patients. Needle electromyography revealed myopathic features in 74%, features of denervation in 16%, and was normal in the remainder. Imaging studies showed cerebral atrophy in 58%, cerebellar atrophy in 16%, and hyperintense lesions of the white matter, pyramidal tract or extrapyramidal system in 16% of the cases. It is concluded that the clinical manifestations of ME can be very variable. Diagnosis of ME should be always considered in young patients presenting with CPEO and muscle weakness. In most cases, diagnosis can be made by a few selected investigations, while detection of genetic abnormalities may lead to the diagnosis in the remaining cases.

Neurologia. 1994 Oct.
Clinical and investigative approaches in mitochondrial diseases. A review of 15 cases. [Article in Spanish]
Arpa J, Campos Y, Cruz Martinez A, Gutierrez Molina M, Arenas J, Alonso M, Plaza I, Morales C, Palomo F, Barreiro P, et al.
Servicio de Neurologia, Hospital La Paz, Madrid.

The results of laboratory investigations in concerning 15 patients suspected of mitochondrial disease (MD) are presented. Our purpose is to provide an outline of the investigative modalities that support the clinical suspicion and have been found to be useful in the diagnosis. Five clinical groups were studied including 5 exercise intolerances (2 with inflammatory myopathy), 3 with myopathies (1 with dilated cardiomyopathy), 2 with progressive external oftalmoplegia (1 associated with cerebellar ataxia+epilepsy+hypertrophic cardiomyopathy+pes cavus), 4 with encephalopathies (3 with myoclonic encephalopathies with ataxia and dementia and 1 with epilepsy and tremor), and 1 with metabolic acidosis and cardiomyopathy. We used the following categories of investigative procedures: clinical phenotype analysis including pedigree study, neurophysiological tests, bicycle ergometric evaluation, neuroimaging, microscopic study of skeletal muscle biopsy, post-mortem examination, biochemical assays and molecular genetic studies. EMG showed myopathic changes in 5 cases, features of neuropathy in 2, mixed myopathic and neuropathic pattern in 1 and nonspecific changes in 3. EMG was normal in 3 patients. The most common skeletal muscle abnormalities were variation in fiber size (60%), lipid inclusions (33.3%), oxidative subsarcolemmal aggregates (26.7%) and ragged-red fibers (26.7%). Electron microscopy revealed mitochondrial abnormalities in 8 out of 14 patients' muscle biopsies, and in myocardiac and hepatic tissues of another. Site of biochemical defect was located in 12 patients. Complex I defect in 6, complexes I+IV deficiencies in 3, complex II defect in 1, complex IV deficiency in 1, complexes II+IV deficiencies in 1, and complex III defect in 1. In 2 patients the biochemical defect was not located. Mitochondrial DNA alterations were not found in 7 investigated patients. The clinical spectrum of MD has become increasingly wider. After the clinica suspicion, the diagnosis depends up on the appropriate use of skeletal muscle biopsy, biochemical investigations and molecular genetic techniques. Conventional EMG and automatic measurement of the electromyogram are particularly helpful in confirming the clinical suspicion in patients with predominantly central nervous system disease or in cases in which clinical signs are few.

Brain Dev. 1993 Jan-Feb.
The expanding clinical spectrum of mitochondrial diseases.
De Vivo DC.
Division of Pediatric Neurology, Columbia-Presbyterian Medical Center, New York, NY.

The mitochondrion is the only extranuclear organelle containing DNA (mtDNA). As such, genetically determined mitochondrial diseases may result from a molecular defect involving the mitochondrial or the nuclear genome. The first is characterized by maternal inheritance and the second by Mendelian inheritance. Ragged-red fibers (RRF) are commonly seen with primary lesions of mtDNA, but this association is not invariant. Conversely, RRF are seldom associated with primary lesions of nuclear DNA. Large-scale rearrangements (deletions and insertions) and point mutations of mtDNA are commonly associated with RRF and lactic acidosis, e.g. Kearns-Sayre syndrome (KSS) (major large-scale rearrangements), Pearson syndrome (large-scale rearrangements), myoclonus epilepsy with RRF (MERRF) (point mutation affecting tRNA(lys) gene), mitochondrial myopathy, lactic acidosis, and stroke-like episodes (MELAS) (two point mutations affecting tRNA(leu)(UUR) gene) and a maternally-inherited myopathy with cardiac involvement (MIMyCa) (point mutation affecting tRNA(leu)(UUR) gene). However, RRF and lactic acidosis are absent in Leber hereditary optic neuropathy (LHON) (one point mutation affecting ND4 gene, two point mutations affecting ND1 gene, and one point mutation affecting the apocytochrome b subunit of complex III), and the condition associated with maternally inherited sensory neuropathy (N), ataxia (A), retinitis pigmentosa (RP), developmental delay, dementia, seizures, and limb weakness (NARP) (point mutation affecting ATPase subunit 6 gene). The point mutations in MELAS, MIMyCa, and MERRF, and the large-scale mtDNA rearrangements in KSS and Pearson syndrome have a broader biochemical impact since these molecular defects involve the translational sequence of mitochondrial protein synthesis. The nuclear defects involving mitochondrial function generally are not associated with RRF. The biochemical classification of mitochondrial diseases principally catalogues these nuclear defects. This classification divides mitochondrial diseases into five categories. Primary and secondary deficiencies of carnitine are examples of a substrate transport defect. A lipid storage myopathy is often present. Disturbances of pyruvate or fatty acid metabolism are examples of substrate utilization defects. Only four defects of the Krebs cycle are known: fumarase deficiency, dihydrolipoyl dehydrogenase deficiency, alpha-ketoglutarate dehydrogenase deficiency, and combined defects of muscle succinate dehydrogenase and aconitase. Luft disease is the singular example of a defect in oxidation-phosphorylation coupling. Defects of respiratory chain function are manifold. Two clinical syndromes predominate, one involving limb weakness, and the other primarily affecting brain function. Leigh syndrome may result from different enzyme defects, most notably pyruvate dehydrogenase complex deficiency, cytochrome c oxidase deficiency, complex I deficiency, and complex V deficiency associated with the recently described NARP point mutation. A new group of mitochondrial diseases has emerged.