|
PWS Articles PWS Research
Other |
[ Printable Page | Edit ]
Mol Med. 2002 Nov;8(11):742-9. BACKGROUND: Although the immunologic effects of endogenous and synthetic estrogens are well studied, few studies have examined the hormonal effects of phytoestrogens (i.e., plant-derived estrogens) on the immune system. The primary goal of this study was to compare the effects of perinatal exposure with life-long exposure to genistein, an estrogenic compound in soy, on the endocrine and immune system in adulthood. MATERIALS AND METHODS: Pregnant female rats were exposed to no, low (5 mg/kg diet), or high (300 mg/kg diet) genistein diets throughout gestation and lactation. At weaning, male offspring exposed to genistein perinatally were either switched to the genistein-free diet or remained on the genistein-dosed diets. At 70 days of age, immune organ masses, lymphocyte subpopulations, cytokine concentrations, and testosterone concentrations were assessed in male offspring. RESULTS: Data were analyzed based on the diets that males were exposed to during gestation and lactation because life-long exposure to genistein had no additional effect on any of the dependent measures. Relative thymus masses were greater among males exposed to the high genistein diet than among males exposed to no genistein. Although the proportions of splenic and thymic CD4+ T cells were not altered by genistein, the percentages of CD4+CD8+ thymocytes, CD8+ splenocytes, and total T cells in the spleen were higher and the percentages of CD4-CD8- thymocytes were lower among males exposed to genistein than among males not exposed to genistein. Synthesis of interferon-gamma (IFN-gamma) was marginally higher and testosterone concentrations were lower among genistein-exposed than genistein-free males. DISCUSSION: These data illustrate that exposure to genistein during pregnancy and lactation exerts long-lasting effects on the endocrine and immune systems in adulthood. Whether exposure to phytoestrogens during early development affects responses to infectious or autoimmune diseases, as well as cancers, later in life requires investigation. From the full text article: Sex steroid hormones affect the immune system and susceptibility to disease (1). Generally, in nonpregnant animals, estrogens enhance immune function, reduce susceptibility to infectious diseases, and increase susceptibility to autoimmune diseases (1–3). Although estrogens can enhance both cell-mediated and humoral immune responses, there are reports of estrogens suppressing some cell-mediated immune responses (4,5). Exposure of human natural killer (NK) cells to 17-estradiol in vitro enhances NK cytotoxicity (6). Estrogens stimulate synthesis of proinflammatory cytokines (e.g., interleukin 1 (IL-1) and IL-6) suggesting that they are potent activators of macrophages (2). Estrogens also affect the transcription and synthesis of helper T-cell type 1 (Th1)-related (e.g., interferon- [IFN-] and IL-2) and Th2-related (e.g., IL-4, IL-5, and IL-10) cytokines (1–3,7). In contrast, androgens suppress several aspects of immune function and increase susceptibility to infection in males (1–3). For example, androgens can inhibit the production of proinflammatory cytokines by macrophages, reduce antibody production by B cells, and lower the numbers of CD4 and CD8 T cells in tissue and circulation (3). Although the effects of estrogens in females are well studied, there are few reports of the effects of estrogen exposure on immune function in males (7). Estrogen receptor- (ER) and ER have been identified throughout the immune system and androgens can be aromatized intracellularly into estrogens in males (8,9). In addition to exposure to endogenous hormones, both humans and nonhuman animals are exposed to estrogenic chemicals in the environment (10,11). These compounds, of both natural and synthetic origin, can either mimic or block the effects of endogenous hormones and are hypothesized to affect physiology and behavior (11–13). These chemicals bind to sex steroid receptors, but with a lower affinity than endogenous steroid hormones (14). In addition to effects on ligand receptors, estrogenic chemicals affect several intracellular molecules, including tyrosine kinase and glucose, indicating that environmental estrogens may exert their effects through cell signaling pathways (15,16). To date, most studies have focused on the effects of estrogenic pesticides and toxic substances on immune function (17–19); less attention has been paid to the effects of naturally occurring phytoestrogens on the immune system (20–22). With the increase in human consumption of phytoestrogens (e.g., via soy supplements, food products, and infant formulas), studies that address the physiologic consequences of phytoestrogen exposure are required (23). The effects of phytoestrogen exposure may vary depending on when during ontogeny exposure occurs (11). In vertebrates, sex steroid hormones affect sex-specific differentiation at two distinct times during development (24). During perinatal development (i.e., during gestation and lactation in rodents), sex steroids cause permanent changes in the development of the brain and peripheral organs, such as the gonads and thymus gland (organizational effects). After puberty, exposure to sex steroids transiently activates preexisting hormonal targets (activational effects). Studies examining the effects of phytoestrogens, such as genistein (the estrogenic compound in soy), on the immune system typically expose animals to genistein after the critical period of sex differentiation. These studies reveal that exposure to genistein at puberty or during adulthood can affect the immune system. For example, adult exposure of intact female mice to the phytoestrogen genistein increases the development of pre-B cells in bone marrow, cytotoxic T-cell activity, NK cell activity, and lymphocyte proliferation in the spleen, and reduces tumor development (25,26). In contrast, both adult and pubertal exposure of gonadectomized male and female mice to genistein reduces thymus size, lowers CD4CD8 numbers in the thymus, increases thymocyte apoptosis, and decreases antibody responses against an innocuous antigen (22). The organizational effects of perinatal exposure to phytoestrogens on the immune system have not been reported. Studies of the effects of phytoestrogens on reproduction illustrate that endocrine disrupting chemicals can have both organizational and activational effects in adulthood (27–29). Therefore, we designed our study to determine whether the effects of genistein on the immune and endocrine systems required exposure from gestation through adulthood (organizational and activational hypothesis) or if exposure during perinatal development was sufficient to alter endocrine and immune responses in adulthood (organizational hypothesis alone). Because the perinatal hormonal milieu is critical for normal physiologic development, we hypothesized that exposure to genistein solely during pregnancy and lactation may cause lasting immunologic alterations in adult male offspring. Perinatal exposure to estrogens enhances immune function in adult animals (7,24); therefore, we speculated that exposure to genistein during gestation and lactation may increase immune responses in adult males. Because perinatal exposure to phytoestrogens reduces testosterone concentrations in males (30), we hypothesized that the immunoenhancing effects of genistein may indirectly be caused by reductions in testosterone concentrations. [...] Males exposed to genistein early during development had heavier thymus masses, a higher percentage of CD8 T cells in the spleen, more total T cells in the spleen, a reduced percentage of CD4CD8 thymocytes, more double-positive CD4CD8 T cells in the thymus, and marginally higher concentrations of IFN- in both the spleen and thymus than genisteinfree males. Males exposed to genistein also had lower testosterone concentrations than males not exposed to genistein. Thus, these data illustrate that exposure to genistein during the sensitive period of sex differentiation affects both the endocrine and immune systems of males. Testosterone concentrations were lower among males exposed to genistein. Males with lower testosterone concentrations had higher CD4CD8 T-cell numbers than males with higher testosterone concentrations. Generally, testosterone is considered immunosuppressive and is thought to underlie increased infection rates and reduced susceptibility to autoimmune diseases in males compared with females (1,2,36). Castrated male rodents, male rodents that possess defective androgen receptors (i.e., the testicular feminization mouse model [Tfm]), and male rodents that do not produce sex steroids (i.e., hypogonadal mice) have enlarged thymus glands and elevated B cell production (36–38). ''Similar to males with gonadal dysfunctional, males exposed to the high dose of genistein had larger thymus glands than males not exposed to genistein.'' In the present study, the enlarged thymus glands and increased percentage of double-positive CD4 CD8 T cells in the thymuses of males exposed to dietary genistein may be indicative of the suppressive effects of genistein on testosterone. Although percentages of CD4CD8 T cells in the thymus were negatively correlated with testosterone concentrations, when CD4CD8 (double stained) cells were examined, males with lower testosterone concentrations had lower cell counts. Studies examining the effects of genistein on immune function in castrated and intact males and females are required to determine whether genistein affects immune function directly or via changes in testosterone concentrations. Genistein administered to adult gonadectomized male and female mice decreases numbers of CD4 CD8 and CD4CD8 thymocytes (22). If estrogen receptors (both and ) are blocked using fulvestrant, then the effects of genistein on the immune system are only partially reversed, illustrating that genistein can affect the immune system through sex steroid-independent mechanisms (22). Whether genistein affects the affinity or distribution of sex steroid receptors, including androgen receptors or steroid receptor coactivators (39) in immune cells should be examined. The increased number of double-positive T cells (immature thymocytes) in genistein-exposed males may be beneficial because, following selection processes in the thymus, these cells mature into either CD4 or CD8 T cells and migrate to secondary lymphoid organs, such as the spleen. Although exposure to genistein had no effect on the numbers of B cells or CD4 T cells, genistein significantly increased the number of CD8 splenocytes. B-cells, with the help of CD4 T cells, produce antibodies and form the cornerstone of humoral immunity. The data from the present study suggest that humoral immunity may not be affected by early genistein exposure in males. Because changes in numbers of immune cells do not necessarily equate with functional differences, future studies should examine the effects of early genistein exposure on antibody responses to microbial (infectious) and self- (autoimmune) antigens. To date, the effects of phytoestrogens on cytokine production and release have not been reported. Helper T cells are functionally and phenotypically heterogeneous and can be differentiated based on the cytokines they release. In the present study, although the overall percentage of helper (CD4) T cells was not altered by genistein, genistein-exposed males had marginally higher IFN- concentrations (a Th1 response) than males not exposed to genistein. IL-4 concentrations (a Th2 response) did not differ between males exposed to genistein and those not exposed. Dietary genistein exposure increased the proportion of cytotoxic (CD8) T cells and the overall percentage of total T cells in the spleen suggesting that cell-mediated immunity is enhanced by perinatal genistein exposure. Because cell-mediated immune responses are instrumental for fighting infection and suppressing tumor growth, these data imply that exposure to genistein may reduce susceptibility to certain diseases. In contrast to our study, adult exposure to genistein in gonadectomized mice reduces the proportion of CD4T cells in both the thymus and spleen as well as the percentage of CD8 splenocytes (22). Thus, phytoestrogens may exert differential effects depending on gonadal status and the timing of exposure. In the present study, extending genistein exposure past weaning did not affect organ masses, lymphocyte subpopulations (percentages of the total lymphocyte population), cytokine production, or hormone concentrations. These data suggest that adult exposure to genistein is not required to permanently alter endocrine or immune responses in males. The critical period of exposure to genistein appears to occur during prenatal and neonatal development. These data are reminiscent of the effects of neonatal exposure to sex steroids on play behavior in rodents (40) and suggest that early exposure to genistein may have organizational effects on the endocrine and immune systems later in life. To determine the overall impact of genistein on physiology, examination of the effects of endocrine disrupters on multiple biological systems is required. Although perinatal exposure to genistein appears to have beneficial effects on the immune system, studies conducted by our laboratory and others reveal that perinatal exposure to phytoestrogens has detrimental effects on reproductive physiology and behavior in male offspring (10–13,24,33,41). In addition to lower testosterone concentrations, males exposed to genistein perinatally have reduced anogenital distance, delayed pubertal development, and reduced mating behavior as adults (i.e., ejaculations) compared with males not exposed to genistein (33). Because testosterone supports male-typic reproductive development and behavior and suppresses immune function, we hypothesize that suppression of testosterone underlies the demasculinizing effects of genistein on both the reproductive and immune systems. Future studies should continue to examine the effects of genistein on the dynamic relationship that exists among hormones, reproduction, and immune function in both males and females. In summary, the data from the present study illustrate that exposure to phytoestrogens during early development has lasting effects on the endocrine and immune systems of male offspring. In the present study, the effects of genistein were more pronounced on cell-mediated than on humoral immune responses. Soy proteins are immunomodulatory and their effects during pregnancy or lactation require additional investigation. Presumably, enhanced immune responses may underlie some of the beneficial health-related outcomes associated with phytoestrogen consumption, including decreased incidences of breast and prostate cancer (42). Whether perinatal exposure to phytoestrogens affects susceptibility to diseases caused by infectious pathogens or autoimmune disorders requires investigation (42). Categories: 2002, Soy, Phytoestrogens, Immunological, Endocrine, Sexual development, Testosterone, Thymus, Nutrition and diet |