Suppression of steroidogenesis and activator protein-1 transcription factor activity in rat adrenals by vitamin E deficiency-induced chronic oxidative stress

Vitamin E (Alpha-Tocopherol) Metabolism and Nutrition in Chronic Kidney Disease

Vitamin E (alpha-tocopherol) is an essential micronutrient and fat-soluble antioxidant with proposed role in protecting tissues from uncontrolled lipid peroxidation. This vitamin has also important protein function and gene modulation effects. The metabolism of vitamin E depends on hepatic binding proteins that selectively retain food alpha-tocopherol for incorporation into nascent VLDL and tissue distribution together with esterified cholesterol and triglycerides. Chronic kidney disease (CKD) is a condition of oxidative stress and increased lipid peroxidation, that are associated with alterations of alpha-tocopherol metabolism and function. Specific changes have been reported for the levels of its enzymatic metabolites, including both short-chain and long-chain metabolites, the latter being endowed with regulatory functions on enzymatic and gene expression processes important for the metabolism of lipids and xenobiotics detoxification, as well as for the control of immune and inflammatory processes. Vitamin E therapy has been investigated in CKD using both oral vitamin E protocols and vitamin E-coated hemodialyzers, showing promising results in the secondary prevention of cardiovascular disease, as well as of immune and hematological complications. These therapeutic approaches are reviewed in the present article, together with a narrative excursus on the main findings indicating CKD as a condition of relative deficiency and impaired metabolism of vitamin E.

SOD2 deficiency-induced oxidative stress attenuates steroidogenesis in mouse ovarian granulosa cells

This study investigated the effects of SOD2 (MnSOD)-deficiency-induced excessive oxidative stress on ovarian steroidogenesis in vivo and isolated and cultured granulosa cells using WT and Sod2+/- mice. Basal and 48 h eCG-stimulated plasma progesterone levels were decreased ~50% in female Sod2+/- mice, whereas plasma progesterone levels were decreased ~70% in Sod2+/- mice after sequential stimulation with eCG followed by hCG. Sod2+/- deficiency caused about 50% reduction in SOD2 activity in granulosa cells. SOD2-deficiency also caused a marked reduction in progestins and estradiol in isolated granulosa cells. qRT-PCR measurements indicated that the mRNA expression levels of StAR protein and steroidogenic enzymes are decreased in the ovaries of Sod2+/- mice. Further studies showed a defect in the movement of mobilized cytosolic cholesterol to mitochondria. The ovarian membrane from Sod2+/- mice showed higher susceptibility to lipid peroxidation. These data indicates that SOD2-deficiency induced oxidative stress inhibits ovarian granulosa cell steroidogenesis primarily by interfering with cholesterol transport to mitochondria and attenuating the expression of Star protein gene and key steroidogenic enzyme genes.

BMI1 promotes steroidogenesis through maintaining redox homeostasis in mouse MLTC-1 and primary Leydig cells

In males, aging is accompanied by decline in serum testosterone levels due to impairment of testicular Leydig cells. The polycomb protein BMI1 has recently been identified as an anti-aging factor. In our previous study, BMI1 null mice showed decreased serum testosterone and Leydig cell population, excessive oxidative stress and p16/p19 signaling activation. However, a cause-and-effect relationship between phenotypes and pathways was not investigated. Here, we used the rescue approach to study the role of oxidative stress or p16/p19 in BMI1-mediated steroidogenesis. Our results revealed that treatment with antioxidant NAC, but not down-regulation of p16/p19, largely rescued cell senescence, DNA damage and steroidogenesis in BMI1-deficient mouse MLTC-1 and primary Leydig cells. Collectively, our study demonstrates that BMI1 orchestrates steroidogenesis mainly through maintaining redox homeostasis, and thus, BMI1 may be a novel and potential therapeutic target for treatment of hypogonadism.

Steroidogenesis in Leydig cells: effects of aging and environmental factors

Serum testosterone (TS) levels decrease with aging in both humans and rodents. Using the rat as a model system, it was found that age-related reductions in serum TS were not due to loss of Leydig cells, but rather to the reduced ability of the Leydig cells to produce TS in response to luteinizing hormone (LH). Detailed analyses of the steroidogenic pathway have suggested that two defects along the pathway, LH-stimulated cAMP production and cholesterol transport to and into the mitochondria, are of particular importance in age-related reductions in TS production. Although the mechanisms involved in these defects are far from certain, increasing oxidative stress appears to play a particularly important role. Interestingly, increased oxidative stress also appears to be involved in the suppressive effects of endocrine disruptors on Leydig cell TS production.

Effect of Argan and Olive Oil Consumption on the Hormonal Profile of Androgens Among Healthy Adult Moroccan Men

This study aimed to assess the effect of virgin argan oil (VAO) and extra virgin olive oil (EVO) on the hormonal profile of androgens and anthropometric parameters among healthy adult Moroccan men during a controlled nutritional intervention. The study was carried out on 60 young and healthy male volunteers aged between 23 and 40 years old. During a stabilization period of 2 weeks they consumed butter. The group was then randomized into two categories, the first one consuming VAO and the second EVO for 3 weeks. Testosterone (T), luteinizing hormone (LH) and dehydroepiandrosterone (DHEAS) serum concentrations were measured at the beginning of the study and at the end of each period. The Mann-Whitney test was used to compare the two groups (VAO and EVO) during each step of the study. Differences in androgens and anthropometric parameters between the baseline and after 3 weeks of the diet in the VAO and EVO groups were analyzed using the Wilcoxon test. T and LH serum concentrations significantly increased after the intervention period. T levels increased by 19.9% and 17.4% (p < 0.0001), and LH levels by 18.5% (p < 0.007) and 42.6% ( p < 0.0001), respectively, for VAO and EVO ( p < 0.0001). However, DHEAS serum concentrations, body weight, body mass index, arterial pressure and daily energetic intake did not show any significant variation after the intervention with either argan or olive oils. The results suggest that consumption of AVO and EVO might be the origin of a positive action on the androgen hormonal profile of men.

Leydig cells: From stem cells to aging

Leydig cells are the testosterone-producing cells of the testis. The adult Leydig cell population ultimately develops from undifferentiated mesenchymal-like stem cells present in the interstitial compartment of the neonatal testis. Four distinct stages of adult Leydig cell development have been identified and characterized: stem Leydig cells, progenitor Leydig cells, immature Leydig cells and adult Leydig cells. The stem Leydig cells are undifferentiated cells that are capable of indefinite self-renewal, differentiation, and replenishment of the Leydig cell niche. Progenitor Leydig cells are derived from the stem Leydig cells. These spindle-shaped cells are luteinizing hormone (LH) receptor positive, have high mitotic activity, and produce little testosterone but rather testosterone metabolites. The progenitor Leydig cells give rise to immature Leydig cells which are round, contain large amounts of smooth endoplasmic reticulum, and produce some testosterone but also very high levels of testosterone metabolites. A single division of these cells produces adult Leydig cells, which are terminally differentiated cells that produce high levels of testosterone. As men age, serum testosterone levels decline, and this is associated with alterations in body composition, energy level, muscle strength, physical, sexual and cognitive functions, and mood. In the Brown Norway rat, used extensively as a model for male reproductive aging, age-related reductions in serum testosterone result from significant decline in the ability of aged Leydig cells to produce testosterone in response to LH stimulation. This review describes Leydig cell development and aging. Additionally, the molecular mechanisms by which testosterone synthesis declines with aging are discussed.

Dietary vitamin E deficiency increases anxiety-related behavior in rats under stress of social isolation

It has been demonstrated that vitamin E deficiency from birth increases anxiety-related behavior using knockout animals with no vitamin E transfer proteins. The current study was undertaken to elucidate the effect of dietary vitamin E deficiency on anxiety-related behavior of rats in different housing conditions. Male Wistar strain rats were divided into two groups during the weaning period and fed a control or vitamin E-deficient diet. All rats were housed in groups (three rats per cage) for 3 weeks. In the fourth week, half of the rats in each dietary treatment were kept in social housing and the other half were kept in individual housing. Before sacrifice, rota-rod and elevated plus-maze (EPM) tests were performed to measure motor coordination and anxiety, respectively. The EPM test revealed that vitamin E-deficient rats spent less time in the open arms and showed more stretch-out posture than the control rats, showing that anxiety increased with dietary vitamin E deficiency. Furthermore, vitamin E deficiency-induced anxiety behavior was observed more prominent in individual housed rats than in social housed rats. On the basis of these results, we conclude that dietary vitamin E deficiency induces anxiety in rats especially under stress of social isolation.

Vitamin E: the shrew waiting to be tamed

Vitamin E is the last of all vitamins whose essentiality is not yet understood. Its widely accepted role as a lipophilic antioxidant has been questioned, since proof of its in vivo relevance remained scarce. The influence of vitamin E on biomarkers of oxidative stress in vivo is inconsistent and metabolites of vitamin E having reacted as an antioxidant are hardly detectable. Novel functions of vitamin E include the regulation of enzymes, most of which are membrane bound or activated by membrane recruitment. Also, expression of genes responds to vitamin E. The search for a transcription factor common to all regulated genes failed so far and a receptor that specifically binds vitamin E has not yet been identified. According to microarray data, pathways preferentially affected by the vitamin E status are the inflammatory response and cellular traffic. A role of vitamin E in cellular trafficking could best explain the neurological symptoms seen in vitamin E deficiency. Emerging knowledge on vitamin E is compiled here with the perspective to unravel the molecular mechanisms that could more likely explain the essentiality of the vitamin than its ability to scavenge free radicals.

alpha- and gamma-Tocopherol prevent age-related transcriptional alterations in the heart and brain of mice

We used high-density oligonucleotide arrays to measure transcriptional alterations in the heart and brain (neocortex) of 30-mo-old B6C3F(1) mice supplemented with alpha-tocopherol (alphaT) and gamma-tocopherol (gammaT) since middle age (15 mo). Gene expression profiles were obtained from 5- and 30-mo-old control mice and 30-mo-old mice supplemented with alphaT (1 g/kg) or a mixture of alphaT and gammaT (500 mg/kg of each tocopherol) from middle age (15 mo). In the heart, both tocopherol-supplemented diets were effective in inhibiting the expression of genes previously associated with cardiomyocyte hypertrophy and increased innate immunity. In the brain, induction of genes encoding ribosomal proteins and proteins involved in ATP biosynthesis was observed with aging and was markedly prevented by the mixture of alphaT and gammaT supplementation but not by alphaT alone. These results demonstrate that middle age-onset dietary supplementation with alphaT and gammaT can partially prevent age-associated transcriptional changes and that these effects are tissue and tocopherol specific.

Evidence that age-related changes in p38 MAP kinase contribute to the decreased steroid production by the adrenocortical cells from old rats

The current studies were initiated to investigate whether excessive oxidative stress exerts its antisteroidogenic action through modulation of oxidant-sensitive mitogen-activated protein kinase (MAPK) signaling pathways. Western blot analysis indicated that aging caused increased phosphorylation and activation of rat adrenal p38 MAPK, but not the ERK1/2 or JNK1/2. Lipid peroxidation measurements (an index of cellular oxidative stress) indicated that adrenal membranes from young animals contained only minimal levels of endogenous thiobarbituric acid-reactive substances (TBARS), and exposure of membranes to enzymatic and non-enzymatic pro-oxidants enhanced TBARS formation approximately 12- and 20-fold, respectively. The adrenal membranes from old animals showed much more susceptibility to lipid peroxidation and exhibited roughly 4- to 6-fold higher TBARS formation than young controls both under basal conditions and in response to pro-oxidants. Qualitatively similar results were obtained when lipid peroxide formation was measured using a sensitive FOXRS (ferrous oxidation-xylenol orange-reactive substances) technique. We next tested whether aging-induced excessive oxidative insult alters steroidogenesis through modulation of MAPK signaling pathway. Treatment of adrenocortical cells from old rats with specific p38 MAPK inhibitors restored Bt(2)cAMP-stimulated steroidogenesis approximately 60-70% of the value seen in cells of young animals. Likewise, pretreatment of cells with reactive oxygen species (ROS) scavengers MnTMPyP and N-acetyl cysteine also partially rescued age-induced loss of steroid production. In contrast, simultaneous treatment of cells with ROS scavengers and p38 MAPK inhibitor did not produce any additional effect suggesting that both types of inhibitors exert their stimulatory action through inhibition of p38 MAPK activation. Collectively, these results indicate that p38 MAPK functions as a signaling effector in oxidative stress-induced inhibition of steroidogenesis during aging.

Vitamin E, aging and Leydig cell steroidogenesis

Previous studies have suggested that oxidant-induced damage may play a role in the reduced ability of aged Brown Norway rat Leydig cells to produce testosterone. We reasoned that if this was the case, antioxidants such as vitamin E (VE) would be expected to have protective effects on steroidogenesis. To test this hypothesis, the effects of VE on Leydig cell steroidogenesis were examined both in vitro and in vivo. In vitro studies were conducted using Leydig cells isolated from the testes of young adult Brown Norway rats. In one experiment, isolated cells were incubated with luteinizing hormone (LH) alone or with LH plus VE (1.3-40 microg/ml). At each of 3, 5 and 7 days thereafter, the ability of the cells to produce testosterone was greater in the presence of VE than in its absence, and depended upon VE dose. Culturing the Leydig cells with the antioxidants melatonin or N-tert-butyl-alpha-phenylnitrone also protected Leydig cell steroidogenic function. Additionally, VE was found to suppress Fe2+/sodium ascorbate-induced lipid peroxidation in Leydig cells. These studies strongly supported the contention that VE has a protective effect on Leydig cell steroidogenesis. These in vitro results prompted us to ask whether, in vivo, VE also would affect steroidogenesis as Leydig cells age. To this end, rats were provided one of three diets, begun when the rats were 6 months of age and carried out through age 25 months: VE-deficient, VE-control, or VE-supplemented. The VE-deficient diet had no effect on the age-related reductions in Leydig cell testosterone production observed in VE-control rats. The VE-supplemented diet did not prevent age-related reductions in steroidogenesis, but the reductions at ages 23 and 25 months were significantly less than those seen in Leydig cells from VE-control or VE-deficient rats. Taken together, the results of the in vitro and in vivo studies reported herein are consistent with the conclusion that vitamin E exerts a protective effect on Leydig cell steroidogenesis.

Oxidative damage and age-related functional declines

Most organisms experience progressive declines in physiological function as they age. Since this senescence of function is thought to underlie the decrease in quality of life in addition to the increase in susceptibility to disease and death associated with aging, identifying the mechanisms involved would be highly beneficial. One of the leading mechanistic theories for aging is the oxidative damage hypothesis. A number of studies in a variety of species support a strong link between oxidative damage and life span determination. The role of oxidative damage in functional senescence has also been investigated, albeit not as comprehensively. Here, we review these investigations. Several studies show that the age-related loss of a number of functions is associated with an accrual of oxidative damage in the tissues mediating those functions. Additionally, treatments that increase the accumulation of oxidative damage with age frequently exacerbate functional losses. Moreover, treatments that reduce the accumulation of oxidative damage often attenuate or delay the loss of function associated with aging. These data provide the foundation for a link between oxidative damage and functional senescence, thereby supporting the oxidative damage hypothesis of aging within the context of age-related functional decline.

Inhibition of transcription factor activity by nuclear compartment-associated Bcl-2

Using a reporter gene assay in PC12, HEK293, HeLa, and NIH-3T3 cells, we show that the anti-apoptotic protein Bcl-2 significantly inhibits transcriptional activation of various transcription factors, including NF kappa B, AP1, CRE, and NFAT. A Bcl-2 mutant lacking its BH4 domain (Delta BH4) also inhibited transcription, whereas a Bcl-2 mutant lacking its transmembrane domain (Delta TM) was ineffective. Furthermore, Bcl-2 chimeric proteins containing transmembrane domains from the mitochondrial protein monoamine oxidase B (MaoB) or the endoplasmic reticulum protein cytochrome b(5) showed no effect on transcription factor activity. Subcellular localization studies showed that under conditions of transient transfection, the active Bcl-2 forms (wild type and Delta BH4) were predominantly found in the nuclear fraction, whereas the non-active forms (Delta TM, MaoB, and cytochrome b(5)) were in the non-nuclear fraction. Additionally, stably expressed Bcl-2 loses its ability to inhibit transcriptional activation and localizes predominantly to the non-nuclear fraction. Expression of FKBP38 (a chaperone that shuttles Bcl-2 to the mitochondria) removes co-expressed Bcl-2 from the nuclear fraction and reverses its effect on transcription factor activity. Finally, using an inducible gene expression system, we show that nuclear compartment-associated Bcl-2 prevents entry of NF kappa B subunits to the nucleus without affecting NF kappa B release from its cytosolic inhibitory sub-unit I kappa B alpha. These results suggest that (a) Bcl-2 suppresses transcriptional activity of multiple transcription factors; (b) Bcl-2 does not interfere with NF kappa B activation but prevents entrance of its active subunits to the nucleus; (c) membrane anchoring is required for this function of Bcl-2; and (d) association of Bcl-2 with the nuclear compartment is also necessary. We speculate that nuclear compartment-associated Bcl-2 may affect nuclear trafficking of multiple factors necessary for transcriptional activity.