The effect of long-term DHEA treatment on glucose metabolism, hydrogen peroxide and thioredoxin levels in the skeletal muscle of diabetic rats

DHEA Treatment Effects on Redox Environment in Skeletal Muscle of Young and Aged Healthy Rats

Background:

Dehydroepiandrosterone (DHEA) is an important precursor of active ster-oid hormone, produced abundantly by the adrenal cortex with an age-dependent pattern.

Objective:

We investigated whether chronic DHEA administration impacts on redox status and on Akt protein activation in skeletal muscle during the aging process (3 and 24 months-old rats).

Methods:

Rats received one weekly dose/5 weeks of DHEA (10 mg/kg) or vehicle. Gastrocnemius muscle was removed to evaluate glutathione system, hydrogen peroxide, antioxidant enzymes, and expression of Akt kinase protein.

Results:

In the 3-months-old rats DHEA induced an increase in hydrogen peroxide when compared both to its control (276%) and the 24-months-old DHEA group (485%). Moreover, in the 24-months-old rats DHEA caused an increase in GSSG (41 and 28%), a decrease in reduced-GSH (55 and 51%), and a more oxidized redox status (reduction in GSH/GSSG ratio, 47 and 65%) when compared to 3-month-old DHEA and to 24-months-old control groups, respectively. Both older groups had increased G6PDH (2.7 fold) and GST (1.7 fold) activities when compared to younger groups, independently of any DHEA treatment. However, there was no modulation of Akt protein (phosphorylated/total isoform).

Conclusion:

The results show that chronic DHEA administration to 3 and 24-months-old rats may not present positive effects regarding the redox environment in skeletal muscle without modulation of pro-survival Akt kinase. Due to the large-scale self-administration of DHEA as an “anti-aging” die-tary supplement, it is crucial to investigate its molecular mechanisms over oxidative stress-induced related diseases.

Effect of dehydroepiandrosterone on the immune function of mice in vivo and in vitro

Dehydroepiandrosterone (DHEA) has anti-inflammatory, anti-oxidant and immune-regulating properties, while the mechanism of DHEA actions remains unclear. The present study aims to investigate the effect and possible mechanism of DHEA on immune function of mice in vivo and in vitro. In vivo, a lipopolysaccharide (LPS)-induced experimental inflammation model was constructed to analyze the regulation of DHEA on anti-oxidative and immune function in ICR mice; In vitro, the effects of DHEA on the biological functions of lymphocytes and macrophages were studied. The results showed that DHEA increased the activity of total antioxidant capacity and superoxide dismutase, while it decreased the level of reactive oxygen species in LPS-induced mice. Meanwhile, DHEA increased the proportion of T lymphocytes and decreased that of B lymphocytes in primary cultured spleen lymphocytes, and markedly enhanced the Th1/Th2 ratio in spleen T lymphocytes. Furthermore, DHEA significantly increased the Th1 type cytokine (IL-2 and IFN-α) and decreased the Th2 type cytokine (IL-4 and IL-10) levels in LPS-induced mice or in primary cultured spleen T lymphocytes. In addition, DHEA improved the phagocytic ability, enhanced the NO production and increased the iNOS activity in peritoneal macrophages. Our data indicates that DHEA increases the macrophages function via improving NO content and up-regulating TNF-α expression levels; and it evoked a Th1 immuno-response and repressed a Th2 immuno-response through promoting a shift in Th1/Th2 balance toward Th1-dominant immunity in vivo and in vitro. These results provide substantial evidence on the mechanism of DHEA-mediated immune function and the efficient protection against infectious and inflammatory response in animals and humans.

Effect of Dehydroepiandrosterone (DHEA) on Diabetes Mellitus and Obesity

Type 2 diabetes is a metabolic disorder that is characterized by an impaired capacity to secrete insulin, insulin resistance, or both. Dehydroepiandrosterone (DHEA), a steroid hormone produced by the adrenal cortex, has been reported to have beneficial effects on diabetes mellitus and obesity in animal models. DHEA and DHEA-sulfate (DHEA-S) have been reported to increase not only insulin secretion of the pancreas but also insulin sensitivity of the liver, adipose tissue, and muscle. We investigated the effects of DHEA on glucose metabolism in animal models and reported decrease of liver gluconeogenesis. Recently, we reported the effect of DHEA on the liver and muscle by using insulin-stimulated insulin receptor substrate 1 and 2 (IRS1 and IRS2)-deficient mice. DHEA increased Akt phosphorylation in the liver of C57BL6 IRS1- and IRS2-deficient mice fed with a high-fat diet (HFD), which suggests that the increase in DHEA-induced Akt signaling is sufficient in the presence of IRS1 or IRS2. In addition, other studies have also reported the effect of DHEA on diabetes mellitus in the liver, muscle, adipose tissue, and pancreatic β-cell and its effect on obesity in animal models. A meta-analysis in elderly men and women has found that DHEA supplementation has no effects on blood glucose levels. However, DHEA supplementation to patients with type 2 diabetes has not been fully elucidated. Therefore, further studies are needed to provide greater insight into the effect of DHEA on diabetes and obesity in animal and human models.

Sex-specific effects of dehydroepiandrosterone (DHEA) on glucose metabolism in the CNS

DHEA is a neuroactive steroid, due to its modulatory actions on the central nervous system (CNS). DHEA is able to regulate neurogenesis, neurotransmitter receptors and neuronal excitability, function, survival and metabolism. The levels of DHEA decrease gradually with advancing age, and this decline has been associated with age related neuronal dysfunction and degeneration, suggesting a neuroprotective effect of endogenous DHEA. There are significant sex differences in the pathophysiology, epidemiology and clinical manifestations of many neurological diseases. The aim of this study was to determine whether DHEA can alter glucose metabolism in different structures of the CNS from male and female rats, and if this effect is sex-specific. The results showed that DHEA decreased glucose uptake in some structures (cerebral cortex and olfactory bulb) in males, but did not affect glucose uptake in females. When compared, glucose uptake in males was higher than females. DHEA enhanced the glucose oxidation in both males (cerebral cortex, olfactory bulb, hippocampus and hypothalamus) and females (cerebral cortex and olfactory bulb), in a sex-dependent manner. In males, DHEA did not affect synthesis of glycogen, however, glycogen content was increased in the cerebral cortex and olfactory bulb. DHEA modulates glucose metabolism in a tissue-, dose- and sex-dependent manner to increase glucose oxidation, which could explain the previously described neuroprotective role of this hormone in some neurodegenerative diseases.

Dehydroepiandrosterone inhibits cell proliferation and improves viability by regulating S phase and mitochondrial permeability in primary rat Leydig cells

Dehydroepiandrosterone (DHEA) is widely used as a nutritional supplement and exhibits putative anti-aging properties. However, the molecular basis of the actions of DHEA, particularly on the biological characteristics of target cells, remain unclear. The aim of the current study was to investigate the effects of DHEA on cell viability, cell proliferation, cell cycle and mitochondrial function in primary rat Leydig cells. Adult Leydig cells were purified by Percoll gradient centrifugation, and cell proliferation was detected using a Click-iT^® EdU Assay kit and cell cycle assessment performed using flow cytometry. Mitochondrial membrane potential was detected using JC-1 staining assay. The results of the current study demonstrate that DHEA decreased cell proliferation in a dose-dependent manner, whereas it improved cell viability in a time-dependent and dose-dependent manner. Flow cytometry analysis demonstrated that DHEA treatment increased the S phase cell population and decreased the G2/M cell population. Cyclin A and CDK2 mRNA levels were decreased in primary rat Leydig cells following DHEA treatment. DHEA treatment decreased the transmembrane electrical gradient in primary Leydig cells, whereas treatment significantly increased succinate dehydrogenase activity. These results indicated that DHEA inhibits primary rat Leydig cell proliferation by decreasing cyclin mRNA level, whereas it improves cells viability by modulating the permeability of the mitochondrial membrane and succinate dehydrogenase activity. These findings may demonstrate an important molecular mechanism by which DHEA activity is mediated.

Effect of dehydroepiandrosterone (DHEA) on Akt and protein kinase C zeta (PKCζ) phosphorylation in different tissues of C57BL6, insulin receptor substrate (IRS)1(-/-), and IRS2(-/-) male mice fed a high-fat diet

We have previously reported that dehydroepiandrosterone (DHEA) suppresses the activity and mRNA expression of the hepatic gluconeogenic enzyme glucose-6-phosphatase (G6Pase), and hepatic glucose production in db/db mice. Tyrosine phosphorylation levels of Insulin receptor substrate (IRS)1 and IRS2 reportedly differ between the liver and muscle tissue and the effect of DHEA on insulin signaling has not been elucidated. Therefore, we examined DHEA's effect on the liver and muscle tissue of IRS1(-/-) and IRS2(-/-) mice. Eight-week-old male C57BL6, IRS1(-/-), and IRS2(-/-) mice were fed a high-fat diet (HFD), or an HFD containing 0.2% DHEA for 4 weeks. In a separate experiment, 8-week-old male C57BL6 mice were fed an HFD or an HFD containing 0.2% androstenedione for 4 weeks. In an insulin tolerance test, DHEA administration decreased the initial plasma glucose levels in the C57BL6, IRS1(-/-), and IRS2(-/-) mice but did not decrease the ratios to the basal blood glucose level. Although DHEA administration increased Akt phosphorylation in the liver of the C57BL6, IRS1(-/-), and IRS2(-/-) mice, androstenedione administration did not increase Akt phosphorylation in the liver of C57BL6 mice. DHEA administration did not increase Akt and PKCζ phosphorylation in the muscle tissue of C57BL6, IRS1(-/-), or IRS2(-/-) mice. However, androstenedione administration increased Akt and PKCζ phosphorylation in the muscle tissue of C57BL6 mice. These findings suggest that the effect of DHEA on insulin action in the liver is self-mediated by DHEA or DHEA sulfate (DHEA-S) in the presence of IRS1, IRS2, or both.

Effect of dehydroepiandrosterone on cell growth and mitochondrial function in TM-3 cells

Dehydroepiandrosterone (DHEA), a major steroid hormone, decreases with age, and this reduction has been shown to be associated with physical health. In the present study, the effect of DHEA on cell growth and mitochondrial function was investigated using TM-3 cells, a Leydig cell line. The growth of TM-3 cells exposed to 100 μM DHEA for 24h was inhibited due to cell cycle arrest, primarily in the S and G2/M phases, and this effect was caused by decreased activity of glucose-6-phosphate dehydrogenase (G6PD) and reduced expression of cyclinA and cyclinB mRNA. A novel finding was that DHEA improved TM-3 cell viability in a markedly time-dependent manner. Although no differences were observed in the configuration or number of TM-3 cell mitochondria following DHEA treatment, mitochondrial membrane permeability and the activity of succinate dehydrogenase (SDH) increased subsequent to 24h treatment of cells with 100 μM DHEA. Overall, the data demonstrate that DHEA inhibited TM-3 cell growth by decreasing G6PD activity and the expression of cyclin mRNAs, whereas it improved TM-3 cell viability by increasing mitochondrial membrane permeability and the activity of SDH. This could be one of mechanisms of DHEA exerts its biological function.

Dehydroepiandrosterone inhibits the Src/STAT3 constitutive activation in pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is an obstructive vasculopathy characterized by enhanced pulmonary artery smooth muscle cell (PASMC) proliferation and suppressed apoptosis. This phenotype is sustained by the activation of the Src/signal transducer and activator of transcription 3 (STAT3) axis, maintained by a positive feedback loop involving miR-204 and followed by an aberrant expression/activation of its downstream targets such as Pim1 and nuclear factor of activated T-cells (NFATc2). Dehydroepiandrosterone (DHEA) is a steroid hormone shown to reverse vascular remodeling in systemic vessels. Since STAT3 has been described as modulated by DHEA, we hypothesized that DHEA reverses human pulmonary hypertension by inhibiting Src/STAT3 constitutive activation. Using PASMCs isolated from patients with PAH (n = 3), we demonstrated that DHEA decreases both Src and STAT3 activation (Western blot and nuclear translocation assay), resulting in a significant reduction of Pim1, NFATc2 expression/activation (quantitative RT-PCR and Western blot), as well as Survivin and upregulation of bone morphogenetic protein receptor 2 (BMPR2) and miR-204. Src/STAT3 axis inhibition by DHEA is associated with 1) mitochondrial membrane potential (tetramethylrhodamine methyl-ester perchlorate; n = 150; P < 0.05) depolarization increasing apoptosis by 25% (terminal deoxynucleotidyl transferase dUTP-mediated nick-end labeling; n = 150; P < 0.05); and 2) decreased intracellular Ca(2+) concentration (fluo-3 AM; n = 150; P < 0.05) and proliferation by 30% (PCNA). Finally, in vivo similarly to STAT3 inhibition DHEA improves experimental PAH (monocrotaline rats) by decreasing mean PA pressure and right ventricle hypertrophy. These effects were associated with the inhibition of Src, STAT3, Pim1, NFATc2, and Survivin and the upregulation of BMPR2 and miR-204. We demonstrated that DHEA reverses pulmonary hypertension in part by inhibiting the Src/STAT3.

Associations of polychlorinated biphenyl exposure and endogenous hormones with diabetes in post-menopausal women previously employed at a capacitor manufacturing plant

There is an increasing body of literature showing associations of organochlorine exposure with risk of diabetes and insulin resistance. Some studies suggest that associations differ by gender and that diabetes risk, in turn, may be affected by endogenous steroid hormones. This report examines the relationships of serum PCBs and endogenous hormones with history of diabetes in a cohort of persons previously employed at a capacitor manufacturing plant. A total of 118 women were post-menopausal with complete data, of whom 93 were not using steroid hormones in 1996, at the time of examination, which included a survey of exposure and medical history, height, weight and collection of blood and urine for measurements of lipids, liver function, hematologic markers and endogenous hormones. This analysis examines relationships of serum polychlorinated biphenyls (PCBs), work exposure and endogenous hormones with self-reported history of diabetes after control for potential confounders. All PCB exposure groups were significantly related to history of diabetes, but not to insulin resistance as measured by the homeostatic model assessment of insulin resistance (HOMA-IR) in non-diabetics. Diabetes was also independently and inversely associated with follicle stimulating hormone (FSH), dehydroepiandrosterone sulfate (DHEAS) and triiodothyronine (T3) uptake. HOMA-IR was positively associated with body mass index (BMI) and C-reactive protein (CRP) and inversely associated with sex hormone binding globulin (SHBG) and T3 uptake after control for PCB exposure. Possible biologic mechanisms are discussed. This study confirms previous reports relating PCB exposure to diabetes and suggests possible hormonal pathways deserving further exploration.

The effect of dehydroepiandrosterone (DHEA) on renal function and metabolism in diabetic rats

Dehydroepiandrosterone (DHEA) is an endogenous steroid hormone involved in a number of biological actions in humans and rodents, but its effects on renal tissue have not yet been fully understood. The aim of this study is to assess the effect of DHEA treatment on diabetic rats, mainly in relation to renal function and metabolism. Diabetic rats were treated with subcutaneous injections of a 10mg/kg dose of DHEA diluted in oil. Plasma glucose and creatinine, in addition to urine creatinine, were quantified espectophotometrically. Glucose uptake and oxidation were quantified using radioactive glucose, the urinary Transforming Growth Factor β(1) (TGF-β(1)) was assessed by enzyme immunoassay, and the total glutathione in the renal tissue was also measured. The diabetic rats displayed higher levels of glycemia, and DHEA treatment reduced hyperglycemia. Plasmatic creatinine levels were higher in the diabetic rats treated with DHEA, while creatinine clearance was lower. Glucose uptake and oxidation were lower in the renal medulla of the diabetic rats treated with DHEA, and urinary TGF-β(1), as well as total gluthatione levels, were higher in the diabetic rats treated with DHEA. DHEA treatment was not beneficial to renal tissue, since it reduced the glomerular filtration rate and renal medulla metabolism, while increasing the urinary excretion of TGF-β(1) and the compensatory response by the glutathione system, probably due to a mechanism involving a pro-oxidant action or a pro-fibrotic effect of this androgen or its derivatives. In conclusion, this study reports that DHEA treatment may be harmful to renal tissue, but the mechanisms of this action have not yet been fully understood.