The phosphatidylinositol/AKT/atypical PKC pathway is involved in the improved insulin sensitivity by DHEA in muscle and liver of rats in vivo

Low serum dehydroepiandrosterone is associated with diabetic dyslipidemia risk in males with type 2 diabetes

Objective

Sex steroid hormones are associated with the advancement of metabolic diseases such as dyslipidemia. This cross-sectional study aimed to investigate the relationship between dehydroepiandrosterone, dehydroepiandrosterone sulfate, androstenedione, and testosterone levels and the risk of dyslipidemia in people with type 2 diabetes mellitus.

Materials and Methods

The analysis included 1,927 patients with type 2 diabetes mellitus. Serum dehydroepiandrosterone, dehydroepiandrosterone sulfate, androstenedione, and testosterone levels were determined using lipid chromatography-tandem mass spectrometry. Multivariable analyses were performed to investigate the association between the variables and dyslipidemia.

Results

The multivariable-adjusted odds ratio (OR) and 95% confidence interval (CI) of dyslipidemia across DHEA tertiles were 0.39 and 0.24-0.64, respectively (p trend = 0.001). This relationship was still maintained when analyzed as a continuous variable (odds ratio, 0.96; 95% confidence interval, 0.92-0.99; P < 0.01). However, in males with type 2 diabetes mellitus, no significant correlations were found between rising levels of dehydroepiandrosterone sulfate, androstenedione, and total testosterone and the risk of dyslipidemia (all P > 0.05). Furthermore, there was no significant association between androgen precursors and total testosterone with regard to the risk of developing dyslipidemia (all P > 0.05).

Conclusions

Serum dehydroepiandrosterone levels were substantially and adversely correlated with dyslipidemia in adult men with T2DM. These results indicated that dehydroepiandrosterone may have an essential role in the development of dyslipidemia. More prospective research is required to validate this link.

Methionine adenosyltransferase2A inhibition restores metabolism to improve regenerative capacity and strength of aged skeletal muscle

We investigate the age-related metabolic changes that occur in aged and rejuvenated myoblasts using in vitro and in vivo models of aging. Metabolic and signaling experiments reveal that human senescent myoblasts and myoblasts from a mouse model of premature aging suffer from impaired glycolysis, insulin resistance, and generate Adenosine triphosphate by catabolizing methionine via a methionine adenosyl-transferase 2A-dependant mechanism, producing significant levels of ammonium that may further contribute to cellular senescence. Expression of the pluripotency factor NANOG downregulates methionine adenosyltransferase 2 A, decreases ammonium, restores insulin sensitivity, increases glucose uptake, and enhances muscle regeneration post-injury. Similarly, selective inhibition of methionine adenosyltransferase 2 A activates Akt2 signaling, repairs pyruvate kinase, restores glycolysis, and enhances regeneration, which leads to significant enhancement of muscle strength in a mouse model of premature aging. Collectively, our investigation indicates that inhibiting methionine metabolism may restore age-associated impairments with significant gain in muscle function.

Mechanical stretch activates glycometabolism-related enzymes via estrogen in C2 C12 myoblasts

Moderate exercise improves glycometabolic disorder and type 2 diabetes mellitus in menopausal females. So far, the effect of exercise-induced estrogen on muscular glycometabolism is not well defined. The current study was designed to explore the effect of mechanical stretch-induced estrogen on glycometabolism in mouse C₂ C₁₂ myoblasts. The mouse C₂ C₁₂ myoblasts in vitro were assigned randomly to the control (C), stretch (S), and stretch plus aromatase inhibitor anastrozole (SA) groups. Cells in the S group were stretched by the Flexcell FX-5000™ system (15% magnitude, 1 Hz frequency, and 6-hr duration) whereas those in the SA group were treated with 400 μg/ml anastrozole before the same stretching. Glucose uptake, estradiol levels, PFK-1 levels, and oxygen consumption rate were determined, and the expression of HK, PI3K, p-AKT, AKT, and GLUT4 proteins were semiquantified with western blot analysis. Compared to the control, the estradiol level, oxygen consumption rate, expression of HK, PI3K, and PFK-1 proteins, the ratio of p-AKT to AKT, and the ratio of GLUT4 in the cell membrane to that in the whole cell were higher in the S group. On the other hand, the estradiol level, glucose uptake, expression of PFK-1 and GLUT4 proteins, oxygen consumption rate, expression of HK protein, and the ratio of p-AKT/AKT were lower in the myoblasts in the SA group than those in the S group. The level of estradiol was positively correlated with glucose uptake (p < .01, r = .818). Therefore, mechanical stretch-induced estrogen increased the expression of glycometabolism-related enzymes and proteins in the mouse C₂ C₁₂ myoblasts.

Dehydroepiandrosterone protects against hepatic glycolipid metabolic disorder and insulin resistance induced by high fat via activation of AMPK-PGC-1α-NRF-1 and IRS1-AKT-GLUT2 signaling pathways

BACKGROUND/OBJECTIVES

Mitochondrial dysfunction, oxidative stress, or fatty liver are the key pathophysiological features for insulin resistance and obesity. Dehydroepiandrosterone (DHEA) can ameliorate obesity and insulin resistance; however, the mechanisms of these actions are poorly understood. The present study aimed to investigate the effect and possible mechanism of DHEA against glycolipid metabolic disorder and insulin resistance.

SUBJECTS/METHODS

Rats fed a high-fat diet (HFD) and palmitic acid (PA)-induced BRL-3A cells were employed to analyze the effect of DHEA on factors related to metabolic disorder and insulin resistance in vivo and in vitro.

RESULTS

DHEA prevented lipid metabolism disorders by enhancing phospho (p)-protein kinase AMP-activated catalytic subunit alpha (AMPKα) (Thr172) protein level and its downstream lipid metabolism-related factors in liver of rats fed an HFD or in PA-induced BRL-3A cells. Meanwhile, DHEA ameliorated mitochondrial dysfunction through activation of the AMPK-peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α)-nuclear respiratory factor-1 (NRF-1) pathway, which represented as the enhancing of the mtDNA copy number, ATP level, and membrane potential, and decreasing of reactive oxygen species production. Moreover, DHEA alleviated insulin resistance via increasing the phosphorylated insulin receptor substrate 1 (p-IRS1) (Tyr612) level and decreasing that of p-IRS1 (Ser307) level in liver of rats fed an HFD or in PA-induced BRL-3A cells, which subsequently enhanced p-protein kinase B (AKT) (Ser473) and membrane glucose transporter type 2 (GLUT2) expression levels.

CONCLUSIONS

The protective effect of DHEA on high-fat-induced hepatic glycolipid metabolic disorder and insulin resistance are achieved through activation of the AMPK-PGC-1α-NRF-1 and IRS1-AKT-GLUT2 signaling pathways. The results provide compelling evidence for the mechanism by which DHEA prevents glycolipid metabolic disorder, and suggest its potential applications for controlling diabetes and obesity in animals and humans.

Anabolic Hormones Deficiencies in Heart Failure With Preserved Ejection Fraction: Prevalence and Impact on Antioxidants Levels and Myocardial Dysfunction

Purpose: In heart failure with reduced ejection fraction, catabolic mechanisms have a strong negative impact on mortality and morbidity. The relationship between anabolic hormonal deficiency and heart failure with preserved ejection fraction (HFpEF) has still been poorly investigated. On the other hand, oxidative stress is recognized as a player in the pathogenesis of HFpEF. Therefore, we performed a cohort study in HFpEF aimed to (1) define the multi-hormonal deficiency prevalence in HFpEF patients; (2) investigate the relationships between hormonal deficiencies and echocardiographic indexes; (3) explore the modulatory activity of anabolic hormones on antioxidant systems. Methods: 84 patients with diagnosis of HFpEF were enrolled in the study. Plasma levels of N-terminal pro-brain natriuretic peptide, fasting glucose, insulin, lipid pattern, insulin-like growth factor-1, dehydroepiandrosterone-sulfate (DHEA-S), total testosterone (T, only in male subjects) were evaluated. Hormonal deficiencies were defined according to T.O.S.C.A. multi-centric study, as previously published. An echocardiographic evaluation was performed. Plasma total antioxidant capacity (TAC) was measured using the system metmyoglobin -H₂O₂ and the chromogen ABTS, whose radical form is spectroscopically revealed; latency time (LAG) in the appearance of ABTS• is proportional to antioxidants in sample. Results: Multiple deficiencies were discovered. DHEA-S deficiency in 87% of patients, IGF-1 in 67% of patients, T in 42%. Patients with DHEA-S deficiency showed lower levels of TAC expressed by LAG (mean ± SEM 91.25 ± 9.34 vs. 75.22 ± 4.38 s; p < 0.05). No differences between TAC in patients with or without IGF-1 deficiency were found. A trend toward high level of TAC in patients without hormonal deficiencies compared with patients with one or multiple deficiencies was found. Regarding echocardiographic parameters, Left Atrial and Left Atrial Volume Index were significantly higher in patients with low IGF-1 values (mean ± SD 90.84 ± 3.86 vs. 72.83 ± 3.78 mL; 51.03 ± 2.33 vs. 40.56 ± 2.46 mL/m², respectively; p < 0.05). Conclusions: Our study showed high prevalence of anabolic deficiencies in HFpEF. DHEA-S seems to influence antioxidant levels; IGF-1 deficiency was associated with alteration in parameters of myocardial structure and dysfunction. These data suggest a role of anabolic hormones in the complex pathophysiological mechanisms of HFpEF and could represent the basis for longitudinal studies and investigations on possible benefits of replacement therapy.

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.

Oncogenic PIK3CA mutations increase dependency on the mRNA cap methyltransferase, RNMT, in breast cancer cells

Basic mechanisms in gene expression are currently being investigated as targets in cancer therapeutics. One such fundamental process is the addition of the cap to pre-mRNA, which recruits mediators of mRNA processing and translation initiation. Maturation of the cap involves mRNA cap guanosine N-7 methylation, catalysed by RNMT (RNA guanine-7 methyltransferase). In a panel of breast cancer cell lines, we investigated whether all are equivalently dependent on RNMT for proliferation. When cellular RNMT activity was experimentally reduced by 50%, the proliferation rate of non-transformed mammary epithelial cells was unchanged, whereas a subset of breast cancer cell lines exhibited reduced proliferation and increased apoptosis. Most of the cell lines which exhibited enhanced dependency on RNMT harboured oncogenic mutations in PIK3CA, which encodes the p110α subunit of PI3Kα. Conversely, all cell lines insensitive to RNMT depletion expressed wild-type PIK3CA. Expression of oncogenic PIK3CA mutants, which increase PI3K p110α activity, was sufficient to increase dependency on RNMT. Conversely, inhibition of PI3Kα reversed dependency on RNMT, suggesting that PI3Kα signalling is required. Collectively, these findings provide evidence to support RNMT as a therapeutic target in breast cancer and suggest that therapies targeting RNMT would be most valuable in a PIK3CA mutant background.

Dehydroepiandrosterone supplementation is not beneficial in the late postmenopausal period in diet-induced obese rats

AIMS

Dehydroepiandrosterone (DHEA) is an adrenal steroid hormone that is a precursor of sexual hormones. It is reduced during aging and is strongly associated with insulin resistance and obesity. There is evidence for beneficial effects of this steroid, in both human and animal models, during perimenopause. However, the impact of DHEA treatment during late postmenopause on glucose metabolism is not clearly documented. We tested the hypothesis that DHEA supplementation could improve insulin sensitivity in an ovariectomized obese rat model (OVX) that was fed a high-fat diet for 11 weeks.

MAIN METHODS

Female Wistar rats at 8 weeks of age were OVX or SHAM-operated. Eight weeks after the surgery, the animals were randomly treated with vehicle or DHEA for 3 weeks. Food intake, metabolic parameters and insulin sensitivity were evaluated.

KEY FINDINGS

Following the ovariectomy, increased body weight gain, adiposity index, and feeding efficiency were observed, despite there being no change in food and energy intake. The OVX rats also displayed glucose intolerance, insulin resistance, decreased insulin-induced IRS1/2 tyrosine phosphorylation in the skeletal muscle, and reduced serum VLDL-c and TAG levels. OVX rats treated with 10 mg/kg DHEA (OVX + DHEA) exhibited estradiol (E₂) serum levels similar to SHAM animals, with no change in uterus mass. DHEA treatment also resulted in an increase in energy intake.

SIGNIFICANCE

Despite the positive effects of DHEA supplementation observed in menopausal women and ovariectomized rats, a potential negative effect on glucose metabolism and insulin action in the late postmenopausal condition in diet-induced obese OVX rats are reported.

Mechanisms of Action of Dehydroepiandrosterone

Dehydroepiandrosterone (3β-hydroxy-5-androsten-17-one, DHEA) and its sulfated metabolite DHEA-S are the most abundant steroids in circulation and decline with age. Rodent studies have shown that DHEA has a wide variety of effects on liver, kidney, adipose, reproductive tissues, and central nervous system/neuronal function. The mechanisms by which DHEA and DHEA-S impart their physiological effects may be direct actions on plasma membrane receptors, including a DHEA-specific, G-protein-coupled receptor in endothelial cells; various neuroreceptors, e.g., aminobutyric-acid-type A, N-methyl-d-aspartate (NMDA), and sigma-1 (S1R) receptors; by binding steroid receptors: androgen and estrogen receptors (ARs, ERα, or ERβ); or by their metabolism to more potent sex steroid hormones, e.g., testosterone, dihydrotestosterone, and estradiol, which bind with higher affinity to ARs and ERs. DHEA inhibits voltage-gated T-type calcium channels. DHEA activates peroxisome proliferator-activated receptor (PPARα) and CAR by a mechanism apparently involving PP2A, a protein phosphatase dephosphorylating PPARα and CAR to activate their transcriptional activity. We review our recent study showing DHEA activated GPER1 (G-protein-coupled estrogen receptor 1) in HepG2 cells to stimulate miR-21 transcription. This chapter reviews some of the physiological, biochemical, and molecular mechanisms of DHEA and DHEA-S activity.

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.

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.

Dehydroepiandrosterone Supplementation Combined with Whole-Body Vibration Training Affects Testosterone Level and Body Composition in Mice

Dehydroepiandrosterone (DHEA), the most abundant sex steroid, is primarily secreted by the adrenal gland and a precursor hormone used by athletes for performance enhancement. Whole-body vibration (WBV) is a well-known light-resistance exercise by automatic adaptations to rapid and repeated oscillations from a vibrating platform, which is also a simple and convenient exercise for older adults. However, the potential effects of DHEA supplementation combined with WBV training on to body composition, exercise performance, and hormone regulation are currently unclear. The objective of the study is to investigate the effects of DHEA supplementation combined with WBV training on body composition, exercise performance, and physical fatigue-related biochemical responses and testosterone content in young-adult C57BL/6 mice. In this study, male C57BL/6 mice were divided into four groups (n = 8 per group) for 6-weeks treatment: sedentary controls with vehicle (SC), DHEA supplementation (DHEA, 10.2 mg/kg), WBV training (WBV; 5.6 Hz, 2 mm, 0.13 g), and WBV training with DHEA supplementation (WBV+DHEA; WBV: 5.6 Hz, 2 mm, 0.13 g and DHEA: 10.2 mg/kg). Exercise performance was evaluated by forelimb grip strength and exhaustive swimming time, as well as changes in body composition and anti-fatigue levels of serum lactate, ammonia, glucose, creatine kinase (CK), and blood urea nitrogen (BUN) after a 15-min swimming exercise. In addition, the biochemical parameters and the testosterone content were measured at the end of the experiment. Six-week DHEA supplementation alone significantly increased mice body weight (BW), muscle weight, testosterone level, and glycogen contents (liver and muscle) when compared with SC group. DHEA supplementation alone had no negative impact on all tissue and biochemical profiles, but could not improve exercise performance. However, WBV+DHEA supplementation also significantly decreased BW, testosterone level and glycogen content of liver, as well as serum lactate and ammonia levels after the 15-min swimming exercise when compared with DHEA supplementation alone. Although DHEA supplementation alone had no beneficial effect in the exercise performance of mice, the BW, testosterone level and glycogen content significantly increased. On the other hand, WBV training combined with DHEA decreased the BW gain, testosterone level and glycogen content caused by DHEA supplementation. Therefore, WBV training could inhibit DHEA supplementation to synthesis the testosterone level or may decrease the DHEA supplement absorptive capacity in young-adult mice.

Sex-related differences in the effects of high-fat diets on DHEA-treated rats

Several studies have investigated the beneficial effects of dehydroepiandrosterone (DHEA) on lipid and glucose metabolism. However, many of these studies are inconclusive about the effects of DHEA administration on metabolic disorders, and there appear to be sex-related differences in the effects of DHEA treatment. Few animal studies have addressed the effects of DHEA on diet-induced metabolic disorders. The present study sought to ascertain whether sex differences exist in the effects of a high-fat diet (HFD) on weight gain, adiposity, and biochemical and hormonal parameters in DHEA-treated rats. Rats were fed a HFD for 4 weeks and simultaneously received treatment with DHEA (10 mg/kg by subcutaneous injection) once weekly. Body weight, retroperitoneal fat depot weight, serum glucose, insulin, and leptin levels, and hepatic lipids were measured. HFD exposure increased the adiposity index in both sexes, the hepatic triglyceride content in both sexes, and the hepatic total cholesterol level in males. Moreover, the HFD induced an increase in blood glucose levels in both sexes, and hyperinsulinemia in males. In this experimental model, DHEA treatment reduced hepatic triglyceride levels only in females, regardless of HFD exposure. Exposure to a HFD, even if it does not cause obesity, may enhance risk factors for metabolic disorders, and males are more sensitive to this effect. DHEA treatment can help prevent metabolic derangements, but its effect varies with sex.

An analysis of DNA methylation in human adipose tissue reveals differential modification of obesity genes before and after gastric bypass and weight loss

Background

Environmental factors can influence obesity by epigenetic mechanisms. Adipose tissue plays a key role in obesity-related metabolic dysfunction, and gastric bypass provides a model to investigate obesity and weight loss in humans.

Results

Here, we investigate DNA methylation in adipose tissue from obese women before and after gastric bypass and significant weight loss. In total, 485,577 CpG sites were profiled in matched, before and after weight loss, subcutaneous and omental adipose tissue. A paired analysis revealed significant differential methylation in omental and subcutaneous adipose tissue. A greater proportion of CpGs are hypermethylated before weight loss and increased methylation is observed in the 3′ untranslated region and gene bodies relative to promoter regions. Differential methylation is found within genes associated with obesity, epigenetic regulation and development, such as CETP, FOXP2, HDAC4, DNMT3B, KCNQ1 and HOX clusters. We identify robust correlations between changes in methylation and clinical trait, including associations between fasting glucose and HDAC4, SLC37A3 and DENND1C in subcutaneous adipose. Genes investigated with differential promoter methylation all show significantly different levels of mRNA before and after gastric bypass.

Conclusions

This is the first study reporting global DNA methylation profiling of adipose tissue before and after gastric bypass and associated weight loss. It provides a strong basis for future work and offers additional evidence for the role of DNA methylation of adipose tissue in obesity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0569-x) contains supplementary material, which is available to authorized users.

DHEA supplementation in ovariectomized rats reduces impaired glucose-stimulated insulin secretion induced by a high-fat diet

Dehydroepiandrosterone (DHEA) and the dehydroepiandrosterone sulfate (DHEA-S) are steroids produced mainly by the adrenal cortex. There is evidence from both human and animal models suggesting beneficial effects of these steroids for obesity, diabetes mellitus, hypertension, and osteoporosis, conditions associated with the post-menopausal period. Accordingly, we hypothesized that DHEA supplementation in ovariectomized (OVX) female rats fed a high-fat diet would maintain glucose-induced insulin secretion (GSIS) and pancreatic islet function. OVX resulted in a 30% enlargement of the pancreatic islets area compared to the control rats, which was accompanied by a 50% reduction in the phosphorylation of AKT protein in the pancreatic islets. However, a short-term high-fat diet induced insulin resistance, accompanied by impaired GSIS in isolated pancreatic islets. These effects were reversed by DHEA treatment, with improved insulin sensitivity to levels similar to the control group, and with increased serine phosphorylation of the AKT protein. These data confirm the protective effect of DHEA on the endocrine pancreas in a situation of diet-induced overweight and low estrogen concentrations, a phenotype similar to that of the post-menopausal period.

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Dehydroepiandrosterone (DHEA) is a physiological precursor of androgens and estrogens.

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Ovariectomized rats fed a high-fat diet showed insulin resistance and impaired glucose-induced insulin secretion.

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These effects were reversed by DHEA treatment, with improved insulin secretion and sensitivity.

Dehydroepiandrosterone improves hepatic antioxidant reserve and stimulates Akt signaling in young and old rats

This study examined, in the liver of young and old (3- and 24-month-old, respectively) healthy Wistar rats, the in vivo effect of dehydroepiandrosterone (DHEA) (10mg/kg body weight) administered subcutaneously for 5 weeks. Reduced (GSH) and oxidized (GSSG) glutathione levels, glucose-6-phosphate dehydrogenase (G6PDH), glutathione-S-transferase (GST), glutathione peroxidase (GPx) and catalase (CAT) activities, hydrogen peroxide concentration, GST and p-Akt/Akt immunocontent ratio were assessed in hepatic tissue. DHEA treatment significantly increased total glutathione content (17%) and GSH (22%) in 3- and 24-month-old treated groups when compared to control groups. The aging factor increased G6PDH (51%) and GPx (22%) activities as well as the hydrogen peroxide concentration (33%), independently of treatment. DHEA treatment increased p-Akt (54%) and p-Akt/Akt ratio (36%) immunocontents in both treated groups. Increased serum levels of alanine aminotransferase (ALT) in aged rats were reduced by DHEA treatment (34%).

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.

Dehydroepiandrosterone protects against oxidative stress-induced endothelial dysfunction in ovariectomized rats

Cardiovascular disease is less frequent in premenopausal women than in age-matched men or postmenopausal women. Moreover, the marked age-related decline in serum dehydroepiandrosterone (DHEA) level has been associated to cardiovascular disease. The aim of this study was to evaluate the effects of DHEA treatment on vascular function in ovariectomized rats. At 8 weeks of age, female Wistar rats were ovariectomized (OVX) or sham (SHAM) operated and 8 weeks after surgery both groups were treated with vehicle or DHEA (10mg kg⁻¹ week⁻¹) for 3 weeks. Aortic rings were used to evaluate the vasoconstrictor response to phenylephrine (PHE) and the relaxation responses to acetylcholine (ACh) and sodium nitroprusside (SNP). Tissue reactive oxygen species (ROS) production and SOD, NADPH oxidase and eNOS protein expression were analysed. PHE-induced contraction was increased in aortic rings from OVX compared to SHAM, associated with a reduction in NO bioavailability. Furthermore, the relaxation induced by ACh was reduced in arteries from OVX, while SNP relaxation did not change. The incubation of aortic rings with SOD or apocynin restored the enhanced PHE-contraction and the impaired ACh-relaxation only in OVX. DHEA treatment corrected the increased PHE contraction and the impaired ACh-induced relaxation observed in OVX by an increment in NO bioavailability and decrease in ROS production. Besides, DHEA treatment restores the reduced Cu/Zn-SOD protein expression and eNOS phosphorylation and the increased NADPH oxidase protein expression in the aorta of OVX rats. The present results suggest an important action of DHEA, improving endothelial function in OVX rats by acting as an antioxidant and enhancing the NO bioavailability.

Dehydroepiandrosterone effects on Akt signaling modulation in central nervous system of young and aged healthy rats

Dehydroepiandrosterone (DHEA) is a steroid synthesized in adrenal cortex as well as in the nervous system. DHEA effects on central nervous system (CNS) have been associated with several brain functions such as marked neurotrophic and neuroprotective activity. DHEA plasma concentration decreases steadily with aging and studies have reported an inverse correlation between levels of DHEA and neurological diseases age-associated. Nonetheless, its mechanisms of action are not yet fully understood. Akt signaling pathway is one protein kinase which has been related to be DHEA modulated. The goal of this study was to investigate whether short-term (6 or 24h) or chronic (5 weeks) DHEA treatment modulates Akt in CNS of adult (3 months) and aged (18 and 24 months) healthy rats. Hypothalamus and hippocampus homogenates were prepared to quantify total-Akt and phosphorylated Akt at Ser(473) (pAkt). The results here presented have shown that acute (50mg/kg) and chronic (10mg/kg) DHEA injections modulate total and pAkt levels. This effect was dose and time-dependent as well as age and tissue-dependent. In addition, the age variable also intervenes on total and pAkt levels expression independently of DHEA treatment.

Atypical protein kinase C zeta exhibits a proapoptotic function in ovarian cancer

Intracellular signaling governed by serine/threonine kinases comprises the molecular interface between cell surface receptors and the nuclear transcriptional machinery. The protein kinase C (PKC) family members are involved in the control of many signaling processes directing cell proliferation, motility, and survival. Here, we examined a role of different PKC isoenzymes in protein phosphatase 2A (PP2A) and HRSL3 tumor suppressor-dependent cell death induction in the ovarian carcinoma cell line OVCAR-3. Phosphorylation and activity of PKC isoenzymes were measured in response to PP2A or phosphoinositide 3-kinase inhibition or HRSL3 overexpression. These experiments indicated a regulation of PKC, epsilon, zeta, and iota through PP2A and/or HRSL3, but not of PKCalpha and beta. Using isoform-specific peptide inhibitors and overexpression approaches, we verified a contribution to PP2A- and HRLS3-dependent apoptosis only for PKCzeta, suggesting a proapoptotic function of this kinase. We observed a significant proportion of human ovarian carcinomas expressing high levels of PKCzeta, which correlated with poor prognosis. Primary ovarian carcinoma cells isolated from patients also responded to okadaic acid treatment with increased phosphorylation of PKCzeta and apoptosis induction. Thus, our data indicate a contribution of PKCzeta in survival control in ovarian carcinoma cells and suggest that upregulation or activation of tyrosine kinase receptors in this tumor might impinge onto apoptosis control through the negative regulation of the atypical PKCzeta.

Adiponectin is involved in the protective effect of DHEA against metabolic risk in aged rats

The aim of the present work was to analyze the effect of dehydroepiandrosterone (DHEA) on several metabolic risk factors, including cardiovascular health and insulin resistance, in aged rats submitted to a high-fat diet. For that, weaned rats were fed on a high-fat diet until 20 months of age. In the last 13 weeks of life, a group (n=11) received the diet supplemented with DHEA (0.5%, w/w), serving the rest (n=10) as controls. Body weight, body fat, serum lipids (triglycerides, total cholesterol and non-esterified fatty acids (NEFA)), HOMA index, n-6/n-3 polyunsaturated fatty acid (PUFA) ratios, serum adiponectin, leptin, resistin and TNF-alpha, as well as adiponectin expression in adipose tissue, were measured. A stepwise discriminant test was used to analyze these variables, and an index of overall metabolic risk was generated from them. DHEA treatment resulted in a significantly lower overall metabolic risk index, as generated by the discriminant test (P<0.01). The DHEA group had lower body fat and n-6/n-3 polyunsaturated fatty acid (PUFA) ratios than the control group (P<0.01), and the same trends were observed for serum cholesterol, triglycerides and HOMA index; in contrast, adiponectin expression in adipose tissue increased in DHEA-treated rats (P<0.05). The discriminant analysis revealed that adiponectin, both from serum and adipose tissue, was the most influencing factor, followed by n-6/n-3 ratios in adipose tissue, and by body fat. Our results then suggest that adiponectin is involved in the protective effect of DHEA against metabolic risk demonstrated in the present work.

Activation of p38MAPK contributes to expanded polyglutamine-induced cytotoxicity

Background

The signaling pathways that may modulate the pathogenesis of diseases induced by expanded polyglutamine proteins are not well understood.

Methodologies/Principal Findings

Herein we demonstrate that expanded polyglutamine protein cytotoxicity is mediated primarily through activation of p38MAPK and that the atypical PKC iota (PKCι) enzyme antagonizes polyglutamine-induced cell death through induction of the ERK signaling pathway. We show that pharmacological blockade of p38MAPK rescues cells from polyglutamine-induced cell death whereas inhibition of ERK recapitulates the sensitivity observed in cells depleted of PKCι by RNA interference. We provide evidence that two unrelated proteins with expanded polyglutamine repeats induce p38MAPK in cultured cells, and demonstrate induction of p38MAPK in an in vivo model of neurodegeneration (spinocerebellar ataxia 1, or SCA-1).

Conclusions/Significance

Taken together, our data implicate activated p38MAPK in disease progression and suggest that its inhibition may represent a rational strategy for therapeutic intervention in the polyglutamine disorders.

Testosterone and DHEA activate the glucose metabolism-related signaling pathway in skeletal muscle

Circulating dehydroepiandrosterone (DHEA) is converted to testosterone or estrogen in the target tissues. Recently, we demonstrated that skeletal muscles are capable of locally synthesizing circulating DHEA to testosterone and estrogen. Furthermore, testosterone is converted to 5alpha-dihydrotestosterone (DHT) by 5alpha-reductase and exerts biophysiological actions through binding to androgen receptors. However, it remains unclear whether skeletal muscle can synthesize DHT from testosterone and/or DHEA and whether these hormones affect glucose metabolism-related signaling pathway in skeletal muscles. We hypothesized that locally synthesized DHT from testosterone and/or DHEA activates glucose transporter-4 (GLUT-4)-regulating pathway in skeletal muscles. The aim of the present study was to clarify whether DHT is synthesized from testosterone and/or DHEA in cultured skeletal muscle cells and whether these hormones affect the GLUT-4-related signaling pathway in skeletal muscles. In the present study, the expression of 5alpha-reductase mRNA was detected in rat cultured skeletal muscle cells, and the addition of testosterone or DHEA increased intramuscular DHT concentrations. Addition of testosterone or DHEA increased GLUT-4 protein expression and its translocation. Furthermore, Akt and protein kinase C-zeta/lambda (PKC-zeta/lambda) phosphorylations, which are critical in GLUT-4-regulated signaling pathways, were enhanced by testosterone or DHEA addition. Testosterone- and DHEA-induced increases in both GLUT-4 expression and Akt and PKC-zeta/lambda phosphorylations were blocked by a DHT inhibitor. Finally, the activities of phosphofructokinase and hexokinase, main glycolytic enzymes, were enhanced by testosterone or DHEA addition. These findings suggest that skeletal muscle is capable of synthesizing DHT from testosterone, and that DHT activates the glucose metabolism-related signaling pathway in skeletal muscle cells.

Effect of dehydroepiandrosterone on protein and fat digestibility, body protein and muscular composition in high-fat-diet-fed old rats

The main objective of the present study was to examine the effects of dehydroepiandrosterone (DHEA) on the digestive efficiency of dietary protein and fat. Second, we analysed the specific changes in muscle composition induced by the hormone. DHEA was given in the diet (0·5 %, w/w) to 75-week-old, high-fat-fed Sprague–Dawley rats (n11) for 13 weeks; age- and weight-matched rats fed on the same diet without DHEA supplementation were used as controls (n10). To determine dietary protein and fat apparent digestibility coefficients, 1-week 24 h faecal depositions were collected. In parallel, urine N was assessed. These assays were performed twice, in the short term (2-week treatment) and in the long term (13-week treatment). Body and gastrocnemius muscle compositions were also analysed. The present results show that DHEA decreased energy intake, body weight, body fat, adipocyte size and number (P < 0·001). The feed efficiency ratio indicates that DHEA-treated rats were less efficient in transforming nutrients fed into their own biomass. Also, a short-term reduction in protein digestibility (P < 0·05) and in body-protein degradation (P < 0·01) was found in DHEA-treated rats, resulting in an increased content of body protein (P < 0·05). Gastrocnemius muscles were smaller, as a result of fat (P < 0·05) but not protein reduction. In conclusion, we confirm the slimming effect of DHEA and, for the first time, we demonstrate that DHEA has an effect at the digestive level. The anti-obesity properties of DHEA could be related to a reduction in protein digestibility in the short term and a protective effect on body protein with a selective mass loss from body fat.

Diabetes alters vascular mechanotransduction: pressure-induced regulation of mitogen activated protein kinases in the rat inferior vena cava

Background

Diabetes mellitus is an important risk factor for increased vein graft failure after bypass surgery. However, the cellular and molecular mechanism(s) underlying vessel attrition in this population remain largely unexplored. Recent reports have suggested that the pathological remodeling of vein grafts may be mediated by mechanically-induced activation of the mitogen activated protein kinase (MAPK) signaling pathways and the MAPK-related induction of caspase-3 activity. On the basis of these findings, we hypothesized that diabetes may be associated with alterations in how veins "sense" and "respond" to altered mechanical loading.

Methods

Inferior venae cavae (IVC) from the non-diabetic lean (LNZ) and the diabetic obese (OSXZ) Zucker rats were isolated and incubated ex vivo under basal or pressurized conditions (120 mmHg). Protein expression, basal activation and the ability of increased pressure to activate MAPK pathways and apoptosis-related signaling was evaluated by immunoblot analysis.

Results

Immunoblot analyses revealed differential expression and activation of extracellular signal-regulated kinase (ERK1/2), p38 and c-Jun NH2-terminal kinase (JNK) MAPKs in the IVCs of diabetic rats as compared to non-diabetic rats. In particular, the expression and basal phosphorylation of p38β- (52.3 ± 11.8%; 45.8 ± 18.2%), JNK 1- (21.5 ± 9.3%; 19.4 ± 11.6%) and JNK3-MAPK (16.8 ± 3.3%; 29.5 ± 17.6%) were significantly higher (P < 0.05) in the diabetic vena cava. An acute increase in IVC intraluminal pressure failed to increase the phosphorylation of ERK1-, JNK-2, or any of the p38-MAPKs in the diabetic obese Zucker rats. Also, IVC loading in the LNZ led to a 276.0 ± 36.0% and 85.8 ± 25.1% (P < 0.05) increase in the cleavage of caspase-3 and caspase-9, respectively, with no effect on these molecules in the OSXZ. No differences were found in the regulation of Bax and Bcl-2 between groups. However, basal expression levels of Akt, phospho-Akt, PTEN, phospho-PTEN and phospho-Bad were higher in the diabetic venae cavae (P < 0.05).

Conclusion

These data suggest that diabetes is associated with significant alteration in the ability of the vena cava to activate MAPK- and apoptosis-related signaling. Whether these changes are associated with the increased vein graft attrition seen in the diabetic population will require further investigation.

Dehydroepiandrosterone inhibits intracellular calcium release in beta-cells by a plasma membrane-dependent mechanism

Both dehydroepiandrosterone (DHEA) and DHEA sulfate (DHEAS) affect glucose stimulated insulin secretion, though their cellular mechanisms of action are not well characterized. We tested the hypothesis that human physiological concentrations of DHEA alter insulin secretion by an action initiated at the plasma membrane of beta-cells. DHEA alone had no effect on intracellular calcium concentration ([Ca(2+)](i)) in a rat beta-cell line (INS-1). However, it caused an immediate and dose-dependent inhibition of carbachol-induced Ca(2+) release from intracellular stores, with a 25% inhibition at zero. One nanometer DHEA. DHEA also inhibited the Ca(2+) mobilizing effect of bombesin (29% decrease), but did not inhibit the influx of extracellular Ca(2+) evoked by glyburide (100 microM) or glucose (15 mM). The steroids (androstenedione, 17-alpha-hydroxypregnenolone, and DHEAS) had no inhibitory effect on carbachol-induced intracellular Ca(2+) release. The action of DHEA depended on a signal initiated at the plasma membrane, since membrane impermeant DHEA-BSA complexes also inhibited the carbachol effect on [Ca(2+)](i) (39% decrease). The inhibition of carbachol-induced Ca(2+) release by DHEA was blocked by pertussis toxin (PTX). DHEA also inhibited the carbachol induction of phosphoinositide generation, with a maximal inhibition at 0.1 nM DHEA. Furthermore, DHEA inhibited insulin secretion induced by carbachol in INS-1 cells by 25%, and in human pancreatic islets by 53%. Taken together, this is the first report showing that human physiological concentrations of DHEA decrease agonist-induced Ca(2+) release by a rapid, non-genomic mechanism in INS-1 cells. Furthermore, these data provide evidence consistent with the existence of a specific plasma membrane DHEA receptor, mediating this signal transduction pathway by pertussis toxin-sensitive G-proteins.

Rescue and regeneration of injured peripheral nerve axons by intrathecal insulin

Insulin peptide, acting through tyrosine kinase receptor pathways, contributes to nerve development or repair. In this work, we examined the direction, impact and repertoire of insulin signaling in vivo during peripheral nerve regeneration in rats. First, we demonstrated that insulin receptor is expressed on lumbar dorsal root ganglia neuronal perikarya using immunohistochemistry. Immunoblots and polymerase chain reactions confirmed the presence of both alpha and beta insulin receptor subunits in dorsal root ganglia. In vivo and in vitro assessment of dorsal root ganglion neurons showed preferential localization of insulin receptor to perikaryal sites. In vivo, intrathecal delivery of fluorescein isothiocyanate-labeled insulin identified localization around dorsal root ganglia neurons. The direction and impact of potential insulin signaling was evaluated by concurrently delivering insulin or carrier over a 2 week period using mini-osmotic pumps, either intrathecally, near nerve, or with both deliveries, following a selective sural nerve crush injury. Only intrathecal insulin increased the number and maturity of regenerating sensory sural nerve axons distal to the crush site. As well, only intrathecal insulin rescued retrograde loss of sural axons after crush. In a separate experiment, insulin also rescued retrograde loss and atrophy of deep peroneal, largely motor, axons post-injury. Intrathecal insulin increased the expression of calcitonin-gene-related peptide in regenerating sprouts, increased the number of visualized regenerating fiber clusters, and reduced downregulation of calcitonin-gene-related peptide in dorsal root ganglia neurons. Insulin delivered intrathecally does not appear to influence expression of insulin-like growth factor-1 at dorsal root ganglion neurons or near peripheral nerve injury, but was associated with upregulation of insulin receptor alpha subunit in dorsal root ganglia. Intrathecal insulin delivery was associated with greater recovery of thermal sensation and longer distances to stimulus response with the pinch test following sural nerve crush. Insulin signaling at neuron perikarya can drive distal sensory axon regrowth, rescue retrograde alterations of axons and alter axon peptide expression. Moreover, such actions are associated with upregulation of its own receptor.

Dehydroepiandrosterone increases β-cell mass and improves the glucose-induced insulin secretion by pancreatic islets from aged rats

The effect of dehydroepiandrosterone (DHEA) on pancreatic islet function of aged rats, an animal model with impaired glucose-induced insulin secretion, was investigated. The following parameters were examined: morphological analysis of endocrine pancreata by immunohistochemistry; protein levels of insulin receptor, IRS-1, IRS-2, PI 3-kinase, Akt-1, and Akt-2; and static insulin secretion in isolated pancreatic islets. Pancreatic islets from DHEA-treated rats showed an increased beta-cell mass accompanied by increased Akt-1 protein level but reduced IR, IRS-1, and IRS-2 protein levels and enhanced glucose-stimulated insulin secretion. The present results suggest that DHEA may be a promising drug to prevent diabetes during aging.

Acetoacetate induces CYP2E1 protein and suppresses CYP2E1 mRNA in primary cultured rat hepatocytes

The ketone body acetoacetate (AA) in the absence of insulin or in the presence of diabetic insulin levels decreases CYP2E1 mRNA expression in a concentration- and time-dependent manner in primary cultured rat hepatocytes. AA activates p70 ribosomal S6 kinase (p70S6K) and protein kinase C (PKC) by approximately 2- to 2.5-fold, respectively, following 6-h treatment. The AA-mediated activation of p70S6K, but not PKC, was abolished by inhibition of PI 3-K with LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one] or wortmannin, in agreement with p70S6K being downstream of phosphatidylinositol 3-kinase (PI 3-K). Inhibition of PI 3-K, mTOR with rapamycin, or PKC with bisindolylmaleimide ameliorated the AA-mediated down-regulation of CYP2E1 mRNA expression. Neither the mitogen-activated protein kinase kinase inhibitor PD98059 (2'-amino-3'-methoxyflavone) nor the p38 mitogen-activated protein kinase inhibitor SB203580 [4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole] ameliorated the AA-mediated suppression of CYP2E1 mRNA expression. Heterogeneous nuclear RNA analysis revealed that AA suppressed CYP2E1 gene transcription by approximately 50% and that inhibition of PI 3-K and PKC diminished this AA-mediated effect on transcription. CYP2E1 mRNA half-life slightly increased from approximately 24 h in untreated hepatocytes to approximately 32 h in AA-treated cells. Interestingly, AA increased CYP2E1 protein levels by approximately 2- and 2.5-fold at 24 and 48 h, respectively. DL-beta-hydroxybutyrate was without effect. Polysomal distribution studies revealed that AA increased the proportion of RNA associated with the actively translated polysomal fractions versus the 40S to 60S untranslated fractions by approximately 40%. CYP2E1 protein half-life increased from approximately 8 h in untreated hepatocytes to approximately 24 in AA-treated cells. These data show that AA decreases CYP2E1 mRNA expression through inhibition of gene transcription while simultaneously elevating CYP2E1 protein levels through increased translation and decreased protein degradation.

C19‐5‐ene Steroids in Nature

Dehydroepiandrosterone (DHEA), produced from cholesterol in the adrenals, is the most abundant steroid in our circulation. It is present almost entirely as the sulfate ester, but the free steroid is the form that serves as a precursor of estrogens and androgens, as well as 7- and 16-oxygenated derivatives. Mammalian tissues reduce the 17-keto Group of DHEA to produce androstenediol-a weak estrogen and full-fledged androgen. Its androgen activity is not inhibited by the anti-androgens commonly used to treat prostate cancer. It is probably responsible for the growth of therapy-resistant prostate cancer. DHEA is hydroxylated at the 7 alpha position, and this derivative is oxidized by 11 beta-hydroxysteroid dehydrogenase to form 7-keto DHEA. The latter is reduced by the same dehydrogenase to form 7 beta-hydroxy DHEA. When fed to rats, each of the latter three steroids induce the formation of two thermogenic enzymes in the liver. The late-term human fetus produces relatively large amounts of 16 alphahydroxy DHEA, which serves the mother as a precursor of estriol.