Dehydroepiandrosterone stimulates glucose uptake in human and murine adipocytes by inducing GLUT1 and GLUT4 translocation to the plasma membrane

Synaptotagmins family affect glucose transport in retinal pigment epithelial cells through their ubiquitination-mediated degradation and glucose transporter-1 regulation

BACKGROUND

Synaptotagmins (SYTs) are a family of 17 membrane transporters that function as calcium ion sensors during the release of Ca2+-dependent neurotransmitters and hormones. However, few studies have reported whether members of the SYT family play a role in glucose uptake in diabetic retinopathy (DR) through Ca2+/glucose transporter-1 (GLUT1) and the possible regulatory mechanism of SYTs.

AIM

To elucidate the role of the SYT family in the regulation of glucose transport in retinal pigment epithelial cells and explore its potential as a therapeutic target for the clinical management of DR.

METHODS

DR was induced by streptozotocin in C57BL/6J mice and by high glucose medium in human retinal pigment epithelial cells (ARPE-19). Bioinformatics analysis, reverse transcriptase-polymerase chain reaction, Western blot, flow cytometry, ELISA, HE staining, and TUNEL staining were used for analysis.

RESULTS

Six differentially expressed proteins (SYT2, SYT3, SYT4, SYT7, SYT11, and SYT13) were found between the DR and control groups, and SYT4 was highly expressed. Hyperglycemia induces SYT4 overexpression, manipulates Ca2+ influx to induce GLUT1 fusion with the plasma membrane, promotes abnormal expression of the glucose transporter GLUT1 and excessive glucose uptake, induces ARPE-19 cell apoptosis, and promotes DR progression. Parkin deficiency inhibits the proteasomal degradation of SYT4 in DR, resulting in SYT4 accumulation and enhanced GLUT1 fusion with the plasma membrane, and these effects were blocked by oe-Parkin treatment. Moreover, dysregulation of the myelin transcription factor 1 (Myt1)-induced transcription of SYT4 in DR further activated the SYT4-mediated stimulus-secretion coupling process, and this process was inhibited in the oe-MYT1-treated group.

CONCLUSION

Our study reveals the key role of SYT4 in regulating glucose transport in retinal pigment epithelial cells during the pathogenesis of DR and the underlying mechanism and suggests potential therapeutic targets for clinical DR.

A fingerprint of 2-[18F]FDG radiometabolites - How tissue-specific metabolism beyond 2-[18F]FDG-6-P could affect tracer accumulation

Studies indicate that the radiotracer 2-[18F]fluoro-2-deoxy-D-glucose (2-[18F]FDG) can be metabolized beyond 2-[18F]FDG-6-phosphate (2-[18F]FDG-6-P), but its metabolism is incompletely understood. Most importantly, it remains unclear whether downstream metabolism affects tracer accumulation in vivo. Here we present a fingerprint of 2-[18F]FDG radiometabolites over time in cancer cells, corresponding tumor xenografts and murine organs. Strikingly, radiometabolites representing glycogen metabolism or the oxPPP correlated inversely with tracer accumulation across all examined tissues. Recent studies suggest that not only hexokinase, but also hexose-6-phosphate dehydrogenase (H6PD), an enzyme of the oxidative pentose phosphate pathway (oxPPP), determines 2-[18F]FDG accumulation. However, little is known about the corresponding enzyme glucose-6-phosphate dehydrogenase (G6PD). Our mechanistic in vitro experiments on the role of the oxPPP propose that 2-[18F]FDG can be metabolized via both G6PD and H6PD, but data from separate enzyme knockdown suggest diverging roles in downstream tracer metabolism. Overall, we propose that tissue-specific metabolism beyond 2-[18F]FDG-6-P could matter for imaging.

Sex Hormones and Diabetes in 45- to 74-year-old Men and Postmenopausal Women: The Hispanic Community Health Study

Previous studies demonstrated associations of endogenous sex hormones with diabetes. Less is known about their dynamic relationship with diabetes progression through different stages of the disease, independence of associations, and role of the hypothalamic-pituitary gonadal axis. The purpose of this analysis was to examine relationships of endogenous sex hormones with incident diabetes, prediabetes, and diabetes traits in 693 postmenopausal women and 1015 men aged 45 to 74 years without diabetes at baseline participating in the Hispanic Community Health Study/Study of Latinos and followed for 6 years. Baseline hormones included estradiol, luteinizing hormone (LH), follicle stimulating hormone (FSH), sex hormone-binding globulin (SHBG), dehydroepiandrosterone sulfate (DHEAS), and, in men, testosterone and bioavailable testosterone. Associations were analyzed using multivariable Poisson and linear regressions. In men, testosterone was inversely associated with conversion from prediabetes to diabetes (incidence rate ratio [IRR] for 1 SD increase in testosterone: 0.821; 95% CI, 0.676, 0.997; P = 0.046), but not conversion from normoglycemia to prediabetes. Estradiol was positively associated with increase in fasting insulin and homeostatic model assessment of insulin resistance. In women, SHBG was inversely associated with change in glycosylated hemoglobin, postload glucose, and conversion from prediabetes to diabetes (IRR = 0.62; 95% CI, 0.44, 0.86, P = 0.005) but not from normoglycemia to prediabetes. Relationships with other hormones varied across glycemic measures. Stronger associations of testosterone and SHBG with transition from prediabetes to diabetes than from normoglycemic to prediabetes suggest they are operative at later stages of diabetes development. Biologic pathways by which sex hormones affect glucose homeostasis await future studies.

Adrenal Androgen Predictive Effects on Clinical and Metabolic Abnormalities of Polycystic Ovary Syndrome

OBJECTIVE

 To examine the possible effects of adrenal prohormones in the prediction of clinical and metabolic abnormalities in women with polycystic ovary syndrome (PCOS).

METHODS

 The present study enrolled 299 normal cycling non-PCOS, 156 normoandrogenemic, and 474 hyperandrogenemic women with PCOS. Baseline characteristics were compared using a chi-squared test or analysis of variance (ANOVA) as appropriate. The roles of adrenal prohormones and their ratios with total testosterone in predicting co-occurring morbidities in women PCOS were evaluated using univariate and multivariate logistic regression analyses.

RESULTS

 Adrenal hyperandrogenism per dehydroepiandrosterone sulfate (DHEAS) levels were found in 32% of women with PCOS. In non-PCOS women, dehydroepiandrosterone (DHEA) and its sulfate had no predictive role concerning clinical, anthropometric, and metabolic parameters. In PCOS women, mainly in the hyperandrogenemic group, DHEA showed to be a significant predictor against most anthropometric-metabolic index abnormalities (odds ratio [OR] = 0.36-0.97; p < 0.05), and an increase in triglycerides (TG) levels (OR = 0.76; p = 0.006). Dehydroepiandrosterone sulfate presented a few predictive effects regarding PCOS-associated disorders. In controls, DHEAS predicted against the increase in estimated average glucose (OR= 0.38; p = 0.036). In the normoandrogenic group, it predicted against elevation in the waist/hip ratio (WHR) (OR= 0.59; p = 0.042), and in hyperandrogenemic PCOS women, it predicted against abnormality in the conicity index (CI) (OR = 0.31; p = 0.028).

CONCLUSION

 Dehydroepiandrosterone was shown to be a better predictor of abnormal anthropometric and biochemical parameters in women with PCOS than DHEAS. Thus, regarding adrenal prohormones, DHEA measurement, instead of DHEAS, should be preferred in PCOS management. The effects of androgen prohormones on the prediction of PCOS abnormalities are weak.

Heat Shock Protein 70 Mediates the Protective Effect of Naringenin on High-Glucose-Induced Alterations of Endothelial Function

Endothelial dysfunction plays a pivotal role in the development and progression of diabetic vascular complications. Naringenin (Nar) is a flavanone bioactive isolated from citrus fruits known to have in vitro and in vivo antidiabetic properties. However, whether Nar affects endothelial function remains unclear in diabetes or under high-glucose (HG) condition. Using an in vitro model of hyperglycemia in human umbilical vein endothelial cells (HUVECs), we found that Nar administration markedly attenuated HG-induced alterations of endothelial function, evidenced by the mitigation of oxidative stress and inflammation, the reduction of cell adhesion molecular expressions, and the improvement of insulin resistance. We also found that HG exposure significantly reduced the levels of intracellular heat shock protein 70 (iHSP70 or iHSPA1A) and the release of HSP70 from HUVECs. HSP70 depletion mimicked and clearly diminished the protective effects of Nar on HG-induced alterations of endothelial function. In addition, Nar treatment significantly enhanced iHSP70 protein levels through a transcription-dependent manner. These results demonstrated that Nar could protect HUVECs against HG-induced alterations of endothelial function through upregulating iHSP70 protein levels. These findings are also helpful in providing new therapeutic strategies that are promising in the clinical use of Nar for the treatment of diabetes and diabetic complications.

Adipocyte and steroidogenic cell cross-talk in polycystic ovary syndrome

BACKGROUND

Metabolic and endocrine alterations in women with polycystic ovary syndrome (PCOS) affect adipose tissue mass and distribution. PCOS is characterised by hyperandrogenism, obesity and adipocyte dysfunction. Hyperandrogenism in PCOS drives dysfunctional adipocyte secretion of potentially harmful adipocytokines. Glucocorticoids and sex-steroids modulate adipocyte development and function. For their part, adipocyte products interact with adrenal and ovarian steroidogenic cells. Currently, the relationship between adipocyte and steroidogenic cells is not clear, and for these reasons, it is important to elucidate the interrelationship between these cells in women with and without PCOS.

OBJECTIVE AND RATIONALE

This comprehensive review aims to assess current knowledge regarding the interrelationship between adipocytes and adrenal and ovarian steroidogenic cells in animal models and humans with or without PCOS.

SEARCH METHODS

We searched for articles published in English and Portuguese in PubMed. Keywords were as follows: polycystic ovary syndrome, steroidogenesis, adrenal glands, theca cells, granulosa cells, adipocytes, adipocytokines, obesity, enzyme activation, and cytochrome P450 enzymes. We expanded the search into the references from the retrieved articles.

OUTCOMES

Glucocorticoids and sex-steroids modulate adipocyte differentiation and function. Dysfunctional adipocyte products play important roles in the metabolic and endocrine pathways in animals and women with PCOS. Most adipokines participate in the regulation of the hypothalamic-pituitary-adrenal and ovarian axes. In animal models of PCOS, hyperinsulinemia and poor fertility are common; various adipokines modulate ovarian steroidogenesis, depending on the species. Women with PCOS secrete unbalanced levels of adipocyte products, characterised by higher levels of leptin and lower levels of adiponectin. Leptin expression positively correlates with body mass index, waist/hip ratio and levels of total cholesterol, triglyceride, luteinising hormone, oestradiol and androgens. Leptin inhibits the production of oestradiol and, in granulosa cells, may modulate 17-hydroxylase and aromatase enzyme activities. Adiponectin levels negatively correlate with fat mass, body mass index, waist-hip ratio, glucose, insulin and triglycerides, and decrease androgen production by altering expression of luteinising hormone receptor, steroidogenic acute regulatory protein, cholesterol-side-chain cleavage enzyme and 17-hydroxylase. Resistin expression positively correlates with body mass index and testosterone, and promotes the expression of 17-hydroxylase enzyme in theca cells. The potential benefits of adipokines in the treatment of women with PCOS require more investigation.

WIDER IMPLICATIONS

The current data regarding the relationship between adipocyte products and steroidogenic cells are conflicting in animals and humans. Polycystic ovary syndrome is an excellent model to investigate the interrelationship among adipocyte and steroidogenic cells. Women with PCOS manifest some pathological conditions associated with hyperandrogenism and adipocyte products. In animals, cross-talk between cells may vary according to species, and the current review suggests opportunities to test new medications to prevent or even reverse several harmful sequelae of PCOS in humans. Further studies are required to investigate the possible therapeutic application of adipokines in women with obese and non-obese PCOS. Meanwhile, when appropriate, metformin use alone, or associated with flutamide, may be considered for therapeutic purposes.

DHEA-pretreatment attenuates oxidative stress in kidney-cortex and liver of diabetic rabbits and delays development of the disease

In view of reported discrepancies concerning antioxidant activity of dehydroepiandrosterone (DHEA), a widely used dietary supplement, the current investigation was undertaken to evaluate the antioxidant properties of DHEA in both kidney-cortex and liver of alloxan (ALX)-induced diabetic rabbits, as this diabetogenic compound exhibits the ROS-dependent action. ALX was injected to animals following 7 days of DHEA administration. Four groups of rabbits were used in the experiments: control, DHEA-treated control, diabetic and DHEA-treated diabetic. Our results show for the first time, that in kidney-cortex DHEA resulted in normalization of hydroxyl free radicals (HFR) levels and restoration of catalase (CAT) and glutathione peroxidase (GPx) activities to near the control values, while in liver DHEA prevented the malondialdehyde (MDA) accumulation and normalized glutathione reductase (GR) and glucose-6-phosphate dehydrogenase (G6PDH) activities. Moreover, in both kidney-cortex and liver DHEA supplementation prevented GSSG elevation accompanied by a decrease in GSH/GSSG ratio. Although DHEA attenuated oxidative stress in both kidney-cortex and liver of ALX-induced diabetic rabbits and significantly delayed the onset of diabetes in time, it did not protect against the final development of diabetes. In conclusion, the current investigation underscores the complexity of the antioxidant action of DHEA. The data are of clinical interest since DHEA supplementation could prevent the deleterious effects of ROS and delay, or even prevent the onset of many diseases. However, in view of the reported pro-oxidant effects of high DHEA doses, the potential use of this agent as a supplement needs a careful evaluation.

Transforming Growth Factor Beta 1 Alters Glucose Uptake but Not Insulin Signalling in Human Primary Myotubes From Women With and Without Polycystic Ovary Syndrome

Women with polycystic ovary syndrome (PCOS), commonly have profound skeletal muscle insulin resistance which can worsen other clinical features. The heterogeneity of the condition has made it challenging to identify the precise mechanisms that cause this insulin resistance. A possible explanation for the underlying insulin resistance may be the dysregulation of Transforming Growth Factor-beta (TGFβ) signalling. TGFβ signalling contributes to the remodelling of reproductive and hepatic tissues in women with PCOS. Given the systemic nature of TGFβ signalling and its role in skeletal muscle homeostasis, it may be possible that these adverse effects extend to other peripheral tissues. We aimed to determine if TGFβ1 could negatively regulate glucose uptake and insulin signalling in skeletal muscle of women with PCOS. We show that both myotubes from women with PCOS and healthy women displayed an increase in glucose uptake, independent of changes in insulin signalling, following short term (16 hr) TGFβ1 treatment. This increase occurred despite pro-fibrotic signalling increasing via SMAD3 and connective tissue growth factor in both groups following treatment with TGFβ1. Collectively, our findings show that short-term treatment with TGFβ1 does not appear to influence insulin signalling or promote insulin resistance in myotubes. These findings suggest that aberrant TGFβ signalling is unlikely to directly contribute to skeletal muscle insulin resistance in women with PCOS in the short term but does not rule out indirect or longer-term effects.

Putative Role of Protein Palmitoylation in Cardiac Lipid-Induced Insulin Resistance

In the heart, inhibition of the insulin cascade following lipid overload is strongly associated with contractile dysfunction. The translocation of fatty acid transporter CD36 (SR-B2) from intracellular stores to the cell surface is a hallmark event in the lipid-overloaded heart, feeding forward to intracellular lipid accumulation. Yet, the molecular mechanisms by which intracellularly arrived lipids induce insulin resistance is ill-understood. Bioactive lipid metabolites (diacyl-glycerols, ceramides) are contributing factors but fail to correlate with the degree of cardiac insulin resistance in diabetic humans. This leaves room for other lipid-induced mechanisms involved in lipid-induced insulin resistance, including protein palmitoylation. Protein palmitoylation encompasses the reversible covalent attachment of palmitate moieties to cysteine residues and is governed by protein acyl-transferases and thioesterases. The function of palmitoylation is to provide proteins with proper spatiotemporal localization, thereby securing the correct unwinding of signaling pathways. In this review, we provide examples of palmitoylations of individual signaling proteins to discuss the emerging role of protein palmitoylation as a modulator of the insulin signaling cascade. Second, we speculate how protein hyper-palmitoylations (including that of CD36), as they occur during lipid oversupply, may lead to insulin resistance. Finally, we conclude that the protein palmitoylation machinery may offer novel targets to fight lipid-induced cardiomyopathy.

Hypoxia induces the translocation of glucose transporter 1 to the plasma membrane in vascular endothelial cells

Glucose uptake and adenosine triphosphate (ATP) generation are important for the survival and growth of endothelial cells. An increase of glucose uptake under hypoxia was previously shown to be associated with the increased expression of glucose transporters (GLUTs). However, the regulation of GLUT trafficking to the cell surface has not been examined in detail. Here, we report the characterization of GLUT1 translocation to the plasma membrane during hypoxia in endothelial cells. Human umbilical vein endothelial cells (HUVECs) were exposed to hypoxia (1% O2) for 12 h, which significantly induced GLUT1 expression and translocation to the plasma membrane. GLUT1 translocation was associated with a decrease of intracellular ATP by hypoxia. Decreasing ATP levels with antimycin-A and 2-deoxyglucose induced GLUT1 translocation under normoxia. The induction of hypoxia-inducible factor-1α under normoxia did not influence the cell surface expression of GLUT1 or cellular ATP concentration. Interestingly, the translocation of GLUT1 induced by hypoxia was inhibited by the ATP-sensitive potassium (KATP) channel inhibitor glibenclamide, while the mitochondrial KATP channel inhibitor 5-HD did not influence GLUT1 translocation during hypoxia. These observations indicate that a decrease of intracellular ATP triggers GLUT1 translocation to the plasma membrane and is mediated by KATP channels, which would contribute to glucose uptake in HUVECs during hypoxia.

The Role of Visceral Adiposity Index as Predictor of Metabolic Syndrome in Obese and Nonobese Women with Polycystic Ovary Syndrome

Background: To evaluate anthropometric-metabolic biomarkers as predictors of metabolic syndrome (MS) in women with polycystic ovary syndrome (PCOS) with and without obesity. Methods: This was an observational cross-sectional study. Patients were classified as nonobese-PCOS (body mass index, BMI <30 kg/m², n = 385), and obese-PCOS (BMI ≥30 kg/m², n = 261). The anthropometric parameters waist circumference, waist/hip ratio, lean body mass, fat body mass, visceral adiposity index (VAI), lipid accumulating product, and biomarkers of glucose and lipid metabolisms were compared between groups. Binominal logistic regression analyses were performed to identify predictors of MS. Results: Obesity was diagnosed in 40% of all PCOS women (P < 0.001). Blood pressure and anthropometric abnormalities were significantly more frequent in obese-PCOS women (P < 0.001, for all comparisons). Glucose metabolism markers were higher in obese-PCOS compared with nonobese-PCOS (P < 0.001, for all comparisons). High-density lipoprotein cholesterol was lower in obese group than in nonobese group (1.26 mM vs. 1.08 mM, P < 0.001). MS was found in 23 of 385 (6%) nonobese-PCOS and in 116 of 261 (44.4%) obese-PCOS (P < 0.001). VAI was the best predictor of MS in both nonobese-PCOS (OR = 4.1, 95% CI 1.5-11.1) and obese-PCOS (OR = 12.9, 95% CI 5.7-29.0). Conclusions: MS is more prevalent in PCOS women with obesity. VAI was the strongest predictor of MS in both obese and nonobese PCOS women, and can be applied in clinical practice for early detection of risk for MS and precocious intervention in women with PCOS, particularly in obese women.

Prenatal Nutrition Containing Bisphenol A Affects Placenta Glucose Transfer: Evidence in Rats and Human Trophoblast

This work aims to clarify the effect of dietary supplementation with Bisphenol A (BPA), a chemical widely present in beverage and food containers, on placental glucose transfer and pregnancy outcome. The study was performed on female Sprague Dawley rats fed with a diet containing BPA (2.5, 25 or 250 μg/Kg/day) for a period of a month (virgin state) plus 20 days during pregnancy. Western blot analysis and immunohistochemistry were performed in placental tissues for glucose type 1 transporter (GLUT1). Furthermore, human trophoblast, HTR8-SV/neo cells, were used to evaluate the effect of BPA on glucose transport and uptake. Studies in rats showed that food supplementation with BPA, produces a higher fetal weight (FW) to placenta weight (PW) ratio at the lowest BPA concentration. Such low concentrations also reduced maternal weight gain in late pregnancy and up-regulated placental expression of GLUT1. Treatment of HTR8-SV/neo with the non-toxic dose of 1 nM BPA confirmed up-regulation of GLUT1 expression and revealed higher activity of the transporter with an increase in glucose uptake and GLUT1 membrane translocation. Overall, these results indicate that prenatal exposure to BPA affects pregnancy and fetal growth producing changes in the placental nutrients-glucose transfer.

DNA methylation status influences insulin-induced glucose transport in 3T3-L1 adipocytes by mediating p53 expression

Researchers frequently use 3T3-L1 adipocytes as a fat cell line, but the capacity of this line for insulin-mediated glucose transport is lower than that of primary isolated fat cells. In this study, we found that 5-azacytidine (5-aza-C), DNA methyltransferase 1 inhibitor, enhanced insulin-stimulated 2-deoxyglucose (2-DG) transport in 3T3-L1 cells after adipogenic differentiation. We next examined the expression of the genes related to glucose transport and insulin signal transduction. The insulin independent glucose transporter, glucose transporter 1 (GLUT1), showed lower expression in 5-aza-C pre-treated 3T3-L1 adipocytes, than in un-treated control adipocytes, while the expression of insulin dependent transporter GLUT4 remained unchanged. In addition, insulin receptor substrate-1 (IRS-1) was highly expressed in 5-aza-C pre-treated adipocytes. Based on DNA microarray and functional annotation analysis, we noticed that 5-aza-C pretreatment activated the tumor suppressor p53 pathway. We confirmed that in 5-aza-C adipocytes, p53 expression was markedly higher, and the methylation level of CpGs in its promoter region was lower than in un-treated control adipocytes. Moreover, pharmacological inhibition of p53 restored GLUT1 and IRS-1 expression to the same level as in un-treated 3T3-L1 adipocytes, and significantly decreased insulin-mediated 2-DG uptake. These results suggest that glucose transport capacity in adipocytes is influenced by DNA methylation status, and demethylation induced by 5-aza-C increased it possibly through the p53 signaling pathway.

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.

Dehydroepiandrosterone on metabolism and the cardiovascular system in the postmenopausal period

Dehydroepiandrosterone (DHEA), mostly present as its sulfated ester (DHEA-S), is an anabolic hormone that naturally declines with age. Furthermore, it is the most abundant androgen and estrogen precursor in humans. Low plasma levels of DHEA have been strongly associated with obesity, insulin resistance, dyslipidemia, and high blood pressure, increasing the risk of cardiovascular disease. In this respect, DHEA could be regarded as a promising agent against metabolic syndrome (MetS) in postmenopausal women, since several age-related metabolic diseases are reported during aging. There are plenty of experimental evidences showing beneficial effects after DHEA therapy on carbohydrate and lipid metabolism, as well as cardiovascular health. However, its potential as a therapeutic agent appears to attract controversy, due to the lack of effects on some symptoms related to MetS. In this review, we examine the available literature regarding the impact of DHEA therapy on adiposity, glucose metabolism, and the cardiovascular system in the postmenopausal period. Both clinical studies and in vitro and in vivo experimental models were selected, and where possible, the main cellular mechanisms involved in DHEA therapy were discussed. Schematic representation showing some of the general effects observed after administration DHEA therapy on target tissues of energy metabolism and the cardiovascular system. ↑ represents an increase, ↓ represents a decrease, - represents a worsening and ↔ represents no change after DHEA therapy.

The Effect of Statins on Levels of Dehydroepiandrosterone (DHEA) in Women with Polycystic Ovary Syndrome: A Systematic Review and Meta-Analysis

BACKGROUND Currently, statins are used to treat polycystic ovary syndrome (PCOS). This systematic review and meta-analysis aimed to investigate the effect of statins on serum or plasma levels of dehydroepiandrosterone (DHEA) in women with PCOS. MATERIAL AND METHODS Databases that were searched included PubMed, Embase, and the Cochrane Library from their inception to August of 2018. Published randomized controlled trials (RCTs) were identified that evaluated the impact of statins on plasma DHEA levels in women with PCOS. The Cochrane risk of bias tool was used to assess the quality of the included RCTs. A random-effects model was used to analyze the pooled results. RESULTS Meta-analysis was performed on data from ten published studies that included 735 patients and showed that statin treatment could significantly reduce plasma DHEA levels when compared with controls (SMD, -0.43; 95% CI, -0.81-0.06; p=0.02; I²=82%). Statins were significantly more effective than placebo in reducing the levels of DHEAs. Subgroup analysis based on statin type showed that atorvastatin significantly reduced DHEA levels (SMD, -0.63; 95% CI, -1.20 - -0.05; p=0.03; I²=38%) but simvastatin did not significantly reduce DHEA levels (SMD: -0.14; 95% CI, -0.49-0.28; p=0.43; I²=77%). Subgroup analysis based on duration of treatment showed no significant difference between 12 weeks of statin treatment (SMD, -0.61; 95% CI, -1.23-0.02; p=0.06; I²=85%) and 24 weeks (SMD, -0.34; 95% CI -0.95-0.28; p=0.29; I²=83%). CONCLUSIONS Meta-analysis showed that statins significantly reduced the levels of DHEA when compared with placebo in patients with PCOS.

Gossypol from Cottonseeds Ameliorates Glucose Uptake by Mimicking Insulin Signaling and Improves Glucose Homeostasis in Mice with Streptozotocin-Induced Diabetes

Glucose absorption from the gut and glucose uptake into muscles are vital for the regulation of glucose homeostasis. In the current study, we determined if gossypol (GSP) reduces postprandial hyperglycemia or enhances glucose uptake; we also investigated the molecular mechanisms underlying those processes in vitro and in vivo. GSP strongly and concentration dependently inhibited α-glucosidase by functioning as a competitive inhibitor with IC₅₀ value of 0.67 ± 0.44. GSP activated the insulin receptor substrate 1 (IRS-1)/protein kinase B (Akt) signaling pathways and enhanced glucose uptake through the translocation of glucose transporter 4 (GLUT4) into plasma membrane in C2C12 myotubes. Pretreatment with a specific inhibitor attenuated the in vitro effects of GSP. We used a streptozotocin-induced diabetic mouse model to assess the antidiabetic potential of GSP. Consistent with the in vitro study, a higher dose of GSP (2.5 mg/kg^-1) dramatically decreased the postprandial blood glucose levels associated with the upregulated expressions of GLUT4 and the IRS-1/Akt-mediated signaling cascade in skeletal muscle. GSP treatment also significantly boosted antioxidant enzyme expression and mitigated gluconeogenesis in the liver. Collectively, these data imply that GSP has the potential in managing and preventing diabetes by ameliorating glucose uptake and improving glucose homeostasis.

Amodiaquine improves insulin resistance and lipid metabolism in diabetic model mice

AIMS

Although peroxisome proliferator-activated receptors (PPARs)α/γ dual agonists can be beneficial for treatment of dyslipidemia in patients with type 2 diabetes, their use is limited owing to various side effects, including body weight gain, edema, and heart failure. We aimed to demonstrate that amodiaquine, an antimalarial agent, has potential as a PPARα/γ dual agonist with low risk of adverse effects.

METHODS

We screened a Prestwick library (Prestwick Chemical; Illkirch, France) to identify novel PPARα/γ dual agonists and selected amodiaquine (4-[(7-chloroquinolin-4-yl)amino]-2-[(diethylamino)methyl]phenol), which activated both PPAR-α & -γ, for further investigation. We performed both in vitro, including glucose uptake assay and fatty acid oxidation assay, and in vivo studies to elucidate the anti-diabetic and anti-obesity effects of amodiaquine.

RESULTS

Amodiaquine selectively activated the transcriptional activities of PPARα/γ and enhanced both fatty acid oxidation and glucose uptake without altering insulin secretion in vitro. In high-fat diet-induced obese and genetically modified obese/diabetic mice, amodiaquine not only remarkably ameliorated insulin resistance, hyperlipidemia, and fatty liver but also decreased body weight gain.

CONCLUSION

Our findings suggest that amodiaquine exerts beneficial effects on glucose and lipid metabolism by concurrent activation of PPARα/γ. Furthermore, amodiaquine acts as an alternative insulin-sensitizing agent with a positive influence on lipid metabolism and has potential to prevent and treat type 2 diabetes while reducing the risk of lipid abnormalities.

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.

Cyanidin-3-rutinoside increases glucose uptake by activating the PI3K/Akt pathway in 3T3-L1 adipocytes

In this study, the effect of cyanidin-3-rutinoside (C3R) on glucose uptake by 3T3-L1 adipocytes was studied. C3R significantly increased glucose uptake, which was associated with enhanced plasma membrane glucose transporter type 4 (PM-GLUT4) expression in 3T3-L1 adipocytes. The potentiating effect of C3R on glucose uptake and PM-GLUT4 expression was related to enhanced phosphorylation of insulin receptor substrate 1 (IRS-1) and Akt, as well as augmented activation of phosphatidylinositol-3-kinase (PI3K) in the insulin signaling pathway. C3R induced glucose uptake was inhibited only by the PI3K inhibitor, but not by an AMPK inhibitor in 3T3-L1 adipocytes. Therefore, C3R likely up-regulates glucose uptake and PM-GLUT4 expression in 3T3-L1 adipocytes by activating the PI3K/Akt pathways.

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.

Neurosteroid dehydroepiandrosterone enhances activity and trafficking of astrocytic GLT-1 via σ1 receptor-mediated PKC activation in the hippocampal dentate gyrus of rats

Neurosteroid dehydroepiandrosterone (DHEA) has been reported to exert a potent neuroprotective effect against glutamate-induced excitotoxicity. However, the underlying mechanism remains to be elucidated. One of the possible mechanisms may be an involvement of astrocytic glutamate transporter subtype-1 (GLT-1) that can quickly clear spilled glutamate at the synapse to prevent excitotoxicity. To examine the effect of DHEA on GLT-1 activity, we measured synaptically induced glial depolarization (SIGD) in the dentate gyrus (DG) of adult rats by applying an optical recording technique to the hippocampal slices stained with voltage-sensitive dye RH155. Bath-application of DHEA for 10 min dose-dependently increased SIGD without changing presynaptic glutamate releases, which was sensitive to the GLT-1 blocker DHK. Patch-clamp recordings in astrocytes showed that an application of 50 μM DHEA increased glutamate-evoked inward currents (Iglu) by approximately 1.5-fold, which was dependent on the GLT-1 activity. In addition, the level of biotinylated GLT-1 protein in the surface of astrocytes was significantly elevated by DHEA. The DHEA-increased SIGD, Iglu, and GLT-1 translocation to the cell surface were blocked by the σ₁ R antagonist NE100 and mimicked by the σ₁ R agonist PRE084. DHEA elevated the phosphorylation level of PKC in a σ₁ R-dependent manner. Furthermore, the PKC inhibitor chelerythrine could prevent the DHEA-increased SIGD, Iglu, and GLT-1 translocation. Collectively, present results suggest that DHEA enhances the activity and translocation to cell surface of astrocytic GLT-1 mainly via σ₁ R-mediated PKC cascade.

Antidiabetic effects of Morus alba fruit polysaccharides on high-fat diet- and streptozotocin-induced type 2 diabetes in rats

ETHNOPHARMACOLOGICAL RELEVANCE

Type 2 diabetes mellitus (T2DM) is becoming a serious threat to human health. The fruit of Morus alba L. is widely used as a traditional Chinese medicine for the treatment of DM, dizziness, tinnitus, insomnia, and premature graying, as well as to protect the liver and kidneys. Several studies have demonstrated that the aqueous extracts of the roots bark, leaves, and ramuli of mulberry, which are known to contain polyphenols and polysaccharides, have antihyperglycemic and antihyperlipidemic activities. The aim of the present study was to further investigate the active polysaccharides from M. alba fruit by evaluating the antidiabetic activities of different fractions on T2DM rats and elucidate the mechanism underlying these activities.

MATERIALS AND METHODS

Diabetic rats were treated with two fractions of M. alba fruit polysaccharides (MFP50 and MFP90). The disease models were induced by a high-fat diet and low dose injection of streptozotocin and were compared to normal rats and metformin-treated diabetic rats. After seven weeks, the fasting blood glucose (FBG), oral glucose tolerance test (OGTT), fasting serum insulin (FINS) levels, homeostasis model of assessment-insulin resistance (HOMA-IR), glycated serum protein (GSP), and serum alanine transaminase (ALT) levels, as well as serum lipid profiles and histopathological changes in the pancreas were measured. Next, the expressions of the insulin signaling pathway were measured by western blot analysis to elucidate the potential mechanism underlying these antidiabetic activities.

RESULTS

After seven weeks of treatment, a significant reduction in the FBG levels, OGTT-area under the curve (OGTT-AUC), FINS, HOMA-IR, ALT, and triglyceride (TG) values of the MFP50 group was observed. On the other hand, in the MFP90 group, the FBG, OGTT-AUC, FINS, HOMA-IR, GSP, and TG levels were significantly reduced. The level of high-density lipoprotein cholesterol (HDL-c) and the proportion of HDL-c to total cholesterol (TC) significantly increased in the MFP50 group. Moreover, MFP50 and MFP90 induced repair of damaged pancreatic tissues of the diabetic rats. The hypoglycemic effect of MFP50 was more stable than MFP90, whereas the hypolipidemic effect of MFP90 was slightly better than MFP50. Moreover, the expression levels of InsR, IRS-2, Akt and GLUT4 in the MFP90 group significantly increased relative to that of the T2DM group.

CONCLUSIONS

MFP50 and MFP90 have markedly antihyperglycemic and antihyperlipidemic effects and can clearly relieve diabetes symptoms in the T2DM rat model. The M. alba fruit polysaccharides may potentially be utilized as an effective treatment for T2DM. Further research into the structures of active M. alba fruit polysaccharides and their mechanisms in promoting antidiabetic effects are underway.

Serum dehydroepiandrosterone levels are associated with lower risk of type 2 diabetes: the Rotterdam Study

AIMS/HYPOTHESIS

Previous literature documents controversial results for the impact of dehydroepiandrosterone (DHEA) in glucose metabolism. We aimed to assess the associations between serum levels of DHEA and its main derivatives DHEA sulphate (DHEAS) and androstenedione, as well as the ratio of DHEAS to DHEA, and risk of type 2 diabetes.

METHODS

We used data on serum levels of DHEA, DHEAS and androstenedione from 5189 middle-aged and elderly men and women from the prospective population-based Rotterdam Study. Type 2 diabetes was defined as a fasting blood glucose ≥7.0 mmol/l or a non-fasting blood glucose ≥11.1 mmol/l.

RESULTS

During a median follow-up of 10.9 years, 643 patients with incident type 2 diabetes were identified. After adjusting for age, sex, cohort, fasting status, fasting glucose and insulin, and BMI, both serum DHEA levels (per 1 unit natural log-transformed, HR 0.76, 95% CI 0.67, 0.87) and serum DHEAS levels (per 1 unit natural log-transformed, HR 0.82, 95% CI 0.73, 0.92) were inversely associated with risk of type 2 diabetes in the total population. Further adjustment for alcohol, smoking, physical activity, prevalent cardiovascular disease, serum total cholesterol, use of lipid-lowering medications, systolic BP, treatment for hypertension, C-reactive protein, oestradiol and testosterone did not substantially affect the association between DHEA and incident type 2 diabetes (per 1 unit natural log-transformed, HR 0.80, 95% CI 0.65, 0.99), but abolished the association between DHEAS and type 2 diabetes. Androstenedione was not associated with risk of type 2 diabetes, nor was DHEAS to DHEA ratio.

CONCLUSIONS/INTERPRETATION

DHEA serum levels might be an independent marker of type 2 diabetes.

GLUT1-mediated glucose uptake plays a crucial role during Plasmodium hepatic infection

Intracellular pathogens have evolved mechanisms to ensure their survival and development inside their host cells. Here, we show that glucose is a pivotal modulator of hepatic infection by the rodent malaria parasite Plasmodium berghei and that glucose uptake via the GLUT1 transporter is specifically enhanced in P. berghei‐infected cells. We further show that ATP levels of cells containing developing parasites are decreased, which is known to enhance membrane GLUT1 activity. In addition, GLUT1 molecules are translocated to the membrane of the hepatic cell, increasing glucose uptake at later stages of infection. Chemical inhibition of GLUT1 activity leads to a decrease in glucose uptake and the consequent impairment of hepatic infection, both in vitro and in vivo. Our results reveal that changes in GLUT1 conformation and cellular localization seem to be part of an adaptive host response to maintain adequate cellular nutrition and energy levels, ensuring host cell survival and supporting P. berghei hepatic development.

Long-Term Administration of Dehydroepiandrosterone Accelerates Glucose Catabolism via Activation of PI3K/Akt-PFK-2 Signaling Pathway in Rats Fed a High-Fat Diet

Dehydroepiandrosterone (DHEA) has a fat-reducing effect, while little information is available on whether DHEA regulates glucose metabolism, which would in turn affect fat deposition. To investigate the effects of DHEA on glucose metabolism, rats were administered a high-fat diet containing either 0 (HCG), 25 (HLG), 50 (HMG), or 100 (HHG) mg·kg^-1 DHEA per day via gavage for 8 weeks. Results showed that long-term administration of DHEA inhibited body weight gain in rats on a high-fat diet. No statistical differences in serum glucose levels were observed, whereas hepatic glycogen content in HMG and HHG groups and muscle glycogen content in HLG and HMG groups were higher than those in HCG group. Glucokinase, malate dehydrogenase and phosphofructokinase-2 activities in HMG and HHG groups, pyruvate kinase and succinate dehydrogenase activities in HMG group, and pyruvate dehydrogenase activity in all DHEA treatment groups were increased compared with those in HCG group. Phosphoenolpyruvate carboxykinase and glycogen phosphorylase mRNA levels were decreased in HMG and HHG groups, whereas glycogen synthase-2 mRNA level was increased in HMG group compared with those in HCG. The abundance of Glut2 mRNA in HMG and HHG groups and Glut4 mRNA in HMG group was higher than that in HCG group. DHEA treatment increased serum leptin content in HMG and HHG groups compared with that in HCG group. Serum insulin content and insulin receptor mRNA level in HMG group and insulin receptor substrate-2 mRNA level in HMG and HHG group were increased compared with those in HCG group. Furthermore, Pi3k mRNA level in HMG and Akt mRNA level in HMG and HHG groups were significantly increased than those in HCG group. These data showed that DHEA treatment could enhance glycogen storage and accelerate glucose catabolism in rats fed a high-fat diet, and this effect may be associated with the activation of PI3K/Akt-PFK-2 signaling pathway.

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.

Hyperandrogenism Decreases GRP78 Protein Level and Glucose Uptake in Human Endometrial Stromal Cells

BACKGROUND

Women with polycystic ovary syndrome (PCOS) exhibit a low fertility by chronic hyperandrogenemia. Different evidence have shown that androgens could regulate the endoplasmic reticulum (ER) homeostasis and glucose metabolism. However, it is unclear whether androgens can exert these effects on human endometrial stromal cells. Our goal was to study the protein content of GRP78 (an ER homeostasis marker) in endometria from women with PCOS and healthy women and to assess the GRP78 protein levels and its relationship with glucose uptake on a human endometrial stromal cell line stimulated with testosterone.

METHODS

Immunohistochemistry assays for GRP78 were performed on endometrial samples obtained from women with PCOS (n = 8) and control women subjected to hysterectomy (n = 8). Western blot analysis for GRP78 and glucose uptake was assessed in a telomerase-immortalized human endometrial stromal cell line (T-HESC) exposed to testosterone for 24 or 48 hours and challenged to an insulin short-term stimulation. Tukey test was performed for human samples comparison. Student t test or ANOVA-Bonferroni test was carried out according to the in vitro experiment. P < .05 was considered as significant.

RESULTS

GRP78 stromal immunostaining was reduced in PCOS endometria compared to controls (P < .05). The T-HESC shows a testosterone-dependent downregulation of GRP78 protein content (P < .05), concomitant with half-reduction in glucose uptake compared to controls (P < .05). Moreover, enhanced small interfering RNA against GRP78 messenger RNA leads to a decrease in glucose uptake (P < .05). Such effects were reverted by hydroxyflutamide, an inhibitor of androgen receptor.

CONCLUSION

These results suggest that hyperandrogenemic PCOS environment could compromise the endometrial homeostasis confirmed by the decrease in glucose uptake induced by testosterone and exhibited by stromal cells.

Effects of DHEA on metabolic and endocrine functions of adipose tissue

Dehydroepiandrosterone (DHEA) and its sulfate ester, DHEAS, are the major circulating adrenal steroids and serve as substrates for sex hormone biosynthesis. DHEA is effectively taken up by adipose tissue, where the concentrations of free DHEA are four to ten times higher than those found in the circulation. DHEA reduces adipose tissue mass and inhibits the proliferation and differentiation of adipocytes; it may also protect against obesity by lowering the activity of stearoyl-CoA desaturase 1 in fat cells. Recent studies demonstrate that DHEA stimulates triacylglycerol hydrolysis in adipose tissue by increasing the expression and activity of adipose triglyceride lipase and hormone-sensitive lipase, the key enzymes of lipolysis. DHEA has been shown to modulate insulin signaling pathways, enhance glucose uptake in adipocytes, and increase insulin sensitivity in patients with DHEA deficiency or abnormal glucose tolerance. Additionally, by suppressing the activity of 11β-hydroxysteroid dehydrogenase 1 in adipocytes, DHEA may promote intra-adipose inactivation of cortisol to cortisone. Several studies have demonstrated that DHEA may also regulate the expression and secretion of adipokines such as leptin, adiponectin, and resistin. The effects of DHEA on adipokine expression in adipose tissue are depot-specific, with visceral fat being the most responsive. The mechanisms underlying DHEA actions in adipose tissue are still unclear; however, they involve nuclear receptors such as androgen receptor and peroxisome proliferator-activated receptors γ and α. Because clinical trials investigating the effects of DHEA failed to yield consistent results, further studies are needed to clarify the role of DHEA in the regulation of human adipose tissue physiology.

Inflamed macrophage microvesicles induce insulin resistance in human adipocytes

BACKGROUND

Cytokines secreted by adipose tissue macrophages (ATMs) significantly alter adipocyte function, inducing inflammatory responses and decreasing insulin sensitivity. However, little relevant information is available regarding the role of microvesicles (MVs) derived from ATMs in macrophage-adipocyte crosstalk.

METHODS

MVs were generated by stimulation of M1 or M2 phenotype THP-1 macrophages and incubated with human primary mature adipocytes and differentiated adipocytes. Subsequently, insulin-stimulated phosphorylation of Akt (pAkt) and glucose uptake were determined. Glucose transporter 4 (GLUT4) translocation and nuclear translocation of nuclear factor (NF)-kappa B were also analyzed in treated adipocytes.

RESULTS

M1 macrophage-derived MVs (M1 MVs) significantly reduced protein abundance of insulin-induced Akt phosphorylation in human primary mature adipocytes and differentiated adipocytes, when compared with the same concentration of M2 macrophage-derived MVs (M2 MVs). In contrast to M2 MVs, which enhanced the insulin-induced glucose uptake measured by 2-NBDG, M1 MVs decreased this effect in treated adipocytes. M1 MVs treatment also brought about a significant increase in the nuclear translocation of nuclear factor (NF)-kappa B, coupled with a decrease in pAkt level and GLUT4 translocation compared with M2 MVs-treated adipocytes. These effects were reversed by BAY 11-7085, a NF- kappa B specific inhibitor.

CONCLUSIONS

MVs derived from proinflammatory (M1) macrophages may, at least in part, contribute to the pathogenesis of obesity-induced insulin resistance, reducing insulin signal transduction and decreasing glucose uptake in human adipocytes, through NF-kappa B activation. Therefore, these MVs may be potential therapy candidates for the management of type 2 diabetes mellitus.

Tumor suppressor p53 negatively regulates glycolysis stimulated by hypoxia through its target RRAD

Cancer cells display enhanced glycolysis to meet their energetic and biosynthetic demands even under normal oxygen concentrations. Recent studies have revealed that tumor suppressor p53 represses glycolysis under normoxia as a novel mechanism for tumor suppression. As the common microenvironmental stress for tumors, hypoxia drives the metabolic switch from the oxidative phosphorylation to glycolysis, which is crucial for survival and proliferation of cancer cells under hypoxia. The p53's role and mechanism in regulating glycolysis under hypoxia is poorly understood. Here, we found that p53 represses hypoxia-stimulated glycolysis in cancer cells through RRAD, a newly-identified p53 target. RRAD expression is frequently decreased in lung cancer. Ectopic expression of RRAD greatly reduces glycolysis whereas knockdown of RRAD promotes glycolysis in lung cancer cells. Furthermore, RRAD represses glycolysis mainly through inhibition of GLUT1 translocation to the plasma membrane. Under hypoxic conditions, p53 induces RRAD, which in turn inhibits the translocation of GLUT1 and represses glycolysis in lung cancer cells. Blocking RRAD by siRNA greatly abolishes p53's function in repressing glycolysis under hypoxia. Taken together, our results revealed an important role and mechanism of p53 in antagonizing the stimulating effect of hypoxia on glycolysis, which contributes to p53's function in tumor suppression.

Dehydroepiandrosterone activates AMP kinase and regulates GLUT4 and PGC-1α expression in C2C12 myotubes

Exercise and caloric restriction (CR) have been reported to have anti-ageing, anti-obesity, and health-promoting effects. Both interventions increase the level of dehydroepiandrosterone (DHEA) in muscle and blood, suggesting that DHEA might partially mediate these effects. In addition, it is thought that either 5'-adenosine monophosphate-activated protein kinase (AMPK) or peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) mediates the beneficial effects of exercise and CR. However, the effects of DHEA on AMPK activity and PGC-1α expression remain unclear. Therefore, we explored whether DHEA in myotubes acts as an activator of AMPK and increases PGC-1α. DHEA exposure increased glucose uptake but not the phosphorylation levels of Akt and PKCζ/λ in C2C12 myotubes. In contrast, the phosphorylation levels of AMPK were elevated by DHEA exposure. Finally, we found that DHEA induced the expression of the genes PGC-1α and GLUT4. Our current results might reveal a previously unrecognized physiological role of DHEA; the activation of AMPK and the induction of PGC-1α by DHEA might mediate its anti-obesity and health-promoting effects in living organisms.

Ginsenoside Rb1 ameliorates liver fat accumulation by upregulating perilipin expression in adipose tissue of db/db obese mice

Background

Ginsenoside Rb1 (G-Rb1), the major active constituent of ginseng, improves insulin sensitivity and exerts antidiabetic effects. We tested whether the insulin-sensitizing and antidiabetic effects of G-Rb1 results from a reduction in ectopic fat accumulation, mediated by inhibition of lipolysis in adipocytes.

Methods

Obese and diabetic db/db mice were treated with daily doses of 20 mg/kg G-Rb1 for 14 days. Hepatic fat accumulation was evaluated by measuring liver weight and triglyceride content. Levels of blood glucose and serum insulin were used to evaluate insulin sensitivity in db/db mice. Lipolysis in adipocytes was evaluated by measuring plasma-free fatty acids and glycerol release from 3T3-L1 adipocytes treated with G-Rb1. The expression of relevant genes was analyzed by western blotting, quantitative real-time polymerase chain reaction, and enzyme-linked immunosorbent assay kit.

Results

G-Rb1 increased insulin sensitivity and alleviated hepatic fat accumulation in obese diabetic db/db mice, and these effects were accompanied by reduced liver weight and hepatic triglyceride content. Furthermore, G-Rb1 lowered the levels of free fatty acids in obese mice, which may contribute to a decline in hepatic lipid accumulation. Corresponding to these results, G-Rb1 significantly suppressed lipolysis in 3T3-L1 adipocytes and upregulated the perilipin expression in both 3T3-L1 adipocytes and mouse epididymal fat pads. Moreover, G-Rb1 increased the level of adiponectin and reduced that of tumor necrosis factor-α in obese mice, and these effects were confirmed in 3T3-L1 adipocytes.

Conclusion

G-Rb1 may improve insulin sensitivity in obese and diabetic db/db mice by reducing hepatic fat accumulation and suppressing adipocyte lipolysis; these effects may be mediated via the upregulation of perilipin expression in adipocytes.

Skeletal myopathy in patients with chronic heart failure: significance of anabolic-androgenic hormones

In heart failure, impairment of cardiac muscle function leads to numerous neurohormonal and metabolic disorders, including an imbalance between anabolic and catabolic processes, in favour of the latter. These disorders cause loss of muscle mass with structural and functional changes within the skeletal muscles, known as skeletal myopathy. This phenomenon constitutes an important mechanism that participates in the pathogenesis of chronic heart failure. both its clinical symptoms and the progression of the disease. Attempts to reverse the above-mentioned pathologic processes by exploiting the anabolic action of androgenic hormones could provide a potentially attractive treatment option. The current concepts of anabolic androgen deficiency and resultant skeletal myopathy in patients with heart failure are reviewed, and the potential role of anabolic-androgenic hormones as an emerging therapeutic option for targeting heart failure is discussed.

Apelin-13 decreases lipid storage in hypertrophic adipocytes in vitro through the upregulation of AQP7 expression by the PI3K signaling pathway

BACKGROUND

Adipocyte-secreted apelin contributes to decreased adiposity and to improved insulin resistance, but the mechanisms remain unknown. The present study aimed to assess if apelin-13 is an upstream signal regulation factor of aquaporin 7 (AQP7), a water-glycerol transporter present in the plasma membrane of adipocytes that plays a key role in the regulation of lipid accumulation.

MATERIAL/METHODS

3T3-L1 pre-adipocytes were induced to fully differentiated adipocytes; hypertrophic adipocytes were then induced using palmitate. The effects of apelin-13 on AQP7 expression in hypertrophic adipocytes were investigated before and after treatment with LY249002, a PI3K inhibitor. Accumulation of cytoplasmic triglycerides (TG) in hypertrophic adipocytes was also determined.

RESULTS

We found that 0.1 mM of palmitate induced a model of hypertrophic adipocytes with a lower AQP7 expression (0.26±0.07 vs. 0.46±0.04, P<0.05). Apelin-13 100 nM or 1000 nM upregulated AQP7 mRNA expression (100 nM: 0.54±0.06 and 1000 nM: 0.58±0.09 vs. control: 0.33±0.04, both P<0.05), and decreased accumulation of cytoplasmic triglycerides in hypertrophic adipocytes. Pretreatment using 10 µM LY294002 prevented the increase in AQP7 expression observed when using apelin-13 alone (apelin-13 + LY49002: 0.38±0.03 vs. apelin-13: 0.54±0.06, P<0.05), as well as the decreased cytoplasmic TG accumulation (apelin-13 + LY294002: 3.79±0.04 µM per µg/ml vs. apelin-13: 3.32±0.08 µM per µg/ml, P<0.05).

CONCLUSIONS

Apelin-13 decreases lipid storage in hypertrophic adipocytes in vitro, possibly through the upregulation of AQP7 expression by the PI3K signaling pathway. Treatment using apelin-13 and AQP modulators might represent novel treatment strategies against obesity and its related complications.

Tumour-associated mutant p53 drives the Warburg effect

Tumour cells primarily utilize aerobic glycolysis for energy production, a phenomenon known as the Warburg effect. Its mechanism is not well understood. The tumour suppressor gene p53 is frequently mutated in tumours. Many tumour-associated mutant p53 (mutp53) proteins not only lose tumour suppressive function but also gain new oncogenic functions that are independent of wild-type p53, defined as mutp53 gain of function (GOF). Here we show that tumour-associated mutp53 stimulates the Warburg effect in cultured cells and mutp53 knockin mice as a new mutp53 GOF. Mutp53 stimulates the Warburg effect through promoting GLUT1 translocation to the plasma membrane, which is mediated by activated RhoA and its downstream effector ROCK. Inhibition of RhoA/ROCK/GLUT1 signalling largely abolishes mutp53 GOF in stimulating the Warburg effect. Furthermore, inhibition of glycolysis in tumour cells greatly compromises mutp53 GOF in promoting tumorigenesis. Thus, our results reveal a new mutp53 GOF and a mechanism for controlling the Warburg effect.

Green tea (-)-epigallocatechin gallate suppresses IGF-I and IGF-II stimulation of 3T3-L1 adipocyte glucose uptake via the glucose transporter 4, but not glucose transporter 1 pathway

This study investigated the pathways involved in EGCG modulation of insulin-like growth factor (IGF)-stimulated glucose uptake in 3T3-L1 adipocytes. EGCG inhibited IGF-I and IGF-II stimulation of adipocyte glucose uptake with dose and time dependencies. EGCG at 20μM for 2h decreased IGF-I- and IGF-II-stimulated glucose uptake by 59% and 64%, respectively. Pretreatment of adipocytes with antibody against the EGCG receptor (also known as the 67-kDa laminin receptor; 67LR), prevented the effects of EGCG on IGF-increased glucose uptake, but pretreatment with normal rabbit immunoglobulin did not. This suggests that the 67LR mediates the anti-IGF effect of EGCG on adipocyte glucose uptake. Further analysis indicated EGCG, IGF-I, and IGF-II did not alter total levels of GLUT1 or GLUT4 protein. However, EGCG prevented the IGF-increased GLUT4 levels in the plasma membrane and blocked the IGF-decreased GLUT4 levels in low-density microsomes. Neither EGCG nor its combination with IGF altered GLUT1 protein levels in the plasma membrane and low-density microsomes. EGCG also suppressed the IGF-stimulated phosphorylation of IGF signaling molecules, PKCζ/λ, but not AKT and ERK1/2, proteins. This study suggests that EGCG suppresses IGF stimulation of 3T3-L1 adipocyte glucose uptake through inhibition of the GLUT4 translocation, but not through alterations of the GLUT1 pathway.

Underestimation of the pentose-phosphate pathway in intact primary neurons as revealed by metabolic flux analysis

The rates of glucose oxidized at glycolysis and pentose-phosphate pathway (PPP) in neurons are controversial. Using [3-(3)H]-, [1-(14)C]-, and [6-(14)C]glucose to estimate fluxes through these pathways in resting, intact rat cortical primary neurons, we found that the rate of glucose oxidized through PPP was, apparently, ∼14% of total glucose metabolized. However, inhibition of PPP rate-limiting step, glucose-6-phosphate (G6P) dehydrogenase, increased approximately twofold the glycolytic rate; and, knockdown of phosphoglucose isomerase increased ∼1.8-fold the PPP rate. Thus, in neurons, a considerable fraction of fructose-6-phosphate returning from the PPP contributes to the G6P pool that re-enters PPP, largely underestimating its flux.

Dehydroepiandrosterone exerts antiglucocorticoid action on human preadipocyte proliferation, differentiation, and glucose uptake

Glucocorticoids increase adipocyte proliferation and differentiation, a process underpinned by the local reactivation of inactive cortisone to active cortisol within adipocytes catalyzed by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). The adrenal sex steroid precursor dehydroepiandrosterone (DHEA) has been shown to inhibit 11β-HSD1 in murine adipocytes; however, rodent adrenals do not produce DHEA physiologically. Here, we aimed to determine the effects and underlying mechanisms of the potential antiglucocorticoid action of DHEA and its sulfate ester DHEAS in human preadipocytes. Utilizing a human subcutaneous preadipocyte cell line, Chub-S7, we examined the metabolism and effects of DHEA in human adipocytes, including adipocyte proliferation, differentiation, 11β-HSD1 expression, and activity and glucose uptake. DHEA, but not DHEAS, significantly inhibited preadipocyte proliferation via cell cycle arrest in the G1 phase independent of sex steroid and glucocorticoid receptor activation. 11β-HSD1 oxoreductase activity in differentiated adipocytes was inhibited by DHEA. DHEA coincubated with cortisone significantly inhibited preadipocyte differentiation, which was assessed by the expression of markers of early (LPL) and terminal (G3PDH) adipocyte differentiation. Coincubation with cortisol, negating the requirement for 11β-HSD1 oxoreductase activity, diminished the inhibitory effect of DHEA. Further consistent with glucocorticoid-opposing effects of DHEA, insulin-independent glucose uptake was significantly enhanced by DHEA treatment. DHEA increases basal glucose uptake and inhibits human preadipocyte proliferation and differentiation, thereby exerting an antiglucocorticoid action. DHEA inhibition of the amplification of glucocorticoid action mediated by 11β-HSD1 contributes to the inhibitory effect of DHEA on human preadipocyte differentiation.

Fasting serum lipid and dehydroepiandrosterone sulfate as important metabolites for detecting isolated postchallenge diabetes: serum metabolomics via ultra-high-performance LC-MS

BACKGROUND

Isolated postchallenge diabetes (IPD), a subtype of type 2 diabetes mellitus (T2DM) defined as 2-h postprandial plasma glucose ≥ 200 mg/dL (≥ 11.1 mmol/L) and fasting plasma glucose (FPG) <108 mg/dL (<6.0 mmol/L), is often overlooked during screening for diabetes on the basis of FPG concentrations. A key challenge is early identification of IPD by the use of fasting serum, which is critical for large-scale diabetes screening.

METHODS

We applied a nontargeted metabolomic approach using ultra-high-performance liquid chromatography-quadrupole TOF-mass spectrometry (UPLC-QTOF-MS) to analyze serum samples from 51 patients with IPD, 52 with newly diagnosed T2DM, and 49 healthy individuals. We processed metabolite profiles by multivariate analysis to identify potential metabolites, which were further confirmed by tandem MS (MS/MS). We also used GC-MS and ELISA methods to detect potentially important metabolites. A number of independent samples were selected to validate the identified candidates.

RESULTS

We selected 15 metabolites with a view to distinguishing patients with IPD, whereas 11 were identified with an authentic standard. The selected metabolites included linoleic acid, oleic acid, phospholipids, and dehydroepiandrosterone sulfate (DHEA-S). In IPD samples, significantly higher linoleic and oleic acid (P < 0.001) and lower DHEA-S (P < 0.001) concentrations were observed, compared with controls. The area under the curve from a combination of linoleic acid, oleic acid, and DHEA-S in the validation study was 0.849 for the IPD group.

CONCLUSIONS

The current study provides useful information to bridge the gaps in our understanding of the metabolic alterations associated with IPD and might facilitate the characterization of patients with IPD by the use of fasting serum.

Ceramide 1-phosphate stimulates glucose uptake in macrophages

It is well established that ceramide 1-phosphate (C1P) is mitogenic and antiapoptotic, and that it is implicated in the regulation of macrophage migration. These activities require high energy levels to be available in cells. Macrophages obtain most of their energy from glucose. In this work, we demonstrate that C1P enhances glucose uptake in RAW264.7 macrophages. The major glucose transporter involved in this action was found to be GLUT 3, as determined by measuring its translocation from the cytosol to the plasma membrane. C1P-stimulated glucose uptake was blocked by selective inhibitors of phosphatidylinositol 3-kinase (PI3K) or Akt, also known as protein kinase B (PKB), and by specific siRNAs to silence the genes encoding for these kinases. C1P-stimulated glucose uptake was also inhibited by pertussis toxin (PTX) and by the siRNA that inhibited GLUT 3 expression. C1P increased the affinity of the glucose transporter for its substrate, and enhanced glucose metabolism to produce ATP. The latter action was also inhibited by PI3K- and Akt-selective inhibitors, PTX, or by specific siRNAs to inhibit GLUT 3 expression.

Involvement of distinct PKC gene products in T cell functions

It is well established that members of the protein kinase C (PKC) family seem to have important roles in T cells. Focusing on the physiological and non-redundant PKC functions established in primary mouse T cells via germline gene-targeting approaches, our current knowledge defines two particularly critical PKC gene products, PKCθ and PKCα, as the "flavor of PKC" in T cells that appear to have a positive role in signaling pathways that are necessary for full antigen receptor-mediated T cell activation ex vivo and T cell-mediated immunity in vivo. Consistently, in spite of the current dogma that PKCθ inhibition might be sufficient to achieve complete immunosuppressive effects, more recent results have indicated that the pharmacological inhibition of PKCθ, and additionally, at least PKCα, appears to be needed to provide a successful approach for the prevention of allograft rejection and treatment of autoimmune diseases.

Adrenarche and middle childhood

Middle childhood, the period from 6 to 12 years of age, is defined socially by increasing autonomy and emotional regulation, somatically by the development of anatomical structures for subsistence, and endocrinologically by adrenarche, the adrenal production of dehydroepiandrosterone (DHEA). Here I suggest that DHEA plays a key role in the coordinated development of the brain and body beginning with middle childhood, via energetic allocation. I argue that with adrenarche, increasing levels of circulating DHEA act to down-regulate the release of glucose into circulation and hence limit the supply of glucose which is needed by the brain for synaptogenesis. Furthermore, I suggest the antioxidant properties of DHEA may be important in maintaining synaptic plasticity throughout middle childhood within slow-developing areas of the cortex, including the insula, thamalus, and anterior cingulate cortex. In addition, DHEA may play a role in the development of body odor as a reliable social signal of behavioral changes associated with middle childhood.

Sex differences in human adipose tissues - the biology of pear shape

Women have more body fat than men, but in contrast to the deleterious metabolic consequences of the central obesity typical of men, the pear-shaped body fat distribution of many women is associated with lower cardiometabolic risk. To understand the mechanisms regulating adiposity and adipose tissue distribution in men and women, significant research attention has focused on comparing adipocyte morphological and metabolic properties, as well as the capacity of preadipocytes derived from different depots for proliferation and differentiation. Available evidence points to possible intrinsic, cell autonomous differences in preadipocytes and adipocytes, as well as modulatory roles for sex steroids, the microenvironment within each adipose tissue, and developmental factors. Gluteal-femoral adipose tissues of women may simply provide a safe lipid reservoir for excess energy, or they may directly regulate systemic metabolism via release of metabolic products or adipokines. We provide a brief overview of the relationship of fat distribution to metabolic health in men and women, and then focus on mechanisms underlying sex differences in adipose tissue biology.

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.

Polymethoxyflavonoids tangeretin and nobiletin increase glucose uptake in murine adipocytes

Tangeretin and nobiletin are polymethoxyflavonoids that are contained in citrus fruits. Polymethoxyflavonoids are reported to have several biological functions including anti-inflammatory, anti-atherogenic, or anti-diabetic effects. However, whether polymethoxyflavonoids directly affect glucose uptake in tissues is not well understood. In the current study, we investigated whether tangeretin and nobiletin affect glucose uptake in insulin target cells such as adipocytes. We observed that treatment with tangeretin or nobiletin significantly increased the uptake of [(3) H]-deoxyglucose in differentiated 3T3-F442A adipocytes in a concentration-dependent manner. Data showed that phosphatidyl inositol 3 kinase, Akt1/2, and the protein kinase A pathways were involved in the increase in glucose uptake induced by polymethoxyflavonoids. These data suggest that the anti-diabetic action of polymethoxyflavonoids is partly exerted via these signaling pathways in insulin target tissues.