Adiponectin and resistin in the neonatal rat: effects of dexamethasone and hypoxia

Glucocorticoid/Adiponectin Axis Mediates Full Activation of Cold-Induced Beige Fat Thermogenesis

Glucocorticoids (GCs), a class of corticosteroids produced by the adrenal cortex in response to stress, exert obesity-promoting effects. Although adaptive thermogenesis has been considered an effective approach to counteract obesity, whether GCs play a role in regulating cold stress-induced thermogenesis remains incompletely understood. Here, we show that the circulating levels of stress hormone corticosterone (GC in rodents) were significantly elevated, whereas the levels of adiponectin, an adipokine that was linked to cold-induced adaptive thermogenesis, were decreased 48 h post cold exposure. The administration of a glucocorticoid hydrocortisone downregulated adiponectin protein and mRNA levels in both WAT and white adipocytes, and upregulated thermogenic gene expression in inguinal fat. In contrast, mifepristone, a glucocorticoid receptor antagonist, enhanced adiponectin expression and suppressed energy expenditure in vivo. Mechanistically, hydrocortisone suppressed adiponectin expression by antagonizing PPARγ in differentiated 3T3-L1 adipocytes. Ultimately, adiponectin deficiency restored mifepristone-decreased oxygen consumption and suppressed the expression of thermogenic genes in inguinal fat. Taken together, our study reveals that the GCs/adiponectin axis is a key regulator of beige fat thermogenesis in response to acute cold stress.

Links between HPA axis and adipokines: clinical implications in paradigms of stress-related disorders

INTRODUCTION

In the human organism, a constant interplay exists between the stress system [which includes the activity of the hypothalamic-pituitary-adrenal (HPA) axis] and the adipose tissue. This interplay is mediated by hormones of the HPA axis such as corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and glucocorticoids (GCs) and adipokines secreted by the adipose tissue.

AREAS COVERED

In this critical review, the bi-directional interactions between HPA axis and the most studied adipokines such as leptin and adiponectin, as well as the pro-inflammatory adipocytokines tumor necrosis factor (TNF) and interleukin (IL) 6 are presented. Furthermore, these interactions are described in normalcy as well as in specific clinical paradigms of stress-related disorders such as eating disorders, hypothalamic amenorrhea, and stress-related endogenous hypercortisolism states. Wherever new therapeutic strategies emerge, they are presented accordingly.

EXPERT COMMENTARY

Additional research is needed to clarify the mechanisms involved in the interplay between the HPA axis and the adipose tissue. Research should be focused, in particular, on the development of new therapeutic means targeting dysfunctional adipose tissue in stress-related situations.

Impact of Glucocorticoid Excess on Glucose Tolerance: Clinical and Preclinical Evidence

Glucocorticoids (GCs) are steroid hormones that exert important physiological actions on metabolism. Given that GCs also exert potent immunosuppressive and anti-inflammatory actions, synthetic GCs such as prednisolone and dexamethasone were developed for the treatment of autoimmune- and inflammatory-related diseases. The synthetic GCs are undoubtedly efficient in terms of their therapeutic effects, but are accompanied by significant adverse effects on metabolism, specifically glucose metabolism. Glucose intolerance and reductions in insulin sensitivity are among the major concerns related to GC metabolic side effects, which may ultimately progress to type 2 diabetes mellitus. A number of pre-clinical and clinical studies have aimed to understand the repercussions of GCs on glucose metabolism and the possible mechanisms of GC action. This review intends to summarize the main alterations that occur in liver, skeletal muscle, adipose tissue, and pancreatic islets in the context of GC-induced glucose intolerance. For this, both experimental (animals) and clinical studies were selected and, whenever possible, the main cellular mechanisms involved in such GC-side effects were discussed.

Insights into the molecular mechanisms of diabetes-induced endothelial dysfunction: focus on oxidative stress and endothelial progenitor cells

Diabetes mellitus is a heterogeneous, multifactorial, chronic disease characterized by hyperglycemia owing to insulin insufficiency and insulin resistance (IR). Recent epidemiological studies showed that the diabetes epidemic affects 382 million people worldwide in 2013, and this figure is expected to be 600 million people by 2035. Diabetes is associated with microvascular and macrovascular complications resulting in accelerated endothelial dysfunction (ED), atherosclerosis, and cardiovascular disease (CVD). Unfortunately, the complex pathophysiology of diabetic cardiovascular damage is not fully understood. Therefore, there is a clear need to better understand the molecular pathophysiology of ED in diabetes, and consequently, better treatment options and novel efficacious therapies could be identified. In the light of recent extensive research, we re-investigate the association between diabetes-associated metabolic disturbances (IR, subclinical inflammation, dyslipidemia, hyperglycemia, dysregulated production of adipokines, defective incretin and gut hormones production/action, and oxidative stress) and ED, focusing on oxidative stress and endothelial progenitor cells (EPCs). In addition, we re-emphasize that oxidative stress is the final common pathway that transduces signals from other conditions-either directly or indirectly-leading to ED and CVD.

Mechanical-tactile stimulation (MTS) intervention in a neonatal stress model alters adult adipose tissue deposition and prevents hyperinsulinemia in male rats

Preterm infants are exposed to numerous stressors during hospitalization and by term corrected gestational age they have lower body weight but a greater proportion of total body as well as abdominal visceral adipose tissue (VAT) accumulation. Greater abdominal VAT stores have a known association with metabolic syndrome. Mechanical-tactile stimulation (MTS) improves modulation of stress response in both humans and rodents. We hypothesize that MTS, administered during an established model of neonatal stress, would decrease stress-driven adiposity and prevent associated metabolic imbalances in adult rats. Neonatal stress, administered to rat pups from postnatal days 5 to P9, consisted of needle puncture and hypoxic/hyperoxic challenge during 60 min of maternal separation (STRESS; n=20). Mechanical-tactile stimulation (MTS; n=20) was administered to rat pups for 10 min during maternal separation in the stress protocol. Control animals received standard care (CTL; n=20). MRI measured adult (P120) abdominal total fat mass, subcutaneous (SAT) and visceral adipose tissue (VAT). Body weight and fasting serum adiponectin, leptin, glucose, insulin, and corticosterone were also measured. STRESS results in elevated VAT/SAT ratio compared to CTL but lower abdominal total fat mass and abdominal SAT. STRESS males experience hyperinsulinemia. Both STRESS and MTS had elevated leptin with lower adiponectin and corticosterone compared to CTL. In summary, neonatal stress promotes greater abdominal VAT accumulation and, in males, caused hyperinsulinemia and hypoadiponectinemia. Importantly, MTS normalized the VAT/SAT ratio and prevented hyperinsulinemia. We speculate that MTS ameliorates some of the negative metabolic consequences of early life perturbations due to neonatal stress exposure.

Glucocorticoid effects on adiponectin expression

Maintenance of energy metabolism and glucose homeostasis is achieved by the regulatory effects of many hormones and their interactions. Glucocorticoids produced from adrenal cortex and adiponectin produced by adipose tissue play important roles in the production, distribution, storage, and utilization of energy substrates. Glucocorticoids are involved in the activation of a number of catabolic processes by affecting the expression of a plethora of genes, while adiponectin acts primarily as an insulin sensitizer. Both are regulated by a number of physiological and pharmacological factors. Although the effects of glucocorticoids on adiponectin expression have been extensively studied in different in vitro, animal and clinical study settings, no consensus has been reached. This report reviews the primary literature concerning the effects of glucocorticoids on adiponectin expression and identifies potential reasons for the contradictory results between different studies. In addition, methods to gain better insights pertaining to the regulation of adiponectin expression are discussed.

Mechanistic modeling of the effects of glucocorticoids and circadian rhythms on adipokine expression

A mechanism-based model was developed to describe the effects of methylprednisolone (MPL), circadian rhythms, and the glucose/free fatty acid (FFA)/insulin system on leptin and adiponectin expression in white adipose tissue in rats. Fifty-four normal Wistar rats received 50 mg/kg MPL intramuscularly and were sacrificed at various times. An additional set of 54 normal Wistar rats were sacrificed at 18 time points across the 24-h light/dark cycle and served as controls. Measurements included plasma MPL, glucocorticoid receptor (GR) mRNA, leptin mRNA, adiponectin mRNA, plasma leptin, adiponectin, glucose, FFA, and insulin. MPL pharmacokinetics was described by a two-compartment model with two absorption components. All measured plasma markers and mRNA expression exhibited circadian patterns except for adiponectin and were described by Fourier harmonic functions. MPL caused significant down-regulation in GR mRNA with the nadir occurring at 5 h. MPL disrupted the circadian patterns in plasma glucose and FFA by stimulating their production. Plasma glucose and FFA subsequently caused an increase in plasma insulin. Furthermore, MPL disrupted the circadian patterns in leptin mRNA expression by stimulating its production. This rise was closely followed by an increase in plasma leptin. Both leptin mRNA and plasma leptin peaked at 12 h after MPL and eventually returned back to their circadian baselines. MPL and insulin had opposing effects on adiponectin mRNA expression and plasma adiponectin, which resulted in biphasic pharmacodynamic profiles. This small systems model quantitatively describes, integrates, and provides additional insights into various factors controlling adipokine gene expression.

Circulating adiponectin as a marker for glucocorticoid-related side effects in children and adolescents with inflammatory bowel disease

Glucocorticoid therapy is widely used in clinical practice. However, treatment with steroids carries the risk of side effects. We investigated changes in serum adiponectin and leptin in response to systemic glucocorticoid treatment in 18 pediatric patients with inflammatory bowel disease and contrasted these findings to circulating glucocorticoid bioactivity measured with a mammalian cell bioassay. Interestingly, serum adiponectin levels at 2 to 4 weeks of therapy were significantly higher in patients who experienced acute glucocorticoid-related side effects (22.9 +/- 2.6 microg/mL, n = 7) than in those who did not (16.0 +/- 2.1 microg/mL, n = 11, P < 0.05). Serum leptin was not associated with side effects. Circulating adiponectin may serve as an early and readily available endogenous biomarker for acute glucocorticoid-related side effects in pediatric patients.

Adiponectin, skeletal muscle adiponectin receptor expression and insulin resistance following dexamethasone

OBJECTIVE

Skeletal muscle is a major site of adiponectin action and of glucocorticoid-induced insulin resistance. Little human data exist however, regarding the impact of exogenous glucocorticoids on adiponectin receptors in skeletal muscle.

DESIGN AND PATIENTS

Twelve subjects with type 2 diabetes and 12 controls underwent blood sampling and muscle biopsy of vastus lateralis before and after 4 days of 4 mg dexamethasone.

MEASUREMENTS

(i) Total and high molecular weight (HMW) plasma adiponectin, glucose and insulin; (ii) Skeletal muscle adiponectin receptor AdipoR1 and AdipoR2 mRNA levels by quantitative real time RT-PCR.

RESULTS

Baseline total adiponectin (8.0 +/- 0.89 vs. 12.5 +/- 1.46 microg/ml, P = 0.013), HMW adiponectin (2.8 +/- 0.44 vs. 5.9 +/- 1.04 microg/ml, P = 0.014) and AdipoR2 mRNA levels (mean DeltaC(T )14.71 +/- 0.35 vs. 13.37 +/- 0.28, P = 0.017) were significantly lower in diabetic subjects. After dexamethasone, AdipoR2 mRNA fell in the controls but there was no change in the diabetic group, while there was a significant increase in total (P = 0.002) and HMW adiponectin (P < 0.001) across both groups. Total and HMW plasma adiponectin correlated with clinical and biochemical measures of insulin sensitivity. However following dexamethasone which increased insulin resistance, the relationship between adiponectin and the biochemical measures was lost.

CONCLUSIONS

Plasma adiponectin and skeletal muscle AdipoR2 mRNA expression are reduced in subjects with diabetes; both are likely to contribute to the observed insulin resistance. Dexamethasone inhibits AdipoR2 mRNA expression in nondiabetic subjects, while there is a small rise in plasma adiponectin levels. The close relationship between plasma adiponectin and biochemical measures of insulin sensitivity is lost in the setting of glucocorticoid-induced insulin resistance.

Effects of prenatal betamethasone administration on leptin and adiponectin concentrations in maternal and fetal circulation

OBJECTIVE

The aim of this study was to determine the effects of in vivo administration of prenatal betamethasone on leptin and adiponectin concentration in maternal and fetal circulation.

STUDY DESIGN

Blood samples were collected from 35 pregnant women receiving betamethasone for threatened preterm delivery before and at different time points after drug administration. Cord blood was collected at delivery in infants born from mothers treated with betamethasone and in 15 infants who delivered at the same gestational age not receiving betamethasone.

RESULTS

Betamethasone caused an approximately 170% increase in maternal leptin at 24 hours after betamethasone, whereas it had no effects on adiponectin concentration. Betamethasone affects neonatal leptin and adiponectin levels in a time-dependent manner. The glucocorticoid-induced changes in the relationship between these adipokines in maternal and fetal circulation was long lasting.

CONCLUSION

These results provide the first evidence for in vivo effects of glucocorticoids on maternal and fetal adipokines relationship in human pregnancy.

Hypoxia inducible factor-1 upregulates adiponectin in diabetic mouse hearts and attenuates post-ischemic injury

Adiponectin is a circulating cytokine with important cardioprotective effects. Plasma adiponectin levels are significantly reduced in patients with insulin resistance and type II diabetes mellitus and cardiovascular disease. Although adiponectin is primarily synthesized by adipocytes, new studies reveal that adiponectin is secreted by other cell types, including cardiomyocytes. Control of adiponectin gene expression in heart and microvasculature is poorly understood. We investigated the regulation of adiponectin expression by the transcription factor hypoxia inducible factor-1 (HIF-1) and its role in attenuating cardiac reperfusion injury. HIF-1 regulation of adiponectin was examined by isolating and characterizing the murine adiponectin promoter. HIF-1-dependent activation of the murine adiponectin promoter was verified via electrophoretic mobility shift assays, transient transfection assays, and QPCR. We show for the first time that HIF-1 activation via an siRNA-mediated prolyl 4-hydroxylase-2 gene silencing strategy induced adiponectin mRNA expression in murine microvascular endothelium in vitro (17-fold), intact hearts (22-fold, wild type; 5-fold, obese/diabetic) and white adipose tissue (37-fold, wild-type; 9.6-fold, obese/diabetic). HIF-1-induced adiponectin expression was associated with improved myocardial viability in obese/diabetic mice (32% increase) and preservation of left ventricular function (36% increase in rate pressure product). Our studies suggest that local production of adiponectin by cardiomyocytes/microvascular endothelial cells may regulate cardiac function and indicate a novel strategy for protecting diabetic hearts from ischemia/reperfusion injury.

Epidermal growth factor and parathyroid hormone-related peptide mRNA in the mammary gland and their concentrations in milk: effects of postpartum hypoxia in lactating rats

The physiological adaptations of the neonatal rat to hypoxia from birth include changes in gastrointestinal function and intermediary metabolism. We hypothesized that the hypoxic lactating dam would exhibit alterations in mammary gland function leading to changes in the concentration of milk peptides that are important in neonatal gastrointestinal development. The present study assessed the effects of chronic hypoxia on peptides produced by the mammary glands and present in milk. Chronic hypoxia decreased the concentration of epidermal growth factor (EGF) in expressed milk and pup stomach contents and decreased maternal mammary gland EGF mRNA. The concentration of parathyroid hormone-related protein (PTHrp) was unchanged in milk and decreased in pup stomach contents; however, mammary PTHLH mRNA was increased by hypoxia. There was a significant increase in adiponectin concentrations in milk from hypoxic dams. Chronic hypoxia decreased maternal body weight, and pair feeding normoxic dams an amount of food equivalent to hypoxic dam food intake decreased body weight to an equivalent degree. Decreased food intake did not affect the expression of EGF, PTHLH, or LEP mRNA in mammary tissue. The results indicated that chronic hypoxia modulated mammary function independently of hypoxia-induced decreases in maternal food intake. Decreased EGF and increased adiponectin concentrations in milk from hypoxic dams likely affect the development of neonatal intestinal function.

Resistin is expressed in human hepatocytes and induces insulin resistance

Resistin, known as an adipocyte-specific secretory factor (ADSF), is implicated to modulate insulin resistance in rodents. However, the precise role of this factor for human insulin resistance has remained elusive. Here, we investigate the relationship between human resistin and insulin resistance in hepatocytes and the effect of Metformin on resistin. In this study, the expression of resistin in human hepatocytes and hepatic tissues was examined, and the human resistin eukaryotic expression vector was constructed and stably transfected in HepG2 cells. Data showed that resistin is expressed in human hepatocytes and hepatic tissues. Overexpression of human resistin impaired significantly insulin-stimulated glucose uptake and glycogen synthesis in HepG2 cells. It also decreased the expression of insulin receptor substrate 2 (IRS-2) and c-cbl associated protein (CAP), whereas increased the expression of glycogen synthetase kinase 3beta (GSK-3beta). The result suggested that human resistin induced insulin resistance in hepatocytes by blocking the two insulin signal transduction pathways of PI-3K/Akt and of CAP/c-cbl. We also concluded that Metformin reversed the effect of resistin and downregulated the expression of resistin in hepatocytes.

Glucocorticoids produce whole body insulin resistance with changes in cardiac metabolism

Insulin resistance is viewed as an insufficiency in insulin action, with glucocorticoids being recognized to play a key role in its pathogenesis. With insulin resistance, metabolism in multiple organ systems such as skeletal muscle, liver, and adipose tissue is altered. These metabolic alterations are widely believed to be important factors in the morbidity and mortality of cardiovascular disease. More importantly, clinical and experimental studies have established that metabolic abnormalities in the heart per se also play a crucial role in the development of heart failure. Following glucocorticoids, glucose utilization is compromised in the heart. This attenuated glucose metabolism is associated with altered fatty acid supply, composition, and utilization. In the heart, elevated fatty acid use has been implicated in a number of metabolic, morphological, and mechanical changes and, more recently, in "lipotoxicity". In the present article, we review the action of glucocorticoids, their role in insulin resistance, and their influence in modulating peripheral and cardiac metabolism and heart disease.

Intermittent hypoxia causes insulin resistance in lean mice independent of autonomic activity

RATIONALE AND OBJECTIVES

Although many clinical physiology and epidemiology studies show an association between obstructive sleep apnea (OSA) and markers of insulin resistance, no causal pathway has been established. The purpose of the current study was to determine if the intermittent hypoxia (IH) stimulus that characterizes OSA causes insulin resistance in the absence of obesity. Furthermore, we assessed the impact of IH on specific metabolic function in liver and muscle. Finally, we examined the potential mechanistic role of the autonomic nervous system (ANS) in mediating insulin resistance in response to IH.

METHODS AND RESULTS

Hyperinsulinemic euglycemic clamps were conducted and whole-body insulin sensitivity, hepatic glucose output, and muscle-specific glucose utilization assessed in conscious, chronically instrumented adult male C57BL/6J mice exposed to (1) IH (achieving a nadir of Fi(O(2)) = 5-6% at 60 cycles/h for 9 h), (2) intermittent air as a control, (3) IH with ANS blockade (hexamethonium), or (4) IA with ANS blockade. IH decreased whole-body insulin sensitivity compared with intermittent air (38.8 +/- 2.7 vs. 49.4 +/- 1.5 mg/kg/min, p < 0.005) and reduced glucose utilization in oxidative muscle fibers, but did not cause a change in hepatic glucose output. Furthermore, the reduction in whole-body insulin sensitivity during IH was not restored by ANS blockade.

CONCLUSION

We conclude that IH can cause acute insulin resistance in otherwise lean, healthy animals, and that the response is associated with decreased glucose utilization of oxidative muscle fibers, but that it occurs independently of activation of the ANS.