Changes in adiponectin receptor expression in muscle and adipose tissue of type 2 diabetic patients during rosiglitazone therapy

Sarcopenia and Diabetes: A Detrimental Liaison of Advancing Age

Sarcopenia is an age-related clinical complaint characterized by the progressive deterioration of skeletal muscle mass and strength over time. Type 2 diabetes (T2D) is associated with faster and more relevant skeletal muscle impairment. Both conditions influence each other, leading to negative consequences on glycemic control, cardiovascular risk, general health status, risk of falls, frailty, overall quality of life, and mortality. PubMed/Medline, Scopus, Web of Science, and Google Scholar were searched for research articles, scientific reports, observational studies, clinical trials, narrative and systematic reviews, and meta-analyses to review the evidence on the pathophysiology of di-abetes-induced sarcopenia, its relevance in terms of glucose control and diabetes-related outcomes, and diagnostic and therapeutic challenges. The review comprehensively addresses key elements for the clinical definition and diagnostic criteria of sarcopenia, the pathophysiological correlation be-tween T2D, sarcopenia, and related outcomes, a critical review of the role of antihyperglycemic treatment on skeletal muscle health, and perspectives on the role of specific treatment targeting myokine signaling pathways involved in glucose control and the regulation of skeletal muscle metabolism and trophism. Prompt diagnosis and adequate management, including lifestyle inter-vention, health diet programs, micronutrient supplementation, physical exercise, and pharmaco-logical treatment, are needed to prevent or delay skeletal muscle deterioration in T2D.

Green Coffee Bean Extract Potentially Ameliorates Liver Injury due to HFD/STZ-Induced Diabetes in Rats

The goal of the current study was to examine the therapeutic potential of green coffee bean extract (GCBE) in the treatment of diabetic hepatic damage induced by high-fat diet (HFD) and streptozotocin (STZ) administration. The novelty of this study lies in constructing a newly stabilized in vivo obese diabetic animal model in rats using HFD/STZ for investigating the dose-dependent effect of two commonly used doses of GCBE in hepatoprotection against oxidative stress-induced hepatic damage by measuring many parameters that have not been carried out previously in other studies. GCBE that was used in this study was a hot water extract of green coffee beans with a concentration of 0.1 g ml−1. Male albino rats were given a single dose of STZ (35 mg kg−1), and HFD to induce diabetes mellitus (DM). For 28 days, two separate doses of GCBE 50 mg kg−1 and 100 mg kg−1 were administered orally to diabetic animals. Leptin, liver enzymes, oxidative stress parameters, inflammatory parameters, fasting plasma glucose (FPG), fasting plasma insulin (FPI), and lipid profile levels were examined. Real-time PCR and ELISA were used to quantitatively detect the mRNAs of the genes involved in the insulin signaling pathway, the genes involved in glucose metabolism, and the amounts of proteins. The levels of FPG, lipid profile, liver enzymes, inflammatory markers, and leptin in the HFD/STZ diabetic group revealed a considerable spike, while they considerably decreased after GCBE treatment in a dose-dependent manner. After GCBE treatment, the diabetic group showed a significant rise in the antioxidant markers glutathione, superoxide dismutase, and catalase, as well as a decrease in malondialdehyde and nitric oxide levels. The liver changes caused by HFD/STZ were entirely reversed by GCBE, and most intriguingly, in a dose-dependent manner. We concluded that GCBE can repair the hepatic oxidative damage caused by HFD and STZ by reversing all the previously measured parameters and improving the insulin signaling pathways. GCBE demonstrated strong antifree radical activity and significantly protected cells from oxidative damage caused by HFD/STZ.

Activation of POMC neurons to adiponectin participating in EA-mediated improvement of high-fat diet IR mice

Background

Insulin resistance (IR) is one of the common pathological manifestations of metabolic-related diseases, and the prevalence of relevant diseases is high. Acupuncture is beneficial to IR patients, but the central mechanism underlying this treatment remains unclear. This study provides mechanistic insights into how electroacupuncture (EA) improves IR through the response of Pro-opiomelanocortin (POMC) neurons to adiponectin (Adipo).

Methods

Glucose tolerance tests (GTT), Insulin tolerance tests (ITT) and fasting blood glucose (FBG) were detected by glucometer. Serum insulin, Adipo and skeletal muscle adiponectin receptor 1 (AdipoR1) protein levels were examined by ELISA. Homeostasis model assessment estimated insulin resistance (HOMA-IR) was calculated using the following formula: HOMA-IR = fasting insulin (FINS) (mU/L) × FBG (mmol/L)/22.5. The expression levels of AdipoR1 and Adipo mRNA in skeletal muscle were detected by real-time PCR quantification. The co-marking of c-Fos/AdipoR1 and POMC neurons were investigated using immunofluorescence. Spontaneous excitatory postsynaptic currents (sEPSCs) of POMC neurons and the response of POMC neurons to Adipo were detected via electrophysiology.

Results

EA significantly ameliorated HFD-induced impairment of GTT, ITT, FBG, and HOMA-IR which was correlated with recovery of the expression level of AdipoR1 and Adipo in skeletal muscle. The improved response of POMC neurons to Adipo in the hypothalamus may be a key factor in correcting abnormal glucose tolerance and improving IR.

Conclusion

This study demonstrates that EA can ameliorate HFD-induced impaired glucose tolerance through improved response of POMC neurons to Adipo in the hypothalamus, providing insight into the central mechanism of improving IR through EA.

Identification, characterization, and expression analysis of adiponectin receptors in black carp Mylopharyngodon piceus in response to dietary carbohydrate

In the present study, three cDNAs of AdipoRs (MpAdipoR1a, MpAdipoR1b, and MpAdipoR2) were identified from juvenile black carp Mylopharyngodon piceus. There were 375, 378, and 356 amino acids in the MpAdipoR1a, MpAdipoR1b, and MpAdipoR2, respectively. BLAST analysis reveals that MpAdipoRs share high identities with other known AdipoRs from zebrafish, rainbow trout, human, etc. And there were all seven transmembrane regions in the amino acid sequences of MpAdipoR1s and MpAdipoR2, respectively. The relative expression levels of MpAdipoR1s were higher in the liver, blood, brain, and eyes in black carp (p < 0.05). Relatively higher expression of MpAdipoR2 was detected in the liver (p < 0.05) and then in the adipose tissues and blood by real-time PCR assays. The relative expression levels of AdipoR mRNA in the liver, muscle, brain, blood, and adipose tissues were detected by real-time PCR in black carp fed with four levels of dietary carbohydrate (CHO) (10.65, 19.43, 28.84, and 37.91%) for 9 weeks, respectively. The expression levels of MpAdipoR1s in the liver, muscle, brain, and blood were induced and reached to the maximum at optimal dietary CHO (19.43 or 28.84%) and then were decreased at 37.91% dietary CHO, although there were no significant differences on the expression levels of MpAdipoR1a in the liver between 19.43, 28.84, and 37.91% dietary CHO. Similarly, MpAdipoR2 were also induced to the maximal levels in the liver, muscle, brain, and blood at optimal dietary CHO (19.43 or 28.84%) compared with that at 10.65% dietary CHO, although no significant differences were observed on the expression levels of MpAdipoR2 in the liver and muscle between groups fed 19.43 and 37.91% dietary CHO (p > 0.05). However, the expression levels of MpAdipoRs in the adipose tissues were significantly downregulated at excessive dietary CHO (37.91%) compared with other groups (p < 0.05). These results indicated that MpAdipoRs were inducible proteins and might enhance the understanding of their vital roles in the regulation of glucose metabolic homeostasis in black carp.

Oral Quercetin Supplementation Enhances Adiponectin Receptor Transcript Expression in Polycystic Ovary Syndrome Patients: A Randomized Placebo-Controlled Double-Blind Clinical Trial

OBJECTIVES

Polycystic ovary syndrome (PCOS), an ovarian-pituitary axis androgen disorder, is a common endocrine disease in women. Obesity-induced androgenesis and imbalance of adipokine secretion may lead to some metabolic features of PCOS. The beneficial effects of polyphenolic compounds such as quercetin have been reported, however, the underlying molecular mechanism is not entirely understood. In the present study, we investigated the effect of quercetin supplementation on the expression of adiponectin receptors at the transcript level in peripheral blood mononuclear cells (PBMC) samples of PCOS patients.

MATERIALS AND METHODS

In this randomized clinical trial, 84 PCOS subjects were randomly assigned to two groups; the treatment group received 1 g quercetin (two 500 mg capsules) daily for 12 weeks and the control group received placebo. To examine the effect of quercetin supplementation on PCOS patients in addition to biochemical and anthropometric assessments, the expression of ADIPOR1 and ADIPOR2 at the transcript level and AMPK level were determined by quantitative reverse transcription-polymerase chain reaction (RT-qPCR) and ELISA assays respectively.

RESULTS

Oral quercetin supplementation significantly increased ADIPOR1 and ADIPOR2 transcript expression by 1.32- and 1.46-fold respecetively (P<0.01). In addition, quercetin supplementation enhanced AMPK level by 12.3% compared with the control group (P<0.05).

CONCLUSIONS

Oral quercetin supplementation improves the metabolic features of PCOS patients by upregulating the expression of adiponectin receptors and AMPK (Registration Number: IRCT2013112515536N1).

Macrophage polarization phenotype regulates adiponectin receptor expression and adiponectin anti-inflammatory response

Adiponectin (APN), a pleiotropic adipokine that exerts anti-inflammatory, antidiabetic, and antiatherogenic effects through its receptors (AdipoRs), AdipoR1 and AdipoR2, is an important therapeutic target. Factors regulating AdipoR expression in monocyte/macrophages are poorly understood, and the significance of polarized macrophage activation in controlling AdipoR expression and the APN-mediated inflammatory response has not been investigated. The aim of this study was to investigate whether the macrophage polarization phenotype controls the AdipoR expression and APN-mediated inflammatory response. With the use of mouse bone marrow and peritoneal macrophages, we demonstrate that classical activation (M1) of macrophages suppressed (40-60% of control) AdipoR expression, whereas alternative activation (M2) preserved it. Remarkably, the macrophage polarization phenotypes produced contrasting inflammatory responses to APN (EC50 5 µg/ml). In M1 macrophages, APN induced proinflammatory cytokines, TNF-α, IL-6, and IL-12 (>10-fold of control) and AdipoR levels. In contrast, in M2 macrophages, APN induced the anti-inflammatory cytokine IL-10 without altering AdipoR expression. Furthermore, M1 macrophages adapt to a cytokine environment by reversing AdipoR expression. APN induced AdipoR mRNA and protein expression by up-regulating liver X receptor-α (LXRα) in macrophages. These results provide the first evidence that macrophage polarization is a key determinant regulating AdipoR expression and differential APN-mediated macrophage inflammatory responses, which can profoundly influence their pathogenic role in inflammatory and metabolic disorders.

Adiponectin decreases lipids deposition by p38 MAPK/ATF2 signaling pathway in muscle of broilers

Adiponectin is an adipokine hormone that influences glucose utilization, insulin sensitivity and energy homeostasis. To investigate the effect of adiponectin on lipids deposition in broilers, rosiglitazone and dexamethasone were used to treat broilers. A total of 120 twenty-three-day-old male Cobb broilers were randomly divided into 3 groups for 3 weeks of drug treatment. Serum adiponectin level and fatty acid composition in muscles were measured. Adiponectin, adiponectin receptors (adipoR1, adipoR2) and lipid metabolism-related genes expression levels in muscles were measured using real-time PCR. Western blot was used to measure the expression levels of lipid metabolism-related proteins and the phosphorylation of p38 mitogen-activated protein kinase (p38 MAPK)/activating transcription factor 2 (ATF2) pathway marker proteins. Rosiglitazone increased serum adiponectin concentration and the expression levels of adiponectin and adipoR1 (P < 0.05), while dexamethasone had the opposite effect. Intramuscular fat content, total fatty acid, saturated fatty acid and monounsaturated fatty acid reduced in the rosiglitazone treatment group (P < 0.05). In the rosiglitazone treatment group, the expression levels of lipogenic genes and proteins decreased in the muscles, whereas the expression levels of lipolysis genes increased. Meanwhile, the phosphorylation levels of p38MAPK and ATF2 increased with supplementation of rosiglitazone and decreased in the dexamethasone treatment group (P < 0.01). These results indicated that rosiglitazone and dexamethasone could regulate adiponectin expression in muscle of broilers and adiponectin had an anti-lipogenic effect by p38 MAPK/ATF2 signaling pathway.

AdipoR1 and AdipoR2 gene expression are regulated by thyroid hormones in adipose tissue

The aim of this study was to examine whether the relative gene expression of AdipoR1 and AdipoR2 in rat adipose tissue is altered by thyroid hormones, and whether this might relate to their circulating thyroid hormones and adiponectin levels. Hyper- and hypothyroidism were induced by daily oral administration of levothyroxine and methimazole in rats, respectively, over a 42 days period. Real-time PCR analysis was performed to evaluate the changes in AdipoR1 and AdipoR2 mRNA levels in the adipose tissue on days 15, 28, 42, and also 2 weeks after the cessation of treatment. In response to treatment with methimazole, mRNA levels of AdipoR1 and AdipoR2 decreased in the white adipose tissue compared to the euthyroid rats (p < 0.05). This decline was reversible 2 weeks after treatment cessation. The mRNA levels of AdipoR1 and AdipoR2 were increased in the hyperthyroid group of animals compared to euthyroid control (p < 0.05), and its changes were reversible 2 weeks after treatment cessation (P < 0.05). Adiponectin receptors gene expression levels in the adipose tissue of treated animals have positive correlations with thyroid hormones concentrations. Our results suggest that AdipoR1 and AdipoR2 gene expression is regulated by thyroid hormones in hypo- and hyperthyroidism.

Insulin-sensitizing effects on muscle and adipose tissue after dietary fiber intake in men and women with metabolic syndrome

CONTEXT

Dietary fibers have been associated with a reduced incidence of type 2 diabetes mellitus in epidemiological studies; however, the precise mechanisms are unknown.

OBJECTIVE

The objective of the study was to evaluate the efficacy and site of action of an insoluble dietary fiber derived from maize (HAM-RS2) in improving insulin resistance in subjects at increased risk of type 2 diabetes mellitus.

DESIGN

This study was a randomized, controlled crossover, dietary intervention study.

SETTING

The study was conducted at the Centre for Diabetes, Endocrinology, and Research, Royal Surrey County Hospital, Guildford, United Kingdom.

PARTICIPANTS

Fifteen men and women with insulin resistance participated in the study.

INTERVENTION

The intervention included 40 g/d HAM-RS2 compared with a matched placebo for 8 wk.

MAIN OUTCOME MEASURES

After each supplement, participants underwent a two-step hyperinsulinemic-euglycemic clamp study with the addition of glucose tracers; a meal tolerance test; arteriovenous sampling across forearm muscle tissue; and a sc adipose tissue biopsy for assessment of gene expression.

RESULTS

There was enhanced uptake of glucose into the forearm muscle measured by arteriovenous sampling (65 ± 15% increase after resistant starch; P < 0.001). Adipose tissue function was also affected, with enhanced fatty acid suppression after HAM-RS2 treatment and an increase in gene expression for hormone sensitive lipase (P = 0.005), perilipin (P = 0.011), lipoprotein lipase (P = 0.014), and adipose triglyceride lipase (P = 0.03) in biopsy samples. There was no effect on the insulin sensitivity of hepatic glucose production or plasma lipids after HAM-RS2.

CONCLUSION

HAM-RS2 improved peripheral but not hepatic insulin resistance and requires further study as an intervention in patients with or at risk for type 2 diabetes.

FTO mRNA expression in extremely obese and type 2 diabetic human omental and subcutaneous adipose tissues

BACKGROUND

Fat mass and obesity-associated protein (FTO) gene expression is known to correlate with obesity. Our aim was to investigate the FTO gene expression in paired omental and subcutaneous human adipose tissues from morbid and obese patients. To understand the role of CD68-positive macrophages in adipose tissues, the correlation with adiposity parameters such as adipocyte diameter and adipocyte radius was also measured. Drug and adiposity correlations were also analyzed.

METHODS

Paired omental and subcutaneous adipose tissue were excised during elective surgery from morbidly obese (n = 9) and obese (n = 5) patients. FTO expressions were determined by quantitative PCR. Tissue sections were analyzed for their CD68 protein expressions by immunuhistochemistry.

RESULTS

Omental and subcutaneous adipose tissue FTO gene expression levels were not found to differ significantly among morbidly obese and obese study groups. Serum aspartate aminotransferase e and alanine transaminase levels were found to be in negative correlation with subcutaneous fat tissue FTO expression rate. Antidiabetic drug use was found to be in correlation with adiposity. Both subcutaneous and omental fat cell diameters were found to have correlation with antidiabetic drug use. Omental fat cell diameter was found to enlarge together with omental CD68 protein expression. Subcutaneous macrophage number decreased while omental fat cell radius increased. Omental macrophage number was found in correlation with subcutaneous macrophage number.

CONCLUSIONS

Antidiabetic therapy was found to increase adiposity in omental and subcutaneous fat. Further research is needed with larger samples to explore the exact role of FTO in obesity.

Secretion of adipokines by human adipose tissue in vivo: partitioning between capillary and lymphatic transport

Peptides secreted by adipose tissue (adipokines) may enter blood via capillaries or lymph. The relative importance of these pathways for a given adipokine might influence its biological effects. Because this has not been studied in any species, we measured the concentrations of seven adipokines and eight nonsecreted proteins in afferent peripheral lymph and venous plasma from 12 healthy men. Data for nonsecreted proteins were used to derive indices of microvascular permeability, which in conjunction with the molecular radii of the adipokines were used to estimate the amounts leaving the tissue via capillaries. Transport rates via lymph were estimated from the lymph adipokine concentrations and lymph flow rates and total transport (secretion) as the sum of this and capillary transport. Concentrations of nonsecreted proteins were always lower in lymph than in plasma. With the exception of adiponectin, adipokine concentrations were always higher in lymph (P < 0.01). Leptin and MCP-1 were secreted at the highest rates (means: 43 μg/h or 2.7 nmol/h and 32 μg/h or 2.4 nmol/h, respectively). IL-6 and MCP-1 secretion rates varied greatly between subjects. The proportion of an adipokine transported via lymph was directly related to its molecular radius (r(s) = +0.94, P = 0.025, n = 6), increasing from 14 to 100% as the radius increased from 1.18 (IL-8) to 3.24 nm (TNFα). We conclude that the lymph/capillary partitioning of adipokines is a function of molecular size, which may affect both their regional and systemic effects in vivo. This finding may have implications for the physiology of peptides secreted by other tissues.

Differential expression of novel adiponectin receptor-1 transcripts in skeletal muscle of subjects with normal glucose tolerance and type 2 diabetes

OBJECTIVE

Adiponectin receptor-1 (AdipoR1) expression in skeletal muscle has been suggested to play an important role in insulin resistance and diabetes. We aimed at evaluating the presence of novel AdiopR1 splice variants in human muscle and their regulation under physiological and pathophysiological states.

RESEARCH DESIGN AND METHODS

AdipoR1 5'UTR mRNA transcripts, predicted from bioinformatics data, were evaluated in fetal and adult human tissues. Expression and function of the identified transcripts were assessed in cultured human skeletal muscle cells and in muscle biopsies obtained from individuals with normal glucose tolerance (NGT) and type 2 diabetes (n = 49).

RESULTS

Screening of potential AdipoR1 5'UTR splice variants revealed a novel highly abundant muscle transcript (R1T3) in addition to the previously described transcript (R1T1). Unlike R1T1, R1T3 expression was significantly increased during fetal development and myogenesis, paralleled with increased AdipoR1 protein expression. The 5'UTR of R1T3 was found to contain upstream open reading frames that repress translation of downstream coding sequences. Conversely, AdipoR1 3'UTR was associated with enhanced translation efficiency during myoblast-myotube differentiation. A marked reduction in muscle expression of R1T3, R1T1, and R1T3-to-R1T1 ratio was observed in individuals with type 2 diabetes compared with expression levels of NGT subjects, paralleled with decreased expression of the differentiation marker myogenin. Among NGT subjects, R1T3 expression was positively correlated with insulin sensitivity.

CONCLUSIONS

These results indicate that AdipoR1 receptor expression in human skeletal muscle is subjected to posttranscriptional regulation, including alternative splicing and translational control. These mechanisms play an important role during myogenesis and may be important for whole-body insulin sensitivity.

Low-abundant adiponectin receptors in visceral adipose tissue of humans and rats are further reduced in diabetic animals

BACKGROUND AND AIMS

Adipose tissue is an endocrine organ that releases various proteins that may also exert autocrine/paracrine effects. The antidiabetic adipokine adiponectin acts through two receptors, AdipoR1 and AdipoR2, but so far mainly mRNA expression has been measured in adipocytes and adipose tissues. Therefore, we aimed to analyze AdipoR1 and AdipoR2 proteins in adipocytes and paired samples of subcutaneous and visceral adipocytes/adipose tissue.

METHODS

AdipoR1 and AdipoR2 mRNA and protein expression were determined in adipocytes and paired samples of subcutaneous and visceral adipose tissue of humans and rats.

RESULTS

AdipoR1 and AdipoR2 proteins were similarly abundant in preadipocytes and mature adipocytes despite an induction of mRNA expression during differentiation. Differentiation of 3T3-L1 cells in the presence of palmitic acid did not alter adiponectin receptor proteins but metformin and fenofibrate upregulated AdipoR2 within 24 h of incubation. AdipoR2 protein was significantly lower in human visceral compared to subcutaneous fat, and both receptors were reduced in visceral adipocytes. In rat tissues both receptors were reduced in visceral fat. In diabetic animals AdipoR2 protein, but not mRNA, was lower in both fat depots compared to similarly obese rats with normal glucose disposal. AdipoR1 was only reduced in subcutaneous adipose tissue of diabetic animals where mRNA expression was induced.

CONCLUSIONS

These data indicate that mRNA expression is not suitable to predict adiponectin receptor protein. Low adiponectin receptors in visceral adipocytes and adipose tissue and further suppression in adipose tissue of insulin-resistant animals indicate disturbed adiponectin bioactivity.

Adiponectin receptor 2 is regulated by nutritional status, leptin and pregnancy in a tissue-specific manner

The aim of the present work was to study the regulation of circulating adiponectin levels and the expression of adiponectin receptor 2 (Adipo-R2) in several rat tissues in relation to fasting, leptin challenge, pregnancy, and chronic undernutrition. Using real-time PCR, we found Adipo-R2 mRNA expression in the liver, stomach, white and brown adipose tissues (WAT and BAT) of adult rats. Immunohistochemical studies confirmed protein expression in the same tissues. Adipo-R2 mRNA levels were decreased in liver after fasting, with no changes in the other tissues. Leptin decreased Adipo-R2 expression in liver and stomach, but increased its expression in WAT and BAT. Chronic caloric restriction in normal rats increased Adipo-R2 gene expression in stomach, while it decreased hepatic Adipo-R2 levels in pregnant rats. Using radioimmunoassay, we found that plasma adiponectin levels were diminished by fasting and leptin. Conversely, circulating adiponectin was increased in food-restricted rats, whereas its levels decreased in food-restricted pregnant rats by the end of gestation. In conclusion our findings provide the first evidence that (a) Adipo-R2 mRNA is regulated in a tissue-specific manner by fasting, but leptin is not responsible for those changes; (b) chronic caloric restriction in normal and pregnant rats also regulate Adipo-R2 mRNA in a tissue-specific manner; and (c) Adipo-R2 mRNA does not show a clear correlation with plasma adiponectin levels.

Serum resistin and adiponectin levels in young non-obese women with polycystic ovary syndrome

INTRODUCTION

Although polycystic ovary syndrome (PCOS) was described more than half a century ago, the underlying cause of PCOS is still unknown. The aim of our study was to evaluate whether serum resistin and adipocytokine levels alter and its changes relate with low grade inflammation in non-obese young women with PCOS.

SUBJECTS AND METHODS

Newly diagnosed 31 young non-obese women with PCOS (mean age 21.8 +/- 5.4 years; body mass index (BMI): 23.8 +/- 6.6 kg/m(2)) and 25 BMI- and age-matched, regular-cycling, healthy women (mean age 24.9 +/- 5.7 years; BMI: 23.1 +/- 5.8 kg/m(2)) were included the study Anthropometric measurements were evaluated. Resistin, adiponectin, glucose, insulin, hormone profiles, Lipoprotein (Lp)(a), high sensitive C reactive protein (hs-CRP), and homocysteine levels were measured in the beginning of oral glucose tolerance test. Homeostasis model assessment of insulin resistance (HOMA-IR) was calculated.

RESULTS

Non-obese young women with PCOS had high adiponectin levels (28.01 +/- 6.47 ng/ml in PCOS vs. 23.89 +/- 7.70 ng/ml in control subjects, p = 0.034), whereas serum resistin levels were not significantly different compared with healthy controls (14.14 +/- 6.6 ng/ml in PCOS vs. 13.78 +/- 4.26 ng/ml in control subjects). There were no significant differences between two groups in terms of fasting insulin, Lp(a), homocysteine, and hs-CRP levels. Mean HOMA-IR value of patients with PCOS was similar with control subjects (1.93 +/- 0.73 in PCOS; 1.15 +/- 0.54 in control group).

CONCLUSIONS

Resistin levels did not change in non-obese young women with PCOS whereas adiponectin level in non-obese young women with PCOS was significantly higher than control subjects, perhaps, because of no insulin resistance. Circulating resistin levels may not be candidate to play a role in pathogenesis of PCOS without insulin resistance or obesity.

Pleiotropic effects of thiazolidinediones on traditional and non-traditional atherosclerotic risk factors

BACKGROUND

The thiazolidinediones pioglitazone and rosiglitazone have established efficacy in improving insulin sensitivity, glycaemic control, dyslipidaemia, hypertension and microalbuminuria in patients with type 2 diabetes. As specific agonists of peroxisome proliferator-activated receptor-gamma, thiazolidinediones have also demonstrated protective effects on a variety of atherosclerosis biomarkers and surrogate measures of cardiovascular disease.

AIM

This paper reviews the evidence for pleiotropic effects on a variety of non-traditional atherosclerotic risk factors.

DISCUSSION

Thiazolidinediones attenuate circulating levels of pro-inflammatory mediators in patients with type 2 diabetes, including C-reactive protein, interleukin-6, CD40L, monocyte chemoattractant protein-1 and metalloproteinase-9. These agents also increase levels of the vascular protective adipokine, adiponectin. The clinical significance of these findings is supported by evidence of improved endothelial dysfunction, reduced carotid intima media thickness and improvements in stenosis following coronary artery stent implantation in patients treated with thiazolidinediones. Limited data suggest that thiazolidinediones might also improve the circulating levels and functional activity of angiogenic endothelial progenitor cells, which independently predict the incidence of cardiovascular events and death. It should be noted that the US Food and Drug Administration and the European Medicines Agency have requested changes to the prescribing information for rosiglitazone to highlight the possibility of an increased risk with this agent in patients with ischaemic heart disease; on review, no such amendment was required for the pioglitazone prescribing information. Both agencies continue to suggest that the benefits of both thiazolidinediones outweight any possible detrimental effects. Further research remains to be conducted to elucidate the potentially differential vascular protective effects of thiazolidinediones. In the US, there are black box heart failure warnings for both agents.

CONCLUSION

In light of the established importance of reducing cardiovascular risk in patients with type 2 diabetes, current evidence continues to support the use of pioglitazone within multifactorial risk management strategies.

Pioglitazone stimulates AMP-activated protein kinase signalling and increases the expression of genes involved in adiponectin signalling, mitochondrial function and fat oxidation in human skeletal muscle in vivo: a randomised trial

AIMS/HYPOTHESIS

The molecular mechanisms by which thiazolidinediones improve insulin sensitivity in type 2 diabetes are not fully understood. We hypothesised that pioglitazone would activate the adenosine 5'-monophosphate-activated protein kinase (AMPK) pathway and increase the expression of genes involved in adiponectin signalling, NEFA oxidation and mitochondrial function in human skeletal muscle.

METHODS

A randomised, double-blind, parallel study was performed in 26 drug-naive type 2 diabetes patients treated with: (1) pioglitazone (n = 14) or (2) aggressive nutritional therapy (n = 12) to reduce HbA(1c) to levels observed in the pioglitazone-treated group. Participants were assigned randomly to treatment using a table of random numbers. Before and after 6 months, patients reported to the Clinical Research Center of the Texas Diabetes Institute for a vastus lateralis muscle biopsy followed by a 180 min euglycaemic-hyperinsulinaemic (80 mU m(-2) min(-1)) clamp.

RESULTS

All patients in the pioglitazone (n = 14) or nutritional therapy (n = 12) group were included in the analysis. Pioglitazone significantly increased plasma adiponectin concentration by 79% and reduced fasting plasma NEFA by 35% (both p < 0.01). Following pioglitazone, insulin-stimulated glucose disposal increased by 30% (p < 0.01), and muscle AMPK and acetyl-CoA carboxylase (ACC) phosphorylation increased by 38% and 53%, respectively (p < 0.05). Pioglitazone increased mRNA levels for adiponectin receptor 1 and 2 genes (ADIPOR1, ADIPOR2), peroxisome proliferator-activated receptor gamma, coactivator 1 gene (PPARGC1) and multiple genes involved in mitochondrial function and fat oxidation. Despite a similar reduction in HbA(1c) and similar improvement in insulin sensitivity with nutritional therapy, there were no significant changes in muscle AMPK and ACC phosphorylation, or the expression of ADIPOR1, ADIPOR2, PPARGC1 and genes involved in mitochondrial function and fat oxidation. No adverse (or unexpected) effects or side effects were reported from the study.

CONCLUSIONS/INTERPRETATIONS

Pioglitazone increases plasma adiponectin levels, stimulates muscle AMPK signalling and increases the expression of genes involved in adiponectin signalling, mitochondrial function and fat oxidation. These changes may represent an important cellular mechanism by which thiazolidinediones improve skeletal muscle insulin sensitivity.

TRIAL REGISTRATION

NCT 00816218 FUNDING: This trial was funded by National Institutes of Health Grant DK24092, VA Merit Award, GCRC Grant RR01346, Executive Research Committee Research Award from the University of Texas Health Science Center at San Antonio, American Diabetes Association Junior Faculty Award, American Heart Association National Scientist Development Grant, Takeda Pharmaceuticals North America Grant and Canadian Institute of Health Research Grant.

Short-term beta-adrenergic regulation of leptin, adiponectin and interleukin-6 secretion in vivo in lean and obese subjects

AIM

Adipose tissue and skeletal muscle are endocrine organs, secreting substances that have been implicated in obesity-related disorders. This study examined short-term beta-adrenergic regulation of circulating leptin, adiponectin and interleukin-6 (IL-6) concentrations and secretion from abdominal subcutaneous adipose tissue and muscle (IL-6) in vivo in lean and obese subjects.

METHODS

Systemic concentrations and net fluxes of leptin, adiponectin and IL-6 across abdominal subcutaneous adipose tissue and forearm skeletal muscle (IL-6) were assessed before and during beta-adrenergic stimulation (intravenous isoprenaline infusion) in 13 lean and 10 obese men.

RESULTS

Basal circulating leptin concentrations were higher in the obese (p < 0.001), while circulating adiponectin (p = 0.45) and IL-6 concentrations (p = 0.41) were not different between groups. beta-Adrenergic stimulation decreased leptin concentrations in both groups (p < 0.01), but did not reduce net abdominal subcutaneous adipose tissue leptin release. Increased leptin clearance and/or decreased leptin secretion from other fat depots may explain the reduction in leptin concentrations. Adiponectin concentrations remained unchanged during beta-adrenergic stimulation in both groups. beta-Adrenergic stimulation increased IL-6 concentration, which was more pronounced in the obese (p = 0.01 vs. lean). This cannot be explained by increased IL-6 release per unit abdominal subcutaneous adipose tissue and muscle but might be because of the increased fat mass and fat-free mass at whole-body level.

CONCLUSIONS

Short-term beta-adrenergic stimulation decreases leptin concentrations, which cannot be explained by reduced net leptin release from abdominal subcutaneous adipose tissue, while it elevates IL-6 concentration partly by increased release from this fat depot and muscle. Finally, beta-adrenergic stimulation has no short-term regulatory role in adiponectin secretion.

The endocrine profile of subcutaneous and visceral adipose tissue of obese patients

The aim of the present study was to evaluate the expression profile of genes potentially related to metabolic complications of obesity in the whole adipose tissue and isolated adipocytes from subcutaneous (SAT) and visceral adipose tissue (VAT) from 12 non-diabetic obese women and 12 lean women. Real-time polymerase chain reaction was used for expression analysis of 41 genes of interest and two housekeeping genes. We found increased expression of specific proinflammatory and adipogenic genes and reduced expression of specific lipogenic and insulin signaling pathway genes in obese relative to lean women with no preferable localization in SAT or VAT depot. The gene expression significantly differed between adipocytes and adipose tissue but both contributed to the proinflammatory profile in obesity. We conclude that both SAT and VAT exhibit alterations in the expression of specific genes possibly contributing to proinflammatory and insulin resistance state and consequently to metabolic complications of obesity.

Adiponectin receptors: expression in Zucker diabetic rats and effects of fenofibrate and metformin

The insulin-sensitizing adipokine, adiponectin, acts through 2 receptors, AdipoR1 and AdipoR2. A decreased expression of these receptors could contribute to insulin resistance and diabetes. We determined if the expression of adiponectin receptors is decreased in an experimental model, the Zucker diabetic rat (ZDF), and if a peroxisome proliferator-activated receptor alpha agonist, fenofibrate, and metformin could increase these expressions. The ZDF and control (L) rats were studied at 7, 14, and 21 weeks. After initial study at 7 weeks, ZDF received no treatment (n = 10), metformin (n = 10), or fenofibrate (n = 10) until final studies at 14 or 21 weeks. The L rats received no treatment. AdipoR1 and R2 expressions were measured in liver, muscle, and white adipose tissue (WAT). As expected, ZDF rats were insulin resistant at 7 weeks, had type 2 diabetes mellitus at 14 weeks, and had diabetes with insulin deficiency at 21 weeks. Compared with L rats, AdipoRs messenger RNA was decreased only in the WAT (P < .05) of 7-week-old ZDF rats, but was unchanged in muscle and increased in liver. Metformin and fenofibrate decreased plasma triacylglycerols (P < .01) as expected. The only effect of fenofibrate on AdipoRs was a moderate increase (P < .01) of both receptors' messenger RNA in liver. Metformin increased AdipoR1 and R2 expression in muscle (P < .01) and AdipoR1 (P < .01) in WAT. These results do not support an important role for decreased AdipoRs expression in the development of insulin resistance and diabetes. Parts of the actions of fenofibrate and of metformin could be mediated by a stimulation of the expression of these receptors in liver and in insulin-sensitive, glucose-utilizing tissues (muscle, WAT), respectively.

Effects of high levels of glucose on the steroidogenesis and the expression of adiponectin receptors in rat ovarian cells

BACKGROUND

Reproductive dysfunction in the diabetic female rat is associated with altered folliculogenesis and steroidogenesis. However, the molecular mechanisms involved in the reduction of steroid production have not been described. Adiponectin is an adipocytokine that has insulin-sensitizing actions including stimulation of glucose uptake in muscle and suppression of glucose production in liver. Adiponectin acts via two receptor isoforms - AdipoR1 and AdipoR2 - that are regulated by hyperglycaemia and hyperinsulinaemia in liver and muscle. We have recently identified AdipoR1 and AdipoR2 in rat ovary. However, their regulation in ovaries of diabetic female rat remains to be elucidated.

METHODS

We incubated rat primary granulosa cells in vitro with high concentrations of glucose (5 or 10 g/l) + or - FSH (10-8 M) or IGF-1 (10-8 M), and we studied the ovaries of streptozotocin-induced diabetic rats (STZ) in vivo. The levels of oestradiol and progesterone in culture medium and serum were measured by RIA. We used immunoblotting to assay key steroidogenesis factors (3beta HSD, p450scc, p450 aromatase, StAR), and adiponectin receptors and various elements of signalling pathways (MAPK ERK1/2 and AMPK) in vivo and in vitro. We also determined cell proliferation by [3H] thymidine incorporation.

RESULTS

Glucose (5 or 10 g/l) impaired the in vitro production in rat granulosa cells of both progesterone and oestradiol in the basal state and in response to FSH and IGF-1 without affecting cell proliferation and viability. This was associated with substantial reductions in the amounts of 3beta HSD, p450scc, p450 aromatase and StAR proteins and MAPK ERK1/2 phosphorylation. In contrast, glucose did not affect the abundance of AdipoR1 or AdipoR2 proteins. In vivo, as expected, STZ treatment of rats caused hyperglycaemia and insulin, adiponectin and resistin deficiencies. Plasma progesterone and oestradiol levels were also reduced in STZ rats. However, the amounts of 3beta HSD and p450 aromatase were the same in STZ rat ovary and controls, and the amounts of StAR and p450scc were higher. Streptozotocin treatment did not affect adiponectin receptors in rat ovary but it increased AMPK phosphorylation without affecting MAPK ERK1/2 phosphorylation.

CONCLUSION

High levels of glucose decrease progesterone and oestradiol production in primary rat granulosa cells and in STZ-treated rats. However, the mechanism that leads to reduced ovarian steroid production seems to be different. Furthermore, adiponectin receptors in ovarian cells are not regulated by glucose.

Role of adiponectin and PBEF/visfatin as regulators of inflammation: involvement in obesity-associated diseases

Obesity and obesity-related disorders play an important role in clinical medicine. Adipose tissue, with its soluble mediators called adipocytokines, has emerged as a major endocrine organ. These adipocytokines comprise many mediators such as adiponectin, PBEF (pre-B-cell-enhancing factor)/visfatin, leptin, resistin, retinol-binding protein-4 and others. They play major roles in key aspects of metabolism, such as insulin resistance, fatty acid oxidation, inflammation and immunity. Adiponectin, a prototypic adipocytokine, is of importance in the regulation of insulin resistance, as circulating levels are decreased in obesity and diseases associated with insulin resistance. Besides its major role in regulation of insulin sensitivity, recent evidence suggests potent anti-inflammatory functions for adiponectin. These effects are paralleled by other immune-regulatory properties, such as regulation of endothelial cell function. The in vitro effects of adiponectin have been corroborated by several studies demonstrating potent in vivo anti-inflammatory effects. Many other adipocytokines, such as PBEF/visfatin, leptin, resistin or retinol binding protein-4, are involved in the physiology and pathophysiology of adipocytes, adipose tissue and related diseases. PBEF/visfatin, another recently characterized adipocytokine, has been linked to several inflammatory disease states beyond insulin resistance, such as acute lung injury or inflammatory bowel diseases. It has been recognized for many decades that obesity is accompanied by an increase in cancer and potentially some immune-mediated diseases. Understanding this new exciting world of adipocytokines will be of importance in the development of novel therapies for obesity-associated diseases.

Impaired expression of cardiac adiponectin in leptin-deficient mice with viral myocarditis

A mouse model of encephalomyocarditis (EMC) virus-induced myocarditis was used to investigate the expression of adiponectin in damaged cardiomyocytes. We intraperitoneally injected EMC virus into leptin-deficient ob/ob (OB) mice and wild-type (WT) mice. OB mice were divided into two subgroups consisting of mice with no intervention and mice receiving leptin replacement starting simultaneously with viral inoculation. We determined differences in heart weight, cardiac histological score, numbers of infiltrating and apoptotic cells in the myocardium, expression levels of adiponectin and TNF-alpha mRNA in the heart, adiponectin immunoreactivity in myocytes, adiponectin and TNF-alpha concentrations in the heart, and immunoreactivity of adiponectin receptors in myocytes between OB mice and WT mice. There was significantly decreased adiponectin mRNA expression, immunoreactivity, and protein level in the heart, and reduced immunoreactivity of adiponectin receptor 1 in myocytes from OB mice on days 4 and 8 after viral inoculation as compared with those in WT mice, together with increased cardiac weight, severe inflammatory myocardial damage, and increased levels of cardiac TNF-alpha mRNA and protein. Replacement of leptin in OB mice inhibited the development of severe myocarditis through augmentation of adiponectin mRNA, immunoreactivity, and protein level, increased adiponectin receptor 1 immunoreactivity in myocytes, and suppressed levels of TNF-alpha mRNA and protein. These results suggest that impaired expression of cardiac adiponectin may contribute to the progression of viral myocarditis through enhanced expression of TNF-alpha under a leptin-deficient condition.

Circulating adiponectin and adiponectin receptor expression in skeletal muscle: effects of exercise

Excess visceral fat can regulate insulin sensitivity and energy metabolism by releasing adipokines into the circulation which then bind with their cognate receptors in various tissues and alter glucose and lipid metabolism. Circulating levels of adiponectin, which promotes glucose uptake into skeletal muscle and increases fat oxidation rates, are decreased in obesity. Strategies to enhance the insulin-like and insulin-sensitizing actions of adiponectin have been shown to be effective in improving metabolic abnormalities associated with obesity and diabetes. Interestingly, the insulin-sensitizing effects of exercise have similar metabolic effects as adiponectin in that exercise also promotes glucose uptake into muscle and increases rates of fatty acid oxidation. Recent studies have begun to examine the potential role of adiponectin in mediating the insulin-sensitizing action of exercise by investigating changes in plasma adiponectin levels and tissue-specific adiponectin receptor (AdipoR) expression. In this review, we have summarized the key findings to date which suggest that changes in expression of AdipoR isoforms in skeletal muscle, rather than circulating total adiponectin levels, may be of physiological importance.

Effects of lactogen resistance and GH deficiency on mouse metabolism: pancreatic hormones, adipocytokines, and expression of adiponectin and insulin receptors

We recently described a novel mouse model that combines resistance to lactogenic hormones with GH deficiency (GHD). The GHD/lactogen-resistant males develop obesity and insulin resistance with age. We hypothesized that altered production of pancreatic hormones and dysregulation of adipocytokine secretion and action contribute to the pathogenesis of their insulin resistance. Double-mutant males (age 12-16 months) had fasting hyperinsulinemia, hyperamylinemia, hyperleptinemia, and a decreased ratio of adiponectin to leptin. Adiponectin receptor 1 and 2 (AdipoR1 and R2) mRNA levels in liver and skeletal muscle were normal but hepatic insulin receptor mRNA was increased. Relative to double-mutant males, GHD males had lower levels of insulin, amylin, and leptin, higher levels of adiponectin, and higher expression of hepatic AdipoR1 and insulin receptor mRNAs. Lactogen-resistant mice had reduced hepatic adipoR2 mRNA. In response to stress the plasma concentrations of MCP-1 and IL-6 increased in double-mutant males but not GHD or lactogen-resistant males. Our findings suggest that the insulin resistance of GHD/lactogen-resistant males is accompanied by dysregulation of pancreatic hormone and adipocytokine secretion and receptor expression. Phenotypic differences between double-mutant and GHD males suggest that lactogens and GH exert differential but overlapping effects on fat deposition and adipocytokine secretion and action.

The cardiovascular effects of the thiazolidinediones: a review of the clinical data

Beyond glycemic control, the thiazolidinediones (TZDs) provide numerous cardiovascular benefits. Clinical data support a role for the TZDs in lowering blood pressure, correcting dyslipidemia, improving vascular structure and function, decreasing inflammation, improving the adipokine profile, reducing systemic oxidative stress, and possibly in stabilizing coronary plaques that may be prone to rupture. Data from the first outcomes trial assessing a TZD in reducing cardiovascular morbidity and mortality have recently been reported. Results were promising, but not conclusive. Therefore, other large studies currently underway should provide greater insight into the role of the TZDs in modifying cardiovascular risk in patients with type 2 diabetes. Reported side effects of the TZDs include fluid retention, worsening of heart failure, and weight gain. Recent research is beginning to clarify the mechanisms associated with these potential side effects and may result in the expanded use of this drug class in patients with heart failure. Because of the unique mechanism of action of this drug class that addresses a fundamental pathophysiolgical phenomenon in type 2 diabetes, namely, improving insulin resistance, and the growing body of evidence supporting cardiovascular benefits, strong consideration should be given to utilizing the TZDs early in the clinical course of diabetes.

Rosiglitazone for type 2 diabetes mellitus

BACKGROUND

Diabetes has long been recognised as a strong, independent risk factor for cardiovascular disease, a problem which accounts for approximately 70% of all mortality in people with diabetes. Prospective studies show that compared to their non-diabetic counterparts, the relative risk of cardiovascular mortality for men with diabetes is two to three and for women with diabetes is three to four. The two biggest trials in type 2 diabetes, the United Kingdom Prospective Diabetes Study (UKPDS) and the University Group Diabetes Program (UGDP) study did not reveal a reduction of cardiovascular endpoints through improved metabolic control. Theoretical benefits of the peroxisome proliferator activated receptor gamma (PPAR-gamma) activator rosiglitazone on endothelial function and cardiovascular risk factors might result in fewer macrovascular disease events in people with type 2 diabetes mellitus.

OBJECTIVES

To assess the effects of rosiglitazone in the treatment of type 2 diabetes.

SEARCH STRATEGY

Studies were obtained from computerised searches of MEDLINE, EMBASE and The Cochrane Library.

SELECTION CRITERIA

Studies were included if they were randomised controlled trials in adult people with type 2 diabetes mellitus and had a trial duration of at least 24 weeks.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality and extracted data. Pooling of studies by means of fixed-effects meta-analysis could be performed for adverse events only.

MAIN RESULTS

Eighteen trials which randomised 3888 people to rosiglitazone treatment were identified. Longest duration of therapy was four years with a median of 26 weeks. Published studies of at least 24 weeks rosiglitazone treatment in people with type 2 diabetes mellitus did not provide evidence that patient-oriented outcomes like mortality, morbidity, adverse effects, costs and health-related quality of life are positively influenced by this compound. Metabolic control measured by glycosylated haemoglobin A1c (HbA1c) as a surrogate endpoint did not demonstrate clinically relevant differences to other oral antidiabetic drugs. Occurrence of oedema was significantly raised (OR 2.27, 95% confidence interval (CI) 1.83 to 2.81). The single large RCT (ADOPT - A Diabetes Outcomes Progression Trial) indicated increased cardiovascular risk. New data on raised fracture rates in women reveal extensive action of rosiglitazone in various body tissues.

AUTHORS' CONCLUSIONS

New studies should focus on patient-oriented outcomes to clarify the benefit-risk ratio of rosiglitazone therapy. Safety data and adverse events of all investigations (published and unpublished) should be made available to the public.

Pattern of expression of adiponectin receptors in human adipose tissue depots and its relation to the metabolic state

OBJECTIVE

To investigate whether adiponectin receptor genes (AdipoR1 and AdipoR2) expression in human subcutaneous (SAT) and visceral (VAT) adipose tissue in severely obese patients with or without diabetes is related to adiponectin gene (APM1) expression and in vivo metabolic parameters.

DESIGN

Cross-sectional, clinical research study.

SUBJECTS

Total RNA was extracted from SAT and VAT tissue obtained during surgery from 13 lean controls, 30 obese diabetic patients, 19 obese glucose-intolerant patients and 54 obese subjects with normal glucose tolerance.

MEASUREMENTS

Tissue expression of APM1, AdipoR1 and AdipoR2, tissue concentration of adiponectin (ApN), and metabolic variables.

RESULTS

APM1 expression was higher in SAT than VAT (1.06+/-0.76 vs 0.69+/-0.52, P<0.0001) as was AdipoR1 (1.17+/-0.70 vs 0.66+/-0.38, P<0.0001) and AdipoR2 (7.02+/-6.19 vs 0.75+/-0.64, P<0.0001). In SAT, APM1 and AdipoR1 expression tended to be lower - by 0.38+/-0.22 and 0.35+/-0.22, respectively - and AdipoR2 expression was markedly depressed - by 4.82+/-1.93 - in association with obesity, whereas presence of diabetes had no additional effect. In VAT, APM1 and AdipoR1 expressions were also reduced - by 0.36+/-0.16 and 0.30+/-0.11, respectively - in association with obesity. Within both SAT and VAT, expression levels of APM1, AdipoR1 and AdipoR2 were all positively interrelated. Tissue ApN concentrations in SAT were similar across groups, whereas ApN levels in VAT were substantially lower in association with obesity (by an average of 63+/-12 ng/mg total protein, P<0.0001). In multivariate models adjusting for sex, age and obesity, serum triglyceride concentrations were reciprocally related to APM1 (r=-0.27, P<0.02), AdipoR1 (r=-0.37, P<0.002 and AdipoR2 expression (r=-0.37, P<0.002) in VAT. Likewise, plasma insulin concentrations were inversely related only to APM1 in VAT (r=-0.25, P<0.03).

CONCLUSIONS

Severe obesity is associated with suppressed expression of both ApN and its receptors in both SAT and VAT, the expression levels in VAT are specifically linked with hyperinsulinemia and dyslipidemia.

Insulin-sensitizing effects of thiazolidinediones are not linked to adiponectin receptor expression in human fat or muscle

Circulating adiponectin levels are increased by the thiazolidinedione (TZD) class of PPARgamma agonists in concert with their insulin-sensitizing effects. Two receptors for adiponectin (AdipoR1 and AdipoR2) are widely expressed in many tissues, but their physiological significance to human insulin resistance remains to be fully elucidated. We examined the expression patterns of AdipoR1 and AdipoR2 in fat and skeletal muscle of human subjects, their relationship to insulin action, and whether they are regulated by TZDs. Expression patterns of both AdipoRs were similar in subcutaneous and omental fat depots, with higher expression in adipocytes than in stromal cells and macrophages. To determine the effects of TZDs on AdipoR expression, subcutaneous fat and quadriceps muscle were biopsied in 14 insulin-resistant subjects with type 2 diabetes mellitus after 45 mg pioglitazone or placebo for 21 days. This duration of pioglitazone improved insulin's suppression of glucose production by 41% and enhanced stimulation of glucose uptake by 27% in concert with increased gene expression and plasma levels of adiponectin. Pioglitazone did not affect AdipoR expression in muscle, whole fat, or cellular adipose fractions, and receptor expression did not correlate with baseline or TZD-enhanced insulin action. In summary, both adiponectin receptors are expressed in cellular fractions of human fat, particularly adipocytes. TZD administration for sufficient duration to improve insulin action and increase adiponectin levels did not affect expression of AdipoR1 or AdipoR2. Although TZDs probably exert many of their effects via adiponectin, changes in these receptors do not appear to be necessary for their insulin-sensitizing effects.

Adiponectin receptors gene expression in lymphocytes of obese and anorexic patients

AIM

Two adiponectin receptors (ADIPORs), ADIPOR1 and ADIPOR2, are widely expressed in tissues. Whether changes in the expression of ADIPORs are associated with obesity and insulin resistance in humans is still unclear. The aim of this study was to explore whether lymphocyte ADIPOR1 and ADIPOR2 mRNA expression is associated with obesity, insulin resistance, first-phase insulin secretion and serum adiponectin levels.

METHODS

Using reverse transcription-polymerase chain reaction, we measured ADIPOR1 and ADIPOR2 mRNA levels in the lymphocytes of 59 obese patients, of whom 39 had normal glucose tolerance, 8 had impaired glucose tolerance or impaired fasting glucose, and 12 had type 2 diabetes, and of 21 women with restrictive anorexia nervosa.

RESULTS

In all subjects, ADIPOR1 expression was 2.2-fold higher than that of ADIPOR2 (p < 0.0001). The mRNA expression level of both receptors correlated with each other (p < 0.0001). After adjustment for age and sex, lymphocyte ADIPORs mRNA expression (ADIPOR1, p < 0.005; ADIPOR2, p < 0.05) and serum adiponectin (p < 0.0001) were significantly lower in obese patients than in anorexic subjects. In a multivariate analysis with ADIPOR1 as the dependent variable and body mass index (BMI), blood pressure and adiponectin as the independent variables, only serum adiponectin remained positively and independently correlated with ADIPOR1 (p < 0.05). Adiponectin was independently and negatively related to BMI and sex.

CONCLUSIONS

We have demonstrated in this study that lymphocytes express ADIPORs and that, similar to serum adiponectin, ADIPORs expression is markedly reduced in obese subjects. ADIPORs expression is not independently related to BMI, insulin resistance and beta-cell function.

Adiponectin and cardiovascular disease: state of the art?

The cardiometabolic syndrome, associated with increased cardiovascular disease risk in the industrialized world, is estimated to affect one in four adults. Although the mechanisms linking obesity and cardiovascular disease remain unclear, research continues to unravel the molecular pathways behind this pandemic. Adipose tissue has emerged as a metabolically active participant in mediating vascular complications, serving as an active endocrine and paracrine organ secreting adipokines, which participate in diverse metabolic processes. Among these adipokines is adiponectin, which seems to possess antiatherogenic and anti-inflammatory effects and may be protective against cardiovascular disease development. The current review describes the pathophysiology of adiponectin in atherosclerotic disease.

Regulation of adiponectin and its receptors in response to development of diet-induced obesity in mice

Adiponectin and its receptors play an important role in energy homeostasis and insulin resistance, but their regulation remains to be fully elucidated. We hypothesized that high-fat diet would decrease adiponectin but increase adiponectin receptor (AdipoR1 and AdipoR2) expression in diet-induced obesity (DIO)-prone C57BL/6J and DIO-resistant A/J mice. We found that circulating adiponectin and adiponectin expression in white adipose tissue are higher at baseline in C57BL/6J mice compared with A/J mice. Circulating adiponectin increases at 10 wk but decreases at 18 wk in response to advancing age and high-fat feeding. However, adiponectin levels corrected for visceral fat mass and adiponectin mRNA expression in WAT are affected by high-fat feeding only, with both being decreased after 10 wk in C57BL/6J mice. Muscle AdipoR1 expression in both C57BL/6J and A/J mice and liver adipoR1 expression in C57BL/6J mice increase at 18 wk of age. High-fat feeding increases both AdipoR1 and AdipoR2 expression in liver in both strains of mice and increases muscle AdipoR1 expression in C57BL/6J mice after 18 wk. Thus advanced age and high-fat feeding, both of which are factors that predispose humans to obesity and insulin resistance, are associated with decreasing adiponectin and increasing AdipoR1 and/or AdipoR2 levels.

Acute and selective regulation of glyceroneogenesis and cytosolic phosphoenolpyruvate carboxykinase in adipose tissue by thiazolidinediones in type 2 diabetes

AIMS/HYPOTHESIS

Regulation of glyceroneogenesis and its key enzyme cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C) plays a major role in the control of fatty acid release from adipose tissue. Here we investigate the effect of rosiglitazone on the expression of genes involved in fatty acid metabolism and the resulting metabolic consequences.

MATERIALS AND METHODS

Rosiglitazone was administered to Zucker fa/fa rats for 4 days and to 24 diabetic patients for 12 weeks, then mRNA expression for the genes encoding PEPCK-C, mitochondrial PEPCK, adipocyte lipid-binding protein, glycerol kinase, lipoprotein lipase and glycerol-3-phosphate dehydrogenase was examined in s.c. adipose tissue by real-time RT-PCR. Glyceroneogenesis was determined using [1-(14)C]pyruvate incorporation into lipids. Cultured adipose tissue explants from overweight women undergoing plastic surgery were incubated with rosiglitazone for various times before mRNA determination and analysis of PEPCK-C protein, activity and glyceroneogenesis.

RESULTS

Rosiglitazone administration to rats induced the expression of the gene encoding PEPCK-C mRNA (PCK1) and PEPCK-C activity in adipose tissue with a resulting 2.5-fold increase in glyceroneogenesis. This was accompanied by an improvement in dyslipidaemia as demonstrated by the decrease in plasma NEFAs and triacylglycerol. In rosiglitazone-treated diabetic patients, PCK1 mRNA was raised 2.5-fold in s.c. adipose tissue. Rosiglitazone treatment of adipose tissue explants from overweight women caused a selective augmentation in PCK1 mRNA which reached a maximum of 9-fold at 14 h, while mRNA for other genes remained unaffected. Experiments with inhibitors showed a direct and transcription-only effect, which was followed by an increase in PEPCK-C protein, enzyme activity and glyceroneogenesis.

CONCLUSIONS/INTERPRETATION

These results favour adipocyte glyceroneogenesis as the initial thiazolidinedione-responsive pathway leading to improvement in dyslipidaemia.

Deficiency of adiponectin receptor 2 reduces diet-induced insulin resistance but promotes type 2 diabetes

Adiponectin/adiponectin receptors (AdipoR) are involved in energy homeostasis and inflammatory pathways. To investigate the role of AdipoR2 in metabolic control, we studied the lipid and glucose metabolic phenotypes in AdipoR2-deficient mice. AdipoR2 deletion diminished high-fat diet-induced dyslipidemia and insulin resistance yet deteriorated glucose homeostasis as high-fat feeding continued, which resulted from the failure of pancreatic beta-cells to adequately compensate for the moderate insulin resistance. A defect in the AdipoR2 gene may represent a mechanism underlying the etiology of certain subgroups of type 2 diabetic patients who eventually develop overt diabetes, whereas other obese patients do not.

Upregulation of adiponectin receptor 1 and 2 mRNA and protein in adipose tissue and adipocytes in insulin-resistant women with polycystic ovary syndrome

AIMS/HYPOTHESIS

Polycystic ovary syndrome (PCOS) is a multifaceted metabolic disease linked with insulin resistance (IR) and obesity. Adiponectin, which is lower in IR states, exerts its glucose-lowering and anti-inflammatory effects by activating two receptors, ADIPOR1 and ADIPOR2. There are no data on the relative expression of these receptors in adipose tissue of PCOS women.

METHODS

We investigated the expression of adiponectin receptors from corresponding s.c. and omental (o.m.) adipose tissue in women with PCOS compared with matched non-PCOS women. As there is a disturbance in the steroid milieu in PCOS women, we also assessed the effects of testosterone and oestradiol on adiponectin receptors using adipocytes and adipocyte explants. Real-time RT-PCR and western blotting were used to assess the relative adiponectin receptor mRNA expression and protein production, respectively. Biochemical measurements were performed in our hospital's laboratory.

RESULTS

We are the first to describe adiponectin receptor expression and production, in corresponding s.c. and o.m. human adipose tissues at the mRNA and protein level. We demonstrate the upregulation of mRNA expression and protein production of adiponectin receptors in women with PCOS, in s.c. and o.m. adipose tissue. Treatment of adipose tissue explants and adipocytes with testosterone and oestradiol induced the expression of adiponectin receptor mRNA and protein. There was a significant positive association between ADIPOR1/R2 expression and homeostasis model assessment, testosterone, oestradiol and triglycerides and a negative relationship with sex hormone-binding globulin.

CONCLUSIONS/INTERPRETATION

The precise reason for the upregulation of adiponectin receptors seen in PCOS women, a pro-diabetic state, is unknown, but it appears that sex steroids may play a role in their regulation in adipose tissue.

Thiazolidinediones, insulin resistance and obesity: Finding a balance

The clinical efficacy of currently available thiazolidinediones (TZDs) in improving glycaemic control and ameliorating several risk factors for cardiovascular disease (linked to their insulin-sensitising actions as well as direct vascular effects) is well established. Treatment-associated weight gain, however, which has been identified as a class effect of the TZDs, is seen in a number of patients. The magnitude of weight gain correlates in part with improved metabolic control, i.e. better responders are more prone to increases in body weight. The cardiovascular risk associated with obesity appears to be depot specific; while peripheral obesity is associated with a low risk of cardiovascular complications, central obesity confers a greater degree of risk. Evidence is reviewed that increases in body weight associated with TZD treatment are associated with neutral effects (or even, decreases) in visceral fat, the adipose depot that is associated with central obesity.

Association of sequence variations in the gene encoding adiponectin receptor 1 (ADIPOR1) with body size and insulin levels. The Finnish Diabetes Prevention Study

AIMS/HYPOTHESIS

Adiponectin is a circulating peptide derived from adipose tissue. It mediates its insulin-sensitising and anti-atherogenic effects on target tissues through two known receptors, adiponectin receptors 1 and 2 (ADIPOR1; ADIPOR2), which are encoded by the genes ADIPOR1 and ADIPOR2. Our aim was to study the association of ADIPOR1 gene variations with body size and risk of type 2 diabetes in subjects with impaired glucose tolerance, who participated in the Finnish Diabetes Prevention Study (DPS).

SUBJECTS AND METHODS

We selected seven single nucleotide polymorphisms (SNPs) of the ADIPOR1 gene to perform association studies with anthropometrics and metabolic parameters at baseline, and with the risk of type 2 diabetes during the 3-year follow-up in the DPS study population. Both single SNP analysis and haplotype effects were studied.

RESULTS

Three out of seven markers studied (rs10920534, rs22757538 and rs1342387) were significantly associated with various body size measurements including weight, height, waist and hip circumference, sagittal diameter and body mass index. Furthermore, three markers (rs10920534, rs12045862 and rs7539542), of which two were different from those associating with body size, were linked to fasting and 2-h insulin levels, particularly in men at baseline. The haplotype analysis with five markers revealed seven major haplotypes in the DPS study population. The haplotype effects on body size measures were in line with those of single SNP analysis. However, none of the markers were associated with the risk of type 2 diabetes.

CONCLUSIONS/INTERPRETATION

Our findings suggest that ADIPOR1 has a putative role in the development of body size, and that traits for central adiposity and insulin resistance may be dissociated from each other.

Expression of adiponectin receptors and its possible implication in the human endometrium

Adiponectin, a pleiotropic cytokine, exerts its effects via the specific receptors AdipoR1 and AdipoR2. Whereas circulating adiponectin concentrations decrease in women with endometriosis and endometrial cancer, possible effects of adiponectin and the presence of the receptors in the endometrium have not been determined. In this study, we examined the expression of adiponectin receptors AdipoR1 and AdipoR2 in the human endometrium and assessed effects of adiponectin in endometrial cells. Expression of AdipoR1 and AdipoR2 in endometrial tissues was evaluated by real-time quantitative PCR, in situ hybridization, and Western blotting. The effects of adiponectin on phosphorylation of AMP-activated protein kinase, a regulator of energy homeostasis, in cultured endometrial stromal cells (ESCs) and epithelial cells (EECs) were studied by Western blotting. The effects of adiponectin on IL-1beta-induced secretion of IL-6, IL-8, and monocyte chemoattractant protein 1 from cultured ESCs were determined using specific ELISAs. The expression of AdipoR1 and AdipoR2 was detected in the endometrium. The expression of both genes was increased in the midluteal phase, the period of embryo implantation. In situ hybridization revealed that both AdipoR1 and AdipoR2 appeared to be equally expressed in the epithelial cells and in the stromal cells. Adiponectin increased phosphorylation of AMP-activated protein kinase in ESCs and EECs. Adiponectin decreased IL-1beta-induced secretion of IL-6, IL-8, and monocyte chemoattractant protein 1 from ESCs. These findings suggest that adiponectin exerts energy-homeostatic and antiinflammatory effects in the endometrium, and these effects might be relevant to pathological and physiological endometrium-related events such as implantation and endometriosis.

Regulation of adiponectin receptors in hepatocytes by the peroxisome proliferator-activated receptor-gamma agonist rosiglitazone

AIMS/HYPOTHESIS

Adiponectin is an adipocyte-derived hormone that plays a critical role in the development of type 2 diabetes via interaction with adiponectin receptors 1 (ADIPOR1) and 2 (ADIPOR2). Rosiglitazone is a peroxisome proliferator-activated receptor-gamma (PPARG) agonist that is widely used in the treatment of type 2 diabetes. We hypothesised that rosiglitazone regulates lipid and glucose metabolism through modulation of the expression of adiponectin receptors in the liver.

METHODS

The expression of ADIPOR1 and ADIPOR2 was analysed in HepG2 hepatocytes. The promoters of adiponectin receptors were isolated and used to analyse the transcriptional regulation. The expression of adiponectin receptors in the liver was determined in mice treated with rosiglitazone.

RESULTS

Rosiglitazone elevated the mRNA and protein levels of ADIPOR2 and stimulated ADIPOR2 promoter in HepG2 cells. Analysis with the ADIPOR2 promoter revealed a putative rosiglitazone-responsive region that contained a glucocorticoid receptor (GR)-binding element. The GR agonist dexamethasone synergised with rosiglitazone to stimulate the ADIPOR2 promoter wheras the GR antagonist RU486 abolished this stimulation. Treatment of mice with rosiglitazone elevated the expression of ADIPOR2 in the liver.

CONCLUSIONS/INTERPRETATION

This study indicates that rosiglitazone can elevate the expression of ADIPOR2 in hepatocytes. Our data also suggest that the PPARG agonist rosiglitazone can interact functionally with a GR element in the ADIPOR2 promoter to mediate stimulation of transcription. This study thus reveals a new paradigm underlying the therapeutic effect of PPARG activators in the treatment of type 2 diabetes.