Insulin/Foxo1 pathway regulates expression levels of adiponectin receptors and adiponectin sensitivity

Early lesion formation in colorectal carcinogenesis is associated with adiponectin status whereas neoplastic lesions are associated with diet and sex in C57BL/6J mice

Adiponectin is an antiinflammatory and insulin-sensitizing hormone that is decreased in obesity. Although controversial, it has been suggested that decreased adiponectin contributes to colorectal cancer risk in obesity. To further investigate the role of adiponectin in obesity-linked colorectal carcinogenesis, we used male and female adiponectin knockout (KO) and wild-type (Wt) C57BL/6J mice. Tumorigenesis was induced in all mice with the combined treatment of azoxymethane (AOM) and dextran sodium sulfate (DSS). Following AOM/DSS treatment, mice were fed a low-fat control (LFC), or high-fat lard (HFL) diet for 7 1/2 wk. KO mice developed fewer total lesions than Wt mice, males developed fewer lesions than females, and mice fed the HFL diet developed fewer lesions than those fed the LFC diet. Early lesion multiplicity was influenced by genotype, whereas advanced lesion development was influenced by sex and diet. Moreover, lesion types were differentially correlated with serum adipokines and colon gene expression of adiponectin receptors, insulin receptor, and toll-like receptor 4. These data suggest that in the AOM/DSS model of carcinogenesis, adiponectin functions to promote early lesion development whereas sex and diet are important regulators of advanced lesion development through pathways involved in inflammation and insulin signaling.

Dietary capsaicin attenuates metabolic dysregulation in genetically obese diabetic mice

Metabolic dysregulation (e.g., hyperglycemia, hyperinsulinemia, hyperlipidemia, etc.) is a hallmark of obesity-related diseases such as insulin resistance, type 2 diabetes, and fatty liver disease. In this study, we assessed whether dietary capsaicin attenuated the metabolic dysregulation in genetically obese diabetic KKAy mice, which have severe diabetic phenotypes. Male KKAy mice fed a high-fat diet for 2 weeks received a 0.015% capsaicin supplement for a further 3 weeks and were compared with nonsupplemented controls. Dietary capsaicin markedly decreased fasting glucose/insulin and triglyceride levels in the plasma and/or liver, as well as expression of inflammatory adipocytokine genes (e.g., monocyte chemoattractant protein-1 and interleukin-6) and macrophage infiltration. At the same time expression of the adiponectin gene/protein and its receptor, AdipoR2, increased in adipose tissue and/or plasma, accompanied by increased activation of hepatic AMP-activated protein kinase, a marker of fatty acid oxidation. These findings suggest that dietary capsaicin reduces metabolic dysregulation in obese/diabetic KKAy mice by enhancing expression of adiponectin and its receptor. Capsaicin may be useful as a dietary factor for reducing obesity-related metabolic dysregulation.

Functional adiponectin resistance and exercise intolerance in heart failure

The contribution of skeletal muscle myopathy to the phenotype of patients with chronic heart failure (CHF) has become generally accepted. Besides the macro- and microscopic changes that develop during the progressive process of muscular wasting, functional abnormalities manifest in an earlier stage. Analogous to the failing heart, alterations in skeletal muscle energy metabolism, including insulin resistance, are increasingly recognized. In the search for factors causing this observed myopathy, adipokines receive growing attention. In particular, adiponectin is of special interest due to its fundamental role in skeletal muscle energy metabolism. In strong contrast with patients at risk for cardiovascular disease, circulating adiponectin levels are increased in patients with CHF, and this finding is associated with adverse outcome. Recently, the concept of functional skeletal muscle adiponectin resistance has been suggested to explain compensatory elevated adiponectin levels in CHF. Unraveling of adiponectin's complex downstream signalling pathways and insights into the concept of adiponectin resistance hopefully will disengage the road for targeted therapeutic interventions.

N-acetylcysteine and allopurinol synergistically enhance cardiac adiponectin content and reduce myocardial reperfusion injury in diabetic rats

Background

Hyperglycemia-induced oxidative stress plays a central role in the development of diabetic myocardial complications. Adiponectin (APN), an adipokine with anti-diabetic and anti-ischemic effects, is decreased in diabetes. It is unknown whether or not antioxidant treatment with N-acetylcysteine (NAC) and/or allopurinol (ALP) can attenuate APN deficiency and myocardial ischemia reperfusion (MI/R) injury in the early stage of diabetes.

Methodology/Principal Findings

Control or streptozotocin (STZ)-induced diabetic rats were either untreated (C, D) or treated with NAC (1.5 g/kg/day) or ALP (100 mg/kg/day) or their combination for four weeks starting one week after STZ injection. Plasma and cardiac biochemical parameters were measured after the completion of treatment, and the rats were subjected to MI/R by occluding the left anterior descending artery for 30 min followed by 2 h reperfusion. Plasma and cardiac APN levels were decreased in diabetic rats accompanied by decreased cardiac APN receptor 2 (AdipoR2), reduced phosphorylation of Akt, signal transducer and activator of transcription 3 (STAT3) and endothelial nitric oxide synthase (eNOS) but increased IL-6 and TNF-α (all P<0.05 vs. C). NAC but not ALP increased cardiac APN concentrations and AdipoR2 expression in diabetic rats. ALP enhanced the effects of NAC in restoring cardiac AdipoR2 and phosphorylation of Akt, STAT3 and eNOS in diabetic rats. Further, NAC and ALP, respectively, decreased postischemic myocardial infarct size and creatinine kinase-MB (CK-MB) release in diabetic rats, while their combination conferred synergistic protective effects. In addition, exposure of cultured rat cardiomyocytes to high glucose resulted in significant reduction of cardiomyocyte APN concentration and AdipoR2 protein expression. APN supplementation restored high glucose induced AdipoR2 reduction in cardiomyocytes.

Conclusions/Significance

NAC and ALP synergistically restore myocardial APN and AdipoR2 mediated eNOS activation. This may represent the mechanism through which NAC and ALP combination greatly reduces MI/R injury in early diabetic rats.

Caloric restriction increases adiponectin expression by adipose tissue and prevents the inhibitory effect of insulin on circulating adiponectin in rats

Aging is associated with redistribution of body fat and the development of insulin resistance. White adipose tissue emerges as an important organ in controlling life span. Caloric restriction (CR) delays the rate of aging possibly modulated partly by altering the amount and function of adipose tissue. Adiponectin is a major adipose-derived adipokine that has anti-inflammatory and insulin-sensitizing properties. This study examined the effects of CR on adiposity and gene expression of adiponectin, its receptors (AdipoR1 and AdipoR2) in adipose tissue and in isolated adipocytes of Brown Norway rats that had undergone CR for 4 months or fed ad libitum. The study also determined plasma concentrations of adiponectin and insulin in these animals and whether insulin infusion for 7 days affects adiponectin expression and its circulating concentrations under CR conditions. CR markedly reduced body weight as anticipated, epididymal fat mass and adipocyte size. CR led to an increase in plasma free fatty acid and glycerol (both twofold), and adipose triglyceride lipase messenger RNA (mRNA) in adipose tissue and isolated adipocytes (both >2-fold). Adiponectin mRNA levels were elevated in adipose tissue and adipocytes (both >2-fold) as was plasma adiponectin concentration (2.8-fold) in CR rats. However, CR did not alter tissue or cellular AdipoR1 and AdipoR2 expression. Seven days of insulin infusion decreased adiponectin mRNA in adipose tissue but did not reverse the CR-induced up-regulation of circulating adiponectin levels. Our results suggest that the benefits of CR could be, at least in part, dependent on enhanced expression and secretion of adiponectin by adipocytes.

Metabolic factors in the development of hepatic steatosis and altered mitochondrial gene expression in vivo

The objective of the study was to understand the role in vivo of elevated plasma free fatty acids (FFA), insulin, and glucose levels in the development of steatosis and altered mitochondrial gene/protein expression. We studied 4 groups of Sprague-Dawley rats: (1) high-fat diet (HFD), (2) high-dose streptozotocin-induced diabetes (T1DM), (3) low-dose streptozotocin-induced diabetic rats on an HFD (T2DM), and (4) controls. Liver histology and expression of genes/proteins related to mitochondrial fatty acid oxidation and biogenesis were analyzed. Despite an attempt to compensate by increasing expression of genes of fatty acid oxidation (carnitine palmitoyl transferase-1/medium chain acyl-CoA dehydrogenase), the HFD and diabetic groups developed marked steatosis and suffered a significant reduction in mitochondrial biogenesis gene expression (nuclear respiratory factor 1/transcriptional factor A, mitochondrial). In T2DM rats, the combination of high glucose and FFA unexpectedly did not lead to greater fat accumulation than HFD alone. Greater steatosis in HFD vs T2DM (P < .001) correlated with impairment in the gene expression of PPAR-α (ie, fatty acid oxidation) and PGC1α, a major coactivator for mitochondrial biogenesis. Steatosis was not severe in insulin-deficient T1DM rats despite very elevated FFA and glucose levels. Increased carnitine palmitoyl transferase-1/medium chain acyl-CoA dehydrogenase/PPAR-α gene expression suggested inadequate adaptation to high FFA in both T1DM/T2DM rats. Hyperinsulinemia combined with elevated FFA is the key metabolic factor driving hepatic lipogenesis in vivo (HFD rats). Mitochondrial biogenesis (nuclear respiratory factor 1; transcriptional factor A, mitochondrial) is highly susceptible to FFA-induced steatosis. In contrast, hyperglycemia does not have an additive effect (T2DM) and leads to only a modest degree of steatosis in the absence of hyperinsulinemia, even when FFA are extremely elevated as in T1DM rats.

Increased abundance of the adaptor protein containing pleckstrin homology domain, phosphotyrosine binding domain and leucine zipper motif (APPL1) in patients with obesity and type 2 diabetes: evidence for altered adiponectin signalling

AIMS/HYPOTHESIS

The adiponectin signalling pathway is largely unknown, but recently the adaptor protein containing pleckstrin homology domain, phosphotyrosine binding domain and leucine zipper motif (APPL1), has been shown to interact directly with adiponectin receptor (ADIPOR)1. APPL1 is present in C2C12 myoblasts and mouse skeletal muscle, but its presence in human skeletal muscle has not been investigated.

METHODS

Samples from type 2 diabetic, and lean and non-diabetic obese participants were analysed by: immunoprecipitation and western blot; HPLC-electrospray ionisation (ESI)-mass spectrometry (MS) analysis; peak area analysis by MS; HPLC-ESI-MS/MS/MS analysis; and RT-PCR analysis of APPL1 mRNA.

RESULTS

Immunoprecipitation and western blot indicated a band specific to APPL1. Tryptic digestion and HPLC-ESI-MS analysis of whole-muscle homogenate APPL1 unambiguously identified APPL1 with 56% sequence coverage. Peak area analysis by MS validated western blot results, showing APPL1 levels to be significantly increased in type 2 diabetic and obese as compared with lean participants. Targeted phosphopeptide analysis by HPLC-ESI-MS/MS/MS showed that APPL1 was phosphorylated specifically on Ser(401). APPL1 mRNA expression was significantly increased in obese and type 2 diabetic participants as compared with lean participants. After bariatric surgery in morbidly obese participants with subsequent weight loss, skeletal muscle APPL1 abundance was significantly reduced (p < 0.05) in association with an increase in plasma adiponectin (p < 0.01), increased levels of ADIPOR1 (p < 0.05) and increased muscle AMP-activated protein kinase (AMPK) phosphorylation (p < 0.05).

CONCLUSIONS/INTERPRETATION

APPL1 abundance is significantly higher in type 2 diabetic muscle; APPL1 is phosphorylated in vivo on Ser(401). Improvements in hyperglycaemia and hypoadiponectinaemia following weight loss are associated with reduced skeletal muscle APPL1, and increased plasma adiponectin levels and muscle AMPK phosphorylation.

Fibrosis is associated with adiponectin resistance in chronic hepatitis C virus infection

BACKGROUND

Chronic hepatitis C virus (HCV) infection is frequently associated with insulin resistance which has been suggested to promote fibrotic progression. Adiponectin, an adipocyte-derived insulin-sensitizing hormone, might play a protective role against hepatic fibrosis.

MATERIALS AND METHODS

This observational case-control study investigated the adiponectin status in insulin resistant, nondiabetic, chronic HCV-infected patients (n=54; 13 women, 41 men) compared with age-, sex- and BMI-matched healthy controls. Liver biopsies from patients with chronic HCV hepatitis were analysed for the adiponectin and adiponectin receptors (ADIPOR) 1 and 2 mRNA and protein expressions.

RESULTS

Serum adiponectin levels were higher in patients with chronic HCV hepatitis than in healthy controls (12·1±4·7 vs. 9·5±4·4 mg L(-1) in men, P = 0·01; 18·2±4·4 vs. 13·6±5·3mgL(-1) in women, P=0·02). BMI, HDL cholesterol and triglycerides levels correlated with adiponectin levels both in patients and in controls, while no correlation with glucose, insulin and HOMA-IR values could be detected. Nonetheless, insulin resistance was predictive of steatosis and fibrosis in chronic HCV-infected patients. Interestingly, patients with none or mild fibrosis showed serum adiponectin levels similar to those in healthy controls, while hyperadiponectinemia was associated with moderate to severe stages of fibrosis. Hyperadiponectinemia was unlikely sustained by liver production as hepatocytes did not express the protein. ADIPOR1 mRNA, but not ADIPOR2 levels, was reduced in chronic HCV hepatitis. The reduced ADIPOR1 expression was confirmed by immunohistochemistry.

CONCLUSIONS

In patients with chronic HCV hepatitis, fibrosis was associated with hyperadiponectinemia. Chronic HCV-infected hepatocytes showed reduced ADIPOR1 expression, suggesting a pattern of adiponectin resistance.

Role of SIRT1-FoxO1 signaling in dietary saturated fat-dependent upregulation of liver adiponectin receptor 2 in ethanol-administered mice

The aim of the present study is to examine the effects of dietary saturated fatty acids on liver adiponectin receptor 1 (AdipoR1) and adiponectin receptor 2 (AdipoR2) in ethanol-administered animals and in ethanol-exposed cultured hepatic cells, and to explore the underlying molecular mechanisms. The mRNA and protein levels of hepatic AdipoR2 were selectively increased by chronic ethanol feeding to mice consuming a diet high in saturated fat (HSF). Administration of an HSF diet blocked hyperacetylation of forkhead transcription factor 1 (FoxO1), a known target of sirtuin 1 (SIRT1), increased nuclear FoxO1 protein levels, and enhanced association of FoxO1 with the AdipoR2 promoter in the livers of ethanol-fed mice. Treatment of cultured hepatic cells with palmitic acid (a major saturated fatty acid in HSF diet) in the presence of ethanol robustly increased AdipoR2 mRNA expression and enhanced activity of a mouse AdipoR2 promoter. Knocking down SIRT1 or FoxO1 using the small silencing SIRT1 or FoxO1 plasmid blunted the palmitic acid effect. Taken together, these results reveal that dietary saturated fat selectively upregulates hepatic AdipoR2 through modulation of SIRT1-FoxO1 signaling in ethanol fed mice, and this effect may contribute to the protective effect of the HSF diet against alcoholic fatty liver.

Adiponectin, a key adipokine in obesity related liver diseases

Non-alcoholic fatty liver disease (NAFLD) comprising hepatic steatosis, non-alcoholic steatohepatitis (NASH), and progressive liver fibrosis is considered the most common liver disease in western countries. Fatty liver is more prevalent in overweight than normal-weight people and liver fat positively correlates with hepatic insulin resistance. Hepatic steatosis is regarded as a benign stage of NAFLD but may progress to NASH in a subgroup of patients. Besides liver biopsy no diagnostic tools to identify patients with NASH are available, and no effective treatment has been established. Visceral obesity is a main risk factor for NAFLD and inappropriate storage of triglycerides in adipocytes and higher concentrations of free fatty acids may add to increased hepatic lipid storage, insulin resistance, and progressive liver damage. Most of the adipose tissue-derived proteins are elevated in obesity and may contribute to systemic inflammation and liver damage. Adiponectin is highly abundant in human serum but its levels are reduced in obesity and are even lower in patients with hepatic steatosis or NASH. Adiponectin antagonizes excess lipid storage in the liver and protects from inflammation and fibrosis. This review aims to give a short survey on NAFLD and the hepatoprotective effects of adiponectin.

Regulation of synthesis and oxidation of fatty acids by adiponectin receptors (AdipoR1/R2) and insulin receptor substrate isoforms (IRS-1/-2) of the liver in a nonalcoholic steatohepatitis animal model

Nonalcoholic steatohepatitis (NASH) is one of the most frequent causes of abnormal liver dysfunction associated with synthesis and oxidation of fatty acids. Adiponectin receptors (AdipoR1/R2) and insulin receptor substrates (IRS-1/-2) are known as modulators of these fatty acid metabolisms in the liver; however, the regulatory roles of these receptors in the synthesis and oxidation of fatty acids are unclear in the liver of NASH. In this study, we examined the roles of hepatic AdipoR1/R2 and IRS-1/-2 in NASH using an animal model. After feeding a high-fat and high-cholesterol diet to obese fa/fa Zucker rats for 8 weeks, rats showed fatty liver spontaneously with inflammation and fibrosis that are characteristic of NASH. The expression levels of AdipoR1/R2 and IRS-2 were significantly decreased, whereas IRS-1 was significantly increased, in NASH. As a result of the decrease of AdipoR1/R2 expression, the messenger RNA expression levels of genes located downstream of AdipoR1/R2, adenosine monophosphate-activated protein kinase α1/α2, which inhibits fatty acid synthesis, and peroxisome proliferator-activated receptor α, which activates fatty acid oxidation, also decreased. Expression level of sterol regulatory element binding protein-1c was found to be elevated, suggesting the up-regulation of IRS-1, and resulted in increased fatty acid synthesis. Furthermore, increase of forkhead box protein A2 expression was observed, which might be associated with the down-regulation of IRS-2, facilitating fatty acid oxidation. Taken together, increased synthesis and oxidation of fatty acids by up- or down-regulation of AdipoR or IRS may contribute to the progression of NASH. Thus, AdipoR and IRS might be crucially important regulators for the synthesis and oxidation of fatty acids in the liver of NASH.

Loss of adiponectin promotes intestinal carcinogenesis in Min and wild-type mice

BACKGROUND & AIMS

Metabolic syndrome- and obesity-associated cancers, including colon cancer, are common in Western countries. Visceral fat accumulation and decreased levels of plasma adiponectin (APN) have been associated with development of human colorectal adenoma. We investigated the function of APN in intestinal carcinogenesis.

METHODS

APN+/+, APN+/-, or APN-/- mice (C57BL/6J) were given injections of azoxymethane (AOM), which led to development of intestinal tumors; these strains of mice were also crossed with Min mice to assess polyp formation. Adipocytokine levels and phosphorylation/activation of AMP-activated protein kinase (AMPK) were evaluated to investigate the mechanisms of APN in tumor growth.

RESULTS

The total number of polyps in the intestines of male APN+/-Min and APN-/-Min mice increased 2.4- and 3.2-fold, respectively, by the age of 9 weeks and 3.2- and 3.4-fold, respectively, by 12 weeks, compared with those of APN+/+Min mice. Similar results were obtained from female mice. AOM induced colon tumor formation in 40% of APN+/+, 50% of APN+/-, and 71% of APN-/- (P<.05) mice, respectively; mean values for tumor multiplicity of each genotype were 0.5, 0.6, and 1.1 (P<.05), respectively. Phosphorylation of AMPK decreased in intestinal epithelial cells of APN-/- mice compared with APN+/+ mice. Among serum adipocytokines, plasminogen activator inhibitor-1 levels increased in APN-/-Min mice and APN-/- mice that received injections of AOM. Activation of AMPK suppressed expression of plasminogen activator inhibitor-1 in Min mice.

CONCLUSIONS

Mice with disruptions in APN develop more intestinal tumors and have decreased activation (phosphorylation) of AMPK and increased levels of plasminogen activator inhibitor-1, compared with wild-type mice. APN and its receptor might be developed as targets for cancer chemopreventive agents.

Hormonal consequences and prognosis of chronic heart failure

PURPOSE OF REVIEW

Chronic heart failure (CHF) is a major public health problem. The failure to provide peripheral tissues with sufficient amounts of oxygen is accompanied by maladaptive responses that include pathophysiological pathways that may lead to an anabolic-catabolic imbalance with the development of cardiac cachexia. This review aims to highlight players of the catabolic-anabolic imbalance, regulators or appetite, and other mediators that are involved in the progression of CHF to cachexia.

RECENT FINDINGS

Clinical research has buttressed the view that deficiencies or resistance to growth hormone and testosterone plays an important role in the pathophysiology of CHF. The role of appetite regulation in the development of cardiac cachexia is also subject of recent studies. The resistance of CHF patients to the effects of appetite-stimulating peptide ghrelin may be one of the contributing factors. These circumstances drive muscle, bone, and fat wasting. Plasma levels of the adipokines leptin and adiponectin may have a role in the detection of such wasting processes.

SUMMARY

Hormonal signaling pathways play an essential role in the development of cardiac cachexia. Recent findings enhance our understanding of the complex interplay between these regulators and may serve as a hub for the development of therapeutic interventions to prevent or potentially even to treat cardiac cachexia.

Influence of the metabolic syndrome on leptin and leptin receptor in breast cancer

Obesity and its associated metabolic syndrome (MetS) are recognized risk factors for breast cancer. The molecular basis for this association remains largely unknown. Adipokines, in particular leptin and adiponectin, are thought to form part of the mechanism linking obesity with cancer through their altered expression/production either systemically (endocrine pathway) or locally (paracrine/autocrine pathway). Using quantitative PCR, mRNA expression of adiponectin (AdipoQ) and leptin (Ob) in mammary adipose tissue (MAT), intratumoral leptin and associated ligand receptors (ObR, AdipoR1, and AdipoR2) was examined in 77 patients with complete anthropomorphic and serological data. Expression of Ob in MAT, and ObR in matched tumor tissue was significantly higher in patients with MetS compared to obese only or normal weight cancer patients (P < 0.005). There was no difference in intratumoral leptin adiponectin or its ligand receptors in the same groups. Individual features of MetS correlated with Ob and ObR expression, but not obesity markers (BMI, waist circumference). mRNA expression of leptin (Ob) and ObR, in adipose tissue and matched tumor samples, respectively, appear to be associated with obesity status in breast cancer. Increasing insulin resistance is a predominant feature of this higher Ob/ObR expression observed. These novel data indicate that the MetS may be an amenable risk factor for breast cancer.

Insulin resistance and other metabolic risk factors in the pathogenesis of hepatocellular carcinoma

Coinciding with the increased incidence of hepatocellular carcinoma (HCC), there has been a significant increase in the global incidence of obesity and diabetes mellitus (DM), the two major risk factors for nonalcoholic steatohepatitis (NASH). There are many causes of HCC, and nonalcoholic fatty liver disease/NASH is now emerging as a leading risk factor owing to the epidemic of obesity and type 2 DM. The mechanisms leading to HCC in obesity and type 2 DM likely involve interactions between several signaling pathways, including oxidative stress, inflammation, oncogenes, adiponectins, and insulin resistance associated with visceral adiposity and diabetes.

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.

Adiponectin Inhibits Spontaneous and Catecholamine-Induced Lipolysis in Human Adipocytes of Non-Obese Subjects Through AMPK-Dependent Mechanisms

Adiponectin is an adipokine increasing glucose and fatty acid metabolism and improving insulin sensitivity. The aim of this study was to investigate the role of adiponectin in the regulation of adipocyte lipolysis. Human adipocytes isolated from biopsies obtained during surgical operations from 16 non-obese and 17 obese subjects were incubated with 1) human adiponectin (20 µg/ml) or 2) 0.5 mM AICAR – activator of AMPK (adenosine monophosphate activated protein kinase). Following these incubations, isoprenaline was added (10-6 M) to investigate the influence of adiponectin and AICAR on catecholamine-induced lipolysis. Glycerol concentration was measured as lipolysis marker. We observed that adiponectin suppressed spontaneous lipolysis by 21 % and isoprenaline-induced lipolysis by 14 % in non-obese subjects. These effects were not detectable in obese individuals, but statistically significant differences in the effect of adiponectin between obese and non-obese were not revealed by two way ANOVA test. The inhibitory effect of AICAR and adiponectin on lipolysis was reversed by Compound C. Our results suggest, that adiponectin in physiological concentrations inhibits spontaneous as well as catecholamine-induced lipolysis. This effect might be lower in obese individuals and this regulation seems to involve AMPK.

The myocyte expression of adiponectin receptors and PPARδ is highly coordinated and reflects lipid metabolism of the human donors

Muscle lipid oxidation is stimulated by peroxisome proliferator-activated receptor (PPAR) δ or adiponectin receptor signalling. We studied human myocyte expression of the PPARδ and adiponectin receptor genes and their relationship to lipid parameters of the donors. The mRNA levels of the three adiponectin receptors, AdipoR1, AdipoR2, and T-cadherin, were highly interrelated (r ≥ 0.91). However, they were not associated with GPBAR1, an unrelated membrane receptor. In addition, the adiponectin receptors were positively associated with PPARδ expression (r ≥ 0.75). However, they were not associated with PPARα. Using stepwise multiple linear regression analysis, PPARδ was a significant determinant of T-cadherin (P = .0002). However, pharmacological PPARδ activation did not increase T-cadherin expression. The myocyte expression levels of AdipoR1 and T-cadherin were inversely associated with the donors' fasting plasma triglycerides (P < .03). In conclusion, myocyte expression of PPARδ and the adiponectin receptors are highly coordinated, and this might be of relevance for human lipid metabolism in vivo.

High-fat diet and glucocorticoid treatment cause hyperglycemia associated with adiponectin receptor alterations

BACKGROUND

Adiponectin is the most abundant plasma protein synthesized for the most part in adipose tissue, and it is an insulin-sensitive hormone, playing a central role in glucose and lipid metabolism. In addition, it increases fatty acid oxidation in the muscle and potentiates insulin inhibition of hepatic gluconeogenesis. Two adiponectin receptors have been identified: AdipoR1 is the major receptor expressed in skeletal muscle, whereas AdipoR2 is mainly expressed in liver. Consumption of high levels of dietary fat is thought to be a major factor in the promotion of obesity and insulin resistance. Excessive levels of cortisol are characterized by the symptoms of abdominal obesity, hypertension, glucose intolerance or diabetes and dyslipidemia; of note, all of these features are shared by the condition of insulin resistance. Although it has been shown that glucocorticoids inhibit adiponectin expression in vitro and in vivo, little is known about the regulation of adiponectin receptors. The link between glucocorticoids and insulin resistance may involve the adiponectin receptors and adrenalectomy might play a role not only in regulate expression and secretion of adiponectin, as well regulate the respective receptors in several tissues.

RESULTS

Feeding of a high-fat diet increased serum glucose levels and decreased adiponectin and adipoR2 mRNA expression in subcutaneous and retroperitoneal adipose tissues, respectively. Moreover, it increased both adipoR1 and adipoR2 mRNA levels in muscle and adipoR2 protein levels in liver. Adrenalectomy combined with the synthetic glucocorticoid dexamethasone treatment resulted in increased glucose and insulin levels, decreased serum adiponectin levels, reduced adiponectin mRNA in epididymal adipose tissue, reduction of adipoR2 mRNA by 7-fold in muscle and reduced adipoR1 and adipoR2 protein levels in muscle. Adrenalectomy alone increased adiponectin mRNA expression 3-fold in subcutaneous adipose tissue and reduced adipoR2 mRNA expression 2-fold in liver.

CONCLUSION

Hyperglycemia as a result of a high-fat diet is associated with an increase in the expression of the adiponectin receptors in muscle. An excess of glucocorticoids, rather than their absence, increase glucose and insulin and decrease adiponectin levels.

The Relationship between Preheparin Lipoprotein Lipase and Metabolic Derangements in Obese Japanese Children

The aim of this study was to clarify the relationship between preheparin lipoprotein lipase (LPL) and derangements of metabolic status in obese Japanese children. We examined 102 obese children (55 boys and 47 girls; mean age 10.9 yr). Anthropometry, blood pressure and levels of liver transaminases, serum lipids and lipoproteins, uric acid, fasting blood glucose (FBG), serum insulin, LPL, leptin and adiponectin were measured. The subjects were divided into the metabolic syndrome (MS) and non-MS groups. The levels of LPL were compared between these groups. Statistical analysis showed that the LPL levels were significantly lower in the MS group compared with the non-MS group, with the levels decreasing progressively as the number of MS components increased. We conclude that LPL levels decrease also in obese Japanese children with a deteriorated metabolic status in the same way as in adults.

A polymorphism in the gene encoding AdipoR1 affects olfactory recognition

Polymorphisms in the gene encoding adiponectin receptor 1 (AdipoR1) are associated with insulin resistance, fatty liver, increased risk for type 2 diabetes and cardiovascular disease. AdipoR1 is expressed in the central nervous system and in the olfactory mucosa of mice and humans. We therefore hypothesized that a common polymorphism in AdipoR1 might alter olfactory function. We investigated a group of 222 healthy subjects (male: n = 147, female: n = 75) for olfactory recognition, and genotyped them for the polymorphism rs6666089 in the human AdipoR1 gene. This polymorphism has been previously shown to be associated with insulin resistance. Olfactory recognition was tested using standardized sniffing sticks, and parameters of glucose metabolism and serum adiponectin levels were assessed. We found a significant olfactory impairment in carriers of the AdipoR1 polymorphism rs6666089 (olfactory recognition: GG: 89.4 ± 1.2%, GA: 86.9 ± 1.4%, AA: 77.2 ± 4.8%, additive model, P = 0.0004, adjusted for age). Adiponectin levels had no impact on olfactory recognition. Fasting plasma glucose, fasting plasma insulin, body mass index and HbA1c did not differ between the genotype groups. In conclusion, the presence of a genetic variation in AdipoR1 is associated with decreased olfactory recognition in healthy subjects. Adiponectin signalling may have an important role in olfactory function and regulation of appetite.

Effect of telmisartan on the expression of cardiac adiponectin and its receptor 1 in type 2 diabetic rats

OBJECTIVES

This study investigated the effect of telmisartan on the expression of cardiac adiponectin and its receptor 1 in type 2 diabetic rats.

METHODS

Thirty-six male Wistar rats were randomly divided into control (C, n = 10) and diabetic (n = 26) groups. Type 2 diabetes was induced by high-fat and high-sugar diet and intraperitoneal injection of a low dose of streptozotocin (STZ). After induction of diabetes, diabetic rats were again randomly divided into diabetic (D, n = 10) and diabetic treated (DT, n = 10) groups. Telmisartan (5 mg/kg/day) was administrated to diabetic treated rats by gavage for 12 weeks. Twelve weeks later, the heart function was investigated. Plasma and myocardial adiponectin levels were detected by enzyme-linked immunosorbent assay (ELISA). The cardiac mRNA expression of adiponectin receptor 1 (adipiR1) was assayed by reverse transcript-polymerase chain reaction (RT-PCR). The cardiac protein expression of adipiR1, AMP-activated protein kinase (AMPK)-α, phospho-AMPK-α (Thr172) and glucose transporter 4(GLUT4) was determined by Western blotting.

KEY FINDINGS

The ratio of heart weight to body weight was significantly increased in diabetic rats compared with control. The decreased levels of plasma and myocardial adiponectin and the decreased protein and mRNA expression of myocardial adipoR1 led to the decreased myocardial phosphorylation of AMPK-α (Thr172) and the decreased protein expression of myocardial GLUT4 in diabetic rats. Consequently, the heart function was decreased in diabetic rats. Telmisartan treatment significantly attenuated the increased ratio of heart weight to body weight in diabetic rats. The levels of plasma and myocardial adiponectin and the expression of myocardial adipoR1 in diabetic rats were upregulated by telmisartan. Subsequently, the levels of myocardial phospho-AMPK-α (Thr172) and the expression of myocardial GLUT4 in diabetic rats were increased by telmisartan. Consequently, the heart function was improved in diabetic rats treated with telmisartan.

CONCLUSIONS

These results suggest that the levels of myocardial adiponectin and its receptor 1 are decreased in type 2 diabetic rats. Telmisartan treatment up-regulates the levels of myocardial adiponectin and its receptor 1, resulting in the increase in myocardial phospho-AMPK-α (Thr172) and GLUT4 expression, which may contribute to the improvement of heart function and the decrease in cardiac hypertrophy in diabetic rats.

Study of adiponectin in chronic liver disease and cholestasis

PURPOSE

Adiponectin is an adipocytokine suggested to have a hepatoprotective effect. To date, little information is available in the literature regarding changes in serum adiponectin levels in cirrhosis and cholestasis and the associated metabolic disturbances. In order to elucidate the role of adiponectin in chronic liver disease our aim was to determine serum adiponectin in patients with different grades of cirrhosis and cholestasis and to correlate it with markers of liver injury, inflammation and cholestasis. We also aimed to correlate adiponectin with markers of metabolic syndrome such as body mass index and insulin resistance.

METHODS

Forty patients with cirrhosis; 30 patients with cirrhosis and cholestasis; and 20 matched controls were studied. They were subjected to clinical assessment, laboratory investigations: serum bilirubin, ALT, AST, alkaline phosphatase, GGT, albumin, C-reactive protein, prothrombin activity, fasting blood sugar, insulin. HOMA index was calculated. Abdominal ultrasonography and upper GI endoscopy were performed.

RESULTS

Adiponectin was elevated in patients with cirrhosis and cirrhosis/cholestasis and was significantly higher in Child A and B. Adiponectin showed correlation with liver cell injury, marker of inflammation, synthetic liver function and markers of cholestasis. Adiponectin did not correlate with complications of cirrhosis as ascites and esophageal varices nor did it correlate with BMI or HOMA.

CONCLUSIONS

Adiponectin is elevated in cirrhosis and shows correlation with degree of hepatocellular injury and cholestasis. Finally, adiponectin levels in cirrhosis do not correlate with parameters of body composition or metabolism but exclusively with reduced liver function.

Adiponectin resistance and vascular dysfunction in the hyperlipidemic state

Insulin plays an important role in the stimulation of vascular nitric oxide production, with both short term (vasomotility and anti-thrombotic effects) and long term (smooth muscle cell growth and migration inhibition) benefits. Impaired vasodilatory response to insulin, the hallmark of vascular insulin resistance (IR), has important implications for circulatory pathophysiology. An association between adipokines and IR has been observed in both diabetic and nondiabetic states. Adiponectin (APN) is an insulin-sensitizing adipokine known to stimulate skeletal muscle fatty acid (FA) oxidation and reduce lipid accumulation. Recent demonstrations of potential cross-talk between APN and insulin in vascular function regulation are particularly interesting. The lipid accumulation observed after chronic high-fat (HF) diets and in the obese state may reduce vascular response to APN, a pathologic state termed as APN resistance. This review highlights the importance of insulin sensitivity and APN activity in the maintenance of endothelial function. It explores the relationships between vascular IR and APN resistance in the hyperlipidemic pathological condition, representative of the metabolic syndrome. The investigation of vascular insulin and APN resistance provides not only better understanding of vascular pathophysiology, but also an opportunity for therapeutic targeting in individuals affected by the metabolic syndrome.

Adiponectin receptors are downregulated in human gastric cancer

BACKGROUND

Adiponectin has been shown to have suppressive effects on tumor development, but the expression of adiponectin receptors in tumor tissue has not been fully elucidated. The purpose of this study was to quantitatively evaluate the expression of two adiponectin receptors, AdipoR1 and AdipoR2, in gastric cancer tissue.

METHODS

The mRNA levels of AdipoR1 and AdipoR2 were evaluated by quantitative reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemical staining in 67 gastric cancer tissues and their normal counterparts. In addition, the effects of cytokines on AdipoR1 and AdipoR2 expression in cultured gastric cancer cells were examined.

RESULTS

As compared to findings in the normal counterparts, AdipoR1 mRNA expression, standardized by β-actin mRNA, tended to be lower (cancer 0.488 ± 0.039, normal 0.955 ± 0.281, p = 0.0726) and AdipoR2 expression was significantly lower (0.818 ± 0.081, 1.500 ± 0.222, p = 0.0035) in gastric cancer tissue. Immunohistochemical examination showed the same tendency for AdipoR1 and AdipoR2 expression in epithelial cells. Moreover, AdipoR2 was strongly expressed in interstitial cells. However, the expression levels of these receptors did not show a strong correlation with various pathological factors. An in vitro experiment using two gastric cancer cell lines, MKN-74 and NUGC-3, showed that the expression levels of AdipoR1 and AdipoR2 were significantly decreased by transforming growth factor (TGF)-β in a dose-dependent manner.

CONCLUSIONS

Two major adiponectin receptors were decreased in gastric cancer as compared to findings in normal gastric epithelium. TGF-β may be involved in this receptor downregulation. This downregulation may be an ideal strategy for cancer cells to escape the antiproliferative effects of adiponectin in the initial phase of tumor development.

Anti-diabetic effects including diabetic nephropathy of anti-osteoporotic trace minerals on diabetic mice

OBJECTIVE

In our previous study to evaluate the effects of soluble silicon (Si) on bone metabolism, Si and coral sand (CS) as a natural Si-containing material suppressed peroxisome proliferator-activated receptor γ (PPARγ), which regulates both glucose and bone metabolism and increases adipogenesis at the expense of osteogenesis, leading to bone loss. In this study, we investigated the anti-diabetic effects of bone-seeking elements, Si and stable strontium (Sr), and CS as a natural material containing these elements using obese diabetic KKAy mice.

METHODS

Weanling male mice were fed diets containing 1% Ca supplemented with CaCO(3) as the control and CS, and diets supplemented with 50 ppm Si or 750 ppm Sr to control diet for 56 d. The mRNA expressions related to energy expenditure in the pancreas and kidney were quantified by real-time polymerase chain reaction.

RESULTS

At the end of feeding, plasma glucose, insulin, leptin, and adiponectin levels decreased significantly in three test groups, while pancreatic PPARγ and adiponectin mRNA expression levels increased significantly toward the normal level, improving the glucose sensitivity of β-cells and inducing a significant decrease in insulin expression. The renal PPARγ, PPARα, and adiponectin expression levels, histologic indices of diabetic glomerulopathy, and plasma indices of renal function were also improved significantly in the test groups.

CONCLUSION

Taken together, anti-osteoporotic trace minerals, Si and Sr, and CS containing them showed novel anti-diabetic effects of lowering blood glucose level, improving the tolerance to insulin, leptin, and adiponectin, and reducing the risk of glomerulopathy through modulation of related gene expression in the pancreas and kidney.

Obesity, hyperinsulinemia and breast cancer: novel targets and a novel role for metformin

The relationship between obesity, metabolic syndrome, diabetes and cancer has been recognized for many years. Multiple studies conducted in the last 20 years have identified molecular mechanisms responsible for this phenomenon. Elucidation of the important role of insulin, IGF receptor, mTOR and AMP-activated protein kinase in breast cancer biology has led to the development and subsequent clinical evaluation of novel targeted therapies, including IGF-1 receptor-specific antibodies or tyrosine kinase inhibitors and inhibitors of mTOR. There is also a growing interest in the use of metformin, which has been shown to possess antitumor activity resulting from activation of AMP-activated protein kinase and subsequent inhibiton of mTOR, as well as from decreased circulating insulin levels. Metformin has been shown to inhibit proliferation, invasion and angiogenesis of neoplastic cells and to overcome resistance of breast cancer to chemotherapy, hormonal therapy and HER2 inhibition. Recently, metformin has been demonstrated to inhibit breast cancer stem cell growth and to synergize with chemotherapy in suppression of tumor growth and prolongation of survival of breast tumor-bearing animals. Several currently ongoing Phase II and III clinical studies are evaluating the therapeutic efficacy of metformin in the treatment of early and advanced breast cancer patients.

ATF3 negatively regulates adiponectin receptor 1 expression

Adiponectin is an adipocyte-derived hormone that has antidiabetic and antiatherogenic effects through two membrane receptors, adiponectin receptor 1 (AdipoR1) and adiponectin receptor 2 (AdipoR2). Although it has been reported that the expression of AdipoR1 and AdipoR2 is regulated under physiological and pathophysiological states, their regulation is largely unknown. Previously, we demonstrated that endoplasmic reticulum (ER) stress or obesity-inducible ATF3 negatively regulates the expression of adiponectin and AdipoR2. Here, we investigated the regulation of another adiponectin receptor, AdipoR1 by ATF3, to determine if ATF3 may contribute to impairment of adiponectin signaling by repressing the expression of both adiponectin and adiponectin receptors. We found that treatment with thapsigargin, a stimulator of ATF3 expression as an inducer of ER stress, decreased AdipoR1 expression in insulin-sensitive cells (HepG2, C2C12) and insulin secreting cells (MIN6N8). Furthermore, overexpression of lentivirus carrying-ATF3 decreased AdipoR1 expression in those cells, demonstrating that ATF3 downregulates AdipoR1 expression. Next, we investigated the effects of ATF3 on human AdipoR1 promoter activity and identified an ATF3-responsive region in the promoter. Both thapsigargin treatment and ATF3 expression repressed AdipoR1 promoter activity. Transfection studies using mutant constructs containing 5'-deletions in the human AdipoR1 promoter revealed that putative ATF/CRE site is located between the -248 and -224, TGACGCGG. Chromatin immunoprecipitation assay demonstrated that ATF3 directly binds to human AdipoR1 promoter spanning from -248 to -224. Finally, deletion of the putative ATF/CRE site abrogated ATF3-mediated transrepression of the AdipoR1 promoter. Importantly, ATF3 expression was increased in hyperglycemia or TNF-α-treated C2C12 cells in which AdipoR1 expression was decreased, suggesting that ATF3 may contribute to downregulation of AdipoR1 by hyperglycemia and TNF-α. Collectively, these results demonstrate that ATF3 negatively regulates human AdipoR1 expression via binding to an ATF3-responsive region in the promoter, which plays an important role in attenuation of adiponectin signaling and induction of insulin resistance.

Skeletal muscle inflammation is not responsible for the rapid impairment in adiponectin response with high-fat feeding in rats

Adiponectin (Ad) is an insulin-sensitizing adipokine known to stimulate fatty acid (FA) oxidation in skeletal muscle. Skeletal muscle can become resistant to Ad very rapidly, after only 3 days of high saturated fat feeding in rats. Whether the same occurs following a high polyunsaturated fat diet is unknown. Obesity, insulin resistance, and hyperlipidemia are recognized as low-grade inflammatory diseases; therefore, we hypothesized that high-fat feeding induces inflammation, which interferes with Ad action at skeletal muscle. To this end, rats were placed into one of three dietary groups, control (CON, 10% kcal from fat), high saturated (SAT), or high polyunsaturated (PUFA) fat (60% kcal from fat) for 3 days to determine whether Ad resistance develops. Half of the animals from each group were further supplemented with aspirin, a common anti-inflammatory drug. Ad stimulated FA metabolism, Ad signaling intermediates [AdipoR1, APPL1, LKB1, AMPK, and acetyl-CoA carboxylase (ACC)], and inflammatory proteins [Toll-like receptor (TLR4), IKKα/β, IκBα, NF-κB, suppressor of cytokine signaling-3 (SOCS3), and JNK] were measured in soleus muscle. Three days of SAT feeding induced Ad resistance in soleus muscle, assessed as an inability of Ad to phosphorylate ACC and increase FA oxidation. In PUFA-fed animals, Ad-stimulated FA oxidation and ACC phosphorylation to the same degree as CON animals (FA oxidation: +35%, +41%; pACC +29%, +19%; CON, PUFA, P < 0.05). However, neither SAT nor PUFA feeding for 3 days induced skeletal muscle inflammation. Surprisingly, aspirin prevented Ad-stimulated increases in FA oxidation. In conclusion, FA type is critical in the development of Ad resistance, but this does not appear to be mediated by inflammation.

Naringenin chalcone improves adipocyte functions by enhancing adiponectin production

Naringenin chalcone is a flavonoid contained in tomato peel. In this study, we investigated its effects on adipocyte functions related to metabolic processes, including adipocytokine production. Naringenin chalcone promoted the gene expression (8.0-fold, p<0.001) and protein secretion (2.2-fold, p<0.001) of adiponectin from 3T3-L1 adipocytes. Reporter gene assays revealed that naringenin enhanced the activity of peroxisome proliferator-activated receptor gamma. DNA microarray experiments and Gene Ontology analysis revealed that naringenin chalcone also up-regulated the genes associated with mitochondrial energy metabolism, reflecting its insulin-sensitizing effects. Conversely, genes in categories such as those for cell adhesion were down-regulated. The expression of one adiponectin receptor, AdipoR2, was also increased (1.8-fold, p<0.01), suggesting that naringenin chalcone could activate the adiponectin pathway through the elevation of both the ligand and its receptor. These results indicate that naringenin chalcone is a potent tomato flavonoid that improves adipocyte metabolic functions and exerts insulin-sensitizing effects by activating an adiponectin-related pathway.

AdipoR2 is transcriptionally regulated by ER stress-inducible ATF3 in HepG2 human hepatocyte cells

Adiponectin acts as an insulin-sensitizing adipokine that protects against obesity-linked metabolic disease, which is generally associated with endoplasmic reticulum (ER) stress. The physiological effects of adiponectin on energy metabolism in the liver are mediated by its receptors. We found that the hepatic expression of adiponectin receptor 2 (AdipoR2) was lower, but the expression of markers of the ER stress pathway, 78 kDa glucose-regulated protein (GRP78) and activating transcription factor 3 (ATF3), was higher in the liver of ob/ob mice compared with control mice. To investigate the regulation of AdipoR2 by ER stress, we added thapsigargin, an ER stress inducer, to a human hepatocyte cell line, HepG2. Addition of the ER stress inducer increased the levels of GRP78 and ATF3, and decreased that of AdipoR2, whereas addition of a chemical chaperone, 4-phenyl butyric acid (PBA), could reverse them. Up- or down-regulation of ATF3 modulated the AdipoR2 protein levels and AdipoR2 promoter activities. Reporter gene assays using a series of 5'-deleted AdipoR2 promoter constructs revealed the location of the repressor element responding to ER stress and ATF3. In addition, using electrophoretic mobility shift and chromatin immunoprecipitation assays, we identified a region between nucleotides -94 and -86 of the AdipoR2 promoter that functions as a putative ATF3-binding site in vitro and in vivo. Thus, our findings suggest that the ER stress-induced decrease in both protein and RNA of AdipoR2 results from a concomitant increase in expression of ATF3, which may play a role in the development of obesity-induced insulin resistance and related ER stress in hepatocytes.

B-cell chronic lymphocytic leukemia risk in association with serum leptin and adiponectin: a case-control study in Greece

AIM

Leptin and adiponectin are two well-studied adipokines in relation to malignancies. In this study, we examined the association between leptin/adiponectin and risk of B-cell chronic lymphocytic leukemia (B-CLL), as well as the relationships between adipokines and several established prognostic factors of B-CLL.

METHODS

Ninety-five patients with incident B-CLL and 95 hospital controls matched on age and gender were studied between 2001 and 2007, and blood samples were collected. Leptin, total and high molecular weight adiponectin, and prognostic markers of B-CLL were determined.

RESULTS

Cases had a higher body mass index (BMI) than controls (p = 0.01) and lower levels of leptin (p < 0.01). Significantly more cases than controls presented a family history of lymphohematopoietic cancer (LHC) (p = 0.01). Higher serum leptin levels were associated with lower risk of B-CLL adjusting for age, gender, family history of LHC, BMI and serum adiponectin; the multivariate odds ratio comparing highest to lowest tertile was 0.05 (95% CI 0.01-0.29, p trend < 0.001); Adiponectin was not significantly different between cases and controls.

CONCLUSION

Leptin was found to be inversely associated with risk of CLL but in contrast to prior studies of CLL and hematologic malignancies, this study found no significant association between CLL and adiponectin.

Impaired liver regeneration of steatotic rats after portal vein ligation: a particular emphasis on (99m)Tc-DISIDA scintigraphy and adiponectin signaling

BACKGROUND & AIMS

Portal vein ligation (PVL) is increasingly employed prior to major hepatectomy in order to enhance the volume of the future liver remnant (FLR) and to avoid post-hepatectomy liver failure. The efficacy of PVL on subjects with non-alcohol fatty liver disease (NAFLD) is largely unknown.

METHODS

Sprague-Dawley rats fed with normal diet (control) and methionine-choline deficient diet (MCD) were used. The animals underwent PVL and were sacrificed at indicated time points.

RESULTS

Livers from MCD rats exhibited a decreased BrdU and Ki-67 labelling index, and an increased apoptotic index after PVL compared to normal rats; as a net effect, MCD rats exhibited a decrease in their restituted liver mass and redistributed volume ratio, compared to normal rats. Normal rats displayed similar serum levels of ICG15-R before and after PVL; whereas MCD rats displayed reduced ICG15-R after PVL. Using (99m)Tc-DISIDA scintigraphy examination, livers from MCD rats exhibited decreased HEF and prolonged TE(1/2) of FLR after PVL, indicating deteriorating hepatocyte function despite the shift in volume. The basal level of plasma TNFalpha, IL-1alpha, IL-1beta, and IL-10 of MCD rats was significantly increased before PVL compared to normal rats; however their plasma level did not increase in response to PVL as in normal rats. Hepatic adiponectin mRNA surged in MCD rats after PVL, whereas its receptors, AdipoR1 and AdipoR2, were paradoxically down-regulated. PPARalpha, a down-stream molecule of AdipoR2 axis, was also decreased in MCD rats.

CONCLUSIONS

Reduced regenerated liver mass and deteriorated hepatocyte function of the FLR from steatotic rats after PVL may be associated with deranged Kupffer cell-mediated cytokine expression and disrupted adiponectin signalling.

Effect of Renin-Angiotensin system blockade on insulin resistance and inflammatory parameters in patients with impaired glucose tolerance

OBJECTIVE

The study investigated the effect of angiotensin receptor blockers (ARB) on glucose homeostasis and inflammatory parameters in patients with impaired glucose tolerance (IGT).

RESEARCH DESIGN AND METHODS

We prospectively studied the insulin sensitivity index (ISI) and homeostasis model assessment-insulin resistance (HOMA-IR) in 13 obese males with IGT and in 13 matched control subjects with normal glucose tolerance (NGT) during hyperglycemic testing over 90 min. Adiponectin, retinol-binding protein 4 (RBP4), and high-sensitive C-reactive protein (hsCRP) were analyzed. Measurements were performed at baseline and after a 4-week treatment with 160 mg/day valsartan. The results of the IGT and NGT groups were compared.

RESULTS

At baseline, HOMA-IR (IGT 4.1 +/- 3 vs. NGT 2.3 +/- 1.0, P < 0.01), hsCRP (IGT 3.9 +/- 1.9 vs. NGT 1.8 +/- 1 mg/l, P < 0.05), and RBP4 (IGT 27.1 +/- 2.1 vs. NGT 24.0 +/- 2.0 ng/ml, P < 0.05) were significantly higher, whereas ISI (IGT 1.5 +/- 0.9 vs. NGT 1.8 +/- 1.2, P < 0.05) and plasma adiponectin (IGT 3.2 +/- 0.9, NGT 5.2 +/- 2.4 microg/ml, P < 0.05) were significantly lower in the IGT group compared with the NGT group. Under ARB, there was an increase in both groups of adiponectin (IGT 4.1 +/- 1.9 microg/ml, NGT 6.3 +/- 2.9 microg/ml, P < 0.05) and an increase in ISI (IGT 1.5 +/- 0.9 to 2.3 +/- 1 microg/ml, NGT 1.8 +/- 1 to 2.5 +/- 2 microg/ml, P < 0.05). HOMA-IR (4.1 +/- 3 to 2.6 +/- 2; P < 0.01), hsCRP (3.9 +/- 1.9 to 1.8 +/- 1 mg/l, P < 0.05), and RBP4 (27.1 +/- 2.1 to 22.1 +/- 1.8 ng/ml, P < 0.01) decreased significantly in the IGT group.

CONCLUSIONS

Insulin sensitivity and associated inflammatory factors improve under ARB in IGT patients.

Dimerization of adiponectin receptor 1 is inhibited by adiponectin

AdipoR1 and AdipoR2 are newly discovered members of the huge family of seven-transmembrane receptors, but both receptors are structurally and functionally different from G-protein-coupled receptors. Little is known about the oligomerization of the AdipoRs. Here, we show the presence of endogenous AdipoR1 dimers in various cell lines and human muscle tissue. To directly follow and localize the dimerization, we applied bimolecular fluorescence complementation (BiFC) in combination with flow cytometry. We visualized and quantified AdipoR1 homodimers in HEK293 cells. Moreover, we identified a GxxxG dimerization motif in the fifth transmembrane domain of the AdipoR1. By mutating both glycine residues to phenylalanine or glutamic acid, we were able to modulate the dimerization of AdipoR1, implicating a role for the GxxxG motif in AdipoR1 dimerization. Furthermore, we tested whether the AdipoR1 ligand adiponectin had any influence on receptor dimerization. Interestingly, we found that adiponectin decreases the receptor dimerization in a concentration-dependent manner. This effect is mainly mediated by segments of the collagen-like domain of full-length adiponectin. Accordingly, this is the first direct read-out signal of adiponectin at the AdipoR1 receptor, which revealed the involvement of specific amino acids of both the receptor and the ligand to modulate the quaternary structure of the AdipoR1.

Diabetes mellitus, inflammation, obesity: proposed treatment pathways for current and future therapies

OBJECTIVE

To review the pathophysiology, pharmacology, and current or future therapies under study for use in treating diabetes mellitus, inflammation associated with diabetes mellitus, and/or obesity related to diabetes mellitus, through 1 of 4 investigational pathways: adiponectin, ghrelin, resveratrol, or leptin.

DATA SOURCES

A literature search using MEDLINE (1966-December 12, 2009), PubMed (1950-December 12, 2009), Science Direct (1994-December 12, 2009), and International Pharmaceutical Abstracts (1970-December 12, 2009) was performed using the terms adiponectin, ghrelin, resveratrol, leptin, inflammation, obesity, and diabetes mellitus. English-language, original research, and review articles were examined, and citations from these articles were assessed as well.

STUDY SELECTION AND DATA EXTRACTION

Clinical studies and in vitro studies were included in addition to any Phase 1, 2, or 3 clinical trials.

DATA SYNTHESIS

Mechanistic pathways regarding adiponectin, ghrelin, resveratrol, and leptin are of interest as future treatment options for diabetes mellitus. Each of these pathways has produced significant in vitro and in vivo clinical data warranting further research as a possible treatment pathway for diabetes-related inflammation and/or obesity reduction. While research is still underway to determine the exact effects these pathways have on metabolic function, current data suggest that each of these compounds may be of interest for future therapies.

CONCLUSIONS

While several pathways under investigation may offer additional benefits in the treatment of diabetes mellitus and associated impairments, further investigation is necessary for both investigational and approved therapies to ensure that the impact in new pathways does not increase risks to patient safety and outcomes.

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.

Correlation of adiponectin receptor expression with cytokines and insulin sensitivity in growth hormone (GH)-treated children with Prader-Willi syndrome and in non-GH-treated obese children

CONTEXT

Prader-Willi syndrome (PWS), a genetic disorder characterized by obesity in early childhood, is reported to have elevated levels of adiponectin. The effects of adiponectin are mediated by adiponectin receptors (ADIPORs) that include ADIPOR1 and ADIPOR2. There is evidence that several cytokines, including adiponectin, TNF-alpha, and IL-6, are involved in insulin sensitivity.

OBJECTIVE AND METHODS

We measured the relative expression of adiponectin, ADIPORs, several proinflammatory cytokines including TNF-alpha, and IL-6 expression in peripheral blood mononuclear cells (PBMCs) of children with PWS and obese comparators using real-time PCR. Their correlation with homeostasis model assessment insulin resistance index (HOMA-IR) was analyzed.

PATIENTS

Thirty children with PWS (median age 7.1 yr, 18 males, 12 females) that were being treated with GH and 32 obese children not receiving GH treatment (median age 9.1 yr, 15 males, 17 females) for comparison were enrolled.

RESULTS

The PWS children had increased expression of ADIPOR2 (P = 0.02) and decreased expression of IL-6 (P = 0.03) compared with the comparison group. Moreover, there was a significant positive correlation between the ADIPORs and TNF-alpha (ADIPOR1 vs. TNF-alpha: r = 0.66, P < 0.001 in PWS, r = 0.80, P < 0.001 in comparison group; ADIPOR2 vs. TNF-alpha: r = 0.69, P < 0.001 in comparison group). The ADIPORs in the comparison group showed significant negative correlation with HOMA-IR (ADIPOR1 vs. HOMA-IR; rho = -0.41, P = 0.02, ADIPOR2 vs. HOMA-IR; rho = -0.46, P < 0.01).

CONCLUSION

The results of this study showed that inflammatory cytokine expression was closely associated with the expression of the ADIPORs in the PBMCs of both the children with PWS and the comparison group. Moreover, ADIPOR2 expression was highly expressed in the PBMCs of the children with PWS. A further study on the mechanism of increased expression of ADIPOR2 and its correlation with the expression of TNF-alpha in the PBMCs using the non-GH-treated PWS and obese control will be warranted because this study compared GH-treated PWS with an obese comparator group.

The Fox genes in the liver: from organogenesis to functional integration

Formation and function of the liver are highly controlled, essential processes. Multiple signaling pathways and transcriptional regulatory networks cooperate in this complex system. The evolutionarily conserved FOX, for Forkhead bOX, class of transcriptional regulators is critical to many aspects of liver development and function. The FOX proteins are small, mostly monomeric DNA binding factors containing the so-called winged helix DNA binding motif that distinguishes them from other classes of transcription factors. We discuss the biochemical and genetic roles of Foxa, Foxl1, Foxm1, and Foxo, as these have been shown to regulate many processes throughout the life of the organ, controlling both formation and function of the liver.

Hepatic adiponectin receptors (ADIPOR) 1 and 2 mRNA and their relation to insulin resistance in obese humans

OBJECTIVE

Adiponectin signalling attenuates insulin resistance (IR) and steatosis hepatis in animal models. As adiponectin receptor (ADIPOR)1 and ADIPOR2 are critical components in the adiponectin signalling cascade, we studied hepatic ADIPOR1/2 mRNA levels in humans and their relation to IR.

DESIGN

We determined metabolic risk factors and levels of hepatic mRNA transcribed from ADIPOR1, ADIPOR2 and FOXO1, a putative up-stream regulator, in 43 and 34 obese subjects with low and high homeostasis model assessment-IR, respectively.

RESULTS

Plasma adiponectin and metabolic risk factors showed associations with IR as expected. Both hepatic ADIPOR1 and ADIPOR2 mRNA expression levels were higher in insulin-resistant subjects (P<0.0035). ADIPOR1 mRNA correlated with FOXO1 mRNA in obese insulin resistant (P=0.0034), but not insulin-sensitive subjects, while no correlations of ADIPOR2 with FOXO1 mRNA were noted. FOXO1 enhanced transcription from the ADIPOR1, but not the ADIPOR2 promoter in HepG2 cells.

CONCLUSION

Increased hepatic ADIPOR1 and ADIPOR2 mRNA in insulin-resistant obese subjects may, at least in part, reflect a compensatory mechanism for reduced plasma adiponectin. FOXO1 may contribute to enhanced ADIPOR1, but not ADIPOR2 transcription in IR.