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PubMed2007

Adiponectin represents an independent risk factor for hypertension in middle aged Korean women.

Adiponectin, which is secreted specifically by adipose tissue, has been shown to act as an anti-atherosclerotic protein. Several studies have shown that adiponectin levels are lower in individuals with obesity, diabetes and cardiovascular disease. The present study investigated relationships between serum adiponectin levels and body mass index (BMI), waist-to-hip ratio (WHR), blood pressure (BP) and lipid profiles in 300 middle-aged Korean women (mean age 50.6 +/- 6.2; BMI 25.78 +/- 3.68 kg/m(2)). The serum adiponectin level was positively associated with high density lipoprotein (HDL)-cholesterol (r = 0.29) and negatively associated with BMI, WHR, percent body fat, triglyceride (TG), systolic BP, and diastolic BP. Multivariate logistic regression analysis revealed that increasing concentrations of adiponectin were associated with lower risk of hypertension. In overall odds ratios (95% CIs) for hypertension, those in the second, third, and fourth (versus the first) quartile of adiponectin after adjustment for age were 0.59 (0.297-1.185), 0.47 (0.236 - 0.938), and 0.32 (0.16 - 0.648), respectively. Regardless of BMI, WHR and percent body fat, higher adiponectin was independently associated with a lower risk of hypertension. These findings suggest that the serum adiponectin level is decreased with atherogenic lipid phenotype including hypertriglyceridemia and low HDL-cholesterol. Furthermore, low serum adiponectin concentration may be an independent risk factor for hypertension in middle-aged Korean women.

Adiponectin↗
PubMed2005

Changes of adiponectin oligomer composition by moderate weight reduction.

Adiponectin affects lipid metabolism and insulin sensitivity. However, adiponectin circulates in three different oligomers that may also have distinct biological functions. We aimed to analyze the role of these oligomers in obesity and lipid metabolism after weight reduction. A total of 17 obese volunteers (15 women and 2 men) participated in a weight reduction program. Individuals were characterized before and after 6 months of a balanced diet. Adiponectin was determined by enzyme-linked immunosorbent assay, and oligomers were detected by nondenaturating Western blot. BMI decreased (35.1 +/- 1.2 to 32.8 +/- 1.1 kg/m(2), P < 0.001), which was associated with an improved metabolite profile. Total adiponectin increased from 5.3 +/- 0.5 to 6.1 +/- 0.6 microg/ml (P = 0.076). High (HMW) and medium molecular weight (MMW) adiponectin oligomers significantly increased during weight reduction (HMW: 0.37 +/- 0.07 to 0.4 +/- 0.08 microg/ml, P = 0.042; MMW: 2.3 +/- 0.2 to 2.9 +/- 0.3 microg/ml, P = 0.007), while low molecular weight (LMW) did not significantly change. Body weight inversely correlated with HMW (r = -0.695, P = 0.002) and positively with LMW (r = 0.579, P = 0.015). Interestingly, HDL cholesterol and HMW were strongly correlated (r = 0.665, P = 0.007). Indeed, HMW and free fatty acids before weight reduction predicted approximately 60% of HDL changes during intervention. In conclusion, weight reduction results in a relative increase of HMW/MMW adiponectin and a reduction of LMW adiponectin. Total adiponectin and especially HMW adiponectin are related to circulating HDL cholesterol.

Female↗
PubMed2004

Globular adiponectin increases GLUT4 translocation and glucose uptake but reduces glycogen synthesis in rat skeletal muscle cells.

AIMS/HYPOTHESIS: The aim of this study was to determine whether adiponectin elicits glucose uptake via increased GLUT4 translocation and to investigate the metabolic fate of glucose in skeletal muscle cells treated with globular adiponectin. MATERIALS AND METHODS: Basal and insulin-stimulated 2-deoxy-D: -[(3)H]glucose uptake, cell surface myc-tagged GLUT4 content, production of (14)CO(2) by oxidation of D: -[U-(14)C]glucose and [1-(14)C]oleate, and incorporation of D: -[U-(14)C]glucose into glycogen and lactate were measured in the presence and absence of globular adiponectin. RESULTS: RT-PCR and Western blot analysis revealed that L6 cells and rat skeletal muscle cells express AdipoR1 mRNA and protein. Globular adiponectin increased both GLUT4 translocation and glucose uptake by increasing the transport V(max) of glucose without altering the K(m). Interestingly, the incorporation of D: -[U-(14)C]glucose into glycogen under basal and insulin-stimulated conditions was significantly decreased by globular adiponectin, whereas lactate production was increased. Furthermore, globular adiponectin did not affect glucose oxidation, but enhanced phosphorylation of AMP kinase and acetyl-CoA carboxylase, and fatty acid oxidation. CONCLUSIONS/INTERPRETATION: The present study is the first to show that globular adiponectin increases glucose uptake in skeletal muscle cells via GLUT4 translocation and subsequently reduces the rate of glycogen synthesis and shifts glucose metabolism toward lactate production. These effects are consistent with the increased phosphorylation of AMP kinase and acetyl-CoA carboxylase and oxidation of fatty acids induced by globular adiponectin.

Adenylate Kinase↗
PubMed2006

Adiponectin mediates antiproliferative and apoptotic responses in human MCF7 breast cancer cells.

It is well established that obesity is a risk factor for breast cancer and that blood levels of adiponectin, a hormone mainly secreted by white adipocytes, are inversely correlated with the body fat mass. As adiponectin elicits anti-proliferative effects in some cell types, we tested the hypothesis that adiponectin could influence human breast cancer MCF-7 cell growth. Here we show that MCF-7 cells express adiponectin receptors and respond to human recombinant adiponectin by reducing their growth, AMPkinase activation, and p42/p44 MAPkinase inactivation. Further, we demonstrate that the anti-proliferative effect of adiponectin involves activation of cell apoptosis and inhibition of cell cycle. These findings suggest that adiponectin could act in vivo as a paracrine/endocrine growth inhibitor towards mammary epithelial cells. Moreover, adipose adiponectin production being strongly reduced in obesity, this study may help to explain why obesity is a risk factor of developing breast cancers.

Adiponectin↗
PubMed2006

Demonstration of adiponectin receptors 1 and 2 mRNA expression in human breast cancer cells.

Recently, we have shown that low adiponectin levels are significantly associated with an increased breast cancer risk. It seems to be very important to study the expression of adiponectin receptor 1 (AdipoR1) and receptor 2 (AdipoR2) in the human breast epithelial cells and breast cancer cells in order to clarify whether or not adiponectin exerts its effects directly on these cells. Expression of adiponectin, AdipoR1, and AdipoR2 mRNA was determined by RT-PCR assay using the RNA samples obtained from human breast cancer cell lines (MCF-7, T47D, SKBR3, and MDA-MB231), HMEC (primary culture of normal human mammary epithelial cells), adipose tissues (axilla) as well as breast cancer cells and normal breast epithelial cells selectively collected from breast cancer tissues by laser microdissection (LMD). Adiponectin mRNA expression was observed only in the adipose tissues. On the other hand, AdipoR1 and AdipoR2 mRNA expression was observed in all four breast cancer cell lines, HMEC, adipose tissues as well as breast cancer cells and normal breast epithelial cells selectively collected by LMD. In addition, AdipoR1 and AdipoR2 expression in both normal breast epithelial cells and breast cancer cells was confirmed by immunohistochemistry. These results suggest a possibility that adiponectin might modulate the growth of normal breast epithelial cells and breast cancer cells directly through AdipoR1 and AdipoR2 receptors, and that the association of low serum adiponectin levels with a high breast cancer risk might be explained, at least in part, by the direct effect of adiponectin on the breast epithelial cells.

Adiponectin↗
PubMed2006

Expression of adiponectin and its receptors (AdipoR1 and AdipoR2) in chicken ovary: potential role in ovarian steroidogenesis.

Adiponectin and its receptors (AdipoR1 and AdipoR2) mRNAs are expressed in various chicken tissues including ovary. However, the cellular expression and the role of adiponectin system have never been investigated in chicken ovary. Here, we have shown that the level of adiponectin mRNA is about 10- to 30-fold higher (p<0.001) in theca cells than in granulosa cells from each hierarchical yellow follicle studied (F4-F1). In contrast, the level of AdipoR1 mRNA expression was about two-fold lower in theca cells than in granulosa cells (p<0.05) whereas those of AdipoR2 was similar in both ovarian cells. Whereas expression of adiponectin mRNA increased with follicular differentiation in theca cells, it decreased in granulosa cells. In contrast, mRNA expression of AdipoR1 and AdipoR2 in both theca and granulosa cells remained stable during yellow follicle development. To determine whether adiponectin is involved in the ovarian steroidogenesis, LH (100 ng/ml)-, FSH (100 ng/ml)- and IGF-1 (100 ng/ml)-induced progesterone production was measured in absence or presence of human recombinant adiponectin (10 microg/ml) for 36 h in cultured granulosa cells from F1, F2 and mixed F3 and F4 follicles. In absence of LH, FSH and IGF-1, adiponectin treatment had no effects on progesterone production whatever vitollegenic follicle studied. However, it increased by about two-fold IGF-1-induced progesterone secretion in F2 and F3/4 follicles whereas it halved progesterone production in response to gonadotropins (LH and FSH) in F3/4 follicles. Thus, in chicken, adiponectin, mainly expressed in theca cells, could exert paracrine or autocrine effect on the ovarian steroidogenesis.

AMP-Activated Protein Kinases↗
PubMed2006

Adiponectin and its receptors: partners contributing to the "vicious circle" leading to the metabolic syndrome?

Although already described five years ago, it is only from year 2000, following intensive research in the field of genetics that the adiponectin protein was related with insulin sensitivity, type 2 diabetes and the metabolic syndrome. The story began with a paradox as this protein exclusively secreted by fat tissue was dramatically decreased in patients presenting an excess of fat mass. Later this decrease was reported with insulin resistance and metabolic syndrome associated phenotypes. The search for genetic variants in the adiponectin encoding ACDC gene and epidemio genetic investigations allowed to associate genetic variations of the gene and phenotypic traits of the metabolic syndrome. One of the major points was the correlation of the levels of circulating adiponectin with insulin sensitivity, leading to a better knowledge of the role of adiponectin. Indeed it is now clearly admitted that adiponectin is an insulin sensitizing cytokine. Recently two adiponectin receptors were described and genetic variations in their genes were associated with features of the metabolic syndrome. Interactions of adiponectin with various partners are discussed in view of a better understanding of adiponectin resistance and insulin resistance.

Adenylate Kinase↗
PubMed2005

Adiponectin and its receptors in non-alcoholic steatohepatitis.

BACKGROUND: Adiponectin, an adipocyte derived polypeptide, has been shown to alleviate steatosis and inflammation in mice with non-alcoholic fatty liver disease. AIM: In the present study, we wished to define liver expression of adiponectin and its receptors in morbidly obese patients undergoing bariatric surgery. Patients with non-alcoholic steatohepatitis (NASH) or simple steatosis were investigated to test whether dysregulation of this system might be involved in these disorders. PATIENTS AND METHODS: Liver mRNA expression of adiponectin and its recently cloned receptors RI and RII (adipoRI and adipoRII) were analysed by fluorescence based real time polymerase chain reaction in 13 patients with NASH and nine with simple steatosis. Adiponectin and adipoRII protein expression were assessed by immunohistochemistry in a subgroup of patients. RESULTS: Adiponectin and adipoRII mRNA expression were significantly reduced in liver biopsies of patients with NASH compared with simple steatosis while no difference was found in adipoRI mRNA expression. In NASH, adipoRII mRNA expression was negatively correlated with serum aspartate aminotransferase levels, serum alanine aminotransferase levels, and grade of fibrosis. Liver adiponectin protein expression was mainly found in endothelial cells of portal vessels and liver sinusoids whereas adipoRII expression was seen in hepatocytes only. Adiponectin and adipoRII staining were lower in biopsies of subjects with NASH compared with simple steatosis. CONCLUSION: Reduced hepatic expression of adiponectin and adipoRII might be of pathophysiological relevance in non-alcoholic fatty liver diseases.

Adiponectin↗
PubMedDate not supplied

Adiponectin replacement therapy attenuates myocardial damage in leptin-deficient mice with viral myocarditis.

The effects of adiponectin replacement therapy on myocardial damage were studied in leptin-deficient (OB) mice with acute viral myocarditis. Encephalomyocarditis virus was injected intraperitoneally into OB and wild-type (WT) mice. One subgroup of OB mice received no intervention and another subgroup received daily adiponectin replacement, simultaneously with viral inoculation. Differences in heart weight, cardiac histological score, numbers of infiltrating or apoptotic cells in the myocardium and the immunoreactivity of adiponectin receptors in myocytes were determined. The reactivity of adiponectin receptor 1 in myocytes from OB mice on day 4 and day 8 after viral inoculation was significantly decreased compared with that in myocytes from WT mice; the OB mice also had elevated cardiac weights and severe inflammatory myocardial damage. Adiponectin replacement in OB mice inhibited the development of severe myocarditis by augmenting myocyte adiponectin receptor 1 reactivity. Exogenously administered adiponectin may inhibit the progression of viral myocarditis through binding to the adiponectin receptor 1 in leptin-deficient conditions.

Adiponectin↗
PubMed2006

Area postrema neurons are modulated by the adipocyte hormone adiponectin.

Adiponectin is an adipocyte-derived peptide hormone involved in energy homeostasis and the pathogenesis of obesity, including hypertension. Area postrema (AP) lacks a blood-brain barrier and is a critical homeostatic integration center for humoral and neural signals. Here we investigate the role of AP in adiponectin signaling. We show that rat AP expresses AdipoR1 and AdipoR2 adiponectin receptor mRNA. We used current-clamp electrophysiology to investigate whether adiponectin influenced membrane properties of AP neurons and found that approximately 60% of rat AP neurons tested were sensitive to adiponectin. Additional electrophysiology experiments coupled with single-cell reverse transcription-PCR indicated that all neurons that expressed both subtypes of receptor were sensitive to adiponectin, whereas neurons expressing only one subtype were predominantly insensitive. Last, microinjection of adiponectin into AP caused significant increases in arterial blood pressure, with no change in heart rate, suggesting that adiponectin acts at AP to provide a possible link between control of energy homeostasis and cardiovascular function.

Adipocytes↗
PubMed2004

[Adiponectin--adipocytokine with a broad clinical spectrum].

Adiponectin (also called AdipoQ, gelatin-binding protein 28, Acrp30) is a novel adipocytokine with important metabolic effects. It is physiologically released from adipose tissue and circulates in serum as a hexamer and larger multimeric structure of high molecular weight. Serum level of the protein correlates with systemic insulin sensitivity. Recently adiponectin receptors AdipoR1 and AdipoR2 have been discovered by expression cloning. AdipoR1 is abundantly expressed in skeletal muscles, whereas AdipoR2 is predominantly expressed in the liver. Marked expression of mRNA for AdipoR1 and AdipoR2 has been lately reported in pancreatic beta cells. Both of the receptors activate AMPK and PPAR alpha metabolic pathways leading to an increase in fatty acid oxidation, glucose uptake and a decreased rate of gluconeogenesis, thus enhancing insulin sensitivity. Moreover effects of adiponectin mimic many metabolic actions of insulin such as augmenting blood flow and glucose disposal in NO-dependent manner. The precise mechanism of regulation of plasma adiponectin level is unknown. Recently the mechanism of transcriptional activation of adiponectin gene via PPAR gamma was described. Its level seems to be decreased by TNFalfa and beta-adrenergic agonists. Furthermore there is increasing evidence that some genetic variants in the adiponectin gene may be associated with its ethnical differences in level as well as its likely clinical consequences. Hipoadiponectynemia is associated with obesity, metabolic syndrome, diabetes type 2, cardiovascular disease, lipodystrophy in AIDS. In patients with chronic renal failure, anorexia nervosa plasma adlponectin level is increased. Weight loss and therapy with thlazolidinediones are proved to enhance endogenous adlponectin production in humans. In summary, the ability of adiponectin to increase insulin sensitivity in conjunction with its anti-inflammatory and antiatherogenic properties have made this novel adipocytokine a promising therapeutic tool for the future, especially in individuals with low plasma levels of adiponectin.

Adiponectin↗
PubMed2006

Serum adiponectin levels in cholesterol and pigment cholelithiasis.

BACKGROUND: Altered adiponectin levels are associated with metabolic abnormalities. The aim of this study was to explore the role of adiponectin in cholelithiasis. METHODS: A radioimmunoassay was used to determine serum adiponectin levels in 58 patients with cholesterol gallstones and 47 with pigment gallstones, and 101 healthy controls. The chemical composition of extracted gallstones was determined by Fourier transform infrared spectroscopy. RESULTS: The mean(s.d.) adiponectin level was decreased in patients with cholesterol gallstones (7.6(4.1) microg/ml; P < 0.001) but raised in patients with pigment gallstones (17.9(9.0) microg/ml; P < 0.001) in comparison with healthy controls (11.7(6.5) microg/ml). Decreased adiponectin levels (odds ratio (OR) 0.85 (95 per cent confidence interval (c.i.) 0.76 to 0.96); P = 0.008) and female sex (OR 6.06 (95 per cent c.i. 2.10 to 17.46); P = 0.001) were associated with cholesterol gallstone formation. Increased adiponectin levels (OR 1.11 (95 per cent c.i. 1.01 to 1.22); P = 0.025) and increased age (OR 1.06 (95 per cent c.i. 1.01 to 1.12); P = 0.029) were associated with pigment gallstone formation. Raised serum aspartate aminotransferase concentration was a risk factor for both cholesterol (OR 1.16 (95 per cent c.i. 1.03 to 1.30); P = 0.013) and pigment (OR 1.23 (95 per cent c.i. 1.10 to 1.38); P < 0.001) gallstones. CONCLUSION: Gallstone formation is associated with altered serum adiponectin levels. Serum adiponectin might serve as a novel marker for cholesterol and pigment cholelithiasis.

Adiponectin↗
PubMed2006

Association between adiponectin, insulin resistance, and endometrial cancer.

BACKGROUND: Obesity is a well known risk factor for the development of endometrial cancer; however, weight alone does not account for all cases. The authors hypothesized that insulin resistance also contributes to an increased risk for endometrial cancer. Adiponectin is a protein secreted by adipose cells and has been shown to be a surrogate marker for insulin resistance, with low levels of adiponectin correlated with hyperinsulinemia and degree of insulin resistance. The purpose of the current study was to determine whether there was an independent association between adiponectin level and endometrial cancer. METHODS: A case-control study was performed on 117 endometrial cancer patients (cases) and 238 women with no history of cancer (controls). Serum adiponectin levels were measured using enzyme-linked immunoadsorbent assay and examined for their association with endometrial cancer. Univariate and multivariate logistic regression analyses were performed with adjustment for confounding factors. RESULTS: The mean serum adiponectin levels were significantly lower among cases (88.8+/-63.3 ng/mL) than among controls (148.2+/-68.3; P<.001). This inverse correlation continued to be observed after controlling for age, body mass index, diabetes, and hypertension. Cases were significantly more likely to have serum adiponectin levels in the lowest (odds ratio [OR] of 10.5; 95% confidence interval [95% CI], 4.49-24.57 [P<.001]) and intermediate tertiles (OR of 2.5; 95% CI, 1.01-6.21 [P=.05]) when compared with controls. CONCLUSIONS: Adiponectin level was found to be independently and inversely associated with endometrial cancer. Women with endometrial cancer were more likely to have low adiponectin levels than controls, even after adjusting for body mass index. This suggested that insulin resistance is independently associated with endometrial cancer.

Adiponectin↗
PubMed2004

Adiponectin protects LPS-induced liver injury through modulation of TNF-alpha in KK-Ay obese mice.

Adiponectin, an adipocytokine, has been identified in adipose tissue, and its receptors are widely distributed in many tissues, including the liver. The present study was performed to clarify the role of adiponectin in lipopolysaccharide (LPS)-induced liver injury using KK-Ay obese mice. We analyzed the effects of adiponectin pretreatment on liver injury induced by D-galactosamine/LPS (GalN/LPS) in KK-Ay obese mice. GalN/LPS treatment induced significant increases in aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels in the blood, apoptotic and necrotic changes in hepatocytes, and/or showed a high degree of lethality. The GalN/LPS-induced liver injury was more pronounced in KK-Ay obese mice than in lean controls. Pretreatment with adiponectin ameliorated the GalN/LPS-induced elevation of serum AST and ALT levels and the apoptotic and necrotic changes in hepatocytes, resulting in a reduction in lethality. In addition, pretreatment with adiponectin attenuated the GalN/LPS-induced increases in serum and hepatic tumor necrosis factor alpha (TNF-alpha) levels and increased peroxisome proliferator-activated receptor (PPAR) alpha messenger RNA expression in the liver. Furthermore, abdominal macrophages from KK-Ay obese mice pretreated with adiponectin in vitro exhibited decreased LPS-induced TNF-alpha production compared with controls. Finally, adiponectin pretreatment also ameliorated TNF-alpha-induced liver injury. In conclusion, these findings suggest that adiponectin prevents LPS-induced hepatic injury by inhibiting the synthesis and/or release of TNF-alpha of KK-Ay obese mice.

Adiponectin↗
PubMed2007

Low adiponectin levels are associated with renal cell carcinoma: a case-control study.

Adiponectin is a novel endogenous insulin sensitizer, secreted by mature adipocytes. Circulating levels of adiponectin are inversely associated with obesity and insulin resistance. Because obesity is a risk factor for renal cell carcinoma (RCC), we hypothesized that low adiponectin levels are associated with RCC. To evaluate this hypothesis, we conducted a case- control study of 70 patients with histologically confirmed RCC and 280 healthy controls matched by gender, age and county of residence. Study subjects were interviewed and blood samples were collected during a 32-month period in Athens, Greece. Serum adiponectin levels were statistically, significantly and inversely associated with RCC when compared with controls (OR=0.76, p=0.05) and this association remained practically unchanged after controlling for BMI; the introduction of waist to hip ratio along with adiponectin in the multiple logistic regression analysis model rendered the association between adiponectin and RCC risk insignificant, indicating that altered levels of adiponectin may mediate the effect of central or intra-abdominal obesity on RCC. Prospective studies as well as studies exploring underlying mechanisms are needed to fully explore the role of adiponectin in predicting future risk of RCC in humans.

Adiponectin↗
PubMed2004

Proteomic and functional characterization of endogenous adiponectin purified from fetal bovine serum.

Adiponectin is a plasma protein exclusively secreted from fat tissue. Many recent pharmacological studies suggest that recombinant adiponectin has multiple therapeutic potentials for obesity-related metabolic disorders, including type 2 diabetes, dyslipidemia, insulin resistance and atherosclerosis. However, the physiological relevance of these findings remains to be further established. In the present study, we have purified endogenous adiponectin from fetal bovine serum and characterized its post-translational modifications and physiological functions in animal models. Endogenous bovine serum adiponectin consists predominantly of full-length proteins that form multiple oligomeric complexes, including trimers, hexamers and higher molecular species. Two-dimensional gel electrophoresis revealed that bovine serum adiponectin exists as multiple post-translationally modified isoforms with distinct molecular weight and isoelectric point. Further analysis using mass spectrometry and Edman degradation sequencing demonstrated that five conserved lysine residues (Lys 28, 60, 63, 72 and 96) within the collagenous domain of bovine adiponectin are hydroxylated and glycosylated by a glucosyl alpha(1-2)galactosyl group. Injection of endogenous bovine adiponectin into C57 mice potently decreased circulating glucose levels and enhanced lipid clearance after a high fat meal. Chronic administration of this protein for a period of two weeks significantly increased insulin sensitivity and glucose tolerance, and depleted hepatic lipid accumulation in high-fat fed mice. These results provide direct evidence that endogenous bovine adiponectin is a physiological hormone that can regulate lipid and glucose metabolism.

Adiponectin↗
PubMed2006

Proteomic characterization of human serum proteins associated with the fat-derived hormone adiponectin.

Adiponectin is a fat cell-secreted hormone with antidiabetic and anti-inflammatory activities. The reduced adiponectin levels are associated with obesity-related metabolic syndrome. Replenishment of this hormone into animal models can improve insulin sensitivity, decrease blood glucose and lipid levels, and prevent the development of atherosclerosis and fatty liver injury. Despite these findings, the underlying molecular mechanisms remain largely unknown. Here, we have used affinity chromatography to purify the protein complexes that are associated with adiponectin in human serum. The nature of these adiponectin-binding proteins was analyzed by MS/MS. Eight proteins from the adiponectin-containing protein mixtures have been identified. Many of them, including thrombospondin-1 (TSP-1), histidine-rich glycoprotein, kininogen 1, and alpha 2 macroglobulin (alpha2M), are well-known glycoproteins involved in the regulation of inflammation, angiogenesis, and tissue remodeling. Coimmunoprecipitation and radioligand competitive-binding assays confirmed the direct interactions between adiponectin and alpha2M, or TSP-1. Moreover, these specific bindings were also detected in the serum samples derived from both healthy human subjects and patients with type 2 diabetes. In summary, our study demonstrated that, in the circulation, adiponectin forms protein complexes with other serum proteins. These proteins might serve as the physiological-binding partners of adiponectin and regulate its bioavailability and biological activities.

Adiponectin↗
PubMed2006

Effects of eicosapentaenoic acid (EPA) on adiponectin gene expression and secretion in primary cultured rat adipocytes.

Adiponectin, a hormone produced by adipocytes, is involved in glucose metabolism and insulin sensitivity. The production of this adipokine is impaired in obesity and insulin resistance. Eicosapentaenoic acid (EPA) is a dietary n-3 polyunsaturated fatty acid that improves insulin sensitivity in several models of obesity and diabetes, which has been suggested to be related to adiponectin induction. An increase in adiponectin production has been also associated with an up-regulation of the transcriptional factor PPARgamma. The aim of this trial was to evaluate the direct effects of EPA on adiponectin gene expression and protein secretion in isolated rat adipocytes as well as to explore the potential mechanisms involved. A comparative study with troglitazone, a PPARgamma agonist, was also performed. For these purposes, primary rat adipocytes were cultured with EPA (100 and 200 microM) and with troglitazone (10 microM) for 96 hours. Both EPA and troglitazone improved glucose utilization by adipocytes. As expected, troglitazone enhanced adiponectin secretion and increased PPARgamma gene expression. However, EPA significantly decreased adiponectin gene expression and protein secretion and reduced PPARy mRNA levels, suggesting that the inhibition of adiponectin by EPA is likely to be secondary to the down-regulation of this adipogenic transcription factor. Moreover, these results suggest that other mechanisms different from the direct stimulation of adiponectin by the fatty acid are underlying the insulin-sensitizing properties observed after EPA treatment in vivo.

Adipocytes↗