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PubMed2006

Post-translational modifications of the four conserved lysine residues within the collagenous domain of adiponectin are required for the formation of its high molecular weight oligomeric complex.

Adiponectin is a multifunctional adipokine that circulates as several oligomeric complexes in the blood stream. However, the molecular basis that regulates the production of the adiponectin oligomers remains largely elusive. We have shown previously that several conserved lysine residues (positions 68, 71, 80, and 104) within the collagenous domain of adiponectin are modified by hydroxylation and glycosylation (Wang, Y., Xu, A., Knight, C., Xu, L. Y., and Cooper, G. J. (2002) J. Biol. Chem. 277, 19521-19529). Here, we investigated the potential roles of these post-translational modifications in oligomeric complex formation of adiponectin. Gel filtration chromatography revealed that adiponectin produced from mammalian cells formed trimeric, hexameric, and high molecular weight (HMW) oligomeric complexes. These three oligomeric forms were differentially glycosylated, with the HMW oligomer having the highest carbohydrate content. Disruption of hydroxylation and glycosylation by substitution of the four conserved lysines with arginines selectively abrogated the intracellular assembly of the HMW oligomers in vitro as well as in vivo. In type 2 diabetic patients, both the ratios of HMW to total adiponectin and the degree of adiponectin glycosylation were significantly decreased compared with healthy controls. Functional studies of adiponectin-null mice revealed that abrogation of lysine hydroxylation/glycosylation markedly decreased the ability of adiponectin to stimulate phosphorylation of AMP-activated protein kinase in liver tissue. Chronic treatment of db/db diabetic mice with wild-type adiponectin alleviated hyperglycemia, hypertriglyceridemia, hepatic steatosis, and insulin resistance, whereas full-length adiponectin without proper post-translational modifications and HMW oligomers showed substantially decreased activities. Taken together, these data suggest that hydroxylation and glycosylation of the lysine residues within the collagenous domain of adiponectin are critically involved in regulating the formation of its HMW oligomeric complex and consequently contribute to the insulin-sensitizing activity of adiponectin in hepatocytes.

Adipocytes↗
PubMed2005

Serum adiponectin concentration and cardiovascular risk factors in climacteric women.

OBJECTIVE: Adiponectin plays a significant role in the modulation of glucose tolerance and insulin sensitivity. We attempted to evaluate the relationship between adiponectin level and parameters of the menopausal metabolic syndrome: body mass index, waist-to-hip ratio, lipid profile and insulin resistance indices. SUBJECTS AND METHODS: Thirty-two women and ten men aged 40-63 years were included. The percentage of body fat and of abdominal fat deposits were measured with dual-energy X-ray absorptiometry. Serum adiponectin, tumour necrosis factor-a (TNFalpha) and leptin were measured with commercially available radioimmunoassay kits. To exclude the influence of nutritional factors on adiponectin secretion, diet content was analysed in the preceding three days. RESULTS: Postmenopausal non-obese women had a non-significantly lower level of adiponectin compared with premenopausal women of corresponding body mass. Serum adiponectin level was significantly lower in postmenopausal obese women than in non-obese women (p = 0.0023). Men with similar age and body mass to the women had the lowest level of adiponectin (p = 0.06). Three months of estrogen replacement therapy in women with surgical menopause did not significantly change the serum level of adiponectin. We found a negative correlation of adiponectin with leptin, insulin resistance index and total cholesterol, and a positive correlation with high-density lipoprotein cholesterol. Adiponectin level was negatively correlated with free testosterone, but we did not find such a relationship with estradiol. There was no correlation of adiponectin level with TNFalpha; however, serum TNFalpha correlated positively with leptin. The dietary analysis showed no differences between the diets of obese and non-obese women over the preceding three days. Moreover, mean diastolic and systolic blood pressures were noted to be significantly lower in premenopausal women than in postmenopausal non-obese women (p = 0.05). CONCLUSIONS: Our results suggest that adiponectin could be a marker of risk for developing menopausal metabolic syndrome. Moreover, it is possible that sex steroids have an influence on adiponectin secretion.

Absorptiometry, Photon↗
PubMed2004

Adiponectin in chronic kidney disease is related more to metabolic disturbances than to decline in renal function.

BACKGROUND: Adiponectin, a newly discovered collagen-like protein of the collectin family exclusively produced by adipocytes, possesses anti-inflammatory properties. Plasma adiponectin is associated with a decreased cardiovascular risk in non-renal patients, and is reduced in obesity and insulin-resistant states. Although reports show an increase in the adiponectin level in maintenance haemodialysis, peritoneal dialysis and end-stage renal disease, there is no documentation of adiponectin levels and regulation in the early stages of chronic kidney disease (CKD). METHODS: We prospectively measured glomerular filtration rate (GFR) in 48 patients with CKD using inulin clearance. Fasting blood was drawn to determine insulin, leptin, adiponectin and C-reactive protein (CRP) levels. Body fat mass was calculated using skinfold thickness measurements. RESULTS: The patients' mean GFR was 53.5+/-24.9 (SD) ml/min/1.73 m2. Adiponectin was in the normal range in men (9.8+/-2.9 mg/l) and women (16.6+/-5.0 mg/l) with CKD, being significantly higher in women than men (P<0.001). Serum leptin was above normal (10.4+/-10.7 microg/l), whereas serum insulin and CRP were within their normal ranges (3.5+/-3.3 microU/ml and 2.6+/-5.0 mg/l, respectively). In linear regression analysis, adiponectin was negatively correlated with GFR (P = 0.02), fat mass (P = 0.03) and body mass index (P = 0.002), and strongly positively correlated with serum leptin (P = 0.003). A positive relationship was also found between plasma adiponectin and the urinary albumin/creatinine ratio (P = 0.007). No relationship was found between adiponectin and insulin or adiponectin and CRP. In multiple regression analysis, adiponectin was significantly positively correlated with leptin (P<0.0001), negatively with body mass index (P<0.0001) and only weakly with GFR (P = 0.04). CONCLUSIONS: Despite an adverse metabolic environment in chronic renal insufficiency, serum adiponectin increases in non-obese patients when renal function deteriorates. Adiponectin is only weakly affected by renal function per se, but appears influenced by proteinuria, and more significantly by body mass index and the change in serum leptin that accompanies decline in renal function.

Adiponectin↗
PubMed2005

Is adiponectin involved in the pathogenesis of nonalcoholic steatohepatitis? A preliminary human study.

BACKGROUND: Animal studies have suggested that adiponectin may play a role in the pathogenesis of alcoholic and nonalcoholic fatty liver disease. Studies are limited that evaluated the role of adiponectin in the pathogenesis of nonalcoholic steatohepatitis (NASH). METHODS: To further our understanding of the role of adiponectin in the pathogenesis of NASH, the following studies were conducted. Serum adiponectin was measured and correlated with anthropometric and nutritional variables in 21 patients with biopsy-proven NASH and 19 age-, gender-, body mass index-, and body fat-matched controls. The effect of a mixed meal on serum adiponectin levels in a subgroup of patients (n = 24) with NASH and controls was assessed. In a separate cohort, liver samples belonging to healthy (n = 11), steatotic (n = 12), and NASH (n = 12) patients were used to further explore the role of adiponectin by measuring the expression of adiponectin and adiponectin receptor (AdipoR2) mRNA. RESULTS: Patients with NASH had significantly lower levels of serum adiponectin than controls (4.9 +/- 2.7 vs. 7.3 +/- 3.5 microg/mL, P = 0.02). While no significant correlation existed between serum adiponectin and anthropometric or nutritional variables, it was independently associated with age, high density lipoprotein, and triglycerides. Mixed meal had no effect on serum adiponectin either in patients with NASH or in controls. There was no expression of adiponectin mRNA in any of liver samples studied. However, AdipoR2 mRNA expression was higher in NASH than in steatotic and normal liver tissue. CONCLUSION: These data show that adiponectin may have a role in the pathogenesis of human NASH and should be investigated further.

Adiponectin↗
PubMed2003

Regulation of adiponectin by adipose tissue-derived cytokines: in vivo and in vitro investigations in humans.

Adiponectin is an adipose tissue-specific protein that is abundantly present in the circulation and suggested to be involved in insulin sensitivity and development of atherosclerosis. Because cytokines are suggested to regulate adiponectin, the aim of the present study was to investigate the interaction between adiponectin and three adipose tissue-derived cytokines (IL-6, IL-8, and TNF-alpha). The study was divided into three substudies as follows: 1) plasma adiponectin and mRNA levels in adipose tissue biopsies from obese subjects [mean body mass index (BMI): 39.7 kg/m2, n = 6] before and after weight loss; 2) plasma adiponectin in obese men (mean BMI: 38.7 kg/m2, n = 19) compared with lean men (mean BMI: 23.4 kg/m2, n = 10) before and after weight loss; and 3) in vitro direct effects of IL-6, IL-8, and TNF-alpha on adiponectin mRNA levels in adipose tissue cultures. The results were that 1) weight loss resulted in a 51% (P < 0.05) increase in plasma adiponectin and a 45% (P < 0.05) increase in adipose tissue mRNA levels; 2) plasma adiponectin was 53% (P < 0.01) higher in lean compared with obese men, and plasma adiponectin was inversely correlated with adiposity, insulin sensitivity, and IL-6; and 3) TNF-alpha (P < 0.01) and IL-6 plus its soluble receptor (P < 0.05) decreased adiponectin mRNA levels in vitro. The inverse relationship between plasma adiponectin and cytokines in vivo and the cytokine-induced reduction in adiponectin mRNA in vitro suggests that endogenous cytokines may inhibit adiponectin. This could be of importance for the association between cytokines (e.g., IL-6) and insulin resistance and atherosclerosis.

Adiponectin↗
PubMed2006

Plasma adiponectin, T94G gene polymorphism and PAI-1 in patients with and without hypertension.

BACKGROUND: Reduced adiponectin level has been associated with metabolic syndrome, type 2 diabetes, coronary artery disease and gene polymorphisms, but the interrelationships of T94G genotype, plasma adiponectin and plasminogen activator inhibitor-1 (PAI-1) are less understood. PATIENTS AND METHODS: The T94G genotypes and plasma levels of adiponectin, and PAI-1 were determined in 568 Chinese patients, 212 with and 356 without hypertension, to study the possible associations of T94G genotype, plasma adiponectin, PAI-1 and blood pressure. RESULTS: Hypertensive patients showed significantly lower plasma adiponectin (9.7 +/- 11.1 vs. 11.5 +/- 10.0 microg/ml, p = 0.04) and higher PAI-1 (p < 0.001) levels but not significantly greater adiponectin TT genotype percentage (38.7 vs. 33.5%) and T allele frequency (0.620 vs. 0.585) than normotensive subjects. Plasma adiponectin was inversely related to PAI-1 activity (r = -0.09, p = 0.03) and antigen (r = -0.202, p < 0.001). Furthermore, the TT genotypic group showed significantly lower plasma adiponectin level (10.4 +/- 10.5 vs. 13.4 +/- 10.8 mug/ml, p = 0.03) and higher plasma PAI-1 activity (17.0 +/- 9.7 vs. 13.5 +/- 7.6 IU/ml, p = 0.003) and antigen (32.3 +/- 22.7 vs. 25.9 +/- 14.7 ng/ml, p = 0.01) than the GG genotypic group. Multiple linear regression analysis in all study subjects, in men and in normotensives documented an impact of adiponectin T94G genotype on plasma levels of adiponectin (p = 0.007, 0.003 and 0.03) and PAI-1 activity (p = 0.02, 0.03 and 0.04) and antigen (p = 0.03, 0.007 and 0.04) after adjustment for potential confounding factors. CONCLUSIONS: The present study demonstrated a significant correlation of the TT genotype with lower plasma adiponectin and higher plasma PAI-1 levels in a Chinese population. The contribution of this genotype seemed greater in men and normotensives. It suggested the adiponectin gene T94G polymorphism might affect the regulation of circulating adiponectin and PAI-1.

Adiponectin↗
PubMed2001

Adipocyte-derived plasma protein, adiponectin, suppresses lipid accumulation and class A scavenger receptor expression in human monocyte-derived macrophages.

BACKGROUND: Excessive lipid accumulation in macrophages plays an important role in the development of atherosclerosis. Recently, we discovered an adipocyte-specific plasma protein, adiponectin, that is decreased in patients with coronary artery disease. We previously demonstrated that adiponectin acts as a modulator for proinflammatory stimuli and inhibits monocyte adhesion to endothelial cells. The present study investigated the effects of adiponectin on lipid accumulation in human monocyte-derived macrophages. METHODS AND RESULTS: Human monocytes were differentiated into macrophages by incubation in human type AB serum for 7 days, and the effects of adiponectin were investigated at different time intervals. Treatment with physiological concentrations of adiponectin reduced intracellular cholesteryl ester content, as determined using the enzymatic, fluorometric method. The adiponectin-treated macrophages contained fewer lipid droplets stained by oil red O. Adiponectin suppressed the expression of the class A macrophage scavenger receptor (MSR) at both mRNA and protein levels by Northern and immunoblot analyses, respectively, without affecting the expression of CD36, which was quantified by flow cytometry. Adiponectin reduced the class A MSR promoter activity, as measured by luciferase reporter assay. Adiponectin treatment dose-dependently decreased class A MSR ligand binding and uptake activities. The mRNA level of lipoprotein lipase as a marker of macrophage differentiation was decreased by adiponectin treatment, but that of apolipoprotein E was not altered. Adiponectin was detected around macrophages in the human injured aorta by immunohistochemistry. CONCLUSIONS: The adipocyte-derived plasma protein adiponectin suppressed macrophage-to-foam cell transformation, suggesting that adiponectin may act as a modulator for macrophage-to-foam cell transformation.

Adipocytes↗
PubMed2006

Adiponectin-induced secretion of interleukin-6 (IL-6), monocyte chemotactic protein-1 (MCP-1, CCL2) and interleukin-8 (IL-8, CXCL8) is impaired in monocytes from patients with type I diabetes.

BACKGROUND: Systemic adiponectin is reduced in patients with cardiovascular disease (CVD) and low adiponectin may contribute to the pathogenesis of atherosclerosis. However, circulating adiponectin is elevated in type 1 diabetes (T1D) patients, who have also a higher incidence to develop CVD. Because monocytes play an important role in atherosclerosis, we analysed the influence of adiponectin on cytokine and chemokine release in monocytes from T1D patients and controls. METHODS: Systemic adiponectin was determined in the plasma and the high-molecular weight (HMW) form of adiponectin was analysed by immunoblot. Monocytes were isolated from T1D patients and controls and the adiponectin-stimulated release of interleukin-6 (IL-6), monocyte chemotactic protein-1 (MCP-1, CCL2) and interleukin-8 (IL-8, CXCL8) was analysed. RESULTS: Systemic adiponectin was higher in T1D patients. Immunoblot analysis of the plasma indicate abundance of HMW adiponectin in T1D patients and controls. IL-6, CCL2 and CXCL8 secretion in response to adiponectin were found induced in monocytes from controls whereas only IL-6 was upregulated in T1D cells. The induction of IL-6 by adiponectin was abrogated by an inhibitor of the NFkappaB pathway. CONCLUSION: These data indicate that adiponectin-mediated induction of IL-6, CCL2 and CXCL8 is disturbed in monocytes from T1D patients and therefore elevated systemic adiponectin in T1D patients may be less protective when compared to controls.

Adiponectin↗
PubMed2003

Serum adiponectin levels are inversely associated with overall and central fat distribution but are not directly regulated by acute fasting or leptin administration in humans: cross-sectional and interventional studies.

Adiponectin is an adipocyte-secreted protein that circulates in high concentrations in the serum and acts to increase insulin sensitivity. Previous studies have shown that serum adiponectin is inversely associated with fat mass and insulin resistance in humans and that acute fasting decreases adipose tissue adiponectin mRNA expression in rodents. Whether acute energy deprivation, body fat distribution, or serum hormone levels are associated with circulating adiponectin in humans remains largely unknown. To identify predictors of serum adiponectin levels, we evaluated the association of adiponectin with several anthropometric, metabolic, and hormonal variables in a cross-sectional study of 121 women without a known history of diabetes. We also performed interventional studies to assess whether fasting for 48 h and/or leptin administration regulates serum adiponectin in healthy men and women. Our cross-sectional study shows that, in addition to overall obesity, central fat distribution is an independent negative predictor of serum adiponectin and suggests that adiponectin may represent a link between central obesity and insulin resistance. In addition, estradiol is negatively and independently associated with adiponectin, whereas there is no association between serum adiponectin and leptin, cortisol, or free testosterone levels. Our interventional studies demonstrate that neither fasting for 48 h, resulting in a low leptin state, nor leptin administration at physiological or pharmacological doses alters serum adiponectin levels. Further studies are needed to fully elucidate the physiology of adiponectin in humans and its role in the pathogenesis of insulin-resistant states.

Adiponectin↗
PubMed2006

Adiponectin in umbilical cord blood is inversely related to low-density lipoprotein cholesterol but not ethnicity.

CONTEXT: Adiponectin is a recognized protective risk marker for cardiovascular disease in adults and is associated with an optimal lipid profile. The role of adiponectin at birth is not well understood, and its relationship with the neonatal lipid profile is unknown. Because ethnic disparities in cardiovascular risk have been attributed to low adiponectin and its associated low high-density lipoprotein cholesterol (HDL-C), investigation at birth may help determine the etiology of these risk patterns. OBJECTIVE: Our objective was to investigate the relationship between neonatal adiponectin and lipid profile at birth in two ethnic groups in cord blood. DESIGN, SETTING, AND PARTICIPANTS: Seventy-four healthy mothers and their newborns of South Asian and White European origin were studied in this cross-sectional study at St. Mary's Hospital, Manchester, United Kingdom. MAIN OUTCOME MEASURES: Serum adiponectin, total cholesterol, HDL-C, low-density lipoprotein cholesterol (LDL-C), and triglyceride levels were measured in umbilical venous blood at birth and in maternal blood collected at 28 wk gestation. RESULTS: Cord adiponectin was significantly inversely associated with cord LDL-C (r = -0.32; P = 0.005) but not HDL-C. In a multiple regression analysis, cord LDL-C remained the most significant association of cord adiponectin (beta = -0.13; P < 0.001). We did not find any significant ethnic differences in cord adiponectin or lipids with the exception of triglycerides, which were significantly lower in South Asian newborns (P < 0.05). CONCLUSION: This is the first report of an inverse relationship between cord adiponectin and LDL-C at birth. In contrast to adult studies, we found no significant association between adiponectin and HDL-C in cord blood. Our results and the strong independent association between adiponectin and HDL-C observed in adult studies suggest a role for adiponectin in lipid metabolism. Ethnic differences in adiponectin may arise after birth.

Adiponectin↗
PubMed2003

Role of adiponectin in insulin-resistant hypertension and atherosclerosis.

Insulin resistance is one of the major risk factors associated with development of hypertension and atherosclerosis. Recent studies have shown that adiponectin, an adipocyte-derived hormone, may be involved in insulin resistance and development of atherosclerosis in diabetes patients. The aim of this study was to examine adiponectin levels in patients with essential hypertension to determine the relationships between adiponectin levels and insulin sensitivity and to examine the relationship of adiponectin with pulse wave velocity (PWV) in a general population based on the results of an epidemiological survey in Japan. In a clinical study, 20 normotensives (NT) and 30 non-treated essential hypertensives (EHT) were hospitalized, and euglycemic hyperinsulinemic glucose clamp (GC) was performed to evaluate insulin sensitivity defined as M value. EHT were divided into insulin-resistant EHT (EHT-R) and insulin-nonresistant EHT (EHT-N) according to the mean -1 SD of the M value of NT as a cut-off point. Fasting plasma glucose (FPG), immunoreactive insulin (IRI), and adiponectin concentrations were measured. There were no significant differences in body mass index (BMI) or FPG among the NT, EHT-N, and EHT-R groups. The M value and adiponectin concentration in EHT-R were significantly lower than those in the NT or EHT-N. The IRI level in the EHT-R was significantly higher than those in the other groups. A positive correlation between adiponectin concentration and M value was found in all subjects, and adiponectin concentration and M value were found to be significant determinants of each other in multiple regression analysis. In an epidemiological study, we studied 391 male inhabitants of rural communities in Hokkaido, Japan. Systolic blood pressure (SBP), BMI, FPG, IRI, and adiponectin were measured in all subjects early in the morning. Homeostasis model assessment (HOMA) values were calculated as an index of insulin sensitivity, and PWV was used as an index of atherosclerosis. A negative correlation between HOMA values and adiponectin concentration was found in all of the subjects. Multiple regression analysis revealed that adiponectin was a significant determinant for PWV in subjects less than 70 years of age. The results of the clinical study indicate that EHT-R had not only hyperinsulinemia but also a low concentration of adiponectin. The results of multiple regression analysis for determinants of degree of PWV using data obtained in the epidemiological study suggest that adiponectin plays a role in antiatherosclerosis, partly through improvement of insulin resistance.

Adiponectin↗
PubMed2005

Circulating adiponectin and plasma fatty acid profile.

BACKGROUND: The amount and type of fat in the diet influence the development of obesity and related inflammatory activity. Knowledge of the possible influence of dietary habits on circulating adiponectin, a molecule with putative antiinflammatory properties, may be helpful in preventing atherosclerosis and type 2 diabetes. METHODS: The association between dietary fat, as inferred from plasma fatty acid composition (gas-liquid chromatography), and circulating adiponectin (RIA) was evaluated in 116 healthy individuals. RESULTS: The proportion of saturated fatty acids in plasma was significantly associated with circulating adiponectin concentration (r = -0.24; P = 0.01). Specifically, percentage of palmitic acid (C16:0) was significantly associated with lower adiponectin concentration (r = -0.28; P = 0.002), particularly among women (r = -0.37; P = 0.02) and nonsmokers (r = -0.30; P = 0.007). Percentage of myristic acid (C14:0) was also significantly associated with lower adiponectin among nonsmokers (r = -0.26; P = 0.02) and women (r = -0.39; P = 0.01). The other fatty acids were not significantly associated with adiponectin except for eicosanoic acid (C20:1 omega-9), which was significantly and positively associated with adiponectin in all individuals (r = 0.23; P = 0.01). This latter association was most significant in smokers (r = 0.43; P = 0.007). In a multivariate regression analysis to predict circulating adiponectin, after controlling for age, body mass index, waist-to-hip ratio, and the individual remaining fatty acids, the percentages of palmitic (P = 0.005) and eicosanoic acid (P = 0.03) contributed independently (6% and 3%, respectively) to adiponectin variance. Among nonsmokers, the percentages of palmitic acid (P = 0.01) and omega-3 fatty acids contributed 8% and 7%, respectively, to adiponectin variance. Among smokers, the percentage of eicosanoic acid (P = 0.03) contributed to 10% of adiponectin variance, independently of body mass index, age, waist-to hip ratio, and the remaining individual fatty acids. CONCLUSIONS: Saturated and omega-3 fatty acids of dietary origin (as inferred from plasma fatty acid concentration) are associated with circulating adiponectin concentrations in healthy humans. The proportion of eicosanoic acid also appears to be positively associated with circulating adiponectin. The knowledge of how these interactions occur may be helpful in the planning of dietary measures aimed at the modulation of inflammatory activity.

Adiponectin↗
PubMed2006

Adiponectin multimeric complexes and the metabolic syndrome trait cluster.

Adiponectin circulates in human plasma mainly as a 180-kDa low molecular weight (LMW) hexamer and a high molecular weight (HMW) multimer of approximately 360 kDa. We comprehensively examined the relationships between circulating levels of total adiponectin, adiponectin multimers, and the relative distribution (i.e., ratio) of multimeric forms with key features of the metabolic syndrome. Total adiponectin (r = 0.45), HMW (r = 0.47), LMW (r = 0.31), and HMW-to-total adiponectin ratio (r = 0.29) were significantly correlated with insulin-stimulated glucose disposal rate. Similarly, total (r = -0.30), HMW (r = -0.38), and HMW-to-total adiponectin ratio (r = -0.34) were correlated with central fat distribution but not with total fat mass or BMI. Regarding energy metabolism, although there were no effects on resting metabolic rate, total (r = 0.41) and HMW (r = 0.44) were associated with increasing rates of fat oxidation. HMW-to-total adiponectin ratio increased as a function of total adiponectin, and it was HMW quantity (not total or HMW-to-total adiponectin ratio or LMW) that was primarily responsible for all of these relationships. Impact on nuclear magnetic resonance lipoprotein subclasses was assessed. HMW and total adiponectin were correlated with decreases in large VLDL (r = -0.44 and -0.41); decreases in small LDL (r = -0.41 and -0.36) and increases in large LDL (r = 0.36 and 0.30) particle concentrations accompanied by increased LDL particle size (r = 0.47 and 0.39); and increases in large HDL (r = 0.45 and 0.37) and HDL particle size (r = 0.53 and 0.47). Most of these correlations persisted after adjustment for metabolic covariables. In conclusion, first, serum adiponectin is associated with increased insulin sensitivity, reduced abdominal fat, and high basal lipid oxidation; however, it is HMW quantity, not total or HMW-to-total adiponectin ratio, that is primarily responsible for these relationships. Second, reduced quantities of HMW independently recapitulate the lipoprotein subclass profile associated with insulin resistance after correcting for glucose disposal rate and BMI. Finally, HMW adiponectin is an important factor in explaining the metabolic syndrome.

Adiponectin↗
PubMed2006

Adiponectin--a key adipokine in the metabolic syndrome.

Adiponectin is a recently described adipokine that has been recognized as a key regulator of insulin sensitivity and tissue inflammation. It is produced by adipose tissue (white and brown) and circulates in the blood at very high concentrations. It has direct actions in liver, skeletal muscle and the vasculature, with prominent roles to improve hepatic insulin sensitivity, increase fuel oxidation [via up-regulation of adenosine monophosphate-activated protein kinase (AMPK) activity] and decrease vascular inflammation. Adiponectin exists in the circulation as varying molecular weight forms, produced by multimerization. Recent data indicate that the high-molecular weight (HMW) complexes have the predominant action in the liver. In contrast to other adipokines, adiponectin secretion and circulating levels are inversely proportional to body fat content. Levels are further reduced in subjects with diabetes and coronary artery disease. Adiponectin antagonizes many effects of tumour necrosis factor-alpha(TNF-alpha) and this, in turn, suppresses adiponectin production. Furthermore, adiponectin secretion from adipocytes is enhanced by thiazolidinediones (which also act to antagonize TNF-alpha effects). Thus, adiponectin may be the common mechanism by which TNF-alpha promotes, and the thiazolidinediones suppress, insulin resistance and inflammation. Two adiponectin receptors, termed AdipoR1 and AdipoR2, have been identified and these are ubiquitously expressed. AdipoR1 is most highly expressed in skeletal muscle and has a prominent action to activate AMPK, and hence promote lipid oxidation. AdipoR2 is most highly expressed in liver, where it enhances insulin sensitivity and reduces steatosis via activation of AMPK and increased peroxisome-proliferator-activated receptor alpha ligand activity. T-cadherin, which is expressed in endothelium and smooth muscle, has been identified as an adiponectin-binding protein with preference for HMW adiponectin multimers. Given the low levels of adiponectin in subjects with the metabolic syndrome, and the beneficial effect of the adipokine in animal studies, there is exciting potential for adiponectin replacement therapy in insulin resistance and related disorders.

Adiponectin↗
PubMed2006

Role of adiponectin receptors in endothelin-induced cellular hypertrophy in cultured cardiomyocytes and their expression in infarcted heart.

Adiponectin, an adipocyte-derived protein, has cardioprotective actions. We elucidated the role of the adiponectin receptors AdipoR1 and AdipoR2 in the effects of adiponectin on endothelin-1 (ET-1)-induced hypertrophy in cultured cardiomyocytes, and we examined the expression of adiponectin receptors in normal and infarcted mouse hearts. Recombinant full-length adiponectin suppressed the ET-1-induced increase in cell surface area and [(3)H]leucine incorporation into cultured cardiomyocytes compared with cells treated with ET-1 alone. Transfection of small interfering RNA (siRNA) specific for AdipoR1 or AdipoR2 reversed the suppressive effects of adiponectin on ET-1-induced cellular hypertrophy in cultured cardiomyocytes. Adiponectin induced phosphorylation of AMP-activated protein kinase (AMPK) and inhibited ET-1-induced ERK1/2 phosphorylation, which were also reversible by transfection of siRNA for AdipoR1 or AdipoR2 in cultured cardiomyocytes. Transfection of siRNA for alpha(2)-catalytic subunits of AMPK reduced the inhibitory effects of adiponectin on ET-1-induced cellular hypertrophy and ERK1/2 phosphorylation. Effects of globular adiponectin were similar to those of full-length adiponectin, and siRNA for AdipoR1 reversed the actions of globular adiponectin. Compared with normal left ventricle, expression levels of AdipoR1 mRNA and protein were decreased in the remote, as well as the infarcted, area after myocardial infarction in mouse hearts. In conclusion, AdipoR1 and AdipoR2 mediate the suppressive effects of full-length and globular adiponectin on ET-1-induced hypertrophy in cultured cardiomyocytes, and AMPK is involved in signal transduction through these receptors. AdipoR1 and AdipoR2 might play a role in the pathogenesis of ET-1-related cardiomyocyte hypertrophy after myocardial infarction.

Adiponectin↗
PubMed2005

Adiponectin is functionally active in human islets but does not affect insulin secretory function or beta-cell lipoapoptosis.

CONTEXT: The adipokine adiponectin has insulin-sensitizing, antiatherogenic, and antiinflammatory properties. Mouse and human adiponectin receptor-1 and -2 have been cloned, both of which are expressed in various tissues and mediate effects of globular and full-length adiponectin. Whether adiponectin affects insulin secretion and beta-cell apoptosis and whether plasma adiponectin is associated with beta-cell function in humans is under investigation. DESIGN AND METHODS: In human islets from multiorgan donors, we investigated expression of adiponectin receptor-1 and -2. Furthermore, glucose-stimulated insulin secretion was determined by RIA. In addition, we investigated fatty acid-induced beta-cell apoptosis by terminal dUTP nick end labeling and flow-cytometric cell cycle analysis (sub-G1 formation). In humans in vivo, insulin secretory function was measured during hyperglycemic clamps in 65 normal glucose-tolerant subjects. We determined first and second phase of glucose-stimulated, glucagon-like peptide-1-stimulated, and arginine-stimulated insulin secretion. RESULTS: Adiponectin receptor-1 and -2 are expressed in human islets at the mRNA and protein level. Moreover, full-length adiponectin induces phosphorylation of acetyl coenzyme A carboxylase. However, adiponectin did not affect basal or glucose-stimulated insulin secretion or basal or fatty acid-induced beta-cell apoptosis. In vivo, fasting plasma adiponectin concentrations were not associated with glucose-stimulated first- and second-phase insulin secretion or with glucagon-like peptide-1- or arginine-stimulated insulin secretion (all P > 0.42). CONCLUSIONS: These data support a regulatory role of adiponectin in human islets; however, adiponectin does not seem to affect insulin secretion or basal/fatty acid-induced beta-cell apoptosis in humans.

Adiponectin↗
PubMed2004

Serum adiponectin in women with polycystic ovarian syndrome and its relation to clinical, metabolic and endocrine parameters.

UNLABELLED: Several studies have demonstrated that low levels of serum adiponectin are present in obesity, insulin resistance, hypertension and hyperlipidemias. The aim of our study was to determine whether serum adiponectin level is different between patients with polycystic ovarian syndrome (PCOS) and control subjects. We also investigated relationships between various cardiovascular risk factors, levels of serum adiponectin and other hormones, such as androstendione, testosterone, estradiol, DHEAS, sex hormone binding globulin (SHBG), and leptin. We also analysed the correlation between serum adiponectin and free androgen index. Ninety-one women with clinical diagnosed PCOS and 53 healthy control subjects, carefully matched by body mass index (BMI) and age, were enrolled in the study. The fasting blood samples were obtained and all participants underwent an oral 75 g glucose tolerance test. The prevalences of impaired glucose tolerance (IGT), hypertension and hypertriglyceridemia were higher in the PCOS group. PCOS women had increased androgen concentrations and higher free androgen index and decreased level of serum SHBG. Lower serum adiponectin concentrations were observed among cases than in controls (median 13.7 microg/ml vs 17.8 microg/ml, p<0.001) despite being matched by BMI. In the PCOS group adiponectin levels correlated significantly with: BMI (r=-0.32, p=0.002), waist circumference (r=-0.32, p=0.003), waist-to-hip ratio (WHR, r=-0.38, p=0.001), triglycerides (r=-0.31, p=0.007), SHBG (r=0.30, p=0.003) and free androgen index (r=-0.29, p=0.02). In contrast, the adiponectin level does not appear to be related to total testosterone, DHEAS and leptin levels. The adiponectin and SHBG levels were found to be decreased in PCOS women with IGT compared to PCOS women with normal glucose tolerance, but after adjustment by BMI or WHR, the differences were no longer statistically significant. To exclude a possible confounding effect due to a higher prevalence of IGT in the PCOS group, this comparison was repeated for the subgroup of 58 PCOS women and 48 control women after excluding those with IGT. Neither adiponectin nor SHBG were significantly different between those subgroups. Multiple regression analysis revealed that serum adiponectin concentrations were best predicted by WHR, free androgen index and presence of IGT when all patients were considered. In PCOS subjects, the only independent predictor of adiponectin concentrations was glucose tolerance status. CONCLUSIONS: Lower adiponectin levels were observed in PCOS group than in control women, and these differences were probably due to higher prevalence of IGT in these cases.

Adiponectin↗
PubMed2005

Determinants of plasma adiponectin levels in patients with anorexia nervosa examined before and after weight gain.

OBJECTIVE: To examine the determinants of adiponectin levels (i) in 23 women with anorexia nervosa (mean BMI 15.0 +/- 1.2) and 43 healthy normal weight females (mean BMI 22.3 +/- 2.3; cross-sectional design) as well as (ii) after six and twelve weeks of weight gain in subgroups of 18 and 11 anorectic patients (mean weight gain 5.8 kg; longitudinal design). Plasma adiponectin and leptin concentrations were measured and their relationships to body composition (fat mass by bioelectrical impedance analysis and anthropometrics), different hormones and metabolic parameters (insulin, ACTH, cortisol, glucose, FFA, lipid profile) were investigated. RESULTS: In anorectic patients, adiponectin levels were higher (+29 %) and leptin levels were lower (-75 %) than in control subjects. There was a high variance in adiponectin levels in patients ranging from 2.6 to 18 nM. Combining patients and controls, an inverse linear correlation was observed between adiponectin levels and fat mass (r = -0.36, p < 0.05), while a positive exponential relation was found between leptin levels and fat mass (r = 0.82, p < 0.001). In anorectic patients, there were no significant correlations between adiponectin and hormonal or metabolic parameters. Weight gain resulted in increasing leptin (+0.17 +/- 0.12 nM; p < 0.001) and a nonsignificant decrease in adiponectin concentrations (-1.12 +/- 2.51 nM). Changes in leptin levels were mainly explained by a gain in fat mass (r = 0.85, p < 0.001). In contrast, changes in adiponectin levels were closely linked to initial adiponectin levels (r = -0.84, p < 0.001) but not to changes in fat mass or BMI. CONCLUSION: Cross-sectionally serum adiponectin concentration followed a linear inverse function with fat mass when patients and controls were combined. Longitudinally gain in fat mass was not associated with changes in adiponectin levels suggesting other yet unidentified influences on adiponectin secretion in anorexia nervosa.

Adiponectin↗