Androgens decrease plasma adiponectin, an insulin-sensitizing adipocyte-derived protein

Disturbed secretion of mutant adiponectin associated with the metabolic syndrome

Adiponectin, an adipocyte-derived protein, consists of collagen-like fibrous and complement C1q-like globular domains, and circulates in human plasma in a multimeric form. The protein exhibits anti-diabetic and anti-atherogenic activities. However, adiponectin plasma concentrations are low in obese subjects, and hypoadiponectinemia is associated with the metabolic syndrome, which is a cluster of insulin resistance, type 2 diabetes mellitus, hypertension, and dyslipidemia. We have recently reported a missense mutation in the adiponectin gene, in which isoleucine at position 164 in the globular domain is substituted with threonine (I164T). Subjects with this mutation showed markedly low level of plasma adiponectin and clinical features of the metabolic syndrome. Here, we examined the molecular characteristics of the mutant protein associated with a genetic cause of hypoadiponectinemia. The current study revealed (1) the mutant protein showed an oligomerization state similar to the wild-type as determined by gel filtration chromatography and, (2) the mutant protein exhibited normal insulin-sensitizing activity, but (3) pulse-chase study showed abnormal secretion of the mutant protein from adipose tissues. Our results suggest that I164T mutation is associated with hypoadiponectinemia through disturbed secretion into plasma, which may contribute to the development of the metabolic syndrome.

Novel interactions of adiponectin with the endocrine system and inflammatory parameters

Several markers of chronic immune activation have been found in association with obesity and insulin resistance. We aimed to study the interaction of adiponectin with chronic inflammation and known components of the insulin resistance syndrome. Insulin sensitivity (minimal model analysis) and plasma soluble fractions of TNF-alpha receptor 1 (sTNFR1) and 2 (sTNFR2), adrenal and thyroid function, and adiponectin were evaluated in 68 apparently healthy subjects. An additional group of type 2 diabetic patients (n = 19) similarly studied, except for insulin sensitivity, were also included in the analysis. As reported by others, serum adiponectin concentrations were higher in women than in men (13.55 +/- 9.79 vs. 8.64 +/- 7.83 mg/liter; P = 0.018). They were also higher in healthy subjects compared with diabetic patients (10.35 +/- 8.48 vs. 7.41 +/- 8.31 mg/liter; P = 0.021). As expected also, circulating adiponectin was significantly associated with waist to hip ratio (r = -0.28; P = 0.013), diastolic blood pressure (r = -0.25; P = 0.027), fasting plasma high-density lipoprotein cholesterol (r = 0.35; P = 0.001), triglycerides (r = -0.37; P = 0.001), and insulin sensitivity (r = 0.30; P = 0.011). Additionally, subjects in the higher quartile of circulating adiponectin had lower sTNFR2 concentrations (3.05 vs. 4.37 microg/liter; P = 0.012), a trend to lower sTNFR1 concentrations (1.76 vs. 2.20 microg/liter; P = 0.055), higher concentration of serum morning cortisol (16.86 vs. 13.52 microg/dl; P = 0.027), and higher serum free T(4) levels (1.31 vs. 1.20 ng/dl; P = 0.038). Multiple regression analysis models were constructed to predict adiponectin concentrations. Predictive variables in these models included insulin sensitivity, waist to hip ratio and free T(4), contributing to 17%, 10%, and 8% of adiponectin variance, respectively, These findings suggest that circulating adiponectin differentially modulates insulin action and that thyroid-axis, inflammatory cytokines, and the adrenal cortex might intervene in this modulation.

Relationship of adiponectin to body fat distribution, insulin sensitivity and plasma lipoproteins: evidence for independent roles of age and sex

AIMS/HYPOTHESIS

Increased intra-abdominal fat is associated with insulin resistance and an atherogenic lipoprotein profile. Circulating concentrations of adiponectin, an adipocyte-derived protein, are decreased with insulin resistance. We investigated the relationships between adiponectin and leptin, body fat distribution, insulin sensitivity and lipoproteins.

METHODS

We measured plasma adiponectin, leptin and lipid concentrations, intra-abdominal and subcutaneous fat areas by CT scan, and insulin sensitivity index (S(I)) in 182 subjects (76 M/106F).

RESULTS

Adiponectin concentrations were higher in women than in men (7.4+/-2.9 vs 5.4+/-2.3 micro g/ml, p<0.0001) as were leptin concentrations (19.1+/-13.7 vs 6.9+/-5.1 ng/ml, p<0.0001). Women were more insulin sensitive (S(I): 6.8+/-3.9 vs 5.9+/-4.4 x 10(-5) min(-1)/(pmol/l), p<0.01) and had more subcutaneous (240+/-133 vs 187+/-90 cm(2), p<0.01), but less intra-abdominal fat (82+/-57 vs 124+/-68 cm(2), p<0.0001). By simple regression, adiponectin was positively correlated with age ( r=0.227, p<0.01) and S(I) ( r=0.375, p<0.0001), and negatively correlated with BMI ( r=-0.333, p<0.0001), subcutaneous ( r=-0.168, p<0.05) and intra-abdominal fat ( r=-0.35, p<0.0001). Adiponectin was negatively correlated with triglycerides ( r=-0.281, p<0.001) and positively correlated with HDL cholesterol ( r=0.605, p<0.0001) and Rf, a measure of LDL particle buoyancy ( r=0.474, p<0.0001). By multiple regression analysis, adiponectin was related to age ( p<0.0001), sex ( p<0.005) and intra-abdominal fat ( p<0.01). S(I) was related to intra-abdominal fat ( p<0.0001) and adiponectin ( p<0.0005). Both intra-abdominal fat and adiponectin contributed independently to triglycerides, HDL cholesterol and Rf.

CONCLUSION/INTERPRETATION

These data suggest that adiponectin concentrations are determined by intra-abdominal fat mass, with additional independent effects of age and sex. Adiponectin could link intra-abdominal fat with insulin resistance and an atherogenic lipoprotein profile.

Plasma Adiponectin and Hyperglycaemia in Diabetic Patients

The insulin-sensitising adipose hormone adiponectin is reduced in type 2 diabetic patients. We assessed the relationships between plasma adiponectin and chronic hyperglycaemia. Adiponectin levels and glycated haemoglobin (HbA1c) were measured at enrolment and after 90 days in 16 patients with type 2 diabetes aged (mean +/- SEM) 63.0 +/- 0.6 years, with body mass index (BMI) 30.2 +/- 0.5 kg/m2 and HbA1c concentration 7.4 +/- 0.1%, who did not modify their hypoglycaemic treatment during the observation period. Furthermore, plasma adiponectin was measured in 29 adult patients with type 1 diabetes and compared with 29 control subjects matched for sex, age, BMI, waist circumference and bioimpedance-estimated fat mass. In type 2 diabetic patients at enrolment, adiponectin concentration correlated with BMI (r = -0.46; p < 0.05), but not with HbA1c. During the prospective observation, variations of adiponectin showed a significant correlation with variations of BMI (r = -0.47; p < 0.01), but not with variations of HbA1c concentration. These results were confirmed by multivariate analysis after adjustment for sex and age. Adiponectin levels in type 1 diabetic patients (380.8 +/- 13.7 ng/ml in women, 192.5 +/- 13.9 ng/ml in men) were significantly (p < 0.05) higher than in control subjects (277.6 +/- 11.0 ng/ml in women, 102.7 +/- 5.1 ng/ml in men); plasma adiponectin correlated significantly with BMI and waist circumference, but not with HbA1c. In conclusion, the reduction of plasma adiponectin levels in type 2 diabetic patients does not appear to be determined by chronic hyperglycaemia. Adiponectin levels are increased in type 1 diabetes, but this phenomenon is not attributable to differences in nutritional status or body composition.

Association of hypoadiponectinemia with coronary artery disease in men

BACKGROUND

Adiponectin is an adipocyte-derived plasma protein that accumulates in the injured artery and has potential antiatherogenic properties. This study was designed to determine whether a decreased plasma adiponectin level (hypoadiponectinemia) can be independently associated with the prevalence of coronary artery disease (CAD).

METHODS AND RESULTS

The consecutive 225 male patients were enrolled from inpatients who underwent coronary angiography. Voluntary blood donors (n=225) matched for age served as controls. Plasma adiponectin levels in the CAD patients were significantly lower than those in the control subjects. Multiple logistic regression analysis including plasma adiponectin level, diabetes mellitus, dyslipidemia, hypertension, smoking habits, and body mass index revealed that hypoadiponectinemia was significantly and independently correlated with CAD (P<0.0088). The entire study population was categorized in quartiles based on the distribution of plasma adiponectin levels. The interquartile cutoff points were 4.0, 5.5, and 7.0 microg/mL. The multivariate-adjusted odds ratios for CAD in the first, second, and third quartiles were 2.051 (95% confidence interval [CI], 1.288 to 4.951), 1.221 (95% CI, 0.684 to 2.186), and 0.749 (95%CI, 0.392 to 1.418), respectively.

CONCLUSIONS

Male patients with hypoadiponectinemia (<4.0 microg/mL) had a significant 2-fold increase in CAD prevalence, independent of well-known CAD risk factors.