Plasma adiponectin in overweight, nondiabetic individuals with or without insulin resistance

Adiponectin is a protein produced exclusively by adipocytes with putative insulin-sensitizing and anti-atherogenic properties. This cross-sectional study investigated the relationship between plasma adiponectin and a range of anthropometric, glycaemic, lipid and inflammatory parameters in overweight and obese subjects expressing characteristics of the metabolic syndrome.

Subjects were selected for the study from a clinical database, if they were non-diabetic, overweight [body mass index (BMI) > 25] and had features of the metabolic syndrome. The subjects were grouped according to BMI (25-30, 31-35 and >35 kg/m2) and then stratified for insulin resistance [homeostasis model assessment (HOMA) %S]. One hundred and ninety-seven patients (109 males and 88 females) were selected for the study by taking an equal number with the highest and lowest HOMA indices from each of the three BMI groups. Plasma adiponectin concentration was measured in duplicate by radioimmunoassay, and the relationship between these levels and the other parameters was investigated using correlation and multiple linear regression analyses.

Plasma adiponectin concentration was higher in females than males (median 10.3 vs. 7.1 micro g/ml, p < 0.001) despite being matched for BMI. In both genders, adiponectin levels were inversely related to BMI, waist circumference, percentage body fat, insulin resistance and the fasting plasma concentration of leptin. A direct correlation in both sexes was found between adiponectin levels and high-density lipoprotein (HDL)-cholesterol, apolipoprotein A1 and age. Multiple linear regression analyses showed that the independent determinants of low plasma adiponectin concentrations were gender, age, BMI, insulin resistance and HDL-cholesterol. An association between reduced adiponectin and increased high-sensitivity plasma C-reactive protein concentration was observed only in female subjects and was independent of anthropometric variables. Our observation that adiponectin levels increase with age differs from the majority of other studies and may simply reflect the demographics of the population studied.

This study shows that adiponectin is an important molecular link between obesity, insulin resistance and atherogenic lipoproteins. It is possible that plasma adiponectin concentration may be a convenient marker for identifying subjects with the metabolic syndrome who may progress to impaired glucose tolerance. Longitudinal studies are required in order to verify this clinical application of adiponectin.