Effect of the interleukin-6 (-174) g/c promoter polymorphism on adiponectin and insulin sensitivity.

We investigated the relation among the interleukin (IL)-6 (-174) G/C promoter polymorphism, adipose tissue gene expression of IL6, circulating adiponectin, and systemic insulin sensitivity. Eighty-five Swedish male subjects who had participated in our previous prediabetic phenotype characterization study were genotyped for the IL6 (-174) G/C polymorphism. Subcutaneous adipose tissue gene expression of IL6 and adiponectin was measured in 44 subjects. The IL6 (-174) G allele carriers had higher fasting plasma insulin levels (C/C, 7.8 +/- 1.1; G/C, 9.0 +/- 0.6; G/G, 10.5 +/- 1.0 mU/L) and higher homeostasis model assessment for insulin resistance (C/C, 1.6 +/- 0.2; G/C, 1.9 +/- 0.1; G/G, 2.2 +/- 0.2) compared with subjects with the C/C genotype. The circulating adiponectin levels were lower in the G allele carriers (C/C, 7.93 +/- 0.45; G/C, 7.05 +/- 0.44; G/G, 7.02 +/- 0.46 microg/mL), whereas the IL-6 levels did not differ among the three genotypes. Adipose tissue IL6 gene expression was significantly higher in the G allele carriers compared with the subjects homozygous for the C allele (C/C, 0.29 +/- 0.15; G/C, 0.84 +/- 0.29; G/G, 0.62 +/- 0.35). Our results suggest that IL6 (-174) G/C polymorphism is associated with insulin resistance and increased adipose tissue IL6 gene expression, which can impair adiponectin production.

A novel cellular marker of insulin resistance and early atherosclerosis in humans is related to impaired fat cell differentiation and low adiponectin.

The epidemic increase in type 2 diabetes can be prevented only if markers of risk can be identified and used for early intervention. We examined the clinical phenotype of individuals characterized by normal or low IRS-1 protein expression in fat cells as well as the potential molecular mechanisms related to the adipose tissue. Twenty-five non-obese individuals with low or normal IRS-1 expression in subcutaneous abdominal fat cells were extensively characterized and the results compared with 71 carefully matched subjects with or without a known genetic predisposition for type 2 diabetes. In contrast to the commonly used risk marker, known heredity for diabetes, low cellular IRS-1 identified individuals who were markedly insulin resistant, had high proinsulin and insulin levels, and exhibited evidence of early atherosclerosis measured as increased intima media thickness in the carotid artery bulb. Circulating levels of adiponectin were also significantly reduced. Gene analyses of fat cells in a parallel study showed attenuated expression of several genes related to fat cell differentiation (adiponectin, aP2, PPARgamma, and lipoprotein lipase) in the group of individuals characterized by a low IRS-1 expression and insulin resistance. A low IRS-1 expression in fat cells is a marker of insulin resistance and risk for type 2 diabetes and is associated with evidence of early vascular complications. Impaired adipocyte differentiation, including low gene expression and circulating levels of adiponectin, can provide a link between the cellular marker and the in vivo phenotype.