Biological background and role of adiponectin as marker for insulin resistance and cardiovascular risk.

Adiponectin is a serum protein secreted by adipocytes and accounts for approximately 0.01% of total plasma protein. In healthy patient populations adiponectin can be found in concentrations of 7-12 mg/l. Unlike other adipocyte products, adiponectin correlates with decreased free fatty acid blood concentrations and reduced body mass index or body weight. Adiponectin protects from vascular diseases by inhibiting local proinflammatory signals, preventing preatherogenic plaque formation, and by impeding arterial wall thickening. Proinflammatory state and endothelial dysfunction are nominators of the metabolic syndrome, a complex set of risk factors including vascular and metabolic insulin resistance with hyperglycemia, hypertension, and dyslipidemia. Over the past years, thiazolidinediones, like rosiglitazone or pioglitazone, became known as a therapeutic option for patients suffering from the metabolic syndrome. It is considered that insulin sensitizers exert their benefit through indirect induction of adiponectin expression. Clinical studies have confirmed that treatment with thiazolidinediones may increase adiponectin concentrations in patients with type 2 diabetes independent from improvements in blood glucose control or parallel treatment with insulinotropic drugs. These findings suggest that adiponectin may have a diagnostic value and can be used especially for monitoring treatment success. This review summarizes recent biological and clinical data indicating that adiponectin may be the molecular link between obesity and insulin resistance and may serve as a biomarker for the metabolic syndrome.