Adiponectin: a key player in obesity related disorders

Recent studies revealed that adipose tissue is not only an energy storing organ, but is a kind of endocrine organ which secretes a variety of bioactive substances, so-called adipokines or adipocytokines. Visceral fat accumulation is associated with hypersecretion of adipocytokines such as tumor necrosis factor-alpha and plasminogen activator inhibitor-1 which may regulate inflammatory and atherogenic diseases. Adiponectin is a relatively new adipocytokine which we discovered in 1996 and has anti-diabetic, anti-atherogenic and anti-inflammatory properties. Adiponectin is present in plasma at a very high concentration, but in contrast to other adipocytokines, its production is reduced in subjects with visceral fat accumulation and the plasma levels are negatively correlated with visceral adiposity. Hypoadiponectinemia induced by visceral fat accumulation is closely associated with type 2 diabetes, lipid disorders, hypertension and also certain inflammatory diseases. In this review, the mechanisms of obesity-related diseases including nonalcoholic fatty liver disease will be discussed from the aspect of important roles of adipocytokines, especially adiponectin.