Review article: adipocytokines and insulin resistance

Insulin resistance has been implicated as one possible factor that links visceral obesity to unfavourable metabolic and cardiovascular consequences. However, the mechanism whereby adipose tissue causes alterations in insulin action remains unclear. White adipose tissue is secreting several hormones, particularly leptin and adiponectin, and a variety of other protein signals: the adipocytokines. They include proteins involved in the regulation of energy balance, lipid and glucose metabolism as well as angiogenesis, vascular and blood pressure regulation. Visceral obesity and inflammation within white adipose tissue may be a crucial step contributing to the emergence of insulin resistance, type 2 diabetes and atherosclerosis. A growing list of adipocytokines involved in inflammation (IL-1beta, IL-6, IL-8, IL-10, TNF-alpha, TGF-beta,) and the acute-phase response (serum amyloid A, PAI-1) have been found to be increased in the metabolic syndrome. It is, however, unclear as to the extent adipose tissue contributes quantitatively to the elevated circulating levels of these factors in obesity and how they may affect the insulin-dependent tissues. This review describes the role of the currently known adipocytokines and hormones released by adipose tissue in generating the insulin resistance state and the chronic inflammatory profile which frequently goes together with visceral obesity.