Adiponectin and resistin--new hormones of white adipose tissue

Adiponectin and resistin are recently described secretory products of adipose tissue. Adiponectin is secreted by fat cells and circulates in the blood. Plasma adiponectin concentration is reduced in obese animals and humans and in patients with type 2 diabetes mellitus. Adiponectin stimulates fatty acids oxidation, decreases plasma triglycerides, and improves glucose metabolism by increasing insulin sensitivity. In addition, adiponectin inhibits the inflammatory process and possibly atherogenesis by suppressing the migration of monocytes/macrophages and their transformation into foam cells. Plasma adiponectin is lower in patients with ischemic heart disease than in body mass index-matched healthy individuals. Hypoadiponectinemia may contribute to insulin resistance and accelerated atherogenesis associated with obesity. Resistin/FIZZ3 is a member of the newly discovered cysteine-reach secretory protein family, referred to as 'resistin-like molecules' (RELM) or 'found in inflammatory zone' (FIZZ), together with FIZZ1/RELMalpha and FIZZ2/RELMbeta. Each of these has unique tissue distribution. Both resistin and FIZZ1/RELMalpha are expressed in adipose tissue. Initial studies in rodents suggested that resistin is upregulated in obesity and may be involved in the development of insulin resistance. Later studies failed to confirm this hypothesis and demonstrated reduced resistin expression in adipose tissue of obese animals. In human adipose tissue resistin is detectable at a very low level, and there is no relationship between resistin expression and obesity. Although the role of resistin in linking human obesity with type 2 diabetes is thus questionable, this protein is detected in peripheral blood monocytes,