[Adipocytokines and life style-related disease]

The adipose tissue produces and secretes many bioactive substances, which we conceptualized as Adipocytokines (Nature Medicine 1996). Adiponectin is a novel adipocytokine, which we identified by screening the adipose-specific genes from human fat. Adiponectin is a secreted protein, the concentration of which reaches as high as 5-15 micrograms/ml in human plasma. Adiponectin mRNA is expressed exclusively in adipose tissues. The adiponectin mRNAs and its plasma levels are reduced in obesity, type 2 diabetes and atherosclerosis. Hyperinsulinemic euglycemic clamp studies in humans and monkeys, and several recent studies from others revealed that adiponectin is an insulin-sensitizing hormone. Furthermore, adiponectin exhibited anti-atherogenic moieties, decreasing the attachment of monocytes to endothelial cells through inhibiting the expression levels of adhesion molecules. It reduced the lipid accumulation in macrophages through reducing the expression of scavenger receptor, and inhibited the cytokine-stimulated proliferation of smooth muscle cells. The genetic mutation of the adiponectin gene accompanying hypoadiponectinemia was strongly associated with the incidence of type 2 diabetes and atherosclerosis in Japanese subjects. Hypoadiponectinemia was the strongest predictor for the development of type 2 diabetes in humans. Adiponectin knockout mice exhibited diet-induced diabetes and severer atherosclerotic response by vascular injury. Adiponectin supplement reversed the insulin resistance syndrome including diabetes and atherosclerotic change in the knockout mice. We conclude that "Hypoadiponectinemia" stands upstream of the pathophysiology of metabolic syndrome, hence, can be a direct target of drug intervention to tackle life style-related disease rampant in developed countries.