Adipose tissue, insulin action and vascular disease: inflammatory signals

Insulin resistance, both in nondiabetic and diabetic subjects, is frequently associated with obesity, particularly an excess of central fat. Many of the features that have been ascribed to the metabolic or insulin-resistance syndrome are also more commonly found in obese subjects. These phenotypes include diabetic dyslipidaemia, elevation of levels of plasminogen activator inhibitor-1, microalbuminuria and endothelial dysfunction. More recently, features of acute-phase activation and low-grade inflammation, including elevated levels of fibrinogen, C-reactive protein and interleukin-6, have been associated with (central) obesity. Adipose tissue generation of cytokines has been shown in vitro and in vivo, and a number of novel cytokine-like molecules, collectively termed adipocytokines, have been identified as adipocyte products. While several of these, such as tumour necrosis factor-α, may act predominantly in autocrine or paracrine fashion, others are released into the systemic circulation, acting as signalling molecules to remote tissues, including liver, skeletal muscle and endothelium. A clearer understanding of adipose tissue signalling, and its contribution to the state of low-grade inflammation of obesity, will require physiological, as well as cellular and molecular, studies.