Adipocytokines as driving forces in rheumatoid arthritis and related inflammatory diseases?

Adipose tissue is ubiquitously present in the human organism. It is a structural component of many organs including the skin, the intestinal tract, and the joints. Besides its central function in energy metabolism, adipose tissue usually serves as a bolster in gaps or intersections between tissues. The dominant cell type, adipocytes, secretes highly bioactive substances, the socalled adipokines or adipocytokines (Table 1). Adipokines include a growing number of pluripotent factors such as adiponectin, resistin, leptin, and visfatin/pre–B cell colony-enhancing factor (PBEF) (1,2). Table 2 provides an overview of several characteristics of these adipokines, and their respective functional aspects are discussed below. There is also increasing evidence that adipocytes actively secrete additional proinflammatory factors operative in the pathophysiology of inflamed joints, such as tumor necrosis factor (TNF ), interleukin-6 (IL-6), factors of the complement system, growth factors, and adhesion molecules (2–4). Moreover, adipokines are able to actively modulate inflammation and the innate immune system (1,5). In this review, the current knowledge about the influence of central adipokines in rheumatic diseases, highlighting several aspects of the role of adipokines in chronic inflammation, is summarized.