Obesity and inflammation--targets for OA therapy.

Obesity is one of the main risk factors for osteoarthritis (OA). For many years the association of obesity and OA has been simply attributed to the effects of overload on weight-bearing joints, and epidemiological surveys have shown a strict correlation between an increased body mass index and the severity of knee or hip OA, as well as some relief of pain and disability following weight loss. Instead, there is now a growing body of evidence that obesity is a complex syndrome in which an abnormal activation of neuroendocrine and pro-inflammatory pathways leads to an altered control of food intake, fat expansion and metabolic changes. Activated white adipose tissue increases the synthesis of pro-inflammatory cytokines, such as IL-6, IL-1, IL-8, TNFalpha, IL-18, while regulatory cytokines, such as IL-10, are decreased. Adipocytes also produce peculiar cytokines, namely adipokines, that exert multiple effects, being capable of promoting synovial inflammation, cartilage degrading enzymes, and bone matrix remodeling. Furthermore, pro-inflammatory cytokines stimulate adipocytes to synthesize neuropeptides, such as substance P and nerve growth factor, that have been shown to be critical in regulating both the appetite and cartilage homeostasis. In this scenario, where the influence of obesity on OA stems from a complex interaction of genetic, metabolic, neuroendocrine, and biomechanical factors, there may be various different potential targets for OA therapy.