[Evidence of inflammatory mechanisms in osteoarthritis]

Classically, osteoarthritis (OA) is not considered an inflammatory arthropathy, because of the presence of a small number of neutrophils in the synovial fluid and the absence of systemic manifestations of inflammation. Besides, the characteristics of articular cartilage (avascular, alymphatic and aneural) do disable to fulfill with the classical signs of inflammation (redness, swelling, heat, pain). However, thanks to development of molecular and cellular biology, there are multiple studies which shown that different proinflammatory mediators, such as the cytokines IL-1β and TNFα, could be important in the development of this disease. Therefore, the stimulation of chondrocytes, the only cell type living in the cartilage matrix and for this reason the principal responsible of integrity of cartilage matrix extracellular, with these proinflamatory cytokines increases the production of metalloproteinases, keys molecules in the irreversible degradation of normal architecture of cartilage. As well, inhibits the synthesis of cartilage proteoglycans and type II collagen, stimulates the production of reactive oxygen species such as nitric oxide, and increases the production of prostaglandin E(2). Likewise, the effects of synovial inflammation expected contribute to deregulation of chondrocyte function in a similar fashion, favouring the lost of equilibrium between the catabolic and anabolic activities of the chondrocyte necessary for maintaining the extracellular cartilage matrix.