Therefore, expression of tumor necrosis factor (TNF)‐α and inflammatory factors such as interleukin (IL)‐1β by chondrocytes as well as synovial cells occurs at advanced stages of osteoarthritis, and consequently, the levels of MMPs and some pro‐inflammatory factors such as prostaglandin E2 (PGE2), IL‐8, IL‐6, and nitric oxide increase (Krasnokutsky et al., 2008). This evidence concerns the gene TNF and osteoarthritis.