TNF and osteoarthritis: In hemophilic arthropathy, pro-inflammatory cytokines such as interleukin (IL)-1β [6–8] and tumor necrosis factor (TNF)-α [6, 9] are produced in the hemosiderin-laden synovial tissue, and these cytokines trigger catabolic programs, activating nitric oxide (NO) [1, 6] and matrix metalloproteinase (MMP) expression [6], osteoarthritis [10], and rheumatoid arthritis.