Mitogen-activated protein kinase pathways are involved in adiponectin induced NO, IL-6, MMP-1 and MMP-3 production in osteoarthritis cartilage. The effects of mitogen-activated protein kinase inhibitors on adiponectin-induced NO production (A), inducible nitric oxide synthase (iNOS) expression (B), IL-6 production (C), matrix metalloproteinase 1 (MMP-1) production (D) and MMP-3 production (E) in human osteoarthritis cartilage. Cartilage explants were incubated for 42 hours with adiponectin (1 μg/ml) and the inhibitor indicated. Samples were collected from six patients in (A) and (B) and from five patients in (C) through (E). Results are expressed as means ± SEM. #P < 0.1, *P < 0.05, **P < 0.01 and ***P < 0.001 compared to explants treated with adiponectin alone. PD98059 = extracellular signal-regulated kinase 1/2 (Erk1/2) inhibitor; SB220025 = p38 inhibitor; SP600125 = c-Jun N-terminal kinase (JNK) inhibitor. The inhibitor concentrations used were based on previous studies in our laboratory [30–32].