Production of visfatin/Nampt by human osteoarthritic joint tissues. Human osteoarthritic joint tissues were incubated for 24 hours in serum-free medium (6 ml/g tissue). Retrieved media were considered conditioned media. (A) Western blot analysis of visfatin/nicotinamide phosphoribosyltransferase (Nampt) protein level in conditioned media. Left panel: denaturing conditions, showing monomeric conformation. Right panel: nondenaturing conditions, showing dimeric conformation. Arrows show bands specific to visfatin/Nampt. (B) Enzyme-linked immunosorbent assay of visfatin/Nampt released by cartilage (n = 15), synovial membrane (n = 13) and subchondral bone (n = 13). **P < 0.001, ***P < 0.0005. Horizontal lines are medians. Each dot represents one sample.