Effect of piperine on the production of extracelluar matrix degradation enzymes (matrix metalloproteinases (MMPs)). (a) ELISA results show that piperine inhibited the production of MMP13, but not MMP1 proteins, in interleukin (IL)1β-stimulated fibroblast-like synoviocytes (FLSs) in a dose dependent manner. (b) mRNA levels were measured by semiquantitative RT-PCR. Experiments were performed with synovial cells derived from patients with rheumatoid arthritis. Values are expressed ± standard error of the mean (SEM). ***P < 0.001 vs IL1β treated group without piperine.