Effect of piperine on the production of proinflammatory mediators. (a) ELISA results show that piperine inhibited the production of interleukin (IL)6 and prostaglandin E2 (PGE2) in IL1β-stimulated fibroblast-like synoviocytes (FLSs) in a dose-dependent manner. (b) Piperine effects on IL6 and cyclo-oxygenase (COX)-2 mRNA expression measured by semiquantitative RT-PCR. (c) Piperine effects on COX-2 protein expression measured by western blot. Experiments were performed with synovial cells derived from patients with rheumatoid arthritis. Values are expressed ± standard error of the mea (SEM). ***P < 0.001 vs IL1β treated group without piperine.