Inhibition of sPLA2-IIA release into medium by PIP-18 in RA and OA SF cultures. Confluent synovial fibroblast (SF) cells in 75 cm2 flasks were serum-starved for overnight (16 hours) before incubation for one hour with 5 μM PIP-18, LY315920, matrix metalloproteinase inhibitor II (MMP-II), or with vehicle (0.5% dimethyl sulfoxide final concentration in medium), and stimulation with hrIL-1β (10 ng/ml) for 24 hours. Rheumatoid arthritis (RA)/osteoarthritis (OA) SFs cultured without IL-1β or the inhibitors served as controls. (a) Immunoreactive secretory phospholipase A2 (sPLA2) released in the culture medium was determined by sPLA2 human type IIA enzyme-linked immunoassay kit. (b) sPLA2 enzymatic activity was measured with an Escherichia coli membrane assay as described . Data shown are the mean ± standard error of the mean of the combined data of triplicate determination of triplicate experiments performed on a pool of RA SF cultures from five RA patients. One-way analysis of variance with post hoc test was done using Bonferroni's correction. *P < 0.05, **P < 0.001, ***P < 0.001 for pair-wise comparisons of each inhibitor type (IL without inhibitor versus IL with inhibitor). PIP = phospholipase inhibitor from python.