Inhibitory effect of triptolide on interleukin-18 and its receptor in rheumatoid arthritis synovial fibroblasts

Objective: To determine the effects of triptolide (TP) on the expression of interleukin-18 (IL-18) and its receptor in phorbol 12-myristate 13-acetate (PMA)-stimulated rheumatoid arthritis synovial fibroblasts (RASF). Materials and Methods: RASF were obtained from the synovial tissue of patients with RA. RASF were pretreated with TP (0 similar to 100 ng/ml) for 2 h before stimulation with PMA (50ng/ml). The bioactivity of IL-18 in the supernatant was detected based on IFN-gamma secretion from IL-18-responding human myelomonocytic KG-I cells. IL-18 level was analyzed by ELISA. In situ expression of IL-18R alpha was determined by immunofluorescence assay. To estimate the protein and mRNA expression of IL-18 and IL-18R alpha in RASE western blot and quantitative RT-PCR were performed. Nuclear factor-kappa B (NF-kappa B) activity in the whole-cell extract of treated RASF was also measured using an ELISA-based method. Results: TP effectively inhibited the bioactivity of IL-18 in PMA-stimulated RASE The expression of IL-18 and IL-18R at protein and gene levels was reduced by TP. NF-kappa B activity in PMA-stimulated RASF was profoundly suppressed by TP. These effects showed a high correlation with TP concentration (0 similar to 100ng/ml). Conclusion: TP effectively inhibited the expression of IL-18 and its receptor in PMA-stimulated RASE These results suggest a mechanism of TP in RA therapy.