Objective: Various extracts of the Chinese herbal remedy Tripterygium wilfordii Hook. f. (TWHF) have been reported to be therapeutically efficacious in rheumatoid arthritis (RA) in China, but their mechanism of action remains unclear. We investigated the effect of triptolide, a diterpenoid triepoxide from TWHF, on the production of pro-matrix metalloproteinase 1 (proMMP-1; or procollagenase 1 or pro-interstitial collagenase 1), proMMP-3 (or prostromelysin 1), tissue inhibitors of metalloproteinases (TIMPs), and proinflammatory cytokines in human synovial fibroblasts and J774A.1 mouse macrophages.
Methods: Human synovial fibroblasts and mouse macrophages were cultured with interleukin-1alpha (IL-1alpha) or lipopolysaccharide (LPS) in the presence or absence of triptolide. The production of proMMPs 1 and 3, TIMPs 1 and 2, cyclooxygenase 1 (COX-1) and COX-2, prostaglandin E2 (PGE2), IL-1beta, and IL-6 was assayed by Western blot analysis and enzyme-linked immunosorbent assay. Gene expression of proMMPs 1 and 3, TIMPs 1 and 2, COX-1 and COX-2, IL-1alpha, IL-1beta, tumor necrosis factor alpha (TNFalpha), and IL-6 was also monitored by Northern blot analysis and reverse transcriptase-polymerase chain reaction.
Results: Triptolide suppressed the IL-1alpha-induced production of proMMPs 1 and 3 and decreased their messenger RNA levels in human synovial fibroblasts. In contrast, the IL-1alpha-induced gene expression and production of TIMPs 1 and 2 were further augmented by triptolide in the synovial cells. Triptolide also inhibited the IL-1alpha-induced production of PGE2 by selectively suppressing the gene expression and production of COX-2, but not those of COX-1. In addition, triptolide suppressed the LPS-induced production of PGE2 in mouse macrophages. Furthermore, the gene expression of IL-1alpha, IL-1beta, TNFalpha, and IL-6, as well as the production of IL-1beta and IL-6, were inhibited by triptolide in the LPS-treated mouse macrophages.
Conclusion: We have demonstrated for the first time that the therapeutic effects of TWHF in RA are due in part to the novel chondroprotective effect of triptolide via the direct suppression of the production of proMMPs 1 and 3 and the simultaneous up-regulation of TIMPs in IL-1-treated synovial fibroblasts. Triptolide's interference with gene expression of proinflammatory cytokines and its known inhibitory effects on PGE2 production are also probably very effective.