Downregulation of lymphocyte activity and human synovial fibroblast growthin rheumatoid arthritis by triptolide

The antirheumatic effects of triptolide, a purified component derived from a Chinese herb, Tripterygium wilfordii Hook f. (TWH), was examined. Periphe ral blood mononuclear cells (PBMC), T cells, or human synovial fibroblasts isolated from healthy controls or rheumatoid arthritis (RA) patients were c ultured in vitro in the absence or presence of triptolide. Estimated by ELI SA, immunoglobulin synthesis in pokeweed mitogen or Staphylococcus aureus C owan 1 strain stimulated PBMC was significantly impaired by triptolide in a concentration-dependent manner (1-10 nM). Similarly, proliferation of PBMC in response to phytohemagglutinin (PHA-M), interleukin-2, or phorbol 12-my ristate 15-acetate (PMA)/ionomycin estimated by incorporation of [H-3]-thym idine was inhibited by triptolide. Cell viability was not affected at the i mmunosuppressive concentrations of triptolide. No abnormality of intracellu lar Ca2+ flux as estimated by flow cytometry was detected in PHA-M-stimulat ed T cells by triptolide. Biosynthesis of cellular protein estimated by inc orporation of [H-3]-leucine was significantly reduced in PMA/ionomycin stim ulated PBMC by triptolide at concentrations above 7.5 nM. Proliferation of human synovial fibroblasts as estimated by crystal violet staining was sign ificantly inhibited by triptolide at 30 nM. The present data demonstrate th at triptolide is a potent immunosuppressant and has an antiproliferative ef fect on synovial fibroblast. The immunosuppressive activity of triptolide i s not due to cytotoxicity, nor is it targeted at the initial membrane signa l transduction process and the generation of second messengers. Inhibition of cellular protein synthesis by triptolide during lymphocyte activation ma y account for its inhibitory activity. The precise mechanism of action of t riptolide needs to be defined in order to develop improved versions of the molecule for the potential treatment of RA. (C) 1999 Wiley-Liss, Inc.