Triptolide, an active component of the Chinese herbal remedy Tripterygium wilfordii Hook F, inhibits production of nitric oxide by decreasing inducible nitric oxide synthase gene transcription

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Abstract
Objective The ethyl acetate (EA) extract of Tripterygium wilfordii Hook F (TWHF) and its major active component, triptolide, have been reported to be effective in the treatment of rheumatoid arthritis and other autoimmune inflammatory diseases. Nitric oxide (NO) has been recognized as an important mediator of inflammation. This study was therefore undertaken to examine the effects of the EA extract and triptolide on the production of NO and inducible NO synthase (iNOS) gene expression and transcription in vivo and in vitro. Methods Peritoneal macrophages from C57BL/6J mice treated orally with the EA extract of TWHF were assayed for NO production and iNOS messenger RNA (mRNA) expression by reverse transcriptase–polymerase chain reaction. The murine fibroblast cell line NIH3T3 was also assessed for NO production and iNOS mRNA expression, as well as for iNOS promoter activation, Oct-1 nuclear binding capacity, and Oct-1 protein content by transient transfection, electrophoretic mobility shift assay, and immunoblotting, respectively. Results NO production and iNOS mRNA expression by macrophages from C57BL/6J mice immunized with trinitrophenyl–bovine serum albumin in Freund's complete adjuvant were significantly inhibited by oral administration of the EA extract (52.3% and 59.8% of control, respectively, at one-eighth of the dose that is lethal for 50% of the animals [LD50] and 21.0% and 38.1% of control, respectively, at one-fourth the LD50). Moreover, the EA extract and triptolide significantly inhibited NO production in vitro in activated peritoneal macrophages, which reflected a decreased level of iNOS mRNA. Finally, triptolide inhibited promoter activity of the iNOS gene and induction of the activity of the regulator of iNOS transcription, Oct-1. Conclusion The EA extract of TWHF and triptolide inhibit transcription of the iNOS gene. This may contribute to the antiinflammatory effects of this traditional herbal remedy.

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