| Abstract: | Objective The cytochrome P450 enzyme CYP7B catalyzes the conversion of dehydroepiandrosterone (DHEA) into 7α‐hydroxy‐DHEA (7α‐OH‐DHEA). This metabolite can stimulate the immune response. We previously reported that the severity of murine collagen‐induced arthritis is correlated with CYP7B messenger RNA (mRNA) expression and activity in the arthritic joint. The purpose of this study was to investigate the presence of 7α‐OH‐DHEA in synovial samples and the cytokine regulation of CYP7B activity in fibroblast‐like synoviocytes (FLS) from patients with rheumatoid arthritis (RA). Methods The presence of 7α‐OH‐DHEA was examined in synovial biopsy tissues, synovial fluid, and serum by radioimmunoassay. The effect of cytokines on CYP7B mRNA expression and CYP7B activity in FLS was examined by determining the formation of the CYP7B enzyme product 7α‐OH‐DHEA with the use of high‐performance liquid chromatography. Results The CYP7B enzyme product 7α‐OH‐DHEA was found in synovial biopsy tissues, synovial fluid, and serum from RA patients. The proinflammatory cytokines tumor necrosis factor α (TNFα), interleukin‐1α (IL‐1α), IL‐1β, and IL‐17 up‐regulated CYP7B activity in an FLS cell line 2–10‐fold. Enhanced CYP7B activity was correlated with an increase in CYP7B mRNA. The cytokine transforming growth factor β inhibited CYP7B activity. Moreover, CYP7B activity was detected in 10 of 13 unstimulated synovial fibroblast cell lines. Stimulation with TNFα increased CYP7B activity in all cell lines tested. Conclusion Exposure to the proinflammatory cytokines TNFα, IL‐1α, IL‐1β, and IL‐17 increases CYP7B activity in synovial tissue. Increased CYP7B activity leads to higher levels of the DHEA metabolite 7α‐OH‐DHEA in synovial fluid, which may contribute to the maintenance of the chronic inflammation observed in RA patients. |
