Severity of murine collagen‐induced arthritis correlates with increased CYP7B activity: Enhancement of dehydroepiandrosterone metabolism by interleukin‐1β

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Abstract
Objective: The endogenous steroid dehydroepiandrosterone (DHEA) has been reported to play a role in rheumatoid arthritis (RA). DHEA is metabolized by the P450 enzyme CYP7B into 7α‐OH‐DHEA, which has immunostimulating properties. This study was undertaken to investigate the putative role of CYP7B in arthritis using murine collagen‐induced arthritis (CIA), an interleukin‐1β (IL‐1β)–dependent model.Methods: DBA/1J mice were immunized and administered a booster with type II collagen. The presence of 7α‐OH‐DHEA was determined in both arthritic and nonarthritic joints and the serum of CIA mice by radioimmunoassay. CYP7B messenger RNA (mRNA) expression was analyzed in synovial biopsy samples, and in fibroblast‐like synoviocytes (FLS) isolated from these synovial biopsy samples, by reverse transcriptase–polymerase chain reaction (RT‐PCR). In addition, the regulatory role of IL‐1β on CYP7B activity in FLS was determined using RT‐PCR, Western blotting, and high‐performance liquid chromatography.Results: In knee joint synovial biopsy samples from arthritic mice, 7α‐OH‐DHEA levels were 5‐fold higher than in nonarthritic mice. Elevated levels of 7α‐OH‐DHEA were accompanied by an increase in CYP7B mRNA expression and were positively correlated with disease severity. In serum, no differences in 7α‐OH‐DHEA levels were observed between arthritic and nonarthritic mice. Incubation of FLS with IL‐1β resulted in a dose‐dependent increase in 7α‐OH‐DHEA formation. In addition, IL‐1β enhanced CYP7B mRNA and CYP7B protein levels in FLS.Conclusion: Disease progression in CIA is correlated with enhanced CYP7B activity, which leads to locally enhanced 7α‐OH‐DHEA levels. Elevated IL‐1β levels within the arthritic joint may regulate this increase in CYP7B activity.

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