Beta-endorphin ameliorates synovial cell hyperfunction in the collagen-induced arthritis rat model by specific downregulation of NF-kappa B activity

Objectives: To observe the multiple immunoregulating effects of beta-endorphin (beta-END) on synovium cells of collagen-induced arthritis ( CIA) in rats and to determine whether the regulation involves the transcriptional factor-kappa B (NF-kappa B) signal pathway. Methods: CIA was induced in female Wistar rats by immunization with native bovine type-II collagen emulsified with complete Freund's adjuvant. Synovial cells in the knees of the CIA rats were cultivated, and the effects of beta-END, beta-END receptor inhibitor ( naloxone, Nal) in proliferation and apoptosis of the synovial cells were assayed by 3-(4,5-dimethylthiazol- 2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)- 2H-tetrazolium, flow cytometry, and DNA integrity, respectively. The effects of beta-END and Nal on mRNA expression of several cytokines in the synovial cells, including tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta ( IL-1 beta), IL-6, regulated upon activation normal T-cell expressed and secreted ( RANTES), inducible nitric oxide synthase ( iNOS), matrix metalloproteinase-2 (MMP-2) and MMP-9 were estimated by quantitative reverse transcription-polymerase chain reaction. Effects of beta-END and Nal on NF-kappa B activity were analyzed using luciferase gene reporter assays. The effects of beta-END and Nal on p65NF-kappa B expression of the synovial cells were examined using Western blot. Results: 75% of the rats were demonstrated to have established the CIA model successfully. beta-END was shown to exert multiple effects on synovial cells of CIA rats including decreased proliferation, induced apoptosis, and downregulation of TNF-alpha, IL-1 beta, IL-6, RANTES, iNOS, MMP-2 and MMP-9 mRNA expression. beta-END seemed to play an immunoregulating role by downregulating the activity and expression of NF-kappa B. It was found that the beta-END receptor blockage could counteract all the effects. Conclusions: beta-END ameliorates synovial cell functions of CIA rats through binding with receptors and downregulating the NF-kappa B signal pathway. This suggests that beta-END, by blocking the activity and expression of NF-kappa B, is a potential antiinflammatory and anti-rheumatic agent against CIA. Copyright (C) 2005 S. Karger AG, Basel.