The Therapetutic Potential Of Cannabinoid Receptor2Activation In The Treatment Of Rheumatoid Arthritis

Backgrounds and Objectives:Rheumatoid arthritis (RA) is an immune-mediated inflammatory disease of unknown etiology, which is characterized by chronic inflammatory infiltrationof the synovium, leading to eventual cartilage and bone destruction. As a typical hisopathological feature of RA, a hyperplastic and hypercellular synovial membrane is built up in which lymphocytes, macrophage-like cells and fibroblast-like cells accumulate. Fibroblast-like synoviocytes (FLS) are recognized as both propagator of the immune response and the engine of joint damage in RA. In spite of significant improvements in the treatment of RA, there is still a need for the identification of new pathways involved in the modulation of inflammation in order to further increase efficacy, particularly in patients in whom the disease dose not respond to current therapies. Cannabinoid receptor2(CB2R) is mainly expressed in peripheral immune system and is being studied in many diseases because of its function against inflammation. The present study is designed to investigate the therapeutic potential of CB2R activation in the treatment of RA.Methods:Expression of CB2R in synovial tissue and FLS was studied by immunohistochemistry, Western blotting and Revers-transcription PCR. A murine model of collagen-induced arthritis (CIA) was used to evaluate the therapeutic efficacy of HU-308, a selective CB2R agonist. HU-308with doses of0.3and1.0mg/kg was administered i.p. for consecutive7days from the day before the booster immunization. The disease severity was evaluated by semi-quantitative scoring, hitological assessment and radiographic assessment. The expression level of mRNA was quantitatively analyzed by real-time RT-PCR. The concentrations of anti-collagen Ⅱ antibodies, cytokines, and matrix metalloproteinases (MMPs) in sera and/or culture supernatants were determined by ELISA. Intracellular proteins were analyzed by Western blot. Proliferation of FLS was assayed with Cell counting kit-8(CCK-8).Results:1. The expression of CB2R was found in synovial tissue and cultured FLS with slight higher levels in RA patients than in OA patients. In cultured FLS, all of IL-1β, TNF-a and lipopolysaccharide upregulated expression of CB2R. Compared with naive mice, expression of CB2R increased significantly in livers and spleens of CIA mice.2. In CIA, treatment with HU-308(1mg/kg) significantly decreased joint swelling, synovial inflammation, and joint destruction, as well as serum levels of anti-collagen II antibodies.3. Ex vivo, HU-308inhibited IL-1β-induced proliferation of FLS as well as IL-1β-induced production of MMP-3,-13and IL-6in FLS in a dose-dependent manner.4. In murine peritoneal macrophages, HU-308significantly suppressed lipopolysaccharide-induced IL-6and TNF-α production in a dose-dependent manner, which was abolished by knockout of CB2R gene.5. HU-308also suppressed IL-1β-induced activation of ERK1/2and p38MAPK in FLS.Conclusion:Activation of CB2R by HU-308has therapeutic potential for RA to suppress synovitis and alleviate joint destruction via inhibiting the production of autoantibodies, proinflammatory cytokines and MMPs, as well as the proliferation of FLS.