Arsenic trioxide (ATO) alleviated the symptoms and joint destruction of CIA mice. (a) ATO and Vitamin D (Vit D) alleviate joint destruction and significantly elevated mean CT values in collagen-induced arthritis (CIA) mice compared with normal control (NC) mice (n=6; ∗p<0.05, ∗∗p<0.01, ∗∗∗p<0.001). Data are expressed as mean ± SEM. (b) The severity of arthritis in CIA mice was measured by H&E staining of knee joints. ATO treatment (2 mg/kg/d) and Vit D (400 ng/kg/d) significantly reduced the histological scores, including synovial hyperplasia, cartilage and bone erosion, and joint inflammation compared with NC (n=6; ∗p<0.05, ∗∗p<0.01, ∗∗∗p<0.001). Magnification = 20×. Bars = 50 μm. Data are expressed as mean ± SEM. (c) Collagen-induced arthritis- (CIA-) saline mice (saline) showed a significant decrease in weight and increased paw thickness and arthritis scores compared with the normal control (NC) group. Arsenic trioxide (ATO) at 2.0 mg/kg/day, Vitamin D (Vit D), and methotrexate (MTX) (n=6) significantly increased bodyweight and decreased paw thickness and arthritis scores (n=6, ∗p<0.05, ∗∗p<0.01, ∗∗∗p<0.001, treatment versus saline). Data are expressed as means ± SEM.