Impact of 6-mercaptopurine and 6-mercaptopurine riboside on pro-inflammatory cytokines and oxidative stress in blood plasma of rats with complete Freund’s adjuvant (CFA) arthritis

Inflammatory arthritis is a chronic autoimmune disorder characterized by joint inflammation and pain, often requiring effective immunosuppressive treatment. In a rat model of inflammatory arthritis, the anti-immunosuppressive effects of 6-mercaptopurine (6-MP) and its derivatives were evaluated. Paw edema was induced via subplantar injection of CFA, followed by oral administration of 6-MP and 6-MP riboside (3, 6, or 10 mg/kg). Footpad thickness was measured to assess edema, and blood plasma samples were analyzed for pathogenic mediators (PGE2), oxidative stress biomarkers (H2O2), and pro-inflammatory cytokines (TNF-α, IL-1, IL-6) using ELISA. Results showed that 6-MP reduced PGE2 and pro-inflammatory cytokines in a dose-dependent manner, significantly decreasing edema. Repeated 6-MP doses (6 and 10 mg/kg) dramatically lowered pro-inflammatory cytokine production, similar to the NSAID diclofenac. Plasma PGE2 levels for 6 and 10 mg/kg 6-MP were 2357±624.7 pg/mL and 1670±150.2 pg/mL, respectively, compared to control. For 6-MP riboside, levels were 1931±305.2 pg/mL and 1710±249.2 pg/mL. TNF-α concentrations decreased significantly in plasma treated with 6 mg/kg 6-MP (36.18±4.71 pg/mL) and 10 mg/kg 6-MP riboside (42.02±3.46 pg/mL). IL-6 levels also showed significant reductions, while IL-1 remained unchanged. Additionally, peroxide and glutathione levels improved. Notably, the 10 mg/kg dose of both compounds exhibited superior immunosuppressive potency compared to diclofenac. These findings suggest that 6-MP and its riboside suppress pro-inflammatory mediators while enhancing antioxidant defense. Thus, 6-MP possesses anti-inflammatory and immunosuppressive properties beneficial for early-stage inflammatory arthritis and may serve as a promising disease-modifying anti-rheumatic drug (DMARD).