Protective effect of lappaconitine on Freund's complete adjuvant-induced arthritis exerted through P2X7 receptor-mediated regulation of M1/M2 balance in rats.

Abstract

Objective: to investigate the anti-arthritic effects of lappaconitine (LA) on adjuvant-induced arthritis in Sprague-Dawley rats and its possible involvement in the regulation of M1/M2 macrophage balance through the P2X7 receptor (P2X7r).

Methods: Rats were immunized with complete Freund's adjuvant and then intraperitoneally administered LA (2, 4, or 8 mg·kg^-1·d^-1) or methotrexate (0.5 mg/kg per 3 d) for 14 d. The anti-arthritic effects of LA were evaluated through arthritis index (AI) assessment, ankle diameter measurement, and histopathological staining analysis. The analgesic effect of LA on arthritis was measured using mechanical withdrawal threshold testing and gait scoring. The impacts of LA on macrophage polarization, the expression of pro-/anti-inflammatory cytokines and P2X7r were analyzed using quantitative real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and Western blotting.

Results: LA treatment significantly reduced AI scores, paw swelling, joint destruction, and inflammatory cell infiltration, and alleviated arthritis pain. Additionally, LA promoted a balanced M1/M2 ratio by increasing the mRNA expression level of M2 marker arginase 1 and decreasing those of M1 markers inducible nitric oxide synthase and interleukin (IL)-1β in synovial tissues. Furthermore, LA lowered the levels of three M1-related cytokines, namely tumor necrosis factor-α, IL-1β and IL-18, and raised the level of the M2-related cytokine IL-10. Further research showed that treatment with LA inhibited the expression of P2X7r.

Conclusion: Our findings indicate that the notable therapeutic and analgesic effects of LA on AIA rats are exerted through balancing the M1/M2 ratio, probably via P2X7r.