Anti-inflammatory Effects of Botulinum Toxin Type A in a Complete Freund’s Adjuvant-Induced Arthritic Knee Joint of Hind Leg on Rat Model

The objective of the study is to verify histopathologically the anti-inflammatory effect of botulinum toxin type A (BoNT-A) in a Complete Freund’s Adjuvant (CFA)-induced arthritic knee joint of hind leg on rat model using immunofluorescent staining of anti-ionized calcium-binding adaptor molecule 1 (Iba-1) and interleukin-1β (IL-1β) antibody. Twenty-eight experimental rats were injected with 0.1 ml of CFA solution in the knee joint of the hind leg bilaterally. Three weeks after CFA injection, the BoNT-A group (N = 14) was injected with 20 IU (0.1 ml) of BoNT-A bilaterally while the saline group (N = 14) was injected with 0.1 ml of saline in the knee joint of the hind leg bilaterally. One and two weeks after BoNT-A or saline injection, joint inflammation was investigated in seven rats from each group using histopathological and immune-fluorescent staining of Iba-1 and IL-1β antibody. The number of Iba-1 and IL-1β immune-reactive (IR) cells was counted in the BoNT-A and saline groups for comparison. There was a significant reduction in joint inflammation and destruction in the BoNT-A group at 1 and 2 weeks after BoNT-A injection compared with the saline group. The binding of Iba-1 and IL-1β antibody was significantly lower in the BoNT-A group than the saline group at 1 and 2 weeks after BoNT-A injection. The number of Iba-1 and IL-1β-IR cells at 1 and 2 weeks after the injection of BoNT-A were significantly different from the corresponding number of Iba-1 and IL-1β-IR cells in the saline group. To conclude, BoNT-A had an anti-inflammatory effect in a CFA-induced arthritic rat model, indicating that BoNT-A could potentially be used to treat inflammatory joint pain.