Prophylactic Effects of Combined Bosentan and Nintedanib on Early Post-Traumatic Joint Contracture Formation in a Rat...

Background/Objectives: Post-traumatic joint contracture (PTJC) is a common complication in orthopedic surgery characterized by fibrosis and restricted joint mobility. Previous work by our multi-arm study demonstrated that nintedanib monotherapy could effectively mitigate PTJC by targeting fibroblast activation pathways. Since PTJC involves multiple simultaneously activated signaling pathways, we hypothesized that combination therapy targeting both inflammation and fibrosis might be advantageous for improving outcomes. As a candidate for combination treatment with nintedanib, bosentan, an endothelin receptor antagonist that modulates inflammatory responses, was chosen to assess whether this approach could improve the prevention of PTJC. Methods: Thirty-nine Sprague Dawley rats were randomized evenly into three groups after undergoing a standardized hyperextension trauma of the knee and K-wire arthrodesis over a period of two weeks. The experimental groups (n = 13 each) received a combination (COMB) of nintedanib (5 mg/kg/d, twice daily) and bosentan (50 mg/kg/d, twice daily), or nintedanib (5 mg/kg/d, twice daily) alone throughout the immobilization period. The control group (n = 13), meanwhile, was given a placebo. Joint mobility was evaluated quantitatively by measuring the contracture angle (CA) and resistance to extension. Additionally, tissue from the posterior joint capsule was collected for histological analysis. Quantitative PCR was used to analyze tissue and assess the expression levels of genes involved in the pro-fibrotic process, including, Il-6, Tgf-β, Nf-κb, Ctgf, and α-Sma. Statistical analysis involved Kruskal-Wallis and ANOVA tests with post hoc methods, with significance defined at p < 0.05. Results: Both combination therapy and nintedanib monotherapy significantly reduced the contracture angle compared to placebo (p ≤ 0.05 and p ≤ 0.01, respectively), with no significant difference between treatments. Histological analysis showed significantly fewer myofibroblasts in the COMB and nintedanib groups versus placebo (p < 0.05). α-SMA expression was significantly decreased by 8-fold (COMB) and 11-fold (nintedanib) compared to placebo (p < 0.05), with no differences between treatments. No significant differences were detected in upstream pro-fibrotic gene expression among groups. Conclusions: Based on results comparable to those achieved with nintedanib monotherapy, the additional administration of bosentan does not appear to offer any further benefit at the given experimental setup.