Defective lymphangiogenesis and iron removal after hemarthrosis in factor VIII-deficient mice are rectified with therapeutic factor VIII administration-implications for joint health.

Background: Maladaptive lymphangiogenesis after hemarthrosis in factor(F)VIII-deficient (knockout [KO]) mice facilitates synovial iron accumulation.

Objectives: To investigate the effect of FVIII treatment on lymphangiogenesis, iron clearance, and joint health after hemarthrosis.

Methods: Two days after knee injury/bleed (subpatellar needle puncture) FVIII-KO mice were separated into 3 groups receiving (1) intravenous saline, (2) recombinant human FVIII for 2 days, or (3) murine (m)FcFVIII for 14 days. FVIII activity levels were measured repeatedly (peak/trough) for 14 days. Joint tissues were processed at 2 and 4 weeks postbleed for Prussian blue staining (iron), CD68 (macrophage), αSMA (vascular remodeling), and LYVE1 (lymphangiogenesis) immunohistochemistry, and Safranin-O-Green staining (cartilage health).

Results: Joint injury caused profound hemarthrosis. Mice treated with mFcFVIII maintained stable FVIII activity levels for 14 days (troughs 29%-38%). Pronounced synovial iron accumulation colocalizing with macrophages, along with severely impaired lymphangiogenesis and joint health parameters, were present in saline-treated mice at 2 and 4 weeks when compared with baseline. Short-term recombinant human FVIII administration resulted in partially impaired lymphangiogenesis and iron clearance with delayed recovery of joint health parameters. In contrast, mice treated with mFcFVIII experienced rapid iron clearance alongside normal lymphangiogenesis, associated with fast and effective normalization of joint health parameters, particularly with respect to cartilage health.

Conclusion: Prolonged FVIII availability in the "mild hemophilia range" (± Fc-mediated effects) after hemarthrosis seem critical for lymphangiogenesis, rapid iron removal, and joint repair, including glycosaminoglycan-dependent cartilage restoration. Intensified courses of FVIII treatment in patients may therefore be beneficial for postbleed management.