Abstract
Hemophilic arthropathy is the major morbidity of congenital factor VIII and IX deficiency. Therapies localized to hemophilic joints could provide adjunctive protection, in addition to that provided by systemic factor replacement. However, the ability of extravascular clotting factors to contribute to hemostatic protection within joint tissue is unknown. We hypothesized that replacing deficient factor VIII or IX within the injured joint capsule of mice with hemophilia A (FVIII −/ −) or hemophilia B (FIX −/ −), respectively, would decrease the progression of synovitis. We developed a bleeding model consisting of a unilateral knee joint capsule needle puncture to induce hemorrhage in hemophilic mice. Pathology of the joint at two weeks after the injury is graded 0 to 10 using a murine hemophilic synovitis grading system (Valentino, Hakobyan. Haemophilia, 2006). Hemostatically normal mice do not develop synovitis following this injury, but > 95% of FIX −/ − mice develop bleeding and synovitis with a mean grade of 3–4 or greater. Coincident with needle puncture, recombinant human coagulation factor doses ranging from 0 to 20 IU/kg body weight of factor IX or 0 to 25 IU/kg of factor VIII were instilled intraarticularly (I.A.). Comparison groups received the same injury and intravenous (I.V.) factor IX or VIII doses of 25 IU/kg to 100 IU/kg (n= 4–7 mice per study group). Joint bleeding phenotype of the two strains of mice was similar. Mice receiving only saline injection at the time of needle puncture developed mean synovitis scores of 5 ±0.5 in the FVIII −/ − mice and 6 ±0.5 in the FIX −/ − mice. Protection by human clotting factor in the mouse coagulation system was incomplete; mice receiving 100 IU/kg I.V. of factor VIII or factor IX developed synovitis scores of 2.6 ± 1.7 and 2.1 ± 0.2, respectively. In contrast, pathology grade of FVIII −/ − mice dosed with 25 IU/kg I.A. was 0.67 ± 0.3 (p = 0.05 for comparison of 25 IU/kg I.A. with 100 IU/kg IV); FIX−/ − mice receiving 20 IU/kg I.A. had synovitis scores of 0.45 ± 0.58 (p < 0.01 for comparison of 25 IU/kg I.A. with 100 IU/kg I.V.). We next ruled out the possibility that I.A. factor was entering the circulation, and via that route resulting in joint protection, either through technical error at the time of injection, or from a depot effect in the joint with late equilibration into the circulation. Additional groups of mice received factor VIII or IX intravenously at 100 IU/kg, or intraarticularly at 4 times the doses used in the hemarthrosis challenge (80 IU/kg FIX or 100 IU/kg FVIII), and factor activity assays were performed at 1, 4, 12, 24, and 48 hours. Expected circulation kinetics were seen following I.V. dosing; no increase in circulating factor VIII or IX activity were seen in the intraarticular dosing groups at any timepoint. In considering the potential immunogenicity of an intraarticular therapy approach for hemophilic joint therapy, factor VIII −/ − mice were treated with three doses of human factor VIII 100 IU/kg at five day intervals either I.V. or I.A. At two weeks after exposure, 5/5 I.V.-treated mice developed inhibitor antibodies with titers ranging 0.8–7.2 BU; 2/5 I.A.-treated mice had detectable low-titer antibodies (1.3 BU), indicating no greater immunogenicity in the I.A. model. Extravascular factor VIII and factor IX can contribute to protection against blood-induced joint deterioration; enhancing local tissue hemostasis with protein or gene therapy may prove a useful adjunct to systemic replacement.
Biological Rationale for New Drugs in the Bleeding Disorders Pipeline
