Individuals with hemophilia have abnormally low bone density, despite prophylactic factor infusion with the associated reduction in the joint disabling complications of bleeding. Previously, we demonstrated decreased bone mineral density, skeletal strength, and increased bone resorption in factor VIII (FVIII)-deficient mice without differences in physical activity or joint bleeding compared to control mice. Thus, we hypothesize that factor deficiency is an independent risk factor for decreased skeletal health.
To test this hypothesis, we evaluated platelet-poor plasma from 80 male subjects with severe FVIII deficiency, 20 male patients with severe factor IX (FIX) deficiency and 52 healthy male controls. Samples were assessed for three markers of bone turnover: receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG) and carboxy-terminal collagen crosslinks (CTX-1). RANKL binding to the RANK receptor induces the proliferation and differentiation of osteoclasts resulting in increased bone resorption. OPG competitively inhibits RANKL binding to RANK, blocking these osteoclastic effects. CTX-1 is formed through the degradation of bone and thus is a direct marker of bone resorption.
No differences in RANKL levels are seen between any of the groups. A significant increase in OPG is identified in plasma from FIX-deficient subjects compared to FVIII-deficient subjects (p = 0.0046) and control subjects (p = 0.0095), without differences seen between FVIII-deficient and control subjects (p = 0.920). CTX-1 is higher in samples from FVIII-deficient subjects compared to FIX-deficient subjects (p = 0.020) and control subjects (p = 0.0024), without differences seen between FIX-deficient and control subjects (p = 0.947) samples. In a subset analysis, subjects receiving FVIIII concentrate replacement within 12 hours of plasma collection have decreased CTX-1 (p = 0.022) but not OPG (p= 0.850) compared to those subjects receiving factor concentrate replacement greater than12 hours from plasma collection. We are currently evaluating other plasma markers of bone turnover and cytokine expression in the same cohort of samples.
Subjects with FVIII deficiency but not FIX deficiency have evidence of increased bone resorption compared to control samples. Increased OPG levels are present in FIX-deficient plasma and may contribute to the differences seen in CTX-1 production between subjects with FIX and FVIII deficiency. Furthermore, FVIII replacement within 12 hours of plasma collection reverses CTX-1 elevation seen in FVIII-deficiency. This study suggests that bone disease is intrinsic to FVIII-deficiency and that aggressive FVIII replacement may ameliorate this pathology.
Manco-Johnson:Novo Nordisk: Membership on an entity’s Board of Directors or advisory committees; Biogen Idec: Membership on an entity’s Board of Directors or advisory committees; Baxter BioScience: Membership on an entity’s Board of Directors or advisory committees; CSL Behring: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Bayer HealthCare: Membership on an entity’s Board of Directors or advisory committees, Research Funding; Eisai: Research Funding. Taylor:Novo Nordisk: Research Funding; Baxter BioScience: Research Funding.
Asterisk with author names denotes non-ASH members.