Heterogeneity in bleeding tendency and arthropathy development in individuals with hemophilia

People with hemophilia (PWH) have an increased tendency to bleed, often into their joints, causing debilitating joint disease if left untreated. To reduce the incidence of bleeding events, PWH receive prophylactic replacement therapy with recombinant factor VIII (FVIII) or FIX. Bleeding events in PWH are typically proportional to their plasma FVIII or IX levels; however, in many PWH, bleeding tendency and the likelihood of developing arthropathy often varies independently of endogenous factor levels. Consequently, many PWH suffer repeated bleeding events before correct dosing of replacement factor can be established. Diagnostic approaches to define an individual's bleeding tendency remain limited. Multiple modulators of bleeding phenotype in PWH have been proposed, including the type of disease-causing variant, age of onset of bleeding episodes, plasma modifiers of blood coagulation or clot fibrinolysis pathway activity, interindividual differences in platelet reactivity, and endothelial anticoagulant activity. In this review, we summarize current knowledge of established factors modulating bleeding tendency and discuss emerging concepts of additional biological elements that may contribute to variable bleeding tendency in PWH. Finally, we consider how variance in responses to new gene therapies may also necessitate consideration of patient-specific tailoring of treatment. Cumulatively, these studies highlight the need to reconsider the current one size fits all approach to treatment regimens for PWH and consider therapies guided by the bleeding phenotype of each individual PWH at the onset of therapy. Further characterization of the biological bases of bleeding heterogeneity in PWH, combined with the development of novel diagnostic assays to identify those factors that modulate bleeding risk in PWH, will be required to meet these aspirations

Biological mechanisms underlying inter-individual variation in factor VIII clearance in haemophilia

Previous studies have highlighted marked inter-individual variations in factor VIII (FVIII) clearance between patients with haemophilia (PWH). The half-life of infused FVIII has been reported to vary from as little as 5.3 hours in some adult PWH, up to as long as 28.8 hours in other individuals. These differences in clearance kinetics have been consistently observed using a number of different plasma-derived and recombinant FVIII products. Furthermore, recent studies have demonstrated that half-life for extended half-life (EHL-) FVIII products also demonstrates significant inter-patient variation. Since time spent with FVIII trough levels <1% has been shown to be associated with increased bleeding risk in PWH on prophylaxis therapy, this variability in FVIII clearance clearly has major clinical significance. Recent studies have provided significant novel insights into the cellular basis underlying FVIII clearance pathways. In addition, accumulating data have shown that endogenous plasma VWF levels, ABO blood group and age, all play important roles in regulating FVIII half-life in PWH. Indeed, multiple regression analysis suggests that together these factors account for approximately 34% of the total inter-individual variation in FVIII clearance observed between subjects with severe haemophilia A. In this review, we consider these and other putative modulators of FVIII half-life, and discuss the biological mechanisms through which these factors impact upon FVIII clearance in vivo

Pain and functional disability amongst adults with moderate and severe haemophilia from the Irish personalised approach to the treatment of haemophilia (iPATH) study

ObjectivesTo establish the prevalence of pain and functional disability in Irish adults with moderate and severe haemophilia, and to examine demographic and lifestyle influences.MethodsMales ≥18 years with moderate or severe haemophilia participated. Pain and function were examined using the PROBE questionnaire.ResultsOf 49 participants [median age 44 (IQR 32, 52) years], most had severe haemophilia (Factor VIII = 30; Factor IX = 13) and were on regular prophylaxis (88%). Those with moderate haemophilia (Factor VIII = 5; Factor IX = 1) treated on demand (12%). Acute (72%) and chronic pain (71%), functional difficulties (58%), and analgesic requirements (92%) were prevalent. Age was significantly associated with more advanced haemophilic arthropathy (p = .002), chronic pain (p = .029) and functional difficulties (p = .036). Adults who reported chronic pain commenced prophylaxis significantly later in life [32 (20, 51) vs. 8 (1, 23) years; p = .004]. Physical activity was significantly lower in those with functional difficulties (p < .05). A disparity between self-perceived ‘target joints’ and clinically defined target joints was also identified (76% vs. 23%).ConclusionHaemophilic arthropathy, pain and functional disability were prevalent amongst Irish adults with moderate and severe haemophilia. Age-dependent lifestyle, analgesic and treatment influences on pain and function warrant further investigation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/172836/1/ejh13763.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/172836/2/ejh13763_am.pd

Macrophage galactose lectin contributes to the regulation of FVIII (Factor VIII) clearance in mice - brief report

Background: Although most plasma FVIII (Factor VIII) circulates in complex with VWF (von Willebrand factor), a minority (3%-5%) circulates as free-FVIII, which is rapidly cleared. Consequently, 20% of total FVIII may be cleared as free-FVIII. Critically, the mechanisms of free-FVIII clearance remain poorly understood. However, recent studies have implicated the MGL (macrophage galactose lectin) in modulating VWF clearance. Methods: Since VWF and FVIII share similar glycosylation, we investigated the role of MGL in FVIII clearance. FVIII binding to MGL was assessed in immunosorbent and cell-based assays. In vivo, FVIII clearance was assessed in MGL1-/- and VWF-/-/FVIII-/- mice. Results: In vitro-binding studies identified MGL as a novel macrophage receptor that binds free-FVIII in a glycan-dependent manner. MGL1-/- and MGL1-/- mice who received an anti-MGL1/2 blocking antibody both showed significantly increased endogenous FVIII activity compared with wild-type mice (P=0.036 and PFVIII-/- mice. To assess whether MGL plays a role in the clearance of free FVIII in a VWF-independent manner, in vivo clearance experiments were repeated in dual VWF-/-/FVIII-/- mice. Importantly, the rapid clearance of free FVIII in VWF-/-/FVIII-/- mice was significantly (P=0.012) prolonged in the presence of anti-MGL1/2 antibodies. Finally, endogenous plasma FVIII levels in VWF-/- mice were significantly increased following MGL inhibition (P=0.016). Conclusions: Cumulatively, these findings demonstrate that MGL plays an important role in regulating macrophage-mediated clearance of both VWF-bound FVIII and free-FVIII in vivo. We propose that this novel FVIII clearance pathway may be of particular clinical importance in patients with type 2N or type 3 Von Willebrand disease.</p