Active von Willebrand Factor in patients with a bleeding diathesis

Introduction: Increased levels of circulating von Willebrand Factor (VWF) in its active, platelet-binding conformation have been implicated in the pathogenesis of several thrombotic conditions as well as bleeding conditions characterized by severe thrombocytopenia. However, it is unclear whether the proportion of activated VWF in the circulation also plays a role in patients with mild to moderate bleeding without thrombocytopenia. Methods: Citrated plasma samples were collected from 145 patients with a bleeding diathesis with unknown cause. Active VWF levels were measured with an in-house developed ELISA assay. In addition, VWF antigen (VWF:Ag), VWF ristocetin cofactor activity (VWF:RCo) and (flow-cytometric) platelet-VWF binding (Plt:VWF) were determined. Results: Active VWF levels were on average mildly, but not significantly, lowered in patients with a bleeding diathesis compared to the reference interval (especially in individuals with non-O blood groups). Active VWF was not significantly different for subjects with (median 107.4%, IQR 18.3) versus without (median 111.1%, IQR 32.3%) an increased bleeding score, nor between subjects with suspected VWD (median 104%, IQR 20.6%) versus other suspected causes of bleeding diathesis (median 111.7%, IQR 33.3%). Conclusion: In this clinically heterogeneous population of patients with a mild bleeding phenotype, quantification of active VWF levels does not have added diagnostic value to VWF:Ag and VWF activity assays in the diagnosis of unexplained bleeding disorders

Mutation in human CLPX elevates levels of δ-aminolevulinate synthase and protoporphyrin IX to promote erythropoietic protoporphyria

Loss-of-function mutations in genes for heme biosynthetic enzymes can give rise to congenital porphyrias, eight forms of which have been described. The genetic penetrance of the porphyrias is clinically variable, underscoring the role of additional causative, contributing, and modifier genes. We previously discovered that the mitochondrial AAA+ unfoldase ClpX promotes heme biosynthesis by activation of δ-aminolevulinate synthase (ALAS), which catalyzes the first step of heme synthesis. CLPX has also been reported to mediate heme-induced turnover of ALAS. Here we report a dominant mutation in the ATPase active site of human CLPX, p.Gly298Asp, that results in pathological accumulation of the heme biosynthesis intermediate protoporphyrin IX (PPIX). Amassing of PPIX in erythroid cells promotes erythropoietic protoporphyria (EPP) in the affected family. The mutation in CLPX inactivates its ATPase activity, resulting in coassembly of mutant and WT protomers to form an enzyme with reduced activity. The presence of low-activity CLPX increases the posttranslational stability of ALAS, causing increased ALAS protein and ALA levels, leading to abnormal accumulation of PPIX. Our results thus identify an additional molecular mechanism underlying the development of EPP and further our understanding of the multiple mechanisms by which CLPX controls heme metabolism. Keywords: heme biosynthesis; porphyria; ALAS; protein unfoldases; AAA+ ATPaseNational Institutes of Health (U.S.) (Grant F32 DK095726)National Institutes of Health (U.S.) (Grant R01 GM049224

25-OH Vitamin D concentrations measured by LC-MS/MS are equivalent in serum and EDTA plasma.

peer reviewedIn contrast to a recent study reporting an unexpected significant difference for total 25-hydroxyvitamin D (25(OH)D) between serum and EDTA plasma, we demonstrate that concentrations of total 25(OH)D, 25(OH)D2, 25(OH)D3 and 24,25(OH)2D3 do not differ between matched serum and EDTA plasma samples, using two well-characterized LC-MS/MS methods

25-OH Vitamin D concentrations measured by LC-MS/MS are equivalent in serum and EDTA plasma

In contrast to a recent study reporting an unexpected significant difference for total 25-hydroxyvitamin D (25(OH)D) between serum and EDTA plasma, we demonstrate that concentrations of total 25(OH)D, 25(OH)D2, 25(OH)D3 and 24,25(OH)2D3 do not differ between matched serum and EDTA plasma samples, using two well-characterized LC-MS/MS methods

Analytical characterization and reference interval of an enzyme-linked immunosorbent assay for active von Willebrand factor.

BackgroundInteraction of von Willebrand factor (VWF) with platelets requires a conformational change that exposes an epitope within the VWF A1 domain, enabling platelet glycoprotein Ibα binding. Quantification of this ''active" conformation of VWF has been shown to provide pathophysiological insight into conditions characterized by excessive VWF-platelet interaction.MethodsWe developed an immunosorbent assay based on a variable heavy chain antibody fragment against the VWF A1 domain as a capture antibody. Assay performance in terms of specificity (binding to active R1306W- and sheared VWF), precision, accuracy, linearity, limits of detection and stability were determined. Active VWF, VWF antigen, VWF ristocetin cofactor activity, VWF:GP1bM and VWF propeptide were measured in citrated plasma and platelet-VWF binding in whole blood from 120 healthy individuals to establish a reference interval for active VWF and to assess associations with other VWF parameters.ResultsIntra- and inter-assay CVs were between 2.4-7.2% and 4.1-9.4%, depending on the level. Mean recovery of spiked recombinant R1306W VWF was 103±3%. The assay was linear in the range of 90.1-424.5% and had a limit of quantification of 101%. The reference interval for active VWF was 91.6-154.8% of NPP. Significant, positive correlations between active VWF and all other VWF parameters were found, with the strongest correlation with VWF:GP1bM binding.ConclusionsWe developed and validated an immunosorbent assay for the accurate detection of active VWF levels in plasma. The assay fulfilled all analytical criteria in this study and a reference interval was established, allowing its use to quantify active VWF in pathological conditions for future research