Deficient Activity of von Willebrand Factor–Cleaving Protease in Chronic Relapsing Thrombotic Thrombocytopenic Purpura

Abstract

In patients with thrombotic thrombocytopenic purpura (TTP), excessive intravascular platelet aggregation has been associated with appearance in plasma of unusually large von Willebrand factor (vWF ) multimers. These extremely adhesive vWF multimers may arise due to deficiency of a “depolymerase” cleaving vWF to smaller molecular forms, either by reducing the interdimeric disulfide bridges or by proteolytic degradation. We studied the activity of a recently described vWF-cleaving protease in four patients with chronic relapsing TTP. Diluted plasma samples of TTP patients were incubated with purified normal human vWF in the presence of a serine protease inhibitor, at low ionic strength, and in the presence of urea and barium ions. The extent of vWF degradation was assayed by electrophoresis in sodium dodecyl sulfate-agarose gels and immunoblotting. Four patients, that included two brothers, with chronic relapsing TTP displayed either substantially reduced levels or a complete absence of vWF-cleaving protease activity. In none of these patient plasmas was an inhibitor of or an antibody against the vWF-cleaving protease established. Our data suggest that the unusually large vWF multimers found in TTP patients may be caused by deficient vWF-cleaving protease activity. Deficiency of this protease may be inherited in an autosomal recessive manner and seems to predispose to chronic relapsing TTP. The assay of the vWF-cleaving protease activity may be used as a sensitive diagnostic tool for identification of subjects with a latent TTP tendency.

Prolonged inhibition of von Willebrand factor‐cleaving protease after splenectomy in a 22‐year‐old patient with acute and plasma refractory thrombotic thrombocytopenic purpura

“…Persistent protease deficiency also resulted in the transient appearance of UL-VWF multimers in the PP (Fig 2A) as reflected by increased ratios of VWF:CBA/VWF:Ag on d 131, 180 and 269 ( Fig 1A). Whereas Furlan et al (1997) concluded that the ratio of VWF ristocetin cofactor activity to VWF:Ag was apparently not a reliable parameter for documenting the presence of UL-VWF multimers, we suggest that calculation of the VWF:CBA/VWF:Ag ratio may be more suitable for this purpose. Disappearance of the inhibitor and slight protease recovery (10%) were first detectable as late as 9 months after splenectomy ( Fig 1A).…”

Microangiopathic haemolytic anaemia in metastasizing malignant tumours is not associated with a severe deficiency of the von Willebrand factor‐cleaving protease

“…Laboratory tests were performed on blood samples taken during the first days of hospitalization and are reported in Table I and Fig 1. Haemoglobin, platelet count, reticulocyte count, LDH and bilirubin were assayed using routine methods. VWF ristocetin co-factor activity (VWF:Rcof), VWF antigen (VWF:Ag), VWF multimer analysis, immunoblotting and collagen binding assays of VWF-cp activity were performed on citrated plasma samples as previously described (Furlan et al, 1997;Gerritsen et al, 1999).…”

“…Haemolytic± uraemic syndrome (HUS) is a clinically similar disease in which renal dysfunction predominates. Severe deficiency of von Willebrand Factor-cleaving protease (VWF-cp), resulting in the presence of very adhesive unusually large VWF multimers in plasma has been consistently found in patients with TTP, whereas VWF-cp was normal in patients diagnosed with HUS (Furlan et al, 1997;Furlan et al, 1998a, b;Tsai & Lian, 1998). Oleksowicz et al (1999) reported VWF-cp deficiency (< 15%) in patients with metastasizing malignancies, whereas in patients with localized tumours VWF-cp activity was found to be normal (> 88%).…”

Thrombotic thrombocytopenic purpura after allogeneic stem cell transplantation: a survey of the European Group for Blood and Marrow Transplantation (EBMT)

“…A large number of abnormalities in blood parameters and endothelial function have been reported in TTP, but their role in the pathogenesis has remained unclear (Pettitt & Clark, 1994;Moake, 1997;Schriber & Herzig, 1997;Sniecinski & O'Donnell, 1998;Wright et al, 1999;Rock, 2000). Progress has been recently made in the understanding of the pathogenesis of de novo TTP with the demonstration of deficient von Willebrand factor-cleaving protease activity, which may be inherited or caused by an antibody (Furlan et al, 1997;Cines et al, 2000). Such an enzyme defect does not seem to have a role in stem cell transplantation-associated TTP (van der Plas et al, 1999) and endothelial injury is likely to be the primary event (Cohen et al, 1989;Holler et al, 1989;Sarode et al, 1995;Schriber & Herzig, 1997).…”