Subunit composition of plasma von Willebrand factor in patients with the myeloproliferative syndrome

Abstract

In order to evaluate the role of proteolysis in acquired von Willebrand's disease (vWD) associated with the myeloproliferative syndrome, we have determined the relative quantity of von Willebrand factor (vWF) fragments as compared with the intact 225 kDa subunit in four patients. The plasma vWF of each individual lacked large multimers; each had a prolonged bleeding time; and both platelet and leukocyte counts were elevated. Plasma was obtained from blood drawn into 1 mmol/L leupeptin, 6 mmol/L N-ethylmaleimide, and 5 mmol/L EDTA to prevent in vitro proteolysis. vWF was isolated from plasma by immunoadsorbent chromatography, reduced, subjected to SDS-5% polyacrylamide gel electrophoresis, and immunoblotted with a mixture of 55 anti-vWF monoclonal antibodies. In three patients with essential thrombocytosis (ET) the 176 and 140 kDa fragments were increased in proportion to the intact 225 kDa subunit indicating increased proteolysis. Treatment of one ET patient with CCNU (Lomustine) decreased the platelet count and, to a lesser extent, the white blood cell count. This was associated with a correction of the bleeding time, a partial correction of the multimeric abnormality, and a lessening of vWF cleavage. In a patient with polycythemia rubra vera (PRV) the proportion of the 176 kDa fragment was increased to the upper limit of normal but there was no definite evidence of increased proteolysis. These studies provide evidence that proteolysis plays a role in the acquired von Willebrand's disease associated with the myeloproliferative syndrome. However, other mechanisms must also be considered.

Decreased half‐life time of plasma von Willebrand factor collagen binding activity in essential thrombocythaemia: normalization after cytoreduction of the increased platelet count

“…Interestingly, increased amounts of proteolytic fragments of VWF have been found in vivo in patients with reactive thrombocytosis, as well as in patients with essential thrombocythaemia (Budde et al, 1986(Budde et al, , 1993Lopez-Fernandez et al, 1987). In the latter group of patients, cytoreduction of the increased platelet count resulted in an abatement of proteolysis of VWF.…”

Multimeric composition of plasma von Willebrand factor in chronic myeloproliferative disorders

“…Recent studies have indicated that platelet calcium-activated protease and neutral proteases of polymorphonuclear leucocytes can degrade the vWf molecule in vitro (Kopec et al 1980;Kunicki, Montgomery & Shulleck 1985;Thompson & Howard 1986). More recently, it has been shown that vWf fragmentation occurs due to in-vivo proteolysis in the patients with CMPD (Budde et al 1986;Lopez-Fernandez et al 1987), and that abnormal vWf structure was not corrected even if blood was obtained in the presence of protease inhibitors (Lopez-Fernandez et al 1987). It is important to determine whether or not these vWf abnormalities are present in each patient with CMPD, because when bleeding episodes occur, the administration of cryoprecipitate or desmopressin (DDAVP) may be effective, as demonstrated in several patients with acquired vWf abnormalities (Budde et al 1984;Mannucci et al 1984;Takahashi et al 1986b).…”

Abnormalities of platelet aggregation in chronic myeloproliferative disorders

“…The causes of these abnormalities may include: 1. defects in arachidonic acid metabolism (decrease in agonist-induced release of arachidonic acid from membrane phospholipids; reduced conversion of arachidonic acid to prostaglandine endoperoxides or lipoxygenase products; reduced platelet responsiveness to tromboxane A 2 ) [9][10][11]; 2. abnormalities of platelet granules (increased platelet alpha-granule secretion and an aquired storage pool defect of dense granules) [3,12,13]; 3. decreased number of á 2 -adrenergic receptors, abnormalities of specific platelet membrane glycoproteins (GP) such as GPIIb/IIIa, GP Ib/IX or increased number of GPIV molecules and receptors for the Fc component of IgG [3,[14][15][16]]. An aquired von Willebrand disease [17,18], a reduction of platelet procoagulant activity and an aquired form of Bernard-Soulier syndrome were also reported in these disorders [19].…”