Are Increased Levels of von Willebrand Factor in Chronic Coronary Heart Disease Caused by Decrease in von Willebrand Factor Cleaving Protease Activity?

Low levels of von Willebrand factor (VWF) in von Willebrand's disease type 2A (VWD 2A) result from increased cleavage of the bond 842Tyr–843Met in the VWF protein by VWF cleaving protease. On the other hand, decreased levels of this protease result in unusually large VWF in thrombotic thrombcytopenic purpura with thrombotic complications. In the present study, we designed an enzyme-liked immunosorbent assay of VWF cleaving protease activity to be used to assess whether the high levels of VWF in coronary heart disease (CHD) relate to a deficiency of this protease. Plasma samples with added Pefabloc and CaCl2 were incubated with purified VWF coated on a microtiter plate. The remaining undigested multimers were quantified by an antibody directed against the intact 842Tyr–843Met bond of the VWF protein. Phosphate-buffered saline (PBS), instead of plasma, was used to obtain the initial level of coated undigested VWF. The reduction in absorbance at 492 nm between PBS and the unknown sample was taken as a measure of the protease activity. The assay was applied to plasma samples from 21 senior women with chronic CHD (cases) and 34 age-matched controls, as well as to samples from three patients with VWD 2A. The protease activity was similar in the two women groups (P>.05), although the VWF antigen levels were higher in the cases (P<.01). The VWD 2A patients had similar plasma levels of the protease to that in normal pooled plasma (NPP). In the senior controls, the protease activity correlated with the subject age (r's=−.61, P<.01, n=34). In conclusion, the developed method is specific for evaluating the protease function on VWF cleavage. The moderate increase of VWF antigen in chronic CHD may not depend on the protease activity. The age influence on the protease levels supports earlier findings of higher VWF levels in healthy older subjects. A high sensitivity of the mutated protein of VWF for the protease effect rather than increases in activity or quantity of the enzyme is probably involved in the pathogenesis of VWD 2A.