Are increased levels of von Willebrand factor in chronic coronary heart disease caused by decrease in von Willebrand factor cleaving protease activity? A study by an immunoassay with antibody against intact bond 842Tyr-843Met of the von Willebrand factor protein

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 thrombcytopeni c 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 (C HID) relate to a deficiency of this protease. Plasma samples with added Pef abloc and CaCl2 were incubated with purified VWF coated on a microtiter pla te. The remaining undigested multimers were quantified by an antibody direc ted against the intact 842Tyr-843Met bond of the VWF protein. Phosphate-buf fered saline (PBS), instead of plasma, was used to obtain the initial level of coated undigested VWF. The reduction in absorbance at 492 run between P BS 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 C HID (cases) and 34 age-matched controls, as well as to samples from three p atients with VWD 2A. The protease activity was similar in the two women gro ups (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 th at in normal pooled plasma (NPP). In the senior controls, the protease acti vity correlated with the subject age (r's = -.61, P < .01, n = 34). In conc lusion, the developed method is specific for evaluating the protease functi on 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 lev els supports earlier findings of higher VWF levels in healthy older subject s. 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 in volved in the pathogenesis of VWD 2A. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.