Abnormal degradation of von Willebrand factor main subunit in pulmonary hypertension

We wished to investigate whether the abnormalities in multimeric structure and biological function of von Willebrand factor (vWF) observed in pulmonary hypertensive patients could be related to increased proteolytic degradation. We therefore analysed plasma vWF subunit composition in 24 pulmonary hypertensive patients, aged 1.2-45 yrs. After immunoisolation, vWF was subjected to 5.5% sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) followed by Western immunoblotting, vWF intact subunit (225 kDa) and four proteolytic fragments (189, 176, 150 and 140 kDa) were visualized by peroxidase staining and analysed in a laser densitometer. In pulmonary hypertensive patients, the relative density of the intact subunit was decreased, and this was associated with an increase in the 176 kDa proteolytic fragment. The mean densities of the other fragments were not significantly changed, but in some patients the 150 and 140 kDa polypeptides were markedly increased. Abnormalities in multimeric structure of vWF (loss of high molecular weight multimers and increase in low molecular weight forms in comparison with controls), were associated with a significant decrease in biological activity (62-92% activity, 95% confidence interval (CI) for the mean). Total proteolytic fragment density correlated positively with multimeric abnormalities (rs = 0.45), and negatively with biological activity of vWF (rs = -0.49). Thus, in pulmonary hypertension, multimeric abnormalities and decreased biological activity are related to proteolytic degradation of vWF main subunit, possibly reflecting extensive endothelial dysfunction.