Interventional Thermal Injury of the Arterial Wall: Unfolding of von Willebrand Factor and Its Increased Binding to Collagen after 55° C Heating

Abstract

Thermal angioplasty alters the thrombogenicity of the arterial wall. In previous studies, platelet adhesion was found to increase after heating human subendothelium to 55 degrees C and decrease after heating to 90 degrees C. In the present electron microscopic study, the mechanism of this temperature-dependent platelet adhesion to the heated arterial wall is elucidated by investigating temperature-dependent conformational changes of von Willebrand factor (vWF) and collagen types I and III and the binding of vWF to heated collagen. Purified vWF and/or collagen was applied to electron microscopic grids and heated by floating on a salt-solution of 37 degrees C, 55 degrees C or 90 degrees C for 15 s. After incubation with a polyclonal antibody against vWF and incubation with protein A/gold, the grids were examined by electron microscopy. At 37 degrees C, vWF was coiled. At 55 degrees C, vWF unfolded, whereas heating at 90 degrees C caused a reduction in antigenicity. Collagen fibers heated to 37 degrees C were 60.3 +/- 3.1 nm wide. Heating to 55 degrees C resulted in the unwinding of the fibers, increasing the width to 87.5 +/- 8.2 nm (p < 0.01). Heating to 90 degrees C resulted in denatured fibers with an enlarged width of 85.1 +/- 6.1 nm (p < 0.05). Heating of collagen to 55 degrees C resulted in an increased vWF binding as compared to collagen heated to 37 degrees C or to 90 degrees C. Incubation of collagen with vWF, prior to heating, resulted in a vWF binding after heating to 55 degrees C that was similar to the 37 degrees C binding and a decreased binding after 90 degrees C. After 55 degrees C heating, the von Willebrand factor molecule unfolds and collagen types I and III exhibit an increased adhesiveness for von Willebrand factor. Heating to 90 degrees C denatures von Willebrand factor and collagen. The conformation changes of von Willebrand factor and its altered binding to collagen type I and III may explain the increased and decreased platelet adhesion to subendothelium after 55 degrees C and 90 degrees C heating, respectively.