Summary
Purpose. Thermal angioplasty alters the thrombogenicity of the arterial wall. In previous studies, platelet adhesion was found to increase after heating human subendothelium to 55° C and decrease after heating to 90° 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.
Methods. Purified vWF and/or collagen was applied to electron microscopic grids and heated by floating on a salt-solution of 37° C, 55° C or 90° 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.
Results. At 37° C, vWF was coiled. At 55° C, vWF unfolded, whereas heating at 90° C caused a reduction in antigenicity. Collagen fibers heated to 37° C were 60.3 ± 3.1 nm wide. Heating to 55° C resulted in the unwinding of the fibers, increasing the width to 87.5 ± 8.2 nm (p < 0.01). Heating to 90° C resulted in denatured fibers with an enlarged width of 85.1 ± 6.1 nm (p < 0.05). Heating of collagen to 55° C resulted in an increased vWF binding as compared to collagen heated to 37° C or to 90° C. Incubation of collagen with vWF, prior to heating, resulted in a vWF binding after heating to 55° C that was similar to the 37° C binding and a decreased binding after 90° C.
Conclusions. After 55° 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° 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° C and 90° C heating, respectively.