INTERVENTIONAL THERMAL-INJURY OF THE ARTERIAL-WALL - UNFOLDING OF VON-WILLEBRAND-FACTOR AND ITS INCREASED BINDING TO COLLAGEN AFTER 55-DEGREES-C HEATING

Purpose. Thermal angioplasty alters the thrombogenicity of the arteria l wall. In previous studies, platelet adhesion was found to increase a fter heating human subendothelium to 55 degrees C and decrease after h eating to 90 degrees C. In the present electron microscopic study, the mechanism of this temperature-dependent platelet adhesion to the heat ed arterial wall is elucidated by investigating temperature-dependent conformational changes of von Willebrand factor (vWF) and collagen typ es I and III and the binding of VWF to heated collagen. Methods. Purif ied 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 ag ainst VWF and incubation with protein A/gold, the grids were examined by electron microscopy. Results. At 37 degrees C, VWF was coiled. At 5 5 degrees C, VWF unfolded, whereas heating at 90 degrees C caused a re duction in antigenicity. Collagen fibers healed to 37 degrees C were 6 0.3 +/- 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). Hea ting to 90 degrees C resulted in denatured fibers with an enlarged wid th of 85.1 +/- 6.1 nm (p< 0.05). Heating of collagen to 55 degrees C r esulted in an increased VWF binding as compared to collagen heated to 37 degrees C or to 90 degrees C. Incubation of collagen with VWF, prio r 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 a fter 90 degrees C. Conclusions. After 55 degrees C heating, the von Wi llebrand factor molecule unfolds and collagen types I and III exhibit an increased adhesiveness for von Willebrand factor. Heating to 90 deg rees C denatures von Willebrand factor and collagen. The conformation changes of von Willebrand factor and its altered binding to collagen t ype I and III may explain the increased and decreased platelet adhesio n to subendothelium after 55 degrees C and 90 degrees C heating, respe ctively.