BOTH INCREASED AND DECREASED PLATELET-ADHESION TO THERMALLY INJURED SUBENDOTHELIUM IS CAUSED BY DENATURATION OF VON-WILLEBRAND-FACTOR

Background. Thermal angioplasty methods heat the arterial wall. We related platelet adhesion to the temperature to which subendothelium and purified adhesive proteins had been exposed. Methods and Results. Cultured subendothelium, purified von Willebrand factor, collagen types I and III, or fibronectin was applied to glass coverslips. Coverslips were mounted on a heating device that applied a temperature gradient from 30 to 100-degrees-C. De-endothelialized umbilical arteries were heated by immersion in phosphate-buffered saline. After cooling to room temperature, the surfaces were perfused with blood at 37-degrees-C (shear rate, 1600 sec-1). Compared with 37-degrees-C, platelet adhesion to endothelial cell matrix was significantly reduced by 25%, 50%, or 75% after heating to 69+/-1-degrees-C (mean+/-SEM, P<.05), 72+/-1-degrees-C, or 75+/-1-degrees-C, respectively. Platelet coverage to umbilical artery subendothelium was in the same way significantly reduced after heating to 71+/-1-degrees-C, 74+/-1-degrees-C, or 77+/-1-degrees-C, respectively. In contrast to endothelial cell matrix, however, heating to about 55-degrees-C increased platelet coverage from 30+/-5% to 54+/-6% (P<.05). Both platelet adhesion to von Willebrand factor and monoclonal antibody binding against the GpIb binding site of von Willebrand factor showed a comparable temperature dependence as platelet adhesion to subendothelium, provided the proper von Willebrand factor concentration was used. Platelet adhesion to heated collagen types I and III was increased and maximal at 57+/-2-degrees-C and 62+/-2-degrees-C, respectively. Preincubation of collagen III with proteins resulted in decreased platelet adhesion with increasing temperatures. Heating did not affect the reactivity of fibronectin. Conclusions. In vitro platelet adhesion to human subendothelium is reduced by more than 50% after heating it briefly to more than 74-degrees-C. Temperatures in excess of 80-degrees-C reduce platelet adhesion by at least 85%. Thermal denaturation of von Willebrand factor is responsible not only for the decreased thrombogenicity above 71-degrees-C but also for the increased thrombogenicity near 55-degrees-C, provided that the von Willebrand factor concentration is low.