Irradiated endothelial cells promote platelet aggregates at high wall shear rate

Abstract number: P0163

Gaugler M. H., Vereycken-Holler V., Aigueperse J.

Institut de Radioprotection et de Sureté Nucléaire, France

The purpose of this study was to investigate the interactions of platelets with endothelial cells (EC) activated by irradiation. These interactions were studied in a parallel plate flow chamber at different wall shear rates simulating physiological shear flow. Confluent monolayers of human microvascular endothelial cell-lung (HMVEC-L) irradiated at 10 Gy or not (137 Cs source, 0.7 Gy min^-1) were placed in the flow chamber 7, 14 or 21 days after irradiation. Fluorescently labeled whole blood was perfused over EC at wall shear rates of 25, 75 and 500 s^-1 corresponding to those observed in the microvessels which are the most sensitive to ionizing radiation. Adhesion of single platelets and platelet aggregates was quantified by image analysis coupled to real-time videomicroscopy and expressed as the surface covered by those platelets. Whatever the wall shear rate and the time after irradiation, irradiated EC promoted platelet adhesion to a greater extent than nonirradiated EC. A about 2-fold increase in the surface covered with platelets (single + aggregates) was observed after irradiation. However, the surface covered with platelets augmented with increasing wall shear rates. Seven days after irradiation and at wall shear rate of 25 s^-1 , this surface was 2460 ± 96 µm²/field (nonirradiated EC) and 3563 ± 148 µm² per field (irradiated EC) as compared to 4088 ± 436 µm² per field (nonirradiated EC) and 8114 ± 859 µm² per field (irradiated EC) at wall shear rate of 500 s^-1 0. This increase in the surface covered with platelets at high shear rate is more pronounced on irradiated EC as compared to nonirradiated EC and involved mostly platelet aggregates. In fact, 7 days after irradiation and at wall shear rate of 25 s^-1, the surface occupied with platelet aggregates represented 28% (nonirradiated EC) and 26% (irradiated EC) of the total surface (single + aggregates). At wall shear rate of 500 s^-1, this surface corresponded to 64% (nonirradiated EC) and 86% (irradiated EC) of the total surface. In conclusion, this study shows that irradiation induced a sustain increase in the prothrombotic properties of EC. Such maintenance could contribute to microvascular occlusion, which is a common deleterious late effect of radiation.