Summary

Ebselen, a seleno-organic compound showing glutathione peroxidase-like activity, has potent anti-inflammatory and anti-oxidanteffects. Since selenium deficiency is thought to be associatedwith an increased incidence of vascular thrombosis, we studiedthe effect of ebselen on blood cell aggregate formation andvessel occlusion in vivo. In individual microvessels of rat cremastermuscle preparations, photochemically induced thrombusformation was analyzed in detail using intravital fluorescencemicroscopy. In ebselen-pretreated animals (30mg/kg ip), venularthrombus formation was significantly delayed (50% vesselocclusion: 535±34s; initial stasis: 872±82s; complete occlusion:908±87s) as compared to vehicle-treated controls (416±42;612±49; 647±51). Moreover, ebselen significantly prolonged thekinetics of arteriolar thrombus formation and even completelyprevented blood cell aggregate and thrombus formation in88.9% of all arterioles studied (p<0.05 vs controls: 37.5%). Antithromboticproperties of ebselen could also be observed in amodel of ferric chloride-induced microvascular thrombosis,with a low dose (5mg/kg ip) being as effective as a high dosepretreatment (30mg/kg ip). As assessed by flow cytometry ofplatelet P-selectin immunfluorescence, whole blood isolatedfrom ebselen-treated animals revealed a significantly lower fractionof P-selectin expressing platelets when compared with thatof DMSO-treated controls. In addition, oxidant stress-inducedupregulation of P-selectin on isolated platelets was found dose-dependentlyinhibited by increasing concentrations of ebselen(10-100µM). Moreover, ebselen dose-dependently inhibitedH₂O₂ -induced platelet-leukocyte aggregate formation in wholeblood in vitro, suggesting that the anti-thrombotic effect of ebselenis achieved by attenuation of P-selectin dependent platelet-leukocyteaggregation.Thus, ebselen represents preventive andtherapeutic value for disorders with increased risk for oxidantstress-associated thrombotic events.