Utility of Platelet Endothelial Cell Adhesion Molecule 1 in the Platelet Activity Assessment in Mouse and Human Blood.

In our previous study, we introduced the platelet endothelial cell adhesion molecule 1 (PECAM-1)/thrombus ratio, which is a parameter indicating the proportion of PECAM-1 in laser-induced thrombi in mice. Because PECAM-1 is an antithrombotic molecule, the higher the PECAM-1/thrombus ratio, the less activated the platelets. In this study, we used an extracorporeal model of thrombosis (flow chamber model) to verify its usefulness in the assessment of the PECAM-1/thrombus ratio in animal and human studies. Using the lipopolysaccharide (LPS)-induced inflammation model, we also evaluated whether the PECAM-1/thrombus ratio determined in the flow chamber (without endothelium) differed from that calculated in laser-induced thrombosis (with endothelium). We observed that acetylsalicylic acid (ASA) decreased the area of the thrombus while increasing the PECAM-1/thrombus ratio in healthy mice and humans in a dose-dependent manner. In LPS-treated mice, the PECAM-1/thrombus ratio decreased as the dose of ASA increased in both thrombosis models, but the direction of change in the thrombus area was inconsistent. Our study demonstrates that the PECAM-1/thrombus ratio can more accurately describe the platelet activation status than commonly used parameters such as the thrombus area, and, hence, it can be used in both human and animal studies.

New approaches for the assessment of platelet activation status in thrombus under flow condition using confocal microscopy.

The goal of the study was the assessment of heterogeneous platelet activation status in thrombus. In a ferric(III) chloride (FeCl3) thrombosis (intravital) model of C57BL/6 J mice, the area of irreversibly activated (phosphatidylserine (PS)-positive) platelets was assessed after 1-s exposure of a vessel to FeCl3. In a laser-induced thrombosis (intravital) model of GFP mice, the area of the thrombus composed of PS-negative platelets was evaluated. The ratio of the area of PECAM-1 to the area of the thrombus was used as a marker to assess the activity of PS-negative platelets. In the in vitro flow chamber model, the thrombus area (PS-negative and PS-positive platelets) and the platelet activation index (ratio of the area of PS-positive platelets to the area of thrombus) were determined. To assess platelet activation status with these models, acetylsalicylic acid (ASA) and iloprost (Ilo) were used. In the FeCl3 thrombosis, ASA (10 mg/kg, 100 mg/kg) decreased the area of PS-positive platelets. In the laser thrombosis, ASA (10 mg/kg) decreased the thrombus area, but the decrease in platelet activity was evident even at 3 mg/kg by an increased PECAM-1/thrombus ratio. In the flow chamber, ASA (0.02 mg/ml, 0.2 mg/ml) equally decreased the platelet activation index, whereas only at 0.2 mg/ml, it decreased the thrombus area. Ilo (3.6 ng/ml, 36 ng/ml) decreased the thrombus area but at 36 ng/ml increased the platelet activation index. We showed that intravital models and flow chamber provide a detailed assessment of platelet activation status and the mechanism of drug action.