Abstract 5451: Deficiency of Glutathione Peroxidase-3 Promotes Platelet Activation in vivo
Plasma glutathione peroxidase (GPx-3) is a selenocysteine-containing protein with antioxidant properties. GPx-3 plays an important role in plasma against oxidant stress by scavenging reactive oxygen species. A deficiency of this enzyme has been associated with platelet dependent thrombosis. We recently developed an animal model to assess platelet function in GPx-3 deficient mice. We hypothesized that GPx-3 deficiency induces platelet activation in vivo. GPx-3 (−/−) mice showed an attenuated bleeding time compared with wild-type mice (94.5 ± 28.8 s versus 153.4 ± 32.3, P<0.05). We also noted an increase in the plasma levels of soluble P-selectin, a marker of platelet activation and prothrombotic activity, in GPx-3 (−/−) mice compared with wild-type mice (137.8 ± 12.3 ng/ml plasma versus 101.5 ± 8.8, P<0.05). Cyclic GMP, a key intracellular second messenger molecule and marker for activation of soluble guanylyl cyclase by nitric oxide, was decreased in the plasma of GPx-3 (−/−) mice compared with wild-type mice (5.38 ± 1.75 pmol/ml plasma versus 23.67 ± 3.59, P<0.001), consistent with less bioactive NO in GPx-3 (−/−) mice. ADP was infused into the right ventricle of mice to induce platelet aggregation in the pulmonary vasculature; this assay resulted in higher pulmonary artery pressure in GPx-3 (−/−) compared with wild-type mice suggesting a more robust platelet activation response in the GPx-3 (−/−) mice. To confirm this interpretation, histological sections from the pulmonary vasculature of GPx-3 (−/−) compared with wild-type mice showed increased thrombi per 7.5 mm2 section normalized to wild-type mice based on staining intensity for P-selectin (1.7 ± 0.4 versus 1.0 ± 0.1, P<0.001), as well as a higher percentage of occluded vessels (0.82 ± 0.16 % versus 0.54 ± 0.21, P<0.05). These findings demonstrate that GPx-3 deficiency causes platelet activation resulting in a prothrombotic state. These data illustrate the importance of this plasma antioxidant enzyme in regulating platelet activity and platelet-dependent thrombosis.