Platelet Activation: Association with NADPH Oxidase Expression and Reactive Oxygen Species Generation in High-Shear Environments

Abstract

Thromboembolic complications remain a major cause of morbidity and mortality among patients with mechanical circulatory support devices for heart failure. Mechanical circulatory support devices, including ventricular assist devices (VADs), artificial hearts, and other cardiovascular therapeutic devices, produce significant intravascular shear which leads to turbulent blood flow and enhanced thrombotic activity. Reactive oxygen species (ROS) have been implicated as inflammatory mediators of platelet activation and thrombosis. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase plays an important role in ROS production. To further evaluate the role of NADPH oxidase 4 (NOX4) and ROS in shear conditions seen in VADs, this study examined the effect of hemodynamic shear stress on NOX4 expression and subsequent production of ROS in human platelets with fluorescent immunostaining to show NOX4 localization. Additionally, this study explored the effect of hydrogen peroxide (H2O2) on shear-mediated platelet activation. Correspondingly, ROS levels were positively correlated with an increase in NOX4 expression; excess ROS most likely resulted in exacerbation of shear-mediated platelet activation. Also, H2O2 resulted in an additive effect on shear-mediated platelet activation. Our results suggest a possible link between shear-mediated activation of platelets and NOX4-induced ROS production. Shear-mediated platelet activation is a dynamic process involving multiple biologic and mechanical elements. These findings contribute to a better understanding of thrombotic complications in patients with flow-altering implantable cardiovascular devices.