Molecular Imaging of Platelets and Oxidative Stress in Atherosclerosis

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SUMMARY Methods for non-invasive in vivo molecular imaging of cardiovascular disease have been developed, in large part, for their potential to improve patient care. These methods are already playing an important role in the research setting to discover potentially treatable pathobiology and to assess new therapies in clinical and pre- clinical studies. Our laboratory has pioneered novel contrast-enhanced ultrasound (CEU) molecular imaging techniques that rely on the detection of encapsulated microbubble (MB) contrast agents. This approach uniquely characterizes the endothelial-blood pool interface. In the prior funding period of this award, we used CEU molecular imaging to better understand how endothelial activation and platelet-endothelial interactions help to promote early atherogenesis and contribute to high-risk features in chronic late-stage atherosclerosis. We demonstrated that platelet adhesion occurs primarily because of excess endothelial-associated Von Willebrand factor (VWF) that happens in situations or regions of increased oxidative stress. The overall goal of this proposal is to leverage this knowledge in order to evaluate potentially treatable origins of acute cardiovascular complications that are attributable to the pro-inflammatory and pro-thrombotic effects of platelet adhesion to the endothelium, either in large vessels or the coronary microcirculation. We will also test novel therapies that prevent these events. In Aim 1, molecular imaging of inflammatory activation, VWF, and platelet adhesion in atherosclerotic mice will be used to characterize global endothelial events that occur after a focal ischemic event (myocardial infarction [MI] or acute limb ischemia), and that we believe contribute to remote plaque activation in non-culprit arteries. We will also test whether platelet-endothelial interactions contribute to remote plaque inflammation; and will assess innovative treatment strategies that are based on their potential to reduce endothelial VWF and suppress platelet-endothelial interactions, including inhibitors of ROS and of Factor XI (FXI). In Aim 2, we will integrate data from CEU molecular imaging and perfusion imaging in various gene-targeted murine strains undergoing MI in order to assess the contribution of VWF-mediated platelet adhesion to microvascular no-reflow, post-reperfusion inflammatory response, and infarct size. Again, we will test innovative pharmacologic interventions capable of rescuing the activity of the enzyme responsible for preventing excess endothelial VWF (ADAMTS13), including inhibitors of ROS and FXI, and recombinant ADAMTS13. In Aim 3, myocardial ischemia-reperfusion injury will be performed in obese, atherosclerotic non- human primates (rhesus macaques on Western diet for >2 years). We will integrate data from molecular imaging, perfusion imaging, and morphologic imaging to evaluate the most promising therapies from Aim 1 and Aim 2 for preventing either: (a) impaired microvascular reflow; or (b) remote plaque activation in the carotid artery after MI. These studies are designed as a translational model to test efficacy, proof-of-mechanism, and safety of therapies that we can then apply in humans.