Myocardial infarction is induced by an ischemic event and often leads to damage of the myocardium and potentially death. Approximately 150,000 deaths occur each year in the United States due to acute myocardial infarction and a similar number go on to suffer from debilitating heart failure due to the infarction. The primary clinical goal during treatment of myocardial infarction is to restore blood flow to the myocardium as quickly as possible. However, paradoxically, the reperfusion can cause significant damage to the myocardium. Of the total infarcted volume, potentially up to 50% can be attributed to reperfusion and not ischemia. The reperfusion injury occurs, in part, due to the ischemic tissue converting the newfound supply of oxygen into reactive oxygen species. Reactive oxygen species can significantly damage a cell and lead to cell death. This project will develop an ultrasound-based oxygen scavenging approach to enable controlled hypoxemic reperfusion in order to reduce cell death from reactive oxygen species. The technique relies on a process known as acoustic droplet vaporization, where a liquid droplet is phase-transitioned into a gas microbubble when exposed to ultrasound. The microbubble acts a sink for oxygen in whole blood, effectively sequestering the oxygen within the microbubble so that less oxygen diffuses into the tissue. In turn, less oxygen in the tissue may reduce oxidative stress and cell death. Our central hypothesis is that ultrasound-mediated oxygen scavenging during reperfusion, following an ischemic event, increases cell and tissue viability. In vitro cell culture and ex vivo tissue models of ischemia-reperfusion injury have been used to obtain preliminary data supporting this hypothesis. Our proof-of-principle data demonstrates that oxygen scavenging can be done using intravascular ultrasound devices, which simplifies in vivo ultrasound targeting and would allow for a percutaneous approach that can be integrated into existing percutaneous treatments. We have also demonstrated the ability to tune the amount of oxygen scavenging by modifying droplet properties, droplet concentrations, and ultrasound insonation parameters. We will test the hypothesis through studies focusing on the efficiency and efficacy of oxygen scavenging in vitro, ex vivo, and in vivo.
The first aim i s to adapt our current technology into a translationally relevant working system. Studies will investigate droplet manufacturing and ultrasound insonation approaches.
The second aim will investigate how the magnitude and duration of oxygen scavenging effect reperfusion injury using an isolated whole heart with Langendorff preparation that enables measurement of both infarct size and ventricular function. These protocols will be translated to an in vivo porcine model of ischemia-reperfusion injury. The primary outcomes within that model will include infarct size measurement and oximetry. The progression of these experiments will ensure a thorough understanding of the therapy and how modifications to the approach can be made to improve therapeutic efficacy.
While new therapies to restore blood flow can be life-saving, up to half of the volume of heart tissue at risk during a heart attack dies, paradoxically, due to the return of blood flow. The previously oxygen-starved heart muscle responds to the influx of oxygen by creating free radicals that damage the patient?s heart cells, so- called reperfusion injury. This project uses a novel, ultrasound-based technique to sequester oxygen from the blood to reduce reperfusion injury.
