Contrast Ultrasound Imaging of the Aorta Does Not Affect Progression of Atherosclerosis or Cardiovascular Biomarkers in ApoE−/−Mice

Ultrasound contrast agents (UCAs) are used to enhance ultrasound imaging of the cardiovascular system. Ultrasound contrast agents are administered intravenously as a solution of micrometer-sized bubbles, consisting of an inert gas encased in a shell of phospholipid or albumin. When ultrasound is applied to the heart or blood vessels, the ultrasonic waves interact with UCAs in the circulation, causing the bubbles to oscillate or collapse. The interaction of ultrasound with UCAs opacifies the blood, allowing for improved imaging of cardiac structure and function,1 arterial stenosis,2 vascularization of atherosclerotic plaques,3 and other aspects of the cardiovascular system. When used for cardiac left ventricular opacification, UCAs can enhance the visual quality of ultrasound scans in patients who are difficult to image and improve diagnostic accuracy.4,5 While UCAs have clear clinical utility in detection and diagnosis of cardiovascular disease, concerns have been raised over their safety. There have been reports of adverse cardiovascular events after ultrasound with UCA administration in animal models and humans. In experimental studies from our research group and others, UCAs have been shown to induce cardiac arrhythmias6 and hemorrhage,7–9 impair endothelium-dependent vasodilatation,10 and alter atheroma thickness and the circulating biomarker von Willebrand Factor (vWF).11 Reports of cardiopulmonary complications and deaths in human clinical patients associated with UCA administration added to these concerns, and patients with preexisting cardiovascular disease appeared to be at increased risk.12 As a result, the US Food and Drug Administration (FDA) mandated warning labels for 2 commercially available UCAs, Definity (Lantheus Medical Imaging, North Billerica, MA) and Optison (GE Healthcare, Princeton, NJ) in 2007. The reported adverse events highlight the importance of further research in this area. The biological effects of contrast ultrasound may be a function of the ultrasound pressure level or UCA concentration, so it is necessary to test for adverse events using a variety of scenarios and experimental models. In this study, we used the ApoE−/− mouse model of atherosclerosis to determine thresholds for arterial damage at several different ultrasound pressure levels, with concomitant UCA administration. We fed groups of mice either a standard chow diet or a high-fat, high-sugar, cholesterol-containing Western diet to modulate the progression of atherosclerosis after a single contrast ultrasound exposure. We hypothesized that contrast ultrasound would induce vascular injury and accelerate the progression of atherosclerosis, that this effect would be pressure dependent, and that the threshold for effects of contrast ultrasound on biomarkers would be lower than FDA limits established for clinical ultrasound imaging.