Targeted ultrasound contrast agents: in vitro assessment of endothelial dysfunction and multi-targeting to ICAM-1 and sialyl Lewisx

An ultrasound-based molecular imaging technique capable of detecting endothelial cell markers of inflammation may allow early, non-invasive assessment of vascular disease. Clinical application of targeted, acoustically-active microbubbles requires optimization of microbubble-endothelial adhesion strength to maximize image signal-to-noise ratio, as well as the ability to discern the degree of inflammation along a continuum of dysfunction. Accordingly, we hypothesized that adhesion of intercellular adhesion molecule-1 (ICAM-1)-targeted microbubbles is dependent on the degree of endothelial inflammation, and that microbubbles multi-targeted to both ICAM-1 (via anti-ICAM-1 antibodies) and selectins (via sialyl Lewisx) demonstrate greater adhesion strength than microbubbles targeted to either inflammatory marker alone. In a radial flow chamber, microbubbles were perfused across endothelial cells activated with interleukin-1beta to four different levels of inflammation, as assessed by quantitative ICAM-1 expression. ICAM-1-targeted microbubble adhesion strength increased with increasing degree of inflammation, with a relationship that was both positive and linear (r > 0.99). Microbubble adhesion strength was significantly higher for the multi-targeted microbubbles than either of the single-targeted microbubbles. These data thus demonstrate that multi-targeting of contrast microbubbles may offer improved adhesion characteristics, allowing for greater sensitivity to inflammation. Furthermore, the adhesion strength of targeted microbubbles is linearly dependent on the degree of inflammation, suggesting that targeted ultrasound imaging may offer differentiation between various degrees of endothelial dysfunction, and thus detect not only the presence, but also the severity of inflammatory disease processes.