Microbubbles targeted to intercellular adhesion molecule-1 bind to activated coronary artery endothelial cells

Preclinical atherosclerosis is associated with increased endothelial cell (EC) expression of leukocyte adhesion molecules (LAMs), which mediate monocyte adhesion during atherogenesis. Identification of cell-surface LAMs may uniquely allow assessment of endothelial function, but there are no in vivo methods for detecting LAMs. We tested a new microbubble designed to bind to and allow specific ultrasound detection of intercellular adhesion molecule-1 (ICAM-1).

A perfluorobutane gas-filled lipid-derived microsphere with monoclonal antibody to ICAM-1 covalently bound to the bubble shell was synthesized. Bubbles with either nonspecific IgG or no protein on the shell were synthesized as controls. Coverslips of cultured human coronary artery ECs were placed in a parallel-plate perfusion chamber and exposed to 1 of the 3 microbubble species, followed by perfusion with culture medium. Experiments were performed with either normal or interleukin-1beta-activated ECs overexpressing ICAM-1, and bubble adherence was quantified with epifluorescent videomicroscopy. There was limited adherence of control bubbles to normal or activated ECs, whereas a 40-fold increase in adhesion occurred when anti-ICAM-1-conjugated bubbles were exposed to activated ECs compared with normal ECs (8.1+/-3.5 versus 0.21+/-0.09 bubbles per cell, respectively, P<0.001). Although diminished, this difference persisted even after perfusion at higher wall shear rates.

A gas-filled microbubble with anti-ICAM-1 antibody on its shell specifically binds to activated ECs overexpressing ICAM-1. Diagnostic ultrasound in conjunction with targeted contrast agents has the unique potential to characterize cell phenotype in vivo.