Albumin Microbubble Adherence to Human Coronary Endothelium: Implications for Assessment of Endothelial Function Using Myocardial Contrast Echocardiography

Objectives. We hypothesized that sonicated 5% human albumin microbubbles (Albunex) adhere to disrupted vascular endothelium and that this interaction is marker of endothelial integrity. This study sought to identify sites and determinants of Albunex–endothelial cell (EC) attachment. Background. Under normal conditions, Albunex microbubbles used in myocardial contrast echocardiography (MCE) pass unimpeded through the coronary microcirculation. During pathophysiologic states associated with endothelial dysfunction, however, microbubbles linger in the myocardium despite normal flow. The sites and conditions regulating microbubble adhesion are unknown. Methods. Coverslips with cultured human coronary artery ECs were mounted in parallel plate perfusion system and perfused with suspension of fluorescein-labeled Albunex in culture medium, followed by bubble-free wash at wall shear rate of 100 s−1. To create inflammatory ECs, phorbol myristate acetate was added 4.5 h before perfusion, and flow cytometry was used to confirm an inflammatory response. Perfusions were performed under normal and inflammatory conditions using surfaces of confluent and subconfluent ECs and isolated extracellular matrix. Bubble adherence was quantified in 20 random fields per coverslip using epifluorescent video microscopy. Results. No microbubbles adhered to normal confluent ECs, although small numbers adhered to inflamed ECs (0.03 ± 0.01 bubbles/cell, p < 0.01 vs. normal cells). Fewer microbubbles attached to normal versus inflamed matrix of both partially exposed (1,800 ± 520 vs. 4,100 ± 1,000 bubbles/mm2, p = 0.05) and completely denuded (2,700 ± 1,300 vs. 7,200 ± 1,100 bubbles/mm2, p < 0.03) endothelium. Conclusions. Albunex microbubbles preferentially adhere to inflammatory endothelial extracellular matrix. These dat suggest that MCE can be used to noninvasively study endothelial integrity and may have implications for the assessment of preclinical atherosclerotic heart disease.