ALBUMIN MICROBUBBLE ADHERENCE TO HUMAN CORONARY ENDOTHELIUM - IMPLICATIONS FOR ASSESSMENT OF ENDOTHELIAL FUNCTION USING MYOCARDIAL CONTRASTECHOCARDIOGRAPHY

Objectives. We hypothesized that sonicated 5% human albumin microbubbl es (Albunex) adhere to disrupted vascular endothelium and that this in teraction is a marker of endothelial integrity. This study sought to i dentify sites and determinants of Albunex-endothelial cell (EC) attach ment. Background. Under normal conditions, Albunex microbubbles used i n myocardial contrast echocardiography (MCE) pass unimpeded through th e coronary microcirculation. During pathophysiologic states associated with endothelial dysfunction, however, microbubbles linger in the myo cardium despite normal flow. The sites and conditions regulating micro bubble adhesion are unknown. Methods. Coverslips with cultured human c oronary artery ECs were mounted in a parallel plate perfusion system a nd perfused with a suspension of fluorescein labeled Albunex in cultur e medium, followed by a bubble-free wash at a 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 infl ammatory response. Perfusions were performed under normal and inflamma tory conditions using surfaces of confluent and subconfluent ECs and i solated extracellular matrix. Bubble adherence was quantified in 20 ra ndom fields per coverslip using epifluorescent video microscopy. Resul ts. No microbubbles adhered to normal confluent ECs, although small nu mbers 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 b ubbles/mm(2), p = 0.05) and completely denuded (2,700 +/- 1,300 vs. 7, 200 +/- 1,100 bubbles/mm(2), p < 0.03) endothelium. Conclusions. Albun ex microbubbles preferentially adhere to inflammatory endothelial extr acellular matrix. These data suggest that MCE can be used to noninvasi vely study endothelial integrity and may have implications for the ass essment of preclinical atherosclerotic heart disease. (C) 1997 by the American College of Cardiology.