Adhesion of bio-functionalized ultrasound microbubbles to endothelial cells by targeting to vascular cell adhesion molecule-1 under shear flow

The expression of certain endothelial cell adhesion molecules is increased during endothelial dysfunction or inflammatory activation. This has led to the concept of using microbubbles for targeted molecular imaging or drug delivery. In this approach, microbubbles with a specific ligand to receptors expressed at the site of specific diseases are constructed. The present study aimed to engineer a novel type of bio-functionalized microbubbles (vascular cell adhesion molecule 1 [VCAM-1]-targeted microbubbles), and determine whether VCAM-1-targeted microbubbles exhibit specific adhesion to lipopolysaccharide (LPS)-activated endothelial cells. Our data showed that VCAM-1 expression was significantly upregulated in both LPS-activated endothelial cells in vitro and endothelium in a rat atherosclerosis model in vivo. Targeted microbubbles were designed by conjugating anti-VCAM-1 monoclonal antibodies to the shell of microbubbles using biotin-avidin bridging chemistry methods. Microbubble adhesion to endothelial cells was assessed in a flow chamber at two shear stress conditions (6.3 and 10.4 dynes/cm²). Our data showed that microbubble adhesion depends on both the surface anti-VCAM-1 antibody densities and the exposed shear stresses. Adhesion of VCAM-1-targeted microbubbles onto LPS-activated endothelial cells increased with the surface antibody densities, and decreased with the exposed shear stresses. These findings showed that the specific ligand-carrying microbubbles have considerable potential in targeted ultrasound molecular imaging or ultrasound-assisted drug/gene delivery applications.