Intravascular Ultrasound Molecular Imaging of Atheroma Components in Vivo

Objectives: Our purpose was to quantitate and confirm specific echogenic immunoliposome (ELIP) atheroma component enhancement in vivo.

Background: Targeted ELIPs for ultrasonic detection and staging of active molecular components of endothelium and atheroma have been developed.

Methods: In Yucatan miniswine, the endothelium was injured from one femoral and one carotid artery, and animals were fed a high-cholesterol diet for two months to create various stages of atheroma. Arteries were imaged with intravascular ultrasound (IVUS) 5 and 10 min after ELIP injection (5-mg dose). Anti-intercellular adhesion molecule-1 (ICAM-1), anti-vascular cell adhesion molecule-1 (VCAM-1), anti-fibrin, anti-fibrinogen, and anti-tissue factor (TF) conjugated ELIPs were used, and immunohistochemistry (IHC) confirmed the presence or absence of molecular expression. Two blinded observers determined if each segment was enhanced by ELIP. Three-dimensional image reconstruction and videodensitometric analysis determined the mean gray-scale (MGS) change of the luminal border.

Results: To determine endothelial injury component enhancement, anti-fibrinogen ELIP enhanced exposed fibrin in all arteries (MGS increased 22 +/- 5%; 6 arteries; 2 animals). To determine enhancement of molecular components in atherosclerotic arteries, observers detected enhancement 5 min after anti-VCAM, anti-ICAM, anti-TF, anti-fibrin, and anti-fibrinogen conjugated ELIPs. Furthermore, ELIP enhanced atheroma MGS by 39 +/- 18% (n = 8). The IHC staining confirmed the expression of respective molecular targets in all enhanced segments.

Conclusions: It was shown that ELIPs specifically enhance endothelial injury/atheroma components. This allows better characterization of the type and extent of active atheroma components and may allow more directed therapy.