Development of a lipid-rich, soft plaque in rabbits, monitored by histology and intravascular ultrasound

Lipid rich, soft plaques in the clinic are a common forerunner to occlusive thrombus formation, even with modest arterial stenosis. Animal models of atherosclerosis, obtained by various methods, do not generally allow direct in vivo evaluation of the lesion and, furthermore, cannot be examined more than once. The aim of the study was the generation of a rabbit model of atherosclerosis, with morphological characteristics similar to human lipid-rich, soft atheromatous plaques, and the evaluation of the reliability of intravascular ultrasound (IVUS) technology in the study of the development of atherosclerotic lesions in this model. Briefly, New Zealand white rabbits undergo perivascular electrical injury at both common carotid arteries, together with a 1.5% cholesterol diet for up to 90 days. The lesioned arterial segments show progressive changes, from diffuse cellular mortality, to macrophage infiltration in the media, up to the final migration of macrophages to the neointima, resulting in bulky, eccentric, macrophage and lipid-rich lesions. At IVUS, the produced lesions clearly resemble those described as 'soft plaques' in the clinical setting, with minimal calcification and reduced echo-reflectivity versus the adventitial layer. Quantitative and morphometric analysis of plaques shows a significant correlation between histological and IVUS measurements at each time point. In conclusion, vascular injury in the common carotids of rabbits generates atherosclerotic lipid-rich, soft plaques, that can be properly assessed by the IVUS methodology. The easy accessibility of the arterial lesion allows serial IVUS investigations and the direct evaluation of a number of locally or generally delivered therapeutic agents.