Swine model of carotid artery atherosclerosis: experimental induction by surgical partial ligation and dietary hypercholesterolemia

Abstract

Introduction: Limited availability of a large animal model of carotid atherosclerosis has limited preclinical evaluation of endovascular therapeutic devices. The present study is aimed at developing such animal models with a novel approach, emphasizing the role of hemodynamics.

Methods: Using 18 carotid arteries from 9 miniswine, surgical partial ligation (approximately 80% stenosis) was carried out in untreated (group I; n = 6) and balloon-injured arteries (group II; n = 9). Three arteries were subjected to sham-operation for control (group III; n = 3). All animals were fed with a high-fat diet until sacrifice. Angiograms and histologic sections of the vessels were analyzed to evaluate both models.

Results: Atherosclerotic changes were confirmed in 6 of 6 in group I and 6 of 9 arteries in group II, whereas all in group III remained intact. Three arteries in group II resulted in thrombotic occlusion. Advanced plaques with intraplaque hemorrhage and/or calcification were seen in 4 of 6 arteries in group I but none in group II. The cross-sectional area stenosis and atherosclerotic stage for plaques in group I were both significantly higher than that in groups II and III.

Conclusion: In this series, surgical partial ligation with concomitant dietary hyperlipidemia is an appropriate experimental technique to develop advanced atherosclerotic plaques with minimal technical complications. This model showed no evidence of such benefits when applied in balloon-injured arteries.

Fig 1.

A, Intraoperative photograph showing a ligated carotid artery with a spacer on the external surface of the artery. This spacer was subsequently removed, leaving a tight stenosis, but not occlusion. B, Angiogram showing a partially ligated artery with approximately 80% stenosis immediately after the procedure. C, Angiogram obtained 3 months after the procedure. Note luminal narrowing proximal and extensive dilation distal to the surgically created stenosis.

Fig 2.

Representative photographs of hematoxylin-eosin-stained cross-sections for carotid arteries from each group. A, Group I (Ib; 6 months). Eccentric advanced atherosclerotic plaque located proximal to the surgical stenosis. Arrow indicates calcium deposits at the bottom of the plaque. Note that the entire plaque is covered by a fibromuscular cap, suggesting the similarity to human lesions. B, Group II (IIb; 6 months). Concentric intimal thickening. Note that in contrast with A, no advanced features of atherosclerosis are seen. C, Group III (6 months). No atherosclerotic change is observed. Scale bar, 500 μm.

Fig 3.

Histologic features of various atheromatous plaques in carotid arteries in group I. All sections are from 1 animal sacrificed at 6 months after the surgical procedure. A, Low magnification micrograph (H-E-stained section) shows a large eccentric plaque in the portion proximal to the surgical stenosis featuring a fibromuscular cap, intra- and extracellular lipid deposition, and massive intraplaque hemorrhage (white arrowheads). Scale bar, 1 mm. B, anti-SMA immunostaining clearly showing a fibromuscular cap covering a large collection of foamy macrophages at the bottom. Note that smooth muscle cells are scattered throughout the plaque and line its luminal surface (at the top). Scale bar, 100 μm. C, Base of plaque immunostained with anti-SMA showing necrotic portion. Scale bar, 100 μm. D, Anti-SMA immunostaining clearly showing calcification at the bottom of plaque (black arrowhead). E, EVG-stained section of plaque shows abundant collagen deposition as well as focally defective internal elastic lamina (arrows). Scale bar, 100 μm. H-E, hematoxylin and eosin; SMA, smooth muscle actin; EVG, Van Gieson’s elastic

Fig 4.

Bar graphs of cross-sectional area stenosis (%) and plaque stage score. A, Area stenosis (%) and plaque stage score versus groups. B, Area stenosis (%) and plaque stage score versus subgroups.