Disturbed Laminar Blood Flow Vastly Augments Lipoprotein Retention in the Artery Wall: A Key Mechanism Distinguishing Susceptible From Resistant Sites.

OBJECTIVE: Atherosclerosis develops initially at branch points and in areas of high vessel curvature. Moreover, experiments in hypercholesterolemic mice have shown that the introduction of disturbed flow in straight, atherosclerosis-resistant arterial segments turns them highly atherosclerosis susceptible. Several biomechanical mechanisms have been proposed, but none has been demonstrated. In the present study, we examined whether a causal link exists between disturbed laminar flow and the ability of the arterial wall to retain lipoproteins. APPROACH AND RESULTS: Lipoprotein retention was detected at natural predilection sites of the murine thoracic aorta 18 hours after infusion of fluorescently labeled low-density lipoprotein. To test for causality between blood flow and the ability of these areas to retain lipoproteins, we manipulated blood flow in the straight segment of the common carotid artery using a constrictive collar. Disturbed laminar flow did not affect low-density lipoprotein influx, but increased the ability of the artery wall to bind low-density lipoprotein. Concordantly, disturbed laminar flow led to differential expression of genes associated with phenotypic modulation of vascular smooth muscle cells, increased expression of proteoglycan core proteins associated with lipoprotein retention, and of enzymes responsible for chondroitin sulfate glycosaminoglycan synthesis and sulfation. CONCLUSIONS: Blood flow regulates genes associated with vascular smooth muscle cell phenotypic modulation, as well as the expression and post-translational modification of lipoprotein-binding proteoglycan core proteins, and the introduction of disturbed laminar flow vastly augments the ability of a previously resistant, straight arterial segment to retain lipoproteins.

Induction of atherosclerosis in mice and hamsters without germline genetic engineering.

RATIONALE: Atherosclerosis can be achieved in animals by germline genetic engineering, leading to hypercholesterolemia, but such models are constrained to few species and strains, and they are difficult to combine with other powerful techniques involving genetic manipulation or variation. OBJECTIVE: To develop a method for induction of atherosclerosis without germline genetic engineering. METHODS AND RESULTS: Recombinant adeno-associated viral vectors were engineered to encode gain-of-function proprotein convertase subtilisin/kexin type 9 mutants, and mice were given a single intravenous vector injection followed by high-fat diet feeding. Plasma proprotein convertase subtilisin/kexin type 9 and total cholesterol increased rapidly and were maintained at high levels, and after 12 weeks, mice had atherosclerotic lesions in the aorta. Histology of the aortic root showed progression of lesions to the fibroatheromatous stage. To demonstrate the applicability of this method for rapid analysis of the atherosclerosis susceptibility of a mouse strain and for providing temporal control over disease induction, we demonstrated the accelerated atherosclerosis of mature diabetic Akita mice. Furthermore, the versatility of this approach for creating atherosclerosis models also in nonmurine species was demonstrated by inducing hypercholesterolemia and early atherosclerosis in Golden Syrian hamsters. CONCLUSIONS: Single injections of proprotein convertase subtilisin/kexin type 9-encoding recombinant adeno-associated viral vectors are a rapid and versatile method to induce atherosclerosis in animals. This method should prove useful for experiments that are high-throughput or involve genetic techniques, strains, or species that do not combine well with current genetically engineered models.

Wall shear stress and local plaque development in stenosed carotid arteries of hypercholesterolemic minipigs.

BACKGROUND: Wall shear stress is thought to play a critical role in the local development of atherosclerotic plaque and to affect plaque vulnerability. However, current models and hypotheses do not fully explain the link between wall shear stress and local plaque development. We aimed to investigate the relation between wall shear stress and local plaque development in surgically induced common carotid artery stenoses of hypercholesterolemic minipigs. MATERIALS, METHODS AND RESULTS: We created a surgically induced stenosis of the common carotid artery in 10 minipigs using a perivascular collar. We documented the flow and shear stress changes by ultrasound, magnetic resonance imaging, and computational fluid dynamics. Carotid plaques were documented by microscopy. Atherosclerotic lesions, in both pre-stenotic and post-stenotic segments, were associated with thrombus in the stenosed segment. In patent carotid arteries, atherosclerotic lesions were found in the post-stenotic segments only. Atherosclerotic lesions developed where low and oscillatory shear stress were present simultaneously, whereas low or oscillatory shear stress alone did not lead to lesion formation. CONCLUSIONS: Low and oscillatory shear stress in combination promoted plaque development, including plaques with necrotic cores that are the key and dangerous characteristic of vulnerable plaques.

Oversized vein grafts develop advanced atherosclerosis in hypercholesterolemic minipigs.

BACKGROUND: Accelerated atherosclerosis is the main cause of late aortocoronary vein graft failure. We aimed to develop a large animal model for the study of pathogenesis and treatment of vein graft atherosclerosis. METHODS: An autologous reversed jugular vein graft was inserted end-to-end into the transected common carotid artery of ten hypercholesteroemic minipigs. The vein grafts were investigated 12-14 weeks later with ultrasound and angiograpy in vivo and microscopy post mortem. RESULTS: One minipig died during follow up (patent vein graft at autopsy), and one vein graft thrombosed early. In the remaining eight patent vein grafts, the mean (standard deviation) intima-media thickness was 712 µm (276 µm) versus 204 µm (74 µm) in the contralateral control internal jugular veins (P < .01). Advanced atherosclerotic plaques were found in three of four oversized vein grafts (diameter of graft > diameter of artery). No plaques were found in four non-oversized vein grafts (P < .05). CONCLUSIONS: Our model of jugular vein graft in the common carotid artery of hypercholesterolemic minipigs displayed the components of human vein graft disease, i.e. thrombosis, intimal hyperplasia, and atherosclerosis. Advanced atherosclerosis, the main cause of late failure of human aortocoronary vein grafts was only seen in oversized grafts. This finding suggests that oversized vein grafts may have detrimental effects on patient outcome.

Familial hypercholesterolaemic downsized pig with human-like coronary atherosclerosis: a model for preclinical studies.

AIMS: A manageable and reproducible large animal model of human-like coronary atherosclerosis is lacking but highly needed for translational research in percutaneous coronary interventions and imaging. Farm pigs with familial hypercholesterolaemia develop advanced atherosclerosis in two to three years but then weigh >200 kg making them impractical and costly. We aimed at down-sizing this pig and accelerating coronary plaque development to make the model more useful and affordable. METHODS AND RESULTS: Familial hypercholesterolaemic farm pigs were downsized by crossing them with smaller pigs while preserving their hypercholesterolaemic trait ascribed to a mutation in the low density lipoprotein receptor. We accelerated coronary plaque development by atherogenic diet feeding whereby plasma total cholesterol rose to >20 mmol/l (>800 mg/dl). We further accelerated coronary plaque development site-specifically by inflicting coronary artery balloon injury. Both spontaneously developed and balloon accelerated coronary plaques mirrored pertinent human plaque features, including a large necrotic core covered by a thin and inflamed fibrous cap as seen in the most common type of thrombosis-prone (vulnerable) plaque in humans. Associated vulnerable plaque features included neovascularisation, intraplaque haemorrhage, and expansive remodelling. CONCLUSIONS: This human-like porcine model of coronary atherosclerosis is practical and highly relevant for translational research in percutaneous coronary interventions and imaging.

Unreliable assessment of necrotic core by virtual histology intravascular ultrasound in porcine coronary artery disease.

BACKGROUND: Intravascular ultrasound-derived virtual histology (VH IVUS) is used increasingly in clinical research to assess composition and vulnerability of coronary atherosclerotic lesions. However, the ability of VH IVUS to quantify individual plaque components, in particular the size of the destabilizing necrotic core, has never been validated. We tested for correlation between VH IVUS necrotic core size and necrotic core size by histology in porcine coronary arteries with human-like coronary disease. METHODS AND RESULTS: In adult atherosclerosis-prone minipigs, 18 advanced coronary lesions were assessed by VH IVUS in vivo followed by postmortem microscopic examination (histology). We found no correlation between the size of the necrotic core determined by VH IVUS and histology. VH IVUS displayed necrotic cores in lesions lacking cores by histology. CONCLUSIONS: We found no correlation between necrotic core size determined by VH IVUS and real histology, questioning the ability of VH IVUS to detect rupture-prone plaques, so-called thin-cap fibroatheromas.