A noninjury, diet-induced swine model of atherosclerosis for cardiovascular-interventional research

A novel rabbit model of atherosclerotic vulnerable plaque established by cryofluid-induced endothelial injury

Acute thrombosis secondary to atherosclerotic plaque rupture is the main cause of acute cardiac and cerebral ischemia. An animal model of unstable atherosclerotic plaques is highly important for investigating the mechanism of plaque rupture and thrombosis. However, current animal models involve complex operations, are costly, and have plaque morphologies that are different from those of humans. We aimed to establish a simple animal model of vulnerable plaques similar to those of humans. Rabbits were randomly divided into three groups. Group A was given a normal formula diet for 13 weeks. Group C underwent surgery on the intima of the right carotid artery with - 80 °C cryofluid-induced injury after 1 week of a high-fat diet and further feeding a 12-week high-fat diet. Group B underwent the same procedure as Group C but without the - 80 °C cryofluid. Serum lipid levels were detected via ELISA. The plaque morphology, stability and degree of stenosis were evaluated through hematoxylin-eosin (HE) staining, Masson trichrome staining, Elastica van Gieson staining (EVG), and oil red O staining. Macrophages and inflammatory factors in the plaques were assessed via immunohistochemical analysis. The serum low-density lipoprotein cholesterol (LDL-C), triglyceride (TG), and total cholesterol (TC) levels in groups B and C were significantly greater than those in group A. No plaque formation was observed in group A. The plaques in group B were very small. In group C, obvious plaques were observed in the blood vessels, and the plaques exhibited a thin fibrous cap, a large lipid core, and partially visible neovascularization, which is consistent with the characteristics of vulnerable plaques. In the plaques of group C, a large number of macrophages were present, and matrix metalloproteinase 9 (MMP-9) and lectin-like oxidized LDL receptor 1 (LOX-1) were abundantly expressed. We successfully established a rabbit model of vulnerable carotid plaque similar to that of humans through the combination of cryofluid-induced endothelial injury and a high-fat diet, which is feasible and cost effective.

Accelerated miniature swine models of advanced atherosclerosis: A review based on morphology

In order to accelerate development of atherosclerosis(AS) in miniature swine models, varieties of strategies and methods have been explored. In addition to traditional methods such as high cholesterol feeding and balloon injury, new methods such as familial hypercholesterolemia induced by gene editing and intramural injection have been applied in recent years. Although it has been claimed that these methods have successfully aggravated lesion areas and stenosis, lesion features induced by different strategies have shown heterogeneity in morphology. In addition, time consumption, high cost, and unavailability are problems that restrict application of these AS models. Here, we summarize strategies and methods to accelerate AS models and further analyze their values, advantages, and shortcomings.

Ginsenoside Rb1 for Myocardial Ischemia/Reperfusion Injury: Preclinical Evidence and Possible Mechanisms

Ginseng is an important herbal drug that has been used worldwide for many years. Ginsenoside Rb1 (G-Rb1), the major pharmacological extract from ginseng, possesses a variety of biological activities in the cardiovascular systems. Here, we conducted a preclinical systematic review to investigate the efficacy of G-Rb1 for animal models of myocardial ischemia/reperfusion injury and its possible mechanisms. Ten studies involving 211 animals were identified by searching 6 databases from inception to May 2017. The methodological quality was assessed by using the CAMARADES 10-item checklist. All the data were analyzed using RevMan 5.3 software. As a result, the score of study quality ranged from 3 to 7 points. Meta-analyses showed that G-Rb1 can significantly decrease the myocardial infarct size and cardiac enzymes (including lactate dehydrogenase, creatine kinase, and creatine kinase-MB) when compared with control group (P < 0.01). Significant decrease in cardiac troponin T and improvement in the degree of ST-segment depression were reported in one study (P < 0.05). Additionally, the possible mechanisms of G-Rb1 for myocardial infarction are antioxidant, anti-inflammatory, antiapoptosis, promoting angiogenesis and improving the circulation. Thus, G-Rb1 is a potential cardioprotective candidate for further clinical trials of myocardial infarction.

Atherosclerosis Induced by a High-Cholesterol and High-Fat Diet in the Inbred Strain of the Wuzhishan Miniature Pig

Coronary artery disease has a significant genetic predisposition, which mainly results from atherosclerosis. Miniature pig is an excellent model to investigate atherosclerosis. This study investigated whether the occurrence and development of atherosclerosis in the Wuzhishan miniature pigs (WZSPs) that were closely bred 12 generations had better consistency. The WZSPs (n = 9) were fed a high-cholesterol and high-fat diet (HCFD). After continuous feeding, 3 WZSPs each were sacrificed at 6, 8, and 12 months, respectively, and the general clinical manifestations and serological indexes were detected. The pathological changes of the major arteries and main organs were recorded. The results showed WZSPs were quite susceptible to the HCFD. At 6 months, plaque lesions appeared in the abdominal aorta and iliac artery, while at 8 months, they appeared in the coronary artery. At 12 months, atherosclerotic lesions could be found in all major arteries, while lipid core, cholesterol precipitation, and calcium deposition appeared in the most serious sites. The progression of arterial lesions and distribution of the lesions were highly consistent in the pigs. However, apparent variations in serum markers were observed. In conclusion, inbred WZSP is a good model to investigate atherosclerosis and has good predictability for the occurrence and development of the disease.

Development of Accelerated Coronary Atherosclerosis Model Using Low Density Lipoprotein Receptor Knock-Out Swine with Balloon Injury

Background

Several animal models have facilitated the evaluation and pathological understanding of atherosclerosis, but a definitive animal model of coronary atherosclerosis is not available. We therefore developed low density lipoprotein receptor knockout (LDLR-KO) pigs with hypercholesterolemia, a model which rapidly developed coronary atherosclerosis following balloon injury.

Methods and Results

We deleted LDLR exon regions from cultured porcine fetal fibroblasts and cloned LDLR knockout (LDLR-KO) embryos microinjecting fetal fibroblast nuclei into enucleated oocytes. Twelve LDLR-KO pigs were fed a 2.0% cholesterol and 20% fat diet. Baseline serum LDL cholesterol level was 510.0±86.1 mg/dL. Balloon injury was created in 46 coronary segments and necropsy were obtained 2, 4, 8 and 12 weeks later. Coronary artery sections were reviewed to evaluate lesion progression. We found lipid accumulation with foam cells and inflammatory cells beginning four weeks after balloon injury. The mean ratio of macrophages to plaque area was significantly higher in the four- weeks and eight-week animals compared with those at 2-weeks (8.79% ± 5.98% and 17.00% ± 10.38% vs. 1.14% ± 1.88%, P < 0.0001). At 12 weeks the ratio decreased toward the level at 2 week level (4.00% ± 4.56%, P = 0.66 vs. baseline). Advanced coronary atherosclerotic lesions contained lipid pools at eight-weeks with fibrous components beginning at 12 weeks.

Conclusions

We developed a model of rapid coronary atherosclerosis using LDLR KO pigs with balloon injury. This model may be useful for preclinical evaluation of medication or devices, and may also help investigate mechanisms of plaque progression.

Vitamin D machinery and metabolism in porcine adipose-derived mesenchymal stem cells

BACKGROUND

Vitamin D, a hormone once thought to have a role limited to calcium homeostasis and bone mineralization, has pleiotropic effects on different types of cells. Vitamin D receptors are reported in vascular smooth muscle cells, endothelial cells, and cardiomyocytes. Adipose-derived MSCs (ADMSCs) are multipotent cells with the capacity to differentiate into cells of different lineages. To our knowledge, the presence of vitamin D machinery on porcine ADMSCs has not yet been examined. In this study, we investigated the presence of vitamin D machinery and metabolism in ADMSCs by analyzing the expression levels of vitamin D receptor (VDR), vitamin D metabolizing enzymes (CYP24A1 and CYP27B1) after in vitro stimulation with active vitamin D, calcitriol.

METHODS AND RESULTS

ADMSCs isolated from porcine adipose tissue were characterized by positive staining for ADMSC markers, CD44, CD73, and CD90, and negative staining for macrophage marker CD11b and hematopoietic stem cell markers CD34 and CD45, and trilineage differentiation to osteocytes, chondrocytes, and adipocytes. No cytotoxicity was observed when MSCs were stimulated with 0.1-10 nM calcitriol. The ADMSCs were analyzed for mRNA and protein expression of CYP24A1, CYP27B1, and VDR by immunostaining, qPCR, and ELISA. A significant increase (p <0.01) in the mRNA expression of CYP24A1, CYP27B1, and VDR was observed after stimulation of ADMSCs with calcitriol (10 nM). The in vitro time-dependent effect of calcitriol (10 nM) on the components of vitamin D machinery in cultured MSCs was determined by qPCR. The VDR and CYP27B1 expression peaked at 3 h and CYP24A1 at 24 h, respectively. The in vitro biosynthesis of 1, 25(OH)2D3 by ADMSCs was analyzed by ELISA and Western blot. The levels of the active form of vitamin D were significantly decreased once the CYP enzymes were inhibited (p <0.01), demonstrating the ability of ADMSCs to convert inactive vitamin D into active vitamin D for cellular action.

CONCLUSIONS

Porcine ADMSCs possess vitamin D hydrolases and VDR to metabolize and respond to vitamin D. Hence, in vivo circulating 25-hydroxy vitamin D levels may have a significant role in regulating the differentiation of ADMSCs into different lineages, which might assist in stem cell-based therapy.

Role of Animal Models in Coronary Stenting

Coronary angioplasty initially employed balloon dilatation only. This technique revolutionized the treatment of coronary artery disease, although outcomes were compromised by acute vessel closure, late constrictive remodeling, and restenosis due to neointimal proliferation. These processes were studied in animal models, which contributed to understanding the biology of endovascular arterial injury. Coronary stents overcome acute recoil, with improvements in the design and metallurgy since then, leading to the development of drug-eluting stents and bioresorbable scaffolds. These devices now undergo computer modeling and benchtop and animal testing before evaluation in clinical trials. Animal models, including rabbit, sheep, dog and pig are available, all with individual benefits and limitations. In smaller mammals, such as mouse and rabbit, the target for stenting is generally the aorta; whereas in larger animals, such as the pig, it is generally the coronary artery. The pig coronary stenting model is a gold-standard for evaluating safety; but insights into biomechanical properties, the biology of stenting, and efficacy in controlling neointimal proliferation can also be gained. Intra-coronary imaging modalities such as intravascular ultrasound and optical coherence tomography allow precise serial evaluation in vivo, and recent developments in genetically modified animal models of atherosclerosis provide realistic test beds for future stents and scaffolds.

Suppressor of cytokine signaling-3 and intimal hyperplasia in porcine coronary arteries following coronary intervention

AIMS

The growth and differentiation of cells is regulated by cytokines by binding to cell-surface receptors and activating intracellular signal transduction cascade. Suppressor of cytokine signaling (SOCS)-3 is a negative regulator of cytokines. In this study we examined the expression of SOCS-3 in porcine coronary artery smooth muscle cells (PCASMCs) in vitro and in proliferating smooth muscle cells of neointimal lesions after coronary artery intervention in a swine model.

METHODS AND RESULTS

PCASMCs were cultured and stimulated with TNF-α and/or IGF-1 individually or in combination. Protein expression of SOCS-3 was examined using Western blot. For in vivo studies, six female Yucatan miniswine were fed with special high cholesterol diet for 8 months. At 4 months of high cholesterol diet, animals underwent coronary balloon angioplasty. At the end of 8 months animals were euthanized, coronary arteries were isolated and morphological and histological studies were performed. Western blot data revealed significantly high SOCS-3 expression in PCASMCs in the presence of either TNF-α or IGF-1 (5-6 fold) alone. However, in the presence of both TNF-α and IGF-1 the SOCS-3 expression was significantly decreased (4-5 fold). Results from morphological studies including, H&E and Masson's trichrome stain showed typical lesions with significant neointimal proliferation. Histological evaluation showed expression of smooth muscle α-actin and significantly increased proliferating cell nuclear antigen (PCNA) in neointimal lesion. Interestingly, there was significantly decreased expression of SOCS-3 in smooth muscle cells of neointima as compared to control.

CONCLUSIONS

These data suggest that SOCS-3 expression is decreased in proliferating smooth muscle cells of neointimal lesions. This leads to uncontrolled growth of vascular smooth muscle cells in injured arteries leading to restenosis. Therefore, local delivery of SOCS-3 gene at the site of injury after coronary artery intervention could regulate the proliferation of vascular smooth muscle cells and help in preventing the neointimal hyperplasia and restenosis.

Endovascular needle injection of cholesteryl linoleate into the arterial wall produces complex vascular lesions identifiable by intravascular ultrasound: early development in a porcine model of vulnerable plaque

BACKGROUND

We attempted to create a pig model of complex arterial lesions through the percutaneous injection of cholesteryl linoleate into the vessel wall.

METHODS AND RESULTS

A total of 81 arterial segments (27 arteries) underwent percutaneous intramural injection of cholesteryl linoleate, in eight pigs. Intravascular ultrasound (IVUS) analysis and corresponding histology were obtained for analysis at 2 and 4 weeks after injection. Overall, 18 out of 27 (67%) of the injected arterial segments displayed lesions identifiable by IVUS as an eccentric echolucent zone present within the deeper layer of the lesion. Quantitative IVUS analysis demonstrated that these lesions were non-occlusive (36+/-8% area stenosis), eccentric (eccentricity index, 0.78+/-0.07) and located into positively remodeled vessels (remodeling index, 1.45+/-0.24). By histology, these lesions were eccentric and comprised less than a third of the vessel circumference. Medial thickening and a thickened intima containing lipid droplets and mononuclear cells were consistently found. The presence of lipids or local wall thickening seen by histology colocalized with the presence of echolucent structures seen by IVUS in 65% of the coronary segments and 70% of the iliac segments.

CONCLUSIONS

The intramural deposition of cholesteryl linoleate results in the development of complex, lipid-containing inflammatory lesions in less than 4 weeks. These lesions are already identifiable by IVUS at 2 weeks and colocalize with histologic findings. Further development of this model may allow the validation of technologies designed to detect and treat high-risk atherosclerotic lesions.

Development of an animal model of selective coronary atherosclerosis

BACKGROUND

Atherosclerosis causes over 40% of all deaths in the USA and Western Europe. Although several hypotheses have been proposed, the etiology and pathogenesis of the atherosclerosis remain unknown.

OBJECTIVE

To develop a model of selective coronary atherosclerosis in pigs.

DESIGN

An animal model of selective coronary atherosclerosis was developed by combining a guide-wire-induced endothelial injury and cholesterol-enriched diet.

METHODS

Twelve pigs were subjected to guide-wire-induced injury to endothelium of left anterior descending (LAD) coronary artery. Six animals (control group) were fed a standard pig food; the remaining six animals (cholesterol group) were fed a 6%-cholesterol-enriched diet. Three animals from the control group were killed immediately after the endothelial injury (acute control group). The other three animals in the control group (chronic control group) and all animals in the cholesterol-fed group were killed 4 weeks after the injury.

RESULTS

The endothelial surface and the media of the left circumflex coronary artery LCX in all animals were intact. Long eccentric areas of endothelial injury were found in the LAD coronary arteries of animals in the acute control group. Numerous fibrous atherosclerotic plaques in LAD coronary arteries were found in animals in the chronic control group as well as in animals in the cholesterol-fed group, but were highly pronounced in animals in the last group. No accumulation of lipids was found in the plaques of animals in both groups.

CONCLUSIONS

Administration of a 6%-cholesterol diet for 6 weeks is not sufficient to cause coronary atherosclerosis in pigs. Selective coronary atherosclerosis can be induced within 4 weeks with the same diet when the blood vessel has been injured with a guide wire.