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

Integrating Computational and Biological Hemodynamic Approaches to Improve Modeling of Atherosclerotic Arteries

Atherosclerosis is the primary cause of cardiovascular disease, resulting in mortality, elevated healthcare costs, diminished productivity, and reduced quality of life for individuals and their communities. This is exacerbated by the limited understanding of its underlying causes and limitations in current therapeutic interventions, highlighting the need for sophisticated models of atherosclerosis. This review critically evaluates the computational and biological models of atherosclerosis, focusing on the study of hemodynamics in atherosclerotic coronary arteries. Computational models account for the geometrical complexities and hemodynamics of the blood vessels and stenoses, but they fail to capture the complex biological processes involved in atherosclerosis. Different in vitro and in vivo biological models can capture aspects of the biological complexity of healthy and stenosed vessels, but rarely mimic the human anatomy and physiological hemodynamics, and require significantly more time, cost, and resources. Therefore, emerging strategies are examined that integrate computational and biological models, and the potential of advances in imaging, biofabrication, and machine learning is explored in developing more effective models of atherosclerosis.

Progression of Arterial Vasa Vasorum from Regulator of Arterial Homeostasis to Promoter of Atherogenesis

The vasa vasorum (vessels of vessels) are a dynamic microvascular system uniquely distributed to maintain physiological homeostasis of the artery wall by supplying nutrients and oxygen to the outer layers of the artery wall, adventitia, and perivascular adipose tissue, and in large arteries, to the outer portion of the medial layer. Vasa vasorum endothelium and contractile mural cells regulate direct access of bioactive cells and factors present in both the systemic circulation and the arterial perivascular adipose tissue and adventitia to the artery wall. Experimental and human data show that proatherogenic factors and cells gain direct access to the artery wall via the vasa vasorum and may initiate, promote, and destabilize the plaque. Activation and growth of vasa vasorum occur in all blood vessel layers primarily by angiogenesis, producing fragile and permeable new microvessels that may cause plaque hemorrhage and fibrous cap rupture. Ironically, invasive therapies, such as angioplasty and coronary artery bypass grafting, injure the vasa vasorum, leading to treatment failures. The vasa vasorum function both as a master integrator of arterial homeostasis and, once perturbed or injured, as a promotor of atherogenesis. Future studies need to be directed at establishing reliable in vivo and in vitro models to investigate the cellular and molecular regulation of the function and dysfunction of the arterial vasa vasorum.

Translating atherosclerosis research from bench to bedside: navigating the barriers for effective preclinical drug discovery

Cardiovascular disease (CVD) remains the leading cause of death worldwide. An ongoing challenge remains the development of novel pharmacotherapies to treat CVD, particularly atherosclerosis. Effective mechanism-informed development and translation of new drugs requires a deep understanding of the known and currently unknown biological mechanisms underpinning atherosclerosis, accompanied by optimization of traditional drug discovery approaches. Current animal models do not precisely recapitulate the pathobiology underpinning human CVD. Accordingly, a fundamental limitation in early-stage drug discovery has been the lack of consensus regarding an appropriate experimental in vivo model that can mimic human atherosclerosis. However, when coupled with a clear understanding of the specific advantages and limitations of the model employed, preclinical animal models remain a crucial component for evaluating pharmacological interventions. Within this perspective, we will provide an overview of the mechanisms and modalities of atherosclerotic drugs, including those in the preclinical and early clinical development stage. Additionally, we highlight recent preclinical models that have improved our understanding of atherosclerosis and associated clinical consequences and propose model adaptations to facilitate the development of new and effective treatments.

Survival intravascular photoacoustic imaging of lipid-rich plaque in cholesterol fed rabbits

Intravascular photoacoustic (IVPA) imaging is a promising modality for quantitative assessment of lipid-laden atherosclerotic plaques. Yet, survival IVPA imaging of the same plaque in the same animal is not demonstrated. Here, using a sheathed IVUS/PA catheter of 0.9 mm in diameter, we demonstrate MRI-guided survival IVPA imaging of same plaque in an aorta of a well-established rabbit model mimicking atherosclerosis in human patients. The IVUS/PA results were confirmed by histology. These advances open the opportunity to evaluate the effectiveness of a therapy that aims to reduce the size of atherosclerotic plaques and demonstrates the potential of translating the IVPA catheter into clinic for detection of lipid-rich plaques that are at high risk for thrombosis.

Preclinical techniques to investigate exercise training in vascular pathophysiology

Atherosclerosis is a dynamic process starting with endothelial dysfunction and inflammation and eventually leading to life-threatening arterial plaques. Exercise generally improves endothelial function in a dose-dependent manner by altering hemodynamics, specifically by increased arterial pressure, pulsatility, and shear stress. However, athletes who regularly participate in high-intensity training can develop arterial plaques, suggesting alternative mechanisms through which excessive exercise promotes vascular disease. Understanding the mechanisms that drive atherosclerosis in sedentary versus exercise states may lead to novel rehabilitative methods aimed at improving exercise compliance and physical activity. Preclinical tools, including in vitro cell assays, in vivo animal models, and in silico computational methods, broaden our capabilities to study the mechanisms through which exercise impacts atherogenesis, from molecular maladaptation to vascular remodeling. Here, we describe how preclinical research tools have and can be used to study exercise effects on atherosclerosis. We then propose how advanced bioengineering techniques can be used to address gaps in our current understanding of vascular pathophysiology, including integrating in vitro, in vivo, and in silico studies across multiple tissue systems and size scales. Improving our understanding of the antiatherogenic exercise effects will enable engaging, targeted, and individualized exercise recommendations to promote cardiovascular health rather than treating cardiovascular disease that results from a sedentary lifestyle.

Effect of pemafibrate (K-877), a novel selective peroxisome proliferator-activated receptor α modular (SPPARMα), in atherosclerosis model using low density lipoprotein receptor knock-out swine with balloon injury

Background

Peroxisome proliferator-activated receptor α (PPARα) is a nuclear receptor that has key roles of lipid metabolism and inflammation. The PPARα may affects the initiation and progression of atherosclerosis by reducing inflammatory responses. Pemafibrate (K-877) is a novel selective PPARα modulator (SPPARMα), which was designed to possess higher PPARα potency and selectivity than existing PPARα agonists. The aim of this study is to evaluate the effect of pemafibrate on vascular response in coronary atherosclerosis model using low density lipoprotein receptor knock-out (LDLR-KO) pigs with balloon injury.

Methods and results

Ten LDLR-KO pigs were randomly allocated to two groups [pemafibrate (n = 5) and control (n = 5)] and fed with a diet containing 2.0% cholesterol and 20% lard throughout the study. Balloon injury was created in 40 coronary segments two weeks after starting the oral administration of pemafibrate or placebo. Necropsy was conducted 8 weeks later. Coronary artery sections were reviewed to evaluate lesion progression and the mRNA expression levels for C-Jun, NFκ B, CCL2, CCR7, CD163 and MMP9 determined using real-time RT-PCR. LDL cholesterol at baseline was about 700 mg/dL. The mean ratio of macrophages to plaque area was significantly lower in pemafibrate group compared with control one (7.63±1.16 vs 14.04±4.51, P = 0.02) whereas no differences were observed in intimal area between groups. The mRNA levels of C-Jun, NFκB and MMP9 were significantly decreased in pemafibrate group.

Conclusions

Pemafibrate was associated with inhibition of inflammatory responses in coronary artery atherosclerosis model using LDLR-KO swine with balloon injury.

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.

Modelling of atherosclerosis in genetically modified animals

Atherosclerosis is a lipid-driven, chronic inflammatory disease that leads to plaque formation at specific sites of the arterial tree. Being the common cause of many cardiovascular disorders, atherosclerosis makes a tremendous impact on morbidity and mortality rates of cardiovascular diseases (CVDs) in countries with higher income. Animal models of atherosclerosis are utilized as useful tools for studying the aetiology, pathogenesis and complications of atherosclerosis, thus, providing a valuable platform for the efficacy testing of different pharmacological therapies and validation of imaging techniques. To date, a large variety of models is available. Pathophysiological changes can be induced in animals by either an atherogenic diet or genetic manipulations. The discussion of advantages and disadvantages of some murine, rabbit and porcine genetic models currently available for the atherosclerosis research is the scope of the following review.

[Current progress of research and use of microminipigs in drug development]

The use of minipigs has been increasing in the areas of pharmacology researches and drug development. The microminipig developed by Fuji Micra Inc. (Shizuoka, Japan) inherits characteristics of other pig strains showing several similarities to humans in anatomy, physiology, omnivorousness and diurnal, but at the same time has several advantages over other pig strains because of its small size which allows easy keeping, handling and dosing, and saving of test substances. The microminipig weighs about 10 kg at the age of 6 months. Canine cages can be used to keep the animal. Swine leukocyte antigens (SLA) are defined in each individual animal which is useful for testing immunological reactions. As there are many similarities in metabolic enzymes and transporters to those in humans, the microminipig is a powerful animal model for toxicokinetic studies. Unfortunately as in other minipigs the microminipig is not appropriate for embryo-fetal development studies of antibody drugs due to its poor placental transfer, but can be used for other reproductive and developmental studies. Repeat dose toxicity, safety pharmacology, immunotoxicity and local tolerance studies should be also other arenas of this animal model.

An update on the tools for creating transgenic animal models of human diseases - focus on atherosclerosis

Animal models of diseases are invaluable tools of modern medicine. More than forty years have passed since the first successful experiments and the spectrum of available models, as well as the list of methods for creating them, have expanded dramatically. The major step forward in creating specific disease models was the development of gene editing techniques, which allowed for targeted modification of the animal's genome. In this review, we discuss the available tools for creating transgenic animal models, such as transgenesis methods, recombinases, and nucleases, including zinc finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), and CRISPR/Cas9 systems. We then focus specifically on the models of atherosclerosis, especially mouse models that greatly contributed to improving our understanding of the disease pathogenesis and we outline their characteristics and limitations.

A new perspective on lipid research in age-related macular degeneration

There is an urgency to find new treatment strategies that could prevent or delay the onset or progression of AMD. Different classes of lipids and lipoproteins metabolism genes have been associated with AMD in a multiple ways, but despite the ever-increasing knowledge base, we still do not understand fully how circulating lipids or local lipid metabolism contribute to AMD. It is essential to clarify whether dietary lipids, systemic or local lipoprotein metabolismtrafficking of lipids in the retina should be targeted in the disease. In this article, we critically evaluate what has been reported in the literature and identify new directions needed to bring about a significant advance in our understanding of the role for lipids in AMD. This may help to develop potential new treatment strategies through targeting the lipid homeostasis.

CRISPR/Cas9-mediated ApoE-/- and LDLR-/- double gene knockout in pigs elevates serum LDL-C and TC levels

The traditional method to establish a cardiovascular disease model induced by high fat and high cholesterol diets is time consuming and laborious and may not be appropriate in all circumstances. A suitable pig model to study metabolic disorders and subsequent atherosclerosis is not currently available. For this purpose, we applied the CRISPR/Cas9 system to Bama minipigs, targeting apolipoprotein E (ApoE) and low density lipoprotein receptor (LDLR) gene simultaneously. Six biallelic knockout pigs of these two genes were obtained successfully in a single step. No off-target incidents or mosaic mutations were detected by an unbiased analysis. Serum biochemical analyses of gene-modified piglets showed that the levels of low density lipoprotein choleserol (LDL-C), total cholesterol (TC) and apolipoprotein B (APOB) were elevated significantly. This model should prove valuable for the study of human cardiovascular disease and related translational research.

A novel swine model for evaluation of dyslipidemia and atherosclerosis induced by human CETP overexpression

Background

The mechanism of cholesteryl ester transfer protein (CETP) in lipid metabolism is still unclear. Furthermore, the relationship of CETP and atherosclerosis (AS) has been controversial. As pigs are a good model for both lipid and AS research, we investigated the lipid metabolism of human CETP (hCETP) transgenic pigs and explored the mechanism of CETP in lipid modulation.

Methods

Plasmids expressing the hCETP gene were designed, successfully constructed, and transfected into porcine fetal fibroblasts by liposomes. Using somatic cell nuclear transfer technology and embryonic transfer, hCETP transgenic pigs were generated. After the DNA, RNA, and protein levels were identified, positive hCETP transgenic pigs were selected. Blood samples were collected at different ages to evaluate the phenotypes of biochemical markers, and the metabolomes of plasma samples were analyzed by liquid mass spectrometry.

Results

Eight positive hCETP transgenic pigs and five negative cloned pigs were generated by transgenic technology. Finally, five hCETP transgenic and five cloned pigs were grown healthily. After feeding with a normal diet, hCETP transgenic pigs compared with unmodified pigs had no significant differences in body weight, liver function, kidney function, or plasma ions, while total cholesterol and low-density lipoprotein were higher than in unmodified pigs, and high-density lipoprotein was significantly decreased. Metabolomics analysis showed that there were differences in metabolic components between hCETP transgenic pigs, cloned pigs, and unmodified pigs.

Conclusions

In this study, we created hCETP transgenic pigs that could serve as an excellent model for lipid disorders and atherosclerosis.

Electronic supplementary material

The online version of this article (10.1186/s12944-017-0563-x) contains supplementary material, which is available to authorized users.