Structural and biomechanical alterations in rabbit thoracic aortas are associated with the progression of atherosclerosis

A study on the ultimate mechanical properties of middle-aged and elderly human aorta based on uniaxial tensile test

Background

The mechanical properties of the aorta are particularly important in clinical medicine and forensic science, serving as basic data for further exploration of aortic disease or injury mechanisms.

Objective

To study the influence of various factors (age, gender, test direction, anatomical location, and pathological characteristics) on the mechanical properties and thickness of the aorta.

Methods

In this study, a total of 24 aortas (age range: 54-88 years old) were collected, one hundred and seventy-four dog-bone-shaped samples were made, and then the uniaxial tensile test was run, finally, pathological grouping was performed through histological staining.

Results

Atherosclerotic plaques were mainly distributed near the openings of blood vessel branches. The distribution was most severe in the abdominal aorta, followed by the aortic arch. Aortic atherosclerosis was a more severe trend in the male group. In the comparison of thickness, there were no significant differences in age (over 50 years) and test direction, the average thickness of the aorta was greater in the male group than the female group and decreased progressively from the ascending aorta to the abdominal aorta. Comparing the mechanical parameters, various parameters are mainly negatively correlated with age, especially in the circumferential ascending aorta (εp "Y = -0.01402*X + 1.762, R2 = 0.6882", εt "Y = -0.01062*X + 1.250, R2 = 0.6772"); the parameters of males in the healthy group were larger, while the parameters of females were larger in atherosclerosis group; the aorta has anisotropy, the parameters in the circumferential direction were greater than those in the axial direction; the parameters of the ascending aorta were the largest in the circumferential direction, the ultimate stress [σp "1.69 (1.08,2.32)"] and ultimate elastic modulus [E2"8.28 (6.67,10.25)"] of the abdominal aorta were significantly larger in the axial direction; In the circumferential direction, the stress [σp "2.2 (1.31,3.98)", σt "0.13 (0.09,0.31)"] and ultimate elastic modulus (E2 "14.10 ± 7.21") of adaptive intimal thickening were greater than those of other groups, the strain (εp "0.82 ± 0.17", εt "0.53 ± 0.14") of pathological intimal thickening was the largest in the pathological group.

Conclusion

The present study systematically analyzed the influence of age, sex, test direction, anatomical site, and pathological characteristics on the biomechanical properties of the aorta, described the distribution of aortic atherosclerosis, and illustrated the characteristics of aortic thickness changes. At the same time, new insights into the grouping of pathological features were presented.

Differential Biological Effects of Dietary Lipids and Irradiation on the Aorta, Aortic Valve, and the Mitral Valve

Aims

Dietary cholesterol and palmitic acid are risk factors for cardiovascular diseases (CVDs) affecting the arteries and the heart valves. The ionizing radiation that is frequently used as an anticancer treatment promotes CVD. The specific pathophysiology of these distinct disease manifestations is poorly understood. We, therefore, studied the biological effects of these dietary lipids and their cardiac irradiation on the arteries and the heart valves in the rabbit models of CVD.

Methods and Results

Cholesterol-enriched diet led to the thickening of the aortic wall and the aortic valve leaflets, immune cell infiltration in the aorta, mitral and aortic valves, as well as aortic valve calcification. Numerous cells expressing α-smooth muscle actin were detected in both the mitral and aortic valves. Lard-enriched diet induced massive aorta and aortic valve calcification, with no detectable immune cell infiltration. The addition of cardiac irradiation to the cholesterol diet yielded more calcification and more immune cell infiltrates in the atheroma and the aortic valve than cholesterol alone. RNA sequencing (RNAseq) analyses of aorta and heart valves revealed that a cholesterol-enriched diet mainly triggered inflammation-related biological processes in the aorta, aortic and mitral valves, which was further enhanced by cardiac irradiation. Lard-enriched diet rather affected calcification- and muscle-related processes in the aorta and aortic valve, respectively. Neutrophil count and systemic levels of platelet factor 4 and ent-8-iso-15(S)-PGF2α were identified as early biomarkers of cholesterol-induced tissue alterations, while cardiac irradiation resulted in elevated levels of circulating nucleosomes.

Conclusion

Dietary cholesterol, palmitic acid, and cardiac irradiation combined with a cholesterol-rich diet led to the development of distinct vascular and valvular lesions and changes in the circulating biomarkers. Hence, our study highlights unprecedented specificities related to common risk factors that underlie CVD.

Experimental Setting for Applying Mechanical Stimuli to Study the Endothelial Response of Ex Vivo Vessels under Realistic Pathophysiological Environments

This paper describes the design, construction and testing of an experimental setting, making it possible to study the endothelium under different pathophysiological conditions. This novel experimental approach allows the application of the following stimuli to an ex vivo vessel in a physiological bath: (a) a realistic intravascular pressure waveform defined by the user; (b) shear stress in the endothelial layer since, in addition to the pressure waveform, the flow through the vessel can be independently controlled by the user; (c) conditions of hypo/hyperoxia and hypo/hypercapnia in an intravascular circulating medium. These stimuli can be applied alone or in different combinations to study possible synergistic or antagonistic effects. The setting performance is illustrated by a proof of concept in an ex vivo rabbit aorta. The experimental setting is easy to build by using very low-cost materials widely available. Online Supplement files provide all the technical information (e.g., circuits, codes, 3D printer drivers) following an open-source hardware approach for free replication.

The impact of plaque type on strut embedment/protrusion and shear stress distribution in bioresorbable scaffold

AIMS

Scaffold design and plaque characteristics influence implantation outcomes and local flow dynamics in treated coronary segments. Our aim is to assess the impact of strut embedment/protrusion of bioresorbable scaffold on local shear stress distribution in different atherosclerotic plaque types.

METHODS AND RESULTS

Fifteen Absorb everolimus-eluting Bioresorbable Vascular Scaffolds were implanted in human epicardial coronary arteries. Optical coherence tomography (OCT) was performed post-scaffold implantation and strut embedment/protrusion were analysed using a dedicated software. OCT data were fused with angiography to reconstruct 3D coronary anatomy. Blood flow simulation was performed and wall shear stress (WSS) was estimated in each scaffolded surface and the relationship between strut embedment/protrusion and WSS was evaluated. There were 9083 struts analysed. Ninety-seven percent of the struts (n = 8840) were well-apposed and 243 (3%) were malapposed. At cross-section level (n = 1289), strut embedment was significantly increased in fibroatheromatous plaques (76 ± 48 µm) and decreased in fibrocalcific plaques (35 ± 52 µm). Compatible with strut embedment, WSS was significantly higher in lipid-rich fibroatheromatous plaques (1.50 ± 0.81 Pa), whereas significantly decreased in fibrocalcified plaques (1.05 ± 0.91 Pa). After categorization of WSS as low (<1.0 Pa) and normal/high WSS (≥1.0 Pa), the percent of low WSS in the plaque subgroups were 30.1%, 31.1%, 25.4%, and 36.2% for non-diseased vessel wall, fibrous plaque, fibroatheromatous plaque, and fibrocalcific plaque, respectively (P-overall < 0.001).

CONCLUSION

The composition of the underlying plaque influences strut embedment which seems to have effect on WSS. The struts deeply embedded in lipid-rich fibroatheromas plaques resulted in higher WSS compared with the other plaque types.

Inhibition of Atherosclerosis Progression, Intimal Hyperplasia, and Oxidative Stress by Simvastatin and Ivabradine May Reduce Thoracic Aorta's Stiffness in Hypercholesterolemic Rabbits

AIMS

This study aims to evaluate atherosclerosis, oxidative stress, and arterial stiffness attenuation by simvastatin and ivabradine in hyperlipidemic rabbits.

METHODS AND RESULTS

Forty rabbits were randomly divided into 4 groups: atherogenic diet (group C), atherogenic diet plus simvastatin (group S), atherogenic diet plus ivabradine (group I), and atherogenic diet plus simvastatin and ivabradine (group S + I). After 9 weeks, rabbits were euthanized and descending aortas excised for mechanical testing. Atherogenic diet induced the development of significant atherosclerotic lesions in group C animals but in none of groups S, I, and S + I. RAM-11 and HHF-35-positive cells were significantly reduced in groups S, I, and S + I compared with group C (P < .001). A significant neointimal hyperplasia and intima-media ratio reduction was demonstrated in groups S (P = .015 and P < .001), I (P = .021 and P < .001), and S + I (P = .019 and P < .001) compared with group C. Protein nitrotyrosine levels were significantly decreased in group S compared with group C (P = .009), and reactive oxygen species levels were decreased in group I compared with group C (P = .011). Aortic stiffness was significantly reduced in groups S, I, and S + I compared with group C (P = .003, P = .011, and P = .029).

CONCLUSION

Simvastatin and ivabradine significantly inhibited intimal hyperplasia and oxidative stress contributing to aortic stiffness reduction in hyperlipidemic rabbits.

Determination of Mechanical Properties of Rat Aorta Using Ring-Shaped Specimen

Ring-shaped specimen is commonly used in tests for determination of mechanical properties for arteries in hoop direction, especially for small mammals such as rats or mice. Although ring test is a lot more convenient than the tests concerning strip specimens, interpretation of the experimental data might be inconclusive – it is difficult distinguish whether it's still straightening up or the actual tension begins. The basic problem is to properly define initial length of specimen, which is essential for strain calculation. The purpose of this study was to evaluate various methods for strain evaluation. Ten Wistar Albino Glaxo male rats (3 months old, body weight about 200g) were sacrificed by decapitation and arteries were immediately removed. Three specimens, each approximately 2–3mm long, from each rat were excised adjacent to the aortic arch. Couple different initial lengths, as well as Digital Image Correlation based extensometer results were used for strain-stress response calculations. In addition a 3D Finite Element model, with an Ogden constitutive model based material, was made for deeper investigation of specimen behavior. This study has shown that the testing procedure for determination of mechanical properties of arteries, based on ring-shaped specimen, is prone to errors. Stiffness calculations are very sensitive to the choice of initial length of the specimen. As the use of DIC proved to give very good correlation with experimental data this method will be used in further studies.

Magnetomotive optical coherence tomography for the assessment of atherosclerotic lesions using αvβ3 integrin-targeted microspheres

PURPOSE

We investigated the early-stage fatty streaks/plaques detection using magnetomotive optical coherence tomography (MM-OCT) in conjunction with αvβ3 integrin-targeted magnetic microspheres (MSs). The targeting of functionalized MSs was investigated by perfusing ex vivo aortas from an atherosclerotic rabbit model in a custom-designed flow chamber at physiologically relevant pulsatile flow rates and pressures.

PROCEDURES

Aortas were extracted and placed in a flow chamber. Magnetic MS contrast agents were perfused through the aortas and MM-OCT, fluorescence confocal, and bright field microscopy were performed on the ex vivo aorta specimens for localizing the MSs.

RESULTS

The results showed a statistically significant and stronger MM-OCT signal (3.30 ± 1.73 dB) from the aorta segment perfused with targeted MSs, compared with the nontargeted MSs (1.18 ± 0.94 dB) and control (0.78 ± 0.41 dB) aortas. In addition, there was a good co-registration of MM-OCT signals with confocal microscopy.

CONCLUSIONS

Early-stage fatty streaks/plaques have been successfully detected using MM-OCT in conjunction with αvβ3 integrin-targeted magnetic MSs.

The relationship between the mechanical properties of heel-pad and common clinical measures associated with foot ulcers in patients with diabetes

AIM

The present study aims at investigating the correlation between the mechanical properties of the heel-pad of people with type-2 diabetes and the clinical parameters used to monitor their health and ulceration risk.

METHODS

A new device for the in-vivo testing of plantar soft tissues was built and pilot-tested. This device consists of an ultrasound probe connected in series with a dynamometer. Loading is applied manually using a ball-screw actuator. A total of 35 volunteers with type-2 diabetes were recruited and the thickness, stiffness of their heel-pads as well as the energy absorbed during loading were assessed. The participants with diabetes also underwent blood tests and measurements of Ankle Brachial Index and Vibration Perception Threshold.

RESULTS

Pearson correlation analysis revealed strong correlations between triglycerides and heel-pad stiffness (r=0.675, N=27, p<0.001) and between triglycerides and energy (r=-0.598, N=27, p=0.002). A correlation of medium strength was found between Fasting Blood Sugar (FBS) and stiffness (r=0.408, N=29, p=0.043).

CONCLUSIONS

People with type-2 diabetes and high levels of triglycerides and FBS are more likely to have stiffer heel-pads. Increased stiffness could limit the tissues' ability to evenly distribute loads making them more vulnerable to trauma and ulceration.

Effects of everolimus on macrophage-derived foam cell behavior

PURPOSE

The purpose of this study was to investigate the effects of everolimus on foam cell (FC) viability, mRNA levels, and inflammatory cytokine production to better understand its potential inhibitory effects on atheroma progression.

METHODS AND MATERIALS

Human THP1 macrophage-derived FC were formed using acetylated LDL (acLDL, 100 μg/mL) for 72 hours, followed by everolimus treatment (10(-5)-10(-11) M) for 24 hours. FC viability was quantified using fluorescent calcein AM/DAPI staining. FC lysates and media supernatants were analyzed for apoptosis and necrosis using a Cell Death ELISA(PLUS) assay. FC lysates and media supernatants were also analyzed for inflammatory cytokine (IL1β, IL8, MCP1, TNFα) mRNA levels and protein expression using quantitative reverse transcription real-time polymerase chain reaction (QPCR) and a Procarta® immunoassay, respectively. mRNA levels of autophagy (MAP1LC3), apoptosis (survivin, clusterin), and matrix degradation (MMP1, MMP9) markers were evaluated by Quantigene® Plex assay and verified with QPCR. Additionally, hypercholesterolemic rabbits received everolimus-eluting stents (EES) for 28 or 60 days. RAM-11 immunohistochemical staining was performed to compare %RAM-11 positive area between stented sections and unstented proximal sections. Statistical significance was calculated using one-way ANOVA (p≤0.05).

RESULTS

Calcein AM/DAPI staining showed that FC exposed to everolimus (10(-5) M) had significantly decreased viability compared to control. FC apoptosis was significantly increased at a high dose of everolimus (10(-5)M), with no necrotic effects at any dose tested. Everolimus did not affect endothelial (HUVEC) and smooth muscle (HCASMC) cell apoptosis or necrosis. Everolimus (10(-5)M) significantly increased MAP1LC3, caused an increased trend in clusterin (p=0.10), and significantly decreased survivin and MMP1 mRNA levels in FC. MCP1 cytokine mRNA levels and secreted protein expression was significantly decreased by everolimus (10(-5) M) in FC. Percentage of RAM-11 positive area exhibited a reduction trend within sections stented with EES compared to unstented proximal sections at 60 days (p=0.09).

CONCLUSION

Everolimus, a potent anti-proliferative agent used in drug-eluting stents and bioresorbable vascular scaffolds, may inhibit atheroma progression and/or promote atheroma stabilization through diminished viability of FC, decreased matrix degradation, and reduced pro-inflammatory cytokine secretion.

EXECUTIVE SUMMARY

We explored the effects of everolimus on the behavior of human THP1 macrophage-derived foam cells in culture, including cell viability, mRNA levels, and pro-inflammatory cytokine production. We conclude that everolimus, a potent anti-proliferative agent used in drug-eluting stents/bioresorbable vascular scaffolds, may potentially inhibit atheroma progression and/or promote atheroma stabilization through diminished viability of foam cells, decreased matrix degradation, and reduced pro-inflammatory cytokine secretion.

Transauricular balloon angioplasty in rabbit thoracic aorta: a novel model of experimental restenosis

BACKGROUND

The aim of this study was to demonstrate a percutaneous transauricular method of balloon angioplasty in high-cholesterol fed rabbits, as an innovative atherosclerosis model.

METHODS

Twenty male New Zealand rabbits were randomly divided into two groups of ten animals, as follows: atherogenic diet plus balloon angioplasty (group A) and atherogenic diet alone (group B). Balloon angioplasty was performed in the descending thoracic aorta through percutaneous catheterization of the auricular artery. Eight additional animals fed regular diet were served as long term control. At the end of 9 week period, rabbits were euthanized and thoracic aortas were isolated for histological, immunohistochemical and biochemical analysis.

RESULTS

Atherogenic diet induced severe hypercholesterolemia in both group A and B (2802 ± 188.59 and 4423 ± 493.39 mg/dl respectively) compared to the control animals (55.5 ± 11.82 mg/dl; P < 0.001). Group A atherosclerotic lesions appeared to be more advanced histologically (20% type IV and 80% type V) compared to group B lesions (50% type III and 50% type IV). Group A compared to group B atherosclerotic lesions demonstrated similar percentage of macrophages (79.5 ± 9.56% versus 84 ± 12.2%; P = 0.869), more smooth muscle cells (61 ± 14.10% versus 40.5 ± 17.07; P = 0.027), increased intima/media ratio (1.20 ± 0.50 versus 0.62 ± 0.13; P = 0.015) despite the similar degree of intimal hyperplasia (9768 ± 1826.79 μm² versus 12205 ± 8789.23 μm²; P = 0.796), and further significant lumen deterioration (23722 ± 4508.11 versus 41967 ± 20344.61 μm²; P = 0.05) and total vessel area reduction (42350 ± 5819.70 versus 73190 ± 38902.79 μm²; P = 0.022). Group A and B animals revealed similar nitrated protein percentage (P = NS), but significantly higher protein nitration compared to control group (P < 0.01; P < 0.01, respectively). No deaths or systemic complications were reported.

CONCLUSION

Transauricular balloon angioplasty constitutes a safe, minimally invasive and highly successful model of induced atherosclerosis in hyperlipidaemic rabbits.