Prediction of fibre architecture and adaptation in diseased carotid bifurcations

Many studies have used patient-specific finite element models to estimate the stress environment in atherosclerotic plaques, attempting to correlate the magnitude of stress to plaque vulnerability. In complex geometries, few studies have incorporated the anisotropic material response of arterial tissue. This paper presents a fibre remodelling algorithm to predict the fibre architecture, and thus anisotropic material response in four patient-specific models of the carotid bifurcation. The change in fibre architecture during disease progression and its affect on the stress environment in the plaque were predicted. The mean fibre directions were assumed to lie at an angle between the two positive principal strain directions. The angle and the degree of dispersion were assumed to depend on the ratio of principal strain values. Results were compared with experimental observations and other numerical studies. In non-branching regions of each model, the typical double helix arterial fibre pattern was predicted while at the bifurcation and in regions of plaque burden, more complex fibre architectures were found. The predicted change in fibre architecture in the arterial tissue during plaque progression was found to alter the stress environment in the plaque. This suggests that the specimen-specific anisotropic response of the tissue should be taken into account to accurately predict stresses in the plaque. Since determination of the fibre architecture in vivo is a difficult task, the system presented here provides a useful method of estimating the fibre architecture in complex arterial geometries.     

A computational model for collagen fibre remodelling in the arterial wall

As the interaction between tissue adaptation and the mechanical condition within tissues is complex, mathematical models are desired to study this interrelation. In this study, a mathematical model is presented to investigate the interplay between collagen architecture and mechanical loading conditions in the arterial wall. It is assumed that the collagen fibres align along preferred directions, situated in between the principal stretch directions. The predicted fibre directions represent symmetrically arranged helices and agree qualitatively with morphometric data from literature. At the luminal side of the arterial wall, the fibres are oriented more circumferentially than at the outer side. The discrete transition of the fibre orientation at the media-adventitia interface can be explained by accounting for the different reference configurations of both layers. The predicted pressure-radius relations resemble experimentally measured sigma-shaped curves. As there is a strong coupling between the collagen architecture and the mechanical loading condition within the tissue, we expect that the presented model for collagen remodelling is useful to gain further insight into the processes involved in vascular adaptation, such as growth and smooth muscle tone adaptation.     

Study of carotid arterial plaque stress for symptomatic and asymptomatic patients

Stroke is one of the leading causes of death in the world, resulting mostly from the sudden ruptures of atherosclerosis carotid plaques. Until now, the exact plaque rupture mechanism has not been fully understood, and also the plaque rupture risk stratification. The advanced multi-spectral magnetic resonance imaging (MRI) has allowed the plaque components to be visualized in-vivo and reconstructed by computational modeling. In the study, plaque stress analysis using fully coupled fluid structure interaction was applied to 20 patients (12 symptomatic and 8 asymptomatic) reconstructed from in-vivo MRI, followed by a detailed biomechanics analysis, and morphological feature study. The locally extreme stress conditions can be found in the fibrous cap region, 85% at the plaque shoulder based on the present study cases. Local maximum stress values predicted in the plaque region were found to be significantly higher in symptomatic patients than that in asymptomatic patients (200 ± 43 kPa vs. 127 ± 37 kPa, p=0.001). Plaque stress level, defined by excluding 5% highest stress nodes in the fibrous cap region based on the accumulative histogram of stress experienced on the computational nodes in the fibrous cap, was also significantly higher in symptomatic patients than that in asymptomatic patients (154 ± 32 kPa vs. 111 ± 23 kPa, p<0.05). Although there was no significant difference in lipid core size between the two patient groups, symptomatic group normally had a larger lipid core and a significantly thinner fibrous cap based on the reconstructed plaques using 3D interpolation from stacks of 2D contours. Plaques with a higher stenosis were more likely to have extreme stress conditions upstream of plaque throat. The combined analyses of plaque MR image and plaque stress will advance our understanding of plaque rupture, and provide a useful tool on assessing plaque rupture risk.     

Oxysterols and symptomatic versus asymptomatic human atherosclerotic plaque

Atherosclerosis is the most common cause of mortality in the Western world, contributing to about 50% of all deaths. Atherosclerosis is characterized by deposition of lipids onto the coronary or carotid arterial wall and formation of an atherosclerotic plaque. Atherosclerotic plaques are categorized into two groups: symptomatic and asymptomatic. The symptomatic plaques tend to be unstable and prone to rupture, and are associated with an increase in ischemic events. Oxysterols, products of cholesterol oxidation, are cytotoxic materials. Their level and type may be associated with plaque formation, development and stability. Oxysterols stimulate the formation of foam cells, advance atherosclerotic plaque progression, and contribute to plaque vulnerability and instability due to their cytotoxicity and their ability to induce cell apoptosis. Studies indicate that plasma 7β-OH CH level can be used as a biomarker for detecting carotid and coronary artery disease. Further clinical studies are needed to evaluate the potential of oxysterols for use as biomarkers for plaque vulnerability and instability. The identification of biomarkers in the blood that can distinguish between symptomatic and asymptomatic plaques remains an unresolved issue.     

Remodelling of continuously distributed collagen fibres in soft connective tissues

Extracellular matrix remodelling plays an essential role in tissue engineering of load-bearing structures. The goal of this study is to model changes in collagen fibre content and orientation in soft connective tissues due to mechanical stimuli. A theory is presented describing the mechanical condition within the tissue and accounting for the effects of collagen fibre alignment and changes in fibre content. A fibre orientation tensor is defined to represent the continuous distribution of collagen fibre directions. A constitutive model is introduced to relate the fibre configuration to the macroscopic stress within the material. The constitutive model is extended with a structural parameter, the fibre volume fraction, to account for the amount of fibres present within the material. It is hypothesised that collagen fibre reorientation is induced by macroscopic deformations and the amount of collagen fibres is assumed to increase with the mean fibre stretch. The capabilities of the model are demonstrated by considering remodelling within a biaxially stretched cube. The model is then applied to analyse remodelling within a closed stented aortic heart valve. The computed preferred fibre orientation runs from commissure to commissure and resembles the fibre directions in the native aortic valve.     

Effects of short length immobilization of medial gastrocnemius muscle of growing young adult rats.

Effects of four and six weeks of immobilization at short length of gastrocnemius muscle on its architecture at optimum muscle length and length-force characteristics were studied. In general, immobilization effects were similar after 4 and 6 weeks. Smaller physiological cross-sectional area and lower muscle force were found as a consequence of immobilization. Muscle and aponeurosis were shorter. This was shown to be quantitatively related to atrophy i.e. smaller fibre diameter. Despite this atrophy no effects of immobilization on fibre and aponeurosis angles could be shown. Adaptation of the number of sarcomeres in series was found exclusively in distal fibres after 4 weeks of immobilization. No significant effects were found for proximal fibres of muscles at this time nor for any fibres after 6 weeks of immobilization. The effects of immobilization on muscle architecture did not affect the length range of active force exertion. It is concluded that muscle length adaptation as a consequence of short length immobilization is not related to adaptation of number of sarcomeres in series but to the occurrence of atrophy. It is also concluded that atrophy of pennate muscles does not have to be accompanied by a lower fibre and aponeurosis angle. Comparison of immobilized and control group rats indicates that the effects of immobilization can be characterized as a combination of retarded development of several variables and the influence of atrophy and its consequences.     

Oxytalan fibre organization in marsupial mandibular periodontal tissues

The arrangement and distribution of oxytalan fibers in Australian marsupials has not previously been reported. Periodontal tissues of wombat, wallaby, possum, and marsupial mouse were examined to ascertain oxytalan fibre organization. Despite adaptation of the marsupial masticatory apparatus to different diets the oxytalan fibre organization in the periodontal ligament shows a basic pattern which corresponds with that reported in other animals. The oxytalan system forms a continuous meshwork of fine, branching fibres which completely invests each tooth root and connects adjacent teeth. Thick ribbon-like apico-occlusally orientated oxytalan fibres, thought to form by the coalescence of thinner fibres, are restricted to the periodontal ligament. The oxytalan fibres are embedded in cementum and attached to blood vessels in the periodontal ligament. Oxytalan fibres do not insert into alveolar bone. Histological evidence indicates functional remodelling of the oxytalan fibre system in continuously erupting teeth.     

Autophagic Marker MAP1LC3B Expression Levels Are Associated with Carotid Atherosclerosis Symptomatology

Objectives

The mechanism by which atheroma plaque becomes unstable is not completely understood to date but analysis of differentially expressed genes in stable versus unstable plaques may provide clues. This will be crucial toward disclosing the mechanistic basis of plaque instability, and may help to identify prognostic biomarkers for ischaemic events. The objective of our study was to identify differences in expression levels of 59 selected genes between symptomatic patients (unstable plaques) and asymptomatic patients (stable plaques).

Methods

80 carotid plaques obtained by carotid endarterectomy and classified as symptomatic (>70% stenosis) or asymptomatic (>80% stenosis) were used in this study. The expression levels of 59 genes were quantified by qPCR on RNA extracted from the carotid plaques obtained by endarterectomy and analyzed by means of various bioinformatic tools.

Results

Several genes associated with autophagy pathways displayed differential expression levels between asymptomatic and symptomatic (i.e. MAP1LC3B, RAB24, EVA1A). In particular, mRNA levels of MAP1LC3B, an autophagic marker, showed a 5−fold decrease in symptomatic samples, which was confirmed in protein blots. Immune system−related factors and endoplasmic reticulum-associated markers (i.e. ERP27, ITPR1, ERO1LB, TIMP1, IL12B) emerged as differently expressed genes between asymptomatic and symptomatic patients.

Conclusions

Carotid atherosclerotic plaques in which MAP1LC3B is underexpressed would not be able to benefit from MAP1LC3B−associated autophagy. This may lead to accumulation of dead cells at lesion site with subsequent plaque destabilization leading to cerebrovascular events. Identified biomarkers and network interactions may represent novel targets for development of treatments against plaque destabilization and thus for the prevention of cerebrovascular events.     

Humanin, a Cytoprotective Peptide, Is Expressed in Carotid Artherosclerotic Plaques in Humans

Objective

The mechanism of atherosclerotic plaque progression leading to instability, rupture, and ischemic manifestation involves oxidative stress and apoptosis. Humanin (HN) is a newly emerging endogenously expressed cytoprotective peptide. Our goal was to determine the presence and localization of HN in carotid atherosclerotic plaques.

Methods and Results

Plaque specimens from 34 patients undergoing carotid endarterectomy were classified according to symptomatic history. Immunostaining combined with digital microscopy revealed greater expression of HN in the unstable plaques of symptomatic compared to asymptomatic patients (29.42±2.05 vs. 14.14±2.13% of plaque area, p<0.0001). These data were further confirmed by immunoblot (density of HN/β-actin standard symptomatic vs. asymptomatic 1.32±0.14 vs. 0.79±0.11, p<0.01). TUNEL staining revealed a higher proportion of apoptotic nuclei in the plaques of symptomatic patients compared to asymptomatic (68.25±3.61 vs. 33.46±4.46% of nuclei, p<0.01). Double immunofluorescence labeling revealed co-localization of HN with macrophages (both M1 and M2 polarization), smooth muscle cells, fibroblasts, and dendritic cells as well as with inflammatory markers MMP2 and MMP9.

Conclusions

The study demonstrates a higher expression of HN in unstable carotid plaques that is localized to multiple cell types within the plaque. These data support the involvement of HN in atherosclerosis, possibly as an endogenous response to the inflammatory and apoptotic processes within the atheromatous plaque.     

Imaging cellulose fibre interfaces with fluorescence microscopy and resonance energy transfer

Future developments in cellulosic materials are predicated by the need to understand the fundamental interactions that occur at cellulose fibre interfaces. These interfaces strongly influence the material properties of fibre networks and fibre reinforced composites. This study takes advantage of fluorescence resonance energy transfer (FRET) and fluorescence microscopy to image cellulose interfaces. Steady-state epi-fluorescence microscopy suggests that energy transfer from coumarin dyed fibres to fluorescein dyed fibres is occurring at the fibre–fibre interface. The FRET response for natural spruce fibre interfaces is distinctly different from that observed in synthetic viscose fibres. This approach constitutes a novel methodology for the characterization of soft material interfaces on the molecular scale, and represents a major opportunity for advancing the understanding of fibrous network structures.     

Intraplaque Stretch in Carotid Atherosclerotic Plaque – an Effective Biomechanical Predictor for Subsequent Cerebrovascular Ischemic Events

Background

Stretch is a mechanical parameter, which has been proposed previously to affect the biological activities in different tissues. This study explored its utility in determining plaque vulnerability.

Methods

One hundred and six patients with mild to moderate carotid stenosis were recruited in this study (53 symptomatic and 53 asymptomatic). High resolution, multi-sequence magnetic resonance (MR) imaging was performed to delineate various plaque components. Finite element method was used to predict high stretch concentration within the plaque.

Results

During a two-year follow-up, 11 patients in symptomatic group and 3 in asymptomatic group experienced recurrent cerebrovascular events. Plaque stretch at systole and stretch variation during one cardiac cycle was greater in symptomatic group than those in the asymptomatic. Within the symptomatic group, a similar trend was observed in patients with recurrent events compared to those without.

Conclusion

Plaques with high stretch concentration and large stretch variation are associated with increased risk of future cerebrovascular events.     

Numerical simulation of the remodelling process of trabecular architecture around dental implants

Dental implants may alter the mechanical environment in the jawbone, thereby causing remodelling and adaptation of the surrounding trabecular bone tissues. To improve the efficacy of dental implant systems, it is necessary to consider the effect of bone remodelling on the performance of the prosthetic systems. In this study, finite element simulations were implemented to predict the evolution of microarchitecture around four implant systems using a previously developed model that combines both adaptive and microdamage-based mechano-sensory mechanisms in bone remodelling process. Changes in the trabecular architecture around dental implants were mainly focused. The simulation results indicate that the orientational and ladder-like architecture around the implants predicted herein is in good agreement with those observed in animal experiments and clinical observations. The proposed algorithms were shown to be effective in simulating the remodelling process of trabecular architecture around dental implant systems. In addition, the architectural features around four typical dental implant systems in alveolar bone were evaluated comparatively.     

An investigation into the role of different constituents in damage accumulation in arterial tissue and constitutive model development

Carotid atherosclerotic plaque rupture is one of the leading causes of stroke. Treatments for atherosclerosis can induce tissue damage during the deployment of an intravascular device or through external tissue clamping during surgery. In this paper, a constituent specific study was performed to investigate the role of the ground matrix and collagen fibres of arterial tissue in response to supra-physiological loads. Cyclic mechanical tests were conducted on intact and collagenase-digested strips of porcine common carotid arteries. Using these tests, four passive damage-relevant phenomena were studied, namely (i) Mullins effect, (ii) hysteresis, (iii) permanent set and (iv) matrix failure and fibre rupture. A constitutive model was also developed to capture all of these damage-relevant phenomena using a continuum damage mechanics approach. The implemented constitutive model was fit to experimental results for both intact and digested samples. The results of this work demonstrate the important role of the ground matrix in the permanent deformation of the arterial tissue under high loads. Supra-physiological load-induced tissue damage may play a key role in vascular remodelling in arteries with atherosclerosis or following interventional procedures.     

Differential effects of insulin-like growth factor-1 and atheroma-associated cytokines on cell proliferation and apoptosis in plaque smooth muscle cells of symptomatic and asymptomatic patients with carotid stenosis

Morbidity and mortality from atherosclerosis are associated with complicated atherosclerotic lesions due to plaque rupture, which is regulated by a balance between proliferation and apoptosis of vascular smooth muscle cells (VSMC). We examined insulin-like growth factor-1 (IGF-1)-induced survival of plaque VSMC from carotid endarterectomy specimens and investigated the underlying cellular mechanisms in the presence and absence of IL-12 and IFN-gamma. Both IL-12 and IFN-gamma were strongly expressed in symptomatic atherosclerotic plaques as compared with asymptomatic plaques. In asymptomatic plaque VSMC, IGF-1 induced the survival and proliferation of VSMC and accelerated VSMC into S-phase. IL-12 or IFN-gamma inhibited proliferation and VSMC were arrested in the G0-G1 phase. IGF-1 markedly inhibited the expression of p27(kip) and p21(cip) and significantly induced cyclin E and cyclin D. Both cytokines by themselves increased the expression of p27(kip) and p21(cip) and inhibited cyclin E and cyclin D. On the contrary, in symptomatic VSMC there was already increased apoptosis of VSMC and there was no significant effect of IGF-1 or inflammatory cytokines on proliferation, apoptosis or the expression of p27(kip) and p21(cip) and cyclin D and E. These data suggest that IGF-1 is more potent in inducing the survival of VSMC from the endarterectomy specimens of asymptomatic patients as compared to that of symptomatic subjects and cytokines associated with atheroma lesions decrease the activity of IGF-1-induced survival in the VSMC of asymptomatic plaques. The different expression and activity of cell cycle regulatory proteins could be responsible for apoptosis of VSMC and destabilization of atherosclerotic plaques.     

Single‐cell transcriptional profiling of human carotid plaques reveals a subpopulation of endothelial cells associated with stroke incidences

The differences in plaque histology between symptomatic and asymptomatic patients have been widely accepted. Whether there is a heterogeneity of cells between symptomatic and asymptomatic plaques remains largely unclear. To reveal the potential heterogeneity within different plaques, which may contribute to different stroke incidences, we obtained the scRNA‐seq data from symptomatic and asymptomatic patients and identified eight cell types present in plaques. Further analysis of endothelial cells (ECs) revealed three distinct EC subpopulations appeared to be endowed with specific biological functions such as antigen processing and presentation, cell adhesion, and smooth muscle cell proliferation. Of note, the differentially expressed genes of the EC 2 subpopulation showed that the genes involved in cell adhesion were up‐regulated in asymptomatic plaques compared to symptomatic plaques. Integrating the data of intraplaque haemorrhage and plaque stability, the 5th top‐enriched biological process was cell adhesion in the stable or non‐haemorrhaged plaques compared to unstable plaques or haemorrhaged plaques. Among these cell adhesion‐related genes, the intersection gene AOC3 may play a vital role in plaque haemorrhage and plaque stability. Targeting cell adhesion and the specialized genes may provide potential new therapeutic directions to prevent asymptomatic patients from stroke.     

Relationship between Framingham risk score and subclinical atherosclerosis in carotid plaques:an in vivo study using multi-contrast MRI

The assessment and management of early-stage atherosclerosis are important for the prevention of cardiovascular disease(CVD).In this study,we used multi-contrast magnetic resonance imaging(MRI) to investigate the carotid plaque feature in asymptomatic,at-risk subjects;we also evaluated the correlation between MRI findings and Framingham risk score(FRS).One hundred sixty-six asymptomatic individuals with risk factors for CVD underwent multi-contrast MRI.After the arterial morphology and plaque components were outlined,the differences in carotid plaque burden among the various risk categories were analyzed.The FRS analysis showed that high-risk individuals had thicker vessel wall and higher plaque lipid content than did low risk participants.A substantial proportion of advanced carotid plaques occurred in low and intermediate-risk groups.Multi-contrast MRI may provide incremental value to the FRS in managing asymptomatic at-risk population.     

Osteoprotegerin,Pericytes and Bone-Like Vascular Calcification Are Associated with Carotid Plaque Stability

Background and Purpose

Vascular calcification, recapitulating bone formation, has a profound impact on plaque stability. The aim of the present study was to determine the influence of bone-like vascular calcification (named osteoid metaplasia = OM) and of osteoprotegerin on plaque stability.

Methods

Tissue from carotid endarterectomies were analysed for the presence of calcification and signs of vulnerability according to AHA grading system. Osteoprotegerin (OPG), pericytes and endothelial cells were sought using immuno-histochemistry. Symptoms and preoperative imaging findings (CT-scan, MRI and Doppler-scan) were analyzed. Human pericytes were cultured to evaluate their ability to secrete OPG and to influence mineralization in the plaque.

Results

Seventy-three carotid plaques (49 asymptomatic and 24 symptomatic) were harvested. A significantly higher presence of OM (18.4% vs 0%, p<0.01), OPG (10.2% of ROI vs 3.4% of ROI, p<0.05) and pericytes (19% of ROI vs 3.8% of ROI, p<0.05) were noted in asymptomatic compared to symptomatic plaques. Consistently, circulating OPG levels were higher in the plasma of asymptomatic patients (3.2 ng/mL vs 2.5 ng/mL, p = 0.05). In vitro, human vascular pericytes secreted considerable amounts of OPG and underwent osteoblastic differentiation. Pericytes also inhibited the osteoclastic differentiation of CD14+ cells through their secretion of OPG.

Conclusions

OPG (intraplaque an plasmatic) and OM are associated with carotid plaque stability. Pericytes may be involved in the secretion of intraplaque OPG and in the formation of OM.     

超声造影技术评价颈动脉粥样硬化斑块稳定性的临床研究

目的:探讨超声造影技术评价颈动脉粥样硬化斑块稳定性的临床价值,为动脉粥样硬化诊断准确性提供参考。方法:根据实时超声造影检查的回声图像特点将该院53例(59个斑块)颈动脉粥样硬化斑块患者分为软斑组(24个)、混合斑组(18个)、硬斑组(17个),比较3组的造影增强率、造影增强程度分级,并对各类型斑块的时间-强度进行定量分析。结果:59个斑块中有40个呈现不同程度的增强,增强率为67.80%,其中软斑组、混合斑组、硬斑组超声增强率分别为87.50%、72.22%、35.29%,差异具有统计学意义(P0.05);造影增强程度Ⅰ级和Ⅲ级在三组间差异具有统计学意义(P0.05),其中硬斑组造影增强程度Ⅰ级个数较软斑组和混合斑组多,软斑组造影增强程度Ⅲ级个数较混合斑组和硬斑组多,差异均有统计学意义(P0.05);软斑组达峰时间、平均渡越时间均低于混合斑组和硬斑组,斑块峰值强度高于混合斑组和硬斑组,混合斑组达峰时间、平均渡越时间均低于硬斑组,斑块峰值强度高于硬斑组,差异均具有统计学意义(P0.05)。结论:超声造影技术可无创性地通过造影增强实时反映出颈动脉粥样硬化斑块内的新生血管情况,提供参数成像与定量分析,正确评价斑块的稳定性。