Haemodynamic Effects on the Development and Stability of Atherosclerotic Plaques in Arterial Blood Vessel

Studying the formation and stability of atherosclerotic plaques in the hemodynamic field is essential for understanding the growth mechanism and preventive treatment of atherosclerotic plaques. In this paper, based on a multiplayer porous wall model, we established a two-way fluid-solid interaction with time-varying inlet flow. The lipid-rich necrotic core (LRNC) and stress in atherosclerotic plaque were described for analyzing the stability of atherosclerotic plaques during the plaque growth by solving advection-diffusion-reaction equations with finite-element method. It was found that LRNC appeared when the lipid levels of apoptotic materials (such as macrophages, foam cells) in the plaque reached a specified lower concentration, and increased with the plaque growth. LRNC was positively correlated with the blood pressure and was negatively correlated with the blood flow velocity. The maximum stress was mainly located at the necrotic core and gradually moved toward the left shoulder of the plaque with the plaque growth, which increases the plaque instability and the risk of the plaque shedding. The computational model may contribute to understanding the mechanisms of early atherosclerotic plaque growth and the risk of instability in the plaque growth.

Bifurcation analysis of a free boundary model of vascular tumor growth with a necrotic core and chemotaxis

A considerable number of research works has been devoted to the study of tumor models. Several biophysical factors, such as cell proliferation, apoptosis, chemotaxis, angiogenesis and necrosis, have been discovered to have an impact on the complicated biological system of tumors. An indicator of the aggressiveness of tumor development is the instability of the shape of the tumor boundary. Complex patterns of tumor morphology have been explored in Lu et al. (J Comput Phys 459:111153, 2022). In this paper, we continue to carry out a bifurcation analysis on such a vascular tumor model with a controlled necrotic core and chemotaxis. This bifurcation analysis, to the parameter of cell proliferation, is built on the explicit formulas of radially symmetric steady-state solutions. By perturbing the tumor free boundary and establishing rigorous estimates of the free boundary system, we prove the existence of the bifurcation branches with Crandall-Rabinowitz theorem. The parameter of chemotaxis is found to influence the monotonicity of the bifurcation point as the mode l increases both theoretically and numerically.

Myeloid-associated lipin-1 transcriptional co-regulatory activity is atheroprotective

BACKGROUND AND AIMS

Atherosclerosis is the most prominent underlying cause of cardiovascular disease (CVD). It is initiated by cholesterol deposition in the arterial intima, which causes macrophage recruitment and proinflammatory responses that promote plaque growth, necrotic core formation, and plaque rupture. Lipin-1 is a phosphatidic acid phosphohydrolase for glycerolipid synthesis. We have shown that lipin-1 phosphatase activity promotes macrophage pro-inflammatory responses when stimulated with modified low-density lipoprotein (modLDL) and accelerates atherosclerosis. Lipin-1 also independently acts as a transcriptional co-regulator where it enhances the expression of genes involved in β-oxidation. In hepatocytes and adipocytes, lipin-1 augments the activity of transcription factors such as peroxisome proliferator-activated receptor (PPARs). PPARs control the expression of anti-inflammatory genes in macrophages and slow or reduce atherosclerotic progression. Therefore, we hypothesize myeloid-derived lipin-1 transcriptional co-regulatory activity reduces atherosclerosis.

METHODS

We used myeloid-derived lipin-1 knockout (lipin-1mKO) and littermate control mice and AAV8-PCSK9 along with high-fat diet to elicit atherosclerosis.

RESULTS

Lipin-1mKO mice had larger aortic root plaques than littermate control mice after 8 and 12 weeks of a high-fat diet. Lipin-1mKO mice also had increased serum proinflammatory cytokine concentrations, reduced apoptosis in plaques, and larger necrotic cores in the plaques compared to control mice.

CONCLUSIONS

Combined, the data suggest lipin-1 transcriptional co-regulatory activity in myeloid cells is atheroprotective.

Dead cell and debris clearance in the atherosclerotic plaque: Mechanisms and therapeutic opportunities to promote inflammation resolution

Phagocytic clearance of dead cells and debris is critical for inflammation resolution and maintenance of tissue homeostasis. Consequently, defective clearance of dead cells and debris is associated with initiation and exacerbation of several autoimmune disorders and chronic inflammatory diseases such as atherosclerosis. The progressive loss of dead cell clearance capacity within the atherosclerotic plaque leads to accumulation of necrotic cells, chronic non-resolving inflammation, and expansion of the necrotic core, which triggers atherosclerotic plaque rupture and clinical manifestation of acute thrombotic cardiovascular adverse events. In this review, we describe the fundamental molecular and cellular mechanisms of dead cell clearance and how it goes awry in atherosclerosis. Finally, we highlight novel therapeutic strategies that enhance dead cell and debris clearance within the atherosclerotic plaque to promote inflammation resolution and atherosclerotic plaque stabilization.

Association of culprit lesion plaque characteristics with flow restoration post-fibrinolysis in ST-segment elevation myocardial infarction: an intravascular ultrasound-virtual histology study

Background

Not every patient achieves normal coronary flow following fibrinolysis in STEMI (ST-segment elevation myocardial infarction). The culprit lesion plaque characteristics play a prominent role in the coronary flow before and during percutaneous coronary intervention. The main purpose was to determine the culprit lesion plaque features by virtual histology-intravascular ultrasound (VH-IVUS) in patients with STEMI following fibrinolysis in relation to baseline coronary angiogram TIMI (thrombolysis in myocardial infarction) flow. Pre-intervention IVUS was undertaken in 61 patients with STEMI after successful fibrinolysis. After the coronary angiogram, they were separated into the TIMI1–2 flow group (n = 31) and TIMI 3 flow group (n = 30). Culprit lesion plaque composition was evaluated by VH-IVUS.

Results

On gray-scale IVUS, the lesion external elastic membrane cross-sectional area (EEM CSA) was significantly higher in the TIMI 1–2 groups as compared to the TIMI 3 group (15.71 ± 3.73 mm² vs 13.91 ± 2.94 mm², p = 0.041) with no significant difference in plaque burden (82.42% vs. 81.65%, p = 0.306) and plaque volume (108.3 mm³ vs. 94.3 mm³, p = 0.194). On VH-IVUS, at the minimal luminal area site (MLS), the fibrous area (5.83 mm² vs. 4.37 mm², p = 0.024), necrotic core (NC) area (0.95 mm² vs. 0.59 mm², p < 0.001), and NC percentage (11% vs. 7.1%, p = 0.024) were higher in the TIMI 1–2 groups in contrast to the TIMI 3 group. The absolute necrotic core (NC) volume (8.3 mm³ vs. 3.65 mm³, p < 0.001) and NC percentage (9.3% vs. 6.0%, p = 0.007) were significantly higher in the TIMI 1–2 groups as compared to the TIMI 3 group. Absolute dense calcium (DC) volume was higher in TIMI 1–2 groups with a trend towards significance (1.0 mm³ vs.0.75 mm³, p = 0.051). In multivariate analysis, absolute NC volume was the only independent predictor of TIMI 1–2 flow (odds ratio = 1.561; 95% CI 1.202–2.026, p = 0.001). Receiver operating characteristic curves showed absolute NC volume has best diagnostic accuracy (AUC = 0.816, p < 0.001) to predict TIMI 1–2 flow with an optimal cutoff value of 4.5 mm³ with sensitivity and specificity of 79% and 61%, respectively.

Conclusions

This study exemplifies that the necrotic core component of the culprit lesion plaque in STEMI is associated with the coronary flow after fibrinolysis. The absolute necrotic core volume is a key determinant of flow restoration post-fibrinolysis and aids in prognostication of less than TIMI 3 flow.

The Interplay between Features of Plaque Vulnerability and Hemodynamic Relevance of Coronary Artery Stenoses

Fractional flow reserve (FFR) may not be immune from hemodynamic perturbations caused by both vessel and lesion related factors. The aim of this study was to investigate the impact of plaque- and vessel wall-related features of vulnerability on the hemodynamic effect of intermediate coronary stenoses. Methods and Results: In this cross-sectional study, patients referred to catheterization laboratory for clinically indicated coronary angiography were prospectively screened for angiographically intermediate stenosis (50-80%). Seventy lesions from 60 patients were evaluated. Mean angiographic stenosis was 62.1 ± 16.3%. After having performed FFR assessment, intravascular ultrasound (IVUS) was performed over the FFR wire. Virtual histology IVUS was used to identify the plaque components and thin cap fibroatheroma (TCFA). TCFA was significantly more frequent (65 vs. 38%, p = 0.026), and necrotic core volume (26.15 ± 14.22 vs. 16.21 ± 8.93 mm3, p = 0.04) was significantly larger in the positively remodeled than non-remodeled vessels. Remodeling index correlated with necrotic core volume (r = 0.396, p = 0.001) and with FFR (r = -0. 419, p = 0.001). With respect to plaque components, only necrotic core area (r = -0.262, p = 0.038) and necrotic core volume (r = -0.272, p = 0.024) were independently associated with FFR. In the multivariable model, presence of TCFA was independently associated with significantly lower mean FFR value as compared to absence of TCFA (adjusted, 0.71 vs. 0.78, p = 0.034). Conclusion: The current study demonstrated that for a given stenosis geometry, features of plaque vulnerability such as necrotic core volume, TCFA, and positive remodeling may influence the hemodynamic relevance of intermediate coronary stenoses.

Drug delivery to solid tumors with heterogeneous microvascular networks: Novel insights from image-based numerical modeling

The present study examines chemotherapy by incorporating multi-scale mathematical modeling to predict drug delivery and its effects. This approach leads to a more-realistic physiological tumor model than is possible with previous approaches, as it obtains the capillary network geometry from an image, and also considers the tumor's necrotic core, drug binding, and cellular uptake. Modeling of the fluid flow and drug transport is then performed in the extracellular matrix. The results demonstrate a 10% drop in the fraction of killed cancer cells 69% rather than the 79% reported earlier for a tumor of similar geometry a more-accurate value. This study examines how tumor-related parameters including the necrotic core size and tumor size, and also drug-related parameters drug dosage, binding affinity of drug, and drug degradation can affect the delivery of the drug to solid tumors. Results indicate that concentration of drug are high in the tumor, low in normal tissue, and remarkably low in the necrotic core. Results also offer a treatment of tumors with smaller necrotic core. Tumor size, which implies the tumor progression, has a considerable impact on treatment outcomes, so to be more effective, treatment should be applied at a specific size of tumor. It is demonstrated that binding affinity of drugs to cell-surface receptors and drug dosage have significant impact on treatment efficacy, so they should be regulated based on a balanced quantification between maximum treatment efficacy and minimum side effects. On the other hand, considering the effects of drug degradation in the model has not significant effect on treatment efficacy. The findings of the present study provide insight into the mechanism of drug delivery to solid tumors based on analyzing the effective parameters and modeling how their behavior in the tumor microenvironment affects treatment efficacy.

Comparison of angioscopy and histopathology for the evaluation of carotid plaque characteristics: an ex vivo validation study

Intravascular angioscopy is widely used for evaluating plaque characteristics through the plaque color in the coronary artery. This study evaluated whether angioscopy is capable of identifying various plaque morphologies, including necrotic core and intraplaque hemorrhage (IPH) in the carotid artery. Nine patients underwent carotid endarterectomy for carotid artery stenosis, and these specimens were imaged ex vivo by angioscopy within 6 h. An angioscopic examination of carotid plaque evaluated its color intensity as follows: white, yellow, or red. The IPH area, necrotic core area, and fibrous cap thickness was measured on histological sections at each site. A total of 7 plaques were graded as white plaques, 10 as yellow, and 8 as red by angioscopy. The IPH area and the percent area occupied by IPH were larger in red and yellow plaques than in white plaques (10.7 ± 9.3 mm², 9.4 ± 7.8 mm², and 2.2 ± 1.7 mm², respectively, P = 0.074; and 25 ± 10%, 19 ± 13%, and 7 ± 5%, respectively, P = 0.008). Furthermore, the thickness of the fibrous cap was significantly thinner in red plaques than in yellow and white plaques (128 ± 34 µm, 328 ± 136 µm, and 285 ± 102 µm, respectively, P = 0.002). The ROC analysis for predicting a presence of red plaques identified that the optimal cutoff value of fibrous cap thickness was 181 µm (area under the curve = 0.987, 100% sensitivity, 90% specificity). The prevalence of red plaques on intravascular angioscopy may represent the existence of plaques containing relatively larger necrotic core and IPH with a thin fibrous cap.

Ultramorphological analysis of plaque advancement and cholesterol crystal formation in Ldlr knockout mouse atherosclerosis

BACKGOUND AND AIMS

The low-density lipoprotein receptor-deficient (Ldlr^-/-) mouse has been utilized by cardiovascular researchers for more than two decades to study atherosclerosis. However, there has not yet been a systematic effort to document the ultrastructural changes that accompany the progression of atherosclerotic plaque in this model.

METHODS

Employing several different staining and microscopic techniques, including immunohistochemistry, as well as electron and polarized microscopy, we analyzed atherosclerotic lesion development in Ldlr^-/- mice fed an atherogenic diet over time.

RESULTS

Lipid-like deposits occurred in the subendothelial space after only one week of atherogenic diet. At two weeks, cholesterol crystals (CC) formed and increased thereafter. Lipid, CC, vascular smooth muscles cells, and collagen progressively increased over time, while after 4 weeks, relative macrophage content decreased. Accelerated accumulation of plate- and needle-shaped CC accompanied plaque core necrosis. Lastly, CC were surrounded by cholesterol microdomains, which co-localized with CC through all stages of atherosclerosis, indicating that the cholesterol microdomains may be a source of CC.

CONCLUSIONS

Here, we have documented, for the first time in a comprehensive way, atherosclerotic plaque morphology and composition from early to advanced stages in the Ldlr^-/- mouse, one of the most commonly used animal models utilized in atherosclerosis research.

In vivo mimicking model for solid tumor towards hydromechanics of tissue deformation and creation of necrosis

The present work addresses transvascular and interstitial fluid transport inside a solid tumor surrounded by normal tissue (close to an in vivo mimicking setup). In general, biological tissues behave like a soft porous material and show mechanical behavior towards the fluid motion through the interstitial space. In general, forces like viscous drag that are associated with the fluid flow may compress the tissue material. On the macroscopic level, we try to model the motion of fluids and macromolecules through the interstitial space of solid tumor and the normal tissue layer. The transvascular fluid transport is assumed to be governed by modified Starling's law. The poroelastohydrodynamics (interstitial hydrodynamics and the deformation of tissue material) inside the tumor and normal tissue regions is modeled using linearized biphasic mixture theory. Correspondingly, the velocity distribution of fluid is coupled to the displacement field of the solid phase (mainly cellular phase and extracellular matrix) in both the normal and tumor tissue regions. The corresponding velocity field is used within the transport reaction equation for fluids and macromolecules through interstitial space to get the overall solute (e.g., nutrients, drug, and other macromolecules) distribution. This study justifies that the presence of the normal tissue layer plays a significant role in delaying/assisting necrosis inside the tumor tissue. It is observed that the exchange process of fluids and macromolecules across the interface of the tumor and normal tissue affects the effectiveness factor corresponding to the tumor tissue.

Lipocalin-2 contributes to experimental atherosclerosis in a stage-dependent manner

BACKGROUND AND AIMS

Lipocalin-2 (Lcn2) is a glycoprotein which can be secreted by immune cells. Several studies in humans have suggested Lcn2 can be used as a biomarker for the detection of unstable atherosclerotic lesions, partly as it is known to interact with MMP-9.

METHODS

In this study, we generated Ldlr^-/-Lcn2^-/- mice to assess the functional role of Lcn2 in different stages of atherosclerosis. Atherosclerotic lesions were characterized through histological analysis and myeloid cell populations were examined using flow cytometry.

RESULTS

We show that Ldlr^-/-Lcn2^-/- mice developed larger atherosclerotic lesions during earlier stages of atherosclerosis and had increased circulating Ly6C^hi inflammatory monocytes compared to Ldlr^-/- mice. Advanced atherosclerotic lesions from Ldlr^-/-Lcn2^-/- mice had decreased necrotic core area, suggesting Lcn2 deficiency may affect lesion stability. Furthermore, MMP-9 activity was diminished in plaques from Ldlr^-/-Lcn2^-/- mice.

CONCLUSIONS

Altogether, these findings suggest that Lcn2 deficiency promotes lesion growth in earlier stages of the disease while it decreases MMP-9 activity and necrotic core size in advanced atherosclerosis.

Microfluidic device flow field characterization around tumor spheroids with tunable necrosis produced in an optimized off-chip process

Tumor spheroids are a 3-D tumor model that holds promise for testing cancer therapies in vitro using microfluidic devices. Tailoring the properties of a tumor spheroid is critical for evaluating therapies over a broad range of possible indications. Using human colon cancer cells (HCT-116), we demonstrate controlled tumor spheroid growth rates by varying the number of cells initially seeded into microwell chambers. The presence of a necrotic core in the spheroids could be controlled by changing the glucose concentration of the incubation medium. This manipulation had no effect on the size of the tumor spheroids or hypoxia in the spheroid core, which has been predicted by a mathematical model in computer simulations of spheroid growth. Control over the presence of a necrotic core while maintaining other physical parameters of the spheroid presents an opportunity to assess the impact of core necrosis on therapy efficacy. Using micro-particle imaging velocimetry (micro-PIV), we characterize the hydrodynamics and mass transport of nanoparticles in tumor spheroids in a microfluidic device. We observe a geometrical dependence on the flow rate experienced by the tumor spheroid in the device, such that the "front" of the spheroid experiences a higher flow velocity than the "back" of the spheroid. Using fluorescent nanoparticles, we demonstrate a heterogeneous accumulation of nanoparticles at the tumor interface that correlates with the observed flow velocities. The penetration depth of these nanoparticles into the tumor spheroid depends on nanoparticle diameter, consistent with reports in the literature.

Non-invasive and invasive imaging of vulnerable coronary plaque

Vulnerable plaque is characterized by a large necrotic core and an overlying thin fibrous cap. Non-invasive imaging modalities such as computed tomography angiography (CTA) and magnetic resonance imaging (MRI) allow for the assessment of morphological plaque characteristics, while positron emission tomography (PET) enables the detection of metabolic activity within the atherosclerotic lesions. Invasive imaging modalities such as intravascular ultrasound (IVUS), optical-coherence tomography (OCT), and intravascular MRI (IV-MRI) display plaques at a high spatial resolution. Near-infrared spectroscopy (NIRS) allows for the detection of chemical components of atherosclerotic plaques. In this review, we describe state-of-the-art non-invasive and invasive imaging modalities and stress the combination of their advantages to identify vulnerable plaque features.

Hydrodynamics and convection enhanced macromolecular fluid transport in soft biological tissues: Application to solid tumor

This work addresses a theoretical framework for transvascular exchange and extravascular transport of solute macromolecules through soft interstitial space inside a solid tumor. Most of the soft biological tissues show materialistic properties similar to deformable porous material. They exhibit mechanical behavior towards the fluid motion since the solid phase of the tumor tissue gets compressed by the drag force that is associated with the extracellular fluid flow. This paper presents a general view about the transvascular and interstitial transport of solute nutrients inside a tumor in the macroscopic level. Modified Starling׳s equation is used to describe transvascular nutrient transport. On the macroscopic level, motion of extracellular fluid within the tumor interstitium is modeled with the help of biphasic mixture theory and a spherical symmetry solution is given as a simpler case. This present model describes the average interstitial fluid pressure (IFP), extracellular fluid velocity (EFV) and flow rate of extracellular fluid, as well as the deformation of the solid phase of the tumor tissue as an immediate cause of extracellular fluid flow. When the interstitial transport is diffusion dominated, an analytical treatment of advection-diffusion-reaction equation finds the overall nutrient distribution. We propose suitable criteria for the formation of necrosis within the tumor interstitium. This study introduces some parameters that represent the nutrient supply from tumor blood vessels into the tumor extracellular space. These transport parameters compete with the reversible nutrient metabolism of the tumor cells present in the interstitium. The present study also shows that the effectiveness factor corresponding to a first order nutrient metabolism may reach beyond unity if the strength of the distributive solute source assumes positive non-zero values.

Dual-energy computed tomography imaging to determine atherosclerotic plaque composition: a prospective study with tissue validation

Background

Identifying vulnerable coronary plaque with coronary CT angiography is limited by overlap between attenuation of necrotic core and fibrous plaque. Using x-rays with differing energies alters attenuation values of these components, depending on their material composition.

Objectives

We sought to determine whether dual-energy CT (DECT) improves plaque component discrimination compared with single-energy CT (SECT).

Methods

Twenty patients underwent DECT and virtual histology intravascular ultrasound (VH-IVUS). Attenuation changes at 100 and 140 kV for each plaque component were defined, using 1088 plaque areas co-registered with VH-IVUS. Hounsfield unit thresholds that best detected necrotic core were derived for SECT (conventional attenuation values) and for DECT (using dual-energy indices, defined as difference in Hounsfield unit values at the 2 voltages/their sum). Sensitivity of SECT and DECT to detect plaque components was determined in 77 segments from 7 postmortem coronary arteries. Finally, we examined 60 plaques in vivo to determine feasibility and sensitivity of clinical DECT to detect VH-IVUS–defined necrotic core.

Results

In contrast to conventional SECT, mean dual-energy indices of necrotic core and fibrous tissue were significantly different with minimal overlap of ranges (necrotic core, 0.007 [95% CI, –0.001 to 0.016]; fibrous tissue, 0.028 [95% CI, 0.016–0.050]; P < .0001). DECT increased diagnostic accuracy to detect necrotic core in postmortem arteries (sensitivity, 64%; specificity, 98%) compared with SECT (sensitivity, 50%; specificity, 94%). DECT sensitivity to detect necrotic core was lower when analyzed in vivo, although still better than SECT (45% vs 39%).

Conclusions

DECT improves the differentiation of necrotic core and fibrous plaque in ex vivo postmortem arteries. However, much of this improvement is lost when translated to in vivo imaging because of a reduction in image quality.