Deposition Of Low-density Lipoprotein Research Articles

HDL and plaque regression in a multiphase model of early atherosclerosis

Atherosclerosis is a chronic disease of the arteries characterised by the accumulation of lipids and lipid-engorged cells in the artery wall. Early plaque growth is aggravated by the deposition of low density lipoproteins (LDL) in the wall and the subsequent immune response. High density lipoproteins (HDL) counterbalance the effects of LDL by accepting cholesterol from macrophages and removing it from the plaque. In this paper, we develop a free boundary multiphase model to investigate the effects of LDL and HDL on early plaque development. We examine how the rates of LDL and HDL deposition affect cholesterol accumulation in macrophages, and how this impacts cell death rates and emigration. We identify a region of LDL–HDL parameter space where plaque growth stabilises for low LDL and high HDL influxes, due to macrophage emigration and HDL clearance that counterbalances the influx of new cells and cholesterol. We explore how the efferocytic uptake of dead cells and the recruitment of new macrophages affect plaque development for a range of LDL and HDL influxes. Finally, we consider how changes in the LDL–HDL profile can change the course of plaque development. We show that changes towards lower LDL and higher HDL can slow plaque growth and even induce regression. We find that these changes have less effect on larger, more established plaques, and that temporary changes will only slow plaque growth in the short term.

Abstract 133: Trem2 Agonist Promotes Atherosclerotic Plaque Stability

Atherosclerosis is an inflammatory disease of the arteries that is a major cause of cardiovascular disease (CVD). Atherosclerotic plaque progression is driven by the deposition of low-density lipoprotein (LDL) within the intima, which is internalized by macrophages, forming lipid-engorged foamy cells. Importantly, the accumulation of excess LDL within foamy macrophages is cytotoxic, driving apoptosis, which ultimately promotes necrotic core formation and increased potential for plaque rupture. Recently, our lab identified the lipid receptor Trem2 to be highly expressed by foamy macrophages and regulate cell survival, proliferation, and cholesterol efflux. Thus, we tested whether agonizing Trem2 could drive macrophage survival to promote plaque stability. Using a Trem2 agonist antibody (AL002a, Alector Inc.), we treated Ldlr -/- mice that had preexisting atherosclerotic plaque with either isotype control or AL002a antibody for 8 weeks. AL002a treated mice showed an increase in plaque size in the aortic arch and aortic sinus. Plaque analysis determined that this was primarily due to an expansion of macrophage cellularity, through promotion of cell survival and proliferation. Furthermore, we found that plaques from AL002a treated mice had decreased necrotic core formation, increased fibrous cap size, and increased collagen deposition, consistent with improved stability. Single cell RNA-sequencing of atherosclerotic aortae from isotype and AL002a treated mice found that Trem2-agonism dramatically reshaped transcriptomes of both foamy macrophages and smooth muscle cells, including upregulation of oxidative phosphorylation (OXPHOS), cholesterol efflux, collagen, and pro-survival genes while downregulating inflammatory pathways. In vitro studies using bone marrow derived macrophages confirmed AL002a’s ability to drive cell survival, proliferation, OXPHOS, and cholesterol efflux in culture. Finally, we determined that AL002a’s ability to reshape aspects of foamy macrophage function was dependent on its ability to activate the kinase SYK downstream of Trem2. Overall, this data identifies Trem2 as a viable therapeutic target for promoting atherosclerotic plaque stability and improving outcomes in CVD.

Apolipoprotein A1 and high-density lipoprotein limit low-density lipoprotein transcytosis by binding SR-B1

Atherosclerosis results from the deposition and oxidation of LDL and immune cell infiltration in the sub-arterial space leading to arterial occlusion. Studies have shown that transcytosis transports circulating LDL across endothelial cells lining blood vessels. LDL transcytosis is initiated by binding to either scavenger receptor B1 (SR-B1) or activin A receptor-like kinase 1 on the apical side of endothelial cells leading to its transit and release on the basolateral side. HDL is thought to partly protect individuals from atherosclerosis due to its ability to remove excess cholesterol and act as an antioxidant. Apolipoprotein A1 (APOA1), an HDL constituent, can bind to SR-B1, raising the possibility that APOA1/HDL can compete with LDL for SR-B1 binding, thereby limiting LDL deposition in the sub-arterial space. To examine this possibility, we used in vitro approaches to quantify the internalization and transcytosis of fluorescent LDL in coronary endothelial cells. Using microscale thermophoresis and affinity capture, we find that SR-B1 and APOA1 interact and that binding is enhanced when using the cardioprotective variant of APOA1 termed Milano (APOA1-Milano). In male mice, transiently increasing the levels of HDL reduced the acute deposition of fluorescently labeled LDL in the atheroprone inner curvature of the aorta. Reduced LDL deposition was also observed when increasing circulating wild-type APOA1 or the APOA1-Milano variant, with a more robust inhibition from the APOA1-Milano. The results suggest that HDL may limit SR-B1-mediated LDL transcytosis and deposition, adding to the mechanisms by which it can act as an atheroprotective particle.

Influence of morphological characteristics on the deposition of low-density lipoprotein in intracranial bifurcation aneurysms

The increasingly demonstrated association of wall enhancement (WE) measured by vascular wall imaging with the instability/rupture of intracranial aneurysms (IAs) implies the significance of investigating the transport and accumulation of blood substances [e.g., low-density lipoprotein (LDL), lipoprotein (a)] related to WE in IAs. In the present study, we perform numerical simulations to explore the relationships between the distribution/severity of LDL deposition on the lumen surface and the morphological characteristics of aneurysm and its adjacent arteries as well as the underlying fluid dynamic mechanisms. Bifurcation aneurysms located at the middle cerebral artery are selected as the subject of investigation and for which both idealized and patient-specific models are built. Studies on the idealized models reveal that the aneurysm–parent (AP) artery angle is more powerful than other morphological parameters [e.g., daughter–parent (DP) artery angle, nonsphericity index (NI) of aneurysm] in determining the severity of LDL deposition. A bleb (i.e., secondary sac) can enhance local LDL deposition, especially when located in an LDL deposition-prone aneurysm wall region. In patient-specific models, the dominant effect on the LDL deposition of the AP angle remains identifiable, whereas the effects of the DP angle and NI are overwhelmed by confounding factors. Enhanced LDL deposition prefers to appear in wall regions perpendicular to the intra-aneurysmal vortex centerline. In comparison with wall shear stress magnitude, the normal-to-tangential near-wall velocity ratio and particle residence time can better predict the localization of enhanced LDL deposition.

Repetitive Antigen Responses of LDL-Reactive CD4+ T Cells Induce Tr1 Cell-Mediated Immune Tolerance.

Inflammation triggered by the deposition of LDL (low-density lipoprotein) in the arterial wall leads to the development of atherosclerosis. Regulatory T (Treg) cells inhibit vascular inflammation through the induction of immune tolerance toward LDL-related antigens. However, tolerogenic mechanisms that promote the generation of LDL-specific Treg cells in vivo remain unclear. We identified LDL-specific T cells by activation-induced marker expression and analyzed expression profiles and suppressive functions of TCR (T-cell antigen receptor)-transgenic T cells upon repetitive transfer into antigen-transgenic mice via flow cytometry. We investigated the naturally occurring Treg-cell response against human LDL in standard chow diet-fed mice that are transgenic for human ApoB100 (apolipoprotein B100). We found that IL (interleukin)-10 expression in LDL-specific T cells from spleen increases with age, albeit LDL-specific populations do not enlarge in older mice. To investigate the generation of IL-10-producing LDL-specific T cells, we transferred naive CD4+ T cells recognizing human ApoB100 from TCR-transgenic mice into human ApoB100-transgenic mice. Adoptive transfer of human ApoB100-specific T cells induced immune tolerance in recipient mice and effectively inhibited activation of subsequently transferred naive T cells of the same specificity in vivo. Moreover, repetitive transfers increased the population of Treg type 1 cells that suppress ApoB100-specific responses via IL-10. In a translational approach, LDL-specific Treg type 1 cells from blood of healthy donors suppressed the activation of monocytic THP-1 cells in an IL-10-dependent manner. We show that repetitive transfer of naive ApoB100-specific T cells and recurrent LDL-specific T-cell stimulation induces Treg type 1 cell-mediated immune tolerance against LDL in vivo. Our results provide insight into the generation of autoantigen-specific anti-inflammatory T cells under tolerogenic conditions.

A mathematical model that describes the relation of low-density lipoprotein and oxygen concentrations in a stenosed artery

The cellular activities of the endothelium layer between lumen and intima are significantly linked to the origin of the disease atherosclerosis. Three stages of atherosclerosis were investigated in this study (40%-mild, 50%-modest, and 60%-acute) concerning the coronary arterial segment. The essence of the hemodynamic factors like flow velocity, pressure, and wall shear stress has been investigated, as well as the interrelationships between them. At all degrees of stenosis, the biophysical relationship between convection-diffusion of low-density lipoproteins (LDL) and convection-diffusion of oxygen in the bloodstream is investigated. The Finite Element Methods (FEM) are used to solve the modeled partial differential equation systems. The method adopted is numerical in nature providing accurate graphical solutions to the framed systems. The physical effects of the deposition of LDL on the arterial wall, like a decrease in the diameter of the lumen, and toughening of the walls, are analyzed through the evaluation of the physical parameters. The study revealed that the deposition of LDL molecules in the post stenotic region leads to the depletion of oxygen in the region leading to the rapid dysfunctioning of the endothelial layer of the lumen-intima boundary.

Cholesterol Paradigm and Beyond in Atherosclerotic Cardiovascular Disease: Cholesterol, Sterol Regulatory Element-Binding Protein, Inflammation, and Vascular Cell Mobilization in Vasculopathy.

Hypercholesterolemia is a well-established risk factor for atherosclerotic cardiovascular disease (ASCVD). How cholesterol and its carrier lipoproteins are involved in ASCVD is still under extensive investigation. Satins are thus far the best-proven class of cholesterol-lowering medications to improve the clinical outcomes of ASCVD. Statins specifically inhibit the rate-limiting enzyme 3-hydroxy-3-methylglutaryl-CoA reductase of the mevalonate pathway for cholesterol biosynthesis. The widely accepted theory is that statins inhibit the hepatic cholesterol synthesis causing upregulation of hepatocyte low-density lipoprotein (LDL) receptor; receptor-mediated LDL uptake and metabolism in the liver results in reduction of circulating LDL cholesterol, which subsequently reduces vascular deposition and retention of cholesterol or LDL in atherogenesis. Nevertheless, cholesterol biosynthesis is ubiquitous, also in extrahepatic cells including those in vascular wall, under tight regulation by sterol regulatory element-binding protein (SREBP), the master gene transcription factor governing cholesterol biosynthesis. Studies have shown that SREBP can be upregulated in vascular wall subject to injury or stent implantation. SREBP can be activated by proinflammatory and mitogenic factors in vascular cells, leading to hyperactive mevalonate pathway, which promotes vascular cell mobilization, further proinflammatory and mitogenic factor release from vascular cells, and vascular inflammation. In this article, we review the cellular cholesterol homeostasis regulation by SREBP and SREBP-mediated vascular hyperactive cholesterol biosynthesis, we term vascular hypercholesterolism, in the pathogenesis of ASCVD and vasculopathy. SREBP functions as a platform bridging cholesterol, inflammation, and vascular cell mobilization in ASCVD pathogenesis. Targeting vascular hypercholesterolism could open a new avenue in fighting against ASCVD.

A computational model for cardiovascular hemodynamics and protein transport phenomena

The hemodynamics plays a key role in the transport processes, in the blood stream, and thus, on the accumulation and deposition of lipids and medication on the vessel’s wall. Therefore, understanding the hemodynamics of the arterial veins can advance the understanding of transport phenomena and prediction of deposition and buildup of the low-density lipoproteins (LDL) and particulate medication, on the arterial surfaces. Previous studies have showed that for pulsatile flow, laminar-turbulent flow transition may occur, particularly during intense exercises. Experimental and computational studies, of hemodynamics and transport phenomena, pose significant challenges due to the complex aorta’s geometry and arterial fluid dynamics. In the present study, we propose a large-eddy simulation (LES), computational approach, to carry out the hemodynamics and medication dispersion and deposition studies, inside the descending aorta. The analysis reveals that the flow separation causes a preferential deposition and build-up of low-density lipoproteins (LDL) on the arterial surface. Our study also shows that the flow boundary-layer separation is associated with an increase in deposition of the low-density lipoproteins. The analysis reveals the presence of Dean vortices, inside the aorta branches, which contribute to the reduction of the deposition and build-up of low-density lipoproteins on the arterial surfaces. The analysis of medication dispersion and deposition, inside the descending aorta, shows that the total medication deposition increases with the increase of particle size and density. Particles of fiber-like shape are more prone to deposition, and this is due to the fact that fiber-like particles align perfectly with the flow streamlines. Thus, the interaction of complex turbulent eddies with vessel’s wall causes medication deposition. The research shows that LES is a promising tool in the analysis of hemodynamics and medication transport and therefore, it may assist medical planning by providing surgeons with the elements of the blood flow such as, pressure, velocity, vorticity, wall-shear stresses, which cannot be measured in vivo and obtained with imaging techniques.

MLKL Aggravates Ox-LDL-Induced Cell Pyroptosis via Activation of NLRP3 Inflammasome in Human Umbilical Vein Endothelial Cells.

Atherosclerosis is a progressive chronic inflammation in the arterial walls. It is believed that the deposition of low-density lipoprotein (LDL) and its damage to endothelial cells play a vital role in atherosclerosis. Oxidized LDL (Ox-LDL) was confirmed to induce endothelial cell pyroptosis which plays an important role in intima inflammation and the development of atherosclerosis, but the underlying molecular mechanism needs to be explored. Here, we showed that ox-LDL upregulated the expression of mixed lineage kinase domain-like (MLKL) protein at both the mRNA and protein levels in endothelial cells, associated with the augment of pro-caspase-1 cleavage, interleukin-1β (IL-1β) maturation, pro-IL-1β production, and lactate dehydrogenase (LDH) release. Overexpression of MLKL substantially aggravated ox-LDL-induced increasing levels of caspase-1, IL-1β, pro-IL-1β, and LDH. MLKL-induced caspase-1 activation and IL-1β maturation were abolished by NLR family, pyrin domain-containing 3 (NLRP3) specific inhibitor MCC950, or extracellular high potassium concentration. Our findings indicated that MLKL is essential for regulation of ox-LDL-induced pyroptosis and inflammation through the activation of NLRP3 inflammasome, and suggested that MLKL could act as potential therapeutic targets to ameliorate atherosclerosis-related diseases.

Opposing effects of HNP1 (α-defensin-1) on plasma cholesterol and atherogenesis.

Atherosclerosis, the predominant cause of death in well-resourced countries, may develop in the presence of plasma lipid levels within the normal range. Inflammation may contribute to lesion development in these individuals, but the underlying mechanisms are not well understood. Transgenic mice expressing α-def-1 released from activated neutrophils develop larger lipid and macrophage-rich lesions in the proximal aortae notwithstanding hypocholesterolemia caused by accelerated clearance of α-def-1/low-density lipoprotein (LDL) complexes from the plasma. The phenotype does not develop when the release of α-def-1 is prevented with colchicine. However, ApoE-/- mice crossed with α-def-1 mice or given exogenous α-def-1 develop smaller aortic lesions associated with reduced plasma cholesterol, suggesting a protective effect of accelerated LDL clearance. Experiments were performed to address this seeming paradox and to determine if α-def-1 might provide a means to lower cholesterol and thereby attenuate atherogenesis. We confirmed that exposing ApoE-/- mice to α-def-1 lowers total plasma cholesterol and decreases lesion size. However, lesion size was larger than in mice with total plasma cholesterol lowered to the same extent by inhibiting its adsorption or by ingesting a low-fat diet. Furthermore, α-def-1 levels correlated independently with lesion size in ApoE-/- mice. These studies show that α-def-1 has competing effects on atherogenesis. Although α-def-1 accelerates LDL clearance from plasma, it also stimulates deposition and retention of LDL in the vasculature, which may contribute to development of atherosclerosis in individuals with normal or even low plasma levels of cholesterol. Inhibiting α-def-1 may attenuate the impact of chronic inflammation on atherosclerotic vascular disease.

Modeling and simulation of blood flow with magnetic nanoparticles as carrier for targeted drug delivery in the stenosed artery

A systematic study on targeted drug delivery is carried out in an unsteady flow of blood infused with magnetic nanoparticles with an aim to understand the flow pattern and nanoparticle aggregation in a diseased arterial segment having atherosclerosis. The magnetic NPs(nanoparticles) are supervised by a magnetic field, which is significant for the therapeutic treatment of arterial diseases, tumors, and cancer cells and removing blood clots. Coupled thermal energy equation has been modeled by considering the dissipation of energy that encounters due to the application of the magnetic field and the presence of high viscosity of blood. The simulation technique used to solve the mathematical model is vorticity-stream function formulations in the diseased artery. An elevation in SLP (Specific loss power) is noted in the aortic bloodstream when the agglomeration of nanoparticles is higher. This phenomenon has potential applications in the treatment of hyperthermia. The study focuses on the lowering of WSS (wall shear stress) with increasing particle concentration at the downstream of the stenosis, which depicts the vigorous flow circulation zone. These low shear stress regions prolong the residing time of the nanoparticles carrying drugs, which soaks up the LDL (Low-Density Lipoprotein) deposition. Moreover, an increase in NP concentration enhances the Nusselt number, which marks the increase of heat transfer from the arterial wall to the surrounding tissues to destroy tumor and cancer cells without affecting the healthy cells. The results have a significant influence on the study of medicine to treat arterial diseases such as atherosclerosis without the need for surgery, which can minimize the expenditures on cardiovascular treatments and post-surgical complications in patients.

Influence of wall shear stress and geometry on the lumen surface concentration of low density lipoprotein in a model abdominal aortic aneurysm

In this work, the correlation between the wall shear stress (WSS) and the surface concentration variation of low density lipoprotein (LDL) on the walls of an idealized abdominal aortic aneurysm (AAA) is explored. It is observed that on the walls of AAA, the WSS has a significant effect on the LDL deposition pattern and a region of low WSS does not always correspond to a locally high concentration of LDL. The correlation between the WSS and the LDL deposition is found to be linked to the local fluid-flow pattern. This is explained by conducting an analysis on simplified geometries using steady inflow conditions that produced a fluid-flow pattern similar to that in the original AAA under physiologically relevant pulsatile inflow conditions. Furthermore, the influence of geometric parameters, such as the height, the width, and the shape of the aneurysm, on the surface concentration of LDL is studied. The width of the aneurysm is found to have a strong influence on the variation of the LDL surface concentration.

Analysis of non-Newtonian effects on Low-Density Lipoprotein accumulation in an artery

In this work, non-Newtonian effects on Low-Density Lipoprotein (LDL) transport across an artery are analyzed with a multi-layer model. Four rheological models (Carreau, Carreau–Yasuda, power-law and Newtonian) are used for the blood flow through the lumen. For the non-Newtonian cases, the arterial wall is modeled with a generalized momentum equation. Convection–diffusion equation is used for the LDL transport through the lumen, while Staverman–Kedem–Katchalsky, combined with porous media equations, are used for the LDL transport through the wall. Results are presented in terms of filtration velocity, Wall Shear Stresses (WSS) and concentration profiles. It is shown that non-Newtonian effects on mass transport are negligible for a healthy intramural pressure value. Non-Newtonian effects increase slightly with intramural pressure, but Newtonian assumption can still be considered reliable. Effects of arterial size are also analyzed, showing that Newtonian assumption can be considered valid for both medium and large arteries, in predicting LDL deposition. Finally, non-Newtonian effects are also analyzed for an aorta–common iliac bifurcation, showing that Newtonian assumption is valid for mass transport at low Reynolds numbers. At a high Reynolds number, it has been shown that a non-Newtonian fluid model can have more impact due to the presence of flow recirculation.

α-Defensins Induce a Post-translational Modification of Low Density Lipoprotein (LDL) That Promotes Atherosclerosis at Normal Levels of Plasma Cholesterol

Approximately one-half of the patients who develop clinical atherosclerosis have normal or only modest elevations in plasma lipids, indicating that additional mechanisms contribute to pathogenesis. In view of increasing evidence that inflammation contributes to atherogenesis, we studied the effect of human neutrophil α-defensins on low density lipoprotein (LDL) trafficking, metabolism, vascular deposition, and atherogenesis using transgenic mice expressing human α-defensins in their polymorphonuclear leukocytes (Def(+/+)). Accelerated Def(+/+) mice developed α-defensin·LDL complexes that accelerate the clearance of LDL from the circulation accompanied by enhanced vascular deposition and retention of LDL, induction of endothelial cathepsins, increased endothelial permeability to LDL, and the development of lipid streaks in the aortic roots when fed a regular diet and at normal plasma levels of LDL. Transplantation of bone marrow from Def(+/+) to WT mice increased LDL clearance, increased vascular permeability, and increased vascular deposition of LDL, whereas transplantation of WT bone marrow to Def(+/+) mice prevented these outcomes. The same outcome was obtained by treating Def(+/+) mice with colchicine to inhibit the release of α-defensins. These studies identify a potential new link between inflammation and the development of atherosclerosis.

Abstract 122: Ceramide Activation of Macrophage RhoA/Rho Kinase/LIM Kinase Signaling Impairs Aggregated LDL Degradation and Foam Cell Formation

Introduction: One of the initiating events in atherogenesis is the deposition of low-density lipoproteins (LDL) in the arterial wall. This LDL becomes modified, aggregated and retained. Macrophages form a degradative contact (a lysosomal synapse or LS) with the aggregated LDL (agLDL) through local actin polymerization. Degradation of agLDL releases free cholesterol, which is taken up by macrophages and results in foam cell formation. Characterization of proteins regulating actin polymerization that allows LS formation may identify new therapeutic targets to inhibit foam cell formation and halt the progression of atherosclerosis. Hypothesis: Small GTPases of the Rho family such as RhoA are key regulators of actin polymerization. Further, many lipids in the micro-environment of the atherosclerotic plaque, such as ceramide, are known to modulate RhoA activity. Therefore we tested the hypothesis that RhoA is important in actin polymerization and foam cell formation in response to macrophage catabolism of agLDL and that this process can be modulated by ceramide. Methods: We overexpressed RhoA in RAW264.7 macrophages prior to treatment with agLDL to test the role of RhoA in LS formation and foam cell formation. We used bone marrow derived macrophages (BMM) from Sphingosine Kinase 2 knockout mice (SK2 KO) as a model for macrophages loaded with long chain ceramides and wild-type BMM loaded with C2-ceramide to test the role of ceramide. We also used inhibitors of Rho Kinase ROCK and LIM Kinase to assess their role in LS formation. Results and Conclusions: Overexpression of wild-type and constitutive active RhoA in RAW264.7 macrophages significantly impaired actin polymerization and foam cell formation in response to agLDL treatment. Using SK2KO BMM and wild-type BMM loaded with C2- ceramide, we find that macrophages loaded with ceramide display increased levels of activated RhoA. This leads to impaired actin polymerization and foam cell formation which could be rescued by RNAi mediated silencing of RhoA, inhibition of ROCK or inhibition of LIMK. In conclusion, these results suggest that RhoA/ROCK/LIMK signaling negatively regulates agLDL degradation and foam cell formation and that this process can be directly modulated by ceramide through activation of RhoA.

Naringenin and Atherosclerosis: A Review of Literature

Atherosclerosis is a multifactorial disease mainly caused by deposition of low-density lipoprotein (LD) cholesterol in macrophages of arterial walls. Atherosclerosis leads to heart attacks as well as stroke. Epidemiological studies showed that there is an inverse correlation between fruit and vegetable consumption and the risk of atherosclerosis. The promising effect of high vegetable and fruit containing diet on atherosclerosis is approved by several experimental studies on isolated phytochemicals such as flavonoids. Flavonoids are known to up-regulate endogenous antioxidant system, suppress oxidative and nitrosative stress, decrease macrophage oxidative stress through cellular oxygenase inhibition as well as interaction with several signal transduction pathways and from these ways, have therapeutic effects against atherosclerosis. Naringenin is a well known flavonoid belonging to the chemical class of flavanones. It is especially abundant in citrus fruits, especially grapefruits. A plethora of evidences ascribes to naringenin antiatherosclerotic effects. Naringenin abilities to decrease LDL and triglycerides as well as inhibit glucose uptake; increase high-density lipoprotein (HDL); co-oxidation of NADH; suppress protein oxidation; protect against intercellular adhesion molecule-1(ICAM-1); suppress macrophage inflammation; inhibit leukotriene B4, monocyte adhesion and foam cell formation; induce of HO-1 and G 0/G 1 cell cycle arrest in vascular smooth muscle cells (VSMC) and down regulate atherosclerosis related genes are believed to have crucial role in the promising role against atherosclerosis. In the present review, we have summarized the available literature data on the anti-atherosclerotic effects of naringenin and its possible mechanisms of action.

Aortic valve calcification: Association with apoE and PON1 serum levels

Oxidation and deposition of low density lipoproteins in aortic valve cusps play a significant role in pathogenesis of the aortic valve calcification (AVC). This process is regulated by paraoxonase 1 (PON1) and apolipoprotein E (aроЕ). The aim of the study was to investigate the serum levels of PON1 and aроЕ in patients with AVC. Seventy patients (mean age 72.5 ± 7.5 years, 48.5% — men) with proven AVC were collected. 36 controls without AVC but with the similar profile of cardiovascular background, match for age, sex, the presence of coronary artery disease and treatment were included. Serum levels of ionized calcium (Са2+), PON1 and aроЕ were assessed by ELISA. Serum levels of PON1 in AVC patients (55.6 ± 27.3 mkg/ml) were higher than in the control group (39.4 ± 21.2 mkg/ml, р < 0.05). Negative correlation of PON1 with low density lipoproteins (r = −0.25, р < 0.05) and very low density lipoprotein (r = −0.28, р < 0.05) concentrations were revealed. Са2+ serum levels in AVC patients (1.12 ± 0.06 mmol/l) were lower than in controls (1.26 ± 0.15 mmol/l, p < 0.05). Са2+ serum levels negatively correlated with aроЕ levels (r = −0.27, р < 0.05). Patients with AVC also demonstrated increased aроЕ serum levels (0.6 ± 0.03 mg/l vs 0.03 ± 0.02 mg/l, р < 0.01). All subjects with AVC were divided into two groups depending on Са2+ serum concentration: normal (1.15–1.3 mmol/l) or low (<1.15 mmol/l). The highest aроЕ average serum level (0.09 ± 0.07 mg/l) was detected in AVC patients with low Са2+ serum concentration in comparison with patients with normal Са2+ level (0.05 ± 0.03 mg/l, р < 0.05) and controls (p < 0.01). Serum levels of Са2+, PON1 and apoE didn't depend on stenosis of calcified aortic valve as well as on degree of stenosis. In previous studies it was established that decrease of PON1 activity is associated with increased risk of atherosclerosis, ischemic heart disease and myocardial infarction. The data obtained on PON1 activity in patients with AVC are inconsistent. In the present study we have detected increase of aроЕ serum concentration in the cases of aortic valve calcification. apoE plays a key role in interactions of lipoproteins and cell receptors. Involvement of aроЕ in the earliest stages of aortic valve calcification was established in the experimental studies. This fact is consistent with our data obtained in vivo. The early in vitro investigations have revealed functional relations between aроЕ and intracellular Са2+ level. There is an opinion that aроЕ contributes to mobilization of cellular Са2+ pool in macrophages, and aроЕ expression in macrophages is Са2+-dependent process. We believe that identified relation between apоЕ and Са2+ serum levels in AVC undoubtedly confirms their complex involvement in the pathogenesis of aortic valve calcification. But what changes are primary is still unclear and requires further advanced study. The data obtained demonstrate increased PON1 and apoE serum levels and decreased Са2+ serum concentration in patients with aortic valve calcification. Valid negative correlation of Са2+ and aроЕ serum levels was identified.

Plasmin Promotes Foam Cell Formation by Increasing Macrophage Catabolism of Aggregated Low-Density Lipoprotein

The plasmin/plasminogen system is involved in atherosclerosis. However, the mechanisms by which it stimulates disease are not fully defined. A key event in atherogenesis is the deposition of low-density lipoprotein (LDL) on arterial walls where it is modified, aggregated, and retained. Macrophages are recruited to clear the lipoproteins, and they become foam cells. The goal of this study was to assess the role of plasmin in macrophage uptake of aggregated LDL and foam cell formation. Plasminogen treatment of macrophages catabolizing aggregated LDL significantly accelerated foam cell formation. Macrophage interaction with aggregated LDL increased the surface expression of urokinase-type plasminogen activator receptor and plasminogen activator activity, resulting in increased ability to generate plasmin at the cell surface. The high local level of plasmin cleaves cell-associated aggregated LDL, allowing a portion of the aggregate to become sequestered in a nearly sealed, yet extracellular, acidic compartment. The low pH in the plasmin-induced compartment allows lysosomal enzymes, delivered via lysosome exocytosis, greater activity, resulting in more efficient cholesteryl ester hydrolysis and delivery of a large cholesterol load to the macrophage, thereby promoting foam cell formation. These findings highlight a critical role for plasmin in the catabolism of aggregated LDL by macrophages and provide a new context for considering the atherogenic role of plasmin.

Abstract 189: The Role of Spleen Tyrosine Kinase, Syk, in CD36-Toll Like Receptor Cooperative Signaling in Atherosclerosis

Atherosclerosis is characterized by chronic sterile inflammation of the artery wall in which cells of the monocyte lineage accumulate in response to the deposition of low density lipoprotein (LDL). We previously established that recognition of oxidized LDL (oxLDL) by CD36 triggers assembly of a novel Toll-like receptor heterodimer composed of TLR4 and TLR6. Here we set out to understand the molecular mechanisms of CD36/TLR4/TLR6 activation and establish how it triggers downstream signals that lead to the expression of the pro-inflammatory mediators that have been directly implicated in the deleterious effects of oxLDL and atherosclerosis progression. By confocal microscopy we demonstrate that oxLDL induces CD36, TLR4 and TLR6 co-localization in intracellular compartments, but not on the cell surface of macrophages. Notably, inhibition of oxLDL endocytosis (with Dynasore) or lysosomal maturation (with Bafilomycin A or NH4Cl) blocks CD36-TLR4-TLR6 complex formation and oxLDL-induced cytokine responses in macrophages. These data indicate that both ligand internalization and lysosomal acidification are required for assembly of a functional CD36/TLR4/TLR6 signaling complex. Notably, CD36 contains a hemi-ITIM motif in the C-terminus that is reported to interact with the spleen tyrosine kinase Syk through its SH2 domain. As Syk has recently been implicated in the trafficking of CD14 and TLR4 to the endosome in response to LPS, we investigated the role of this kinase in CD36/TLR4/TLR6 signaling. We find that Syk is required for CD36 internalization and TLR4/TLR6 heterodimerization. Using a pharmacological inhibitor, we show that inhibition of Syk activity blocks oxLDL-induced TLR4-TLR6 co-precipitation and abrogates macrophage expression of both MyD88- (IL-1b, CXCL1) and TRIF-dependent (CCL5) cytokines/chemokines. Together, our data are consistent with a key role for Syk in the trafficking of CD36 and oxLDL to the lysosome, where it coordinates the assembly of a functional TLR4-TLR6 heterodimer to initiate signaling. This model highlights the importance of CD36 as a co-receptor that orchestrates TLR4-TLR6 trafficking and assembly to initiate the detrimental inflammatory responses that promote the progression of atherosclerosis.

Patient-specific computational modeling of subendothelial LDL accumulation in a stenosed right coronary artery: effect of hemodynamic and biological factors

Atherosclerosis is a systemic disease with local manifestations. Low-density lipoprotein (LDL) accumulation in the subendothelial layer is one of the hallmarks of atherosclerosis onset and ignites plaque development and progression. Blood flow-induced endothelial shear stress (ESS) is causally related to the heterogenic distribution of atherosclerotic lesions and critically affects LDL deposition in the vessel wall. In this work we modeled blood flow and LDL transport in the coronary arterial wall and investigated the influence of several hemodynamic and biological factors that may regulate LDL accumulation. We used a three-dimensional model of a stenosed right coronary artery reconstructed from angiographic and intravascular ultrasound patient data. We also reconstructed a second model after restoring the patency of the stenosed lumen to its nondiseased state to assess the effect of the stenosis on LDL accumulation. Furthermore, we implemented a new model for LDL penetration across the endothelial membrane, assuming that endothelial permeability depends on the local lumen LDL concentration. The results showed that the presence of the stenosis had a dramatic effect on the local ESS distribution and LDL accumulation along the artery, and areas of increased LDL accumulation were observed in the downstream region where flow recirculation and low ESS were present. Of the studied factors influencing LDL accumulation, 1) hypertension, 2) increased endothelial permeability (a surrogate of endothelial dysfunction), and 3) increased serum LDL levels, especially when the new model of variable endothelial permeability was applied, had the largest effects, thereby supporting their role as major cardiovascular risk factors.