Inflammation and atherosclerosis: mechanisms underlying vulnerable plaque

Shear stress induces human aortic endothelial cell apoptosis via interleukin‑1 receptor‑associated kinase 2‑induced endoplasmic reticulum stress

Atherosclerosis is characterized by localized lesions distributed in the arterial tree due to the shear stress produced by blood flow. Endothelial cells are directly affected by alterations in blood flow. Dysfunction and injury to endothelial cells has been hypothesized to initiate the pathological processes of atherosclerosis. The present study aimed to investigate the mechanism of shear stress-induced endothelial cellular apoptosis. Shear stress was generated using an artificial device to mimic the impact of disturbed blood flow on cultured human aortic endothelial cells (HAECs). Cellular apoptosis was assessed using a terminal deoxynucleotidyl transferase dUTP nick end labeling assay; an ELISA assay was used to detect the produced interleukin (IL)-1β; specific small interfering (si)RNA was used to knockdown the expression of interleukin-1 receptor-associated kinase 2 (IRAK2) in HAECs and the expression levels of 78 kDa glucose-regulated protein, DNA damage-inducible transcript 3 protein (CHOP), IRAK2 and IL-1β were evaluated using western blotting. The results of the present study demonstrated that artificial shear stress induced endoplasmic reticulum (ER) stress, IL-1β production and apoptosis in HAECs in a time-dependent manner. The inhibition of ER stress, and treatment with interleukin-1 receptor antagonist protein and siRNA against IRAK2 attenuated shear stress-induced CHOP signaling-mediated cellular apoptosis. Therefore, overproduction of IL-1β exacerbated shear stress-induced ER stress-mediated apoptosis via the IRAK2/CHOP signaling pathway in endothelial cells.

MCS-18, a natural product isolated from Helleborus purpurascens, inhibits maturation of dendritic cells in ApoE-deficient mice and prevents early atherosclerosis progression

INTRODUCTION

Inflammation accelerates both plaque progression and instability in the pathogenesis of atherosclerosis. The inhibition of dendritic cell (DC) maturation is a promising approach to suppress excessive inflammatory immune responses and has been shown to be protective in several autoimmune models. The aim of this study was to investigate the immune modulatory effects of the natural substance MCS-18, an inhibitor of DC maturation, regarding the progression of atherosclerosis in ApoE-deficient mice.

MATERIALS AND METHODS

ApoE-deficient mice were fed for twelve weeks with a Western-type diet (n = 32) or normal chow (control group; n = 16). Animals receiving high-fat diet were treated with MCS-18 (500 μg/kg body weight, n = 16) or saline (n = 16) twice a week. After 12 weeks, animals were transcardially perfused and sacrificed. The percentage of mature DCs (CD3(-)/CD19(-)/CD14(-)/NK1.1(-)/CD11c(+)/MHCII(+)/CD83(+)/CD86(+)) and T cell subpopulations (CD4(+)/CD25(+)/Foxp3(+), CD3/CD4/CD8) was analyzed in peripheral blood and in the spleen using flow cytometry. Plaque size was determined in the aortic root and the thoracoabdominal aorta using en-face staining. Immunohistochemical stainings served to detect inflammatory cells in the aortic root. Several cytokines and chemokines were determined in serum using multiplex assays.

RESULTS

In splenic cells derived from saline-treated atherosclerotic mice an increased DC maturation, reflected by the upregulation of CD83 and CD86 expression, was observed. The enhanced expression of both maturation markers was absent in MCS-18 treated atherosclerotic mice. While the percentage of splenic Foxp3 expressing Treg was increased in animals receiving MCS-18 compared to saline-treated atherosclerotic mice, cytotoxic T cells were reduced in the spleen and in atherosclerotic lesions of the aortic root. Furthermore, proatherogenic cytokines (e.g. IL-6 and IFN-γ) and chemokines (e.g. MIP-1β) were decreased in serum of MCS-18-treated animals when compared to saline-treated atherosclerotic mice. Also plaque size in the aortic root and the thoracoabdominal aorta was significantly lower following administration of MCS-18.

CONCLUSION

This study provides for the first time evidence that MCS-18 is able to prevent the onset of atherosclerosis in ApoE-deficient mice. The observed anti-atherogenic effect is associated with the suppression of DC maturation and an inhibited migration and proliferation of cytotoxic T cells.

Atherosclerosis and infection: is the jury still not in?

Atherosclerosis is a chronic inflammatory process accounting for increased cardiovascular and cerebrovascular morbidity and mortality. A wealth of recent data has implicated several infectious agents, mainly Chlamydophila pneumoniae, Helicobacter pylori, CMV and periodontal pathogens, in atherosclerosis. Thus, we sought to comprehensively review the available data on the topic, exploring in particular the pathogenetic mechanisms, and discuss anticipated future directions.

A-002 (Varespladib), a phospholipase A2 inhibitor, reduces atherosclerosis in guinea pigs

BACKGROUND

The association of elevated serum levels of secretory phospholipase A2 (sPLA2) in patients with cardiovascular disease and their presence in atherosclerotic lesions suggest the participation of sPLA2 enzymes in this disease. The presence of more advanced atherosclerotic lesions in mice that overexpress sPLA2 enzymes suggest their involvement in the atherosclerotic process. Therefore, the sPLA2 family of enzymes could provide reasonable targets for the prevention and treatment of atherosclerosis. Thus, A-002 (varespladib), an inhibitor of sPLA2enzymes, is proposed to modulate the development of atherosclerosis.

METHODS

Twenty-four guinea pigs were fed a high saturated fat, high cholesterol diet (0.25%) for twelve weeks. Animals were treated daily with A-002 (n = 12) or vehicle (10% aqueous acacia; n = 12) by oral gavage. After twelve weeks, animals were sacrificed and plasma, heart and aorta were collected. Plasma lipids were measured by enzymatic methods, lipoprotein particles size by nuclear magnetic resonance, aortic cytokines by a colorimetric method, and aortic sinus by histological analyses.

RESULTS

Plasma total cholesterol, HDL cholesterol and triglycerides were not different among groups. However, the levels of inflammatory cytokines interleukin (IL)-10, IL-12 and granulocyte-macrophage colony-stimulating factor (GM-CSF) were significantly reduced in the treatment group. This group also had a significant 27% reduction in cholesterol accumulation in aorta compared with placebo group. Morphological analysis of aortic sinus revealed that the group treated with A-002 reduced atherosclerotic lesions by 24%.

CONCLUSION

The use of A-002 may have a beneficial effect in preventing diet-induced atherosclerosis in guinea pigs.

Potential of magnetic resonance plaque imaging using superparamagnetic particles of iron oxide for the detection of carotid plaque

Macrophages and by-products are important in plaque destabilization in atherosclerosis. Ultra-small superparamagnetic particles of iron oxide (SPIO)-enhanced magnetic resonance (MR) imaging may be suitable for the detection of macrophages in atherosclerotic plaques. The present study investigated the potential of MR plaque imaging using SPIO in 10 patients scheduled for carotid endarterectomy before and 24-43 hours after administration of SPIO (fercarbotran, 0.016 ml/kg). Three-dimensional gradient recalled acquisition in the steady state (3D-GRASS) was used for detecting macrophages within plaques. Signal loss on the post-contrast 3D-GRASS images was found in 5 of 10 cases, and accumulation of SPIO particles in the vessel wall was confirmed in 4 of these 5 cases. Intracytoplasmic localization of SPIO particles within recruited macrophages was verified by double staining analysis. A correlation between MR plaque imaging using SPIO and localization of macrophages was demonstrated in 6 of 10 patients. This study indicates that MR plaque imaging using SPIO is a potential functional imaging tool to detect infiltration of macrophages in human atherosclerotic carotid plaque.

Controlling cardiac transport and plaque formation

Macro-particles transported in the bloodstream, such as LDL particles and macrophages, are considered to be one of the initiating factors of atherosclerotic plaque development. LDL infiltration from the bloodstream into a blood vessel's wall, whether the coronary, peripheral, or carotid arteries, is considered a major inflammatory factor, recruiting macrophages from the blood flow and leading to the formation of vulnerable atherosclerotic plaques. Infiltration sites are influenced by patterns of blood flow, as regions of lower shear stresses and high oscillations may give rise to higher infiltration rates through the endothelium, exacerbating the growth of a plaque and its tendency to rupture. Previous studies demonstrated a high prevalence of rupture sites proximal to the minimum lumen area, which raised the question of whether the existence of two distinct adjacent plaques, in which the distal plaque is more severe, can give rise to hemodynamic forces that can push the non-stenotic plaque to rupture. Models of the coronary arteries with one and two eccentric and concentric stenotic narrowings were built into a closed flow loop. The single stenosis model had a 75% area reduction narrowing (representing the vunerable atherosclerotic plaque) with relevant elastic properties. The double stenosis model included an additional distal 84% area reduction narrowing. The flow in the area between the two stenoses was recorded and analyzed using continuous doppler particle image velocimetry (CDPIV), together with the hydrostatic pressure acting on the proximal plaque. Results indicated that the combined shear rates and pressure effects in a model with a significant distal stenosis can contribute to the increase in plaque instability by LDL and enhanced macrophage uptake. The highly oscillatory nature of the disturbed flow near the shoulder of the vulnerable atherosclerotic plaque enriches its lipid soft core, and the high hydrostatic pressures acting on the same lesion in this geometry induce high internal maximal stresses that can trigger the rupture of the plaque.

Audit of cardiovascular disease risk factors among supported adults with intellectual disability attending an ageing clinic

BACKGROUND

Little is known about the cardiovascular disease (CVD) risk factor profile for older adults with intellectual disability (ID). As many CVD risk factors are treatable by lifestyle changes, confirmation of the risk factor profile for older adults with ID could substantially impact upon preventive health practices for this group.

METHOD

Medical charts of all adults aged 40 years or over attending a specialised ageing clinic for adults with ID between January 2002 and June 2005 were reviewed.

RESULTS

Overall, 155 adults' charts were reviewed and 8 (5%) had diagnosed CVD. Risk factor assessments found 18% with hypertension (of 73% checked), 8% with elevated glucose (of 97% checked), 27% with elevated total cholesterol (of 94% checked), 70% overweight or obese (of 55% checked), 11% current or ex-smokers (100% checked), and 96% with inadequate daily exercise (100% checked). Only the prevalence of hypertension and smoking increased significantly with age.

CONCLUSION

Apart from lack of exercise (which was much more prevalent than for the general population) and overweight or obesity, the overall CVD risk factor profile of supported older adults with ID appears generally more favourable compared to the age-matched general population, although the occurrence of all risk factors is still common. Healthy lifestyle programs for this population should focus on implementation of exercise and nutrition strategies.

The expression of vascular dendritic cells in human atherosclerotic carotid plaques

Atherosclerosis is currently considered a chronic inflammatory disease, and evidence is accumulating for a role of the immune system in the progression of atherosclerosis. Dendritic cells are specialized antigen-presenting cells with the unique ability to initiate a primary immune response to certain antigens by the activation of naive T-lymphocytes. Although dendritic cells are well known to be important in the development of different diseases, studies of vascular dendritic cells in atherosclerosis are rare, and their role is not clearly understood. Therefore, we investigated the immunohistochemical expression of vascular dendritic cells in atherosclerotic plaques. Between April 2003 and December 2005, carotid endarterectomy was performed in 26 consecutive patients, and 27 carotid plaque specimens were analyzed. We investigated the immunohistochemical expression of vascular dendritic cells in human carotid plaques by measuring the signal intensity of fascin-positive cells using an image analyzer. In addition, these immunohistochemical results were related to clinical data. The highest signal intensity of dendritic cells was found in plaque shoulders, and the mean signal intensity of dendritic cells was significantly higher in complicated than in uncomplicated plaques (P = .0029). Moreover, the mean signal intensity of dendritic cells in plaques from symptomatic patients was significantly elevated compared with plaques from asymptomatic patients (P = .0004). Although atherosclerotic plaque instability is determined by multiple factors, the immune and inflammatory pathways play a particularly important role. Dendritic cells play a role in atherosclerosis, and the present study suggests that the expression of dendritic cells in human carotid arteries may be strongly associated with the occurrence of ischemic stroke.

Optical coherence tomography for imaging the vulnerable plaque

While our understanding of vulnerable coronary plaque is still at an early stage, the concept that certain types of plaques predispose patients to developing an acute myocardial infarction continues to be at the forefront of cardiology research. Intracoronary optical coherence tomography (OCT) has been developed to both identify and study these lesions due to its distinct resolution advantage over other imaging modalities. We review clinical research conducted at the Massachusetts General Hospital over the past five years to develop, validate, and utilize this technology to improve our understanding of vulnerable plaque. Our results show that intracoronary OCT may be safely conducted in patients and that it provides abundant information regarding plaque microscopic morphology, which is essential to the identification and study of high-risk lesions. Even though many basic biological, clinical, and technological challenges must be addressed prior to widespread use of this technology, the unique capabilities of OCT ensure that it will have a prominent role in shaping the future of cardiology.