Human Carotid Atherosclerosis Research Articles

Identification of cholesteryl esters in human carotid atherosclerosis by ex vivo image-guided proton MRS

Vulnerable atherosclerotic plaques may be identified by their large lipid component, particularly liquid cholesteryl ester (CE), covered by a fibrous cap. We hypothesized that image-guided 1H proton magnetic resonance spectroscopy (MRS) would identify mobile CE in discrete, preselected regions of atherosclerotic plaque. Human carotid endarterectomy specimens (n = 10) were imaged ex vivo by magnetic resonance imaging (MRI) at high field (11.7 T) utilizing standard T1- and T2-weighted spin echo protocols. MRS spectra were acquired from 1 mm3 voxels, localized to plaque regions that we judged by MRI to be lipid rich or lipid poor. The spectra revealed methyl and methylene resonances of fatty acyl chains with relative intensities and linewidths characteristic of pure CE, by comparison with lipid standards. Regions judged to be lipid rich by MRI showed much more intense CE resonances than did lipid-poor regions. The integrated intensities of lipid peaks were 5.5 +/- 2.0% (lipid-rich regions) versus 0.9 +/- 0.6% (lipid-poor regions) of the unsuppressed water peak (P < 0.0001). Lipid distribution by histology, MRS, and MRI showed strong correlation. Image-guided proton MRS accurately identified CE in selected regions of atherosclerotic plaque as small as 1 mm3 in an ex vivo setting. This procedure may permit the noninvasive detection and quantification of CE in atherosclerotic plaque in vivo.

Tracking regression and progression of atherosclerosis in human carotid arteries using high-resolution magnetic resonance imaging

Magnetic resonance imaging (MRI) can accurately and reproducibly measure the volume of atherosclerotic plaque in human carotid arteries. Atherosclerotic plaques may either progress or regress over time, depending on individual risk factors and treatment regimens. This study was designed to determine if regression or progression of human carotid atherosclerosis in patients receiving statin therapy over 24 months can be detected by high-resolution MRI. In 11 subjects who had undergone unilateral carotid endarterectomy and were on statin therapy, volumes for total carotid artery, concentric wall (normal wall), eccentric wall (plaque), and lumen were quantified at 0, 16 and 24 months using a 1.5-T human imager equipped with 6-cm phased array coils. The interobserver mean coefficient of variation (CV) was lowest for the lumen volume (3.1%) and highest for the plaque volume (9.8%). The interscan mean CV was lowest for the total artery volume (3.2%) and highest for the plaque volume (9.9%). As much as 26% regression and 35% progression were observed in individual subject's carotid artery eccentric wall (plaque) volumes over time. Mean eccentric wall volume increased 5% by 16 months and 8% by 24 months. Mean total wall volume increased slightly at both 16 and 24 months (+1.2% and +1.8%). High-resolution MRI provides a noninvasive reproducible method of tracking changes in carotid atherosclerosis. This pilot study detected changes in individual subjects at both 16 and 24 months. MRI tracking of changes in atherosclerotic plaques should prove useful in assessing vascular disease risk and monitoring the efficacy of interventions designed to induce regression or retard progression.

Osteoprotegerin and osteopontin are expressed at high concentrations within symptomatic carotid atherosclerosis.

The aim of this study was to compare the concentration of osteoprotegerin (OPG), receptor activator of nuclear factor kappaB ligand (RANKL), and osteopontin (OPN) in stable (asymptomatic) and unstable (symptomatic) carotid atherosclerosis. In addition, we were interested in the effect of angiotensin II blockade on the secretion of these proteins by unstable atherosclerosis. Endarterectomy samples removed from patients with recent (within 6 weeks) or no previous focal neurological symptoms were assessed by immunohistochemistry, Western analysis, and explant culture. Concentrations of OPG, RANKL, and OPN were measured by mean optical density (MOD), densitometry of protein bands, and enzyme-linked immunosorbent assay of supernatants from explant culture, and compared between symptomatic and asymptomatic patients. The concentration of OPG and OPN within the proximal internal carotid (PIC) part of the endarterectomy specimen removed from symptomatic patients was elevated 2- and 4-fold, respectively. Although the concentration of RANKL did not differ according to patients' symptoms, the quantity of OPG secreted by explants of the PIC was greater in explants from symptomatic patients and could be significantly reduced within 48 hours of incubation with the angiotensin II blocker irbesartan. OPG and OPN are upregulated in symptomatic human carotid atherosclerosis with possible implications for plaque stability. Angiotensin II blockade is able to downregulate OPG secretion in vitro.

1P-0250 p53 mediated apoptosis in human carotid atherosclerosis and cystic medial degeneration of aorta

1P-0250 p53 mediated apoptosis in human carotid atherosclerosis and cystic medial degeneration of aorta

Clinicopathological significance of lipid peroxidation in carotid plaques

Several reports have suggested an association between lipid peroxidation and human carotid atherosclerosis, but few reports have demonstrated a link between lipid peroxidation and carotid plaques in humans. In this study, we investigated the relationship between clinical features, histopathological characteristics and lipid peroxidation in patients undergoing carotid endarterectomy (CEA). Forty-one carotid plaques were obtained. A portion of the most severe lesions was subjected to histopathologic examination, and the remainder of the plaques examined for lipid peroxidation. Thiobarbituric acid-reactive substances (TBARS) values were determined as a marker for lipid peroxidation. The lipid-rich core (LC) and macrophage infiltration (Mφ) component as a percentage of total plaque area were measured morphometrically. Based on the results, all plaques were classified into four groups. Group I (GI): LC <10%; Group IIa (GIIa): LC 10–30%, Mφ <5%; Group IIb (GIIb): LC 10–30%, Mφ ≥5%, and Group III (GIII): LC ≥30%. The plaque TBARS values of GIII were significantly higher than those of GI, GIIa, and GIIb. The TBARS values of GIIb were one-and-a-half times higher than those of GIIa. Our results show that lipid peroxidation in carotid plaques is significantly associated with carotid atherosclerosis, especially plaque instability. These findings provide direct evidence of an association between lipid peroxidation and human atherosclerosis.

Smoking-Induced Vascular Disease

Polycyclic aromatic hydrocarbons (PAHs) are recognized widely as potential environmental procarcinogens and have attracted their share of attention from both funding agencies and scientists interested in biomedical research. Curiously, their potential relevance to cardiovascular disease, rather than cancer, has stirred less emotion. This imbalance of attention is reflected also in society’s response to that most intimate form of self-pollution with PAHs (and much else), cigarette smoking. While the States have chosen to allocate varying proportions of their Tobacco Settlements to research, cancer tends to dominate the agenda. Yet, tobacco-related cardiovascular disease yields an even more striking burden on the public health than cancer. It has been estimated that cardiovascular morbidity and mortality are increased 4-fold in smokers and by one third in passive smokers.1 One might think that such daunting figures would prompt advocacy groups, such as the American Heart Association, to lobby vigorously at the State level for an appropriate allocation of the Tobacco Settlements to cardiovascular research. Our understanding of the mechanisms by which smoking mediates cardiovascular injury and the factors that determine interindividual susceptibility to smoking-induced tissue injury is remarkably limited. In this issue of Circulation Research , Kerzee and Ramos2 draw our attention to a mechanism of potential relevance to acceleration of atherogenesis by PAHs, including those in cigarette smoke. The aryl hydrocarbon receptor (Ahr) is a member of the family of basic helix loop helix proteins (bHLHs) that contain PAS domains. This family includes proteins related to differentiation, such as MyoD, the response to hypoxia, such as Hif1α, and circadian rhythms, such as CLOCK, …

Localization of Tissue Transglutaminase in Human Carotid and Coronary Artery Atherosclerosis: Implications for Plaque Stability and Progression

Although atherosclerosis progresses in an indolent state for decades, the rupture of plaques creates acute ischemic syndromes that may culminate in myocardial infarction and stroke. Mechanical forces and matrix metalloproteinase activity initiate plaque rupture, whereas tissue inhibitors of metalloproteinases have an important (albeit indirect) role in plaque stabilization. In this paper, an enzyme that could directly stabilize the plaque is described. Tissue transglutaminase (TG) catalyzes the formation of ε(γ-glutamyl)lysine isopeptide bonds that are resistant to enzymatic, mechanical, and chemical degradation. We performed immunohistochemistry for TG in atherosclerotic human coronary and carotid arteries. TG was most prominent along the luminal endothelium and in the medium of the vessels with a distribution mirroring that of smooth muscle cells. Variable, often prominent, immunoreactivity for TG was also seen in the intima, especially in regions with significant neovascularization. Additionally, TG was detected in fibrous caps and near the “shoulder regions” of some plaques. A monoclonal antibody to the transglutaminase product ε(γ-glutamyl)lysine isopeptide demonstrated co-localization with TG antigen. Transglutaminase activity was found in 6 of 14 coronary artery atherectomy samples. Cross-linking of TG substrates such as fibrinogen, fibronectin, vitronectin, collagen type I, and protease inhibitors stabilized the plaque. Furthermore, the activation of transforming growth factor–beta-1 by TG might be an additional mechanism for the promotion of plaque stabilization and progression by increasing the synthesis of extracellular matrix components.

Analysis of the measurement precision of arterial lumen and wall areas using high-resolution MRI.

High-resolution MRI may be used to monitor the progression of human carotid atherosclerosis by measuring the lumen and wall area changes over time. The purpose of this study was to analyze the precision of quantitative measurements of lumen and wall areas. Two independent MR scans near the carotid bifurcation were conducted on eight patients within 2 weeks. The error of lumen area measurement was 6. 2%, 9.2%, and 9.7% for T(1), proton density, and T(2)-weighted images, respectively, and the error of wall area measurement was 10. 8%, 10.9%, and 12.0%. The precision of area measurement correlates strongly with image quality.

The relationship of hydroxyeicosatetraenoic acids and F2-isoprostanes to plaque instability in human carotid atherosclerosis.

Evidence for increased oxidant stress has been reported in human atherosclerosis. However, no information is available about the importance of in situ oxidant stress in relation to plaque stability. This information is relevant because the morbidity and mortality of atherosclerosis are essentially the consequences of acute ischemic syndromes due to unstable plaques. We studied 30 carotid atherosclerotic plaques retrieved by endarterectomy from 18 asymptomatic (stable plaques) and 12 symptomatic patients (unstable plaques). Four normal arteries served as controls. After lipid extraction and ester hydrolysis, quantitation of different indices of oxidant stress were analyzed, including hydroxyeicosatetraenoic acids (HETEs), epoxyeicosatetraenoic acids (EETs), ketoeicosatetraenoic acids (oxo-ETEs), and F2-isoprostanes using online reverse-phase high-performance liquid chromatography tandem mass spectrometry (LC/MS/MS). All measurements were carried out in a strictly double-blind procedure. We found elevated levels of the different compounds in atherosclerotic plaques. Levels of HETEs were 24 times higher than EETs, oxo-ETEs, or F2-isoprostanes. Levels of HETEs, but not those of EETs, oxo-ETEs or F2-isoprostanes, were significantly elevated in plaques retrieved from symptomatic patients compared with those retrieved from asymptomatic patients (1, 738 +/- 274 vs. 1,002 +/- 107 pmol/ micromol lipid phosphorous, respectively; P < 0.01). One monooxygenated arachidonate species, 9-HETE, which cannot be derived from known enzymatic reactions, was the most abundant and significant compound observed in plaques, suggesting that nonenzymatic lipid peroxidation predominates in advanced atherosclerosis and may promote plaque instability.

Interstitial Collagenase (MMP-1) Expression in Human Carotid Atherosclerosis

In human atherosclerosis, most clinical events occur when plaque integrity is compromised and hemorrhage and thrombosis result. One mechanism for this might be the release by plaque cells of matrix-degrading proteases, such as interstitial collagenase (matrix metalloproteinase-1, MMP-1), which degrades two major plaque structural proteins, types I and III collagen. This study was undertaken to determine whether MMP-1 is expressed in human atherosclerotic plaques. To determine the cellular source and location of MMP-1 in human carotid atherosclerotic lesions, in situ hybridization and immunohistochemistry were performed on 20 endarterectomy specimens. Six nonatherosclerotic carotid arteries also were studied. Intense MMP-1 expression (mRNA and protein) was detected in a subset of plaque macrophages located at the borders of the lipid cores adjacent to fibrous caps and shoulder regions. Subsets of plaque smooth muscle cells and endothelial cells also expressed MMP-1. There was a strong correlation between the percentage of the lipid core occupied by hemorrhage and the percentage of the lipid core perimeter positive for MMP-1 (r = .823, P = .0001). MMP-1 was not detected in any cell type in nonatherosclerotic carotid arteries. This study demonstrates that MMP-1 is expressed by several cell types in human carotid atherosclerosis and that there is a correlation between the expression of the protease and histopathological evidence of plaque instability. Since MMP-1 may degrade the major structural collagens of the plaque, expression of the protease by macrophages in regions critical to plaque integrity could contribute to plaque expansion, rupture, and hemorrhage.

Ultrasound observation on pulsation in human carotid artery lesions

B-mode ultrasound imaging was used to compare pulsation in moderately advanced, non-calcific, common carotid atherosclerotic lesions with adjacent carotid artery walls where no lesions were visible. Subjects were 13 men with proven coronary atherosclerosis. Average age was 54 years and subjects did not have cerebral symptoms or carotid bruits. E p , the pressure-strain modulus, was estimated using brachial artery blood pressures recorded on the same clinic visit. E p values in lesion areas were significantly greater than in nonlesion areas. Two extremely high E p lesion values were found which could not be explained on the basis of focal calcification as determined by ultrasonic or angiographic images. Study of lesion pulsation by ultrasound imaging is proposed as a new noninvasive procedure for characterizing human carotid atherosclerosis.