Marina S. Ferguson

Vascular cell adhesion molecule-1 is expressed in human coronary atherosclerotic plaques. Implications for the mode of progression of advanced coronary atherosclerosis.

Endothelial attachment is the initial step in leukocyte recruitment into developing atherosclerotic lesions. To determine whether vascular cell adhesion molecule-1 (VCAM-1) expression may play a role in inflammatory cell recruitment into human atherosclerotic lesions, immunohistochemistry was performed with a polyclonal rabbit antisera, raised against recombinant human VCAM-1, on 24 atherosclerotic coronary plaques and 11 control coronary segments with nonatherosclerotic diffuse intimal thickening from 10 patients. Immunophenotyping was performed on adjacent sections to identify smooth muscle cells, macrophages, and endothelial cells. To confirm VCAM-1-expressing cell types, double immunostaining with VCAM-1 antisera and each of the cell-specific markers and in situ hybridization were performed. All atherosclerotic plaques contained some VCAM-1, compared to 45% of control segments. VCAM-1 was found infrequently on endothelial cells at the arterial lumen din both plaques (21%) and in control segments (27%), but was prevalent in areas of neovascularization and inflammatory infiltrate in the base of plaques. Double immunostaining and in situ hybridization confirmed that most VCAM-1 was expressed by subsets of plaque smooth muscle cells and macrophages. The results document the presence of VCAM-1 in human atherosclerosis, demonstrate VCAM-1 expression by human smooth muscle cells in vivo, and suggest that intimal neovasculature may be an important site of inflammatory cell recruitment into advanced coronary lesions.

Association Between Carotid Plaque Characteristics and Subsequent Ischemic Cerebrovascular Events A Prospective Assessment With MRI—Initial Results

Background and Purpose— MRI is able to quantify carotid plaque size and composition with good accuracy and reproducibility and provides an opportunity to prospectively examine the relationship between plaque features and subsequent cerebrovascular events. We tested the hypothesis that the characteristics of carotid plaque, as assessed by MRI, are possible predictors of future ipsilateral cerebrovascular events. Methods— A total of 154 consecutive subjects who initially had an asymptomatic 50% to 79% carotid stenosis by ultrasound with ≥12 months of follow-up were included in this study. Multicontrast-weighted carotid MRIs were performed at baseline, and participants were followed clinically every 3 months to identify symptoms of cerebrovascular events. Results— Over a mean follow-up period of 38.2 months, 12 carotid cerebrovascular events occurred ipsilateral to the index carotid artery. Cox regression analysis demonstrated a significant association between baseline MRI identification of the following plaque characteristics and subsequent symptoms during follow-up: presence of a thin or ruptured fibrous cap (hazard ratio, 17.0; P≤0.001), intraplaque hemorrhage (hazard ratio, 5.2; P=0.005), larger mean intraplaque hemorrhage area (hazard ratio for 10 mm2 increase, 2.6; P=0.006), larger maximum %lipid-rich/necrotic core (hazard ratio for 10% increase, 1.6; P=0.004), and larger maximum wall thickness (hazard ratio for a 1-mm increase, 1.6; P=0.008). Conclusions— Among patients who initially had an asymptomatic 50% to 79% carotid stenosis, arteries with thinned or ruptured fibrous caps, intraplaque hemorrhage, larger maximum %lipid-rich/necrotic cores, and larger maximum wall thickness by MRI were associated with the occurrence of subsequent cerebrovascular events. Findings from this prospective study provide a basis for larger multicenter studies to assess the risk of plaque features for subsequent ischemic events.

Classification of Human Carotid Atherosclerotic Lesions With In Vivo Multicontrast Magnetic Resonance Imaging

Background—Recent studies demonstrated that in vivo and ex vivo MRI can characterize the components of the carotid atherosclerotic plaque, such as fibrous tissue, lipid/necrotic core, calcium, hemorrhage, and thrombus. The purpose of this study was to determine whether in vivo high-resolution multicontrast MRI could accurately classify human carotid atherosclerotic plaque according to the American Heart Association classification. Methods and Results—Sixty consecutive patients (mean age 70 years; 54 males) scheduled for carotid endarterectomy were imaged with a 1.5-T scanner after informed consent was obtained. A standardized protocol was used to obtain 4 different contrast-weighted images (time of flight and T1-, PD-, and T2-weighted) of the carotid arteries. Best voxel size was 0.25×0.25×1 mm3. Carotid plaques were removed intact and processed for histological examination. Both MR images and histological sections were independently reviewed, categorized, and compared. Overall, the classification obtained by MRI and the American Heart Association classifications showed good agreement, with Cohen’s &kgr; (95% CI) of 0.74 (0.67 to 0.82) and weighted &kgr; of 0.79. The sensitivity and specificity, respectively, of MRI classification were as follows: type I-II lesions, 67% and 100%; type III lesions, 81% and 98%; type IV-V lesions, 84% and 90%; type VI lesions, 82% and 91%; type VII lesions, 80% and 94%; and type VIII lesions, 56% and 100%. Conclusions—In vivo high-resolution multicontrast MRI is capable of classifying intermediate to advanced atherosclerotic lesions in the human carotid artery and is also capable of distinguishing advanced lesions from early and intermediate atherosclerotic plaque.

Quantitative Evaluation of Carotid Plaque Composition by In Vivo MRI

Objective— This study evaluates the ability of MRI to quantify all major carotid atherosclerotic plaque components in vivo. Methods and Results— Thirty-one subjects scheduled for carotid endarterectomy were imaged with a 1.5T scanner using time-of-flight–, T1-, proton density–, and T2-weighted images. A total of 214 MR imaging locations were matched to corresponding histology sections. For MRI and histology, area measurements of the major plaque components such as lipid-rich/necrotic core (LR/NC), calcification, loose matrix, and dense (fibrous) tissue were recorded as percentages of the total wall area. Intraclass correlation coefficients (ICCs) were computed to determine intrareader and inter-reader reproducibility. MRI measurements of plaque composition were statistically equivalent to those of histology for the LR/NC (23.7 versus 20.3%; P=0.1), loose matrix (5.1 versus 6.3%; P=0.1), and dense (fibrous) tissue (66.3% versus 64%; P=0.4). Calcification differed significantly when measured as a percentage of wall area (9.4 versus 5%; P<0.001). Intrareader and inter-reader reproducibility was good to excellent for all tissue components, with ICCs ranging from 0.73 to 0.95. Conclusions— MRI-based tissue quantification is accurate and reproducible. This application can be used in therapeutic clinical trials and in prospective longitudinal studies to examine carotid atherosclerotic plaque progression and regression.

Presence of Intraplaque Hemorrhage Stimulates Progression of Carotid Atherosclerotic Plaques A High-Resolution Magnetic Resonance Imaging Study

Background—Previous studies suggest that erythrocyte membranes from intraplaque hemorrhage into the necrotic core are a source of free cholesterol and may become a driving force in the progression of atherosclerosis. We have shown that MRI can accurately identify carotid intraplaque hemorrhage and precisely measure plaque volume. We tested the hypothesis that hemorrhage into carotid atheroma stimulates plaque progression. Methods and Results—Twenty-nine subjects (14 cases with intraplaque hemorrhage and 15 controls with comparably sized plaques without intraplaque hemorrhage at baseline) underwent serial carotid MRI examination with a multicontrast weighted protocol (T1, T2, proton density, and 3D time of flight) over a period of 18 months. The volumes of wall, lumen, lipid-rich necrotic core, calcification, and intraplaque hemorrhage were measured with a custom-designed image analysis tool. The percent change in wall volume (6.8% versus −0.15%; P=0.009) and lipid-rich necrotic core volume (28.4% versus −5.2%; P=0.001) was significantly higher in the hemorrhage group than in controls over the course of the study. Furthermore, those with intraplaque hemorrhage at baseline were much more likely to have new plaque hemorrhages at 18 months compared with controls (43% versus 0%; P=0.006). Conclusions—Hemorrhage into the carotid atherosclerotic plaque accelerated plaque progression in an 18-month period. Repeated bleeding into the plaque may produce a stimulus for the progression of atherosclerosis by increasing lipid core and plaque volume and creating new destabilizing factors.

In Vivo Quantitative Measurement of Intact Fibrous Cap and Lipid-Rich Necrotic Core Size in Atherosclerotic Carotid Plaque: Comparison of High-Resolution, Contrast-Enhanced Magnetic Resonance Imaging and Histology

Background— Previous studies with contrast-enhanced magnetic resonance imaging (CEMRI) have shown that the fibrous cap (FC) in atherosclerotic carotid plaques enhances with gadolinium-based contrast agents. Conversely, the lipid-rich necrotic core (LR-NC), lacking both vasculature and matrix, shows no or only slight enhancement. The goal of this study was to assess whether CEMRI can be used to accurately measure the dimensions of the intact FC and LR-NC. Methods and Results— Twenty-one patients scheduled for carotid endarterectomy were imaged with a 1.5-T scanner. Precontrast images and CEMRI were obtained. One hundred eight locations with an intact FC were matched between MRI and the excised histology specimens. Quantitative measurements of FC length along the lumen circumference, FC area, and LR-NC area were collected from CEMRI images and histology sections. Blinded comparison of corresponding MR images and histology slices showed moderate to good correlation for length (r=0.73, P<0.001) and area (r=0.80, P<0.001) of the intact FC. The mean percentage LR-NC areas (LR-NC area/wall area) measured by CEMRI and histology were 30.1% and 32.7%, respectively, and were strongly correlated across locations (r=0.87, P<0.001). Conclusions— In vivo high-resolution CEMRI is capable of quantitatively measuring the dimensions of the intact FC and LR-NC. These new parameters may be useful to evaluate plaque vulnerability and provide continuous variables for characterizing the intact FC and LR-NC in progression and regression studies.

Contrast-enhanced high resolution MRI for atherosclerotic carotid artery tissue characterization.

To determine if a gadolinium‐based contrast agent provides additional information for characterization of human plaque tissues, particularly neovasculature. Although high‐resolution magnetic resonance imaging (MRI) has been used to identify plaque constituents in advanced atherosclerosis, some constituents, such as neovascularized tissue, defy detection.

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

BACKGROUND 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. METHODS AND RESULTS 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. CONCLUSIONS 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.

Proliferation in primary and restenotic coronary atherectomy tissue. Implications for antiproliferative therapy.

On the basis of animal models of arterial injury, smooth muscle cell proliferation has been posited as a dominant event in restenosis. Unfortunately, little is known about this proliferation in the human restenotic lesion. The purpose of this study was to determine the extent and time course of proliferation in primary and restenotic coronary atherectomy-derived tissue. Primary (n = 118) and restenotic (n = 100) coronary atherectomy specimens were obtained from 211 nonconsecutive patients. Immunocytochemistry for the proliferating cell nuclear antigen (PCNA) was used to gauge proliferation in the atherectomy specimens. The identity of PCNA-positive cells was then determined using immunohistochemical cell-specific markers. Eighty-two percent of primary specimens and 74% of restenotic specimens had no evidence of PCNA labeling. The majority of the remaining specimens had only a modest number of PCNA-positive cells per slide (typically < 50 cells per slide). In the restenotic specimens, PCNA labeling was detected over a wide time interval after the initial procedure (eg, 1 to 390 days), with no obvious proliferative peak. Cell-specific immunohistochemical markers identified primary and restenotic PCNA-positive cells as smooth muscle cells, macrophages, and endothelial cells. In conclusion, the findings were as follows: (1) Proliferation in primary and restenotic coronary atherectomy specimens, as indicated by PCNA labeling, occurs infrequently and at low levels. (2) The response to injury in existing animal models of angioplasty may follow a very different course of events from the clinical reality in human atherosclerotic coronary arteries and may help explain why current approaches to restenosis therapy have been ineffective.

Hemorrhage in the Atherosclerotic Carotid Plaque: A High-Resolution MRI Study

Background and Purpose— High-resolution, multicontrast magnetic resonance imaging (MRI) has developed into an effective tool for the identification of carotid atherosclerotic plaque components, such as necrotic core, fibrous matrix, and hemorrhage/thrombus. Factors that may lead to plaque instability are lipid content, thin fibrous cap, and intraplaque hemorrhage. Determining the age of intraplaque hemorrhage can give insight to the history and current condition of the biologically active plaque. The aim of this study was to develop criteria for the identification of the stages of intraplaque hemorrhage using high-resolution MRI. Methods— Twenty-seven patients, scheduled for carotid endarterectomy (CEA), were imaged on a 1.5-T GE SIGNA scanner (sequences: 3-dimensional time of flight, double-inversion recovery, T1-weighted (T1W), PDW and T2W). Two readers, blinded to histology, reviewed MR images and grouped hemorrhage into fresh, recent, and old categories using a modified cerebral hemorrhage criteria. The CEA specimens were serially sectioned and graded as to presence and stage of hemorrhage. Results— Hemorrhage was histologically identified and staged in 145/189 (77%) of carotid artery plaque locations. MRI detected intraplaque hemorrhage with high sensitivity (90%) but moderate specificity (74%). Moderate agreement in classifying stages occurred between MRI and histology (Cohen κ = 0.7, 95% CI: 0.5 to 0.8 for reviewer 1 and 0.4, 95% CI: 0.2 to 0.6 for reviewer 2), with moderate agreement between the 2 MRI readers (κ = 0.4, 95% CI: 0.3 to 0.6). Conclusion— Multicontrast MRI can detect and classify carotid intraplaque hemorrhage with high sensitivity and moderate specificity.