Atherosclerotic plaques composed of a large core of foam cells covered with thin fibrous caps in twice-injured carotid arterial specimens obtained from high cholesterol diet-fed rabbits

Evaluation of plaque stabilization by fluvastatin with carotid intima- medial elasticity measured by a transcutaneous ultrasonic-based tissue characterization system

AIM

As an approach to tissue characterization, we attempted to classify in vivo carotid plaque tissues in terms of arterial wall elasticity instead of echogenicity on B-mode scanning and investigated whether the effect of fluvastatin on carotid elasticity can be detected in hypercholesterolemic patients.

METHODS

In 170 subjects, simultaneous measurements of intima-media thickness (IMT) and elastic modulus in the circumferential direction (E(theta)) were performed using a new transcutaneous high-resolution Doppler technique.

RESULTS

From the observation of various tissues, an elasticity library was obtained as follows: lipid core, 22+/-15 kPa; calcification, 674+/-384 kPa; lipid core- and calcification-free plaques, 173+/-69 kPa; smooth muscle, 104+/-32 kPa; blood clot, 85+/-68 kPa; fibrosis, 273+/-173 kPa.The effect of fluvastatin (30 mg/day, n=62) was assessed over 12 months using the elasticity distribution and serum markers. The statin reduced low-density lipoprotein cholesterol, high-sensitivity CRP, mean IMT and mean E(theta), and increased nitrite/nitrate. In the max IMT > or =1.1 mm group, both E(theta) and IMT decreased significantly. On the other hand, in the max IMT <1.1 mm group, E(theta) but not IMT decreased significantly. The histogram of the subgroups showing increased E(theta) with max IMT> or =1.1 mm revealed a decrease in areas corresponding to E(theta) of 20200 kPa (lipid/smooth muscle-rich tissue) and an increase in relatively hardened areas of <250 kPa (collagen fibers).

CONCLUSION

Non-invasive echographic carotid arterial elasticity measurement is useful for the classification of atherosclerotic plaques and evaluation of chronological and histopathological changes.

Effects of antiatherosclerosis in carotid artery by RNAi-mediated silencing of MCP-1 expression

BACKGROUND

Our objective was to identify the effects of MCP-1 siRNA in vivo transfection in an atherosclerosis model on local expression of MCP-1 and pathogenesis of atherosclerosis.

METHODS

Carotid atherosclerosis was induced in 28 New Zealand white rabbits. Rabbits were divided into three groups randomly: RNAi group, model group, and blank plasmid group. siRNA-expressing vector was transfected to blood vessels by liposomes. The carotid arteries were processed for morphological evaluation. Local expression of MCP-1 was detected by immunohistochemistry, RT-PCR, and Western blot.

RESULTS

On hematoxylin and eosin-stained sections, partial endothelial cells detached while intimae were less thickened in the RNAi group compared to the model and blank plasmid groups; the I:M ratio was significantly reduced to 1.46 in the RNAi group compared to the model and blank plasmid groups (5.55 and 5.27, respectively). The results of immunohistochemistry showed that MCP-1 expression was less colorized and less positive in the RNAi group. RT-PCR and Western blot showed reduced expression in the RNAi group than in the model and blank plasmid groups. There were highly positive correlations between semiquantitative RT-PCR and the I:M ratio (r = 0.968).

CONCLUSION

Expression of MCP-1 was successfully inhibited by transfecting MCP-1 siRNA expression plasmid to the carotid artery, and the progression of atherosclerosis was restricted by RNAi-mediated silencing of MCP-1 expression.

Association of cholesterol levels and occurrence of angiographically detectable endothelial disruption during coronary angioplasty

BACKGROUND

Disruption of the atherosclerotic plaque is a common feature of both acute coronary syndromes and balloon dilatation of coronary artery stenoses.

HYPOTHESIS

The study was undertaken to evaluate whether the known association of cholesterol levels and acute coronary syndromes also exists for the occurrence of angiographically detectable endothelial disruption (ED) following coronary angioplasty.

METHODS

For this purpose, we examined 79 consecutive patients (men/women 58/21; mean age: 62 +/- 11 years), with a noncalcified, de novo, significant stenosis in a single native coronary artery, undergoing elective coronary intervention because of stable effort angina. Coronary angioplasty was performed using regular balloon catheters, aiming for a balloon/ artery ratio of 1, with stent implantation allowed only provisionally. Following balloon dilatation, patients were divided into two groups according to the presence or absence of angiographically detectable ED.

RESULTS

Endothelial disruption occurred in 28 patients (35%). The two groups with and without ED were comparable with respect to clinical, angiographic, and procedural parameters. A history of hypercholesterolemia was significantly more frequent in patients with ED (93 vs. 2%; p < 0.001). Total and low-density lipoprotein (LDL) cholesterol levels were significantly higher in the group with ED (230.1 +/- 46.5 vs. 204.4 +/- 30.2 mg/dl, p < 0.05; and 150.6 +/- 39.2 vs. 125.8 +/- 26 mg/dl, p < 0.03, respectively). A cut-off value of LDL cholesterol > or = 135 mg/dl identified patients at higher risk of developing ED.

CONCLUSION

High cholesterol levels appear to favor the occurrence of ED during coronary angioplasty. Aggressive lipid-lowering therapy and a more careful procedural approach may be warranted in patients with hypercholesterolemia undergoing coronary interventions in order to decrease the occurrence of ED and the associated clinical (acute ischemia) and procedural (stent implantation) consequences.

Effect of Fluid Shear Stress on Migration of Vascular Smooth Muscle Cells in Cocultured Model

Migration of smooth muscle cells (SMCs) in hyperplasia is thought to have a correlation with blood flow conditions. In this study, the effect of shear stress applied to endothelial cells (ECs) on SMC migration was examined using a newly designed EC-SMC coculture model (CM), in which bovine SMCs and ECs were separated by a collagen layer and a membrane filter. After exposing the CM to shear stresses of 0.5, 1.0, or 1.5 Pa for 48 h, the number of SMCs migrating into the collagen layer was counted. Under static conditions, the migration of SMCs in the CM increased compared with SMCs cultured alone. Shear stress of 1.5 Pa significantly suppressed the SMC migration (p < 0.05) compared with the static CM. Media conditioned with the CM exposed to shear stress of 1.0 Pa (p < 0.05) and 1.5 Pa (p < 0.005) exhibited reduction in activated matrix metalloproteinase-2 (MMP-2) compared with the static CM, as analyzed by zymography. Addition of an inhibitor of nitric oxide (NO) synthase, N (omega)-nitro-L: -arginine methyl ester, to the media inhibited the effect of 1.5 Pa shear stress on SMC migration but MMP-2 activity was unaffected. These results suggest that physiological shear stress has protective roles in atherosclerogenesis.

Physical activity and atherosclerosis: which animal model?

Atherosclerosis is a progressive disease that is the most important single contributor to human cardiovascular morbidity and mortality. Epidemiologic studies show that physical activity, or routine exercise, reduces the risk of developing cardiovascular disease. The mechanisms through which exercise may function in primary or secondary prevention of atherosclerosis remain largely to be established. Most studies in humans are performed after the onset of clinical signs when disease is well advanced and the prescription of exercise is based on empirical evidence of benefit in secondary prevention. Animal models per-mit the study of the initiation and progression of preclinical stages of atherosclerosis. In order to provide information relevant to treatment and prevention, these models should mimic human disease and interactions of physical activity with disease processes as closely as possible. The purpose of this review is to compare animal models of atherosclerosis and to summarize the available data in those models in regard to the effects of exercise.

Atherosclerosis and Matrix Dystrophy

Atherosclerosis is characterized by inflammatory metabolic change with lipid accumulation in the artery. Atherosclerotic plaque occurs at discrete locations in the arterial system and involves the proliferation of smooth muscle cells (SMCs) together with imbalance of the extracellular matrix elements, elastic fiber in particular. The role of elastin in arterial development and disease was confirmed by generating mice that lack elastin. Thus, elastin is a critical regulatory molecule that regulates the phenotypic modulation, proliferation and migration of SMCs. We estimated that elastin expression and SMC proliferation are coupled inversely: potent stimulators of cell proliferation may potentially inhibit elastin expression and potent inhibitors of cell proliferation can stimulate elastin expression. Moreover, elastin was found to be expressed maximally at the G(0) and minimally at the G(2)/M phase during the cell cycle, suggesting that its expression is regulated by the cell growth state. The elastin peptide VPGVG enhanced SMC proliferation, resulting in the reduction of elastin expression. The inhibition of elastin expression by elastin fragments may be reflected in the negative feedback regulatory mechanism. The relationship between cell proliferation and elastin expression may be changed in atherosclerosis. Areas of atherosclerotic plaque show abnormality of elasticity and permeability from the viewpoint of the physiological function of the arterial wall. The etiology was estimated to be that cholesterol and calcium are deposited on the elastic fiber, resulting in decreased elastin synthesis and cross-linking formation. In addition, these dysfunctions of elastin fiber are also associated, in that the down-regulation of elastin and its related components (fibrillin-1 and lysyl oxidase) are directly related to calcification in SMCs. The denatured arterial elastin by cholesterol and calcium accumulation was also susceptible to proteolytic enzymes such as elastase and matrix metalloproteinase (MMP). Therefore, metabolic change in elastic fiber induces decreased elasticity and is associated with essential hypertension. Vitamin K(2) is used in drug therapy against atherosclerosis, or calcification in diabetes mellitus or dialysis, due to its promotion of the carboxylation of the matrix Gla protein.

Changes in aspects such as the collagenous fiber density and foam cell size of atherosclerotic lesions composed of foam cells, smooth muscle cells and fibrous components in rabbits caused by all-cis-5, 8, 11, 14, 17-icosapentaenoic acid

Atherosclerotic plaques composed of foamed macrophages, smooth muscle cells and fibrous components in the twice-injured carotid artery from 1% cholesterol diet (HCD)-fed rabbits were prepared and the effects of all-cis-5, 8, 11, 14, 17-icosapentaenoic acid (EPA) on the histopathological properties of atherosclerotic lesions were examined. During the test period, there was no significant difference between the control and the EPA-treated groups in serum lipid levels. In the control group, atherosclerotic lesions were composed of foamed macrophages, smooth muscle cells and fibrous components. Some of the lesions had a large core of foamed macrophages covered with a thin cap of smooth muscle cells and fibrous components, and were morphologically similar to human vulnerable plaques. The classification of plaques, composing atherosclerotic lesions based on collagenous fiber density and foam cell size indicated that over 70% of plaques in the control group were poor in collagenous fiber, while about 20% of plaques contained only large foam cells. In contrast to the control group, over 70% of plaques in the EPA-treated group were rich in collagenous fiber and only 3% consisted of large foam cells. These results suggest that EPA changes certain aspects of pre-existing atherosclerotic lesions.