The Mikamo Lecture 2002. Therapeutic targets for the treatment of atherothrombosis in the new millennium--clinical frontiers in atherosclerosis research

Acute myocardial infarction caused by a floating thrombus in the ascending aorta: A role of CD34-positive endothelial cells

A 49-year-old woman was transferred to our hospital with acute-onset chest pain. Her electrocardiogram showed complete atrioventricular block and bradycardia with ST-segment elevation in the inferior leads, and she presented with cardiogenic shock. She was diagnosed with inferior acute myocardial infarction (AMI), and subsequent emergency cardiac catheterization was performed. Selective coronary angiography showed neither stenosis nor obstruction in any of the coronary arteries. Left ventriculography showed a large floating object located on the ascending aortic wall above the ostium of the right coronary artery (RCA). Chest enhanced computed tomography confirmed the floating object in the ascending aorta. These findings suggested that the floating object was associated with the RCA occlusion. To remove the floating object, emergency surgery was performed. The floating object was a large thrombus derived from the localized atheromatous plaque in the ascending aorta. Specialized immunostaining for surface antigen CD34 revealed that regenerated endothelial cells were present on the erosion, along the stalk, and on the floating thrombus. These findings indicate that the CD34-positive endothelial precursor cells strayed into the surface and/or inside of the thrombus, and consequently the floating thrombus supported by these regenerated endothelial cells occluded the RCA, causing AMI. <Learning objective: A free floating thrombus formed in the ascending aorta can cause obstruction of the coronary artery ostium, leading to AMI. This unusual cause of AMI mostly occurs in females, and shows high mortality rates. Although the risk factors are known to be current smoking, oral hormone therapy, and hypercoagulable state such as pregnancy, the underlying mechanism of thrombus formation is still unclear. This report describes a possible role of CD-34 positive regenerated endothelial cells in thrombus formation.>.

Two consecutive fatal cases of acute myocardial infarction caused by free floating thrombus in the ascending aorta and review of literature

Free floating thrombus in the ascending aorta is an uncommon source of acute myocardial infarction. We report on two cases of young women who died of acute myocardial infarction caused by a free floating thrombus in the sinus of Valsalva obstructing the coronary arteries' ostia. The first case reports on a 30-year-old pregnant woman who anamnestically had episodes with short loss of consciousness and weakness. The second case presents a 37-year-old woman suffering from multiple sclerosis with no previous history of thrombotic events. The review of literature revealed a predominance of women (eight females and three males). Interestingly, the coronary arteries bear no preference concerning the right (RCA) or left coronary artery (LCA) being more often occluded by a free floating thrombus. Especially, younger women (mean age 45.5 years, range 30-59 years) with no history of cardiac symptoms and without atherosclerotic changes seem to be predispositioned. The hypothesis that thrombus formation in cases without plaque disruption may depend on an endothelial erosion which seems to be more common in younger women and promoted by a hyperthrombogenic state is supported by our two cases. A comprehensive literature search revealed, that these are the first two reports on a free floating thrombus being the cause of fatal acute myocardial infarction in a pregnant woman, respectively, a woman suffering from multiple sclerosis.

Fenofibrate induces plaque regression in hypercholesterolemic atherosclerotic rabbits: In vivo demonstration by high-resolution MRI

INTRODUCTION

Fenofibrate has shown to reduce major cardiovascular events and slow angiographic progression of coronary atherosclerosis. The postulated mechanism of action is via the activation of peroxisomal proliferator-activated receptor-alpha (PPAR-alpha), a nuclear transcription factor that controls a variety of cellular functions. We investigated the anti-atherogenic effects of fenofibrate on previously established experimental atherosclerotic lesions.

METHOD

Atherosclerotic lesions were induced in the abdominal aorta of New Zealand white (NZW) rabbits (n=19) by a combination of a double-balloon injury and a 9-month hypercholesterolemic diet. The rabbits were randomized into placebo or fenofibrate group. The corresponding treatments were added to the hypercholesterolemic diet. All rabbits underwent MRI examination at randomization and after 6 months of treatment, and were then sacrificed for histopathology.

RESULTS

LDL-cholesterol was similarly elevated at randomization and follow-up, and was not significantly modified by fenofibrate therapy. HDL-cholesterol decreased (-27+/-10%, p=0.04) in the placebo and increased (+36.8+/-2%, p=0.04) in the fenofibrate group. MRI showed comparable vessel wall area (VWA) at randomization in both groups. At 15months, a significant increase in VWA was seen in the placebo group (15+/-4%, p=0.007), while fenofibrate treatment was associated with a regression (-11+/-4%, p=0.041) of previously established lesions. Fenofibrate also decreased macrophage and increased smooth muscle cell/collagen content of atherosclerotic lesions.

CONCLUSION

MRI measurements can, in conjunction with in vitro histological measurements, contribute to the understanding of the actions of pharmacologic agents in experimental models of atherosclerosis. Fenofibrate significantly regresses atherosclerotic lesions and induced changes in plaque composition associated with a more "stable" phenotype (reduced macrophages and increased SMC). These observations support the potential anti-atherogenic effects of PPAR-alpha agonists.

Statins: potent vascular anti-inflammatory agents

Atherosclerosis is a multifactorial condition that can result in cardiovascular disease. Statin therapy is thought to mediate cardioprotective effects that influence endothelial function, inflammatory responses, plaque stability and thrombus formation, processes involved in atherosclerosis. Although reduction in low-density lipoprotein cholesterol (LDL-C) potentially plays a role in all of these effects, several lines of evidence also implicate nonlipidmediated 'pleiotropic' effects. For example, statin therapy confers a lower risk for coronary heart disease than placebo in patients with comparable serum cholesterol levels, and confers a greater magnitude of clinical benefit than expected based on LDL-C levels alone. Moreover, while nonstatin lipid-lowering therapy does not necessarily reduce stroke risk, statins have shown a significant reduction in stroke. Statins exert their pleiotropic effects, in part, by improving endothelial function via up-regulation of endothelial nitric oxide synthase enzyme activity. Markers of inflammation such as high sensitivity C-reactive protein have been also shown to add further prognostic information about patients at risk of cardiovascular disease who may benefit from statin therapy. Further studies are still needed to determine whether statins have direct effects on inflammatory pathways.

Vasa vasorum in plaque angiogenesis, metabolic syndrome, type 2 diabetes mellitus, and atheroscleropathy: a malignant transformation

BACKGROUND

Vascularization is an exciting and complex mechanism involving angiogenesis and arteriogenesis. The metabolic syndrome (MS) and type 2 diabetes mellitus (T2DM) are associated with multiple metabolic toxicities, which result in reactive oxygen species (ROS) due to an elevated tension of oxidative-redox stress and an accelerated atherosclerosis termed atheroscleropathy.

RESULTS

This atheroscleropathy is associated with accelerated angiogenesis within the vulnerable, thin-cap fibro-atheroma, prone to rupture resulting in acute coronary syndromes (ACS). The resulting intimopathy with its neovascularization due to angiogenesis of the adventitial vasa vasorum (Vv) is prone to intraplaque hemorrhage (IPH). These IPH are associated with destabilization of the vulnerable plaques resulting in plaque erosion and plaque rupture resulting in ACS. In atheroscleropathy the adventitial Vv invades the plaque in a malignant-like fashion and concurrently is associated with chronic inflammation, as macrophages are being deposited within the shoulder regions of these vulnerable plaques. These angiogenic Vv provide a custom delivery vascular network for multiple detrimental substrates, which further accelerates the growth of these vulnerable plaques and atheroscleropathy. There exists a vascularization paradox in MS and T2DM, in that, angiogenesis within the plaque is induced and arteriogenesis is impaired.

CONCLUSION

This review will attempt to provide a database of knowledge regarding the vascularization process (angiogenesis and arteriogenesis) and its mechanisms to better understand the increased cardiovascular risk and the increased morbidity and mortality associated with MS and T2DM.

R353Q Polymorphism, Activated Factor VII, and Risk of Premature Myocardial Infarction in Japanese Men

BACKGROUND

The association between myocardial infarction (MI) and the R353Q polymorphism of the Factor VII (FVII) gene, which reportedly influences FVII concentrations, activated Factor VII (FVIIa), or FVII antigen (FVIIag), remains controversial.

METHODS AND RESULTS

The present case - control study in 127 Japanese men with their first MI at or before 45 years of age and 150 matched healthy controls was designed to clarify this association in premature MI. R353Q polymorphism was determined by polymerase chain reaction, and plasma concentrations of FVIIa and FVIIag were assayed. The distribution of the RR, RQ, and QQ genotypes with respect to R353Q polymorphism was 117, 10, and 0 in the patients, and 131, 17, and 2 in the controls. The Q allele was negatively associated with premature MI (odds ratio =0.41, p=0.038). The plasma concentration of FVIIa was slightly higher in patients (55.1+/-40.9 U/L) than in controls (44.8+/-20.2 U/L), but not significantly (p=0.078); the plasma concentration of FVIIag did not differ between patients (88.7+/-15.7%) and controls (87.0+/-9.0%) (p=0.557). Plasma FVIIa concentrations were influenced by R353Q polymorphism (p<0.001).

CONCLUSIONS

The Q allele may be protective against premature MI.

TWEAK Can Induce Pro-Inflammatory Cytokines and Matrix Metalloproteinase-9 in Macrophages

The expression of TWEAK (TNFSF12) and TweakR/Fn14 was detected in regions rich in macrophage/foam cells in atherosclerotic plaques. The role of TWEAK in monocytes in relation to atherogenesis was investigated by analyzing the cellular events induced by TWEAK in a human macrophage-like cell line, THP-1. TWEAK induced various molecular mediators of atherogenesis, such as IL-6, MCP-1, IL-8 and MMP-9, and the induction was augmented by interferon-gamma. TWEAK-induced activation of MMP-9 was mediated by activation of NF-kappaB. These results suggest that TWEAK is involved in atherosclerosis by inducing pro-inflammatory cytokines and extracellular matrix degrading enzymes, which reduce plaque stability.

Giant Organized Thrombus in the Left Sinus of Valsalva Causing Intermittent Left Coronary Obstruction-An Unusual Case of Acute Myocardial Infarction-

A 48-year-old Japanese man was admitted to hospital for acute myocardial infarction associated with a giant organized thrombus occupying the left sinus of Valsalva. Cardiac catheterization revealed no organic stenosis in either coronary artery, but left ventriculography and aortography showed a filling defect above the left coronary cusp. Transesophageal echocardiography was immediately performed and showed a round mass filling the left sinus of Valsalva. A solid, round mass approximately 2.5 cm in diameter was removed during emergency surgery and determined to be a thrombus on the basis of microscopic findings. This is the second report of a giant organized thrombus occupying the entire left sinus of Valsalva, obstructing the ostium of the left coronary artery intermittently, and leading to acute myocardial infarction.

Elevated Concentration of Soluble Vascular Endothelial Cadherin Is Associated With Coronary Atherosclerosis

BACKGROUND

Vascular endothelial (VE)-cadherin, a Ca(2+)-dependent cell adhesion molecule, is expressed in atherosclerotic lesions by endothelial cells and is associated with neovascularization, although the relationship between circulating VE-cadherin and coronary artery disease has not been studied.

METHODS AND RESULTS

The plasma concentration of VE-cadherin was measured in peripheral blood (femoral artery) and the coronary sinus of 24 patients with acute myocardial infarction (AMI), 26 with stable angina pectoris (AP), 18 with old myocardial infarction (OMI), and 30 control subjects (Control) who had no coronary artery stenosis on angiography. For the patients with AMI, blood samples were obtained in the acute (day 1) and chronic (day 21) phases. The plasma concentration of VE-cadherin was measured by enzyme-linked immunosorbent assay. The correlation between the plasma VE-cadherin concentration and the Gensini score was also determined as an index of the severity of coronary atherosclerosis. The plasma concentrations of VE-cadherin (ng/ml) in both the peripheral and coronary sinus blood were higher in patients with AMI, AP, and OMI than in the control subjects, and were similar in the 3 groups with coronary artery disease (femoral artery: AMI 5.1+/-2.5, AP 4.7+/-2.4, OMI 4.5+/-3.3, Control 2.6+/-2.3; coronary sinus: AMI 5.6+/-2.6, AP 5.0+/-2.3, OMI 5.0+/-2.9, Control 2.4+/-2.1, respectively). Plasma VE-cadherin concentrations were higher in the coronary sinus than peripheral blood samples in patients with AMI (p<0.01), AP (p<0.01), and OMI (p<0.05). The plasma VE-cadherin concentration was the same in the acute and chronic phases in patients with AMI. In the 3 groups of patients with coronary disease, both the peripheral plasma VE-cadherin concentration and the coronary sinus concentration correlated with the Gensini score (r=0.32, p<0.01 and r=0.42, p<0.001, respectively). Multiple regression analysis revealed that the plasma VE-cadherin concentration predicted the Gensini score independently of sex, age, hypertension, diabetes mellitus, smoking, and the lipid profiles.

CONCLUSION

Increased secretion of VE-cadherin from the epicardial arteries is associated with the degree of coronary atherosclerosis, indicating the presence of atherosclerosis rather than disease activity.