Extracellular Matrix in Vascular Disease,Part 2/4: JACC Focus Seminar

Medium-sized and large arteries consist of 3 layers: the tunica intima, tunica media, and tunica adventitia. The tunica media accounts for the bulk of the vessel wall and is the chief determinant of mechanical compliance. It is primarily composed of circumferentially arranged layers of vascular smooth muscle cells that are separated by concentrically arranged elastic lamellae; a form of extracellular matrix (ECM). The tunica media is separated from the tunica intima and tunica adventitia, the innermost and outermost layers, respectively, by the internal and external elastic laminae. This second part of a 4-part JACC Focus Seminar discusses the contributions of the ECM to vascular homeostasis and pathology. Advances in genetics and proteomics approaches have fostered significant progress in our understanding of vascular ECM. This review highlights the important role of the ECM in vascular disease and the prospect of translating these discoveries into clinical disease biomarkers and potential future therapies.     

Invasion of atheromatous plaques into tunica media causes coronary outward remodeling in WHHLMI rabbits

To clarify the mechanism of coronary outward remodeling, we examined atherosclerotic coronary arteries morphologically using WHHLMI rabbits that develop coronary atherosclerosis spontaneously. Perfusion-fixed coronary segments of WHHLMI rabbits were prepared at 500microm intervals. After immunohistochemical staining and histopathological staining, the areas and lengths of the arterial wall and the lesions were measured. Obvious outward remodeling was observed in coronary sections with greater than 40% cross-sectional narrowing. In coronary sections with greater than 40% cross-sectional narrowing, the tunica media was thick at the shoulder of atheromatous plaque and was thin beneath the atheromatous plaques. Macrophages infiltrated those attenuated tunica media expressed matrix metalloproteinases and oxidized LDL was accumulated in those areas. In those areas, collagen fibers and the internal elastic lamina had disappeared partly and apoptotic smooth muscle cells were observed. Proliferation of smooth muscle cells was observed at the attenuated tunica media and adjacent adventitia. The present results suggest that invasion of atheromatous plaques into the tunica media causes coronary outward remodeling.     

Intravascular ultrasound imaging: in vitro validation and pathologic correlation

Intravascular ultrasound imaging is a new method in which high resolution images of the arterial wall are obtained with use of a catheter placed within an artery. An in vitro Plexiglas well model was used to validate measurements of the luminal area, and an excellent correlation was obtained. One hundred thirty segments of fresh peripheral arteries underwent ultrasound imaging and the findings were compared with the corresponding histopathologic sections. Luminal areas determined with ultrasound imaging correlated well with those calculated from microscopic slides (r = 0.98). Three patterns were identified on the ultrasound images: 1) distinct interface between media and adventitia, 2) indistinct interface between media and adventitia but different echo density layers, and 3) diffuse homogeneous appearance. The types of patterns depended on the relative composition of the media and adventitia. Calcification of intimal plaque obscured underlying structures. Atherosclerotic plaque was readily visualized but could not always be differentiated from the underlying media.     

Evaluation of changes in myocardial perfusion and function on exercise in patients with coronary artery disease by gated MIBI scintigraphy.

OBJECTIVE--To investigate the ability of gated methoxy-isobutylisonitrile (MIBI) scintigraphy to measure changes in myocardial function as well as perfusion with exercise. SETTING--Regional cardiothoracic centre. PATIENTS--43 presenting with chest pain, 28 with coronary artery disease on angiography, and 15 with normal coronary arteriograms. RESULTS--Gated perfusion images showed an improvement in detecting regions with stenosed arteries compared with non-gated images (38/55 v 31/55, p < or = 0.01)). Functional analysis showed an increase in fractional shortening of 4.11% in subjects with normal coronary arteries, whereas in those with coronary disease a fall of 0.57% was found (p < or = 0.01). Both perfusion and function imaging showed an improved sensitivity compared with standard exercise testing (p < or = 0.01). When both function and perfusion imaging were analysed all patients with coronary disease were detected. There was agreement in abnormal regions in 33/55 territories supplied by a stenosed artery. Combined perfusion and function detected 49/55 (89%) of abnormal regions, thus improving the overall sensitivity from 38/55 (69%) by perfusion imaging alone (p < or = 0.01). CONCLUSIONS--Gated methoxy-isobutylisonitrile scintigraphy can successfully evaluate perfusion and function on exercise, so improving the diagnostic usefulness of this agent.     

Morphology of the coronary arteries following percutaneous transluminal coronary angioplasty with hemopericardium

Autopsy findings in a patient with cardiac tamponade following percutaneous transluminal coronary angioplasty (PTCA) are reported. Angiography during PTCA demonstrated coronary dissection without extravasation of contrast medium at the site of angioplasty. Histologic examination of the dilated coronary segment revealed longitudinal splitting of intima and media as well as circumferential subintimal and submedial dissection. Hemorrhage into plaque, intima, media, adventitia and dissection lumina was found. Disruption of the adventitia was not present. Cardiac tamponade may occur transadventitially without complete disruption of the coronary artery and without extravasation of contrast medium.     

Spontaneous coronary artery dissection: a neglected cause of acute myocardial ischaemia and sudden death.

Spontaneous coronary artery dissection is a rare cause of acute myocardial ischaemia. Eight consecutive fatal cases which occurred in women aged 34-54 years (mean 43) are described. The dissection involved the left anterior descending coronary artery in four, the left main trunk in two, the right coronary artery in one, and both left anterior descending and circumflex arteries in one. The clinical presentation was sudden death in six cases, and acute myocardial infarction in two. Diagnosis was made at necropsy in every case but one, in which coronary dissection was diagnosed during life by selective coronary angiography. The only ascertained risk factor was hypertension in one patient; none of the women was in the puerperium, and Marfan syndrome was excluded in all. Histology showed a haematoma between the coronary tunica media and adventitia, that flattened and occluded the lumen; a coronary intimal tear was detected in only two cases. Unusual histological findings were cystic medial necrosis in one case, eosinophilic inflammatory infiltrates in four, and angiomatosis of the tunica adventitia in one. Patients dying of spontaneous coronary dissection are usually middle aged women, with no coronary atherosclerosis and apparently no risk factors. Spontaneous coronary artery dissection is unpredictable, and sudden death is the usual mode of clinical presentation. Prompt diagnosis and life saving treatment is far from being achieved.     

A Adiponectina Previne a Reestenose pela Inibição da Proliferação Celular em um Modelo de Enxerto Venoso em Ratos

Background:Coronary artery bypass grafting (CABG) continues to be an effective therapy for coronary artery disease patients, but the vein graft is prone to restenosis or occlude. Adiponectin (ADP) is a plasma hormone protein with the function of regulating cell proliferation.Objective:This study used two different doses of ADP protein in a rat vein graft model to stimulate vein graft change. The aim of our study was to investigate the effect of ADP on vein graft restenosis.Methods:Autologous jugular veins were implanted as carotid interposition grafts through the anastomotic cuff technique in Sprague Dawley rats. Adiponectin (2.5 μg and 7.5 μg) was delivered to the vein bypass grafts in a perivascular fashion, suspended in a 30% Pluronic-F127 gel. No treatment (bypass only) and vehicle loaded Pluronic gel served as controls. Comparisons were made with one-way analysis of variance and a post-hoc test, with p < 0.05 considered significant.Results:Cell proliferation (PCNA index) was significantly low in adiponectin-treated versus control and vehicle-gel-treated grafts, both in intima and adventitia, as of day 3 (p < 0.01). VCAM-1 and ICAM-1 evaluated by immunohistochemistry significantly down-regulated in the adiponectin-treated vein grafts in the fourth week (p <0.01). Treatment of vein grafts with adiponectin-loaded gels reduced intimal, media, and adventitia thickness when compared with the control and vehicle-gel-treated vein grafts at day 28 (p < 0.01).Conclusions:Our studies provide further support for the potential therapeutic role of adiponectin in modulating vascular injury and repair.     

Surface organization of aqueous MgCl2 and application to atmospheric marine aerosol chemistry

Inorganic salts in marine aerosols play an active role in atmospheric chemistry, particularly in coastal urban regions. The study of the interactions of these ions with water molecules at the aqueous surface helps to elucidate the role of inorganic cations and anions in atmospheric processes. We present surface vibrational sum frequency generation (SFG) spectroscopic and molecular dynamics (MD) studies of aqueous MgCl₂ surfaces as models of marine aerosol. Spectroscopy results reveal that the disturbance of the hydrogen bonding environment of the air/aqueous interface is dependent on the MgCl₂ concentration. At low concentrations (< 1 M) minor changes are observed. At concentrations above 1 M the hydrogen bonding environment is highly perturbed. The 2.1 M intermediate concentration solution shows the largest SFG response relative to the other solutions including concentrations as high as 4.7 M. The enhancement of SFG signal observed for the 2.1 M solution is attributed to a larger SFG-active interfacial region and more strongly oriented water molecules relative to other concentrations. MD simulations reveal concentration dependent compression of stratified layers of ions and water orientation differences at higher concentrations. SFG and MD studies of the dangling OH of the surface water reveal that the topmost water layer is affected structurally at high concentrations (> 3.1 M). Finally, the MgCl₂ concentration effect on a fatty acid coated aqueous surface was investigated and SFG spectra reveal that deprotonation of the carboxylic acid of atmospherically relevant palmitic acid (PA) is accompanied by binding of the Mg²⁺ to the PA headgroup.     

冠状动脉夹层的成因、影像学诊断及治疗策略

冠状动脉夹层是指冠状动脉内膜撕裂,血液进入冠状动脉中膜或内膜下血肿形成,可导致管腔急剧变窄和血流严重受阻。若诊治不及时,冠状动脉夹层可能会引发受累冠状动脉的破裂、急性心肌梗死、心源性休克、猝死等严重临床后果。本文就冠状动脉夹层的分类及成因、影像学诊断、治疗策略作一综述。     

Collagen biomechanics in cerebral arteries and bifurcations assessed by polarizing microscopy

Collagen is the main matrix protein of the artery wall. We have used the known correlation between collagen birefringence and its mechanical properties to assess the wall structural integrity in brain arteries and their bifurcation regions, which are the sites of formation of saccular aneurysms. Segments of 28 brain arteries, including bifurcations, were pressure fixed and sectioned in one of three orthogonal planes. Measurements were taken by polarizing microscopy of the birefringence of collagen fibers at the apex of bifurcations and in the main layers of the artery wall - adventitia, media and intima. Dimensional data were obtained of the layers in order to estimate wall properties. Along the apex of the flow divider we measured a narrow band of collagen (birefringence 30% higher than the adjacent adventitia) providing strength and stiffness in that region. There is a thin cell-free outer layer of the tunica media (mean thickness 11 microm) comprised of densely packed coaligned collagen with high birefringence. From the fiber birefringence and directional alignment of the individual layers we calculated that the adventitia contributes about one third of circumferential and almost all of longitudinal strength of intracranial arteries.     

Left Ventricular Systolic Function Changes in Primary Hypertension Patients Detected by the Strain of Different Myocardium Layers

This study investigated left ventricular (LV) systolic dysfunction associated with differential strain among myocardial layers in primary hypertension (PH) patients with or without LV hypertrophy (LVH), and normal patients.In 63 PH and 42 healthy patients, two-dimensional speckle tracking echocardiography was used to measure the peak systolic longitudinal and circumferential strain of the myocardial subendocardial, middle and subepicardial layers, and the peak systolic radial strain. To assess LV systolic function, the apical long axis, 4- and 2-chamber views, and parasternal short axis at the basal, middle, and apical levels were acquired by cardiovascular ultrasound (Vivid E9, GE Healthcare, USA).Overall, the pattern in peak systolic longitudinal strain among myocardial layers was subendocardial > middle > subepicardial. In the peak systolic circumferential strain, this was middle > subepicardial > subendocardial. The peak systolic longitudinal strain was normal > NLVH > LVH. Among the groups, the peak systolic circumferential strain at the basal parasternal short-axis level was statistically similar, but at the middle and the apical parasternal short-axis levels were NLVH > normal > LVH. In normal and NLVH patients, the peak radial strain was middle > apical > basal, and in LVH patients was apical > middle > basal. The peak averages of the longitudinal and subendocardial circumferential strains differed significantly when LVH compared with NLVH and normal patients.The systolic function of PH patients was damaged in comparison with normal individuals, which could be detected conveniently and accurately using two-dimensional speckle tracking echocardiography.     

Dipyridamole is superior to dobutamine for thallium stress imaging: a randomised crossover study.

OBJECTIVE--To assess the value of dobutamine over dipyridamole as a pharmacological stressing agent in myocardial perfusion imaging with thallium-201. DESIGN--Stress and redistribution tomographic images were taken in a group of patients in a randomised crossover study of both agents. The scans were scored to give a value for the stress and redistribution images and a reversibility score (redistribution--stress). All patients had coronary angiography that was also scored. Differences between the two agents were compared by a paired t test. PATIENTS--30 patients aged 51-70 years with chest pain thought to be caused by myocardial ischaemia. 11 had had previously myocardial infarction. RESULTS--Dipyridamole caused adverse symptoms in six patients whereas dobutamine caused symptoms in 21 patients (chi 2 = 15.15, p < 0.0001). Dobutamine stress took considerably longer than dipyridamole (31 v 6 minutes) and cost more (17 pounds v 1.50 pounds). There were no significant differences between the agents in terms of total stress or redistribution scores, but regional analysis showed that dipyridamole showed significantly more defects during stress at the apex and lateral wall (p < 0.05), with no significant difference at redistribution. Dipyridamole stress also caused significantly more reversible defects at the apex (p < 0.05) and gave a better correlation than dobutamine with coronary score (dipyridamole r = 0.80, p < 0.001 v dobutamine r = 0.64, p < 0.001). In six patients who had continued to take beta blockers the results of dobutamine stress did not correlate with coronary score, r = 0.34 (NS), whereas dipyridamole studies were not affected. CONCLUSION--Compared with dobutamine, dipyridamole was as effective in producing overall perfusion defects and more effective in provoking defects at the apex and lateral segment. The dipyridamole study correlated better with coronary score and was not affected by concurrent beta blocker treatment. It was also better tolerated by the patients, was less time consuming, and was much cheaper.     

Cholinergic properties of the bronchial artery and contribution of the endothelium

Using selective agonists and antagonists, both muscarinic and nicotinic receptors were identified in the bovine bronchial artery. The helical bronchial artery strips contracted to acetylcholine and methacholine and responses to both were blocked by atropine. Nicotine contractions were blocked by both atropine and hexamethonium. Longitudinal strips responded poorly to both acetylcholine and nicotine. Sixty-five percent of pre-contracted bronchial arterial strips with intact endothelium relaxed in the presence of low concentrations of acetylcholine (1 X 10(-9)M to 1 X 10(-7)M), while those strips without endothelium did not. The presence or absence of endothelium was shown histologically, as was the identification of cholinergic fibers located in the adventitia and outer layers of the tunica media of the bronchial artery. These data confirm the hypothesis of vagal innervation of the bronchial artery and also suggest a role for the endothelium in modulating this artery's response to acetylcholine stimulation in obstructive airway diseases.     

DNA strand breaking by the hydroxyl radical is governed by the accessible surface areas of the hydrogen atoms of the DNA backbone

Despite extensive study, there is little experimental information available as to which of the deoxyribose hydrogen atoms of duplex DNA reacts most with the hydroxyl radical. To investigate this question, we prepared a set of double-stranded DNA molecules in which deuterium had been incorporated specifically at each position in the deoxyribose of one of the four nucleotides. We then measured deuterium kinetic isotope effects on the rate of cleavage of DNA by the hydroxyl radical. These experiments demonstrate that the hydroxyl radical reacts with the various hydrogen atoms of the deoxyribose in the order 5′ H > 4′ H > 3′ H ≈ 2′ H ≈ 1′ H. This order of reactivity parallels the exposure to solvent of the deoxyribose hydrogens. Our work therefore reveals the structural basis of the reaction of the hydroxyl radical with DNA. These results also provide information on the mechanism of DNA damage caused by ionizing radiation as well as atomic-level detail for the interpretation of hydroxyl radical footprints of DNA-protein complexes and chemical probe experiments on the structure of RNA and DNA in solution.     

Assessment of normal and atherosclerotic arterial wall thickness with an intravascular ultrasound imaging catheter

A prototype intravascular ultrasound imaging catheter with a 20 MHz transducer was used to obtain 59 cross-sectional images in 14 segments of human atherosclerotic arteries. Three distinct components of the arterial wall were visualized on the ultrasound images: a highly reflective intima, an echolucent media, and a moderately reflective adventitia. Images were obtained at 1 mm increments in vitro and were compared with histologic sections at the same levels. Measurements of the arterial layers showed a close correlation between ultrasound images and histologic sections for the thickness of the intimal plaque (r = 0.91), the media (r = 0.83), and the total wall thickness (r = 0.85). The ultrasound images overestimated the mean intimal and total wall thickness by 0.3 mm and 0.7 mm compared to measurements in histologic sections (p less than 0.001). Intravascular imaging with high-frequency ultrasound is an accurate method for measuring microanatomic arterial dimensions and the extent of atheromatous involvement of the arterial wall. This method could represent an important adjunct to traditional angiographic techniques for assessing the severity of atherosclerosis.     

Neurotrophins and neurotrophin receptors in human pulmonary arteries

The localization of neurotrophins (NTs) and NT receptors was analyzed in sections of human extra- and intrapulmonary arteries by Western blot analysis and immunohistochemistry. In extrapulmonary branches of human pulmonary artery, NT and NT receptor immunoreactivity was located in the tunica intima, within endothelium, in the tunica media, within smooth muscle and in the tunica adventitia. In different sized intrapulmonary arteries, NT and NT receptor immunoreactivity was observed primarily in the tunica adventitia. A faint NT and NT receptor immunoreactivity was observed in the tunica media of large-sized branches of intrapulmonary arteries, but not within medium- or small-sized intrapulmonary vessels or in tunica intima of different sized intrapulmonary arteries. These findings suggest that NTs may have a role in the control of vascular responses in the pulmonary system acting as local paracrine or autocrine mediators. The possible relevance of the NT system in human pulmonary vasculature identified in this study is discussed.     

Role of matrix metalloproteinases and their tissue inhibitors in the regulation of coronary cell migration.

The migration of vascular cells is regulated by matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs). Because the activation of adventitial fibroblasts has been implicated in coronary repair, we have examined regional differences in cell outgrowth and the synthesis of MMPs/TIMPs in different layers of porcine coronary arteries. Coronary medial explants demonstrated significantly slower cell outgrowth than coronary adventitia in culture (P<0.001). These observations were paralleled by the predominant expression of TIMP-1 and -2 in the media (14-fold and 37-fold higher than in adventitia, respectively, P<0.001), whereas higher gelatinolytic activities (MMP-2 and -9) were released from adventitial explants. Smooth muscle cell outgrowth from the media was regulated by endogenous TIMPs, since TIMP inhibition (recombinant MMP-2 or neutralizing anti-TIMP antibodies) facilitated cell outgrowth (P<0.001). In contrast, the addition of recombinant TIMP-1 or -2 decreased adventitial cell outgrowth. In the coculture experiments, the presence of coronary media retarded adventitial cell outgrowth, whereas medial damage abrogated these effects, allowing for fibroblast migration (P<0.001). In conclusion, this study demonstrated differential migratory properties and distinct MMP/TIMP synthesis by coronary fibroblasts and smooth muscle cells. Endogenous TIMPs in the media may play an important role in maintaining coronary arterial wall homeostasis, whereas high levels of matrix-degrading activities confer the "invasive" characteristics of adventitial fibroblasts.     

The mechanism of transluminal angioplasty

Normal coronary arteries in dogs, atherosclerotic human coronary arteries at autopsy, and rabbit iliac arteries with experimental atherosclerosis were subjected to angioplasty and studied histologically or by electron microscopy. The studies showed desquamation of endothelium, deposition of platelets in the area of angioplasty, and splitting of atheromatous plaques frequently down to the internal elastic membrane. Human coronary arteries studied at post-mortem after successful angioplasty also have demonstrated splitting of the atheromatous plaque at its weakest point. Compression of atheromatous material from the plaque has not been demonstrated experimentally. The mechanism of angioplasty is complex. As the angioplasty balloon expands, splitting of the atheromatous plaque occurs at its weakest, thinnest point. The media and adventitia of the artery are then stretched, producing an enlarged lumen and increased blood flow. Splitting of the atherosclerotic plaque explains the angiographic appearance frequently seen after angioplasty--a separate column of angiographic dye or a small radiolucent filling defect in the area of successful angioplasty.