Hypercholesterolemic Arteries Research Articles

Sonographic Assessment of Atherosclerotic and Hypercholesterolemic Artery Using the Echo-Tracking Technique in an Animal Model

The purpose of this study was to ascertain the utility of sonography with the echo-tracking (ET) technique to assess vascular stiffness in rabbits with hypercholesterolemia and atherosclerosis. Grayscale sonography associated with the ET technique was used to measure the elastic modulus (Ep) of the aorta in cholesterol-fed rabbits (group T1, n = 44, for 4 weeks; group T2, n = 44, for 12 weeks) and normal control rabbits (group C1, n = 44; group C2, n = 44). The aortic Ep values and blood biochemical markers between groups were compared using analysis of covariance. Light and transmission electron microscopic evaluation were used to demonstrate atherosclerotic changes in the aorta. The Ep values of the aorta in group T1 and T2 rabbits were significantly higher than those of group C1 and C2 controls (88.74 +/- 27.99 and 100.96 +/- 24.81 vs 64.38 +/- 20.23 and 72.35 +/- 18.43, p = .124). Also, the Ep values of the aorta between group T1 and T2 rabbits were significantly different (p = .033). Light and transmission electron microscopy confirmed morphologic typical changes of aortic atherosclerosis in groups T1 and T2. Grayscale sonography with the ET method could be used to evaluate tissue elastic changes in arterial walls associated with atherosclerosis and hypercholesterolemia.

Endothelial dysfunction and improvement of the angiotensin II-reactivity in hypercholesterolemic rabbits: Role of cyclooxygenase metabolites

The aim of this paper was to study the effect of high cholesterol diet on endothelial function and vascular reactivity to angiotensin II and to test the role of vasoconstrictor cyclooxygenase metabolites in this experimental condition. Rabbits were fed with either normal chow or a diet containing 1% cholesterol for 6–7-week. Isometric contractions were measured in rubbed or unrubbed aortic rings. Arteries were contracted with noradrenaline and then exposed to one cumulative dose–response curve to acetylcholine in absence (control) or in presence of indomethacin, ( N-[2-cyvlohexyloxy)-4-nitrophenyl]-methanesulfonamide) (NS 398) or 4-hydroxy-2,2,6,6-tetraethylpiperidine- N-oxyl (tempol). After washing the arteries, one cumulative dose–response curve to angiotensin II was constructed in absence or presence of indomethacin, NS 398, [1 S-[1 alpha,2 beta (5 Z),3 beta,4 alpha]-7-[3-[[2-[(phenylamino) carbonyl]hydrazino]methyl]-7-oxabicyclo[2.2.1] hept-2-yl]-5-heptenoic acid (SQ29548) or 17-octadecynoic acid (17-ODYA). In other group, resting potential was recorded in basal and angiotensin II-stimulated conditions. Indomethacin, NS 398 or 17-ODYA were added to the bath before angiotensin II-stimulation. Rabbits fed on a diet enriched with cholesterol showed higher plasma levels of total cholesterol and LDL. Hypercholesterolemic diet impaired acetylcholine relaxation. Indomethacin normalized endothelium-dependent relaxation whereas NS 398 and tempol had no effect on this phenomenon. Angiotensin II-reactivity was increased in endothelium intact hypercholesterolemic aortic rings and indomethacin, SQ29548 or 17-ODYA blocked this effect. The resting potential of unrubbed hypercholesterolemic arteries was significantly less negative to control after angiotensin II-stimulation. 17-ODYA but not indomethacin prevented angiotensin II-depolarization. High cholesterol diet caused endothelial dysfunction and increased the angiotensin II-reactivity. Both effects were cyclooxygenase1-dependent. Deficit in the NO-production might improve 20-hydroxyeicosatrienoic acid availability, which induces depolarization and angiotensin II-sensitization. In addition, 20-hydroxyeicosatrienoic acid would be metabolized by cyclooxygenase1 to 20-endoperoxides which act through thromboxane A 2/prostaglandin H 2 receptors contributing to angiotensin II-reactivity increase.

Effect of atherosclerosis on transmural convection an arterial ultrastructure. Implications for local intravascular drug delivery.

Local infusion of agents through perforated catheters may reduce neointimal formation following vascular angioplasty. Such treatment will succeed only if the drug is retained within the arterial intima long enough to promote repair. Drugs will be dispersed throughout the wall predominantly by transmural convection instead of diffusion if the Peclet number, Pe = J (1-delta f)/P, is greater than unity, where J is the transmural fluid flow per unit surface area and delta(f) and P are the reflection and permeability coefficients to the drug, respectively. Although the targets of local drug delivery will be atherosclerotic vessels, little is known about the transport properties of these vessels. Accordingly, we evaluated the effects of hypercholesterolemia and atherosclerosis on J per unit pressure (hydraulic conductance, Lp) and on ultrastructure in femoral arteries. Measurements were made at 30, 60, and 90 mm Hg in anesthetized New Zealand white rabbits fed a normal diet (n = 6) and after 3 weeks of lipid feeding (n = 19). Atherosclerosis was induced in six lipid-fed animals by air desiccation of a femoral artery. Hydraulic conductance was significantly greater in vessels from hypercholesterolemic than from normal animals and decreased with pressure only in hypercholesterolemic arteries. Atherosclerosis did not augment hydraulic conductance compared with hypercholesterolemia alone. Electron microscopic examination demonstrated damaged endothelium in hypercholesterolemic arteries and both altered endothelium and less tightly packed medial tissue, compared with controls, in atherosclerotic vessels, at least at lower pressures. Peclet numbers for macromolecules exceeded unity for all three groups of arteries and reached 0.3 to 0.4 for molecules as small as heparin. Thus, convection plays a dominant role in the distribution of macromolecular agents following local delivery and may result in their rapid transport to the adventitia in the femoral artery.

Percutaneous transluminal in vivo gene transfer by recombinant adenovirus in normal porcine coronary arteries, atherosclerotic arteries, and two models of coronary restenosis.

Gene therapy has been proposed as a possible solution to the problem of restenosis after coronary angioplasty. The current study was undertaken to assess conventional methods of gene transfer and to develop percutaneous techniques for introducing genes directly into the coronary arteries of large mammals. Since the anticipated targets of gene therapy against restenosis include atherosclerotic and previously instrumented arteries, we also evaluated gene transfer in atherosclerotic coronary arteries and in two porcine models of restenosis: one using intracoronary stents and a second using balloon overstretch angioplasty. The conventional method of using perforated balloon catheters to deliver Lipofectin-DNA complexes directly into the coronary arteries of intact animals was applied to 18 porcine coronary arteries including normal arteries, hypercholesterolemic arteries, and those simulating restenosis. The results of this study were consistent with previously published results indicating that only low levels of luciferase gene expression could be obtained by Lipofectin-mediated gene transfer. We therefore undertook a second, parallel study to evaluate percutaneous transluminal in vivo gene transfer using a replication-deficient adenoviral vector. A comparison of the two studies revealed that the mean level of reporter gene expression in the cohort undergoing adenoviral infection was 100-fold higher than in the cohort undergoing Lipofection. Analysis of luciferase activity over time in normal arteries revealed that recombinant gene expression was half-maximal after 1 day, peaked within 1 week, was still half-maximal at 2 weeks, and declined to low levels by 4 weeks. Histochemical analysis of coronary arteries treated with a second adenovirus expressing a nuclear-localized beta-galactosidase gene demonstrated gene transfer to a limited number of cells in the media and adventitia. Immunohistochemical analysis of Ad5-infused arteries using a monoclonal antibody directed against CD44 identified a periadventitial infiltrate composed of leukocytes. The recombinant adenoviral vectors proved to be far more effective than Lipofectin at delivering foreign genes directly into the coronary arteries of living mammals. Furthermore, the influences of hypercholesterolemia and arterial injury appeared to have little effect on the levels of gene expression obtained using either method. The results demonstrate that low-level recombinant gene expression, the major obstacle impeding gene therapy for the prevention of restenosis, can potentially be overcome by using adenoviral vectors to mediate coronary gene transfer in vivo. The duration of gene expression provided by these vectors and their effective deployment in atherosclerotic, balloon-overstretched, and stented coronary arteries suggest that recombinant adenovirus may have potential for evaluating gene therapy in the clinically informative porcine models of coronary restenosis.

Enhanced role of potassium channels in relaxations to acetylcholine in hypercholesterolemic rabbit carotid artery.

The effect of hypercholesterolemia for 10 wk on endothelium-dependent relaxations to acetylcholine was studied in isolated rings of rabbit carotid artery and abdominal aorta contracted with phenylephrine or elevated potassium. In these arteries obtained from hypercholesterolemic rabbits, endothelium-dependent relaxations to acetylcholine were not significantly different from those of normal rabbits. In normal and hypercholesterolemic arteries, partial relaxation persisted in the presence of NG-nitro-L-arginine methyl ester (L-NAME), which blocked acetylcholine-induced increases in arterial guanosine 3',5'-cyclic monophosphate (cGMP). Combined treatment with L-NAME and the calcium-dependent potassium-channel inhibitor, charybdotoxin, blocked relaxations in both groups, suggesting that L-NAME-resistant relaxations are mediated by an endothelium-derived hyperpolarizing factor. Charybdotoxin alone or depolarizing potassium had no significant effect on normal carotid artery or normal and hypercholesterolemic abdominal aorta but significantly inhibited relaxations of the carotid artery from cholesterol-fed rabbits. The enhanced role of calcium-dependent potassium channels and the hyperpolarizing factor in relaxation of the hypercholesterolemic carotid artery suggested by these results was likely related to the fact that acetylcholine failed to stimulate cGMP only in that artery. These data suggest that endothelium-dependent relaxation in these rabbit arteries is mediated by nitric oxide-cGMP-dependent and -independent mechanisms. In hypercholesterolemia, the contribution of nitric oxide-cGMP in the carotid artery is reduced, but a hyperpolarizing factor and calcium-dependent potassium channels maintain normal acetylcholine-induced relaxation.