Antiatherogenic effect of angiotensin converting enzyme inhibitor (benazepril) and angiotensin II receptor antagonist (valsartan) in the cholesterol-fed rabbits

The purpose of this study was to determine whether an angiotensin converting enzyme (ACE) inhibitor, benazepril, and an angiotensin receptor antagonist, valsartan, would decrease atherosclerotic severity in cholesterol-fed rabbits. Male rabbits were fed either: (a) normal rabbit chow; (b) 2% cholesterol diet; (c) 2% cholesterol diet supplemented by benazepril (3 mg/kg per day, subcutaneous injection); or (d) 2% cholesterol diet supplemented by valsartan (1 mg/kg per day, subcutaneous injection). After 12 weeks, the arteries were harvested for histomorphometry and immunohistochemistry. We observed that decreases in serum triglyceride (TG) and total cholesterol (TC) and ACE activity with benazepril-treatment were more than 60, 30, and 84%, respectively, in comparison with the cholesterol group; with valsartan-treatment, TG levels were 53% lower than in the cholesterol group, however, there was no significant difference in TC and ACE activity. The percentage of aortic surface atherosclerotic area, intimal thickness and the ratio of aortic intimal area to medial area were about 40% lower in the benazepril-treated group in comparison with those of the cholesterol group; the difference was more than 60% in the thoracic aorta. The valsartan-treated group had 23% less atherosclerotic area, less effective than benazepril treatment. The percent of PCNA-positive cells and the number of intimal proliferative cells/mm2 were significantly less in the benazepril-treated group compared with the cholesterol group (by 55 and 63%); these parameters were 35 and 17% lower, respectively, with valsartan. The ratio of proliferating macrophages to smooth muscle cells (SMCs) was 3:1 in the cholesterol group, 1:1 in the benazepril and 2:1 in the valsartan-treated group. These results indicate that benazepril could reduce atherosclerotic progression by decreasing macrophage proliferation and accumulation in the arterial wall. The mechanisms for reducing atherosclerotic progression by benazepril and valsartan may be related to reduction of TG and blockade of the angiotensin II action.

Enhanced reduction of atherosclerosis in hamsters treated with pravastatin and captopril: ACE in atheromas provides cellular targets for captopril

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase and angiotensin-converting enzyme (ACE) reduce experimental atherosclerosis by different mechanisms. To determine whether dual-drug therapy additively retards the progression of early lesions, control hyperlipidemic hamsters were compared with those treated with pravastatin, captopril, and pravastatin plus captopril. After 8 weeks of treatment, pravastatin (34 mg/kg/day) reduced plasma total cholesterol and triglycerides by 41 and 84%, respectively, whereas captopril (100 mg/kg/day) reduced normal blood pressure by 21%. The combination of pravastatin and captopril (33 and 100 mg/kg/day) decreased plasma total cholesterol and triglycerides by 44 and 84%, and blood pressure was decreased by 14%. In the aortic arch, pravastatin reduced macrophage-foam cell size and fatty streak area by 21 and 31%, respectively, whereas captopril decreased macrophage-foam cell number and fatty streak area by 34 and 35%. Pravastatin plus captopril decreased macrophage-foam cell number, foam cell size, and fatty streak area by 38, 24, and 67%. ACE inhibitors were previously reported to retard atherosclerosis without affecting blood pressure, suggesting that these agents acted on the artery wall. Therefore the expression of arterial ACE was determined in normal and atherosclerotic hamster aortas. ACE messenger RNA (mRNA) and protein were detected in endothelial cells, intimal macrophage-foam cells and medial smooth-muscle cells of atherosclerotic arteries indicating an upregulation of ACE expression with hyperlipidemia and atherosclerosis. In conclusion, dual-therapy with pravastatin and captopril produced an additive reduction in fatty streak area compared with either drug alone and suggested that atherogenesis can be retarded beyond the level achieved with monotherapy. The presence of ACE in endothelial cells and intimal macrophage-foam cells provides cellular targets for captopril to directly modify the formation of early atherosclerotic lesions.

Induction of angiotensin converting enzyme and angiotensin II receptors in the atherosclerotic aorta of high-cholesterol fed Cynomolgus monkeys

Antiatherogenic effects of imidapril and involvement of renin angiotensin system were examined in experimental atherosclerosis induced by feeding a high-cholesterol diet to Cynomolgus monkeys. Eighteen male monkeys were divided into three groups and placed under (1) normal diet (normal group), (2) high-cholesterol diet (control group), (3) high-cholesterol diet with imidapril (20 mg/kg body wt/day, orally) treatment (imidapril group). At the end of the experiment, the normal group showed no apparent atherosclerosis in their aorta evaluated by oil red-O staining, while the control group exhibited marked atherosclerotic involvement of the intimal surface of the aorta (58.4 +/- 9.3%, P < 0.01). Imidapril reduced systolic blood pressure and atherosclerotic involvement (24.1 +/- 5.5%, P < 0.05). Total cholesterol content of the descending thoracic aorta was also significantly reduced in the imidapril group. In the atherosclerotic vessels, angiotensin converting enzyme (ACE) activity evaluated by quantitative in vitro autoradiography was significantly increased in the intimal lesion. Further evaluation revealed angiotensin II (Ang II) type I (AT1) receptor density was significantly increased in the medial lesion and type II (AT2) receptor density in the adventitia. When the progression of atherosclerosis was impeded by imidapril treatment, the ACE activity level as well as the AT1 and AT2 receptor density remained at normal. Expression of mRNA for fibronectin, TGF-beta1, types I and III collagen was studied by Northern blot analysis. No significant differences in types I and III collagen mRNA levels were found between the control and imidapril group. On the other hand, mRNA expression for fibronectin and TGF-beta1 were much lower in the imidapril group than in the control group. These results suggest that increased production of Ang II and activated receptors may be involved in atherosclerotic process in this model and also antiatherogenic effect of imidapril may be derived from reduction of local Ang II production as well as its hypotensive action.

Delapril slows the progression of atherosclerosis and maintains endothelial function in cholesterol-fed rabbits

The renin-angiotensin system is an important modulator of arterial blood pressure and inhibitors of the angiotensin-converting enzyme (ACE-Is) and are currently used in the treatment of hypertension. The pleiotropic actions exerted by angiotensin II (AngII) on the functionality of the vessel wall may have pro-atherosclerotic outcomes; evidence for an anti-atherosclerotic effect of ACE-Is has been presented and an antioxidant effect has been attributed to thiol-containing ACE-Is, like Captopril. The present study has been undertaken to investigate the effect of Delapril, a lipophilic ACE-I, on the development of atherosclerosis in cholesterol-fed rabbits. While it did not correct hyperlipidemia, Delapril dose dependently inhibited the development of atherosclerosis, expressed as aortic area covered by lesions (23.3+/-4.1, 21.3+/-2.4 and 18.5+/-3.3% with Delapril at the daily dose of 5, 10 and 20 mg/kg, respectively, versus 38.2%+/-6.4 for control animals) and its effect was similar to that of Captopril (14.5+/-5.1% at the daily dose of 25 mg/kg). Furthermore, Delapril partially and dose dependently restored endothelium-dependent relaxation, which is impaired in vessels from hypercholesterolemic animals (51.80+/-12.18, 59.74+/-5.16, 69.13+/-8.70 maximal percent relaxation versus 48.26+/-3.05% for the untreated control and 67.67+/-6.72% for Captopril-treated animals). An antioxidant mechanism is unlikely to explain this data, since Delapril does not contain thiol groups. These observations suggest that Delapril may represent an effective pharmacological approach for the treatment of atherosclerosis during its early phases.

Angiotensin II induction of osteopontin expression and DNA replication in rat arteries

We recently identified the adhesive protein osteopontin as a novel smooth muscle cell product overexpressed in rat developing neointima and human atheroma. Although osteopontin is a candidate stimulant for intimal lesion progression because of its chemotactic and calcium binding functions, factors controlling osteopontin expression in arteries remain poorly defined. In vitro, smooth muscle cell expression of osteopontin is associated with cell cycle transit or alterations in cell phenotype, and it is increased by angiotensin II (Ang II) stimulation. In the present studies, we investigated both osteopontin expression and DNA replication in the arterial wall in response to chronic Ang II infusion in vivo. Rat carotid arteries with or without intimal thickening (induced by balloon catheterization) were examined. Ang II (250 ng/kg per minute) or vehicle was coinfused with bromodeoxyuridine (to label replicating DNA in vivo) for 2 weeks beginning 4 weeks after injury. With Ang II, smooth muscle cells overexpressed osteopontin as shown by protein immunohistochemistry, in situ hybridization, and Northern blot analyses. Osteopontin mRNA levels were increased markedly (approximately fivefold) in the normal artery media and injured artery neointima, but levels remained low in the injured artery media, in positive correlation (R2 = 0.88, P < .001) with DNA replication in the smooth muscle layers, further suggesting that osteopontin may be a growth-associated, phenotype-dependent gene for smooth muscle cells. However, osteopontin expression in neointima was not restricted to areas showing DNA replication, suggesting a nonobligatory association. Ang II induced severe hypertension. Arterial osteopontin expression was increased also by chronic catecholamine infusion, a model of vascular growth stimulation showing labile pressure elevations. Osteopontin induction in smooth muscle cells may contribute to Ang II-dependent intimal lesion progression and vascular remodeling events associated with renovascular diseases or hyperadrenergic disorders.

Smooth muscle DNA replication in response to angiotensin II is regulated differently in the neointima and media at different times after balloon injury in the rat carotid artery. Role of AT1 receptor expression

We have reported that angiotensin II (Ang II) infusion to rats during the third and fourth weeks after vascular injury stimulates DNA replication in a larger proportion of smooth muscle cells (SMCs) in the arterial neointima than in the underlying media or the normal arterial media. Whether this increased responsiveness to Ang II is a transient or stable property of neointimal cells after vascular injury remained unclear. The present study examined smooth muscle DNA replication in response to Ang II infusion (250 ng.kg-1.min-1 for 2 weeks) at 3 to 4, 9 to 10, or 27 to 28 weeks after balloon injury to the rat carotid artery. Control rats received Ringer's lactate. BrdU (0.8 mg.kg-1.d-1) was coinfused to label replicating DNA. The increased replicative response to Ang II in the neointima versus the normal arterial media did not persist beyond the period of rapid lesion growth shortly after injury, even in neointimal areas without endothelial regeneration. By 9 to 10 weeks after injury, replication frequencies were comparable in the neointima and the normal arterial wall. In the presence of a regenerated endothelium, neointimal DNA replication was lowered but not abolished. After the early period, however, the most marked difference may be the loss of ability of medial SMCs to respond mitogenically to systemic Ang II. As a consequence, Ang II-induced DNA replication in injured arteries was greater in the neointima than in the underlying media at all times studied after injury. DNA replication levels correlated with AT1 receptor levels in the injured artery neointima but not media, as shown by receptor binding in vascular sections at 3 and 10 weeks after injury. The growth response to systemic Ang II is differentially regulated in adjacent smooth muscle layers in the injured arterial wall in vivo via mechanisms that include, but are not restricted to, the regulation of AT1 receptor expression in SMCs.

Inhibitors of angiotensin converting enzyme decrease early atherosclerosis in hyperlipidemic hamsters. Fosinopril reduces plasma cholesterol and captopril inhibits macrophage-foam cell accumulation independently of blood pressure and plasma lipids

The effect of two angiotensin converting enzyme (ACE) inhibitors on the development of atherosclerosis was determined in hyperlipidemic hamsters. Preliminary studies indicated that only fosinopril (50 mg/kg) temporarily decreased mean arterial pressure, while after chronic dosing fosinopril and captopril (50 mg/kg) were ineffective. The same dose of fosinopril and captopril inhibited the angiotensin I pressor response, indicating these agents suppressed ACE activity in vivo. In the 3 week atherosclerosis experiment, all hamsters were fed chow supplemented with 0.05% cholesterol and 10% coconut oil. Control hamsters were compared with those receiving either 50 mg/kg per day of fosinopril or 50 mg/kg per day of captopril. After 3 weeks, fosinopril reduced plasma total cholesterol, low density lipoprotein (LDL) plus very low density lipoprotein cholesterol and total triglycerides by 17%, 27% and 45%, respectively. Captopril only reduced high density lipoprotein cholesterol by 20%. Neither fosinopril or captopril altered blood pressure at 3 weeks. Atherosclerosis was quantified from en face preparations of the lesion-prone aortic arch that were stained with oil red O (for cholesteryl ester and triglycerides). In control hamsters, oil red O labeled numerous subendothelial macrophage-foam cells located along the inner curvature of the aortic arch. Compared with controls, fosinopril reduced the number of intimal macrophage-foam cells/mm2, foam cell size and the fatty streak area by 85%, 38% and 90%, respectively. Captopril decreased these parameters by 44%, 16% and 53%. Thus captopril decreased early atherosclerosis without affecting plasma LDL cholesterol or blood pressure, which suggested that inhibiting ACE (or kininase II) directly impeded the accumulation and formation of macrophage-foam cells.(ABSTRACT TRUNCATED AT 250 WORDS)