Vascular angiotensin-converting enzyme activity in cholesterol-fed rabbits: effects of enalapril

Vitamin C Lowers Blood Pressure in Spontaneously Hypertensive Rats by Targeting Angiotensin-Converting Enzyme I Production in a Frequency-Dependent Manner

The lowering blood pressure effect of vitamin C (VC) has been evaluated in various models. As VC has a fast degradation rate in the body after consumption, a study of the frequency-dependent manner of VC is essential for the sustained antihypertension effect of VC. In this study, we investigated the frequency and dose dependency of vitamin C (VC) on blood pressure reduction in spontaneously hypertensive rats (SHRs). Wistar–Kyoto rats (WKYs) and SHRs were orally administered tap water or VC (250, 500, 1000, and 2000 mg/60 kg/day). Blood pressures were measured using the tail-cuff method, and thoracic aortas, liver, and blood were harvested from sacrificed rats after 8 weeks to measure angiotensinogen, angiotensin-converting enzyme (ACE) I, endothelial nitric oxide synthase (eNOS), and total nitric oxide (NOx) concentration. VC decreased blood pressure from the fourth week with no significant differences between doses. The twice-a-day administration of VC decreased blood pressure from the second week, and the blood pressure in these groups was close to that of the WKY group in the eighth week. Treatment with once a day VC decreased ACE I production which was further significantly reduced in twice a day groups. Angiotensinogen and eNOS production were increased upon VC treatment but were not significant among groups. The NOx content was decreased by VC treatment. These results suggest that VC lowers blood pressure in SHRs by directly targeting ACE I production in a frequency-dependent manner and may improve endothelial function depending on the frequency of administration.

Lack of an association between angiotensin converting enzyme gene polymorphism and peripheral arterial occlusive disease

Numerous factors have been reported to influence the pathogenesis of atherosclerosis. The angiotensin I converting enzyme (ACE) gene is a candidate gene for atherosclerotic-related disease. In the present study, the association between the polymorphism of the ACE gene and peripheral arterial occlusive disease (PAOD) was investigated. Using polymerase chain reaction techniques, 100 patients (age 66.7-7.7 years) with PAOD and 100 age-matched controls were divided into the three ACE genotypes: II, ID and DD (Insertion I and Deletion D). There was no evidence of any association between ACE gene polymorphism and the presence of PAOD (odds ratio 0.759; 95% confidence interval 0.418-1.377). These results indicate an absence of association between DD genotype and PAOD. Further evaluation in a larger population study is required to examine the possibility of an increased risk of PAOD in DD homozygotes.

Investigating the cardio-protective abilities of supplemental L-arginine on parameters of endothelial function in a hypercholesterolemic animal model

Endothelial dysfunction is now widely recognized as an early marker of cardiovascular disease, making its treatment, or complete avoidance, an emerging, interesting therapeutic target. This study investigated the ability of the highly intriguing amino acid L-arginine to influence endothelial function. Its therapeutic potential is also compared to that of known cardiovascular medications, namely nitroglycerin [a nitric oxide (NO) donor] and enalapril [an angiotensin-converting enzyme (ACE) inhibitor]. Fifty male New Zealand rabbits were included in the study, divided into 5 equal groups: control, hypercholesterolemia (untreated), hypercholesterolemia (+L-arginine), hypercholesterolemia (+enalapril), and hypercholesterolemia (+nitroglycerin). Biochemical investigations included measurement of circulating NOx, malondialdehyde (MDA), and lipid profile markers, as well as dimethylarginine dimethylaminohydrolase (DDAH) and ACE activities. Furthermore, aortic ACE activity and blood platelet aggregation were estimated. A histopathological examination and intimal thickness measurement were also conducted. Compared to the untreated hypercholesterolemic group, all agents were capable of positively influencing MDA levels, platelet aggregation and intimal thickness; however, only the L-arginine group was capable of beneficially and significantly altering both NOx levels and serum and aortic ACE activities. No agents were capable of modulating serum DDAH activity inhibited by hypercholesterolemia. Based on the results of this study, L-arginine appears to be a novel cardio-protective agent, illustrated by its ability to ameliorate the deleterious effects of hypercholesterolemia on endothelial function, in a manner comparable to, and sometimes more potent than, commonly used cardiovascular medications.

Effect of Angiotensin-converting enzyme inhibitors and Angiotensin receptor antagonists in atherosclerosis prevention

Atherosclerosis is a highly complex biological process that has become the scourge of modern civilization. Endothelial dysfunction is the first step in the development of atherosclerosis. The renin-angiotensin-aldosterone system (RAAS) plays an important role in the development of endothelial dysfunction and atherosclerosis. Several studies have shown that in vitro blockade of the RAAS is associated with improvement in markers of endothelial dysfunction and inflammation. Many clinical trials have demonstrated a clear benefit of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) manifested by a reduction of cardiovascular events. These findings suggest that ACEIs and ARBs can play an important role in prevention of atherosclerosis and in the delay of its progression. In this review we focus on the importance of RAAS blockade to prevent or delay progression of atherosclerosis and its impact on reduction of cardiovascular events.

Modification of the coronary artery disease risk associated with the presence of traditional risk factors by insertion/deletion polymorphism of the ACE gene

Cigarette smoking, hypercholesterolemia, and obesity influence the renin-angiotensin system (RAS) functions including an increased synthesis of the angiotensin I converting enzyme (ACE). Thus in the present work we explore the interactions of the ACE gene insertion/deletion (I/D) polymorphism and traditional risk factors. The study cohort included 341 subjects composed of 172 patients with angiographically confirmed CAD and 169 blood donors without a history of cardiovascular diseases. The I/D polymorphism was genotyped using polymerase chain reaction (PCR) methodology. To determine the interactions between the ACE genotypes and traditional risk factors the epidemiologic approach was used (4 x 2 tables and the synergy measures). The frequency of the DD genotype was significantly higher in patients than in controls (33.7% versus 21.3%, odds ratio [OR] = 1.88, 95% CI; 1.13-3.15, p = 0.010), but greater differences were found in males (35.7% versus 20.5%, OR = 2.15, 95% CI: 1.14-4.04, p = 0.010). We found a synergy of the DD genotype with smoking (SI = 1.88, SIM = 1.22), total cholesterol > or =5 mmol/l (SI = 2.12, SIM = 1.31) and elevated low density lipoprotein (LDL) cholesterol level (> or =3 mmol/l) (SI = 1.78, SIM = 1.14). The presence of the D allele (DD + ID subjects) also increased the risk of coronary artery disease (CAD) associated with the presence of elevated total cholesterol and LDL cholesterol (SI = 1.69, SIM = 1.18, in both cases), elevated level (> or =1.7 mmol/l) of triacylglycerols (SI = 1.81, SIM = 1.18) and overweight/obesity (SI = 4.25, SIM = 2.36). In each case the estimated CAD risk was greater than that predicted by assuming the additivity of effects (the risk increased from 69% for the D allele - total cholesterol interaction to 325% for the D allele - overweight/obesity). The statistical significance was also confirmed by a multiplicative model of synergy. The DD genotype/D allele of the ACE gene increases the risk of CAD associated with the presence of traditional risk factors.

Addition of eplerenone to an angiotensin-converting enzyme inhibitor effectively improves nitric oxide bioavailability

Angiotensin II and aldosterone both promote endothelial dysfunction and atherosclerosis. We investigated the effect of a combination of eplerenone, a selective aldosterone antagonist, and enalapril, an angiotensin-converting enzyme inhibitor, on NO bioavailability and spontaneous atherosclerotic changes. Twenty-four myocardial infarction-prone Watanabe heritable hyperlipidemic rabbits were treated with vehicle (control), eplerenone (50 mg/kg per day), enalapril (3 mg/kg per day), or eplerenone plus enalapril for 8 weeks (n=6 in each group). After treatment, acetylcholine-induced NO production was measured as a surrogate for endothelium-protective function, and vascular peroxynitrite (a product of superoxide and NO) was measured to assess dysfunctional endothelial NO synthase activity. Plaque area was quantified by histology. Intra-aortic infusion of acetylcholine produced an increase in plasma NO concentration that was significantly higher with all of the drug treatments compared with the control. Eplerenone and enalapril, in combination, increased acetylcholine-induced NO by 7.9 nM, which was significantly higher than with either eplerenone or enalapril alone. Vascular peroxynitrite was significantly higher in the control group (1.3 pmol/mg of protein) and significantly lower with combination treatment (0.4 pmol/mg of protein) compared with the enalapril or eplerenone group. The highest tetrahydrobiopterin levels were observed after cotreatment with eplerenone and enalapril. Histology of the thoracic aorta showed a significantly decreased plaque area with combination therapy compared with monotherapy. Combined treatment with a selective aldosterone antagonist and an angiotensin-converting enzyme inhibitor has additive protective effects on endothelial function and on atherosclerotic changes via decreased nitrosative stress.

Microalbuminuria

Microalbuminuria, originally described more than 3 decades ago as a predictor of nephropathy in patients who had type 1 diabetes mellitus and associated with higher cardiovascular risk, is now linked with increased risk for cardiovascular events rather than progression to end-stage kidney disease. This article reviews the role of microalbuminuria in the context of atherosclerotic vascular disease. It presents the methods for microalbuminuria assessment in clinical practice, its relations with other cardiovascular risk factors, and the pathophysiologic associations between microalbuminuria and vascular damage. In addition, this article discusses the prognostic significance of microalbuminuria for cardiovascular disease as well as existing therapeutic interventions for reducing urine albumin excretion in patients who are at high cardiovascular risk.

Diabetes mellitus-associated atherosclerosis: mechanisms involved and potential for pharmacological invention

While diabetes mellitus is most often associated with hypertension, dyslipidemia, and obesity, these factors do not fully account for the increased burden of cardiovascular disease in patients with the disease. This strengthens the need for comprehensive studies investigating the underlying mechanisms mediating diabetic cardiovascular disease and, more specifically, diabetes-associated atherosclerosis. In addition to the recognized metabolic abnormalities associated with diabetes mellitus, upregulation of putative pathological pathways such as advanced glycation end products, the renin-angiotensin system, oxidative stress, and increased expression of growth factors and cytokines have been shown to play a causal role in atherosclerotic plaque formation and may explain the increased risk of macrovascular complications. This review discusses the methods used to assess the development of atherosclerosis in the clinic as well as addressing novel biomarkers of atherosclerosis, such as low-density lipoprotein receptor-1. Experimental models of diabetes-associated atherosclerosis are discussed, such as the streptozocin-induced diabetic apolipoprotein E knockout mouse. Results of major clinical trials with inhibitors of putative atherosclerotic pathways are presented. Other topics covered include the role of HMG-CoA reductase inhibitors and fibric acid derivatives with respect to their lipid-altering ability, as well as their emerging pleiotropic anti-atherogenic actions; the effect of inhibiting the renin-angiotensin system by either ACE inhibition or angiotensin II receptor antagonism; the effect of glycemic control and, in particular, the promising role of thiazolidinediones with respect to their direct anti-atherogenic actions; and newly emerging mediators of diabetes-associated atherosclerosis, such as advanced glycation end products, vascular endothelial growth factor and platelet-derived growth factor. Overall, this review aims to highlight the observation that various pathways, both independently and in concert, appear to contribute toward the pathology of diabetes-associated atherosclerosis. Furthermore, it reflects the need for combination therapy to combat this disease.

High glucose levels abolish antiatherosclerotic benefits of ACE inhibition in alloxan-induced diabetes in rabbits

Renin-angiotensin system activation is recognized to play an important role in atherosclerosis. This study aimed to verify the antiatherosclerotic effects of ACE inhibition on an experimental model of diabetes and hypercholesterolemia. Diabetes was induced in New Zealand male rabbits with a single dose of alloxan (100 mg/kg, i.v.), and, according to plasma glucose levels obtained after 1 week, the animals were divided into 2 groups (> or =250 mg/dL or <250 mg/dL). Each group was randomly assigned to receive or not quinapril (30 mg/d) added to a 0.5% cholesterol-enriched diet. Animals with high glucose levels at 1 week and that remained high after 12 weeks presented higher triglyceride levels (P < 0.02 versus basal). Those initially hyperglycemic but presenting <250 mg/dL glucose at the end of study formed an additional group. Plasma ACE activity was lower in quinapril-treated animals (P < 0.01 versus untreated groups). However, aorta intima/media ratio and intima area were lower only in the subgroups of quinapril-treated animals with low glucose levels (P < 0.05). Our results support the hypothesis that high plasma glucose may abolish the antiatherosclerotic effect of ACE inhibitors.

Enalapril attenuates angiotensin II-induced atherosclerosis and vascular inflammation

Angiotensin converting enzyme (ACE) inhibitors prevent a wide variety of key events underlying atherogenesis. Whether these actions depend solely on reduction of angiotensin II (Ang II) generation is still to be determined. This study was undertaken to determine whether enalapril, an ACE inhibitor, prevents atherosclerosis and vascular inflammation induced by Ang II in apolipoprotein E-deficient (apoE-KO) mice. Subcutaneous infusion of Ang II (1.44 mg/(kg day)) for 4 weeks increased blood pressure and accelerated atherosclerosis development in the carotid arteries. The expression of the endothelial adhesion molecules E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), as well as the chemokines monocyte chemotactic protein-1 (MCP-1) and macrophage-colony stimulating factor (M-CSF) was up-regulated in the aortas of Ang II-treated mice. Enalapril co-treatment (25 mg/(kg day), in drinking water) prevented the development of atherosclerosis without affecting blood pressure or circulating cholesterol. In addition to preventing the Ang II-induced over-expression of adhesion molecules and chemokines in the aorta, enalapril up-regulated the expression of peroxisome proliferator-activated receptors (PPARs)-alpha and -gamma, potential anti-inflammatory transcription factors. In the aortic arch, a lesion-prone site, the co-treatment with enalapril reduced the percentage of arterial wall occupied by macrophages and foam cells, medial sclerosis and elastin reduplication. Together, these data suggest an important role for Ang II-independent mechanisms in the antiatherogenic and anti-inflammatory effects of ACE inhibitors.

Angiotensin converting anzyme (ACE) activity in porcine ocular tissue: effects of diet and ACE inhibitors

The aim of the present experiments was to determine angiotensin converting enzyme (ACE) activity in different parts of the porcine eye, and to examine whether an atherogenic diet influenced ACE activity. Female mini-pigs were fed a standard diet or a diet with high cholesterol to produce atherosclerosis. The animals were killed by an overdose of pentobarbital, and the eyes were enucleated and dissected into iris, ciliary body, retina, and choroid. Crude tissue homogenates were used for determination of ACE activity, which was done with a radioenzymatic assay. In pigs fed a normal diet, basal ACE activity was 18.1 +/- 1.6, 13.6 +/- 1.9, 4.4 +/- 0.6, and 44.7 +/- 8.5 units/mg for iris, ciliary body, retina, and choroid, respectively. The ACE activities in ocular tissues from the pigs that had been fed an atherogenic diet were not significantly different. Nor was the ACE activity in the abdominal aorta and serum significantly different between the two groups. In both groups, the ACE inhibitors captopril and enalaprilat, caused a significant inhibition of the ACE activity in the choroid and ciliary body, with enalaprilat being more potent. In the retina, ACE activity was inhibited significantly only in the group fed a normal diet, whereas ACE activity in the iris was not significantly inhibited in either group. We did not find any differences in ACE activity between pigs fed a normal diet and pigs fed an atherogenic diet, which is in disagreement with previous studies that showed an increased ACE activity in aorta from atherosclerotic mini-pigs. The reason for this discrepancy is not clear, but lower cholesterol levels are one possibility.

Hydrochlorothiazide abolishes the anti-atherosclerotic effect of quinapril

1. Antihypertensive treatment has been demonstrated to result in persistent reductions in morbidity and mortality due to stroke. However, the coronary risk attributable to hypertension has been only partially reversed. We hypothesized that diuretics could have unfavourable effects on atherosclerosis. 2. New Zealand rabbits were fed a 0.5% cholesterol-enriched diet for 12 weeks, followed by a 0.1% cholesterol diet for another 12 weeks. During the last 12 week period, 40 animals were randomly assigned to one of four groups: (i) group I was the control group; (ii) group II received hydrochlorothiazide (10 mg/day); (iii) group III received quinapril (30 mg/day); and (iv) group IV was treated with hydrochlorothiazide (10 mg/day) plus quinapril (30 mg/day). 3. The treatments did not affect either the lipid profile or serum electrolytes and oxidative stress. However, endothelium-dependent vasorelaxation in isolated aortic rings was significantly improved with quinapril (group III) treatment (P < 0.001 vs other groups). In addition, therapy with quinapril promoted a significant reduction in atherosclerosis (intima area, intima/media ratio and perimeter of vessel with plaque; P < 0.05 vs other groups), as well as in cholesterol content of the aorta (P < 0.05 vs groups II and IV). 4. In conclusion, hydrochlorothiazide did not modify atherosclerosis and, when added to quinapril treatment, impaired the anti-atherosclerotic effect seen with quinapril alone.

Dietary cholesterol alters Na+/K+ selectivity at intracellular Na+/K+ pump sites in cardiac myocytes

A modest diet-induced increase in serum cholesterol in rabbits increases the sensitivity of the sarcolemmal Na+/K+ pump to intracellular Na+, whereas a large increase in cholesterol levels decreases the sensitivity to Na+. To examine the mechanisms, we isolated cardiac myocytes from controls and from rabbits with diet-induced increases in serum cholesterol. The myocytes were voltage clamped with the use of patch pipettes that contained osmotically balanced solutions with Na+ in a concentration of 10 mM and K+ in concentrations ([K+]pip) ranging from 0 to 140 mM. There was no effect of dietary cholesterol on electrogenic Na+/K+ current (Ip) when pipette solutions were K+ free. A modest increase in serum cholesterol caused a [K+]pip-dependent increase in Ip, whereas a large increase caused a [K+]pip-dependent decrease in Ip. Modeling suggested that pump stimulation with a modest increase in serum cholesterol can be explained by a decrease in the microscopic association constant KK describing the backward reaction E1 + 2K+ --> E2(K+)2, whereas pump inhibition with a large increase in serum cholesterol can be explained by an increase in KK. Because hypercholesterolemia upregulates angiotensin II receptors and because angiotensin II regulates the Na+/K+ pump in cardiac myocytes in a [K+]pip-dependent manner, we blocked angiotensin synthesis or angiotensin II receptors in vivo in cholesterol-fed rabbits. This abolished cholesterol-induced pump inhibition. Because the epsilon-isoform of protein kinase C (epsilonPKC) mediates effects of angiotensin II on the pump, we included specific epsilonPKC-blocking peptide in patch pipette filling solutions. The peptide reversed cholesterol-induced pump inhibition.

Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers in atherosclerosis

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) effectively interfere with the renin-angiotensin system and exert various beneficial actions on cardiac and vascular structure and function, beyond their blood pressure-lowering effects. Randomized, controlled clinical trials have shown that ACE inhibitors improve endothelial function, cardiac and vascular remodeling, retard the anatomic progression of atherosclerosis, and reduce the risk of myocardial infarction, stroke, and cardiovascular death. Therefore, these agents are recommended in the treatment of a wide range of patients at risk for adverse cardiovascular outcomes, including those with coronary disease, prior stroke, peripheral arterial disease, high-risk diabetes, hypertension, and heart failure. ARBs are effective blood pressure- lowering and renoprotective agents and can be used in heart failure in patients who do not tolerate ACE inhibitors. The role of ARBs in the prevention of atherosclerosis and its sequelae is currently under investigation. The use of combined ACE inhibitor plus ARB therapy offers theoretical advantages over the use of each of these agents alone and is also under investigation in large, randomized clinical trials.

Two angiotensin AT1 receptor antagonists, irbesartan and losartan, effects in cholesterol-fed rabbits

This study was performed to examine the long-term effects of irbesartan and losartan, two angiotensin (AT(1)) receptor antagonists, on lipoproteins and vascular responsiveness in vessels isolated from hypercholesterolemic rabbits. Four groups of rabbits (n=40) were used: Group 0 (control group), Group 1 [hypercholesterolemic group, 0.5% (wt./wt.) cholesterol-enriched diet], Group 2 (hypercholesterolemic+irbesartan 10 mg/kg/day) and Group 3 (hypercholesterolemic+losartan 10 mg/kg/day). After 17 weeks of treatment, total cholesterol and low-density lipoproteins levels in irbesartan- and losartan-treated groups were significantly lower than those of Group 1 (alpha=0.05). Furthermore, levels of high-density lipoproteins were higher in the treated groups than in the hypercholesterolemic (alpha=0.05) when we consider the same level of total cholesterol in the hypercholesterolemic and the treated groups. Despite the effect of the drugs on the abovementioned parameters, treatment with irbesartan or losartan did not improve endothelium-dependent and independent relaxation in aortic and mesenteric rings. Treatment with irbesartan and losartan decreased noradrenaline-induced contraction in aortic rings with respect to that in the hypercholesterolemic group (alpha=0.05). In addition, irbesartan treatment improved the increase in serotonin-induced contraction in proximal coronary arteries with respect to that in the hypercholesterolemic group (alpha=0.05). These results indicate that irbesartan and losartan restore noradrenaline-induced contraction in hypercholesterolemic rabbit-isolated arteries and improve lipoprotein profile in cholesterol-fed rabbits.

Influence of baroreflex on volume elasticity of heart and aorta in the rabbit

Optimal ventriculoaortic coupling includes tuning of elastic properties. The ratio of effective arterial elastance and left ventricular endsystolic elastance is often taken as a measure for mechanical and energetical efficiency. The present study determined the time course of ventricular and aortic volume elasticity (VE = dp/dV) throughout a complete heartbeat. This was achieved by using changes of eigenfrequency of two catheter-transducer systems under closed chest conditions in rabbits. Short-term VE modulation was studied by a baroreflex response, as induced by pressure changes applied to the carotid sinus. Long-term changes were studied in atherosclerotic rabbits (12 wk of high-cholesterol feeding). The time course and mean values of ventricular and aortic VE were changed by the baroreflex stimulus. Cholesterol feeding diminished the response. The degree of ventriculoaortic coupling, as quantified by VE(Aorta)/VE(Ventricle) ratio, varied during a single ejection period. The large span allows either maximal energetical efficiency or maximal stroke work. Although normal rabbits adjusted their ventriculoaortic coupling during baroreflex input, the cholesterol-fed rabbits failed to do so.

Ramipril administration to atherosclerotic mice reduces oxidized low-density lipoprotein uptake by their macrophages and blocks the progression of atherosclerosis

Foam cell formation, the hallmark of early atherosclerosis, results from cholesterol accumulation in arterial macrophages. Angiotensin-II stimulates foam cell formation and angiotensin converting enzyme (ACE) inhibitors reduce atherosclerosis in animal models. The goal of the present study was to determine the effect of the ACE inhibitor Ramipril on the progression of atherosclerosis in apolipoprotein-E-deficient (E0) mice with already advanced atherosclerosis. Therefore, 4-month-old atherosclerotic E0 mice were treated with Ramipril for 2 and 4 months and compared to age-matched placebo-treated mice, as well as to control young (4-month-old) non-treated E0 mice, for their atherosclerosis. Histomorphometry showed that Ramipril treatment substantially inhibited atherogenesis as shown by 48 and 72% reduction in lesion size at 6 and 8 months of age, respectively, compared to the lesion size in age-matched placebo-treated mice. Moreover, the size of the atherosclerotic lesions in 6- and 8-month-old Ramipril-treated mice was almost identical to the size of atherosclerosis of the 4-month-old control mice. Moreover, Ramipril treatment of E0 mice, significantly reduced oxidized low-density lipoprotein (Ox-LDL) uptake by their peritoneal macrophages (MPM) by 32%, compared to Ox-LDL uptake by MPM from 6-month-old placebo mice, and even reduced it by 12% in comparison to Ox-LDL uptake by MPM from 4-month-old control mice. A significant decrease in the mRNA levels of the Ox-LDL receptor CD36 by 58% was observed in macrophages from 6-month-old Ramipril-treated mice compared to macrophages from the 6-month-old placebo-treated mice. There was even a significant reduction (by 32%) in CD36 mRNA levels in macrophages from the 6-month-old Ramipril-treated mice, compared to the CD36 mRNA levels in macrophages from the 4-month-old control mice. We thus conclude that administration of the ACE inhibitor Ramipril to E0 mice, which already exhibit significant atherosclerosis, blocked the progression of the atherosclerotic lesion build-up, a phenomenon that could be related to Ramipril-induced inhibition of Ox-LDL uptake by macrophages.

Potential indications for angiotensin-converting enzyme inhibitors in atherosclerotic vascular disease

Angiotensin-converting enzyme (ACE) inhibitors are well established as first-line therapy for patients with left ventricular dysfunction, diabetic patients with hypertension or renal disease, and patients recovering from myocardial infarction. Angiotensin II and bradykinin regulate cellular proliferation, inflammation, and endothelial function, thus playing an important role in the pathogenesis of atherosclerosis. A large body of experimental evidence reporting that ACE inhibitors limit these effects has formed the rationale for major clinical trials of these drugs in the management of atherosclerotic vascular disease. The first trial to be completed demonstrated that ACE inhibition improves the prognosis of patients who have, or are at risk of, atherosclerotic vascular disease, independent of its effects on left ventricular function and hypertension. Expanding the indications for ACE inhibitors is now evidence driven, although the choice of agent for these new indications remains to be determined by further research.

Increased angiotensin-converting enzyme activity in coronary artery specimens from patients with acute coronary syndrome

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors are effective in the secondary prevention of ischemic heart disease, but they do not reduce the rate of restenosis. Vascular ACE activity in the culprit coronary lesions of these patients, however, has never been quantified.

METHODS AND RESULTS

We measured the ACE activity of vascular tissue obtained by directional coronary atherectomy in patients with acute coronary syndrome (n=17) and in patients with stable ischemic heart disease (n=36), with and without restenosis. The ACE activity of the culprit coronary lesions was significantly increased in patients with acute coronary syndrome (0.87+/-0.12 nmol. min(-1). mg protein(-1); P:<0.01) but not in patients with ischemic heart disease with restenosis (n=11, 0.19+/-0.05 nmol. min(-1). mg protein(-1)) when compared with those patients with ischemic heart disease without restenosis (n=25, 0.20+/-0.05 nmol. min(-1). mg protein(-1)). There was no difference between the ACE activity of the coronary tissue of the in-stent (n=5) and stent-unrelated (n=6) restenosis patients (0.24+/-0.10 versus 0.15+/-0.04 nmol. min(-1). mg protein(-1)). Serum ACE activity did not differ significantly among the patients.

CONCLUSIONS

The present study demonstrates increased ACE activity in culprit lesions in acute coronary syndrome, indicating that enhanced ACE activity is related to the causative mechanism of active coronary lesions.

Antiatherosclerotic effects of ACE inhibitors: where are we now?

ACE inhibitors have been used extensively in the management of patients with hypertension and heart failure. Over the past decade, a large body of evidence has emerged indicating that ACE inhibition also favorably affects the vasculature, and that these effects are associated with improved patient outcomes. Such evidence is provided by several sources: (i) experimental studies, which demonstrate that in addition to blood pressure lowering, ACE inhibitors improve endothelial function and have a host of other beneficial effects on the arterial wall; (ii) epidemiologic studies, which link the renin-angiotensin-aldosterone system to increased risk for myocardial infarction, and (iii) clinical trials, which demonstrate that treatment with these agents reduces the risk for acute ischemic events, improves the function of the arterial endothelium and can retard the progression of the anatomic extent of atherosclerosis.

Angiotensin II promotes atherosclerotic lesions and aneurysms in apolipoprotein E-deficient mice

Increased plasma concentrations of angiotension II (Ang II) have been implicated in atherogenesis. To examine this relationship directly, we infused Ang II or vehicle for 1 month via osmotic minipumps into mature apoE(-/-) mice. These doses of Ang II did not alter arterial blood pressure, body weight, serum cholesterol concentrations, or distribution of lipoprotein cholesterol. However, Ang II infusions promoted an increased severity of aortic atherosclerotic lesions. These Ang II-induced lesions were predominantly lipid-laden macrophages and lymphocytes; moreover, Ang II promoted a marked increase in the number of macrophages present in the adventitial tissue underlying lesions. Unexpectedly, pronounced abdominal aortic aneurysms were present in apoE(-/-) mice infused with Ang II. Sequential sectioning of aneurysmal abdominal aorta revealed two major characteristics: an intact artery that is surrounded by a large remodeled adventitia, and a medial break with pronounced dilation and more modestly remodeled adventitial tissue. Although no atherosclerotic lesions were visible at the medial break point, the presence of hyperlipidemia was required because infusions of Ang II into apoE(+/+) mice failed to generate aneurysms. These results demonstrate that increased plasma concentrations of Ang II have profound and rapid effects on vascular pathology when combined with hyperlipidemia, in the absence of hemodynamic influences.

CD143 in the development of atherosclerosis

The expression of CD143 (angiotensin-I-converting enzyme, ACE) in cardiovascular diseases may be an important determinant of local angiotensin and kinin concentrations. Much of the experimental and clinical evidence suggests a crucial role for Ang II in fibrogenesis and the development of atherosclerosis. Therefore, we have studied the distribution of CD143 in atherosclerotic and non-atherosclerotic segments isolated from different parts of the human vascular tree, including aorta and coronary, carotid, brachial, renal, iliac and femoral arteries, and staged according to the AHA. Two hundred and thirty native and formalin-fixed specimens of 80 patients were analysed by sensitive APAAP-technique using ten different monoclonal and polyclonal antibodies to human CD143 and several controls. In non-atherosclerotic segments or intimal thickening, CD143 was found almost restricted to the endothelial cells of adventitial arterioles and small muscular arteries. In contrast, a striking accumulation of CD143 was detected in all early and advanced atherosclerotic lesions. This de-novo occurrence of CD143 within the intimal vascular wall was caused by spindle-shaped subendothelial cells with macrophagic/histocytic features, activated macrophages and foam cells. In addition, advanced lesions of atherosclerosis showed a marked neo-expression of CD143 in newly formed intimal microvessels. Hypocellular fibrotic plaques depleted in microvessels and macrophages showed only little CD143. The de-novo occurrence of CD143 was dependent on the stage of atherosclerosis but not on its particular localisation within the vascular system. This early and obligatory CD143 expression at an unusual vascular site may contribute to unusual tissue levels of angiotensins as indicated by co-localisation of immunoreactive Ang II. Thus, it may be an important pathogenetic step in the development of atherosclerosis and an established target for pharmacological prevention.

Differential effects of long-term renin-angiotensin system blockade on limitation of infarct size in cholesterol-fed rabbits

We evaluated the effects of chronic inhibition of angiotensin-converting enzyme (ACE) or receptor blockade of angiotensin II type I on the size of myocardial infarcts induced by coronary occlusion-reperfusion in rabbits fed a high-cholesterol or normal diet for 10 weeks. In treated rabbits, myocardial infarction occurred 24 h after the last dose of enalapril or L-158809, an angiotensin II type I receptor antagonist, because of the drugs' waning effects on hemodynamic parameters. The size of the infarct was significantly larger in cholesterol-fed rabbits than in rabbits fed a normal diet. This augmentation of infarct size in cholesterol-fed rabbits was reversed by long-term treatment with enalapril, but not L-158809. The favorable effects of enalapril treatment disappeared after pretreatment with the bradykinin B(2) receptor blocker HOE 140. Long-term enalapril or L-158809 administration did not reduce the size of the infarct in rabbits fed a normal diet. ACE activity in ischemic myocardium significantly exceeded that in nonischemic myocardium and was further increased in cholesterol-fed rabbits, but was significantly reduced by long-term enalapril, but not L-158809. Moreover, treatment with enalapril, but not L-158809, restored acetylcholine-induced endothelium-dependent relaxation of aortic rings from cholesterol-fed rabbits. These results demonstrate that long-term ACE inhibition, but not angiotensin II type I receptor blockade, effectively reduces the size of myocardial infarcts in cholesterol-fed rabbits. The favorable effects of enalapril treatment may involve primarily a bradykinin B(2) receptor-mediated pathway.

Pathogenic role of oxidative stress in vascular angiotensin-converting enzyme activation in long-term blockade of nitric oxide synthesis in rats

Inhibition of nitric oxide (NO) synthesis with N(omega)-nitro-L-arginine methyl ester (L-NAME) activates vascular angiotensin-converting enzyme (ACE) and causes oxidative stress. We investigated the role of oxidative stress in the pathogenesis of ACE activation in rats. Studies involved aortas of rats receiving no treatment, L-NAME, L-NAME plus L-arginine, or L-NAME plus an antioxidant drug (N-acetylcysteine, allopurinol, or ebselen) for 7 days. L-NAME significantly increased oxidative stress (O(2)(-)) and ACE activity. The increased O(2)(-) production was normalized by removal of endothelium. Immunohistochemistry showed the increased ACE activity in the endothelial layer. Treatment with antioxidant drugs did not affect the L-NAME-induced increase in systolic arterial pressure but did prevent increases in vascular O(2)(-) production and ACE activity. These results implicate oxidative stress in the pathogenesis of vascular ACE activation in rats with long-term inhibition of NO synthesis. The observed effects of antioxidant drugs on ACE activation do not appear to involve the hypertension induced by L-NAME.

In vivo renal vascular and tubular function in experimental hypercholesterolemia

Hypercholesterolemia (HC) is often associated with impaired peripheral and coronary vascular responses to endothelium-dependent vasodilators, which are probably due to low bioavailability of nitric oxide. To examine the effect of HC on renal vascular and tubular function, 22 domestic pigs were studied after being fed a 12-week normal (n=11) or HC (n=11) diet. Renal regional perfusion and intratubular contrast media concentration in each nephron segment (representing fluid reabsorption) were quantified in vivo with electron-beam computed tomography before and after a suprarenal infusion of either acetylcholine (6 pigs of each diet) or sodium nitroprusside (SNP; 5 pigs of each diet). An increase in cortical perfusion, observed in normal pigs with acetylcholine (+35+/-6%, P=0. 002) and SNP (+12+/-4%, P=0.005), was blunted in the HC group (+8. 8+/-4.0, P=0.01, and -4.6+/-4.0%, P=0.1, respectively, P=0.003 and P=0.005 compared with normal) as was an increase in medullary perfusion (+58+/-21 in normal versus +24+/-11% in HC, P=0.04). A decrease in the intratubular contrast media concentration in the distal tubule and collecting duct of normal pigs was observed in all tubular segments (and was significantly enhanced in the proximal tubule and Henle's loop) in the HC group, which was associated with increased sodium excretion. The tubular and renal excretory responses to SNP were similar between the groups. In conclusion, early experimental HC in the pig attenuates renal perfusion response to both endothelium-dependent and -independent vasodilators possibly because of decreased bioavailability or decreased vascular responsiveness to nitric oxide. This vascular impairment may play a role in maladjusted renovascular responses and contribute to renal damage in later stages of atherosclerosis.

Angiotensin-converting enzyme and cardiovascular disease risk

The published studies of the association of the angiotensin-converting enzyme (ACE) genotype with cardiovascular disease have used many different diagnostic criteria for cardiovascular disease and have drawn their samples from different patient groups and different populations. This review examines the association of the ACE DD genotype with cardiovascular disease risk in studies grouped by their case criterion, the geographical region of the population samples, and by the cardiovascular risk level of the patient sample. In studies where the underlying odds ratios are determined to be homogeneous, the overall odds ratios for myocardial infarction and coronary artery disease with regard to the ACE DD genotype are estimated using the Mantel-Haenszel method.

Antiatherosclerotic activity of drugs in relation to nitric oxide function

Many studies have shown that loss of endothelium-derived nitric oxide is a major factor of ischemic episodes in patients with coronary artery disease and there is increasing evidence to suggest that nitric oxide might exert antiatherosclerotic actions. Based on these concepts, the results of animal studies on the effects of lipid lowering drugs, antioxidants, angiotensin converting enzyme inhibitors, Ca2+ channel blockers, estrogens and agents which modulate nitric oxide bioavailability are presented and compared to the results of patient studies and clinical trials. In spite of encouraging results obtained with antioxidants in animals, clinical trials could only show a clear positive effect of vitamin E treatment on the outcome of cardiovascular disease. Angiotensin converting enzyme inhibitors can ameliorate endothelial dysfunction in coronary heart disease, but their impact on disease progression remains unclear. There is evidence that estrogen replacement therapy in post-menopausal women may increase the bioavailability of nitric oxide. Finally, improved endothelial function and plaque stability clearly contribute to the clinical benefits of lipid lowering interventions, statins in particular. Taken together, these studies lend support to the concept that improving endothelial function and nitric oxide release might serve as valuable elements in the prevention or therapy of cardiovascular disease.

Special considerations in the therapy of diabetic hypertension

Patients with diabetes mellitus have an increased prevalence of hypertension and associated cardiovascular disease (CVD), including coronary and cerebrovascular disease. The risk of an individual of developing CVD is much greater when both diseases coexist and is further magnified by their frequent association with dyslipidemia, coagulation, platelet, and endothelial abnormalities. Metabolic abnormalities frequently associated with hypertension are insulin resistance, enhanced coagulation, and decreased fibrinolytic activity. Drug treatment of hypertension in diabetic subjects is fraught with potential difficulties, including altered efficacy of medications, possible side effects, worsening of glycemic control, and impairment of lipid metabolism. Because hypertension is a major contributor to morbidity and mortality in diabetes, it should be recognized and treated early and aggressively despite these difficulties. This article reviews the efficacy and side effects of the various classes of antihypertensive agents in patients with diabetes mellitus.

Amelioration by quinapril of myocardial infarction induced by coronary occlusion/reperfusion in a rabbit model of atherosclerosis: possible mechanisms

BACKGROUND

The increased severity of the myocardial injury produced by coronary occlusion-reperfusion in models of atherosclerosis is associated with an increase in leukocyte accumulation in the ischemic myocardium. Expression of P-selectin, an adhesion molecule involved in the interaction between leukocytes and endothelium, is increased in atherosclerotic vessels. Long-term angiotensin-converting enzyme (ACE) inhibition has been shown to reduce atherosclerotic vascular change in experimental models.

METHODS AND RESULTS

We examined changes in the size of the infarct resulting from coronary occlusion/reperfusion in normally fed and cholesterol-fed rabbits that were chronically treated with quinapril. Infarct size was significantly larger in the cholesterol-fed versus normally fed rabbits. ACE activity in the ischemic and nonischemic myocardium was significantly reduced by quinapril. Chronic quinapril administration significantly ameliorated the increased myocardial injury in cholesterol-fed rabbits. Quinapril administration markedly increased the myocardial cGMP content and reduced the myeloperoxidase activity in the border region of the ischemic myocardium in cholesterol-fed rabbits. The enhanced expression of P-selectin in myocardial tissue of cholesterol-fed rabbits was also effectively reduced by quinapril treatment. The above effects of quinapril were eliminated by blockade of bradykinin B2 receptors or inhibition of nitric oxide synthesis.

CONCLUSIONS

Chronic quinapril treatment ameliorated the severity of myocardial injury produced by coronary occlusion/reperfusion in cholesterol-fed rabbits, possibly because of reversal of the enhanced interaction between leukocytes and endothelium in the ischemic myocardium via a bradykinin-related pathway.

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.