Effects of ramipril and vitamin E on atherosclerosis: the study to evaluate carotid ultrasound changes in patients treated with ramipril and vitamin E (SECURE)

Antioxidant vitamins and the risk of carotid atherosclerosis. The Perth Carotid Ultrasound Disease Assessment study (CUDAS)

OBJECTIVES

This study examined whether dietary intake or plasma levels of antioxidant vitamins were independently associated with common carotid artery intima-media (wall) thickness (IMT) or focal plaque, or both, in a large, randomly selected community population.

BACKGROUND

Oxidation of low-density lipoprotein (LDL) cholesterol is thought to be important in early atherogenesis. Antioxidant micronutrients may therefore protect against lipid peroxidation and atherosclerotic vascular disease.

METHODS

We studied 1,111 subjects (558 men and 553 women; age 52 +/- 13 years [mean +/- SD], range 27 to 77). We measured dietary vitamin intake and fasting plasma levels of vitamins A, C and E, lycopene and alpha- and beta-carotene and performed bilateral carotid artery B-mode ultrasound imaging. RESULTS; After adjustment for age and conventional risk factors, there was a progressive decrease in mean IMT, with increasing quartiles of dietary vitamin E intake in men (p = 0.02) and a nonsignificant trend in women (p = 0.10). Dietary vitamin E levels accounted for 1% of the variance in measured IMT in men. For plasma antioxidant vitamins, there was an inverse association between carotid artery mean IMT and plasma lycopene in women (p = 0.047), but not in men. None of the other dietary or plasma antioxidant vitamins, nor antioxidant vitamin supplements, were associated with carotid artery IMT or focal carotid artery plaque.

CONCLUSIONS

This study provides limited support for the hypothesis that increased dietary intake of vitamin E and increased plasma lycopene may decrease the risk of atherosclerosis. No benefit was demonstrated for supplemental antioxidant vitamin use.

The relevance of tissue angiotensin-converting enzyme: manifestations in mechanistic and endpoint data

Angiotensin-converting enzyme (ACE) is primarily localized (>90%) in various tissues and organs, most notably on the endothelium but also within parenchyma and inflammatory cells. Tissue ACE is now recognized as a key factor in cardiovascular and renal diseases. Endothelial dysfunction, in response to a number of risk factors or injury such as hypertension, diabetes mellitus, hypercholesteremia, and cigarette smoking, disrupts the balance of vasodilation and vasoconstriction, vascular smooth muscle cell growth, the inflammatory and oxidative state of the vessel wall, and is associated with activation of tissue ACE. Pathologic activation of local ACE can have deleterious effects on the heart, vasculature, and the kidneys. The imbalance resulting from increased local formation of angiotensin II and increased bradykinin degradation favors cardiovascular disease. Indeed, ACE inhibitors effectively reduce high blood pressure and exert cardio- and renoprotective actions. Recent evidence suggests that a principal target of ACE inhibitor action is at the tissue sites. Pharmacokinetic properties of various ACE inhibitors indicate that there are differences in their binding characteristics for tissue ACE. Clinical studies comparing the effects of antihypertensives (especially ACE inhibitors) on endothelial function suggest differences. More comparative experimental and clinical studies should address the significance of these drug differences and their impact on clinical events.

The role of angiotensin-converting enzyme inhibitors in the treatment of hypertension

Angiotensin-converting enzyme (ACE) inhibitors continue to find new uses. The Heart Outcomes Prevention Evaluation study has demonstrated their wide application as a preventive measure for patients at high risk of cardiovascular disease, but the available clinical trials in hypertensive subjects do not so far suggest any clear superiority over conventional treatment. The available trials may have been underpowered to detect non-blood pressure-related benefits on smooth muscle growth, endothelial function, left ventricular hypertrophy, and plaque rupture, when used in relatively low-risk subjects with uncomplicated hypertension. Clinical trials have also shown that two or more drugs are needed to lower blood pressure even to 140/90. Few patients have uncomplicated hypertension, so the choice of their drugs will be powerfully influenced by their other clinical problems. Nevertheless, there is a strong case for an attack on the renin-angiotensin system. Whether this will be by ACE inhibition, angiotensin-II receptor blockade, or both, is the subject of current clinical trials.

The clinical implication of tissue renin angiotensin systems

The presence, and in many cases the regulated synthesis, of components of the renin-angiotensin system have been demonstrated in multiple tissues, indicating the existence of tissue angiotensin-generating systems. These vary with respect to which renin-angiotensin system components are synthesized locally and which are taken up from plasma. Enzymes unrelated to the classical renin-angiotensin system may also contribute to tissue angiotensin synthesis. However, based on the available data, the prevailing opinion that kidney-derived renin is in all cases the only physiologically relevant renin in tissues must be revised. Also there is evidence indicating a role for tissue angiotensin systems in the pathogenesis of cardiovascular disease and in cardiovascular structural remodeling. The angiotensin-regulated synthesis of aldosterone in cardiac tissue has been described, suggesting the possibility that a renin-angiotensin-aldosterone system exists in the heart. In addition, intracellular (intracrine) sites of angiotensin action have been reported. Some of these findings have implications for therapeutics and, in particular, for the use of angiotensin converting-enzyme inhibitors and angiotensin receptor blockers. Finally, tissue angiotensin systems outside the cardiovascular system also appear to be physiologically relevant.

Vitamin E: protective role of a Janus molecule

Since the discovery of vitamin E in 1922, its deficiency has been associated with various disorders, particularly atherosclerosis, ischemic heart disease, and the development of different types of cancer. A neurological syndrome associated with vitamin E deficiency resembling Friedreich ataxia has also been described. Whereas epidemiological studies have indicated the role of vitamin E in preventing the progression of atherosclerosis and cancer, intervention trials have produced contradictory results, indicating strong protection in some cases and no significant effect in others. Although it is commonly believed that phenolic compounds like vitamin E exert only a protective role against free radical damage, antioxidant molecules can exert other biological functions. For instance, the antioxidant activity of 17-beta-estradiol is not related to its role in determining secondary sexual characters, and the antioxidant capacity of all-trans-retinal is distinguished from its role in rhodopsin and vision. Thus, it is not unusual that alpha-tocopherol (the most active form of vitamin E) has properties independent of its antioxidant/radical scavenging ability. The Roman god Janus, shown in ancient coins as having two faces in one body, inspired the designation of 'Janus molecules' for these substances. The new biochemical face of vitamin E was first described in 1991, with an inhibitory effect on cell proliferation and protein kinase C activity. After a decade, this nonantioxidant role of vitamin E is well established, as confirmed by authoritative studies of signal transduction and gene regulation. More recently, a tocopherol binding protein with possible receptor function has been discovered. Despite such important developments in understanding the molecular mechanism and the targets of vitamin E, its new Janus face is not fully elucidated. Greater knowledge of the molecular events related to vitamin E will help in selecting the parameters for clinical intervention studies such as population type, dose response effects, and possible synergism with other compounds.

Inflammatory pathways in atherosclerosis and acute coronary syndromes

Evidence from a broad range of studies demonstrates that atherosclerosis is a chronic disease that, from its origins to its ultimate complications, involves inflammatory cells (T cells, monocytes, macrophages), inflammatory proteins (cytokines, chemokines), and inflammatory responses from vascular cells (endothelial cell expression of adhesion molecules). Investigators have identified a variety of proteins whose levels might predict cardiovascular risk. Of these candidates, C-reactive protein, tumor necrosis factor-alpha, and interleukin-6 have been most widely studied. There is also the prospect of inflammation as a therapeutic target, with investigators currently debating to what extent the decrease in cardiovascular risk seen with statins, angiotensin-converting enzyme inhibitors, and peroxisome proliferator-activated receptor ligands derives from changes in inflammatory parameters. These advances in basic and clinical science have placed us on a threshold of a new era in cardiovascular medicine.

Why vascular biology matters

Cardiovascular disease has been the leading cause of death for men and women in this country since 1921 and is currently the leading cause of death in the world. Adding to the sense of urgency about disease prevention is the recent finding that the initial lesions of atherosclerotic vascular disease may begin within the first year of life-or even earlier, during fetal growth. However, the pathobiology of atherosclerosis (and in particular, the key role of low-density lipoprotein cholesterol) is now well understood. Activation of 3 major oxidative systems as well as the renin-angiotensin system-all located in the vascular wall-is an early step. In fact, the effects of statins and angiotensin-converting enzyme inhibitors on the vascular wall (improved endothelial function, inhibition of platelet aggregation, and plaque stabilization) are an important mechanism of benefit, independent of their systemic effects. Several very positive trials with these agents have been completed. However, if this information is not incorporated into clinical practice in a timely manner, cardiovascular disease will continue to present a major cause of morbidity and mortality worldwide.

Drugs for cardiovascular risk reduction in the diabetic patient

The diabetic patient is at increased risk for cardiac events. Lowering hemoglobin A1c levels even within the normal range is associated with less cardiac risk. Oral agents for diabetes that reduce insulin resistance and its associated cardiac risk factors in addition to lowering glucose should be used. Energetic reduction of blood pressure with an emphasis on the use of angiotensin-converting enzyme inhibitors and beta blockers will further reduce cardiac risk. Reduction of low-density lipoprotein and triglyceride levels and elevation of high-density lipoprotein levels through judicious use of statins and other anti-lipid agents is essential and will lower the rate of cardiac events in the diabetic patients even more than in the nondiabetic patients. In addition, aspirin and folic acid supplementation should be utilized. Use of a multiple risk factor management strategy with these drugs will lower morbidity and mortality, improve quality of life, and save cost for the diabetic patient.

Therapeutic potential of anti-oxidants and diabetic retinopathy

Retinopathy, a severely disabling complication of diabetes mellitus, is today the leading cause of acquired blindness among young adults in developed countries. Good glycaemic control can attenuate the development of diabetic retinopathy but such metabolic control is often difficult to achieve and maintain and additional therapies need to be identified by which retinopathy can be prevented or arrested. Hyperglycaemia plays a critical role in the development and progression of retinopathy, but the mechanism by which hyperglycaemia results in the development of retinopathy is not clear. Oxidative stress is increased in the retina in diabetes. The possible sources of increased oxidative stress might include increased generation of free radicals or impaired anti-oxidant defence system. Dietary supplementation with anti-oxidants in animal models of diabetic retinopathy inhibits retinal metabolic abnormalities and retinal histopathology, suggesting that oxidative stress is associated with the development of retinopathy. The mechanism by which anti-oxidants inhibit retinopathy in diabetes warrants further investigation, but animal studies show that increasing the diversity of anti-oxidants provides significantly more protection than using any single anti-oxidant. Thus, supplementation with anti-oxidants represents an achievable adjunct therapy to help preserve vision in diabetic patients.

Targeting kinin receptors for the treatment of tissue ischaemia

Kinins, the biological end-products of the kallikrein-kininogen system, influence many aspects of the cellular function. Interest in this peptidergic system has been renewed recently by the discovery that kinins exert cardiovascular protective effects and promote post-ischaemic recovery by stimulating vascular growth. Pharmacological and genetic studies indicate that induction of kallikrein and kinin receptors by ischaemia is functionally relevant in the natural host response that permits perfusion recovery and tissue healing. Furthermore, potentiation of the generation of kinins by continuous supply of tissue kallikrein promotes reparative angiogenesis through stimulation of the release of nitric oxide and prostaglandins. Strategies that activate kinin receptors might be applicable to the treatment of occlusive vascular disease, whereas kinin receptor antagonists could represent therapeutic reagents against pathological angiogenesis in cancer and chronic inflammatory conditions.

Oxidants and antioxidants in atherosclerosis

The oxidative theory suggests that LDL oxidation contributes to atherogenesis, implying that attenuation of this process by antioxidants should decrease atherosclerosis. However, a causative link between LDL oxidation and atherogenesis is not firmly established. It requires the identification of the oxidants that are responsible for the initiation of LDL oxidation, and an understanding of the modified moieties that are responsible for the proatherogenic activities of oxidized LDL. The present review summarizes recent data on potential biological oxidants for LDL in the vessel wall, and discusses the antiatherogenic role(s) of selected antioxidants.

The antiatherogenic effects of antihypertensive treatment: trials completed and ongoing

B-mode ultrasonography provides a reliable means of measuring carotid artery wall intima-media thickness. Because carotid intima-media thickness is correlated with blood pressure and is predictive of future cardiovascular events, it can be used as an endpoint in intervention trials. Inclusion of carotid bifurcation in the measurements appears necessary for inferences about atherosclerosis. Several intervention studies using antihypertensive agents have been completed and others are ongoing. Placebo-controlled studies have shown beneficial effects of calcium antagonists and beta-blockers, and contradictory responses with angiotensin converting enzyme inhibitors, but none of these studies have been performed in hypertensive patients. In hypertensive patients, three studies comparing different antihypertensive agents have been completed, with some evidence favoring calcium antagonists over diuretics. Two studies are ongoing, and should be completed and published soon.

Effects of ramipril on coronary events in high-risk persons: results of the Heart Outcomes Prevention Evaluation Study

BACKGROUND

In trials of patients with left ventricular dysfunction or heart failure, ACE inhibitor use was unexpectedly associated with reduced myocardial infarction (MI). Using the Heart Outcomes Prevention Evaluation (HOPE) trial data, we tested prospectively whether ramipril, an ACE inhibitor, could reduce coronary events and revascularization procedures among patients with normal left ventricular function.

METHODS AND RESULTS

In the HOPE trial, 9297 high-risk men and women, >/=55 years of age with previous cardiovascular disease or diabetes plus 1 risk factor, were randomly assigned to ramipril (up to 10 mg/d), vitamin E (400 IU/d), their combination, or matching placebos. During the mean follow-up of 4.5 years, there were 482 (10.4%) patients with clinical MI and unexpected cardiovascular death in the ramipril group compared with 604 (12.9%) in the placebo group [relative risk reduction (RRR), 21% (95% CI) (11,30); P<0.0003]. Ramipril was associated with a trend toward less fatal MI and unexpected death [4.0% versus 4.7%; RRR, 16% (-3, 31)] and with a significant reduction in nonfatal MI [5.6% versus 7.2%; RRR, 23% (9,34)]. Risk reductions in MI were documented in participants taking or not taking beta-blockers, lipid lowering, and/or antiplatelet agents. Although ramipril had no impact on hospitalizations for unstable angina [11.9% versus 12.2%; RRR, 3% (-9,14)], it reduced the risk of worsening and new angina [27.2% versus 30.0%; RRR, 12% (5,18); P<0.0014] and coronary revascularizations [12.5% versus 14.8%; RRR, 18%; (8,26) P<0.0005].

CONCLUSIONS

In this high-risk cohort, ramipril reduced the risk of MI, worsening and new angina, and the occurrence of coronary revascularizations.

Are all angiotensin-converting enzyme inhibitors interchangeable?

In the treatment of most medical conditions, there are many choices. A critical question for practicing clinicians is: "Are all drugs within a class interchangeable?" In the past decade, the market has seen a proliferation of drugs within popular drug classes. The original drugs within a class typically have better scientific documentation than the newer ones, which are often referred to as "me-too" drugs. Due to a lesser financial investment, the latter may be available at a lower cost. Good reasons exist for grouping drugs, however, there is no accepted definition of the term "class effect." Although members of a drug class share main actions, they may have clinically important differences in terms of efficacy and safety. There are many such examples in the literature. This article reviews the class effect concept as it applies to the angiotensin-converting enzyme (ACE) inhibitors. Only half of the 10 ACE inhibitors available in the U.S. have been shown to improve survival and reduce morbidity in patients with heart failure or myocardial infarction. It is unknown whether the other five have the same safety and efficacy profiles or what their optimal doses are. Thus, we do not know whether all ACE inhibitors are fully interchangeable. The practice of medicine ought to be based on solid scientific evidence, not on assumptions or extrapolations. For our patients, such practice is a legitimate expectation. Therefore, it seems prudent to recommend that patients requiring ACE inhibitor therapy be prescribed one that has been proven effective and safe.

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.

Dose response of ACE inhibitors: implications of the SECURE trial

The choice of the appropriate dosage of ACE inhibitor in clinical practice is an important one. The available evidence suggests that in chronic heart failure as well as in chronic coronary artery disease, high doses of angiotensin-converting enzyme (ACE) inhibitor are more effective than low ones. The current recommended clinical approach is to target ACE inhibitor dosing regimens to be similar to those used in the clinical trials, which demonstrated mortality and morbidity benefits. When titrated appropriately, ACE inhibitors are generally well tolerated and target doses can be achieved and maintained in the majority of patients with atherosclerotic vascular disease, with or without heart failure.