Angiotensin receptor blockers: evidence for preserving target organs

Hypertension is a major problem throughout the developed world. Although current antihypertensive treatment regimens reduce morbidity and mortality, patients are often noncompliant, and medications may not completely normalize blood pressure. As a result, current therapy frequently does not prevent or reverse the cardiovascular remodeling that often occurs when blood pressure is chronically elevated. Blockade of the renin-angiotensin system (RAS) is effective in controlling hypertension and treating congestive heart failure. Both angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) inhibit the activity of the RAS, but these two classes of antihypertensive medications have different mechanisms of action and different pharmacologic profiles. Angiotensin-converting enzyme inhibitors block a single pathway in the production of angiotensin II (Ang II). In addition, angiotensin I is not the only substrate for ACE. The ACE inhibitors also block the degradation of bradykinin that may have potential benefits in cardiovascular disease. Bradykinin is, however, the presumed cause of cough associated with ACE inhibitor therapy. Data from clinical trials on ACE inhibitors serve to support the involvement of the RAS in the development of cardiovascular disease. Angiotensin receptor blockers act distally in the RAS to block the Ang II type 1 (AT1) receptor selectively. Thus, ARBs are more specific agents and avoid many side effects. Experimental and clinical trials have documented the efficacy of ARBs in preserving target-organ function and reversing cardiovascular remodeling. In some instances, maximal benefit may be obtained with Ang II blockade using both ARBs and ACE inhibitors. This review describes clinical trials that document the efficacy of ARBs in protecting the myocardium, blood vessels, and renal vasculature.     

Use of angiotensin-converting enzyme inhibitor/angiotensin II receptor blocker therapy to reduce cardiovascular events in high-risk patients: Part 1

Cardiovascular disease is understood as a continuum; risk factors induce a pathophysiologic cascade that culminates in end-organ failure. The renin-angiotensin system (RAS) influences multiple aspects of the pathophysiology via hemodynamic and nonhemodynamic effects. Many long-term clinical trials provide overwhelming evidence of benefits of angiotensin-converting enzyme (ACE) inhibitors and angiotensin II receptor blockers (ARBs) across the cardiovascular continuum, including benefits regarding hypertension, myocardial infarction, stroke, renal disease, and heart failure. Trials also indicate additive or synergistic effects of combination therapy in renal disease and heart failure, a possibility supported by the basic biochemistry of the agents. Discussion of these trials is included in part 1 of this 2-part review. Part 2 of the review will discuss the extensive interaction of the RAS with the cellular and molecular pathophysiology of cardiovascular disease and the cross-continuum effects of ARBs and ACE inhibitors, which raise the possibility that RAS inhibition can offer protection in high-risk patients who do not have symptoms. The benefits of combined ACE inhibitor/ARB therapy in high-risk patients await confirmation; ongoing clinical research in this area will be discussed.     

Treating patients for cardiovascular protection: combination therapy to achieve complete renin-angiotensin system blockade

Inhibition of the renin-angiotensin system (RAS) with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) is a proven antihypertensive strategy. Understanding of the pathophysiologic effects of chronic RAS activation and clinical data indicate that RAS inhibition may exert beneficial effects in addition to blood pressure reduction. Studies indicate that monotherapy with ACE inhibitors and ARBs slows progression of diabetic and non-diabetic renal disease. Vascular protective effects of RAS inhibition have also been demonstrated in patients at high risk for cardiovascular events in the absence of significant blood pressure elevation or left ventricular dysfunction. Combining the complementary effects of ACE inhibitors and ARBs to achieve more complete RAS blockade is a promising approach to further reducing cardiovascular risk. This review will present the rationale for dual RAS inhibition, clinical data relating to its efficacy, and ongoing studies designed to evaluate its utility in patients at high risk for cardiovascular events.     

Clinical update: the role of angiotensin II receptor blockers in patients with left ventricular dysfunction (Part II of II)

Almost 5 million individuals in the United States have chronic heart failure (HF), which is increasing in prevalence. Angiotensin-converting enzyme (ACE) inhibitors are standard therapies for HF, although more than 10% of patients with HF are unable to tolerate these agents. Furthermore, ACE inhibitors may not provide complete blockade of the renin-angiotensin system (RAS) in the long term. Because angiotensin II receptor blockers (ARBs) may block the RAS more completely than ACE inhibitors and are better tolerated, several large-scale ARB trials have been performed exploring their potential role in treating patients with symptomatic HF and left ventricular systolic dysfunction. The Losartan Heart Failure Survival Study (ELITE II) demonstrated no significant differences in morbidity and mortality between the ARB losartan and the ACE inhibitor captopril among elderly patients with HF. The Valsartan Heart Failure Trial (Val-HeFT) demonstrated reductions in hospitalizations for HF with the ARB valsartan when added to standard HF therapy, with no effect on mortality. Both trials suggested a potential negative interaction between ARB and beta-blocker therapy. The Candesartan in Heart failure-Assessment of Reduction in Mortality and morbidity (CHARM) program demonstrated significant reductions in morbidity and mortality with the ARB candesartan in patients with HF due to systolic dysfunction, with or without ACE inhibitors and with or without beta blockers. Thus, the addition of ARBs to the treatment regimen of patients with symptomatic HF should be strongly considered.     

Angiotensin II receptor blockers in the treatment of heart failure

Heart failure treatment centers on antagonism of the renin-angiotensin-aldosterone system and adrenergic nervous system. Angiotensin-converting enzyme (ACE) inhibitors have been shown to benefit patients with left ventricular systolic dysfunction irrespective of symptoms. Despite ACE inhibitor use, left ventricular dysfunction continues to progress in most patients. In addition, ACE inhibitors are substantially underused in patients who would benefit, in large part due to physician concern over potential adverse effects. Angiotensin receptor blockers (ARBs) have been proposed as either potential substitutes for ACE inhibitors or as additive therapy for heart failure patients. The authors will review the importance of the renin-angiotensin-aldosterone system in the progression of heart failure, as well as the mechanisms by which ACE inhibitors and ARBs counteract this effect. The clinical evidence to date supporting the use of ARBs in heart failure also will be reviewed. Based on current trials, ARBs are suitable substitutes for ACE inhibitors in patients who have true ACE inhibitor intolerance, but ACE inhibitors should still be considered first-line therapy in the treatment of left ventricular systolic dysfunction and heart failure. ARBs are a reasonable additive therapy in patients on maximal ACE inhibitor therapy who remain symptomatic, especially in patients unable to tolerate beta blockade.     

Rationale for the use of combination angiotensin-converting enzyme inhibitor/angiotensin II receptor blocker therapy in heart failure

BACKGROUND: Heart failure (HF) is a major cause of morbidity and mortality in the United States. The renin-angiotensin system (RAS) plays a major role in its pathophysiology, and angiotensin-converting enzyme (ACE) inhibitors are the cornerstone of therapy. However, HF continues to progress despite this therapy, perhaps because of production of angiotensin II by alternative pathways, which lead to direct stimulation of the angiotensin II receptor. Angiotensin II receptor blocker (ARB) therapy alone or in combination with the ACE inhibitor is a promising approach to block the RAS and slow HF progression more completely. METHODS: The current medical literature on the pathophysiology of HF and the use of ACE inhibitors and ARBs was extensively reviewed. RESULTS: Evidence from basic science, experimental animals, and clinical trials provides data on the safety and efficacy of RAS inhibition with ACE inhibitors and ARBs as monotherapy and in combination. Data from the Evaluation of Losartan in the Elderly (ELITE) II trial indicate that ARBs alone do not appear to be more effective than ACE inhibitors in HF, but studies evaluating their use in combination are currently ongoing. CONCLUSIONS: The addition of an ARB offers more complete angiotensin II receptor blockade of the RAS than can be obtained by ACE inhibitors alone. Combination therapy preserves the benefits of bradykinin potentiation offered by ACE inhibitors while providing potential antitrophic influences of AT(2) receptor stimulation and may play an increased role in the treatment of chronic HF in the future.     

How high should an ACE inhibitor or angiotensin receptor blocker be dosed in patients with diabetic nephropathy?

Angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs), two drug classes that effectively block the actions of the renin-angiotensin system (RAS), have unique capabilities as antihypertensive agents. Recent landmark clinical trials have demonstrated their important roles as primary therapy for the prevention of renal disease in diabetes. The optimal dosage of these RAS blockers required to slow the progression of renal disease or impair the development of cardiovascular risk is not known. However, data from many studies strongly support the use of the higher doses of ACE inhibitors or ARBs to reduce proteinuria. All studies of kidney disease progression demonstrate benefit on slowing only when blood pressure is reduced when using higher doses. In order to accrue the optimum benefit from ACE inhibitors and ARBs, the dose-response relationship for diabetic renal disease will have to be determined. The best strategy, ie, supramaximal doses of ACE inhibitors or ARBs or combining them, is still a matter of debate but may be resolved soon by results of ongoing studies.     

Angiotensin II receptor blockers in congestive heart failure

The benefits of angiotensin-converting enzyme (ACE) inhibitors for the treatment of congestive heart failure (CHF) are well-established. A newer class of medications, angiotensin II receptor blockers (ARBs), may be a suitable replacement for ACE inhibitors as a result of a more complete inhibition of angiotensin II and better tolerability among patients. To examine the current literature on the efficacy and safety of ARBs in the setting of CHF, a Medline search was conducted of the English language literature for the years 1987 to 2005. Clinical trials that reported data on cardiac outcomes were reviewed. The earlier trials were direct ARB to ACE inhibitor comparisons (ELITE I and ELITE II). These studies indicated that ARBs do not confer an improvement in cardiac outcomes over ACE inhibitors. RESOLVD, Val-HeFT, and the 3 separate trials of the CHARM program investigated the addition of an ARB to standard therapy. The RESOLVD trial showed no significant differences in clinical events among ACE inhibitor, ARB, and their combination. Although no mortality benefit was evident in the Val-HeFT trial, a substantial reduction in CHF rehospitalizations was reported among patients who were not receiving ACE inhibitor therapy. The CHARM-Overall program demonstrated a significant benefit in cardiovascular death and hospital admissions for CHF with the addition of ARB to standard therapy, a benefit that was more pronounced in patients with depressed left ventricular ejection fraction. In the setting of CHF, rates of cardiac outcomes do not differ substantially between ARBs and ACE inhibitors. However, their combination may improve outcomes for patients with CHF.     

Is There a Place on the Shelf for Aliskiren?

Increased renin-angiotensin-aldosterone system (RAAS) activity contributes to target-organ damage and increases cardiovascular risk by elevating blood pressure (BP) and through direct effects on the heart, kidneys, brain, and vascular endothelium. Pharmacologic blockade of RAAS effectively reduces BP and limits or reverses various forms of target-organ damage, including cardiac heart failure, coronary artery disease, chronic kidney disease, and left ventricular hypertrophy. Direct renin inhibitors selectively inhibit human renin and have a therapeutic potential similar to angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers. Aliskiren is the only orally active direct renin inhibitor that has been approved for the treatment of hypertension and has been shown to have favorable effects on target-organ damage. It effectively reduces BP and has favorable effects on heart failure and proteinuria in diabetic patients. Additional outcome trials are needed to establish the role of this new class of antihypertensive medication in preventing cardiovascular outcomes.     

Renin inhibition: A new modality for hypertension management

Renin is the first and rate-limiting step cleaving angiotensinogen to angiotensin I, thus influencing angiotensin II (Ang II) formation. Inhibition of the renin-angiotensin system (RAS) with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) is effective in management of several cardiovascular diseases; however, control continues to be difficult and requires multiple drug therapy. Use of RAS inhibitors does not totally prevent Ang II formation, which could continue to contribute to development of end-organ damage. Over the past two decades, renin inhibition seemed to be an attractive approach for complete blockade of the RAS. Recently, aliskiren, a renin inhibitor, was approved as the first of a new class of antihypertension drugs. Clinical trials demonstrated significant blood pressure reduction in hypertensive patients with aliskiren used alone or combined with hydrochlorothiazide, ACE inhibitors, or ARBs. Studies are in progress to evaluate the potential role for renin inhibition in management of kidney and cardiac diseases.     

Rationale for the use of angiotensin II receptor blockers in patients with left ventricular dysfunction (part I of II)

Almost 5 million individuals in the United States are diagnosed with chronic heart failure (HF), and the prevalence is increasing. Angiotensin-converting enzyme (ACE) inhibitors and beta blockers, neurohormonal antagonists that block the renin-angiotensin system (RAS) and the sympathetic nervous system, respectively, have been shown in clinical trials to reduce morbidity and mortality in patients with HF, and these therapies are now integral components of standard HF treatment. Yet, morbidity and mortality rates in HF remain unacceptably high, and the limitations of current standard therapies are becoming increasingly apparent. About 10% of patients with HF are unable to tolerate ACE inhibitors, often because of cough. In addition, ACE inhibition may not completely block the RAS because angiotensin II, the main end product of the RAS, can be generated via non-ACE enzymatic pathways. Angiotensin II receptor blockers (ARBs) may exert more complete RAS blockade than ACE inhibitors by interfering with the binding of angiotensin II at the receptor level, regardless of the enzymatic pathway of production. They are also better tolerated than ACE inhibitors and have been shown to improve symptoms and function in clinical trials in patients with HF. These factors provide a strong rationale for the study of the clinical effects of ARBs in patients with HF.     

Target‐organ protection with combination renin‐angiotensin‐system blockade

Pharmacologic blockade of the renin‐angiotensin‐aldosterone system (RAS) has antihypertensive, anti‐atherogenic, antioxidant, and anti‐inflammatory effects. Treatment with angiotensin‐converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) has been demonstrated to prevent atrial fibrillation and new‐onset diabetes, and provide cardiac, cerebral, and renal protection. Combination therapy with ACEIs and ARBs, compared with monotherapy, provides enhanced reno‐ and cardioprotection, although available data indicate that combination RAS blockade may be beneficial only in select patient groups, such as those with diabetes mellitus, chronic kidney disease, or heart failure (HF). In certain high‐risk patients, the use of ARBs provides comparable efficacy to that observed with ACEIs. The efficacy of these agents may stem from pleiotropic effects beyond blood pressure (BP) reduction. Several studies demonstrate achievement of clinical endpoints without significant effects on BP. Copyright © 2009 Wiley Periodicals, Inc.     

Angiotensin-converting enzyme inhibitors or angiotensin receptor blockers for prevention of type 2 diabetes: a meta-analysis of randomized clinical trials

OBJECTIVES: We sought to investigate the role of angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) in preventing the new onset of type 2 diabetes mellitus. BACKGROUND: Diabetes is a public health problem of epidemic proportions and its prevalence is on the rise. The typical American born today has a one in three chance of developing type 2 diabetes. This diagnosis is associated with an adverse cardiovascular prognosis and is considered the risk equivalent of established coronary disease. Even in high-risk individuals, diabetes is a preventable disease. Several studies have shown that ACE inhibitors and ARBs decrease the incidence of new-onset type 2 diabetes. However, the exact role of these agents in diabetes prevention has not yet been fully elucidated. METHODS: We conducted a meta-analysis of 12 randomized controlled clinical trials of ACE inhibitors or ARBs, identified through a MEDLINE search and a review of reports from scientific meetings, to study the efficacy of these medications in diabetes prevention. RESULTS: This showed that ACE inhibitors and ARBs were associated with reductions in the incidence of newly diagnosed diabetes by 27% and 23%, respectively, and by 25% in the pooled analysis. CONCLUSIONS: The use of an ACE inhibitor or ARB should be considered in patients with pre-diabetic conditions such as metabolic syndrome, hypertension, impaired fasting glucose, family history of diabetes, obesity, congestive heart failure, or coronary heart disease.     

Angiotensin receptor blockers: therapeutic targets and cardiovascular protection

In the prevention and treatment of cardiovascular disease, pharmacological treatment strategies should have several aims: (i) in individuals without overt cardiovascular disease, but with risk factors such as hypertension and/or diabetes, pharmacotherapy should prevent or delay disease development; (ii) in patients who have already progressed to cardiovascular disease, pharmacotherapy should help either to prevent or regress target organ damage (TOD); and (iii) in patients with TOD, pharmacotherapy should prevent events. Any medication intended for long-term therapy also should be well tolerated. Inhibiting the renin-angiotensin system has proven a successful therapeutic strategy in cardiovascular and renal medicine. Angiotensin-converting enzyme (ACE) inhibitors have demonstrated important advantages over conventional agents such as beta-blockers and thiazide diuretics, and have become a relevant part of treatment for heart failure post-myocardial infarction, left ventricular dysfunction and renal disease. Tolerability concerns may prevent their use in some patients, however. Angiotensin AT1 receptor blockers (ARBs) provide a different form of blockade of the renin-angiotensin system and a growing body of evidence suggests that this alternative approach may confer additional cardiovascular protection for some patient subgroups. In addition, ARBs generally are better tolerated than ACE inhibitors, enhancing patient compliance and persistence with long-term therapy. Furthermore, evidence in favour of combining an ACE inhibitor and an ARB in certain circumstances is continuously growing.     

Renin Inhibitors and Cardiovascular and Renal Protection: An Endless Quest?

Renin-angiotensin system (RAS) blockade with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) has become a major therapeutic approach in medicine since the end of the 1970’s. Although these molecules were the first RAS blockers to be developed, it would have been physiologically and pharmacologically more pertinent to selectively inhibit renin itself. Indeed, the reaction between renin and its unique substrate, angiotensinogen, is the highly regulated and rate-limiting step of the RAS. The development of direct renin inhibitors (DRI) has been a slow and complex process and the synthesis of the first orally active DRI, aliskiren, was only achieved in the 2000’s. Its pharmacological profile in patients with hypertension, diabetic nephropathy or heart failure, in addition to experimental evidence, suggests that aliskiren may be of value for the management of cardiovascular and renal diseases. However, the long-term, randomized, placebo-controlled, morbidity/mortality trial, ALTITUDE, which included 8,600 patients with type 2 diabetes, proteinuria and a high cardiovascular risk already treated with ACE inhibitors or ARBs was terminated in December 2011 because of futility and an increased incidence of serious adverse events in the aliskiren 300 mg arm. Other long-term studies are still ongoing to demonstrate the safety and efficacy of aliskiren to reduce cardiovascular morbidity and mortality in patients with heart failure and in elderly individuals (≥65 years) with systolic blood pressure of 130 to 159 mmHg, no overt cardiovascular disease, and a high cardiovascular risk profile. In the meantime, according to the European Medicines Agency recommendations, aliskiren should not be prescribed to diabetic patients in combination with ACE inhibitors or ARBs.     

The role of angiotensin receptor blockers in the management of chronic heart failure

Clinical and basic science research has repeatedly confirmed the importance of the renin-angiotensin-aldosterone system in the pathophysiology of chronic heart failure. Accordingly, blockade of this system by angiotensin-converting enzyme (ACE) inhibitors has assumed a central role in the treatment of heart failure. Recently, angiotensin II receptor blockers (ARBs) have gained prominence as a possible substitute for ACE inhibitors in therapy for heart failure. However, clinical data compiled on this use of ARBs have shown them to be useful only as alternative therapy in ACE inhibitor-intolerant patients. Continuing large-scale clinical investigations may lead to an expansion of their role in therapy for various cardiovascular diseases.     

Renin-angiotensin-system blockade in the prevention of diabetes

Type 2 diabetes often occurs in association with hypertension and cardiovascular disease, and markedly increases cardiovascular risk. Strategies to reduce the incidence of diabetes in patients with cardiovascular disease or at high risk for such disease are therefore important. Certain classes of antihypertensive agents, namely the thiazide diuretics and beta-blockers, have an adverse impact on the metabolic profile and increase the risk for new-onset diabetes in hypertensive subjects. In contrast, angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs), which are blockers of the renin-angiotensin system (RAS), have been shown to increase insulin sensitivity. They may also reduce the risk of diabetes in patients with hypertension or cardiovascular disorders. Some of the evidence in favour of ACE inhibitors and ARBs has come from studies with active comparators that have potential adverse metabolic effects. However, the Candesartan in Heart failure-Assessment of Reduction in Mortality and morbidity (CHARM) programme demonstrated that the ARB candesartan reduced the incidence of diabetes in heart failure patients in comparison to placebo. The mechanisms responsible for the beneficial effects of RAS blockade remain to be established. Nevertheless, a treatment that can control hypertension and reduce the risk of onset of type 2 diabetes at the same time is certainly desirable.     

Modulating atherosclerosis through inhibition or blockade of angiotensin

Angiotensin-convertng enzyme (ACE) inhibitors are well recognized for their benefits in treating hypertension and congestive heart failure and preventing postmyocardial infarction heart failure or left ventricular (LV) dysfunction. Recently, blockade of the angiotensin II type 1 (AT1) receptor was shown to reduce cardiovascular events in hypertensive subjects with LV hypertrophy. Several lines of evidence are now converging to show that ACE inhibitors may affect the atherosclerotic process itself. Emerging clinical data indicate that angiotensin-receptor blockers (ARBs) may possibly modulate atherosclerosis as well. The antiatherogenic properties of ACE inhibitors and ARBs may derive from inhibition or blockade of angiotensin II, now recognized as an agent that increases oxidative stress.Angiotensin-converting enzyme inhibition and angiotensin-receptor blockade also increase endothelial nitric oxide formation, which improves endothelial function. In contrast to the effects of ARBs, the vascular effects of ACE inhibitors may, in part, be mediated by an increase in bradykinin. This article reviews some of the biologic mechanisms whereby ACE inhibitors and ARBs may modulate atherosclerosis.