Angiotensin II receptor antagonist improves age-related endothelial dysfunction

BACKGROUND : We previously demonstrated that the angiotensin converting enzyme (ACE) inhibitor, enalapril, prevents the age-related impairment of endothelium-dependent hyperpolarization and relaxation mediated by endothelium-derived hyperpolarizing factor (EDHF). OBJECTIVE : To test whether angiotensin II type 1 (AT1) receptor antagonists would also improve age-related endothelial dysfunction. METHODS : Normotensive Wistar-Kyoto (WKY) rats were treated for 3 months with either the AT1 receptor antagonist, candesartan cilexetil (3.5 mg/kg per day; candesartan group), or the ACE inhibitor, enalapril (20 mg/kg per day; enalapril group), from 9 to 12 months of age. Untreated 12-month-old WKY rats (old group) served as controls (n = 7-12). RESULTS : The two treatments decreased systolic blood pressure comparably. EDHF-mediated hyperpolarization in response to acetylcholine (ACh; 10(-5) mol/l) in the presence of norepinephrine in mesenteric arteries was improved in both the candesartan and enalapril groups to a similar extent compared with the old group (candesartan group, -24 +/- 3 mV; enalapril group, -21 +/- 2 mV; old group, -13 +/- 2 mV). EDHF-mediated relaxation was similarly improved in the candesartan and enalapril groups (maximum relaxation: candesartan group, 70 +/- 7%; enalapril group, 63 +/- 8%; old group, 33 +/- 9%). Hyperpolarization and relaxation responses to levcromakalim, an ATP-sensitive K+-channel opener, were similar in all groups. CONCLUSIONS : These findings suggest that the AT1 receptor antagonist is as effective as the ACE inhibitor in improving the age-related decline in EDHF-mediated hyperpolarization and relaxation in normotensive rats. Thus AT1 receptor antagonists might serve as novel tools with which to prevent endothelial dysfunction associated with aging.     

Angiotensin II receptor blockers in older patients

Older patients with hypertension are often inadequately treated due to misconceptions regarding reasonable goal blood pressures or concerns about treatment side effects. Adequately treating hypertension can yield impressive benefits in terms of improved morbidity and enhanced quality of life in persons of any age. Antagonists of the renin-angiotensin-aldosterone system are especially effective in older persons, many of whom have concomitant conditions such as diabetes mellitus, renal dysfunction, and other cardiovascular risk factors. Treatment with angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers has been shown to improve many of the complications of hypertension, including left ventricular hypertrophy and renal disease. Results of recent key studies such as Losartan Intervention For Endpoint Reduction in Hypertension (LIFE), Valsartan in Heart Failure Trial (Val-HeFT), Candesartan in Heart Failure Assessment of Reduction in Mortality and Morbidity (CHARM), and Valsartan in Acute Myocardial Infarction (VALIANT) add to the evidence that angiotensin II receptor blockers are well suited for the treatment of hypertension in older patients. These trials also indicate that they are appropriate therapy for heart failure patients and for patients who have experienced acute myocardial infarction, particularly those who are unable to tolerate an angiotensin-converting enzyme inhibitor.     

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.     

Cognitive dysfunction associated with metabolic syndrome

Metabolic syndrome which includes visceral obesity, elevated triglycerides, elevated fasting blood sugar, high blood pressure and a decrease in high-density lipoprotein cholesterol levels comprises the most common chronic physical illnesses in modern society. Components of the metabolic syndrome play a role in the pathogenesis of a plethora of medical illnesses. Evidence has emerged highlighting the detrimental effects of metabolic syndrome and its constituent features on the cognitive aspects of neurological function. The precise mechanisms underlying this association are not known but a combination of neuroanatomical changes and neuroendocrine consequences of somatic dysregulation may be relevant. As the population ages and the prevalence of metabolic syndrome increases, it is important that this clinically relevant association be recognized.     

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.     

Angiotensin II receptor pharmacology and AT1-receptor blockers

Angiotensin II (Ang II) has diverse physiological actions leading, for example, to increases in extracellular volume, peripheral vascular resistance and blood pressure, and has also been implicated in the regulation of cell growth and differentiation. Molecular cloning and pharmacological studies have defined two major classes of Ang II receptors, designated as AT1 and AT2. Most effects of Ang II are mediated by AT1 receptors. Much less is known about the physiological role of AT2 receptors. Recent evidence suggests involvement of AT2 receptors in development, cell differentiation, apoptosis and regeneration in various tissues. AT1 and AT2 receptors have been shown to exert counteracting effects on cellular growth and differentiation, vascular tone and the release of arginine vasopressin (AVP). In each condition the AT2 receptor appears to down-modulate actions mediated by the AT1 receptor, resulting in decreased cellular proliferation, decreased levels of serum AVP levels or decreased vasoconstrictor responses. In addition, in neuronal cell lines, the AT2 receptor reportedly exerts antiproliferative effects and promotes neurite outgrowth, an effect accompanied by significant changes in the gene expression pattern of growth- and differentiation-related genes.     

Angiotensin II receptor blockers and risk of cancer in patients with systemic hypertension

Recently, concerns have been raised that angiotensin II receptor blockers (ARBs) may be associated with an increased risk for cancer development. However, the relation between ARBs and cancer is still unclear. Therefore, a nationwide population-based study was conducted to investigate the possible influence of ARBs on the occurrence of new cancers in patients with hypertension by using the Taiwan National Health Insurance database. A total of 109,002 patients with newly diagnosed hypertension were identified from a cohort database of 1 million individuals from January 1, 1998, to December 31, 2006. Among them, 40,124 (36.8%) had received ARBs for hypertension. The end point was the development of any type of cancer before the end of 2007. During an average of 5.7 ± 2.6 years of follow-up, a total of 9,067 cases of new cancer occurrence were observed. The log-rank test showed that the occurrence rate of newly diagnosed cancers in the subjects receiving ARBs was significantly lower than those receiving treatment without ARBs (ARBs vs controls 3,082 vs 5,985, p <0.001). After adjusting for age, gender, co-morbidities, and medications for hypertension control, ARB use was found to be independently associated with a decreased risk for cancer occurrence (hazard ratio 0.66, 95% confidence interval 0.63 to 0.68, p <0.001). In conclusion, long-term use of ARBs is associated with a lower incidence of cancer occurrence, thereby suggesting that ARBs may prevent cancer development.     

Angiotensin II subtype 1 receptor blockers and renal function.

Blood pressure reduction is the most significant factor in delaying onset and progression of renal disease. Blockade of the renin-angiotensin system (RAS) using angiotensin-converting enzyme inhibitors (ACEIs) delays renal disease progression. More recently, agents that block the RAS by preventing angiotensin II from binding to its subtype 1 receptor (ARBs) have been developed in an effort to prevent deleterious consequences of pathologic levels of angiotensin II and to reduce the adverse effects of RAS blockade associated with ACEIs. Human studies with a variety of ARBs have clearly demonstrated the antihypertensive and antiproteinuric efficacy of these agents in patients with progressive renal diseases. Moreover, the effects of ARBs are similar or identical to those of ACEIs. Ongoing long-term clinical trials are designed to determine whether ARBs also preserve renal function similar to ACEIs. Specifically, the role of ARBs in patients with hypertension and type 2 diabetes is being evaluated in 3 large trials, including Appropriate Blood Pressure Control in Diabetes-Part 2 With Valsartan, the Losartan Renal Protection Study, and the Irbesartan Diabetic Nephropathy Trial. Definitive evidence of the long-term protective effects of ARBs in chronic progressive renal disease is expected from these important studies.     

Angiotensin receptor blockers in diabetic nephropathy

Where shall we place angiotensin receptor blockers in the scheme of the prevention of diabetic nephropathy? Only the results of a large, randomized double-blind trial with a comparable and appropriate alternative would prove therapeutic efficacy. The results of several trials with angiotensin-converting enzyme (ACE) inhibitors have proven them to be the standard of care for diabetics and their kidneys. As reviewed in this article, the results of three large such clinical trials have recently been completed with angiotensin receptor blockers in patients with type 2 diabetes mellitus. Initial results appear favorable. However, whether angiotensin blockers have more to offer than ACE inhibitors is still speculative. The renin-angiotensin system plays an important role in the pathogenesis of diabetic nephropathy. Since alternative pathways to ACE have been uncovered in the formation of angiotensin II, inhibition at the final end point would provide favored blockade. Because angiotensin receptor blockers do provide this specific blockade, they offer far more promise than ACE inhibitors.     

Mechanisms of endothelial dysfunction in the metabolic syndrome

Cardiovascular disease is a leading cause of death and disability in patients with diabetes or metabolic syndrome (MS). The available data suggest that many patients with diabetes or MS already have vascular abnormalities by the time they are diagnosed with their metabolic disorder. Endothelial dysfunction (ED), which is one of the initial steps in the process of vascular disease, is often present in patients with diabetes or MS. Although the precise mechanism(s by which diabetes or MS causes ED remains to be elucidated, several possibilities exist. Hyperglycemia, hyperinsulinemia, increased oxidative stress, and diabetic dyslipidemia can all contribute to ED individually or in concert with one another. ED in the setting of diabetes or MS can subsequently result in the activation of a variety of pathways that alter vascular function and participate in the process of vascular remodeling and atherosclerosis. Because insulin resistance is the predominant mechanism responsible for various perturbations seen in MS or diabetes, it is essential to develop a therapeutic strategy that can improve insulin sensitivity with the hope that such interventions would reduce the risk of future cardiovascular events.     

Angiotensin converting enzyme inhibitors and angiotensin II receptor blockers in atrial fibrillation

Atrial fibrillation is the most prevalent clinically relevant arrhythmia; a major cause of morbidity and hospitalization. Additionally, atrial fibrillation carries a significant risk of thrombo-embolic events, specifically cerebrovascular accident. Among the most prevalent risk factors for atrial fibrillation, hypertension not only has the strongest correlation but is also the most prevalent. The renin-angiotensin-aldosterone system represents a prime target for the treatment of hypertension through the use of angiotensin-converting enzymes inhibitors and angiotensin II receptor blockers. In addition to blood pressure control, these medications have been shown to reduce the occurrence of atrial fibrillation. They have been shown to have effects at the cellular level in preventing atrial fibrosis. Additionally, these medications may prevent the development ofatrial fibrillation, reduce the duration of atrial fibrillation, and facilitate electrical cardioversion in patients with the arrhythmia. Therefore, patients with, or at risk for atrial fibrillation may benefit from treatment with renin-angiotensin-aldosterone system antagonists; deriving benefits from these medications beyond simple blood pressure control.     

Angiotensin II receptor blockers and myocardial infarction: deeds and misdeeds

BACKGROUND: A recent editorial published by Verma and Strauss, entitled 'Angiotensin receptor blockers and myocardial infarction', examined, through a partial analysis of individual trials, the use of angiotensin receptor blockers (ARBs) in a variety of clinical settings. This editorial was reported widely in the lay press and media, and generated disappointment and concern among physicians in many countries, probably because of its provocative subtitle in the British Medical Journal: 'These drugs may increase myocardial infarction and patients may need to be told'. OBJECTIVE AND METHODS: In order to explore the influence of ARBs on myocardial infarction, we performed a more comprehensive and updated meta-analysis, taking into account all major international, randomized trials using ARBs compared with another active drug or conventional therapy (placebo), and reporting information on rates of myocardial infarction. RESULTS: We found no significant differences in fatal and non-fatal myocardial infarction between treatment with ARBs, placebo or active treatment, and the same result was obtained when considering only trials in which ARBs were compared with angiotensin-converting enzyme inhibitors (ACEIs), or when pooling all trials together. The pooled analysis of these trials shows that the relative risk of myocardial infarction lies substantially on the indifference line. CONCLUSION: Our analysis demonstrates that, at this time, there is no evidence of increased risk of myocardial infarction in patients treated with ARBs.