The renin angiotensin system and cardiovascular disease: hope or hype?

The Role of Oxidative Stress in Cardiovascular Aging and Cardiovascular Diseases

Aging can be seen as process characterized by accumulation of oxidative stress induced damage. Oxidative stress derives from different endogenous and exogenous processes, all of which ultimately lead to progressive loss in tissue and organ structure and functions. The oxidative stress theory of aging expresses itself in age-related diseases. Aging is in fact a primary risk factor for many diseases and in particular for cardiovascular diseases and its derived morbidity and mortality. Here we highlight the role of oxidative stress in age-related cardiovascular aging and diseases. We take into consideration the molecular mechanisms, the structural and functional alterations, and the diseases accompanied to the cardiovascular aging process.

Treating hypertension in the patient with overt diabetic nephropathy

Arterial blood pressure is a major determinant of renal and cardiovascular outcomes in diabetic nephropathy. There is a proportional relationship between the systolic blood pressure and renal and mortality outcomes. Decreasing the diastolic pressure does not significantly decrease these outcomes. Irrespective of the magnitude of pretreatment systolic hypertension in the patient with type 2 diabetic nephropathy, the systolic pressure achieved with antihypertensive therapy is the important determinant of renal and cardiovascular risk. Achieving a lower systolic pressure down to 120 mm Hg is associated with substantial risk reduction. Although the data are limited, systolic blood pressure less than 120 mm Hg may be associated with increased all-cause mortality in this patient population, increasing the possibility of a J-curve response. A marked decrease in diastolic pressure, which is a danger when undertaking aggressive therapy with the goal of decreasing the systolic pressure to 130 mm Hg, can be associated with an increased risk of cardiac events. The renoprotective and proteinuria-decreasing effects of angiotensin-converting enzyme inhibitors and angiotensin-receptor blockers recommend these agents as the standard of care in type 2 diabetic nephropathy. In addition to angiotensin-converting enzyme inhibitor and angiotensin-receptor blocker therapy, controlling the systolic blood pressure in this difficult to control patient population may require the use of 3 or more antihypertensive agents.

Renin: friend or foe?

Renin maintains blood pressure through vasoconstriction when there is inadequate salt to maintain volume. In populations where blood pressure is more often high than low, and vascular death more common than haemorrhage or dehydration, therapeutic reductions in renin secretion or response are valuable. Whether long-term benefits are due entirely to blood pressure reduction remains unproved. The pathway can be blocked at its rate-limiting step (beta blockade or direct renin inhibition), the synthesis of the active product, angiotensin II, or at the receptor for angiotensin. Because renin and sodium are the two main factors in blood pressure control, and renin levels vary inversely with sodium load, blood pressure control requires a combination of natriuresis and blocking the consequential increase in renin activity. Being a large and stable molecule, renin is among the easiest and cheapest of hormone measurements. Understanding the simple biochemistry and physiology of renin permits optimal use of the drugs acting to raise or suppress this hormone.

Recent hypertension trials: implications and controversies

The pharmacologic treatment of hypertension has been extensively studied by clinical trials. These studies have provided definitive evidence of a treatment benefit, and the weight and consistency of the clinical evidence has led to uniformity in many aspects of treatment recommendations worldwide. However, controversies remain-in particular, whether specific classes of drug therapy offer benefits for cardiovascular disease prevention beyond the expected benefits of blood pressure lowering per se. Updated large-scale epidemiologic studies and the meta-analysis of clinical trial data have better informed this debate and emphasized that the main driver of clinical benefit from blood pressure-lowering therapy is the magnitude of blood pressure reduction and perhaps the speed at which it is achieved. However, clinical trials are of short duration, and there are more marked drug-specific differences in intermediate cardiovascular structure, functional, and metabolic end points. The challenge is to interpret their significance with regard to longer term outcomes. Finally, although blood pressure lowering is undoubtedly beneficial, the concepts of single risk factor intervention and arbitrary blood pressure thresholds and treatment goals are being challenged by the recognition that the real target is cardiovascular disease risk. Undoubtedly, the most effective way to "go beyond blood pressure" is to add a statin.

Protection against stroke and dementia: an update on the latest clinical trial evidence

Recent meta-analyses have examined the relationship between lowering blood pressure (BP) and reducing the risk for stroke and dementia. Studies have shown that drug therapy that successfully reduces systolic BP by only 10 mm Hg results in significant protection against stroke. Controversy exists regarding the most effective regimen, with supporters for the standards of diuretics and beta-blockers, or angiotensin-converting enzyme inhibitors and calcium-channel blockers, pitted against the increasing evidence of the effectiveness of angiotensin-receptor blockers or statins. Additionally, the most effective strategy for delivery of BP-reducing therapy is being examined, with some studies supporting use of standards for primary prevention of stroke and reserving the newer drugs for secondary prevention. Ultimately, however, all agree that for patients with the highest risk for cardiovascular and cerebrovascular complications, the strategy of intervention is immaterial, and drug therapy, including low-dose aspirin, is vital.

Office compared with ambulatory blood pressure in assessing response to antihypertensive treatment: a meta-analysis

OBJECTIVE

To undertake a systematic review of the studies on the effect of antihypertensive treatment on ambulatory (ABP) and office blood pressure in order to obtain a differential assessment of the magnitude of the reduction in (1) office blood pressure compared with 24-h average ABP values, and (2) daytime compared with night-time average blood pressure values.

DATA SOURCES

Medline search, Cochrane Library.

REVIEW METHODS

This review is based on a meta-analysis (carried out according to the Quality of Reports of Meta-analyses of Randomized Controlled Trials Group statement, whenever applicable) of papers on the effect of antihypertensive drugs on blood pressure. Papers were selected if they provided information on drug-induced changes in one or both of: (1) both office blood pressure and 24-h ABP, and/or (2) both daytime and night-time average blood pressure. Additional inclusion criteria were administration of antihypertensive drugs for at least 1 week and good quality ABP, according to current guidelines. Comparison between the effect of treatment on blood pressure values was made by meta-regression of the data provided by the individual studies (weighted by their size) and by calculating differences between weighted average values obtained by pooling the results of individual papers.

RESULTS

We identified 984 papers on this issue by Medline search, with no additional information from the Cochrane Library. The inclusion criteria were satisfied by only 44 papers, which were included in the final analysis. The results showed that treatment-induced reduction in blood pressure is both smaller for the 24-h average than for the office systolic and diastolic blood pressure and smaller for night-time than for daytime average diastolic blood pressure, the average ratio ranging from 0.67 to 0.75. A different ratio characterized the treatment-induced changes in office blood pressure and ABP in the Heart Outcomes Prevention Evaluation (HOPE) ABP substudy.

CONCLUSIONS

The effect of antihypertensive treatment is greater on office blood pressure than on ABP, and is unevenly distributed between day and night. This suggests caution when interpreting trials on cardiovascular protection by antihypertensive treatment that are based only on office blood pressure readings, and advocates a more systematic adoption of ABP monitoring in these trials. The conflicting data provided by the main HOPE study and by the HOPE-ABP monitoring substudy on the role of blood pressure reduction in explaining the reduced event rates associated with treatment by angiotensin-converting enzyme inhibitors are a clear example of the importance of performing ABP monitoring in trials on cardiovascular protection.

From CONSENSUS to CHARM—how do ACEI and ARB produce clinical benefits in CHF?

Two decades of research from CONSENSUS to CHARM using modulators of the renin-angiotensin-aldosterone system (RAAS) in chronic heart failure (CHF) patients have shown convincing clinical benefits, but the majority of clinicians prescribing these drugs are still unclear about what mechanisms are responsible for the observed benefits. Of the candidate mechanisms hitherto proposed, there emerges a theme that best fits the spectrum of known factors from pathophysiology of heart failure to how the drugs enhance longevity of patients. This concept can be summarised as follows: after the onset of heart failure, neurohormones are activated resulting in raised levels of angiotensin, aldosterone and catecholamines, which are all known cardiotoxic agents. Cumulatively over time, they are responsible for accelerated cardiomyocyte attrition, manifesting as a faster reduction of cardiac pumping reserve, leading to worsening heart failure, more neurohormonal activation, thus propagating a vicious cycle spiralling towards an earlier fatality. The vicious cycle can be interrupted by dampening the excessive neurohormonal activities, thereby minimising cardiomyocyte losses and preserving cardiac functional reserve for longer. This culminates in maintenance of a reasonable quality of life and enhanced longevity. Such a mechanistic understanding would enable clinicians to have a better perspective on how to apply data from various clinical trials involving these drugs into clinical practice, to optimise and tailor therapy to the individual patient so that each patient can gain maximal benefits.

New evidence on the importance of the renin-angiotensin system in the treatment of higher-risk patients with hypertension

We reviewed the drug treatment of hypertension in the light of recent trials. beta-Blockers and diuretics clearly reduce mortality, strokes, and coronary heart disease (CHD) in hypertension. Recent trials assessed whether newer agents that block the renin-angiotensin-aldosterone system, or calcium blockers, offer any additional advantage, or have benefits in high-risk individuals with conventionally 'normal' blood pressure. The recent ALLHAT study claimed no differences in CHD or mortality when chlorthalidone, amlodipine, and lisinopril were compared. However, the decrease in blood pressure was not the same with the three agents, and a substantial proportion of patients enrolled did not have clinical disease. In contrast, the LIFE study (comparing losartan and a beta-blocker) and the ANBP-2 study [comparing angiotensin-converting enzyme (ACE) inhibition and a diuretic] reduced blood pressure similarly, yet demonstrated benefits in favour of angiotensin II type 1 receptor blockers (ARBs) and ACE inhibitors. Other trials indicated similar advantages of ACE inhibitors or ARBs in patients with diabetic nephropathy. Among high-risk patients with initial blood pressure in the 'normal' range, ACE inhibitors significantly reduce clinical events (mortality, strokes, and myocardial infarction), despite modest decreases in blood pressure, suggesting that additional mechanisms are responsible. Recent results of the Prospective Studies Collaboration show lower risk, even in the normal blood pressure range; high-risk patients will benefit further from ACE inhibitors and ARBs (and beta-blockers after myocardial infarction). Data for other blood pressure decreasing agents are unavailable in such populations. We conclude that blood pressure decreasing per se is of clinical benefit, but drugs that block the renin-angiotensin system offer additional advantages. Drug choice is best determined by the patient's clinical condition.

Better blood pressure control: how to combine drugs

Prospective comparisons of different drug classes have shown that differences in blood pressure control, rather than differences between drug classes, have the over-riding influence on overall outcome. The same studies have also reinforced the need, in the majority of patients, to use combinations of drugs in order to achieve the target of <140/85 mmHg. By contrast, most patients in routine practice receive single agents and consequently fail to achieve target blood pressure. This failure reflects in part the emphasis in individual studies and subsequent guidelines on comparison of individual drugs. In this article we show how the consistency of both theory and a broad range of evidence permits a didactic approach to combination therapy. Our advice is based on the growing recognition that essential hypertension and its treatment fall into two main categories. Younger Caucasians usually have renin-dependent hypertension that responds well to angiotensin-converting-enzyme inhibition or angiotensin receptor blockade (A) or ss blockade (B). Most other patients have low-renin hypertension that responds better to calcium channel blockade (C) or diuretics (D). These latter drugs activate the renin system rendering patients responsive to the addition of renin suppressive therapy. Coincidence of the initials of these main drug classes with the first four letters of the alphabet permits an AB/CD rule, according to which recommended combinations are one drug from each of the "AB" and "CD" categories of drugs. However, the diabetogenic potential of the older "B" and "D" classes leads us to advise against combining "B" and "D" in older patients, and to recommend "A" + "C" + "D" as standard triple therapy for resistant hypertension.