Angiotensin-Converting Enzyme Inhibitors and Stroke Risk: Benefit Beyond Blood Pressure Reduction?

Angiotensin-converting enzyme inhibitors stimulate cerebral arteriogenesis

AIM

Arteriogenesis constitutes the most efficient endogenous rescue mechanism in cases of cerebral ischaemia. The aim of this work was to investigate whether angiotensin-converting enzyme inhibitors (ACEi) stimulates, and angiotensin II receptor type 1 blockers (ARB) inhibits cerebral collateral growth by applying a three-vessel occlusion (3-VO) model in rat.

METHODS

Cerebral collateral growth was measured post 3-VO (1) by assessing blood flow using the cerebrovascular reserve capacity (CVRC) technique, and (2) by assessing vessel diameters in the posterior cerebral artery (PCA) via the evaluation of latex angiographies. A stimulatory effect on arteriogenesis was investigated for ACEi administration ± bradykinin receptor 1 (B1R) and 2 (B2R) blockers, and an inhibitory effect was analysed for ARB administration. Results were validated by immunohistochemical analysis and mechanistic data were collected by human umbilical vein endothelial cell (HUVEC) viability or scratch assay and monocyte (THP-1) migration assay.

RESULTS

An inhibitory effect of ARB on arteriogenesis could not be demonstrated. However, collateral growth measurements demonstrated a significantly increased CVRC and PCA diameters in the ACEi group. ACEi stimulates cell viability and migration, which could be partially reduced by additional administration of bradykinin receptor 1 inhibitor (B1Ri). ACEi inhibits the degradation of pro-arteriogenic bradykinin derivatives, but combined ACEi + B1Ri + B1Ri (BRB) treatment did not reverse the stimulatory effect. Yet, co-administration of ACEi + BRB enhances arteriogenesis and cell migration.

CONCLUSION

We demonstrate a potent stimulatory effect of ACEi on cerebral arteriogenesis in rats, presumable via B1R. However, results imply a pleiotropic and compensatory effect of ACEi on bradykinin receptor-stimulated arteriogenesis.

Intraclass differences among antihypertensive drugs

The four major classes of antihypertensive drugs—diuretics, β-blockers, calcium channel blockers, and renin-angiotensin system inhibitors (including angiotensin-converting enzyme inhibitors and angiotensin receptor blockers)—have significant qualitative and quantitative differences in the adverse effects they cause. Structural and chemical differences have been identified within these classes, especially among the calcium channel blockers and, to a lesser extent, among the thiazide/thiazide-like diuretics. However, it has been more difficult to demonstrate that these differences translate into differential effects with respect to either the surrogate endpoint of blood pressure reduction or, more importantly, hypertension-related cardiovascular complications. Based on a hierarchy-of-evidence approach, differences are apparent between hydrochlorothiazide and chlorthalidone based on evidence of moderate quality. Low-quality evidence suggests atenolol is less effective than other β-blockers. However, no significant intraclass differences have been established among the other classes of antihypertensive drugs.

Interaction between mineralocorticoid receptor and epidermal growth factor receptor signaling

The mineralocorticoid receptor (MR) is a steroid receptor that physiologically regulates water and electrolyte homeostasis but that can also induce pathophysiological effects in the renocardiovascular system. Classically, the MR acts as a transcription factor at glucocorticoid response elements but additional protein-protein interactions with other signaling cascades have been described. Of these, the crosstalk with EGFR signaling is especially interesting because various vasoactive substances like angiotensin II and endothelin-1 also mediate their pathophysiological effects via the EGFR. Recently, the MR has been shown to interact nongenomically (via transactivation) and genomically with the epidermal growth factor receptor (via altered expression). These interactions seem to contribute to physiological (e.g. salt homeostasis) as well as pathophysiological (e.g. vascular function) MR effects. The current knowledge on the mechanisms of interaction and on the possible cellular and systemic physiological as well as pathophysiological relevance is reviewed in this article.

Aliskiren: An orally active renin inhibitor

Renin inhibitors are antihypertensive drugs that block the first step in the renin-angiotensin system. Their mechanism of action differs from that of the angiotensin-converting enzyme inhibitors and angiotensin-receptor antagonists, but like these drugs, renin inhibitors interrupt the negative feedback effects of angiotensin II on renin secretion. The renin–angiotensin–aldosterone system (RAAS) has long been recognized to play a significant role in hypertension pathophysiology. Certain agents that modify the RAAS can control blood pressure and improve cardiovascular outcomes. Optimization of this compound by Novartis led to the development of aliskiren – the only direct renin inhibitor which is clinically used as an antihypertensive drug. Aliskiren is the first of a new class of antihypertensive agents. Aliskiren is a new renin inhibitor of a novel structural class that has recently been shown to be efficacious in hypertensive patients after once-daily oral dosing. In short-term studies, it was effective in lowering blood pressure either alone or in combination with valsartan and hydrochlorothiazide, and had a low incidence of serious adverse effects. It was approved by the Food and Drug Administration in 2007 for the use as a monotherapy or in combination with other antihypertensives. Greater reductions in blood pressure have been achieved when aliskiren was used in combination with hydrochlorothiazide or an angiotensin-receptor blocker. The most common adverse effects reported in clinical trials were headache, fatigue, dizziness, diarrhea, and nasopharyngitis. Aliskiren has not been studied in patients with moderate renal dysfunction; as an RAAS-acting drug, it should be prescribed for such patients only with caution.

Angiotensin II type 1 receptor antagonists in the treatment of hypertension in elderly patients: focus on patient outcomes

Hypertension in the elderly is one of the main risk factors of cardiovascular and cerebrovascular diseases. Knowledge regarding the mechanisms of hypertension and specific considerations in managing hypertensive elderly through pharmacological intervention(s) is fundamental to improving clinical outcomes. Recent clinical studies in the elderly have provided evidence that angiotensin II type 1 (AT(1)) receptor antagonists can improve clinical outcomes to a similar or, in certain populations, an even greater extent than other classical arterial blood pressure-lowering agents. This newer class of antihypertensive agents presents several benefits, including potential for improved adherence, excellent tolerability profile with minimal first-dose hypotension, and a low incidence of adverse effects. Thus, AT(1) receptor antagonists represent an appropriate option for many elderly patients with hypertension, type 2 diabetes, heart failure, and/or left ventricular dysfunction.

Are there effects of renin-angiotensin system antagonists beyond blood pressure control?

Angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) are recognized to reduce cardiovascular and renal morbidity and mortality, which is primarily attributed to their antihypertensive effects. Activation of the renin-angiotensin system (RAS) may also play an important role in the pathogenesis of cardiovascular and renal disease through blood pressure-independent mechanisms mediated by angiotensin II. Thus, inhibiting the RAS with either an ARB or an ACE inhibitor may confer additional benefit in people with advanced nephropathy that cannot be explained totally by reductions in blood pressure. Preclinical evidence suggests that blood pressure lowering is not solely responsible for the organ and tissue protective effects of ACE inhibitors or ARBs. Furthermore, clinical studies evaluating effects on end organs and surrogate markers have shown that these agents have blood pressure-independent effects. There is also intriguing evidence that agents in the same class may differ in their effects on renal function despite similar blood pressure control. Support for blood pressure-independent effects comes from outcome studies. Agents evaluated in such studies and that appear to have effects independent of blood pressure lowering include irbesartan, losartan, ramipril, and telmisartan. Taken together, this body of evidence indicates that the clinical benefits of ARBs and ACE inhibitors in patients with advanced nephropathy extend beyond blood pressure reduction. Therefore, although antihypertensive efficacy is of primary importance in choosing a treatment to provide cardiovascular and renal protection, consideration should be given to the effects of an agent that extend beyond blood pressure.

Aliskiren: renin inhibitor for hypertension management

BACKGROUND

The renin-angiotensin-aldosterone system (RAAS) has long been recognized to play a significant role in hypertension pathophysiology. Certain agents that modify the RAAS can control blood pressure and improve cardiovascular outcomes. Aliskiren is the first of a new class of antihypertensive agents known as renin inhibitors.

OBJECTIVE

The goal of this article was to discuss the clinical pharmacology of aliskiren and its use in the management of hypertension, as well as potential uses in other cardiovascular disorders.

METHODS

Peer-reviewed articles and abstracts were identified from the MEDLINE and Current Contents databases (both 1966-October 1, 2007) using the search terms aliskiren, drug interaction, pharmacokinetics, and pharmacology. Citations from available articles were reviewed for additional references. Abstracts presented at recent professional meetings were also examined.

RESULTS

Nine published clinical studies have evaluated the effect of aliskiren in lowering blood pressure in hypertensive patients, either alone or in combination with other antihypertensive agents. This review summarizes those studies. Patients treated with aliskiren had significantly lower blood pressure compared with patients with mild to moderate hypertension (systolic blood pressure [SBP] 140-180 mm Hg and diastolic blood pressure [DBP] 95-110 mm Hg) who received placebo. Aliskiren in doses of 75 to 300 mg daily produced reductions of SBP (-5.3 to -15.8 mm Hg) and DBP (-5.8 to -12.3 mm Hg); placebo produced reductions of SBP that ranged from -2.85 to -10.0 mm Hg and DBP reductions from -3.26 to -8.6 mm Hg (P < 0.05 in all studies between aliskiren and placebo). Aliskiren's blood pressure-lowering effect at doses of 75 to 300 mg daily was comparable to irbesartan 150 mg daily and valsartan 80 to 360 mg daily alone. When aliskiren was added to ramipril, hydrochlorothiazide, amlodipine, irbesartan, or valsartan, significant additive blood pressure-lowering effects were reported (P < 0.05 in all clinical trials). The total incidence of adverse events was similar to placebo and other comparative agents, including irbesartan, valsartan, losartan, ramipril, and hydrochlorothiazide. The overall adverse-event rates were 22%, 35% to 52%, 25% to 52%, 34% to 55%, and 33% to 52% for aliskiren 37.5, 75, 150, 300, and 600 mg, respectively. The most commonly reported adverse events included headache, dizziness, and fatigue. Studies with cardiovascular outcomes as end points have not been performed with aliskiren.

CONCLUSIONS

Aliskiren is an effective alternative agent for blood pressure management. Before aliskiren can be recommended as a routine first-line agent, however, clinical studies must explore if the blood pressure-lowering effect will translate into improvement in cardiovascular outcomes.

Is the mineralocorticoid receptor a potential target for stroke prevention?

In recent years, it has become increasingly clear that the extra-renal effects of aldosterone play an important role in the pathogenesis of cardiovascular disease. Stroke is one of the leading causes of death in the Western world, and MR (mineralocorticoid receptor) antagonism is a potential preventative therapy for patients at risk of both ischaemic and haemorrhagic strokes. This protective effect of MR antagonism appears to occur at the level of the cerebral vasculature and may be related to the expression and activation of the EGFR (epidermal growth factor receptor) and the degree of vessel wall collagen deposition.

National Stroke Association guidelines for the management of transient ischemic attacks

OBJECTIVE

Transient ischemic attacks are common and important harbingers of subsequent stroke. Management varies widely, and most published guidelines have not been updated in several years. We sought to create comprehensive, unbiased, evidence-based guidelines for the management of patients with transient ischemic attacks.

METHODS

Fifteen expert panelists were selected based on objective criteria, using publication metrics that predicted nomination by practitioners in the field. Prior published guidelines were identified through systematic review, and recommendations derived from them were rated independently for quality by the experts. Highest quality recommendations were selected and subsequently edited by the panelists using a modified Delphi approach with multiple iterations of questionnaires to reach consensus on new changes. Experts were provided systematic reviews of recent clinical studies and were asked to justify wording changes based on new evidence and to rate the final recommendations based on level of evidence and quality. No expert was allowed to contribute to recommendations on a topic for which there could be any perception of a conflict of interest.

RESULTS

Of 257 guidelines documents identified by systematic review, 13 documents containing 137 recommendations met all entry criteria. Six iterations of questionnaires were required to reach consensus on wording of 53 final recommendations. Final recommendations covered initial management, evaluation, medical treatment, surgical treatment, and risk factor management.

INTERPRETATION

The final recommendations on the care of patients with transient ischemic attacks emphasize the importance of urgent evaluation and treatment. The novel approach used to develop these guidelines is feasible, allows for rapid updating, and may reduce bias.

Aldosterone: good guy or bad guy in cerebrovascular disease?

Stroke is a leading cause of disability in the Western world, yet the choices for therapeutic intervention are few. The complex role played by aldosterone in the pathogenesis of stroke is beginning to emerge. Chronic mineralocorticoid receptor (MR) blockade reduces the incidence of hemorrhagic strokes and the severity of damage caused by ischemic strokes. This appears to be a vascular phenomenon because MR blockade increases vessel lumen diameter, which presumably increases blood flow and perfusion of the tissue to reduce ischemic damage. However, the vascular protection afforded by MR antagonism is at odds with the results seen within the brain, where MR activation is required for neuronal survival. Both of these divergent effects have possible therapeutic implications for stroke.

Angiotensin II, angiotensin II antagonists and spironolactone and their modulation of cardiac repolarization

Angiotensin II and aldosterone produce pro-arrhythmic effects by several mechanisms, including the modulation of voltage-dependent K(+) channels involved in human cardiac repolarization. Drugs that inhibit the renin-angiotensin-aldosterone system exert anti-arrhythmic actions that are related to the blockade of the pro-arrhythmic actions of angiotensin II and aldosterone. These anti-arrhythmic actions include inhibition of electrical and structural cardiac remodeling, inhibition of neurohumoral activation, reduction of blood pressure and stabilization of electrolyte disturbances. In this article, several angiotensin II AT(1) receptor antagonists (candesartan, E3174, eprosartan, irbesartan and losartan) and aldosterone receptor antagonists (canrenoic acid and spironolactone) that directly modulate the activity of the voltage-dependent K(+) channels are reviewed; the effects of these antagonists might be useful in the prevention and treatment of cardiac arrhythmias.