The difficult conception, birth and delivery of a renin inhibitor: controversies around aliskiren

Direct renin inhibition: extricating facts from façades

The renin–angiotensin system (RAS) affects vascular tone, cardiac output and kidney function. By these means the RAS plays a key role in the pathogenesis of arterial hypertension. As a result, RAS inhibition is highly effective not only in lowering blood pressure but also in reducing kidney disease progression (particularly when associated with proteinuria) and cardiovascular events.

Among RAS blocking agents, direct renin inhibitors have shown not only excellent efficacy in hypertension control but also pharmacologic tolerance that is comparable with other renin–angiotensin suppressors. Indeed, aliskiren, the only direct renin inhibitor available is effective in controlling blood pressure as monotherapy or in combination with other antihypertensive drugs, irrespective of patient’s age, ethnicity or sex. It is also effective in patients with metabolic syndrome, obesity and diabetes. Long-term studies comparing ‘hard endpoints’ of aliskiren therapy versus treatment with other RAS inhibitors, including cardiac and kidney protection, are currently ongoing. Combined with other antihypertensive agents, aliskiren not only improves their hypotensive response but may also lessen the adverse effects of other drugs. In high-risk patients, however, precautions should be taken when combining two or more renin–angiotensin inhibiting agents, as tissue perfusion may be highly renin-dependent in these patients and serious adverse side effects could take place.

Comparison of aliskiren/hydrochlorothiazide combination therapy and amlodipine monotherapy in patients with stage 2 systolic hypertension and type 2 diabetes mellitus

Patients with stage 2 hypertension and diabetes are at high cardiovascular risk and require large blood pressure (BP) reductions to reach treatment goals. This randomized double-blind study compared aliskiren/hydrochlorothiazide (HCTZ) combination therapy with amlodipine monotherapy in 860 patients with mean sitting systolic BP (msSBP) ≥160 mm Hg to <200 mm Hg and type 2 diabetes. Patients received either once-daily aliskiren/HCTZ 150/12.5 mg or amlodipine 5 mg for 1 week then force-titrated to double the doses for 7 weeks. Baseline BP was 167.7/91.4 mm Hg. At week 8 end point, aliskiren/HCTZ provided significantly greater reductions in msSBP than amlodipine (28.8 mm Hg vs 26.2 mm Hg; P<.05). Mean sitting diastolic BP reductions were similar with aliskiren/HCTZ (9.9 mm Hg) and amlodipine (9.0 mm Hg). Achievement of BP control (<130/80 mm Hg) was significantly greater with aliskiren/HCTZ (23.2%) than amlodipine (13.8%; P<.0001). Aliskiren/HCTZ provides substantial msSBP reductions and greater BP control rates than amlodipine, and offers an attractive treatment option for patients with hypertension and diabetes mellitus.

Signal transduction of the (pro)renin receptor as a novel therapeutic target for preventing end-organ damage

The (pro)renin receptor ((P)RR) not only represents a novel component of the renin-angiotensin system but is also a promising novel drug target because of its crucial involvement in the pathogenesis of renal and cardiac end-organ damage. This review discusses the signal transduction of the (P)RR with its adapter protein promyelocytic zinc-finger protein, the impact of this receptor, especially on cardiovascular disease, and its putative interaction with renin inhibitors such as aliskiren. Furthermore, the increasing complexity regarding the cellular function of the (P)RR is addressed, which arises by the intimate link with proton pumps and the phosphatase PRL-1, as well as by the presence of different subcellular localizations and of a soluble isoform of the (P)RR. Finally, the rationale and strategy for the development of small-molecule antagonists of the (P)RR, called renin/prorenin receptor blockers, are presented.

Aliskiren monotherapy does not cause paradoxical blood pressure rises: meta-analysis of data from 8 clinical trials

Angiotensin receptor blockers, angiotensin-converting enzyme inhibitors, and diuretics all cause reactive rises in plasma renin concentration, but particularly high levels have been reported with aliskiren. This prompted speculation that blockade of plasma renin activity with aliskiren could be overwhelmed, leading to paradoxical increases in blood pressure. This meta-analysis of data from 4877 patients from 8 randomized, double-blind, placebo- and/or active-controlled trials examined this hypothesis. The analysis focused on the incidence of paradoxical blood pressure increases above predefined thresholds, after > or =4 weeks of treatment with 300 mg of aliskiren, angiotensin receptor blockers (300 mg of irbesartan, 100 mg of losartan, or 320 mg of valsartan), 10 mg of ramipril, 25 mg of hydrochlorothiazide, or placebo. There were no significant differences in the frequency of increases in systolic (>10 mm Hg; P=0.30) or diastolic (>5 mm Hg; P=0.65) pressure among those treated with aliskiren (3.9% and 3.1%, respectively), angiotensin receptor blockers (4.0% and 3.7%), ramipril (5.7% and 2.6%), or hydrochlorothiazide (4.4% and 2.7%). Increases in blood pressure were considerably more frequent in the placebo group (12.6% and 11.4%; P<0.001). None of the 536 patients with plasma renin activity data who received 300 mg of aliskiren exhibited an increase in systolic pressure >10 mm Hg that was associated with an increase in plasma renin activity >0.1 ng/mL per hour. In conclusion, the incidence of blood pressure increases with aliskiren was similar to that during treatment with other antihypertensive drugs. Blood pressure rises on aliskiren treatment were not associated with increases in plasma renin activity. This meta-analysis found no evidence that aliskiren uniquely causes paradoxical rises in blood pressure.

Comparative effects of aliskiren-based and ramipril-based therapy on the renin system during long-term (6 months) treatment and withdrawal in patients with hypertension

INTRODUCTION

This subgroup analysis assessed the effects of treatment based on the direct renin inhibitor, aliskiren, or the angiotensin-converting enzyme inhibitor, ramipril, on plasma renin activity (PRA), plasma renin concentration (PRC) and other biomarkers in a 26-week randomised, double-blind trial. Changes in PRA and PRC after stopping treatment were also assessed.

METHODS

After placebo run-in, 842 patients (mean sitting diastolic blood pressure (BP) 95-109 mmHg) were randomised to aliskiren 150 mg or ramipril 5 mg. Dose titration and hydrochlorothiazide addition were allowed after Week 6 and 12, respectively, for inadequate BP control. Patients completing active treatment were re-randomised to current regimen or placebo during a 4-week posttreatment phase.

RESULTS

BP reductions were independent of baseline PRA at Week 12, were greater with aliskiren- than ramipril-based therapy at Week 26 (17.9/13.3 vs. 15.2/12.0 mmHg, p<0.05) and persisted for longer after stopping aliskiren. Aliskiren-based therapy reduced geometric mean PRA (-63%, p<0.05; n=103), while ramipril-based therapy increased PRA (+143%, p<0.05; n=100) at Week 26; PRC increased in both groups (aliskiren: +224% [n=33], ramipril: +145% [n=39], both p<0.05). Four weeks after stopping aliskiren-based therapy, PRA remained 52% below pre-treatment baseline; PRA returned to baseline 2 weeks after stopping ramipril-based therapy.

CONCLUSIONS

Aliskiren-based therapy produced sustained BP and PRA reductions over 26 weeks; ramipril-based therapy lowered BP and increased PRA. PRA reductions persisted 4 weeks after stopping aliskiren, suggesting an inhibitory effect beyond the elimination half-life of the drug.

Role of aliskiren in cardio-renal protection and use in hypertensives with multiple risk factors

The renin–angiotensin–aldosterone system (RAAS) is a key mediator of blood pressure (BP) and volume regulation in both normotensive and hypertensive persons. Stimulation of RAAS also contributes to hypertension-related target organ damage. The renin–angiotensinogen reaction is the first and rate-limiting step in the generation of angiotensin II (Ang II) and has been a target of antihypertensive drug development for decades. Aliskiren is the first in a new class of orally effective direct renin inhibitors (DRIs) and is approved for the treatment of hypertension in humans. It effectively reduces BP in the general population of hypertensive patients and has a tolerability and safety profile similar to placebo. Aliskiren has favorable effects on vascular inflammation and remodeling, on neurohumoral mediators of various forms of cardiovascular disease, including heart failure, and on proteinuria in diabetic patients. Additional outcome trials are needed to establish the role of this novel class of antihypertensive medication in preventing cardiovascular disease morbidity and mortality.

Role of aliskiren in cardio-renal protection and use in hypertensives with multiple risk factors

The renin-angiotensin-aldosterone system (RAAS) is an important mediator of blood pressure (BP) and volume regulation in both normotensive and hypertensive persons and is a major contributor to hypertension-related target organ damage. The concept of renin inhibition for managing hypertension by blocking the RAAS pathway at its point of activation is very attractive since the renin-angiotensinogen reaction is the first and rate-limiting step in the generation of angiotensin II (Ang II). Aliskiren, the first in a new class of orally effective direct renin inhibitors (DRIs), is approved for the treatment of hypertension. It is effective in reducing BP in the general population of hypertensive patients and in special patient groups such as obese persons, and has a tolerability and safety profile similar to placebo. Aliskiren has renoprotective, cardioprotective and anti-atherosclerotic effects in animal models that appear to be independent of BP lowering. It reduces proteinuria in diabetic patients and has favorable neurohumoral effects in patients with symptomatic heart failure. Additional outcome trials are needed to establish the role of this novel class of antihypertensive medication in the therapeutic armamentarium.

Managing cardiovascular and renal risk: the potential of direct renin inhibition

Aliskiren is the first direct renin inhibitor for the treatment of hypertension. Clinical experience from studies in over 14,000 patients has shown that aliskiren, alone or in combination with other antihypertensive therapies, provides effective blood pressure lowering with a good safety and tolerability profile.The ultimate aim of antihypertensive therapy, however, is to reduce the risk of adverse cardiovascular and renal outcomes.The effect of aliskiren on surrogate markers of organ damage and clinical outcomes is being assessed in the ongoing ASPIRE HIGHER programme, the largest clinical trials programme in the cardio-renal disease area. Results from the ALOFT, AVOID and ALLAY studies suggest that aliskiren has positive effects on markers of cardiovascular and renal damage in patients with type 2 diabetes and nephropathy, heart failure and left ventricular hypertrophy.ASPIRE HIGHER also includes four large-scale studies assessing the potential outcome benefits of aliskiren, and the results of these trials will help define the clinical utility of aliskiren in the treatment of cardiovascular and renal diseases. In this article, we review the antihypertensive efficacy of aliskiren and explore its potential in the management of cardiovascular and renal risk.

Renin inhibition with aliskiren in hypertension: focus on aliskiren/hydrochlorothiazide combination therapy

Hypertension is a major risk factor for the development of cardiovascular and renal disease. The incidence of hypertension is increasing globally and the rate of blood pressure control remains inadequate. Renin-angiotensin-aldosterone system (RAAS) plays a crucial role in volume regulation and maintenance of blood pressure. Pathological activation of RAAS results in chronic hypertension and consequent end organ damage. Most patients with hypertension require combination therapy using agents with complimentary mechanisms of action. Hydrochlorothiazide (HCTZ) together with an agent blocking the RAAS such as an angiotensin converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) are widely used effective anti-hypertensive therapy. Aliskiren is an orally effective direct renin inhibitor that blocks the generation of angiotensin I from angiotensinogen, the rate limiting step of RAAS activation. Studies have shown equivalent antihypertensive efficacy of aliskiren when compared to existing medications such as HCTZ, ACE inhibitors and ARBs. Aliskiren has also been tested in combination therapies. The current review aims to look at the efficacy of aliskiren therapy in hypertension and the evidence for using aliskiren in combination with HCTZ.

Aliskiren fails to lower blood pressure in patients who have either low PRA levels or whose PRA falls insufficiently or reactively rises

BACKGROUND

Suppressed baseline plasma renin activity (PRA) levels or large reactive increases in renin secretion are two possible reasons for treatment failure with antirenin system drugs.

METHODS

To investigate their prevalence we reanalyzed data from three published clinical trials of the renin inhibitor aliskiren.

RESULTS

Aliskiren failed to lower systolic blood pressure (SBP) by at least 10 mm Hg in half of all patients. It was very effective in two-thirds of medium- to high-renin patients (-19 mm Hg). But BP did not fall in most low-renin patients, or in 30% of medium- to high-renin patients. BP actually rose by >10 mm Hg in 5% of patients taking aliskiren and in >10% of patients when aliskiren was added to an angiotensin receptor blocker (ARB) or angiotensin converting enzyme inhibitor (ACEI). PRA changed in parallel with BP. Although PRA fell in most patients, it actually rose in 5% and in up to 30% when aliskiren was added to an ARB or ACEI.

CONCLUSIONS

There are two reasons for treatment failure with aliskiren. Many hypertensive patients have large BP falls. But, BP does not fall in most low-renin patients or in medium- to high-renin patients whose PRA levels do not fall sufficiently. If the concept of that treatment resistance is caused by excessive reactive increases in renin secretion is confirmed, then a PRA determination during treatment could be used to guide subsequent addition or subtraction of either natriuretic or antirenin drug types, to thereby correct BP and reduce cardiovascular risk.

Renal and hormonal responses to direct renin inhibition with aliskiren in healthy humans

BACKGROUND

Pharmacological interruption of the renin-angiotensin system focuses on optimization of blockade. As a measure of intrarenal renin activity, we have examined renal plasma flow (RPF) responses in a standardized protocol. Compared with responses with angiotensin-converting enzyme inhibition (rise in RPF approximately 95 mL x min(-1) x 1.73 m(-2)), greater renal vasodilation with angiotensin receptor blockers (approximately 145 mL x min(-1) x 1.73 m(-2)) suggested more effective blockade. We predicted that blockade with the direct oral renin inhibitor aliskiren would produce renal vascular responses exceeding those induced by angiotensin-converting enzyme inhibitors and angiotensin receptor blockers.

METHODS AND RESULTS

Twenty healthy normotensive subjects were studied on a low-sodium (10 mmol/d) diet, receiving separate escalating doses of aliskiren. Six additional subjects received captopril 25 mg as a low-sodium comparison and also received aliskiren on a high-sodium (200 mmol/d) diet. RPF was measured by clearance of para-aminohippurate. Aliskiren induced a remarkable dose-related renal vasodilation in low-sodium balance. The RPF response was maximal at the 600-mg dose (197+/-27 mL x min(-1) x 1.73 m(-2)) and exceeded responses to captopril (92+/-20 mL x min(-1) x 1.73 m(-2); P<0.01). Furthermore, significant residual vasodilation was observed 48 hours after each dose (P<0.01). The RPF response on a high-sodium diet was also higher than expected (47+/-17 mL x min(-1) x 1.73 m(-2)). Plasma renin activity and angiotensin levels were reduced in a dose-related manner. As another functional index of the effect of aliskiren, we found significant natriuresis on both diets.

CONCLUSIONS

Renal vasodilation in healthy people with the potent renin inhibitor aliskiren exceeded responses seen previously with angiotensin-converting enzyme inhibitors and angiotensin receptor blockers. The effects were longer lasting and were associated with significant natriuresis. These results indicate that aliskiren may provide more complete and thus more effective blockade of the renin-angiotensin system.

Review: The therapeutic role of RAS blockade in chronic heart failure

Cardiovascular disease represents a continuum that starts with risk factors such as hypertension and progresses to atherosclerosis, end-organ damage, and ultimately to chronic heart failure (CHF) and premature death. Renin-angiotensin system (RAS) blockade with angiotensin converting enzyme (ACE) inhibitors and/or angiotensin II type 1 receptor blockers (ARBs) has turned out to be beneficial at all stages of this continuum. Several mechanisms govern the progression of structural myocardial damage to end-stage CHF. Chronic neuroendocrine activation fosters left ventricular remodeling and dilatation and leads to clinical symptoms of CHF via forward/backward failure. RAS inhibition is a cornerstone of neuroendocrine blockade in CHF patients, and combined RAS blockade is especially effective in patients presenting with repetitive cardiac decompensations. This review focuses on the therapeutic role of inhibitors of different RAS components in chronic heart failure caused by systolic left ventricular dysfunction.