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

Therapeutic Renin Inhibition in Diabetic Nephropathy-A Review of the Physiological Evidence

The purpose of this systematic review was to investigate the scientific evidence to support the use of direct renin inhibitors (DRIs) in diabetic nephropathy (DN). MEDLINE was searched for articles reported until 2018. A standardized dataset was extracted from articles describing the effects of DRIs on plasma renin activity (PRA) in DN. A total of three clinical articles studying PRA as an outcome measure for DRIs use in DN were identified. These clinical studies were randomized controlled trials (RCTs): one double-blind crossover, one post hoc of a double-blind and placebo-controlled study, and one open-label and parallel-controlled study. Two studies reported a significant decrease of albuminuria associated with PRA reduction. One study had a DRI as monotherapy compared with placebo, and two studies had DRI as add-in to an angiotensin II (Ang II) receptor blocker (ARB). Of 10,393 patients with DN enrolled in five studies with DRI, 370 (3.6%) patients had PRA measured. Only one preclinical study was identified that determined PRA when investigating the effects of aliskiren in DN. Moreover, most of observational preclinical and clinical studies identified report on a low PRA or hyporeninemic hypoaldosteronism in DM. Renin inhibition has been suggested for DN, but proof-of-concept studies for this are scant. A small number of clinical and preclinical studies assessed the PRA effects of DRIs in DN. For a more successful translational research for DRIs, specific patient population responsive to the treatment should be identified, and PRA may remain a biomarker of choice for patient stratification.

Juxtaglomerular Cell Tumor: Reviewing a Cryptic Cause of Surgically Correctable Hypertension

Juxtaglomerular cell tumor (JGCT), or reninoma, is a typically benign neoplasm generally affecting adolescents and young adults due to modified smooth muscle cells from the afferent arteriole of the juxtaglomerular apparatus. Patients experience symptoms related to hypertension and hypoka-lemia due to renin-secretion by the tumor. MRI, PET, CT, and renal vein catheterizations can be used to capture JGCTs, with laparoscopic ultrasonography being most cost-efective. Surgical removal is the best option for management; electrolyte imbalances are a potential complication which may be assuaged via pre-surgical administration of aliskiren, a renin inhibitor. Considering the vast etiology for hypertension and rarity of JGCT, the diagnosing physician must have a high index of suspicion for JGCT. Early recognition and management can help prevent cardiovascular or pregnancy complications and fatalities, vascular invasion and metastasis, improve quality of life, and limit socioeconomic liabilities. Herein we review the epidemiology, genetics, histopathol-ogy, clinical presentation, and management of this rare condition. The impact of genetics on prognosis warrant further research.

Rationale for nebivolol/valsartan combination for hypertension: review of preclinical and clinical data

To treat hypertension, combining two or more antihypertensive drugs from different classes is often necessary. β-Blockers and renin–angiotensin–aldosterone system inhibitors, when combined, have been deemed ‘less effective’ based on partially overlapping mechanisms of action and limited evidence. Recently, the single-pill combination (SPC) of nebivolol (Neb) 5 mg – a vasodilatory β1-selective antagonist/β3 agonist – and valsartan 80 mg, an angiotensin II receptor blocker, was US Food and Drug Administration-approved for hypertension. Pharmacological profiles of Neb and valsartan, alone and combined, are well characterized. In addition, a large 8-week randomized trial in stages I–II hypertensive patients (N = 4161) demonstrated greater blood pressure-reducing efficacy for Neb/valsartan SPCs than component monotherapies with comparable tolerability. In a biomarkers substudy (N = 805), Neb/valsartan SPCs prevented valsartan-induced increases in plasma renin, and a greater reduction in plasma aldosterone was observed with the highest SPC dose vs. valsartan 320 mg/day. This review summarizes preclinical and clinical evidence supporting Neb/valsartan as an efficacious and well tolerated combination treatment for hypertension.

The Potential Role of Primary Care in Case Detection/Screening of Primary Aldosteronism

Endocrine hypertension, particularly primary aldosteronism (PA), was previously considered to account for less than 1% of all hypertension and was suspected only when patients presented with spontaneous hypokalemia. However, the last 20 years of PA research has now clearly shown that PA is not a rarity, but rather, may account for up to 13% of unselected hypertensive individuals and between 10% and 20% of those with resistant hypertension. Most of these patients do not have spontaneous hypokalemia. The population prevalence of PA likely far exceeds actual detection rates in routine clinical care. As PA represents one of the most common, potentially reversible causes of hypertension, and is associated with significant cardiovascular complications over the long term, it is clear that a pragmatic strategy for targeted case detection in primary care is needed.

Advances in understanding the renin-angiotensin-aldosterone system (RAAS) in blood pressure control and recent pivotal trials of RAAS blockade in heart failure and diabetic nephropathy

The renin-angiotensin-aldosterone system (RAAS) plays a fundamental role in the physiology of blood pressure control and the pathophysiology of hypertension (HTN) with effects on vascular tone, sodium retention, oxidative stress, fibrosis, sympathetic tone, and inflammation. Fortunately, RAAS blocking agents have been available to treat HTN since the 1970s and newer medications are being developed. In this review, we will (1) examine new anti-hypertensive medications affecting the RAAS, (2) evaluate recent studies that help provide a better understanding of which patients may be more likely to benefit from RAAS blockade, and (3) review three recent pivotal randomized trials that involve newer RAAS blocking agents and inform clinical practice.

Correlations of plasma renin activity and aldosterone concentration with ambulatory blood pressure responses to nebivolol and valsartan, alone and in combination, in hypertension

After demonstration of the antihypertensive efficacy of the combination of the beta-blocker nebivolol and the angiotensin receptor blocker valsartan in an 8-week, randomized, placebo-controlled trial (N = 4161), we now report the effects of this treatment on the renin-angiotensin-aldosterone system in a substudy (n = 805). Plasma renin activity increased with valsartan (54%-73%) and decreased with nebivolol (51%-65%) and the combination treatment (17%-39%). Plasma aldosterone decreased with individual treatments (valsartan, 11%-22%; nebivolol, 20%-26%), with the largest reduction (35%) observed with maximum combination dose (20 mg nebivolol/320 mg valsartan). Baseline ln(plasma renin activity) correlated with the 8-week reductions in 24-hour systolic and diastolic BP following treatments with the combination (all doses combined, P = .003 and P < .001) and nebivolol (both, P < .001), but not with valsartan. Baseline ln(aldosterone) correlated with 24-hour systolic and diastolic BP reductions following combination treatment only (P < .001 and P = .005). The implications of the renin-angiotensin-aldosterone system effects of this beta blocker-angiotensin receptor blocker combination should be explored further.

Pressor response to initial blood pressure monotherapy is associated with cardiovascular mortality

BACKGROUND

A paradoxical pressor systolic response to initial antihypertensive monotherapy has been observed in 8% of hypertensive patients. The long-term consequences of this finding are unknown.

METHODS

We included 945 hypertensive patients with baseline systolic blood pressure (SBP) ≥140mm Hg. A 4-week washout period free of antihypertensive drugs was allowed for those already on treatment at entry. Mortality outcomes were ascertained from the National Death Index. Subjects were categorized by SBP response into depressor (≥10mm Hg fall), nonresponder, and pressor (≥10mm Hg rise) categories.

RESULTS

There were 268 fatalities. Of these, 100 (37%) were from cardiovascular disease (CVD), of which 70 (70%) were due to coronary artery disease (CAD). A pressor response was associated with higher SBP at 1 year compared with the nonresponder or depressor response (141 vs. 136 vs. 136mm Hg). CVD mortality was greater in pressors than depressors (hazard ratio (HR) = 3.0; 95% confidence interval (CI) = 1.4-6.4; P = 0.004], as was CAD (HR = 3.1; 95% CI = 1.4-6.8; P < 0.01) and all-cause mortality (HR = 1.7; 95% CI = 1.1-2.6; P = 0.02), after adjusting for 1-year SBP and other possible confounders.

CONCLUSIONS

We found the incidence of a pressor response to monotherapy at 3 months was significantly, specifically, and independently associated with higher subsequent cardiovascular mortality.

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.

The plasma renin test reveals the contribution of body sodium-volume content (V) and renin-angiotensin (R) vasoconstriction to long-term blood pressure

Body sodium works together with the plasma renin-angiotensin system to ensure adequate blood flow to the tissues. Body sodium content determines the extracellular fluid (ECF) volume ensuring that, with each heart beat, a sufficient volume of fluid is delivered into the arterial space. At the same time the kidneys monitor ECF volume and blood pressure (BP), so that the juxtaglomerular cells can adjust their net secretion rate of renin to maintain an appropriate plasma renin activity (PRA) level. Plasma renin produces angiotensin II (Ang II) to constrict the arterioles and thereby ensure sufficient BP to deliver an appropriate rate of flow for cardiovascular homeostasis. The low renin, sodium-volume dependent (V) form of essential hypertension occurs whenever body sodium content increases beyond the point where plasma renin-angiotensin vasoconstrictor activity is turned off. In contrast, medium to high renin (R) hypertension occurs when too much renin is secreted relative to the body sodium content. Thus, BP = V × R. This volume-vasoconstriction dual support of long-term hypertension is validated by the fact that all effective long-term antihypertensive drug types are either (i) natriuretic to reduce body salt and volume content (anti-V), or (ii) antirenin to reduce or block the activity of the circulating renin-angiotensin system (anti-R). The PRA test defines the relative participation of the concurrent volume and vasoconstrictor factors. In the hypertensive patient PRA testing can guide initiation, addition or subtraction of anti-V or anti-R antihypertensive drug types to thereby improve BP control and prognosis while reducing drug type usage and cost.

Combined aliskiren-amlodipine treatment for hypertension in African Americans: clinical science and management issues

While it may seem at first that antihypertensive drug combinations run counter to the desire to 'personalize' the management of hypertension, the best combinations have predictable efficacy in different individuals and subpopulations. Race is probably not a valid surrogate for clinically meaningful genetic variation or guide to therapy. Most guidelines suggest similar blood pressure goals for different races but drug treatment recommendations have diverged. In the United States, race is not considered to be a major factor in drug choice, but in England and other countries, initial therapy with renin-angiotensin system blocking drugs is not recommended in Blacks. In this review we: (1) examine new trends in race-based research; (2) emphasize the weaknesses of race-based treatment recommendations; and (3) explore the effects of a new combination, renin inhibition (aliskiren) and amlodipine, in African Americans.

Vaccines in the management of hypertension

IMPORTANCE OF THE FIELD

In the USA only 35% of patients with hypertension achieve adequate blood pressure control. Non-compliance is one of the main barriers to treatment. Vaccine against hypertension is an innovative treatment, injected every 4 - 6 months, to combat non-compliance.

AREAS COVERED IN THIS REVIEW

Pathogenesis of hypertension and progress towards developing a hypertension vaccine, including the virus-like-particle-based approach, new adjuvant molecules and the potential toxicity of hypertension vaccine.

WHAT THE READER WILL GAIN

The pathogenesis of hypertension is multifactorial. The most common cause is disruption of the Renin-angiotensin-aldosterone system (RAAS), and the first vaccine study was carried out against renin. While the vaccine reduced blood pressure in animal models, it also caused autoimmune disease. In the last decade, vaccines against angiotensin I, angiotensin II, and angiotensin II-type 1 receptors have demonstrated acceptable safety profiles in animal and human studies.

TAKE HOME MESSAGE

Reduction in blood pressure can be achieved by inducing immunity against targets in the RAAS. The target antigen and selection of adjuvant are crucial factors determining effectiveness and safety of the vaccine. CYT006-AngQb (angiotensin II vaccine) reduced blood pressure in humans but the results were not reproducible with more frequent dosing. Vaccines for hypertension are still in the early phase. We hope for an effective vaccine for hypertension in the years to come.

Pressor responses to antihypertensive drug types

BACKGROUND

Pressor responses to antihypertensive drugs are not addressed in treatment guidelines although they have been described in various clinical situations. We now report the incidence of pressor responses to initiation of monotherapy using four antihypertensive drug types, and the influence of plasma renin activity (PRA) status, among participants in a worksite-based antihypertensive treatment program.

METHODS

Systolic blood pressure (SBP) response was evaluated among 945 participants with no prior treatment who were given either a diuretic or calcium-channel blocker (natriuretic antivolume V drugs, n = 537) or a beta-blocker or angiotensin-converting enzyme (ACE) inhibitor (antirenin R drugs n = 408). PRA was categorized by low, middle, and high tertiles (L, M, and H). SBP rise > or =10 mm Hg was considered pressor.

RESULTS

More pressor responses occurred with R than V drugs (11% vs. 5%, P = 0.001). L, M, and H renin tertiles had similar frequencies with V drugs (6, 4, and 6%), but low and middle tertiles given R had greater pressor frequencies (17% P = 0.003 vs. V and 10% P = 0.02 vs. V). Treatment SBP > or =160 mm Hg occurred more frequently with R than V drugs (19% vs. 13%; P = 0.007); moreover, in the lowest renin tertile 35% R vs. 13% V (P = 0.001) had SBP > or =160 mm Hg. Treatment SBP <130 mm Hg was more frequent in V patients in the lowest tertile (18% vs. 5%; P = 0.003), and in R patients in the highest tertile (26% vs. 12%, P = 0.002).

CONCLUSIONS

Pressor responses to antihypertensive monotherapy occur sufficiently frequently to be of concern, especially in lower renin patients given a beta-blocker or ACE inhibitor (ACEI).

Direct renin inhibitors as antihypertensive agents

Hypertension, a serious disease affecting almost a billion people (25% of adults) worldwide, is a major modifiable risk factor for cardiovascular (CV) and renal disease. Despite numerous advances in the pharmacologic treatment of high blood pressure (BP) and availability of several antihypertensive drugs to treat hypertension, a significant proportion of treated hypertensive patients still have uncontrolled high BP, and thus, face serious morbidity and mortality. Furthermore, it is not sufficient to aim for optimum BP control, but to treat all CV risk factors, protect end-organ damage, prevent progression of disease, and prevent long-range adverse effects of the drugs. Therefore, new therapeutic modalities have to be developed to achieve the above objectives. Some years ago, investigators identified renin inhibition as the preferred pharmacologic approach to blockade of the renin-angiotensin system. Renin is a monospecific enzyme that catalyzes the rate-limiting step in the synthesis of angiotensin II. Amplified enzymatic activity and additional physiologic effects occur when renin and prorenin bind to the (pro)renin receptor. Until very recently, development of clinically effective renin inhibitors remained elusive but molecular modeling was used to develop aliskiren and other renin inhibitors that produce sustained suppression of plasma renin activity after oral administration with a dose-dependent BP. Additional studies will ultimately determine the place of renin inhibition in the treatment of hypertension and related CV disorders.

New approaches to blockade of the renin-angiotensin-aldosterone system: characteristics and usefulness of the direct renin inhibitor aliskiren

Since renin inhibition interferes with the first and rate-limiting steps in the renin-angiotensin system, the renin step is a very attractive target for lowering blood pressure and minimizing target-organ damage. The newly developed direct renin inhibitor aliskiren has several attractive characteristics: it definitively reduces plasma renin activity among inhibitors of the renin-angiotensin system, is remarkably specific for human renin, exhibits a long half-life in plasma comparable to that of amlodipine, and has a high affinity for renal glomeruli and vasculature. Although these characteristics suggest the clinical usefulness and safety of aliskiren, several problems remain unsolved. Why does aliskiren have beneficial effects on the heart and kidneys of patients treated with angiotensin-converting enzyme (ACE) inhibitors and/or angiotensin II type 1-receptor blockers (ARBs)? Is the blood-pressure-lowering effect of aliskiren dependent on the plasma renin activity? Does aliskiren exert a possible adverse effect via (pro)renin receptor-dependent intracellular signals? Here, we review the characteristics and usefulness of aliskiren and discuss the current issues associated with this direct renin inhibitor.

Unmet needs in managing hypertension: potential role of direct renin inhibition

Hypertension is the most prevalent and important risk factor for cardiovascular and renal disease worldwide. Despite the large armamentarium of available blood pressure-lowering agents, the need remains for safer and more effective antihypertensive treatment. Based on current target levels of < 140/90 mm Hg, only one-third of hypertensive Americans have achieved goal blood pressure. Several strategies can help address these challenges, including increasing public awareness, and improving physician awareness of evidence-based therapeutic guidelines. There also remains a need for new therapeutic options. This review examines new developments among those agents having inhibitory activity on the renin-angiotensin-aldosterone system (RAAS). All currently available RAAS blockers cause a reactive increase in plasma renin concentration. However, the direct renin inhibitors are the only class that diminishes plasma renin activity, an effect that may provide additional cardiovascular and/or renoprotective benefit. Aliskiren is the first clinically available direct renin inhibitor that has been shown to be effective and well tolerated both as monotherapy and in combination with other established agents in hypertensive patients. Randomized clinical trials are underway to explore the extent to which direct renin inhibition provides additive protection against cardiovascular and renal disease events.

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.

The increase in renin during renin inhibition: does it result in harmful effects by the (pro)renin receptor?

Renin inhibitors, similar to all renin-angiotensin system (RAS) blockers, increase the plasma concentration of renin because they attenuate the negative feedback effect of angiotensin (Ang) II on renin release. The increase in renin has been suggested to be higher than that during other types of RAS blockade. This could potentially limit the effectiveness of renin inhibition, either because Ang II generation might occur again ('Ang II escape'), possibly even at the levels above baseline, as has been described before for angiotensin-converting enzyme inhibitors, or because high levels of renin will stimulate the recently discovered (pro)renin receptor, and thus induce effects in an Ang-independent manner. This review shows first that the cause(s) of the renin increase during treatment with the renin inhibitor aliskiren is the consequence of a combination of factors, including an assay artifact, allowing the detection of prorenin as renin, and a change in renin half-life. When correcting for these phenomena the increase is unlikely to be as excessive as originally thought. The review then critically describes the consequence(s) of such a increase, concluding (i) that an Ang II escape is highly unlikely, given the [aliskiren]/[renin] stoichiometry, and (ii) that renin and prorenin downregulate their receptor (similar to many agonists). On the basis of the latter, one could even speculate that this will be more substantial when the renin and prorenin levels are higher. Thus, from this point of view the larger increase in renin during renin inhibition will cause a stronger reduction in (pro)renin receptor expression, and a greater suppression of (pro)renin receptor-mediated effects than other renin-Ang blockers.

Is there a role for direct renin inhibitors in chronic kidney disease?

PURPOSE OF REVIEW

To evaluate the evidence supporting the use of renin inhibitors to control hypertension, limit kidney disease progression, and decrease cardiovascular risk in patients with chronic kidney disease (CKD).

RECENT FINDINGS

The literature on the subject is still limited. Most of the studies have used aliskiren as the study drug. Animal models show improved survival and decreased renal injury in animals receiving aliskiren. Human studies in patients with normal renal function show effective blood pressure control alone or in combination with different agents. There are no studies focusing on blood pressure control in patients with CKD, though the drug has been safely used in CKD. In a randomized clinical trial, aliskiren decreased albuminuria when added to losartan in patients with early diabetic nephropathy. Ongoing studies are evaluating the role of renin inhibitors in the prevention of cardiovascular events and slowing of kidney disease progression in CKD.

SUMMARY

Renin inhibitors, specifically aliskiren, effectively decrease albuminuria. Their role in improving hard renal endpoints and decreasing cardiovascular events in CKD still remains to be established.

Dual blockade of the renin-angiotensin-aldosterone system: beyond the ACE inhibitor and angiotensin-II receptor blocker combination

The renin-angiotensin-aldosterone system (RAAS), an important regulator of blood pressure as well as fluid and electrolyte balance, plays an important role in the pathophysiology of cardiovascular and kidney diseases. Blockade of the RAAS with angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin-II (ANG-II) receptor blockers (ARBs) lowers blood pressure, decreases morbidity and mortality in patients with chronic heart failure, and decreases proteinuria and the rate of decline in renal function in patients with chronic kidney disease. Although these drugs are highly effective and are widely used in the management of cardiovascular and kidney diseases, current treatment regimens with ACEIs and ARBs may not completely suppress the RAAS. Combinations of ACEIs and ARBs have been shown to be superior to either agent alone for some, but certainly not all, composite cardiovascular and kidney outcomes. With the growing appreciation of the role of aldosterone in the pathogenesis of cardiorenal diseases and the recent approval of the direct renin inhibitor (DRI), aliskiren, additional combination strategies have emerged that may offer novel ways to more fully suppress the RAAS. This review examines what is presently known about ACEI/ARB combination therapy and explores alternative combination strategies that include DRIs and mineralocorticoid receptor blockers (MRBs).

Adapter proteins and promoter regulation of the angiotensin AT2 receptor — implications for cardiac pathophysiology

The angiotensin AT 2 receptor (AT2R) represents an important component of the renin-angiotensin system since it is involved in the (patho) physiology of different cardiovascular and neuronal diseases. Furthermore, AT2 receptors can partly mediate beneficial effects of angiotensin AT 1 receptor (AT1R) blockers, and direct pharmacological AT 2 receptor agonism emerges as a novel therapeutic strategy. This review discusses the constitutive and ligand-mediated activity as well as the signal transduction of the AT2 receptor, focusing on adapter proteins which directly bind to this receptor. Direct protein-protein interaction partners of the AT2 receptor described so far include the transcription factor promyelocytic zinc finger protein, AT2 receptor binding protein and the AT1 receptor. In addition, the putative crosstalk of the AT2 receptor with the renin/ prorenin receptor (RER) via the promyelocytic zinc finger protein (PLZF) and the role of oestrogens on the regulation of the AT2 receptor are presented. Conceiving the coupling of the AT2 receptor to different adapter proteins with distinct and partly opposing cellular effects and the implications of its constitutive activity might help to overcome the current controversies on the (patho)physiological role of the AT2 receptor.

Aliskiren monotherapy results in the greatest and the least blood pressure lowering in patients with high- and low-baseline PRA levels, respectively

Hypertensive patients with low-baseline plasma renin activity (PRA) are known to respond best to natriuretic drugs, and those with high PRA respond best to renin-angiotensin system (RAS) blockade. However, there has been recent speculation that blood pressure (BP)-lowering responses to the renin inhibitor, aliskiren, might also be blunted in some patients with medium-to-high baseline PRA. It has been suggested that treatment resistance in these patients may result from excessive reactive increases in renin secretion, such that aliskiren's blockade of PRA is overwhelmed. In order to test for evidence in support of this hypothesis, we conducted a reanalysis of original data from three published clinical trials of aliskiren. When aliskiren was administered as a monotherapy, or in combination with other blockers of the RAS, changes in PRA were closely correlated with baseline PRA. Patients with low-baseline PRA demonstrated small reductions or rises in PRA, rather than patients with medium-to-high baseline PRA. We confirmed that ambulatory BP-lowering responses to full dose aliskiren monotherapy were greatest and least among patients with high- and low-baseline PRA, respectively. However no such association was demonstrated during aliskiren combination therapy. With either monotherapy or combination therapy, no patient with a baseline PRA >0.65 ng/ml/h was observed to have a rise in both PRA and BP. We conclude, therefore, that there is only evidence for one type of resistance to aliskiren--as with all blockers of the RAS, lesser BP-lowering responses to aliskiren occur in those with the least renin to block.

Plasma Renin test-guided drug treatment algorithm for correcting patients with treated but uncontrolled hypertension: a randomized controlled trial

BACKGROUND

Undefined pathophysiologic mechanisms likely contribute to unsuccessful antihypertensive drug therapy. The renin test-guided therapeutic (RTGT) algorithm is based on the concept that, irrespective of current drug treatments, subnormal plasma renin activity (PRA) (<0.65 ng/ml/h) indicates sodium-volume excess "V" hypertension, whereas values >or=0.65 indicate renin-angiotensin vasoconstriction excess "R" hypertension.

METHODS

The RTGT algorithm was applied to treated, uncontrolled hypertensives and compared to clinical hypertension specialists' care (CHSC) without access to PRA. RTGT protocol: "V" patients received natriuretic anti-"V" drugs (diuretics, spironolactone, calcium antagonists, or alpha(1)-blockers) while withdrawing antirenin "R" drugs (converting enzyme inhibitors, angiotensin receptor antagonists, or beta-blockers). Converse strategies were applied to "R" patients. Eighty-four ambulatory hypertensives were randomized and 77 qualified for the intention-to-treat analysis including 38 in RTGT (63.9 +/- 1.8 years; baseline blood pressure (BP) 157.0 +/- 2.6/87.1 +/- 2.0 mm Hg; PRA 5.8 +/- 1.6; 3.1 +/- 0.3 antihypertensive drugs) and 39 in CHSC (58.0 +/- 2.0 years; BP 153.6 +/- 2.3/91.9 +/- 2.0; PRA 4.6 +/- 1.1; 2.7 +/- 0.2 drugs).

RESULTS

BP was controlled in 28/38 (74% (RTGT)) vs. 23/39 (59% (CHSC)), P = 0.17, falling to 127.9 +/- 2.3/73.1 +/- 1.8 vs. 134.0 +/- 2.8/79.8 +/- 1.9 mm Hg, respectively. Systolic BP (SBP) fell more with RTGT (-29.1 +/- 3.2 vs. -19.2 +/- 3.2 mm Hg, P = 0.03), whereas diastolic BP (DBP) declined similarly (P = 0.32). Although final antihypertensive drug numbers were similar (3.1 +/- 0.2 (RTGT) vs. 3.0 +/- 0.3 (CHSC), P = 0.73) in "V" patients, 60% (RTGT) vs. 11% (CHSC) of "R" drugs were withdrawn and BP medications were reduced (-0.5 +/- 0.3 vs. +0.7 +/- 0.3, P = 0.01).

CONCLUSIONS

In treated but uncontrolled hypertension, RTGT improves control and lowers BP equally well or better than CHSC, indicating that RTGT provides a reasonable strategy for correcting treated but uncontrolled hypertension.

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.

Newer Insights into the Biochemical Physiology of the Renin–Angiotensin System: Role of Angiotensin-(1-7), Angiotensin Converting Enzyme 2, and Angiotensin-(1-12)

Knowledge of the mechanisms by which the rennin–angiotensin system contributes to cardiovascular pathology continues to advance at a rapid pace as newer methods and therapies uncover the nature of this complex system and its fundamental role in the regulation of blood pressure and tissue function. The characterization of the biochemical pathways and functions mediated by angiotensin-(1-7) [Ang-(1-7)], angiotensin converting enzyme 2 (ACE2), and the mas receptor has revealed a vasodepressor and antiproliferative axis that within the rennin–angiotensin system opposes the biological actions of angiotensin II (Ang II). In addition, new research expands on this knowledge by demonstrating additional mechanisms for the formation of Ang II and Ang-(1-7) through the existence of an alternate form of the angiotensinogen substrate [angiotensin-(1-12)] which generates Ang II and even Ang-(1-7) through a non-renin dependent action. Altogether, this research paves the way for a better understanding of the intracellular mechanisms involved in the synthesis of angiotensin peptides and its consequences in terms of cell function in both physiology and pathology.