Renin inhibition with aliskiren: where are we now, and where are we going?

Effective Management of Hypertensive Emergencies with Aliskiren Treatment in a Patient before and after Introducing Hemodialysis Secondary to Scleroderma Renal Crisis-like Condition under Corticosteroid Treatment for Sjögren Syndrome-associated Multiple Mononeuropathy

A middle-aged woman presented with hypertensive emergency after corticosteroid treatment for Sjögren syndrome-associated multiple mononeuropathy with suspected systemic sclerosis. Hypertensive heart failure with hyperreninemia improved with antihypertensives, including aliskiren; however, she became hemodialysis-dependent. Clinical findings and biopsy-proven thrombotic microangiopathy indicated conditions resembling scleroderma renal crisis (SRC). Severe hypertension and heart failure with hyperreninemia occurred after stopping aliskiren for hypotension due to diverticular bleeding, which improved after the reintroduction of aliskiren. Aliskiren appears to be effective in managing hypertensive heart failure in patients with SRC. Nevertheless, hemodialysis remained necessary in our case, and whether or not aliskiren can restore the renal function is unclear.

N-(Heteroaryl)thiophene sulfonamides as angiotensin AT2 receptor ligands

Two series of N-(heteroaryl)thiophene sulfonamides, encompassing either a methylene imidazole group or a tert-butylimidazolylacetyl group in the meta position of the benzene ring, have been synthesized. An AT2R selective ligand with a Ki of 42 nM was identified in the first series and in the second series, six AT2R selective ligands with significantly improved binding affinities and Ki values of <5 nM were discovered. The binding modes to AT2R were explored by docking calculations combined with molecular dynamics simulations. Although some of the high affinity ligands exhibited fair stability in human liver microsomes, comparable to that observed with C21 undergoing clinical trials, most ligands displayed a very low metabolic stability with t½ of less than 10 min in human liver microsomes. The most promising ligand, with an AT2R Ki value of 4.9 nM and with intermediate stability in human hepatocytes (t½ = 77 min) caused a concentration-dependent vasorelaxation of pre-contracted mouse aorta.

Nanoparticle approaches for the renin-angiotensin system

The renin-angiotensin system (RAS) is a hormonal cascade that contributes to several disorders: systemic hypertension, heart failure, kidney disease, and neurodegenerative disease. Activation of the RAS can promote inflammation and fibrosis. Drugs that target the RAS can be classified into 3 categories, AT1 angiotensin receptor blockers (ARBs), angiotensin-converting enzyme (ACE) inhibitors, and renin inhibitors. The therapeutic efficacy of current RAS-inhibiting drugs is limited by poor penetration across the blood-brain barrier, low bioavailability, and to some extent, short half-lives. Nanoparticle-mediated drug delivery systems (DDSs) are possible emerging alternatives to overcome such limitations. Nanoparticles are ideally 1-100 nm in size and are considered efficient DDSs mainly due to their unique characteristics, including water dispersity, prolonged half-life in blood circulation, smaller size, and biocompatibility. Nano-scale DDSs can reduce the drug dosage frequency and acute toxicity of drugs while enhancing therapeutic success. Different types of nanoparticles, such as chitosan, polymeric, and nanofibers, have been examined in RAS-related studies, especially in hypertension, cardiovascular disease, and COVID-19. In this review article, we summarize the physical and chemical characteristics of each nanoparticle to elaborate on their potential use in RAS-related nano-drug delivery research and clinical application.

Cluster analysis of angiotensin biomarkers to identify antihypertensive drug treatment in population studies

BACKGROUND

The recent progress in molecular biology generates an increasing interest in investigating molecular biomarkers as markers of response to treatments. The present work is motivated by a study, where the objective was to explore the potential of the molecular biomarkers of renin-angiotensin-aldosterone system (RAAS) to identify the undertaken antihypertensive treatments in the general population. Population-based studies offer an opportunity to assess the effectiveness of treatments in real-world scenarios. However, lack of quality documentation, especially when electronic health record linkage is unavailable, leads to inaccurate reporting and classification bias.

METHOD

We present a machine learning clustering technique to determine the potential of measured RAAS biomarkers for the identification of undertaken treatments in the general population. The biomarkers were simultaneously determined through a novel mass-spectrometry analysis in 800 participants of the Cooperative Health Research In South Tyrol (CHRIS) study with documented antihypertensive treatments. We assessed the agreement, sensitivity and specificity of the resulting clusters against known treatment types. Through the lasso penalized regression, we identified clinical characteristics associated with the biomarkers, accounting for the effects of cluster and treatment classifications.

RESULTS

We identified three well-separated clusters: cluster 1 (n = 444) preferentially including individuals not receiving RAAS-targeting drugs; cluster 2 (n = 235) identifying angiotensin type 1 receptor blockers (ARB) users (weighted kappa κw = 74%; sensitivity = 73%; specificity = 83%); and cluster 3 (n = 121) well discriminating angiotensin-converting enzyme inhibitors (ACEi) users (κw = 81%; sensitivity = 55%; specificity = 90%). Individuals in clusters 2 and 3 had higher frequency of diabetes as well as higher fasting glucose and BMI levels. Age, sex and kidney function were strong predictors of the RAAS biomarkers independently of the cluster structure.

CONCLUSIONS

Unsupervised clustering of angiotensin-based biomarkers is a viable technique to identify individuals on specific antihypertensive treatments, pointing to a potential application of the biomarkers as useful clinical diagnostic tools even outside of a controlled clinical setting.

Discovery of Novel 2-Carbamoyl Morpholine Derivatives as Highly Potent and Orally Active Direct Renin Inhibitors

The renin-angiotensin-aldosterone system (RAAS) plays a key role in the regulation of blood pressure. Renin, the first and rate-limiting enzyme of the RAAS, is an attractive target for the treatment of hypertension and cardiovascular/renal diseases. Therefore, various direct renin inhibitors (DRIs) have been researched over recent decades; however, most exhibited poor pharmacokinetics and oral bioavailability due to the peptidomimetic or nonpeptidomimetic structures with a molecular weight (MW) of >600, and only aliskiren is approved. This study introduces a novel class of DRIs comprised of a 2-carbamoyl morpholine scaffold. These compounds have a nonpeptidomimetic structure and a MW of <500. The representative compound 26 was highly potent despite not occupying S1'-S2' sites or the opened flap region used by other DRIs and exerted a significant antihypertensive efficacy via oral administration on double transgenic mice carrying both the human angiotensinogen and the human renin genes.

Discovery of SPH3127: A Novel, Highly Potent, and Orally Active Direct Renin Inhibitor

Renin is the rate-limiting enzyme in the renin-angiotensin-aldosterone system (RAAS) which regulates blood pressure and renal function and hence is an attractive target for the treatment of hypertension and cardiovascular/renal diseases. However, the development of direct renin inhibitors (DRIs) with favorable oral bioavailability has been a longstanding challenge for many years. This problem was thought to be because most of the reported DRIs were peptide-like structures or nonpeptide-like structures with a molecular weight (MW) of > 600. Therefore, we tried to find nonpeptidomimetic DRIs with a MW of < 500 and discovered the promising 2-carbamoyl morpholine derivative 4. In our efforts to improve the pharmacokinetic profile of 4 without a significant increase in the MW, we discovered compound 18 (SPH3127), which demonstrated higher bioavailability and a more potent antihypertensive effect in preclinical models than aliskiren and has completed a phase II clinical trial for essential hypertension.

N-(Methyloxycarbonyl)thiophene sulfonamides as high affinity AT2 receptor ligands

A series of meta-substituted acetophenone derivatives, encompassing N-(alkyloxycarbonyl)thiophene sulfonamide fragments have been synthesized. Several selective AT2 receptor ligands were identified, among those a tert-butylimidazole derivative (20) with a K_i of 9.3 nM, that demonstrates a high stability in human liver microsomes (t_½ = 62 min) and in human hepatocytes (t_½ = 194 min). This methyloxycarbonylthiophene sulfonamide is a 20-fold more potent binder to the AT2 receptor and is considerably more stable in human liver microsomes, than a previously reported and broadly studied structurally related AT₂R prototype antagonist 3 (C38). Ligand 20 acts as an AT₂R agonist and caused an AT₂R mediated concentration-dependent vasorelaxation of pre-contracted mouse aorta. Furthermore, in contrast to imidazole derivative C38, the tert-butylimidazole derivative 20 is a poor inhibitor of CYP3A4, CYP2D6 and CYP2C9. It is demonstrated herein that smaller alkyloxycarbonyl groups make the ligands in this series of AT₂R selective compounds less prone to degradation and that a high AT2 receptor affinity can be retained after truncation of the alkyloxycarbonyl group. Binding modes of the most potent AT₂R ligands were explored by docking calculations combined with molecular dynamics simulations.

ACE2 as a Therapeutic Target for COVID-19; its Role in Infectious Processes and Regulation by Modulators of the RAAS System

Angiotensin converting enzyme 2 (ACE2) is the recognized host cell receptor responsiblefor mediating infection by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). ACE2bound to tissue facilitates infectivity of SARS-CoV-2; thus, one could argue that decreasing ACE2tissue expression would be beneficial. However, ACE2 catalytic activity towards angiotensin I (AngI) and II (Ang II) mitigates deleterious effects associated with activation of the renin-angiotensinaldosteronesystem (RAAS) on several organs, including a pro-inflammatory status. At the tissuelevel, SARS-CoV-2 (a) binds to ACE2, leading to its internalization, and (b) favors ACE2 cleavage toform soluble ACE2: these actions result in decreased ACE2 tissue levels. Preserving tissue ACE2activity while preventing ACE2 shredding is expected to circumvent unrestrained inflammatoryresponse. Concerns have been raised around RAAS modulators and their effects on ACE2expression or catalytic activity. Various cellular and animal models report conflicting results invarious tissues. However, recent data from observational and meta-analysis studies in SARS-CoV-2-infected patients have concluded that RAAS modulators do not increase plasma ACE2 levels orsusceptibility to infection and are not associated with more severe diseases. This review presentsour current but evolving knowledge of the complex interplay between SARS-CoV-2 infection, ACE2levels, modulators of RAAS activity and the effects of RAAS modulators on ACE2 expression.

Evolution of Angiotensin Peptides and Peptidomimetics as Angiotensin II Receptor Type 2 (AT2) Receptor Agonists

Angiotensin II receptor type 1 and 2 (AT1R and AT2R) are two G-protein coupled receptors that mediate most biological functions of the octapeptide Angiotensin II (Ang II). AT2R is upregulated upon tissue damage and its activation by selective AT2R agonists has become a promising approach in the search for new classes of pharmaceutical agents. We herein analyzed the chemical evolution of AT2R agonists starting from octapeptides, through shorter peptides and peptidomimetics to the first drug-like AT2R-selective agonist, C21, which is in Phase II clinical trials and aimed for idiopathic pulmonary fibrosis. Based on the recent crystal structures of AT1R and AT2R in complex with sarile, we identified a common binding model for a series of 11 selected AT2R agonists, consisting of peptides and peptidomimetics of different length, affinity towards AT2R and selectivity versus AT1R. Subsequent molecular dynamics simulations and free energy perturbation (FEP) calculations of binding affinities allowed the identification of the bioactive conformation and common pharmacophoric points, responsible for the key interactions with the receptor, which are maintained by the drug-like agonists. The results of this study should be helpful and facilitate the search for improved and even more potent AT2R-selective drug-like agonists.

The use of aliskiren as an antifibrotic drug in experimental models: A systematic review

Aliskiren is an oral antihypertensive medication that acts by directly inhibiting renin. High levels of circulating renin and prorenin activate the pathological signaling pathway of fibrosis. This drug also reduces oxidative stress. Thus, the aim of this systematic review is to analyze experimental studies that show the actions of aliskiren on fibrosis. PubMed and LILACS databases were consulted using the keywords aliskiren and fibrosis within the period between 2005 and 2017. Fifty-three articles were analyzed. In the heart, aliskiren attenuated remodeling, hypertrophy, inflammatory cytokines, collagen deposition, and oxidative stress. In the kidneys, there was a reduction in interstitial fibrosis, the infiltration of inflammatory cells, apoptosis, proteinuria, and in the recruitment of macrophages. In diabetic models, an improvement in the albumin/creatinine relationship and in the insulin pathway in skeletal muscles was observed; aliskiren was beneficial to pancreatic function and glucose tolerance. In the liver, aliskiren reduced fibrosis, steatosis, inflammatory cytokines, and collagen deposition. In the lung and peritoneal tissues, there was a reduction in fibrosis. Many studies have reported on the beneficial effects of aliskiren on endothelial function and arterial rigidity. A reduction in fibrosis in different organs is cited by many authors, which complies with the results found in this review. However, studies diverge on the use of the drug in diabetic patients. Aliskiren has antifibrotic potential in several experimental models, interfering with the levels of fibrogenic cytokines and oxidative stress. Therefore, its use in diseases in which fibrosis plays an important pathophysiological role is suggested.

Renin Activity in Heart Failure with Reduced Systolic Function-New Insights

Regardless of the cause, symptomatic heart failure (HF) with reduced ejection fraction (rEF) is characterized by pathological activation of the renin–angiotensin–aldosterone system (RAAS) with sodium retention and extracellular fluid expansion (edema). Here, we review the role of active renin, a crucial, upstream enzymatic regulator of the RAAS, as a prognostic and diagnostic plasma biomarker of heart failure with reduced ejection fraction (HFrEF) progression; we also discuss its potential as a pharmacological bio-target in HF therapy. Clinical and experimental studies indicate that plasma renin activity is elevated with symptomatic HFrEF with edema in patients, as well as in companion animals and experimental models of HF. Plasma renin activity levels are also reported to be elevated in patients and animals with rEF before the development of symptomatic HF. Modulation of renin activity in experimental HF significantly reduces edema formation and the progression of systolic dysfunction and improves survival. Thus, specific assessment and targeting of elevated renin activity may enhance diagnostic and therapeutic precision to improve outcomes in appropriate patients with HFrEF.

Long-term safety and tolerability of valsartan in children aged 6 to 17 years with hypertension

OBJECTIVE

The present study aimed to assess the long-term safety and tolerability of valsartan in hypertensive children aged 6-17 years, with or without chronic kidney disease (CKD).

METHODS

This was an 18-month, open-label, multicentre, prospective study conducted in 150 patients with history of hypertension with or without CKD. The primary endpoint was long-term safety and tolerability of valsartan and valsartan-based treatments, assessed in terms of adverse events (AEs), serious AEs, laboratory measurements, estimated glomerular filtration rate (eGFR), urinalysis and electrocardiogram.

RESULTS

Of 150 enrolled patients, 117 (78%) completed the study. At week 78, a clinically and statistically significant reduction in mean sitting systolic and diastolic blood pressures was observed in all patients (- 14.9 mmHg and - 10.6 mmHg, respectively). Within the first 3 months of treatment, mean urine albumin creatinine ratio decreased in CKD population, which was sustained. A higher percentage of CKD patients had at least one AE compared to non-CKD patients (85.3% vs. 73.3%, respectively). The majority of AEs were mild (50.7%) or moderate (18.7%) in severity. As expected, in patients with underlying CKD, increases in serum potassium, creatinine and blood urea nitrogen were more commonly reported compared to non-CKD patients. A > 25% decrease in Schwartz eGFR was observed in 28.4% of CKD patients and 13.5% of non-CKD patients.

CONCLUSIONS

Valsartan was generally well tolerated, with an AE profile consistent with angiotensin receptor blockers in the overall population and in patients with underlying CKD. Long-term efficacy was maintained and a beneficial effect on proteinuria was observed.

The comparative efficacy of renin-angiotensin system blockers in schistosomal hepatic fibrosis

Schistosomiasis mansoni is involved in hepatic fibrogenesis and portal hypertension. Previous studies proved that blockade of some components of the renin-angiotensin system (RAS) reduce liver fibrogenesis. However, the effects of inhibition of early stages of RAS pathway in schistosomal fibrosis have not been studied yet. Thus, the aim of this study was to compare the role of different antihypertensive drugs on hepatic fibrosis in murine schistosomiasis. BALB/c mice (n = 50) weighing 20g were subjected to inoculation of 50 cercariae and submitted to different treatments: aliskiren, 50 mg/kg (n = 10); bradykinin, 2 μg/kg (n = 5); losartan, 10 mg/kg (n = 10); lisinopril 10 mg/kg (n = 5) and control, proportional volume vehicle (n = 5); daily for 14 weeks. Six animals were not subjected to cercariae inoculation or any type of treatment. Ultrasound, histological, immunohistochemical and proteomic analyzes were performed to evaluate markers associated with hepatic fibrogenesis. The hepatic areas stained with Sirius red and thenumber of cells marked by α-SMA in animals treated with aliskiren, bradykinin, lisinopril and losartan were diminished when compared to control group, demonstrating reduced hepatic fibrosis after RAS blockade. These results were reinforced by ultrasonography analysis and protein expression of TGFβ. These findings demonstrated the effect of RAS inhibition on hepatic fibrosis in murine schistosomiasis, with the most evident results being observed in the losartan and aliskiren treated groups. The main mechanisms underlying this process appear to involve anti-fibrogenic activity through the inhibition of collagen and TGFβ synthesis.

Sequence, Structural Analysis and Metrics to Define the Unique Dynamic Features of the Flap Regions Among Aspartic Proteases

Aspartic proteases are a class of hydrolytic enzymes that have been implicated in a number of diseases such as HIV, malaria, cancer and Alzheimer's. The flap region of aspartic proteases is a characteristic unique structural feature of these enzymes; and found to have a profound impact on protein overall structure, function and dynamics. Flap dynamics also plays a crucial role in drug binding and drug resistance. Therefore, understanding the structure and dynamic behavior of this flap regions is crucial in the design of potent and selective inhibitors against aspartic proteases. Defining metrics that can describe the flap motion/dynamics has been a challenging topic in literature. This review is the first attempt to compile comprehensive information on sequence, structure, motion and metrics used to assess the dynamics of the flap region of different aspartic proteases in "one pot". We believe that this review would be of critical importance to the researchers from different scientific domains.

Effects of Direct Renin Blockade on Renal & Systemic Hemodynamics and on RAAS Activity, in Weight Excess and Hypertension: A Randomized Clinical Trial

Aim

The combination of weight excess and hypertension significantly contributes to cardiovascular risk and progressive kidney damage. An unfavorable renal hemodynamic profile is thought to contribute to this increased risk and may be ameliorated by direct renin inhibition (DRI). The aim of this trial was to assess the effect of DRI on renal and systemic hemodynamics and on RAAS activity, in men with weight excess and hypertension.

Methods

A randomized, double-blind, cross-over clinical trial to determine the effect of DRI (aliskiren 300 mg/day), with angiotensin converting enzyme inhibition (ACEi; ramipril 10 mg/day) as a positive control, on renal and systemic hemodynamics, and on RAAS activity (n = 15).

Results

Mean (SEM) Glomerular filtration rate (101 (5) mL/min/1.73m²) remained unaffected by DRI or ACEi. Effective renal plasma flow (ERPF; 301 (14) mL/min/1.73m²) was increased in response to DRI (320 (14) mL/min/1.73m², P = 0.012) and ACEi (317 (15) mL/min/1.73m², P = 0.045). Filtration fraction (FF; 34 (0.8)%) was reduced by DRI only (32 (0.7)%, P = 0.044). Mean arterial pressure (109 (2) mmHg) was reduced by DRI (101 (2) mmHg, P = 0.008) and ACEi (103 (3) mmHg, P = 0.037). RAAS activity was reduced by DRI and ACEi. Albuminuria (20 [9–42] mg/d) was reduced by DRI only (12 [5–28] mg/d, P = 0.030).

Conclusions

In men with weight excess and hypertension, DRI and ACEi improved renal and systemic hemodynamics. Both DRI and ACEi reduced RAAS activity. Thus, DRI provides effective treatment in weight excess and hypertension.

Trial Registration

Dutch trial register, registration number: 2532 www.trialregister.nl

New therapeutic agents in diabetic nephropathy

Studies investigating diabetic nephropathy (DN) have mostly focused on interpreting the pathologic molecular mechanisms of DN, which may provide valuable tools for early diagnosis and prevention of disease onset and progression. Currently, there are few therapeutic drugs for DN, which mainly consist of antihypertensive and antiproteinuric measures that arise from strict renin-angiotensin-aldosterone system inactivation. However, these traditional therapies are suboptimal and there is a clear, unmet need for treatments that offer effective schemes beyond glucose control. The complexity and heterogeneity of the DN entity, along with ambiguous renal endpoints that may deter accurate appraisal of new drug potency, contribute to a worsening of the situation. To address these issues, current research into original therapies to treat DN is focusing on the intrinsic renal pathways that intervene with intracellular signaling of anti-inflammatory, antifibrotic, and metabolic pathways. Mounting evidence in support of the favorable metabolic effects of these novel agents with respect to the renal aspects of DN supports the likelihood of systemic beneficial effects as well. Thus, when translated into clinical use, these novel agents would also address the comorbid factors associated with diabetes, such as obesity and risk of cardiovascular disease. This review will provide a discussion of the promising and effective therapeutic agents for the management of DN.

Aliskiren effect on non-alcoholic steatohepatitis in metabolic syndrome

BACKGROUND

Non-alcoholic steatohepatitis (NASH) is highly associated with metabolic syndrome, a major cause of morbidity in the globalized society. The renin-angiotensin system (RAS) influences hepatic fatty acid metabolism, inflammation and fibrosis. Thus, in the present study, we aimed to evaluate the effect of aliskiren, a direct renin inhibitor, on metabolic syndrome-related NASH.

METHODS

C57BL/6 male mice (n = 45) were divided into three groups: controls; animals inoculated with streptozotocin (STZ) (40 mg/kg/day) for 5 days and fed with high fat diet (HFD) for 8 weeks; and animals inoculated with STZ for 5 days, fed with HFD for 8 weeks and treated with aliskiren (100 mg/kg/day) for the final 2 weeks. Glycemic and insulin levels, hepatic lipid profile, histological parameters and inflammatory protein expression were analyzed.

RESULTS

Aliskiren normalized plasma glucose and insulin levels, reduced cholesterol, triglycerides and total fat accumulation in liver and diminished hepatic injury, steatosis and fibrosis. These results could be explained by the ability of aliskiren to block angiotensin-II, lowering oxidative stress and inflammation in liver. Also, it exhibited a beneficial effect in increasing insulin sensitivity.

CONCLUSION

These findings support the use of aliskiren in the treatment of metabolic syndrome underlying conditions. However, clinical studies are indispensable to test its effectiveness in the treatment of patients with metabolic syndrome.

Aliskiren for Renin Inhibition: A New Class of Antihypertensives

Objective:

To review the safety, efficacy, pharmacology, pharmacokinetics, and drug interactions of aliskiren for the treatment of mild-to-moderate hypertension.

Data Sources:

A literature search was conducted using MEDLINE (1966'January 2007), International Pharmaceutical Abstracts (1970'January 2007), and Cochrane database (2006) for the key words aliskiren or SPP100. References of selected articles were also reviewed. Abstract data were included only in the absence of significant published data.

Study Selection And Data Extraction:

Available English-language data from reviews, abstracts, and clinical trials were selected. For review of efficacy, randomized controlled trials were preferred.

Data Synthesis:

Aliskiren is a renin inhibitor, the first in a new class of antihypertensives. As renin catalyzes the rate-limiting step of the renin–angiotensin system (RAS), renin inhibition may offer a theoretical advantage over other RAS inhibitors, such as angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs). In short-term clinical trials (≤8 wk) of subjects with mild-to-moderate hypertension, single daily doses of aliskiren 150–300 mg produced significant systolic and diastolic blood pressure reduction similar to that achieved with ACE inhibitors and ARBs, with placebo-like tolerability, without an elevation in heart rate or evidence of tolerance.

Conclusions:

Aliskiren appears to be a safe and effective treatment option in mild-to-moderate hypertension. Although long-term outcome data have not been published, aliskiren is a promising option for RAS inhibition.

Pathophysiological Mechanisms and Correlates of Therapeutic Pharmacological Interventions in Essential Arterial Hypertension

Treating arterial hypertension (HT) remains a hard task. The hypertensive patient is often a subject with several comorbidities and metabolic abnormalities. Clinicians everyday have to choose the right drug for the single patient among the different classes of antihypertensives. Apart from lowering blood pressure, a main therapeutic target should be that of counteracting all the possible pathophysiological mechanisms involved in HT itself and in existing/potential comorbidities. All the ancillary positive and negative effects of the administered drugs should be considered: in particular, since hypertensive patients are often glucose intolerant/diabetic, carrier of serum lipids disorder, have already developed atherosclerotic diseases and endothelial dysfunction, they should not be treated with drugs negatively interfering with these conditions but with molecules that, if possible, improve them. The main pathophysiological mechanisms and correlates of therapeutic pharmacological interventions in essential HT are reviewed here.

Antihypertensive Efficacy of the Direct Renin Inhibitor Aliskiren as Add-on Therapy in Patients with Poorly Controlled Hypertension

OBJECTIVE

A direct renin inhibitor, aliskiren, has a longer stable antihypertensive effect compared with other renin-angiotensin-aldosterone system (RAAS) inhibitors.

METHODS

This study was a 6-month, single-center, open trial conducted between December 2010 and November 2011 to assess the antihypertensive effect of adding aliskiren (300 mg) to the treatment of essential hypertension patients whose target blood pressure (BP) had not been achieved and to assess whether it was possible to reduce the amount of antihypertensive drugs used.

RESULTS

The results showed an overall improvement in the target BP achievement rate of 60% for clinic BP and 52% for home BP measurements (75 cases total). The mean number of drugs before treatment with aliskiren was 3.28±1.52, whereas at the end of the six months the mean number of drugs prescribed other than aliskiren was 2.85±1.72 (p<0.0001). Moreover, no worsening of the renal function was observed in patients with diabetes or chronic kidney disease (CKD) who were being treated with other RAAS inhibitors in combination to aliskiren.

CONCLUSION

These results showed that when aliskiren was added to the treatment of poorly controlled hypertension, the BP achievement rate increased, and it was possible to reduce the amount of antihypertensive drugs used in combination with aliskiren. Moreover, as a result of careful monitoring of the renal function or decreasing the amounts of drugs used in combination, no worsening of the renal function was observed even in the cases complicated by diabetes or CKD being treated with other RAAS inhibitors.

Effects of treatment withdrawal on brachial and central aortic pressure after direct renin inhibition or angiotensin receptor blockade

INTRODUCTION

Whilst sustained lowering of brachial systolic blood pressure (Br-SBP) and central aortic systolic pressure (CASP) have been demonstrated in patients with hypertension, effects of treatment withdrawal on these parameters have not been investigated. The ASSERTIVE study previously reported more sustained control of Br-SBP with aliskiren versus telmisartan in patients with hypertension, following 7-days treatment withdrawal. In this ASSERTIVE sub-study, we hypothesised that aliskiren would similarly exert more sustained control of CASP than telmisartan during treatment withdrawal.

METHODS

We investigated the effects of treatment withdrawal on both Br-SBP and CASP following 12-weeks treatment with either aliskiren (300 mg) or telmisartan (80 mg). Br-SBP and CASP were measured at the end of treatment, and at days 2 and 7 following treatment withdrawal in 303 patients (CASP randomised set).

RESULTS

Of the CASP randomised set, 94 patients completed CASP measurements at all time points (CASP completer set). After 7 days of treatment withdrawal, aliskiren demonstrated lesser increases in both Br-SBP and CASP than telmisartan; Br-SBP change: -2.0±1.6 vs. +5.6±1.7 mmHg, p = 0.001; CASP change: -0.4±1.6 vs. +4.6±1.7 mmHg, p = 0.041, n = 94. Similar findings were obtained for the CASP randomised set.

CONCLUSIONS

Following treatment withdrawal, aliskiren demonstrated more sustained control of both brachial and central SBP than telmisartan.

Neuropeptides: metabolism to bioactive fragments and the pharmacology of their receptors

The proteolytic processing of neuropeptides has an important regulatory function and the peptide fragments resulting from the enzymatic degradation often exert essential physiological roles. The proteolytic processing generates, not only biologically inactive fragments, but also bioactive fragments that modulate or even counteract the response of their parent peptides. Frequently, these peptide fragments interact with receptors that are not recognized by the parent peptides. This review discusses tachykinins, opioid peptides, angiotensins, bradykinins, and neuropeptide Y that are present in the central nervous system and their processing to bioactive degradation products. These well-known neuropeptide systems have been selected since they provide illustrative examples that proteolytic degradation of parent peptides can lead to bioactive metabolites with different biological activities as compared to their parent peptides. For example, substance P, dynorphin A, angiotensin I and II, bradykinin, and neuropeptide Y are all degraded to bioactive fragments with pharmacological profiles that differ considerably from those of the parent peptides. The review discusses a selection of the large number of drug-like molecules that act as agonists or antagonists at receptors of neuropeptides. It focuses in particular on the efforts to identify selective drug-like agonists and antagonists mimicking the effects of the endogenous peptide fragments formed. As exemplified in this review, many common neuropeptides are degraded to a variety of smaller fragments but many of the fragments generated have not yet been examined in detail with regard to their potential biological activities. Since these bioactive fragments contain a small number of amino acid residues, they provide an ideal starting point for the development of drug-like substances with ability to mimic the effects of the degradation products. Thus, these substances could provide a rich source of new pharmaceuticals. However, as discussed herein relatively few examples have so far been disclosed of successful attempts to create bioavailable, drug-like agonists or antagonists, starting from the structure of endogenous peptide fragments and applying procedures relying on stepwise manipulations and simplifications of the peptide structures.

trans-(3S,4S)-Disubstituted pyrrolidines as inhibitors of the human aspartyl protease renin. Part I: prime site exploration using an amino linker

Recently, we reported on the discovery of (3S,4S)-disubstituted pyrrolidines (e.g., 2) as inhibitors of the human aspartyl protease renin. In our effort to further expand the scope of this novel class of direct renin inhibitors, a new sub-series was designed in which the prime site substituents are linked to the pyrrolidine core by a (3S)-amino functional group. In particular, analogs bearing the corresponding sulfonamide spacer (50, 51 and 54a) demonstrated a pronounced increase in in vitro potency compared to compound 2.

Effects of the inhibition of intestinal P-glycoprotein on aliskiren pharmacokinetics in cynomolgus monkeys

Aliskiren is a substrate for P-glycoprotein (P-gp) and is metabolized via cytochrome P450 3A4 (CYP3A4). The aim of the present study was to assess whether P-gp influenced the pharmacokinetics of aliskiren and also if drug-drug interactions (DDIs) mediated through P-gp could be reproduced in cynomolgus monkeys. The study investigated the pharmacokinetics of aliskiren in mdr1a/1b gene-deficient (P-gp KO) and wild-type (WT) mice. The area under the plasma concentration-time curve (AUC) following the oral administration of aliskiren was 6.9-fold higher in P-gp KO mice than in WT mice, while no significant differences were observed in the AUC or total plasma clearance following the intravenous administration of aliskiren to P-gp KO mice. Then the pharmacokinetics of aliskiren were evaluated and DDIs between aliskiren and P-gp inhibitors, such as cyclosporin A (CsA) and zosuquidar, examined in cynomolgus monkeys. The AUC for aliskiren were 8.3- and 42.1-fold higher after the oral administration of aliskiren with the concomitant oral administration of zosuquidar and CsA at doses of 10 and 30 mg/kg, respectively. In contrast, the AUC after the intravenous and oral administration of aliskiren was not significantly affected by the oral administration of zosuquidar or intravenous administration of CsA, respectively. These results indicated that P-gp strictly limited the intestinal absorption of aliskiren in mice and monkeys, and also that the effects of intestinal P-gp inhibition by CsA or zosuquidar on the pharmacokinetics of aliskiren were sensitively reproduced in monkeys. In conclusion, aliskiren can be used as a sensitive substrate to evaluate intestinal P-gp inhibition in monkeys.

Aliskiren, the first direct renin inhibitor: assessing a role in pediatric hypertension and kidney diseases

This article provides a review of the role of aliskiren, a direct renin inhibitor, in pediatric hypertension and kidney diseases. Among the many mechanisms involved in regulating blood pressure, the renin-angiotensin-aldosterone system (RAAS) plays a major role. Additionally, the RAAS has been identified as a contributing factor to cardiovascular and renal diseases for more than three decades. The potential benefits of inhibiting the RAAS by aliskiren alone or in combination with other RAAS blockers (ACEIs, ARBs) seem to be theoretically promising. However, caution should be exercised in treating children, especially in those with significant chronic kidney disease until there is more evidence regarding the safety and efficacy of this new drug in the pediatric population from ongoing clinical trials.

Aliskiren, the future of renin–angiotensin system blockade?

The suppression of the renin-angiotensin system by angiotensin-converting enzyme inhibitors and angiotensin receptor blockers has been proven in many studies to treat hypertension and reduce cardiovascular events; however, reducing angiotensin I receptor stimulation results in the loss of the negative-feedback signal, leading to increased plasma renin activity. Numerous direct renin inhibitors were synthesized, but abandoned owing to low potency, poor bioavailability and short half-life. Aliskiren, a direct renin inhibitor of a novel structural class, inhibits the activity of the renin produced and, thus, its capacity to form angiotensin I, as measured by plasma renin activity. Aliskiren has been recently shown to be efficacious in hypertensive patients at once-daily oral dosing with favorable pharmacokinetics and the potential to improve end-organ protection.

Aliskiren toxicity in juvenile rats is determined by ontogenic regulation of intestinal P-glycoprotein expression

Juvenile rat toxicity studies with the direct renin inhibitor aliskiren were initiated to support treatment in the pediatric population. In Study 1, aliskiren was administered orally to juvenile rats at doses of 0, 30, 100 or 300 mg/kg/day with repeated dosing from postpartum day (PPD) 8 to PPD 35/36. In-life, clinical pathology, anatomic pathology, and toxicokinetics evaluations were performed. In Study 2, single oral doses of aliskiren (0, 100 or 300 mg/kg) were given to 14-, 21-, 24-, 28-, 31- or 36-day-old rats; in-life data and toxicokinetics were evaluated. Study 3 was a single dose (3 mg/kg i.v.) pharmacokinetic study in juvenile rats on PPD 8, 14, 21 and 28. In Study 4, naïve rats were used to investigate ontogenic changes of the multidrug-resistant protein 1 (MDR1) and the organic anion transporting polypeptide (OATP) mRNA in several organs. Oral administration of aliskiren at 100 and 300 mg/kg caused unexpected mortality and severe morbidity in 8-day-old rats. Aliskiren plasma and tissue concentrations were increased in rats aged 21days and younger. Expression of MDR1 and OATP mRNA in the intestine, liver and brain was significantly lower in very young rats. In conclusion, severe toxicity and increased exposure in very young rats after oral administration of aliskiren are considered to be the result of immature drug transporter systems. Immaturity of MDR1 in enterocytes appears to be the most important mechanism responsible for the high exposure.

Renin-sensitive microRNAs correlate with atherosclerosis plaque progression

Recent trials with inhibition of the renin-angiotensin-aldosterone system (RAAS) in patients with established atherosclerosis have been equivocal. MicroRNAs (miRs) are known to affect multiple pathways relevant to atherosclerosis, including RAAS. We postulated that the use of a direct renin antagonist would result in differential regulation of miRs. We examined monocyte miR expression before and after treatment with renin antagonist, Aliskiren, in patients with established cardiovascular disease as part of a prospective, single-center, randomized, double-blind and placebo-controlled clinical trial (NCT01417104). After screening, patients (mean age 62±3 years) were randomized to placebo or Aliskiren. Three-dimensional dark-blood magnetic resonance imaging assessment of atherosclerosis in the thoracic and abdominal aorta was conducted at baseline and at study completion (19-36 weeks). MiR expression arrays were performed on RNA from peripheral blood mononuclear cells collected at baseline and 12 weeks following randomization to placebo or Aliskiren and showed that hsa-miR-106b-5p, 27a-3p and 18b-5p were significantly downregulated with Aliskiren. Baseline expression of these miRs positively correlated with normalized total wall volume in subjects taking Aliskiren (miR-106b, R=0.62; miR-27a, R=0.63; miR-18b, R=0.77; P<0.05). Hsa-miR-106b-5p, 27a-3p and 18b-5p may represent pathway-specific adaptations to renin inhibition relevant to atherosclerosis.

Aliskiren: review of efficacy and safety data with focus on past and recent clinical trials

Aliskiren is the newest antihypertensive drug and the first orally active direct renin inhibitor to become available for clinical use. Clinical data have substantiated that the antihypertensive effectiveness of aliskiren is similar to that of the other major antihypertensive agents. Furthermore, aliskiren has a similar safety profile to placebo. Combination treatment with aliskiren showed significant blood pressure and proteinuria reductions compared with monotherapy. Aliskiren decreases plasma renin activity in contrast to other renin-angiotensin-aldosterone related drugs. The efficacy of aliskiren in treating major cardiovascular events and the prevention of end-organ damage are being investigated in the ASPIRE HIGHER program. Although the first studies of the ASPIRE HIGHER program such as ALOFT, AVOID, AGELESS showed favorable findings, ASPIRE and AVANT-GARDE studies provided contradictory results. Subsequently, the ALTITUDE study was terminated early because of safety issues and lack of beneficial effects. Most recently, the ASTRONAUT trial showed no reduction in cardiovascular death or heart failure rehospitalization with the addition of aliskiren to standard therapy in patients who were hospitalized for heart failure and with reduced left-ventricular ejection fraction. The results of ongoing studies in other patient groups such as the ATMOSPHERE trial are awaited.

Renin inhibitors and cardiovascular and renal protection: an endless quest?

Renin-angiotensin system (RAS) blockade with angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) has become a major therapeutic approach in medicine since the end of the 1970's. Although these molecules were the first RAS blockers to be developed, it would have been physiologically and pharmacologically more pertinent to selectively inhibit renin itself. Indeed, the reaction between renin and its unique substrate, angiotensinogen, is the highly regulated and rate-limiting step of the RAS. The development of direct renin inhibitors (DRI) has been a slow and complex process and the synthesis of the first orally active DRI, aliskiren, was only achieved in the 2000's. Its pharmacological profile in patients with hypertension, diabetic nephropathy or heart failure, in addition to experimental evidence, suggests that aliskiren may be of value for the management of cardiovascular and renal diseases. However, the long-term, randomized, placebo-controlled, morbidity/mortality trial, ALTITUDE, which included 8,600 patients with type 2 diabetes, proteinuria and a high cardiovascular risk already treated with ACE inhibitors or ARBs was terminated in December 2011 because of futility and an increased incidence of serious adverse events in the aliskiren 300 mg arm. Other long-term studies are still ongoing to demonstrate the safety and efficacy of aliskiren to reduce cardiovascular morbidity and mortality in patients with heart failure and in elderly individuals (≥65 years) with systolic blood pressure of 130 to 159 mmHg, no overt cardiovascular disease, and a high cardiovascular risk profile. In the meantime, according to the European Medicines Agency recommendations, aliskiren should not be prescribed to diabetic patients in combination with ACE inhibitors or ARBs.

Potential of RAS inhibition to improve metabolic bone disorders

Metabolic bone disorder is usually caused by abnormalities of minerals and hormones metabolism. Recently, it has been proved by several studies that the renin-angiotensin system (RAS) in local bone tissue is directly involved in bone metabolism. Activation of skeletal RAS plays an important role in bone metabolic disorders. Based on in vitro, in vivo, and clinical studies, this review explains the roles of RAS in bone metabolism and also covers the potential approaches and beneficial effects of RAS inhibition on bone health. Differential strategies for inhibiting RAS can be employed to maintain bone health, which are attributed primarily to the reduced level of angiotensin II (AngII) and suppressed stimulation of the AngII signaling pathway. The use of renin inhibitors, angiotensin-converting enzyme inhibitors, and AngII receptor blockers either individually or in combination with each other could have promising results in fighting bone metabolic disorders associated with other cardiovascular diseases as well as independent bone injuries.

Aliskiren effect on plaque progression in established atherosclerosis using high resolution 3D MRI (ALPINE): a double-blind placebo-controlled trial

Background

The renin–angiotensin system is well recognized as a mediator of pathophysiological events in atherosclerosis. The benefits of renin inhibition in atherosclerosis, especially when used in combination with angiotensin-converting enzyme inhibitors/angiotensin receptor blockers (ACEIs/ARBs) are currently not known. We hypothesized that treatment with the renin inhibitor aliskiren in patients with established cardiovascular disease will prevent the progression of atherosclerosis as determined by high-resolution magnetic resonance imaging (MRI) measurements of arterial wall volume in the thoracic and abdominal aortas of high-risk patients with preexisting cardiovascular disease.

Methods and Results

This was a single-center, randomized, double-blind, placebo-controlled trial in patients with established cardiovascular disease. After a 2-week single-blind placebo phase, patients were randomized to receive either placebo (n=37, mean±SD age 64.5±8.9 years, 3 women) or 150 mg of aliskiren (n=34, mean±SD age 63.9±11.5 years, 9 women). Treatment dose was escalated to 300 mg at 2 weeks and maintained during the remainder of the study. Patients underwent dark-blood, 3-dimensional MRI assessment of atherosclerotic plaque in the thoracic and abdominal segments at baseline and on study completion or termination (up to 36 weeks of drug or matching placebo). Aliskiren use resulted in significant progression of aortic wall volume (normalized total wall volume 5.31±6.57 vs 0.15±4.39 mm³, P=0.03, and percentage wall volume 3.37±2.96% vs 0.97±2.02%, P=0.04) compared with placebo. In a subgroup analysis of subjects receiving ACEI/ARB therapy, atherosclerosis progression was observed only in the aliskiren group, not in the placebo group.

Conclusions

MRI quantification of atheroma plaque burden demonstrated that aliskiren use in patients with preexisting cardiovascular disease resulted in an unexpected increase in aortic atherosclerosis compared with placebo. Although preliminary, these results may have implications for the use of renin inhibition as a therapeutic strategy in patients with cardiovascular disease, especially in those receiving ACEI/ARB therapy.

Clinical Trial Registration

URL: http://ClinicalTrials.gov Unique identifier: NCT01417104.

Effectiveness and safety of aliskiren and aliskiren hydrochlorothiazide (HCT) in a multiethnic, real-world setting

INTRODUCTION

Numerous randomized clinical trials have demonstrated the efficacy and tolerability of aliskiren and aliskiren hydrochlorothiazide (aliskiren HCT) single-pill combination therapy in patients with hypertension. The objective of the present study was to evaluate the effectiveness and safety of aliskiren-based therapy under daily life conditions in a multiethnic population.

METHODS

This observational, multicenter, noninterventional study, conducted at 420 centers in Asia and the Middle East, included adult patients with hypertension who received treatment with aliskiren or aliskiren HCT as single or add-on therapy for a planned treatment period of at least 26 weeks. The main effectiveness assessments included the proportion of patients achieving therapeutic blood pressure (BP) goal (defined as systolic BP [SBP]/diastolic BP [DBP]<140/90 mmHg, or <130/80 mmHg in patients with diabetes) and BP response, and change in mean sitting BP from baseline to study end.

RESULTS

Of 4,826 patients (mean age 51.4 years, 65.9% male, 64.5% Asian, 41.5% diabetic) included in the study, 3,473 received aliskiren and 1,353 received aliskiren HCT. Almost half the study population (48.1%) received aliskiren or aliskiren HCT as add-on therapy. The therapeutic BP goal was achieved in 49.5% of patients treated with aliskiren and 48.3% of patients receiving aliskiren HCT; attainment of BP goal increased to more than 70% when a classic BP target of <140/90 mmHg was applied for all patients. Reductions in mean sitting SBP/DBP were significantly lower versus baseline for both aliskiren (24.1/12.2 mmHg) and aliskiren HCT (27.6/14.1 mmHg) and BP response rates were consistently achieved in more than 80% of all patients during the study. Aliskiren treatment was well tolerated with only a small proportion of patients experiencing adverse events (AEs; 2.1%) and serious AEs (0.3%).

CONCLUSION

In this real-world, naturalistic setting, antihypertensive treatment with an aliskiren-based regimen was effective and well-tolerated in this multiethnic population with arterial hypertension.

Discovery of inhibitors of insulin-regulated aminopeptidase as cognitive enhancers

The hexapeptide angiotensin IV (Ang IV) is a metabolite of angiotensin II (Ang II) and plays a central role in the brain. It was reported more than two decades ago that intracerebroventricular injection of Ang IV improved memory and learning in the rat. Several hypotheses have been put forward to explain the positive effects of Ang IV and related analogues on cognition. It has been proposed that the insulin-regulated aminopeptidase (IRAP) is the main target of Ang IV. This paper discusses progress in the discovery of inhibitors of IRAP as potential enhancers of cognitive functions. Very potent inhibitors of the protease have been synthesised, but pharmacokinetic issues (including problems associated with crossing the blood-brain barrier) remain to be solved. The paper also briefly presents an overview of the status in the discovery of inhibitors of ACE and renin, and of AT1R antagonists and AT2R agonists, in order to enable other discovery processes within the RAS system to be compared. The paper focuses on the relationship between binding affinities/inhibition capacity and the structures of the ligands that interact with the target proteins.