Determinants of angiotensin II generation during converting enzyme inhibition

(Pro)renin Receptor and Blood Pressure Regulation: A Focus on the Central Nervous System

The renin-angiotensin system (RAS) is classically described as a hormonal system in which angiotensin II (Ang II) is one of the main active peptides. The action of circulating Ang II on its cognate Ang II type-1 receptor (AT1R) in circumventricular organs has important roles in regulating the autonomic nervous system, blood pressure (BP) and body fluid homeostasis, and has more recently been implicated in cardiovascular metabolism. The presence of a local or tissue RAS in various tissues, including the central nervous system (CNS), is well established. However, because the level of renin, the rate-limiting enzyme in the systemic RAS, is very low in the brain, how endogenous angiotensin peptides are generated in the CNS-the focus of this review-has been the subject of considerable debate. Notable in this context is the identification of the (pro)renin receptor (PRR) as a key component of the brain RAS in the production of Ang II in the CNS. In this review, we highlight cellular and anatomical locations of the PRR in the CNS. We also summarize studies using gain- and loss-of function approaches to elucidate the functional importance of brain PRR-mediated Ang II formation and brain RAS activation, as well as PRR-mediated Ang II-independent signaling pathways, in regulating BP. We further discuss recent developments in PRR involvement in cardiovascular and metabolic diseases and present perspectives for future directions.

The Human Explanted Heart Program: A translational bridge for cardiovascular medicine

The progression of cardiovascular research is often impeded by the lack of reliable disease models that fully recapitulate the pathogenesis in humans. These limitations apply to both in vitro models such as cell-based cultures and in vivo animal models which invariably are limited to simulate the complexity of cardiovascular disease in humans. Implementing human heart tissue in cardiovascular research complements our research strategy using preclinical models. We established the Human Explanted Heart Program (HELP) which integrates clinical, tissue and molecular phenotyping thereby providing a comprehensive evaluation into human heart disease. Our collection and storage of biospecimens allow them to retain key pathogenic findings while providing novel insights into human heart failure. The use of human non-failing control explanted hearts provides a valuable comparison group for the diseased explanted hearts. Using HELP we have been able to create a tissue repository which have been used for genetic, molecular, cellular, and histological studies. This review describes the process of collection and use of explanted human heart specimens encompassing a spectrum of pediatric and adult heart diseases, while highlighting the role of these invaluable specimens in translational research. Furthermore, we highlight the efficient procurement and bio-preservation approaches ensuring analytical quality of heart specimens acquired in the context of heart donation and transplantation.

Should ACE inhibitors and ARBs be used in combination in children?

The renin-angiotensin-aldosterone system (RAAS) plays a pivotal role in a host of renal and cardiovascular functions. Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs), drugs that disrupt RAAS function, are effective in treating hypertension and offer other renoprotective effects independent of blood pressure (BP) reduction. As our understanding of RAAS physiology and the feedback mechanisms of ACE inhibition and angiotensin receptor blockade have improved, questions have been raised as to whether combination ACEI/ARB therapy is warranted in certain patients with incomplete angiotensin blockade on one agent. In this review, we discuss the rationale for combination ACEI/ARB therapy and summarize the results of key adult studies and the limited pediatric literature that have investigated this therapeutic approach. We additionally review novel therapies that have been developed over the past decade as alternative approaches to combination ACEI/ARB therapy, or that may be potentially used in combination with ACEIs or ARBs, in which further adult and pediatric studies are needed.

Renin angiotensin aldosterone inhibition in the treatment of cardiovascular disease

A collective century of discoveries establishes the importance of the renin angiotensin aldosterone system in maintaining blood pressure, fluid volume and electrolyte homeostasis via autocrine, paracrine and endocrine signaling. While research continues to yield new functions of angiotensin II and angiotensin-(1-7), the gap between basic research and clinical application of these new findings is widening. As data accumulates on the efficacy of angiotensin converting enzyme inhibitors and angiotensin II receptor blockers as drugs of fundamental importance in the treatment of cardiovascular and renal disorders, it is becoming apparent that the achieved clinical benefits is suboptimal and surprisingly no different than what can be achieved with other therapeutic interventions. We discuss this issue and summarize new pathways and mechanisms effecting the synthesis and actions of angiotensin II. The presence of renin-independent non-canonical pathways for angiotensin II production are largely unaffected by agents inhibiting renin angiotensin system activity. Hence, new efforts should be directed to develop drugs that can effectively block the synthesis and/or action of intracellular angiotensin II. Improved drug penetration into cardiac or renal sites of disease, inhibiting chymase the primary angiotensin II forming enzyme in the human heart, and/or inhibiting angiotensinogen synthesis would all be more effective strategies to inhibit the system. Additionally, given the role of angiotensin II in the maintenance of renal homeostatic mechanisms, any new inhibitor should possess greater selectivity of targeting pathogenic angiotensin II signaling processes and thereby limit inappropriate inhibition.

Angiotensin-converting enzyme 2 amplification limited to the circulation does not protect mice from development of diabetic nephropathy

Blockers of the renin-angiotensin system are effective in the treatment of experimental and clinical diabetic nephropathy. An approach different from blocking the formation or action of angiotensin II (1-8) that could also be effective involves fostering its degradation. Angiotensin-converting enzyme 2 (ACE2) is a monocarboxypeptidase that cleaves angiotensin II (1-8) to form angiotensin (1-7). Therefore, we examined the renal effects of murine recombinant ACE2 in mice with streptozotocin-induced diabetic nephropathy as well as that of amplification of circulating ACE2 using minicircle DNA delivery prior to induction of experimental diabetes. This delivery resulted in a long-term sustained and profound increase in serum ACE2 activity and enhanced ability to metabolize an acute angiotensin II (1-8) load. In mice with streptozotocin-induced diabetes pretreated with minicircle ACE2, ACE2 protein in plasma increased markedly and this was associated with a more than 100-fold increase in serum ACE2 activity. However, minicircle ACE2 did not result in changes in urinary ACE2 activity as compared to untreated diabetic mice. In both diabetic groups, glomerular filtration rate increased significantly and to the same extent as compared to non-diabetic controls. Albuminuria, glomerular mesangial expansion, glomerular cellularity, and glomerular size were all increased to a similar extent in minicircle ACE2-treated and untreated diabetic mice, as compared to non-diabetic controls. Recombinant mouse ACE2 given for 4 weeks by intraperitoneal daily injections in mice with streptozotocin-induced diabetic nephropathy also failed to improve albuminuria or kidney pathology. Thus, a profound augmentation of ACE2 confined to the circulation failed to ameliorate the glomerular lesions and hyperfiltration characteristic of early diabetic nephropathy. These findings emphasize the importance of targeting the kidney rather than the circulatory renin angiotensin system to combat diabetic nephropathy.

Pharmacodynamic Impact of Carboxylesterase 1 Gene Variants in Patients with Congestive Heart Failure Treated with Angiotensin-Converting Enzyme Inhibitors

BACKGROUND

Variation in the carboxylesterase 1 gene (CES1) may contribute to the efficacy of ACEIs. Accordingly, we examined the impact of CES1 variants on plasma angiotensin II (ATII)/angiotensin I (ATI) ratio in patients with congestive heart failure (CHF) that underwent ACEI dose titrations. Five of these variants have previously been associated with drug response or increased CES1 expression, i.e., CES1 copy number variation, the variant of the duplicated CES1 gene with high transcriptional activity, rs71647871, rs2244613, and rs3815583. Additionally, nine variants, representatives of CES1Var, and three other CES1 variants were examined.

METHODS

Patients with CHF, and clinical indication for ACEIs were categorized according to their CES1 genotype. Differences in mean plasma ATII/ATI ratios between genotype groups after ACEI dose titration, expressed as the least square mean (LSM) with 95% confidence intervals (CIs), were assessed by analysis of variance.

RESULTS

A total of 200 patients were recruited and 127 patients (63.5%) completed the study. The mean duration of the CHF drug dose titration was 6.2 (SD 3.6) months. After ACEI dose titration, there was no difference in mean plasma ATII/ATI ratios between subjects with the investigated CES1 variants, and only one previously unexplored variation (rs2302722) qualified for further assessment. In the fully adjusted analysis of effects of rs2302722 on plasma ATII/ATI ratios, the difference in mean ATII/ATI ratio between the GG genotype and the minor allele carriers (GT and TT) was not significant, with a relative difference in LSMs of 0.67 (95% CI 0.43-1.07; P = 0.10). Results of analyses that only included enalapril-treated patients remained non-significant after Bonferroni correction for multiple parallel comparisons (difference in LSM 0.60 [95% CI 0.37-0.98], P = 0.045).

CONCLUSION

These findings indicate that the included single variants of CES1 do not significantly influence plasma ATII/ATI ratios in CHF patients treated with ACEIs and are unlikely to be primary determinants of ACEI efficacy.

Combined Treatment With Angiotensin-Converting Enzyme Inhibitors and Angiotensin II Receptor Blockers: A Review of the Current Evidence

Several studies have shown that angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers are useful in the treatment of hypertension, cardiovascular disease, chronic heart failure, and some types of nephropathy. In this context, dual renin-angiotensin system blockade with both angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers may be more effective than treatment with each agent alone. Many clinical trials have demonstrated the beneficial effect of this combined treatment on proteinuria, hypertension, heart failure, and cardiovascular events. Moreover, these studies demonstrated that dual renin-angiotensin system blockade is generally safe and well tolerated. Long-term studies are under way to confirm these effects and also investigate the effectiveness of dual reninangiotensin system blockade on cerebrovascular disease and prevention of type 2 diabetes mellitus. These studies are expected to define the optimal use of combination treatment in everyday clinical practice. This review considers the most important clinical trials that evaluated the effect of dual renin-angiotensin system blockade on blood pressure, heart failure, and renal function.

Use of plasma renin activity to monitor mineralocorticoid treatment in dogs with primary hypoadrenocorticism: desoxycorticosterone versus fludrocortisone

Background

Measurement of plasma renin activity (PRA) is the gold standard for monitoring mineralocorticoid treatment in humans with primary hypoadrenocorticism (PH).

Objectives

To compare PRA in dogs with newly diagnosed PH, dogs with diseases mimicking PH, and healthy dogs, and evaluate measurement of PRA to monitor therapeutic effects in dogs with PH treated with different mineralocorticoids.

Animals

Eleven dogs with newly diagnosed PH (group 1), 10 dogs with diseases mimicking PH (group 2), 21 healthy dogs (group 3), 17 dogs with treated PH (group 4).

Methods

In group 1, PRA was measured before treatment and at different times after initiating treatment. In groups 2 and 3, PRA was measured at initial presentation only. In group 4, no baseline PRA was obtained but PRA was measured once or every 1–6 months during treatment. Mineralocorticoid treatment consisted of fludrocortisone acetate (FC) or desoxycorticosterone pivalate (DOCP).

Results

Plasma renin activity before treatment was increased in dogs with PH compared to normal dogs and dogs with diseases mimicking PH with median activity of 27, 0.8, and 1.0 ng/mL/h, respectively. In dogs with PH, PRA decreased and normalized with mineralocorticoid treatment using DOCP but not with FC. In dogs treated with DOCP, PRA was lower than in dogs treated with FC. Plasma sodium concentrations were higher and potassium concentrations were lower with DOCP treatment compared to FC treatment.

Conclusion and Clinical Importance

Plasma renin activity is a reliable tool for monitoring mineralocorticoid treatment. DOCP treatment more effectively suppresses PRA compared to FC in dogs with PH.

A core promoter variant of angiotensinogen gene and interindividual variation in response to angiotensin-converting enzyme inhibitors

INTRODUCTION

The polymorphic angiotensinogen (AGT) gene is one of the most promising candidates for essential hypertension. The aim of this study was to examine the association between the A-6G variant of the AGT gene and the blood pressure response to angiotensin-converting enzyme (ACE) inhibitors in hypertensive subjects.

METHODS

Five hundred and nine mildly to moderately hypertensive subjects received ACE inhibitors for six weeks after a two-week run-in period. AGT genotyping was performed by direct polymerase chain reaction amplification and deoxyribonucleic acid (DNA) nucleotide sequencing from peripheral blood.

RESULTS

The AA genotype, AG genotype, and GG genotype were present in 301 (59.1%), 186 (36.6%), and 22 (4.3%) of patients, respectively. As compared with patients carrying the AA or AG genotype, those carrying the GG genotype had significantly greater reductions in systolic blood pressure, diastolic blood pressure, pulse pressure and mean arterial pressure (p=0.007, 0.014, 0.027 and 0.005, respectively). Moreover, stepwise multiple linear regression analysis showed that the A-6G genotype was a significant predictor of systolic blood pressure and pulse pressure reductions (p=0.040 and 0.019, respectively).

CONCLUSION

Our study indicates that the A-6G variant of the AGT gene may be an important determinant of interindividual variation in the response to ACE inhibitors.

Manipulating angiotensin metabolism with angiotensin converting enzyme 2 (ACE2) in heart failure

•

Heart failure is increasing in prevalence associated with a huge economic burden.

•

ACE2 is a negative regulator of the renin–angiotensin system.

•

Elevated ACE2 activity is a biomarker in heart failure.

•

Enhancing ACE2 action may have unique therapeutic effects in patients with heart failure.

Angiotensin converting enzyme 2 (ACE2), is a monocarboxypeptidase which metabolizes several peptides including the degradation of Ang II, a peptide with vasoconstrictive/proliferative/effects, to generate Ang 1–7, which acting through its receptor Mas exerts vasodilatory/anti-proliferative actions. The classical pathway of the RAS involving the ACE-Ang II-AT₁ receptor axis is antagonized by the second arm constituted by the ACE2-Ang 1–7/Mas receptor axis. Loss of ACE2 enhances the adverse pathological remodeling susceptibility to pressure-overload and myocardial infarction. Human recombinant ACE2 is also a negative regulator of Ang II-induced myocardial hypertrophy, fibrosis and diastolic dysfunction and suppresses pressure-overload induced heart failure. Due to its characteristics, the ACE2-Ang 1–7/Mas axis may represent new possibilities for developing novel therapeutic strategies for the treatment of heart failure. Human recombinant ACE2 has been safely administered to healthy human volunteers intravenously resulting in sustained lowering of plasma Ang II levels. In this review, we will summarize the beneficial effects of ACE2 in heart disease and the potential use of human recombinant ACE2 as a novel therapy for heart failure.

Use of the ACE inhibitor zofenopril in the treatment of ischemic heart disease

Zofenopril, an inhibitor of the angiotensin-converting enzyme (ACE), has recently been widely introduced into the pharmaceutical market. Its clinical safety and efficacy has been demonstrated in patients with hypertension and in patients with acute myocardial infarction (AMI). The Survival of Myocardial Infarction Long-term Evaluation (SMILE) project provided valuable information regarding the safety of early onset ACE inhibition with zofenopril after AMI and a greater perception of the early and late benefits. The SMILE-I study demonstrated that most benefits of ACE inhibition may be obtained early after AMI and persist after discontinuation of treatment. The SMILE-II study demonstrated that early zofenopril treatment (initiated <12 h) is safe and associated with a low rate of severe hypotension in thrombolyzed patients with acute myocardial infarction when administered in accordance with an adequate dose-titration scheme. Many other studies of clinical ACE-inhibitors (ACEIs) over the last 30 years have provided us with information in order to understand the effects of ACEIs and have demonstrated that patients benefit from ACEI treatment at different stages of the pathophysiological continuum of cardiovascular diseases. The current guidelines recommend that ACEIs should be used for routine secondary prevention in all patients with coronary artery disease and should be considered for all other patients with coronary or other vascular disease unless contraindicated.

Role of angiotensin-converting enzyme 2 (ACE2) in diabetic cardiovascular complications

Diabetes mellitus results in severe cardiovascular complications, and heart disease and failure remain the major causes of death in patients with diabetes. Given the increasing global tide of obesity and diabetes, the clinical burden of diabetes-induced cardiovascular disease is reaching epidemic proportions. Therefore urgent actions are needed to stem the tide of diabetes which entails new prevention and treatment tools. Clinical and pharmacological studies have demonstrated that AngII (angiotensin II), the major effector peptide of the RAS (renin–angiotensin system), is a critical promoter of insulin resistance and diabetes mellitus. The role of RAS and AngII has been implicated in the progression of diabetic cardiovascular complications and AT1R (AngII type 1 receptor) blockers and ACE (angiotensin-converting enzyme) inhibitors have shown clinical benefits. ACE2, the recently discovered homologue of ACE, is a monocarboxypeptidase which converts AngII into Ang-(1–7) [angiotensin-(1–7)] which, by virtue of its actions on the MasR (Mas receptor), opposes the effects of AngII. In animal models of diabetes, an early increase in ACE2 expression and activity occurs, whereas ACE2 mRNA and protein levels have been found to decrease in older STZ (streptozotocin)-induced diabetic rats. Using the Akita mouse model of Type 1 diabetes, we have recently shown that loss of ACE2 disrupts the balance of the RAS in a diabetic state and leads to AngII/AT1R-dependent systolic dysfunction and impaired vascular function. In the present review, we will discuss the role of the RAS in the pathophysiology and treatment of diabetes and its complications with particular emphasis on potential benefits of the ACE2/Ang-(1–7)/MasR axis activation.

Evaluation of a rapid pressor response test in healthy cats

OBJECTIVE

To evaluate angiotensin I and angiotensin II rapid pressor response tests in healthy cats.

ANIMALS

6 purpose-bred sexually intact male cats.

PROCEDURES

Telemetric blood pressure (BP) implants were placed in all cats. After 2 weeks, cats were anesthetized for challenge with exogenous angiotensin I or angiotensin II. Continuous direct arterial BP was recorded during and immediately after IV administration of boluses of angiotensin I or angiotensin II at increasing doses. Blood pressure responses were evaluated for change in systolic BP (SBP), change in diastolic BP (DBP), and rate of increase of SBP by 4 observers.

RESULTS

Following IV angiotensin I and angiotensin II administration, transient, dose-dependent increases in BP (mean ± SEM change in SBP, 25.7 ± 5.2 and 45.0 ± 9.1; change in DBP, 23.4 ± 4.7 mm Hg and 36.4 ± 7.8 mm Hg; for 100 ng of angiotensin I/kg and angiotensin II/kg, respectively) and rate of increase of SBP were detected. At angiotensin I and II doses < 2.0 ng/kg, minimal responses were detected, with greater responses at doses ranging from 20 to 1,000 ng/kg. A significant effect of observer was not found. No adverse effects were observed.

CONCLUSIONS AND CLINICAL RELEVANCE

The rapid pressor response test elicited dose-dependent, transient increases in SBP and DBP. The test has potential as a means of objectively evaluating the efficacy of various modifiers of the renin-angiotensin-aldosterone system in cats. Ranges of response values are provided for reference in future studies.

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.

Where hypertension happens

Essential hypertension, which accounts for 90%-95% of all cases of hypertension seen in the clinic, is also referred to as idiopathic hypertension, because we simply don't understand the cause(s). Although many theories have been advanced, in the current issue of the JCI, Gonzalez-Villalobos et al. present further evidence implicating the intrarenal renin-angiotensin system and take us one step further by proposing a mechanism underlying this pathology.

An integrated physiology-based model for the interaction of RAA system biomarkers with drugs

The renin angiotensin aldosterone system (RAAS) is a paramount target for the pharmacological treatment of cardiovascular diseases. As modeling and simulation techniques are becoming increasingly utilized in cardiovascular research, our aim was to develop a physiology-based model that describes the effect of different drugs at different doses on the RAAS and integrates physiology-based description drug pharmacokinetics (PK). First, a basic RAAS model was developed in which equations for drug effects were included and missing parameters estimated. Next, a physiology-based PK model for enalapril and enalaprilat was developed and coupled to the RAAS model. Simulation of the effects of angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and aliskiren administration on angiotensins I and II did not reveal significant overestimation or underestimation. For all drugs, the error numerics were acceptable. The model also encompassed the PK of intravenous and oral enalapril and its conversion to enalaprilat. In summary, we report a physiology-based model for the interaction of the RAAS biomarkers angiotensin I and II with enalapril, benazepril, aliskiren, and losartan that allows for an adequate description of the RAAS response after single administration of the drugs. Such a comprehensive description may lead to a better understanding of the effects of pharmacological interventions in the RAAS.

A detailed physiologically based model to simulate the pharmacokinetics and hormonal pharmacodynamics of enalapril on the circulating endocrine Renin-Angiotensin-aldosterone system

The renin-angiotensin-aldosterone system (RAAS) plays a key role in the pathogenesis of cardiovascular disorders including hypertension and is one of the most important targets for drugs. A whole body physiologically based pharmacokinetic (wb PBPK) model integrating this hormone circulation system and its inhibition can be used to explore the influence of drugs that interfere with this system, and thus to improve the understanding of interactions between drugs and the target system. In this study, we describe the development of a mechanistic RAAS model and exemplify drug action by a simulation of enalapril administration. Enalapril and its metabolite enalaprilat are potent inhibitors of the angiotensin-converting-enzyme (ACE). To this end, a coupled dynamic parent-metabolite PBPK model was developed and linked with the RAAS model that consists of seven coupled PBPK models for aldosterone, ACE, angiotensin 1, angiotensin 2, angiotensin 2 receptor type 1, renin, and prorenin. The results indicate that the model represents the interactions in the RAAS in response to the pharmacokinetics (PK) and pharmacodynamics (PD) of enalapril and enalaprilat in an accurate manner. The full set of RAAS-hormone profiles and interactions are consistently described at pre- and post-administration steady state as well as during their dynamic transition and show a good agreement with literature data. The model allows a simultaneous representation of the parent-metabolite conversion to the active form as well as the effect of the drug on the hormone levels, offering a detailed mechanistic insight into the hormone cascade and its inhibition. This model constitutes a first major step to establish a PBPK-PD-model including the PK and the mode of action (MoA) of a drug acting on a dynamic RAAS that can be further used to link to clinical endpoints such as blood pressure.

Haemodynamic effects of aliskiren in decompensated severe heart failure

Aim: The renin–angiotensin–aldosterone system (RAAS) has dual pathways to angiotensin II production; therefore, multiple blockages may be useful in heart failure. In this study, we evaluated the short-term haemodynamic effects of aliskiren, a direct renin inhibitor, in patients with decompensated severe heart failure who were also taking angiotensin-converting enzyme (ACE) inhibitors.

Materials and methods: A total of 16 patients (14 men, two women, mean age: 60.3 years) were enrolled in the study. The inclusion criteria included hospitalisation due to decompensated heart failure, ACE inhibitor use, and an ejection fraction < 40% (mean: 21.9 ± 6.7%). The exclusion criteria were: creatinine > 2.0 mg/dl, cardiac pacemaker, serum K+ > 5.5 mEq/l, and systolic blood pressure < 70 mmHg. Patients either received 150 mg/d aliskiren for 7 days (aliskiren group, n = 10) or did not receive aliskiren (control group, n = 6). Primary end points were systemic vascular resistance and cardiac index values. Repeated-measures analysis of variance (ANOVA) was used to assess variables before and after intervention. A two-sided p-value < 0.05 was considered statistically significant.

Results: Compared to pre-intervention levels, systemic vascular resistance was reduced by 20.4% in aliskiren patients, but it increased by 2.9% in control patients ( p = 0.038). The cardiac index was not significantly increased by 19.0% in aliskiren patients, but decreased by 8.4% in control patients ( p = 0.127). No differences in the pulmonary capillary or systolic blood pressure values were observed between the groups.

Conclusion: Aliskiren use reduced systemic vascular resistance in patients with decompensated heart failure taking ACE inhibitors.

Active renin mass concentration to determine aldosterone-to-renin ratio in screening for primary aldosteronism

Background:

Active renin mass concentration (ARC) is independent of the endogenous level of angiotensinogen, and less variable and more reproducible than plasma renin activity. Reference values for the aldosterone-to-renin ratio (ARR) using ARC are still undefined. The objective of the present study was to determine the threshold of ARR using ARC measurement to screen for primary aldosteronism.

Methods:

A total of 211 subjects were included in the study, comprising 78 healthy normotensive controls, 95 patients with essential hypertension, and 38 patients with confirmed primary aldosteronism (20 with surgery-confirmed aldosterone-producing adenoma and 18 with idiopathic adrenal hyperplasia). Blood samples were drawn from ambulatory patients and volunteers in the mid-morning without specific dietary restriction for measuring plasma aldosterone concentration, ARC, and serum potassium.

Results:

Most normotensive controls and essential hypertension patients had ARR results below 100 pmol/ng, a value which corresponded to 3.3 times the median of these two groups.

Conclusion:

Patients with ARR values above this level should be considered for further investigation (confirmatory tests) or for repeat testing should ARR values be borderline. This study indicates that ARC can be used reliably in determining ARR for primary aldosteronism screening.

Potential benefits of aliskiren beyond blood pressure reduction

There is now clear evidence that reducing blood pressure (BP) with a broad range of agents, including angiotensin converting enzyme inhibitors and angiotensin receptor blockers, improves cardiovascular and renal outcomes. There is also evidence suggesting that these drugs have beneficial effects that are independent of BP lowering. Aliskiren is a direct renin inhibitor that interrupts the renin-angiotensin-aldosterone system (RAAS) at its rate-limiting step. Unlike angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, aliskiren produces a sustained reduction in plasma renin activity and reduces plasma levels of angiotensin II and aldosterone. Preclinical data and clinical trials in high-risk patients using surrogate markers increasingly suggest that aliskiren can reduce the progression of end-organ damage beyond that afforded by BP control. With its unique mechanism of action, combining aliskiren with another RAAS-blocking agent that has a different mechanism of action may provide more comprehensive blockade of the RAAS, potentially conferring additional clinical benefits. Evaluation of these end-organ effects in humans is underway in clinical trials designed to assess the effects of aliskiren alone and in combination with other antihypertensive agents on cardiovascular and renal outcomes.

Angiotensin-converting enzyme inhibition augments the expression of rat elastase-2, an angiotensin II-forming enzyme

Mounting evidence suggest that tissue levels of angiotensin (ANG) II are maintained in animals submitted to chronic angiotensin-converting enzyme (ACE) inhibitor treatment. We examined the expression levels of transcripts for elastase-2, a chymostatin-sensitive serine protease identified as the alternative pathway for ANG II generation from ANG I in the rat vascular tissue and the relative role of ACE-dependent and -independent pathways in generating ANG II in the rat isolated carotid artery rings of spontaneously hypertensive rats (SHR) and Wistar normotensive rats (WNR) treated with enalapril for 7 days. Enalapril treatment decreased blood pressure of SHR only and resulted in significantly more elastase-2 mRNA expression in carotid artery of both enalapril-treated WNR and SHR. Captopril induced a comparable rightward shift of concentration-response curves to ANG I in vehicle and enalapril-treated rats, although this effect was of lesser magnitude in SHR group. Chymostatin induced a rightward shift of the dose response to ANG I in vehicle-treated and a decrease in maximal effect of 22% in enalapril-treated WNR group. Maximal response induced by ANG I was remarkably reduced by chymostatin in enalapril-treated SHR carotid artery (by 80%) compared with controls (by 23%). Our data show that chronic ACE inhibition was associated with augmented functional role of non-ACE pathway in generating ANG II and increased elastase-2 gene expression, suggesting that this protease may contribute as an alternative pathway for ANG II generation when ACE is inhibited in the rat vascular tissue.

Antihypertensive and organ-protective effects of benazepril

Benazepril is a nonsulfhydryl ACE inhibitor with favorable pharmacodynamic and pharmacokinetic properties, well-established antihypertensive effects and a good tolerability profile. Recent clinical studies have demonstrated that patients treated with benazepril alone or in combination with hydrochlorothiazide or amlodipine may achieve beneficial renal outcomes that extend beyond blood pressure control. Furthermore, the recent Avoiding Cardiovascular Events Through Combination Therapy in Patients Living with Systolic Hypertension (ACCOMPLISH) trial showed decreased cardiovascular morbidity and mortality with benazepril when administered as a cotreatment. An additional novel therapeutic area for benazepril is atrial fibrillation. Differences between combination therapies have implications for which patients may be best suited to particular interventions, and further studies are required to fully ascertain this potential.

The relationship between ACE gene insertion/deletion polymorphism and diabetic retinopathy in Iranian patients with type 2 diabetes

BACKGROUND

The role of genetic factors in diabetic retinopathy (DR) is unclear. We investigated the relationship between DR and an insertion/deletion polymorphism in the angiotensin-converting enzyme (ACE) gene in Iranian patients with type 2 diabetes without overt nephropathy.

METHODS

A total of 178 consecutive type 2 diabetic patients with DR (Group A) and 206 type 2 diabetic patients without DR (Group B) were studied. The following variables were determined: age, sex, body mass index, diabetes duration, medications used, history of coronary artery disease and its complications, blood pressure (systolic and diastolic), fasting plasma glucose, hemoglobin A1c, total cholesterol, low- and high-density lipoproteins, triglycerides, plasma creatinine, and 24-h urine albumin excretion.

RESULTS

The groups were statistically similar in all variables except diabetes duration (P = 0.037), ACE activity (P < 0.001), and ACE genotype (P = 0.008). The DD genotype was significantly more common in Group A (32.6% versus 19.2% in Group B; P = 0.009). In multivariate regression analysis, the ID genotype (compared to the II genotype) was an independent predictor of DR (OR = 1.831, 95% CI = 1.074-3.124; P = 0.026).

CONCLUSIONS

The D allele of the ACE gene is independently associated with DR in Iranian type 2 diabetic patients.

Blocking the RAAS at different levels: an update on the use of the direct renin inhibitors alone and in combination

The renin–angiotensin–aldosterone system (RAAS), an important regulator of blood pressure and mediator of hypertension-related complications, is a prime target for cardiovascular drug therapy. Angiotensin-converting enzyme inhibitors (ACEIs) were the first drugs to be used to block the RAAS. Angiotensin II receptor blockers (ARBs) have also been shown to be equally effective for treatment. Although these drugs are highly effective and are widely used in the management of hypertension, current treatment regimens with ACEIs and ARBs are unable to completely suppress the RAAS. Combinations of ACEIs and ARBs have been shown to be superior than to either agent alone for some, but certainly not all, composite cardiovascular and kidney outcomes, but dual RAAS blockade with the combination of an ACEI and an ARB is sometimes associated with an increase in the risk for adverse events, primarily hyperkalemia and worsening renal function. The recent introduction of the direct renin inhibitor, aliskiren, has made available new combination strategies to obtain a more complete blockade of the RAAS with fewer adverse events. Renin system blockade with aliskiren and another RAAS agent has been, and still is, the subject of many large-scale clinical trials and furthermore, is already available in some countries as a fixed combination.

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).

The role of the renin-angiotensin-aldosterone system in cardiovascular progenitor cell function

Intervention in the RAAS (renin-angiotensin-aldosterone system) is one of the leading pharmacotherapeutic strategies, among others, used for the treatment of cardiovascular disease to improve the prognosis after myocardial infarction and to reduce hypertension. Recently, regenerative progenitor cell therapy has emerged as a possible alternative for pharmacotherapy in patients after myocardial infarction or ischaemic events elsewhere, e.g. in the limbs. Angiogenic cell therapy to restore the vascular bed in ischaemic tissues is currently being tested in a multitude of clinical studies. This has prompted researchers to investigate the effect of modulation of the RAAS on progenitor cells. Furthermore, the relationship between hypertension and endothelial progenitor cell function is being studied. Pharmacotherapy by means of angiotensin II type 1 receptor antagonists or angiotensin-converting enzyme inhibitors has varying effects on progenitor cell levels and function. These controversial effects may be explained by involvement of multiple mediators, e.g. angiotensin II and angiotensin-(1-7), that have differential effects on mesenchymal stem cells, haematopoietic progenitor cells and endothelial progenitor cells. Importantly, angiotensin II can either stimulate endothelial progenitor cells by improvement of vascular endothelial growth factor signalling, or invoke excessive production of reactive oxygen species causing premature senescence of these cells. On the other hand, angiotensin-(1-7) stimulates haematopoietic cells and possibly also endothelial progenitor cells. Furthermore, aldosterone, bradykinin and Ac-SDKP (N-acetyl-Ser-Asp-Lys-Pro) may also affect progenitor cell populations. Alternatively, the variability in effects of angiotensin II type 1 receptor and angiotensin-converting enzyme inhibition on cardiovascular progenitor cells might reflect differences between the various models or diseases with respect to circulating and local tissue RAAS activation. In the present review we discuss what is currently known with respect to the role of the RAAS in the regulation of cardiovascular progenitor cells.

Bradykinin protects against oxidative stress-induced endothelial cell senescence

Premature aging (senescence) of endothelial cells might play an important role in the development and progression of hypertension and atherosclerosis. We hypothesized that bradykinin, a hormone that mediates vasoprotective effects of angiotensin-converting enzyme inhibitors, protects endothelial cells from oxidative stress-induced senescence. Bradykinin treatment (0.001 to 1 nmol/L) dose-dependently decreased senescence induced by 25 micromol/L of H(2)O(2) in cultured bovine aortic endothelial cells, as witnessed by a complete inhibition of increased senescent cell numbers and a 34% reduction of the levels of the senescence-associated cell cycle protein p21. Because H(2)O(2) induces senescence through superoxide-induced DNA damage, single-cell DNA damage was measured by comet assay. Bradykinin reduced DNA damage to control levels. The protective effect of bradykinin also resulted in a significant increase in the migration of H(2)O(2)-treated bovine aorta endothelial cells in an in vitro endothelial injury model, or "scratch" assay. The protective effect of bradykinin was abolished by the bradykinin B2 receptor antagonist HOE-140 and the NO production inhibitor N(omega)-methyl-L-arginine acetate salt. Therefore, we conclude that bradykinin protects endothelial cells from superoxide-induced senescence through bradykinin B2 receptor- and NO-mediated inhibition of DNA damage.

Intracellular angiotensin II production in diabetic rats is correlated with cardiomyocyte apoptosis, oxidative stress, and cardiac fibrosis

OBJECTIVE

Many of the effects of angiotensin (Ang) II are mediated through specific plasma membrane receptors. However, Ang II also elicits biological effects from the interior of the cell (intracrine), some of which are not inhibited by Ang receptor blockers (ARBs). Recent in vitro studies have identified high glucose as a potent stimulus for the intracellular synthesis of Ang II, the production of which is mainly chymase dependent. In the present study, we determined whether hyperglycemia activates the cardiac intracellular renin-Ang system (RAS) in vivo and whether ARBs, ACE, or renin inhibitors block synthesis and effects of intracellular Ang II (iAng II).

RESEARCH DESIGN AND METHODS

Diabetes was induced in adult male rats by streptozotocin. Diabetic rats were treated with insulin, candesartan (ARB), benazepril (ACE inhibitor), or aliskiren (renin inhibitor).

RESULTS

One week of diabetes significantly increased iAng II levels in cardiac myocytes, which were not normalized by candesartan, suggesting that Ang II was synthesized intracellularly, not internalized through AT(1) receptor. Increased intracellular levels of Ang II, angiotensinogen, and renin were observed by confocal microscopy. iAng II synthesis was blocked by aliskiren but not by benazepril. Diabetes-induced superoxide production and cardiac fibrosis were partially inhibited by candesartan and benazepril, whereas aliskiren produced complete inhibition. Myocyte apoptosis was partially inhibited by all three agents.

CONCLUSIONS

Diabetes activates the cardiac intracellular RAS, which increases oxidative stress and cardiac fibrosis. Renin inhibition has a more pronounced effect than ARBs and ACE inhibitors on these diabetes complications and may be clinically more efficacious.

Renal effects of dual renin-angiotensin-aldosterone system blockade in patients with diabetic nephropathy

Evidence from recent studies indicates that in patients with diabetic nephropathy combined therapy with ACE inhibitors (ACEI) and AT1-receptor antagonists (ARB) results in more complete blockade of the renin-angiotensin-aldosterone system (RAS) than monotherapy, and reduces proteinuria. Most of these trials, however, had short follow-up, included a small number of patients, and were heterogeneous, so the opportunity to start this treatment in these patients remains unclear. This review summarizes the results of these studies, describing the renal effects of dual RAS blockade in both type 1 and type 2 diabetic patients.

Current possibilities of ACE inhibitor and ARB combination in arterial hypertension and its complications

The renin-angiotensin-aldosterone system (RAAS) plays a crucial role in blood pressure regulation and hypertension-related complications. Angiotensin-converting enzyme inhibitors (ACEIs) were the first to be used to block the RAAS and now have many compelling indications in the treatment of hypertension and its cardiovascular and renal complications. Angiotensin II receptor blockers (ARBs), introduced 20 years later, have been shown to be equally as effective as antihypertensive treatment and are also associated with a lower number of side effects. Furthermore, in clinical trials ARBs and ACEIs were associated with comparable benefits for their most typical indications. This was confirmed in the 2007 New European Society of Hypertension/European Society of Cardiology (ESH/ESC) guidelines for the management of hypertension by comparable specific recommendations for ARB and ACEI treatment. There is sufficient theoretical background and, in some cases, also clinical evidence that combination therapy with ACEIs and ARBs may be more beneficial than monotherapy with either of the groups alone, both in uncomplicated hypertension and with concomitant heart failure or renal dysfunction. However, the combination of ACEI and ARB was not recommended in the ESH/ESC 2007 Guidelines. This may change after the publication of the Ongoing Telmisartan Alone and in Combination with Ramipril Global End point Trial (ONTARGET) study, the preliminary results of which have just been presented. In heart failure, recent studies have shown that the combination of ACEI and ARB decreases cardiovascular mortality and the number of hospitalizations due to aggravation of heart failure. These results have been reflected in the newest ESC guidelines of the heart failure treatment. Nephroprotective properties of the combination of ACEs and ARBs have been proved both in studies on nondiabetic and diabetic nephropathy. The potential benefits, indications in prespecified groups of patients, the most recent data from clinical trials and latest research regarding dual blockade of RAAS will be reviewed in this article.

Effects of dual blockade of Renin-Angiotensin system on concentric left ventricular hypertrophy in essential hypertension: a randomized, controlled pilot study

BACKGROUND

The renin-angiotensin system (RAS) plays a major role in promoting left ventricular (LV) remodeling in essential hypertension. We designed a controlled, randomized pilot study aimed to test the hypothesis that the dual RAS blockade with angiotensin-converting enzyme (ACE) inhibitor (ACEi) + angiotensin II receptor blocker (ARB) can be more effective in decreasing LV hypertrophy and improving diastolic function than a largely employed association such as ACEi + calcium-antagonist (Ca-A).

METHODS

Twenty-four never-treated hypertensive patients with LV concentric hypertrophy were randomized to ramipril + candesartan or ramipril + lercanidipine. Before and after the 6-month treatment they underwent a 24-h blood pressure (BP) monitoring and echocardiographic examination.

RESULTS

At baseline, age, body mass index (BMI), 24-h BP, and LV morpho-functional parameters were similar between the two groups. The 6-month treatment induced in both groups a significant decrease of 24-h BP, septal and posterior wall thickness, and LV mass index (LVMi) (ACEi + ARB 155 +/- 19 to 122 +/- 17 g/m(2), P < 0.0001; ACEi + Ca-A 146 +/- 18 to 127 +/- 20 g/m(2), P < 0.0001). Systolic function remained unchanged; LV diastolic parameters increased significantly in both groups. The extent of 24-h BP decrease was similar between the two groups (-13.3/16.3% vs. -12.3/15.8%, P = 0.63/P = 0.71), whereas the decrease of LV mass (-22% vs. -12.8%, P < 0.005) and the improvement of diastolic function were greater in ACEi + ARB group.

CONCLUSIONS

In comparison with ACEi + Ca-A, ACEi + ARB treatment showed a greater antiremodeling effect, that can be reasonably ascribed to a BP-independent effect of the dual RAS blockade.

The role of angiotensin II type 1 receptor blockers in the prevention and management of diabetes mellitus

Angiotensin II Receptor blockers (ARBs) are an important addition to the current range of medications available for treating a wide spectrum of diseases including cardiovascular diseases. Coronary heart disease (CHD) is the most common cause of death in the United Kingdom and worldwide. More importantly, the presence of the metabolic syndrome and the likelihood of diabetes mellitus taking on epidemic proportions in the years to come all threaten to maintain the mortality rate due to CHD. This review article focuses on the clinical studies that have helped define the trends in the usage of these agents in the prevention and treatment of diabetes mellitus and its complications and also explores possible mechanisms of action and future developments.

Rationale for Combining Blockers of the Renin-Angiotensin System

Blockade of the renin-angiotensin system (RAS) with angiotensin I-converting enzyme (ACE) inhibitors and AT1-receptor (AT1R) blockers has become one of the most successful therapeutic approaches in medicine. The question is no longer whether RAS inhibition helps, but rather how we can optimize inhibition to achieve optimal cardiovascular and renal protection. Indeed, numerous data have shown that the RAS is not blocked fully over 24 hours with current doses of RAS blockers because they trigger a counter-regulatory renin release that can offset pharmacologic inhibition of the RAS. This absence of full blockade may have clinical implications. Combination therapy with ACE inhibitors and AT1R antagonists thus has been proposed to inhibit the biological effects of the reactive renin release triggered by single-site RAS inhibition. By using this approach, numerous experimental and clinical studies have suggested that this combination therapy has additive or synergistic effects on blood pressure and on the prevention of cardiovascular and renal lesions. Although similar intensity of RAS blockade can be achieved by either combination therapy or by using high doses of an AT1-receptor antagonist given alone, the ACE inhibitor present in the combination interferes with the bradykinin-nitric oxide pathway and the N-acetyl-Ser-Asp-Lys-Pro metabolism, which both may have additional biological effects.

Hormonal and hemodynamic effects of aliskiren and valsartan and their combination in sodium-replete normotensive individuals

BACKGROUND AND OBJECTIVES

An AT1 receptor antagonist induces a counterregulatory renin release whose intensity and duration reflect the magnitude of the renin-angiotensin blockade. We investigated whether a renin inhibitor may neutralize this counterregulation and amplify the effects of AT1 receptor antagonists.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In 12 normotensive male individuals who were on a high-sodium diet, a double-blind, placebo-controlled, randomized, crossover design was used to study the hormonal and BP effects of single oral administrations of 300 mg of the renin inhibitor aliskiren, 320 mg of valsartan, and a combination of these two drugs, each at half dosage (150 mg of aliskiren and 160 mg of valsartan).

RESULTS

Valsartan (320 mg) increased plasma renin activity and angiotensin I and angiotensin II levels, but 300 mg of aliskiren decreased them for 48 h. Aliskiren (300 mg) stimulated immunoreactive renin release more strongly than 320 mg of valsartan, decreased urinary aldosterone excretion for longer than 320 mg of valsartan, and had a similar BP-lowering effect as 320 mg of valsartan. In combination, 150 mg of aliskiren neutralized the valsartan (160 mg)-induced increase in plasma angiotensins for 48 h. The renin and aldosterone effects of the combination of 150 mg of aliskiren and 160 mg of valsartan were similar to those of 300 mg of aliskiren and greater than those of 320 mg of valsartan. When plasma drug concentrations were taken into account, the combination of 150 mg of aliskiren and 160 mg of valsartan had a synergistic effect on renin release. The BP-lowering effect of 150 mg of aliskiren and 160 mg of valsartan was similar to that of 300 mg of aliskiren and 320 mg of valsartan at peak but was more prolonged.

CONCLUSION

The stronger and longer lasting effects on plasma active renin and urinary aldosterone of aliskiren, alone or in combination, demonstrate a more effective blockade of the renin-angiotensin system than that obtained with 320 mg of valsartan alone.