Direct renin inhibition: clinical pharmacology

Antihypertensive Properties of a Pea Protein Hydrolysate during Short- and Long-Term Oral Administration to Spontaneously Hypertensive Rats

This study investigated short-term (24 h) and long-term (5 wk) systolic blood pressure (SBP)-lowering effects in spontaneously hypertensive rats (SHR) of a 5 kDa membrane pea protein hydrolysate permeate (PPH-5) produced through thermoase hydrolysis of pea protein isolate (PPI). Amino acid analysis showed that the PPH-5 had lower contents of sulfur-containing amino acids than the PPI. Size-exclusion chromatography indicated mainly low molecular weight (<10 kDa) peptides in PPH-5 but not in the PPI. The PPH-5 had renin and angiotensin converting enzyme inhibition IC50 values of 0.57 and 0.10 mg/mL (P < 0.05), respectively, and consisted mainly of peptides with 2 to 6 amino acids. Mass spectrometry analysis revealed mainly hydrophilic tetrapeptide sequences. After a single oral administration (100 mg/kg body weight) to SHR, the unheated PPI showed weakest (P < 0.05) SBP-lowering effect with a -4 mm Hg maximum when compared to -25 mm Hg for heat-treated PPI and -36 mm Hg for PPH-5. Incorporation of the PPH-5 as 0.5% or 1% (w/w) casein substitute in the SHR diet produced maximum SBP reductions of -22 or -26 mm Hg (P < 0.05), respectively after 3 wk. In comparison, the unhydrolyzed PPI produced a maximum SBP reduction of -17 mm Hg also after 3 wk. Potency of the pea products decreased in the 4th and 5th wk, though SBP values of the treated rats were still lower than the untreated control. We conclude that the antihypertensive potency of PPH-5 may have been due to the presence of easily absorbed hydrophilic peptides.

Aliskiren, exendin-4, and insulin: their impact on endothelin receptor subtype(s) regulation/binding in type 1 diabetic rat hearts

This study focuses on the impact of aliskiren and (or) glucagon-like peptide-1 analogue on the binding affinity/regulation of endothelin-1 (ET-1) to its receptor subtypes A (ETAR) and B (ETBR) at the level of the coronary endothelium and the cardiomyocytes in a type-1 diabetic rat model. Seven groups were used: (i) normal rats, (ii) rats with induced diabetes, (iii) rats with induced diabetes that were treated with insulin, (iv) rats with induced diabetes that were treated with exendin-4, (v) rats with induced diabetes that were treated with aliskiren, (vi) rats with induced diabetes that were co-treated with insulin plus aliskiren, and (vii) rats with induced diabetes that were co-treated with exendin-4 plus aliskiren. Heart perfusion with [125I]-ET-1 was employed to estimate ET-1 binding affinity (τ = 1/K–n) to ETAR and ETBR at the level of the coronary endothelium and the cardiomyocytes. Plasma ET-1 levels were measured using enzyme immunoassay, whereas densities of ETAR and ETBR were detected using Western blot. No significance differences were detected in the τ of ETAR and ETBR between normal and diabetic in cardiomyocytes and the coronary endothelium. Exendin-4 normalized the τ value for ETAR and ETBR on coronary endothelium, while aliskiren normalized it on cardiomyocytes. Furthermore, ETAR and ETBR densities were normalized with monotreatments of aliskiren and exendin-4, compared with up-regulated ETAR and down-regulated ETBR band densities in the diabetic animals. Our data indicate that aliskiren alleviates diabetes-associated hypertrophy in type 1 diabetes mellitus.

Aliskiren penetrates adipose and skeletal muscle tissue and reduces renin-angiotensin system activity in obese hypertensive patients

OBJECTIVE

In animals, the direct renin inhibitor aliskiren showed extensive tissue binding in the kidney and long-lasting renal effects. Aliskiren provides prolonged blood pressure-lowering effects following treatment discontinuation in patients. Therefore, we investigated whether aliskiren attains tissue concentrations sufficient to inhibit local renin-angiotensin system (RAS) activity in patients.

METHODS

We included 10 hypertensive patients with abdominal adiposity in an open-label study. Following 1-2 weeks washout, patients received 2 weeks placebo, then 4 weeks aliskiren 300 mg once daily, followed by 4 weeks washout, and then 4 weeks amlodipine 5 mg once daily. Drug concentrations and RAS biomarkers were measured in interstitial fluid using microdialysis and in biopsies from abdominal subcutaneous adipose and skeletal muscle.

RESULTS

We detected aliskiren in all compartments. After 4 weeks of treatment, microdialysate aliskiren concentrations (ng/ml) were 2.4 ± 2.1 (adipose) and 7.1 ± 4.2 (skeletal muscle), similar to plasma concentrations (8.4 ± 4.4); tissue concentrations (ng/g) were 29.0 ± 16.7 (adipose) and 107.3 ± 68.6 (skeletal muscle). Eight weeks after discontinuation, aliskiren was measurable in tissue biopsies but not in plasma or in interstitial fluid. Pooled microdialysate samples from two sets of four patients suggested reduction in tissue angiotensin II with aliskiren but not with amlodipine.

CONCLUSION

In obese hypertensive patients, aliskiren penetrates adipose and skeletal muscle tissue at levels that are apparently sufficient to reduce tissue RAS activity. Furthermore, tissue binding may contribute to aliskiren's prolonged blood pressure-lowering effect following discontinuation.

The role of renin inhibition in treating the hypertensive patient with diabetes: a summary of preclinical and clinical evidence

Comorbid hypertension and diabetes is common and associated with substantially greater cardiovascular and renal risk relative to hypertension alone. Tissue renin-angiotensin system (RAS) overactivity is a hallmark of diabetes and contributes to target organ damage. Treatment guidelines recommend angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) for reducing cardiorenal risk in patients with hypertension plus diabetes. However, these agents only partially prevent cardiovascular and renal morbidity/mortality. Further attempts to improve clinical outcomes have focused on the use of an ACE inhibitor plus an ARB, but this combination has not demonstrated a favorable risk-benefit profile. Direct renin inhibitors provide a more comprehensive blockade of the RAS compared with ACE inhibitors or ARBs, and may be of particular benefit in counteracting tissue RAS overactivity. In this article, the role of the RAS in diabetic hypertension and the preclinical and clinical effects of direct renin inhibitor therapy on target organs are reviewed.

Direct renin inhibition: update on clinical investigations with aliskiren

The renin–angiotensin–aldosterone system (RAAS) plays a pivotal role in regulating blood pressure, volume, and electrolytes. The final product of RAAS cascade is angiotensin II, which exerts diverse biological activities via binding to one of three known receptor types, with different binding consequences. Despite the success with conventional strategies to limit angiotensin II production and action, these agents promote a reflex rise in plasma renin activity, which is thought to be associated with an increased incidence of cardiovascular events. Several renin inhibitors have been synthesized in order to counteract deleterious consequences of renin activity and RAAS activation; aliskiren is the first of these new non-peptide direct renin inhibitors to be approved for the treatment of hypertension. The paper reviews pharmacokinetics of aliskiren and its role in hypertension, with particular regard to those studies that compared clinical efficacy of aliskiren in comparison and in addition to other antihypertensive drug strategies.

Direct renin inhibitors as antihypertensive agents

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

A reduction of unilateral ureteral obstruction-induced renal fibrosis by a therapy combining valsartan with aliskiren

The protective effect of combination therapy with valsartan and aliskiren against renal fibrosis remains to be defined. This study was undertaken to examine the protective effects of the combination of valsartan and aliskiren against renal fibrosis induced by unilateral ureteral obstruction (UUO). Combination therapy with valsartan (15 mg·kg(-1)·day(-1)) and aliskiren (10 mg·kg(-1)·day(-1)), valsartan monotherapy (30 mg·kg(-1)·day(-1)), and aliskiren monotherapy (20 mg·kg(-1)·day(-1)) all significantly ameliorated the increase in blood urea nitrogen and the degree of hydronephrosis determined by the increase in weight and length of the obstructed kidney. The dose titration study and blood pressure measurement confirmed that the combination therapy provided a greater benefit independent of the vasodilatory effect. There were no significant changes in serum levels of creatinine, sodium, and potassium in UUO rats and any treatment groups. Combination therapy also attenuated UUO-related increases in the scores of tubular dilatation, interstitial volume, interstitial collagen deposition, α-smooth muscle actin, the activation of ERK 1/2, the infiltration of monocytes/macrophages, the mRNA expression of snail-1, and transforming growth factor-β1 to a greater extent compared with aliskiren or valsartan used alone. The mRNA expression of renin and the (pro)renin receptor significantly increased after UUO. Combination therapy and monotherapy of valsartan and aliskiren had a comparable enhancing effect on the mRNA expression of renin, whereas all these treatments did not affect the expression of the (pro)renin receptor. In conclusion, a direct renin inhibitor in conjunction with an angiotensin II receptor blocker exerts increased renal protection against renal fibrosis and inflammation during obstruction over either agent alone.

Potential roles of melatonin and chronotherapy among the new trends in hypertension treatment

The number of well-controlled hypertensives is unacceptably low worldwide. Respecting the circadian variation of blood pressure, nontraditional antihypertensives, and treatment in early stages of hypertension are potential ways to improve hypertension therapy. First, prominent variations in circadian rhythm are characteristic for blood pressure. The revolutionary MAPEC (Ambulatory Blood Pressure Monitoring and Cardiovascular Events) study, in 3000 adult hypertensives investigates, whether chronotherapy influences the cardiovascular prognosis beyond blood pressure reduction per se. Second, melatonin, statins and aliskiren are hopeful drugs for hypertension treatment. Melatonin, through its scavenging and antioxidant effects, preservation of NO availability, sympatholytic effect or specific melatonin receptor activation exerts antihypertensive and anti-remodeling effects and may be useful especially in patients with nondipping nighttime blood pressure pattern or with nocturnal hypertension and in hypertensives with left ventricular hypertrophy (LVH). Owing to its multifunctional physiological actions, this indolamine may offer cardiovascular protection far beyond its hemodynamic benefit. Statins exert several pleiotropic effects through inhibition of small guanosine triphosphate-binding proteins such as Ras and Rho. Remarkably, statins reduce blood pressure in hypertensive patients and more importantly they attenuate LVH. Addition of statins should be considered for high-risk hypertensives, for hypertensives with LVH, and possibly for high-risk prehypertensive patients. The direct renin inhibitor, aliskiren, inhibits catalytic activity of renin molecules in circulation and in the kidney, thus lowering angiotensin II levels. Furthermore, aliskiren by modifying the prorenin conformation may prevent prorenin activation. At present, aliskiren should be considered in hypertensive patients not sufficiently controlled or intolerant to other inhibitors of renin-angiotensin system. Third, TROPHY (Trial of Preventing Hypertension) is the first pharmacological intervention for prehypertensive patients revealing that treatment with angiotensin II type 1 receptor blocker attenuates hypertension development and thus decreases the risk of cardiovascular events.

Development of a homogeneous immunoassay for the detection of angiotensin I in plasma using AlphaLISA acceptor beads technology

Plasma renin activity (PRA) is a well-established biomarker for assessing the efficacy of various antihypertensive agents such as direct renin inhibitors, angiotensin receptor blockers, and angiotensin-converting enzyme inhibitors (ACEIs). PRA measurements are obtained through the detection and quantification of angiotensin I (Ang I) produced by the action of renin on its natural substrate angiotensinogen. The most accepted and reproducible method for PRA measurement uses an antibody capture Ang I methodology that employs specific antibodies that recognize and protect Ang I against angiotensinase activities contained in plasma. The amount of Ang I is then quantified by either radioimmunoassay (RIA) or enzyme immunoassay (EIA). In the current report, we describe the optimization of a novel homogeneous immunoassay based on the AlphaScreen technology for the detection and quantification of antibody-captured Ang I using AlphaLISA acceptor beads in buffer and in the plasma of various species (human, rat, and mouse). Ex vivo measurements of renin activity were performed using 10 microl or less of a reaction mixture, and concentrations as low as 1 nM Ang I were quantified. Titration curves obtained for the quantification of Ang I in buffer and plasma gave similar EC(50) values of 5.6 and 14.4 nM, respectively. Both matrices generated an equivalent dynamic range that varies from approximately 1 to 50 nM. Renin inhibitors have been successfully titrated and IC(50) values obtained correlated well with those obtained using EIA methodology (r(2)=0.80). This assay is sensitive, robust, fast, and less tedious than measurements performed using nonhomogeneous EIA. The AlphaLISA methodology is homogeneous, does not require wash steps prior to the addition of reagents, and does not generate radioactive waste.