Combination angiotensin converting enzyme and direct renin inhibition in heart failure following experimental myocardial infarction

Normalizing Plasma Renin Activity in Experimental Dilated Cardiomyopathy: Effects on Edema, Cachexia, and Survival

Heart failure (HF) patients frequently have elevated plasma renin activity. We examined the significance of elevated plasma renin activity in a translationally-relevant model of dilated cardiomyopathy (DCM), which replicates the progressive stages (A–D) of human HF. Female mice with DCM and elevated plasma renin activity concentrations were treated with a direct renin inhibitor (aliskiren) in a randomized, blinded fashion beginning at Stage B HF. By comparison to controls, aliskiren treatment normalized pathologically elevated plasma renin activity (p < 0.001) and neprilysin levels (p < 0.001), but did not significantly alter pathological changes in plasma aldosterone, angiotensin II, atrial natriuretic peptide, or corin levels. Aliskiren improved cardiac systolic function (ejection fraction, p < 0.05; cardiac output, p < 0.01) and significantly reduced the longitudinal development of edema (extracellular water, p < 0.0001), retarding the transition from Stage B to Stage C HF. The normalization of elevated plasma renin activity reduced the loss of body fat and lean mass (cachexia/sarcopenia), p < 0.001) and prolonged survival (p < 0.05). In summary, the normalization of plasma renin activity retards the progression of experimental HF by improving cardiac systolic function, reducing the development of systemic edema, cachexia/sarcopenia, and mortality. These data suggest that targeting pathologically elevated plasma renin activity may be beneficial in appropriately selected HF patients.

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.

Epoxyeicosatrienoic Acid-Based Therapy Attenuates the Progression of Postischemic Heart Failure in Normotensive Sprague-Dawley but Not in Hypertensive Ren-2 Transgenic Rats

Epoxyeicosatrienoic acids (EETs) and their analogs have been identified as potent antihypertensive compounds with cardio- and renoprotective actions. Here, we examined the effect of EET-A, an orally active EET analog, and c-AUCB, an inhibitor of the EETs degrading enzyme soluble epoxide hydrolase, on the progression of post-myocardial infarction (MI) heart failure (HF) in normotensive Hannover Sprague-Dawley (HanSD) and in heterozygous Ren-2 transgenic rats (TGR) with angiotensin II-dependent hypertension. Adult male rats (12 weeks old) were subjected to 60-min left anterior descending (LAD) coronary artery occlusion or sham (non-MI) operation. Animals were treated with EET-A and c-AUCB (10 and 1 mg/kg/day, respectively) in drinking water, given alone or combined for 5 weeks starting 24 h after MI induction. Left ventricle (LV) function and geometry were assessed by echocardiography before MI and during the progression of HF. At the end of the study, LV function was determined by catheterization and tissue samples were collected. Ischemic mortality due to the incidence of sustained ventricular fibrillation was significantly higher in TGR than in HanSD rats (35.4 and 17.7%, respectively). MI-induced HF markedly increased LV end-diastolic pressure (P_ed) and reduced fractional shortening (FS) and the peak rate of pressure development [+(dP/dt)_max] in untreated HanSD compared to sham (non-MI) group [P_ed: 30.5 ± 3.3 vs. 9.7 ± 1.3 mmHg; FS: 11.1 ± 1.0 vs. 40.8 ± 0.5%; +(dP/dt)_max: 3890 ± 291 vs. 5947 ± 309 mmHg/s]. EET-A and c-AUCB, given alone, tended to improve LV function parameters in HanSD rats. Their combination amplified the cardioprotective effect of single therapy and reached significant differences compared to untreated HanSD controls [P_ed: 19.4 ± 2.2 mmHg; FS: 14.9 ± 1.0%; +(dP/dt)_max: 5278 ± 255 mmHg/s]. In TGR, MI resulted in the impairment of LV function like HanSD rats. All treatments reduced the increased level of albuminuria in TGR compared to untreated MI group, but neither single nor combined EET-based therapy improved LV function. Our results indicate that EET-based therapy attenuates the progression of post-MI HF in HanSD, but not in TGR, even though they exhibited renoprotective action in TGR hypertensive rats.

Intermedin improves cardiac function and sympathetic neural remodeling in a rat model of post myocardial infarction heart failure

Emerging evidence has suggested that intermedin (IMD), a novel member of the calcitonin gene-related peptide (CGRP) family, has a wide range of cardioprotective effects. The present study investigated the effects of long-term administration of IMD on cardiac function and sympathetic neural remodeling in heart failure (HF) rats, and studied potential underlying mechanism. HF was induced in rats by myocardial infarction (MI). Male Sprague Dawley rats were randomly assigned to either saline or IMD (0.6 µg/kg/h) treatment groups for 4 weeks post-MI. Another group of sham-operated rats served as controls. Cardiac function was assessed by echocardiography, cardiac catheterization and plasma level of B-type natriuretic peptide (BNP). Cardiac sympathetic neural remodeling was assessed by immunohistochemistical study of tyrosine hydroxylase (TH) and growth associated protein 43 (GAP43) immunoreactive nerve fibers. The protein expression levels of nerve growth factor (NGF), TH and GAP43 in the ventricular myocardium were studied by western blotting. Ventricular fibrillation threshold (VFT) was determined to evaluate the incidence of ventricular arrhythmia. Oxidative stress was assessed by detecting the activity of superoxide dismutase and the level of malondialdehyde. Compared with rats administrated with saline, IMD significantly improved cardiac function, decreased the plasma BNP level, attenuated sympathetic neural remodeling, increased VFT and suppressed oxidative stress. In conclusion, these results indicated that IMD prevents ventricle remodeling and improves the performance of a failing heart. In addition, IMD attenuated sympathetic neural remodeling and reduced the incidence of ventricular arrhythmia, which may contribute to its anti-oxidative property. These results implicate IMD as a potential therapeutic agent for the treatment of HF.

Enzyme inhibition kinetics and molecular interactions of patatin peptides with angiotensin I-converting enzyme and renin

In this work, the inhibitory effects of potato patatin-derived peptides Trp-Gly (WG) and Pro-Arg-Tyr (PRY) on angiotensin I-converting enzyme (ACE) and renin activities were investigated using kinetics, intrinsic fluorescence and molecular docking. The results indicated that PRY was a more potent ACE- and renin-inhibitory peptide than WG. Enzyme inhibition kinetics showed that WG and PRY inhibited ACE activity through mixed-type and competitive modes, respectively. The inhibitory mechanism of WG and PRY towards renin was determined to be mixed-type. PRY exhibited stronger affinity towards ACE and renin molecules, when compared to WG as determined by intrinsic fluorescence intensity. Molecular docking data confirmed that the higher inhibitory potency of PRY might be attributed to formation of more hydrogen bonds with the enzyme's active site or non-active sites that distorted the configuration necessary for catalysis.

Moderate additive effects of endothelin receptor A blockade in Ren-2 transgenic rats subjected to various types of RAS blockade

AIMS

Chronic endothelin receptor A (ETA) blockade lowered blood pressure (BP) by decreasing angiotensin-dependent vasoconstriction and attenuating calcium influx. We tested whether the addition of ETA blockade to renin-angiotensin system (RAS) blockade would have further effects on the principal vasoactive systems contributing to BP maintenance in Ren-2 transgenic rats (TGR).

METHODS

Four-week-old TGR rats were fed with normal-salt diet and given either different renin-angiotensin system (RAS) blockers [angiotensin receptor blocker losartan, angiotensin converting enzyme inhibitor captopril, direct renin inhibitor aliskiren], or ETA blocker (atrasentan) alone, or a combination of atrasentan with RAS blockers for 4weeks. At the end of the study, basal BP and acute BP responses to sequential blockade of renin-angiotensin (RAS), sympathetic nervous (SNS), and nitric oxide (NO) systems were determined in conscious rats. Thereafter, BP responses to acute inhibition of nifedipine-sensitive calcium influx through voltage-dependent calcium channels (L-VDCC) were measured.

KEY FINDINGS

All RAS blockers similarly decreased BP to normotension, their effects being mediated through substantially attenuated RAS-dependent and moderately decreased SNS-dependent vasoconstriction. Atrasentan alone partially lowered BP, while BP was normalized by combination of atrasentan with either RAS blocker. In combination therapies, BP lowering effects resulted from the attenuation of both RAS- and SNS-dependent vasoconstriction. Moreover, atrasentan-treated groups had substantially reduced NO-dependent vasodilation and significantly decreased calcium influx through L-VDCC.

CONCLUSIONS

Although the BP-lowering effect of combined ETA and RAS blockades in TGR is predominantly dependent on the effects exerted by RAS blockade, further effects are attributable to decreased calcium influx due to chronic ETA blockade.

Evaluating molecular mechanism of hypotensive peptides interactions with renin and angiotensin converting enzyme

Our previous study showed that three rapeseed protein-derived peptides (TF, LY and RALP) inhibited the in vitro activities of angiotensin converting enzyme (ACE) and renin. Oral administration of these peptides to spontaneously hypertensive rats led to reductions in systolic blood pressure. In the present work, we examined the potential molecular mechanisms responsible for the ACE- and renin-inhibitory activities of these peptides. Enzyme inhibition kinetics showed competitive, non-competitive and mixed-type peptide-dependent inhibition of renin and ACE activities. Intrinsic fluorescence intensity data showed that LY and RALP have stronger binding effects on ACE molecule compared to that of TF. LY and RALP showed the highest inhibition of ACE and renin activities, respectively. Circular dichroism data showed that the inhibitory mechanism involved extensive peptide-dependent reductions in α-helix and β-sheet fractions of ACE and renin protein conformations. Molecular docking studies confirmed that the higher renin-inhibitory activity of RALP may be due to formation of several hydrogen bonds (H-bonds) with the enzyme’s active site residues. The rapeseed peptides inhibited renin and ACE activities mostly through binding to enzyme active site or non-active sites and forming extensive H-bonds that distorted the normal configuration required for catalysis. Data presented from this work could enhance development of highly potent antihypertensive natural peptides or peptidomimetics.