Effects of long-term enalapril and losartan therapy of heart failure on cardiovascular aldosterone

Losartan attenuates acetic acid enema-induced visceral hypersensitivity by inhibiting the ACE1/Ang II/AT1 receptor axis in enteric glial cells

Enteric glial cells (EGCs) play an important role in visceral hypersensitivity associated with irritable bowel syndrome (IBS). Losartan (Los) is known to reduce pain; however, its function in IBS is unclear. The present study aimed to investigate Los's therapeutic effect on visceral hypersensitivity in IBS rats. Thirty rats were randomly divided into control, acetic acid enema (AA), AA + Los low, medium and high dose groups in vivo. EGCs were treated with lipopolysaccharide (LPS) and Los in vitro. The molecular mechanisms were explored by assessing the expression of EGC activation markers, pain mediators, inflammatory factors and angiotensin-converting enzyme 1(ACE1)/angiotensin II (Ang II)/Ang II type 1 (AT1) receptor axis molecules in colon tissue and EGCs. The results showed that the rats in the AA group showed significantly higher visceral hypersensitivity than the control rats, which was alleviated by different doses of Los. The expression of GFAP, S100β, substance P (SP), calcitonin gene-related peptide (CGRP), transient receptor potential vanilloid 1 (TRPV1), tumor necrosis factor (TNF), interleukin-1β (IL-1β) and interleukin-6 (IL-6) was considerably increased in colonic tissues of AA group rats and LPS-treated EGCs compared with control rats and EGCs, and reduced by Los. In addition, Los reversed ACE1/Ang II/AT1 receptor axis upregulation in AA colon tissues and LPS-treated EGCs. These results show that Los inhibits ACE1/Ang II/AT1 receptor axis upregulation by suppressing EGC activation, resulting in reduced expression of pain mediators and inflammatory factors, thereby alleviating visceral hypersensitivity.

LCZ696 Therapy Reduces Ventricular Tachyarrhythmia Inducibility in a Myocardial Infarction-Induced Heart Failure Rat Model

Background

LCZ696 (valsartan/sacubitril) therapy significantly reduced mortality in patients with heart failure (HF). Although a clinical trial (PARADISE-MI Trial) has been ongoing to examine the effects of LCZ696 in myocardial infarction (MI) patients, the effects of LCZ696 on remodeling of cardiac electrophysiology in animal models remain largely unclear.

Methods

We performed coronary artery ligation to create MI in Sprague-Dawley rats. Echocardiography was performed one week after MI to confirm the development of HF with left ventricular ejection fraction ≤ 40%. MI rats were randomly assigned to receive medical therapy for 4 weeks: LCZ696, enalapril, or vehicle. The sham-operation rats received sham operation without MI creation. In vivo electrophysiological exams were performed under general anesthesia. Western blot analyses were conducted to quantify ion channel proteins.

Results

The HF-vehicle group did not show significant changes in LVEF. Both enalapril and LCZ696 therapy significantly improved LVEF. The HF-vehicle group had higher ventricular arrhythmia (VA) inducibility than the sham group. As compared with the HF-vehicle group, LCZ696 therapy significantly reduced VA inducibility, but enalapril therapy did not. Western blot analyses showed significant downregulation of Na_V1.5, ERG, KCNE1, and KCNE2 channel proteins in the HF vehicle group compared with the sham group. LCZ696 therapy upregulated protein expression of ERG, KCNE1, and KCNE2.

Conclusion

As compared with enalapril therapy, LCZ696 therapy led to improvement of LVEF, reduced VA inducibility, and upregulated expression of K⁺ channel proteins.

Aldosterone and cardiovascular remodelling: focus on myocardial failure

Heart failure is a clinical syndrome that may result from different disease states or conditions that injure the myocardium. The activation of circulating neurohormones, particularly aldosterone, may play a pivotal role in left ventricular (LV) remodelling. The Randomized Aldactone Evaluation Study and Eplerenone Post-Acute Myocardial Infarction Heart Failure Efficacy and Survival trial have emphasised the clinical importance of aldosterone. This review addresses some of the proposed mechanisms of LV remodelling in heart failure.

Cardiac hypertrophy and fibrosis in the metabolic syndrome: a role for aldosterone and the mineralocorticoid receptor

Obesity and hypertension, major risk factors for the metabolic syndrome, render individuals susceptible to an increased risk of cardiovascular complications, such as adverse cardiac remodeling and heart failure. There has been much investigation into the role that an increase in the renin-angiotensin-aldosterone system (RAAS) plays in the pathogenesis of metabolic syndrome and in particular, how aldosterone mediates left ventricular hypertrophy and increased cardiac fibrosis via its interaction with the mineralocorticoid receptor (MR). Here, we review the pertinent findings that link obesity with elevated aldosterone and the development of cardiac hypertrophy and fibrosis associated with the metabolic syndrome. These studies illustrate a complex cross-talk between adipose tissue, the heart, and the adrenal cortex. Furthermore, we discuss findings from our laboratory that suggest that cardiac hypertrophy and fibrosis in the metabolic syndrome may involve cross-talk between aldosterone and adipokines (such as adiponectin).

Markedly increased Rho-kinase activity in circulating leukocytes in patients with chronic heart failure

BACKGROUND

The small guanosine triphosphatase Rho and its target Rho-kinase have significant roles in experimental remodeling and ventricular dysfunction, but no data are available on Rho-kinase activation in patients with heart failure (HF). We hypothesized that, in patients with chronic HF, Rho-kinase in circulating leukocytes is activated and related to left ventricular (LV) remodeling and dysfunction.

METHODS

Accordingly, Rho-kinase activity, assessed by the levels of phosphorylated to total myosin light chain phosphatase 1 (MYPT1-P/T) in circulating leukocytes, and echocardiographic LV function data were compared between patients with HF New York Heart Association functional class II or III due to systolic dysfunction (n = 17), healthy controls (n = 17), and hypertensive patients without HF (n = 17).

RESULTS

In the control subjects, mean MYPT1-P/T ratio was 1.2 ± 0.2 (it was similar in the hypertensive patients without HF), whereas in patients with HF, it was significantly increased by >100-fold (P < .001). Both MYPT1-P/T and log MYPT1-P/T ratios were inversely correlated with ejection fraction (r = -0.54, P < .03 and r = -0.86, P < .001, respectively). Furthermore, in patients with HF with LV end-diastolic diameter <60 mm, MYPT1-P/T ratio was 35.8 ± 18.1, whereas it was significantly higher in patients with LV diameter ≥60 mm (P < .05).

CONCLUSIONS

Rho-Kinase activity is markedly increased in patients with stable chronic HF under optimal medical treatment, and it is associated with pathologic LV remodeling and systolic dysfunction. Mechanisms of Rho-kinase activation in patients with HF, its role in the progression of the disease, and the direct effect of Rho-kinase inhibition need further investigation.

Aldosterone and the cardiovascular system: a dangerous association

Initial studies have focussed on the actions of aldosterone in renal electrolyte handling and, as a consequence, blood pressure control. More recently, attention has primarily been focussed on its actions on the heart and vascular system, where it is locally produced. Aldosterone by binding mineralocorticoid receptors causes oxidative stress, fibrosis and triggers an inflammatory response in the cardiovascular system. All these effects could be underlying the role of aldo-sterone on cardiac and vascular remodelling associated with different pathological situations. At the vascular level, aldo-sterone affects endothelial function because administration of aldosterone to rats impaired endothelium-dependent relaxations. In addition, the administration of mineralocorticoid receptor antagonists ameliorates endothelium-dependent relaxation in models of both hypertension and atherosclerosis, and in patients with heart failure. Several mechanisms can participate in this effect, including production of vasoconstrictor factors and a reduction in nitric oxide levels. This reduction can involve both a decrease in its production as well as an increase in its degradation by reactive oxygen species. Aldosterone can produce oxidative stress by the activation of transcription factors such as the NF-κB system, which can also trigger an inflammatory process through the production of different cytokines. At cardiac level, high levels of aldosterone can also adversely impact heart function by producing cardiac hypertrophy, diastolic dysfunction and electrical remodelling through changes in ionic channels. All these effects can explain the beneficial effect of mineralocorticoid blockade in the cardiovascular system.

AT1 Receptor Blockade Prevents Cardiac Dysfunction after Myocardial Infarction in Rats

Myocardial infarction (MI) can induce severe alterations of contractile function that can, in turn, lead to heart failure. In a previous study, we have demonstrated that TNF-alpha was involved in cardiac contractile dysfunction 7 days after coronary artery ligation in rats. Since Angiotensin II type 1 (AT1) receptor can be involved in TNF-alpha production, we have investigated whether early short-term treatment with irbesartan, an AT1 receptor blocker, is able to limit TNF-alpha production within the heart and to improve cardiac function and geometry following MI in rats. Male Wistar rats were subjected to permanent coronary artery ligation and received either a placebo or irbesartan (50 mg/kg/day) per os daily from day 3 to day 6 after surgery. On day 7, cardiac TNF-alpha was significantly reduced in MI rats receiving irbesartan (p < 0.05). Moreover, irbesartan improved residual LV end-diastolic pressure under both basal conditions and after volume overload (p < 0.01). In addition, a significant leftward shift of the pressure-volume curve in the irbesartan-treated group was found versus placebo. Finally, infarct expansion index was also significantly improved by irbesartan (p < 0.01). In conclusion, early, short-term AT1 receptor blockade limits post-infarct cardiac TNF-alpha production and diminishes myocardial alterations observed 7 days after MI in the rat.

Persistent Cardiac Aldosterone Synthesis in Angiotensin II Type 1A Receptor–Knockout Mice After Myocardial Infarction

Background— The renin-angiotensin-aldosterone system is implicated in the pathogenesis of heart failure. Pharmacological blockade of angiotensin II (Ang II)–dependent signaling is clinically effective in reducing cardiovascular events after myocardial infarction (MI) but still fails to completely prevent remodeling. The molecular basis underlying this Ang II–independent remodeling is unclear.

Methods and Results— Acute MI was induced by coronary ligation in wild-type (WT) and angiotensin II type IA receptor–knockout (AT 1A -KO) mice. Left ventricular (LV) geometry, hemodynamics, and cardiac gene expression were evaluated on day 28. Severe LV remodeling and resultant cardiac dysfunction were observed in WT mice, whereas less marked, but still significant, LV remodeling and cardiac dysfunction were induced in AT 1A -KO mice. Gene expression levels of aldosterone synthase and the cardiac aldosterone content were both elevated in the MI hearts, even in AT 1A -KO mice. In AT 1A -KO mice treated with spironolactone (20 mg/kg per day), LV remodeling, cardiac dysfunction, and cardiac gene expression of collagens and natriuretic peptides were almost normalized.

Conclusions— Our results indicate that genetic blockade of AT 1A signaling fails to arrest aldosterone production in cardiac tissues and that cardiac aldosterone plays a critical role in post-MI LV remodeling. The results suggest that spironolactone could be potentially effective in patients with MI, when used in combination with renin-angiotensin system blockade, by blocking the actions of aldosterone produced by Ang II–independent mechanisms.

Effects of differential blockade of the renin-angiotensin system in postinfarcted rats

The present study compared short-term effects of the AT(1)-receptor antagonist, irbesartan with the angiotensin-converting enzyme (ACE) inhibitor, enalapril on systemic haemodynamics and cardiac remodelling in post-myocardia-infarcted (MI) rats. MI Sprague-Dawley rats were orally treated for 4 weeks with irbesartan (50 mg/kg/day) or enalapril (10 mg/kg/day). Then, cardiac and systemic haemodynamics were measured. Compared with the sham-operated group, left ventricular end-diastolic pressure (LVEDP), diastolic pressure (LVDP), heart weight to body weight ratio were all significantly increased in the MI group while the LV contractility (dP/dt) and pulsatile arterial pressure were significantly reduced. Both drugs reduced the elevated LVEDP and LVDP and prevented cardiac hypertrophy. Furthermore, irbesartan attenuated the right shift of the pressure-volume curves, prevented postinfarction-induced increase in urinary cyclic guanosine monophosphate and reduced urinary aldosterone excretion. Although both drugs were able to prevent further cardiac hypertrophy and improved cardiac filling pressure, only irbesartan limited LV dilatation. These data indicate that blockade of the renin-angiotensin system at the level of AT1 receptors may have a better cardioprotective benefit than reducing angiotensin II levels by ACE inhibition.

RAAS escape: a real clinical entity that may be important in the progression of cardiovascular and renal disease

Interruption of the renin-angiotensin-aldosterone system (RAAS) at different levels is target-organ protective in several disease states; however, complete blockade is unlikely to be achieved due to escape mechanisms whenever blockade is attempted, incomplete knowledge of the role of all elements of the RAAS, and lack of pharmacotherapy against some elements that have been shown to contribute to disease states. Aldosterone has been overlooked as a mediator of RAAS escape and a key factor in target-organ injury despite the use of available RAAS blockers. Aldosterone is thought to play a role in the development of hypertension, alteration in vascular structure, vascular smooth muscle hypertrophy, endothelial dysfunction, structural renal injury, proteinuria, left ventricular remodeling, collagen synthesis, and myocardial fibrosis. Aldosterone receptor antagonists have been shown to antagonize all these effects in experimental models. Clinical trials with aldosterone antagonists showed an improvement in survival and left ventricular mass index in patients with congestive heart failure, and a reduction in urinary protein excretion and left ventricular mass index in patients with type 2 diabetes and early nephropathy who developed aldosterone synthesis escape. Consequently, aldosterone receptor antagonists may have specific benefits for reducing target-organ injury, particularly if there is evidence of RAAS escape.