Vasopeptidase inhibition reverses myocardial vasoactive intestinal peptide depletion and decreases fibrosis in salt sensitive hypertension

Future pharmacological therapy in hypertension

PURPOSE OF REVIEW

Hypertension (HTN) is a widespread and growing disease, with medication intolerance and side-effect present among many. To address these obstacles novel pharmacotherapy is an active area of drug development. This review seeks to explore future drug therapy for HTN in the preclinical and clinical arenas.

RECENT FINDINGS

The future of pharmacological therapy in HTN consists of revisiting old pathways to find new targets and exploring wholly new approaches to provide additional avenues of treatment. In this review, we discuss the current status of the most recent drug therapy in HTN. New developments in well trod areas include novel mineralocorticoid antagonists, aldosterone synthase inhibitors, aminopeptidase-A inhibitors, natriuretic peptide receptor agonists, or the counter-regulatory angiotensin converting enzyme 2/angiotensin (Ang) (1-7)/Mas receptor axis. Neprilysin inhibitors popularized for heart failure may also still hold HTN potential. Finally, we examine unique systems in development never before used in HTN such as Na/H exchange inhibitors, vasoactive intestinal peptide agonists, and dopamine beta hydroxylase inhibitors.

SUMMARY

A concise review of future directions of HTN pharmacotherapy.

Endopeptidase inhibition attenuates the contraction induced by big endothelin-1 of isolated human penile erectile tissue

Peptides, such as C-type natriuretic peptide (CNP), vasoactive intestinal polypeptide (VIP) and endothelin 1 (ET-1), are involved in the control of penile erectile tissue (corpus cavernosum = CC). Inhibiting the degradation of CNP and VIP or conversion of Big ET-1 into ET-1 by endopeptidase enzymes should result in an enhancement of CC smooth muscle relaxation. Using the tissue bath technique, responses of isolated CC, challenged by noradrenaline (NA, 1 μm), to increasing concentrations of the endopeptidase inhibitor KC 12615 (1 nm - 10 μm), CNP and VIP (0.1 nm - 1 μm), were investigated. Effects of CNP, VIP and Big ET-1 (0.1 nm - 100 nm) on the tissue tension were also evaluated following pre-exposure to 10 μm of KC 12615. Big ET-1 induced contraction of the CC amounting to a force generation of 1,200 mg. The contraction was attenuated in the presence of KC 12615 by 35% and 50%, respectively. The tension induced by NA was reversed by VIP and CNP to 38.7% ± 15.8% and 61% ± 13%, respectively, of the initial force. The findings might be of significance with regard to future pharmacological treatment options for male ED, where an endothelial dysfunction exists.

Effects of endopeptidase inhibition on the relaxation response of isolated human penile erectile tissue to vasoactive peptides

Peptides, such as CNP, CGRP and VIP, are involved in the function of male penile erectile tissue. Tissue levels of said peptides are controlled by the endopeptidase enzymes. Theoretically, the inhibition of the degradation of CNP, CGRP and/or VIP should result in an enhancement in penile smooth muscle relaxation. The effects were investigated of CNP or VIP (0.1 nm-1 μm), without and following pre-exposure of the tissue to a threshold concentration of the endopeptidase inhibitor KC 12615 (10 μm, for 20 min), on the reversion of tension induced by means of electrical field stimulation. Drug effects on the production of cyclic AMP/GMP were also evaluated. Neither KC 12615, CNP and VIP nor the combination of CNP plus KC 12615 or VIP plus KC 12615 increased the response of the tissue to EFS. While no effects were observed of a pre-exposure of the tissue to KC 12615 on the production of cyclic AMP in the presence of VIP, an enhancement was registered in the accumulation of cyclic AMP in the presence of CNP plus KC 12615. Further studies are indicated to investigate whether endopeptidase inhibitors might tend to be more effective in tissues affected by a decreased local production of vasoactive peptides.

New developments in the pharmacological treatment of hypertension: dead-end or a glimmer at the horizon?

Arterial hypertension is the most prevalent controllable disease world-wide. Yet, we still need to further improve blood pressure control, deal with resistant hypertension, and we hope to reduce risk "beyond blood pressure." The number of candidate molecules aspiring for these aims is constantly declining. The new possible approaches to combat high blood pressure include neprilysin/neutral endopeptidase (NEP) inhibition, particularly when combined with an angiotensin receptor blockade (such as the ARNI, LCZ696), phosphodiesterase 5 (PDE5) inhibition (KD027/Slx-2101), natriuretic agents (PL3994), or a long-lasting vasointestinal peptide (VIP) analogue (PB1046). Other options exploit the protective arm of the renin-angiotensin-aldosterone system by stimulating the angiotensin AT2 receptor (compound 21), the Mas receptor (AVE-0991), or the angiotensin converting enzyme 2. Finally, we review the possibilities how to optimize the use of the available treatment options by using drug combinations or by tailoring therapy to each patient's angiotensin peptide profile.

Role of neuropeptides in cardiomyopathies

The role of neuropeptides in cardiomyopathy-associated heart failure has been garnering more attention. Several neuropeptides--Neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), calcitonin gene related peptide (CGRP), substance P (SP) and their receptors have been studied in the various types of cardiomyopathies. The data indicate associations with the strength of the association varying depending on the kind of neuropeptide and the nature of the cardiomyopathy--diabetic, ischemic, inflammatory, stress-induced or restrictive cardiomyopathy. Several neuropeptides appear to alter regulation of genes involved in heart failure. Demonstration of an association is an essential first step in proving causality or establishing a role for a factor in a disease. Understanding the complexity of neuropeptide function should be helpful in establishing new or optimal therapeutic strategies for the treatment of heart failure in cardiomyopathies.

Human VIP-alpha: a long-acting, biocompatible and biodegradable peptide nanomedicine for essential hypertension

We have previously shown that self-association of human vasoactive intestinal peptide with sterically stabilized liposomes (VIP-alpha) alters peptide conformation from random coil in aqueous solution to alpha-helix. This, in turn, protects the peptide from hydrolysis and amplifies and prolongs its bioactivity. The purpose of this study was to determine whether a single, intravenous injection of low-dose human VIP-alpha normalizes systemic arterial pressure in anesthetized spontaneously hypertensive hamsters for a prolonged period of time in a selective fashion. We found that intravenous injection of human VIP-alpha, VIP alone (each, 1.0 nmol) and empty liposomes had no significant effects on mean arterial pressure (MAP) in normotensive hamsters. By contrast, human VIP-alpha (0.01-1.0 nmol) evoked a significant concentration-dependent decrease in MAP to the normative range in spontaneously hypertensive hamsters that lasted throughout the observation period (6 h; p<0.05). VIP alone and empty liposomes had no significant effects on MAP in these animals. We conclude that a single, low-dose intravenous injection of human VIP-alpha normalizes systemic arterial pressure in spontaneously hypertensive hamsters for a prolonged period of time in a selective fashion. We suggest that human VIP-alpha should be further developed as a long-acting, biocompatible and biodegradable peptide nanomedicine for essential hypertension.

Anti-atherosclerotic and renoprotective effects of combined angiotensin-converting enzyme and neutral endopeptidase inhibition in diabetic apolipoprotein E-knockout mice

OBJECTIVE

To investigate the effects of the combined angiotensin-converting enzyme (ACE)/neutral endopeptidase (NEP) inhibitor omapatrilat on atherosclerosis and renal injury in a model of diabetes-associated accelerated atherosclerosis and renal injury.

DESIGN

The study was performed using diabetic apolipoprotein E-knockout (apo E-KO) mice, a model combining hyperlipidemia and hyperglycemia, which leads to accelerated atherosclerosis and renal injury.

METHODS

Diabetes was induced by the injection of streptozotocin in 6-week old apo E-KO mice. Diabetic animals received no treatment (n = 12) or treatment with the ACE/NEP inhibitor omapatrilat (30 mg/kg per day, via gavage, n = 12) or quinapril (10 mg/kg per day, in drinking water, n = 12) for 20 weeks. Non-diabetic apo E-KO mice (n = 12) served as controls.

RESULTS

Omapatrilat reduced atherosclerosis and protected the mice from renal structural injury and albuminuria. The protective effects were associated with tissue inhibition of aortic and renal ACE and NEP as well as a significant reduction in blood pressure. Omapatrilat had similar anti-atherosclerotic effects compared with the ACE inhibitor quinapril in association with an almost complete inhibition of aortic ACE activity by both drugs. Omapatrilat conferred superior renoprotection in the diabetic apo E-KO mouse compared with quinapril in the context of greater renal ACE inhibition by omapatrilat than seen with quinapril, additional renal NEP inhibition and a modestly enhanced antihypertensive response.

CONCLUSIONS

These studies demonstrate the anti-atherosclerotic and renoprotective effects of omapatrilat in diabetic apo E-KO mice, a model of accelerated atherosclerosis and renal injury. These effects were observed in association with the local inhibition of ACE and NEP at the tissue level in the aorta and kidney. These results suggest that the anti-atherosclerotic effect conferred by omapatrilat treatment in the diabetic apo E-KO mouse is predominantly mediated by its capacity to inhibit local vascular ACE. By contrast, in the kidney, local renal ACE and NEP inhibition and the superior antihypertensive effect of omapatrilat all contribute to the renoprotective effect conferred by omapatrilat treatment in the diabetic apo E-KO mouse.

Pituitary adenylate cyclase activating polypeptide protects cardiomyocytes against oxidative stress-induced apoptosis

Pituitary adenylate cyclase activating polypeptide (PACAP) has well-known neuroprotective effects, and one of the main factors leading to neuroprotection seems to be its anti-apoptotic effects. The peptide and its receptors are present also in the heart, but whether PACAP can be protective in cardiomyocytes, is not known. Therefore, the aim of the present study was to investigate the effects of PACAP on oxidative stress-induced apoptosis in cardiomyocytes. Our results show that PACAP increased cell viability by attenuating H2O2-induced apoptosis in a cardiac myocyte culture. PACAP also decreased caspase-3 activity and increased the expression of the anti-apoptotic markers Bcl-2 and phospho-Bad. These effects of PACAP were counteracted by the PACAP antagonist PACAP6-38. In summary, our results show that PACAP is able to attenuate oxidative stress-induced cardiomyocyte apoptosis.

Clinical endocrinology and metabolism. Potential clinical applications of vasoactive intestinal peptide: a selected update

Neuropeptides are expressed in neurons innervating endocrine cells or in endocrine cells and cancer cells, and are released on site to act as hormones and growth factors. Vasoactive intestinal peptide (VIP) was first discovered in the early 1970s and has since become the area of research for many laboratories. VIP has a neuroendocrine role as it is intimately involved with the synthesis, secretion and action of other neuroendocrine hormones as well as cytokines and chemokines. Major outcomes of VIP downregulation encompass developmental and behavioral dysfunctions, including impaired diurnal rhythms. Overexpression of VIP has been associated with diarrhea and cancer, and overexpression of VIP receptors is associated with cancerous growth. This short review outlines some of the recent progress made in VIP research.