Characterization of Relaxant Responses to Natriuretic Peptides in the Human MicrocirculationIn VitroandIn Vivo

Exploring the Therapeutic Potential of C-Type Natriuretic Peptide for Preeclampsia

BACKGROUND

Preeclampsia is a serious condition of pregnancy, complicated by aberrant maternal vascular dysfunction. CNP (C-type natriuretic peptide) contributes to vascular homeostasis, acting through NPR-B (natriuretic peptide receptor-B) and NPR-C (natriuretic peptide receptor-C). CNP mitigates vascular dysfunction of arteries in nonpregnant cohorts; this study investigates whether CNP can dilate maternal arteries in ex vivo preeclampsia models.

METHODS

Human omental arteries were dissected from fat biopsies collected during cesarean section. CNP, NPR-B, and NPR-C mRNA expression was assessed in arteries collected from pregnancies complicated by preeclampsia (n=6) and normotensive controls (n=11). Using wire myography, we investigated the effects of CNP on dilation of arteries from normotensive pregnancies. Arteries were preconstricted with either serum from patients with preeclampsia (n=6) or recombinant ET-1 (endothelin-1; vasoconstrictor elevated in preeclampsia; n=6) to model vasoconstriction associated with preeclampsia. Preconstricted arteries were treated with recombinant CNP (0.001-100 µmol/L) or vehicle and vascular relaxation assessed. In further studies, arteries were preincubated with NPR-B (5 µmol/L) and NPR-C (10 µmol/L) antagonists before serum-induced constriction (n=4-5) to explore mechanistic signaling.

RESULTS

CNP, NPR-B, and NPR-C mRNAs were not differentially expressed in omental arteries from preeclamptic pregnancies. CNP potently stimulated maternal artery vasorelaxation in our model of preeclampsia (using preeclamptic serum). Its vasodilatory actions were driven through the activation of NPR-B predominantly; antagonism of this receptor alone dampened CNP vasorelaxation. Interestingly, CNP did not reduce ET-1-driven omental artery constriction.

CONCLUSIONS

Collectively, these data suggest that enhancing CNP signaling through NPR-B offers a potential therapeutic strategy to reduce systemic vascular constriction in preeclampsia.

Endothelial cyclooxygenase-1 paradoxically drives local vasoconstriction and atherogenesis despite underpinning prostacyclin generation

Endothelial cyclooxygenase-1-derived prostanoids, including prostacyclin, have clear cardioprotective roles associated with their anti-thrombotic potential but have also been suggested to have paradoxical pathological activities within arteries. To date it has not been possible to test the importance of this because no models have been available that separate vascular cyclooxygenase-1 products from those generated elsewhere. Here, we have used unique endothelial-specific cyclooxygenase-1 knockout mice to show that endothelial cyclooxygenase-1 produces both protective and pathological products. Functionally, however, the overall effect of these was to drive pathological responses in the context of both vasoconstriction in vitro and the development of atherosclerosis and vascular inflammation in vivo. These data provide the first demonstration of a pathological role for the vascular cyclooxygenase-1 pathway, highlighting its potential as a therapeutic target. They also emphasize that, across biology, the role of prostanoids is not always predictable due to unique balances of context, products, and receptors.

Heart-Microcirculation Connection: Effects of ANP (Atrial Natriuretic Peptide) on Pericytes Participate in the Acute and Chronic Regulation of Arterial Blood Pressure

Cardiac ANP (atrial natriuretic peptide) moderates arterial blood pressure. The mechanisms mediating its hypotensive effects are complex and involve inhibition of the renin-angiotensin-aldosterone system, increased natriuresis, endothelial permeability, and vasodilatation. The contribution of the direct vasodilating effects of ANP to blood pressure homeostasis is controversial because variable levels of the ANP receptor, GC-A (guanylyl cyclase-A), are expressed among vascular beds. Here, we show that ANP stimulates GC-A/cyclic GMP signaling in cultured microvascular pericytes and thereby the phosphorylation of the regulatory subunit of myosin phosphatase 1 by cGMP-dependent protein kinase I. Moreover, ANP prevents the calcium and contractile responses of pericytes to endothelin-1 as well as microvascular constrictions. In mice with conditional inactivation (knock-out) of GC-A in microcirculatory pericytes, such vasodilating effects of ANP on precapillary arterioles and capillaries were fully abolished. Concordantly, these mice have increased blood pressure despite preserved renal excretory function. Furthermore, acute intravascular volume expansion, which caused release of cardiac ANP, did not affect blood pressure of control mice but provoked hypertensive reactions in pericyte GC-A knock-out littermates. We conclude that GC-A/cGMP-dependent modulation of pericytes and microcirculatory tone contributes to the acute and chronic moderation of arterial blood pressure by ANP. Graphic Abstract A graphic abstract is available for this article.

Intradermal Administration of Atrial Natriuretic Peptide Attenuates Cutaneous Vasodilation but Not Sweating in Young Men during Exercise in the Heat

INTRODUCTION

Prolonged exercise in the heat stimulates plasma release of atrial natriuretic peptide (ANP) in association with dehydration-induced reductions in blood volume. Elevated plasma ANP levels under these conditions may indirectly attenuate cutaneous blood flow and sweating responses due to the effects of this hormone on central blood volume and plasma osmolality and the resulting stimulation of nonthermal reflexes. However, it remains unclear whether cutaneous blood flow and sweating are directly modulated by ANP at the level of the cutaneous end organs (cutaneous microvessels and eccrine sweat glands) during prolonged exercise in the heat.

OBJECTIVE

Therefore, we evaluated the effects of local ANP administration on forearm cutaneous vascular conductance (CVC) and local sweat rate (LSR) during rest and exercise in the heat.

METHODS

In 9 habitually active young men (26 ± 6 years) CVC and LSR were evaluated at 3 intradermal microdialysis sites continuously perfused with lactated Ringer solution (control) or ANP (0.1 or 1.0 μM). Participants rested in a non-heat-stress condition (25°C) for approximately 60 min followed by 70 min in the heat (35°C). They then performed 50 min of moderate-intensity cycling (approx. 55% VO2 peak), with a 30-min recovery. Thereafter, 50 mM sodium nitroprusside was administered at all sites to elicit maximum CVC, which was subsequently used to normalize all values (CVC%max).

RESULTS

No effects of ANP on CVC%max were observed in the non-heat-stress resting condition compared to the untreated control site (both p > 0.05). Conversely during rest in the heat there was an 11% (5-17%) reduction in CVC%max at the 1.0 μM ANP site relative to the untreated control site (p < 0.05). At the end of exercise CVC%max was attenuated by 12% (1-23%) at the 0.1 μM ANP site and by 21% (7-35%) at the 1.0 μM ANP site relative to the untreated control site (all p < 0.05). Conversely, neither concentration of ANP influenced sweating at any time point (all p > 0.05).

CONCLUSION

Intradermal ANP administration directly attenuated cutaneous blood flow, but not sweating, in habitually active young men during rest and exercise in the heat.

Effects of dual angiotensin type 1 receptor/neprilysin inhibition vs. angiotensin type 1 receptor inhibition on target organ injury in the stroke-prone spontaneously hypertensive rat

OBJECTIVES

The combination of AT1 blocker/neutroendopeptidase neprilysin inhibition (ARNi) represents an interesting approach to reduce cardiovascular risk in hypertension. We assessed the efficacy of ARNi, compared with angiotensin II type 1 receptor blockade alone, on blood pressure (BP) and on protection from target organ damage development in the stroke-prone spontaneously hypertensive rat (SHRSP).

METHODS

In high-salt fed SHRSP, we assessed plasma and tissue natriuretic peptides, urinary volume, BP and body weight over a short-term treatment (6 weeks) with either ARNi (sacubitril/valsartan 68 mg/kg per day) or valsartan (30 mg/kg per day), protection from stroke and renal damage (as documented by proteinuria) over 4 months of treatment with either sacubitril/valsartan or valsartan; the ability of either treatment to reduce progression of cerebrovascular and renal damage after 2 weeks of high-salt diet.

RESULTS

Higher levels of plasma and tissue atrial natriuretic peptide, of urinary cyclic guanosine 3'5'monophosphate and urine volumes, along with lower BP levels, were found upon sacubitril/valsartan as compared with valsartan over the short-term treatment. Sacubitril/valsartan caused a significant reduction of both BP and proteinuria levels and complete prevention of stroke over the long-term treatment. Once organ damage was established, a significant delay of its progression was observed with sacubitril/valsartan.

CONCLUSION

The dual angiotensin II type 1 receptor/neutroendopeptidase inhibition significantly increased atrial natriuretic peptide level and reduced BP. Complete prevention of stroke was achieved in this model. The ability of sacubitril/valsartan to reduce organ damage progression was superior to that of valsartan alone. ARNi may represent a highly effective therapeutic agent to protect from target organ damage development in hypertension.

C-type Natriuretic Peptide: A Multifaceted Paracrine Regulator in the Heart and Vasculature

C-type natriuretic peptide (CNP) is an autocrine and paracrine mediator released by endothelial cells, cardiomyocytes and fibroblasts that regulates vital physiological functions in the cardiovascular system. These roles are conveyed via two cognate receptors, natriuretic peptide receptor B (NPR-B) and natriuretic peptide receptor C (NPR-C), which activate different signalling pathways that mediate complementary yet distinct cellular responses. Traditionally, CNP has been deemed the endothelial component of the natriuretic peptide system, while its sibling peptides, atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP), are considered the endocrine guardians of cardiac function and blood volume. However, accumulating evidence indicates that CNP not only modulates vascular tone and blood pressure, but also governs a wide range of cardiovascular effects including the control of inflammation, angiogenesis, smooth muscle and endothelial cell proliferation, atherosclerosis, cardiomyocyte contractility, hypertrophy, fibrosis, and cardiac electrophysiology. This review will focus on the novel physiological functions ascribed to CNP, the receptors/signalling mechanisms involved in mediating its cardioprotective effects, and the development of therapeutics targeting CNP signalling pathways in different disease pathologies.

Host Peptidic Hormones Affecting Bacterial Biofilm Formation and Virulence

Bacterial biofilms constitute a critical problem in hospitals, especially in resuscitation units or for immunocompromised patients, since bacteria embedded in their own matrix are not only protected against antibiotics but also develop resistant variant strains. In the last decade, an original approach to prevent biofilm formation has consisted of studying the antibacterial potential of host communication molecules. Thus, some of these compounds have been identified for their ability to modify the biofilm formation of both Gram-negative and Gram-positive bacteria. In addition to their effect on biofilm production, a detailed study of the mechanism of action of these human hormones on bacterial physiology has allowed the identification of new bacterial pathways involved in biofilm formation. In this review, we focus on the impact of neuropeptidic hormones on bacteria, address some future therapeutic issues, and provide a new view of inter-kingdom communication.

A Novel Paradigm for Sacubitril/Valsartan: Beta-Endorphin Elevation as a Contributor to Exercise Tolerance Improvement in Rats With Preexisting Heart Failure Induced by Pressure Overload

BACKGROUND

Simultaneous angiotensin receptor (AT1) blockade and neprilysin inhibition with the use of sacubitril/valsartan has been recently approved to treat patients with heart failure (HF). Therapeutic benefits of this therapy have been attributed to natriuretic peptide elevation and AT1 receptor blockade. However, that pharmacologic picture may not be complete. The aims of this study were to investigate the pharmacology of sacubitril/valsartan compared with sacubitril and valsartan alone and to examine their impact on peptides up-regulated by neprilysin inhibition, such as beta-endorphin.

METHODS AND RESULTS

An HF model was induced by pressure overload via constriction of the suprarenal abdominal aorta in rats. Sacubitril/valsartan (68 mg/kg), valsartan (31 mg/kg), sacubitril (31 mg/kg), or placebo was administered by daily oral gavage (starting 4 weeks after pressure overload onset and continued for 4 additional weeks; n = 8 in each group). Exercise tolerance testing was conducted using a rodent treadmill and hemodynamic assessments were conducted under anesthesia with the use of Millar left ventricular (LV) conductance technology. Pressure overload led to exercise intolerance by 4 weeks and to hypertension and LV dysfunction and remodeling by 8 weeks. Both sacubitril/valsartan and sacubitril elevated beta-endorphin levels, by 40% and 54%, respectively, and improved exercise tolerance, by 93% and 112%, whereas valsartan did not. Indices of LV dysfunction persisted with the use of sacubitril/valsartan and valsartan therapies and even deteriorated in sacubitril group.

CONCLUSIONS

When added to valsartan, sacubitril increases beta-endorphin concentrations and improves exercise tolerance. These data suggest beta-endorphin elevation as a potential mechanism of action leading to improvement in exercise tolerance that is seen with sacubitril/valsartan. This therapeutic benefit is potentially independent from LV function.

Natriuretic Peptides and Normal Body Fluid Regulation

Natriuretic peptides are structurally related, functionally diverse hormones. Circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are delivered predominantly by the heart. Two C-type natriuretic peptides (CNPs) are paracrine messengers, notably in bone, brain, and vessels. Natriuretic peptides act by binding to the extracellular domains of three receptors, NPR-A, NPR-B, and NPR-C of which the first two are guanylate cyclases. NPR-C is coupled to inhibitory proteins. Atrial wall stress is the major regulator of ANP secretion; however, atrial pressure changes plasma ANP only modestly and transiently, and the relation between plasma ANP and atrial wall tension (or extracellular volume or sodium intake) is weak. Absence and overexpression of ANP-related genes are associated with modest blood pressure changes. ANP augments vascular permeability and reduces vascular contractility, renin and aldosterone secretion, sympathetic nerve activity, and renal tubular sodium transport. Within the physiological range of plasma ANP, the responses to step-up changes are unimpressive; in man, the systemic physiological effects include diminution of renin secretion, aldosterone secretion, and cardiac preload. For BNP, the available evidence does not show that cardiac release to the blood is related to sodium homeostasis or body fluid control. CNPs are not circulating hormones, but primarily paracrine messengers important to ossification, nervous system development, and endothelial function. Normally, natriuretic peptides are not powerful natriuretic/diuretic hormones; common conclusions are not consistently supported by hard data. ANP may provide fine-tuning of reno-cardiovascular relationships, but seems, together with BNP, primarily involved in the regulation of cardiac performance and remodeling. © 2017 American Physiological Society. Compr Physiol 8:1211-1249, 2018.