Guanylyl cyclase / atrial natriuretic peptide receptor-A: role in the pathophysiology of cardiovascular regulation

Cardiac cGMP Regulation and Therapeutic Applications

cGMP plays a central role in cardiovascular regulation in health and disease. It is synthesized by NO or natriuretic peptide activated cyclases and hydrolyzed to 5'GMP by select members of the PDEs (phosphodiesterase) superfamily. The primary downstream effector is cGMP-dependent protein kinase, primarily cGK-1a (cyclic GMP-dependent protein kinase 1 alpha) also known as protein kinase G 1a in the heart and vasculature. cGMP signaling is controlled in intracellular nanodomains to regulate myocyte growth, survival, metabolism, protein homeostasis, G-protein-coupled receptor signaling, and other critical functions. The vascular effects of cGMP signaling have been dominated by its lowering of smooth muscle tone, but other cellular processes are also engaged. Localization of cyclases and corresponding PDEs within intracellular domains, along with their varying expression across different cell types, adds multiorgan complexity to cGMP signaling. This diversity can be leveraged therapeutically by targeting selective pathway components to impact some but not other cGMP signaling effects. Here, we review the generation and regulation of cGMP by PDEs and cyclases, focusing mainly on their role in cardiac physiology and pathophysiology. Current therapeutic uses of cGMP modulation and ongoing trials testing new potential applications are discussed.

Timeline of Changes in Biomarkers Associated with Spinal Cord Injury-Induced Polyuria

Deficits in upper and lower urinary tract function, which include detrusor overactivity, urinary incontinence, detrusor-sphincter dyssynergia, and polyuria, are among the leading issues that arise after spinal cord injury (SCI) affecting quality of life. Given that overproduction of urine (polyuria) has been shown to be associated with an imbalance in key regulators of body fluid homeostasis, the current study examined the timing of changes in levels of various relevant hormones, peptides, receptors, and channels post-contusion injury in adult male Wistar rats. The results show significant up- or downregulation at various time points, beginning at 7 days post-injury, in levels of urinary atrial natriuretic peptide, serum arginine vasopressin (AVP), kidney natriuretic peptide receptor-A, kidney vasopressin-2 receptor, kidney aquaporin-2 channels, and kidney epithelial sodium channels (β- and γ-, but not α-, subunits). The number of AVP-labeled neurons in the hypothalamus (supraoptic and -chiasmatic, but not paraventricular, nuclei) was also significantly altered at one or more time points. These data show significant fluctuations in key biomarkers involved in body fluid homeostasis during the post-SCI secondary injury phase, suggesting that therapeutic interventions (e.g., desmopressin, a synthetic analogue of AVP) should be considered early post-SCI.

Sex-dependent compensatory mechanisms preserve blood pressure homeostasis in prostacyclin receptor-deficient mice

Inhibitors of microsomal prostaglandin E synthase 1 (mPGES-1) are in the early phase of clinical development. Deletion of mPges-1 in mice confers analgesia, restrains atherogenesis, and fails to accelerate thrombogenesis, while suppressing prostaglandin E2 (PGE2), but increasing the biosynthesis of prostacyclin (PGI2). In low-density lipoprotein receptor-deficient (Ldlr-/-) mice, this last effect represents the dominant mechanism by which mPges-1 deletion restrains thrombogenesis, while suppression of PGE2 accounts for its antiatherogenic effect. However, the effect of mPges-1 depletion on blood pressure (BP) in this setting remains unknown. Here, we show that mPges-1 depletion significantly increased the BP response to salt loading in male Ldlr-/- mice, whereas, despite the direct vasodilator properties of PGI2, deletion of the I prostanoid receptor (Ipr) suppressed this response. Furthermore, combined deletion of the Ipr abrogated the exaggerated BP response in male mPges-1-/- mice. Interestingly, these unexpected BP phenotypes were not observed in female mice fed a high-salt diet (HSD). This is attributable to the protective effect of estrogen in Ldlr-/- mice and in Ipr-/- Ldlr-/- mice. Thus, estrogen compensates for a deficiency in PGI2 to maintain BP homeostasis in response to high salt in hyperlipidemic female mice. In male mice, by contrast, the augmented formation of atrial natriuretic peptide (ANP) plays a similar compensatory role, restraining hypertension and oxidant stress in the setting of Ipr depletion. Hence, men with hyperlipidemia on a HSD might be at risk of a hypertensive response to mPGES-1 inhibitors.

High protein diet leads to prediabetes remission and positive changes in incretins and cardiovascular risk factors

BACKGROUND AND AIMS

High Protein diets may be associated with endocrine responses that favor improved metabolic outcomes. We studied the response to High Protein (HP) versus High Carbohydrate (HC) Diets in terms of incretin hormones GLP-1 and GIP, the hunger hormone ghrelin and BNP, which is associated with cardiac function. We hypothesized that HP diets induce more pronounced release of glucose lowering hormones, suppress hunger and improve cardiac function.

METHODS AND RESULTS

24 obese women and men with prediabetes were recruited and randomized to either a High Protein (HP) (n = 12) or High Carbohydrate (HC) (n = 12) diet for 6 months with all food provided. OGTT and MTT were performed and GLP-1, GIP, Ghrelin, BNP, insulin and glucose were measured at baseline and 6 months on the respective diets. Our studies showed that subjects on the HP diet had 100% remission of prediabetes compared to only 33% on the HC diet with similar weight loss. HP diet subjects had a greater increase in (1) OGTT GLP-1 AUC(p = 0.001) and MTT GLP-1 AUC(p = 0.001), (2) OGTT GIP AUC(p = 0.005) and MTT GIP AUC(p = 0.005), and a greater decrease in OGTT ghrelin AUC(p = 0.005) and MTT ghrelin AUC(p = 0.001) and BNP(p = 0.001) compared to the HC diet at 6 months.

CONCLUSIONS

This study demonstrates that the HP diet increases GLP-1 and GIP which may be responsible in part for improved insulin sensitivity and β cell function compared to the HC diet. HP ghrelin results demonstrate the HP diet can reduce hunger more effectively than the HC diet. BNP and other CVRF, metabolic parameters and oxidative stress are significantly improved compared to the HC diet. CLINICALTRIALS.

GOV IDENTIFIER

NCT01642849.

Modern trends in diuretics development

Diuretics are the first-line therapy for widespread cardiovascular and non-cardiovascular diseases. Traditional diuretics are commonly prescribed for treatment in patients with hypertension, edema and heart failure, as well as with a number of kidney problems. They are diseases with high mortality, and the number of patients suffering from heart and kidney diseases is increasing year by year. The use of several classes of diuretics currently available for clinical use exhibits an overall favorable risk/benefit balance. However, they are not devoid of side effects. Hence, pharmaceutical researchers have been making efforts to develop new drugs with a better pharmacological profile. High-throughput screening, progress in protein structure analysis and modern methods of chemical modification have opened good possibilities for identification of new promising agents for preclinical and clinical testing. In this review, we provide an overview of the medicinal chemistry approaches toward the development of small molecule compounds showing diuretic activity that have been discovered over the past decade and are interesting drug candidates. We have discussed promising natriuretics/aquaretics/osmotic diuretics from such classes as: vasopressin receptor antagonists, SGLT2 inhibitors, urea transporters inhibitors, aquaporin antagonists, adenosine receptor antagonists, natriuretic peptide receptor agonists, ROMK inhibitors, WNK-SPAK inhibitors, and pendrin inhibitors.

Phosphodiesterase Inhibitors for Alzheimer's Disease: A Systematic Review of Clinical Trials and Epidemiology with a Mechanistic Rationale

BACKGROUND

Preclinical studies, clinical trials, and reviews suggest increasing 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) with phosphodiesterase inhibitors is disease-modifying in Alzheimer's disease (AD). cAMP/protein kinase A (PKA) and cGMP/protein kinase G (PKG) signaling are disrupted in AD. cAMP/PKA and cGMP/PKG activate cAMP response element binding protein (CREB). CREB binds mitochondrial and nuclear DNA, inducing synaptogenesis, memory, and neuronal survival gene (e.g., brain-derived neurotrophic factor) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α). cAMP/PKA and cGMP/PKG activate Sirtuin-1, which activates PGC1α. PGC1α induces mitochondrial biogenesis and antioxidant genes (e.g.,Nrf2) and represses BACE1. cAMP and cGMP inhibit BACE1-inducing NFκB and tau-phosphorylating GSK3β.

OBJECTIVE AND METHODS

We review efficacy-testing clinical trials, epidemiology, and meta-analyses to critically investigate whether phosphodiesteraseinhibitors prevent or treat AD.

RESULTS

Caffeine and cilostazol may lower AD risk. Denbufylline and sildenafil clinical trials are promising but preliminary and inconclusive. PF-04447943 and BI 409,306 are ineffective. Vinpocetine, cilostazol, and nicergoline trials are mixed. Deprenyl/selegiline trials show only short-term benefits. Broad-spectrum phosphodiesterase inhibitor propentofylline has been shown in five phase III trials to improve cognition, dementia severity, activities of daily living, and global assessment in mild-to-moderate AD patients on multiple scales, including the ADAS-Cogand the CIBIC-Plus in an 18-month phase III clinical trial. However, two books claimed based on a MedScape article an 18-month phase III trial failed, so propentofylline was discontinued. Now, propentofylline is used to treat canine cognitive dysfunction, which, like AD, involves age-associated wild-type Aβ deposition.

CONCLUSION

Phosphodiesterase inhibitors may prevent and treat AD.

Sacubitril/Valsartan Decreases Cardiac Fibrosis in Left Ventricle Pressure Overload by Restoring PKG Signaling in Cardiac Fibroblasts

Background Heart failure (HF) is invariably accompanied by development of cardiac fibrosis, a form of scarring that increases muscular tissue rigidity and decreases cardiac contractility. Cardiac fibrosis arises from a pathological attempt to repair tissue damaged during maladaptive remodeling. Treatment options to block or reverse fibrosis have proven elusive. Neprilysin is an endopeptidase that degrades vasoactive peptides, including atrial natriuretic peptide. Thus, neprilysin inhibition reduces hypertension, ultimately limiting maladaptive cardiac remodeling. LCZ696, which consists of an angiotensin receptor blocker (valsartan [VAL]) and a neprilysin inhibitor (sacubitril [SAC]), was shown to be well tolerated and significantly reduced the risk of death and hospitalization in HF patients with reduced ejection fraction. We hypothesized that SAC/VAL directly inhibits fibroblast activation and development of pathological fibrosis. Methods and Results We used a mouse model of left ventricle pressure overload coupled to in vitro studies in primary mouse and human cardiac fibroblasts (CFs) to study the impact of SAC/VAL on CF activation and cardiac fibrosis. SAC/VAL significantly ameliorated pressure overload-induced cardiac fibrosis by blocking CF activation and proliferation, leading to functional improvement. Mechanistically, the beneficial impact of SAC/VAL at least partially stemmed from restoration of PKG (protein kinase G) signaling in HF patient-derived CF, which inhibited Rho activation associated with myofibroblast transition. Conclusions This study reveals that SAC/VAL acts directly on CF to prevent maladaptive cardiac fibrosis and dysfunction during pressure overload-induced hypertrophy and suggests that SAC/VAL should be evaluated as a direct antifibrotic therapeutic for conditions such as HF with preserved ejection fraction.

Differential effects of atrial and brain natriuretic peptides on human pulmonary artery: An in vitro study

BACKGROUND

The prevalence of cardiovascular diseases, especially heart failure, continues to rise worldwide. In heart failure, increasing levels of circulating atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) are associated with a worsening of heart failure and a poor prognosis.

AIM

To test whether a high concentration of BNP would inhibit relaxation to ANP.

METHODS

Pulmonary arteries were dissected from disease-free areas of lung resection, as well as pulmonary artery rings of internal diameter 2.5–3.5 mm and 2 mm long, were prepared. Pulmonary artery rings were mounted in a multiwire myograph, and a basal tension of 1.61gf was applied. After equilibration for 60 min, rings were pre-constricted with 11.21 µmol/L PGF_2α (EC₈₀), and concentration response curves were constructed to vasodilators by cumulative addition to the myograph chambers.

RESULTS

Although both ANP and BNP were found to vasodilate the pulmonary vessels, ANP is more potent than BNP. pEC50 of ANP and BNP were 8.96 ± 0.21 and 7.54 ± 0.18, respectively, and the maximum efficacy (E_max) for ANP and BNP was -2.03 gf and -0.24 gf, respectively. After addition of BNP, the E_max of ANP reduced from -0.96gf to -0.675gf (P = 0.28).

CONCLUSION

BNP could be acting as a partial agonist in small human pulmonary arteries, and inhibits relaxation to ANP. Elevated levels of circulating BNP could be responsible for the worsening of decompensated heart failure. This finding could also explain the disappointing results seen in clinical trials of ANP and BNP analogues for the treatment of heart failure.

Race, Natriuretic Peptides, and High-Carbohydrate Challenge: A Clinical Trial

RATIONALE

Lower NP (natriuretic peptide) levels may contribute to the development of cardiometabolic diseases. Blacks have lower NP levels than middle-aged and older white adults. A high-carbohydrate challenge causes an upregulation of a negative ANP regulator microRNA-425 (miR-425), which reduces ANP (atrial-NP) levels in whites.

OBJECTIVES

We designed a prospective trial to study racial differences in (1) NP levels among young adults, (2) NP response to a high-carbohydrate challenge, and (3) explore underlying mechanisms for race-based differences.

METHODS AND RESULTS

Healthy self-identified blacks and whites received 3 days of study diet followed by a high-carbohydrate challenge. Gene expression from whole blood RNA was assessed in the trial participants. Additionally, atrial and ventricular tissue samples from the Myocardial Applied Genomics Network repository were examined for NP system gene expression. Among 72 healthy participants, we found that B-type-NP, NT-proBNP (N-terminal-pro-B-type NP), and MRproANP (midregional-pro-ANP) levels were 30%, 47%, and 18% lower in blacks compared with whites (P≤0.01), respectively. The decrease in MRproANP levels in response to a high-carbohydrate challenge differed by race (blacks 23% [95% CI, 19%-27%] versus whites 34% [95% CI, 31%-38]; P_interaction<0.001), with no change in NT-proBNP levels. We did not observe any racial differences in expression of genes encoding for NPs (NPPA/NPPB) or NP signaling (NPR1) in atrial and ventricular tissues. NP processing (corin), clearance (NPR3), and regulation (miR-425) genes were ≈3.5-, ≈2.5-, and ≈2-fold higher in blacks than whites in atrial tissues, respectively. We also found a 2-and 8-fold higher whole blood RNA expression of gene encoding for Neprilysin (MME) and miR-425 among blacks than whites.

CONCLUSIONS

Racial differences in NP levels are evident in young, healthy adults suggesting a state of NP deficiency exists in blacks. Impaired NP processing and clearance may contribute to race-based NP differences. Higher miR-425 levels in blacks motivate additional studies to understand differences in NP downregulation after physiological perturbations.

CLINICAL TRIAL REGISTRATION

URL: https://clinicaltrials.gov/ct2/show/NCT03072602. Unique identifier: NCT03072602.

The left atrial appendage in humans: structure, physiology, and pathogenesis

For many years, the left atrial appendage (LAA) was considered a dormant embryological remnant; however, it is a structurally complex and functional organ that contributes to cardiac haemodynamic changes and volume homeostasis through both its contractile properties and neurohormonal peptide secretion. When dysfunctional, the LAA contributes to thrombogenesis and subsequent increased predisposition to cardioembolic events. Consequently, the LAA has gained much attention as a therapeutic target to lower this risk. In addition, attention has focused on the LAA in its role as an electrical trigger for atrial tachycardia and atrial fibrillation with ablation of the LAA to achieve electrical isolation showing promising results in the maintenance of sinus rhythm. This in-depth review explores the structure, physiology and pathophysiology of the LAA, as well as LAA intervention and their sequelae.

Pulmonary Arterial Hypertension Due to NPR-C Mutation: A Novel Paradigm for Normal and Pathologic Remodeling?

Idiopathic Pulmonary Arterial Hypertension (IPAH) is a deadly and disabling disease characterized by severe vascular remodeling of small pulmonary vessels by fibroblasts, myofibroblasts and vascular smooth muscle cell proliferation. Recent studies suggest that the Natriuretic Peptide Clearance Receptor (NPR-C) signaling pathways may play a crucial role in the development of IPAH. Reduced expression or function of NPR-C signaling in pulmonary artery smooth muscle cells may contribute to the pulmonary vascular remodeling, which is characteristic of this disease. The likely mechanisms may involve an impaired interaction between NPR-C, specific growth factors and other signal transduction pathways including but not limited to Gqα/mitogen-activated protein kinase (MAPK)/PI3K and AKT signaling. The resulting failure of growth suppression in pulmonary artery smooth muscle cells provides critical clues to the cellular pathobiology of IPAH. The reciprocal regulation of NPR-C signaling in models of tissue remodeling may thus provide new insights to our understanding of IPAH.

Molecular and genetic aspects of guanylyl cyclase natriuretic peptide receptor-A in regulation of blood pressure and renal function

Natriuretic peptides (NPs) exert diverse effects on several biological and physiological systems, such as kidney function, neural and endocrine signaling, energy metabolism, and cardiovascular function, playing pivotal roles in the regulation of blood pressure (BP) and cardiac and vascular homeostasis. NPs are collectively known as anti-hypertensive hormones and their main functions are directed toward eliciting natriuretic/diuretic, vasorelaxant, anti-proliferative, anti-inflammatory, and anti-hypertrophic effects, thereby, regulating the fluid volume, BP, and renal and cardiovascular conditions. Interactions of NPs with their cognate receptors display a central role in all aspects of cellular, biochemical, and molecular mechanisms that govern physiology and pathophysiology of BP and cardiovascular events. Among the NPs atrial and brain natriuretic peptides (ANP and BNP) activate guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) and initiate intracellular signaling. The genetic disruption of Npr1 (encoding GC-A/NPRA) in mice exhibits high BP and hypertensive heart disease that is seen in untreated hypertensive subjects, including high BP and heart failure. There has been a surge of interest in the NPs and their receptors and a wealth of information have emerged in the last four decades, including molecular structure, signaling mechanisms, altered phenotypic characterization of transgenic and gene-targeted animal models, and genetic analyses in humans. The major goal of the present review is to emphasize and summarize the critical findings and recent discoveries regarding the molecular and genetic regulation of NPs, physiological metabolic functions, and the signaling of receptor GC-A/NPRA with emphasis on the BP regulation and renal and cardiovascular disorders.

A rapid reporter assay for recombinant human brain natriuretic peptide (rhBNP) by GloSensor technology

Accurate determination of biological activity is essential in quality control of recombinant human brain natriuretic peptide (rhBNP). In previous study, we successfully developed a genetically modified cell line 293GCAC3-based ELISA assay for rhBNP. But ELISA procedure is still tedious, so this study was aimed to develop a rapid and simple bioassay for rhBNP using GloSensor technology, which provides a platform of flexible luciferase-based biosensors for real-time detection of signaling events in live cells, including cGMP production. A reporter cell line 293GCAGlo-G1 was constructed by transfecting pGloSensor™ 40 F plasmid into 293GCAC3. The reporter assay based on 293GCAGlo-G1 showed high precision with intra-assay CV being 8.3% and inter-assay CV being 14.1%; high accuracy with 80%, 100% and 120% recovery rate being 99.2%, 102.4% and 99.0% respectively; and great linearity with R² of linear fitting equation being 0.99. Besides, no significant difference was found in test results of reporter assay and 293GCAC3-based ELISA assay (paired t test, p = 0.630). All these results suggested that the reporter assay was a viable assay for biological determination of rhBNP.

Cardiac Hypertrophy and Brain Natriuretic Peptide Levels in an Ovariectomized Rat Model Fed a High-Fat Diet

BACKGROUND Heart failure in women increases around the time of menopause when high-fat diets may result in obesity. The heart produces brain natriuretic peptide (BNP), also known as B-type natriuretic peptide. This aims of this study were to assess cardiac hypertrophy and BNP levels in ovariectomized rats fed a high-fat diet. MATERIAL AND METHODS Forty-eight female Wistar rats were divided into four groups: sham-operated rats fed a control diet (SC) (n=12); ovariectomized rats fed a control diet (OC) (n=12); sham-operated rats fed a high-fat diet (SF) (n=12); and ovariectomized rats fed a high-fat diet (OF) (n=12). Body weight and blood pressure were measured weekly for 24 weeks. Rats were then euthanized, and plasma samples and heart tissue were studied for gene expression, hydroxyproline levels, and histological examination. RESULTS A high-fat diet and ovariectomy (group OF) increased the weight body and the systolic blood pressure after three months and five months, respectively. Cardiomyocyte hypertrophy was associated with increased expression of ventricular BNP, decreased natriuretic peptide receptor (NPR)-A and increased levels of hydroxyproline and transforming growth factor (TGF)-β. The plasma levels of BNP and estradiol were inversely correlated; expression of estrogen receptor (ER)β and ERα were reduced. CONCLUSIONS The findings of this study showed that, in the ovariectomized rats fed a high-fat diet, the BNP-NPR-A receptor complex was involved in cardiac remodeling. BNP may be a marker of cardiac hypertrophy in this animal model.

Heads and Tails of Natriuretic Peptides: Neuroprotective Role of Brain Natriuretic Peptide

Background

Besides the relevant role of brain‐type natriuretic peptide (BNP) as biomarker of cardioembolic strokes, new experimental evidences suggest that this peptide may mediate neuroprotective effects. In this study, we have evaluated for the first time the clinical association between BNP (by means of proBNP) and good outcome in ischemic stroke patients, and analyzed the effect of blood BNP increase in an ischemic animal model.

Methods and Results

A retrospective study with 2 different cohorts (262 patients in cohort I and 610 in cohort II) from the same prospective stroke registry was performed. proBNP concentration was analyzed within the first 12 hours from stroke onset. The primary predictor variable was functional outcome evaluated by modified Rankin Scale at 3 months. For the experimental study, BNP pretreatment was tested in an ischemic animal model subjected to a transient occlusion of the cerebral artery, and the infarct volume and sensorimotor deficit were evaluated for 14 days. Cardioembolic strokes presented a positive correlation between proBNP concentration and modified Rankin Scale at 3 months; however, noncardioembolic strokes presented a negative correlation. In the logistic regression analysis, noncardioembolic strokes with concentrations of proBNP ≥340 pg/mL were associated with a good outcome. In line with these clinical findings, the experimental study revealed that those BNP pretreated animals presented a reduction on infarct volumes at 24 hours and functional recovery at days 7 and 14 compared with the control groups.

Conclusions

These clinical and experimental evidences support the potential role of BNP as a protective factor against cerebral ischemia.

DNA methylation dysregulations in valvular atrial fibrillation

BACKGROUND

The epigenetic changes underlying the development of atrial fibrillation (AF) remain incompletely understood. Limited evidence suggests that abnormal DNA methylation might be involved in the pathogenesis of AF. In the present study, we evaluated the methylation status of genomic DNA from myocardial tissue in AF patients and sinus rhythm (SR) patients systematically.

HYPOTHESIS

DNA methylation dysregulations will be associated with valvular AF.

METHODS

Right atrial myocardial tissue was obtained from rheumatic valvular patients who had undergone valve replacement surgery (SR group, n = 10; AF group, n = 10). The global DNA methylation level, the promoter methylation level of the natriuretic peptide receptor-A gene (NPRA), and its correlation with the mRNA expression level of DNA methyltransferase genes were detected.

RESULTS

The global DNA methylation level was significantly higher in the AF group than in the SR group (P < 0.05). The NPRA mRNA expression was decreased and the NPRA gene was hypermethylated in the AF group (P < 0.05). Meanwhile, the NPRA mRNA expression level has a negative correlation with the mean methylation level in the promoter region of the NPRA gene.

CONCLUSIONS

DNA methylation dysregulations may be relevant in the pathogenesis of AF. DNA methyltransferase 3B likely plays an essential role in the DNA methylation dysregulations in AF.

The multifaceted role of natriuretic peptides in metabolic syndrome

Due to globalization and sophisticated western and sedentary lifestyle, metabolic syndrome has emerged as a serious public health challenge. Obesity is significantly increasing worldwide because of increased high calorie food intake and decreased physical activity leading to hypertension, dyslipidemia, atherosclerosis, and insulin resistance. Thus, metabolic syndrome constitutes cardiovascular disease, type 2 diabetes, obesity, and nonalcoholic fatty liver disease (NAFLD) and recently some cancers are also considered to be associated with this syndrome. There is increasing evidence of the involvement of natriuretic peptides (NP) in the pathophysiology of metabolic diseases. The natriuretic peptides are cardiac hormones, which are produced in the cardiac atrium, ventricles of the heart and the endothelium. These peptides are involved in the homeostatic control of body water, sodium intake, potassium transport, lipolysis in adipocytes and regulates blood pressure. The three known natriuretic peptide hormones present in the natriuretic system are atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and c-type natriuretic peptide (CNP). These three peptides primarily function as endogenous ligands and mainly act via their membrane receptors such as natriuretic peptide receptor A (NPR-A), natriuretic peptide receptor B (NPR-B) and natriuretic peptide receptor C (NPR-C) and regulate various physiological and metabolic functions. This review will shed light on the structure and function of natriuretic peptides and their receptors and their role in the metabolic syndrome.

Association of NPR3 polymorphism with risk of essential hypertension in a Chinese population

WHAT IS KNOWN AND OBJECTIVE

Essential hypertension (EH) is a common disease exhibiting large individual difference in occurrence, development and treatment response. Genetic factors are implicated in the development and progression of EH. This study aimed to explore the association between NPR3 single nucleotide polymorphism rs2270915 (A/G, Asn521Asp) and the risk of EH in a Chinese Han population by a case-control study.

METHODS

The study was a single-centre, case-control trial, in which a total of 287 EH patients and 289 age- and sex-matched healthy controls were enrolled. The inclusion criteria were as follows: Han Chinese origin, male or female patients, systolic blood pressure (SBP) ≥140 mm Hg and/or diastolic blood pressure (DBP) ≥90 mm Hg. The healthy controls were subjects without histories of cardiovascular or cerebrovascular diseases. NPR3 rs2270915 polymorphism was genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). In addition, primary human umbilical vein endothelial cells (HUVECs) were isolated from 19 fresh human umbilical cords and cultured. Atrial natriuretic peptide (ANP) concentration in cell medium was determined by enzyme-linked immunosorbent assay (ELISA). NPR3 mRNA expression was determined by real-time semi-quantitative PCR.

RESULTS AND DISCUSSION

No significant difference in genotype distribution of NPR3 rs2270915 polymorphism was observed between cases and controls (P>.05). Patients carrying the rs2270915 G allele showed decreased SBP, and the difference was marginal. As compared with cells carrying the rs2270915 AA genotype, those with the AG genotype showed significantly lower NPR3 mRNA expression levels (P<.05) and lower medium ANP concentration (P<.001).

WHAT IS NEW AND CONCLUSION

This study suggested that NPR3 rs2270915 polymorphism was associated with decreased SBP level marginally in EH patients in a Chinese Han population, and the polymorphism may function through decreasing NPR3 mRNA expression and ANP level.

Renal adaptive changes and sodium handling in the fetal-to-newborn transition

Appropriate fluid and electrolyte management is critical for optimal care of very low birth weight or sick infants. Delivery of such care requires an understanding of developmental changes in renal water and salt handling that occur with advancing gestational age as well as postnatal age. This review focuses on the principles of sodium homeostasis during fetal and postnatal life. The physiology of renal tubular transport mechanisms, as well as neurohumoral factors impacting renal tubular transport are highlighted. Clinical implications and guidelines to the provision of sodium to this vulnerable population are also discussed.

Differential expression and regulation of anti-hypertrophic genes Npr1 and Npr2 during β-adrenergic receptor activation-induced hypertrophic growth in rats

We sought to determine the effect of chronic activation of β-adrenergic receptor (β-AR) on the left ventricular (LV) expression profile of Npr1 and Npr2 (coding for NPR-A and NPR-B, respectively) genes, and the functional activity of these receptors in adult Wistar rat hearts. The Npr1 gene expression was markedly reduced (3.5-fold), while the Npr2 gene expression was up regulated (4-fold) in Isoproterenol (ISO)-treated heart as compared with controls. A gradual reduction in NPR-A protein (3-fold), cGMP levels (75%) and a steady increased expression of NPR-B protein (4-fold), were noticed in ISO hearts. Further, in-vitro membranes assay shows that NPR-A dependent guanylyl cyclase (GC) activity was down-regulated (2-fold), whereas NPR-B dependent GC activity was increased (5-fold) in ISO treated hearts. Atenolol treatment normalized the altered expression of Npr1 and Npr2 genes. In conclusion, the chronic β-AR activation differentially regulates Npr1 and Npr2 genes in the heart. Npr1 down regulation is positively associated with the development of left ventricular hypertrophy (LVH) in ISO rats.

Adipose tissue natriuretic peptide receptor expression is related to insulin sensitivity in obesity and diabetes

OBJECTIVE

Cardiac natriuretic peptides (NPs) bind to two receptors (NPRA-mediator of signaling; NPRC-clearance receptor) whose ratio, NPRR (NPRA/NPRC), determines the NP bioactivity. This study investigated the relationship of NP receptor gene expression in adipose tissue and muscle with obesity and glucose intolerance. Prospectively, the study also assessed whether changes in NP receptor expression and thermogenic gene markers accompanied improvements of insulin sensitivity.

METHODS

A cross-sectional study of subjects with a wide range of BMI and glucose tolerance (n = 50) was conducted, as well as a randomized 12-week trial of subjects with type 2 diabetes mellitus (T2DM) treated with pioglitazone (n = 9) or placebo (n = 10).

RESULTS

NPRR mRNA was significantly lower in adipose tissue of subjects with obesity when compared with lean subjects (P ≤ 0.001). NPRR decreased with progression from normal glucose tolerance to T2DM (P < 0.01) independently of obesity. Treatment of subjects with T2DM with pioglitazone increased NPRR in adipose tissue (P ≤ 0.01) in conjunction with improvements in insulin sensitivity and increases of the thermogenic markers PPARγ coactivator-1α and uncoupling protein 1 (P ≤ 0.01).

CONCLUSIONS

Decreased adipose tissue NPRR was associated with obesity, glucose intolerance, and insulin resistance. This relationship was not observed for skeletal muscle NPRR. Pharmacological improvement of insulin sensitivity in subjects with T2DM was tied to improvement in NPRR and increased expression of genes involved in thermogenic processes.

NPs/NPRs Signaling Pathways May Be Involved in Depression-Induced Loss of Gastric ICC by Decreasing the Production of mSCF

It is well known that natriuretic peptides (NPs) are involved in the regulation of gastrointestinal motility. Interstitial cells of Cajal (ICC) are the pacemaker cells of gastrointestinal motility and gastrointestinal dyskinesia is one of the important digestive tract symptoms of depression. However, it is unclear whether they are involved in depression-induced loss of ICC. The aim of the present study was to investigate the relationship between the natriuretic peptide signaling pathway and depression-induced loss of gastric ICC in depressed rats. These results showed that the expression of c-kit and stem cell factor (SCF) in smooth muscle layers of stomach were down-regulated in depressed rats at the mRNA and protein levels. The expression of natriuretic peptide receptor (NPR)-A, B and C were up-regulated in the stomach of depressed rats at the mRNA and protein levels. NPR-A, B and C can significantly decrease the expression of SCF to treat cultured gastric smooth muscle cells (GSMCs) obtained from normal rats with different concentrations of C-type natriuretic peptide (CNP). Pretreatment of cultured GSMCs with 8-Brom-cGMP (8-Br-cGMP, a membrane permeable cGMP analog), cANF (a specific NPR-C agonist) and CNP (10⁻⁶ mol/L) demonstrated that 8-Br-cGMP had a similar effect as CNP, but treatment with cANF did not. The results of the methyl thiazolyl tetrazolium bromide (MTT) assay indicated that high concentrations of cANF (10⁻⁶ mol/L) restrained the proliferation of cultured GSMCs. Taken together, these results indicate that the up-regulation of the NPs/NPR-C and NPs/NPR-A, B/cGMP signaling pathways may be involved in depression-induced loss of gastric ICC.

Impaired atrial natriuretic peptide-mediated lipolysis in obesity

BACKGROUND

Catecholamines and natriuretic peptides (NPs) are the only hormones with pronounced lipolytic effects in human white adipose tissue. Although catecholamine-induced lipolysis is well known to be impaired in obesity and insulin resistance, it is not known whether the effect of NPs is also altered.

METHODS

Catecholamine- and atrial NP (ANP)-induced lipolysis was investigated in abdominal subcutaneous adipocytes in vitro and in situ by microdialysis.

RESULTS

In a cohort of 122 women, both catecholamine- and ANP-induced lipolysis in vitro was markedly attenuated in obesity (n=87), but normalized after substantial body weight loss (n=52). The impairment of lipolysis differed between the two hormones when expressing lipolysis per lipid weight, the ratio of stimulated over basal (spontaneous) lipolysis rate or per number of adipocytes. Thus, while the response to catecholamines was lower when expressed as the former two measures, it was higher when expressed per cell number, a consequence of the significantly larger fat cell size in obesity. In contrast, although ANP-induced lipolysis was also attenuated when expressed per lipid weight or the ratio stimulated/basal, it was similar between non-obese and obese subjects when expressed per cell number suggesting that the lipolytic effect of ANP may be even more sensitive to the effects of obesity than catecholamines. Obesity was characterized by a decrease in the protein expression of the signaling NP A receptor (NPRA) and a trend toward increased levels of the clearance receptor NPRC. The impairment in ANP-induced lipolysis observed in vitro was corroborated by microdialysis experiments in situ in a smaller cohort of lean and overweight men.

CONCLUSIONS

ANP- and catecholamine-induced lipolysis is reversibly attenuated in obesity. The pro-lipolytic effects of ANP are relatively more impaired compared with that of catecholamines, which may in part be due to specific changes in NP receptor expression.

Ularitide: a natriuretic peptide candidate for the treatment of acutely decompensated heart failure

Treatment for acutely decompensated heart failure (ADHF) has not changed much in the last two decades. Currently available therapies have variable efficacy and can be associated with adverse outcomes. Natriuretic peptides properties include diuresis, natriuresis, vasorelaxation, inhibition of renin-angiotensin-aldosterone system, and are thus chosen in the treatment of ADHF. Two forms of natriuretic peptides are currently available for the treatment of ADHF. Urodilatin (INN: ularitide) represents another member of the natriuretic peptide family with a unique molecular structure that may provide distinct benefits in the treatment of ADHF. Early clinical exploratory and Phase II studies have demonstrated that ularitide has potential cardiovascular and renal benefits. Ularitide is currently being tested in the Phase III TRUE-AHF clinical study. TRUE-AHF has features that may be different when compared with other recent outcome studies in ADHF. These distinct differences aim to maximize clinical effects and minimize potential adverse events of ularitide. However, whether this rationale translates into a better outcome needs to be awaited.

Systemic, but not cardiomyocyte-specific, deletion of the natriuretic peptide receptor guanylyl cyclase A increases cardiomyocyte number in neonatal mice

Guanylyl cyclase A (GC-A), the receptor for atrial and B-type natriuretic peptides, is implicated in the regulation of blood pressure and cardiac growth. We used design-based stereological methods to examine the effect of GC-A inactivation on cardiomyocyte volume, number and subcellular composition in postnatal mice at day P2. In mice with global, systemic GC-A deletion, the cardiomyocyte number was significantly increased, demonstrating that hyperplasia is the main cause for the increase in ventricle weight in these early postnatal animals. In contrast, conditional, cardiomyocyte-restricted inactivation of GC-A had no significant effect on ventricle weight or cardiomyocyte number. The mean volume of cardiomyocytes and the myocyte-related volumes of the four major cell organelles (myofibrils, mitochondria, nuclei and sarcoplasm) were similar between genotypes. Taken together, systemic GC-A deficiency induces cardiac enlargement based on a higher number of normally composed and sized cardiomyocytes early after birth, whereas cardiomyocyte-specific GC-A abrogation is not sufficient to induce cardiac enlargement and has no effect on number, size and composition of cardiomyocytes. We conclude that postnatal cardiac hyperplasia in mice with global GC-A inactivation is provoked by systemic alterations, e.g., arterial hypertension. Direct GC-A-mediated effects in cardiomyocytes seem not to be involved in the regulation of myocyte proliferation at this early stage.

Glipizide suppresses embryonic vasculogenesis and angiogenesis through targeting natriuretic peptide receptor A

Glipizide, a second-generation sulfonylurea, has been widely used for the treatment of type 2 diabetes. However, it is controversial whether or not glipizide would affect angiogenesis or vasculogenesis. In the present study, we used early chick embryo model to investigate the effect of glipizide on angiogenesis and vasculogenesis, which are the two major processes for embryonic vasculature formation as well as tumor neovascularization. We found that Glipizide suppressed both angiogenesis in yolk-sac membrane (YSM) and blood island formation during developmental vasculogenesis. Glipizide did not affect either the process of epithelial to mesenchymal transition (EMT) or mesoderm cell migration. In addition, it did not interfere with separation of smooth muscle cell progenitors from hemangioblasts. Moreover, natriuretic peptide receptor A (NPRA) has been identified as the putative target for glipizide׳s inhibitory effect on vasculogenesis. When NPRA was overexpressed or activated, blood island formation was reduced. NPRA signaling may play a crucial role in the effect of glipizide on vasculogenesis during early embryonic development.

Atrial natriuretic peptide (ANP) inhibits DMBA/croton oil induced skin tumor growth by modulating NF-κB, MMPs, and infiltrating mast cells in swiss albino mice

Cardiac hormone atrial natriuretic peptide (ANP) and its receptor, natriuretic peptide receptor-A (NPR-A) are implicated as a vital regulator of cancer cell growth and tumor progression. However, the underlying mechanism by which ANP opposes the cancer growth in in-vivo remains unknown. Herein, we investigated the anti-cancer activity of ANP on 7, 12-dimethyl benzanthracence (DMBA)/Croton oil- induced two-step skin carcinogenic mouse model. Skin tumor incidence and tumor volume were recorded during the experimental period of 16 weeks. ANP (1 μg/kg body weight/alternate days for 4 weeks) was injected subcutaneously from the 13th week of DMBA/Croton oil induction. ANP treatment markedly inhibited the skin tumor growth (P<0.001). A significant reduction in the level of NF-κB activation (P<0.001), infiltrating mast cell count (P<0.01) and MMP-2/-9 (P<0.001, respectively) were noticed in the ANP treated mice skin tissue. Further, ANP treatment revert back the altered levels of serum LDH-4, C-reactive protein (CRP), and enzymatic antioxidants (SOD and CAT activities) to near normal level. Taken together, the results of this study suggest that ANP opposes the skin carcinogenesis by suppressing the inflammatory response and MMPs.

Novel diuretic strategies for the treatment of heart failure in Japan

Fluid management is of paramount importance in the treatment strategy of heart failure (HF), but the therapeutic efficacy of loop diuretic-based treatment for HF patients is limited by insufficient response and adverse effects. Clinical data establishing the efficacy and safety of tolvaptan, a selective oral vasopressin V2 receptor antagonist that induces aquaresis, have recently been accumulated over 3 years of daily clinical experience in Japan. Intravenous infusion of carperitide, a synthetic α-human atrial natriuretic peptide, has also been widely used as acute-phase therapy for acute decompensated HF in Japan. Combination therapy using loop diuretics, tolvaptan, and carperitide with differing and complementary mechanisms of action may maximize therapeutic activity, to minimize the dosage of loop diuretics and thereby reduce the adverse effects not only for volume removal but also for the stability of cardiorenal hemodynamics.

Atrial natriuretic factor receptor guanylate cyclase, ANF-RGC, transduces two independent signals, ANF and Ca(2+)

Atrial natriuretic factor receptor guanylate cyclase (ANF-RGC), was the first discovered member of the mammalian membrane guanylate cyclase family. The hallmark feature of the family is that a single protein contains both the site for recognition of the regulatory signal and the ability to transduce it into the production of the second messenger, cyclic GMP. For over two decades, the family has been classified into two subfamilies, the hormone receptor subfamily with ANF-RGC being its paramount member, and the Ca²⁺ modulated subfamily, which includes the rod outer segment guanylate cyclases, ROS-GC1 and 2, and the olfactory neuroepithelial guanylate cyclase. ANF-RGC is the receptor and the signal transducer of the most hypotensive hormones, ANF– and B-type natriuretic peptide (BNP). After binding these hormones at the extracellular domain it, at its intracellular domain, signals activation of the C-terminal catalytic module and accelerates the production of cyclic GMP. Cyclic GMP then serves the second messenger role in biological responses of ANF and BNP such as natriuresis, diuresis, vasorelaxation, and anti-proliferation. Very recently another modus operandus for ANF-RGC was revealed. Its crux is that ANF-RGC activity is also regulated by Ca²⁺. The Ca²⁺ sensor neurocalcin d mediates this signaling mechanism. Strikingly, the Ca²⁺ and ANF signaling mechanisms employ separate structural motifs of ANF-RGC in modulating its core catalytic domain in accelerating the production of cyclic GMP. In this review the biochemistry and physiology of these mechanisms with emphasis on cardiovascular regulation will be discussed.

Histone deacetylase inhibitors modulate the transcriptional regulation of guanylyl cyclase/natriuretic peptide receptor-a gene: interactive roles of modified histones, histone acetyltransferase, p300, AND Sp1

Atrial natriuretic peptide (ANP) binds guanylyl cyclase-A/natriuretic peptide receptor-A (GC-A/NPRA) and produces the intracellular second messenger, cGMP, which regulates cardiovascular homeostasis. We sought to determine the function of histone deacetylases (HDACs) in regulating Npr1 (coding for GC-A/NPRA) gene transcription, using primary mouse mesangial cells treated with class-specific HDAC inhibitors (HDACi). Trichostatin A, a pan inhibitor, and mocetinostat (MGCD0103), a class I HDAC inhibitor, significantly enhanced Npr1 promoter activity (by 8- and 10-fold, respectively), mRNA levels (4- and 5.3-fold, respectively), and NPRA protein (2.7- and 3.5-fold, respectively). However, MC1568 (class II HDAC inhibitor) had no discernible effect. Overexpression of HDAC1 and HDAC2 significantly attenuated Npr1 promoter activity, whereas HDAC3 and HDAC8 had no effect. HDACi-treated cultured cells in vitro and intact animals in vivo showed significantly reduced binding of HDAC1 and -2 and increased accumulation of acetylated H3-K9/14 and H4-K12 at the Npr1 promoter. Deletional analyses of the Npr1 promoter along with ectopic overexpression and inhibition of Sp1 confirmed that HDACi-induced Npr1 gene transcription is accomplished by Sp1 activation. Furthermore, HDACi attenuated the interaction of Sp1 with HDAC1/2 and promoted Sp1 association with p300 and p300/cAMP-binding protein-associated factor; it also promoted the recruitment of p300 and p300/cAMP-binding protein-associated factor to the Npr1 promoter. Our results demonstrate that trichostatin A and MGCD0103 enhanced Npr1 gene expression through inhibition of HDAC1/2 and increased both acetylation of histones (H3-K9/14, H4-K12) and Sp1 by p300, and their recruitment to Npr1 promoter. Our findings define a novel epigenetic regulatory mechanism that governs Npr1 gene transcription.

Natriuretic peptides and fat metabolism

PURPOSE OF REVIEW

Cardiac natriuretic peptides have emerged as potent metabolic hormones during the past decade. We here discuss recent work highlighting the potential importance of these hormones in metabolic physiology and diseases.

RECENT FINDINGS

Natriuretic peptides signal through a cyclic guanosine monophosphate pathway to convey their biological effects at the cell level. Similarly to cyclic adenosine monophosphate, activation of cyclic guanosine monophosphate signaling induces a browning of white fat and thermogenesis. Natriuretic peptides also enhance oxidative capacity and fat oxidation in skeletal muscle of mice and humans. The molecular mechanism involves an upregulation of mitochondrial fat oxidative capacity and respiration. This may be particularly relevant to relay the physiological adaptations of chronic exercise. Population-based studies indicate that circulating natriuretic peptides are lowered in obesity and predict type 2 diabetes. Recent work also directly link natriuretic peptides with type 2 diabetes through a gut-heart axis.

SUMMARY

Natriuretic peptides exhibit a wide range of biological actions to control metabolic homeostasis. Natriuretic peptides deficiency in obesity may trigger metabolic dysfunction and lead to type 2 diabetes. Increasing circulating natriuretic peptides level and tissue signaling may help to fight against metabolic complications of obesity.

Pathological ventricular remodeling: mechanisms: part 1 of 2

Despite declines in heart failure morbidity and mortality with current therapies, rehospitalization rates remain distressingly high, substantially affecting individuals, society, and the economy. As a result, the need for new therapeutic advances and novel medical devices is urgent. Disease-related left ventricular remodeling is a complex process involving cardiac myocyte growth and death, vascular rarefaction, fibrosis, inflammation, and electrophysiological remodeling. Because these events are highly interrelated, targeting a single molecule or process may not be sufficient. Here, we review molecular and cellular mechanisms governing pathological ventricular remodeling.

Functional silencing of guanylyl cyclase/natriuretic peptide receptor-A by microRNA interference: analysis of receptor endocytosis

Guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) is the principal receptor for the regulatory action of atrial and brain natriuretic peptides (ANP and BNP) and an important effector molecule in controlling of extracellular fluid volume and blood pressure homeostasis. We have utilized RNA interference to silence the expression of GC-A/NPRA gene (Npr1), providing a novel system to study the internalization and trafficking of NPRA in intact cells. MicroRNA (miRNA)-mediated small interfering RNA (siRNA) elicited functional gene-knockdown of NPRA in stably transfected human embryonic kidney 293 (HEK-293) cells expressing a high density of recombinant NPRA. We artificially expressed three RNA polymerase II-driven miRNAs that specifically targeted the Npr1 gene, but shared no significant sequence homology with any other known mouse genes. Reverse transcription-PCR (RT-PCR) and Northern blot analyses identified two highly efficient Npr1 miRNA sequences to knockdown the expression of NPRA. The Npr1 miRNA in chains or clusters decreased NPRA expression more than 90% as compared with control cells. ANP-dependent stimulation of intracellular accumulation of cGMP and guanylyl cyclase activity of NPRA were significantly reduced in Npr1 miRNA-expressing cells by 90-95% as compared with control cells. Treatment with Npr1 miRNA caused a drastic reduction in the receptor density subsequently a deceased internalization of radiolabeled (125)I-ANP-NPRA ligand-receptor complexes. Only 12%-15% of receptor population was localized in the intracellular compartments of microRNA silenced cells as compared to 70%-80% in control cells.

The ANF-RGC gene motif (669)WTAPELL(675) is vital for blood pressure regulation: biochemical mechanism

ANF-RGC is the prototype membrane guanylate cyclase, both the receptor and the signal transducer of the hormones ANF and BNP. After binding them at the extracellular domain, it, at its intracellular domain, signals activation of the C-terminal catalytic module and accelerates production of the second messenger, cyclic GMP. This, in turn, controls the physiological processes of blood pressure, cardiovascular function, fluid secretion, and others: metabolic syndrome, obesity, and apoptosis. The biochemical mechanism by which this single molecule controls these diverse processes, explicitly blood pressure regulation, is the subject of this study. In line with the concept that the structural modules of ANF-RGC are designed to respond to more than one yet distinctive signals, the study demonstrates the construction of a novel ANF-RGC-In-gene-(669)WTAPELL(675) mouse model. Through this model, the study establishes that (669)WTAPELL(675) is a vital ANF signal transducer motif of the guanylate cyclase. Its striking physiological features linked with their biochemistry are the following. (1) It controls the hormonally dependent cyclic GMP production in the kidney and the adrenal gland. Its deletion causes (2) hypertension and (3) cardiac hypertrophy. (4) These mice show higher levels of the plasma aldosterone. For the first time, a mere seven-amino acid-encoded motif of the mouse gene has been directly linked with the physiological control of blood pressure regulation, a detailed biochemistry of this linkage has been established, and a model for this linkage has been described.

[The heart as an endocrine organ]

The discovery of cardiac hormone production significantly changed the evaluation of the function of the heart, which is rather regarded as a determining factor of the electrolyte and hemodynamic homeostasis cooperating with other organ systems instead of a mechanical pump. The most important hormones produced by the heart are the natriuretic peptides that have the primary role of protection against volume overload through natriuretic, diuretic, vasodilator and antiproliferative effects. They are integrative markers of the cardiac, vascular and renal functions and marking cardiorenal distress. Brain natriuretic peptide and the N-terminal pro-hormone (NT-proBNP) became generally accepted markers of heart failure exceeding traditional pathophysiological significance of those. They are useful in the diagnosis, estimation of prognosis and therapy guidance and their therapeutic administration is also available. Although the detection of extraadrenal aldosterone production is an exciting new discovery, intracardial aldosterone production is not significant in human beings. The intracardial thyroid hormone production is regulated by deiodinase activity. The role of elevated T3 concentration was suggested in the development of cardiac hypertrophy, while low T3 is assumed to be important in adaptation to hypoxia. An unexpected, complex relation can be determined between epicardial adipose tissue and coronary artery diseases, cytokine and adipokine production of adipocytes might be a part of the self-enhancing process of atherosclerosis.

Natriuretic peptides and cGMP signaling control of energy homeostasis

Since the discovery of natriuretic peptides (NPs) by de Bold et al. in 1981, the cardiovascular community has been well aware that they exert potent effects on vessels, heart remodeling, kidney function, and the regulation of sodium and water balance. Who would have thought that NPs are also able to exert metabolic effects and contribute to an original cross talk between heart, adipose tissues, and skeletal muscle? The attention on the metabolic role of NPs was awakened in the year 2000 with the discovery that NPs exert potent lipolytic effects mediated by the NP receptor type A/cGMP pathway in human fat cells and that they contribute to lipid mobilization in vivo. In this review, we will discuss the biological effects of NPs on the main tissues involved in the regulation of energy metabolism (i.e., white and brown adipose tissues, skeletal muscle, liver, and pancreas). These recent results on NPs are opening a new chapter into the physiological properties and therapeutic usefulness of this family of hormones.

A novel bioassay for the activity determination of therapeutic human brain natriuretic peptide (BNP)

Background

Recombinant human brain natriuretic peptide (rhBNP) is an important peptide-based therapeutic drug indicated for the treatment of acute heart failure. Accurate determination of the potency of therapeutic rhBNP is crucial for the safety and efficacy of the drug. The current bioassay involves use of rabbit aortic strips, with experiments being complicated and time-consuming and markedly variable in results. Animal-less methods with better precision and accuracy should be explored. We have therefore developed an alternative cell-based assay, which relies on the ability of BNP to induce cGMP production in HEK293 cells expressing BNP receptor guanylyl cyclase-A.

Methodology/Principal Findings

An alternative assay based on the measurement of BNP-induced cGMP production was developed. Specifically, the bioassay employs cells engineered to express BNP receptor guanylyl cyclase-A (GCA). Upon rhBNP stimulation, the levels of the second messager cGMP in these cells drastically increased and subsequently secreted into culture supernatants. The quantity of cGMP, which corresponds to the rhBNP activity, was determined using a competitive ELISA developed by us. Compared with the traditional assay, the novel cell-based assay demonstrated better reproducibility and precision.

Conclusion/Significance

The optimized cell-based assay is much simpler, more rapid and precise compared with the traditional assay using animal tissues. To our knowledge, this is the first report on a novel and viable alternative assay for rhBNP potency analysis.

Ca(2+) modulation of ANF-RGC: new signaling paradigm interlocked with blood pressure regulation

ANF-RGC is the prototype receptor membrane guanylate cyclase that is both the receptor and the signal transducer of the most hypotensive hormones, ANF and BNP. It is a single-transmembrane protein. After binding these hormones at the extracellular domain, ANF-RGC at its intracellular domain signals the activation of the C-terminal catalytic module and accelerates the production of the second messenger, cyclic GMP, which controls blood pressure, cardiac vasculature, and fluid secretion. At present, this is the sole transduction mechanism and the physiological function of ANF-RGC. Through comprehensive studies involving biochemistry, immunohistochemistry, and blood pressure measurements in mice with targeted gene deletions, this study demonstrates a new signaling model of ANF-RGC that also controls blood pressure. In this model, (1) ANF-RGC is not the transducer of ANF and BNP, (2) its extracellular domain is not used for signaling, and (3) the signal flow is not downstream from the extracellular domain to the core catalytic domain. Instead, the signal is the intracellular Ca(2+), which is translated at the site of its reception, at the core catalytic domain of ANF-RGC. A model for this Ca(2+) signal transduction is diagrammed. It captures Ca(2+) through its Ca(2+) sensor myristoylated neurocalcin δ and upregulates ANF-RGC activity with a K(1/2) of 0.5 μM. The neurocalcin δ-modulated domain resides in the (849)DIVGFTALSAESTPMQVV(866) segment of ANF-RGC, which is a part of the core catalytic domain. Thereby, ANF-RGC is primed to receive, transmit, and translate the Ca(2+) signals into the generation of cyclic GMP at a rapid rate. The study defines a new paradigm of membrane guanylate cyclase signaling, which is linked to the physiology of cardiac vasculature regulation and possibly also to fluid secretion.

Key advances in antihypertensive treatment

Although various effective treatments for hypertension are available, novel therapies to reduce elevated blood pressure, improve blood-pressure control, treat resistant hypertension, and reduce the associated cardiovascular risk factors are still required. A novel angiotensin-receptor blocker (ARB) was approved in 2011, and additional compounds are in development or being tested in clinical trials. Several of these agents have innovative mechanisms of action (an aldosterone synthase inhibitor, a natriuretic peptide agonist, a soluble epoxide hydrolase inhibitor, and an angiotensin II type 2 receptor agonist) or dual activity (a combined ARB and neutral endopeptidase inhibitor, an ARB and endothelin receptor A blocker, and an endothelin-converting enzyme and neutral endopeptidase inhibitor). In addition, several novel fixed-dose combinations of existing antihypertensive agents were approved in 2010-2011, including aliskiren double and triple combinations, and an olmesartan triple combination. Upcoming fixed-dose combinations are expected to introduce calcium-channel blockers other than amlodipine and diuretics other than hydrochlorothiazide. Finally, device-based approaches to the treatment of resistant hypertension, such as renal denervation and baroreceptor activation therapy, have shown promising results in clinical trials. However, technical improvements in the implantation procedure and devices used for baroreceptor activation therapy are required to address procedural safety concerns.