Discovery of small molecule guanylyl cyclase A receptor positive allosteric modulators.

The particulate guanylyl cyclase A receptor (GC-A), via activation by its endogenous ligands atrial natriuretic peptide (ANP) and b-type natriuretic peptide (BNP), possesses beneficial biological properties such as blood pressure regulation, natriuresis, suppression of adverse remodeling, inhibition of the renin-angiotensin-aldosterone system, and favorable metabolic actions through the generation of its second messenger cyclic guanosine monophosphate (cGMP). Thus, the GC-A represents an important molecular therapeutic target for cardiovascular disease and its associated risk factors. However, a small molecule that is orally bioavailable and directly targets the GC-A to potentiate cGMP has yet to be discovered. Here, we performed a cell-based high-throughput screening campaign of the NIH Molecular Libraries Small Molecule Repository, and we successfully identified small molecule GC-A positive allosteric modulator (PAM) scaffolds. Further medicinal chemistry structure-activity relationship efforts of the lead scaffold resulted in the development of a GC-A PAM, MCUF-651, which enhanced ANP-mediated cGMP generation in human cardiac, renal, and fat cells and inhibited cardiomyocyte hypertrophy in vitro. Further, binding analysis confirmed MCUF-651 binds to GC-A and selectively enhances the binding of ANP to GC-A. Moreover, MCUF-651 is orally bioavailable in mice and enhances the ability of endogenous ANP and BNP, found in the plasma of normal subjects and patients with hypertension or heart failure, to generate GC-A-mediated cGMP ex vivo. In this work, we report the discovery and development of an oral, small molecule GC-A PAM that holds great potential as a therapeutic for cardiovascular, renal, and metabolic diseases.

Sex-based differences in metabolic protection by the ANP genetic variant rs5068 in the general population.

Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are produced in the heart and secreted into the circulation. As hormones, both peptides activate the guanylyl cyclase receptor A (GC-A), playing a role in blood pressure (BP) regulation. A significant role for ANP and BNP includes favorable actions in metabolic homeostasis. Sex-based high prevalence of risk factors for cardiovascular disease in males compared with females is well established, but sex-based differences on cardiometabolic protection have not been investigated in relation to ANP (NPPA) and BNP (NPPB) gene variants. We included 1,146 subjects in the general population from Olmsted County, Minnesota. Subjects were genotyped for the ANP gene variant rs5068 and BNP gene variant rs198389. Cardiometabolic parameters and medical records were reviewed. In the presence of the minor allele of rs5068, diastolic BP, creatinine, body mass index (BMI), waist measurement, insulin, and prevalence of obesity and metabolic syndrome were lower, whereas HDL was higher in males with only trends observed in females. We observed no associations of the minor allele with echocardiographic parameters in either males or females. Regarding rs198389 genotype, the minor allele was not associated with any BP, metabolic, renal, or echocardiographic parameters in either sex. In the general community, the minor allele of the ANP gene variant rs5068 is associated with a favorable metabolic phenotype in males. No associations were observed with the BNP gene variant rs198389. These studies support a protective role of the ANP pathway on metabolic function and underscore the importance of sex in relationship to natriuretic peptide responses.NEW & NOTEWORTHY Males are characterized by lower ANP and BNP with greater prevalence of cardiometabolic disease. The ANP genetic variant rs5068 was associated with less metabolic dysfunction in males, whereas no metabolic profile was related to the BNP genetic variant rs198389 in the general population. ANP may play a more biological role in metabolic homeostasis compared with BNP in the general population with greater physiological metabolic actions in males compared with females.

CRED9: A differentially expressed elncRNA regulates expression of transcription factor CEBPA.

Enhancer RNAs (eRNA) are non-coding transcripts produced from active enhancers and have potential gene regulatory function. CCAAT enhancer-binding protein alpha (CEBPA) is a transcription factor generally involved in metabolism, cell cycle inhibition, hematopoiesis, adipogenesis, hepatogenesis, and is associated with tumorigenesis. In this study, we demonstrate that an enhancer-associated long non-coding RNA (elncRNA), transcribed from an enhancer located 9kb downstream from the transcriptional start site (TSS) of CEBPA, positively regulates the expression of CEBPA. As a result, we named this elncRNA 'CEBPA regulatory elncRNA downstream 9kb' or 'CRED9'. CRED9 expression level positively correlates with CEBPA mRNA expression across multiple cell lines as detected by RT droplet digital PCR. Knockdown of CRED9 resulted in a reduction of CEBPA mRNA expression in Hep3B cells. Additionally, CRED9 knockdown in Hep3B and HepG2 cells resulted in lower CEBPA protein expression. We also found that knockdown of CRED9 in Hep3B cells caused a 57.8% reduction in H3K27ac levels at the +9kb CEBPA enhancer. H3K27ac has previously been described as a marker of active enhancers. Taken together, the evidence presented here supports a previously proposed model whereby, in some contexts, eRNA transcripts are necessary to amplify and maintain H3K27ac levels at a given enhancer. Ultimately, this study adds to the growing body of evidence that elncRNA transcripts have important roles in enhancer function and gene regulation.

Novel Humanized Peripheral Blood Mononuclear Cell Mouse Model with Delayed Onset of Graft-versus-Host Disease for Preclinical HIV Research.

Humanized mouse models are based on the engraftment of human cells in immunodeficient mouse strains, most notably the NSG strain. Most used models have a major limitation in common, the development of graft-versus-host disease (GVHD). GVHD not only introduces variabilities into the research data but also leads to animal welfare concerns. A new mouse strain, B6.129S-Rag2tm1Fwa CD47tm1Fpl Il2rgtm1Wjl/J, which lacks Rag1, IL2rg, and CD47 (triple knockout [TKO]), is resistant to GVHD development. We transplanted TKO mice with human peripheral blood mononuclear cells (PBMCs) to establish a new humanized PBMC (hu-PBMC) mouse model. A cohort of these mice was infected with HIV-1 and monitored for plasma HIV viremia and CD4+ T cell depletion. The onset and progression of GVHD were monitored by clinical signs. This study demonstrates that TKO mice transplanted with human PBMCs support engraftment of human immune cells in primary and secondary lymphoid tissues, rectum, and brain. Moreover, the TKO hu-PBMC model supports HIV-1 infection via the intraperitoneal, rectal, or vaginal route, as confirmed by robust plasma HIV viremia and CD4+ T cell depletion. Lastly, TKO mice showed a delayed onset of GVHD clinical signs (∼24 days) and exhibited significant decreases in plasma levels of tumor necrosis factor beta (TNF-ß). Based on these results, the TKO hu-PBMC mouse model not only supports humanization and HIV-1 infection but also has a delayed onset of GVHD development, making this model a valuable tool in HIV research. IMPORTANCE Currently, there is no cure or vaccine for HIV infection; thus, continued research is needed to end the HIV pandemic. While many animal models are used in HIV research, none is used more than the humanized mouse model. A major limitation with current humanized mouse models is the development of graft-versus-host disease (GVHD). Here, we describe a novel humanized-PBMC mouse model that has a delayed onset GVHD development and supports and models HIV infection comparably to well-established humanized mouse models.

Evidence for Angiotensin II as a Naturally Existing Suppressor for the Guanylyl Cyclase A Receptor and Cyclic GMP Generation.

The natriuretic peptide system (NPS) and renin-angiotensin-aldosterone system (RAAS) function oppositely at multiple levels. While it has long been suspected that angiotensin II (ANGII) may directly suppress NPS activity, no clear evidence to date supports this notion. This study was designed to systematically investigate ANGII-NPS interaction in humans, in vivo, and in vitro. Circulating atrial, b-type, and c-type natriuretic peptides (ANP, BNP, CNP), cyclic guanosine monophosphate (cGMP), and ANGII were simultaneously investigated in 128 human subjects. Prompted hypothesis was validated in vivo to determine the influence of ANGII on ANP actions. The underlying mechanisms were further explored via in vitro approaches. In humans, ANGII demonstrated an inverse relationship with ANP, BNP, and cGMP. In regression models predicting cGMP, adding ANGII levels and the interaction term between ANGII and natriuretic peptides increased the predictive accuracy of the base models constructed with either ANP or BNP, but not CNP. Importantly, stratified correlation analysis further revealed a positive association between cGMP and ANP or BNP only in subjects with low, but not high, ANGII levels. In rats, co-infusion of ANGII even at a physiological dose attenuated cGMP generation mediated by ANP infusion. In vitro, we found the suppressive effect of ANGII on ANP-stimulated cGMP requires the presence of ANGII type-1 (AT1) receptor and mechanistically involves protein kinase C (PKC), as this suppression can be substantially rescued by either valsartan (AT1 blocker) or Go6983 (PKC inhibitor). Using surface plasmon resonance (SPR), we showed ANGII has low binding affinity to the guanylyl cyclase A (GC-A) receptor compared to ANP or BNP. Our study reveals ANGII is a natural suppressor for the cGMP-generating action of GC-A via AT1/PKC dependent manner and highlights the importance of dual-targeting RAAS and NPS in maximizing beneficial properties of natriuretic peptides in cardiovascular protection.

Novel Therapeutic Approaches Targeting the Renin-Angiotensin System and Associated Peptides in Hypertension and Heart Failure.

Despite the success of renin-angiotensin system (RAS) blockade by angiotensin-converting enzyme (ACE) inhibitors and angiotensin II type 1 receptor (AT1R) blockers, current therapies for hypertension and related cardiovascular diseases are still inadequate. Identification of additional components of the RAS and associated vasoactive pathways, as well as new structural and functional insights into established targets, have led to novel therapeutic approaches with the potential to provide improved cardiovascular protection and better blood pressure control and/or reduced adverse side effects. The simultaneous modulation of several neurohumoral mediators in key interconnected blood pressure-regulating pathways has been an attractive approach to improve treatment efficacy, and several novel approaches involve combination therapy or dual-acting agents. In addition, increased understanding of the complexity of the RAS has led to novel approaches aimed at upregulating the ACE2/angiotensin-(1-7)/Mas axis to counter-regulate the harmful effects of the ACE/angiotensin II/angiotensin III/AT1R axis. These advances have opened new avenues for the development of novel drugs targeting the RAS to better treat hypertension and heart failure. Here we focus on new therapies in preclinical and early clinical stages of development, including novel small molecule inhibitors and receptor agonists/antagonists, less conventional strategies such as gene therapy to suppress angiotensinogen at the RNA level, recombinant ACE2 protein, and novel bispecific designer peptides.

CRRL269.

RATIONALE: Acute kidney injury (AKI) has a high prevalence and mortality in critically ill patients. It is also a powerful risk factor for heart failure incidence driven by hemodynamic changes and neurohormonal activation. However, no drugs have been approved by the Food and Drug Administration. Endogenous pGC-A (particulate guanylyl cyclase A receptor) activators were reported to preserve renal function and improve mortality in AKI patients, although hypotension accompanied by pGC-A activators have limited their therapeutic potential. OBJECTIVE: We investigated the therapeutic potential of a nonhypotensive pGC-A activator/designer natriuretic peptide, CRRL269, in a short-term, large animal model of ischemia-induced AKI and also investigated the potential of uCNP (urinary C-type natriuretic peptide) as a biomarker for AKI. METHODS AND RESULTS: We first showed that CRRL269 stimulated cGMP generation, suppressed plasma angiotensin II, and reduced cardiac filling pressures without lowering blood pressure in the AKI canine model. We also demonstrated that CRRL269 preserved glomerular filtration rate, increased renal blood flow, and promoted diuresis and natriuresis. Further, CRRL269 reduced kidney injury and apoptosis as evidenced by ex vivo histology and tissue apoptosis analysis. We also showed, compared with native pGC-A activators, that CRRL269 is a more potent inhibitor of apoptosis in renal cells and induced less decreases in intracellular Ca2+ concentration in vascular smooth muscle cells. The renal antiapoptotic effects were at least mediated by cGMP/PKG pathway. Further, CRRL269 inhibited proapoptotic genes expression using a polymerase chain reaction gene array. Additionally, we demonstrated that AKI increased uCNP levels. CONCLUSIONS: Our study supports developing CRRL269 as a novel renocardiac protective agent for AKI treatment.

Discovery of O-glycans on atrial natriuretic peptide (ANP) that affect both its proteolytic degradation and potency at its cognate receptor.

Atrial natriuretic peptide (ANP) is a peptide hormone that in response to atrial stretch is secreted from atrial myocytes into the circulation, where it stimulates vasodilatation and natriuresis. ANP is an important biomarker of heart failure where low plasma concentrations exclude cardiac dysfunction. ANP is a member of the natriuretic peptide (NP) family, which also includes the B-type natriuretic peptide (BNP) and the C-type natriuretic peptide. The proforms of these hormones undergo processing to mature peptides, and for proBNP, this process has previously been demonstrated to be regulated by O-glycosylation. It has been suggested that proANP also may undergo post-translational modifications. Here, we conducted a targeted O-glycoproteomics approach to characterize O-glycans on NPs and demonstrate that all NP members can carry O-glycans. We identified four O-glycosites in proANP in the porcine heart, and surprisingly, two of these were located on the mature bioactive ANP itself. We found that one of these glycans is located within a conserved sequence motif of the receptor-binding region, suggesting that O-glycans may serve a function beyond intracellular processing and maturation. We also identified an O-glycoform of proANP naturally occurring in human circulation. We demonstrated that site-specific O-glycosylation shields bioactive ANP from proteolytic degradation and modifies potency at its cognate receptor in vitro Furthermore, we showed that ANP O-glycosylation attenuates acute renal and cardiovascular ANP actions in vivo The discovery of novel glycosylated ANP proteoforms reported here significantly improves our understanding of cardiac endocrinology and provides important insight into the etiology of heart failure.

Long-term blood pressure lowering and cGMP-activating actions of the novel ANP analog MANP.

Based on the cardiac hormone atrial natriuretic peptide (ANP) and its seminal role in blood pressure (BP) homeostasis, we investigated the chronic BP lowering actions of a novel ANP analog currently entering clinical trials for hypertension. Previous reports demonstrate that this analog MANP activates the guanylyl cyclase A receptor (GC-A) and results in more potent biological actions compared with ANP; thus, it may represent a new therapeutic drug for hypertension. A major goal of this study was to establish that chronic subcutaneous delivery of MANP is feasible and hypotensive together with cGMP effects. We investigated the BP-lowering and cGMP-activating actions of acute and chronic subcutaneous delivery in normal and hypertensive rats. Furthermore, we explored vascular mechanisms of MANP in human aortic smooth muscle cells (HASMC) and ex vivo in isolated arteries. In normal rats with a single subcutaneous injection, MANP promoted robust dose-dependent BP-lowering actions and natriuresis, together with cGMP activation. Most importantly in hypertensive rats, once-a-day subcutaneous injection of MANP for 7 days induced cGMP elevation and long-term BP reduction compared with vehicle. Mechanistically, in HASMC, MANP activated cGMP and attenuated angiotensin II-mediated increases in intracellular Ca2+ levels while directly vasorelaxing arterial rings. Our study demonstrates for the first time the effectiveness of subcutaneous administration of MANP for 7 days and provides innovative, vascular mechanisms of BP regulation supporting its continued development as a novel therapeutic for hypertension.

C53: A novel particulate guanylyl cyclase B receptor activator that has sustained activity in vivo with anti-fibrotic actions in human cardiac and renal fibroblasts.

The native particulate guanylyl cyclase B receptor (pGC-B) activator, C-type natriuretic peptide (CNP), induces anti-remodeling actions in the heart and kidney through the generation of the second messenger 3', 5' cyclic guanosine monophosphate (cGMP). Indeed fibrotic remodeling, particularly in cardiorenal disease states, contributes to disease progression and thus, has been a key target for drug discovery and development. Although the pGC-B/cGMP system has been perceived as a promising anti-fibrotic pathway, its therapeutic potential is limited due to the rapid degradation and catabolism of CNP by neprilysin (NEP) and natriuretic peptide clearance receptor (NPRC). The goal of this study was to bioengineer and test in vitro and in vivo a novel pGC-B activator, C53. Here we established that C53 selectively generates cGMP via the pGC-B receptor and is highly resistant to NEP and has less interaction with NPRC in vitro. Furthermore in vivo, C53 had enhanced cGMP-generating actions that paralleled elevated plasma CNP-like levels, thus indicating a longer circulating half-life compared to CNP. Importantly in human cardiac fibroblasts (HCFs) and renal fibroblasts (HRFs), C53 exerted robust cGMP-generating actions, inhibited TGFß-1 stimulated HCFs and HRFs proliferation chronically and suppressed the differentiation of HCFs and HRFs to myofibroblasts. The current findings advance innovation in drug discovery and highlight C53 as a novel pGC-B activator with sustained in vivo activity and anti-fibrotic actions in vitro. Future studies are warranted to explore the efficacy and therapeutic opportunity of C53 targeting fibrosis in cardiorenal disease states and beyond.

HIV Replication and Latency in a Humanized NSG Mouse Model during Suppressive Oral Combinational Antiretroviral Therapy.

Although current combinatorial antiretroviral therapy (cART) is therapeutically effective in the majority of HIV patients, interruption of therapy can cause a rapid rebound in viremia, demonstrating the existence of a stable reservoir of latently infected cells. HIV latency is therefore considered a primary barrier to HIV eradication. Identifying, quantifying, and purging the HIV reservoir is crucial to effectively curing patients and relieving them from the lifelong requirement for therapy. Latently infected transformed cell models have been used to investigate HIV latency; however, these models cannot accurately represent the quiescent cellular environment of primary latently infected cells in vivo For this reason, in vivo humanized murine models have been developed for screening antiviral agents, identifying latently infected T cells, and establishing treatment approaches for HIV research. Such models include humanized bone marrow/liver/thymus mice and SCID-hu-thy/liv mice, which are repopulated with human immune cells and implanted human tissues through laborious surgical manipulation. However, no one has utilized the human hematopoietic stem cell-engrafted NOD/SCID/IL2rγnull (NSG) model (hu-NSG) for this purpose. Therefore, in the present study, we used the HIV-infected hu-NSG mouse to recapitulate the key aspects of HIV infection and pathogenesis in vivo Moreover, we evaluated the ability of HIV-infected human cells isolated from HIV-infected hu-NSG mice on suppressive cART to act as a latent HIV reservoir. Our results demonstrate that the hu-NSG model is an effective surgery-free in vivo system in which to efficiently evaluate HIV replication, antiretroviral therapy, latency and persistence, and eradication interventions.IMPORTANCE HIV can establish a stably integrated, nonproductive state of infection at the level of individual cells, known as HIV latency, which is considered a primary barrier to curing HIV. A complete understanding of the establishment and role of HIV latency in vivo would greatly enhance attempts to develop novel HIV purging strategies. An ideal animal model for this purpose should be easy to work with, should have a shortened disease course so that efficacy testing can be completed in a reasonable time, and should have immune correlates that are easily translatable to humans. We therefore describe a novel application of the hematopoietic stem cell-transplanted humanized NSG model for dynamically testing antiretroviral treatment, supporting HIV infection, establishing HIV latency in vivo The hu-NSG model could be a facile alternative to humanized bone marrow/liver/thymus or SCID-hu-thy/liv mice in which laborious surgical manipulation and time-consuming human cell reconstitution is required.

Atrial Natriuretic Peptide: A Molecular Target of Novel Therapeutic Approaches to Cardio-Metabolic Disease.

Atrial natriuretic peptide (ANP) is a cardiac hormone with pleiotropic cardiovascular and metabolic properties including vasodilation, natriuresis and suppression of the renin-angiotensin-aldosterone system. Moreover, ANP induces lipolysis, lipid oxidation, adipocyte browning and ameliorates insulin sensitivity. Studies on ANP genetic variants revealed that subjects with higher ANP plasma levels have lower cardio-metabolic risk. In vivo and in humans, augmenting the ANP pathway has been shown to exert cardiovascular therapeutic actions while ameliorating the metabolic profile. MANP is a novel designer ANP-based peptide with greater and more sustained biological actions than ANP in animal models. Recent studies also demonstrated that MANP lowers blood pressure and inhibits aldosterone in hypertensive subjects whereas cardiometabolic properties of MANP are currently tested in an on-going clinical study in hypertension and metabolic syndrome. Evidence from in vitro, in vivo and in human studies support the concept that ANP and related pathway represent an optimal target for a comprehensive approach to cardiometabolic disease.

New Pharmacological Strategies to Increase cGMP.

The intracellular nucleotide cyclic guanosine monophosphate (cGMP) is found in many human organ tissues. Its concentration increases in response to the activation of receptor enzymes called guanylyl cyclases (GCs). Different ligands bind GCs, generating the second messenger cGMP, which in turn leads to a variety of biological actions. A deficit or dysfunction of this pathway at the cardiac, vascular, and renal levels manifests in cardiovascular diseases such as heart failure, arterial hypertension, and pulmonary arterial hypertension. An impairment of the cGMP pathway also may be involved in the pathogenesis of obesity as well as dementia. Therefore, agents enhancing the generation of cGMP for the treatment of these conditions have been intensively studied. Some have already been approved, and others are currently under investigation. This review discusses the potential of novel drugs directly or indirectly targeting cGMP as well as the progress of research to date.

CRRL269: a novel designer and renal-enhancing pGC-A peptide activator.

The natriuretic peptides (NPs) B-type NP (BNP) and urodilatin (URO) exert renal protective properties via the particulate guanylyl cyclase A receptor (pGC-A). As a potential renal-enhancing strategy, we engineered a novel designer peptide that we call CRRL269. CRRL269 was investigated in human cell lines and in normal canines to define potential cardiorenal enhancing actions. The mechanism of its cardiorenal selective properties was also investigated. In vitro NP receptor activity was quantified with guanosine 3',5'-cyclic monophosphate generation. In vivo effects were determined in normal canine acute infusion studies. We observed that CRRL269 demonstrated enhanced pGC-A activity in renal compared with nonrenal cell lines. CRRL269 exerted enhanced resistance to neprilysin compared with URO. Importantly, CRRL269 exhibited significant and greater increases in urinary sodium excretion and diuresis, with less blood pressure reduction, than BNP or URO in normal canines. CRRL269 retained potent renin-angiotensin-aldosterone system (RAAS) suppressing properties shared by URO and BNP. Also, CRRL269 exerted less arterial relaxation and higher cAMP cardiomyocytes generation than BNP. CRRL269 possessed superior renal and pGC-A activating properties compared with BNP or URO in vitro. CRRL269 exerted enhanced renal actions while suppressing RAAS in vivo and with less hypotension compared with URO or BNP. Together, our study suggests that CRRL269 is a promising innovative renal-enhancing drug, with favorable protective actions targeting cardiorenal disease states through the pGC-A receptor.

Particulate Guanylyl Cyclase A/cGMP Signaling Pathway in the Kidney: Physiologic and Therapeutic Indications.

The particulate guanylyl cyclase A (pGC-A)/cGMP pathway plays important roles in regulating renal physiological function and as well as in counteracting pathophysiological conditions. Naturally occurring peptide pGC-A activators consist of atrial natriuretic peptide (ANP), b-type NP (BNP), and urodilatin (URO). These activators bind and activate pGC-A, generating the second messenger cyclic 3',5' guanosine monophosphate (cGMP). Cyclic GMP binds to downstream pathway effector molecules including protein kinase G (PKG), cGMP-gated ion channels, and phosphodiesterases (PDEs). These mediators result in a variety of physiological actions in the kidney, including diuresis, natriuresis, increased glomerular filtration rate (GFR) and organ protection, thus, opposing renal cellular injury and remodeling. Downstream proteins regulated by PKG include collagen 1 (Col-1), transforming growth factor beta (TGF-ß) and apoptosis-related proteins. In addition to their physiological regulatory effects, pGC-A/cGMP signaling is critical for preserving renal homeostasis in different renal diseases such as acute kidney injury (AKI). Regarding therapeutic options, native pGC-A activators have short half-lives and their activity can be further enhanced by advances in innovative peptide engineering. Thus, novel designer peptide pGC-A activators with enhanced renal activity are under development.

Experimental cardiac radiation exposure induces ventricular diastolic dysfunction with preserved ejection fraction.

Breast cancer radiotherapy increases the risk of heart failure with preserved ejection fraction (HFpEF). Cardiomyocytes are highly radioresistant, but radiation specifically affects coronary microvascular endothelial cells, with subsequent microvascular inflammation and rarefaction. The effects of radiation on left ventricular (LV) diastolic function are poorly characterized. We hypothesized that cardiac radiation exposure may result in diastolic dysfunction without reduced EF. Global cardiac expression of the sodium-iodide symporter (NIS) was induced by cardiotropic gene (adeno-associated virus serotype 9) delivery to 5-wk-old rats. SPECT/CT (125I) measurement of cardiac iodine uptake allowed calculation of the 131I doses needed to deliver 10- or 20-Gy cardiac radiation at 10 wk of age. Radiated (Rad; 10 or 20 Gy) and control rats were studied at 30 wk of age. Body weight, blood pressure, and heart rate were similar in control and Rad rats. Compared with control rats, Rad rats had impaired exercise capacity, increased LV diastolic stiffness, impaired LV relaxation, and elevated filling pressures but similar LV volume, EF, end-systolic elastance, preload recruitable stroke work, and peak +dP/dt Pathology revealed reduced microvascular density, mild concentric cardiomyocyte hypertrophy, and increased LV fibrosis in Rad rats compared with control rats. In the Rad myocardium, oxidative stress was increased and in vivo PKG activity was decreased. Experimental cardiac radiation exposure resulted in diastolic dysfunction without reduced EF. These data provide insight into the association between cardiac radiation exposure and HFpEF risk and lend further support for the importance of inflammation-related coronary microvascular compromise in HFpEF.NEW & NOTEWORTHY Cardiac radiation exposure during radiotherapy increases the risk of heart failure with preserved ejection fraction. In a novel rodent model, cardiac radiation exposure resulted in coronary microvascular rarefaction, oxidative stress, impaired PKG signaling, myocardial fibrosis, mild cardiomyocyte hypertrophy, left ventricular diastolic dysfunction, and elevated left ventricular filling pressures despite preserved ejection fraction.

Biochemistry, Therapeutics, and Biomarker Implications of Neprilysin in Cardiorenal Disease.

BACKGROUND: Neprilysin (NEP) is a membrane-bound neutral endopeptidase that degrades a variety of bioactive peptides. The substrates include natriuretic peptides (NPs), which are important regulating mediators for cardiovascular and renal biology. Inhibition of NEP activity and exogenous NP administration thus have emerged as potential therapeutic strategies for treating cardiorenal diseases. More recently, B-type natriuretic peptide (BNP) or N-terminal-proBNP (NT-proBNP), 3'-5' cyclic guanosine monophosphate (cGMP), and soluble NEP as biomarkers have also been investigated in heart failure (HF) trials and their predictive value are beginning to be recognized. CONTENT: The biological functions of NEP and NPs are discussed. Enhancing NPs through NEP inhibition combined with renin-angiotensin-aldosterone system (RAAS) antagonism has proved to be successful in HF treatment, although future surveillance studies will be required. Direct NP enhancement through peptide delivery may have fewer potentially hazardous effects compared to NEP inhibition. Strategies of combined inhibition on NEP with other cardiorenal pathophysiological pathways are promising. Finally, monitoring BNP/NT-proBNP/cGMP concentrations during NEP inhibition treatment may provide supplemental benefits to conventional biomarkers, and the identification of soluble NEP as a novel biomarker for HF needs further investigation. SUMMARY: In this review, the biology of NEP is summarized, with a focus on NP regulation. The degradation of NPs by NEP provides the rationale for NEP inhibition as a strategy for cardiorenal disease treatment. We also describe the current therapeutic strategies of NEP inhibition and NP therapeutics in cardiorenal diseases. Moreover, the discovery of its circulating form, soluble NEP, as a biomarker is also discussed.

Atrial Natriuretic Peptide　- Old But New Therapeutic in Cardiovascular Diseases.

With the discovery of atrial natriuretic peptide (ANP), the heart as an endocrine organ was established. Basic science revealed that ANP, through the particulate guanylyl cyclase A receptor and cGMP, plays a fundamental role in cardiorenal biology. This work has led to the development of ANP as a therapeutic, especially in heart failure (HF). Human genomics has strengthened our understanding of ANP, revealing specific ANP gene variants that may be associated with biological dysfunction, but also may mediate protective properties, including in metabolic syndrome. Advances in understanding the processing and degradation of ANP molecular forms have resulted in therapeutic breakthroughs, especially inhibition of ANP degradation by neprilysin inhibitors. Although ANP is administered intravenously for acute HF, a novel therapeutic strategy is its chronic delivery by subcutaneous injection. An innovative therapeutic development is engineering to develop ANP-based peptides for chronic use. These interconnected topics of ANP biology and therapeutics will be reviewed in detail.