Burnett, John C.

Introduction: Atrial natriuretic peptide (ANP) is the most potent endogenous activator of the guanylyl cyclase A receptor (GC-A) mediating cardiorenal protective actions by increasing cGMP production. To test the hypothesis that acute decompensated heart failure (ADHF) is associated with increased circulating ANP but with reduced GC-A potency, we developed an ex-vivo precision medicine assay to quantify the potency of circulating ANP in plasma from healthy and ADHF subjects. Further, we assessed the ex-vivo potency of MANP, a novel ANP analog with greater cGMP activation than ANP, also using plasma of healthy and ADHF subjects. Methods: For the potency assay, we engineered HEK293 cells to overexpress human GC-A. Plasma from individual healthy (n=4) and ADHF (n=4) subjects was incubated in the assay and cGMP was assessed. The endogenous ANP derived cGMP was evaluated against the cGMP response of equimolar synthetic ANP (S ANP ) to assess potency of ANP from each cohort. MANP mediated cGMP generation was also assessed in the assay using healthy and ADHF plasma. Results: Healthy plasma, in which plasma ANP was 26±5 pg/mL, generated 10.3±0.7 pmol/mL of cGMP. S ANP added to the assay to mimic endogenous ANP levels in healthy subjects produced 7.8±0.5 pmol/mL of cGMP. ADHF plasma with markedly elevated ANP (350±57pg/mL) generated 23.5±3.1 pmol/mL of cGMP. S ANP mimicking plasma ANP in ADHF produced 59.7±13.8 pmol/mL of cGMP, which was greater than cGMP generated from ADHF patient-derived plasma (p<0.05), consistent with reduced potency of endogenous ANP in ADHF. Low treatment dose of MANP (LD MANP ; 10 -8 M) in healthy plasma increased cGMP to 45±5.5 pmol/ml while high treatment dose (HD MANP ; 10 -6 M) increased cGMP to 167.1±14.1 pmol/mL. In markedly elevated ANP ADHF plasma, LD MANP increased cGMP to 60.4±9.7 pmol/mL while HD MANP increased cGMP to 200.8±5.4 pmol/mL (p<0.03 for both) demonstrating similar cGMP production by MANP in healthy and ADHF plasma. Conclusions: Employing a novel ex-vivo precision medicine ANP/GC-A/cGMP assay, we conclude that ADHF is characterized by elevated ANP yet with impaired potency in GC-A activation and cGMP generation. MANP overcomes this impairment and serves as a potential efficacious GC-A activating therapeutic in heart failure.

Introduction: Hypertension (HTN) represents one of the greatest burdens in human health and is associated with increased morbidity and mortality. Despite the availability of several antihypertensive drugs, most patients have suboptimal blood pressure (BP) control, thus underscoring the need for new therapeutic drugs. The natriuretic peptide receptor A (NPRA) possesses potent vasodilating, natriuretic and diuretic actions via activation by ANP or BNP and generation of its second messenger, cGMP. Recently, we reported the discovery of a small molecule positive allosteric modulator (PAM) for NPRA, MCUF-651, which enhances the ANP/BNP/NPRA/cGMP pathway (PNAS,2021). To date, the in vivo actions of MCUF-651 remains unknown. Here we tested the hypothesis that MCUF-651 would have BP lowering and renal enhancing properties in experimental HTN. Methods: A single IV bolus of MCUF-651 (10mg/kg; n=4) or vehicle (V; n=5) was injected into anesthetized spontaneous hypertensive rats (SHRs). Plasma and urinary cGMP (PcGMP and UcGMP), mean arterial pressure (MAP) and urinary volume (UV) and sodium (UNa) excretion were assessed at baseline (BL) and over 60-mins post-bolus. Results: In SHRs, PcGMP and UcGMP were significantly elevated with MCUF-651 compared to the vehicle group (ΔPcGMP MCUF-651: 16±5, ΔPcGMP V: -2±3, pmol/mL; P =0.003; ΔUcGMP MCUF-651: 78±29, ΔUcGMP V: 30±8, pmol/min, P =0.01), thus supporting NPRA target engagement. Notably, the elevations in cGMP with MCUF-651 were associated with a significant reduction in MAP at 15-mins post bolus compared to vehicle (ΔMAP MCUF-651: -29±14, ΔMAP V: -6±2 mmHg; P =0.04) and this MAP reduction was sustained over 60 mins. Further, UV and UNa excretion were significantly increased, from BL, with MCUF-651 (BL UV: 6 ± 2, 60 mins post bolus UV: 56± 18 μL/min, P <0.001; BL UNa: 1±0.2, 60 mins post bolus UNa: 8±2 μmol/min, P <0.001). Conclusions: We report for the first time that MCUF-651, a novel NPRA small molecule PAM, engages NPRA, increases cGMP and reduces MAP while enhancing sodium and water excretion in experimental HTN. These findings support the development of MCUF-651 as a potential new therapeutic modality to optimize BP lowering goals and reduce adverse outcomes in human HTN.

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.

Introduction: The atrial natriuretic peptide (ANP) regulates blood pressure (BP) and cardiorenal homeostasis via activation of guanylyl cyclase A (GC-A) receptor and second messenger cGMP. We recently demonstrated the safety, tolerability, and BP-lowering properties of MANP, an ANP analog and best-in-class GC-A activator, in subjects with essential hypertension (HTN). However, the effects of MANP on human metabolome during HTN remains undefined. Hypothesis: A single subcutaneous (SQ) administration of MANP can trigger metabolomic changes in humans. Methods: Twenty-two patients with HTN and metabolic syndrome (MetS) were randomized to receive placebo (N=5) or MANP (N=17, 2.5 μg/kg). Untargeted liquid chromatography mass spectrometry-based metabolomics and informatics were conducted on plasma of all subjects at baseline, 1 h post injection (hpi), and 6 hpi. Top circulating metabolites associated with MANP treatment were identified via a comparison of abundance between before and after MANP administration. Results: Compared to placebo, MANP resulted in the most prominent cGMP increase at 1 hpi and BP lowering effect at 6 hpi. With untargeted approach, we identified totally 1384 circulating metabolites. Principal component analysis supported distinct metabolic signatures at baseline, 1 hpi and 6 hpi in subjects receiving MANP. In MANP group, we found 31 metabolites at 1 hpi and 148 metabolites at 6 hpi showing significant change in abundance (adjusted P value < 0.05) compared to baseline. By contrast, <10 metabolites with difference in circulating abundance at either 1 hpi or 6 hpi compared to baseline were found in placebo group. Specifically, 8 annotated metabolites were identified with significant and progressive changes at both 1 and 6 hpi after treatment of MANP but not placebo, which included spisulosine, paecilaminol, quinine ethyl carbonate, thyrotropin releasing hormone, 3-epideoxycholic acid, hellicoside, pentanorvitamin D3, and tetracosanal. Conclusion: SQ administration of MANP triggers changes in a wide range of circulating metabolites beyond cGMP activation and BP reduction in humans. The biological outcome and clinical impact of these MANP-associated metabolites may help guide a precision medicine approach in HTN with MetS.

Abstract The discovery of the heart as an endocrine organ resulted in a remarkable recognition of the natriuretic peptide system (NPS). Specifically, research has established the production of atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) from the heart, which exert pleiotropic cardiovascular, endocrine, renal, and metabolic actions via the particulate guanylyl cyclase A receptor (GC-A) and the second messenger, cGMP. C-type natriuretic peptide (CNP) is produced in the endothelium and kidney and mediates important protective auto/paracrine actions via GC-B and cGMP. These actions, in part, participate in the efficacy of sacubitril/valsartan in heart failure (HF) due to the augmentation of the NPS. Here, we will review important insights into the biology of the NPS, the role of precision medicine, and focus on the phenotypes of human genetic variants of ANP and BNP in the general population and the relevance to HF. We will also provide an update of the existence of NP deficiency states, including in HF, which provide the rationale for further therapeutics for the NPS. Finally, we will review the field of peptide engineering and the development of novel designer NPs for the treatment of HF. Notably, the recent discovery of a first-in-class small molecule GC-A enhancer, which is orally deliverable, will be highlighted. These innovative designer NPs and small molecule possess enhanced and novel properties for the treatment of HF and cardiovascular diseases.

Background: Aldosterone is a critical pathological driver for cardiac and renal diseases. We recently discovered that mutant atrial natriuretic peptide (MANP), a novel atrial natriuretic peptide (ANP) analog, possessed more potent aldosterone inhibitory action than ANP in vivo. MANP and natriuretic peptide (NP)-augmenting therapy sacubitril/valsartan are under investigations for human hypertension treatment. Understanding the elusive mechanism of aldosterone inhibition by NPs remains to be a priority. Conflicting results were reported on the roles of the pGC-A (particulate guanylyl cyclase A receptor) and NP clearance receptor in aldosterone inhibition. Furthermore, the function of PKG (protein kinase G) and PDEs (phosphodiesterases) on aldosterone regulation are not clear. Methods: In the present study, we investigated the molecular mechanism of aldosterone regulation in a human adrenocortical cell line H295R and in mice. Results: We first provided evidence to show that pGC-A, not NP clearance receptor, mediates aldosterone inhibition. Next, we confirmed that MANP inhibits aldosterone via PDE2 (phosphodiesterase 2) not PKG, with specific agonists, antagonists, siRNA silencing, and fluorescence resonance energy transfer experiments. Further, the inhibitory effect is mediated by a reduction of intracellular Ca2+ levels. We then illustrated that MANP directly reduces aldosterone synthase CYP11B2 (cytochrome p450 family 11 subfamily b member 2) expression via PDE2. Last, in PDE2 knockout mice, consistent with in vitro findings, embryonic adrenal CYP11B2 is markedly increased. Conclusions: Our results innovatively explore and expand the NP/pGC-A/3',5', cyclic guanosine monophosphate (cGMP)/PDE2 pathway for aldosterone inhibition by MANP in vitro and in vivo. In addition, our data also support the development of MANP as a novel ANP analog drug for aldosterone excess treatment.

Introduction: Therapeutic strategies dual-targeting renin-angiotensin system (RAS) and natriuretic peptide system (NPS), such as Sacubitril/Valsartan, have been proven promising in treating cardiorenal disease (CRD). However, mechanisms behind the crosstalk between RAS and NPS remain to be fully elucidated. While angiotensin II (ANGII), the central RAS hormone, is thought to interact with NPS at multiple levels, whether and how it may influence the actions of particulate guanylyl cyclase A (pGC-A), the receptor activated by ANP and BNP to increase its second messenger cGMP, has not been investigated. Hypothesis: We hypothesize ANGII naturally suppresses pGC-A activity and inhibition of this ANGII mediated action can be a new strategy to combat CRD. Methods: Studies consist of biomarker analyses in plasma from healthy humans, drug infusions in normal rats, molecular characterization in human HEK293 cells, and in vitro assessment of CRRL290, an innovative dual-functional peptide designed to activate pGC-A and inhibit protein kinase C (PKC). Results: In 128 healthy humans, plasma cGMP was positively associated with ANP or BNP in low (≤ 4.5 pg/mL) but not those with high (> 4.5 pg/mL) ANGII levels. Infusion of ANP (300 pmol/kg/min) in normal rats increased plasma and urinary cGMP, however ANP mediated cGMP generation was reduced in the presence of ANGII. Interestingly, suppression effect of ANGII on pGC-A was only recapitulated in HEK293 cell overexpressing both pGC-A and AT1R, but not in HEK293 cell overexpressing pGC-A alone. We also found PKC, a known downstream target of AT1R, was a key mediator as the suppression effect of ANGII was largely ablated by Go6983, a pan PKC inhibitor. Accordingly, we designed and synthesized CRRL290. Notably, CRRL290 had superior potency in cGMP generation compared to the currently best-in-class ANP-analog, MANP, in HEK293 cells. Conclusions: We demonstrate that ANGII is a natural suppressor of pGC-A via AT1R and PKC signaling. We also report for the first time that CRRL290, a novel bioengineered peptide that activates pGC-A receptor while inhibiting PKC signaling, potently generates cGMP. Our study provides new insights into the RAS-NPS interaction, and highlights a novel and mechanism-based therapeutic avenue for treating CRD.

Introduction: The cardiac hormone atrial natriuretic peptide (ANP) plays a key role in blood pressure (BP) and metabolic homeostasis through guanylyl cyclase receptor-A. While the role of ANP in cardiovascular disease (CVD) has been extensively investigated, its role in metabolic regulation has only recently emerged. A genetic variant of the ANP gene (rs5068), which increases production of ANP and NT-proANP, is associated with lower blood pressure (BP), reduced risk for hypertension and a decreased prevalence of obesity and metabolic syndrome. Hypothesis: We hypothesized that sex differences in ANP may have an important role in cardiometabolic disease together with cardiovascular (CV) morbidity and mortality. Methods: We studied 1176 subjects (age > 45 years) in the general population from Olmsted County MN. Plasma ANP molecular forms were quantified. Metabolic and cardiorenal parameters, and detailed medical records were reviewed. The cardiometabolic protective action of the ANP gene variant rs5068 was also assessed. Subjects were followed for all-cause mortality and morbidity for 12 years. Results: Plasma ANP molecular forms were significantly lower in males compared to females. Males had higher BMI and greater incidence of myocardial infarction (MI), coronary artery disease and heart failure (HF). Males also had lower EF and HDL cholesterol and higher LA volume and LV mass, serum glucose, insulin and diastolic pressure. The presence of the rs5068 minor allele improved the cardiometabolic phenotype including BP and widespread metabolic parameters in males but not females. After adjustment by age, males had increased risk of all-cause mortality, HF, MI, and stroke. Conclusions: Males are characterized by a relative ANP deficiency compared to females and widespread prevalence of cardiometabolic disease and increased CV morbidity and mortality in the general population. We demonstrate that the cardiometabolic protective action of the ANP gene variant rs5068 minor allele is sex dependent and protective in males. These findings have diagnostic and therapeutic implications, particularly in males.

Rationale: The role of cardiac natriuretic peptides (NPs) in peripheral arterial disease (PAD) or thromboangiitis obliterans (TA) is unknown. Recent studies in mice suggested that BNP may be produced outside the heart in the ischemic limbs contributing to peripheral angiogenesis. Objective: Determine if synthesis or consumption/degradation of NPs occur in the ischemic legs of patients with PAD or TA. Methods: 32 patients with critical limb ischemia (CLI) or claudication (PAD n=31; TA n=1; 20 males; mean age 72.9 years) underwent diagnostic angiography or revascularization. We determined differences of concentrations of BNP, NT-proBNP, and CNP in the blood of proximal veins and arteries of both legs. Concentrations differences were then compared between the more ischemic target and the contralateral self-control legs. Results: Values are means ± SD. P values <0.05 were considered significant. In the PAD group, in the target extremity, concentration step-ups of NT-proBNP (11±68; p=0.40) and CNP (0.45±6.22; p=0.71) were not significant from the arterial to venous blood. In the contralateral self-control legs, NT-proBNP and CNP concentrations drops were also not significant (-37±160, p=0.7; -0.89±4.09, p=0.23). Venous BNP concentrations were significantly lower than arterial both in the target (-66±153, p<0.001) and self-control legs (-59±107, p<0.001). BNP concentrations drops were greater in the CLI than claudication cases driving the overall significance. In the patient with TA, whose only identifiable PAD risk factor was smoking, arterial concentrations of NPs were generally low (NT-proBNP 81; BNP 46; CNP 8.2), but higher than venous concentrations (80; 41; 6.7). Conclusion: Significantly lower venous BNP concentrations suggest possible BNP consumption/degradation in the ischemic legs. Concentrations of NT-proBNP, that has a longer half-life than BNP, were more stable suggesting no significant local production or conversion to BNP. CNP concentrations were stable. Recognizing the angiogenic properties of NPs and lack of evidence of peripheral production, studies are warranted in humans with PAD to determine the potential angiogenic properties of exogenous NPs supplementation in what could be considered a local NPs deficiency state.