Iyer, Seethalakshmi

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.

M-atrial natriuretic peptide (MANP) is a novel ANP (atrial natriuretic peptide) analog engineered to be an innovative particulate GC-A (guanylyl cyclase A) receptor activator. The rationale for its design was to develop a best-in-class GC-A activator with enhanced cGMP activating, natriuretic, aldosterone-suppressing, and blood pressure–lowering actions, compared with endogenous ANP, for the treatment of hypertension. Here, we report the first-in-human study on the safety, tolerability, neurohumoral, renal, and blood pressure–lowering properties of MANP in hypertension subjects. This was an open-label sequential single ascending dose design in which all subjects stopped all antihypertensive agents for 14 days before receiving a single subcutaneous injection of MANP. MANP was safe, well tolerated, activated cGMP, induced natriuresis, reduced aldosterone, and decreased blood pressure at or below the maximal tolerated dose. Thus, MANP has a favorable safety profile and produced expected pharmacological effects in human hypertension. Our results support further investigations of MANP as a potential future blood pressure–lowering, natriuretic and aldosterone-suppressing drug for hypertension especially resistant hypertension.

Aldosterone is a critical driver for cardiovascular disease (CVD). We recently discovered that MANP, a novel atrial natriuretic peptide (ANP) analog, possessed more potent aldosterone inhibitory action than ANP. MANP is currently entering clinical trials for hypertension and thus understanding its aldosterone suppressing mechanism is important. The mechanism of aldosterone inhibition by natriuretic peptides (NPs) remains to be clearly defined. Conflicting results were reported on the roles of particulate guanylyl cyclase A receptor (pGC-A) and NP clearance receptor (NPRC) in aldosterone inhibition. Furthermore, the functions of protein kinase G (PKG) and phosphodiesterases (PDE) on aldosterone regulation are not clear. Herein, we investigated the molecular mechanism of aldosterone regulation in the human adrenocortical cell line H295R and in mice. We firstly showed that pGC-A mediates aldosterone inhibition. In contrast, with NPRC agonist and antagonist, we showed that NPRC did not inhibit aldosterone. Next, we confirmed that MANP inhibits aldosterone via PDE2, not PKG, with specific agonists, antagonists, siRNA silencing, and fluorescence resonance energy transfer (FRET) experiments. Specifically, MANP suppressed ANGII mediated activation of aldosterone (fold change) MANP+ANGII 3.2±0.1* vs. ANGII 3.8±0.1 (*p<0.05) with IBMX, a PDEs inhibitor and the PDE2 antagonist Bay 60-7550 reversed MANP-mediated aldosterone suppression (IBMX+MANP+ANGII 3.9±0.2 and Bay+MANP+ANGII 4.1±0.1). With PKG agonists and inhibitors, aldosterone levels were not changed. In PDE2 activity FRET studies, aldosterone control was 3.7±0.4 and with MANP 0.9±0.2* supporting PDE2 activation by MANP. Further, the inhibitory effect of PDE2 is mediated by a reduction of intracellular Ca2+ concentration (~22%). We then showed that MANP directly reduced aldosterone synthase CYP11B2 expression in vitro. Lastly, in PDE2 knockout mice (embryonic lethal), embryonic adrenal CYP11B2 expression is markedly increased (wild type: 1±0.2, KO: 2.8±0.5*). Our findings innovatively elucidate the pGC-A/cGMP/PDE2 pathway in aldosterone inhibition by MANP in vitro and in vivo. Additionally, our data also support the development of MANP as a novel ANP analog drug for CVD.

Introduction: Atrial natriuretic peptide (ANP) plays an important role in blood pressure (BP) regulation via the second messenger cGMP. ANP also induces lipolysis by increasing plasma levels of non-esterified fatty acids (NEFA). MANP is a new Mayo Clinic designed ANP analog consisting of the native ANP with a novel 12-amino-acid C-terminus extension. In experimental models, MANP is more potent than ANP in reducing BP and inducing natriuresis. These actions are mediated by the activation of the pGC-A receptor and generation of cGMP. To date, the BP pressure lowering, cGMP generating and lipolytic actions of MANP remain unexplored along with its safety and tolerability in subjects with hypertension (HTN) associated with metabolic disease. Hypothesis: In subjects with HTN, obesity and metabolic syndrome (MS), MANP administration is safe, well tolerated, activates cGMP and exerts BP lowering and lipolytic properties. Methods: Double-blind, placebo-control clinical trial in 22 subjects (17 receiving MANP) with HTN, obesity and MS involving a single subcutaneous (SQ) injection of MANP (2.5 μg/Kg) or placebo. Subjects were monitored and cardiovascular, cGMP and metabolic parameters were collected during 24 hours after the injection. Results: In all subjects, MANP was safe and well-tolerated with no serious adverse side effects. MANP increased mean cGMP plasma levels after 30 minutes (delta: 4.8 ± 2.0 pmol/mL, p=0.02) and 1 hour (delta: 2.9 ±1.3 pmol/mL, p=0.03) when compared to baseline. Six hours after MANP injection systolic BP decreased by 5.7 ± 2.9 mmHg (p=0.06) whereas subjects receiving placebo had no decrease in blood pressure values compared to baseline. During fasting period, one hour after the administration of MANP, NEFA plasma levels increased by 108.2 ± 37.4 μM (p=0.01). Conclusions: In subjects with HTN, obesity and MS, SQ MANP is safe, well tolerated and activates the pGC-A receptor as measured by a significant increase in the second messenger cGMP. Subjects receiving MANP showed a borderline significant decrease in systolic BP and a significant increase in NEFA circulating levels supporting anti-hypertensive and lipolytic properties. Our findings support MANP as a potential novel therapy for HTN associated with metabolic disease.

The importance of canonical versus noncanonical mechanisms for the generation of angiotensins remains a major challenge that, in part, is heavily swayed by the relative efficacy of therapies designed to inhibit renin, ACE (angiotensin-converting enzyme), or the Ang II (Angiotensin II) receptor. Ang (1–12) (angiotensin [1-12]) is an Ang II forming substrate serving as a source for Ang II–mediated tissue actions. This study identifies for the first time the presence of Ang (1–12) in the blood of 52 normal (22 women) and 19 (13 women) patients with hypertension not receiving antihypertensive medication at the time of the study. Normal subjects of comparable ages and body habitus had similar circulating plasma Ang (1–12) concentrations (women: 2.02±0.62 [SD] ng/mL; men 2.05±0.55 [SD] ng/mL, P >0.05). The higher values of plasma Ang (1–12) concentrations in hypertensive men (2.51±0.49 ng/mL, n=6) and women (2.33±0.63 [SD] ng/mL, n=13) were statistically significant ( P <0.02) and correlated with elevated plasma renin activity, systolic and pulse pressure, and plasma concentrations of NT-proBNP (N-terminal prohormone BNP). The increased plasma Ang (1–12) in patients with hypertension was not mirrored by similar changes in plasma angiotensinogen and Ang II concentrations. The first identification of an age-independent presence of Ang (1–12) in the blood of normotensive subjects and patients with hypertension, irrespective of sex, implicates this non-renin dependent substrate as a source for Ang II production in the blood and its potential contribution to the hypertensive process.

Atrial and B-type natriuretic peptides (ANP and BNP) are cardiac hormones secreted as compensatory measures to preserve cardiorenal homeostasis. Treating heart failure (HF) with sacubitril/valsartan increased ANP and not BNP, suggesting the ANP system may confer therapeutic benefit. Thus, the presence of an ANP deficient subgroup of HF patients possibly posing higher risk for HF severity, underscores a need to characterize both, the biologically active and inactive (NT-proANP and NT-proBNP) natriuretic peptides (NPs)(latter resistant to degradation), to highlight the extent of NP production in HF. Characterizing neprilysin (NEP) activity may also provide insights into the degree of NP degradation in HF. This study aims to both highlight the cardiac NP response in acute decompensated HF(ADHF) by measuring molecular forms of ANP and BNP together with defining circulating soluble NEP activity as to assess mechanisms impairing the NP response in HF. We recruited 47 healthy individuals with neither cardiovascular nor metabolic disease and compared ANP, BNP, NT-proANP, NT-proBNP, and NEP activity levels with 107 recruited ADHF patients. In ADHF, compared to a healthy setting, median ANP, BNP, NT-proANP, and NT-proBNP were all elevated (15.7 vs. 118.1 pg/mL , p<0.0001; 23 vs. 515 pg/ml, p<0.0001; 60.1 vs. 651.6 pg/mL, p<0.0001; 46 vs. 3330 pg/mL, p<0.0001, respectively). However, circulating NEP activity was significantly lower in ADHF than in healthy circulation (32 vs. 12.3 nM/mL/min, p<0.0001). NPs did not correlate with NEP activity in healthy circulation. However, only ANP (r = 0.4788, p<0.0001) and NT-proANP (r = 0.6819, p<0.0001) correlated with NEP activity in ADHF. The presence of an impaired ANP response in ADHF, underscored by insufficient increases in NT-proANP than NT-proBNP, suggests decreased ANP production may induce not only an ANP deficient ADHF state, but be characteristic of ADHF. The presence of NEP activity in ADHF circulation, despite lower NEP activity compared to healthy individuals, suggests ANP degradation may second impaired production, further lowering ADHF ANP levels. Our studies support augmenting the ANP system in ADHF through either endogenous stimulation or exogenous supplementation as optimal therapeutic strategies.

Background Ang‐(1‐12) is a primary non‐renin dependent substrate for direct tissue angiotensin II (Ang II) formation by chymase. This discovery challenges conventional thinking and explains the large residual risk of cardiovascular events in patients medicated with blockers of the renin angiotensin system (RAS). Here we report the first demonstration of circulating Ang‐(1‐12) as a biomarker of essential hypertension (EH) and cardio‐renal remodeling. Methods The cohort of patients from Olmsted County MN included 52 healthy adult volunteers (21 females), age 54 ± 8 years, and 23 essential hypertensive (EH) patients (14 females) age 61 ± 8 years with systolic blood pressure (SBP) ≥140 mm Hg prior to recruitment. Clinical examination, standardized BP measurements, and venous blood were obtained for measurements of plasma concentrations of angiotensinogen (AGT), Ang‐(1‐12), Ang II, aldosterone, renin activity, N‐terminal pro–B‐type natriuretic peptide (NT‐proBNP) and atrial and brain natriuretic peptides (ANP and BNP, respectively). All values are Means ± SD. Data were analyzed by 2‐way ANOVA for sex and hypertension. Results Plasma Ang‐(1‐12) levels in EHs [SBP: 134 ± 14 mm Hg; Ang‐(1‐12): 1,463 ± 446] were higher than normotensives [SBP: 117 ± 13 mm Hg; Ang‐(1‐12): 1,353 ± 379 fmol/mL, hypertension effect: P<0.05], irrespective of sex. Hypertension associated with increases in pulse pressure, PRA, and plasma AGT and NT‐proBNP concentrations (see Figure ). The elevation in circulating NT‐proBNP levels with hypertension was accounted for by a 4.6‐fold increase in hypertensive males (165 ± 134 pg/mL) while the 1.5‐fold rise in plasm NT‐proBNP did reach significance (134 ± 127 pg/mL, p> 0.05). Conclusions We show for the first time that Ang‐(1‐12) circulates in humans and its concentrations are elevated by chronic hypertension. We further demonstrate a sexual dimorphic pattern in hypertensives with respect to NT‐proBNP, the latter a biomarker for cardiac remodeling. Whether this represents a natriuretic system‐related compensatory mechanism, or worsening pathology, due to an elevated noncanonical RAS specific to male hypertensives remains to be studied. Further investigation to fully define the role of Ang‐(1‐12) as a cardiac disease biomarker in a larger, gender and ethnic diverse population and its relationship to hypertension and myocardial structure is warranted. Support or Funding Information Supported by grant HL‐051952 from the NHLBI of the NIH Lines are means ± SD Figure 1

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.

Background Neprilysin is a metalloprotease involved in proteolysis of numerous peptides, including natriuretic peptides, and is of prognostic and therapeutic importance in heart failure with reduced ejection fraction. No studies have investigated circulating neprilysin in the community, its clinical correlates, or its relationship to cardiovascular disease in the general population. Methods and Results Plasma neprilysin was measured in 1536 participants from Olmsted County, Minnesota, using a commercially available sandwich ELISA assay. Clinical and echocardiographic correlates and subsequent outcomes were determined. Soluble neprilysin is non‐normally distributed in the community (median: 3.9 ng/mL; interquartile range: 1.0–43.0 ng/mL). There was no relationship between plasma neprilysin and age (Spearman correlation: −0.04, P =0.16); body mass index (Spearman correlation: −0.04, P =0.16); glomerular filtration rate (Spearman correlation: −0.007, P =0.8); or A‐, B‐, or C‐type natriuretic peptides (Spearman correlation: 0.03, P =0.22; −0.001, P =0.96; 0.01, P =0.67, respectively). Among tertiles of neprilysin, the lowest tertile group had the highest prevalence of smokers ( P <0.001), hypertension ( P =0.04), dyslipidemia ( P =0.03), and diastolic dysfunction ( P =0.02). Soluble neprilysin was not prospectively associated with death or heart failure over a median of 10.7 years. Conclusions In a large community‐based cohort, for the first time, we described the distribution of circulating neprilysin in the general community. We observed that neprilysin does not correlate with natriuretic peptide levels and is not independently associated with adverse outcomes. The novel associations observed between low soluble neprilysin levels and an adverse cardiometabolic and smoking profile requires further investigation.

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 Ca 2+ 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.