Burnett, John C.

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.

Objective B-type natriuretic peptide (BNP) has favourable effects on left ventricular remodelling, including antifibrotic and antiapoptotic properties. We tested the hypothesis that infusion of BNP after an acute myocardial infarction would reduce left ventricular systolic and diastolic volumes and improve left ventricular ejection fraction compared with placebo. Methods A total of 58 patients who underwent successful revascularisation for an acute ST elevation anterior myocardial infarction were randomised to receive 72-hour infusion of BNP at 0.006 µg/kg/min or placebo. Left ventricular end diastolic and systolic volumes and left ventricular ejection fraction were measured at baseline and at 30 days by multigated acquisition scan. Left ventricular infarction size was measured by cardiac MRI. Results BNP infusion led to significantly higher BNP levels and plasma cyclic guanosine monophosphate at 72 hours. No significant difference in change of left ventricular volumes or ejection fraction from baseline to 30 days was observed between groups. Although left ventricular infarction size measured by cardiac MRI was not significantly different between BNP infusion versus placebo (p=0.39), there was a trend towards reduced infarction size in patients with a baseline ejection fraction of <40% (p=0.14). Conclusions Infusion of BNP in patients with an anterior myocardial infarction did not affect parameters of left ventricular remodelling. Patients treated with BNP who had a baseline left ventricular ejection fraction of <40% had a trend towards reduced left ventricular infarction size compared with placebo. These results do not support the use of intravenous BNP in patients after recent myocardial infarction. Trial registration number NCT00573144.

Abstract C-type natriuretic peptide (CNP) is an endothelium-drived vasorelaxing factor which is present in human plasma, urine and renal epithelial cells. Endothelin (ET) is a potent renal and systemic vasoconstrictor and sodium regulating peptide. To date, the localization of C-type natriuretic peptide and endothelin gene expression in human kidney remains poorly defined. We determined the co-localization of C-type natriuretic peptide and endothelin mRNA in normal human kidney using in situ hybridization (ISH) with synthesized human C-type natriuretic peptide or human endothelin oligonucleotide probes together with immunohistochemical staining (IHCS) with human CNP-22 and ET-1 antibodies with no crossreactivity. The sections treated with nonimmune rabbit serum (NRS) demonstrated no immunoperoxidase activity. Human renal tissue (n=7) was obtained from biopsy of normal cadaveric donor kidneys and normal autopsy specimens. In situ hybridization (Figure 1) demonstrated that C-type natriuretic peptide and endothelin mRNA presence in human kidney which was localized to proximal and distal tubes with similar intensities.

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

Cardiorenal syndrome (CRS) is a multi‐organ disease, encompassing heart, kidney and vascular system dysfunction. CRS is a worldwide problem, with high morbidity, mortality, and inflicts a significant burden on the health care system. The pathophysiology is complex, involving interactions between neurohormones, inflammatory processes, oxidative stress and metabolic derangements. Therapies remain inadequate, mainly comprising symptomatic care with minimal prospect of full recovery. Challenges include limiting the contradictory effects of multi‐organ targeted drug prescriptions and continuous monitoring of volume overload. Novel strategies such as multi‐organ transplantation and innovative dialysis modalities have been considered but lack evidence in the CRS context. The adjunct use of pharmaceuticals targeting alternative pathways showing positive results in preclinical models also warrants further validation in the clinic. In recent years, studies have identified the involvement of gut dysbiosis, uraemic toxin accumulation, sphingolipid imbalance and other unconventional contributors, which has encouraged a shift in the paradigm of CRS therapy.