Cataliotti, Alessandro

Since the discovery of the cardiac hormone atrial natriuretic peptide by de Bold and colleagues in 1981, the field of natriuretic peptides has significantly advanced with translation of new knowledge to the clinical practice of heart failure. This new knowledge builds on the importance of cardiorenal mechanisms that contribute to optimal cardiovascular regulation. Recent investigations by our group and others have also established the direct myocardial actions of the natriuretic peptides, broadening their therapeutic potential beyond renal mechanisms. Indeed, a potential therapeutic target is cardiac remodeling and fibrosis based on the unique cardiorenal and humoral protective properties that natriuretic peptides possess. We review new insights into the natriuretic peptide system and specifically focus on the possible role of natriuretic peptides as a new therapeutic strategy to limit cardiac remodeling and fibrosis to delay worsening of cardiac function and the progression of heart failure.

Unlike healthy subjects, overt congestive heart failure cannot “escape” the sodium- and water-retaining actions of mineralocorticoid excess. It is undefined whether escape occurs in asymptomatic left ventricular dysfunction (ALVD), which is characterized by preserved sodium homeostasis, natriuretic peptide activation, and normal circulating aldosterone. We hypothesized that, in ALVD, mineralocorticoid excess with exogenous deoxycorticosterone acetate (DOCA) would overwhelm renal compensatory mechanisms, resulting in sodium and water retention, and promote renal and cardiac collagen deposition. ALVD was induced in 2 groups (N=5 each) of dogs by tachypacing at 180 bpm. Urine was collected daily and blood drawn at baseline and days 2, 5, 8, and 11. One group served as control (ALVD), and the other received DOCA (ALVD+DOCA) starting at day 2 of pacing. Urine flow and sodium excretion were unchanged in the ALVD group. In ALVD+DOCA, urine flow and sodium excretion decreased on the first 2 days DOCA was given but normalized starting day 4. Urine flow and urinary cGMP excretion increased in ALVD+DOCA after DOCA escape. Plasma atrial natriuretic peptide, B-type natriuretic peptide, and cGMP increased equally in both groups. There were no differences in cardiorenal and hemodynamic parameters in an acute study on day 11. Although renal collagen area fraction was similar, left ventricular collagen area fraction in ALVD+DOCA was significantly higher than in ALVD (3.3±0.4% versus 2.0±0.2%; P =0.012). We conclude that ALVD can escape the sodium- and water-retaining effects of mineralocorticoid excess. Despite renal escape, increased left ventricular collagen deposition suggests that the heart but not the kidney failed to escape the tissue effects of DOCA.

Recent studies support the speculation that different molecular forms of the cardiac hormone BNP with differential biological activity may circulate in heart failure and be detected by conventional assays. In the current study we determined the ability of 3 widely used conventional assays to detect these different forms thought to circulate in heart failure. We also evaluated the ability of pro-BNP (1-108), N-terminal peptide (NT)–pro-BNP (1-76), and BNP 3-32, the latter a cleavage product of BNP 1-32 by dipeptidyl peptidase IV, on an equimolar basis to activate cGMP in cultured cardiac fibroblasts and cardiomyocytes compared with the biologically active mature BNP 1-32. Specifically, we observed that the Roche NT–pro-BNP assay detected both NT–pro-BNP 1-76 and pro-BNP 1-108 and that Biosite Triage and Shionogi detected both mature BNP 1-32 and the shortened BNP 3-32. Moreover, in cultured cardiac fibroblasts and cardiomyocytes, BNP 1-32 (10 −6 mol/L) activated cGMP. BNP 3-32 demonstrated a similar cGMP activating property in both cardiac cell types. In contrast, the cGMP response to pro-BNP 1-108 and NT–pro-BNP 1-76 was not significantly greater than no treatment alone. We conclude that widely used commercial assays for NT–pro-BNP 1-76 and BNP 1-32 cannot differentiate among pro-, processed, or degraded forms and, thus, may not thoroughly identify circulating BNP forms in heart failure patients. These findings also demonstrate differential cGMP activating properties of BNP forms and, importantly, that pro-BNP 1-108 and NT–pro-BNP 1-76 have reduced cGMP activity in vitro that may have biological relevance to human heart failure.

Soluble guanylate cyclase is a heterodimeric enzyme with a prosthetic heme group that, on binding of its main ligand, NO, generates the second messenger cGMP. Unlike conventional nitrovasodilators, the novel direct NO- and heme-independent soluble guanylate cyclase activator BAY 58-2667 is devoid of non-cGMP actions, lacks tolerance development, and preferentially activates NO-insensitive heme-free or oxidized soluble guanylate cyclase. BAY 58-2667, therefore, represents a novel therapeutic advance in mediating vasodilation. To date, its cardiorenal actions in congestive heart failure (CHF) are undefined. We, therefore, hypothesized that BAY 58-2667 would have beneficial preload- and afterload-reducing actions in experimental severe CHF together with renal vasodilating properties. We assessed the cardiorenal actions of intravenous administration of 2 doses of BAY 58-2667 (0.1 and 0.3 μg/kg per minute, respectively) in a model of tachypacing-induced severe CHF. In CHF, BAY 58-2667 dose-dependently reduced mean arterial, right atrial, pulmonary artery, and pulmonary capillary wedge pressure (from baseline 19±1 to 12±2 mm Hg). Cardiac output (2.4±0.3 to 3.2±0.4 L/min) and renal blood flow increased. Glomerular filtration rate and sodium and water excretion were maintained. Consistent with cardiac unloading, atrial and B-type natriuretic peptide decreased. Plasma renin activity ( P =0.31) and aldosterone remained unchanged ( P =0.19). In summary, BAY 58-2667 in experimental CHF potently unloaded the heart, increased cardiac output and renal blood flow, and preserved glomerular filtration rate and sodium and water excretion without further neurohumoral activation. These beneficial properties make direct soluble guanylate cyclase stimulation with BAY 58-2667 a promising new therapeutic strategy for cardiovascular diseases, such as heart failure.

Recent studies report that, in the absence of heart failure and renal failure, plasma B-type natriuretic peptide (BNP) has prognostic value for mortality. We sought to confirm and extend these previous studies to assess BNP, measured by 3 distinct assays, as a biomarker for mortality in a strategy to enhance efforts at primary prevention and to better understand the clinical phenotype of such subjects at risk. We used a community-based cohort of 2042 subjects from Olmsted County, Minn, and individuals with heart or renal failure were excluded. BNP was assessed using 3 assays including Biosite and Shionogi for mature, biologically active BNP and the Roche assay for apparently nonbiologically active amino-terminal pro-BNP (NT-proBNP). Thorough echocardiographic and clinical data were recorded for all of the participants. Median follow-up for mortality was 5.6 years. BNP by all 3 of the assays was predictive of mortality. NT-proBNP and Biosite assays remained significant even after adjustment for traditional clinical risk factors and echocardiographic abnormalities including left ventricular hypertrophy and diastolic dysfunction. Echocardiography documented widespread structural changes in those with increasing BNP levels yet below levels observed in heart failure. We report in a large, well-characterized community-based cohort, free of heart failure, the first study to compare 3 distinct BNP assays as biomarkers for mortality in the same cohort. Our findings confirm the potential use of NT-proBNP and BNP biomarkers for future events and underscore that these peptides may also serve as biomarkers for underlying cardiac remodeling secondary to diverse cardiovascular disease entities.

Abstract Background BNP is a cardiac peptide with vasodilating, lusitropic and natriuretic properties mediated by the second messenger cGMP. We have previously shown that chronic subcutaneous (SQ) administration of BNP in experimental CHF resulted in improved haemodynamics and unloading of the heart. However, it is unknown if this will lead to the development of tolerance to exogenous BNP. Methods The current study extends our previous study and compares the cardiorenal effects of acute administration of SQ BNP (5 μg/kg) in a group of dogs (n = 5) with rapid ventricular pacing induced CHF (180 bpm for 10 days) to a separate group of CHF dogs (n = 6), who received chronic SQ BNP (5 μg/kg) three times a day for 10 days. Results Acute administration of SQ BNP resulted in similar increases in both plasma cGMP (35 ± 5 vs. 29 + 2 pmol/ml) and urinary cGMP excretion (UcGMPV) (6000 ±1000 vs. 4000 ± 600 pmol/min) in both the Chronic SQ BNP treated and the Untreated CHF groups (P>0.05). These were associated with decreased cardiac filling pressures and increased urine flow, which were also similar in both groups. Conclusion In experimental CHF, chronic SQ BNP administration did not result in the development of tolerance as demonstrated by increases in both plasma cGMP and UcGMPV following acute administration of SQ BNP. This may have important clinical implications, suggesting that chronic BNP administration does not lead to the development of tolerance to acute BNP administration.

C-terminal brain (B-type) natriuretic peptide (BNP)-32 is a widely used clinical biomarker for the diagnosis, prognosis, and treatment of heart failure (HF). The 32-aa peptide is synthesized primarily in the atrial and ventricular myocardium and constitutes the mature biologically active form of immature BNP (pro-BNP). There has been mounting evidence that suggests BNP circulates in different structural forms that impact HF diagnosis and in vivo activity. Herein, we have developed and used an immunoaffinity purification assay to isolate endogenous BNP-32 from New York Heart Association class IV patient plasma for subsequent analysis by nano-liquid chromatography (LC) electrospray ionization Fourier transform ion cyclotron resonance (FT-ICR) MS. We have introduced stable isotope-labeled BNP-32 to the assayed plasma to enable quantification of endogenous levels of BNP-32. Unlike the chemically nonspecific point-of-care tests (POCTs) and RIAs used worldwide to quantify BNP-32 from plasma, FT-ICR-MS (unprecedented mass measurement accuracy) coupled with LC (retention time) affords extraordinary molecular specificity, and when combined with the use of internal standards is able to confidently identify and quantify BNP-32. The significance of this work is despite exceedingly high circulating levels of BNP-32 in the New York Heart Association class IV patients as determined by POCTs (>290 fmol/ml) nano-LC-electrospray ionization-FT-ICR-MS data did not reveal any endogenous BNP-32. These results provide molecularly specific evidence for the absence of circulating BNP-32 in advanced-stage HF patients and suggest the existence of altered forms of BNP that are contributing to the POCT values.

Background— The objective of this study was to address the feasibility and the biological activity of orally administered human brain natriuretic peptide (hBNP). Proprietary technology has been developed in which short, amphiphilic oligomers are covalently attached to peptides. The conjugated peptides are intended to have an improved pharmacokinetic profile and to enable oral administration. We hypothesized that novel oral conjugated hBNP (CONJ-hBNP) increases plasma hBNP, activates cGMP, and reduces mean arterial pressure (MAP). Methods and Results— This randomized crossover-designed study tested the biological activity of oral CONJ-hBNP compared with oral native hBNP in normal conscious dogs. Measurements of MAP, plasma hBNP, and cGMP were made at baseline (BL) and repeated at 10, 30, 60, 120, 180, and 240 minutes after oral administration. Plasma hBNP was not detectable in dogs at BL. Plasma hBNP was detected after native hBNP and CONJ-HBNP administration. However, plasma hBNP concentration was significantly higher after CONJ-hBNP than after native hBNP administration ( P =0.0374 between groups). Plasma cGMP increased after CONJ-hBNP for 60 minutes (from 10.8±3 to 36.8±26 pmol/mL; P <0.05), whereas it did not change after native hBNP ( P =0.001 between groups). MAP decreased at 10 minutes and remained decreased for 60 minutes after CONJ-hBNP (from 113±8 to 101±12 mm Hg after 10 minutes to 97.5±10 mm Hg after 30 minutes to 99±13 mm Hg after 60 minutes) while remaining unchanged after native hBNP ( P =0.0387 between groups). Conclusions— This study reports for the first time that novel conjugated oral BNP activates cGMP and significantly reduces MAP, thus implying an efficacious coupling of CONJ-hBNP to the natriuretic receptor-A. These data advance a new concept of orally administered chronic BNP therapy for cardiovascular diseases.

Background— The renal actions of brain natriuretic peptide (BNP) in congestive heart failure (CHF) are associated with increased diuresis and natriuresis, preserved glomerular filtration rate (GFR), and lack of activation of the renin-angiotensin-aldosterone system (RAAS). In contrast, diuretic-induced natriuresis may be associated with reduced GFR and RAAS activation. The objective of this study was to test the hypothesis that exogenous BNP enhances the renal diuretic and natriuretic actions of furosemide (Fs) and retards the activation of aldosterone in a model of CHF. Methods and Results— CHF was produced in 2 groups of dogs by ventricular pacing. One group received continuous (90-minute) intravenous Fs (1 mg · kg −1 · h −1 ). A second group (Fs+BNP) received 45-minute intravenous coinfusion of Fs (1 mg · kg −1 · h −1 ) and low-dose (2 pmol · kg −1 · min −1 ) BNP followed by 45-minute coinfusion of Fs (1 mg · kg −1 · h −1 ) and high-dose (10 pmol · kg −1 · min −1 ) BNP. Fs increased urinary flow, but the effect of Fs+BNP was greater. Similarly, urinary sodium excretion was higher in the Fs+BNP group. Although GFR tended to decrease in the Fs group, it increased in the Fs+BNP group (35±3 to 56±4*) (* indicates P <0.05 versus baseline) ( P <0.0001 between groups). Plasma aldosterone increased with Fs (41±10 to 100±11* ng/dL) but was attenuated in the Fs+BNP group (44±11 to 54±9 ng/dL low-dose and to 47±7 ng/dL high-dose) ( P =0.0007 between groups). Conclusions— Fs+BNP has more profound diuretic and natriuretic responses than Fs alone and also increases GFR without activation of aldosterone. Coadministration of BNP and loop diuretic is effective in maximizing natriuresis and diuresis while preserving renal function and inhibiting activation of aldosterone.