Pro-B-type natriuretic peptide-1-108 processing and degradation in human heart failure.

BACKGROUND: We have reported that pro-B-type natriuretic peptide (BNP)-1-108 circulates and is processed to mature BNP1-32 in human blood. Building on these findings, we sought to determine whether proBNP1-108 processed forms in normal circulation are biologically active and stimulate cGMP, and whether proBNP1-108 processing and activity are altered in human heart failure (HF) compared with normal. Because BNP1-32 is deficient whereas proBNP1-108 is abundant in HF, we hypothesize that proBNP1-108 processing and degradation are impaired in HF patients ex vivo. METHODS AND RESULTS: We measured circulating molecular forms, including BNP1-32, proBNP1-108, and N-terminal-proBNP, and all were significantly higher in patients with HF when compared with that in normals. Fresh serum samples from normals or patients with HF were incubated with or without exogenous nonglycosylated proBNP1-108 tagged with 6 C-terminal Histidines to facilitate peptide isolation. His-tag proBNP1-108 was efficiently processed into BNP1-32/3-32 at 5 minutes in normal serum, persisted for 15 minutes, then disappeared. Delayed processing of proBNP1-108 was observed in HF samples, and the degradation pattern differed depending on left ventricular function. The 5-minute processed forms from both normal and HF serums were active and generated cGMP via guanylyl cyclase-A receptors; however, the 180-minute samples were not active. The proBNP1-108 processing enzyme corin and BNP-degrading enzyme dipeptidyl peptidase-4 were reduced in HF versus normal, perhaps contributing to differential BNP metabolism in HF. CONCLUSIONS: Exogenous proBNP1-108 is processed into active BNP1-32 and ultimately degraded in normal circulation. The processing and degradation of BNP molecular forms were altered but complete in HF, which may contribute to the pathophysiology of HF.

Cardiac fibrosis in end-stage human heart failure and the cardiac natriuretic peptide guanylyl cyclase system: regulation and therapeutic implications.

Left ventricular assist device (LVAD) support has been used in the treatment of end-stage heart failure (HF), however use of anti-fibrotic co-therapies may improve prognosis. Natriuretic peptides (NPs) possess anti-fibrotic properties through their receptors, GC-A/GC-B/NPR-C. We sought to evaluate cardiac fibrosis and the endogenous NP system in end-stage HF with and without LVAD therapy and to assess the anti-fibrotic actions of the dual GC-A/-B activator CD-NP in vitro. Collagen (Col) protein content was assessed by Picrosirius Red staining and NPs, NP receptors, and Col I mRNA expression were determined by qPCR in LV tissue from patients in end-stage HF (n=13), after LVAD support (n=5) and in normal subjects (n=6). Col I mRNA and protein levels in cardiac fibroblasts (CFs) pretreated with CD-NP were compared to those of BNP or CNP pretreatment. The LV in end-stage HF was characterized by higher Col I mRNA expression and Col protein deposition compared to normal which was sustained after LVAD support. ANP and BNP mRNA expressions were higher while CNP was lower in end-stage HF LV. GC-A expression did not change while GC-B and NPR-C increased compared to normal LV. The changes in NP system expression were not reversed after LVAD support. In vitro, CD-NP reduced Col I production stimulated by TGF-beta 1 greater than BNP or CNP in CFs. We conclude that the failing LV is characterized by increased fibrosis and reduced CNP gene expression. LVAD support did not reverse Col deposition nor restore CNP production, suggesting a therapeutic opportunity for CD-NP.

Urinary C-type natriuretic peptide: a new heart failure biomarker.

OBJECTIVES: This study was conducted to determine whether urinary excretion of C-type natriuretic peptide (CNP) is elevated in acute decompensated heart failure (ADHF) and whether elevated levels predict adverse outcomes. BACKGROUND: Urinary CNP has been detected in patients with heart failure, but its clinical significance and prognostic utility, compared to established kidney injury biomarkers, in ADHF is unknown. METHODS: We measured 24-h urinary excretion and concurrent plasma concentrations of CNP22, CNP53, and NT-CNP53 in 58 ADHF patients and 20 healthy control subjects. Urinary kidney injury molecule (KIM)-1 and neutrophil gelatinase­associated lipocalin (NGAL) and plasma N-terminal pro-B type natriuretic peptide (NT-proBNP) were also measured. Mortality and all-cause rehospitalization/death were assessed over a follow-up of 1.5 ± 0.9 years. RESULTS: ADHF patients had higher urinary excretion of all 3 CNP molecular forms than did controls. Plasma CNP22 and CNP53 were elevated in ADHF but showed limited correlation with urinary excretion, suggesting that mainly renal-derived CNP appears in urine. Plasma NT-proBNP and urinary KIM-1 were also elevated in ADHF (p < 0.0001); urinary NGAL was similar to that in controls. At 6 months, event-free survival values in ADHF patients were 86% for mortality and 59% for all-cause rehospitalization/death. On Cox regression analysis, urinary NT-CNP53 was the only predictor of mortality (hazard ratio: 1.7; 95% confidence interval: 1.1 to 2.4; p = 0.01) and all-cause rehospitalization/death (hazard ratio: 1.8; 95% confidence interval: 1.3 to 2.4; p = 0.0004), even after adjustment. Integrated discrimination analysis suggested that urinary NT-CNP53 combined with plasma NT-proBNP improved the prediction of adverse outcomes. CONCLUSIONS: The findings from this study support the clinical utility of urinary CNP molecular forms. In ADHF, urinary NT-CNP53 correlated with prognosis, better predicted outcomes than did urinary NGAL and KIM-1, and improved the prognostic value of plasma NT-proBNP.

Endothelial permeability in vitro and in vivo: protective actions of ANP and omapatrilat in experimental atherosclerosis.

Increased arterial endothelial cell permeability (ECP) is considered an initial step in atherosclerosis. Atrial natriuretic peptide (ANP) which is rapidly degraded by neprilysin (NEP) may reduce injury-induced endothelial cell leakiness. Omapatrilat represents a first in class of pharmacological agents which inhibits both NEP and angiotensin converting enzyme (ACE). We hypothesized that ANP prevents thrombin-induced increases of ECP in human aortic ECs (HAECs) and that omapatrilat would reduce aortic leakiness and atherogenesis and enhance ANP mediated vasorelaxation of isolated aortas. Thrombin induced ECP determined by I(125) albumin flux was assessed in HAECs with and without ANP pretreatment. Next we examined the effects of chronic oral administration of omapatrilat (12 mg/kg/day, n=13) or placebo (n=13) for 8 weeks on aortic leakiness, atherogenesis and ANP-mediated vasorelaxation in isolated aortas in a rabbit model of atherosclerosis produced by high cholesterol diet. In HAECs, thrombin-induced increases in ECP were prevented by ANP. Omapatrilat reduced the area of increased aortic leakiness determined by Evans-blue dye and area of atheroma formation assessed by Oil-Red staining compared to placebo. In isolated arterial rings, omapatrilat enhanced vasorelaxation to ANP compared to placebo with and without the endothelium. ANP prevents thrombin-induced increases in ECP in HAECs. Chronic oral administration of omapatrilat reduces aortic leakiness and atheroma formation with enhanced endothelial independent vasorelaxation to ANP. These studies support the therapeutic potential of dual inhibition of NEP and ACE in the prevention of increased arterial ECP and atherogenesis which may be linked to the ANP/cGMP system.

Corin is present in the normal human heart, kidney, and blood, with pro-B-type natriuretic peptide processing in the circulation.

BACKGROUND: B-type natriuretic peptide (BNP), which is activated in heart failure (HF), is processed to an active form by corin. The corin gene is expressed in the human heart and kidney, but corin protein expression in the heart, kidney, and circulation, along with whether proBNP is processed by circulating corin, remains unknown. METHODS: We examined corin protein expression by immunostaining and Western blot in human heart and kidney, and we assessed the circulating corin concentration by ELISA. We examined histidine-tagged (His-tag) proBNP(1-108) processing in serum and plasma by immunoprecipitation and Western blot and sequenced the processed form. RESULTS: Normal human heart and kidney displayed the presence of corin, especially in cells around the vasculature. Both corin and proBNP(1-108) were present in the plasma of healthy human subjects, with circulating corin significantly higher in men than women (P < 0.0001) and a positive correlation of corin to age (P = 0.0497, r = 0.27). In fresh normal plasma and serum, His-tag proBNP(1-108) was processed to a lower molecular weight form confirmed to be BNP. Processed BNP was higher in men than women (P = 0.041) and was positively correlated to plasma corin concentrations (P = 0.041, r = 0.65). CONCLUSIONS: Our results support the concept that proBNP(1-108) may be processed outside of the heart in the circulation where the proprotein convertase is present. Moreover, sex may impact this process, since corin concentrations are higher in men. These findings may have important physiologic and pathophysiologic implications for the proBNP/corin system in the human.

A novel chimeric natriuretic peptide reduces cardiomyocyte hypertrophy through the NHE-1-calcineurin pathway.

AIMS: Natriuretic peptides (NPs) inhibit cardiomyocyte hypertrophy through a cyclic GMP (cGMP)-dependent process, although these effects are associated with substantial vasodilatation. In this study, we used CU-NP, a non-vasodilatating novel NP synthesized from the ring structure of human C-type NP (CNP) and both C- and N-termini of urodilatin, and investigated whether it can directly modulate cardiomyocyte hypertrophy. METHODS AND RESULTS: Experiments were carried out in cultured neonatal rat ventricular myocytes exposed to phenylephrine, angiotensin II, or endothelin-1 in the absence or presence of CU-NP. CU-NP produced a concentration- and time-dependent increase in intracellular cGMP levels. The hypertrophic responses to all agonists were abrogated by 10 nM CU-NP. CU-NP treatment also prevented increased activity, gene and protein expression of sodium-hydrogen exchanger-1 (NHE-1) as well as elevations in intracellular Na(+) concentrations caused by hypertrophic agents. In addition, these effects were associated with a more than two-fold increase in activity of the Ca(2+)-dependent protein phosphatase calcineurin that peaked 6 h after addition of hypertrophic stimuli. Early (1-3 h) calcineurin activation was unaffected by CU-NP, although activation at 6 and 24 h was prevented by CU-NP as was the resultant translocation of the transcriptional factor NFAT into nuclei. CONCLUSION: Our study demonstrates a direct anti-hypertrophic effect of the chimeric peptide CU-NP via NHE-1 inhibition, thereby preventing calcineurin activation and NFAT nuclear import. Thus, CU-NP represents a novel fusion peptide of CNP and urodilatin that has the potential to be developed into a therapeutic agent to treat cardiac hypertrophy and heart failure.

Distinct roles for renal particulate and soluble guanylyl cyclases in preserving renal function in experimental acute heart failure.

Worsening renal function in the setting of human acute heart failure (AHF) predicts poor outcomes, such as rehospitalization and increased mortality. Understanding potential renoprotective mechanisms is warranted. The guanylate cyclase (GC) enzymes and their second messenger cGMP are the target of two important circulating neurohumoral systems with renoprotective properties. Specifically, natriuretic peptides (NP) released from the heart with AHF target particulate GC in the kidney, while the nitric oxide (NO) system is an activator of renal soluble GC. We hypothesized that both systems are essential to preserve renal excretory and hemodynamic function in AHF but with distinct roles. We investigated these roles in three groups of anesthetized dogs (6 each) with AHF induced by rapid ventricular pacing. After a baseline AHF clearance, each group received intrarenal vehicle (control), N(G)-monomethyl-l-arginine (l-NMMA), a competitive NO inhibitor (50 microg.kg(-1).min(-1)) or a specific NP receptor antagonist, HS-142-1 (0.5 mg/kg). We observed that intrarenal l-NMMA decreased renal blood flow (RBF) without significant decreases in glomerular filtration rate (GFR), urinary sodium excretion (UNaV), or urinary cGMP. In contrast, HS-142-1 resulted in a decrease in UNaV and cGMP excretion together with a reduction in GFR and an increase in distal fractional tubular sodium reabsorption. We conclude that in AHF, the NP system plays a role in maintaining sodium excretion and GFR, while the function of NO is in the maintenance of RBF. These studies have both physiological and therapeutic implications warranting further research into cardiorenal interactions in this syndrome of AHF.

Immunoreactivity and guanosine 3',5'-cyclic monophosphate activating actions of various molecular forms of human B-type natriuretic peptide.

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.

BNP-induced activation of cGMP in human cardiac fibroblasts: interactions with fibronectin and natriuretic peptide receptors.

Cardiac remodeling involves the accumulation of extracellular matrix (ECM) proteins including fibronectin (FN). FN contains RGD motifs that bind integrins at DDX sequences allowing signaling from the ECM to the nucleus. We noted that the natriuretic peptide receptor A (NPR-A) sequence contains both RGD and DDX sequences. The goal of the current investigation was to determine potential interactions between FN and NPR-A on BNP induction of cGMP in cultured human cardiac fibroblasts (CFs). Further, we sought to determine whether a Mayo designed NPR-A specific RGD peptide could modify this interaction. Here we reconfirm the presence of all three natriuretic peptide receptors (NPR) in CFs. CFs plated on FN demonstrated a pronounced increase in cGMP production to BNP compared to non-coated plates. This production was also enhanced by the NPR-A specific RGD peptide, which further augmented FN associated cGMP production. Addition of HS-142-1, a NPR-A/B antagonist, abrogated the responses of BNP to both FN and the NPR-A specific RGD peptide. Finally, we defined a possible role for the NPR-C through non-cGMP mechanisms in mediating the anti-proliferative actions of BNP in CFs where the NPR-C antagonist cANF 4-28 but not HS-142-1 blocked BNP-mediated inhibition of proliferation of CFs. We conclude that NPR-A interacts with components of the ECM such as FN to enhance BNP activation of cGMP and that a small NPR-A specific RGD peptide augments this action of BNP with possible therapeutic implications. Lastly, the NPR-C may also have a role in mediating anti-proliferative actions of BNP in CFs.

Oral human brain natriuretic peptide activates cyclic guanosine 3',5'-monophosphate and decreases mean arterial pressure.

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.

The potential of brain natriuretic peptide as a biomarker for New York Heart Association class during the outpatient treatment of heart failure.

BACKGROUND: Plasma C-terminal atrial natriuretic peptide (C-ANP), N-terminal ANP (N-ANP), and brain natriuretic peptide (BNP) have diagnostic utility in detecting left ventricular dysfunction. Their relative value in monitoring symptom status during the chronic treatment of congestive heart failure (CHF) remains undefined. METHODS AND RESULTS: Ninety-eight subjects with CHF were evaluated. Baseline natriuretic peptides were measured by radioimmunoassay, left ventricular ejection fraction (LVEF) was estimated with echocardiography, and New York Heart Association (NYHA) class was determined independently by attending heart failure specialists. Forty-one subjects were restudied during a 6- to 12-month follow-up period after optimizing therapy. At baseline, all natriuretic peptides and LVEF correlated positively with NYHA class (P <.005). Plasma BNP, however, correlated best with NYHA class. At follow-up, only changes of BNP correlated to changes of NYHA class (P =.04). BNP decreased (-45% +/- 12%, N = 14, P =.002) in subjects whose NYHA class improved whereas BNP remained unchanged (-1% +/- 10%, N = 25, P =.95) in those whose NYHA class was stable. CONCLUSIONS: This investigation demonstrates the superiority of plasma BNP as compared to ANP and LVEF in objectively assessing NYHA class during the chronic treatment of CHF. Given that clinical assessment of CHF is subjective, plasma BNP is a useful objective biomarker in monitoring human CHF in the outpatient setting.