McKie, Paul M.

Myocardial aging is characterized by left ventricular (LV) fibrosis leading to diastolic and systolic dysfunction. Studies have established the potent antifibrotic and antiproliferative properties of C-type natriuretic peptide (CNP); however, the relationship between circulating CNP, LV fibrosis, and associated changes in LV function with natural aging are undefined. Accordingly, we characterized the relationship of plasma CNP with LV fibrosis and function in 2-, 11-, and 20-month–old male Fischer rats. Further in vitro, we established the antiproliferative actions of CNP and the participation of the clearance receptor using adult human cardiac fibroblasts. Here we establish for the first time that a progressive decline in circulating CNP characterizes natural aging and is strongly associated with a reciprocal increase in LV fibrosis that precedes impairment of diastolic and systolic function. Additionally, we demonstrate in cultured adult human cardiac fibroblasts that the direct antiproliferative actions of high-dose CNP may involve a non-cGMP pathway via the clearance receptor. Together, these studies provide new insights into myocardial aging and the relationship to the antifibrotic and antiproliferative peptide CNP.

BACKGROUNDB-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.METHODSWe 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) proBNP1–108 processing in serum and plasma by immunoprecipitation and Western blot and sequenced the processed form.RESULTSNormal human heart and kidney displayed the presence of corin, especially in cells around the vasculature. Both corin and proBNP1–108 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 proBNP1–108 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).CONCLUSIONSOur results support the concept that proBNP1–108 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.

M-atrial natriuretic peptide (ANP; M-ANP) is a novel next generation 40 amino acid peptide based on ANP, which is highly resistant to enzymatic degradation and has greater and more sustained beneficial actions compared with ANP. The current study was designed to advance our understanding of the therapeutic potential of M-ANP in a canine model of acute angiotensin II–induced hypertension with elevated cardiac filling pressures and aldosterone activation. We compare M-ANP with vehicle and equimolar human B-type natriuretic peptide, which possesses the most potent in vivo actions of the native natriuretic peptides. M-ANP significantly lowered mean arterial pressure and systemic vascular resistance. Importantly, despite a reduction in blood pressure, renal function was enhanced with significant increases in renal blood flow, glomerular filtration rate, diuresis, and natriuresis after M-ANP infusion. Although angiotensin II induced an acute increase in pulmonary capillary wedge pressure, M-ANP significantly lowered pulmonary capillary wedge pressure, pulmonary artery pressure, and right atrial pressure. Further, M-ANP significantly suppressed angiotensin II–induced activation of aldosterone. These cardiovascular and renal enhancing actions of M-ANP were accompanied by significant increases in plasma and urinary cGMP, the second messenger molecule of the natriuretic peptide system. When compared with human B-type natriuretic peptide, M-ANP had comparable cardiovascular actions but resulted in a greater natriuretic effect. These results suggest that M-ANP, which is more potent than ANP in normal canines, has potent blood pressure lowering and renal enhancing properties and may, therefore, serve as an ANP based therapeutic for acute hypertension.

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.

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.