Sangaralingham, S. Jeson

We sought to investigate the role of aldosterone as a mediator of disease and its relationship with the counter-regulatory natriuretic peptide (NP) system. We measured plasma aldosterone (n=1674; aged≥45 years old) in a random sample of the general population from Olmsted County, MN. In a multivariate logistic regression model, aldosterone analyzed as a continuous variable was associated with hypertension (odds ratio [OR]=1.75; 95% confidence interval [CI]=1.57–1.96; P <0.0001), obesity (OR=1.34; 95% CI=1.21–1.48; P <0.0001), chronic kidney disease (OR=1.39; 95% CI=1.22–1.60; P <0.0001), central obesity (OR=1.47; 95% CI=1.32–1.63; P <0.0001), metabolic syndrome (OR=1.41; 95% CI=1.26–1.58; P <0.0001), high triglycerides (OR=1.23; 95% CI=1.11–1.36; P <0.0001), concentric left ventricular hypertrophy (OR=1.22; 95% CI=1.09–1.38; P =0.0007), and atrial fibrillation (OR=1.24; 95% CI=1.01–1.53; P =0.04), after adjusting for age and sex. The associations with hypertension, central obesity, metabolic syndrome, triglycerides, and concentric left ventricular hypertrophy remained significant after further adjustment for body mass index, NPs, and renal function. Furthermore, aldosterone in the highest tertile correlated with lower NP levels and increased mortality. Importantly, most of these associations remained significant even after excluding subjects with aldosterone levels above the normal range. In conclusion, we report that aldosterone is associated with hypertension, chronic kidney disease, obesity, metabolic syndrome, concentric left ventricular hypertrophy, and lower NPs in the general community. Our data suggest that aldosterone, even within the normal range, may be a biomarker of cardiorenal and metabolic disease. Further studies are warranted to evaluate a therapeutic and preventive strategy to delay the onset and progression of disease, using mineralocorticoid antagonists or chronic NP administration in high-risk subjects identified by plasma aldosterone.

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.

BackgroundSystemic hypertension is a common characteristic in acute heart failure (HF). This increasingly recognized phenotype is commonly associated with renal dysfunction and there is an unmet need for renal enhancing therapies. In a canine model ofHFand acute vasoconstrictive hypertension we characterized and compared the cardiorenal actions ofM‐atrial natriuretic peptide (M‐ANP), a novel particulate guanylyl cyclase (pGC) activator, and nitroglycerin, a soluble guanylyl cyclase (sGC) activator.Methods and ResultsHFwas induced by rapid RV pacing (180 beats per minute) for 10 days. On day 11, hypertension was induced by continuous angiotensin II infusion. We characterized the cardiorenal and humoral actions prior to, during, and following intravenousM‐ANP(n=7), nitroglycerin (n=7), and vehicle (n=7) infusion. Mean arterial pressure (MAP) was reduced byM‐ANP(139±4 to 118±3 mm Hg,P<0.05) and nitroglycerin (137±3 to 116±4 mm Hg,P<0.05); similar findings were recorded for pulmonary wedge pressure (PCWP) withM‐ANP(12±2 to 6±2 mm Hg,P<0.05) and nitroglycerin (12±1 to 6±1 mm Hg,P<0.05).M‐ANPenhanced renal function with significant increases (P<0.05) in glomerular filtration rate (38±4 to 53±5 mL/min), renal blood flow (132±18 to 236±23 mL/min), and natriuresis (11±4 to 689±37 mEq/min) and also inhibited aldosterone activation (32±3 to 23±2 ng/dL,P<0.05), whereas nitroglycerin had no significant (P>0.05) effects on these renal parameters or aldosterone activation.ConclusionsOur results advance the differential cardiorenal actions ofpGC(M‐ANP) andsGC(nitroglycerin) mediatedcGMPactivation. These distinct renal and aldosterone modulating actions makeM‐ANPan attractive therapeutic forHFwith concomitant hypertension, where renal protection is a key therapeutic goal.

In heart failure (HF), the cardiac hormone natriuretic peptides (NPs) atrial (ANP), B-type (BNP), and C-type (CNP) play a key role to protect cardiac remodeling. The proprotein convertases corin and furin process their respective pro-NPs into active NPs. Here we define in a canine model of HF furin and corin gene and protein expression in normal and failing left atrium (LA) or ventricle (LV) testing the hypothesis that the NP proproteins convertases production is altered in experimental HF. Experimental canine HF was produced by rapid right ventricular pacing for 10 days. NPs, furin, and corin mRNA expression were determined by quantitative RT-PCR. Protein concentration or expression was determined by immunostaining, radioimmunoassay, or Western blot. Furin and corin proteins were present in normal canine LA and LV myocardium and vasculature and in smooth muscle cells. In normal canines, expression of NPs was dominant in the atrium compared with the ventricle. In experimental early stage HF characterized with marked atrial fibrosis, ANP, BNP, and CNP mRNA, and protein concentrations were higher in HF LA but not HF LV compared with normals. In LA, corin mRNA and protein expressions in HF were lower, whereas furin mRNA and protein expressions were higher than normals. NPs and furin expressions were augmented in the atrium in experimental early stage HF and, conversely, corin mRNA and protein expressions were decreased with atrial remodeling. Selective changes of these NP convertases may have significance in the regulation of pro-NP processing and atrial remodeling in early stage HF.

Background— Alterations at the level of the coronary circulation with aging may play an important role in the evolution of age-associated changes in left ventricular (LV) fibrosis and function. However these age-associated changes in the coronary vasculature remain poorly defined primarily due to the lack of high resolution imaging technologies. The current study was designed to utilize cardiac micro–computed tomography (micro-CT) technology as a novel imaging strategy, to define the 3-dimensional coronary circulation in the young and aged heart and its relationship to LV fibrosis and function. Methods and Results— Young (2 months old; n=10) and aged (20 months old; n=10) Fischer rats underwent cardiac micro-CT imaging as well as echocardiography, blood pressure, and fibrosis analysis. Importantly, when indexed to LV mass, which increased with age, the total and intramyocardial vessel volumes were lower, whereas the epicardial vessel volume, with and without indexing to LV mass, was significantly higher in the aged hearts compared with the young hearts. Moreover, the aged hearts had a significantly lower percentage of intramyocardial vessel volume and a significantly higher percentage of epicardial vessel volume, when normalized to the total vessel volume, compared with the young hearts. Further, the aged hearts had significant LV fibrosis and mild LV dysfunction compared with the young hearts. Conclusions— This micro-CT imaging study reports the reduction in normalized intramyocardial vessel volume within the aged heart, in association with increased epicardial vessel volume, in the setting of increased LV fibrosis, and mild LV dysfunction.

Impaired renal function with loss of nephron number in chronic renal disease (CKD) is associated with increased cardiovascular morbidity and mortality. However, the structural and functional cardiac response to early and mild reduction in renal mass is poorly defined. We hypothesized that mild renal impairment produced by unilateral nephrectomy (UNX) would result in early cardiac fibrosis and impaired diastolic function, which would progress to a more global left ventricular (LV) dysfunction. Cardiorenal function and structure were assessed in rats at 4 and 16 wk following UNX or sham operation (Sham); ( n = 10 per group). At 4 wk, blood pressure (BP), aldosterone, glomerular filtration rate (GFR), proteinuria, and plasma B-type natriuretic peptide (BNP) were not altered by UNX, representing a model of mild early CKD. However, UNX was associated with significantly greater LV myocardial fibrosis compared with Sham. Importantly, terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining revealed increased apoptosis in the LV myocardium. Further, diastolic dysfunction, assessed by strain echocardiography, but with preserved LVEF, was observed. Changes in genes related to the TGF-β and apoptosis pathways in the LV myocardium were also observed. At 16 wk post-UNX, we observed persistent LV fibrosis and impairment in LV diastolic function. In addition, LV mass significantly increased, as did LVEDd, while there was a reduction in LVEF. Aldosterone, BNP, and proteinuria were increased, while GFR was decreased. The myocardial, structural, and functional alterations were associated with persistent changes in the TGF-β pathway and even more widespread changes in the LV apoptotic pathway. These studies demonstrate that mild renal insufficiency in the rat results in early cardiac fibrosis and impaired diastolic function, which progresses to more global LV remodeling and dysfunction. Thus, these studies importantly advance the concept of a kidney-heart connection in the control of myocardial structure and function.

Renal aging is characterized by structural changes in the kidney including fibrosis, which contributes to the increased risk of kidney and cardiac failure in the elderly. Studies involving healthy kidney donors demonstrated subclinical age-related nephropathy on renal biopsy that was not detected by standard diagnostic tests. Thus there is a high-priority need for novel noninvasive biomarkers to detect the presence of preclinical age-associated renal structural and functional changes. C-type natriuretic peptide (CNP) possesses renoprotective properties and is present in the kidney; however, its modulation during aging remains undefined. We assessed circulating and urinary CNP in a Fischer rat model of experimental aging and also determined renal structural and functional adaptations to the aging process. Histological and electron microscopic analysis demonstrated significant renal fibrosis, glomerular basement membrane thickening, and mesangial matrix expansion with aging. While plasma CNP levels progressively declined with aging, urinary CNP excretion increased, along with the ratio of urinary to plasma CNP, which preceded significant elevations in proteinuria and blood pressure. Also, CNP immunoreactivity was increased in the distal and proximal tubules in both the aging rat and aging human kidneys. Our findings provide evidence that urinary CNP and its ratio to plasma CNP may represent a novel biomarker for early age-mediated renal structural alterations, particularly fibrosis. Thus urinary CNP could potentially aid in identifying subjects with preclinical structural changes before the onset of symptoms and disease, allowing for the initiation of strategies designed to prevent the progression of chronic kidney disease particularly in the aging population.

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.

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.