Search

Baroreflex control of cardiac contraction (positive inotropy) through sympathetic nerve activation is important for cardiocirculatory homeostasis. Transient receptor potential canonical subfamily (TRPC) channels are responsible for α 1 -adrenoceptor (α 1 AR)-stimulated cation entry and their upregulation is associated with pathological cardiac remodeling. Whether TRPC channels participate in physiological pump functions remains unclear. We demonstrate that TRPC6-specific Zn 2+ influx potentiates β-adrenoceptor (βAR)-stimulated positive inotropy in rodent cardiomyocytes. Deletion of trpc6 impairs sympathetic nerve-activated positive inotropy but not chronotropy in mice. TRPC6-mediated Zn 2+ influx boosts α 1 AR-stimulated βAR/G s -dependent signaling in rat cardiomyocytes by inhibiting β-arrestin-mediated βAR internalization. Replacing two TRPC6-specific amino acids in the pore region with TRPC3 residues diminishes the α 1 AR-stimulated Zn 2+ influx and positive inotropic response. Pharmacological enhancement of TRPC6-mediated Zn 2+ influx prevents chronic heart failure progression in mice. Our data demonstrate that TRPC6-mediated Zn 2+ influx with α 1 AR stimulation enhances baroreflex-induced positive inotropy, which may be a new therapeutic strategy for chronic heart failure., (© 2022. The Author(s).)

Background: This study aimed to investigate the association between changes in brain natriuretic peptide (BNP) from discharge to 6-month visit and subsequent clinical outcomes in patients with acute heart failure (AHF)., Methods: Among 1246 patients enrolled in the prospective longitudinal follow-up study nested from the Kyoto Congestive Heart Failure registry, this study population included 446 patients with available paired BNP data at discharge and 6-month index visit. This study population was classified into 3 groups by percent change in BNP from discharge to 6-month visit; the low tertile (≤-44%, N = 149), the middle tertile (>-44% and ≤22%, N = 149) and the high tertile (>22%, N = 148)., Findings: The cumulative 180-day incidence after the index visit of the primary outcome measure (a composite endpoint of all-cause death or hospitalization for HF) was significantly higher in the high and middle tertiles than in the low tertile (26.8% and 14.4% versus 6.9%, log-rank P<0.0001). The adjusted excess risk of the high tertile relative to the low tertile remained significant for the primary outcome measure (hazard ratio: 3.43, 95% confidence interval: 1.51-8.46, P = 0.003)., Conclusions: Percent change in BNP was associated with a subsequent risk for a composite of all-cause death and hospitalization for HF after adjustment of the absolute BNP values, suggesting that observing the change in BNP levels, in addition to absolute BNP levels themselves, helps us to manage patient with HF., Competing Interests: The authors have declared that no competing interests exist.

Background: During the development of heart failure, a fetal cardiac gene program is reactivated and accelerates pathological cardiac remodeling. We previously reported that a transcriptional repressor, NRSF (neuron restrictive silencer factor), suppresses the fetal cardiac gene program, thereby maintaining cardiac integrity. The underlying molecular mechanisms remain to be determined, however., Methods: We aim to elucidate molecular mechanisms by which NRSF maintains normal cardiac function. We generated cardiac-specific NRSF knockout mice and analyzed cardiac gene expression profiles in those mice and mice cardiac-specifically expressing a dominant-negative NRSF mutant., Results: We found that cardiac expression of Gα o , an inhibitory G protein encoded in humans by GNAO1 , is transcriptionally regulated by NRSF and is increased in the ventricles of several mouse models of heart failure. Genetic knockdown of Gnao1 ameliorated the cardiac dysfunction and prolonged survival rates in these mouse heart failure models. Conversely, cardiac-specific overexpression of GNAO1 in mice was sufficient to induce cardiac dysfunction. Mechanistically, we observed that increasing Gα o expression increased surface sarcolemmal L-type Ca 2+ channel activity, activated CaMKII (calcium/calmodulin-dependent kinase-II) signaling, and impaired Ca 2+ handling in ventricular myocytes, which led to cardiac dysfunction., Conclusions: These findings shed light on a novel function of Gα o in the regulation of cardiac Ca 2+ homeostasis and systolic function and suggest Gα o may be an effective therapeutic target for the treatment of heart failure.

Aims: The methodology to distinguish between the heart failure (HF) with recovered ejection fraction (HFrecEF) and those with continuously reduced ejection fraction (EF) (HFcrEF) on admission has not been established. We recently demonstrated that the ratio of plasma levels of pro-B-type natriuretic peptide (proBNP) to total BNP (proBNP plus mature BNP) is decreased on admission in patients with mild acute HF, but not in severe acute HF as a compensatory mechanism for activating cyclic GMP via increases of bioactive mature BNP. We aimed to test the hypothesis that the ratio of bioactive mature BNP to total BNP is associated with reverse remodelling capacity in patients with HF with reduced EF., Methods and Results: Plasma proBNP and total BNP were measured in patients with acute decompensated HF by using specific and sensitive enzyme immunochemiluminescent assay. Estimated percent mature BNP (%emBNP) was calculated as ([total BNP - proBNP]/total BNP) × 100. We retrospectively identified the patients with reduced EF (≤40%, on admission) who had echocardiographic data after discharge (n = 93). We defined patients with increased EF by >10% during the follow-up term (median, 545 days) after the admission as HFrecEF group. We compared patient characteristics, %emBNP, and other biomarkers between HFrecEF and HFcrEF. Of the enrolled patients with HFrecEF (n = 32) and HFcrEF (n = 61), on admission, %emBNP was significantly higher in HFrecEF than in HFcrEF (44.1% vs. 36.9%; P < 0.05). There were no significant differences in left ventricular EF on admission between the two groups. The univariate analysis revealed that %emBNP on admission was associated with HFrecEF occurrence rate (P < 0.05), in contrast both total BNP and high-sensitive cardiac troponin-T levels were not associated with HFrecEF occurrence rate., Conclusions: The ratio of mature BNP to total BNP in plasma at the time of hospital admission may be predictive of left ventricular contractile recovery. Preservation of the capacity to convert proBNP to mature BNP, but not myocardial injury itself, is associated with future ventricular contractile recovery., (© 2021 The Authors. ESC Heart Failure published by John Wiley & Sons Ltd on behalf of European Society of Cardiology.)

B-type (or brain) natriuretic peptide (BNP) is synthesized in cardiac myocytes and released constitutively into the circulation. Pressure/volume overload, neurohumoral factors, cytokines, and ischemia enhance BNP gene expression, and then precursor proBNP is produced. It has been thought that proBNP is cleaved into active BNP molecule and inactive marker molecule NT-proBNP intracellularly by processing enzyme furin, and they are released into the circulation. However, recent studies have shown that considerable amount of uncleaved proBNP circulates in the blood. The commercially available BNP assay kits consist of two antibodies that sandwich the BNP molecule. Therefore, if proBNP is present, BNP assay kit cross-reacts to proBNP and measures it as BNP. Therefore, it should be noted that the current BNP value is proBNP plus BNP. BNP and NT-proBNP have been established as a biomarker for heart failure patients presenting dyspnea. But many pitfalls are present for interpreting the BNP value. For example, the presence of renal dysfunction, age, female sex, atrial fibrillation, inflammation, hyperthyroidism, use of sacubitril/valsartan, and macro-proBNPemia overestimate BNP value, whereas the presence of obesity, immediately after acute coronary syndrome onset, and pericardial effusion underestimate BNP value. In the management for heart failure patients, BNP plays an important role. Therefore, clinicians should note the pitfall of interpretation of BNP and we describe the mechanism involved., (Copyright © 2021. Published by Elsevier Ltd.)

Despite recent developments in various therapies, heart failure remains a leading cause of morbidity and mortality worldwide. New pharmacological approaches are therefore needed to improve the outcomes of patients with heart failure. Diabetes mellitus is an important risk factor for heart failure, but until recently there had been no evidence that hypoglycemic agents prevent heart failure. Sodium-glucose cotransporter-2 (SGLT2) inhibitors have now been shown to prevent cardiovascular events, especially hospitalization for heart failure, in three large randomized clinical trials: EMPA-REG OUTCOME, the CANVAS program, and the DECLARE-TIMI58 trial. It is expected, therefore, that SGLT2 inhibitors will be useful therapeutic agents for the treatment of heart failure. The DAPA-HF trial recently demonstrated that dapagliflozin significantly reduces cardiovascular death and hospitalization for heart failure in patients with heart failure with reduced ejection fraction (HFrEF). Importantly, these benefits of dapagliflozin were similarly observed in patients with or without diabetes, suggesting the drug's efficacy is independent of glycemic reduction. The results of that study highlight the significance of SGLT2 inhibition as a novel therapeutic approach to treating HFrEF, irrespective of the presence or absence of diabetes. Findings of the DAPA-HF trial may also challenge current assumptions about the mechanisms underlying the cardioprotective action of SGLT2 inhibitors. It is anticipated that ongoing clinical trials, mainly using dapagliflozin and empagliflozin, will provide further insight into the clinical importance of these drugs for the treatment of heart failure, including heart failure with preserved ejection fraction (HFpEF), and also the mechanisms underlying those clinical benefits., (Copyright © 2020. Published by Elsevier Ltd.)

Background Early detection for worsening renal function (WRF) is indispensable in patients with acute decompensated heart failure (HF). We tested the hypothesis that the difference in the circulating levels of each B-type or brain natriuretic peptide (BNP) molecular form is associated with the occurrence of WRF. Methods and Results Circulating levels of proBNP, the NT-proBNP (N-terminal proBNP), and total BNP (proBNP+mature BNP) were prospectively measured in patients with acute decompensated HF using specific and sensitive enzyme immunochemiluminescent assays. An estimated mature BNP (emBNP) concentration was calculated by subtracting proBNP levels from total BNP levels. WRF was defined as a >20% decrease in the estimated glomerular filtration rate during the hospitalization. One-way repeated-measures ANOVA was used to compare the changes of variables between the patients with and without WRF. In patients with acute decompensated HF (New York Heart Association class III-IV; 96%) hospitalized for HF, NT-proBNP levels did not differ during the hospitalization between patients with and without WRF (n=42 and 140, respectively). By contrast, emBNP levels were lower in patients with WRF than in those without WRF on day 3 after admission. NT-proBNP/emBNP molar ratios were elevated on day 3 after admission in the patients with WRF, before estimated glomerular filtration rate declined, but were unchanged in patients without WRF. On day 3 after hospital admission, NT-proBNP/emBNP ratios were strongly associated with percentage decreases in estimated glomerular filtration rate. Conclusions These findings suggest that elevation of NT-proBNP/emBNP ratio precedes WRF in patients with acute HF and can be a potentially useful biomarker for risk stratification of cardiorenal syndrome.

The natriuretic peptide family consists of three biologically active peptides: atrial natriuretic peptide (ANP), brain (or B-type) natriuretic peptide (BNP), and C-type natriuretic peptide (CNP). Among these, ANP and BNP are secreted by the heart and act as cardiac hormones. Both ANP and BNP preferentially bind to natriuretic peptide receptor-A (NPR-A or guanylyl cyslase-A) and exert similar effects through increases in intracellular cyclic guanosine monophosphate (cGMP) within target tissues. Expression and secretion of ANP and BNP are stimulated by various factors and are regulated via multiple signaling pathways. Human ANP has three molecular forms, α-ANP, β-ANP, and proANP (or γ-ANP), with proANP predominating in healthy atrial tissue. During secretion proANP is proteolytically processed by corin, resulting in secretion of bioactive α-ANP into the peripheral circulation. ProANP and β-ANP are minor forms in the circulation but are increased in patients with heart failure. The human BNP precursor proBNP is proteolytically processed to BNP 1-32 and N-terminal proBNP (NT-proBNP) within ventricular myocytes. Uncleaved proBNP as well as mature BNP 1-32 and NT-proBNP is secreted from the heart, and its secretion is increased in patients with heart failure. Mature BNP, its metabolites including BNP 3-32 , BNP 4-32 , and BNP 5-32 , and proBNP are all detected as immunoreactive-BNP by the current BNP assay system. We recently developed an assay system that specifically detects human proBNP. Using this assay system, we observed that miR30-GALNTs-dependent O-glycosylation in the N-terminal region of proBNP contributes to regulation of the processing and secretion of proBNP from the heart., (Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.)

Brain (or B-type) natriuretic peptide (BNP) is a cardiac hormone produced in the heart and an established biochemical marker for heart failure (HF) because the level in plasma increases in proportion to disease severity. Recently, the diversity of BNP molecular forms in the peripheral circulation, which includes mature BNP (BNP 1-32 ) and its metabolites (BNP 3-32 , BNP 4-32 , and BNP 5-32 ), was demonstrated. Moreover, studies showed that unprocessed BNP prohormone (proBNP) is also secreted from the heart, and its secretion is increased in patients with HF. Interestingly, BNP 1-32 , its metabolites, and proBNP are all detected as immunoreactive BNP by the currently available BNP assay system. Current N-terminal proBNP (NT-proBNP) assay systems also can react to both NT-proBNP and proBNP. In addition, the N-terminal region of proBNP and NT-proBNP are often O-glycosylated, which may result in underestimation of total NT-proBNP level, which includes both glycosylated and non-glycosylated NT-proBNP, by the NT-proBNP assay system. More recently, we have shown that miR30-GALNT-dependent O-glycosylation in the N-terminal region of proBNP affects the processing of proBNP and contributes to its secretion from the heart. The level of proBNP relative to BNP (proBNP/BNP ratio) in the coronary sinus is higher in patients with more severe HF. The proBNP/BNP ratio and the deglycosylated NT-proBNP level may be new and clinically useful biomarkers of HF.

Background: A recent study showed that both glycosylation of pro-B-type natriuretic peptide (BNP) and the proBNP/total BNP ratio are decreased in acute decompensated heart failure (ADHF). However, the following points regarding the proBNP/total BNP ratio have not been determined in patients with ADHF: 1) the relationship with the severity of ADHF, 2) the changes in the ratio during treatment, and 3) the relationship with cyclic guanosine monophosphate (cGMP)-generating activity., Methods: Plasma proBNP and total BNP (proBNP+mature BNP) were measured in patients with ADHF (n=154). Measurement was performed on admission, 3 and 7days after admission, and before discharge using recently developed sandwich chemiluminescence enzyme immunoassays. The percent proBNP was calculated as: (proBNP/total BNP)×100., Results: On admission, %proBNP was higher in patients with severe ADHF than in patients with mild ADHF (median: 61.7% vs. 56.2%, respectively; p<0.01), while the plasma cGMP/total BNP ratio, an index of the biological activity of BNP, was lower (p<0.001). In patients with severe ADHF, the higher %proBNP and lower cGMP/total BNP ratio were unchanged during hospitalization, whereas %proBNP increased gradually in patients with mild ADHF and the cGMP/total BNP ratio also increased at 3days after admission., Conclusion: These findings suggest that in patients with mild ADHF, compensation for heart failure occurs via increased proBNP processing, leading to increase of mature BNP and activation of the BNP/cGMP cascade. In contrast, this compensatory mechanism may be impaired in patients with severe ADHF and a vicious cycle can potentially occur., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Adrenomedullin (AM) is a vasodilatory peptide originally discovered in human pheochromocytoma tissue. Although AM is highly expressed in the adrenal glands, heart, lungs, and kidneys, vascular endothelium and smooth muscle are thought to be the main source of plasma AM. The AM precursor is processed to AM-glycine, which is then converted to AM-mature through C-terminal amidation. In this process, mid-regional pro-adrenomedullin (MR-proAM) is also produced. Plasma AM, AM-mature, AM-glycine, and MR-proAM levels are all higher in patients with heart failure than healthy subjects in proportional to the disease severity. All molecular forms of AM are prognostic markers for heart failure., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Background: Recent studies have shown that plasma levels of the biologically inactive prohormone for brain natriuretic peptide (proBNP) are increased in patients with heart failure. This can contribute to a reduction in the effectiveness of circulating BNP and exacerbate heart failure progression. The precise mechanisms governing the increase in proBNP remain unclear, however., Methods and Results: We used our recently developed, highly sensitive human proBNP assay system to investigate the mechanisms underlying the increase in plasma proBNP levels. We divided 53 consecutive patients hospitalized with heart failure into 2 groups based on their aortic plasma levels of immunoreactive BNP. Patients with higher levels exhibited more severe heart failure, a higher proportion of proBNP among the immunoreactive BNP forms secreted from failing hearts, and a weaker effect of BNP as estimated from the ratio of plasma cyclic guanosine monophosphate levels to log-transformed plasma BNP levels. Glycosylation at threonines 48 and 71 of human proBNP contributed to the increased secretion of proBNP by attenuating its processing, and GalNAc-transferase (GALNT) 1 and 2 mediated the glycosylation-regulated increase in cardiac human proBNP secretion. Cardiac GALNT1 and 2 expression was suppressed by microRNA (miR)-30, which is abundantly expressed in the myocardium of healthy hearts, but is suppressed in failing hearts., Conclusions: We have elucidated a novel miR-30-GALNT1/2 axis whose dysregulation increases the proportion of inactive proBNP secreted by the heart and impairs the compensatory actions of BNP during the progression of heart failure., (© 2017 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.)

Aims: Dysregulation of autonomic nervous system activity can trigger ventricular arrhythmias and sudden death in patients with heart failure. N-type Ca(2+) channels (NCCs) play an important role in sympathetic nervous system activation by regulating the calcium entry that triggers release of neurotransmitters from peripheral sympathetic nerve terminals. We have investigated the ability of NCC blockade to prevent lethal arrhythmias associated with heart failure., Methods and Results: We compared the effects of cilnidipine, a dual N- and L-type Ca(2+) channel blocker, with those of nitrendipine, a selective L-type Ca(2+) channel blocker, in transgenic mice expressing a cardiac-specific, dominant-negative form of neuron-restrictive silencer factor (dnNRSF-Tg). In this mouse model of dilated cardiomyopathy leading to sudden arrhythmic death, cardiac structure and function did not significantly differ among the control, cilnidipine, and nitrendipine groups. However, cilnidipine dramatically reduced arrhythmias in dnNRSF-Tg mice, significantly improving their survival rate and correcting the imbalance between cardiac sympathetic and parasympathetic nervous system activity. A β-blocker, bisoprolol, showed similar effects in these mice. Genetic titration of NCCs, achieved by crossing dnNRSF-Tg mice with mice lacking CACNA1B, which encodes the α1 subunit of NCCs, improved the survival rate. With restoration of cardiac autonomic balance, dnNRSF-Tg;CACNA1B(+/-) mice showed fewer malignant arrhythmias than dnNRSF-Tg;CACNA1B(+/+) mice., Conclusions: Both pharmacological blockade of NCCs and their genetic titration improved cardiac autonomic balance and prevented lethal arrhythmias in a mouse model of dilated cardiomyopathy and sudden arrhythmic death. Our findings suggest that NCC blockade is a potentially useful approach to preventing sudden death in patients with heart failure., (Published on behalf of the European Society of Cardiology. All rights reserved. © The Author 2014. For permissions please email: journals.permissions@oup.com.)

Background: The efficacy of pharmacological interventions to prevent sudden arrhythmic death in patients with chronic heart failure remains limited. Evidence now suggests increased ventricular expression of hyperpolarization-activated cation (HCN) channels in hypertrophied and failing hearts contributes to their arrythmicity. Still, the role of induced HCN channel expression in the enhanced arrhythmicity associated with heart failure and the capacity of HCN channel blockade to prevent lethal arrhythmias remains undetermined., Methods and Results: We examined the effects of ivabradine, a specific HCN channel blocker, on survival and arrhythmicity in transgenic mice (dnNRSF-Tg) expressing a cardiac-specific dominant-negative form of neuron-restrictive silencer factor, a useful mouse model of dilated cardiomyopathy leading to sudden death. Ivabradine (7 mg/kg per day orally) significantly reduced ventricular tachyarrhythmias and improved survival among dnNRSF-Tg mice while having no significant effect on heart rate or cardiac structure or function. Ivabradine most likely prevented the increase in automaticity otherwise seen in dnNRSF-Tg ventricular myocytes. Moreover, cardiac-specific overexpression of HCN2 in mice (HCN2-Tg) made hearts highly susceptible to arrhythmias induced by chronic β-adrenergic stimulation. Indeed, ventricular myocytes isolated from HCN2-Tg mice were highly susceptible to β-adrenergic stimulation-induced abnormal automaticity, which was inhibited by ivabradine., Conclusions: HCN channel blockade by ivabradine reduces lethal arrhythmias associated with dilated cardiomyopathy in mice. Conversely, cardiac-specific overexpression of HCN2 channels increases arrhythmogenicity of β-adrenergic stimulation. Our findings demonstrate the contribution of HCN channels to the increased arrhythmicity seen in failing hearts and suggest HCN channel blockade is a potentially useful approach to preventing sudden death in patients with heart failure.

Background: Recent studies have shown that in addition to brain (or B-type) natriuretic peptide (BNP) and the N-terminal proBNP fragment, levels of intact proBNP are also increased in heart failure. Moreover, present BNP immunoassays also measure proBNP, as the anti-BNP antibody cross-reacts with proBNP. It is important to know the exact levels of proBNP in heart failure, because elevation of the low-activity proBNP may be associated with the development of heart failure., Methodology/principal Findings: We therefore established a two-step immunochemiluminescent assay for total BNP (BNP+proBNP) and proBNP using monoclonal antibodies and glycosylated proBNP as a standard. The assay enables measurement of plasma total BNP and proBNP within only 7 h, without prior extraction of the plasma. The detection limit was 0.4 pmol/L for a 50-µl plasma sample. Within-run CVs ranged from 5.2%-8.0% in proBNP assay and from 7.0%-8.4% in total BNP assay, and between-run CVs ranged from 5.3-7.4% in proBNP assay and from 2.9%-9.5% in total BNP assay, respectively. The dilution curves for plasma samples showed good linearity (correlation coefficients   = 0.998-1.00), and analytical recovery was 90-101%. The mean total BNP and proBNP in plasma from 116 healthy subjects were 1.4 ± 1.2 pM and 1.0 ± 0.7 pM, respectively, and were 80 ± 129 pM and 42 ± 70 pM in 32 heart failure patients. Plasma proBNP levels significantly correlate with age in normal subjects., Conclusions/significance: Our immunochemiluminescent assay is sufficiently rapid and precise for routine determination of total BNP and proBNP in human plasma.

Objective: Pro-brain natriuretic peptide (proBNP)-108 and N-terminal proBNP-76 (NT-BNP) contain seven sites for O-linked oligosaccharide attachment. Currently, levels of glycosylated NT-BNP are probably underestimated because it is not recognised by one antibody in the sandwich assay system. The pathophysiological significance of cardiac and plasma levels of non-glycosylated (nonglyNT-BNP) and glycosylated NT-BNP (glyNT-BNP) in heart failure (HF) and chronic renal failure (CRF) was investigated., Methods: Plasma samples from 186 patients with HF and 76 patients with CRF on haemodialysis were studied, together with 11 atrial tissue samples. To measure nonglyNT-BNP and glyNT-BNP, samples were incubated with or without deglycosylating enzymes and NT-BNP was measured using Roche Elecsys proBNP I. The percentage glyNT-BNP was calculated as glyNT-BNP/(glyNT-BNP + nonglyNT-BNP)., Results: In HF, plasma BNP, nonglyNT-BNP and glyNT-BNP levels all increased with increasing disease severity (New York Heart Association class; p<0.0001), though the molar ratio remained constant (molar ratio, BNP:nonglyNT-BNP:glyNT-BNP = 1:2.4:9.6). Before haemodialysis for CRF, plasma BNP and nonglyNT-BNP were somewhat elevated, and glyNT-BNP was markedly increased (molar ratio, BNP:nonglyNT-BNP:glyNT-BNP = 1:8.5:82). After haemodialysis, plasma BNP, nonglyNT-BNP, atrial natriuretic protein and cGMP all declined (p<0.0001), but glyNT-BNP was unchanged. Notably, the percentage of glyNT-BNP was elevated before haemodialysis, and was further increased after haemodialysis (p<0.0001). Atrial tissue levels of BNP, nonglyNT-BNP and glyNT-BNP were similar., Conclusion: THE findings suggest that most endogenous plasma NT-BNP is glycosylated and therefore undetectable with the current assay system, and that the relative glycosylation level is increased by haemodialysis.

Background: Angiotensin II plays a prominent role in the progression of heart failure after acute myocardial infarction (AMI). Although both angiotensin type 1 (AT1) and type 2 (AT2) receptors are known to be present in the heart, comparatively little is known about the latter. We therefore examined the role played by AT2 receptors in post-AMI heart failure., Methods and Results: In wild-type mice subjected to AMI by coronary artery ligation, AT2 receptor immunoreactivity is upregulated in the infarct and border areas. Among AT2 receptor-null (-/-) mice, the 7-day survival rate after AMI was significantly lower than among wild-type mice (43% versus 67%; P<0.05). All sham-operated animals of both genotypes survived through the study. Ventricular mRNA levels for brain natriuretic peptide were elevated in both genotypes 24 hours after coronary occlusion, with levels in AT2-/- significantly higher than in wild-type mice, as were their lung weights, and histological examination revealed marked pulmonary congestion in the AT2-/- mice. Cardiac function was significantly decreased in AT2-/- mice 2 days after AMI., Conclusions: AT2 receptor deficiency exacerbates short-term death rates and heart failure after experimental AMI in mice. The AT2 receptor may thus exert a protective effect on the heart after AMI.

Baroreflex control of cardiac contraction (positive inotropy) through sympathetic nerve activation is important for cardiocirculatory homeostasis. Transient receptor potential canonical subfamily (TRPC) channels are responsible for α1-adrenoceptor (α1AR)-stimulated cation entry and their upregulation is associated with pathological cardiac remodeling. Whether TRPC channels participate in physiological pump functions remains unclear. We demonstrate that TRPC6-specific Zn2+ influx potentiates β-adrenoceptor (βAR)-stimulated positive inotropy in rodent cardiomyocytes. Deletion of trpc6 impairs sympathetic nerve–activated positive inotropy but not chronotropy in mice. TRPC6-mediated Zn2+ influx boosts α1AR-stimulated βAR/Gs-dependent signaling in rat cardiomyocytes by inhibiting β-arrestin-mediated βAR internalization. Replacing two TRPC6-specific amino acids in the pore region with TRPC3 residues diminishes the α1AR-stimulated Zn2+ influx and positive inotropic response. Pharmacological enhancement of TRPC6-mediated Zn2+ influx prevents chronic heart failure progression in mice. Our data demonstrate that TRPC6-mediated Zn2+ influx with α1AR stimulation enhances baroreflex-induced positive inotropy, which may be a new therapeutic strategy for chronic heart failure. Baroreflex control of cardiac contractility is essential to maintain cardiocirculatory homeostasis. Here, Oda et al show that α1 adrenoceptor-stimulated Zn2+ entry through TRPC6 channels boosts β adrenoceptor-dependent myocardial positive inotropy. [ABSTRACT FROM AUTHOR]

Simple Summary: Active BNP-32, less active proBNP-108, and inactive N-terminal proBNP-76 all circulate in the blood. The circulating protease neprilysin has lower substrate specificity for BNP than ANP, while proBNP and N-terminal proBNP are not degraded by neprilysin. Currently available BNP immunoassays react with both mature BNP and proBNP; therefore, measured plasma BNP is mature BNP + proBNP. Because ARNI administration increases mature BNP, measured plasma BNP initially increases with ARNI administration by the amount of the increase in mature BNP. Later, ARNI administration reduces myocardial wall stress, and the resultant reduction in BNP production more than offsets the increase of mature BNP due to inhibition of degradation by neprilysin, resulting in lower plasma BNP levels. In the ARNI era, BNP remains a useful biomarker for heart failure, though mild increases early during ARNI administration should be taken into consideration. Myocardial wall stress, cytokines, hormones, and ischemia all stimulate B-type (or brain) natriuretic peptide (BNP) gene expression. Within the myocardium, ProBNP-108, a BNP precursor, undergoes glycosylation, after which a portion is cleaved by furin into mature BNP-32 and N-terminal proBNP-76, depending on the glycosylation status. As a result, active BNP, less active proBNP, and inactive N-terminal proBNP all circulate in the blood. There are three major pathways for BNP clearance: (1) cellular internalization via natriuretic peptide receptor (NPR)-A and NPR-C; (2) degradation by proteases in the blood, including neprilysin, dipeptidyl-peptidase-IV, insulin degrading enzyme, etc.; and (3) excretion in the urine. Because neprilysin has lower substrate specificity for BNP than atrial natriuretic peptide (ANP), the increase in plasma BNP after angiotensin receptor neprilysin inhibitor (ARNI) administration is much smaller than the increase in plasma ANP. Currently available BNP immunoassays react with both mature BNP and proBNP. Therefore, BNP measured with an immunoassay is mature BNP + proBNP. ARNI administration increases mature BNP but not proBNP, as the latter is not degraded by neprilysin. Consequently, measured plasma BNP initially increases with ARNI administration by the amount of the increase in mature BNP. Later, ARNI reduces myocardial wall stress, and the resultant reduction in BNP production more than offsets the increase in mature BNP mediated by inhibiting degradation by neprilysin, which lowers plasma BNP levels. These results suggest that even in the ARNI era, BNP can be used for diagnosis and assessment of the pathophysiology and prognosis of heart failure, though the mild increases early during ARNI administration should be taken into consideration. [ABSTRACT FROM AUTHOR]

Aims: A sodium glucose cotransporter 2 (SGLT2) inhibitor was recently found to reduce heart failure hospitalization in the EMPA‐REG OUTCOME trial. We have hypothesized that autonomic nerve activity may be modulated by SGLT2 inhibition. The current study aims to investigate the impact of empagliflozin on sympathetic and parasympathetic nerve activity in patients with type 2 diabetes mellitus. Methods and results: This ongoing study is a prospective, randomized, open‐label, multicentre investigation of 134 patients with type 2 diabetes mellitus. The patients are randomly allocated to receive either empagliflozin or sitagliptin with the treatment goal of the Japan Diabetes Society guidelines. Ambulatory electrocardiographic monitoring is performed at the baseline and at 12 and 24 weeks of treatment. Analyses of heart rate variability are conducted using the MemCalc method, which is a combination of the maximum entropy method for spectral analysis and the non‐linear least squares method for square analysis. The primary endpoint is the change in the low‐frequency (0.04–0.15 Hz)/high‐frequency (0.15–0.4 Hz) ratio from baseline to 24 weeks. Conclusions: This investigation on the effect of EMPagliflozin on cardiac sYmpathetic and parasympathetic neRve activity in JapanEse pAtieNts with type 2 diabetes (EMPYREAN study) offers an important opportunity to understand the impact of SGLT2 inhibition on autonomic nerve activity in patients with type 2 diabetes. [ABSTRACT FROM AUTHOR]

B-type natriuretic peptide (BNP) is a cardiac hormone widely used as a biomarker for heart failure. Here, we present the first report of extremely high levels of immunoreactive BNP caused by formation of macro-proBNP. A 70-year-old woman with left ventricular hypertrophy and normal systolic function presented with extremely high plasma levels of BNP (35,374 pg/ml) and N-terminal proBNP (NT-proBNP; 30,600 pg/ml). Our recently developed proBNP immunoassay showed that nearly 100% of her immunoreactive BNP was proBNP. Polyethylene glycol precipitation tests reported extremely low BNP recovery (1.3%), while protein G addition tests also reported a remarkably low BNP fraction (3.3%). Gel filtration chromatography with normal elution buffer combined with BNP immunoassays showed a BNP peak with a retention time slightly shorter than that of IgG. With acidic elution buffer (pH 3.0), however this peak disappeared and a new BNP peak consistent with glycosylated human proBNP appeared. These results suggest that in this case most BNP immunoreactivity consisted of macro-proBNP, which is an immune complex composed of proBNP and an anti-proBNP autoantibody. Gel filtration chromatography combined with NT-proBNP immunoassays revealed that the NT-proBNP assay cross-reacts with both the proBNP-IgG complex and proBNP. In addition, with acidic buffer, a new large peak appeared with a retention time the same as that of glycosylated NT-proBNP. These results suggest spuriously high levels of BNP and NT-proBNP are caused by macro-proBNP. Macro-NT-proBNP is not detected by the currently available NT-proBNP assay system. [ABSTRACT FROM AUTHOR]

Background and Purpose Angiotensin II has been implicated in the development of various cardiovascular ailments, including cardiac hypertrophy and heart failure. The fact that inhibiting its signalling reduced the incidences of both sudden cardiac death and heart failure in several large-scale clinical trials suggests that angiotensin II is involved in increased cardiac arrhythmogenicity during the development of heart failure. However, because angiotensin II also promotes structural remodelling, including cardiomyocyte hypertrophy and cardiac fibrosis, it has been difficult to assess its direct contribution to cardiac arrhythmogenicity independently of the structural effects. Experimental Approach We induced cardiac hypertrophy in wild-type ( WT) and angiotensin II type 1a receptor knockout ( AT1aR- KO) mice by transverse aortic constriction ( TAC). The susceptibility to ventricular tachycardia ( VT) assessed in an in vivo electrophysiological study was compared in the two genotypes. The effect of acute pharmacological blockade of AT1 R on the incidences of arrhythmias was also assessed. Key Results As described previously, WT and AT1aR- KO mice with TAC developed cardiac hypertrophy to the same degree, but the incidence of VT was much lower in the latter. Moreover, although TAC induced an increase in tyrosine phosphorylation of connexin 43, a critical component of gap junctional channels, and a reduction in ventricular levels of connexin 43 protein in both genotypes, the effect was significantly ameliorated in AT1aR- KO mice. Acute pharmacological blockade of AT1R also reduced the incidence of arrhythmias. Conclusions and Implications Our findings demonstrate that AT1aR-mediated signalling makes a direct contribution to the increase in arrhythmogenicity in hypertrophied hearts independently of structural remodelling. [ABSTRACT FROM AUTHOR]

Abstract: Neuron-restrictive silencer factor (NRSF) is a zinc-finger transcription factor that binds to specific DNA sequences (NRSE) to repress transcription. By down-regulating the transcription of its target genes, NRSF contributes to the regulation of various biological processes, including neuronal differentiation, carcinogenesis and cardiovascular homeostasis. We previously reported that NRSF regulates expression of the cardiac fetal gene program, and that attenuation of NRSF-mediated repression contributes to genetic remodeling in hearts under pathological conditions. The precise molecular mechanisms and signaling pathways via which NRSF activity is regulated in pathological conditions of the heart remain unclear, however. In this study, to search for regulators of NRSF, we carried out yeast two-hybrid screening using NRSF as bait and identified zinc-finger protein (Zfp) 90 as a novel NRSF-binding protein. NRSF and Zfp90 colocalized in the nucleus, with the zinc-finger DNA-binding domain of the former specifically interacting with the latter. Zfp90 inhibited the repressor activity of NRSF by inhibiting its binding to DNA, thereby derepressing transcription of NRSF-target genes. Knockdown of Zfp90 by siRNA led to reduced expression of NRSF-target fetal cardiac genes, atrial and brain natriuretic peptide genes, and conversely, overexpression of Zfp90 in ventricular myocardium resulted in significant increases in the expression of these genes. Notably, expression of Zfp90 mRNA was significantly upregulated in mouse and human hearts with chronic heart failure. Collectively, these results suggest that Zfp90 functions as a negative regulator of NRSF and contributes to genetic remodeling during the development of cardiac dysfunction. [Copyright &y& Elsevier]

Introduction: Recently, we reported continuous elevation in the pro B-type natriuretic peptide (BNP) to total BNP ratio during hospitalization in patients with severe acute heart failure (HF). On the other hand, although atrial natriuretic peptide (ANP) is known to elevate acutely after cardiac stress, little is unknown about the clinical significance of proANP measurement on admission in patients with acute HF. Hypothesis: We hypothesized that the elevations in pro-natriuretic peptide (NP) family on admission have a greater predictability than BNP level measured by the conventional assay. Methods: We prospectively evaluated plasma levels of proANP, proBNP, and BNP, in 173 patients with acute HF (NYHA3-4) on admission by using our recently developed chemiluminescence enzyme immunoassay for each NP. Results: During follow-up (median: 469 days), composite clinical events (all causes of death or re-hospitalization for HF) occurred in 67 patients (38.7 %). Interestingly, the association with the frequency of composite events was strongest for proANP (hazard ratio: 1.18, 95% CI: 1.03, 1.34, p=0.017), although only borderline significances were found in the other two NPs on admission (proBNP, p=0.058; BNP, p=0.101). Then, we analyzed the clinical features of the patients with higher proANP/BNP ratio. The patients with above median proANP/BNP presented lower systolic blood pressure (BP), left ventricular ejection fraction (LVEF) and larger LV end-diastolic diameter (LVDd); Figure A-C, respectively; p<0.05 vs. below median proANP/BNP. The age- and sex-adjusted multivariate model for higher proANP ratio showed that the significance of systolic BP, LVEF and LVDd persisted (p<0.05). Conclusion: ProANP level on admission is a stronger predictor of future adverse events than BNP or proBNP level. Due to the association of higher proANP ratio with LV structure and function, proANP may be a better marker for hemodynamic stress to the LV than BNP in the acute heart failure. [ABSTRACT FROM AUTHOR]