Mechanisms of renal hyporesponsiveness to ANP in heart failure

The impact of phosphodiesterase-5 inhibition or angiotensin-converting enzyme inhibition on right and left ventricular remodeling in heart failure due to chronic volume overload

While phosphodiesterase-5 inhibition (PED5i) may prevent hypertrophy and failure in pressure-overloaded heart in an experimental model, the impact of PDE5i on volume-overload (VO)-induced hypertrophy is unknown. It is also unclear whether the hypertrophied right ventricle (RV) and left ventricle (LV) differ in their responsiveness to long-term PDE5i and if this therapy affects renal function. The goal of this study was to elucidate the effect of PDE5i treatment in VO due to aorto-caval fistula (ACF) and to compare PDE5i treatment with standard heart failure (HF) therapy with angiotensin-converting enzyme inhibitor (ACEi). ACF/sham procedure was performed on male HanSD rats aged 8 weeks. ACF animals were randomized for PDE5i sildenafil, ACEi trandolapril, or placebo treatments. After 20 weeks, RV and LV function (echocardiography, pressure-volume analysis), myocardial gene expression, and renal function were studied. Separate rat cohorts served for survival analysis. ACF led to biventricular eccentric hypertrophy (LV: +68%, RV: +145%), increased stroke work (LV: 3.6-fold, RV: 6.7-fold), and reduced load-independent systolic function (PRSW, LV: -54%, RV: -51%). Both ACF ventricles exhibited upregulation of the genes of myocardial stress and glucose metabolism. ACEi but not PDE5i attenuated pulmonary congestion, LV remodeling, albuminuria, and improved survival (median survival in ACF/ACEi was 41 weeks vs. 35 weeks in ACF/placebo, p = .02). PDE5i increased cyclic guanosine monophosphate levels in the lungs, but not in the RV, LV, or kidney. PDE5i did not improve survival rate and cardiac and renal function in ACF rats, in contrast to ACEi. VO-induced HF is not responsive to PDE5i therapy.

The Importance of Optimal Hydration in Patients with Heart Failure-Not Always Too Much Fluid

Heart failure (HF) is a leading cause of morbidity and mortality and a major public health problem. Both overhydration and dehydration are non-physiological states of the body that can adversely affect human health. Congestion and residual congestion are common in patients hospitalized for HF and are associated with poor prognosis and high rates of rehospitalization. However, the clinical problem of dehydration is also prevalent in healthcare and community settings and is associated with increased morbidity and mortality. This article provides a comprehensive review of the issue of congestion and dehydration in HF, including HF guidelines, possible causes of dehydration in HF, confirmed and potential new diagnostic methods. In particular, a full database search on the relationship between dehydration and HF was performed and all available evidence in the literature was reviewed. The novel hypothesis of chronic subclinical hypohydration as a modifiable risk factor for HF is also discussed. It is concluded that maintaining euvolemia is the cornerstone of HF management. Physicians have to find a balance between decongestion therapy and the risk of dehydration.

Atrial Natriuretic Peptides as a Bridge between Atrial Fibrillation, Heart Failure, and Amyloidosis of the Atria

ANP is mainly synthesized by the atria, and upon excretion, it serves two primary purposes: vasodilation and increasing the renal excretion of sodium and water. The understanding of ANP's role in cardiac systems has improved considerably in recent decades. This review focuses on several studies demonstrating the importance of analyzing the regulations between the endocrine and mechanical function of the heart and emphasizes the effect of ANP, as the primary hormone of the atria, on atrial fibrillation (AF) and related diseases. The review first discusses the available data on the diagnostic and therapeutic applications of ANP and then explains effect of ANP on heart failure (HF) and atrial fibrillation (AF) and vice versa, where tracking ANP levels could lead to understanding the pathophysiological mechanisms operating in these diseases. Second, it focuses on conventional treatments for AF, such as cardioversion and catheter ablation, and their effects on cardiac endocrine and mechanical function. Finally, it provides a point of view about the delayed recovery of cardiac mechanical and endocrine function after cardioversion, which can contribute to the occurrence of acute heart failure, and the potential impact of restoration of the sinus rhythm by extensive ablation or surgery in losing ANP-producing sites. Overall, ANP plays a key role in heart failure through its effects on vasodilation and natriuresis, leading to a decrease in the activity of the renin-angiotensin-aldosterone system, but it is crucial to understand the intimate role of ANP in HF and AF to improve their diagnosis and personalizing the patients' treatment.

Pathophysiology-Based Management of Acute Heart Failure

Even though acute heart failure (AHF) is one of the most common admission diagnoses globally, its pathogenesis is poorly understood, and there are few effective treatments available. Despite an heterogenous onset, congestion is the leading contributor to hospitalization, making it a crucial therapeutic target. Complete decongestion, nevertheless, may be hard to achieve, especially in patients with reduced end organ perfusion. In order to promote a personalised pathophysiological-based therapy for patients with AHF, we will address in this review the pathophysiological principles that underlie the clinical symptoms of AHF as well as examine how to assess them in clinical practice, suggesting that gaining a deeper understanding of pathophysiology might result in significant improvements in HF therapy.

Sexual dimorphism in acute myocardial infarction-induced acute kidney injury: cardiorenal deteriorating effects of ovariectomy in premenopausal female mice

Acute kidney injury (AKI) is a common complication of cardiovascular diseases (CVDs) in both males and females, increasing mortality rate substantially. Premenopausal females appear to be more protected, suggesting a potential protective role of female sex hormones. Here, we tested the hypothesis that ovariectomy (OVX) eliminates the beneficial effect of female sex on renal protection following acute myocardial infarction (MI). Seven days post-MI, both sexes exhibited worsened kidney function and a substantial decrease in total kidney NAD levels. Unlike MI female mice, MI males showed exacerbated morphological alterations with increased proinflammatory, proapoptotic, and profibrotic biomarkers. The expression of NAD+ biosynthetic enzymes NAMPT and NMRK-1 was increased in MI females only, while males showed a substantial increase in NAD+ consuming enzyme PARP-1. OVX did not eliminate the female-sex protection of glomerular morphology but was associated with swelling of proximal convoluted tubules with MI as in males. With OVX, MI females had enhanced proinflammatory cytokine release, and a further decrease in creatinine clearance and urine output was observed. Our findings suggest that MI induced AKI in both sexes with pre-menopausal female mice being more protected. Ovariectomy worsens aspects of AKI in females after MI, which may portend increased risk for development of chronic kidney disease.

Augmentation of Natriuretic Peptide Bioactivity via Combined Inhibition of Neprilysin and Phosphodiesterase-9 in Heart Failure

BACKGROUND

The natriuretic peptides (NPs) are potent natriuretic/diuretic and vasodilatory factors, and augmentation of their levels or signaling via inhibition of the enzymes neprilysin (NEP) and phosphodiesterase 9 (PDE9), respectively, has beneficial actions in heart failure (HF).

OBJECTIVES

The authors investigated dual enhancement of NP bioactivity by combining PDE9 inhibition and NEP inhibition in HF using an ovine model.

METHODS

Eight sheep with pacing-induced HF received on 4 separate days intravenous PDE9 inhibition (PF-04749982), NEP inhibition (SCH-32615), PDE9 inhibition + NEP inhibition (PI+NI), and vehicle control treatment.

RESULTS

Compared with the control treatment, NEP inhibition significantly increased plasma NP concentrations with a corresponding rise in second messenger cyclic guanosine monophosphate (cGMP), whereas PDE9 inhibition increased circulating cGMP with a negligible effect on NP levels. Combined PI+NI elevated plasma NPs to an extent comparable to that seen with NEP inhibition alone but further increased cGMP, resulting in a rise in the cGMP-to-NP ratio. All active treatments reduced mean arterial pressure, left atrial pressure, pulmonary arterial pressure, and peripheral resistance, with combined PI+NI further reducing mean arterial pressure and left atrial pressure relative to either inhibitor separately. Active treatments increased urine volume and sodium, potassium and creatinine excretion, and creatinine clearance, in association with rises in urine cGMP levels. PI+NI induced a significantly greater natriuresis and increase in urinary cGMP relative to either inhibitor singly.

CONCLUSIONS

The present study demonstrates for the first time that combined PI+NI has additional beneficial hemodynamic and renal effects when compared with either PDE9 inhibition or NEP inhibition alone. The superior efficacy of this 2-pronged augmentation of NP bioactivity supports PI+NI as a potential therapeutic strategy for HF.

Edema formation in congestive heart failure and the underlying mechanisms

Congestive heart failure (HF) is a complex disease state characterized by impaired ventricular function and insufficient peripheral blood supply. The resultant reduced blood flow characterizing HF promotes activation of neurohormonal systems which leads to fluid retention, often exhibited as pulmonary congestion, peripheral edema, dyspnea, and fatigue. Despite intensive research, the exact mechanisms underlying edema formation in HF are poorly characterized. However, the unique relationship between the heart and the kidneys plays a central role in this phenomenon. Specifically, the interplay between the heart and the kidneys in HF involves multiple interdependent mechanisms, including hemodynamic alterations resulting in insufficient peripheral and renal perfusion which can lead to renal tubule hypoxia. Furthermore, HF is characterized by activation of neurohormonal factors including renin-angiotensin-aldosterone system (RAAS), sympathetic nervous system (SNS), endothelin-1 (ET-1), and anti-diuretic hormone (ADH) due to reduced cardiac output (CO) and renal perfusion. Persistent activation of these systems results in deleterious effects on both the kidneys and the heart, including sodium and water retention, vasoconstriction, increased central venous pressure (CVP), which is associated with renal venous hypertension/congestion along with increased intra-abdominal pressure (IAP). The latter was shown to reduce renal blood flow (RBF), leading to a decline in the glomerular filtration rate (GFR). Besides the activation of the above-mentioned vasoconstrictor/anti-natriuretic neurohormonal systems, HF is associated with exceptionally elevated levels of atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). However, the supremacy of the deleterious neurohormonal systems over the beneficial natriuretic peptides (NP) in HF is evident by persistent sodium and water retention and cardiac remodeling. Many mechanisms have been suggested to explain this phenomenon which seems to be multifactorial and play a major role in the development of renal hyporesponsiveness to NPs and cardiac remodeling. This review focuses on the mechanisms underlying the development of edema in HF with reduced ejection fraction and refers to the therapeutic maneuvers applied today to overcome abnormal salt/water balance characterizing HF.

Neuroendocrine hormone status and diuretic response to atrial natriuretic peptide in patients with acute heart failure

AIMS

Given the various effects of sacubitril/valsartan in heart failure, a deeper understanding of atrial natriuretic peptide (ANP) actions is warranted. Natriuresis is a fundamental action of ANP in acute heart failure (AHF), whereas the diuretic effect of ANP is different in each patient according to the diversity of renal response to ANP, which is affected by baseline plasma ANP status and deficiency of circulating ANP. Meanwhile, associations between other neuroendocrine hormones and the diuretic response to ANP are unclear. This study investigated the impact of pivotal neuroendocrine hormones on the diuretic effects of exogenous ANP, carperitide.

METHODS AND RESULTS

Plasma ANP, renin, aldosterone, and vasopressin levels and the diuretic effect of 0.0125 μg/kg/min of carperitide alone for the first 6 h were prospectively evaluated in 75 patients with AHF. Lower ANP levels were significantly associated with a greater diuretic response to exogenous ANP (r = -0.35, P = 0.002). Additionally, higher vasopressin levels were significantly related to the poor diuretic effects of exogenous ANP (r = -0.54, P < 0.001). Plasma ANP and vasopressin concentrations were not significantly correlated (r = 0.19, P = 0.10). Baseline systolic blood pressure, renal function, and prior use of loop diuretics did not predict the diuretic response to exogenous ANP, whereas vasopressin levels independently predicted a diuretic response to exogenous ANP (P < 0.001), as well as lower plasma ANP levels (P = 0.027).

CONCLUSIONS

Vasopressin status was significantly associated with the diuretic response to exogenous ANP in AHF, independent of plasma ANP status. The results may provide a better understanding of the actions of sacubitril/valsartan.

The Beneficial Effects of Chinese Herbal Monomers on Ameliorating Diabetic Cardiomyopathy via Nrf2 Signaling

Diabetic cardiomyopathy (DCM) is the main factor responsible for poor prognosis and survival in patients with diabetes. The highly complex pathogenesis of DCM involves multiple signaling pathways, including nuclear factor-κB (NF-κB) signaling pathway, adenosine monophosphate-activated protein kinase (AMPK) signaling pathway, phosphatidylinositol 3-kinase-protein kinase B (Akt) signaling pathway, mitogen-activated protein kinase (MAPK) signaling pathway, and transforming growth factor-β (TGF-β) signaling pathway. Nuclear factor erythroid-2-related factor 2 (Nrf2) seems essential to the amelioration of the progression of DCM, not only through counterbalancing oxidative stress, but also through interacting with other signaling pathways to combat inflammation, the disorder in energy homeostasis and insulin signaling, and fibrosis. It has been evidenced that Chinese herbal monomers could attenuate DCM through the crosstalk of Nrf2 with other signaling pathways. This article has summarized the pathogenesis of DCM (especially in oxidative stress), the beneficial effects of ameliorating DCM via the Nrf2 signaling pathway and its crosstalk, and examples of Chinese herbal monomers. It will facilitate pharmacological research and development to promote the utilization of traditional Chinese medicine in DCM.

Hormonal Regulation of Renal Fibrosis

Fibrosis is a severe complication of many acute and chronic kidney pathologies. According to current concepts, an imbalance in the synthesis and degradation of the extracellular matrix by fibroblasts is considered the key cause of the induction and progression of fibrosis. Nevertheless, inflammation associated with the damage of tissue cells is among the factors promoting this pathological process. Most of the mechanisms accompanying fibrosis development are controlled by various hormones, which makes humoral regulation an attractive target for therapeutic intervention. In this vein, it is particularly interesting that the kidney is the source of many hormones, while other hormones regulate renal functions. The normal kidney physiology and pathogenesis of many kidney diseases are sex-dependent and thus modulated by sex hormones. Therefore, when choosing therapy, it is necessary to focus on the sex-associated characteristics of kidney functioning. In this review, we considered renal fibrosis from the point of view of vasoactive and reproductive hormone imbalance. The hormonal therapy possibilities for the treatment or prevention of kidney fibrosis are also discussed.

Schisandrin A protects against isoproterenol‑induced chronic heart failure via miR‑155

Schisandrin A (Sch A) has a protective effect on cardiomyocytes. Circulating miR-155 levels are related to chronic heart failure (CHF). The present study aimed to clarify the role and the molecular mechanism of Sch A in CHF. C57BL/6JGpt mice were used for an isoproterenol (ISO)-induced CHF model to collect heart samples. Echocardiography was employed to detect heartbeat indicators. The degree of myocardial hypertrophy was evaluated based on the measurement of heart weight (HW), body weight (BW) and tibia length (TL) and the observation using hematoxylin-eosin staining. Sprague-Dawley rats were purchased for the separation of neonatal rat ventricular myocytes (NRVMs), which were treated with ISO for 24 h. Transfection regulated the level of miR-155. The viability of NRVMs was detected via MTT assay. The mRNA and protein levels were measured via reverse transcription-quantitative PCR and western blotting and immunofluorescence was used to detect the content of α-smooth muscle actin (α-SMA). Treatment with ISO resulted in rising left ventricular posterior wall thickness, intra-ventricular septum diastole, left ventricular end diastolic diameter, left ventricular end systolic diameter, HW/BW, HW/TL and falling ejection fraction and fractional shortening, the trend of which could be reversed by Sch A. Sch A ameliorated myocardial hypertrophy in CHF mice. In addition, Sch A inhibited ISO-induced upregulated expressions of atrial natriuretic peptide, B-type natriuretic peptide, B-myosin heavy chain and miR-155 in myocardial tissue. Based on the results in vitro, Sch A had no significant effect on the viability of NRVMs when its concentration was <24 µmol/l. Sch A inhibited the levels of miR-155, α-SMA and the phosphorylation levels of AKT and cyclic AMP response-element binding protein (CREB) in ISO-induced NRVMs, which was reversed by the upregulation of miR-155. Schisandrin A mediated the AKT/CREB signaling pathway to prevent CHF by regulating the expression of miR-155, which may shed light on a possible therapeutic target for CHF.

Distribution of Cardiac and Renal Corin and Proprotein Convertase Subtilisin/Kexin-6 in the Experimental Model of Cardio-Renal Syndrome of Various Severities

Congestive heart failure (CHF) often leads to progressive cardiac hypertrophy and salt/water retention. However, its pathogenesis remains largely unclarified. Corin, a cardiac serine protease, is responsible for converting proANP and proBNP to biologically active peptides. Although the involvement of corin in cardiac hypertrophy and heart failure was extensively studied, the alterations in corin and proprotein convertase subtilisin/kexin-6 (PCSK6), a key enzyme in the conversion of procorin to corin, has not been studied simultaneously in the cardiac and renal tissues in cardiorenal syndrome. Thus, this study aims to examine the status of PCSK6/corin in the cardiac and renal tissues of rats with CHF induced by the creation of aorto-caval fistula (ACF). We divided rats with ACF into two subgroups based on the pattern of their urinary sodium excretion, namely, compensated and decompensated. Placement of ACF led to cardiac hypertrophy, pulmonary congestion, and renal dysfunction, which were more profound in the decompensated subgroup. Corin immunoreactive peptides were detected in all heart chambers at the myocyte membranal and cytosolic localization and in the renal tissue, especially in the apical membrane of the proximal tubule, mTAL, and the collecting duct. Interestingly, the expression and abundance of corin in both the cardiac ventricles and renal tissues were significantly increased in compensated animals as compared with the decompensated state. Noteworthy, the abundance of PCSK6 in these tissues followed a similar pattern as corin. In contrast, furin expression was upregulated in the cardiac and renal tissues in correlation with CHF severity. We hypothesize that the obtained upregulation of cardiac and renal PCSK6/corin in rats with compensated CHF may represent a compensatory response aiming at maintaining normal Na⁺ balance, whereas the decline in these two enzymes may contribute to the pathogenesis of avid sodium retention, cardiac hypertrophy, and blunted atrial natriuretic peptide/brain natriuretic peptide actions in decompensated CHF.

Relevance of Neutrophil Neprilysin in Heart Failure

Significant expression of neprilysin (NEP) is found on neutrophils, which present the transmembrane integer form of the enzyme. This study aimed to investigate the relationship of neutrophil transmembrane neprilysin (mNEP) with disease severity, adverse remodeling, and outcome in HFrEF. In total, 228 HFrEF, 30 HFpEF patients, and 43 controls were enrolled. Neutrophil mNEP was measured by flow-cytometry. NEP activity in plasma and blood cells was determined for a subset of HFrEF patients using mass-spectrometry. Heart failure (HF) was characterized by reduced neutrophil mNEP compared to controls (p < 0.01). NEP activity on peripheral blood cells was almost 4-fold higher compared to plasma NEP activity (p = 0.031) and correlated with neutrophil mNEP (p = 0.006). Lower neutrophil mNEP was associated with increasing disease severity and markers of adverse remodeling. Higher neutrophil mNEP was associated with reduced risk for mortality, total cardiovascular hospitalizations, and the composite endpoint of both (p < 0.01 for all). This is the first report describing a significant role of neutrophil mNEP in HFrEF. The biological relevance of neutrophil mNEP and exact effects of angiotensin-converting-enzyme inhibitors (ARNi) at the neutrophil site have to be determined. However, the results may suggest early initiation of ARNi already in less severe HF disease, where effects of NEP inhibition may be more pronounced.

Chlorine-binding structures: role and organization in different proteins

The review focuses on chloride-binding structures in the proteins of bacteria, plants, viruses and animals. The structure and amino acid composition of the chloride-binding site and its role in the functioning of structural, regulatory, transport, receptor, channel proteins, transcription factors and enzymes are considered. Data on the important role of chloride-binding structures and chloride anions in the polymerization of fibrin are presented.

Atrial Natriuretic Peptide31-67: A Novel Therapeutic Factor for Cardiovascular Diseases

The characterization of the cardiac hormone atrial natriuretic peptide (ANP_99–126), synthesized and secreted predominantly by atrial myocytes under stimulation by mechanical stretch, has established the heart as an endocrine organ with potent natriuretic, diuretic, and vasodilating actions. Three additional distinct polypeptides resulting from proteolytic cleavage of proANP have been identified in the circulation in humans. The mid-sequence proANP fragment 31–67 (also known as proANP_31–67) has unique potent and prolonged diuretic and natriuretic properties. In this review, we report the main effects of this circulating hormone in different tissues and organs, and its mechanisms of actions. We further highlight recent evidence on the cardiorenal protective actions of chronic supplementation of synthetic proANP_31–67 in preclinical models of cardiorenal disease. Finally, we evaluate the use of proANP_31–67 as a new therapeutic strategy to repair end-organ damage secondary to hypertension, diabetes mellitus, renal diseases, obesity, heart failure, and other morbidities that can lead to impaired cardiac function and structure.

Potential Utility of Cardiorenal Biomarkers for Prediction and Prognostication of Worsening Renal Function in Acute Heart Failure

BACKGROUND

Multiple different pathophysiologic processes can contribute to worsening renal function (WRF) in acute heart failure.

METHODS AND RESULTS

We retrospectively analyzed 787 patients with acute heart failure for the relationship between changes in serum creatinine and biomarkers including brain natriuretic peptide, high sensitivity cardiac troponin I, galectin 3, serum neutrophil gelatinase-associated lipocalin, and urine neutrophil gelatinase-associated lipocalin. WRF was defined as an increase of greater than or equal to 0.3 mg/dL or 50% in creatinine within first 5 days of hospitalization. WRF was observed in 25% of patients. Changes in biomarkers and creatinine were poorly correlated (r ≤ 0.21) and no biomarker predicted WRF better than creatinine. In the multivariable Cox analysis, brain natriuretic peptide and high sensitivity cardiac troponin I, but not WRF, were significantly associated with the 1-year composite of death or heart failure hospitalization. WRF with an increasing urine neutrophil gelatinase-associated lipocalin predicted an increased risk of heart failure hospitalization.

CONCLUSIONS

Biomarkers were not able to predict WRF better than creatinine. The 1-year outcomes were associated with biomarkers of cardiac stress and injury but not with WRF, whereas a kidney injury biomarker may prognosticate WRF for heart failure hospitalization.

The therapeutic effect of B-type natriuretic peptides in acute decompensated heart failure

B-type natriuretic peptide (BNP) exhibits roles in natriuresis and diuresis, making it an ideal drug that may aid in diuresing a fluid-overloaded patient with poor or worsening renal function. Several randomized clinical trials have tested the hypothesis that infusions of pharmacological doses of BNP to acute heart failure (HF) patients may enhance decongestion and preserve renal function in this clinical setting. Unfortunately, none of these have demonstrated beneficial outcomes. The current challenge for BNP research in acute HF lies in addressing a failure of concept and a reluctance to abandon an ineffective research model. Future success will necessitate a detailed understanding of the mechanism of action of BNP, as well as better integration of basic and clinical science.

Sex-based differences in myocardial infarction-induced kidney damage following cigarette smoking exposure: more renal protection in premenopausal female mice

The impact of cigarette smoking (CS) on kidney homeostasis in the presence of myocardial infarction (MI) in both males and females remains poorly elucidated. C57BL6/J mice were exposed to 2 weeks of CS prior to MI induction followed by 1 week of CS exposure in order to investigate the impact of CS on kidney damage in the presence of MI. Cardiac hemodynamic analysis revealed a significant decrease in ejection fraction (EF) in CS-exposed MI male mice when compared with the relative female subjects, whereas cardiac output (CO) comparably decreased in CS-exposed MI mice of both sexes. Kidney structural alterations, including glomerular retraction, proximal convoluted tubule (PCT) cross-sectional area, and total renal fibrosis were more pronounced in CS-exposed MI male mice when compared with the relative female group. Although renal reactive oxygen species (ROS) generation and glomerular DNA fragmentation significantly increased to the same extent in CS-exposed MI mice of both sexes, alpha-smooth muscle actin (α-SMA) and connective tissue growth factor (CTGF) significantly increased in CS-exposed MI male mice, only. Metabolically, nicotinamide phosphoribosyltransferase (NAMPT) and nicotinamide riboside-1 (NMRK-1) substantially increased in CS-exposed MI female mice only, whereas sirtuin (SIRT)-1 and SIRT-3 substantially decreased in CS-exposed MI male mice compared with their relative female group. Additionally, renal NAD levels significantly decreased only in CS-exposed MI male mice. In conclusion, MI female mice exhibited pronounced renal protection following CS when compared with the relative male groups.

Hemodynamic, Hormonal, and Renal Actions of Phosphodiesterase-9 Inhibition in Experimental Heart Failure

BACKGROUND

Phosphodiesterase-9 (PDE9) reduces natriuretic peptide (NP) signaling and may be involved in the pathophysiology of heart failure (HF).

OBJECTIVES

This study investigated for the first time the integrated hemodynamic, endocrine, and renal effects of phosphodiesterase-9 inhibition (PDE9-I).

METHODS

A total of 8 normal sheep and 8 sheep with pacing-induced HF received incremental intravenous boluses of PDE9-I (30, 100, and 300 mg PF-04749982 at 1-h intervals).

RESULTS

PDE9-I dose-dependently increased plasma cyclic guanosine monophosphate (cGMP) in normal sheep (p < 0.05) while concurrently reducing circulating atrial natriuretic peptide levels (p < 0.01). Similar trends were evident in HF, resulting in significant elevations in the cGMP/NP ratio in both states (p < 0.001 and p < 0.05, respectively). PDE9-I also produced progressive falls in arterial pressure (HF: p < 0.001), atrial pressure (Normal: p < 0.001; HF: p < 0.001), and peripheral resistance (HF: p < 0.001), and transiently increased cardiac output at the top dose (Normal: p < 0.05; HF: p < 0.001). Inhibition of PDE9 had a negligible effect on circulating hormones at the lower doses, but post-high dose, acutely increased renin activity (Normal: p < 0.001; HF: p < 0.05), vasopressin (Normal: p < 0.001; HF: p < 0.01), and cyclic adenosine monophosphate (HF: p < 0.001). Plasma aldosterone increased briefly after high-dose PDE9-I in normal sheep, and fell following the top dose in HF. PDE9-I dose-dependently increased urinary cGMP in both states (both p < 0.001). In HF, this was associated with increases in urine volume (p < 0.01), sodium excretion (p < 0.01), and creatinine clearance (p < 0.001).

CONCLUSIONS

PDE9-I improves NP efficacy in conjunction with beneficial hemodynamic and renal effects in experimental HF. These results support a role for PDE9 in HF pathophysiology and suggest its inhibition may constitute a novel therapeutic approach to this disease.

NO mediates the effect of the synthetic natriuretic peptide NPCdc on kidney and aorta in nephrectomised rats

NPCdc is a synthetic natriuretic peptide that was originally derived from another peptide, the NP2_Casca, isolated from Crotalus durissus cascavella venom. These molecules share 70% structural homology with natriuretic peptides obtained from different species, including humans. NP2_Casca induces vasorelaxation and increases nitric oxide levels independently of natriuretic peptide receptors A and B. This study aimed to investigate whether NPCdc-induced hypotension in control rats and rats with a reduced kidney mass is associated with effects on the glomerular filtration rate, NADPH oxidase activity and components downstream of natriuretic peptide receptor C (NPR-C). Anaesthetized Wistar rats that were subjected to a sham operation and 5/6 nephrectomy (5/6Nx) were infused with saline (vehicle) or NPCdc (7.5 μg/kg/min) for 70 min. The NPCdc treatment decreased the mean arterial pressure and NADPH oxidase activity while simultaneously increasing the glomerular filtration rate, fractional Na⁺ excretion and nitric oxide level. After 70 min, the levels of p-AKT ^Ser-473, p-eNOS ^Ser-1177, p-nNOS ^Ser-1417 and p-iNOS^Tyr-151 were not affected. However, p-ERK1/2 ^{Thr-202/Tyr-204} levels were altered. Thus, nitric oxide and components of NPR-C signalling mediate the effects of NPCdc. The results suggest a potential therapeutic application of this peptide for cardiorenal syndrome.

Down-Regulation of miR-34a-5p Potentiates Protective Effect of Adipose-Derived Mesenchymal Stem Cells Against Ischemic Myocardial Infarction by Stimulating the Expression of C1q/Tumor Necrosis Factor-Related Protein-9

Adipose-derived stem cells (ADSCs) have shown great promise for the treatment of myocardial infarction (MI), although their potential therapeutic mechanism remains poorly understood. Growing evidence has implicated microRNAs (miRNAs or miRs) in the biological processes whereby ADSCs could ameliorate cardiovascular disease. In this study, we explored the contribution of miR-34a-5p down-regulation to the protective actions of ADSCs against MI. We initially identified the interaction between miR-34a-5p and C1q/tumor necrosis factor-related protein-9 (CTRP9) through in silico analysis. We next tested the effects of miR-34a-5p and CTRP9 on the expression of extracellular signal-regulated kinase 1 (ERK1), matrix metalloproteinase-9 (MMP-9), nuclear factor (erythroid-derived 2)-like 2 (NRF2), and antioxidant proteins [manganese superoxide dismutase (MnSOD), and heme oxygenase-1 (HO-1)] through gain- and loss-of-function tests. In other experiments, we assessed the proliferation, migration, and apoptosis of ADSCs using the EdU assay, scratch test, Transwell assay, and flow cytometry. Finally, we studied whether miR-34a-5p/CTRP9 axis could modulate the protective effect of ADSCs against MI during stem cell transplantation in MI mouse models. miR-34a-5p could target and down-regulate CTRP9 in cardiomyocytes. Down-regulated miR-34a-5p increased the expression of ERK1, MMP-9, NRF2, MnSOD, and HO-1, whereas down-regulation of miR-34a-5p or up-regulation of CTRP9 in vitro promoted ADSC proliferation and migration and inhibited ADSC apoptosis. Moreover, miR-34a-5p down-regulation or CTRP9 up-regulation promoted the protective role of ADSCs against MI damage in vivo. Thus, inhibition of miR-34a-5p may facilitate ADSC’s protective function against MI damage by stimulating the expression of CTRP9.

The Endocrine Function of the Heart: Physiology and Involvements of Natriuretic Peptides and Cyclic Nucleotide Phosphodiesterases in Heart Failure

Besides pumping, the heart participates in hydro-sodium homeostasis and systemic blood pressure regulation through its endocrine function mainly represented by the large family of natriuretic peptides (NPs), including essentially atrial natriuretic (ANP) and brain natriuretic peptides (BNP). Under normal conditions, these peptides are synthesized in response to atrial cardiomyocyte stretch, increase natriuresis, diuresis, and vascular permeability through binding of the second intracellular messenger’s guanosine 3′,5′-cyclic monophosphate (cGMP) to specific receptors. During heart failure (HF), the beneficial effects of the enhanced cardiac hormones secretion are reduced, in connection with renal resistance to NP. In addition, there is a BNP paradox characterized by a physiological inefficiency of the BNP forms assayed by current methods. In this context, it appears interesting to improve the efficiency of the cardiac natriuretic system by inhibiting cyclic nucleotide phosphodiesterases, responsible for the degradation of cGMP. Recent data support such a therapeutic approach which can improve the quality of life and the prognosis of patients with HF.

Cardiovascular Pleiotropic Effects of Natriuretic Peptides

Atrial natriuretic peptide (ANP) is a cardiac hormone belonging to the family of natriuretic peptides (NPs). ANP exerts diuretic, natriuretic, and vasodilatory effects that contribute to maintain water–salt balance and regulate blood pressure. Besides these systemic properties, ANP displays important pleiotropic effects in the heart and in the vascular system that are independent of blood pressure regulation. These functions occur through autocrine and paracrine mechanisms. Previous works examining the cardiac phenotype of loss-of-function mouse models of ANP signaling showed that both mice with gene deletion of ANP or its receptor natriuretic peptide receptor A (NPR-A) developed cardiac hypertrophy and dysfunction in response to pressure overload and chronic ischemic remodeling. Conversely, ANP administration has been shown to improve cardiac function in response to remodeling and reduces ischemia-reperfusion (I/R) injury. ANP also acts as a pro-angiogenetic, anti-inflammatory, and anti-atherosclerotic factor in the vascular system. Pleiotropic effects regarding brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) were also reported. In this review, we discuss the current evidence underlying the pleiotropic effects of NPs, underlying their importance in cardiovascular homeostasis.

Rosiglitazone treatment restores renal responsiveness to atrial natriuretic peptide in rats with congestive heart failure

The thiazolidinedione (TZD) class of Peroxisome proliferator‐activated receptor gamma agonists has restricted clinical use for diabetes mellitus due to fluid retention and potential cardiovascular risks. These side effects are attributed in part to direct salt‐retaining effect of TZDs at the renal collecting duct. A recent study from our group revealed that prolonged rosiglitazone (RGZ) treatment caused no Na+/H₂O retention or up‐regulation of Na⁺ transport‐linked channels/transporters in experimental congestive heart failure (CHF) induced by surgical aorto‐caval fistula (ACF). The present study examines the effects of RGZ on renal and cardiac responses to atrial natriuretic peptide (ANP), Acetylcholine (Ach) and S‐Nitroso‐N‐acetylpenicillamine (SNAP‐NO donor). Furthermore, we assessed the impact of RGZ on gene expression related to the ANP signalling pathway in animals with ACF. Rats subjected to ACF (or sham) were treated with either RGZ (30 mg/kg/day) or vehicle for 4 weeks. Cardiac chambers pressures and volumes were assessed invasively via Miller catheter. Kidney excretory and renal hemodynamic in response to ANP, Ach and SNAP were examined. Renal clearance along with cyclic guanosine monophosphate (cGMP), gene expression of renal CHF‐related genes and ANP signalling in the kidney were determined. RGZ‐treated CHF rats exhibited significant improvement in the natriuretic responses to ANP infusion. This ‘sensitization’ to ANP was not associated with increases in neither urinary cGMP nor in vitro cGMP production. However, RGZ caused down‐regulation of several genes in the renal cortex (Ace, Nos3 and Npr1) and up‐regulation of ACE2, Agtrla, Mme and Cftr along down‐regulation of Avpr2, Npr1,2, Nos3 and Pde3 in the medulla. In conclusion, CHF+RGZ rats exhibited significant enhancement in the natriuretic responses to ANP infusion, which are known to be blunted in CHF. This ‘sensitization’ to ANP is independent of cGMP signalling, yet may involve post‐cGMP signalling target genes such as ACE2, CFTR and V2 receptor. The possibility that TZD treatment in uncomplicated CHF may be less detrimental than thought before deserves additional investigations.

Role of Neprilysin Inhibitors in Heart Failure

Heart failure (HF) is a complex multifactorial medical condition that should be addressed according to its complexity and diversity. Currently, there is a medical arsenal available for the management of HF, but despite the advance in medical resources, its prevalence and social and financial impacts are still worrisome for the medical community and society. Among the numerous therapeutic options for the treatment of HF, neprilysin inhibitors have changed the perspective of the approach to titrate patients who suffer from this condition because neprilysin plays a role in the degradation of natriuretic peptides and various other vasoactive compounds that are crucial to counteract the devastating pathophysiology of HF. The purpose of this review was to analyze the role of neprilysin inhibitors in HF, focusing on newer therapy such as LCZ696 and studies that sustain its potential benefits in this medical entity.

Synthesis, secretion, function, metabolism and application of natriuretic peptides in heart failure

As a family of hormones with pleiotropic effects, natriuretic peptide (NP) system includes atrial NP (ANP), B-type NP (BNP), C-type NP (CNP), dendroaspis NP and urodilatin, with NP receptor-A (guanylate cyclase-A), NP receptor-B (guanylate cyclase-B) and NP receptor-C (clearance receptor). These peptides are genetically distinct, but structurally and functionally related for regulating circulatory homeostasis in vertebrates. In humans, ANP and BNP are encoded by NP precursor A (NPPA) and NPPB genes on chromosome 1, whereas CNP is encoded by NPPC on chromosome 2. NPs are synthesized and secreted through certain mechanisms by cardiomyocytes, fibroblasts, endotheliocytes, immune cells (neutrophils, T-cells and macrophages) and immature cells (embryonic stem cells, muscle satellite cells and cardiac precursor cells). They are mainly produced by cardiovascular, brain and renal tissues in response to wall stretch and other causes. NPs provide natriuresis, diuresis, vasodilation, antiproliferation, antihypertrophy, antifibrosis and other cardiometabolic protection. NPs represent body's own antihypertensive system, and provide compensatory protection to counterbalance vasoconstrictor-mitogenic-sodium retaining hormones, released by renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS). NPs play central roles in regulation of heart failure (HF), and are inactivated through not only NP receptor-C, but also neutral endopeptidase (NEP), dipeptidyl peptidase-4 and insulin degrading enzyme. Both BNP and N-terminal proBNP are useful biomarkers to not only make the diagnosis and assess the severity of HF, but also guide the therapy and predict the prognosis in patients with HF. Current NP-augmenting strategies include the synthesis of NPs or agonists to increase NP bioactivity and inhibition of NEP to reduce NP breakdown. Nesiritide has been established as an available therapy, and angiotensin receptor blocker NEP inhibitor (ARNI, LCZ696) has obtained extremely encouraging results with decreased morbidity and mortality. Novel pharmacological approaches based on NPs may promote a therapeutic shift from suppressing the RAAS and SNS to re-balancing neuroendocrine dysregulation in patients with HF. The current review discussed the synthesis, secretion, function and metabolism of NPs, and their diagnostic, therapeutic and prognostic values in HF.

The use of nesiritide in patients with critical cardiac disease

OBJECTIVE

We evaluated the use of nesiritide in children with critical CHD, pulmonary congestion, and inadequate urine output despite undergoing conventional diuretic therapy.

DESIGN

We conducted a retrospective analysis of 11 patients with critical CHD, comprising 18 infusions, each of which occurred during separate hospitalisations. Haemodynamic parameters were assessed, and the stage of acute kidney injury was determined before and throughout the duration of therapy using a standardised definition of acute kidney injury - The Kidney Disease: Improving Global Outcomes criteria. Patients Children with critical CHD, pulmonary congestion, and inadequate urinary output despite undergoing diuretic therapy were included. Measurements and main results The use of nesiritide was associated with a significant decrease in the maximum and minimum heart rate values and with a trend towards a significant decrease in maximum systolic blood pressure and maximum and minimum central venous pressures. Urine output increased but was not significant. Serum creatinine levels decreased significantly during the course of therapy (-0.26 mg/dl [-0.50, 0.0], p=0.02), and the number of patients who experienced a decrease in the stage of acute kidney injury of 2 or more - where a change in the stage of acute kidney disease of 2 or more was possible, that is, baseline stage >1 - was highly significant (five of 12 patients, 42%, p<0.001).

CONCLUSIONS

Nesiritide had a favourable impact on haemodynamics, and its use was not associated with deterioration of renal function in patients with critical CHD.

Importance of endogenous compensatory vasoactive peptides in broadening the effects of inhibitors of the renin-angiotensin system for the treatment of heart failure

The magnitude of the clinical benefits produced by inhibitors of the renin-angiotensin system in heart failure has been modest, possibly because of the ability of renin-angiotensin activity to escape from suppression during long-term treatment. Efforts to intensify pharmacological blockade by use of dual inhibitors that interfere with the renin-angiotensin system at multiple sites have not yielded consistent incremental clinical benefits, but have been associated with serious adverse reactions. By contrast, potentiation of endogenous compensatory vasoactive peptides can act to enhance the survival effects of inhibitors of the renin-angiotensin system, as evidenced by trials that have compared angiotensin-converting enzyme inhibitors with drugs that inhibit both the renin-angiotensin system and neprilysin. Several endogenous vasoactive peptides act as adaptive mechanisms, and their augmentation could help to broaden the benefits of renin-angiotensin system inhibitors for patients with heart failure.

The Use of Nesiritide in Children With Congenital Heart Disease

OBJECTIVE

We evaluated the use of nesiritide in children with critical congenital heart disease, pulmonary congestion, and inadequate urine output despite conventional diuretic therapy.

DESIGN

We conducted a retrospective analysis of 26 consecutive patients, comprising 37 infusions occurring during separate hospitalizations. Hemodynamic variables, urine output, and serum creatinine levels were monitored prior to and throughout the duration of therapy with nesiritide. In addition, the stage of acute kidney injury was determined prior to and throughout the duration of the therapy using a standardized definition of acute kidney injury-The Kidney Disease: Improving Global Outcomes criteria.

SETTING

Cardiac ICU.

PATIENTS

Pediatric patients with critical congenital heart disease, pulmonary congestion, and inadequate urinary output despite diuretic therapy.

INTERVENTION

Nesiritide infusion.

MEASUREMENTS AND MAIN RESULTS

The use of nesiritide was associated with a significant decrease in the central venous pressure and heart rate with a trend toward a significant increase in urine output. During the course of therapy with nesiritide, the serum creatinine and stage of acute kidney injury decreased significantly. The decrease in stage of acute kidney injury became significant by day 4 (p = 0.006) and became more significant with time (last day of therapy compared with baseline; p < 0.001). During 12 of the 37 infusions, the stage of acute kidney injury decreased by two or more (p < 0.001).

CONCLUSIONS

Nesiritide had a favorable impact on hemodynamics and urine output in children with critical congenital heart disease and pulmonary congestion, and there was no worsening of renal function.

Chronic heart failure as a state of reduced effectiveness of the natriuretic peptide system: implications for therapy

Natriuretic peptides (NPs) promote diuresis, natriuresis and vasodilation in early chronic heart failure (CHF), countering renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS) overstimulation. Despite dramatic increases in circulating NP concentrations as CHF progresses, their effects become blunted. Increases in diuresis, natriuresis, and vasodilation after administration of exogenous atrial (ANP) or brain (BNP) natriuretic peptides are attenuated in patients with advanced CHF compared with controls. Several major factors may account for the reduced effectiveness of the natriuretic peptide system (NPS) in CHF. First, there is reduced availability of active forms of NPs, namely BNP. Second, target organ responsiveness becomes diminished. Third, the counter-regulatory hormones of the RAAS and SNS, and endothelin-1 become over-activated. Therefore, pharmacological approaches to enhance the functional effectiveness of the NPS in CHF have been explored in recent years. In terms of clinical outcomes, studies of synthetic BNP, or of neprilysin inhibitors alone or associated with an angiotensin converting enzyme inhibitor, have been controversial for several reasons. Recently, however, encouraging results have been obtained with the angiotensin receptor neprilysin inhibitor sacubitril/valsartan. The available data show that treatment with sacubitril/valsartan is associated with increased levels of NPs and their intracellular mediator cyclic guanosine monophosphate, suggesting improved functional effectiveness of the NPS, in addition to beneficial effects on mortality and morbidity outcomes. Therefore, combined targeting of the NPS and RAAS with sacubitril/valsartan emerges as the current optimal approach for redressing the neurohormonal imbalance in CHF.

Heart Failure and Kidney Disease

Kidney disease is commonly found in heart failure (HF) patients. They share many risk factors and common pathophysiological pathways which often lead to mutual dysfunction. Both haemodynamic and non-haemodynamic mechanisms are involved in the development of renal impairment in heart failure patients. Moreover, the presence of a chronic kidney disease is a significant independent predictor of worse outcome in chronic as well as in acute decompensated HF. As a consequence, an accurate evaluation of renal function plays a key role in the management of HF patients. Serum creatinine levels and glomerular filtration rate (GFR) estimates are the corner stones of renal function evaluation in clinical practice. However, to overcome their limits, several emerging glomerular and tubular biomarkers have been proposed over the last years. Alongside the renal biomarkers, imaging techniques could complement the laboratory data exploring different pathophysiological pathways. In particular, Doppler evaluation of renal circulation is a highly feasible technique that can effectively identify HF patients prone to develop renal dysfunction and with a worse outcome. Finally, some classes of drugs currently used in heart failure treatment can affect renal function and their use can be influenced by the presence of chronic kidney disease.

Localization of corin and atrial natriuretic peptide expression in human renal segments

Atrial natriuretic peptide (ANP)-mediated natriuretic response is a well-established cardiac endocrine function. Corin is a transmembrane protease that activates ANP in the heart. Corin expression has been detected in non-cardiac tissues including the kidney. Here we examined corin, pro-ANP/ANP and natriuretic peptide receptor-A (NPR-A) expression in human renal segments. By immunostaining and in situ hybridization, we found similar corin, pro-ANP/ANP and NPR-A protein and mRNA expression in human renal segments. The expression was most abundant in the proximal convoluted tubules and the medullary connecting ducts. In the proximal tubules, corin protein was present in the apical membrane region underneath the brush border where the ANP-degrading protease neprilysin was abundant. These results suggest that corin-mediated pro-ANP activation may occur in renal segments and that locally produced ANP may act in an autocrine manner to regulate sodium and water reabsorption in situ Our results also point to the proximal convoluted tubules as a major site for local ANP action. Such a renal corin/ANP autocrine mechanism may differ from the cardiac corin/ANP endocrine mechanism in regulating sodium homoeostasis under physiological and pathological conditions.

The natriuretic peptides system in the pathophysiology of heart failure: from molecular basis to treatment

After its discovery in the early 1980s, the natriuretic peptide (NP) system has been extensively characterized and its potential influence in the development and progression of heart failure (HF) has been investigated. HF is a syndrome characterized by the activation of different neurohormonal systems, predominantly the renin-angiotensin (Ang)-aldosterone system (RAAS) and the sympathetic nervous system (SNS), but also the NP system. Pharmacological interventions have been developed to counteract the neuroendocrine dysregulation, through the down modulation of RAAS with ACE (Ang-converting enzyme) inhibitors, ARBs (Ang receptor blockers) and mineralcorticoid antagonists and of SNS with β-blockers. In the last years, growing attention has been paid to the NP system. In the present review, we have summarized the current knowledge on the NP system, focusing on its role in HF and we provide an overview of the pharmacological attempts to modulate NP in HF: from the negative results of the study with neprilysin (NEP) inhibitors, alone or associated with an ACE inhibitor and vasopeptidase inhibitors, to the most recently and extremely encouraging results obtained with the new pharmacological class of Ang receptor and NEP inhibitor, currently defined ARNI (Ang receptor NEP inhibitor). Indeed, this new class of drugs to manage HF, supported by the recent results and a vast clinical development programme, may prompt a conceptual shift in the treatment of HF, moving from the inhibition of RAAS and SNS to a more integrated target to rebalance neurohormonal dysregulation in HF.

The pathophysiological role of natriuretic peptide-RAAS cross talk in heart failure

Chronic Heart Failure (HF) is still a disease state characterized by elevated morbidity and mortality and represents an unresolved problem for its socio-economic impact. Besides many of the pathophysiological events leading to advanced HF have been widely disclosed in the past decades, the role of neuro-hormonal dysregulation accompanying HF has to be clearly assessed with the objective of better therapeutic approaches in treating such a disease. In the present review article, alongside with a brief re-evaluation of general aspects of HF physiopathology, we summarize recent advances in the cross talk between renin-angiotensin-aldosterone system (RAAS) with natriuretic peptides (NPs) which have been shown to play a relevant role in the development of severe HF. The role of RAAS-NPs interplay has been shown to be crucial in both hemodynamic and tissue remodeling associated to cardiomyocyte dysfunction, leading to advanced impairment of left ventricular performance. On the basis of these results, the development of drugs resetting both RAAS and NPs system seems to be promising for a successful long term treatment of chronic HF.

The kidney in heart failure: an update

Heart and kidney are closely related in the clinical syndrome of heart failure (HF). It is now sufficiently clear that renal dysfunction occurs frequently in all phenotypes of HF, and when present, it is associated with higher mortality and morbidity. While the pathophysiology is multifactorial, the most important factors are a reduced renal perfusion and venous congestion. Recent interest has focused on worsening renal function (WRF), a situation strongly related to mortality, but seemingly only when HF status deteriorates. Unfortunately, to date clinicians are unable to identify specifically those patients with a grim prognosis following WRF. Although much has been learned on cardiorenal interaction in HF, still more questions have been left unanswered. The coming decade should provide us with more dedicated epidemiologic, mechanistic, and controlled trials in HF patients with reduced renal function. An updated classification of the cardiorenal syndrome that incorporates recent evidence and points towards areas of interest and uncertainties, and areas where progress is needed could facilitate this process. Ultimately, this should lead to preventive and treatment strategies that can preserve renal function and associated outcome in patients with HF.

Angiotensin-converting enzyme inhibition prevents myocardial infarction-induced increase in renal cortical cGMP and cAMP phosphodiesterase activities

We investigated whether myocardial infarction (MI) enhances renal phosphodiesterases (PDE) activities, investigating particularly the relative contribution of PDE1-5 isozymes in total PDE activity involved in both cGMP and cAMP pathways, and whether angiotensin-converting enzyme inhibition (ACEi) decreases such renal PDE hyperactivities. We also investigated whether ACEi might thereby improve atrial natriuretic peptide (ANP) efficiency. We studied renal cortical PDE1-5 isozyme activities in sham (SH)-operated, MI rats and in MI rats treated with perindopril (ACEi) 1 month after coronary artery ligation. Circulating atrial natriuretic peptide (ANP), its second intracellular messenger cyclic guanosine monophosphate (cGMP) and cGMP/ANP ratio were also determined. Cortical cGMP-PDE2 (80.3 vs. 65.1 pmol/min/mg) and cGMP-PDE1 (50.7 vs. 30.1 pmol/min/mg), and cAMP-PDE2 (161 vs. 104.1 pmol/min/mg) and cAMP-PDE4 (307.5 vs. 197.2 pmol/min/mg) activities were higher in MI than in SH rats. Despite increased ANP plasma level, ANP efficiency tended to be decreased in MI compared to SH rats. Perindopril restored PDE activities and tended to improve ANP efficiency in MI rats. One month after coronary ligation, perindopril treatment of MI rats prevents the increase in renal cortical PDE activities. This may contribute to increase renal ANP efficiency in MI rats.

Mechanisms of renal hyporesponsiveness to BNP in heart failure

The B-type natriuretic peptide (BNP), a member of the family of vasoactive peptides, is a potent natriuretic, diuretic, and vasodilatory peptide that contributes to blood pressure and volume homeostasis. These attributes make BNP an ideal drug that could aid in diuresing a fluid-overloaded patient who had poor or worsening renal function. Despite the potential benefits of BNP, accumulating evidence suggests that simply increasing the amount of circulating BNP does not necessarily increase natriuresis in patients with heart failure (HF). Moreover, despite high BNP levels, natriuresis falls when HF progresses from a compensated to a decompensated state, suggesting the emergence of renal resistance to BNP. Although likely multifactorial, several mechanisms have been proposed to explain renal hyporesponsiveness in HF, including, but not limited to, decreased renal BNP availability, down-regulation of natriuretic peptide receptors, and altered BNP intracellular signal transduction pathways. Thus, a better understanding of renal hyporesponsiveness in HF is required to devise strategies to develop novel agents and technologies that directly restore renal BNP efficiency. It is hoped that development of these new therapeutic approaches will serve to limit sodium retention in patients with HF, which may ultimately delay the progression to overt HF.

Potential role of dipeptidyl peptidase IV in the pathophysiology of heart failure

Dipeptidyl peptidase IV (DPPIV) is a widely expressed multifunctional serine peptidase that exists as a membrane-anchored cell surface protein or in a soluble form in the plasma and other body fluids. Numerous substrates are cleaved at the penultimate amino acid by DPPIV, including glucagon-like peptide-1 (GLP-1), brain natriuretic peptide (BNP) and stromal cell-derived factor-1 (SDF-α), all of which play important roles in the cardiovascular system. In this regard, recent reports have documented that circulating DPPIV activity correlates with poorer cardiovascular outcomes in human and experimental heart failure (HF). Moreover, emerging evidence indicates that DPPIV inhibitors exert cardioprotective and renoprotective actions in a variety of experimental models of cardiac dysfunction. On the other hand, conflicting results have been found when translating these promising findings from preclinical animal models to clinical therapy. In this review, we discuss how DPPIV might be involved in the cardio-renal axis in HF. In addition, the potential role for DPPIV inhibitors in ameliorating heart disease is revised, focusing on the effects of the main DPPIV substrates on cardiac remodeling and renal handling of salt and water.

Ularitide for the treatment of acute decompensated heart failure: from preclinical to clinical studies

The short- and long-term morbidity and mortality in acute heart failure is still unacceptably high. There is an unmet need for new therapy options with new drugs with a new mode of action. One of the drugs currently in clinical testing in Phase III is ularitide, which is the chemically synthesized form of the human natriuretic peptide urodilatin. Urodilatin is produced in humans by differential processing of pro-atrial natriuretic peptide in distal renal tubule cells. Physiologically, urodilatin appears to be the natriuretic peptide involved in sodium homeostasis. Ularitide exerts its pharmacological actions such as vasodilation, diuresis, and natriuresis through the natriuretic peptide receptor/particulate guanylate cyclase/cyclic guanosine monophosphate pathway. In animal models of heart failure as well as Phase I and II clinical studies in heart failure patients, ularitide demonstrated beneficial effects such as symptom relief and vasodilation, while still preserving renal function. Subsequently, the pivotal acute decompensated heart failure (ADHF) Phase III study, called TRUE-AHF, was started with the objectives to evaluate the effects of ularitide infusion on the clinical status and cardiovascular mortality of patients with ADHF compared with placebo. This review summarizes preclinical and clinical data supporting the potential use of ularitide in the treatment of ADHF.

ANP-induced signaling cascade and its implications in renal pathophysiology

The balance between vasoconstrictor/sodium-retaining and vasodilator/natriuretic systems is essential for maintaining body fluid and electrolyte homeostasis. Natriuretic peptides, such as atrial natriuretic peptide (ANP), belong to the vasodilator/natriuretic system. ANP is produced by the conversion of pro-ANP into ANP, which is achieved by a proteolytical cleavage executed by corin. In the kidney, ANP binds to the natriuretic peptide receptor-A (NPR-A) and enhances its guanylyl cyclase activity, thereby increasing intracellular cyclic guanosine monophosphate production to promote natriuretic and renoprotective responses. In the glomerulus, ANP increases glomerular permeability and filtration rate and antagonizes the deleterious effects of the renin-angiotensin-aldosterone system activation. Along the nephron, natriuretic and diuretic actions of ANP are mediated by inhibiting the basolaterally expressed Na(+)-K(+)-ATPase, reducing apical sodium, potassium, and protein organic cation transporter in the proximal tubule, and decreasing Na(+)-K(+)-2Cl(-) cotransporter activity and renal concentration efficiency in the thick ascending limb. In the medullary collecting duct, ANP reduces sodium reabsorption by inhibiting the cyclic nucleotide-gated cation channels, the epithelial sodium channel, and the heteromeric channel transient receptor potential-vanilloid 4 and -polycystin 2 and diminishes vasopressin-induced water reabsorption. Long-term ANP treatment may lead to NPR-A desensitization and ANP resistance, resulting in augmented sodium and water reabsorption. In mice, corin deficiency impairs sodium excretion and causes salt-sensitive hypertension. Characteristics of ANP resistance and corin deficiency are also encountered in patients with edema-associated diseases, highlighting the importance of ANP signaling in salt-water balance and renal pathophysiology.

Diuretic response in acute heart failure-pathophysiology, evaluation, and therapy

The administration of loop diuretics to achieve decongestion is the cornerstone of therapy for acute heart failure. Unfortunately, impaired response to diuretics is common in these patients and associated with adverse outcomes. Diuretic resistance is thought to result from a complex interplay between cardiac and renal dysfunction, and specific renal adaptation and escape mechanisms, such as neurohormonal activation and the braking phenomenon. However, our understanding of diuretic response in patients with acute heart failure is still limited and a uniform definition is lacking. Three objective methods to evaluate diuretic response have been introduced, which all suggest that diuretic response should be determined based on the effect of diuretic dose administered. Several strategies have been proposed to overcome diuretic resistance, including combination therapy and ultrafiltration, but prospective studies in patients who are truly unresponsive to diuretics are lacking. An enhanced understanding of diuretic response should ultimately lead to an improved, individualized approach to treating patients with acute heart failure.

Diastolic heart failure: a confusing concept

Descriptions of the pathophysiology of heart failure have gone through a substantial evolution in the last 50 years. It is now recognised that heart failure can occur in the presence and also in the absence of a reduction in left ventricular function. In the former situation, this classically has been described to lead to hypotension and secondary salt and volume retention by the kidneys, further aggravating cardiac function. In the latter, this has been described to lead to pulmonary congestion because of impaired cardiac diastolic filling. These concepts have further evolved in the discrimination of 'acute vascular' versus 'acute congestive' heart failure. The current paper builds the argument from numerous smaller observational studies that irrespective of the clinical presentation of heart failure, fluid congestion is the key. If left ventricular function is preserved, fluid retention is probably due to the inability of damaged kidneys to excrete the large amounts of salt ingested with modern diet. In the extreme of end-stage renal disease requiring haemodialysis, heart failure is frequent, but can be prevented almost entirely by strict volume control. Unfortunately, the absence of systematic studies describing fluid volumes and renal haemodynamic and reabsorptive function in patients with acute heart failure precludes the final proof of our concept. This paper therefore is a strong call for mechanistic research in this area.

Systems biology and biomechanical model of heart failure

Heart failure is seen as a complex disease caused by a combination of a mechanical disorder, cardiac remodeling and neurohormonal activation. To define heart failure the systems biology approach integrates genes and molecules, interprets the relationship of the molecular networks with modular functional units, and explains the interaction between mechanical dysfunction and cardiac remodeling. The biomechanical model of heart failure explains satisfactorily the progression of myocardial dysfunction and the development of clinical phenotypes. The earliest mechanical changes and stresses applied in myocardial cells and/or myocardial loss or dysfunction activate left ventricular cavity remodeling and other neurohormonal regulatory mechanisms such as early release of natriuretic peptides followed by SAS and RAAS mobilization. Eventually the neurohormonal activation and the left ventricular remodeling process are leading to clinical deterioration of heart failure towards a multi-organic damage. It is hypothesized that approaching heart failure with the methodology of systems biology we promote the elucidation of its complex pathophysiology and most probably we can invent new therapeutic strategies.

Natriuretic peptide-guided therapy: further research required for still-unresolved issues

It has been asserted that serial measurements of natriuretic peptides (NPs), i.e., B-type natriuretic peptide (BNP) or the amino-terminal fragment of pro-B-type natriuretic peptide (NT-pro BNP), could help modulate more accurately the intensity of drug treatment in patients with chronic heart failure (CHF). Nevertheless, there are still several open questions about the presumed role of NP-guided pharmacologic adjustment as a valuable strategy in this setting. In this review, we outline the main randomized controlled trials (RCTs) carried out to date regarding NP-guided therapy in CHF patients and we focus on some of the still-unresolved issues. In particular, we discuss which NP plasma level should be assumed as the optimal target level to be attained, and we debate the possible influence exerted by different age classes on clinical end points during NP-guided therapy. The possible advantages and limitations for the cardiovascular system arising from the functional activation of NPs in CHF patients are also discussed. Although the pooling of data derived from the RCTs demonstrates an overall effect of slightly significant improvement in clinical outcomes with the NP-guided approach, we have noted that there are some relatively large studies that failed to document a significant clinical improvement in terms of mortality and morbidity using an NP-guided strategy. Thus, in our opinion, larger and better conducted trials addressing the unresolved issues of NP-guided therapy should be undertaken in the future.