Preischemic infusion of alpha-human atrial natriuretic peptide elicits myoprotective effects against ischemia reperfusion in isolated rat hearts

Data-Independent Acquisition Proteomics and N-Terminomics Methods Reveal Alterations in Mitochondrial Function and Metabolism in Ischemic-Reperfused Hearts

Myocardial ischemia-reperfusion (IR) (stunning) injury triggers changes in the proteome and degradome of the heart. Here, we utilize quantitative proteomics and comprehensive degradomics to investigate the molecular mechanisms of IR injury in isolated rat hearts. The control group underwent aerobic perfusion, while the IR injury group underwent 20 min of ischemia and 30 min of reperfusion to induce a stunning injury. As MMP-2 activation has been shown to contribute to myocardial injury, hearts also underwent IR injury with ARP-100, an MMP-2-preferring inhibitor, to dissect the contribution of MMP-2 to IR injury. Using data-independent acquisition (DIA) and mass spectroscopy, we quantified 4468 proteins in ventricular extracts, whereby 447 proteins showed significant alterations among the three groups. We then used subtiligase-mediated N-terminomic labeling to identify more than a hundred specific cleavage sites. Among these protease substrates, 15 were identified following IR injury. We identified alterations in numerous proteins involved in mitochondrial function and metabolism following IR injury. Our findings provide valuable insights into the biochemical mechanisms of myocardial IR injury, suggesting alterations in reactive oxygen/nitrogen species handling and generation, fatty acid metabolism, mitochondrial function and metabolism, and cardiomyocyte contraction.

NPPA/atrial natriuretic peptide is an extracellular modulator of autophagy in the heart

NPPA/atrial natriuretic peptide (natriuretic peptide type A) exerts critical pleiotropic effects in the cardiovascular system, limiting cardiomyocyte hypertrophy and death, reducing cardiac fibrosis and promoting vascular integrity. However, the molecular mechanisms underlying these beneficial effects still need to be clarified. We demonstrated for the first time that macroautophagy/autophagy is involved in the local protective effects of NPPA in cardiomyocytes (CMs), both in vitro and in vivo. Exogenous NPPA rapidly activates autophagy in CMs through NPR1/type A natriuretic peptide receptor and PRKG/protein kinase G signaling and also increases cardiac autophagy in mice. Remarkably, endogenous NPPA is secreted by CMs in response to glucose deprivation or hypoxia, thereby stimulating autophagy through autocrine/paracrine mechanisms. NPPA preserves cell viability and reduces hypertrophy in response to stress through autophagy activation. In vivo, we found that Nppa knockout mice undergoing ischemia-reperfusion (I/R) show increased infarct size and reduced autophagy. Reactivation of autophagy by Tat-Beclin D11 limits I/R injury. We also found that the protective effects of NPPA in reducing infarct size are abrogated in the presence of autophagy inhibition. Mechanistically, we found that NPPA stimulates autophagy through the activation of TFEB (transcription factor EB). Our data suggest that NPPA is a novel extracellular regulator of autophagy in the heart.

Identification of a novel native peptide derived from 60S ribosomal protein L23a that translationally regulates p53 to reduce myocardial ischemia-reperfusion

Myocardial ischemia-reperfusion (I/R) is a severe disease，but its underlying mechanism is not fully elucidated and no effective clinical treatment is available. Utilizing intracellular peptidomics, we identified a novel native peptide PDRL23A (Peptide Derived from RPL23A), that is intimately related to hypoxic stress. We further show that PDRL23A effectively alleviates hypoxia-induced cardiomyocyte injury in vitro, along with improvements in mitochondrial function and redox homeostasis, including ROS accumulation, oxidative phosphorylation, and mitochondrial membrane potential. Strikingly, the in vivo results indicate that, short-term pretreatment with PDRL23A could effectively inhibit I/R-induced cardiomyocyte death, myocardial fibrosis and decreased cardiac function. Interestingly, PDRL23A was found to interact with 60 S ribosomal protein L26 (RPL26), hampering RPL26-governed p53 translation, and resulting in a reduction in the level of p53 protein, which in turn reduced p53-mediated apoptosis under hypoxic conditions. Collectively, a native peptide, PDRL23A, which translationally regulates p53 to protect against myocardial I/R injury, has been identified for the first time. Our findings provide insight into the adaptive mechanisms of hypoxia and present a potential new treatment for myocardial I/R.

The Role of Natriuretic Peptides in the Regulation of Cardiac Tolerance to Ischemia/Reperfusion and Postinfarction Heart Remodeling

In the past 10 years, mortality from acute myocardial infarction has not decreased despite the widespread introduction of percutaneous coronary intervention. The reason for this situation is the absence in clinical practice of drugs capable of preventing reperfusion injury of the heart with high efficiency. In this regard, noteworthy natriuretic peptides (NPs) which have the infarct-limiting effect, prevent reperfusion cardiac injury, prevent adverse post-infarction remodeling of the heart. Atrial natriuretic peptide does not have the infarct-reducing effect in rats with alloxan-induced diabetes mellitus. NPs have the anti-apoptotic and anti-inflammatory effects. There is indirect evidence that NPs inhibit pyroptosis and autophagy. Published data indicate that NPs inhibit reactive oxygen species production in cardiomyocytes, aorta, heart, kidney and the endothelial cells. NPs can suppress aldosterone, angiotensin II, endothelin-1 synthesize and secretion. NPs inhibit the effects aldosterone, angiotensin II on the post-receptor level through intracellular signaling events. NPs activate guanylyl cyclase, protein kinase G and protein kinase A, and reduce phosphodiesterase 3 activity. NO-synthase and soluble guanylyl cyclase are involved in the cardioprotective effect of NPs. The cardioprotective effect of natriuretic peptides is mediated via activation of kinases (AMPK, PKC, PI3 K, ERK1/2, p70s6 k, Akt) and inhibition of glycogen synthase kinase 3β. The cardioprotective effect of NPs is mediated via sarcolemmal K_ATP channel and mitochondrial K_ATP channel opening. The cardioprotective effect of brain natriuretic peptide is mediated via MPT pore closing. The anti-fibrotic effect of NPs may be mediated through inhibition TGF-β1 expression. Natriuretic peptides can inhibit NF-κB activity and activate GATA. Hemeoxygenase-1 and peroxisome proliferator-activated receptor γ may be involved in the infarct-reducing effect of NPs. NPs exhibit the infarct-limiting effect in patients with acute myocardial infarction. NPs prevent post-infarction remodeling of the heart. To finally resolve the question of the feasibility of using NPs in AMI, a multicenter, randomized, blind, placebo-controlled study is needed to assess the effect of NPs on the mortality of patients after AMI.

Cardiac Ischemic Preconditioning Promotes MG53 Secretion Through H2O2-Activated Protein Kinase C-δ Signaling

BACKGROUND

Ischemic heart disease is the leading cause of morbidity and mortality worldwide. Ischemic preconditioning (IPC) is the most powerful intrinsic protection against cardiac ischemia/reperfusion injury. Previous studies have shown that a multifunctional TRIM family protein, MG53 (mitsugumin 53; also called TRIM72), not only plays an essential role in IPC-mediated cardioprotection against ischemia/reperfusion injury but also ameliorates mechanical damage. In addition to its intracellular actions, as a myokine/cardiokine, MG53 can be secreted from the heart and skeletal muscle in response to metabolic stress. However, it is unknown whether IPC-mediated cardioprotection is causally related to MG53 secretion and, if so, what the underlying mechanism is.

METHODS

Using proteomic analysis in conjunction with genetic and pharmacological approaches, we examined MG53 secretion in response to IPC and explored the underlying mechanism using rodents in in vivo, isolated perfused hearts, and cultured neonatal rat ventricular cardiomyocytes. Moreover, using recombinant MG53 proteins, we investigated the potential biological function of secreted MG53 in the context of IPC and ischemia/reperfusion injury.

RESULTS

We found that IPC triggered robust MG53 secretion in rodents in vivo, perfused hearts, and cultured cardiac myocytes without causing cell membrane leakage. Mechanistically, IPC promoted MG53 secretion through H₂O₂-evoked activation of protein kinase-C-δ. Specifically, IPC-induced myocardial MG53 secretion was mediated by H₂O₂-triggered phosphorylation of protein kinase-C-δ at Y311, which is necessary and sufficient to facilitate MG53 secretion. Functionally, systemic delivery of recombinant MG53 proteins to mimic elevated circulating MG53 not only restored IPC function in MG53-deficient mice but also protected rodent hearts from ischemia/reperfusion injury even in the absence of IPC. Moreover, oxidative stress by H₂O₂ augmented MG53 secretion, and MG53 knockdown exacerbated H₂O₂-induced cell injury in human embryonic stem cell-derived cardiomyocytes, despite relatively low basal expression of MG53 in human heart.

CONCLUSIONS

We conclude that IPC and oxidative stress can trigger MG53 secretion from the heart via an H₂O₂-protein kinase-C-δ-dependent mechanism and that extracellular MG53 can participate in IPC protection against cardiac ischemia/reperfusion injury.

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.

Flavonoids Extraction from Propolis Attenuates Pathological Cardiac Hypertrophy through PI3K/AKT Signaling Pathway

Propolis, a traditional medicine, has been widely used for a thousand years as an anti-inflammatory and antioxidant drug. The flavonoid fraction is the main active component of propolis, which possesses a wide range of biological activities, including activities related to heart disease. However, the role of the flavonoids extraction from propolis (FP) in heart disease remains unknown. This study shows that FP could attenuate ISO-induced pathological cardiac hypertrophy (PCH) and heart failure in mice. The effect of the two fetal cardiac genes, atrial natriuretic factor (ANF) and β-myosin heavy chain (β-MHC), on PCH was reversed by FP. Echocardiography analysis revealed cardiac ventricular dilation and contractile dysfunction in ISO-treated mice. This finding is consistent with the increased heart weight and cardiac ANF protein levels, massive replacement fibrosis, and myocardial apoptosis. However, pretreatment of mice with FP could attenuate cardiac dysfunction and hypertrophy in vivo. Furthermore, the cardiac protection of FP was suppressed by the pan-PI3K inhibitor wortmannin. FP is a novel cardioprotective agent that can attenuate adverse cardiac dysfunction, hypertrophy, and associated disorder, such as fibrosis. The effects may be closely correlated with PI3K/AKT signaling. FP may be clinically used to inhibit PCH progression and heart failure.

Long-term effects and prognosis in acute heart failure treated with tolvaptan: the AVCMA trial

Background. Diuresis is a major therapy for the reduction of congestive symptoms in acute decompensated heart failure (ADHF) patients. We previously reported the efficacy and safety of tolvaptan compared to carperitide in hospitalized patients with ADHF. There were some reports of cardio- and renal-protective effects in carperitide; therefore, the purpose of this study was to compare the long-term effects of tolvaptan and carperitide on cardiorenal function and prognosis. Methods and Results. One hundred and five ADHF patients treated with either tolvaptan or carperitide were followed after hospital discharge. Levels of plasma B-type natriuretic peptide, serum sodium, potassium, creatinine, and estimated glomerular filtration rate were measured before administration of tolvaptan or carperitide at baseline, the time of discharge, and one year after discharge. These data between tolvaptan and carperitide groups were not different one year after discharge. Kaplan-Meier survival curves demonstrated that the event-free rate regarding all events, cardiac events, all cause deaths, and rehospitalization due to worsening heart failure was not significantly different between tolvaptan and carperitide groups. Conclusions. We demonstrated that tolvaptan had similar effects on cardiac and renal function and led to a similar prognosis in the long term, compared to carperitide.

Role of atrial natriuretic Peptide in oxytocin induced cardioprotection

BACKGROUND

The purpose of this study was to determine whether endogenous atrial natriuretic peptide (ANP) contributes to the protective effect of neurohypophysial hormone oxytocin (OT) in heart preconditioning.

METHODS

Sprague-Dawley male rats were subjected to 25 min regional ischaemia and 120 min reperfusion and were divided into eight groups. Oxytocin or an equivalent volume of saline was administrated intraperitoneally, 30 min before ischaemia. The OT receptor antagonist (atosiban), ANP receptor antagonist (anantin) and nitric oxide synthase inhibitor (L-NAME) were injected 10 min before OT. In other groups, atosiban, anantin and L-NAME were only administered 40 min prior to ischaemia.

RESULTS

Compared with the ischaemia/reperfusion group (I/R), alterations in infarct size, biochemical parameters [LDH (lactate dehydrogenase), CK-MB (creatine kinase-MB), MDA (malondialdehyde) plasma levels] and severity of ventricular arrhythmia due to I/R injury were attenuated and VF was abolished by OT treatment. These OT effects were eliminated by OT and ANP receptor blockers and nitric oxide synthase inhibitor, but anantin did not reverse the effect of OT in lipid peroxidation.

CONCLUSIONS

These findings demonstrate an important contributory role of ANP in the OT induced protection in myocardial ischaemia reperfusion. OT also reduced lipid peroxidation with a NO-dependent mechanism.

Natriuretic peptides in cardiometabolic regulation and disease

In the 30 years since the identification of the natriuretic peptides, their involvement in regulating fluid and blood pressure has become firmly established. Data indicating a role for these hormones in lifestyle-related metabolic and cardiovascular disorders have also accumulated over the past decade. Dysregulation of the natriuretic peptide system has been associated with obesity, glucose intolerance, type 2 diabetes mellitus, and essential hypertension. Moreover, the natriuretic peptides have been implicated in the protection against atherosclerosis, thrombosis, and myocardial ischaemia. All these conditions can coexist and potentially lead to heart failure, a syndrome associated with a functional natriuretic peptide deficiency despite high circulating concentrations of immunoreactive peptides. Therefore, dysregulation of the natriuretic peptide system, a 'natriuretic handicap', might be an important factor in the initiation and progression of metabolic dysfunction and its accompanying cardiovascular complications. This Review provides a summary of the natriuretic peptide system and its involvement in these cardiometabolic conditions. We propose that these peptides might have an integrating role in lifestyle-related metabolic and cardiovascular disorders.

Effects of atrial natriuretic peptide after prolonged hypothermic storage of the isolated rat heart

Primary graft failure (PGF) caused by ischemia-reperfusion injury (IRI) is the strongest determinant of perioperative mortality after heart transplantation. Atrial natriuretic peptide (ANP) has been found to reduce the IRI of cardiomyocytes and may be beneficial in alleviating PGF after heart transplantation, although there is a lack of evidence to support this issue. The purpose of this study was to investigate the cardioprotective effects of ANP after prolonged hypothermic storage. For this purpose, an isolated working-heart rat model was used. After the preparation, the hearts were arrested with and stored in an extracellular-based cardioplegic solution at 3-4°C for 6 h and followed by 25 min of reperfusion. The hearts were divided into four groups (n = 7 in each group) according to the timing of ANP administration: Group 1 (in perfusate before storage), Group 2 (in cardioplegia), Group 3 (in reperfusate), and control (no administration of ANP). Left ventricular functional recovery and the incidence of ventricular fibrillation (VF) were compared. ANP administration at the time of reperfusion improved the percent recovery of left ventricular developed pressure (control, 45.5 ± 10.2; Group 1, 47.4 ± 8.8; Group 2, 45.3 ± 12 vs. Group 3, 76.3 ± 7; P < 0.05) and maximum first derivative of the left ventricular pressure (control, 47.9 ± 8.7; Group 1, 46.7 ± 8.8; Group 2, 49.6 ± 10.8 vs. Group 3, 76.6 ± 7.5; P < 0.05). The incidence of VF after reperfusion did not differ significantly among these four groups (71.4, 85.7, 57.1, and 85.7% in Groups 1, 2, 3, and control, respectively). This result suggests that the administration of ANP at the time of reperfusion may have the potential to decrease the incidence of PGF after heart transplantation.

Targeting reperfusion injury in acute myocardial infarction: a review of reperfusion injury pharmacotherapy

INTRODUCTION

Acute myocardial infarction (AMI) (secondary to lethal ischemia-reperfusion [IR]) contributes to much of the mortality and morbidity from ischemic heart disease. Currently, the treatment for AMI is early reperfusion; however, this itself contributes to the final myocardial infarct size, in the form of what has been termed 'lethal reperfusion injury'. Over the last few decades, the discovery of the phenomena of ischemic preconditioning and postconditioning, as well as remote preconditioning and remote postconditioning, along with significant advances in our understanding of the cardioprotective pathways underlying these phenomena, have provided the possibility of successful mechanical and pharmacological interventions against reperfusion injury.

AREAS COVERED

This review summarizes the evidence from clinical trials evaluating pharmacological agents as adjuncts to standard reperfusion therapy for ST-elevation AMI.

EXPERT OPINION

Reperfusion injury pharmacotherapy has moved from bench to bedside, with clinical evaluation and ongoing clinical trials providing us with valuable insights into the shortcomings of current research in establishing successful treatments for reducing reperfusion injury. There is a need to address some key issues that may be leading to lack of translation of cardioprotection seen in basic models to the clinical setting. These issues are discussed in the Expert opinion section.

Cardiac-specific overexpression of caveolin-3 attenuates cardiac hypertrophy and increases natriuretic peptide expression and signaling

OBJECTIVES

We hypothesized that cardiac myocyte-specific overexpression of caveolin-3 (Cav-3), a muscle-specific caveolin, would alter natriuretic peptide signaling and attenuate cardiac hypertrophy.

BACKGROUND

Natriuretic peptides modulate cardiac hypertrophy and are potential therapeutic options for patients with heart failure. Caveolae, microdomains in the plasma membrane that contain caveolin proteins and natriuretic peptide receptors, have been implicated in cardiac hypertrophy and natriuretic peptide localization.

METHODS

We generated transgenic mice with cardiac myocyte-specific overexpression of caveolin-3 (Cav-3 OE) and also used an adenoviral construct to increase Cav-3 in cardiac myocytes.

RESULTS

The Cav-3 OE mice subjected to transverse aortic constriction had increased survival, reduced cardiac hypertrophy, and maintenance of cardiac function compared with control mice. In left ventricle at baseline, messenger ribonucleic acid for atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were increased 7- and 3-fold, respectively, in Cav-3 OE mice compared with control subjects and were accompanied by increased protein expression for ANP and BNP. In addition, ventricles from Cav-3 OE mice had greater cyclic guanosine monophosphate levels, less nuclear factor of activated T-cell nuclear translocation, and more nuclear Akt phosphorylation than ventricles from control subjects. Cardiac myocytes incubated with Cav-3 adenovirus showed increased expression of Cav-3, ANP, and Akt phosphorylation. Incubation with methyl-β-cyclodextrin, which disrupts caveolae, or with wortmannin, a PI3K inhibitor, blocked the increase in ANP expression.

CONCLUSIONS

These results imply that cardiac myocyte-specific Cav-3 OE is a novel strategy to enhance natriuretic peptide expression, attenuate hypertrophy, and possibly exploit the therapeutic benefits of natriuretic peptides in cardiac hypertrophy and heart failure.

[Physiology and clinical role of natriuretic peptides]

In the last three decades many members of the natriuretic peptide family was isolated. The function and physiological role of these peptides are pleiotropic. All natriuretic peptides are synthesized from polypeptide precursors. Together with the sympathetic nervous system and other hormones they play key roles, like an endogenous system in the regulation of the body fluid homeostasis and blood pressure. Changes in this balance lead to dysfunction in the endothel and left ventricle, which can cause severe complications. In many cardiovascular diseases natriuretic peptides serve not only as marker for diagnosis and prognosis but they have therapeutic importance. In the last years the potential use of the elevated BNP levels for diagnosis of pre-eclampsia was examined. In our review we discuss the current understanding of molecular biology, biochemistry and clinical relevance of natriuretic peptides.

Heme oxygenase-1 induction enhances cell survival and restores contractility to unvascularized three-dimensional adult cardiomyocyte grafts implanted in vivo

Autologous adult cardiomyocytes are not utilized for heart repair strategies because of their rapid apoptosis after implantation. We examined whether induction of heme oxygenase-1 (HO-1), a mediator of preconditioning, could enhance early postimplant myocyte survival. Three-dimensional 5×5 mm patches of full-thickness adult murine atrial wall, including cardiomyocytes, capillary networks, and extracellular matrix, were cultured with or without HO-1 inducer cobalt protoporphyrin (CoPP), or the HO-1 inhibitor, tin protoporphyrin (SnPP), or both. Patches were then implanted subcutaneously. Freshly procured atrial wall patches implanted without preculturing served as additional controls. By 14 days postimplant, graft cardiomyocyte content was significantly greater in CoPP-treated patches than in either control group (p<0.02). Adult cardiomyocytes did not contract in culture or immediately after implantation. However, by 14 days postimplant, spontaneous contraction had recovered in 47% of CoPP-treated patches, but in only 6% of precultured patches without CoPP, 0% of SnPP-treated patches, and 0% of uncultured patches (p<0.03). CoPP-treated adult cardiomyocyte patches were also observed to remodel spontaneously into endothelial-lined chambers that pumped nonclotting blood. These findings demonstrate that adult cardiomyocytes have more plasticity and capacity for functional recovery than previously recognized and could have application as an autologous cardiomyocyte source for tissue engineering.

Mast cells, peptides and cardioprotection - an unlikely marriage?

1 Mast cells have classically been regarded as the 'bad guys' in the setting of acute myocardial ischaemia, where their released contents are believed to contribute both to tissue injury and electrical disturbances resulting from ischaemia. Recent evidence suggests, however, that if mast cell degranulation occurs in advance of ischaemia onset, this may be cardioprotective by virtue of the depletion of mast cell contents that can no longer act as instruments of injury when the tissue becomes ischaemic. 2 Many peptides, such as ET-1, adrenomedullin, relaxin and atrial natriuretic peptide, have been demonstrated to be cardioprotective when given prior to the onset of myocardial ischaemia, although their physiological functions are varied and the mechanisms of their cardioprotective actions appear to be diverse and often ill defined. However, one common denominator that is emerging is the ability of these peptides to modulate mast cell degranulation, raising the possibility that peptide-induced mast cell degranulation or stabilization may hold the key to a common mechanism of their cardioprotection. 3 The aim of this review was to consolidate the evidence implying that mast cell degranulation could play both a detrimental and protective role in myocardial ischaemia, depending upon when it occurs, and that this may underlie the cardioprotective effects of a range of diverse peptides that exerts physiological effects within the cardiovascular system.

Post-ischemic infusion of atrial natriuretic peptide attenuates warm ischemia-reperfusion injury in rat lung

BACKGROUND

The serious shortage of organs for transplantation, especially lungs, has drawn increasing attention to donation after cardiac death and protection of organs against warm ischemic injury. Atrial natriuretic peptide (ANP) activates guanylate cyclase receptors and increases cyclic guanosine monophosphate (cGMP) levels, which decrease in the lung during ischemia. In this study we investigated the effect on lung ischemia-reperfusion injury of administering synthetic ANP (carperitide) at the onset of reperfusion after warm ischemia.

METHODS

An isolated rat lung perfusion model was used. The rats were allocated into three groups: the control group; the ANP group; and the sham group. In the control and ANP groups, the heart-lung block was exposed to 60 minutes of ischemia at 37 degrees C, and subsequently reperfused for 60 minutes. At the onset of reperfusion, either saline or ANP was added to the perfusate. In the sham group, lungs were continuously perfused without ischemia and only saline was added to the perfusate.

RESULTS

ANP significantly reduced pulmonary vascular resistance and pulmonary edema, and improved oxygenation. It also significantly increased cGMP levels in reperfused lungs. Histologically, lungs in the ANP group showed significantly fewer signs of injury and fewer cells demonstrated apoptotic changes or single-stranded DNA than lungs in the control group.

CONCLUSIONS

Our results indicate that ANP administered at the onset of reperfusion increases cGMP in lung tissue and attenuates warm ischemia-reperfusion injury in isolated perfused rat lung.

Hypothermic Circulatory Arrest: Renal Protection by Atrial Natriuretic Peptide

Moderate hypothermic circulatory arrest with selective cerebral perfusion has been developed for cerebral protection during thoracic aortic surgery. However, visceral organs, particularly the kidneys, suffer greater tissue damage under moderate hypothermic circulatory arrest, and acute renal failure after hypothermic circulatory arrest is an independent risk factor for early and late mortality. This study investigated whether atrial natriuretic peptide could prevent the reduction in renal perfusion and protect renal function after moderate hypothermic circulatory arrest. Twelve pigs cooled to 30°C during cardiopulmonary bypass were randomly assigned to a peptide-treated group of 6 and a control group of 6. Moderate hypothermic circulatory arrest was induced for 60 min. Systemic arterial mean pressure and renal artery flow did not differ between groups during the study. However, renal medullary blood flow increased significantly in the peptide-treated group after hypothermic circulatory arrest. Myeloperoxidase activity was significantly reduced in the medulla of the peptide-treated group. Renal medullary ischemia after hypothermic circulatory arrest was ameliorated by atrial natriuretic peptide which increased medullary blood flow and reduced sodium reabsorption in the medulla. Atrial natriuretic peptide also reduced the release of an inflammatory marker after ischemia in renal tissue.

Glycogen Synthase Kinase-3 Inactivation Is Not Required for Ischemic Preconditioning or Postconditioning in the Mouse

The inactivation of glycogen synthase kinase-3β (GSK-3β) is proposed as the event integrating protective pathways initiated by preconditioning and other interventions. The inactivation of GSK-3 is thought to decrease the probability of opening of the mitochondrial permeability transition pore. The aim of this study was to verify the role of GSK-3 using a targeted mouse line lacking the critical N-terminal serine within GSK-3β (Ser9) and the highly homologous GSK-3α (Ser21), which when phosphorylated results in kinase inactivation. Postconditioning with 10 cycles of 5 seconds of reperfusion/5 seconds of ischemia and preconditioning with 6 cycles of 4 minutes of ischemia/6 minutes of reperfusion, similarly reduced infarction of the isolated perfused mouse heart in response to 30 minutes of global ischemia and 120 minutes of reperfusion. Preconditioning caused noticeable inactivating phosphorylation of GSK-3. However, both preconditioning and postconditioning still protected hearts of homozygous GSK-3 double knockin mice. Moreover, direct pharmacological inhibition of GSK-3 catalytic activity with structurally diverse inhibitors before or after ischemia failed to recapitulate conditioning protection. Nonetheless, cyclosporin A, a direct mitochondrial permeability transition pore inhibitor, reduced infarction in hearts from both wild-type and homozygous GSK-3 double knockin mice. Furthermore, in adult cardiac myocytes from GSK-3 double knockin mice, insulin exposure was still as effective as cyclosporin A in delaying mitochondrial permeability transition pore opening. Our results, which include a novel genetic approach, suggest that the inhibition of GSK-3 is unlikely to be the key determinant of cardioprotective signaling in either preconditioning or postconditioning in the mouse.

B-type natriuretic peptide at early reperfusion limits infarct size in the rat isolated heart

Natriuretic peptides are regulatory autacoids in the mammalian myocardium whose functions, mediated via particulate guanylyl cyclase/cGMP, may include cytoprotection against ischaemia-reperfusion injury. Previous work has identified that B-type natriuretic peptide (BNP) limits infarct size when administered prior to and during coronary occlusion through a K(ATP) channel-dependent mechanism. The present study examined the hypothesis that the protection afforded by BNP is mediated specifically at reperfusion in a postconditioning-like manner. Langendorff-perfused rat hearts were subjected to 35 min coronary artery occlusion and 120 min reperfusion, and infarct size was determined by tetrazolium staining. Postconditioning was effected by applying six 10-second periods of global ischaemia at the onset of reperfusion.Treatment with either BNP 10 nM or the NO donor S-nitroso-N-acetylpenicillamine (SNAP) 1-10 microM was commenced 5 min prior to reperfusion and continued until 10 min after reperfusion. Control infarct size (% of ischaemic risk zone) was 40.8 +/- 3.7%.BNP at reperfusion induced a significant limitation of infarct size (BNP 22.9 +/- 4.1% P<0.05 vs. control). Co-treatment at reperfusion with BNP and the K(ATP) channel blockers 5-hydroxydecanote (5HD, 100 microM), glibenclamide (Glib; 10 microM) or HMR1098 (10 microM) abolished the infarct-limiting effect of BNP (BNP + 5HD 41.0 +/- 3.9%, BNP + Glib 39.8 +/- 5.6%, BNP + HMR 1098 46.0 +/- 7.1%,P < 0.05 vs. BNP). BNP given together with L-NAME (100 microM) at reperfusion resulted in a marked loss of protection (BNP + L-NAME 53.1 +/- 3.8% P < 0.001 vs. BNP). In a second series of experiments, SNAP (1-10 microM) given at reperfusion was found not to be protective (SNAP 1 microM 30.2 +/- 4.9%, SNAP 2 microM 27.5 +/- 9.5%, SNAP 5 microM 39.2 +/- 5.7%, SNAP 10 microM 33.7 +/- 6.4%, not significant vs. control). In a third series of experiments, postconditioning significantly limited infarct size (14.9 +/- 3.6 % vs. control 34.5 +/- 4.9%, P < 0.01) and this effect of postconditioning was abolished in the presence of isatin (100 microM), a non-specific blocker of particulate guanylyl cyclases (35.1 +/- 6%, P < 0.05 vs. postconditioning). In conclusion, pharmacological activation of pGC by BNP can effectively induce protection against reperfusion injury, by mechanisms involving K(ATP) channel opening and endogenous NO synthase activation. Furthermore, endogenous activation of pGC could play a role in the mechanism of postconditioning.

Cyclic GMP and protein kinase-G in myocardial ischaemia-reperfusion: opportunities and obstacles for survival signaling

It is clear that multiple signalling pathways regulate the critical balance between cell death and survival in myocardial ischaemia-reperfusion. Recent attention has focused on the activation of survival or salvage kinases, particularly during reperfusion, as a common mechanism of many cardioprotective interventions. The phosphatidyl inositol 3'-hydroxy kinase/Akt complex (PI3K/Akt) and p42/p44 mitogen-activated protein kinase cascades have been widely promoted in this respect but the cyclic guanosine 3',5'-monophosphate/cGMP-dependent protein kinase (cGMP/PKG) signal transduction cassette has been less systematically investigated as a survival cascade. We propose that activation of the cGMP/PKG signalling pathway, following activation of soluble or particulate guanylate cyclases, may play a pivotal role in survival signalling in ischaemia-reperfusion, especially in the classical preconditioning, delayed preconditioning and postconditioning paradigms. The resurgence of interest in reperfusion injury, largely as a result of postconditioning-related research, has confirmed that the cGMP/PKG pathway is a pivotal salvage mechanism in reperfusion. Numerous studies suggest that the infarct-limiting effects of preconditioning and postconditioning, exogenously donated nitric oxide (NO), natriuretic peptides, phosphodiesterase inhibitors, and other diverse drugs and mediators such as HMG co-A reductase inhibitors (statins), Rho-kinase inhibitors and adrenomedullin, whether given before and during ischaemia, or specifically at the onset of reperfusion, may be mediated by activation or enhancement of the cGMP pathway, either directly or indirectly via endogenous NO generation downstream of PI3K/Akt. Putative mechanisms of protection include PKG regulation of Ca(2+) homeostasis through the modification of sarcoplasmic reticulum Ca(2+) uptake mechanisms, and PKG-induced opening of ATP-sensitive K(+) channels during ischaemia and/or reperfusion. At present, significant technical obstacles in defining the precise roles played by cGMP/PKG signalling include the heavy reliance on pharmacological PKG inhibitors of uncertain selectivity, difficulties in determining PKG activity in intact tissue, and the growing recognition that intracellular compartmentalisation of the cGMP pool may contribute markedly to the nucleotide's biological actions and biochemical determination. Overall, the body of experimental evidence suggests that cGMP/PKG survival signalling ameliorates irreversible injury associated with ischaemia-reperfusion and may be a tractable therapeutic target.

Atrial natriuretic peptide reduces ischemia/reperfusion-induced spinal cord injury in rats by enhancing sensory neuron activation

We recently demonstrated that calcitonin gene-related peptide (CGRP) released from sensory neurons reduces spinal cord injury (SCI) by inhibiting neutrophil activation through an increase in the endothelial production of prostacyclin (PGI(2)). Carperitide, a synthetic alpha-human atrial natriuretic peptide (ANP), reduces ischemia/reperfusion (I/R)-induced tissue injury. However, its precise therapeutic mechanism(s) remains to be elucidated. In the present study, we examined whether ANP reduces I/R-induced spinal cord injury by enhancing sensory neuron activation using rats. ANP increased CGRP release and cellular cAMP levels in dorsal root ganglion neurons isolated from rats in vitro. The increase in CGRP release induced by ANP was reversed by pretreatment with capsazepine, an inhibitor of vanilloid receptor-1 activation, or with (9S, 10S, 12R)-2,3,9,10,11,12-hexahydro-10-hydroxy-9-methyl-1-oxo-9,12-epoxy-1H-diindolo[1,2,3-fg:3',2',1'-kl]pyrrolo[3,4-i][1,6]-benzodiazocine-10-carboxylic acid hexyl ester (KT5720), an inhibitor of protein kinase A (PKA), suggesting that ANP might increase CGRP release from sensory neurons by activating PKA through an increase in the cellular cAMP level. Spinal cord ischemia was induced in rats using a balloon catheter placed in the aorta. ANP reduced mortality and motor disturbances by inhibiting reduction of the number of motor neurons in animals subjected to SCI. ANP significantly enhanced I/R-induced increases in spinal cord tissue levels of CGRP and 6-keto-prostaglandin F(1alpha). a stable metabolite of PGI(2). ANP inhibited I/R-induced increases in spinal cord tissue levels of tumor necrosis factor and myeloperoxidase. Pretreatment with 4'-chloro-3-methoxycinnamanilide (SB366791), a specific vanilloid receptor-1 antagonist, and indomethacin reversed the effects of ANP. These results strongly suggest that ANP might reduce I/R-induced SCI in rats by inhibiting neutrophil activation through enhancement of sensory neuron activation.

Cardioprotective actions of peptide hormones in myocardial ischemia

The myocardium represents a major source of several families of peptide hormones under normal physiological conditions and the plasma concentrations of many of these "cardiac peptides" (or related pro-peptide fragments) are substantially augmented in many cardiac disease states. In addition to well-characterised endocrine functions of several of the cardiac peptides, pleiotropic functions within the myocardium and the coronary vasculature represent a significant aspect of their actions in health and disease. Here, we focus specifically on the cardioprotective roles of four major peptide families in myocardial ischemia and reperfusion: adrenomedullin, kinins, natriuretic peptides and the urocortins. The patterns of early release of all these peptides are consistent with roles as autacoid cardioprotective mediators. Clinical and experimental research indicates the early release and upregulation of many of these peptides by acute ischemia and there is a convincing body of evidence showing that exogenously administered adrenomedullin, bradykinin, ANP, BNP, CNP and urocortins are all markedly protective against experimental myocardial ischemia-reperfusion injury through a conserved series of cytoprotective signal transduction pathways. Intriguingly, all the peptides examined so far have the potential to salvage against infarction when administered specifically during early reperfusion. Thus, the myocardial secretion of peptide hormones likely represents an early protective response to ischemia. Further work is required to explore the potential therapeutic manipulation of these peptides in acute coronary syndromes and their promise as biomarkers of acute myocardial ischemia.

Cardiomyocyte-restricted over-expression of C-type natriuretic peptide prevents cardiac hypertrophy induced by myocardial infarction in mice

OBJECTIVE

Infused C-type natriuretic peptide (CNP) was recently found to play a cardioprotective role in preventing myocardial ischaemia/reperfusion (I/R) injury and improving cardiac remodelling after myocardial infarction (MI) in rats. Our study aimed to investigate the effect of cardiomyocyte-specific CNP over-expression on I/R injury and MI in transgenic mice.

METHODS AND RESULTS

We generated transgenic (TG) mice over-expressing CNP in cardiomyocytes. Elevated CNP expression on RNA and protein levels was demonstrated by RNase-protection assay and radioimmunoassay. Male TG mice and age-matched wild-type (WT) littermates were subjected to 1-hour global myocardial ischaemia and 23 h of reperfusion or permanent ligation of the coronary artery for 3 weeks. Infarct size did not differ between the WT and TG groups in mice subjected to I/R. In mice that underwent permanent ligation of coronary arteries, both left and right ventricular hypertrophy were prevented by CNP over-expression 3 weeks post-MI. Histological analysis revealed less necrosis, muscular degeneration and inflammation in infarcted TG mice. Impairment of cardiac function was less pronounced in transgenic animals than in the wild-type controls.

CONCLUSIONS

Over-expression of CNP in cardiomyocytes does not affect I/R-induced infarct size but prevents cardiac hypertrophy induced by MI. Therefore, CNP may represent a potent therapeutic target for the treatment of patients with cardiac hypertrophy induced by myocardial infarction or other aetiology.

Effects of Intravenous Atrial Natriuretic Peptide on Cardiac Sympathetic Nerve Activity and Left Ventricular Remodeling in Patients With First Anterior Acute Myocardial Infarction

OBJECTIVES

We sought to evaluate the effects of atrial natriuretic peptide (ANP) on cardiac sympathetic nerve activity (CSNA) and left ventricular (LV) remodeling in patients with first anterior acute myocardial infarction (AMI) after primary coronary angioplasty.

BACKGROUND

The activation of the renin-angiotensin-aldosterone system (RAAS) prevents the uptake of norepinephrine in the myocardium. Atrial natriuretic peptide, a circulating hormone of cardiac origin, has vasodilatory and diuretic properties, and can inhibit the RAAS.

METHODS

We studied 50 patients with first anterior AMI who were randomly assigned to receive ANP (group A) or isosorbide dinitrate (group B) before and after primary coronary angioplasty. The ANP or ISDN was continuously infused >48 h. The extent score (ES) was determined from 99mTc-pyrophosphate scintigraphy to evaluate the area of initial myocardial damage 3 to 5 days after primary angioplasty. The LV end-diastolic volume (LVEDV) and LV ejection fraction (LVEF) were determined by left ventriculography 2 weeks later. The delayed heart/mediastinum count (H/M) ratio, delayed total defect score (TDS), and washout rate (WR) were determined from 123I-meta-iodobenzylguanidine scintigraphy after 3 weeks.

RESULTS

After primary angioplasty, age, gender, risk factors, peak serum creatine phosphokinase concentration, recanalization time, and ES were similar in the 2 groups. However, in group A (n = 25), the TDS was significantly lower (34 +/- 8 vs. 41 +/- 8; p < 0.05), the H/M ratio was significantly higher (1.96 +/- 0.18 vs. 1.74 +/- 0.23; p < 0.05), and the WR was significantly lower (35 +/- 8% vs. 44 +/- 12%; p < 0.005) than in group B (n = 25). Moreover, the LVEDV and LVEF in group A were better than in group B (LVEDV: 85.5 +/- 28.5 ml vs. 106.3 +/- 39.4 ml [p < 0.05]; LVEF: 47.9 +/- 10.2% vs. 41.5 +/- 11.8% [p < 0.05]).

CONCLUSIONS

Intravenous ANP improves CSNA and prevents LV remodeling in patients with first anterior AMI.

Post-conditioning induced cardioprotection requires signaling through a redox-sensitive mechanism, mitochondrial ATP-sensitive K+ channel and protein kinase C activation

Post-conditioning (Post-C) induced cardioprotection involves activation of guanylyl-cyclase. In the ischemic preconditioning scenario, the downstream targets of cGMP include mitochondrial ATP-sensitive K(+) (mK(ATP)) channels and protein kinase C (PKC), which involve reactive oxygen species (ROS) production. This study tests the hypothesis that mK(ATP), PKC and ROS are also involved in the Post-C protection. Isolated rat hearts underwent 30 min global ischemia (I) and 120 min reperfusion (R) with or without Post-C (i.e., 5 cycles of 10 s R/I immediately after the 30 min ischemia). In 6 groups (3 with and 3 without Post-C) either mK(ATP) channel blocker, 5- hydroxydecanoate (5-HD), or PKC inhibitor, chelerythrine (CHE) or ROS scavenger, N-acetyl-cysteine (NAC), were given during the entire reperfusion (120 min). In other 6 groups (3 with and 3 without Post-C), 5-HD, CHE or NAC were infused for 117 min only starting after 3 min of reperfusion not to interfere with the early effects of Post-C and/or reperfusion. In an additional group NAC was given during Post-C maneuvers (i.e., 3 min only). Myocardial damage was evaluated using nitro-blue tetrazolium staining and lactate dehydrogenase (LDH) release. Post-C attenuated myocardial infarct size (21 +/- 3% vs. 64 +/- 5% in control; p < 0.01). Such an effect was abolished by 5-HD or CHE given during either the 120 or 117 min of reperfusion as well as by NAC given during the 120 min or the initial 3 min of reperfusion. However, delayed NAC (i.e., 117 min infusion) did not alter the protective effect of Post- C (infarct size 32 +/- 5%; p < 0.01 vs. control, NS vs. Post-C). CHE, 5-HD or NAC given in the absence of Post-C did not alter the effects of I/R. Similar results were obtained in terms of LDH release. Our data show that Post-C induced protection involves an early redox-sensitive mechanism as well as a persistent activation of mK(ATP) and PKC, suggesting that the mK(ATP)/ROS/PKC pathway is involved in post-conditioning.

Atrial natriuretic peptide reverses the negative functional effects of stunning in rabbit myocardium

We tested the hypothesis that atrial natriuretic peptide (ANP) would decrease both the effects of myocardial stunning and oxygen consumption in rabbit hearts. In two groups of anesthetized open-chest rabbits, myocardial stunning was produced by two 15 min occlusions of the left anterior descending (LAD) artery separated by 15 min of reperfusion. Either ANP (0.2 mg) or vehicle (lactated Ringers) was then injected into the affected area of the left ventricle. In a third group, ANP was injected into the LAD region of non-stunned rabbits. Hemodynamic (heart rate, aortic and left ventricular pressures) and functional (wall thickening (WT), delay of onset of WT, and rate of WT) parameters were measured. Coronary blood flow (microspheres) and O2 extraction (microspectrophotometry) were used to determine myocardial O2 consumption. Stunning was demonstrated by an increase in the time delay to contraction and depressed WT. In the control group, baseline delay to contraction was 25+/-7 ms, and this increased to 84+/-16 following stunning and vehicle administration. In the ANP group, baseline delay was 20+/-6 at baseline and after stunning and ANP administration it was 30+/-7. Wall thickening decreased by approximately 30% with stunning and vehicle but only 8% in the ANP treated hearts. Stunning did not affect regional O2 consumption (6.0+/-1.1 stunned vs. 7.4+/-1.2 mlO2/min/100g non-stunned). ANP administration did not affect O2 consumption (7.3+/-1.7 stunned vs. 6.4+/-1.0 non-stunned). We therefore concluded that ANP administration reversed the effects of stunning without alteration in local O2 consumption in stunned myocardium.

Effect of sildenafil on reperfusion function, infarct size, and cyclic nucleotide levels in the isolated rat heart model

We have previously shown that NO-donor induced elevation in myocardial cGMP levels is associated with improved reperfusion function of the isolated rat heart. The phosphodiesterase 5 (PDE 5) inhibitor, sildenafil could potentially increase myocardial cGMP levels and thus protect the heart against ischaemic/reperfusion injury.

METHODS

To test our hypothesis we treated the isolated working rat heart with vehicle, OR sildenafil (10, 20, 50, 100, 200 nM), OR sildenafil (50 nM) plus a sarcolemmal (HMR 1098) or a mitochondrial (5-Hydroxydecanoate (5-HD)) K(ATP) channel blocker. Hearts were then subjected to 20 min global, or 35 min regional ischaemia at 37( composite function)C before reperfusion function (aortic output, coronary flow and aortic pressure) and infarct size were documented. Pre-ischaemic, ischaemic and reperfusion myocardial cAMP and cGMP concentrations were determined.

RESULTS

Low concentrations of sildenafil (10, 20 and 50 nM) improved reperfusion aortic output (AO) recovery (61.4+/- 4.5%, 64.8 +/- 5.2% and 62.3 +/- 5.0% vs. 45.4 +/- 3.8% for controls (p < 0.05)) and infarct size, while high concentrations (200 nM) worsened AO recovery (24.9 +/- 4.9.0%, p < 0.05). Myocardial cGMP levels of ischaemic tissue were elevated (34.7 +/- 2.4 vs. 27.3 +/- 2.2 pmol/g ww) and cAMP levels were suppressed (0.59 +/- 0.03 vs. 0.87 +/- 0.06 nmol/g ww) in the sildenafil (50 nM) treated hearts. Co-perfusion with sildenafil plus HMR 1098 decreased AO recovery (21.7 +/- 7.6% vs. 62.3 +/- 5.0% for sildenafil alone, p < 0.05) and increased infarct size (29.7 +/- 2.04% vs. 8.6 +/- 2.39% for sildenafil alone, p < 0.05).Similarly, sildenafil plus 5-HD decreased reperfusion AO recovery (44.4 +/- 6.0% vs. 62.3 +/- 5.0% for sildenafil alone, p < 0.05) and increased infarct size (33.8 +/- 1.62% vs. 8.6 +/- 2.39% for sildenafil alone, p < 0.05).

CONCLUSIONS

(1) Pretreatment with low concentrations of sildenafil (20-50 nM) improves, while higher concentrations (200 nM) worsen reperfusion function in this model. (2) Low concentrations of sildenafil (20-50 nM) decrease infarct size while the higher concentrations had no effect. (3) These protective properties of low concentrations of sildenafil may be related to its cGMP elevating and cAMP suppressing effects in the ischaemic heart. (4) Possible end-effectors for sildenafil in the ischaemic heart include the mitochondrial and sarcolemmal K(ATP) channel.

The role of atrial natriuretic peptide in the immune system

Atrial natriuretic peptide (ANP) is a hormone predominately produced by the heart atria which regulates the water and salt balance as well as blood pressure homeostasis. Being expressed in various parts of the immune system a link of the peptide to the immune system has been proposed. In fact, this review focus on effects of ANP in the immune system and reports about the role of the peptide in innate immune functions as well as in the adaptive immune response.

ANP-induced decrease of iron regulatory protein activity is independent of HO-1 induction

Atrial natriuretic peptide (ANP)-preconditioned livers are protected from ischemia-reperfusion injury. ANP-treated organs show increased expression of heme oxygenase (HO)-1. Because HO-1 liberates bound iron, the aim of our study was to determine whether ANP affects iron regulatory protein (IRP) activity and, thus, the levels of ferritin. Rat livers were perfused with Krebs-Henseleit buffer [+/-ANP, 8-bromo-cGMP (8-Br-cGMP), and tin protoporphyrin, 20 min], stored in University of Wisconsin solution (4 degrees C, 24 h), and reperfused (120 min). IRP activity was assessed by gel-shift assays, and ferritin, IRP phosphorylation, and PKC localization were assessed by Western blot. Control livers displayed decreased IRP activity at the end of ischemia but no change in ferritin content during ischemia and reperfusion. ANP-pretreated livers showed reduced IRP activity, an effect mimicked by 8-Br-cGMP. Ferritin levels were increased in ANP-pretreated organs. Simultaneous perfusion of livers with ANP and tin protoporphyrin did not reduce ANP-induced action, arguing against a role for HO-1 in changes in IRP activity. ANP and 8-Br-cGMP decreased membrane localization of PKC-alpha and PKC-epsilon, but this modulation of PKC seems unrelated to inhibition of IRP binding. This work shows the cGMP-mediated attenuation of IRP binding activity by ANP, which results in increased hepatic ferritin levels. This change in IRPs is independent of ANP-induced HO-1 and reduced PKC activation.