Protection against hypoxia-reoxygenation in the absence of poly (ADP-ribose) synthetase in isolated working hearts

NAD+ Metabolism as an Emerging Therapeutic Target for Cardiovascular Diseases Associated With Sudden Cardiac Death

In addition to its central role in mediating oxidation reduction in fuel metabolism and bioenergetics, nicotinamide adenine dinucleotide (NAD⁺) has emerged as a vital co-substrate for a number of proteins involved in diverse cellular processes, including sirtuins, poly(ADP-ribose) polymerases and cyclic ADP-ribose synthetases. The connection with aging and age-associated diseases has led to a new wave of research in the cardiovascular field. Here, we review the basics of NAD⁺ homeostasis, the molecular physiology and new advances in ischemic-reperfusion injury, heart failure, and arrhythmias, all of which are associated with increased risks for sudden cardiac death. Finally, we summarize the progress of NAD⁺-boosting therapy in human cardiovascular diseases and the challenges for future studies.

Regulation of cell death in the cardiovascular system

The adult heart is a post-mitotic terminally differentiated organ; therefore, beyond development, cardiomyocyte cell death is maladaptive. Heart disease is the leading cause of death in the world and aberrant cardiomyocyte cell death is the underlying problem for most cardiovascular-related diseases and fatalities. In this chapter, we will discuss the different cell death mechanisms that engage during normal cardiac development, aging, and disease states. The most abundant loss of cardiomyocytes occurs during a myocardial infarction, when the blood supply to the heart is obstructed, and the affected myocardium succumbs to cell death. Originally, this form of cell death was considered to be unregulated; however, research from the last half a century clearly demonstrates that this form of cell death is multifaceted and employees various degrees of regulation. We will explore all of the cell death pathways that have been implicated in this disease state and the potential interplay between them. Beyond myocardial infarction, we also explore the role and mechanisms of cardiomyocyte cell death in heart failure, myocarditis, and chemotherapeutic-induced cardiotoxicity. Inhibition of cardiomyocyte cell death has extensive therapeutic potential that will increase the longevity and health of the human heart.

Fundamental Mechanisms of Regulated Cell Death and Implications for Heart Disease

Twelve regulated cell death programs have been described. We review in detail the basic biology of nine including death receptor-mediated apoptosis, death receptor-mediated necrosis (necroptosis), mitochondrial-mediated apoptosis, mitochondrial-mediated necrosis, autophagy-dependent cell death, ferroptosis, pyroptosis, parthanatos, and immunogenic cell death. This is followed by a dissection of the roles of these cell death programs in the major cardiac syndromes: myocardial infarction and heart failure. The most important conclusion relevant to heart disease is that regulated forms of cardiomyocyte death play important roles in both myocardial infarction with reperfusion (ischemia/reperfusion) and heart failure. While a role for apoptosis in ischemia/reperfusion cannot be excluded, regulated forms of necrosis, through both death receptor and mitochondrial pathways, are critical. Ferroptosis and parthanatos are also likely important in ischemia/reperfusion, although it is unclear if these entities are functioning as independent death programs or as amplification mechanisms for necrotic cell death. Pyroptosis may also contribute to ischemia/reperfusion injury, but potentially through effects in non-cardiomyocytes. Cardiomyocyte loss through apoptosis and necrosis is also an important component in the pathogenesis of heart failure and is mediated by both death receptor and mitochondrial signaling. Roles for immunogenic cell death in cardiac disease remain to be defined but merit study in this era of immune checkpoint cancer therapy. Biology-based approaches to inhibit cell death in the various cardiac syndromes are also discussed.

Prolonging hypothermic ischaemic cardiac and vascular storage by inhibiting the activation of the nuclear enzyme poly(adenosine diphosphate-ribose) polymerase

OBJECTIVES

Heart transplantation is the standard treatment in end-stage heart failure and at shortage of cardiac allografts is its major limiting factor. Striving to optimize the use of this limited resource, the aspect that long distance procurement may increase the available donor pool must be taken into consideration. As poly(ADP-ribose)polymerase (PARP)-activation has been identified as a key pathway of reperfusion injury, we assessed the hypothesis that its inhibition would allow an extension of cold preservation time and protect the graft against ischaemia/reperfusion injury.

METHODS

Hearts from donor rats were explanted, stored in a preservation solution (Custodiol) at 4 °C for 4 h or 8 h, and heterotopically transplanted. A vehicle or the PARP-inhibitor, INO-1001 (5 mg/kg), was administered during the reperfusion period. We evaluated post-transplant graft function with a Millar micromanometer at different left-ventricular volumes. Additionally, in organ bath experiments the effect of PARP-inhibition on endothelium-dependent and -independent vasorelaxation was evaluated after long-term cold ischaemic storage/warm reperfusion.

RESULTS

PARP-inhibition resulted in a better systolic functional recovery of grafts submitted to 4 h and 8 h ischaemia. Furthermore, INO-1001 decreased the left-ventricular end-diastolic pressure after 8 h of ischaemia. Coronary blood flow was significantly higher after PARP-inhibition in comparison to controls. Endothelium-dependent vasorelaxation was significantly better in the INO-1001-groups than in the vehicle-treated transplant groups. After 24-h hypothermic storage, treatment of aortic ring with INO-1001 during reoxygenation significantly improved endothelial dysfunction.

CONCLUSIONS

By inhibiting the PARP activation, INO-1001 can protect the graft and endothelium from the injury that is caused by prolonged cold myocardial ischaemia/reperfusion, thereby improving post-transplant graft function.

Olaparib protects cardiomyocytes against oxidative stress and improves graft contractility during the early phase after heart transplantation in rats

BACKGROUND AND PURPOSE

Olaparib, rucaparib and niraparib, potent inhibitors of poly(ADP-ribose) polymerase (PARP) are approved as anti-cancer drugs in humans. Considering the previously demonstrated role of PARP in various forms of acute and chronic myocardial injury, we tested the effects of olaparib in in-vitro models of oxidative stress in cardiomyocytes, and in an in vivo model of cardiac transplantation.

EXPERIMENTAL APPROACH

H9c2-embryonic rat heart-derived myoblasts pretreated with vehicle or olaparib (10μM) were challenged with either hydrogen peroxide (H₂ O₂ ) or with glucose oxidase (GOx, which generates H₂ O₂ in the tissue culture medium). Cell viability assays (MTT, lactate dehydrogenase) and Western blotting for PARP and its product, PAR was performed. Heterotopic heart transplantation was performed in Lewis rats; recipients were treated either with vehicle or olaparib (10 mg kg^-1 ). Left ventricular function of transplanted hearts was monitored via a Millar catheter. Multiple gene expression in the graft was measured by qPCR.

KEY RESULTS

Olaparib blocked autoPARylation of PARP1 and attenuated the rapid onset of death in H9c2 cells, induced by H₂ O₂ , but did not affect cell death following chronic, prolonged oxidative stress induced by GOx. In rats, after transplantation, left ventricular systolic and diastolic function were improved by olaparib. In the transplanted hearts, olaparib also reduced gene expression for c-jun, caspase-12, catalase, and NADPH oxidase-2.

CONCLUSIONS AND IMPLICATIONS

Olaparib protected cardiomyocytes against oxidative stress and improved graft contractility in a rat model of heart transplantation. These findings raise the possibility of repurposing this clinically approved oncology drug, to be used in heart transplantation.

LINKED ARTICLES

This article is part of a themed section on Inventing New Therapies Without Reinventing the Wheel: The Power of Drug Repurposing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.2/issuetoc.

Continuous inhibition of poly(ADP-ribose) polymerase does not reduce reperfusion injury in isolated rat heart

Poly(ADP-ribose) polymerase (PARP), an enzyme that is important to the regulation of nuclear function, is activated by DNA strand breakage. In massive DNA damage, PARP is overactivated, exhausting nicotinamide adenine dinucleotide and leading to cell death. Recent studies have succeeded in reducing cellular damage in ischemia/reperfusion by inhibiting PARP. However, PARP plays an important part in the DNA repair system, and its inhibition may be hazardous in certain situations. We compared the short-time inhibition of PARP against continuous inhibition during ischemia/reperfusion using isolated rat hearts. The hearts were reperfused after 21 minutes of ischemia with a bolus injection of 3-aminobenzamide (3-AB) (10 mg/kg) followed by continuous 3-AB infusion (50 μM) for the whole reperfusion period or for the first 6 minutes or without 3-AB. At the end of reperfusion, contractile function, high-energy phosphate content, nicotinamide adenine dinucleotide content, and infarcted area were significantly preserved in the 3-AB 6-minute group. In the 3-AB continuous group, these advantages were not apparent. At the end of reperfusion, PARP cleavage had significantly proceeded in the 3-AB continuous group, indicating initiation of the apoptotic cascade. Thus, continuous PARP inhibition by 3-AB does not reduce reperfusion injury in the isolated rat heart, which may be because of acceleration of apoptosis.

Therapeutic applications of PARP inhibitors: anticancer therapy and beyond

The aim of this article is to describe the current and potential clinical translation of pharmacological inhibitors of poly(ADP-ribose) polymerase (PARP) for the therapy of various diseases. The first section of the present review summarizes the available preclinical and clinical data with PARP inhibitors in various forms of cancer. In this context, the role of PARP in single-strand DNA break repair is relevant, leading to replication-associated lesions that cannot be repaired if homologous recombination repair (HRR) is defective, and the synthetic lethality of PARP inhibitors in HRR-defective cancer. HRR defects are classically associated with BRCA1 and 2 mutations associated with familial breast and ovarian cancer, but there may be many other causes of HRR defects. Thus, PARP inhibitors may be the drugs of choice for BRCA mutant breast and ovarian cancers, and extend beyond these tumors if appropriate biomarkers can be developed to identify HRR defects. Multiple lines of preclinical data demonstrate that PARP inhibition increases cytotoxicity and tumor growth delay in combination with temozolomide, topoisomerase inhibitors and ionizing radiation. Both single agent and combination clinical trials are underway. The final part of the first section of the present review summarizes the current status of the various PARP inhibitors that are in various stages of clinical development. The second section of the present review summarizes the role of PARP in selected non-oncologic indications. In a number of severe, acute diseases (such as stroke, neurotrauma, circulatory shock and acute myocardial infarction) the clinical translatability of PARP inhibition is supported by multiple lines of preclinical data, as well as observational data demonstrating PARP activation in human tissue samples. In these disease indications, PARP overactivation due to oxidative and nitrative stress drives cell necrosis and pro-inflammatory gene expression, which contributes to disease pathology. Accordingly, multiple lines of preclinical data indicate the efficacy of PARP inhibitors to preserve viable tissue and to down-regulate inflammatory responses. As the clinical trials with PARP inhibitors in various forms of cancer progress, it is hoped that a second line of clinical investigations, aimed at testing of PARP inhibitors for various non-oncologic indications, will be initiated, as well.

PARP inhibition attenuates histopathological lesion in ischemia/reperfusion renal mouse model after cold prolonged ischemia

We test the hypothesis that PARP inhibition can decrease acute tubular necrosis (ATN) and other renal lesions related to prolonged cold ischemia/reperfusion (IR) in kidneys preserved at 4°C in University of Wisconsin (UW) solution. Material and Methods. We used 30 male Parp1^+/+ wild-type and 15 male Parp1^0/0 knockout C57BL/6 mice. Fifteen of these wild-type mice were pretreated with 3,4-dihydro-5-[4-(1-piperidinyl)butoxyl]-1(2H)-isoquinolinone (DPQ) at a concentration of 15 mg/kg body weight, used as PARP inhibitor. Subgroups of mice were established (A: IR 45 min/6 h; B: IR + 48 h in UW solution; and C: IR + 48 h in UW solution plus DPQ). We processed samples for morphological, immunohistochemical, ultrastructural, and western-blotting studies. Results. Prolonged cold ischemia time in UW solution increased PARP-1 expression and kidney injury. Preconditioning with PARP inhibitor DPQ plus DPQ supplementation in UW solution decreased PARP-1 nuclear expression in renal tubules and renal damage. Parp1^0/0 knockout mice were more resistant to IR-induced renal lesion. In conclusion, PARP inhibition attenuates ATN and other IR-related renal lesions in mouse kidneys under prolonged cold storage in UW solution. If confirmed, these data suggest that pharmacological manipulation of PARP activity may have salutary effects in cold-stored organs at transplantation.

Pathophysiology of perinatal asphyxia: can we predict and improve individual outcomes?

Perinatal asphyxia occurs still with great incidence whenever delivery is prolonged, despite improvements in perinatal care. After asphyxia, infants can suffer from short- to long-term neurological sequelae, their severity depend upon the extent of the insult, the metabolic imbalance during the re-oxygenation period and the developmental state of the affected regions. Significant progresses in understanding of perinatal asphyxia pathophysiology have achieved. However, predictive diagnostics and personalised therapeutic interventions are still under initial development. Now the emphasis is on early non-invasive diagnosis approach, as well as, in identifying new therapeutic targets to improve individual outcomes. In this review we discuss (i) specific biomarkers for early prediction of perinatal asphyxia outcome; (ii) short and long term sequelae; (iii) neurocircuitries involved; (iv) molecular pathways; (v) neuroinflammation systems; (vi) endogenous brain rescue systems, including activation of sentinel proteins and neurogenesis; and (vii) therapeutic targets for preventing or mitigating the effects produced by asphyxia.

Improved poststorage cardiac function by poly (ADP-ribose) polymerase inhibition: role of phosphatidylinositol 3-kinase Akt pathway

BACKGROUND

Inhibition of poly(ADP-ribose) polymerase 1 (PARP) has been shown to be effective in minimizing cardiac ischemia reperfusion injury. We investigated the cardioprotective effect of the PARP inhibitor, INO-1153, in isolated working rat hearts after 6 hr of hypothermic storage in Celsior.

METHODS

Hearts were treated with 1 muM INO-1153 before hypothermic storage, at cardioplegia and storage or after hypothermic storage. Hearts not exposed to INO-1153 served as controls. Another group was pretreated with the phosphatidylinositol 3-kinase inhibitor Wortmannin (0.1 muM) before storage in INO-1153-supplemented Celsior. After baseline measurement of aortic flow, heart rate, coronary flow, and cardiac output were obtained, hearts were arrested and stored in Celsior at 2-3 degrees C for 6 hr. After storage, hearts were reperfused for 15 min before performing work for a further 30 min, at which time poststorage indices of cardiac function were remeasured then heart tissue was stored at -80 degrees C for Western blot analysis.

RESULTS

The presence of INO-1153 during prestorage perfusion or during cardioplegia and storage significantly improved poststorage cardiac function. Functional improvements produced by INO-1153 were completely abolished by Wortmnanin pretreatment. Western blots showed a significant increase in phospho-Akt in presence of INO-1153, which was inhibited by Wortmannin.

CONCLUSION

Activation of the prosurvival phosphatidylinositol 3-kinase-Akt pathway was involved in the protective action of PARP inhibition in this model of donor heart procurement and hypothermic storage. Importantly for the logistics of clinical organ procurement, maximum protection is observed when the PARP inhibitor is included in the cardioplegic storage solution.

Novel pharmacological approaches to the treatment of renal ischemia-reperfusion injury: a comprehensive review

Renal ischemia-reperfusion (I-R) contributes to the development of ischemic acute renal failure (ARF). Multi-factorial processes are involved in the development and progression of renal I-R injury with the generation of reactive oxygen species, nitric oxide and peroxynitrite, and the decline of antioxidant protection playing major roles, leading to dysfunction, injury, and death of the cells of the kidney. Renal inflammation, involving cytokine/adhesion molecule cascades with recruitment, activation, and diapedesis of circulating leukocytes is also implicated. Clinically, renal I-R occurs in a variety of medical and surgical settings and is responsible for the development of acute tubular necrosis (a characteristic feature of ischemic ARF), e.g., in renal transplantation where I-R of the kidney directly influences graft and patient survival. The cellular mechanisms involved in the development of renal I-R injury have been targeted by several pharmacological interventions. However, although showing promise in experimental models of renal I-R injury and ischemic ARF, they have not proved successful in the clinical setting (e.g., atrial natriuretic peptide, low-dose dopamine). This review highlights recent pharmacological developments, which have shown particular promise against experimental renal I-R injury and ischemic ARF, including novel antioxidants and antioxidant enzyme mimetics, nitric oxide and nitric oxide synthase inhibitors, erythropoietin, peroxisome-proliferator-activated receptor agonists, inhibitors of poly(ADP-ribose) polymerase, carbon monoxide-releasing molecules, statins, and adenosine. Novel approaches such as recent research involving combination therapies and the potential of non-pharmacological strategies are also considered.

Role of poly(ADP-ribose) polymerase 1 (PARP-1) in cardiovascular diseases: the therapeutic potential of PARP inhibitors

Accumulating evidence suggests that the reactive oxygen and nitrogen species are generated in cardiomyocytes and endothelial cells during myocardial ischemia/reperfusion injury, various forms of heart failure or cardiomyopathies, circulatory shock, cardiovascular aging, diabetic complications, myocardial hypertrophy, atherosclerosis, and vascular remodeling following injury. These reactive species induce oxidative DNA damage and consequent activation of the nuclear enzyme poly(ADP-ribose) polymerase 1 (PARP-1), the most abundant isoform of the PARP enzyme family. PARP overactivation, on the one hand, depletes its substrate, NAD+, slowing the rate of glycolysis, electron transport, and ATP formation, eventually leading to the functional impairment or death of the endothelial cells and cardiomyocytes. On the other hand, PARP activation modulates important inflammatory pathways, and PARP-1 activity can also be modulated by several endogenous factors such as various kinases, purines, vitamin D, thyroid hormones, polyamines, and estrogens, just to mention a few. Recent studies have demonstrated that pharmacological inhibition of PARP provides significant benefits in animal models of cardiovascular disorders, and novel PARP inhibitors have entered clinical development for various cardiovascular indications. Because PARP inhibitors can enhance the effect of anticancer drugs and decrease angiogenesis, their therapeutic potential is also being explored for cancer treatment. This review discusses the therapeutic effects of PARP inhibitors in myocardial ischemia/reperfusion injury, various forms of heart failure, cardiomyopathies, circulatory shock, cardiovascular aging, diabetic cardiovascular complications, myocardial hypertrophy, atherosclerosis, vascular remodeling following injury, angiogenesis, and also summarizes our knowledge obtained from the use of PARP-1 knockout mice in the various preclinical models of cardiovascular diseases.

Poly(ADP-ribose) polymerase-1 hyperactivation and impairment of mitochondrial respiratory chain complex I function in reperfused mouse hearts

Poly(ADP-ribose) polymerase-1 (PARP-1), the most abundant member of the PARP family, is a nuclear enzyme that catalyzes ADP-ribose transfer from NAD+ to specific acceptor proteins in response to DNA damage. Excessive PARP-1 activation is an important cause of infarction and contractile dysfunction in heart tissue during interruptions of blood flow. The mechanisms by which PARP-1 inhibition and disruption dramatically improve metabolic recovery and reduce oxidative stress during cardiac reperfusion have not been fully explored. We developed a mouse heart experimental protocol to test the hypothesis that mitochondrial respiratory complex I is a downstream mediator of beneficial effects of PARP-1 inhibition or disruption. Pharmacological inhibition of PARP-1 activity produced no deterioration of hemodynamic function in C57BL/6 mouse hearts. Hearts from PARP-1 knockout mice also exhibited normal baseline contractility. Prolonged ischemia-reperfusion produced a selective defect in complex I function distal to the NADH dehydrogenase component. PARP-1 inhibition and PARP-1 gene disruption conferred equivalent protection against mitochondrial complex I injury and were strongly associated with improvement in myocardial energetics, contractility, and tissue viability. Interestingly, ischemic preconditioning abolished cardioprotection stimulated by PARP-1 gene disruption. Treatment with the antioxidant N-(2-mercaptopropionyl)-glycine or xanthine oxidase inhibitor allopurinol restored the function of preconditioned PARP-1 knockout hearts. This investigation establishes a strong association between PARP-1 hyperactivity and mitochondrial complex I dysfunction in cardiac myocytes. Our findings advance understanding of metabolic regulation in myocardium and identify potential therapeutic targets for prevention and treatment of ischemic heart disease.

Cardioprotective effects of poly(ADP-ribose) polymerase inhibition

Free radical and oxidant production in cardiac myocytes during ischemia/reperfusion, cardiomyopathy, cardiotoxic drug exposure and ageing leads to DNA strand-breakage which activates the nuclear enzyme poly(ADP-ribose) polymerase (PARP) and initiates an energy consuming, inefficient cellular metabolic cycle with transfer of the ADP-ribosyl moiety of NAD+ to protein acceptors. These processes lead to the functional impairment of the myocytes and promote myocyte death. During the last decade a growing number of experimental studies demonstrated the beneficial effects of PARP inhibition in cell cultures through rodent models and more recently in pre-clinical large animal models of regional and global ischemia/reperfusion injury and various forms of heart failure. The current article provides an overview of the experimental evidence implicating PARP as a pathophysiological modulator of cardiac myocyte injury in vitro and in vivo.

Beneficial effects of 5-aminoisoquinolinone, a novel, potent, water-soluble, inhibitor of poly (ADP-ribose) polymerase, in a rat model of splanchnic artery occlusion and reperfusion

Poly(ADP-ribose) polymerase (PARP), a nuclear enzyme activated by strand breaks in DNA, plays an important role in the tissue injury associated with ischemia-reperfusion and inflammation. Splanchnic artery occlusion and reperfusion causes an enhanced formation of reactive oxygen species which contribute to the pathophysiology of shock. The aim of the present study was to investigate the effects of 5-aminoisoquinolinone (5-AIQ), a potent water-soluble inhibitor of poly(ADP-ribose) polymerase (PARP), in the pathogenesis of splanchnic artery occlusion shock. Splanchnic artery occlusion shock was induced in rats by clamping both the superior mesenteric artery and the celiac artery for 45 min, followed thereafter by release of the clamp (reperfusion). At 60 min after reperfusion, all animals were sacrificed for histological examination and biochemical studies. Treatment of rats with 5-AIQ (3 mg/kg i.v.), attenuated the fall of mean arterial blood pressure caused by splanchnic artery occlusion shock. 5-AIQ also attenuated the ileum injury as well as the increase in the tissue levels of myeloperoxidase and malondialdehyde caused by splanchnic artery occlusion shock in the ileum. The immunohistochemical examination also demonstrated a marked increase in the immunoreactivity to PAR, nitrotyrosine, and intercellular adhesion molecule (ICAM-1) in the necrotic ileum from splanchnic artery occlusion-shocked rats. 5-AIQ treatment significantly reduced the increase of positive staining for PAR, nitrotyrosine and ICAM-I. In conclusion, these results show that 5-AIQ, a new water-soluble potent inhibitor of poly(ADP-ribose) polymerase, exerts multiple protective effects in splanchnic artery occlusion/reperfusion shock.

Poly(ADP-Ribose) Polymerase Contributes to the Development of Myocardial Infarction in Diabetic Rats and Regulates the Nuclear Translocation of Apoptosis-Inducing Factor

Activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP)-1 by oxidant-mediated DNA damage is an important pathway of cell dysfunction and tissue injury during myocardial infarction. Because diabetes mellitus can substantially alter cellular signal transduction pathways, we have now investigated whether the PARP pathway also contributes to myocardial ischemia/reperfusion (MI/R) injury in diabetes mellitus in rodents. Myocardial ischemia/reperfusion in control and streptozotocin-diabetic rats was induced by transient ligation of the left anterior descending coronary artery. PARP activation was inhibited by the isoindolinone derivative PARP inhibitor INO-1001. In diabetic rats, a more pronounced degree of myocardial contractile dysfunction developed, which also was associated with a larger infarct size, and significant mortality compared with nondiabetic rats. Inhibition of PARP provided a similar degree of myocardial protective effect in diabetic and nondiabetic animals and reduced infarct size and improved myocardial contractility. In diabetic rats, PARP inhibition reduced mortality during the reperfusion phase. There was marked activation of PARP in the ischemic/reperfused myocardium, which was blocked by INO-1001. In addition, there was a significant degree of mitochondrial-to-nuclear translocation of the cell death effector apoptosis-inducing factor (AIF) in myocardial infarction, which was blocked by pharmacological inhibition of PARP. The role of PARP in regulating AIF translocation in myocytes also was confirmed in an isolated perfused heart preparation. Overall, the current results demonstrate the importance of the PARP pathway in diabetic rats subjected to myocardial infarction and demonstrate the role of PARP in regulating AIF translocation in MI/R.

5-Aminoisoquinolinone reduces renal injury and dysfunction caused by experimental ischemia/reperfusion

BACKGROUND

Poly (ADP-ribose) polymerase (PARP), a nuclear enzyme activated by strand breaks in DNA, plays an important role in the development of ischemia/reperfusion (I/R) injury. The aim of this study was to investigate the effects of a water-soluble and potent PARP inhibitor, 5-aminoisoquinolinone (5-AIQ), on the renal injury and dysfunction caused by oxidative stress of the rat kidney in vitro and in vivo.

METHODS

Primary cultures of rat renal proximal tubular cells, subjected to oxidative stress caused by hydrogen peroxide (H2O2), were incubated with increasing concentrations of 5-AIQ (0.01 to 1 mmol/L) after which PARP activation, cellular injury, and cell death were measured. In in vivo experiments, anesthetized male Wistar rats were subjected to renal bilateral ischemia (45 minutes) followed by reperfusion (6 hours) in the absence or presence of 5-AIQ (0.3 mg/kg) after which renal dysfunction, injury and PARP activation were assessed.

RESULTS

Incubation of proximal tubular cells with H2O2 caused a substantial increase in PARP activity, cellular injury, and cell death, which were all significantly reduced in a concentration-dependent by 5-AIQ [inhibitory concentration 50 (IC50) approximately 0.03 mmol/L]. In vivo, renal I/R resulted in renal dysfunction, injury, and PARP activation, primarily in the proximal tubules of the kidney. Administration of 5-AIQ significantly reduced the biochemical and histologic signs of renal dysfunction and injury and markedly reduced PARP activation caused by I/R.

CONCLUSION

This study demonstrates that 5-AIQ is a potent, water soluble inhibitor of PARP activity, which can significantly reduce (1) cellular injury and death caused to primary cultures of rat proximal tubular cells by oxidative stress in vitro, and (2) renal injury and dysfunction caused by I/R of the kidney of the rat in vivo.

Poly-ADP-ribose polymerase inhibition protects against myocardial and endothelial reperfusion injury after hypothermic cardiac arrest

OBJECTIVE

Free radical production and related cytotoxicity during ischemia and reperfusion might lead to DNA strand breakage, which activates the nuclear enzyme poly-ADP-ribose synthetase and initiates an energy-consuming and inefficient cellular metabolic cycle with transfer of the adenosine diphosphate-ribosyl moiety of nicotinamide adenine dinucleotide (NAD(+)) to protein acceptors. We investigated the effects of poly-ADP-ribose synthetase inhibition on myocardial and endothelial function during reperfusion in an experimental model of cardiopulmonary bypass.

METHODS

Twelve anesthetized dogs underwent hypothermic cardiopulmonary bypass. After 60 minutes of hypothermic cardiac arrest, reperfusion was started after application of either saline vehicle (control, n = 6) or PJ34 (10 mg/kg), a potent poly-ADP-ribose synthetase inhibitor (n = 6). Biventricular hemodynamic variables were measured by means of a combined pressure-volume conductance catheter, and the slope of the end-systolic pressure-volume relationships was calculated at baseline and after 60 minutes of reperfusion. Left anterior descending coronary blood flow, endothelium-dependent vasodilatation to acetylcholine, and endothelium-independent vasodilatation to sodium nitroprusside were also determined.

RESULTS

The administration of PJ34 led to a significantly better recovery of left and right ventricular systolic function (P <.05) after 60 minutes of reperfusion. In addition, the inotropic adaptation potential of the right ventricle to an increased afterload was better preserved in the PJ34 group. Coronary blood flow was also significantly higher in the PJ34 group (P <.05). Although the vasodilatory response to sodium nitroprusside was similar in both groups, acetylcholine resulted in a significantly higher increase in coronary blood flow in the PJ34 group (P <.05).

CONCLUSIONS

Poly-ADP-ribose synthetase inhibition improves the recovery of myocardial and endothelial function after cardiopulmonary bypass with hypothermic cardiac arrest.

Poly(ADP-ribose) polymerase inhibition improves postischemic myocardial function after cardioplegia-cardiopulmonary bypass

BACKGROUND

Poly(ADP-ribose) polymerase activation has been shown to contribute to the pathogenesis of myocardial ischemia-reperfusion injury. We hypothesized that a novel poly(ADP-ribose) polymerase inhibitor, INO-1001, provides myocardial protection and improves cardiac function after regional ischemia and cardioplegia-cardiopulmonary bypass (CPB).

STUDY DESIGN

Pigs were subjected to 30 minutes of regional ischemia by distal left anterior descending coronary artery ligation followed by CPB (60 minutes) with hyperkalemic cardioplegia (45 minutes). The myocardium then was reperfused post-CPB for 90 minutes. After 15 minutes of ischemia, the treatment group (n = 6) received an INO-1001 bolus (1mg/kg) before a continuous infusion (1mg/kg/hour). Control pigs (n = 6) received vehicle solution. Left ventricular pressure was monitored, from which the maximum, positive first derivative of left ventricular pressure over time (+dP/dt) was calculated. Regional myocardial function in the ischemic area was determined by sonomicrometric analysis. Infarct size was measured as the percent of the ischemic area by tetrazolium staining. Myocardial sections were immunohistochemically stained for poly(ADP-ribose) as a measure of poly(ADP-ribose) polymerase activity and inhibition.

RESULTS

Pigs treated with INO-1001 showed improvements in the +dP/dt at 60 and 90 minutes of post-CPB reperfusion (both p = 0.03) and percent segmental shortening at 30, 60, and 90 minutes of post-CPB reperfusion (p = 0.03, 0.009, and 0.03, respectively). Infarct size was decreased in the treatment group (18.5 +/- 5.7% versus 52.0 +/- 7.7%, INO-1001 versus control, p = 0.03). Poly(ADP-ribose) was reduced in myocardial sections from INO-1001-treated animals compared with controls.

CONCLUSIONS

These results suggest that INO-1001 provides myocardial protection by reducing the extent of infarction and improves cardiac function after regional ischemia and cardioplegia-CPB.

Effects of peroxynitrite on isolated cardiac trabeculae: selective impact on myofibrillar energetic controllers

Formation of peroxynitrite and cardiac protein nitration have been implicated in multiple cardiac disease states, but their contributions to disease initiation remain undefined. We have previously observed nitration of myofibrillar regions of cardiac myocytes in several experimental and clinical settings of cardiac myocyte dysfunction and postulated that oxidative insult to key components of the contractile apparatus may be initiating events. Here we tested the hypothesis that peroxynitrite alters myofibrillar contractile function, and investigated a mechanistic role for nitration in this process. Isolated rat ventricular trabeculae were exposed to physiologically relevant concentrations of peroxynitrite and ATP-dependent contractile responses were measured. Maximal trabecular force generation was significantly impaired following 300 nM peroxynitrite exposures. Several myofibrillar proteins demonstrated increased tyrosine nitration, the most significant increases occurred in the myosin heavy chain and the myofibrillar isoform of creatine kinase. Additional functional experiments were conducted using phosphocreatine (high energy phosphate substrate for myofibrillar creatine kinase) as the primary energy substrate. Myofibrillar creatine kinase-dependent force generation was impaired at peroxynitrite concentrations as low as 50 nM, suggesting potent inactivation of the enzyme. Extent of tyrosine nitration of myofibrillar creatine kinase was negatively correlated to myofibrillar creatine kinase-dependent force generation. These data demonstrate that the cardiac contractile apparatus is highly sensitive to peroxynitrite, and that MM-CK may be a uniquely vulnerable target.

Role of poly(ADP-ribose) polymerase activation in endotoxin-induced cardiac collapse in rodents

Reactive oxygen and nitrogen species are overproduced in the cardiovascular system during circulatory shock. Oxidant-induced cell injury involves the activation of poly(ADP-ribose) polymerase (PARP). Using a dual approach of PARP-1 suppression, by genetic deletion or pharmacological inhibition with the new potent phenanthridinone PARP inhibitor PJ34 [the hydrochloride salt of N-(oxo-5,6-dihydro-phenanthridin-2-yl)-N,N-dimethylacetamide], we studied whether the impaired cardiac function in endotoxic shock is dependent upon the PARP pathway. Escherichia coli endotoxin (lipopolysaccharide, LPS) at 55 mg/kg, i.p., induced a severe depression of the systolic and diastolic contractile function, tachycardia, and a reduction in mean arterial blood pressure in both rats and mice. Treatment with PJ34 significantly improved cardiac function and increased the survival of rodents. In addition, LPS-induced depression of left ventricular performance was significantly less pronounced in PARP-1 knockout mice (PARP(-/-)) as compared with their wild-type littermates (PARP(+/+)). Thus, PARP activation in the cardiovascular system is an important contributory factor to the cardiac collapse and death associated with endotoxin shock.

Peroxynitrite in myocardial ischemia-reperfusion injury

Peroxynitrite is a highly reactive oxidant which is produced during reperfusion of the ischemic heart. The role that this molecule plays in reperfusion injury has been controversial. Many investigations have demonstrated toxic effects of peroxynitrite, whereas others have found it to be protective during reperfusion. This review surveys evidence supporting both sides and proposes that peroxynitrite is a dichotomous molecule with beneficial and detrimental effects on the reperfused heart. Its toxic effects are mediated by modification and activation of a variety of targets (including poly (ADP) ribose synthetase and matrix metalloproteinases) while its beneficial effects are primarily mediated through its reaction with thiols, resulting in the formation of NO donor compounds (S-nitrosothiols).

Pharmacologic inhibition of poly(adenosine diphosphate-ribose) polymerase may represent a novel therapeutic approach in chronic heart failure

OBJECTIVES

We investigated the effects of a novel ultrapotent poly(adenosine diphosphate-ribose) polymerase (PARP) inhibitor, PJ34, on cardiac and endothelial dysfunction in a rat model of chronic heart failure (CHF).

BACKGROUND

Overactivation of the nuclear enzyme PARP importantly contributes to the development of cell dysfunction and tissue injury in various pathophysiologic conditions associated with oxidative stress, including myocardial reperfusion injury, heart transplantation, stroke, shock, and diabetes.

METHODS

Chronic heart failure was induced in Wistar rats by chronic ligation of the left anterior descending coronary artery. Left ventricular (LV) function and ex vivo vascular contractility and relaxation were measured 10 weeks after the surgery. Nitrotyrosine (NT) formation and PARP activation were detected by immunohistochemistry.

RESULTS

Chronic heart failure induced increased NT formation and PARP activation in the myocardium and intramural vasculature, depressed LV performance, and impaired vascular relaxation of aortic rings. PJ34 significantly decreased myocardial PARP activation but not NT formation, and improved both cardiac dysfunction and vascular relaxation.

CONCLUSIONS

Poly(ADP-ribose) polymerase inhibition represents a novel approach for the experimental treatment of CHF.

Protective effect of a novel, potent inhibitor of poly(adenosine 5'-diphosphate-ribose) synthetase in a porcine model of severe bacterial sepsis

OBJECTIVE

To determine whether activation of the nuclear enzyme poly(adenosine 5'-diphosphate [ADP]-ribose) synthetase (PARS) contributes to mortality rate, myocardial dysfunction, and cardiovascular collapse in a porcine model of sepsis induced by implantation of an infected clot.

DESIGN

Prospective, random animal study.

SETTING

Research laboratory at Rush Presbyterian St. Luke's Medical Center.

SUBJECTS

Twenty pigs were chronically instrumented with intracardiac transducers to measure left ventricular pressure, sonomicrometer crystals in the left ventricle to measure short axis diameter, an ultrasonic flow meter to measure cardiac output, and catheters in the pulmonary artery and aorta to measure blood pressures and collect samples.

INTERVENTIONS

By using a randomized study design, we administered either the novel potent PARS inhibitor PJ34 (10 mg/kg for 1 hr, 2 mg x kg(-1) x hr(-1) for 96 hrs) or vehicle to pigs immediately before intraperitoneal implantation of Escherichia coli 0111.B4 (2.3 +/- 0.1 x 10(10) colony-forming units/kg)-laden fibrin clots to produce peritonitis and bacteremia.

MEASUREMENTS AND MAIN RESULTS

In vehicle-treated pigs, 12% survival was recorded at 24 hrs, whereas 83% and 66% survival was recorded in the PJ34-treated animals at 24 and 96 hrs, respectively (p <.05). PJ34 treatment attenuated bacteremia-induced increases in systemic and pulmonary vascular resistances. In controls, peritonitis induced rapid increase in plasma tumor necrosis factor-alpha. PJ34 treatment significantly attenuated this cytokine response. The formation of peroxynitrite and the activation of PARS were confirmed in hearts and lungs of the septic pigs by the immunohistochemical detection of nitrotyrosine and poly(ADP-ribose), respectively. Inhibition of PARS with PJ34 abolished poly(ADP-ribose) formation in septic animals.

CONCLUSIONS

Treatment with a potent PARS inhibitor improved survival and cardiovascular status and attenuated an important mediator component of the inflammatory response in a lethal porcine model of sepsis.

Activation of poly(ADP-ribose) polymerase contributes to development of doxorubicin-induced heart failure

Activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) by oxidant-mediated DNA damage is an important pathway of cell dysfunction and tissue injury in conditions associated with oxidative stress. Increased oxidative stress is a major factor implicated in the cardiotoxicity of doxorubicin (DOX), a widely used antitumor anthracycline antibiotic. Thus, we hypothesized that the activation of PARP may contribute to the DOX-induced cardiotoxicity. Using a dual approach of PARP-1 suppression, by genetic deletion or pharmacological inhibition with the phenanthridinone PARP inhibitor PJ34, we now demonstrate the role of PARP in the development of cardiac dysfunction induced by DOX. PARP-1+/+ and PARP-1-/- mice received a single injection of DOX (25 mg/kg i.p). Five days after DOX administration, left ventricular performance was significantly depressed in PARP-1+/+ mice, but only to a smaller extent in PARP-1-/- ones. Similar experiments were conducted in BALB/c mice treated with PJ34 or vehicle. Treatment with a PJ34 significantly improved cardiac dysfunction and increased the survival of the animals. In addition PJ34 significantly reduced the DOX-induced increase in the serum lactate dehydrogenase and creatine kinase activities but not metalloproteinase activation in the heart. Thus, PARP activation contributes to the cardiotoxicity of DOX. PARP inhibitors may exert protective effects against the development of severe cardiac complications associated with the DOX treatment.

The role of poly(ADP-ribose) polymerase activation in the development of myocardial and endothelial dysfunction in diabetes

Patients with diabetes exhibit a high incidence of diabetic cardiomyopathy and vascular complications, which underlie the development of retinopathy, nephropathy, and neuropathy and increase the risk of hypertension, stroke, and myocardial infarction. There is emerging evidence that the activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) importantly contributes to the development of endothelial dysfunction in a streptozotocin-induced model of diabetes. We investigated the role of PARP activation in the pathogenesis of cardiac dysfunction in streptozotocin-induced and genetic (nonobese diabetic) models of diabetes in rats and mice. Development of diabetes was accompanied by hyperglycemia, cardiac PARP activation, a selective loss of endothelium-dependent vasodilation in the thoracic aorta, and an early diastolic dysfunction of the heart. Treatment with a novel potent phenanthridinone-based PARP inhibitor, PJ34, starting 1 week after the onset of diabetes, restored normal vascular responsiveness and significantly improved cardiac dysfunction, despite the persistence of severe hyperglycemia. The beneficial effect of PARP inhibition persisted even after several weeks of discontinuation of the treatment. Thus, PARP activation plays a central role in the pathogenesis of diabetic cardiovascular (cardiac as well as endothelial) dysfunction. PARP inhibitors may exert beneficial effects against the development of cardiovascular complications in diabetes.

Potential clinical applications of poly(ADP-ribose) polymerase (PARP) inhibitors

Poly(ADP-ribose) polymerases (PARPs) are defined as cell signaling enzymes that catalyze the transfer of ADP-ribose units from NAD(+)to a number of acceptor proteins. PARP-1, the best characterized member of the PARP family, that presently includes six members, is an abundant nuclear enzyme implicated in cellular responses to DNA injury provoked by genotoxic stress (oxygen radicals, ionizing radiations and monofunctional alkylating agents). Due to its involvement either in DNA repair or in cell death, PARP-1 is regarded as a double-edged regulator of cellular functions. In fact, when the DNA damage is moderate, PARP-1 participates in the DNA repair process. Conversely, in the case of massive DNA injury, elevated PARP-1 activation leads to rapid NAD(+)/ATP consumption and cell death by necrosis. Excessive PARP-1 activity has been implicated in the pathogenesis of numerous clinical conditions such as stroke, myocardial infarction, shock, diabetes and neurodegenerative disorders. PARP-1 could therefore be considered as a potential target for the development of pharmacological strategies to enhance the antitumor efficacy of radio- and chemotherapy or to treat a number of clinical conditions characterized by oxidative or NO-induced stress and consequent PARP-1 activation. Moreover, the discovery of novel functions for the multiple members of the PARP family might lead in the future to additional clinical indications for PARP inhibitors.

Poly(ADP-Ribose) polymerase inhibition reduces reperfusion injury after heart transplantation

The aim of the present study was to investigate the effects of the novel poly(ADP-ribose) polymerase (PARP) inhibitor PJ34 (N-(6-oxo-5,6-dihydro-phenanthridin-2-yl)-N,N-dimethylacetamide) on myocardial and endothelial function after hypothermic ischemia and reperfusion in a heterotopic rat heart transplantation model. After a 1-hour ischemic preservation, reperfusion was started either after application of placebo or PJ34 (3 mg/kg). The assessment of left ventricular pressure-volume relations, total coronary blood flow, endothelial function, myocardial high energy phosphates, and histological analysis were performed at 1 and 24 hours of reperfusion. After 1 hour, myocardial contractility and relaxation, coronary blood flow, and endothelial function were significantly improved and myocardial high energy phosphate content was preserved in the PJ34-treated animals. Improved transplant function was also seen with treatment with another, structurally different PARP inhibitor, 5-aminoisoquinoline. The PARP inhibitors did not affect baseline cardiac function. Immunohistological staining confirmed that PJ34 prevented the activation of PARP in the transplanted hearts. The activation of P-selectin and ICAM-1 was significantly elevated in the vehicle-treated heart transplantation group. Thus, pharmacological PARP inhibition reduces reperfusion injury after heart transplantation due to prevention of energy depletion and downregulation of adhesion molecules and exerts a beneficial effect against reperfusion-induced graft coronary endothelial dysfunction.

5-aminoisoquinolinone, a potent inhibitor of poly (adenosine 5'-diphosphate ribose) polymerase, reduces myocardial infarct size

This study investigates the effects of a novel, water-soluble inhibitor of the activity of poly (adenosine 5'-diphosphate ribose) polymerase, 5-aminoisoquinolinone [5-aminoisoquinolin-1(2H)-one], on (i) poly (adenosine 5'-diphosphate ribose) polymerase activity in rat cardiac myoblasts and (ii) the infarct size caused by regional myocardial ischaemia and reperfusion in the rat. Exposure of H9c2 cells to hydrogen peroxide (H2O2, 1 mM) caused a significant increase in poly (adenosine 5'-diphosphate ribose) polymerase activity and an 80-90% reduction in mitochondrial respiration (cellular injury). Pretreatment of these cells with 5-aminoisoquinolinone (0.003-1 mM) caused a concentration-dependent inhibition of poly (adenosine 5'-diphosphate ribose) polymerase activity (IC50: approximately 4.5 microM, n=6-9) and cell injury (EC50: approximately 4.45 microM, n=9). In a rat model of myocardial infarction, left anterior descending coronary artery occlusion (25 min) and reperfusion (2 h) resulted in an infarct size of 50+/-3%. Administration (1 min before reperfusion) of 5-aminoisoquinolinone reduced myocardial infarct size in a dose-related fashion. Thus, 5-aminoisoquinolinone is a potent inhibitor of poly (adenosine 5'-diphosphate ribose) polymerase activity in cardiac myoblasts and reduces myocardial infarct size in vivo.

Suppression of poly (ADP-ribose) polymerase activation by 3-aminobenzamide in a rat model of myocardial infarction: long-term morphological and functional consequences

1. Recent studies demonstrated that inhibition or genetic inactivation of the enzyme poly (ADP-ribose) polymerase (PARP) is beneficial in myocardial reperfusion injury. PARP activation in the reperfused myocardium has been assumed, but not directly demonstrated. Furthermore, the issue whether pharmacological PARP inhibition affords long-term functional benefit in the reperfused myocardium has not been explored. These questions were addressed in the present study. 2. In a rat model of myocardial ischemia (1 h) and reperfusion (up to 24 h), there was a marked and significant activation of PARP in the ischemic borderzone, as determined by poly(ADP-ribose) (PAR) immunohistochemistry. PAR localized to the nuclei of myocytes and infiltrating mononuclear cells. In the core of the infarction, necrotic tissues and diffuse PAR staining were observed. PARP activation remained markedly detectable 24 h after reperfusion. The PARP inhibitor 3-aminobenzamide (20 mg kg(-1) intraperitoneally 10 min before reperfusion, and every 2 h thereafter for 6 h) markedly reduced the activation of the enzyme in myocytes. 3. 3-aminobenzamide significantly protected against myocardial morphological and functional alterations at 24 h post-reperfusion. Notably, infarct size was reduced, circulating creatine kinase activity was attenuated, and myocardial contractility (dP dt(-1)) was restored by 3-aminobenzamide. 4. Our results demonstrate a significant and prolonged activation of PARP in the reperfused myocardium, localizing to the necrotic area and the ischaemic borderzone. Furthermore, the studies demonstrate that PARP inhibition affords long-term beneficial morphological and functional effects in the reperfused myocardium. These data strengthen the notion that pharmacological PARP inhibition is a viable novel experimental approach for protection against myocardial reperfusion injury.

Effect of poly(ADP-ribose) polymerase inhibitors on the ischemia-reperfusion-induced oxidative cell damage and mitochondrial metabolism in Langendorff heart perfusion system

Ischemia-reperfusion induces reactive oxygen species (ROS) formation, and ROS lead to cardiac dysfunction, in part, via the activation of the nuclear poly(ADP-ribose) polymerase (PARP, called also PARS and ADP-RT). ROS and peroxynitrite induce single-strand DNA break formation and PARP activation, resulting in NAD(+) and ATP depletion, which can lead to cell death. Although protection of cardiac muscle by PARP inhibitors can be explained by their attenuating effect on NAD(+) and ATP depletion, there are data indicating that PARP inhibitors also protect mitochondria from oxidant-induced injury. Studying cardiac energy metabolism in Langendorff heart perfusion system by (31)P NMR, we found that PARP inhibitors (3-aminobenzamide, nicotinamide, BGP-15, and 4-hydroxyquinazoline) improved the recovery of high-energy phosphates (ATP, creatine phosphate) and accelerated the reutilization of inorganic phosphate formed during the ischemic period, showing that PARP inhibitors facilitate the faster and more complete recovery of the energy production. Furthermore, PARP inhibitors significantly decrease the ischemia-reperfusion-induced increase of lipid peroxidation, protein oxidation, single-strand DNA breaks, and the inactivation of respiratory complexes, which indicate a decreased mitochondrial ROS production in the reperfusion period. Surprisingly, PARP inhibitors, but not the chemically similar 3-aminobenzoic acid, prevented the H(2)O(2)-induced inactivation of cytochrome oxidase in isolated heart mitochondria, suggesting the presence of an additional mitochondrial target for PARP inhibitors. Therefore, PARP inhibitors, in addition to their important primary effect of decreasing the activity of nuclear PARP and decreasing NAD(+) and ATP consumption, reduce ischemia-reperfusion-induced endogenous ROS production and protect the respiratory complexes from ROS induced inactivation, providing an additional mechanism by which they can protect heart from oxidative damages.

The effect of agmatine administration on ischemic-reperfused isolated rat heart

BACKGROUND

The natural polyamine Agmatine (Ag) plays a significant role in protection of nerve cell ischemic injury. A previous report indicated that Ag given intraperitoneally to rats enhanced the recovery of the heart from ischemic injury. Based on this initial observation, a larger investigation was undertaken to explore a dose-response effect and possible mechanisms underlying the protective effects.

METHODS

Using the modified Langendorff model, 36 isolated hearts were divided into five groups: group 1, hearts receiving 100 microM/L Ag pre-ischemia (n=7); group 2, hearts receiving 100 microM/L Ag pre- and post-ischemia, (n=7); group 3, hearts receiving 250 microM/L Ag pre-ischemia (n=7); group 4, hearts receiving 250 microM/L Ag pre- and postischemia (n=7); and group 5, hearts receiving Krebs-Hensleit solution served as control (n=8). The study design included 20 minutes of perfusion, 30 minutes of global ischemia, and 30 minutes of reperfusion.

RESULTS

After ischemia, group 2 developed higher left ventricular pressure P(max) (P<0.01), improved first-derivative of the rise (dP/dt max; P<0.02), and fall (dP/dt min; P<0.04) in left ventricular pressure, and the area calculated under the left-ventricle developed pressure curve (pressure-time integral; P<0.015), but coronary flow was not significantly increased (P=0.06) compared to the control group. Group 1 had improved diastolic recovery: dP/dt min (P<0.05) and coronary flow (P<0.03), compared with the control group. Group 3 had improved P(max) (P<0.01), dP/dt min (P<0.01), and coronary flow (P<0.02); group 4 had no improvement in all hemodynamic parameters.

CONCLUSION

Low doses of Ag given pre- and post-ischemia, and high doses given only pre-ischemia have favorable, protective effects on the hemodynamic recovery of isolated rat heart undergoing global ischemia and reperfusion.

GPI 6150 prevents H(2)O(2) cytotoxicity by inhibiting poly(ADP-ribose) polymerase

GPI 6150 (1,11b-dihydro-[2H]benzopyrano[4,3,2-de]isoquinolin-3-one) is a novel inhibitor of poly(ADP-ribose) polymerase (PARP). It has demonstrated efficacy in rodent models of focal cerebral ischemia, traumatic brain injury, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine damage to dopaminergic neurons, regional myocardial ischemia, streptozotocin-induced diabetes, septic shock, and arthritis. Here we report the structure of GPI 6150, its enzymatic characteristics, and biochemical property in cytoprotection. As a competitive PARP inhibitor (K(i) = 60 nM), GPI 6150 protected the P388D1 cells against hydrogen peroxide cytotoxicity, by preventing PARP activation and the depletion of NAD(+), the substrate for PARP. To address the concerns of potential side effects of PARP inhibition, we tested GPI 6150 and found it had no effect on the repair and expression of a plasmid DNA damaged by N-methyl-N'-nitro-N-nitrosoguanidine. Neither did it affect dehydrogenases with NAD co-enzyme. GPI 6150 was much less potent to inhibit mono-ADP-ribosyltransferase. There was no selectivity for GPI 6150 between PARP isozymes. These attributes render GPI 6150 a useful tool to probe the functions of PARP.

Effects of inhibitors of the activity of poly (ADP-ribose) synthetase on the organ injury and dysfunction caused by haemorrhagic shock

1 Poly (ADP-ribose) synthetase (PARS) is a nuclear enzyme activated by strand breaks in DNA, which are caused by reactive oxygen species (ROS). Here we investigate the effects of the PARS inhibitors 3-aminobenzamide (3-AB), nicotinamide and 1,5-dihydroxyisoquinoline (ISO) on the circulatory failure and the organ injury/dysfunction caused by haemorrhage and resuscitation in the anaesthetized rat. 2 Haemorrhage (sufficient to lower mean arterial blood pressure to 50 mmHg for 90 min) and subsequent resuscitation with shed blood resulted (within 4 h after resuscitation) in a delayed fall in blood pressure to 66+/-4 mmHg (control, n=13). This circulatory failure was not affected by administration (5 min prior to resuscitation) of 3-AB (10 mg kg-1 i.v., n=7), nicotinamide (10 mg kg-1 i.v., n=6) or ISO (3 mg kg-1 i.v., n=6). 3 Haemorrhage and resuscitation also resulted in rises in the serum levels of urea and creatinine. This renal dysfunction was attenuated by 3-AB and nicotinamide, but not by nicotinic acid (n=7), an inactive analogue of nicotinamide. Although ISO (n=6) also attenuated the renal dysfunction caused by haemorrhage and resuscitation, its vehicle (10% DMSO, n=4) had the same effect. 4 Haemorrhagic shock resulted in enhanced serum levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT) and lipase, indicating the development of hepatocellular and pancreatic injury, respectively. Similarly, haemorrhagic shock also resulted in an increase in the serum levels of creatine kinase (CK) indicating the development of neuromuscular injury. This was attenuated by 3-AB and nicotinamide, but not by nicotinic acid. Although ISO also attenuated the liver, pancreatic and neuromuscular injury caused by haemorrhagic shock, its vehicle had the same effect. 5 Thus, activation of PARS contributes to the organ injury and dysfunction caused by haemorrhage and resuscitation in the rat.

An inhibitor of poly (ADP-ribose) synthetase activity reduces contractile dysfunction and preserves high energy phosphate levels during reperfusion of the ischaemic rat heart

The cardioprotective properties of inhibition of poly (ADP-ribose) synthetase (PARS) were investigated in the isolated perfused heart of the rat. Hearts were perfused in the Langendorff mode and subjected to 23 min total global ischaemia and reperfused for 60 min. Left ventricular function was assessed by means of an intra-ventricular balloon. High energy phosphates were measured by 31P-NMR spectroscopy. Intracellular levels of NAD were measured by capillary electrophoresis of perchloric acid extracts of hearts at the end of reperfusion. Reperfusion in the presence of the PARS inhibitor 1,5 didroxyisoquinoline (ISO, 100 microM) attenuated the mechanical dysfunction observed following 1 h of reperfusion; 27+/-13 and 65+/-8% recovery of preischaemic rate pressure product for control and 100 microM ISO, respectively. This cardioprotection was accompanied by a preservation of intracellular high-energy phosphates during reperfusion; 38+/-2 vs 58+/-4% (P<0.05) of preischaemic levels of phosphocreatine (PCr) for control and 100 microM ISO respectively and 23+/-1 vs 31+/-3% (P < 0.05) of preischaemic levels of ATP for control and 100 microM ISO respectively. Cellular levels of NAD were higher in ISO treated hearts at the end of reperfusion; 2.56+/-0.45 vs 4.76+/-1.12 micromoles g(-1) dry weight (P<0.05) for control and ISO treated. These results demonstrate that the cardioprotection afforded by inhibition of PARS activity with ISO is accompanied by a preservation of high-energy phosphates and cellular NAD levels and suggest that the mechanism responsible for this cardioprotection may involve prevention of intracellular ATP depletion.