Poly(ADP-ribose) polymerase gene disruption renders mice resistant to cerebral ischemia

Novel modulators of poly(ADP-ribose) polymerase

The nuclear enzyme poly(ADP-ribose) polymerase (PARP)-1 has an important role in regulating cell death and cellular responses to DNA repair. Pharmacological inhibitors of PARP have entered clinical testing as cytoprotective agents in cardiovascular diseases and as adjunct antitumor therapeutics. Initially, it was assumed that the regulation of PARP occurs primarily at the level of DNA breakage: recognition of DNA breaks was considered to be the primary regulator (activator) or the catalytic activity of PARP. Recent studies have provided evidence that PARP-1 activity can also be modulated by several endogenous factors, including various kinases, purines and caffeine metabolites. There is a gender difference in the contribution of PARP-1 to stroke and inflammatory responses, which is due, at least in part, to endogenous estrogen levels. Several tetracycline antibiotics are also potent PARP-1 inhibitors. In this article, we present an overview of novel PARP-1 modulators.

Poly(ADP-ribose) (PAR) polymer is a death signal

Excessive activation of the nuclear enzyme, poly(ADP-ribose) polymerase-1 (PARP-1) plays a prominent role in various of models of cellular injury. Here, we identify poly(ADP-ribose) (PAR) polymer, a product of PARP-1 activity, as a previously uncharacterized cell death signal. PAR polymer is directly toxic to neurons, and degradation of PAR polymer by poly(ADP-ribose) glycohydrolase (PARG) or phosphodiesterase 1 prevents PAR polymer-induced cell death. PARP-1-dependent, NMDA excitotoxicity of cortical neurons is reduced by neutralizing antibodies to PAR and by overexpression of PARG. Neuronal cultures with reduced levels of PARG are more sensitive to NMDA excitotoxicity than WT cultures. Transgenic mice overexpressing PARG have significantly reduced infarct volumes after focal ischemia. Conversely, mice with reduced levels of PARG have significantly increased infarct volumes after focal ischemia compared with WT littermate controls. These results reveal PAR polymer as a signaling molecule that induces cell death and suggests that interference with PAR polymer signaling may offer innovative therapeutic approaches for the treatment of cellular injury.

Apoptosis-inducing factor mediates poly(ADP-ribose) (PAR) polymer-induced cell death

Apoptosis-inducing factor (AIF), a mitochondrial oxidoreductase, is released into the cytoplasm to induce cell death in response to poly(ADP-ribose) (PAR) polymerase-1 (PARP-1) activation. How PARP-1 activation leads to AIF release is not known. Here we identify PAR polymer as a cell death signal that induces release of AIF. PAR polymer induces mitochondrial AIF release and translocation to the nucleus. PAR glycohydrolase, which degrades PAR polymer, prevents PARP-1-dependent AIF release. Cells with reduced levels of AIF are resistant to PARP-1-dependent cell death and PAR polymer cytotoxicity. These results reveal PAR polymer as an AIF-releasing factor that plays important roles in PARP-1-dependent cell death.

Caspase inhibitors promote alternative cell death pathways

The use of caspase inhibitors has revealed the existence of alternative backup cell death programs for apoptosis. The broad-spectrum caspase inhibitor zVAD-fmk modulates the three major types of cell death. Addition of zVAD-fmk blocks apoptotic cell death, sensitizes cells to necrotic cell death, and induces autophagic cell death. Several studies have shown a crucial role for the kinase RIP1 and the adenosine nucleotide translocator (ANT)-cyclophilin D (CypD) complex in necrotic cell death. The underlying mechanism of zVAD-fmk-mediated sensitization to necrotic cell death involves the inhibition of caspase-8-mediated proteolysis of RIP1 and disturbance of the ANT-CypD interaction. RIP1 is also involved in autophagic cell death. Caspase inhibitors and knockdown studies have revealed negative roles for catalase and caspase-8 in autophagic cell death. The positive role of RIP1 and the negative role of caspase-8 in both necrotic and autophagic cell death suggest that the pathways of these two types of cell death are interconnected. Necrotic cell death represents a rapid cellular response involving mitochondrial reactive oxygen species (ROS) production, decreased adenosine triphosphate concentration, and other cellular insults, whereas autophagic cell death first starts as a survival attempt by cleaning up ROS-damaged mitochondria. However, when this process occurs in excess, autophagy itself becomes cytotoxic and eventually leads to autophagic cell death. A better understanding of the molecular mechanisms of these alternative cell death pathways may provide therapeutic tools to combat cell death associated with neurodegenerative diseases, ischemia-reperfusion pathologies, and infectious diseases, and may also facilitate the development of alternative cytotoxic strategies in cancer treatment.

Nicotinamide prevents the effect of perinatal asphyxia on dopamine release evaluated with in vivo microdialysis 3 months after birth

The present study shows that nicotinamide prevents the long-term effect of perinatal asphyxia on dopamine release monitored with in vivo microdialysis in the neostriatum of 3-month-old rats. Perinatal asphyxia was induced by immersing foetuses-containing uterine horns removed from ready-to-deliver rats into a water bath for 16 or 20 min. Sibling, spontaneous, and caesarean-delivered pups were used as controls. Saline or nicotinamide (0.8 mmol/kg, i.p.) was administered to control and asphyxia-exposed animals 24, 48, and 72 h after birth. After weaning, the rats were randomly distributed in laboratory cages for animal care under standard ad libitum laboratory conditions. Approximately 3 months after birth, control and asphyxia-exposed animals were implanted with microdialysis probes into the lateral neostriatum for measuring extracellular monoamine and metabolite levels with HPLC-coupled to an electrochemical detection system under basal, D-amphetamine, and K(+)-depolarising conditions. There was an asphyxia-dependent decrease of extracellular dopamine levels, mainly observed during the periods when D-amphetamine (100 microM) or KCl (100 mM) was added into the perfusion medium. Compared to that observed in caesarean-delivered controls, the effect of D-amphetamine on dopamine levels was decreased by approximately 30 and 70% in animals exposed to 16 and 20 min of perinatal asphyxia, respectively. The effect of K(+)-depolarisation was decreased by 45 and 83% in animals exposed to the same periods of asphyxia, respectively. Both effects were prevented by nicotinamide, even if the treatment started 24 h after the insult. The present results support the idea of nicotinamide as an interesting molecule, useful for protecting against anoxia/ischemia occurring at neonatal stages. Nicotinamide can help to restore NADH/NAD+ depletion, but also to inhibit PARP-1 overactivation, a mechanism of action that has attracted attention, representing a novel target for neuroprotection following insults involving energy failure.

Influence of duration of focal cerebral ischemia and neuronal nitric oxide synthase on translocation of apoptosis-inducing factor to the nucleus

Translocation of apoptosis-inducing factor (AIF) from the mitochondria to the nucleus can play a major role in neuronal death elicited by oxidant stress. The time course of nuclear translocation of AIF after experimental stroke may vary with the severity of injury and may be accelerated by oxidant stress associated with reperfusion and nitric oxide (NO) production. Western immunoblots of AIF on nuclear fractions of ischemic hemisphere of male mice showed no significant increase with 1 h of middle cerebral artery occlusion and no reperfusion, whereas increases were detectable after 6 and 24 h of permanent ischemia. However, as little as 20 min of reperfusion after 1 h of middle cerebral artery occlusion resulted in an increase in nuclear AIF coincident with an increase in poly(ADP-ribose) polymer (PAR) formation. Further nuclear AIF accumulation was seen at 6 and 24 h of reperfusion. In contrast, 20 min of reperfusion after 2 h of occlusion did not increase nuclear AIF. In this case, nuclear AIF became detectable at 6 and 24 h of reperfusion. With brief occlusion of 30 min duration, nuclear AIF remained undetectable at both 20 min and 6 h and became evident only after 24 h of reperfusion. Inhibition of neuronal NO synthase attenuated formation of PAR and nuclear AIF accumulation. Gene deletion of neuronal NO synthase also attenuated nuclear AIF accumulation. Therefore, reperfusion accelerates AIF translocation to the nucleus when focal ischemia is of moderate duration (1 h), but is markedly delayed after brief ischemia (30 min). Nuclear translocation of AIF eventually occurs with prolonged focal ischemia with or without reperfusion. Neuronally-derived NO is a major factor contributing to nuclear AIF accumulation after stroke.

Evolving therapeutic approaches to treating acute ischemic stroke

Stroke contributes significantly to death, disability, and healthcare costs; however, recombinant tissue plasminogen activator (rt-PA) is the only approved thrombolytic therapy for acute ischemic stroke. One area of development for new ischemic stroke treatment options is focused on neuroprotection of viable tissue in the ischemic vascular bed. The ischemic penumbra is recognizable on MRI by decreased perfusion, in contrast to the core area of ischemia, which includes diffusion and perfusion abnormalities. Understanding the mechanisms of neuronal death, including the role of excitotoxic neurotransmitters, free radical production, and apoptotic pathways, is important in developing new therapies for stroke. This article reviews these causes and results of stroke, as well as current and future neuroprotective treatment options. Several compounds have shown neuroprotective effects in animal studies, but have failed to be effective in human clinical trials. Several promising therapeutic areas include targeting of free radicals, modulation of glutamatergic transmission, and membrane stabilization via ion channels.

Diabetes-induced cerebrovascular dysfunction: role of poly(ADP-ribose) polymerase

Our goal was to identify the role of poly(ADP-ribose) polymerase (PARP) in cerebrovascular dysfunction in Type 1 diabetes mellitus (T1D). In a first series of studies, rats were assigned to nondiabetic and diabetic (streptozotocin; 50 mg/kg IP) groups. Two to three months after injection of streptozotocin, we examine in vivo responses of pial arterioles to nitric oxide synthase (NOS)-dependent (adenosine diphosphate (ADP), acetylcholine and histamine) and -independent (nitroglycerin) agonists. After the initial examination of reactivity to the agonists, we treated pial arterioles acutely with an inhibitor of PARP (PJ-34; 1 microM), and then we again examined responses to the agonists. In a second series of studies, we examine superoxide production (lucigenin chemiluminescence) by parietal cortex tissue in nondiabetic and diabetic rats. We found that dilation of pial arterioles in response to ADP, acetylcholine and histamine, but not to nitroglycerin, was impaired in diabetic compared to nondiabetic rats. In addition, although PJ-34 did not alter responses in nondiabetic rats, PJ-34 alleviated T1D-induced impairment of NOS-dependent vasodilation. We also found that basal production of superoxide was increased in diabetic compared to nondiabetic rats and that PJ-34 decreased this basal production of superoxide. Our findings suggest that T1D impairs NOS-dependent reactivity of cerebral arterioles by a mechanism that appears to be related to the formation of superoxide via activation of PARP.

Phorbol 12-myristate 13-acetate protects against tumor necrosis factor (TNF)-induced necrotic cell death by modulating the recruitment of TNF receptor 1-associated death domain and receptor-interacting protein into the TNF receptor 1 signaling complex: Implication for the regulatory role of protein kinase C

Protein kinase C (PKC) triggers cellular signals that regulate proliferation or death in a cell- and stimulus-specific manner. Although previous studies have demonstrated that activation of PKC with phorbol 12-myristate 13-acetate (PMA) protects cells from apoptosis induced by a number of mechanisms, including death receptor ligation, little is known about the effect or mechanism of PMA in the necrotic cell death. Here, we demonstrate that PMA-mediated activation of PKC protects against tumor necrosis factor (TNF)-induced necrosis by disrupting formation of the TNF receptor (TNFR)1 signaling complex. Pretreatment with PMA protected L929 cells from TNF-induced necrotic cell death in a PKC-dependent manner, but it did not protect against DNA-damaging agents, including doxorubicin (Adriamycin) and camptothecin. Analysis of the upstream signaling events affected by PMA revealed that it markedly inhibited the TNF-induced recruitment of TNFR1-associated death domain protein (TRADD) and receptor-interacting protein (RIP) to TNFR1, subsequently inhibiting TNF-induced activation of nuclear factor-kappaB and c-Jun NH2-terminal kinase (JNK). However, JNK inhibitors do not significantly affect TNF-induced necrosis, suggesting that the inhibition of JNK activation by PMA is not part of the antinecrotic mechanism. In addition, PMA acted as an antagonist of TNF-induced reactive oxygen species (ROS) production, thereby suppressing activation of ROS-mediated poly(ADP-ribose)polymerase (PARP), and thus inhibiting necrotic cell death. Furthermore, during TNF-induced necrosis, PARP was significantly activated in wild-type mouse embryonic fibroblast (MEF) cells but not in RIP-/- or TNFR-associated factor 2-/-MEF cells. Taken together, these results suggest that PKC activation ensures effective shutdown of the death receptor-mediated necrotic cell death pathway by modulating formation of the death receptor signaling complex.

Blockade of PARP activity attenuates poly(ADP-ribosyl)ation but offers only partial neuroprotection against NMDA-induced cell death in the rat retina

Recent reports have linked neuronal cell death by necrosis to poly(ADP-ribose) polymerase-1 (PARP-1) hyperactivation. It is believed that under stress, the activity of this enzyme is up-regulated, resulting in extensive poly(ADP-ribosyl)ation of nuclear proteins, using NAD(+) as its substrate, which, in turn, leads to the depletion of NAD(+). In efforts to restore the level of NAD(+), depletion of ATP occurs, resulting in the shutdown of ATP-dependent ionic pumps. This results in cell swelling and eventual loss of membrane selectivity, hallmarks of necrosis. Reports from in vitro and in vivo studies in the brain have shown that NMDA receptor activation stimulates PARP activity and that blockade of the enzyme provides substantial neuroprotection. The present study was undertaken to determine whether PARP activity is regulated by NMDA in the rat retina, and whether blockade of PARP activity provides protection against toxic effects of NMDA. Rat retinas exposed to intravitreal injections containing NMDA, with or without the PARP inhibitor N-(6-oxo-5, 6-dihydrophenanthridin-2-yl)-(N,-dimethylamino) acetamide hydrochloride (PJ-34), were assessed for changes in PARP-1 activity as evidenced by poly(ADP-ribosyl)ation (PAR), loss of membrane integrity, morphological indicators of apoptosis and necrosis, and ganglion cell loss. Results showed that: NMDA increased PAR formation in a concentration-dependent manner and caused a decline in retinal ATP levels; PJ-34 blockade attenuated the NMDA-induced formation of PAR and decline in ATP; NMDA induced the loss of membrane selectivity to ethidium bromide (EtBr) in inner retinal neurons, but loss of membrane selectivity was not prevented by blocking PARP activity; cells stained with EtBr, or reacted for TUNEL-labeling, displayed features characteristic of both apoptosis and necrosis. In the presence of PJ-34, greater numbers of cells exhibited apoptotic features; PJ-34 provided partial neuroprotection against NMDA-induced ganglion cell loss. These findings suggest that although blockade of PARP activity fully attenuates NMDA-induced PAR formation and loss of retinal ATP content, and improves the survival of select populations of ganglion cells, this approach does not provide full neuroprotection. In contrast, blockade of PARP activity promotes apoptotic-like cell death in the majority of cells undergoing cell death. Furthermore, these studies show that the loss of membrane selectivity is not dependent upon PAR formation or the resulting decline of ATP, and suggests that an alternative pathway, other than PARP activation, exists to mediate this event.

Poly(ADP-ribose) polymerase-1 inhibition protects the brain against systemic inflammation

Poly(ADP-ribose) polymerase-1 (PARP-1) is involved in DNA repair, but its overactivation can induce cell death. Our aim was to investigate the role of PARP-1 in activation of programmed cell death processes in the brain during systemic inflammation. Our data indicated that lipopolysaccharide (1mg/kgb.w., i.p.)-evoked systemic inflammation enhanced PARP-1 activity in the mouse brain, leading to the lowering of beta-NAD(+) concentration, to translocation of apoptosis inducing factor from mitochondria to the nucleus, and to enhanced lipid peroxidation. Inhibitor of PARP-1, 3-aminobenzamide (30 mg/kgb.w., i.p.), protected the brain against prooxidative and cell death processes, suggesting involvement of PARP-1 in systemic inflammation-related processes in the brain.

Sigma 1 receptor agonists act as neuroprotective drugs through inhibition of inducible nitric oxide synthase

Postischemic administration of the sigma-1 agonists reduces ischemic brain injury; however, the mechanism is unclear. We hypothesized that the sigma-1 agonist (+)isoform of pentazocine (P(+)) reduces damage in part by ameliorating cell death mediated via inducible nitric oxide synthase (iNOS) and that the (-)isoform (P(-)) lacks this effect. We compared treatment with P(+) with or without the iNOS inhibitor aminoguanidine (AG) and also the effects of P(+) in iNOS deficient (iNOSKO) mice. A possible mechanism of neuroprotection is inhibition of iNOS expression. Male C57/Bl6 mice were subjected to transient middle cerebral artery occlusion (90 min) and drugs were administered with reperfusion: 1) P(+) with AG (P+/AG), 2) P(+), 3) P(-), 4) AG, or 5) placebo. iNOSKOs were treated with either P(+) or placebo. Infarction (triphenyltetrazolium chloride histology, 72 h) was reduced by P(+) treatment in striatum by 44% and in neocortex by 23% versus placebo (P < 0.05), a reduction comparable to AG effect. P(-) did not attenuate brain injury. There was no difference in P(+)/AG treatment compared with showed the same level of neuroprotection as P(+) alone. P(+) also did not provide further neuroprotection for iNOSKOs. We conclude that postischemic administration of P(+) reduces infarct volume in mice. Because AG provides no additional benefit to P(+) treatment and iNOSKOs do not benefit from P(+), we speculate that P(+) acts by suppressing cell death resulting from iNOS toxicity.

Plasticity of the central nervous system (CNS) following perinatal asphyxia: does nicotinamide provide neuroprotection?

We have investigated the idea that nicotinamide, a non-selective inhibitor of the sentinel enzyme Poly(ADP-ribose) polymerase-I (PARP-1), provides neuroprotection against the long-term neurological changes induced by perinatal asphyxia. Perinatal asphyxia was induced in vivo by immersing foetuses-containing uterine horns removed from ready-to-deliver rats into a water bath for 20 min. Sibling caesarean-delivered pups were used as controls. The effect of perinatal asphyxia on neurocircuitry development was studied in vitro with organotypic cultures from substantia nigra, neostriatum and neocortex, platted on a coverslip 3 days after birth. After approximately one month in vitro (DIV 25), the cultures were treated for immunocytochemistry to characterise neuronal phenotype with markers against the N-methyl-D-aspartate receptor subunit 1 (NR1), the dopamine pacemaker enzyme tyrosine hydroxylase (TH), and nitric oxide synthase (NOS), the enzyme regulating the bioavailability of NO. Nicotinamide (0.8 mmol/kg, i.p.) or saline was administered to asphyctic and caesarean-delivered pups 24, 48 and 72 h after birth. It was found that nicotinamide treatment prevented the effect of perinatal asphyxia on several neuronal parameters, including TH- and NOS-positive neurite atrophy and NOS-positive neuronal loss; supporting the idea that nicotinamide constitutes a therapeutic alternative for the effects produced by sustained energy-failure conditions, as occurring during perinatal asphyxia.

New tricks for old drugs: the anticarcinogenic potential of DNA repair inhibitors

Defective or abortive repair of DNA lesions has been associated with carcinogenesis. Therefore it is imperative for a cell to accurately repair its DNA after damage if it is to return to a normal cellular phenotype. In certain circumstances, if DNA damage cannot be repaired completely and with high fidelity, it is more advantageous for an organism to have some of its more severely damaged cells die rather than survive as neoplastic transformants. A number of DNA repair inhibitors have the potential to act as anticarcinogenic compounds. These drugs are capable of modulating DNA repair, thus promoting cell death rather than repair of potentially carcinogenic DNA damage mediated by error-prone DNA repair processes. In theory, exposure to a DNA repair inhibitor during, or immediately after, carcinogenic exposure should decrease or prevent tumorigenesis. However, the ability of DNA repair inhibitors to prevent cancer development is difficult to interpret depending upon the system used and the type of genotoxic stress. Inhibitors may act on multiple aspects of DNA repair as well as the cellular signaling pathways activated in response to the initial damage. In this review, we summarize basic DNA repair mechanisms and explore the effects of a number of DNA repair inhibitors that not only potentiate DNA-damaging agents but also decrease carcinogenicity. In particular, we focus on a novel anti-tumor agent, beta-lapachone, and its potential to block transformation by modulating poly(ADP-ribose) polymerase-1.

Necrosis, a well-orchestrated form of cell demise: signalling cascades, important mediators and concomitant immune response

Necrosis has long been described as a consequence of physico-chemical stress and thus accidental and uncontrolled. Recently, it is becoming clear that necrotic cell death is as well controlled and programmed as caspase-dependent apoptosis, and that it may be an important cell death mode that is both pathologically and physiologically relevant. Necrotic cell death is not the result of one well-described signalling cascade but is the consequence of extensive crosstalk between several biochemical and molecular events at different cellular levels. Recent data indicate that serine/threonine kinase RIP1, which contains a death domain, may act as a central initiator. Calcium and reactive oxygen species (ROS) are main players during the propagation and execution phases of necrotic cell death, directly or indirectly provoking damage to proteins, lipids and DNA, which culminates in disruption of organelle and cell integrity. Necrotically dying cells initiate pro-inflammatory signalling cascades by actively releasing inflammatory cytokines and by spilling their contents when they lyse. Unravelling the signalling cascades contributing to necrotic cell death will permit us to develop tools to specifically interfere with necrosis at certain levels of signalling. Necrosis occurs in both physiological and pathophysiological processes, and is capable of killing tumour cells that have developed strategies to evade apoptosis. Thus detailed knowledge of necrosis may be exploited in therapeutic strategies.

Diabetic neuropathy and oxidative stress

This review will focus on the impact of hyperglycemia-induced oxidative stress in the development of diabetes-related neural dysfunction. Oxidative stress occurs when the balance between the production of reactive oxygen species (ROS) and the ability of cells or tissues to detoxify the free radicals produced during metabolic activity is tilted in the favor of the former. Although hyperglycemia plays a key role in inducing oxidative stress in the diabetic nerve, the contribution of other factors, such as endoneurial hypoxia, transition metal imbalances, and hyperlipidemia have been also suggested. The possible sources for the overproduction of ROS in diabetes are widespread and include enzymatic pathways, auto-oxidation of glucose, and mitochondrial superoxide production. Increase in oxidative stress has clearly been shown to contribute to the pathology of neural and vascular dysfunction in diabetes. Potential therapies for preventing increased oxidative stress in diabetic nerve dysfunction will be discussed.

Minocycline inhibits poly(ADP-ribose) polymerase-1 at nanomolar concentrations

Poly(ADP-ribose) polymerase-1 (PARP-1), when activated by DNA damage, promotes both cell death and inflammation. Here we report that PARP-1 enzymatic activity is directly inhibited by minocycline and other tetracycline derivatives that have previously been shown to have neuroprotective and anti-inflammatory actions. These agents were evaluated by using cortical neuron cultures in which PARP-1 activation was induced by the genotoxic agents N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) or 3-morpholinosydnonimine (SIN-1). In both conditions, neuronal death was reduced by >80% either by 10 muM 3,4-dihydro-5-[4-(1-piperidinyl)butoxy]-1(2H)-isoquinolinone, an established PARP inhibitor, or by 100 nM minocycline. Neuronal NAD(+) depletion and poly(ADP-ribose) formation, which are biochemical markers of PARP-1 activation, were also blocked by 100 nM minocycline. A direct, competitive inhibition of PARP-1 by minocycline (K(i) = 13.8 +/- 1.5 nM) was confirmed by using recombinant PARP-1 in a cell-free assay. Comparison of several tetracycline derivatives showed a strong correlation (r(2) = 0.87) between potency as a PARP-1 inhibitor and potency as a neuroprotective agent during MNNG incubations, with the rank order of potency being minocycline > doxycycline > demeclocycline > chlortetracycline. These compounds are known to have other actions that could contribute their neuroprotective effects, but at far higher concentrations than shown here to inhibit PARP-1. The neuroprotective and antiinflammatory effects of minocycline and other tetracycline derivatives may be attributable to PARP-1 inhibition in some settings.

Switch from caspase-dependent to caspase-independent death during heart development: essential role of endonuclease G in ischemia-induced DNA processing of differentiated cardiomyocytes

Differentiated cardiomyocytes are resistant to caspase-dependent cell death; however, the mechanisms involved are still uncertain. We previously reported that low Apaf1 expression partially accounts for cardiomyocyte resistance to apoptosis. Here, we extend the knowledge on the molecular basis of cardiac resistance to caspase activation by showing that the whole caspase-dependent pathway is silenced during heart development. Experimental ischemia triggers caspase activation in embryonic cardiomyocytes and proliferating fibroblasts, but not in neonatal and adult cardiomyocytes. Ischemia induces the release of the proapoptotic factors cytochrome c, truncated-AIF, and EndoG from mitochondria in postnatal cardiomyocytes in the absence of caspase activation. On the one hand, lentiviral-driven knockdown of EndoG shows that this gene is essential for ischemia-induced DNA degradation in neonatal cardiomyocytes, but not in proliferating fibroblasts; on the other hand, the AIF gene is essential for high molecular DNA cleavage in fibroblasts, but not in postmitotic cardiomyocytes, where it plays a prosurvival role during reoxygenation. These results show the switch from caspase-dependent to caspase-independent death pathways after cardiac cell differentiation, and disclose the relevance of EndoG in the caspase-independent DNA processing of differentiated cardiomyocytes.

Role of changes in cardiac metabolism in development of diabetic cardiomyopathy

In patients with diabetes, an increased risk of symptomatic heart failure usually develops in the presence of hypertension or ischemic heart disease. However, a predisposition to heart failure might also reflect the effects of underlying abnormalities in diastolic function that can occur in asymptomatic patients with diabetes alone (termed diabetic cardiomyopathy). Evidence of cardiomyopathy has also been demonstrated in animal models of both Type 1 (streptozotocin-induced diabetes) and Type 2 diabetes (Zucker diabetic fatty rats and ob/ob or db/db mice). During insulin resistance or diabetes, the heart rapidly modifies its energy metabolism, resulting in augmented fatty acid and decreased glucose consumption. Accumulating evidence suggests that this alteration of cardiac metabolism plays an important role in the development of cardiomyopathy. Hence, a better understanding of this dysregulation in cardiac substrate utilization during insulin resistance and diabetes could provide information as to potential targets for the treatment of cardiomyopathy. This review is focused on evaluating the acute and chronic regulation and dysregulation of cardiac metabolism in normal and insulin-resistant/diabetic hearts and how these changes could contribute toward the development of cardiomyopathy.

Oxygen Radicals Induce Poly(ADP-Ribose) Polymerase-Dependent Cell Death in Cytotoxic Lymphocytes

Cytotoxic T cells and NK cells will acquire features of apoptosis when exposed to oxygen radicals, but the molecular mechanisms underlying this phenomenon are incompletely understood. We have investigated the role of two enzyme systems responsible for execution of cell death, caspases and the poly(ADP-ribose) polymerase (PARP). We report that although human cytotoxic lymphocytes were only marginally protected by caspase inhibitors, PARP inhibitors completely protected lymphocytes from radical-induced apoptosis and restored their cytotoxic function. The radical-induced, PARP-dependent cell death was accompanied by nuclear accumulation of apoptosis-inducing factor and a characteristic pattern of large-fragment DNA degradation. It is concluded that the PARP/apoptosis-inducing factor axis is critically involved in oxygen radical-induced apoptosis in cytotoxic lymphocytes.

Oxidative Stress as the Leading Cause of Acute Myocardial Infarction in Diabetics

The risk factors, such as hypertension and metabolic syndrome, tend to promote heart pathology. These risk factors can aggravate concomitant heart insults as well. Diabetes mellitus represents one of the most important risk factors for the development of heart pathology. By itself it represents a source of vascular and heart dysfunction through formation of reactive oxygen species (ROS) and can compromise the recovery from cardiovascular diseases. This review focuses on the evidence that cellular oxidative stress is the leading cause of the worst outcome of myocardial infarction (MI) in diabetics. Hyperglycemia is viewed in this article as the primary mediator of a cascade of heart damaging events, starting from ROS formation and leading to myocardial ischemia, inflammation and death of myocytes. This article also provides insights into why diverse therapeutic interventions, which have in common the ability to reduce oxidative stress and inflammation, can impede or delay the onset of complications of myocardial infarction in diabetic patients.

Players in the PARP-1 cell-death pathway: JNK1 joins the cast

The nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) triggers a cell-death pathway in which mitochondria play an integral part, but it remains uncertain how PARP-1 activation in the nucleus is signaled to the mitochondria. A recent report by Xu and colleagues suggests that Jun kinase-1, a member of the mitogen-activated protein kinase family, might have a crucial role in this signaling pathway.

Apoptosis: Future Targets for Neuroprotective Strategies

Focal permanent or transient cerebral artery occlusion produces massive cell death in the central core of the infarction, whereas in the peripheral zone (penumbra) nerve cells are subjected to various determining survival and death signals. Cell death in the core of the infarction and in the adult brain is usually considered a passive phenomenon, although events largely depend on the partial or complete disruption of crucial metabolic pathways. Cell death in the penumbra is currently considered an active process largely dependent on the activation of cell death programs leading to apoptosis. Yet cell death in the penumbra includes apoptosis, necrosis, intermediate and other forms of cell death. A rather simplistic view implies poor prospects regarding cell survival in the core of the infarction and therapeutic expectations in the control of cell death and cell survival in the penumbra. However, the capacity for neuroprotection depends on multiple factors, primarily the use of the appropriate agent, at the appropriate time and during the appropriate interval. Understanding the mechanisms commanding cell death and survival area is as important as delimiting the therapeutic time window and the facility of a drug to effectively impact on specific targets. Moreover, the detrimental effects of homeostasis and the activation of multiple pathways with opposing signals following ischemic stroke indicate that better outcome probably does not depend on a single compound but on several drugs acting in combination at the optimal time in a particular patient.

Immunopathogenesis of cerebral malaria

Malaria is one of the most important global health problems, potentially affecting more than one third of the world's population. Cerebral malaria (CM) is a deadly complication of Plasmodium falciparum infection, yet its pathogenesis remains incompletely understood. In this review, we discuss some of the principal pathogenic events that have been described in murine models of the disease and relate them to the human condition. One of the earliest events in CM pathogenesis appears to be a mild increase in the permeability to protein of the blood-brain barrier. Recent studies have shown a role for CD8+T cells in mediating damage to the microvascular endothelium and this damage can result in the leakage of cytokines, malaria antigens and other potentially harmful molecules across the blood-brain barrier into the cerebral parenchyma. We suggest that this, in turn, leads to the activation of microglia and the activation and apoptosis of astrocytes. The role of hypoxia in the pathogenesis of cerebral malaria is also discussed, with particular reference to the local reduction of oxygen consumption in the brain as a consequence of vascular obstruction, to cytokine-driven changes in glucose metabolism, and to cytopathic hypoxia. Interferon-gamma, a cytokine known to be produced in malaria infection, induces increased expression, by microvascular endothelial cells, of the haem enzyme indoleamine 2,3-dioxygenase, the first enzyme in the kynurenine pathway of tryptophan metabolism. Enhanced indoleamine 2,3-dioxygenase expression leads to increased production of a range of biologically active metabolites that may be part of a tissue protective response. Damage to astrocytes may result in reduced production of the neuroprotectant molecule kynurenic acid, leading to a decrease in its ratio relative to the neuroexcitotoxic molecule quinolinic acid, which might contribute to some of the neurological symptoms of cerebral malaria. Lastly, we discuss the role of other haem enzymes, cyclooxygenase-2, inducible nitric oxide synthase and haem oxygenase-1, as potentially being components of mechanisms that protect host tissue against the effects of cytokine- and leukocyte-mediated stress induced by malaria infection.

Binding mode of novel 1-substituted quinazoline derivatives to poly(ADP-ribose) polymerase-catalytic domain, revealed by X-ray crystal structure analysis of complexes

In order to clarify the role of the 1-substituent of quinazoline derivatives in their inhibitory activity against poly(ADP-ribose) polymerase (PARP), two novel inhibitors, 1 [8-hydroxy-1-(3-morpholinopropyl)-quinazoline-2,4(1H,3H)-dione] and 2 [8-hydroxy-1-(3-phenoxypropyl)-quinazoline-2,4(1H,3H)-dione], were synthesized and subjected to X-ray crystal analysis in complex with the PARP C-terminal catalytic domain (PARP-CD), which requires NAD+ coenzyme for biological function. The nicotinamide-mimicking part of the quinazoline skeleton of 1 and 2 were both located at the nicotinamide subsite of the NAD+-binding pocket in the same manner as previously reported inhibitors: three hydrogen bonds [(Gly-863)NH-O12, (Gly-863)O-HN3 and (Ser-904)O(gamma)-O12] and stacking interaction between the Tyr-907 phenol and the quinazoline ring. On the other hand, the N-morpholinoprop-3-yl moiety introduced at the 1-position of the quinazoline ring in 1 bridged the large gap between the donor site and the acceptor site through a (Met-890)NH-O20(morpholine) hydrogen bond, where the donor and the acceptor sites are classified as the binding sites of NAD+ and the ADP moiety of the poly(ADP-ribose) chain, respectively. In contrast, the N-phenoxyprop-3-yl moiety in 2 formed hydrophobic interactions close to the adenosine-binding site of NAD+, unlike the hydrogen bond such as in 1. As the inhibitory activities of 1 and 2 for PARP were much more potent than those of the unsubstituted nicotinamide analogues, these results suggest that the occupation of the proximal region of the ADP phosphate-and adenosine-binding subsite of the donor site or that of the gap between the donor and the acceptor site by the 1-substituent of quinazoline may increase the inhibitory activity considerably. The nearly equal inhibitory activities of 1 and 2, despite of their different binding modes at the active site, indicate that this 1-substituent is promising in improving the bioavailability of the inhibitor without compromising its inhibitory activity.

The human apurinic/apyrimidinic endonuclease-1 suppresses activation of poly(adp-ribose) polymerase-1 induced by DNA single strand breaks

DNA single-strand breaks (SSB) activate poly (ADP-ribose) polymerase 1 (PARP1), which then polymerizes ADP-ribosyl groups on various nuclear proteins, consuming cellular energy. Although PARP1 has a role in repairing SSB, activation of PARP1 also causes necrosis and inflammation due to depletion of cellular energy. Here we show that the major mammalian apurinic/apyrimidinic (AP) endonuclease-1 (APE1), an essential DNA repair protein, binds to SSB and suppresses the activation of PARP1. APE1's high affinity for SSB requires Arg177, which is unique in mammalian APEs. PARP1's binding to the cleaved DNA was inhibited, and PARP1 activation was suppressed by the wild-type APE1, but not by the R177A mutant APE1 protein. Cells transiently transfected with the wild-type APE1 decreased the PARP1 activation after H2O2 treatment, while such suppression did not occur with the expression of the R177A APE1 mutant. These results suggest that APE1 suppresses the activation of PARP1 during the repair process of the DNA damage generated by oxidative stress, which may have an important implication for cells to avoid necrosis due to energy depletion.

Poly(ADP-ribose) polymerase-1-deficient mice are protected from angiotensin II-induced cardiac hypertrophy

Poly(ADP-ribose) polymerase-1 (PARP), a chromatin-bound enzyme, is activated by cell oxidative stress. Because oxidative stress is also considered a main component of angiotensin II-mediated cell signaling, it was postulated that PARP could be a downstream target of angiotensin II-induced signaling leading to cardiac hypertrophy. To determine a role of PARP in angiotensin II-induced hypertrophy, we infused angiotensin II into wild-type (PARP(+/+)) and PARP-deficient mice. Angiotensin II infusion significantly increased heart weight-to-tibia length ratio, myocyte cross-sectional area, and interstitial fibrosis in PARP(+/+) but not in PARP(-/-) mice. To confirm these results, we analyzed the effect of angiotensin II in primary cultures of cardiomyocytes. When compared with PARP(-/-) cardiomyocytes, angiotensin II (1 microM) treatment significantly increased protein synthesis in PARP(+/+) myocytes, as measured by (3)H-leucine incorporation into total cell protein. Angiotensin II-mediated hypertrophy of myocytes was accompanied with increased poly-ADP-ribosylation of nuclear proteins and depletion of cellular NAD content. When cells were treated with cell death-inducing doses of angiotensin II (10-20 microM), robust myocyte cell death was observed in PARP(+/+) but not in PARP(-/-) myocytes. This type of cell death was blocked by repletion of cellular NAD levels as well as by activation of the longevity factor Sir2alpha deacetylase, indicating that PARP induction and subsequent depletion of NAD levels are the sequence of events causing angiotensin II-mediated cardiomyocyte cell death. In conclusion, these results demonstrate that PARP is a nuclear integrator of angiotensin II-mediated cell signaling contributing to cardiac hypertrophy and suggest that this could be a novel therapeutic target for the management of heart failure.

Direct phosphorylation and regulation of poly(ADP-ribose) polymerase-1 by extracellular signal-regulated kinases 1/2

Sustained activation of poly(ADP-ribose) polymerase-1 (PARP-1) and extracellular signal-regulated kinases 1/2 (ERK1/2) both promote neuronal death. Here we identify a direct link between these two cell death pathways. In a rat model of hypoglycemic brain injury, neuronal PARP-1 activation and subsequent neuronal death were blocked by the ERK1/2 inhibitor 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one (PD98059). In neuron cultures, PARP-1-mediated neuronal death induced by N-methyl-d-aspartate, peroxynitrite, or DNA alkylation was similarly blocked by ERK1/2 pathway inhibitors. These inhibitors also blocked PARP-1 activation and PARP-1-mediated death in astrocytes. siRNA down-regulation of ERK2 expression in astrocytes also blocked PARP-1 activation and cell death. Direct effects of ERK1/2 on PARP-1 were evaluated by using isolated recombinant enzymes. The activity of recombinant human PARP-1 was reduced by incubation with alkaline phosphatase and restored by incubation with active ERK1 or ERK2. Putative ERK1/2 phosphorylation sites on PARP-1 were identified by mass spectrometry. Using site-directed mutagenesis, these sites were replaced with alanine (S372A and T373A) to block phosphorylation, or with glutamate (S372E and T373E) to mimic constitutive phosphorylation. Transfection of PARP-1 deficient mouse embryonic fibroblasts with the mutant PARP-1 species showed that the S372A and T373A mutations impaired PARP-1 activation, whereas the S372E and T373E mutations increased PARP-1 activity and eliminated the effect of ERK1/2 inhibitors on PARP-1 activation. These results suggest that PARP1 phosphorylation by ERK1/2 is required for maximal PARP-1 activation after DNA damage.

Oxidative metabolism, apoptosis and perinatal brain injury

Perinatal hypoxic-ischaemic injury (HII) is a significant cause of neurodevelopmental impairment and disability. Studies employing 31P magnetic resonance spectroscopy to measure phosphorus metabolites in situ in the brains of newborn infants and animals have demonstrated that transient hypoxia-ischaemia leads to a delayed disruption in cerebral energy metabolism, the magnitude of which correlates with the subsequent neurodevelopmental impairment. Prominent among the biochemical features of HII is the loss of cellular ATP, resulting in increased intracellular Na+ and Ca2+, and decreased intracellular K+. These ionic imbalances, together with a breakdown in cellular defence systems following HII, can contribute to oxidative stress with a net increase in reactive oxygen species. Subsequent damage to lipids, proteins, and DNA and inactivation of key cellular enzymes leads ultimately to cell death. Although the precise mechanisms of neuronal loss are unclear, it is now clear both apoptosis and necrosis are the significant components of cell death following HII. A number of different factors influence whether a cell will undergo apoptosis or necrosis, including the stage of development, cell type, severity of mitochondrial injury and the availability of ATP for apoptotic execution. This review will focus on some pathological mechanisms of cell death in which there is a disruption to oxidative metabolism. The first sections will discuss the process of damage to oxidative metabolism, covering the data collected both from human infants and from animal models. Following sections will deal with the molecular mechanisms that may underlie cerebral energy failure and cell death in this form of brain injury, with a particular emphasis on the role of apoptosis and mitochondria.

Poly(ADP-ribose) Polymerase-1 Signaling to Mitochondria in Necrotic Cell Death Requires RIP1/TRAF2-mediated JNK1 Activation

Poly(ADP-ribose) polymerase-1 (PARP-1) hyperactivation-induced necrosis has been implicated in several pathophysiological conditions. Although mitochondrial dysfunction and apoptosis-inducing factor translocation from the mitochondria to the nucleus have been suggested to play very important roles in PARP-1-mediated cell death, the signaling events downstream of PARP-1 activation in initiating mitochondria dysfunction are not clear. Here we used the DNA alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine, a potent PARP-1 activator, to study PARP-1 activation-mediated cell death. We found, based on genetic knockouts and pharmacological inhibition, that c-Jun N-terminal kinase (JNK), especially JNK1, but not the other groups of mitogen-activated protein kinase, is required for PARP-1-induced mitochondrial dysfunction, apoptosis-inducing factor translocation, and subsequent cell death. We reveal that receptor-interacting protein 1 (RIP1) and tumor necrosis factor receptor-associated factor 2 (TRAF2), are upstream of JNK in PARP-1 hyperactivated cells, because PARP-1-induced JNK activation was attenuated in RIP1-/- and TRAF2-/- mouse embryonic fibroblast cells. Consistently, knockouts of RIP1 and TRAF2 caused a resistance to PARP-1-induced cell death. Therefore, our study uncovers that RIP1, TRAF2, and JNK comprise a pathway to mediate the signaling from PARP-1 overactivation to mitochondrial dysfunction.

Parp-1 protects homologous recombination from interference by Ku and Ligase IV in vertebrate cells

Parp-1 and Parp-2 are activated by DNA breaks and have been implicated in the repair of DNA single-strand breaks (SSB). Their involvement in double-strand break (DSB) repair mediated by homologous recombination (HR) or nonhomologous end joining (NHEJ) remains unclear. We addressed this question using chicken DT40 cells, which have the advantage of carrying only a PARP-1 gene but not a PARP-2 gene. We found that PARP-1(-/-) DT40 mutants show reduced levels of HR and are sensitive to various DSB-inducing genotoxic agents. Surprisingly, this phenotype was strictly dependent on the presence of Ku, a DSB-binding factor that mediates NHEJ. PARP-1/KU70 double mutants were proficient in the execution of HR and displayed elevated resistance to DSB-inducing drugs. Moreover, we found deletion of Ligase IV, another NHEJ gene, suppressed the camptothecin of PARP-1(-/-) cells. Our results suggest a new critical function for Parp in minimizing the suppressive effects of Ku and the NHEJ pathway on HR.

Caspase-3 deficiency during development increases vulnerability to hypoxic-ischemic injury through caspase-3-independent pathways

Neonatal hypoxia-ischemia (H-I) is a common cause of perinatal morbidity and mortality leading to prominent activation of caspase-3 in the brain. Previous studies have shown that acute inhibition of caspase-3 can protect against neonatal H-I in rats. In this study, we investigated brain injury following neonatal H-I in mice deficient in caspase-3. Wild-type, caspase-3+/- and caspase-3-/- mice underwent unilateral carotid ligation at postnatal day (P) 7, followed by 45 min of exposure to 8% oxygen. Surprisingly, tissue loss at P14 was significantly higher in caspase-3-/- mice when compared to wild-type littermates. As in rats, we found that acute inhibition of caspase-3 in mice leads to decrease in tissue loss at P14. There was no difference in nuclear morphology, DNA laddering or calpain activation between caspase-3-/-caspase-3+/- and wild-type mice subjected to H-I, and there was no evidence for compensatory activation of other caspases in caspase-3-/- mice. Also, all genotypes showed evidence of mitochondrial dysfunction after H-I, suggesting that this is a critical point in regulation of neuronal cell death following neonatal H-I. Our results suggest that long-term inhibition of caspase-3 during development, unlike acute inhibition, leads to upregulation of caspase-3-independent cell death pathways and increases the vulnerability of the developing brain to neonatal H-I injury.

Ischemic preconditioning in the rat brain enhances the repair of endogenous oxidative DNA damage by activating the base-excision repair pathway

The development of ischemic tolerance in the brain, whereby a brief period of sublethal 'preconditioning' ischemia attenuates injury from subsequent severe ischemia, may involve the activation of multiple intracellular signaling events that promote neuronal survival. In this study, the potential role of inducible DNA base-excision repair (BER), an endogenous adaptive response that prevents the detrimental effect of oxidative DNA damage, has been studied in the rat model of ischemic tolerance produced by three episodes of ischemic preconditioning (IP). This paradigm of IP, when applied 2 and 5 days before 2-h middle cerebral artery occlusion (MCAO), significantly decreased infarct volume in the frontal-parietal cortex 72 h later. Correlated with this protective effect, IP markedly attenuated the nuclear accumulations of several oxidative DNA lesions, including 8-oxodG, AP sites, and DNA strand breaks, after 2-h MCAO. Consequently, harmful DNA damage-responsive events, including NAD depletion and p53 activation, were reduced during postischemic reperfusion in preconditioned brains. The mechanism underlying the decreased DNA damage in preconditioned brain was then investigated by measuring BER activities in nuclear extracts. Beta-polymerase-mediated BER activity was markedly increased after IP, and this activation occurred before (24 h) and during the course of ischemic tolerance (48 to 72 h). In similar patterns, the activities for AP site and 8-oxodG incisions were also upregulated after IP. The upregulation of BER activities after IP was likely because of increased expression of repair enzymes beta-polymerase, AP endonuclease, and OGG1. These results suggest that the activation of the BER pathway may contribute to IP-induced neuroprotection by enhancing the repair of endogenous oxidative DNA damage after ischemic injury.

Does apoptosis-inducing factor (AIF) have both life and death functions in cells?

Apoptosis-inducing factor (AIF) is expelled from mitochondria after some apoptotic stimuli and translocates to the nucleus, which may contribute to DNA and nuclear fragmentation in some non-physiological mammalian cell deaths. Conversely, the requirement for mitochondrial AIF in oxidative phosphorylation and energy generation provides a plausible explanation for the embryonic lethality or neurodegeneration that has been found in different AIF-deficient mouse models. These findings may help illuminate the ability of mitochondrial AIF to suppress cytoplasmic stress granule formation and to promote the tumorigenic growth of cancer cells. AIF is ideally located in the mitochondrion to perform a vital normal function in energy production. Once it translocates to the nucleus, however, the cell might die either of energy failure or nuclear fragmentation (or both). We propose that the main function of AIF is to support energy production in both normal and transformed cell physiology, whereas nuclear-translocated AIF might contribute to stress-induced or pathological cell death in certain scenarios.

Differential effect of PARP-2 deletion on brain injury after focal and global cerebral ischemia

Poly(ADP-ribose) polymerase-2 (PARP-2) is a member of the PARP enzyme family, and, similarly to PARP-1, catalyzes the formation of ADP-ribose polymers in response to DNA damage. While PARP-1 overactivation contributes to ischemic cell death, no information is available regarding the role of PARP-2. In this study, we evaluated the impact of PARP-2 deletion on histopathological outcome from two different experimental models of cerebral ischemia. Male PARP-2-/- mice and wild-type (WT) littermates were subjected to either 2 h of middle cerebral artery occlusion (MCAO) followed by 22 h reperfusion, or underwent 10 mins of KCl-induced cardiac arrest (CA) followed by cardiopulmonary resuscitation (CPR) and 3-day survival. After MCAO, infarct volume was reduced in PARP-2-/- mice (38%+/-12% of contralateral hemisphere) compared with WT (64%+/-16%). After CA/CPR, PARP-2 deletion significantly increased neuronal cell loss in the hippocampal CA1 field (65%+/-36% ischemic neurons) when compared with WT mice (31%+/-33%), with no effect in either striatum or cortex. We conclude that PARP-2 is a novel executioner of cell death pathways in focal cerebral ischemia, but might be a necessary survival factor after global ischemia to mitigate hippocampal delayed cell death.

Treatment with PARP-1 inhibitors, GPI 15427 or GPI 16539, ameliorates intestinal damage in rat models of colitis and shock

Poly (ADP-ribose) polymerase-1 (PARP-1), a nuclear enzyme activated by DNA strand breaks, plays a detrimental role during inflammation. As inflammation is important in the development of colitis and ischemia/reperfusion (I/R) injury of the intestine, we investigated the effects of 10-(4-methyl-piperazin-1-ylmethyl)-2H-7-oxa-1,2-diaza-benzo[de]anthracen-3-one (GPI 15427) and 2-(4-methyl-piperazin-1-yl)-5H-benzo[c][1,5]naphthyridin-6-one (GPI 16539), two novel and potent inhibitors of PARP-1, in a rat model of gut injury and inflammation, splanchnic artery occlusion (SAO)shock and dinitrobenzene sulfonic acid (DNBS)-induced colitis. We report here for the first time that post-injury administration of GPI 15427 and GPI 16539 exerts potent anti-inflammatory effects by reducing inflammatory cell infiltration and histological injury, and delaying the development of clinical signs in both in vivo models. Furthermore, GPI 15427 and GPI 16539 treatment diminished the accumulation of poly(ADP-ribose) in the ileum of splanchnic artery occlusion-shocked rats and in the colons of dinitrobenzene sulfonic acid-treated rats. Thus, GPI 15427 and GPI 16539 exhibited anti-inflammation activity against damage caused by intestinal ischemia/reperfusion and colitis. GPI 15427 and GPI 16539 may be useful for treating gut ischemia and inflammation.

Poly(ADP-ribose)polymerase Activation Mediates Lung Epithelial Cell DeathIn Vitrobut Is Not Essential in Hyperoxia-Induced Lung Injury

Hyperoxia induces extensive DNA damage and lung cell death by apoptotic and nonapoptotic pathways. We analyzed the regulation of Poly(ADP-ribose)polymerase-1 (PARP-1), a nuclear enzyme activated by DNA damage, and its relation to cell death during hyperoxia in vitro and in vivo. In lung epithelial-derived A549 cells, which are known to die by necrosis when exposed to oxygen, a minimal amount of PARP-1 was cleaved, correlating with the absence of active caspase-3. Conversely, in primary lung fibroblasts, which die mainly by apoptosis, the complete cleavage of PARP-1 was concomitant to the induction of active caspase-3, as assessed by Western blot and caspase activity. Blockade of caspase activity by Z-VAD reduced the amount of cleaved PARP-1 in fibroblasts. Hyperoxia induced PARP activity in both cell types, as revealed by poly-ADP-ribose accumulation. In A549 cells, the final outcome of necrosis was dependent on PARP activity because it was prevented by the PARP inhibitor 3-aminobenzamide. In contrast, apoptosis of lung fibroblasts was not sensitive to 3-aminobenzamide and was not affected by PARP-1 deletion. In vivo, despite evidence of PARP activation in hyperoxia-exposed mouse lungs, absence of PARP-1 did not change the extent of lung damage, arguing for redundant oxidative stress-induced cell death pathways.

Role of poly(ADP-ribose) polymerase-1 activation in the pathogenesis of diabetic complications: endothelial dysfunction, as a common underlying theme

Hyperglycemia-induced overproduction of superoxide by mitochondrial electron-transport chain triggers several pathways of injury involved in the pathogenesis of diabetic complications [protein kinase C (PKC), hexosamine and polyol pathway fluxes, advanced glycation end product (AGE) formation] by inhibiting glyceraldehyde- 3-phosphate dehydrogenase (GAPDH) activity. Increased oxidative and nitrosative stress activates the nuclear enzyme, poly(ADP-ribose) polymerase-1 (PARP). PARP activation, on the one hand, depletes its substrate, NAD+, slowing the rate of glycolysis, electron transport, and ATP formation. On the other hand, it inhibits GAPDH by poly(ADP-ribosy)lation. These processes result in acute endothelial dysfunction in diabetic blood vessels, which importantly contributes to the development of various diabetic complications. Accordingly, hyperglycemia-induced activation of PKC isoforms, hexosaminase pathway flux, and AGE formation is prevented by blocking PARP activity. Furthermore, inhibition of PARP protects against diabetic cardiovascular dysfunction in preclinical models. PARP activation is present in microvasculature of human diabetic subjects. The oxidative/nitrosative stress-PARP pathway leads to diabetes-induced endothelial dysfunction, which may be an important underlying mechanism for the pathogenesis of other diabetic complications (cardiomyopathy, nephropathy, neuropathy, and retinopathy). This review focuses on the role of PARP in diabetic complications and the unique therapeutic potential of PARP inhibition in the prevention or reversal of diabetic complications.

Sex differences in cell death

Female patients experience substantial neuroprotection after experimental stroke compared with male patients, a finding attributed to the protective effects of gonadal hormones. This study examined the response of male- and female-derived organotypic hippocampal slices to oxidative and excitotoxic injury. Both oxygen and glucose deprivation and N-methyl-D-aspartic acid exposure led to neuronal death; however, female-derived cultures sustained less injury than male-derived cultures. Cell death after oxygen and glucose deprivation was ameliorated in male cultures, but not female cultures, by the addition of 7-nitroindazole, a neuronal nitric oxide synthase inhibitor. These studies have relevance to researchers investigating neuroprotective agents in mixed sex experiments.

Identification of three critical acidic residues of poly(ADP-ribose) glycohydrolase involved in catalysis: determining the PARG catalytic domain

PARG [poly(ADP-ribose) glycohydrolase] catalyses the hydrolysis of alpha(1''-->2') or alpha(1'''-->2'') O-glycosidic linkages of ADP-ribose polymers to produce free ADP-ribose. We investigated possible mechanistic similarities between PARG and glycosidases, which also cleave O-glycosidic linkages. Glycosidases typically utilize two acidic residues for catalysis, thus we targeted acidic residues within a conserved region of bovine PARG that has been shown to contain an inhibitor-binding site. The targeted glutamate and aspartate residues were changed to asparagine in order to minimize structural alterations. Mutants were purified and assayed for catalytic activity, as well as binding, to an immobilized PARG inhibitor to determine ability to recognize substrate. Our investigation revealed residues essential for PARG catalytic activity. Two adjacent glutamic acid residues are found in the conserved sequence Gln755-Glu-Glu757, and a third residue found in the conserved sequence Val737-Asp-Phe-Ala-Asn741. Our functional characterization of PARG residues, along with recent identification of an inhibitor-binding residue Tyr796 and a glycine-rich region Gly745-Gly-Gly747 important for PARG function, allowed us to define a PARG 'signature sequence' [vDFA-X3-GGg-X6-8-vQEEIRF-X3-PE-X14-E-X12-YTGYa], which we used to identify putative PARG sequences across a range of organisms. Sequence alignments, along with our mapping of PARG functional residues, suggest the presence of a conserved catalytic domain of approx. 185 residues which spans residues 610-795 in bovine PARG.

NADH can enter into astrocytes and block poly(ADP-ribose) polymerase-1-mediated astrocyte death

Poly(ADP-ribose) polymerase-1 consumes NAD to catalyze poly(ADP-ribosyl)ation of target proteins, which modulates various biological functions. However, excessive poly(ADP-ribose) polymerase-1 activation mediates oxidative cell death. Our recent studies have indicated that NAD can enter into astrocytes to prevent poly(ADP-ribose) polymerase-1 cytotoxicity. In this study, we show that NADH can also enter into astrocytes, which can significantly decrease poly(ADP-ribose) polymerase-1-induced astrocyte death even when applied 3-4 h after poly(ADP-ribose) polymerase-1 activation. The protective effects can be produced by 10 muM NADH, which is significantly lower than that required for NAD to be protective. These results provide novel information suggesting that NADH can be used for decreasing poly(ADP-ribose) polymerase-1 toxicity, and extracellular NADH can enter into astrocytes to influence cellular functions.

Neuroprotective effects of KCL-440, a new poly(ADP-ribose) polymerase inhibitor, in the rat middle cerebral artery occlusion model

It is reported that ischemic brain injury is mediated by the activation of poly(ADP-ribose) polymerase (PARP). In this study, we examined the pharmacological profile of KCL-440, a new PARP inhibitor, and its neuroprotective effects in the rat acute cerebral infarction model induced by photothrombotic middle cerebral artery (MCA) occlusion. In an in vitro study, KCL-440 exhibited potency with regard to inhibition of PARP activity, with an IC50 value of 68 nM. An in vivo pharmacokinetic study showed that the brain concentration of KCL-440 was sufficient to inhibit PARP activity during the intravenous infusion of KCL-440 at the rate of 1 mg/kg/h. KCL-440 at various doses or saline was administered for 24 h immediately after the MCA occlusion. Administration of KCL-440 led to a dose-dependent reduction in the infarct size at 24 h after MCA occlusion. Infarct sizes were 44.8% +/- 3.0% (n = 8), 40.5% +/- 1.1% (n = 8), 38.2% +/- 1.4% (n = 8), 35.1% +/- 2.1% (n = 8), 34.2% +/- 2.3% (n = 7), 32.6% +/- 1.9% (n = 8), and 31.0% +/- 2.1% (n = 5) at doses of 0, 0.01, 0.03, 0.1, 0.3, 1.0, and 3.0 mg/kg/h. When compared to the control group, a statistically significant difference was observed in the doses that were higher than 0.03 mg/kg/h. When the infusion of KCL-440 (1 mg/kg/h, n = 8) was started at 1 h after the MCA occlusion, a significant reduction in infarct size was observed; this was not observed when KCL-440 infusion was started 2 or 3 h after the MCA occlusion. Furthermore, increased poly(ADP-ribose) immunostaining was confirmed at the ischemic border zone 2 h after the MCA occlusion, and it was reduced by KCL-440 treatment. These results suggest that KCL-440 is a possible neuroprotective agent with high blood-brain barrier permeability and high PARP inhibitory activity.

Mediation of cell death by poly(ADP-ribose) polymerase-1

Poly(ADP-ribosyl)ation plays an important role in modulating the cellular response to stress. The extent of poly(ADP-ribosyl)ation, chiefly via the activation of the poly(ADP-ribose) polymerase-1 (PARP-1), correlates with the severity of genotoxic stress and this determines the cellular response. Under mild and moderate stress, it plays important roles in DNA processing and it participates in the proinflammatory/cellular defense via transcriptional regulation. However, severe stress following acute neuronal injury causes the overactivation of PARP-1, which results in unregulated poly(ADP-ribose) (PAR) synthesis and widespread neuronal cell death. Previously, this PARP-1-dependent cell death mechanism was manifest solely through necrosis, but apoptotic mechanisms are also evident. Poly(ADP-ribosyl)ation directly induces the nuclear translocation of apoptosis-inducing factor, which results in caspase-independent cell death significant in many neurodegenerative conditions. Further, the hydrolysis of PAR by poly(ADP-ribose) glycohydrolase (PARG) has a protective role, since the accumulation of PAR leads to cell death by apoptosis. Thus, PAR signaling, regulated by PARP-1 and PARG, mediates cell death. Accordingly, modulation of PAR synthesis or degradation through the targeting of PARP-1 or PARG holds particular promise in the treatment of conditions such as cancer, stroke, and Parkinson's disease.

Poly(ADP-ribosyl)ation and stroke

Over the past decade, poly(ADP-ribosyl)ation has emerged as a crucial event in the pathogenesis of ischemic stroke. A large body of evidence unambiguously demonstrates that activity of poly(ADP-ribose) polymerase-1 (PARP-1) significantly increases during brain ischemia, and that inhibition of this enzymatic activity affords substantial neuroprotection from ischemic brain injury. This review strictly focuses on literature on poly(ADP-ribosyl)ation and ischemic stroke, highlighting the pathogenetic role of poly(ADP-ribose) in ischemic neuronal death, and the therapeutic relevance of drugs modulating its metabolism to pharmacological treatment of cerebral ischemia.

Shock, inflammation and PARP

The activation of poly(ADP-ribose) polymerase (PARP) is well considered to play an important role in various patho-physiological conditions like inflammation and shock. A vast amount of circumstantial evidence implicates oxygen-derived free radicals (especially, superoxide and hydroxyl radical) and high-energy oxidants (such as peroxynitrite) as mediators of inflammation and shock. ROS (e.g., superoxide, peroxynitrite, hydroxyl radical and hydrogen peroxide) are all potential reactants capable of initiating DNA single strand breakage, with subsequent activation of the nuclear enzyme poly(ADP-ribose) synthetase (PARS), leading to eventual severe energy depletion of the cells, and necrotic-type cell death. During the last years, numerous experimental studies have clearly demonstrated the beneficial effects of PARP inhibition in cell cultures through rodent models and more recently in pre-clinical large animal models of acute and chronic inflammation. The aim of this review is to describe recent experimental evidence implicating PARP as a pathophysiological modulator of acute and chronic inflammation.

Role of poly(ADP-ribose) glycohydrolase (PARG) in shock, ischemia and reperfusion

Poly(ADP-ribosyl)ation is regulated by the synthesizing enzyme poly(ADP-ribose) polymerase-1 (PARP-1) and the degrading enzyme poly(ADP-ribose) glycohydrolase (PARG). Homeostasis of poly(ADP-ribosyl)ation has been proposed to be an important regulator for pathogenesis in multi-cellular organisms. Although the role of PARP-1 in tissue damage, inflammation and ischemia has been extensively studied, the function of PARG in various cellular processes is largely unknown. Recent studies using chemical inhibitors of PARG and genetically engineered Drosophila and mouse models that carry a disrupted PARG gene have started to shed new light on the biological function of PARG in vivo. These animal models and cells isolated from them will be useful for further validation of PARG as a potential pharmaceutical target to intervene the pathogenesis induced by acute tissue injury, ischemia and inflammation.