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

Calpain activation and Na+/Ca2+ exchanger degradation occur downstream of calcium deregulation in hippocampal neurons exposed to excitotoxic glutamate

Delayed calcium deregulation (DCD) plays an essential role in glutamate excitotoxicity, a major detrimental factor in stroke, traumatic brain injury, and various neurodegenerations. In the present study, we examined the role of calpain activation and Na(+)/Ca(2+) exchanger (NCX) degradation in DCD and excitotoxic cell death in cultured hippocampal neurons. Exposure of neurons to glutamate caused DCD accompanied by secondary mitochondrial depolarization. Activation of calpain was evidenced by detecting NCX isoform 3 (NCX3) degradation products. Degradation of NCX isoform 1 (NCX1) was below the detection limit of Western blotting. Degradation of NCX3 was detected only after 1 hr of incubation with glutamate, whereas DCD occurred on average within 15 min after glutamate application. Calpeptin, an inhibitor of calpain, significantly attenuated NCX3 degradation but failed to inhibit DCD and excitotoxic neuronal death. Calpain inhibitors I, III, and VI also failed to influence DCD and glutamate-induced neuronal death. On the other hand, MK801, an inhibitor of the NMDA subtype of glutamate receptors, added shortly after the initial glutamate-induced jump in cytosolic Ca(2+), completely prevented DCD and activation of calpain and strongly protected neurons against excitotoxicity. Taken together, our results suggest that, in glutamate-treated hippocampal neurons, the initial increase in cytosolic Ca(2+) that precedes DCD is insufficient for sustained calpain activation, which most likely occurs downstream of DCD.

Astrocytic poly(ADP-ribose) polymerase-1 activation leads to bioenergetic depletion and inhibition of glutamate uptake capacity

Poly(ADP-ribose) polymerase-1 (PARP-1) is a ubiquitous nuclear enzyme involved in genomic stability. Excessive oxidative DNA strand breaks lead to PARP-1-induced depletion of cellular NAD(+), glycolytic rate, ATP levels, and eventual cell death. Glutamate neurotransmission is tightly controlled by ATP-dependent astrocytic glutamate transporters, and thus we hypothesized that astrocytic PARP-1 activation by DNA damage leads to bioenergetic depletion and compromised glutamate uptake. PARP-1 activation by the DNA alkylating agent, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), caused a significant reduction of cultured cortical astrocyte survival (EC(50) = 78.2 +/- 2.7 microM). HPLC revealed MNNG-induced time-dependent reductions in NAD(+) (98%, 4 h), ATP (71%, 4 h), ADP (63%, 4 h), and AMP (66%, 4 h). The maximal [(3)H]glutamate uptake rate (V(max)) also declined in a manner that corresponded temporally with ATP depletion, falling from 19.3 +/- 2.8 in control cells to 2.1 +/- 0.8 nmol/min/mg protein 4 h post-MNNG. Both bioenergetic depletion and loss of glutamate uptake capacity were attenuated by genetic deletion of PARP-1, directly indicating PARP-1 involvement, and by adding exogenous NAD(+) (10 mM). In mixed neurons/astrocyte cultures, MNNG neurotoxicity was partially mediated by extracellular glutamate and was reduced by co-culture with PARP-1(-/-) astrocytes, suggesting that impairment of astrocytic glutamate uptake by PARP-1 can raise glutamate levels sufficiently to have receptor-mediated effects at neighboring neurons. Taken together, these experiments showed that PARP-1 activation leads to depletion of the total adenine nucleotide pool in astrocytes and severe reduction in neuroprotective glutamate uptake capacity.

Influence of PARP-1 polymorphisms in patients after traumatic brain injury

Poly(ADP-ribose) polymerase-1 (PARP-1) plays an important role in the cellular response to stress and DNA damage. However, excessive activity of PARP-1 exacerbates brain injury via NAD+ depletion and energy failure. The purpose of this study was to determine if tagging single nucleotide polymorphisms (tSNPs) covering multiple regions of the PARP-1 gene are related to outcome after traumatic brain injury (TBI) in humans. DNA from 191 adult patients with severe TBI was assayed for four tSNPs corresponding to haplotype blocks spanning the PARP-1 gene. Categorization as favorable or poor outcome was based on Glasgow Outcome Scale (GOS) score assigned at 6 months. PARP-1 enzyme activity was indirectly evaluated by quantifying poly-ADP-ribose (PAR)-modified proteins in cerebrospinal fluid (CSF) using an enzyme-linked immunosorbent assay. In multiple logistic regression analysis controlling for age, initial Glasgow Coma Scale score, and gender, the AA genotype of SNP rs3219119 was an independent predictor of favorable neurologic outcome. This SNP tags a haplotype block spanning the automodification and catalytic domains of the PARP-1 gene. SNP rs2271347 correlated with CSF PAR-modified protein level. This SNP, which did not correlate with outcome, tags a haplotype block spanning the promoter region of the PARP-1 gene. We conclude that after severe TBI in humans, a PARP-1 polymorphism within the automodification-catalytic domain is associated with neurological outcome, while a polymorphism within the promoter region was associated with CSF PAR-modified protein level. These findings must be replicated in a prospective study before the relevance of PARP-1 polymorphisms after TBI can be established.

Protective effect of nicotinamide against poly(ADP-ribose) polymerase-1-mediated astrocyte death depends on its transporter-mediated uptake

AIM

Poly(ADP-ribose) polymerase-1 (PARP-1) is a DNA repair enzyme, and its excessive activation, following ischemia, trauma, etc., depletes cellular nicotinamide adenine dinucleotide (NAD(+)) as a substrate and eventually leads to brain cell death. Nicotinamide, an NAD(+) precursor and a PARP-1 inhibitor, is known to prevent PARP-1-triggered cell death, but there is no available information on the mechanisms involved in its transport. Here we clarified the transport characteristics of nicotinamide in primary cultured mouse astrocytes.

MAIN METHODS

Uptake characteristics of [(14)C]nicotinamide were assessed by a conventional method with primary cultured mouse astrocytes. Cell viability and PARP-1 activity were determined with intracellular LDH activity and immunocytochemical detection of PAR accumulation, respectively.

KEY FINDINGS

PARP-1 activation was induced by treatment of astrocytes with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), an alkylating agent. MNNG-triggered astrocyte death and PAR accumulation were completely inhibited by treatment with nicotinamide as with DPQ (3,4-dihydro-5-(4-(1-piperidinyl)butoxy)-1(2H)-isoquinolinone), a second generation PARP inhibitor. The uptake of [(14)C]nicotinamide was time-, temperature-, concentration- and pH-dependent, and was inhibited and stimulated by co- and pre-treatment with N-methylnicotinamide, a representative substrate of an organic cation transport system, respectively. Co-treatment of astrocytes with nicotinamide and N-methylnicotinamide resulted in a decrease in PAR accumulation and absolute prevention of cell death.

SIGNIFICANCE

These findings suggest that nicotinamide has a protective effect against PARP-1-induced astrocyte death and that its transporter-mediated uptake, which is extracellular pH-sensitive and common to N-methylnicotinamide, is critical for prevention of PARP-1-triggered cell death.

PISA, a novel pharmacodynamic assay for assessing poly(ADP-ribose) polymerase (PARP) activity in situ

INTRODUCTION

Poly ADP-ribose polymerase (PARP) maintains genomic integrity by repairing DNA strand breaks, however over-activation of PARP following neural tissue injury is hypothesized to cause neuronal death. Therefore, PARP inhibitors have potential for limiting neural injury under certain conditions. A reliable method for assessing PARP activity in brain is critical for development of novel inhibitors with CNS activity. We developed the PARP In Situ Activity (PISA) assay to provide a direct, quantitative assessment of CNS PARP activity in vitro or in vivo.

METHODS

The assay utilized brain sections from rats with striatal kainic acid (KA) lesions and 3H- or biotinylated NAD+ as the substrate to assess PARP activity. Following optimization of the assay, it was used to assess in vitro and in vivo efficacy of known and novel PARP inhibitors. The assay also was used to assess PARP activity in male and female gonad-intact and ovariectomized rats.

RESULTS

Using 3H-NAD+ as the substrate, PARP activity was greater (p<0.01) in tissue from KA-lesioned vs. non-lesioned rats. Using biotinylated NAD+ it was revealed that PARP activity was present ipsilateral to the KA injection site, and labeling was blocked by incubation with excess unlabeled NAD+ or PARP inhibitors. The PARP inhibitor, 3-aminobenzamide and several novel inhibitors reduced (p<0.01) polymerase activity in vitro. Furthermore, the inhibitor MRLSD303 reduced (p<0.001) PARP activity in vivo in both male and female rats. Finally, administration of the novel PARP inhibitor MRLIT115 dose-dependently reduced (p<0.001) polymerase activity in vivo.

DISCUSSION

The PISA assay provides a direct, quantitative method for assessing PARP activity in vitro and provides critical information on factors underlying in vivo efficacy of chemical inhibitors including brain penetration and target engagement. These findings support use of the PISA assay as a screening tool for testing efficacy of PARP inhibitors in brain.

Parp1 activation in mouse embryonic fibroblasts promotes Pol beta-dependent cellular hypersensitivity to alkylation damage

Alkylating agents induce cell death in wild-type (WT) mouse embryonic fibroblasts (MEFs) by multiple mechanisms, including apoptosis, autophagy and necrosis. DNA polymerase beta (Pol beta) knockout (KO) MEFs are hypersensitive to the cytotoxic effect of alkylating agents, as compared to WT MEFs. To test the hypothesis that Parp1 is preferentially activated by methyl methanesulfonate (MMS) exposure of Pol beta KO MEFs, we have examined the relationship between Pol beta expression, Parp1 activation and cell survival following MMS exposure in a series of WT and Pol beta deficient MEF cell lines. Consistent with our hypothesis, we observed elevated Parp1 activation in Pol beta KO MEFs as compared to matched WT MEFs. Both the MMS-induced activation of Parp1 and the MMS-induced cytotoxicity of Pol beta KO MEFs are attenuated by pre-treatment with the Parp1/Parp2 inhibitor PJ34. Further, elevated Parp1 activation is observed following knockdown (KD) of endogenous Pol beta, as compared to WT cells. Pol beta KD MEFs are hypersensitive to MMS and both the MMS-induced hypersensitivity and Parp1 activation is prevented by pre-treatment with PJ34. In addition, the MMS-induced cellular sensitivity of Pol beta KO MEFs is reversed when Parp1 is also deleted (Pol beta/Parp1 double KO MEFs) and we observe no MMS sensitivity differential between Pol beta/Parp1 double KO MEFs and those that express recombinant mouse Pol beta. These studies suggest that Parp1 may function as a sensor of BER to initiate cell death when BER is aborted or fails. Parp1 may therefore function in BER as a tumor suppressor by initiating cell death and preventing the accumulation of cells with chromosomal damage due to a BER defect.

Oxidative Stress Induced Mitochondrial Failure and Vascular Hypoperfusion as a Key Initiator for the Development of Alzheimer Disease

Mitochondrial dysfunction may be a principal underlying event in aging, including age-associated brain degeneration. Mitochondria provide energy for basic metabolic processes. Their decay with age impairs cellular metabolism and leads to a decline of cellular function. Alzheimer disease (AD) and cerebrovascular accidents (CVAs) are two leading causes of age-related dementia. Increasing evidence strongly supports the theory that oxidative stress, largely due to reactive oxygen species (ROS), induces mitochondrial damage, which arises from chronic hypoperfusion and is primarily responsible for the pathogenesis that underlies both disease processes. Mitochondrial membrane potential, respiratory control ratios and cellular oxygen consumption decline with age and correlate with increased oxidant production. The sustained hypoperfusion and oxidative stress in brain tissues can stimulate the expression of nitric oxide synthases (NOSs) and brain endothelium probably increase the accumulation of oxidative stress products, which therefore contributes to blood brain barrier (BBB) breakdown and brain parenchymal cell damage. Determining the mechanisms behind these imbalances may provide crucial information in the development of new, more effective therapies for stroke and AD patients in the near future.

Bioenergetic metabolites regulate base excision repair-dependent cell death in response to DNA damage

Base excision repair (BER) protein expression is important for resistance to DNA damage-induced cytotoxicity. Conversely, BER imbalance [DNA polymerase beta (Polbeta) deficiency or repair inhibition] enhances cytotoxicity of radiation and chemotherapeutic DNA-damaging agents. Whereas inhibition of critical steps in the BER pathway result in the accumulation of cytotoxic DNA double-strand breaks, we report that DNA damage-induced cytotoxicity due to deficiency in the BER protein Polbeta triggers cell death dependent on poly(ADP-ribose) (PAR) polymerase activation yet independent of PAR-mediated apoptosis-inducing factor nuclear translocation or PAR glycohydrolase, suggesting that cytotoxicity is not from PAR or PAR catabolite signaling. Cell death is rescued by the NAD(+) metabolite beta-nicotinamide mononucleotide and is synergistic with inhibition of NAD(+) biosynthesis, showing that DNA damage-induced cytotoxicity mediated via BER inhibition is primarily dependent on cellular metabolite bioavailability. We offer a mechanistic justification for the elevated alkylation-induced cytotoxicity of Polbeta-deficient cells, suggesting a linkage between DNA repair, cell survival, and cellular bioenergetics.

Poly (ADP-ribose) polymerase-1 initiated neuronal cell death pathway--do androgens matter?

Activation of poly (ADP-ribose) polymerases (PARP) contributes to ischemic damage by causing neuronal nicotinamide adenine dinucleotide (NAD(+)) depletion, release of apoptosis-inducing factor and consequent caspase-independent cell death. PARP-mediated cell death is sexually dimorphic, participating in ischemic damage in the male brain, but not the female brain. We tested the hypothesis that androgen signaling is required for this male-specific neuronal cell death pathway. We observed smaller damage following focal cerebral ischemia (MCAO) in male PARP-1 knockout mice compared to wild type (WT) as well as decreased damage in male mice treated with the PARP inhibitor PJ34. Protection from ischemic damage provided by PJ-34 in WT mice is lost after removal of testicular androgens (CAST) and rescued by androgen replacement. CAST PARP-1 KO mice exhibit increased damage compared to intact male KO mice, an effect reversed by androgen replacement in an androgen receptor-dependent manner. Lastly, we observed that ischemia causes an increase in PARP-1 expression that is diminished in the absence of testicular androgens. Our data indicate that PARP-mediated neuronal cell death in the male brain requires intact androgen-androgen receptor signaling.

Mitochondrial calpain system: an overview

Calpain system is generally known to be comprised of three molecules: two Ca2+-dependent proteases: mu- and m-calpains, and their endogenous inhibitor, calpastatin. While calpains have previously been considered as the cytoplasmic enzymes, research in the recent past demonstrated that mu-calpain, m-calpain and calpain 10 are present in mitochondria, which play important roles in a variety of pathophysiological conditions including necrotic and apoptotic cell death phenomena. Although a number of original research articles on mitochondrial calpain system are available, yet to the best of our knowledge, a precise review article on mitochondrial calpain system has, however, not been available. This review outlines the key features of the mitochondrial calpain system, and its roles in several cellular and biochemical events under normal and some pathophysiological conditions.

Recent advances in physiological and pathological significance of NAD+ metabolites: roles of poly(ADP-ribose) and cyclic ADP-ribose in insulin secretion and diabetogenesis

Poly(ADP-ribose) synthetase/polymerase (PARP) activation causes NAD+ depletion in pancreatic beta-cells, which results in necrotic cell death. On the other hand, ADP-ribosyl cyclase/cyclic ADP-ribose hydrolase (CD38) synthesizes cyclic ADP-ribose from NAD+, which acts as a second messenger, mobilizing intracellular Ca2+ for insulin secretion in response to glucose in beta-cells. PARP also acts as a regenerating gene (Reg) transcription factor to induce beta-cell regeneration. This provides the new concept that NAD+ metabolism can control the cellular function through gene expression. Clinically, PARP could be one of the most important therapeutic targets; PARP inhibitors prevent cell death, maintain the formation of a second messenger, cyclic ADP-ribose, to achieve cell function, and keep PARP functional as a transcription factor for cell regeneration.

Discovery and SAR of novel, potent and selective hexahydrobenzonaphthyridinone inhibitors of poly(ADP-ribose)polymerase-1 (PARP-1)

A novel hexahydrobenzonaphthyridinone PARP-1 pharmacophore is reported, subsequent SAR exploration around this scaffold led to selective PARP-1 inhibitors with low nanomolar enzyme potency, displaying good cellular activity and promising rat PK properties.

Outer mitochondrial membrane localization of apoptosis-inducing factor: mechanistic implications for release

Poly(ADP-ribose) polymerase-1-dependent cell death (known as parthanatos) plays a pivotal role in many clinically important events including ischaemia/reperfusion injury and glutamate excitotoxicity. A recent study by us has shown that uncleaved AIF (apoptosis-inducing factor), but not calpain-hydrolysed truncated-AIF, was rapidly released from the mitochondria during parthanatos, implicating a second pool of AIF that might be present in brain mitochondria contributing to the rapid release. In the present study, a novel AIF pool is revealed in brain mitochondria by multiple biochemical analyses. Approx. 30% of AIF loosely associates with the outer mitochondrial membrane on the cytosolic side, in addition to its main localization in the mitochondrial intermembrane space attached to the inner membrane. Immunogold electron microscopic analysis of mouse brain further supports AIF association with the outer, as well as the inner, mitochondrial membrane in vivo. In line with these observations, approx. 20% of uncleaved AIF rapidly translocates to the nucleus and functionally causes neuronal death upon NMDA (N-methyl-d-aspartate) treatment. In the present study we show for the first time a second pool of AIF in brain mitochondria and demonstrate that this pool does not require cleavage and that it contributes to the rapid release of AIF. Moreover, these results suggest that this outer mitochondrial pool of AIF is sufficient to cause cell death during parthanatos. Interfering with the release of this outer mitochondrial pool of AIF during cell injury paradigms that use parthanatos hold particular promise for novel therapies to treat neurological disorders.

Brain ischemic preconditioning does not require PARP-1

BACKGROUND AND PURPOSE

Poly(ADP-ribose) polymerase-1 (PARP-1) is involved in ischemic preconditioning of the heart and cultured neurons, but its role in brain ischemic preconditioning is unknown. Summary of Report- We report that 5-minute bilateral common carotid artery occlusion (BCCAO) in the mouse prompted reduction of infarct volumes triggered 24 hours later by 20-minute middle cerebral artery occlusion (MCAO). Pharmacological PARP-1 inhibition between BCCAO and MCAO did not impair preconditioning. The contents of the PARP-1 substrate NAD, those of its product poly(ADP-ribose), caspase-3 activation, and PARP-1 expression did not change after BCCAO within the preconditioned tissue. PARP-1 KO mice were similarly protected by the 5-minute BCCAO.

CONCLUSIONS

Data demonstrate that, at variance with the heart, PARP-1 is dispensable for brain ischemic preconditioning.

Mitochondria, oxidative metabolism and cell death in stroke

Stroke most commonly results from occlusion of a major artery in the brain and typically leads to the death of all cells within the affected tissue. Mitochondria are centrally involved in the development of this tissue injury due to modifications of their major role in supplying ATP and to changes in their properties that can contribute to the development of apoptotic and necrotic cell death. In animal models of stroke, the limited availability of glucose and oxygen directly impairs oxidative metabolism in severely ischemic regions of the affected tissue and leads to rapid changes in ATP and other energy-related metabolites. In the less-severely ischemic "penumbral" tissue, more moderate alterations develop in these metabolites, associated with near normal glucose use but impaired oxidative metabolism. This tissue remains potentially salvageable for at least the first few hours following stroke onset. Early restoration of blood flow can result in substantial recovery of energy-related metabolites throughout the affected tissue. However, glucose oxidation is markedly decreased due both to lower energy requirements in the post-ischemic tissue and limitations on the mitochondrial oxidation of pyruvate. A secondary deterioration of mitochondrial function subsequently develops that may contribute to progression to cell loss. Mitochondrial release of multiple apoptogenic proteins has been identified in ischemic and post-ischemic brain, mostly in neurons. Pharmacological interventions and genetic modifications in rodent models strongly implicate caspase-dependent and caspase-independent apoptosis and the mitochondrial permeability transition as important contributors to tissue damage, particularly when induced by short periods of temporary focal ischemia.

Aldosterone-induced endothelial dysfunction of rat aorta: role of poly(ADP-ribose) activation

Introduction. The aim of this study was to investigate whether activation of the nuclear enzyme poly(ADP-ribose) polymerase (PARP) contributes to the development of aldosterone-induced endothelial dysfunction and treatment with the potent PARP inhibitor 1,5-isoquinolinediol (3 mg/kg/day, i.p.) could prevent endothelial dysfunction caused by aldosterone.

Methods. Infusion of subpressor doses of aldosterone with subcutaneously implanted mini-osmotic pumps (0.05 mg/kg/day) to rats for 21 days induced the development of endothelial dysfunction. In order to evaluate endothelial function, isometric tension studies were performed in response to acetylcholine and sodium nitroprusside.Additionally, PAR (the end product of activated PARP) and PARP-1 expressions in the endothelium of thoracic aortas were evaluated by immunohistochemistry.

Results. There was a significant loss of endothelium-dependent vasodilatation in response to acetylcholine in aldosterone-infused rats. In animals treated with 1,5-isoquinolinediol, the effect of aldosterone on vascular responsiveness was less than the untreated groups. Immunohistochemical studies demonstrated that aldosterone administration increased PAR and PARP-1 expressions in the endothelium of thoracic aortas, whereas PARP inhibition decreased their expressions to control levels.

Conclusion. Our results indicate that PARP activation in the vascular system may be a contributory factor to the impaired endothelial function associated with aldosterone administration.

Mechanisms of gender-linked ischemic brain injury

Biological sex is an important determinant of stroke risk and outcome. Women are protected from cerebrovascular disease relative to men, an observation commonly attributed to the protective effect of female sex hormones, estrogen and progesterone. However, sex differences in brain injury persist well beyond the menopause and can be found in the pediatric population, suggesting that the effects of reproductive steroids may not completely explain sexual dimorphism in stroke. We review recent advances in our understanding of sex steroids (estradiol, progesterone and testosterone) in the context of ischemic cell death and neuroprotection. Understanding the molecular and cell-based mechanisms underlying sex differences in ischemic brain injury will lead to a better understanding of basic mechanisms of brain cell death and is an important step toward designing more effective therapeutic interventions in stroke.

Nicotinamide rescues human embryonic stem cell-derived neuroectoderm from parthanatic cell death

Abundant cell death is observed when human embryonic stem cells (hESCs) undergo neuralization, a critical first step for future cell-based therapies addressing neurodegeneration. Using hESC neuralization as an in vitro model of human development, we demonstrated that the developing neuroepithelium acquires increased susceptibility to spontaneous cell death. We found that poly(ADP-ribose) polymerase-1 (PARP1)/apoptosis-inducing factor (AIF)-mediated cell death (parthanatos) is a dominant mechanism responsible for cell loss during hESC neuralization. The demise of neural progenitor cells, at least in part, is due to decreased endogenous antioxidant defenses and enhanced reactive oxygen species leakage from mitochondria fuelled by nonphysiological culture conditions. Under such conditions, PARP1 overactivation triggered cell death through the mitochondrial-nuclear translocation of AIF. Blocking PARP1 activity with small hairpin RNA interference or nicotinamide dramatically enhanced hESC neuralization, providing optimal survival of the developing neuroepithelium. Because nicotinamide is a physiological metabolite, our results raise the possibility that neural stem/progenitor cell survival in vivo requires a metabolic niche. We argue that small natural metabolites provide a powerful physiological tool to optimize hESC differentiation compatible with the requirements of regenerative medicine.

Poly(ADP-ribose) polymerase-1 modulation of in vivo response of brain hypoxia-inducible factor-1 to hypoxia/reoxygenation is mediated by nitric oxide and factor inhibiting HIF

Poly(ADP-ribose) polymerase-1 (PARP-1) is a nuclear protein that once activated by genotoxic agents, modulates its own activity and that of several other nuclear proteins. The absence or pharmacological inhibition of this protein has been proven to be beneficial in the treatment of different diseases involving a hypoxic situation. We previously reported that PARP-1 modulates the hypoxia-inducible factor-1 (HIF-1) response in vitro, but this effect has not yet been demonstrated in vivo. The brain is especially susceptible to hypoxic injury, and the present study demonstrates that PARP-1 plays a major role in the post-hypoxic response of HIF-1alpha in the cerebral cortex. Immediate post-hypoxic HIF-1alpha accumulation was higher in the presence of PARP-1, and this differential response was mediated by nitric oxide and to a lesser extent, reactive oxygen species. PARP-1 was also found to induce a more rapid but less sustained HIF-1 transcriptional activity by up-regulating the factor inhibiting HIF. The implication of PARP-1 in these results was further demonstrated by pharmacologically inhibiting PARP in wild-type mice. In conclusion, our data suggest that PARP-1 has an important regulatory role in the in vivo response of brain HIF-1 to hypoxia/reoxygenation.

PARP inhibitors: new partners in the therapy of cancer and inflammatory diseases

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, which currently comprises 18 members, is an abundant nuclear enzyme implicated in cellular responses to DNA injury provoked by genotoxic stress. PARP is involved in DNA repair and transcriptional regulation and is now recognized as a key regulator of cell survival and cell death as well as a master component of a number of transcription factors involved in tumor development and inflammation. PARP-1 is essential to the repair of DNA single-strand breaks via the base excision repair pathway. Inhibitors of PARP-1 have been shown to enhance the cytotoxic effects of ionizing radiation and DNA-damaging chemotherapy agents, such as the methylating agents and topoisomerase I inhibitors. There are currently at least five PARP inhibitors in clinical trial development. Recent in vitro and in vivo evidence suggests that PARP inhibitors could be used not only as chemo/radiotherapy sensitizers, but also as single agents to selectively kill cancers defective in DNA repair, specifically cancers with mutations in the breast cancer-associated genes (BRCA1 and BRCA2). PARP becomes activated in response to oxidative DNA damage and depletes cellular energy pools, thus leading to cellular dysfunction in various tissues. The activation of PARP may also induce various cell death processes and promotes an inflammatory response associated with multiple organ failure. Inhibition of PARP activity is protective in a wide range of inflammatory and ischemia-reperfusion-associated diseases, including cardiovascular diseases, diabetes, rheumatoid arthritis, endotoxic shock, and stroke. The aim of this review is to overview the emerging data in the literature showing the role of PARP in the pathogenesis of cancer and inflammatory diseases and unravel the solid body of literature that supports the view that PARP is an important target for therapeutic intervention in critical illness.

Poly(ADP-ribose) polymerase-1 regulates the progression of autoimmune nephritis in males by inducing necrotic cell death and modulating inflammation

Necrotic lesions and necrotic cell death characterize severe autoimmune nephritides, and contribute to local inflammation and to progression of the disease. Poly(ADP-ribose) polymerase-1 (PARP-1), a DNA repair enzyme, is involved in the induction of necrosis and is a key player in the acute and chronic inflammation. Therefore, we hypothesized that PARP-1 controls the severity of nephritis by mediating the induction of necrosis in the kidney. We used lupus and anti-glomerular basement membrane models of nephritis to determine the effects of PARP-1 on the inflammatory response in the kidney. We show in this study that PARP-1 is indeed activated during the course of glomerulonephritis. We also show that the absence of PARP-1 or its pharmacological inhibition results in milder nephritis, with lower blood urea nitrogen levels, reduced necrotic lesions, and higher survival rates. The relevance of PARP-1 showed a strong male sex specificity, and treatment of male mice with 17beta-estradiol prolonged their survival during the course of nephritis. PARP-1 also regulated TNF-alpha expression and up-regulation of adhesion molecules, further supporting a role of PARP-1 in the inflammatory process within the kidney. Our results demonstrate that PARP-1 activation and consequent necrotic cell death play an important role in the pathogenesis of male nephritis, and suggest that PARP-1 can be a novel therapeutic target in glomerulonephritis.

Calpain activation is not required for AIF translocation in PARP-1-dependent cell death (parthanatos)

Apoptosis-inducing factor (AIF) is critical for poly(ADP-ribose) polymerase-1 (PARP-1)-dependent cell death (parthanatos). The molecular mechanism of mitochondrial AIF release to the nucleus remains obscure, although a possible role of calpain I has been suggested. Here we show that calpain is not required for mitochondrial AIF release in parthanatos. Although calpain I cleaved recombinant AIF in a cell-free system in intact cells under conditions where endogenous calpain was activated by either NMDA or N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) administration, AIF was not cleaved, and it was released from mitochondria to the nucleus in its 62-kDa uncleaved form. Moreover, NMDA administration under conditions that failed to activate calpain still robustly induced AIF nuclear translocation. Inhibition of calpain with calpastatin or genetic knockout of the regulatory subunit of calpain failed to prevent NMDA- or MNNG-induced AIF nuclear translocation and subsequent cell death, respectively, which was markedly prevented by the PARP-1 inhibitor, 3,4-dihydro-5-[4-(1-piperidinyl)butoxyl]-1(2H)-iso-quinolinone. Our study clearly shows that calpain activation is not required for AIF release during parthanatos, suggesting that other mechanisms rather than calpain are involved in mitochondrial AIF release in parthanatos.

Mitochondrial mechanisms of cell death and neuroprotection in pediatric ischemic and traumatic brain injury

There are several forms of acute pediatric brain injury, including neonatal asphyxia, pediatric cardiac arrest with global ischemia, and head trauma, that result in devastating, lifelong neurologic impairment. The only clinical intervention that appears neuroprotective is hypothermia initiated soon after the initial injury. Evidence indicates that oxidative stress, mitochondrial dysfunction, and impaired cerebral energy metabolism contribute to the brain cell death that is responsible for much of the poor neurologic outcome from these events. Recent results obtained from both in vitro and animal models of neuronal death in the immature brain point toward several molecular mechanisms that are either induced or promoted by oxidative modification of macromolecules, including consumption of cytosolic and mitochondrial NAD(+) by poly-ADP ribose polymerase, opening of the mitochondrial inner membrane permeability transition pore, and inactivation of key, rate-limiting metabolic enzymes, e.g., the pyruvate dehydrogenase complex. In addition, the relative abundance of pro-apoptotic proteins in immature brains and neurons, and particularly within their mitochondria, predisposes these cells to the intrinsic, mitochondrial pathway of apoptosis, mediated by Bax- or Bak-triggered release of proteins into the cytosol through the mitochondrial outer membrane. Based on these pathways of cell dysfunction and death, several approaches toward neuroprotection are being investigated that show promise toward clinical translation. These strategies include minimizing oxidative stress by avoiding unnecessary hyperoxia, promoting aerobic energy metabolism by repletion of NAD(+) and by providing alternative oxidative fuels, e.g., ketone bodies, directly interfering with apoptotic pathways at the mitochondrial level, and pharmacologic induction of antioxidant and anti-inflammatory gene expression.

Calcium dysregulation induces apoptosis-inducing factor release: cross-talk between PARP-1- and calpain-signaling pathways

Recent discoveries show that caspase-independent cell death pathways are a pervasive mechanism in neurodegenerative diseases, and apoptosis-inducing factor (AIF) is an important effector of this mode of neuronal death. There are currently two known mechanisms underlying AIF release following excitotoxic stress, PARP-1 and calpain. To test whether there is an interaction between PARP-1 and calpain in triggering AIF release, we used the NMDA toxicity model in rat primary cortical neurons. Exposure to NMDA resulted in AIF truncation and nuclear translocation, and shRNA-mediated knockdown of AIF resulted in neuroprotection. Both calpain and PARP-1 are involved with AIF processing as AIF truncation, nuclear translocation and neuronal death were attenuated by calpain inhibition using adeno-associated virus-mediated overexpression of the endogenous calpain inhibitor, calpastatin, or treatment with the PARP-1 inhibitor 3-ABA. Activation of PARP-1 is necessary for calpain activation as PARP-1 inhibition blocked mitochondrial calpain activation. Finally, NMDA toxicity induces mitochondrial Ca(2+) dysregulation in a PARP-1 dependent manner. Thus, PARP-1 and mitochondrial calpain activation are linked via PARP-1-induced alterations in mitochondrial Ca(2+) homeostasis. Collectively, these findings link the two seemingly independent mechanisms triggering AIF-induced neuronal death.

The effects of nicotinamide adenine dinucleotide on intracerebral hemorrhage-induced brain injury in mice

In the present study, we investigated whether the administration of nicotinamide adenine dinucleotide (NAD+) provides brain protection in a mouse model of intracerebral hemorrhage (ICH). Male CD-1 mice were divided into sham, ICH treated with vehicle and ICH treated with NAD+ (10 or 20 mg/kg, intranasal) groups. Intranasal delivery of NAD+ resulted in an increase in NAD+ contents in the brains. ICH was induced by collagenase injection. Neurological function, hemorrhage volume and brain edema were measured 24 hours after injection. ICH caused significant neurological deficit with associated brain edema. NAD+ (10 and 20 mg/kg) failed to reduce brain injury after ICH. These results suggest that NAD+ has no neuroprotective effect at 24 hours after ICH.

Sex differences in the response to activation of the poly (ADP-ribose) polymerase pathway after experimental stroke

It is increasingly recognized that histological and functional outcomes after stroke are shaped by biologic sex. Emerging data suggests that ischemic cell death pathways are sexually dimorphic (Hurn, P., Vannucci, S., Hagberg, H. (2005) Adult or perinatal brain injury: does sex matter?. Stroke 36, 193-195 ; Lang, J.T., McCullough, L.D. (2008) Pathways to ischemic neuronal cell death: are sex differences relevant?. J. Transl. Med. 6). Reducing neuronal nitric oxide (NO) or poly-ADP-ribose polymerase (PARP1) activation protects only the male brain (Hagberg, H., et al. PARP-1 gene disruption in mice preferentially protects males from perinatal brain injury. J. Neurochem. 90, 1068-1075 (2004)), and paradoxically enhances ischemic injury in females (McCullough, L.D., et al. Ischemic nitric oxide and poly (ADP-ribose) polymerase-1 in cerebral ischemia: male toxicity, female protection. J. Cereb. Blood Flow Metab. 25, 502-512 (2005)). In this study, we examined downstream mediators of NO/PARP activation to investigate possible mediators of ischemic sexual dimorphism. Nuclear translocation of Apoptosis Inducing Factor (AIF) was equivalent in wild type males and females after stroke and was unaffected by estrogen exposure. Deletion of PARP1 led to a dramatic reduction in stroke-induced poly (ADP-ribose) polymerase (PAR) formation and AIF translocation in both sexes, yet ischemic damage was reduced only in males. Subsequent examination of AIF-deficient Harlequin mice demonstrated that male Harlequin mice had less PAR formation, reduced AIF translocation and less ischemic damage than male wild type mice. In contrast, female Harlequin mice had no neuroprotective effect of gene deletion despite robust reductions in PAR formation and AIF translocation. Although equivalent activation of this cell death pathway occurs in both sexes after ischemia, detrimental effects are only present in males. AIF translocation and PAR formation do not mediate ischemic injury in the female brain, therefore agents designed to reduce PARP1 activation are unlikely to benefit females.

Neuroprotective strategies targeting apoptotic and necrotic cell death for stroke

It has been a major challenge to develop effective therapeutics for stroke, a leading cause of death and serious debilitation. Intensive research in the past 15 years have implicated many regulators and the related mechanisms by which neuronal cell death is regulated. It is now clear that even a brief ischemic stroke may trigger complex cellular events that lead to both apoptotic and necrotic neuronal cell death in a progressive manner. Although efforts at developing specific chemical inhibitors for validated targets have been successful for in vitro enzymatic assays, the development of some of such inhibitors into human therapy has been often hindered by their in vivo bioavailability profile. Considerations for the ability to chemically target a cellular mechanism in manner compatible with disease targets in vivo might be emphasized early in the development process by putting a priority on identifying key targets that can be effectively targeted chemically. Thorough interrogation of cellular pathways by saturation chemical genetics may provide a novel strategy to identify multiple key molecular entities that can be targeted chemically in order to select a target suitable for the treatment of intended human diseases such as stroke.

Sex differences in minocycline-induced neuroprotection after experimental stroke

Minocycline is neuroprotective in clinical and experimental stroke studies, due in part to its ability to inhibit poly (ADP-ribose) polymerase. Previous preclinical data have shown that interference with poly (ADP-ribose) polymerase signaling leads to sex-specific neuroprotection, reducing stroke injury only in males. In this study, we show that minocycline is ineffective at reducing ischemic damage in females after middle cerebral artery occlusion, likely due to effects on poly (ADP-ribose) polymerase signaling. Clinical trials must consider possible sex differences in the response to neuroprotective agents, if we hope to translate promising therapies to stroke patients of both sexes.

Poly(ADP-ribose) signals to mitochondrial AIF: a key event in parthanatos

Poly(ADP-ribose) polymerase-1 (PARP-1) plays a pivotal role in multiple neurologic diseases by mediating caspase-independent cell death, which has recently been designated parthanatos to distinguish it from other forms of cell death such as apoptosis, necrosis and autophagy. Mitochondrial apoptosis-inducing factor (AIF) release and translocation to the nucleus is the commitment point for parthanatos. This process involves a pathogenic role of poly(ADP-ribose) (PAR) polymer. It generates in the nucleus and translocates to the mitochondria to mediate AIF release following lethal PARP-1 activation. PAR polymer itself is toxic to cells. Thus, PAR polymer signaling to mitochondrial AIF is the key event initiating the deadly crosstalk between the nucleus and the mitochondria in parthanatos. Targeting PAR-mediated AIF release could be a potential approach for the therapy of neurologic disorders.

Attenuation of neuronal degeneration in thioredoxin-1 overexpressing mice after mild focal ischemia

Thioredoxin (Trx) is a 12-kDa protein ubiquitously expressed in all living cells that fulfills a variety of biological functions related to cell proliferation and apoptosis. It is characterized by the highly conserved reduction/oxidation (redox)-active site sequence Trp-Cys-Gly-Pro-Cys-Lys. Trx acts as a powerful antioxidant and plays an important role in maintaining critical protein thiols in the reduced state. Moreover, it has been shown to scavenge reactive oxygen species (ROS) and to protect against oxidative stress. We have reported that Trx-1 protects against neuronal damage during focal ischemia. However, the mechanisms underlying this protective effect and the effect of Trx-1 on neuronal apoptosis during ischemia have not been fully clarified. In this study, we analyzed the effect of Trx-1 overexpression against neuronal degeneration after a short duration of transient brain ischemia. Mild focal ischemia was reported to induce neuronal death through apoptosis. We employed Fluorojade-B staining to detect neuronal degeneration. In Trx transgenic mice, a smaller number of Fluorojade-B-positive neurons were detected after ischemia-reperfusion than in wild-type mice. In addition, we detected cleaved caspase-3- and TUNEL-positive cells, which indicated caspase-dependent apoptosis. Fewer caspase-3- and TUNEL-positive neurons were detected after ischemia-reperfusion in Trx transgenic mice than in wild-type mice. Furthermore, Akt signaling was reported to play a role in neuronal survival in Trx-1 overexpressing mice. After ischemia-reperfusion, Western blot and immunohistochemical analysis indicated that phosphorylation of Akt was enhanced in Trx transgenic mice after ischemia-reperfusion. Intraventricular injection of LY294002,which is a phosphoinositide 3-kinase (PI3K), vanished the neuroprotective effect in Trx-1 transgenic mice. These results indicate that Trx-1 overexpression protects neurons from apoptosis after ischemia-reperfusion.

Sex differences in caspase activation after stroke

BACKGROUND AND PURPOSE

Over the past 5 years, experimental data have emerged that ischemia-induced cell death pathways may differ in males and females. Cell death in males is triggered by poly(ADP-ribose) polymerase activation and nuclear translocation of apoptosis-inducing factor. We have previously shown that interference with this pathway benefits males but not females after an experimental stroke. In contrast, caspase activation may be the major pathway activated after ischemic injury in females. The aim of this study is to examine whether sex differences exist in caspase activation in adult mice after stroke and to determine if interference with stroke-induced caspase activation preferentially protects females.

METHODS

Focal stroke was induced by reversible middle cerebral artery occlusion (90 minutes) in young and aging C57BL/6 mice of both sexes. The pan-caspase inhibitor, quinoline-Val-Asp(Ome)-CH2-O-phenoxy was administered at reperfusion. Histological outcomes were assessed 48 hours after middle cerebral artery occlusion. Separate cohorts were used for protein analysis of key cell death proteins, including caspase-3, caspase-8, cytochrome C, and apoptosis-inducing factor.

RESULTS

Drug-treated female mice had significantly decreased infarct volumes and improved neurological deficits after stroke compared to vehicle-treated mice. Quinoline-Val-Asp(Ome)-CH2-O-phenoxy administration had no effect in male mice. The expression of cytochrome C and nuclear caspase-8 levels were increased in females after stroke.

CONCLUSIONS

Female mice had an early release of cytochrome C and enhanced caspase activation after middle cerebral artery occlusion. Caspase inhibition benefited females but not males. Sex differences exist in both the response to ischemic injury and the efficacy of neuroprotective agents.

Antimycin A-induced cell death depends on AIF translocation through NO production and PARP activation and is not involved in ROS generation, cytochrome c release and caspase-3 activation in HL-60 cells

A respiratory inhibitor, antimycin A (AA), induced an apoptotic-like cell death characterized by nuclear and DNA fragmentation in human leukemia HL-60 cells. This cell death was significantly restricted by a nitric oxide synthase (NOS) inhibitor, N(G)-monomethyl-L-arginine (L-NMMA), and a poly(ADP-ribose) polymerase (PARP) inhibitor, 5-aminoisoquinoline (AIQ). Indeed, NO production and PARP overactivation were detected in the cells treated with AA. On the one hand, L-NMMA partly eliminated NO production and on the other, AIQ and L-NMMA also restricted PARP activation. Excessive signals related to PARP overactivation induce the translocation of an apoptosis-inducing factor (AIF) from the mitochondria to the nuclei, resulting in DNA fragmentation. In AA-treated cells, the nuclear translocation of AIF occurred. This translocation was restricted by pretreatment with AIQ and L-NMMA. Although pretreatment with ascorbic acid eliminated the reactive oxygen species (ROS) generation induced by the blockade of complex III by AA, the pretreatment did not protect the cells from AA-induced cell death. Furthermore, cytochrome c release or caspase-3 activation was not observed in the cells treated with AA. These results suggest that AA-induced cell death does not depend on respiratory inhibition and the succeeding cascades, but on NO production, PARP overactivation and AIF translocation.

Apoptotic mechanisms after cerebral ischemia

BACKGROUND AND PURPOSE

Traditionally, cell death after cerebral ischemia was considered to be exclusively necrotic in nature, but research over the past decade has revealed that after a stroke, many neurons in the ischemic penumbra will undergo apoptosis.

SUMMARY OF REVIEW

This brief review provides a general overview and update of various signaling pathways in the development of apoptosis in ischemic lesions. Cerebral ischemia triggers two general pathways of apoptosis: the intrinsic pathway, originating from mitochondrial release of cytochrome c and associated stimulation of caspase-3; and the extrinsic pathway, originating from the activation of cell surface death receptors, resulting in the stimulation of caspase-8. Although many of the key apoptotic proteins have been identified, our understanding of the complex underlying mechanisms remains poor and hence treatment of stroke patients by manipulating apoptotic pathways remains a daunting task. However, recent advances in the field have helped broaden our knowledge of apoptosis after cerebral ischemia. Further to the simplistic concept that stroke-induced apoptosis occurs predominantly in neurons and is caspase-dependent, accumulating evidence now indicates that apoptosis is prevalent in nonneuronal cells and that caspase-independent mechanisms also play a key role.

CONCLUSIONS

Although the ischemic penumbra is under threat of infarction, it is potentially salvageable and thus represents an opportunity for therapeutic intervention.

The importance of NAD in multiple sclerosis

The etiology of multiple sclerosis (MS) is unknown but it manifests as a chronic inflammatory demyelinating disease in the central nervous system (CNS). During chronic CNS inflammation, nicotinamide adenine dinucleotide (NAD) concentrations are altered by (T helper) Th1-derived cytokines through the coordinated induction of both indoleamine 2,3-dioxygenase (IDO) and the ADP cyclase CD38 in pathogenic microglia and lymphocytes. While IDO activation may keep auto-reactive T cells in check, hyper-activation of IDO can leave neuronal CNS cells starving for extracellular sources of NAD. Existing data indicate that glia may serve critical functions as an essential supplier of NAD to neurons during times of stress. Administration of pharmacological doses of non-tryptophan NAD precursors ameliorates pathogenesis in animal models of MS. Animal models of MS involve artificially stimulated autoimmune attack of myelin by experimental autoimmune encephalomyelitis (EAE) or by viral-mediated demyelination using Thieler's murine encephalomyelitis virus (TMEV). The Wld(S) mouse dramatically resists razor axotomy mediated axonal degeneration. This resistance is due to increased efficiency of NAD biosynthesis that delays stress-induced depletion of axonal NAD and ATP. Although the Wld(S) genotype protects against EAE pathogenesis, TMEV-mediated pathogenesis is exacerbated. In this review, we contrast the role of NAD in EAE versus TMEV demyelinating pathogenesis to increase our understanding of the pharmacotherapeutic potential of NAD signal transduction pathways. We speculate on the importance of increased SIRT1 activity in both PARP-1 inhibition and the potentially integral role of neuronal CD200 interactions through glial CD200R with induction of IDO in MS pathogenesis. A comprehensive review of immunomodulatory control of NAD biosynthesis and degradation in MS pathogenesis is presented. Distinctive pharmacological approaches designed for NAD-complementation or targeting NAD-centric proteins (SIRT1, SIRT2, PARP-1, GPR109a, and CD38) are outlined towards determining which approach may work best in the context of clinical application.

Parthanatos, a messenger of death

Poly-ADP-ribose polymerase-1 (PARP-1)'s roles in the cell span from maintaining life to inducing death. The processes PARP-1 is involved in include DNA repair, DNA transcription, mitosis, and cell death. Of PARP-1's different cellular functions, its role in cell death is of particular interest to designing therapies for diseases. Genetic deletion of PARP-1 revealed that PARP-1 overactivation underlies cell death in models of stroke, diabetes, inflammation and neurodegeneration. Since interfering with PARP-1 mediated cell death will be clinically beneficial, great effort has been invested into understanding mechanisms downstream of PARP-1 overactivation. Recent evidence shows that poly-ADP ribose (PAR) polymer itself can act as a cell death effector downstream of PARP-1. We coined the term parthanatos after Thanatos, the personification of death in Greek mythology, to refer to PAR-mediated cell death. In this review, we will present evidence and questions raised by these recent findings, and summarize the proposed mechanisms by which PARP-1 overactivation kills. It is evident that further understanding of parthanatos opens up new avenues for therapy in ameliorating diseases related to PARP-1 overactivation.

Essential role for zinc-triggered p75NTR activation in preconditioning neuroprotection

Ischemic preconditioning (PC) of the brain is a phenomenon by which mild ischemic insults render neurons resistant to subsequent strong insults. Key steps in ischemic PC of the brain include caspase-3 activation and poly(ADP-ribose) polymerase-1 (PARP-1) cleavage, but upstream events have not been clearly elucidated. We have tested whether endogenous zinc is required for ischemic PC of the brain in rats. Mild, transient zinc accumulation was observed in certain neurons after ischemic PC. Moreover, intraventricular administration of CaEDTA during ischemic PC abrogated both zinc accumulation and the protective effect against subsequent full ischemia. To elucidate the mechanism of the zinc-triggered PC (Zn PC) effect, cortical cultures were exposed to sublethal levels of zinc, and 18 h later to lethal levels of zinc or NMDA. Zn PC exhibited the characteristic features of ischemic PC, including caspase-3 activation, PARP-1 cleavage, and HSP70 induction, all of which are crucial for subsequent neuroprotection against NMDA or zinc toxicity. HSP70 induction was necessary for protection, as it halted caspase-3 activation before apoptosis. Interestingly, in both Zn PC in vitro and ischemic PC in vivo, p75(NTR) was necessary for neuroprotection. These results suggest that caspase-3 activation during ischemic PC, a necessary event for subsequent neuroprotection, may result from mild zinc accumulation and the consequent p75(NTR) activation in neurons.

Imidazoquinolinone, imidazopyridine, and isoquinolindione derivatives as novel and potent inhibitors of the poly(ADP-ribose) polymerase (PARP): a comparison with standard PARP inhibitors

We have identified three novel structures for inhibitors of the poly(ADP-ribose) polymerase (PARP), a nuclear enzyme activated by strand breaks in DNA and implicated in DNA repair, apoptosis, organ dysfunction or necrosis. 2-[4-(5-Methyl-1H-imidazol-4-yl)-piperidin-1-yl]-4,5-dihydro-imidazo[4,5,1-i,j]quinolin-6-one (BYK49187), 2-(4-pyridin-2-yl-phenyl)-4,5-dihydro-imidazo[4,5,1-i,j]quinolin-6-one (BYK236864), 6-chloro-8-hydroxy-2,3-dimethyl-imidazo-[1,2-alpha]-pyridine (BYK20370), and 4-(1-methyl-1H-pyrrol-2-ylmethylene)-4H-isoquinolin-1,3-dione (BYK204165) inhibited cell-free recombinant human PARP-1 with pIC(50) values of 8.36, 7.81, 6.40, and 7.35 (pK(i) 7.97, 7.43, 5.90, and 7.05), and murine PARP-2 with pIC(50) values of 7.50, 7.55, 5.71, and 5.38, respectively. BYK49187, BYK236864, and BYK20370 displayed no selectivity for PARP-1/2, whereas BYK204165 displayed 100-fold selectivity for PARP-1. The IC(50) values for inhibition of poly(ADP-ribose) synthesis in human lung epithelial A549 and cervical carcinoma C4I cells as well in rat cardiac myoblast H9c2 cells after PARP activation by H(2)O(2) were highly significantly correlated with those at cell-free PARP-1 (r(2) = 0.89-0.96, P < 0.001) but less with those at PARP-2 (r(2) = 0.78-0.84, P < 0.01). The infarct size caused by coronary artery occlusion and reperfusion in the anesthetized rat was reduced by 22% (P < 0.05) by treatment with BYK49187 (3 mg/kg i.v. bolus and 3 mg/kg/h i.v. during 2-h reperfusion), whereas the weaker PARP inhibitors, BYK236864 and BYK20370, were not cardioprotective. In conclusion, the imidazoquinolinone BYK49187 is a potent inhibitor of human PARP-1 activity in cell-free and cellular assays in vitro and reduces myocardial infarct size in vivo. The isoquinolindione BYK204165 was found to be 100-fold more selective for PARP-1. Thus, both compounds might be novel and valuable tools for investigating PARP-1-mediated effects.

Protein nitration and poly-ADP-ribosylation in brain after rapid exsanguination cardiac arrest in a rat model of emergency preservation and resuscitation

BACKGROUND

Emergency preservation and resuscitation (EPR) of 60 min in rats is achievable with favorable outcome, while 75 min is associated with substantial mortality and impaired neurological outcome in survivors. We hypothesized that 75 min but not 60 min of EPR would be associated with activation of two potential secondary injury cascades in brain as reflected by protein nitration and poly (ADP-ribose) polymerase (PARP) activation.

METHODS

Rats were rapidly exsanguinated over 5 min. After 1 min of cardiac arrest (CA), rats were cooled to a target tympanic temperature of 15 degrees C. After either 60 min or 75 min of CA, resuscitation was achieved via cardiopulmonary bypass (CPB). Rats subjected to CPB only served as controls. Overall performance category (OPC) and neurologic deficit score (NDS) were assessed at 24 h. Protein nitration and poly-ADP-ribosylation were assessed by Western blotting and immunohistochemistry for 3-nitrotyrosine and poly-ADP ribose polymers, respectively, in multiple brain regions.

RESULTS

Neurologic outcome was better in the 60 min vs. the 75 min EPR group (OPC, P<0.001; NDS, P=0.001). Densitometric analysis of the major 64 kD band showed that nitration and PARP activation were significantly increased in hippocampus, cortex and striatum in the 75 min EPR group vs. other groups. However, there were no differences in cerebellum. Analysis of the full protein spectrum showed significantly increased PARP activation only in hippocampus in the 75 min EPR group vs. other groups.

CONCLUSIONS

Extending the duration of EPR beyond the limit that can yield favorable recovery in rats was associated with increased nitration and ribosylation of selected proteins in selectively vulnerable brain regions. The impact of these mechanisms on the outcome remains to be determined.

Tissue-type plasminogen activator and the low-density lipoprotein receptor-related protein induce Akt phosphorylation in the ischemic brain

Tissue-type plasminogen activator (tPA) is found in the intravascular space and in the central nervous system. The low-density lipoprotein receptor-related protein (LRP) is expressed in neurons and in perivascular astrocytes. During cerebral ischemia, tPA induces the shedding of LRP's extracellular domain from perivascular astrocytes, and this is followed by the development of cerebral edema. Protein kinase B (Akt) is a serine/threonine kinase that plays a critical role not only in cell survival but also in the regulation of the permeability of the blood-brain barrier. We found that, in the early phases of the ischemic insult, the interaction between tPA and LRP induces Akt phosphorylation (pAkt) in perivascular astrocytes and inhibits pAkt in neurons. Coimmunoprecipitation studies indicate that pAkt and LRP's intracellular domain interact in perivascular astrocytes and that this interaction is dependent on the presence of tPA and results in the development of edema. Together, these results indicate that, in the early stages of cerebral ischemia, the interaction between tPA and LRP in perivascular astrocytes induces the activation of a cell signaling event mediated by pAkt that leads to increase in the permeability of the blood-brain barrier.

Caspase inhibitor zVAD.fmk reduces infarct size after myocardial ischaemia and reperfusion in rats but not in mice

OBJECTIVE

Apoptosis of cardiomyocytes has been suggested to contribute to outcome following myocardial ischaemia and reperfusion (MI/R). Caspase inhibitors were developed as potential therapeutics for MI/R. However, various reports using the broad-spectrum caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD.fmk) in the latter setting present conflicting results. Therefore, it is still unclear whether inhibition of apoptosis by caspase inhibitors promotes cardioprotection.

MATERIALS AND METHODS

This study evaluated whether zVAD.fmk or novel caspase inhibitor quinoline-Val-Asp(Ome)-CH2-O-phenoxy (Q-VD-OPh) reduce myocardial infarct size in mice. Secondly, we tested zVAD.fmk's potential infarct-sparing effects in rats and whether these are accompanied by improved left ventricular function.

RESULTS

In mice neither zVAD.fmk nor Q-VD-OPh reduced infarct size. In rats, however, zVAD.fmk reduced infarct size following ischaemia (25min) and reperfusion (7 days) by approximately 53%. This was, however, accompanied by an increase in left ventricular end-diastolic pressure.

CONCLUSION

This study provides further evidence that abrogation of apoptosis via caspase inhibition might not be sufficient to effectively limit infarct size following MI/R.

Quantification of poly(ADP-ribose)-modified proteins in cerebrospinal fluid from infants and children after traumatic brain injury

Poly-ADP-ribosylation (PAR) of proteins by poly(ADP-ribose) polymerases (PARP) occurs after experimental traumatic brain injury (TBI) and modulates neurologic outcome. Several promising pharmacological PARP inhibitors have been developed for use in humans, but there is currently no clinically relevant means of monitoring treatment effects. We therefore used an enzyme-linked immunosorbent assay to measure PAR-modified proteins in cerebrospinal fluid (CSF). Cerebrospinal fluid samples from 17 pediatric TBI patients and 15 controls were plated overnight and then incubated with polyclonal antibody against PAR. Histone-1, a PARP substrate, was incubated with active PARP, NAD, and nicked DNA, and served as the standard. Both peak and mean CSF PAR-modified proteins were increased in TBI patients versus controls. Peak CSF PAR-modified protein levels occurred on day 1 and levels remained increased on day 2 after TBI. Increases in peak CSF PAR-modified protein concentrations were independently associated with age and male sex, but not initial Glasgow Coma Scale score, Glasgow outcome score, or mechanism of injury. The increase in PAR-modified proteins in CSF after TBI may be because of increased PARP activation, decreased PAR degradation, or both. As PAR-modified protein concentration correlated with age and male sex, developmental and sex-dependent roles for PARP after TBI are implicated.

Parp and cell death or protection in rat primary astroglial cell cultures under LPS/IFNgamma induced proinflammatory conditions

The enzyme poly(ADP-ribose)polymerase (PARP) has a leader role in the DNA damage survey mechanisms by its nick-sensor function, but it is also involved in the early events of the programmed cell death, particularly during inflammatory injury, as a coactivator of NF-kB. In the present study, we evaluated the PARP involvement in the mechanisms of protection and/or cell death in rat astroglial cell cultures during the early phase of proinflammatory commitment after lipopolysaccharide and interferon gamma treatment. According with the recent findings that PARP-1 phosphorylation by MAPK/ERK-2 pathway seems to modulate PARP activation, in time course experiments we demonstrated that a very early PARP activation and expression is able to trigger a cell death pathway, DNA damage independent, during strong proinflammatory insults, maintaining its role of guardian of the genome stability only during the normal cell cycling.

Ethanol-mediated DNA damage and PARP-1 apoptotic responses in cultured fetal cortical neurons

BACKGROUND

Prior studies by many laboratories have illustrated that ethanol can elicit a cascade of caspase-dependent apoptotic events in cultured neurons. Studies in our laboratory have connected this to oxidative stress and effects on fetal cortical neuron glutathione homeostasis.

AIMS

The intent of the following studies is to address mechanisms underlying ethanol-associated DNA damage that may be connected to apoptotic death of neurons.

METHODS

Cultures of fetal rat cerebral cortical neurons were utilized. Estimates of DNA damage was determined by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining and nuclear condensation; Poly(ADP-ribose) polymerase-1 (PARP-1) expression was determined by immunostaining and Western blotting; and occurrence of parylation and AIF translocations were assessed by Western blotting.

RESULTS

Ethanol treatment of the neurons generated increases in DNA damage by 4 hours while nuclear condensation was low at the short exposure period but increased markedly by 24 hours. This was temporally related to a marked up-regulation of PARP-1 expression. Activity of PARP-1, as assessed by PolyADP-ribose (PAR) formation, occurred within 15 minutes and peaked by 6 to 8 hours of ethanol treatment. An almost complete translocation of apoptosis inducing factor (AIF) from mitochondria to the nucleus occurred by 24 hours of ethanol treatment (4.0 mg/ml). Ethanol treatment for 4, 12, and 24 hours elicited an increasing caspase-mediated cleavage of PARP-1 to its 24 kDa fragment.

CONCLUSIONS

These data illustrate the rapid occurrence of DNA damage following ethanol exposure and that PARP-1 pathways may play a role in the subsequent apoptotic death of these neurons.

Dantrolene: mechanisms of neuroprotection and possible clinical applications in the neurointensive care unit

Calcium plays a central role in neuronal function and injury. Dantrolene, an inhibitor of the ryanodine receptor, inhibits intracellular calcium release from the sarco-endoplasmic reticulum. We review the available data of dantrolene as a potential neuroprotective agent and briefly summarize its other pharmacologic effects that may have potential applications for patients in the neurointensive care unit (NICU). Areas with the need for continued research are identified.

Protective effects of cilostazol against transient focal cerebral ischemia and chronic cerebral hypoperfusion injury

Cilostazol increases intracellular cyclic adenosine monophosphate (cyclic AMP) levels by inhibiting type III phosphodiesterase. It was approved by the Food and Drug Administration for the treatment of intermittent claudication. Its principal actions include inhibition of platelet aggregation, antithrombotic action in cerebral ischemia, and vasodilation, mediated by increased cyclic AMP levels. In a multicenter, randomized, placebo-controlled, double-blind clinical trial, cilostazol has been shown to protect patients from recurrent cerebral infarction. It has been recently suggested that cilastozol could be useful in the treatment of transient focal cerebral ischemic injury. Beneficial effects of cilostazol in cerebral ischemic infarction and edema formation has been confirmed in rats by the magnetic resonance imaging (MRI). The preventive effect was ascribed to cAMP-dependent protein kinase (PKA)-coupled maxi-K channel activation with additional antioxidant and poly(adenosine diphosphate [ADP]-ribose) polymerase inhibitory actions. Most recently, cilostazol has been shown to prevent vacuolation and rarefaction in the white matter of the rats subjected to chronic cerebral hypoperfusion in association with suppression of astrocyte and microglial activation. Taken together, recent experimental studies with cilostazol showed promising results in cerebral ischemia and chronic cerebral hypoperfusion.