NAD+ depletion or PAR polymer formation: which plays the role of executioner in ischaemic cell death?

Increasing adult neurogenesis protects mice from epilepsy

Neurogenesis occurs in the adult brain in the hippocampal dentate gyrus, an area that contains neurons which are vulnerable to insults and injury, such as severe seizures. Previous studies showed that increasing adult neurogenesis reduced neuronal damage after these seizures. Because the damage typically is followed by chronic life-long seizures (epilepsy), we asked if increasing adult neurogenesis would prevent epilepsy. Adult neurogenesis was selectively increased by deleting the pro-apoptotic gene Bax from Nestin-expressing progenitors. Tamoxifen was administered at 6 weeks of age to conditionally delete Bax in Nestin-CreERT2 Bax fl/fl mice. Six weeks after tamoxifen administration, severe seizures (status epilepticus; SE) were induced by injection of the convulsant pilocarpine. After mice developed epilepsy, seizure frequency was quantified for 3 weeks. Mice with increased adult neurogenesis exhibited fewer chronic seizures. Postictal depression was reduced also. These results were primarily in female mice, possibly because they were the more affected by Bax deletion than males, consistent with sex differences in Bax. The female mice with enhanced adult neurogenesis also showed less neuronal loss of hilar mossy cells and hilar somatostatin-expressing neurons than wild type females or males, which is notable because these two hilar cell types are implicated in epileptogenesis. The results suggest that selective Bax deletion to increase adult neurogenesis can reduce experimental epilepsy, and the effect shows a striking sex difference. The results are surprising in light of past studies showing that suppressing adult-born neurons can also reduce chronic seizures.

The sex-dependent response to psychosocial stress and ischaemic heart disease

Stress is an important risk factor for modern chronic diseases, with distinct influences in males and females. The sex specificity of the mammalian stress response contributes to the sex-dependent development and impacts of coronary artery disease (CAD). Compared to men, women appear to have greater susceptibility to chronic forms of psychosocial stress, extending beyond an increased incidence of mood disorders to include a 2- to 4-fold higher risk of stress-dependent myocardial infarction in women, and up to 10-fold higher risk of Takotsubo syndrome-a stress-dependent coronary-myocardial disorder most prevalent in post-menopausal women. Sex differences arise at all levels of the stress response: from initial perception of stress to behavioural, cognitive, and affective responses and longer-term disease outcomes. These fundamental differences involve interactions between chromosomal and gonadal determinants, (mal)adaptive epigenetic modulation across the lifespan (particularly in early life), and the extrinsic influences of socio-cultural, economic, and environmental factors. Pre-clinical investigations of biological mechanisms support distinct early life programming and a heightened corticolimbic-noradrenaline-neuroinflammatory reactivity in females vs. males, among implicated determinants of the chronic stress response. Unravelling the intrinsic molecular, cellular and systems biological basis of these differences, and their interactions with external lifestyle/socio-cultural determinants, can guide preventative and therapeutic strategies to better target coronary heart disease in a tailored sex-specific manner.

1H NMR Spectroscopy-Based Metabolomics Approach to Study the Anti-Stroke Activity of G-3702, a Novel Better Alternative to DL-3-n-Butylphthalide

Cerebrovascular disease is the leading cause of disability and death, and ischemic stroke accounts for most stroke cases. However, few effective drugs are available for the treatment of ischemic stroke; thus, there is an urgent need to develop effective drugs to treat ischemic stroke. DL-3-n-butylphthalide (NBP) is clinically approved as an anti-ischemic drug in China, but its potential hepatotoxicity limits its use. G-3702 (a structural analogue of NBP) is synthesized with the boron hydroxyl group replacing carbonyl group. G-3702 significantly enhanced the survival of middle cerebral artery occlusion (MCAO) rats, decreased neurobehavioral deficit scores and cerebral infarct volume, comparable with NBP, which was also supported by tissue damage assessment, immunohistochemistry staining, biochemical parameters and ELISA assay. G-3702 showed better anti-stroke activity than NBP according to ¹H NMR spectroscopy-based metabolomics analysis, demonstrating the feasibility of metabolomics approach to assess drug efficacy. G-3702 markedly ameliorated energy metabolism, attenuated oxidative and inflammatory stress during ischemia/reperfusion (I/R). G-3702 exhibited good neuroprotective effects against I/R induced injury and favorable little possibility of hepatotoxicity, which made it a promising anti-stroke drug and better NBP alternative.

SLC25A22 promotes proliferation and metastasis by activating MAPK/ERK pathway in gallbladder cancer

Background

SLC25A22, a member of mitochondrial carrier system (MCS) family encoding a mitochondrial glutamate transporter, has been reported to have vital roles in promoting proliferation and migration in cancer. Gallbladder cancer (GBC) is the most common biliary tract malignancy and has a poor prognosis. We aimed to determine the expression and function of SLC25A22 in GBC.

Methods

Immunohistochemistry (IHC) staining analysis and quantitative real-time PCR (qRT-PCR) were conducted to determine the expression of SLC25A22 in GBC tissues. Human NOZ and GBC-SD cells were used to perform the experiments. The protein expression was detected by western-blot analysis. Cell viability was evaluated via CCK-8 assay and colony formation assay. Cell migration and invasion in vitro were investigated by wound healing and transwell assay. Annexin V/PI staining assay for apoptosis were measured by flow cytometry. The effect of SLC25A22 in vivo was conducted with subcutaneous xenograft.

Results

We indicated that the expression of SLC25A22 was significantly upregulated in GBC tumor tissues as well as cell lines. Downregulation of SLC25A22 inhibited GBC cell growth and proliferation in vitro and in vivo and also had an effect on metastasis of GBC cells through the EMT processes. In addition, inhibition of SLC25A22 promoted mitochondrial apoptosis via downregulating BCL-2 and upregulating cleaved PARP, Cytochrome-c, and BAX mediated by MAPK/ERK pathway.

Conclusions

Our study identified that SLC25A22 promoted development of GBC activating MAPK/ERK pathway. SLC25A22 has a potential to be used as a target for cancer diagnosis of GBC and related therapies.

Hydroquinone induces TK6 cell growth arrest and apoptosis through PARP-1/p53 regulatory pathway

Hydroquinone (HQ), one of the most important metabolites derived from benzene, induces cell cycle arrest and apoptosis. Poly(ADP-ribose) polymerase-1 (PARP-1) participates in various biological processes, including DNA repair and cell cycle regulation. To explore whether PARP-1 regulatory pathway mediated HQ-induced cell cycle arrest and apoptosis, we assessed the effect of PARP-1 suppression on induction of apoptosis analyzed by FACSCalibur flow cytometer in PARP-1 deficientTK6 cells (TK6-shPARP-1). We observed an increase in the fraction of cells in G1 phase by 7.6% and increased apoptosis by 4.5% in PARP-1-deficient TK6 cells (TK6-shPARP-1) compared to those negative control cells (TK6-shNC cells) in response to HQ treatment. Furthermore, HQ might activate the extrinsic pathways of apoptosis via up-regulation of Fas expression, followed by caspase-3 activation, apoptotic body, and sub G1 accumulation. Enhanced p53 expression was observed in TK6-shPARP-1 cells than in TK6-shNC cells after HQ treatment. In contrast, Fas expression was lower in TK6-shPARP-1 cells than in TK6-shNC cells. Therefore, we conclude that HQ may activate apoptotic signals via Fas up-regulation and p53-mediated apoptosis in TK6-shNC cells. The reduction of PARP-1 expression further intensified up-regulation of p53 in TK6-shPARP-1 cells, resulting in an increased G1→S phase cell arrest and apoptosis in TK6-shPARP-1 cells compared to TK6-shNC cells.

Mitochondrial maintenance failure in aging and role of sexual dimorphism

Gene expression changes during aging are partly conserved across species, and suggest that oxidative stress, inflammation and proteotoxicity result from mitochondrial malfunction and abnormal mitochondrial-nuclear signaling. Mitochondrial maintenance failure may result from trade-offs between mitochondrial turnover versus growth and reproduction, sexual antagonistic pleiotropy and genetic conflicts resulting from uni-parental mitochondrial transmission, as well as mitochondrial and nuclear mutations and loss of epigenetic regulation. Aging phenotypes and interventions are often sex-specific, indicating that both male and female sexual differentiation promote mitochondrial failure and aging. Studies in mammals and invertebrates implicate autophagy, apoptosis, AKT, PARP, p53 and FOXO in mediating sex-specific differences in stress resistance and aging. The data support a model where the genes Sxl in Drosophila, sdc-2 in Caenorhabditis elegans, and Xist in mammals regulate mitochondrial maintenance across generations and in aging. Several interventions that increase life span cause a mitochondrial unfolded protein response (UPRmt), and UPRmt is also observed during normal aging, indicating hormesis. The UPRmt may increase life span by stimulating mitochondrial turnover through autophagy, and/or by inhibiting the production of hormones and toxic metabolites. The data suggest that metazoan life span interventions may act through a common hormesis mechanism involving liver UPRmt, mitochondrial maintenance and sexual differentiation.

The activity and inhibition of poly(ADP-ribose) polymerase-1 in equine peripheral blood mononuclear cells in vitro

OBJECTIVES

To evaluate the poly (ADP-ribose) polymerase-1 (PARP1) enzyme and its inhibition in horses and explore its potential as a novel therapeutic target for equine intestinal ischemia-reperfusion injury by (1) identifying poly (ADP-ribose) (PAR) as an indication of PARP1 activation in equine cells using available immunoblot analytical techniques, (2) inducing PARP1 activation in an in vitro oxidative DNA damage model, (3) and demonstrating the inhibition of PARP1 in equine cells using commercially available PARP1 inhibitors.

DESIGN

Experimental study.

ANIMALS

Blood samples were collected from systemically healthy ponies (n = 3) and horses (n = 3).

INTERVENTIONS

(1) Equine peripheral blood mononuclear cells were exposed to 3 different concentrations of hydrogen peroxide (H2 O2 ) and were lysed at specific time points. PARP1 activity was then assessed by using immunoblot analyses to determine PAR levels. (2) Equine peripheral blood mononuclear cells were preincubated with defined concentrations of PARP1 inhibitors prior to H2 O2 -mediated PARP1 stimulation. PAR levels reflecting PARP1 activity were determined using immunoblot analyses.

MEASUREMENTS AND MAIN RESULTS

Commercially available anti-PAR antibodies were used successfully to identify equine PAR. There was a significant increase in PAR accumulation following treatment with H2 O2 . All of the tested PARP inhibitors significantly reduced PAR accumulation to or below basal levels following treatment with H2 O2 .

CONCLUSIONS

This proof of principle study demonstrated that PAR, an indicator of PARP1 activity, can be identified in the equine species using immunoblot techniques, that equine PARP1 can be activated by H2 O2 -induced DNA damage, and that this activation can be inhibited by PARP1 enzyme inhibitors. The data suggest that the PARP1 pathway plays a role in the equine cellular response to oxidative DNA damage and supports its potential as a novel therapeutic target. Further research documenting an increase in PAR levels in vivo and the efficacy of PARP1 inhibitors in an equine intestinal ischemia-reperfusion model is needed.

Regulation of NAD biosynthetic enzymes modulates NAD-sensing processes to shape mammalian cell physiology under varying biological cues

In addition to its role as a redox coenzyme, NAD is a substrate of various enzymes that split the molecule to either catalyze covalent modifications of target proteins or convert NAD into biologically active metabolites. The coenzyme bioavailability may be significantly affected by these reactions, with ensuing major impact on energy metabolism, cell survival, and aging. Moreover, through the activity of the NAD-dependent deacetylating sirtuins, NAD behaves as a beacon molecule that reports the cell metabolic state, and accordingly modulates transcriptional responses and metabolic adaptations. In this view, NAD biosynthesis emerges as a highly regulated process: it enables cells to preserve NAD homeostasis in response to significant NAD-consuming events and it can be modulated by various stimuli to induce, via NAD level changes, suitable NAD-mediated metabolic responses. Here we review the current knowledge on the regulation of mammalian NAD biosynthesis, with focus on the relevant rate-limiting enzymes. This article is part of a Special Issue entitled: Cofactor-dependent proteins: evolution, chemical diversity and bio-applications.

Neuronal death induced by misfolded prion protein is due to NAD+ depletion and can be relieved in vitro and in vivo by NAD+ replenishment

The mechanisms of neuronal death in protein misfolding neurodegenerative diseases such as Alzheimer's, Parkinson's and prion diseases are poorly understood. We used a highly toxic misfolded prion protein (TPrP) model to understand neurotoxicity induced by prion protein misfolding. We show that abnormal autophagy activation and neuronal demise is due to severe, neuron-specific, nicotinamide adenine dinucleotide (NAD(+)) depletion. Toxic prion protein-exposed neuronal cells exhibit dramatic reductions of intracellular NAD(+) followed by decreased ATP production, and are completely rescued by treatment with NAD(+) or its precursor nicotinamide because of restoration of physiological NAD(+) levels. Toxic prion protein-induced NAD(+) depletion results from PARP1-independent excessive protein ADP-ribosylations. In vivo, toxic prion protein-induced degeneration of hippocampal neurons is prevented dose-dependently by intracerebral injection of NAD(+). Intranasal NAD(+) treatment of prion-infected sick mice significantly improves activity and delays motor impairment. Our study reveals NAD(+) starvation as a novel mechanism of autophagy activation and neurodegeneration induced by a misfolded amyloidogenic protein. We propose the development of NAD(+) replenishment strategies for neuroprotection in prion diseases and possibly other protein misfolding neurodegenerative diseases.

Bortezomib inhibits gastric carcinoma HGC-27 cells through the phospho-Jun N-terminal kinase (p-JNK) pathway in vitro

The study is designed to explore the anticancer mechanism of Bortezomib. The effects of Bortezomib on the proliferation of human gastric cancer cells HGC-27 and expression levels of the phospho-Jun N-terminal kinase (p-JNK) pathway-related proteins in vitro were investigated. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay revealed that the Bortezomib significantly decreased the viability of HGC-27 cells and induced apoptosis. Western blot showed that the Bortezomib strongly increased the levels of p-JNK, caspase-3, PARP, and bax proteins while it increased the level of bcl-2. However, SP600125 can significantly decrease antitumour effects of Bortezomib in HGC-27 cells. It can be concluded that Bortezomib has significant inhibitory effects on the growth of HGC-27 cells. The effect may be achieved partly via upregulating JNK pathway and its down-stream apoptosis-related proteins. Therefore, Bortezomib may be beneficial in gastric carcinoma treatment.

Sorbitol dehydrogenase inhibitor protects the liver from ischemia/reperfusion-induced injury via elevated glycolytic flux and enhanced sirtuin 1 activity

Sorbitol dehydrogenase (SDH), a key enzyme of the polyol pathway, has recently been demonstrated to have an important role in mediating tissue ischemia/reperfusion (I/R) injury. The present study investigated how this enzyme may affect the ischemic liver and the mechanism underlying its effect. Firstly, C57BL/6 mice were subjected to oral administration of CP-470,711 (5 mg/kg body weight/day for five days) and 70% hepatic I/R. Next the present study further investigated the changes in liver function, histology, inflammation, apoptosis and necrosis; the cytosolic adenosine triphosphate (ATP) and nictotinamide adenine dinucleotide [NAD(H)] contents and the protein level of caspase 3 and sirtuin 1 (SIRT1). The data demonstrated that sorbitol dehydrogenase inhibitor (SDI)-administration significantly alleviated I/R-induced liver injury, palliated histological changes and lowered the level of hepatocyte apoptosis and necrosis. In addition, SDI-pretreatment in ischemic liver markedly maintained the cytosolic ATP and NAD(H) proportion, enhanced SIRT1 and suppressed the activation of caspase 3 at the protein level. The findings in the present study revealed that the flux through SDH may render the liver more vulnerable to I/R-induced injury and interventions targeting this enzyme may provide a novel adjunctive approach to protect from severe tissue injury following liver ischemia.

ARTD1 (PARP1) activation and NAD(+) in DNA repair and cell death

Nicotinamide adenine dinucleotide, NAD(+), is a small metabolite coenzyme that is essential for the progress of crucial cellular pathways including glycolysis, the tricarboxylic acid cycle (TCA) and mitochondrial respiration. These processes consume and produce both oxidative and reduced forms of NAD (NAD(+) and NADH). NAD(+) is also important for ADP(ribosyl)ation reactions mediated by the ADP-ribosyltransferase enzymes (ARTDs) or deacetylation reactions catalyzed by the sirtuins (SIRTs) which use NAD(+) as a substrate. In this review, we highlight the significance of NAD(+) catabolism in DNA repair and cell death through its utilization by ARTDs and SIRTs. We summarize the current findings on the involvement of ARTD1 activity in DNA repair and most specifically its involvement in the trigger of cell death mediated by ARTD1 activation and energy depletion. By sharing the same substrate, the activities of ARTDs and SIRTs are tightly linked, are dependent on each other and are thereby involved in the same cellular processes that play an important role in cancer biology, inflammatory diseases and ischaemia/reperfusion.

Polyol pathway exacerbated ischemia/reperfusion-induced injury in steatotic liver

Background. The polyol pathway, a bypass pathway of glucose metabolism initiated by aldose reductase (AR), has been shown to play an important role in mediating tissue ischemia/reperfusion (I/R) impairment recently. Here, we investigated how and why this pathway might affect the fatty liver following I/R. Methods. Two opposite models were created: mice with high-fat-diet-induced liver steatosis were treated with aldose reductase inhibition (ARI) and subsequent I/R; and AR-overexpressing L02 hepatocytes were sequentially subjected to steatosis and hypoxia/reoxygenation. We next investigated (a) the hepatic injuries, including liver function, histology, and hepatocytes apoptosis/necrosis; (b) the NAD(P)(H) contents, redox status, and mitochondrial function; and (c) the flux through the caspase-dependent apoptosis pathway. Results. AR-inhibition in vivo markedly attenuated the I/R-induced liver injuries, maintained the homeostasis of NAD(P)(H) contents and redox status, and suppressed the caspase-dependent apoptosis pathway. Correspondingly, AR overexpression in vitro presented the opposite effects. Conclusion. The flux through the polyol pathway may render steatotic liver greater vulnerability to I/R. Interventions targeting this pathway might provide a novel adjunctive approach to protect fatty liver from ischemia.

Review of poly (ADP-ribose) polymerase (PARP) mechanisms of action and rationale for targeting in cancer and other diseases

Poly (ADP-ribose) polymerases (PARPs) are a family of related enzymes that share the ability to catalyze the transfer of ADP-ribose to target proteins. PARPs play an important role in various cellular processes, including modulation of chromatin structure, transcription, replication, recombination, and DNA repair. The role of PARP proteins in DNA repair is of particular interest, in view of the finding that certain tumors defective in homologous recombination mechanisms, may rely on PARP-mediated DNA repair for survival, and are sensitive to its inhibition. PARP inhibitors may also increase tumor sensitivity to DNA-damaging agents. Clinical trials of PARP inhibitors are investigating the utility of these approaches in cancer. The hyperactivation of PARP has also been shown to result in a specific programmed cell death pathway involving NAD+/ATP depletion, mu-calpain activation, loss of mitochondrial membrane potential, and the release of apoptosis inducing factor. Hyperactivation of the PARP pathway may be exploited to selectively kill cancer cells. Other PARP forms, including tankyrase 1 (PARP 5a), which plays an important role in enhancing telomere elongation by telomerase, have been found to be potential targets in cancer therapy. The PARP pathway and its inhibition thus offers a number of opportunities for therapeutic intervention in both cancer and other disease states.

Cerebral ischemia is exacerbated by extracellular nicotinamide phosphoribosyltransferase via a non-enzymatic mechanism

Intracellular nicotinamide phosphoribosyltransferase (iNAMPT) in neuron has been known as a protective factor against cerebral ischemia through its enzymatic activity, but the role of central extracellular NAMPT (eNAMPT) is not clear. Here we show that eNAMPT protein level was elevated in the ischemic rat brain after middle-cerebral-artery occlusion (MCAO) and reperfusion, which can be traced to at least in part from blood circulation. Administration of recombinant NAMPT protein exacerbated MCAO-induced neuronal injury in rat brain, while exacerbated oxygen-glucose-deprivation (OGD) induced neuronal injury only in neuron-glial mixed culture, but not in neuron culture. In the mixed culture, NAMPT protein promoted TNF-α release in a time- and concentration-dependent fashion, while TNF-α neutralizing antibody protected OGD-induced, NAMPT-enhanced neuronal injury. Importantly, H247A mutant of NAMPT with essentially no enzymatic activity exerted similar effects on ischemic neuronal injury and TNF-α release as the wild type protein. Thus, eNAMPT is an injurious and inflammatory factor in cerebral ischemia and aggravates ischemic neuronal injury by triggering TNF-α release from glia cells, via a mechanism not related to NAMPT enzymatic activity.

Nicotinamide adenine dinucleotide prevents neuroaxonal degeneration induced by manganese in cochlear organotypic cultures

Manganese (Mn) is an essential trace mineral for normal growth and development. Persistent exposures to high atmospheric levels of Mn have deleterious effects on CNS and peripheral nerves including those associated with the auditory system. Nicotinamide adenine dinucleotide (NAD) is a coenzyme which functions in the electron transfer system within the mitochondria. One of the most notable protective functions of NAD is to delay axonal degenerations caused by various neurodegenerative injuries. We hypothesized that NAD might also protect auditory nerve fibers (ANF) and SGN from Mn injury. To test this hypothesis, cochlear organotypic cultures were treated with different doses of Mn (0.5-3.0 mM) alone or combined with 20 mM NAD. Results demonstrate that the percentage of hair cells, ANF and SGN decreased with increasing Mn concentration. The addition of 20 mM NAD did not significantly reduce hair cells loss in the presence of Mn, whereas the density of ANF and SGN increased significantly in the presence of NAD. NAD suppressed Mn-induced TUNEL staining and caspase activation suggesting it prevents apoptotic cell death. These results suggest that excess Mn has ototoxic and neurotoxic effects on the auditory system and that NAD may prevent Mn-induced axonal degeneration and avoid or delay hearing loss caused by excess Mn exposure.

Therapeutic applications of PARP inhibitors: anticancer therapy and beyond

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

Cluster of differentiation 38 (CD38) mediates bile acid-induced acinar cell injury and pancreatitis through cyclic ADP-ribose and intracellular calcium release

Aberrant Ca(2+) signals within pancreatic acinar cells are an early and critical feature in acute pancreatitis, yet it is unclear how these signals are generated. An important mediator of the aberrant Ca(2+) signals due to bile acid exposure is the intracellular Ca(2+) channel ryanodine receptor. One putative activator of the ryanodine receptor is the nucleotide second messenger cyclic ADP-ribose (cADPR), which is generated by an ectoenzyme ADP-ribosyl cyclase, CD38. In this study, we examined the role of CD38 and cADPR in acinar cell Ca(2+) signals and acinar injury due to bile acids using pharmacologic inhibitors of CD38 and cADPR as well as mice deficient in Cd38 (Cd38(-/-)). Cytosolic Ca(2+) signals were imaged using live time-lapse confocal microscopy in freshly isolated mouse acinar cells during perifusion with the bile acid taurolithocholic acid 3-sulfate (TLCS; 500 μM). To focus on intracellular Ca(2+) release and to specifically exclude Ca(2+) influx, cells were perifused in Ca(2+)-free medium. Cell injury was assessed by lactate dehydrogenase leakage and propidium iodide uptake. Pretreatment with either nicotinamide (20 mM) or the cADPR antagonist 8-Br-cADPR (30 μM) abrogated TLCS-induced Ca(2+) signals and cell injury. TLCS-induced Ca(2+) release and cell injury were reduced by 30 and 95%, respectively, in Cd38-deficient acinar cells compared with wild-type cells (p < 0.05). Cd38-deficient mice were protected against a model of bile acid infusion pancreatitis. In summary, these data indicate that CD38-cADPR mediates bile acid-induced pancreatitis and acinar cell injury through aberrant intracellular Ca(2+) signaling.

Protective effect of nicotinamide on high glucose/palmitate-induced glucolipotoxicity to INS-1 beta cells is attributed to its inhibitory activity to sirtuins

This study was initiated to determine whether the protective effect of nicotinamide (NAM) on high glucose/palmitate (HG/PA)-induced INS-1 beta cell death was due to its role as an anti-oxidant, nicotinamide dinucleotide (NAD+) precursor, or inhibitor of NAD+-consuming enzymes such as poly (ADP-ribose) polymerase (PARP) or sirtuins. All anti-oxidants tested were not protective against HG/PA-induced INS-1 cell death. Direct supplementation of NAD+ or indirect supplementation through NAD+ salvage or de novo pathway did not protect the death. Knockdown of the NAD+ salvage pathway enzymes such as nicotinamide phosphoribosyl transferase (NAMPT) or nicotinamide mononucleotide adenyltransferase (NMNAT) did not augment death. On the other hand, pharmacological inhibition or knockdown of PARP did not affect death. However, sirtinol as an inhibitor of NAD-dependant deacetylase or knockdown of SIRT3 or SIRT4 significantly reduced the HG/PA-induced death. These data suggest that protective effect of NAM on beta cell glucolipotoxicity is attributed to its inhibitory activity on sirtuins.

NAD+ and nicotinamide: sex differences in cerebral ischemia

BACKGROUND

Previous literature suggests that cell death pathways activated after cerebral ischemia differ between the sexes. While caspase-dependent mechanisms predominate in the female brain, caspase-independent cell death induced by the activation of poly(ADP-ribose) polymerase (PARP) predominates in the male brain. PARP-1 gene deletion decreases infarction volume in the male brain, but paradoxically increases damage in PARP-1 knockout females.

PURPOSE

This study examined stroke-induced changes in NAD+, a key energy molecule involved in PARP-1 activation in both sexes.

METHODS

Mice were subjected to middle cerebral artery occlusion and NAD+ levels were assessed. Caspase-3 activity and nuclear translocation were assessed 6h after ischemia. In additional cohorts, Nicotinamide (500 mg/kg i.p.) a precursor of NAD+ or vehicle was administered and infarction volume was measured 24h after ischemia.

RESULTS

Males have higher baseline NAD+ levels than females. Significant stroke-induced NAD+ depletion occurred in males and ovariectomized females but not in intact females. PARP-1 deletion prevented the stroke-induced loss in NAD+ in males, but worsened NAD+ loss in PARP-1 deficient females. Preventing NAD+ loss with nicotinamide reduced infarct in wild-type males and PARP-1 knockout mice of both sexes, with no effect in WT females. Caspase-3 activity was significantly increased in PARP-1 knockout females compared to males and wild-type females, this was reversed with nicotinamide.

CONCLUSIONS

Sex differences exist in baseline and stroke-induced NAD+ levels. Nicotinamide protected males and PARP knockout mice, but had minimal effects in the wild-type female brain. This may be secondary to differences in energy metabolism between the sexes.

Novel directions for diabetes mellitus drug discovery

INTRODUCTION

Diabetes mellitus impacts almost 200 million individuals worldwide and leads to debilitating complications. New avenues of drug discovery must target the underlying cellular processes of oxidative stress, apoptosis, autophagy, and inflammation that can mediate multi-system pathology during diabetes mellitus.

AREAS COVERED

The authors examine the novel directions for drug discovery that involve: the β-nicotinamide adenine dinucleotide (NAD(+)) precursor nicotinamide, the cytokine erythropoietin, the NAD(+)-dependent protein histone deacetylase SIRT1, the serine/threonine-protein kinase mammalian target of rapamycin (mTOR), and the wingless pathway. Furthermore, the authors present the implications for the targeting of these pathways that oversee gluconeogenic genes, insulin signaling and resistance, fatty acid beta-oxidation, inflammation, and cellular survival.

EXPERT OPINION

Nicotinamide, erythropoietin, and the downstream pathways of SIRT1, mTOR, forkhead transcription factors, and wingless signaling offer exciting prospects for novel directions of drug discovery for the treatment of metabolic disorders. Future investigations must dissect the complex relationship and fine modulation of these pathways for the successful translation of robust reparative and regenerative strategies against diabetes mellitus and the complications of this disorder.

Erythropoietin: new directions for the nervous system

New treatment strategies with erythropoietin (EPO) offer exciting opportunities to prevent the onset and progression of neurodegenerative disorders that currently lack effective therapy and can progress to devastating disability in patients. EPO and its receptor are present in multiple systems of the body and can impact disease progression in the nervous, vascular, and immune systems that ultimately affect disorders such as Alzheimer's disease, Parkinson's disease, retinal injury, stroke, and demyelinating disease. EPO relies upon wingless signaling with Wnt1 and an intimate relationship with the pathways of phosphoinositide 3-kinase (PI 3-K), protein kinase B (Akt), and mammalian target of rapamycin (mTOR). Modulation of these pathways by EPO can govern the apoptotic cascade to control β-catenin, glycogen synthase kinase-3β, mitochondrial permeability, cytochrome c release, and caspase activation. Yet, EPO and each of these downstream pathways require precise biological modulation to avert complications associated with the vascular system, tumorigenesis, and progression of nervous system disorders. Further understanding of the intimate and complex relationship of EPO and the signaling pathways of Wnt, PI 3-K, Akt, and mTOR are critical for the effective clinical translation of these cell pathways into robust treatments for neurodegenerative disorders.

Potential role of poly(ADP-ribose) polymerase (PARP) activation in methotrexate-induced nephrotoxicity and tubular apoptosis

Nephrotoxicity is one of the serious dose-limiting complications of methotrexate (MTX) when used in the treatment of various malignancies and nononcological diseases. The aim of this study was to investigate the role of poly(adenosine diphosphate ribose) polymerase (PARP) activity in MTX-induced nephrotoxicity. Rats were divided into 4 groups as control, MTX treated (MTX, 7 mg/kg per d, intraperitoneally [ip], once daily for 3 consecutive days), MTX plus 1,5-isoquinelinediol (ISO, a PARP inhibitor, 3 mg/kg per d, i.p.) treated, or ISO treated. Histopathology of kidneys was evaluated by light microscopy. Terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end labeling assay was used to analyze apoptosis in kidney sections. Blood urea nitrogen (BUN), serum creatinine, and urinary N-acetyl-β-d-glucosaminidase (NAG) were used as biochemical markers of MTX-induced renal injury. Our results showed that MTX administration significantly increased BUN, serum creatinine, and urinary NAG levels. The PARP-1 and PAR (a product of PARP activity) expression and apoptotic cell death were also markedly increased in renal tubules after MTX administration. The ISO treatment attenuated MTX-induced renal injury, as indicated by BUN and serum creatinine levels, urinary NAG excretion, and renal histology. The PARP inhibitor treatment reduced PARP-1 and PAR expression to levels similar to that of controls. These results revealed that ISO may have a protective effect against the nephrotoxic effects of MTX by inhibiting PARP activation. This is the first study that demonstrates the role of PARP activation in MTX-induced nephrotoxicity and tubular apoptosis.

A dual role for poly(ADP-ribose) polymerase-1 during caspase-dependent apoptosis

2,3,5-Tris(glutathion-S-yl)hydroquinone (TGHQ), a metabolite of benzene, catalyzes the generation of reactive oxygen species (ROS) and caspase-dependent apoptosis in human promyelocytic leukemia (HL-60) cells. We now report that TGHQ induces severe DNA damage, as evidenced by DNA ladder formation and H2AX phosphorylation. The subsequent activation of the DNA nick sensor enzyme, poly(ADP-ribose) polymerase-1 (PARP-1), leads to the rapid depletion of ATP and NAD and the concomitant formation of poly(ADP-ribosylated) proteins (PARs). PJ-34 (a PARP-1 inhibitor) completely prevented the formation of PARs, partially attenuated TGHQ-mediated ATP depletion, but had little effect on NAD depletion. Intriguingly, although z-vad-fmk (a pan-caspase inhibitor) attenuated TGHQ-induced apoptosis, cotreatment with PJ-34 led to a further decrease in apoptosis, suggesting that PARP-1 participates in caspase-dependent apoptosis. Indeed, PARP-1 inhibition reduced TGHQ-induced caspase-3, -7, and -9 activation, at least partially by attenuating cytochrome c translocation from mitochondria to the cytoplasm. In contrast, PJ-34 potentiated TGHQ-induced caspase-8 activation, suggesting that PARP-1 plays a dual role in regulating TGHQ-induced apoptosis via opposing effects on the intrinsic (mitochondrial) and extrinsic (death-receptor) pathways. PARP-1 knockdown in HL-60 cells confirmed that PARP-1 participates in effector caspase activation. Finally, PJ-34 also inhibited TGHQ-induced apoptosis-inducing factor (AIF) nuclear translocation, but neither c-jun NH(2)-terminal kinase nor p38 MAPK (p38 mitogen-activated protein kinase) activation was required for AIF translocation. In summary, TGHQ-induced apoptosis of HL-60 cells is accompanied by PARP-1, caspase activation, and AIF nuclear translocation. TGHQ-induced apoptosis appears to primarily occur via engagement of the mitochondrial-mediated pathway in a process amenable to PARP inhibition. Residual cell death in the presence of PJ-34 is likely mediated via the extrinsic apoptotic pathway.

Poly(ADP-ribose) polymerase-1 inhibition by arsenite promotes the survival of cells with unrepaired DNA lesions induced by UV exposure

Human arsenic exposure is associated with increased risk of skin cancer, and arsenite greatly enhances ultraviolet (UV)-induced skin tumors in a mouse model of carcinogenesis. Inhibition of DNA repair is one proposed mechanism for the observed cocarcinogenicity. We have previously demonstrated that low concentrations of arsenite inhibit poly(ADP-ribose) polymerase (PARP)-1, thus interfering with DNA repair process triggered by UV radiation. Because overactivation of PARP-1 often leads to apoptotic cell death, and unrepaired DNA lesions promote genomic instability and carcinogenesis, we hypothesized that inhibition of PARP-1 by arsenic may promote the survival of potentially "initiated carcinogenic cells," i.e., cells with unrepaired DNA lesions. In the present study, we tested this hypothesis on UV-challenged HaCat cells. Cells were pretreated with 2μM arsenite for 24 h before UV exposure. Outcome parameters included apoptotic death rate, PARP-1 activation, apoptotic molecules, and retention of DNA lesions. UV exposure induced PARP-1 activation and associated poly(ADP-ribose) production, apoptosis-inducing factor release, cytochrome C release, and caspases activation, which led to apoptotic death in HaCat cells. Pretreatment with 2μM arsenite significantly inhibited UV-induced cell death as well as the associated molecular events. Notably, knockdown of PARP-1 with small interfering RNA completely abolished the antagonism of arsenite. Furthermore, arsenite pretreatment led to long-term retention of UV-induced cyclobutane pyrimidine dimers. Together, these results suggest that low concentration of arsenite reduces UV-induced apoptosis via inhibiting PARP-1, thus promoting the survival of cells with unrepaired DNA lesions, which may be an important mechanism underlying arsenic cocarcinogenic action.

Inverse susceptibility to oxidative death of lymphocytes obtained from Alzheimer's patients and skin cancer survivors: increased apoptosis in Alzheimer's and reduced necrosis in cancer

A paucity of cancer in individuals with Alzheimer's disease (AD) and low rates of AD in cancer survivors has been reported in epidemiological studies. Deregulation in opposite directions of biological mechanisms, such as susceptibility to cell death, might be shared in the two disorders. We analyzed lymphocytes from AD and skin cancer patients as well as healthy controls and found significantly increased vulnerability of AD lymphocytes to H(2)O(2)-induced apoptotic death and higher resistance to death of skin cancer lymphocytes, due to reduced necrosis, as compared with healthy controls by pairwise comparisons adjusted for age and sex. H(2)O(2)-induced death in lymphocytes was caspase independent and significantly reduced by PARP-1 inhibition in all three groups. These differences in the susceptibility to cell death observed for lymphocytes from AD and skin cancer patients may be one of the mechanisms that help explain the inverse correlation detected between these diseases in epidemiological studies.

Regulated hepatic reperfusion mitigates ischemia-reperfusion injury and improves survival after prolonged liver warm ischemia: a pilot study on a novel concept of organ resuscitation in a large animal model

BACKGROUND

Ischemia-reperfusion injury (IRI) can occur during hepatic surgery and transplantation. IRI causes hepatic mitochondrial and microcirculatory impairment, resulting in acute liver dysfunction and failure. We proposed a novel strategy of regulated hepatic reperfusion (RHR) to reverse the cellular metabolic deficit that incurred during organ ischemia by using a substrate-enriched, oxygen-saturated, and leukocyte-depleted perfusate delivered under regulated reperfusion pressure, temperature, and pH. We investigate the use of RHR in mitigating IRI after a prolonged period of warm ischemia.

METHODS

Using a 2-hour liver warm ischemia swine model, 2 methods of liver reperfusion were compared. The control group (n = 6) received conventional reperfusion with unmodified portal venous blood under unregulated reperfusion pressure, temperature, and pH. The experimental group (n = 6) received RHR. We analyzed the effects of RHR on post-reperfusion hemodynamic changes, liver function, and 7-day animal survival.

RESULTS

RHR resulted in 100% survival compared with 50% in the control group (p = 0.05). Post-reperfusion syndrome was not observed in the RHR group, but it occurred in 83% of the control group. RHR resulted in a lesser degree of change from baseline serum alanine aminotransferase levels, aspartate aminotransferase, and lactate dehydrogenase after reperfusion compared with the control group. Histopathologic evaluation showed minimal ischemic changes in the RHR group, whereas a considerable degree of coagulative hepatocellular necrosis was observed in the control group.

CONCLUSIONS

Regulated hepatic reperfusion mitigates IRI, facilitates liver function recovery, and improves survival after a prolonged period of hepatic warm ischemia. This novel strategy has potential applicability to clinical hepatic surgery and liver transplantation when marginal grafts are used.

Xenotransplantation of mitochondrial electron transfer enzyme, Ndi1, in myocardial reperfusion injury

A significant consequence of ischemia/reperfusion (I/R) is mitochondrial respiratory dysfunction, leading to energetic deficits and cellular toxicity from reactive oxygen species (ROS). Mammalian complex I, a NADH-quinone oxidoreductase enzyme, is a multiple subunit enzyme that oxidizes NADH and pumps protons across the inner membrane. Damage to complex I leads to superoxide production which further damages complex I as well as other proteins, lipids and mtDNA. The yeast, S. cerevisiae, expresses internal rotenone insensitive NADH-quinone oxidoreductase (Ndi1); a single 56kDa polypeptide which, like the multi-subunit mammalian complex I, serves as the entry site of electrons to the respiratory chain, but without proton pumping. Heterologous expression of Ndi1 in mammalian cells results in protein localization to the inner mitochondrial membrane which can function in parallel with endogenous complex I to oxidize NADH and pass electrons to ubiquinone. Expression of Ndi1 in HL-1 cardiomyocytes and in neonatal rat ventricular myocytes protected the cells from simulated ischemia/reperfusion (sI/R), accompanied by lower ROS production, and preservation of ATP levels and NAD+/NADH ratios. We next generated a fusion protein of Ndi1 and the 11aa protein transduction domain from HIV TAT. TAT-Ndi1 entered cardiomyocytes and localized to mitochondrial membranes. Furthermore, TAT-Ndi1 introduced into Langendorff-perfused rat hearts also localized to mitochondria. Perfusion of TAT-Ndi1 before 30 min no-flow ischemia and up to 2 hr reperfusion suppressed ROS production and preserved ATP stores. Importantly, TAT-Ndi1 infused before ischemia reduced infarct size by 62%; TAT-Ndi1 infused at the onset of reperfusion was equally cardioprotective. These results indicate that restoring NADH oxidation and electron flow at reperfusion can profoundly ameliorate reperfusion injury.

Translating cell survival and cell longevity into treatment strategies with SIRT1

The sirtuin SIRT1, a class III NAD(+)-dependent protein histone deacetylase, is present throughout the body that involves cells of the central nervous system, immune system, cardiovascular system, and the musculoskeletal system. SIRT1 has broad biological effects that affect cellular metabolism as well as cellular survival and longevity that can impact both acute and chronic disease processes that involve neurodegenerative disease, diabetes mellitus, cardiovascular disease, and cancer. Given the intricate relationship SIRT1 holds with a host of signal transduction pathways ranging from transcription factors, such as forkhead, to cytokines and growth factors, such as erythropoietin, it becomes critical to elucidate the cellular pathways of SIRT1 to safely and effectively develop and translate novel avenues of treatment for multiple disease entities.