Local administration of the poly(ADP-ribose) polymerase inhibitor INO-1001 prevents NAD+ depletion and improves water maze performance after traumatic brain injury in mice

Nicotinamide Adenine Dinucleotide (NAD+)-Dependent Signaling in Neurological Disorders

Significance: Nicotinamide adenine dinucleotide (NAD+) participates in redox reactions and NAD+-dependent signaling processes, which couples the enzymatic degradation of NAD+ to posttranslational modifications of proteins or the production of second messengers. Cellular NAD+ levels are dynamically controlled by synthesis and degradation, and dysregulation of this balance has been associated with acute and chronic neuronal dysfunction. Recent Advances: A decline in NAD+ has been observed during normal aging and since aging is the primary risk factor for many neurological disorders, NAD+ metabolism has become a promising therapeutic target and prolific research field in recent years. Critical Issues: In many neurological disorders, either as a primary feature or as consequence of the pathological process, neuronal damage is accompanied by dysregulated mitochondrial homeostasis, oxidative stress, or metabolic reprogramming. Modulating NAD+ availability appears to have a protective effect against such changes observed in acute neuronal damage and age-related neurological disorders. Such beneficial effects could be, at least in part, due to the activation of NAD+-dependent signaling processes. Future Directions: While in many instances the protective effect has been ascribed to the activation of sirtuins, approaches that directly test the role of sirtuins or that target the NAD+ pool in a cell-type-specific manner may be able to provide further mechanistic insight. Likewise, these approaches may afford greater efficacy to strategies aimed at harnessing the therapeutic potential of NAD+-dependent signaling in neurological disorders. Antioxid. Redox Signal. 39, 1150-1166.

Application of P7C3 Compounds to Investigating and Treating Acute and Chronic Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading worldwide cause of disability, and there are currently no medicines that prevent, reduce, or reverse acute or chronic neurodegeneration in TBI patients. Here, we review the target-agnostic discovery of nicotinamide adenine dinucleotide (NAD+)/NADH-stabilizing P7C3 compounds through a phenotypic screen in mice and describe how P7C3 compounds have been applied to advance understanding of the pathophysiology and potential treatment of TBI. We summarize how P7C3 compounds have been shown across multiple laboratories to mitigate disease progression safely and effectively in a broad range of preclinical models of disease related to impaired NAD+/NADH metabolism, including acute and chronic TBI, and note the reported safety and neuroprotective efficacy of P7C3 compounds in nonhuman primates. We also describe how P7C3 compounds facilitated the recent first demonstration that chronic neurodegeneration 1 year after TBI in mice, the equivalent of many decades in people, can be reversed to restore normal neuropsychiatric function. We additionally review how P7C3 compounds have facilitated discovery of new pathophysiologic mechanisms of neurodegeneration after TBI. This includes the role of rapid TBI-induced tau acetylation that drives axonal degeneration, and the discovery of brain-derived acetylated tau as the first blood-based biomarker of neurodegeneration after TBI that directly correlates with the abundance of a therapeutic target in the brain. We additionally review the identification of TBI-induced tau acetylation as a potential mechanistic link between TBI and increased risk of Alzheimer's disease. Lastly, we summarize historical accounts of other successful phenotypic-based drug discoveries that advanced medical care without prior recognition of the specific molecular target needed to achieve the desired therapeutic effect.

P7C3-A20 Attenuates Microglial Inflammation and Brain Injury after ICH through Activating the NAD+/Sirt3 Pathway

Intracerebral hemorrhage (ICH) is lethal but lacks effective therapies. Nicotinamide adenine dinucleotide (NAD⁺) is a central metabolite indispensable for a broader range of fundamental intracellular biological functions. Reduction of NAD⁺ usually occurs after acute brain insults, and supplementation of NAD⁺ has been proven neuroprotective. P7C3-A20 is a novel compound featuring its ability to facilitate the flux of NAD⁺. In this study, we sought to determine the potential therapeutic value of P7C3-A20 in ICH. In collagenase-induced ICH mouse models, we found that P7C3-A20 treatment could diminish lesion volume, reduce blood-brain barrier (BBB) damage, mitigate brain edema, attenuate neural apoptosis, and improve neurological outcomes after ICH. Further, RNA sequencing and subsequent experiments revealed that ICH-induced neuroinflammation and microglial proinflammatory activities were significantly suppressed following P7C3-A20 treatment. Mitochondrial damage is an important trigger of inflammatory response. We examined mitochondrial morphology and function and found that P7C3-A20 could attenuate OxyHb-induced impairment of mitochondrial dynamics and functions in vitro. Mechanistically, Sirt3, an NAD⁺-dependent deacetylase located in mitochondria, was then found to play a vital role in the protection of P7C3-A20 against mitochondrial damage and inflammatory response. In rescue experiments, P7C3-A20 failed to exert those protective effects in microglia-specific Sirt3 conditional knockout (CKO) mice. Finally, preclinical research revealed a correlation between the plasma NAD⁺ level and the neurological outcome in ICH patients. These results demonstrate that P7C3-A20 is a promising therapeutic agent for neuroinflammatory injury after ICH and exerts protective actions, at least partly, in a Sirt3-dependent manner.

The role of regulatory necrosis in traumatic brain injury

Traumatic brain injury (TBI) is a major cause of death and disability in the population worldwide, of which key injury mechanism involving the death of nerve cells. Many recent studies have shown that regulatory necrosis is involved in the pathological process of TBI which includes necroptosis, pyroptosis, ferroptosis, parthanatos, and Cyclophilin D (CypD) mediated necrosis. Therefore, targeting the signaling pathways involved in regulatory necrosis may be an effective strategy to reduce the secondary injury after TBI. Meanwhile, drugs or genes are used as interference factors in various types of regulatory necrosis, so as to explore the potential treatment methods for the secondary injury after TBI. This review summarizes the current progress on regulatory necrosis in TBI.

Oxidative stress and mitochondrial dysfunction following traumatic brain injury: From mechanistic view to targeted therapeutic opportunities

Traumatic brain injury (TBI) is one of the most prevalent causes of permanent physical and cognitive disabilities. TBI pathology results from primary insults and a multi-mechanistic biochemical process, termed as secondary brain injury. Currently, there are no pharmacological agents for definitive treatment of patients with TBI. This article is presented with the purpose of reviewing molecular mechanisms of TBI pathology, as well as potential strategies and agents against pathological pathways. In this review article, materials were obtained by searching PubMed, Scopus, Elsevier, Web of Science, and Google Scholar. This search was considered without time limitation. Evidence indicates that oxidative stress and mitochondrial dysfunction are two key mediators of the secondary injury cascade in TBI pathology. TBI-induced oxidative damage results in the structural and functional impairments of cellular and subcellular components, such as mitochondria. Impairments of mitochondrial electron transfer chain and mitochondrial membrane potential result in a vicious cycle of free radical formation and cell apoptosis. The results of some preclinical and clinical studies, evaluating mitochondria-targeted therapies, such as mitochondria-targeted antioxidants and compounds with pleiotropic effects after TBI, are promising. As a proposed strategy in recent years, mitochondria-targeted multipotential therapy is a new hope, waiting to be confirmed. Moreover, based on the available findings, biologics, such as stem cell-based therapy and transplantation of mitochondria are novel potential strategies for the treatment of TBI; however, more studies are needed to clearly confirm the safety and efficacy of these strategies.

Radiation-induced neuroinflammation: a potential protective role for poly(ADP-ribose) polymerase inhibitors?

Radiotherapy (RT) plays a fundamental role in the treatment of glioblastoma (GBM). GBM are notoriously invasive and harbor a subpopulation of cells with stem-like features which exhibit upregulation of the DNA damage response (DDR) and are radioresistant. High radiation doses are therefore delivered to large brain volumes and are known to extend survival but also cause delayed toxicity with 50%-90% of patients developing neurocognitive dysfunction. Emerging evidence identifies neuroinflammation as a critical mediator of the adverse effects of RT on cognitive function. In addition to its well-established role in promoting repair of radiation-induced DNA damage, activation of poly(ADP-ribose) polymerase (PARP) can exacerbate neuroinflammation by promoting secretion of inflammatory mediators. Therefore, PARP represents an intriguing mechanistic link between radiation-induced activation of the DDR and subsequent neuroinflammation. PARP inhibitors (PARPi) have emerged as promising new agents for GBM when given in combination with RT, with multiple preclinical studies demonstrating radiosensitizing effects and at least 3 compounds being evaluated in clinical trials. We propose that concomitant use of PARPi could reduce radiation-induced neuroinflammation and reduce the severity of radiation-induced cognitive dysfunction while at the same time improving tumor control by enhancing radiosensitivity.

DNA damage and repair following traumatic brain injury

Traumatic brain injury (TBI) is known to promote significant DNA damage irrespective of age, sex, and species. Chemical as well as structural DNA modification start within minutes and persist for days after TBI. Although several DNA repair pathways are induced following TBI, the simultaneous downregulation of some of the genes and proteins of these pathways leads to an aberrant overall DNA repair process. In many instances, DNA damages escape even the most robust repair mechanisms, especially when the repair process becomes overwhelmed or becomes inefficient by severe or repeated injuries. The persisting DNA damage and/or lack of DNA repair contributes to long-term functional deficits. In this review, we discuss the mechanisms of TBI-induced DNA damage and repair. We further discussed the putative experimental therapies that target the members of the DNA repair process for improved outcome following TBI.

Poly(ADP-ribose) polymerase inhibition: past, present and future

The process of poly(ADP-ribosyl)ation and the major enzyme that catalyses this reaction, poly(ADP-ribose) polymerase 1 (PARP1), were discovered more than 50 years ago. Since then, advances in our understanding of the roles of PARP1 in cellular processes such as DNA repair, gene transcription and cell death have allowed the investigation of therapeutic PARP inhibition for a variety of diseases - particularly cancers in which defects in DNA repair pathways make tumour cells highly sensitive to the inhibition of PARP activity. Efforts to identify and evaluate potent PARP inhibitors have so far led to the regulatory approval of four PARP inhibitors for the treatment of several types of cancer, and PARP inhibitors have also shown therapeutic potential in treating non-oncological diseases. This Review provides a timeline of PARP biology and medicinal chemistry, summarizes the pathophysiological processes in which PARP plays a role and highlights key opportunities and challenges in the field, such as counteracting PARP inhibitor resistance during cancer therapy and repurposing PARP inhibitors for the treatment of non-oncological diseases.

Alternative substrate metabolism depends on cerebral metabolic state following traumatic brain injury

Decreases in energy metabolism following traumatic brain injury (TBI) are attributed to impairment of glycolytic flux and oxidative phosphorylation. Glucose utilization post-TBI is decreased while administration of alternative substrates has been shown to be neuroprotective. Changes in energy metabolism following TBI happens in two phases; a period of hyper-metabolism followed by prolonged hypo-metabolism. It is not understood how different cerebral metabolic states may impact substrate metabolism and ultimately mitochondrial function. Adult male or female Sprague Dawley rats were given sham surgery or controlled cortical impact (CCI) and were assigned one of two administration schemes. Glucose, lactate or beta-hydroxybutyrate (BHB) were infused i.v. either starting immediately after injury or beginning 6 h post-injury for 3 h to reflect the hyper- and hypo-metabolic stages. Animals were euthanized 24 h post-injury. The peri-contusional cortex was collected and assayed for mitochondrial respiration peroxide production, and citrate synthase activity. Tissue acetyl-CoA, ATP, glycogen and HMGB1 were also quantified. Sex differences were observed in injury pattern. Administration based on cerebral metabolic state identified that only early lactate and late BHB improved mitochondrial function and peroxide production and TCA cycle intermediates in males. In contrast, both early and late BHB had deleterious effects on all aspects of metabolic measurements in females. These data stress there is no one optimal alternative substrate, but rather the fuel type used should be guided by both cerebral metabolic state and sex.

Cell Death and Recovery in Traumatic Brain Injury

Traumatic brain injury (TBI) is the leading cause of morbidity and mortality worldwide. Although TBI leads to mechanical damage during initial impact, secondary damage also occurs as results from delayed neurochemical process and intracellular signaling pathways. Accumulated animal and human studies demonstrated that apoptotic mechanism contributes to overall pathology of TBI. Apoptotic cell death has been identified within contusional brain lesion at acute phase of TBI and in region remote from the site directly injured in days to weeks after trauma. TBI is also dynamic conditions that cause neuronal decline overtime and is likely due to neurodegenerative mechanisms years after trauma. Current studies have even suggested association of neuronal damage through apoptotic pathway with mild TBI, which contributes chronic persistent neurological symptoms and cognitive deficits. Thus, a better understanding of the acute and chronic consequences of apoptosis following TBI is required. The purpose of this review is to describe (1) neuronal apoptotic pathway following TBI, (2) contribution of apoptosis to acute and chronic phase of TBI, and (3) current treatment targeting on apoptotic pathway.

NAD+ therapy in age-related degenerative disorders: A benefit/risk analysis

Nicotinamide adenine dinucleotide (NAD+) is an essential pyridine nucleotide that is present in all living cells. NAD+ acts as an important cofactor and substrate for a multitude of biological processes including energy production, DNA repair, gene expression, calcium-dependent secondary messenger signalling and immunoregulatory roles. The de novo synthesis of NAD+ is primarily dependent on the kynurenine pathway (KP), although NAD+ can also be recycled from nicotinic acid (NA), nicotinamide (NAM) and nicotinamide riboside (NR). NAD+ levels have been reported to decline during ageing and age-related diseases. Recent studies have shown that raising intracellular NAD+ levels represents a promising therapeutic strategy for age-associated degenerative diseases in general and to extend lifespan in small animal models. A systematic review of the literature available on Medline, Embase and Pubmed was undertaken to evaluate the potential health and/or longevity benefits due to increasing NAD+ levels. A total of 1545 articles were identified and 147 articles (113 preclinical and 34 clinical) met criteria for inclusion. Most studies indicated that the NAD+ precursors NAM, NR, nicotinamide mononucleotide (NMN), and to a lesser extent NAD+ and NADH had a favourable outcome on several age-related disorders associated with the accumulation of chronic oxidative stress, inflammation and impaired mitochondrial function. While these compounds presented with a limited acute toxicity profile, evidence is still quite limited and long-term human clinical trials are still nascent in the current literature. Potential risks in raising NAD+ levels in various clinical disorders using NAD+ precursors include the accumulation of putative toxic metabolites, tumorigenesis and promotion of cellular senescence. Therefore, NAD+ metabolism represents a promising target and further studies are needed to recapitulate the preclinical benefits in human clinical trials.

Genetic Influences on Patient-Oriented Outcomes in Traumatic Brain Injury: A Living Systematic Review of Non-Apolipoprotein E Single-Nucleotide Polymorphisms

There is a growing literature on the impact of genetic variation on outcome in traumatic brain injury (TBI). Whereas a substantial proportion of these publications have focused on the apolipoprotein E (APOE) gene, several have explored the influence of other polymorphisms. We undertook a systematic review of the impact of single-nucleotide polymorphisms (SNPs) in non–apolipoprotein E (non-APOE) genes associated with patient outcomes in adult TBI). We searched EMBASE, MEDLINE, CINAHL, and gray literature from inception to the beginning of August 2017 for studies of genetic variance in relation to patient outcomes in adult TBI. Sixty-eight articles were deemed eligible for inclusion into the systematic review. The SNPs described were in the following categories: neurotransmitter (NT) in 23, cytokine in nine, brain-derived neurotrophic factor (BDNF) in 12, mitochondrial genes in three, and miscellaneous SNPs in 21. All studies were based on small patient cohorts and suffered from potential bias. A range of SNPs associated with genes coding for monoamine NTs, BDNF, cytokines, and mitochondrial proteins have been reported to be associated with variation in global, neuropsychiatric, and behavioral outcomes. An analysis of the tissue, cellular, and subcellular location of the genes that harbored the SNPs studied showed that they could be clustered into blood–brain barrier associated, neuroprotective/regulatory, and neuropsychiatric/degenerative groups. Several small studies report that various NT, cytokine, and BDNF-related SNPs are associated with variations in global outcome at 6–12 months post-TBI. The association of these SNPs with neuropsychiatric and behavioral outcomes is less clear. A definitive assessment of role and effect size of genetic variation in these genes on outcome remains uncertain, but could be clarified by an adequately powered genome-wide association study with appropriate recording of outcomes.

Neurotherapeutic capacity of P7C3 agents for the treatment of Traumatic Brain Injury

Traumatic brain injury (TBI) is a significant public health problem around the world. A promising area of research is the characterization of small, drug-like molecules that have potent clinical properties. One pharmacotherapeutic agent in particular, an aminopropyl carbazole called P7C3, was discovered using an in vivo screen to identify new agents that augmented the net magnitude of adult hippocampal neurogenesis. P7C3 greatly enhanced neurogenesis by virtue of increasing survival rates of immature neurons. The potent neuroprotective efficacy of P7C3 is likely due to enhanced nicotinamide phosphoribosyltransferase (NAMPT) activity, which supports critical cellular processes. The scaffold of P7C3 was found to have favorable pharmacokinetic properties, good bioavailability, and was nontoxic. Preclinical studies have shown that administration of the P7C3-series of neuroprotective compounds after TBI can rescue and reverse detrimental cellular events leading to improved functional recovery. In several TBI models and across multiple species, P7C3 and its analogues have produced significant neuroprotection, axonal preservation, robust increases in the net magnitude of adult neurogenesis, protection from injury-induced LTP deficits, and improvement in neurological functioning. This review will elucidate the exciting and diverse therapeutic findings of P7C3 administration in the presence of a complex and multifactorial set of cellular and molecular challenges brought forth by experimental TBI. The clinical potential and broad therapeutic applicability of P7C3 warrants much needed investigation into whether these remedial effects can be replicated in the clinic. P7C3 may serve as an important step forward in the design, understanding, and implementation of pharmacotherapies for treating patients with TBI. This article is part of the Special Issue entitled "Novel Treatments for Traumatic Brain Injury".

Effects of Veliparib on Microglial Activation and Functional Outcomes after Traumatic Brain Injury in the Rat and Pig

The inflammation response induced by brain trauma can impair recovery. This response requires several hours to develop fully and thus provides a clinically relevant therapeutic window of opportunity. Poly(ADP-ribose) polymerase inhibitors suppress inflammatory responses, including brain microglial activation. We evaluated delayed treatment with veliparib, a poly(ADP-ribose) polymerase inhibitor, currently in clinical trials as a cancer therapeutic, in rats and pigs subjected to controlled cortical impact (CCI). In rats, CCI induced a robust inflammatory response at the lesion margins, scattered cell death in the dentate gyrus, and a delayed, progressive loss of corpus callosum axons. Pre-determined measures of cognitive and motor function showed evidence of attentional deficits that resolved after three weeks and motor deficits that recovered only partially over eight weeks. Veliparib was administered beginning 2 or 24 h after CCI and continued for up to 12 days. Veliparib suppressed CCI-induced microglial activation at doses of 3 mg/kg or higher and reduced reactive astrocytosis and cell death in the dentate gyrus, but had no significant effect on delayed axonal loss or functional recovery. In pigs, CCI similarly induced a perilesional microglial activation that was attenuated by veliparib. CCI in the pig did not, however, induce detectable persisting cognitive or motor impairment. Our results showed veliparib suppression of CCI-induced microglial activation with a delay-to-treatment interval of at least 24 h in both rats and pigs, but with no associated functional improvement. The lack of improvement in long-term recovery underscores the complexities in translating anti-inflammatory effects to clinically relevant outcomes.

Metabolic fate of glucose in rats with traumatic brain injury and pyruvate or glucose treatments: A NMR spectroscopy study

Administration of sodium pyruvate (SP; 9.08 μmol/kg, i.p.), ethyl pyruvate (EP; 0.34 μmol/kg, i.p.) or glucose (GLC; 11.1 μmol/kg, i.p.) to rats after unilateral controlled cortical impact (CCI) injury has been reported to reduce neuronal loss and improve cerebral metabolism. In the present study these doses of each fuel or 8% saline (SAL; 5.47 nmoles/kg) were administered immediately and at 1, 3, 6 and 23 h post-CCI. At 24 h all CCI groups and non-treated Sham injury controls were infused with [1,2 ¹³C] glucose for 68 min ¹³C nuclear magnetic resonance (NMR) spectra were obtained from cortex + hippocampus tissues from left (injured) and right (contralateral) hemispheres. All three fuels increased lactate labeling to a similar degree in the injured hemisphere. The amount of lactate labeled via the pentose phosphate and pyruvate recycling (PPP + PR) pathway increased in CCI-SAL and was not improved by SP, EP, and GLC treatments. Oxidative metabolism, as assessed by glutamate labeling, was reduced in CCI-SAL animals. The greatest improvement in oxidative metabolism was observed in animals treated with SP and fewer improvements after EP or GLC treatments. Compared to SAL, all three fuels restored glutamate and glutamine labeling via pyruvate carboxylase (PC), suggesting improved astrocyte metabolism following fuel treatment. Only SP treatments restored the amount of [4 ¹³C] glutamate labeled by the PPP + PR pathway to sham levels. Milder injury effects in the contralateral hemisphere appear normalized by either SP or EP treatments, as increases in the total pool of ¹³C lactate and labeling of lactate in glycolysis, or decreases in the ratio of PC/PDH labeling of glutamine, were found only for CCI-SAL and CCI-GLC groups compared to Sham. The doses of SP, EP and GLC examined in this study all enhanced lactate labeling and restored astrocyte-specific PC activity but differentially affected neuronal metabolism after CCI injury. The restoration of astrocyte metabolism by all three fuel treatments may partially underlie their abilities to improve cerebral glucose utilization and to reduce neuronal loss following CCI injury.

Acute Axonal Degeneration Drives Development of Cognitive, Motor, and Visual Deficits after Blast-Mediated Traumatic Brain Injury in Mice

Axonal degeneration is a prominent feature of many forms of neurodegeneration, and also an early event in blast-mediated traumatic brain injury (TBI), the signature injury of soldiers in Iraq and Afghanistan. It is not known, however, whether this axonal degeneration is what drives development of subsequent neurologic deficits after the injury. The Wallerian degeneration slow strain (WldS) of mice is resistant to some forms of axonal degeneration because of a triplicated fusion gene encoding the first 70 amino acids of Ufd2a, a ubiquitin-chain assembly factor, that is linked to the complete coding sequence of nicotinamide mononucleotide adenylyltransferase 1 (NMAT1). Here, we demonstrate that resistance of WldS mice to axonal degeneration after blast-mediated TBI is associated with preserved function in hippocampal-dependent spatial memory, cerebellar-dependent motor balance, and retinal and optic nerve–dependent visual function. Thus, early axonal degeneration is likely a critical driver of subsequent neurobehavioral complications of blast-mediated TBI. Future therapeutic strategies targeted specifically at mitigating axonal degeneration may provide a uniquely beneficial approach to treating patients suffering from the effects of blast-mediated TBI.

A Combination Therapy of Nicotinamide and Progesterone Improves Functional Recovery following Traumatic Brain Injury

Neuroprotection, recovery of function, and gene expression were evaluated in an animal model of traumatic brain injury (TBI) after a combination treatment of nicotinamide (NAM) and progesterone (Prog). Animals received a cortical contusion injury over the sensorimotor cortex, and were treated with either Vehicle, NAM, Prog, or a NAM/Prog combination for 72 h and compared with a craniotomy only (Sham) group. Animals were assessed in a battery of behavioral, sensory, and both fine and gross motor tasks, and given histological assessments at 24 h post-injury to determine lesion cavity size, degenerating neurons, and reactive astrocytes. Microarray-based transcriptional profiling was used to determine treatment-specific changes on gene expression. Our results confirm the beneficial effects of treatment with either NAM or Prog, demonstrating significant improvements in recovery of function and a reduction in lesion cavitation, degenerating neurons, and reactive astrocytes 24 h post-injury. The combination treatment of NAM and Prog led to a significant improvement in both neuroprotection at 24 h post-injury and recovery of function in sensorimotor related tasks when compared with individual treatments. The NAM/Prog-treated group was the only treatment group to show a significant reduction of cortical loss 24 h post-injury. The combination appears to affect inflammatory and immune processes, reducing expression of a significant number of genes in both pathways. Further preclinical trials using NAM and Prog as a combination treatment should be conducted to identify the window of opportunity, determine the optimal duration of treatment, and evaluate the combination in other pre-clinical models of TBI.

Permeability transition pore-dependent and PARP-mediated depletion of neuronal pyridine nucleotides during anoxia and glucose deprivation

Exposure of rat cortical neurons to combined oxygen and glucose deprivation results in loss of NAD(P)H autofluorescence that is only partially reversible following restoration of oxygen and glucose, suggesting catabolism of pyridine nucleotides. This study tested the hypothesis that metabolic inhibition caused by cyanide-induced chemical anoxia plus glucose deprivation promotes both release of mitochondrial NAD(H) in response to opening of the permeability transition pore (PTP) and NAD(P)(H) degradation through activation of poly (ADP-ribose) polymerase (PARP). The NAD(P)H autofluorescence of rat neonatal cortical neurons was monitored during and following acute (10-30 min) exposure to the respiratory inhibitor, cyanide, in the absence and presence of glucose. Because nitric oxide-derived peroxynitrite is a known activator of PARP, we additionally assessed the effect of a nitric oxide generating agent on the NAD(P)H autofluorescence response to chemical anoxia plus glucose deprivation. Cyanide induced a rapid increase in autofluorescence, followed by a steady decline promoted by the presence of nitric oxide. This decline was primarily due to NAD(H) catabolism, as verified by measurements of total NAD(H) present in cellular extracts. Catabolism was partially blocked by an inhibitor of PARP, by a PTP inhibitor, and by either glucose or pyruvate as a source of reducing power. Overall, data suggest that metabolic, oxidative, and nitrosative stress during in vitro neuronal anoxia and glucose deprivation result in release of mitochondrial pyridine nucleotides in response to PTP opening and rapid, extensive NAD(H) degradation mediated by PARP activation. These events may contribute to the metabolic dysfunction that occurs in vivo during cerebral ischemia and reperfusion and therefore represent prime targets for neuroprotection.

Sex differences in mitochondrial (dys)function: Implications for neuroprotection

Decades of research have revealed numerous differences in brain structure size, connectivity and metabolism between males and females. Sex differences in neurobehavioral and cognitive function after various forms of central nervous system (CNS) injury are observed in clinical practice and animal research studies. Sources of sex differences include early life exposure to gonadal hormones, chromosome compliment and adult hormonal modulation. It is becoming increasingly apparent that mitochondrial metabolism and cell death signaling are also sexually dimorphic. Mitochondrial metabolic dysfunction is a common feature of CNS injury. Evidence suggests males predominantly utilize proteins while females predominantly use lipids as a fuel source within mitochondria and that these differences may significantly affect cellular survival following injury. These fundamental biochemical differences have a profound impact on energy production and many cellular processes in health and disease. This review will focus on the accumulated evidence revealing sex differences in mitochondrial function and cellular signaling pathways in the context of CNS injury mechanisms and the potential implications for neuroprotective therapy development.

Traumatic brain injury alters long-term hippocampal neuron morphology in juvenile, but not immature, rats

PURPOSE

Pediatric traumatic brain injury (TBI) represents a prominent yet understudied medical condition that can profoundly impact brain development. As the juvenile injured brain matures in the wake of neuropathological cascades during potentially critical periods, circuit alterations may explain neurological consequences, including cognitive deficits. We hypothesize that experimental brain injury in juvenile rats, with behavioral deficits that resolve, will lead to quantifiable structural changes in hippocampal neurons at chronic time points post-injury.

METHODS

Controlled cortical impact (CCI), a model of focal TBI with contusion, was used to induce brain injury on post-natal day (PND) 17 juvenile rats. The histological consequence of TBI was quantified in regions of the hippocampus at post-injury day 28 (PID28) on sections stained using a variation of the Golgi-Cox staining method. Individual neuronal morphologies were digitized from the dentate gyrus (DG), CA3, and CA1 regions.

RESULTS

Soma area in the ipsilateral injured DG and CA3 regions of the hippocampus increased significantly at PID28 in comparison to controls. In CA1, dendritic length and dendritic branching decreased significantly in comparison to controls and the contralateral hemisphere, without change in soma area. To extend the study, we examined neuronal morphology in rats with CCI at PND7. On PID28 after CCI on PND7 rats, CA1 neurons showed no injury-induced change in morphology, potentially indicating an age-dependent morphological response to injury.

CONCLUSIONS

Long-lasting structural alterations in hippocampal neurons of brain-injured PND17 juvenile animals, but not PND7 immature animals, suggest differential plasticity depending on age-at-injury, with potential consequences for later function.

Targeting poly(ADP-ribose)polymerase1 in neurological diseases: A promising trove for new pharmacological interventions to enter clinical translation

The highly conserved abundant nuclear protein poly(ADP-ribose)polymerase1 (PARP1) functions at the center of cellular stress response and is mainly implied in DNA damage repair mechanism. Apart from its involvement in DNA damage repair, it does sway multiple vital cellular processes such as cell death pathways, cell aging, insulator function, chromatin modification, transcription and mitotic apparatus function. Since brain is the principal organ vulnerable to oxidative stress and inflammatory responses, upon stress encounters robust DNA damage can occur and intense PARP1 activation may result that will lead to various CNS diseases. In the context of soaring interest towards PARP1 as a therapeutic target for newer pharmacological interventions, here in the present review, we are attempting to give a silhouette of the role of PARP1 in the neurological diseases and the potential of its inhibitors to enter clinical translation, along with its structural and functional aspects.

Neurological and histological consequences induced by in vivo cerebral oxidative stress: evidence for beneficial effects of SRT1720, a sirtuin 1 activator, and sirtuin 1-mediated neuroprotective effects of poly(ADP-ribose) polymerase inhibition

Poly(ADP-ribose)polymerase and sirtuin 1 are both NAD⁺-dependent enzymes. In vitro oxidative stress activates poly(ADP-ribose)polymerase, decreases NAD⁺ level, sirtuin 1 activity and finally leads to cell death. Poly(ADP-ribose)polymerase hyperactivation contributes to cell death. In addition, poly(ADP-ribose)polymerase inhibition restores NAD⁺ level and sirtuin 1 activity in vitro. In vitro sirtuin 1 induction protects neurons from cell loss induced by oxidative stress. In this context, the role of sirtuin 1 and its involvement in beneficial effects of poly(ADP-ribose)polymerase inhibition were evaluated in vivo in a model of cerebral oxidative stress induced by intrastriatal infusion of malonate in rat. Malonate promoted a NAD⁺ decrease that was not prevented by 3-aminobenzamide, a poly(ADP-ribose)polymerase inhibitor, at 4 and 24 hours. However, 3-aminobenzamide increased nuclear SIRT1 activity/expression ratio after oxidative stress. Malonate induced a neurological deficit associated with a striatal lesion. Both were reduced by 3-aminobenzamide and SRT1720, a sirtuin 1 activator, showing beneficial effects of poly(ADP-ribose)polymerase inhibition and sirtuin 1 activation on oxidative stress consequences. EX527, a sirtuin 1 inhibitor, given alone, modified neither the score nor the lesion, suggesting that endogenous sirtuin 1 was not activated during cerebral oxidative stress. However, its association with 3-aminobenzamide suppressed the neurological improvement and the lesion reduction induced by 3-aminobenzamide. The association of 3-aminobenzamide with SRT1720, the sirtuin 1 activator, did not lead to a better protection than 3-aminobenzamide alone. The present data represent the first demonstration that the sirtuin 1 activator SRT1720 is neuroprotective during in vivo cerebral oxidative stress. Furthermore sirtuin 1 activation is involved in the beneficial effects of poly(ADP-ribose)polymerase inhibition after in vivo cerebral oxidative stress.

PARP-1 inhibition attenuates neuronal loss, microglia activation and neurological deficits after traumatic brain injury

Traumatic brain injury (TBI) causes neuronal cell death as well as microglial activation and related neurotoxicity that contribute to subsequent neurological dysfunction. Poly (ADP-ribose) polymerase (PARP-1) induces neuronal cell death through activation of caspase-independent mechanisms, including release of apoptosis inducing factor (AIF), and microglial activation. Administration of PJ34, a selective PARP-1 inhibitor, reduced cell death of primary cortical neurons exposed to N-Methyl-N'-Nitro-N-Nitrosoguanidine (MNNG), a potent inducer of AIF-dependent cell death. PJ34 also attenuated lipopolysaccharide and interferon-γ-induced activation of BV2 or primary microglia, limiting NF-κB activity and iNOS expression as well as decreasing generation of reactive oxygen species and TNFα. Systemic administration of PJ34 starting as late as 24 h after controlled cortical impact resulted in improved motor function recovery in mice with TBI. Stereological analysis demonstrated that PJ34 treatment reduced the lesion volume, attenuated neuronal cell loss in the cortex and thalamus, and reduced microglial activation in the TBI cortex. PJ34 treatment did not improve cognitive performance in a Morris water maze test or reduce neuronal cell loss in the hippocampus. Overall, our data indicate that PJ34 has a significant, albeit selective, neuroprotective effect after experimental TBI, and its therapeutic effect may be from multipotential actions on neuronal cell death and neuroinflammatory pathways.

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.

Nicotinamide pre-treatment ameliorates NAD(H) hyperoxidation and improves neuronal function after severe hypoxia

Prolonged hypoxia leads to irreversible loss of neuronal function and metabolic impairment of nicotinamide adenine dinucleotide recycling (between NAD(+) and NADH) immediately after reoxygenation, resulting in NADH hyperoxidation. We test whether the addition of nicotinamide (to enhance NAD(+) levels) or PARP-1 inhibition (to prevent consumption of NAD(+)) can be effective in improving either loss of neuronal function or hyperoxidation following severe hypoxic injury in hippocampal slices. After severe, prolonged hypoxia (maintained for 3min after spreading depression) there was hyperoxidation of NADH following reoxygenation, an increased soluble NAD(+)/NADH ratio, loss of neuronal field excitatory post-synaptic potential (fEPSP) and decreased ATP content. Nicotinamide incubation (5mM) 2h prior to hypoxia significantly increased total NAD(H) content, improved neuronal recovery, enhanced ATP content, and prevented NADH hyperoxidation. The nicotinamide-induced increase in total soluble NAD(H) was more significant in the cytosolic compartment than within mitochondria. Prolonged incubation with PJ-34 (>1h) led to enhanced baseline NADH fluorescence prior to hypoxia, as well as improved neuronal recovery, NADH hyperoxidation and ATP content on recovery from severe hypoxia and reoxygenation. In this acute model of severe neuronal dysfunction prolonged incubation with either nicotinamide or PJ-34 prior to hypoxia improved recovery of neuronal function, enhanced NADH reduction and ATP content, but neither treatment restored function when administered during or after prolonged hypoxia and reoxygenation.

Insights into the metabolic response to traumatic brain injury as revealed by (13)C NMR spectroscopy

The present review highlights critical issues related to cerebral metabolism following traumatic brain injury (TBI) and the use of (13)C labeled substrates and nuclear magnetic resonance (NMR) spectroscopy to study these changes. First we address some pathophysiologic factors contributing to metabolic dysfunction following TBI. We then examine how (13)C NMR spectroscopy strategies have been used to investigate energy metabolism, neurotransmission, the intracellular redox state, and neuroglial compartmentation following injury. (13)C NMR spectroscopy studies of brain extracts from animal models of TBI have revealed enhanced glycolytic production of lactate, evidence of pentose phosphate pathway (PPP) activation, and alterations in neuronal and astrocyte oxidative metabolism that are dependent on injury severity. Differential incorporation of label into glutamate and glutamine from (13)C labeled glucose or acetate also suggest TBI-induced adaptations to the glutamate-glutamine cycle.

Prevention of traumatic brain injury-induced neuron death by intranasal delivery of nicotinamide adenine dinucleotide

Traumatic brain injury (TBI) is one of the most devastating injuries experienced by military personnel, as well as the general population, and can result in acute and chronic complications such as cognitive impairments. Since there are currently no effective tools for the treatment of TBI, it is of great importance to determine the mechanisms of neuronal death that characterize this insult. Several studies have indicated that TBI-induced neuronal death arises in part due to excessive activation of poly(ADP-ribose) polymerase-1 (PARP-1), which results in nicotinamide adenine dinucleotide (NAD⁺) depletion and subsequent energy failure. In this study, we investigated whether intranasal administration of NAD⁺ could reduce neuronal death after TBI. Rats were subjected to a weight-drop TBI model that induces cortical and hippocampal neuronal death. The intranasal administration of NAD⁺ (20 mg/kg) immediately after TBI protected neurons in CA1, CA3, and dentate gyrus of the hippocampus, but not in the cortex. In addition, delayed microglial activation normally seen after TBI was reduced by NAD⁺ treatment at 7 days after insult. Neuronal superoxide production and PARP-1 accumulation after TBI were not inhibited by NAD⁺ treatment, indicating that reactive oxygen species (ROS) production and PARP-1 activation are events that occur upstream of NAD⁺ depletion. This study suggests that intranasal delivery of NAD⁺ represents a novel, inexpensive, and non-toxic intervention for preventing TBI-induced neuronal death.

Microglial activation induced by brain trauma is suppressed by post-injury treatment with a PARP inhibitor

BACKGROUND

Traumatic brain injury (TBI) induces activation of microglia. Activated microglia can in turn increase secondary injury and impair recovery. This innate immune response requires hours to days to become fully manifest, thus providing a clinically relevant window of opportunity for therapeutic intervention. Microglial activation is regulated in part by poly(ADP-ribose) polymerase-1 (PARP-1). Inhibition of PARP-1 activity suppresses NF-kB-dependent gene transcription and thereby blocks several aspects of microglial activation. Here we evaluated the efficacy of a PARP inhibitor, INO-1001, in suppressing microglial activation after cortical impact in the rat.

METHODS

Rats were subjected to controlled cortical impact and subsequently treated with 10 mg/kg of INO-1001 (or vehicle alone) beginning 20 - 24 hours after the TBI. Brains were harvested at several time points for histological evaluation of inflammation and neuronal survival, using markers for microglial activation (morphology and CD11b expression), astrocyte activation (GFAP), and neuronal survival (NeuN). Rats were also evaluated at 8 weeks after TBI using measures of forelimb dexterity: the sticky tape test, cylinder test, and vermicelli test.

RESULTS

Peak microglial and astrocyte activation was observed 5 to 7 days after this injury. INO-1001 significantly reduced microglial activation in the peri-lesion cortex and ipsilateral hippocampus. No rebound inflammation was observed in rats that were treated with INO-1001 or vehicle for 12 days followed by 4 days without drug. The reduced inflammation was associated with increased neuronal survival in the peri-lesion cortex and improved performance on tests of forelimb dexterity conducted 8 weeks after TBI.

CONCLUSIONS

Treatment with a PARP inhibitor for 12 days after TBI, with the first dose given as long as 20 hours after injury, can reduce inflammation and improve histological and functional outcomes.

Impact of pharmacological treatments on outcome in adult rodents after traumatic brain injury: a meta-analysis

Pharmacological treatments have been widely investigated in pre-clinical animal trials to evaluate their usefulness in reducing cognitive, behavioural and motor problems after traumatic brain injury (TBI). However, the relative efficacy of these agents has yet to be evaluated, making it difficult to assess the strength of evidence for their use in a clinical population. A meta-analytic review of research (1980-2009) was therefore conducted to examine the impact of pharmacological treatments administered to adult male rodents after experimental TBI on cognitive, behavioural, and motor outcome. The PubMed and PsycInfo databases were searched using 35 terms. Weighted Cohen's d effect sizes, percent overlap, Fail-Safe N statistics and confidence intervals were calculated for each treatment. In total, 91 treatments were evaluated in 223 pre-clinical trials, comprising 5988 rodents. Treatments that were investigated by multiple studies and showed large and significant treatment effects were of greatest interest. Of the 16 treatments that were efficacious, six improved cognition, 10 improved motor function and no treatment improved behaviour (depression/anxiety, aggression, zoosocial behaviour). Treatment benefits were found across a range of TBI models. Drug dosage and treatment interval impacted on treatment effects.

Brain energy depletion in a rodent model of diffuse traumatic brain injury is not prevented with administration of sodium lactate

Lactate has been identified as an alternative fuel for the brain in situations of increased energy demand, as following a traumatic brain injury (TBI). This study investigates the effect of treatment with sodium lactate (NaLac) on the changes in brain energy state induced by a severe diffuse TBI. Rats were assigned to one of the eight groups (n=10 per group): 1-sham, normal saline; 2-TBI, normal saline; 3-TBI, hypertonic saline; 4-TBI, 100mM NaLac, 5-TBI, 500 mM NaLac; 6-TBI, 1280 mM NaLac; 7-TBI, 2000 mM NaLac and 8-TBI-500 mM NaLac+magnesium sulfate. Cerebrums were removed 6h after trauma. Metabolites representative of the energy state (ATP, ATP-catabolites), N-acetylaspartate (NAA), antioxidant defenses (ascorbic acid, glutathione), markers of oxidative stress (malondialdehyde, ADP-ribose) and nicotinic coenzymes (NAD(+)) were measured by HPLC. TBI induced a marked decrease in the cerebral levels of ATP, NAA, ascorbic acid, glutathione and NAD(+) and a significant rise in the content of ATP-catabolites, malondialdehyde and ADP-ribose. These alterations were not ameliorated with NaLac infusion. We observed a significant reduction in cerebral NAD(+), an essential co-enzyme for mitochondrial lactate-dehydrogenase that converts lactate into pyruvate and thus replenishes the tricarboxylic acid cycle. These results suggest that the metabolic pathway necessary to consume lactate may be compromised following a severe diffuse TBI in rats.

Inhibition of the kynurenine-NAD+ pathway leads to energy failure and exacerbates apoptosis in pneumococcal meningitis

Pneumococcal meningitis causes neurological sequelae, including learning and memory deficits in up to half of the survivors. In both humans and in animal models of the disease, there is apoptotic cell death in the hippocampus, a brain region involved in learning and memory function. We previously demonstrated that in an infant rat model of pneumococcal meningitis, there is activation of the kynurenine (KYN) pathway in the hippocampus, and that there was a positive correlation between the concentration of 3-hydroxykynurenine and the extent of hippocampal apoptosis. To clarify the role of the KYN pathway in the pathogenesis of hippocampal apoptosis in pneumococcal meningitis, we specifically inhibited 2 key enzymes of the KYN pathway and assessed hippocampal apoptosis, KYN pathway metabolites, and nicotinamide adenine dinucleotide (NAD) concentrations by high-performance liquid chromatography. Pharmacological inhibition of kynurenine 3-hydroxylase and kynureninase led to decreased cellular NAD levels and increased apoptosis in the hippocampus. The cerebrospinal fluid levels of tumor necrosis factor and interleukin-1α and -β were not affected. Our data suggest that activation of the KYN pathway in pneumococcal meningitis is neuroprotective by compensating for an increased NAD demand caused by infection and inflammation;this mechanism may prevent energy failure and apoptosis in the hippocampus.

Neuroprotection for traumatic brain injury: translational challenges and emerging therapeutic strategies

Traumatic brain injury (TBI) causes secondary biochemical changes that contribute to subsequent tissue damage and associated neuronal cell death. Neuroprotective treatments that limit secondary tissue loss and/or improve behavioral outcome have been well established in multiple animal models of TBI. However, translation of such neuroprotective strategies to human injury have been disappointing, with the failure of more than thirty controlled clinical trials. Both conceptual issues and methodological differences between preclinical and clinical injury have undoubtedly contributed to these translational difficulties. More recently, changes in experimental approach, as well as altered clinical trial methodologies, have raised cautious optimism regarding the outcomes of future clinical trials. Here we critically review developing experimental neuroprotective strategies that show promise, and we propose criteria for improving the probability of successful clinical translation.

Metabolic and histologic effects of sodium pyruvate treatment in the rat after cortical contusion injury

This study determined the effects of intraperitoneal sodium pyruvate (SP) treatment on the levels of circulating fuels and on cerebral microdialysis levels of glucose (MD(glc)), lactate (MD(lac)), and pyruvate (MD(pyr)), and the effects of SP treatment on neuropathology after left cortical contusion injury (CCI) in rats. SP injection (1000 mg/kg) 5 min after sham injury (Sham-SP) or CCI (CCI-SP) significantly increased arterial pyruvate (p < 0.005) and lactate (p < 0.001) compared to that of saline-treated rats with CCI (CCI-Sal). Serum glucose also increased significantly in CCI-SP compared to that in CCI-Sal rats (p < 0.05), but not in Sham-SP rats. MD(pyr) was not altered after CCI-Sal, whereas MD(lac) levels within the cerebral cortex significantly increased bilaterally (p < 0.05) and those for MD(glc) decreased bilaterally (p < 0.05). MD(pyr) levels increased significantly in both Sham-SP and CCI-SP rats (p < 0.05 vs. CCI-Sal) and were higher in left/injured cortex of the CCI-SP group (p < 0.05 vs. sham-SP). In CCI-SP rats the contralateral MD(lac) decreased below CCI-Sal levels (p < 0.05) and the ipsilateral MD(glc) levels exceeded those of CCI-Sal rats (p < 0.05). Rats with a single low (500 mg/kg) or high dose (1000 mg/kg) SP treatment had fewer damaged cortical cells 6 h post-CCI than did saline-treated rats (p < 0.05), but three hourly injections of SP (1000 mg/kg) were needed to significantly reduce contusion volume 2 weeks after CCI. Thus, a single intraperitoneal SP treatment increases circulating levels of three potential brain fuels, attenuates a CCI-induced reduction in extracellular glucose while increasing extracellular levels of pyruvate, but not lactate, and can attenuate cortical cell damage occurring within 6 h of injury. Enduring (2 week) neuronal protection was achieved only with multiple SP treatments within the first 2 h post-CCI, perhaps reflecting the need for additional fuel throughout the acute period of increased metabolic demands induced by CCI.

NAD+ depletion is necessary and sufficient for poly(ADP-ribose) polymerase-1-mediated neuronal death

Poly(ADP-ribose)-1 (PARP-1) is a key mediator of cell death in excitotoxicity, ischemia, and oxidative stress. PARP-1 activation leads to cytosolic NAD(+) depletion and mitochondrial release of apoptosis-inducing factor (AIF), but the causal relationships between these two events have been difficult to resolve. Here, we examined this issue by using extracellular NAD(+) to restore neuronal NAD(+) levels after PARP-1 activation. Exogenous NAD(+) was found to enter neurons through P2X(7)-gated channels. Restoration of cytosolic NAD(+) by this means prevented the glycolytic inhibition, mitochondrial failure, AIF translocation, and neuron death that otherwise results from extensive PARP-1 activation. Bypassing the glycolytic inhibition with the metabolic substrates pyruvate, acetoacetate, or hydroxybutyrate also prevented mitochondrial failure and neuron death. Conversely, depletion of cytosolic NAD(+) with NAD(+) glycohydrolase produced a block in glycolysis inhibition, mitochondrial depolarization, AIF translocation, and neuron death, independent of PARP-1 activation. These results establish NAD(+) depletion as a causal event in PARP-1-mediated cell death and place NAD(+) depletion and glycolytic failure upstream of mitochondrial AIF release.

Neuroanatomical correlation of behavioral deficits in the CCI model of TBI

Traumatic brain injury (TBI) is the leading cause of death and disability both in combat and civilian situations with limited treatment options including surgical removal of hematoma, ventricular drainage and use of hyperosmotic agents that restrict secondary injury following TBI. Availability of appropriate model system with full-range characterization of anatomical and behavioral components correlative with brain injury provides a pre-clinical platform to test candidate therapies for clinical translation. Modeling of TBI using controlled cortical impact injury (CCI) is largely considered to be close to clinical TBI and hence CCI models have been widely used in pre-clinical TBI research. Most studies reported so far using CCI models were presented with a limited behavioral characterization and lacked its correlation with the signature histopathology of TBI. Current investigation validated a detailed sensomotor and cognitive behavioral characterization correlative with diffuse axonal injury-the signature histopathology of TBI, in the CCI mouse model of TBI. Present study offers a comprehensively characterized model of TBI that can be used to investigate cellular and molecular mechanisms underlying TBI and to test candidate therapies in developing novel and effective treatments for TBI.

A novel PARP inhibitor L-2286 in a rat model of impact acceleration head injury: an immunohistochemical and behavioral study

We examined the neuro/axono-protective potential of a novel poly (ADP-ribose) polymerase (PARP) inhibitor L-2286 in a rat impact acceleration brain injury model. Male Wistar rats (n = 70) weighing 300–350 grams were used to determine the most effective intracerebroventricular (i.c.v.) dose of L-2286 administered 30 min after injury, and to test the neuroprotective effect at two time points (immediately, and 30 min after injury). The neuroprotective effect of L-2286 was tested using immunohistochemical (amyloid precursor protein and mid-sized mouse anti-neurofilament clone RMO-14.9 antibody) and behavioral tests (beam-balance, open-field and elevated plus maze). At both time-points, a 100 μg/rat dose of i.c.v. L-2286 significantly (p < 0.05) reduced the density of damaged axons in the corticospinal tract and medial longitudinal fascicle compared to controls. In the behavioral tests, treatment 30 min post-injury improved motor function, while the level of anxiety was reduced in both treatment protocols.

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.

Sustained delivery of nicotinamide limits cortical injury and improves functional recovery following traumatic brain injury

Previously, we have demonstrated that nicotinamide (NAM), a neuroprotective soluble B-group vitamin, improves recovery of function following traumatic brain injury (TBI). However, no prior studies have examined whether NAM is beneficial following continuous infusions over 7 days post-TBI. The purpose of this study was to investigate the preclinical efficacy of NAM treatment as it might be delivered clinically; over several days by slow infusion. Rats were prepared with either unilateral controlled cortical impact (CCI) injuries or sham procedures and divided into three groups: CCI-NAM, CCI-vehicle, and sham. Thirty minutes following CCI, Alzet osmotic mini-pumps were implanted subcutaneously. NAM was delivered at a rate of 50 mg/kg/day for 7 days immediately post-CCI. On day 7 following injury, the pumps were removed and blood draws were collected for serum NAM and nicotinamide adenine dinucleotide (NAD+) analyses. Starting on day 2 post-CCI, animals were tested on a battery of sensorimotor tests (bilateral tactile adhesive removal, locomotor placing, and limb-use asymmetry). Continuous infusion of NAM resulted in a significant serum elevation in NAM, but not NAD+. Statistical analyses of the tactile removal and locomotor placing data revealed that continuous administration of NAM significantly reduced the initial magnitude of the injury deficit and improved overall recovery compared to the vehicle-treated animals. NAM treatment also significantly decreased limb-use asymmetries compared to vehicle-treated animals. The overall extent of the cortical damage was also reduced by NAM treatment. No detrimental effects were seen following continuous infusion. The present results suggest that NAM delivered via a clinically relevant therapeutic regimen may truncate behavioral damage following TBI. Thus our results offer strong support for translation into the clinical population.

Cell death mechanisms and modulation in traumatic brain injury

Cell death after traumatic brain injury (TBI) is a major cause of neurological deficits and mortality. Understanding the mechanisms of delayed post-traumatic cell loss may lead to new therapies that improve outcome. Although TBI induces changes in multiple cell types, mechanisms of neuronal cell death have been the predominant focus. Recent work has emphasized the diversity of neuronal death phenotypes, which have generally been defined by either morphological or molecular changes. This diversity has led to confusing and at times contradictory nomenclature. Here we review the historical basis of proposed definitions of neuronal cell death, with the goal of clarifying critical research questions and implications for therapy in TBI. We believe that both morphological and molecular features must be used to clarify post-traumatic cell death and related therapeutic targets. Further, we underscore that the most effective neuroprotective strategies will need to target multiple pathways to reflect the regional and temporal changes underlying diverse neuronal cell death phenotypes.

Hypoxic-ischemic encephalopathy in the term infant

Hypoxia-ischemia in the perinatal period is an important cause of cerebral palsy and associated disabilities in children. There has been significant research progress in hypoxic-ischemic encephalopathy over the last 2 decades, and many new molecular mechanisms have been identified. Despite all these advances, therapeutic interventions are still limited. In this article the authors discuss several molecular pathways involved in hypoxia-ischemia, and potential therapeutic targets.

Drug targets for traumatic brain injury from poly(ADP-ribose)polymerase pathway modulation

The deleterious pathophysiological cascade induced after traumatic brain injury (TBI) is initiated by an excitotoxic process triggered by excessive glutamate release. Activation of the glutamatergic N-methyl-D-aspartate receptor, by increasing calcium influx, activates nitric oxide (NO) synthases leading to a toxic production of NO. Moreover, after TBI, free radicals are highly produced and participate to a deleterious oxidative stress. Evidence has showed that the major toxic effect of NO comes from its combination with superoxide anion leading to peroxynitrite formation, a highly reactive and oxidant compound. Indeed, peroxynitrite mediates nitrosative stress and is a potent inducer of cell death through its reaction with lipids, proteins and DNA. Particularly DNA damage, caused by both oxidative and nitrosative stresses, results in activation of poly(ADP-ribose) polymerase (PARP), a nuclear enzyme implicated in DNA repair. In response to excessive DNA damage, massive PARP activation leads to energetic depletion and finally to cell death. Since 10 years, accumulating data have showed that inactivation of PARP, either pharmacologically or using PARP null mice, induces neuroprotection in experimental models of TBI. Thus TBI generating NO, oxidative and nitrosative stresses promotes PARP activation contributing in post-traumatic motor, cognitive and histological sequelae. The mechanisms by which PARP inhibitors provide protection might not entirely be related to the preservation of cellular energy stores, but might also include other PARP-mediated mechanisms that needed to be explored in a TBI context. Ten years of experimental research provided rational basis for the development of PARP inhibitors as treatment for TBI.

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.

Histological and functional outcomes after traumatic brain injury in mice null for the erythropoietin receptor in the central nervous system

Erythropoietin (EPO) and its receptor (EPOR), essential for erythropoiesis, are expressed in the nervous system. Recombinant human EPO treatment promotes functional outcome after traumatic brain injury (TBI) and stroke, suggesting that the endogenous EPO/EPOR system plays an important role in neuroprotection and neurorestoration. This study was designed to investigate effects of the EPOR on histological and functional outcomes after TBI. Experimental TBI was induced in adult EPOR-null and wild-type mice by controlled cortical impact. Neurological function was assessed using the modified Morris Water Maze and footfault tests. Animals were sacrificed 35 days after injury and brain sections stained for immunohistochemistry. As compared to the wild-type injured mice, EPOR-null mice did not exhibit higher susceptibility to TBI as exemplified by tissue loss in the cortex, cell loss in the dentate gyrus, impaired spatial learning, angiogenesis and cell proliferation. We observed that less cortical neurogenesis occurred and that sensorimotor function (i.e., footfault) was more impaired in the EPOR-null mice after TBI. Co-accumulation of amyloid precursor protein (axonal injury marker) and calcium was observed in the ipsilateral thalamus in both EPOR-null and wild-type mice after TBI with more calcium deposits present in the wild-type mice. This study demonstrates for the first time that EPOR null in the nervous system aggravates sensorimotor deficits, impairs cortical neurogenesis and reduces thalamic calcium precipitation after TBI.