Effects of L-NAME and 7-NI on NOS catalytic activity and behavioral outcome after traumatic brain injury in the rat

Mild traumatic brain injury in Drosophila melanogaster alters reactive oxygen and nitrogen species in a sex-dependent manner

Traumatic brain injury (TBI) is an outside force causing a modification in brain function and/or structural brain pathology that upregulates brain inducible nitric oxide synthase (iNOS), instigating increased levels of nitric oxide activity which is implicated in secondary pathology leading to behavioral deficits (Hall et al., 2012; Garry et al., 2015; Kozlov et al., 2017). In mammals, TBI-induced NO production activates an immune response and potentiates metabolic crisis through mitochondrial dysfunction coupled with vascular dysregulation; however, the direct influence on pathology is complicated by the activation of numerous secondary cascades and activation of other reactive oxygen species. Drosophila TBI models have demonstrated key features of mammalian TBI, including temporary incapacitation, disorientation, motor deficits, activation of innate immunity (inflammation), and autophagy responses observed immediately after injury (Katzenberger et al., 2013; Barekat et al., 2016; Simon et al., 2017; Anderson et al., 2018; Buhlman et al., 2021b). We hypothesized that acute behavioral phenotypes would be associated with deficits in climbing behavior and increased oxidative stress. Because flies lack mammalian-like cardiovascular and adaptive immune systems, we were able to make our observations in the absence of vascular disruption and adaptive immune system interference in a system where highly targeted interventions can be rapidly evaluated. To demonstrate the induction of injury, ten-day-old transgenic flies received an injury of increasing angles from a modified high impact trauma (HIT) device where angle-dependent increases occurred for acute neurological behavior assessments and twenty-four-hour mortality, and survival was significantly decreased. Injury caused sex-dependent effects on climbing activity and measures of oxidative stress. Specifically, after a single 60-degree HIT, female flies exhibited significant impairments in climbing activity beyond that observed in male flies. We also found that several measures of oxidative stress, including Drosophila NOS (dNOS) expression, protein nitration, and hydrogen peroxide production were significantly decreased in female flies. Interestingly, protein nitration was also decreased in males, but surpassed sham levels with a more severe injury. We also observed decreased autophagy demand in vulnerable dopaminergic neurons in female, but not male flies. In addition, mitophagy initiation was decreased in females. Collectively, our data suggest that TBI in flies induces acute behavioral phenotypes and climbing deficits that are analogous to mammalian TBI. We also observed that various indices of oxidative stress, including dNOS expression, protein tyrosine nitration, and hydrogen peroxide levels, as well as basal levels of autophagy, are altered in response to injury, an effect that is more pronounced in female flies.

Are We Ready for Clinical Therapy based on Cerebral Autoregulation? A Pro-con Debate

Cerebral autoregulation (CA) is a physiological mechanism that maintains constant cerebral blood flow regardless of changes in cerebral perfusion pressure and prevents brain damage caused by hypoperfusion or hyperperfusion. In recent decades, researchers have investigated the range of systemic blood pressures and clinical management strategies over which cerebral vasculature modifies intracranial hemodynamics to maintain cerebral perfusion. However, proposed clinical interventions to optimize autoregulation status have not demonstrated clear clinical benefit. As future trials are designed, it is crucial to comprehend the underlying cause of our inability to produce robust clinical evidence supporting the concept of CA-targeted management. This article examines the technological advances in monitoring techniques and the accuracy of continuous assessment of autoregulation techniques used in intraoperative and intensive care settings today. It also examines how increasing knowledge of CA from recent clinical trials contributes to a greater understanding of secondary brain injury in many disease processes, despite the fact that the lack of robust evidence influencing outcomes has prevented the translation of CA-guided algorithms into clinical practice.

Revisiting Traumatic Brain Injury: From Molecular Mechanisms to Therapeutic Interventions

Studying the complex molecular mechanisms involved in traumatic brain injury (TBI) is crucial for developing new therapies for TBI. Current treatments for TBI are primarily focused on patient stabilization and symptom mitigation. However, the field lacks defined therapies to prevent cell death, oxidative stress, and inflammatory cascades which lead to chronic pathology. Little can be done to treat the mechanical damage that occurs during the primary insult of a TBI; however, secondary injury mechanisms, such as inflammation, blood-brain barrier (BBB) breakdown, edema formation, excitotoxicity, oxidative stress, and cell death, can be targeted by therapeutic interventions. Elucidating the many mechanisms underlying secondary injury and studying targets of neuroprotective therapeutic agents is critical for developing new treatments. Therefore, we present a review on the molecular events following TBI from inflammation to programmed cell death and discuss current research and the latest therapeutic strategies to help understand TBI-mediated secondary injury.

Nitric oxide synthase mediates cerebellar dysfunction in mice exposed to repetitive blast-induced mild traumatic brain injury

We investigated the role of nitric oxide synthase (NOS) in mediating blood-brain barrier (BBB) disruption and peripheral immune cell infiltration in the cerebellum following blast exposure. Repetitive, but not single blast exposure, induced delayed-onset BBB disruption (72 hours post-blast) in cerebellum. The NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) administered after blast blocked BBB disruption and prevented CD4⁺ T-cell infiltration into cerebellum. L-NAME also blocked blast-induced increases in intercellular adhesion molecule-1 (ICAM-1), a molecule that plays a critical role in regulating blood-to-brain immune cell trafficking. Blocking NOS-mediated BBB dysfunction during this acute/subacute post-blast interval (24-71 hours after the last blast) also prevented sensorimotor impairment on a rotarod task 30 days later, long after L-NAME cleared the body. In postmortem brains from Veterans/military Servicemembers with blast-related TBI, we found marked Purkinje cell dendritic arbor structural abnormalities, which were comparable to neuropathologic findings in the blast-exposed mice. Taken collectively, these results indicate that blast provokes delayed-onset of NOS-dependent pathogenic cascades that can later emerge as behavioral dysfunction. These results also further implicate the cerebellum as a brain region vulnerable to blast-induced mTBI.

Arginase overexpression in neurons and its effect on traumatic brain injury

Arginine is a semi-essential amino acid which serves as a substrate for nitric oxide (NO) production by nitric oxide synthase (NOS) and a precursor for various metabolites including ornithine, creatine, polyamines, and agmatine. Arginase competes with nitric oxide synthase for substrate arginine to produce orthinine and urea. There is contradictory evidence in the literature on the role of nitric oxide in the pathophysiology of traumatic brain injury (TBI). These contradictory perspectives are likely due to different NOS isoforms - endothelial (eNOS), inducible (iNOS) and neuronal (nNOS) which are expressed in the central nervous system. Of these, the role of nNOS in acute injury remains less clear. This study aimed to employ a genetic approach by overexpressing arginase isoforms specifically in neurons using a Thy-1 promoter to manipulate cell autonomous NO production in the context of TBI. The hypothesis was that increased arginase would divert arginine from pathological NO production. We generated 2 mouse lines that overexpress arginase I (a cytoplasmic enzyme) or arginase II (a mitochondrial enzyme) in neurons of FVB mice. We found that two-weeks after induction of controlled cortical injury, overexpressing arginase I but not arginase II in neurons significantly reduced contusion size and contusion index compared to wild-type (WT) mice. This study establishes enhanced neuronal arginase levels as a strategy to affect the course of TBI and provides support for the potential role of neuronal NO production in this condition.

Blast exposure elicits blood-brain barrier disruption and repair mediated by tight junction integrity and nitric oxide dependent processes

Mild blast-induced traumatic brain injury (TBI) is associated with blood-brain barrier (BBB) disruption. However, the mechanisms whereby blast disrupts BBB integrity are not well understood. To address this issue BBB permeability to peripherally injected ¹⁴C-sucrose and ^99mTc-albumin was quantified in ten brain regions at time points ranging from 0.25 to 72 hours. In mice, repetitive (2X) blast provoked BBB permeability to ¹⁴C-sucrose that persisted in specific brain regions from 0.25 to 72 hours. However, ^99mTc-albumin revealed biphasic BBB disruption (open-closed-open) over the same interval, which was most pronounced in frontal cortex and hippocampus. This indicates that blast initiates interacting BBB disruption and reparative processes in specific brain regions. Further investigation of delayed (72 hour) BBB disruption revealed that claudin-5 (CLD5) expression was disrupted specifically in the hippocampus, but not in dorsal striatum, a brain region that showed no blast-induced BBB permeability to sucrose or albumin. In addition, we found that delayed BBB permeability and disrupted CLD5 expression were blocked by the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). These data argue that latent nitric oxide-dependent signaling pathways initiate processes that result in delayed BBB disruption, which are manifested in a brain-region specific manner.

Effects of Dimeric PSD-95 Inhibition on Excitotoxic Cell Death and Outcome After Controlled Cortical Impact in Rats

Therapeutic effects of PSD-95 inhibition have been demonstrated in numerous studies of stroke; however only few studies have assessed the effects of PSD-95 inhibitors in traumatic brain injury (TBI). As the pathophysiology of TBI partially overlaps with that of stroke, PSD-95 inhibition may also be an effective therapeutic strategy in TBI. The objectives of the present study were to assess the effects of a dimeric inhibitor of PSD-95, UCCB01-144, on excitotoxic cell death in vitro and outcome after experimental TBI in rats in vivo. In addition, the pharmacokinetic parameters of UCCB01-144 were investigated in order to assess uptake of the drug into the central nervous system of rats. After a controlled cortical impact rats were randomized to receive a single injection of either saline or two different doses of UCCB01-144 (10 or 20 mg/kg IV) immediately after injury. Spatial learning and memory were assessed in a water maze at 2 weeks post-trauma, and at 4 weeks lesion volumes were estimated. Overall, UCCB01-144 did not protect against NMDA-toxicity in neuronal cultures or experimental TBI in rats. Important factors that should be investigated further in future studies assessing the effects of PSD-95 inhibitors in TBI are discussed.

Gas Diffusion in the CNS

Gases have been long known to have essential physiological functions in the CNS such as respiration or regulation of vascular tone. Since gases have been classically considered to freely diffuse, research in gas biology has so far focused on mechanisms of gas synthesis and gas reactivity, rather than gas diffusion and transport. However, the discovery of gas pores during the last two decades and the characterization of diverse diffusion patterns through different membranes has raised the possibility that modulation of gas diffusion is also a physiologically relevant parameter. Here we review the means of gas movement into and within the brain through "free" diffusion and gas pores, notably aquaporins, discussing the role that gas diffusion may play in the modulation of gas function. We highlight how diffusion is relevant to neuronal signaling, volume transmission, and cerebrovascular control in the case of NO, one of the most extensively studied gases. We point out how facilitated transport can be especially relevant for gases with low permeability in lipid membranes like NH₃ and discuss the possible implications of NH₃ -permeable channels in physiology and hyperammonemic encephalopathy. We identify novel research questions about how modulation of gas diffusion could intervene in CNS pathologies. This emerging area of research can provide novel and interesting insights in the field of gas biology.

The effects of 7-nitroindazole on serum neuron-specific enolase and astroglia-derived protein (S100β) levels after traumatic brain injury

We investigated the possible role of 7-nitroindazole (7-NI) in regulating serum neuron-specific enolase (NSE) and S100β levels in a rat model of traumatic brain injury (TBI). We also explored the possible mechanism by which 7-NI may affect the level of NSE and S100β. A total of 160 healthy adult male Sprague-Dawley rats were randomly divided into 2 groups: i) The saline-treated group and ii) the 7-NI-treated group. Using the random number table, the groups were further divided into four subgroups: i) The sham-injured group; ii) the TBI 6 h group; iii) the TBI 12 h group; and iv) the TBI 24 h group (n=20). Controlled cortical impact in rats was established. Serum NSE and S100β levels, nitric oxide (NO) level, water content, Evans blue (EB) content, malondialdehyde (MDA) level and total superoxide dismutase (T-SOD) level in the brain tissue were measured. NO synthase (NOS) activity was measured at 6, 12 and 24 h after TBI. Pathological changes in brain tissue were studied by hematoxylin and eosin (H&E) staining at each time-point. NSE and S100β levels, NO content, water content, EB content and MDA level in the brain tissue increased significantly after TBI. NOS activity was also increased significantly after TBI while T-SOD content in brain tissue was significantly reduced after TBI. H&E staining showed that brain damage was aggravated gradually after TBI. We concluded that the early application of 7-NI significantly reduced serum NSE and S100β levels after TBI. The neuroprotective effects of 7-NI may be associated with reduced NOS activity, reduced NO content, alleviated brain edema, lower blood-brain barrier permeability and oxidative stress. Serum NSE and S100β levels can reflect the therapeutic effect of 7-NI, which suggest a good diagnostic value.

Endothelial nitric oxide synthase mediates arteriolar vasodilatation after traumatic brain injury in mice

Brain edema and increased cerebral blood volume (CBV) contribute to intracranial hypertension and hence to unfavorable outcome after traumatic brain injury (TBI). The increased post-traumatic CBV may be caused in part by arterial vasodilatation. The aim of the current study was to uncover the largely unknown mechanisms of post-traumatic arteriolar vasodilatation. The diameter of pial arterioles and venules was monitored by intravital fluorescence microscopy before (baseline) and for 30 min after controlled cortical impact in C57BL/6 and endothelial nitric oxide synthase (eNOS)-/- mice (n=5-6/group) and in C57BL/6 mice (n=6/group) receiving vehicle (phosphate-buffered saline [PBS]) or 4-amino-tetrahydro-L-biopterine (VAS203), a NOS inhibitor previously shown to reduce post-traumatic intracranial hypertension. Temperature, end-tidal partial pressure of carbon dioxide (pCO₂), and mean arterial blood pressure were kept within the physiological range throughout the experiments. Arteriolar diameters were stable during baseline monitoring but increased significantly in C57BL/6 mice after controlled cortical impact (136±7% of baseline; p<0.001 vs. baseline). This response was reduced by 78% in eNOS-/- mice (108±3% of baseline; p<0.005 vs. wild-type). Application of VAS203, a NOS inhibitor, or PBS did not affect vessels diameter before TBI. After trauma, however, administration of VAS203 reduced arteriolar diameter to 92±2% of baseline (p<0.05). The diameter of pial veins was not affected. Our results suggest that arteriolar vasodilatation after TBI is largely mediated by excess production of endothelial nitric oxide. Accordingly, our data may explain the beneficial effects of the NOS inhibitor VAS203 in the early phase after TBI and suggest that inhibition of excess endothelial nitric oxide production may represent a novel therapeutic strategy following TBI.

HOE-140, an antagonist of B2 receptor, protects against memory deficits and brain damage induced by moderate lateral fluid percussion injury in mice

RATIONALE

There are evidences indicating the role of kinins in pathophysiology of traumatic brain injury, but little is known about their action on memory deficits.

OBJECTIVES

Our aim was to establish the role of bradykinin receptors B₁ (B₁R) and B₂ (B₂R) on the behavioral, biochemical, and histologic features elicited by moderate lateral fluid percussion injury (mLFPI) in mice.

METHODS

The role of kinin B₁ and B₂ receptors in brain damage, neuromotor, and cognitive deficits induced by mLFPI, was evaluated by means of subcutaneous injection of B₂R antagonist (HOE-140; 1 or 10 nmol/kg) or B₁R antagonist (des-Arg9-[Leu8]-bradykinin (DAL-Bk; 1 or 10 nmol/kg) 30 min and 24 h after brain injury. Brain damage was evaluated in the cortex, being considered as lesion volume, inflammatory, and oxidative damage. The open field and elevated plus maze tests were performed to exclude the nonspecific effects on object recognition memory test.

RESULTS

Our data revealed that HOE-140 (10 nmol/kg) protected against memory impairment. This treatment attenuated the brain edema, interleukin-1β, tumor necrosis factor-α, and nitric oxide metabolites content elicited by mLFPI. Accordingly, HOE-140 administration protected against the increase of nicotinamide adenine dinucleotide phosphate oxidase activity, thiobarbituric-acid-reactive species, protein carbonylation generation, and Na⁺ K⁺ ATPase inhibition induced by trauma. Histologic analysis showed that HOE-140 reduced lesion volume when analyzed 7 days after brain injury.

CONCLUSIONS

This study suggests the involvement of the B₂ receptor in memory deficits and brain damage caused by mLFPI in mice.

Endogenous nitric-oxide synthase inhibitor ADMA after acute brain injury

Previous results on nitric oxide (NO) metabolism after traumatic brain injury (TBI) show variations in NO availability and controversial effects of exogenous nitric oxide synthase (NOS)-inhibitors. Furthermore, elevated levels of the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) were reported in cerebro-spinal fluid (CSF) after traumatic subarachnoid hemorrhage (SAH). Therefore, we examined whether ADMA and the enzymes involved in NO- and ADMA-metabolism are expressed in brain tissue after TBI and if time-dependent changes occur. TBI was induced by controlled cortical impact injury (CCII) and neurological performance was monitored. Expression of NOS, ADMA, dimethylarginine dimethylaminohydrolases (DDAH) and protein-arginine methyltransferase 1 (PRMT1) was determined by immunostaining in different brain regions and at various time-points after CCII. ADMA and PRMT1 expression decreased in all animals after TBI compared to the control group, while DDAH1 and DDAH2 expression increased in comparison to controls. Furthermore, perilesionally ADMA is positively correlated with neuroscore performance, while DDAH1 and DDAH2 are negatively correlated. ADMA and its metabolizing enzymes show significant temporal changes after TBI and may be new targets in TBI treatment.

Traumatic brain injury: oxidative stress and neuroprotection

SIGNIFICANCE

A vast amount of circumstantial evidence implicates high energy oxidants and oxidative stress as mediators of secondary damage associated with traumatic brain injury. The excessive production of reactive oxygen species due to excitotoxicity and exhaustion of the endogenous antioxidant system induces peroxidation of cellular and vascular structures, protein oxidation, cleavage of DNA, and inhibition of the mitochondrial electron transport chain.

RECENT ADVANCES

Different integrated responses exist in the brain to detect oxidative stress, which is controlled by several genes termed vitagens. Vitagens encode for cytoprotective heat shock proteins, and thioredoxin and sirtuins.

CRITICAL ISSUES AND FUTURE DIRECTIONS

This article discusses selected aspects of secondary brain injury after trauma and outlines key mechanisms associated with toxicity, oxidative stress, inflammation, and necrosis. Finally, this review discusses the role of different oxidants and presents potential clinically relevant molecular targets that could be harnessed to treat secondary injury associated with brain trauma.

Changes in mouse cognition and hippocampal gene expression observed in a mild physical- and blast-traumatic brain injury

Warfare has long been associated with traumatic brain injury (TBI) in militarized zones. Common forms of TBI can be caused by a physical insult to the head-brain or by the effects of a high velocity blast shock wave generated by the detonation of an explosive device. While both forms of trauma are distinctly different regarding the mechanism of trauma induction, there are striking similarities in the cognitive and emotional status of survivors. Presently, proven effective therapeutics for the treatment of either form of TBI are unavailable. To be able to develop efficacious therapies, studies involving animal models of physical- and blast-TBI are required to identify possible novel or existing medicines that may be of value in the management of clinical events. We examined indices of cognition and anxiety-like behavior and the hippocampal gene transcriptome of mice subjected to both forms of TBI. We identified common behavioral deficits and gene expression regulations, in addition to unique injury-specific forms of gene regulation. Molecular pathways presented a pattern similar to that seen in gene expression. Interestingly, pathways connected to Alzheimer's disease displayed a markedly different form of regulation depending on the type of TBI. While these data highlight similarities in behavioral outcomes after trauma, the divergence in hippocampal transcriptome observed between models suggests that, at the molecular level, the TBIs are quite different. These models may provide tools to help define therapeutic approaches for the treatment of physical- and blast-TBIs. Based upon observations of increasing numbers of personnel displaying TBI related emotional and behavioral changes in militarized zones, the development of efficacious therapies will become a national if not a global priority.

Inhaled nitric oxide reduces secondary brain damage after traumatic brain injury in mice

Ischemia, especially pericontusional ischemia, is one of the leading causes of secondary brain damage after traumatic brain injury (TBI). So far efforts to improve cerebral blood flow (CBF) after TBI were not successful because of various reasons. We previously showed that nitric oxide (NO) applied by inhalation after experimental ischemic stroke is transported to the brain and induces vasodilatation in hypoxic brain regions, thus improving regional ischemia, thereby improving brain damage and neurological outcome. As regional ischemia in the traumatic penumbra is a key mechanism determining secondary posttraumatic brain damage, the aim of the current study was to evaluate the effect of NO inhalation after experimental TBI. NO inhalation significantly improved CBF and reduced intracranial pressure after TBI in male C57 Bl/6 mice. Long-term application (24 hours NO inhalation) resulted in reduced lesion volume, reduced brain edema formation and less blood-brain barrier disruption, as well as improved neurological function. No adverse effects, e.g., on cerebral auto-regulation, systemic blood pressure, or oxidative damage were observed. NO inhalation might therefore be a safe and effective treatment option for TBI patients.

Edaravone increases regional cerebral blood flow after traumatic brain injury in mice

Traumatic brain injury (TBI) is a major cause of preventable death and serious morbidity, with subsequent low cerebral blood flow (CBF) considered to be associated with poor prognosis. In the present study, we demonstrated the effect of the free radical scavenger edaravone on regional CBF (rCBF) after TBI. Male mice (C57/BL6) were subjected to TBI using a controlled cortical impactor device. Immediately after TBI, the animals were intravenously administered 3.0 mg/kg of edaravone or a vehicle saline solution. Two-dimensional rCBF images were acquired before and 24 h post-TBI, and were quantified in the ipsilateral and contralateral hemispheres (n = 5 animals per group). CBF in the vehicle-treated animals decreased broadly over the ipsilateral hemisphere, with the region of low rCBF spreading from the frontal cortex to the occipital lobe. The zone of lowest rCBF matched that of the contusion area. The mean rCBF at 24 h for a defined elliptical region between the bregma and lambda was 73.7 ± 5.8 %. In comparison, the reduction of rCBF in edaravone-treated animals was significantly attenuated (93.4 ± 5.7 %, p < 0.05). The edaravone-treated animals also exhibited higher rCBF in the contralateral hemisphere compared with that seen in -vehicle-treated animals. It is suggested that edaravone reduces neuronal damage by scavenging reactive oxygen species (ROS) and by maintaining intact the autoregulation of the cerebral vasculature.

Relationship of nitric oxide synthase induction to peroxynitrite-mediated oxidative damage during the first week after experimental traumatic brain injury

We have previously shown the pathophysiological importance of the reactive nitrogen species peroxynitrite (PN) formed from the reaction of nitric oxide (•NO) and superoxide (O(2)(•-)) radicals and its involvement in lipid peroxidation (LP) and protein nitration damage in brain tissue following traumatic brain injury (TBI). Nitric oxide is produced by at least three isoforms of the enzyme nitric oxide synthase (NOS) including: endothelial NOS (eNOS) in the CNS vasculature, neuronal NOS (nNOS), and inducible NOS (iNOS) in macrophages/microglia. In view of the requirement of •NO synthesis for PN formation, we sought to address the time course of NOS expression (mRNA by real time quantitative PCR and protein by western blot) after TBI in comparison with the time course of PN-mediated protein nitration (3-nitrotyrosine, 3-NT) in ipsilateral cortex (CTX) and hippocampus (HIPP) between 3 hours and 1 week post-injury using a controlled cortical impact (CCI) mouse model of TBI in young adult CF-1 mice. Protein nitration showed a progressive posttraumatic increase that became significant in CTX at 24 hours and then peaked at 72 hours in both CTX and HIPP. During the increase in PN-derived 3-NT, there was no increase in either CTX or HIPP eNOS mRNA levels, whereas eNOS protein levels were significantly (p<0.05) increased at 48 and 72 hours in both brain regions. There was a significant decrease in HIPP, but not CTX nNOS mRNA; however, nNOS protein did not change except for a significant increase in CTX at 1 week. There was significantly increased CTX and HIPP iNOS mRNA levels at 24, 48, and 72 hours (p<.05) post-injury. In contrast, no change was seen in CTX or HIPP iNOS protein at any timepoint. Taken together, eNOS protein expression and iNOS mRNA appear to bear a coincident temporal relationship to the time course of PN-mediated protein nitrative damage after CCI-TBI suggesting that both constitutive and inducible NOS isoforms contribute •NO for PN formation and 3-NT protein modification after TBI.

Neuroprotective effects of almond skins in experimental spinal cord injury

BACKGROUND & AIMS

Functional deficits following spinal cord injury (SCI) arise from both mechanical injury and from secondary tissue reactions involving inflammation. Natural almond skins (NS) were tested to evaluate anti-inflammatory effects on an animal model of SCI.

METHODS

SCI was induced by the application of vascular clips to the dura via a four-level T5-T8 laminectomy. In the present study, to elucidate whether the protective effects of NS are related to the total phenolic content, we also investigated the effect of a blanched (BS) almond skins (industrially obtained by removing bran from the nut) in SCI. NS and BS (30 mg/kg respectively) were administered per os, 1 h and 6 h, after SCI.

RESULTS

SCI in mice resulted in severe injury characterized by edema, tissue damage, production of inflammatory mediators and apoptosis (measured by Bax, Bcl-2 and Tunel assay). NS treatment, 1 and 6 h after SCI, reduced all parameters of inflammation as neutrophil infiltration, NF-κB activation, PAR formation, iNOS expression and apoptosis. However, treatment with BS did not exert any protective effect.

CONCLUSIONS

Our results suggest that NS treatment, reducing the development of inflammation and tissue injury, may be useful in the treatment of SCI.

Glutamate receptors, neurotoxicity and neurodegeneration

Glutamate excitotoxicity is a hypothesis that states excessive glutamate causes neuronal dysfunction and degeneration. As glutamate is a major excitatory neurotransmitter in the central nervous system (CNS), the implications of glutamate excitotoxicity are many and far-reaching. Acute CNS insults such as ischaemia and traumatic brain injury have traditionally been the focus of excitotoxicity research. However, glutamate excitotoxicity has also been linked to chronic neurodegenerative disorders such as amyotrophic lateral sclerosis, multiple sclerosis, Parkinson's disease and others. Despite the continued research into the mechanisms of excitotoxicity, there are currently no pharmacological interventions capable of providing significant neuroprotection in the clinical setting of brain ischaemia or injury. This review addresses the current state of excitotoxic research, focusing on the structure and physiology of glutamate receptors; molecular mechanisms underlying excitotoxic cell death pathways and their interactions with each other; the evidence for glutamate excitotoxicity in acute neurologic diseases; laboratory and clinical attempts at modulating excitotoxicity; and emerging targets for excitotoxicity research.

Antioxidant therapies for traumatic brain injury

Free radical-induced oxidative damage reactions, and membrane lipid peroxidation (LP), in particular, are among the best validated secondary injury mechanisms in preclinical traumatic brain injury (TBI) models. In addition to the disruption of the membrane phospholipid architecture, LP results in the formation of cytotoxic aldehyde-containing products that bind to cellular proteins and impair their normal functions. This article reviews the progress of the past three decades in regard to the preclinical discovery and attempted clinical development of antioxidant drugs designed to inhibit free radical-induced LP and its neurotoxic consequences via different mechanisms including the O(2)(*-) scavenger superoxide dismutase and the lipid peroxidation inhibitor tirilazad. In addition, various other antioxidant agents that have been shown to have efficacy in preclinical TBI models are briefly presented, such as the LP inhibitors U83836E, resveratrol, curcumin, OPC-14177, and lipoic acid; the iron chelator deferoxamine and the nitroxide-containing antioxidants, such as alpha-phenyl-tert-butyl nitrone and tempol. A relatively new antioxidant mechanistic strategy for acute TBI is aimed at the scavenging of aldehydic LP byproducts that are highly neurotoxic with "carbonyl scavenging" compounds. Finally, it is proposed that the most effective approach to interrupt posttraumatic oxidative brain damage after TBI might involve the combined treatment with mechanistically complementary antioxidants that simultaneously scavenge LP-initiating free radicals, inhibit LP propagation, and lastly remove neurotoxic LP byproducts.

The novel nitric oxide synthase inhibitor 4-amino-tetrahydro-L-biopterine prevents brain edema formation and intracranial hypertension following traumatic brain injury in mice

Brain edema formation, resulting in increased intracranial pressure (ICP), is one of the most deleterious consequences of traumatic brain injury (TBI). Nitric oxide (NO) has previously been shown to be involved in the damage of the blood-brain barrier (BBB) and, thus, in the formation of post-traumatic brain edema; however, this knowledge never resulted in a clinically relevant therapeutic option because available NO synthase inhibitors have serious side effects in man. The aim of the current study was to investigate the therapeutic efficacy of VAS203, a novel tetrahydrobiopterine (BH3)-based NOS inhibitor, in experimental TBI. When added to isolated vessels rings obtained from rat basilar and middle cerebral arteries (n = 32-35) VAS203 showed the same vasoconstrictive effect as the classical NO synthase inhibitor L-(G)-nitro-arginine-methylester (L-NAME). VAS203 passed the BBB both in healthy and traumatized mouse brain (C57/BL6, n = 5 per group) and did not show any systemic side effects at therapeutic concentrations. When administered 30 min after experimental TBI (controlled cortical impact, 2.2 mg/kg/min i.v., n = 7 per group), VAS203 prevented any further increase in ICP or deterioration of cerebral blood flow. This effect was dose-dependent and long-lasting (i.e., 24 h after trauma, brain edema formation was still significantly reduced [-40%, p < 0.008; n = 7 per group] and functional improvements were present up to 7 days after TBI [p < 0.02 on post-trauma day 6; n = 8 per group]). Therefore, VAS203 may represent a promising candidate for the treatment of acute intracranial hypertension following TBI.

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.

Investigation of neuroprotective effect of dexamethasone by using nitric oxide and leukocyte levels in experimental head trauma

The objective of the present study was to determine the levels of nitric oxide (NO) and white blood cells (WBCs), which are assumed to play a role in secondary cerebral damage by increasing to pathological levels during cranial trauma, and to investigate the neuroprotective effect of dexamethasone on NO and WBC levels in experimental cranial trauma. For this purpose, adult Sprague-Dawley male rats were used. Blood NO and WBC levels were investigated in one group of non-trauma rats (control group, n = 10) after 6 h; in a group of rats with experimental post-cranial trauma (trauma group, n = 10) after 6 and 24 h; and in a third group of rats with experimental cranial trauma, intraperitoneally injected with 10 mg/kg dexamethasone after 1 and 12 h (trauma + dexamethasone group, n = 10), WBC and NO levels were measured after 6 and 24 h. Determination of NO levels was carried out by assaying serum nitrite and nitrate levels. The increases in post-trauma serum NO (nitrite and nitrate) and WBC levels were statistically significant for the trauma and trauma + dexamethasone groups compared to controls. There was no significant difference between serum NO and WBC levels in rats in the trauma + dexamethasone and those in the trauma group. The study demonstrated no significant inhibition of NO and WBC levels by dexamethasone, a drug used for its anti-edema and anti-inflammatory effects and its influence on membrane stabilization and in avoiding oscillation stress. In the present study, dexamethasone was found to be ineffective in decreasing NO and WBC levels to avoid secondary cerebral damage after cranial trauma.

Nitric oxide in the injured spinal cord: synthases cross-talk, oxidative stress and inflammation

Nitric oxide (NO) is a unique informational molecule involved in a variety of physiological processes in the central nervous system (SNS). It has been demonstrated that it can exert both protective and detrimental effects in several diseases states of the CNS, including spinal cord injury (SCI). The effects of NO on the spinal cord depend on several factors such as: concentration of produced NO, activity of different synthase isoforms, cellular source of production and time of release. Basically, it has been shown that low NO concentrations may play a role in physiologic processes, whereas large amounts of NO may be detrimental by increasing oxidative stress. However, this does not explain all the discrepancies evidenced studying the effects of NO in SCI models. The analysis of the different synthase isoforms, of their temporal profile of activation and cellular source has shed light on this topic. Two post-injury time intervals can be defined with reference to the NO production: immediately after injury and several hours-to-days later. The initial immediate peak of NO production after injury is due to the up-regulation of the neuronal NO synthase (nNOS) in resident spinal cord cells. The late peak is due primarily to the activity of inducible NOS (nNOS) produced by inflammatory infiltrating cells. High NO levels produced by up-regulated nNOS and iNOS are neurotoxic; the down-regulation of nNOS corresponds temporally to the expression of iNOS. On the bases of the evidence, therapeutic approaches should be aimed: (1) to reduce the NO-elicited damage by inhibition of specific synthases according to the temporal profile of activation; (2) by maintaining physiologic amount of NO to keep the induction of iNOS.

Neuronal NOS-mediated nitration and inactivation of manganese superoxide dismutase in brain after experimental and human brain injury

Manganese superoxide dismutase (MnSOD) provides the first line of defense against superoxide generated in mitochondria. SOD competes with nitric oxide for reaction with superoxide and prevents generation of peroxynitrite, a potent oxidant that can modify proteins to form 3-nitrotyrosine. Thus, sufficient amounts of catalytically competent MnSOD are required to prevent mitochondrial damage. Increased nitrotyrosine immunoreactivity has been reported after traumatic brain injury (TBI); however, the specific protein targets containing modified tyrosine residues and functional consequence of this modification have not been identified. In this study, we show that MnSOD is a target of tyrosine nitration that is associated with a decrease in its enzymatic activity after TBI in mice. Similar findings were obtained in temporal lobe cortical samples obtained from TBI cases versus control patients who died of causes not related to CNS trauma. Increased nitrotyrosine immunoreactivity was detected at 2 h and 24 h versus 72 h after experimental TBI and co-localized with the neuronal marker NeuN. Inhibition and/or genetic deficiency of neuronal nitric oxide synthase (nNOS) but not endothelial nitric oxide synthase (eNOS) attenuated MnSOD nitration after TBI. At 24 h after TBI, there was predominantly polymorphonuclear leukocytes accumulation in mouse brain whereas macrophages were the predominant inflammatory cell type at 72 h after injury. However, a selective inhibitor or genetic deficiency of inducible nitric oxide synthase (iNOS) failed to affect MnSOD nitration. Nitration of MnSOD is a likely consequence of peroxynitrite within the intracellular milieu of neurons after TBI. Nitration and inactivation of MnSOD could lead to self-amplification of oxidative stress in the brain progressively enhancing peroxynitrite production and secondary damage.

EFFECTS OF HYPERTONIC ARGININE ON CEREBRAL BLOOD FLOW AND INTRACRANIAL PRESSURE AFTER TRAUMATIC BRAIN INJURY COMBINED WITH HEMORRHAGIC HYPOTENSION

Hypertonic saline solutions improve cerebral blood flow (CBF) when used for acute resuscitation from hemorrhagic hypotension accompanying some models of traumatic brain injury (TBI); however, the duration of increased CBF is brief. Because the nitric oxide synthase substrate l-arginine provides prolonged improvement in CBF after TBI, we investigated whether a hypertonic resuscitation fluid containing l-arginine would improve CBF in comparison to hypertonic saline without l-arginine in a model of moderate, paramedian, fluid-percussion TBI followed immediately by hemorrhagic hypotension (mean arterial pressure [MAP] = 60 mm Hg for 45 min). Sprague-Dawley rats were anesthetized with 4.0% isoflurane, intubated and ventilated with 1.5%-2.0% isoflurane in oxygen/air (50:50). After preparation for TBI and measurement of CBF using laser Doppler flowmetry and measurement of intracranial pressure (ICP) using an implanted transducer, rats were subjected to moderate (2.0 atm) TBI, hemorrhaged for 45 min, and randomly assigned to receive an infusion of hypertonic saline (7.5%, 2,400 mOsm total; 6 mL/kg; n = 6) or hypertonic saline with 50, 100, or 300 mg/kg L-arginine (2,400 mOsm; 6 mL/kg; n = 6 in each of the three dose groups) and then monitored for 120 min after the end of infusion. CBF was measured continuously and calculated as a percent of the pre-TBI baseline during the hemorrhage period, after reinfusion of one of the hypertonic arginine solutions, and 30, 60, and 120 min after reinfusion. All four hypertonic solutions initially improved MAP, which, by 120 min after infusion, had decreased nearly to the levels observed during hemorrhage. ICP remained below baseline levels during resuscitation in all groups, although ICP was slightly greater (P = NS) than baseline in the hypertonic saline group. CBF increased similarly in all groups during infusion and then decreased similarly in all groups. At 120 min after infusion, CBF was highest in the group infused with hypertonic saline, but the difference was not significant. We conclude that the improvement of MAP, ICP, and CBF produced by hypertonic saline alone after TBI and hemorrhagic hypotension is not significantly enhanced by the addition of L-arginine at these doses.

Reduced neuronal injury after treatment with NG-nitro-L-arginine methyl ester (L-NAME) or 2-sulfo-phenyl-N-tert-butyl nitrone (S-PBN) following experimental brain contusion

OBJECTIVE

Nitric oxide (NO) and oxygen free radicals are implicated in the pathophysiology of traumatic brain injury (TBI). Peroxynitrite formation from NO and superoxide contributes to secondary neuronal injury but the neuroprotective effects of nitric oxide synthase (NOS)-inhibitors have been contradictory. This study was undertaken to examine whether PTtic administration of the (NOS)-inhibitor N-nitro-l-arginine methyl ester (L-NAME), and a combination of L-NAME and the nitrone radical scavenger 2-sulfo-phenyl-N-tert-butyl nitrone (S-PBN) favorable affects neuronal injury in a model of TBI.

METHODS

A weight-drop model of TBI was used. The animals received L-NAME, S-PBN or a combination of the drugs 15 minutes prothrombin time (PT) and sacrificed after 24 hours or six days. NOS activity was measured by the conversion of L-[U-C]arginine to L-[U-C]citrulline. Peroxynitrite formation, cellular apoptosis, neuronal degeneration and survival were assessed by nitrotyrosine-, TUNEL-, Fluoro-Jade- and NeuN-stainings.

RESULTS

eNOS and nNOS activity was significantly reduced in animals that received L-NAME alone or the combination with S-PBN. iNOS activity or iNOS immunoreactivity was not affected. All treatments significantly reduced neuronal degeneration and nitrotyrosine immunoreactivity at 24 hours and increased neuronal survival at six days PT. No differences were detected between L-NAME and L-NAME + S-PBN groups.

CONCLUSION

NO from NOS contributes to secondary neuronal injury in this TBI-model. PTtic treatment does not inhibit early beneficial NO-related effects. L-NAME and S-PBN limit peroxynitrite formation, promoting neuronal survival. The combination of L-NAME and S-PBN was neuroprotective; surprisingly no additive effects were found on nitrotyrosine formation, apoptosis or neuronal survival.

[Anti-inflammatory modulators in traumatic brain injury]

Traumatic brain injury leads to primary and secondary brain injuries. Primary brain injury results from mechanical forces applied to the head at the time of impact. Secondary brain injury occurs at some time after the primary impact. Numerous pathophysiological mechanisms have been postulated to explain the progressive tissue damage produced by secondary injuries. The endogenous neuroinflammatory response after traumatic brain injury contributes to the development of blood-brain barrier breakdown, cerebral oedema and neuronal cell death and this has led to various pharmacological therapies to try to limit this type of damage. Studies employing glutamate receptor antagonist for cerebral protection have yielded promising results in laboratory animals but failed to produce clinically significant improvements. The present review will summarize the mechanisms of post traumatic cerebral inflammation with a special focus on the anti-inflammatory drug targets.

The role of inducible nitric oxide synthase following spinal cord injury in rat

Acute spinal cord injury (SCI) is two-step process that first involves the primary mechanical injury and then the secondary injury is induced by various biochemical reactions. Apoptosis is one of secondary SCI mechanisms and it is thought to play an important role for the delayed neuronal injury. The enhanced formation of nitric oxide (NO) via inducible nitric oxide synthase (iNOS) has been implicated in the pathogenesis of apoptosis in SCI. The level of .iNOS mRNA peaked at 6 hr after SCI and it declined until 72 hr after SCI in a rat model. Double-immunofluorescence staining revealed that iNOS positive cells were stained for ED-1, synaptophysin, GFAP, and oligodendrocyte marker. The terminal deoxynucleotidyl-transferase-mediated dUDP-biotin nick end-labeling (TUNEL) positive cell count was higher for the 72 hr post-SCI group than for the 24 hr post-SCI group. This cell count was also higher going in the caudal direction than in the rostral direction from the epicenter, and especially for the 72 hr group. Treatment with a selective iNOS inhibitor resulted in the reduction of TUNEL-positive cells at the lesion site. These findings suggest that nitric oxide generated by the iNOS of macrophages, neurons, oligodentrocytes, and astrocytes plays an important role for the acute secondary SCI that results from apoptotic cell death.

Combined effects of mechanical and ischemic injury to cortical cells: secondary ischemia increases damage and decreases effects of neuroprotective agents

Traumatic brain injury (TBI) involves direct mechanical damage, which may be aggravated by secondary insults such as ischemia. We utilized an in vitro model of stretch-induced injury to investigate the effects of mechanical and combined mechanical/ischemic insults to cultured mouse cortical cells. Stretch injury alone caused significant neuronal loss and increased uptake of the dye, propidium iodide, suggesting cellular membrane damage to both glia and neurons. Exposure of cultures to ischemic conditions for 24h, or a combination of stretch and 24h of ischemia, caused greater neuronal loss compared to stretch injury alone. Next, we tested the neuroprotective effects of superoxide dismutase (SOD), and the nitric oxide (NO) synthase inhibitors 7-nitroindazole (7-NINA) and lubeluzole. In general, these agents decreased neuronal loss following stretch injury alone, but were relatively ineffective against the combined injury paradigm. A combination of SOD with 7-NINA or lubeluzole offered no additional protection than single drug treatment against stretch alone or combined injury. These results suggest that the effects of primary mechanical damage and secondary ischemia to cortical neurons are cumulative, and drugs that scavenge superoxide or reduce NO production may not be effective for treating the secondary ischemia that often accompanies TBI.

Lateral fluid percussion brain injury: a 15-year review and evaluation

This article comprehensively reviews the lateral fluid percussion (LFP) model of traumatic brain injury (TBI) in small animal species with particular emphasis on its validity, clinical relevance and reliability. The LFP model, initially described in 1989, has become the most extensively utilized animal model of TBI (to date, 232 PubMed citations), producing both focal and diffuse (mixed) brain injury. Despite subtle variations in injury parameters between laboratories, universal findings are evident across studies, including histological, physiological, metabolic, and behavioral changes that serve to increase the reliability of the model. Moreover, demonstrable histological damage and severity-dependent behavioral deficits, which partially recover over time, validate LFP as a clinically-relevant model of human TBI. The LFP model, also has been used extensively to evaluate potential therapeutic interventions, including resuscitation, pharmacologic therapies, transplantation, and other neuroprotective and neuroregenerative strategies. Although a number of positive studies have identified promising therapies for moderate TBI, the predictive validity of the model may be compromised when findings are translated to severely injured patients. Recently, the clinical relevance of LFP has been enhanced by combining the injury with secondary insults, as well as broadening studies to incorporate issues of gender and age to better approximate the range of human TBI within study design. We conclude that the LFP brain injury model is an appropriate tool to study the cellular and mechanistic aspects of human TBI that cannot be addressed in the clinical setting, as well as for the development and characterization of novel therapeutic interventions. Continued translation of pre-clinical findings to human TBI will enhance the predictive validity of the LFP model, and allow novel neuroprotective and neuroregenerative treatment strategies developed in the laboratory to reach the appropriate TBI patients.

Administration of Ginseng radix decreases nitric oxide synthase expression in the hippocampus of streptozotocin-induced diabetic rats

Nitric oxide (NO) is synthesized from L-arginine by nitric oxide synthase (NOS). Alternation of NOS expression is implicated in the pathogenesis of numerous secondary complications of diabetes. Aqueous extract of Ginseng radix has traditionally been used for the various disorders including diabetes. In this study, the effect of Ginseng radix on the NOS expression in the hippocampus of streptozotocin (STZ)-induced diabetic rats was investigated via nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry. Enhanced NOS expression was detected in the hippocampus of diabetic rats and administration of Ginseng radix suppressed NOS expression. Ginseng radix may aid the treatment of central nervous system complications in diabetes.

Characterization of a rat model to study acute neuroinflammation on histopathological, biochemical and functional outcomes

Neuroinflammation is one of the events occurring after acute brain injuries. The aim of the present report was to characterize a rat model to study acute neuroinflammation on the histopathological, biochemical and functional outcomes. Lipopolysaccharide (LPS), known as a strong immunostimulant, was directly injected into the hippocampus. The spatiotemporal evolution of inducible NOS (iNOS) and cell death was studied from 6 h to 7 days. A perfect time course correlation was observed between iNOS immunoreactivity and iNOS activity showing an acute, expansive and transient iNOS induction in the hippocampus with a peak at 24 h. It was associated with a marked increase in NO metabolite (NO(x)) levels, and a high level of myeloperoxidase (MPO) activity. This inflammation precedes a massive cellular loss including at least neurons and astrocytes, and a drop of constitutive NOS activity, restrictive to the ipsilateral hippocampus from 48 h after LPS injection. Moreover, sensorimotor function impairment occurred from 24 h to 7 days with a maximum at 24 h post-LPS injection. Therefore, we characterized an in vivo model of acute neuroinflammation and neurodegeneration, in relation with a neurological deficit, which may be a powerful tool for mechanistic studies and for further evaluation of the potential neuroprotective agents.

Nitric oxide in traumatic brain injury

Nitric oxide (NO) is a gaseous chemical messenger which has functions in the brain in a variety of broad physiological processes, including control of cerebral blood flow, interneuronal communications, synaptic plasticity, memory formation, receptor functions, intracellular signal transmission, and release of neurotransmitters. As might be expected from the numerous and complex roles that NO normally has, it can have both beneficial and detrimental effects in disease states, including traumatic brain injury. There are two periods of time after injury when NO accumulates in the brain, immediately after injury and then again several hours-days later. The initial immediate peak in NO after injury is probably due to the activity of endothelial NOS and neuronal NOS. Pre-injury treatment with 7-nitroindazole, which probably inhibits this immediate increase in NO by neuronal NOS, is effective in improving neurological outcome in some models of traumatic brain injury (TBI). After the initial peak in NO, there can be a period of relative deficiency in NO. This period of low NO levels is associated with a low cerebral blood flow (CBF). Administration of L-arginine at this early time improves CBF, and outcome in many models. The late peak in NO after traumatic injury is probably due primarily to the activity of inducible NOS. Inhibition of inducible NOS has neuroprotective effects in most models.

Peroxynitrite-mediated protein nitration and lipid peroxidation in a mouse model of traumatic brain injury

The role of reactive oxygen-induced oxidative damage to lipids (i.e., lipid peroxidation, LP) and proteins has been strongly supported in previous work. Most notably, a number of free radical scavengers and lipid antioxidants have been demonstrated to be neuroprotective in traumatic brain injury (TBI) models. However, the specific sources of reactive oxygen species (ROS), the time course of oxidative damage and its relationship to post-traumatic neurodegeneration in the injured brain have been incompletely defined. The present study was directed at an investigation of the role of the ROS, peroxynitrite (PON), in the acute pathophysiology of TBI and its temporal relationship to neurodegeneration in the context of the mouse model of diffuse head injury model. Male CF-1 mice were subjected to a moderately severe head injury and assessed at 1-, 3-, 6-, 12-, 24-, 48-, 72, 96- and 120-h post-injury for neurodegeneration using quantitative image analysis of silver staining and semi-quantitative analysis of PON-mediated oxidative damage to proteins (3-nitrotyrosine, 3-NT) and lipids (4-hydroxynonenal, 4-HNE). Significant evidence of silver staining was not apparent until 24-h post-injury, with peak staining seen between 72- and 120-h. This time-course of neurodegeneration was preceded by intense immunostaining for 3-NT and 4-HNE, which occurred within the first hour post-injury. The time course and staining pattern for 3-NT and 4-HNE were similar, with the highest staining intensity noted within the first 48-h in areas surrounding trauma-induced contusions. In the case of 3-NT, neuronal perikarya and processes and microvessels displayed staining. The temporal and spatial coincidence of protein nitration and LP damage suggests that PON is involved in both. However, lipid-peroxidative (4-HNE) immunoreactivity was broader and more diffuse than 3-NT, suggesting that other reactive oxygen mechanisms, such as iron-dependent LP, may also contribute to the more widespread 4-HNE immunoreactivity. This indicates that optimal pharmacological inhibition of post-traumatic oxidative damage in TBI may need to combine two functionalities: one to scavenge PON or PON-derived radicals, and the second to inhibit LP caused by multiple ROS species.

The neuronal nitric oxide synthase inhibitor, TRIM, as a neuroprotective agent: effects in models of cerebral ischaemia using histological and magnetic resonance imaging techniques

Most neuroprotective compounds that appear promising in the pre-clinical phase of testing are subsequently dismissed as relatively ineffective when entered into large-scale clinical trials. Many pre-clinical studies of potential neuroprotective candidates evaluate efficacy in only one or possibly two different models of ischaemia. In this study we examined the effects of 1,2-trifluoromethylphenyl imidazole (TRIM), a novel neuronal nitric oxide synthase (nNOS) inhibitor, in three models of cerebral ischaemia (global gerbil, global rat and focal rat). In addition, to follow the progression of the pathology, we also compared traditional histology methods with more advanced magnetic resonance imaging (MRI) as endpoint measures for neurological damage and neuroprotection. TRIM (50 mg/kg i.p.) prevented ischaemia-induced hippocampal damage following global ischaemia in gerbils when administered before or immediately post-occlusion, but failed to protect when administration was delayed until 30 min post-occlusion. Further studies indicated that the compound (administered at 50 mg/kg, i.p., immediately after occlusion) also protected in a rat four-vessel occlusion (4-VO) model using both histological and diffusion-weighted (DW) imaging techniques. In a final study, TRIM (50 mg/kg i.p. 30 min after occlusion) provided a significant reduction in infarct volume at 4 and 24 h as measured using diffusion-weighted (DW) and proton density (PD)-weighted magnetic resonance imaging (MRI). This was confirmed using histological techniques. These studies confirm that nNOS inhibitors may have utility in stroke and provide evidence that combined magnetic resonance and histological methods can provide a powerful method of assessing neuronal damage in rodent models of cerebral ischaemia.

Elevated nitric oxide levels in childhood brain tumors

OBJECTIVES

One of the fundamental aspects of nitric oxide (NO) is the regulation of the inflammatory processes involved in neuronal apoptosis. Expressions of NO and NO synthase (NOS) are considered to be involved in brain tissue injuries and brain tumors. The purpose of our study was to investigate the roles of NO and inducible-form NOS (iNOS) in the pathogenesis of brain tumors.

METHODS

NO levels in the cerebrospinal fluid (CSF) of 36 brain tumor patients were detected utilizing the NO-chemiluminescence method. Deparaffinized tissue sections were immunostained for the presence of antibodies against iNOS and for apoptosis using the TUNEL stain. The results were compared with 10 control patients (with epilepsy and hydrocephalus).

CONCLUSIONS

Higher levels of NO and iNOS activities may induce immune responses and neurotoxicities. This preliminary study revealed elevated NO and NOS activities with an increased amount of apoptotic processes in brain tumor tissues, which may indicate the possible roles of NO in the formation of brain tumors.

The Role of Endothelial Nitric Oxide Synthase in the Cerebral Hemodynamics after Controlled Cortical Impact Injury in Mice

Traumatic brain injury causes a reduction in cerebral blood flow, which may cause additional damage to the brain. The purpose of this study was to examine the role of nitric oxide produced by endothelial nitric oxide synthase (eNOS) in these vascular effects of trauma. To accomplish this, cerebral hemodynamics were monitored in mice deficient in eNOS and wild-type control mice that underwent lateral controlled cortical impact injury followed by administration of either L-arginine, 300 mg/kg, or saline at 5 min after the impact injury. The eNOS deficient mice had a greater reduction in laser Doppler flow (LDF) in the contused brain tissue at the impact site after injury, despite maintaining a higher blood pressure. L-Arginine administration increased LDF post-injury only in the wild-type mice. L-Arginine administration also resulted in a reduction in contusion volume, from 2.4 +/- 1.5 to 1.1 +/- 1.2 mm(3) in wild-type mice. Contusion volume in the eNOS deficient mice was not significantly altered by L-arginine administration. These differences in cerebral hemodynamics between the eNOS-deficient and the wild-type mice suggest an important role for nitric oxide produced by eNOS in the preservation of cerebral blood flow in contused brain following traumatic injury, and in the improvement in cerebral blood flow with L-arginine administration.

Traumatic Cerebral Vascular Injury: The Effects of Concussive Brain Injury on the Cerebral Vasculature

In terms of human suffering, medical expenses, and lost productivity, head injury is one of the major health care problems in the United States, and inadequate cerebral blood flow is an important contributor to mortality and morbidity after traumatic brain injury. Despite the importance of cerebral vascular dysfunction in the pathophysiology of traumatic brain injury, the effects of trauma on the cerebral circulation have been less well studied than the effects of trauma on the brain. Recent research has led to a better understanding of the physiologic, cellular, and molecular components and causes of traumatic cerebral vascular injury. A more thorough understanding of the direct and indirect effects of trauma on the cerebral vasculature will lead to improvements in current treatments of brain trauma as well as to the development of novel and, hopefully, more effective therapeutic strategies.

Measurement of the nitric oxide metabolites nitrate and nitrite in the human brain by microdialysis

To examine the feasibility of measuring the nitric oxide (NO) metabolites nitrate and nitrite in microdialysate samples from the human brain, microdialysis probes were placed in normal appearing cerebral cortex of severely head injured patients in the Neurosurgical Intensive Care Unit at Ben Taub General Hospital. Nitrate/nitrite analysis was performed using NO chemiluminescence. Low micromolar levels of NO metabolites were consistently and easily detected. These levels seen are comparable to levels reported in CSF but tissue tortuosity and probe recovery considerations suggest that the absolute concentrations at the probe site are probably ten fold higher. Microdialysis with measurement of nitric oxide metabolites is technically feasible and may provide valuable insights into both normal neurochemistry and neurochemical derangements in disease.

Reversal of attenuation of cerebrovascular reactivity to hypercapnia by a nitric oxide donor after controlled cortical impact in a rat model of traumatic brain injury

OBJECT

Traumatic brain injury (TBI) attenuates the cerebral vasodilation to hypercapnia. Cortical spreading depression (CSD) also transiently reduces hypercapnic vasodilation. The authors sought to determine whether the CSD elicited by a controlled cortical impact (CCI) injury masks the true effect of TBI on hypercapnic vasodilation, and whether a nitric oxide (NO) donor can reverse the attenuation of hypercapnic vasodilation following CCI.

METHODS

Anesthetized rats underwent moderate CCI. Cerebral blood flow was monitored with laser Doppler flowmetry and the response to hypercapnia was determined for injured and sham-injured animals. The effect of the NO donor, S-nitroso-N-acetylpenicillamine (SNAP), on this response was also assessed. At an uninjured cortical site ipsilateral to the CCI, a single wave of CSD was recorded and the CO2 response at this location was significantly attenuated for up to 30 minutes (seven rats, p < 0.05). At the injured cortex, hypercapnic vasodilation continued to be attenuated for 7 hours. The cerebral vasodilation to CO2 was 37 +/- 5% in injured rats (six) compared with 84 +/- 10% in the sham-injured group (five rats, p < 0.05). After 30 minutes of topical superfusion with SNAP, hypercapnic vasodilation was restored to 74 +/- 7% (nine rats, p > 0.1 compared with that in the sham-injured group). In contrast, papaverine, an NO-independent vasodilator, failed to reverse the attenuation of the CO2 response to CCI.

CONCLUSIONS

The authors conclude that CSD elicited by CCI can mask the true effect of TBI on hypercapnic vasodilation for at least 30 minutes. Exogenous NO, but not papaverine, can reverse the attenuation of cerebrovascular reactivity to CO2 caused by TBI. This result supports the hypothesis that NO production is reduced after TBI and that the NO donor has a potential beneficial role in the clinical management of head injury.

Cerebral ischemia and trauma-different etiologies yet similar mechanisms: neuroprotective opportunities

Cerebral ischemia leads to brain damage caused by pathogenetic mechanisms that are also activated by neurotrauma. These mechanisms include among others excitotoxicity, over production of free radicals, inflammation and apoptosis. Furthermore, cerebral ischemia and trauma both trigger similar auto-protective mechanisms including the production of heat shock proteins, anti-inflammatory cytokines and endogenous antioxidants. Neuroprotective therapy aims at minimizing the activation of toxic pathways and at enhancing the activity of endogenous neuroprotective mechanisms. The similarities in the damage-producing and endogenous auto-protective mechanisms may imply that neuroprotective compounds found to be active against one of these conditions may indeed be also protective in the other. This review summarizes the pathogenetic events of ischemic and traumatic brain injury and reviews the neuroprotective strategies employed thus far in each of these conditions with a special emphasize on their clinical relevance and on future directions in the field of neuronal protection.

The association between neuronal nitric oxide synthase and neuronal sensitivity in the brain after brain injury

Injury to the central nervous system is the leading cause of disability in the United States. Neuronal death is one of the causes of disability. Among patients who survive this type of injury, various degrees of recovery in brain function are observed. The molecular basis of functional recovery is poorly understood. Clinical observations and research using experimental injury models have implicated several metabolites in the cascade of events that lead to neuronal degeneration. The levels of intracellular ATP (energy source) and pH are decreased, whereas levels of extracellular glutamate, intracellular calcium ions, and oxidative damage to RNA/DNA, protein, and lipid are increased. These initiating events can be associated with energy failure and mitochondrial dysfunction, resulting in functional or structural brain damage. The injured brain is known to express immediate early genes. Recent studies show that reactive oxygen species (ROS) cause lesions in genes from which mRNA is transcribed as part of the endogenous neuroprotective response. Although degenerating proteins and lipids may contribute to necrosis significantly after severe injury, abnormalities in genetic material, if not repaired, disturb cellular function at every level by affecting replication, transcription, and translation. These lesions include abnormal nucleic acids, known as oxidative lesions of DNA (ODLs) or of RNA (ORLs). In this review, we focus on our current understanding of the various effects of neuronal nitric oxide synthase on the formation of modified bases in DNA and RNA that are induced in the brain after injury, and how ODLs and ORLs affect cell function.

The effects of L-arginine on cerebral hemodynamics after controlled cortical impact injury in the mouse

Traumatic brain injury (TBI) induces vascular changes that may influence neurological outcome by causing the brain to be more susceptible to secondary ischemic insults. In rat models of TBI, L-arginine administration has been shown to restore cerebral blood flow and improve neurological outcome. The purpose of this study was to determine if hypoperfusion occurs in a mouse model of TBI and if L-arginine administration has the same beneficial effects after injury in the mouse. C57BL6 mice were anesthetized with isoflurane, intubated and mechanically ventilated, and underwent a 3-m/sec, 1.5-mm deformation cortical impact injury. Five minutes after injury, L-arginine, 300 mg/kg, or saline were administered. Arterial blood pressure, intracranial pressure, and laser Doppler flow at the impact site were monitored for 3 h after the injury. The cerebral hemodynamic effects of the TBI induced by cortical impact injury were similar to that previously observed in rats. Intracranial hypertension, with ICP peaking at 46+/-2 mm Hg, and systemic hypotension both contributed to a reduction in CPP. In addition, LDF decreased significantly at the impact site. L-Arginine administration restored LDF to near baseline levels without increasing ICP. These studies demonstrate that cerebral hemodynamics can be measured in mouse models of TBI. The changes in cerebral hemodynamics are relatively simlar to those see in the rat model of cortical impact injury and suggest an important role for nitric oxide metabolism in the maintenance of cerebral blood flow following TBI.