L-arginine and superoxide dismutase prevent or reverse cerebral hypoperfusion after fluid-percussion traumatic brain injury

THE NEUROENDOTHELIAL AXIS IN TRAUMATIC BRAIN INJURY: MECHANISMS OF MULTIORGAN DYSFUNCTION, NOVEL THERAPIES, AND FUTURE DIRECTIONS

ABSTRACT

Severe traumatic brain injury (TBI) often initiates a systemic inflammatory response syndrome, which can potentially culminate into multiorgan dysfunction. A central player in this cascade is endotheliopathy, caused by perturbations in homeostatic mechanisms governed by endothelial cells due to injury-induced coagulopathy, heightened sympathoadrenal response, complement activation, and proinflammatory cytokine release. Unique to TBI is the potential disruption of the blood-brain barrier, which may expose neuronal antigens to the peripheral immune system and permit neuroinflammatory mediators to enter systemic circulation, propagating endotheliopathy systemically. This review aims to provide comprehensive insights into the "neuroendothelial axis" underlying endothelial dysfunction after TBI, identify potential diagnostic and prognostic biomarkers, and explore therapeutic strategies targeting these interactions, with the ultimate goal of improving patient outcomes after severe TBI.

Targeting hydrogen sulfide and nitric oxide to repair cardiovascular injury after trauma

The systemic cardiovascular effects of major trauma, especially neurotrauma, contribute to death and permanent disability in trauma patients and treatments are needed to improve outcomes. In some trauma patients, dysfunction of the autonomic nervous system produces a state of adrenergic overstimulation, causing either a sustained elevation in catecholamines (sympathetic storm) or oscillating bursts of paroxysmal sympathetic hyperactivity. Trauma can also activate innate immune responses that release cytokines and damage-associated molecular patterns into the circulation. This combination of altered autonomic nervous system function and widespread systemic inflammation produces secondary cardiovascular injury, including hypertension, damage to cardiac tissue, vascular endothelial dysfunction, coagulopathy and multiorgan failure. The gasotransmitters nitric oxide (NO) and hydrogen sulfide (H2S) are small gaseous molecules with potent effects on vascular tone regulation. Exogenous NO (inhaled) has potential therapeutic benefit in cardio-cerebrovascular diseases, but limited data suggests potential efficacy in traumatic brain injury (TBI). H2S is a modulator of NO signaling and autonomic nervous system function that has also been used as a drug for cardio-cerebrovascular diseases. The inhaled gases NO and H2S are potential treatments to restore cardio-cerebrovascular function in the post-trauma period.

Impaired capillary-to-arteriolar electrical signaling after traumatic brain injury

Traumatic brain injury (TBI) acutely impairs dynamic regulation of local cerebral blood flow, but long-term (>72 h) effects on functional hyperemia are unknown. Functional hyperemia depends on capillary endothelial cell inward rectifier potassium channels (Kir2.1) responding to potassium (K+) released during neuronal activity to produce a regenerative, hyperpolarizing electrical signal that propagates from capillaries to dilate upstream penetrating arterioles. We hypothesized that TBI causes widespread disruption of electrical signaling from capillaries-to-arterioles through impairment of Kir2.1 channel function. We randomized mice to TBI or control groups and allowed them to recover for 4 to 7 days post-injury. We measured in vivo cerebral hemodynamics and arteriolar responses to local stimulation of capillaries with 10 mM K+ using multiphoton laser scanning microscopy through a cranial window under urethane and α-chloralose anesthesia. Capillary angio-architecture was not significantly affected following injury. However, K+-induced hyperemia was significantly impaired. Electrophysiology recordings in freshly isolated capillary endothelial cells revealed diminished Ba2+-sensitive Kir2.1 currents, consistent with a reduction in channel function. In pressurized cerebral arteries isolated from TBI mice, K+ failed to elicit the vasodilation seen in controls. We conclude that disruption of endothelial Kir2.1 channel function impairs capillary-to-arteriole electrical signaling, contributing to altered cerebral hemodynamics after TBI.

Detecting Behavioral Deficits in Rats After Traumatic Brain Injury

With the increasing incidence of traumatic brain injury (TBI) in both civilian and military populations, TBI is now considered a chronic disease; however, few studies have investigated the long-term effects of injury in rodent models of TBI. Shown here are behavioral measures that are well-established in TBI research for times early after injury, such as two weeks, until two months. Some of these methods have previously been used at later times after injury, up to one year, but by very few laboratories. The methods demonstrated here are a short neurological assessment to test reflexes, a Beam-Balance to test balance, a Beam-Walk to test balance and motor coordination, and a working memory version of the Morris water maze that can be sensitive to deficits in reference memory. Male rats were handled and pre-trained to neurological, balance, and motor coordination tests prior to receiving parasagittal fluid percussion injury (FPI) or sham injury. Rats can be tested on the short neurological assessment (neuroscore), the beam-balance, and the Beam-Walk multiple times, while testing on the water maze can only be done once. This difference is because rats can remember the task, thus confounding the results if repeated testing is attempted in the same animal. When testing from one to three days after injury, significant differences are detected in all three non-cognitive tasks. However, differences in the Beam-Walk task were not detectable at later time points (after 3 months). Deficits were detected at 3 months in the Beam-Balance and at 6 months in the neuroscore. Deficits in working memory were detected out to 12 months after injury, and a deficit in a reference memory first appeared at 12 months. Thus, standard behavioral tests can be useful measures of persistent behavioral deficits after FPI.

Effects of Mild Blast Traumatic Brain Injury on Cerebral Vascular, Histopathological, and Behavioral Outcomes in Rats

To determine the effects of mild blast-induced traumatic brain injury (bTBI), several groups of rats were subjected to blast injury or sham injury in a compressed air-driven shock tube. The effects of bTBI on relative cerebral perfusion (laser Doppler flowmetry [LDF]), and mean arterial blood pressure (MAP) cerebral vascular resistance were measured for 2 h post-bTBI. Dilator responses to reduced intravascular pressure were measured in isolated middle cerebral arterial (MCA) segments, ex vivo, 30 and 60 min post-bTBI. Neuronal injury was assessed (Fluoro-Jade C [FJC]) 24 and 48 h post-bTBI. Neurological outcomes (beam balance and walking tests) and working memory (Morris water maze [MWM]) were assessed 2 weeks post-bTBI. Because impact TBI (i.e., non-blast TBI) is often associated with reduced cerebral perfusion and impaired cerebrovascular function in part because of the generation of reactive oxygen and nitrogen species such as peroxynitrite (ONOO-), the effects of the administration of the ONOO- scavenger, penicillamine methyl ester (PenME), on cerebral perfusion and cerebral vascular resistance were measured for 2 h post-bTBI. Mild bTBI resulted in reduced relative cerebral perfusion and MCA dilator responses to reduced intravascular pressure, increases in cerebral vascular resistance and in the numbers of FJC-positive cells in the brain, and significantly impaired working memory. PenME administration resulted in significant reductions in cerebral vascular resistance and a trend toward increased cerebral perfusion, suggesting that ONOO- may contribute to blast-induced cerebral vascular dysfunction.

Rheological effects of drag-reducing polymers improve cerebral blood flow and oxygenation after traumatic brain injury in rats

Cerebral ischemia has been clearly demonstrated after traumatic brain injury (TBI); however, neuroprotective therapies have not focused on improvement of the cerebral microcirculation. Blood soluble drag-reducing polymers (DRP), prepared from high molecular weight polyethylene oxide, target impaired microvascular perfusion by altering the rheological properties of blood and, until our recent reports, has not been applied to the brain. We hypothesized that DRP improve cerebral microcirculation and oxygenation after TBI. DRP were studied in healthy and traumatized rat brains and compared to saline controls. Using in-vivo two-photon laser scanning microscopy over the parietal cortex, we showed that after TBI, nanomolar concentrations of intravascular DRP significantly enhanced microvascular perfusion and tissue oxygenation in peri-contusional areas, preserved blood-brain barrier integrity and protected neurons. The mechanisms of DRP effects were attributable to reduction of the near-vessel wall cell-free layer which increased near-wall blood flow velocity, microcirculatory volume flow, and number of erythrocytes entering capillaries, thereby reducing capillary stasis and tissue hypoxia as reflected by a reduction in NADH. Our results indicate that early reduction in CBF after TBI is mainly due to ischemia; however, metabolic depression of contused tissue could be also involved.

Persistent Behavioral Deficits in Rats after Parasagittal Fluid Percussion Injury

Although traumatic brain injury (TBI) is now considered a chronic disease, few studies have investigated the long-term behavioral deficits elicited by a well-established rodent model of injury. Here we evaluate behavioral measures, commonly used in TBI research, to determine which tests are useful for studying long-term effects of brain injury in rats. Male Sprague-Dawley rats were handled and pre-trained to neurological, balance, and motor coordination tests prior to receiving parasagittal fluid-percussion injury (FPI), sham injury, or maintenance as naïve cohorts. Rats underwent neuroscore, beam-balance, and beam-walk tests for 3 days after injury. Subsequently, in separate groups at 3, 6, or 12 months, they were re-tested on the same tasks followed by a working memory version of the Morris water maze. On post-injury days (PIDs) 1-3, significant effects of injury on neuroscore, beam-balance, and beam-walk were observed. Differences in the beam-walk task were not detectable at any of the later time-points. However, deficits persisted in beam-balance out to 3 months and neuroscore out to 6 months. Working memory deficits persisted out to 12 months, at which time a reference memory deficit was also evident. These data suggest that balance and motor coordination recovered more quickly than neurological deficits. Furthermore, while deficits in working memory remained stable over the 12-month period, the late onset of the reference memory deficit points to the progressive nature of the injury, or an age/TBI interaction. In conclusion, standard behavioral tests are useful measures of persistent behavioral deficits after parasagittal FPI and provide evidence that TBI is a chronic condition that can change over time and worsen with age.

A time course of NADPH-oxidase up-regulation and endothelial nitric oxide synthase activation in the hippocampus following neurotrauma

Nicotinamide adenine dinucleotide phosphate oxidase (NADPH-oxidase; NOX) is a complex enzyme responsible for increased levels of reactive oxygen species (ROS), superoxide (O2(•-)). NOX-derived O2(•-) is a key player in oxidative stress and inflammation-mediated multiple secondary injury cascades (SIC) following traumatic brain injury (TBI). The O2(•-) reacts with nitric oxide (NO), produces various reactive nitrogen species (RNS), and contributes to apoptotic cell death. Following a unilateral cortical contusion, young adult rats were killed at various times postinjury (1, 3, 6, 12, 24, 48, 72, and 96 h). Fresh tissue from the hippocampus was analyzed for NOX activity, and level of O2(•-). In addition we evaluated the translocation of cytosolic NOX proteins (p67(Phox), p47(Phox), and p40(Phox)) to the membrane, along with total NO and the activation (phosphorylation) of endothelial nitric oxide synthase (p-eNOS). Results show that both enzymes and levels of O2(•-) and NO have time-dependent injury effects in the hippocampus. Translocation of cytosolic NOX proteins into membrane, NOX activity, and O2(•-) were also increased in a time-dependent fashion. Both NOX activity and O2(•-) were increased at 6 h. Levels of p-eNOS increased within 1h, with significant elevation of NO at 12h post-TBI. Levels of NO failed to show a significant association with p-eNOS, but did associate with O2(•-). NOX up-regulation strongly associated with both the levels of O2(•-) and the total NO. The initial 12 h post-TBI are very important as a possible window of opportunity to interrupt SIC. It may be important to selectively target the translocation of cytosolic subunits for the modulation of NOX function.

Traumatic brain injury in vivo and in vitro contributes to cerebral vascular dysfunction through impaired gap junction communication between vascular smooth muscle cells

Gap junctions (GJs) contribute to cerebral vasodilation, vasoconstriction, and, perhaps, to vascular compensatory mechanisms, such as autoregulation. To explore the effects of traumatic brain injury (TBI) on vascular GJ communication, we assessed GJ coupling in A7r5 vascular smooth muscle (VSM) cells subjected to rapid stretch injury (RSI) in vitro and VSM in middle cerebral arteries (MCAs) harvested from rats subjected to fluid percussion TBI in vivo. Intercellular communication was evaluated by measuring fluorescence recovery after photobleaching (FRAP). In VSM cells in vitro, FRAP increased significantly (p<0.05 vs. sham RSI) after mild RSI, but decreased significantly (p<0.05 vs. sham RSI) after moderate or severe RSI. FRAP decreased significantly (p<0.05 vs. sham RSI) 30 min and 2 h, but increased significantly (p<0.05 vs. sham RSI) 24 h after RSI. In MCAs harvested from rats 30 min after moderate TBI in vivo, FRAP was reduced significantly (p<0.05), compared to MCAs from rats after sham TBI. In VSM cells in vitro, pretreatment with the peroxynitrite (ONOO(-)) scavenger, 5,10,15,20-tetrakis(4-sulfonatophenyl)prophyrinato iron[III], prevented RSI-induced reductions in FRAP. In isolated MCAs from rats treated with the ONOO(-) scavenger, penicillamine, GJ coupling was not impaired by fluid percussion TBI. In addition, penicillamine treatment improved vasodilatory responses to reduced intravascular pressure in MCAs harvested from rats subjected to moderate fluid percussion TBI. These results indicate that TBI reduced GJ coupling in VSM cells in vitro and in vivo through mechanisms related to generation of the potent oxidant, ONOO(-).

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.

Erythropoietin improves motor and cognitive deficit, axonal pathology, and neuroinflammation in a combined model of diffuse traumatic brain injury and hypoxia, in association with upregulation of the erythropoietin receptor

Background

Diffuse axonal injury is a common consequence of traumatic brain injury (TBI) and often co-occurs with hypoxia, resulting in poor neurological outcome for which there is no current therapy. Here, we investigate the ability of the multifunctional compound erythropoietin (EPO) to provide neuroprotection when administered to rats after diffuse TBI alone or with post-traumatic hypoxia.

Methods

Sprague–Dawley rats were subjected to diffuse traumatic axonal injury (TAI) followed by 30 minutes of hypoxic (Hx, 12% O₂) or normoxic ventilation, and were administered recombinant human EPO-α (5000 IU/kg) or saline at 1 and 24 hours post-injury. The parameters examined included: 1) behavioural and cognitive deficit using the Rotarod, open field and novel object recognition tests; 2) axonal pathology (NF-200); 3) callosal degradation (hematoxylin and eosin stain); 3) dendritic loss (MAP2); 4) expression and localisation of the EPO receptor (EpoR); 5) activation/infiltration of microglia/macrophages (CD68) and production of IL-1β.

Results

EPO significantly improved sensorimotor and cognitive recovery when administered to TAI rats with hypoxia (TAI + Hx). A single dose of EPO at 1 hour reduced axonal damage in the white matter of TAI + Hx rats at 1 day by 60% compared to vehicle. MAP2 was decreased in the lateral septal nucleus of TAI + Hx rats; however, EPO prevented this loss, and maintained MAP2 density over time. EPO administration elicited an early enhanced expression of EpoR 1 day after TAI + Hx compared with a 7-day peak in vehicle controls. Furthermore, EPO reduced IL-1β to sham levels 2 hours after TAI + Hx, concomitant to a decrease in CD68 positive cells at 7 and 14 days.

Conclusions

When administered EPO, TAI + Hx rats had improved behavioural and cognitive performance, attenuated white matter damage, resolution of neuronal damage spanning from the axon to the dendrite, and suppressed neuroinflammation, alongside enhanced expression of EpoR. These data provide compelling evidence of EPO’s neuroprotective capability. Few benefits were observed when EPO was administered to TAI rats without hypoxia, indicating that EPO’s neuroprotective capacity is bolstered under hypoxic conditions, which may be an important consideration when EPO is employed for neuroprotection in the clinic.

Behavioral and histopathological alterations resulting from mild fluid percussion injury

The majority of people who sustain a traumatic brain injury (TBI) have an injury that can be classified as mild (often referred to as concussion). Although head CT scans for most subjects who have sustained a mild TBI (mTBI) are negative, these persons may still suffer from neurocognitive and neurobehavioral deficits. In order to expedite pre-clinical research and develop therapies, there is a need for well-characterized animal models of mTBI that reflect the neurological, neurocognitive, and pathological changes seen in human patients. In the present study, we examined the motor, cognitive, and histopathological changes resulting from 1.0 and 1.5 atmosphere (atm) overpressure fluid percussion injury (FPI). Both 1.0 and 1.5 atm FPI injury caused transient suppression of acute neurological functions, but did not result in visible brain contusion. Animals injured with 1.0 atm FPI did not show significant motor, vestibulomotor, or learning and memory deficits. In contrast, 1.5 atm injury caused transient motor disturbances, and resulted in a significant impairment of spatial learning and short-term memory. In addition, 1.5 atm FPI caused a marked reduction in cerebral perfusion at the site of injury that lasted for several hours. Consistent with previous studies, 1.5 atm FPI did not cause visible neuronal loss in the hippocampus or in the neocortex. However, a robust inflammatory response (as indicated by enhanced GFAP and Iba1 immunoreactivity) in the corpus callosum and the thalamus was observed. Examination of fractional anisotropy color maps after diffusion tensor imaging (DTI) revealed a significant decrease of FA values in the cingulum, an area found to have increased silver impregnation, suggesting axonal injury. Increased silver impregnation was also observed in the corpus callosum, and internal and external capsules. These findings are consistent with the deficits and pathologies associated with mild TBI in humans, and support the use of mild FPI as a model to evaluate putative therapeutic options.

Inflammatory consequences in a rodent model of mild traumatic brain injury

Mild traumatic brain injury (mTBI), particularly mild "blast type" injuries resulting from improvised exploding devices and many sport-caused injuries to the brain, result in long-term impairment of cognition and behavior. Our central hypothesis is that there are inflammatory consequences to mTBI that persist over time and, in part, are responsible for resultant pathogenesis and clinical outcomes. We used an adaptation (1 atmosphere pressure) of a well-characterized moderate-to-severe brain lateral fluid percussion (LFP) brain injury rat model. Our mild LFP injury resulted in acute increases in interleukin-1α/β and tumor necrosis factor alpha levels, macrophage/microglial and astrocytic activation, evidence of heightened cellular stress, and blood-brain barrier (BBB) dysfunction that were evident as early as 3-6 h postinjury. Both glial activation and BBB dysfunction persisted for 18 days postinjury.

Neurogenic and neuro-protective potential of a novel subpopulation of peripheral blood-derived CD133+ ABCG2+CXCR4+ mesenchymal stem cells: development of autologous cell-based therapeutics for traumatic brain injury

INTRODUCTION

Nervous system injuries comprise a diverse group of disorders that include traumatic brain injury (TBI). The potential of mesenchymal stem cells (MSCs) to differentiate into neural cell types has aroused hope for the possible development of autologous therapies for central nervous system injury.

METHODS

In this study we isolated and characterized a human peripheral blood derived (HPBD) MSC population which we examined for neural lineage potential and ability to migrate in vitro and in vivo. HPBD CD133+, ATP-binding cassette sub-family G member 2 (ABCG2)+, C-X-C chemokine receptor type 4 (CXCR4)+ MSCs were differentiated after priming with β-mercaptoethanol (β-ME) combined with trans-retinoic acid (RA) and culture in neural basal media containing basic fibroblast growth factor (FGF2) and epidermal growth factor (EGF) or co-culture with neuronal cell lines. Differentiation efficiencies in vitro were determined using flow cytometry or fluorescent microscopy of cytospins made of FACS sorted positive cells after staining for markers of immature or mature neuronal lineages. RA-primed CD133+ABCG2+CXCR4+ human MSCs were transplanted into the lateral ventricle of male Sprague-Dawley rats, 24 hours after sham or traumatic brain injury (TBI). All animals were evaluated for spatial memory performance using the Morris Water Maze (MWM) Test. Histological examination of sham or TBI brains was done to evaluate MSC survival, migration and differentiation into neural lineages. We also examined induction of apoptosis at the injury site and production of MSC neuroprotective factors.

RESULTS

CD133+ABCG2+CXCR4+ MSCs consistently expressed markers of neural lineage induction and were positive for nestin, microtubule associated protein-1β (MAP-1β), tyrosine hydroxylase (TH), neuron specific nuclear protein (NEUN) or type III beta-tubulin (Tuj1). Animals in the primed MSC treatment group exhibited MWM latency results similar to the uninjured (sham) group with both groups showing improvements in latency. Histological examination of brains of these animals showed that in uninjured animals the majority of MSCs were found in the lateral ventricle, the site of transplantation, while in TBI rats MSCs were consistently found in locations near the injury site. We found that levels of apoptosis were less in MSC treated rats and that MSCs could be shown to produce neurotropic factors as early as 2 days following transplantation of cells. In TBI rats, at 1 and 3 months post transplantation cells were generated which expressed markers of neural lineages including immature as well as mature neurons.

CONCLUSIONS

These results suggest that PBD CD133+ABCG2+CXCR4+ MSCs have the potential for development as an autologous treatment for TBI and neurodegenerative disorders and that MSC derived cell products produced immediately after transplantation may aid in reducing the immediate cognitive defects of TBI.

Detection of structural and metabolic changes in traumatically injured hippocampus by quantitative differential proteomics

Traumatic brain injury (TBI) is a complex and common problem resulting in the loss of cognitive function. In order to build a comprehensive knowledge base of the proteins that underlie these cognitive deficits, we employed unbiased quantitative mass spectrometry, proteomics, and bioinformatics to identify and quantify dysregulated proteins in the CA3 subregion of the hippocampus in the fluid percussion model of TBI in rats. Using stable isotope 18O-water differential labeling and multidimensional tandem liquid chromatography (LC)-MS/MS with high stringency statistical analyses and filtering, we identified and quantified 1002 common proteins, with 124 increased and 76 decreased. The ingenuity pathway analysis (IPA) bioinformatics tool identified that TBI had profound effects on downregulating global energy metabolism, including glycolysis, the Krebs cycle, and oxidative phosphorylation, as well as cellular structure and function. Widespread upregulation of actin-related cytoskeletal dynamics was also found. IPA indicated a common integrative signaling node, calcineurin B1 (CANB1, CaNBα, or PPP3R1), which was downregulated by TBI. Western blotting confirmed that the calcineurin regulatory subunit, CANB1, and its catalytic binding partner PP2BA, were decreased without changes in other calcineurin subunits. CANB1 plays a critical role in downregulated networks of calcium signaling and homeostasis through calmodulin and calmodulin-dependent kinase II to highly interconnected structural networks dominated by tubulins. This large-scale knowledge base lays the foundation for the identification of novel therapeutic targets for cognitive rescue in TBI.

Effects of hemodilution after traumatic brain injury in juvenile rats

BACKGROUND

Normovolemic hemodilution (HD) in adult animal studies has shown exacerbation of traumatic brain injury (TBI) lesion volumes. Similar studies in juvenile rats have not been reported and outcomes are likely to be different. This study investigated the effects of normovolemic hemodilution (21% hematocrit) in a juvenile TBI (jTBI) model.

METHODS

Twenty 17-day-old rats underwent moderate cortical contusion impact injury (CCI) and were divided into four groups: CCI/hemodilution (HD) (group HD), CCI/no HD (group C), Sham/HD (group SHD), and Sham/no HD (group S). Regional laser Doppler flowmetry (LDF), edema formation (MRI-T2WI), water mobility assessed using diffusion weighted imaging (MRI-DWI), open field activity tests, and histological analyses were evaluated for lesion characteristics.

RESULTS

Hemodilution significantly increased blood flow in the HD compared to the C group after TBI. T2WI revealed a significantly increased extravascular blood volume in HD at 1, 7, and 14 days post-CCI. Edematous tissue and total contusional lesion volume were higher in HD-treated animals at 1 and 14 days. DWI revealed that HD, SHD, and C groups had elevated water mobility compared to S groups in the ipsilateral cortex and striatum. Histology showed a larger cortical lesion in the C than HD group. Open field activity was increased in HD, C, and SHD groups compared to the S group.

CONCLUSIONS

Hemodilution results in significant brain hyperemia with increased edema formation, extravascular blood volume, and water mobility after jTBI. Hemodilution results in less cortical damage but did not alter behavior. Hemodilution is likely not to be clinically beneficial following jTBI.

Magnetic resonance imaging of regional hemodynamic and cerebrovascular recovery after lateral fluid-percussion brain injury in rats

Hemodynamic and cerebrovascular factors are crucially involved in secondary damage after traumatic brain injury (TBI). With magnetic resonance imaging, this study aimed to quantify regional cerebral blood flow (CBF) by arterial spin labeling and cerebral blood volume by using an intravascular contrast agent, during 14 days after lateral fluid-percussion injury (LFPI) in rats. Immunohistochemical analysis of vessel density was used to evaluate the contribution of vascular damage. Results show widespread ipsilateral and contralateral hypoperfusion, including both the cortex and the hippocampus bilaterally, as well as the ipsilateral thalamus. Hemodynamic unrest may partly be explained by an increase in blood vessel density over a period of 2 weeks in the ipsilateral hippocampus and perilesional cortex. Furthermore, three phases of perilesional alterations in CBF, progressing from hypoperfusion to normal and back to hypoperfusion within 2 weeks were shown for the first time in a rat TBI model. These three phases were similar to hemodynamic fluctuations reported in TBI patients. This makes it feasible to use LFPI in rats to study mechanisms behind hemodynamic changes and to explore novel therapeutic approaches for secondary brain damage after TBI.

L-arginine reactivity in cerebral vessels after severe traumatic brain injury

OBJECTIVES

Traumatic brain injury (TBI) causes an early reduction of cerebral blood flow (CBF). The purpose was to study cerebrovascular endothelial function by examining the reactivity of cerebral vessels to L-arginine.

METHODS

Fifty-one patients with severe TBI were prospectively studied by measuring cerebral hemodynamics before and after the administration of L-arginine, 300 mg/kg at 12 hours and at 48 hours after injury. These hemodynamic measurements, using transcranial Doppler techniques, included internal carotid flow volume as an estimate of hemispheric CBF, flow velocity in intracranial vessels, CO(2) reactivity, and dynamic pressure autoregulation using thigh cuff deflation and carotid compression methods. Changes in the hemodynamics with L-arginine administration were analyzed using a general linear mixed model.

RESULTS

L-arginine produced no change in mean arterial pressure, intracranial pressure, or brain oxygenation. Overall, L-arginine induced an 11.3% increase in internal carotid artery flow volume (P=0.0190). This increase was larger at 48 hours than at 12 hours (P=0.0045), and tended to be larger in the less injured hemisphere at both time periods. The response of flow velocity in the intracranial vessels was similar, but smaller differences with administration of L-arginine were observed. There was a significant improvement in CO(2) reactivity with L-arginine, but no change in dynamic pressure autoregulation.

DISCUSSION

The low response of the cerebral vessels to L-arginine at 12 hours post-injury with improvement at 48 hours suggests that dysfunction of cerebrovascular endothelium plays a role in the reduced CBF observed after TBI.

Impact of arginase II on CBF in experimental cortical impact injury in mice using MRI

Traumatic brain injury (TBI) results in reduced cerebral blood flow (CBF) and low levels of the vasodilator nitric oxide (NO) may be involved. Arginase II negatively regulates NO production through competition for the substrate L-arginine. We determined whether arginase II-deficient (ArgII(-/-)) mice would show improved CBF after TBI through arterial spin-labeling magnetic resonance imaging (MRI). The ArgII(-/-) mice exhibit a significantly improved CBF recovery after trauma in the perilesional brain (P=0.0015) and in various other brain regions. In conclusion, arginase II deficiency leads to a better CBF recovery after TBI and implicates arginase II in hemodynamic processes.

Hemodynamic and histological effects of traumatic brain injury in eNOS-deficient mice

Microvascular dysfunction in the brain, characterized by vasoconstriction, vascular occlusion, and disruption of the blood brain barrier, may adversely affect outcome following traumatic brain injury (TBI). Because of its vasodilating and antiaggregative properties, nitric oxide (NO) produced by nitric oxide synthase in the endothelium (eNOS) is a key regulator of vascular homeostasis. The objective of the present study was to evaluate the role of eNOS in vascular disturbances and histological outcome in the brain following TBI. Cortical blood flow ([(14)C]-iodoantipyrine technique), number of perfused capillaries (FITC-dextran technique), brain water content (wet vs. dry weight), and the transfer constant (K(i)) for [(51)Cr]-EDTA, reflecting permeability, were analyzed 3 h and 24 h after a controlled cortical impact injury (CCI) in eNOS-deficient (eNOS-KO) and wild-type (WT) mice. Cortical contusion volume and cell count in the hippocampus were evaluated 3 weeks after injury. Blood flow in the injured cortex decreased in both groups following trauma. There were no significant differences between the groups at 3 h, but blood flow was lower in eNOS-KO mice than in WT mice 24 h after trauma. Brain water content was higher in the WT mice than in eNOS-KO mice at 24 h. Number of perfused capillaries, K(i), and histological outcome were similar in both groups. We conclude that eNOS is important for maintenance of cerebral blood flow after trauma and that eNOS promotes edema formation by mechanisms other than increased permeability. The vascular effects of eNOS do not, however, influence histological outcome.

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.

L-Arginine decreases fluid-percussion injury-induced neuronal nitrotyrosine immunoreactivity in rats

Peroxynitrite is a powerful oxidant capable of nitrating phenolic moieties, such as tyrosine or tyrosine residues in proteins and increases after traumatic brain injury (TBI). First, we tested the hypothesis that TBI increases nitrotyrosine (NT) immunoreactivity in the brain by measuring the number of NT-immunoreactive neurons in the cerebral cortex and hippocampus of rats subjected to parasagittal fluid-percussion TBI. Second, we tested the hypothesis that treatment with L-arginine, a substrate for nitric oxide synthase, further increases NT immunoreactivity over TBI alone. Rats were anesthetized with isoflurane and subjected to TBI, sham TBI, or TBI followed by treatment with L-arginine (100 mg/kg). Twelve, 24, or 72 h after TBI, brains were harvested. Coronal sections (10 microm) were incubated overnight with rabbit polyclonal anti-NT antibody, rinsed, and incubated with a biotinylated secondary antibody. The antigen-antibody complex was visualized using a peroxidase-conjugated system with diaminobenzidine as the chromagen. The number of NT-positive cortical and hippocampal neurons increased significantly in both ipsilateral and contralateral hemispheres up to 72 h after TBI compared with the sham-injured group. Remarkably, treatment with L-arginine reduced the number of NT-positive neurons after TBI in both cortex and hippocampus. Our results indicate that L-arginine actually prevents TBI-induced increases in NT immunoreactivity.

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.

[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.

Endothelial influences on cerebrovascular tone

The cerebrovascular endothelium exerts a profound influence on cerebral vessels and cerebral blood flow. This review summarizes current knowledge of various dilator and constrictor mechanisms intrinsic to the cerebrovascular endothelium. The endothelium contributes to the resting tone of cerebral arteries and arterioles by tonically releasing nitric oxide (NO•). Dilations can occur by stimulated release of NO•, endothelium-derived hyperpolarization factor, or prostanoids. During pathological conditions, the dilator influence of the endothelium can turn to that of constriction by a variety of mechanisms, including decreased NO• bioavailability and release of endothelin-1. The endothelium may participate in neurovascular coupling by conducting local dilations to upstream arteries. Further study of the cerebrovascular endothelium is critical for understanding the pathogenesis of a number of pathological conditions, including stroke, traumatic brain injury, and subarachnoid hemorrhage.

Characterization of the effects of adenosine receptor agonists on cerebral blood flow in uninjured and traumatically injured rat brain using continuous arterial spin-labeled magnetic resonance imaging

Hypoperfusion after traumatic brain injury may exacerbate damage. Adenosine, a vasodilator, regulates cerebral blood flow (CBF). Treatment with adenosine receptor agonists has shown benefit in experimental CNS trauma; however, their effects on CBF after injury remain undefined. We used magnetic resonance imaging to assess CBF in uninjured rats both early and at 24 h after intrahippocampal administration of either the nonselective adenosine receptor agonist 2-chloroadenosine (2-CA, 12 nmol) or the A(2A)-receptor agonist 2-p-(2-carboxyethyl)-phenethylamino-5'-N-ethylcarbox-amidoadenosine (CGS 21680, 6 nmol). We also assessed the effects of these agents on cerebral metabolic rate for glucose (CMRglu). We then assessed the effect of 2-CA on CBF at 3.5 to 5 h after controlled cortical impact (CCI). Injection of 2-CA into uninjured rat brain produced marked increases in CBF in ipsilateral hippocampus and cortex versus vehicle (P<0.05); CBF increases persisted even at 24 h. Measurement of hippocampal levels of 2-CA showed persistent increases to 24 h. CGS 21680 produced even more marked global increases in CBF than seen with 2-CA (2-6-fold versus vehicle, P<0.05 in 10/12 regions of interest (ROIs)). Neither agonist altered CMRglu versus vehicle. After CCI, 2-CA increased CBF in ipsilateral hippocampal and hemispheric ROIs (P<0.05 versus vehicle), but the response was attenuated at severe injury levels. We report marked increases in CBF after injection of adenosine receptor agonists into uninjured rat brain despite unaltered CMRglu. 2-Chloroadenosine produced enduring increases in CBF in uninjured brain and attenuated posttraumatic hypoperfusion. Future studies of adenosine-related therapies in CNS injury should address the role of CBF.

Enhanced oxidative stress in iNOS-deficient mice after traumatic brain injury: support for a neuroprotective role of iNOS

Studies in experimental traumatic brain injury (TBI) suggest both deleterious and protective effects of inducible nitric oxide synthase (iNOS). Early after injury, iNOS may be detrimental via formation of peroxynitrite and iNOS inhibitors are protective. In contrast, we reported impaired long-term functional outcome after TBI in iNOS knockout (ko) versus wild-type (wt) mice. To elucidate potential neuroprotective and neurotoxic mechanisms for iNOS, we studied nitric oxide formation by electron paramagnetic resonance (EPR) spectroscopy using diethyldithiocarbamate-iron (DETC-Fe) as a spin trap and markers of nitrosative (S-nitrosothiol (RSNO, Fluorescent assay); nitrotyrosine (3NT, ELISA)) and oxidative stress (ascorbate, HPLC) at 72 h after controlled cortical impact (CCI) in iNOS ko and wt and in uninjured iNOS ko and wt mice. 3NT immunostaining with macrophage and myeloperoxidase (MPO) dual labeling was also assessed in brain sections. Brain DETC-Fe-NO low-temperature EPR signal intensity was approximately 2-fold greater in wt versus iNOS ko at 72 h after CCI. Ascorbate levels decreased in injured hemisphere in wt and iNOS ko versus uninjured -this decrease was more pronounced in iNOS ko. In wt mice, RSNO and 3NT levels were increased after CCI versus uninjured (50% and 400%, respectively, P < 0.05). RSNO levels were not increased in iNOS ko after CCI. Nitrotyrosine levels increased after CCI in wt and ko versus respective uninjured -this increase was more pronounced in wt (2.34 +/- 0.95 versus 1.27 +/- 0.49 pmol/mg protein, P < 0.05). Increased 3NT immunoreactivity was detected in wt versus iNOS ko at 72 h after CCI, and colocalized with macrophage marker and MPO. Our data support a role for iNOS-derived NO as an endogenous antioxidant after CCI. iNOS also contributes protein nitrosylation and nitration. Colocalization of 3NT with macrophages and MPO suggests generation of nitrating agents by macrophages and/or phagocytosis of nitrated proteins.

The effects of traumatic brain injury on cerebral blood flow and brain tissue nitric oxide levels and cytokine expression

Adult, male, Sprague-Dawley rats were anesthetized, intubated, and mechanically ventilated with 1.5-2.0% isoflurane in oxygen (30%) and air. Rats were prepared for fluid percussion traumatic brain injury (TBI), laser Doppler flowmetry, and measurement of brain tissue nitric oxide (NO) levels using an ISO-NO electrode system. After preparation, isoflurane was reduced to 1.5%, and the rats were randomly assigned to receive sham (n = 6), moderate (1.9 atm, n = 6), or severe (2.8 atm, n = 6) parasagittal fluid percussion TBI. CBF and brain tissue NO levels were measured for 4 h, and then isoflurane levels were increased to 4.0% and the rats were decapitated and the brains were removed. Total RNA was isolated from rat brains and cytokine expression was determined. Laser Doppler flow velocity remained constant in the sham-injured rats but decreased significantly in rats subjected to moderate (p < 0.05) or severe (p < 0.05) TBI. Brain tissue NO levels remained constant in the sham-injured rats but decreased significantly (p < 0.01) after moderate TBI. Severe TBI produced slight, insignificant reductions in NO levels. Cytokine expression was very low in the shaminjured rats. TBI-induced expression of mRNAs for interleukin-1 alpha (IL-1alpha), IL-1beta, IL-6, and tumor necrosis factor-alpha (TNFa). IL-1alpha and IL-1beta mRNA expression increased significantly (p < 0.05 vs. sham-injury) after severe TBI and IL-6 and TNFa mRNA expression increased significant (p < 0.05 vs. sham-injury) after both moderate and severe TBI. Other cytokine mRNA expression was unchanged after TBI.

Cerebral pressure autoregulation is intact and is not influenced by hypothermia after traumatic brain injury in rats

In head-injured patients and experimental traumatic brain injury (TBI), important cerebrovascular abnormalities include decreases in cerebral blood flow (CBF) and impairment of cerebral pressure autoregulation. We evaluated CBF and pressure autoregulation after fluid percussion injury (FPI) and hypothermia in rats with the hypothesis that hypothermia would ameliorate changes in posttraumatic CBF. Male Sprague-Dawley rats, intubated and mechanically ventilated, were prepared for parasagittal FPI (1.8 atm) and laser Doppler CBF flow (LDF) measurement. The abdominal aorta was cannulated for rapid removal and reinfusion of blood. Baseline autoregulatory testing in all groups consisted of LDF measurements at normothermia and a mean arterial pressure (MAP) of 100 mm Hg, followed by randomly ordered changes of MAP to 80, 60, and 40 mm Hg. Animals were then randomized to one of five groups: normothermic control without FPI; normothermia with FPI; hypothermic control (32 degrees C) without FPI; hypothermia initiated before FPI; and hypothermia initiated immediately after FPI injury. For each group, a complete, randomly ordered autoregulatory sequence was performed at 30 and 60 min after FPI or sham TBI. In a second study, rats were prepared identically, maintained at normothermic temperatures and autoregulation was tested before and after TBI using a set of randomly ordered levels of hypotension or using progressive reductions in MAP (i.e., 80, 60, 40 mm Hg) with the hypothesis that the technical manner and timing of decreasing of the blood pressure would effect CBF after TBI. Due to high acute mortality, the group in which hypothermia was induced before FPI was excluded from the analysis. At baseline, autoregulation was similar in all groups. There was no change in CBF or autoregulation in the normothermic control group at 30 and 60 min. In the other groups at 30 and 60 min, there was a similar, statistically significant decrease in absolute CBF (i.e., a decrease of 27-57% of baseline values), but pressure autoregulation was intact except at the lowest blood pressure tested at 60 min, where there was a slight improvement in the hypothermic group. Thus, in these experiments, absolute CBF decreased with hypothermia and FPI, while neither hypothermia nor FPI significantly altered autoregulation. In the second study, autoregulatory function was not different before TBI when comparing random and sequential blood pressure changes, but, when comparing the groups after TBI at the 60 mm Hg blood pressure level, CBF was significantly lower in the sequential group than in the random order group. This suggests that the mechanism of creating hypotension, whether random or sequential, significantly affects the measurement of CBF and autoregulation after TBI in rats.

Comparison of tetrahydrobiopterin and L-arginine on cerebral blood flow after controlled cortical impact injury in rats

The purpose of this study was to compare the effects of L-arginine and tetrahydrobiopterin administration on post-traumatic cerebral blood flow (CBF) and tissue levels of NO in injured brain tissue. Rats were anesthetized with isoflurane. Mean blood pressure, intracranial pressure, cerebral blood flow using laser Doppler flowmetry (LDF) and brain tissue nitric oxide (NO) concentrations were measured prior to, and for 2 h after a controlled cortical impact injury. L-arginine, 300 mg/kg, tetrahydrobiopterin, 10 mg/kg, or equal volume of saline was given at 5 min after injury. In the saline-treated animals, LDF decreased to 34 +/- 4% of baseline values after injury. NO concentration also decreased by approximately 20 pmol/ml from baseline values. L-arginine and tetrahydrobiopterin administration both resulted in a significant preservation of tissue NO concentrations and an improvement in LDF, compared to control animals given saline. These studies demonstrate that tetrahydrobiopterin administration has a beneficial effect on cerebral blood flow that is similar to L-arginine administration, and may suggest that depletion of tetrahydrobiopterin plays a role in the post-traumatic hypoperfusion of the brain.

Laser Doppler Flow and Brain Tissue PO2 after Cortical Impact Injury Complicated by Secondary Ischemia in Rats Treated with Arginine

BACKGROUND

Traumatic brain injury (TBI) makes the brain susceptible to secondary insults such as ischemia. This study tested the hypothesis that L-arginine would increase regional CBF (rCBF) and brain tissue PO2 (PbtO2) at the injury site.

METHODS

A secondary insult model was employed in rodents. rCBF was measured with laser doppler flowmetry (LDF) and PbtO2 with a PO2 catheter at the impact site. Animals were randomized to receive L-arginine, D-arginine or saline intravenously, 5 minutes after impact.

RESULTS

In animals who received L-arginine, the percentage rCBF from baseline (%CBF) was higher at the impact site after impact (p < 0.001), during bilateral carotid occulation (BCO) (p = 0.001) and during reperfusion (p = 0.032). In contrast, PbtO2 was not significantly increased throughout the experiment for the L-arginine group.

CONCLUSIONS

Administration of L-arginine increased rCBF in the injured brain tissue, and resulted in better preservation of CBF during BCO than D-arginine and saline.

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.

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.

F2-isoprostane and neuron-specific enolase in cerebrospinal fluid after severe traumatic brain injury in infants and children

It has been hypothesized that oxidative stress plays an important role in mediating secondary damage after traumatic brain injury (TBI). To study the relationship between lipid peroxidation, clinical variables, and neuronal damage in pediatric TBI, we measured levels of F2-isoprostane, a marker of lipid peroxidation, and neuron-specific enolase (NSE), a marker of neuronal damage, in serial cerebrospinal fluid (CSF) samples from 23 infants and children with severe TBI (Glasgow Coma Scale score <8). These were compared to CSF samples from 10 uninjured pediatric controls. On d1 after injury, F2-isoprostane was increased 6-fold vs. control (36.59+/-8.96 pg/ml vs. 5.64+/-8.08 pg/ml, p=0.0035) and NSE was increased 10-fold (100.62+/-17.34 ng/ml vs. 8.63+/-2.76 ng/ml, p=0.0002). Multivariate analysis of F2-isoprostane levels and selected clinical variables showed a trend toward an inverse association with time after injury (p=0.0708). Multivariate analysis of NSE levels and selected variables showed a positive association between d1 NSE and F2-isoprostane (p=0.0426). CSF F2-isoprostane increases early after TBI in infants and children and is correlated with NSE, supporting a role for oxidative stress in the evolution of secondary damage early after severe TBI in infants and children.

Upregulation of neurogenesis and reduction in functional deficits following administration of DEtA/NONOate, a nitric oxide donor, after traumatic brain injury in rats

OBJECT

Neurogenesis, which is upregulated by neural injury in the adult mammalian brain, may be involved in the repair of the injured brain and functional recovery. Therefore, the authors sought to identify agents that can enhance neurogenesis after brain injury, and they report that (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA/NONOate), a nitric oxide donor, upregulates neurogenesis and reduces functional deficits after traumatic brain injury (TBI) in rats.

METHODS

The agent DETA/NONOate (0.4 mg/kg) was injected intraperitoneally into 16 rats daily for 7 days, starting 1 day after TBI induced by controlled cortical impact. Bromodeoxyuridine (100 mg/kg) was also injected intraperitoneally daily for 14 days after TBI to label the newly generated cells in the brain. A neurological functional evaluation was performed in all rats and the animals were killed at 14 or 42 days postinjury. Immunohistochemical staining was used to identify proliferating cells.

CONCLUSIONS

Compared with control rats, the proliferation, survival, migration and differentiation of neural progenitor cells were all significantly enhanced in the hippocampus, subventricular zone, striatum, corpus callosum, and the boundary zone of the injured cortex, as well as in the contralateral hemisphere in rats with TBI that received DETA/ NONOate treatment. Neurological functional outcomes in the DETA/NONOate-treated group were also significantly improved compared with the untreated group. These data indicate that DETA/NONOate may be useful in the treatment of TBI.

Traumatic brain injury in infants and children: mechanisms of secondary damage and treatment in the intensive care unit

Unfortunately no specific pharmacologic therapies are available for the treatment of TBI in patients. Current investigation of contemporary therapies for the treatment of TBI consists of recycling of previously tested therapies in the era of contemporary neurointensive care. These therapies include hypothermia, decompressive craniectomy, osmotherapy, and controlled hyperventilation. It is hoped that more detailed knowledge regarding the dominant pathophysiologic mechanisms associated with TBI-excitotoxicity, CBF dysregulation, oxidative stress, and programmed cell death-will catapult an efficacious intervention from the laboratory bench to the bedside. This intervention may be a potent agent targeting a single dominant pathway, a broad-spectrum intervention such as hypothermia, or, more likely, a combination of therapies. Meanwhile, practitioners must offer meticulous supportive neurointensive care using clinically proven therapies aimed at minimizing cerebral swelling for the management of pediatric patients who are victims of TBI.

Neuroprotective effects of L-arginine administration after cortical impact injury in rats: dose response and time window

Administration of L-arginine has been shown to increase cerebral blood flow and reduce neurological damage after experimental traumatic brain injury. The purpose of this study was to examine the optimal dose and time window for these neuroprotective effects. In a dose response experiment, doses of L-arginine ranging from 37.5 to 600 mg/kg were administered 5 min after a 5-m/s, 3-mm, controlled cortical impact in rats. The amount of brain injury found at 2 weeks after injury, both at the contusion site and in the ipsilateral hippocampus, were inversely related to the dose of L-arginine administered. Both 300- and 600-mg/kg doses of L-arginine significantly reduced contusion volume. The 300-mg/kg dose significantly increased the neuron density in the CA1 region of the hippocampus. Physiological effects of L-arginine were also dose-related. The greatest reduction in intracranial pressure occurred with the 300-mg/kg dose of L-arginine. Doses up to 300 mg/kg were well tolerated, but the 600-mg/kg dose resulted in transient hypotension. In another experiment, 300 mg/kg L-arginine was administered at times varying from 5 min to 48 h after injury. Contusion volume was significantly reduced when the L-arginine was given at 5 min and 1 h after injury. The protective effect was less when the same dose was given at the later times, but there was no evidence of an adverse effect even when the L-arginine was administered 48 h after injury.

L-arginine and free radical scavengers increase cerebral blood flow and brain tissue nitric oxide concentrations after controlled cortical impact injury in rats

To examine the mechanism of the increase in cerebral blood flow induced by L-arginine administration after traumatic brain injury, the cerebral hemodynamic effects of L-arginine, D-arginine, and the free radical scavengers superoxide dismutase (SOD) and catalase were compared in the controlled cortical impact injury model in rats. Animals were anesthetized with isoflurane. Measured parameters included mean blood pressure, intracranial pressure, cerebral blood flow using laser Doppler flowmetry (LDF) and brain tissue nitric oxide (NO) concentrations using an NO electrode. L-arginine, but not D-arginine, administration resulted in a significant increase in tissue NO concentrations and an improvement in LDF at the impact site, compared to control animals given saline. Administration of SOD alone and in combination with catalase resulted in a significant increase in brain tissue NO concentrations. However, LDF was consistently improved only when both SOD and catalase were given. These studies support the theory that L-arginine administration improves post-traumatic cerebral blood flow by increasing NO production. Free radical production after trauma may also contribute to the reduction in CBF by inactivating NO.

Promising strategies to minimize secondary brain injury after head trauma

OBJECTIVE

To review novel therapeutic approaches in the treatment of severe traumatic brain injury.

DESIGN

Eighty-three studies were reviewed specific to the treatment of traumatic brain injury, in either experimental models or in patients.

CONCLUSION

Four therapeutic strategies appear to be the most promising approaches currently in clinical trials for severe traumatic brain injury: a) the novel pharmacologic agent dexanabinol; b) hypertonic saline; c) mild hypothermia; and d) decompressive craniectomy. Each of these therapies share the common feature of targeting multiple mechanisms, suggesting this may be an important factor to the development of a successful approach to severe traumatic brain injury.

Increased S-nitrosothiols and S-nitrosoalbumin in cerebrospinal fluid after severe traumatic brain injury in infants and children: indirect association with intracranial pressure

Nitric oxide (NO) is implicated in both secondary damage and recovery after traumatic brain injury (TBI). Transfer of NO groups to cysteine sulfhydryls on proteins produces S-nitrosothiols (RSNO). S-nitrosothiols may be neuroprotective after TBI by nitrosylation of N-methyl-D-aspartate receptor and caspases. S-nitrosothiols release NO on decomposition for which endogenous reductants (i.e., ascorbate) are essential, and ascorbate is depleted in cerebrospinal fluid (CSF) after pediatric TBI. This study examined the presence and decomposition of RSNO in CSF and the association between CSF RSNO level and physiologic parameters after severe TBI. Cerebrospinal fluid samples (n = 72) were obtained from 18 infants and children on days 1 to 3 after severe TBI (Glasgow Coma Scale score < 8) and 18 controls. Cerebrospinal fluid RSNO levels assessed by fluorometric assay peaked on day 3 versus control (1.42 +/- 0.11 micromol/L vs. 0.86 +/- 0.04, P< 0.05). S-nitrosoalbumin levels were also higher after TBI (n = 8, 0.99 +/- 0.09 micromol/L on day 3 vs. n = 6, 0.42 +/- 0.02 in controls, P< 0.05). S-nitrosoalbumin decomposition was decreased after TBI. Multivariate analysis showed an inverse relation between CSF RSNO and intracranial pressure and a direct relation with barbiturate treatment. Using a novel assay, the presence of RSNO and S-nitrosoalbumin in human CSF, an approximately 1.7-fold increase after TBI, and an association with low intracranial pressure are reported, supporting a possible neuroprotective role for RSNO. The increase in RSNO may result from increased NO production and/or decreased RSNO decomposition.

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.

Management of head trauma

Traumatic brain injury (TBI) is a major cause of disability and death in most Western nations and consumes an estimated $100 billion annually in the United States alone. In the last 2 decades, the management of TBI has evolved dramatically, as a result of a more thorough understanding of the physiologic events leading to secondary neuronal injury as well as advances in the care of critically ill patients. However, it is likely that many patients with TBI are not treated according to current treatment principles. This article presents an overview of the current management of patients with TBI.