Restoration of cerebrovascular responsiveness to hyperventilation by the oxygen radical scavenger n-acetylcysteine following experimental traumatic brain injury

A Modern Approach to the Treatment of Traumatic Brain Injury

Background: Traumatic brain injury manifests itself in various forms, ranging from mild impairment of consciousness to severe coma and death. Traumatic brain injury remains one of the leading causes of morbidity and mortality. Currently, there is no therapy to reverse the effects associated with traumatic brain injury. New neuroprotective treatments for severe traumatic brain injury have not achieved significant clinical success. Methods: A literature review was performed to summarize the recent interdisciplinary findings on management of traumatic brain injury from both clinical and experimental perspective. Results: In the present review, we discuss the concepts of traditional and new approaches to treatment of traumatic brain injury. The recent development of different drug delivery approaches to the central nervous system is also discussed. Conclusions: The management of traumatic brain injury could be aimed either at the pathological mechanisms initiating the secondary brain injury or alleviating the symptoms accompanying the injury. In many cases, however, the treatment should be complex and include a variety of medical interventions and combination therapy.

N-Acetylcysteine and Probenecid Adjuvant Therapy for Traumatic Brain Injury

N-Acetylcysteine (NAC) has shown promise as a putative neurotherapeutic for traumatic brain injury (TBI). Yet, many such promising compounds have limited ability to cross the blood-brain barrier (BBB), achieve therapeutic concentrations in brain, demonstrate target engagement, among other things, that have hampered successful translation. A pharmacologic strategy for overcoming poor BBB permeability and/or efflux out of the brain of organic acid-based, small molecule therapeutics such as NAC is co-administration with a targeted or nonselective membrane transporter inhibitor. Probenecid is a classic ATP-binding cassette and solute carrier inhibitor that blocks transport of organic acids, including NAC. Accordingly, combination therapy using probenecid as an adjuvant with NAC represents a logical neurotherapeutic strategy for treatment of TBI (and other CNS diseases). We have completed a proof-of-concept pilot study using this drug combination in children with severe TBI-the Pro-NAC Trial (ClinicalTrials.gov NCT01322009). In this review, we will discuss the background and rationale for combination therapy with probenecid and NAC in TBI, providing justification for further clinical investigation.

Drug Repurposing in the Treatment of Traumatic Brain Injury

Traumatic brain injury (TBI) is the most common cause of morbidity among trauma patients; however, an effective pharmacological treatment has not yet been approved. Individuals with TBI are at greater risk of developing neurological illnesses such as Alzheimer's disease (AD) and Parkinson's disease (PD). The approval process for treatments can be accelerated by repurposing known drugs to treat the growing number of patients with TBI. This review focuses on the repurposing of N-acetyl cysteine (NAC), a drug currently approved to treat hepatotoxic overdose of acetaminophen. NAC also has antioxidant and anti-inflammatory properties that may be suitable for use in therapeutic treatments for TBI. Minocycline (MINO), a tetracycline antibiotic, has been shown to be effective in combination with NAC in preventing oligodendrocyte damage. (-)-phenserine (PHEN), an anti-acetylcholinesterase agent with additional non-cholinergic neuroprotective/neurotrophic properties initially developed to treat AD, has demonstrated efficacy in treating TBI. Recent literature indicates that NAC, MINO, and PHEN may serve as worthwhile repositioned therapeutics in treating TBI.

An Overview and Therapeutic Promise of Nutraceuticals against Sports-Related Brain Injury

Sports-related traumatic brain injury (TBI) is one of the common neurological maladies experienced by athletes. Earlier the term 'punch drunk syndrome' was used in the case TBI of boxers and now this term is replaced by chronic traumatic encephalopathy (CTE). Sports-related brain injury can either be short term or long term. A common instance of brain injury encompasses subdural hematoma, concussion, cognitive dysfunction, amnesia, headache, vision issue, axonopathy, or even death if remain undiagnosed or untreated. Further, chronic TBI may lead to pathogenesis of neuroinflammation and neurodegeneration via tauopathy, formation of neurofibrillary tangles, and damage to the blood-brain barrier, microglial, and astrocyte activation. Thus, altered pathological, neurochemical, and neurometabolic attributes lead to the modulation of multiple signaling pathways and cause neurological dysfunction. Available pharmaceutical interventions are based on one drug one target hypothesis and thereby unable to cover altered multiple signaling pathways. However, in recent time's pharmacological intervention of nutrients and nutraceuticals have been explored as they exert a multifactorial mode of action and maintain over homeostasis of the body. There are various reports available showing the positive therapeutic effect of nutraceuticals in sport-related brain injury. Therefore, in the current article we have discussed the pathology, neurological consequence, sequelae, and perpetuation of sports-related brain injury. Further, we have discussed various nutraceutical supplements as well as available animal models to explore the neuroprotective effect/ upshots of these nutraceuticals in sports-related brain injury.

New Insights into Oxidative Damage and Iron Associated Impairment in Traumatic Brain Injury

:

Traumatic Brain Injury is considered one of the most prevalent causes of death around the world; more than seventy millions of individuals sustain the condition per year. The consequences of traumatic brain injury on brain tissue are complex and multifactorial, hence, the current palliative treatments are limited to improve patients’ quality of life. The subsequent hemorrhage caused by trauma and the ongoing oxidative process generated by biochemical disturbances in the in the brain tissue may increase iron levels and reactive oxygen species. The relationship between oxidative damage and the traumatic brain injury is well known, for that reason, diminishing factors that potentiate the production of reactive oxygen species have a promissory therapeutic use. Iron chelators are molecules capable of scavenging the oxidative damage from the brain tissue and are currently in use for ironoverload- derived diseases.

:

Here, we show an updated overview of the underlying mechanisms of the oxidative damage after traumatic brain injury. Later, we introduced the potential use of iron chelators as neuroprotective compounds for traumatic brain injury, highlighting the action mechanisms of iron chelators and their current clinical applications.

Systematic Review of Human and Animal Studies Examining the Efficacy and Safety of N-Acetylcysteine (NAC) and N-Acetylcysteine Amide (NACA) in Traumatic Brain Injury: Impact on Neurofunctional Outcome and Biomarkers of Oxidative Stress and Inflammation

Background

No new therapies for traumatic brain injury (TBI) have been officially translated into current practice. At the tissue and cellular level, both inflammatory and oxidative processes may be exacerbated post-injury and contribute to further brain damage. N-acetylcysteine (NAC) has the potential to downregulate both processes. This review focuses on the potential neuroprotective utility of NAC and N-acetylcysteine amide (NACA) post-TBI.

Methods

Medline, Embase, Cochrane Library, and ClinicalTrials.gov were searched up to July 2017. Studies that examined clinical and laboratory effects of NAC and NACA post-TBI in human and animal studies were included. Risk of bias was assessed in human and animal studies according to the design of each study (randomized or not). The primary outcome assessed was the effect of NAC/NACA treatment on functional outcome, while secondary outcomes included the impact on biomarkers of inflammation and oxidation. Due to the clinical and methodological heterogeneity observed across studies, no meta-analyses were conducted.

Results

Our analyses revealed only three human trials, including two randomized controlled trials (RCTs) and 20 animal studies conducted using standardized animal models of brain injury. The two RCTs reported improvement in the functional outcome post-NAC/NACA administration. Overall, the evidence from animal studies is more robust and demonstrated substantial improvement of cognition and psychomotor performance following NAC/NACA use. Animal studies also reported significantly more cortical sparing, reduced apoptosis, and lower levels of biomarkers of inflammation and oxidative stress. No safety concerns were reported in any of the studies included in this analysis.

Conclusion

Evidence from the animal literature demonstrates a robust association for the prophylactic application of NAC and NACA post-TBI with improved neurofunctional outcomes and downregulation of inflammatory and oxidative stress markers at the tissue level. While a growing body of scientific literature suggests putative beneficial effects of NAC/NACA treatment for TBI, the lack of well-designed and controlled clinical investigations, evaluating therapeutic outcomes, prognostic biomarkers, and safety profiles, limits definitive interpretation and recommendations for its application in humans at this time.

Repositioning drugs for traumatic brain injury - N-acetyl cysteine and Phenserine

Traumatic brain injury (TBI) is one of the most common causes of morbidity and mortality of both young adults of less than 45 years of age and the elderly, and contributes to about 30% of all injury deaths in the United States of America. Whereas there has been a significant improvement in our understanding of the mechanism that underpin the primary and secondary stages of damage associated with a TBI incident, to date however, this knowledge has not translated into the development of effective new pharmacological TBI treatment strategies. Prior experimental and clinical studies of drugs working via a single mechanism only may have failed to address the full range of pathologies that lead to the neuronal loss and cognitive impairment evident in TBI and other disorders. The present review focuses on two drugs with the potential to benefit multiple pathways considered important in TBI. Notably, both agents have already been developed into human studies for other conditions, and thus have the potential to be rapidly repositioned as TBI therapies. The first is N-acetyl cysteine (NAC) that is currently used in over the counter medications for its anti-inflammatory properties. The second is (-)-phenserine ((-)-Phen) that was originally developed as an experimental Alzheimer's disease (AD) drug. We briefly review background information about TBI and subsequently review literature suggesting that NAC and (-)-Phen may be useful therapeutic approaches for TBI, for which there are no currently approved drugs.

Hippocampal Neurophysiologic Changes after Mild Traumatic Brain Injury and Potential Neuromodulation Treatment Approaches

Traumatic brain injury (TBI) is the leading cause of death and disability in individuals below age 45, and five million Americans live with chronic disability as a result. Mild TBI (mTBI), defined as TBI in the absence of major imaging or histopathological defects, is responsible for a majority of cases. Despite the lack of overt morphological defects, victims of mTBI frequently suffer lasting cognitive deficits, memory difficulties, and behavioral disturbances. There is increasing evidence that cognitive and memory dysfunction is related to subtle physiological changes that occur in the hippocampus, and these impact both the phenotype of deficits observed and subsequent recovery. Therapeutic modulation of physiological activity by means of medications commonly used for other indications or brain stimulation may represent novel treatment approaches. This review summarizes the present body of knowledge regarding neurophysiologic changes that occur in the hippocampus after mTBI, as well as potential targets for therapeutic modulation of neurologic activity.

Novel pharmaceutical treatments for minimal traumatic brain injury and evaluation of animal models and methodologies supporting their development

BACKGROUND

The need for effective pharmaceuticals within animal models of traumatic brain injury (TBI) continues to be paramount, as TBI remains the major cause of brain damage for children and young adults. While preventative measures may act to reduce the incidence of initial blunt trauma, well-tolerated drugs are needed to target the neurologically damaging internal cascade of molecular mechanisms that follow. Such processes, known collectively as the secondary injury phase, include inflammation, excitotoxicity, and apoptosis among other changes still subject to research. In this article positive treatment findings to mitigate this secondary injury in rodent TBI models will be overviewed, and include recent studies on Exendin-4, N-Acetyl-l-cycteine, Salubrinal and Thrombin.

CONCLUSIONS

These studies provide representative examples of methodologies that can be combined with widely available in vivo rodent models to evaluate therapeutic approaches of translational relevance, as well as drug targets and biochemical cascades that may slow or accelerate the degenerative processes induced by TBI. They employ well-characterized tests such as the novel object recognition task for assessing cognitive deficits. The application of such methodologies provides both decision points and a gateway for implementation of further translational studies to establish the feasibility of clinical efficacy of potential therapeutic interventions.

Fetal and Neonatal Effects of N-Acetylcysteine When Used for Neuroprotection in Maternal Chorioamnionitis

OBJECTIVE

To evaluate the clinical safety of antenatal and postnatal N-acetylcysteine (NAC) as a neuroprotective agent in maternal chorioamnionitis in a randomized, controlled, double-blinded trial.

STUDY DESIGN

Twenty-two mothers >24 weeks gestation presenting within 4 hours of diagnosis of clinical chorioamnionitis were randomized with their 24 infants to NAC or saline treatment. Antenatal NAC (100 mg/kg/dose) or saline was given intravenously every 6 hours until delivery. Postnatally, NAC (12.5-25 mg/kg/dose, n = 12) or saline (n = 12) was given every 12 hours for 5 doses. Doppler studies of fetal umbilical and fetal and infant cerebral blood flow, cranial ultrasounds, echocardiograms, cerebral oxygenation, electroencephalograms, and serum cytokines were evaluated before and after treatment, and 12, 24, and 48 hours after birth. Magnetic resonance spectroscopy and diffusion imaging were performed at term age equivalent. Development was followed for cerebral palsy or autism to 4 years of age.

RESULTS

Cardiovascular measures, cerebral blood flow velocity and vascular resistance, and cerebral oxygenation did not differ between treatment groups. Cerebrovascular coupling was disrupted in infants with chorioamnionitis treated with saline but preserved in infants treated with NAC, suggesting improved vascular regulation in the presence of neuroinflammation. Infants treated with NAC had higher serum anti-inflammatory interleukin-1 receptor antagonist and lower proinflammatory vascular endothelial growth factor over time vs controls. No adverse events related to NAC administration were noted.

CONCLUSIONS

In this cohort of newborns exposed to chorioamnionitis, antenatal and postnatal NAC was safe, preserved cerebrovascular regulation, and increased an anti-inflammatory neuroprotective protein.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT00724594.

N-acetylcysteine amide confers neuroprotection, improves bioenergetics and behavioral outcome following TBI

Traumatic brain injury (TBI) has become a growing epidemic but no approved pharmacological treatment has been identified. Our previous work indicates that mitochondrial oxidative stress/damage and loss of bioenergetics play a pivotal role in neuronal cell death and behavioral outcome following experimental TBI. One tactic that has had some experimental success is to target glutathione using its precursor N-acetylcysteine (NAC). However, this approach has been hindered by the low CNS bioavailability of NAC. The current study evaluated a novel, cell permeant amide form of N-acetylcysteine (NACA), which has high permeability through cellular and mitochondrial membranes resulting in increased CNS bioavailability. Cortical tissue sparing, cognitive function and oxidative stress markers were assessed in rats treated with NACA, NAC, or vehicle following a TBI. At 15days post-injury, animals treated with NACA demonstrated significant improvements in cognitive function and cortical tissue sparing compared to NAC or vehicle treated animals. NACA treatment also was shown to reduce oxidative damage (HNE levels) at 7days post-injury. Mechanistically, post-injury NACA administration was demonstrated to maintain levels of mitochondrial glutathione and mitochondrial bioenergetics comparable to sham animals. Collectively these data provide a basic platform to consider NACA as a novel therapeutic agent for treatment of TBI.

Efficacy of N-acetyl cysteine in traumatic brain injury

In this study, using two different injury models in two different species, we found that early post-injury treatment with N-Acetyl Cysteine (NAC) reversed the behavioral deficits associated with the TBI. These data suggest generalization of a protocol similar to our recent clinical trial with NAC in blast-induced mTBI in a battlefield setting, to mild concussion from blunt trauma. This study used both weight drop in mice and fluid percussion injury in rats. These were chosen to simulate either mild or moderate traumatic brain injury (TBI). For mice, we used novel object recognition and the Y maze. For rats, we used the Morris water maze. NAC was administered beginning 30-60 minutes after injury. Behavioral deficits due to injury in both species were significantly reversed by NAC treatment. We thus conclude NAC produces significant behavioral recovery after injury. Future preclinical studies are needed to define the mechanism of action, perhaps leading to more effective therapies in man.

The chemistry and biological activities of N-acetylcysteine

BACKGROUND

N-acetylcysteine (NAC) has been in clinical practice for several decades. It has been used as a mucolytic agent and for the treatment of numerous disorders including paracetamol intoxication, doxorubicin cardiotoxicity, ischemia-reperfusion cardiac injury, acute respiratory distress syndrome, bronchitis, chemotherapy-induced toxicity, HIV/AIDS, heavy metal toxicity and psychiatric disorders.

SCOPE OF REVIEW

The mechanisms underlying the therapeutic and clinical applications of NAC are complex and still unclear. The present review is focused on the chemistry of NAC and its interactions and functions at the organ, tissue and cellular levels in an attempt to bridge the gap between its recognized biological activities and chemistry.

MAJOR CONCLUSIONS

The antioxidative activity of NAC as of other thiols can be attributed to its fast reactions with OH, NO2, CO3(-) and thiyl radicals as well as to restitution of impaired targets in vital cellular components. NAC reacts relatively slowly with superoxide, hydrogen-peroxide and peroxynitrite, which cast some doubt on the importance of these reactions under physiological conditions. The uniqueness of NAC is most probably due to efficient reduction of disulfide bonds in proteins thus altering their structures and disrupting their ligand bonding, competition with larger reducing molecules in sterically less accessible spaces, and serving as a precursor of cysteine for GSH synthesis.

GENERAL SIGNIFICANCE

The outlined reactions only partially explain the diverse biological effects of NAC, and further studies are required for determining its ability to cross the cell membrane and the blood-brain barrier as well as elucidating its reactions with components of cell signaling pathways.

Blast-induced brain injury and posttraumatic hypotension and hypoxemia

Explosive munitions account for more than 50% of all wounds sustained in military combat, and the proportion of civilian casualties due to explosives is increasing as well. But there has been only limited research on the pathophysiology of blast-induced brain injury, and the contributions of alterations in cerebral blood flow (CBF) or cerebral vascular reactivity to blast-induced brain injury have not been investigated. Although secondary hypotension and hypoxemia are associated with increased mortality and morbidity after closed head injury, the effects of secondary insults on outcome after blast injury are unknown. Hemorrhage accounted for approximately 50% of combat deaths, and the lungs are one of the primary organs damaged by blast overpressure. Thus, it is likely that blast-induced lung injury and/or hemorrhage leads to hypotensive and hypoxemic secondary injury in a significant number of combatants exposed to blast overpressure injury. Although the effects of blast injury on CBF and cerebral vascular reactivity are unknown, blast injury may be associated with impaired cerebral vascular function. Reactive oxygen species (ROS) such as the superoxide anion radical and other ROS, likely major contributors to traumatic cerebral vascular injury, are produced by traumatic brain injury (TBI). Superoxide radicals combine with nitric oxide (NO), another ROS produced by blast injury as well as other types of TBI, to form peroxynitrite, a powerful oxidant that impairs cerebral vascular responses to reduced intravascular pressure and other cerebral vascular responses. While current research suggests that blast injury impairs cerebral vascular compensatory responses, thereby leaving the brain vulnerable to secondary insults, the effects of blast injury on the cerebral vascular reactivity have not been investigated. It is clear that further research is necessary to address these critical concerns.

Inhibitory effect on cerebral inflammatory response following traumatic brain injury in rats: a potential neuroprotective mechanism of N-acetylcysteine

Although N-acetylcysteine (NAC) has been shown to be neuroprotective for traumatic brain injury (TBI), the mechanisms for this beneficial effect are still poorly understood. Cerebral inflammation plays an important role in the pathogenesis of secondary brain injury after TBI. However, it has not been investigated whether NAC modulates TBI-induced cerebral inflammatory response. In this work, we investigated the effect of NAC administration on cortical expressions of nuclear factor kappa B (NF-kappaB) and inflammatory proteins such as interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and intercellular adhesion molecule-1 (ICAM-1) after TBI. As a result, we found that NF-kappaB, proinflammatory cytokines, and ICAM-1 were increased in all injured animals. In animals given NAC post-TBI, NF-kappaB, IL-1beta, TNF-alpha, and ICAM-1 were decreased in comparison to vehicle-treated animals. Measures of IL-6 showed no change after NAC treatment. NAC administration reduced brain edema, BBB permeability, and apoptotic index in the injured brain. The results suggest that post-TBI NAC administration may attenuate inflammatory response in the injured rat brain, and this may be one mechanism by which NAC ameliorates secondary brain damage following TBI.

Neuroprotective Effects of N-acetylcysteine on Experimental Closed Head Trauma in Rats

N-acetylcysteine (NAC) is a precursor of glutathione, a potent antioxidant, and a free radical scavenger. The beneficial effect of NAC on nervous system ischemia and ischemia/reperfusion models has been well documented. However, the effect of NAC on nervous system trauma remains less understood. Therefore, we aimed to investigate the therapeutic efficacy of NAC with an experimental closed head trauma model in rats. Thirty-six adult male Sprague-Dawley rats were randomly divided into three groups of 12 rats each: Group I (control), Group II (trauma-alone), and Group III (trauma+NAC treatment). In Groups II and III, a cranial impact was delivered to the skull from a height of 7 cm at a point just in front of the coronal suture and over the right hemisphere. Rats were sacrificed at 2 h (Subgroups I-A, II-A, and III-A) and 12 h (Subgroups I-B, II-B, and III-B) after the onset of injury. Brain tissues were removed for biochemical and histopathological investigation. The closed head trauma significantly increased tissue malondialdehyde (MDA) levels (P < 0.05), and significantly decreased tissue superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities (P < 0.05), but not tissue catalase (CAT) activity, when compared with controls. The administration of a single dose of NAC (150 mg/kg) 15 min after the trauma has shown protective effect via decreasing significantly the elevated MDA levels (P < 0.05) and also significantly (P < 0.05) increasing the reduced antioxidant enzyme (SOD and GPx) activities, except CAT activity. In the trauma-alone group, the neurons became extensively dark and degenerated into picnotic nuclei. The morphology of neurons in the NAC treatment group was well protected. The number of neurons in the trauma-alone group was significantly less than that of both the control and trauma+NAC treatment groups. In conclusion, the NAC treatment might be beneficial in preventing trauma-induced oxidative brain tissue damage, thus showing potential for clinical implications.

Early, Transient Increase in Complexin I and Complexin II in the Cerebral Cortex following Traumatic Brain Injury Is Attenuated by N-Acetylcysteine

Alteration of excitatory neurotransmission is a key feature of traumatic brain injury (TBI) in which extracellular glutamate levels rise. Although increased synaptic release of glutamate occurs at the injury site, the precise mechanism is unclear. Complexin I and complexin II constitute a family of cytosolic proteins involved in the regulation of neurotransmitter release, competing with the chaperone protein alpha-SNAP (soluble N-ethylmaleimide-sensitive factor-attachment protein) for binding to the synaptic vesicle protein synaptobrevin as well as the synaptic membrane proteins SNAP-25 and syntaxin, which together form the SNAP receptor (SNARE) complex. Complexin I is predominantly a marker of axosomatic (inhibitory) synapses, whereas complexin II mainly labels axodendritic and axospinous synapses, the majority of which are excitatory. In order to examine the role of these proteins in TBI, we have studied levels of both complexins in the injured hemisphere by immunoblotting over a time period ranging from 6 h to 7 days following lateral fluid-percussion brain injury in the rat. Transient increases in the levels of complexin I and complexin II proteins were detected in the injured cerebral cortex 6 h following TBI. This increase was followed by a decrease of complexin I in the injured cortex and hippocampus, and a decrease in both complexins in the injured thalamus region at day 3 and day 7 post-injury. The early, transient increase in the injured cortex was completely blocked by N-acetylcysteine (NAC) administered 5 min following trauma, suggesting an involvement of oxidative stress. Neuronal loss was also reduced in the injured hemisphere with post-TBI NAC treatment. Our findings suggest a dysregulation of both inhibitory and excitatory neurotransmission following traumatic injury that is responsive to antioxidant treatment. These alterations in complexin levels may also play an important role in neuronal cell loss following TBI, and thus contribute to the pathophysiology of cerebral damage following brain injury.

The emerging functions of UCP2 in health, disease, and therapeutics

The uncoupling proteins (UCPs) are attracting an increased interest as potential therapeutic targets in a number of important diseases. UCP2 is expressed in several tissues, but its physiological functions as well as potential therapeutic applications are still unclear. Unlike UCP1, UCP2 does not seem to be important to thermogenesis or weight control, but appears to have an important role in the regulation of production of reactive oxygen species, inhibition of inflammation, and inhibition of cell death. These are central features in, for example, neurodegenerative and cardiovascular disease, and experimental evidence suggests that an increased expression and activity of UCP2 in models of these diseases has a beneficial effect on disease progression, implicating a potential therapeutic role for UCP2. UCP2 has an important role in the pathogenesis of type 2 diabetes by inhibiting insulin secretion in islet beta cells. At the same time, type 2 diabetes is associated with increased risk of cardiovascular disease and atherosclerosis where an increased expression of UCP2 appears to be beneficial. This illustrates that therapeutic applications involving UCP2 likely will have to regulate expression and activity in a tissue-specific manner.

The effect of N-acetylcysteine on posttraumatic changes after controlled cortical impact in rats

OBJECTIVE

The antioxidant potential N-Acetylcysteine (NAC) and its improvement of posttraumatic mitrochondrial dysfunction have been reported. This study investigated the effect of NAC on posttraumatic changes after controlled cortical Impact (CCI) injury.

DESIGN AND SETTING

Prospective randomized controlled animal study.

METHODS

A moderate left focal cortical contusion was induced using CCI. Either NAC (163 mg/kg bw) or physiological saline was administered intraperitoneally immediately and 2 and 4 h after trauma. Blood gases, temperature, mean arterial blood pressure (MABP), and intracranial pressure (ICP) were monitored. Twenty-four hours after trauma brains were removed and either posttraumatic edema was quantified gravimetrically (n=24], or contusion volume was determined morphometrically using slices staining and computerized image analysis (n=24]. Laser Doppler flowmetry was used to assess pericontusional cortical perfusion before trauma, 30 min and 4 and 24 h after trauma (n=14].

MEASUREMENTS AND RESULTS

Physiological parameters remained within normal limits. ICP measurements and water content in traumatized hemispheres did not differ between the groups. Relative contusion volume of the left hemisphere was slightly but nonsignificantly diminished in NAC-treated animals (4.7+/-0.4% vs. 5.9+/-0.5% in controls). In both groups pericontusional perfusion was significantly reduced at 4 h followed by a state of hyperperfusion at 24 h with no differences between the groups.

CONCLUSIONS

Despite previously reported neuroprotective abilities of NAC, no positive effect on posttraumatic perfusion, brain edema formation, or contusion volume after focal brain injury was observed in this study.

N-acetylcysteine attenuates early induction of heme oxygenase-1 following traumatic brain injury

Traumatic brain injury (TBI) results in a cascade of events that includes the production of reactive oxygen species. Heme oxygenase-1 (HO-1) is induced in glial cells following head trauma, suggestive of oxidative stress. We have studied the temporal and spatial effects of the antioxidant N-acetylcysteine (NAC) on HO-1 levels following lateral fluid-percussion injury by immunoblotting and immunohistochemistry. In the injured cerebral cortex, maximal HO-1 induction was seen 6 h post-TBI and was maintained for up to 24 h following the insult, while the ipsilateral hippocampus and thalamus showed marked induction at 24 h postinjury. In all three brain regions, little or no HO-1 immunoreactivity was observed on the contralateral side. Astrocytes exhibited positive immunoreactivity for HO-1 in the injured cerebral cortex, hippocampus, and thalamus, while some neurons and microglia were also immunoreactive in the injured cortex. The administration of NAC 5 min following TBI resulted in a marked reduction in this widespread induction of HO-1, concomitant with a decrease in the volume of injury in all three brain regions. Together, these findings indicate that HO-1 induction is related to both oxidative and injury characteristics of the affected tissue, suggesting that protein expression of this gene is a credible marker of oxidative damage in this model of TBI.

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.

The neurophysiology of brain injury

OBJECTIVE

This article reviews the mechanisms and pathophysiology of traumatic brain injury (TBI).

METHODS

Research on the pathophysiology of diffuse and focal TBI is reviewed with an emphasis on damage that occurs at the cellular level. The mechanisms of injury are discussed in detail including the factors and time course associated with mild to severe diffuse injury as well as the pathophysiology of focal injuries. Examples of electrophysiologic procedures consistent with recent theory and research evidence are presented.

RESULTS

Acceleration/deceleration (A/D) forces rarely cause shearing of nervous tissue, but instead, initiate a pathophysiologic process with a well defined temporal progression. The injury foci are considered to be diffuse trauma to white matter with damage occurring at the superficial layers of the brain, and extending inward as A/D forces increase. Focal injuries result in primary injuries to neurons and the surrounding cerebrovasculature, with secondary damage occurring due to ischemia and a cytotoxic cascade. A subset of electrophysiologic procedures consistent with current TBI research is briefly reviewed.

CONCLUSIONS

The pathophysiology of TBI occurs over time, in a pattern consistent with the physics of injury. The development of electrophysiologic procedures designed to detect specific patterns of change related to TBI may be of most use to the neurophysiologist.

SIGNIFICANCE

This article provides an up-to-date review of the mechanisms and pathophysiology of TBI and attempts to address misconceptions in the existing literature.

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.

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.

Oxidative stress in brain during experimental bacterial meningitis: differential effects of alpha-phenyl-tert-butyl nitrone and N-acetylcysteine treatment

Antioxidant treatment has previously been shown to be neuroprotective in experimental bacterial meningitis. To obtain quantitative evidence for oxidative stress in this disease, we measured the major brain antioxidants ascorbate and reduced glutathione, and the lipid peroxidation endproduct malondialdehyde in the cortex of infant rats infected with Streptococcus pneumoniae. Cortical levels of the two antioxidants were markedly decreased 22 h after infection, when animals were severely ill. Total pyridine nucleotide levels in the cortex were unaltered, suggesting that the loss of the two antioxidants was not due to cell necrosis. Bacterial meningitis was accompanied by a moderate, significant increase in cortical malondialdehyde. While treatment with either of the antioxidants alpha-phenyl-tert-butyl nitrone or N-acetylcysteine significantly inhibited this increase, only the former attenuated the loss of endogenous antioxidants. Cerebrospinal fluid bacterial titer, nitrite and nitrate levels, and myeloperoxidase activity at 18 h after infection were unaffected by antioxidant treatment, suggesting that they acted by mechanisms other than modulation of inflammation. The results demonstrate that bacterial meningitis is accompanied by oxidative stress in the brain parenchyma. Furthermore, increased cortical lipid peroxidation does not appear to be the result of parenchymal oxidative stress, because it was prevented by NAC, which had no effect on the loss of brain antioxidants.

Effects of nimodipine and magnesium sulfate on endogenous antioxidant levels in brain tissue after experimental head trauma

To examine the effects of calcium antagonists nimodipine and magnesium sulfate (MgSO4) on tissue endogenous antioxidant levels, the authors studied superoxide dismutase (SOD) and glutathione peroxidase (GPx) levels in rabbit brain 1 hour after experimental head trauma. Forty New Zealand rabbits were anesthetized and randomly divided into four groups. Group 1 (n = 10) was the sham operated group. Group 2 (n = 10), the control group, received head trauma and no treatment. Group 3 (n = 10) received head trauma and intravenous (IV) 2 microgr/kg nimodipine. Group 4 (n = 10) received head trauma and IV 100 mg/kg MgSO4. Head trauma was delivered by performing a craniectomy over the right hemisphere and dropping a weight of 20 g from a height of 40 cm. In the right (traumatized) hemisphere, SOD and GPx decreased by 57.60% +/- 9.60% and 72.93% +/- 5.51% respectively from sham values. Magnesium sulfate, but not nimodipine, reduced the magnitude of decrease of SOD and GPx to 19.43% +/- 7.15% and 39.01% +/- 7.92% respectively from sham values. In the left (nontraumatized) hemisphere, MgSO4 increased SOD to 42.43% +/- 24.76% above sham values. The authors conclude that MgSO4 treatment inhibited the decrease in SOD and GPx levels in experimental brain injury.

Therapeutic potential of N-acetylcysteine in age-related mitochondrial neurodegenerative diseases

Increasing lines of evidence suggest a key role for mitochondrial damage in neurodegenerative diseases. Brain aging, Parkinson's disease, Alzheimer's disease, Huntington's disease and Friedreich's ataxia have been associated with several mitochondrial alterations including impaired oxidative phosphorylation. Mitochondrial impairment can decrease cellular bioenergetic capacity, which will then increase the generation of reactive oxygen species resulting in oxidative damage and programmed cell death. This paper reviews the mechanisms of N-acetylcysteine action at the cellular level, and the possible usefulness of this antioxidant for the treatment of age-associated neurodegenerative diseases. First, this thiol can act as a precursor for glutathione synthesis as well as a stimulator of the cytosolic enzymes involved in glutathione regeneration. Second, N-acetylcysteine can act by direct reaction between its reducing thiol group and reactive oxygen species. Third, it has been shown that N-acetylcysteine can prevent programmed cell death in cultured neuronal cells. And finally, N-acetylcysteine also increases mitochondrial complex I and IV specific activities both in vitro and in vivo in synaptic mitochondrial preparations from aged mice. In view of the above, and because of the ease of its administration and lack of toxicity in humans, the potential usefulness of N-acetylcysteine in the treatment of age-associated mitochondrial neurodegenerative diseases deserves investigation.

Alterations in cerebral energy metabolism induced by traumatic brain injury

Energy metabolism of the brain is unique, possessing high aerobic metabolism with no significant capacity for anaerobic glycolysis and limited tissue stores of glucose. A steady supply of oxygen and glucose is essential in order to maintain cerebral function and integrity. Extensive research in experimental and human head injury has been conducted regarding the delivery of oxygen and outcome. This research has provided evidence which indicates that in addition to the availability of oxygen and glucose, other factors, such as perturbation of mitochondrial energy transducing processes which also follow head trauma, play significant roles. In this paper, the salient findings from biochemical studies of experimental and clinical brain injury are summarized and indicate that the mitochondrial respiratory chain-linked oxidative phosphorylation and calcium transport are compromised by trauma-induced brain injury and support the idea that oxidative stress and perturbation of cellular calcium homeostasis play significant roles in traumatic brain injury.

L-arginine partially restores the diminished CO2 reactivity after mild controlled cortical impact injury in the adult rat

Using an open cranial window technique, the authors investigated the mechanisms associated with the suppressed CO2 reactivity after mild controlled cortical impact (CCI) injury in rats. The dilation of arterioles (n = 7) to hypercapnia before injury was 38 +/- 12%, which was significantly reduced both at 1 hour (23 +/- 15% dilation) and at 2 hours after injury (11 +/- 19% dilation). In the presence of L-arginine (10 mmol/L topical suffusion, 300 mg/kg intravenous infusion), the dilation of pial arterioles (n = 6) to hypercapnia was partially restored to 30 +/- 6% at 2 hours after injury. In the presence of the nitric oxide (NO) donor, S-nitroso-N-acetylpenicillamine (SNAP) (10(-8) mol/L topical suffusion), the dilation of pial arterioles (n = 5) to hypercapnia remained diminished (5 +/- 7%) at 2 hours after injury. The dilation of pial arterioles (n = 4) to hypercapnia also remained suppressed (5 +/- 6%) with topical suffusion of the free radical scavengers, polyethylene glycol-superoxide dismutase (60 units/mL) and polyethylene glycol-catalase (40 units/mL). The authors have shown that L-arginine at least partially restores the diminished response to hypercapnia after mild CCI injury. Furthermore, these data suggest that the beneficial effects of L-arginine are mediated by a combination of providing substrate for NO synthase and scavenging free radicals.

In-vivo glutathione elevation protects against hydroxyl free radical-induced protein oxidation in rat brain

Glutathione deficiency has been associated with a number of neurodegenerative diseases including Lou Gehrig's disease, Parkinson's disease, and HIV. A crucial role for glutathione is as a free radical scavenger. Alzheimer's disease (AD) brain is characterized by oxidative stress, manifested by protein oxidation, lipid oxidation, oxidized glutathione, and decreased activity of glutathione S-transferase, among others. Reasoning that elevated levels of endogenous glutathione would offer protection against free radical-induced oxidative stress, rodents were given in vivo injections of N-acetylcysteine (NAC), a known precursor of glutathione, to study the vulnerability of isolated synaptosomal membranes treated with Fe2+/H2O2, a known hydroxyl free radical producer. Protein carbonyls, a marker of protein oxidation, were measured. NAC significantly increased endogenous glutathione levels in cortical synaptosome cytosol (P < 0.01). As reported previously, protein carbonyl levels of the Fe2+/H2O2-treated synaptosomes were significantly higher compared to that of non-treated controls (P < 0.01), consistent with increased oxidative stress. In contrast, protein carbonyl levels in Fe2+/H2O2-treated synaptosomes isolated from NAC-injected animals were not significantly different from saline-injected non-treated controls, demonstrating protection against hydroxyl radical induced oxidative stress. These results are consistent with the notion that methods to increase endogenous glutathione levels in neurodegenerative diseases associated with oxidative stress, including AD, may be promising.

Effect of N-acetylcysteine on mitochondrial function following traumatic brain injury in rats

Efficacy of N-acetylcysteine (NAC) in traumatic brain injury (TBI)-induced mitochondrial dysfunction was evaluated following controlled cortical impact injury in rats. Respiratory function and calcium transport of rat forebrain mitochondria from injured and uninjured hemispheres were examined. NAC significantly restored mitochondrial electron transfer, energy coupling capacity, calcium uptake activity and reduced calcium content absorbed to brain mitochondrial membranes when examined 12 h post-TBI if NAC was administered i.p. 5 min before injury or 30 min or 1 h postinjury. Glutathione (reduced form, GSH) levels in brain tissues were decreased at all time points examined over a 14-day observation period, while mitochondrial GSH levels significantly decreased only at 3 days and 14 days following TBI. NAC treatment given within 1 h greatly restored brain GSH levels from 1 h to 14 days and mitochondrial GSH levels from 12 h to 14 days post-TBI. NAC did not show protective effects when given 2 h postinjury. Our data indicate that NAC administered postinjury at an early stage can effectively restore TBI-induced mitochondrial dysfunction and the protective effect of NAC may be related to its restoration of GSH levels in the brain.

Amyloid beta but not bradykinin induces phosphatidylcholine hydrolysis in immortalized rat brain endothelial cells

We describe the inhibitory effect of A beta (25-35) fragment of amyloid-beta peptide and bradykinin (BK) on phosphatidylcholine (PtdCho) metabolism in immortalized rat brain GP8.39 endothelial cells (EC). Cultures were incubated either with A beta for 24-48 h, or with BK for 30 min-4 h. The peroxidation indices (malondialdehyde, conjugated dienes) and lactate dehydrogenase (LDH) release significantly increased after A beta peptide (10-50 microM) treatment. The BK (10 microM) stimulation of cells brought about an increase in conjugated dienes and LDH release only after 4 h. Following 24 h treatment with 50 microM A beta peptide, the [Me-3H]choline incorporation into PtdCho strongly decreased while the [3H]choline release increased, indicating PtdCho hydrolysis. The effect was most likely due to peptide prooxidant effect. After 4 h preincubation with BK, the [Me-3H]choline incorporation into PtdCho strongly decreased, but no significant [3H]choline release was found. Following long-term treatment, the action of 50 microM A beta on [3H]choline release was not enhanced by 10 microM BK. Cell exposure to alpha-tocopherol (1 mM) prior to the addition of both agents did not abolish stimulated PtdCho breakdown. The data suggest that: (a) A beta peptide and BK may modulate phospholipid turnover in microvessel cells; (b) they could not synergistically interact in vascular EC damage during processes involving amyloid accumulation and inflammatory response.

Hypothesis: can N-acetylcysteine be beneficial in Parkinson's disease?

Based on the finding of decreased mitochondrial complex I activity in the substantia nigra of patients with Parkinson's disease, we propose that the consequent reduction of ATP synthesis and increased generation of reactive oxygen species may be a possible cause of nigrostriatal cell death. Since sulfhydryl groups are essential in oxidative phosphorylation, thiolic antioxidants may contribute to the preservation of these proteins against oxidative damage. In the present paper, we hypothesize that treatment with a sulfur-containing antioxidant such as N-acetylcysteine may provide a new neuroprotective therapeutic strategy for Parkinson's disease.

The consequences of traumatic brain injury on cerebral blood flow and autoregulation: a review

In this decade, the brain argueably stands as one of the most exciting and challenging organs to study. Exciting in as far as that it remains an area of research vastly unknown and challenging due to the very nature of its anatomical design: the skull provides a formidable barrier and direct observations of intraparenchymal function in vivo are impractical. Moreover, traumatic brain injury (TBI) brings with it added complexities and nuances. The development of irreversible damage following TBI involves a plethora of biochemical events, including impairment of the cerebral vasculature, which render the brain at risk to secondary insults such as ischemia and intracranial hypertension. The present review will focus on alterations in the cerebrovasculature following TBI, and more specifically on changes in cerebral blood flow (CBF), mediators of CBF including local chemical mediators such as K+, pH and adenosine, endothelial mediators such as nitric oxide and neurogenic mediators such as catecholamines, as well as pressure autoregulation. It is emphasized that further research into these mechanisms may help attenuate the prevalence of secondary insults and therefore improve outcome following TBI.

The 21-aminosteroid U-74389G reduces cerebral superoxide anion concentration following fluid percussion injury of the brain

We examined the effects of the 21-aminosteroid antioxidant U-74389G (16-desmethyl-tirilazad) on the concentration of extracellular superoxide anion following fluid percussion traumatic brain injury (TBI) measured by a cytochrome c-coated electrode and on local cerebral perfusion (CBFld) measured by laser Doppler flowmetry (LDF). U-74389G in a dose of 3 mg/kg reduced superoxide anion concentrations 60 min after TBI significantly but had no significant effect on CBFld. These results indicate that reduction of CBF after TBI can be dissociated from superoxide anion production. Persistent ischemia may limit neuroprotection efficacy and may contribute to divergent outcome results in clinical and animal trials using agents to modify reactive oxygen species.

N-acetylcysteine protects against age-related increase in oxidized proteins in mouse synaptic mitochondria

Since it has been proposed that oxidized protein accumulation plays a critical role in brain aging, we have investigated the effect of a thiolic antioxidant on protein carbonyl content in synaptic mitochondria from female OF-1 mice. At 48 weeks of age, a control group was fed standard food pellets and another group received pellets containing 0.3% (w/w) of N-acetylcysteine. A 24-week treatment resulted in a significant decrease in protein carbonyl content in synaptic mitochondria of the N-acetylcysteine-treated animals as compared to age-matched controls.

Isoprostanes: free radical-generated prostaglandins with constrictor effects on cerebral arterioles

BACKGROUND AND PURPOSE

Isoprostanes are generated by cyclooxygenase-independent free radical attack of arachidonic acid and are potent constrictors of the peripheral vasculature. Traumatic brain injury stimulates oxygen radical production and is associated with cerebral blood flow reduction. However, no specific vasoconstrictor has been identified as the cause of posttraumatic blood flow reduction. The purpose of this study was to determine whether isoprostanes constrict cerebral arterioles.

METHODS

The effects of 10(-9) to 10(-5) mol/L 8-iso-prostaglandin F2 alpha (8-iso-PGF2 alpha), 8-iso-prostaglandin E2 (8-iso-PGE2), and prostaglandin F2 alpha (PGF2 alpha) on pial arteriolar diameter were measured in anesthetized rats using a closed cranial window and in vivo microscopy.

RESULTS

All prostanoids produced vasoconstriction. Of these, 8-iso-PGF2 alpha produced the greatest vasoconstriction (34% +/- 2), followed by 8-iso-PGE2 (25% +/- 4) and PGF2 alpha (20% +/- 2). After six cerebrospinal fluid washouts of the cranial window, both 8-iso-PGF2 alpha- and 8-iso-PGE2-treated vessels remained slightly constricted, whereas the PGF2 alpha-treated vessels returned to control diameter. Coapplication of the semiselective thromboxane A2/prostaglandin H2 receptor antagonist SQ29548 completely blocked the vasoconstriction induced by 8-iso-PGF2 alpha and 8-iso-PGE2.

CONCLUSIONS

Isoprostanes are potent constrictors of cerebral arterioles and appear to act at a receptor that is similar to the thromboxane A2/prostaglandin H2 receptor. Isoprostanes may play a role in the reduction of cerebral blood flow that occurs after brain injury and subsequent oxygen radical production.

Secondary insults increase injury after controlled cortical impact in rats

Secondary ischemic insults are common after severe head injury and contribute to poor neurological outcome. To study the increased vulnerability of the traumatized brain to secondary insults, bilateral carotid occlusion was produced after a controlled cortical impact injury in rats. The injury produced by either the impact injury or the bilateral carotid occlusion was mild to moderate when studied individually. The 1 and 3 m/sec impact injuries alone caused no detectable contusion at the impact side and minimal neuronal loss in the hippocampus. The 5 m/sec impact injury alone resulted in a small contusion with a median volume of 5.4 mm3. The 40-min period of bilateral carotid occlusion alone caused no cortical injury and no neuronal loss in the CA1 region of the hippocampus. When the 40 min of bilateral carotid occlusion was produced 1 h after the impact injury, there was an increase in the damage produced. The contusion volume was significantly larger after the 3 and 5 m/sec impact injuries and the hippocampal neuronal loss was significantly greater after the 1 and 3 m/sec impact injuries. When varying durations of bilateral carotid occlusion were produced 1 h after a 3 m/sec impact injury, contusion volume was significantly larger after bilateral carotid occlusion duration of 40 min, and CA1 neuronal loss was significantly greater after bilateral carotid occlusion durations of 30 and 40 min. When 40 min of bilateral carotid occlusion was produced at different time intervals after a 3 m/sec injury, the increased contusion volume was maximal when bilateral carotid occlusion occurred at 4 h after the impact injury, and the increased neuronal loss in the CA3 region of the hippocampus was maximal when bilateral carotid occlusion occurred at 1 h after the impact injury. By 24 h after the impact injury, 40 min of bilateral carotid occlusion had minimal consequences, similar to the effect in sham-injured animals. These results mimic the clinical situation where secondary insults of a severity that would not cause permanent neurological damage in a normal person are associated with a marked worsening of neurological outcome after head injury and where the injured brain is most susceptible to secondary insults in the first few hours after injury.

Reduction of traumatic brain injury-induced cerebral oedema by a free radical scavenger

Oxygen derived free radicals have been proposed to be in part responsible for the cerebral oedema resulting from head injury. In the present study the effects of free radical suppression with MDL 74,180 (2,3-dihydro-2,2,4,6,7-pentamethyl-3-(4-methylpiperazino)-methyl-1 - benzofuran-5-ol dihydrochloride), an alpha-tocopherol analogue free radical scavenger, on the development of cerebral oedema resulting from head injury has been assessed. Fluid percussion head injury in rats caused a regional oedema 48 h after injury. Infusion of MDL 74,180 for 2 h after the injury significantly attenuated oedema development in a dose-related manner. Using magnetic resonance imaging, cerebral oedema development was monitored in head injured mice. Oedema was apparent 4 h after head injury and was greatest in the vicinity of the olfactory bulb and surrounding the ventricles. Treatment with MDL 74,180 (1-10 micrograms/kg intravenously, administered 3-5 min after the injury) significantly reduced the oedema development. MDL 74,180 is a potential treatment for the oedema caused as a result of head injury.

Susceptibility of the injured rat brain to CNS oxygen toxicity

The possibility of an altered susceptibility of the injured brain to central nervous system (CNS) oxygen toxicity was examined in awake rats. Moderate to severe closed head injury with diffuse axonal damage was produced in anesthetized rats by the fluid percussion method (2-2.5 atm), after which chronic EEG electrodes were implanted. Twenty-four hours later, the rats were exposed to 5 atm abs (506.5 kPa) oxygen and the time to appearance of paroxysmal EEG patterns was noted. The difference between the 19 minute median latency of this group and 16 minute of a control group which underwent a sham operation did not reach statistical significance. Some injured animals convulsed with minimal or no EEG changes. The clinical implication could be that brain injured patients are not at higher risk of CNS oxygen toxicity but the EEG alterations that could potentially be used to forecast incipient convulsions, or be the indication of actual convulsions in the intact brain of a paralyzed patient, may not always be present.

Superoxide dismutase improves posttraumatic cortical blood flow in rats

Oxygen free radicals, such as the superoxide anion, are known to mediate damage to the cerebral microcirculation following traumatic brain injury. The purpose of this study was to determine if superoxide dismutase (SOD), a scavenger of superoxide anion, could alter posttraumatic cortical blood flow. Following barbiturate anesthesia, rats were surgically prepared for moderate fluid percussion brain injury. Cortical blood flow contralateral to the site of injury was measured using laser-Doppler flowmetry. Laser-Doppler flowmetry assesses flow by measuring cell volume and velocity, which are multiplied electronically to give flow. Starting 10 min before injury, animals received either superoxide dismutase (24,000 U/kg bolus, followed by continuous infusion of 1600 U/kg/min) or an equal volume of saline. Blood pressure, heart rate, and cortical blood flow were measured up to 1 h posttrauma. Rats receiving superoxide dismutase had significantly higher cortical blood flow posttrauma (F = 6.91, p < 0.02). One hour posttrauma, the blood flow in SOD-treated rats was 89 +/- 8% of preinjury baseline, whereas this value was only 66 +/- 6% of control in saline-treated rats. SOD caused not only greater blood velocity but also less reduction in cortical blood volume after injury. There were no significant differences between the groups with respect to blood pressure or heart rate. This study further supports the role of oxygen radical-mediated cerebrovascular dysfunction following traumatic brain injury and is the first to show the beneficial effect of SOD on cortical blood flow following fluid percussion brain injury.

The effect of acute cocaine or lidocaine on behavioral function following fluid percussion brain injury in rats

One of the goals of our laboratory is to examine how the presence of drugs of abuse will influence traumatic brain injury. Previous studies in our laboratory have shown that cocaine or lidocaine treatment before experimental fluid percussion brain injury in rats reduces the cortical hypoperfusion normally found in the early posttraumatic period. The purpose of the current study was to determine if pretreatment with cocaine or lidocaine is also associated with changes in trauma-induced suppression of reflexes and motor and cognitive dysfunction that occurs following traumatic brain injury (TBI). Twenty-four hours after surgical preparation, rats were randomly assigned to a saline or drug pretreatment group, cocaine (0.5, 2, or 5 mg/kg) or lidocaine (2 mg/kg), which was injected via the tail vein. None of the drug pretreatments worsened injury. Lidocaine and cocaine decreased the duration of suppression of some neurological reflexes and reduced posttraumatic body weight losses. Lidocaine and cocaine both decreased postinjury motor deficits. Lidocaine and cocaine did not affect cognitive function on days 11-15 postinjury. The mechanism by which lidocaine improves acute neurological and motor function following brain injury is unknown, but may involve improved posttraumatic cortical blood flow, as seen in our previous study. Our results, along with other studies showing lidocaine to be neuroprotective in animal models of ischemia, suggest that studies of the effect of posttraumatic administration of lidocaine are warranted.

N-acetylcysteine enhances hippocampal neuronal survival after transient forebrain ischemia in rats

BACKGROUND AND PURPOSE

Free radical scavengers enhance neuronal survival in some models of transient forebrain ischemia. Recent experiments have suggested that N-acetylcysteine prevents cellular injury after a reperfusion injury. No information is available regarding the neuroprotective potential of the free radical scavenger N-acetylcysteine after transient forebrain ischemia. In this study we evaluated the potential of N-acetylcysteine to improve hippocampal neuronal survival after transient forebrain ischemia in the rat.

METHODS

In series A and B, ventilated, paralyzed, normothermic rats had 10 minutes of transient forebrain ischemia induced by bilateral carotid occlusion with hypotension induced by blood withdrawal (mean arterial blood pressure, 45 mm Hg). In series A, animals were administered N-acetylcysteine (163 mg/kg) 30 minutes and 5 minutes before transient forebrain ischemia. In series B, N-acetylcysteine (326 mg/kg) was administered 15 minutes after transient forebrain ischemia. In series C, N-acetylcysteine (326 mg/kg) was administered 15 minutes after transient forebrain ischemia in animals with a mean arterial blood pressure of 30 mm Hg during transient forebrain ischemia. All series had normal control, sham, and vehicle treatment groups. In all series, the rats were allowed to recover and were killed at 7 days after ischemia. The effect of forebrain ischemia was assessed by evaluating the number of viable neurons at bregma sections -3.3, -3.8, and -4.3 of the CA1 region of the hippocampus.

RESULTS

The results demonstrated no physiological difference among the various treatment groups. There were no differences in the number of viable neurons between the transient forebrain ischemia with no treatment group and the vehicle (saline)-treated transient forebrain ischemic groups. Animals pretreated with N-acetylcysteine (mean number of neurons, 84 +/- 6) had a significant increase (P < .05) in neuronal survival compared with vehicle-treated animals (mean number of neurons, 43 +/- 4). Animals posttreated with N-acetylcysteine (mean number of neurons, 89 +/- 9) had a significant increase in neuronal survival compared with vehicle-treated animals (mean number of neurons, 7 +/- 1). However, N-acetylcysteine protection was only partial at 45 mm Hg and did not improve neuronal survival (mean number of neurons, 22 +/- 3) in animals with a more severe ischemic insult (mean arterial blood pressure, 30 mm Hg during transient forebrain ischemia) compared with vehicle-treated animals (mean number of neurons, 10 +/- 1).

CONCLUSIONS

N-Acetylcysteine partially improved neuronal survival when administered before or after ischemia following transient cerebral ischemia (mean arterial blood pressure, 45 mm Hg) but not with a more severe ischemic insult of 10 minutes of transient cerebral ischemia with a mean arterial blood pressure of 30 mm Hg.

Continuous monitoring of posttraumatic cerebral blood flow using laser-Doppler flowmetry

Traumatic brain injury causes alterations in cerebral blood flow that are thought to influence secondary pathophysiology and neurologic outcome in humans. Since it is difficult to study early changes in blood flow in head-injured patients, animal models of brain injury must be employed. However, techniques to monitor brain blood flow in animals are labor intensive and generally provide discontinuous flow measurements. The present study examines the application of laser-Doppler flowmetry for measurement of cerebral blood flow following experimental brain injury. This method allows continuous monitoring of local cerebral blood flow before, during, and after injury. Rats (n = 9) were prepared for lateral fluid percussion injury under barbiturate anesthesia. Injury (2.10 +/- 0.02 atm) was induced over the right parietal cortex, and blood flow was monitored in the contralateral cortex. Seconds after the peak hypertension after injury, blood flow in the left parietal cortex increased 226% +/- 18% (means +/- SEM). This increase was transient, with blood flow falling below control values within minutes. Five minutes after injury, blood flow was 83% +/- 8% of control, and at 1 h, this value had fallen to 56% +/- 6%. Blood flow at 60 min was 93% +/- 5% of control in the sham-injured group (n = 10). The reduction in cerebral blood flow in our laser-Doppler study was of similar magnitude as previously reported in rats injured at a similar intensity when blood flow was examined with radiolabeled microspheres. Given these results, we believe laser-Doppler flowmetry can be used to continuously monitor posttraumatic blood flow following experimental brain injury.