Structural and Functional Damage Sustained by Mitochondria After Traumatic Brain Injury in the Rat: Evidence for Differentially Sensitive Populations in the Cortex and Hippocampus:

Synaptic Mitochondria Sustain More Damage than Non-Synaptic Mitochondria after Traumatic Brain Injury and Are Protected by Cyclosporine A

Currently, there are no Food and Drug Administration (FDA)-approved pharmacotherapies for the treatment of those with traumatic brain injury (TBI). As central mediators of the secondary injury cascade, mitochondria are promising therapeutic targets for prevention of cellular death and dysfunction after TBI. One of the most promising and extensively studied mitochondrial targeted TBI therapies is inhibition of the mitochondrial permeability transition pore (mPTP) by the FDA-approved drug, cyclosporine A (CsA). A number of studies have evaluated the effects of CsA on total brain mitochondria after TBI; however, no study has investigated the effects of CsA on isolated synaptic and non-synaptic mitochondria. Synaptic mitochondria are considered essential for proper neurotransmission and synaptic plasticity, and their dysfunction has been implicated in neurodegeneration. Synaptic and non-synaptic mitochondria have heterogeneous characteristics, but their heterogeneity can be masked in total mitochondrial (synaptic and non-synaptic) preparations. Therefore, it is essential that mitochondria targeted pharmacotherapies, such as CsA, be evaluated in both populations. This is the first study to examine the effects of CsA on isolated synaptic and non-synaptic mitochondria after experimental TBI. We conclude that synaptic mitochondria sustain more damage than non-synaptic mitochondria 24 h after severe controlled cortical impact injury (CCI), and that intraperitoneal administration of CsA (20 mg/kg) 15 min after injury improves synaptic and non-synaptic respiration, with a significant improvement being seen in the more severely impaired synaptic population. As such, CsA remains a promising neuroprotective candidate for the treatment of those with TBI.

Striatal Mitochondrial Disruption following Severe Traumatic Brain Injury

Traumatic brain injury (TBI) results in oxidative stress and calcium dysregulation in mitochondria. However, little work has examined perturbations of mitochondrial homeostasis in peri-injury tissue. We examined mitochondrial homeostasis after a unilateral controlled cortical impact over the sensorimotor cortex in adult male rats. There was a significant reduction in peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) messenger RNA (mRNA) at post-injury days 3 and 6 and a transient reduction in mitochondrial DNA copy number at 3 days post-injury that recovered by 6 days in the ipsi-injury striatum. In ipsilateral cortex, PGC-1α mRNA was reduced only at 6 days post-injury. Additionally, expression of mitochondrial-encoded mRNAs, cytochrome c oxidase subunit 1 and NADH dehydrogenase subunit 1, was decreased at 3 and 6 days post-injury in ipsilesional striatum and at 6 days post-injury in ipsilesional cortex. There was no observable decrease in nuclear-encoded mRNAs mitochondrial transcription factor A or NADH dehydrogenase (ubiquinone) Fe-S protein 1. We detected an acute increase in superoxide dismutase 2 mRNA expression, as well as an induction of microRNA (miR)-21 and miR-155, which have been previously demonstrated to disrupt mitochondrial homeostasis. Behaviorally, rats with TBI exhibited marked error rates in contrainjury forelimb performance on the ladder test. These findings reveal that there may be differential susceptibilities of various peri-injury brain structures to mitochondrial dysfunction and associated behavioral deficits, and that molecular pathways demonstrated to interfere with mitochondrial homeostasis and function are activated subacutely post-TBI.

Altered Mitochondrial Dynamics and TBI Pathophysiology

Mitochondrial function is intimately linked to cellular survival, growth, and death. Mitochondria not only generate ATP from oxidative phosphorylation, but also mediate intracellular calcium buffering, generation of reactive oxygen species (ROS), and apoptosis. Electron leakage from the electron transport chain, especially from damaged or depolarized mitochondria, can generate excess free radicals that damage cellular proteins, DNA, and lipids. Furthermore, mitochondrial damage releases pro-apoptotic factors to initiate cell death. Previous studies have reported that traumatic brain injury (TBI) reduces mitochondrial respiration, enhances production of ROS, and triggers apoptotic cell death, suggesting a prominent role of mitochondria in TBI pathophysiology. Mitochondria maintain cellular energy homeostasis and health via balanced processes of fusion and fission, continuously dividing and fusing to form an interconnected network throughout the cell. An imbalance of these processes, particularly an excess of fission, can be detrimental to mitochondrial function, causing decreased respiration, ROS production, and apoptosis. Mitochondrial fission is regulated by the cytosolic GTPase, dynamin-related protein 1 (Drp1), which translocates to the mitochondrial outer membrane (MOM) to initiate fission. Aberrant Drp1 activity has been linked to excessive mitochondrial fission and neurodegeneration. Measurement of Drp1 levels in purified hippocampal mitochondria showed an increase in TBI animals as compared to sham controls. Analysis of cryo-electron micrographs of these mitochondria also showed that TBI caused an initial increase in the length of hippocampal mitochondria at 24 h post-injury, followed by a significant decrease in length at 72 h. Post-TBI administration of Mitochondrial division inhibitor-1 (Mdivi-1), a pharmacological inhibitor of Drp1, prevented this decrease in mitochondria length. Mdivi-1 treatment also reduced the loss of newborn neurons in the hippocampus and improved novel object recognition (NOR) memory and context-specific fear memory. Taken together, our results show that TBI increases mitochondrial fission and that inhibition of fission improves hippocampal-dependent learning and memory, suggesting that strategies to reduce fission may have translational value after injury.

S100B and Glial Fibrillary Acidic Protein as Indexes to Monitor Damage Severity in an In Vitro Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is a leading and rising cause of death and disability worldwide. There is great interest in S100B and Glial Fibrillary Acid Protein (GFAP) as candidate biomarkers of TBI for diagnosis, triage, prognostication and drug development. However, conflicting results especially on S100B hamper their routine application in clinical practice. To try to address this question, we mimicked TBI damage utilizing a well-validated, simplified in vitro model of graded stretch injury induced in rat organotypic hippocampal slice cultures (OHSC). Different severities of trauma, from mild to severe, have been tested by using an equi-biaxial stretch of the OHSCs at a specified Lagrangian strain of 0 (controls), 5, 10, 20 and 50 %. OHSC were analysed at 3, 6, 18, 24, 48 and 96 h post-injury. Cell death, gene expressions and release into the culture medium of S100B and GFAP were determined at each time point. Gene expression and release of S100B slightly increased only in 20 and 50 % stretched OHSC. GFAP over-expression occurred in 10, 20 and 50 % and was inversely correlated with time post-injury. GFAP release significantly increased with time at any level of injury (p < 0.01 with respect to controls). Consequently, the total amount of GFAP released showed a strong linear relationship with the severity of injury (R(2) = 0.7662; p < 0.001). Under these experimental conditions, S100B seems to be useful in diagnosing only moderate to severe TBI-like injuries. Differently, GFAP demonstrates adequate biomarker requisites since its cellular release is affected by all grades of injury severity.

Cerebral glucose metabolism in an immature rat model of pediatric traumatic brain injury

Altered cerebral metabolism and mitochondrial function have been identified in experimental and clinical studies of pediatric traumatic brain injury (TBI). Metabolic changes detected using (1)H (proton) magnetic resonance spectroscopy correlate with long-term outcomes in children after severe TBI. We previously identified early (4-h) and sustained (24-h and 7-day) abnormalities in brain metabolites after controlled cortical impact (CCI) in immature rats. The current study aimed to identify specific alterations of cerebral glucose metabolism at 24 h after TBI in immature rats. Rats (postnatal days 16-18) underwent CCI to the left parietal cortex. Sham rats underwent craniotomy only. Twenty-four hours after CCI, rats were injected (intraperitoneally) with [1,6-(13)C]glucose. Brains were removed, separated into hemispheres, and frozen. Metabolites were extracted with perchloric acid and analyzed using (1)H and (13)C-nuclear magnetic resonance spectroscopy. TBI resulted in decreases in N-acetylaspartate in both hemispheres, compared to sham contralateral. At 24 h after TBI, there was significant decrease in the incorporation of (13)C label into [3-(13)C]glutamate and [2-(13)C]glutamate in the injured brain. There were no differences in percent enrichment of [3-(13)C]glutamate, [4-(13)C]glutamate, [3-(13)C]glutamine, or [4-(13)C]glutamine. There was significantly lower percent enrichment of [2-(13)C]glutamate in both TBI sides and the sham craniotomy side, compared to sham contralateral. No differences were detected in enrichment of (13)C glucose label in [2-(13)C]glutamine, [2-(13)C]GABA (gamma-aminobutyric acid), [3-(13)C]GABA, or [4-(13)C]GABA, [3-(13)C]lactate, or [3-(13)C]alanine between groups. Results suggest that overall oxidative glucose metabolism in the immature brain recovers at 24 h after TBI. Specific reductions in [2-(13)C]glutamate could be the result of impairments in either neuronal or astrocytic metabolism. Future studies should aim to identify pathways leading to decreased metabolism and develop cell-selective "metabolic rescue."

Neuroprotection by genipin against reactive oxygen and reactive nitrogen species-mediated injury in organotypic hippocampal slice cultures

Genipin, the multipotent ingredient in Gardenia jasmenoides fruit extract (GFE), may be an effective candidate for treatment following stroke or traumatic brain injury (TBI). Secondary injury includes damage mediated by reactive oxygen species (ROS) and reactive nitrogen species (RNS), which can alter the biological function of key cellular structures and eventually lead to cell death. In this work, we studied the neuroprotective potential of genipin against damage stemming from ROS and RNS production in organotypic hippocampal slice cultures (OHSC), as well as its potential as a direct free radical scavenger. A 50 µM dose of genipin provided significant protection against tert-butyl hydroperoxide (tBHP), a damaging organic peroxide. This dosage of genipin significantly reduced cell death at 48 h compared to vehicle control (0.1% DMSO) when administered 0, 1, 6, and 24 h after addition of tBHP. Similarly, genipin significantly reduced cell death at 48 h when administered 0, 1, 2, and 6h after addition of rotenone, which generates reactive oxygen species via a more physiologically relevant mechanism. Furthermore, genipin significantly reduced both cell death and nitrite levels at 24 h caused by S-nitroso-N-acetylpenicillamine (SNAP), a direct nitric oxide (NO) donor, and successfully quenched 1,1-Diphenyl-2-picryl-hydrazyl (DPPH), a stable free radical, suggesting that genipin may act as a direct free radical scavenger. Our encouraging findings suggest that genipin should be tested in animal models of CNS injury with a significant component of ROS- and RNS-mediated damage, such as TBI and stroke, to assess its in vivo efficacy.

Mitochondrial polymorphisms impact outcomes after severe traumatic brain injury

Patient outcomes are variable following severe traumatic brain injury (TBI); however, the biological underpinnings explaining this variability are unclear. Mitochondrial dysfunction after TBI is well documented, particularly in animal studies. The aim of this study was to investigate the role of mitochondrial polymorphisms on mitochondrial function and patient outcomes out to 1 year after a severe TBI in a human adult population. The Human MitoChip V2.0 was used to evaluate mitochondrial variants in an initial set of n=136 subjects. SNPs found to be significantly associated with patient outcomes [Glasgow Outcome Scale (GOS), Neurobehavioral Rating Scale (NRS), Disability Rating Scale (DRS), in-hospital mortality, and hospital length of stay] or neurochemical level (lactate:pyruvate ratio from cerebrospinal fluid) were further evaluated in an expanded sample of n=336 subjects. A10398G was associated with DRS at 6 and 12 months (p=0.02) and a significant time by SNP interaction for DRS was found (p=0.0013). The A10398 allele was associated with greater disability over time. There was a T195C by sex interaction for GOS (p=0.03) with the T195 allele associated with poorer outcomes in females. This is consistent with our findings that the T195 allele was associated with mitochondrial dysfunction (p=0.01), but only in females. This is the first study associating mitochondrial DNA variation with both mitochondrial function and neurobehavioral outcomes after TBI in humans. Our findings indicate that mitochondrial DNA variation may impact patient outcomes after a TBI potentially by influencing mitochondrial function, and that sex of the patient may be important in evaluating these associations in future studies.

Cellular alterations in human traumatic brain injury: changes in mitochondrial morphology reflect regional levels of injury severity

Mitochondrial dysfunction may be central to the pathophysiology of traumatic brain injury (TBI) and often can be recognized cytologically by changes in mitochondrial ultrastructure. This study is the first to broadly characterize and quantify mitochondrial morphologic alterations in surgically resected human TBI tissues from three contiguous cortical injury zones. These zones were designated as injury center (Near), periphery (Far), and Penumbra. Tissues from 22 patients with TBI with varying degrees of damage and time intervals from TBI to surgical tissue collection within the first week post-injury were rapidly fixed in the surgical suite and processed for electron microscopy. A large number of mitochondrial structural patterns were identified and divided into four survival categories: normal, normal reactive, reactive degenerating, and end-stage degenerating profiles. A tissue sample acquired at 38 hours post-injury was selected for detailed mitochondrial quantification, because it best exhibited the wide variation in cellular and mitochondrial changes consistently noted in all the other cases. The distribution of mitochondrial morphologic phenotypes varied significantly between the three injury zones and when compared with control cortical tissue obtained from an epilepsy lobectomy. This study is unique in its comparative quantification of the mitochondrial ultrastructural alterations at progressive distances from the center of injury in surviving TBI patients and in relation to control human cortex. These quantitative observations may be useful in guiding the translation of mitochondrial-based neuroprotective interventions to clinical implementation.

Mitochondrial calcium uniporter blocker effectively prevents brain mitochondrial dysfunction caused by iron overload

AIMS

Although iron overload induces oxidative stress and brain mitochondrial dysfunction, and is associated with neurodegenerative diseases, brain mitochondrial iron uptake has not been investigated. We determined the role of mitochondrial calcium uniporter (MCU) in brain mitochondria as a major route for iron entry. We hypothesized that iron overload causes brain mitochondrial dysfunction, and that the MCU blocker prevents iron entry into mitochondria, thus attenuating mitochondrial dysfunction.

MAIN METHODS

Isolated brain mitochondria from male Wistar rats were used. Iron (Fe(2+) and Fe(3+)) at 0-286 μM were applied onto mitochondria at various incubation times (5-30 min), and the mitochondrial function was determined. Effects of MCU blocker (Ru-360) and iron chelator were studied.

KEY FINDINGS

Both Fe(2+) and Fe(3+) entered brain mitochondria and caused mitochondrial swelling in a dose- and time-dependent manner, and caused mitochondrial depolarization and increased ROS production. However, Fe(2+) caused more severe mitochondrial dysfunction than Fe(3+). Although all drugs attenuated mitochondrial dysfunction caused by iron overload, only an MCU blocker could completely prevent ROS production and mitochondrial depolarization.

SIGNIFICANCE

Our findings indicated that iron overload caused brain mitochondrial dysfunction, and that an MCU blocker effectively prevented this impairment, suggesting that MCU could be the major portal for brain mitochondrial iron uptake.

Potentially neuroprotective gene modulation in an in vitro model of mild traumatic brain injury

In this study, we investigated the hypothesis that mild traumatic brain injury (mTBI) triggers a controlled gene program as an adaptive response finalized to neuroprotection, similar to that found in hibernators and in ischemic preconditioning. A stretch injury device was used to produce an equi-biaxial strain field in rat organotypic hippocampal slice cultures at a specified Lagrangian strain of 10 % and a constant strain rate of 20 s(-1). After 24 h from injury, propidium iodide staining, HPLC analysis of metabolites and microarray analysis of cDNA were performed to evaluate cell viability, cell energy state and gene expression, respectively. Compared to control cultures, 10 % stretch injured cultures showed no change in viability, but demonstrated a hypometabolic state (decreased ATP, ATP/ADP, and nicotinic coenzymes) and a peculiar pattern of gene modulation. The latter was characterized by downregulation of genes encoding for proteins of complexes I, III, and IV of the mitochondrial electron transport chain and of ATP synthase; downregulation of transcriptional and translational genes; downregulation and upregulation of genes controlling the synthesis of glutamate and GABA receptors, upregulation of calmodulin and calmodulin-binding proteins; proper modulation of genes encoding for proapoptotic and antiapoptotic proteins. These results support the hypothesis that, following mTBI, a hibernation-type response is activated in non-hibernating species. Unlike in hibernators and ischemic preconditioning, this adaptive gene programme, aimed at achieving maximal neuroprotection, is not triggered by decrease in oxygen availability. It seems rather activated to avoid increase in oxidative/nitrosative stress and apoptosis during a transient period of mitochondrial malfunctioning.

Pyruvate dehydrogenase phosphatase1 mRNA expression is divergently and dynamically regulated between rat cerebral cortex, hippocampus and thalamus after traumatic brain injury: a potential biomarker of TBI-induced hyper- and hypo-glycaemia and neuronal vulnerability

Cerebral pyruvate depletion and lactate acidosis are common metabolic characteristics of patients with traumatic brain injury (TBI) and are associated with poor prognosis. Pyruvate dehydrogenase (PDH) is the rate-limiting enzyme coupling glycolysis to mitochondrial tricarboxylic acid (TCA) cycle. Brain PDH activity is regulated by its phosphorylation status and other effectors. Phosphorylation of PDH E1α1 subunit by PDH kinase inhibits PDH activity while dephosphorylation of phosphorylated PDHE1α1 by PDH phosphatase (PDP1) restores PDH activity. In situ hybridization showed that PDP1 mRNA is highly expressed in the cerebral cortex, hippocampus and thalamus of rat. Controlled cortical impact (CCI) induced a significant increase in PDP1 mRNA expression in ipsilateral cerebral cortex at 4 h (P<0.05) and 24 h post CCI (P<0.01) that returned to basal level 72 h post CCI. PDP1 mRNA level increased transiently in ipsilateral hippocampal dentate gyrus and CA1-3 subfields 4 h post CCI (P<0.01) but decreased significantly 24 h and 72 h (P<0.01) post CCI, coinciding with a marked increase in neuronal apoptosis in ipsilateral hippocampus 24 h post CCI. PDP1 mRNA expression in thalamus and other subcortical regions decreased persistently post CCI. Contralateral CCI and craniotomy showed similar effects on PDP1 mRNA expression as ipsilateral CCI. Because GFAP mRNA expression was induced in brain regions where PDP1 expression was altered, further study should determine the potential relationship between astrocyte activation, PDP1 alteration, and pyruvate metabolism following TBI.

Neuroglobin upregulation offers neuroprotection in traumatic brain injury

OBJECTIVES

The aim of this study was to investigate rat neuroglobin (rNGB) expression level after traumatic brain injury (TBI) and further study its neuroprotective effects in TBI when it was overexpressed in adenoviral vector.

METHODS

The Wistar rats (280-320 g) were divided into control, 12 and 36 hours after TBI groups (n = 3) and their TBI model was established. Subsequently, NGB expression level was examined by Western blot and immunohistochemical. Beyond that, adenoviral vectors pAdEasy-rNGB-GFP and pAdEasy-GFP were constructed and transfected into the rat brain respectively (pAdEasy-GFP was control), and the neuroprotective effects were examined by immunohistochemical.

RESULTS

Immunohistochemical and Western blot results demonstrated that NGB expression level was increased at 12 and 36 hours after TBI injury compare with control. Meanwhile, the pAdEasy-rNGB-GFP transfected rats suffered less necrosis and apoptosis compare to control.

CONCLUSIONS

NGB was upregulated in TBI and overexpressed rNGB had a significant neuroprotection in TBI. However, the mechanism remained unknown. This study suggested that rNGB overexpression may be a new strategy for treating of TBI.

Caffeic Acid phenethyl ester protects blood-brain barrier integrity and reduces contusion volume in rodent models of traumatic brain injury

A number of studies have established a deleterious role for inflammatory molecules and reactive oxygen species (ROS) in the pathology of traumatic brain injury (TBI). Caffeic acid phenethyl ester (CAPE) has been shown to exert both antioxidant and anti-inflammatory effects. The primary objective of the present study was to examine if CAPE could be used to reduce some of the pathological consequences of TBI using rodent models. Male Sprague-Dawley rats and C57BL/6 mice were subjected to controlled cortical impact (CCI) injury. Blood-brain barrier (BBB) integrity was assessed by examining claudin-5 expression and the extravasation of Evans blue dye. The effect of post-injury CAPE administration on neurobehavioral function was assessed using vestibulomotor, motor, and two hippocampus-dependent learning and memory tasks. We report that post-TBI administration of CAPE reduces Evans blue extravasation both in rats and mice. This improvement was associated with preservation of the levels of the tight junction protein claudin-5. CAPE treatment did not improve performance in either vestibulomotor/motor function (tested using beam balance and foot-fault tests), or in learning and memory function (tested using the Morris water maze and associative fear memory tasks). However, animals treated with CAPE were found to have significantly less cortical tissue loss than vehicle-treated controls. These findings suggest that CAPE may provide benefit in the treatment of vascular compromise following central nervous system injury.

Traumatic brain injury in adult rats causes progressive nigrostriatal dopaminergic cell loss and enhanced vulnerability to the pesticide paraquat

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the loss of nigrostriatal dopaminergic neurons and the accumulation of alpha-synuclein. Both traumatic brain injury (TBI) and pesticides are risk factors for PD, but whether TBI causes nigrostriatal dopaminergic cell loss in experimental models and whether it acts synergistically with pesticides is unknown. We have examined the acute and long-term effects of TBI and exposure to low doses of the pesticide paraquat, separately and in combination, on nigrostriatal dopaminergic neurons in adult male rats. In an acute study, rats received moderate TBI by lateral fluid percussion (LFP) injury, were injected with saline or paraquat (10 mg/kg IP) 3 and 6 days after LFP, were sacrificed 5 days later, and their brains processed for immunohistochemistry. TBI alone increased microglial activation in the substantia nigra, and caused a 15% loss of dopaminergic neurons ipsilaterally. Paraquat increased the TBI effect, causing a 30% bilateral loss of dopaminergic neurons, reduced striatal tyrosine hydroxylase (TH) immunoreactivity more than TBI alone, and induced alpha-synuclein accumulation in the substantia nigra pars compacta. In a long-term study, rats received moderate LFP, were injected with saline or paraquat at 21 and 22 weeks post-injury, and were sacrificed 4 weeks later. At 26 weeks post injury, TBI alone induced a 30% bilateral loss of dopaminergic neurons that was not exacerbated by paraquat. These data suggest that TBI is sufficient to induce a progressive degeneration of nigrostriatal dopaminergic neurons. Furthermore, TBI and pesticide exposure, when occurring within a defined time frame, could combine to increase the PD risk.

Post-injury administration of the mitochondrial permeability transition pore inhibitor, NIM811, is neuroprotective and improves cognition after traumatic brain injury in rats

Mitochondrial dysfunction is known to play a pivotal role in cell death mechanisms following traumatic brain injury (TBI). N-methyl-4-isoleucine-cyclosporin (NIM811), a non-immunosuppressive cyclosporin A (CsA) analog, inhibits the mitochondrial permeability transition pore (mPTP) and has been shown to be neuroprotective following TBI in mice. However, the translation of the neuroprotective effects of mPTP inhibitors, including CsA and NIM811, into improved cognitive end points has yet to be fully investigated. Therefore, to build upon these results, a severe unilateral controlled cortical impact model of TBI was used in the present study to establish a dose-response curve for NIM811 in rats. The findings demonstrate that the neuroprotection afforded by NIM811 is dose dependent, with the 10 mg/kg dose being the most effective dose. Once the dose response was established, we evaluated the effect of the optimal dose of NIM811 on behavior, mitochondrial bioenergetics, and mitochondrial oxidative damage following TBI. For behavioral studies, rats were administered NIM811 at 15 min and 24 h post-injury, with cognitive testing beginning 10 days post-injury. Mitochondrial studies involved a single injection of NIM811 at 15 min post-injury followed by mitochondrial isolation at 6 h post-injury. The results revealed that the optimal dose of NIM811 improves cognition, improves mitochondrial functioning, and reduces oxidative damage following TBI.

Improvement of cerebral metabolism mediated by Ro5-4864 is associated with relief of intracranial pressure and mitochondrial protective effect in experimental brain injury

PURPOSE

To investigate the possible impact of reduction of mitochondrial membrane permeabilization by modulation of the 18 kDa translocator protein mediated by Ro5-4864 over post-traumatic cerebral edema and metabolic crisis.

METHODS

Cerebral microdialysis and intracranial pressure (ICP) monitoring were performed in Sprague-Dawley rats treated by intraperitoneal injection of either dimethylsulfoxide (vehicle) or Ro5-4864 following cortical contusion and further correlated with quantitative assessment of mitochondrial damage, water content in the injured tissue, modified neurological severity score, and lesion size.

RESULTS

Ro5-4864 resulted in a profound decrease in ICP that correlated with improved cerebral metabolism characterized by significantly higher glucose and pyruvate and lower lactate concentrations in the pericontusional area in comparison with vehicle-treated animals. Reduced ICP correlated with reduced water content in the injured tissue; improved metabolism was associated with reduced mitochondrial damage evidenced by electron microscopy. Both effects were associated with a profound and significant reduction in glycerol release and lesion size, and correlated with improved neurological recovery.

CONCLUSIONS

The present study shows that Ro5-4864 has a favorable effect on the fate of injured brain, presumably mediated by improvement of metabolism. It further suggests that improvement of metabolism may contribute to ICP relief.

Therapeutic window analysis of the neuroprotective effects of cyclosporine A after traumatic brain injury

Mitochondrial dysfunction plays a pivotal role in secondary cell death mechanisms following traumatic brain injury (TBI). Several reports have demonstrated that inhibition of the mitochondrial permeability transition pore with the immunosuppressant drug cyclosporine A (CsA) is efficacious. Accordingly, CsA is being moved forward into late-stage clinical trials for the treatment of moderate and severe TBI. However, several unknowns exist concerning the optimal therapeutic window for administering CsA at the proposed dosages to be used in human studies. The present study utilized a moderate (1.75 mm) unilateral controlled cortical impact model of TBI to determine the most efficacious therapeutic window for initiating CsA therapy. Rats were administered an IP dose of CsA (20 mg/kg) or vehicle at 1, 3, 4, 5, 6, and 8 h post-injury. Immediately following the initial IP dose, osmotic mini-pumps were implanted at these time points to deliver 10 mg/kg/d of CsA or vehicle. Seventy-two hours following the initiation of treatment the pumps were removed to stop CsA administration. Quantitative analysis of cortical tissue sparing 7 days post-injury revealed that CsA treatment initiated at any of the post-injury initiation times out to 8 h resulted in significantly less cortical damage compared to animals receiving vehicle treatment. However, earlier treatment begun in the first 3 h was significantly more protective than that begun at 4 and 8 h. Treatment initiated at 1 h post-injury (∼68% decrease) was not significantly different than that seen at 3 h (∼46% decrease), but resulted in significantly greater cortical tissue sparing compared to CsA treatment initiated at least 4 h post-injury (28% decrease). Together these results illustrate the importance of initiating therapeutic interventions such as CsA as soon as possible following TBI, preferably within 4 h post-injury, to achieve the best possible neuroprotective effect. However, the drug appears to retain some protective efficacy even when initiated as late as 8 h post-injury.

Astrocyte oxidative metabolism and metabolite trafficking after fluid percussion brain injury in adult rats

Despite various lines of evidence pointing to the compartmentation of metabolism within the brain, few studies have reported the effect of a traumatic brain injury (TBI) on neuronal and astrocyte compartments and/or metabolic trafficking between these cells. In this study we used ex vivo ¹³C NMR spectroscopy following an infusion of [1-¹³C] glucose and [1,2-¹³C₂] acetate to study oxidative metabolism in neurons and astrocytes of sham-operated and fluid percussion brain injured (FPI) rats at 1, 5, and 14 days post-surgery. FPI resulted in a decrease in the ¹³C glucose enrichment of glutamate in neurons in the injured hemisphere at day 1. In contrast, enrichment of glutamine in astrocytes from acetate was not significantly decreased at day 1. At day 5 the ¹³C enrichment of glutamate and glutamine from glucose in the injured hemisphere of FPI rats did not differ from sham levels, but glutamine derived from acetate metabolism in astrocytes was significantly increased. The ¹³C glucose enrichment of the C3 position of glutamate (C3) in neurons was significantly decreased ipsilateral to FPI at day 14, whereas the enrichment of glutamine in astrocytes had returned to sham levels at this time point. These findings indicate that the oxidative metabolism of glucose is reduced to a greater extent in neurons compared to astrocytes following a FPI. The increased utilization of acetate to synthesize glutamine, and the acetate enrichment of glutamate via the glutamate-glutamine cycle, suggests an integral protective role for astrocytes in maintaining metabolic function following TBI-induced impairments in glucose metabolism.

Early mitochondrial dysfunction after cortical contusion injury

Following traumatic brain injury, mitochondria sustain structural and functional impairment, which contributes to secondary damage that can continue for days after the initial injury. The present study investigated mitochondrial bioenergetic changes in the rat neocortex at 1 and 3 h after mild, moderate, and severe injuries. Brains from young adult Sprague-Dawley rats were harvested from the injured and contralateral cortex to assess possible changes in mitochondrial respiration abilities following a unilateral cortical contusion injury. Differential centrifugation was used to isolate synaptic and extrasynaptic mitochondria from cortical tissue. Bioenergetics was assessed using a Clark-type electrode and results were graphed as a function of injury severity and time post-injury. Respiration was significantly affected by all injury severity levels compared to uninjured tissue. Complex 1- and complex 2-driven respirations were affected proportionally to the severity of the injury, indicating that damage to mitochondria may occur on a gradient. Total oxygen utilization, respiratory control ratio, ATP production, and maximal respiration capabilities were all significantly decreased in the injured cortex at both 1 and 3 h post-trauma. Although mitochondria displayed bioenergetic deficits at 1 h following injury, damage was not exacerbated by 3 h. This study stresses the importance of early therapeutic intervention and suggests a window of approximately 1-3 h before greater dysfunction occurs.

Use of magnesium in traumatic brain injury

Depletion of magnesium is observed in animal brain and in human blood after brain injury. Treatment with magnesium attenuates the pathological and behavioral changes in rats with brain injury; however, the therapeutic effect of magnesium has not been consistently observed in humans with traumatic brain injury (TBI). Secondary brain insults are observed in patients with brain injury, which adversely affect clinical outcome. Systemic administration studies in rats have shown that magnesium enters the brain; however, inducing hypermagnesemia in humans did not concomitantly increase magnesium levels in the CSF. We hypothesize that the neuroprotective effects of magnesium in TBI patients could be observed by increasing its brain bioavailability with mannitol. Here, we review the role of magnesium in brain injury, preclinical studies in brain injury, clinical safety and efficacy studies in TBI patients, brain bioavailability studies in rat, and pharmacokinetic studies in humans with brain injury. Neurodegeneration after brain injury involves multiple biochemical pathways. Treatment with a single agent has often resulted in poor efficacy at a safe dose or toxicity at a therapeutic dose. A successful neuroprotective therapy needs to be aimed at homeostatic control of these pathways with multiple agents. Other pharmacological agents, such as dexanabinol and progesterone, and physiological interventions, with hypothermia and hyperoxia, have been studied for the treatment of brain injury. Treatment with magnesium and hypothermia has shown favorable outcome in rats with cerebral ischemia. We conclude that coadministration of magnesium and mannitol with pharmacological and physiological agents could be an effective neuroprotective regimen for the treatment of TBI.

Tempol protection of spinal cord mitochondria from peroxynitrite-induced oxidative damage

Peroxynitrite (PN)-mediated mitochondrial dysfunction has been implicated in the secondary injury process after traumatic spinal cord injury (SCI). This study investigated the detrimental effects of the PN donor SIN-1 (3-morpholinosydnonimine) on isolated healthy spinal cord mitochondria and the protective effects of tempol, a catalytic scavenger of PN-derived radicals. A 5 min exposure of the mitochondria to SIN-1 caused a dose-dependent decrease in the respiratory control ratio (RCR) that was accompanied by significant increases in complex I-driven states II and IV respiration rates and decreases in states III and V. These impairments occurred together with an increase in mitochondrial protein 3-nitrotyrosine (3-NT), but not in lipid peroxidation (LP)-related 4-hydroxynonenal (4-HNE). Tempol significantly antagonized the respiratory effects of SIN-1 in parallel with an attenuation of 3-NT levels. These results show that the exogenous PN donor, SIN-1, rapidly causes mitochondrial oxidative damage and complex I dysfunction identical to traumatic spinal cord mitochondrial impairment and that this is mainly due to tyrosine nitration. Consistent with that, the protection of mitochondrial respiratory function by tempol is associated with a decrease in 3-NT levels in mitochondrial proteins also similar to the previously reported antioxidant actions of tempol in traumatically-injured spinal cord mitochondria.

Duration of ATP reduction affects extent of CA1 cell death in rat models of fluid percussion injury combined with secondary ischemia

Secondary ischemia (SI) following traumatic brain injury (TBI) increases damage to the brain in both animals and humans. The current study determined if SI after TBI alters the extent or duration of reduced energy production within the first 24 h post-injury and hippocampal cell loss at one week post-injury. Adult male rats were subjected to sham injury, lateral (LFPI) or central fluid percussion injury (CFPI) only, or to combined LFPI or CFPI with SI. The SI was 8 min of bilateral forebrain ischemia combined with hemorrhagic hypotension, applied at 1 h following FPI. After LFPI alone adenosine triphosphate (ATP) levels within the ipsilateral CA1 were reduced at 2 h (p < 0.05) and subsequently recovered. After LFPI+SI the ATP reductions in CA1 ipsilateral to FPI persisted for 24 h (p < 0.01). ATP levels in the contralateral CA1 were not affected by LFPI alone or LFPI+SI. After CFPI alone CA1 ATP levels were depressed bilaterally only at 2 h (p < 0.05). Similar to the LFPI paradigm, CFPI+SI reduced ATP levels for 24 h (p < 0.01), with bilateral ATP reductions seen after CFPI+SI. Cell counts in the CA1 region at 7 days post-injury revealed no significant neuronal cell loss after LFPI or CFPI alone. Significant neuronal cell loss was present only within the ipsilateral (p < 0.001) CA1 after LFPI+SI, but cell loss was bilateral (p < 0.001) after CFPI+SI. Thus, SI prolongs ATP reductions induced by LFPI and CFPI within the CA1 region and this SI-induced energy reduction appears to adversely affect regional neuronal viability.

Heterogeneous regional and temporal energetic impairment following controlled cortical impact injury in rats

OBJECTIVES

Following traumatic brain injury metabolic stability is impaired. Duration and reversibility of these changes might be important to guide specific interventions.

METHODS

To characterize temporal and regional changes in cerebral metabolism, 68 male Sprague-Dawley rats were subjected to a focal cortical contusion. Lesion progression and mitochondrial impairment were determined by magnetic resonance imaging (MRI) and triphenyl tetrazolium chloride (TTC) staining, respectively. Metabolic alterations were determined at hours 6 and 24 and day 7 by measuring extracellular glucose, lactate and hypoxanthine levels with microdialysis catheters placed adjacent and distant to the contusion and by quantifying changes in tissue ATP, lactate and glucose using bioluminescence imaging.

RESULTS

The cortical lesion reached its maximal extent at hour 24 and remained confined to the ipsilateral hemisphere. In microdialysate, at hour 6, extracellular hypoxanthine and lactate reached maximal values, thereafter hypoxanthine normalized while lactate remained increased. Extracellular glucose reached the highest values at hour 24 and remained elevated. Bioluminescence imaging revealed heterogeneous changes in areas distant to the contusion. No significant changes were found in ATP content. Slightly elevated tissue glucose until 24 hours in the ipsilateral hemisphere was observed. Following a continuous increase, lactate levels were the highest by 6 hours in the ipsilateral cortex and hippocampus.

DISCUSSION

CCI is associated with disturbances in energetic metabolism. Metabolic perturbation is not restricted to the early phase and the contusional region following focal cortical contusion, but also involves hippocampus and primarily uninjured parts of the hemisphere.

The protective role of cellular glutathione peroxidase against trauma-induced mitochondrial dysfunction in the mouse brain

Reactive oxygen species are believed to participate in the pathogenesis of traumatic brain injury (TBI). To evaluate the role of cellular glutathione peroxidase (Gpx1), a selenium-containing enzyme functioning in reduction of hydrogen peroxide and alkyl hyperoxides, in protecting animals against TBI, a line of Gpx1 transgenic mice was generated. Overexpression of Gpx1 was found in many organs including the brain of the transgenic mice. This line of transgenic mice and knockout mice deficient in Gpx1 were used in a model of controlled cortical impact injury and the efficiency of oxidative phosphorylation in brain mitochondria was determined. Although a 2-mm depth of mechanical impact caused a drastic decrease in NAD-linked electron transfer activities and energy-coupling capacities in brain mitochondria of nontransgenic mice, the decrease in mitochondrial function was completely prevented by overexpression of Gpx1 in Gpx1 transgenic mice. In addition, a 1-mm deformation depth hardly affected brain mitochondrial function in wild-type (Gpx1+/+) mice, yet resulted in a significant decrease in mitochondrial bioenergetic capacity in brains of homozygous Gpx1 knockout (Gpx1-/-) mice. Further experiments showed that inclusion of calcium chelator egtazic acid in measurement of mitochondrial respiration could completely restore the efficiency of mitochondrial respiration in injured brains of nontransgenic mice and Gpx1-/- mice, suggesting that the observed mitochondrial dysfunction is a direct result of increase in mitochondrion-associated calcium, which is secondary to the increased oxidative stress. These studies not only establish the role of Gpx1 in preventing mitochondrial dysfunction in mouse brain after TBI, but also suggest the species of reactive oxygen responsible for this event.

Region-specific tolerance criteria for the living brain

Computational models of traumatic brain injury (TBI) can predict injury-induced brain deformation. However, predicting the biological consequences (i.e. cell death or dysfunction) of induced brain deformation requires tolerance criteria. Here, we present a tolerance criterion for the cortex which exhibits important differences from that of the hippocampus. Organotypic slice cultures of the rat cortex, which maintain tissue architecture and cell content consistent with that in vivo, were mechanically injured with an in vitro model described previously. Cultures were stretched equibiaxially up to 0.35 Lagrangian strain at strain rates up to 50 s(-1). Cell death was quantified at 1, 2, 3, and 4 days following injury. Statistical analysis (repeated measures ANOVA) showed that all three factors (Strain, Strain Rate, and Time post-injury) significantly affected cell death. An equation describing cell death as a function of the significant parameters was then fit to the data. Compared to the hippocampus, the cortex was less vulnerable to stretch-induced injury and demonstrated a strain threshold below 0.20. Strain rate was also a significant factor for cortical but not hippocampal cell death. Cortical cell death began at an earlier time point than in the hippocampus, with cell death evident at 1 day post-injury versus 3 days in the hippocampus. In conclusion, different regions of the brain respond differently to identical mechanical stimuli, and this difference should be incorporated into finite element models of TBI if they are to more accurately predict in vivo consequences of TBI.

Post-Injury Administration of Mitochondrial Uncouplers Increases Tissue Sparing and Improves Behavioral Outcome following Traumatic Brain Injury in Rodents

Following experimental traumatic brain injury (TBI), a rapid and significant necrosis occurs at the site of injury which coincides with significant mitochondrial dysfunction. The present study is driven by the hypothesis that TBI-induced glutamate release increases mitochondrial Ca(2+)cycling/overload, ultimately leading to mitochondrial dysfunction. Based on this premise, mitochondrial uncoupling during the acute phases of TBI-induced excitotoxicity should reduce mitochondrial Ca(2+) uptake (cycling) and reactive oxygen species (ROS) production since both are mitochondrial membrane potential dependent. In the present study, we utilized a cortical impact model of TBI to assess the potential use of mitochondrial uncouplers (2,4-DNP, FCCP) as a neuroprotective therapy. Young adult male rats were intraperitoneally administered vehicle (DMSO), 2,4-DNP (5 mg/kg), or FCCP (2.5 mg/kg) at 5 min post-injury. All animals treated with the uncouplers demonstrated a significant reduction in the amount of cortical damage and behavioral improvement following TBI. In addition, mitochondria isolated from the injured cortex at 3 or 6 h post-injury demonstrated that treatment with the uncouplers significantly improved several parameters of mitochondrial bioenergetics. These results demonstrate that post-injury treatment with mitochondrial uncouplers significantly (p < 0.01) increases cortical tissue sparing ( approximately 12%) and significantly (p< 0.01) improves behavioral outcome following TBI. The mechanism of neuroprotection most likely involves the maintenance of mitochondrial homeostasis by reducing mitochondrial Ca(2+) loading and subsequent mitochondrial dysfunction. These results further implicate mitochondrial dysfunction as an early event in the pathophysiology of TBI and that targeting acute mitochondrial events can result in long-term neuroprotection and improve behavioral outcome following brain injury.

Mitochondrial dysfunction early after traumatic brain injury in immature rats

Mitochondria play central roles in acute brain injury; however, little is known about mitochondrial function following traumatic brain injury (TBI) to the immature brain. We hypothesized that TBI would cause mitochondrial dysfunction early (<4 h) after injury. Immature rats underwent controlled cortical impact (CCI) or sham injury to the left cortex, and mitochondria were isolated from both hemispheres at 1 and 4 h after TBI. Rates of phosphorylating (State 3) and resting (State 4) respiration were measured with and without bovine serum albumin. The respiratory control ratio was calculated (State 3/State 4). Rates of mitochondrial H(2)O(2) production, pyruvate dehydrogenase complex enzyme activity, and cytochrome c content were measured. Mitochondrial State 4 rates (ipsilateral/contralateral ratios) were higher after TBI at 1 h, which was reversed with bovine serum albumin. Four hours after TBI, pyruvate dehydrogenase complex activity and cytochrome c content (ipsilateral/contralateral ratios) were lower in TBI mitochondria. These data demonstrate abnormal mitochondrial function early (<or=4 h) after TBI in the developing brain. Future studies directed at reversing mitochondrial abnormalities could guide neuroprotective interventions after pediatric TBI.

Mitochondrial heat shock protein 60 is increased in cerebrospinal fluid following pediatric traumatic brain injury

Mitochondrial dysfunction occurs after traumatic brain injury (TBI) and contributes significantly to subsequent cell death. Heat shock protein 60 (hsp60) is a predominantly mitochondrial protein with important homeostatic functions. Induction of hsp60 has been demonstrated in cerebral ischemia models, possibly reflecting mitochondrial stress. We measured hsp60 concentration in the cerebrospinal fluid (CSF) of 34 infants and children after severe TBI and of 7 control patients by ELISA. Peak CSF hsp60 concentration was increased in TBI patients versus controls (0.84 ng/ml, range 0-44.59, vs. 0.0 ng/ml, range 0-0.48; p<0.05). Induction of hsp60 occurred early after the injury. Peak hsp60 concentration was independently associated with the severity of injury, defined as the admission Glasgow Coma Scale score. These data suggest that increased hsp60 in CSF might reflect the severity of early mitochondrial stress or damage after TBI.

Relationship of calpain-mediated proteolysis to the expression of axonal and synaptic plasticity markers following traumatic brain injury in mice

The role of neuronal plasticity and repair on the final functional outcome following traumatic brain injury (TBI) remains poorly understood. Moreover, the relationship of the magnitude of post-traumatic secondary injury and neurodegeneration to the potential for neuronal repair has not been explored. To address these questions, we employed Western immunoblotting techniques to examine how injury severity affects the spatial and temporal expression of markers of axonal growth (growth-associated protein GAP-43) and synaptogenesis (pre-synaptic vesicular protein synaptophysin) following either moderate (0.5 mm, 3.5 M/s) or severe (1.0 mm, 3.5 M/s) lateral controlled cortical impact traumatic brain injury (CCI-TBI) in young adult male CF-1 mice. Moderate CCI increased GAP-43 levels at 24 and 48 h post-insult in the ipsilateral hippocampus relative to sham, non-injured animals. This increase in axonal plasticity occurred prior to maximal hippocampal neurodegeneration, as revealed by de Olmos silver staining, at 72 h. However, moderate CCI-TBI did not elevate GAP-43 expression in the ipsilateral cortex where neurodegeneration was extensive by 6 h post-TBI. In contrast to moderate injury, severe CCI-TBI failed to increase hippocampal GAP-43 levels and instead resulted in depressed GAP-43 expression in the ipsilateral hippocampus and cortex at 48 h post-insult. In regards to injury-induced changes in synaptogenesis, we found that moderate CCI-TBI elevated synaptophysin levels in the ipsilateral hippocampus at 24, 48, 72 h and 21 days, but this effect was not present after severe injury. Together, these data highlights the adult brain's ability for axonal and synaptic plasticity following a focal cortical injury, but that severe injuries may diminish these endogenous repair mechanisms. The differential effects of moderate versus severe TBI on the post-traumatic plasticity response may be related to the calpain-mediated proteolytic activity occurring after a severe injury preventing increased expression of proteins required for plasticity. Supporting this hypothesis is the fact that GAP-43 is a substrate for calpain along with our data demonstrating that calpain-mediated degradation of the cytoskeletal protein, alpha-spectrin, is approximately 10 times greater in ipsilateral hippocampal tissue following severe compared to moderate CCI-TBI. Thus, TBI severity has a differential effect on the injury-induced neurorestorative response with calpain activation being one putative factor contributing to neuroregenerative failure following severe CCI-TBI. If true, then calpain inhibition may lead to both neuroprotective effects and an enhancement of neuronal plasticity/repair mechanisms post-TBI.

Photon correlation spectroscopy of brain mitochondrial populations: Application to traumatic brain injury

Mitochondrial dysfunction and pathology that contribute to a host of neurodegenerative diseases are deduced from changes in ultrastructure, routinely examined by a host of optical techniques. We adapted the technique of photon correlation spectroscopy (PCS) to evaluate calcium-induced structural alterations in isolated viable cortical and hippocampal mitochondria. In detecting calcium-induced reductions in light intensity, PCS was more sensitive than absorbance across varying calcium concentrations. Mitochondrial populations encompass a broad distribution of sizes, confirmed by ultrastructural profiles, both which remain unaffected by calcium exposure. Cortical and hippocampal populations show fractional calcium-induced reductions in light scatter compared to subsequent maximal alamethicin-induced reductions. Although reductions in light scatter (refractive index) have been interpreted as mitochondrial swelling, PCS quantification of the mean mitochondrial radius demonstrates that mitochondrial size is unaffected by calcium exposure, but not alamethicin. Likewise, the population distribution histograms remain stable with calcium exposure, but shift to larger radii after alamethicin exposure. Furthermore, hippocampal mitochondrial populations from a neurodegenerative model of traumatic brain injury, lateral fluid percussion, demonstrate greater calcium-induced reductions in scatter intensity, which are associated with an initial population of large mitochondria becoming smaller. The disparate responses to calcium and subsequent alamethicin of mitochondria at 3 and 24 h after injury attest to an acute disruption of membrane permeability in mitochondria from injured brain. PCS provides quantitative indices of refractive index and size in isolated mitochondrial populations, aiding the evaluation of mitochondria in degenerative diseases.

Upregulation of pentose phosphate pathway and preservation of tricarboxylic acid cycle flux after experimental brain injury

The metabolic fate of [1,2 13C]-labeled glucose was determined in male control and unilateral controlled cortical impact (CCI) injured rats at 3.5 and 24 h after surgery. The concentration of 13C-labeled glucose, lactate, glutamate and glutamine were measured in the injured and contralateral cortex. CCI animals showed a 145% increase in 13C lactate in the injured cortex at 3.5 h, but not at 24 h after injury, indicating increased glycolysis in neurons and/or astrocytes ipsilateral to CCI. Total levels of 13C glutamate in cortical tissue extracts did not differ between groups. However, 13C glutamine increased by 40% in the left and 98% in the right cortex at 3.5 h after injury, most likely resulting from an increase in astrocytic metabolism of glutamate. Levels of 13C incorporation into the glutamine isotopomers had returned to control levels by 24 h after CCI. The singlet to doublet ratio of the lactate C3 resonances was calculated to estimate the flux of glucose through the pentose phosphate pathway (PPP). CCI resulted in bilateral increases (9-12%) in the oxidation of glucose via the PPP, with the largest increase occurring at 24 h. Since an increase in PPP activity is associated with NADPH generation, the data suggest that there was an increasing need for reducing equivalents after CCI. Furthermore, 13C was incorporated into glutamate and glutamine isotopomers associated with multiple turns of the tricarboxylic acid (TCA) cycle, indicating that oxidative phosphorylation of glucose was maintained in the injured cortex at 3.5 and 24 h after a moderate to severe CCI injury.

An in vitro model of traumatic brain injury utilising two-dimensional stretch of organotypic hippocampal slice cultures

Traumatic brain injury (TBI) is caused by rapid deformation of the brain, resulting in a cascade of pathological events and ultimately neurodegeneration. Understanding how the biomechanics of brain deformation leads to tissue damage remains a considerable challenge. We have developed an in vitro model of TBI utilising organotypic hippocampal slice cultures on deformable silicone membranes, and an injury device, which generates tissue deformation through stretching the silicone substrate. Our injury device controls the biomechanical parameters of the stretch via feedback control, resulting in a reproducible and equi-biaxial deformation stimulus. Organotypic cultures remain well adhered to the membrane during deformation, so that tissue strain is 93 and 86% of the membrane strain in the x- and y-axis, respectively. Cell damage following injury is positively correlated with strain. In conclusion, we have developed a unique in vitro model to study the effects of mechanical stimuli within a complex cellular environment that mimics the in vivo environment. We believe this model could be a powerful tool to study the acute phases of TBI and the induced cell degeneration could provide a good platform for the development of potential therapeutic approaches and may be a useful in vitro alternative to animal models of TBI.

Prevention of mitochondrial dysfunction in post-traumatic mouse brain by superoxide dismutase

Reactive oxygen species (ROS) are known to be involved in the pathogenesis of traumatic brain injury (TBI). Previous studies have shown that the susceptibility of mice to TBI-induced formation of cortical lesion is determined by the expression levels of copper-zinc and manganese superoxide dismutase (CuZnSOD and MnSOD, respectively). However, the underlying biochemical mechanisms are not understood. In this study, we measured the efficiency of mitochondrial respiration in mouse brains with altered expression of these two enzymes. While controlled cortical impact injury (CCII) with a deformation depth of 2 mm caused a drastic decrease in NAD-linked bioenergetic capacity in brain mitochondria of wild-type mice, the functional decrease was not observed in brains of littermate transgenic mice overexpressing CuZnSOD or MnSOD. In addition, a 1 mm CCII greatly compromised brain mitochondrial function in mice deficient in CuZnSOD or MnSOD, but not wild-type mice. Inclusion of the calcium-chelating agent, EGTA, in the assay solution could completely prevent dysfunction of oxidative phosphorylation in all mitochondrial samples, suggesting that the observed impairment of mitochondrial function was a result of calcium overloading. In conclusion, our results imply that mitochondrial dysfunction induced by superoxide anion radical contributes to lesion formation in mouse brain following physical trauma.

Critical appraisal of neuroprotection trials in head injury: what have we learned?

To date, despite very encouraging preclinical results, almost all phase II/III clinical neuroprotection trials in traumatic brain injury (TBI) have failed to show any consistent improvement in outcome for TBI patients. To understand the reasons behind such developments we need to review and evaluate the evolution of trial design as a result of our changing understanding of the pathophysiology of brain cell death and progress of translational research from the laboratory bench to the bedside. This paper attempts to critically appraise these neuroprotection trials, rationalize the paucity of effectiveness, review any recent developments in the field, and try to draw some conclusions on how to move forward.

Secondary hypoxia exacerbates acute disruptions of energy metabolism in rats resulting from fluid percussion injury

The purpose of these experiments was to determine whether secondary hypoxia exacerbates the metabolic consequences of fluid percussion injury (FPI). In Experiment I, rats were trained to press a lever for their entire daily ration of food at any time during a 12-h light/dark cycle and run in an activity wheel. After food intake and body weight stabilized, rats were surgically prepared, assigned to one of four groups [FPI+Hypoxia (IH), FPI+Normoxia (IN), Sham Injury+Hypoxia (SH), Sham Injury+Normoxia (SN)] and, after recovery from surgery, anesthetized with halothane delivered by a 21% O2 source. Immediately after injury or sham injury, the O2 source was switched to 13% for rats in Groups IH and SH for 30 min. Post-traumatic hypoxemia exacerbated the ensuing FPI-induced reductions of food intake and body weight, but did not change FPI-induced reduction in wheel running. In Experiment II, rats were assigned to one of three groups (SH, IN, or IH) and subjected to sham injury and 13% O2 or FPI and either 13 or 21% O2. Immediately after 30 min of hypoxia or normoxia, rats were confined to metabolism cages that were used to quantify rates of oxygen consumption (VO2), carbon dioxide production (VCO2), and heat production (H). Post-traumatic hypoxia exacerbated the FPI-induced increases in VO2, VCO2, and H. The results of Experiments I and II provide convergent confirmation that secondary hypoxemia exacerbates the FPI-induced hypermetabolic state in rats and therefore might significantly exacerbate the brain injury-induced disruptions of energy metabolism in humans.

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

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

Brain-derived respiring mitochondria exhibit homogeneous, complete and cyclosporin-sensitive permeability transition

The mitochondrial permeability transition (mPT) is increasingly implicated in neuronal cell death. In the present study, isolated respiring brain mitochondria were examined for their ability to undergo calcium-induced mPT and their sensitivity to mPT inhibition by cyclosporin A (CsA). Previous studies have suggested a heterogeneous response to calcium, a limitation of CsA inhibition, and a relative resistance in the ability of respiring brain mitochondria to undergo mPT. Using fluorometric and electron microscopic analyses, we found that virtually the whole population of respiring brain mitochondria readily undergo mPT and swell upon calcium exposure. Further, brain mitochondria were highly sensitive to CsA which potentiated morphological recovery after transient swelling as well as completely blocked mPT induction in the presence of a low concentration of ADP. Using flow cytometry, which allows analysis of individual mitochondria, we demonstrate that both brain and liver mitochondria display homogeneous responses to calcium-induced mPT. We conclude that the mPT is one likely target for the broad in vivo neuroprotective effects displayed by CsA when allowed to penetrate the blood-brain barrier, and that development of compounds inhibiting mPT may prove beneficial for the treatment of severe brain disease.

Moderate and severe traumatic brain injury: epidemiologic, imaging and neuropathologic perspectives

This article examines 3 contexts in which moderate or severe traumatic brain injury can be approached. The epidemiologic background of moderate and severe traumatic brain injury is presented, with particular attention paid to new findings from the study of a national hospital inpatient database. We review aspects of neuroimaging and how new imaging modalities can reveal fine detail about traumatic brain injury. Finally we examine the current state of neuropathologic evaluation of, and recent developments in, understanding of the neural disruptions that occur following traumatic brain injury, together with cellular reactions to these disruptions.

Hyperoxia in head injury

PURPOSE OF REVIEW

Currently, no neuroprotective therapies have been shown to reduce the secondary neuronal damage occurring after traumatic brain injury. Recent studies have addressed the potentiality of hyperoxia to ameliorate brain metabolism after traumatic brain injury. In this article, we present the principles of oxygen transport to the brain, the effects of hyperoxia on cerebral metabolism, and the role of lactate in brain metabolism after traumatic brain injury.

RECENT FINDINGS

It has been shown that hyperoxia obtained by increasing the inspired fraction of oxygen results in a decreased cerebral lactate concentration measured in the extracellular space using the microdialysis. However, the brain oxygen delivery is not substantially improved by eubaric hyperoxia and the ratio between lactate and pyruvate (a better indicator of the cellular redox state than lactate alone) is not changed by hyperoxia. In addition, it has been shown the lactate might be an alternative fuel for neurons during the acute postinjury phase.

SUMMARY

At present, there is no evidence supporting any clinical benefit of hyperoxia in brain-injured patients, and the meaning of posttraumatic brain extracellular lactate accumulation should be further investigated.

Voluntary exercise following traumatic brain injury: brain-derived neurotrophic factor upregulation and recovery of function

Voluntary exercise leads to an upregulation of brain-derived neurotrophic factor (BDNF) and associated proteins involved in synaptic function. Activity-induced enhancement of neuroplasticity may be considered for the treatment of traumatic brain injury (TBI). Given that during the first postinjury week the brain is undergoing dynamic restorative processes and energetic changes that may influence the outcome of exercise, we evaluated the effects of acute and delayed exercise following experimental TBI. Male Sprague-Dawley rats underwent either sham or lateral fluid-percussion injury (FPI) and were housed with or without access to a running wheel (RW) from postinjury days 0-6 (acute) or 14-20 (delayed). FPI alone resulted in significantly elevated levels of hippocampal phosphorylated synapsin I and phosphorylated cyclic AMP response element-binding-protein (CREB) at postinjury day 7, of which phosphorylated CREB remained elevated at postinjury day 21. Sham and delayed FPI-RW rats showed increased levels of BDNF, following exercise. Exercise also increased phosphorylated synapsin I and CREB in sham rats. In contrast to shams, the acutely exercised FPI rats failed to show activity-dependent BDNF upregulation and had significant decreases of phosphorylated synapsin I and total CREB. Additional rats were cognitively assessed (learning acquisition and memory) by utilizing the Morris water maze after acute or delayed RW exposure. Shams and delayed FPI-RW animals benefited from exercise, as indicated by a significant decrease in the number of trials to criterion (ability to locate the platform in 7 s or less for four consecutive trials), compared with the delayed FPI-sedentary rats. In contrast, cognitive performance in the acute FPI-RW rats was significantly impaired compared with all the other groups. These results suggest that voluntary exercise can endogenously upregulate BDNF and enhance recovery when it is delayed after TBI. However, when exercise is administered to soon after TBI, the molecular response to exercise is disrupted and recovery may be delayed.

Temporal alterations in cellular Bax:Bcl-2 ratio following traumatic brain injury in the rat

Cell death/survival following CNS injury may be a result of alterations in the intracellular ratio of death and survival factors. Using immunohistochemistry, Western analysis and in situ hybridization, the expression of the anti-cell death protein, Bcl-2, and the pro-cell death protein, Bax, was evaluated following lateral fluid-percussion (FP) brain injury of moderate severity (2.3-2.6 atm) in adult male Sprague-Dawley rats. By 2 h post-injury, a marked reduction of cellular Bcl-2-immunoreactivity (IR) and a mild decrease in cellular Bax IR were observed in the temporal and occipital cortices, and in the hippocampal CA3 ipsilateral to the site of impact. These decreases in Bcl-2 and Bax IR appeared to precede the overt cell loss in these regions that was evident at 24 h. Immunoblot analysis supported the immunohistochemical data, with a modest but significant reduction in the intensities of both the Bcl-2 and Bax protein bands at 2 h (p < 0.05 compared to sham levels). However, the Bax:Bcl-2 ratio increased significantly at 2 h (2.28 +/- 0.13) and remained elevated up to 7 days (2.05 +/- 0.13) post-injury compared to sham-injured control tissue (1.62 +/- 0.10, p < 0.05). Furthermore, cortical, but not hippocampal, levels of Bax protein increased by 25% (p < 0.05 compared to sham-injured controls) at 24 h post-injury, and returned to control levels by 7 days. In situ hybridization analysis of Bax mRNA revealed increased cellular grain density in the injured cortex (p < 0.05 compared to sham-injured brains), but not in the CA3 region of the injured hippocampus. No injury-induced changes in the expression of Bcl-2 mRNA were observed in any brain region. Taken together, these data suggest that the association between regional post-traumatic cell death and alterations in the cellular ratio of Bcl-2 and Bax may be, in part, due to alterations in mRNA and/or protein expression of the Bcl-2 family of proteins.

Age-associated mitochondrial DNA deletions are not evident chronically after experimental brain injury in the rat

The enduring cognitive and sensorimotor deficits that result from traumatic brain injury (TBI) are associated with metabolic stress and free radical cascades, which establish conditions that may promote mitochondrial DNA (mtDNA) deletion and oxidation, often observed as a consequence of normal aging. Without substantial mtDNA repair mechanisms, permanent alterations to essential mitochondrial enzymes could perpetuate post-injury pathologic cascades. To determine whether mitochondria from the injured cortex and hippocampus sustain mtDNA damage after TBI, we evaluated mtDNA deletion and oxidation following lateral fluid percussion TBI in the anesthetized adult Sprague-Dawley rat (4 months) compared with uninjured adult and aged rats (n = 4/group). The presence of the 4.8-KB common deletion in mtDNA was assessed by conventional PCR to generate products representing total, non-deleted wild-type, and deleted mtDNA in homogenized tissue and isolated mitochondria 3 and 14 days following TBI. Total and wild-type mtDNA amplification products were obtained from cortical and hippocampal tissue and mitochondria for all conditions. Although no mtDNA deletions were observed following experimental TBI, mtDNA deletion was detected in cortical tissue, but not isolated mitochondria, of naive, aged (24 months) Sprague-Dawley rats, suggesting that the isolation protocol may exclude mitochondria harboring mtDNA damage. Oxidative mtDNA damage in isolated mitochondria assayed by ELISA for 8-hydroxy-2'-deoxyguanosine (8-OHdG) from cortical (0.50 +/- 0.08 pg 8-OHdG/ micro g mitochondria) and hippocampal (0.35 +/- 0.02) regions were unaffected by TBI. However, mitochondrial protein yields from injured and aged brains were comparable and significantly lower than uninjured brain, suggesting that the underlying pathology between TBI and aging may be similar.