Effects of traumatic brain injury on cerebral high-energy phosphates and pH: a 31P magnetic resonance spectroscopy study

Tracing the path of disruption: 13C isotope applications in traumatic brain injury-induced metabolic dysfunction

Cerebral metabolic dysfunction is a critical pathological hallmark observed in the aftermath of traumatic brain injury (TBI), as extensively documented in clinical investigations and experimental models. An in-depth understanding of the bioenergetic disturbances that occur following TBI promises to reveal novel therapeutic targets, paving the way for the timely development of interventions to improve patient outcomes. The 13C isotope tracing technique represents a robust methodological advance, harnessing biochemical quantification to delineate the metabolic trajectories of isotopically labeled substrates. This nuanced approach enables real-time mapping of metabolic fluxes, providing a window into the cellular energetic state and elucidating the perturbations in key metabolic circuits. By applying this sophisticated tool, researchers can dissect the complexities of bioenergetic networks within the central nervous system, offering insights into the metabolic derangements specific to TBI pathology. Embraced by both animal studies and clinical research, 13C isotope tracing has bolstered our understanding of TBI-induced metabolic dysregulation. This review synthesizes current applications of isotope tracing and its transformative potential in evaluating and addressing the metabolic sequelae of TBI.

Changes in Brain Energy and Membrane Metabolism in Glioblastoma following Chemoradiation

Brain parenchyma infiltration with glioblastoma (GB) cannot be entirely visualized by conventional magnetic resonance imaging (MRI). The aim of this study was to investigate changes in the energy and membrane metabolism measured with phosphorous MR spectroscopy (31P-MRS) in the presumably “normal-appearing” brain following chemoradiation therapy (CRT) in GB patients in comparison to healthy controls. Twenty (seven female, thirteen male) GB patients underwent a 31P-MRS scan prior to surgery (baseline) and after three months of standard CRT (follow-up examination. The regions of interest “contrast-enhancing (CE) tumor” (if present), “adjacent to the (former) tumor”, “ipsilateral distant” hemisphere, and “contralateral” hemisphere were compared, differentiating between patients with stable (SD) and progressive disease (PD). Metabolite ratios PCr/ATP, Pi/ATP, PCr/Pi, PME/PDE, PME/PCr, and PDE/ATP were investigated. In PD, energy and membrane metabolism in CE tumor areas have a tendency to “normalize” under therapy. In different “normal-appearing” brain areas of GB patients, the energy and membrane metabolism either “normalized” or were “disturbed”, in comparison to baseline or controls. Differences were also detected between patients with SD and PD. 31P-MRS might contribute as an additional imaging biomarker for outcome measurement, which remains to be investigated in a larger cohort.

Phosphorous Magnetic Resonance Spectroscopy and Molecular Markers in IDH1 Wild Type Glioblastoma

Simple Summary

Gliobastoma is one of the deadliest tumors overall, yet the most common malignant brain tumor. The new World Health Organization Classification of Brain Tumors brought changes in how we look at this type of malignancy. Now we know that glioblastoma is rather a spectrum of similar tumors, but with some distinct characteristics that include molecular footprint, response to therapy and with that overall survival, among others. We hypothesised that by employing phosphorous magnetic resonance we will be able to show differences in cellular energy metabolism in these various subtypes of glioblastoma. For example, we found indices of faster cell reproduction and tumor growth in MGMT-methylated and EGFR-amplified tumors. These tumors also could have reduced energetic state or tissue oxygenation due to the increased necrosis. Tumors with EGFR-amplification could have increased apoptotic activity regardless of their MGMT status. Our study indicated various differences in energetic metabolism in tumors with different molecular characteristics, which could potentially be important in future therapeutic strategies.

Abstract

The World Health Organisation’s (WHO) classification of brain tumors requires consideration of both histological appearance and molecular characteristics. Possible differences in brain energy metabolism could be important in designing future therapeutic strategies. Forty-three patients with primary, isocitrate dehydrogenase 1 (IDH1) wild type glioblastomas (GBMs) were included in this study. Pre-operative standard MRI was obtained with additional phosphorous magnetic resonance spectroscopy (31-P-MRS) imaging. Following microsurgical resection of the tumors, biopsy specimens underwent neuropathological diagnostics including standard molecular diagnosis. The spectroscopy results were correlated with epidermal growth factor (EGFR) and O6-Methylguanine-DNA methyltransferase (MGMT) status. EGFR amplified tumors had significantly lower phosphocreatine (PCr) to adenosine triphosphate (ATP)-PCr/ATP and PCr to inorganic phosphate (Pi)-PCr/Pi ratios, and higher Pi/ATP and phosphomonoesters (PME) to phosphodiesters (PDE)-PME/PDE ratio than those without the amplification. Patients with MGMT-methylated tumors had significantly higher cerebral magnesium (Mg) values and PME/PDE ratio, while their PCr/ATP and PCr/Pi ratios were lower than in patients without the methylation. In survival analysis, not-EGFR-amplified, MGMT-methylated GBMs showed the longest survival. This group had lower PCr/Pi ratio when compared to MGMT-methylated, EGFR-amplified group. PCr/Pi ratio was lower also when compared to the MGMT-unmethylated, EGFR not-amplified group, while PCr/ATP ratio was lower than all other examined groups. Differences in energy metabolism in various molecular subtypes of wild-type-GBMs could be important information in future precision medicine approach.

Repeated 31P-MRS in severe traumatic brain injury: Insights into cerebral energy status and altered metabolism

Phosphorous magnetic resonance spectroscopy (31P-MRS) is suited to non-invasively investigate energy metabolism and to detect molecules containing phosphorus in the human brain. The aim of this longitudinal study was to perform 31P-MRS at two different time points (within 72 hours and between day 10-14) after severe traumatic brain injury (sTBI) to reveal alterations in cerebral energy metabolism. Twenty-six ventilated sTBI patients, aged between 20 to 75 years, with a median initial GCS of 5 were prospectively analyzed. 31P-MRS data of the structurally more affected side were compared to data from contralateral normal appearing areas and to data of age- and gender-matched healthy controls. There were no significant intraindividual differences between the lesioned and the less affected side at either of time points. In the acute phase, PCr/ATP and PCr/Pi were significantly elevated whereas PME/PDE and Pi/ATP were significantly decreased in contrast to healthy controls. In the subacute phase these differences gradually dissipated, remaining lower Pi/ATP ratio, and only partly altered levels of PCr/Pi and PME/PDE. Our data affirm that cerebral metabolism is globally altered after sTBI, demonstrating the diffuse impairment of brain bioenergetics at multiple levels, with resultant developments in terms of time.

Phosphorous Magnetic Resonance Spectroscopy to Detect Regional Differences of Energy and Membrane Metabolism in Naïve Glioblastoma Multiforme

Simple Summary

Glioblastoma multiforme is a highly aggressive brain tumor, tending to infiltrate even larger zones of brain tissue than visible on conventional magnetic resonance imaging. By application of phosphorus magnetic resonance spectroscopy in patients with naïve glioblastoma multiforme, we tried to demonstrate changes in energy and membrane metabolism not only in affected regions but also in distant brain regions, the opposite brain hemisphere, and in comparison to healthy volunteers. We found reduced energetic states and signs of increased cell membrane turnover in regions of visible tumor and differences to and between the “normal-appearing” brains of glioblastoma patients and the brains of healthy volunteers. Our pilot study confirmed the feasibility of the method, so differences between various genetic mutations or clinical applicability for follow-up monitoring can be assessed in larger cohorts.

Abstract

Background: Glioblastoma multiforme (GBM) is a highly malignant primary brain tumor with infiltration of, on conventional imaging, normal-appearing brain parenchyma. Phosphorus magnetic resonance spectroscopy (31P-MRS) enables the investigation of different energy and membrane metabolites. The aim of this study is to investigate regional differences of 31P-metabolites in GBM brains. Methods: In this study, we investigated 32 patients (13 female and 19 male; mean age 63 years) with naïve GBM using 31P-MRS and conventional MRI. Contrast-enhancing (CE), T2-hyperintense, adjacent and distant ipsilateral areas of the contralateral brain and the brains of age- and gender-matched healthy volunteers were assessed. Moreover, the 31P-MRS results were correlated with quantitative diffusion parameters. Results: Several metabolite ratios between the energy-dependent metabolites and/or the membrane metabolites differed significantly between the CE areas, the T2-hyperintense areas, the more distant areas, and even the brains of healthy volunteers. pH values and Mg²⁺ concentrations were highest in visible tumor areas and decreased with distance from them. These results are in accordance with the literature and correlated with quantitative diffusion parameters. Conclusions: This pilot study shows that 31P-MRS is feasible to show regional differences of energy and membrane metabolism in brains with naïve GBM, particularly between the different “normal-appearing” regions and between the contralateral hemisphere and healthy controls. Differences between various genetic mutations or clinical applicability for follow-up monitoring have to be assessed in a larger cohort.

Impact of CNS Diseases on Drug Delivery to Brain Extracellular and Intracellular Target Sites in Human: A "WHAT-IF" Simulation Study

The blood-brain barrier (BBB) is equipped with unique physical and functional processes that control central nervous system (CNS) drug transport and the resulting concentration-time profiles (PK). In CNS diseases, the altered BBB and CNS pathophysiology may affect the CNS PK at the drug target sites in the brain extracellular fluid (brainECF) and intracellular fluid (brainICF) that may result in changes in CNS drug effects. Here, we used our human CNS physiologically-based PK model (LeiCNS-PK3.0) to investigate the impact of altered cerebral blood flow (CBF), tight junction paracellular pore radius (pararadius), brainECF volume, and pH of brainECF (pHECF) and of brainICF (pHICF) on brainECF and brainICF PK for 46 small drugs with distinct physicochemical properties. LeiCNS-PK3.0 simulations showed a drug-dependent effect of the pathophysiological changes on the rate and extent of BBB transport and on brainECF and brainICF PK. Altered pararadius, pHECF, and pHICF affected both the rate and extent of BBB drug transport, whereas changes in CBF and brainECF volume modestly affected the rate of BBB drug transport. While the focus is often on BBB paracellular and active transport processes, this study indicates that also changes in pH should be considered for their important implications on brainECF and brainICF target site PK.

The voltage-gated proton channel Hv1 plays a detrimental role in contusion spinal cord injury via extracellular acidosis-mediated neuroinflammation

Tissue acidosis is an important secondary injury process in the pathophysiology of traumatic spinal cord injury (SCI). To date, no studies have examined the role of proton extrusion as mechanism of pathological acidosis in SCI. In the present study, we hypothesized that the phagocyte-specific proton channel Hv1 mediates hydrogen proton extrusion after SCI, contributing to increased extracellular acidosis and poor long-term outcomes. Using a contusion model of SCI in adult female mice, we demonstrated that tissue pH levels are markedly lower during the first week after SCI. Acidosis was most evident at the injury site, but also extended into proximal regions of the cervical and lumbar cord. Tissue reactive oxygen species (ROS) levels and expression of Hv1 were significantly increased during the week of injury. Hv1 was exclusively expressed in microglia within the CNS, suggesting that microglia contribute to ROS production and proton extrusion during respiratory burst. Depletion of Hv1 significantly attenuated tissue acidosis, NADPH oxidase 2 (NOX2) expression, and ROS production at 3 d post-injury. Nanostring analysis revealed decreased gene expression of neuroinflammatory and cytokine signaling markers in Hv1 knockout (KO) mice. Furthermore, Hv1 deficiency reduced microglia proliferation, leukocyte infiltration, and phagocytic oxidative burst detected by flow cytometry. Importantly, Hv1 KO mice exhibited significantly improved locomotor function and reduced histopathology. Overall, these data suggest an important role for Hv1 in regulating tissue acidosis, NOX2-mediated ROS production, and functional outcome following SCI. Thus, the Hv1 proton channel represents a potential target that may lead to novel therapeutic strategies for SCI.

Cerebral Energy Status and Altered Metabolism in Early Severe TBI: First Results of a Prospective 31P-MRS Feasibility Study

OBJECTIVE

Severe traumatic brain injury (sTBI) represents a serious public health issue with high morbidity and mortality. Neuroimaging plays a crucial role in the evaluation of sTBI patients. Phosphorous magnetic resonance spectroscopy (³¹P-MRS) is an imaging technique for evaluation of energy metabolites. The aim of this study is to evaluate the feasibility and the diagnostic potential of ultra-early ³¹P-MRS to detect changes in cerebral energy metabolism in sTBI.

METHODS

Adult patients with sTBI presenting with GCS ≤ 8 being eligible for MRI were prospectively included in the study and MRI was performed within 72 h after trauma. Imaging was performed using a 3 Tesla MRI. ³¹P-MRS data from the structurally affected side were compared to data from normal appearing contralateral areas symmetrically to the location of the traumatic lesions, and to data of matched healthy controls.

RESULTS

Ten sTBI patients (3 female, 7 male), aged between 20 and 75 years, with a mean initial GCS of 6 were analyzed. MRI was performed 61 h (mean, range 37-71 h) after trauma. Statistical analysis revealed no significant differences between the lesioned side and contralaterally. An increased PCr/ATP ratio and a decreased PME/PDE ratio were present in structurally normal appearing, but traumatized tissue when compared to the healthy population, thus indicating significant differences in ATP resynthesis and membrane turnover (F (2,33), P = 0.005 and, P = 0.027, respectively).

CONCLUSION

³¹P-MRS could provide a better understanding of pertinent global changes in cerebral energy metabolism in sTBI patients under general anesthesia.

Phosphorus spectroscopy in acute TBI demonstrates metabolic changes that relate to outcome in the presence of normal structural MRI

Metabolic dysfunction is a key pathophysiological process in the acute phase of traumatic brain injury (TBI). Although changes in brain glucose metabolism and extracellular lactate/pyruvate ratio are well known, it was hitherto unknown whether these translate to downstream changes in ATP metabolism and intracellular pH. We have performed the first clinical voxel-based in vivo phosphorus magnetic resonance spectroscopy (³¹P MRS) in 13 acute-phase major TBI patients versus 10 healthy controls (HCs), at 3T, focusing on eight central 2.5 × 2.5 × 2.5 cm³ voxels per subject. PCr/γATP ratio (a measure of energy status) in TBI patients was significantly higher (median = 1.09) than that of HCs (median = 0.93) (p < 0.0001), due to changes in both PCr and ATP. There was no significant difference in PCr/γATP between TBI patients with favourable and unfavourable outcome. Cerebral intracellular pH of TBI patients was significantly higher (median = 7.04) than that of HCs (median = 7.00) (p = 0.04). Alkalosis was limited to patients with unfavourable outcome (median = 7.07) (p < 0.0001). These changes persisted after excluding voxels with > 5% radiologically visible injury. This is the first clinical demonstration of brain alkalosis and elevated PCr/γATP ratio acutely after major TBI. ³¹P MRS has potential for non-invasively assessing brain injury in the absence of structural injury, predicting outcome and monitoring therapy response.

Lactate infusion increases brain energy content during euglycemia but not hypoglycemia in healthy men

A special characteristic of the brain is the usage of lactate as alternative fuel instead of glucose to preserve its energy homeostasis. This physiological function is valid for sufficient cerebral glucose supply, as well as presumably during hypoglycemia, given that exogenous lactate infusion suppresses hormonal counterregulation. However, it is not yet clarified whether this effect is mediated by the use of lactate as an alternative cerebral energy substrate or any other mechanism. We hypothesized that under conditions of limited access to glucose (ie, during experimental hypoglycemia) lactate infusion would prevent hypoglycemia-induced neuroenergetic deficits in a neuroprotective way. In a randomized, double-blind, crossover study, lactate vs placebo infusion was compared during hyperinsulinemic-hypoglycemic clamps in 16 healthy young men. We measured the cerebral high-energy phosphate content - ie, adenosine triphosphate (ATP), phosphocreatine (PCr) and inorganic phosphate (Pi) levels - by ³¹ P-magnetic resonance spectroscopy as well as the neuroendocrine stress response. During euglycemia, lactate infusion increased ATP/Pi as well as PCr/Pi ratios compared with baseline values and placebo infusion. During hypoglycemia, there were no differences between the lactate and the placebo condition in both ratios. Hormonal counterregulation was significantly diminished upon lactate infusion. Our data demonstrate an elevated cerebral high-energy phosphate content upon lactate infusion during euglycemia, whereas there was no such effect during experimental hypoglycemia. Nevertheless, lactate infusion suppressed hypoglycemic hormonal counterregulation. Lactate thus adds to cerebral energy provision during euglycemia and may contribute to an increase in ATP reserves, which in turn protects the brain against neuroglucopenia under recurrent hypopglycemic conditions, eg, in diabetic patients.

pH-weighted molecular MRI in human traumatic brain injury (TBI) using amine proton chemical exchange saturation transfer echoplanar imaging (CEST EPI)

Cerebral acidosis is a consequence of secondary injury mechanisms following traumatic brain injury (TBI), including excitotoxicity and ischemia, with potentially significant clinical implications. However, there remains an unmet clinical need for technology for non-invasive, high resolution pH imaging of human TBI for studying metabolic changes following injury. The current study examined 17 patients with TBI and 20 healthy controls using amine chemical exchange saturation transfer echoplanar imaging (CEST EPI), a novel pH-weighted molecular MR imaging technique, on a clinical 3T MR scanner. Results showed significantly elevated pH-weighted image contrast (MTRasym at 3 ppm) in areas of T2 hyperintensity or edema (P < 0.0001), and a strong negative correlation with Glasgow Coma Scale (GCS) at the time of the MRI exam (R2 = 0.4777, P = 0.0021), Glasgow Outcome Scale - Extended (GOSE) at 6 months from injury (R2 = 0.5334, P = 0.0107), and a non-linear correlation with the time from injury to MRI exam (R2 = 0.6317, P = 0.0004). This evidence suggests clinical feasibility and potential value of pH-weighted amine CEST EPI as a high-resolution imaging tool for identifying tissue most at risk for long-term damage due to cerebral acidosis.

The effect of succinate on brain NADH/NAD+ redox state and high energy phosphate metabolism in acute traumatic brain injury

A key pathophysiological process and therapeutic target in the critical early post-injury period of traumatic brain injury (TBI) is cell mitochondrial dysfunction; characterised by elevation of brain lactate/pyruvate (L/P) ratio in the absence of hypoxia. We previously showed that succinate can improve brain extracellular chemistry in acute TBI, but it was not clear if this translates to a change in downstream energy metabolism. We studied the effect of microdialysis-delivered succinate on brain energy state (phosphocreatine/ATP ratio (PCr/ATP)) with 31P MRS at 3T, and tissue NADH/NAD+ redox state using microdialysis (L/P ratio) in eight patients with acute major TBI (mean 7 days). Succinate perfusion was associated with increased extracellular pyruvate (+26%, p < 0.0001) and decreased L/P ratio (-13%, p < 0.0001) in patients overall (baseline-vs-supplementation over time), but no clear-cut change in 31P MRS PCr/ATP existed in our cohort (p > 0.4, supplemented-voxel-vs-contralateral voxel). However, the percentage decrease in L/P ratio for each patient following succinate perfusion correlated significantly with their percentage increase in PCr/ATP ratio (Spearman's rank correlation, r = -0.86, p = 0.024). Our findings support the interpretation that L/P ratio is linked to brain energy state, and that succinate may support brain energy metabolism in select TBI patients suffering from mitochondrial dysfunction.

Large animal models of traumatic brain injury

Purpose/Aim: Animal models of traumatic brain injury (TBI) provide powerful tools to study TBI in a controlled, rigorous and cost-efficient manner. The mostly used animals in TBI studies so far are rodents. However, compared with rodents, large animals (e.g. swine, rabbit, sheep, ferret, etc.) show great advantages in modeling TBI due to the similarity of their brains to human brain. The aim of our review was to summarize the development and progress of common large animal TBI models in past 30 years.

MATERIALS AND METHODS

Mixed published articles and books associated with large animal models of TBI were researched and summarized.

RESULTS

We majorly sumed up current common large animal models of TBI, including discussion on the available research methodologies in previous studies, several potential therapies in large animal trials of TBI as well as advantages and disadvantages of these models.

CONCLUSIONS

Large animal models of TBI play crucial role in determining the underlying mechanisms and screening putative therapeutic targets of TBI.

Assessing Metabolism and Injury in Acute Human Traumatic Brain Injury with Magnetic Resonance Spectroscopy: Current and Future Applications

Traumatic brain injury (TBI) triggers a series of complex pathophysiological processes. These include abnormalities in brain energy metabolism; consequent to reduced tissue pO₂ arising from ischemia or abnormal tissue oxygen diffusion, or due to a failure of mitochondrial function. In vivo magnetic resonance spectroscopy (MRS) allows non-invasive interrogation of brain tissue metabolism in patients with acute brain injury. Nuclei with “spin,” e.g., ¹H, ³¹P, and ¹³C, are detectable using MRS and are found in metabolites at various stages of energy metabolism, possessing unique signatures due to their chemical shift or spin–spin interactions (J-coupling). The most commonly used clinical MRS technique, ¹H MRS, uses the great abundance of hydrogen atoms within molecules in brain tissue. Spectra acquired with longer echo-times include N-acetylaspartate (NAA), creatine, and choline. NAA, a marker of neuronal mitochondrial activity related to adenosine triphosphate (ATP), is reported to be lower in patients with TBI than healthy controls, and the ratio of NAA/creatine at early time points may correlate with clinical outcome. ¹H MRS acquired with shorter echo times produces a more complex spectrum, allowing detection of a wider range of metabolites.³¹ P MRS detects high-energy phosphate species, which are the end products of cellular respiration: ATP and phosphocreatine (PCr). ATP is the principal form of chemical energy in living organisms, and PCr is regarded as a readily mobilized reserve for its replenishment during periods of high utilization. The ratios of high-energy phosphates are thought to represent a balance between energy generation, reserve and use in the brain. In addition, the chemical shift difference between inorganic phosphate and PCr enables calculation of intracellular pH.¹³ C MRS detects the ¹³C isotope of carbon in brain metabolites. As the natural abundance of ¹³C is low (1.1%), ¹³C MRS is typically performed following administration of ¹³C-enriched substrates, which permits tracking of the metabolic fate of the infused ¹³C in the brain over time, and calculation of metabolic rates in a range of biochemical pathways, including glycolysis, the tricarboxylic acid cycle, and glutamate–glutamine cycling. The advent of new hyperpolarization techniques to transiently boost signal in ¹³C-enriched MRS in vivo studies shows promise in this field, and further developments are expected.

Traumatic brain injury decreases AMP-activated protein kinase activity and pharmacological enhancement of its activity improves cognitive outcome

Prolonged metabolic suppression in the brain is a well-characterized secondary pathology of both experimental and clinical traumatic brain injury (TBI). AMP-activated kinase (AMPK) acts as a cellular energy sensor that, when activated, regulates various metabolic and catabolic pathways to decrease ATP consumption and increase ATP synthesis. As energy availability after TBI is suppressed, we questioned if increasing AMPK activity after TBI would improve cognitive outcome. TBI was delivered using the electromagnetic controlled cortical impact model on male Sprague-Dawley rats (275-300 g) and C57BL/6 mice (20-25 g). AMPK activity within the injured parietal cortex and ipsilateral hippocampus was inferred by western blots using phospho-specific antibodies. The consequences of acute manipulation of AMPK signaling on cognitive function were assessed using the Morris water maze task. We found that AMPK activity is decreased as a result of injury, as indicated by reduced AMPK phosphorylation and corresponding changes in the phosphorylation of its downstream targets: ribosomal protein S6 and Akt Substrate of 160 kDa (AS160). Increasing AMPK activity after injury using the drugs 5-amino-1-β-d-ribofuranosyl-imidazole-4-carboxamide or metformin did not affect spatial learning, but significantly improved spatial memory. Taken together, our results suggest that decreased AMPK activity after TBI may contribute to the cellular energy crisis in the injured brain, and that AMPK activators may have therapeutic utility. Increased phosphorylation of Thr172 activates AMP-activated protein kinase (AMPK) under conditions of low cellular energy availability. This leads to inhibition of energy consuming, while activating energy generating, processes. Hill et al., present data to indicate that TBI decreases Thr172 phosphorylation and that its stimulation by pharmacological agents offers neuroprotection and improves memory. These results suggest that decreased AMPK phosphorylation after TBI incorrectly signals the injured brain that excess energy is available, thereby contributing to the cellular energy crisis and memory impairments.

Glucose metabolism following human traumatic brain injury: methods of assessment and pathophysiological findings

The pathophysiology of traumatic brain (TBI) injury involves changes to glucose uptake into the brain and its subsequent metabolism. We review the methods used to study cerebral glucose metabolism with a focus on those used in clinical TBI studies. Arterio-venous measurements provide a global measure of glucose uptake into the brain. Microdialysis allows the in vivo sampling of brain extracellular fluid and is well suited to the longitudinal assessment of metabolism after TBI in the clinical setting. A recent novel development is the use of microdialysis to deliver glucose and other energy substrates labelled with carbon-13, which allows the metabolism of glucose and other substrates to be tracked. Positron emission tomography and magnetic resonance spectroscopy allow regional differences in metabolism to be assessed. We summarise the data published from these techniques and review their potential uses in the clinical setting.

Systemic, local, and imaging biomarkers of brain injury: more needed, and better use of those already established?

Much progress has been made over the past two decades in the treatment of severe acute brain injury, including traumatic brain injury and subarachnoid hemorrhage, resulting in a higher proportion of patients surviving with better outcomes. This has arisen from a combination of factors. These include improvements in procedures at the scene (pre-hospital) and in the hospital emergency department, advances in neuromonitoring in the intensive care unit, both continuously at the bedside and intermittently in scans, evolution and refinement of protocol-driven therapy for better management of patients, and advances in surgical procedures and rehabilitation. Nevertheless, many patients still experience varying degrees of long-term disabilities post-injury with consequent demands on carers and resources, and there is room for improvement. Biomarkers are a key aspect of neuromonitoring. A broad definition of a biomarker is any observable feature that can be used to inform on the state of the patient, e.g., a molecular species, a feature on a scan, or a monitoring characteristic, e.g., cerebrovascular pressure reactivity index. Biomarkers are usually quantitative measures, which can be utilized in diagnosis and monitoring of response to treatment. They are thus crucial to the development of therapies and may be utilized as surrogate endpoints in Phase II clinical trials. To date, there is no specific drug treatment for acute brain injury, and many seemingly promising agents emerging from pre-clinical animal models have failed in clinical trials. Large Phase III studies of clinical outcomes are costly, consuming time and resources. It is therefore important that adequate Phase II clinical studies with informative surrogate endpoints are performed employing appropriate biomarkers. In this article, we review some of the available systemic, local, and imaging biomarkers and technologies relevant in acute brain injury patients, and highlight gaps in the current state of knowledge.

Two aspects of ASIC function: Synaptic plasticity and neuronal injury

Extracellular brain pH fluctuates in both physiological and disease conditions. The main postsynaptic proton receptor is the acid-sensing ion channels (ASICs). During the past decade, much progress has been made on protons, ASICs, and neurological disease. This review summarizes the recent progress on synaptic role of protons and our current understanding of how ASICs contribute to various types of neuronal injury in the brain. This article is part of the Special Issue entitled 'Acid-Sensing Ion Channels in the Nervous System'.

Arylsulfatase B improves locomotor function after mouse spinal cord injury

Bacterial chondroitinase ABC (ChaseABC) has been used to remove the inhibitory chondroitin sulfate chains from chondroitin sulfate proteoglycans to improve regeneration after rodent spinal cord injury. We hypothesized that the mammalian enzyme arylsulfatase B (ARSB) would also enhance recovery after mouse spinal cord injury. Application of the mammalian enzyme would be an attractive alternative to ChaseABC because of its more robust chemical stability and reduced immunogenicity. A one-time injection of human ARSB into injured mouse spinal cord eliminated immunoreactivity for chondroitin sulfates within five days, and up to 9 weeks after injury. After a moderate spinal cord injury, we observed improvements of locomotor recovery assessed by the Basso Mouse Scale (BMS) in ARSB treated mice, compared to the buffer-treated control group, at 6 weeks after injection. After a severe spinal cord injury, mice injected with equivalent units of ARSB or ChaseABC improved similarly and both groups achieved significantly more locomotor recovery than the buffer-treated control mice. Serotonin and tyrosine hydroxylase immunoreactive axons were more extensively present in mouse spinal cords treated with ARSB and ChaseABC, and the immunoreactive axons penetrated further beyond the injury site in ARSB or ChaseABC treated mice than in control mice. These results indicate that mammalian ARSB improves functional recovery after CNS injury. The structural/molecular mechanisms underlying the observed functional improvement remain to be elucidated.

Therapeutic targets for neuroprotection and/or enhancement of functional recovery following traumatic brain injury

Traumatic brain injury (TBI) is a significant public health concern. The number of injuries that occur each year, the cost of care, and the disabilities that can lower the victim's quality of life are all driving factors for the development of therapy. However, in spite of a wealth of promising preclinical results, clinicians are still lacking a therapy. The use of preclinical models of the primary mechanical trauma have greatly advanced our knowledge of the complex biochemical sequela that follow. This cascade of molecular, cellular, and systemwide changes involves plasticity in many different neurochemical systems, which represent putative targets for remediation or attenuation of neuronal injury. The purpose of this chapter is to highlight some of the promising molecular and cellular targets that have been identified and to provide an up-to-date summary of the development of therapeutic compounds for those targets.

Posthypothermic rewarming considerations following traumatic brain injury

To date, considerable attention has been focused upon the use of hypothermia as a therapeutic strategy for attenuating many of the damaging consequences of traumatic brain injury (TBI). Despite the promise of hypothermic intervention following TBI, many questions remain regarding the optimal use of hypothermic intervention, including, but not limited to, the rewarming rates needed to assure optimal brain protection. In this review, we revisit the relatively limited literature examining the issue of hypothermia and differing rewarming rates following TBI. Considering both experimental and clinical literature, evidence is presented that the rate of posthypothermic rewarming is an important variable for influencing the protective effects of hypothermic intervention following TBI. In the experimental setting, posttraumatic hypothermia followed by slow rewarming appears to provide maximal protection in terms of traumatically induced axonal damage, microvascular damage and dysfunction, and contusional expansion. In contrast, hypothermia followed by rapid rewarming not only reverses the protective effects associated with hypothermic intervention, but in many cases, exacerbates the traumatically induced pathology and its functional consequences. While similar evaluations have not been conducted in the clinical setting, multiple lines of clinical evidence suggest the benefits of posttraumatic hypothermia are optimized through the use of slow rewarming, with the suggestion that such a strategy reduces the potential for rebound vasodilation, elevated intracranial pressure (ICP), and impaired neurocognitive recovery. Collectively, this review highlights not only the benefits of hypothermic intervention, but also the rate of posthypothermic rewarming as an important variable in assuring maximal efficacy following the use of hypothermic intervention.

Combination therapies for traumatic brain injury: prospective considerations

Traumatic brain injury (TBI) initiates a cascade of numerous pathophysiological events that evolve over time.Despite the complexity of TBI, research aimed at therapy development has almost exclusively focused on single therapies, all of which have failed in multicenter clinical trials. Therefore, in February 2008 the National Institute of Neurological Disorders and Stroke, with support from the National Institute of Child Health and Development, the National Heart, Lung, and Blood Institute, and the Department of Veterans Affairs, convened a workshop to discuss the opportunities and challenges of testing combination therapies for TBI. Workshop participants included clinicians and scientists from a variety of disciplines, institutions, and agencies. The objectives of the workshop were to: (1) identify the most promising combinations of therapies for TBI; (2) identify challenges of testing combination therapies in clinical and pre-clinical studies; and (3) propose research methodologies and study designs to overcome these challenges. Several promising combination therapies were discussed, but no one combination was identified as being the most promising. Rather, the general recommendation was to combine agents with complementary targets and effects (e.g., mechanisms and time-points), rather than focusing on a single target with multiple agents. In addition, it was recommended that clinical management guidelines be carefully considered when designing pre-clinical studies for therapeutic development.To overcome the challenges of testing combination therapies it was recommended that statisticians and the U.S. Food and Drug Administration be included in early discussions of experimental design. Furthermore, it was agreed that an efficient and validated screening platform for candidate therapeutics, sensitive and clinically relevant biomarkers and outcome measures, and standardization and data sharing across centers would greatly facilitate the development of successful combination therapies for TBI. Overall there was great enthusiasm for working collaboratively to act on these recommendations.

Effect of profound hypothermia on genomics of hippocampus following complete cerebral ischemia in rats

OBJECTIVE

To determine differential gene expression of hippocampus in rats following complete cerebral ischemia with treatment of profound hypothermia compared to normothermia.

METHODS

Six rats got 5 minutes of complete cerebral ischemia with circulatory arrest and randomly divided into two groups: normothermia ischemia group (37 +/- 0.3 degrees C, n = 3) and profound hypothermia ischemia group (18 +/- 0.5 degrees C, n = 3). Affymetrix U34A rat arrays were applied to detect the difference of gene expression profile in hippocampus between the two groups.

RESULTS

Expression profiles of a total of 75 transcripts in the profound hypothermia ischemia group were statistically different from those of the normothermia ischemia group, and 33 of them were significantly up-regulated and other 42 were significantly down-regulated (p < 0.07).

CONCLUSIONS

Compared with normothermia, profound hypothermia had a significant effect on the gene expression profiles following complete cerebral ischemia, which may be involved in the mechanisms of cerebral protection by profound hypothermia.

Differential hippocampal protection when blocking intracellular sodium and calcium entry during traumatic brain injury in rats

This study investigated the contributions of the reverse mode of the sodium-calcium exchanger (NCX) and the type 1 sodium-proton antiporter (NHE-1) to acute astrocyte and neuronal pathology in the hippocampus following fluid percussion traumatic brain injury (TBI) in the rat. KB-R7943, EIPA, or amiloride, which respectively inhibit NCX, NHE-1, or NCX, NHE-1, and ASIC1a (acid-sensing ion channel type 1a), was infused intraventricularly over a 60-min period immediately prior to TBI. Astrocytes were immunostained for glial fibrillary acidic protein (GFAP), and degenerating neurons were identified by Fluoro-Jade staining at 24 h after injury. Stereological analysis of the CA2/3 sub-regions of the hippocampus demonstrated that higher doses of KB-R7943 (2 and 20 nmoles) significantly reduced astrocyte GFAP immunoreactivity compared to vehicle-treated animals. EIPA (2-200 nmoles) did not alter astrocyte GFAP immunoreactivity. Amiloride (100 nmoles) significantly attenuated the TBI-induced acute reduction in astrocyte GFAP immunoreactivity. Of the three compounds examined, only amiloride (100 nmoles) reduced hippocampal neuronal degeneration assessed with Fluoro-Jade. The results provide additional evidence of acute astrocyte pathology in the hippocampus following TBI, while suggesting that activation of NHE-1 and the reverse mode of NCX contribute to both astrocyte and neuronal pathology following experimental TBI.

Traumatic brain injury causes a long-lasting calcium (Ca2+)-plateau of elevated intracellular Ca levels and altered Ca2+ homeostatic mechanisms in hippocampal neurons surviving brain injury

Traumatic brain injury (TBI) survivors often suffer chronically from significant morbidity associated with cognitive deficits, behavioral difficulties and a post-traumatic syndrome and thus it is important to understand the pathophysiology of these long-term plasticity changes after TBI. Calcium (Ca2+) has been implicated in the pathophysiology of TBI-induced neuronal death and other forms of brain injury including stroke and status epilepticus. However, the potential role of long-term changes in neuronal Ca2+ dynamics after TBI has not been evaluated. In the present study, we measured basal free intracellular Ca2+ concentration ([Ca2+](i)) in acutely isolated CA3 hippocampal neurons from Sprague-Dawley rats at 1, 7 and 30 days after moderate central fluid percussion injury. Basal [Ca2+](i) was significantly elevated when measured 1 and 7 days post-TBI without evidence of neuronal death. Basal [Ca2+](i) returned to normal when measured 30 days post-TBI. In contrast, abnormalities in Ca2+ homeostasis were found for as long as 30 days after TBI. Studies evaluating the mechanisms underlying the altered Ca2+ homeostasis in TBI neurons indicated that necrotic or apoptotic cell death and abnormalities in Ca2+ influx and efflux mechanisms could not account for these changes and suggested that long-term changes in Ca2+ buffering or Ca2+ sequestration/release mechanisms underlie these changes in Ca2+ homeostasis after TBI. Further elucidation of the mechanisms of altered Ca2+ homeostasis in traumatized, surviving neurons in TBI may offer novel therapeutic interventions that may contribute to the treatment and relief of some of the morbidity associated with TBI.

Energy metabolic changes in the early post-injury period following traumatic brain injury in rats

Impaired cerebral energy metabolism may be a major contributor to the secondary injury cascade that occurs following traumatic brain injury (TBI). To estimate the cortical energy metabolic state following mild and severe controlled cortical contusion (CCC) TBI in rats, ipsi-and contralateral cortical tissues were frozen in situ at 15 and 40 min post-injury and adenylate (ATP, ADP, AMP) levels were analyzed using high-performance liquid chromatography (HPLC) and the energy charge (EC) was calculated. At 15 min post-injury, mildly brain-injured animals showed a 43% decrease in cortical ATP levels and a 2.4-fold increase in AMP levels (P < 0.05), and there was a significant reduction of the ipsilateral cortical EC when compared to sham-injured animals (P < 0.05). At 40 min post-injury, the ipsilateral adenylate levels and EC had recovered to the values observed in the sham-injury group. In the severe CCC group, there was a 51% decrease in ipsilateral cortical ATP levels and a 5.3-fold increase in AMP levels with a significant reduction of cortical EC at 15 min post-injury (P < 0.05). At 40 min post-injury, a 2.6-fold ipsilateral increase in AMP levels and an 11% and 44% decrease in EC and ATP levels, respectively, remained (P < 0.05). A 37-38% reduction of the total adenylate pool was observed ipsilaterally in both CCC severity groups at the early time-point, and a 19% and 28% decrease remained in the mild and severe CCC groups, respectively, at 40 min post-injury. Significant contralateral ATP and EC changes were only observed in the severe CCC group at 40 min post-injury (P < 0.05). The energy-requiring secondary injury cascades that occur early post-injury do not challenge the brain tissue to the extent of ATP depletion and may provide a window of opportunity for therapeutic intervention.

Effect of long-term mild hypothermia or short-term mild hypothermia on outcome of patients with severe traumatic brain injury

To compare the effect of long-term mild hypothermia versus short-term mild hypothermia on the outcome of 215 severe traumatic brain injured patients with cerebral contusion and intracranial hypertension. At three medical centers, 215 patients aged 18 to 45 years old with an admission Glasgow Coma Scale < or =8 within 4 h after injury were randomly divided into two groups: long-term mild hypothermia group (n = 108) for 5+/-1.3 days mild hypothermia therapy and short-term mild hypothermia group (n = 107) for 2+/-0.6 days mild hypothermia therapy. All patients had intracranial hypertension and frontotemporoparietal contusion with midline shift >1 cm confirmed on computed tomographic scan. Glasgow Outcome Scale at 6-month follow-up, 47 cases had favorable outcome (43.5%), and other 61 cases had unfavorable outcome (56.5%) in the long-term mild hypothermia group. However, only 31 cases had favorable outcome (29.0%), and other 76 cases had unfavorable outcome (71.0%) in the short-term mild hypothermia group (P < 0.05). The intracranial pressure significantly rebounded after rewarming in the short-term mild hypothermia group, but not in the long-term mild hypothermia (P < 0.05). Furthermore, the incidence of stress ulcer, epilepsy, pulmonary infection, intracranial infection did not significantly differ between the two groups (P > 0.05). Compared with short-term mild hypothermia, long-term mild hypothermia significantly improves the outcome of severe traumatic brain injured patients with cerebral contusion and intracranial hypertension without significant complications. Our data suggest that 5 days of long-term cooling is more efficacious than 2 days of short-term cooling when mild hypothermia is used to control refractory intracranial hypertension in patients with severe traumatic brain injury.

Evaluation of traumatic brain injured patients in correlation with functional status by localized 1H-MR spectroscopy

OBJECTIVE

To determine whether proton magnetic resonance spectroscopy (1H-MRS) could be a useful tool for detecting microscopic diffuse axonal injury to evaluate the functional status of patients with traumatic brain injury (TBI).

DESIGN

A comparative study.

SETTING

An inpatient rehabilitation unit in Korea.

SUBJECTS

We examined eight adult patients who had severe TBI approximately five months before. Fourteen normal controls were employed for comparison.

MAIN MEASURES

Image-guided localized in vivo 1H-MRS was performed in the parietal white matter and occipital grey matter regions in brain in which no definite abnormalities in MR imaging were found at the time of 1H-MRS examination. We evaluated functional status for all patients with the Functional Independence Measure (FIM) on the same day as the 1H-MRS examination and compared the results.

RESULTS

In the parietal white matter, the [N-acetyl aspartate/creatine] ratios were significantly lower, and the [choline/creatine] and [myo-inositol/creatine] ratios were significantly higher than those of normal controls. Significant correlations of the IN-acetyl aspartate/creatine] and [myo-inositol/creatine] ratios in the parietal white matter with FIM scores were observed (p < 0.05).

CONCLUSIONS

A spectral feature of the decreased [N-acetyl aspartate/creatine] and increased [choline/creatine] and [myo-inositol/creatine] ratios in parietal white matter may be a marker for diffuse axonal injury in patients with TBI and has a significant correlation with the functional status of the patients. Localized 1H-MRS has the potential to be used for detecting diffuse axonal injury in vivo in TBI patients, which can be used to guide evaluation of the functional status of TBI patients receiving rehabilitation.

Metabolic changes in the vicinity of brain contusions: a proton magnetic resonance spectroscopy and histology study

Proton MR spectroscopy (1H-MRS) has been previously used to monitor metabolic changes in areas of diffuse brain injury. We studied metabolism in the close vicinity of experimental traumatic brain contusions and remote on the contralateral side from 1h to 28d post-injury. Changes of creatine and phosphocreatine (Cr&PCr), N-acetylaspartate (NAA), choline (Cho), inositol (Ino), taurine (Tau), glutamate (Glu), and lactate (Lac) were assessed and compared to neuronal, glial and inflammatory changes in histology. In the pericontusional zone Cr&PCr, NAA, and Glu decreased immediately after trauma by -35%, -60%, and -37%, respectively, related to primary cell disintegration and secondary perturbations as reflected in histology. These metabolites partially recovered at 7d (-15%, -37%, and -21% respectively), in parallel to indicators of repair in immunhistochemistry. Control levels were not regained at 28d, in correlation to a decrease of viable neurons. Cho and Ino, initially lowered by -26% and -31% respectively, increased at 7d by +74% and 31%, reflecting glial activation and proliferation. The signal including the lactate resonance increased by >1000% with a maximum at 7d, possibly related to energy failure, inflammation and glial activation. A partial contribution of lipids to this signal cannot be fully excluded. The contralateral side showed mild astroglial activation in histology, but no changes in 1H-MRS. The study demonstrates the feasibility of volume selective 1H-MRS using the LCModel (Linear Combination of Model in vitro spectra of metabolites solutions) to monitor metabolic changes close to focal traumatic lesions and suggests how metabolic alterations can be differentiated in cause.

Novel diketopiperazine enhances motor and cognitive recovery after traumatic brain injury in rats and shows neuroprotection in vitro and in vivo

The authors developed a novel diketopiperazine that shows neuroprotective activity in a variety of in vitro models, as well as in a clinically relevant experimental model of traumatic brain injury (TBI) in rats. Treatment with 1-ARA-35b (35b), a cyclized dipeptide derived from a modified thyrotropin-releasing hormone (TRH) analog, significantly reduced cell death associated with necrosis (maitotoxin), apoptosis (staurosporine), or mechanical injury in neuronal-glial cocultures. Rats subjected to lateral fluid percussion-induced TBI and then treated with 1 mg/kg intravenous 35b thirty minutes after trauma showed significantly improved motor recovery and spatial learning compared with vehicle-treated controls. Treatment also significantly reduced lesion volumes as shown by magnetic resonance imaging, and decreased the number of TUNEL-positive neurons observed in ipsilateral hippocampus. Unlike TRH or traditional TRH analogs, 35b treatment did not change mean arterial pressure, body temperature, or thyroid-stimulating hormone release, and did not have analeptic activity. Moreover, in contrast to TRH or typical TRH analogs, 35b administration after TBI did not alter free-magnesium concentration or cellular bioenergetic state. Receptor-binding studies showed that 35b did not act with high affinity at 50 classical receptors, channels, or transporters. Thus, 35b shows none of the typical physiologic actions associated with TRH, but possesses neuroprotective actions in vivo and in vitro, and appears to attenuate both necrotic and apoptotic cell death.

Delayed changes in regional brain energy metabolism following cerebral concussion in rats

Traumatic brain injury (TBI) results in an acute altered metabolic profile of brain tissue which resolves within hours of initial insult and yet some of the functional deficits and cellular perturbations persist for days. It is hypothesized that a delayed change in energy status does occur and is a factor in the neural tissue's ability to survive and regain function. Regional metabolic profile and glucose consumption were determined at either 1 or 3 days following two different intensities of parasagittal fluid-percussion (F-P). A significant decrease in both 1CMRgluc and levels of ATP and P-creatine was evident in the hemisphere ipsilateral to the trauma at 1 day after the insult. The effect was greater in the cortical than the subcortical regions and was more pronounced at the higher trauma intensity. Normalization of glucose consumption and energy levels was essentially complete by 3 days. It would appear that the delayed metabolic changes at 1 day postinsult cannot be explained by a secondary ischemia since the changes in the metabolite profile do not elicit an increase in the consumption of glucose. These changes in energy metabolites may account for and contribute to the chronic neurological deficits following TBI.

1H-MR spectroscopic monitoring of posttraumatic metabolism following controlled cortical impact injury: pilot study

Proton magnetic resonance spectroscopy (1H-MRS) has been increasingly utilised in experimental traumatic brain injury for characterisation of posttraumatic metabolic dysfunction. Following human brain injury pathological findings correlated with outcome measures. Combined with conventional T2-weighted MR imaging MRS is a sensitive tool to evaluate metabolic changes in brain tissue following trauma. Studies have been restricted so far to diffuse axonal injury models and fluid percussion injury. Using a high resolution scanner at 4.7 T, MRI combined with 1H-MRS was applied in a pilot study to the controlled cortical impact injury model of experimental brain contusion (CCII). Eight Sprague-Dawley rats were investigated, of which two served as controls. Four animals were injured 24 h after craniotomy, two investigated at 72 h post craniotomy. MRS/MRI indicated a transient brain oedema development and metabolic changes induced by the craniotomy itself. Following CCII MRI demonstrated that the area of contusion as well as the surrounding brain oedema increased twofold in size within 24 h (p < 0.05). MRS showed an immediate increase of N-acetylaspartate (NAA) and glutamate ipsilateral to the contusion and a drop of NAA on the contralateral side. MRS/MRI investigations in the CCII model demonstrated a potential to further elucidate the pathophysiology following traumatic brain contusion.

Small shifts in craniotomy position in the lateral fluid percussion injury model are associated with differential lesion development

Previous studies have shown that location and direction of injury may affect outcome in experimental models of traumatic brain injury. Significant variability in outcome data has also been noted in studies using the lateral fluid percussion brain injury model (FPI) in rats. In recent studies from our laboratory, we observed considerable variability in localization and severity of tissue damage as a function of small changes in craniotomy position. To further address this issue, we examined the relationship between craniotomy position and brain lesion size/location in rats subjected to moderate FPI (2.28 +/- 0.18 atmospheres). With placement of a 5-mm craniotomy adjacent to the sagittal suture, there was both ipsilateral and contralateral damage as detected at 3 weeks posttrauma using T2-weighted magnetic resonance imaging (MRI). The MRI lesions were generally restricted to the hippocampus and subcortical layers. Shifting of the craniotomy site laterally was associated with increased ipsilateral tissue damage and a greater cortical component that correlated with distance from the sagittal suture. In contrast, the contralateral MRI lesion did not change significantly in size or location unless the center of the craniotomy was placed more than 3.5 mm from the sagittal suture, under which condition contralateral damage could no longer be detected. Ipsilateral tissue damage as determined from the MRI scans was linearly correlated to motor outcome but not with cognitive outcome as assessed by the Morris Water Maze. We conclude that craniotomy position is critical in determining extent and location of tissue injury produced during the lateral FPI model in rats. Addressing such potential variability is essential for studies that address either injury mechanisms or therapeutic treatments.

Altered cellular metabolism following traumatic brain injury: a magnetic resonance spectroscopy study

Experimental studies have reported early reductions in pH, phosphocreatine, and free intracellular magnesium following traumatic brain injury using phosphorus magnetic resonance spectroscopy. Paradoxically, in clinical studies there is some evidence for an increase in the pH in the subacute stage following traumatic brain injury. We therefore performed phosphorus magnetic resonance spectroscopy on seven patients in the subacute stage (mean 9 days postinjury) following traumatic brain injury to assess cellular metabolism. In areas of normal-appearing white matter, the pH was significantly alkaline (patients 7.09 +/- 0.04 [mean +/- SD], controls 7.01 +/- 0.04, p = 0.008), the phosphocreatine to inorganic phosphate ratio (PCr/Pi) was significantly increased (patients 4.03 +/- 1.18, controls 2.64 +/- 0.71, p = 0.03), the inorganic phosphate to adenosine triphosphate ratio (Pi/ATP) was significantly reduced (patients 0.37 +/- 0.10, controls 0.56 +/- 0.19, p = 0.04), and the PCr/ATP ratio was nonsignificantly increased (patients 1.53 +/- 0.29, controls 1.34 +/- 0.19, p = 0.14) in patients compared to controls. Furthermore, the calculated free intracellular magnesium was significantly increased in the patients compared to the controls (patients 0.33 +/- 0.09 mM, controls 0.22 +/- 0.09 mM, p = 0.03)). Proton spectra, acquired from similar regions showed a significant reduction in N-acetylaspartate (patients 9.64 +/- 2.49 units, controls 12.84 +/- 2.35 units, p = 0.03) and a significant increase in choline compounds (patients 7.96 +/- 1.02, controls 6.67 +/- 1.01 units, p = 0.03). No lactate was visible in any patient or control spectrum. The alterations in metabolism observed in these patients could not be explained by ongoing ischemia but might be secondary to a loss of normal cellular homeostasis or a relative alteration in the cellular population, in particular an increase in the glial cell density, in these regions.

Effect of long-term mild hypothermia therapy in patients with severe traumatic brain injury: 1-year follow-up review of 87 cases

OBJECT

The goal of this study was to investigate the protective effects of long-term (3-14 days) mild hypothermia therapy (33-35 degrees C) on outcome in 87 patients with severe traumatic brain injury (TBI) (Glasgow Coma Scale score < or = 8).

METHODS

In 43 patients assigned to a mild hypothermia group, body temperatures were cooled to 33 to 35 degrees C a mean of 15 hours after injury and kept at 33 to 35 degrees C for 3 to 14 days. Rewarming commenced when the individual patient's intracranial pressure (ICP) returned to the normal level. Body temperatures in 44 patients assigned to a normothermia group were maintained at 37 to 38 degrees C. Each patient's outcome was evaluated 1 year later by using the Glasgow Outcome Scale. One year after TBI, the mortality rate was 25.58% (11 of 43 patients) and the rate of favorable outcome (good recovery or moderate disability) was 46.51% (20 of 43 patients) in the mild hypothermia group. In the normothermia group, the mortality rate was 45.45% (20 of 44 patients) and the rate of favorable outcome was 27.27% (12 of 44 patients) (p < 0.05). Induced mild hypothermia also markedly reduced ICP (p < 0.01) and inhibited hyperglycemia (p < 0.05). The rates of complication were not significantly different between the two groups.

CONCLUSIONS

The data produced by this study demonstrate that long-term mild hypothermia therapy significantly improves outcomes in patients with severe TBI.

Severity of experimental brain injury on lactate and free fatty acid accumulation and Evans blue extravasation in the rat cortex and hippocampus

Lactate and free fatty acids (FFAs) were extracted from the cortices and hippocampi of rats subjected to sham operation, or mild (1.25 atm) or moderate (2.0 atm) fluid percussion (FP) injury, and their total tissue concentrations were measured. The elevation of lactate in the injured left cortex (IC) and ipsilateral hippocampus (IH) was significantly greater in the moderate-injury than in the mild-injury group at most test times between 5 min and 48 h after injury. Levels of total FFAs were elevated in the IC and IH to a greater extent and for a longer period after injury in the moderate-injury (up to 48 h) than in the mild-injury group (up to 20 min). In general, the extent and duration of the elevation of most of the individual FFAs (palmitic, stearic, oleic, and arachidonic acids) in the IC and IH were also greater in the moderate-injury group than in the mild-injury group. In the contralateral cortex (CC) and hippocampus (CH), the elevation of lactate and total FFAs (and individual stearic and arachidonic acids) were also greater in the moderate-injury group than in the low-injury group at 5 min after injury. The extravasation of Evans blue in the IC and IH from 3 to 6 h after injury was also the greatest in the moderate-injury group. The hippocampal CA3 neuronal cell loss, but not cortical lesion volume, also increased with the severity of injury. These findings suggest that certain neurochemical, physiological (blood-brain barrier permeability), and morphologic responses increase with the severity of FP brain injury, and such relationships are consistent with the increased behavioral deficits observed with the increase of severity of brain injury.

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.

Axonal injury alters alternative splicing of the retinal NR1 receptor: the preferential expression of the NR1b isoforms is crucial for retinal ganglion cell survival

Cellular-specific splicing of the retinal NMDAR1 receptor (NR1) and expression of NMDAR2 receptor (NR2) subunits in response to optic nerve injury was investigated by in situ hybridization in adult rats. A controlled optic nerve crush led to a clear alteration in the expression of alternatively spliced NR1 variants in the retinal ganglion cell layer (GCL). The NR1-2b and NR1-4b isoforms were preferentially expressed between 2 d and 1 week after injury, whereas expression for all other isoforms remained either unchanged or decreased to barely detectable levels within 4 weeks. Cellular silver grain density for NR2 subunits also declined in the GCL after trauma. To directly test the hypothesis that NR1b expression is crucial for cell survival after axonal trauma, we administered intraocularly an antisense oligonucleotide against the NR1b isoform 2 and 3 d after injury. This led to a drastic loss of retrogradely labeled retinal ganglion cells (RGCs). Antisense targeting clearly reduced retinal NR1 protein levels, as judged by Western blot analysis, but had no effect on the cell number in control retinas. These findings point toward injury-specific changes in alternative splicing of the NR1 receptor, which are crucial for the survival of RGCs after partial axonal trauma. We therefore propose that this reflects an adaptive, rather than a pathogenic, cellular response to neurotrauma.

Failure of cerebral autoregulation in an experimental diffuse brain injury model

The normal cerebral circulation has the ability to maintain a stable cerebral blood flow over a wide range of cerebral perfusion pressures and this is known as cerebral autoregulation. Autoregulation may be impaired in the injured brain. Closed head injury was induced in 28 Sprague-Dawley rats weighing 400-450 g. Four groups were studied: control and groups, head injured by weight drop from one meter height using 350 g, 400 g and 450 g respectively. CBF was monitored using laser-Doppler flowmetry along with monitoring of ICP and arterial blood pressure. If the correlation coefficient between CBF and CPP was > 0.85 and CPP was within normal range, loss of autoregulation was hypothesized. Loss of autoregulation was seen in all groups of injured rats during first four hours. A statistically significant difference (p = 0.041) was seen in the trequency of loss of autoregulation between injured and control animals. No loss of autoregulation was observed in the control group. In conclusion CBF and CPP provide information about loss of autoregulation in diffuse brain injury. Decrease in CBF and increase of ICP is observed as a result of loss of cerebral autoregulation. Knowledge of loss of autoregulation could help in the management of head injured patients.

pH dependency of mu-calpain and m-calpain activity assayed by casein zymography following traumatic brain injury in the rat

Studies employing casein zymographic assays analyzed the effects of varying pH (from pH 6.8 to pH 8.0) on changes in mu-calpain and m-calpain activity in naive, sham-injured and injured rat cortex 3 h following unilateral cortical impact injury. Mu-calpain activity following cortical impact injury was enhanced between pH values of 7.2 and 7.8, with pH 7.5 being optimal. m-Calpain activity was readily detected only between pH values of 7.2 and 7.4, with pH 7.3 producing the most prominent proteolytic activity. These observations suggest that strict control of pH is an important consideration in assessments of brain pH activation by casein zymography. Moreover, activation of different calpain isoforms, especially after traumatic brain injury, may be differentially influenced by smaller changes in physiological pH than previously recognized.

Amelioration of mitochondrial function by a novel antioxidant U-101033E following traumatic brain injury in rats

In the present study, a severe traumatic brain injury (TBI) was produced over the right parietal cortex of rats using the controlled cortical impact injury (CCII) model. TBI perturbed calcium homeostasis and impaired electron transfer and energy coupling activities of forebrain mitochondria isolated from injured hemispheres with a maximal injury at 12-72 h. Efficacy of the blood-brain barrier penetrating antioxidant U-101033E on TBI-induced mitochondrial impairment was evaluated. In the dose-response experiment, two i.v. boluses (vehicle or 1-10 mg/kg of U-101033E) were administered at 5 min and 2h post-TBI. Forebrain mitochondria from each hemisphere were examined at 12 h post-injury. With respect to forebrain mitochondrial dysfunction, the drug showed a bell-shaped dose-response curve with an optimal dose of 3 mg/kg (n = 5, p < 0.05 vs. vehicle). In the time-course experiment, two i.v. boluses of 3 mg U-101033E/kg (the optimal dose) were given at 5 min and 2 h post-injury and forebrain mitochondria were examined at 6 h-14 days post-injury. U-101033E significantly restored electron transfer, energy coupling capacity, and Ca2+ transport capacity during 6 h to 14 days post-injury. Our data indicate that the antioxidant U-101033E administered post-injury at proper dosage can effectively restore TBI-induced mitochondrial dysfunction and support the contention that oxidative stress plays an important role in the pathogenesis of TBI.

Effects of six weeks of chronic ethanol administration on lactic acid accumulation and high energy phosphate levels after experimental brain injury in rats

The effects of 6 weeks of chronic ethanol administration on the lateral fluid percussion (FP) brain injury-induced regional accumulation of lactate and on the levels of total high-energy phosphates were examined in rats. In both the chronic ethanol diet (ethanol diet) and pair-fed isocaloric sucrose control diet (control diet) groups, tissue concentrations of lactate were elevated in the cortices and hippocampi of both the ipsilateral and contralateral hemispheres at 5 min after brain injury. In both diet groups, concentrations of lactate were elevated only in the injured left cortex and the ipsilateral hippocampus at 20 min after FP brain injury. No significant differences were found in the levels of lactate in the cortices and hippocampi of sham animals and brain-injured animals between the ethanol and control diet groups at 5 min and 20 min after injury. In the ethanol and control diet groups, tissue concentrations of total high-energy phosphates (ATP + PCr) were not affected in the cortices and hippocampi at 5 min and 20 min after lateral FP brain injury. No significant differences were found in the levels of total high-energy phosphates in the cortices and hippocampi of the sham and brain-injured animals between the ethanol and control diet groups at 5 min and 20 min after injury. Histologic studies revealed a similar extent of damage in the cortex and in the CA3 region of the ipsilateral hippocampus in both diet groups at 14 days after lateral FP brain injury. These findings suggest that 6 weeks of chronic ethanol administration does not alter brain injury-induced accumulation of lactate, levels of total high energy phosphates, and extent of morphological damage.

Riluzole reduces brain lesions and improves neurological function in rats after a traumatic brain injury

Riluzole (2-amino 6-trifluoromethoxy-benzothiazole) was studied in a rat model of traumatic brain injury (TBI) induced by a fluid percussion applied laterally to the right parietal cortex. Study I: vehicle or riluzole (4 or 8 mg/kg) was administered 15 min (i.v.), 6 h and 24 h (s.c.), after TBI. Brain lesions were quantified 1 week after insult. Riluzole significantly reduced the size of TBI-induced lesions by approximately 44% with either dose regime (P < 0.05). Study II: vehicle or riluzole (8 mg/kg) was administered 15 min (i.v.), 6 h (i.p.) and then twice daily (i.p.) for 6 days, after injury. One, 2 and 3 weeks after TBI, a neurological examination was performed. Control injured rats had a significant neurological deficit at 1, 2 and 3 weeks (P < 0.001). Riluzole treatment did not modify the neurological status evaluated for the first 2 weeks after TBI. However at 3 weeks, riluzole significant improved the neurological function of injured rats (P < 0.05). These results suggest that riluzole may be beneficial in the clinical treatment of TBI. The protective action of riluzole may result from (i) stabilization of the inactivated state of voltage-dependent sodium channels, (ii) indirect action on the glutamatergic pathway, and/or (iii) indirect neurotrophic effect.

Blood glucose concentration does not affect outcome in brain trauma: A 31P MRS study

Effects of blood glucose concentration on biochemical and neurologic outcome following lateral fluid percussion-induced traumatic injury of moderate severity (2.8 atm) in rats were studied using radioactive phosphorus (31P) magnetic resonance spectroscopy (MRS) and a battery of tests designed to evaluate posttraumatic neurologic motor function. Prior to injury, male Sprague-Dawley rats (n = 18) were randomly assigned to receive either dextrose, 2 ml 50% (wt/vol), zinc insulin (10 IU/kg) or no treatment, thus dividing the animals into hyperglycemic, hypoglycemic, and normoglycemic groups, respectively. Animals were then injured, monitored for 4 h by 31P MRS before being allowed to recover, and assessed for posttraumatic motor function. Following brain injury, there was no difference in brain intracellular pH between groups over the 4-h posttraumatic MRS monitoring period. Similarly, intracellular free magnesium, cytosolic phosphorylation potential, and neurologic outcome posttrauma were not significantly different between groups. We conclude that, unlike models of ischemia, blood glucose concentration may not be a significant factor affecting outcome in traumatic brain injury.

Diffusion- and T2-weighted MRI of closed-head injury in rats: a time course study and correlation with histology

Diffusion- and T2-weighted MRI were used to evaluate changes in brain water characteristics following closed-head injury in rats. Images were collected within the first 2 h and at 24 h and 7 days following the traumatic event and then compared with histology. The ratios between the apparent diffusion coefficients (ADCs) of the traumatized tissues and normal brain tissues were significantly different from unity and were found to be 0.79 +/- 0.25 (p < 0.01), 0.49 +/- 0.33 (p < 0.0002), and 3.47 +/- 1.36 (p < 10(-6)) at 1-2 h, 24 h, and 1 week after the trauma, respectively. In severe trauma, areas of hyperintensity which were not apparent on the T2-weighted images could be detected on the diffusion-weighted images within 1-2 h after the trauma. At 24 h following the traumatic event, large areas of hyperintensity are observed in both types of images. One week following the trauma, the ADCs of the traumatized tissues (1.84 +/- 0.69 x 10(-5) cm2/s) are much larger than those of normal brain (0.57 +/- 0.19 x 10(-5) cm2/s) and approach the value of free water. At 7 days, the areas of hyperintensity in the T2-weighted images seem to underestimate the injured areas found by histology. At this time point a good correlation is obtained between the areas of hypointensity observed on the diffusion-weighted images and the infarct areas obtained by histology (r = 0.88).

Detection of acute pathologic changes following experimental traumatic brain injury using diffusion-weighted magnetic resonance imaging

Standard magnetic resonance imaging (MRI) has been shown to be remarkably insensitive to acute changes following traumatic brain injury. Because diffusion-weighted MRI has recently demonstrated excellent sensitivity to acute ischemic injury and other CNS abnormalities, we evaluated the use of diffusion MRI for the detection of pathologic changes in the rat brain during the first hours following parasagittal fluid percussion brain injury. Diffusion MRI was able to demonstrate a significant diffusion decrease in the primary cortical contusion injury and a comparable decrease in the ipsilateral thalamus. Tissue damage in the thalamus region is much weaker than in the cortex, but the thalamus is a primary site of axonal and dendritic injury in this model. T2 imaging in the same subjects showed slight enhancement in the neighborhood of the injured cortex but was unable to demonstrate injury elsewhere. Diffusion imaging was superior to T2 at demonstrating injury and the prominent diffusion decrease in the thalamus suggests that diffusion MRI is preferentially sensitive to axonal or dendritic injury.

Effect of magnesium given 1 hour after head trauma on brain edema and neurological outcome

Excitatory amino acids (EAA), mainly glutamate and aspartate, are released in excessive amounts from terminals of ischemic or traumatically injured neurons. These excessive levels of EAAs initiate a cascade of events believed to lead to secondary delayed damage to the surrounding brain. The N-methyl-D-aspartate receptor antagonists MK-801 and ketamine are reported to suppress excessive EAA release and to attenuate the development of focal brain edema following neuronal injury. Magnesium is also reported to work at the postsynaptic receptor to reduce the neurotoxic effect of glutamate. The present study was undertaken to examine the effect of postinjury treatment with Mg++ on brain edema and neurological outcome after traumatic brain injury. Sixty-nine rats that survived halothane anesthesia and closed head trauma (CHT) were randomly assigned to one of seven experimental groups: sham, CHT, and CHT with administration of Mg++ 1 hour postinjury. At 48 hours, brain tissue Mg++ concentration (calculated from optical density using a standard curve) was significantly increased compared to baseline levels (10.06 +/- 2.44 mg/g vs. 6.83 +/- 0.81 mg/g, p < 0.01 calculated by one-way analysis of variance). Also at 48 hours postinjury, brain tissue specific gravity in the contused hemisphere of Mg(++)-treated rats was significantly greater than that in the contused hemisphere of untreated rats, indicating attenuation of brain edema formation by Mg++. The neurological severity score (NSS) of rats treated with Mg++ improved significantly at both 18 and 48 hours, compared to baseline values obtained 1 hour after CHT but prior to administration of Mg++ (11.2 +/- 2.5 vs. 15.2 +/- 4.1, p = 0.03; and 12.3 +/- 6.1 vs. 17.3 +/- 3.6, p = 0.004, respectively). In the untreated groups, the NSS at 18 and 48 hours was not significantly different from baseline values (that is, no neurological improvement). The present study indicates that postinjury treatment with Mg++ attenuates brain edema formation and improves neurological outcome after experimental CHT.