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

Evaluation of microglia activation related markers following a clinical course of TBS: A non-human primate study

While the applicability and popularity of theta burst stimulation (TBS) paradigms remain, current knowledge of their neurobiological effects is still limited, especially with respect to their impact on glial cells and neuroinflammatory processes. We used a multimodal imaging approach to assess the effects of a clinical course of TBS on markers for microglia activation and tissue injury as an indirect assessment of neuroinflammatory processes. Healthy non-human primates received continuous TBS (cTBS), intermittent TBS (iTBS), or sham stimulation over the motor cortex at 90% of resting motor threshold. Stimulation was delivered to the awake subjects 5 times a week for 3-4 weeks. Translocator protein (TSPO) expression was evaluated using Positron Emission Tomography and [11C]PBR28, and myo-inositol (mI) and N-acetyl-aspartate (NAA) concentrations were assessed with Magnetic Resonance Spectroscopy. Animals were then euthanized, and immunofluorescence staining was performed using antibodies against TSPO. Paired t-tests showed no significant changes in [11C]PBR28 measurements after stimulation. Similarly, no significant changes in mI and NAA concentrations were found. Post-mortem TSPO evaluation showed comparable mean immunofluorescence intensity after active TBS and sham delivery. The current study suggests that in healthy brains a clinical course of TBS, as evaluated with in-vivo imaging techniques (PET and MRS), did not measurably modulate the expression of glia related markers and metabolite associated with neural viability.

Spreading depolarizations pose critical energy challenges in acute brain injury

Spreading depolarization (SD) is an electrochemical wave of neuronal depolarization mediated by extracellular K+ and glutamate, interacting with voltage-gated and ligand-gated ion channels. SD is increasingly recognized as a major cause of injury progression in stroke and brain trauma, where the mechanisms of SD-induced neuronal injury are intimately linked to energetic status and metabolic impairment. Here, I review the established working model of SD initiation and propagation. Then, I summarize the historical and recent evidence for the metabolic impact of SD, transitioning from a descriptive to a mechanistic working model of metabolic signaling and its potential to promote neuronal survival and resilience. I quantify the energetic cost of restoring ionic gradients eroded during SD, and the extent to which ion pumping impacts high-energy phosphate pools and the energy charge of affected tissue. I link energy deficits to adaptive increases in the utilization of glucose and O2, and the resulting accumulation of lactic acid and CO2 downstream of catabolic metabolic activity. Finally, I discuss the neuromodulatory and vasoactive paracrine signaling mediated by adenosine and acidosis, highlighting these metabolites' potential to protect vulnerable tissue in the context of high-frequency SD clusters.

Cerebrospinal fluid purinomics as a biomarker approach to predict outcome after severe traumatic brain injury

Severe traumatic brain injury (TBI) is associated with high rates of mortality and long-term disability linked to neurochemical abnormalities. Although purine-derivatives play important roles in TBI pathogenesis in preclinical models, little is known about potential changes in purine levels and their implications in human TBI. We assessed cerebrospinal fluid (CSF) levels of purines in severe TBI patients as potential biomarkers that predict mortality and long-term dysfunction. This was a cross-sectional study performed in 17 severe TBI patients (Glasgow Coma Scale < 8) and 51 controls. Two to four hours after admission to ICU, patients were submitted to ventricular drainage and CSF collection for quantification of adenine and guanine purine-derivatives by HPLC. TBI patients survival was followed up to 3 days from admission. A neurofunctional assessment was performed through the modified Rankin Scale (mRS) two years after ICU admission. Purine levels were compared between control and TBI patients, and between surviving and non-surviving patients. Relative to controls, TBI patients presented increased CSF levels of GDP, guanosine, adenosine, inosine, hypoxanthine, and xanthine. Further, GTP, GDP, IMP, and xanthine levels were different between surviving and non-surviving patients. Among the purines, guanosine was associated with improved mRS (p=0.042; r= -0.506). Remarkably, GTP displayed predictive value (AUC=0.841, p=0.024) for discriminating survival vs. non-survival patients up to three days from admission. These results support TBI-specific purine signatures, suggesting GTP as a promising biomarker of mortality, and guanosine as an indicator of long-term functional disability.

Glial immune-related pathways mediate effects of closed head traumatic brain injury on behavior and lethality in Drosophila

In traumatic brain injury (TBI), the initial injury phase is followed by a secondary phase that contributes to neurodegeneration, yet the mechanisms leading to neuropathology in vivo remain to be elucidated. To address this question, we developed a Drosophila head-specific model for TBI termed Drosophila Closed Head Injury (dCHI), where well-controlled, nonpenetrating strikes are delivered to the head of unanesthetized flies. This assay recapitulates many TBI phenotypes, including increased mortality, impaired motor control, fragmented sleep, and increased neuronal cell death. TBI results in significant changes in the transcriptome, including up-regulation of genes encoding antimicrobial peptides (AMPs). To test the in vivo functional role of these changes, we examined TBI-dependent behavior and lethality in mutants of the master immune regulator NF-κB, important for AMP induction, and found that while sleep and motor function effects were reduced, lethality effects were enhanced. Similarly, loss of most AMP classes also renders flies susceptible to lethal TBI effects. These studies validate a new Drosophila TBI model and identify immune pathways as in vivo mediators of TBI effects.

Traumatic brain injury in Drosophila causes sleep and motor impairments, as well as a strong activation of the innate immune response that is crucial for survival. This study leverages Drosophila as a model organism to reveal neuroprotective and neurotoxic injury mechanisms more quickly using high throughout approaches.

In Vivo Detection of Extracellular Adenosine Triphosphate in a Mouse Model of Traumatic Brain Injury

Traumatic brain injury (TBI) is traditionally characterized by primary and secondary injury phases, both contributing to pathological and morphological changes. The mechanisms of damage and chronic consequences of TBI remain to be fully elucidated, but synaptic homeostasis disturbances and impaired energy metabolism are proposed to be a major contributor. It has been proposed that an increase of extracellular (eATP) adenosine triphosphate (ATP) in the area immediately surrounding impact may play a pivotal role in this sequence of events. After tissue injury, rupture of cell membranes allows release of intracellular ATP into the extracellular space, triggering a cascade of toxic events and inflammation. ATP is a ubiquitous messenger; however, simple and reliable techniques to measure its concentration have proven elusive. Here, we integrate a sensitive bioluminescent eATP sensor known as pmeLUC, with a controlled cortical impact mouse model to monitor eATP changes in a living animal after injury. Using the pmeLUC probe, a rapid increase of eATP is observed proximal to the point of impact within minutes of the injury. This event is significantly attenuated when animals are pretreated with an ATP hydrolyzing agent (apyrase) before surgery, confirming the contribution of eATP. This new eATP reporter could be useful for understanding the role of eATP in the pathogenesis in TBI and may identify a window of opportunity for therapeutic intervention.

Targeting higher levels of lactate in the post-injury period following traumatic brain injury

BACKGROUND

Secondary traumatic brain injury (TBI) consequences continue multiple cascades of biochemical reactions caused by initial neurotrauma and one of the important pathogenetic processes is mitochondrial dysfunction partly characterized by elevation of lactate/pyruvate ratio in brain following metabolic failure.

OBJECTIVE

To identify lactate, pyruvate, lactate dehydrogenase, tau protein, ceruloplasmin blood levels in the post-injury period following TBI in relation to its different forms.

PATIENTS AND METHODS

Ninety-six patients (mean age ± SD 38.8 ± 10.39 years) at 12 months post-injury follow-ups TBI (post-TBI) were investigated; plasma lactate and pyruvate levels were measured by the spectrophotometric method according to the manufacturer protocols; tau protein, ceruloplasmin and lactate dehydrogenase (LDH) were measured in sera by enzyme-linked immunosorbent assays. Group 1 was comprised of 54 participants who had a history of mild TBI, group 2 was comprised of 42 patients who had a history of moderate TBI.

RESULTS

In this work, we found the highest plasma lactate levels in the patients with the post-injury period following moderate TBI as compared to controls (p = 0.0047, t = 2.924, 95 % CI -0.2154 to -0.04071) where the median lactate level was 0.832 ± 0.033 and 0704 ± 0.021 mmol/L in controls. No significant differences were seen between mild and moderate post-TBI (p = 0.079; t = 1.772); significant difference was also seen between general post-TBI group versus controls (p = 0.0181; t = 2.396; 95 % CI -0.1627 to -0.01551) with the median total lactate level of 0.793 ± 0.019 mmol/L. Lactate data did not distinguish with the respect to gender or age. The results showed no significant differences in tau protein, pyruvate, LDH and ceruloplasmin levels.

CONCLUSION

This study shows higher lactate levels in the post-injury period following TBI that reflect post-injury oxidative dysmetabolism and are more expressed in the post-injury period following moderate TBI.

Thermoregulation in brain injury

Different mechanisms explain thermoregulatory dysfunction following ischemic stroke, hemorrhagic stroke, and traumatic brain injury. Temperature instability following brain injury likely involves hypothalamic injury, pathologic changes in cerebral blood flow, metabolic derangement, and a neurogenic inflammatory response. Although targeted temperature management (TTM) exerts pleiotropic effects, the heterogeneity of brain injury has hindered identification of patient subsets most likely to benefit from TTM. Early optimism about TTM's role in brain injury has been tempered by the failure of successive clinical trials to show improved patient outcomes. However, given the deleterious effects of fever, aggressive fever management is still warranted in the critically ill neurologic patient.

Traumatic Brain Injury Alters the Metabolism and Facilitates Alzheimer's Disease in a Murine Model

A majority of Alzheimer's disease (AD) cases are sporadic without known cause. People who suffered from traumatic brain injury (TBI) are more likely to develop neurodegeneration and cognitive impairments. However, the role of TBI in pathophysiology of AD remains elusive. The present study intended to explore the effect of TBI on metabolism and its role in AD pathogenesis. We subjected double transgenic AD model mice APP23/PS45 to TBI. We found that TBI promoted β-secretase cleavage of amyloid β precursor protein and amyloid β protein deposition, and exuberated the cognitive impairments in AD mouse models. ¹H nuclear magnetic resonance (¹H-NMR)-based metabolomics with multivariate analysis was performed to investigate the characteristic metabolites and the related metabolic pathways in the serum and urine samples of the mice. TBI affected the metabolic patterns, methylamine metabolism, and amino acid metabolism in serum samples. Urinary metabolites showed that glycolysis and the tricarboxylic acid (TCA) cycle were perturbed. The results indicate that TBI might facilitate Alzheimer's pathogenesis by altering metabolism and inducing mitochondrial dysfunction. The study suggests that metabolite changes could also serve as biomarkers for TBI-induced neurodegeneration.

Metabolic fate of glucose in rats with traumatic brain injury and pyruvate or glucose treatments: A NMR spectroscopy study

Administration of sodium pyruvate (SP; 9.08 μmol/kg, i.p.), ethyl pyruvate (EP; 0.34 μmol/kg, i.p.) or glucose (GLC; 11.1 μmol/kg, i.p.) to rats after unilateral controlled cortical impact (CCI) injury has been reported to reduce neuronal loss and improve cerebral metabolism. In the present study these doses of each fuel or 8% saline (SAL; 5.47 nmoles/kg) were administered immediately and at 1, 3, 6 and 23 h post-CCI. At 24 h all CCI groups and non-treated Sham injury controls were infused with [1,2 ¹³C] glucose for 68 min ¹³C nuclear magnetic resonance (NMR) spectra were obtained from cortex + hippocampus tissues from left (injured) and right (contralateral) hemispheres. All three fuels increased lactate labeling to a similar degree in the injured hemisphere. The amount of lactate labeled via the pentose phosphate and pyruvate recycling (PPP + PR) pathway increased in CCI-SAL and was not improved by SP, EP, and GLC treatments. Oxidative metabolism, as assessed by glutamate labeling, was reduced in CCI-SAL animals. The greatest improvement in oxidative metabolism was observed in animals treated with SP and fewer improvements after EP or GLC treatments. Compared to SAL, all three fuels restored glutamate and glutamine labeling via pyruvate carboxylase (PC), suggesting improved astrocyte metabolism following fuel treatment. Only SP treatments restored the amount of [4 ¹³C] glutamate labeled by the PPP + PR pathway to sham levels. Milder injury effects in the contralateral hemisphere appear normalized by either SP or EP treatments, as increases in the total pool of ¹³C lactate and labeling of lactate in glycolysis, or decreases in the ratio of PC/PDH labeling of glutamine, were found only for CCI-SAL and CCI-GLC groups compared to Sham. The doses of SP, EP and GLC examined in this study all enhanced lactate labeling and restored astrocyte-specific PC activity but differentially affected neuronal metabolism after CCI injury. The restoration of astrocyte metabolism by all three fuel treatments may partially underlie their abilities to improve cerebral glucose utilization and to reduce neuronal loss following CCI injury.

Metabolic, enzymatic and gene involvement in cerebral glucose dysmetabolism after traumatic brain injury

In this study, the metabolic, enzymatic and gene changes causing cerebral glucose dysmetabolism following graded diffuse traumatic brain injury (TBI) were evaluated. TBI was induced in rats by dropping 450g from 1 (mild TBI; mTBI) or 2m height (severe TBI; sTBI). After 6, 12, 24, 48, and 120h gene expressions and enzymatic activities of glycolysis and pentose phosphate pathway (PPP) enzymes, and levels of lactate, ATP, ADP, ATP/ADP (indexing mitochondrial phosphorylating capacity), NADP(+), NADPH and GSH were determined in whole brain extracts (n=9 rats at each time for both TBI levels). Sham-operated animals (n=9) were used as controls. Results demonstrated that mTBI caused a late increase (48-120h post injury) of glycolytic gene expression and enzymatic activities, concomitantly with mitochondrial functional recovery (ATP and ATP/ADP normalization). No changes in lactate and PPP genes and enzymes, were accompanied by transient decrease in GSH, NADP(+), NADPH and NADPH/NADP(+). Animals following sTBI showed early increase (6-24h post injury) of glycolytic gene expression and enzymatic activities, occurring during mitochondrial malfunctioning (50% decrease in ATP and ATP/ADP). Higher lactate and lower GSH, NADP(+), NADPH, NADPH/NADP(+) than controls were recorded at anytime post injury (p<0.01). Both TBI levels caused metabolic and gene changes affecting glucose metabolism. Following mTBI, increased glucose flux through glycolysis is coupled to mitochondrial glucose oxidation. "True" hyperglycolysis occurs only after sTBI, where metabolic changes, caused by depressed mitochondrial phosphorylating capacity, act on genes causing net glycolytic flux increase uncoupled from mitochondrial glucose oxidation.

Mitochondrial response in a toddler-aged swine model following diffuse non-impact traumatic brain injury

Traumatic brain injury (TBI) is an important health problem, and a leading cause of death in children worldwide. Mitochondrial dysfunction is a critical component of the secondary TBI cascades. Mitochondrial response in the pediatric brain has limited investigation, despite evidence that the developing brain's response differs from that of the adult, especially in diffuse non-impact TBI. We performed a detailed evaluation of mitochondrial bioenergetics using high-resolution respirometry in a swine model of diffuse TBI (rapid non-impact rotational injury: RNR), and examined the cortex and hippocampus. A substrate-uncoupler-inhibitor-titration protocol examined the role of the individual complexes as well as the uncoupled maximal respiration. Respiration per mg of tissue was also related to citrate synthase activity (CS) as an attempt to control for variability in mitochondrial content following injury. Diffuse RNR stimulated increased complex II-driven respiration relative to mitochondrial content in the hippocampus compared to shams. LEAK (State 4o) respiration increased in both regions, with decreased respiratory ratios of convergent oxidative phosphorylation through complex I and II, compared to sham animals, indicating uncoupling of oxidative phosphorylation at 24h. The study suggests that proportionately, complex I contribution to convergent mitochondrial respiration was reduced in the hippocampus after RNR, with a simultaneous increase in complex-II driven respiration. Mitochondrial respiration 24h after diffuse TBI varies by location within the brain. We concluded that significant uncoupling of oxidative phosphorylation and alterations in convergent respiration through complex I- and complex II-driven respiration reveals therapeutic opportunities for the injured at-risk pediatric brain.

Chaperone-Mediated Autophagy after Traumatic Brain Injury

Chaperone-mediated autophagy (CMA) and the ubiquitin-proteasomal system (UPS) are two major protein degradation systems responsible for maintaining cellular homeostasis, but how these two systems are regulated after traumatic brain injury (TBI) remains unknown. TBI produces primary mechanical damage that must be repaired to maintain neuronal homeostasis. The level of lysosomal-associated membrane protein type 2A (LAMP2A) is the hallmark of CMA activity. The level of polyubiquitinated proteins (ubi-proteins) reflects UPS activity. This study utilized a moderate fluid percussion injury model in rats to investigate the changes in CMA and the UPS after TBI. Induction of CMA was manifested by significant upregulation of LAMP2A and secondary lysosomes during the periods of 1-15 days of recovery after TBI. In comparison, the levels of ubi-proteins were increased only moderately after TBI. The increases in the levels of LAMP2A and 70 kDa heat-shock protein for CMA after TBI were seen mainly in the secondary lysosome-containing fractions. Confocal and electron microscopy further showed that increased LAMP2A or lysosomes were found mainly in neurons and proliferated microglia. Because CMA and the UPS are two major routes for elimination of different types of cellular aberrant proteins, the consecutive activation of these two pathways may serve as a protective mechanism for maintaining cellular homeostasis after TBI.

Imaging of cerebral blood flow in patients with severe traumatic brain injury in the neurointensive care

Ischemia is a common and deleterious secondary injury following traumatic brain injury (TBI). A great challenge for the treatment of TBI patients in the neurointensive care unit (NICU) is to detect early signs of ischemia in order to prevent further advancement and deterioration of the brain tissue. Today, several imaging techniques are available to monitor cerebral blood flow (CBF) in the injured brain such as positron emission tomography (PET), single-photon emission computed tomography, xenon computed tomography (Xenon-CT), perfusion-weighted magnetic resonance imaging (MRI), and CT perfusion scan. An ideal imaging technique would enable continuous non-invasive measurement of blood flow and metabolism across the whole brain. Unfortunately, no current imaging method meets all these criteria. These techniques offer snapshots of the CBF. MRI may also provide some information about the metabolic state of the brain. PET provides images with high resolution and quantitative measurements of CBF and metabolism; however, it is a complex and costly method limited to few TBI centers. All of these methods except mobile Xenon-CT require transfer of TBI patients to the radiological department. Mobile Xenon-CT emerges as a feasible technique to monitor CBF in the NICU, with lower risk of adverse effects. Promising results have been demonstrated with Xenon-CT in predicting outcome in TBI patients. This review covers available imaging methods used to monitor CBF in patients with severe TBI.

Impaired cortical mitochondrial function following TBI precedes behavioral changes

Traumatic brain injury (TBI) pathophysiology can be attributed to either the immediate, primary physical injury, or the delayed, secondary injury which begins minutes to hours after the initial injury and can persist for several months or longer. Because these secondary cascades are delayed and last for a significant time period post-TBI, they are primary research targets for new therapeutics. To investigate changes in mitochondrial function after a brain injury, both the cortical impact site and ipsilateral hippocampus of adult male rats 7 and 17 days after a controlled cortical impact (CCI) injury were examined. State 3, state 4, and uncoupler-stimulated rates of oxygen consumption, respiratory control ratios (RCRs) were measured and membrane potential quantified, and all were significantly decreased in 7 day post-TBI cortical mitochondria. By contrast, hippocampal mitochondria at 7 days showed only non-significant decreases in rates of oxygen consumption and membrane potential. NADH oxidase activities measured in disrupted mitochondria were normal in both injured cortex and hippocampus at 7 days post-CCI. Respiratory and phosphorylation capacities at 17 days post-CCI were comparable to naïve animals for both cortical and hippocampus mitochondria. However, unlike oxidative phosphorylation, membrane potential of mitochondria in the cortical lining of the impact site did not recover at 17 days, suggesting that while diminished cortical membrane potential at 17 days does not adversely affect mitochondrial capacity to synthesize ATP, it may negatively impact other membrane potential-sensitive mitochondrial functions. Memory status, as assessed by a passive avoidance paradigm, was not significantly impaired until 17 days after injury. These results indicate pronounced disturbances in cortical mitochondrial function 7 days after CCI which precede the behavioral impairment observed at 17 days.

N-Acetylaspartate reductions in brain injury: impact on post-injury neuroenergetics, lipid synthesis, and protein acetylation

N-Acetylaspartate (NAA) is employed as a non-invasive marker for neuronal health using proton magnetic resonance spectroscopy (MRS). This utility is afforded by the fact that NAA is one of the most concentrated brain metabolites and that it produces the largest peak in MRS scans of the healthy human brain. NAA levels in the brain are reduced proportionately to the degree of tissue damage after traumatic brain injury (TBI) and the reductions parallel the reductions in ATP levels. Because NAA is the most concentrated acetylated metabolite in the brain, we have hypothesized that NAA acts in part as an extensive reservoir of acetate for acetyl coenzyme A synthesis. Therefore, the loss of NAA after TBI impairs acetyl coenzyme A dependent functions including energy derivation, lipid synthesis, and protein acetylation reactions in distinct ways in different cell populations. The enzymes involved in synthesizing and metabolizing NAA are predominantly expressed in neurons and oligodendrocytes, respectively, and therefore some proportion of NAA must be transferred between cell types before the acetate can be liberated, converted to acetyl coenzyme A and utilized. Studies have indicated that glucose metabolism in neurons is reduced, but that acetate metabolism in astrocytes is increased following TBI, possibly reflecting an increased role for non-glucose energy sources in response to injury. NAA can provide additional acetate for intercellular metabolite trafficking to maintain acetyl CoA levels after injury. Here we explore changes in NAA, acetate, and acetyl coenzyme A metabolism in response to brain injury.

Downregulation of Src-kinase and glutamate-receptor phosphorylation after traumatic brain injury

Phosphorylation of N-methyl-D-aspartate (NMDA) receptors is a major regulatory mechanism underlying synaptic plasticity. However, changes in NMDA receptors and phosphorylation after traumatic brain injury (TBI) remain incompletely understood. Using an animal TBI model, we observed that the protein level of NMDA receptor subunit NR2B was downregulated in synaptosomal fractions obtained from the ipsilateral neocortical injury region, whereas the levels of NR2A, NR1, and PSD93 were not significantly altered at 4 and 24 hours after TBI. Further investigation showed that tyrosine phosphorylations of NR2B Y1472 and PSD93 Y340 in synaptosomal fractions were significantly decreased relative to their total protein level after TBI. Correspondingly, phosphorylation of the Src-kinase-inhibitory site Y527 was increased, whereas phosphorylation of the activation site Y416 was decreased, indicating that the activity of Src kinase is significantly inhibited after TBI. In comparison, other Src family kinase substrates of NMDA receptor, NR2A Y1246, NR2A Y1325, and NR2B Y1070 were not obviously affected after TBI. The results suggest that TBI downregulates the Src-kinase-mediated phosphorylation of NR2 and PSD93 to destabilize the synaptic localization of NMDA receptors. Therefore, post-TBI loss of NMDA receptors may contribute to the depression of synaptic activity after TBI.

Bioenergetic study of murine hepatic tissue treated in vitro with atorvastatin

Atorvastatin (a 3-hydroxy-3-methylglutaryl coenzyme-A reductase inhibitor) is a widely used cholesterol-lowering drug, which is recognized for its potential hepatotoxicity. This study investigated in vitro effects of this agent on hepatic tissue respiration, ATP content, caspase activity, urea synthesis and histology. Liver fragments from Taylor Outbred and C57Bl/6 mice were incubated at 37°C in Krebs-Henseleit buffer continuously gassed with 95% O₂: 5% CO₂ in the presence and absence of atorvastatin. Phosphorescence O₂ analyzer that measured dissolved [O₂] as a function of time was used to monitor cellular mitochondrial O₂ consumption. The caspase-3 substrate N-acetyl-asp-glu-val-asp-7-amino-4-methylcoumarin was used to monitor caspase activity. The rates of hepatocyte respiration (μM O₂ min^-1 mg^-1) in untreated samples were 0.15 ± 0.07 (n = 31). The corresponding rates for samples treated with 50 nM (therapeutic concentration), 150 nM or 1.0 μM atorvastatin for ≤13 h were 0.13 ± 0.05 (n = 19), p = 0.521. The contents of hepatocyte ATP (pmol^-1 mg^-1) in untreated samples were 40.3 ± 14.0 and in samples treated with 1.0 μM atorvastatin for ≤4.5 h were 48.7 ± 23.9 (p = 0.7754). The concentrations of urea (mg/dL mg^-1, produced over 50 min) for untreated samples were 0.061 ± 0.020 (n = 6) and for samples treated with 1.0 μM atorvastatin for ≤6 h were 0.072 ± 0.022 (n = 6), p = 0.3866. Steadily, hepatocyte caspase activity and histology were unaffected by treatments with up to 1.0 μM atorvastatin for ≤6 h. Thus, the studied murine model showed preserved hepatocyte function and structure in the presence of high concentrations of atorvastatin.

The neuroprotective effect of lactate is not due to improved glutamate uptake after controlled cortical impact in rats

For many years lactate was considered to be a waste product of glycolysis. Data are accumulating that suggest that lactate is an important energy substrate for neurons during activation. In severe traumatic brain injury (TBI) glutamate release and ischemic cerebral blood flow (CBF) are major factors for a mismatch between energy demand and supply and for neuronal cell death. Although ATP and behavior could be improved by lactate treatment after TBI, no histological correlate nor any linkage to better astrocytic glutamate uptake or CBF as possible mechanisms have been described. We subjected male rats to a controlled cortical impact (CCI; 5 m/sec, 2.5 mm). To study the effects of lactate treatment on lesion volume, glutamate release, and CBF, animals were infused with either NaCl or 100 mM lactate for up to 3 h. The role of endogenous lactate was investigated by inhibiting transport with α-cyano-4-hydroxy-cinnamic acid (4-CIN; 90 mg/kg). Lactate treatment 15 min post-CCI reduced lesion volume from 21.1±2.8 mm³ to 12.1±1.9 mm³ at day 2 after CCI. Contusion produced a significant three- to fourfold increase of glutamate in microdialysates, but there was no significant difference between treatments that began 30 min before CCI. In this experiment lesion volume was significantly reduced by lactate at day 7 post-CCI (23.7±4 to 9.3±1-2 mm³). CBF increased immediately after CCI and dropped thereafter below baseline in all animals. Lactate infusion 15 min post-CCI elevated CBF for 20 min in 7 of 10 animals, whereas 7 of 8 NaCl-treated animals showed a further CBF decline. Neuroprotection was achieved by lactate treatment following contusion injury, whereas blocking of endogenous lactate transport exerted no adverse effects. Neuroprotection was not achieved by improved glutamate uptake into astrocytes, but was supported by augmented CBF following CCI. Due to its neuroprotective property, lactate might be a beneficial pharmacological treatment for TBI patients.

Do β-defensins and other antimicrobial peptides play a role in neuroimmune function and neurodegeneration?

It is widely accepted that the brain responds to mechanical trauma and development of most neurodegenerative diseases with an inflammatory sequelae that was once thought exclusive to systemic immunity. Mostly cationic peptides, such as the β-defensins, originally assigned an antimicrobial function are now recognized as mediators of both innate and adaptive immunity. Herein supporting evidence is presented for the hypothesis that neuropathological changes associated with chronic disease conditions of the CNS involve abnormal expression and regulatory function of specific antimicrobial peptides. It is also proposed that these alterations exacerbate proinflammatory conditions within the brain that ultimately potentiate the neurodegenerative process.

Rational design of surface/interface chemistry for quantitative in vivo monitoring of brain chemistry

To understand the molecular basis of brain functions, researchers would like to be able to quantitatively monitor the levels of neurochemicals in the extracellular fluid in vivo. However, the chemical and physiological complexity of the central nervous system (CNS) presents challenges for the development of these analytical methods. This Account describes the rational design and careful construction of electrodes and nanoparticles with specific surface/interface chemistry for quantitative in vivo monitoring of brain chemistry. We used the redox nature of neurochemicals at the electrode/electrolyte interface to establish a basis for monitoring specific neurochemicals. Carbon nanotubes provide an electrode/electrolyte interface for the selective oxidation of ascorbate, and we have developed both in vivo voltammetry and an online electrochemical detecting system for continuously monitoring this molecule in the CNS. Although Ca(2+) and Mg(2+) are involved in a number of neurochemical signaling processes, they are still difficult to detect in the CNS. These divalent cations can enhance electrocatalytic oxidation of NADH at an electrode modified with toluidine blue O. We used this property to develop online electrochemical detection systems for simultaneous measurements of Ca(2+) and Mg(2+) and for continuous selective monitoring of Mg(2+) in the CNS. We have also harnessed biological schemes for neurosensing in the brain to design other monitoring systems. By taking advantage of the distinct reaction properties of dopamine (DA), we have developed a nonoxidative mechanism for DA sensing and a system that can potentially be used for continuously sensing of DA release. Using "artificial peroxidase" (Prussian blue) to replace a natural peroxidase (horseradish peroxidase, HRP), our online system can simultaneously detect basal levels of glucose and lactate. By substituting oxidases with dehydrogenases, we have used enzyme-based biosensing schemes to develop a physiologically relevant system for detecting glucose and lactate in rat brain. Because of their unique optical properties and modifiable surfaces, gold nanoparticles (Au-NPs) have provided a platform of colorimetric assay for in vivo cerebral glucose quantification. We designed and modified the surfaces of Au-NPs and then used a sequence of reactions to produce hydroxyl radicals from glucose.

Effects of enoxaparin in the rat hippocampus following traumatic brain injury

Purpose of this study was to investigate the effects of low molecular weight heparin, enoxaparin, on different parameters of the hippocampal damage following traumatic brain injury (TBI) in the rat. TBI of moderate severity was performed over the left parietal cortex using the lateral fluid percussion brain injury model. Animals were s.c. injected with either enoxaparin (1mg/kg) or vehicle 1, 7, 13, 19, 25, 31, 37, and 43 h after the TBI induction. Sham-operated, vehicle-treated animals were used as the control group. Rats were sacrificed 48h after the induction of TBI. Hippocampi were processed for spectrophotometric measurements of the products of oxidative lipid damage, thiobarbituric acid-reactive substances (TBARS) levels, as well as the activities of antioxidant enzymes, superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px). Moreover, the Western blotting analyses of the oxidized protein levels, expressions of cyclooxygenase-2 (COX-2), inducible nitric oxide synthase (iNOS), pro- and mature-interleukin-1β (pro-, and mature-IL-1β), and active caspase-3 were performed. COX-2 expressions were also explored by using immunohistochemistry. Glial fibrillary acidic protein immunochistochemistry was performed with the aim to assess the level of astrocytic activity. Fluoro-Jade B staining was used to identify the level and extent of hippocampal neuronal injury. TBI caused statistically significant increases of the hippocampal TBARS and oxidized protein levels as well as COX-2, pro-IL-1β, and active caspase-3 overexpressions, but it did not significantly affect the SOD and GSH-Px activities, the iNOS, and mature-IL-1β expression levels. TBI also induced hippocampal reactive astrocytosis and neurodegeneration. Enoxaparin significantly decreased the hippocampal TBARS and oxidized protein levels, COX-2 overexpression and reactive gliosis, but it did not influence the SOD and GSH-Px activities, pro-IL-1β and active caspase-3 overexpressions as well as neurodegeneration following TBI. These findings demonstrate that enoxaparin may reduce oxidative damage, inflammation and astrocytosis following TBI in the rat and could be a candidate drug for neuroprotective treatment of this injury.

Ketogenic diet prevents alterations in brain metabolism in young but not adult rats after traumatic brain injury

Previous studies have shown that the change of cerebral metabolic rate of glucose (CMRglc) in response to traumatic brain injury (TBI) is different in young (PND35) and adult rats (PND70), and that prolonged ketogenic diet treatment results in histological and behavioral neuroprotection only in younger rat brains. However, the mechanism(s) through which ketones act in the injured brain and the biochemical markers of their action remain unknown. Therefore, the current study was initiated to: 1) determine the effect of injury on the neurochemical profile in PND35 compared to PND70 rats; and 2) test the effect of early post-injury administration of ketogenic diet on brain metabolism in PND35 versus PND70 rats. The data show that alterations in energy metabolites, amino acid, and membrane metabolites were not evident in PND35 rats on standard diet until 24  h after injury, when the concentration of most metabolites was reduced from sham-injured values. In contrast, acute, but transient deficits in energy metabolism were measured at 6  h in PND70 rats, together with deficits in N-acetylaspartate that endured until 24  h. Administration of a ketogenic diet resulted in significant increases in plasma β-hydroxybutyrate (βOHB) levels. Similarly, brain βOHB levels were significantly elevated in all injured rats, but were elevated by 43% more in PND35 rats compared to PND70 rats. As a result, ATP, creatine, and phosphocreatine levels at 24  h after injury were significantly improved in the ketogenic PND35 rats, but not in the PND70 group. The improvement in energy metabolism in the PND35 brains was accompanied by the recovery of NAA and reduction of lactate levels, as well as amelioration of the deficits of other amino acids and membrane metabolites. These results indicate that the PND35 brains are more resistant to the injury, indicated by a delayed deficit in energy metabolism. Moreover, the younger brains revert to ketones metabolism more quickly than do the adult brains, resulting in better neurochemical and cerebral metabolic recovery after injury.

Clinical characteristics and pathophysiological mechanisms of focal and diffuse traumatic brain injury

Traumatic brain injury (TBI) is a frequent and clinically highly heterogeneous neurological disorder with large socioeconomic consequences. TBI severity classification, based on the hospital admission Glasgow Coma Scale (GCS) score, ranges from mild (GCS 13-15) and moderate (GCS 9-12) to severe (GCS ≤ 8). The GCS reflects the risk of dying from TBI, which is low after mild (∼1%), intermediate after moderate (up to 15%) and high (up to 40%) after severe TBI. Intracranial damage can be focal, such as epidural and subdural haematomas and parenchymal contusions, or diffuse, for example traumatic axonal injury and diffuse cerebral oedema, although this distinction is somewhat arbitrary. Study of the cellular and molecular post-traumatic processes is essential for the understanding of TBI pathophysiology but even more to find therapeutic targets for the development of neuroprotective drugs to be eventually used in human beings. To date, studies in vitro and in vivo, mainly in animals but also in human beings, are unravelling the pathological TBI mechanisms at high pace. Nevertheless, TBI pathophysiology is all but completely elucidated. Neuroprotective treatment studies in human beings have been disappointing thus far and have not resulted in commonly accepted drugs. This review presents an overview on the clinical aspects and the pathophysiology of focal and diffuse TBI, and it highlights several acknowledged important events that occur on molecular and cellular level after TBI.

Age-related mitochondrial changes after traumatic brain injury

Mitochondrial dysfunction is known to occur following traumatic brain injury (TBI) and has been well characterized. This study assessed possible age-related changes in the cortical mitochondrial bioenergetics following TBI. Three hours following a moderate TBI, tissue from the ipsilateral hemisphere (site of impact and penumbra) and the corresponding contralateral region were harvested from young (3- to 5-month-old) and aged (22- to 24-month-old) Fischer 344 rats. Synaptic and extrasynaptic mitochondria were isolated using a Ficoll gradient, and several bioenergetic parameters were examined using a Clark-type electrode. Injury-related respiration deficits were observed in both young and aged rats. Synaptic mitochondria showed an age-related decline in the rate of ATP production, and a decline in respiratory control ratios (RCR), which were not apparent in the extrasynaptic fraction. Following respiration analysis, mitochondrial samples were probed for oxidative damage (3-nitrotyrosine [3-NT], 4-hydroxynonenal [4-HNE], and protein carbonyls [PC]). All markers of oxidative damage were elevated with injury and age in the synaptic fraction, but only with injury in the extrasynaptic fraction. Synaptic mitochondria displayed the highest levels of oxidative damage and may contribute to the synaptic bioenergetic deficits seen following injury. Data indicate that cortical synaptic mitochondria appear to have an increased susceptibility to perturbation with age, suggesting that the increased mitochondrial dysfunction observed following injury may impede recovery in aged animals.

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.

Physical exercise and cognitive recovery in acquired brain injury: a review of the literature

OBJECTIVE

Physical exercise has been shown to play an ever-broadening role in the maintenance of overall health and has been implicated in the preservation of cognitive function in both healthy elderly and demented populations. Animal and human studies of acquired brain injury (ABI) from trauma or vascular causes also suggest a possible role for physical exercise in enhancing cognitive recovery.

DATA SOURCES

A review of the literature was conducted to explore the current understanding of how physical exercise impacts the molecular, functional, and neuroanatomic status of both intact and brain-injured animals and humans.

STUDY SELECTION

Searches of the MEDLINE, CINHAL, and PsychInfo databases yielded an extensive collection of animal studies of physical exercise in ABI. Animal studies strongly tie physical exercise to the upregulation of multiple neural growth factor pathways in brain-injured animals, resulting in both hippocampal neurogenesis and functional improvements in memory.

DATA EXTRACTION

A search of the same databases for publications involving physical exercise in human subjects with ABI yielded 24 prospective and retrospective studies.

DATA SYNTHESIS

Four of these evaluated cognitive outcomes in persons with ABI who were involved in physical exercise. Three studies cited a positive association between exercise and improvements in cognitive function, whereas one observed no effect. Human exercise interventions varied greatly in duration, intensity, and level of subject supervision, and tools for assessing neurocognitive changes were inconsistent.

CONCLUSIONS

There is strong evidence in animal ABI models that physical exercise facilitates neurocognitive recovery. Physical exercise interventions are safe in the subacute and rehabilitative phases of recovery for humans with ABI. In light of strong evidence of positive effects in animal studies, more controlled, prospective human interventions are warranted to better explore the neurocognitive effects of physical exercise on persons with ABI.

Metabolic biomarkers related to energy metabolism in Saudi autistic children

OBJECTIVES

Energy metabolism is usually manipulated in many neurodegenerative diseases. Autism is considered a definable systemic disorder resulting in a number of diverse factors that may affect the brain development and functions both pre and post natal. The increased prevalence of autism will have enormous future public implications and has stimulated intense research into potential etiologic factors. This study aims to establish a connection between autism and the deterioration accompanied it, especially in the brain cognitive areas through a postulation of energy manipulation.

MATERIALS AND METHODS

The biochemical changes in activities of enzymes and pathways that participate in the production of ATP as the most important high-energy compound needed by the human brain were measured in Saudi autistic children. Na(+)/K(+)ATPase, ectonucleotidases (NTPDases) (ADPase and ATPase) and creatine kinase (CK), were assessed in plasma of 30 Saudi autistic patients and compared to 30 age-matching control samples. In addition, adenosine mono, di and trinucleotides (ATP, ADP, and AMP) were measured calorimetrically in the red blood cells of both groups and the adenylate energy charge (AEC) was calculated. Moreover, lactate concentration in plasma of both groups was monitored.

RESULTS

The obtained data recorded 148.77% and 72.35% higher activities of Na(+)/K(+)ATPase and CK respectively in autistic patients which prove the impairment of energy metabolism in these children compared to age and sex matching healthy controls. While ADPase was significantly higher in autistic patients, ATPase were non-significantly elevated compared to control. In spite of the significant increase of Na(+)/K(+)ATPase activity in autistic patients, there was no significant difference in the levels of ATP, ADP, and AMP in both groups and the calculated AEC values were 0.814+/-0.094 and 0.806+/-0.081 for autistic and control groups respectively. The unchanged AEC value in autistic patients was easily correlated with the induced activity of CK and ADPase as two enzymes playing a critical role in the stabilization of AEC. Lactate as an important energy metabolite for the brain was significantly higher in autistic patients compared to control showing about 40% increase.

CONCLUSION

The present study confirmed the impairment of energy metabolism in Saudi autistic patients which could be correlated to the oxidative stress previously recorded in the same investigated samples. The identification of biochemical markers related to autism would be advantageous for earlier clinical diagnosis and intervention.

Traumatic brain injury-induced expression and phosphorylation of pyruvate dehydrogenase: a mechanism of dysregulated glucose metabolism

Dysregulated brain glucose metabolism and lactate accumulation are seen following traumatic brain injury (TBI). The underlying molecular mechanism is poorly understood. Pyruvate dehydrogenase (PDH), the rate-limiting enzyme coupling cytosolic glycolysis to mitochondrial citric acid cycle, plays a critical role in maintaining homeostasis of brain glucose metabolism. PDH activity is maintained by the expression of its E1alpha1 subunit 1 (PDHE1alpha1) and is inhibited by the phosphorylation of PDHE1alpha1 (p-PDHE1alpha1). We hypothesized that PDHE1alpha1 expression and phosphorylation was altered in rat brain following controlled cortical impact (CCI)-induced TBI. Compared to naïve controls (=100%), PDHE1alpha1 protein decreased significantly ipsilateral to CCI (62%, P<0.05; 75%, P<0.05; 57%, P<0.05; and 39%, P<0.01) and contralateral to CCI (77%, 78%, 78% and 36% P<0.01) at 4h, 24h, 3- and 7-day post-CCI, respectively. PDHE1alpha1 protein phosphorylation level also decreased significantly ipsilateral to CCI (31%, P<0.01; 102%, P>0.05; 64%, P<0.05; and 14%, P<0.01) and to contralateral CCI (35%, 74%, P<0.05; 60%, P<0.05; 20%, P<0.01) at 4h, 24h, 3- and 7-day post-CCI, respectively. Similar reduction in PDHE1alpha1 and p-PDHE1alpha1 protein was found in the craniotomy (sham CCI) group. TBI-induced change in PDHE1alpha1 expression and phosphorylation could alter brain PDH activity and glucose metabolism.

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.

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.