The potential role of mitochondria in pediatric traumatic brain injury

Initial dysnatremia and clinical outcomes in pediatric traumatic brain injury: a multicenter observational study

PURPOSE

We aimed to investigate the association between initial dysnatremia (hyponatremia and hypernatremia) and in-hospital mortality, as well as between initial dysnatremia and functional outcomes, among children with traumatic brain injury (TBI).

METHOD

We performed a multicenter observational study among 26 pediatric intensive care units from January 2014 to August 2022. We recruited children with TBI under 18 years of age who presented to participating sites within 24 h of injury. We compared demographics and clinical characteristics between children with initial hyponatremia and eu-natremia and between those with initial hypernatremia and eu-natremia. We defined poor functional outcome as a discharge Pediatric Cerebral Performance Category (PCPC) score of moderate, severe disability, coma, and death, or an increase of at least 2 categories from baseline. We performed multivariable logistic regression for mortality and poor PCPC outcome.

RESULTS

Among 648 children, 84 (13.0%) and 42 (6.5%) presented with hyponatremia and hypernatremia, respectively. We observed fewer 14-day ventilation-free days between those with initial hyponatremia [7.0 (interquartile range (IQR) = 0.0-11.0)] and initial hypernatremia [0.0 (IQR = 0.0-10.0)], compared to eu-natremia [9.0 (IQR = 4.0-12.0); p = 0.006 and p < 0.001]. We observed fewer 14-day ICU-free days between those with initial hyponatremia [3.0 (IQR = 0.0-9.0)] and initial hypernatremia [0.0 (IQR = 0.0-3.0)], compared to eu-natremia [7.0 (IQR = 0.0-11.0); p = 0.006 and p < 0.001]. After adjusting for age, severity, and sex, presenting hyponatremia was associated with in-hospital mortality [adjusted odds ratio (aOR) = 2.47, 95% confidence interval (CI) = 1.31-4.66, p = 0.005] and poor outcome (aOR = 1.67, 95% CI = 1.01-2.76, p = 0.045). After adjustment, initial hypernatremia was associated with mortality (aOR = 5.91, 95% CI = 2.85-12.25, p < 0.001) and poor outcome (aOR = 3.00, 95% CI = 1.50-5.98, p = 0.002).

CONCLUSION

Among children with TBI, presenting dysnatremia was associated with in-hospital mortality and poor functional outcome, particularly hypernatremia. Future research should investigate longitudinal sodium measurements in pediatric TBI and their association with clinical outcomes.

FAM3A Ameliorates Brain Impairment Induced by Hypoxia-Ischemia in Neonatal Rat

Hypoxia-ischemia (HI) during crucial periods of brain formation can lead to changes in brain morphology, propagation of neuronal stimuli, and permanent neurodevelopmental impairment, which can have profound effects on cognitive function later in life. FAM3A, a subgroup of family with sequence similarity 3 (FAM3) gene family, is ubiquitously expressed in almost all cells. Overexpression of FAM3A has been evidenced to reduce hyperglycemia via the PI3K/Akt signaling pathway and protect mitochondrial function in neuronal HT22 cells. This study aims to evaluate the protective role of FAM3A in HI-induced brain impairment. Experimentally, maternal rats underwent uterine artery bilateral ligation to induce neonatal HI on day 14 of gestation. At 6 weeks of age, cognitive development assessments including NSS, wire grip, and water maze were carried out. The animals were then sacrificed to assess cerebral mitochondrial function as well as levels of FAM3A, TNF-α and IFN-γ. Results suggest that HI significantly reduced FAM3A expression in rat brain tissues, and that overexpression of FAM3A through lentiviral transduction effectively improved cognitive and motor functions in HI rats as reflected by improved NSS evaluation, cerebral water content, limb strength, as well as spatial learning and memory. At the molecular level, overexpression of FAM3A was able to promote ATP production, balance mitochondrial membrane potential, and reduce levels of pro-inflammatory cytokines TNF-α and IFN-γ. We conclude that FAM3A overexpression may have a protective effect on neuron morphology, cerebral mitochondrial as well as cognitive function. Created with Biorender.com.

Neuroprotective and Anti-inflammatory Effects of Pioglitazone on Traumatic Brain Injury

Traumatic brain injury (TBI) is still a major cause of concern for public health, and out of all the trauma-related injuries, it makes the highest contribution to death and disability worldwide. Patients of TBI continue to suffer from brain injury through an intricate flow of primary and secondary injury events. However, when treatment is provided in a timely manner, there is a significant window of opportunity to avoid a few of the serious effects. Pioglitazone (PG), which has a neuroprotective impact and can decrease inflammation after TBI, activates peroxisome proliferator-activated receptor-gamma (PPARγ). The objective of the study is to examine the existing literature to assess the neuroprotective and anti-inflammatory impact of PG in TBI. It also discusses the part played by microglia and cytokines in TBI. According to the findings of this study, PG has the ability to enhance neurobehavior, decrease brain edema and neuronal injury following TBI. To achieve the protective impact of PG the following was required: (1) stimulating PPARγ; (2) decreasing oxidative stress; (3) decreasing nuclear factor kappa B (NF-κB), interleukin 6 (IL-6), interleukin-1β (IL-1β), cyclooxygenase-2 (COX-2), and C-C motif chemokine ligand 20 (CCL20) expression; (4) limiting the increase in the number of activated microglia; and (5) reducing mitochondrial dysfunction. The findings indicate that when PIG is used clinically, it may serve as a neuroprotective anti-inflammatory approach in TBI.

Oxygen-Glucose Deprivation/Reperfusion-Induced Sirt3 Reduction Facilitated Neuronal Injuries in an Apoptosis-Dependent Manner During Prolonged Reperfusion

Cerebral ischemia is a major cause of morbidity and permanent disability. To date, no treatments for cerebral ischemia/reperfusion injury can be effectively administered beyond 4-6 h after the ischemic insult. Our study aimed to clarify the significance of Sirt3 during acute cerebral ischemia and explore Sirt3-targeted therapy for ischemic injuries. Upon establishing the oxygen-glucose deprivation/reperfusion (OGD/R) cell model, changes of Sirt3 protein levels and the effects of Sirt3 overexpression on primary hippocampal neurons were detected at indicated time points. Moreover, mitochondrial damage was observed in neurons upon OGD/R injury. The results showed that compared with the normoxia group, Sirt3 protein was significantly decreased in hippocampal neurons exposed to 1 h of OGD followed by 12 h of reperfusion. In addition, the reduction of Sirt3 protein levels contributed to OGD/R-induced neuronal injuries, a higher ratio of neuronal apoptosis, and extensive production of reactive oxygen species (ROS). However, all neuronal injuries were partly rescued by Sirt3 overexpression induced by lentivirus transfection. Mitochondrial morphologies were significantly impaired after OGD/R, but partly salvaged by Sirt3 overexpression. We further explored whether pharmacologically activating Sirt3 is protective for neurons, and found that treatment with honokiol (a Sirt3 agonist) after OGD exposure activated Sirt3 during reperfusion and significantly alleviated OGD/R-induced neuronal injuries. Because mitochondrial functions are essential for neuronal survival, the current results indicate that Sirt3 may be an efficient target to suppress ischemic injuries via maintenance of mitochondrial homeostasis. Our current findings shed light on a novel therapeutic strategy against subacute ischemic injuries.

Pathophysiology of Pediatric Traumatic Brain Injury

The national incidence of traumatic brain injury (TBI) exceeds that of any other disease in the pediatric population. In the United States the Centers for Disease Control and Prevention (CDC) reports 697,347 annual TBIs in children ages 0–19 that result in emergency room visits, hospitalization or deaths. There is a bimodal distribution within the pediatric TBI population, with peaks in both toddlers and adolescents. Preclinical TBI research provides evidence for age differences in acute pathophysiology that likely contribute to long-term outcome differences between age groups. This review will examine the timecourse of acute pathophysiological processes during cerebral maturation, including calcium accumulation, glucose metabolism and cerebral blood flow. Consequences of pediatric TBI are complicated by the ongoing maturational changes allowing for substantial plasticity and windows of vulnerabilities. This review will also examine the timecourse of later outcomes after mild, repeat mild and more severe TBI to establish developmental windows of susceptibility and altered maturational trajectories. Research progress for pediatric TBI is critically important to reveal age-associated mechanisms and to determine knowledge gaps for future studies.

Transcriptional activation of antioxidant gene expression by Nrf2 protects against mitochondrial dysfunction and neuronal death associated with acute and chronic neurodegeneration

Mitochondria are both a primary source of reactive oxygen species (ROS) and a sensitive target of oxidative stress; damage to mitochondria can result in bioenergetic dysfunction and both necrotic and apoptotic cell death. These relationships between mitochondria and cell death are particularly strong in both acute and chronic neurodegenerative disorders. ROS levels are affected by both the production of superoxide and its toxic metabolites and by antioxidant defense mechanisms. Mitochondrial antioxidant activities include superoxide dismutase 2, glutathione peroxidase and reductase, and intramitochondrial glutathione. When intracellular conditions disrupt the homeostatic balance between ROS production and detoxification, a net increase in ROS and an oxidized shift in cellular redox state ensues. Cells respond to this imbalance by increasing the expression of genes that code for proteins that protect against oxidative stress and inhibit cytotoxic oxidation of proteins, DNA, and lipids. If, however, the genomic response to mitochondrial oxidative stress is insufficient to maintain homeostasis, mitochondrial bioenergetic dysfunction and release of pro-apoptotic mitochondrial proteins into the cytosol initiate a variety of cell death pathways, ultimately resulting in potentially lethal damage to vital organs, including the brain. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a translational activating protein that enters the nucleus in response to oxidative stress, resulting in increased expression of numerous cytoprotective genes, including genes coding for mitochondrial and non-mitochondrial antioxidant proteins. Many experimental and some FDA-approved drugs promote this process. Since mitochondria are targets of ROS, it follows that protection against mitochondrial oxidative stress by the Nrf2 pathway of gene expression contributes to neuroprotection by these drugs. This document reviews the evidence that Nrf2 activation increases mitochondrial antioxidants, thereby protecting mitochondria from dysfunction and protecting neural cells from damage and death. New experimental results are provided demonstrating that post-ischemic administration of the Nrf2 activator sulforaphane protects against hippocampal neuronal death and neurologic injury in a clinically-relevant animal model of cardiac arrest and resuscitation.

Mitochondrial function and brain Metabolic Score (BMS) in ischemic Stroke: Evaluation of "neuroprotectants" safety and efficacy

The initial and significant event developed in ischemic stroke is the sudden decrease in blood flow and oxygen supply to brain tissue, leading to dysfunction of the mitochondria. Many attempts were and are being made to develop new drugs and treatments that will save the ischemic brain, but the efficacy is not optimal and in many patients, irreversible damage to the brain will persist. We review a unique approach to evaluate mitochondrial function and microcirculatory hemodynamic in real time in vivo. Three out of four monitored physiological parameters are integrated into a new Brain Metabolic Score (BMS) calculated in real time and is correlated to Brain Oxygen Balance. The technology was adapted to various experimental as well as clinical situations for monitoring the brain in real time. The developed protocols could be used in testing the efficacy and safety of new drugs in experimental animals. Few models of brain monitoring during partial or complete ischemia were developed and used in naive animals or under brain activation protocols. It was found that mitochondrial function/dysfunction is the major and dominant parameter affecting the calculated Brain Metabolic Score. Using our monitoring system and protocols will provide direct information regarding the ability of the tested brain to provide enough oxygen consumed by the mitochondria in the "resting" or in the "activated" brain in vivo and in real-time. Preliminary studies, indicated that testing the efficacy and safety of new neuroprotectant drugs provided significant results to the R&D studies of ischemic stroke related to mitochondrial function.

Administration of a 20-Hydroxyeicosatetraenoic Acid Synthesis Inhibitor Improves Outcome in a Rat Model of Pediatric Traumatic Brain Injury

The arachidonic acid pathway metabolite 20-hydroxyeicosatetraenoic acid (20-HETE) contributes to ischemia/reperfusion brain injury. Inhibition of 20-HETE formation can protect the developing brain from global ischemia. Here, we examined whether treatment with the 20-HETE synthesis inhibitor N-hydroxy-N-4-butyl-2-methylphenylformamidine (HET0016) can protect the immature brain from traumatic brain injury (TBI). Male rats at postnatal day 9-10 underwent controlled cortical impact followed by intraperitoneal injection with vehicle or HET0016 (1 mg/kg, 5 min and 3 h post-injury). HET0016 decreased the lesion volume by over 50% at 3 days of recovery, and this effect persisted at 30 days as the brain matured. HET0016 decreased peri-lesion gene expression of proinflammatory cytokines (tumor necrosis factor-α [TNF-α], interleukin-1β [IL-1β]) at 1 day and increased reparative cytokine (IL-4, IL-10) expression at 3 days. It also partially preserved microglial ramified processes, consistent with less activation. HET0016 decreased contralateral hindlimb foot faults and improved outcome on the novel object recognition memory task 30 days after TBI. In cultured BV2 microglia, HET0016 attenuated the lipopolysaccharide-evoked increase in release of TNF-α. Our data show that HET0016 improves acute and long-term histologic and functional outcomes, in association with an attenuated neuroinflammatory response after contusion of an immature rat brain.

Sex differences in pediatric traumatic brain injury

The response of the developing brain to traumatic injury is different from the response of the mature, adult brain. There are critical developmental trajectories in the young brain, whereby injury can lead to long term functional abnormalities. Emerging preclinical and clinical literature supports the presence of significant sex differences in both the response to and the recovery from pediatric traumatic brain injury (TBI). These sex differences are seen at all pediatric ages, including neonates/infants, pre-pubertal children, and adolescents. As importantly, the response to neuroprotective therapies or treatments can differ between male and females subjects. These sex differences can result from several biologic origins, and may manifest differently during the various phases of brain and body development. Recognizing and understanding these potential sex differences is crucial, and should be considered in both preclinical and clinical studies of pediatric TBI.

Sex-dependent and chronic alterations in behavior and mitochondrial function in a rat model of pediatric mild traumatic brain injury

OBJECTIVE

To determine if chronic changes in mitochondrial function occur following a mild traumatic brain injury in young rats.

RESEARCH DESIGN

Closed-head, weight drop model was used to cause mTBI by applying rotational forces to the brain without surgery. Behavioral battery was used to assess multiple dimensions of impairment across time. Analysis of brain tissue carried out at three-weeks post-injury represents a chronic time point to complement previous work examining acute time points.

METHODS AND PROCEDURES

Twenty-three male and 22 female rats one month of age were divided equally into sham and mTBI groups with the latter undergoing the weight drop. Multiple behavioral tests in combination with energetic (oxygen consumption), molecular (immunoblotting), and imaging (electron microscopy) characterization of brain mitochondria were performed.

MAIN OUTCOMES AND RESULTS

Mitochondria isolated from sham juvenile female rats had higher basal oxygen consumption compared to juvenile male rats (514.875 ± 171.091 pmol/min vs. 267 ± 73.906 pmol/min, p < 0.0001). Chronic sex-dependent differences were observed in females after mTBI in basal (514.875 ± 171.091 pmol/min vs. 600.688 ± 124.422 pmol/min, p = 0.0264) and maximal oxygen consumption (298.938 ± 119.964 pmol/min vs. 403.281 ± 112.922 pmol/min, p = 0.0001) and proton leak (59.46 ± 7.807 vs. 84.32 ± 5.80 pmol/min, p = 0.0001).

CONCLUSIONS

The juvenile rat brain displays sex differences in mitochondrial function at (1) baseline and (2) in long-term outcomes after mTBI. These results offer new insight into a potential mechanism for persistent, individualized impairments following pediatric mTBI.

Early behavioral and metabolomic change after mild to moderate traumatic brain injury in the developing brain

Pathophysiology of developmental traumatic brain injury (TBI) is unique due to intrinsic differences in the developing brain. Energy metabolic studies of the brain during early development (P13 to P30) have indicated acute oxidative energy metabolic decreases below 24 h after TBI, which generally recovered by 48 h. However, marked neurodegeneration and altered neural functional connectivity have been observed at later stages into adolescence. As secondary neurodegeneration is most prominent during the first week after TBI in the rat model, we hypothesized that the subacute TBI-metabolome may contain predictive markers of neurodegeneration. Sham and TBI metabolomes were examined at 72 h after a mild to moderate intensity TBI in male Sprague-Dawley rats aged P31. Sensorimotor behavior was assessed at 24, 48 and 72 h after injury, followed by 72-hour postmortem brain removal for metabolomics using Liquid Chromatography/Mass Spectrometry (LC-MS) measurement. Broad TBI-induced metabolomic shifts occurred with relatively higher intensity in the injury-lateralized (ipsilateral) hemisphere. Intensity of metabolomic perturbation correlated with the extent of sensorimotor behavioral deficit. N-acetyl-aspartate (NAA) levels at 72 h after TBI, predicted the extent of neurodegeneration assessed histochemically 7-days post TBI. Results from the multivariate untargeted approach clearly distinguished metabolomic shifts induced by TBI. Several pathways including amino acid, fatty acid and energy metabolism continued to be affected at 72 h after TBI, whose collective effects may determine the overall pathological response after TBI in early development including neurodegeneration.

Sex differences in the mitochondrial bioenergetics of astrocytes but not microglia at a physiologically relevant brain oxygen tension

Biological sex is thought to influence mitochondrial bioenergetic function. Previous respiration measurements examining brain mitochondrial sex differences were made at atmospheric oxygen using isolated brain mitochondria. Oxygen is 160 mm Hg (21%) in the atmosphere, while the oxygen tension in the brain generally ranges from ∼5 to 45 mm Hg (∼1-6% O2). This study tested the hypothesis that sex and/or brain physiological oxygen tension influence the mitochondrial bioenergetic properties of primary rat cortical astrocytes and microglia. Oxygen consumption was measured with a Seahorse XF24 cell respirometer in an oxygen-controlled environmental chamber. Strikingly, male astrocytes had a higher maximal respiration than female astrocytes when cultured and assayed at 3% O2. Three percent O2 yielded a low physiological dissolved O2 level of ∼1.2% (9.1 mm Hg) at the cell monolayer during culture and 1.2-3.0% O2 during assays. No differences in bioenergetic parameters were observed between male and female astrocytes at 21% O2 (dissolved O2 of ∼19.7%, 150 mm Hg during culture) or between either of these cell populations and female astrocytes at 3% O2. In contrast to astrocytes, microglia showed no sex differences in mitochondrial bioenergetic parameters at either oxygen level, regardless of whether they were non-stimulated or activated to a proinflammatory state. There were also no O2- or sex-dependent differences in proinflammatory TNF-α or IL-1β cytokine secretion measured at 18 h activation. Overall, results reveal an intriguing sex variance in astrocytic maximal respiration that requires additional investigation. Findings also demonstrate that sex differences can be masked by conducting experiments at non-physiological O2.

Adaptive responses of neuronal mitochondria to bioenergetic challenges: Roles in neuroplasticity and disease resistance

An important concept in neurobiology is "neurons that fire together, wire together" which means that the formation and maintenance of synapses is promoted by activation of those synapses. Very similar to the effects of the stress of exercise on muscle cells, emerging findings suggest that neurons respond to activity by activating signaling pathways (e.g., Ca²⁺, CREB, PGC-1α, NF-κB) that stimulate mitochondrial biogenesis and cellular stress resistance. These pathways are also activated by aerobic exercise and food deprivation, two bioenergetic challenges of fundamental importance in the evolution of the brains of all mammals, including humans. The metabolic 'switch' in fuel source from liver glycogen store-derived glucose to adipose cell-derived fatty acids and their ketone metabolites during fasting and sustained exercise, appears to be a pivotal trigger of both brain-intrinsic and peripheral organ-derived signals that enhance learning and memory and underlying synaptic plasticity and neurogenesis. Brain-intrinsic extracellular signals include the excitatory neurotransmitter glutamate and the neurotrophic factor BDNF, and peripheral signals may include the liver-derived ketone 3-hydroxybutyrate and the muscle cell-derived protein irisin. Emerging findings suggest that fasting, exercise and an intellectually challenging lifestyle can protect neurons against the dysfunction and degeneration that they would otherwise suffer in acute brain injuries (stroke and head trauma) and neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's disease. Among the prominent intracellular responses of neurons to these bioenergetic challenges are up-regulation of antioxidant defenses, autophagy/mitophagy and DNA repair. A better understanding of such fundamental hormesis-based adaptive neuronal response mechanisms is expected to result in the development and implementation of novel interventions to promote optimal brain function and healthy brain aging.

Imaging mass spectrometry reveals loss of polyunsaturated cardiolipins in the cortical contusion, hippocampus, and thalamus after traumatic brain injury

Traumatic brain injury (TBI) leads to changes in ion fluxes, alterations in mitochondrial function, and increased generation of reactive oxygen species, resulting in secondary tissue damage. Mitochondria play important signaling roles in coordination of multiple metabolic platforms in addition to their well-known role in bioenergetics. Mitochondrial signaling strongly depends on cardiolipin (CL), a mitochondria-specific structurally unusual anionic phospholipid containing four fatty acyl chains. While our previous reports indicated that CL is selectively oxidized and presents itself as a target for the redox therapy following TBI, the topography of changes of CL in the injured brain remained to be defined. Here, we present a matrix-assisted laser desorption/ionization imaging study which reports regio-specific changes in CL, in a controlled cortical impact model of TBI in rats. Matrix-assisted laser desorption/ionization imaging revealed that TBI caused early decreases in CL in the contusional cortex, ipsilateral hippocampus, and thalamus with the most highly unsaturated CL species being most susceptible to loss. Phosphatidylinositol was the only other lipid species that exhibited a significant decrease, albeit to a lesser extent than CL. Signals for other lipids remained unchanged. This is the first study evaluating the spatial distribution of CL loss after acute brain injury. We propose that the CL loss may constitute an upstream mechanism for CL-driven signaling in different brain regions as an early response mechanism and may also underlie the bioenergetic changes that occur in hippocampal, cortical, and thalamic mitochondria after TBI.

Expected pairwise congruence among gene trees under the coalescent model

Although it is widely appreciated that gene trees may differ from the overall species tree and from one another due to various evolutionary processes (e.g., incomplete lineage sorting (ILS), horizontal gene transfer, etc.), the extent of this incongruence is rarely quantified and discussed. Here we consider the expected amount of incongruence arising from ILS, as modeled by the coalescent process. In particular, we compute the probability that two gene trees randomly sampled from the same species tree agree with one another as well as the distribution of the Robinson-Foulds distance between them, for species trees with three to eight taxa. We demonstrate that, as expected under the coalescent model, the amount of discordance is affected by species tree-specific factors such as speciation times and effective population sizes for the species under consideration. Our results highlight the fact that substantial discordance may occur, even when the number of species is very small, which has implications both for larger taxon samples and for any method that uses estimated gene trees as the basis for further statistical inference. The amount of incongruence is substantial enough that such methods may need to be modified to account for variability in the underlying gene trees.

Increased platelet mitochondrial respiration after cardiac arrest and resuscitation as a potential peripheral biosignature of cerebral bioenergetic dysfunction

Cardiac arrest (CA) results in a sepsis-like syndrome with activation of the innate immune system and increased mitochondrial bioenergetics.

OBJECTIVE

To determine if platelet mitochondrial respiration increases following CA in a porcine pediatric model of asphyxia-associated ventricular fibrillation (VF) CA, and if this readily obtained biomarker is associated with decreased brain mitochondrial respiration. CA protocol: 7 min of asphyxia, followed by VF, protocolized titration of compression depth to systolic blood pressure of 90 mmHg and vasopressor administration to a coronary perfusion pressure greater than 20 mmHg.

PRIMARY OUTCOME

platelet integrated mitochondrial electron transport system (ETS) function evaluated pre- and post-CA/ROSC four hours after return of spontaneous circulation (ROSC). Secondary outcome: correlation of platelet mitochondrial bioenergetics to cerebral bioenergetic function. Platelet maximal oxidative phosphorylation (OXPHOSCI+CII), P < 0.02, and maximal respiratory capacity (ETSCI+CII), P < 0.04, were both significantly increased compared to pre-arrest values. This was primarily due to a significant increase in succinate-supported respiration through Complex II (OXPHOSCII, P < 0.02 and ETSCII, P < 0.03). Higher respiration was not due to uncoupling, as the LEAKCI + CII respiration (mitochondrial respiration independent of ATP-production) was unchanged after CA/ROSC. Larger increases in platelet mitochondrial respiratory control ratio (RCR) compared to pre-CA RCR were significantly correlated with lower RCRs in the cortex (P < 0.03) and hippocampus (P < 0.04) compared to sham respiration. Platelet mitochondrial respiration is significantly increased four hours after ROSC. Future studies will identify mechanistic relationships between this serum biomarker and altered cerebral bioenergetics function following cardiac arrest.

Establishing a Clinically Relevant Large Animal Model Platform for TBI Therapy Development: Using Cyclosporin A as a Case Study

We have developed the first immature large animal translational treatment trial of a pharmacologic intervention for traumatic brain injury (TBI) in children. The preclinical trial design includes multiple doses of the intervention in two different injury types (focal and diffuse) to bracket the range seen in clinical injury and uses two post-TBI delays to drug administration. Cyclosporin A (CsA) was used as a case study in our first implementation of the platform because of its success in multiple preclinical adult rodent TBI models and its current use in children for other indications. Tier 1 of the therapy development platform assessed the short-term treatment efficacy after 24 h of agent administration. Positive responses to treatment were compared with injured controls using an objective effect threshold established prior to the study. Effective CsA doses were identified to study in Tier 2. In the Tier 2 paradigm, agent is administered in a porcine intensive care unit utilizing neurological monitoring and clinically relevant management strategies, and intervention efficacy is defined as improvement in longer term behavioral endpoints above untreated injured animals. In summary, this innovative large animal preclinical study design can be applied to future evaluations of other agents that promote recovery or repair after TBI.

Peripheral Blood Mitochondrial DNA as a Biomarker of Cerebral Mitochondrial Dysfunction following Traumatic Brain Injury in a Porcine Model

BACKGROUND

Traumatic brain injury (TBI) has been shown to activate the peripheral innate immune system and systemic inflammatory response, possibly through the central release of damage associated molecular patterns (DAMPs). Our main purpose was to gain an initial understanding of the peripheral mitochondrial response following TBI, and how this response could be utilized to determine cerebral mitochondrial bioenergetics. We hypothesized that TBI would increase peripheral whole blood relative mtDNA copy number, and that these alterations would be associated with cerebral mitochondrial bioenergetics triggered by TBI.

METHODOLOGY

Blood samples were obtained before, 6 h after, and 25 h after focal (controlled cortical impact injury: CCI) and diffuse (rapid non-impact rotational injury: RNR) TBI. PCR primers, unique to mtDNA, were identified by aligning segments of nuclear DNA (nDNA) to mtDNA, normalizing values to nuclear 16S rRNA, for a relative mtDNA copy number. Three unique mtDNA regions were selected, and PCR primers were designed within those regions, limited to 25-30 base pairs to further ensure sequence specificity, and measured utilizing qRT-PCR.

RESULTS

Mean relative mtDNA copy numbers increased significantly at 6 and 25 hrs after following both focal and diffuse traumatic brain injury. Specifically, the mean relative mtDNA copy number from three mitochondrial-specific regions pre-injury was 0.84 ± 0.05. At 6 and 25 h after diffuse non-impact TBI, mean mtDNA copy number was significantly higher: 2.07 ± 0.19 (P < 0.0001) and 2.37 ± 0.42 (P < 0.001), respectively. Following focal impact TBI, relative mtDNA copy number was also significantly higher, 1.35 ± 0.12 (P < 0.0001) at 25 hours. Alterations in mitochondrial respiration in the hippocampus and cortex post-TBI correlated with changes in the relative mtDNA copy number measured in peripheral blood.

CONCLUSIONS

Alterations in peripheral blood relative mtDNA copy numbers may be a novel biosignature of cerebral mitochondrial bioenergetics with exciting translational potential for non-invasive diagnostic and interventional studies.

Mitochondrial bioenergetic alterations after focal traumatic brain injury in the immature brain

Traumatic brain injury (TBI) is one of the leading causes of death in children worldwide. Emerging evidence suggests that alterations in mitochondrial function are critical components of secondary injury cascade initiated by TBI that propogates neurodegeneration and limits neuroregeneration. Unfortunately, there is very little known about the cerebral mitochondrial bioenergetic response from the immature brain triggered by traumatic biomechanical forces. Therefore, the objective of this study was to perform a detailed evaluation of mitochondrial bioenergetics using high-resolution respirometry in a high-fidelity large animal model of focal controlled cortical impact injury (CCI) 24h post-injury. This novel approach is directed at analyzing dysfunction in electron transport, ADP phosphorylation and leak respiration to provide insight into potential mechanisms and possible interventions for mitochondrial dysfunction in the immature brain in focal TBI by delineating targets within the electron transport system (ETS). Development and application of these methodologies have several advantages, and adds to the interpretation of previously reported techniques, by having the added benefit that any toxins or neurometabolites present in the ex-vivo samples are not removed during the mitochondrial isolation process, and simulates the in situ tricarboxylic acid (TCA) cycle by maximizing key substrates for convergent flow of electrons through both complexes I and II. To investigate alterations in mitochondrial function after CCI, ipsilateral tissue near the focal impact site and tissue from the corresponding contralateral side were examined. Respiration per mg of tissue was also related to citrate synthase activity (CS) and calculated flux control ratios (FCR), as an attempt to control for variability in mitochondrial content. Our biochemical analysis of complex interdependent pathways of electron flow through the electron transport system, by most measures, reveals a bilateral decrease in complex I-driven respiration and an increase in complex II-driven respiration 24h after focal TBI. These alterations in convergent electron flow though both complex I and II-driven respiration resulted in significantly lower maximal coupled and uncoupled respiration in the ipsilateral tissue compared to the contralateral side, for all measures. Surprisingly, increases in complex II and complex IV activities were most pronounced in the contralateral side of the brain from the focal injury, and where oxidative phosphorylation was increased significantly compared to sham values. We conclude that 24h after focal TBI in the immature brain, there are significant alterations in cerebral mitochondrial bioenergetics, with pronounced increases in complex II and complex IV respiration in the contralateral hemisphere. These alterations in mitochondrial bioenergetics present multiple targets for therapeutic intervention to limit secondary brain injury and support recovery.

Forensic medical evaluations of child maltreatment: a proposed research agenda

Physicians play an important role in the forensic evaluation of suspected child abuse and neglect. There has been considerable progress in the medical field, helping distinguish findings related to maltreatment from other conditions or circumstances. Nevertheless, important questions remain. This article covers several of these questions and proposes a research agenda concerning five main topics: sexual abuse, neglect, fractures, abusive head trauma, and physicians work in interdisciplinary settings. The suggestions are hardly inclusive, but offer suggestions the authors think are priorities, and ones that research could reasonably address. By providing some background to gaps in our knowledge, this paper should be of interest to a broader audience than just medical professionals.

Sex differences in mitochondrial (dys)function: Implications for neuroprotection

Decades of research have revealed numerous differences in brain structure size, connectivity and metabolism between males and females. Sex differences in neurobehavioral and cognitive function after various forms of central nervous system (CNS) injury are observed in clinical practice and animal research studies. Sources of sex differences include early life exposure to gonadal hormones, chromosome compliment and adult hormonal modulation. It is becoming increasingly apparent that mitochondrial metabolism and cell death signaling are also sexually dimorphic. Mitochondrial metabolic dysfunction is a common feature of CNS injury. Evidence suggests males predominantly utilize proteins while females predominantly use lipids as a fuel source within mitochondria and that these differences may significantly affect cellular survival following injury. These fundamental biochemical differences have a profound impact on energy production and many cellular processes in health and disease. This review will focus on the accumulated evidence revealing sex differences in mitochondrial function and cellular signaling pathways in the context of CNS injury mechanisms and the potential implications for neuroprotective therapy development.

Shedding light on mitochondrial function by real time monitoring of NADH fluorescence: I. Basic methodology and animal studies

Normal mitochondrial function in the process of metabolic energy production is a key factor in maintaining cellular activities. Many pathological conditions in animals, as well as in patients, are directly or indirectly related to dysfunction of the mitochondria. Monitoring the mitochondrial activity by measuring the autofluorescence of NADH has been the most practical approach since the 1950s. This review presents the principles and technological aspects, as well as typical results, accumulated in our laboratory since the early 1970s. We were able to apply the fiber-optic-based NADH fluorometry to many organs monitored in vivo under various pathophysiological conditions in animals. These studies were the basis for the development of clinical monitoring devices as presented in accompanying article. The encouraging experimental results in animals stimulated us to apply the same technology in patients after technological adaptations as described in the accompanying article. Our medical device was approved for clinical use by the FDA.

Neuroglobin upregulation offers neuroprotection in traumatic brain injury

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Mitochondrial glutaminase release contributes to glutamate-mediated neurotoxicity during human immunodeficiency virus-1 infection

Human immunodeficiency virus (HIV) induces a neurological disease culminating in frank dementia referred to as HIV-associated dementia (HAD). Neurotoxins from HIV-1-infected and activated mononuclear phagocytes contribute to the neuropathogenesis of HAD. Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system (CNS) and functions through activation of multiple receptors. Excessive glutamate production by HIV-infected macrophages in HAD may contribute to neuronal injury. Our previous studies have suggested that mitochondrial glutaminase is responsible for the excessive production of glutamate. However, how HIV-1 infection regulates glutamate over-production remains unclear. In this study, we propose that HIV infection-induced oxidative stress contributes to mitochondrial glutaminase release, which results in the excessive production of glutamate and subsequent neuronal injury. We collected conditioned media from HIV-1 infected macrophages and analyzed glutamate concentration in the media by RP-HPLC, and found that the cyclosporine A (CsA), an inhibitor of HIV-1 replication and mitochondrial permeability transition pore, and N-acetylcysteine (NAC), a remover of reactive oxygen species (ROS), not only blocked the excessive glutamate production, but also decreased the glutamate-mediated neurotoxicity. In addition, HIV-infection-induced ROS generation was accompanied with the excessive glutamate production, suggesting that oxidative stress was involved in glutamate regulation. Using the isolated rat brain mitochondria as an ex vivo model and over-expressing GFP-glutaminase fusion protein in mammalian cells as a cell model, we confirm oxidative stress-mediated mitochondrial glutaminase release during HIV-1 infection contributes to glutamate over-production and the subsequent neurotoxicity. These results may provide insight into HAD pathogenesis and a therapeutic strategy for HAD treatment.

Facts and fiction: the impact of hypothermia on molecular mechanisms following major challenge

Numerous multiple trauma and surgical patients suffer from accidental hypothermia. While induced hypothermia is commonly used in elective cardiac surgery due to its protective effects, accidental hypothermia is associated with increased posttraumatic complications and even mortality in severely injured patients. This paper focuses on protective molecular mechanisms of hypothermia on apoptosis and the posttraumatic immune response. Although information regarding severe trauma is limited, there is evidence that induced hypothermia may have beneficial effects on the posttraumatic immune response as well as apoptosis in animal studies and certain clinical situations. However, more profound knowledge of mechanisms is necessary before randomized clinical trials in trauma patients can be initiated.

Polymorphisms in the brain-derived neurotrophic factor gene influence memory and processing speed one month after brain injury

Brain-derived neurotrophic factor (BDNF) plays a role in cognition, as well as neural survival and plasticity. There are several common polymorphisms in the BDNF gene, one of which (rs6265) is an extensively studied non-synonymous coding polymorphism (Val66Met) which has been linked to cognitive performance in healthy controls and some clinical populations. We hypothesized that the Met allele of rs6265 would be associated with poorer cognitive performance in individuals with mild-to-moderate traumatic brain injury, and that other polymorphisms in the BDNF gene would also affect cognition. Genotype at 9 single-nucleotide polymorphisms (SNPs) in the BDNF gene, and measures of speed of information processing, learning, and memory were assessed in 75 patients with mTBI and 38 healthy subjects. Consistent with previous reports, the Met allele of rs6265 was associated with cognition (slower processing speed) in the entire group. Two other SNPs were associated with processing speed in the mTBI group, but both are in linkage disequilibrium with rs6265, and neither remained significant after adjustment for rs6265 status. Within the mTBI group, but not the controls, 4 SNPs, but not rs6265, were associated with memory measures. These associations were not affected by adjustment for rs6265 status. Polymorphisms in BDNF influence cognitive performance shortly after mTBI. The results raise the possibility that a functional polymorphism other than rs6265 may contribute to memory function after mTBI.

Depression of whole-brain oxygen extraction fraction is associated with poor outcome in pediatric traumatic brain injury

INTRODUCTION

Traumatic brain injury (TBI) is a leading cause of death and disability in children. Metabolic failure is an integral component of the pathological aftermath of TBI. The oxygen extraction fraction (OEF) is a valuable parameter for characterization and description of metabolic abnormalities; however, OEF measurement has required either invasive procedures or the use of ionizing radiation, which significantly limits its use in pediatric research.

RESULTS

Patients with TBI had depressed OEF levels that correlated with the severity of injury. In addition, the OEF measured within 2 weeks of injury was predictive of patient outcome at 3 mo after injury. In pediatric TBI patients, low OEF-a marker of metabolic dysfunction-correlates with the severity of injury and outcome.

DISCUSSION

Our findings support previous literature on the role of metabolic dysfunction after TBI.

METHODS

Using a recently developed magnetic resonance (MR) technique for the measurement of oxygen saturation, we determined the whole-brain OEF in both pediatric TBI patients and in healthy controls. Injury and outcome were classified using pediatric versions of the Glasgow Coma Scale (GCS) and Glasgow Outcome Scale-Extended (GOS-E), respectively.

CSF Bcl-2 and cytochrome C temporal profiles in outcome prediction for adults with severe TBI

The biochemical cascades associated with cell death after traumatic brain injury (TBI) involve both pro-survival and pro-apoptotic proteins. We hypothesized that elevated cerebrospinal fluid (CSF) Bcl-2 and cytochrome C (CytoC) levels over time would reflect cellular injury response and predict long-term outcomes after TBI. Cerebrospinal fluid Bcl-2 and CytoC levels were measured for 6 days after injury for adults with severe TBI (N=76 subjects; N=277 samples). Group-based trajectory analysis was used to generate distinct temporal biomarker profiles that were compared with Glasgow Outcome Scale (GOS) and Disability Rating Scale (DRS) scores at 6 and 12 months after TBI. Subjects with persistently elevated temporal Bcl-2 and CytoC profiles compared with healthy controls had the worst outcomes at 6 and 12 months (P≤0.027). Those with CytoC profiles near controls had better long-term outcomes, and those with declining CytoC levels over time had intermediate outcomes. Subjects with Bcl-2 profiles that remained near controls had better outcomes than those with consistently elevated Bcl-2 profiles. However, subjects with Bcl-2 values that started near controls and steadily rose over time had 100% good outcomes by 12 months after TBI. These results show the prognostic value of Bcl-2 and CytoC profiles and suggest a dynamic apoptotic and pro-survival response to TBI.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Cyclosporin A preserves mitochondrial function after traumatic brain injury in the immature rat and piglet

Cyclosporin A (CsA) has been shown to be neuroprotective in mature animal models of traumatic brain injury (TBI), but its effects on immature animal models of TBI are unknown. In mature animal models, CsA inhibits the opening of the mitochondrial permeability transition pore (MPTP), thereby maintaining mitochondrial homeostasis following injury by inhibiting calcium influx and preserving mitochondrial membrane potential. The aim of the present study was to evaluate CsA's ability to preserve mitochondrial bioenergetic function following TBI (as measured by mitochondrial respiration and cerebral microdialysis), in two immature models (focal and diffuse), and in two different species (rat and piglet). Three groups were studied: injured+CsA, injured+saline vehicle, and uninjured shams. In addition, we evaluated CsA's effects on cerebral hemodynamics as measured by a novel thermal diffusion probe. The results demonstrate that post-injury administration of CsA ameliorates mitochondrial dysfunction, preserves cerebral blood flow (CBF), and limits neuropathology in immature animals 24 h post-TBI. Mitochondria were isolated 24 h after controlled cortical impact (CCI) in rats and rapid non-impact rotational injury (RNR) in piglets, and CsA ameliorated cerebral bioenergetic crisis with preservation of the respiratory control ratio (RCR) to sham levels. Results were more dramatic in RNR piglets than in CCI rats. In piglets, CsA also preserved lactate pyruvate ratios (LPR), as measured by cerebral microdialysis and CBF at sham levels 24 h after injury, in contrast to the significant alterations seen in injured piglets compared to shams (p<0.01). The administration of CsA to piglets following RNR promoted a 42% decrease in injured brain volume (p<0.01). We conclude that CsA exhibits significant neuroprotective activity in immature models of focal and diffuse TBI, and has exciting translational potential as a therapeutic agent for neuroprotection in children.

Pioglitazone attenuates mitochondrial dysfunction, cognitive impairment, cortical tissue loss, and inflammation following traumatic brain injury

Following traumatic brain injury (TBI) there is significant neuropathology which includes mitochondrial dysfunction, loss of cortical gray matter, microglial activation, and cognitive impairment. Previous evidence has shown that activation of the peroxisome proliferator-activated receptors (PPARs) provide neuroprotection following traumatic brain and spinal injuries. In the current study we hypothesized that treatment with the PPAR ligand Pioglitazone would promote neuroprotection following a rat controlled cortical impact model of TBI. Animals received a unilateral 1.5mm controlled cortical impact followed by administration of Pioglitazone at 10mg/kg beginning 15min after the injury and subsequently every 24h for 5days. Beginning 1day after the injury there was significant impairment in mitochondrial bioenergetic function which was attenuated by treatments with Pioglitazone at 15min and 24h (p<0.05). In an additional set of animals, cognitive function was assessed using the Morris Water Maze (MWM) and it was observed that over the course of 4days of testing the injury produced a significant increase in both latency (p<0.05) and distance (p<0.05) to the platform. Animals treated with Pioglitazone performed similarly to sham animals and did not exhibit any impairment in MWM performance. Sixteen days after the injury tissue sections through the lesion site were quantified to determine the size of the cortical lesion. Vehicle-treated animals had an average lesion size of 5.09±0.73mm(3) and treatment with Pioglitazone significantly reduced the lesion size by 55% to 2.27±0.27mm(3) (p<0.01). Co-administration of the antagonist T0070907 with Pioglitazone blocked the protective effect seen with administration of Pioglitazone by itself. Following the injury there was a significant increase in the number of activated microglia in the area of the cortex adjacent to the site of the lesion (p<0.05). Treatment with Pioglitazone prevented the increase in the number of activated microglia and no difference was observed between sham and Pioglitazone-treated animals. From these studies we conclude that following TBI Pioglitazone is capable ameliorating multiple aspects of neuropathology. These studies provide further support for the use of PPAR ligands, specifically Pioglitazone, for neuroprotection.

NMDA receptor antagonist MK-801 reduces neuronal damage and preserves learning and memory in a rat model of traumatic brain injury

OBJECTIVE

NMDA receptor channel plays an important role in the pathophysiological process of traumatic brain injury (TBI). The present study aims to study the pathological mechanism of TBI and the impairment of learning and memory after TBI, and to investigate the mechanism of the protective effect of NMDA receptor antagonist MK-801 on learning and memory disorder after TBI.

METHODS

Forty Sprague-Dawley rats (weighing approximately 200 g) were randomized into 5 groups (n = 8 in each group): control group, model group, low-dose group (MK-801 0.5 mg/kg), middle-dose group (MK-801 2 mg/kg), and high-dose group (MK-801 10 mg/kg). TBI model was established using a weight-drop head injury mode. After 2-month drug treatment, learning and memory ability was evaluated by using Morris water maze test. Then the animals were sacrificed, and brain tissues were taken out for morphological and immunohistochemical assays.

RESULTS

The ability of learning and memory was significantly impaired in the TBI model animals. Besides, the neuronal caspase-3 expression, neuronal nitric oxide synthase (nNOS)-positive neurons and OX-42-positive microglia were all increased in TBI animals. Meanwhile, the number of neuron synapses was decreased, and vacuoles degeneration could be observed in mitochondria. After MK-801 treatment at 3 different dosages, the ability of learning and memory was markedly improved, as compared to that of the TBI model animals. Moreover, neuronal caspase-3 expression, OX-42-positive microglia and nNOS-positive neurons were all significantly decreased. Meanwhile, the mitochondria degeneration was greatly inhibited.

CONCLUSION

MK-801 could significantly inhibit the degeneration and apoptosis of neurons in damaged brain areas. It could also inhibit TBI-induced increase in nNOS-positive neurons and OX-42-positive microglia. Impairment in learning and memory in TBI animals could be repaired by treatment with MK-801.

Huperzine A protects isolated rat brain mitochondria against beta-amyloid peptide

Our previous work in cells and animals showed that mitochondria are involved in the neuroprotective effect of huperzine A (HupA). In this study, the effects of HupA on isolated rat brain mitochondria were investigated. In addition to inhibiting the Abeta(25-35) (40 microM)-induced decrease in mitochondrial respiration, adenosine 5'-triphosphate (ATP) synthesis, enzyme activity, and transmembrane potential, HupA (0.01 or 0.1 microM) effectively prevented Abeta-induced mitochondrial swelling, reactive oxygen species increase, and cytochrome c release. More interestingly, administration of HupA to isolated mitochondria promoted the rate of ATP production and blocked mitochondrial swelling caused by normal osmosis. These results indicate that HupA protects mitochondria against Abeta at least in part by preserving membrane integrity and improving energy metabolism. These direct effects on mitochondria further extend the noncholinergic functions of HupA.

Delayed cerebral oxidative glucose metabolism after traumatic brain injury in young rats

Traumatic brain injury (TBI) results in a cerebral metabolic crisis that contributes to poor neurologic outcome. The aim of this study was to characterize changes in oxidative glucose metabolism in early periods after injury in the brains of immature animals. At 5 h after controlled cortical impact TBI or sham surgery to the left cortex, 21-22 day old rats were injected intraperitoneally with [1,6-13C]glucose and brains removed 15, 30 and 60 min later and studied by ex vivo 13C-NMR spectroscopy. Oxidative metabolism, determined by incorporation of 13C into glutamate, glutamine and GABA over 15-60 min, was significantly delayed in both hemispheres of brain from TBI rats. The most striking delay was in labeling of the C4 position of glutamate from neuronal metabolism of glucose in the injured, ipsilateral hemisphere which peaked at 60 min, compared with the contralateral and sham-operated brains, where metabolism peaked at 30 and 15 min, respectively. Our findings indicate that (i) neuronal-specific oxidative metabolism of glucose at 5-6 h after TBI is delayed in both injured and contralateral sides compared with sham brain; (ii) labeling from metabolism of glucose via the pyruvate carboxylase pathway in astrocytes was also initially delayed in both sides of TBI brain compared with sham brain; (iii) despite this delayed incorporation, at 6 h after TBI, both sides of the brain showed apparent increased neuronal and glial metabolism, reflecting accumulation of labeled metabolites, suggesting impaired malate aspartate shuttle activity. The presence of delayed metabolism, followed by accumulation of labeled compounds is evidence of severe alterations in homeostasis that could impair mitochondrial metabolism in both ipsilateral and contralateral sides of brain after TBI. However, ongoing oxidative metabolism in mitochondria in injured brain suggests that there is a window of opportunity for therapeutic intervention up to at least 6 h after injury.

Mitochondrial mechanisms of cell death and neuroprotection in pediatric ischemic and traumatic brain injury

There are several forms of acute pediatric brain injury, including neonatal asphyxia, pediatric cardiac arrest with global ischemia, and head trauma, that result in devastating, lifelong neurologic impairment. The only clinical intervention that appears neuroprotective is hypothermia initiated soon after the initial injury. Evidence indicates that oxidative stress, mitochondrial dysfunction, and impaired cerebral energy metabolism contribute to the brain cell death that is responsible for much of the poor neurologic outcome from these events. Recent results obtained from both in vitro and animal models of neuronal death in the immature brain point toward several molecular mechanisms that are either induced or promoted by oxidative modification of macromolecules, including consumption of cytosolic and mitochondrial NAD(+) by poly-ADP ribose polymerase, opening of the mitochondrial inner membrane permeability transition pore, and inactivation of key, rate-limiting metabolic enzymes, e.g., the pyruvate dehydrogenase complex. In addition, the relative abundance of pro-apoptotic proteins in immature brains and neurons, and particularly within their mitochondria, predisposes these cells to the intrinsic, mitochondrial pathway of apoptosis, mediated by Bax- or Bak-triggered release of proteins into the cytosol through the mitochondrial outer membrane. Based on these pathways of cell dysfunction and death, several approaches toward neuroprotection are being investigated that show promise toward clinical translation. These strategies include minimizing oxidative stress by avoiding unnecessary hyperoxia, promoting aerobic energy metabolism by repletion of NAD(+) and by providing alternative oxidative fuels, e.g., ketone bodies, directly interfering with apoptotic pathways at the mitochondrial level, and pharmacologic induction of antioxidant and anti-inflammatory gene expression.

Therapeutic hypothermia preserves antioxidant defenses after severe traumatic brain injury in infants and children

OBJECTIVE

Oxidative stress contributes to secondary damage after traumatic brain injury (TBI). Hypothermia decreases endogenous antioxidant consumption and lipid peroxidation after experimental cerebral injury. Our objective was to determine the effect of therapeutic hypothermia on oxidative damage after severe TBI in infants and children randomized to moderate hypothermia vs. normothermia.

DESIGN

Prospective randomized controlled study.

SETTING

Pediatric intensive care unit of Pittsburgh Children's Hospital.

PATIENTS

The study included 28 patients.

MEASUREMENTS AND MAIN RESULTS

We compared the effects of hypothermia (32 degrees C-33 degrees C) vs. normothermia in patients treated in a single center involved in a multicentered randomized controlled trial of hypothermia in severe pediatric TBI (Glasgow Coma Scale score <or=8). The patients randomized to hypothermia (n = 13) were cooled to target temperature within approximately 6 to 24 hours for 48 hours and then rewarmed. Antioxidant status was assessed by measurements of total antioxidant reserve and glutathione. Protein oxidation and lipid peroxidation were assessed by measurements of protein thiols and F2-isoprostane, respectively, in ventricular cerebrospinal fluid (CSF) samples (n = 76) obtained on day 1-3 after injury. The association between Glasgow Coma Scale score, age, gender, treatment, temperature, time after injury, and CSF antioxidant reserve, glutathione, protein-thiol, F2-isoprostane levels were assessed by bivariate and multiple regression models. Demographic and clinical characteristics were similar between the two treatment groups. Mechanism of injury included both accidental injury and nonaccidental injury. Multiple regression models revealed preservation of CSF antioxidant reserve by hypothermia (p = 0.001). Similarly, a multiple regression model showed that glutathione levels were inversely associated with patient temperature at the time of sampling (p = 0.002). F2-isoprostane levels peaked on day 1 after injury and were progressively decreased thereafter. Although F2-isoprostane levels were approximately three-fold lower in patients randomized to hypothermia vs. normothermia, this difference was not statistically significant.

CONCLUSION

To our knowledge, this is the first study demonstrating that hypothermia attenuates oxidative stress after severe TBI in infants and children. Our data also support the concept that CSF represents a valuable tool for monitoring treatment effects on oxidative stress after TBI.

Deleterious effects of minocycline after in vivo target deprivation of thalamocortical neurons in the immature, metallothionein-deficient mouse brain

Compared with adults, immature metallothionein I and II knockout (MT(-/-)) mice incur greater neuronal loss and a more rapid rate of microglia accumulation after target deprivation-induced injury. Because minocycline has been proposed to inhibit microglial activation and associated production of neuroinflammatory factors, we investigated its ability to promote neuronal survival in the immature, metallothionein-deficient brain. After ablation of the visual cortex, 10-day-old MT(-/-) mice were treated with minocycline or saline and killed 24 or 48 hr after injury. By means of stereological methods, the number of microglia and neurons were estimated in the ipsilateral dorsal lateral geniculate nucleus (dLGN) by an investigator blinded to the treatment. No effect on neuronal survival was observed at 24 hr, but 48 hr after injury, an unanticipated but significant minocycline-mediated increase in neuronal loss was detected. Further, while failing to inhibit microglial accumulation, minocycline treatment increased the proportion of amoeboid microglia in the ipsilateral dLGN. To understand the molecular mechanisms underlying this neurotoxic response, we identified minocycline-mediated changes in the expression of three potentially proapoptotic/inflammatory genes: growth arrest- and DNA damage-inducible gene 45gamma (GADD45gamma); interferon-inducible protein 1 (IFI1), and cytokine-induced growth factor. We also observed increased mitogen-activated protein kinase p38 phosphorylation with minocycline treatment. Although minocycline inhibited calpain activity at 12 hr after injury, this effect was not sustained at 24 hr. Together, these results help to explain how minocycline has a deleterious effect on neuronal survival in this injury model.

Use of NADH fluorescence to determine mitochondrial function in vivo

Normal mitochondrial function is a critical factor in maintaining cellular homeostasis in various organs of the body. Due to the involvement of mitochondrial dysfunction in many pathological states, the real-time in vivo monitoring of the mitochondrial metabolic state is crucially important. This type of monitoring in animal models as well as in patients provides real-time data that can help interpret experimental results or optimize patient treatment. In this paper we are summarizing the following items: (1) presenting the solid scientific ground underlying nicotine amide adenine dinucleotide (NADH) NADH fluorescence measurements based on published materials. (2) Presenting NADH fluorescence monitoring and its physiological significance. (3) Providing the reader with basic information on the methodologies of the fluorometers reflectometers. (4) Clarifying various factors affecting the monitored signals, including artifacts. (5) Presenting the potential use of monitoring mitochondrial function in vivo for the evaluation of drug development. The large numbers of publications by different groups testify to the valuable information gathered in various experimental conditions. The monitoring of NADH levels in the tissue provides the most important information on the metabolic state of the mitochondria in terms of energy production and intracellular oxygen levels. Although NADH signals are not calibrated in absolute units, their trend monitoring is important for the interpretation of physiological or pathological situations. To better understand the tissue function, the multiparametric approach has been developed where NADH serves as the key parameter to be monitored.

Early and sustained alterations in cerebral metabolism after traumatic brain injury in immature rats

Although studies have shown alterations in cerebral metabolism after traumatic brain injury (TBI), clinical data in the developing brain is limited. We hypothesized that post-traumatic metabolic changes occur early (<24 h) and persist for up to 1 week. Immature rats underwent TBI to the left parietal cortex. Brains were removed at 4 h, 24 h, and 7 days after injury, and separated into ipsilateral (injured) and contralateral (control) hemispheres. Proton nuclear magnetic resonance (NMR) spectra were obtained, and spectra were analyzed for N-acetyl-aspartate (NAA), lactate (Lac), creatine (Cr), choline, and alanine, with metabolite ratios determined (NAA/Cr, Lac/Cr). There were no metabolic differences at any time in sham controls between cerebral hemispheres. At 4 and 24 h, there was an increase in Lac/Cr, reflecting increased glycolysis and/or decreased oxidative metabolism. At 24 h and 7 days, there was a decrease in NAA/Cr, indicating loss of neuronal integrity. The NAA/Lac ratio was decreased ( approximately 15-20%) at all times (4 h, 24 h, 7 days) in the injured hemisphere of TBI rats. In conclusion, metabolic derangements begin early (<24 h) after TBI in the immature rat and are sustained for up to 7 days. Evaluation of early metabolic alterations after TBI could identify novel targets for neuroprotection in the developing brain.

Postnatal developmental regulation of Bcl-2 family proteins in brain mitochondria

Although it has been long recognized that the relative balance of pro- and antiapoptotic Bcl-2 proteins is critical in determining the susceptibility to apoptotic death, only a few studies have examined the level of these proteins specifically at mitochondria during postnatal brain development. In this study, we examined the age-dependent regulation of Bcl-2 family proteins using rat brain mitochondria isolated at various postnatal ages and from the adult. The results indicate that a general down-regulation of most of the proapoptotic Bcl-2 proteins present in mitochondria occurs during postnatal brain development. The multidomain proapoptotic Bax, Bak, and Bok are all expressed at high levels in mitochondria early postnatally but decline in the adult. Multiple BH3-only proteins, including direct activators (Bid, Bim, and Puma) and the derepressor BH3-only protein Bad, are also present in immature brain mitochondria and are down-regulated in the adult brain. Antiapoptotic Bcl-2 family members are differentially regulated, with a shift from high Bcl-2 expression in immature mitochondria to predominant Bcl-x(L) expression in the adult. These results support the concept that developmental differences in upstream regulators of the mitochondrial apoptotic pathway are responsible for the increased susceptibility of cells in the immature brain to apoptosis following injury.

Temporal window of metabolic brain vulnerability to concussions: oxidative and nitrosative stresses--part II

OBJECTIVE

In the present study, we investigated the occurrence of oxidative and nitrosative stresses in rats undergoing repeat mild traumatic brain injury (mTBI) delivered with increasing time intervals.

METHODS

Rats were subjected to two diffuse mTBIs (450 g/1 m height), with the second mTBI delivered after 1 (n = 6), 2 (n = 6), 3 (n = 6), 4 (n = 6), or 5 days (n = 6). The rats were sacrificed 48 hours after the last mTBI. Sham-operated animals were used as controls (n = 6). Concentrations of biochemical indices of oxidative stress (malondialdehyde, ascorbic acid, reduced and oxidized glutathione) and nitrosative stress (nitrite, nitrate) were synchronously measured by high-performance liquid chromatography in deproteinized tissue extracts (three right + three left hemispheres for each group of animals).

RESULTS

Increase of malondialdehyde, reduced/oxidized glutathione ratio, nitrite, nitrate, and decrease of ascorbic acid and glutathione were dependent on the interval between impacts with maximal changes recorded when mTBIs were spaced by 3 days. Biochemical markers of oxidative and nitrosative stresses were near control levels only in animals receiving mTBIs 5 days apart.

CONCLUSION

This study shows the remarkable negative contribution of reactive oxygen species overproduction and activation of inducible nitric oxide synthase in repeat mTBI. Because these effects were maximal when mTBIs were spaced by 3 days, it can be inferred that occurrence of a second mTBI within the temporal window of brain vulnerability not only causes profound derangement of mitochondrial functions, but also induces sustained oxidative and nitrosative stresses. Both phenomena certainly play a major role in the overall brain tissue damage occurring under these pathological conditions.

Stem cell therapies for perinatal brain injuries

This chapter reviews four groups of paediatric brain injury. The pathophysiology of these injuries is discussed to establish which cells are damaged and therefore which cells represent targets for cell replacement. Next, we review potential sources of cellular replacements, including embryonic stem cells, fetal and neonatal neural stem cells and a variety of mesenchymal stem cells. The advantages and disadvantages of each source are discussed. We review published studies to illustrate where stem cell therapies have been evaluated for therapeutic gain and discuss the hurdles that will need to be overcome to achieve therapeutic benefit. Overall, we conclude that children with paediatric brain injuries or inherited genetic disorders that affect the brain are worthy candidates for stem cell therapeutics.

The effects of head trauma on hypothalamic-pituitary function in children and adolescents

PURPOSE OF REVIEW

Endocrine dysfunctions have been increasingly recognized following traumatic brain injury. Ever more numerous studies on acute head-injured adults have also raised concern about this risk in children and adolescents who have experienced head injury. The current review of the pediatric literature summarizes recent findings on acute-phase dysfunction and traumatic brain injury-associated hypopituitarism.

RECENT FINDINGS

The pathophysiologic mechanisms underlying acute-phase hyponatremic and hypernatremic disorders have been elucidated. Prospective studies on traumatic brain injury-associated hypopituitarism in pediatric patients are ongoing and preliminary data are available.

SUMMARY

Traumatic brain injury, a 'silent epidemic' that carries a considerable burden of disabilities, leads to a variety of endocrine dysfunctions in 28-69% of adult acute head-injured patients. In the acute posttraumatic phase, adrenal insufficiency and electrolyte disorders are critical conditions. Neurosurgical patients, particularly those prone to neurological damage, require prompt diagnosis. Hypopituitarism may be diagnosed months or years after a traumatic brain injury event. Since growth hormone and gonadotropin secretion are most frequently compromised, careful follow-up of growth and pubertal development is mandatory in children hospitalized for traumatic brain injury.

Pediatric traumatic brain injury: not just little adults

PURPOSE OF REVIEW

This review will update the reader on the most significant recent findings with regards to both the clinical research and basic science of pediatric traumatic brain injury.

RECENT FINDINGS

The developing brain is not simply a smaller version of the mature brain. Studies have uncovered important distinctions of the younger brain after traumatic brain injury, including an increased propensity for apoptosis, age-dependent parameters for cerebral blood flow and metabolism, development-specific biomarkers, increased likelihood of early posttraumatic seizures, differential sensitivity to commonly used neuroactive medications and altered neuroplasticity during recovery from injury. Specifically, there is strong preclinical evidence for increased neuronal apoptosis in the developing brain being triggered by anesthetics and anticonvulsants, making it paramount that future studies more clearly delineate preferred agents and specific indications for use, incorporating long-term functional outcomes as well as short-term benefits. In addition, the young brain may actually benefit from therapeutic interventions that have been less effective following adult traumatic brain injury, such as decompressive craniectomy and hypothermia.

SUMMARY

An increasing body of evidence demonstrates the importance of establishing age-dependent guidelines for physiological monitoring, pharmacological intervention, management of intracranial pressure and facilitating recovery of function.

Mitochondrial dysfunction early after traumatic brain injury in immature rats

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