The effects of age and ketogenic diet on local cerebral metabolic rates of glucose after controlled cortical impact injury in rats

Differences in Volatile Organic Compounds Between Concussed and Non-concussed Division I Athletes

Introduction Diagnosing a concussion is challenging because of complex and variable symptoms. Establishing a viable biomarker of injury may rely on physiologic measurements rather than symptomology. Volatile organic compounds (VOCs) such as breath acetone have been identified as potential physiological markers that can capture changes in the utilization of energy substrates post-concussion. Here, we aimed to explore whether differences in VOCs exist between concussed and non-concussed athletes at the initial and later stages of injury recovery. Methods Six (N=6) non-concussed athletes were enrolled as control participants prior to the competitive season. Control participants' breath acetone, heart rate, and anthropometric measures were obtained at rest and throughout a single exercise challenge by breathalyzer. Six (N=6) athletes diagnosed with concussion during the competitive season had breath acetone measured daily until cleared to return to activity or approximately four weeks following enrollment where they participated in an exit exercise challenge having breath acetone, heart rate, and anthropometric measures obtained. Comparisons were made between at-rest measures of concussed and non-concussed participants at multiple time points during the recovery period. Paired t-test comparisons with individuals serving as their own control were used to determine individual differences in recovery. Visual graphs were used to demonstrate differences in obtained measures amongst individuals and between groups during the exercise challenges. Results Results demonstrated statistically significant differences in breath acetone between concussed and control participants when the highest day measured during the first week of concussion was compared to the control participant's resting values (P=0.017). Additionally, when the concussed participants served as their own control and their highest measured day of the first week post-concussion was compared to values when cleared to return to activity or at 26 days post-concussion, there was a significant difference in breath acetone (P=0.028). Comparing breath acetone during exercise between non-concussed and cleared concussed participants or four weeks post-injury, demonstrated no significant differences throughout the challenge or at rest prior. Visual graph comparisons in a single participant before and after concussion suggest differences may appear following exercise during the recovery period. Discussion These results suggest VOCs, particularly breath acetone, have the potential to serve as diagnostic markers of concussion. However, longitudinal research within larger cohorts and with equipment able to expel VOCs other than acetone from measures are needed to make informed recommendations.

Non-pharmacological interventions for traumatic brain injury

Heterogeneity and variability of symptoms due to the type, site, age, sex, and severity of injury make each case of traumatic brain injury (TBI) unique. Considering this, a universal treatment strategy may not be fruitful in managing outcomes after TBI. Most of the pharmacological therapies for TBI aim at modifying a particular pathway or molecular process in the sequelae of secondary injury rather than a holistic approach. On the other hand, non-pharmacological interventions such as hypothermia, hyperbaric oxygen, preconditioning with dietary adaptations, exercise, environmental enrichment, deep brain stimulation, decompressive craniectomy, probiotic use, gene therapy, music therapy, and stem cell therapy can promote healing by modulating multiple neuroprotective mechanisms. In this review, we discussed the major non-pharmacological interventions that are being tested in animal models of TBI as well as in clinical trials. We evaluated the functional outcomes of various interventions with an emphasis on the links between molecular mechanisms and outcomes after TBI.

Ketogenic Diet for Neonatal Hypoxic-Ischemic Encephalopathy

The prevalence of neonatal hypoxic-ischemic encephalopathy (HIE), a devastating neurological injury, is increasing; thus, effective treatments and preventions are urgently needed. The underlying pathology of HIE remains unclear; recent research has focused on elucidating key features of the disease. A variety of diseases can be alleviated by consuming a ketogenic diet (KD) despite differences in pathogenesis and features, given the common mechanisms of KD-induced effects. Dietary modification is the most translatable, cost-efficient, and safest approach to treat acute or chronic neurological disorders and reduces reliance on pharmaceutical treatments. Evidence suggests that the KD can exert beneficial effects in animal models and in humans with brain injuries. The efficacy of the KD in preventing neuronal damage, motor alterations, and cognitive decline varies. Moreover, the KD may provide an alternative source of energy, enhance mitochondrial function, and reduce the expression of inflammatory and apoptotic mediators. Thus, this diet has attracted interest as a potential therapy for HIE. This review examined the role of the KD in HIE treatment and described the mechanisms by which ketone bodies (KBs) exert effects under pathological conditions and protect against brain damage; the evidence supports the implementation of dietary interventions as a therapeutic strategy for HIE. Future research should aim to elucidate the underlying mechanisms of the KD in patients with HIE and determine whether the effect of the KD on clinical outcomes can be reproduced in humans.

Exogenous Ketones and Lactate as a Potential Therapeutic Intervention for Brain Injury and Neurodegenerative Conditions

Metabolic dysfunction is a ubiquitous underlying feature of many neurological conditions including acute traumatic brain injuries and chronic neurodegenerative conditions. A central problem in neurological patients, in particular those with traumatic brain injuries, is an impairment in the utilization of glucose, which is the predominant metabolic substrate in a normally functioning brain. In such patients, alternative substrates including ketone bodies and lactate become important metabolic candidates for maintaining brain function. While the potential neuroprotective benefits of ketosis have been recognized for up to almost a century, the majority of work has focused on the use of ketogenic diets to induce such a state, which is inappropriate in cases of acute disease due to the prolonged periods of time (i.e., weeks to months) required for the effects of a ketogenic diet to be seen. The following review seeks to explore the neuroprotective effects of exogenous ketone and lactate preparations, which have more recently become commercially available and are able to induce a deep ketogenic response in a fraction of the time. The rapid response of exogenous preparations makes their use as a therapeutic adjunct more feasible from a clinical perspective in both acute and chronic neurological conditions. Potentially, their ability to globally moderate long-term, occult brain dysfunction may also be relevant in reducing lifetime risks of certain neurodegenerative conditions. In particular, this review explores the association between traumatic brain injury and contusion-related dementia, assessing metabolic parallels and highlighting the potential role of exogenous ketone and lactate therapies.

Feasibility of an MI-CBT ketogenic adherence program for older adults with mild cognitive impairment

BACKGROUND

The National Institutes of Health Obesity-Related Behavioral Intervention Trials model for intervention development was used to establish the feasibility and proof of concept of a motivational ketogenic nutrition adherence program for older adults with mild cognitive impairment.

METHODS

This was a single-arm, single-center feasibility trial. A comprehensive assessment protocol, including a clinical interview, neuropsychological testing, and genetic sequencing was used as an initial screening. Nine participants (aged 64-75) with possible amnestic mild cognitive impairment were consented for the intervention. Participants completed pre- and post-intervention neuropsychological assessments using the updated Repeatable Battery for Assessment of Neuropsychological Status. Participants tracked their macronutrient consumption using food diaries and ketone levels using urinalysis test strips daily. Mood and other psychosocial variables were collected through surveys, and qualitative exit interviews were completed.

RESULTS

100% of participants who began the trial completed the 6-week ketogenic nutrition adherence program, including completion of the pre- and post-assessments. Eight participants achieved measurable levels of ketones during the program. The average self-rated adherence across the program was 8.7 out of 10. A Wilcoxon Signed-Rank test demonstrated significant improvement in cognitive performance from baseline (median = 88) to follow up (median = 96, Z = - 2.26, p = .024). The average difference in cognitive performance from baseline to follow-up was - 7.33 (95% CI - 12.85, - 1.82).

CONCLUSIONS

Results supported the feasibility for moving to the next phase and demonstrated proof of concept for the intervention. The next step is a randomized pilot trial to test clinical signals of effect compared to a control condition.

TRIAL REGISTRATION

This trial was retrospectively registered with clinicaltrials.gov on July 13, 2021. The trial number is NCT04968041.

Ketogenic diets and the nervous system: a scoping review of neurological outcomes from nutritional ketosis in animal studies

OBJECTIVES

Ketogenic diets have reported efficacy for neurological dysfunctions; however, there are limited published human clinical trials elucidating the mechanisms by which nutritional ketosis produces therapeutic effects. The purpose of this present study was to investigate animal models that report variations in nervous system function by changing from a standard animal diet to a ketogenic diet, synthesise these into broad themes, and compare these with mechanisms reported as targets in pain neuroscience to inform human chronic pain trials.

METHODS

An electronic search of seven databases was conducted in July 2020. Two independent reviewers screened studies for eligibility, and descriptive outcomes relating to nervous system function were extracted for a thematic analysis, then synthesised into broad themes.

RESULTS

In total, 170 studies from eighteen different disease models were identified and grouped into fourteen broad themes: alterations in cellular energetics and metabolism, biochemical, cortical excitability, epigenetic regulation, mitochondrial function, neuroinflammation, neuroplasticity, neuroprotection, neurotransmitter function, nociception, redox balance, signalling pathways, synaptic transmission and vascular supply.

DISCUSSION

The mechanisms presented centred around the reduction of inflammation and oxidative stress as well as a reduction in nervous system excitability. Given the multiple potential mechanisms presented, it is likely that many of these are involved synergistically and undergo adaptive processes within the human body, and controlled animal models that limit the investigation to a particular pathway in isolation may reach differing conclusions. Attention is required when translating this information to human chronic pain populations owing to the limitations outlined from the animal research.

Systematic Review - Neuroprotection of ketosis in acute injury of the mammalian central nervous system: A meta-analysis

To evaluate the neuroprotection exerted by ketosis against acute damage of the mammalian central nervous system (CNS). Search engines were interrogated to identify experimental studies comparing the mitigating effect of ketosis (intervention) versus non-ketosis (control) on acute CNS damage. Primary endpoint was a reduction in mortality. Secondary endpoints were a reduction in neuronal damage and dysfunction, and an 'aggregated advantage' (composite of all primary and secondary endpoints). Hedges' g was the effect measure. Subgroup analyses evaluated the modulatory effect of age, insult type, and injury site. Meta-regression evaluated timing, type, and magnitude of intervention as predictors of neuroprotection. The selected publications were 49 experimental murine studies (period 1979-2020). The intervention reduced mortality (g 2.45, SE 0.48, p < .01), neuronal damage (g 1.96, SE 0.23, p < .01) and dysfunction (g 0.99, SE 0.10, p < .01). Reduction of mortality was particularly pronounced in the adult subgroup (g 2.71, SE 0.57, p < .01). The aggregated advantage of ketosis was stronger in the pediatric (g 3.98, SE 0.71, p < .01), brain (g 1.96, SE 0.18, p < .01), and ischemic insult (g 2.20, SE 0.23, p < .01) subgroups. Only the magnitude of intervention was a predictor of neuroprotection (g 0.07, SE 0.03, p 0.01 per every mmol/L increase in ketone levels). Ketosis exerts a potent neuroprotection against acute damage to the mammalian CNS in terms of reduction of mortality, of neuronal damage and dysfunction. Hematic levels of ketones are directly proportional to the effect size of neuroprotection.

Microglial Metabolism After Pediatric Traumatic Brain Injury - Overlooked Bystanders or Active Participants?

Microglia play an integral role in brain development but are also crucial for repair and recovery after traumatic brain injury (TBI). TBI induces an intense innate immune response in the immature, developing brain that is associated with acute and chronic changes in microglial function. These changes contribute to long-lasting consequences on development, neurologic function, and behavior. Although alterations in glucose metabolism are well-described after TBI, the bulk of the data is focused on metabolic alterations in astrocytes and neurons. To date, the interplay between alterations in intracellular metabolic pathways in microglia and the innate immune response in the brain following an injury is not well-studied. In this review, we broadly discuss the microglial responses after TBI. In addition, we highlight reported metabolic alterations in microglia and macrophages, and provide perspective on how changes in glucose, fatty acid, and amino acid metabolism can influence and modulate the microglial phenotype and response to injury.

A new ketogenic formulation improves functional outcome and reduces tissue loss following traumatic brain injury in adult mice

Rationale: Traumatic brain injury (TBI) leads to neurological impairment, with no satisfactory treatments available. Classical ketogenic diets (KD), which reduce reliance on carbohydrates and provide ketones as fuel, have neuroprotective potential, but their high fat content reduces compliance, and experimental evidence suggests they protect juvenile brain against TBI, but not adult brain, which would strongly limit their applicability in TBI. Methods: We designed a new-KD with a fat to carbohydrate plus protein ratio of 2:1, containing medium chain triglycerides (MCT), docosahexaenoic acid (DHA), low glycaemic index carbohydrates, fibres and the ketogenic amino acid leucine, and evaluated its neuroprotective potential in adult TBI. Adult male C57BL6 mice were injured by controlled cortical impact (CCI) and assessed for 70 days, during which they received a control diet or the new-KD. Results: The new-KD, that markedly increased plasma Beta-hydroxybutyrate (β-HB), significantly attenuated sensorimotor deficits and corrected spatial memory deficit. The lesion size, perilesional inflammation and oxidation were markedly reduced. Oligodendrocyte loss appeared to be significantly reduced. TBI activated the mTOR pathway and the new-KD enhanced this increase and increased histone acetylation and methylation. Conclusion: The behavioural improvement and tissue protection provide proof of principle that this new formulation has therapeutic potential in adult TBI.

The ketone ester, 3-hydroxybutyl-3-hydroxybutyrate, attenuates neurobehavioral deficits and improves neuropathology following controlled cortical impact in male rats

Traumatic brain injury (TBI) is a leading cause of human death and disability with no effective therapy to fully prevent long-term neurological deficits in surviving patients. Ketone ester supplementation is protective in animal models of neurodegeneration, but its efficacy against TBI pathophysiology is unknown. Here, we assessed the neuroprotective effect of the ketone monoester, 3-hydroxybutyl-3-hydroxybutyrate, (KE) in male Sprague Dawley rats (n=32). TBI was induced using the controlled cortical impact (CCI) with Sham animals not receiving the brain impact. KE was administered daily by oral gavage (0.5 ml/kg/day) and provided ad libitum at 0.3% (v/v) in the drinking water. KE supplementation started immediately after TBI and lasted for the duration of the study. Motor and sensory deficits were assessed using the Neurobehavioral Severity Scale-Revised (NSS-R) at four weeks post-injury. The NSS-R total score in CCI + KE (1.2 ± 0.4) was significantly lower than in CCI + water (4.4 ± 0.5). Similarly, the NSS-R motor scores in CCI + KE (0.6 ± 0.7) were significantly lower than CCI + water (2.9 ± 1.5). Although the NSS-R sensory score in the CCI + KE group (0.5 ± 0.2) was significantly lower compared to CCI + water (1.8 ± 0.4), no difference was observed between CCI + water and Sham + water (1.0 ± 0.2) groups. The lesion volume was smaller in the CCI + KE (10 ± 3 mm³) compared to CCI + water (47 ± 11 mm³; p < 0.001). KE significantly decreased Iba1⁺ stained areas in the cortex and hippocampus, and GFAP⁺ stained areas in all brain regions analyzed - prefrontal cortex, hippocampus, cortex, amygdala (p < 0.01). In summary, our results indicate that KE can protect against TBI-induced morphological and functional deficits when administered immediately after an insult.

Nutritional interventions to improve neurophysiological impairments following traumatic brain injury: A systematic review

Traumatic brain injury (TBI) accounts for significant global health burden. Effects of TBI can become chronic even following mild injury. There is a need to develop effective therapies to attenuate the damaging effects of TBI and improve recovery outcomes. This literature review using a priori criteria (PROSPERO; CRD42018100623) summarized 43 studies between January 1998 and July 2019 that investigated nutritional interventions (NUT) delivered with the objective of altering neurophysiological (NP) outcomes following TBI. Risk of bias was assessed for included studies, and NP outcomes recorded. The systematic search resulted in 43 of 3,748 identified studies met inclusion criteria. No studies evaluated the effect of a NUT on NP outcomes of TBI in humans. Biomarkers of morphological changes and apoptosis, oxidative stress, and plasticity, neurogenesis, and neurotransmission were the most evaluated NP outcomes across the 43 studies that used 2,897 animals. The risk of bias was unclear in all reviewed studies due to poorly detailed methodology sections. Taking these limitations into account, anti-oxidants, branched chain amino acids, and ω-3 polyunsaturated fatty acids have shown the most promising pre-clinical results for altering NP outcomes following TBI. Refinement of pre-clinical methodologies used to evaluate effects of interventions on secondary damage of TBI would improve the likelihood of translation to clinical populations.

The Ketogenic Diet in the Treatment of Post-concussion Syndrome-A Feasibility Study

Concussion is the most common form of mild traumatic brain injury (mTBI). Although most patients' symptoms resolve within a month, patients with post-concussion syndrome (PCS) may continue to experience symptoms for years and have limited treatment options. This pilot study assessed the feasibility and symptom-related effects of a ketogenic diet (KD) in patients with PCS symptoms. The Ketogenic Diet in Post-Concussion Syndrome (KD-PCS) was a single-arm trial of a 2-month KD high in non-starchy vegetables and supplemented with medium-chain triglyceride (MCT) oil. Macronutrient targets were ≥70% fat, ≤10% carbohydrate, and the remainder as protein as energy. We assessed feasibility by daily self-reported measure of urine acetoacetate and collection of 3-day food records and serum beta-hydroxybutyrate at multiple timepoints. We assessed symptoms by administering the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) and Modified Balance Error Scoring System (M-BESS) at baseline and month 2 and the Post-Concussion Symptom Scale (PCSS) at baseline, month 1, and month 2. Fourteen participants enrolled in the KD-PCS. Twelve participants completed the study and 11 implemented the KD (73% fat, 9% carbohydrate, and 18% protein) and achieved ketosis. One participant complained of MCT-related diarrhea that resolved and another reported nausea and fatigue that resulted in withdrawal from the study. Among compliant participants, the visual memory domain of the ImPACT improved by 12 points (p = 0.02) and PCSS scores improved by 9 points, although not statistically significant. This pilot trial suggests that the KD is a feasible experimental treatment for PCS and justifies further study of its efficacy.

Application of ketogenic diets for pediatric neurocritical care

In this review, we summarize the general mechanisms of the ketogenic diet, and the application of a ketogenic diet in pediatric intensive care units for the neurological disorders of children and young infants. A ketogenic diet is a high-fat, low-carbohydrate, adequate-protein diet. It can alter the primary cerebral energy metabolism from glucose to ketone bodies, which involves multiple mechanisms of antiepileptic action, antiepileptogenic properties, neuro-protection, antioxidant and anti-inflammatory effects, and it is potentially a disease-modifying intervention. Although a ketogenic diet is typically used for the chronic stage of pharmacoresistant of epilepsy, recent studies have shown its efficacy in patients with the acute stage of refractory/super-refractory status epilepticus. The application of a ketogenic diet in pediatric intensive care units is a challenge because of the critical status of the patients, who are often in a coma or have a nothing by mouth order. Moreover, a ketogenic diet needs to be started early and sometimes through parenteral administration in patients with critical conditions such as refractory status epilepticus or febrile infection-related epilepsy syndrome. Animal models and some case reports have shown that the neuro-protective effects of a ketogenic diet can be extended to other emergent neurological diseases, such as traumatic brain injury and ischemic stroke.

A Western diet impairs CNS energy homeostasis and recovery after spinal cord injury: Link to astrocyte metabolism

A diet high in fat and sucrose (HFHS), the so-called Western diet promotes metabolic syndrome, a significant co-morbidity for individuals with spinal cord injury (SCI). Here we demonstrate that the spinal cord of mice consuming HFHS expresses reduced insulin-like growth factor 1 (IGF-1) and its receptor and shows impaired tricarboxylic acid cycle function, reductions in PLP and increases in astrogliosis, all prior to SCI. After SCI, Western diet impaired sensorimotor and bladder recovery, increased microgliosis, exacerbated oligodendrocyte loss and reduced axon sprouting. Direct and indirect neural injury mechanisms are suggested since HFHS culture conditions drove parallel injury responses directly and indirectly after culture with conditioned media from HFHS-treated astrocytes. In each case, injury mechanisms included reductions in IGF-1R, SIRT1 and PGC-1α and were prevented by metformin. Results highlight the potential for a Western diet to evoke signs of neural insulin resistance and injury and metformin as a strategy to improve mechanisms of neural neuroprotection and repair.

Alternative substrate metabolism depends on cerebral metabolic state following traumatic brain injury

Decreases in energy metabolism following traumatic brain injury (TBI) are attributed to impairment of glycolytic flux and oxidative phosphorylation. Glucose utilization post-TBI is decreased while administration of alternative substrates has been shown to be neuroprotective. Changes in energy metabolism following TBI happens in two phases; a period of hyper-metabolism followed by prolonged hypo-metabolism. It is not understood how different cerebral metabolic states may impact substrate metabolism and ultimately mitochondrial function. Adult male or female Sprague Dawley rats were given sham surgery or controlled cortical impact (CCI) and were assigned one of two administration schemes. Glucose, lactate or beta-hydroxybutyrate (BHB) were infused i.v. either starting immediately after injury or beginning 6 h post-injury for 3 h to reflect the hyper- and hypo-metabolic stages. Animals were euthanized 24 h post-injury. The peri-contusional cortex was collected and assayed for mitochondrial respiration peroxide production, and citrate synthase activity. Tissue acetyl-CoA, ATP, glycogen and HMGB1 were also quantified. Sex differences were observed in injury pattern. Administration based on cerebral metabolic state identified that only early lactate and late BHB improved mitochondrial function and peroxide production and TCA cycle intermediates in males. In contrast, both early and late BHB had deleterious effects on all aspects of metabolic measurements in females. These data stress there is no one optimal alternative substrate, but rather the fuel type used should be guided by both cerebral metabolic state and sex.

Modulation of cerebral ketone metabolism following traumatic brain injury in humans

Adaptive metabolic response to injury includes the utilization of alternative energy substrates - such as ketone bodies (KB) - to protect the brain against further damage. Here, we examined cerebral ketone metabolism in patients with traumatic brain injury (TBI; n = 34 subjects) monitored with cerebral microdialysis to measure total brain interstitial tissue KB levels (acetoacetate and β-hydroxybutyrate). Nutrition - from fasting vs. stable nutrition state - was associated with a significant decrease of brain KB (34.7 [10th-90th percentiles 10.7-189] µmol/L vs. 13.1 [6.5-64.3] µmol/L, p < 0.001) and blood KB (668 [168.4-3824.9] vs. 129.4 [82.6-1033.8] µmol/L, p < 0.01). Blood KB correlated with brain KB (Spearman's rho 0.56, p = 0.0013). Continuous feeding with medium-chain triglycerides-enriched enteral nutrition did not increase blood KB, and provided a modest increase in blood and brain free medium chain fatty acids. Higher brain KB at the acute TBI phase correlated with age and brain lactate, pyruvate and glutamate, but not brain glucose. These novel findings suggest that nutritional ketosis was the main determinant of cerebral KB metabolism following TBI. Age and cerebral metabolic distress contributed to brain KB supporting the hypothesis that ketones might act as alternative energy substrates to glucose. Further studies testing KB supplementation after TBI are warranted.

Concussion Pathophysiology and Injury Biomechanics

PURPOSE OF REVIEW

The concussion public health burden has increased alongside our knowledge of the pathophysiology of mild traumatic brain injury (mTBI). The purpose of this review is to summarize our current understanding of mTBI pathophysiology and biomechanics and how these underlying principles correlate with clinical manifestations of mTBI.

RECENT FINDINGS

Changes in post-mTBI glutamate and GABA concentrations seem to be region-specific and time-dependent. Genetic variability may predict recovery and symptom severity while gender differences appear to be associated with the neuroinflammatory response and neuroplasticity. Ongoing biomechanical research has shown a growing body of evidence in support of an "individual-specific threshold" for mTBI that varies based on individual intrinsic factors. The literature demonstrates a well-characterized timeframe for mTBI pathophysiologic changes in animal models while work in this area continues to grow in humans. Current human research shows that these underlying post-mTBI effects are multifactorial and may correlate with symptomatology and recovery. While wearable sensor technology has advanced biomechanical impact research, a definitive concussion threshold remains elusive.

How to Translate Time: The Temporal Aspects of Rodent and Human Pathobiological Processes in Traumatic Brain Injury

Traumatic brain injury (TBI) triggers multiple pathobiological responses with differing onsets, magnitudes, and durations. Identifying the therapeutic window of individual pathologies is critical for successful pharmacological treatment. Dozens of experimental pharmacotherapies have been successfully tested in rodent models, yet all of them (to date) have failed in clinical trials. The differing time scales of rodent and human biological and pathological processes may have contributed to these failures. We compared rodent versus human time scales of TBI-induced changes in cerebral glucose metabolism, inflammatory processes, axonal integrity, and water homeostasis based on published data. We found that the trajectories of these pathologies run on different timescales in the two species, and it appears that there is no universal "conversion rate" between rodent and human pathophysiological processes. For example, the inflammatory process appears to have an abbreviated time scale in rodents versus humans relative to cerebral glucose metabolism or axonal pathologies. Limitations toward determining conversion rates for various pathobiological processes include the use of differing outcome measures in experimental and clinical TBI studies and the rarity of longitudinal studies. In order to better translate time and close the translational gap, we suggest 1) using clinically relevant outcome measures, primarily in vivo imaging and blood-based proteomics, in experimental TBI studies and 2) collecting data at multiple post-injury time points with a frequency exceeding the expected information content by two or three times. Combined with a big data approach, we believe these measures will facilitate the translation of promising experimental treatments into clinical use.

Bridging the gap: Mechanisms of plasticity and repair after pediatric TBI

Traumatic brain injury is the leading cause of death and disability in the United States, and may be associated with long lasting impairments into adulthood. The multitude of ongoing neurobiological processes that occur during brain maturation confer both considerable vulnerability to TBI but may also provide adaptability and potential for recovery. This review will examine and synthesize our current understanding of developmental neurobiology in the context of pediatric TBI. Delineating this biology will facilitate more targeted initial care, mechanism-based therapeutic interventions and better long-term prognostication and follow-up.

Metabolic perturbations after pediatric TBI: It's not just about glucose

Improved patient survival following pediatric traumatic brain injury (TBI) has uncovered a currently limited understanding of both the adaptive and maladaptive metabolic perturbations that occur during the acute and long-term phases of recovery. While much is known about the redundancy of metabolic pathways that provide adequate energy and substrates for normal brain growth and development, the field is only beginning to characterize perturbations in these metabolic pathways after pediatric TBI. To date, the majority of studies have focused on dysregulated oxidative glucose metabolism after injury; however, the immature brain is well-equipped to use alternative substrates to fuel energy production, growth, and development. A comprehensive understanding of metabolic changes associated with pediatric TBI cannot be limited to investigations of glucose metabolism alone. All energy substrates used by the brain should be considered in developing nutritional and pharmacological interventions for pediatric head trauma. This review summarizes post-injury changes in brain metabolism of glucose, lipids, ketone bodies, and amino acids with discussion of the therapeutic potential of altering substrate utilization to improve pediatric TBI outcomes.

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.

Midline (central) fluid percussion model of traumatic brain injury in pediatric and adolescent rats

OBJECTIVE Experimental traumatic brain injury (TBI) models hold significant validity to the human condition, with each model replicating a subset of clinical features and symptoms. TBI is the leading cause of mortality and morbidity in children and teenagers; thus, it is critical to develop preclinical models of these ages to test emerging treatments. Midline fluid percussion injury (FPI) might best represent mild and diffuse clinical brain injury because of the acute behavioral deficits, the late onset of behavioral morbidities, and the absence of gross histopathology. In this study, the authors sought to adapt a midline FPI to postnatal day (PND) 17 and 35 rats. The authors hypothesized that scaling the craniectomy size based on skull dimensions would result in a reproducible injury comparable to the standard midline FPI in adult rats. METHODS PND17 and PND35 rat skulls were measured, and trephines were scaled based on skull size. Custom trephines were made. Rats arrived on PND10 and were randomly assigned to one of 3 cohorts: PND17, PND35, and 2 months old. Rats were subjected to midline FPI, and the acute injury was characterized. The right reflex was recorded, injury-induced apnea was measured, injury-induced seizure was noted, and the brains were immediately examined for hematoma. RESULTS The authors' hypothesis was supported; scaling the trephines based on skull size led to a reproducible injury in the PND17 and PND35 rats that was comparable to the injury in a standard 2-month-old adult rat. The midline FPI suppressed the righting reflex in both the PND17 and PND35 rats. The injury induced apnea in PND17 rats that lasted significantly longer than that in PND35 and 2-month-old rats. The injury also induced seizures in 73% of PND17 rats compared with 9% of PND35 rats and 0% of 2-month-old rats. There was also a significant relationship between the righting reflex time and presence of seizure. Both PND17 and PND35 rats had visible hematomas with an intact dura, indicative of diffuse injury comparable to the injury observed in 2-month-old rats. CONCLUSIONS With these procedures, it becomes possible to generate brain-injured juvenile rats (pediatric [PND17] and adolescent [PND35]) for studies of injury-induced pathophysiology and behavioral deficits, for which rational therapeutic interventions can be implemented.

The ketogenic diet as a treatment for traumatic brain injury: a scoping review

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality worldwide. The ketogenic diet (KD) has been identified as a potential therapy to enhance recovery after TBI. The purpose of this study is to complete a scoping review and synthesize the evidence regarding the KD and its therapeutic effects in TBI. The methodological framework of Arksey and O'Malley was employed. Databases searched include Medline, EMBASE, CCRCT, CINAHL and WebOfScience. Two reviewers independently screened titles, abstracts and full texts in a two-step screening protocol to determine inclusion. Abstracted data included study setting and therapeutic mechanism. The KD was demonstrated to reduce cerebral oedema, apoptosis, improve cerebral metabolism and behavioural outcomes in rodent TBIs. Additionally, the KD affected rodent TBIs in an age-dependent manner. Due to a lack of relevant outcome measures, the human trials did not establish much evidence with respect to the KD as a treatment for TBI; only its safety was established. The KD is an effective treatment for TBI recovery in rats and shows potential in humans. Future research should aim to better elucidate the KD's mechanisms of action in human TBIs and determine if the KD's effectiveness on clinical outcomes can be reproduced in humans.

Concussion: pathophysiology and clinical translation

The majority of the 3.8 million estimated annual traumatic brain injuries (TBI) in the United States are mild TBIs, or concussions, and they occur primarily in adolescents and young adults. A concussion is a brain injury associated with rapid brain movement and characteristic clinical symptoms, with no associated objective biomarkers or overt pathologic brain changes, thereby making it difficult to diagnose by neuroimaging or other objective diagnostic tests. Most concussion symptoms are transient and resolve within 1-2 weeks. Concussions share similar acute pathophysiologic perturbations to more severe TBI: there is a rapid release of neurotransmitters, which causes ionic disequilibrium across neuronal membranes. Re-establishing ionic homeostasis consumes energy and leads to dynamic changes in cerebral glucose uptake. The magnitude and duration of these changes are related to injury severity, with milder injuries showing faster normalization. Cerebral sex differences add further variation to concussion manifestation. Relative to the male brain, the female brain has higher overall cerebral blood flow, and demonstrates regional differences in glucose metabolism, inflammatory responses, and connectivity. Understanding the pathophysiology and clinical translation of concussion can move research towards management paradigms that will minimize the risk for prolonged recovery and repeat injury.

Glucose metabolism in pediatric traumatic brain injury

Traumatic brain injury is the number one cause of death and disability among the pediatric population in the USA. The heterogeneity of the pediatric population is reflected by both the normal cerebral maturation and the age differences in the causes of TBI, which generate unique age-related pathophysiology responses and recovery profiles. This review will address the normal changes in cerebral glucose metabolism throughout developmental phases and how TBI alters glucose metabolism. Evidence has shown that TBI disrupts the biochemical processing of glucose to energy. This brings to question, "What is the optimal substrate to manage a pediatric TBI patient?" Issues related to glycemic control and alternative substrate metabolism are addressed specifically in regard to pediatric TBI. Research into pediatric glucose metabolism after TBI is limited, and understanding these age-related differences within the pediatric population have great potential to improve support for the injured younger brain.

Functional Neuroimaging in Traumatic Brain Injury: From Nodes to Networks

Since the invention of functional magnetic resonance imaging (fMRI), thousands of studies in healthy and clinical samples have enlightened our understanding of the organization of cognition in the human brain and neuroplastic changes following brain disease and injury. Increasingly, studies involve analyses rooted in complex systems theory and analysis applied to clinical samples. Given the complexity in available approaches, concise descriptions of the theoretical motivation of network techniques and their relationship to traditional approaches and theory are necessary. To this end, this review concerns the use of fMRI to understand basic cognitive function and dysfunction in the human brain scaling from emphasis on basic units (or "nodes") in the brain to interactions within and between brain networks. First, major themes and theoretical issues in the scientific study of the injured brain are introduced to contextualize these analyses, particularly concerning functional "brain reorganization." Then, analytic approaches ranging from the voxel level to the systems level using graph theory and related approaches are reviewed as complementary approaches to examine neurocognitive processes following TBI. Next, some major findings relevant to functional reorganization hypotheses are discussed. Finally, major open issues in functional network analyses in neurotrauma are discussed in theoretical, analytic, and translational terms.

Hyperbaric Environment: Oxygen and Cellular Damage versus Protection

The elevation of tissue pO2 induced by hyperbaric oxygen (HBO) is a physiological stimulus that elicits a variety of cellular responses. These effects are largely mediated by, or in response to, an increase in the production of reactive oxygen and nitrogen species (RONS). The major consequences of elevated RONS include increased oxidative stress and enhanced antioxidant capacity, and modulation of redox-sensitive cell signaling pathways. Interestingly, these phenomena underlie both the therapeutic and potentially toxic effects of HBO. Emerging evidence indicates that supporting mitochondrial health is a potential method of enhancing the therapeutic efficacy of, and preventing oxygen toxicity during, HBO. This review will focus on the cellular consequences of HBO, and explore how these processes mediate a delicate balance of cellular protection versus damage. © 2017 American Physiological Society. Compr Physiol 7:213-234, 2017.

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.

Ketogenic diet decreases oxidative stress and improves mitochondrial respiratory complex activity

Cerebral metabolism of ketones after traumatic brain injury (TBI) improves neuropathology and behavior in an age-dependent manner. Neuroprotection is attributed to improved cellular energetics, although other properties contribute to the beneficial effects. Oxidative stress is responsible for mitochondrial dysfunction after TBI. Ketones decrease oxidative stress, increase antioxidants and scavenge free radicals. It is hypothesized that ketogenic diet (KD) will decrease post-TBI oxidative stress and improve mitochondria. Postnatal day 35 (PND35) male rats were given sham or controlled cortical impact (CCI) injury and placed on standard (STD) or KD. Ipsilateral cortex homogenates and mitochondria were assayed for markers of oxidative stress, antioxidant expression and mitochondrial function. Oxidative stress was significantly increased at 6 and 24 h post-injury and attenuated by KD while inducing protein expression of antioxidants, NAD(P)H dehydrogenase quinone 1 (NQO1) and superoxide dismutase (SOD1/2). Complex I activity was inhibited in STD and KD groups at 6 h and normalized by 24 h. KD significantly improved Complex II-III activity that was reduced in STD at 6 h. Activity remained reduced at 24 h in STD and unchanged in KD animals. These results strongly suggest that ketones improve post-TBI cerebral metabolism by providing alternative substrates and through antioxidant properties, preventing oxidative stress-mediated mitochondrial dysfunction.

Pyruvate treatment attenuates cerebral metabolic depression and neuronal loss after experimental traumatic brain injury

Experimental traumatic brain injury (TBI) is known to produce an acute increase in cerebral glucose utilization, followed rapidly by a generalized cerebral metabolic depression. The current studies determined effects of single or multiple treatments with sodium pyruvate (SP; 1000mg/kg, i.p.) or ethyl pyruvate (EP; 40mg/kg, i.p.) on cerebral glucose metabolism and neuronal injury in rats with unilateral controlled cortical impact (CCI) injury. In Experiment 1 a single treatment was given immediately after CCI. SP significantly improved glucose metabolism in 3 of 13 brain regions while EP improved metabolism in 7 regions compared to saline-treated controls at 24h post-injury. Both SP and EP produced equivalent and significant reductions in dead/dying neurons in cortex and hippocampus at 24h post-CCI. In Experiment 2 SP or EP were administered immediately (time 0) and at 1, 3 and 6h post-CCI. Multiple SP treatments also significantly attenuated TBI-induced reductions in cerebral glucose metabolism (in 4 brain regions) 24h post-CCI, as did multiple injections of EP (in 4 regions). The four pyruvate treatments produced significant neuroprotection in cortex and hippocampus 1day after CCI, similar to that found with a single SP or EP treatment. Thus, early administration of pyruvate compounds enhanced cerebral glucose metabolism and neuronal survival, with 40mg/kg of EP being as effective as 1000mg/kg of SP, and multiple treatments within 6h of injury did not improve upon outcomes seen following a single treatment.

Metabolic Response of Pediatric Traumatic Brain Injury

Traumatic brain injury (TBI) in the pediatric brain presents unique challenges as the complex cascades of metabolic and biochemical responses to TBI are further complicated ongoing maturational changes of the developing brain. TBIs of all severities have been shown to significantly alter metabolism and hormones which impair the ability of the brain to process glucose for cellular energy. Under these conditions, the brain's primary fuel (glucose) becomes a less favorable fuel and the ability of the younger brain to revert to ketone metabolism can an advantage. This review addresses the potential of alternative substrate metabolic intervention as a logical pediatric TBI neuroprotective strategy.

Glucose administration after traumatic brain injury exerts some benefits and no adverse effects on behavioral and histological outcomes

The impact of hyperglycemia after traumatic brain injury (TBI), and even the administration of glucose-containing solutions to head injured patients, remains controversial. In the current study adult male Sprague-Dawley rats were tested on behavioral tasks and then underwent surgery to induce sham injury or unilateral controlled cortical impact (CCI) injury followed by injections (i.p.) with either a 50% glucose solution (Glc; 2g/kg) or an equivalent volume of either 0.9% or 8% saline (Sal) at 0, 1, 3 and 6h post-injury. The type of saline treatment did not significantly affect any outcome measures, so these data were combined. Rats with CCI had significant deficits in beam-walking traversal time and rating scores (p's < 0.001 versus sham) that recovered over test sessions from 1 to 13 days post-injury (p's < 0.001), but these beam-walking deficits were not affected by Glc versus Sal treatments. Persistent post-CCI deficits in forelimb contraflexion scores and forelimb tactile placing ability were also not differentially affected by Glc or Sal treatments. However, deficits in latency to retract the right hind limb after limb extension were significantly attenuated in the CCI-Glc group (p < 0.05 versus CCI-Sal). Both CCI groups were significantly impaired in a plus maze test of spatial working memory on days 4, 9 and 14 post-surgery (p < 0.001 versus sham), and there was no effect of Glc versus Sal on this cognitive outcome measure. At 15 days post-surgery the loss of cortical tissue volume (p < 0.001 versus sham) was significantly less in the CCI-Glc group (30.0%; p < 0.05) compared to the CCI-Sal group (35.7%). Counts of surviving hippocampal hilar neurons revealed a significant (~40%) loss ipsilateral to CCI (p < 0.001 versus sham), but neuronal loss in the hippocampus was not different in the CCI-Sal and CCI-Glc groups. Taken together, these results indicate that an early elevation of blood glucose may improve some neurological outcomes and, importantly, the induction of hyperglycemia after isolated TBI did not adversely affect any sensorimotor, cognitive or histological outcomes.

Cerebral metabolism following traumatic brain injury: new discoveries with implications for treatment

Because it is the product of glycolysis and main substrate for mitochondrial respiration, lactate is the central metabolic intermediate in cerebral energy substrate delivery. Our recent studies on healthy controls and patients following traumatic brain injury (TBI) using [6,6-(2)H2]glucose and [3-(13)C]lactate, along with cerebral blood flow (CBF) and arterial-venous (jugular bulb) difference measurements for oxygen, metabolite levels, isotopic enrichments and (13)CO2 show a massive and previously unrecognized mobilization of lactate from corporeal (muscle, skin, and other) glycogen reserves in TBI patients who were studied 5.7 ± 2.2 days after injury at which time brain oxygen consumption and glucose uptake (CMRO2 and CMRgluc, respectively) were depressed. By tracking the incorporation of the (13)C from lactate tracer we found that gluconeogenesis (GNG) from lactate accounted for 67.1 ± 6.9%, of whole-body glucose appearance rate (Ra) in TBI, which was compared to 15.2 ± 2.8% (mean ± SD, respectively) in healthy, well-nourished controls. Standard of care treatment of TBI patients in state-of-the-art facilities by talented and dedicated heath care professionals reveals presence of a catabolic Body Energy State (BES). Results are interpreted to mean that additional nutritive support is required to fuel the body and brain following TBI. Use of a diagnostic to monitor BES to provide health care professionals with actionable data in providing nutritive formulations to fuel the body and brain and achieve exquisite glycemic control are discussed. In particular, the advantages of using inorganic and organic lactate salts, esters and other compounds are examined. To date, several investigations on brain-injured patients with intact hepatic and renal functions show that compared to dextrose + insulin treatment, exogenous lactate infusion results in normal glycemia.

Decreased carbon shunting from glucose toward oxidative metabolism in diet-induced ketotic rat brain

The mechanistic link of ketosis to neuroprotection under certain pathological conditions continues to be explored. We investigated whether chronic ketosis induced by ketogenic diet results in the partitioning of ketone bodies toward oxidative metabolism in brain. We hypothesized that diet-induced ketosis results in increased shunting of ketone bodies toward citric acid cycle and amino acids with decreased carbon shunting from glucose. Rats were fed standard (STD) or ketogenic (KG) diets for 3.5 weeks and then infused with [U-(13) C]glucose or [U-(13) C]acetoacetate tracers. Concentrations and (13) C-labeling pattern of citric acid cycle intermediates and amino acids were analyzed from brain homogenates using stable isotopomer mass spectrometry analysis. The contribution of [U-(13) C]glucose to acetyl-CoA and amino acids decreased by ~ 30% in the KG group versus STD, whereas [U-(13) C]acetoacetate contributions were more than two-fold higher. The concentration of GABA remained constant across groups; however, the (13) C labeling of GABA was markedly increased in the KG group infused with [U-(13) C]acetoacetate compared to STD. This study reveals that there is a significant contribution of ketone bodies to oxidative metabolism and GABA in diet-induced ketosis. We propose that this represents a fundamental mechanism of neuroprotection under pathological conditions.

The collective therapeutic potential of cerebral ketone metabolism in traumatic brain injury

The postinjury period of glucose metabolic depression is accompanied by adenosine triphosphate decreases, increased flux of glucose through the pentose phosphate pathway, free radical production, activation of poly-ADP ribose polymerase via DNA damage, and inhibition of glyceraldehyde dehydrogenase (a key glycolytic enzyme) via depletion of the cytosolic NAD pool. Under these post-brain injury conditions of impaired glycolytic metabolism, glucose becomes a less favorable energy substrate. Ketone bodies are the only known natural alternative substrate to glucose for cerebral energy metabolism. While it has been demonstrated that other fuels (pyruvate, lactate, and acetyl-L-carnitine) can be metabolized by the brain, ketones are the only endogenous fuel that can contribute significantly to cerebral metabolism. Preclinical studies employing both pre- and postinjury implementation of the ketogenic diet have demonstrated improved structural and functional outcome in traumatic brain injury (TBI) models, mild TBI/concussion models, and spinal cord injury. Further clinical studies are required to determine the optimal method to induce cerebral ketone metabolism in the postinjury brain, and to validate the neuroprotective benefits of ketogenic therapy in humans.

Influences of developmental age on the resolution of diffuse traumatic intracranial hemorrhage and axonal injury

This study investigated the age-dependent injury response of diffuse traumatic axonal injury (TAI) and regional subdural and subarachnoid intracranial hemorrhage (ICH) in two pediatric age groups using a porcine head injury model. Fifty-five 5-day-old and 40 four-week-old piglets-which developmentally correspond to infants and toddlers, respectively-underwent either a sham injury or a single rapid non-impact rotational injury in the sagittal plane and were grouped by post-TBI survival time (sham, 3-8 h, one day, 3-4 days, and 5-6 days). Both age groups exhibited similar initial levels of ICH and a significant reduction of ICH over time (p<0.0001). However, ICH took longer to resolve in the five-day-old age group. At 5-6 days post-injury, ICH in the cerebrum had returned to sham levels in the four-week-old piglets, while the five-day-olds still had significantly elevated cerebral ICH (p=0.012). Both ages also exhibited similar resolution of axonal injury with a peak in TAI at one day post-injury (p<0.03) and significantly elevated levels even at 5-6 days after the injury (p<0.008), which suggests a window of vulnerability to a second insult at one day post-injury that may extend for a prolonged period of time. However, five-day-old piglets had significantly more TAI than four-week-olds overall (p=0.016), which presents some evidence for an increased vulnerability to brain injury in this age group. These results provide insight into an optimal window for clinical intervention, the period of increased susceptibility to a second injury, and an age dependency in brain injury tolerance within the pediatric population.

The pathophysiology of traumatic brain injury at a glance

Traumatic brain injury (TBI) is defined as an impact, penetration or rapid movement of the brain within the skull that results in altered mental state. TBI occurs more than any other disease, including breast cancer, AIDS, Parkinson's disease and multiple sclerosis, and affects all age groups and both genders. In the US and Europe, the magnitude of this epidemic has drawn national attention owing to the publicity received by injured athletes and military personnel. This increased public awareness has uncovered a number of unanswered questions concerning TBI, and we are increasingly aware of the lack of treatment options for a crisis that affects millions. Although each case of TBI is unique and affected individuals display different degrees of injury, different regional patterns of injury and different recovery profiles, this review and accompanying poster aim to illustrate some of the common underlying neurochemical and metabolic responses to TBI. Recognition of these recurrent features could allow elucidation of potential therapeutic targets for early intervention.

Glucose administration after traumatic brain injury improves cerebral metabolism and reduces secondary neuronal injury

Clinical studies have indicated an association between acute hyperglycemia and poor outcomes in patients with traumatic brain injury (TBI), although optimal blood glucose levels needed to maximize outcomes for these patients' remain under investigation. Previous results from experimental animal models suggest that post-TBI hyperglycemia may be harmful, neutral, or beneficial. The current studies determined the effects of single or multiple episodes of acute hyperglycemia on cerebral glucose metabolism and neuronal injury in a rodent model of unilateral controlled cortical impact (CCI) injury. In Experiment 1, a single episode of hyperglycemia (50% glucose at 2 g/kg, i.p.) initiated immediately after CCI was found to significantly attenuate a TBI-induced depression of glucose metabolism in cerebral cortex (4 of 6 regions) and subcortical regions (2 of 7) as well as to significantly reduce the number of dead/dying neurons in cortex and hippocampus at 24 h post-CCI. Experiment 2 examined effects of more prolonged and intermittent hyperglycemia induced by glucose administrations (2 g/kg, i.p.) at 0, 1, 3 and 6h post-CCI. The latter study also found significantly improved cerebral metabolism (in 3 of 6 cortical and 3 of 7 subcortical regions) and significant neuroprotection in cortex and hippocampus 1 day after CCI and glucose administration. These results indicate that acute episodes of post-TBI hyperglycemia can be beneficial and are consistent with other recent studies showing benefits of providing exogenous energy substrates during periods of increased cerebral metabolic demand.

Ketosis proportionately spares glucose utilization in brain

The brain is dependent on glucose as a primary energy substrate, but is capable of utilizing ketones such as β-hydroxybutyrate and acetoacetate, as occurs with fasting, starvation, or chronic feeding of a ketogenic diet. The relationship between changes in cerebral metabolic rates of glucose (CMRglc) and degree or duration of ketosis remains uncertain. To investigate if CMRglc decreases with chronic ketosis, 2-[(18)F]fluoro-2-deoxy-D-glucose in combination with positron emission tomography, was applied in anesthetized young adult rats fed 3 weeks of either standard or ketogenic diets. Cerebral metabolic rates of glucose (μmol/min per 100 g) was determined in the cerebral cortex and cerebellum using Gjedde-Patlak analysis. The average CMRglc significantly decreased in the cerebral cortex (23.0±4.9 versus 32.9±4.7) and cerebellum (29.3±8.6 versus 41.2±6.4) with increased plasma ketone bodies in the ketotic rats compared with standard diet group. The reduction of CMRglc in both brain regions correlates linearly by ∼9% for each 1 mmol/L increase of total plasma ketone bodies (0.3 to 6.3 mmol/L). Together with our meta-analysis, these data revealed that the degree and duration of ketosis has a major role in determining the corresponding change in CMRglc with ketosis.

Repeated mild traumatic brain injury: mechanisms of cerebral vulnerability

Among the 3.5 million annual new head injury cases is a subpopulation of children and young adults who experience repeated traumatic brain injury (TBI). The duration of vulnerability after a single TBI remains unknown, and biomarkers have yet to be determined. Decreases in glucose metabolism (cerebral metabolic rate of glucose [CMRglc]) are consistently observed after experimental and human TBI. In the current study, it is hypothesized that the duration of vulnerability is related to the duration of decreased CMRglc and that a single mild TBI (mTBI) increases the brain's vulnerability to a second insult for a period, during which a subsequent mTBI will worsen the outcome. Postnatal day 35 rats were given sham, single mTBI, or two mTBI at 24-h or 120-h intervals. (14)C-2-deoxy-D-glucose autoradiography was conducted at 1 or 3 days post-injury to calculate CMRglc. At 24 h after a single mTBI, CMRglc is decreased by 19% in both the parietal cortex and hippocampus, but approached sham levels by 3 days post-injury. When a second mTBI is introduced during the CMRglc depression of the first injury, the consequent CMRglc is depressed (36.5%) at 24 h and remains depressed (25%) at 3 days. In contrast, when the second mTBI is introduced after the metabolic recovery of the first injury, the consequent CMRglc depression is similar to that seen with a single injury. Results suggest that the duration of metabolic depression reflects the time-course of vulnerability to second injury in the juvenile brain and could serve as a valuable biomarker in establishing window of vulnerability guidelines.

Exploring temporospatial changes in glucose metabolic disorder, learning, and memory dysfunction in a rat model of diffuse axonal injury

Diffuse axonal injury (DAI) is the predominant effect of severe traumatic brain injury and contributes significantly to cognitive deficits. The mechanisms underlying these cognitive deficits are often associated with complex metabolic alterations. However, the relationships between temporospatial alterations in cerebral glucose metabolism and the pathophysiology of DAI-related learning and memory dysfunction are not yet completely understood. We used a small animal positron emission tomography (PET) scanner with 2-[F-18]-fluoro-2-deoxy-D-glucose (¹⁸F-FDG) as a molecular probe to evaluate temporospatial glucose metabolism in vulnerable areas of rats with DAI. The Morris water maze (MWM) was used to evaluate the development and progression of learning and memory dysfunction. Compared to the sham-treated group, PET-MRI fusion images showed that glucose metabolism was reduced in animals with DAI. In addition, the standardized uptake value (SUV) of ¹⁸F-FDG was significantly decreased in the sensorimotor cortex, hippocampus, corpus callosum, caudate putamen, brain stem, and cerebellum at days 1, 3, and 7 after injury. SUV returned to baseline levels by 30 days after injury. The escape latency of the injured group was significantly increased, and the percentages of distance travelled and time spent in the target quadrant were significantly decreased 1 month after injury. These effects persisted for 3 months. SUVs in the hippocampus at the acute stage were significantly correlated with MWM performance during the recovery stage of DAI. These results demonstrate that microstructural injury-induced hypometabolism in the hippocampus at the acute stage are all significantly correlated with learning and memory dysfunctions during the recovery stage of DAI.

Noninvasive image derived heart input function for CMRglc measurements in small animal slow infusion FDG PET studies

Absolute quantitation of the cerebral metabolic rate for glucose (CMRglc) can be obtained in positron emission tomography (PET) studies when serial measurements of the arterial [(18)F]-fluoro-deoxyglucose (FDG) input are available. Since this is not always practical in PET studies of rodents, there has been considerable interest in defining an image-derived input function (IDIF) by placing a volume of interest (VOI) within the left ventricle of the heart. However, spill-in arising from trapping of FDG in the myocardium often leads to progressive contamination of the IDIF, which propagates to underestimation of the magnitude of CMRglc. We therefore developed a novel, non-invasive method for correcting the IDIF without scaling to a blood sample. To this end, we first obtained serial arterial samples and dynamic FDG-PET data of the head and heart in a group of eight anaesthetized rats. We fitted a bi-exponential function to the serial measurements of the IDIF, and then used the linear graphical Gjedde-Patlak method to describe the accumulation in myocardium. We next estimated the magnitude of myocardial spill-in reaching the left ventricle VOI by assuming a Gaussian point-spread function, and corrected the measured IDIF for this estimated spill-in. Finally, we calculated parametric maps of CMRglc using the corrected IDIF, and for the sake of comparison, relative to serial blood sampling from the femoral artery. The uncorrected IDIF resulted in 20% underestimation of the magnitude of CMRglc relative to the gold standard arterial input method. However, there was no bias with the corrected IDIF, which was robust to the variable extent of myocardial tracer uptake, such that there was a very high correlation between individual CMRglc measurements using the corrected IDIF with gold-standard arterial input results. Based on simulation, we furthermore find that electrocardiogram-gating, i.e. ECG-gating is not necessary for IDIF quantitation using our approach.

Caprylic triglyceride as a novel therapeutic approach to effectively improve the performance and attenuate the symptoms due to the motor neuron loss in ALS disease

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder of motor neurons causing progressive muscle weakness, paralysis, and finally death. ALS patients suffer from asthenia and their progressive weakness negatively impacts quality of life, limiting their daily activities. They have impaired energy balance linked to lower activity of mitochondrial electron transport chain enzymes in ALS spinal cord, suggesting that improving mitochondrial function may present a therapeutic approach for ALS. When fed a ketogenic diet, the G93A ALS mouse shows a significant increase in serum ketones as well as a significantly slower progression of weakness and lower mortality rate. In this study, we treated SOD1-G93A mice with caprylic triglyceride, a medium chain triglyceride that is metabolized into ketone bodies and can serve as an alternate energy substrate for neuronal metabolism. Treatment with caprylic triglyceride attenuated progression of weakness and protected spinal cord motor neuron loss in SOD1-G93A transgenic animals, significantly improving their performance even though there was no significant benefit regarding the survival of the ALS transgenic animals. We found that caprylic triglyceride significantly promoted the mitochondrial oxygen consumption rate in vivo. Our results demonstrated that caprylic triglyceride alleviates ALS-type motor impairment through restoration of energy metabolism in SOD1-G93A ALS mice, especially during the overt stage of the disease. These data indicate the feasibility of using caprylic acid as an easily administered treatment with a high impact on the quality of life of ALS patients.