Temporal Alterations in Cerebrovascular Glycocalyx and Cerebral Blood Flow after Exposure to a High-Intensity Blast in Rats.

The glycocalyx is a proteoglycan-glycoprotein structure lining the luminal surface of the vascular endothelium and is susceptible to damage due to blast overpressure (BOP) exposure. The glycocalyx is essential in maintaining the structural and functional integrity of the vasculature and regulation of cerebral blood flow (CBF). Assessment of alterations in the density of the glycocalyx; its components (heparan sulphate proteoglycan (HSPG/syndecan-2), heparan sulphate (HS), and chondroitin sulphate (CS)); CBF; and the effect of hypercapnia on CBF was conducted at 2-3 h, 1, 3, 14, and 28 days after a high-intensity (18.9 PSI/131 kPa peak pressure, 10.95 ms duration, and 70.26 PSI·ms/484.42 kPa·ms impulse) BOP exposure in rats. A significant reduction in the density of the glycocalyx was observed 2-3 h, 1-, and 3 days after the blast exposure. The glycocalyx recovered by 28 days after exposure and was associated with an increase in HS (14 and 28 days) and in HSPG/syndecan-2 and CS (28 days) in the frontal cortex. In separate experiments, we observed significant decreases in CBF and a diminished response to hypercapnia at all time points with some recovery at 3 days. Given the role of the glycocalyx in regulating physiological function of the cerebral vasculature, damage to the glycocalyx after BOP exposure may result in the onset of pathogenesis and progression of cerebrovascular dysfunction leading to neuropathology.

The Neurovascular Unit as a Locus of Injury in Low-Level Blast-Induced Neurotrauma.

Blast-induced neurotrauma has received much attention over the past decade. Vascular injury occurs early following blast exposure. Indeed, in animal models that approximate human mild traumatic brain injury or subclinical blast exposure, vascular pathology can occur in the presence of a normal neuropil, suggesting that the vasculature is particularly vulnerable. Brain endothelial cells and their supporting glial and neuronal elements constitute a neurovascular unit (NVU). Blast injury disrupts gliovascular and neurovascular connections in addition to damaging endothelial cells, basal laminae, smooth muscle cells, and pericytes as well as causing extracellular matrix reorganization. Perivascular pathology becomes associated with phospho-tau accumulation and chronic perivascular inflammation. Disruption of the NVU should impact activity-dependent regulation of cerebral blood flow, blood-brain barrier permeability, and glymphatic flow. Here, we review work in an animal model of low-level blast injury that we have been studying for over a decade. We review work supporting the NVU as a locus of low-level blast injury. We integrate our findings with those from other laboratories studying similar models that collectively suggest that damage to astrocytes and other perivascular cells as well as chronic immune activation play a role in the persistent neurobehavioral changes that follow blast injury.

Brain and blood biomarkers of tauopathy and neuronal injury in humans and rats with neurobehavioral syndromes following blast exposure.

Traumatic brain injury (TBI) is a risk factor for the later development of neurodegenerative diseases that may have various underlying pathologies. Chronic traumatic encephalopathy (CTE) in particular is associated with repetitive mild TBI (mTBI) and is characterized pathologically by aggregation of hyperphosphorylated tau into neurofibrillary tangles (NFTs). CTE may be suspected when behavior, cognition, and/or memory deteriorate following repetitive mTBI. Exposure to blast overpressure from improvised explosive devices (IEDs) has been implicated as a potential antecedent for CTE amongst Iraq and Afghanistan Warfighters. In this study, we identified biomarker signatures in rats exposed to repetitive low-level blast that develop chronic anxiety-related traits and in human veterans exposed to IED blasts in theater with behavioral, cognitive, and/or memory complaints. Rats exposed to repetitive low-level blasts accumulated abnormal hyperphosphorylated tau in neuronal perikarya and perivascular astroglial processes. Using positron emission tomography (PET) and the [18F]AV1451 (flortaucipir) tau ligand, we found that five of 10 veterans exhibited excessive retention of [18F]AV1451 at the white/gray matter junction in frontal, parietal, and temporal brain regions, a typical localization of CTE tauopathy. We also observed elevated levels of neurofilament light (NfL) chain protein in the plasma of veterans displaying excess [18F]AV1451 retention. These findings suggest an association linking blast injury, tauopathy, and neuronal injury. Further study is required to determine whether clinical, neuroimaging, and/or fluid biomarker signatures can improve the diagnosis of long-term neuropsychiatric sequelae of mTBI.

Neuroendocrine function and associated mental health outcomes following mild traumatic brain injury in OEF-deployed service members.

Mild traumatic brain injury (mTBI) has been linked to mental health disorders (MHDs) and pituitary function alterations. Due to the complex relationship of mTBI, the neuroendocrine system, and MHDs, we propose that neuroendocrine dysfunction (NED) may play a role in negative long-term health outcomes. The goal of this study was to determine if blast-concussed service members (SMs) have a stronger likelihood of developing NED. We hypothesized that NED either pre- or post-injury is associated with poor mental and physical health outcomes. Serum samples from the Armed Forces Health Surveillance Branch were obtained from concussed (n = 59) and non-concussed (n = 72) SMs treated at the Concussion Restoration Care Center (CRCC) in Afghanistan. Serum was collected within 2 years prior to deployment and one or two times within 3 years following their CRCC visit. Samples were analyzed for luteinizing hormone (LH), testosterone, human growth hormone, cortisol, and prolactin to assess post-injury neuroendocrine function. Results indicate that SMs who incurred an mTBI exhibited long-term LH and testosterone deficiencies 3 years following injury compared to controls. Specifically, 47.6% of head-injured SMs displayed hypofunction in at least one of five hormones at 3 years post-injury. Anxiety disorders were the most common MHD observed in concussed SMs with hypopituitarism, while there was also a trend for SMs with chronic pituitary dysfunction to have MHD diagnoses. Findings indicate blast-related mTBI may be associated with long-term health outcomes following a period of incubation. Neuroendocrine screenings may increase treatment opportunities, inform rehabilitation strategies, and improve overall quality of life for patients.

Blast exposure results in tau and neurofilament light chain changes in peripheral blood.

OBJECTIVES: To evaluate how blast exposure impacts peripheral biomarkers.in military personnel enrolled in 10-day blast training. METHODS: On day 7, 21 military personnel experienced peak overpressure <2 pounds per square inch (psi); while 29 military personnel experienced peak overpressure ≥5 psi. Blood samples were collected each day to measure changes in amyloid beta (Aß), neurofilament light chain (NFL), and tau concentrations. RESULTS: Within 24 hours following exposure ≥5 psi, the ≥5 psi group had lower Aß42 (p = .004) and NFL (p < .001) compared to the <2 psi group and lower Aß42 (9.35%) and NFL (22.01%) compared to baseline. Twenty-four hours after ≥5 psi exposure, the ≥5 psi group had lower tau (p < .001) and NFL (p < .001) compared to the <2 psi group and baseline. Seventy-two hours after exposure ≥5 psi, tau increased in the ≥5 psi group compared to the <2 psi group (p = .02) and baseline. The tau:Aß42 ratio 24 hours after blast (p = .012), and the Aß40:Aß42 ratio 48 hours after blast (p = .04) differed in the ≥5 psi group compared to the <2 psi group. CONCLUSIONS: These findings provide an initial report of acute alterations in biomarker concentrations following blast exposure.

Supervised learning technique for the automated identification of white matter hyperintensities in traumatic brain injury.

BACKGROUND: White matter hyperintensities (WMHs) are foci of abnormal signal intensity in white matter regions seen with magnetic resonance imaging (MRI). WMHs are associated with normal ageing and have shown prognostic value in neurological conditions such as traumatic brain injury (TBI). The impracticality of manually quantifying these lesions limits their clinical utility and motivates the utilization of machine learning techniques for automated segmentation workflows. METHODS: This study develops a concatenated random forest framework with image features for segmenting WMHs in a TBI cohort. The framework is built upon the Advanced Normalization Tools (ANTs) and ANTsR toolkits. MR (3D FLAIR, T2- and T1-weighted) images from 24 service members and veterans scanned in the Chronic Effects of Neurotrauma Consortium's (CENC) observational study were acquired. Manual annotations were employed for both training and evaluation using a leave-one-out strategy. Performance measures include sensitivity, positive predictive value, [Formula: see text] score and relative volume difference. RESULTS: Final average results were: sensitivity = 0.68 ± 0.38, positive predictive value = 0.51 ± 0.40, [Formula: see text] = 0.52 ± 0.36, relative volume difference = 43 ± 26%. In addition, three lesion size ranges are selected to illustrate the variation in performance with lesion size. CONCLUSION: Paired with correlative outcome data, supervised learning methods may allow for identification of imaging features predictive of diagnosis and prognosis in individual TBI patients.

Characterization of acute stress reaction following an IED blast-related mild traumatic brain injury.

PRIMARY OBJECTIVE: To characterize an acute stress reaction (ASR) following an improvised explosive device (IED) blast-related mild traumatic brain injury (mTBI). RESEARCH DESIGN: Participants were male, US military personnel treated in Afghanistan within 4 days following an IED-related mTBI event (n = 239). METHODS AND PROCEDURES: Demographics, diagnosis of ASR, injury history and self-reported mTBIs, blast exposures and psychological health histories were recorded. MAIN OUTCOMES AND RESULTS: In total, 12.5% of patients met ASR criteria. Patients with ASR were significantly younger and junior in rank (p < 0.05). Patients with ASR were more likely to experience the IED-blast while dismounted, report a loss of consciousness (LOC) and higher pain levels (p < 0.05). Adjusting for age and rank, multivariate logistic regression showed an association between mTBI history and ASR (AOR = 1.405; 95% CI = 1.105-1.786, p < 0.01). Adjusting for mechanism of injury (dismounted vs. mounted), LOC and pain, multivariate logistic regression showed an association between mTBI history and ASR (AOR = 1.453; 95% CI = 1.132-1.864, p < 0.01). Prior blast exposure and past psychological health issues were not associated with ASR. CONCLUSIONS: A history of multiple mTBIs is associated with increased risk of ASR. Future research is warranted.

Exposure to Low-Intensity Blast Increases Clearance of Brain Amyloid Beta.

The long-term effects of exposure to blast overpressure are an important health concern in military personnel. Increase in amyloid beta (Aß) has been documented after non-blast traumatic brain injury (TBI) and may contribute to neuropathology and an increased risk for Alzheimer's disease. We have shown that Aß levels decrease following exposure to a low-intensity blast overpressure event. To further explore this observation, we examined the effects of a single 37 kPa (5.4 psi) blast exposure on brain Aß levels, production, and clearance mechanisms in the acute (24 h) and delayed (28 days) phases post-blast exposure in an experimental rat model. Aß and, notably, the highly neurotoxic detergent soluble Aß42 form, was reduced at 24 h but not 28 days after blast exposure. This reduction was not associated with changes in the levels of Aß oligomers, expression levels of amyloid precursor protein (APP), or increase in enzymes involved in the amyloidogenic cleavage of APP, the ß- and ϒ-secretases BACE1 and presenilin-1, respectively. The levels of ADAM17 α-secretase (also known as tumor necrosis factor α-converting enzyme) decreased, concomitant with the reduction in brain Aß. Additionally, significant increases in brain levels of the endothelial transporter, low-density related protein 1 (LRP1), and enhancement in co-localization of aquaporin-4 (AQP4) to perivascular astrocytic end-feet were observed 24 h after blast exposure. These findings suggest that exposure to low-intensity blast may enhance endothelial clearance of Aß by LRP1-mediated transcytosis and alter AQP4-aided glymphatic clearance. Collectively, the data demonstrate that low-intensity blast alters enzymatic, transvascular, and perivascular clearance of Aß.

Neurological Effects of Repeated Blast Exposure in Special Operations Personnel.

Exposure to blast overpressure has been a pervasive feature of combat-related injuries. Studies exploring the neurological correlates of repeated low-level blast exposure in career "breachers" demonstrated higher levels of tumor necrosis factor alpha (TNFα) and interleukin (IL)-6 and decreases in IL-10 within brain-derived extracellular vesicles (BDEVs). The current pilot study was initiated in partnership with the U.S. Special Operations Command (USSOCOM) to explore whether neuroinflammation is seen within special operators with prior blast exposure. Data were analyzed from 18 service members (SMs), inclusive of 9 blast-exposed special operators with an extensive career history of repeated blast exposures and 9 controls matched by age and duration of service. Neuroinflammation was assessed utilizing positron emission tomography (PET) imaging with [18F]DPA-714. Serum was acquired to assess inflammatory biomarkers within whole serum and BDEVs. The Blast Exposure Threshold Survey (BETS) was acquired to determine blast history. Both self-report and neurocognitive measures were acquired to assess cognition. Similarity-driven Multi-view Linear Reconstruction (SiMLR) was used for joint analysis of acquired data. Analysis of BDEVs indicated significant positive associations with a generalized blast exposure value (GBEV) derived from the BETS. SiMLR-based analyses of neuroimaging demonstrated exposure-related relationships between GBEV, PET-neuroinflammation, cortical thickness, and volume loss within special operators. Affected brain networks included regions associated with memory retrieval and executive functioning, as well as visual and heteromodal processing. Post hoc assessments of cognitive measures failed to demonstrate significant associations with GBEV. This emerging evidence suggests neuroinflammation may be a key feature of the brain response to blast exposure over a career in operational personnel. The common thread of neuroinflammation observed in blast-exposed populations requires further study.

Metabotropic Glutamate Receptor 2 Expression Is Chronically Elevated in Male Rats With Post-Traumatic Stress Disorder Related Behavioral Traits Following Repetitive Low-Level Blast Exposure.

Many military veterans who experienced blast-related traumatic brain injuries in the conflicts in Iraq and Afghanistan currently suffer from chronic cognitive and mental health problems that include depression and post-traumatic stress disorder (PTSD). Male rats exposed to repetitive low-level blast develop cognitive and PTSD-related behavioral traits that are present for more than 1 year after exposure. We previously reported that a group II metabotropic receptor (mGluR2/3) antagonist reversed blast-induced behavioral traits. In this report, we explored mGluR2/3 expression following blast exposure in male rats. Western blotting revealed that mGluR2 protein (but not mGluR3) was increased in all brain regions studied (anterior cortex, hippocampus, and amygdala) at 43 or 52 weeks after blast exposure but not at 2 weeks or 6 weeks. mGluR2 RNA was elevated at 52 weeks while mGluR3 was not. Immunohistochemical staining revealed no changes in the principally presynaptic localization of mGluR2 by blast exposure. Administering the mGluR2/3 antagonist LY341495 after behavioral traits had emerged rapidly reversed blast-induced effects on novel object recognition and cued fear responses 10 months following blast exposure. These studies support alterations in mGluR2 receptors as a key pathophysiological event following blast exposure and provide further support for group II metabotropic receptors as therapeutic targets in the neurobehavioral effects that follow blast injury.

Differential effects on TDP-43, piezo-2, tight-junction proteins in various brain regions following repetitive low-intensity blast overpressure.

Introduction: Mild traumatic brain injury (mTBI) caused by repetitive low-intensity blast overpressure (relBOP) in military personnel exposed to breaching and heavy weapons is often unrecognized and is understudied. Exposure to relBOP poses the risk of developing abnormal behavioral and psychological changes such as altered cognitive function, anxiety, and depression, all of which can severely compromise the quality of the life of the affected individual. Due to the structural and anatomical heterogeneity of the brain, understanding the potentially varied effects of relBOP in different regions of the brain could lend insights into the risks from exposures. Methods: In this study, using a rodent model of relBOP and western blotting for protein expression we showed the differential expression of various neuropathological proteins like TDP-43, tight junction proteins (claudin-5, occludin, and glial fibrillary acidic protein (GFAP)) and a mechanosensitive protein (piezo-2) in different regions of the brain at different intensities and frequency of blast. Results: Our key results include (i) significant increase in claudin-5 after 1x blast of 6.5 psi in all three regions and no definitive pattern with higher number of blasts, (ii) significant increase in piezo-2 at 1x followed by significant decrease after multiple blasts in the cortex, (iii) significant increase in piezo-2 with increasing number of blasts in frontal cortex and mixed pattern of expression in hippocampus and (iv) mixed pattern of TDP-3 and GFAP expression in all the regions of brain. Discussion: These results suggest that there are not definitive patterns of changes in these marker proteins with increase in intensity and/or frequency of blast exposure in any particular region; the changes in expression of these proteins are different among the regions. We also found that the orientation of blast exposure (e.g. front vs. side exposure) affects the altered expression of these proteins.

Progressive Transcriptional Changes in the Amygdala Implicate Neuroinflammation in the Effects of Repetitive Low-Level Blast Exposure in Male Rats.

Chronic mental health problems are common among military veterans who sustained blast-related traumatic brain injuries. The reasons for this association remain unexplained. Male rats exposed to repetitive low-level blast overpressure (BOP) exposures exhibit chronic cognitive and post-traumatic stress disorder (PTSD)-related traits that develop in a delayed fashion. We examined blast-induced alterations on the transcriptome in four brain areas (anterior cortex, hippocampus, amygdala, and cerebellum) across the time frame over which the PTSD-related behavioral phenotype develops. When analyzed at 6 weeks or 12 months after blast exposure, relatively few differentially expressed genes (DEGs) were found. However, longitudinal analysis of amygdala, hippocampus, and anterior cortex between 6 weeks and 12 months revealed blast-specific DEG patterns. Six DEGs (hyaluronan and proteoglycan link protein 1 [Hapln1], glutamate metabotropic receptor 2 [Grm2], purinergic receptor P2y12 [P2ry12], C-C chemokine receptor type 5 [Ccr5], phenazine biosynthesis-like protein domain containing 1 [Pbld1], and cadherin related 23 [Cdh23]) were found altered in all three brain regions in blast-exposed animals. Pathway enrichment analysis using all DEGs or those uniquely changed revealed different transcription patterns in blast versus sham. In particular, the amygdala in blast-exposed animals had a unique set of enriched pathways related to stress responses, oxidative phosphorylation, and mitochondrial dysfunction. Upstream analysis implicated tumor necrosis factor (TNF)α signaling in blast-related effects in amygdala and anterior cortex. Eukaryotic initiating factor eIF4E (EIF4e), an upstream regulator of P2ry12 and Ccr5, was predicted to be activated in the amygdala. Quantitative polymerase chain reaction (qPCR) validated longitudinal changes in two TNFα regulated genes (cathepsin B [Ctsb], Hapln1), P2ry12, and Grm2. These studies have implications for understanding how blast injury damages the brain and implicates inflammation as a potential therapeutic target.

(2R,6R)-Hydroxynorketamine Treatment of Rats Exposed to Repetitive Low-Level Blast Injury.

Many military veterans who experienced blast-related traumatic brain injuries (TBIs) in the conflicts in Iraq and Afghanistan suffer from chronic cognitive and mental health problems, including post-traumatic stress disorder (PTSD). Male rats subjected to repetitive low-level blast exposure develop chronic cognitive and PTSD-related traits that develop in a delayed manner. Ketamine has received attention as a treatment for refractory depression and PTSD. (2R,6R)-hydroxynorketamine [(2R,6R)-HNK] is a ketamine metabolite that exerts rapid antidepressant actions. (2R,6R)-HNK has become of clinical interest because of its favorable side-effect profile, low abuse potential, and oral route of administration. We treated three cohorts of blast-exposed rats with (2R,6R)-HNK, beginning 7-11 months after blast exposure, a time when the behavioral phenotype is established. Each cohort consisted of groups (n = 10-13/group) as follows: 1) Sham-exposed treated with saline, 2) blast-exposed treated with saline, and 3) blast-exposed treated with a single dose of 20 mg/kg of (2R,6R)-HNK. (2R,6R)-HNK rescued blast-induced deficits in novel object recognition (NOR) and anxiety-related features in the elevated zero maze (EZM) in all three cohorts. Exaggerated acoustic startle was reversed in cohort 1, but not in cohort 3. (2R,6R)-HNK effects were still present in the EZM 12 days after administration in cohort 1 and 27 days after administration in NOR testing of cohorts 2 and 3. (2R,6R)-HNK may be beneficial for the neurobehavioral syndromes that follow blast exposure in military veterans. Additional studies will be needed to determine whether higher doses or more extended treatment regimens may be more effective.

Late chronic local inflammation, synaptic alterations, vascular remodeling and arteriovenous malformations in the brains of male rats exposed to repetitive low-level blast overpressures.

In the course of military operations in modern war theaters, blast exposures are associated with the development of a variety of mental health disorders associated with a post-traumatic stress disorder-related features, including anxiety, impulsivity, insomnia, suicidality, depression, and cognitive decline. Several lines of evidence indicate that acute and chronic cerebral vascular alterations are involved in the development of these blast-induced neuropsychiatric changes. In the present study, we investigated late occurring neuropathological events associated with cerebrovascular alterations in a rat model of repetitive low-level blast-exposures (3 × 74.5 kPa). The observed events included hippocampal hypoperfusion associated with late-onset inflammation, vascular extracellular matrix degeneration, synaptic structural changes and neuronal loss. We also demonstrate that arteriovenous malformations in exposed animals are a direct consequence of blast-induced tissue tears. Overall, our results further identify the cerebral vasculature as a main target for blast-induced damage and support the urgent need to develop early therapeutic approaches for the prevention of blast-induced late-onset neurovascular degenerative processes.

Elevations in Tumor Necrosis Factor Alpha and Interleukin 6 From Neuronal-Derived Extracellular Vesicles in Repeated Low-Level Blast Exposed Personnel.

Objective: The purpose of this pilot study was to determine if military service members with histories of hundreds to thousands of low-level blast exposures (i. e., experienced breachers) had different levels of serum and neuronal-derived extracellular vesicle (EV) concentrations of interleukin (IL)-6, IL-10, and tumor necrosis factor alpha (TNFα), compared to matched controls, and if these biomarkers related to neurobehavioral symptoms. Methods: Participants were experienced breachers (n = 20) and matched controls without blast exposures (n = 14). Neuronal-derived EVs were isolated from serum and identified with mouse anti-human CD171. Serum and neuronal-derived EVs were analyzed for IL-6, IL-10, and TNFα using an ultra-sensitive assay. Results: Serum TNFα concentrations were decreased in breachers when compared to control concentrations (p < 0.01). There were no differences in serum concentrations of IL-6, IL-10, or the IL-6/IL-10 ratio between breachers and controls (p's > 0.01). In neuronal-derived EVs, TNFα and IL-6 levels were increased in breachers compared to controls (p's < 0.01), and IL-10 levels were decreased in the breacher group compared to controls (p < 0.01). In breachers the IL-6/IL-10 ratio in neuronal-derived EVs was higher compared to controls, which correlated with higher total Rivermead Post-concussion Questionnaire (RPQ) scores (p's < 0.05). Conclusions: These findings suggest that exposure of personnel to high numbers of low-level blast over a career may result in enduring central inflammation that is associated with chronic neurological symptoms. The data also suggest that peripheral markers of inflammation are not necessarily adequate surrogates for central neuroinflammation.

A Pilot Study of Whole-Blood Transcriptomic Analysis to Identify Genes Associated with Repetitive Low-Level Blast Exposure in Career Breachers.

Repetitive low-level blast exposure is one of the major occupational health concerns among US military service members and law enforcement. This study seeks to identify gene expression using microRNA and RNA sequencing in whole-blood samples from experienced breachers and unexposed controls. We performed experimental RNA sequencing using Illumina's HiSeq 2500 Sequencing System, and microRNA analysis using NanoString Technology nCounter miRNA expression panel in whole-blood total RNA samples from 15 experienced breachers and 14 age-, sex-, and race-matched unexposed controls. We identified 10 significantly dysregulated genes between experienced breachers and unexposed controls, with FDR corrected <0.05: One upregulated gene, LINC00996 (long intergenic non-protein coding RNA 996); and nine downregulated genes, IGLV3-16 (immunoglobulin lambda variable 3-16), CD200 (CD200 molecule), LILRB5 (leukocyte immunoglobulin-like receptor B5), ZNF667-AS1 (ZNF667 antisense RNA 1), LMOD1 (leiomodin 1), CNTNAP2 (contactin-associated protein 2), EVPL (envoplakin), DPF3 (double PHD fingers 3), and IGHV4-34 (immunoglobulin heavy variable 4-34). The dysregulated gene expressions reported here have been associated with chronic inflammation and immune response, suggesting that these pathways may relate to the risk of lasting neurological symptoms following high exposures to blast over a career.

Development of a Blast Exposure Estimator from a Department of Defense-Wide Survey Study on Military Service Members.

Long-term, repeated exposure to low-intensity blast overpressure is a potential causal factor of lasting outcomes reminiscent of post-concussion syndrome. Wearable blast sensor engineers are exploring elements of blast that are associated with outcomes. Currently, however, there are no devices that can truly record all blasts experienced by an individual. Military service members (n = 984) were surveyed about their lifelong exposure and behavioral health. Using heavy-arms-associated target outcomes, we calculated a generalized blast exposure value (GBEV) for each participant. A threshold of 200,000 GBEV units was established at which a participant was likely to report more intense symptomology. If repetitive, low-intensity blast exposure has even a subtle effect over time, operational readiness could be negatively impacted. A threshold of exposure can inform decisions about how to reduce detrimental exposure. The GBEV can be used to track ongoing exposure and potentially identify those who may be at risk for developing blast-related outcomes.

Roadmap for Advancing Pre-Clinical Science in Traumatic Brain Injury.

Pre-clinical models of disease have long played important roles in the advancement of new treatments. However, in traumatic brain injury (TBI), despite the availability of numerous model systems, translation from bench to bedside remains elusive. Integrating clinical relevance into pre-clinical model development is a critical step toward advancing therapies for TBI patients across the spectrum of injury severity. Pre-clinical models include in vivo and ex vivo animal work-both small and large-and in vitro modeling. The wide range of pre-clinical models reflect substantial attempts to replicate multiple aspects of TBI sequelae in humans. Although these models reveal multiple putative mechanisms underlying TBI pathophysiology, failures to translate these findings into successful clinical trials call into question the clinical relevance and applicability of the models. Here, we address the promises and pitfalls of pre-clinical models with the goal of evolving frameworks that will advance translational TBI research across models, injury types, and the heterogenous etiology of pathology.

Impact of ketogenic diet and ketone diester supplementation on body weight, blood glucose, and ketones in Sprague Dawley rats fed over two weeks.

Ketogenic diets consist of low carbohydrate/high fat, shifting energy reliance from glucose to ketone bodies. Ketone diester supplement to a standard diet (ketone ester) increases ketone bodies by adding a substance without altering other consumed foods. We evaluated weight, glucose, and ketone concentrations in rats fed ketogenic diet and ketone ester feeds. We hypothesized that these feeds would increase ketones and decrease glucose and weight. We tested 16 male and 16 female Sprague Dawley rats randomly assigned to standard diet, ketogenic diet, or ketone ester for two weeks. Weight and blood glucose and ketones were measured daily. Group means were compared by analysis of variance. Ketogenic diet and ketone ester both increased ketones and decreased weight compared to standard diet (p < 0.001). Glucose decreased only in ketogenic diet (p = 0.010), driven by a decrease from higher starting concentrations observed in standard diet males. Sex interacted with weight, with male gains impacted more by both ketogenic diet and ketone ester than female gains. Ketogenic diet had a larger effect size than ketone ester with regard to increased ketones and decreased weight. Ketogenic diet glucose significantly decreased over time because standard diet concentrations in males were high prior to initializing ketogenic diet. This suggests sex differences in energy substrate utilization. Ketogenic diet ketones peaked at 72 h then decreased to near basal levels at about 10 days, suggesting "fat adaption." While this work is part of a larger project examining blast exposure, these results are relevant to any military forces considering ketone-increasing foods.

Blast-induced temporal alterations in blood-brain barrier properties in a rodent model.

The consequences of blast-induced traumatic brain injury (bTBI) on the blood-brain barrier (BBB) and components of the neurovascular unit are an area of active research. In this study we assessed the time course of BBB integrity in anesthetized rats exposed to a single blast overpressure of 130 kPa (18.9 PSI). BBB permeability was measured in vivo via intravital microscopy by imaging extravasation of fluorescently labeled tracers (40 kDa and 70 kDa molecular weight) through the pial microvasculature into brain parenchyma at 2-3 h, 1, 3, 14, or 28 days after the blast exposure. BBB structural changes were assessed by immunostaining and molecular assays. At 2-3 h and 1 day after blast exposure, significant increases in the extravasation of the 40 kDa but not the 70 kDa tracers were observed, along with differential reductions in the expression of tight junction proteins (occludin, claudin-5, zona occluden-1) and increase in the levels of the astrocytic water channel protein, AQP-4, and matrix metalloprotease, MMP-9. Nearly all of these measures were normalized by day 3 and maintained up to 28 days post exposure. These data demonstrate that blast-induced changes in BBB permeability are closely coupled to structural and functional components of the BBB.