Lung Injury and Recovery After Exposure to Blast Overpressure

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.

High-energy open-fracture model with initial experience of fluorescence-guided bone perfusion assessment

High-energy orthopedic injuries cause severe damage to soft tissues and are prone to infection and healing complications, making them a challenge to manage. Further research is facilitated by a clinically relevant animal model with commensurate fracture severity and soft-tissue damage, allowing evaluation of novel treatment options and techniques. Here we report a reproducible, robust, and clinically relevant animal model of high-energy trauma with extensive soft-tissue damage, based on compressed air-driven membrane rupture as the blast wave source. As proof-of-principle showing the reproducibility of the injury, we evaluate changes in tissue and bone perfusion for a range of different tibia fracture severities, using dynamic contrast-enhanced fluorescence imaging and microcomputed tomography. We demonstrate that fluorescence tracer temporal profiles for skin, femoral vein, fractured bone, and paw reflect the increasing impact of more powerful blasts causing a range of Gustilo grade I-III injuries. The maximum fluorescence intensity of distal tibial bone following 0.1 mg/kg intravenous indocyanine green injection decreased by 35% (p < 0.01), 75% (p < 0.001), and 87% (p < 0.001), following grade I, II, and III injuries, respectively, compared to uninjured bone. Other kinetic parameters of bone and soft tissue perfusion extracted from series of fluorescence images for each animal also showed an association with severity of trauma. In addition, the time-intensity profile of fluorescence showed marked differences in wash-in and wash-out patterns for different injury severities and anatomical locations. This reliable and realistic high-energy trauma model opens new research avenues to better understand infection and treatment strategies. Level of evidence: Level III; Case-control.

Single and Multiplex Immunohistochemistry to Detect Platelets and Neutrophils in Rat and Porcine Tissues

Platelet–neutrophil complexes (PNCs) occur during the inflammatory response to trauma and infections, and their interactions enable cell activation that can lead to tissue destruction. The ability to identify the accumulation and tissue localisation of PNCs is necessary to further understand their role in the organs associated with blast-induced shock wave trauma. Relevant experimental lung injury models often utilise pigs and rats, species for which immunohistochemistry protocols to detect platelets and neutrophils have yet to be established. Therefore, monoplex and multiplex immunohistochemistry protocols were established to evaluate the application of 22 commercially available antibodies to detect platelet (nine rat and five pig) and/or neutrophil (four rat and six pig) antigens identified as having potential selectivity for porcine or rat tissue, using lung and liver sections taken from models of polytrauma, including blast lung injury. Of the antibodies evaluated, one antibody was able to detect rat neutrophil elastase (on frozen and formalin-fixed paraffin embedded (FFPE) sections), and one antibody was successful in detecting rat CD61 (frozen sections only); whilst one antibody was able to detect porcine MPO (frozen and FFPE sections) and antibodies, targeting CD42b or CD49b antigens, were able to detect porcine platelets (frozen and FFPE and frozen, respectively). Staining procedures for platelet and neutrophil antigens were also successful in detecting the presence of PNCs in both rat and porcine tissue. We have, therefore, established protocols to allow for the detection of PNCs in lung and liver sections from porcine and rat models of trauma, which we anticipate should be of value to others interested in investigating these cell types in these species.

Tourniquet use following blast-associated complex lower limb injury and traumatic amputation promotes end organ dysfunction and amplified heterotopic ossification formation

BACKGROUND

Traumatic heterotopic ossification (tHO) is characterized by ectopic bone formation in extra-skeletal sites leading to impaired wound healing, entrapment of neurovascular structures, pain, and reduced range of motion. HO has become a signature pathology affecting wounded military personnel who have sustained blast-associated traumatic amputations during the recent conflicts in Iraq and Afghanistan and can compound recovery by causing difficulty with prosthesis limb wearing. Tourniquet use to control catastrophic limb hemorrhage prior to surgery has become almost ubiquitous during this time, with the recognition the prolonged use may risk an ischemia reperfusion injury and associated complications. While many factors influence the formation of tHO, the extended use of tourniquets to limit catastrophic hemorrhage during prolonged field care has not been explored.

METHODS

Utilizing an established pre-clinical model of blast-associated complex lower limb injury and traumatic amputation, we evaluated the effects of tourniquet use on tHO formation. Adult male rats were subjected to blast overpressure exposure, femur fracture, and soft tissue crush injury. Pneumatic tourniquet (250-300 mmHg) applied proximal to the injured limb for 150-min was compared to a control group without tourniquet, before a trans-femoral amputation was performed. Outcome measures were volume to tHO formation at 12 weeks and changes in proteomic and genomic markers of early tHO formation between groups.

RESULTS

At 12 weeks, volumetric analysis with microCT imaging revealed a 70% increase in total bone formation (p = 0.007) near the site of injury compared to rats with no tourniquet time in the setting of blast-injuries. Rats subjected to tourniquet usage had increased expression of danger-associated molecular patterns (DAMPs) and end organ damage as early as 6 h and as late as 7 days post injury. The expressions of pro-inflammatory cytokines and chemokines and osteochondrogenic genes using quantitative RT-PCR similarly revealed increased expression as early as 6 h post injury, and these genes along with hypoxia associated genes remained elevated for 7 days compared to no tourniquet use.

CONCLUSION

These findings suggest that tourniquet induced ischemia leads to significant increases in key transcription factors associated with early endochondral bone formation, systemic inflammatory and hypoxia, resulting in increased HO formation.

Low-level blast exposure induces chronic vascular remodeling, perivascular astrocytic degeneration and vascular-associated neuroinflammation

Cerebral vascular injury as a consequence of blast-induced traumatic brain injury is primarily the result of blast wave-induced mechanical disruptions within the neurovascular unit. In rodent models of blast-induced traumatic brain injury, chronic vascular degenerative processes are associated with the development of an age-dependent post-traumatic stress disorder-like phenotype. To investigate the evolution of blast-induced chronic vascular degenerative changes, Long-Evans rats were blast-exposed (3 × 74.5 kPa) and their brains analyzed at different times post-exposure by X-ray microcomputed tomography, immunohistochemistry and electron microscopy. On microcomputed tomography scans, regional cerebral vascular attenuation or occlusion was observed as early as 48 h post-blast, and cerebral vascular disorganization was visible at 6 weeks and more accentuated at 13 months post-blast. Progression of the late-onset pathology was characterized by detachment of the endothelial and smooth muscle cellular elements from the neuropil due to degeneration and loss of arteriolar perivascular astrocytes. Development of this pathology was associated with vascular remodeling and neuroinflammation as increased levels of matrix metalloproteinases (MMP-2 and MMP-9), collagen type IV loss, and microglial activation were observed in the affected vasculature. Blast-induced chronic alterations within the neurovascular unit should affect cerebral blood circulation, glymphatic flow and intramural periarterial drainage, all of which may contribute to development of the blast-induced behavioral phenotype. Our results also identify astrocytic degeneration as a potential target for the development of therapies to treat blast-induced brain injury.

NF-κB and FosB mediate inflammation and oxidative stress in the blast lung injury of rats exposed to shock waves

Blast lung injury (BLI) is the major cause of death in explosion-derived shock waves; however, the mechanisms of BLI are not well understood. To identify the time-dependent manner of BLI, a model of lung injury of rats induced by shock waves was established by a fuel air explosive. The model was evaluated by hematoxylin and eosin staining and pathological score. The inflammation and oxidative stress of lung injury were also investigated. The pathological scores of rats' lung injury at 2 h, 24 h, 3 days, and 7 days post-blast were 9.75±2.96, 13.00±1.85, 8.50±1.51, and 4.00±1.41, respectively, which were significantly increased compared with those in the control group (1.13±0.64; P<0.05). The respiratory frequency and pause were increased significantly, while minute expiratory volume, inspiratory time, and inspiratory peak flow rate were decreased in a time-dependent manner at 2 and 24 h post-blast compared with those in the control group. In addition, the expressions of inflammatory factors such as interleukin (IL)-6, IL-8, FosB, and NF-κB were increased significantly at 2 h and peaked at 24 h, which gradually decreased after 3 days and returned to normal in 2 weeks. The levels of total antioxidant capacity, total superoxide dismutase, and glutathione peroxidase were significantly decreased 24 h after the shock wave blast. Conversely, the malondialdehyde level reached the peak at 24 h. These results indicated that inflammatory and oxidative stress induced by shock waves changed significantly in a time-dependent manner, which may be the important factors and novel therapeutic targets for the treatment of BLI.

Red Blood Cells Elicit Platelet-Dependent Neutrophil Recruitment Into Lung Airspaces

ABSTRACT

Hemolysis that occurs in intravascular hemolytic disorders, such as sickle cell disease and malaria, is associated with inflammation and platelet activation. Alveolar hemorrhage, for example following primary blast lung injury or acute respiratory distress syndrome, results in the escape of erythrocytes (RBCs) into alveolar spaces, where they subsequently lyse and release their intracellular contents. However, the inflammatory effects of RBCs in the airways are not fully understood. We hypothesized that RBCs in the airway induce an inflammatory response, associated with platelet activation. By instilling whole RBCs or lysed RBCs into the airways of mice, we have demonstrated that whole RBCs elicit macrophage accumulation in the lung. On the other hand, lysed RBCs induce significant inflammatory cell recruitment, particularly neutrophils and this was associated with a 50% increase in circulating platelet neutrophil complexes. Platelet depletion prior to lysed RBC exposure in the lung resulted in reduced neutrophil recruitment, suggesting that the presence of intracellular RBC components in the airways can elicit inflammation that is platelet dependent. To identify specific platelet-dependent signaling pathways involved in neutrophil recruitment, anti-P-selectin ligand and anti-PSGL1 blocking antibodies were tested; however, neither affected neutrophil recruitment. These findings implicate an involvement for other, as yet unidentified platelet-dependent signaling and adhesion mechanisms. Further understanding of how platelets contribute to lung inflammation induced by the presence of RBCs could offer novel therapeutic approaches to attenuate inflammation that occurs in conditions associated with alveolar hemorrhage.

Pulmonary injury risk curves and behavioral changes from blast overpressure exposures of varying frequency and intensity in rats

At present, there are no set guidelines establishing cumulative limits for blast exposure numbers and intensities in military personnel, in combat or training operations. The objective of the current study was to define lung injury, pathology, and associated behavioral changes from primary repeated blast lung injury under appropriate exposure conditions and combinations (i.e. blast overpressure (BOP) intensity and exposure frequency) using an advanced blast simulator. Male Sprague Dawley rats were exposed to BOP frontally and laterally at a pressure range of ~ 8.5-19 psi, for up to 30 daily exposures. The extent of lung injury was identified at 24 h following BOP by assessing the extent of surface hemorrhage/contusion, Hematoxylin and Eosin staining, and behavioral deficits with open field activity. Lung injury was mathematically modeled to define the military standard 1% lung injury threshold. Significant levels of histiocytosis and inflammation were observed in pressures ≥ 10 psi and orientation effects were observed at pressures ≥ 13 psi. Experimental data demonstrated ~ 8.5 psi is the threshold for hemorrhage/contusion, up to 30 exposures. Modeling the data predicted injury risk up to 50 exposures with intensity thresholds at 8 psi for front exposure and 6psi for side exposures, which needs to be validated further.

Global gene expression profiling of blast lung injury of goats exposed to shock wave

PURPOSE

Blast lung injury (BLI) is the most common damage resulted from explosion-derived shock wave in military, terrorism and industrial accidents. However, the molecular mechanisms underlying BLI induced by shock wave are still unclear.

METHODS

In this study, a goat BLI model was established by a fuel air explosive power. The key genes involved in were identified. The goats of the experimental group were fixed on the edge of the explosion cloud, while the goats of the control group were 3 km far away from the explosive environment. After successful modeling for 24 h, all the goats were sacrificed and the lung tissue was harvested for histopathological observation and RNA sequencing. Gene ontology (GO) and kyoto encyclopedia of genes and genomes (KEGG) analysis were performed to identify the main enriched biological functions of differentially expressed genes (DEGs). Quantitative real-time polymerase chain reaction (qRT-PCR) was used to verify the consistency of gene expression.

RESULTS

Of the sampled goat lungs, 895 genes were identified to be significantly differentially expressed, and they were involved in 52 significantly enriched GO categories. KEGG analysis revealed that DEGs were highly enriched in 26 pathways, such as cytokine-cytokine receptor interaction, antifolate resistance, arachidonic acid metabolism, amoebiasis and bile secretion, JAK-STAT, and IL-17 signaling pathway. Furthermore, 15 key DEGs involved in the biological processes of BLI were confirmed by qRT-PCR, and the results were consistent with RNA sequencing.

CONCLUSION

Gene expression profiling provide a better understanding of the molecular mechanisms of BLI, which will help to set strategy for treating lung injury and preventing secondary lung injury induced by shock wave.

Androgens are essential for epithelial cell recovery after efferent duct ligation in the initial segment of the mouse epididymis†

Efferent duct ligation (EDL) induces epithelial cell degeneration followed by regeneration in the epididymal initial segment. We tested here the role of androgens in the recovery phase. EDL was performed at post-natal weeks (PNW) 3, 4, 5, 6, and 7, and apoptotic and proliferating epithelial cells were quantified 24 h, and at days 2 and 2.5 post-EDL, respectively. A progressive increase in the number of apoptotic basal cells (BCs) and principal cells (PCs) was detected from PNW3 to 6, 24 h after EDL. Two days after EDL, no increase in proliferating BCs and PCs was observed at PNW3 and 4, despite the induction of apoptosis by EDL. A progressive increase in the number of proliferating BCs was then observed from PNW5 to 6, while the number of proliferating PCs remained low. 2.5 days after EDL, the number of proliferating BCs and PCs remained low at PNW3, 4, and 5, but a marked increase in the number of proliferating PCs was observed at PNW6. Flutamide pretreatment for 3 weeks followed by EDL at PNW7 dramatically decreased the number of proliferating BCs on EDL day 2, and the number of proliferating PCs on EDL day 2.5, compared to controls. We conclude that (1) BCs are the first to show recovery after EDL, followed by PCs; (2) androgens are essential for BC and PC repair after injury in the postpubertal epididymis; and (3) the prepubertal epididymis lacks repair ability following injury.

Hypobaria during aeromedical evacuation exacerbates histopathological injury and modifies inflammatory response in rats exposed to blast overpressure injury

BACKGROUND

Aeromedical evacuation (AE) is often used as a rapid and effective way to evacuate patients. However, little is known about the possible effects of AE on patients with blast and traumatic brain injury. In the current study, we used blast overpressure (BOP) as a method to introduce traumatic brain injury in rats and investigated the effects of hypobaria during AE on histology and inflammatory response.

METHODS

Animals were exposed to a 12-hour flight 2 days after BOP and euthanized 48 hours after flight. Control animals were kept at normobaria.

RESULTS

Overall, BOP animals exposed to flight demonstrated higher histopathologic injury scores as compared to control animals in lungs, brain, kidney, heart, and intestine. The BOP animals exposed to normobaria exhibited a proinflammatory response compared to those that were not blasted, an observation that was not seen in BOP animals exposed to hypobaria.

CONCLUSION

These data suggest that AE 48 hours post blast may lead to impairment in the inflammatory process and worsening of long-term outcomes.

LEVEL OF EVIDENCE

Animal research, level II.

The effect of aerosolized indomethacin on lung inflammation and injury in a rat model of blunt chest trauma

Background

Acute lung contusion from blunt chest trauma (BCT) is characterized by an intense inflammatory response in the pulmonary parenchyma, which is associated with acute lung injury (ALI), acute respiratory distress syndrome and ventilator-associated pneumonia. We hypothesized that aerosolized indomethacin may reduce pulmonary inflammation and ALI in a rat model of BCT.

Methods

Sprague-Dawley rats were anesthetized and received a tracheotomy for administration of aerosolized medication through a catheter. The BCT procedure involved free-dropping a hollow metal weight (200 g) from a height of 25.5, 38.3 or 51.2 cm onto the right thorax. We administered 1 mg/kg of indomethacin or 1 mL/kg of saline intratracheally 15 minutes after BCT. The sham group had a similar procedure without the exposure to BCT and treatment. Three hours postimpact, we obtained arterial blood gas and analyzed bronchoalveolar lavage for protein concentration, polymorphonuclear leukocytes (PMN) and cytokine levels, and lung tissue samples were taken for histopathological analysis.

Results

The rats’ mean arterial pressure and heart rate dropped immediately postimpact but recovered close to that of the sham group after 30 minutes in both control and treatment groups. Compared to BCT alone, indomethacin significantly reduced the total protein level in the lungs (1.06 ± 0.39 mg/mL v. 3.75 ± 1.95 mg/mL, p = 0.006) and alveolar FD-70 leak (0.23 ± 0.19 μg/mL v. 0.53 ± 0.19 μg/mL, p = 0.02). Indomethacin also significantly attenuated the acute inflammatory response in percent PMN (13.33 ±7.5% v. 28.0 ± 12.96%, p = 0.04). Tumour necrosis factor-α and interleukin-6 decreased in the indomethacin group, but the decreases were not significant compared with other groups.

Conclusion

Aerosolized indomethacin has a protective effect against alveloar tissue permeability and inflammatory response induced by BCT.

Low-level blast exposure disrupts gliovascular and neurovascular connections and induces a chronic vascular pathology in rat brain

Much concern exists over the role of blast-induced traumatic brain injury (TBI) in the chronic cognitive and mental health problems that develop in veterans and active duty military personnel. The brain vasculature is particularly sensitive to blast injury. The aim of this study was to characterize the evolving molecular and histologic alterations in the neurovascular unit induced by three repetitive low-energy blast exposures (3 × 74.5 kPa) in a rat model mimicking human mild TBI or subclinical blast exposure. High-resolution two-dimensional differential gel electrophoresis (2D-DIGE) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry of purified brain vascular fractions from blast-exposed animals 6 weeks post-exposure showed decreased levels of vascular-associated glial fibrillary acidic protein (GFAP) and several neuronal intermediate filament proteins (α-internexin and the low, middle, and high molecular weight neurofilament subunits). Loss of these proteins suggested that blast exposure disrupts gliovascular and neurovascular interactions. Electron microscopy confirmed blast-induced effects on perivascular astrocytes including swelling and degeneration of astrocytic endfeet in the brain cortical vasculature. Because the astrocyte is a major sensor of neuronal activity and regulator of cerebral blood flow, structural disruption of gliovascular integrity within the neurovascular unit should impair cerebral autoregulation. Disrupted neurovascular connections to pial and parenchymal blood vessels might also affect brain circulation. Blast exposures also induced structural and functional alterations in the arterial smooth muscle layer. Interestingly, by 8 months after blast exposure, GFAP and neuronal intermediate filament expression had recovered to control levels in isolated brain vascular fractions. However, despite this recovery, a widespread vascular pathology was still apparent at 10 months after blast exposure histologically and on micro-computed tomography scanning. Thus, low-level blast exposure disrupts gliovascular and neurovascular connections while inducing a chronic vascular pathology.

Caffeine attenuates brain injury but increases mortality induced by high-intensity blast wave exposure

Caffeine is a substance that is consumed worldwide, and it may exert neuroprotective effects against various cerebral insults, including neurotrauma, which is the most prevalent injury among military personnel. To investigate the effects of caffeine on high-intensity blast wave-induced severe blast injury in mice, three different paradigms of caffeine were applied to male C57BL/6 mice with severe whole body blast injury (WBBI). The results demonstrated that chronic caffeine treatment alleviated blast-induced traumatic brain injury (bTBI); however, both chronic and acute caffeine treatments exacerbated blast-induced lung injuries and, more importantly, increased both the cumulative and time-segmented mortalities postinjury. Interestingly, withdrawing caffeine intake preinjury resulted in favorable outcomes in mortality and lung injury, similar to the findings in water-treated mice, and had the trend to attenuate brain injury. These findings demonstrated that although drinking coffee or caffeine preparations attenuated blast-induced brain trauma, these beverages may place personnel in the battlefield at high risk of casualties, which will help us re-evaluate the therapeutic strategy of caffeine application, particularly in multiple-organ-trauma settings. Furthermore, these findings provided possible strategies for reducing the risk of casualties with caffeine consumption, which may help to change the coffee-drinking habits of military personnel.

Effect of acute restraint stress in a polytrauma rat model

INTRODUCTION

A stressful environment may contribute to poor outcomes after TBI. The current study evaluates the impact of acute stress in a polytrauma rat model.

METHODS

Rats were stressed by a 45-minute immobilization period before instrumentation under ketamine (t1). Polytrauma was produced by blast overpressure and controlled hemorrhage (t2). Rats were euthanized immediately after a 3 h simulated Medevac-transport time (t3) or after 72 h post-trauma (t4). Corticosterone, ACTH, and ACTH receptor gene expression were measured at these time points. Physiological parameters were monitored throughout the study.

RESULTS

HR was higher in stressed compared to unstressed animals at t1. Corticosterone and ACTH levels were similar for all conditions at t1 and t2; ACTH and corticosterone became elevated in all groups at t3 and at t4, respectively. The ACTH receptor gene expression trended towards higher values at t4 for the stressed animals whether being injured or not. Survival after injury was 83% in both unstressed and stressed animals.

CONCLUSION

Overall, corticosterone was not significantly affected following acute stress in ketamine-anesthetized rats. Early mortality was primarily due to polytrauma and change in the animal's biochemical parameters appeared at t4 post trauma. The findings indicate that ketamine-anesthesia and/or surgery may have overshadowed the effect of the initial stress.

Shock waves increase pulmonary vascular leakage, inflammation, oxidative stress, and apoptosis in a mouse model

Severe lung damage is a major cause of death in blast victims, but the mechanisms of pulmonary blast injury are not well understood. Therefore, it is important to study the injury mechanism of pulmonary blast injury. A model of lung injury induced by blast exposure was established by using a simulation blast device. The effectiveness and reproducibility of the device were investigated. Eighty mice were randomly divided into eight groups: control group and 3 h, 6 h, 12 h, 24 h, 48 h, 7 days and 14 days post blast. The explosive device induced an explosion injury model of a single lung injury in mice. The success rate of the model was as high as 90%, and the degree of lung injury was basically the same under the same pressure. Under the same conditions, the thickness of the aluminum film can be from 0.8 mm to 1.6 mm, and the peak pressure could be from 95.85 ± 15.61 PSI to 423.32 ± 11.64 PSI. There is no statistical difference in intragroup comparison. A follow-up lung injury experiment using an aluminum film thickness of 1.4 mm showed a pressure of 337.46 ± 18.30 PSI induced a mortality rate of approximately 23.2%. Compared with the control group (372 ± 23 times/min, 85.9 ± 9.4 mmHg, 4.34 ± 0.09), blast exposed mice had decreased heart rate (283 ± 21 times/min) and blood pressure (73.6 ± 3.6 mmHg), and increased lung wet/dry weight ratio(2.67 ± 0.11), marked edematous lung tissue, ruptured blood vessels, infiltrating inflammatory cells, increased NF-κB (4.13 ± 0.01), TNF-α (4.13 ± 0.01), IL-1β (2.43 ± 0.01) and IL-6 (4.65 ± 0.01) mRNA and protein, decreased IL-10(0.18 ± 0.02) mRNA and protein ( P < 0.05). The formation of ROS and the expression of MDA5 (4.46 ± 0.01) and IREα (3.43 ± 0.00) mRNA and protein were increased and the expression of SOD-1 (0.28 ± 0.02) mRNA and protein was decreased ( P < 0.05). Increased expression of Bax (3.54 ± 0.00) and caspase 3 (4.18 ± 0.01) mRNA and protein inhibited the expression of Bcl-2 (0.39 ± 0.02) mRNA and protein. The changes of pulmonary edema, inflammatory cell infiltration, and cell damage factor expression increased gradually with time, and reached the peak at 12-24 h after the outbreak, and returned to normal at 7-14 days. Detonation injury can lead to edema of lung tissue, pulmonary hemorrhage, rupture of pulmonary vessels, induction of early inflammatory responses accompanied by increased oxidative stress in lung tissue cells and increased apoptosis in mice experiencing blast injury. The above results are consistent with those reported in other literatures. It is showed that the mouse lung blast injury model is successfully modeled, and the device can be used for the study of pulmonary blast injury. Impact statement The number of patients with explosive injury has increased year by year, but there is no better treatment. However, the research on detonation injury is difficult to carry out. One of the factors is the difficulty in making the model of blast injury. The laboratory successfully developed and produced a simulation device of explosive knocking through a large amount of literature data and preliminary experiments, and verified the preparation of the simulation device through various experimental techniques. The results showed that the device could simulate the shock wave-induced acute lung injury generated, which was similar to the actual knocking injury. The experimental process was controlled. Under the same condition, there was no statistical difference between the groups. It is possible to realize miniaturization and precision of an explosive knocking simulation device, which is a good experimental tool for further research on the mechanism of organ damage caused by detonation and the development of protective drugs.

Neurological heterotopic ossification: Current understanding and future directions

Neurological heterotopic ossification (NHO) involves the formation of bone in soft tissue following a neurological condition, of which the most common are brain and spinal cord injuries. NHO often forms around the hip, knee and shoulder joints, causing severe pain and joint deformation which is associated with significant morbidity and reduced quality of life. The cellular and molecular events that initiate NHO have been the focus of an increasing number of human and animal studies over the past decade, with this work largely driven by the need to unearth potential therapeutic interventions to prevent the formation of NHO. This review provides an overview of the present understanding of NHO pathogenesis and pathobiology, current treatments, novel therapeutic targets, potential biomarkers and future directions.

Chronic post-traumatic stress disorder-related traits in a rat model of low-level blast exposure

The postconcussion syndrome following mild traumatic brain injuries (mTBI) has been regarded as a mostly benign syndrome that typically resolves in the immediate months following injury. However, in some individuals, symptoms become chronic and persistent. This has been a striking feature of the mostly blast-related mTBIs that have been seen in veterans returning from the recent conflicts in Iraq and Afghanistan. In these veterans a chronic syndrome with features of both the postconcussion syndrome and post-traumatic stress disorder has been prominent. Animal modeling of blast-related TBI has developed rapidly over the last decade leading to advances in the understanding of blast pathophysiology. However, most studies have focused on acute to subacute effects of blast on the nervous system and have typically studied higher intensity blast exposures with energies more comparable to that involved in human moderate to severe TBI. Fewer animal studies have addressed the chronic effects of lower level blast exposures that are more comparable to those involved in human mTBI or subclinical blast. Here we describe a rat model of repetitive low-level blast exposure that induces a variety of anxiety and PTSD-related behavioral traits including exaggerated fear responses that were present when animals were tested between 28 and 35 weeks after the last blast exposure. These animals provide a model to study the chronic and persistent behavioral effects of blast including the relationship of PTSD to mTBI in dual diagnosis veterans.

Pattern and nature of Neyshabur train explosion blast injuries

Background

Explosions are classified as both man-made and complex accidents. Explosive events can cause serious damage to people, property, and the environment. This study aimed to investigate the pattern and nature of damage incurred to the victims of the Neyshabur Train Explosion.

Methods

The current study is a descriptive cross-sectional study that was retrospectively performed on 99 individuals using census method and documents victims hospitalized due to the Neyshabur train disaster (February 2004) in 2016. In this study, different variables such as age, sex, type of injury, treatment, etc. were examined using a questionnaire and were analyzed using SPSS16.

Results

The results showed that 50.5% of victims were males with mean age of 30.33 ± 4.27 years and most of them were in 20- to 40-year age group. A total of 98 victims were discharged after treatment, and 1 victim died due to the severity of injuries after 3 days of hospitalization. Second type of injuries caused by the explosion accounted for most of the injuries (55.6%), and most treatments (54.5%) were related to the specific field of orthopedics.

Conclusion

Handling and transportation of fuels and chemicals via rail transport system is one of the potential hazards that threatens human life. The results showed that the highest numbers of victims were in 20- to 40-year age group, which is the age of economic efficiency. The prevention and reduction of human and financial losses resulting from accidents require proper national planning.

Effects of Mild Blast Traumatic Brain Injury on Cerebral Vascular, Histopathological, and Behavioral Outcomes in Rats

To determine the effects of mild blast-induced traumatic brain injury (bTBI), several groups of rats were subjected to blast injury or sham injury in a compressed air-driven shock tube. The effects of bTBI on relative cerebral perfusion (laser Doppler flowmetry [LDF]), and mean arterial blood pressure (MAP) cerebral vascular resistance were measured for 2 h post-bTBI. Dilator responses to reduced intravascular pressure were measured in isolated middle cerebral arterial (MCA) segments, ex vivo, 30 and 60 min post-bTBI. Neuronal injury was assessed (Fluoro-Jade C [FJC]) 24 and 48 h post-bTBI. Neurological outcomes (beam balance and walking tests) and working memory (Morris water maze [MWM]) were assessed 2 weeks post-bTBI. Because impact TBI (i.e., non-blast TBI) is often associated with reduced cerebral perfusion and impaired cerebrovascular function in part because of the generation of reactive oxygen and nitrogen species such as peroxynitrite (ONOO-), the effects of the administration of the ONOO- scavenger, penicillamine methyl ester (PenME), on cerebral perfusion and cerebral vascular resistance were measured for 2 h post-bTBI. Mild bTBI resulted in reduced relative cerebral perfusion and MCA dilator responses to reduced intravascular pressure, increases in cerebral vascular resistance and in the numbers of FJC-positive cells in the brain, and significantly impaired working memory. PenME administration resulted in significant reductions in cerebral vascular resistance and a trend toward increased cerebral perfusion, suggesting that ONOO- may contribute to blast-induced cerebral vascular dysfunction.

CD43Lo classical monocytes participate in the cellular immune response to isolated primary blast lung injury

BACKGROUND

Understanding of the cellular immune response to primary blast lung injury (PBLI) is limited, with only the neutrophil response well documented. Moreover, its impact on the immune response in distal organs remains poorly understood. In this study, a rodent model of isolated primary blast injury was used to investigate the acute cellular immune response to isolated PBLI in the circulation and lung, including the monocyte response, and investigate distal subacute immune effects in the spleen and liver 6 hours after injury.

METHODS

Rats were subjected to a shock wave (~135 kPa overpressure, 2 ms duration) inducing PBLI or sham procedure. Rat physiology was monitored, and at 1, 3, and 6 hours thereafter, blood, lung, and bronchoalveolar lavage fluid (BALF) were collected and analyzed by flow cytometry, enzyme-linked immunosorbent assay, and histologic examination. In addition, at 6 hours, spleen and liver were collected and analyzed by flow cytometry.

RESULTS

Lung histology confirmed pulmonary barotrauma and inflammation. This was associated with rises in CXCL-1, interleukin 6 (IL-6), tumor necrosis factor α and albumin protein in the BALF. Significant acute increases in blood and lung neutrophils and CD43Lo/His48Hi (classical) monocytes/macrophages were detected. No significant changes were seen in blood or lung "nonclassical" monocyte and in natural killler, B, or T cells. In the BALF, significant increases were seen in neutrophils, CD43Lo monocyte-macrophages and monocyte chemoattractant protein-1. Significant increases in CD43Lo and Hi monocyte-macrophages were detected in the spleen at 6 hours.

CONCLUSION

This study reveals a robust and selective response of CD43Lo/His48Hi (classical) monocytes, in addition to neutrophils, in blood and lung tissue following PBLI. An increase in monocyte-macrophages was also observed in the spleen at 6 hours. This profile of immune cells in the blood and BALF could present a new research tool for translational studies seeking to monitor, assess, or attenuate the immune response in blast-injured patients.

Perfluorocarbon reduces cell damage from blast injury by inhibiting signal paths of NF-κB, MAPK and Bcl-2/Bax signaling pathway in A549 cells

Background and objective

Blast lung injury is a common type of blast injury and has very high mortality. Therefore, research to identify medical therapies for blast injury is important.

Perfluorocarbon (PFC) is used to improve gas exchange in diseased lungs and has anti-inflammatory functions in vitro and in vivo. The aim of this study was to determine whether PFC reduces damage to A549 cells caused by blast injury and to elucidate its possible mechanisms of action.

Study design and methods

A549 alveolar epithelial cells exposed to blast waves were treated with and without PFC. Morphological changes and apoptosis of A549 cells were recorded. PCR and enzyme-linked immunosorbent assay (ELISA) were used to measure the mRNA or protein levels of IL-1β, IL-6 and TNF-α. Malondialdehyde (MDA) levels and superoxide dismutase (SOD) activity levels were detected. Western blot was used to quantify the expression of NF-κB, Bax, Bcl-2, cleaved caspase-3 and MAPK cell signaling proteins.

Results

A549 cells exposed to blast wave shrank, with less cell-cell contact. The morphological change of A549 cells exposed to blast waves were alleviated by PFC. PFC significantly inhibited the apoptosis of A549 cells exposed to blast waves. IL-1β, IL-6 and TNF-α cytokine and mRNA expression levels were significantly inhibited by PFC. PFC significantly increased MDA levels and decreased SOD activity levels. Further studies indicated that NF-κB, Bax, caspase-3, phospho-p38, phosphor-ERK and phosphor-JNK proteins were also suppressed by PFC. The quantity of Bcl-2 protein was increased by PFC.

Conclusion

Our research showed that PFC reduced A549 cell damage caused by blast injury. The potential mechanism may be associated with the following signaling pathways:

1) the signaling pathways of NF-κB and MAPK, which inhibit inflammation and reactive oxygen species (ROS); and 2) the signaling pathways of Bcl-2/Bax and caspase-3, which inhibit apoptosis.

Exposure to a Predator Scent Induces Chronic Behavioral Changes in Rats Previously Exposed to Low-level Blast: Implications for the Relationship of Blast-Related TBI to PTSD

Blast-related mild traumatic brain injury (mTBI) has been unfortunately common in veterans who served in the recent conflicts in Iraq and Afghanistan. The postconcussion syndrome associated with these mTBIs has frequently appeared in combination with post-traumatic stress disorder (PTSD). The presence of PTSD has complicated diagnosis, since clinically, PTSD and the postconcussion syndrome of mTBI have many overlapping symptoms. In particular, establishing how much of the symptom complex can be attributed to the psychological trauma associated with PTSD in contrast to the physical injury of traumatic brain injury has proven difficult. Indeed, some have suggested that much of what is now being called blast-related postconcussion syndrome is better explained by PTSD. The relationship between the postconcussion syndrome of mTBI and PTSD is complex. Association of the two disorders might be viewed as additive effects of independent psychological and physical traumas suffered in a war zone. However, we previously found that rats exposed to repetitive low-level blast exposure in the absence of a psychological stressor developed a variety of anxiety and PTSD-related behavioral traits that were present months following the last blast exposure. Here, we show that a single predator scent challenge delivered 8 months after the last blast exposure induces chronic anxiety related changes in blast-exposed rats that are still present 45 days later. These observations suggest that in addition to independently inducing PTSD-related traits, blast exposure sensitizes the brain to react abnormally to a subsequent psychological stressor. These studies have implications for conceptualizing the relationship between blast-related mTBI and PTSD and suggest that blast-related mTBI in humans may predispose to the later development of PTSD in reaction to subsequent psychological stressors.

Primary blast causes mild, moderate, severe and lethal TBI with increasing blast overpressures: Experimental rat injury model

Injury severity in blast induced Traumatic Brain Injury (bTBI) increases with blast overpressure (BOP) and impulse in dose-dependent manner. Pure primary blast waves were simulated in compressed gas shock-tubes in discrete increments. Present work demonstrates 24 hour survival of rats in 0–450 kPa (0–800 Pa∙s impulse) range at 10 discrete levels (60, 100, 130, 160, 190, 230, 250, 290, 350 and 420 kPa) and determines the mortality rate as a non-linear function of BOP. Using logistic regression model, predicted mortality rate (PMR) function was calculated, and used to establish TBI severities. We determined a BOP of 145 kPa as upper mild TBI threshold (5% PMR). Also we determined 146–220 kPa and 221–290 kPa levels as moderate and severe TBI based on 35%, and 70% PMR, respectively, while BOP above 290 kPa is lethal. Since there are no standards for animal bTBI injury severity, these thresholds need further refinements using histopathology, immunohistochemistry and behavior. Further, we specifically investigated mild TBI range (0–145 kPa) using physiological (heart rate), pathological (lung injury), immuno-histochemical (oxidative/nitrosative and blood-brain barrier markers) as well as blood borne biomarkers. With these additional data, we conclude that mild bTBI occurs in rats when the BOP is in the range of 85–145 kPa.

Prolonged but not short-duration blast waves elicit acute inflammation in a rodent model of primary blast limb trauma

BACKGROUND

Blast injuries from conventional and improvised explosive devices account for 75% of injuries from current conflicts; over 70% of injuries involve the limbs. Variable duration and magnitude of blast wave loading occurs in real-life explosions and is hypothesised to cause different injuries. While a number of in vivo models report the inflammatory response to blast injuries, the extent of this response has not been investigated with respect to the duration of the primary blast wave. The relevance is that explosions in open air are of short duration compared to those in confined spaces.

METHODS

Hindlimbs of adult Sprauge-Dawley rats were subjected to focal isolated primary blast waves of varying overpressure (1.8-3.65kPa) and duration (3.0-11.5ms), utilising a shock tube and purpose-built experimental rig. Rats were monitored during and after the blast. At 6 and 24h after exposure, blood, lungs, liver and muscle tissues were collected and prepared for histology and flow cytometry.

RESULTS

At 6h, increases in circulating neutrophils and CD43Lo/His48Hi monocytes were observed in rats subjected to longer-duration blast waves. This was accompanied by increases in circulating pro-inflammatory chemo/cytokines KC and IL-6. No changes were observed with shorter-duration blast waves irrespective of overpressure. In all cases, no histological damage was observed in muscle, lung or liver. By 24h post-blast, all inflammatory parameters had normalised.

CONCLUSIONS

We report the development of a rodent model of primary blast limb trauma that is the first to highlight an important role played by blast wave duration and magnitude in initiating acute inflammatory response following limb injury in the absence of limb fracture or penetrating trauma. The combined biological and mechanical method developed can be used to further understand the complex effects of blast waves in a range of different tissues and organs in vivo.

In Silico Modeling of Novel Drug Ligands for Treatment of Concussion Associated Tauopathy

The objective of this study was to develop an in silico screening model for characterization of potential novel ligands from commercial drug libraries able to functionally activate certain olfactory receptors (ORs), which are members of the class A rhodopsin-like family of G protein couple receptors (GPCRs), in the brain of murine models of concussion. We previously found that concussions may significantly influence expression of certain ORs, for example, OR4M1 in subjects with a history of concussion/traumatic brain injury (TBI). In this study, we built a 3-D OR4M1 model and used it in in silico screening of potential novel ligands from commercial drug libraries. We report that in vitro activation of OR4M1 with the commercially available ZINC library compound 10915775 led to a significant attenuation of abnormal tau phosphorylation in embryonic cortico-hippocampal neuronal cultures derived from NSE-OR4M1 transgenic mice, possibly through modulation of the JNK signaling pathway. The attenuation of abnormal tau phosphorylation was rather selective since ZINC10915775 significantly decreased tau phosphorylation on tau Ser202/T205 (AT8 epitope) and tau Thr212/Ser214 (AT100 epitope), but not on tau Ser396/404 (PHF-1 epitope). Moreover, no response of ZINC10915775 was found in control hippocampal neuronal cultures derived from wild type littermates. Our in silico model provides novel means to pharmacologically modulate select ubiquitously expressed ORs in the brain through high affinity ligand activation to prevent and eventually to treat concussion induced down regulation of ORs and subsequent cascade of tau pathology. J. Cell. Biochem. 117: 2241-2248, 2016. © 2016 Wiley Periodicals, Inc.

Time Course and Size of Blood-Brain Barrier Opening in a Mouse Model of Blast-Induced Traumatic Brain Injury

An increasing number of studies have reported blood-brain barrier (BBB) dysfunction after blast-induced traumatic brain injury (bTBI). Despite this evidence, there is limited quantitative understanding of the extent of BBB opening and the time course of damage after blast injury. In addition, many studies do not report kinematic parameters of head motion, making it difficult to separate contributions of primary and tertiary blast-loading. Detailed characterization of blast-induced BBB damage may hold important implications for serum constituents that may potentially cross the compromised barrier and contribute to neurotoxicity, neuroinflammation, and persistent neurologic deficits. Using an in vivo bTBI model, systemic administration of sodium fluorescein (NaFl; 376 Da), Evans blue (EB; 69 kDa when bound to serum albumin), and dextrans (3-500 kDa) was used to estimate the pore size of BBB opening and the time required for recovery. Exposure to blast with 272 ± 6 kPa peak overpressure, 0.69 ± 0.01 ms duration, and 65 ± 1 kPa*ms impulse resulted in significant acute extravasation of NaFl, 3 kDa dextran, and EB. However, there was no significant acute extravasation of 70 kDa or 500 kDa dextrans, and minimal to no extravasation of NaFl, dextrans, or EB 1 day after exposure. This study presents a detailed analysis of the time course and pore size of BBB opening after bTBI, supported by a characterization of kinematic parameters associated with blast-induced head motion.

Physiological and immune-biological characterization of a long-term murine model of blunt chest trauma

Blunt chest trauma causes pulmonary and systemic inflammation. It is still a matter of debate whether the long-term course of this inflammatory response is associated with persistent impairment of lung function. We hypothesized that an increase of inflammatory biomarkers may still be present at later time points after blunt chest trauma, eventually, despite normalized lung mechanics and gas exchange. Anesthetized spontaneously breathing male C57BL/6J mice underwent a blast wave-induced blunt chest trauma or sham procedure. Twelve and 24 h later, blood gases and lung mechanics were measured, together with blood, bronchoalveolar lavage (BAL), and tissue cytokine concentrations (multiplex cytokine kit); heme oxygenase 1 (HO-1), activated caspase-3, Bcl-xL, and Bax expression (Western blotting); nuclear factor-κB activation (electrophoretic mobility shift assay); nitrotyrosine formation; and purinergic (P2XR4 and P2XR7) receptor expression (immunohistochemistry). Histological damage was assessed by hematoxylin and eosin and periodic acid-Schiff staining. High-resolution respirometry allowed assessing mitochondrial respiration in diaphragm biopsies. Chest trauma significantly increased tissue and BAL cytokine levels, associated with a significant increase in HO-1, purinergic receptor expression, and tissue nitrotyrosine formation. In contrast, lung mechanics, gas exchange, and histological damage did not show any significant difference between sham and trauma groups. Activation of the immune response remains present at later time points after murine blunt chest trauma. Discordance of the increased local inflammatory response and preserved pulmonary function may be explained by a dissociation of the immune response and lung function, such as previously suggested after experimental sepsis.

Neuronal DNA Methylation Profiling of Blast-Related Traumatic Brain Injury

Long-term molecular changes in the brain resulting from blast exposure may be mediated by epigenetic changes, such as deoxyribonucleic acid (DNA) methylation, that regulate gene expression. Aberrant regulation of gene expression is associated with behavioral abnormalities, where DNA methylation bridges environmental signals to sustained changes in gene expression. We assessed DNA methylation changes in the brains of rats exposed to three 74.5 kPa blast overpressure events, conditions that have been associated with long-term anxiogenic manifestations weeks or months following the initial exposures. Rat frontal cortex eight months post-exposure was used for cell sorting of whole brain tissue into neurons and glia. We interrogated DNA methylation profiles in these cells using Expanded Reduced Representation Bisulfite Sequencing. We obtained data for millions of cytosines, showing distinct methylation profiles for neurons and glia and an increase in global methylation in neuronal versus glial cells (p<10(-7)). We detected DNA methylation perturbations in blast overpressure-exposed animals, compared with sham blast controls, within 458 and 379 genes in neurons and glia, respectively. Differentially methylated neuronal genes showed enrichment in cell death and survival and nervous system development and function, including genes involved in transforming growth factor β and nitric oxide signaling. Functional validation via gene expression analysis of 30 differentially methylated neuronal and glial genes showed a 1.2 fold change in gene expression of the serotonin N-acetyltransferase gene (Aanat) in blast animals (p<0.05). These data provide the first genome-based evidence for changes in DNA methylation induced in response to multiple blast overpressure exposures. In particular, increased methylation and decreased gene expression were observed in the Aanat gene, which is involved in converting serotonin to the circadian hormone melatonin and is implicated in sleep disturbance and depression associated with traumatic brain injury.

Steroid-Loaded Hemostatic Nanoparticles Combat Lung Injury after Blast Trauma

In response to the lack of therapeutics for internal bleeding following a traumatic event, we synthesized hemostatic dexamethasone nanoparticles (hDNP) to help alleviate internal hemorrhaging. hDNP consist of a block copolymer, poly(lactic-co-glycolic acid)-poly(l-lysine)-poly(ethylene glycol) conjugated to a peptide, glycine-arginine-glycine-aspartic acid-serine (GRGDS). These particles were evaluated as treatment for primary blast lung injury in a rodent model. Animals were randomly placed into test and control groups, exposed to blast and given immediate injection. Recovery was assessed using physiological parameters and immunohistochemistry. We found that dexamethasone-loaded hemostatic nanoparticles alleviate physiological deprivation caused by blast injury and reduce lung injury damage.

The role of plasma gelsolin in cardiopulmonary bypass induced acute lung injury in infants and young children: a pilot study

BACKGROUND

Acute lung injury (ALI) induced by cardiopulmonary bypass (CPB, CPB-ALI) is a common and serious complication after cardiac surgery. And infants and young children are more prone to CPB-ALI. The purpose of this study was to investigate the perioperative changes of plasma gelsolin (pGSN) in patients below 3 years of age with cardiac surgeries and CPB, and determine whether pGSN are associated with the occurrence and severity of CPB-ALI.

METHODS

Seventy-seven consecutive patients ≤3 years of age with congenital heart diseases (CHD) performed on open heart surgery with CPB were finally enrolled, and assigned to ALI and non-ALI groups according to the American-European Consensus Criteria. Plasma concentrations of gelsolin and total protein were measured at following 8 time points: before CPB (a), after CPB (b), 2 hours after CPB (c), 6 hours after CPB (d), 12 hours after CPB (e), 24 hours after CPB (f), 48 hours after CPB (g) and 72 hours after CPB (h).

RESULTS

Twenty-seven (35.1%) patients developed CPB-ALI in the study, including eleven (14.3%) patients with ARDS. The earliest significant drop of pGSN and normalized pGSN (pGSNN) of ALI group both occurred at 6 hours after CPB (p = 0.04 and p < 0.01), which was much earlier than those of non-ALI group (48 hours, p = 0.03 and 24 hours, p < 0.01); PGSN of ALI group before CPB and 6 hours after CPB were both significantly lower than those of non-ALI group (p < 0.01); PGSNN of ALI group before CPB and 6 hours after CPB were both significantly lower than those of non-ALI group (p < 0.01, p = 0.04); PGSN before CPB was the only independent risk factor predicting the occurrence of CPB-ALI (OR, 1.023; 95% CI, 1.007-1.039; p < 0.01) with an AUC of 0.753 (95% CI, 0.626-0.880); The optimal cutoff value of pGSN before CPB was 264.2 mg/L, with a sensitivity of 58.3% and a specificity 94.7%. And lower pGSN before CPB was significantly associated with the severity of CS-AKI (r = -0.45, p < 0.01).

CONCLUSIONS

Patients developing CPB-ALI had lower plasma gelsolin reservoir and a much more amount and rapid consumption of plasma gelsolin early after operation. PGSN before CPB was an early and sensitive predictor of CPB-ALI in infants and young children undergoing cardiac surgery, and was negatively correlated with the severity of CPB-ALI.

Blast TBI Models, Neuropathology, and Implications for Seizure Risk

Traumatic brain injury (TBI) due to explosive blast exposure is a leading combat casualty. It is also implicated as a key contributor to war related mental health diseases. A clinically important consequence of all types of TBI is a high risk for development of seizures and epilepsy. Seizures have been reported in patients who have suffered blast injuries in the Global War on Terror but the exact prevalence is unknown. The occurrence of seizures supports the contention that explosive blast leads to both cellular and structural brain pathology. Unfortunately, the exact mechanism by which explosions cause brain injury is unclear, which complicates development of meaningful therapies and mitigation strategies. To help improve understanding, detailed neuropathological analysis is needed. For this, histopathological techniques are extremely valuable and indispensable. In the following we will review the pathological results, including those from immunohistochemical and special staining approaches, from recent preclinical explosive blast studies.

Blast overpressure induces shear-related injuries in the brain of rats exposed to a mild traumatic brain injury

Background

Blast-related traumatic brain injury (TBI) has been a significant cause of injury in the military operations of Iraq and Afghanistan, affecting as many as 10-20% of returning veterans. However, how blast waves affect the brain is poorly understood. To understand their effects, we analyzed the brains of rats exposed to single or multiple (three) 74.5 kPa blast exposures, conditions that mimic a mild TBI.

Results

Rats were sacrificed 24 hours or between 4 and 10 months after exposure. Intraventricular hemorrhages were commonly observed after 24 hrs. A screen for neuropathology did not reveal any generalized histopathology. However, focal lesions resembling rips or tears in the tissue were found in many brains. These lesions disrupted cortical organization resulting in some cases in unusual tissue realignments. The lesions frequently appeared to follow the lines of penetrating cortical vessels and microhemorrhages were found within some but not most acute lesions.

Conclusions

These lesions likely represent a type of shear injury that is unique to blast trauma. The observation that lesions often appeared to follow penetrating cortical vessels suggests a vascular mechanism of injury and that blood vessels may represent the fault lines along which the most damaging effect of the blast pressure is transmitted.

Mechanisms of hearing loss after blast injury to the ear

Given the frequent use of improvised explosive devices (IEDs) around the world, the study of traumatic blast injuries is of increasing interest. The ear is the most common organ affected by blast injury because it is the body's most sensitive pressure transducer. We fabricated a blast chamber to re-create blast profiles similar to that of IEDs and used it to develop a reproducible mouse model to study blast-induced hearing loss. The tympanic membrane was perforated in all mice after blast exposure and found to heal spontaneously. Micro-computed tomography demonstrated no evidence for middle ear or otic capsule injuries; however, the healed tympanic membrane was thickened. Auditory brainstem response and distortion product otoacoustic emission threshold shifts were found to be correlated with blast intensity. As well, these threshold shifts were larger than those found in control mice that underwent surgical perforation of their tympanic membranes, indicating cochlear trauma. Histological studies one week and three months after the blast demonstrated no disruption or damage to the intra-cochlear membranes. However, there was loss of outer hair cells (OHCs) within the basal turn of the cochlea and decreased spiral ganglion neurons (SGNs) and afferent nerve synapses. Using our mouse model that recapitulates human IED exposure, our results identify that the mechanisms underlying blast-induced hearing loss does not include gross membranous rupture as is commonly believed. Instead, there is both OHC and SGN loss that produce auditory dysfunction.

Rat injury model under controlled field-relevant primary blast conditions: acute response to a wide range of peak overpressures

We evaluated the acute (up to 24 h) pathophysiological response to primary blast using a rat model and helium driven shock tube. The shock tube generates animal loadings with controlled pure primary blast parameters over a wide range and field-relevant conditions. We studied the biomechanical loading with a set of pressure gauges mounted on the surface of the nose, in the cranial space, and in the thoracic cavity of cadaver rats. Anesthetized rats were exposed to a single blast at precisely controlled five peak overpressures over a wide range (130, 190, 230, 250, and 290 kPa). We observed 0% mortality rates in 130 and 230 kPa groups, and 30%, 24%, and 100% mortality rates in 190, 250, and 290 kPa groups, respectively. The body weight loss was statistically significant in 190 and 250 kPa groups 24 h after exposure. The data analysis showed the magnitude of peak-to-peak amplitude of intracranial pressure (ICP) fluctuations correlates well with mortality rates. The ICP oscillations recorded for 190, 250, and 290 kPa are characterized by higher frequency (10-20 kHz) than in other two groups (7-8 kHz). We noted acute bradycardia and lung hemorrhage in all groups of rats subjected to the blast. We established the onset of both corresponds to 110 kPa peak overpressure. The immunostaining against immunoglobulin G (IgG) of brain sections of rats sacrificed 24-h post-exposure indicated the diffuse blood-brain barrier breakdown in the brain parenchyma. At high blast intensities (peak overpressure of 190 kPa or more), the IgG uptake by neurons was evident, but there was no evidence of neurodegeneration after 24 h post-exposure, as indicated by cupric silver staining. We observed that the acute response as well as mortality is a non-linear function over the peak overpressure and impulse ranges explored in this work.

Acute blast injury reduces brain abeta in two rodent species

Blast-induced traumatic brain injury (TBI) has been a major cause of morbidity and mortality in the conflicts in Iraq and Afghanistan. How the primary blast wave affects the brain is not well understood. In particular, it is unclear whether blast injures the brain through mechanisms similar to those found in non-blast closed impact injuries (nbTBI). The β-amyloid (Aβ) peptide associated with the development of Alzheimer’s disease is elevated acutely following TBI in humans as well as in experimental animal models of nbTBI. We examined levels of brain Aβ following experimental blast injury using enzyme-linked immunosorbent assays for Aβ 40 and 42. In both rat and mouse models of blast injury, rather than being increased, endogenous rodent brain Aβ levels were decreased acutely following injury. Levels of the amyloid precursor protein (APP) were increased following blast exposure although there was no evidence of axonal pathology based on APP immunohistochemical staining. Unlike the findings in nbTBI animal models, levels of the β-secretase, β-site APP cleaving enzyme 1, and the γ-secretase component presenilin-1 were unchanged following blast exposure. These studies have implications for understanding the nature of blast injury to the brain. They also suggest that strategies aimed at lowering Aβ production may not be effective for treating acute blast injury to the brain.

Wartime spine injuries: understanding the improvised explosive device and biophysics of blast trauma

The improvised explosive device (IED) has been the most significant threat by terrorists worldwide. Blast trauma has produced a wide pattern of combat spinal column injuries not commonly experienced in the civilian community. Unfortunately, explosion-related injuries have also become a widespread reality of civilian life throughout the world, and civilian medical providers who are involved in emergency trauma care must be prepared to manage casualties from terrorist attacks using high-energy explosive devices. Treatment decisions for complex spine injuries after blast trauma require special planning, taking into consideration many different factors and the complicated multiple organ system injuries not normally experienced at most civilian trauma centers. Therefore, an understanding about the effects of blast trauma by spine surgeons in the community has become imperative, as the battlefield has been brought closer to home in many countries through domestic terrorism and mass casualty situations, with the lines blurred between military and civilian trauma. We set out to provide the spine surgeon with a brief overview on the use of IEDs for terrorism and the current conflicts in Iraq and Afghanistan and also a perspective on the biophysics of blast trauma.

Blast exposure induces post-traumatic stress disorder-related traits in a rat model of mild traumatic brain injury

Blast related traumatic brain injury (TBI) has been a major cause of injury in the wars in Iraq and Afghanistan. A striking feature of the mild TBI (mTBI) cases has been the prominent association with post-traumatic stress disorder (PTSD). However, because of the overlapping symptoms, distinction between the two disorders has been difficult. We studied a rat model of mTBI in which adult male rats were exposed to repetitive blast injury while under anesthesia. Blast exposure induced a variety of PTSD-related behavioral traits that were present many months after the blast exposure, including increased anxiety, enhanced contextual fear conditioning, and an altered response in a predator scent assay. We also found elevation in the amygdala of the protein stathmin 1, which is known to influence the generation of fear responses. Because the blast overpressure injuries occurred while animals were under general anesthesia, our results suggest that a blast-related mTBI exposure can, in the absence of any psychological stressor, induce PTSD-related traits that are chronic and persistent. These studies have implications for understanding the relationship of PTSD to mTBI in the population of veterans returning from the wars in Iraq and Afghanistan.

Blast-induced color change in photonic crystals corresponds with brain pathology

A high incidence of blast exposure is a 21st century reality in counter-insurgency warfare. However, thresholds for closed-head blast-induced traumatic brain injury (bTBI) remain unknown. Moreover, without objective information about relative blast exposure, warfighters with bTBI may not receive appropriate medical care and may remain in harm's way. Accordingly, we have engineered a blast injury dosimeter (BID) using a photonic crystalline material that changes color following blast exposure. The photonic crystals are fabricated using SU-8 via multi-beam interference laser lithography. The final BID is similar in appearance to an array of small colored stickers that may be affixed to uniforms or helmets in multiple locations. Although durable under normal conditions, the photonic crystalline micro- and nano-structure are precisely altered by blast to create a color change. These BIDs were evaluated using a rat model of bTBI, for which blast shockwave exposure was generated via a compressed air-driven shock tube. With prototype BID arrays affixed to the animals, we found that BID color changes corresponded with subtle brain pathologies, including neuronal degeneration and reactive astrocytosis. These subtle changes were most notable in the dentate gyrus of the hippocampus, cerebral cortex, and cerebellum. These data demonstrate the feasibility of using a materials-based, power-free colorimetric BID as the first self-contained blast sensor calibrated to correspond with brain pathology.

Blast-induced moderate neurotrauma (BINT) elicits early complement activation and tumor necrosis factor α (TNFα) release in a rat brain

Blast-induced neurotrauma (BINT) is a major medical concern yet its etiology is largely undefined. Complement activation may play a role in the development of secondary injury following traumatic brain injury; however, its role in BINT is still undefined. The present study was designed to characterize the complement system and adaptive immune-inflammatory responses in a rat model of moderate BINT. Anesthetized rats were exposed to a moderate blast (120 kPa) using an air-driven shock tube. Brain tissue injury, systemic and local complement, cerebral edema, inflammatory cell infiltration, and pro-inflammatory cytokine production were measured at 0.5, 3, 48, 72, 120, and 168 h. Injury to brain tissue was evaluated by histological evaluation. Systemic complement was measured via ELSIA. The remaining measurements were determined by immunohistoflourescent staining. Moderate blast triggers moderate brain injuries, elevated levels of local brain C3/C5b-9 and systemic C5b-9, increased leukocyte infiltration, unregulated tumor necrosis factor alpha (TNFα), and aquaporin-4 in rat brain cortex at 3- and 48-hour post blast. Early immune-inflammatory response to BINT involves complement and TNFα, which correlates with hippocampus and cerebral cortex damage. Complement and TNFα activation may be a novel therapeutic target for reducing the damaging effects of BINT inflammation.

MicroRNA let-7i is a promising serum biomarker for blast-induced traumatic brain injury

Blast-induced traumatic brain injury (TBI) is of significant concern in soldiers returning from the current conflicts in Iraq and Afghanistan. Incidents of TBI have increased significantly in the current conflicts compared to previous wars, and a majority of these injuries are caused by improvised explosive devices. Currently, no specific technique or biomarker is available for diagnosing TBI when no obvious clinical symptoms are present. Micro-RNAs are small RNA (~ 22nts) molecules that are expressed endogenously and play an important role in regulating gene expression. MicroRNAs have emerged as novel serum diagnostic biomarkers for various diseases. In this study, we studied the effect of blast overpressure injury on the microRNA signatures in the serum of rats. Rats were exposed to three serial 120-kPa blast overpressure exposures through a shockwave tube. Blood and cerebrospinal fluid were collected at various time points after injury, and microRNA modulation was analyzed using real-time PCR. Five microRNAs were significantly modulated in the serum samples of these animals at three time points post-injury. Further, we also found that the levels of microRNA let-7i are also elevated in cerebrospinal fluid post-blast wave exposure. The presence of microRNA in both serum and cerebrospinal fluid immediately after injury makes microRNA let-7i an ideal candidate for further studies of biomarkers in TBI.