A closed-body preclinical model to investigate blast-induced spinal cord injury

Blast-induced spinal cord injuries (bSCI) are common and account for 75% of all combat-related spinal trauma. It remains unclear how the rapid change in pressure contributes to pathological outcomes resulting from these complex injuries. Further research is necessary to aid in specialized treatments for those affected. The purpose of this study was to develop a preclinical injury model to investigate the behavior and pathophysiology of blast exposure to the spine, which will bring further insight into outcomes and treatment decisions for complex spinal cord injuries (SCI). An Advanced Blast Simulator was used to study how blast exposure affects the spinal cord in a non-invasive manner. A custom fixture was designed to support the animal in a position that protects the vital organs while exposing the thoracolumbar region of the spine to the blast wave. The Tarlov Scale and Open Field Test (OFT) were used to detect changes in locomotion or anxiety, respectively, 72 h following bSCI. Spinal cords were then harvested and histological staining was performed to investigate markers of traumatic axonal injury (β-APP, NF-L) and neuroinflammation (GFAP, Iba1, S100β). Analysis of the blast dynamics demonstrated that this closed-body model for bSCI was found to be highly repeatable, administering consistent pressure pulses following a Friedlander waveform. There were no significant changes in acute behavior; however, expression of β-APP, Iba1, and GFAP significantly increased in the spinal cord following blast exposure (p < 0.05). Additional measures of cell count and area of positive signal provided evidence of increased inflammation and gliosis in the spinal cord at 72 h after blast injury. These findings indicated that pathophysiological responses from the blast alone are detectable, likely contributing to the combined effects. This novel injury model also demonstrated applications as a closed-body SCI model for neuroinflammation enhancing relevance of the preclinical model. Further investigation is necessary to assess the longitudinal pathological outcomes, combined effects from complex injuries, and minimally invasive treatment approaches.

Development of a Minipig Model of BINT From Blast Exposure Using a Repeatable Mobile Shock Expansion Tube

INTRODUCTION

The Office of Naval Research (ONR) sponsored the Blast Load Assessment Sense and Test (BLAST) program to provide an approach to operationally relevant monitoring and analysis of blast exposure for optimization of service member performance and health. Of critical importance in this effort was the development of a standardized methodology for preclinical large animal studies that can reliably produce outcome measures that cannot be measured in human studies to support science-based guidelines. The primary advantage of this approach is that, because animal studies report physiological measures that correlate with human neuropathology, these data can be used to evaluate potential risks to service members by accounting for the anatomical and physiological differences between humans and large animal models. This article describes the methodology used to generate a comprehensive outcome measure dataset correlated with controlled blast exposure.

METHODS AND MATERIALS

To quantify outcomes associated with a single exposure to blast, 23 age- and weight-matched Yucatan minipigs were exposed to a single blast event generated by a large-bore, compressed gas shock tube. The peak pressure ranged from 280 to 525 kPa. After a post-exposure 72-hour observation period, the physiological response was quantified using a comprehensive set of neurological outcome measures that included neuroimaging, histology, and behavioral measures. Responses of the blast-exposed animals were compared to the sham-treated cohort to identify statistically significant and physiologically relevant differences between the two groups.

RESULTS

Following a single exposure, the minipigs were assessed for structural, behavioral, and cellular changes for 3 days after exposure. The following neurological changes were observed: Structural-Using Diffusion Tensor Imaging, a statistically significant decrement (P < .001) in Fractional Anisotropy across the entire volume of the brain was observed when comparing the exposed group to the sham group. This finding indicates that alterations in brain tissue following exposure are not focused at a single location but instead a diffuse brain volume that can only be observed through a systematic examination of the neurological tissue. Cellular-The histopathology results from several large white matter tract locations showed varied cellular responses from six different stains. Using standard statistical methods, results from stains such as Fluoro-Jade C and cluster of differentiation 68 in the hippocampus showed significantly higher levels of neurodegeneration and increased microglia/macrophage activation in blast-exposed subjects. However, other stains also indicated increased response, demonstrating the need for multivariate analysis with a larger dataset. Behavioral-The behavior changes observed were typically transient; the animals' behavior returned to near baseline levels after a relatively short recovery period. Despite behavioral recovery, the presence of active neurodegenerative and inflammatory responses remained.

CONCLUSIONS

The results of this study demonstrate that (1) a shock tube provides an effective tool for generating repeatable exposures in large animals and (2) exposure to blast overpressure can be correlated using a combination of imaging, behavioral, and histological analyses. This research demonstrates the importance of using multiple physiological indicators to track blast-induced changes in minipigs. The methodology and findings from this effort were central to developing machine-learning models to inform the development of blast exposure guidelines.

MRI brain templates of the male Yucatan minipig

The pig is growing in popularity as an experimental animal because its gyrencephalic brain is similar to humans. Currently, however, there is a lack of appropriate brain templates to support functional and structural neuroimaging pipelines. The primary contribution of this work is an average volume from an iterative, non-linear registration of 70 five- to seven-month-old male Yucatan minipigs. In addition, several aspects of this study are unique, including the comparison of linear and non-linear template generation, the characterization of a large and homogeneous cohort, an analysis of effective resolution after averaging, and the evaluation of potential in-template bias as well as a comparison with a template from another minipig species using a "left-out" validation set. We found that within our highly homogeneous cohort, non-linear registration produced better templates, but only marginally so. Although our T1-weighted data were resolution limited, we preserved effective resolution across the multi-subject average, produced templates that have high gray-white matter contrast and demonstrate superior registration accuracy compared to an alternative minipig template.

Pre-Clinical Testing of Therapies for Traumatic Brain Injury

Despite the large number of promising neuroprotective agents identified in experimental traumatic brain injury (TBI) studies, none has yet shown meaningful improvements in long-term outcome in clinical trials. To develop recommendations and guidelines for pre-clinical testing of pharmacological or biological therapies for TBI, the Moody Project for Translational Traumatic Brain Injury Research hosted a symposium attended by investigators with extensive experience in pre-clinical TBI testing. The symposium participants discussed issues related to pre-clinical TBI testing including experimental models, therapy and outcome selection, study design, data analysis, and dissemination. Consensus recommendations included the creation of a manual of standard operating procedures with sufficiently detailed descriptions of modeling and outcome measurement procedures to permit replication. The importance of the selection of clinically relevant outcome variables, especially related to behavior testing, was noted. Considering the heterogeneous nature of human TBI, evidence of therapeutic efficacy in multiple, diverse (e.g., diffuse vs. focused) rodent models and a species with a gyrencephalic brain prior to clinical testing was encouraged. Basing drug doses, times, and routes of administration on pharmacokinetic and pharmacodynamic data in the test species was recommended. Symposium participants agreed that the publication of negative results would reduce costly and unnecessary duplication of unsuccessful experiments. Although some of the recommendations are more relevant to multi-center, multi-investigator collaborations, most are applicable to pre-clinical therapy testing in general. The goal of these consensus guidelines is to increase the likelihood that therapies that improve outcomes in pre-clinical studies will also improve outcomes in TBI patients.

Keratin biomaterials augment anti-inflammatory macrophage phenotype in vitro

Tissue regeneration following injury is mediated by macrophage recruitment and differentiation in response to environmental signals. In general, macrophages adopt either a classically M1 (M[IFN-γ, LPS]) or alternatively activated M2 (M[IL-4, IL-13] or M[IL-10]) phenotype. Recent studies have highlighted the importance of alternatively activated macrophages in tissue remodeling and repair as well as the contribution of an imbalance of classically and alternatively activated macrophages to tissue degeneration and disease progression. Keratin biomaterials have recently demonstrated their ability to promote alternatively activated macrophage polarization in an in vitro model using a monocytic cell line. In the present study, the ability of extracted human hair keratins to influence alternative activation of human primary monocytes in vitro is assessed by evaluating changes in surface receptor expression, inflammatory cytokine secretion, and phagocytic activity. The impact of keratin molecular weight fractionation on these outcomes was also investigated. High and low molecular weight fractions of the oxidized form of extractable human hair keratins - referred to as keratose (KOS^H and KOS^P, respectively) - were characterized by size exclusion chromatography, mass spectrometry, and Western blot. Primary macrophages underwent traditional differentiation to the M[IFN-γ, LPS], M[IL-4, IL-13], or M[IL-10]) phenotypes or were plated on different molecular weight keratin coatings (KOS^H and KOS^P). Macrophages plated on keratin and analyzed via flow cytometry yielded the largest CD163⁺ cell populations and CD163 mean fluorescence intensities. Cells in the KOS^P group were significantly more phagocytic than all other cell types at the 1.5 and 3 h time points and exhibited behavior and a cytokine production profile most similar to the M[IL-10] treated group. These findings may have important implications for understanding and evaluating the ability of keratin biomaterials to influence inflammation and tissue regeneration in disease and injury models.

STATEMENT OF SIGNIFICANCE

Biomaterials made from human hair keratins have previously been shown to elicit anti-inflammatory responses from naïve macrophages and polarize them toward an M2 phenotype. In this work we show for the first time that primary human cells respond similarly, that it is the M2c phenotype that predominates, that a sub-fraction of hydrolyzed keratin peptides are most likely responsible for the response, and that immobilization of the keratin peptides to a surface is required. Keratin biomaterials have been used to regenerate several tissues such as skin, muscle, bone, nerve, and cornea, in vitro and in animal studies. Our current findings will help guide the development of keratin-based biomaterials that seek to direct responses toward regenerative outcomes by attenuating inflammation.

Primary Blast Brain Injury Mechanisms: Current Knowledge, Limitations, and Future Directions

Mild blast traumatic brain injury (bTBI) accounts for the majority of brain injury in United States service members and other military personnel worldwide. The mechanisms of primary blast brain injury continue to be disputed with little evidence to support one or a combination of theories. The main hypotheses addressed in this review are blast wave transmission through the skull orifices, direct cranial transmission, skull flexure dynamics, thoracic surge, acceleration, and cavitation. Each possible mechanism is discussed using available literature with the goal of focusing research efforts to address the limitations and challenges that exist in blast injury research. Multiple mechanisms may contribute to the pathology of bTBI and could be dependent on magnitudes and orientation to blast exposure. Further focused biomechanical investigation with cadaver, in vivo, and finite element models would advance our knowledge of bTBI mechanisms. In addition, this understanding could guide future research and contribute to the greater goal of developing relevant injury criteria and mandates to protect our soldiers on the battlefield.

Blast overpressure induced axonal injury changes in rat brainstem and spinal cord

Introduction:

Blast induced neurotrauma has been the signature wound in returning soldiers from the ongoing wars in Iraq and Afghanistan. Of importance is understanding the pathomechansim(s) of blast overpressure (OP) induced axonal injury. Although several recent animal models of blast injury indicate the neuronal and axonal injury in various brain regions, animal studies related to axonal injury in the white matter (WM) tracts of cervical spinal cord are limited.

Objective:

The purpose of this study was to assess the extent of axonal injury in WM tracts of cervical spinal cord in male Sprague Dawley rats subjected to a single insult of blast OP.

Materials and Methods:

Sagittal brainstem sections and horizontal cervical spinal cord sections from blast and sham animals were stained by neurofilament light (NF-L) chain and beta amyloid precursor protein immunocytochemistry and observed for axonal injury changes.

Results:

Observations from this preliminary study demonstrate axonal injury changes in the form of prominent swellings, retraction bulbs, and putative signs of membrane disruptions in the brainstem and cervical spinal cord WM tracts of rats subjected to blast OP.

Conclusions:

Prominent axonal injury changes following the blast OP exposure in brainstem and cervical spinal WM tracts underscores the need for careful evaluation of blast induced injury changes and associated symptoms. NF-L immunocytochemistry can be considered as an additional tool to assess the blast OP induced axonal injury.

Two and Three-Dimensional in Vitro Models of Blast-Induced Neurotrauma

Blast-induced neurotrauma (BINT) has become an increasingly significant concern in Veterans returning from warfare. Associated brain injury and cognitive deficits are difficult to diagnose as the nature of this injury is progressive. In order to better understand the mechanisms of BINT at the microscopic level, two- and three-dimensional models of astrocytes were studied. The 3-D model was developed using Matrigel® to embed the cells. Injury was induced by exposure to an overpressure of 20 psi (140 kPa) using a shock wave generator which simulates a free field blast profile. Cellular viability was measured by MTT assays conducted at 24 and 48 hours post-blast. Gene expression levels of glial-fibrillary acidic protein (GFAP), ß-actin, and vinculin were analyzed as potential structural biomarkers of injury at 48 and 72 hours post-blast. Results indicated that glial cells survived and became activated by 72 hours following exposure. Specifically, gene expression of GFAP was elevated in simulated blast cultures as compared to controls. Moreover, 2- and 3-D cultures were observed to have different time periods of activation. These activation markers may be useful when designing therapeutic targets to mitigate injury progression.

Examining lethality risk for rodent studies of primary blast lung injury

While protective measures have been taken to mitigate injury to the thorax during a blast exposure, primary blast lung injury (PBLI) is still evident in mounted/in vehicle cases during military conflicts. Moreover, civilians, who are unprotected from blast exposure, can be severely harmed by terrorist attacks that use improvised explosive devices (IEDs). Since the lungs are the most susceptible organ due to their air-filled nature, PBLI is one of the most serious injuries seen in civilian blast cases. Determining lethality threshold for rodent studies is crucial to guide experimental designs centered on therapies for survival after PBLI or mechanistic understanding of the injury itself. Using an Advanced Blast Simulator, unprotected rats were exposed to a whole body blast to induce PBLI. The one-hour survival rate was assessed to determine operating conditions for a 50% lethality rate. Macroscopic and histological analysis of lung was conducted using hematoxylin and eosin staining. Results demonstrated lethality risk trends based on static blast overpressure (BOP) for rodent models, which may help standardized animal studies and contribute to scaling to the human level. The need for a standardized method of producing PBLI is pressing and establishing standard curves, such as a lethality risk curve for lung blasts, is crucial for this condensing of BOP methods.

IL-5; a diffuse biomarker associated with brain inflammation after blast exposure

Detailed biomolecular mechanisms underlying cognitive issues following blast exposure are unknown. Recently, studies confined to the hippocampus have shown elevated pro-inflammatory factors after blast exposure. In an attempt to understand the diffuse effects from blast, an established rodent model of blast neurotrauma was used. Animals were exposed to a peak overpressure of 117kPa, while controls animals underwent similar conditions however were not exposed to overpressure. Six brain regions were collected at 24 hours following blast and analyzed for various cytokine and chemokine levels using a multiplex bead array. Results indicated that a significant increase in IL-5 was observed in nucleus accumbens (NAC), anterior motor cortex (AMC), prefrontal cortex (PFC), and anterior striatum (AST). While other cytokines had significant variations when compared to controls (GM-CSF, TNF-a, IFN-? and IL-1a), IL-5 had a diffuse presence after blast. In addition, it was noteworthy that NAC had 17/23 cytokines elevated significantly in the blast group which may indicate that NAC is more susceptible to blast injury. Although the role of IL-5 in brain injury is unknown, it has been previously demonstrated that IL-5 is co-expressed with MCP-1 under cell death conditions to initiate the inflammatory process. We speculate that IL-5 could be a key regulator in inflammation after blast injury.

Effects of blast-induced neurotrauma on the nucleus accumbens

Blast-induced neurotrauma (BINT) leads to deterioration at the cellular level, with adverse cognitive and behavioral outcomes. The nucleus accumbens (NAC) plays an important role in reward, addiction, aggression, and fear pathways. To identify the molecular changes and pathways affected at an acute stage in the NAC, this study focused on a time course analysis to determine the effects of blast on neurochemical and apoptotic pathways. By using a rodent model of BINT, acute damage to the NAC was assessed by proton magnetic resonance spectroscopy (¹H-MRS), high-performance liquid chromatography, immunohistochemistry, and Western blotting. The results demonstrated ongoing neuroprotective effects from elevated levels of Bcl-2, an antiapoptotic marker, at 24 hr and N-acetyl aspartate glutamate at 48 hr following blast exposure. Selective loss of serotonin levels at 24 hr, increased levels of inflammation (elevated glycerophosphocholine at 48 and 72 hr), and increased levels of glial fibrillary acidic protein were also observed at 24 and 48 hr, leading to disruptive energy status. Furthermore, active cell death was indicated by the increased levels of the apoptotic marker Bax, decreased actin levels, and signs excitotoxicity (glutamate/creatine). In addition, increased levels of caspase-3, an apoptotic marker, confirm active cell death in NAC. It is hypothesized that blast overpressure causes inflammation and neurochemical changes that trigger apoptosis in NAC. This cascade of events may lead to stress-related behavioral outcomes and psychiatric sequelae.

Blast-induced tinnitus and hearing loss in rats: behavioral and imaging assays

Abstract The current study used a rat model to investigate the underlying mechanisms of blast-induced tinnitus, hearing loss, and associated traumatic brain injury (TBI). Seven rats were used to evaluate behavioral evidence of tinnitus and hearing loss, and TBI using magnetic resonance imaging following a single 10-msec blast at 14 psi or 194 dB sound pressure level (SPL). The results demonstrated that the blast exposure induced early onset of tinnitus and central hearing impairment at a broad frequency range. The induced tinnitus and central hearing impairment tended to shift towards high frequencies over time. Hearing threshold measured with auditory brainstem responses also showed an immediate elevation followed by recovery on day 14, coinciding with behaviorally-measured results. Diffusion tensor magnetic resonance imaging results demonstrated significant damage and compensatory plastic changes to certain auditory brain regions, with the majority of changes occurring in the inferior colliculus and medial geniculate body. No significant microstructural changes found in the corpus callosum indicates that the currently adopted blast exposure mainly exerts effects through the auditory pathways rather than through direct impact onto the brain parenchyma. The results showed that this animal model is appropriate for investigation of the mechanisms underlying blast-induced tinnitus, hearing loss, and related TBI. Continued investigation along these lines will help identify pathology with injury/recovery patterns, aiding development of effective treatment strategies.

Skull flexure as a contributing factor in the mechanism of injury in the rat when exposed to a shock wave

The manner in which energy from an explosion is transmitted into the brain is currently a highly debated topic within the blast injury community. This study was conducted to investigate the injury biomechanics causing blast-related neurotrauma in the rat. Biomechanical responses of the rat head under shock wave loading were measured using strain gauges on the skull surface and a fiber optic pressure sensor placed within the cortex. MicroCT imaging techniques were applied to quantify skull bone thickness. The strain gauge results indicated that the response of the rat skull is dependent on the intensity of the incident shock wave; greater intensity shock waves cause greater deflections of the skull. The intracranial pressure (ICP) sensors indicated that the peak pressure developed within the brain was greater than the peak side-on external pressure and correlated with surface strain. The bone plates between the lambda, bregma, and midline sutures are probable regions for the greatest flexure to occur. The data provides evidence that skull flexure is a likely candidate for the development of ICP gradients within the rat brain. This dependency of transmitted stress on particular skull dynamics for a given species should be considered by those investigating blast-related neurotrauma using animal models.

Autoimmunity to the M(r) 32,000 subunit of replication protein A in breast cancer

PURPOSE

We sought to identify autoantigens recognized by antibodies in breast cancer patient sera with potential diagnostic or prognostic significance.

EXPERIMENTAL DESIGN

Serum from a female breast cancer patient exhibiting a high titer antinuclear antibody was used to screen a HeLa cDNA expression library, leading to the cloning of a cDNA for the M(r) 32,000 subunit of replication protein A (RPA32). RPA32 expression and localization were assayed in autologous tumor by monoclonal antibody staining. A specific ELISA using recombinant protein was used to screen sera from 801 breast cancer patients and 65 controls.

RESULTS

A relationship between anti-replication protein A (RPA) antibodies and the ductal breast carcinoma of the proband was suggested by overexpression and aberrant localization of RPA32 in tumor cells as compared with surrounding normal ductal tissue and by the presence of anti-RPA32 antibodies before the diagnosis. The prevalence of anti-RPA32 antibodies was significantly higher (P < 0.01) among breast cancer patients (87 of 801 patients) than among noncancer controls (0 of 65 controls). Similarly, anti-RPA32 antibodies were present in 4 of 39 patients with intraductal in situ carcinoma. No associations were found between anti-RPA antibodies and survival, occurrence of a second tumor, metastases, or antibodies to p53. Reactivity to RPA32 also was detected in sera from 3 of 47 patients with other cancers.

CONCLUSIONS

In view of the central role of RPA in DNA replication, recombination, and repair, we suggest that autoimmunity to RPA32 may reflect molecular changes involved in the process of tumorigenesis. The finding of antibodies to RPA32 before diagnosis and their prevalence in in situ carcinoma suggest that they are potentially useful markers of early disease.