Trials and tribulations of using β-amyloid precursor protein immunohistochemistry to evaluate traumatic brain injury in adults

Background characteristics and neuropathology findings of medico-legal autopsy cases with and without β-amyloid precursor protein positive diffuse traumatic axonal injury

The postmortem diagnosis of diffuse traumatic axonal injury (dTAI) relies on β-amyloid precursor protein (β-APP) immunohistochemistry. Most reports of factors associating with dTAI are decades old. We compared background characteristics and neuropathology findings of today's Finnish medico-legal autopsy cases with and without β-APP-positive dTAI (dTAI+ and dTAI-, respectively). The cases had suffered a head injury prior to death and underwent a full neuropathological examination including β-APP stain. Background and circumstantial data as well as neuropathology findings were collected from police documents, medical records, and autopsy and neuropathology reports. Prevalence ratios were calculated for each factor to facilitate comparisons between the dTAI+ and dTAI- groups. The dataset comprised 57 cases (66.7% males), with 17 classified as dTAI+ and 40 as dTAI-. Based on prevalence ratios, the factors that had at least two-fold prevalence among dTAI+ cases compared to dTAI- cases were: an unknown injury mechanism; concurrent epidural or subdural haemorrhage; and an accidental manner of death. In contrast, the factors that had at least two-fold prevalence among dTAI- cases compared to dTAI+ cases were: a short postinjury survival (<30 min); concurrent intracerebral/ventricular haemorrhage or contusion; vermal atrophy; and a natural or homicidal manner of death. This study revealed differences in circumstantial features and neuropathology findings between dTAI+ and dTAI- cases in today's medico-legal autopsy material. Data on typical case profiles may help estimate the prior probability of dTAI not only in medico-legal autopsies but also among living patients with head injuries.

Temporal and structural sensitivities of major biomarkers for detecting neuropathology after traumatic brain injury in the mouse

Traumatic brain injury (TBI) is a leading cause of morbidity and mortality, especially in teenagers to young adults. In recent decades, different biomarkers and/or staining protocols have been employed to evaluate the post-injury development of pathological structures, but they have produced many contradictory findings. Since correctly identifying the underlying neuroanatomical changes is critical to advancing TBI research, we compared three commonly used markers for their ability to detect TBI pathological structures: Fluoro-Jade C, the rabbit monoclonal antibody Y188 against amyloid precursor protein and the NeuroSilver kit were used to stain adjacent slices from naïve or injured mouse brains harvested at different time points from 30 min to 3 months after lateral fluid percussion injury. Although not all pathological structures were stained by all markers at all time points, we found damaged neurons and deformed dendrites in gray matter, punctate and perivascular structures in white matter, and axonal blebs and Wallerian degeneration in both gray and white matter. The present study demonstrates the temporal and structural sensitivities of the three biomarkers: each marker is highly effective for a set of pathological structures, each of which in turn emerges at a particular time point. Furthermore, the different biomarkers showed different abilities at detecting identical types of pathological structures. In contrast to previous studies that have used a single biomarker at a single time range, the present report strongly recommends that a combination of different biomarkers should be adopted and different time points need to be checked when assessing neuropathology after TBI.

Frequent Alzheimer's disease neuropathological change in patients with glioblastoma

Background

The incidence of brain cancer and neurodegenerative diseases is increasing with a demographic shift towards aging populations. Biological parallels have been observed between glioblastoma and Alzheimer's disease (AD), which converge on accelerated brain aging. Here, we aimed to map the cooccurrence of AD neuropathological change (ADNC) in the tumor-adjacent cortex of patients with glioblastoma.

Methods

Immunohistochemical screening of AD markers amyloid beta (Abeta), amyloid precursor protein (APP), and hyperphosphorylated tau (pTau) was conducted in 420 tumor samples of 205 patients. For each cortex area, we quantified ADNC, neurons, tumor cells, and microglia.

Results

Fifty-two percent of patients (N = 106/205) showed ADNC (Abeta and pTau, Abeta or pTau) in the tumor-adjacent cortex, with histological patterns widely consistent with AD. ADNC was positively correlated with patient age and varied spatially according to Thal phases and Braak stages. It decreased with increasing tumor cell infiltration (P < .0001) and was independent of frequent expression of APP in neuronal cell bodies (N = 182/205) and in tumor necrosis-related axonal spheroids (N = 195/205; P = .46). Microglia response was most present in tumor cell infiltration plus ADNC, being further modulated by patient age and sex. ADNC did not impact patient survival in the present cohort.

Conclusions

Our findings highlight the frequent presence of ADNC in the glioblastoma vicinity, which was linked to patient age and tumor location. The cooccurrence of AD and glioblastoma seemed stochastic without clear spatial relation. ADNC did not impact patient survival in our cohort.

Detection and verification of neurodegeneration after traumatic brain injury in the mouse: Immunohistochemical staining for amyloid precursor protein

Previous studies of human traumatic brain injury (TBI) have shown diffuse axonal injury as varicosities or spheroids in white matter (WM) bundles when using immunoperoxidase-ABC staining with 22C11, a mouse monoclonal antibody against amyloid precursor protein (APP). These findings have been interpreted as TBI-induced axonal pathology. In a mouse model of TBI however, when we used immunofluorescent staining with 22C11, as opposed to immunoperoxidase staining, we did not observe varicosities or spheroids. To explore this discrepancy, we performed immunofluorescent staining with Y188, an APP knockout-validated rabbit monoclonal that shows baseline immunoreactivity in neurons and oligodendrocytes of non-injured mice, with some arranged-like varicosities. In gray matter after injury, Y188 intensely stained axonal blebs. In WM, we encountered large patches of heavily stained puncta, heterogeneous in size. Scattered axonal blebs were also identified among these Y188-stained puncta. To assess the neuronal origin of Y188 staining after TBI we made use of transgenic mice with fluorescently labeled neurons and axons. A close correlation was observed between Y188-stained axonal blebs and fluorescently labeled neuronal cell bodies/axons. By contrast, no correlation was observed between Y188-stained puncta and fluorescent axons in WM, suggesting that these puncta in WM did not originate from axons, and casting further doubt on the nature of previous reports with 22C11. As such, we strongly recommend Y188 as a biomarker for detecting damaged neurons and axons after TBI. With Y188, stained axonal blebs likely represent acute axonal truncations that may lead to death of the parent neurons. Y188-stained puncta in WM may indicate damaged oligodendrocytes, whose death and clearance can result in secondary demyelination and Wallerian degeneration of axons. We also provide evidence suggesting that 22C11-stained varicosities or spheroids previously reported in TBI patients might be showing damaged oligodendrocytes, due to a cross-reaction between the ABC kit and upregulated endogenous biotin.

Expanded ischemic lesion due to herniation leads to axonal injury in a site remote to the primary lesion on autopsy brain with acute focal cerebral ischemia

Cerebral ischemia may lead to axonal injury not only at the site of the primary lesion but also in a region remote to the site of insult. In this study, we investigated the effect of herniation on the development of axonal injury at a site remote to the primary lesion during the acute phase of cerebral ischemia. We obtained postmortem brains of 13 cases with acute phase of unilateral cerebral infarction in the territory of the internal carotid artery or middle cerebral artery and seven controls. We classified the brain tissues into herniation and non-herniation groups. Then we examined whether axonal and ischemic changes existed in the corpus callosum contralateral to the ischemic hemisphere and the upper pons. In the herniation group, we detected white-matter lesions by Klüver-Barrera staining, microglial loss by immunohistochemistry for ionized calcium-binding adaptor molecule 1, and axonal injury by immunohistochemistry for amyloid precursor protein. However, none of the aforementioned findings were observed in the non-herniation group. These findings suggest the existence of regional overlap in axonal and ischemic pathologies in remote regions in the presence of herniation. We concluded that herniation may play a significant role in the development of axonal and ischemic changes in the remote region. Our results suggest that axonal injury in a remote region may result from expanded ischemic lesions due to herniation.

Pathological Spectrum and β-APP Immunoreactivity as a Diagnostic Tool of Diffuse Axonal Injury following Traumatic Brain Injury: A Novel Classification

Aim  Different deposition patterns and grading systems used to define and identify DAI remain discordant and to date these are a challenge in clinical practice. Our main objective was to study the post-mortem axonal changes and develop a grading system to identify DAI on the basis of histopathological and immunoreactive β-amyloid precursor protein (β-APP) observations in severe TBI cases. Methods  Prospective study with 35 decedents with sTBI (GCS score ≤ 8) was conducted and samples were collected from three different sites-corpus callosum, thalamus and brain stem. Serial sections from each site were stained with hematoxylin and eosin (H&E), and immunohistochemistry (IHC) of β-APP. Results  We developed a grading system based on histopathological characteristics to assess the overall damage of axonal injury. We found maximum histopathological changes in cases with prolonged stay. Corpus callosum showed maximum changes in both gradings. Curiously, we also detected axonal swellings with H&E staining. Usually neglected, the thalamus also showed significant histopathological and immunoreactive changes for sTBI. Conclusion  Our study based on histopathological and β-APP scoring system to define and identify DAI thus facilitates accurate diagnosis of DAI post mortem, which has forensic implications, and may further contribute toward survival and improvement of quality of life of sTBI patients.

Traumatic axonal injury: neuropathological features, postmortem diagnostic methods, and strategies

Traumatic brain injury (TBI) has high morbidity and poor prognosis and imposes a serious socioeconomic burden. Traumatic axonal injury (TAI), which is one of the common pathological changes in the primary injury of TBI, is often caused by the external force to the head that causes the white matter bundles to generate shear stress and tension; resulting in tissue damage and leading to the cytoskeletal disorder. At present, the forensic pathological diagnosis of TAI-caused death is still a difficult problem. Most of the TAI biomarkers studied are used for the prediction, evaluation, and prognosis of TAI in the living state. The research subjects are mainly humans in the living state or model animals, which are not suitable for the postmortem diagnosis of TAI. In addition, there is still a lack of recognized indicators for the autopsy pathological diagnosis of TAI. Different diagnostic methods and markers have their limitations, and there is a lack of systematic research and summary of autopsy diagnostic markers of TAI. Therefore, this study mainly summarizes the pathological mechanism, common methods, techniques of postmortem diagnosis, and corresponding biomarkers of TAI, and puts forward the strategies for postmortem diagnosis of TAI for forensic cases with different survival times, which is of great significance to forensic pathological diagnosis.

Distribution of amyloid-β precursor protein-immunoreactive axons differs according to the severity of cerebral ischemia in autopsy brains

Amyloid-β precursor protein (APP) immunohistochemistry has been used to detect axonal injury in forensic neuropathology. However, axonal injury caused by cerebral ischemia has not been investigated by APP immunohistochemistry in detail. In particular, it is unknown if there is a correlation between the prognosis of cerebral ischemia and the distribution of axonal injury detected by APP immunohistochemistry. To address this issue, we compared the distribution of APP-immunoreactive axons in autopsy brains including lesions of acute phase of cerebral infarction in the territory of the middle cerebral artery (MCA) or internal carotid artery (ICA) with the degree of severity. The presence or absence of a midline shift was used as an indicator of the severity of cerebral ischemia. We identified a difference in the distribution of APP-immunoreactive axons between cases with and without a midline shift. In both the groups, APP-immunoreactive axons were detected at the margin of the ischemic lesions; however, only in cases with a midline shift, intense APP-immunoreactive axons were also found in areas other than the MCA and ICA territories, including the white matter of the cerebral hemispheres ipsilateral and contralateral to the ischemic lesions. This distribution was different from that of acute global cerebral ischemia cases reported previously. Our results indicate that the distribution of APP-immunoreactive axons differs according to the severity and type of cerebral ischemia, suggesting that the distribution of APP-immunoreactive axons is associated with the prognosis of cerebral ischemia.

Axonal injury is detected by βAPP immunohistochemistry in rapid death from head injury following road traffic collision

The accumulation of βAPP caused by axonal injury is an active energy-dependent process thought to require blood circulation; therefore, it is closely related to the post-injury survival time. Currently, the earliest reported time at which axonal injury can be detected in post-mortem traumatic brain injury (TBI) tissue by βAPP (Beta Amyloid Precursor Protein) immunohistochemistry is 35 min. The aim of this study is to investigate whether βAPP staining for axonal injury can be detected in patients who died rapidly after TBI in road traffic collision (RTC), in a period of less than 30 min.

We retrospectively studied thirty-seven patients (group 1) died very rapidly at the scene; evidenced by forensic assessment of injuries short survival, four patients died after a survival period of between 31 min and 12 h (group 2) and eight patients between 2 and 31 days (group 3). The brains were comprehensively examined and sampled at the time of the autopsy, and βAPP immunohistochemistry carried out on sections from a number of brain areas.

βAPP immunoreactivity was demonstrated in 35/37 brains in group 1, albeit with a low frequency and in a variable pattern, and with more intensity and frequency in all brains of group 2 and 7/8 brains from group 3, compared with no similar βAPP immunoreactivity in the control group. The results suggest axonal injury can be detected in those who died rapidly after RTC in a period of less than 30 min, which can help in the diagnosis of severe TBI with short survival time.

[Problems of forensic diagnosis of diffuse axonal brain injury in the acute post-traumatic period]

The article refers to actual problems of forensic diagnostics of diffuse axonal brain injury in the acute post-traumatic period, that is of particular importance in the case of head trauma in conditions of non-evidence. To solve the existing problems, it is necessary to conduct a comprehensive study aimed at improving the diffuse axonal brain injury examination by developing a unified methodological approach to running the forensic medical diagnostics of this form of traumatic brain injury and determining the duration of the acute (up to three days) post-traumatic period.

Heterogeneous immunoreactivity of axonal spheroids in focal symmetrical encephalomalacia produced by Clostridium perfringens type D epsilon toxin in sheep

Since axonal injury (AI) is an important component of many veterinary neurologic disorders, we assessed the relative ability of a panel of antibodies (amyloid precursor protein, 3 subunits of neurofilament protein, protein gene product 9.5, ubiquitin, and synaptophysin) to detect axonal swellings or spheroids. Abundant axonal spheroids found in necrotic internal capsule foci produced in 4 sheep by chronic Clostridium perfringens type D epsilon neurotoxicity provided a model system in which to evaluate this important diagnostic tool. There was heterogeneous labeling of subsets of spheroids by the respective antibodies, suggesting that, in order to detect the complete spectrum of AI in diagnostic cases, a range of antibodies should be used, not only when spheroids are plentiful but also when they are few in number or incompletely developed. The application of insufficient markers in the latter cases can potentially lead to the contribution of AI to lesion pathogenesis being underappreciated.

CLARITY reveals a more protracted temporal course of axon swelling and disconnection than previously described following traumatic brain injury

Diffuse axonal injury (DAI) is an important consequence of traumatic brain injury (TBI). At the moment of trauma, axons rarely disconnect, but undergo cytoskeletal disruption and transport interruption leading to protein accumulation within swellings. The amyloid precursor protein (APP) accumulates rapidly and the standard histological evaluation of axonal pathology relies upon its detection. APP+ swellings first appear as varicosities along intact axons, which can ultimately undergo secondary disconnection to leave a terminal "axon bulb" at the disconnected, proximal end. However, sites of disconnection are difficult to determine with certainty using standard, thin tissue sections, thus limiting the comprehensive evaluation of axon degeneration. The tissue-clearing technique, CLARITY, permits three-dimensional visualization of axons that would otherwise be out of plane in standard tissue sections. Here, we examined the morphology and connection status of APP+ swellings using CLARITY at 6 h, 24 h, 1 week and 1 month following the controlled cortical impact (CCI) model of TBI in mice. Remarkably, many APP+ swellings that appeared as terminal bulbs when viewed in standard 8-µm-thick regions of tissue were instead revealed to be varicose swellings along intact axons when three dimensions were fully visible. Moreover, the percentage of these potentially viable axon swellings differed with survival from injury and may represent the delayed onset of distinct mechanisms of degeneration. Even at 1-month post-CCI, ~10% of apparently terminal bulbs were revealed as connected by CLARITY and are thus potentially salvageable. Intriguingly, the diameter of swellings decreased with survival, including varicosities along intact axons, and may reflect reversal of, or reduced, axonal transport interruption in the chronic setting. These data indicate that APP immunohistochemistry on standard thickness tissue sections overestimates axon disconnection, particularly acutely post-injury. Evaluating cleared tissue demonstrates a surprisingly delayed process of axon disconnection and thus longer window of therapeutic opportunity than previously appreciated. Intriguingly, a subset of axon swellings may also be capable of recovery.

Traumatic axonal injury revealed by postmortem magnetic resonance imaging: A case report

In forensic investigations, it is important to detect traumatic axonal injuries (TAIs) to reveal head trauma that might otherwise remain occult. These lesions are subtle and frequently ambiguous on macroscopic evaluations. We present a case of TAI revealed by pre-autopsy postmortem magnetic resonance imaging (PMMR). A man in his sixties was rendered unconscious in a motor vehicle accident. CT scans revealed traumatic mild subarachnoid hemorrhage. Two weeks after the accident he regained consciousness, but displayed an altered mental state. Seven weeks after the accident, he suddenly died in hospital. Postmortem computed tomography (PMCT) and PMMR were followed by a forensic autopsy. PMMR showed low-intensity lesions in parasagittal white matter, deep white matter, and corpus callosum on three-dimensional gradient-echo T1-weighted imaging (3D-GRE T1WI). In some of these lesions, T2∗-weighted imaging also showed low-intensity foci suggesting hemorrhagic axonal injury. The lesions were difficult to find on PMCT and macroscopic evaluation, but were visible on antemortem MRI and confirmed as TAIs on histopathology. From this case, it can be said that PMMR can detect subtle TAIs missed by PMCT and macroscopic evaluation. Hence, pre-autopsy PMMR scanning could be useful for identifying TAIs during forensic investigations.

Histology of Brain Trauma and Hypoxia-Ischemia

Forensic pathologists encounter hypoxic-ischemic (HI) brain damage or traumatic brain injuries (TBI) on an almost daily basis. Evaluation of the findings guides decisions regarding cause and manner of death. When there are gross findings of brain trauma, the cause of death is often obvious. However, microscopic evaluation should be used to augment the macroscopic diagnoses. Histology can be used to seek evidence for TBI in the absence of gross findings, e.g., in the context of reported or suspected TBI. Estimating the survival interval after an insult is often of medicolegal interest; this requires targeted tissue sampling and careful histologic evaluation. Retained tissue blocks serve as forensic evidence and also provide invaluable teaching and research material. In certain contexts, histology can be used to demonstrate nontraumatic causes of seemingly traumatic lesions. Macroscopic and histologic findings of brain trauma can be confounded by concomitant HI brain injury when an individual survives temporarily after TBI. Here we review the histologic approaches for evaluating TBI, hemorrhage, and HI brain injury. Amyloid precursor protein (APP) immunohistochemistry is helpful for identifying damaged axons, but patterns of damage cannot unambiguously distinguish TBI from HI. The evolution of hemorrhagic lesions will be discussed in detail; however, timing of any lesion is at best approximate. It is important to recognize artifactual changes (e.g., dark neurons) that can resemble HI damage. Despite the shortcomings, histology is a critical adjunct to the gross examination of brains.

Mechanical disruption of the blood-brain barrier following experimental concussion

Although concussion is now recognized as a major health issue, its non-lethal nature has limited characterization of the underlying pathophysiology. In particular, potential neuropathological changes have typically been inferred from non-invasive techniques or post-mortem examinations of severe traumatic brain injury (TBI). Here, we used a swine model of head rotational acceleration based on human concussion to examine blood-brain barrier (BBB) integrity after injury in association with diffuse axonal injury and glial responses. We then determined the potential clinical relevance of the swine concussion findings through comparisons with pathological changes in human severe TBI, where post-mortem examinations are possible. At 6-72 h post-injury in swine, we observed multifocal disruption of the BBB, demonstrated by extravasation of serum proteins, fibrinogen and immunoglobulin-G, in the absence of hemorrhage or other focal pathology. BBB disruption was observed in a stereotyped distribution consistent with biomechanical insult. Specifically, extravasated serum proteins were frequently observed at interfaces between regions of tissue with differing material properties, including the gray-white boundary, periventricular and subpial regions. In addition, there was substantial overlap of BBB disruption with regions of axonal pathology in the white matter. Acute perivascular cellular uptake of blood-borne proteins was observed to be prominent in astrocytes (GFAP-positive) and neurons (MAP-2-positive), but not microglia (IBA1-positive). Parallel examination of human severe TBI revealed similar patterns of serum extravasation and glial uptake of serum proteins, but to a much greater extent than in the swine model, attributed to the higher injury severity. These data suggest that BBB disruption represents a new and important pathological feature of concussion.

Neurotrauma

Traumatic brain injury remains a major cause of morbidity and mortality throughout the world, affecting young and old alike. Pathologic data have been developed through observations of human autopsies and developing animal models to investigate mechanisms, although animal models do not represent the polypathology of human brain injury and there are likely to be significant differences in the anatomic basis of injury and cellular responses between species. Traumatic brain injury can be defined pathologically as either focal or diffuse, and can be considered to be either primary, directly related to the force associated with the neurotrauma, or secondary, developing as a downstream consequence of the neurotrauma. While neuropathology has traditionally focused on severe head injury, there is increasing recognition of the long-term consequences of traumatic brain injury, particularly repetitive mild traumatic brain injury, and a possible long-term association with chronic traumatic encephalopathy.

Diffuse Axonal Injury and Oxidative Stress: A Comprehensive Review

Traumatic brain injury (TBI) is one of the world’s leading causes of morbidity and mortality among young individuals. TBI applies powerful rotational and translational forces to the brain parenchyma, which results in a traumatic diffuse axonal injury (DAI) responsible for brain swelling and neuronal death. Following TBI, axonal degeneration has been identified as a progressive process that starts with disrupted axonal transport causing axonal swelling, followed by secondary axonal disconnection and Wallerian degeneration. These modifications in the axonal cytoskeleton interrupt the axoplasmic transport mechanisms, causing the gradual gathering of transport products so as to generate axonal swellings and modifications in neuronal homeostasis. Oxidative stress with consequent impairment of endogenous antioxidant defense mechanisms plays a significant role in the secondary events leading to neuronal death. Studies support the role of an altered axonal calcium homeostasis as a mechanism in the secondary damage of axon, and suggest that calcium channel blocker can alleviate the secondary damage, as well as other mechanisms implied in the secondary injury, and could be targeted as a candidate for therapeutic approaches. Reactive oxygen species (ROS)-mediated axonal degeneration is mainly caused by extracellular Ca²⁺. Increases in the defense mechanisms through the use of exogenous antioxidants may be neuroprotective, particularly if they are given within the neuroprotective time window. A promising potential therapeutic target for DAI is to directly address mitochondria-related injury or to modulate energetic axonal energy failure.

Application of FTIR spectroscopy for traumatic axonal injury: a possible tool for estimating injury interval

Traumatic axonal injury (TAI) is a progressive and secondary injury following traumatic brain injury (TBI). Despite extensive investigations in the field of forensic science and neurology, no effective methods are available to estimate TAI interval between injury and death. In the present study, Fourier transform IR (FTIR) spectroscopy with IR microscopy was applied to collect IR spectra in the corpus callosum (CC) of rats subjected to TAI at 12, 24, and 72 h post-injury compared with control animals. The classification amongst different groups was visualized based on the acquired dataset using hierarchical cluster analysis (HCA) and partial least square (PLS). Furthermore, the established PLS models were used to predict injury interval of TAI in the unknown sample dataset. The results showed that samples at different time points post-injury were distinguishable from each other, and biochemical changes in protein, lipid, and carbohydrate contributed to the differences. Then, the established PLS models provided a satisfactory prediction of injury periods between different sample groups in the external validation. The present study demonstrated the great potential of FTIR-based PLS algorithm as an objective tool for estimating injury intervals of TAI in the field of forensic science and neurology.

Extent of impaired axoplasmic transport and neurofilament compaction in traumatically injured axon at various strains and strain rates

PRIMARY OBJECTIVE

Secondary axotomy is more prevalent than the primary axotomy and involves subtle intraaxonal changes in response to the injury leading to cytoskeletal disruptions including neurofilament (NF) misalignment and compaction, which is associated with the genesis of impaired axoplasmic transport (IAT). Recent studies have reported two differential axonal responses to injury, one associated with the cytoskeletal collapse and another with the IAT. The objective of this study was to determine the extent of IAT and early NF changes in axons that were subjected to a stretch of various degrees at different strain rates.

RESEARCH DESIGN AND METHODS

Fifty-six L5 dorsal spinal nerve roots were subjected to a predetermined strain at a specified displacement rate (0.01 and 15 mm/second) only once. The histological changes were determined by performing standard immunohistochemical procedures using beta amyloid precursor protein (β APP) and NF-68 kDa antibodies.

RESULTS AND CONCLUSIONS

No significant differences in the occurrence rate of either of the staining in the axons were observed when subjected to similar loading conditions, and the occurrence rate of both β APP and NF68 staining was strain and rate-dependent.

Traumatic axonal injury, a clinical-pathological correlation

Traumatic axonal injury (TAI) is a distinct clinicopathological entity that can cause serious impairment of the brain function and can sometimes be found as a concrete cause of death. It has been discussed from the perspective of its biomechanical importance, and also from the standpoint of certain criteria for the pathological diagnosis of TAI. However, since the time when DAI (diffuse axonal injury) was initially described, there have been few, if any, discussions about the clinical-pathological correlation in TAI. This paper is an attempt to address this issue. For the purpose of certain pathological diagnoses of TAI, 63 cases with closed head injuries have been subjected to the complete forensic-neuropathological examination, involving immunohistochemistry with antibody against β-APP. In the diagnosis of TAI strict criteria have been followed. Then, retrograde analysis of the clinical parameters has been performed in order to determine some clinical-pathological correlation. The following two most reliable parameters of the impairment of the brain function have been analyzed: the impairment of the consciousness and the time of survival. Comparing the two groups, the one with TAI and the other without TAI, and using appropriate statistical evaluation, our results show that TAI is not a significant contributing factor to the lethal outcome in the early post injury period (24 h), but it is undoubtedly a contributing factor for the severe impairment of the brain function indicated through the status of the consciousness.

A Conceptual Overview of Axonopathy in Infants and Children with Allegedly Inflicted Head Trauma

Fatal, allegedly inflicted pediatric head trauma remains a controversial topic in forensic pathology. Recommendations for systematic neuropathologic evaluation of the brains of supposedly injured infants and children usually include the assessment of long white matter tracts in search of axonopathy - specifically, diffuse axonal injury. The ability to recognize, document, and interpret injuries to axons has significant academic and medicolegal implications. For example, more than two decades of inconsistent nosology have resulted in confusion about the definition of diffuse axonal injury between various medical disciplines including radiology, neurosurgery, pediatrics, neuropathology, and forensic pathology. Furthermore, in the pediatric setting, acceptance that "pure" shaking can cause axonal shearing in infants and young children is not widespread. Additionally, controversy abounds whether or not axonal trauma can be identified within regions of white matter ischemia - a debate with very significant implications. Immunohistochemistry is often used not only to document axonal injury, but also to estimate the time since injury. As a result, the estimated post-injury interval may then be used by law enforcement officers and prosecutors to narrow "exclusive opportunity" and thus, identify potential suspects. Fundamental to these highly complicated and controversial topics is a philosophical understanding of the diffuse axonal injury spectrum disorders.

Diffuse Axonal Injury-A Distinct Clinicopathological Entity in Closed Head Injuries

The knowledge about the diffuse axonal injury (DAI) as a clinicopathological entity has matured in the last 30 years. It has been defined clinically (immediate and prolonged unconsciousness leading to death or severe disability) and pathologically (the triad of DAI specific changes). In terms of its biomechanics, DAI is occurring as a result of acceleration forces of longer duration and has been fully reproduced experimentally.In the process of diagnosing DAI, the performance of a complete forensic neuropathological examination is essential and the immunohistochemistry method using antibodies against β-amyloid precursor protein (β-APP) has been proved to be highly sensitive and specific, selectively targeting the damaged axons.In this review, we are pointing to the significant characteristics of DAI as a distinct clinicopathological entity that can cause severe impairment of the brain function, and in the forensic medicine setting, it can be found as the concrete cause of death. We are discussing not only its pathological feature, its mechanism of occurrence, and the events on a cellular level but also the dilemmas about DAI that still exist in science: (1) regarding the strict criteria for its diagnosis and (2) regarding its biomechanical significance, which can be of a big medicolegal importance.

Axonal Injury in Stroke: A Forensic Neuropathology Perspective

The use of β-amyloid precursor protein (β-APP) immunocytochemistry is standard practice in forensic neuropathology to assess the presence and severity of traumatic axonal injury. However, axonal injury has many causes, in addition to trauma. The principal complicating factor in interpretation is where traumatic brain injury is associated with brain swelling or hemorrhage, resulting in ischemic axonal injury. Although it has been claimed that different patterns of β-APP immunoreactivity are seen in trauma, as opposed to hypoxia-ischemia, there have been few systematic studies of β-APP immunostaining patterns in ischemic or hemorrhagic stroke. This study investigated staining patterns in 96 cases of stroke with no history of head injury and found complex staining patterns, some of which were indistinguishable from those said to be specific for trauma. A questioning approach to the assessment of β-APP immunostaining patterns in cases of head injury is proposed to ensure that the possibility of some or much of the staining being due to ischemia has been excluded, before concluding that the axonal injury identified is traumatic in causation.

Interleukin (IL)-8 immunoreactivity of injured axons and surrounding oligodendrocytes in traumatic head injury

Interleukin (IL)-8 has been suggested to be a positive regulator of myelination in the central nervous system, in addition to its principal role as a chemokine for neutrophils. Immunostaining for beta-amyloid precursor protein (AβPP) is an effective tool for detecting traumatic axonal injury, although AβPP immunoreactivity can also indicate axonal injury due to hypoxic causes. In this study, we examined IL-8 and AβPP immunoreactivity in sections of corpus callosum obtained from deceased patients with blunt head injury and from equivalent control tissue. AβPP immunoreactivity was detected in injured axons, such as axonal bulbs and varicose axons, in 24 of 44 head injury cases. These AβPP immunoreactive cases had survived for more than 3h. The AβPP immunostaining pattern can be classified into two types: traumatic (Pattern 1) and non-traumatic (Pattern 2) axonal injuries, which we described previously [Hayashi et al. Int. J. Legal Med. 129 (2015) 1085-1090]. Three of 44 control cases also showed AβPP immunoreactive injured axons as Pattern 2. In contrast, IL-8 immunoreactivity was detected in 7 AβPP immunoreactive and in 2 non-AβPP immunoreactive head injury cases, but was not detected in any of the 44 control cases, including the 3 AβPP immunoreactive control cases. The IL-8 immunoreactive cases had survived from 3 to 24 days, whereas those cases who survived less than 3 days (n=29) and who survived 90 days (n=1) were not IL-8 immunoreactive. Moreover, IL-8 was detected as Pattern 1 axons only. In addition, double immunofluorescence analysis showed that IL-8 is expressed by oligodendrocytes surrounding injured axons. In conclusion, our results suggest that immunohistochemical detection of IL-8 may be useful as a complementary diagnostic marker of traumatic axonal injury.

Cerebral amyloid-β accumulation and deposition following traumatic brain injury--A narrative review and meta-analysis of animal studies

Traumatic brain injury (TBI) increases the risk of neurodegenerative disorders many years post-injury. However, molecular mechanisms underlying the relationship between TBI and neurodegenerative diseases, such as Alzheimer's disease (AD), remain to be elucidated. Nevertheless, previous studies have demonstrated a link between TBI and increased amyloid-β (Aβ), a protein involved in AD pathogenesis. Here, we review animal studies that measured Aβ levels following TBI. In addition, from a pool of initially identified 1209 published papers, we examined data from 19 eligible animal model studies using a meta-analytic approach. We found an acute increase in cerebral Aβ levels ranging from 24h to one month following TBI (overall log OR=2.97 ± 0.40, p<0.001). These findings may contribute to further understanding the relationship between TBI and future dementia risk. The methodological inconsistencies of the studies discussed in this review suggest the need for improved and more standardised data collection and study design, in order to properly elucidate the role of TBI in the expression and accumulation of Aβ.

SNTF immunostaining reveals previously undetected axonal pathology in traumatic brain injury

Diffuse axonal injury (DAI) is a common feature of severe traumatic brain injury (TBI) and may also be a predominant pathology in mild TBI or "concussion". The rapid deformation of white matter at the instant of trauma can lead to mechanical failure and calcium-dependent proteolysis of the axonal cytoskeleton in association with axonal transport interruption. Recently, a proteolytic fragment of alpha-II spectrin, "SNTF", was detected in serum acutely following mild TBI in patients and was prognostic for poor clinical outcome. However, direct evidence that this fragment is a marker of DAI has yet to be demonstrated in either humans following TBI or in models of mild TBI. Here, we used immunohistochemistry (IHC) to examine for SNTF in brain tissue following both severe and mild TBI. Human severe TBI cases (survival <7d; n = 18) were compared to age-matched controls (n = 16) from the Glasgow TBI archive. We also examined brains from an established model of mild TBI at 6, 48 and 72 h post-injury versus shams. IHC specific for SNTF was compared to that of amyloid precursor protein (APP), the current standard for DAI diagnosis, and other known markers of axonal pathology including non-phosphorylated neurofilament-H (SMI-32), neurofilament-68 (NF-68) and compacted neurofilament-medium (RMO-14) using double and triple immunofluorescent labeling. Supporting its use as a biomarker of DAI, SNTF immunoreactive axons were observed at all time points following both human severe TBI and in the model of mild TBI. Interestingly, SNTF revealed a subpopulation of degenerating axons, undetected by the gold-standard marker of transport interruption, APP. While there was greater axonal co-localization between SNTF and APP after severe TBI in humans, a subset of SNTF positive axons displayed no APP accumulation. Notably, some co-localization was observed between SNTF and the less abundant neurofilament subtype markers. Other SNTF positive axons, however, did not co-localize with any other markers. Similarly, RMO-14 and NF-68 positive axonal pathology existed independent of SNTF and APP. These data demonstrate that multiple pathological axonal phenotypes exist post-TBI and provide insight into a more comprehensive approach to the neuropathological assessment of DAI.

Two different immunostaining patterns of beta-amyloid precursor protein (APP) may distinguish traumatic from nontraumatic axonal injury

Immunostaining for beta-amyloid precursor protein (APP) is recognized as an effective tool for detecting traumatic axonal injury, but it also detects axonal injury due to ischemic or other metabolic causes. Previously, we reported two different patterns of APP staining: labeled axons oriented along with white matter bundles (pattern 1) and labeled axons scattered irregularly (pattern 2) (Hayashi et al. (Leg Med (Tokyo) 11:S171-173, 2009). In this study, we investigated whether these two patterns are consistent with patterns of trauma and hypoxic brain damage, respectively. Sections of the corpus callosum from 44 cases of blunt head injury and equivalent control tissue were immunostained for APP. APP was detected in injured axons such as axonal bulbs and varicose axons in 24 of the 44 cases of head injuries that also survived for three or more hours after injury. In 21 of the 24 APP-positive cases, pattern 1 alone was observed in 14 cases, pattern 2 alone was not observed in any cases, and both patterns 1 and 2 were detected in 7 cases. APP-labeled injured axons were detected in 3 of the 44 control cases, all of which were pattern 2. These results suggest that pattern 1 indicates traumatic axonal injury, while pattern 2 results from hypoxic insult. These patterns may be useful to differentiate between traumatic and nontraumatic axonal injuries.

Expression of amyloid-β protein and amyloid-β precursor protein after primary brain-stem injury in rats

Amyloid-β (Aβ) protein and its precursor, amyloid-β precursor protein (β-APP), have traditionally been used in the diagnosis of Alzheimer disease. Their use in diagnosis of traumatic brain injury by forensic analysis is becoming more widespread. However, to date, no reliable small animal model exists to evaluate these brain injury indicators. To address this, we have studied primary brain-stem injury in rats to assess the appearance of diffuse axonal injury in brain sections and correlate these findings with appearance of Aβ and relative β-APP mRNA levels. Using an EnVision 2-step immunohistochemical staining method to measure axon diameter, we found that there was significant difference in axon diameters within the medulla oblongata and several time points after brain injury, ranging from 3 to 24 hours. In addition, mRNA expression levels of β-APP increased following brain injury, peaking 3 hours following injury and decreasing back to baseline levels by 24 hours after injury. These results suggest that using immunohistochemistry and reverse transcription-polymerase chain reaction to detect changes in Aβ-associated axonal changes and β-APP mRNA levels, respectively, can be useful for the diagnosis of diffuse axonal injury during autopsy at early time points following fatal brain injury.

Decompressive craniectomy reduces white matter injury after controlled cortical impact in mice

Reduction and avoidance of increases in intracranial pressure (ICP) after severe traumatic brain injury (TBI) continue to be the mainstays of treatment. Traumatic axonal injury is a major contributor to morbidity after TBI, but it remains unclear whether elevations in ICP influence axonal injury. Here we tested the hypothesis that reduction in elevations in ICP after experimental TBI would result in decreased axonal injury and white matter atrophy in mice. Six-week-old male mice (C57BL/6J) underwent either moderate controlled cortical impact (CCI) (n=48) or Sham surgery (Sham, n=12). Immediately after CCI, injured animals were randomized to a loose fitting plastic cap (Open) or replacement of the previously removed bone flap (Closed). Elevated ICP was observed in Closed animals compared with Open and Sham at 15 min (21.4±4.2 vs. 12.3±2.9 and 8.8±1.8 mm Hg, p<0.0001) and 1 day (17.8±3.7 vs. 10.6±2.0 and 8.9±1.9 mm Hg, p<0.0001) after injury. Beta amyloid precursor protein staining in the corpus callosum and ipsilateral external capsule revealed reduced axonal swellings and bulbs in Open compared with Closed animals (32% decrease, p<0.01 and 40% decrease, p<0.001 at 1 and 7 days post-injury, respectively). Open animals were also found to have decreased neurofilament-200 stained axonal swellings at 7 days post-injury compared with Open animals (32% decrease, p<0.001). At 4 weeks post-injury, Open animals had an 18% reduction in white matter volume compared with 34% in Closed animals (p<0.01). Thus, our results indicate that CCI with decompressive craniectomy was associated with reductions in ICP and reduced pericontusional axonal injury and white matter atrophy. If similar in humans, therapeutic interventions that ameliorate intracranial hypertension may positively influence white matter injury severity.

Forensic molecular pathology: its impacts on routine work, education and training

The major role of forensic pathology is the investigation of human death in relevance to social risk management to determine the cause and process of death, especially in violent and unexpected sudden deaths, which involve social and medicolegal issues of ultimate, personal and public concerns. In addition to the identification of victims and biological materials, forensic molecular pathology contributes to general explanation of the human death process and assessment of individual death on the basis of biological molecular evidence, visualizing dynamic functional changes involved in the dying process that cannot be detected by morphology (pathophysiological or molecular biological vital reactions); the genetic background (genomics), dynamics of gene expression (up-/down-regulation: transcriptomics) and vital phenomena, involving activated biological mediators and degenerative products (proteomics) as well as metabolic deterioration (metabolomics), are detected by DNA analysis, relative quantification of mRNA transcripts using real-time reverse transcription-PCR (RT-PCR), and immunohisto-/immunocytochemistry combined with biochemistry, respectively. Thus, forensic molecular pathology involves the application of omic medical sciences to investigate the genetic basis, and cause and process of death at the biological molecular level in the context of forensic pathology, that is, 'advanced molecular autopsy'. These procedures can be incorporated into routine death investigations as well as guidance, education and training programs in forensic pathology for 'dynamic assessment of the cause and process of death' on the basis of autopsy and laboratory data. Postmortem human data can also contribute to understanding patients' critical conditions in clinical management.

Axonal pathology in traumatic brain injury

Over the past 70years, diffuse axonal injury (DAI) has emerged as one of the most common and important pathological features of traumatic brain injury (TBI). Axons in the white matter appear to be especially vulnerable to injury due to the mechanical loading of the brain during TBI. As such, DAI has been found in all severities of TBI and may represent a key pathologic substrate of mild TBI (concussion). Pathologically, DAI encompasses a spectrum of abnormalities from primary mechanical breaking of the axonal cytoskeleton, to transport interruption, swelling and proteolysis, through secondary physiological changes. Depending on the severity and extent of injury, these changes can manifest acutely as immediate loss of consciousness or confusion and persist as coma and/or cognitive dysfunction. In addition, recent evidence suggests that TBI may induce long-term neurodegenerative processes, such as insidiously progressive axonal pathology. Indeed, axonal degeneration has been found to continue even years after injury in humans, and appears to play a role in the development of Alzheimer's disease-like pathological changes. Here we review the current understanding of DAI as a uniquely mechanical injury, its histopathological identification, and its acute and chronic pathogenesis following TBI.

Disconnection of the ascending arousal system in traumatic coma

Traumatic coma is associated with disruption of axonal pathways throughout the brain, but the specific pathways involved in humans are incompletely understood. In this study, we used high angular resolution diffusion imaging to map the connectivity of axonal pathways that mediate the 2 critical components of consciousness-arousal and awareness-in the postmortem brain of a 62-year-old woman with acute traumatic coma and in 2 control brains. High angular resolution diffusion imaging tractography guided tissue sampling in the neuropathologic analysis. High angular resolution diffusion imaging tractography demonstrated complete disruption of white matter pathways connecting brainstem arousal nuclei to the basal forebrain and thalamic intralaminar and reticular nuclei. In contrast, hemispheric arousal pathways connecting the thalamus and basal forebrain to the cerebral cortex were only partially disrupted, as were the cortical "awareness pathways." Neuropathologic examination, which used β-amyloid precursor protein and fractin immunomarkers, revealed axonal injury in the white matter of the brainstem and cerebral hemispheres that corresponded to sites of high angular resolution diffusion imaging tract disruption. Axonal injury was also present within the gray matter of the hypothalamus, thalamus, basal forebrain, and cerebral cortex. We propose that traumatic coma may be a subcortical disconnection syndrome related to the disconnection of specific brainstem arousal nuclei from the thalamus and basal forebrain.

Therapy development for diffuse axonal injury

Diffuse axonal injury (DAI) remains a prominent feature of human traumatic brain injury (TBI) and a major player in its subsequent morbidity. The importance of this widespread axonal damage has been confirmed by multiple approaches including routine postmortem neuropathology as well as advanced imaging, which is now capable of detecting the signatures of traumatically induced axonal injury across a spectrum of traumatically brain-injured persons. Despite the increased interest in DAI and its overall implications for brain-injured patients, many questions remain about this component of TBI and its potential therapeutic targeting. To address these deficiencies and to identify future directions needed to fill critical gaps in our understanding of this component of TBI, the National Institute of Neurological Disorders and Stroke hosted a workshop in May 2011. This workshop sought to determine what is known regarding the pathogenesis of DAI in animal models of injury as well as in the human clinical setting. The workshop also addressed new tools to aid in the identification of this axonal injury while also identifying more rational therapeutic targets linked to DAI for continued preclinical investigation and, ultimately, clinical translation. This report encapsulates the oral and written components of this workshop addressing key features regarding the pathobiology of DAI, the biomechanics implicated in its initiating pathology, and those experimental animal modeling considerations that bear relevance to the biomechanical features of human TBI. Parallel considerations of alternate forms of DAI detection including, but not limited to, advanced neuroimaging, electrophysiological, biomarker, and neurobehavioral evaluations are included, together with recommendations for how these technologies can be better used and integrated for a more comprehensive appreciation of the pathobiology of DAI and its overall structural and functional implications. Lastly, the document closes with a thorough review of the targets linked to the pathogenesis of DAI, while also presenting a detailed report of those target-based therapies that have been used, to date, with a consideration of their overall implications for future preclinical discovery and subsequent translation to the clinic. Although all participants realize that various research gaps remained in our understanding and treatment of this complex component of TBI, this workshop refines these issues providing, for the first time, a comprehensive appreciation of what has been done and what critical needs remain unfulfilled.

Two patterns of beta-amyloid precursor protein (APP) immunoreactivity in cases of blunt head injury

Immunostaining for beta-amyloid precursor protein (APP) is widely recognized as an effective tool for detecting diffuse traumatic axonal injury (TAI). APP selectively labels injured axons, such as axonal bulbs and varicose axons. However, it has been reported that axonal bulbs are detected in cases of cerebral hypoxia without head injury. Therefore, we examined whether there are differences in the morphological pattern of axonal bulbs between trauma and hypoxia. Sections of the corpus callosum from 25 cases of head injury and 23 control cases were immunostained for APP. APP staining detected axonal bulbs in 14 cases of head injury, who survived more than several hours, although it failed to label axons in control cases. In addition, two patterns of immunoreactivity were identified in several cases of head injury. The first pattern showed that labeled axons were oriented along with white matter bundles; the second demonstrated that the axons were scattered irregularly. The first pattern alone was found in 5 of 14 cases, while cases of the second pattern alone were not observed. Both patterns were detected in 5 cases and in the remaining 4 cases, clear patterns were not found. From these findings, we speculated that the first pattern may represent TAI. Further examinations are required for determining whether these two patterns are identical with patterns of trauma and hypoxic brain damage as indicated by [Oehmichen M, Meissner C, Schmidt V, Pedal I, König HG, Saternus KS. Axonal injury--a diagnostic tool in forensic neuropathology? A review. Forensic Sci Int 1998;95:67-83] and [Graham DI, Smith C, Reichard R, Leclercq PD, Gentleman SM. Trials and tribulations of using beta-amyloid precursor protein immunohistochemistry to evaluate traumatic brain injury in adults. Forensic Sci Int 2004;146:89-96].

Shaken baby syndrome: re-examination of diffuse axonal injury as cause of death

The discussion surrounding shaken baby syndrome (SBS) arose from the lack of evidence implicating diffuse axonal injury (DAI) as a cause of death. It was assumed instead that injury to the cervical cord, medulla, and nerve roots played a causal role. The present pathomorphological study examines 18 selected infants (<1-year-old) whose deaths were highly suspicious for SBS, exhibiting the classical SBS triad of acute subdural hemorrhage (SDH), retinal bleeding, and encephalopathy. Gross autopsy and microscopic findings of these infants were compared with those of 19 victims of sudden infant death syndrome (SIDS; control group 1) and of 14 infants who died of disease or injuries/violence not involving the head, neck or eyes (control group 2). Symptoms of mechanical impact to the head were evident in seven of the SBS infants, but in none of the control infants. DAI was not detected in either the SBS or control cases. Localized axonal injury (AI) was regularly present in the brains of the SBS infants surviving longer than 1.5-3.0 h, but only occasionally in the craniocervical junction and within the nerve roots of the upper cervical cord; it was never present in the medulla. Epidural hemorrhage of the cervical cord was seen in four of the ten examined SBS cases, but in none of the control cases. Based on the absence of DAI in the brain and of signs of generalized cervical cord or nerve root injuries, we conclude that the cause of death in the SBS victims was a global cerebral ischemia secondary to SDH, focal vasospasm, trauma-induced transitory respiratory and/or circulatory failure.

Early diagnosis of diffuse brain damage resulting from a blunt head injury

Diffuse types of traumatic brain injury (TBI) are more difficult to diagnose than focal types in forensic postmortem examination, since macroscopic abnormalities may be minimal. In addition, most microscopic findings are not specific to TBI and are sometimes not obvious in cases when the survival period is short. Therefore, early diagnosis of diffuse TBI is most difficult. Histopathological and immunohistochemical examinations of various elements including axons, nerve cells, and glial cells in a sufficient number of blocks are indispensable. Mapping of changes in these elements with complicated focal lesions, even if the lesions are trivial, on anatomical diagrams would be useful. The combination of histopathological and immunohistochemical examinations as well as analysis of the exact history of the trauma, if possible, and elimination of other causes of death would lead to accurate diagnosis of diffuse types of TBI in cases when the survival period is brief.

An overview of inflicted head injury in infants and young children, with a review of beta-amyloid precursor protein immunohistochemistry

CONTEXT

Inflicted traumatic brain injury of infants and young children results in a complex array of autopsy findings. In many cases, immunostains for beta-amyloid precursor protein are used to detect axonal injury. Interpretation of the gross, microscopic, and immunostaining results requires the integration of the many facets of the individual case.

OBJECTIVE

In this article we review the gross and microscopic findings associated with inflicted traumatic brain injury. The application and interpretation of beta-amyloid precursor protein immunostains are discussed and photomicrographs are used to illustrate immunostaining patterns.

DATA SOURCES

The pertinent literature is integrated into a review of the subject.

CONCLUSIONS

Inflicted traumatic brain injury often results in subdural, subarachnoid, retinal, and optic nerve sheath hemorrhage. These findings must be interpreted within the entire context of the case. Beta-amyloid precursor protein immunostains may be helpful in illustrating the traumatic nature of the injuries in some cases.