Pascale D. Leclercq

The neuroinflammatory response in humans after traumatic brain injury.

Traumatic brain injury is a significant cause of morbidity and mortality worldwide. An epidemiological association between head injury and long‐term cognitive decline has been described for many years and recent clinical studies have highlighted functional impairment within 12 months of a mild head injury. In addition chronic traumatic encephalopathy is a recently described condition in cases of repetitive head injury. There are shared mechanisms between traumatic brain injury and Alzheimers disease, and it has been hypothesized that neuroinflammation, in the form of microglial activation, may be a mechanism underlying chronic neurodegenerative processes after traumatic brain injury.

Amyloid-Beta Peptide Is Toxic to Neurons In Vivo via Indirect Mechanisms

We have studied the neurotoxicity of amyloid-beta (Abeta) after a single unilateral intravitreal injection. Within the retina apoptotic cells were seen throughout the photoreceptor layer and the inner nuclear layer but not in the ganglion cell layer at 48 h after injection of Abeta(1-42) compared to vehicle control and control peptide. At 5 months, there was a significant reduction in total cell numbers in the ganglion cell layer in Nissl stained retinas. There was glial cell dysfunction with upregulation of glial fibrillary acidic protein and a reduction in the expression of Müller cell associated proteins in the injected retinas. These results suggest an indirect cytotoxic effect of Abeta on retinal neurons and an important role for dysfunction of Müller glia in mediating Abeta neurotoxicity.

Axonal Injury Is Accentuated in the Caudal Corpus Callosum of Head-Injured Patients

Amyloid precursor protein (APP) accumulation is a sensitive marker for the axonal damage that is commonly seen in the brain as the result of head injury. This form of damage is particularly associated with midline structures such as the corpus callosum, although it is not clear whether some areas are more susceptible than others. The aim of this study was to determine if there was a differential distribution of axonal injury throughout the corpus callosum after head injury in an unselected group of cases. Coronal tissue sections from eight cases were taken at different levels through the corpus callosum, including the genu, body, and splenium. The sections were immunostained with an antibody to APP, and the amount of axonal damage at the different levels was quantified using computer image analysis to build up a rostro-caudal profile for each case. The profiles revealed a significantly higher APP load in caudal parts of the corpus callosum. This supports previous nonquantitative reports in the literature and has important implications in terms of choosing where tissue should be sampled to maximize the chance of detecting axonal injury post mortem.

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

Axonal pathology is increasingly identified by beta-amyloid precursor protein (betaAPP) immunohistochemistry in the brains of patients who may or may not have a history of trauma. The presence of betaAPP-IR(+) has been variously interpreted as either that diffuse traumatic axonal injury (TAI) is indeed a universal finding in cases of fatal traumatic brain injury (TBI) or there are other causes of betaAPP-IR(+) axons which under certain circumstances may be sufficient to mimic TBI and therefore make the medico-legal interpretation of certain cases very difficult. To address some of the uncertainties we have undertaken a detailed analysis of the amount and distribution of betaAPP immunohistochemistry in 63 cases of fatal TBI, 17 cases of patients dying after cardiac arrest, 12 cases dying in association with status epilepticus, 3 cases of carbon monoxide (CO) poisoning, 13 cases of hypoglycaemia and in 60 controls. Three patterns of betaAPP-IR(+) were identified. First, diffuse multi-focal, second, corresponding to the outline of an infarct or haematoma, and thirdly a mixture of the two. The first pattern was seen in cases of the lesser grades of TAI, CO poisoning, and hypoglycaemia, the second pattern in cases in which there was evidence of raised intracranial pressure and the third in cases of severe TAI. It is concluded that the proper interpretation of cases requires the examination of a sufficient number of blocks ( [Formula: see text] ), processing using standardised protocols including betaAPP immunohistochemistry and in some cases the mapping of any IR(+) on anatomical line diagrams. betaAPP carried out on a small number of randomly taken blocks is likely to lead to misinterpretation of the clinico-pathological correlations and possibly to a miscarriage of justice.

Cerebral amyloid angiopathy in traumatic brain injury: association with apolipoprotein E genotype

Objective: In view of the association of the apolipoprotein E (APOE) ε4 allele with poor outcome after traumatic brain injury we determined the frequency of cerebral amyloid angiopathy (CAA) and the extent of haemorrhagic pathology in relation to APOE genotype in an autopsy series of 88 head injured cases. Methods: Tissue sections from the frontal and temporal lobes were immunostained for amyloid-β peptide (Aβ) and stained for Congo red to identify vascular amyloid pathology. A semiquantitative assessment of contusions, the total contusion index, was used to estimate the severity of the haemorrhagic pathology. APOE genotypes were determined by polymerase chain reaction of genomic DNA extracted from paraffin embedded tissue sections. Results: CAA was present in 7/40 (18%) ε4 carriers compared with 1/48 (2%) non-ε4 carriers (p = 0.021, 95% confidence interval (CI) for difference in proportions with CAA 3% to 29%) with 6/40 (4 with CAA) ε4 carriers being homozygotes. Thus the risk of having CAA for ε4 carriers was 8.4 times that for the non-ε4 carriers. However, there was no clear tendency for patients with CAA to have more severe or more numerous contusions (median contusion index 19 (CAA) v 14.5, p = 0.23, 95% CI for difference in medians −5 to 14). Conclusions: Presence of CAA in head injured cases was significantly associated with possession of an APOE ε4 allele but not with the severity of contusions.

Simple Morphometry of Axonal Swellings Cannot Be Used in Isolation for Dating Lesions after Traumatic Brain Injury

Disruption of fast axonal transport as a result of traumatic brain injury is characterized by the accumulation of beta-amyloid precursor protein (APP) in axonal swellings. A recent report has suggested a correlation between the size of axonal swellings and survival time up to about 85 h after blunt head injury. The authors of the report concluded that this correlation, in conjunction with other evidence, might be useful in forensic science for timing injuries. To test this hypothesis we have used image analysis software to measure a number of different morphological parameters of axonal swellings. Paraffin sections from 63 cases of fatal head injury were stained with an antibody raised against the N-terminus of APP and counterstained with haematoxylin. Three different measurements were made of the APP-immunoreactive axonal swellings from the corpus callosum: (i) minimum and (ii) maximum Feret diameters, and (iii) area. Linear regression revealed a significant correlation between survival time and the minimum Feret diameter (p < 0.0001) and the area (p < 0.001) of axonal swellings. Our findings are in agreement with the previous study in that there is a significant correlation between axonal swelling size and survival time. However, we would suggest that the large variability in swelling size within individual cases and the heterogeneity of the original trauma seriously compromise the utility of such information in the timing of lesions.