Faculty Bibliography

Traumatic brain injury (TBI) and Alzheimer's disease (AD) are devastating neurological disorders, whose complex relationship is not completely understood. Cerebrovascular pathology, a key element in both conditions, could represent a mechanistic link between Aβ/tau deposition after TBI and the development of post concussive syndrome, dementia and chronic traumatic encephalopathy (CTE). In addition to debilitating acute effects, TBI-induced neurovascular injuries accelerate amyloid β (Aβ) production and perivascular accumulation, arterial stiffness, tau hyperphosphorylation and tau/Aβ-induced blood brain barrier damage, giving rise to a deleterious feed-forward loop. We postulate that TBI can initiate cerebrovascular pathology, which is causally involved in the development of multiple forms of neurodegeneration including AD-like dementias. In this review, we will explore how novel biomarkers, animal and human studies with a focus on cerebrovascular dysfunction are contributing to the understanding of the consequences of TBI on the development of AD-like pathology.

Posttraumatic stress disorder (PTSD) is associated with abnormalities in functional connectivity of a specific cortico-limbic network; however, less is known about white matter abnormalities providing structural connections for this network. This study investigated whether the diagnosis and symptoms of PTSD are associated with alterations in fractional anisotropy (FA), an index reflecting white matter organization, across six, a priori-defined tracts. White matter FA was quantified by diffusion tensor imaging using 3 T-MRI among 57 male, combat-exposed veterans with no history of moderate to severe head injuries or current alcohol dependence: 31 met criteria for PTSD and 26 were demographically comparable, combat-exposed controls without PTSD. Clinician-administered and self-report questionnaires assessed PTSD severity, dissociation, and mood. PTSD + veterans had significantly higher FA than exposed controls in the superior fronto-occipital fasciculus (SFOF) and borderline higher FA in the anterior corona radiata (ACR) and cingulum (CGC), controlling for age and neurovascular comorbidities. When lifetime alcohol use disorders was included, only the association of PTSD with SFOF-FA remained significant. Among PTSD + veterans, higher SFOF-FA was associated with greater mood disturbance, dissociative symptoms, and re-experiencing, while lower FA of the uncinate fasciculus (UF) was associated with greater mood disturbance symptoms. Compared to combat-exposed controls without PTSD, veterans with PTSD exhibited higher white matter FA in the SFOF, and a similar tendency in the ACR and CGC, tracts involved in conflict-processing and spatial attention. Prior alcohol use might explain the associations of PTSD with ACR-FA and CGC-FA but not the association with SFOF-FA.

OBJECTIVE: Acute leukemia (AL) is associated with an immediate threat to life, an unpredictable clinical course, and substantial physical suffering. Traumatic stress symptoms that may meet criteria for acute stress disorder (ASD) may be common and disabling in this context, but have received little clinical attention. We investigated the incidence over time and risk factors for traumatic stress symptoms and ASD in the 3 months following diagnosis or relapse of AL. METHODS: Individuals with AL were recruited at a tertiary cancer centre in Canada within one month of diagnosis or relapse. Participants (N=230) completed self-report measures, including the Stanford Acute Stress Reaction Questionnaire, at baseline and monthly over 3 months. The incidence of traumatic stress symptoms over time was examined and a generalized logistic model was used to identify factors associated with ASD. RESULTS: Participants were 60% male, with a mean age of 48.9+/-15.2 years. Symptoms of ASD were identified in 24.3% of participants at baseline. Of these participants, ASD was identified in 37.3% at one follow-up and in 55.3% at >/=2 follow-ups. ASD was associated with having young children, being unmarried, acute lymphocytic leukemia (ALL), and greater physical symptom burden. Persistent or recurrent ASD was associated with female sex, ALL, greater attachment anxiety, less spiritual well-being, and less satisfactory patient-clinician communication. CONCLUSIONS: Symptoms of ASD are common and often persist or recur following diagnosis or relapse of AL. Research is urgently needed to determine the impact of interventions to prevent and treat psychological distress in this population.

Glutamate is the principal excitatory neurotransmitter in the central nervous system, and is thought to be involved in the process of memory encoding and storage. Glutamate disturbances have also been reported in psychiatric disorders, such as schizophrenia and major depressive disorder (MDD), and in Alzheimer's disease. In this paper, we set out to study the relationship between cerebrospinal fluid (CSF) glutamate levels and memory performance, which we believe has not been reported previously. In particular, we focused on recall performance broken down by serial position. Our prediction was that the recency ratio (Rr), a novel cognitive marker of intellectual impairment, would be linked with CSF glutamate levels. We studied data from a group of cognitively intact elderly individuals, 28 of whom had MDD, while 19 were controls. Study results indicated that Rr levels, but no other memory score, were inversely correlated with CSF glutamate levels, although this was found only in individuals with late-life MDD. For comparison, glutamine or GABA were not correlated with any memory performance measure.

Inflammation is reported in post-traumatic stress disorder (PTSD). Few studies have investigated circulating blood cells that may contribute to inflammation. We assessed circulating platelets, white blood cells (WBC) and red blood cells (RBC) in PTSD and assessed their relationship to inflammation and symptom severity. One-hundred and sixty-three male combat-exposed veterans (82 PTSD, 81 non-PTSD) had blood assessed for platelets, WBC, and RBC. Data were correlated with symptom severity and inflammation. All cell counts were significantly elevated in PTSD. There were small mediation effects of BMI and smoking on these relationships. After adjusting for these, the differences in WBC and RBC remained significant, while platelet count was at trend level. In all subjects, all of the cell counts correlated significantly with inflammation. Platelet count correlated with inflammation only in the PTSD subjects. Platelet count, but none of the other cell counts, was directly correlated with PTSD severity ratings in the PTSD group. Combat PTSD is associated with elevations in RBC, WBC, and platelets. Dysregulation of all three major lineages of hematopoietic cells in PTSD, as well as their significant correlation with inflammation, suggest clinical significance of these changes.

This study examined whether reduced performance on two neuropsychological tasks, cognitive flexibility and working memory, were associated with higher levels of trauma centrality. A growing body of research has shown that trauma centrality, the extent to which a person believes a potentially traumatic event has become central to their self-identity and life story, is associated with post-traumatic stress disorder (PTSD). Furthermore, PTSD is often associated with alterations in neuropsychological functioning. The relationship between neuropsychological processes and trauma centrality, however, has yet to be explored. OEF/OIF combat veterans (N = 41) completed the Post-traumatic Diagnostic Scale (PDS), the Beck Depression Inventory-II (BDI-II), the Centrality of Event Scale (CES), and on-line measures of cognitive flexibility and working memory assessed via WebNeuro. Bivariate Pearson correlations showed that CES scores were positively correlated with PDS and BDI scores, and negatively correlated with cognitive flexibility and working memory. Linear regressions revealed that working memory significantly predicted CES when controlling for depression and PTSD severity while cognitive flexibility approached significance when controlling for these same variables. This study employed a cross-sectional design, precluding causality. The small sample size, entirely male sample, and use of an online neuropsychological assessment warrant follow-up research. Although numerous studies have found an association between CES and PTSD, this is the first to suggest that neuropsychological processes underlie the construct of trauma centrality. Given the importance of maladaptive cognitive processes underlying the pathogenesis of PTSD, these data suggest that future studies aimed at examining the link between neuropsychological processes and maladaptive cognitive processes, such as trauma centrality, may help to characterize and treat PTSD.

Emerging knowledge suggests that post-traumatic stress disorder (PTSD) pathophysiology is linked to the patients' epigenetic changes, but comprehensive studies examining genome-wide methylation have not been performed. In this study, we examined genome-wide DNA methylation in peripheral whole blood in combat veterans with and without PTSD to ascertain differentially methylated probes. Discovery was initially made in a training sample comprising 48 male Operation Enduring Freedom (OEF)/Operation Iraqi Freedom (OIF) veterans with PTSD and 51 age/ethnicity/gender-matched combat-exposed PTSD-negative controls. Agilent whole-genome array detected ~5600 differentially methylated CpG islands (CpGI) annotated to ~2800 differently methylated genes (DMGs). The majority (84.5%) of these CpGIs were hypermethylated in the PTSD cases. Functional analysis was performed using the DMGs encoding the promoter-bound CpGIs to identify networks related to PTSD. The identified networks were further validated by an independent test set comprising 31 PTSD+/29 PTSD- veterans. Targeted bisulfite sequencing was also used to confirm the methylation status of 20 DMGs shown to be highly perturbed in the training set. To improve the statistical power and mitigate the assay bias and batch effects, a union set combining both training and test set was assayed using a different platform from Illumina. The pathways curated from this analysis confirmed 65% of the pool of pathways mined from training and test sets. The results highlight the importance of assay methodology and use of independent samples for discovery and validation of differentially methylated genes mined from whole blood. Nonetheless, the current study demonstrates that several important epigenetically altered networks may distinguish combat-exposed veterans with and without PTSD.