Effects of traumatic brain injury and posttraumatic stress disorder on development of Alzheimer's disease in Vietnam Veterans using the Alzheimer's Disease Neuroimaging Initiative: Preliminary Report

No association between head injury with loss of consciousness and Alzheimer disease pathology-Findings from the University of Manchester Longitudinal Study of Cognition in Normal Healthy Old Age

OBJECTIVES

Head injury with loss of consciousness (HI-LOC) is a common occurrence. Some studies have linked such injuries with an increased risk of Alzheimer disease (AD). However, recent large clinicopathologic studies have failed to find a clear relationship between HI-LOC and the pathological changes associated with AD. The present study aims to further investigate the relationship between HI-LOC and AD pathology in the elderly.

METHODS/DESIGN

History of HI-LOC in participants in the University of Manchester Longitudinal Study of Cognition in Normal Healthy Old Age was ascertained. The donated brains of 110 of these individuals were assessed for AD pathology using consensus guidelines. Analyses aimed to elucidate relationships between HI-LOC and AD pathology.

RESULTS

No associations were found between incidence of HI-LOC and regional AD pathology or any of the three established measures of the neuropathology associated with AD: CERAD score, Thal phase, or Braak stage.

CONCLUSIONS

Single incidences of HI-LOC may not be sufficient to cause the pathology associated with late-stage AD. Other routes of damage, such as diffuse axonal injury or Lewy body pathology, may play a greater role in causing cognitive impairment associated with head injury.

Response to the letter concerning the publication: Amyloid pathology fingerprint differentiates post-traumatic stress disorder and traumatic brain injury. Mohamed AZ, et al. NeuroImage Clinical 2018 June 5;19:716-726

In August 2018, Weiner and colleagues raised a red flag concerning certain errors in the tables and figures of our article, “Amyloid pathology fingerprint differentiates post-traumatic stress disorder and traumatic brain injury. NeuroImage Clinical 2018 Jun 5;19:716–726”. We have addressed this in detail in our published “Corrigendum to ‘Amyloid pathology fingerprint differentiates post-traumatic stress disorder and traumatic brain injury’ NeuroImage: Clinical. 19 (2018) 716–726”. However, recently Prof. Weiner and colleagues have raised a new issue in indicating that they could not 'replicate our results, despite accurately emulating our methods. We have prepared this letter in response to their recent letter.

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The methods used by Prof Weiner and colleagues are different than those described in our paper.

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PTSD increases amyloid at cerebral cortex and TBI with PTSD at white matter.

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After APOE4 and age correction, white matter changes in TBI with PTSD were no longer significant.

Failure to detect an association between self-reported traumatic brain injury and Alzheimer's disease neuropathology and dementia

INTRODUCTION

Recent research with neuropathologic or biomarker evidence of Alzheimer's disease (AD) casts doubt on traumatic brain injury (TBI) as a risk factor for AD. We leveraged the National Alzheimer's Coordinating Center to examine the association between self-reported TBI with loss of consciousness and AD neuropathologic changes, and with baseline and longitudinal clinical status.

METHODS

The sample included 4761 autopsy participants (453 with remote TBI with loss of consciousness; 2822 with AD neuropathologic changes) from National Alzheimer's Coordinating Center.

RESULTS

Self-reported TBI did not predict AD neuropathologic changes (P > .10). Reported TBI was not associated with baseline or change in dementia severity or cognitive function in participants with or without autopsy-confirmed AD.

DISCUSSION

Self-reported TBI with loss of consciousness may not be an independent risk factor for clinical or pathological AD. Research that evaluates number and severity of TBIs is needed to clarify the neuropathological links between TBI and dementia documented in other large clinical databases.

Gene-environment interactions in Alzheimer's disease: A potential path to precision medicine

Alzheimer's disease (AD) is the leading cause of dementia in the United States and afflicts >5.7 million Americans in 2018. Therapeutic options remain extremely limited to those that are symptom targeting, while no drugs have been approved for the modification or reversal of the disease itself. Risk factors for AD including aging, the female sex, as well as carrying an APOE4 genotype. These risk factors have been extensively examined in the literature, while less attention has been paid to modifiable risk factors, including lifestyle, and environmental risk factors such as exposures to air pollution and pesticides. This review highlights the most recent data on risk factors in AD and identifies gene by environment interactions that have been investigated. It also provides a suggested framework for a personalized therapeutic approach to AD, by combining genetic, environmental and lifestyle risk factors. Understanding modifiable risk factors and their interaction with non-modifiable factors (age, susceptibility alleles, and sex) is paramount for designing personalized therapeutic interventions.

Interactive Effect of Traumatic Brain Injury and Psychiatric Symptoms on Cognition among Late Middle-Aged Men: Findings from the Vietnam Era Twin Study of Aging

Traumatic brain injury (TBI), post-traumatic stress disorder (PTSD), and depressive symptoms each increase the risk for cognitive impairment in older adults. We investigated whether TBI has long-term associations with cognition in late middle-aged men, and examined the role of current PTSD/depressive symptoms. Participants were 953 men (ages 56-66) from the Vietnam Era Twin Study of Aging (VETSA), who were classified by presence or absence of (1) history of TBI and (2) current elevated psychiatric symptoms (defined as PTSD or depressive symptoms above cutoffs). TBIs had occurred an average of 35 years prior to assessment. Participants completed cognitive testing examining nine domains. In mixed-effects models, we tested the effect of TBI on cognition including for interactions between TBI and elevated psychiatric symptoms. Models adjusted for age, pre-morbid cognitive ability assessed at average age 20 years, apolipoprotein E genotype, and substance abuse; 33% (n = 310) of participants had TBI, mostly mild and remote; and 23% (n = 72) of those with TBI and 18% (n = 117) without TBI had current elevated psychiatric symptoms. TBI and psychiatric symptoms had interactive effects on cognition, particularly executive functioning. Group comparison analyses showed that men with both TBI and psychiatric symptoms demonstrated deficits primarily in executive functioning. Cognition was largely unaffected in men with either risk factor in isolation. Among late middle-aged men, the combination of even mild and very remote TBI with current elevated psychiatric symptoms is associated with deficits in executive function and related abilities. Future longitudinal studies should investigate how TBI and psychiatric factors interact to impact brain aging.

Causes and Patterns of Dementia: An Update in the Era of Redefining Alzheimer's Disease

The burden of dementia continues to increase as the population ages, with no disease-modifying treatments available. However, dementia risk appears to be decreasing, and progress has been made in understanding its multifactorial etiology. The 2018 National Institute on Aging-Alzheimer's Association (NIA-AA) research framework for Alzheimer's disease (AD) defines AD as a biological process measured by brain pathology or biomarkers, spanning the cognitive spectrum from normality to dementia. This framework facilitates interventions in the asymptomatic space and accommodates knowledge that many additional pathologies (e.g., cerebrovascular) contribute to the Alzheimer's dementia syndrome. The framework has implications for how we think about risk factors for "AD": Many commonly accepted risk factors are not related to AD pathology and would no longer be considered risk factors for AD. They may instead be related to other pathologies or resilience to pathology. This review updates what is known about causes, risk factors, and changing patterns of dementia, addressing whether they are related to AD pathology/biomarkers, other pathologies, or resilience.

The long-term consequences of repetitive head impacts: Chronic traumatic encephalopathy

Chronic traumatic encephalopathy (CTE) is a neurodegenerative disease associated with exposure to repetitive head impacts (RHI). Although described in boxers for almost a century, scientific and public interest in CTE grew tremendously following a report of postmortem evidence of CTE in the first former professional American football player in 2005. Neuropathologic diagnostic criteria for CTE have been defined, with abnormal perivascular deposition of hyperphosphorylated tau at the sulcal depths as the pathognomonic feature. CTE can currently only be diagnosed postmortem, but clinical research criteria for the in vivo diagnosis of CTE have been proposed. The clinical phenotype of CTE is still ill-defined and there are currently no validated biomarkers to support an in-life diagnosis of "Probable CTE." Many knowledge gaps remain regarding the neuropathologic and clinical make-up of CTE. An increased understanding of CTE is critical given the millions that could potentially be impacted by this disease. This chapter describes the state of the literature on CTE. The historical origins of CTE are first presented, followed by a comprehensive description of the neuropathologic and clinical features. The chapter concludes with discussion on future research directions, emphasizing the importance of diagnosing CTE during life to facilitate development of preventative and intervention strategies.

Military-related risk factors for dementia

INTRODUCTION

In recent years, there has been growing discussion to better understand the pathophysiological mechanisms of traumatic brain injury and post-traumatic stress disorder and how they may be linked to an increased risk of neurodegenerative diseases including Alzheimer's disease in veterans.

METHODS

Building on that discussion, and subsequent to a special issue of Alzheimer's & Dementia published in June 2014, which focused on military risk factors, the Alzheimer's Association convened a continued discussion of the scientific community on December 1, 2016.

RESULTS

During this meeting, participants presented and evaluated progress made since 2012 and identified outstanding knowledge gaps regarding factors that may impact veterans' risk for later life dementia.

DISCUSSION

The following is a summary of the invited presentations and moderated discussions of both the review of scientific understanding and identification of gaps to inform further investigations.

Microglia in Alzheimer's Disease: Risk Factors and Inflammation

Microglia are resident immune cells in the central nervous system (CNS) that originate from myeloid progenitor cells in the embryonic yolk sac and are maintained independently of circulating monocytes throughout life. In the healthy state, microglia are highly dynamic and control the environment by rapidly extending and retracting their processes. When the CNS is inflamed, microglia can give rise to macrophages, but the regulatory mechanisms underlying this process have not been fully elucidated. Recent genetic studies have suggested that microglial function is compromised in Alzheimer's disease (AD), and that environmental factors such as diet and brain injury also affect microglial activation. In addition, studies of triggering receptor expressed on myeloid cells 2-deficiency in AD mice revealed heterogeneous microglial reactions at different disease stages, complicating the therapeutic strategy for AD. In this paper, we describe the relationship between genetic and environmental risk factors and the roles of microglia in AD pathogenesis, based on studies performed in human patients and animal models. We also discuss the mechanisms of inflammasomes and neurotransmitters in microglia, which accelerate the development of amyloid-β and tau pathology.

The Early Events That Initiate β-Amyloid Aggregation in Alzheimer's Disease

Alzheimer’s disease (AD) is characterized by the development of amyloid plaques and neurofibrillary tangles (NFTs) consisting of aggregated β-amyloid (Aβ) and tau, respectively. The amyloid hypothesis has been the predominant framework for research in AD for over two decades. According to this hypothesis, the accumulation of Aβ in the brain is the primary factor initiating the pathogenesis of AD. However, it remains elusive what factors initiate Aβ aggregation. Studies demonstrate that AD has multiple causes, including genetic and environmental factors. Furthermore, genetic factors, many age-related events and pathological conditions such as diabetes, traumatic brain injury (TBI) and aberrant microbiota also affect the aggregation of Aβ. Here we provide an overview of the age-related early events and other pathological processes that precede Aβ aggregation.

Neurocognitive and Information Processing Biases in Posttraumatic Stress Disorder

PURPOSE OF REVIEW

We review recent research addressing neurocognitive and information processing abnormalities in posttraumatic stress disorder (PTSD), including studies informing direction of causality. We additionally consider neurocognition in the context of co-morbid mild traumatic brain injury (TBI) and psychosocial treatments for PTSD.

RECENT FINDINGS

Learning, memory, attention, inhibitory functions, and information processing biases frequently accompany PTSD, reflecting potential bi-directional relationships with PTSD. Although mild TBI is associated with increased risk of PTSD development and maintenance, TBI does not typically contribute significantly to sustained neurocognitive deficits in individuals with PTSD. Whereas better learning and memory is associated with mildly enhanced response to psychosocial interventions, such interventions may also improve neurocognitive performance and can be effectively provided to patients with TBI history. PTSD is associated with cognitive abnormalities in processing both emotionally relevant and emotionally neutral information and, although mild, may underlie some PTSD symptom expression.

Amyloid pathology fingerprint differentiates post-traumatic stress disorder and traumatic brain injury

Introduction

Traumatic brain injury (TBI) and post-traumatic stress disorder (PTSD) are risk factors for early onset of Alzheimer's disease (AD) and may accelerate the progression rate of AD pathology. As amyloid-beta (Aβ) plaques are a hallmark of AD pathology, we hypothesized that TBI and PTSD might increase Aβ accumulation in the brain.

Methods

We examined PET and neuropsychological data from Vietnam War veterans compiled by the US Department of Defense Alzheimer's Disease Neuroimaging Initiative, to examine the spatial distribution of Aβ in male veterans' who had experienced a TBI and/or developed PTSD. Subjects were classified into controls, TBI only, PTSD only, and TBI with PTSD (TBI_PTSD) groups and data were analyzed using both voxel-based and ROI-based approaches.

Results

Compared to controls, all three clinical groups showed a pattern of mainly increased referenced standard uptake values (SUVR) for the amyloid tracer [18F]-AV45 PET, with rank order PTSD > TBI_PTSD > TBI > Control, and same rank order was seen in the deficits of cognitive functions. SUVR increase was observed in widespread cortical regions of the PTSD group; in white matter of the TBI_PTSD group; and cerebellum and precuneus area of the TBI group, in contrast with controls. The [18F]-AV45 SUVR correlated negatively with cerebrospinal fluid (CSF) amyloid levels and positively with the CSF tau concentrations.

Conclusion

These results suggest that both TBI and PTSD are substantial risk factors for cognition decline and increased Aβ deposition resembling that in AD. In addition, both PTSD and TBI_PTSD have a different pathways of Aβ accumulation.

Neuro-Immuno-Gene- and Genome-Editing-Therapy for Alzheimer's Disease: Are We There Yet?

Alzheimer's disease (AD) is a highly complex neurodegenerative disorder and the current treatment strategies are largely ineffective thereby leading to irreversible and progressive cognitive decline in AD patients. AD continues to defy successful treatment despite significant advancements in the field of molecular medicine. Repeatedly, early promising preclinical and clinical results have catapulted into devastating setbacks leading to multi-billion dollar losses not only to the top pharmaceutical companies but also to the AD patients and their families. Thus, it is very timely to review the progress in the emerging fields of gene therapy and stem cell-based precision medicine. Here, we have made sincere efforts to feature the ongoing progress especially in the field of AD gene therapy and stem cell-based regenerative medicine. Further, we also provide highlights in elucidating the molecular mechanisms underlying AD pathogenesis and describe novel AD therapeutic targets and strategies for the new drug discovery. We hope that the quantum leap in the scientific advancements and improved funding will bolster novel concepts that will propel the momentum toward a trajectory leading to a robust AD patient-specific next generation precision medicine with improved cognitive function and excellent life quality.

Traumatic brain injury may not increase the risk of Alzheimer disease

Traumatic brain injury (TBI) commonly occurs in civilian and military populations. Some epidemiologic studies previously have associated TBI with an increased risk of Alzheimer disease (AD). Recent clinicopathologic and biomarker studies have failed to confirm the relationship of TBI to the development of AD dementia or pathologic changes, and suggest that other neurodegenerative processes might be linked to TBI. Additional studies are required to determine the long-term consequences of TBI.