Volume 88, Number 3, 2022

Mini-Forum: Alzheimer’s Disease, Brain Over-Excitation, and EEG Signatures: Preclinical and Clinical Evidence (Guest Editor: Claudio Babiloni)

Pages 801-807

Claudio Babiloni
The Dark Side of Alzheimer’s Disease: Neglected Physiological Biomarkers of Brain Hyperexcitability and Abnormal Consciousness Level

Pages 809-836

Sean Tok, Abdallah Ahnaou, Wilhelmus Drinkenburg
Functional Neurophysiological Biomarkers of Early-Stage Alzheimer’s Disease: A Perspective of Network Hyperexcitability in Disease Progression
Abstract: Network hyperexcitability (NH) has recently been suggested as a potential neurophysiological indicator of Alzheimer’s disease (AD), as new, more accurate biomarkers of AD are sought. NH has generated interest as a potential indicator of certain stages in the disease trajectory and even as a disease mechanism by which network dysfunction could be modulated. NH has been demonstrated in several animal models of AD pathology and multiple lines of evidence point to the existence of NH in patients with AD, strongly supporting the physiological and clinical relevance of this readout. Several hypotheses have been put forward to explain the prevalence of NH in animal models through neurophysiological, biochemical, and imaging techniques. However, some of these hypotheses have been built on animal models with limitations and caveats that may have derived NH through other mechanisms or mechanisms without translational validity to sporadic AD patients, potentially leading to an erroneous conclusion of the underlying cause of NH occurring in patients with AD. In this review, we discuss the substantiation for NH in animal models of AD pathology and in human patients, as well as some of the hypotheses considering recently developed animal models that challenge existing hypotheses and mechanisms of NH. In addition, we provide a preclinical perspective on how the development of animal models incorporating AD-specific NH could provide physiologically relevant translational experimental data that may potentially aid the discovery and development of novel therapies for AD.

Pages 837-847
Milan Stoiljkovic, Karel Otero Gutierrez, Craig Kelley, Tamas L. Horvath, Mihály Hajós
TREM2 Deficiency Disrupts Network Oscillations Leading to Epileptic Activity and Aggravates Amyloid-β-Related Hippocampal Pathophysiology in Mice
Abstract: Background: Genetic mutations in triggering receptor expressed on myeloid cells-2 (TREM2) have been strongly associated with increased risk of developing Alzheimer’s disease (AD) and other progressive dementias. In the brain, TREM2 protein is specifically expressed on microglia suggesting their active involvement in driving disease pathology. Using various transgenic AD models to interfere with microglial function through TREM2, several recent studies provided important data indicating a causal link between TREM2 and underlying amyloid-β (Aβ) and tau pathology. However, mechanisms by which TREM2 contributes to increased predisposition to clinical AD and influences its progression still remain largely unknown. Objective: Our aim was to elucidate the potential contribution of TREM2 on specific oscillatory dynamic changes associated with AD pathophysiology. Methods: Spontaneous and brainstem nucleus pontis oralis stimulation-induced hippocampal oscillation paradigm was used to investigate the impact of TREM2 haploinsufficiency TREM2(Het) or total deficiency TREM2(Hom) on hippocampal network function in wild-type and Aβ overproducing Tg2576 mice under urethane anesthesia. Results: Partial (TREM2(Het)) or total (TREM2(Hom)) deletion of TREM2 led to increased incidence of spontaneous epileptiform seizures in both wild-type and Tg2576 mice. Importantly, deficiency of TREM2 in Tg2576 mice significantly diminished power of theta oscillation in the hippocampus elicited by brainstem-stimulation compared to wild-type mice. However, it did not affect hippocampal theta-phase gamma-amplitude coupling significantly, since over a 60% reduction was found in coupling in Tg2576 mice regardless of TREM2 function. Conclusion: Our findings indicate a role for TREM2-dependent microglial function in the hippocampal neuronal excitability in both wild type and Aβ overproducing mice, whereas deficiency in TREM2 function exacerbates disruptive effects of Aβ on hippocampal network oscillations.

Pages 849-865

Nanxiang Jin, Claudio Babiloni, Wilhelmus H. Drinkenburg, Mihály Hajós, Haakon B. Nygaard, Heikki Tanila
Recommendations for Preclinical Testing of Treatments Against Alzheimer’s Disease-Related Epileptiform Spikes in Transgenic Rodent Models
Abstract: Recent evidence suggests that about 30% of patients with mild to moderate Alzheimer’s disease (AD) without a known diagnosis of epilepsy may display epileptiform spikes during electroencephalographic (EEG) recordings. These abnormal discharges occur predominantly during sleep and may be associated with accelerated disease progression. Subclinical spikes may represent a relevant target for clinical drug interventions, and there is a clear unmet need for preclinical testing of novel disease modifying agents in suitable animal models. Transgenic rodent models of AD pathology exhibit various forms of epileptiform EEG activity related to the abnormal levels of amyloid species in the brain. Among them, large-amplitude cortical and hippocampal EEG spikes in mouse and rat AD models may be reminiscent of the subclinical epileptiform EEG spikes recorded in some AD patients. This article reports the recommendations of a multidisciplinary panel of experts on optimal EEG markers and experimental designs to measure and report epileptiform activities and their response to symptomatic and disease-modifying drugs in transgenic AD model rodents. These recommendations may harmonize future preclinical EEG studies in the drug discovery research and may increase the comparability of experimental outcomes and their translational clinical value.

Pages 867-891
Shaylyn Joseph, Rachel Patterson, Wei Wang, Daniel M. Blumberger, Tarek Rajji, Sanjeev Kumar
Quantitative Assessment of Cortical Excitability in Alzheimer’s Dementia and Its Association with Clinical Symptoms: A Systematic Review and Meta-Analyses
Abstract: Background: Alzheimer’s disease (AD) is characterized by cognitive and neuropsychiatric symptoms (NPS) due to underlying neurodegenerative pathology. Some studies using electroencephalography (EEG) have shown increased epileptiform and epileptic activity in AD. Objective: This review and meta-analyses aims to synthesize the existing evidence for quantitative abnormalities of cortical excitability in AD and their relationship with clinical symptoms. Methods: We systematically searched and reviewed publications that quantitatively assessed cortical excitability, using transcranial magnetic stimulation (TMS) resting motor threshold (rMT), active motor threshold (aMT), motor evoked potential (MEP) or directly from the cortex using TMS-EEG via TMS-evoked potential (TEP). We meta-analyzed studies that assessed rMT and aMT using random effects model. Results: We identified 895 publications out of which 37 were included in the qualitative review and 30 studies using rMT or aMT were included in the meta-analyses. The AD group had reduced rMT (Hedges’ g = -0.99, 95% CI [-1.29, -0.68], p < 0.00001) and aMT (Hedges’ g = -0.87, 95% CI [-1.50, -0.24], p < 0.00001) as compared with control groups, indicative of higher cortical excitability. Qualitative review found some evidence of increased MEP amplitude, whereas findings related to TEP were inconsistent. There was some evidence supporting an inverse association between cortical excitability and global cognition. No publications reported on the relationship between cortical excitability and NPS. Conclusion: There is strong evidence of increased motor cortex excitability in AD and some evidence of an inverse association between excitability and cognition. Future studies should assess cortical excitability from non-motor areas using TMS-EEG and examine its relationship with cognition and NPS.

Pages 893-901
Cinzia Costa, Fabrizio Vecchio, Michele Romoli, Francesca Miraglia, Elena Nardi Cesarini, Francesca Alù, Paolo Calabresi, Paolo Maria Rossini
Cognitive Decline Risk Stratification in People with Late-Onset Epilepsy of Unknown Etiology: An Electroencephalographic Connectivity and Graph Theory Pilot Study
Abstract: Background: Although people with late onset epilepsy of unknown etiology (LOEU) are at higher risk of cognitive decline compared to the general population, we still lack affordable tools to predict and stratify their risk of dementia. Objective: This pilot-study investigates the potential application of electroencephalography (EEG) network small-world (SW) properties in predicting cognitive decline among patients with LOEU. Methods: People diagnosed with LOEU and normal cognitive examination at the time of epilepsy diagnosis were included. Cerebrospinal fluid biomarkers, brain imaging, and neuropsychological assessment were performed at the time of epilepsy diagnosis. Baseline EEG was analyzed for SW properties. Patients were followed-up over time with neuropsychological testing to define the trajectory of cognitive decline. Results: Over 5.1 years of follow-up, among 24 patients diagnosed with LOEU, 62.5% were female, mean age was 65.3 years, thirteen developed mild cognitive impairment (MCI), and four developed dementia. Patients with LOEU developing MCI had lower values of SW coefficients in the delta (p=0.03) band and higher SW values in the alpha frequency bands (p=0.02) compared to patients having normal cognition at last follow-up. The two separate ANOVAs, for low and alpha bands, confirmed an interaction between SW and cognitive decline at follow-up. A similar gradient was confirmed for patients developing dementia compared to those with normal cognitive function as well as to those developing MCI. Conclusion: Baseline EEG analysis through SW is worth investigating as an affordable, widely available tool to stratify LOEU patients for their risk of cognitive decline.

Pages 903-931
Claudio Babiloni, Giuseppe Noce, Carlo Di Bonaventura, Roberta Lizio, Ali Eldellaa, Federico Tucci, Enrico M. Salamone, Raffaele Ferri, Andrea Soricelli, Flavio Nobili, Francesco Famà, Dario Arnaldi, Eleonora Palma, Pierangelo Cifelli, Moira Marizzoni, Fabrizio Stocchi, Giuseppe Bruno, Giancarlo Di Gennaro, Giovanni B. Frisoni, Claudio Del Percio
Alzheimer’s Disease with Epileptiform EEG Activity: Abnormal Cortical Sources of Resting State Delta Rhythms in Patients with Amnesic Mild Cognitive Impairment
Abstract: Background: Patients with amnesic mild cognitive impairment due to Alzheimer’s disease (ADMCI) typically show a "slowing" of cortical resting-state eyes-closed electroencephalographic (rsEEG) rhythms. Some of them also show subclinical, non-convulsive, and epileptiform EEG activity (EEA) with an unclear relationship with that "slowing." Objective: Here we tested the hypothesis that the "slowing" of rsEEG rhythms is related to EEA in ADMCI patients. Methods: Clinical and instrumental datasets in 62 ADMCI patients and 38 normal elderly (Nold) subjects were available in a national archive. No participant had received a clinical diagnosis of epilepsy. The eLORETA freeware estimated rsEEG cortical sources. The area under the receiver operating characteristic curve (AUROCC) indexed the accuracy of eLORETA solutions in the classification between ADMCI-EEA and ADMCI-noEEA individuals. Results: EEA was observed in 15% (N=8) of the ADMCI patients. The ADMCI-EEA group showed: 1) more abnormal Aβ42 levels in the cerebrospinal fluid as compared to the ADMCI-noEEA group and 2) higher temporal and occipital delta (< 4 Hz) rsEEG source activities as compared to the ADMCI-noEEA and Nold groups. Those source activities showed moderate accuracy (AUROCC = 0.70-0.75) in the discrimination between ADMCI-noEEA versus ADMCI-EEA individuals. Conclusion: It can be speculated that in ADMCI-EEA patients, AD-related amyloid neuropathology may be related to an over-excitation in neurophysiological low-frequency (delta) oscillatory mechanisms underpinning cortical arousal and quiet vigilance.

Regular Section

Pages 933-941
Andrea McGrattan, Christopher J. Stewart, Aedín Cassidy, Jayne V. Woodside, Claire T. McEvoy
Diet Patterns, the Gut Microbiome, and Alzheimer’s Disease
Abstract: Given the complex bidirectional communication system that exists between the gut microbiome and the brain, there is growing interest in the gut microbiome as a novel and potentially modifiable risk factor for Alzheimer’s disease (AD). Gut dysbiosis has been implicated in the pathogenesis and progression of AD by initiating and prolonging neuroinflammatory processes. The metabolites of gut microbiota appear to be critical in the mechanism of the gut-brain axis. Gut microbiota metabolites, such as trimethylamine-n-oxide, lipopolysaccharide, and short chain fatty acids, are suggested to mediate systemic inflammation and intracerebral amyloidosis via endothelial dysfunction. Emerging data suggest that the fungal microbiota (mycobiome) may also influence AD pathology. Importantly, ~60% of variation in the gut microbiome is attributable to diet, therefore modulating the gut microbiome through dietary means could be an effective approach to reduce AD risk. Given that people do not eat isolated nutrients and instead consume a diverse range of foods and combinations of nutrients that are likely to be interactive, studying the effects of whole diets provides the opportunity to account for the interactions between different nutrients. Thus, dietary patterns may be more predictive of real-life effect on gut microbiome and AD risk than foods or nutrients in isolation. Accumulating evidence from experimental and animal studies also show potential effects of gut microbiome on AD pathogenesis. However, data from human dietary interventions are lacking. Well-designed intervention studies are needed in diverse populations to determine the influence of diet on gut microbiome and inform the development of effective dietary strategies for prevention of AD.

Pages 943-948
Short Communication

Leon Flicker, Kaarin J. Anstey, Osvaldo P. Almeida, Michael Waller, Patrick Fitzgerald, Fleur de Crespigny, Thao Vu, Annette J. Dobson (Handling Associate Editor: Nasser Bagheri)
Differing Methodologies Are Required to Estimate Prevalence of Dementia: Single Study Types Are No Longer Reliable
Abstract: Population-based surveys were used to estimate community prevalence of dementia, but have low response fractions due, among other things, to difficulties in obtaining informed consent from people with diminished capacity. Cohort studies of younger people are subject to recruitment bias and non-random drop-outs. Dementia registries can delineate sub-types of dementia but have limited population coverage and are costly to maintain. Administrative datasets have low costs but may be subject to selection bias and uncertain sensitivity. We propose that astute combination of methodologies, including assessment of coverage and validity of administrative datasets, is the most cost-effective process to estimate and monitor community prevalence.

Pages 949-955
Short Communication

Rana Mabrouk*, Maria Gotkiewicz*, Tuomas Rauramaa, Heikki Tanila (Handling Associate Editor: M. Paul Murphy) *These authors contributed equally to this work.
DAPI (4',6-diamidino-2-phenylindole) Stains Compact Amyloid Plaques
Abstract: DAPI is conventionally used as a nuclear stain for cells in culture or tissue. Here we demonstrate that it binds specifically to the β-sheet core of amyloid-β plaques but not diffuse amyloid-β at the plaque periphery. The specific DAPI induced blue fluorescence is much stronger than amyloid plaque autofluorescence. DAPI staining of fibrillar amyloid deposit may yield a misleading impression of damaged or dying cells. On the other hand, it provides a handy and low-cost means of staining compact amyloid plaques together with cell nuclei in double or triple immunofluorescent studies.

Pages 957-970
Hannah Jester, Saahj Gosrani, Huiping Ding, Xueyan Zhou, Mei-Chuan Ko, Tao Ma (Handling Associate Editor: Chengxin Gong)
Characterization of Early Alzheimer’s Disease-Like Pathological Alterations in Non-Human Primates with Aging: A Pilot Study
Abstract: Background: Sporadic or late onset Alzheimer’s disease (LOAD) is a multifactorial neurodegenerative disease with aging the most known risk factor. Non-human primates (NHPs) may serve as an excellent model to study LOAD because of their close similarity to humans in many aspects including neuroanatomy and neurodevelopment. Recent studies reveal AD-like pathology in old NHPs. Objective: In this pilot study, we took advantage of brain samples from 6 Cynomolgus macaques that were divided into two groups: middle aged (average age 14.81 years) and older (average age 19.33 years). We investigated whether AD-like brain pathologies are present in the NHPs. Methods: We used immunohistochemical method to examine brain Aβ pathology and neuron density. We applied biochemical assays to measure tau phosphorylation and multiple signaling pathways indicated in AD. We performed electron microscopy experiments to study alterations of postsynaptic density and mitochondrial morphology in the brain of NHPs. Results: We found multiple AD-like pathological alteration in the prefrontal cortex (but not in the hippocampus) of the older NHPs including tau hyperphosphorylation, increased activity of AMP-activated protein kinase (AMPK), decreased expression of protein phosphatase 2A (PP2A), impairments in mitochondrial morphology, and postsynaptic densities formation. Conclusion: These findings may provide insights into the factors contributing to the development of LOAD, particularly during the early stage transitioning from middle to old age. Future endeavors are warranted to elucidate mechanisms underlying the regional (and perhaps cellular) vulnerability with aging and the functional correlation of such pathological changes in NHPs.

Pages 971-984
Birgit Teichmann, Mara Gkioka, Andreas Kruse, Magda Tsolaki
Informal Caregivers’ Attitude Toward Dementia: The Impact of Dementia Knowledge, Confidence in Dementia Care, and the Behavioral and Psychological Symptoms of the Person with Dementia. A Cross-Sectional Study
Abstract: Background: Dementia is rapidly increasing worldwide due to demographic aging. More than two-thirds of patients are cared by family members. The quality of care depends on the caregivers’ attitude toward dementia influencing patient care decisions. Objective: The aim of this study is to examine the factors that influence the caregivers’ attitude and whether there is an association between participation in a psycho-educational program and attitude. Methods: We performed a cross-sectional study using a structured closed-ended questionnaire to retrieve socio-demographic information from caregivers and the persons with dementia (N=86). The study included validated scales such as the Dementia Attitude Scale, the Dementia Knowledge Assessment Tool 2, the Positive Aspects of Caregiving, the Zarit Burden Interview, the Confidence in Dementia Scale, and Spielberger’s State-Trait Anxiety Inventory, as well as a neuropsychological battery to assess the condition of people with dementia. Results: Our final model explains 55.6% of the total variance and shows a significant correlation of five factors with attitude toward dementia: confidence, behavioral and psychological symptoms of dementia, anxiety as a trait, positive aspects of caregiving, and dementia knowledge. The caregivers who participated in a psycho-educational program showed a significantly more positive attitude toward dementia, better dementia knowledge, higher confidence in dementia care, and lower anxiety as a state. Conclusion: The strong correlation of attitude and knowledge, as well as confidence in dementia care, supports the tripartite model of attitude, which hypothesizes the interrelation of affect, cognition, and behavior.

Pages 985-993
Kevin S. Heffernan, Lee Stoner, Michelle L. Meyer, Paul D. Loprinzi
Association Between Estimated Pulse Wave Velocity and Cognitive Performance in Older Black and White Adults in NHANES
Abstract: Background: Aging-associated cognitive decline is greater in non-Hispanic Black (NHB) adults than non-Hispanic White (NHW) adults. An important risk factor for cognitive decline with aging is arterial stiffening, though the importance to racial variation remains poorly understood. Objective: We examined the association of an estimate of arterial stiffness with cognitive function in a bi-racial sample of 60–85-year-old adults (N= 3,616, 26.5% NHB) enrolled in the National Health and Nutrition Examination Survey (NHANES) between 1999-2002 and 2011-2014. Methods: As a measure of vascular aging, pulse wave velocity was estimated (ePWV) using an equation incorporating age and mean arterial pressure and expressed as m/s. Using the digit symbol substitution test (DSST), cognitive function was expressed as the number of correctly matched symbols (out of 133) within 120 s. Linear regression models examined associations between ePWV and DSST. Results: In models that adjusted for sex, education, smoking, body mass index, history of cardiovascular disease, and hypertension, ePWV was inversely associated with DSST score in NHB adults (β = -3.47, 95% CI = -3.9 to -3.0; p<0.001) and NHW adults (β = -3.51, 95% CI = -4.4 to -2.6; p<0.001). Conclusion: ePWV is inversely associated with a measure of cognitive function in older Black and White adults. ePWV may be a useful measure of vascular aging that can offer insight into cognitive aging.

Pages 995-1005
Gali H. Weissberger, Anya Samek, Laura Mosqueda, Annie L. Nguyen, Aaron C. Lim, Laura Fenton, S. Duke Han
Increased Financial Altruism is Associated with Alzheimer’s Disease Neurocognitive Profile in Older Adults
Abstract: Background: Older age is associated with an increase in altruistic behaviors such as charitable giving. However, few studies have investigated the cognitive correlates of financial altruism in older adults. Objective: This study investigated the cognitive correlates of financial altruism measured using an altruistic choice paradigm in a community-based sample of older adults. Methods: In the present study, a sample of older adults (N = 67; M age = 69.21, SD = 11.23; M education years = 15.97, SD = 2.51; 58.2% female; 71.6% Non-Hispanic White) completed a comprehensive neuropsychological assessment and an altruistic choice paradigm in which they made decisions about allocating money between themselves and an anonymous person. Results: In multiple linear regression analyses that controlled for age, education, and sex, financial altruism was negatively associated with performance on cognitive measures typically sensitive to early Alzheimer’s disease (including word list learning and recall, delayed story recall, and animal fluency). Conclusion: Findings of this study point to a negative relationship between financial altruism and cognitive functioning in older adults on measures known to be sensitive to Alzheimer’s disease. Findings also point to a potential link between financial exploitation risk and Alzheimer’s disease in older age.

Pages 1007-1016
Alexandra Horvath, Patrick Quinlan, Carl Eckerström, N. David Åberg, Anders Wallin, Johan Svensson
Low Serum Insulin-like Growth Factor-I Is Associated with Decline in Hippocampal Volume in Stable Mild Cognitive Impairment but not in Alzheimer’s Disease
Abstract: Background: Serum insulin-like growth factor-I (IGF-I) has shown some association with hippocampal volume in healthy subjects, but this relation has not been investigated in stable mild cognitive impairment (sMCI) or Alzheimer’s disease (AD). Objective: At a single memory clinic, we investigated whether serum IGF-I was associated with baseline magnetic resonance imaging (MRI)-estimated brain volumes and longitudinal alterations, defined as annualized changes, up to 6 years of follow-up. Methods: A prospective study of patients with sMCI (n = 110) and AD (n = 60). Brain regions included the hippocampus and amygdala as well as the temporal, parietal, frontal, and occipital lobes, respectively. Results: Serum IGF-I was statistically similar in sMCI and AD patients (112 versus 123 ng/mL, p = 0.31). In sMCI, serum IGF-I correlated positively with all baseline MRI variables except for the occipital lobe, and there was also a positive correlation between serum IGF-I and the annualized change in hippocampal volume (rs = 0.32, p = 0.02). Furthermore, sMCI patients having serum IGF-I above the median had lower annual loss of hippocampal volume than those with IGF-I below the median (p = 0.02). In contrast, in AD patients, IGF-I did not associate with baseline levels or annualized changes in brain volumes. Conclusion: In sMCI patients, our results suggest that IGF-I exerted neuroprotective effects on the brain, thereby maintaining hippocampal volume. In AD, serum IGF-I did not associate with brain volumes, indicating that IGF-I could not induce neuroprotection in this disease. This supports the notion of IGF-I resistance in AD.

Pages 1017-1027
Jing Tian, Tienju Wang, Kun Jia, Lan Guo, Russell H. Swerdlow, Heng Du
Nonobese Male Patients with Alzheimer’s Disease Are Vulnerable to Decrease in Plasma Leptin
Abstract: Background: Metabolic dysfunction links to cognitive deficits in Alzheimer’s disease (AD). Leptin is an anti-obesity hormone that modulates energy homeostasis and memory function. Although leptin deregulation is implicated in mouse models of AD-like brain pathology, clinical studies have shown inconsistent results regarding an association of leptin with the development of this neurodegenerative disorder. Objective: We investigated the changes of plasma leptin and the correlation of sex-stratified circulating leptin with cognitive performance, AD-related biological markers, and metabolic status in patients with AD and cognitively unimpaired (CU) counterparts. Methods: We used nonobese AD patients and CU controls in a University of Kansas Medical Center (KUMC) cohort. Plasma leptin levels, circulating AD-related molecules and metabolic profiles were examined and analyzed. Results: In contrast to unchanged circulating leptin in females, male patients exhibited decreased plasma leptin levels compared with male CU counterparts. Moreover, plasma leptin showed no correlation with cognitive performance and AD blood biomarkers in patients with either sex. Of note, females but not males demonstrated an association of plasma leptin with body mass index, high density lipoprotein-cholesterol and its ratio with total cholesterol and triglycerides. Conclusion: Our findings suggest that leptin deficiency is associated with nonobese male AD patients, supporting systemic dysmetabolism in the development of this neurodegenerative disorder in certain populations. Although plasma leptin may have limited capacity to reflect disease severity or progression, future mechanistic studies on the regulation of leptin in nonobese patients with AD would deepen our understanding of the sex-related disparity of AD etiopathogenesis.

Pages 1029-1035
Jakob Leonhardi*, Henryk Barthel*, Sven Speerforck, Jens Dietzel, Matthias L. Schroeter, Dorothee Saur, Solveig Tiepolt, Michael Rullmann, Marianne Patt, Joseph Claßen, Georg Schomerus, Osama Sabri *These authors contributed equally to this work.
Differential Diagnosis Between Alzheimer’s Disease-Related Depression and Pseudo-Dementia in Depression: A New Indication for Amyloid-β Imaging?
Abstract: Background: Alzheimer’s disease and depression can start with combined cognitive and depressive symptoms [1, 2]. Accurate differential diagnosis is desired to initiate specific treatment. Objective: We investigated whether amyloid-β PET imaging can discriminate both entities. Methods: This retrospective observational study included 39 patients (20 female, age=70±11years) with both cognitive and depressive symptoms who underwent amyloid-β PET imaging and in whom clinical follow-up data was available. Amyloid-β PET was carried out applying [18F]Florbetaben or [11C]PiB. The PET images were analyzed by standardized visual and relative-quantitative evaluation. Based on clinical follow-up (median of 2.4 years [range 0.3 to 7.0 years, IQR=3.7 years] after amyloid PET imaging which was not considered in obtaining a definite diagnosis), discrimination ability between AD-related depression and pseudo-dementia in depression/depression with other comorbidities was determined. Results: Visually, all 10 patients with pseudo-dementia in depression and all 15 patients with other depression were rated as amyloid-β-negative; 2 of 14 patients with AD-related depression were rated amyloid-β−negative. ROC curve analysis of the unified composite standardized uptake value ratios (cSUVRs) was able to discriminate pseudo-dementia in depression from AD-related depression with high accuracy (AUC=0.92). Optimal [18F]Florbetaben discrimination cSUVR threshold was 1.34. In congruence with the visual PET analysis, the resulting sensitivity of the relative-quantitative analysis was 86% with a specificity of 100%. Conclusion: Amyloid-β PET can differentiate AD-related depression and pseudo-dementia in depression. Prospective clinical studies are warranted to confirm this result and to potentially broaden the spectrum of clinical applications for amyloid-β PET imaging.

Pages 1037-1048
Jinghuan Gan, Shuai Liu, Zhichao Chen, Yaqi Yang, Lingyun Ma, Qingbo Meng, Xiao-Dan Wang, Chunyan Liu, Xudong Li, Wei Zhang, Yong Ji
Elevated Plasma Orexin-A Levels in Prodromal Dementia with Lewy Bodies
Abstract: Background: Studies on plasma orexin-A levels in prodromal dementia with Lewy bodies (DLB) and the relationship with clinical manifestations are rare. Objective: To assess plasma orexin-A levels and evaluate the correlation with clinical features in patients with mild cognitive impairment with Lewy bodies (MCI-LB) and DLB. Methods Plasma orexin-A levels were measured in 41 patients with MCI-LB, 53 with DLB, and 48 healthy controls (HCs). Informant-based history, neurological examinations, neuropsychological assessments, laboratory tests, and neuroimaging were collected and the correlation between orexin-A and various indicators evaluated. Results: Plasma orexin-A levels in patients with MCI-LB (1.18 ± 0.33 ng/mL, p = 0.014) or DLB (1.20 ± 0.44 ng/mL, p = 0.011) were significantly higher than in HCs (1.02 ± 0.32 ng/mL) and associated with gender and age. DLB patients with fluctuating cognition (FC) (1.01 ± 0.23 versus 1.31 ± 0.50, p = 0.007) or parkinsonism (PARK) (0.98 ± 0.19 versus 1.25 ± 0.47, p = 0.030) had significantly lower plasma orexin-A levels than subjects without FC or PARK. Plasma orexin-A levels were significantly negatively correlated with irritability and UPDRS-III scores and significantly positively correlated with disinhibition scores. Conclusion: This is the first report in which elevated plasma orexin-A levels were observed in patients with MCI-LB or DLB. In addition, lower orexin-A levels were found in patients with DLB and FC or PARK compared with HCs. The plasma orexin-A levels were associated with the presence of core features and motor and neuropsychiatric symptoms in patients with MCI-LB and DLB.

Pages 1049-1059
Michelle M. Mielke, Jeanine E. Ransom, Jay Mandrekar, Pierpaolo Turcano, Rodolfo Savica, Allen W. Brown
Traumatic Brain Injury and Risk of Alzheimer’s Disease and Related Dementias in the Population
Abstract: Background: Epidemiological studies examining associations between traumatic brain injury (TBI) and Alzheimer’s disease and related dementias (ADRD) have yielded conflicting results, which may be due methodological differences. Objective: To examine the relationship between the presence and severity of TBI and risk of ADRD using a population-based cohort with medical record abstraction for confirmation of TBI and ADRD. Methods: All TBI events among Olmsted County, Minnesota residents aged >40 years from 1985-1999 were confirmed by manual review and classified by severity. Each TBI case was randomly matched to two age-, sex-, and non-head injury population-based referents without TBI. For TBI events with non-head trauma, the Trauma Mortality Prediction Model was applied to assign an overall measure of non-head injury severity and corresponding referents were matched on this variable. Medical records were manually abstracted to confirm ADRD diagnosis. Cox proportional hazards models examined the relationship between TBI and severity with risk of ADRD. Results: A total of 1,418 residents had a confirmed TBI (865 Possible, 450 Probable, and 103 Definite) and were matched to 2,836 referents. When combining all TBI severities, the risk of any ADRD was significantly higher for those with a confirmed TBI compared to referents (HR=1.32, 95% CI: 1.11, 1.58). Stratifying by TBI severity, Probable (HR=1.42, 95% CI: 1.05, 1.92) and Possible (HR=1.29, 95% CI: 1.02-1.62) TBI was associated with an increased risk of ADRD, but not Definite TBI (HR=1.22, 95% CI: 0.68, 2.18). Conclusion: Our analyses support including TBI as a potential risk factor for developing ADRD.

Pages 1061-1074
Avram S. Bukhbinder*, Yaobin Ling*, Omar Hasan*, Xiaoqian Jiang, Yejin Kim, Kamal N. Phelps, Rosemarie E. Schmandt, Albert Amran, Ryan Coburn, Srivathsan Ramesh, Qian Xiao, Paul E. Schulz (Handling Associate Editor: Karel Kostev) *These authors contributed equally to this work.
Risk of Alzheimer’s Disease Following Influenza Vaccination: A Claims-Based Cohort Study Using Propensity Score Matching
Abstract: Background: Prior studies have found a reduced risk of dementia of any etiology following influenza vaccination in selected populations, including Veterans and patients with serious chronic health conditions. However, the effect of influenza vaccination on Alzheimer’s disease (AD) risk in a general cohort of older US adults has not been characterized. Objective: To compare the risk of incident AD between patients with and without prior influenza vaccination in a large US claims database. Methods: Deidentified claims data spanning September 1, 2009 through August 31, 2019 were used. Eligible patients were free of dementia during the 6-year look-back period and ≥65 years old by the start of follow-up. Propensity-score matching (PSM) was used to create flu-vaccinated and flu-unvaccinated cohorts with similar baseline demographics, medication usage, and comorbidities. Relative risk (RR) and absolute risk reduction (ARR) were estimated to assess the effect of influenza vaccination on AD risk during the 4-year follow-up. Results: From the unmatched sample of eligible patients (n=2,356,479), PSM produced a sample of 935,887 flu–vaccinated-unvaccinated matched pairs. The matched sample was 73.7 (SD, 8.7) years of age and 56.9% female, with median follow-up of 46 (IQR, 29-48) months; 5.1% (n=47,889) of the flu-vaccinated patients and 8.5% (n=79,630) of the flu-unvaccinated patients developed AD during follow-up. The RR was 0.60 (95% CI, 0.59-0.61) and ARR was 0.034 (95% CI, 0.033-0.035), corresponding to a number needed to treat of 29.4. Conclusion: This study demonstrates that influenza vaccination is associated with reduced AD risk in a nationwide sample of US adults aged 65 and older.

Pages 1075-1089
Masatomo Kobayashi*, Yasunori Yamada*, Kaoru Shinkawa, Miyuki Nemoto, Kiyotaka Nemoto, Tetsuaki Arai (Handling Associate Editor: Catherine Price) *These authors contributed equally to this work.
Automated Early Detection of Alzheimer’s Disease by Capturing Impairments In Multiple Cognitive Domains with Multiple Drawing Tasks
Abstract: Background: Automatic analysis of the drawing process using a digital tablet and pen has been applied to successfully detect Alzheimer's disease (AD) and mild cognitive impairment (MCI). However, most studies focused on analyzing individual drawing tasks separately, and the question of how a combination of drawing tasks could improve the detection performance thus remains unexplored. Objective: We aimed to investigate whether analysis of the drawing process in multiple drawing tasks could capture different, complementary aspects of cognitive impairments, with a view toward combining multiple tasks to effectively improve the detection capability. Methods: We collected drawing data from 144 community-dwelling older adults (27 AD, 65 MCI, and 52 cognitively normal, or CN) who performed five drawing tasks. We then extracted motion- and pause-related drawing features for each task and investigated the associations of the features with the participants' diagnostic statuses and cognitive measures. Results: The drawing features showed gradual changes from CN to MCI and then to AD, and the changes in the features for each task were statistically associated with cognitive impairments in different domains. For classification into the three diagnostic categories, a machine learning model using the features from all five tasks achieved a classification accuracy of 75.2%, an improvement by 7.8% over that of the best single-task model. Conclusion: Our results demonstrate that a common set of drawing features from multiple drawing tasks can capture different, complementary aspects of cognitive impairments, which may lead to a scalable way to improve the automated, reliable detection of AD and MCI.

Pages 1091-1101
Belinda M. Brown, Jaisalmer de Frutos Lucas, Tenielle Porter, Natalie Frost, Michael Vacher, Jeremiah J. Peiffer, Simon M. Laws
Non-Modifiable Factors as Moderators of the Relationship Between Physical Activity and Brain Volume: A Cross-Sectional UK Biobank Study
Abstract: Background: Previous research suggests physical activity attenuates grey and white matter loss; however, there appears to be individual variability in this effect. Understanding factors that can influence the relationship between physical activity and brain volume may enable prediction of individual response. Objective: The current study examined the relationship between objectively-measured physical activity and brain volume; and whether this relationship is moderated by age, sex, or a priori candidate genetic factors, brain-derived neurotrophic factor (BDNF) Val66Met, or apolipoprotein (APOE) ε4 allele carriage. Methods: Data from 10,083 men and women (50 years and over) of the UK Biobank were used to examine the study objectives. All participants underwent a magnetic resonance imaging scan to quantify grey and white matter volumes, physical activity monitoring via actigraphy, and genotyping. Results: Physical activity was associated with total grey matter volume, total white matter volume, and right hippocampal volume. Only males had an association between higher physical activity levels and greater cortical grey matter volume, total grey matter volume, and right hippocampal volume. Age moderated the relationship between physical activity and white matter volume. Conclusion: Our results indicate that in males, but not females, an association exists between objectively-measured physical activity and grey matter volume. Age may also play a role in impacting the relationship between physical activity and brain volume. Future research should evaluate longitudinal brain volumetrics to better understand the nature of age and sex-effects on the physical activity and brain volume relationship.

Pages 1103-1114
Eman M. Khedr, Nehad Omeran, Haidi Karam-Allah Ramadan, Gellan K. Ahmed, Ahmed M. Abdel Warith
Alteration of Gut Microbiota in Alzheimer’s Disease and Their Relation to the Cognitive Impairment
Abstract: Background: Dysbiosis of gut microbiota has been reported to be enrolled in the pathogenesis of Alzheimer’s disease (AD). However, there is a lack of relevant studies on this topic in Egyptian patients with AD. Objective: To investigate different species of gut microbiota in Egyptian patients with AD and correlate microbiota bacterial abundance with clinical data. Methods: The study included 25 patients with AD and 25 healthy volunteers as age and sex-matched controls. Clinical data was taken for each patient, including medical history and examination; Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA) were assessed for each participant. Bacterial DNA was extracted from stool, and abundance quantified via qPCR using 16S rRNA group-specific primers. Results: Akkermansia, Enterobacteria, Bacteroidetes, Bacillus cereus, Prevotella, and Clostridium cluster IV were more abundant in the AD group than in the control group, although there was significantly less abundance of Bifidobacterium spp., Firmicutes, and Actinobacteria in patients with AD than in controls, whereas no such significance was found for lactic acid bacteria between both groups. Lactic acid bacteria and Prevotella abundance was negatively correlated with cognitive impairment (p=0.03 with MMSE, and p=0.03 with MoCA). Prevotella abundance was positively correlated with age of onset and duration of illness and negatively correlated with smoking and coronary heart disease (p=0.007, p=0.03, p=0.035, and p=0.047, respectively). Conclusion: The current work highlighted a significant relationship between AD and gut microbiota dysbiosis. A higher abundance of Prevotella species and lactic acid bacteria was correlated with cognition.

Pages 1115-1125
Rui Pan*, Shuyi Luo*, Qing Huang, Weiwei Li, Tianshu Cai, Kelin Lai, Xiaolei Shi, for the Alzheimer’s Disease Neuroimaging Initiative *These authors contributed equally to this study.
The Associations of Cerebrospinal Fluid Ferritin with Neurodegeneration and Neuroinflammation Along the Alzheimer’s Disease Continuum
Abstract: Background: Increasing evidence has suggested that iron accumulation plays an important role in the onset and development of Alzheimer’s disease (AD). However, the potential mechanism remains unclear. Objective: The present study investigated the associations of cerebrospinal fluid (CSF) ferritin, an indicator for brain iron load, with neurodegenerative and inflammatory changes in AD. Methods: The study involved 302 participants from the Alzheimer’s Disease Neuroimaging Initiative (ADNI). They were classified as normal controls (A-T-N-, n = 48), AD continuum (A+TN-, n = 46; A+TN+, n = 166), and suspected non-AD pathology (A-TN+, n = 42), according to the amyloid/tau/neurodegeneration (ATN) system. Group comparisons of CSF ferritin among groups were performed using one-way ANOVA. Linear regression models were used to test the relationships between CSF ferritin and cognitive assessments, and the associations between CSF ferritin and other biomarkers, respectively. Results: We found that CSF ferritin showed significant differences among the ATN groups, with higher concentration in more advanced categories (A+TN+). Furthermore, CSF ferritin level was independently related to cognitive performance (MMSE, ADAS-Cog13, and ADNI-mem). Linear regression analysis indicated positive relationships between CSF ferritin and phosphorylated tau and total tau, rather than Aβ42. Significant associations were revealed between CSF ferritin and inflammatory proteins, including TNF-α, TNFR1, TNFR2, ICAM1, VCAM1, TGF-β1, IL-9, and IP-10, respectively. Conclusion: Our results provide new insight into iron dysfunction in AD pathology and highlight elevated brain iron as a possible mechanism of neurodegeneration and neuroinflammation along AD continuum.

Pages 1127-1135
Doaa G. Ali, Ahmed A. Bahrani, Justin M. Barber, Riham H. El Khouli, Brian T. Gold, Jordan P. Harp, Yang Jiang, Donna M. Wilcock, Gregory A. Jicha
Amyloid-PET Levels in the Precuneus and Posterior Cingulate Cortices Are Associated with Executive Function Scores in Preclinical Alzheimer’s Disease Prior to Overt Global Amyloid Positivity
Abstract: Background: Global amyloid-β (Aβ) deposition in the brain can be quantified by Aβ-PET scans to support or refute a diagnosis of preclinical Alzheimer’s disease (pAD). Yet, Aβ-PET scans enable quantitative evaluation of regional Aβ elevations in pAD, potentially allowing even earlier detection of pAD, long before global positivity is achieved. It remains unclear as to whether such regional changes are clinically meaningful. Objective: Test the hypothesis that early focal regional amyloid deposition in the brain is associated with cognitive performance in specific cognitive domain scores in pAD. Methods: Global and regional standardized uptake value ratios (SUVr) from 18F-florbetapir PET/CT scanning were determined using the Siemens Syngo.via® Neurology software package across a sample of 99 clinically normal participants with Montreal Cognitive Assessment (MoCA) scores ≥23. Relationships between regional SUVr and cognitive test scores were analyzed using linear regression models adjusted for age, sex, and education. Participants were divided into two groups based on SUVr in the posterior cingulate and precuneus gyri (SUVR≥1.17). Between group differences in cognitive test scores were analyzed using ANCOVA models. Results: Executive function performance was associated with increased regional SUVr in the precuneus and posterior cingulate regions only (p<0.05). There were no significant associations between memory and Aβ-PET SUVr in any regions of the brain. Conclusion: These data demonstrate that increased Aβ deposition in the precuneus and posterior cingulate (the earliest brain regions affected with Aβ pathology) is associated with changes in executive function that may precede memory decline in pAD.

Pages 1137-1145
Patricia Aguilar-Calvo, Alejandro M. Sevillano, Suhail Rasool, Kevin J. Cao, Lyndsay M. Randolph, Robert A. Rissman, Stella T. Sarraf, Jerry Yang, Christina J. Sigurdson (Handling Associate Editor: Inga Zerr)
Noninvasive Antemortem Detection of Retinal Prions by a Fluorescent Tracer
Abstract: Background: Neurodegenerative diseases are widespread yet challenging to diagnose and stage antemortem. As an extension of the central nervous system, the eye harbors retina ganglion cells vulnerable to degeneration, and visual symptoms are often an early manifestation of neurodegenerative disease. Objective: Here we test whether prion protein aggregates could be detected in the eyes of live mice using an amyloid-binding fluorescent probe and high-resolution retinal microscopy. Methods: We performed retinal imaging on an experimental mouse model of prion-associated cerebral amyloid angiopathy in a longitudinal study. An amyloid-binding fluorophore was intravenously administered, and retinal imaging was performed at timepoints corresponding to early, mid-, and terminal prion disease. Retinal amyloid deposits were quantified and compared to the amyloid load in the brain. Results: We report that by mid-prion disease (50% timepoint), discrete fluorescent foci appeared adjacent to the optic disc. By later timepoints, the fluorescent foci partly surrounded the optic disc and tracked along retinal vasculature. Conclusion: The progression of perivascular amyloid can be directly monitored in the eye by live imaging, illustrating the utility of this technology for diagnosing and monitoring the progression of cerebral amyloid-angiopathy.

Pages 1147-1155
Jan S. Novotný, Juan P. Gonzalez-Rivas, Maria Vassilaki, Janina Krell-Roesch, Yonas E. Geda, Gorazd B. Stokin
Natural Pattern of Cognitive Aging
Abstract: Background: Considering the world’s rapidly increasing life expectancy, with people working and maintaining active lifestyles longer than ever before, addressing the effects of aging on cognition is of utmost importance. A greater understanding of cognitive aging may also be critical in distinguishing natural cognitive aging from pre-clinical stages of Alzheimer’s disease and related cognitive disorders. Objective: To systematically examine the association between aging and cognitive performance in a cognitively and otherwise healthy probability population-based sample using a computer-based method. Methods: This cross-sectional study enrolled 673 cognitively and otherwise healthy participants aged 25-89 years (mean age 52.3 ±14.2 years, 52.5% of whom were female) from the Kardiovize study cohort. Mild cognitive impairment and dementia cases were excluded, followed by measurement of cognitive performance with the computer-administered Cogstate Brief Battery. We used ANCOVA and Modified Signed-Likelihood Ratio tests to examine patterns of cognition across age groups. Results: We found a gradual decrease in cognitive performance across the lifespan, which required two decades to demonstrate significant changes. In contrast to attention and learning, psychomotor speed and working memory showed the most significant age-related decrease and variability in performance. The established pattern of cognitive aging was not altered by sex or education. Conclusion: These findings corroborate, validate, and extend the current understanding of natural cognitive aging and pinpoint specific cognitive domains with the most extensive age-related interindividual differences. This will contribute to the development of strategies to preserve cognition with aging and may also serve to improve early diagnostics of cognitive disorders using computer-based methods.

Pages 1157-1165
Dorothea Dumuid, Maddison L. Mellow, Tim Olds, Emma Tregoweth, Danielle Greaves, Hannah Keage, Ashleigh E. Smith
Does APOE ε4 Status Change How 24-Hour Time-Use Composition Is Associated with Cognitive Function? An Exploratory Analysis Among Middle-to-Older Adults
Abstract: Background: The 24-h time-use composition of physical activity, sedentary behavior, and sleep is linked to cognitive function in adults and may contribute to future dementia risk. However, the impact of reallocating time between behaviors may differ depending on an individual’s genetic dementia risk. Objective: To explore if there is an interaction between 24-h time-use composition and genetic dementia risk in relation to cognitive function, and to simulate how time-reallocations are associated with cognitive function across different levels of genetic dementia risk. Methods: Cross-sectional global cognition, executive function, genetic dementia risk (at least one apolipoprotein (APOE) ε4 allele versus none) and 7 days of 24-h accelerometry (average daily time-use composition of moderate-to-vigorous physical activity (MVPA), light physical activity, sedentary time, sleep) were collected from 82 adults (65.6±7.5 years, 49 females). Linear regression was used to explore the relationship between time-use composition and cognitive measures, testing for interaction between APOE ε4 status and time-use composition. The models were used to simulate time reallocations in both APOE ε4 status groups. Results: The 24-h time-use composition was associated with global cognition (F=2.4, p=0.02) and executive function (F=2.6, p=0.01). For both measures, the association differed according to genetic risk (interactions p<0.001). In both APOE ε4 groups, reallocating time to MVPA was beneficially associated with measures of cognitive function, but associations were larger among those with at least one APOE ε4 allele. Conclusion: Genetic dementia risk may impact the effectiveness of activity interventions. Increasing MVPA may provide greater benefits among those with higher genetic dementia risk.

Pages 1167-1177
Rania M. Khalil, Shereen Alaa, Hanan Eissa, Ibrahim Youssef
Early Prediction of a Pre-Symptomatic Neurodegeneration Disorder by Measuring Macrophage Inhibitory Factor Level in Diabetic Patients
Abstract: Background: The relationship between diabetes mellitus and neurodegenerative disorders has been of great interest. Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine in which a variety of signaling cascades are activated through it. MIF has been involved in the pathogenesis of several diseases and can predict early pre-symptomatic stages of neurodegeneration in diabetic patients. Objective: To investigate whether serum MIF could predict brain neurodegeneration at the early pre-symptomatic stages in diabetic patients. Methods: We examined adults with type 2 diabetes mellitus and compared with normal control adults using a short form of the IQCODE and biochemical examination, including assessment of HA1C, fasting blood glucose, lipid profile, and MIF which was measured by ELISA technique. Correlations between parameters were studied. Computational PathLinker bioinformatic tool was used to search for potential pathway reconstructions for the insulin/amyloid-β/MIF signaling. Results: We demonstrated that MIF level was increased in the serum at the early pre-symptomatic stages of neurodegenerative disorder in diabetic patients. In addition, network analysis demonstrates that insulin receptor substrate 1 can ameliorate amyloid-β protein precursor through COP9 signalosome complex subunit 5 that enhances MIF elevation. Conclusion: Diagnosis processes could not be used as routine examinations for still pre-symptomatic neurodegenerative disorders. This may be due to the time constraints and the heavy dependence on the physician’s experience. Therefore, serum MIF level could predict brain neurodegeneration at the early pre-symptomatic stages in diabetic patients which may support its potential utility as a clinically useful biomarker.

Pages 1179-1187
Flavia Loreto*, Anna Fitzgerald*, Mara Golemme, Stephen Gunning, Zarni Win, Neva Patel, Christopher Carswell, Richard Perry, Angus Kennedy, Paul Edison, Paresh Malhotra *These authors contributed equally to this work.
Prevalence of Depressive Symptoms in a Memory Clinic Cohort: A Retrospective Study
Abstract: Background: Depression has been suggested to be a cause of reversible cognitive impairment but also a risk factor for neurodegenerative disease. Studies suggest that depression prevalence may be high in early onset dementia, particularly Alzheimer’s disease, but this has not been systematically assessed in a biomarker-validated clinical dementia cohort to date. Objective: To examine the prevalence, features, and association with amyloid pathology of lifetime depressive symptoms in a memory clinic cohort meeting appropriate use criteria for amyloid PET imaging. Methods: We included 300 patients from a single-center memory clinic cohort that received diagnostic biomarker evaluation with amyloid PET imaging according to appropriate use criteria. History of lifetime depressive symptoms was retrospectively assessed through structured review of clinical correspondence. Results: One hundred forty-two (47%) patients had a history of significant depressive symptoms (‘D+’). Of these, 89% had ongoing symptoms and 60% were on antidepressants at the time of presentation to our Clinic. Depressive symptoms were equally highly prevalent in the amyloid-positive and the heterogeneous group of amyloid-negative patients. Conclusion: Approximately half of patients who meet appropriate use criteria for amyloid PET had a history of depressive symptoms. We suggest that depression is an important feature of both neurodegenerative and non-neurodegenerative cognitive impairment and may contribute to the diagnostic uncertainty behind referral to amyloid PET.

Pages 1189-1200
Dana M. Cairns, Ruth F. Itzhaki, David L. Kaplan
Potential Involvement of Varicella Zoster Virus in Alzheimer’s Disease via Reactivation of Quiescent Herpes Simplex Virus Type 1
Abstract: Background: Varicella zoster virus (VZV) has been implicated in Alzheimer’s disease (AD), and vaccination against shingles, caused by VZV, has been found to decrease the risk of AD/dementia. VZV might reside latently in brain, and on reactivation might cause direct damage leading to AD, as proposed for herpes simplex virus type 1 (HSV-1), a virus strongly implicated in AD. Alternatively, shingles could induce neuroinflammation and thence, reactivation of HSV-1 in brain. Objective: To investigate these possibilities by comparing the effects of VZV and HSV-1 infection of cultured cells, and the action of VZV infection on cells quiescently infected with HSV-1. Methods: We infected human-induced neural stem cell (hiNSC) cultures with HSV-1 and/or VZV and sought the presence of AD-related phenotypes such as amyloid-β (Aβ) and P-tau accumulation, gliosis, and neuroinflammation. Results: Cells infected with VZV did not show the main AD characteristics, Aβ and P-tau accumulation, which HSV-1 does cause, but did show gliosis and increased levels of pro-inflammatory cytokines, suggesting that VZV’s action relating to AD/dementia is indirect. Strikingly, we found that VZV infection of cells quiescently infected with HSV-1 causes reactivation of HSV-1 and consequent AD-like changes, including Aβ and P-tau accumulation. Conclusion: Our results are consistent with the suggestion that shingles causes reactivation of HSV1 in brain and with the protective effects against AD of various vaccines, as well as the decrease in herpes labialis reported after certain types of vaccination. They support an indirect role for VZV in AD/dementia via reactivation of HSV-1 in brain.

Pages 1201-1202
Book Review
Releasing the Butterfly: A Love Affair in Four Acts by Max Sherman, 2020, 280 pp. Reviewed by Jenny Sarpalius