Pages 1111-1129
Review
Amy Loughman, Christina Adler, Helen Macpherson
Unlocking Modifiable Risk Factors for Alzheimer’s Disease: Does the Oral Microbiome Hold Some of the Keys?
Abstract: Advancing age is recognized as the primary risk factor for Alzheimer’s disease (AD); however approximately one third of dementia cases are attributable to modifiable risk factors such as hypertension, diabetes, smoking, and obesity. Recent research also implicates oral health and the oral microbiome in AD risk and pathophysiology. The oral microbiome contributes to the cerebrovascular and neurodegenerative pathology of AD via the inflammatory, vascular, neurotoxic, and oxidative stress pathways of known modifiable risk factors. This review proposes a conceptual framework that integrates the emerging evidence regarding the oral microbiome with established modifiable risk factors. There are numerous mechanisms by which the oral microbiome may interact with AD pathophysiology. Microbiota have immunomodulatory functions, including the activation of systemic pro-inflammatory cytokines. This inflammation can affect the integrity of the blood-brain barrier, which in turn modulates translocation of bacteria and their metabolites to brain parenchyma. Amyloid-β is an antimicrobial peptide, a feature which may in part explain its accumulation. There are microbial interactions with cardiovascular health, glucose tolerance, physical activity, and sleep, suggesting that these modifiable lifestyle risk factors of dementia may have microbial contributors. There is mounting evidence to suggest the relevance of oral health practices and the microbiome to AD. The conceptual framework presented here additionally demonstrates the potential for the oral microbiome to comprise a mechanistic intermediary between some lifestyle risk factors and AD pathophysiology. Future clinical studies may identify specific oral microbial targets and the optimum oral health practices to reduce dementia risk.
Pages 1131-1146
Review
Jay Shah, Md Mahfuzur Rahman Siddiquee, Janina Krell-Roesch, Jeremy A. Syrjanen, Walter K. Kremers, Maria Vassilaki, Erica Forzani, Teresa Wu, Yonas E. Geda
Neuropsychiatric Symptoms and Commonly Used Biomarkers of Alzheimer’s Disease: A Literature Review from a Machine Learning Perspective
Abstract: There is a growing interest in the application of machine learning (ML) in Alzheimer’s disease (AD) research. However, neuropsychiatric symptoms (NPS), frequent in subjects with AD, mild cognitive impairment (MCI), and other related dementias have not been analyzed sufficiently using ML methods. To portray the landscape and potential of ML research in AD and NPS studies, we present a comprehensive literature review of existing ML approaches and commonly studied AD biomarkers. We conducted PubMed searches with keywords related to NPS, AD biomarkers, machine learning, and cognition. We included a total of 38 articles in this review after excluding some irrelevant studies from the search results and including 6 articles based on a snowball search from the bibliography of the relevant studies. We found a limited number of studies focused on NPS with or without AD biomarkers. In contrast, multiple statistical machine learning and deep learning methods have been used to build predictive diagnostic models using commonly known AD biomarkers. These mainly included multiple imaging biomarkers, cognitive scores, and various omics biomarkers. Deep learning approaches that combine these biomarkers or multi-modality datasets typically outperform single-modality datasets. We conclude ML may be leveraged to untangle the complex relationships of NPS and AD biomarkers with cognition. This may potentially help to predict the progression of MCI or dementia and develop more targeted early intervention approaches based on NPS.
Pages 1147-1171
Review
Sara E. Dingle, Melissa S. Bujtor, Catherine M. Milte, Steven J. Bowe, Robin M. Daly, Susan J. Torres
Statistical Approaches for the Analysis of Combined Health-Related Factors in Association with Adult Cognitive Outcomes: A Scoping Review
Abstract: Background: Dementia prevention is a global health priority, and there is emerging evidence to support associations between individual modifiable health behaviors and cognitive function and dementia risk. However, a key property of these behaviors is they often co-occur or cluster, highlighting the importance of examining them in combination. Objective: To identify and characterize the statistical approaches used to aggregate multiple health-related behaviors/modifiable risk factors and assess associations with cognitive outcomes in adults. Methods: Eight electronic databases were searched to identify observational studies exploring the association between two or more aggregated health-related behaviors and cognitive outcomes in adults. Results: Sixty-two articles were included in this review. Fifty articles employed co-occurrence approaches alone to aggregate health behaviors/other modifiable risk factors, eight studies used solely clustering-based approaches, and four studies used a combination of both. Co-occurrence methods include additive index-based approaches and presenting specific health combinations, and whilst simple to construct and interpret, do not consider the underlying associations between co-occurring behaviors/risk factors. Clustering-based approaches do focus on underlying associations, and further work in this area may aid in identifying at-risk subgroups and understanding specific combinations of health-related behaviors/risk factors of particular importance in the scope of cognitive function and neurocognitive decline. Conclusion: A co-occurrence approach to aggregating health-related behaviors/risk factors and exploring associations with adult cognitive outcomes has been the predominant statistical approach used to date, with a lack of research employing more advanced statistical methods to explore clustering-based approaches.
Pages 1173-1198
Review
Yunlong Xu, Fuxiang Zheng, Qi Zhong, Yingjie Zhu (Handling Associate Editor: Jianping Jia)
Ketogenic Diet as a Promising Non-Drug Intervention for Alzheimer’s Disease: Mechanisms and Clinical Implications
Abstract: Alzheimer's disease (AD) is a progressive neurodegenerative disorder that is mainly characterized by cognitive deficits. Although many studies have been devoted to developing disease-modifying therapies, there has been no effective therapy until now. However, dietary interventions may be a potential strategy to treat AD. The ketogenic diet (KD) is a high-fat and low-carbohydrate diet with adequate protein. KD increases the levels of ketone bodies, providing an alternative energy source when there is not sufficient energy supply because of impaired glucose metabolism. Accumulating preclinical and clinical studies have shown that a KD is beneficial to AD. The potential underlying mechanisms include improved mitochondrial function, optimization of gut microbiota composition, and reduced neuroinflammation and oxidative stress. The review provides an update on clinical and preclinical research on the effects of KD or medium-chain triglyceride supplementation on symptoms and pathophysiology in AD. We also detail the potential mechanisms of KD, involving amyloid and tau proteins, neuroinflammation, gut microbiota, oxidative stress, and brain metabolism. We aimed to determine the function of the KD in AD and outline important aspects of the mechanism, providing a reference for the implementation of the KD as a potential therapeutic strategy for AD.
Pages 1199-1217
Systematic Review
Deborah A. Jehu, Jennifer C. Davis, Jessica Gill, Olabamibo Oke, Teresa Liu-Ambrose
The Effect of Exercise on Falls in People Living with Dementia: A Systematic Review
Abstract: Background: People living with dementia (PWD) are at a heightened risk for falls. However, the effects of exercise on falls in PWD are unclear. Objective: To conduct a systematic review of randomized controlled trials (RCTs) examining the efficacy of exercise to reduce falls, recurrent falls, and injurious falls relative to usual care among PWD. Methods: We included peer-reviewed RCTs evaluating any exercise mode on falls and related injuries among medically diagnosed PWD aged ≥55years (international prospective register of systematic reviews (PROSPERO) ID:CRD42021254637). We excluded studies that did not solely involve PWD and were not the primary publication examining falls. We searched the Cochrane Dementia and Cognitive Improvement Group’s Specialized Register and grey literature on 08/19/2020 and 04/11/2022; topical categories included dementia, exercise, RCTs, and falls. We evaluated the risk of bias (ROB) using the Cochrane ROB Tool-2 and study quality using the Consolidated Standards of Reporting Trials. Results: Twelve studies were included (n=1,827; age=81.3±7.0 years; female=59.3%; Mini-Mental State Examination=20.1±4.3 points; intervention duration=27.8±18.5 weeks; adherence=75.5±16.2%; attrition=21.0±12.4%). Exercise reduced falls in two studies [Incidence Rate Ratio (IRR) range=0.16 to 0.66; fall rate range: intervention=1.35-3.76 falls/year, control=3.07-12.21 falls/year]; all other studies (n=10) reported null findings. Exercise did not reduce recurrent falls (n=0/2) or injurious falls (n=0/5). The RoB assessment ranged from some concerns (n=9) to high RoB (n=3); no studies were powered for falls. The quality of reporting was good (78.8±11.4%). Conclusion: There was insufficient evidence to suggest that exercise reduces falls, recurrent falls, or injurious falls among PWD. Well-designed studies powered for falls are needed.
Pages 1219-1227
Short Communication
Angela C. Golas*, Patrick Salwierz*, Tarek K. Rajji, Christopher R. Bowie, Meryl A. Butters, Corinne E. Fischer, Alastair J. Flint, Nathan Herrmann, Linda Mah, Benoit H. Mulsant, Bruce G. Pollock, Foad Taghdiri, Wei Wang, M. Carmela Tartaglia0 on behalf of the PACt-MD Study Group *These authors contributed equally to this work.
Assessing the Role of Past Depression in Patients with Mild Cognitive Impairment, with and without Biomarkers for Alzheimer’s Disease
Abstract: Major depressive disorder (MDD) is a risk factor for Alzheimer’s disease (AD). Cerebrovascular disease (CVD) is implicated in MDD and AD. Our study compared participants with AD positive and negative cerebrospinal fluid (CSF) biomarkers on neuropsychological performance, remitted MDD status, and CVD burden. Next, we compared AD-CSF biomarkers and white matter hyperintensities (WMH) burden among three groups: mild cognitive impairment (MCI) (n=12), MCI with remitted MDD (MDD+MCI) (n=12), and remitted MDD alone (MDD) (n=7). Few participants (18%) with MCI+MDD exhibited AD(+) biomarkers. Nearly all participants had moderate-severe WMH. WMH may contribute to cognitive impairment or depression in MCI patients with AD(-) biomarkers.
Pages 1229-1239
Ann Abraham Daniel, Talisa Silzer, Jie Sun, Zhengyang Zhou, Courtney Hall, Nicole Phillips, Robert Barber
Hypermethylation at CREBBP Is Associated with Cognitive Impairment in a Mexican American Cohort
Abstract: Background: The aging Mexican American (MA) population is the fastest growing ethnic minority group in the US. MAs have a unique metabolic-related risk for Alzheimer’s disease (AD) and mild cognitive impairment (MCI), compared to non-Hispanic whites (NHW). This risk for cognitive impairment (CI) is multifactorial involving genetics, environmental, and lifestyle factors. Changes in environment and lifestyle can alter patterns and even possibly reverse derangement of DNA methylation (a form of epigenetic regulation). Objective: We sought to identify ethnicity-specific DNA methylation profiles that may be associated with CI in MAs and NHWs. Methods: DNA obtained from peripheral blood of 551 participants from the Texas Alzheimer's Research and Care Consortium was typed on the Illumina Infinium® MethylationEPIC chip array, which assesses over 850K CpG genomic sites. Within each ethnic group (N=299 MAs, N=252 NHWs), participants were stratified by cognitive status (control versus CI). Beta values, representing relative degree of methylation, were normalized using the Beta MIxture Quantile dilation method and assessed for differential methylation using the Chip Analysis Methylation Pipeline (ChAMP), limma and cate packages in R. Results: Two differentially methylated sites were significant: cg13135255 (MAs) and cg27002303 (NHWs) based on an FDR p<0.05. Three suggestive sites obtained were cg01887506 (MAs) and cg10607142 and cg13529380 (NHWs). Most methylation sites were hypermethylated in CI compared to controls, except cg13529380 which was hypomethylated. Conclusion: The strongest association with CI was at cg13135255 (FDR-adjusted p=0.029 in MAs), within the CREBBP gene. Moving forward, identifying additional ethnicity-specific methylation sites may be useful to discern CI risk in MAs.
Pages 1241-1256
Yi Li, Jin-zhao Wang, Yue-ming Deng, Kun Wang, Li Yang, Cheng Long (Handling Associate Editor: Ling-Qiang Zhu)
Amyloid-β Protein Precursor Regulates Electrophysiological Properties in the Hippocampus via Altered Kv1.4 Expression and Function in Mice
Abstract: Background: Amyloid-β protein precursor (AβPP) is enriched in neurons. However, the mechanism underlying AβPP regulation of neuronal activity is poorly understood. Potassium channels are critically involved in neuronal excitability. In hippocampus, A-type potassium channels are highly expressed and involved in determining neuronal spiking. Objective: We explored hippocampal local field potential (LFP) and spiking in the presence and absence of AβPP, and the potential involvement of an A-type potassium channel. Methods: We used in vivo extracellular recording and whole-cell patch-clamp recording to determine neuronal activity, current density of A-type potassium currents, and western blot to detect changes in related protein levels. Results: Abnormal LFP was observed in AβPP-/- mice, including reduced beta and gamma power, and increased epsilon and ripple power. The firing rate of glutamatergic neurons reduced significantly, in line with an increased action potential rheobase. Given that A-type potassium channels regulate neuronal firing, we measured the protein levels and function of two major A-type potassium channels and found that the post-transcriptional level of Kv1.4, but not Kv4.2, was significantly increased in the AβPP-/- mice. This resulted in a marked increase in the peak time of A-type transient outward potassium currents in both glutamatergic and gamma-aminobutyric acid-ergic (GABAergic) neurons. Furthermore, a mechanistic experiment using human embryonic kidney 293 (HEK293) cells revealed that the AβPP deficiency-induced increase in Kv1.4 may not involve protein-protein interaction between AβPP and Kv1.4. Conclusion: This study suggests that AβPP modulates neuronal firing and oscillatory activity in the hippocampus, and Kv1.4 may be involved in mediating the modulation.
Pages 1257-1267
Elizabeth Mahanna-Gabrielli, Sayaka Kuwayama, Wassim Tarraf, Sonya Kaur, Delia Cabrera DeBuc, Jianwen Cai, Martha L. Daviglus, Charlotte E. Joslin, David J. Lee, Carlos Mendoza-Santiesteban, Ariana M. Stickel, Diane Zheng, Hector M. González, Alberto R. Ramos (Handling Associate Editor: Mohammad Nami)
The Effect of Self-Reported Visual Impairment and Sleep on Cognitive Decline: Results of the Hispanic Community Health Study/Study of Latinos
Abstract: Background: Visual impairment could worsen sleep/wake disorders and cognitive decline. Objective: To examine interrelations among self-reported visual impairment, sleep, and cognitive decline in the Hispanic Community Health Study/Study of Latinos (HCHS/SOL) Miami-site. Method: HCHS/SOL Miami-site participants ages 45-74 years (n=665) at Visit-1, who returned for cognitive test 7-years later (SOL-INCA). Participants completed the National Eye Institute Visual Functioning Questionnaire (NEI-VFQ), validated sleep questionnaires and test for obstructive sleep apnea (OSA) at Visit-1. We obtained verbal episodic learning and memory, verbal fluency, processing speed, and executive functioning at Visit-1 and at SOL-INCA. Processing speed/executive functioning were added to SOL-INCA. We examined global cognition and change using a regression-based reliable change index, adjusting for the time lapse between Visit-1 and SOL-INCA. We used regression models to test whether 1) persons with OSA, self-reported sleep duration, insomnia, and sleepiness have an increased risk for visual impairment, 2a) visual impairment is associated with worse cognitive function and/or decline, and 2b) sleep disorders attenuate these associations. Result: Sleepiness (β=0.04; p<0.01) and insomnia (β=0.04; p<0.001) were cross-sectionally associated with visual impairment, adjusting for sociodemographic characteristics, behavioral factors, acculturation, and health conditions. Visual impairment was associated with lower global cognitive function at Visit-1 (β=-0.16; p<0.001) and on average 7-years later (β=-0.18; p<0.001). Visual impairment was also associated with a change in verbal fluency (β=-0.17; p<0.01). OSA, self-reported sleep duration, insomnia, and sleepiness did not attenuate any of the associations. Conclusion: Self-reported visual impairment was independently associated with worse cognitive function and decline.
Pages 1269-1282
Deirdre M. O’Shea, James E. Galvin (Handling Associate Editor: Maheen Adamson)
Female APOE ε4 Carriers with Slow Rates of Biological Aging Have Better Memory Performances Compared to Female ε4 Carriers with Accelerated Aging
Abstract: Background: Evidence suggests that APOE ε4 carriers have worse memory performances compared to APOE ε4 non-carriers in older adults and effects may vary by sex and age. Estimates of biological age, using DNA methylation age estimates may enhance understanding of the associations between sex and APOE ε4 on cognition. Objective: To investigate whether associations between APOE ε4 status and memory vary according to rates of biological aging, using a DNA methylation age biomarker, in older men and women without dementia. Methods: Data were obtained from 1,771 adults enrolled in the 2016 wave of the Health and Retirement Study. A series of ANCOVAs were used to test the interaction effects of APOE ε4 status and aging rates (defined as 1 standard deviation below (i.e., slow rate), or above (i.e., fast rate) their sex-specific mean rate of aging on a composite measure of verbal learning and memory. Results: APOE ε4 female carriers with slow rates of GrimAge had significantly better memory performances compared to fast and average aging APOE ε4 female carriers. There was no effect of aging group rate on memory in the female non-carriers and no significant differences in memory according to age rate in either male APOE ε4 carriers or non-carriers. Conclusion: Slower rates of aging in female APOE ε4 carriers may buffer against the negative effects of the ε4 allele on memory. However, longitudinal studies with larger sample sizes are needed to evaluate risk of dementia/memory impairment based on rates of aging in female APOE ε4 carriers.
Pages 1283-1287
Hanxiang Liu, Gavin P. Reynolds, Xianwen Wei
The Influence of Agricultural Work and Plasma Uric Acid on Hospital Admission for Alzheimer’s Disease
Abstract: Background: Exposure to environmental neurotoxins associated with agricultural work, such as pesticides, may be a risk factor for neurodegenerative disorders such as Alzheimer’s (AD) and Parkinson’s (PD) diseases. There is strong evidence that such exposure is associated with the development of PD; for AD the current evidence is equivocal. Several mechanisms are proposed to mediate this environmental toxicity, one of which is oxidative stress. Uric acid (UA) is an endogenous antioxidant, low levels of which are also implicated in neurodegenerative disease. Objective: This study aimed to determine whether agricultural work was a risk factor for AD in a population in which its association with PD was established, and whether UA was also associated with AD in this cohort. Methods: Hospital records of subjects meeting criteria for AD (n=128) or vascular dementia (VaD) (n=178) after hospital admission for symptoms of dementia were studied. History of agricultural work and plasma UA were recorded and their relationship to diagnosis determined. Results: In contrast to previous findings in this population in which agricultural work was strongly associated with PD, a history of agricultural work was not over-represented in hospital admission for AD versus VaD. AD was associated with a reduced level of circulating UA compared with VaD. Conclusion: Agricultural work as a likely proxy for exposure to pesticides appears not to be a risk factor for AD to the extent found in PD, perhaps reflecting their differences in neuronal pathology. Nevertheless, findings with UA suggests that oxidative stress may be an important factor in AD pathogenesis.
Pages 1289-1302
Maria I. Lazarova, Lyubka P. Tancheva, Krasimira N. Tasheva, Petko N. Denev, Diamara N. Uzunova, Miroslava O. Stefanova, Elina R. Tsvetanova, Almira P. Georgieva, Reni E. Kalfin
Effects of Sideritis scardica Extract on Scopolamine-Induced Learning and Memory Impairment in Mice
Abstract: Background: The neurodegenerative process in Alzheimer's disease, one of the most common types of dementia worldwide, mostly affects the cholinergic neurotransmitter system and, to a lesser extent, the monoaminergic one. The antioxidant acetylcholinesterase (AChE) and triple monoamine reuptake inhibitory activity of Sideritis scardica (S. scardica) and other Sideritis species has already been reported. Objective: To investigate the effects of S. scardica water extracts on the learning and memory processes, anxiety-like behavior, and locomotor activities in scopolamine (Sco)-induced dementia in mice. Methods: Male Albino IRC mice were used. The plant extract was administered for 11 consecutive days in the presence or absence of Sco (1 mg/kg, i.p). The behavioural performance of the animals was evaluated by passive avoidance, T-maze, and hole-board tests. The effects of extract on AChE activity, brain noradrenalin (NA), and serotonin (Sero) content, аnd antioxidant status were also monitored. Results: Our experimental data revealed that the S. scardica water extract caused a reduction in degree of memory impairment and anxiety-like behaviour in mice with scopolamine-induced dementia. The extract did not affect changed by the Sco AChE activity but impact reduced brain NA and Sero levels and demonstrated moderate antioxidant activity. In healthy mice we did not confirm the presence of anxiolytic-like and AChE inhibitory effects of the S. scardica water extract. The extract did not change the control Sero brain levels and reduce those of NA. Conclusion: S. scardica water extract demonstrated memory preserving effect in mice with scopolamine-induced dementia and deserve further attention.
Pages 1303-1321
Greta García-Escobar, Albert Puig-Pijoan, Víctor Puente-Periz, Aida Fernández-Lebrero, Rosa María Manero, Irene Navalpotro-Gómez, Marc Suárez-Calvet, Oriol Grau-Rivera, José Contador-Muñana, Diego Cascales-Lahoz, Xavier Duran-Jordà, Núncia Boltes, Maria Claustre Pont-Sunyer, Jordi Ortiz-Gil, Sara Carrillo-Molina, María Dolores López-Villegas, María Teresa Abellán-Vidal, María Isabel Martínez-Casamitjana, Juan José Hernández-Sánchez, Anna Padrós-Fluvià, Jordi Peña-Casanova, Gonzalo Sánchez-Benavides
NEURONORMA Cognitive Battery Associations with Cerebrospinal Fluid Amyloid-β and Tau Levels in the Continuum of Alzheimer’s Disease
Abstract: Background: Neuropsychological assessments are essential to define the cognitive profile and contribute to the diagnosis of Alzheimer’s disease (AD). The progress in knowledge about the pathophysiological process of the disease has allowed conceptualizing AD through biomarkers as a biological continuum that encompasses different clinical stages. Objective: To explore the association between cerebrospinal fluid (CSF) biomarkers of AD and cognition using the NEURONORMA battery, in a sample of cognitively unimpaired (CU), mild cognitive impaired (MCI), and mild dementia of the Alzheimer type (DAT) subjects, and to characterize the cognitive profiles in MCI subjects classified by A/T/N system. Methods: 42 CU, 35 MCI, and 35 mild DAT were assessed using the NEURONORMA battery. Core AD biomarkers [amyloid-β 42 (Aβ42) peptide, total tau (t-tau), and phosphorylated tau 181 (p-tau181)] proteins were measured in CSF. Correlation coefficients, multivariate regression, and effect sizes were calculated. We explored the age- and education-adjusted cognitive profiles by A/T/N variants within the MCI group. Results: Cognitive outcomes were directly associated with CSF Aβ42 and inversely with CSF tau measures. We found differences in both biomarkers and cognitive outcomes comparing all pairs except for CSF measures between cognitively impaired groups. The highest effect size was in memory tasks and biomarkers ratios. Lower performances were in memory and executive domains in MCI subjects with AD pathology (A+T+N±) compared to those with normal levels of AD biomarkers (A-T-N). Conclusion: This study provides further evidence of the validity of Spanish NEURONORMA cognitive battery to characterize cognitive impairment in the AD pathological continuum.
Pages 1323-1339
Avram S. Bukhbinder*, Miriam Hinojosa*, Kristofer Harris*, Xiaojin Li, Christine M. Farrell, Madison Shyer, Nathan Goodwin, Sahar Anjum, Omar Hasan, Susan Cooper, Lois Sciba, Amanda Falk Vargas, David H. Hunter, Guadalupe J. Ortiz, Karen Chung, Licong Cui, Guo-Qiang Zhang, Susan P. Fisher-Hoch, Joseph B. McCormick, Paul E. Schulz *These authors contributed equally to this work.
Population-Based Mini-Mental State Examination Norms in Adults of Mexican Heritage in the Cameron County Hispanic Cohort
Abstract: Background: Accurately identifying cognitive changes in Mexican American (MA) adults using the Mini-Mental State Examination (MMSE) requires knowledge of population-based norms for the MMSE, a scale which has widespread use in research settings. Objective: To describe the distribution of MMSE scores in a large cohort of MA adults, assess the impact of MMSE requirements on their clinical trial eligibility, and explore which factors are most strongly associated with their MMSE scores. Methods: Visits between 2004–2021 in the Cameron County Hispanic Cohort were analyzed. Eligible participants were ≥18 years old and of Mexican descent. MMSE distributions before and after stratification by age and years of education (YOE) were assessed, as was the proportion of trial-aged (50-85–year-old) participants with MMSE <24, a minimum MMSE cutoff most frequently used in Alzheimer’s disease (AD) clinical trials. As a secondary analysis, random forest models were constructed to estimate the relative association of the MMSE with potentially relevant variables. Results: The mean age of the sample set (n=3,404) was 44.4 (SD, 16.0) years old and 64.5% female. Median MMSE was 28 (IQR, 28-29). The percentage of trial-aged participants (n=1,267) with MMSE < 24 was 18.6% overall and 54.3% among the subset with 0-4 YOE (n=230). The five variables most associated with the MMSE in the study sample were education, age, exercise, C-reactive protein, and anxiety. Conclusion: The minimum MMSE cutoffs in most phase III prodromal-to-mild AD trials would exclude a significant proportion of trial-aged participants in this MA cohort, including over half of those with 0-4 YOE.
Pages 1341-1355
Feng Zhang*, Long Niu*, Rujia Zhong*, Song Li, Weidong Le *These authors contribute equally to this work.
Chronic Sleep Disturbances Alters Sleep Structure and Tau Phosphorylation in AβPP/PS1 AD Mice and Their Wild-Type Littermates
Abstract: Background: Emerging evidence indicates that sleep disorders are the common non-cognitive symptoms of Alzheimer’s disease (AD), and they may contribute to the pathogenesis of this disease. Objective: In this study, we aim to investigate the effect of chronic sleep deprivation (CSD) on AD-related pathologies with a focus on tau phosphorylation and the underlying DNA methylation regulation. Methods: AβPPswe/PS1ΔE9 AD mice and their wild-type (WT) littermates were subjected to a two-month CSD followed by electroencephalography and electromyography recording. The mice were examined for learning and memory evaluation, then pathological, biochemical, and epigenetic assessments including western blotting, immunofluorescence, dot blotting, and bisulfite sequencing. Results: The results show that CSD caused sleep disorders shown as sleep pattern change, poor sleep maintenance, and increased sleep fragmentation. CSD increased tau phosphorylation at different sites and increased the level of tau kinases in AD and WT mice. The increased expression of cyclin-dependent kinase 5 (CDK5) may result from decreased DNA methylation of CpG sites in the promoter region of CDK5 gene, which might be associated with the downregulation of DNA methyltransferase 3A and 3B. Conclusion: CSD altered AD-related tau phosphorylation through epigenetic modification of tau kinase gene. The findings in this study may give insights into the mechanisms underlying the effects of sleep disorders on AD pathology and provide new therapeutic targets for the treatment of this disease.
Pages 1357-1365
Shan Xu*, Linyun Xie*, Yao Zhang, Xiao Wu, Hui Hong, Ruiting Zhang, Qingze Zeng, Kaicheng Li, Xiao Luo, Minming Zhang, Jianzhong Sun, Peiyu Huang and for behalf of Alzheimer’s Disease Neuroimaging Initiative* *These authors contributed equally to this work.
Inferior Frontal Sulcal Hyperintensity on FLAIR Is Associated with Small Vessel Disease but not Alzheimer’s Disease Pathology
Abstract: Background: The inferior frontal sulci are essential sites on the route of cerebrospinal fluid outflow. A recent study suggests that inferior frontal sulcal hyperintensities (IFSH) on FLAIR images might be related to glymphatic dysfunction. Objective: To investigate whether IFSH is associated with Alzheimer’s disease (AD) pathology and cerebral small vessel disease (SVD) burden. Methods: We retrospectively collected data from 272 non-demented subjects in the ADNI3 database. The IFSH was assessed on 3D fluid-attenuated inversion recovery images. The standardized uptake value ratios of amyloid and tau PET were used to reflect the AD pathology burden. To measure the SVD burden, we assessed white matter hyperintensities (WMH), dilation of perivascular spaces, microbleeds, and lacunes. Finally, we performed ordinal logistic regression analyses to investigate the associations between the IFSH score and AD pathology and SVD burden. Results: The IFSH score was associated with the deep WMH score (OR, 1.79; 95% CI, 1.24 - 2.59) controlling for age and sex. The association remained significant in the multivariable regression models. There was no association between the IFSH score and AD pathology burden. Conclusion: This study suggests that the IFSH sign is associated with SVD but not AD pathology. Further studies are needed to confirm the findings.
Pages 1367-1384
Seyyed M.H. Haddad, Frederico Pieruccini-Faria, Manuel Montero-Odasso, Robert Bartha
Localized White Matter Tract Integrity Measured by Diffusion Tensor Imaging Is Altered in People with Mild Cognitive Impairment and Associated with Dual-Task and Single-Task Gait Speed
Abstract: Background: Altered white matter (WM) tract integrity may contribute to mild cognitive impairment (MCI) and gait abnormalities. Objective: The purpose of this study was to determine whether diffusion tensor imaging (DTI) metrics were altered in specific portions of WM tracts in people with MCI and to determine whether gait speed variations were associated with the specific DTI metric changes. Methods: DTI was acquired in 44 people with MCI and 40 cognitively normal elderly controls (CNCs). Fractional anisotropy (FA) and radial diffusivity (RD) were measured along 18 major brain WM tracts using probabilistic tractography. The average FA and RD along the tracts were compared between the groups using MANCOVA and post-hoc tests. The tracts with FA or RD differences between the groups were examined using an along-tract exploratory analysis to identify locations that differed between the groups. Associations between FA and RD in whole tracts and in the segments of the tracts that differed between the groups and usual/dual-task gait velocities and gross cognition were examined. Results: Lower FA and higher RD was observed in right cingulum-cingulate gyrus endings (rh.ccg) of the MCI group compared to the CNC group. These changes were localized to the posterior portions of the rh.ccg and correlated with gait velocities. Conclusion: Lower FA and higher RD in the posterior portion of the rh.ccg adjacent to the posterior cingulate suggests decreased microstructural integrity in the MCI group. The correlation of these metrics with gait velocities suggests an important role for this tract in maintaining normal cognitive-motor function.
Pages 1385-1397
Chiara Giuseppina Bonomi, Martina Assogna, Martina Gaia Di Donna, Francesca Bernocchi, Vincenzo De Lucia, Marzia Nuccetelli, Denise Fiorelli, Stefano Loizzo, Nicola Biagio Mercuri, Giacomo Koch, Alessandro Martorana, Caterina Motta (Handling Associate Editor: Marco Bozzali)
Cerebrospinal Fluid sTREM-2, GFAP, and β-S100 in Symptomatic Sporadic Alzheimer’s Disease: Microglial, Astrocytic, and APOE Contributions Along the Alzheimer’s Disease Continuum
Abstract: Background: Many transversal mechanisms act synergistically at different time-points in the cascade of Alzheimer’s disease (AD), since amyloid-β (Aβ) deposition, tau pathology, and neuroinflammation influence each other. Objective: We explored the contributions of microglia and astrocytes in patients with symptomatic sporadic AD stratified according to AT(N) system and APOE genotype. Methods: We compared the cerebrospinal fluid (CSF) levels of sTREM-2 and markers of astrocytic activation (GFAP; β-S100) from 71 patients with AD (23 A+T-,48 A+T+; 38 APOE ε3, 33 APOE ε4) and 30 healthy controls (HC). With multivariate analyses we investigated associations between glial biomarkers, Aβ42, and p-tau in all subgroups. Results: CSF sTREM-2 was higher in A+T+ [1.437 (0.264)] and A+T- [1.355 (0.213)] than in HC [1.042 (0.198); both p<0.001]; GFAP and β-S100 were comparable across groups. Considering all patients, sTREM-2 positively associated with Aβ42 (p=0.04) and p-tau (=0.016), with the first being present only in the A+T- subgroup (p=0.023). GFAP positively associated with Aβ42 in all patients (p=0.020) and in the A+T+ subgroup (p=0.04). Stratifying by APOE, a positive association of sTREM-2 and p-tau was confirmed selectively in carriers of ε4 (p=0.018). Finally, sTREM-2 positively correlated with β-S100 in all subgroups, and with GFAP in A+T+ (p=0.042). Conclusion: Our results confirm the increase of CSF sTREM-2 in AD, which associates with reduced amyloidopathy in A+T- patients. Moreover, microglial activation seems to increase CSF tau levels in carriers of APOE ε4, is associated with astrocytic reactivity (GFAP) in A+T+, and likely leads the acquisition of a more neurotoxic astrocytic phenotype (β-S100).
Pages 1399-1412
Yasmin Hollenbenders, Monika Pobiruchin, Alexandra Reichenbach, for the Alzheimer‘s Disease Neuroimaging Initiative (Handling Associate Editor: Jeffrey Prescott)
Two Routes to Alzheimer’s Disease Based on Differential Structural Changes in Key Brain Regions
Abstract: Background: Alzheimer's disease (AD) is a neurodegenerative disorder with homogenous disease patterns. Neuropathological changes precede symptoms by up to two decades making neuroimaging biomarkers a prime candidate for early diagnosis, prognosis, and patient stratification. Objective: The goal of the study was to discern intermediate AD stages and their precursors based on neuroanatomical features for stratifying patients on their progression through different stages. Methods: Data include grey matter features from 14 brain regions extracted from longitudinal structural MRI and cognitive data obtained from 1,017 healthy controls and AD patients of ADNI. AD progression was modeled with a Hidden Markov Model, whose hidden states signify disease stages derived from the neuroanatomical data. To tie the progression in brain atrophy to a behavioral marker, we analyzed the ADAS-cog sub-scores in the stages. Results: The optimal model consists of eight states with differentiable neuroanatomical features, forming two routes crossing once at a very early point and merging at the final state. The cortical route is characterized by early and sustained atrophy in cortical regions. The limbic route is characterized by early decrease in limbic regions. Cognitive differences between the two routes are most noticeable in the memory domain with subjects from the limbic route experiencing stronger memory impairments. Conclusion: Our findings corroborate that more than one pattern of grey matter deterioration with several discernable stages can be identified in the progression of AD. These neuroanatomical subtypes are behaviorally meaningful and provide a door into early diagnosis of AD and prognosis of the disease’s progression.
Pages 1413-1426
Yan He*, Junjie Li*, Liling Yi, Xiaohuan Li, Man Luo, Yayan Pang, Maoju Wang, Zhaolun Li, Mingliang Xu, Zhifang Dong, Yehong Du (Handling Associate Editor: Ling-Qiang Zhu) *These authors contributed equally to this work.
Octadecaneuropeptide Ameliorates Cognitive Impairments Through Inhibiting Oxidative Stress in Alzheimer’s Disease Models
Abstract: Background: Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by amyloid-β peptide (Aβ) deposition. Aβ accumulation induces oxidative stress, leading to mitochondrial dysfunction, apoptosis, and so forth. Octadecaneuropeptide (ODN), a diazepam-binding inhibitor (DBI)-derived peptide, has been reported to have antioxidant properties. However, it is unclear whether ODN has neuroprotective effects in AD. Objective: To profile the potential effects of ODN on AD. Methods: We established a mouse model of AD via microinjection of Aβ in the lateral ventricle. Utilizing a combination of western blotting assays, electrophysiological recordings, and behavioral tests, we investigated the neuroprotective effects of ODN on AD. Results: DBI expression was decreased in AD model mice and cells. Meanwhile, ODN decreased Aβ generation by downregulating amyloidogenic AβPP processing in HEK-293 cells stably expressing human Swedish mutant APP695 and BACE1 (2EB2). Moreover, ODN could inhibit Aβ-induced oxidative stress in primary cultured cells and mice, as reflected by a dramatic increase in antioxidants and a decrease in pro-oxidants. We also found that ODN could reduce oxidative stress-induced apoptosis by restoring mitochondrial membrane potential, intracellular Ca2+ and cleaved caspase-3 levels in Aβ-treated primary cultured cells and mice. More importantly, intracerebroventricular injection of ODN attenuated cognitive impairments as well as long-term potentiation in Aβ-treated mice. Conclusion: These results suggest that ODN may exert a potent neuroprotective effect against Aβ-induced neurotoxicity and memory decline via its antioxidant effects, indicating that ODN may be a potential therapeutic agent for AD.
Pages 1427-1438
Ifrah Zawar*, Meghan K. Mattos*, Carol Manning, James Patrie, Mark Quigg (Handling Associate Editor: Gabrielle Britton) *These authors contributed equally to this work.
Sleep Disturbances Predict Cognitive Decline in Cognitively Healthy Adults
Abstract: Background: The effect of nighttime behaviors on cognition has not been studied independently from other neuropsychiatric symptoms. Objective: We evaluate the following hypotheses that sleep disturbances bring increased risk of earlier cognitive impairment, and more importantly that the effect of sleep disturbances is independent from other neuropsychiatric symptoms that may herald dementia. Methods: We used the National Alzheimer’s Coordinating Center database to evaluate the relationship between Neuropsychiatric Inventory Questionnaire (NPI-Q) determined nighttime behaviors which served as surrogate for sleep disturbances and cognitive impairment. Montreal Cognitive Assessment scores defined two groups: conversion from 1) normal to mild cognitive impairment (MCI) and 2) MCI to dementia. The effect of nighttime behaviors at initial visit and covariates of age, sex, education, race, and other neuropsychiatric symptoms (NPI-Q), on conversion risk were analyzed using Cox regression. Results: Nighttime behaviors predicted earlier conversion time from normal cognition to MCI (hazard ratio (HR): 1.09; 95% CI: [1.00, 1.48], p=0.048) but were not associated with MCI to dementia conversion (HR: 1.01; [0.92, 1.10], p=0.856). In both groups, older age, female sex, lower education, and neuropsychiatric burden increased conversion risk. Conclusion: Our findings suggest that sleep disturbances predict earlier cognitive decline independently from other neuropsychiatric symptoms that may herald dementia.
Pages 1439-1450
Sirong Piao*, Keliang Chen*, Na Wang*, Yifang Bao, Xueling Liu, Bin Hu, Yucheng Lu, Liqin Yang, Daoying Geng, Yuxin Li* *These authors contributed equally to this work.
Modular Level Alterations Of Structural-Functional Connectivity Coupling in Mild Cognitive Impairment Patients and Interactions with Age Effect
Abstract: Background: Structural-functional connectivity (SC–FC) coupling is related to various cognitive functions and more sensitive for the detection of subtle brain alterations. Objective: To investigate whether decoupling of SC-FC was detected in mild cognitive impairment (MCI) patients on a modular level, the interaction effect of aging and disease, and its relationship with network efficiency. Methods: 73 patients with MCI and 65 healthy controls were enrolled who underwent diffusion tensor imaging and resting-state functional MRI to generate structural and functional networks. Five modules were defined based on automated anatomical labeling 90 atlas, including default mode network (DMN), frontoparietal attention network (FPN), sensorimotor network (SMN), subcortical network (SCN), and visual network (VIS). Intra-module and inter-module SC-FC coupling were compared between two groups. The interaction effect of aging and group on modular SC-FC coupling was further analyzed by two-way ANOVA. The correlation between the coupling and network efficiency was finally calculated. Results: In MCI patients, aberrant intra-module coupling was noted in SMN, and altered inter-module coupling was found in the other four modules. Intra-module coupling exhibited significant age-by-group effects in DMN and SMN, and inter-module coupling showed significant age-by-group effects in DMN and FPN. In MCI patients, both positive or negative correlations between coupling and network efficiency were found in DMN, FPN, SCN, and VIS. Conclusion: SC-FC coupling could reflect the association of SC and FC, especially in modular levels. In MCI, SC-FC coupling could be affected by the interaction effect of aging and disease, which may shed light on advancing the pathophysiological mechanisms of MCI.
Pages 1451-1458
Shulei Man*, Boran Chen*, Yifan Zhang, Hanyue Xu, Yu Liu, Yuzhu Gao, Yi Chen, Qing Chen, Ming Zhang *These authors contributed equally to this work.
The Associations Between Cataracts and Alzheimer’s Disease: A Bidirectional Two-Sample Mendelian Randomization Study
Abstract: Background: The relationship between cataracts and Alzheimer’s disease (AD) has been reported in recent observational studies. However, it is still unclear whether a causal effect of cataracts on AD or reverse causation exists. Objective: To explore the association between cataracts and AD genetically, we performed a bidirectional two-sample Mendelian randomization study. Methods: We obtained genetic instrumental variables related to cataracts and AD from recently published genome-wide association studies (GWASs). SNP-outcome associations for AD were obtained from a GWAS with 111,326 cases and 677,663 controls. SNP-outcome associations for cataracts were drawn from two sources: a GWAS with 67,844 cases and 517,399 controls and the FinnGen consortium (42,843 cases and 262,698 controls). Inverse variance weighted (IVW) was used as the primary method for Mendelian randomization (MR) analyses. Results: No genetic evidence suggested that cataracts were associated with the risk of AD (IVW odds ratio =1.04, 95% confidence interval: 0.98-1.10, p=0.199). In contrast, an effect of genetically determined AD on a decreased risk of cataract was observed with suggestive evidence (IVW odds ratio =0.96, 95% confidence interval: 0.93-0.99, p=0.004). However, this result might be distorted by survival bias. Conclusion: Genetically determined cataracts were not related to AD, as demonstrated by our study. In contrast, there was suggestive evidence that AD might prevent cataract development, but there might be potential survival bias. To define the exact association between the two diseases, more prospective research and studies on the pathogenesis are needed.
Pages 1459-1472
Ran Li, Beibei Song, Lu Xu, Jiali Zheng, Wenhao Pan, Fang Cai, Juelu Wang , Yili Wu, Weihong Song (Handling Associate Editor: Peng Lei)
Regulation of USP25 by SP1 Associates with Amyloidogenesis
Abstract: Background: Trisomy 21, an extra copy of human chromosome 21 (HSA21), causes most Down’s syndrome (DS) cases. Individuals with DS inevitably develop Alzheimer’s disease (AD) neuropathological phenotypes after middle age including amyloid plaques and tau neurofibrillary tangles. Ubiquitin Specific Peptidase 25 (USP25), encoding by USP25 gene located on HSA21, is a deubiquitinating enzyme, which plays an important role in both DS and AD pathogenesis. However, the regulation of USP25 remains unclear. Objective: We aimed to determine the regulation of USP25 by specificity protein 1 (SP1) in neuronal cells and its potential role in amyloidogenesis. Methods: The transcription start site and promoter activity was identified by SMART-RACE and Dual-luciferase assay. Functional SP1-responsive elements were examined by EMSA. USP25 expression was examined by RT-PCR and immunoblotting. Student’s t-test or one-way ANOVA were applied for statistical analysis. Results: The transcription start site of human USP25 gene was identified. Three functional SP1 responsive elements in human USP25 gene were revealed. SP1 promotes USP25 transcription and subsequent USP25 protein expression, while SP1 inhibition significantly reduces USP25 expression in both non-neuronal and neuronal cells. Moreover, SP1 inhibition dramatically reduces amyloidogenesis. Conclusion: We demonstrates that transcription factor SP1 regulates USP25 gene expression, which associates with amyloidogenesis. It suggests that SP1 signaling may play an important role in USP25 regulation and contribute to USP25-mediated DS and AD pathogenesis.
Pages 1473-1485
Kaijus Ervasti, Toomas Kotkas, Mervi Issakainen, Minna Teiska, Anna Mäki-Petäjä-Leinonen
In the Shadow of COVID-19: The Well-Being and Rights of People Living with Dementia in Finland During the Pandemic
Abstract: Background: Exceptional circumstances such as the COVID-19 pandemic increase the risk for vulnerability among people living with dementia. Objective: This article discusses the well-being and rights of people living with dementia in Finland during the pandemic and analyses the legal framework covering the restrictions of their rights during that period. Methods: The empirical research comprises a survey of persons with dementia (n=31) and their family members (n=168). The participants completed a total of 13 survey items involving questions about their well-being during the pandemic, restrictions on freedom, access to services, information on pandemic regulations and guidelines as well as possible problems with authorities. The survey included both multiple choice and open-ended questions. Results: According to people with dementia and their family members, by spring 2021, the pandemic had reduced meaningful activities available to people living with dementia in Finland and decreased the number of meetings between them and other people. Many reported a decline in their physical and/or mental well-being or greater difficulty or delays in accessing social and health services. Over a third of respondents found that the right to meet people was restricted among people with dementia, and almost half of the respondents took the view that their freedom of movement was restricted. There were also major shortcomings in terms of information on restrictions. Conclusion: The results highlight the importance of bearing in mind the negative effects that restrictions on mobility, meeting other people and meaningful activities can have on the well-being of people living with dementia. This should be considered, for example, when reforming legislation.
Pages 1487-1497
Sayeh Bayat, Catherine M. Roe, Suzanne Schindler, Samantha A. Murphy, Jason M. Doherty, Ann M. Johnson, Alexis Walker, Beau M. Ances, John C. Morris, Ganesh M. Babulal
Everyday Driving and Plasma Biomarkers in Alzheimer’s Disease: Leveraging Artificial Intelligence to Expand Our Diagnostic Toolkit
Abstract: Background: Driving behavior as a digital marker and recent developments in blood-based biomarkers show promise as a widespread solution for the early identification of Alzheimer’s disease (AD). Objective: This study used artificial intelligence methods to evaluate the association between naturalistic driving behavior and blood-based biomarkers of AD. Methods: We employed an artificial neural network (ANN) to examine the relationship between everyday driving behavior and plasma biomarker of AD. The primary outcome was plasma Aβ42/Aβ40, and Aβ42/Aβ40<0.1013 was used to define amyloid positivity. Two ANN models were trained and tested for predicting the outcome. The first model architecture only includes driving variables as input, whereas the second architecture includes the combination of age, APOE ε4 status, and driving variables. Results: All 142 participants (mean [SD] age 73.9 [5.2] years; 76 [53.5%] men; 80 participants [56.3%] with amyloid positivity based on plasma Aβ42/Aβ40) were cognitively normal. The six driving features, included in the ANN models, were the number of trips during rush hour, the median and standard deviation of jerk, the number of hard braking incidents and night trips, and the standard deviation of speed. The F1 score of the model with driving variables alone was 0.75 [0.023] for predicting plasma Aβ42/Aβ40. Incorporating age and APOE ε4 carrier status improved the diagnostic performance of the model to 0.80 [0.051]. Conclusion: Blood-based AD biomarkers offer a novel opportunity to establish the efficacy of naturalistic driving as an accessible digital marker for AD pathology in driving research.
Pages 1499-1500
Book Review
Minding the Future: Approaching Aging with a Plan. A review of Aging with a Plan, Second Edition: How a Little Thought Today Can Vastly Improve Your Tomorrow by Sharona Hoffman, JD, LLM, SJD, First Hill Books, London, United Kingdom, 2022, 220 pp. Reviewed by Alan J. Lerner, MD
