Fifteen Years of the Australian Imaging, Biomarkers and Lifestyle (AIBL) Study: Progress and Observations from 2,359 Older Adults Spanning the Spectrum from Cognitive Normality to Alzheimer's Disease

Background:

The Australian Imaging, Biomarkers and Lifestyle (AIBL) Study commenced in 2006 as a prospective study of 1,112 individuals (768 cognitively normal (CN), 133 with mild cognitive impairment (MCI), and 211 with Alzheimer’s disease dementia (AD)) as an ‘Inception cohort’ who underwent detailed ssessments every 18 months. Over the past decade, an additional 1247 subjects have been added as an ‘Enrichment cohort’ (as of 10 April 2019).

Objective:

Here we provide an overview of these Inception and Enrichment cohorts of more than 8,500 person-years of investigation.

Methods:

Participants underwent reassessment every 18 months including comprehensive cognitive testing, neuroimaging (magnetic resonance imaging, MRI; positron emission tomography, PET), biofluid biomarkers and lifestyle evaluations.

Results:

AIBL has made major contributions to the understanding of the natural history of AD, with cognitive and biological definitions of its three major stages: preclinical, prodromal and clinical. Early deployment of Aβ-amyloid and tau molecular PET imaging and the development of more sensitive and specific blood tests have facilitated the assessment of genetic and environmental factors which affect age at onset and rates of progression.

Conclusion:

This fifteen-year study provides a large database of highly characterized individuals with longitudinal cognitive, imaging and lifestyle data and biofluid collections, to aid in the development of interventions to delay onset, prevent or treat AD. Harmonization with similar large longitudinal cohort studies is underway to further these aims.

Longitudinal Trajectories in Cortical Thickness and Volume Atrophy: Superior Cognitive Performance Does Not Protect Against Brain Atrophy in Older Adults

Background:

Previous research has identified a small subgroup of older adults that maintain a high level of cognitive functioning well into advanced age. Investigation of those with superior cognitive performance (SCP) for their age is important, as age-related decline has previously been thought to be inevitable.

Objective:

Preservation of cortical thickness and volume was evaluated in 76 older adults with SCP and 100 typical older adults (TOAs) assessed up to five times over six years.

Methods:

Regions of interest (ROIs) found to have been associated with super-aging status (a construct similar to SCP status) in previous literature were investigated, followed by a discovery phase analyses of additional regions. SCPs were aged 70 + at baseline, scoring at/above normative memory (CVLT-II) levels for demographically similar individuals aged 30–44 years old, and in the unimpaired range for all other cognitive domains over the course of the study.

Results:

In linear mixed models, following adjustment for multiple comparisons, there were no significant differences between rates of thinning or volume atrophy between SCPs and TOAs in previously identified ROIs, or the discovery phase analyses. With only amyloid-β negative individuals in the analyses, again there were no significant differences between SCPs and TOAs.

Conclusion:

The increased methodological rigor in classifying groups, together with the influence of cognitive reserve, are discussed as potential factors accounting for our findings as compared to the extant literature on those with superior cognitive performance for their age.

Flavonoid intake and incident dementia in the Danish Diet, Cancer, and Health cohort

INTRODUCTION

Prospective studies investigating flavonoid intake and dementia risk are scarce. The aims of this study were to examine associations between flavonoid intake and the risk of incident dementia and to investigate whether this association differs in the presence of lifestyle risk factors for dementia.

METHODS

We examined associations in 55,985 participants of the Danish Diet, Cancer, and Health Study followed for 23 years. The Phenol-Explorer database was used to estimate flavonoid intakes. Information on incident dementia and dementia subtypes was obtained using Danish patient and prescription registries. Hazard ratios (HRs) were calculated using restricted cubic splines in multivariable-adjusted Cox proportional hazards models.

RESULTS

For incident dementia, moderate compared to low intakes of flavonols (HR: 0.90 [0.82, 0.99]), flavanol oligo+polymers (HR: 0.87 [0.79, 0.96]), anthocyanins (HR: 0.84 [0.76, 0.93]), flavanones (HR: 0.89 [0.80, 0.99]), and flavones (HR: 0.85 [0.77, 0.95]) were associated with a lower risk. For vascular dementia, moderate intakes of flavonols (HR: 0.69 [0.53, 0.89]) and flavanol oligo + polymers (HR: 0.65 [0.51, 0.83]) were associated with lower risk. Flavonoid intakes were not significantly associated with Alzheimer's disease or unspecified dementia. The inverse association between total flavonoid intake and incident dementia was stronger in "ever" smokers than in "never" smokers and in those without hypercholesterolemia versus those with hypercholesteremia. Furthermore, the inverse association of vascular dementia with a moderate total flavonoid intake was stronger in "ever" smokers and those who were "normal" to "overweight" versus "never" smokers or those who were "obese," respectively.

CONCLUSION

A moderate intake of flavonoid-rich foods may help to reduce dementia risk.

Relationship of Established Cardiovascular Risk Factors and Peripheral Biomarkers on Cognitive Function in Adults at Risk of Cognitive Deterioration

BACKGROUND

There is a paucity of information on the role of microvascular and inflammatory biomarkers in cognitive dysfunction.

OBJECTIVE

This study sought to evaluate the relationships between established and a number of peripheral biomarkers on cognitive patterns in 108 older adults with memory complaints.

METHODS

Participants in the AIBL Active study aged 60 years and older with at least one vascular risk factor and memory complaints completed a neuropsychological test battery and provided cross-sectional health data. Linear regression models adjusted for covariates examined associations between cognitive performance and a panel of vascular risk factors (Framingham cardiovascular scores, hs-CRP, homocysteine, fasting glucose, LDL-cholesterol) and peripheral biomarkers (TNF-α, BDNF, VCAM-1, ICAM-1, PAI-1, CD40L).

RESULTS

Higher fasting glucose and homocysteine levels were independent factors associated with poorer performance in Trail Making Test (TMT) B (adjusted β= 0.40±0.10 and 0.43±0.09, respectively). Increasing homocysteine levels were weakly associated with poorer global cognition and delayed recall (adjusted β= 0.23±0.10 and -0.20±0.10 respectively). Increasing Framingham cardiovascular scores were related to poorer performance in TMT B (β  = 0.42±0.19). There was early evidence of associations between increasing plasma TNF-α and poorer TMT B (adjusted β  = 0.21±0.10) and between increasing BDNF and better global cognition (β= -0.20±0.09).

CONCLUSION

This study provides evidence to support the associations between vascular risk factors (Framingham scores, fasting glucose, and homocysteine) and poorer cognitive functions. Additionally, we measured several peripheral biomarkers to further investigate their associations with cognition. The relationship between TNF-α, BDNF, and cognitive performance in various domains may offer new insights into potential mechanisms in vascular cognitive impairment.

PRKAG2 Gene Expression Is Elevated and its Protein Levels Are Associated with Increased Amyloid-β Accumulation in the Alzheimer's Disease Brain

Increased amyloid-β (Aβ) accumulation associated with abnormal autophagy-lysosomal activity and nutrient kinase dysregulation are common features in Alzheimer’s disease (AD) brain. Recent studies have identified PRKAG2 and TIPRL genes that control nutrient kinase regulated autophagy, and here we determined if their expression is altered in postmortem AD brains. Gene and protein expression of TIPRL were unchanged. However, gene expression of PRKAG2 was increased 3-fold and its protein levels positively correlated with Aβ accumulation in the AD brain. In summary, our findings suggest that increased PRKAG2 is an important contributing factor to Aβ accumulation in the AD brain.

Sodium Butyrate Reduces Brain Amyloid-β Levels and Improves Cognitive Memory Performance in an Alzheimer's Disease Transgenic Mouse Model at an Early Disease Stage

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline and neuropathological features, including abnormal deposition of amyloid-β (Aβ) peptides, intracellular neurofibrillary tangles, and neuronal death. Identifying therapeutics which can reduce memory deficits at an early stage of the disease has the advantage of slowing or even reversing disease progression before irreversible brain damage has occurred. Consequently, in this study, we investigated the ability of the histone deacetylase inhibitor sodium butyrate (NaB) to attenuate memory deficits in the 5xFAD mouse model of AD following a 12-week feeding regimen. 5xFAD mice demonstrate a unique time course of Aβ pathology, developing Aβ plaques as early as 2 months. Male mice were assigned to either a control diet or a NaB-supplemented diet which was administered at either 5 mg/kg/day, or 15 mg/kg/day for 12 weeks (each group, N = 15). Supplementation commenced at an early disease stage (8-10 weeks of age). Behavioral testing (contextual and cued fear conditioning) was undertaken, and brain Aβ levels measured, at the end of the 12-week intervention. NaB had profound effects on Aβ levels and on associative learning and cognitive functioning. A 40% reduction in brain Aβ levels and a 25% increase in fear response in both the cued and contextual testing was observed in the NaB-treated animals compared to the control group. These findings suggest that NaB warrants further investigation as a potential therapeutic agent in the treatment of cognitive deficits associated with early stages of AD.

Relationships Between Plasma Lipids Species, Gender, Risk Factors, and Alzheimer's Disease

Background:

Lipid metabolism is altered in Alzheimer’s disease (AD); however, the relationship between AD risk factors (age, APOEɛ4, and gender) and lipid metabolism is not well defined.

Objective:

We investigated whether altered lipid metabolism associated with increased age, gender, and APOE status may contribute to the development of AD by examining these risk factors in healthy controls and also clinically diagnosed AD individuals.

Methods:

We performed plasma lipidomic profiling (582 lipid species) of the Australian Imaging, Biomarkers and Lifestyle flagship study of aging cohort (AIBL) using liquid chromatography-mass spectrometry. Linear regression and interaction analysis were used to explore the relationship between risk factors and plasma lipid species.

Results:

We observed strong associations between plasma lipid species with gender and increasing age in cognitively normal individuals. However, APOEɛ4 was relatively weakly associated with plasma lipid species. Interaction analysis identified differential associations of sphingolipids and polyunsaturated fatty acid esterified lipid species with AD based on age and gender, respectively. These data indicate that the risk associated with age, gender, and APOEɛ4 may, in part, be mediated by changes in lipid metabolism.

Conclusion:

This study extends our existing knowledge of the relationship between the lipidome and AD and highlights the complexity of the relationships between lipid metabolism and AD at different ages and between men and women. This has important implications for how we assess AD risk and also for potential therapeutic strategies involving modulation of lipid metabolic pathways.

Androgen receptor CAG repeat length as a moderator of the relationship between free testosterone levels and cognition

Age-related decrease in testosterone levels is a potential risk factor for cognitive decline in older men. However, observational studies and clinical trials have reported inconsistent results on the effects of testosterone on individual cognitive domains. Null findings may be attributed to factors that studies have yet to consider. In particular, individual variations in polyglutamine (CAG) length in the androgen receptor (AR) gene could alter androgenic activity in brain regions associated with cognitive processes including memory and executive functions. However, the role of AR CAG repeat length as a moderator of the relationship between testosterone levels and cognition has not been investigated. Therefore, we aimed to examine the relationship between baseline calculated free testosterone (cFT) levels, change in cFT levels over 18 months and CAG repeat length on cognitive performance in memory, executive function, language, attention and processing speed domains. These relationships were examined in 304 cognitively normal older male participants of the Australian Imaging, Biomarkers and Lifestyle (AIBL) Study of Ageing. In the attention and processing speed domain, a short CAG repeat length appears to exacerbate the effects of low baseline cFT levels that are also lower than expected at follow-up. These results highlight that individual variations in AR CAG repeat length should be considered in future studies and clinical trials that examine the complex relationship between testosterone and cognition.

Relevance of a Truncated PRESENILIN 2 Transcript to Alzheimer's Disease and Neurodegeneration

BACKGROUND

The PRESENILIN genes (PSEN1, PSEN2) encoding for their respective proteins have critical roles in many aspects of Alzheimer's disease (AD) pathogenesis. The PS2V transcript of PSEN2 encodes a truncated protein and is upregulated in AD brains; however, its relevance to AD and disease progression remains to be determined.

OBJECTIVE

Assess transcript levels in postmortem AD and non-AD brain tissue and in lymphocytes collected under the Australian Imaging Biomarker and Lifestyle (AIBL) study.

METHODS

Full length PSEN2 and PS2V transcript levels were assessed by quantitative digital PCR in postmortem brain tissue (frontal cortex and hippocampus) from control, AD, frontotemporal dementia (FTD), and Lewy body dementia (LBD). Transcript levels were also assessed in lymphocytes obtained from the Perth subset of the AIBL study (n = 160). Linear regression analysis was used to assess correlations between transcript copy number and brain volume and neocortical amyloid load.

RESULTS

PS2V levels increased in AD postmortem brain but PS2V was also present at significant levels in FTD and LBD brains. PS2V transcript was detected in lymphocytes and PS2V/PSEN2 ratios were increased in mild cognitive impairment (p = 0.024) and AD (p = 0.019) groups compared to control group. Increased ratios were significantly correlated with hippocampal volumes only (n = 62, β= -0.269, p = 0.03).

CONCLUSION

Taken together, these results suggest that PS2V may be a marker of overall neurodegeneration.

Core Alzheimer's disease cerebrospinal fluid biomarker assays are not affected by aspiration or gravity drip extraction methods

BACKGROUND

CSF biomarkers are well-established for routine clinical use, yet a paucity of comparative assessment exists regarding CSF extraction methods during lumbar puncture. Here, we compare in detail biomarker profiles in CSF extracted using either gravity drip or aspiration.

METHODS

Biomarkers for β-amyloidopathy (Aβ1-42, Aβ1-40), tauopathy (total tau), or synapse pathology (BACE1, Neurogranin Trunc-p75, α-synuclein) were assessed between gravity or aspiration extraction methods in a sub-population of the Australian Imaging, Biomarkers and Lifestyle (AIBL) study (cognitively normal, N = 36; mild cognitive impairment, N = 8; Alzheimer's disease, N = 6).

RESULTS

High biomarker concordance between extraction methods was seen (concordance correlation > 0.85). Passing Bablock regression defined low beta coefficients indicating high scalability.

CONCLUSIONS

Levels of these commonly assessed CSF biomarkers are not influenced by extraction method. Results of this study should be incorporated into new consensus guidelines for CSF collection, storage, and analysis of biomarkers.

Segregation of functional networks is associated with cognitive resilience in Alzheimer's disease

Cognitive resilience is an important modulating factor of cognitive decline in Alzheimer's disease, but the functional brain mechanisms that support cognitive resilience remain elusive. Given previous findings in normal ageing, we tested the hypothesis that higher segregation of the brain's connectome into distinct functional networks represents a functional mechanism underlying cognitive resilience in Alzheimer's disease. Using resting-state functional MRI, we assessed both resting-state functional MRI global system segregation, i.e. the balance of between-network to within-network connectivity, and the alternate index of modularity Q as predictors of cognitive resilience. We performed all analyses in two independent samples for validation: (i) 108 individuals with autosomal dominantly inherited Alzheimer's disease and 71 non-carrier controls; and (ii) 156 amyloid-PET-positive subjects across the spectrum of sporadic Alzheimer's disease and 184 amyloid-negative controls. In the autosomal dominant Alzheimer's disease sample, disease severity was assessed by estimated years from symptom onset. In the sporadic Alzheimer's sample, disease stage was assessed by temporal lobe tau-PET (i.e. composite across Braak stage I and III regions). In both samples, we tested whether the effect of disease severity on cognition was attenuated at higher levels of functional network segregation. For autosomal dominant Alzheimer's disease, we found higher functional MRI-assessed system segregation to be associated with an attenuated effect of estimated years from symptom onset on global cognition (P = 0.007). Similarly, for patients with sporadic Alzheimer's disease, higher functional MRI-assessed system segregation was associated with less decrement in global cognition (P = 0.001) and episodic memory (P = 0.004) per unit increase of temporal lobe tau-PET. Confirmatory analyses using the alternate index of modularity Q revealed consistent results. In conclusion, higher segregation of functional connections into distinct large-scale networks supports cognitive resilience in Alzheimer's disease.

Plasma Amyloid-Beta Levels in a Pre-Symptomatic Dutch-Type Hereditary Cerebral Amyloid Angiopathy Pedigree: A Cross-Sectional and Longitudinal Investigation

Plasma amyloid-beta (Aβ) has long been investigated as a blood biomarker candidate for Cerebral Amyloid Angiopathy (CAA), however previous findings have been inconsistent which could be attributed to the use of less sensitive assays. This study investigates plasma Aβ alterations between pre-symptomatic Dutch-type hereditary CAA (D-CAA) mutation-carriers (MC) and non-carriers (NC) using two Aβ measurement platforms. Seventeen pre-symptomatic members of a D-CAA pedigree were assembled and followed up 3–4 years later (NC = 8; MC = 9). Plasma Aβ1-40 and Aβ1-42 were cross-sectionally and longitudinally analysed at baseline (T1) and follow-up (T2) and were found to be lower in MCs compared to NCs, cross-sectionally after adjusting for covariates, at both T1(Aβ1-40: p = 0.001; Aβ1-42: p = 0.0004) and T2 (Aβ1-40: p = 0.001; Aβ1-42: p = 0.016) employing the Single Molecule Array (Simoa) platform, however no significant differences were observed using the xMAP platform. Further, pairwise longitudinal analyses of plasma Aβ1-40 revealed decreased levels in MCs using data from the Simoa platform (p = 0.041) and pairwise longitudinal analyses of plasma Aβ1-42 revealed decreased levels in MCs using data from the xMAP platform (p = 0.041). Findings from the Simoa platform suggest that plasma Aβ may add value to a panel of biomarkers for the diagnosis of pre-symptomatic CAA, however, further validation studies in larger sample sets are required.

SPON1 Is Associated with Amyloid-β and APOE ε4-Related Cognitive Decline in Cognitively Normal Adults

Abstract.

High-intensity exercise and cognitive function in cognitively normal older adults: a pilot randomised clinical trial

Background

Physical inactivity has been consistently linked to increased risk of cognitive decline; however, studies examining the impact of exercise interventions on cognition have produced inconsistent findings. Some observational studies suggest exercise intensity may be important for inducing cognitive improvements; however, this has yet to be thoroughly examined in older adult cohorts. The objective of the current study was to evaluate the effect of systematically manipulated high-intensity and moderate-intensity exercise interventions on cognition.

Methods

This multi-arm pilot randomised clinical trial investigated the effects of 6 months of high-intensity exercise and moderate-intensity exercise, compared with an inactive control, on cognition. Outcome measures were assessed at pre- (baseline), post- (6 months), and 12 months post-intervention. Ninety-nine cognitively normal men and women (aged 60–80 years) were enrolled from October 2016 to November 2017. Participants that were allocated to an exercise group (i.e. high-intensity or moderate-intensity) engaged in cycle-based exercise two times per week for 6 months. Cognition was assessed using a comprehensive neuropsychological test battery. Cardiorespiratory fitness was evaluated by a graded exercise test.

Results

There was a dose-dependent effect of exercise intensity on cardiorespiratory fitness, whereby the high-intensity group experienced greater increases in fitness than the moderate-intensity and control groups. However, there was no direct effect of exercise on cognition.

Conclusions

We did not observe a direct effect of exercise on cognition. Future work in this field should be appropriately designed and powered to examine factors that may contribute to individual variability in response to intervention.

Trial registration

This study is registered with the Australian New Zealand Clinical Trials Registry (ACTRN12617000643370). Registered on 3 May 2017—retrospectively registered. https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=372780

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-021-00774-y.

A Randomized Controlled Trial of High-Intensity Exercise and Executive Functioning in Cognitively Normal Older Adults

BACKGROUND

There is a paucity of interventional research that systematically assesses the role of exercise intensity and cardiorespiratory fitness, and their relationship with executive function in older adults. To address this limitation, we have examined the effect of a systematically manipulated exercise intervention on executive function.

METHODS

Ninety-nine cognitively normal participants (age = 69.10 ± 5.2 years; n = 54 female) were randomized into either a high-intensity cycle-based exercise, moderate-intensity cycle-based exercise, or no-intervention control group. All participants underwent neuropsychological testing and fitness assessment at baseline (preintervention), 6-month follow-up (postintervention), and 12-month postintervention. Executive function was measured comprehensively, including measures of each subdomain: Shifting, Updating/ Working Memory, Inhibition, Verbal Generativity, and Nonverbal Reasoning. Cardiorespiratory fitness was measured by analysis of peak aerobic capacity; VO₂peak.

RESULTS

First, the exercise intervention was found to increase cardiorespiratory fitness (VO₂peak) in the intervention groups, in comparison to the control group (F =10.40, p≤0.01). However, the authors failed to find mean differences in executive function scores between the high-intensity, moderate intensity, or inactive control group. On the basis of change scores, cardiorespiratory fitness was found to associate positively with the executive function (EF) subdomains of Updating/Working Memory (β = 0.37, p = 0.01, r = 0.34) and Verbal Generativity (β = 0.30, p = 0.03, r = 0.28) for intervention, but not control participants.

CONCLUSION

At the aggregate level, the authors failed to find evidence that 6-months of high-intensity aerobic exercise improves EF in older adults. However, it remains possible that individual differences in experimentally induced changes in cardiorespiratory fitness may be associated with changes in Updating/ Working Memory and Verbal Generativity.

Improving Prospective Memory Performance in Community-dwelling Older Adults: Goal Management Training and Implementation Intentions

Aim: The present study tested a compensatory executive intervention for prospective memory (goal management training) for the first time in older adults. Prospective memory (the ability to remember and execute a task in the future) declines with age, with significant implications for older adults' activities of daily living and quality of life. Prospective memory interventions have focused primarily on the retrospective component of prospective memory (e.g., implementation intentions). However, executive dysfunction is also implicated in age-related prospective memory decline.Methods: Community-dwelling older adults were randomly allocated to receive goal management training, implementation intentions or no intervention. Prospective memory was assessed before and after the intervention with a well-validated laboratory-based prospective memory measure. Results: Contrary to predictions, neither goal management training nor implementation intentions were successful at improving prospective memory in healthy older adults. Participants who received goal management training were more likely to have difficulty comprehending the intervention. Post-hoc analyses suggested implementation intentions improved prospective memory specifically for participants with poorer baseline prospective memory. Conclusions: These results represent important cautionary findings about the possible limitations of goal management training to improve prospective memory in older adults. Future research should also consider the role of baseline prospective memory ability in affecting response to compensatory intervention.

Plasma glial fibrillary acidic protein is elevated in cognitively normal older adults at risk of Alzheimer's disease

Glial fibrillary acidic protein (GFAP), an astrocytic cytoskeletal protein, can be measured in blood samples, and has been associated with Alzheimer's disease (AD). However, plasma GFAP has not been investigated in cognitively normal older adults at risk of AD, based on brain amyloid-β (Aβ) load. Cross-sectional analyses were carried out for plasma GFAP and plasma Aβ1-42/Aβ1-40 ratio, a blood-based marker associated with brain Aβ load, in participants (65-90 years) categorised into low (Aβ-, n = 63) and high (Aβ+, n = 33) brain Aβ load groups via Aβ positron emission tomography. Plasma GFAP, Aβ1-42, and Aβ1-40 were measured using the Single molecule array (Simoa) platform. Plasma GFAP levels were significantly higher (p < 0.00001), and plasma Aβ1-42/Aβ1-40 ratios were significantly lower (p < 0.005), in Aβ+ participants compared to Aβ- participants, adjusted for covariates age, sex, and apolipoprotein E-ε4 carriage. A receiver operating characteristic curve based on a logistic regression of the same covariates, the base model, distinguished Aβ+ from Aβ- (area under the curve, AUC = 0.78), but was outperformed when plasma GFAP was added to the base model (AUC = 0.91) and further improved with plasma Aβ1-42/Aβ1-40 ratio (AUC = 0.92). The current findings demonstrate that plasma GFAP levels are elevated in cognitively normal older adults at risk of AD. These observations suggest that astrocytic damage or activation begins from the pre-symptomatic stage of AD and is associated with brain Aβ load. Observations from the present study highlight the potential of plasma GFAP to contribute to a diagnostic blood biomarker panel (along with plasma Aβ1-42/Aβ1-40 ratios) for cognitively normal older adults at risk of AD.

Investigating Auditory Electrophysiological Measures of Participants with Mild Cognitive Impairment and Alzheimer's Disease: A Systematic Review and Meta-Analysis of Event-Related Potential Studies

BACKGROUND

Objectively measuring auditory functions has been proposed as an avenue in differentiating normal age-related cognitive dysfunction from Alzheimer's disease (AD) and its prodromal states. Previous research has suggested auditory event-related potentials (AERPs) to be non-invasive, cost-effective, and efficient biomarkers for the diagnosis of AD.

OBJECTIVE

The objective of this paper is to review the published literature on AERPs measures in older adults diagnosed with AD and those at higher risk of developing AD, i.e., mild cognitive impairment (MCI) and subjective cognitive decline.

METHODS

The search was performed on six major electronic databases (Ovid MEDLINE, OVID EMBASE, PsycINFO, PubMed, Scopus, and CINAHL Plus). Articles identified prior to 7 May 2019 were considered for this review. A random effects meta-analysis and analysis of between study heterogeneity was conducted using the Comprehensive Meta-Analysis software.

RESULTS

The search identified 1,076 articles; 74 articles met the full inclusion criteria and were included in the systematic review, and 47 articles were included into the analyses. Pooled analysis suggests that AD participants can be differentiated from controls due to significant delays in ABR, N100, P200, N200, and P300 latencies. P300 amplitude was significantly smaller in AD participants compared to controls. P300 latencies differed significantly between MCI participants and controls based on the pooled analysis.

CONCLUSION

The findings of this review indicate that some AERPs may be valuable biomarkers of AD. In conjunction with currently available clinical and neuropsychological assessments, AERPs can aid in screening and diagnosis of prodromal AD.

Targeting Mitophagy in Alzheimer's Disease

Mitochondria perform many essential cellular functions including energy production, calcium homeostasis, transduction of metabolic and stress signals, and mediating cell survival and death. Maintaining viable populations of mitochondria is therefore critical for normal cell function. The selective disposal of damaged mitochondria, by a pathway known as mitophagy, plays a key role in preserving mitochondrial integrity and quality. Mitophagy reduces the formation of reactive oxygen species and is considered as a protective cellular process. Mitochondrial dysfunction and deficits of mitophagy have important roles in aging and especially in neurodegenerative disorders such as Alzheimer's disease (AD). Targeting mitophagy pathways has been suggested to have potential therapeutic effects against AD. In this review, we aim to briefly discuss the emerging concepts on mitophagy, molecular regulation of the mitophagy process, current mitophagy detection methods, and mitophagy dysfunction in AD. Finally, we will also briefly examine the stimulation of mitophagy as an approach for attenuating neurodegeneration in AD.