Amyloid Accumulation and Cognitive Decline in Clinically Normal Older Individuals: Implications for Aging and Early Alzheimer's Disease

The duality of amyloid-β: its role in normal and Alzheimer's disease states

Alzheimer's disease (AD) is a degenerative neurological condition that gradually impairs cognitive abilities, disrupts memory retention, and impedes daily functioning by impacting the cells of the brain. A key characteristic of AD is the accumulation of amyloid-beta (Aβ) plaques, which play pivotal roles in disease progression. These plaques initiate a cascade of events including neuroinflammation, synaptic dysfunction, tau pathology, oxidative stress, impaired protein clearance, mitochondrial dysfunction, and disrupted calcium homeostasis. Aβ accumulation is also closely associated with other hallmark features of AD, underscoring its significance. Aβ is generated through cleavage of the amyloid precursor protein (APP) and plays a dual role depending on its processing pathway. The non-amyloidogenic pathway reduces Aβ production and has neuroprotective and anti-inflammatory effects, whereas the amyloidogenic pathway leads to the production of Aβ peptides, including Aβ40 and Aβ42, which contribute to neurodegeneration and toxic effects in AD. Understanding the multifaceted role of Aβ, particularly in AD, is crucial for developing effective therapeutic strategies that target Aβ metabolism, aggregation, and clearance with the aim of mitigating the detrimental consequences of the disease. This review aims to explore the mechanisms and functions of Aβ under normal and abnormal conditions, particularly in AD, by examining both its beneficial and detrimental effects.

NLRP3 inflammasome signalling in Alzheimer's disease

Every year, 10 million people develop dementia, the most common of which is Alzheimer's disease (AD). To date, there is no way to prevent cognitive decline and therapies are limited. This review provides a neuroimmunological perspective on the progression of AD, and discusses the immune-targeted therapies that are in preclinical and clinical trials that may impact the development of this disease. Specifically, we look to the role of the NLRP3 inflammasome, its triggers in the brain and how its activation can contribute to the progression of dementia. We summarise the range of inhibitors targeting the NLRP3 inflammasome and its downstream pathways that are under investigation, and discuss future therapeutic perspectives for this devastating condition.

Assessing amyloid PET positivity and cognitive function in Down syndrome to guide clinical trials targeting amyloid

INTRODUCTION

Trisomy 21, or Down syndrome (DS), predisposes individuals to early-onset Alzheimer's disease (AD). While monoclonal antibodies (mAbs) targeting amyloid are approved for older AD patients, their efficacy in DS remains unexplored. This study examines amyloid positron emission tomography (PET) positivity (A+), memory function, and clinical status across ages in DS to guide mAb trial designs.

METHODS

Cross-sectional data from the Alzheimer Biomarker Consortium-Down Syndrome (ABC-DS) was analyzed. PET amyloid beta in Centiloids classified amyloid status using various cutoffs. Episodic memory was assessed using the modified Cued Recall Test, and clinical status was determined through consensus processes.

RESULTS

Four hundred nine DS adults (mean age = 44.83 years) were evaluated. A+ rates increased with age, with mean amyloid load rising significantly. Memory decline and cognitive impairment are also correlated with age.

DISCUSSION

These findings emphasize the necessity of tailoring mAb trials for DS, considering age-related AD characteristics.

HIGHLIGHTS

There is rapid increase in prevalence of amyloid beta (Aβ) positron emission tomography (PET) positivity in Down syndrome (DS) after the age of 40 years. Aβ PET positivity thresholds have significant impact on prevalence rates in DS. There is a significant lag between Aβ PET positivity and clinical symptom onset in DS.

Amyloid-beta and tau protein beyond Alzheimer's disease

ABSTRACT

The aggregation of amyloid-beta peptide and tau protein dysregulation are implicated to play key roles in Alzheimer's disease pathogenesis and are considered the main pathological hallmarks of this devastating disease. Physiologically, these two proteins are produced and expressed within the normal human body. However, under pathological conditions, abnormal expression, post-translational modifications, conformational changes, and truncation can make these proteins prone to aggregation, triggering specific disease-related cascades. Recent studies have indicated associations between aberrant behavior of amyloid-beta and tau proteins and various neurological diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, as well as retinal neurodegenerative diseases like Glaucoma and age-related macular degeneration. Additionally, these proteins have been linked to cardiovascular disease, cancer, traumatic brain injury, and diabetes, which are all leading causes of morbidity and mortality. In this comprehensive review, we provide an overview of the connections between amyloid-beta and tau proteins and a spectrum of disorders.

Integrative Multimodal Metabolomics to Early Predict Cognitive Decline Among Amyloid Positive Community-Dwelling Older Adults

Alzheimer's disease is strongly linked to metabolic abnormalities. We aimed to distinguish amyloid-positive people who progressed to cognitive decline from those who remained cognitively intact. We performed untargeted metabolomics of blood samples from amyloid-positive individuals, before any sign of cognitive decline, to distinguish individuals who progressed to cognitive decline from those who remained cognitively intact. A plasma-derived metabolite signature was developed from Supercritical Fluid chromatography coupled with high-resolution mass spectrometry (SFC-HRMS) and nuclear magnetic resonance (NMR) metabolomics. The 2 metabolomics data sets were analyzed by Data Integration Analysis for Biomarker discovery using Latent approaches for Omics studies (DIABLO), to identify a minimum set of metabolites that could describe cognitive decline status. NMR or SFC-HRMS data alone cannot predict cognitive decline. However, among the 320 metabolites identified, a statistical method that integrated the 2 data sets enabled the identification of a minimal signature of 9 metabolites (3-hydroxybutyrate, citrate, succinate, acetone, methionine, glucose, serine, sphingomyelin d18:1/C26:0 and triglyceride C48:3) with a statistically significant ability to predict cognitive decline more than 3 years before decline. This metabolic fingerprint obtained during this exploratory study may help to predict amyloid-positive individuals who will develop cognitive decline. Due to the high prevalence of brain amyloid-positivity in older adults, identifying adults who will have cognitive decline will enable the development of personalized and early interventions.

Age and beta amyloid deposition impact gait speed, stride length, and gait smoothness while transitioning from an even to an uneven walking surface in older adults

BACKGROUND

Capturing a measure of movement quality during a complex walking task may indicate the earliest signs of detrimental changes to the brain due to beta amyloid (Aβ) deposition and be a potential differentiator of older adults at elevated and low risk of developing Alzheimer's disease. This study aimed to determine: 1) age-related differences in gait speed, stride length, and gait smoothness while transitioning from an even to an uneven walking surface, by comparing young adults (YA) and older adults (OA), and 2) if gait speed, stride length, and gait smoothness in OA while transitioning from an even to an uneven walking surface is influenced by the amount of Aβ deposition present in an OA's brain.

METHODS

Participants included 56 OA (>70 years of age) and 29 YA (25-35 years of age). In OA, Aβ deposition in the brain was quantified by PET imaging. All participants completed a series of cognitive assessments, a functional mobility assessment, and self-report questionnaires. Then participants performed two sets of walking trials on a custom-built walkway containing a mixture of even and uneven surface sections, including three trials with a grass uneven surface and three trials with a rocks uneven surface. Gait data were recorded using a wireless inertial measurement unit system. Stride length, gait speed, and gait smoothness (i.e., log dimensionless lumbar jerk) in the anteroposterior (AP), mediolateral (ML), and vertical (VT) directions were calculated for each stride. Outcomes were retained for five stride locations immediately surrounding the surface transition.

RESULTS

OA exhibited slower gait (Grass: p < 0.001; Rocks: p = 0.006), shorter strides (Grass: p < 0.001; Rocks: p = 0.008), and smoother gait (Grass AP: p < 0.001; Rocks AP: p = 0.002; Rocks ML: p = 0.02) than YA, but they also exhibited greater reductions in gait speed and stride length than YA while transitioning to the uneven grass and rocks surfaces. Within the OA group, those with greater Aβ deposition exhibited decreases in smoothness with age (Grass AP: p = 0.02; Rocks AP: p = 0.03; Grass ML: p = 0.04; Rocks ML: p = 0.03), while those with lower Aβ deposition exhibited increasing smoothness with age (Grass AP: p = 0.01; Rocks AP: p = 0.02; Grass ML: p = 0.08; Rocks ML: p = 0.07). Better functional mobility was associated with less smooth gait (Grass ML: p = 0.02; Rocks ML: p = 0.05) and with less variable gait smoothness (Grass and Rocks AP: both p = 0.04) in the OA group.

CONCLUSION

These results suggest that, relative to YA, OA may be adopting more cautious, compensatory gait strategies to maintain smoothness when approaching surface transitions. However, OA with greater Aβ deposition may have limited ability to adopt compensatory gait strategies to increase the smoothness of their walking as they get older because of neuropathological changes altering the sensory integration process and causing worse dynamic balance (i.e., jerkier gait). Functional mobility, in addition to age and Aβ deposition, may be an important factor of whether or not an OA chooses to employ compensatory strategies to prioritize smoothness while walking and what type of compensatory strategy an OA chooses.

A Pragmatic, Investigator-Driven Process for Disclosure of Amyloid PET Scan Results to ADNI-4 Research Participants

BACKGROUND

Prior studies of Alzheimer's disease (AD) biomarker disclosure have answered important questions about individuals' safety after learning and comprehending their amyloid PET results; however, these studies have typically employed highly structured disclosure protocols and focused on the psychological impact of disclosure (e.g., anxiety, depression, and suicidality) in homogeneous populations. More work is needed to develop flexible disclosure protocols and study outcomes in ethnoculturally representative samples.

METHODS

The Alzheimer's Disease Neuroimaging Initiative (ADNI) is formally incorporating amyloid PET disclosure into the newest protocol (ADNI-4). Participants across the cognitive spectrum who wish to know their amyloid PET results may learn them. The pragmatic disclosure process spans four timepoints: (1) a pre-disclosure visit, (2) the PET scan and its read, (3) a disclosure visit, and (4) a post-disclosure check-in. This process applies to all participants, with slight modifications to account for their cognitive status. In designing this process, special emphasis was placed on utilizing investigator discretion. Participant measures include perceived risk of dementia, purpose in life, and disclosure satisfaction. Investigator assessment of the disclosure visit (e.g., challenges encountered, topics discussed, etc.) is also included.

RESULTS

Data collection is ongoing. Results will allow for more robust characterization of the impact of learning amyloid PET results on individuals and describe the perspectives of investigators.

CONCLUSION

The pragmatic design of the disclosure process in ADNI-4 coupled with the novel participant and investigator data will inform future disclosure practices. This is especially important as disclosure of biomarker results expands in research and care.

Mixed Medicinal Mushroom Mycelia Attenuates Alzheimer's Disease Pathologies In Vitro and In Vivo

Alzheimer's disease (AD) is characterized by memory impairment and existence of amyloid-β (Aβ) plaques and neuroinflammation. Due to the pivotal role of oxidative damage in AD, natural antioxidative agents, such as polyphenol-rich fungi, have garnered scientific scrutiny. Here, the aqueous extract of mixed medicinal mushroom mycelia (MMMM)-Phellinus linteus, Ganoderma lucidum, and Inonotus obliquus-cultivated on a barley medium was assessed for its anti-AD effects. Neuron-like PC12 cells, which were subjected to Zn2+, an Aβ aggregator, were employed as an in vitro AD model. The cells pretreated with or without MMMM were assayed for Aβ immunofluorescence, cell viability, reactive oxygen species (ROS), apoptosis, and antioxidant enzyme activity. Then, 5XFAD mice were administered with 30 mg/kg/day MMMM for 8 weeks and underwent memory function tests and histologic analyses. In vitro results demonstrated that the cells pretreated with MMMM exhibited attenuation in Aβ immunofluorescence, ROS accumulation, and apoptosis, and incrementation in cell viability and antioxidant enzyme activity. In vivo results revealed that 5XFAD mice administered with MMMM showed attenuation in memory impairment and histologic deterioration such as Aβ plaque accumulation and neuroinflammation. MMMM might mitigate AD-associated memory impairment and cerebral pathologies, including Aβ plaque accumulation and neuroinflammation, by impeding Aβ-induced neurotoxicity.

Decoding the heterogeneity of Alzheimer's disease diagnosis and progression using multilayer networks

Alzheimer's disease (AD) is a multifactorial and heterogeneous disorder, which makes early detection a challenge. Studies have attempted to combine biomarkers to improve AD detection and predict progression. However, most of the existing work reports results in parallel or compares normalized findings but does not analyze data simultaneously. We tested a multi-dimensional network framework, applied to 490 subjects (cognitively normal [CN] = 147; mild cognitive impairment [MCI] = 287; AD = 56) from ADNI, to create a single model capable of capturing the heterogeneity and progression of AD. First, we constructed subject similarity networks for structural magnetic resonance imaging, amyloid-β positron emission tomography, cerebrospinal fluid, cognition, and genetics data and then applied multilayer community detection to find groups with shared similarities across modalities. Individuals were also followed-up longitudinally, with AD subjects having, on average, 4.5 years of follow-up. Our findings show that multilayer community detection allows for accurate identification of present and future AD (≈90%) and is also able to identify cases that were misdiagnosed clinically. From all MCI participants who developed AD or reverted to CN, the multilayer model correctly identified 90.8% and 88.5% of cases respectively. We observed similar subtypes across the full sample and when examining multimodal data from subjects with no AD pathology (i.e., amyloid negative). Finally, these results were also validated using an independent testing set. In summary, the multilayer framework is successful in detecting AD and provides unique insight into the heterogeneity of the disease by identifying subtypes that share similar multidisciplinary profiles of neurological, cognitive, pathological, and genetics information.

Early Life Obesity Increases Neuroinflammation, Amyloid Beta Deposition, and Cognitive Decline in a Mouse Model of Alzheimer's Disease

Obesity, a known risk factor of Alzheimer's disease (AD), increases the activation of microglia, leading to a proinflammatory phenotype. Our previous work shows that a high fat diet (HFD) can cause neuroinflammation and cognitive decline in mice. We hypothesized that proinflammatory activation of brain microglia in obesity exacerbates AD pathology and increases the accumulation of amyloid beta (Aβ) plaques. Presently, we tested cognitive function in 8-month-old male and female APP/PS1 mice fed a HFD, starting at 1.5 months of age. Locomotor activity, anxiety-like behavior, behavioral despair, and spatial memory were all assessed through behavioral tests. Microgliosis and Aβ deposition were measured in multiple brain regions through immunohistochemical analysis. Our results show that a HFD decreases locomotor activity, while increasing anxiety-like behavior and behavioral despair independent of genotype. A HFD led to increased memory deficits in both sexes, with HFD-fed APP/PS1 mice performing the worst out of all groups. Immunohistochemical analysis showed increased microgliosis in mice fed a HFD. This was accompanied by an increase in Aβ deposition in the HFD-fed APP/PS1 mice. Together, our results support that HFD-induced obesity exacerbates neuroinflammation and Aβ deposition in a young adult AD mouse model, leading to increased memory deficits and cognitive decline in both sexes.

Early and late chaperone intervention therapy boosts XBP1s and ADAM10, restores proteostasis, and rescues learning in Alzheimer's Disease mice

Alzheimer's disease (AD) is a debilitating neurodegenerative disorder that is pervasive among the aging population. Two distinct phenotypes of AD are deficits in cognition and proteostasis, including chronic activation of the unfolded protein response (UPR) and aberrant Aβ production. It is unknown if restoring proteostasis by reducing chronic and aberrant UPR activation in AD can improve pathology and cognition. Here, we present data using an APP knock-in mouse model of AD and several protein chaperone supplementation paradigms, including a late-stage intervention. We show that supplementing protein chaperones systemically and locally in the hippocampus reduces PERK signaling and increases XBP1s, which is associated with increased ADAM10 and decreased Aβ42. Importantly, chaperone treatment improves cognition which is correlated with increased CREB phosphorylation and BDNF. Together, this data suggests that chaperone treatment restores proteostasis in a mouse model of AD and that this restoration is associated with improved cognition and reduced pathology.

One-sentence summary

Chaperone therapy in a mouse model of Alzheimer's disease improves cognition by reducing chronic UPR activity.

Upregulation of extracellular proteins in a mouse model of Alzheimer's disease

Various risk factors of Alzheimer's disease (AD) are known, such as advanced age, possession of certain genetic variants, accumulation of toxic amyloid-β (Aβ) peptides, and unhealthy lifestyle. An estimate of heritability of AD ranges from 0.13 to 0.25, indicating that its phenotypic variation is accounted for mostly by non-genetic factors. DNA methylation is regarded as an epigenetic mechanism that interfaces the genome with non-genetic factors. The Tg2576 mouse model has been insightful in AD research. These transgenic mice express a mutant form of human amyloid precursor protein linked to familial AD. At 9-13 months of age, these mice show elevated levels of Aβ peptides and cognitive impairment. The current literature lacks integrative multiomics of the animal model. We applied transcriptomics and DNA methylomics to the same brain samples from ~ 11-month-old transgenic mice. We found that genes involved in extracellular matrix structures and functions are transcriptionally upregulated, and genes involved in extracellular protein secretion and localization are differentially methylated in the transgenic mice. Integrative analysis found enrichment of GO terms related to memory and synaptic functionability. Our results indicate a possibility of transcriptional modulation by DNA methylation underlying AD neuropathology.

Activated gliosis, accumulation of amyloid β, and hyperphosphorylation of tau in aging canines with and without cognitive decline

Canine cognitive dysfunction (CCD) syndrome is a well-recognized naturally occurring disease in aged dogs, with a remarkably similar disease course, both in its clinical presentation and neuropathological changes, as humans with Alzheimer's disease (AD). Similar to human AD patients this naturally occurring disease is found in the aging canine population however, there is little understanding of how the canine brain ages pathologically. It is well known that in neurodegenerative diseases, there is an increase in inflamed glial cells as well as an accumulation of hyperphosphorylation of tau (P-tau) and amyloid beta (Aβ_1-42). These pathologies increase neurotoxic signaling and eventual neuronal loss. We assessed these brain pathologies in aged canines and found an increase in the number of glial cells, both astrocytes and microglia, and the activation of astrocytes indicative of neuroinflammation. A rise in the aggregated protein Aβ_1-42 and hyperphosphorylated tau, at Threonine 181 and 217, in the cortical brain regions of aging canines. We then asked if any of these aged canines had CCD utilizing the only current diagnostic, owner questionnaires, verifying positive or severe CCD had pathologies of gliosis and accumulation of Aβ_1-42 like their aged, matched controls. However uniquely the CCD dogs had P-tau at T217. Therefore, this phosphorylation site of tau at threonine 217 may be a predictor for CCD.

Directed Functional Brain Connectivity is Altered in Sub-threshold Amyloid-β Accumulation in Cognitively Normal Individuals

Several studies have shown that amyloid-β (Aβ) deposition below the clinically relevant cut-off levels is associated with subtle changes in cognitive function and increases the risk of developing future Alzheimer's disease (AD). Although functional MRI is sensitive to early alterations occurring during AD, sub-threshold changes in Aβ levels have not been linked to functional connectivity measures. This study aimed to apply directed functional connectivity to identify early changes in network function in cognitively unimpaired participants who, at baseline, exhibit Aβ accumulation below the clinically relevant threshold. To this end, we analyzed baseline functional MRI data from 113 cognitively unimpaired participants of the Alzheimer's Disease Neuroimaging Initiative cohort who underwent at least one 18F-florbetapir-PET after the baseline scan. Using the longitudinal PET data, we classified these participants as Aβ negative (Aβ-) non-accumulators (n = 46) and Aβ- accumulators (n = 31). We also included 36 individuals who were amyloid-positive (Aβ+) at baseline and continued to accumulate Aβ (Aβ+ accumulators). For each participant, we calculated whole-brain directed functional connectivity networks using our own anti-symmetric correlation method and evaluated their global and nodal properties using measures of network segregation (clustering coefficient) and integration (global efficiency). When compared to Aβ- non-accumulators, the Aβ- accumulators showed lower global clustering coefficient. Moreover, the Aβ+ accumulator group exhibited reduced global efficiency and clustering coefficient, which at the nodal level mainly affected the superior frontal gyrus, anterior cingulate cortex, and caudate nucleus. In Aβ- accumulators, global measures were associated with lower baseline regional PET uptake values, as well as higher scores on the Modified Preclinical Alzheimer Cognitive Composite. Our findings indicate that directed connectivity network properties are sensitive to subtle changes occurring in individuals who have not yet reached the threshold for Aβ positivity, which makes them a potentially viable marker to detect negative downstream effects of very early Aβ pathology.

Classification and prediction of cognitive trajectories of cognitively unimpaired individuals

Objectives

Efforts to prevent Alzheimer's disease (AD) would benefit from identifying cognitively unimpaired (CU) individuals who are liable to progress to cognitive impairment. Therefore, we aimed to develop a model to predict cognitive decline among CU individuals in two independent cohorts.

Methods

A total of 407 CU individuals from the Alzheimer's Disease Neuroimaging Initiative (ADNI) and 285 CU individuals from the Samsung Medical Center (SMC) were recruited in this study. We assessed cognitive outcomes by using neuropsychological composite scores in the ADNI and SMC cohorts. We performed latent growth mixture modeling and developed the predictive model.

Results

Growth mixture modeling identified 13.8 and 13.0% of CU individuals in the ADNI and SMC cohorts, respectively, as the "declining group." In the ADNI cohort, multivariable logistic regression modeling showed that increased amyloid-β (Aβ) uptake (β [SE]: 4.852 [0.862], p < 0.001), low baseline cognitive composite scores (β [SE]: -0.274 [0.070], p < 0.001), and reduced hippocampal volume (β [SE]: -0.952 [0.302], p = 0.002) were predictive of cognitive decline. In the SMC cohort, increased Aβ uptake (β [SE]: 2.007 [0.549], p < 0.001) and low baseline cognitive composite scores (β [SE]: -4.464 [0.758], p < 0.001) predicted cognitive decline. Finally, predictive models of cognitive decline showed good to excellent discrimination and calibration capabilities (C-statistic = 0.85 for the ADNI model and 0.94 for the SMC model).

Conclusion

Our study provides novel insights into the cognitive trajectories of CU individuals. Furthermore, the predictive model can facilitate the classification of CU individuals in future primary prevention trials.

Brain β-Amyloid Links the Association of Change in Body Mass Index With Cognitive Decline in Community-Dwelling Older Adults

BACKGROUND

We tested the hypothesis that indices of Alzheimer's disease and related dementia (ADRD) pathologies may explain associations between change in body mass index (BMI) and cognitive decline in old age.

METHOD

We used data from 436 older decedents participating in a prospective longitudinal cohort study who had undergone annual cognitive and BMI assessments and postmortem collection of indices of 12 brain pathologies. We identified ADRD brain pathologies associated with BMI range, a previously published metric of change in BMI. We employed sigmoidal mixed-effect models of cognitive decline to examine the associations of change in BMI and cognitive decline with and without terms for ADRD brain pathologies.

RESULTS

Average age at baseline was 78.6 years, SD = 6.5 years with 64% female. On average, 9 cognitive assessments were obtained with average age at death 88.4 years (SD = 6.2 years). Change in BMI as measured by BMI range was associated with cognitive decline (θ 2 = 0.260). β-Amyloid, hippocampal sclerosis, and substantia nigra neuronal loss were associated with BMI range. β-Amyloid strongly attenuated the association of BMI range with cognitive decline. Hippocampal sclerosis showed only partial attenuation of the association of BMI range and cognitive decline and nigral neuronal loss did not attenuate this association.

CONCLUSION

Changes in BMI and cognitive decline in older adults may be affected by similar mechanisms underlying the accumulation of brain pathologies like β-amyloid in aging brains. Elucidating the molecular mechanisms underlying these associations may provide novel targets for developing interventions that maintain brain health and metabolic homeostasis in old age.

Urolithin A reduces amyloid-beta load and improves cognitive deficits uncorrelated with plaque burden in a mouse model of Alzheimer's disease

In the present study, we investigated the effects of urolithin A (UA), a metabolite generated from ellagic acid via its metabolism by gut bacteria, as an autophagy activator with potential neuroprotective activity. WT and 3xTg-AD mice were administered long-term intermittent dietary supplementation with UA. UA was found to prevent deficits in spatial memory, cued fear response, and exploratory behavior in this model. It also decreased the Aβ plaque burden in areas of the hippocampus where these protein deposits are prominent in the model. Interestingly, correlation analyses demonstrate that Aβ plaque burden positively correlates with enhanced spatial memory in 3xTg-AD mice on a control diet but not in those supplemented with UA. In contrast, Aβ42 abundance in cortical and hippocampal homogenates negatively correlate with spatial memory in UA-fed mice. Our data suggest that plaque formation may be a protective mechanism against neurodegeneration and cognitive decline and that targeting the generation of proteotoxic Aβ species might be a more successful approach in halting disease progression. UA was also found to extend lifespan in normal aging mice. Mechanistically, we demonstrate that UA is able to induce autophagy and to increase Aβ clearance in neuronal cell lines. In summary, our studies reveal UA, likely via its actions as a autophagy inducer, is capable of removing Aβ from neurons and its dietary administration prevents the onset of cognitive deficits associated with pathological Aβ deposition in the 3xTg-AD mouse model as well as extending lifespan in normal aging mice.

Increasing empathic concern relates to salience network hyperconnectivity in cognitively healthy older adults with elevated amyloid-β burden

Enhanced emotional empathy, the ability to share others' affective experiences, can be a feature of Alzheimer's disease (AD), but whether emotional empathy increases in the preclinical phase of the disease is unknown. We measured emotional empathy over time (range = 0 - 7.3 years, mean = 2.4 years) in 86 older adults during a period in which they were cognitively healthy, functionally normal, and free of dementia symptoms. For each participant, we computed longitudinal trajectories for empathic concern (i.e., an other-oriented form of emotional empathy that promotes prosocial actions) and emotional contagion (i.e., a self-focused form of emotional empathy often accompanied by feelings of distress) from informant ratings of participants' empathy on the Interpersonal Reactivity Index. Amyloid-β (Aβ) positron emission tomography (PET) scans were used to classify participants as either Aβ positive (Aβ+, n = 23) or negative (Aβ-, n = 63) based on Aβ-PET cortical binding. Participants also underwent structural and task-free functional magnetic resonance imaging approximately two years on average after their last empathy assessment, at which time most participants remained cognitively healthy. Results indicated that empathic concern, but not emotional contagion, increased more over time in Aβ+ participants than in Aβ- participants despite no initial group difference at the first measurement. Higher connectivity between certain salience network node-pairs (i.e., pregenual anterior cingulate cortex and periaqueductal gray) predicted longitudinal increases in empathic concern in the Aβ+ group but not in the Aβ- group. The Aβ+ participants also had higher overall salience network connectivity than Aβ- participants despite no differences in gray matter volume. These results suggest gains in empathic concern may be a very early feature of AD pathophysiology that relates to hyperconnectivity in the salience network, a system that supports emotion generation and interoception. A better understanding of emotional empathy trajectories in the early stages of AD pathophysiology will broaden the lens on preclinical AD changes and help clinicians to identify older adults who should be screened for AD biomarkers.

Change in brain amyloid load and cognition in patients with amnestic mild cognitive impairment: a 3-year follow-up study

Background

Our aim was to investigate the discriminative value of ¹⁸F-Flutemetamol PET in longitudinal assessment of amyloid beta accumulation in amnestic mild cognitive impairment (aMCI) patients, in relation to longitudinal cognitive changes.

Methods

We investigated the change in ¹⁸F-Flutemetamol uptake and cognitive impairment in aMCI patients over time up to 3 years which enabled us to investigate possible association between changes in brain amyloid load and cognition over time. Thirty-four patients with aMCI (mean age 73.4 years, SD 6.6) were examined with ¹⁸F-Flutemetamol PET scan, brain MRI and cognitive tests at baseline and after 3-year follow-up or earlier if the patient had converted to Alzheimer´s disease (AD). ¹⁸F-Flutemetamol data were analyzed both with automated region-of-interest analysis and voxel-based statistical parametric mapping.

Results

¹⁸F-flutemetamol uptake increased during the follow-up, and the increase was significantly higher in patients who were amyloid positive at baseline as compared to the amyloid-negative ones. At follow-up, there was a significant association between ¹⁸F-Flutemetamol uptake and MMSE, logical memory I (immediate recall), logical memory II (delayed recall) and verbal fluency. An association was seen between the increase in ¹⁸F-Flutemetamol uptake and decline in MMSE and logical memory I scores.

Conclusions

In the early phase of aMCI, presence of amyloid pathology at baseline strongly predicted amyloid accumulation during follow-up, which was further paralleled by cognitive declines. Inversely, some of our patients remained amyloid negative also at the end of the study without significant change in ¹⁸F-Flutemetamol uptake or cognition. Future studies with longer follow-up are needed to distinguish whether the underlying pathophysiology of aMCI in such patients is other than AD.

Statistical Parametric Mapping in Amyloid Positron Emission Tomography

Alzheimer's disease (AD), the most common cause of dementia, has limited treatment options. Emerging disease modifying therapies are targeted at clearing amyloid-β (Aβ) aggregates and slowing the rate of amyloid deposition. However, amyloid burden is not routinely evaluated quantitatively for purposes of disease progression and treatment response assessment. Statistical Parametric Mapping (SPM) is a technique comparing single-subject Positron Emission Tomography (PET) to a healthy cohort that may improve quantification of amyloid burden and diagnostic performance. While primarily used in 2-[18F]-fluoro-2-deoxy-D-glucose (FDG)-PET, SPM's utility in amyloid PET for AD diagnosis is less established and uncertainty remains regarding optimal normal database construction. Using commercially available SPM software, we created a database of 34 non-APOE ε4 carriers with normal cognitive testing (MMSE > 25) and negative cerebrospinal fluid (CSF) AD biomarkers. We compared this database to 115 cognitively normal subjects with variable AD risk factors. We hypothesized that SPM based on our database would identify more positive scans in the test cohort than the qualitatively rated [11C]-PiB PET (QR-PiB), that SPM-based interpretation would correlate better with CSF Aβ42 levels than QR-PiB, and that regional z-scores of specific brain regions known to be involved early in AD would be predictive of CSF Aβ42 levels. Fisher's exact test and the kappa coefficient assessed the agreement between SPM, QR-PiB PET, and CSF biomarkers. Logistic regression determined if the regional z-scores predicted CSF Aβ42 levels. An optimal z-score cutoff was calculated using Youden's index. We found SPM identified more positive scans than QR-PiB PET (19.1 vs. 9.6%) and that SPM correlated more closely with CSF Aβ42 levels than QR-PiB PET (kappa 0.13 vs. 0.06) indicating that SPM may have higher sensitivity than standard QR-PiB PET images. Regional analysis demonstrated the z-scores of the precuneus, anterior cingulate and posterior cingulate were predictive of CSF Aβ42 levels [OR (95% CI) 2.4 (1.1, 5.1) p = 0.024; 1.8 (1.1, 2.8) p = 0.020; 1.6 (1.1, 2.5) p = 0.026]. This study demonstrates the utility of using SPM with a "true normal" database and suggests that SPM enhances diagnostic performance in AD in the clinical setting through its quantitative approach, which will be increasingly important with future disease-modifying therapies.

AuNPs- Aβ-Ni-HRP sandwich assay: A new sensitive colorimetric method for the detection of Aβ 1-40

Amyloid β-peptide (Aβ) is a key predictor for preclinical diagnosis of Alzheimer's disease (AD) and vascular diseases. In this work, we propose a gold nanoparticle (AuNPs)-Aβ-nickel (Ni)-horseradish peroxidase (HRP) based colorimetric assay for the detection of Aβ_1-40. The consecutive binding of Aβ_1-40 to AuNPs and metal ions is designed and examined for Aβ-specific aggregation of AuNPs and the generation of quantitative colorimetric signals. The affinity of Aβ_1-40 towards various metal ions was studied first, and two metal ions, Cu and Ni, were specifically tested with Metal Ion-Binding Site Prediction (MIB) and High-resolution Electrospray Ionization Mass Spectrometry (HR-ESI-MS). Subsequently, the binding of Aβ_1-40 and AuNPs was examined, and the binding between Aβ-AuNPs and Ni-HRP was finally analyzed by UV-Vis and nano-zetasizer. Based on the characterized dual binding of Aβ_1-40, a colorimetric sandwich assay was developed and the analytical performance of the developed assay has been evaluated with standard solutions and human serum samples. Good linearity within a range from 0 nM to 10 nM was found. The detection limits of 0.22 nM in the standard sample and 0.23 nM in the human serum sample have been demonstrated. The newly developed colorimetric sandwich assay is a short, simple, antibody-free assay and achieves high sensitivity with only 100 μL Aβ_1-40 samples. The assay has immense potential for the detection of Aβ_1-40 in biological or biomedical diagnosis.

Assessing and disclosing test results for ‘mild cognitive impairment’: the perspective of old age psychiatrists in Scotland

Background

Mild cognitive impairment (MCI) is a condition that exists between normal healthy ageing and dementia with an uncertain aetiology and prognosis. This uncertainty creates a complex dynamic between the clinicians’ conception of MCI, what is communicated to the individual about their condition, and how the individual responds to the information conveyed to them. The aim of this study was to explore clinicians’ views around the assessment and communication of MCI in memory clinics.

Method

As part of a larger longitudinal study looking at patients’ adjustment to MCI disclosure, we interviewed Old Age Psychiatrists at the five participating sites across Scotland. The study obtained ethics approvals and the interviews (carried out between Nov 2020–Jan 2021) followed a semi-structured schedule focusing on [1] how likely clinicians are to use the term MCI with patients; [2] what tests clinicians rely on and how much utility they see in them; and [3] how clinicians communicate risk of progression to dementia. The interviews were voice recorded and were analysed using reflective thematic analysis.

Results

Initial results show that most clinicians interviewed (Total N = 19) considered MCI to have significant limitations as a diagnostic term. Nevertheless, most clinicians reported using the term MCI (n = 15/19). Clinical history was commonly described as the primary aid in the diagnostic process and also to rule out functional impairment (which was sometimes corroborated by Occupational Therapy assessment). All clinicians reported using the Addenbrooke’s Cognitive Examination-III as a primary assessment tool. Neuroimaging was frequently found to have minimal usefulness due to the neuroradiological reports being non-specific.

Conclusion

Our study revealed a mixture of approaches to assessing and disclosing test results for MCI. Some clinicians consider the condition as a separate entity among neurodegenerative disorders whereas others find the term unhelpful due to its uncertain prognosis. Clinicians report a lack of specific and sensitive assessment methods for identifying the aetiology of MCI in clinical practice. Our study demonstrates a broad range of views and therefore variability in MCI risk disclosure in memory assessment services which may impact the management of individuals with MCI.

No Influence of Age-Related Hearing Loss on Brain Amyloid-β

BACKGROUND

Hearing loss is independently associated with a faster rate of cognitive decline in older adults and has been identified as a modifiable risk factor for dementia. The mechanism for this association is unknown, and there has been limited exploration of potential casual pathology.

OBJECTIVE

Our objective was to investigate whether there was an association between degree of audiometrically measured hearing loss (HL) and brain amyloid-β (Aβ) in a pre-clinical sample.

METHODS

Participants of the Australian Imaging and Biomarker Longitudinal Study (AIBL; n = 143) underwent positron emission tomography (PET) imaging and objective measurement of hearing thresholds within 5 years of imaging, as well as cognitive assessment within 2 years of imaging in this observational cohort study.

RESULTS

With one exception, study participants who had cognitive assessments within 2 years of their PET imaging (n = 113) were classified as having normal cognition. There was no association between cognitive scores and degree of hearing loss, or between cognitive scores and Aβ load. No association between HL and Aβ load was found once age was controlled for. As previously reported, positive Apolipoprotein E4 (APOE4) carrier status increased the risk of being Aβ positive (p = 0.002).

CONCLUSION

Degree of HL was not associated with positive Aβ status.

Association between serum urate and CSF markers of Alzheimer's disease pathology in a population-based sample of 70-year-olds

INTRODUCTION

The relationship between urate and biomarkers for Alzheimer's disease (AD) pathophysiology has not been investigated.

METHODS

We examined whether serum concentration of urate was associated with cerebrospinal fluid biomarkers, amyloid beta (Aβ)42, Aβ40, phosphorylated tau (p-tau), total tau (t-tau), neurofilament light (NfL), and Aβ42/Aβ40 ratio, in cognitively unimpaired 70-year-old individuals from Gothenburg, Sweden. We also evaluated whether possible associations were modulated by the apolipoprotein E (APOE) ε4 allele.

RESULTS

Serum urate was positively associated with Aβ42 in males (β = 0.55 pg/mL, P = .04). There was a positive urate-APOE ε4 interaction (1.24 pg/mL, P interaction = .02) in relation to Aβ42 association. The positive urate and Aβ42 association strengthened in male APOE ε4 carriers (β = 1.28 pg/mL, P = .01).

DISCUSSION

The positive association between urate and Aβ42 in cognitively healthy men may suggest a protective effect of urate against deposition of amyloid protein in the brain parenchyma, and in the longer term, maybe against AD dementia.

Characteristics of Bipolar Patients with Cognitive Impairment of Suspected Neurodegenerative Origin: A Multicenter Cohort

Bipolar disorder is associated with an increased risk of dementia with aging. Little is known regarding this association, limiting appropriate diagnosis and management. We aimed to describe the characteristics of bipolar patients with late cognitive impairment for whom the hypothesis of an underlying neurodegenerative disease had been raised. We performed a retrospective multicenter study, recruiting bipolar patients over 50 years old from five French tertiary memory centers who had undergone cerebrospinal fluid (CSF) biomarker assessment for Alzheimer’s disease (AD). Clinical, neuropsychological, and paraclinical characteristics were analyzed and 78 patients were included. The mean age at the onset of cognitive impairment was 62.4 years (±9.2). The mean MMSE score was 22.8 (±4.5), the mean FAB was 11.7 (±3.9), and the mean FCRST was 15.8 (±7.4)/36.8 (±9.7) (free/total recall). A total of 48.6% of the patients displayed cognitive fluctuations, and 38.2% showed cognitive improvement during follow-ups; and 56.3% of the patients showed Parkinsonism, of which 12.7% had never received antipsychotics. Among patients who underwent DAT-scans, 35.3% displayed dopaminergic denervation; 10.3% of patients had CSF AD biological signature (“A+ T+” profile), while 56.4% had other abnormal CSF profiles. Thus, clinical presentation was dominated by executive dysfunction, episodic memory impairment, fluctuating cognition, and a high frequency of Parkinsonism. Specifically, high frequency of delusional episodes suggests limited tolerance of psychotropic drugs. Most patients had abnormal CSF biomarker profiles, but only a minority displayed AD’s specific biomarker signature. Therefore, while our results unveil shared common neurocognitive features in bipolar patients with cognitive impairment of suspected neurodegenerative origin they suggest a participation of various underlying pathologies rather than a common degenerative mechanism in the pathophysiology of this condition.

What Radiologists Should Know About Normal Pressure Hydrocephalus

BACKGROUND

 Normal pressure hydrocephalus is a disease in elderly patients and one of the most common causes of treatable dementia. It occurs frequently with microangiopathy and Alzheimer's disease, so that differential diagnosis plays an important role. This is crucially determined by imaging findings. Therapy consists of cerebrospinal fluid drainage through a shunt, which should be performed as early as possible to improve the chances of success.

METHOD

 This report is based on a summary of the relevant literature that has been reviewed in PubMed with reference to epidemiology, symptoms, pathophysiology, diagnostics, and therapy. The results were supplemented by the joint guidelines of the German Society of Neurology and the German Society of Neurosurgery.

RESULTS AND CONCLUSION

 The understanding of the pathophysiologic changes leading to normal pressure hydrocephalus has expanded significantly in recent years to include concepts explaining relevant comorbidities. Diagnosis is based on radiological and clinical indicators, although accurate differentiation with respect to comorbidities is not always possible. A high response rate to treatment can be achieved by good patient selection. Positive prognostic markers for therapeutic success include Disproportionately Enlarged Subarachnoid Space Hydrocephalus (DESH), short disease duration, predominant gait disturbance, and few comorbidities.

KEY POINTS

  · Normal pressure hydrocephalus mainly affects patients older than 65 years of age with high comorbidity rate for microangiopathy and Alzheimer's disease. · Radiologic findings play an important role in the diagnosis and follow-up after shunting. · The earlier a shunt is placed, the better the outcome.

CITATION FORMAT

· Illies T, Eckert B, Kehler U. What Radiologists Should Know About Normal Pressure Hydrocephalus. Fortschr Röntgenstr 2021; 193: 1197 - 1206.

Selective Secretase Targeting for Alzheimer's Disease Therapy

Alzheimer's disease (AD) is associated with marked atrophy of the cerebral cortex and accumulation of amyloid plaques and neurofibrillary tangles. Amyloid plaques are formed by oligomers of amyloid-β (Aβ) in the brain, with a length of 42 and 40 amino acids. α-secretase cleaves amyloid-β protein precursor (AβPP) producing the membrane-bound fragment CTFα and the soluble fragment sAβPPα with neuroprotective activity; β-secretase produces membrane-bound fragment CTFβ and a soluble fragment sAβPPβ. After α-secretase cleavage of AβPP, γ-secretase cleaves CTFα to produce the cytoplasmic fragment AICD and P3 in the non-amyloidogenic pathway. CTFβ is cleaved by γ-secretase producing AICD as well as Aβ in amyloidogenic pathways. In the last years, the study of natural products and synthetic compounds, such as α-secretase activity enhancers, β-secretase inhibitors (BACE-1), and γ-secretase activity modulators, have been the focus of pharmaceuticals and researchers. Drugs were improved regarding solubility, blood-brain barrier penetration, selectivity, and potency decreasing Aβ42. In this regard, BACE-1 inhibitors, such as Atabecestat, NB-360, Umibecestat, PF-06751979 Verubecestat, LY2886721, Lanabecestat, LY2811376 and Elenbecestat, were submitted to phase I-III clinical trials. However, inhibition of Aβ production did not recover cognitive functions or reverse disease progress. Novel strategies are being developed, aiming at a partial reduction of Aβ production, such as the development of γ-secretase modulators or α-secretase activity enhancers. Such therapeutic tools shall focus on slowing down or minimizing the progression of neuronal damage. Here, we summarize structures and activities of the latest compounds designed for AD treatment, with remarkable in vitro, in vivo, and clinical phase activities.

Amyloid Deposition Is Greater in Cerebral Gyri than in Cerebral Sulci with Worsening Clinical Diagnosis Across the Alzheimer's Disease Spectrum

BACKGROUND

Histopathologic studies have demonstrated differential amyloid-β (Aβ) burden between cortical sulci and gyri in Alzheimer's disease (AD), with sulci having a greater Aβ burden.

OBJECTIVE

To characterize Aβ deposition in the sulci and gyri of the cerebral cortex in vivo among subjects with normal cognition (NC), mild cognitive impairment (MCI), and AD, and to evaluate if these differences could improve discrimination between diagnostic groups.

METHODS

T1-weighted 3T MR and florbetapir (amyloid) positron emission tomography (PET) data were obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI). T1 images were segmented and the cortex was separated into sulci/gyri based on pial surface curvature measurements. T1 images were registered to PET images and regional standardized uptake value ratios (SUVr) were calculated. A linear mixed effects model was used to analyze the relationship between clinical variables and amyloid PET SUVr measurements in the sulci/gyri. Receiver operating characteristic (ROC) analysis was performed to define amyloid positivity. Logistic models were used to evaluate predictive performance of clinical diagnosis using amyloid PET SUVr measurements in sulci/gyri.

RESULTS

719 subjects were included: 272 NC, 315 MCI, and 132 AD. Gyral and sulcal Aβ increased with worsening cognition, however there was a greater increase in gyral Aβ. Females had a greater gyral and sulcal Aβ burden. Focusing on sulcal and gyral Aβ did not improve predictive power for diagnostic groups.

CONCLUSION

While there were significant differences in Aβ deposition in cerebral sulci and gyri across the AD spectrum, these differences did not translate into improved prediction of diagnosis. Females were found to have greater gyral and sulcal Aβ burden.

Grey Matter Loss at Different Stages of Cognitive Decline: A Role for the Thalamus in Developing Alzheimer's Disease

Background:

Alzheimer’s disease (AD) is characterized by cognitive impairment and large loss of grey matter volume and is the most prevalent form of dementia worldwide. Mild cognitive impairment (MCI) is the stage that precedes the AD dementia stage, but individuals with MCI do not always convert to the AD dementia stage, and it remains unclear why.

Objective:

We aimed to assess grey matter loss across the brain at different stages of the clinical continuum of AD to gain a better understanding of disease progression.

Methods:

In this large-cohort study (N = 1,386) using neuroimaging data from the Alzheimer’s Disease Neuroimaging Initiative, voxel-based morphometry analyses were performed between healthy controls, individuals with early and late and AD dementia stage.

Results:

Clear patterns of grey matter loss in mostly hippocampal and temporal regions were found across clinical stages, though not yet in early MCI. In contrast, thalamic volume loss seems one of the first signs of cognitive decline already during early MCI, whereas this volume loss does not further progress from late MCI to AD dementia stage. AD dementia stage converters already show grey matter loss in hippocampal and mid-temporal areas as well as the posterior thalamus (pulvinar) and angular gyrus at baseline.

Conclusion:

This study confirms the role of temporal brain regions in AD development and suggests additional involvement of the thalamus/pulvinar and angular gyrus that may be linked to visuospatial, attentional, and memory related problems in both early MCI and AD dementia stage conversion.

Metabolism navigates neural cell fate in development, aging and neurodegeneration

An uninterrupted energy supply is critical for the optimal functioning of all our organs, and in this regard the human brain is particularly energy dependent. The study of energy metabolic pathways is a major focus within neuroscience research, which is supported by genetic defects in the oxidative phosphorylation mechanism often contributing towards neurodevelopmental disorders and changes in glucose metabolism presenting as a hallmark feature in age-dependent neurodegenerative disorders. However, as recent studies have illuminated roles of cellular metabolism that span far beyond mere energetics, it would be valuable to first comprehend the physiological involvement of metabolic pathways in neural cell fate and function, and to subsequently reconstruct their impact on diseases of the brain. In this Review, we first discuss recent evidence that implies metabolism as a master regulator of cell identity during neural development. Additionally, we examine the cell type-dependent metabolic states present in the adult brain. As metabolic states have been studied extensively as crucial regulators of malignant transformation in cancer, we reveal how knowledge gained from the field of cancer has aided our understanding in how metabolism likewise controls neural fate determination and stability by directly wiring into the cellular epigenetic landscape. We further summarize research pertaining to the interplay between metabolic alterations and neurodevelopmental and psychiatric disorders, and expose how an improved understanding of metabolic cell fate control might assist in the development of new concepts to combat age-dependent neurodegenerative diseases, particularly Alzheimer's disease.

Practical recommendations for timely, accurate diagnosis of symptomatic Alzheimer's disease (MCI and dementia) in primary care: a review and synthesis

The critical role of primary care clinicians (PCCs) in Alzheimer's disease (AD) prevention, diagnosis and management must evolve as new treatment paradigms and disease-modifying therapies (DMTs) emerge. Our understanding of AD has grown substantially: no longer conceptualized as a late-in-life syndrome of cognitive and functional impairments, we now recognize that AD pathology builds silently for decades before cognitive impairment is detectable. Clinically, AD first manifests subtly as mild cognitive impairment (MCI) due to AD before progressing to dementia. Emerging optimism for improved outcomes in AD stems from a focus on preventive interventions in midlife and timely, biomarker-confirmed diagnosis at early signs of cognitive deficits (i.e. MCI due to AD and mild AD dementia). A timely AD diagnosis is particularly important for optimizing patient care and enabling the appropriate use of anticipated DMTs. An accelerating challenge for PCCs and AD specialists will be to respond to innovations in diagnostics and therapy for AD in a system that is not currently well positioned to do so. To overcome these challenges, PCCs and AD specialists must collaborate closely to navigate and optimize dynamically evolving AD care in the face of new opportunities. In the spirit of this collaboration, we summarize here some prominent and influential models that inform our current understanding of AD. We also advocate for timely and accurate (i.e. biomarker-defined) diagnosis of early AD. In doing so, we consider evolving issues related to prevention, detecting emerging cognitive impairment and the role of biomarkers in the clinic.

Current advances in digital cognitive assessment for preclinical Alzheimer's disease

There is a pressing need to capture and track subtle cognitive change at the preclinical stage of Alzheimer's disease (AD) rapidly, cost-effectively, and with high sensitivity. Concurrently, the landscape of digital cognitive assessment is rapidly evolving as technology advances, older adult tech-adoption increases, and external events (i.e., COVID-19) necessitate remote digital assessment. Here, we provide a snapshot review of the current state of digital cognitive assessment for preclinical AD including different device platforms/assessment approaches, levels of validation, and implementation challenges. We focus on articles, grants, and recent conference proceedings specifically querying the relationship between digital cognitive assessments and established biomarkers for preclinical AD (e.g., amyloid beta and tau) in clinically normal (CN) individuals. Several digital assessments were identified across platforms (e.g., digital pens, smartphones). Digital assessments varied by intended setting (e.g., remote vs. in-clinic), level of supervision (e.g., self vs. supervised), and device origin (personal vs. study-provided). At least 11 publications characterize digital cognitive assessment against AD biomarkers among CN. First available data demonstrate promising validity of this approach against both conventional assessment methods (moderate to large effect sizes) and relevant biomarkers (predominantly weak to moderate effect sizes). We discuss levels of validation and issues relating to usability, data quality, data protection, and attrition. While still in its infancy, digital cognitive assessment, especially when administered remotely, will undoubtedly play a major future role in screening for and tracking preclinical AD.

Synergistic Neuroprotective Effects of a Natural Product Mixture against AD Hallmarks and Cognitive Decline in Caenorhabditis elegans and an SAMP8 Mice Model

The study of different natural products can provide a wealth of bioactive compounds, and more interestingly, their combination can exert a new strategy for several neurodegenerative diseases with major public health importance, such as Alzheimer’s disease (AD). Here, we investigated the synergistic neuroprotective effects of a mixed extract composed of docosahexaenoic acid, Ginkgo biloba, D-pinitol, and ursolic acid in several transgenic Caenorhabditis elegans (C. elegans) and a senescence-accelerated prone mice 8 (SAMP8) model. First, we found a significantly higher survival percentage in the C. elegans group treated with the natural product mixture compared to the single extract-treated groups. Likewise, we found a significantly increased lifespan in group of C. elegans treated with the natural product mixture compared to the other groups, suggesting synergistic effects. Remarkably, we determined a significant reduction in Aβ plaque accumulation in the group of C. elegans treated with the natural product mixture compared to the other groups, confirming synergy. Finally, we demonstrated better cognitive performance in the group treated with the natural product mixture in both AD models (neuronal Aβ C. elegans strain CL2355 and the SAMP8 mice model), confirming the molecular results and unraveling the synergist effects of this combination. Therefore, our results proved the potential of this new natural product mixture for AD therapeutic strategies.

Treatment by low-dose brain radiation therapy improves memory performances without changes of the amyloid load in the TgF344-AD rat model

Alzheimer's disease (AD) is a neurodegenerative condition affecting memory performance. This pathology is characterized by intracerebral amyloid plaques and tau tangles coupled with neuroinflammation. During the last century, numerous therapeutic trials unfortunately failed highlighting the need to find new therapeutic approaches. Low-dose brain radiotherapy (LD-RT) showed efficacy to reduce amyloid load and inflammation in patients with peripheral diseases. In this study, the therapeutic potential of 2 LD-RT schedules was tested on the TgF344-AD rat model of AD. Fifteen-month-old rats were irradiated with 5 fractions of 2 Gy delivered either daily or weekly. The daily treatment induced an improvement of memory performance in the Y-maze. In contrast, the weekly treatment increased the microglial reactivity in the hippocampus. A lack of effect of both regimens on amyloid pathology was unexpectedly observed. The positive effect on cognition encourages to further evaluate the LD-RT therapeutic potential and highlights the impact of the design choice of the LD-RT regimen.

Pathobiolgy and Management of Alzheimer's Disease

Amyloid and tau protein abnormalities have been identified as the main causes of Alzheimer's disease but exact mechanisms remain to be revealed. Especially, amyloid beta and tau protein coupling and neuroinflammatory and neurovascular contributions to Alzheimer disease are quite mysterious. Many animal models and basic biological research are trying to solve these puzzles. Known as aging processes, autophagy, mitochondrial degeneration with generation of reactive oxygen species, and age-related epigenetic modifications are also known to be associated with development of Alzheimer's disease. Environmental factors such as bacterial and viral infections, heavy metal ions, diet, sleep, stress, and gut microbiota are also risk factors of Alzheimer's disease. Future development of preventive and therapeutic modalities may be dependent on the pathobiology of Alzheimer's disease.

Early-Stage Alzheimer's Disease Does Not Alter Pupil Responses to Colored Light Stimuli

BACKGROUND

Pathologic changes in cerebral and retinal structures governing the pupillary light reflex occur in Alzheimer's disease (AD). Analysis of pupillary responses originating from different retinal cells may allow for non-invasive detection of cerebral AD pathology.

OBJECTIVE

This study aimed to quantify the pupil light reflex using a portable chromatic pupillometer in patients with early stage AD and compare their responses to those of a healthy control group.

METHODS

Participants in this case-control pilot study were recruited from a well-characterized cohort of elderly people participating in a larger prospective study on early AD. Cognitive testing, volumetric brain imaging, and lumbar puncture were performed in all participants to define two groups: early AD, i.e., cognitively impaired subjects with biomarker-confirmed AD pathology, and control group of subjects with normal cognition and normal CSF biomarker profile. Pupil responses to red and blue light stimuli intended to activate cone photoreceptors and melanopsin ganglion cells were recorded under photopic conditions.

RESULTS

Sixteen patients with AD (mean age 77 years) and sixteen controls (mean age 71 years) were tested. Baseline pupil size was significantly smaller in AD patients. Pupillary contraction amplitude to all red and blue lights was also smaller in AD patients but did not reach statistical significance. The post-illumination pupillary response was the same between the two groups.

CONCLUSION

Compared to healthy controls, we found only a smaller resting size of the pupil in patients with early AD. The pupillary dynamics to light stimulation remained relatively preserved.

Disclosure of preclinical Alzheimer's disease biomarker results in research and clinical settings: Why, how, and what we still need to know

Disclosure of personal disease-related information to asymptomatic adults has been debated over the last century in medicine and research. Recently, Alzheimer's disease (AD) has been conceptualized as a continuum that begins with a "preclinical" stage in which biomarkers are present in the absence of cognitive impairment. Studies have begun assessing the safety, psychological, and behavioral effects of disclosing both AD-related genetic and biomarker information to cognitively unimpaired older adults. Yet, debate continues over the appropriate circumstances and methods for returning such information. This article outlines concerns with and rationale for AD biomarker disclosure and summarizes findings from prior studies. Overall, this article aims to describe and respond to key questions concerning disclosure of amyloid positron emission tomography scan results to asymptomatic adults in a research setting. Moving forward, such conditions are important to consider as interventions target the preclinical phase of AD and normalize disclosing biomarker information to cognitively unimpaired persons.

The search for a convenient procedure to detect one of the earliest signs of Alzheimer's disease: A systematic review of the prediction of brain amyloid status

INTRODUCTION

Convenient, cost-effective tests for amyloid beta (Aβ) are needed to identify those at higher risk for developing Alzheimer's disease (AD). This systematic review evaluates recent models that predict dichotomous Aβ. (PROSPERO: CRD42020144734).

METHODS

We searched Embase and identified 73 studies from 29,581 for review. We assessed study quality using established tools, extracted information, and reported results narratively.

RESULTS

We identified few high-quality studies due to concerns about Aβ determination and analytical issues. The most promising convenient, inexpensive classifiers consist of age, apolipoprotein E genotype, cognitive measures, and/or plasma Aβ. Plasma Aβ may be sufficient if pre-analytical variables are standardized and scalable assays developed. Some models lowered costs associated with clinical trial recruitment or clinical screening.

DISCUSSION

Conclusions about models are difficult due to study heterogeneity and quality. Promising prediction models used demographic, cognitive/neuropsychological, imaging, and plasma Aβ measures. Further studies using standardized Aβ determination, and improved model validation are required.

Preclinical and clinical biomarker studies of CT1812: A novel approach to Alzheimer's disease modification

INTRODUCTION

Amyloid beta (Aβ) oligomers are one of the most toxic structural forms of the Aβ protein and are hypothesized to cause synaptotoxicity and memory failure as they build up in Alzheimer's disease (AD) patients' brain tissue. We previously demonstrated that antagonists of the sigma-2 receptor complex effectively block Aβ oligomer toxicity. CT1812 is an orally bioavailable, brain penetrant small molecule antagonist of the sigma-2 receptor complex that appears safe and well tolerated in healthy elderly volunteers. We tested CT1812's effect on Aβ oligomer pathobiology in preclinical AD models and evaluated CT1812's impact on cerebrospinal fluid (CSF) protein biomarkers in mild to moderate AD patients in a clinical trial (ClinicalTrials.gov NCT02907567).

METHODS

Experiments were performed to measure the impact of CT1812 versus vehicle on Aβ oligomer binding to synapses in vitro, to human AD patient post mortem brain tissue ex vivo, and in living APP_Swe /PS1dE9 transgenic mice in vivo. Additional experiments were performed to measure the impact of CT1812 versus vehicle on Aβ oligomer-induced deficits in membrane trafficking rate, synapse number, and protein expression in mature hippocampal/cortical neurons in vitro. The impact of CT1812 on cognitive function was measured in transgenic Thy1 huAPP^Swe/Lnd+ and wild-type littermates. A multicenter, double-blind, placebo-controlled parallel group trial was performed to evaluate the safety, tolerability, and impact on protein biomarker expression of CT1812 or placebo given once daily for 28 days to AD patients (Mini-Mental State Examination 18-26). CSF protein expression was measured by liquid chromatography with tandem mass spectrometry or enzyme-linked immunosorbent assay in samples drawn prior to dosing (Day 0) and at end of dosing (Day 28) and compared within each patient and between pooled treated versus placebo-treated dosing groups.

RESULTS

CT1812 significantly and dose-dependently displaced Aβ oligomers bound to synaptic receptors in three independent preclinical models of AD, facilitated oligomer clearance into the CSF, increased synaptic number and protein expression in neurons, and improved cognitive performance in transgenic mice. CT1812 significantly increased CSF concentrations of Aβ oligomers in AD patient CSF, reduced concentrations of synaptic proteins and phosphorylated tau fragments, and reversed expression of many AD-related proteins dysregulated in CSF.

DISCUSSION

These preclinical studies demonstrate the novel disease-modifying mechanism of action of CT1812 against AD and Aβ oligomers. The clinical results are consistent with preclinical data and provide evidence of target engagement and impact on fundamental disease-related signaling pathways in AD patients, supporting further development of CT1812.

Plasma Amyloid Beta Concentrations in Aged and Cognitively Impaired Pet Dogs

Longevity-associated neurological disorders have been observed across human and canine aging populations. Alzheimer's disease (AD) and canine cognitive dysfunction syndrome (CDS) represent comparable diseases affecting both species as they age. Translational diagnostic and therapeutic research is needed for these incurable diseases. The amyloid β (Aβ) peptide family are AD-associated peptides with identical amino acid sequences between dogs and humans. Plasma Aβ42 concentration increases with age and decreases with AD in humans, and cerebrospinal fluid (CSF) concentration decreases in AD and correlates inversely with the amyloid load within the brain. Similarly, CSF Aβ42 concentrations decrease in dogs with CDS but there is limited and conflicting information on plasma Aβ42 concentrations in aging dogs and dogs with CDS. We measured plasma concentrations of Aβ42 and Aβ40 with an ultrasensitive single-molecule array assay (SIMOA) in a population of healthy aging dogs of different life stages (n = 36) and dogs affected with CDS (n = 11). In addition, the ratio of Aβ42/β40 was calculated. The mean plasma concentrations of Aβ42 and Aβ40 increased significantly with age (r2 = 0.27, p = 0.001; and r2 = 0.42, p < 0.001, respectively) and with life stage: puppy/junior group (0.43-2 years): 1.23 ± 0.95 and 38.26 ± 49.43 pg/mL; adult/mature group (2.1-9 years): 10.99 ± 5.45 and 131.05 ± 80.17 pg/mL; geriatric/senior group (9.3-14.5 years): 18.65 ± 16.65 and 192.88 ± 146.38 pg/mL, respectively. Concentrations of Aβ42 and Aβ40 in dogs with CDS (11.0-15.6 years) were significantly lower than age-matched healthy dogs at 11.61 ± 6.39 and 150.23 ± 98.2 pg/mL (p = 0.0048 and p = 0.001), respectively. Our findings suggest the dynamics of canine plasma amyloid concentrations are analogous to that found in aging humans with and without AD.

Proper names from story recall are associated with beta-amyloid in cognitively unimpaired adults at risk for Alzheimer's disease

Due to advances in the early detection of Alzheimer's disease (AD) biomarkers including beta-amyloid (Aβ), neuropsychological measures that are sensitive to concurrent, subtle changes in cognition are critically needed. Story recall tasks have shown sensitivity to early memory declines in persons with mild cognitive impairment (MCI) and early stage dementia, as well as in persons with autosomal dominantly inherited AD up to 10 years prior to a dementia diagnosis. However, the evidence is inconclusive regarding relationships between evidence of Aβ and story recall measures. Because story recall tasks require the encoding and delayed retrieval of several lexical-semantic categories, such as proper names, verbs, and numerical expressions, and because lexical categories have been shown to be differentially impaired in persons with MCI, we focused on item-level analyses of lexical-semantic retrieval from a quintessential story recall task, Logical Memory from the Wechsler Memory Scale-Revised. Our objective was to investigate whether delayed recall of lexical categories (proper names, verbs and/or numerical expressions), as well as the traditional total score measure, was associated with "preclinical AD," or cognitively unimpaired adults with positive Aβ deposition on positron emission tomography (PET) neuroimaging using Pittsburgh Compound B (PiB). We developed an item-level scoring system, in which we parsed items into lexical categories and examined the immediate and delayed recall of these lexical categories from 217 cognitively unimpaired participants from the Wisconsin Registry for Alzheimer's Prevention (WRAP). We performed binary logistic regression models with story recall score as predictor and Aβ status (positive/negative) as the outcome. Using baseline Logical Memory data, proper names from delayed story recall were significantly associated with Aβ status, such that participants who recalled more proper names were less likely to be classified as PiB(+) (odds ratio = .58, p = .01). None of the other story recall variables, including total score, were associated with PiB status. Secondary analyses determined that immediate recall of proper names was not significantly associated with Aβ, suggesting a retrieval deficit rather than that of encoding. The present findings suggest that lexical semantic retrieval measures from existing story recall tasks may be sensitive to Aβ deposition, and may provide added utility to a widely-used, long-standing neuropsychological test for early detection of cognitive decline on the AD continuum.

The Dichotomy of Alzheimer's Disease Pathology: Amyloid-β and Tau

In this issue, an article by Tiepolt et al. shows that PET scanning using [¹¹C]PiB can demonstrate both cerebral blood flow (CBF) changes and amyloid-β (Aβ) deposition in patients with mild cognitive dysfunction or mild dementia of Alzheimer’s disease (AD). The CBF changes can be determined because the early scan counts (1–9 minutes) reflect the flow of the radiotracer in the blood passing through the brain, while the Aβ levels are measured by later scan counts (40–70 minutes) after the radiotracer has been cleared from regions to which the radiotracer did not bind. Thus, two different diagnostic measures are obtained with a single injection. Unexpectedly, the mild patients with Aβ positivity had scan data with only a weak relationship to memory, while the relationships to executive function and language function were relatively strong. This divergence of findings from studies of severely impaired patients highlights the importance of determining how AD pathology affects the brain. A possibility suggested in this commentary is that Aβ deposits occur early in AD and specifically in critical areas of the neocortex affected only later by the neurofibrillary pathology indicating a different role of the amyloid-β protein precursor (AβPP) in the development of those neocortical regions, and a separate component of AD pathology may selectively impact functions of these neocortical regions. The effects of adverse AβPP metabolism in the medial temporal and brainstem regions occur later possibly because of different developmental issues, and the later, different pathology is clearly more cognitively and socially devastating.

What works and what does not work in Alzheimer's disease? From interventions on risk factors to anti-amyloid trials

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with no approved disease-modifying therapy (DMT). In this review, we summarize the various past approaches taken in an attempt to find treatments capable of altering the long-term course for individuals with AD, including: translating epidemiological observations into potential treatment options; seeking a single-treatment approach across the continuum of AD severity; utilizing biomarkers for assessing target engagement; using biomarkers as early surrogates of clinical efficacy; and enriching study populations to demonstrate adequate placebo decline during the limited duration of clinical trials. Although targeting the amyloid-β (Aβ) pathway has been central to the search for an effective DMT, to date, trials of anti-Aβ monoclonal antibodies have failed to consistently demonstrate significant clinical efficacy. Key learnings from these anti-Aβ trials, as well as the trials that came before them, have shifted the focus within clinical development programs to identifying target populations thought most likely to benefit from treatments (i.e., individuals at an earlier stage of disease). Other learnings include strategies to increase the likelihood of showing measurable improvements within the clinical trial setting by better predicting decline in placebo participants, as well as developing measures to quantify the needed treatment exposure (e.g., higher doses). Given the complexity associated with AD pathology and progression, treatments targeting non-amyloid AD pathologies in combination with anti-amyloid therapies may offer an alternative for the successful development of DMTs.

Distinct Neural Correlates of Executive Function by Amyloid Positivity and Associations with Clinical Progression in Mild Cognitive Impairment

PURPOSE

This study aimed to identify the neural basis of executive function (EF) in amnestic mild cognitive impairment (aMCI) according to beta-amyloid (Aβ) positivity. Furthermore, we explored if the identified brain areas could serve as predictors for clinical progression.

MATERIALS AND METHODS

We included individuals with aMCI using data from [¹⁸F]-florbetapir-positron emission tomography (PET), fluorodeoxyglucose-PET, and EF scores, as well as follow-up clinical severity scores at 1 and 5 years from baseline from the Alzheimer's Disease Neuroimaging Initiative database. The correlations between EF score and regional cerebral glucose metabolism (rCMglc) were analyzed separately for aMCI with low Aβ burden (aMCI Aβ-, n=230) and aMCI with high Aβ burden (aMCI Aβ+, n=268). Multiple linear regression analysis was conducted to investigate the associations between rCMglc and clinical progression.

RESULTS

Longitudinal courses differed between aMCI Aβ- and aMCI Aβ+ groups. On average, aMCI Aβ- subjects maintained their level of clinical severity, whereas aMCI Aβ+ subjects showed progression. EF impairment in aMCI Aβ- was related to the anterior cingulate cortex (ACC), whereas that in aMCI Aβ+ was related to Alzheimer's Disease-vulnerable brain regions. ACC and the posterior cingulate cortex were associated with clinical progression in aMCI Aβ- and aMCI Aβ+, respectively.

CONCLUSION

Our findings suggest that although MCI subjects showed similar behavioral phenotypes at the time of diagnosis, EF and further progression were associated with different brain regions according to Aβ burden. Clarification of the etiologies and nature of EF impairment in aMCI are critical for disease prognosis and management.

'Obesageing': Linking obesity & ageing

Obesity is one of the leading causes of preventable mortalities in many parts of the globe. The rise in geriatric population due to better treatment opportunities has also emerged as a major public health challenge. Both of these health challenges have impacted developed as well as developing countries. Obesity is attributed as a powerful risk factor of a variety of health problems such as cardiovascular diseases, hypertension, type 2 diabetes, dementia, neuropsychiatric diseases and many more. On the other hand, ageing is a natural process involving a gradual decline in physiological functions and is associated with similar co-morbidities as obesity. This review discusses about the commonalities (termed as ‘Obesageing') between the pathological phenomenon of obesity and normal physiological process of ageing. A unique rodent model of obesageing has been developed (WNIN/Ob) that has characteristics of morbid obesity as well as premature ageing. Such a novel animal model would facilitate the understanding of the complex interplay of different mechanisms that are common to obesity and ageing and help to devise strategies in future to tackle the growing burden of obesity and ageing.

Microstructural White Matter Alterations in Mild Cognitive Impairment and Alzheimer's Disease : Study Based on Neurite Orientation Dispersion and Density Imaging (NODDI)

PURPOSE

To investigate microstructural alterations in white matter in mild cognitive impairment (MCI) and Alzheimer's disease (AD) using neurite orientation dispersion and density imaging (NODDI) and to assess the potential diagnostic performance of NODDI-derived parameters.

METHODS

In this study 14 MCI patients, 14 AD patients, and 14 healthy controls (HC) were recruited. The diffusion tensor imaging(DTI)-derived fractional anisotropy (FA) and NODDI-derived neurite density index (NDI), orientation dispersion index (ODI), and volume fraction of isotropic water molecules (Viso) were calculated from the diffusion data. The tract-based spatial statistics (TBSS) method was used for statistical analysis with one-way ANOVA. The correlations between the parameter values and mini-mental state examination (MMSE) and Montreal cognitive assessment (MoCA) scores were examined. A receiver operating characteristic (ROC) curve was conducted to assess the diagnostic performance of different parameters.

RESULTS

Compared with the HC group, the NDI and ODI values decreased significantly and the Viso values were significantly increased in the MCI and AD groups (p < 0.01, threshold-free cluster enhancement (TFCE)-corrected); however, there were no significant differences in FA values in the MCI group. The NDI, ODI, and Viso values of multiple fibers were significantly correlated with MMSE and MoCA scores. For the diagnosis of AD, the area under the ROC curve (AUC) for the NDI value of the splenium of corpus callosum was larger than the FA value (AUC = 0.885, 0.714, p = 0.042). The AUC of the Viso value of the right cerebral peduncle was larger than FA value (AUC = 0.934, 0.531, p = 0.004).

CONCLUSION

The NDI is more sensitive to white matter microstructural changes than FA and NODDI could be superior to DTI in the diagnosis of AD.