Is There Any Evidence of Monocytes Involvement in Alzheimer's Disease? A Pilot Study on Human Postmortem Brain

Background

The role of neuroinflammation has become more evident in the pathogenesis of neurodegenerative diseases. Increased expression of microglial markers is widely reported in Alzheimer's disease (AD), but much less is known about the role of monocytes in AD pathogenesis. In AD animal models, bone marrow-derived monocytes appear to infiltrate the parenchyma and contribute to the phagocytosis of amyloid-β depositions, but this infiltration has not been established in systematic studies of the human brain postmortem.

Objective

In addition to assessing the distribution of different subtypes of microglia by immunostaining for CD68, HLA-DR, CD163, and CD206, we focused on the involvement of C-chemokine receptor type2 (CCR2) positive monocytes during the AD course.

Methods

We used formalin-fixed and paraffin-embedded tissue from four vulnerable brain regions (hippocampus, occipital lobe, brainstem, and cerebellum) from neuropathologically characterized AD cases at different Braak stages and age-matched controls.

Results

Only singular migrated CCR2-positive cells were found in all brain regions and stages. The brainstem showed the highest number of positive cells overall, followed by the hippocampus. This mechanism of recruitment seems to work less efficiently in the human brain at an advanced age, and the ingress of monocytes obviously takes place in much reduced numbers or not at all.

Conclusion

In contrast to studies on animal models, we observed only a quite low level of myeloid monocytes associated with AD pathology. Furthermore, we provide evidence associating early microglial reactions carried out in particular by pro-inflammatory cells with early effects on tangle- and plaque-positive vulnerable brain regions.

Proportion of Women and Reporting of Outcomes by Sex in Clinical Trials for Alzheimer Disease: A Systematic Review and Meta-analysis

IMPORTANCE

Women represent two-thirds of patients with Alzheimer disease (AD), and sex differences might affect results of randomized clinical trials (RCTs). However, little information exists on differences in sex as reported in RCTs for AD.

OBJECTIVE

To assess the ratio of females to males and the reporting of sex-stratified data in large pharmaceutical RCTs for AD.

DATA SOURCES

A search for pharmaceutical RCTs for AD was conducted on September 4, 2019, using ClinicalTrials.gov with the key word Alzheimer disease, and articles related to those trials were identified using the PubMed, Scopus, and Google Scholar databases. Searches were conducted between September 4 and October 31, 2019, and between April 15 and May 31, 2020.

STUDY SELECTION

Controlled RCTs that had more than 100 participants and tested the efficacy of drugs or herbal extracts were included. Of 1047 RCTs identified, 409 were published and therefore screened. A total of 77 articles were included in the final analysis, including 56 primary articles on AD, 13 secondary articles on AD, and 8 articles on mild cognitive impairment.

DATA EXTRACTION AND SYNTHESIS

The location and date of publication; number, sex, and age of patients enrolled; disease severity; experimental or approved status of the drug; and whether the study included a sex-stratified analysis in the protocol, methods, or results were extracted by 1 reviewer for each article, and the meta-analysis followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline. Data were analyzed using a mixed-effects model.

MAIN OUTCOMES AND MEASURES

The mean proportion of women enrolled in the trials and the associations between prespecified variables were analyzed. The proportion of articles that included sex-stratified results and the temporal trends in the reporting of these results were also studied.

RESULTS

In this review of 56 RCTs for AD involving 39 575 participants, 23 348 women (59.0%) were included. The mean (SD) proportion of women in RCTs of approved drugs was 67.3% (6.9%), and in RCTs of experimental drugs was 57.9% (5.9%). The proportion of women in RCTs of experimental drugs was significantly lower than the proportion of women in the general population with AD in the US (62.1%; difference, -4.56% [95% CI, -6.29% to -2.87%]; P < .001) and Europe (68.2%; difference, -10.67% [95% CI, -12.39% to -8.97%]; P < .001). Trials of approved drugs had a higher probability of including women than trials of experimental drugs (odds ratio [OR], 1.26; 95% CI, 1.05-1.52; P = .02). Both the severity of AD at baseline and the trial location were associated with the probability of women being enrolled in trials (severity: OR, 0.98; 95% CI, 0.97-1.00; P = .02; location in Europe: OR, 1.26; 95% CI, 1.05-1.52; P = .01; location in North America: OR, 0.81; 95% CI, 0.71-0.93; P = .002). Only 7 articles (12.5%) reported sex-stratified results, with an increasing temporal trend (R, 0.30; 95% CI, 0.05-0.59; P = .03).

CONCLUSIONS AND RELEVANCE

In this systematic review and meta-analysis, the proportion of women in RCTs for AD, although higher than the proportion of men, was significantly lower than that in the general population. Only a small proportion of trials reported sex-stratified results. These findings support strategies to improve diversity in enrollment and data reporting in RCTs for AD.

The connectivity between the olfactory and auditory cortex predicts an individual's sleep quality

Sleep disorders and multiple sensory impairments have been noticed as the potential first sign of neurodegenerative diseases such as the Parkinson disease. The relationship between sleep quality and the sensory neural basis would help us consider their combination in early diagnosis. In the present study, 32 out of 45 healthy subjects' resting-state functional magnetic resonance imaging data survived from motion correction and entered into the connectivity analysis. We found that the connectivity between two regions of interest (the left olfactory gyrus and the left superior temporal pole) and the regional homogeneity in the left middle temporal gyrus were negatively correlated with their Pittsburgh sleep quality index. These results suggest that these sensory-related brain regions are related to sleep quality and they may together predict the diseases.

Renin-Angiotensin System and Alzheimer's Disease Pathophysiology: From the Potential Interactions to Therapeutic Perspectives

New roles of the Renin-Angiotensin System (RAS), apart from fluid homeostasis and Blood Pressure (BP) regulation, are being progressively unveiled, since the discoveries of RAS alternative axes and local RAS in different tissues, including the brain. Brain RAS is reported to interact with pathophysiological mechanisms of many neurological and psychiatric diseases, including Alzheimer's Disease (AD). Even though AD is the most common cause of dementia worldwide, its pathophysiology is far from elucidated. Currently, no treatment can halt the disease course. Successive failures of amyloid-targeting drugs have challenged the amyloid hypothesis and increased the interest in the inflammatory and vascular aspects of AD. RAS compounds, both centrally and peripherally, potentially interact with neuroinflammation and cerebrovascular regulation. This narrative review discusses the AD pathophysiology and its possible interaction with RAS, looking forward to potential therapeutic approaches. RAS molecules affect BP, cerebral blood flow, neuroinflammation, and oxidative stress. Angiotensin (Ang) II, via angiotensin type 1 receptors may promote brain tissue damage, while Ang-(1-7) seems to elicit neuroprotection. Several studies dosed RAS molecules in AD patients' biological material, with heterogeneous results. The link between AD and clinical conditions related to classical RAS axis overactivation (hypertension, heart failure, and chronic kidney disease) supports the hypothesized role of this system in AD. Additionally, RAStargeting drugs as Angiotensin Converting Enzyme inhibitors (ACEis) and Angiotensin Receptor Blockers (ARBs) seem to exert beneficial effects on AD. Results of randomized controlled trials testing ACEi or ARBs in AD are awaited to elucidate whether AD-RAS interaction has implications on AD therapeutics.

Test-retest reliability of spatial navigation in adults at-risk of Alzheimer's disease

The Virtual Supermarket Task (VST) and Sea Hero Quest detect high-genetic-risk Alzheimer`s disease (AD). We aimed to determine their test-retest reliability in a preclinical AD population. Over two time points, separated by an 18-month period, 59 cognitively healthy individuals underwent a neuropsychological and spatial navigation assessment. At baseline, participants were classified as low-genetic-risk of AD or high-genetic-risk of AD. We calculated two-way mixed effects intraclass correlation coefficients (ICC) for task parameters and used repeated measures ANOVAS to determine whether genetic risk or sex contributed to test-retest variability. The egocentric parameter of the VST measure showed the highest test-retest reliability (ICC = .72), followed by the SHQ distance travelled parameter (ICC = .50). Post hoc longitudinal analysis showed that boundary-based navigation predicts worsening episodic memory concerns in high-risk (F = 5.01, P = 0.03), but in not low-risk, AD candidates. The VST and the Sea Hero Quest produced parameters with acceptable test-retest reliability. Further research in larger sample sizes is desirable.

An application of machine learning with feature selection to improve diagnosis and classification of neurodegenerative disorders

Background

The analysis of health and medical data is crucial for improving the diagnosis precision, treatments and prevention. In this field, machine learning techniques play a key role. However, the amount of health data acquired from digital machines has high dimensionality and not all data acquired from digital machines are relevant for a particular disease. Primary Progressive Aphasia (PPA) is a neurodegenerative syndrome including several specific diseases, and it is a good model to implement machine learning analyses. In this work, we applied five feature selection algorithms to identify the set of relevant features from 18F-fluorodeoxyglucose positron emission tomography images of the main areas affected by PPA from patient records. On the other hand, we carried out classification and clustering algorithms before and after the feature selection process to contrast both results with those obtained in a previous work. We aimed to find the best classifier and the more relevant features from the WEKA tool to propose further a framework for automatic help on diagnosis. Dataset contains data from 150 FDG-PET imaging studies of 91 patients with a clinic prognosis of PPA, which were examined twice, and 28 controls. Our method comprises six different stages: (i) feature extraction, (ii) expertise knowledge supervision (iii) classification process, (iv) comparing classification results for feature selection, (v) clustering process after feature selection, and (vi) comparing clustering results with those obtained in a previous work.

Results

Experimental tests confirmed clustering results from a previous work. Although classification results for some algorithms are not decisive for reducing features precisely, Principal Components Analisys (PCA) results exhibited similar or even better performances when compared to those obtained with all features.

Conclusions

Although reducing the dimensionality does not means a general improvement, the set of features is almost halved and results are better or quite similar. Finally, it is interesting how these results expose a finer grain classification of patients according to the neuroanatomy of their disease.

Sex differences in Alzheimer disease - the gateway to precision medicine

Alzheimer disease (AD) is characterized by wide heterogeneity in cognitive and behavioural syndromes, risk factors and pathophysiological mechanisms. Addressing this phenotypic variation will be crucial for the development of precise and effective therapeutics in AD. Sex-related differences in neural anatomy and function are starting to emerge, and sex might constitute an important factor for AD patient stratification and personalized treatment. Although the effects of sex on AD epidemiology are currently the subject of intense investigation, the notion of sex-specific clinicopathological AD phenotypes is largely unexplored. In this Review, we critically discuss the evidence for sex-related differences in AD symptomatology, progression, biomarkers, risk factor profiles and treatment. The cumulative evidence reviewed indicates sex-specific patterns of disease manifestation as well as sex differences in the rates of cognitive decline and brain atrophy, suggesting that sex is a crucial variable in disease heterogeneity. We discuss critical challenges and knowledge gaps in our current understanding. Elucidating sex differences in disease phenotypes will be instrumental in the development of a 'precision medicine' approach in AD, encompassing individual, multimodal, biomarker-driven and sex-sensitive strategies for prevention, detection, drug development and treatment.

Toward personalized cognitive diagnostics of at-genetic-risk Alzheimer's disease

Spatial navigation is emerging as a critical factor in identifying preclinical Alzheimer's disease (AD). However, the impact of interindividual navigation ability and demographic risk factors (e.g., APOE, age, and sex) on spatial navigation make it difficult to identify persons "at high risk" of AD in the preclinical stages. In the current study, we use spatial navigation big data (n = 27,108) from the Sea Hero Quest (SHQ) game to overcome these challenges by investigating whether big data can be used to benchmark a highly phenotyped healthy aging laboratory cohort into high- vs. low-risk persons based on their genetic (APOE) and demographic (sex, age, and educational attainment) risk factors. Our results replicate previous findings in APOE ε4 carriers, indicative of grid cell coding errors in the entorhinal cortex, the initial brain region affected by AD pathophysiology. We also show that although baseline navigation ability differs between men and women, sex does not interact with the APOE genotype to influence the manifestation of AD-related spatial disturbance. Most importantly, we demonstrate that such high-risk preclinical cases can be reliably distinguished from low-risk participants using big-data spatial navigation benchmarks. By contrast, participants were undistinguishable on neuropsychological episodic memory tests. Taken together, we present evidence to suggest that, in the future, SHQ normative benchmark data can be used to more accurately classify spatial impairments in at-high-risk of AD healthy participants at a more individual level, therefore providing the steppingstone for individualized diagnostics and outcome measures of cognitive symptoms in preclinical AD.

Going beyond the mean: Intraindividual variability of cognitive performance in prodromal and early neurodegenerative disorders

OBJECTIVE

Intraindividual variability (IIV), generally defined as short-term variations in behavior, has been proposed as a sign of subtle early impairment in neurodegenerative disorders, presumably associated with the disintegration of neuronal network connectivity. We aim to provide a review of IIV as a sensitive cognitive marker in prodromal neurodegenerative disorders.

METHOD

A narrative review focusing not only on theoretical and methodological definitions, including an overview on the neural correlates of IIV, but mainly on results from population-based and clinical-based studies on the role of IIV as a reliable predictor of mild cognitive impairment (MCI) and conversion to dementia in neurodegenerative disorders, mostly Alzheimer's and Parkinson's disease.

RESULTS

Most studies focus on MCI and Alzheimer's disease and demonstrate that IIV is a reliable cognitive marker. IIV is partly more sensitive than mean performance in the prediction of cognitive impairment or progressive deterioration and is independent of socio-demographic variables and disease mediators (e.g., genetic susceptibility). Neuroimaging data, mostly from healthy subjects, suggest a relationship between IIV and dysfunction of the default mode network, presumably mediated by white matter disintegration in frontal and parietal areas.

CONCLUSIONS

IIV measures may provide valuable information about diagnosis and progression in prodromal stages of neurodegenerative disorders. Thus, further conceptual and methodological clarifications are needed to justify the inclusion of IIV as a sensible cognitive marker in routine clinical neuropsychological assessment.

Precision medicine and drug development in Alzheimer's disease: the importance of sexual dimorphism and patient stratification

Neurodegenerative diseases (ND) are among the leading causes of disability and mortality. Considerable sex differences exist in the occurrence of the various manifestations leading to cognitive decline. Alzheimer's disease (AD) exhibits substantial sexual dimorphisms and disproportionately affects women. Women have a higher life expectancy compared to men and, consequently, have more lifespan to develop AD. The emerging precision medicine and pharmacology concepts - taking into account the individual genetic and biological variability relevant for disease risk, prevention, detection, diagnosis, and treatment - are expected to substantially enhance our knowledge and management of AD. Stratifying the affected individuals by sex and gender is an important basic step towards personalization of scientific research, drug development, and care. We hypothesize that sex and gender differences, extending from genetic to psychosocial domains, are highly relevant for the understanding of AD pathophysiology, and for the conceptualization of basic/translational research and for clinical therapy trial design.

The Quest for an Alzheimer Therapy

This mini-review considers three different approaches to the therapy and prevention of Alzheimer’s disease (AD): replacement therapy, disease modification, and multi-level interventions. Each of these research frameworks has direct implications at the clinical level, leading to an emphasis on different time points of the AD continuum. While all perspectives continue to play an important role in current efforts to reach the ambitious target of an effective therapy or prevention of AD by 2025, it is clear that novel paradigms are needed, including new models of clinical trial design. This goal can only be accomplished by a concerted effort of academia, governmental agencies, and industry.

Revolution of Alzheimer Precision Neurology. Passageway of Systems Biology and Neurophysiology

The Precision Neurology development process implements systems theory with system biology and neurophysiology in a parallel, bidirectional research path: a combined hypothesis-driven investigation of systems dysfunction within distinct molecular, cellular, and large-scale neural network systems in both animal models as well as through tests for the usefulness of these candidate dynamic systems biomarkers in different diseases and subgroups at different stages of pathophysiological progression. This translational research path is paralleled by an "omics"-based, hypothesis-free, exploratory research pathway, which will collect multimodal data from progressing asymptomatic, preclinical, and clinical neurodegenerative disease (ND) populations, within the wide continuous biological and clinical spectrum of ND, applying high-throughput and high-content technologies combined with powerful computational and statistical modeling tools, aimed at identifying novel dysfunctional systems and predictive marker signatures associated with ND. The goals are to identify common biological denominators or differentiating classifiers across the continuum of ND during detectable stages of pathophysiological progression, characterize systems-based intermediate endophenotypes, validate multi-modal novel diagnostic systems biomarkers, and advance clinical intervention trial designs by utilizing systems-based intermediate endophenotypes and candidate surrogate markers. Achieving these goals is key to the ultimate development of early and effective individualized treatment of ND, such as Alzheimer's disease. The Alzheimer Precision Medicine Initiative (APMI) and cohort program (APMI-CP), as well as the Paris based core of the Sorbonne University Clinical Research Group "Alzheimer Precision Medicine" (GRC-APM) were recently launched to facilitate the passageway from conventional clinical diagnostic and drug development toward breakthrough innovation based on the investigation of the comprehensive biological nature of aging individuals. The APMI movement is gaining momentum to systematically apply both systems neurophysiology and systems biology in exploratory translational neuroscience research on ND.