Preclinical Alzheimer disease: identification of cases at risk among cognitively intact older individuals

Causal association and mediating effect of blood biochemical metabolic traits and brain image-derived endophenotypes on Alzheimer's disease

Background

Recent genetic evidence supports that circulating biochemical and metabolic traits (BMTs) play a causal role in Alzheimer's disease (AD), which might be mediated by changes in brain structure. Here, we leveraged publicly available genome-wide association study data to investigate the intrinsic causal relationship between blood BMTs, brain image-derived phenotypes (IDPs) and AD.

Methods

Utilizing the genetic variants associated with 760 blood BMTs and 172 brain IDPs as the exposure and the latest AD summary statistics as the outcome, we analyzed the causal relationship between blood BMTs and brain IDPs and AD by using a two-sample Mendelian randomization (MR) method. Additionally, we used two-step/mediation MR to study the mediating effect of brain IDPs between blood BMTs and AD.

Results

Twenty-five traits for genetic evidence supporting a causal association with AD were identified, including 12 blood BMTs and 13 brain IDPs. For BMTs, glutamine consistently reduced the risk of AD in 3 datasets. For IDPs, specific alterations of cortical thickness (atrophy in frontal pole and insular lobe, and incrassation in superior parietal lobe) and subcortical volume (atrophy in hippocampus and its subgroups, left accumbens and left choroid plexus, and expansion in cerebral white matter) are vulnerable to AD. In the two-step/mediation MR analysis, superior parietal lobe, right hippocampal fissure and left accumbens were identified to play a potential mediating role among three blood BMTs and AD.

Conclusions

The results obtained in our study suggest that 12 circulating BMTs and 13 brain IDPs play a causal role in AD. Importantly, a subset of BMTs exhibit shared genetic architecture and potentially causal relationships with brain structure, which may contribute to the alteration of brain IDPs in AD.

Baseline structural MRI and plasma biomarkers predict longitudinal structural atrophy and cognitive decline in early Alzheimer's disease

BACKGROUND

Crucial to the success of clinical trials targeting early Alzheimer's disease (AD) is recruiting participants who are more likely to progress over the course of the trials. We hypothesize that a combination of plasma and structural MRI biomarkers, which are less costly and non-invasive, is predictive of longitudinal progression measured by atrophy and cognitive decline in early AD, providing a practical alternative to PET or cerebrospinal fluid biomarkers.

METHODS

Longitudinal T1-weighted MRI, cognitive (memory-related test scores and clinical dementia rating scale), and plasma measurements of 245 cognitively normal (CN) and 361 mild cognitive impairment (MCI) patients from ADNI were included. Subjects were further divided into β-amyloid positive/negative (Aβ+/Aβ-)] subgroups. Baseline plasma (p-tau181 and neurofilament light chain) and MRI-based structural medial temporal lobe subregional measurements and their association with longitudinal measures of atrophy and cognitive decline were tested using stepwise linear mixed effect modeling in CN and MCI, as well as separately in the Aβ+/Aβ- subgroups. Receiver operating characteristic (ROC) analyses were performed to investigate the discriminative power of each model in separating fast and slow progressors (first and last terciles) of each longitudinal measurement.

RESULTS

A total of 245 CN (35.0% Aβ+) and 361 MCI (53.2% Aβ+) participants were included. In the CN and MCI groups, both baseline plasma and structural MRI biomarkers were included in most models. These relationships were maintained when limited to the Aβ+ and Aβ- subgroups, including Aβ- CN (normal aging). ROC analyses demonstrated reliable discriminative power in identifying fast from slow progressors in MCI [area under the curve (AUC): 0.78-0.93] and more modestly in CN (0.65-0.73).

CONCLUSIONS

The present data support the notion that plasma and MRI biomarkers, which are relatively easy to obtain, provide a prediction for the rate of future cognitive and neurodegenerative progression that may be particularly useful in clinical trial stratification and prognosis. Additionally, the effect in Aβ- CN indicates the potential use of these biomarkers in predicting a normal age-related decline.

The role of the hippocampus in statistical learning and language recovery in persons with post stroke aphasia

Although several studies have aimed for accurate predictions of language recovery in post stroke aphasia, individual language outcomes remain hard to predict. Large-scale prediction models are built using data from patients mainly in the chronic phase after stroke, although it is clinically more relevant to consider data from the acute phase. Previous research has mainly focused on deficits, i.e., behavioral deficits or specific brain damage, rather than compensatory mechanisms, i.e., intact cognitive skills or undamaged brain regions. One such unexplored brain region that might support language (re)learning in aphasia is the hippocampus, a region that has commonly been associated with an individual's learning potential, including statistical learning. This refers to a set of mechanisms upon which we rely heavily in daily life to learn a range of regularities across cognitive domains. Against this background, thirty-three patients with aphasia (22 males and 11 females, M = 69.76 years, SD = 10.57 years) were followed for 1 year in the acute (1-2 weeks), subacute (3-6 months) and chronic phase (9-12 months) post stroke. We evaluated the unique predictive value of early structural hippocampal measures for short-term and long-term language outcomes (measured by the ANELT). In addition, we investigated whether statistical learning abilities were intact in patients with aphasia using three different tasks: an auditory-linguistic and visual task based on the computation of transitional probabilities and a visuomotor serial reaction time task. Finally, we examined the association of individuals' statistical learning potential with acute measures of hippocampal gray and white matter. Using Bayesian statistics, we found moderate evidence for the contribution of left hippocampal gray matter in the acute phase to the prediction of long-term language outcomes, over and above information on the lesion and the initial language deficit (measured by the ScreeLing). Non-linguistic statistical learning in patients with aphasia, measured in the subacute phase, was intact at the group level compared to 23 healthy older controls (8 males and 15 females, M = 74.09 years, SD = 6.76 years). Visuomotor statistical learning correlated with acute hippocampal gray and white matter. These findings reveal that particularly left hippocampal gray matter in the acute phase is a potential marker of language recovery after stroke, possibly through its statistical learning ability.

Sporadic Alzheimer's Disease- and Neurotoxicity-Related microRNAs Affecting Key Events of Tau-Driven Adverse Outcome Pathway Toward Memory Loss

BACKGROUND

A complex network of aging-related homeostatic pathways that are sensitive to further deterioration in the presence of genetic, systemic, and environmental risk factors, and lifestyle, is implicated in the pathogenesis of progressive neurodegenerative diseases, such as sporadic (late-onset) Alzheimer's disease (sAD).

OBJECTIVE

Since sAD pathology and neurotoxicity share microRNAs (miRs) regulating common as well as overlapping pathological processes, environmental neurotoxic compounds are hypothesized to exert a risk for sAD initiation and progression.

METHODS

Literature search for miRs associated with human sAD and environmental neurotoxic compounds was conducted. Functional miR analysis using PathDip was performed to create miR-target interaction networks.

RESULTS

The identified miRs were successfully linked to the hypothetical starting point and key events of the earlier proposed tau-driven adverse outcome pathway toward memory loss. Functional miR analysis confirmed most of the findings retrieved from literature and revealed some interesting findings. The analysis identified 40 miRs involved in both sAD and neurotoxicity that dysregulated processes governing the plausible adverse outcome pathway for memory loss.

CONCLUSION

Creating miR-target interaction networks related to pathological processes involved in sAD initiation and progression, and environmental chemical-induced neurotoxicity, respectively, provided overlapping miR-target interaction networks. This overlap offered an opportunity to create an alternative picture of the mechanisms underlying sAD initiation and early progression. Looking at initiation and progression of sAD from this new angle may open for new biomarkers and novel drug targets for sAD before the appearance of the first clinical symptoms.

When Does Alzheimer's Disease Really Start? The Role of Biomarkers

(Appeared originally in Int J Mol Sci 2019, 20 5536).

The striatum, the hippocampus, and short-term memory binding: Volumetric analysis of the subcortical grey matter's role in mild cognitive impairment

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Hippocampal atrophy plays no role in short-term memory binding.

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The globus pallidus could be part of the brain network supporting binding.

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Total brain atrophy does not correlate with striatal grey matter atrophy in MCI.

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Striatal grey matter atrophy reflects in total brain atrophy in controls.

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Hippocampal and parahippocampal volumes correlate in MCI and controls.

Background

Deficits in short-term memory (STM) binding are a distinguishing feature of preclinical stages leading to Alzheimer's disease (AD). However, the neuroanatomical correlates of conjunctive STM binding are largely unexplored. Here we examine the possible association between the volumes of hippocampi, parahippocampal gyri, and grey matter within the subcortical structures – all found to have foci that seemingly correlate with basic daily living activities in AD patients - with cognitive tests related to conjunctive STM binding.

Materials and methods

Hippocampal, thalamic, parahippocampal and corpus striatum volumes were semi-automatically quantified in brain magnetic resonance images from 25 cognitively normal people and 21 patients with Mild Cognitive Impairment (MCI) at high risk of AD progression, who undertook a battery of cognitive tests and the short-term memory binding test. Associations were assessed using linear regression models and group differences were assessed using the Mann-Whitney U test.

Results

Hippocampal and parahippocampal gyrus volumes differed between MCI and control groups. Although the grey matter volume in the globus pallidus (r = -0.71, p < 0.001) and parahippocampal gyry (r = -0.63, p < 0.05) correlated with a STM binding task in the MCI group, only the former remained associated with STM binding deficits in MCI patients, after correcting for age, gender and years of education (β = -0.56,P = 0.042) although with borderline significance.

Conclusions

Loss of hippocampal volume plays no role in the processing of STM binding. Structures within the basal ganglia, namely the globus pallidus, could be part of the extrahippocampal network supporting binding. Replication of this study in large samples is now needed.

Subregional Density of Neurons, Neurofibrillary Tangles and Amyloid Plaques in the Hippocampus of Patients With Alzheimer's Disease

A variety of anatomical alterations have been reported in the hippocampal formation of patients with Alzheimer's Disease (AD) and these alterations have been correlated with cognitive symptoms in the early stages of the disease. Major hallmarks in AD are the presence of paired helical filaments of tau protein (PHF_Tau) within neurons, also known as neurofibrillary tangles (NFTs), and aggregates of amyloid-β protein (Aβ) which form plaques in the extracellular space. Nevertheless, how the density of plaques and NFTs relate to the severity of cell loss and cognitive decline is not yet clear. The aim of the present study was to further examine the possible relationship of both Aβ plaques and NFTs with neuronal loss in several hippocampal fields (DG, CA3, CA1, and subiculum) of 11 demented AD patients. For this purpose, using stereological techniques, we compared neuronal densities (Nissl-stained, and immunoreactive neurons for NeuN) with: (i) numbers of neurons immunostained for two isoforms of PHF_Tau (PHF_Tau-AT8 and PHF_Tau-pS396); and (ii) number of Aβ plaques. We found that CA1 showed the highest number of NFTs and Aβ plaques, whereas DG and CA3 displayed the lowest number of these markers. Furthermore, AD patients showed a variable neuronal loss in CA1 due to tangle-related cell death, which seems to correlate with the presence of extracellular tangles.

When Does Alzheimer's Disease Really Start? The Role of Biomarkers

While Alzheimer’s disease (AD) classical diagnostic criteria rely on clinical data from a stablished symptomatic disease, newer criteria aim to identify the disease in its earlier stages. For that, they incorporated the use of AD’s specific biomarkers to reach a diagnosis, including the identification of Aβ and tau depositions, glucose hypometabolism, and cerebral atrophy. These biomarkers created a new concept of the disease, in which AD’s main pathological processes have already taken place decades before we can clinically diagnose the first symptoms. Therefore, AD is now considered a dynamic disease with a gradual progression, and dementia is its final stage. With that in mind, new models were proposed, considering the orderly increment of biomarkers and the disease as a continuum, or the variable time needed for the disease’s progression. In 2011, the National Institute on Aging and the Alzheimer’s Association (NIA-AA) created separate diagnostic recommendations for each stage of the disease continuum—preclinical, mild cognitive impairment, and dementia. However, new scientific advances have led them to create a unifying research framework in 2018 that, although not intended for clinical use as of yet, is a step toward shifting the focus from the clinical symptoms to the biological alterations and toward changing the future diagnostic and treatment possibilities. This review aims to discuss the role of biomarkers in the onset of AD.

Cracking novel shared targets between epilepsy and Alzheimer's disease: need of the hour

Epilepsy and Alzheimer's disease (AD) are interconnected. It is well known that seizures are linked with cognitive impairment, and there are various shared etiologies between epilepsy and AD. The connection between hyperexcitability of neurons and cognitive dysfunction in the progression of AD or epileptogenesis plays a vital role for improving selection of treatment for both diseases. Traditionally, seizures occur less frequently and in later stages of age in patients with AD which in turn implies that neurodegeneration causes seizures. The role of seizures in early stages of pathogenesis of AD is still an issue to be resolved. So, it is well timed to analyze the common pathways involved in pathophysiology of AD and epilepsy. The present review focuses on similar potential underlying mechanisms which may be related to the causes of seizures in epilepsy and cognitive impairment in AD. The proposed review will focus on many possible newer targets like abnormal expression of various enzymes like GSK-3β, PP2A, PKC, tau hyperphosphorylation, MMPs, caspases, neuroinflammation and oxidative stress associated with number of neurodegenerative diseases linked with epilepsy. The brief about the prospective line of treatment of both diseases will also be discussed in the present review.

A Study of Amyloid-β and Phosphotau in Plaques and Neurons in the Hippocampus of Alzheimer's Disease Patients

The main pathological hallmarks in Alzheimer's disease (AD) are the presence of extracellular amyloid plaques, primarily consisting of amyloid-β (Aβ) peptide, and the accumulation of paired helical filaments of hyperphosphorylated tau protein (PHF-Tau) within neurons. Since CA1 is one of the most affected regions in AD, mainly at early stages, we have performed a detailed analysis of the CA1 region from 11 AD patients (demented and clinically similar; Braak stages IV-VI) to better understand the possible relationship between the presence and distribution of different neurochemical types of Aβ plaques and PHF-Tau immunoreactive  (- ir)  neurons. Hence, we have examined hippocampal sections in confocal microscopy images from double and triple-immunostained sections, to study labeled plaques and PHF-Tau-ir neurons using specific software tools. There are four main findings in the present study. First, the pyramidal layer of proximal CA1 (close to CA2) contains the smallest number of both plaques and PHF-Tau-ir neurons. Second, a large proportion of Aβ-ir plaques were also characterized by the presence of PHF-Tau-ir. Third, all plaques containing one of the two PHF-Tau isoforms also express the other isoform, that is, if a plaque contains PHFpS396, it also contains PHFAT8, and vice versa. Fourth, the coexpression study of both PHF-Tau isoforms in CA1 neurons revealed that most of the labeled neurons express only PHFpS396. Our findings further support the idea that AD is not a unique entity even within the same neuropathological stage, since the microanatomical/neurochemical changes that occur in the hippocampus greatly vary from one patient to another.

Poor Safety and Tolerability Hamper Reaching a Potentially Therapeutic Dose in the Use of Thalidomide for Alzheimer's Disease: Results from a Double-Blind, Placebo-Controlled Trial

INTRODUCTION

To date there is no cure for Alzheimer's disease (AD). After amyloid beta immunotherapies have failed to meet primary endpoints of slowing cognitive decline in AD subjects, the inhibition of the beta-secretase BACE1 appears as a promising therapeutic approach. Pre-clinical data obtained in APP23 mice suggested that the anti-cancer drug thalidomide decreases brainBACE1 and Aβ levels. This prompted us to develop an NIH-supported Phase IIa clinical trial to test the potential of thalidomide for AD. We hypothesized that thalidomide can decrease or stabilize brain amyloid deposits, which would result in slower cognitive decline in drug- versus placebo-treated subjects.

METHODS

This was a 24-week, randomized, double-blind, placebo-controlled, parallel group study with escalating dose regimen of thalidomide with a target dose of 400mg daily in patients with mild to moderate AD. The primary outcome measures were tolerability and cognitive performance assessed by a battery of tests.

RESULTS

A total of 185 subjects have been pre-screened, out of which25 were randomized. Mean age of the sample at baseline was 73.64 (±7.20) years; mean education was 14.24 (±2.3) years; mean MMSE score was 21.00 (±5.32); and mean GDS score was 2.76 (±2.28).Among the 25 participants, 14 (56%) terminated early due to adverse events, dramatically decreasing the power of the study. In addition, those who completed the study (44%) never reached the estimated therapeutic dose of 400 mg/day thalidomide because of reported adverse events. The cognitive data showed no difference between the treated and placebo groups at the end of the trial.

CONCLUSION

This study demonstrates AD patients have poor tolerability for thalidomide, and are unable to reach a therapeutic dose felt to be sufficient to have effects on BACE1. Because of poor tolerability, this study failed to demonstrate a beneficial effect on cognition.

MEG biomarker of Alzheimer's disease: Absence of a prefrontal generator during auditory sensory gating

Magnetoencephalography (MEG), a direct measure of neuronal activity, is an underexplored tool in the search for biomarkers of Alzheimer's disease (AD). In this study, we used MEG source estimates of auditory gating generators, nonlinear correlations with neuropsychological results, and multivariate analyses to examine the sensitivity and specificity of gating topology modulation to detect AD. Our results demonstrated the use of MEG localization of a medial prefrontal (mPFC) gating generator as a discrete (binary) detector of AD at the individual level and resulted in recategorizing the participant categories in: (1) controls with mPFC generator localized in response to both the standard and deviant tones; (2) a possible preclinical stage of AD participants (a lower functioning group of controls) in which mPFC activation was localized to the deviant tone only; and (3) symptomatic AD in which mPFC activation was not localized to either the deviant or standard tones. This approach showed a large effect size (0.9) and high accuracy, sensitivity, and specificity (100%) in identifying symptomatic AD patients within a limited research sample. The present results demonstrate high potential of mPFC activation as a noninvasive biomarker of AD pathology during putative preclinical and clinical stages. Hum Brain Mapp 38:5180-5194, 2017. © 2017 Wiley Periodicals, Inc.

Hippocampal and Amygdala Gray Matter Loss in Elderly Controls with Subtle Cognitive Decline

In contrast to the idea that hippocampal and amygdala volume loss occur in late phases of neurodegeneration, recent contributions point to the relevance of preexisting structural deficits that are associated with aging and are independent of amyloid deposition in preclinical Alzheimer disease cases. The present work explores GM hippocampal and amygdala volumes in elderly controls displaying the first signs of cognitive decline. 455 subjects (263 females), including 374 controls (228 females) and 81 middle cognitive impairment subjects (35 females), underwent two neuropsychological evaluations (baseline and 18 months follow-up) and a MRI-T1 examination (only baseline). Clinical assessment included Mini-Mental State Examination (MMSE), Clinical Dementia Rating scale, Hospitalized Anxiety and Depression scale, the Consortium to Establish a Registry for Alzheimer’s Disease neuropsychological battery and RI-48 Cued Recall Test (RI-48) for episodic memory. Based on their cognitive performance, we defined the controls as stable controls (sCON) and deteriorating controls (dCONs). Analyses included volumetric assessment, shape analyses and linear regressions between GM volume loss and differences in clinical scores between baseline and follow-up. Significant GM volume decrease in hippocampus bilaterally and right amygdala was found in dCON compared to sCON (p < 0.05). Lower right amygdala volumes were measured in mild cognitive impairment (MCI) compared to sCON (p < 0.05). Shape analyses revealed that atrophy was more pronounced at the superior- posterior lateral side of the hippocampus and amygdala. Significant correlations were found between GM volume of left hippocampus and the delta of MMSE and RI-48 scores in dCON and MCI groups separately. Decreased hippocampal and right amygdala volumes precede the first signs of cognitive decline in healthy elderly controls at the pre-MCI state. Left hippocampus volume may also predict short-term changes of overall cognition in these vulnerable cases.

Preclinical Alzheimer's disease: Definition, natural history, and diagnostic criteria

During the past decade, a conceptual shift occurred in the field of Alzheimer's disease (AD) considering the disease as a continuum. Thanks to evolving biomarker research and substantial discoveries, it is now possible to identify the disease even at the preclinical stage before the occurrence of the first clinical symptoms. This preclinical stage of AD has become a major research focus as the field postulates that early intervention may offer the best chance of therapeutic success. To date, very little evidence is established on this "silent" stage of the disease. A clarification is needed about the definitions and lexicon, the limits, the natural history, the markers of progression, and the ethical consequence of detecting the disease at this asymptomatic stage. This article is aimed at addressing all the different issues by providing for each of them an updated review of the literature and evidence, with practical recommendations.

Relationship between Brain Age-Related Reduction in Gray Matter and Educational Attainment

Inter-subject variability in age-related brain changes may relate to educational attainment, as suggested by cognitive reserve theories. This voxel-based morphometry study investigated the impact of very low educational level on the relationship between regional gray matter (rGM) volumes and age in healthy elders. Magnetic resonance imaging data were acquired in elders with low educational attainment (less than 4 years) (n = 122) and high educational level (n = 66), pulling together individuals examined using either of three MRI scanners/acquisition protocols. Voxelwise group comparisons showed no rGM differences (p<0.05, family-wise error corrected for multiple comparisons). When within-group voxelwise patterns of linear correlation were compared between high and low education groups, there was one cluster of greater rGM loss with aging in low versus high education elders in the left anterior cingulate cortex (p<0.05, FWE-corrected), as well as a trend in the left dorsomedial prefrontal cortex (p<0.10). These results provide preliminary indication that education might exert subtle protective effects against age-related brain changes in healthy subjects. The anterior cingulate cortex, critical to inhibitory control processes, may be particularly sensitive to such effects, possibly given its involvement in cognitive stimulating activities at school or later throughout life.

A critical review of chronic traumatic encephalopathy

Chronic traumatic encephalopathy (CTE) has been described in the literature as a neurodegenerative disease with: (i) localized neuronal and glial accumulations of phosphorylated tau (p-tau) involving perivascular areas of the cerebral cortex, sulcal depths, and with a preference for neurons within superficial cortical laminae; (ii) multifocal axonal varicosities and axonal loss involving deep cortex and subcortical white matter; (iii) relative absence of beta-amyloid deposits; (iv) TDP-43 immunoreactive inclusions and neurites; and (v) broad and diverse clinical features. Some of the pathological findings reported in the literature may be encountered with age and other neurodegenerative diseases. However, the focality of the p-tau cortical findings in particular, and the regional distribution, are believed to be unique to CTE. The described clinical features in recent cases are very similar to how depression manifests in middle-aged men and with frontotemporal dementia as the disease progresses. It has not been established that the described tau pathology, especially in small amounts, can cause complex changes in behavior such as depression, substance abuse, suicidality, personality changes, or cognitive impairment. Future studies will help determine the extent to which the neuropathology is causally related to the diverse clinical features.

Free Recall Episodic Memory Performance Predicts Dementia Ten Years prior to Clinical Diagnosis: Findings from the Betula Longitudinal Study

BACKGROUND/AIMS

Early dementia diagnosis is a considerable challenge. The present study examined the predictive value of cognitive performance for a future clinical diagnosis of late-onset Alzheimer's disease or vascular dementia in a random population sample.

METHODS

Cognitive performance was retrospectively compared between three groups of participants from the Betula longitudinal cohort. Group 1 developed dementia 11-22 years after baseline testing (n = 111) and group 2 after 1-10 years (n = 280); group 3 showed no deterioration towards dementia during the study period (n = 2,855). Multinomial logistic regression analysis was used to investigate the predictive value of tests reflecting episodic memory performance, semantic memory performance, visuospatial ability, and prospective memory performance.

RESULTS

Age- and education-corrected performance on two free recall episodic memory tests significantly predicted dementia 10 years prior to clinical diagnosis. Free recall performance also predicted dementia 11-22 years prior to diagnosis when controlling for education, but not when age was added to the model.

CONCLUSION

The present results support the suggestion that two free recall-based tests of episodic memory function may be useful for detecting individuals at risk of developing dementia 10 years prior to clinical diagnosis.

Free Recall Episodic Memory Performance Predicts Dementia Ten Years prior to Clinical Diagnosis: Findings from the Betula Longitudinal Study

BACKGROUND/AIMS

Early dementia diagnosis is a considerable challenge. The present study examined the predictive value of cognitive performance for a future clinical diagnosis of late-onset Alzheimer's disease or vascular dementia in a random population sample.

METHODS

Cognitive performance was retrospectively compared between three groups of participants from the Betula longitudinal cohort. Group 1 developed dementia 11-22 years after baseline testing (n = 111) and group 2 after 1-10 years (n = 280); group 3 showed no deterioration towards dementia during the study period (n = 2,855). Multinomial logistic regression analysis was used to investigate the predictive value of tests reflecting episodic memory performance, semantic memory performance, visuospatial ability, and prospective memory performance.

RESULTS

Age- and education-corrected performance on two free recall episodic memory tests significantly predicted dementia 10 years prior to clinical diagnosis. Free recall performance also predicted dementia 11-22 years prior to diagnosis when controlling for education, but not when age was added to the model.

CONCLUSION

The present results support the suggestion that two free recall-based tests of episodic memory function may be useful for detecting individuals at risk of developing dementia 10 years prior to clinical diagnosis.

Imaging biomarkers associated with cognitive decline: a review

In evaluating disease changes, it is critical to have measurements that are sensitive, specific, and reliable. Cognitive decline, particularly in the context of Alzheimer's disease, is an area that has attracted numerous recent studies, and the proposed biomarkers used in these investigations need to be validated. In this review, we highlight studies with important implications about the role of imaging biomarkers in cognitive decline and dementia as well as in distinguishing preclinical dementia before evidence of cognitive decline. Structural changes determined on cross-sectional and longitudinal magnetic resonance imaging provide early prediction of dementia, particularly when combined with other measures. Molecular imaging using positron emission tomography and single photon emission computed tomography tracers quantify the presence or activity of receptors, transporters, enzymes, metabolic pathways, and proteins. The newest developments in molecular imaging are described, and methods are compared. Distinguishing features of imaging biomarkers among dementias and the spectrum of preclinical Alzheimer's disease, mild cognitive impairment, and Alzheimer's disease are described. Appropriate use criteria for positron emission tomography with amyloid tracers are delineated. Although these efforts are still in the early phase of development, there is great promise for further development in structural magnetic resonance imaging and positron emission tomography technologies.

Alzheimer's disease and vascular dementia: one potentially preventable and modifiable disease. Part I: Pathology, diagnosis and screening

Alzheimer's disease (AD) and vascular dementia (VaD) frequently coexist and their separation may well be a false dichotomy. The neurodegenerative and cerebrovascular changes vary from the extremes of 'pure AD' to 'pure VaD' and a combination of changes is the most frequent. Both changes have a preclinical phase of decades. The clinical presentation is often out of proportion to the neuropathology to a lesser or greater degree. The diagnosis of dementia or mild cognitive impairment is based on clinical assessment and diagnostic criteria have been published. Neuropsychological testing and specialist evaluation may be required. The UK and US governments propose screening of all older adults. The value of routine screening has been questioned. Consent for testing and counseling are essential.

Genetic evidence for the involvement of variants at APOE, BIN1, CR1, and PICALM loci in risk of late-onset Alzheimer's disease and evaluation for interactions with APOE genotypes

Alzheimer's disease (AD) is the most common form of dementia in older population. Growing evidence of genetic background that predisposes individuals to AD has been reported as the risk factors in recent years. The Department of Medical Genetics and the Immunology Research Centre investigated the distribution of 11 polymorphisms in 160 patients with late onset AD (LOAD) and in 163 healthy controls, using the sequencing technique. All participants were of Turkish Azeri ethnicity. We compared allele and genotype frequencies between the LOAD patients and control subjects using a chi-square or Fisher's exact test. Alleles and genotypes of APOE, PICALM rs3851179 and rs541458, and the BIN1 gene rs744373 polymorphism were significantly different between LOAD and control groups. The frequencies of the other investigated alleles were similar in the two groups. We also analyzed the association of BIN1, CR1 and PICALM SNPs with LOAD in subgroups stratified by the presence or absence of the APOE ε4 allele. After adjusting for APOE, statistical analysis revealed that the association with PICALM rs541458 and BIN1 rs744373 were only significant among subjects without the APOE ε4 allele.

Selective alterations of neurons and circuits related to early memory loss in Alzheimer's disease

A progressive loss of episodic memory is a well-known clinical symptom that characterizes Alzheimer’s disease (AD). The beginning of this loss of memory has been associated with the very early, pathological accumulation of tau and neuronal degeneration observed in the entorhinal cortex (EC). Tau-related pathology is thought to then spread progressively to the hippocampal formation and other brain areas as the disease progresses. The major cortical afferent source of the hippocampus and dentate gyrus is the EC through the perforant pathway. At least two main circuits participate in the connection between EC and the hippocampus; one originating in layer II and the other in layer III of the EC giving rise to the classical trisynaptic (ECII → dentate gyrus → CA3 → CA1) and monosynaptic (ECIII → CA1) circuits. Thus, the study of the early pathological changes in these circuits is of great interest. In this review, we will discuss mainly the alterations of the granule cell neurons of the dentate gyrus and the atrophy of CA1 pyramidal neurons that occur in AD in relation to the possible differential alterations of these two main circuits.

Altered proteolysis in fibroblasts of Alzheimer patients with predictive implications for subjects at risk of disease

There is great interest in developing reliable biomarkers to support antemortem diagnosis of late-onset Alzheimer's disease (AD). Early prediction and diagnosis of AD might be improved by the detection of a proteolytic dysfunction in extracts from cultured AD fibroblasts, producing altered isoelectrophoretic forms of the enzyme transketolase (TK-alkaline bands). The TK profile and apolipoprotein E (APOE) genotype were examined in fibroblasts from 36 clinically diagnosed probable late-onset sporadic AD patients and 38 of their asymptomatic relatives, 29 elderly healthy individuals, 12 neurological non-AD patients, and 5 early-onset AD patients. TK alterations occurred in (i) several probable AD patients regardless of age-of-onset and severity of disease; (ii) all early-onset AD patients and APOE ε 4/4 carriers; and (iii) nearly half of asymptomatic AD relatives. Normal subjects and non-AD patients were all negative. Notably, culture conditions promoting TK alterations were also effective in increasing active BACE1 levels. Overall, the TK assay might represent a low-cost laboratory tool useful for supporting AD differential diagnosis and identifying asymptomatic subjects who are at greater risk of AD and who should enter a follow-up study. Moreover, the cultured fibroblasts were confirmed as a useful in vitro model for further studies on the pathogenetic process of AD.

Changes in PINCH levels in the CSF of HIV+ individuals correlate with hpTau and CD4 count

Several studies report associations between the particularly interesting new cysteine histidine-rich (PINCH) protein and HIV-associated CNS disease. PINCH is detected in the CSF of HIV patients, and changes in levels during disease may be indicative of changes in disease status over time. PINCH binds hyperphosphorylated Tau (hpTau) in the brain and CSF, but little is known about the relevance of these interactions to HIV CNS disease. In this study, PINCH and hpTau levels were assessed in three separate CSF samples collected longitudinally from 20 HIV+ participants before and after initiating antiretroviral therapy or before and after a change in the treatment regimen. The intervals were approximately 1 (T2) and 3-7 (T3) months from the initial visit (baseline, T1). Correlational analyses were conducted for CSF levels of PINCH and hpTau and other variables including blood CD4 T-cell count, plasma and CSF viral burden, CSF neopterin, white blood cell (WBC) count, and antiretroviral CNS penetration effectiveness (CPE). Values for PINCH and hpTau were determined for each patient by calculating the fold changes between the second (T2) and third measurements (T3) from the baseline measurement (T1). Statistical analyses showed that the fold changes in CSF PINCH protein from T1 to T2 were significantly higher in participants with CD4 counts >200 cells/mm(3) at T2 compared to those with CD4 counts <200 cells/mm(3) at T2. This trend persisted irrespective of plasma or CSF viral burden or antiretroviral therapy CPE scores. The fold changes in PINCH levels between T1 and T2, and T1 and T3 were highly correlated to the fold changes in hpTau at T2/T1 and T3/T1 (correlation coefficient = 0.69, p < 0.001; correlation coefficient = 0.83, p < 0.0001, respectively). In conclusion, in these HIV participants, changes in CSF levels of PINCH appear to correlate with changes in blood CD4 count and with changes in CSF hpTau levels, but not with plasma or CSF viral burden, neopterin, WBC, or antiretroviral regimen CPE.

Reductive stress in young healthy individuals at risk of Alzheimer disease

Oxidative stress is a hallmark of Alzheimer disease (AD) but this has not been studied in young healthy persons at risk of the disease. Carrying an Apo ε4 allele is the major genetic risk factor for AD. We have observed that lymphocytes from young, healthy persons carrying at least one Apo ε4 allele suffer from reductive rather than oxidative stress, i.e., lower oxidized glutathione and P-p38 levels and higher expression of enzymes involved in antioxidant defense, such as glutamylcysteinyl ligase and glutathione peroxidase. In contrast, in the full-blown disease, the situation is reversed and oxidative stress occurs, probably because of the exhaustion of the antioxidant mechanisms just mentioned. These results provide insights into the early events of the progression of the disease that may allow us to find biomarkers of AD at its very early stages.

Efficient derivation of cortical glutamatergic neurons from human pluripotent stem cells: a model system to study neurotoxicity in Alzheimer's disease

Alzheimer's disease (AD) is among the most prevalent forms of dementia affecting the aging population, and pharmacological therapies to date have not been successful in preventing disease progression. Future therapeutic efforts may benefit from the development of models that enable basic investigation of early disease pathology. In particular, disease-relevant models based on human pluripotent stem cells (hPSCs) may be promising approaches to assess the impact of neurotoxic agents in AD on specific neuronal populations and thereby facilitate the development of novel interventions to avert early disease mechanisms. We implemented an efficient paradigm to convert hPSCs into enriched populations of cortical glutamatergic neurons emerging from dorsal forebrain neural progenitors, aided by modulating Sonic hedgehog (Shh) signaling. Since AD is generally known to be toxic to glutamatergic circuits, we exposed glutamatergic neurons derived from hESCs to an oligomeric pre-fibrillar forms of Aβ known as "globulomers", which have shown strong correlation with the level of cognitive deficits in AD. Administration of such Aβ oligomers yielded signs of the disease, including cell culture age-dependent binding of Aβ and cell death in the glutamatergic populations. Furthermore, consistent with previous findings in postmortem human AD brain, Aβ-induced toxicity was selective for glutamatergic rather than GABAeric neurons present in our cultures. This in vitro model of cortical glutamatergic neurons thus offers a system for future mechanistic investigation and therapeutic development for AD pathology using human cell types specifically affected by this disease.

Alzheimer's disease, dementia, mild cognitive impairment and the menopause: a 'window of opportunity'?

Alzheimer's disease (AD) is not an inevitable consequence of aging and may be modified by both adverse and protective factors. The pathological changes of AD commence in midlife and AD has a long preclinical phase that may be diagnosed by biomarkers in the cerebrospinal fluid and by brain MRI. New clinical criteria for the diagnosis of AD dementia and AD mild cognitive impairment (MCI) have been proposed. MCI and dementia are frequently the result of AD and cerebrovascular disease combined. Over the age of 85 years, MCI and dementia are more common in women than in men. Women with a surgical premature menopause have an increased risk of MCI and AD. Menopausal hormone therapy from the menopause to the age of 60 years, when any risks of menopausal hormone therapy are extremely small, may provide a 'window of opportunity' to reduce the risk of MCI and AD in later life. Many measures may help to prevent, delay or minimize AD in both women and men and should be actively encouraged.