Ratio of Aβ42/P-tau181p in CSF is associated with aberrant default mode network in AD

Default mode network dynamics: An integrated neurocircuitry perspective on social dysfunction in human brain disorders

Our intricate social brain is implicated in a range of brain disorders, where social dysfunction emerges as a common neuropsychiatric feature cutting across diagnostic boundaries. Understanding the neurocircuitry underlying social dysfunction and exploring avenues for its restoration could present a transformative and transdiagnostic approach to overcoming therapeutic challenges in these disorders. The brain's default mode network (DMN) plays a crucial role in social functioning and is implicated in various neuropsychiatric conditions. By thoroughly examining the current understanding of DMN functionality, we propose that the DMN integrates diverse social processes, and disruptions in brain communication at regional and network levels due to disease hinder the seamless integration of these social functionalities. Consequently, this leads to an altered balance between self-referential and attentional processes, alongside a compromised ability to adapt to social contexts and anticipate future social interactions. Looking ahead, we explore how adopting an integrated neurocircuitry perspective on social dysfunction could pave the way for innovative therapeutic approaches to address brain disorders.

A phase 2, open-label study of anti-inflammatory NE3107 in patients with dementias

BACKGROUND

Alzheimer's disease (AD) is a progressive, multifactorial, neurodegenerative disorder affecting >6 million Americans. Chronic, low-grade neuroinflammation, and insulin resistance may drive AD pathogenesis. We explored the neurophysiological and neuropsychological effects of NE3107, an oral, anti-inflammatory, insulin-sensitizing molecule, in AD.

METHODS

In this phase 2, open-label study, 23 patients with mild cognitive impairment or mild dementia received 20-mg oral NE3107 twice daily for 3 months. Primary endpoints assessed changes from baseline in neurophysiological health and oxidative stress (glutathione level) using advanced neuroimaging analyses. Secondary endpoints evaluated changes from baseline in neuropsychological health using cognitive assessments, including the 11-item Alzheimer's Disease Assessment Scale-Cognitive Subscale (ADAS-Cog11), Mini-Mental State Examination (MMSE), Montreal Cognitive Assessment, Clinical Dementia Rating, Quick Dementia Rating Scale, Alzheimer's Disease Composite Score, and Global Rating of Change (GRC). Exploratory endpoints assessed changes from baseline in neuroinflammation biomarkers (tumor necrosis factor alpha, TNF-α) and AD (amyloid beta and phosphorylated tau [P-tau]).

RESULTS

NE3107 was associated with clinician-rated improvements in cerebral blood flow and functional connectivity within the brain. In patients with MMSE ≥ 20 (mild cognitive impairment to mild AD; n = 17), NE3107 was associated with directional, but statistically nonsignificant, changes in brain glutathione levels, along with statistically significant improvements in ADAS-Cog11 (P = .017), Clinical Dementia Rating (P = .042), Quick Dementia Rating Scale (P = .002), Alzheimer's Disease Composite Score (P = .0094), and clinician-rated GRC (P < .001), as well as in cerebrospinal fluid P-tau levels (P = .034) and P-tau:amyloid beta 42 ratio (P = .04). Biomarker analyses also demonstrated directional, but statistically non-significant, changes in plasma TNF-α, consistent with the expected mechanism of NE3107. Importantly, we observed a statistically significant correlation (r = 0.59) between improvements in TNF-α levels and ADAS-Cog11 scores (P = .026) in patients with baseline MMSE ≥ 20.

CONCLUSION

Our results indicate that in this study NE3107 was associated with what appear to be positive neurophysiological and neuropsychological findings, as well as evidence of improvement in biomarkers associated with neuroinflammation and AD in patients diagnosed with dementia. Our findings are consistent with previous preclinical and clinical observations and highlight a central role of neuroinflammation in AD pathogenesis.

Constructing hierarchical attentive functional brain networks for early AD diagnosis

Analyzing functional brain networks (FBN) with deep learning has demonstrated great potential for brain disorder diagnosis. The conventional construction of FBN is typically conducted at a single scale with a predefined brain region atlas. However, numerous studies have identified that the structure and function of the brain are hierarchically organized in nature. This urges the need of representing FBN in a hierarchical manner for more effective analysis of the complementary diagnostic insights at different scales. To this end, this paper proposes to build hierarchical FBNs adaptively within the Transformer framework. Specifically, a sparse attention-based node-merging module is designed to work alongside the conventional network feature extraction modules in each layer. The proposed module generates coarser nodes for further FBN construction and analysis by combining fine-grained nodes. By stacking multiple such layers, a hierarchical representation of FBN can be adaptively learned in an end-to-end manner. The hierarchical structure can not only integrate the complementary information from multiscale FBN for joint analysis, but also reduce the model complexity due to decreasing node sizes. Moreover, this paper argues that the nodes defined by the existing atlases are not necessarily the optimal starting level to build FBN hierarchy and exploring finer nodes may further enrich the FBN representation. In this regard, each predefined node in an atlas is split into multiple sub-nodes, overcoming the scale limitation of the existing atlases. Extensive experiments conducted on various data sets consistently demonstrate the superior performance of the proposed method over the competing methods.

Functional gradients of the medial parietal cortex in a healthy cohort with family history of sporadic Alzheimer's disease

BACKGROUND

The medial parietal cortex is an early site of pathological protein deposition in Alzheimer's disease (AD). Previous studies have identified different subregions within this area; however, these subregions are often heterogeneous and disregard individual differences or subtle pathological alterations in the underlying functional architecture. To address this limitation, here we measured the continuous connectivity gradients of the medial parietal cortex and assessed their relationship with cerebrospinal fluid (CSF) biomarkers, ApoE ε4 carriership and memory in asymptomatic individuals at risk to develop AD.

METHODS

Two hundred sixty-three cognitively normal participants with a family history of sporadic AD who underwent resting-state and task-based functional MRI using encoding and retrieval tasks were included from the PREVENT-AD cohort. A novel method for characterizing spatially continuous patterns of functional connectivity was applied to estimate functional gradients in the medial parietal cortex during the resting-state and task-based conditions. This resulted in a set of nine parameters that described the appearance of the gradient across different spatial directions. We performed correlation analyses to assess whether these parameters were associated with CSF biomarkers of phosphorylated tau181 (p-tau), total tau (t-tau), and amyloid-ß1-42 (Aß). Then, we compared the spatial parameters between ApoE ε4 carriers and noncarriers, and evaluated the relationship between these parameters and memory.

RESULTS

Alterations involving the superior part of the medial parietal cortex, which was connected to regions of the default mode network, were associated with higher p-tau, t-tau levels as well as lower Aß/p-tau levels during the resting-state condition (p < 0.01). Similar alterations were found in ApoE ε4 carriers compared to non-carriers (p < 0.003). In contrast, lower immediate memory scores were associated with changes in the middle part of the medial parietal cortex, which was connected to inferior temporal and posterior parietal regions, during the encoding task (p = 0.001). No results were found when using conventional connectivity measures.

CONCLUSIONS

Functional alterations in the medial parietal gradients are associated with CSF AD biomarkers, ApoE ε4 carriership, and lower memory in an asymptomatic cohort with a family history of sporadic AD, suggesting that functional gradients are sensitive to subtle changes associated with early AD stages.

The recency ratio assessed by story recall is associated with cerebrospinal fluid levels of neurodegeneration biomarkers

Recency refers to the information learned at the end of a study list or task. Recency forgetting, as tracked by the ratio between recency recall in immediate and delayed conditions, i.e., the recency ratio (Rr), has been applied to list-learning tasks, demonstrating its efficacy in predicting cognitive decline, conversion to mild cognitive impairment (MCI), and cerebrospinal fluid (CSF) biomarkers of neurodegeneration. However, little is known as to whether Rr can be effectively applied to story recall tasks. To address this question, data were extracted from the database of the Alzheimer's Disease Research Center at the University of Wisconsin - Madison. A total of 212 participants were included in the study. CSF biomarkers were amyloid-beta (Aβ) 40 and 42, phosphorylated (p) and total (t) tau, neurofilament light (NFL), neurogranin (Ng), and α-synuclein (a-syn). Story Recall was measured with the Logical Memory Test (LMT). We carried out Bayesian regression analyses with Rr, and other LMT scores as predictors; and CSF biomarkers (including the Aβ42/40 and p-tau/Aβ42 ratios) as outcomes. Results showed that models including Rr consistently provided best fits with the data, with few exceptions. These findings demonstrate the applicability of Rr to story recall and its sensitivity to CSF biomarkers of neurodegeneration, and encourage its inclusion when evaluating risk of neurodegeneration with story recall.

Serum-Based Biomarkers in Neurodegeneration and Multiple Sclerosis

Multiple Sclerosis (MS) is a debilitating disease with typical onset between 20 and 40 years of age, so the disability associated with this disease, unfortunately, occurs in the prime of life. At a very early stage of MS, the relapsing-remitting mobility impairment occurs in parallel with a progressive decline in cognition, which is subclinical. This stage of the disease is considered the beginning of progressive MS. Understanding where a patient is along such a subclinical phase could be critical for therapeutic efficacy and enrollment in clinical trials to test drugs targeted at neurodegeneration. Since the disease course is uneven among patients, biomarkers are needed to provide insights into pathogenesis, diagnosis, and prognosis of events that affect neurons during this subclinical phase that shapes neurodegeneration and disability. Thus, subclinical cognitive decline must be better understood. One approach to this problem is to follow known biomarkers of neurodegeneration over time. These biomarkers include Neurofilament, Tau and phosphotau protein, amyloid-peptide-β, Brl2 and Brl2-23, N-Acetylaspartate, and 14-3-3 family proteins. A composite set of these serum-based biomarkers of neurodegeneration might provide a distinct signature in early vs. late subclinical cognitive decline, thus offering additional diagnostic criteria for progressive neurodegeneration and response to treatment. Studies on serum-based biomarkers are described together with selective studies on CSF-based biomarkers and MRI-based biomarkers.

Development of a Low-Molecular-Weight Aβ42 Detection System Using a Enzyme-Linked Peptide Assay

Alzheimer's disease (AD) is a degenerative brain disease that is the most common cause of dementia. The incidence of AD is rapidly rising because of the aging of the world population. Because AD is presently incurable, early diagnosis is very important. The disease is characterized by pathological changes such as deposition of senile plaques and decreased concentration of the amyloid-beta 42 (Aβ42) peptide in the cerebrospinal fluid (CSF). The concentration of Aβ42 in the CSF is a well-studied AD biomarker. The specific peptide probe was screened through four rounds of biopanning, which included the phage display process. The screened peptide showed strong binding affinity in the micromolar range, and the enzyme-linked peptide assay was optimized using the peptide we developed. This diagnostic method showed specificity toward Aβ42 in the presence of other proteins. The peptide-binding site was also estimated using molecular docking analysis. Finally, the diagnostic method we developed could significantly distinguish patients who were classified based on amyloid PET images.

Drug design targeting active posttranslational modification protein isoforms

Modern drug design aims to discover novel lead compounds with attractable chemical profiles to enable further exploration of the intersection of chemical space and biological space. Identification of small molecules with good ligand efficiency, high activity, and selectivity is crucial toward developing effective and safe drugs. However, the intersection is one of the most challenging tasks in the pharmaceutical industry, as chemical space is almost infinity and continuous, whereas the biological space is very limited and discrete. This bottleneck potentially limits the discovery of molecules with desirable properties for lead optimization. Herein, we present a new direction leveraging posttranslational modification (PTM) protein isoforms target space to inspire drug design termed as "Post-translational Modification Inspired Drug Design (PTMI-DD)." PTMI-DD aims to extend the intersections of chemical space and biological space. We further rationalized and highlighted the importance of PTM protein isoforms and their roles in various diseases and biological functions. We then laid out a few directions to elaborate the PTMI-DD in drug design including discovering covalent binding inhibitors mimicking PTMs, targeting PTM protein isoforms with distinctive binding sites from that of wild-type counterpart, targeting protein-protein interactions involving PTMs, and hijacking protein degeneration by ubiquitination for PTM protein isoforms. These directions will lead to a significant expansion of the biological space and/or increase the tractability of compounds, primarily due to precisely targeting PTM protein isoforms or complexes which are highly relevant to biological functions. Importantly, this new avenue will further enrich the personalized treatment opportunity through precision medicine targeting PTM isoforms.

MicroRNA-101a Regulates Autophagy Phenomenon via the MAPK Pathway to Modulate Alzheimer's-Associated Pathogenesis

Alzheimer’s disease (AD) is a type of neurodegenerative disorder and the most common form of dementia. MicroRNA (miRNA) has been shown to play a role in various diseases, including AD. It also has been reported to regulate autophagy. We extracted miRNA from blood samples and constructed an miRNA-101a lentivirus vector. In this study we found the level of miRNA-101a was significantly reduced in the plasma of patients with AD and APPswe/PS1ΔE9 transgenic mice. The relative expression of miRNA-101a exhibited a relatively high diagnostic performance (area under receiver operating characteristic curve: 0.8725) in the prediction of AD with a sensitivity of 0.913 and a specificity of 0.733 at the threshold of 0.6463. Under electron microscopy, autophagic vacuoles in AD-related cells numbered more than the cells up-regulating miRNA-101a in the in vitro experiments. Dual-luciferase reporter assay and Western blot results proved that the MAPK1 pathway plays a role in the formation of autophagic vacuoles in AD. This study found that the autophagy phenomenon regulated by miRNA-101a via the MAPK pathway might be a new mechanism in AD. This could provide new insights into AD formation and treatment.

Brain network alterations in individuals with and without mild cognitive impairment: parallel independent component analysis of AV1451 and AV45 positron emission tomography

BACKGROUND

Amyloid β (Aβ) and tau proteins are considered as critical factors that affect Alzheimer's disease (AD) and mild cognitive impairment (MCI). Although many studies have conducted on these two proteins, little study has investigated the relationship between their spatial distributions. This study aims to explore the associations of spatial patterns between Aβ deposition and tau deposition in patients with MCI and normal control (NC).

METHODS

We used multimodality positron emission tomography (PET) data from a clinically heterogeneous population of patients with MCI and NC. All data were obtained from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database containing information of 65 patients with MCI and 75 NC who both had undergone AV45 (Aβ) and AV1451 (tau) PET. To assess the spatial distribution of Aβ and tau deposition, we employed parallel independent component analysis (pICA), which enabled the joint analysis of multimodal imaging data. pICA was conducted to identify the significant difference and correlation relationship of brain networks between Aβ PET and tau PET in MCI and NC groups.

RESULTS

Our results revealed the strongly correlated network between Aβ PET and tau PET were colocalized with the default-mode network (DMN). Simultaneously, in comparison of the spatial distribution between Aβ PET and tau PET, it was found that the significant differences between MCI and NC were mainly distributed in DMN, cognitive control network and visual networks. The altered brain networks obtained from pICA analysis are consistent with the abnormalities of brain network in MCI patients.

CONCLUSIONS

Findings suggested the abnormal spatial distribution regions of tau PET were correlated with the abnormal spatial distribution regions of Aβ PET, and both of which were located in DMN network. This study revealed that combining pICA with multimodal imaging data is an effective approach for distinguishing MCI patients from NC group.

Cognitive Reserve Relates to Functional Network Efficiency in Alzheimer's Disease

Alzheimer’s disease (AD) is the most common form of dementia, with no means of cure or prevention. The presence of abnormal disease-related proteins in the population is, in turn, much more common than the incidence of dementia. In this context, the cognitive reserve (CR) hypothesis has been proposed to explain the discontinuity between pathophysiological and clinical expression of AD, suggesting that CR mitigates the effects of pathology on clinical expression and cognition. fMRI studies of the human connectome have recently reported that AD patients present diminished functional efficiency in resting-state networks, leading to a loss in information flow and cognitive processing. No study has investigated, however, whether CR modifies the effects of the pathology in functional network efficiency in AD patients. We analyzed the relationship between CR, pathophysiology and network efficiency, and whether CR modifies the relationship between them. Fourteen mild AD, 28 amnestic mild cognitive impairment (aMCI) due to AD, and 28 controls were enrolled. We used education to measure CR, cerebrospinal fluid (CSF) biomarkers to evaluate pathophysiology, and graph metrics to measure network efficiency. We found no relationship between CR and CSF biomarkers; CR was related to higher network efficiency in all groups; and abnormal levels of CSF protein biomarkers were related to more efficient networks in the AD group. Education modified the effects of tau-related pathology in the aMCI and mild AD groups. Although higher CR might not protect individuals from developing AD pathophysiology, AD patients with higher CR are better able to cope with the effects of pathology—presenting more efficient networks despite pathology burden. The present study highlights that interventions focusing on cognitive stimulation might be useful to slow age-related cognitive decline or dementia and lengthen healthy aging.

Sex Differences in Cognitive Decline in Subjects with High Likelihood of Mild Cognitive Impairment due to Alzheimer's disease

Sex differences in Alzheimer’s disease (AD) biology and progression are not yet fully characterized. The goal of this study is to examine the effect of sex on cognitive progression in subjects with high likelihood of mild cognitive impairment (MCI) due to Alzheimer’s and followed up to 10 years in the Alzheimer’s Disease Neuroimaging Initiative (ADNI). Cerebrospinal fluid total-tau and amyloid-beta (Aβ42) ratio values were used to sub-classify 559 MCI subjects (216 females, 343 males) as having “high” or “low” likelihood for MCI due to Alzheimer’s. Data were analyzed using mixed-effects models incorporating all follow-ups. The worsening from baseline in Alzheimer’s Disease Assessment Scale-Cognitive score (mean, SD) (9 ± 12) in subjects with high likelihood of MCI due to Alzheimer’s was markedly greater than that in subjects with low likelihood (1 ± 6, p < 0.0001). Among MCI due to AD subjects, the mean worsening in cognitive score was significantly greater in females (11.58 ± 14) than in males (6.87 ± 11, p = 0.006). Our findings highlight the need to further investigate these findings in other populations and develop sex specific timelines for Alzheimer’s disease progression.

Cerebrospinal Fluid Biomarkers for the Differential Diagnosis between Alzheimer's Disease and Frontotemporal Lobar Degeneration: Systematic Review, HSROC Analysis, and Confounding Factors

BACKGROUND

Differential diagnosis in dementia is at present one of the main challenges both in clinical practice and research. Cerebrospinal fluid (CSF) biomarkers are included in the current diagnostic criteria of Alzheimer's disease (AD) but their clinical utility is still unclear.

OBJECTIVE

We performed a systematic review of studies analyzing the diagnostic performance of CSF Aβ42, total tau (t-tau), and phosphorylated tau (p-tau) in the discrimination between AD and frontotemporal lobar degeneration (FTLD) dementias.

METHODS

The following electronic databases were consulted until May 2016: Medline and PreMedline, EMBASE, PsycInfo, CINAHL, Cochrane Library, and CRD. For the first-time in the field, a Hierarchical Summary Receiver Operating Characteristic (HRSOC) model was applied, which avoids methodological problems of meta-analyses based on summary points of sensitivity and specificity values. We also investigated relevant confounders of CSF biomarkers' diagnostic performance such as age, disease duration, and global cognitive impairment.

RESULTS

The p-tau/Aβ42 ratio showed the best diagnostic performance. No statistically significant effects of the confounders were observed. Nonetheless, the p-tau/Aβ42 ratio may be especially indicated for younger patients. P-tau may be preferable for less cognitively impaired patients (high MMSE scores) and the t-tau/Aβ42 ratio for more cognitively impaired patients (low MMSE scores).

CONCLUSION

The p-tau/Aβ42 ratio has potential for being implemented in the clinical routine for the differential diagnosis between AD and FTLD. It is of utmost importance that future studies report information on confounders such as age, disease duration, and cognitive impairment, which should also stimulate understanding of the role of these factors in disease mechanisms and pathophysiology.

The Effects of Gene Mutations on Default Mode Network in Familial Alzheimer's Disease

Familial Alzheimer's disease (FAD) mutations have very high penetrance but age at onset and rate of disease progression differ. Neuroimaging and cerebrospinal fluid (CSF) examinations in mutation carriers (MCs) may provide an opportunity to identify early biomarkers that can be used to track disease progression from presymptomatic to the dementia stages of disease. The default mode network (DMN) is a resting state neuronal network composed of regions known to associate with amyloid deposition in AD. We hypothesized that functional connectivity in the DMN might change at pre-clinical stages in FAD MCs and correlate with changes in CSF biomarkers as a consequence of AD brain pathology. To test the hypothesis, we compared the functional connectivity in DMN between pre-MCs/MCs and non-carriers (NCs). No significant differences between pre-MCs and NCs were observed. When comparing all MCs with NCs, significant decreased functional connectivity in the right inferior parietal lobule, right precuneus, and left posterior cingulate cortex were found. We also found statistically significant correlations between CSF amyloid-β 42 and tau protein levels and average Z-score, a resting-state functional MRI measurement reflecting the degree of the correlation between a given voxel's time courses and the time courses corresponding to DMN, from the region with statistical difference. The observed disruption of DMN and pathological levels of AD CSF-biomarkers in FAD MCs are similar to the changes described in sporadic AD, which give further support that amyloid and tau pathology impairs neuronal and synaptic function.

Ventricular and Periventricular Anomalies in the Aging and Cognitively Impaired Brain

Ventriculomegaly (expansion of the brain’s fluid-filled ventricles), a condition commonly found in the aging brain, results in areas of gliosis where the ependymal cells are replaced with dense astrocytic patches. Loss of ependymal cells would compromise trans-ependymal bulk flow mechanisms required for clearance of proteins and metabolites from the brain parenchyma. However, little is known about the interplay between age-related ventricle expansion, the decline in ependymal integrity, altered periventricular fluid homeostasis, abnormal protein accumulation and cognitive impairment. In collaboration with the Baltimore Longitudinal Study of Aging (BLSA) and Alzheimer’s Disease Neuroimaging Initiative (ADNI), we analyzed longitudinal structural magnetic resonance imaging (MRI) and subject-matched fluid-attenuated inversion recovery (FLAIR) MRI and periventricular biospecimens to map spatiotemporally the progression of ventricle expansion and associated periventricular edema and loss of transependymal exchange functions in healthy aging individuals and those with varying degrees of cognitive impairment. We found that the trajectory of ventricle expansion and periventricular edema progression correlated with degree of cognitive impairment in both speed and severity, and confirmed that areas of expansion showed ventricle surface gliosis accompanied by edema and periventricular accumulation of protein aggregates, suggesting impaired clearance mechanisms in these regions. These findings reveal pathophysiological outcomes associated with normal brain aging and cognitive impairment, and indicate that a multifactorial analysis is best suited to predict and monitor cognitive decline.

Intranetwork and internetwork connectivity in patients with Alzheimer disease and the association with cerebrospinal fluid biomarker levels

BACKGROUND

In the last decade, many studies have reported abnormal connectivity within the default mode network (DMN) in patients with Alzheimer disease. Few studies, however, have investigated other networks and their association with pathophysiological proteins obtained from cerebrospinal fluid (CSF).

METHODS

We performed 3 T imaging in patients with mild Alzheimer disease, patients with amnestic mild cognitive impairment (aMCI) and healthy controls, and we collected CSF samples from the patients with aMCI and mild Alzheimer disease. We analyzed 57 regions from 8 networks. Additionally, we performed correlation tests to investigate possible associations between the networks' functional connectivity and the protein levels obtained from the CSF of patients with aMCI and Alzheimer disease.

RESULTS

Our sample included 41 patients with Alzheimer disease, 35 with aMCI and 48 controls. We found that the main connectivity abnormalities in those with Alzheimer disease occurred between the DMN and task-positive networks: these patients presented not only a decreased anticorrelation between some regions, but also an inversion of the correlation signal (positive correlation instead of anticorrelation). Those with aMCI did not present statistically different connectivity from patients with Alzheimer disease or controls. Abnormal levels of CSF proteins were associated with functional disconnectivity between several regions in both the aMCI and mild Alzheimer disease groups, extending well beyond the DMN or temporal areas.

LIMITATIONS

The presented data are cross-sectional in nature, and our findings are dependent on the choice of seed regions used.

CONCLUSION

We found that the main functional connectivity abnormalities occur between the DMN and task-positive networks and that the pathological levels of CSF biomarkers correlate with functional connectivity disruption in patients with Alzheimer disease.

A whole-brain computational modeling approach to explain the alterations in resting-state functional connectivity during progression of Alzheimer's disease

Alzheimer's disease (AD) is the most common dementia with dramatic consequences. The research in structural and functional neuroimaging showed altered brain connectivity in AD. In this study, we investigated the whole-brain resting state functional connectivity (FC) of the subjects with preclinical Alzheimer's disease (PAD), mild cognitive impairment due to AD (MCI) and mild dementia due to Alzheimer's disease (AD), the impact of APOE4 carriership, as well as in relation to variations in core AD CSF biomarkers. The synchronization in the whole-brain was monotonously decreasing during the course of the disease progression. Furthermore, in AD patients we found widespread significant decreases in functional connectivity (FC) strengths particularly in the brain regions with high global connectivity. We employed a whole-brain computational modeling approach to study the mechanisms underlying these alterations. To characterize the causal interactions between brain regions, we estimated the effective connectivity (EC) in the model. We found that the significant EC differences in AD were primarily located in left temporal lobe. Then, we systematically manipulated the underlying dynamics of the model to investigate simulated changes in FC based on the healthy control subjects. Furthermore, we found distinct patterns involving CSF biomarkers of amyloid-beta (Aβ1 - 42) total tau (t-tau) and phosphorylated tau (p-tau). CSF Aβ1 - 42 was associated to the contrast between healthy control subjects and clinical groups. Nevertheless, tau CSF biomarkers were associated to the variability in whole-brain synchronization and sensory integration regions. These associations were robust across clinical groups, unlike the associations that were found for CSF Aβ1 - 42. APOE4 carriership showed no significant correlations with the connectivity measures.

Psychosis in parkinsonism: an unorthodox approach

Psychosis in Parkinson's disease (PD) is currently considered as the occurrence of hallucinations and delusions. The historical meaning of the term psychosis was, however, broader, encompassing a disorganization of both consciousness and personality, including behavior abnormalities, such as impulsive overactivity and catatonia, in complete definitions by the International Classification of Diseases-10 (ICD-10) and the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5). Our review is aimed at reminding that complex psychotic symptoms, including impulsive overactivity and somatoform disorders (the last being a recent controversial entity in PD), were carefully described in postencephalitic parkinsonism (PEP), many decades before dopaminergic treatment era, and are now described in other parkinsonisms than PD. Eminent neuropsychiatrists of the past century speculated that studying psychosis in PEP might highlight its mechanisms in other conditions. Yet, functional assessments were unavailable at the time. Therefore, the second part of our article reviews the studies of neural correlates of psychosis in parkinsonisms, by taking into account both theories on the narrative functions of the default mode network (DMN) and hypotheses on DMN modulation.

Disrupted Network Topology in Patients with Stable and Progressive Mild Cognitive Impairment and Alzheimer's Disease

Recent findings suggest that Alzheimer's disease (AD) is a disconnection syndrome characterized by abnormalities in large-scale networks. However, the alterations that occur in network topology during the prodromal stages of AD, particularly in patients with stable mild cognitive impairment (MCI) and those that show a slow or faster progression to dementia, are still poorly understood. In this study, we used graph theory to assess the organization of structural MRI networks in stable MCI (sMCI) subjects, late MCI converters (lMCIc), early MCI converters (eMCIc), and AD patients from 2 large multicenter cohorts: ADNI and AddNeuroMed. Our findings showed an abnormal global network organization in all patient groups, as reflected by an increased path length, reduced transitivity, and increased modularity compared with controls. In addition, lMCIc, eMCIc, and AD patients showed a decreased path length and mean clustering compared with the sMCI group. At the local level, there were nodal clustering decreases mostly in AD patients, while the nodal closeness centrality detected abnormalities across all patient groups, showing overlapping changes in the hippocampi and amygdala and nonoverlapping changes in parietal, entorhinal, and orbitofrontal regions. These findings suggest that the prodromal and clinical stages of AD are associated with an abnormal network topology.

Insulin Resistance is Associated with Higher Cerebrospinal Fluid Tau Levels in Asymptomatic APOEɛ4 Carriers

BACKGROUND

Insulin resistance (IR) is linked with the occurrence of pathological features observed in Alzheimer's disease (AD), including neurofibrillary tangles and amyloid plaques. However, the extent to which IR is associated with AD pathology in the cognitively asymptomatic stages of preclinical AD remains unclear.

OBJECTIVE

To determine the extent to which IR is linked with amyloid and tau pathology in late-middle-age.

METHOD

Cerebrospinal fluid (CSF) samples collected from 113 participants enrolled in the Wisconsin Registry for Alzheimer's Prevention study (mean age = 60.6 years), were assayed for AD-related markers of interest: Aβ₄₂, P-Tau181, and T-Tau. IR was determined using the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). Linear regression was used to test the effect of IR, and APOEɛ4, on tau and amyloid pathology. We hypothesized that greater IR would be associated with higher CSF P-Tau181 and T-Tau, and lower CSF Aβ₄₂.

RESULTS

No significant main effects of HOMA-IR on P-Tau181, T-Tau, or Aβ₄₂ were observed; however, significant interactions were observed between HOMA-IR and APOEɛ4 on CSF markers related to tau. Among APOEɛ4 carriers, higher HOMA-IR was associated with higher P-Tau181 and T-Tau. Among APOEɛ4 non-carriers, HOMA-IR was negatively associated with P-Tau181 and T-Tau. We found no effects of IR on Aβ₄₂ levels in CSF.

CONCLUSION

IR among asymptomatic APOEɛ4 carriers was associated with higher P-Tau181 and T-Tau in late-middle age. The results suggest that IR may contribute to tau-related neurodegeneration in preclinical AD. The findings may have implications for developing prevention strategies aimed at modifying IR in mid-life.

Cerebrospinal fluid lactate levels and brain [18F]FDG PET hypometabolism within the default mode network in Alzheimer's disease

PURPOSE

It has been suggested that neuronal energy metabolism may be involved in Alzheimer's disease (AD). In this view, the finding of increased cerebrospinal fluid (CSF) lactate levels in AD patients has been considered the result of energetic metabolism dysfunction. Here, we investigated the relationship between neuronal energy metabolism, as measured via CSF lactate levels, and cerebral glucose metabolism, as stated at the 2-deoxy-2-(18F)fluoro-D-glucose positron emission tomography ([18F]FDG PET) in AD patients.

METHODS

AD patients underwent lumbar puncture to measure CSF lactate levels and [18F]FDG PET to assess brain glucose metabolism. CSF and PET data were compared to controls. Since patients were studied at rest, we specifically investigated brain areas active in rest-condition owing to the Default Mode Network (DMN). We correlated the CSF lactate concentrations with the [18F]FDG PET data in brain areas owing to the DMN, using sex, age, disease duration, Mini Mental State Examination, and CSF levels of tau proteins and beta-amyloid as covariates.

RESULTS

AD patients (n = 32) showed a significant increase of CSF lactate levels compared to Control 1 group (n = 28). They also showed brain glucose hypometabolism in the DMN areas compared to Control 2 group (n = 30). Within the AD group we found the significant correlation between increased CSF lactate levels and glucose hypometabolism in Broadman areas (BA) owing to left medial prefrontal cortex (BA10, mPFC), left orbitofrontal cortex (BA11, OFC), and left parahippocampal gyrus (BA 35, PHG).

CONCLUSION

We found high CSF levels of lactate and glucose hypometabolism within the DMN in AD patients. Moreover, we found a relationship linking the increased CSF lactate and the reduced glucose consumption in the left mPFC, OFC and PHG, owing to the anterior hub of DMN. These findings could suggest that neural glucose hypometabolism may affect the DMN efficiency in AD, also proposing the possible role of damaged brain energetic machine in impairing DMN.

Test-retest reliability of the default mode network in a multi-centric fMRI study of healthy elderly: Effects of data-driven physiological noise correction techniques

Understanding how to reduce the influence of physiological noise in resting state fMRI data is important for the interpretation of functional brain connectivity. Limited data is currently available to assess the performance of physiological noise correction techniques, in particular when evaluating longitudinal changes in the default mode network (DMN) of healthy elderly participants. In this 3T harmonized multisite fMRI study, we investigated how different retrospective physiological noise correction (rPNC) methods influence the within-site test-retest reliability and the across-site reproducibility consistency of DMN-derived measurements across 13 MRI sites. Elderly participants were scanned twice at least a week apart (five participants per site). The rPNC methods were: none (NPC), Tissue-based regression, PESTICA and FSL-FIX. The DMN at the single subject level was robustly identified using ICA methods in all rPNC conditions. The methods significantly affected the mean z-scores and, albeit less markedly, the cluster-size in the DMN; in particular, FSL-FIX tended to increase the DMN z-scores compared to others. Within-site test-retest reliability was consistent across sites, with no differences across rPNC methods. The absolute percent errors were in the range of 5-11% for DMN z-scores and cluster-size reliability. DMN pattern overlap was in the range 60-65%. In particular, no rPNC method showed a significant reliability improvement relative to NPC. However, FSL-FIX and Tissue-based physiological correction methods showed both similar and significant improvements of reproducibility consistency across the consortium (ICC = 0.67) for the DMN z-scores relative to NPC. Overall these findings support the use of rPNC methods like tissue-based or FSL-FIX to characterize multisite longitudinal changes of intrinsic functional connectivity. Hum Brain Mapp 37:2114-2132, 2016. © 2016 Wiley Periodicals, Inc.

Alzheimer's Biomarkers are Correlated with Brain Connectivity in Older Adults Differentially during Resting and Task States

β-amyloid (Aβ) plaques and tau-related neurodegeneration are pathologic hallmarks of Alzheimer’s disease (AD). The utility of AD biomarkers, including those measured in cerebrospinal fluid (CSF), in predicting future AD risk and cognitive decline is still being refined. Here, we explored potential relationships between functional connectivity (FC) patterns within the default-mode network (DMN), age, CSF biomarkers (Aβ₄₂ and pTau₁₈₁), and cognitive status in older adults. Multiple measures of FC were explored, including a novel time series-based measure [total interdependence (TI)]. In our sample of 27 cognitively normal older adults, no significant associations were found between levels of Aβ₄₂ or pTau₁₈₁ and cognitive scores or regional brain volumes. However, we observed several novel relationships between these biomarkers and measures of FC in DMN during both resting-state and a short-term memory task. First, increased connectivity between bilateral anterior middle temporal gyri was associated with higher levels of CSF Aβ₄₂ and Aβ₄₂/pTau₁₈₁ ratio (reflecting lower AD risk) during both rest and task. Second, increased bilateral parietal connectivity during the short-term memory task, but not during rest, was associated with higher levels of CSF pTau₁₈₁ (reflecting higher AD risk). Third, increased connectivity between left middle temporal and left parietal cortices during the active task was associated with decreased global cognitive status but not CSF biomarkers. Lastly, we found that our new TI method was more sensitive to the CSF Aβ₄₂-connectivity relationship whereas the traditional cross-correlation method was more sensitive to levels of CSF pTau₁₈₁ and cognitive status. With further refinement, resting-state connectivity and task-driven connectivity measures hold promise as non-invasive neuroimaging markers of Aβ and pTau burden in cognitively normal older adults.

Consensus statement for diagnosis of subcortical small vessel disease

Vascular cognitive impairment (VCI) is the diagnostic term used to describe a heterogeneous group of sporadic and hereditary diseases of the large and small blood vessels. Subcortical small vessel disease (SVD) leads to lacunar infarcts and progressive damage to the white matter. Patients with progressive damage to the white matter, referred to as Binswanger's disease (BD), constitute a spectrum from pure vascular disease to a mixture with neurodegenerative changes. Binswanger's disease patients are a relatively homogeneous subgroup with hypoxic hypoperfusion, lacunar infarcts, and inflammation that act synergistically to disrupt the blood-brain barrier (BBB) and break down myelin. Identification of this subgroup can be facilitated by multimodal disease markers obtained from clinical, cerebrospinal fluid, neuropsychological, and imaging studies. This consensus statement identifies a potential set of biomarkers based on underlying pathologic changes that could facilitate diagnosis and aid patient selection for future collaborative treatment trials.

Hydrogen Sulfide Prevents Synaptic Plasticity from VD-Induced Damage via Akt/GSK-3β Pathway and Notch Signaling Pathway in Rats

Our previous study has demonstrated that hydrogen sulfide (H₂S) attenuates neuronal injury induced by vascular dementia (VD) in rats, but the mechanism is still poorly understood. In this study, we aimed to investigate whether the neuroprotection of H₂S was associated with synaptic plasticity and try to interpret the potential underlying mechanisms. Adult male Wistar rats were suffered the ligation of bilateral common carotid arteries. At 24 h after surgery, rats were administered intraperitoneally with sodium hydrosulfide (NaHS, 5.6 mg·kg⁻¹·day⁻¹), a H₂S donor, for 3 weeks in the VD+NaHS group and treated intraperitoneally with saline in the VD group respectively. Our results demonstrated that NaHS significantly decreased the level of glutamate. It obviously ameliorated cognitive flexibility as well as the spatial learning and memory abilities by Morris water maze. Moreover, NaHS significantly improved the long-term depression (LTD), and was able to elevate the expression of N-methyl-d-aspartate receptor subunit 2A, which plays a pivotal role in synaptic plasticity. Interestingly, NaHS decreased the phosphorylation of Akt, and it could maintain the activity of glycogen synthase kinase-3β (GSK-3β). Surprisingly, NaHS triggered the canonical Notch pathway by increasing expressions of Jagged-1 and Hes-1. These findings suggest that NaHS prevents synaptic plasticity from VD-induced damage partly via Akt/GSK-3β pathway and Notch signaling pathway.

Hydrogen sulfide modulated the ratio of NMDAR 2A/2B and improved the synaptic plasticity via Akt/GSK-3β pathway and Notch signaling pathway in VD rats.

CSF proteins and resting-state functional connectivity in Parkinson disease

OBJECTIVE

The purpose of this study was to investigate the relationship between disruption of MRI-measured resting-state functional connectivity (rs-fcMRI) brain networks and CSF levels of potentially pathogenic proteins that reflect brain pathology in Parkinson disease (PD).

METHODS

PD participants without dementia (n = 43) and age-matched controls (n = 22) had lumbar punctures to measure CSF protein levels, Pittsburgh compound B (PiB)-PET imaging, and rs-fcMRI while off medication. Imaging analyses focused on 5 major resting-state networks as well as the striatum.

RESULTS

Participants with PD had significantly reduced sensorimotor functional connectivity, which correlated with reduced CSF levels of α-synuclein. The PD group also had significantly stronger default mode network functional connectivity that did not correlate with CSF β-amyloid (Aβ)42 or PiB uptake. In contrast, default mode network functional connectivity in the control group did correlate with CSF Aβ42 levels. Functional connectivity was similar between groups in the dorsal attention, control, and salience networks.

CONCLUSION

These results suggest that abnormal α-synuclein accumulation, but not Aβ, contributes to the disruption of motor-related functional connectivity in PD. Furthermore, correlating CSF protein measures with the strength of resting-state networks provides a direct link between abnormal α-synuclein metabolism and disrupted brain function in PD.

Network dysfunction in Alzheimer's disease: refining the disconnection hypothesis

Much effort in recent years has focused on understanding the effects of Alzheimer's disease (AD) on neural function. This effort has resulted in an enormous number of papers describing different facets of the functional derangement seen in AD. A particularly important tool for these investigations has been resting-state functional connectivity. Attempts to comprehensively synthesize resting-state functional connectivity results have focused on the potential utility of functional connectivity as a biomarker for disease risk, disease staging, or prognosis. While these are all appropriate uses of this technique, the purpose of this review is to examine how functional connectivity disruptions inform our understanding of AD pathophysiology. Here, we examine the rationale and methodological considerations behind functional connectivity studies and then provide a critical review of the existing literature. In conclusion, we propose a hypothesis regarding the development and spread of functional connectivity deficits seen in AD.

Correlations of amyloid-β concentrations between CSF and plasma in acute Alzheimer mouse model

Amyloid-β (Aβ) is one of the few neuropathological biomarkers associated with transporters of the blood-brain barrier (BBB). Despite the well-characterized clinical indication of decreasing Aβ levels in the cerebrospinal fluid (CSF) during the development of Alzheimer's disease (AD), the link between the alternation of Aβ level in the blood and the progress of the disorder is still controversial. Here, we report a direct correlation of Aβ(1-42) levels between CSF and plasma in AD mouse model. We injected monomeric Aβ(1-42) directly into the intracerebroventricular (ICV) region of normal adult mouse brains to induce AD-like phenotypes. Using sandwich enzyme-linked immunosorbent assays, we observed proportional elevation of Aβ(1-42) levels in both CSF and plasma in a dose-dependent manner. Our findings that plasma Aβ(1-42) reflects the condition of CSF Aβ(1-42) warrant further investigation as a biomarker for the blood diagnosis of AD.

The association between biomarkers in cerebrospinal fluid and structural changes in the brain in patients with Alzheimer's disease

BACKGROUND

Biochemical changes in the cerebrospinal fluid (CSF) could reflect pathophysiological processes in Alzheimer's disease (AD). However, it is still not clear how these processes correlate with grey matter (GM) volume and microstructural changes in the brain.

OBJECTIVE

To assess the relationship between CSF biomarkers and structural brain changes in AD.

DESIGN AND SETTING

Cross-sectional study in a memory clinic-based sample.

SUBJECTS

A total of 78 subjects were included in the study: 22 with subjective cognitive impairment (SCI), 35 with mild cognitive impairment (MCI) and 21 with AD.

MAIN OUTCOME MEASURES

Voxel-wise correlations between CSF biomarkers, including β-amyloid42 (Aβ42), tau phosphorylated at position threonine 181 and total tau protein, and GM volume, self-diffusion fractional anisotropy (FA) and mean diffusivity (MD) maps using voxel-based morphometry and tract-based spatial statistical analyses. FA and MD maps were obtained using diffusion tensor imaging.

RESULTS

In the whole sample (patients with SCI, MCI and AD), there was positive correlation between GM volume and Aβ42 concentration, and negative correlation with total tau protein. Higher FA was only related to higher concentration of Aβ42. MD showed significant negative correlation with Aβ42 and positive correlation with T-tau levels. The majority of brain regions with significant correlation with CSF biomarkers overlapped with the default mode network and extended to the adjacent white matter.

CONCLUSIONS

Early AD pathological changes can be detected with voxel-based morphometric analysis and diffusion tensor imaging measurements. Furthermore, there was an association between CSF AD biomarkers and structural brain changes in areas related to the default mode network.

Cerebrospinal fluid Aβ42, phosphorylated Tau181, and resting-state functional connectivity

IMPORTANCE

Resting-state functional connectivity magnetic resonance imaging has great potential for characterizing pathophysiological changes during the preclinical phase of Alzheimer disease.

OBJECTIVE

To assess the relationship between default mode network integrity and cerebrospinal fluid biomarkers of Alzheimer disease pathology in cognitively normal older individuals.

DESIGN, SETTING, AND PARTICIPANTS

Cross-sectional cohort study at The Charles F. and Joanne Knight Alzheimer's Disease Research Center at Washington University in St Louis, St Louis, Missouri, among 207 older adults with normal cognition (Clinical Dementia Rating, 0).

MAIN OUTCOMES AND MEASURES

Resting-state functional connectivity magnetic resonance imaging measures of default mode network integrity.

RESULTS

Decreased cerebrospinal fluid Aβ42 and increased cerebrospinal fluid phosphorylated tau181 were independently associated with reduced default mode network integrity, with the most prominent decreases in functional connectivity observed between the posterior cingulate and medial temporal regions. Observed reductions in functional connectivity were unattributable to age or structural atrophy in the posterior cingulate and medial temporal areas. Similar resting-state functional connectivity magnetic resonance imaging findings in relation to cerebrospinal fluid biomarkers were obtained using region-of-interest analyses and voxelwise correlation mapping.

CONCLUSIONS AND RELEVANCE

Both Aβ and tau pathology affect default mode network integrity before clinical onset of Alzheimer disease.

Network-based biomarkers in Alzheimer's disease: review and future directions

By 2050 it is estimated that the number of worldwide Alzheimer's disease (AD) patients will quadruple from the current number of 36 million people. To date, no single test, prior to postmortem examination, can confirm that a person suffers from AD. Therefore, there is a strong need for accurate and sensitive tools for the early diagnoses of AD. The complex etiology and multiple pathogenesis of AD call for a system-level understanding of the currently available biomarkers and the study of new biomarkers via network-based modeling of heterogeneous data types. In this review, we summarize recent research on the study of AD as a connectivity syndrome. We argue that a network-based approach in biomarker discovery will provide key insights to fully understand the network degeneration hypothesis (disease starts in specific network areas and progressively spreads to connected areas of the initial loci-networks) with a potential impact for early diagnosis and disease-modifying treatments. We introduce a new framework for the quantitative study of biomarkers that can help shorten the transition between academic research and clinical diagnosis in AD.