CSF biomarkers in relationship to cognitive profiles in Alzheimer disease

The role of perfusion, grey matter volume and behavioural phenotypes in the data-driven classification of cognitive syndromes

BACKGROUND

The use of structural and perfusion brain imaging in combination with behavioural information in the prediction of cognitive syndromes using a data-driven approach remains to be explored. Here, we thus examined the contribution of brain structural and perfusion imaging and behavioural features to the existing classification of cognitive syndromes using a data-driven approach.

METHODS

Study participants belonged to the community-based Biomarker and Cognition Cohort Study in Singapore who underwent neuropsychological assessments, structural-functional MRI and blood biomarkers. Participants had a diagnosis of cognitively normal (CN), subjective cognitive impairment (SCI), mild cognitive impairment (MCI) and dementia. Cross-sectional structural and cerebral perfusion imaging, behavioural scale data including mild behaviour impairment checklist, Pittsburgh Sleep Quality Index and Depression, Anxiety and Stress scale data were obtained.

RESULTS

Three hundred seventy-three participants (mean age 60.7 years; 56% female sex) with complete data were included. Principal component analyses demonstrated that no single modality was informative for the classification of cognitive syndromes. However, multivariate glmnet analyses revealed a specific combination of frontal perfusion and temporo-frontal grey matter volume were key protective factors while the severity of mild behaviour impairment interest sub-domain and poor sleep quality were key at-risk factors contributing to the classification of CN, SCI, MCI and dementia (p < 0.0001). Moreover, the glmnet model showed best classification accuracy in differentiating between CN and MCI cognitive syndromes (AUC = 0.704; sensitivity = 0.698; specificity = 0.637).

CONCLUSIONS

Brain structure, perfusion and behavioural features are important in the classification of cognitive syndromes and should be incorporated by clinicians and researchers. These findings illustrate the value of using multimodal data when examining syndrome severity and provide new insights into how cerebral perfusion and behavioural impairment influence classification of cognitive syndromes.

The Relationship of Cerebrospinal Fluid Biomarkers and Cognitive Performance in Frontotemporal Dementia

Objective

Currently available literature on the relationships between cerebrospinal fluid (CSF) biomarkers and cognitive performance in frontotemporal dementia (FTD) is very limited and inconclusive. In this study, we investigated the association of cognition, as measured with Montreal Cognitive Assessment (MoCA), with CSF levels of total tau (t-tau), phosphorylated tau at threonine 181 (p-tau181), and amyloid β 1-42 (Aβ1-42) in a group of patients with FTD and Alzheimer's disease (AD).

Methods

We conducted a retrospective cohort study with participants selected from the electronic records of patients seen at Yale New Haven Hospital's Memory Clinic, CT, USA. We included 61 patients, 28 with FTD (mean age=64.1) and 33 with AD (mean age=66.8).

Results

T-tau levels negatively and significantly correlated with total MoCA scores as well as the different MoCA index scores in both the FTD (r=-0.469, p<0.05) and AD (r=-0.545, p<0.01) groups. There were no significant associations with MoCA scores and p-tau181 levels in patients with FTD (r=-0.224, p>0.05), unlike patients with AD, who exhibited significant correlations (r=-0.549, p<0.01). Also, Aβ1-42 levels were not significantly correlated with MoCA scores in either of the FTD and AD groups.

Conclusion

CSF concentrations of t-tau are inversely correlated to cognitive performance in patients with FTD and both t-tau and p-tau181 in AD. These findings provide valuable insights into the relationship between clinical cognitive performance and tau-related pathology in FTD.

Exploring cognitive progression subtypes in the Framingham Heart Study

INTRODUCTION

Alzheimer's disease (AD) is a heterogeneous disorder characterized by complex underlying neuropathology that is not fully understood. This study aimed to identify cognitive progression subtypes and examine their correlation with clinical outcomes.

METHODS

Participants of this study were recruited from the Framingham Heart Study. The Subtype and Stage Inference (SuStaIn) method was used to identify cognitive progression subtypes based on eight cognitive domains.

RESULTS

Three cognitive progression subtypes were identified, including verbal learning (Subtype 1), abstract reasoning (Subtype 2), and visual memory (Subtype 3). These subtypes represent different domains of cognitive decline during the progression of AD. Significant differences in age of onset among the different subtypes were also observed. A higher SuStaIn stage was significantly associated with increased mortality risk.

DISCUSSION

This study provides a characterization of AD heterogeneity in cognitive progression, emphasizing the importance of developing personalized approaches for risk stratification and intervention.

Highlights

We used the Subtype and Stage Inference (SuStaIn) method to identify three cognitive progression subtypes.Different subtypes have significant variations in age of onset.Higher stages of progression are associated with increased mortality risk.

Understanding the Episodic Memory and Executive Functioning Axis Impairment in MCI Patients: A Multicenter Study in Comparison with CSF Biomarkers

BACKGROUND

This study aimed to explore the association between a verbal learning task that evaluates the potential mutual dependency between memory and executive functions (i.e., the Test of Memory Strategies, TMS) and cerebrospinal fluid (CSF) Alzheimer's Disease (AD) biomarkers.

METHODS

A sample of 47 mild cognitive impairment (MCI) participants from Poland and Spain were classified according to the Erlangen Score Diagnostic Algorithm (ESA) into CSF- (n = 16) and CSF+ (n = 31) groups. Correlation analyses between TMS word-list conditions and CSF biomarkers were conducted. Additionally, an analysis of covariance was performed to define the effect on ESA classification in the sample, using as a covariable the country of origin of the participants.

RESULTS

Significant associations between the TMS-3 condition and Aβ42, t-tau, and p-tau were observed for the whole sample. In addition, the CSF- participants obtained higher cognitive performance in TMS-3 compared to the CSF+ group. This outcome persisted if the groups were based on Aβ42 scores, but not t-tau or p-tau values.

CONCLUSIONS

These findings could indicate that poor performance on verbal learning tests may be affected by executive dysfunctions. Therefore, future intervention plans focused on training executive functions would be of interest to improve the ability of MCI patients to encode and organize information.

Proteomic clusters underlie heterogeneity in preclinical Alzheimer's disease progression

Heterogeneity in progression to Alzheimer's disease (AD) poses challenges for both clinical prognosis and clinical trial implementation. Multiple AD-related subtypes have previously been identified, suggesting differences in receptivity to drug interventions. We identified early differences in preclinical AD biomarkers, assessed patterns for developing preclinical AD across the amyloid-tau-(neurodegeneration) [AT(N)] framework, and considered potential sources of difference by analysing the CSF proteome. Participants (n = 10) enrolled in longitudinal studies at the Knight Alzheimer Disease Research Center completed four or more lumbar punctures. These individuals were cognitively normal at baseline. Cerebrospinal fluid measures of amyloid-β (Aβ)42, phosphorylated tau (pTau181), and neurofilament light chain (NfL) as well as proteomics values were evaluated. Imaging biomarkers, including PET amyloid and tau, and structural MRI, were repeatedly obtained when available. Individuals were staged according to the amyloid-tau-(neurodegeneration) framework. Growth mixture modelling, an unsupervised clustering technique, identified three patterns of biomarker progression as measured by CSF pTau181 and Aβ42. Two groups (AD Biomarker Positive and Intermediate AD Biomarker) showed distinct progression from normal biomarker status to having biomarkers consistent with preclinical AD. A third group (AD Biomarker Negative) did not develop abnormal AD biomarkers over time. Participants grouped by CSF trajectories were re-classified using only proteomic profiles (AUCAD Biomarker Positive versus AD Biomarker Negative = 0.857, AUCAD Biomarker Positive versus Intermediate AD Biomarkers = 0.525, AUCIntermediate AD Biomarkers versus AD Biomarker Negative = 0.952). We highlight heterogeneity in the development of AD biomarkers in cognitively normal individuals. We identified some individuals who became amyloid positive before the age of 50 years. A second group, Intermediate AD Biomarkers, developed elevated CSF ptau181 significantly before becoming amyloid positive. A third group were AD Biomarker Negative over repeated testing. Our results could influence the selection of participants for specific treatments (e.g. amyloid-reducing versus other agents) in clinical trials. CSF proteome analysis highlighted additional non-AT(N) biomarkers for potential therapies, including blood-brain barrier-, vascular-, immune-, and neuroinflammatory-related targets.

NEURONORMA Cognitive Battery Associations with Cerebrospinal Fluid Amyloid-β and Tau Levels in the Continuum of Alzheimer's Disease

BACKGROUND

Neuropsychological assessments are essential to define the cognitive profile and contribute to the diagnosis of Alzheimer's disease (AD). The progress in knowledge about the pathophysiological process of the disease has allowed conceptualizing AD through biomarkers as a biological continuum that encompasses different clinical stages.

OBJECTIVE

To explore the association between cerebrospinal fluid (CSF) biomarkers of AD and cognition using the NEURONORMA battery, in a sample of cognitively unimpaired (CU), mild cognitive impaired (MCI), and mild dementia of the Alzheimer type (DAT) subjects, and to characterize the cognitive profiles in MCI subjects classified by A/T/N system.

METHODS

42 CU, 35 MCI, and 35 mild DAT were assessed using the NEURONORMA battery. Core AD biomarkers [amyloid-β42 (Aβ42) peptide, total tau (t-tau), and phosphorylated tau 181 (p-tau181)] proteins were measured in CSF. Correlation coefficients, multivariate regression, and effect sizes were calculated. We explored the age- and education-adjusted cognitive profiles by A/T/N variants within the MCI group.

RESULTS

Cognitive outcomes were directly associated with CSF Aβ42 and inversely with CSF tau measures. We found differences in both biomarkers and cognitive outcomes comparing all pairs except for CSF measures between cognitively impaired groups. The highest effect size was in memory tasks and biomarkers ratios. Lower performances were in memory and executive domains in MCI subjects with AD pathology (A+T+N±) compared to those with normal levels of AD biomarkers (A- T- N).

CONCLUSION

This study provides further evidence of the validity of Spanish NEURONORMA cognitive battery to characterize cognitive impairment in the AD pathological continuum.

Exploration of salient risk factors involved in mild cognitive impairment

Mild cognitive impairment (MCI) is a prevalent and complex condition among older adults that often progresses into Alzheimer's disease (AD). Although MCI affects individuals differently, there are specific indicators of risk commonly associated with the development of MCI. The present study explored the prevalence of seven established MCI risk categories within a large sample of older adults with and without MCI. We explored trends across the different diagnostic groups and extracted the most salient risk factors related to MCI using partial least squares. Neuropsychological risk categories showed the largest differences across groups, with the cognitively unimpaired groups outperforming the MCI groups on all measures. Apolipoprotein E4 (ApoE4) carriers were significantly more common among the more severe MCI group, whereas ApoE4 non-carriers were more common in the healthy controls. Participants with subjective and objective cognitive impairment were trending towards AD-like cerebral spinal fluid (CSF) biomarker levels. Increased age, being male and having fewer years of education were identified as important risk factors of MCI. Higher CSF tau levels were correlated with ApoE4 carrier status, age and a decrease in the ability to carry out daily activities across all diagnostic groups. Amyloid beta_1-42 CSF concentration was positively correlated with cognitive and memory performance and non-ApoE4 carrier status regardless of diagnostic status. Unlike previous research, poor cardiovascular health or being female had no relation to MCI. Altogether, the results highlighted risk factors that were specific to persons with MCI, findings that will inform future research in healthy aging, MCI and AD.

Tau as a Biomarker of Neurodegeneration

Less than 50 years since tau was first isolated from a porcine brain, its detection in femtolitre concentrations in biological fluids is revolutionizing the diagnosis of neurodegenerative diseases. This review highlights the molecular and technological advances that have catapulted tau from obscurity to the forefront of biomarker diagnostics. Comprehensive updates are provided describing the burgeoning clinical applications of tau as a biomarker of neurodegeneration. For the clinician, tau not only enhances diagnostic accuracy, but holds promise as a predictor of clinical progression, phenotype, and response to drug therapy. For patients living with neurodegenerative disorders, characterization of tau dysregulation could provide much-needed clarity to a notoriously murky diagnostic landscape.

Episodic recognition memory based on incidental learning of visual associations is largely preserved compared to recall in amnestic mild cognitive impairment and mild Alzheimer's disease

We investigated preserved episodic recognition memory based on incidental learning of visual associations in Alzheimer's disease (AD). In a cross-sectional design, we analyzed episodic memory score profiles of patients with amnestic mild cognitive impairment (a-MCI) (n = 42) or mild AD (n = 19) who had hippocampal atrophy, and healthy elderly controls (n = 43). The Visual Association Test-Extended served as a measure of episodic memory. Multiple-choice cued recognition was compared with paired associate recall and free recall within groups. Results showed that patients recognized learned material much better compared to when they had to recall material, resulting in large effect sizes (Cohen's d) ranging from 1.3 to 3.5. We conclude that episodic recognition memory based on incidental learning of visual associations is largely preserved when compared to recall in a-MCI and mild AD. This suggests that the episodic memory impairment in AD may be characterized as a retrieval impairment rather than a consolidation impairment, indicating that preserved recognition compared to recall may be compatible with AD being the correct diagnosis. Measuring the episodic memory impairment in AD may benefit from using tests that capture different aspects of memory processes such as incidental learning of visual associations.

Comparison of Diagnostic Performances Between Cerebrospinal Fluid Biomarkers and Amyloid PET in a Clinical Setting

The diagnostic performances of cerebrospinal fluid (CSF) biomarkers and amyloid positron emission tomography (PET) were compared by examining the association and concordance or discordance between CSF Aβ1-42 and amyloid PET, after determining our own cut-off values for CSF Alzheimer's disease (AD) biomarkers. Furthermore, we evaluated the ability of CSF biomarkers and amyloid PET to predict clinical progression. CSF Aβ1-42, t-tau, and p-tau levels were analyzed in 203 individuals [27 normal controls, 38 mild cognitive impairment (MCI), 62 AD dementia, and 76 patients with other neurodegenerative diseases] consecutively recruited from two dementia clinics. We used both visual and standardized uptake value ratio (SUVR)-based amyloid PET assessments for analyses. The association of CSF biomarkers with amyloid PET SUVR, hippocampal atrophy, and cognitive function were investigated by linear regression analysis, and the risk of conversion from MCI to AD dementia was assessed using a Cox proportional hazards model. CSF p-tau/Aβ1-42 and t-tau/Aβ1-42 exhibited the best diagnostic accuracies among the CSF AD biomarkers examined. Correlations were observed between CSF biomarkers and global SUVR, hippocampal volume, and cognitive function. Overall concordance and discordance between CSF Aβ1-42 and amyloid PET was 77% and 23%, respectively. Baseline positive CSF Aβ1-42 for MCI demonstrated a 5.6-fold greater conversion risk than negative CSF Aβ1-42 .  However, amyloid PET findings failed to exhibit significant prognostic value. Therefore, despite presence of a significant correlation between the CSF Aβ1-42 level and SUVR of amyloid PET, and a relevant concordance between CSF Aβ1-42 and amyloid PET, baseline CSF Aβ1-42 better predicted AD conversion.

Protective Role of Cerebrospinal Fluid Inflammatory Cytokines in Patients with Amnestic Mild Cognitive Impairment and Early Alzheimer's Disease Carrying Apolipoprotein E4 Genotype

BACKGROUND

Neuroinflammatory cytokines can play a pivotal role in Alzheimer's disease (AD) contributing to the evolution of degenerative processes.

OBJECTIVE

We aimed at evaluating the levels of cerebrospinal fluid (CSF) inflammatory cytokines, chemokines, and growth factors in subjects with diagnosis of amnestic mild cognitive impairment and mild AD.

METHODS

We evaluated CSF contents of inflammatory cytokines in 66 patients divided according to the NIA-AA research framework and the APOE genotype. CSF of a group of cognitively unimpaired individuals (n = 23) was evaluated as control. All patients were evaluated for 24 months using Mini-Mental State Examination (MMSE).

RESULTS

We found significant increased levels of IL-4, IL-6, IL-8, and G-CSF in the CSF of A+/T-APOE4 carriers, respect to A+/T-patients homozygous for APOE3, respect to A+/T+ patients, regardless the APOE status, and respect to controls. Over a period of 24 months, A+/T-APOE4 carriers, with increased levels of cytokines, showed a preserved cognitive evaluation when compared to the other subgroups of patients (delta MMSE at 24 months respect to baseline: 0.10±0.35; p < 0.05).

CONCLUSION

Our data suggest that during early phases of AD, in APOE4 carriers, Aβ pathology likely induces a specific cytokines pattern synthesis associated to cognitive preservation. These data highlight the different role that neuroinflammation can play in AD pathology based on the presence of specific CSF biomarkers and on the APOE status.

TNFRSF1B Gene Variants and Related Soluble TNFR2 Levels Impact Resilience in Alzheimer's Disease

Tumor necrosis factor receptor 2 (TNFR2) promotes neuronal survival downstream. This longitudinal study evaluated whether the TNFRSF1B gene encoding TNFR2 and levels of its soluble form (sTNFR2) affect Alzheimer disease (AD) biomarkers and clinical outcomes. Data analyzed included 188 patients in the Alzheimer's Disease Neuroimaging Initiative (ADNI) who had mild cognitive impairment (MCI) and AD dementia. Further, a replication study was performed in 48 patients with MCI with positive AD biomarkers who were treated at a memory clinic. Cerebrospinal fluid (CSF) sTNFR2 levels along with two related TNFRSF1B gene single nucleotide polymorphisms (SNPs) rs976881 and rs1061622 were assessed. General linear models were used to evaluate the effect of CSF sTNFR2 levels and each SNP in relationship to CSF t-tau and p-tau, cognitive domains, MRI brain measures, and longitudinal cognitive changes after adjustments were made for covariates such as APOE ε4 status. In the ADNI cohort, a significant interaction between rs976881 and CSF sTNFR2 modulates CSF t-tau and p-tau levels; hippocampal and whole brain volumes; and Digit Span Forwards subtest scores. In the replication cohort, a significant interaction between rs976881 and CSF sTNFR2 modulates CSF p-tau. A significant interaction between rs976881 and CSF sTNFR2 also impacts Clinical Dementia Rating Sum of Boxes scores over 12 months in the ADNI cohort. The interaction between TNFRSF1B variant rs976881 and CSF sTNFR2 levels was noted to modulate multiple AD-associated severity markers and cognitive domains. This interaction impacts resilience-related clinical outcomes in AD and lends support to sTNFR2 as a promising candidate for therapeutic targeting to improve clinical outcomes of interest.

Pathophysiological subtypes of Alzheimer's disease based on cerebrospinal fluid proteomics

Alzheimer's disease is biologically heterogeneous, and detailed understanding of the processes involved in patients is critical for development of treatments. CSF contains hundreds of proteins, with concentrations reflecting ongoing (patho)physiological processes. This provides the opportunity to study many biological processes at the same time in patients. We studied whether Alzheimer's disease biological subtypes can be detected in CSF proteomics using the dual clustering technique non-negative matrix factorization. In two independent cohorts (EMIF-AD MBD and ADNI) we found that 705 (77% of 911 tested) proteins differed between Alzheimer's disease (defined as having abnormal amyloid, n = 425) and controls (defined as having normal CSF amyloid and tau and normal cognition, n = 127). Using these proteins for data-driven clustering, we identified three robust pathophysiological Alzheimer's disease subtypes within each cohort showing (i) hyperplasticity and increased BACE1 levels; (ii) innate immune activation; and (iii) blood-brain barrier dysfunction with low BACE1 levels. In both cohorts, the majority of individuals were labelled as having subtype 1 (80, 36% in EMIF-AD MBD; 117, 59% in ADNI), 71 (32%) in EMIF-AD MBD and 41 (21%) in ADNI were labelled as subtype 2, and 72 (32%) in EMIF-AD MBD and 39 (20%) individuals in ADNI were labelled as subtype 3. Genetic analyses showed that all subtypes had an excess of genetic risk for Alzheimer's disease (all P > 0.01). Additional pathological comparisons that were available for a subset in ADNI suggested that subtypes showed similar severity of Alzheimer's disease pathology, and did not differ in the frequencies of co-pathologies, providing further support that found subtypes truly reflect Alzheimer's disease heterogeneity. Compared to controls, all non-demented Alzheimer's disease individuals had increased risk of showing clinical progression (all P < 0.01). Compared to subtype 1, subtype 2 showed faster clinical progression after correcting for age, sex, level of education and tau levels (hazard ratio = 2.5; 95% confidence interval = 1.2, 5.1; P = 0.01), and subtype 3 at trend level (hazard ratio = 2.1; 95% confidence interval = 1.0, 4.4; P = 0.06). Together, these results demonstrate the value of CSF proteomics in studying the biological heterogeneity in Alzheimer's disease patients, and suggest that subtypes may require tailored therapy.

Patterns of CSF Inflammatory Markers in Non-demented Older People: A Cluster Analysis

Objective

In this study, we aimed to examine if patterns of CSF inflammatory markers are correlated with global cognition, episodic memory, hippocampal volume, and CSF AD-related pathologies among non-demented older people.

Methods

We included 217 non-demented older individuals, including 87 subjects with normal cognition (NC) and 130 subjects with mild cognitive impairment (MCI) from the Alzheimer’s Disease Neuroimaging Initiative (ADNI) study. Hierarchical cluster analysis including nine inflammatory markers in CSF [Tumor necrosis factor-α(TNF-α), TNF-R1, TNF-R2, transforming growth factor-β1 (TGF-β1), TGF-β2, TGF-β3, Interleukin-21 (IL-21), IL-6, and IL-7] was conducted.

Results

We identified two clusters among non-demented older people based on nine inflammatory markers in CSF. Compared to the first cluster, the second cluster showed significantly higher levels of CSF inflammatory markers (TNF-R1, TNF-R2, TGF-β1, TGF-β3, and IL-6). Further, the second cluster was also associated with higher levels of t-tau and p-tau levels in CSF.

Conclusion

We observed a subgroup of non-demented older people characterized by increased levels of inflammatory markers in CSF. Further, this subgroup showed higher levels of t-tau and p-tau levels in CSF.

Highly Elevated Cerebrospinal Fluid Total Tau Level Reflects Higher Likelihood of Non-Amnestic Subtype of Alzheimer's Disease

BACKGROUND

Cerebrospinal fluid (CSF) levels of total tau (t-tau) protein are thought to reflect the intensity of the neuronal damage in neurodegeneration, including Alzheimer's disease (AD). The recent link of CSF t-tau to rapidly progressive AD raises the question among other AD clinical variants regarding CSF t-tau. We investigated the clinical phenotypes of AD patients with varying CSF t-tau levels.

OBJECTIVE

We tested the hypothesis that highly elevated CSF t-tau level would have a higher likelihood of presenting with atypical non-amnestic variants of AD.

METHODS

Retrospective comparative case study of 97 patients evaluated in a memory clinic with clinical presentation and CSF biomarkers consistent with AD. We compared the age, sex, education, APOEɛ4 status, Montreal Cognitive Assessment (MoCA) score, clinical phenotype, and MRI volumetric measures by CSF t-tau quartile at baseline. Multivariable logistic regression models were used to evaluate if CSF t-tau levels predict non-amnestic presentations controlling for covariates.

RESULTS

Non-amnestic AD had a higher median CSF t-tau level compared to amnestic-AD (p = 0.014). Each 50 pg/ml increase in CSF t-tau was associated with an increase in the odds of having a non-amnestic presentation (7.4%) and aphasia (10.6 %) as the initial presenting symptom even after taking into account; age, sex, education, APOEɛ4, MoCA, and CSF Aβ42. Logopenic AD had higher t-tau and p-tau levels compared to other variants.

CONCLUSIONS

Highly elevated CSF t-tau levels could indicate more cortical involvement presenting with early non-amnestic symptoms in atypical AD subtypes, particularly in the logopenic variant.

Disentangling Heterogeneity in Alzheimer's Disease and Related Dementias Using Data-Driven Methods

Brain aging is a complex process that includes atrophy, vascular injury, and a variety of age-associated neurodegenerative pathologies, together determining an individual's course of cognitive decline. While Alzheimer's disease and related dementias contribute to the heterogeneity of brain aging, these conditions themselves are also heterogeneous in their clinical presentation, progression, and pattern of neural injury. We reviewed studies that leveraged data-driven approaches to examining heterogeneity in Alzheimer's disease and related dementias, with a principal focus on neuroimaging studies exploring subtypes of regional neurodegeneration patterns. Over the past decade, the steadily increasing wealth of clinical, neuroimaging, and molecular biomarker information collected within large-scale observational cohort studies has allowed for a richer understanding of the variability of disease expression within the aging and Alzheimer's disease and related dementias continuum. Moreover, the availability of these large-scale datasets has supported the development and increasing application of clustering techniques for studying disease heterogeneity in a data-driven manner. In particular, data-driven studies have led to new discoveries of previously unappreciated disease subtypes characterized by distinct neuroimaging patterns of regional neurodegeneration, which are paralleled by heterogeneous profiles of pathological, clinical, and molecular biomarker characteristics. Incorporating these findings into novel frameworks for more differentiated disease stratification holds great promise for improving individualized diagnosis and prognosis of expected clinical progression, and provides opportunities for development of precision medicine approaches for therapeutic intervention. We conclude with an account of the principal challenges associated with data-driven heterogeneity analyses and outline avenues for future developments in the field.

Cerebro-spinal fluid biomarker levels: phosphorylated tau (T) and total tau (N) as markers for rate of progression in Alzheimer's disease

Background

We investigated the potential associations between cerebro-spinal fluid (CSF) levels of phosphorylated tau (P-tau) and total tau (T-tau) with short-term response to cholinesterase inhibitor (ChEI) treatment, longitudinal outcome and progression rates in Alzheimer’s disease (AD).

Methods

This prospective, observational study included 129 participants clinically diagnosed with mild-to-moderate AD, who underwent a lumbar puncture. The CSF biomarkers amyloid-β_1–42 (Aβ₄₂), P-tau and T-tau were analysed with xMAP technology. Cognitive, global, instrumental and basic activities of daily living (ADL) capacities at the start of ChEI therapy and semi-annually over 3 years were evaluated.

Results

All patients had abnormal Aβ₄₂ (A+). Fifty-eight individuals (45%) exhibited normal P-tau and T-tau (A+ T– (N)–), 12 (9%) abnormal P-tau/normal T-tau (A+ T+ (N)–), 17 (13%) normal P-tau/abnormal T-tau (A+ T– (N)+) and 42 (33%) abnormal P-tau and T-tau (A+ T+ (N)+). The participants with A+ T+ (N)+ were younger than A+ T– (N)+ at the estimated onset of AD and the initiation of ChEIs. The proportion of 6-month responders to ChEI and deterioration/year after start of treatment did not differ between the AT(N) profiles in any scales. A higher percentage of globally improved/unchanged patients was exhibited in the A+ T– (N)– group after 12, 30 and 36 months of ChEI therapy but not at other assessments. In apolipoprotein E (APOE) ε4-carriers, linear relationships were found between greater cognitive decline/year and higher tau; Mini-Mental State Examination score – T-tau (r_s = − 0.257, p = 0.014) and Alzheimer’s Disease Assessment Scale–cognitive subscale – P-tau (r_s = − 0.242, p = 0.022). A correlation between faster progression in instrumental ADL (IADL) and higher T-tau was also detected (r_s = − 0.232, p = 0.028). These associations were not demonstrated in non-ε4-carriers.

Conclusions

Younger age and faster global deterioration were observed in AD patients with pathologic tau and neurodegeneration, whereas more rapid cognitive and IADL decline were related to higher P-tau or T-tau in APOE ε4-carriers only. The results might indicate an association between more pronounced tau pathology/neuronal injury and the APOE ε4-allele leading to a worse prognosis. Our findings showed that the AT(N) biomarker profiles have limited utility to predict AD progression rates and, thus, measure change and interpreting outcomes from clinical trials of future therapies.

Detection of early-stage Alzheimer's pathology using blood-based autoantibody biomarkers in elderly hip fracture repair patients

Post-operative delirium (POD) is the most common complication following major surgery in non-demented older (>65 y/o) patients. Patients experiencing POD show increased risk for future cognitive decline, including mild cognitive impairment (MCI) and Alzheimer’s disease (AD) and, conversely, patients with cognitive decline at surgery show increased risk for POD. Here, we demonstrate that a previously established panel of AD-driven MCI (ADMCI) autoantibody (aAB) biomarkers can be used to detect prodromal AD pre-surgically in individuals admitted into the hospital for hip fracture repair (HFR) surgery. Plasma from 39 STRIDE (STRIDE: A Strategy to Reduce the Incidence of Postoperative Delirium in Elderly Patients) HFR patients and sera from 25 age- and sex-matched non-demented and non-surgical controls were screened using human protein microarrays to measure expression of a panel of 44 previously identified MCI aAB biomarkers. The predictive classification accuracy of the aAB biomarker panel was evaluated using Random Forest (RF). The ADMCI aAB biomarkers successfully distinguished 21 STRIDE HFR patients (CDR = 0.5) from 25 matched non-surgical controls with an overall accuracy of 91.3% (sensitivity = 95.2%; specificity = 88.0%). The ADMCI aAB panel also correctly identified six patients with preoperative CDR = 0 who later converted to CDR = 0.5 or >1 at one-year follow-up. Lastly, the majority of cognitively normal (CDR = 0) STRIDE HFR subjects that were positive for CSF AD biomarkers based on the A/T/N classification system were likewise classified as ADMCI aAB-positive using the biomarker panel. Results suggest that pre-surgical detection of ADMCI aAB biomarkers can readily identify HFR patients with likely early-stage AD pathology using pre-surgery blood samples, opening up the potential for early, blood-based AD detection and improvements in peri- and postoperative patient management.

Subtypes Based on Six Apolipoproteins in Non-Demented Elderly Are Associated with Cognitive Decline and Subsequent Tau Accumulation in Cerebrospinal Fluid

Apolipoproteins (APOs) have been implicated in the pathogenesis of Alzheimer's disease (AD). In the present study, we aimed to investigate if patterns of cerebrospinal fluid (CSF) APOs (APOA-I, APOC-III, APOD, APOE, APOH, and APOJ) levels are associated with changes over time in cognition, memory performance, neuroimaging markers, and AD-related pathologies (CSF Aβ42, t-tau, and p-tau) in non-demented older adults. At baseline, a total of 241 non-demented older adults with CSF APOs data was included in the present analysis. Hierarchical agglomerative cluster analysis including the six CSF APOs was carried out. Among non-demented older adults, we identified two clusters. Compare with the first cluster, the second cluster had higher levels of APOs in CSF. Additionally, the second cluster showed a more benign disease course, including slower cognitive decline and slower p-tau accumulation in CSF. Our data highlight the importance of APOs in the pathogenesis of AD.

Diagnosis associated with Tau higher than 1200 pg/mL: Insights from the clinical and laboratory practice

CONTEXT

Cerebrospinal fluid (CSF) biomarkers are valuable tools for the diagnosis of neurological diseases. We aimed to investigate within a retrospective multicentric study the final diagnosis associated with very high CSF Tau levels and to identify patterns of biomarkers that would differentiate them in clinical practice, to help clinical biologists into physicians' counseling.

PATIENTS AND METHODS

Within the national multicentric network ePLM, we included 1743 patients from January 1, 2008, to December 31, 2013, with CSF biomarkers assayed by the same Innotest assays (protein Tau, phospho-Tau [pTau], and Aβ 1-42). We identified 205 patients with protein Tau concentration higher than 1200 pg/mL and final diagnosis.

RESULTS

Among those patients, 105 (51.2%) were suffering from Alzheimer's disease, 37 (18%) from sporadic Creuztfeldt-Jakob disease, and 63 (30.7%) from other neurological diseases including paraneoplastic/ central nervous system tumor, frontotemporal dementia, other diagnoses, amyloid angiopathy, Lewy body dementia, and infections of the central nervous system. Phospho-Tau, Aβ1-42 and Aβ1-42/pTau values differed significantly between the three groups of patients (p < .001). An Aβ1-42/pTau ratio between 4.7 and 9.7 was suggestive of other neurological diseases (threshold in AD: 8.3). CSF 14-3-3 was useful to discriminate Alzheimer's disease from Creuztfeldt-Jakob disease in case of Aβ1-42 concentrations <550 pg/mL or pTau>60 pg/mL.

CONCLUSION

This work emphasizes the interest of a well-thought-out interpretation of CSF biomarkers in neurological diseases, particularly in the case of high Tau protein concentrations in the CSF.

Relevance of the interplay between amyloid and tau for cognitive impairment in early Alzheimer's disease

Amyloid β (Aβ) and tau are key hallmark features of Alzheimer's disease (AD) neuropathology. The interplay of Aβ and tau for cognitive impairment in early AD was examined with cross-sectional analysis, measured by cerebrospinal fluid biomarkers (Aβ_1-42, total tau [t-tau], and phosphorylated tau [p-tau181P]), and on cognitive performance by the repeatable battery for assessment of neuropsychological status (RBANS). Participants (n = 246) included cognitively normal (Aβ-), mild cognitively impaired (Aβ-), preclinical AD (Aβ+), and prodromal AD (Aβ+). Overall, cognitive scores (RBANS total scale score) had a moderate negative correlation to t-tau (n = 246; r = -0.434; p < 0.001) and p-tau181P (r = -0.389; p < 0.001). When classified by Aβ status, this correlation to t-tau was applicable only in Aβ+ participants (n = 139; r = -0.451, p < 0.001) but not Aβ- participants (n = 107; r = 0.137, p = 0.16), with identical findings for p-tau. Both tau (p < 0.0001) and interaction of Aβ_1-42 with tau (p = 0.006) affected RBANS, but not Aβ_1-42 alone. Cognitive/memory performance correlated well with cerebrospinal fluid tau levels across early stages of AD, although the correlation is Aβ dependent.

Stress and the Etiopathogenesis of Alzheimer's Disease and Depression

Alzheimer's disease (AD) is a multifactorial neurodegenerative disorder with a complex physiopathology whose initiators are poorly defined. Accumulating clinical and experimental evidence suggests a causal role of lifetime stress in AD. This chapter summarizes current knowledge about how chronic stress and its accompanying high levels of glucocorticoid (GC) secretion, trigger the two main pathomechanisms of AD: (i) misprocessing of amyloid precursor protein (APP) and the generation of amyloid beta (Aβ) and (ii) Tau hyperphosphorylation and aggregation. Given that depression is a well-known stress-related illness, and the evidence that depression may precede AD, this chapter also explores neurobiological mechanisms that may be common to depressive and AD pathologies. This review also discusses emerging insights into the role of Tau and its malfunction in disrupting neuronal cascades and neuroplasticity and, thus triggering brain pathology.

Decision tree supports the interpretation of CSF biomarkers in Alzheimer's disease

Introduction

We developed and validated a clinically applicable decision tree for the use of cerebrospinal fluid biomarkers in the diagnosis of Alzheimer's disease (AD).

Methods

Subjects with probable AD (n = 1004) and controls (n = 442) were included. A decision tree was modeled using Classification And Regression Tree analysis in a training cohort (AD n = 221; controls n = 221) and validated in an independent cohort (AD n = 783; controls n = 221). Diagnostic performance was compared to previously defined cutoffs (amyloid β 1-42 < 813 pg/ml; tau>375 pg/ml).

Results

Two cerebrospinal fluid AD biomarker profiles were revealed: the “classical” AD biomarker profile (amyloid β 1-42: 647-803 pg/ml; tau >374 pg/ml) and an “atypical” AD biomarker profile with strongly decreased amyloid β 1-42 (<647 pg/ml) and normal tau concentrations (<374 pg/ml). Compared to previous cutoffs, the decision tree performed better on diagnostic accuracy (86% [84-88] vs 80% [78-83]).

Discussion

Two cerebrospinal fluid AD biomarker profiles were identified and incorporated in a readily applicable decision tree, which improved diagnostic accuracy.

•

Classification And Regression Tree analysis revealed two Alzheimer's disease (AD) biomarker profiles based on cerebrospinal fluid amyloid beta 1-42 and tau.

•

A “classical AD-like” profile and an atypical AD profile were identified.

•

Combining both AD biomarker profiles led to a higher diagnostic accuracy.

•

Both biomarker profiles are incorporated in a readily applicable decision tree.

The relationship between CSF biomarkers and cerebral metabolism in early-onset Alzheimer's disease

PURPOSE

One can reasonably suppose that cerebrospinal spinal fluid (CSF) biomarkers can identify distinct subgroups of Alzheimer's disease (AD) patients. In order to better understand differences in CSF biomarker patterns, we used FDG PET to assess cerebral metabolism in CSF-based subgroups of AD patients.

METHODS

Eighty-five patients fulfilling the criteria for probable early-onset AD (EOAD) underwent lumbar puncture, brain ¹⁸F-FDG PET and MRI. A cluster analysis was performed, with the CSF biomarkers for AD as variables. Vertex-wise, partial-volume-corrected metabolic maps were computed for the patients and compared between the clusters of patients. Linear correlations between each CSF biomarker and the metabolic maps were assessed.

RESULTS

Three clusters emerged. The "Aβ42" cluster contained 32 patients with low levels of Aβ42, while tau and p-tau remained within the normal range. The "Aβ42 + tau" cluster contained 41 patients with low levels of Aβ42 and high levels of tau and p-tau. Lastly, the "tau" cluster contained 12 patients with very high levels of tau and p-tau and low-normal levels of Aβ42. There were no inter-cluster differences in age, sex ratio, educational level, APOE genotype, disease duration or disease severity. The "Aβ42 + tau" and "tau" clusters displayed more marked frontal hypometabolism than the "Aβ42" cluster did, and frontal metabolism was significantly negatively correlated with the CSF tau level. The "Aβ42" and "Aβ42 + tau" clusters displayed more marked hypometabolism in the left occipitotemporal region than the "tau" cluster did, and metabolism in this region was significantly and positively correlated with the CSF Aβ42 level.

CONCLUSION

The CSF biomarkers can be used to identify metabolically distinct subgroups of patients with EOAD. Future research should seek to establish whether these biochemical differences have clinical consequences.

Oligomeric forms of amyloid-β protein in plasma as a potential blood-based biomarker for Alzheimer's disease

Background

Soluble amyloid-β (Aβ) oligomers are the major toxic substances associated with the pathology of Alzheimer’s disease (AD). The ability to measure Aβ oligomer levels in the blood would provide simple and minimally invasive tools for AD diagnostics. In the present study, the recently developed Multimer Detection System (MDS) for AD, a new enzyme-linked immunosorbent assay for measuring Aβ oligomers selectively, was used to detect Aβ oligomers in the plasma of patients with AD and healthy control individuals.

Methods

Twenty-four patients with AD and 37 cognitively normal control individuals underwent extensive clinical evaluations as follows: blood sampling; detailed neuropsychological tests; brain magnetic resonance imaging; cerebrospinal fluid (CSF) measurement of Aβ42, phosphorylated tau protein (pTau), and total tau protein (tTau); and ¹¹C-Pittsburgh compound B (PIB) positron emission tomography. Pearson’s correlation analyses between the estimations of Aβ oligomer levels by MDS and other conventional AD biomarkers (CSF Aβ₄₂, pTau, and tTau, as well as PIB standardized uptake value ratio [PIB SUVR]) were conducted. ROC analyses were used to compare the diagnostic performance of each biomarker.

Results

The plasma levels of Aβ oligomers by MDS were higher in patients with AD than in normal control individuals, and they correlated well with conventional AD biomarkers (levels of Aβ oligomers by MDS vs. CSF Aβ₄₂, r = −0.443; PIB SUVR, r = 0.430; CSF pTau, r = 0.530; CSF tTau, r = 0.604). The sensitivity and specificity of detecting plasma Aβ oligomers by MDS for differentiating AD from the normal controls were 78.3% and 86.5%, respectively. The AUC for plasma Aβ oligomers by MDS was 0.844, which was not significantly different from the AUC of other biomarkers (p = 0.250).

Conclusions

Plasma levels of Aβ oligomers could be assessed using MDS, which might be a simple, noninvasive, and accessible assay for evaluating brain amyloid deposition related to AD pathology.

Electronic supplementary material

The online version of this article (doi:10.1186/s13195-017-0324-0) contains supplementary material, which is available to authorized users.

The prevalence and biomarkers' characteristic of rapidly progressive Alzheimer's disease from the Alzheimer's Disease Neuroimaging Initiative database

INTRODUCTION

The prevalence and detailed biomarkers' characteristic of rapidly progressive Alzheimer's disease (rpAD) remain incompletely understood.

METHODS

A total of 312 mild AD patients from the Alzheimer's Disease Neuroimaging Initiative database were chosen and dichotomized into rpAD and non-rpAD groups. We performed the prevalence and comprehensive biomarker evaluation.

RESULTS

The prevalence of rpAD was 17.6% in mild AD. Compared with non-rpAD, there were no differences in APOE ε4/ε4, APOE ε3/ε4, and APOE ε2/ε4 genotype distribution, cerebrospinal fluid tau, phosphorylated tau (p-tau), amyloid-β, hippocampus volume, and amyloid deposition in rpAD. Yet, a lower p-tau/tau ratio was observed in rpAD (P = .04). rpAD showed region-specific hypometabolism ([18F]fluorodeoxyglucose-positron emission tomography [FDG-PET]) (P = .001). Receiver-operating characteristic analysis of FDG-PET demonstrated that left angular and left temporal cortices were the regions with higher area under the curve and predictive value for identifying clinical at-risk rpAD.

DISCUSSION

We identified that rpAD commonly existed in mild AD. Cerebral hypometabolism could provide potential clinical differential value for rpAD in the short-term follow-up period.

Matrix Metalloproteinases in Alzheimer's Disease and Concurrent Cerebral Microbleeds

Matrix metalloproteinases (MMPs) are a family of enzymes able to degrade components of the extracellular matrix, which is important for normal blood-brain barrier function. Their function is regulated by tissue inhibitors of matrix metalloproteinases (TIMPs). We investigated whether MMPs and TIMPs in cerebrospinal fluid (CSF) and plasma were altered in Alzheimer's disease (AD) and vascular dementia (VaD), and whether this effect was modified by presence of cerebral micro-bleeds in AD patients. In addition, we assessed associations of MMPs and TIMPs with CSF amyloid-β(1-42) (Aβ42), tau, and tau phosphorylated at threonine-181 (p-tau). We measured MMP2, MMP9, and MMP10, and TIMP1 and TIMP2 in CSF and plasma of 52 AD patients, 26 matched controls, and 24 VaD patients. AD patients showed higher plasma MMP2 levels compared to VaD patients (p <  0.05), and higher CSF MMP10 levels compared to controls (p <  0.05). Microbleeds in AD were associated with lower CSF TIMP1, TIMP2 and MMP9 in a dose-response relation. In addition, CSF MMP2 was associated with p-tau (St.B 0.23, p <  0.05), and CSF MMP10 with tau (St.B 0.38, p <  0.001) and p-tau (St.B 0.40, p <  0.001). Our findings suggest involvement of MMP2 and MMP10 in AD pathology. Lower levels of TIMPs in AD patients with microbleeds suggest less MMP inhibition in patients with concurrent cerebral microbleeds, which may hypothetically lead to a more vulnerable blood-brain barrier in these patients.

Biomarker clusters are differentially associated with longitudinal cognitive decline in late midlife

The ability to detect preclinical Alzheimer's disease is of great importance, as this stage of the Alzheimer's continuum is believed to provide a key window for intervention and prevention. As Alzheimer's disease is characterized by multiple pathological changes, a biomarker panel reflecting co-occurring pathology will likely be most useful for early detection. Towards this end, 175 late middle-aged participants (mean age 55.9 ± 5.7 years at first cognitive assessment, 70% female) were recruited from two longitudinally followed cohorts to undergo magnetic resonance imaging and lumbar puncture. Cluster analysis was used to group individuals based on biomarkers of amyloid pathology (cerebrospinal fluid amyloid-β42/amyloid-β40 assay levels), magnetic resonance imaging-derived measures of neurodegeneration/atrophy (cerebrospinal fluid-to-brain volume ratio, and hippocampal volume), neurofibrillary tangles (cerebrospinal fluid phosphorylated tau181 assay levels), and a brain-based marker of vascular risk (total white matter hyperintensity lesion volume). Four biomarker clusters emerged consistent with preclinical features of (i) Alzheimer's disease; (ii) mixed Alzheimer's disease and vascular aetiology; (iii) suspected non-Alzheimer's disease aetiology; and (iv) healthy ageing. Cognitive decline was then analysed between clusters using longitudinal assessments of episodic memory, semantic memory, executive function, and global cognitive function with linear mixed effects modelling. Cluster 1 exhibited a higher intercept and greater rates of decline on tests of episodic memory. Cluster 2 had a lower intercept on a test of semantic memory and both Cluster 2 and Cluster 3 had steeper rates of decline on a test of global cognition. Additional analyses on Cluster 3, which had the smallest hippocampal volume, suggest that its biomarker profile is more likely due to hippocampal vulnerability and not to detectable specific volume loss exceeding the rate of normal ageing. Our results demonstrate that pathology, as indicated by biomarkers, in a preclinical timeframe is related to patterns of longitudinal cognitive decline. Such biomarker patterns may be useful for identifying at-risk populations to recruit for clinical trials.

Detection of Alzheimer's disease at mild cognitive impairment and disease progression using autoantibodies as blood-based biomarkers

Introduction

There is an urgent need to identify biomarkers that can accurately detect and diagnose Alzheimer's disease (AD). Autoantibodies are abundant and ubiquitous in human sera and have been previously demonstrated as disease-specific biomarkers capable of accurately diagnosing mild-moderate stages of AD and Parkinson's disease.

Methods

Sera from 236 subjects, including 50 mild cognitive impairment (MCI) subjects with confirmed low CSF Aβ42 levels, were screened with human protein microarrays to identify potential biomarkers for MCI. Autoantibody biomarker performance was evaluated using Random Forest and Receiver Operating Characteristic curves.

Results

Autoantibody biomarkers can differentiate MCI patients from age-matched and gender-matched controls with an overall accuracy, sensitivity, and specificity of 100.0%. They were also capable of differentiating MCI patients from those with mild-moderate AD and other neurologic and non-neurologic controls with high accuracy.

Discussion

Autoantibodies can be used as noninvasive and effective blood-based biomarkers for early diagnosis and staging of AD.

Chronic Stress and Glucocorticoids: From Neuronal Plasticity to Neurodegeneration

Stress and stress hormones, glucocorticoids (GCs), exert widespread actions in central nervous system, ranging from the regulation of gene transcription, cellular signaling, modulation of synaptic structure, and transmission and glial function to behavior. Their actions are mediated by glucocorticoid and mineralocorticoid receptors which are nuclear receptors/transcription factors. While GCs primarily act to maintain homeostasis by inducing physiological and behavioral adaptation, prolonged exposure to stress and elevated GC levels may result in neuro- and psychopathology. There is now ample evidence for cause-effect relationships between prolonged stress, elevated GC levels, and cognitive and mood disorders while the evidence for a link between chronic stress/GC and neurodegenerative disorders such as Alzheimer's (AD) and Parkinson's (PD) diseases is growing. This brief review considers some of the cellular mechanisms through which stress and GC may contribute to the pathogenesis of AD and PD.

The identification of cognitive subtypes in Alzheimer's disease dementia using latent class analysis

OBJECTIVE

Alzheimer's disease (AD) is a heterogeneous disorder with complex underlying neuropathology that is still not completely understood. For better understanding of this heterogeneity, we aimed to identify cognitive subtypes using latent class analysis (LCA) in a large sample of patients with AD dementia. In addition, we explored the relationship between the identified cognitive subtypes, and their demographical and neurobiological characteristics.

METHODS

We performed LCA based on neuropsychological test results of 938 consecutive probable patients with AD dementia using Mini-Mental State Examination as the covariate. Subsequently, we performed multinomial logistic regression analysis with cluster membership as dependent variable and dichotomised demographics, APOE genotype, cerebrospinal fluid biomarkers and MRI characteristics as independent variables.

RESULTS

LCA revealed eight clusters characterised by distinct cognitive profile and disease severity. Memory-impaired clusters-mild-memory (MILD-MEM) and moderate-memory (MOD-MEM)-included 43% of patients. Memory-spared clusters mild-visuospatial-language (MILD-VILA), mild-executive (MILD-EXE) and moderate-visuospatial (MOD-VISP) -included 29% of patients. Memory-indifferent clusters mild-diffuse (MILD-DIFF), moderate-language (MOD-LAN) and severe-diffuse (SEV-DIFF) -included 28% of patients. Cognitive clusters were associated with distinct demographical and neurobiological characteristics. In particular, the memory-spared MOD-VISP cluster was associated with younger age, APOE e4 negative genotype and prominent atrophy of the posterior cortex.

CONCLUSIONS

Using LCA, we identified eight distinct cognitive subtypes in a large sample of patients with AD dementia. Cognitive clusters were associated with distinct demographical and neurobiological characteristics.

Functional correlates of t-Tau, p-Tau and Aβ₁₋₄₂ amyloid cerebrospinal fluid levels in Alzheimer's disease: a ¹⁸F-FDG PET/CT study

AIM

The aim of the study was to investigate the relationships between cerebrospinal fluid (CSF) levels of t-Tau, p-Tau and amyloid-β (Aβ₁₋₄₂) amyloid peptide and fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) brain distribution in a group of patients with Alzheimer's disease.

MATERIALS AND METHODS

The study included 81 newly diagnosed Alzheimer's disease patients according to the NINCDS-ADRDA criteria. The mean (±SD) age of the patients was 70 (±6) years; 44 were male and 37 were female. All patients underwent a CSF assay and MRI before ¹⁸F-FDG PET scanning. The relationships were evaluated by means of statistical parametric mapping (SPM8).

RESULTS

Increased t-Tau CSF levels were related to reduced glucose consumption in a wide portion of the right frontal lobe [Brodmann area (BA 47)] and limbic lobe bilaterally (BA 31,32), whereas no areas of increased ¹⁸F-FDG uptake related to t-Tau levels were detected. Elevated p-Tau concentrations in CSF were related to increased glucose consumption in both the right and the left limbic lobe and in the left frontal lobe (BA 32 and 8). We did not find any specific cortical area of reduced glucose consumption being related to low levels of Aβ₁₋₄₂ in CSF, whereas a spawn of ¹⁸F-FDG uptake was detectable in BA 18,19 and in the right cerebellum.

CONCLUSION

The results of our study suggest that reduced Aβ₁₋₄₂ concentrations in CSF are related to a wide cortical dysfunction, whereas t-Tau and p-Tau are related to more selective cortical metabolic patterns that mainly involve the cingulate cortex.

Linking CSF and cognition in Alzheimer's disease: Reanalysis of clinical data

OBJECTIVES

Memory and executive deficits are important cognitive markers of Alzheimer's disease (AD). Moreover, in the past decade, cerebrospinal fluid (CSF) biomarkers have been increasingly utilized in clinical practice. Both cognitive and CSF markers can be used to differentiate between AD patients and healthy seniors with high diagnostic accuracy. However, the extent to which performance on specific mnemonic or executive tasks enables reliable estimations of the concentrations of different CSF markers and their ratios remains unclear.

METHODS

To address the above issues, we examined the association between neuropsychological data and CSF biomarkers in 51 AD patients using hierarchical multiple regression analyses. In the first step of these analyses, age, education and sex were entered as predictors to control for possible confounding effects. In the second step, data from a neuropsychological test battery assessing episodic memory, semantic memory and executive functioning were included to determine whether these variables significantly increased (compared to step 1) the explained variance in Aβ42 concentration, p-tau concentration, t-tau concentration, Aβ42/t-tau ratio, and Aβ42/Aβ40 ratio.

RESULTS

The different models explained 52% of the variance in Aβ42/t-tau ratio, 27% of the variance in Aβ42 concentration, and 28% of the variance in t-tau concentration. In particular, Aβ42/t-tau ratio was associated with verbal recognition and code shifting, with Aβ42 being related to verbal recognition and t-tau being related to code shifting. By contrast, the inclusion of neuropsychological data did not allow reliable estimations of Aβ42/Aβ40 ratio or p-tau concentration.

CONCLUSION

Our results showed that strong associations exist between the cognitive key symptoms of AD and the concentrations and ratios of specific CSF markers. In addition, we revealed a specific combination of neuropsychological tests that may facilitate reliable estimations of CSF concentrations, thereby providing important diagnostic information for non-invasive early AD detection.

Cerebrospinal Fluid Aβ42 Levels: When Physiological Become Pathological State

Impaired amyloid beta (Aβ) metabolism is currently considered central to understand the pathophysiology of Alzheimer's disease (AD). Measurements of cerebrospinal fluid Aβ levels remain the most useful marker for diagnostic purposes and to individuate people at risk for AD. Despite recent advances criticized the direct role in neurodegeneration of cortical neurons, Aβ is considered responsible for synaptopathy and impairment of neurotransmission and therefore remains the major trigger of AD and future pharmacological treatment remain Aβ oriented. However, experimental and clinical findings showed that Aβ peptides could have a wider range of action responsible for cell dysfunction and for appearance of clinico-pathological entities different from AD. Such findings may induce misunderstanding of the real role played by Aβ in AD and therefore strengthen criticism on its centrality and need for CSF measurements. Aim of this review is to discuss the role of CSF Aβ levels in light of experimental, clinical pathologic, and electrophysiological results in AD and other pathological entities to put in a correct frame the value of Aβ changes.

Cerebrospinal fluid tau and amyloid-β1-42 in patients with dementia

Progressive cognitive decline in combination with a cerebrospinal fluid biomarker pattern of low levels of amyloid-β1-42 and high levels of total tau and phosphorylated tau is typical of Alzheimer's disease. However, several neurodegenerative disorders may overlap with Alzheimer's disease both in regards to clinical symptoms and neuropathology. In a uniquely large cohort of dementia patients, we examined the associations of cerebrospinal fluid biomarkers for Alzheimer's disease molecular pathology with clinical dementia diagnoses and disease severity. We cross-referenced the Swedish Dementia Registry with the clinical laboratory database at the Sahlgrenska University Hospital. The final data set consisted of 5676 unique subjects with a clinical dementia diagnosis and a complete set of measurements for cerebrospinal fluid amyloid-β1-42, total tau and phosphorylated tau. In cluster analysis, disregarding clinical diagnosis, the optimal natural separation of this data set was into two clusters, with the majority of patients with early onset Alzheimer's disease (75%) and late onset Alzheimer's disease (73%) assigned to one cluster and the patients with vascular dementia (91%), frontotemporal dementia (94%), Parkinson's disease dementia (94%) and dementia with Lewy bodies (87%) to the other cluster. Frontotemporal dementia had the highest cerebrospinal fluid levels of amyloid-β1-42 and the lowest levels of total tau and phosphorylated tau. The highest levels of total tau and phosphorylated tau and the lowest levels of amyloid-β1-42 and amyloid-β1-42:phosphorylated tau ratios were found in Alzheimer's disease. Low amyloid-β1-42, high total tau and high phosphorylated tau correlated with low Mini-Mental State Examination scores in Alzheimer's disease. In Parkinson's disease dementia and vascular dementia low cerebrospinal fluid amyloid-β1-42 was associated with low Mini-Mental State Examination score. In the vascular dementia, frontotemporal dementia, dementia with Lewy bodies and Parkinson's disease dementia groups 53%, 34%, 67% and 53% of the subjects, respectively had abnormal amyloid-β1-42 levels, 41%, 41%, 28% and 28% had abnormal total tau levels, and 29%, 28%, 25% and 19% had abnormal phosphorylated tau levels. Cerebrospinal fluid biomarkers were strongly associated with specific clinical dementia diagnoses with Alzheimer's disease and frontotemporal dementia showing the greatest difference in biomarker levels. In addition, cerebrospinal fluid amyloid-β1-42, total tau, phosphorylated tau and the amyloid-β1-42:phosphorylated tau ratio all correlated with poor cognitive performance in Alzheimer's disease, as did cerebrospinal fluid amyloid-β1-42 in Parkinson's disease dementia and vascular dementia. The results support the use of cerebrospinal fluid biomarkers to differentiate between dementias in clinical practice, and to estimate disease severity.

Cerebrospinal fluid biomarkers and cerebral atrophy in distinct clinical variants of probable Alzheimer's disease

Different clinical variants of probable Alzheimer's disease (AD) share underlying plaques and tangles but show distinct atrophy patterns. We included 52 posterior cortical atrophy, 29 logopenic variant primary progressive aphasia, 53 early-onset and 42 late-onset AD patients, selected for abnormal cerebrospinal fluid (CSF)-amyloid-beta42, with CSF and magnetic resonance imaging data available. Bootstrapping revealed no differences in the prevalence of abnormal CSF total-tau and phosphorylated-tau between probable AD variants (range total-tau: 84.9%-92.3%, phosphorylated-tau: 79.2%-93.1%, p > 0.05). Voxelwise linear regressions showed various relationships between lower CSF-Aβ42 and syndrome-specific atrophy, involving precuneus, posterior cingulate, and medial temporal lobe in early-onset AD, occipital cortex and middle temporal gyrus in posterior cortical atrophy; anterior cingulate, insular cortex and precentral gyrus (left > right) in logopenic variant primary progressive aphasia; and medial temporal lobe, thalamus, and temporal pole in late-onset AD (all at p < 0.001 uncorrected). In contrast, CSF-tau was not related to gray matter atrophy in any group. Our findings suggest that lower CSF-amyloid-beta42 - and not increased total-tau and phosphorylated-tau - relates to reduced gray matter volumes, mostly in regions that are typically atrophied in distinct clinical variants of probable AD.

"Is dopamine involved in Alzheimer's disease?"

Alzheimer's Disease (AD) is a neurodegenerative disorder characterized by progressive cognitive decline and dementia. Recent advances indicate that AD pathogenesis appears more complex than its mere neuropathology. Changes in synaptic plasticity, neuronal disarray and cell death are pathways commonly recognized as pathogenic mechanisms of AD. It is thought that the altered metabolism of certain membrane proteins may lead to the production of amyloid (Aβ) oligomers that are characterized by an highly toxic effect on neurotransmission pathways, such as those mediated by Acetylcholine. The interaction of Aβ oligomers with these neurotansmitters systems would in turn induce cell dysfunction, neurotransmitters signaling imbalance and finally lead to the appearance of neurological signs. In this perspective, it is still debated how and if these mechanisms may also engage the dopaminergic system in AD. Recent experimental work revealed that the dopaminergic system may well be involved in the occurrence of cognitive decline, often being predictive of rapidly progressive forms of AD. However, a clear idea on the role of the dopamine system in AD is still missing. Here we review the more recent evidences supporting the notion that the dopaminergic dysfunction has a pathogenic role in cognitive decline symptoms of AD.

Cholinesterase inhibitors and add-on nutritional supplements in Alzheimer's disease: a systematic review of randomized controlled trials

To date, single drug and nutrient-based interventions have failed to show a clinically relevant effect on Alzheimer's disease (AD). Multidomain interventions may alleviate symptoms and alter the disease course in a synergistic manner. This systematic review examines the effect of adding nutritional supplementation to cholinesterase inhibitors. A systematic PubMed and Cochrane search resulted in nine high quality studies. The studies had low to moderate risk of bias and focused on oxidative stress, homocysteine levels, membrane fluidity, inflammation and acetylcholine levels. Only the use of vitamin E supplements could reduce the rate of functional decline when combined with cholinesterase inhibitors in one study, whereas cognition was not affected in both this and other studies. None of the other nutritional supplements showed convincing evidence of a beneficial effect when combined with cholinesterase inhibitors. This shows that cognitive and functional improvement is difficult to achieve in patients with AD, despite epidemiological data and evidence of biological effects of nutritional supplements. Addressing one disease pathway in addition to cholinesterase inhibitor therapy is probably insufficient to alter the course of the disease. Personalized, multifactorial interventions may be more successful in improving cognition and daily functioning.

The cerebrospinal fluid "Alzheimer profile": easily said, but what does it mean?

BACKGROUND

We aimed to identify the most useful definition of the "cerebrospinal fluid Alzheimer profile," based on amyloid-ß1-42 (Aβ42), total tau, and phosphorylated tau (p-tau), for diagnosis and prognosis of Alzheimer's disease (AD).

METHODS

We constructed eight Alzheimer profiles with previously published combinations, including regression formulas and simple ratios. We compared their diagnostic accuracy and ability to predict dementia due to AD in 1385 patients from the Amsterdam Dementia Cohort. Results were validated in an independent cohort (n = 1442).

RESULTS

Combinations outperformed individual biomarkers. Based on the sensitivity of the best performing regression formulas, cutoffs were chosen at 0.52 for the tau/Aβ42 ratio and 0.08 for the p-tau/Aβ42 ratio. Ratios performed similar to formulas (sensitivity, 91%-93%; specificity, 81%-84%). The same combinations best predicted cognitive decline in mild cognitive impairment patients. Validation confirmed these results, especially regarding the tau/Aβ42 ratio.

CONCLUSIONS

A tau/Aβ42 ratio of >0.52 constitutes a robust cerebrospinal fluid Alzheimer profile. We recommend using this ratio to combine biomarkers.

Biological markers of Alzheimer?s disease

The challenges for establishing an early diagnosis of Alzheimer’s disease (AD) have created a need for biomarkers that reflect the core pathology of the disease. The cerebrospinal fluid (CSF) levels of total Tau (T-tau), phosphorylated Tau (P-Tau) and beta-amyloid peptide (Aβ42) reflect, respectively, neurofibrillary tangle and amyloid pathologies and are considered as surrogate markers of AD pathophysiology. The combination of low Aβ42 and high levels of T-tau and P-Tau can accurately identify patients with AD at early stages, even before the development of dementia. The combined analysis of the CSF biomarkers is also helpful for the differential diagnosis between AD and other degenerative dementias. The development of these CSF biomarkers has evolved to a novel diagnostic definition of the disease. The identification of a specific clinical phenotype combined with the in vivo evidence of pathophysiological markers offers the possibility to make a diagnosis of AD before the dementia stage with high specificity.

Fluid biomarkers for diagnosing dementia: rationale and the Canadian Consensus on Diagnosis and Treatment of Dementia recommendations for Canadian physicians

Fluid biomarkers improve the diagnostic accuracy in dementia and provide an objective measure potentially useful as a therapeutic response in clinical trials. The role of fluid biomarkers in patient care is a rapidly evolving field. Here, we provide a review and recommendations regarding the use of fluid biomarkers in clinical practice as discussed at the Fourth Canadian Consensus Conference on the Diagnosis and Treatment of Dementia (CCCDTD4) convened in Montreal, 4 to 5 May 2012. At present, there is no consensus regarding the optimal methodology for conducting quantification of plasma amyloid-beta (Aβ) peptides. In addition, since there is insufficient evidence supporting clinical applications for plasma Aβ-peptide measures, the CCCDTD4 does not recommended plasma biomarkers either for primary care or for specialists. Evidence for CSF Aβ1-42, total tau and phosphorylated tau in the diagnosis of Alzheimer pathology is much stronger, and can be considered at the tertiary care level for selected cases to improve diagnostic certainty, particularly in those cases presenting atypical clinical features.

Propranolol reduces cognitive deficits, amyloid β levels, tau phosphorylation and insulin resistance in response to chronic corticosterone administration

Chronic exposure to glucocorticoids might result not only in insulin resistance or cognitive deficits, but it is also considered as a risk factor for pathologies such as Alzheimer's disease. Propranolol is a β-adrenergic antagonist commonly used in the treatment of hypertension or acute anxiety. The effects of propranolol (5 mg/kg) have been tested in a model of chronic corticosterone administration (100 μg/ml, 4 wk) in drinking water. Corticosterone administration led to cognitive impairment in the novel object recognition test that was reversed by propranolol. Increased levels of Aβ in the hippocampus of corticosterone-treated mice were counteracted by propranolol treatment, purportedly through an increased IDE expression. Chronic corticosterone treatment induced responses characteristic of insulin resistance, as increased peripheral insulin levels, decreased activation of the insulin receptor (pIR) and decreased associated intracellular pathways (pAkt). These effects might be related to a decreased c-Jun N terminal kinase 1 expression. Again, propranolol was able to counteract all corticosterone-induced effects. One of the main kinases involved in tau phosphorylation, glycogen synthase kinase 3β (GSK3β), which is inactivated by phosphorylation by pAkt, was found to be decreased after corticosterone and increased after propranolol treatment. Concomitant changes in pTau expression were found. Overall, these data further strengthen the potential of propranolol as a therapeutic agent for pathologies associated with the interaction glucocorticoids-insulin resistance and the development of relevant cellular processes for Alzheimer's disease.