Detailed comparison of amyloid PET and CSF biomarkers for identifying early Alzheimer disease

Relevance of Aβ42/40 Ratio for Detection of Alzheimer Disease Pathology in Clinical Routine: The PLMR Scale

Background: Cerebrospinal fluid (CSF) biomarkers (Aβ peptides and tau proteins) improved the diagnosis of Alzheimer's disease (AD) in research and clinical settings. We previously described the PLM-scale (Paris-Lille-Montpellier study), which combines Aβ42, tau, and phosphorylated ptau(181) biomarkers in an easy to use and clinically relevant way. The purpose of this work is to evaluate an optimized PLM_R-scale (PLM ratio scale) that now includes the Aβ42/Aβ40 ratio to detect AD versus non-AD (NAD) participants in clinical routine of memory centers. Methods: Both scales were compared using 904 participants with cognitive impairment recruited from two independent cohorts (Mtp-1 and Mtp-2). The CSF Aβ42/Aβ40 ratio was measured systematically in Mtp-1, and only on biologically discordant cases in Mtp-2. Two different ELISA kit providers were also employed. The distribution of AD and NAD patients and the discrepancies of biomarker profiles were computed. Receiver Operating Characteristic curves were used to represent clinical sensitivity and specificity for AD detection. The classification of patients with the net reclassification index (NRI) was also evaluated. Results: Nine hundred and four participants (342 AD and 562 NAD) were studied; 400 in Mtp-1 and 504 in Mtp-2. For AD patients, the mean CSF Aβ42 and CSF Aβ42/40 ratio was 553 ± 216 pg/mL and 0.069 ± 0.022 pg/mL in Mtp-1 and 702 ± 335 pg/mL and 0.045 ± 0.020 pg/mL in Mtp-2. The distribution of AD and NAD differed between the PLM and the PLM_R scales (p < 0.0001). The percentage AD well-classified (class 3) increased with PLM_R from 38 to 83% in Mpt-1 and from 33 to 53% in Mpt-2. A sharp reduction of the discordant profiles going from 34 to 16.3% and from 37.5 to 19.8%, for Mtp-1 and Mtp-2 respectively, was also observed. The AUC of the PLM_R scale was 0.94 in Mtp-1 and 0.87 in Mtp-2. In both cohorts, the PLM_R outperformed CSF Aβ42 or Aβ42/40 ratio. The diagnostic performance was improved with the PLM_R with an NRI equal to 44.3% in Mtp-1 and 28.8% in Mtp-2. Conclusion: The integration of the Aβ42/Aβ40 ratio in the PLM_R scale resulted in an easy-to-use tool which reduced the discrepancies in biologically doubtful cases and increased the confidence in the diagnosis in memory center.

Emerging topics and practical aspects for an appropriate use of amyloid PET in the current Italian context

In May 2017 some representatives of the Italian nuclear medicine and neurological communities spontaneously met to discuss the issues emerged during the first two years of routine application of amyloid PET with fluorinated radiopharmaceuticals in the real world. The limitations of a binary classification of scans, the possibility to obtain early images as a surrogate marker of regional cerebral bloos flow, the need for (semi-)quantification and, thus, the opportunity of ranking brain amyloidosis, the correlation with Aβ42 levels in the cerebrospinal fluid, the occurrence and biological meaning of uncertain/boderline scans, the issue of incidental amyloidosis, the technical pittfalls leading to false negative/positive results, the position of the tool in the diagnostic flow-chart in the national reality, are the main topics that have been discussed. Also, a card to justify the examination to be filled by the dementia specialist and a card for the nuclear medicine physician to report the exam in detail have been approved and are available in the web, which should facilitate the creation of a national register, as previewed by the 2015 intersocietal recommendation on the use of amyloid PET in Italy. The content of this discussion could stimulate both public institutions and companies to support further research on these topics.

Biomarkers study in atypical dementia: proof of a diagnostic work-up

BACKGROUND

An early differentiation between Alzheimer's Disease (AD) and other dementias is crucial for an adequate patients' management, albeit it may result difficult for the occurrence of "atypical presentations." Current diagnostic criteria recognize the importance of biomarkers for AD diagnosis, but still an optimal diagnostic work-up isn't available.

OBJECTIVE

Evaluate the utility and reproducibility of biomarkers and propose an "optimal" diagnostic work-up in atypical dementia.

METHODS

(1) a retrospective selection of "atypical dementia cases"; (2) a repetition of diagnostic assessment by two neurologists following two different diagnostic work-ups, each consisting of multiple steps; (3) a comparison between diagnostic accuracy and confidence reached at each step by both neurologists and evaluation of the inter-rater agreement.

RESULTS

In AD, regardless of the undertaken diagnostic work-up, a significant gain in accuracy was reached by both neurologists after the second step, whereas in frontotemporal dementia (FTD), adding subsequent steps was not always sufficient to increase significantly the baseline accuracy. A relevant increment in diagnostic confidence was detectable after studying pathophysiological markers in AD, and after assessing brain metabolism in FTD. The inter-rater agreement was higher at the second step for the AD group when the pathophysiological markers were available and for the FTD group when the results of FDG-PET were accessible.

CONCLUSIONS

In atypical cases of dementia, biomarkers significantly raise diagnostic accuracy, confidence, and agreement. This study introduces a proof of diagnostic work-up that combines imaging and CSF biomarkers and suggests distinct ways to proceed on the basis of a greater diagnostic likelihood.

The Distinction of Amyloid-β Protein Precursor (AβPP) Ratio in Platelet Between Alzheimer's Disease Patients and Controls: A Systematic Review and Meta-Analysis

To systematically assess the clinical significance of platelet amyloid-β protein precursor (AβPP) ratio between Alzheimer's disease (AD) patients and controls. 14 articles were selected in this analysis by search of databases including PubMed and Web of Science up to December 2016. Random effects models were used to calculate the standardized mean difference (SMD). Subgroup analyses were used to detect the cause of heterogeneity. The result showed a significant drop in platelet AβPP ratio in AD patients compared to controls [SMD: -1.871; 95% CI: (-2.33, -1.41); p < 0.001; I2 = 88.0% ]. Subgroup analysis revealed races or the quality of studies may be the cause of high heterogeneity. This meta-analysis concluded that there is a close association between platelet AβPP ratio and AD. It is necessary to design a sizable sample study to further support that platelet AβPP ratio can be a biomarker of AD.

Identification of Successful Cognitive Aging in the Alzheimer's Disease Neuroimaging Initiative Study

The present prospective observational study aimed to identify the existence of successful cognitive agers among a group of well-defined cognitively healthy older adults (n = 354, mean age = 75 years), and to examine baseline individual-level predictors and associated health outcomes over time. Episodic memory (EM) and executive function (EF) composite scores and multiple health outcomes were obtained annually over 5 years. Potential individual-level predictors that were related to Alzheimer's disease pathology or genetic risk, neurodegeneration, and vascular risks were collected at baseline. Three latent classes with matched age and education were identified using growth mixture modeling: a group of participants who exhibited high, stable EM and EF (40.7% of the sample, "successful agers"); a group who had initial high cognitive performance that declined over time (21.2%, "declining agers"); and a group who had normal (EM) or poor (EF) but stable cognitive performance over time (38.1%, "low stable agers"). The group classification predicted significant differences in the incidence of global cognitive impairment, the development of at least one depressive symptom, and everyday functional impairment. Sex, apolipoprotein E allele 4, amyloid-β1-42, and t-tau significantly contributed to the difference in cognitive trajectories between the successful agers and the other two groups. Characterizing successful cognitive agers who are relatively resistant to both tau and amyloid pathology provides potential pathways for promoting successful cognitive aging and preventing cognitive decline.

Obstructive Sleep Apnea Severity Affects Amyloid Burden in Cognitively Normal Elderly. A Longitudinal Study

RATIONALE

Recent evidence suggests that obstructive sleep apnea (OSA) may be a risk factor for developing mild cognitive impairment and Alzheimer's disease. However, how sleep apnea affects longitudinal risk for Alzheimer's disease is less well understood.

OBJECTIVES

To test the hypothesis that there is an association between severity of OSA and longitudinal increase in amyloid burden in cognitively normal elderly.

METHODS

Data were derived from a 2-year prospective longitudinal study that sampled community-dwelling healthy cognitively normal elderly. Subjects were healthy volunteers between the ages of 55 and 90, were nondepressed, and had a consensus clinical diagnosis of cognitively normal. Cerebrospinal fluid amyloid β was measured using ELISA. Subjects received Pittsburgh compound B positron emission tomography scans following standardized procedures. Monitoring of OSA was completed using a home sleep recording device.

MEASUREMENTS AND MAIN RESULTS

We found that severity of OSA indices (AHIall [F1,88 = 4.26; P < 0.05] and AHI4% [F1,87 = 4.36; P < 0.05]) were associated with annual rate of change of cerebrospinal fluid amyloid β42 using linear regression after adjusting for age, sex, body mass index, and apolipoprotein E4 status. AHIall and AHI4% were not associated with increases in ADPiB-mask (Alzheimer's disease vulnerable regions of interest Pittsburg compound B positron emission tomography mask) most likely because of the small sample size, although there was a trend for AHIall (F1,28 = 2.96, P = 0.09; and F1,28 = 2.32, not significant, respectively).

CONCLUSIONS

In a sample of cognitively normal elderly, OSA was associated with markers of increased amyloid burden over the 2-year follow-up. Sleep fragmentation and/or intermittent hypoxia from OSA are likely candidate mechanisms. If confirmed, clinical interventions for OSA may be useful in preventing amyloid build-up in cognitively normal elderly.

Prevalence of the apolipoprotein E ε4 allele in amyloid β positive subjects across the spectrum of Alzheimer's disease

INTRODUCTION

Apolipoprotein E (APOE) ε4 is the major genetic risk factor for Alzheimer's disease (AD), but its prevalence is unclear because earlier studies did not require biomarker evidence of amyloid β (Aβ) pathology.

METHODS

We included 3451 Aβ+ subjects (853 AD-type dementia, 1810 mild cognitive impairment, and 788 cognitively normal). Generalized estimating equation models were used to assess APOE ε4 prevalence in relation to age, sex, education, and geographical location.

RESULTS

The APOE ε4 prevalence was 66% in AD-type dementia, 64% in mild cognitive impairment, and 51% in cognitively normal, and it decreased with advancing age in Aβ+ cognitively normal and Aβ+ mild cognitive impairment (P < .05) but not in Aβ+ AD dementia (P = .66). The prevalence was highest in Northern Europe but did not vary by sex or education.

DISCUSSION

The APOE ε4 prevalence in AD was higher than that in previous studies, which did not require presence of Aβ pathology. Furthermore, our results highlight disease heterogeneity related to age and geographical location.

Cerebrospinal fluid biomarkers measured by Elecsys assays compared to amyloid imaging

INTRODUCTION

Levels of amyloid β peptide 42 (Aβ42), total tau, and phosphorylated tau-181 are well-established cerebrospinal fluid (CSF) biomarkers of Alzheimer's disease, but variability in manual plate-based assays has limited their use. We examined the relationship between CSF biomarkers, as measured by a novel automated immunoassay platform, and amyloid positron emission tomography.

METHODS

CSF samples from 200 individuals underwent separate analysis for Aβ42, total tau, and phosphorylated tau-181 with automated Roche Elecsys assays. Aβ40 was measured with a commercial plate-based assay. Positron emission tomography with Pittsburgh Compound B was performed less than 1 year from CSF collection.

RESULTS

Ratios of CSF biomarkers (total tau/Aβ42, phosphorylated tau-181/Aβ42, and Aβ42/Aβ40) best discriminated Pittsburgh Compound B-positive from Pittsburgh Compound B-negative individuals.

DISCUSSION

CSF biomarkers and amyloid positron emission tomography reflect different aspects of Alzheimer's disease brain pathology, and therefore, less-than-perfect correspondence is expected. Automated assays are likely to increase the utility of CSF biomarkers.

Young to Middle-Aged Dogs with High Amyloid-β Levels in Cerebrospinal Fluid are Impaired on Learning in Standard Cognition tests

Understanding differences in Alzheimer’s disease biomarkers before the pathology becomes evident can contribute to an improved understanding of disease pathogenesis and treatment. A decrease in amyloid-β (Aβ)₄₂ in cerebrospinal fluid (CSF) is suggested to be a biomarker for Aβ deposition in brain. However, the relevance of CSF Aβ levels prior to deposition is not entirely known. Dogs are similar to man with respect to amyloid-β protein precursor (AβPP)-processing, age-related amyloid plaque deposition, and cognitive dysfunction. In the current study, we evaluated the relation between CSF Aβ₄₂ levels and cognitive performance in young to middle-aged dogs (1.5–7 years old). Additionally, CSF sAβPPα and sAβPPβ were measured to evaluate AβPP processing, and CSF cytokines were measured to determine the immune status of the brain. We identified two groups of dogs showing consistently low or high CSF Aβ₄₂ levels. Based on prior studies, it was assumed that at this age no cerebral amyloid plaques were likely to be present. The cognitive performance was evaluated in standard cognition tests. Low or high Aβ concentrations coincided with low or high sAβPPα, sAβPPβ, and CXCL-1 levels, respectively. Dogs with high Aβ concentrations showed significant learning impairments on delayed non-match to position (DNMP), object discrimination, and reversal learning compared to dogs with low Aβ concentrations. Our data support the hypothesis that high levels of CSF Aβ in dogs coincide with lower cognitive performance prior to amyloid deposition. Further experiments are needed to investigate this link, as well as the relevance with respect to Alzheimer’s disease pathology progression.

The Cerebrospinal Fluid Neurogranin/BACE1 Ratio is a Potential Correlate of Cognitive Decline in Alzheimer's Disease

Background: In diagnosing Alzheimer’s disease (AD), ratios of cerebrospinal fluid (CSF) biomarkers, such as CSF Aβ_1-42/tau, have an improved diagnostic performance compared to the single analytes, yet, still a limited value to predict cognitive decline. Since synaptic dysfunction/loss is closely linked to cognitive impairment, synaptic proteins are investigated as candidate CSF AD progression markers.

Objective: We studied CSF levels of the postsynaptic protein neurogranin and protein BACE1, predominantly localized presynaptically, and their relation to CSF total-tau, Aβ_1-42, Aβ_1-40, and Aβ_1-38. All six analytes were considered as single parameters as well as ratios.

Methods: Every ELISA involved was based on monoclonal antibodies, including the BACE1 and neurogranin immunoassay. The latter specifically targets neurogranin C-terminally truncated at P75, a more abundant species of the protein in CSF. We studied patients with MCI due to AD (n = 38) and 50 dementia due to AD patients, as well as age-matched cognitively healthy elderly (n = 20). A significant subset of the patients was followed up by clinical and neuropsychologically (MMSE) examinations for at least one year.

Results: The single analytes showed statistically significant differences between the clinical groups, but the ratios of analytes indeed had a higher diagnostic performance. Furthermore, only the ratio of CSF neurogranin trunc P75/BACE1 was significantly correlated with the yearly decline in MMSE scores in patients with MCI and dementia due to AD, pointing toward the prognostic value of the ratio.

Conclusion: This is the first study demonstrating that the CSF neurogranin trunc P75/BACE1 ratio, reflecting postsynaptic/presynaptic integrity, is related to cognitive decline.

Optimized Standard Operating Procedures for the Analysis of Cerebrospinal Fluid Aβ42 and the Ratios of Aβ Isoforms Using Low Protein Binding Tubes

Background: Reduced cerebrospinal fluid (CSF) concentration of amyloid-β_1-42 (Aβ_1-42) reflects the presence of amyloidopathy in brains of subjects with Alzheimer’s disease (AD).

Objective: To qualify the use of Aβ_1-42/Aβ_1-40 for improvement of standard operating procedures (SOP) for measurement of CSF Aβ with a focus on CSF collection, storage, and analysis.

Methods: Euroimmun ELISAs for CSF Aβ isoforms were used to set up a SOP with respect to recipient properties (low binding, polypropylene), volume of tubes, freeze/thaw cycles, addition of detergents (Triton X-100, Tween-20) in collection or storage tubes or during CSF analysis. Data were analyzed with linear repeated measures and mixed effects models.

Results: Optimization of CSF analysis included a pre-wash of recipients (e.g., tubes, 96-well plates) before sample analysis. Using the Aβ_1-42/Aβ_1-40 ratio, in contrast to Aβ_1-42, eliminated effects of tube type, additional freeze/thaw cycles, or effect of CSF volumes for polypropylene storage tubes. ‘Low binding’ tubes reduced the loss of Aβ when aliquoting CSF or in function of additional freeze/thaw cycles. Addition of detergent in CSF collection tubes resulted in an almost complete absence of variation in function of collection procedures, but affected the concentration of Aβ isoforms in the immunoassay.

Conclusion: The ratio of Aβ_1-42/Aβ_1-40 is a more robust biomarker than Aβ_1-42 toward (pre-) analytical interfering factors. Further, ‘low binding’ recipients and addition of detergent in collection tubes are able to remove effects of SOP-related confounding factors. Integration of the Aβ_1-42/Aβ_1-40 ratio and ‘low-binding tubes’ into guidance criteria may speed up worldwide standardization of CSF biomarker analysis.

Performance Evaluation of an Automated ELISA System for Alzheimer's Disease Detection in Clinical Routine

The variability of Alzheimer's disease (AD) cerebrospinal fluid (CSF) biomarkers undermines their full-fledged introduction into routine diagnostics and clinical trials. Automation may help to increase precision and decrease operator errors, eventually improving the diagnostic performance. Here we evaluated three new CSF immunoassays, EUROIMMUNtrademark amyloid-β 1-40 (Aβ1-40), amyloid-β 1-42 (Aβ1-42), and total tau (t-tau), in combination with automated analysis of the samples. The CSF biomarkers were measured in a cohort consisting of AD patients (n = 28), mild cognitive impairment (MCI, n = 77), and neurological controls (OND, n = 35). MCI patients were evaluated yearly and cognitive functions were assessed by Mini-Mental State Examination. The patients clinically diagnosed with AD and MCI were classified according to the CSF biomarkers profile following NIA-AA criteria and the Erlangen score. Technical evaluation of the immunoassays was performed together with the calculation of their diagnostic performance. Furthermore, the results for EUROIMMUN Aβ1-42 and t-tau were compared to standard immunoassay methods (INNOTESTtrademark). EUROIMMUN assays for Aβ1-42 and t-tau correlated with INNOTEST (r = 0.83, p < 0.001 for both) and allowed a similar interpretation of the CSF profiles. The Aβ1-42/Aβ1-40 ratio measured with EUROIMMUN was the best parameter for AD detection and improved the diagnostic accuracy of Aβ1-42 (area under the curve = 0.93). In MCI patients, the Aβ1-42/Aβ1-40 ratio was associated with cognitive decline and clinical progression to AD.The diagnostic performance of the EUROIMMUN assays with automation is comparable to other currently used methods. The variability of the method and the value of the Aβ1-42/Aβ1-40 ratio in AD diagnosis need to be validated in large multi-center studies.

Comparing 18F-AV-1451 with CSF t-tau and p-tau for diagnosis of Alzheimer disease

Objective

To compare PET imaging of tau pathology with CSF measurements (total tau [t-tau] and phosphorylated tau [p-tau]) in terms of diagnostic performance for Alzheimer disease (AD).

Methods

We compared t-tau and p-tau and ¹⁸F-AV-1451 in 30 controls, 14 patients with prodromal AD, and 39 patients with Alzheimer dementia, recruited from the Swedish BioFINDER study. All patients with AD (prodromal and dementia) were screened for amyloid positivity using CSF β-amyloid 42. Retention of ¹⁸F-AV-1451 was measured in a priori specified regions, selected for known associations with tau pathology in AD.

Results

Retention of ¹⁸F-AV-1451 was markedly elevated in Alzheimer dementia and moderately elevated in prodromal AD. CSF t-tau and p-tau was increased to similar levels in both AD dementia and prodromal AD. ¹⁸F-AV-1451 had very good diagnostic performance for Alzheimer dementia (area under the receiver operating characteristic curve [AUROC] ∼1.000), and was significantly better than t-tau (0.876), p-tau (0.890), hippocampal volume (0.824), and temporal cortical thickness (0.860). For prodromal AD, there were no significant AUROC differences between CSF tau and ¹⁸F-AV-1451 measures (0.836–0.939), but MRI measures had lower AUROCs (0.652–0.769).

Conclusions

CSF tau and ¹⁸F-AV-1451 have equal performance in early clinical stages of AD, but ¹⁸F-AV-1451 is superior in the dementia stage, and exhibits close to perfect diagnostic performance for mild to moderate AD.

Classification of evidence

This study provides Class III evidence that CSF tau and ¹⁸F-AV-1451 PET have similar performance in identifying early AD, and that ¹⁸F-AV-1451 PET is superior to CSF tau in identifying mild to moderate AD.

Fluid and imaging biomarkers for Alzheimer's disease: Where we stand and where to head to

There is increasing evidence that a number of potentially informative biomarkers for Alzheimer disease (AD) can improve the accuracy of diagnosing this form of dementia, especially when used as a panel of diagnostic assays and interpreted in the context of neuroimaging and clinical data. Moreover, by combining the power of CSF biomarkers with neuroimaging techniques to visualize Aβ deposits (or neurodegenerative lesions), it might be possible to better identify individuals at greatest risk for developing MCI and converting to AD. The objective of this article was to review recent progress in selected imaging and chemical biomarkers for prediction, early diagnosis and progression of AD. We present our view point of a scenario that places CSF and imaging markers on the verge of general utility based on accuracy levels that already match (or even surpass) current clinical precision.

A Systematic Review and Aggregated Analysis on the Impact of Amyloid PET Brain Imaging on the Diagnosis, Diagnostic Confidence, and Management of Patients being Evaluated for Alzheimer's Disease

BACKGROUND

Amyloid PET (aPET) imaging could improve patient outcomes in clinical practice, but the extent of impact needs quantification.

OBJECTIVE

To provide an aggregated quantitative analysis of the value added by aPET in cognitively impaired subjects.

METHODS

Systematic literature searches were performed in Embase and Medline until January 2017. 1,531 cases over 12 studies were included (1,142 cases over seven studies in the primary analysis where aPET was the key biomarker; the remaining cases included as defined groups in the secondary analysis). Data was abstracted by consensus among two observers and assessed for bias. Clinical utility was measured by diagnostic change, diagnostic confidence, and patient management before and after aPET. Three groups were further analyzed: control patients for whom feedback of aPET scan results was delayed; aPET Appropriate Use Criteria (AUC+) cases; and patients undergoing additional FDG/CSF testing.

RESULTS

For 1,142 cases with only aPET, 31.3% of diagnoses were revised, whereas 3.2% of diagnoses changed in the delayed aPET control group (p < 0.0001). Increased diagnostic confidence following aPET was found for 62.1% of 870 patients. Management changes with aPET were found in 72.2% of 740 cases and in 55.5% of 299 cases in the control group (p < 0.0001). The diagnostic value of aPET in AUC+ patients or when FDG/CSF were additionally available did not substantially differ from the value of aPET alone in the wider population.

CONCLUSIONS

Amyloid PET contributed to diagnostic revision in almost a third of cases and demonstrated value in increasing diagnostic confidence and refining management plans.

Amyloid Network Topology Characterizes the Progression of Alzheimer's Disease During the Predementia Stages

There is increasing evidence showing that the accumulation of the amyloid-β (Aβ) peptide into extracellular plaques is a central event in Alzheimer's disease (AD). These abnormalities can be detected as lowered levels of Aβ42 in the cerebrospinal fluid (CSF) and are followed by increased amyloid burden on positron emission tomography (PET) several years before the onset of dementia. The aim of this study was to assess amyloid network topology in nondemented individuals with early stage Aβ accumulation, defined as abnormal CSF Aβ42 levels and normal Florbetapir PET (CSF+/PET-), and more advanced Aβ accumulation, defined as both abnormal CSF Aβ42 and Florbetapir PET (CSF+/PET+). The amyloid networks were built using correlations in the mean 18F-florbetapir PET values between 72 brain regions and analyzed using graph theory analyses. Our findings showed an association between early amyloid stages and increased covariance as well as shorter paths between several brain areas that overlapped with the default-mode network (DMN). Moreover, we found that individuals with more advanced amyloid accumulation showed more widespread changes in brain regions both within and outside the DMN. These findings suggest that amyloid network topology could potentially be used to assess disease progression in the predementia stages of AD.

Concordance Between Different Amyloid Immunoassays and Visual Amyloid Positron Emission Tomographic Assessment

Importance

Visual assessment of amyloid positron emission tomographic (PET) images has been approved by regulatory authorities for clinical use. Several immunoassays have been developed to measure β-amyloid (Aβ) 42 in cerebrospinal fluid (CSF). The agreement between CSF Aβ42 measures from different immunoassays and visual PET readings may influence the use of CSF biomarkers and/or amyloid PET assessment in clinical practice and trials.

Objective

To determine the concordance between CSF Aβ42 levels measured using 5 different immunoassays and visual amyloid PET analysis.

Design, Setting, and Participants

The study included 262 patients with mild cognitive impairment or subjective cognitive decline from the Swedish BioFINDER (Biomarkers for Identifying Neurodegenerative Disorders Early and Reliably) cohort (recruited from September 1, 2010, through December 31, 2014) who had undergone flutemetamol F 18 ([18F]flutemetamol)-labeled PET. Levels of CSF Aβ42 were analyzed using the classic INNOTEST and the newer modified INNOTEST, fully automated Lumipulse (FL), EUROIMMUN (EI), and Meso Scale Discovery (MSD) assays. Concentrations of CSF Aβ were assessed using an antibody-independent mass spectrometry-based reference measurement procedure.

Main Outcomes and Measures

The concordance of CSF Aβ42 levels and Aβ42:Aβ40 and Aβ42:tau ratios with visual [18F]flutemetamol PET status.

Results

Of 262 participants (mean [SD] age, 70.9 [5.5] years), 108 were women (41.2%) and 154 were men (58.8%). The mass spectrometry-derived Aβ42 values showed higher correlations with the modified Aβ42-INNOTEST (r = 0.97), Aβ42-FL (r = 0.93), Aβ42-EI (r = 0.93), and Aβ42-MSD (r = 0.95) assays compared with the classic Aβ42-INNOTEST assay (r = 0.88; P ≤ .01). The signal in the classic Aβ42-INNOTEST assay was partly quenched by recombinant Aβ1-40 peptide. However, the classic Aβ42-INNOTEST assay showed better concordance with visual [18F]flutemetamol PET status (area under the receiver operating characteristic curve [AUC], 0.92) compared with the newer assays (AUCs, 0.87-0.89; P ≤ .01). The accuracies of the newer assays improved significantly when Aβ42:Aβ40 (AUCs, 0.93-0.95; P ≤ .01), Aβ42 to total tau (T-tau) (AUCs, 0.94; P ≤ .05), or Aβ42 to phosphorylated tau (P-tau) (AUCs, 0.94-0.95; P ≤ .001) ratios were used. A combination of the Aβ42:Aβ40 ratio and T-tau or P-tau level did not improve the accuracy compared with the ratio alone.

Conclusions and Relevance

Concentrations of CSF Aβ42 derived from the new immunoassays (modified INNOTEST, FL, EI, and MSD) may correlate better with the antibody-independent mass spectrometry-based reference measurement procedure and may show improved agreement with visual [18F]flutemetamol PET assessment when using the Aβ42:Aβ40 or Aβ42:tau ratios. These findings suggest the benefit of implementing the CSF Aβ42:Aβ40 or Aβ42:tau ratios as a biomarker of amyloid deposition in clinical practice and trials.

Factors influencing accuracy of cortical thickness in the diagnosis of Alzheimer's disease

There is great value to use of structural neuroimaging in the assessment of Alzheimer's disease (AD). However, to date, predictive value of structural imaging tend to range between 80% and 90% in accuracy and it is unclear why this is the case given that structural imaging should parallel the pathologic processes of AD. There is a possibility that clinical misdiagnosis relative to the gold standard pathologic diagnosis and/or additional brain pathologies are confounding factors contributing to reduced structural imaging classification accuracy. We examined potential factors contributing to misclassification of individuals with clinically diagnosed AD purely from cortical thickness measures. Correctly classified and incorrectly classified groups were compared across a range of demographic, biological, and neuropsychological data including cerebrospinal fluid biomarkers, amyloid imaging, white matter hyperintensity (WMH) volume, cognitive, and genetic factors. Individual subject analyses suggested that at least a portion of the control individuals misclassified as AD from structural imaging additionally harbor substantial AD biomarker pathology and risk, yet are relatively resistant to cognitive symptoms, likely due to "cognitive reserve," and therefore clinically unimpaired. In contrast, certain clinical control individuals misclassified as AD from cortical thickness had increased WMH volume relative to other controls in the sample, suggesting that vascular conditions may contribute to classification accuracy from cortical thickness measures. These results provide examples of factors that contribute to the accuracy of structural imaging in predicting a clinical diagnosis of AD, and provide important information about considerations for future work aimed at optimizing structural based diagnostic classifiers for AD.

Combining viscoelasticity, diffusivity and volume of the hippocampus for the diagnosis of Alzheimer's disease based on magnetic resonance imaging

Dementia due to Alzheimer's Disease (AD) is a neurodegenerative disease for which treatment strategies at an early stage are of great clinical importance. So far, there is still a lack of non-invasive diagnostic tools to sensitively detect AD in early stages and to predict individual disease progression. Magnetic resonance elastography (MRE) of the brain may be a promising novel tool. In this proof-of-concept study, we investigated whether multifrequency-MRE (MMRE) can detect differences in hippocampal stiffness between patients with clinical diagnosis of dementia due to AD and healthy controls (HC). Further, we analyzed if the combination of three MRI-derived parameters, i.e., hippocampal stiffness, hippocampal volume and mean diffusivity (MD), improves diagnostic accuracy.

Diagnostic criteria for probable dementia due to AD were in line with the NINCDS-ADRDA criteria and were verified through history-taking (patient and informant), neuropsychological testing, routine blood results and routine MRI to exclude other medical causes of a cognitive decline.

21 AD patients and 21 HC (median age 75 years) underwent MMRE and structural MRI, from which hippocampal volume and MD were calculated. From the MMRE-images maps of the magnitude |G*| and phase angle φ of the complex shear modulus were reconstructed using multifrequency inversion. Median values of |G*| and φ were extracted within three regions of interest (hippocampus, thalamus and whole brain white matter). To test the predictive value of the main outcome parameters, we performed receiver operating characteristic (ROC) curve analyses.

Hippocampal stiffness (|G*|) and viscosity (φ) were significantly lower in the patient group (both p < 0.001). ROC curve analyses showed an area under the curve (AUC) for | G*| of 0.81 [95%CI 0.68–0.94]; with sensitivity 86%, specificity 67% for cutoff at |G*| = 980 Pa) and for φ an AUC of 0.79 [95%CI 0.66–0.93]. In comparison, the AUC of MD and hippocampal volume were 0.83 [95%CI 0.71–0.95] and 0.86 [95%CI 0.74–0.97], respectively. A combined ROC curve of |G*|, MD and hippocampal volume yielded a significantly improved AUC of 0.90 [95%CI 0.81–0.99].

In conclusion, we demonstrated reduced hippocampal stiffness and reduced hippocampal viscosity, as determined by MMRE, in patients with clinical diagnosis of dementia of the AD type. Diagnostic sensitivity was further improved by the combination with two other MRI-based hippocampal parameters. These findings motivate further investigation whether MMRE can detect decreased brain stiffness already in pre-dementia stages, and whether these changes predict cognitive decline.

•

Non-invasive methods for early detection of AD are lacking.

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MRE of the brain is a promising new non-invasive diagnostic tool.

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We demonstrate reduced hippocampal stiffness (|G*|) in AD patients.

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|G*| distinguishes healthy and demented with 86% sensitivity and 67% specificity.

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Combining hippocampal stiffness, MD and volume improved diagnostic accuracy.

Tau-mediated Neurodegeneration and Potential Implications in Diagnosis and Treatment of Alzheimer's Disease

OBJECTIVE

To review recent research advances on tau, a major player in Alzheimer's disease (AD) pathogenesis, a biomarker for AD onset, and potential target for AD therapy.

DATA SOURCES

This review was based on a comprehensive search using online literature databases, including PubMed, Web of Science, and Google Scholar.

STUDY SELECTION

Literature search was based on the following keywords: Alzheimer's disease, tau protein, biomarker, cerebrospinal fluid (CSF), therapeutics, plasma, imaging, propagation, spreading, seeding, prion, conformational templating, and posttranslational modification. Relevant articles were carefully reviewed, with no exclusions applied to study design and publication type.

RESULTS

Amyloid plaques enriched with extracellular amyloid beta (Aβ) and intracellular neurofibrillary tangles comprised of hyperphosphorylated tau proteins are the two main pathological hallmarks of AD. Although the Aβ hypothesis has dominated AD research for many years, clinical Aβ-targeting strategies have consistently failed to effectively treat AD or prevent AD onset. The research focus in AD has recently shifted to the role of tau in AD. In addition to phosphorylation, tau is acetylated and proteolytically cleaved, which also contribute to its physiological and pathological functions. Emerging evidence characterizing pathological tau propagation and spreading provides new avenues for research into the molecular and cellular mechanisms underlying AD pathogenesis. Techniques to detect tau at minute levels in CSF and blood have been developed, and improved tracers have facilitated tau imaging in the brain. These advances have potential to accurately determine tau levels at early diagnostic stages in AD. Given that tau is a potential therapeutic target, anti-tau immunotherapy may potentially be a viable treatment strategy in AD intervention.

CONCLUSION

Detecting changes in tau and targeting tau pathology represent a promising lead in the diagnosis and treatment of AD.

Screening Utility of the King-Devick Test in Mild Cognitive Impairment and Alzheimer Disease Dementia

The King-Devick (K-D) test is a 1 to 2 minute, rapid number naming test, often used to assist with detection of concussion, but also has clinical utility in other neurological conditions (eg, Parkinson disease). The K-D involves saccadic eye and other eye movements, and abnormalities thereof may be an early indicator of Alzheimer disease (AD)-associated cognitive impairment. No study has tested the utility of the K-D in AD and we sought to do so. The sample included 206 [135 controls, 39 mild cognitive impairment (MCI), and 32 AD dementia] consecutive subjects from the Boston University Alzheimer's Disease Center registry undergoing their initial annual evaluation between March 2013 and July 2015. The K-D was administered during this period. Areas under the receiver operating characteristic curves generated from logistic regression models revealed the K-D test distinguished controls from subjects with cognitive impairment (MCI and AD dementia) [area under the curve (AUC)=0.72], MCI (AUC=0.71) and AD dementia (AUC=0.74). K-D time scores between 48 and 52 seconds were associated with high sensitivity (>90.0%) and negative predictive values (>85.0%) for each diagnostic group. The K-D correlated strongly with validated attention, processing speed, and visual scanning tests. The K-D test may be a rapid and simple effective screening tool to detect cognitive impairment associated with AD.

Earliest accumulation of β-amyloid occurs within the default-mode network and concurrently affects brain connectivity

It is not known exactly where amyloid-β (Aβ) fibrils begin to accumulate in individuals with Alzheimer’s disease (AD). Recently, we showed that abnormal levels of Aβ42 in cerebrospinal fluid (CSF) can be detected before abnormal amyloid can be detected using PET in individuals with preclinical AD. Using these approaches, here we identify the earliest preclinical AD stage in subjects from the ADNI and BioFINDER cohorts. We show that Aβ accumulation preferentially starts in the precuneus, medial orbitofrontal, and posterior cingulate cortices, i.e., several of the core regions of the default mode network (DMN). This early pattern of Aβ accumulation is already evident in individuals with normal Aβ42 in the CSF and normal amyloid PET who subsequently convert to having abnormal CSF Aβ42. The earliest Aβ accumulation is further associated with hypoconnectivity within the DMN and between the DMN and the frontoparietal network, but not with brain atrophy or glucose hypometabolism. Our results suggest that Aβ fibrils start to accumulate predominantly within certain parts of the DMN in preclinical AD and already then affect brain connectivity.

Abnormal levels of Aβ42 in the cerebrospinal fluid occur prior to a positive amyloid PET scan in the brain of individuals with Alzheimer’s disease and here the authors use this temporal pattern to identify individuals with very early stage AD. They show that Aβ fibrils start to accumulate in some of the regions of the default mode network and affect brain connectivity before neurodegeneration occurs.

Modeling the Relationships Among Late-Life Body Mass Index, Cerebrovascular Disease, and Alzheimer's Disease Neuropathology in an Autopsy Sample of 1,421 Subjects from the National Alzheimer's Coordinating Center Data Set

The relationship between late-life body mass index (BMI) and Alzheimer's disease (AD) is poorly understood due to the lack of research in samples with autopsy-confirmed AD neuropathology (ADNP). The role of cerebrovascular disease (CVD) in the interplay between late-life BMI and ADNP is unclear. We conducted a retrospective longitudinal investigation and used joint modeling of linear mixed effects to investigate causal relationships among repeated antemortem BMI measurements, CVD (quantified neuropathologically), and ADNP in an autopsy sample of subjects across the AD clinical continuum. The sample included 1,421 subjects from the National Alzheimer's Coordinating Center's Uniform Data Set and Neuropathology Data Set with diagnoses of normal cognition (NC; n = 234), mild cognitive impairment (MCI; n = 201), or AD dementia (n = 986). ADNP was defined as moderate to frequent neuritic plaques and Braak stageIII-VI. Ischemic Injury Scale (IIS) operationalized CVD. Joint modeling examined relationships among BMI, IIS, and ADNP in the overall sample and stratified by initial visit Clinical Dementia Rating score. Subject-specific random intercept for BMI was the predictor for ADNP due to minimal BMI change (p = 0.3028). Analyses controlling for demographic variables and APOE ɛ4 showed lower late-life BMI predicted increased odds of ADNP in the overall sample (p < 0.001), and in subjects with CDR of 0 (p = 0.0021) and 0.5 (p = 0.0012), but not ≥1.0 (p = 0.2012). Although higher IIS predicted greater odds of ADNP (p < 0.0001), BMI did not predict IIS (p = 0.2814). The current findings confirm lower late-life BMI confers increased odds for ADNP. Lower late-life BMI may be a preclinical indicator of underlying ADNP.

Filling the void: a role for exercise-induced BDNF and brain amyloid precursor protein processing

Inactivity, obesity, and insulin resistance are significant risk factors for the development of Alzheimer's disease (AD). Several studies have demonstrated that diet-induced obesity, inactivity, and insulin resistance exacerbate the neuropathological hallmarks of AD. The aggregation of β-amyloid peptides is one of these hallmarks. β-Site amyloid precursor protein-cleaving enzyme 1 (BACE1) is the rate-limiting enzyme in amyloid precursor protein (APP) processing, leading to β-amyloid peptide formation. Understanding how BACE1 content and activity are regulated is essential for establishing therapies aimed at reducing and/or slowing the progression of AD. Exercise training has been proven to reduce the risk of AD as well as decrease β-amyloid production and BACE1 content and/or activity. However, these long-term interventions also result in improvements in adiposity, circulating metabolites, glucose tolerance, and insulin sensitivity making it difficult to determine the direct effects of exercise on brain APP processing. This review highlights this large void in our knowledge and discusses our current understanding of the direct of effect of exercise on β-amyloid production. We have concentrated on the central role that brain-derived neurotrophic factor (BDNF) may play in mediating the direct effects of exercise on reducing brain BACE1 content and activity as well as β-amyloid production. Future studies should aim to generate a greater understanding of how obesity and exercise can directly alter APP processing and AD-related pathologies. This knowledge could provide evidence-based hypotheses for designing therapies to reduce the risk of AD and dementia.

In vivo retention of 18F-AV-1451 in corticobasal syndrome

Objective:

To study the usefulness of ¹⁸F-AV-1451 PET in patients with corticobasal syndrome (CBS).

Methods:

We recruited 8 patients with CBS, 17 controls, 31 patients with Alzheimer disease (AD), and 11 patients with progressive supranuclear palsy (PSP) from the Swedish BioFINDER study. All patients underwent clinical assessment, ¹⁸F-AV-1451 PET, MRI, and quantification of β-amyloid pathology. A subset of participants also underwent ¹⁸F-FDG-PET.

Results:

In the 8 patients with CBS, 6 had imaging findings compatible with the corticobasal degeneration pathology and 2 with typical AD pathology. In the 6 patients with CBS without typical AD pathology, there were substantial retentions of ¹⁸F-AV-1451 in the motor cortex, corticospinal tract, and basal ganglia contralateral to the most affected body side. These patients could be clearly distinguished from patients with AD dementia or PSP using ¹⁸F-AV-1451. However, cortical atrophy was more widespread than the cortical retention of ¹⁸F-AV1451 in these CBS cases, and cortical AV-1451 uptake did not correlate with cortical thickness or glucose hypometabolism. These results are in sharp contrast to AD dementia, where ¹⁸F-AV-1451 retention was more widespread than cortical atrophy, and correlated well with cortical thickness and hypometabolism.

Conclusions:

Patients with CBS without typical AD pathology exhibited AV-1451 retention in the motor cortex, corticospinal tract, and basal ganglia contralateral to the affected body side, clearly different from controls and patients with AD dementia or PSP. However, cortical atrophy measured with MRI and decreased ¹⁸F-fluorodeoxyglucose uptake were more widespread than ¹⁸F-AV-1451 uptake and probably represent earlier, yet less specific, markers of CBS.

Classification of evidence:

This study provides Class III evidence that ¹⁸F-AV-1451 PET distinguishes between CBS and AD or PSP.

Amyloid Beta and Tau as Alzheimer's Disease Blood Biomarkers: Promise From New Technologies

The utility of the levels of amyloid beta (Aβ) peptide and tau in blood for diagnosis, drug development, and assessment of clinical trials for Alzheimer's disease (AD) has not been established. The lack of availability of ultra-sensitive assays is one critical issue that has impeded progress. The levels of Aβ species and tau in plasma and serum are much lower than levels in cerebrospinal fluid. Furthermore, plasma or serum contain high levels of assay-interfering factors, resulting in difficulties in the commonly used singulex or multiplex ELISA platforms. In this review, we focus on two modern immune-complex-based technologies that show promise to advance this field. These innovative technologies are immunomagnetic reduction technology and single molecule array technology. We describe the technologies and discuss the published studies using these technologies. Currently, the potential of utilizing these technologies to advance Aβ and tau as blood-based biomarkers for AD requires further validation using already collected large sets of samples, as well as new cohorts and population-based longitudinal studies.

A Review of Fluid Biomarkers for Alzheimer's Disease: Moving from CSF to Blood

A set of core cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease (AD) includes total tau (T-tau), phosphorylated tau (P-tau) and β-amyloid 42 (Aβ42). These biomarkers reflect some of the key aspects of AD pathophysiology, including neuronal degeneration, tau phosphorylation with tangle formation, and Aβ aggregation with deposition of the peptide into plaques. The core AD CSF biomarkers have been validated clinically in numerous studies, and found to have a very high diagnostic performance to identify AD, both in the dementia and in the mild cognitive impairment stages of the disease. CSF Aβ42 has also been found to show very high concordance with amyloid PET to identify brain amyloid deposition. The synaptic protein neurogranin is a novel candidate CSF biomarker for AD and prodromal AD. High CSF neurogranin predicts future cognitive decline and seems to be more specific for AD than, for example, T-tau. Importantly, technical developments have given ultrasensitive measurement techniques that allow measurement of brain-specific proteins such as tau and neurofilament light (NFL) in blood samples. Both plasma tau and NFL are increased in AD, and a recent study showed that plasma NFL has a diagnostic performance comparable to the core AD CSF biomarkers, and predicted future cognitive decline. Future large longitudinal clinical studies are warranted to determine the potential for plasma tau and NFL to serve as first-in-line screening tools for neurodegeneration in primary care.

A multinational study distinguishing Alzheimer's and healthy patients using cerebrospinal fluid tau/Aβ42 cutoff with concordance to amyloid positron emission tomography imaging

Introduction

Changes in cerebrospinal fluid (CSF) tau and amyloid β (Aβ)42 accompany development of Alzheimer's brain pathology. Robust tau and Aβ42 immunoassays were developed to establish a tau/Aβ42 cutoff distinguishing mild-to-moderate Alzheimer's disease (AD) subjects from healthy elderly control (HC) subjects.

Methods

A CSF tau/Aβ42 cutoff criteria was chosen, which distinguished the groups and maximized concordance with amyloid PET. Performance was assessed using an independent validation cohort.

Results

A tau/Aβ42 = 0.215 cutoff provided 94.8% sensitivity and 77.7% specificity. Concordance with PET visual reads was estimated at 86.9% in a ∼50% PET positive population. In the validation cohort, the cutoff demonstrated 78.4% sensitivity and 84.9% specificity to distinguish the AD and HC populations.

Discussion

A tau/Aβ42 cutoff with acceptable sensitivity and specificity distinguished HC from mild-to-moderate AD subjects and maximized concordance to brain amyloidosis. The defined cutoff demonstrated that CSF analysis may be useful as a surrogate to imaging assessment of AD pathology.

Diagnostic Validity Comparison Between Criteria Based on CSF Alzheimer's Disease Biomarkers

AIM

To compare the diagnostic validity of NIA-AA criteria, for AD CSF biomarkers, with our own new criteria.

MATERIALS AND METHODS

Between 2008 and 2011, 170 patients with Mild Cognitive Impairment (MCI) were included. CSF levels of Aβ1-42, T-tau, P-tau181, and ratios of T-tau/Aβ1-42 and P-tau181/Aβ1-42 were analyzed. In our criteria, we considered 3 or more abnormal variables indicative of a high likelihood of MCI due to AD.

RESULTS

After a clinical follow-up of 4.5 ± 1.2 years, 44 patients remained stable, 95 developed AD, 15 other forms of dementia, 7 died and 9 received other diagnoses. Using the NIA-AA criteria and our own criteria, the diagnostic validity of the CSF biomarkers was 58% versus 85%, specificity 84% versus 72%, PPV 82% versus 79% and NPV 61% versus 79%.

CONCLUSION

The inclusion of the ratios in diagnostic criteria increases sensitivity and NPV for the diagnosis of MCI due to AD.

Alzheimer disease: CSF biomarkers for Alzheimer disease - approaching consensus

A European working group has provided a new set of recommendations for the use of cerebrospinal fluid (CSF) biomarkers in the diagnostic evaluation of Alzheimer disease and mild cognitive impairment. These recommendations represent an important step towards the implementation of CSF biomarker tests in the clinic, but several challenges remain.

Decision-Making Deficits Associated with Amyloidosis in Lewy Body Disorders

Background: Lewy body disorders (LBD) are clinical syndromes characterized by pathological inclusions containing α-synuclein. Cognitive deficits are common or diagnostic in LBD, and may be associated with the presence of beta-amyloid (Aβ), which is a hallmark histopathologic abnormality characteristic of Alzheimer's disease (AD) that can also co-occur with LBD.

Objective: In the present study we evaluated whether social decision-making difficulties in LBD are associated with Aβ burden.

Methods: Decision-making abilities were measured with a simple, untimed, behavioral task previously validated in patients with behavioral variant frontotemporal dementia, and performance was related to gray matter atrophy on MRI. Aβ burden was assessed by examination of cerebrospinal fluid (CSF) level of Aβ₁₋₄₂ and by autopsy confirmation in a subgroup of patients.

Results: The results revealed that LBD patients with evidence of Aβ have reduced social decision-making abilities compared to patients with no evidence of Aβ. The imaging analysis related greater decision-making difficulty in Aβ-positive patients in respect to Aβ-negative patients to gray matter atrophy in medial orbitofrontal. This region is a critical node of a decision-making network as well as a region previously associated with comorbid α-synuclein and Aβ in LBD.

Conclusions: These preliminary findings suggest that cognitive difficulties in LBD extend to include deficits in social decision-making and that this may be related to the presence of Aβ.

Plasma concentrations of free amyloid β cannot predict the development of Alzheimer's disease

INTRODUCTION

Biomarkers that identify individuals at risk of Alzheimer's disease (AD) development would be highly valuable. Plasma concentration of amyloid β (Aβ)-central in the pathogenesis of AD-is a logical candidate, but studies to date have produced conflicting results on its utility.

METHODS

Plasma samples from 339 preclinical AD cases (76.4% women, mean age 61.3 years) and 339 age- and sex-matched dementia-free controls, taken an average of 9.4 years before AD diagnosis, were analyzed using Luminex xMAP technology and INNO-BIA plasma Aβ form assays to determine concentrations of free plasma Aβ₄₀ and Aβ₄₂.

RESULTS

Plasma concentrations of free Aβ₄₀ and Aβ₄₂ did not differ between preclinical AD cases and dementia-free controls, in the full sample or in subgroups defined according to sex and age group (<60 and ≥ 60 years). The interval between sampling and AD diagnosis did not affect the results. Aβ concentrations did not change in the years preceding AD diagnosis among individuals for whom longitudinal samples were available.

DISCUSSION

Plasma concentrations of free Aβ could not predict the development of clinical AD, and Aβ concentrations did not change in the years preceding AD diagnosis in this sample. These results indicate that free plasma Aβ is not a useful biomarker for the identification of individuals at risk of developing clinical AD.

Biomarkers for the Early Detection and Progression of Alzheimer's Disease

The recent failures of potential disease-modifying drugs for Alzheimer's disease (AD) may reflect the fact that the enrolled participants in clinical trials are already too advanced to derive a clinical benefit. Thus, well-validated biomarkers for the early detection and accurate diagnosis of the preclinical stages of AD will be crucial for therapeutic advancement. The combinatorial use of biomarkers derived from biological fluids, such as cerebrospinal fluid (CSF), with advanced molecular imaging and neuropsychological testing may eventually achieve the diagnostic sensitivity and specificity necessary to identify people in the earliest stages of the disease when drug modification is most likely possible. In this regard, positive amyloid or tau tracer retention on positron emission tomography imaging, low CSF concentrations of the amyloid-β 1-42 peptide, high CSF concentrations in total tau and phospho-tau, mesial temporal lobe atrophy on magnetic resonance imaging, and temporoparietal/precuneus hypometabolism or hypoperfusion on 18F-fluorodeoxyglucose positron emission tomography have all emerged as biomarkers for the progression to AD. However, the ultimate AD biomarker panel will likely involve the inclusion of novel CSF and blood biomarkers more precisely associated with confirmed pathophysiologic mechanisms to improve its reliability for detecting preclinical AD. This review highlights advancements in biological fluid and imaging biomarkers that are moving the field towards achieving the goal of a preclinical detection of AD.

Advances in Aβ plaque detection and the value of knowing: overcoming challenges to improving patient outcomes in Alzheimer's disease

Clinical diagnosis of Alzheimer's disease (AD) can be challenging as numerous diseases mimic the characteristics of AD. In this light, recent guidelines developed by different associations and working groups point out the need for biomarkers to support AD diagnosis. This paper discusses 18F-labeled radiotracers (which are indicated for PET imaging of the brain) and ongoing clinical studies that aim to generate new evidence for the usage of amyloid imaging. In addition to their relatively long half-life, these agents are known for their high sensitivity and high negative predictive values for detection of neuritic Aβ plaques. Comparisons with other biomarkers are provided and implications of diagnostic disclosures discussed. Finally, recent data from clinical trials underscore the importance of amyloid PET for detecting, quantifying and monitoring Aβ plaque deposits.

Modeling Strategies for Quantification of In Vivo 18F-AV-1451 Binding in Patients with Tau Pathology

Aggregation of hyperphosphorylated tau is a major hallmark of many neurodegenerative diseases, including Alzheimer disease (AD). In vivo imaging with PET may offer important insights into pathophysiologic mechanisms, diagnosis, and disease progression. We describe different strategies for quantification of ¹⁸F-AV-1451 (T807) tau binding, including models with blood sampling and noninvasive alternatives. Methods: Fifteen subjects (4 controls, 6 AD, 3 progressive supranuclear palsy, 2 cortico basal syndrome) underwent 180-min PET with ¹⁸F-AV-1451 and arterial blood sampling. Modeling with arterial input functions included 1-, 2-, and 3-tissue-compartment models and the Logan plot. Using the cerebellum as reference region, we applied the simplified reference tissue model 2 and Logan reference plot. Finally, simplified outcome measures were calculated as ratio, with reference to cerebellar concentrations (SUV ratio [SUVR]) and SUVs. Results: Tissue compartment models were not able to describe the kinetics of ¹⁸F-AV-1451, with poor fits in 33%-53% of cortical regions and 80% in subcortical areas. In contrast, the Logan plot showed excellent fits and parameter variance (total volume of distribution SE < 5%). Compared with the 180-min arterial-based Logan model, strong agreement was obtained for the Logan reference plot also for a reduced scan time of 100 min (R² = 0.91) and SUVR 100-120 min (R² = 0.94), with 80-100 min already representing a reasonable compromise between duration and accuracy (R² = 0.93). Time-activity curves and kinetic parameters were equal for cortical regions and the cerebellum in control subjects but different in the putamen. Cerebellar total volumes of distribution were higher in controls than patients. For these methods, increased cortical binding was observed for AD patients and to some extent for cortico basal syndrome, but not progressive supranuclear palsy. Conclusion: The Logan plot provided the best estimate of tau binding using arterial input functions. Assuming that the cerebellum is a valid reference region, simplified methods seem to provide robust alternatives for quantification, such as the Logan reference plot with 100-min scan time. Furthermore, SUVRs between target and cerebellar activities obtained from an 80- to 100-min static scan offer promising potential for clinical routine application.

Plasma tau in Alzheimer disease

Objective:

To test whether plasma tau is altered in Alzheimer disease (AD) and whether it is related to changes in cognition, CSF biomarkers of AD pathology (including β-amyloid [Aβ] and tau), brain atrophy, and brain metabolism.

Methods:

This was a study of plasma tau in prospectively followed patients with AD (n = 179), patients with mild cognitive impairment (n = 195), and cognitive healthy controls (n = 189) from the Alzheimer's Disease Neuroimaging Initiative (ADNI) and cross-sectionally studied patients with AD (n = 61), mild cognitive impairment (n = 212), and subjective cognitive decline (n = 174) and controls (n = 274) from the Biomarkers for Identifying Neurodegenerative Disorders Early and Reliably (BioFINDER) study at Lund University, Sweden. A total of 1284 participants were studied. Associations were tested between plasma tau and diagnosis, CSF biomarkers, MRI measures, ¹⁸fluorodeoxyglucose-PET, and cognition.

Results:

Higher plasma tau was associated with AD dementia, higher CSF tau, and lower CSF Aβ₄₂, but the correlations were weak and differed between ADNI and BioFINDER. Longitudinal analysis in ADNI showed significant associations between plasma tau and worse cognition, more atrophy, and more hypometabolism during follow-up.

Conclusions:

Plasma tau partly reflects AD pathology, but the overlap between normal aging and AD is large, especially in patients without dementia. Despite group-level differences, these results do not support plasma tau as an AD biomarker in individual people. Future studies may test longitudinal plasma tau measurements in AD.

Withdrawn: Plasma concentrations of free amyloid-β cannot predict the development of Alzheimer's disease

The Publisher regrets that this article is an accidental duplication of an article that has already been published, DOI of original article: http://dx.doi.org/10.1016/j.jalz.2016.12.004. The duplicate article has therefore been withdrawn. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.

Enrichment of clinical trials in MCI due to AD using markers of amyloid and neurodegeneration

OBJECTIVE

To investigate the effect of enriching mild cognitive impairment (MCI) clinical trials using combined markers of amyloid pathology and neurodegeneration.

METHODS

We evaluate an implementation of the recent National Institute for Aging-Alzheimer's Association (NIA-AA) diagnostic criteria for MCI due to Alzheimer disease (AD) as inclusion criteria in clinical trials and assess the effect of enrichment with amyloid (A+), neurodegeneration (N+), and their combination (A+N+) on the rate of clinical progression, required sample sizes, and estimates of trial time and cost.

RESULTS

Enrichment based on an individual marker (A+ or N+) substantially improves all assessed trial characteristics. Combined enrichment (A+N+) further improves these results with a reduction in required sample sizes by 45% to 60%, depending on the endpoint.

CONCLUSIONS

Operationalizing the NIA-AA diagnostic criteria for clinical trial screening has the potential to substantially improve the statistical power of trials in MCI due to AD by identifying a more rapidly progressing patient population.

Alzheimer's disease due to loss of function: A new synthesis of the available data

Alzheimer's Disease (AD) is a highly complex disease involving a broad range of clinical, cellular, and biochemical manifestations that are currently not understood in combination. This has led to many views of AD, e.g. the amyloid, tau, presenilin, oxidative stress, and metal hypotheses. The amyloid hypothesis has dominated the field with its assumption that buildup of pathogenic β-amyloid (Aβ) peptide causes disease. This paradigm has been criticized, yet most data suggest that Aβ plays a key role in the disease. Here, a new loss-of-function hypothesis is synthesized that accounts for the anomalies of the amyloid hypothesis, e.g. the curious pathogenicity of the Aβ42/Aβ40 ratio, the loss of Aβ caused by presenilin mutation, the mixed phenotypes of APP mutations, the poor clinical-biochemical correlations for genetic variant carriers, and the failure of Aβ reducing drugs. The amyloid-loss view accounts for recent findings on the structure and chemical features of Aβ variants and their coupling to human patient data. The lost normal function of APP/Aβ is argued to be metal transport across neuronal membranes, a view with no apparent anomalies and substantially more explanatory power than the gain-of-function amyloid hypothesis. In the loss-of-function scenario, the central event of Aβ aggregation is interpreted as a loss of soluble, functional monomer Aβ rather than toxic overload of oligomers. Accordingly, new research models and treatment strategies should focus on remediation of the functional amyloid balance, rather than strict containment of Aβ, which, for reasons rationalized in this review, has failed clinically.

Clinical and biomarker profiling of prodromal Alzheimer's disease in workpackage 5 of the Innovative Medicines Initiative PharmaCog project: a 'European ADNI study'

BACKGROUND

In the field of Alzheimer's disease (AD), the validation of biomarkers for early AD diagnosis and for use as a surrogate outcome in AD clinical trials is of considerable research interest.

OBJECTIVE

To characterize the clinical profile and genetic, neuroimaging and neurophysiological biomarkers of prodromal AD in amnestic mild cognitive impairment (aMCI) patients enrolled in the IMI WP5 PharmaCog (also referred to as the European ADNI study).

METHODS

A total of 147 aMCI patients were enrolled in 13 European memory clinics. Patients underwent clinical and neuropsychological evaluation, magnetic resonance imaging (MRI), electroencephalography (EEG) and lumbar puncture to assess the levels of amyloid β peptide 1-42 (Aβ42), tau and p-tau, and blood samples were collected. Genetic (APOE), neuroimaging (3T morphometry and diffusion MRI) and EEG (with resting-state and auditory oddball event-related potential (AO-ERP) paradigm) biomarkers were evaluated.

RESULTS

Prodromal AD was found in 55 aMCI patients defined by low Aβ42 in the cerebrospinal fluid (Aβ positive). Compared to the aMCI group with high Aβ42 levels (Aβ negative), Aβ positive patients showed poorer visual (P = 0.001), spatial recognition (P < 0.0005) and working (P = 0.024) memory, as well as a higher frequency of APOE4 (P < 0.0005), lower hippocampal volume (P = 0.04), reduced thickness of the parietal cortex (P < 0.009) and structural connectivity of the corpus callosum (P < 0.05), higher amplitude of delta rhythms at rest (P = 0.03) and lower amplitude of posterior cingulate sources of AO-ERP (P = 0.03).

CONCLUSION

These results suggest that, in aMCI patients, prodromal AD is characterized by a distinctive cognitive profile and genetic, neuroimaging and neurophysiological biomarkers. Longitudinal assessment will help to identify the role of these biomarkers in AD progression.