Detecting amyloid positivity in early Alzheimer's disease using combinations of plasma Aß42/Aß40 and p-tau.

INTRODUCTION: We studied usefulness of combining blood amyloid beta (Aß)42/Aß40, phosphorylated tau (p-tau)217, and neurofilament light (NfL) to detect abnormal brain Aß deposition in different stages of early Alzheimer's disease (AD). METHODS: Plasma biomarkers were measured using mass spectrometry (Aß42/Aß40) and immunoassays (p-tau217 and NfL) in cognitively unimpaired individuals (CU, N = 591) and patients with mild cognitive impairment (MCI, N = 304) from two independent cohorts (BioFINDER-1, BioFINDER-2). RESULTS: In CU, a combination of plasma Aß42/Aß40 and p-tau217 detected abnormal brain Aß status with area under the curve (AUC) of 0.83 to 0.86. In MCI, the models including p-tau217 alone or Aß42/Aß40 and p-tau217 had similar AUCs (0.86-0.88); however, the latter showed improved model fit. The models were implemented in an online application providing individualized risk assessments (https://brainapps.shinyapps.io/PredictABplasma/). DISCUSSION: A combination of plasma Aß42/Aß40 and p-tau217 discriminated Aß status with relatively high accuracy, whereas p-tau217 showed strongest associations with Aß pathology in MCI but not in CU.

Clinical utility of an antibody-free LC-MS method to detect brain amyloid deposition in cognitively unimpaired individuals from the screening visit of the A4 Study.

INTRODUCTION: This study explored the ability of plasma amyloid beta (Aß)42/Aß40 to identify brain amyloid deposition in cognitively unimpaired (CU) individuals. METHODS: Plasma Aß was quantified with an antibody-free high-performance liquid chromatography tandem mass spectrometry method from Araclon Biotech (ABtest-MS) in a subset of 731 CU individuals from the screening visit of the Anti-Amyloid Treatment in Asymptomatic Alzheimer's (A4) Study, to assess associations of Aß42/Aß40 with Aß positron emission tomography (PET). RESULTS: A model including Aß42/Aß40, age, apolipoprotein E ε4, and recruitment site identified Aß PET status with an area under the curve of 0.88 and an overall accuracy of 81%. A plasma-based pre-screening step could save up to 42% of the total number of Aß PET scans. DISCUSSION: ABtest-MS accurately identified brain amyloid deposition in a population of CU individuals, supporting its implementation in AD secondary prevention trials to reduce recruitment time and costs. Although a certain degree of heterogeneity is inherent to large and multicentric trials, ABtest-MS could be more robust to pre-analytical bias compared to other immunoprecipitation mass spectrometry methods. HIGHLIGHTS: Plasma amyloid beta (Aß)42/Aß40 accurately identified brain Aß deposition in cognitively unimpaired individuals from the Anti-Amyloid Treatment in Asymptomatic Alzheimer's (A4) Study.The inclusion of the recruitment site in the predictive models has a non-negligible effect.A plasma biomarker-based model could reduce recruitment costs in Alzheimer's disease secondary prevention trials.Antibody-free liquid chromatography mass spectrometry methods may be more robust to pre-analytical variability than other platforms.

Clinical performance of an antibody-free assay for plasma Aß42/Aß40 to detect early alterations of Alzheimer's disease in individuals with subjective cognitive decline.

BACKGROUND: Accessible and cost-effective diagnostic tools are urgently needed to accurately quantify blood biomarkers to support early diagnosis of Alzheimer's disease (AD). In this study, we investigated the ability of plasma amyloid-beta (Aß)42/Aß40 ratio measured by an antibody-free mass-spectrometric (MS) method, ABtest-MS, to detect early pathological changes of AD. METHODS: This cohort study included data from the baseline and 2-year follow-up visits from the Fundació ACE Healthy Brain Initiative (FACEHBI) study. Plasma Aß42/Aß40 was measured with ABtest-MS and compared to 18F-Florbetaben PET as the reference standard (cutoff for early amyloid deposition of 13.5 centiloids). Cross-validation was performed in an independent DPUK-Korean cohort. Additionally, associations of plasma Aß42/Aß40 with episodic memory performance and brain atrophy were assessed. RESULTS: The FACEHBI cohort at baseline included 200 healthy individuals with subjective cognitive decline (SCD), of which 36 (18%) were Aß-PET positive. Plasma Aß42/Aß40 levels were significantly lower in Aß-PET positive individuals (median [interquartile range, IQR], 0.215 [0.203-0.236]) versus Aß-PET negative subjects (median [IQR], 0.261 [0.244-0.279]) (P < .001). Plasma Aß42/Aß40 was significantly correlated with Aß-PET levels (rho = -0.390; P < .001) and identified Aß-PET status with an area under the receiver operating characteristic curve (AUC) of 0.87 (95% confidence interval [CI], 0.80-0.93). A cutoff for the Aß42/Aß40 ratio of 0.241 (maximum Youden index) yielded a sensitivity of 86.1% and a specificity of 80.5%. These findings were cross-validated in an independent DPUK-Korean cohort (AUC 0.86 [95% CI 0.77-0.95]). Lower plasma Aß42/Aß40 ratio was associated with worse episodic memory performance and increased brain atrophy. Plasma Aß42/Aß40 at baseline predicted clinical conversion to mild cognitive impairment and longitudinal changes in amyloid deposition and brain atrophy at 2-year follow-up. CONCLUSIONS: This study suggests that plasma Aß42/Aß40, as determined by this MS-based assay, has potential value as an accurate and cost-effective tool to identify individuals in the earliest stages of AD, supporting its implementation in clinical trials, preventative strategies and clinical practice.

Contribution of clinical information to the predictive performance of plasma ß-amyloid levels for amyloid positron emission tomography positivity.

Background: Early detection of ß-amyloid (Aß) accumulation, a major biomarker for Alzheimer's disease (AD), has become important. As fluid biomarkers, the accuracy of cerebrospinal fluid (CSF) Aß for predicting Aß deposition on positron emission tomography (PET) has been extensively studied, and the development of plasma Aß is beginning to receive increased attention recently. In the present study, we aimed to determine whether APOE genotypes, age, and cognitive status increase the predictive performance of plasma Aß and CSF Aß levels for Aß PET positivity. Methods: We recruited 488 participants who underwent both plasma Aß and Aß PET studies (Cohort 1) and 217 participants who underwent both cerebrospinal fluid (CSF) Aß and Aß PET studies (Cohort 2). Plasma and CSF samples were analyzed using ABtest-MS, an antibody-free liquid chromatography-differential mobility spectrometry-triple quadrupole mass spectrometry method and INNOTEST enzyme-linked immunosorbent assay kits, respectively. To evaluate the predictive performance of plasma Aß and CSF Aß, respectively, logistic regression and receiver operating characteristic analyses were performed. Results: When predicting Aß PET status, both plasma Aß42/40 ratio and CSF Aß42 showed high accuracy (plasma Aß area under the curve (AUC) 0.814; CSF Aß AUC 0.848). In the plasma Aß models, the AUC values were higher than plasma Aß alone model, when the models were combined with either cognitive stage (p < 0.001) or APOE genotype (p = 0.011). On the other hand, there was no difference between the CSF Aß models, when these variables were added. Conclusion: Plasma Aß might be a useful predictor of Aß deposition on PET status as much as CSF Aß, particularly when considered with clinical information such as APOE genotype and cognitive stage.

Head-to-Head Comparison of 8 Plasma Amyloid-ß 42/40 Assays in Alzheimer Disease.

Importance: Blood-based tests for brain amyloid-ß (Aß) pathology are needed for widespread implementation of Alzheimer disease (AD) biomarkers in clinical care and to facilitate patient screening and monitoring of treatment responses in clinical trials. Objective: To compare the performance of plasma Aß42/40 measured using 8 different Aß assays when detecting abnormal brain Aß status in patients with early AD. Design, Setting, and Participants: This study included 182 cognitively unimpaired participants and 104 patients with mild cognitive impairment from the BioFINDER cohort who were enrolled at 3 different hospitals in Sweden and underwent Aß positron emission tomography (PET) imaging and cerebrospinal fluid (CSF) and plasma collection from 2010 to 2014. Plasma Aß42/40 was measured using an immunoprecipitation-coupled mass spectrometry developed at Washington University (IP-MS-WashU), antibody-free liquid chromatography MS developed by Araclon (LC-MS-Arc), and immunoassays from Roche Diagnostics (IA-Elc); Euroimmun (IA-EI); and Amsterdam University Medical Center, ADx Neurosciences, and Quanterix (IA-N4PE). Plasma Aß42/40 was also measured using an IP-MS-based method from Shimadzu in 200 participants (IP-MS-Shim) and an IP-MS-based method from the University of Gothenburg (IP-MS-UGOT) and another immunoassay from Quanterix (IA-Quan) among 227 participants. For validation, 122 participants (51 cognitively normal, 51 with mild cognitive impairment, and 20 with AD dementia) were included from the Alzheimer Disease Neuroimaging Initiative who underwent Aß-PET and plasma Aß assessments using IP-MS-WashU, IP-MS-Shim, IP-MS-UGOT, IA-Elc, IA-N4PE, and IA-Quan assays. Main Outcomes and Measures: Discriminative accuracy of plasma Aß42/40 quantified using 8 different assays for abnormal CSF Aß42/40 and Aß-PET status. Results: A total of 408 participants were included in this study. In the BioFINDER cohort, the mean (SD) age was 71.6 (5.6) years and 49.3% of the cohort were women. When identifying participants with abnormal CSF Aß42/40 in the whole cohort, plasma IP-MS-WashU Aß42/40 showed significantly higher accuracy (area under the receiver operating characteristic curve [AUC], 0.86; 95% CI, 0.81-0.90) than LC-MS-Arc Aß42/40, IA-Elc Aß42/40, IA-EI Aß42/40, and IA-N4PE Aß42/40 (AUC range, 0.69-0.78; P < .05). Plasma IP-MS-WashU Aß42/40 performed significantly better than IP-MS-UGOT Aß42/40 and IA-Quan Aß42/40 (AUC, 0.84 vs 0.68 and 0.64, respectively; P < .001), while there was no difference in the AUCs between IP-MS-WashU Aß42/40 and IP-MS-Shim Aß42/40 (0.87 vs 0.83; P = .16) in the 2 subcohorts where these biomarkers were available. The results were similar when using Aß-PET as outcome. Plasma IPMS-WashU Aß42/40 and IPMS-Shim Aß42/40 showed highest coefficients for correlations with CSF Aß42/40 (r range, 0.56-0.65). The BioFINDER results were replicated in the Alzheimer Disease Neuroimaging Initiative cohort (mean [SD] age, 72.4 [5.4] years; 43.4% women), where the IP-MS-WashU assay performed significantly better than the IP-MS-UGOT, IA-Elc, IA-N4PE, and IA-Quan assays but not the IP-MS-Shim assay. Conclusions and Relevance: The results from 2 independent cohorts indicate that certain MS-based methods performed better than most of the immunoassays for plasma Aß42/40 when detecting brain Aß pathology.

Performance of the plasma Aß42/Aß40 ratio, measured with a novel HPLC-MS/MS method, as a biomarker of amyloid PET status in a DPUK-KOREAN cohort.

BACKGROUND: We assessed the feasibility of plasma Aß42/Aß40 determined using a novel liquid chromatography-mass spectrometry method (LC-MS) as a useful biomarker of PET status in a Korean cohort from the DPUK Study. METHODS: A total of 580 participants belonging to six groups, Alzheimer's disease dementia (ADD, n = 134), amnestic mild cognitive impairment (aMCI, n = 212), old controls (OC, n = 149), young controls (YC, n = 15), subcortical vascular cognitive impairment (SVCI, n = 58), and cerebral amyloid angiopathy (CAA, n = 12), were included in this study. Plasma Aß40 and Aß42 were quantitated using a new antibody-free, LC-MS, which drastically reduced the sample preparation time and cost. We performed receiver operating characteristic (ROC) analysis to develop the cutoff of Aß42/Aß40 and investigated its performance predicting centiloid-based PET positivity (PET+). RESULTS: Plasma Aß42/Aß40 were lower for PET+ individuals in ADD, aMCI, OC, and SVCI (p < 0.001), but not in CAA (p = 0.133). In the group of YC, OC, aMCI, and ADD groups, plasma Aß42/Aß40 predicted PET+ with an area under the ROC curve (AUC) of 0.814 at a cutoff of 0.2576. When adding age, APOE4, and diagnosis, the AUC significantly improved to 0.912. CONCLUSION: Plasma Aß42/Aß40, as measured by this novel LC-MS method, showed good discriminating performance based on PET positivity.

Individualized prognosis of cognitive decline and dementia in mild cognitive impairment based on plasma biomarker combinations.

We developed models for individualized risk prediction of cognitive decline in mild cognitive impairment (MCI) using plasma biomarkers of ß-amyloid (Aß), tau and neurodegeneration. A total of 573 patients with MCI from the Swedish BioFINDER study and the Alzheimer's Disease Neuroimaging Initiative (ADNI) were included in the study. The primary outcomes were longitudinal cognition and conversion to Alzheimer's disease (AD) dementia. A model combining tau phosphorylated at threonine 181 (P-tau181) and neurofilament light (NfL), but not Aß42/Aß40, had the best prognosis performance of all models (area under the curve = 0.88 for 4-year conversion to AD in BioFINDER, validated in ADNI), was stronger than a basic model of age, sex, education and baseline cognition, and performed similarly to cerebrospinal fluid biomarkers. A publicly available online tool for individualized prognosis in MCI based on our combined plasma biomarker models is introduced. Combination of plasma biomarkers may be of high value to identify individuals with MCI who will progress to AD dementia in clinical trials and in clinical practice.

The global Alzheimer's Association round robin study on plasma amyloid ß methods.

INTRODUCTION: Blood-based assays to measure brain amyloid beta (Aß) deposition are an attractive alternative to the cerebrospinal fluid (CSF)-based assays currently used in clinical settings. In this study, we examined different blood-based assays to measure Aß and how they compare among centers and assays. METHODS: Aliquots from 81 plasma samples were distributed to 10 participating centers. Seven immunological assays and four mass-spectrometric methods were used to measure plasma Aß concentrations. RESULTS: Correlations were weak for Aß42 while Aß40 correlations were stronger. The ratio Aß42/Aß40 did not improve the correlations and showed weak correlations. DISCUSSION: The poor correlations for Aß42 in plasma might have several potential explanations, such as the high levels of plasma proteins (compared to CSF), sensitivity to pre-analytical sample handling and specificity, and cross-reactivity of different antibodies. Different methods might also measure different pools of plasma Aß42. We, however, hypothesize that greater correlations might be seen in future studies because many of the methods have been refined during completion of this study.

Outstanding Phenotypic Differences in the Profile of Amyloid-ß between Tg2576 and APPswe/PS1dE9 Transgenic Mouse Models of Alzheimer's Disease.

APPswe/PS1dE9 and Tg2576 are very common transgenic mouse models of Alzheimer's disease (AD), used in many laboratories as tools to research the mechanistic process leading to the disease. In order to augment our knowledge about the amyloid-ß (Aß) isoforms present in both transgenic mouse models, we have developed two chromatographic methods, one acidic and the other basic, for the characterization of the Aß species produced in the brains of the two transgenic mouse models. After immunoprecipitation and micro-liquid chromatography-electrospray ionization mass spectrometry/mass spectrometry, 10 species of Aß, surprisingly all of human origin, were detected in the brain of Tg2576 mouse, whereas 39 species, of both murine and human origin, were detected in the brain of the APP/PS1 mouse. To the best of our knowledge, this is the first study showing the identification of such a high number of Aß species in the brain of the APP/PS1 transgenic mouse, whereas, in contrast, a much lower number of Aß species were identified in the Tg2576 mouse. Therefore, this study brings to light a relevant phenotypic difference between these two popular mice models of AD.

Aß1-17 is a major amyloid-ß fragment isoform in cerebrospinal fluid and blood with possible diagnostic value in Alzheimer's disease.

This work was prompted by the finding that Aß1-17 (Aß17) appeared to be the second-most abundant cerebrospinal fluid (CSF) Aß fragment, after Aß40. We developed an ELISA to quantify levels of Aß17 directly accessible in plasma (DA17), recovered from the proteomic plasma matrix (RP17) and associated with the cellular pellet (CP17) that remained after plasma collection. Then, we used a sample of 19 healthy control (HC), 27 mild cognitive impairment (MCI), and 17 mild Alzheimer's disease (AD) patients to explore the association of the diagnostic groups with those direct markers, their ratios or the ratios with their Aß40 or Aß42 counterparts. After dichotomization (d) for the median of the sample population, logistic regression analysis showed that in the AD versus HC subgroup, subjects with a dDA/CP17 higher than the median had a significantly greater risk of being AD than those with marker levels equal to or below the median (odds ratio OR; 95% confidence interval; 17.21; 1.42-208.81). Subjects with dRP17/42 below the median had an increased likelihood of being MCI (20.00; 1.17-333.33) or AD (40.00; 1.87-1000) versus being HC, than those with dRP17/42 higher than the median. Although the confidence intervals are wide, these findings suggest that assessment of Aß17 may increase the diagnostic performance of blood-based Aß tests which might be developed into minimally invasive first-step screening tests for people with increased risk for AD.

Identification of ß-amyloid species in canine cerebrospinal fluid by mass spectrometry.

It is well known that several Aß species, including Aß40 and Aß42, are present in cerebrospinal fluid (CSF). Experimental results suggest that these species could play a role in Alzheimer's disease and might also have diagnostic significance. In the present work, the canine CSF ß-amyloid species profile has been identified by matrix-assisted laser desorption and ionization-time-of-flight/time of flight mass spectrometry (MALDI-TOF/TOF) analysis after immunoprecipitation with different Aß-specific antibodies. The results show that species arising from combined ß- and γ-secretase activities in humans, such as Aß1-33, Aß1-34, Aß1-37, Aß1-38, Aß1-39, Aß1-40, and Aß1-42, are also present in dogs. Species arising from combined α- and ß-secretase activities, as well as other Aß-degrading enzymes, are also present in both human and canine CSF, with the exception of Aß1-13, Aß1-14, and Aß1-18, which are not detected in dogs. A large number of species truncated at Glu-3 and Glu-11 have also been detected. To our knowledge, this work describes a most complete Aß species profile from canine CSF. The similarities between the canine and human CSF Aß profile reinforce the dog as a highly appropriate animal model for research in Alzheimer's disease.