Abstract Body

INTRODUCTION: Synaptic and lysosomal dysfunction are hallmark pathological changes in most neurodegenerative diseases. Thus, identification and validation of biomarkers reflecting synaptic and lysosomal dysfunction to be employed as diagnostic and prognostic biomarkers are greatly needed.

METHOD: Solid-phase extraction and parallel reaction monitoring mass spectrometry methods were used to quantify 17 synaptic proteins and 18 lysosomal proteins in CSF, in cross-sectional studies including Alzheimer's disease (AD) patients, patients with different forms of frontotemporal dementia (FTD), Parkinson's disease (PD) and cognitively normal controls.

RESULTS: Increased concentrations of beta-synuclein, gamma-synuclein, neurogranin, PEBP-1, and 14-3-3 proteins were observed in AD patients compared with controls, while neuronal pentraxin-2 and neuronal pentraxin receptor were decreased. In FTD, multiple markers were abnormal in symptomatic MAPT mutations (beta-synuclein, gamma-synuclein, neurogranin, Rab GDP dissociation factor, 14-3-3 eta, syntaxin 1B, syntaxin 7, PBP1 plus NPTX1 and 2), whilst only neuronal pentraxins were affected in symptomatic C9orf72 and GRN mutation carriers. PD patients showed generally low levels of synaptic and lysosomal proteins in their CSF.

DISCUSSION: We have established methods to quantify synaptic and lysosomal proteins in CSF. The results suggest distinct biomarker patterns across neurodegenerative dementias, which correlate with clinical onset and disease progression. Future studies are now needed to examine how the biomarkers change with time and how they respond to treatment with disease-modifying drug candidates.

Aims

To examine the accuracy of key Alzheimer’s disease (AD) plasma biomarkers for identifying β-amyloid (Aβ) and prediction of AD dementia using fully-automated assays.

Methods

Two independent cohorts (n_total=926): PanelA+ (32 cognitively unimpaired [CU], 106 mild cognitively impaired [MCI], 89 AD participants); BioFINDER (463 CU and 236 MCI). Using novel plasma prototype Elecsys^© immunoassays, Aβ42/Aβ40, two different phospho-tau217 variants (P-tau217-1 and P-tau217-2), apolipoproteinE-ε4 (ApoE4), neurofilament light (NfL) and glial fibrillary acidic protein (GFAP) were analyzed. Accuracy for Aβ positivity (CSF Aβ42/Aβ40) and progression to AD dementia within 6 years was analyzed using the area under the curve (AUC).

Results

Plasma Aβ42/Aβ40 identified Aβ positivity with higher accuracy than previous Elecsys prototype assays (PanelA+ AUC 0.87 vs 0.80, p=0.009; BioFINDER 0.83 vs 0.78; p=0.03). Combining Aβ42/Aβ40, P-tau217-1 and ApoE4 improved the AUCs (PanelA+ 0.92, BioFINDER 0.89; p<0.01). Also including GFAP improved the model fit, but resulted in similar AUCs (PanelA+ 0.93, p=0.10; BioFINDER 0.90, p<0.01). Results were similar in CU/MCI subgroups and when using CSF P-tau/Aβ42 for Aβ status. Dichotomized plasma ApoE4 concentrations had 100% concordance with APOE-ε4 carrier status. In BioFINDER, P-tau217-1, P-tau217-2 and ApoE4 predicted AD dementia among CU participants with an AUC of 0.85. Among MCI participants, P-tau217-1, P-tau217-2 and Aβ42/Aβ40 had an AUC of 0.87.

Conclusions

Using fully-automated assays, a combination of biomarkers accurately identified Aβ positivity in two independent cohorts and predicted AD dementia. Future work will focus on evaluating the feasibility and diagnostic utility of these biomarkers for use in clinical practice and AD trials.

Aims

Plasma tau phosphorylated at threonine 181 (p-tau181) is a promising Alzheimer’s Disease (AD) biomarker. The objectives of this study are to determine if plasma p-tau181 distinguishes pathology-proven AD from cognitively normal adults and determine if p-tau181 levels associate with rate of cognitive and functional decline.

Methods

Thirty-one neuropathology-confirmed AD cases had plasma collected within 3 years of death. Adults with clinical diagnoses of normal cognition (NC, N=241), mild cognitive impairment (MCI, N=91), and AD (N=64) had plasma collected at study entry, and cognitive and functional scales (Mini Mental Status Exam [MMSE] and Clinical Dementia Rating Scale [CDR]) at yearly intervals. P-tau181 was measured in plasma using the Quanterix Simoa HD-X platform. Area under the receiver operating characteristics curve (AUC-ROC) was used to distinguish AD from NC with negative amyloid PET scans. Mixed-effects linear regression and Cox proportional hazards models were used to evaluate ptau181 effect on cognitive and functional decline.

Results

Plasma p-tau181 level differentiated AD from NC with an AUC of 0.9267. A cut-off of 3.44 pg/mL (maximum Youden Index) showed a sensitivity of 0.77, specificity of 0.96, and accuracy of 0.91. High ptau181 associated with faster rate of decline in MMSE in AD and MCI and a shorter time to clinically significant decline in the CDR sum of boxes in all groups.

Conclusions

Plasma ptau-181 differentiates cases with AD pathology from CN with high accuracy. Higher levels of plasma ptau181 are associated with faster cognitive and functional decline in clinically diagnosed groups.

Aims

To systematically investigate the relationship between plasma biomarkers of Alzheimer’s disease pathophysiology with neuropathology and longitudinal cognition.

Methods

Participants were enrolled in the UCSD Shiley-Marcos Alzheimer’s Disease Research Center (ADRC). Participants donated their brain for autopsy, which examined the presence and extent of AD and non-AD pathologies. Additionally, participants underwent annual clinical evaluations, covering both functional and neuropsychological tests. Lastly, participants underwent venipuncture every other year, with measures using single molecule array (Simoa) with either commercial (p-tau181, total-tau, neurofilament light, and Aβ42/40 [Quanterix, Bilerica, MA]) or in-house (p-tau231) assays.

Results

312 participants (mean age from 74.8 years in participants with severe AD to 85.3 in moderate AD) were included. At the last venipuncture antemortem, p-tau231, p-tau181 and were highest in severe AD pathology (p<0.05 to p<0.001), regardless of other concomitant pathologies and increased with higher degree of neuritic plaque pathology (all p<0.01), increasing Braak stage of tau pathology (V-VI > 0-II & III-IV, P<0.001) and NIA-Reagan criteria for AD (high AD > moderate and low AD). Also, both were higher in AD with or without Lewy body disease (LBD) (both p<0.01) and hippocampal sclerosis (HS) (both p<0.05) compared to pure HS and LBD. Finally, p-tau231 and p-tau181 were higher 10 years antemortem and continued to increase in high vs. low and moderate AD, and a high baseline p-tau231 and p-tau181 predicted steeper cognitive decline in subjects with AD postmortem.

Conclusions

Plasma p-tau clearly associates with the neuropathological hallmarks of AD, regardless of co-pathologies as well as predicts the rate of cognitive decline.

Aims

We examined plasma phosphorylated tau (P-tau) 181 and 217 as prognostic biomarkers of incident mild cognitive impairment (MCI) in a community-based study and assessed whether the prognostic value differed by elevated brain amyloid.

Methods

We included 999 cognitively unimpaired participants enrolled in the Mayo Clinic Study on Aging (median age of 73; 54% male, 25% APOE Ɛ4 carriers). P-tau 181 and 217 was measured on the MSD platform; previously developed cutpoints for P-tau181≥1.62 [P-tau181+] and P-tau217≥0.25 [P-tau217+]) were used for analyses. Cox Proportional Hazard models examined P-tau181+ and P-tau217+for risk of incident MCI within 2 years after adjusting for age, sex, APOE, chronic kidney disease, body mass index, stroke, and myocardial infarction. Elevated amyloid (A+) was defined as SUVR≥1.48 using PiB PET in 874 subjects. The risk of MCI among P-tau181+ and P-tau217+ was determined by brain amyloid status (A+ and A-).

Results

There were 64 incident cases of MCI within 2 years. Among all participants the P-tau measures performed similarly for risk of MCI at 2 years (P-tau181: HR 2.49, 95% CI: 1.47, 4.20; P-tau217: HR 2.24, 95% CI: 1.30, 3.85). Among those with amyloid PET, neither P-tau181+ (interactive p-value = 0.64) nor P-tau217+ (interactive p-value = 0.52) for risk of MCI differed by A+ status.

Conclusions

In this community-based sample of cognitively unimpaired participants, plasma P-tau levels can inform on risk of incident MCI within 2 years independent of amyloid PET status.

Aims

To identify which combinations of Alzheimer’s disease (AD) related plasma biomarkers and other easily accessible markers best predict progression to AD dementia in patients with mild cognitive impairment (MCI).

Methods

We included patients with amnestic MCI (n=110) followed prospectively over 3 years and where baseline plasma biomarkers (amyloid-b42/40, phosphorylated tau 217 [p-tau217], neurofilament light and glial fibrillary acidic protein), hippocampal volume, APOE genotype and cognitive tests were available. Performance of different biomarkers and biomarker combinations were investigated using logistic regressions with conversion to amyloid-positive AD dementia as outcome. The first set of analyses included only the plasma biomarkers to determine the ones most related to AD dementia conversion. Second, hippocampal volume, APOE genotype and a brief cognitive composite score (mPACC) were combined with the best plasma biomarker.

Results

Of all plasma biomarker combinations, p-tau217 alone had the best performance for discriminating progression to AD dementia vs all other combinations (AUC 0.84, 95% CI 0.75-0.93). Next, combining p-tau217 with hippocampal volume, cognition and APOE genotype provided the best discrimination between MCI progressors vs. non-progressors (AUC 0.89, 0.83-0.96), with p-tau217 and cognition being the main contributors. The most parsimonious model including p-tau217 and cognition had a similar model fit, but a slightly lower AUC (0.86, 0.78-0.94, p=0.06).

Conclusions

We identified that combining plasma p-tau217 and a brief cognitive composite score was strongly related to greater risk of progression to AD dementia in MCI patients, suggesting that these measures should be key components of future prognostic algorithms for early AD.

Aims

To explore the characteristics of plasma p-tau181 and p-tau231 as biomarkers associated with early Alzheimer’s pathologic change.

Methods

We studied 154 cognitively unimpaired (CU) participants from the TRIAD cohort with available blood biomarkers (plasma p-tau181 and p-tau231) and positron emission tomography (PET) data ([¹⁸F]-AZD4694 amyloid-PET, neocortical composite; [¹⁸F]-MK6240 tau-PET, Braak I-II regions). To understand how these plasma p-tau species are associated with amyloid, tau or both pathologies, we fitted linear regression models in which plasma biomarkers were the response variables, with four different predictor combinations: amyloid-PET (A); tau-PET (T); amyloid- plus tau-PET (A+T); amyloid- and tau-PET interactive effect (A*T). Then, to assess what drives group-level p-tau increases, we plotted plasma p-tau levels as a function of amyloid-PET, stratifying the sample based on tau-PET SUVr tertiles, and as a function of tau-PET, stratifying the sample based on amyloid-PET SUVr tertiles.

Results

In CU individuals, variability of plasma p-tau231 was best explained by the amyloid-PET model, with tau-PET having little explanatory contribution; in contrast, variability in plasma p-tau181 was poorly explained by all evaluated models (Fig. 1). Moreover, increases in plasma p-tau231 were associated with increases in amyloid-PET SUVr in all tau-PET tertile groups, while increases in p-tau181 were not associated with amyloid-PET (Fig. 2). The positive associations between p-tau levels and increases in tau-PET SUVr given amyloid-PET tertiles were similar for 231 and 181 (Fig. 3).

Conclusions

In CU individuals, plasma p-tau231, but not p-tau181, is associated with early amyloid-β deposition, highlighting it’s potential as a biomarker to monitor emerging Alzheimer’s disease pathologic change.

Abstract Body

The study of plasma biomarkers for Alzheimer’s disease (AD) has accelerated greatly in recent years thanks in part to ultra-sensitive, reliable analytic platforms and imaging biomarkers like amyloid and tau-PET. We report here our plasma biomarker findings from a well characterized autopsy cohort.

We identified 90 autopsy cases that had banked plasma within two years of death. We then assayed the last plasma sample prior to death for a battery of biomarkers using Quanterix Simoa assays. Specifically, we measured Aβ40, Aβ42, tau, pTau181, NfL, TNFα, IL6, IL10, GFAP, TGFβ, IL8, MMP9, VEGF-A, PlGF. After log-transforming the data, proportional odds and binary regression models were used to evaluate the relationship between plasma biomarkers and different vascular and AD neuropathological hallmarks. All models were adjusted for age at autopsy and covariates including ApoE genotype, sex, diabetes, and hypertension were included.

Of the AD pathological hallmarks of amyloid plaques and neurofibrillary tangles, we found that the tau/Aβ42 ratio had the greatest association with increased Aβ deposition (Thal score) and neuritic plaques (CERAD neuritic plaque score). In addition, Aβ42/Aβ40 ratio was inversely associated with Aβ deposition and neuritic plaques. Surprisingly, plasma GFAP was associated with Thal and CERAD neuritic plaque scores. Angiogenic factors PlGF, and to a lesser extent VEGF, were associated with worsening CAA, but showed a modest inverse association with arteriolosclerosis and chronic cerebrovascular pathologies.

Overall, we were able to confirm associations of candidate plasma biomarkers with AD pathologies in a well-characterized autopsy cohort and identify unique biomarker changes associated with cerebrovascular pathologies.