Targeted Proteomic Biomarker Profiling Using NULISA in a cohort enriched with risk for Alzheimer's Disease and Related Dementias

Abstract

Introduction: Targeted proteomic assays may be useful for diagnosing and staging Alzheimer's disease and related dementias (ADRD). We evaluated the performance of a 120-marker central nervous system (CNS) NUcleic acid-Linked Immuno-Sandwich Assay (NULISA) panel in samples spanning the AD spectrum.

Methods: Cross-sectional plasma samples (n=252) were analyzed using Alamar's NULISAseq CNS panel. ROC analyses demonstrated NULISAseq-pTau217 accuracy in detecting amyloid (A) and tau (T) PET positivity. Differentially expressed proteins were identified using volcano plots.

Results: NULISAseq-pTau217 accurately classified A/T PET status with ROC AUCs of 0.92/0.86. pTau217 was upregulated in A+, T+, and impaired groups with log2-fold changes of 1.21, 0.57 and 4.63, respectively, compared to A-. Interestingly, pTDP43-409 was also upregulated in the impaired group and correlated with declining hippocampal volume and cognitive trajectories.

Discussion: This study shows the potential of a targeted proteomics panel for characterizing brain changes pertinent to ADRD. The promising pTDP43-409 findings require further replication.

Figure 1.

Performance comparison between NULISA and Simoa for subset of n=218 with both plasma assays and amyloid PET visual read. A) Correlation between NULISA 2NPQ and Simoa pg/mL concentrations. Dashed lines indicate the Youden’s cut-off for the NULISA (vertical line) and Simoa (horizontal line) assays, derived from their respective ROCs for amyloid visual read (red) and tau visual read (purple). B-C) ROC curves from NULISA (blue) and Simoa (yellow), based on amyloid visual read (B) and tau visual read (C).

Figure 2.

Proteinomics analysis across groups of interest. We performed comparisons between binary groups of interest across all biomarkers in the CNS120 panel. We only considered as analytes of interest those that showed a log₂ fold change between categories of at least 0.5 (vertical dashed lines), and that maintained a p-value < 0.05 after FDR correction (horizontal dashed line). Analytes meeting these criteria for each of the tests are highlighted in red. We stratified participants according to four different variables: A) Cognitive diagnosis status (CU vs MCI); B) Amyloid status (A−/T− vs A+/T−); C) Tau status (A+/T− vs A+/T+); D) synSAA status (synSAA− vs synSAA+). See Supplementary Table 1 for details about the proteins differentially expressed in each comparison.

Figure 3.

Distribution of non-AD biomarkers by categories of interest. We first compared plasma biomarker expression in participants with results from the CSF Amprion seed amplification assay (synSAA), classified as synSAA− (n =68) and synSAA+(n = 17). A) plasma Oligo-SNCA and B) plasma monomeric alpha-synuclein (Mono-SNCA). Given the results from the proteinomics analysis identifying expression of plasma biomarkers between CU and MCI individuals, we additionally looked at the distribution of plasma pTDP43 (C) and plasma TARDBP (D) among cognitive diagnosis statuses. We additionally show the A/T PET status in distinct colors in all these panels.

Figure 4.

Estimated and observed longitudinal trajectories among pTDP43 groups. A-B) Predicted slopes across time in each of the pTDP43 groups depending on their A/T status, for the PACC3-TMTB and memory composite scores, respectively. C) Predicted slopes for hippocampal volume across time in each of the pTDP43 groups depending on their A/T status. Solid dark lines represent the marginal effects across time for each pTDP43 group, shaded areas correspond to the SE. Dots and lines in the background represent the observed values from everyone in the sample.