Development and validation of a novel panel of CSF biomarkers for Alzheimer's disease

Background: Using proximity extension proteomic arrays (PEA), we previously identified a nine-biomarker CSF protein panel reflecting different biological processes dysregulated in Alzheimer´s disease (AD) that discriminated AD from non-AD dementias (i.e., dementia with Lewy bodies (DLB) and Frontotemporal dementia (FTD)). We translated this AD-Differential diagnostic panel into immunoassays for large-scale analysis and validated its discriminative performance in an independent cohort.

Method: In-house or commercially available immunoassays for five out of nine proteins (THOP1, ENO2, DDC, MMP7, and ITGB2) were analytically validated on the Ella platform. To verify analytical performance, results in CSF samples (n = 206) were compared between custom-PEA and Ella immunoassays. Clinical validation was performed in patients from the Amsterdam Dementia Cohort, including controls (cognitively unimpaired; n = 55, mean age: 57 ± 4 years, 36% females), amyloid-positive patients with mild cognitive impairment (MCI-Aβ+; n = 39, mean age: 68 ± 4 years, 46% females), AD (n = 47, mean age 66 ± 5 years, 31% females), and a non-AD group including patients with DLB (n = 54, mean age 69 ± 5 years, 17% females) and FTD (n = 50, mean age 64 ± 7 years, 32% females).

Results: Moderate to strong correlations between custom-PEA and Ella immunoassays were observed (Rho’s > 0.646). CSF proteins showed similar though weaker trends compared to custom-PEA results. THOP1 and ENO2 were dysregulated across different AD stages. ENO2 and ITGB2 were increased in AD compared with DLB and FTD, while DDC was specifically increased in DLB. THOP1, ITGB2, and ENO2 correlated strongly with CSF pTau181 and tTau while weak correlations with amyloid were observed. Our CSF panel (THOP1, ENO2, DDC, MMP7, ITGB2) discriminated AD from non-AD dementias with moderate accuracy (AUC = 0.73, 95%CI: 0.64–0.82).

Conclusion: We developed immunoassays for novel AD biomarker candidates, which cover relevant biological processes (i.e., cellular remodeling, neuropeptide degradation, energy metabolic processes, the immune system, and neurotransmitter synthesis) underlying AD pathophysiology. CSF patterns were consistent with our discovery study, albeit diagnostic performance was somewhat lower than observed previously. This highlights the need to further evaluate this panel, which monitors a broader spectrum of biological processes, both in clinical practice and within clinical trial settings.