Beta-Amyloid Peptide in Tears: An Early Diagnostic Marker of Alzheimer's Disease Correlated with Choroidal Thickness

We aimed to evaluate the diagnostic role of Alzheimer's disease (AD) biomarkers in tears as well as their association with retinal and choroidal microstructures. In a cross-sectional study, 35 subjects (age 71.7 +/- 6.9 years) were included: 11 with prodromal AD (MCI), 10 with mild-to-moderate AD, and 14 healthy controls. The diagnosis of AD and MCI was confirmed according to a complete neuropsychological evaluation and PET or MRI imaging. After tear sample collection, beta-amyloid peptide A beta 1-42 concentration was analyzed using ELISA, whereas C-terminal fragments of the amyloid precursor protein (APP-CTF) and phosphorylated tau (p-tau) were assessed by Western blot. Retinal layers and choroidal thickness (CT) were acquired by spectral-domain optical coherence tomography (SD-OCT). A beta 1-42 levels in tears were able to detect both MCI and AD patients with a specificity of 93% and a sensitivity of 81% (AUC = 0.91). Tear levels of A beta 1-42 were lower, both in the MCI (p < 0.01) and in the AD group (p < 0.001) when compared to healthy controls. Further, A beta 1-42 was correlated with psychometric scores (p < 0.001) and CT (p < 0.01). CT was thinner in the affected patients (p = 0.035). No differences were observed for APP-CTF and p-tau relative abundance in tears. Testing A beta 1-42 levels in tears seems to be a minimally invasive, cost-saving method for early detection and diagnosis of AD.

Automated summary

We conducted a study to evaluate the diagnostic role of AD biomarkers in tears and their association with retinal and choroidal microstructures. We found that tear A beta 1-42 levels had a high sensitivity and specificity in detecting MCI and AD patients. Additionally, A beta 1-42 levels were correlated with psychometric scores and choroidal thickness. Testing A beta 1-42 levels in tears could be a minimally invasive and cost-saving method for early detection and diagnosis of AD.