Neuroinflammation Markers in Tear Fluid of Mild Alzheimer's Disease

The protein composition of tear fluid (TF) reflects the severity and progression of many age-related diseases. Here, we evaluated TF proteins from patients with mild Alzheimer's disease (AD) and cognitively healthy controls (CO) to explore potential new biomarker molecules. The aim of this study was to explore potential new biomarker molecules by examining the expression of TF proteins whose function is related to neuroinflammation. We examined 53 participants (34 COs, mean age 71 years, Mini-Mental State Examination (MMSE) score 28.9 ± 1.4; 19 with AD, Clinical Dementia Rating 0.5-1, mean age 72 years, MMSE 23.8 ± 2.8). All participants underwent neurological status examination, cognitive testing, and ophthalmological examination. TF was collected using Schirmer strips, and TF protein content was evaluated using mass spectrometry-based proteomics and label-free quantification. We report 14 TF proteins that showed altered protein expression in the AD group compared to the CO group. Twelve proteins were significantly upregulated (SERPINA3, FGA, SIAS, ORM1, ANXA3, G6PI/NLK, CH3L2, MSLN, CPPED1, JCHAIN, IGHV5-51, SPARCL1) and two were downregulated (PIP, SCGB2A1) (p ≤ 0.05). Observed altered expression of TF proteins in the AD group may have potential in AD pathology. Since inflammation is one of the earliest signs of neurodegeneration in AD, these proteins are putative new biomarker candidates of early AD.