Intraday and day-to-day variability of the tear proteome

Tear film is a dynamic biological fluid that is emerging as an attractive source of non-invasive biomarkers. Due to the minimal volume typically obtained during the collection, the in-depth study of the tear proteome presents significant challenges, particularly for personalized medical approaches. Despite the advances in high-resolution mass spectrometry, which have enabled more detailed profiling of the tear proteome, intraday and day-to-day variability of tear proteins, which could affect their utility as biomarkers, has not been well explored yet. This study aims to investigate the variations in the tear fluid proteome. Building on a foundational study that identified 932 proteins across 23 subjects, tear composition was monitored in two individuals over three weeks, collecting samples weekly both in the morning and in the afternoon. Differential analysis of ultrahigh-resolution shotgun proteomics data revealed a consistent abundance of tear proteins across the weeks, with only 27 proteins showing significant variation throughout the day. These findings enhance the understanding of tear fluid dynamics and support its potential in biomarker research.