Tear proteomics in evaporative dry eye disease

Purpose: To analyze tear protein variations in patients suffering from dry eye symptoms in the presence of tear film instability but without epithelial defects. Methods: Five microlitres of non-stimulated tears from 60 patients, suffering from evaporative dry eye (EDE) with a break-up time (BUT) <10 s, and from 30 healthy subjects as control (no symptoms, BUT >10 s) were collected. Tear proteins were separated by mono and bi-dimensional SDS-PAGE electrophoresis and characterized by immunoblotting and enzymatic digestion. Digested peptides were analyzed by liquid chromatography coupled to electrospray ionization quadrupole-time of flight mass spectrometry followed by comparative data analysis into Swiss-Prot human protein database using Mascot. Statistical analysis were performed by applying a t-test for independent data and a Mann-Whitney test for unpaired data (P<0.05). Results: In EDE patients vs controls, a significant decrease in levels of lactoferrin (data in % +/- SD): 20.15 +/- 2.64 vs 24.56 +/- 3.46 (P = 0.001), lipocalin-1: 14.98 +/- 2.70 vs 17.73 +/- 2.96 (P = 0.0001), and lipophilin A-C: 2.89 +/- 1.06 vs 3.63 +/- 1.37 (P = 0.006) was revealed, while a significant increase was observed for serum albumin: 9.45 +/- 1.87 vs 3.46 +/- 1.87 (P 0.0001). No changes for lysozyme and zinc alpha-2 glycoprotein (P = 0.07 and 0.7, respectively) were shown. Proteomic analysis showed a downregulation of lipophilin A and C and lipocalin-1 in patients, which is suggested to be associated with post-translational modifications. Conclusions: Data show that tear protein changes anticipate the onset of more extensive clinical signs in early stage dry eye disease. Eye (2010) 24, 1396-1402; doi:10.1038/eye.2010.7; published online 12 February 2010