iTRAQ Based Tear Proteomic Profiling Reveals Inflammatory Proteins in Chronic Medicated Glaucoma Eyes

Abstract

Purpose: : Glaucoma, an optic neuropathy characterized by elevated intraocular pressure (IOP) is normally treated in the first instance with eyedrops to lower the IOP, and filtration surgery reserved for individuals refractory to eyedrops alone. Chronic use of eyedrops has been implicated in the exacerbation of ocular surface disease, which not only increases morbidity but also adversely affects surgical outcomes due to prolonged inflammation and post-op scarring. The aim of the study is to describe the effect of chronic use of topical medication on changes in the tear protein profile.

Methods: : Tear samples were collected using Schirmer strips from 18 patients on anti-glaucoma medications and 10 age-matched, healthy unmedicated controls. Tear proteins were analyzed using iTRAQ (Isobaric tags for relative and absolute quantification) based quantitative proteomics.

Results: : Collectively 128 tear proteins were identified (99% confidence, Protscore >=2) in 6 sets of iTRAQ experiments. We found 5 proteins whose iTRAQ ratios showed significant changes (p < 0.05) when comparing non-medicated control group and medicated group. Levels of 4 tear proteins (S100 A8, S100 A9, mammaglobin B and 14-3-3 zeta/delta protein) were elevated and level of proline-rich 4 protein was decreased in medicated samples compared with non-medicated control samples. S100 A8 and A9 protein belong to the S100 calcium-binding protein family and are an inflammation-associated proteins and may reflect the inflammatory status of the ocular surface.

Conclusions: : The chronic use of eyedrops induces an alteration in tear protein profile to a more pro-inflammatory one. The use of proteomics to identify inflammatory biomarkers in the tears will be a useful diagnostic tool to help identify individuals who may be at risk of increased post-operative inflammation and therefore surgical failure.

Keywords: proteomics • cornea: tears/tear film/dry eye