Quantitative analysis of proteins in the tear fluid of patients with diabetic retinopathy

Diabetic retinopathy is the leading cause of new cases of legal blindness among adults in the developed countries. Approximately 40% of all people with diabetes have diabetic retinopathy and 5% of these have sight-threatening form. As the advanced stage, where there is a high risk for vision loss, can develop without any serious symptoms, sometimes it is hard to detect it. A non invasive method to detect biomarkers characteristic for diabetic retinopathy from the tear fluid was developed. Tear samples from diabetic patients with no retinopathy, non proliferative and proliferative stages of diabetic retinopathy were analyzed and the protein content of each sample was compared to the protein content of tear pool from healthy volunteers. The samples were labeled with iTRAQ fourplex labels and were analyzed with nanoHPLC coupled ESI-MS/MS mass spectrometry. The lipocalin 1, lactotransferrin, lacritin, lysozyme C, lipophilin A and immunoglobulin lambda chain were identified as possible biomarker candidates with significantly higher relative levels in the tear of patients with diabetic retinopathy.