Profiling Tear Film Enzymes Reveals Major Metabolic Pathways Involved in the Homeostasis of the Ocular Surface

Abstract Background The role of ocular surface enzymes is of great interest. Therefore, this study first aimed to profile and classify enzymes identified on the ocular surface to describe major biological processes and pathways that are involved in the maintenance of homeostasis. Secondly, we aimed to compare the enzymatic profiles between two main tear collection methods, capillary tubes (CT) and Schirmer strips (ScS). Methods A comprehensive tear proteomic dataset was generated by pooling all identified enzymes from nine tear proteomic analyses of healthy subjects using mass spectrometry. In these studies, tear fluid was collected using CT (n = 4), ScS (n = 4) or both collection methods (n = 1). The classification and functional analysis of enzymes was performed using a combination of bioinformatic tools. Results The generated dataset enabled the identification of 1010 enzymes. The most representative classes were hydrolases (EC 3) and transferases (EC 2). Phosphotransferases, esterases and peptidases were the most represented subclasses. A large part of identified enzymes was common to both collection methods (n = 499). More enzymes were specifically detected in the ScS-extracted proteome. The immune system and metabolism of proteins, carbohydrates and lipids formed the major pathways of the identified enzymes. Metabolic processes of nucleosides, cellular amid, sugar and sulfur compounds constituted the most enriched biological processes. Conclusions Knowledge about these highly druggable molecules could help to predict the metabolism of ophthalmic drugs, and develop novel prodrug strategies as well as new drug delivery systems. Combining extensive knowledge about ocular surface enzymes with new approaches and techniques might open up new avenues for ocular drug metabolisms.