Abstract
PurposeTo establish a robust workflow for combined mass spectrometry–based analysis of metabolites and proteins in tear fluid with regard to clinical applicability.MethodsTear fluid was taken from 12 healthy volunteers at different time points using specially designed Schirmer strips. Following the liquid extraction of metabolites from standardized punches, the remaining material was processed for bottom-up proteomics. Targeted metabolite profiling was performed adapting a metabolomics kit, which targets 188 metabolites from four different analyte classes. Proteomics was performed of the identical samples targeting 15 tear proteins relevant to ocular health.ResultsSixty metabolites could be consistently determined in all tear samples (98 metabolites were detectable in average) covering acylcarnitines, amino acids, biogenic amines, and glycerophospholipids. Following normalization, the majority of metabolites exhibited intraindividual variances of less than 20%, both regarding different times of sampling, and the individual eye. The targeted analysis of tear proteins revealed a mean intraindividual variation of 23% for the three most abundant proteins. Even extreme differences in tear secretion rates resulted in interindividual variability below 30% for 65 metabolites and two proteins.ConclusionsThe newly established workflow can be used for combined targeted detection of metabolites and proteins in one punch of a Schirmer strip in a clinical setting.Translational RelevanceOur data about intra- and interindividual as well as intereye variation provide a valuable basis for the design of clinical studies, and for the applicability of multiplexed “omics” to well accessible tear fluid with regard to future routine use.
Highlights
The tear fluid forms a film that covers the cornea and conjunctiva of the eye
Translational Relevance: Our data about intra- and interindividual as well as intereye variation provide a valuable basis for the design of clinical studies, and for the applicability of multiplexed ‘‘omics’’ to well accessible tear fluid with regard to future routine use
Tear fluid protects epithelial cells against dehydration, removes particles and waste products, and provides nutrients as well as an antimicrobial defense system.[1]. It has been known for a long time that the excretion and constitution of tear fluid are affected by ocular diseases, for example in patients suffering from dry-eye syndrome.[2]
Summary
The tear fluid forms a film that covers the cornea and conjunctiva of the eye. Tear fluid protects epithelial cells against dehydration, removes particles and waste products, and provides nutrients as well as an antimicrobial defense system.[1] It has been known for a long time that the excretion and constitution of tear fluid are affected by ocular diseases, for example in patients suffering from dry-eye syndrome.[2] Thereby, the tear secretion rate is significantly reduced, and the osmolarity and the concentrations of molecular components are altered. Tear fluid has been seen as a gateway for pharmaceutical intervention into the human eye. The classical examples are eye drops that have been formulated to treat infections, glaucoma, and inflammatory disorders.[3]
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