Low molecular weight analysis of tears using matrix assisted laser desorption ionization-time of flight mass spectrometry

Many low molecular weight substances in human tears, including protein and lipid species, have yet to be characterized. Some of these uncharacterized substances may well be important in the pathogenesis of ocular surface dise ase or in ocular discomfort. The aim of this study was to build a biochemic al profile of low molecular weight species in tears, and to determine its r epeatability. A total of 80 tear samples were collected from 11 subjects. T ear samples were dialysed to remove salts, added to a matrix of alpha -cyan o-4- hydroxycinnamic acid, and analysed using matrix-assisted laser desorpt ion ionization-time of flight (MALDI-TOF) mass spectrometry. Species were s eparated based on their mass to charge ratio (m : z). The repeatability of the appearance of the different species was analysed using logistic regress ion and diurnal and day-to-day repeatability were ascertained. Peptides wer e identified in the range of 848-3897 Da. Of these, 39 peptides were found to be present in more than 10 / 80 samples. There was no diurnal variation in the peptides. All species were found to occur repeatably, with the excep tion of peptide 1653 Da. This study has demonstrated that the majority of l ow molecular weight species in tears are repeatably present and do not exhi bit diurnal variation. Further study aims to characterize these species and to identify changes in tear profiles between subject groups.