Purpose:
It is well known that different species have different susceptibilities to ocular diseases. It is also well established that the tear film is vital to ocular surface protection against pathogenic invasion. An understanding of the differences in mucin content of tears in different species would be helpful in determining the basis for predisposition to ocular disease. In this study, we examined the carbohydrate profile of tears of a variety of species as a preliminary step to identifying the types of mucins present.
Methods:
Protein and carbohydrate concentrations of tears, which were collected with IRB & ACUC approvals, from humans, dolphins, seals, sea lions, and camelids, were determined using bicinchoninic acid and sulfuric methods respectively. Monosaccharides were cleaved and released from tear samples using acid hydrolysis. Samples were incubated at 100°C for 4.5 hours with a final concentration of 2N trifluoroacetic acid and then subjected to high performance anion exchange chromatography (HPAEC) on a Dionex CarboPac PA-20 column using isocratic gradient elution.
Results:
Carbohydrate to protein ratios differed across species, with dolphin tears having the highest carbohydrate concentrations, and camelids the highest protein concentrations. HPAEC profiles of hydrolyzed monosaccharides released from tear samples of a variety of animals revealed distinct, species-specific chromatographic patterns. In comparison to humans and pinnipeds, tears of all of the other species analyzed had fewer peaks and different retention times. Seal and sea lion tear chromatograms had similar numbers of peaks and retention times as those of humans.
Conclusions:
Overall, the chromatograms of tears from pinnipeds were the most similar to humans, however each species had a distinct profile. Differences in carbohydrate profiles across species likely indicate variations in mucin composition of tears. It is possible that tear film mucin composition may correlate with differences in species’ vulnerability to ocular surface disease.
Keywords: cornea: tears/tear film/dry eye