Abstract

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 and dryness. An understanding of the differences in mucin content of marine mammal ocular secretions as compared to that of tears of terrestrial mammals would be helpful in determining the basis for predisposition to ocular disease. In this study, we compared the carbohydrate profile of tears from a variety of species as a preliminary step to identifying the types of mucins present. Protein and carbohydrate concentrations of tears, which were collected with IRB & ACUC approvals, from dolphins, seals, sea lions, humans, and camelids, were determined using standard bicinchoninic acid and sulfuric methods. 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 indicate that carbohydrate to protein ratios differ across species, with dolphin tears having the highest carbohydrate concentration, and camelid tears the highest protein concentration. HPAEC profiles of hydrolyzed monosaccharides released from tear samples of marine and terrestrial animals revealed distinct, species-specific chromatographic patterns. In comparison to humans and pinnipeds, tears 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. 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 species-specific differences in vulnerability to ocular surface disease.

Acknowledgments

We thank the staff and trainers at Dolphin Quest Oahu, Oahu, HI; Aquarium of Niagara, Niagara Falls, NY; and New England Aquarium, Boston, MA, for their very generous support in collecting marine mammal tear samples for this project. Grant Support: NIH EY014847 (PA) & RO1EY05612; Arey's Pond Boat Yard, S. Orleans, MA