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Robin Kelleher Davis, Pablo Argueso; Composition of Terrestrial and Marine Mammal Tears is Dependent on Species and Environment. Invest. Ophthalmol. Vis. Sci. 2014;55(13):36.
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© ARVO (1962-2015); The Authors (2016-present)
There are differences in the nature of the tear film of marine mammals as compared to terrestrial, including the absence of a lipid layer in the marine mammal. We hypothesize that in lieu of a lipid layer, mucin-type glycoproteins play a critical role in the health and wellbeing of the sea mammal eye. In this study, we analyzed tears from a variety of sea dwelling species for carbohydrate and protein composition, and compared the results to those obtained from terrestrial mammals.
Tears were collected, using IRB and ACUC approved protocols, from manatees, dolphins, seals, sea lions, camelids and humans. Protein and carbohydrate concentrations of tear samples were determined using standard bicinchoninic acid and sulfuric assays. Monosaccharides were cleaved and released from tear glycoproteins 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.
Carbohydrate to protein (C:P) ratios were 6-18 times greater in tears from manatees, dolphins, seals and sea lions as compared to human tears, whereas camelid C:P ratio was ¼ that of human. Tears from manatees in rehabilitation settings had a 4-fold higher C:P ratio than those in the wild. By HPAEC, dolphin, seal and sea lion tears contained fucose (0.08-0.21 nmol/μg total protein), N-acetylgalactosamine (0.55-6.17 nmol/μg), N-acetylglucosamine (1.43-6.17 nmol/μg), galactose (0.52-2.78 nmol/μg), glucose (0.07-0.90 nmol/μg), and mannose (0.68-2.36 nmol/μg). N-acetylgalactosamine and N-acetylglucosamine were present in higher amounts in dolphin tears (6.57 and 6.17 nmol/μg respectively) than in the other species analyzed, including human (0.89 and 1.86 nmol/μg respectively).
Results from this study demonstrate a higher content of carbohydrates in tears from marine mammals compared to terrestrial species. Of interest, within one family of marine mammal, the manatee, tear carbohydrate content was substantially higher in a controlled rehabilitative facility than in the wild, which may represent a homeostatic response to an artificial environment.
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