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1 Department of Ophthalmology and Graduate School of Biomedical Sciences, UTSouthwestern Medical Center, Dallas, Texas, United States
* To whom correspondence should be addressed. E-mail: igor.butovich{at}utsouthwestern.edu.
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PURPOSE: To qualitatively compare the nonpolar lipids present in meibomian gland (MG) secretions (samples T1) with aqueous tears (AT) collected from the lower tear menisci of healthy, non-dry eye volunteers using either glass microcapillaries (samples T2) or Schirmer test strips (samples T3). METHODS: Samples T1-T3 were analyzed using high pressure liquid chromatography/positive ion mode atmospheric pressure chemical ionization mass spectrometry. Where possible, the unknown lipids were compared with known standards. RESULTS: Samples T1 had the simplest lipid composition among all the tested specimens. Samples T2 and T3 were very similar to each other, but remarkably different from samples T1. In addition to all the compounds detected in samples T1, there were large amounts of lower molecular weight wax esters and other compounds found in samples T2 and T3. No appreciable amounts of fatty acid amides (e.g. oleamide), ceramides, or monoacyl glycerols were routinely detected in any of the samples. The occasionally observed minor signals of oleamide (m/z 282), were attributed to the contamination of the samples with common plasticizers routinely found in plasticware extractives and/or organic solvents. CONCLUSIONS: The MG is a prominent source of lipids for the tear film. However, it would have been a mistake to exclude from consideration other likely sources of lipids such as conjunctiva, cornea, and tears produced by the lacrimal glands. Our data showed that lipids in AT are fundamentally different from, and more complex than, MG secretions, which necessitates a more cautious interpretation of the functions of the latter in the tear film.
Key Words: meibum, tears, meibomian gland, lipids, mass spectrometry, high pressure liquid chromatography
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I. A. Butovich, J. C. Wojtowicz, and M. Molai Human tear film and meibum. Very long chain wax esters and (O-acyl)-omega-hydroxy fatty acids of meibum J. Lipid Res., December 1, 2009; 50(12): 2471 - 2485. [Abstract] [Full Text] [PDF] |
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