Journal
CHEMISTRY AND PHYSICS OF LIPIDS
Volume 170, Issue -, Pages 55-64Publisher
ELSEVIER IRELAND LTD
DOI: 10.1016/j.chemphyslip.2013.03.005
Keywords
Cooperativity; Meibum; Melting; Phase transitions; Microcalorimetry; Wax esters
Categories
Funding
- National Institutes of Health [R01EY019480, 3R01EY019480-01A1S1]
- Research to Prevent Blindness (New York, NY)
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Meibomian gland secretions (or meibum) are produced by holocrine meibomian glands and are secreted in melted form onto the ocular surface of humans and animals to form a protective tear film lipid layer (TFLL). Its protective effect strongly depends on the composition and, hence, thermotropic behavior of meibum. The goal of our study was to quantitatively evaluate the melting characteristics of human meibum and model lipid mixtures using differential scanning microcalorimetry. Standard calorimetric parameters, e.g. changes in calorimetric enthalpy, transition temperatures T-m, cooperativity of melting, etc. were assessed. We found that thermotropic behavior of meibum resembled that of relatively simple mixtures of unsaturated wax esters, but showed a lower change in calorimetric enthalpy, which can be indicative of a looser packing of lipids in meibum compared with pure standards and their simple mixtures. The cooperativity of melting of meibomian lipids was comparable to that of an equimolar mixture of four oleic-acid based wax esters. We demonstrated that the phase transitions in meibum start at about 10-15 degrees C and end at 35-36 degrees C, with Tm being about 30 degrees C. The highly asymmetrical shape of the thermotropic peak of meibum is important for the physiology and biophysics of TFLL. (C) 2013 Elsevier Ireland Ltd. All rights reserved.
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