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Jianzhong CHEN, Kelly K Nichols; Composition of Diesters in Human Meibum. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4818. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Diesters are the third most abundant type of lipids in meibum and account for about 8% of its total lipid content (only less than wax esters and cholesteryl esters). There are two types of diesters: α, ω Type II DEs and ω Type I-St DEs. It was reported recently by our group that diesters were down-regulated in dry eye patients (Chen J, et al., IOVS, 2013; 54:5730–5753; IOVS, 2015; 56:342). The purpose of the present study is to systematically determine the composition of intact molecules of these diesters which can augment our understanding the role of meibum in dry eye diseases.
Meibum samples (~ 13 μg or ~ 16 nL) were collected in microcapillaries directly from meibomian gland orifices. Meibum stock solutions were prepared by dissolving each meibum sample in chloroform-methanol mixture (2:1, v/v) at the concentration of ~13 μg/100 μL. The stock solutions were diluted with methanol by 5 fold. The final working solution contained 0.025% ammonium hydroxide as the additive and was directly infused into a Triple TOF 5600 mass spectrometer (Sciex, Framingham, MA) with electrospray ionization. Mass spectrometry (MS) and tandem mass spectrometry (MS/MS) analysis of meibum samples were acquired in positive ion detection mode. A total of about 40 different ions in the MS analysis, half corresponding to intact α, ω Type II DEs and the other half to ω Type I-St DEs, were analyzed by tandem mass spectrometry. Because there are no commercially available standards for these diesters, the known dissociation patterns of representative, ester bond-containing lipids (cholesteryl esters and wax esters) were used to predict the product ions to be formed.
The major components of the α, ω Type II DEs included one moiety of a C30:1, C32:1, or C34:1 diol and two moieties of C18:1, C16:1, and/or C17:0 fatty acids, linked by two ester bonds. The major components of the ω Type I-St DEs included one moiety of a C18:1, C16:1, or C17:0 fatty acid; one moiety of a C30:1, C32:1 or C34:1 ω-hydroxy fatty acid; and a cholesteryl group, also linked by two ester bonds. The middle moieties for intact molecules of the two types of diesters in human meibum are almost exclusively composed of C30:1, C32:1, and C34:1.
The composition of intact diester molecules is determined, which will be helpful for studies on the function of the tear film lipid layer and the theoretical model of the tear film.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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