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Cameron K Postnikoff, Jianzhong Chen, Jeremy Keirsey, Kari Basso, Kelly K Nichols; Altered Regulation of Expressed Polar Meibum Lipids in Dry Eye Disease. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):343.
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The effect of meibum lipids on dry eye disease is still not well understood. In related studies, we have identified differentially-expressed non-polar lipids in dry eye samples that may be important in retarding tear evaporation. Polar lipids are also believed to play an important role in maintaining the stability of tear film. The purpose of the present study was to determine if polar lipids are differentially-expressed in human meibum and their identity.
Meibum samples (< 13 μg) were collected in microcapillaries directly from meibomian gland orifices. Meibum solution was prepared by dissolving each meibum sample in a chloroform/methanol mixture at the concentration of ~13 μg/500 μL with an addition of 0.1% ammonium hydroxide. The solutions were directly infused into a maXis 4G UHR-QTOF mass spectrometer (Bruker; Billerica, MA), and the lipid peaks were acquired in negative ion detection mode. A total of 26 samples (17 dry eye and 9 normal) were analyzed by mass spectrometry and the resultant peak lists for these samples were statistically analyzed with volcano plots, a combination of fold changes and t-tests, by using the online program MetaboAnalyst.
Volcano plots, plots of log2 (fold change) vs. log10 (p value), were generated to show the differentially expressed lipids. A total of 42 peaks were found differentially expressed (p<0.05) in dry eye meibum samples. Downregulated species include polyunsaturated O-acyl-omega-hydroxy-fatty acids; while upregulated species include saturated fatty acids.
Complementary to nonpolar lipids detected, the differentially-expressed polar species in dry eye meibum helps better understand dry eye disease. Depending on the nature of the polar lipids, they could help or hinder the stability of tear film.
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