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Jianzhong Chen, Jeremy Keirsey, Kari Basso, Kelly K Nichols; Differentially Expressed Non-polar Lipids in Human Meibum of Dry Eye Disease. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):342.
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The role of lipid species and the integration of meibum lipids into the tear film in dry eye disease is poorly understood. In our recent pilot studies (Chen J, et al., IOVS, 2013; 54:5730-5753), we have tentatively identified several differentially expressed non-polar lipids in dry eye versus normal meibum. The purpose of the present study was to confirm our earlier findings and to further explore differentially-expressed lipids with a large number of human meibum samples.
Meibum samples (~ 13 μg) were collected in microcapillaries directly from meibomian gland orifices. Meibum stock solutions were prepared by dissolving each meibum sample in chloroform/methanol mixture at the concentration of ~13 μg/100 μL. The stock solutions were diluted with methanol by 50 fold and then directly infused into a high resolution maXis 4G UHR-QTOF mass spectrometer (Bruker; Billerica, MA), and the lipid peaks were acquired in positive ion detection mode. A total of 84 meibum samples (48 normal, 36 dry eye) were analyzed. The resultant peak lists for these samples were statistically analyzed with volcano plots, a visual statistical tool combining fold change results with t-test results, by using the online program MetaboAnalyst.
Differentially expressed lipids were assessed using a novel technology. Volcano plots, the plot of log2 (fold change) vs. log10 (p value), were generated to show a total of 53 peaks that were differentially expressed (p<0.05) in dry eye meibum samples. Down-regulated species mainly included polyunsaturated wax esters and diesters; while up-regulated species included triacylglycerols (including their fragment ions, possibly from in-source dissociation) as well as wax esters and diesters with low levels of saturation.
With the large number of samples, we not only confirmed many polyunsaturated diesters were down regulated in dry eye samples, but also found other lipid species with altered expression in dry eye disease. Identifying differentially expressed non-polar species in dry eye meibum may lead to the development of new therapeutic approaches and ultimately a better understanding of dry eye disease.
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