Lipids of human meibum: Mass-spectrometric analysis and structural elucidation

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Abstract

The purpose of this study was to structurally characterize the major lipid species present in human meibomian gland secretions (MGS) of individual subjects by means of ion trap atmospheric pressure ionization mass spectrometry analysis (API MSn). The samples of MGS and authentic lipid standards were analyzed in direct infusion and high-pressure liquid chromatography (HPLC) experiments with API MSn detection of the analytes (HPLC API MS n). The major precursor ions were isolated and subjected to further sequential fragmentation in MSn experiments, and their fragmentation patterns were compared with those of authentic lipid standards. Multiple precursor ions were observed in the positive-ion mode. Among those, previously identified cholesterol (Chl; m/z 369; [M - H2O + H]+) and oleic acid (OA; m/z 283; [M + H]+) were found. The other major compounds of the general molecular formula CnH2n-2O 2 were consistent with wax esters (WEs), with OA as fatty acyl component. Accompanying them were two homologous series of compounds that fit the molecular formulas CnH2n-4O2 and C nH2nO2. Subset 2 was found to be a homolog series of linoleic acid-based WEs, whereas subset 3 was, apparently, a mixture of stearic acid-based WEs. HPLC API MSn analysis revealed the presence of large quantities of cholesteryl esters (Chl-Es) in all of the tested samples. Less than 0.1% (w/w) of oleamide was detected in human MGS. In the negative-ion mode, three major compounds with m/z values of 729, 757, and 785 that were apparently related to anionogenic lipids of the diacylglyceryl family were found in all of the samples. Common phospholipids and ceramides (Cers) were not present among the major MGS lipids. Phosphocholine-based lipids were found in MGS in quantities less than 0.01% (w/w), if at all. This ratio is two orders of magnitude lower than reported previously. These observations suggest that MGS are a major source of nonpolar lipids of the WE and Chl-E families for the tear film lipid layer, but not of its previously reported (phospho)lipid, Cer, and fatty acid amide components.

Original languageEnglish (US)
Pages (from-to)2220-2235
Number of pages16
JournalJournal of Lipid Research
Volume48
Issue number10
DOIs
StatePublished - Oct 2007

Fingerprint

Meibomian Glands
Lipids
Waxes
High pressure liquid chromatography
Atmospheric Pressure
Ions
Esters
Atmospheric pressure
Ionization
Mass spectrometry
Mass Spectrometry
High Pressure Liquid Chromatography
Phosphorylcholine
Cholesterol Esters
Ceramides
Linoleic Acid
Oleic Acid
Tears
Application programming interfaces (API)
Amides

Keywords

  • Human meibomian gland
  • Mass spectrometry
  • Oleamide
  • Phospholipids
  • Tear film lipid layer
  • Wax esters

ASJC Scopus subject areas

  • Endocrinology

Cite this

Lipids of human meibum : Mass-spectrometric analysis and structural elucidation. / Butovich, Igor A.; Uchiyama, Eduardo; McCulley, James P.

In: Journal of Lipid Research, Vol. 48, No. 10, 10.2007, p. 2220-2235.

Research output: Contribution to journalArticle

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