title: Polar lipids in human meibomian gland secretions.
abstract: OBJECTIVE
  To determine the polar lipid composition of human meibomian gland secretions and their relationship to the preocular tear film.
  
  
  METHODS
  Meibomian secretions were collected from normals and patients with chronic blepharitis. These lipids (meibum) were first separated by thin layer chromatography. Polar lipids were then separated utilizing high-pressure liquid chromatography with ultraviolet detection. Individual peaks were identified by comparison with standards. Collected sample peaks were subjected to differential transmethylation with sodium methoxide-methanol and the resulting fatty acid methyl esters were analyzed by gas chromatography-mass spectroscopy.
  
  
  RESULTS
  Three phospholipids were identified as phosphatidylcholine, phosphatidylethanolamine and sphingomyelin; other unidentified phospholipids were also present. Also present in secretions were the sphingolipids ceramides and cerebrosides. Fatty acids present were 12-18 carbon chain length. All fatty acids were normal (not branched) saturated fatty acids except in sphingolipids, where hydroxy fatty acids were also present. Unsaturated normal fatty acids were present only in meibum from patients with meibomianitis.
  
  
  CONCLUSIONS
  The composition of the polar lipids in meibomian gland secretions is more complex than previously thought. On the other hand, the type and carbon chain length of the polar lipid fatty acids appears strictly controlled. The relationship of these findings to the preocular tear film should be considered in terms of overall functionality. The polar lipid layer most likely is only one to three molecules thick and serves as a surfactant between aqueous tears and the thicker nonpolar lipid layer.
authors.affiliation: Department of Ophthalmology, The University of Texas Southwestern Medical Center, Dallas, Texas 75390-9057, USA. ward.shine@UTSouthwestern.edu
authors.forename: Ward E
authors.initials: WE
authors.lastname: Shine
authors.forename: James P
authors.initials: JP
authors.lastname: McCulley
mesh_terms: D001762:Blepharitis / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D002908:Chronic Disease; D005227:Fatty Acids / Q000378:metabolism; D008401:Gas Chromatography-Mass Spectrometry; D006801:Humans; D008537:Meibomian Glands / Q000378:metabolism*; D009093:Mucus / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D013107:Sphingolipids / Q000378:metabolism*; D013666:Tears / Q000378:metabolism
chemical_list: D005227:Fatty Acids; D010743:Phospholipids; D013107:Sphingolipids