title: Tear analysis and lens-tear interactions: part II. Ocular lipids-nature and fate of meibomian gland phospholipids.
abstract: OBJECTIVE
  Published data indicate that the polar lipid content of human meibomian gland secretions (MGS) could be anything between 0.5% and 13% of the total lipid. The tear film phospholipid composition has not been studied in great detail and it has been understood that the relative proportions of lipids in MGS would be maintained in the tear film. The purpose of this work was to determine the concentration of phospholipids in the human tear film.
  
  
  METHODS
  Liquid chromatography mass spectrometry (LCMS) and thin layer chromatography (TLC) were used to determine the concentration of phospholipid in the tear film. Additionally, an Amplex Red phosphatidylcholine-specific phospholipase C (PLC) assay kit was used for determination of the activity of PLC in the tear film.
  
  
  RESULTS
  Phospholipids were not detected in any of the tested human tear samples with the low limit of detection being 1.3 μg/mL for TLC and 4 μg/mL for liquid chromatography mass spectrometry. TLC indicated that diacylglycerol (DAG) may be present in the tear film. PLC was in the tear film with an activity determined at approximately 15 mU/mL, equivalent to the removal of head groups from phosphatidylcholine at a rate of approximately 15 μM/min.
  
  
  CONCLUSIONS
  This work shows that phospholipid was not detected in any of the tested human tear samples (above the lower limits of detection as described) and suggests the presence of DAG in the tear film. DAG is known to be at low concentrations in MGS. These observations indicate that PLC may play a role in modulating the tear film phospholipid concentration.
authors.affiliation: Biomaterials Research Unit, Bio-Materials and Molecular Science Group, Chemical Engineering and Applied Chemistry, School of Engineering and Applied Science, Aston University, Aston, Birmingham, West Midlands, United Kingdom. campbeld@aston.ac.uk
authors.forename: Darren
authors.initials: D
authors.lastname: Campbell
authors.forename: Gareth
authors.initials: G
authors.lastname: Griffiths
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Tighe
mesh_terms: D002851:Chromatography, High Pressure Liquid; D002855:Chromatography, Thin Layer; D004075:Diglycerides / Q000032:analysis; D006801:Humans; D013058:Mass Spectrometry; D008537:Meibomian Glands / Q000378:metabolism*; D010743:Phospholipids / Q000032:analysis*; D013048:Specimen Handling; D013666:Tears / Q000737:chemistry*; D010738:Type C Phospholipases / Q000032:analysis
chemical_list: D004075:Diglycerides; D010743:Phospholipids; D010738:Type C Phospholipases