title: The Effect of Ambient Ozone on Unsaturated Tear Film Wax Esters.
abstract: OBJECTIVE
  Tear film lipid layer (TFLL) is constantly exposed to reactive ozone in the surrounding air, which may have detrimental effects on ocular health. Behenyl oleate (BO), a representative tear film wax ester, was used to study the reaction with ozone at the air-water interface.
  
  
  METHODS
  Time-dependent changes in mean molecular area of BO monolayers were measured at different ozone concentrations and surface pressures. In addition, the effect of ascorbic acid on the reaction rate was determined. Reaction was followed using thin-layer chromatography and reaction products were identified using liquid chromatography-electrospray ionization mass spectrometry (LC-MS). Tear fluid samples from healthy subjects were analyzed with LC-MS for any ozonolysis reaction products.
  
  
  RESULTS
  Behenyl oleate was found to undergo rapid ozonolysis at the air-water interface at normal indoor ozone concentrations. The reaction was observed as an initial expansion followed by a contraction of the film area. Ascorbic acid was found to decrease the rate of ozonolysis. Main reaction products were identified as behenyl 9-oxononanoate and behenyl 8-(5-octyl-1,2,4-trioxolan-3-yl)octanoate. Similar ozonolysis products were not detected in the tear fluid samples.
  
  
  CONCLUSIONS
  At the air-water interface, unsaturated wax esters react readily with ozone in ambient air. However, no signs of ozonolysis products were found in the tear fluid. This is most likely due to the antioxidant systems present in tear fluid. Last, the results show that ozonolysis needs to be controlled in future surface chemistry studies on tear film lipids.
authors.affiliation: Helsinki Eye Lab Ophthalmology, University of Helsinki and Helsinki University Hospital, Finland.
authors.forename: Riku O
authors.initials: RO
authors.lastname: Paananen
authors.affiliation: Helsinki Eye Lab Ophthalmology, University of Helsinki and Helsinki University Hospital, Finland.
authors.forename: Antti H
authors.initials: AH
authors.lastname: Rantamäki
authors.affiliation: Laboratory of Analytical Chemistry, Department of Chemistry, University of Helsinki, Finland.
authors.forename: Jevgeni
authors.initials: J
authors.lastname: Parshintsev
authors.affiliation: Helsinki Eye Lab Ophthalmology, University of Helsinki and Helsinki University Hospital, Finland.
authors.forename: Juha M
authors.initials: JM
authors.lastname: Holopainen
mesh_terms: D000328:Adult; D002788:Cholesterol Esters / Q000378:metabolism; D002855:Chromatography, Thin Layer; D004952:Esters / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism; D005260:Female; D006801:Humans; D008246:Lysophospholipids / Q000378:metabolism; D008297:Male; D019301:Oleic Acid / Q000378:metabolism; D010083:Oxidants, Photochemical / Q000494:pharmacology*; D010126:Ozone / Q000494:pharmacology*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods; D013666:Tears / Q000737:chemistry*; D014280:Triglycerides / Q000378:metabolism
chemical_list: D002788:Cholesterol Esters; D004952:Esters; D005227:Fatty Acids; D008246:Lysophospholipids; D010083:Oxidants, Photochemical; D014280:Triglycerides; D019301:Oleic Acid; D010126:Ozone