title: Effects of keratin and lung surfactant proteins on the surface activity of meibomian lipids.
abstract: OBJECTIVE
  In vitro studies indicate that surface tension and surface viscosity of the tear film lipid layer (TFLL) are governed by interactions between meibomian lipids and proteins from the aqueous layer. The role of minor tear proteins with strong lipophilic properties or those correlated with pathological states is still unknown. The discovery of lung surfactant proteins (SPs) in tears and keratin in normal and abnormal meibomian gland excretions warrants investigation into their effects on the surface activity of meibomian lipid films.
  
  
  METHODS
  Commercial keratin and bovine lung SPs were used in vitro to assess the surface pressure of meibomian lipid films using a Langmuir trough.
  
  
  RESULTS
  The pressure-area profiles of meibomian lipid films seeded with SPs (2.5 μL; 0.1 μg) demonstrated hybrid characteristics between meibomian lipid films alone and SPs alone but reached much higher maximum surface pressures (approximately 30 vs. 24 mN/m). Microscopically, the appearance of meibomian lipid films was not altered by SPs. Maximum surface pressure of meibomian films premixed with keratin was much higher than meibum alone. The pressure-area isocycles appeared more like those of meibomian lipids with a low concentration of protein and more like pure keratin films at a high concentration.
  
  
  CONCLUSIONS
  The data strongly indicate that SPs and keratin likely interact with the TFLL. SPs are likely to act as strong surfactants and to reduce the surface tension of the lipid layer. Excess concentrations of keratin as identified in patients with meibomian gland dysfunction could disrupt the normal structure of the meibomian lipid film.
authors.affiliation: School of Science and Health, University of Western Sydney, New South Wales, Australia.
authors.forename: Chendur K
authors.initials: CK
authors.lastname: Palaniappan
authors.forename: Burkhardt S
authors.initials: BS
authors.lastname: Schütt
authors.forename: Lars
authors.initials: L
authors.lastname: Bräuer
authors.forename: Martin
authors.initials: M
authors.lastname: Schicht
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Millar
mesh_terms: D000818:Animals; D002417:Cattle; D007633:Keratins / Q000494:pharmacology*; D008055:Lipids / Q000032:analysis*; D008537:Meibomian Glands / Q000737:chemistry* / Q000187:drug effects; D037661:Pulmonary Surfactant-Associated Proteins / Q000494:pharmacology*; D011663:Pulmonary Surfactants / Q000494:pharmacology; D013499:Surface Properties; D013500:Surface Tension
chemical_list: D008055:Lipids; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants; D007633:Keratins