Tear lipocalins: potential lipid scavengers for the corneal surface.
OBJECTIVE
To investigate the dynamic effect of tear lipocalins (TLs), the major lipid-binding protein in tears, at aqueous-cornea and lipid-aqueous interfaces, and their potential contribution to surface tension in the tear film.


METHODS
Human apo- and holo-TLs were applied to the aqueous subphase in a Langmuir trough, and changes in surface pressure were measured. Changes in the contact angle of tear components were observed on Teflon and ferric-stearate-treated surfaces. A nitroxide-labeled derivative of lauric acid and a fluorescence-labeled derivative of palmitic acid were used to monitor the dynamic interaction of lipid removed from a hydrophobic surface by the major tear components in solution.


RESULTS
TLs increase the surface pressure at the aqueous-air interface by penetrating, spreading, and rearranging on the surface. Apo-TLs show a longer diffusion-dependent induction time than holo-TLs due to more extensive oligomerization of the apoprotein. Kinetic analysis of relaxation time suggests that apo-TLs have more rapid surface penetration and rearrangement than holo-TLs, indicative of a more flexible structure in apo-TLs. TLs reduce the contact angle of solutions on lipid films, a property that is greater with TLs than other tear proteins. TLs, unlike lysozyme and lactoferrin, remove labeled lipids from hydrophobic surfaces and deliver them into solution.


CONCLUSIONS
TLs are potent lipid-binding proteins that increase the surface pressure of aqueous solutions while scavenging lipids from hydrophobic surfaces and delivering them to the aqueous phase of tears. These data suggest important functional roles for TLs in maintaining the integrity of the tear film.
Glasgow
B J
BJ
Department of Pathology, Jules Stein Eye Institute, University of California, School of Medicine, Los Angeles 90095, USA. bglasgow@mednet.ucla.edu
Marshall
G
G
Gasymov
O K
OK
Abduragimov
A R
AR
Yusifov
T N
TN
Knobler
C M
CM
D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002850:Chromatography, Gel; D003315:Cornea / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D007781:Lactoferrin / Q000378:metabolism; D007850:Lauric Acids / Q000378:metabolism*; D054835:Lipocalin 1; D009113:Muramidase / Q000378:metabolism; D010169:Palmitic Acids / Q000378:metabolism*; D013666:Tears / Q000737:chemistry
D002352:Carrier Proteins; D015853:Cysteine Proteinase Inhibitors; C518443:LCN1 protein, human; D007850:Lauric Acids; D054835:Lipocalin 1; D010169:Palmitic Acids; C030358:lauric acid; C047265:16-(9-anthroyloxy)palmitic acid; D009113:Muramidase; D007781:Lactoferrin