Tear lipocalin: evidence for a scavenging function to remove lipids from the human corneal surface.
OBJECTIVE
Lipid contamination of the cornea may create an unwettable surface and result in desiccation of the corneal epithelium. Tear lipocalin (TL), also known as lipocalin-1, is the principal lipid-binding protein in tears. TL has been shown to scavenge lipids from hydrophobic surfaces. The hypothesis that TL can remove contaminating fatty acids and phospholipids from the human corneal surface was tested.


METHODS
TL was purified from pooled human tear samples by size exclusion and ion exchange chromatographies. Tears depleted of TL were reconstituted from fractions eluted by size exclusion chromatography that did not contain TL. Fresh and formalin-fixed human corneas were obtained from exenteration specimens. Fluorescent analogs of either palmitic acid or phosphatidylcholine were applied to the corneal epithelial surface. Tears, TL, or tears depleted of TL were applied over the corneas, and spectrofluorometry and fluorescent stereomicroscopy were used to monitor the removal of fluorescent lipids. Tears used in the experiments were then fractionated by size exclusion chromatography to determine the component of tears associated with fluorescent lipids.


RESULTS
Significant enhancement of fluorescence for 16AP and NBD C(6)-HPC was evident in solutions incubated with whole tears and purified TL but not with tears depleted of TL for fixed and unfixed corneas. After the experiment, size exclusion fractions of tears showed that the fluorescence component coeluted with TL.


CONCLUSIONS
TL scavenges lipids from the human corneal surface and delivers them into the aqueous phase of tears. TL may have an important role in removing lipids from the corneal surface to maintain the wettability and integrity of the ocular surface.
Gasymov
Oktay K
OK
Department of Pathology and Ophthalmology, UCLA School of Medicine, Los Angeles, California, USA.
Abduragimov
Adil R
AR
Prasher
Pawan
P
Yusifov
Taleh N
TN
Glasgow
Ben J
BJ
D002352:Carrier Proteins / Q000302:isolation & purification / Q000502:physiology*; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D003315:Cornea / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000302:isolation & purification / Q000502:physiology*; D005136:Eye Proteins / Q000302:isolation & purification / Q000502:physiology*; D005456:Fluorescent Dyes / Q000378:metabolism; D006801:Humans; D054835:Lipocalin 1; D008856:Microscopy, Fluorescence; D010169:Palmitic Acids / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D010743:Phospholipids / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013666:Tears / Q000737:chemistry
D002352:Carrier Proteins; D015853:Cysteine Proteinase Inhibitors; D005136:Eye Proteins; D005456:Fluorescent Dyes; C518443:LCN1 protein, human; D054835:Lipocalin 1; D010169:Palmitic Acids; D010713:Phosphatidylcholines; D010743:Phospholipids; C042434:tear proteins; C047265:16-(9-anthroyloxy)palmitic acid