Cis-urocanic acid suppresses UV-B-induced interleukin-6 and -8 secretion and cytotoxicity in human corneal and conjunctival epithelial cells in vitro.
OBJECTIVE
Urocanic acid (UCA) is a major ultraviolet (UV)-absorbing endogenous chromophore in the epidermis and is also an efficacious immunosuppressant. The anti-inflammatory and cytoprotective effects of cis-UCA were studied in ocular surface cell cultures exposed to UV-B irradiation.


METHODS
Human corneal epithelial cells (HCE-2) and human conjunctival epithelial cells (HCECs) were incubated with 10, 100, 1,000, and 5,000 microg/ml cis-UCA with and without a single UV-B irradiation dose. The concentrations of IL-1beta, IL-6, IL-8, and TNF-alpha in the culture medium and caspase-3 activity in the cell extract sampled were measured by enzyme-linked immunosorbent assay (ELISA). Cell viability was measured by the colorimetric MTT (3-(4,5-dimethyldiazol- 2-yl)-2,5-diphenyltetrazolium bromide) assay.


RESULTS
UV-B irradiation multiplied interleukin IL-6 and IL-8 secretion levels in HCE-2 cells and HCECs as analyzed with ELISA. Cell viability as measured by the MTT assay declined by 30%-50% in HCE-2 cells and by 20%-40% in HCECs after UV-B irradiation. Moreover, UV-B increased caspase-3 activity in both cell types as analyzed with ELISA. Treatment with 100 microg/ml cis-UCA completely suppressed IL-6 and IL-8 secretion, decreased caspase-3 activity, and improved cell viability against UV-B irradiation. No significant effects on IL-6 or IL-8 secretion, caspase-3 activity, or viability of the non-irradiated cells were observed with 100 microg/ml cis-UCA in both cell types. The 5,000 microg/ml concentration was toxic.


CONCLUSIONS
These findings indicate that cis-UCA may represent a promising anti-inflammatory and cytoprotective treatment option to suppress UV-B-induced inflammation and cellular damage in human corneal and conjunctival epithelial cells.
Viiri
J
J
Department of Ophthalmology, Institute of Clinical Medicine, University of Kuopio, Kuopio, Finland.
Jauhonen
H M
HM
Kauppinen
A
A
Ryhänen
T
T
Paimela
T
T
Hyttinen
J
J
Sorri
I
I
Laihia
J K
JK
Leino
L
L
Kaarniranta
K
K
D053148:Caspase 3 / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects / Q000528:radiation effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D003228:Conjunctiva / Q000166:cytology*; D003470:Culture Media; D004847:Epithelial Cells / Q000166:cytology* / Q000187:drug effects / Q000528:radiation effects; D019573:Epithelium, Corneal / Q000166:cytology*; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism*; D016209:Interleukin-8 / Q000378:metabolism*; D007536:Isomerism; D014466:Ultraviolet Rays; D014560:Urocanic Acid / Q000737:chemistry / Q000494:pharmacology*
D003470:Culture Media; D015850:Interleukin-6; D016209:Interleukin-8; D053148:Caspase 3; D014560:Urocanic Acid