title: Cis-urocanic acid suppresses UV-B-induced interleukin-6 and -8 secretion and cytotoxicity in human corneal and conjunctival epithelial cells in vitro.
abstract: 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.
authors.affiliation: Department of Ophthalmology, Institute of Clinical Medicine, University of Kuopio, Kuopio, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Viiri
authors.forename: H M
authors.initials: HM
authors.lastname: Jauhonen
authors.forename: A
authors.initials: A
authors.lastname: Kauppinen
authors.forename: T
authors.initials: T
authors.lastname: Ryhänen
authors.forename: T
authors.initials: T
authors.lastname: Paimela
authors.forename: J
authors.initials: J
authors.lastname: Hyttinen
authors.forename: I
authors.initials: I
authors.lastname: Sorri
authors.forename: J K
authors.initials: JK
authors.lastname: Laihia
authors.forename: L
authors.initials: L
authors.lastname: Leino
authors.forename: K
authors.initials: K
authors.lastname: Kaarniranta
mesh_terms: 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*
chemical_list: D003470:Culture Media; D015850:Interleukin-6; D016209:Interleukin-8; D053148:Caspase 3; D014560:Urocanic Acid