title: Protection of corneal epithelial stem cells prevents ultraviolet A damage during corneal collagen cross-linking treatment for keratoconus.
abstract: OBJECTIVE
  Cross-linking of the cornea is usually carried out at a young age as a treatment to manage ectasia. The corneal limbal region contains delicate long-lived stem cells, which could potentially be deleteriously affected by Ultraviolet A (UV-A) radiation. Damage to these stem cells may not demonstrate as a clinical problem for many years subsequent to cross-linking treatment. UV-A radiation is known to have potential mutagenic effects upon mammalian DNA and can result in cancer.
  
  
  METHODS
  Cultured corneal epithelial cells and ex vivo corneal tissue were treated with the standard clinical cross-linking protocol for UV-A irradiation. 8-hydroxydeoxyguansoine (8-OHdG) and cyclin-dependent kinase inhibitor genes (CDKN1A and CDKN2A) were assayed as markers of DNA damage using immunohistochemistry, ELISA and quantitative real time PCR.
  
  
  RESULTS
  Staining of treated limbal tissue demonstrated the presence of 8-OHdG within p63 positive basal limbal cells. Levels of 8-OHdG and CDKN1A mRNA were found to be significantly increased in cultured corneal epithelial cells and limbal epithelial cells but no increase was demonstrated with the use of a polymethyl methylacrylate protective cover.
  
  
  CONCLUSIONS
  This study provides evidence that oxidative nuclear DNA damage can occur through cross-linking in layers of corneal epithelial cells at the limbus and that this can be easily prevented by covering the limbus.
authors.affiliation: School of Biomedical Sciences, University of Ulster, , Coleraine, Northern Ireland.
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Moore
authors.forename: Sarah D
authors.initials: SD
authors.lastname: Atkinson
authors.forename: Dimitri T
authors.initials: DT
authors.lastname: Azar
authors.forename: Jenny
authors.initials: J
authors.lastname: Worthington
authors.forename: C Stephen
authors.initials: CS
authors.lastname: Downes
authors.forename: David G
authors.initials: DG
authors.lastname: Courtney
authors.forename: C B Tara
authors.initials: CB
authors.lastname: Moore
mesh_terms: D000080242:8-Hydroxy-2'-Deoxyguanosine / Q000031:analogs & derivatives; D017209:Apoptosis / Q000528:radiation effects; D002460:Cell Line; D003094:Collagen / Q000494:pharmacology*; D004247:DNA / Q000235:genetics; D004249:DNA Damage; D004797:Enzyme-Linked Immunosorbent Assay; D019573:Epithelium, Corneal / Q000166:cytology* / Q000187:drug effects / Q000528:radiation effects; D006147:Guanine / Q000031:analogs & derivatives / Q000378:metabolism; D006801:Humans; D007640:Keratoconus / Q000378:metabolism / Q000473:pathology / Q000628:therapy*; D060888:Real-Time Polymerase Chain Reaction; D013234:Stem Cells / Q000166:cytology* / Q000187:drug effects / Q000528:radiation effects; D014466:Ultraviolet Rays / Q000009:adverse effects*; D014467:Ultraviolet Therapy / Q000009:adverse effects
chemical_list: D006147:Guanine; C078307:8-oxo-7,8-dihydrodeoxyguanine; D000080242:8-Hydroxy-2'-Deoxyguanosine; D003094:Collagen; D004247:DNA
keywords: Cornea; Stem Cells; Treatment Lasers; Vision