title: Radiation cataracts: mechanisms involved in their long delayed occurrence but then rapid progression.
abstract: OBJECTIVE
  This study was directed to assess the DNA damage and DNA repair response to X-ray inflicted lens oxidative damage and to investigate the subsequent changes in lens epithelial cell (LEC) behavior in vivo that led to long delayed but then rapidly developing cataracts.
  
  
  METHODS
  Two-month-old C57Bl/6 female mice received 11 Grays (Gy) of soft x-irradiation to the head only. The animals' eyes were examined for cataract status in 30 day intervals by slit lamp over an 11 month period post-irradiation. LEC migration, DNA fragment, free DNA retention, and reactive oxygen species (ROS) presence were established in the living lenses with fluorescent dyes using laser scanning confocal microscopy (LSCM). The extent and removal of initial LEC DNA damage were determined by comet assay. Immunohistochemistry was used to determine the presence of oxidized DNA and the response of a DNA repair protein in the lenses.
  
  
  RESULTS
  This treatment resulted in advanced cortical cataracts that developed 5-11 months post-irradiation but then appeared suddenly within a 30 day period. The initially incurred DNA strand breaks were repaired within 30 min, but DNA damage remained as shown 72 h post-irradiation by the presence of the DNA adduct, 8-hydroxyguanosine (8-OHG), and a DNA repair protein, XRCC1. This was followed months later by abnormal behavior by LEC descendant cells with abnormal differentiation and migration patterns as seen with LSCM and fluorescent dyes.
  
  
  CONCLUSIONS
  The sudden development of cortical cataracts several months post-irradiation coupled with the above findings suggests an accumulation of damaged descendants from the initially x-irradiated LECs. As these cells migrate abnormally and leave acellular lens surface sites, eventually a crisis point may arrive for lens entry of environmental O(2) with resultant ROS formation that overwhelms protection by resident antioxidant enzymes and results in the coagulation of lens proteins. The events seen in this study indicate the retention and transmission of progenitor cell DNA damage in descendant LEC. The cellular and molecular events parallel those previously reported for LSCM observations in age-related cataracts.
authors.affiliation: Department of Pathology, University of Washington, Seattle, WA 98195-7475, USA. normwolf@u.washington.edu
authors.forename: Norman
authors.initials: N
authors.lastname: Wolf
authors.forename: William
authors.initials: W
authors.lastname: Pendergrass
authors.forename: Narendra
authors.initials: N
authors.lastname: Singh
authors.forename: Karen
authors.initials: K
authors.lastname: Swisshelm
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Schwartz
mesh_terms: D000016:Abnormalities, Radiation-Induced / Q000473:pathology*; D000818:Animals; D002386:Cataract / Q000473:pathology*; D016923:Cell Death / Q000528:radiation effects; D002465:Cell Movement / Q000528:radiation effects; D020552:Comet Assay; D004247:DNA / Q000378:metabolism; D018736:DNA Adducts / Q000378:metabolism; D004249:DNA Damage; D004268:DNA-Binding Proteins / Q000378:metabolism; D018450:Disease Progression; D004847:Epithelial Cells / Q000473:pathology / Q000528:radiation effects; D005136:Eye Proteins / Q000737:chemistry; D005260:Female; D006151:Guanosine / Q000031:analogs & derivatives / Q000378:metabolism; D007904:Lens Cortex, Crystalline / Q000473:pathology / Q000528:radiation effects; D007907:Lens Nucleus, Crystalline / Q000473:pathology / Q000528:radiation effects; D051379:Mice; D008810:Mice, Inbred C57BL; D020836:Protein Structure, Quaternary; D011833:Radiation Injuries, Experimental / Q000473:pathology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D013997:Time Factors; D014965:X-Rays; D000076105:X-ray Repair Cross Complementing Protein 1
chemical_list: D018736:DNA Adducts; D004268:DNA-Binding Proteins; D005136:Eye Proteins; D017382:Reactive Oxygen Species; D000076105:X-ray Repair Cross Complementing Protein 1; C000619352:Xrcc1 protein, mouse; D006151:Guanosine; C046215:8-hydroxyguanosine; D004247:DNA