title: Protein modifications by 4-hydroxynonenal and 4-hydroxyhexenal in light-exposed rat retina.
abstract: OBJECTIVE
  4-Hydroxynonenal (4-HNE) and 4-hydroxyhexenal (4-HHE) are reactive aldehydes derived from the nonenzymatic oxidation of n-6 and n-3 polyunsaturated fatty acids, respectively. Increasing evidence suggests that protein modifications by reactive aldehydes are involved in various diseases. The present study was undertaken to test whether protein modifications by 4-HNE and 4-HHE increase in retinal tissues after exposure of rats to damaging levels of light.
  
  
  METHODS
  Albino rats were exposed to 1 or 5 klux white fluorescent light for 3 hours and, at various times thereafter, the levels and localizations of aldehyde-modified proteins in retinas were assessed by densitometric analysis of semiquantitative Western dot blots and by immunohistochemistry, using 4-HNE- and 4-HHE-specific antibodies. In some rats, the protective antioxidant phenyl-N-tert-butylnitrone (PBN) was injected (50 mg/kg) before exposure to light. To assess retinal damage, outer nuclear layer (ONL) thickness was measured on hematoxylin-eosin (H&E)-stained sections, and apoptosis was semiquantitatively analyzed by TUNEL staining.
  
  
  RESULTS
  By dot blot analysis, 4-HNE- and 4-HHE-modified proteins were significantly increased in retina (both by 1.7-fold) and RPE fraction (1.5- and 1.8-fold, respectively) after 5-klux exposure. In retina, increases in 4-HNE- and 4-HHE-modified proteins were more prominent at 3 hours than at 24 hours or 48 hours after exposure to light. In rod outer segments, only 4-HHE-modified proteins increased significantly (1.4-fold). Retinal thinning, TUNEL staining in ONL, 4-HNE-, and 4-HHE protein modifications were all found in the same retinal regions. PBN treatment inhibited the light-induced increase of 4-HNE and 4-HHE modified proteins in retina and RPE fractions.
  
  
  CONCLUSIONS
  Exposure to intense light increases 4-HNE and 4-HHE protein modifications in the retina, suggesting that free radical initiated, nonenzymatic reactions are involved in this process. These modifications may be early events that precede photoreceptor cell apoptosis.
authors.affiliation: Departments of Ophthalmology, University of Oklahoma Health Sciences Center, Oklahoma City, 73104, USA. masaki-tanito@ouhsc.edu
authors.forename: Masaki
authors.initials: M
authors.lastname: Tanito
authors.forename: Michael H
authors.initials: MH
authors.lastname: Elliott
authors.forename: Yashige
authors.initials: Y
authors.lastname: Kotake
authors.forename: Robert E
authors.initials: RE
authors.lastname: Anderson
mesh_terms: D000447:Aldehydes / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D003497:Cyclic N-Oxides; D005136:Eye Proteins / Q000378:metabolism*; D005260:Female; D016166:Free Radical Scavengers / Q000494:pharmacology; D007124:Immunoenzyme Techniques; D020287:In Situ Nick-End Labeling; D008027:Light; D009589:Nitrogen Oxides / Q000494:pharmacology; D011499:Protein Processing, Post-Translational; D011833:Radiation Injuries, Experimental / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000187:drug effects / Q000473:pathology / Q000528:radiation effects*; D012162:Retinal Degeneration / Q000378:metabolism* / Q000473:pathology / Q000517:prevention & control
chemical_list: D000447:Aldehydes; D003497:Cyclic N-Oxides; D005136:Eye Proteins; D016166:Free Radical Scavengers; D009589:Nitrogen Oxides; C045934:4-hydroxy-2-hexenal; C029217:phenyl-N-tert-butylnitrone; C027576:4-hydroxy-2-nonenal