title: Molecular genetic basis for fluoroquinolone-induced retinal degeneration in cats.
abstract: OBJECTIVE
  Distribution of fluoroquinolones to the retina is normally restricted by ABCG2 at the blood-retinal barrier. As the cat develops a species-specific adverse reaction to photoreactive fluoroquinolones, our goal was to investigate ABCG2 as a candidate gene for fluoroquinolone-induced retinal degeneration and blindness in cats.
  
  
  METHODS
  Feline ABCG2 was sequenced and the consensus amino acid sequence was compared with that of 10 other mammalian species. Expression of ABCG2 in feline retina was assessed by immunoblot. cDNA constructs for feline and human ABCG2 were constructed in a pcDNA3 expression vector and expressed in HEK-293 cells, and ABCG2 expression was analyzed by western blot and immunofluorescence. Mitoxantrone and BODIPY-prazosin efflux measured by flow cytometry and a phototoxicity assay were used to assess feline and human ABCG2 function.
  
  
  RESULTS
  Four feline-specific (compared with 10 other mammalian species) amino acid changes in conserved regions of ABCG2 were identified. Expression of ABCG2 on plasma membranes was confirmed in feline retina and in cells transfected with human and feline ABCG2, although some intracellular expression of feline ABCG2 was detected by immunofluorescence. Function of feline ABCG2, compared with human ABCG2, was found to be deficient as determined by flow cytometric measurement of mitoxantrone and BODIPY-prazosin efflux and enrofloxacin-induced phototoxicity assays.
  
  
  CONCLUSIONS
  Feline-specific amino acid changes in ABCG2 cause a functional defect of the transport protein in cats. This functional defect may be owing, in part, to defective cellular localization of feline ABCG2. Regardless, dysfunction of ABCG2 at the blood-retinal barrier likely results in accumulation of photoreactive fluoroquinolones in feline retina. Exposure of the retina to light would then generate reactive oxygen species that would cause the characteristic retinal degeneration and blindness documented in some cats receiving high doses of some fluoroquinolones. Pharmacological inhibition of ABCG2 in other species might result in retinal damage if fluoroquinolones are concurrently administered.
authors.affiliation: Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University, Pullman, Washington 99164-6610, USA.
authors.forename: Christina J
authors.initials: CJ
authors.lastname: Ramirez
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Minch
authors.forename: John M
authors.initials: JM
authors.lastname: Gay
authors.forename: Sunshine M
authors.initials: SM
authors.lastname: Lahmers
authors.forename: Dan J
authors.initials: DJ
authors.lastname: Guerra
authors.forename: Gary J
authors.initials: GJ
authors.lastname: Haldorson
authors.forename: Terri
authors.initials: T
authors.lastname: Schneider
authors.forename: Katrina L
authors.initials: KL
authors.lastname: Mealey
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001896:Boron Compounds / Q000378:metabolism; D002371:Cat Diseases / Q000139:chemically induced* / Q000235:genetics*; D002415:Cats; D017124:Conserved Sequence / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D017484:Dermatitis, Phototoxic / Q000150:complications / Q000235:genetics / Q000662:veterinary; D005455:Fluorescent Antibody Technique; D024841:Fluoroquinolones / Q000009:adverse effects* / Q000737:chemistry; D057809:HEK293 Cells; D006801:Humans; D008942:Mitoxantrone / Q000494:pharmacology; D008967:Molecular Biology; D008969:Molecular Sequence Data; D011224:Prazosin / Q000031:analogs & derivatives / Q000378:metabolism; D012160:Retina / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D012162:Retinal Degeneration / Q000139:chemically induced / Q000150:complications / Q000235:genetics / Q000662:veterinary*; D014162:Transfection
chemical_list: D018528:ATP-Binding Cassette Transporters; C412306:BODIPY-FL prazosin; D001896:Boron Compounds; D018076:DNA, Complementary; D024841:Fluoroquinolones; D008942:Mitoxantrone; D011224:Prazosin