title: Source-dependent intracellular distribution of iron in lens epithelial cells cultured under normoxic and hypoxic conditions.
abstract: OBJECTIVE
  Intracellular iron trafficking and the characteristics of iron distribution from different sources are poorly understood. We previously determined that the lens removes excess iron from fluids of inflamed eyes. In the current study, we examined uptake and intracellular distribution of ⁵⁹Fe from iron transport protein transferrin or ferric chloride (nontransferrin-bound iron [NTBI]) in cultured canine lens epithelial cells (LECs). Because lens tissue physiologically functions under low oxygen tension, we also tested effects of hypoxia on iron trafficking. Excess iron, not bound to proteins, can be damaging to cells due to its ability to catalyze formation of reactive oxygen species.
  
  
  METHODS
  LECs were labeled with ⁵⁹Fe-Tf or ⁵⁹FeCl₃ under normoxic or hypoxic conditions. Cell lysates were fractioned into mitochondria-rich, nuclei-rich, and cytosolic fractions. Iron uptake and its subcellular distribution were measured by gamma counting.
  
  
  RESULTS
  ⁵⁹Fe accumulation into LECs labeled with ⁵⁹Fe-Tf was 55-fold lower as compared with that of ⁵⁹FeCl₃. Hypoxia (24 hours) decreased uptake of iron from transferrin but not from FeCl₃. More iron from ⁵⁹FeCl₃ was directed to the mitochondria-rich fraction (32.6%-47.7%) compared with ⁵⁹Fe from transferrin (10.6%-12.6%). The opposite was found for the cytosolic fraction (8.7%-18.3% and 54.2%-46.6 %, respectively). Hypoxia significantly decreased iron accumulation in the mitochondria-rich fraction of LECs labeled with ⁵⁹Fe-Tf .
  
  
  CONCLUSIONS
  There are source-dependent differences in iron uptake and trafficking. Uptake and distribution of NTBI are not as strictly regulated as that of iron from transferrin. Excessive exposure to NTBI, which could occur in pathological conditions, may oxidatively damage organelles, particularly mitochondria.
authors.affiliation: Department of Molecular Biomedical Sciences, North Carolina State University, Raleigh, North Carolina.
authors.forename: Małgorzata
authors.initials: M
authors.lastname: Goralska
authors.forename: Steven
authors.initials: S
authors.lastname: Nagar
authors.forename: Lloyd N
authors.initials: LN
authors.lastname: Fleisher
authors.forename: Philip
authors.initials: P
authors.lastname: Mzyk
authors.forename: M Christine
authors.initials: MC
authors.lastname: McGahan
mesh_terms: D000818:Animals; D001692:Biological Transport; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D002470:Cell Survival; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism*; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism*; D005290:Ferric Compounds / Q000378:metabolism*; D000860:Hypoxia / Q000378:metabolism*; D007424:Intracellular Fluid / Q000378:metabolism; D007504:Iron Radioisotopes / Q000378:metabolism; D007908:Lens, Crystalline / Q000166:cytology* / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D014168:Transferrin / Q000378:metabolism*
chemical_list: D002712:Chlorides; D005290:Ferric Compounds; D007504:Iron Radioisotopes; D014168:Transferrin; C024555:ferric chloride
keywords: NTBI; hypoxia; iron trafficking; lens epithelial cells; transferrin