IRON BOUND TO THE LIPOPHILIC IRON CHELATOR, 8-HYDROXYQUINOLINE, CAUSES DNA STRAND BREAKAGE IN CULTURED LUNG-CELLS

The formation of DNA-strand breaks was studied in cultured human lung cells (A 549) subjected to iron, either in the form of iron(III) citra te or in combination with the metal chelators ethylene diamine tetra-a cetic acid (EDTA), nitrilo triacetic acid (NTA), or 8-hydroxyquinoline (8HQ), After 15 min exposure to 5 mu M iron(III) citrate or iron chel ate, the cellular levels of iron were found to be three times higher i n cells subjected to iron-8HQ than in cells subjected to iron(III) cit rate, iron-EDTA or iron-NTA, Exposure to iron-8HQ caused extensive DNA -strand breakage, whereas no such breakage was found in cells exposed to iron-EDTA or iron-NTA, The DNA damage caused by iron-8HQ increased with time and dose, and DNA-strand breakage was clearly demonstrable i n cells after 15 min exposure to as little as 0.1 mu M iron-8HQ, Moreo ver, iron-8HQ was strongly toxic to the cells and inhibited their grow th after exposure, Along with the formation of DNA-strand breaks, the concentration of cellular malondialdehyde increased four-fold after ex posure to iron-8HQ and two-fold after exposure to iron-EDTA or iron-NT A, suggesting that reactive oxygen metabolites might be involved in th e toxic action, Moreover, both iron-EDTA and iron-NTA caused a conside rable hydroxylation of deoxyguanosine (dG) residues in DNA in vitro, w hereas iron(III) citrate and iron-8HQ only caused a minor hydroxylatio n of dG, This points to the possibility that iron-8HQ-mediated DNA-str and breakage in cells might be due to the action of a metal-bound oxyl radical formed from the iron-8HQ complex rather than to the formation of hydroxyl radicals, Altogether, these findings indicate that iron b ound to the lipophilic chelator, 8HQ, has strong toxic properties and that it may cause substantial DNA-strand breakage and lipid peroxidati on in living cells.