Role of iron ion chelation by quinones in their reduction, OH-radical generation and lipid peroxidation

Abstract To study the role of the complex of quinones with iron ions in the processes of quinone reduction and OH-radical generation in the presence of ascorbate (AH) and glutathione (GSH) the quinone-chelators have been used: 2-phenyl-4-butylaminonaphtho[2,3-h]quinolindione-7,12 (Qc) and adriamycin (Adr). 2-Phenyl-5-nitronaphtho[2,3-g]indodione-6,11 (Qn), 2-(3-hydroxypropyl)anthraquinone (AQOP) and 2-dimethvlamino-3-chlor-1,4-naphthoquinone (DCNQ) were chosen as quinones that do not chelate iron ions. It was found that, unlike Adr and nonchelating quinones Qn, AQOP, and DCNQ, addition of Qc to AH and GSH leads to semiquinone EPR spectrum formation and OH-radical generation via the complex of Qc with iron ions. It was demonstrated that all these quinones can be reduced by AH. However, reduction constant of Qc-Fe(3+) by the AH was 98±9 M −1 c −1 , while DCNQ reduction constant was only 0.042±0.005 M −1 c −1 . It was found that in the presence of GSH only complexes of quinones Qc and Adr with iron ions arc reduced. It is concluded that the capability of Qc to reduce and to generate OH-radicals is related to intramolecular electron transfer by the reaction: Fe(2+)-Qc⇔Fe(3+)-Qc ∸ . The capability of Qc to increase generation of oxygen radicals and to inhibit lipid peroxidation may be interesting for designing quinone-containing antibiotics.