Prooxidant and antioxidant properties of iron-hydroquinone and iron-1,2,4-benzenetriol complex. Implications for benzene toxicity.

Bleomycin-dependent degradation of DNA in bone marrow cells was studied in vitro in the presence of iron or iron polyphenol chelates which are formed during biotransformation of benzene. Iron polyphenol chelates markedly enhanced bleomycin-dependent DNA degradation in comparison to iron alone. About 1.5 and 2.5-fold increase was observed in the presence of iron hydroquinone (HQ) chelate and iron 1,2,4-benzenetriol (BT) chelate, respectively. Endogenous iron chelators such as glutamate, citrate, aspartate, glycine, cysteine, dithiothreitol, AMP, ADP and ATP did not enhance iron-catalysed bleomycin-dependent degradation of DNA. By bleomycin assay, the recovery of iron polyphenol chelate added externally to bone marrow lysate was complete. However, the presence of iron polyphenol chelate resulted in less thiobarbituric acid reactive products from glutamate or brain homogenate than with iron alone. The optical spectra of BT were modified in the presence of ferrous sulphate, revealing a new absorption peak at 259 nm indicating complexation with iron. Thus, the iron polyphenol chelate, on one hand, is a more potent DNA cleaving agent in the presence of bleomycin, and on the other hand, it is a less effective free radical generator as compared to iron alone.