Iron mobilization from crocidolite asbestos greatly enhances crocidolite-dependent formation of DNA single-strand breaks in øX174 RFI DNA

Abstract

The ability of the iron associated with asbestos to catalyze damage to phi X174 RFI DNA was determined and compared with iron mobilized from asbestos. Asbestos (1 mg/ml) suspended for 30 min in 50 mM NaCl containing 0.5 micrograms phi X174 RFI DNA, pH 7.5, did not catalyze detectable amounts of DNA single-strand breaks (SSB). However, addition of ascorbate (1 mM) resulted in 19, 26, 7 or 8% DNA with SSB for crocidolite, amosite, chrysotile or tremolite respectively. The percentage of DNA with SSB induced by each form of asbestos was directly related to its iron content. Inclusion of desferrioxamine B, which binds Fe(III) rendering it redox inactive, completely inhibited asbestos-dependent formation of DNA SSB, suggesting that iron was responsible for catalyzing the formation of DNA SSB. Mobilization of Fe(II) from crocidolite by citrate, EDTA or nitrilotriacetate (1 mM) in the absence of ascorbate resulted in 15, 33 or 63% DNA with SSB respectively. This activity was completely inhibited by compounds considered to be .OH scavengers, i.e. mannitol, 5,5-dimethyl-1-pyrroline N-oxide or salicylate (100 mM). Preincubation of crocidolite with citrate (1 mM) for 24 h resulted in mobilization of 52 microM iron and increased ascorbate-dependent induction of DNA SSB compared with crocidolite that was preincubated without citrate. Iron mobilized by citrate was entirely responsible for crocidolite-dependent formation of DNA SSB as evidenced by complete inhibition with desferrioxamine B.…