THE EFFECT OF IRON-BINDING ON THE ABILITY OF CROCIDOLITE ASBESTOS TO CATALYZE DNA SINGLE-STRAND BREAKS

Crocidolite or crocidolite pretreated with desferrioxamine-B (DF croci dolite) was exposed to ferrous chloride solutions to determine whether iron could be bound from solution. Native crocidolite was capable of binding up to 57 nmol Fe2+/mg fiber in 60 min, while the DF crocidolit e was capable of binding only 5.5 nmol Fe2+/mg fiber. The rate of iron binding for the first 5 min of exposure was independent of the concen tration of iron in the solution, suggesting that there was a group of rapidly saturable sites, similar to 1.5x10(18) binding sites/m(2) croc idolite surface, which were responsible for the immediate binding. Thi s process was followed by a slower binding phase, likely occurring at other sites. Crocidolite and DF crocidolite, with various amounts of i ron bound, were assayed for their abilities to catalyze the formation of DNA single-strand breaks (SSBs) in phi X174 RFI DNA. Native crocido lite with additional iron bound did not significantly change in its ab ility to cause DNA SSBs in 15 or 30 min incubations, even though more iron could be mobilized from the iron-treated crocidolite at 4 of 24 h . DF crocidolite, after the addition of iron, had a significantly incr eased ability to form DNA SSBs. DF crocidolite with 0, 3.0 or 5.5 nmol Fe2+/mg catalyzed the formation of DNA SSBs in 21, 42 or 51% of the D NA respectively in the presence of EDTA and ascorbate. Fibers were als o incubated in tissue culture medium with or without iron salts. The f ibers incubated in the iron-containing medium had an increased ability to form DNA SSBs. These results suggest that fibers such as crocidoli te may be capable of binding iron from intracellular sources. This add itional iron may be as reactive as the intrinsic iron and may increase the reactive lifetime of the fiber.