The hypothesis for the proposed research is that iron is responsible for the carcinogenicity of mineral fibers. Fibers can have intrinsic iron, e.g. crocidolite, or can acquire iron which binds to the surface. Either intrinsic or acquired iron may be active at the surface, but mobilization may increase the reactivity of the iron with O2 generating radicals that can cause toxicity and cancer. The in vitro experiments will focus on the effects of iron binding from solution or from cultured macrophages by two forms of asbestos of high iron content, crocidolite and amosite, and a carcinogenic mineral with little or no iron, erionite. Four parameters will be monitored: the surface composition and topography, the surface redox activity, the rate of iron mobilization by chelators, and the ability to induce iron-catalyzed DNA single-strand breaks. The surface composition and topography will be characterized by X-ray photoelectron spectroscopy, Auger electron spectroscopy, and scanning force microscopy. The amount of surface redox active iron will be determined using mediated, thin-layer cell cyclic voltammetry. The intracellular distribution of 55Fe from neutron activated crocidolite in human lung epithelial and mesothelial cells will be compared with that from [55Fe]transferrin, a nontoxic source of iron, and [55Fe]NTA, a toxic source of iron. The amounts of 55Fe in the 10,000 x g supernatant, in immunoprecipitated ferritin, in heme, in <10,000 MW fraction (LMW), and in subcellular organelles will be determined. The nature of the LMW chelator will be determined using laser desorption time-of-flight mass spectrometry, proton nuclear magnetic resonance, and high performance liquid chromatography. The amounts of iron mobilized into the LMW form from neutron-activated crocidolite, amosite, or erionite, unloaded or loaded with iron, will be compared for their relationship with cytotoxicity and ferritin synthesis.
