| Popis: |
Asbestos related research began approximately 60 years ago, yet, the mechanism(s) by which asbestos exerts its biological effects is not well understood. The hypothesis upon which this dissertation is based is that mobilization of iron from asbestos enhances the iron-dependent biochemical reactivity of asbestos in vitro and contributes to asbestos-dependent cytotoxicity. The specific aims for this hypothesis were, 1) to determine whether iron was responsible for the biochemical reactivity of asbestos in vitro and asbestos-induced cytotoxicity in cultured cells, and 2) to determine whether mobilization of iron from asbestos enhanced the reactions catalyzed by asbestos in vitro and contributes to asbestos-induced cytotoxicity. It was shown that a chelator (e.g., citrate) had to be present to mobilize iron from asbestos in vitro at pH 7.5. Factors that affected iron mobilization from asbestos (e.g., chelator, pH, or surface area) were investigated. Iron on crocidolite reacted with reducing agents and o2, catalyzed the formation of hydroxyl radical, and induced the formation of DNA single-strand breaks in vitro. However, mobilization of iron from crocidolite by a chelator greatly enhanced crocidolite-dependent o2 consumption, hydroxyl radical formation, and DNA damage in vitro. Crocidolite was more cytotoxic, as measured by cloning efficiency, to cultured Syrian hamster embryo cells than crocidolite that had been pretreated to reduce the amount of iron associated with the fiber, suggesting that iron was responsible for the cytotoxicity. Crocidolite-dependent transformation of these cells was not detected. Crocidolite-dependent cytotoxicity to the human lung carcinoma cell line, A549, was directly dependent upon dose. Intracellular mobilization of iron (55 Fe) from crocidolite was determined using neutron-activated crocidolite and A549 cells. A time- and dose-dependent increase in the amount of 55 Fe mobilized intracellularly from crocidolite into a soluble, 10,000 x g supernatant fraction of lysed cells was observed for cultured cells treated up to 72 h. All of the results presented here support the hypothesis that iron and/or iron mobilization from asbestos may contribute to the some of the biological effects of asbestos in vivo. |
