Chemical characterization and reactivity of iron chelator-treated amphibole asbestos.

Abstract

Iron in amphibole asbestos is implicated in the pathogenicity of inhaled fibers. Evidence includes the observation that iron chelators can suppress fiber-induced tissue damage. This is believed to occur via the diminished production of fiber-associated reactive oxygen species. The purpose of this study was to explore possible mechanisms for the reduction of fiber toxicity by iron chelator treatments. We studied changes in the amount and the oxidation states of bulk and surface iron in crocidolite and amosite asbestos that were treated with iron-chelating desferrioxamine, ferrozine, sodium ascorbate, and phosphate buffer solutions. The results have been compared with the ability of the fibers to produce free radicals and decompose hydrogen peroxide in a cellfree system in vitro. We found that chelators can affect the amount of iron at the surface of the asbestos fibers and its valence, and that they can modify the chemical reactivity of these surfaces. However, we found no obvious or direct correlations between fiber reactivity and the amount of iron removed, the amount of iron at the fiber surface, or the oxidation state of surface iron. Our results suggest that surface Fe3+ ions may play a role in fiber-related carboxylate radical formation, and that desferrioxamine and phosphate groups detected at treated fiber surfaces may play a role in diminishing and enhancing, respectively, fiber redox activity. It is proposed that iron mobility in the silicate structure may play a larger role in the chemical reactivity of asbestos than previously assumed. Environ Health Perspect 1 05(Suppl 5):1 021-1030 (1997)

The molecular basis of asbestos induced lung injury

“…Moreover, they observed that the iron in asbestos can be repeatedly oxidised and reduced. In contrast, Gold and associates24 found, using atomic absorption spectroscopy and inductively coupled plasma atomic emission spectroscopy, that various chelators remove only approximately 1–5% of the total iron on the surface and that this did not affect the ratio of Fe 3+ to Fe 2+ ions in crocidolite and amosite asbestos (70:30 and 60:40, respectively) or alter the content of redox active Fe 2+ at the surface. These observations may account for the limited efficacy of iron chelators in some bioassays described below.…”

Emission of airborne fibers from mechanically impacted asbestos-cement sheets and concentration of fibrous aerosol in the home environment in Upper Silesia, Poland

“…There are three essential factors that are required to develop such disease [6]: adequate dose, dimensions of the fibers in the alveolar region, and fiber biopersistence. Other fiber properties, such as presence of iron or other transition metals on fibers, ability of fibers to generate free radicals [7,8], and the ability of fibers to interact with and alter biologically relevant molecules, as well as, the ability of fibers to produce reactive oxygen/nitrogen species (ROS) may also be determinants of fiber toxicity [6], especially among biopersistent fibers. Fibers may catalyze the generation of oxidants directly from molecular oxygen or indirectly from reactive oxygen and nitrogen species released by inflammatory cells recruited to the lungs or pleura [9].…”

Cyto-genotoxicity of amphibole asbestos fibers in cultured human lung epithelial cell line: Role of surface iron

“…Iron present at the surface of amphibole fibers is implicated in the pathogenicity of inhaled fibers (Gold et al, 1997) and is thought to get mobilized in cellular systems, finally initiating the ROS generation via Fenton's reaction. Evidence includes the observation that iron chelators can suppress fiber-induced tissue damage (Poser et al, 2004).…”