Iron-Loaded Synthetic Chrysotile:  A New Model Solid for Studying the Role of Iron in Asbestos Toxicity

Abstract

The generation of reactive oxygen species and other radicals, catalyzed by iron ions at the fiber surface, is thought to play an important role in asbestos-induced cytotoxicity and genotoxicity, but a direct confirmation of this statement needs the availability of asbestos samples differing only for their iron content, without the interference of other physicochemical features. Synthetic stoichiometric chrysotile nanofibers, devoid of iron or any other contaminant, did not exert genotoxic and cytotoxic effects nor elicited oxidative stress in a murine alveolar macrophage cell line; on the contrary, the same nanofibers, loaded with 0.57% and 0.94% (w/w) iron, induced DNA strand breaks, lipoperoxidation, inhibition of redox metabolism and alterations of cell integrity, similarly to natural chrysotile. On the other hand, the incubation with ferric nitrilotriacetate, a cell-permeating iron complex, even if it caused an intracellular overloading of iron very similar to that elicited by iron-loaded synthetic chrysotile and by natural chrysotile, did not exert any of these effects. This suggests that chrysotile is not toxic by acting simply as a carrier of iron into the cell, but rather that the redox activity of iron is potentiated when organized at the fibers surface into specific crystallographic sites having coordination states able to activate free radical generation. Synthetic chrysotile fibers may be proposed as a standard reference sample and model solids for experimental studies on asbestos fibers aiming to clarify the mechanisms of its toxicity and to synthesize new fibers devoid of pathogenic effects.

The Role of Iron Impurities in the Toxic Effects Exerted by Short Multiwalled Carbon Nanotubes (MWCNT) in Murine Alveolar Macrophages

“…It is well known how asbestos fibers generate free radicals via different mechanisms including a Fenton reaction catalyzed by Fe ions exposed to their surface (Kamp, 2009). Our research group showed a correlation between the coordination and oxidation state of Fe in asbestos and its toxicity in in vitro cellular systems (Aldieri et al, 2001;Gazzano et al, 2007;Turci et al, 2010). It is thus conceivable to postulate a role for Fe also in MWCNT-induced toxic effects.…”

“…In fact a strict correlation between the presence of Fe at the surface of different types of asbestos fibers in a well-defined redox and coordination state (crocidolite, chrysotile) and related toxicity was previously demonstrated (Aldieri et al, 2001;Gazzano et al, 2007).…”

Adsorption of bovine serum albumin onto synthetic Fe-doped geomimetic chrysotile

“…In a previous study, it was demonstrated that at the low amount of Fe content in the nanocrystals both biological and radical activity were more significant than the nanocrystal with higher Fe content [8,23]. This higher reactivity could be due to the higher percentage of Fe replacing Mg in octahedral position.…”

“…In natural chrysotile (Mg 3 Si 2 O 5 (OH) 4 ), iron is a contaminant (about 0.5-2%, w/w), replacing isomorphously magnesium and silicon that may have important health implications. The role of Fe in the toxicity of natural chrysotile fibres has been widely investigated in the past [3,[5][6][7], while more recent experimental evidences supported the view that the generation of reactive oxygen species and other radicals, catalysed by iron ions at the fibre surface, is implied in asbestos-induced cytotoxicity and genotoxicity [8]. The available data also suggest that the Fe content of asbestos, as well as redox active Fe associated with or mobilized from the surface of the fibres, is important in generating HO.…”

Lichen deterioration of asbestos and asbestiform minerals of serpentinite rocks in Western Alps

“…Iron is indeed chelated by several acidic fungal metabolites, including oxalic acid (Gadd, 1999), and its occurrence in chrysotile accounts for the detrimental surface chemical reactivity (Gazzano et al, 2007). Accordingly, the ROS production is significantly reduced after the leaching of vein E in the laboratory (Fig.…”