Effects of Active Oxygen Species on Particle Uptake

Effects of Active Oxygen Species on Particle Uptake 

Many minerals can spontaneously catalyze the formation of active oxygen species (AOS) in aqueous systems, which in this context include both the cell surface and the cell cytoplasm (5). Most commonly, this process uses surface iron(II) or teachable iron(II) from the mineral particle to reduce molecular oxygen to superoxide anion superoxide anion then dismutates to hydrogen peroxide and, in the presence of iron(II), the hydroxyl radical is formed via the Fenton reaction, along with iron(III). If iron(III) can be reduced (e.g., by additional superoxide anion 

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We have used a rat traeheal explant system to examine the role of AOS in particle uptake. When traeheal explants are briefly immersed in a suspension of a mineral dust, dust partieles adhere to the epithelial cell surfaces if the explants are then maintained in organ eulture in air, the epithelial cells slowly take up particles from the apical surface (see Fig. 1). The relative basal level of uptake of different types of particles is quite different (see Table 3), but every type of mineral particle thus far examined (asbestos, carbon, titanium dioxide, iron oxide, talc, wollastonite, or silicon carbide) enters the epithelial cells (3,4,51-54). This system offers several simplifying advantages for studying particle uptake, ineluding lack of airspace inflammatory cells, maintenance of normal levels of intraeel-lular antioxidant defense (Churg A, unpublished data), and retention of a polarized cell structure with normal apical differentiation. 

In tracheal explants, the basal level of amosite asbestos uptake can be decreased by adding catalase, a scavenger of hydrogen peroxide, to the dust suspension, or by preincubating the dust with the iron chelator, deferoxamine (124), a chelator that prevents the reaction of iron with hydrogen peroxide to form a hydroxyl radical (6). The decreases in particle uptake are scavenger-chelator dose-dependent, but uptake cannot be reduced below about one-third to one-half the basal level (124). Conversely, uptake can be increased if amosite asbestos or titanium dioxide particles are preincubated with iron salt solutions to increase surface iron before they are applied to the explants (125). 

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VII. Effects of Active Oxygen Species on Particle Uptake... 

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