Enhanced Generation of Free Radicals from Phagocytes Induced by Mineral Dusts

Abstract

Several studies have suggested that pulmonary toxicity to asbestos and silica may be mediated through oxidant-induced cell injury. We have reported recently that surface radicals associated with freshly fractured silica may be an important factor in cell injury and induction of pulmonary disease. Although the generation of oxygenated radicals in dust-cell interactions has been demonstrated, there are no data correlating the toxicity of a dust with the level of oxygen radical generation by the dust during its interaction with phagocytic cells. In the present study, we have investigated the in vitro generation of oxygen free radicals from human neutrophils and rat alveolar macrophages stimulated with freshly fractured silica, aged silica, amosite, crocidolite, chrysotile, and nontoxic dust, barite. Electron spin resonance (ESR) with the aid of a spin trap phenyl-N-tert-butyl nitrone (PBN) was used to measure the oxygen radicals generated during phagocytosis of the dusts. The relative toxicity index and ESR peak heights, on an equal surface area basis and normalized to barite as one, showed a direct relationship. The normalized toxicity indices and peak heights were: silica, 3.5 versus 2; chrysotile, 4 versus 2; crocidolite, 11 versus 8; and amosite, 26 versus 13. Addition of hydroxyl radical scavengers such as catalase, dimethyl sulfoxide, 1,3 dimethyl-2-thiourea (DMTU), sodium benzoate, and mannitol prevented the radical generation. Carmustine, a glutathione reductase-glutathione peroxidase inhibitor, caused a 5-fold increase in the radical generation. These results indicate that a nontoxic dust such as barite generates toxic oxygen radicals at a minimal level that can be quenched by the normal cellular defense system. For toxic dusts such as silica, amosite, chrysotile, and crocidolite, the potential for oxygen radical generation is enhanced by their surface properties, physical dimensions, and the surface-based radical-generating redox sites. The enhanced radical generation may impair the cellular defense system, resulting in cell injury. Use of scavengers, chelators, and potentiating agents suggests the membrane-based oxidase system as the probable primary source of the radical-generating system. The data presented herein suggest the generation of oxygen free radicals as an important primary event in silica- as well as asbestos-induced cell injury.

Induction of Activator Protein-1 through Reactive Oxygen Species by Crystalline Silica in JB6 Cells

“…It also blocks the interaction of the silica surface with phosphate groups of DNA in vitro. It has been reported that PVPNO inhibits silicainduced ROS generation in cells (31,32).…”

“…SiOH groups on the silica surface have been proposed to be involved in silica-induced cellular damage. Chemical modification of the silica surface can be used to reduce toxicity in vitro and fibrosis in vivo (31). It is known that when silica particles are exposed to water, surface silicon-oxygen bonds (Si-O) are hydrated, resulting in the formation of SiOH groups.…”

Fluoromicroscopic Studies of Bleomycin-Induced Intracellular Oxidation in Alveolar Macrophages and Its Inhibition by Taurine

“…This is likely, since AM have receptors for bleomycin allowing for the internalization of the drug molecule (28). Other studies have shown that bleomycin possesses a bithiazole ring that can intercalate into the DNA helix, and Fe binding sites involving the pyrimidine and imidazole moieties that are capable of generating oxygen radicals in the vicinity of the DNA molecule (5,6). The role of Fe in bleomycininduced intracellular oxidation is shown in Figure 4.…”

“…The most significant and deleterious consequences of oxidation, such as DNA strand breakage (5), damage to the cytoskeleton (14,15), and a rise in intracellular calcium (16), occur intracellularly and can lead to a cascade of cellular events resulting in cell death. Detection of intracellular oxygen radicals is difficult as they are highly reactive and extracellular modes of detection such as luminol-derived chemiluEnvironmental Health Perspectives 91 minescence or electron spin resonance signals rely on detection of extracellularly generated radicals (17) or leakage from a compromised cell membrane.…”

Oxygen radicals and asbestos carcinogenesis.

“…In fact, Gabrielson et al (7) have been unable to detect generation of hydroxyl radicals by asbestos fibers added to cultures of human mesothelial cells. However, generation of free radicals by phagocytic cells exposed to asbestos fibers has been detected by this technique (8). Phagocytic cells such as neutrophils and macrophages release much higher quantities of oxidants than mesothelial cells (9).…”