Efflux of reduced glutathione after exposure of human lung epithelial cells to crocidolite asbestos.

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Abstract
This study investigated glutathione (GSH) homeostasis in human lung epithelial cells (A549) exposed to crocidolite. Exposure of A549 cells to 3 micrograms/cm2 crocidolite resulted in a decrease in intracellular reduced glutathione by 36% without a corresponding increase in GSH disulfide. After a 24-hr exposure to crocidolite, 75% of the intracellular GSH lost was recovered in the extracellular medium, of which 50% was in reduced form. Since the half-life of reduced GSH in culture medium was less than 1 hr, this suggests that reduced GSH was released continuously from the cells after treatment. The release of GSH did not appear to result from nonspecific membrane damage, as there was no concomitant release of lactate dehydrogenase or 14C-adenine from loaded cells after crocidolite treatment for 24 hr. Crocidolite exposure resulted in the formation of S-nitrosothiols but no increase in the level of GSH-protein mixed disulfides or GSH conjugates. Exposure of A549 cells to crocidolite for 24 hr decreased gamma glutamylcysteine synthetase (gamma-GCS) activity by 47% without changes in the activities of GSH reductase, GSH peroxidase, GSH S-transferase, or glucose-6-phosphate dehydrogenase. Treatment of cells with crocidolite pretreated with the iron chelator desferrioxamine B resulted in the same level of intracellular GSH depletion and efflux and the same decrease in gamma-GCS activity as treatment with unmodified crocidolite, which suggests that iron-catalyzed reactions were not responsible for the GSH depletion.