Exposure of developing oligodendrocytes to cadmium causes HSP72 induction, free radical generation, reduction in glutathione levels, and cell death

Primary cultures of oligodendrocytes were used to study the toxic effects of cadmium chloride. Cell viability was evaluated by the mitochondrial dehydrogenase activity and confirmed by propidium iodide (PI) fluorescence staining. The expression of the 72 kDa stress protein, HSP72, was assayed by Western blot analysis. The results showed that Cd2+-induced toxicity was dependent on the time and dose of exposure, as well as on the developmental stage of the cultures. Oligodendrocyte progenitors were more vulnerable to Cd2+ toxicity than were mature oligodendrocytes. Mature oligodendrocytes accumulated relatively higher levels of Cd2+ than did progenitors, as determined by 109CdCl2 uptake; treatment with the metal ion caused a more pronounced reduction in intracellular glutathione levels and significantly higher free radical accumulation in progenitors. The latter could explain the observed differences in Cd2+ susceptibility. HSP72 protein expression was increased both in progenitors and in mature cells exposed to Cd2+. Pretreatment with N-acetylcysteine, a thiocompound with antioxidant activity and a precursor of glutathione, prevented Cd2+-induced (i) reduction in glutathione levels and (ii) induction of HSP72 and diminished (i) Cd2+ uptake and (ii) Cd2+-evoked cell death. In contrast, buthionine sulfoximine, an inhibitor of γ-glutamyl-cysteine synthetase, depleted glutathione, and potentiated the toxic effect of Cd2+. These results strongly suggest that Cd2+-induced cytotoxicity in oligodendrocytes is mediated by reactive oxygen species and is modulated by glutathione levels.