Cr (VI) induces cell growth arrest through hydrogen peroxide-mediated reactions

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Cr(VI) compounds are widely used in industries and are recognized human carcinogens. The mechanism of carcinogenesis associated with these compounds is not well understood. The present study focused on Cr (VI)-induced cell growth arrest in human lung epithelial A549 cells, using flow cytometric analysis of DNA content. Treatment of the cells with Cr (VI) at 1µM caused a growth arrest at G,/M phase. An increase in Cr (VI) concentration enhanced the growth arrest. At a concentration of 25 µM, Cr (VI)-induced apoptosis became apparent. Superoxide dismutase (SOD) or sodium formate did not alter the Cr (V I)-induced cell growth arrest. While catalase inhibited growth, indicating H2O, is an important mediator in Cr (VI)-induced G,/ M phase arrest. Electron spin resonance (ESR) spin trapping measurements showed that incubation of cells with Cr (VI) generated hydroxyl radical (’0H). Catalase inhibited the ‘OH radical generation, indicating that H_D2was generated from cells stimulated by Cr (VI), and that H02functioned as a precursor for-OH radical generation. The formation of 112O2from Cr (VI)-stimulated cells was also measured by the change in fluorescence of scopoletin in the presence of horseradish peroxidase. The mechanism of reactive oxygen species generation involved the reduction of molecular oxygen as shown by oxygen consumption assay. These results support the following conclusions: (a) Reactive oxygen species are generated in Cr (VI)-stimulatedA549 cells through reduction of molecular oxygen, (b) Among the reactive oxygen species generated, H2O2played a major role in causing G2/M phase arrest in human lung epithelial cells. (Mol Cell Biochem222:77-83,2001)