Two pathways for chromium(VI)-induced DNA damage in 14 day chick embryos: Cr-DNA binding in liver and 8-oxo-2'-deoxyguanosine in red blood cells.

Abstract

Previous studies have shown that chromium(VI) induced cell-specific types of DNA damage, i.e. DNA cross-links in liver and DNA strand breaks in red blood cells, in 14 day chick embryos. Direct and indirect pathways for chromium(VI)-mediated DNA damage, in the form of Cr-DNA binding and 8-oxo-2'-deoxyguanosine (8-oxo-dG) respectively, were examined in liver and red blood cells of 14 day chick embryos. Levels of hepatic Cr-DNA binding increased in a Cr(VI) dose-dependent manner. Cr-DNA binding in red blood cells was 10-fold lower than in liver, although the Cr-uptake in red blood cells was only 2-fold lower than in liver. The level of 8-oxo-dG formation in red blood cells increased at all Cr(VI) doses tested but peaked at 0.10 mmol Cr(VI)/kg, whereas no increase in 8-oxo-dG levels over background levels was observed in liver of Cr(VI)-treated embryos. The possible role of glutathione in modulating Cr(VI)-induced DNA damage was examined by using L-buthionine-R,S-sulfoximine (BSO) to deplete glutathione. No changes in glutathione levels were observed in either liver or red blood cells of embryos treated with Cr(VI) in the presence or absence of BSO pretreatment. Ascorbate levels in liver and red blood cells were not affected by treatment of embryos with chromium(VI), BSO or Cr(VI) and BSO. Depletion of glutathione by BSO resulted in a small increase of chromium uptake in liver of embryos treated with 0.050 and 0.10 mmol Cr(VI)/kg, but had no effect on hepatic chromium uptake at 0.20 mmol Cr(VI)/kg. BSO had no effect on chromium uptake in red blood cells. Depletion of glutathione had no effect on hepatic or red blood cells Cr-DNA binding in embryos treated with Cr(VI). However, depletion of glutathione significantly decreased the 8-oxo-dG levels in red blood cells at all Cr(VI) doses tested. Levels of 8-oxo-dG in liver of Cr(VI)-treated embryos remained at background in the presence or absence of BSO pretreatment. These results indicate that Cr(VI)-induced DNA damage in 14 day chick embryos is through a direct interaction of chromium with DNA in liver, but is through an indirect oxidative pathway in red blood cells. It appears that glutathione plays an important role in chromium(VI)-induced formation of 8-oxo-dG in red blood cells.