Repair of chromate-induced DNA damage in chick embryo hepatocytes

Abstract

The repair of DNA damage caused by chromate was examined in chick embryo hepatocytes. Treatment of chick embryo hepatocytes with 5 μM sodium chromate for 2 h caused the formation of DNA strand breaks, DNA interstrand crosslinks, and DNA-protein cross-links. The maximal level of strand breaks and DNA interstrand cross-links was observed immediately after the 2 h chromate treatment. After removal of the chromate, strand breaks and DNA interstrand cross-links were completely repaired by 3 h and 12 h, respectively. In contrast, DNA-protein cross-links continued to form reaching a maximal level 3 h after chromate removal. Although the level of DNA-protein cross-links decreased at later times, a significant level persisted 40 h after chromate removal. The effect of these persistent DNA-protein cross-links on gene expression was examined by measuring induction of porphyrin accumulation by propylisopropylacetamide and deferoxamine methanesulphonate, a process known to depend on mRNA synthesis. Induction of porphyrin accumulation was decreased immediately following the 2 h chromate treatment. Only partial recovery of induction was observed even 40 h after chromate removal. The effect of chromate treatment on cellular glutathione levels was monitored. No change in cellular glutathione was observed after a 2 h treatment with 5 μM sodium chromate; however, a three-fold increase was observed 12 h after removal of chromate.