Effect of sodium arsenite on heme metabolism in cultured chick embryo hepatocytes

We had previously reported that low concentrations of sodium arsenite (15 m u M) decreased the induction of cytochrome P450 CYP1A and CYP2H in cultured chick embryo hepatocytes in parallel with. increases in heme oxygenase, Ho wever, in those studies exogenous heme did not prevent the decrease in CYPs , In this study, we investigated the effect of arsenite on the synthesis an d degradation of heme. Arsenite had no effect on induction of 5-aminolevuli nic acid synthase mRNA or activity. Arsenite, at concentrations from 1 to 2 5 mu M, had no effect on protoporphyrin synthesis from 5-aminolevulinic aci d and did not increase the accumulation of other porphyrins, indicating tha t the enzymes in the pathway between 5-aminolevulinic acid synthase and fer rochelatase were unaffected by arsenite, Synthesis of heme from radioactive 5-aminolevulinic acid was slightly decreased (less than 20%) by 2.5 mu M a rsenite, a concentration that decreased induction of CYP1A and CYP2H by gre ater than 50%, Rates of biliverdin formation and degradation of exogenous h eme were not different in cultures treated simultaneously with arsenite and heme or with heme alone. However, arsenite treatment increased biliverdin formation from heme synthesized from added 5-aminolevulinic acid by 60% and decreased the endogenous heme content of the cells by 30%, Our results sug gest that although 2.5 mu M arsenite induced heme oxygenase four- to sixfol d, this had no effect on degradation of exogenous heme. Degradation of heme synthesized from 5-aminolevulinic acid was increased but this did not affe ct the regulatory heme pool, (C) 1999 Academic Press.