Studies on the in vitro transfer of DNA binding benzo[a]pyrene metabolites from rat hepatocytes to human fibroblasts

Abstract

The release and reabsorption of benzo[a]pyrene (BP) metabolites were studied in isolated rat hepatocytes incubated with BP. There was a rapid uptake of BP by the hepatocytes followed by an excretion of organic and water-soluble metabolites. Upon further incubation the BP-dihydrodiols and BP-phenols were reabsorbed by the cells and finally excreted as water-soluble conjugates. The metabolism of BP by the hepatocytes also resulted in the formation and release of reactive intermediates to the incubation medium. The DNA-binding intermediates released from the cells were consistent with trans-7,8-dihydroxy-7,8-dihydrobenzo[a]pyrene-9,10-oxide(s) and 9-hydroxybenzo[a]pyrene-4,5-oxide(s). The BP-metabolites were bound to hepatocyte and fibroblast DNA. The degree of DNA binding was estimated as the formation of DNA strand breaks. BP metabolites formed within the hepatocytes and transferred to the fibroblasts induced DNA strand breaks in the latter cells. Addition of DNA to the medium markedly decreased the fraction of single stranded DNA in these cells. Under conditions where the excretion from hepatocytes of BP-phenols and BP-dihydrodiols were increased, the amount of DNA strand breaks in the fibroblasts increased.