Mutagenesis and DMA Binding of Benzo(a)pyrene in Cocultures of Rat Hepatocytes and Human Fibroblasts

The genotoxicity of benzo(a)pyrene (BP) was investigated in combined cultures of rat hepatocytes and human diploid fibroblasts. Freshly isolated rat hepatocytes were shown to activate BP to a species which bound to and damaged hepatocyte and fibroblast DMA. A significant increase in the hypoxanthineguanine phosphoribosyltransferase mutation frequency was induced when 10 to 100 /IM BP was added to the cocultures. A comparative analysis of the binding of BP metabolites to hepatocyte and fibroblast DMA revealed that approximately 4 times more [3H]BP metabolites were bound to the fibroblast DMA than were bound to the hepatocyte DNA (per fig DNA). Activation of BP by the fibroblasts themselves was shown not to be the cause of the relatively greater binding of BP to fibroblast DNA than to the hepatocyte DNA. These results suggest that proximate and/or ultimately carcinogenic metab olites of BP are readily released from isolated hepatocytes and that the metabolites are sufficiently stable and long lived so as to bind to the DNA of an adjacent cell. The relative protection of the hepatocytic DNA from BP metabolites that generated in the cytoplasm of the hepatocyte may be significant in view of the observations that the liver is not under normal conditions a target of BP carcinogenicity in vivo.