title: Comparisons of the effects of chemical carcinogens in mixed cultures of rat hepatocytes and human fibroblasts.
abstract: Unscheduled DNA synthesis (UDS) was measured simultaneously in rat hepatocytes and human fibroblasts when combined cultures of the 2 cell types were exposed to procarcinogens. Human fibroblasts were preincubated with 5-bromo-2'-deoxyuridine (BRdU) to substitute for thymidine in the DNA. Hepatocyte DNA was separated from the heavier BRdU-substituted fibroblast DNA by isopycnic centrifugations in neutral cesium chloride and the specific activities of the DNA's were determined. In the presence of hepatocytes, benzo - [a]pyrene (BP) induced more UDS in the fibroblasts than in the hepatocytes. BP induced no UDS in the fibroblasts in the absence of hepatocytes. Diethylnitrosamine (DEN) and 2-acetylaminofluorene (AAF) stimulated a significant amount of UDS only in the hepatocytes. Thus, the co-cultures of hepatocytes and fibroblasts responded with UDS to these chemical carcinogens in a manner that parallels the tissue specificity of the carcinogenicity of these chemicals in vivo. That is, the known hepatocarcinogens DEN and AAF, only stimulated significant UDS in the hepatocytes, whereas the non-hepatocarcinogen, BP, though activated in these cultures mainly by the hepatocytes, stimulated more UDS in the fibroblasts than in the hepatocytes. The amount of [3H]BP bound to DNA was investigated in the co-cultures and in cultures of fibroblasts alone. When co-cultures were exposed to [3H]BP the fibroblast DNA had approximately 3 times more BP bound to it (per microgram DNA) than did the hepatocyte DNA. The amount of [3H]BP bound to the DNA of cultures of fibroblasts alone was 29% of the amount bound to the DNA of the fibroblasts from the co-cultures. Thus, although the hepatocytes were mainly responsible for the activation of BP, more [3H]BP was bound to the fibroblast DNA. It is suggested that the intercellular distribution of carcinogenic metabolites may be a significant determinant of the carcinogenic effect.
mesh_terms: D015073:2-Acetylaminofluorene / Q000494:pharmacology; D000818:Animals; D001564:Benzo(a)pyrene; D001580:Benzopyrenes / Q000494:pharmacology; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002273:Carcinogens / Q000494:pharmacology*; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis*; D004052:Diethylnitrosamine / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D001580:Benzopyrenes; D002273:Carcinogens; D001564:Benzo(a)pyrene; D004052:Diethylnitrosamine; D004247:DNA; D015073:2-Acetylaminofluorene; D001973:Bromodeoxyuridine