Differences in DNA damage and repair produced by systemic, hepatocarcinogenic and sarcomagenic dibenzocarbazole derivatives in a model of rat liver progenitor cells.
Liver progenitor (oval) cells are a potential target cell population for hepatocarcinogens. Our recent study showed that the liver carcinogens 7H-dibenzo[c,g]carbazole (DBC) and 5,9-dimethyldibenzo[c,g]carbazole (DiMeDBC), but not the sarcomagen N-methyldibenzo[c,g]carbazole (N-MeDBC), induced several cellular events associated with tumor promotion in WB-F344 cells, an in vitro model of liver oval cells [J. Vondracek, L. Svihalkova-Sindlerova, K. Pencikova, P. Krcmar, Z. Andrysik, K. Chramostova, S. Marvanova, Z. Valovicova, A. Kozubik, A. Gabelova, M. Machala, 7H-Dibenzo[c,g]carbazole and 5,9-dimethyldibenzo[c,g]carbazole exert multiple toxic events contributing to tumor promotion in rat liver epithelial 'stem-like' cells, Mutat. Res. Fundam. Mol. Mech. Mutagen. 596 (2006) 43-56]. In this study, we focused on the genotoxic effects generated by these dibenzocarbazoles in WB-F344 cells to better understand the cellular and molecular mechanisms involved in hepatocarcinogenesis. Lower IC(50) values determined for DBC and DiMeDBC, as compared with N-MeDBC, indicated a higher sensitivity of WB-F344 cells towards hepatocarcinogens. Accordingly, DBC produced a dose-dependent DNA-adduct formation resulting in substantial inhibition of DNA replication and transcription. In contrast, DNA-adduct number detected in DiMeDBC-exposed cells was almost negligible, whereas N-MeDBC produced a low level of DNA adducts. Although all dibenzocarbazoles significantly increased the level of strand breaks (p<0.05) and micronuclei (p<0.001) after 2-h treatment, differences in the kinetics of strand break rejoining were found. The strand break level in DiMeDBC- and N-MeDBC-exposed cells returned to near the background level within 24h after treatment, whereas a relatively high DNA damage level was detected in DBC-treated cells up to 48h after exposure. Additional breaks detected after incubation of DiMeDBC-exposed WB-F344 cells with a repair-specific endonuclease, along with a nearly 3-fold higher level of reactive oxygen species found in these cells as compared with control, suggest a possible role of oxidative stress in DiMeDBC genotoxicity. We demonstrated qualitative differences in the DNA damage profiles produced by hepatocarcinogens DBC and DiMeDBC in WB-F344 cells. Different lesions may trigger distinct cellular pathways involved in hepatocarcinogenesis. The low amount of DNA damage, together with an efficient repair, may explain the lack of hepatocarcinogenicity of N-MeDBC.
Laboratory of Mutagenesis and Carcinogenesis, Cancer Reserach Institute, SAS, Vlárska 7, 833 91 Bratislava, Slovakia.
Zuzana
Z
Valovicová
Sona
S
Marvanová
Monika
M
Mészárosová
Annamária
A
Srancíková
Lenka
L
Trilecová
Alena
A
Milcová
Helena
H
Líbalová
Jan
J
Vondrácek
Miroslav
M
Machala
Jan
J
Topinka
Alena
A
Gábelová
D000818:Animals; D002227:Carbazoles / Q000633:toxicity*; D002273:Carcinogens / Q000633:toxicity*; D002460:Cell Line; D018736:DNA Adducts / Q000378:metabolism; D004249:DNA Damage; D004260:DNA Repair; D006657:Histones / Q000378:metabolism; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000139:chemically induced; D008954:Models, Biological; D009153:Mutagens / Q000633:toxicity; D018384:Oxidative Stress / Q000187:drug effects; D051381:Rats; D012513:Sarcoma, Experimental / Q000139:chemically induced; D013234:Stem Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*
D002227:Carbazoles; D002273:Carcinogens; D018736:DNA Adducts; D006657:Histones; D009153:Mutagens; C039387:5,9-dimethyldibenzo(c,g)carbazole; C013478:7H-dibenzo(c,g)carbazole