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  • Title: Role of cytochrome P450 in DNA damage induced by N-nitrosodialkylamines in cultured rat hepatocytes.
    Author: Shu L, Hollenberg PF.
    Journal: Carcinogenesis; 1996 Mar; 17(3):569-76. PubMed ID: 8631147.
    Abstract:
    The involvement of cytochrome P450 in the cytotoxicity and DNA damage-repair induced by N-nitrosodipropylamine (NDPA), N-nitroso-n-butyl-n-propylamine (NBPA), and N-nitrosodibutylamine (NDBA) was investigated in cultured hepatocytes isolated from untreated, phenobarbital (PB)- and pyridine (PYR)-pretreated rats. Pretreatment of rats with PB caused a 10-fold increase in the sensitivity of hepatocytes to the cytotoxic actions of NDPA, NBPA and NDBA as measured by trypan blue exclusion, whereas PYR pretreatment increased the sensitivity of hepatocytes to NDPA and NBPA, but not to NDBA. This elevated sensitivity correlated well with increased 7-pentoxyresorufin depentylase activity catalyzed by P450 2B1 in cultures from PB-pretreated rats and enhanced p-nitrophenol hydroxylase activity of P450 2E1 in cultures of hepatocytes from PYR-pretreated rats. Unscheduled DNA synthesis showed that DNA damage-repair was significantly increased in freshly isolated hepatocytes from PB- and PYR-pretreated rats. With increasing time in culture, however, there was a marked reduction in the DNA damage repair response, concomitant with a decrease in the cytotoxicity of NDPA, NBPA and NDBA in primary cultures of hepatocytes. Coincident with this, a rapid loss in the specific activities of P450 2B1 and 2E1 was detected during the first 48 h in all primary cultures. Although N-nitrosodimethylamine (NDMA), used as a positive control, produced high nuclear grain counts in cultures from PYR-pretreated rats, the toxic effect of NDMA in rat hepatocytes was much weaker than that observed with NDPA, NBPA and NDBA. This result suggests that the type of DNA damage or repair efficiently induced by NDPA, NDBA or NDBA might differ from that due to NDMA.
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