Selective induction of the CYP3A family by endosulfan and DNA-adduct formation in different hepatic and hepatoma cells

Endosulfan, a chlorinated cyclodiene insecticide, is known to cause a significant enhancement of altered hepatic foci in rats and to be a potent inhibitor of gap-junctional intercellular communication in vitro. Both of these features are common to many tumor promoters. However, long-term studies in rodents provide no evidence that it is carcinogenic or genotoxic. In the present study, endosulfan genotoxicity is evaluated and the formation of DNA adducts is investigated in three types of cultured hepatic cells (rodent, bird, and human). DNA-adduct formation in response to endosulfan treatment is measured by the P-32-postlabelling method. The results have shown a high genotoxicity of endosulfan only in rat and human cells. Therefore, to better understand these findings and because nothing is known about the xenobiotic-metabolizing enzymes involved in endosulfan metabolism, we have attempted to identify the cytochromes P450 induced, which can transform endosulfan into reactive intermediates capable of interacting with DNA. To examine if endosulfan induces CYP1A-, CYP2B-, or CYP3A-family transcripts, we measured transcript levels by Northern blot and RT-PCR analyses. Endosulfan appears to selectively induce expression of the CYP3A gene family. It is a potent inducer of CYP3A1 mRNA in rat and is also shown, by RT-PCR, to increase the CYP3A7 transcript level in Hep G2 human hepatoma cells. In contrast, in fetal quail hepatocytes, CYP3A is not expressed and no endosulfan-DNA adducts are formed.