Metabolic bioactivation of oestradiol-17β (E 2β) in mouse colon epithelial cells bearing ApcMin mutation

Abstract

Epidemiological studies have revealed a protective role of oestrogens against the promotion of colorectal cancer (CRC). Therefore, the oestrogen metabolism status of colonic cells is studied to explain it. Loss of function of adenomatous polyposis coli ( Apc) gene product is an early and frequent event in human colorectal carcinogenesis. Normal ( Apc +/+) and premalignant ( Apc multiple intestinal neoplasia ( Min)/+ ) mouse colonic epithelial cells were used to compare their respective metabolic capabilities towards oestradiol-17β (E 2β), with or without an inducer of the CYP1 family, 2,3,7,8-tetrachlorodibenzo- p-dioxin (TCDD). In both cell types, the major metabolite was oestradiol-17β-3-glucuronide. The formation of catechol (CE) metabolites by cytochromes P450 of the CYP1 family and their derivatives was shown. Among these metabolites, several O-methyl-ether derivatives were detected, as unconjugated metabolites in Apc +/+ cells and as glucuroconjugates in Apc Min/+ cells, after TCDD treatment. Apc Min/+ cells are metabolically more competent than Apc +/+ cells to produce different hydroxylated metabolites as well as glucuroconjugates. Quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR) experiments corroborate these results. Indeed, induction by TCDD has prevailing effects in gene expression of CYP1A1, CYP1A2 and CYP1B1 in Apc Min/+ cells, compared with Apc +/+ ones. Apc Min/+ cells displayed higher rates of oestrogen metabolic biotransformation than Apc +/+ ones, but exhibited two opposite tendencies. Apc Min/+ cells were able to detoxify E 2β mainly by the formation of glucuronides and displayed at the same time a striking potential to bioactivate E 2β by producing only the electrophilic 2-CE derivatives, not the 4-CE ones, even though a significant CYP1B1 mRNA induction was noticed. These specific electrophilic metabolites may form DNA adducts but are not prone to generate new mutations. Interestingly, the ultimate 2- O-methyl-ether metabolite of E 2β may be an endogenous protective factor against CRC promotion given its recognised anti-angiogenic and pro-apoptotic properties.