High potency of bioactivation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in mouse colon epithelial cells with Apc(Min) mutation.
2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a prominent heterocyclic aromatic amine (HAA) found in meat and fish cooked at moderate to high temperature. It is considered as a potent dietary factor promoting colon carcinogenesis. However, the role of intestinal cells in PhIP bioactivation has not been fully explained, particularly when cells are pre-malignant. Loss of function of the adenomatous polyposis coli (APC) gene product is an early and frequent event in human colorectal carcinogenesis. Normal (Apc(+/+)) and pre-malignant (Apc(Min/+), where Min=multiple intestinal neoplasia) colonic epithelial cells of mice can be used to study promotion of carcinogenesis, but these cells have not been characterized for bio-activation of HAA. We investigated the metabolism of (14)C-PhIP in these two murine cell lines. Cells induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) metabolized PhIP into 4'-OH-PhIP as the main metabolite in PhiP detoxification. Besides, 5-OH-PhIP was identified, revealing the formation of intermediary reactive metabolites, since it results from a degradation of conjugates of N-acetoxy-PhIP. Apc(Min/+) cells produce significantly higher amounts of these metabolites. Demethylated metabolites are also observed, indicating that the colon contains a significant CYP1 family dependent metabolic activity. A minor hydroxy-glucuronide-PhIP metabolite is observed in Apc(Min/+) cells, the glucuronidation being known as an important step in the detoxification pathway. Quantitative real-time reverse transcription polymerase chain reaction experiments demonstrate that induction by TCDD has prevailing effects in gene expression of CYP1A1, CYP1A2 and CYP1B1 in Apc(Min/+) cells. In these cells, N-acetyltransferase-2 is also expressed at higher levels. So, the more important potency to metabolically bio-activate PhIP, as measured in Apc(Min/+) cells, can be linked to a higher probability to generate new in situ mutations.
Bellocq
Delphine
D
INRA/ENVT, UMR1089 Laboratoire des Xénobiotiques, 180, Chemin de Tournefeuille, F-31931 Toulouse, France.
Molina
Jérôme
J
Rathahao
Estelle
E
Canlet
Cécile
C
Taché
Sylviane
S
Martin
Pascal G P
PG
Pierre
Fabrice
F
Paris
Alain
A
D011125:Adenomatous Polyposis Coli; D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000096:biosynthesis* / Q000235:genetics; D001191:Arylamine N-Acetyltransferase / Q000096:biosynthesis* / Q000235:genetics; D001711:Biotransformation; D002460:Cell Line; D003106:Colon / Q000201:enzymology* / Q000473:pathology; D003296:Cooking; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D017491:Genes, APC; D007093:Imidazoles / Q000378:metabolism / Q000633:toxicity*; D007413:Intestinal Mucosa / Q000201:enzymology* / Q000473:pathology; D008461:Meat Products / Q000009:adverse effects; D051379:Mice; D008817:Mice, Mutant Strains; D008934:Mitogens / Q000378:metabolism / Q000633:toxicity*; D009154:Mutation; D000072317:Polychlorinated Dibenzodioxins / Q000031:analogs & derivatives / Q000494:pharmacology; D017747:Seafood / Q000009:adverse effects
D007093:Imidazoles; D008934:Mitogens; D000072317:Polychlorinated Dibenzodioxins; C445379:1,2,7,8-tetrachlorodibenzo-p-dioxin; C049584:2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine; D001189:Aryl Hydrocarbon Hydroxylases; D001191:Arylamine N-Acetyltransferase; C524206:Nat2 enzyme, mouse