Intestinal absorption and cell transforming potential of PhIP-M1, a bacterial metabolite of the heterocyclic aromatic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)

•The transport of PhIP-M1, a metabolite of the colon carcinogen PhIP produced by gut bacteria, in eight different intestinal segments from male Fischer 344 rats was examined in Ussing chambers.•A very recently developed HPLC method to quantify the concentration of PhIP-M1 in biological fluids as well as in intestinal tissue was applied.•At the most, 10–20% of the PhIP-M1 amount added to the mucosal compartment of the Ussing chambers per segment were absorbed within 90 min.•PhIP-M1 in a concentration of up to 100 μM did not induce the malignant transformation of BALB/c 3T3 cells.•Even if one would assume that 100% of the daily amount of PhIP ingested by a human being is converted into PhIP-M1 in the colon, this concentration most probably would not lead to carcinogenicity in the colorectal mucosa.

Previous studies have shown that in the rat, the colon carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is only absorbed to a limited extent in the small intestines and that a major fraction of unmetabolised PhIP reaches the colon. Moreover, PhIP is extensively metabolised when incubated with human stool samples to a major derivative, 7-hydroxy-5-methyl-3-phenyl-6,7,8,9-tetrahydropyrido [3′,2′:4,5]imidazo[1,2-a]pyrimidin-5-ium chloride (PhIP-M1). In the present study, the uptake and transport of PhIP-M1 in Ussing chamber experiments, its cytotoxicity in the different segments of the Fischer 344 rat gut and its transforming potential in the BALB/c 3T3 cell transformation assay were analysed. At the most, 10–20% of the PhIP-M1 amount added to the mucosal compartment of the Ussing chambers per segment were absorbed within 90 min. Therefore, the amount of PhIP-M1 detected in the tissues as well as in the serosal compartment of the Ussing chambers was extremely low. Moreover, human-relevant concentrations of PhIP-M1 were not cytotoxic and did not induce the malignant transformation of BALB/c 3T3 cells. In conclusion, even if one would assume that 100% of the daily amount of PhIP ingested by a human being is converted into PhIP-M1 in the colon, this concentration most probably would not lead to cytotoxicity and/or carcinogenicity in the colorectal mucosa.