Metabolism of Foodborne Heterocyclic Aromatic Amines by Lactobacillus reuteri DSM 20016.

Abstract

The heterocyclic aromatic amine (HAA) 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is converted into 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) via a chemical reaction with 3-hydroxypropionaldehyde or acrolein derived from glycerol by reuterin producing gut bacteria. Because it is unknown whether this reaction also applies to other HAAs, seven foodborne HAAs (2-amino-9H-pyrido[2,3-b]indole (AαC), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), 2-amino-3-methyl-3H-imidazo[4,5-f]quinoline (IQ), 2-amino-3,4-dimethyl-3H-imidazo[4,5-f]quinoline (MeIQ), 2-amino-3,8-dimethyl-3H-imidazo[4,5-f]quinoxaline (MeIQx), 9H-pyrido[3,4-b]indole (norharman), and 1-methyl-9H-pyrido[3,4-b]indole (harman)) were anaerobically incubated with Lactobacillus reuteri DSM 20016 in the presence of glycerol. The extent of conversion, as analyzed by HPLC-DAD/FLD, was dependent on both the studied HAAs and the glucose/glycerol ratio, indicating reuterin to be involved in HAA metabolism. Based on HRMS analyses, PhIP-M1-type metabolites were detected for AαC, Trp-P-1, IQ, MeIQ, MeIQx, harman, and norharman. In the case of AαC, this was confirmed by metabolite isolation (AαC-M8, 2,3,4,10-tetrahydro-1H-indolo[2,3-b][1,8]naphthyridin-2-ol) and one- (1H) and two-dimensional (HSQC, HMBC, COSY, DOSY) NMR spectroscopy. In addition, based on HRMS and/or NMR spectroscopy, a new type of HAA metabolite, resulting from the reaction with two molecules of 3-hydroxypropionaldehyde or acrolein, is hypothesized for AαC, Trp-P-1, IQ, MeIQ, and MeIQx.