The Human Fecal Microbiota Metabolizes Foodborne Heterocyclic Aromatic Amines by Reuterin Conjugation and Further Transformations

Scope: Heterocyclic aromatic amines (HAAs) are process-induced food contaminants with high mutagenic and/or carcinogenic potential. Although the human gut microbiota is known to affect the metabolism of dietary constituents, its impact on HAA metabolism and toxicity has been little studied. Here, the glycerol-dependent metabolism of seven foodborne HAAs (AaC, Trp-P-1, harman, norharman, PhIP, MeIQx, and MeIQ) by the human fecal microbiota is investigated. Methods and results: As analyzed by HPLC-DAD/FLD, the extent of conversion is strongly dependent on glycerol supplementation and HAA structure. AaC (60-100%) and the 2-aminoimidazoazarenes (up to 58%) are especially prone to microbial conversion. Based on high-resolution MS and/or NMR spectroscopy data, 70 fecal metabolites are identified in total, mainly formed by chemical reactions with one or two molecules of microbially derived reuterin. Moreover, it has been demonstrated that the human fecal microbiota can further transform reuterin adducts by reduction and/or hydroxylation reactions. Upon isolation, some reuterin-induced HAA metabolites appear to be partially unstable, complicating structural identification. Conclusion: The formation of microbial metabolites needs to be incorporated into risk assessment considerations for HAAs in human health. In this study, several HAA metabolites, mainly reuterin-dependent, are identified in vitro, providing the basis for future human studies investigating microbial HAA metabolism.