2-Amino-1-methyl-6-(5-hydroxy-)phenylimidazo[4,5-b]pyridine (5-OH-PhIP), a biomarker for the genotoxic dose of the heterocyclic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP).

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is a mutagenic and carcinogenic heterocyclic amine formed during ordinary cooking. PhIP is metabolically activated by CYP P450 mediated N-hydroxylation followed by phase II esterification. The ultimate mutagenic metabolite reacts with DNA resulting in formation of adducts, and with proteins and other cellular constituents resulting in unstable products which are degraded to 5-hydroxy-PhIP. Rats were dosed orally with PhIP and urine and faeces were collected to 24, 48 and 72 h. Urine and faeces samples were hydrolysed with glucuronidase/sulfatase in order to release conjugated metabolites, followed by purification on C18 columns. The rats excreted 0.88% of the dose as 5-hydroxy-PhIP with the urine to 24 h and 0.04 and 0.01% to 48 and 72 h, respectively. The amounts of 5-hydroxy-PhIP found in faeces were 0.03, 0.1 and 0% to 24, 48 and 72 h. Urinary excretion of 5-hydroxy-PhIP showed a linear dose-response relationship in rats dosed orally with PhIP. This shows that 5-hydroxy-PhIP is also formed in vivo and that 91% is excreted with the urine in 24 h, indicating the possible use of 5-hydroxy-PhIP as a urinary biomarker for the bioactive dose of PhIP. In a preliminary study, using molecular imprinted polymer a specific sorbent for purification, after enzymatic hydrolysis and purification on a C18 column, we have identified 5-OH-PhIP in a 24-h urine sample from a male volunteer who had ingested a fried beef. This indicates that urinary 5-OH-PhIP could be used as an easily obtainable marker for the genotoxic dose of PhIP in human biomonitoring studies.