Modulation of cytochrome P450 1A1 by food-derived heterocyclic aromatic amines.

A short-term effect of a meal of fried meat is a postprandial induction of hepatic and intestinal cytochrome P450 activity. In order to identify the components responsible for this effect we investigated the potency of food derived genotoxic heterocyclic aromatic amines (HA) to induce CYP1A1 in vitro. In two cell lines, the rat hepatoma cell line H4IIE and the human breast cancer cell line MCF-7, we investigated 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeAC), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and Harman representing the different classes of HA at concentrations from 10(-8) to 10(-4) M. Induction of CYP1A1 was analysed on the mRNA level by semi-quantitative RT-PCR and the protein level (western blot using specific antibodies). The relative order of enzyme induction was Trp-P-1 with 1.4 x 10(-6) M (EC50 compared to TCDD 10(-9) M), MeAalphaC (1.4 x 10(-5)), Harman (2.1 x 10(-4)) and MeIQx (1.0 x 10(-3)). Furthermore, CYP1A1 enzyme activity was analysed as ethoxyresorufin-O-deethylase. While protein and mRNA analyses gave similar results, competitive inhibition impaired the enzyme activity assay. Inhibition of CYP1A1 activity was determined using microsomes of heterologous expressed CYP1A1. This dose-dependent inhibitory activity paralleled the induction potency. These results compare well with earlier data published for hepatic enzyme induction by HA observed in animal experiments. However, since the observed activities are rather weak and the amounts of HA ingested with a meal are low, there may be other factors involved in the observed postprandial enzyme induction in humans. On the other hand, concentrations in the micromolar range that are reached in high dosage animal experiments with HA may well influence cytochrome activity and, thus, influence the experimental outcome of these studies.