Down‐regulation of 2‐Amino‐3,8‐dimethylimidazo[4,5‐f]quinoxaline (MeIQx)‐induced CYP1A2 Expression Is Associated with Bovine Lactoferrin Inhibition of MeIQx‐induced Liver and Colon Carcinogenesis in Rats

The inhibitory influence of bovine lactoferrin (bLF) on induction of preneoplastic hepatic glutathione S‐transferase placental form‐positive (GST‐P(+)) cell foci and colon aberrant crypt foci (ACF) by diethylnitrosamine (DEN) and 2‐amino‐3,8‐dimethylimidazo[4,5‐f]quinoxaline (MeIQx) was investigated in F344 rats. Rats were initially treated with DEN, then placed on basal diet containing MeIQx (200 ppm) alone, MeIQx plus 2% bLF, or MeIQx plus 0.2% bLF from week 2 to week 8, with partial hepatectomy performed at week 3. Concomitant administration of 2% or 0.2% bLF with MeIQx caused significant dose‐dependent decreases in both number and unit area of GST‐P(+) cell foci (2% bLF, P <0.001; 0.2% bLF, P <0.01). Similar results were observed for MeIQx‐induced colon ACF in the groups without DEN treatment (2% and 0.2% bLF, P <0.05). To investigate the underlying mechanisms, we analyzed the influence of bLF on levels of cytochrome P4501A2 (CYP1A2), a metabolically activating enzyme of MeIQx in the liver. The results demonstrated that combined administration of 2% bLF significantly reduced levels of MeIQx‐induced CYP1A2 mRNA (P <0.05) and protein (P <0.05) to the normal levels, in association with reduced values for MeIQx‐DNA adducts (P <0.05), liver GST‐P(+) cell foci and colon ACF. These results suggest that bLF is a chemopreventive agent for DEN alone or DEN plus MeIQx‐induced liver, and MeIQx‐induced colon carcinogenesis in rats. One possible mechanism is a normalizing down‐regulation of CYP1A2 expression by bLF, with consequent reduction of carcinogen activation and adduct formation.