Suppressive effect of enzymatically modified isoquercitrin on phenobarbital-induced liver tumor promotion in rats.

To investigate the effect of enzymatically modified isoquercitrin (EMIQ) on hepatocellular tumor promotion induced by phenobarbital (PB), male rats were administered a single intraperitoneal injection of 200 mg/kg N-diethylnitrosamine (DEN) and then fed with a diet containing PB (500 ppm) for 8 weeks, with or without EMIQ (2,000 ppm) in the drinking water. One week after PB administration, rats underwent a two-thirds partial hepatectomy. The PB-induced increase in the number and area of glutathione S-transferase placental form-positive foci and the proliferating cell nuclear antigen-positive ratio was significantly suppressed by EMIQ. Real-time reverse transcription-polymerase chain reaction analysis revealed increases in mRNA expression levels of Cyp2b2 and Mrp2 in the DEN-PB and DEN-PB-EMIQ groups compared with the DEN-alone group, while the level of Mrp2 decreased in the DEN-PB-EMIQ group compared with the DEN-PB group. There were no significant changes in microsomal reactive oxygen species (ROS) production and oxidative stress markers between the DEN-PB and DEN-PB-EMIQ groups. Immunohistochemically, the constitutive active/androstane receptor (CAR) in the DEN-PB group was clearly localized in the nuclei, but its immunoreactive intensity was decreased in the DEN-PB-EMIQ group. These results indicate that EMIQ suppressed the liver tumor-promoting activity of PB by inhibiting nuclear translocation of CAR, and not by suppression of oxidative stress.