Correlation of susceptibility to ortho-aminoazotoluene-induced hepatocarcinogenesis with Car and Ahr signaling pathway activation in mice

Abstract

ortho-Aminoazotoluene (o-AT) is a potent hepatocarcinogen for most mouse strains. Previously, it has been shown that oAT administration activates the aryl hydrocarbon receptor (Ahr) and the constitutive androstane receptor (Car) in the mouse liver. Both receptors are directly involved in hepatocarcinogenesis. In this study, we investigated the effect of chronic o-AT administration on the mRNA expression levels of Ahr, Car, and their target genes Cyp1a1 and Cyp2b10, as well as the correlation of their expression with the degree of inflammatory response in the mouse strains DD/He (DD) and CC57BR/Mv (BR), which are contrasting in their sensitivity to hepatocarcinogenesis. Male mice of both strains received the o-AT oil solution at a dose of 225 mg/kg body weight four times within two months. Control animals received the equivalent solvent amount. The mice were sacrificed after 1 and 4 days since the last o-AT administration. The gene expression levels in the liver were determined by real-time PCR. The inflammatory response was evaluated by the serum concentration of the tumor necrosis factor alpha (TNFα). In resistant BR mice, the o-AT administration induced a more pronounced and prolonged increase in the Cyp1a1 mRNA, indicating the preferential Ahr activation in these animals. At the same time a more pronounced increase in the Cyp2b10 expression level in the sensitive DD mice was observed, suggesting the Car activation. In addition, a strong and prolonged inflammatory response to o-AT administration was noted in the DD mice, but not in BR. It is assumed that the prevalence of the Ahr signaling pathway activation over the Car signaling pathway activation is a factor of the resistance to o-AT-induced hepatocarcinogenesis.