Phenanthrene, but not its isomer anthracene, effectively activates both human and mouse nuclear receptor constitutive androstane receptor (CAR) and induces hepatotoxicity in mice.

Polycyclic aromatic hydrocarbons (PAHs) are a class of pervasive global environmental pollutants and adversely affect human health. Among PAHs, phenanthrene and anthracene are isomers consisting of three benzene rings. In the present study, we have made comparisons of constitutive androstane receptor (CAR) activation and toxic effects on the liver between these two isomers. Phenanthrene, but not anthracene, significantly induced promoter activity and gene expression of human drug metabolizing enzyme CYP2B6 in HepG2 cells and human primary hepatocytes, respectively. Phenanthrene, but not anthracene, significantly increased CYP2B10 expression levels and caused hepatotoxicity in mice. Phenanthrene induced the nuclear accumulation of CAR in the liver of wild-type mice, but not CAR^-/- mice. Hepatocellular necrosis, elevated expression levels of some CAR-related genes such as CYP2B10, CYP3A11, UGT1A1, SULT2A1 and GSTM3, and lower hepatic glutathione levels were found in phenanthrene-exposed wild-type mice but not CAR^-/- mice. Additionally, phenanthrene and anthracene were detected in both raw and grilled lamb samples. The average concentrations of phenanthrene were much higher than those of anthracene in these samples. This study is the first to demonstrate that phenanthrene, but not its isomer anthracene, effectively activates both human and mouse nuclear receptor CAR, and CAR plays a crucial role in phenanthrene-induced mouse hepatotoxicity. Compared with anthracene, K region may be an important electronic structure of phenanthrene for activation of CAR. Dietary consumption of PAHs-contaminated food is an important exposure route for humans. Exposure to phenanthrene may affect human health especially associated with liver.