An In Vitro Bioassay for Xenobiotics Using the SXR-Driven Human CYP3A4/lac Z Reporter Gene

The dose and time effect of nine xenobiotics, including 17β-estradiol, corticosterone, dexamethasone, progesterone, nifedipine, bisphenol A, rifampicin, methamphetamine, and nicotine were investigated, in vitro, using human steroid and xenobiotics receptor (SXR)-binding sites on the human CYP3A4 promoter, which can enhance the linked lac Z reporter gene transcription. To test this, liver-specific SAP (human serum amyloid P component)-SXR (SAP/SXR) and human CYP3A4 promoter-regulated lac Z (h CYP3A4/lac Z) constructs were transiently transfected into Hep G2 and NIH3T3 cells to compare the xenobiotic responsiveness between human and nonhuman cell lines. In the Hep G2 cells, rifampicin, followed by corticosterone, nicotine, methamphetamine, and dexamethasone, exhibited enhanced levels of the lac Z transcript, whereas those of bisphenol A and nifedipine were found to be reduced. No significant responses were observed with 17β-estradiol or progesterone. In addition, 17β-estradiol and progesterone did not change the levels of the lac Z transcripts in the Hep G2 cells, but did induce significant increases in the transcripts of the NIH3T3 cells. Treatment with corticosterone and dexamethasone, which were highly expressed in the Hep G2 cells, did not affect the levels of the lac Z transcript in NIH3T3 cells. These results show that lac Z transcripts can be measured, rapidly and reproducibly, using reverse transcriptase–polymerase chain reaction (RT-PCR) based on the expression of the h CYP3A4/lac Z reporter gene, and was mediated by the SXR. Thus, this in vitro reporter gene bioassay is useful for measuring xenobiotic activities, and is a means to a better relevant bioassay, using human cells, human genes and human promoters, in order to get a closer look at actual human exposure.