Augmentation of 3-methylcholanthrene-induced bioactivation in the human hepatoma cell line HepG2 by the calcium channel blocker nicardipine

Live-cell screening platform using human-induced pluripotent stem cells expressing fluorescence-tagged cytochrome P450 1A1

Human-induced pluripotent stem cells (hiPSCs) are invaluable sources for drug screening and toxicity tests because of their differentiation potential and proliferative capacity. Recently, the CRISPR-Cas9-mediated homologous recombination system has enabled reporter knock-ins at desired loci in hiPSCs, and here, we generated a hiPSC reporter line expressing mCherry-tagged cytochrome P450 1A1 (CYP1A1), which can be utilized to screen for the modulators of aryl hydrocarbon receptor (AHR) in live cells. CYP1A1-mCherry hiPSCs exhibited typical characteristics of pluripotent stem cells such as marker expression, differentiation potential, and normal karyotype. After differentiation into hepatocyte-like cells (HLCs), CYP1A1-mCherry fusion protein was expressed and localized at the endoplasmic reticulum, and induced by AHR agonists. We obtained 23 hits modulating CYP1A1 expression from high-content screening with 241 hepatotoxicity chemicals and nuclear receptor ligands, and identified three upregulating chemicals and two downregulating compounds. Responses of hiPSC-HLCs against an AHR agonist were more similar to human primary hepatocytes than of HepG2 hepatocellular carcinoma cells. This platform has the advantages of live-cell screening without sacrificing cells (unlike previously available CYP1A1 reporter cell lines), as well as an indefinite supply of cells, and can be utilized in a wide range of screening related to AHR- and CYP1A1-associated diseases in desired cell types.

[Sex- and species-differences on xenobiotic-induced toxicity: differences in constitutive and xenobiotic-mediated expression of cytochrome P450 1A subfamily enzymes (CYP1As)]

Cytochrome P450 1A subfamily enzymes (CYP1As) are important molecules in the metabolic activation of carcinogens such as polycyclic aromatic hydrocarbons and heterocyclic amines and are induced by their substrate exposure. There are species, sex, and organ differences in the induction of CYP1As, and susceptibilities to carcinogens are closely related to the constitutive and carcinogen-induced levels of CYP1As in target organs of experimental rodents. In this study, we investigated the induction of CYP1As and their species or sex differences after treatment with various chemicals using experimental animals and cultured cell lines. We found that: 1) newly established reporter cell lines, HepG2-A10 and KanR2-XL8, can be used for determining of activation of the aryl hydrocarbon receptor (AhR), a key transcription factor in the expression of CYP1As; 2) monocyclic aromatic amine (2-methoxy-4-nitroaniline) induced hepatic CYP1As in rats but not in other rodents in an AhR-independent manner; 3) androgen suppressed the constitutive expression or heterocyclic aromatic amine (Trp-P-1)-dependent induction of these enzymes in pigs and mice; and 4) nicardipine, a dihydropyridine calcium channel blocker, increased hepatic CYP1A expression in rats and augmented 3-methylcholanthrene-mediated induction of CYP1As and DNA-adduct formation in HepG2 cells. These findings indicate that there are species or sex differences in the induction of hepatic CYP1As via AhR-independent and unexplained transcriptional mechanisms. The elucidation of these mechanisms will aid in finding new predictors or developing new prevention strategies for chemical-induced carcinogenesis.

Validation of reference gene stability for APAP hepatotoxicity studies in different in vitro systems and identification of novel potential toxicity biomarkers

Liver cell lines and primary hepatocytes are becoming increasingly valuable for in vitro toxicogenomic studies, with RT-qPCR enabling the analysis of gene expression profiles following exposure to potential hepatotoxicants. Supporting the accurate normalisation of RT-qPCR data requires the identification of reference genes which have stable expression during in vitro toxicology studies. Therefore, we performed a comprehensive analysis of reference gene stability in two routinely used cell types, (HepG2 cells and primary rat hepatocytes), and two in vitro culture systems, (2D monolayer and 3D scaffolds). A robust reference gene validation strategy was performed, consisting of geNorm analysis, to test for pair wise variation in gene expression, and statistical analysis using analysis of variance. This strategy identified stable reference genes with respect to acetaminophen treatment and time in HepG2 cells (GAPDH and PPIA), and with respect to acetaminophen treatment and culture condition in primary hepatocytes (18S rRNA and α-tubulin). Following the selection of reference genes, the novel target genes E2F7 and IL-11RA were identified as potential toxicity biomarkers for acetaminophen treatment. We conclude that accurate quantification of gene expression requires the use of a validated normalisation strategy for each species and experimental system employed.