An investigation into 1-methyl-3-octyl imidazolium toxicity in the undifferentiated HepaRG cell line

Abstract

The 1-Methyl-3-Octyl Imidazolium (M8OI) was recently detected in the environment using rat progenitor (B-13) cell lines in a toxicity screen. M8OI has subsequently been proposed as a potential trigger for Primary Biliary Cholangitis (PBC), an autoimmune liver disease. The HepaRG cells were used to investigate the M8OI toxicity because they are human progenitor like cells that can differentiate into both hepatocytes as well as cholangiocytes. In previous studies, undifferentiated HepaRG cells were shown to be relatively insensitive to M8OI toxic effects compared to B13 cells. This study aims to examine the insensitivity of undifferentiated HepaRG cells to M8OI. Increased medium glucose concentrations did not afford protection to undifferentiated HepaRG cells, in contrast to B-13 cells. Seahorse assay indicated that undifferentiated HepaRG cells consumed significantly less oxygen compared to B-13 cells when normalised for protein. Further, M8OI was less potent as an inhibitor of oxygen consumption in HepaRG cells compared to B-13 cells. This study also investigated whether undifferentiated HepaRG cells expressed CYP1A1, which could be capable of converting M8OI into non-toxic compounds. The results of this study indicated that undifferentiated HepaRG cells had negligible CYP1A1 activity although low levels were detectable after treatment with beta-naphthoflavone. These data suggest that undifferentiated HepaRG cells are less sensitive to M8OI toxicity compared to B-13 cells due to reduced reliance on mitochondrial oxidative phosphorylation combined with reduced sensitivity to M8OI inhibitory action on the electron transport chain. Expression of functional CYP1A1 activity was not responsible for reduced sensitivity to M8OI.