Combined exposure to triphenyl phosphate and haloperidol alters hepatic lipid homeostasis and xenobiotic metabolism beyond single-compound effects

Disruption of hepatic lipid metabolism by chemicals can lead to steatosis or phospholipidosis. Toxicological risk assessment mainly focuses on individual compounds rather than on mixtures, which does not well reflect real-life exposure scenarios. Mixture effects of compounds that do not share similar modes of action are increasingly drawing attention, with several studies having shown toxicodynamic and toxicokinetic interactions leading to unexpected mixture effects. The aim of this study was to investigate how the mixture of a phospholipidosis inducer and a steatosis inducer affect hepatic lipid and xenobiotic metabolism in comparison to single-compound treatment. Hence, differentiated HepaRG cells were treated with haloperidol (1–100 µM HLP, phospholipidosis inducer) and triphenyl phosphate (1–100 µM TPP, steatosis inducer), alone and in combination (with 25 µM TPP or 20 µM HLP). Steatosis induction by TPP was diminished when TPP was present in a mixture with HLP, with the antagonistic effects likely being caused by interactions at the transcriptional level. Furthermore, toxicokinetic investigations revealed decreased cytochrome P450 (CYP) expression and activity, leading to synergistic effects of the mixture on cell viability and also a slight increase in phospholipidosis induction by HLP. In conclusion, the investigated mixture of HLP and TPP demonstrated non-additive effects on hepatic lipid and xenobiotic metabolism with complex toxicodynamic and toxicokinetic interplay. These findings highlight the challenges of predicting mixture interactions for risk assessment.