Mixture effects of food-relevant polycyclic aromatic hydrocarbons on the activation of nuclear receptors and gene expression, benzo[a]pyrene metabolite profile and DNA damage in HepaRG cells

Carcinogenic benzo[a]pyrene (BP) and other non-carcinogenic polycyclic aromatic hydrocarbons (PAH) like fluoranthene (FA) and pyrene (PYR) occur as food contaminants. Molecular effects of BP, FA and PYR in human liver cells were investigated using mixtures occurring in grilled meat. Activation of aryl hydrocarbon receptor (AHR) and constitutive androstane receptor (CAR) was investigated along with target gene expression. Mixture effects on BP metabolite profile and DNA-damaging potential were studied as biological downstream effects. Compared to BP, FA and PYR activated the AHR only weakly. Mixtures were less efficient than BP. Analysis of CYP1A1 expression showed synergistic induction after co-exposure in HepaRG cells. FA and PYR were strong CAR agonists, whereas BP was less potent. Mixtures containing BP caused a strong decrease of CAR transactivation in line with lower CYP2B6 expression. The BP metabolite profile and BP-induced DNA damage were only weakly affected. PAH mixtures modulate AHR, CAR activation and their target genes. However, these mixture effects appear not to be reflected at the level of downstream events like BP metabolite formation or BP-induced DNA damage. Our study clearly shows that endpoints at all biological levels should be considered for mixture evaluation, instead of drawing conclusions exclusively based on early molecular events.