Mixture effect of Dexamethasone & Benzo[a]pyrene in the poeciliopsis lucida hepatocellular carcinoma (PLHC-1) cell line

Abstract: At present days, inland water bodies and seashores show significant levels of various pharmaceuticals. This is to a great extent due to the low removal rate of common wastewater treatment plants when it comes to pharmaceuticals. As pharmaceuticals, dosed adequately, are perceived as harmless to humans, the concentrations of pharmaceuticals present in the environment are often not considered problematic. However, several aspects give a reason for concern. Besides the long-term effects of bioaccumulating pharmaceuticals and sensitive, highly-adaptive microorganisms, potential mixture effects are one of the most distressing concerns. While the toxic effects of single, isolated compounds may be known or easily assessable, the “cocktail” effect existing from chemical mixtures is significantly more difficult to predict and investigate. (Backhaus and Karlsson 2014; Lindim et al. 2019; Ukić et al. 2019; Wassmur et al. 2013). In this thesis, we focus on the interactions between two substances, Dexamethasone (DEX) and Benzo[a]pyrene (BaP) in the poeciliopsis lucida hepatocellular carcinoma (PLHC-I) cell line. We tested different mixture compositions to investigate GR-AhR crosstalk in these cells. Our study reveals increased CYP1A (EROD) activity (1.5 to 2-fold) in cells treated with a mixture of DEX and BaP, compared to cells treated with BaP only, whereas DEX alone, did not affect CYP1A induction. Interestingly, the difference in response was less prominent in cells exposed to BaP concentrations below 0.5 µM and in cells exposed to DEX concentrations greater than 2.5 µM. Time-course experiments showed that the synergistic mixture effect on CYP1A induction peaked at 48h after dosing with shorter exposure times showing lower CYP1A induction. To put the interaction between DEX and BaP into perspective, we tested three additional GR agonists and β-naphthoflavone (BNF) as an AhR agonist. Our results showed similar potentiating effects with all four GR agonists combined with the two AhR agonists on CYP1A induction. Our findings confirm previous studies showing exposure to mixtures of GR- and AhR agonists having potentiating effects on CYP1A induction (Celander et al. 1997; Wassmur et al. 2013). By testing several glucocorticoids in combination with two different AhR agonists, we demonstrated that there is consistent GR-AhR crosstalk on CYP1A induction in this fish cell line.