New Conceptual Toxicokinetic Model to Assess Synergistic Mixture Effects between the Aromatic Hydrocarbon β-Naphthoflavone and the Azole Nocodazole on the CYP1A Biomarker in a Fish Cell Line

Abstract

Toxicokinetic interactions with catabolic cytochrome P450 (CYP) enzymes can inhibit chemical elimination pathways and cause synergistic mixture effects. We have created a mathematical bottom-up model for a synergistic mixture effect where we fit a multidimensional function to a given data set using an auxiliary nonadditive approach. The toxicokinetic model is based on the data from a previous study on a fish cell line, where the CYP1A enzyme activity was measured over time after exposure to various combinations of the aromatic hydrocarbon β-naphthoflavone and the azole nocodazole. To describe the toxicokinetic mechanism in this pathway and how that affects the CYP1A biomarker, the model uses ordinary differential equations. Local sensitivity and identifiability analyses revealed that all the 10 parameters estimated in the model were identified uniquely while fitting the model to the data for measuring the CYP1A enzyme activity. The model has a good prediction power and is a promising tool to test the synergistic toxicokinetic interactions between different chemicals.

Biotransformation of 6PPD-quinone In Vitro Using RTL-W1 Cell Line

“…39 Co-exposure with BNF completely inhibited the biotransformation capacity of RTL-W1 cells due to competitive inhibition (data not shown), as BNF is also metabolized by CYP1A. 40 Pre-exposing cells to BNF for 72 h before a 4 h 6PPD-quinone exposure significantly increased biotransformation (Student's t test, p = 0.0467, Figure 2B) and EROD (Dunnett's test, p-adj = 0.0373, Figure 2C) activity compared to PC, supporting CYP1A as the primary enzyme responsible for hydroxylation of 6PPDquinone. 41 No phase II TPs were found in any of the cell media samples after 4 h of exposure.…”

“…The inducers had a minimal effect (rifampicin), and in some cases negative (BNF), on the biotransformation of 6PPD-quinone when pre-exposed for 24 h. A reduction of TPs was observed for the 24 h BNF pre-exposed RTL-W1 cells, indicating that more time was needed to induce CYP1A, as BNF has been shown to induce CYP1A1 expression in primary rainbow trout hepatocytes . Co-exposure with BNF completely inhibited the biotransformation capacity of RTL-W1 cells due to competitive inhibition (data not shown), as BNF is also metabolized by CYP1A . Pre-exposing cells to BNF for 72 h before a 4 h 6PPD-quinone exposure significantly increased biotransformation (Student’s t test, p = 0.0467, Figure B) and EROD (Dunnett’s test, p -adj = 0.0373, Figure C) activity compared to PC, supporting CYP1A as the primary enzyme responsible for hydroxylation of 6PPD-quinone .…”