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

Urban stormwater runoff contains the tire-derived transformation product N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine-quinone (6PPD-quinone), which poses significant environmental risks due to its high toxicity toward certain salmonids. 6PPD-quinone biotransformation has been investigated to explain some of the stark interspecies differences in sensitivity across different fishes; however, the primary mechanisms of 6PPD-quinone biotransformation remain unclear. This work aimed to explore the toxicokinetics of 6PPD-quinone in immortalized rainbow trout (Oncorhynchus mykiss) liver cells (RTL-W1) to identify transformation products, using coexposure with different enzyme inhibitors and inducers. Using high-resolution mass spectrometry, we identified three phase I 6PPD-quinone transformation products, with phenyl ring hydroxylation dominating, followed by hydroxylation of the alkyl side chain, and an unknown transformation product after 4 h of exposure. Co-exposing RTL-W1 cells with α-naphthoflavone and quercetin greatly inhibited the biotransformation of 6PPD-quinone, revealing that CYP1A is primarily involved in phase I biotransformation. Hepatic clearance predicted from in vitro results was further verified based on isolated perfused trout liver experiments. Further studies are necessary on the biotransformation and kinetics of 6PPD-quinone and the detoxification pathways involved in a wide phylogenetic space in fishes.