Development of in vivo biotransformation enzyme assays for ecotoxicity screening: In vivo measurement of phases I and II enzyme activities in freshwater planarians

• Both phase I and II enzyme activities were detectable in planarian culture media.
• In vivo O-deethylation with alkoxycoumarins were present in Dugesia japonica.
• In vivo O-deethylation with alkoxyresorufins were not detected in Dugesia japonica.
• DT-diaphorase and catechol-O-methyltransferase activities were present in planarian.
• UDP-glucuronosyltransferase and arylsulfatase activities were present in planarian.

The development of a high-throughput tool is required for screening of environmental pollutants and assessing their impacts on aquatic animals. Freshwater planarians can be used in rapid and sensitive toxicity bioassays. Planarians are known for their remarkable regeneration ability but much less known for their metabolic and xenobiotic biotransformation abilities. In this study, the activities of different phase I and II enzymes were determined in vivo by directly measuring fluorescent enzyme substrate disappearance or fluorescent enzyme metabolite production in planarian culture media. For phase I enzyme activity, O-deethylation activities with alkoxyresorufin could not be detected in planarian culture media. By contrast, O-deethylation activities with alkoxycoumarin were detected in planarian culture media. Increases in 7-ethoxycoumarin O-deethylase (ECOD) activities was only observed in planarians exposed to 1 μM, but not 10 μM, β-naphthoflavone for 24 h. ECOD activity was inhibited in planarians exposed to 10 and 100 μM rifampicin or carbamazepine for 24 h. For phase II enzyme activity, DT-diaphorase, arylsulfatases, uridine 5′-diphospho (UDP)-glucuronosyltransferase or catechol-O-methyltransferase activity was determined in culture media containing planarians. The results of this study indicate that freshwater planarians are a promising model organism to monitor exposure to environmental pollutants or assess their impacts through the in vivo measurement of phase I and II enzyme activities.

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