In vitro metabolism assessment of thiacloprid in rainbow trout and rat by LC-UV and high resolution-mass spectrometry

Abstract

1. Thiacloprid (THI) is a widely used neonicotinoid insecticide where concerns have been raised regarding low absorption by crops, substantial distribution in surrounding areas, and potential adverse effects to terrestrial and aquatic organisms.

2. Prior to this study, there was very limited information addressing the ex vivo (precision-cut liver slices) metabolism of THI by fish species and the metabolic pathways regulating its potential for adverse effects.

3. The in vitro and ex vivo biotransformation pathway of THI is defined by the formation of three primary metabolites (TM1, TM2 and TM3) via separate paths differentiated by reductive decyanation, reductive dechlorination with hydration and dealkylation processes, respectively.

4. Kinetic rates were calculated for the rat microsomal decyanation of THI into TM1 (K_m = 299.2 µM and V_max = 5.3 pmol/min/mg), and for the dealkylation of THI into TM3 (K_m = 368.9 µM and V_max = 3.95 pmol/min/mg).

5. Formation confirmation and identity inference of THI metabolites in absence of standards were achieved by LC-UV and High Resolution-MS strategies.

6. The in vitro and ex vivo metabolic products of THI are conserved both across species (rat and Rainbow trout) and levels of biological organization (microsomes and liver slices), as previously reported for the neonicotinoid insecticides Imidacloprid and Acetamiprid.

Keywords:

• Chloropyridinyl neonicotinoids
• thiacloprid
• in vitro/ex vivo metabolism
• precision-cut slices
• microsomal fraction
• rainbow trout
• rat
• uHPLC-HR-MS

Acknowledgements

The authors thank Dr. Keith Houck and Tylor Lahren, USEPA/ORD/CCTE for thorough review of this manuscript.

Disclosure statement

The views expressed in this paper are those of the authors and do not necessarily reflect the views or policies of the U.S. Environmental Protection Agency. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. Manuscript review was performed following provisions of the USEPA Office of Research and Development. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. Views presented in the text are those of the authors and not necessarily the opinion of the USEPA. The authors report no conflict of interest.

Data availability statement

All data from associated with this manuscript will be publicly available at the EPA Environmental Dataset Gateway (https://edg.epa.gov/metadata/catalog/main/home.page).

Additional information

Funding

All research reported in this manuscript was funded by the US Environmental Protection Agency (USEPA) and conducted by or under the supervision of USEPA employees.