In vitro metabolism of imidacloprid and acetamiprid in rainbow trout and rat

Abstract

1. Providing an alternative to pyrethroids, organophosphates, and carbamates, the neonicotinoids are now the most widely used insecticides in the world. They are water soluble and relatively stable in soil and water which allows for run-off through surface waters and thus potentially impacting aquatic species and environments.

2. While the mammalian metabolism of neonicotinoids has been studied extensively, there is a lack of understanding of their metabolism in fish species. The current study constitutes the first report of the metabolism of imidacloprid (IMI) and acetamiprid (AC) in rainbow trout.

3. Formation of respective metabolites 5-hydroxy-imidacloprid and N-desmethyl-acetamiprid was conserved across orders of biological organization in both microsomal and liver slice assays.

4. Michaelis–Menten kinetics were determined for the microsomal conversion of IMI to 5-hydroxy-imidacloprid in rainbow trout (Km = 79.2 µM; Vmax = 0.75 pmole/min/mg) and rat (Km = 158.7 µM; Vmax = 38.4 pmole/min/mg). Kinetics for the microsomal demethylation of AC to N-desmethyl-acetamiprid were determined in the rat (Km = 70.9 µM; Vmax = 10 pmoles/min/mg). N-desmethyl-acetamiprid was found in detectable but below quantifiable levels across the range of test concentrations which precluded a calculation of kinetic rate constants in rainbow trout (RBT).

5. Ultimately, the formation of the metabolites 5-hydroxy-imidacloprid and N-desmethyl-acetamiprid was conserved across RBT and rat species.

Keywords:

• Metabolism
• acetamiprid
• imidacloprid
• liver slice
• microsomes
• rainbow trout
• rat
• neonicotinoid

Acknowledgements

The authors thank Keith Sappington and Ideliz Negrón-Encarnación (USEPA/OCSPP/OPP) for inciteful review of the manuscript, as well as Dr. Brett Blackwell (USEPA/CCTE/GLTED) for technical collaboration.

Disclosure statement

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. 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. No potential conflict of interest was reported by the authors.