Metabolism of N-Methyl-2-Pyrrolidone in Honey Bee Adults and Larvae: Exploring Age Related Differences in Toxic Effects

Abstract

In chronic feeding assays, the common agrochemical inert formulant N-methyl-2-pyrrolidone (NMP) is at least 20 times more toxic to honey bee larvae than to adults, but the underlying cause of this difference is unknown. In other taxa, NMP is primarily detoxified via a cytochrome P450 mediated pathway. Using a LC-MS method, putative cytochrome P450 metabolites of NMP were identified and quantified in adults and larvae following chronic exposure to NMP. Major differences in the identities and quantities of the generated metabolites were observed between adults and larvae. One major difference was the higher percentage of the administered NMP recovered as the parent compound in larvae compared to adults. To further explore the apparent difference in metabolic capacity, a spectrofluorometric method was used to compare general cytochrome P450 enzyme activity by monitoring the transformation of a 7-ethoxycoumarin substrate. Higher microsomal levels of 7-ethoxycoumarin-O-deethylase activity in adult fat bodies suggests that the higher percentage of unmetabolized NMP in larvae relative to adults may be due to lower cytochrome P450 enzyme activity in fat bodies. Taken together, these results suggest that larvae may be less able to detoxify xenobiotics encountered in diet than adults, and these findings will help inform future risk assessment.