An integrated approach, based on mass spectrometry, for the assessment of imidacloprid metabolism and penetration into mouse brain and fetus after oral treatment.

ABSTRACT

Imidacloprid is an insecticide belonging to neonicotinoids, a class of agonists of the nicotinic acetylcholine receptors that shows higher affinities in insects compared to mammals. However, recent evidence show that neonicotinoids can bind to the mammalian receptors, leading to detrimental responses in cultured neurons. We developed an analytical strategy which uses mass spectrometry with multiple reaction monitoring (targeted approach) and high-resolution acquisitions (untargeted approach), which were applied to quantify imidacloprid and to identify its metabolites in biological tissues after oral treatments of mice. Mouse dams were treated with doses from 0.118 mg/kg bw day up to 41 mg/kg day between gestational days 6-9. Results showed quantifiable levels of imidacloprid in plasma (from 30.48 to 5705 ng/mL) and brain (from 20.48 to 5852 ng/g) of treated mice, proving the passage through the mammalian blood-brain barrier with a high correspondence between doses and measured concentrations. Untargeted analyses allowed the identification of eight metabolites including imidacloprid-olefin, hydroxy-imidacloprid dihydroxy-imidacloprid, imidacloprid-nitrosimine, desnitro-imidacloprid, 6-chloronicotinic acid, 5-(methylsulfanyl)pyridine-2-carboxylic acid and N-imidazolidin-2-ylidenenitramide in plasma and brain. Moreover, analysis of embryonic tissues after oral treatment of mouse dams showed detectable levels of imidacloprid (816.6 ng/g after a dose of 4.1 mg/Kg bw day and 5646 ng/g after a dose of 41 mg/Kg bw day) and its metabolites, proving the permeability of the placenta barrier. Although many studies have been reported on the neurotoxicity of neonicotinoids, our study paves the way for a risk assessment in neurodevelopmental toxicity, demostrating the capability of imidacloprid and its metabolites to pass the biological barriers.