Neonicotinoid Metabolism: Compounds, Substituents, Pathways, Enzymes, Organisms, and Relevance

Abstract

Neonicotinoids are one of the three principal insecticide chemotypes. The seven major commercial neonicotinoids are readily biodegraded by metabolic attack at their N-heterocyclylmethyl moiety, heterocyclic or acyclic spacer, and N-nitroimine, nitromethylene, or N-cyanoimine tip. Phase I metabolism is largely dependent on microsomal CYP450 isozymes with situ selectivity in hydroxylation, desaturation, dealkylation, sulfoxidation, and nitro reduction. Cytosolic aldehyde oxidase is a nitroreductase for some neonicotinoids. Phase II metabolism involves methylation, acetylation, and formation of glucuronide, glucoside, amino acid, and sulfate- and glutathione-derived conjugates. Some neonicotinoids act as proinsecticides with metabolism to more potent nicotinic agonists. Pest resistance is more commonly due to synergist-reversible CYP450 detoxification than to nAChR mutants or variants. Metabolites in some cases contribute to mammalian hepatotoxicity and carcinogenesis and in others to enhanced plant vigor and stress shields. These relationships explain much of neonicotinoid comparative toxicology and provide the basis for continued and improved safety and effectiveness of this chemotype.

Rapid and efficient pesticide detection via cyclodextrin-promoted energy transfer

“…Reported herein is the use of these pesticides as energy donors in combination with high quantum yield fluorophore acceptors 8-10, and the ability to use such energy transfer as the basis for the highly sensitive detection of these pesticides in both purified buffer solution and in commercially available, unpurified apple juice. The structures of all analytes and fluorophores are shown in Figure 2, and include multiple pesticide classes such as organochlorines (compounds 1 and 2), 20 pyrethroids (compounds 3, 5, and 7), 21 neonicotinoids (compound 4), 22 and carbamates (compound 6). 23 The fluorophores chosen are either commercially available or easily synthesized via literature-…”

Acute Poisoning with Neonicotinoid Insecticide

“…The most active CYP isoenzyme for oxidation of the imidacloprid residue is CYP 3A4 (CYP most abundant in humans), followed by CYP 2C19, 2A6 and 2C9. For nitroreduction, the most active CYP are: CYP 1A2, 2B6, 2D6 and 2E1 [16,17]. …”

Non-target effects of chlorantraniliprole and thiamethoxam on Chrysoperla carnea when employed as sunflower seed treatments

“…Furthermore, the conversion of thiamethoxam into highly toxic metabolites such as clothianidin (Casida 2011) may contribute to increased toxicity to insects, including natural enemies. Nauen et al (2003) demonstrated that clothianidin is one of the primary metabolites of thiamethoxam in true leaves of cotton plants treated via soil drench.…”