Nereistoxin and cartap neurotoxicity attributable to direct block of the insect nicotinic receptor/channel.

Seog-Jong Lee, Motohiro Tomizawa, John E Casida

Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720-3112, USA.

Journal of agricultural and food chemistry 2003 Apr 23

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Nereistoxin (NTX) (4-dimethylamino-1,2-dithiolane) is the naturally occurring prototype for cartap [the bis(thiocarbamate) derivative of the NTX dithiol], which is generally regarded as a proinsecticide reverting to NTX. The aim of this study is to define the target site(s) for dithiolanes and dithiol esters. The affinity of [(3)H]NTX was not suitable for binding assays with honeybee (Apis mellifera) head membranes. However, NTX and cartap are equally potent, direct-acting, and competitive displacers of [(3)H]thienylcyclohexylpiperidine binding at the noncompetitive blocker (NCB) site of the Apis nicotinic acetylcholine receptor (nAChR)/channel. NTX also binds at the Apis [(3)H]imidacloprid agonist site, but cartap does not. As candidate metabolic pathways, sequential N-desmethylation and S-oxidation of NTX progressively reduce its potency at the NCB site and toxicity to houseflies. A P450 inhibitor reduces the toxicity of NTX and enhances it with cartap. Surprisingly, cartap is not just a pro-NTX but instead directly induces inhibitory neurotoxicity by blocking the nAChR/channel, whereas NTX may have dual NCB and agonist targets.

Citation

Seog-Jong Lee, Motohiro Tomizawa, John E Casida. Nereistoxin and cartap neurotoxicity attributable to direct block of the insect nicotinic receptor/channel. Journal of agricultural and food chemistry. 2003 Apr 23;51(9):2646-52