title: Minor structural changes in nicotinoid insecticides confer differential subtype selectivity for mammalian nicotinic acetylcholine receptors.
abstract: The major nitroimine insecticide imidacloprid (IMI) and the nicotinic analgesics epibatidine and ABT-594 contain the 6-chloro-3-pyridinyl moiety important for high activity and/or selectivity. ABT-594 has considerable nicotinic acetylcholine receptor (AChR) subtype specificity which might carry over to the chloropyridinyl insecticides. This study considers nine IMI analogues for selectivity in binding to immuno-isolated alpha1, alpha3 and alpha7 containing nicotinic AChRs and to purported alpha4beta2 nicotinic AChRs. Alpha1- and alpha3-containing nicotinic AChRs (both immuno-isolated by mAb 35, from Torpedo and human neuroblastoma SH-SY5Y cells, respectively) are between two and four times more sensitive to DN-IMI than to (-)-nicotine. With immuno-isolated alpha3 nicotinic AChRs, the tetrahydropyrimidine analogues of IMI with imine or nitromethylene substituents are 3-4 fold less active than (-)-nicotine. The structure-activity profile with alpha3 nicotinic AChRs from binding assays is faithfully reproduced in agonist potency as induction of 86rubidium ion efflux in intact cells. Alpha7-containing nicotinic AChRs of SH-SY5Y cells (immuno-isolated by mAb 306) and rat brain membranes show maximum sensitivity to the tetrahydropyrimidine analogue of IMI with the nitromethylene substituent. The purported alpha4beta2 nicotinic AChRs [mouse (Chao & Casida, 1997) and rat brain] are similar in sensitivity to DN-IMI, the tetrahydropyrimidine nitromethylene and nicotine. The commercial insecticides (IMI, acetamiprid and nitenpyram) have low to moderate potency at the alpha3 and purported alpha4beta2 nicotinic AChRs and are essentially inactive at alpha1 and alpha7 nicotinic AChRs. In conclusion, the toxicity of the analogues and metabolites of nicotinoid insecticides in mammals may involve action at multiple receptor subtypes with selectivity conferred by minor structural changes.
authors.affiliation: Department of Environmental Science, Policy and Management, University of California, Berkeley 94720-3112, USA.
authors.forename: M
authors.initials: M
authors.lastname: Tomizawa
authors.forename: J E
authors.initials: JE
authors.lastname: Casida
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D018678:Cholinergic Agents / Q000737:chemistry / Q000494:pharmacology* / Q000633:toxicity; D004557:Electric Organ / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D007093:Imidazoles / Q000737:chemistry / Q000494:pharmacology* / Q000633:toxicity; D007306:Insecticides / Q000737:chemistry / Q000494:pharmacology* / Q000633:toxicity; D051379:Mice; D000073943:Neonicotinoids; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists / Q000494:pharmacology; D009574:Nitro Compounds; D011869:Radioligand Assay; D051381:Rats; D011978:Receptors, Nicotinic / Q000187:drug effects*; D012414:Rubidium Radioisotopes; D013329:Structure-Activity Relationship; D014101:Torpedo; D014407:Tumor Cells, Cultured
chemical_list: D000911:Antibodies, Monoclonal; D018678:Cholinergic Agents; D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D018722:Nicotinic Agonists; D009574:Nitro Compounds; D011978:Receptors, Nicotinic; D012414:Rubidium Radioisotopes; C082359:imidacloprid; D009538:Nicotine