Impact of a worker bee thoracic ganglion RIC-3 variant on the actions of acetylcholine and neonicotinoids on nicotinic receptors in Apis mellifera.

A transmembrane thioredoxin (TMX3) enables the functional expression of insect nicotinic acetylcholine receptors (nAChRs) in Xenopus laevis oocytes, while co-factors RIC-3 and UNC-50 regulate the receptor expression level. RIC-3 (resistant to inhibitors of cholinesterase 3) has been shown to diversify by its differential mRNA splicing patterns. How such diversity influences neonicotinoid sensitivity of nAChRs of beneficial insect species remains poorly understood. We have identified a RIC-3 variant expressed most abundantly in the thoracic ganglia of honeybee (Apis mellifera) workers and investigated its effects on the functional expression and pharmacology of Amα1/Amα8/Amß1 and Amα1/Amα2/Amα8/Amß1 nAChRs expressed in X. laevis oocytes. The AmRIC-3 enhanced the response amplitude to the acetylcholine (ACh) of these A. mellifera nAChRs when its cRNA was injected into oocytes at low concentrations but suppressed the ACh response amplitude at high concentrations. Co-expression of the AmRIC-3 had a minimal impact on the affinity of ACh, but changed the efficacy of imidacloprid and clothianidin, suggesting that the presence and the level of RIC-3 expression can affect the nAChR responses to ACh and neonicotinoids, depending on nAChR subunit composition in honeybees. © 2024 Society of Chemical Industry.

Unravelling nicotinic receptor and ligand features underlying neonicotinoid knockdown actions on the malaria vector mosquito Anopheles gambiae.

With the spread of resistance to long-established insecticides targeting Anopheles malaria vectors, understanding the actions of compounds newly identified for vector control is essential. With new commercial vector-control products containing neonicotinoids under development, we investigate the actions of 6 neonicotinoids (imidacloprid, thiacloprid, clothianidin, dinotefuran, nitenpyram and acetamiprid) on 13 Anopheles gambiae nicotinic acetylcholine receptor (nAChR) subtypes produced by expression of combinations of the Agα1, Agα2, Agα3, Agα8 and Agß1 subunits in Xenopus laevis oocytes, the Drosophila melanogaster orthologues of which we have previously shown to be important in neonicotinoid actions. The presence of the Agα2 subunit reduces neonicotinoid affinity for the mosquito nAChRs, whereas the Agα3 subunit increases it. Crystal structures of the acetylcholine binding protein (AChBP), an established surrogate for the ligand-binding domain, with dinotefuran bound, shows a unique target site interaction through hydrogen bond formation and CH-N interaction at the tetrahydrofuran ring. This is of interest as dinotefuran is also under trial as the toxic element in baited traps. Multiple regression analyses show a correlation between the efficacy of neonicotinoids for the Agα1/Agα2/Agα8/Agß1 nAChR, their hydrophobicity and their rate of knockdown of adult female An. gambiae, providing new insights into neonicotinoid features important for malaria vector control.

Divergent Nine-Step Syntheses of Perhydrohistrionicotoxin Analogs and Their Inhibition Activity Toward Chicken α4ß2-Neuronal Nicotinic Acetylcholine Receptors.

Histrionicotoxin (HTX) alkaloids, which are isolated from Colombian poison dart frogs, are analgesic neurotoxins that modulate nicotinic acetylcholine receptors (nAChRs) as antagonists. Perhydrohistrionicotoxin (pHTX) is the potent synthetic analogue of HTX and possesses a 1-azaspiro[5.5]undecane skeleton common to the HTX family. Here, we show for the first time the divergent nine-step synthesis of pHTX and its three stereoisomers from the known aldehyde through a one-step construction of the 1-azaspiro[5.5]undecane framework from a linear amino ynone substrate. Surprisingly, some pHTX diastereomers exhibited antagonistic activities on the chicken α4ß2-neuronal nAChRs that were more potent than pHTX.