(-)-Adaline from the Adalia Genus of Ladybirds Is a Potent Antagonist of Insect and Specific Mammalian Nicotinic Acetylcholine Receptors

Ladybird beetles (Coleoptera: Coccinellidae) possess strong chemical defences that are secreted in response to stress and are also found on the coating of eggs, which are rich in alkaloids that are responsible for their toxicity to other species. Recent studies have shown that alkaloids from several species of ladybird beetle can target nicotinic acetylcholine receptors (nAChRs) acting as receptor antagonists. Here, we have explored the actions of (-)-adaline, found in the 2-spot (Adalia bipunctata) and 10-spot (Adalia decempunctata) ladybirds, on both mammalian (alpha 1 beta 1 gamma delta, alpha 7, alpha 4 beta 2, alpha 3 beta 4) and insect nAChRs using patch-clamp of TE671 cells and locust brain neurons natively expressing nAChRs, as well as two-electrode voltage clamp of Xenopus laevis oocytes recombinantly expressing nAChRs. All nAChR subtypes were antagonised by (-)-adaline in a time-dependent, voltage-dependent and non-competitive manner with the lowest IC(50)s at rat alpha 3 beta 4 (0.10 mu M) and locust neuron (1.28 mu M) nAChRs, at a holding potential of -75 mV. The data imply that (-)-adaline acts as an open channel blocker of nAChRs.

Automated summary

Ladybird beetles possess strong chemical defences, and recent studies have shown that their alkaloids can target receptors and act as antagonists. This study explored the actions of one particular alkaloid found in ladybirds on different types of receptors.