Journal Article

The Dinoflagellate Toxin 20-Methyl Spirolide-G Potently Blocks Skeletal Muscle and Neuronal Nicotinic Acetylcholine Receptors

Molgó, Jordi, Aráoz, Rómulo, Servent, Denis, Benoit, Evelyne, Iorga, Bogdan, Reynaud, Morgane, Couesnon, Aurélie

2016

Overview

The cyclic imine toxin 20-methyl spirolide G (20-meSPX-G), produced by the toxigenic dinoflagellate Alexandrium ostenfeldii/Alexandrium peruvianum, has been previously reported to contaminate shellfish in various European coastal locations, as revealed by mouse toxicity bioassay. The aim of the present study was to determine its toxicological profile and its molecular target selectivity. 20-meSPX-G blocked nerve-evoked isometric contractions in isolated mouse neuromuscular preparations, while it had no action on contractions elicited by direct electrical stimulation, and reduced reversibly nerve-evoked compound muscle action potential amplitudes in anesthetized mice. Voltage-clamp recordings in Xenopus oocytes revealed that 20-meSPX-G potently inhibited currents evoked by ACh on Torpedo muscle-type and human α7 nicotinic acetylcholine receptors (nAChR), whereas lower potency was observed in human α4β2 nAChR. Competition-binding assays showed that 20-meSPX-G fully displaced [3H]epibatidine binding to HEK-293 cells expressing the human α3β2 (Ki = 0.040 nM), whereas a 90-fold lower affinity was detected in human α4β2 nAChR. The spirolide displaced [125I]α-bungarotoxin binding to Torpedo membranes (Ki = 0.028 nM) and in HEK-293 cells expressing chick chimeric α7-5HT3 nAChR (Ki = 0.11 nM). In conclusion, this is the first study to demonstrate that 20-meSPX-G is a potent antagonist of nAChRs, and its subtype selectivity is discussed on the basis of molecular docking models.

• Publisher: MDPI,MDPI AG
• Subject: Action Potentials / alpha7 Nicotinic Acetylcholine Receptor / Animals / Binding Sites / Binding, Competitive / Bridged Bicyclo Compounds, Heterocyclic - metabolism / Chickens / CHO Cells / Cholinergic Fibers - drug effects / Cholinergic Fibers - metabolism / competition-binding assays / Cricetinae / Cricetulus / dinoflagellate toxin / Dose-Response Relationship, Drug / Electric Stimulation / Female / HEK293 Cells / Humans / In Vitro Techniques / Isometric Contraction / Isometric Contraction - drug effects / Life Sciences / Marine Toxins / Mice / molecular docking / Molecular Docking Simulation / Muscle Cells / Muscle, Skeletal - drug effects / Muscle, Skeletal - innervation / Muscle, Skeletal - metabolism / Neurobiology / Neuromuscular Junction / Neuromuscular Junction - drug effects / Neuromuscular Junction - metabolism / neuromuscular transmission / Neurons and Cognition / Neurotoxicity Syndromes / nicotinic acetylcholine receptors / Nicotinic Antagonists - chemistry / Nicotinic Antagonists - metabolism / Nicotinic Antagonists - toxicity / nicotinic currents / Oocytes / Patch-Clamp Techniques / Protein Binding / Protein Conformation / Pyridines - metabolism / Receptors, Muscarinic / Receptors, Nicotinic / Receptors, Nicotinic - chemistry / Receptors, Nicotinic - drug effects / Receptors, Nicotinic - genetics / Receptors, Nicotinic - metabolism / Spiro Compounds / Spiro Compounds - chemistry / Spiro Compounds - metabolism / Spiro Compounds - toxicity / spirolides / Structure-Activity Relationship / Torpedo / Toxicology / Transfection / Xenopus / Xenopus laevis / Xenopus oocytes