In vivo and in vitro pinnatoxins A and G reversibly block transmission at the skeletal neuromuscular junction

Evelyne Benoit (1, 2, 3, 4) , Aurélie Couesnon (5) , Jiri Lindovsky (5) , Bogdan Iorga (6) , Armen Zakarian (7) , Denis Servent (4, 2, 3) , Jordi Molgó (4, 1, 2, 3)

1 NeuroPSI - Institut des Neurosciences Paris-Saclay
2 SIMoS - Service d'Ingénierie Moléculaire pour la Santé (ex SIMOPRO)
3 MTS - Médicaments et Technologies pour la Santé
4 SIMOPRO
5 NBCM - Laboratoire de neurobiologie cellulaire et moléculaire
6 ICSN - Institut de Chimie des Substances Naturelles
7 Department of Chemistry and Biochemistry

The dinoflagellate $Vulcanodinium\ rugosum$, first isolated from Ingril, a French Mediterranean lagoon, is known to produce the pinnatoxins (PnTXs) and the portimines. PnTXs (A-H) constitute an emerging family of phycotoxins belonging to the cyclic imine group. Interest has been focused on these fast-acting highly-potent toxins because they are widely found in contaminated shellfish. Despite their highly complex molecular structure, PnTXs have been chemically synthetized by the Zakarian’s group, and demonstrated to act on various nicotinic acetylcholine receptors (nAChRs). To the best of our knowledge, neither PnTX-A nor PnTX-G and analogs, obtained by chemical synthesis with high degree of purity (> 98%), have been studied in vivo or in vitro on adult mouse and isolated nerve-muscle preparations expressing the mature muscletype (a1)2b1de nAChR. Our results show that PnTX-A and PnTX-G acted on the neuromuscular system of anesthetized mice and blocked the compound muscle action potential (CMAP) in a dose- and time-dependent manner with similar ID50 values (dose required to block 50% of the CMAP), as determined using an in vivo minimally invasive electrophysiological method. The decrease of CMAP induced by both toxins in vivo was reversible within 6-8 h. PnTX-A and PnTX-G, applied to isolated extensor digitorum longus (EDL) nerve-muscle preparations, blocked reversibly isometric twitches evoked by nerve stimulation. Both toxins exerted no direct action on the contractile machinery of muscle fibers, as revealed by direct muscle stimulation. In addition, PnTX-A and PnTX-G blocked synaptic transmission at mouse neuromuscular junctions. PnTX-A aminoketone analog (containing an open form of the imine ring) had no effect on neuromuscular transmission. These results indicate the importance of the cyclic imine for interacting with adult mammalian muscle-type nAChR.

Mots clés: pinnatoxins; synaptic potentials; mouse neuromuscular system; compound muscle action potential; cyclic imines; emerging toxins; marine phycotoxins

Domaines: Neurobiologie; Toxicologie

Evelyne Benoit, Aurélie Couesnon, Jiri Lindovsky, Bogdan Iorga, Armen Zakarian, et al.. In vivo and in vitro pinnatoxins A and G reversibly block transmission at the skeletal neuromuscular junction. PHYCOTOX 2019 - GDR Annual Conference on Toxic Microalgae, May 2019, Plouzané, France. . ⟨hal-04467214⟩