The marine phycotoxin gymnodimine targets muscular and neuronal nicotinic acetylcholine receptor subtypes with high affinity

Abstract

Gymnodimines (GYMs) are phycotoxins exhibiting unusual structural features including a spirocyclic imine ring system and a trisubstituted tetrahydrofuran embedded within a 16‐membered macrocycle. The toxic potential and the mechanism of action of GYM‐A, highly purified from contaminated clams, have been assessed. GYM‐A in isolated mouse phrenic hemidiaphragm preparations produced a concentration‐ and time‐dependent block of twitch responses evoked by nerve stimulation, without affecting directly elicited muscle twitches, suggesting that it may block the muscle nicotinic acetylcholine (ACh) receptor (nAChR). This was confirmed by the blockade of miniature endplate potentials and the recording of subthreshold endplate potentials in GYM‐A paralyzed frog and mouse isolated neuromuscular preparations. Patch‐clamp recordings in Xenopus skeletal myocytes revealed that nicotinic currents evoked by constant iontophoretical ACh pulses were blocked by GYM‐A in a reversible manner. GYM‐A also blocked, in a voltage‐independent manner, homomeric human α7 nAChR expressed in Xenopus oocytes. Competition‐binding assays confirmed that GYM‐A is a powerful ligand interacting with muscle‐type nAChR, heteropentameric α3β2, α4β2, and chimeric α7‐5HT3 neuronal nAChRs. Our data show for the first time that GYM‐A broadly targets nAChRs with high affinity explaining the basis of its neurotoxicity, and also pave the way for designing specific tests for accurate GYM‐A detection in shellfish samples.

Structural determinants in phycotoxins and AChBP conferring high affinity binding and nicotinic AChR antagonism

“…2 C and D and Table 2). Antagonism by GYM is consistent with data obtained on Xenopus myocytes and frog and mouse neuromuscular preparations (15). GYM also antagonizes ACh in oocytes expressing α4β2.…”

“…Later reports revealed that 13-desmethyl spirolide C caused dose-dependent, widespread mouse brain neuronal damage and up-regulation of muscarinic and nicotinic ACh receptors (nAChR) transcription in rats (2). In contrast to most peptidic toxins, gymnodimines target both muscle and neuronal nAChRs at subnanomolar concentrations, explaining their neurotoxicity (15).…”

“…1) have been identified from contaminated shellfish or from extracts of the dinoflagellate Karenia selliformis (12)(13)(14)(15). Similar to spirolides, gymnodimines contain a spirocyclic imine but, in contrast to spirolides, they bear a trisubstituted tetrahydrofuran embedded within a 16-membered macrocycle.…”

“…Similar to spirolides, gymnodimines contain a spirocyclic imine but, in contrast to spirolides, they bear a trisubstituted tetrahydrofuran embedded within a 16-membered macrocycle. Gymnodimines also cause rapid neurotoxic mortality (15,16).…”

Identification of gymnodimine D and presence of gymnodimine variants in the dinoflagellate Alexandrium ostenfeldii from the Baltic Sea

“…Compared to other cyclic imines, such as the structurally related pinnatoxins (Araoz et al, 2011) and spirolides (Gueret and Brimble, 2010), knowledge on gymnodimines is still limited. Gymnodimine A is a fast-acting toxin with high intraperitoneal toxicity in mice (LD 50 of 80e96 mg/kg) (Kharrat et al, 2008;Munday et al, 2004) and similar bioactivities have been reported from other cyclic imines (Munday, 2008). Gymnodimine A is of low oral toxicity to mice, and is regarded as low risk for humans (Munday et al, 2004).…”