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

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.


(A) Chemical structure of spirolide A toxin (the first member of the spirolide family described). The positions at which variations in the substitution pattern have been described are numbered, and the size of the macrocyclic is shown in magenta; (B) chemical structure of 20-methyl spirolide G.; (C) chemical structure of 13-desmethyl spirolide C; and (D) chemical structure of gymnodimine A.
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toxins-08-00249-f001: (A) Chemical structure of spirolide A toxin (the first member of the spirolide family described). The positions at which variations in the substitution pattern have been described are numbered, and the size of the macrocyclic is shown in magenta; (B) chemical structure of 20-methyl spirolide G.; (C) chemical structure of 13-desmethyl spirolide C; and (D) chemical structure of gymnodimine A.

Mentions: Spirolides were found in the 1990s in Canada [1,2], when uncommon mouse toxicities were detected with scallop and mussel extracts. Since then, spirolides were shown to have an outstanding diversity in chemical profiles and a world-wide distribution. Spirolides have their place in the cyclic imine group of neurotoxins, which also include prorocentrolides, spiro-prorocentrimine, gymnodimines, pinnatoxins, pteriatoxins, and portimine (for recent reviews see [3,4,5]). At present, sixteen structurally-related spirolides sharing common scaffolds have been reported. The general chemical structure of spirolides is characterized by a macrocycle (with a ring size between 20 and 24, as shown in Figure 1), a seven-membered cyclic imine group, which constitutes a key pharmacophore element, and the spiroketal cyclic, too, which can be 6,5,5-spiroketal (spirolides A–F), 6,5-spiroketal (spirolides H and I), or 6,6,5-spiroketal in the case of spirolide G (Figure 1). The cyclic imine moiety is responsible for the toxicity of these compounds, since spirolides E and F, which have an acyclic aminoketone, exhibit no toxicity [2].


The Dinoflagellate Toxin 20-Methyl Spirolide-G Potently Blocks Skeletal Muscle and Neuronal Nicotinic Acetylcholine Receptors
(A) Chemical structure of spirolide A toxin (the first member of the spirolide family described). The positions at which variations in the substitution pattern have been described are numbered, and the size of the macrocyclic is shown in magenta; (B) chemical structure of 20-methyl spirolide G.; (C) chemical structure of 13-desmethyl spirolide C; and (D) chemical structure of gymnodimine A.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037475&req=5

toxins-08-00249-f001: (A) Chemical structure of spirolide A toxin (the first member of the spirolide family described). The positions at which variations in the substitution pattern have been described are numbered, and the size of the macrocyclic is shown in magenta; (B) chemical structure of 20-methyl spirolide G.; (C) chemical structure of 13-desmethyl spirolide C; and (D) chemical structure of gymnodimine A.
Mentions: Spirolides were found in the 1990s in Canada [1,2], when uncommon mouse toxicities were detected with scallop and mussel extracts. Since then, spirolides were shown to have an outstanding diversity in chemical profiles and a world-wide distribution. Spirolides have their place in the cyclic imine group of neurotoxins, which also include prorocentrolides, spiro-prorocentrimine, gymnodimines, pinnatoxins, pteriatoxins, and portimine (for recent reviews see [3,4,5]). At present, sixteen structurally-related spirolides sharing common scaffolds have been reported. The general chemical structure of spirolides is characterized by a macrocycle (with a ring size between 20 and 24, as shown in Figure 1), a seven-membered cyclic imine group, which constitutes a key pharmacophore element, and the spiroketal cyclic, too, which can be 6,5,5-spiroketal (spirolides A–F), 6,5-spiroketal (spirolides H and I), or 6,6,5-spiroketal in the case of spirolide G (Figure 1). The cyclic imine moiety is responsible for the toxicity of these compounds, since spirolides E and F, which have an acyclic aminoketone, exhibit no toxicity [2].

View Article: PubMed Central - PubMed

ABSTRACT

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.

No MeSH data available.