title: Pinnatoxins E, F and G target multiple nicotinic receptor subtypes.
abstract: Pinnatoxins are members of the cyclic imine group of marine phycotoxins that are highly toxic in in vivo rodent bioassays, causing rapid death due to respiratory depression. Recent studies have shown that pinnatoxins E, F and G, found in New Zealand and Australian shellfish, act as antagonists at muscle-type nicotinic acetylcholine receptors (nAChRs) at the neuromuscular junction. In the present study, binding affinities and modes of these pinnatoxin isomers at neuronal and muscle nAChRs were assessed using radioligand binding, electrophysiological and molecular modelling techniques. Radioligand-binding studies revealed that all three pinnatoxins bound with high affinity to muscle-type nAChRs, as well as to the α7 and α4β2 neuronal receptors, with an order of affinity of muscle type > α7 > α4β2. The rank order of potency at all receptors was pinnatoxin F > G > E. Pinnatoxins F and G also antagonized ACh-evoked responses in α7 and α4β2 neuronal receptors expressed in Xenopus oocytes. Molecular modelling revealed that pinnatoxins E, F and G make multiple hydrogen bond interactions with the binding site of muscle-type and α7 receptors, with few interactions at the α4β2 binding site, reflecting the binding affinity and functional data. This study shows for the first time that pinnatoxins E, F and G bind to, and functionally antagonize neuronal nAChRs, with interactions potentially playing a role in pinnatoxin toxicity.
authors.affiliation: Department of Pharmacology and Toxicology, University of Otago School of Medical Sciences, Dunedin, New Zealand.
authors.forename: Shane D
authors.initials: SD
authors.lastname: Hellyer
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia.
authors.forename: Dinesh
authors.initials: D
authors.lastname: Indurthi
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia.
authors.forename: Thomas
authors.initials: T
authors.lastname: Balle
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia.
authors.forename: Vanda
authors.initials: V
authors.lastname: Runder-Varga
authors.affiliation: Cawthron Institute, Nelson, New Zealand.
authors.forename: Andrew I
authors.initials: AI
authors.lastname: Selwood
authors.affiliation: New Zealand's National School of Pharmacy, University of Otago, Dunedin, New Zealand.
authors.forename: Joel D A
authors.initials: JD
authors.lastname: Tyndall
authors.affiliation: Faculty of Pharmacy, University of Sydney, Sydney, NSW, Australia.
authors.forename: Mary
authors.initials: M
authors.lastname: Chebib
authors.affiliation: Cawthron Institute, Nelson, New Zealand.
authors.forename: Lesley
authors.initials: L
authors.lastname: Rhodes
authors.affiliation: Department of Pharmacology and Toxicology, University of Otago School of Medical Sciences, Dunedin, New Zealand.
authors.forename: D Steven
authors.initials: DS
authors.lastname: Kerr
mesh_terms: D000470:Alkaloids / Q000008:administration & dosage / Q000378:metabolism*; D000818:Animals; D003964:Diaphragm / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D016503:Drug Delivery Systems / Q000379:methods*; D005260:Female; D011485:Protein Binding / Q000502:physiology; D021122:Protein Subunits / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011978:Receptors, Nicotinic / Q000378:metabolism*; D013141:Spiro Compounds / Q000008:administration & dosage / Q000378:metabolism*; D014981:Xenopus
chemical_list: D000470:Alkaloids; D021122:Protein Subunits; D011978:Receptors, Nicotinic; D013141:Spiro Compounds; C552838:pinnatoxin E; C552839:pinnatoxin F; C552840:pinnatoxin G
keywords: neuromuscular; neurotoxins; nicotinic receptors; pinnatoxin; structure-activity