title: Toxicity of the synthetic polymeric 3-alkylpyridinium salt (APS3) is due to specific block of nicotinic acetylcholine receptors.
abstract: The in vivo and in vitro toxic effects of the synthetic polymeric 3-alkylpyridinium salt (APS3), from the Mediterranean marine sponge Reniera sarai, were evaluated on mammals, with emphasis to determine its mode of action. The median lethal doses of APS3 were 7.25 and higher that 20mg/kg in mouse and rat, respectively. Intravenous administration of 7.25 and 20mg/kg APS3 to rat caused a significant fall followed by an increase in mean arterial blood pressure accompanied by tachycardia. In addition, cumulative doses of APS3 (up to 60 mg/kg) inhibited rat nerve-evoked skeletal muscle contraction in vivo, with a median inhibitory dose (ID(50)) of 37.25mg/kg. When administrated locally by intramuscular injection to mouse, APS3 decreased the compound muscle action potential recorded in response to in vivo nerve stimulation, with an ID(50) of 0.5mg/kg. In vitro experiments confirmed the inhibitory effect of APS3 on mouse hemidiaphragm nerve-evoked muscle contraction with a median inhibitory concentration (IC(50)) of 20.3 μM, without affecting directly elicited muscle contraction. The compound inhibited also miniature endplate potentials and nerve-evoked endplate potentials with an IC(50) of 7.28 μM in mouse hemidiaphragm. Finally, APS3 efficiently blocked acetylcholine-activated membrane inward currents flowing through Torpedo nicotinic acetylcholine receptors (nAChRs) incorporated to Xenopus oocytes, with an IC(50) of 0.19 μM. In conclusion, our results strongly suggest that APS3 blocks muscle-type nAChRs, and show for the first time that in vivo toxicity of APS3 is likely to occur through an antagonist action of the compound on these receptors.
authors.affiliation: Institute of Physiology, Pharmacology and Toxicology, Veterinary Faculty, University of Ljubljana, Gerbičeva 60, 1000 Ljubljana, Slovenia.
authors.forename: Marjana
authors.initials: M
authors.lastname: Grandič
authors.forename: Romulo
authors.initials: R
authors.lastname: Aráoz
authors.forename: Jordi
authors.initials: J
authors.lastname: Molgó
authors.forename: Tom
authors.initials: T
authors.lastname: Turk
authors.forename: Kristina
authors.initials: K
authors.lastname: Sepčić
authors.forename: Evelyne
authors.initials: E
authors.lastname: Benoit
authors.forename: Robert
authors.initials: R
authors.lastname: Frangež
mesh_terms: D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D005260:Female; D020128:Inhibitory Concentration 50; D007273:Injections, Intramuscular; D007275:Injections, Intravenous; D007928:Lethal Dose 50; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D009119:Muscle Contraction / Q000187:drug effects; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D018733:Nicotinic Antagonists / Q000008:administration & dosage / Q000302:isolation & purification / Q000633:toxicity*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D011108:Polymers / Q000008:administration & dosage / Q000302:isolation & purification / Q000633:toxicity*; D011161:Porifera / Q000737:chemistry*; D011726:Pyridinium Compounds / Q000008:administration & dosage / Q000302:isolation & purification / Q000633:toxicity*; D051381:Rats; D017208:Rats, Wistar; D011978:Receptors, Nicotinic / Q000187:drug effects* / Q000378:metabolism; D014982:Xenopus laevis
chemical_list: D018733:Nicotinic Antagonists; D011108:Polymers; D011726:Pyridinium Compounds; D011978:Receptors, Nicotinic; C115254:poly-APS