Activation and desensitization of peripheral muscle and neuronal nicotinic acetylcholine receptors by selected, naturally-occurring pyridine alkaloids

Authors: Green, Benedict - Ben; Lee, Stephen; Welch, Kevin; Cook, Daniel; KEM, WILLIAM - University Of Florida

Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2016
Publication Date: 7/4/2016
Publication URL: https://handle.nal.usda.gov/10113/62924
Citation: Green, B.T., Lee, S.T., Welch, K.D., Cook, D., Kem, W.R. 2016. Activation and desensitization of peripheral muscle and neuronal nicotinic acetylcholine receptors by selected, naturally-occurring pyridine alkaloids. Toxins. doi: 10.1016/j.toxicon.2015.09.015.

Interpretive Summary: In this research, we compared nicotinic agonists at µM concentrations (epibatidine, the most potent know nicotinic acetylcholine receptor (nAChR) agonists, nicotine, anabasine, and anabaseine) for their ability to classically desensitize nAChR. We chose to examine classical desensitization based on previous research of the plant toxin induced inhibition of ultrasonically monitored fetal movement in goats. In this study, we used two cell lines that have fetal characteristics to study classical nAChR desensitization. TE-671 cells which express fetal human muscle-type nAChR (a12ß1'd), and SH-SY5Y cells that were derived from embryonic central nervous system tissue and express markers characteristic of immature catecholaminergic neurons. We tested the specific hypothesis that the piperidine alkaloid anabaseine a 1,2-dehydropiperidine and anabasine, its saturated analogue classically desensitize nAChRs expressed by TE-671 cells and SHSY-5Y cells which is the putative receptor-based mechanism of MCC-type defect formation in fetal livestock.

Technical Abstract: Teratogenic alkaloids can cause developmental defects due to inhibition of fetal movement that results from desensitization of fetal muscletype nicotinic acetylcholine receptors (nAChRs). We investigated the ability of two known teratogens, the piperidinyl-pyridine anabasine and its 1,2-dehydropiperidinyl analog anabaseine to activate and desensitize peripheral nAChRs expressed in TE-671 and SH-SY5Y cells. Activation-concentration response curves for each alkaloid were obtained in the same multiwall plate. To measure rapid desensitization, cells were first exposed to five potentially desensitizing concentrations of each alkaloid in log10 molar increments from 10 nM to 100 µM and then to a fixed concentration of acetylcholine (ACh), that alone produces near maximal activation. The fifty percent desensitization concentration (DC50) was calculated from the alkaloid concentration-ACh response curve. Agonist fast desensitization potency was predicted by agonist potency measured in the initial response. Anabaseine was a more potent desensitizer than anabasine. Relative to anabaseine, nicotine was more potent at autonomic nAChRs but less potent at the fetal neuromuscular nAChRs. Our experiments have demonstrated that anabaseine is more effective at desensitizing fetal muscle-type nAChRs than anabasine or nicotine and thus it is predicted to be more teratogenic.