Peimine, an Anti-Inflammatory Compound from Chinese Herbal Extracts, Modulates Muscle-Type Nicotinic Receptors

Abstract

Fritillaria bulbs are used in Traditional Chinese Medicine to treat several illnesses. Peimine (Pm), an anti-inflammatory compound from Fritillaria, is known to inhibit some voltage-dependent ion channels and muscarinic receptors, but its interaction with ligand-gated ion channels remains unexplored. We have studied if Pm affects nicotinic acetylcholine receptors (nAChRs), since they play broad functional roles, both in the nervous system and non-neuronal tissues. Muscle-type nAChRs were incorporated to Xenopus oocytes and the action of Pm on the membrane currents elicited by ACh (IAChs) was assessed. Functional studies were combined with virtual docking and molecular dynamics assays. Co-application of ACh and Pm reversibly blocked IACh, with an IC50 in the low micromolar range. Pm inhibited nAChR by: (i) open-channel blockade, evidenced by the voltage-dependent inhibition of IAch, (ii) enhancement of nAChR desensitization, revealed by both an accelerated IACh decay and a decelerated IACh deactivation, and (iii) resting-nAChR blockade, deduced from the IACh inhibition elicited by Pm when applied before ACh superfusion. In good concordance, virtual docking and molecular dynamics assays demonstrated that Pm binds to different sites at the nAChR, mostly at the transmembrane domain. Thus, Pm from Fritillaria bulbs, considered therapeutic herbs, targets nAChRs with high affinity, which might account for its anti-inflammatory actions.

Xenopus Oocytes as a Powerful Cellular Model to Study Foreign Fully-Processed Membrane Proteins

“…After confirming that purified and reconstituted nAChRs microtransplanted to the oocyte membrane preserve their native biophysical properties [ 67 ], this technique has been used to study the modulation of this complex protein by different molecules of therapeutic relevance. Thus, this experimental approach has been used to assess the allosteric modulation of muscle-type nAChR function by several cholinesterase inhibitors [ 105 , 106 ], local anesthetics such as lidocaine [ 107 ] or akin molecules [ 59 , 60 ], tetracaine [ 108 ], and benzocaine [ 109 ] or natural anti-inflammatory agents such as peimine [ 110 ]. By combining electrophysiological and virtual docking assays, it has been possible to identify specific nAChR residues interacting with different drugs, which support the open-channel blockade elicited by either lidocaine or diethylamine, a molecule resembling the hydrophilic moiety of lidocaine [ 59 , 107 , 110 ] or tetracaine [ 108 ].…”

“…Thus, this experimental approach has been used to assess the allosteric modulation of muscle-type nAChR function by several cholinesterase inhibitors [ 105 , 106 ], local anesthetics such as lidocaine [ 107 ] or akin molecules [ 59 , 60 ], tetracaine [ 108 ], and benzocaine [ 109 ] or natural anti-inflammatory agents such as peimine [ 110 ]. By combining electrophysiological and virtual docking assays, it has been possible to identify specific nAChR residues interacting with different drugs, which support the open-channel blockade elicited by either lidocaine or diethylamine, a molecule resembling the hydrophilic moiety of lidocaine [ 59 , 107 , 110 ] or tetracaine [ 108 ]. Although the kinetic changes elicited by superfusing Xenopus oocytes with modulating drugs are rather slow (usually over 1 s; see above the section of drawbacks of using Xenopus oocytes to study membrane proteins), the kinetics of the open-channel blockade can be resolved at much higher resolution.…”

“…Since quaternary-ammonium cholinesterase inhibitors and many local anesthetics are positively charged molecules, the application of positive voltage pulses removes the drug from the channel, thus unplugging the pore by electrostatic repulsion. If the oocyte is maintained in the presence of ACh and the open-channel blocker, the sudden return of the cell membrane potential to negative values, after the application of a strong positive pulse to vanish the open-channel blockade, allows one to determine the kinetics of open-channel blockade with a fairly high temporal resolution [ 108 , 110 ]. Furthermore, the fraction of the voltage field (δ), sensed by the drug at its binding site, can be computed by using the Woodhull equation [ 111 ] to electrophysiologically estimate the loci where these open-channel blockers bind within the channel pore [ 106 , 107 ].…”

Special Issue: Cholinergic Control of Inflammation

“…This Special Issue, “Cholinergic Control of Inflammation”, arises from the need to implement the knowledge on inflammation regulation by the cholinergic system. It is composed of a collection of one original article [ 6 ], and five reviews [ 7 , 8 , 9 , 10 , 11 ] that discuss different aspects of how the cholinergic system can respond to or can be affected by inflammatory insults, environmental (acrylamide and pesticides) or infectious (SARS-CoV-2), highlighting possible therapeutic applications. The presence of two commentaries [ 12 , 13 ] enriches the discussion on new intriguing aspects of the involvement of the cholinergic system in response to SARS-CoV-2, again suggesting that the cholinergic system is becoming an increasingly considered target in the pharmacological approach to inflammatory-based diseases.…”

“…From the perspective of therapeutic approaches, searching for new molecules with anti-inflammatory activity, the original article by Alberola-Die et al [ 6 ] deals with Peimine, an alkaloid with anti-inflammatory properties, considered one of the main bioactive molecules of Fritillaria bulbs (Fb) extracts. Fb has been used as a therapeutic herb for thousands of years, and there is strong support for its beneficial effects and its weak (or lack of) toxicity.…”