Identification of Antagonistic Action of Pyrrolizidine Alkaloids in Muscarinic Acetylcholine Receptor M1 by Computational Target Prediction Analysis

Abstract

Pyrrolizidine alkaloids (PAs) are one of the largest distributed classes of toxins in nature.They have a wide range of toxicity, such as hepatotoxicity, pulmonary toxicity, neuronal toxicity,and carcinogenesis. Yet, biological targets responsible for these effects are not well addressed.Using methods of computational biology for target identification, we tested more than 200 PAs.We used a machine-learning approach that applies structural similarity for target identification,ChemMapper, and SwissTargetPrediction. The predicted target with high probability was muscarinic acetylcholine receptor M1. The predicted interactions between this target and PAs were further studied by molecular docking-based binding energies using AutoDock and VinaLC, which revealedgood binding affinities. The PAs are bound to the same binding pocket as pirenzepine, a known M1antagonist. These results were confirmed by in vitro assays showing that PAs increased the levels ofintracellular calcium. We conclude that PAs are potential acetylcholine receptor M1 antagonists. This elucidates for the first time the serious neuro-oncological toxicities exerted by PA consumption.