Unraveling anthelmintic targets and mechanisms of action of trans-cinnamaldehyde from cinnamon essential oil

Parasitic nematodes pose a significant global socio-economic threat and contribute to neglected diseases. Current infection control relies on drug therapy, but increasing anthelmintic resistance highlights the urgent need for novel treatments. In this study, we investigate the molecular targets and mechanisms of action of trans-cinnamaldehyde (TCA), a principal component of Cinnamon Essential Oil (Cinnamomum verum EO), using Caenorhabditis elegans as a model organism. Our research offers new insights into the anthelmintic effects of TCA by identifying its specific interactions with key Cys-loop receptors and detailing its inhibitory mechanisms. The anthelmintic activity of C. verum EO and TCA manifests as rapid alterations in locomotor activity and inhibition of egg hatching. TCA screening of mutant worms lacking Cys-loop receptors reveal multiple receptor targets, including the levamisole-sensitive nicotinic ACh receptor (L-AChR), GABA-activated chloride channel (UNC-49) and glutamate-activated chloride channel. The mechanism behind the egg hatching inhibition by TCA remains unclear, as none of the mutants studied were found to be resistant to TCA. Furthermore, TCA increases the paralyzing effects of the anthelmintics levamisole and monepantel in a synergistic manner, offering a route for more effective polytherapy strategies. Electrophysiological studies on C. elegans Cys-loop receptors, in both native and heterologous systems, were used to elucidate the molecular mechanisms of TCA-induced paralysis. TCA reduces ACh- and GABA-elicited macroscopic currents and decreases single-channel activity and open durations of native muscle L-AChR channels, indicating an inhibitory action. Thus, by acting through a different mechanism to that of classical anthelmintics, TCA may be beneficial to counteract resistance in combined anthelmintic therapies. Our findings underscore the potential of the multitarget compound TCA as a valuable tool in integrated pharmacological strategies.