Liriodenine, a molecule isolated from Chinese herb Zanthoxylum nitidum, has been shown to cause diverse biological effects on a variety of organisms, however its potential as an insect control agent has not yet been documented. For this study, we sought to characterize its neurophysiological and insecticidal effects on variety of different insect models. Liriodenine was neuroexcitatory and capable of reversing the effects of GABA when applied by itself on the Drosophila melanogaster central nervous system (CNS). Moreover, liriodenine antagonized the effects of GABA on neurons isolated from the CNS of American cockroaches under patch clamp conditions, with an approximate IC50 of 1 µM. Liriodenine also caused significant depolarization and spontaneous action potentials in giant axons in the ventral nerve cord of American cockroaches, and altered excitatory postsynaptic potentials (EPSPs) on the house fly neuromuscular junction. From these results and in silico molecular modeling, we posit that liriodenine is a structural analog of bicuculine that antagonizes GABA receptors in insects, much like the function of bicuculine on mammalian GABA receptors. We further propose that liriodenine also acts on insect potassium or sodium channels, which may explain the effects of liriodenine on the cockroach giant axon and house fly neuromuscular junctions. Unfortunately, as a topical insecticide on Aedes aegypti mosquitoes, liriodenine was a relatively weak compound, with an LD50 considerably higher than 1 µg per insect. However, its insecticidal character was synergized by both dimethyl sulfoxide (DMSO) and piperonyl butoxide (PBO). These results have important implications for the potential of liriodenine as an insect control agent and will be further discussed.

Neurophysiological and insecticidal effects of liriodenine, an alkaloid isolated from the Chinese herb Zanthoxylum nitidum

ACS Fall 2021

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