Inhibition of acetylcholinesterases of the pinewood nematode, Bursaphelenchus xylophilus, by phytochemicals from plant essential oils.

To understand the nematicidal mode of action of phytochemicals derived from plant essential oils against the pinewood nematode (Bursaphelenchus xylophilus), we evaluated 97 compounds (49 monoterpenes, 17 phenylpropenes, 16 sesquiterpenes, and 15 sulfides) for their inhibitory effects on B. xylophilus acetylcholinesterases (BxACEs). In the primary inhibition assay using B. xylophilus crude protein, more than 50% BxACE inhibition activity was observed with 3 monoterpenes, (+)-α-pinene, (-)-α-pinene, and 3-carene; 2 phenylpropenes, ο-anisaldehyde, and coniferyl alcohol; and 1 sesquiterpene, cis-nerolidol. Other compounds showed moderate or weak inhibitory activity. The inhibitory activities against 3 recombinant BxACEs were subsequently estimated using the identified active compounds in a primary inhibition assay. (+)-α-Pinene showed the strongest inhibition of BxACE-1 followed by 3-carene, coniferyl alcohol, (-)-α-pinene, o-anisaldehyde, and cis-nerolidol. The half maximal inhibitory concentration (IC50) values of (+)-α-pinene, 3-carene, o-anisaldehyde, cis-nerolidol, and (-)-α-pinene against BxACE-2 were found to be 0.64, 1.41, 8.18, 8.53, 15.28, and 18.03mM, respectively. Coniferyl alcohol showed the strongest inhibition of BxACE-3 followed by (+)-α-pinene and cis-nerolidol.