Acetylcholinesterases from entomopathogenic nematode Heterorhabditid bacteriophora: Susceptibility to insecticides and immunological characteristics

Eucalyptus globulus leaf-isolated isorhapontin serves as a natural insecticide via acetylcholinesterase inhibition

Acetylcholinesterase (AChE) inhibitors cause insect death by preventing the hydrolysis of the neurotransmitter acetylcholine, which overstimulates the nervous system. In this study, isorhapontin, isolated from E. globulus leaves, was evaluated as a natural insecticide with AChE inhibition at 12.5 μM. Using kinetic analyses, we found that isorhapontin acted as a competitive inhibitor that binds to the active site of AChE. The inhibition constant (Ki) was 6.1 μM. Furthermore, isorhapontin and resveratrol, which have basic skeletons, were predicted to bind to the active site of AChE via molecular docking. A comparison of the hydrogen bonding between the two stilbenes revealed characteristic differences in their interactions with amino acids. In isorhapontin, Trp83, Gly149, Tyr162, Tyr324, and Tyr370 interacted with the sugar moiety. These results suggest that with further development, isorhapontin can be used as an insecticide alternative.

Metal contamination and heat stress impair swimming behavior and acetylcholinesterase activity in embryo-larval stages of the Mediterranean mussel, Mytilus galloprovincialis

Behavioral parameters are increasingly considered sensitive and early bioindicators of toxicity in aquatic organisms. A video-tracking tool was specifically developed to monitor the swimming behaviour of D-larvae of the Mediterranean mussel, Mytilus galloprovincialis, in controlled laboratory conditions. Both maximum and average swimming speeds and trajectories were recorded. We then investigated the impact of copper and silver with or without a moderate rise of temperature on swimming behavior and acetylcholinesterase (AChE) activity of mussel D-larvae and the possible mechanistic link between both biological responses. Our results showed that copper and/or silver exposure, as well as temperature increase, disrupts the swimming behavior of mussel larvae which could compromise their dispersal and survival. In addition, the combined effect of temperature and metals significantly (p < 0.05) increased AChE activity in mussel larvae. Pearson's correlation analysis was performed and results showed that the AChE activity is positively correlated with maximum speeds (r = 0.71, p < 0.01). This study demonstrates the value of behavioral analyzes of aquatic invertebrates as a sensitive and integrate marker of the effects of stressors.

Purification and characterization of acetylcholinesterase in Rhynchophorus ferrugineus (Olivier) (Coleoptera: Curculionidae)

Red palm weevil (RPW), Rhynchophorus ferrugineus, is one of the most destructive pests of cultivated palm trees. The application of synthetic insecticides is currently a main strategy for RPW control. In this study we estimated the distribution of acetylcholinesterase (AChE), as a detoxifying enzyme and the target site of inhibition by insecticides, using ASChI as substrate in different organs of the pest including whole gut, cuticle, fat body, head and haemolymph. The activity ranged from 314.9 to 3868 U in individual organs while the specific activity ranged from 99 to 340.8 U/mg proteins; the cuticle had the highest enzyme level. During larval development, the 11th instar larvae had the highest enzyme content with 5630 U in the cuticle, with a specific activity of 140 U/mg protein. The two major AChE isoenzymes were purified by chromatography on gel filtration and ion exchange columns. They had specific activities of 3504.3 and 2979 U/mg protein, molecular weights of 33 and 54 kDa and activation energies of 8.3 and 4.4 kcal/mol, respectively. Both isoenzymes had monomeric forms, optimum activity at pH 8.0 and 40 °C, were completely inhibited by Hg²⁺ and Cu² and showed similar trends towards the inhibitors eserine, BW284C51 and iso-OMPA. The catalytic properties were compared with those previously recorded for different insect species. This work will pave the way for more studies for improving the understanding of insecticide resistance and developing the field application of synthetic insecticides for controlling R. ferrugineus to ensure successful application.