Effects of intersubunit amino acid substitutions on GABA receptor sensitivity to the ectoparasiticide fluralaner

Yamato, Kohei; Nakata, Yunosuke; Takashima, Madoka; Ozoe, Fumiyo; Asahi, Miho; Kobayashi, Masaki; Ozoe, Yoshihisa

doi:10.1016/j.pestbp.2019.11.001

Cited by 24 publications

(33 citation statements)

References 25 publications

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“…Whether these differences might be due to the compounds themselves or the pharmacological properties of receptors from different species remain to be investigated. Furthermore, the amino acids implicated in the binding of lotilaner are not known yet although some studies recently suggested that amino acids in theTM1 and TM3 might be critical in RDL from M. domestica [77]. The mechanism of action of lotilaner on RDL receptors at the molecular level are still to be deciphered.…”

Section: Discussionmentioning

confidence: 99%

Distinct molecular targets for macrocyclic lactone and isoxazoline insecticides in the human louse: new prospects for the treatment of pediculosis

Lamassiaude

Toubaté

Neveu

et al. 2020

Preprint

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BackgroundControl of infestation by cosmopolitan lice (Pediculus humanus) is increasingly difficult due to the transmission of resistant parasites to pediculicides. However, since the targets for pediculicides have no been identified in human lice so far, their mechanism of action remain largely unknown. The macrocyclic lactone, ivermectin is active against a broad range of insects including human lice. Isoxazolines are a recent new chemical class targeting the γ-aminobutyric acid (GABA) receptor made of the resistant to dieldrin (RDL) subunit and exhibiting a strong insecticidal potential. Here, we addressed the pediculicidal potential of isoxazolines and deciphered the molecular targets of ivermectin and the novel ectoparasiticide lotilaner in the human body louse species Pediculus humanus humanus.Methods and findingsUsing toxicity bioassays, we showed that fipronil, ivermectin and lotilaner are efficient pediculicides on adult lice. The RDL (Phh-RDL) and glutamate-gated chloride channel subunits (Phh-GluCl) were cloned and characterized by two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes. Phh-RDL and Phh-GluCl formed functional homomeric receptors respectively gated by GABA and L-glutamate with EC50 values of 6.4 µM and 9.3 µM. Importantly, ivermectin displayed a super agonist action on Phh-Glucl whereas Phh-RDL receptors were weakly affected. Reversally, lotilaner strongly inhibited the GABA-evoked currents in Phh-RDL with an IC50 value 0.5 µM, whereas it had no effect on Phh-GluCl.ConclusionsWe report here for the first time the pediculicidal potential of isoxazolines and reveal the distinct mode of action of ivermectin and lotilaner on GluCl and RDL channels from human lice. These results emphasize the clear repurposing future of the isoxazoline drug class to provide new pediculicidal agents to tackle resistant-louse infestations in humans.Autorship summaryWhy was this study done?Human cosmopolitan lice are responsible for pediculosis, which represent a significant public health concern. Resistant lice against insecticides and lack of safety of the treatments for human and environment is a growing issue worldwide. Here we investigated the efficacy on lice of the classical macrocyclic lactone drug, ivermectin, and the novel isoxazoline drug, lotilaner. This study was done to decipher their mode of action at the molecular and funtional levels in order to propose new strategies to control lice infestation.What did the researchers do and find?Our bioassay results indicate that ivermectin and lotilaner were potent at killing human adult lice, with lotilaner showing a higher efficacy than ivermectin. Furthermore, we identified and pharmacologically characterized the first glutamate- and GABA-gated chloride channels ever described in human lice yet. Mechanistically, our molecular biology and electrophysiology findings demonstrate that ivermectin acted preferentially at glutamate channels while lotilaner specifically targeted GABA channels.What do these findings mean?These results provide new insights in the understanding of the insecticide mode of action and highlight the isoxazolines as a new drug-repurposing opportunity for pest control strategies.

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Section: Discussionmentioning

confidence: 99%

Distinct molecular targets for macrocyclic lactone and isoxazoline insecticides in the human louse: new prospects for the treatment of pediculosis

Lamassiaude

Toubaté

Neveu

et al. 2020

Preprint

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“…The binding sites of isoxazolines and meta-diamides are most likely located in the interface between TM1 and TM3 from adjacent subunits of insect GABARs. 67,68…”

Section: Conventional Gabar Nca Insecticidesmentioning

confidence: 99%

“…Insect GABAR A2′ mutants are sensitive to isozazolines and broflanilide, whereas these mutants exhibited low or no sensitivity to fipronil. The binding sites of isoxazolines and meta -diamides are most likely located in the interface between TM1 and TM3 from adjacent subunits of insect GABARs. , …”

Section: Conventional Gabar Nca Insecticidesmentioning

confidence: 99%

Potential of Competitive Antagonists of Insect Ionotropic γ-Aminobutyric Acid Receptors as Insecticides

Liu

Gao

et al. 2020

J. Agric. Food Chem.

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Ionotropic γ-aminobutyric acid (GABA) receptors (GABARs) represent an important insecticide target. Currently used GABAR-targeting insecticides are non-competitive antagonists (NCAs) of these receptors. Recent studies have demonstrated that competitive antagonists (CAs) of GABARs have functions of inhibiting insect GABARs similar to NCAs and that they also exhibit insecticidal activity. CAs have different binding sites and different mechanisms of action compared to those of NCAs. Therefore, GABAR CAs should have the potential to be developed into novel insecticides, which could be used to overcome the developed resistance of insect pests to conventional NCA insecticides. Although research on insect GABAR CAs has lagged behind that on mammalian GABAR CAs, research on the CAs of insect ionotropic GABARs has made great progress in recent years, and several series of heterocyclic compounds, such as 3-isoxazolols and 6-iminopyridazines, have been identified as insect GABAR CAs. In this review, we briefly summarize the design strategies, structures, and biological activities of the novel GABAR CAs that have been found in the past decade. Updated information about GABAR CAs may benefit the design and development of novel GABAR-targeting insecticides.

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“…To date, three candidate genes, RDL (resistance to dieldrin), LCCH3 (ligand-gated chloride channel homologue 3), and GRD (GABA and glycine-like receptor of Drosophila ), are considered as iGABA receptor subunits in insects. ,, RDL has been studied in several insect species, such as fruit fly Drosophila melanogaster, small brown planthopper Laodelphax striatellus, and honeybee Apis mellifera. − Due to amino acid sequence homology, it has been suggested that the 8916 gene is a putative GABA receptor subunit that has been identified in many insect species including D. melanogaster, L.…”

Section: Introductionmentioning

confidence: 99%

Functional Characteristics of the Lepidopteran Ionotropic GABA Receptor 8916 Subunit Interacting with the LCCH3 or the RDL Subunit

Huang

Sheng

Jones

et al. 2021

J. Agric. Food Chem.

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The ionotropic γ-aminobutyric acid (iGABA) receptor is commonly considered as a fast inhibitory channel and is an important insecticide target. Since 1990, RDL, LCCH3, and GRD have been successively isolated and found to be potential subunits of the insect iGABA receptor. More recently, one orphan gene named 8916 was found and considered to be another potential iGABA receptor subunit according to its amino acid sequence. However, little information about 8916 has been reported. Here, the 8916 subunit from Chilo suppressalis was studied to determine whether it can form part of a functional iGABA receptor by co-expressing this subunit with CsRDL1 or CsLCCH3 in the Xenopus oocyte system. Cs8916 or CsLCCH3 did not form functional ion channels when expressed alone. However, Cs8916 was able to form heteromeric ion channels when expressed with either CsLCCH3 or CsRDL1. The recombinant heteromeric Cs8916/LCCH3 channel was a cation-selective channel, which was sensitive to GABA or β-alanine. The current of the Cs8916/LCCH3 channel was inhibited by dieldrin, endosulfan, fipronil, or ethiprole. In contrast, fluralaner, broflanilide, and avermectin showed little effect on the Cs8916/LCCH3 channel (IC50s > 10 000 nM). The Cs8916/RDL1 channel was sensitive to GABA, but was significantly different in EC50 and I max for GABA to those of homomeric CsRDL1. Fluralaner, fipronil, or dieldrin showed antagonistic actions on Cs8916/RDL1. In conclusion, Cs8916 is a potential iGABA receptor subunit, which can interact with CsLCCH3 to generate a cation-selective channel that is sensitive to several insecticides. Also, as Cs8916/RDL1 has a higher EC50 than homomeric CsRDL1, Cs8916 may affect the physiological functions of CsRDL1 and therefore play a role in fine-tuning GABAergic signaling.

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Effects of intersubunit amino acid substitutions on GABA receptor sensitivity to the ectoparasiticide fluralaner

Cited by 24 publications

References 25 publications

Distinct molecular targets for macrocyclic lactone and isoxazoline insecticides in the human louse: new prospects for the treatment of pediculosis

Distinct molecular targets for macrocyclic lactone and isoxazoline insecticides in the human louse: new prospects for the treatment of pediculosis

Potential of Competitive Antagonists of Insect Ionotropic γ-Aminobutyric Acid Receptors as Insecticides

Functional Characteristics of the Lepidopteran Ionotropic GABA Receptor 8916 Subunit Interacting with the LCCH3 or the RDL Subunit

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