Mechanism of action of the insecticides, lindane and fipronil, on glycine receptor chloride channels

Robi Islam, J W Lynch

Research output: Contribution to journalArticleResearchpeer-review

Abstract

BACKGROUND AND PURPOSE: Docking studies predict that the insecticides, lindane and fipronil, block GABAA receptors by binding to 6′ pore-lining residues. However, this has never been tested at any Cys-loop receptor. The neurotoxic effects of these insecticides are also thought to be mediated by GABAA receptors, although a recent morphological study suggested glycine receptors mediated fipronil toxicity in zebrafish. Here we investigated whether human α1, α1β, α2 and α3 glycine receptors were sufficiently sensitive to block by either compound as to represent possible neurotoxicity targets. We also investigated the mechanisms by which lindane and fipronil inhibit α1 glycine receptors.

EXPERIMENTAL APPROACH: Glycine receptors were recombinantly expressed in HEK293 cells and insecticide effects were studied using patch-clamp electrophysiology.

KEY RESULTS:
Both compounds completely inhibited all tested glycine receptor subtypes with IC50 values ranging from 0.2–2 µM, similar to their potencies at vertebrate GABAA receptors. Consistent with molecular docking predictions, both lindane and fipronil interacted with 6′ threonine residues via hydrophobic interactions and hydrogen bonds. In contrast with predictions, we found no evidence for lindane interacting at the 2′ level. We present evidence for fipronil binding in a non-blocking mode in the anaesthetic binding pocket, and for lindane as an excellent pharmacological tool for identifying the presence of β subunits in αβ heteromeric glycine receptors.

CONCLUSIONS AND IMPLICATIONS:
This study implicates glycine receptors as novel vertebrate toxicity targets for fipronil and lindane. Furthermore, lindane interacted with pore-lining 6′ threonine residues, whereas fipronil may have both pore and non-pore binding sites.
Original languageEnglish
Pages (from-to)2707-2720
Number of pages14
JournalBritish Journal of Pharmacology
Volume165
Issue number8
DOIs
Publication statusPublished - 2012
Externally publishedYes

Fingerprint

Glycine Receptors
Lindane
Chloride Channels
Insecticides
GABA-A Receptors
Threonine
Vertebrates
Cysteine Loop Ligand-Gated Ion Channel Receptors
HEK293 Cells
Electrophysiology
Zebrafish
fipronil
Hydrophobic and Hydrophilic Interactions
Inhibitory Concentration 50
Anesthetics
Hydrogen
Binding Sites
Pharmacology

Cite this

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abstract = "BACKGROUND AND PURPOSE: Docking studies predict that the insecticides, lindane and fipronil, block GABAA receptors by binding to 6′ pore-lining residues. However, this has never been tested at any Cys-loop receptor. The neurotoxic effects of these insecticides are also thought to be mediated by GABAA receptors, although a recent morphological study suggested glycine receptors mediated fipronil toxicity in zebrafish. Here we investigated whether human α1, α1β, α2 and α3 glycine receptors were sufficiently sensitive to block by either compound as to represent possible neurotoxicity targets. We also investigated the mechanisms by which lindane and fipronil inhibit α1 glycine receptors.EXPERIMENTAL APPROACH: Glycine receptors were recombinantly expressed in HEK293 cells and insecticide effects were studied using patch-clamp electrophysiology.KEY RESULTS: Both compounds completely inhibited all tested glycine receptor subtypes with IC50 values ranging from 0.2–2 µM, similar to their potencies at vertebrate GABAA receptors. Consistent with molecular docking predictions, both lindane and fipronil interacted with 6′ threonine residues via hydrophobic interactions and hydrogen bonds. In contrast with predictions, we found no evidence for lindane interacting at the 2′ level. We present evidence for fipronil binding in a non-blocking mode in the anaesthetic binding pocket, and for lindane as an excellent pharmacological tool for identifying the presence of β subunits in αβ heteromeric glycine receptors.CONCLUSIONS AND IMPLICATIONS: This study implicates glycine receptors as novel vertebrate toxicity targets for fipronil and lindane. Furthermore, lindane interacted with pore-lining 6′ threonine residues, whereas fipronil may have both pore and non-pore binding sites.",
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Mechanism of action of the insecticides, lindane and fipronil, on glycine receptor chloride channels. / Islam, Robi; Lynch, J W.

In: British Journal of Pharmacology, Vol. 165, No. 8, 2012, p. 2707-2720.

Research output: Contribution to journalArticleResearchpeer-review

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