Merck

Neurotoxicity and mode of action of N, N-diethyl-meta-toluamide (DEET).

PloS one (2014-08-08)
Daniel R Swale, Baonan Sun, Fan Tong, Jeffrey R Bloomquist
ABSTRACT

Recent studies suggest that N, N-diethyl-meta-toluamide (DEET) is an acetylcholinesterase inhibitor and that this action may result in neurotoxicity and pose a risk to humans from its use as an insect repellent. We investigated the mode of action of DEET neurotoxicity in order to define the specific neuronal targets related to its acute toxicity in insects and mammals. Although toxic to mosquitoes (LD50 ca. 1.5 µg/mg), DEET was a poor acetylcholinesterase inhibitor (<10% inhibition), even at a concentration of 10 mM. IC50 values for DEET against Drosophila melanogaster, Musca domestica, and human acetylcholinesterases were 6-12 mM. Neurophysiological recordings showed that DEET had excitatory effects on the housefly larval central nervous system (EC50: 120 µM), but was over 300-fold less potent than propoxur, a standard anticholinesterase insecticide. Phentolamine, an octopamine receptor antagonist, completely blocked the central neuroexcitation by DEET and octopamine, but was essentially ineffective against hyperexcitation by propoxur and 4-aminopyridine, a potassium channel blocker. DEET was found to illuminate the firefly light organ, a tissue utilizing octopamine as the principal neurotransmitter. Additionally, DEET was shown to increase internal free calcium via the octopamine receptors of Sf21 cells, an effect blocked by phentolamine. DEET also blocked Na(+) and K(+) channels in patch clamped rat cortical neurons, with IC50 values in the micromolar range. These findings suggest DEET is likely targeting octopaminergic synapses to induce neuroexcitation and toxicity in insects, while acetylcholinesterase in both insects and mammals has low (mM) sensitivity to DEET. The ion channel blocking action of DEET in neurons may contribute to the numbness experienced after inadvertent application to the lips or mouth of humans.

MATERIALS
Product Number
Brand
Product Description

Supelco
Benzoic acid, Pharmaceutical Secondary Standard; Certified Reference Material
Supelco
Melting point standard 121-123°C, analytical standard
Sigma-Aldrich
Cesium chloride, 99.99% trace metals basis
Sigma-Aldrich
Dimethyl sulfoxide, sterile-filtered, BioPerformance Certified, meets EP, USP testing specifications, suitable for hybridoma
Sigma-Aldrich
8-Octanoyloxypyrene-1,3,6-trisulfonic acid trisodium salt, suitable for fluorescence, ≥90% (HPCE)
Sigma-Aldrich
Toluene, anhydrous, 99.8%
Sigma-Aldrich
Benzoic acid, meets analytical specification of Ph. Eur., BP, USP, FCC, E210, 99.5-100.5% (alkalimetric)
Sigma-Aldrich
Dimethyl sulfoxide, anhydrous, ≥99.9%
Sigma-Aldrich
Acetylthiocholine iodide, ≥99.0% (AT)
Sigma-Aldrich
Dimethyl sulfoxide, BioUltra, for molecular biology, ≥99.5% (GC)
Sigma-Aldrich
Cesium chloride, BioUltra, for molecular biology, ≥99.5% (AT)
Sigma-Aldrich
Benzoic acid, purified by sublimation, ≥99%
Sigma-Aldrich
Benzoic acid, natural, ≥99.5%, FCC, FG
Sigma-Aldrich
Benzoic acid, ≥99.5%, FCC, FG
Sigma-Aldrich
Benzoic acid, ReagentPlus®, 99%
Supelco
Toluene, analytical standard
Supelco
Benzoic acid, certified reference material for titrimetry, certified by BAM, ≥99.5%
Supelco
Dimethyl sulfoxide, analytical standard
Supelco
DEET, PESTANAL®, analytical standard
Sigma-Aldrich
Benzoic acid, puriss. p.a., ACS reagent, reag. Ph. Eur., ≥99.9% (alkalimetric)
Sigma-Aldrich
Cesium chloride, ≥99.999% trace metals basis
Sigma-Aldrich
Sodium phosphate, 96%
Sigma-Aldrich
Benzoic acid, ACS reagent, ≥99.5%
Sigma-Aldrich
Cesium chloride, AnhydroBeads, −10 mesh, 99.999% trace metals basis
Sigma-Aldrich
Cesium chloride, optical grade, ≥99.5% trace metals basis
Sigma-Aldrich
Cesium chloride, Grade I, ≥99.0%
Sigma-Aldrich
Dimethyl sulfoxide, for molecular biology
Sigma-Aldrich
Dimethyl sulfoxide, PCR Reagent
Sigma-Aldrich
Dimethyl sulfoxide, ≥99.5% (GC), suitable for plant cell culture
Sigma-Aldrich
Dimethyl sulfoxide, meets EP testing specifications, meets USP testing specifications