Pyrethroid Target Research Articles

Pertussis toxin modulation of sodium channels in the central neurons of cyhalothrin‐resistant and cyhalothrin‐susceptible cotton bollworm, Helicoverpa armigera

AbstractPertussis toxin (PTX) inhibits the activation of the α‐subunit of the inhibitory heterotrimeric G‐proteins (Gαi./o) and modulates voltage‐gated sodium channels, which may be one of the primary targets of pyrethroids. To investigate the potential mechanisms of agricultural pests resistance to pyrethroid insecticides, we examined the modulations by PTX on sodium channels in the central neurons of the 3rd—4th instar larvae of cyhalothrin‐resistant (Cy‐R) and cyhalothrin‐susceptible (Cy‐S) Helicoverpa armigera by the whole‐cell patch‐clamp technique. The isolated neurons were cultured for 12—16 h in an improved L15 insect culture medium with or without PTX (400 ng/mL). The results showed that both the Cy‐R and Cy‐S sodium channels exhibited fast kinetics and tetrodotoxin (TTX) sensitivity. The Cy‐R sodium channels exhibited not only altered gating properties, including a 8.88‐mV right shift in voltage‐dependent activation (V0.5act) and a 6.54‐mV right shift in voltage‐dependent inactivation (V0.5inact), but also a reduced peak in sodium channel density (Idensity) (55.2% of that in Cy‐S neurons). Cy‐R sodium channels also showed low excitability, as evidenced by right shift of activation potential (Vacti) by 5—10 mV and peak potential (Vpeak) by 20 mV. PTX exerted significant effects on Cy‐S sodium channels, reducing sodium channel density by 70.04%, right shifting V0.5act by 14.41 mV and V0.5inact by 9. 38 mV. It did not cause any significant changes of the parameters mentioned above in the Cy‐R sodium channels. The activation time (Tpeak) from latency to peak at peak voltage and the fast inactivation time constant (τinact) in both Cy‐S and Cy‐R neurons were not affected. The results suggest that cotton bollworm resistant to pyrethroid insecticides involves not only mutations and allosteric alterations of voltage‐gated sodium channels, but also might implicate perturbation of PTX‐sensitive Gαi./o‐coupled signaling transduction pathways.

Differential effects of pyrethroid insecticides on extracellular dopamine in the striatum of freely moving rats

In order to obtain a more complete understanding of pyrethroid neurotoxicity, effects of the pyrethroid insecticides, allethrin (type I), cyhalothrin (type II) and deltamethrin (type II) on extracellular levels of dopamine (DA) and its metabolites in the striatum of conscious rats were studied by in vivo microdialysis. Rats were treated i.p. with pyrethroids or vehicle. Allethrin had a dual effect on DA release. The increase in the extracellular level of striatal DA by 10 mg/kg allethrin reached a maximum of 178% of baseline but 20 and 60 mg/kg inhibited DA release to 63% and 52% of baseline with a peak effect at 60-80 min after injection. Cyhalothrin 10, 20 and 60 mg/kg inhibited DA release to 65%, 56% and 45% of basal release, respectively, with a peak time of inhibition 40-80 min past injection. Deltamethrin (10 and 20 mg/kg) increased DA release to maximum of 187% and 252% of basal release whereas 60 mg/kg first reduced the efflux for 40 min to 50% of basal release and then increased the efflux to a maximum of 344% of basal release with a peak time of 120 min. Local infusion of 1 microM tetrodotoxin, a Na(+) blocker through the dialysis probe completely prevented the effect of allethrin (10 and 60 mg/kg), cyhalothrin (60 mg/kg) and deltamethrin (20 mg/kg) on DA release but only partially blocked the effects of 60 mg/kg deltamethrin. The effect of deltamethrin (60 mg/kg) on DA release was completely prevented by local infusion of 10 microM nimodipine, an L-type Ca(++) channel blocker. All three pyrethroids did not alter the extracellular levels of DOPAC, 3-MT and HVA except that 20 and 60 mg/kg of allethrin and cyhalothrin increased 3-MT levels. Effect of the pyrethroids on synaptosomal DA uptake was also examined. The DA uptake was decreased in rats exposed to 60 mg/kg of allethrin and cyhalothrin but was increased in rats exposed to 60 mg/kg of deltamethrin. Our results demonstrate that striatal DA release and DA uptake are differentially affected by type I and the two type II pyrethroids indicating that dopaminergic circuitry, striatal DA in particular, may be a pyrethroid target and that pyrethroids may be acting on striatal DA by multiple mechanisms.

Novel point mutation in the sodium channel gene of pyrethroid-resistant sea lice Lepeophtheirus salmonis (Crustacea: Copepoda)

Knockdown resistance (kdr) to pyrethroid insecticides is caused by point mutations in the pyrethroid target site, the para-type sodium channel of nerve membranes. This most commonly involves alterations within the domain II (S4-S6) region of the channel protein, where several different mutation sites have been identified across a range of insect species. To investigate the possibility that a kdr-type mechanism is responsible for pyrethroid resistance in sea lice, a domain II region of the Lepeophtheirus salmonis sodium channel gene was PCR amplified and sequenced. To our knowledge, this is the first published sodium channel sequence from a crustacean. Comparison of sequences from a range of samples, including several individuals from areas in which control failures had been reported, failed to identify any of the mutations within this region that have previously been linked with resistance. Instead, a novel glutamine to arginine mutation, Q945R, in transmembrane segment IIS5 was consistently found in the samples from areas of control failure and may therefore be associated with resistance to pyrethroids in this species.

Developmental neurotoxicity of pyrethroid insecticides: critical review and future research needs.

Pyrethroid insecticides have been used for more than 40 years and account for 25% of the worldwide insecticide market. Although their acute neurotoxicity to adults has been well characterized, information regarding the potential developmental neurotoxicity of this class of compounds is limited. There is a large age dependence to the acute toxicity of pyrethroids in which neonatal rats are at least an order of magnitude more sensitive than adults to two pyrethroids. There is no information on age-dependent toxicity for most pyrethroids. In the present review we examine the scientific data related to potential for age-dependent and developmental neurotoxicity of pyrethroids. As a basis for understanding this neurotoxicity, we discuss the heterogeneity and ontogeny of voltage-sensitive sodium channels, a primary neuronal target of pyrethroids. We also summarize 22 studies of the developmental neurotoxicity of pyrethroids and review the strengths and limitations of these studies. These studies examined numerous end points, with changes in motor activity and muscarinic acetylcholine receptor density the most common. Many of the developmental neurotoxicity studies suffer from inadequate study design, problematic statistical analyses, use of formulated products, and/or inadequate controls. These factors confound interpretation of results. To better understand the potential for developmental exposure to pyrethroids to cause neurotoxicity, additional, well-designed and well-executed developmental neurotoxicity studies are needed. These studies should employ state-of-the-science methods to promote a greater understanding of the mode of action of pyrethroids in the developing nervous system.

Identification of mutations associated with pyrethroid resistance in the para-type sodium channel of the cat flea, Ctenocephalides felis

Knockdown resistance (kdr) to pyrethroid insecticides is caused by point mutations in the pyrethroid target site, the para-type sodium channel of nerve membranes. This most commonly involves alterations within the domain II (S4–S6) region of the channel protein where five different mutation sites have been identified across a range of insect species. To investigate the incidence of this mechanism in cat fleas, we have cloned and sequenced the IIS4–IIS6 region of the para sodium channel gene from seven laboratory flea strains. Analysis of these sequences revealed two amino acid replacements at residues previously implicated in pyrethroid resistance. One is the ‘common’ kdr mutation, a leucine to phenylalanine substitution (equivalent to L1014F of housefly) reported previously in several other insects. The other is a threonine to valine substitution (equivalent to T929V) and is a novel variant of the T929I mutation first identified in diamondback moth. The L1014F mutation was found at varying frequency in all of the laboratory flea strains, whereas the T929V mutation was found only in the highly resistant Cottontail strain. We have developed rapid PCR-based diagnostic assays for the detection of these mutations in individual cat fleas and used them to show that both L1014F and T929V are common in UK and US flea populations. This survey revealed a significant number of fleas that carry only the V929 allele indicating that co-expression with the F1014 allele is not necessary for flea viability.

Oestradiol Potentiates the Effects of Certain Pyrethroid Compounds in the MCF7 Human Breast Carcinoma Cell Line

Pyrethroids are the most widely used insecticides for indoor pest control, so human exposure to them is common. The main target of pyrethroids is the nervous system, but their endocrine disrupting capabilities may also be of toxicological concern. In the present study, the proliferation of the breast cancer cell line, MCF7, was studied after a 7-day exposure to various concentrations of pyrethrin, permethrin and cypermethrin. The effects of oestradiol and the combined effects of oestradiol (0.10 nM) and pyrethroids (0.1-100 microM) on MCF7 cell proliferation were also evaluated. Proliferation and cell toxicity were studied by measuring the ATP content with a luminescence method, and mitochondrial metabolic enzyme activity with the WST-1 test. In the ATP test, low concentrations (0.1-1 microM) of pyrethroids in co-exposure with oestradiol caused a clear statistically significant increase in the proliferation of MCF7 cells. This was evident when compared to the proliferative effect caused by 0.1 nM oestradiol alone. High concentrations were cytotoxic, and the greatest cell toxicity was that of cypermethrin, which has a cyano group in its molecular structure.

The synaptosomal membrane bound ATPase as a target for the neurotoxic effects of pyrethroids, permethrin and cypermethrin

Pyrethroids are used widely as insecticides both in agriculture and in households. A cellular target of pyrethroids is the sodium channel in the membrane. In the present study, the activity of the membrane bound integral protein ATPase was studied as a biomarker for the membrane effect of the pyrethroids permethrin and cypermethrin. Male Sprague–Dawley rats were used for cerebral synaptosome preparation. The isolation of synaptosomes was performed with the Percoll gradient method. Both total ATPase and Mg 2+ activated ATPase were studied by determining inorganic phosphate liberated from the substrate ATP. One hour exposure to permethrin (Biokill) and cypermethrin (Ripcord) insecticide products affected ATPase activities. The activity of Na +, K + ATPase decreased dose-dependently in 10–50 μM concentrations of permethrin, and Mg 2+ activated ATPase increased over twofold in the same concentrations of the active components. The effect of the cypermethrin compound Ripcord was not clearly dose-dependent. The activity of total ATPase was almost entirely lost in the concentrations of 100 μM of permethrin and cypermethrin. The results support the idea that membrane ATPases are one target of the neurotoxic effect of pyrethroid compounds.

Molecular and biochemical diagnosis of esterase-mediated pyrethroid resistance in a Mexican strain of Boophilus microplus (Acari: Ixodidae).

We examined pyrethroid resistant Mexican strains of Boophilus microplus using biochemical and molecular tests to determine the mechanisms conferring resistance. Permethrin hydrolysis assays and esterase activity gels indicated enhanced esterase-mediated metabolic detoxification in the Cz strain, while one other pyrethroid resistant strain, SF, and two pyrethroid susceptible strains had lower levels of permethrin hydrolysis. Results from assays using a PCR-based test to detect a pyrethroid target site resistance-associated mutation in the tick sodium channel gene found only low levels of mutations in the Cz strain, while the SF strain had a high level of the mutated sodium channel alleles. A specific esterase, designated CzEst9, believed to be responsible for the esterase-mediated pyrethroid resistance in the Cz strain was purified, and the gene encoding CzEst9 cloned.

Sodium and GABA-activated channels as the targets of pyrethroids and cyclodienes

The symptoms of poisoning by the pyrethroid and cyclodiene insecticides are characterized by hyperexcitation and convulsions followed by paralysis. The main target site of the pyrethroids has been identified to be the sodium channels which are kept open for unusually long periods of time, causing a prolonged sodium current to flow which, in turn, leads to hyperexcitation of the nervous system. We have now found large differential sensitivity to the pyrethroids in two types of sodium channels. The dorsal root ganglion neurons of the rat were endowed with two types of sodium channels, one sensitive to the blocking action of tetrodotoxin (TTX) and the other insensitive to TTX. The type I pyrethroid allethrin and the type II pyrethroid deltamethrin were both effective in prolonging the sodium current in the TXX-resistant sodium channel but had only a small effect on the TTX-sensitive sodium channel. These two types of sodium channels also exhibited marked differences in their physiological properties, including the time course of current, the activation voltage, and the steady-state inactivation. In contrast to the pyrethroids, lindane and the cyclodienes endrin, isobenzan, dieldrin and heptachlor-epoxide suppressed the GABA-induced chloride current. The initial transient component of the chloride current was blocked more than the late sustained component. The suppression of the GABA-mediated synaptic inhibition would cause hyperexcitation of the nervous system. The results are compatible with the convulsant action of these insecticides.

Analysis of pyrethroid binding by use of a photoreactive analogue: Possible role for GTP-binding proteins in pyrethroid activity

Neurotoxicity of pyrethroids has been attributed to their activity on a variety of enzymes, membrane receptors, and ion channels—especially voltage-dependent sodium channels. To study pyrethroid binding, I have synthesized decyanoazidofenvalerate (DeCAF), a photoactivatable arylazide derivative of fenvalerate. DeCAF is insecticidal and induces repetitive firing in invertebrate nerve axons. SDS-PAGE analysis of photoderivatized proteins from rat brain membranes indicated that [ 3H]DeCAF covalently labeled a 36-kDa membrane-bound protein. This labeling was completely abolished by fenvalerate and unlabeled DeCAF, and partially inhibited by other pyrethroids. While labeling was not inhibited by alkaloid toxins or polypeptide venoms that modify voltage-dependent sodium channels, photolabeling was stimulated by tetrodotoxin and saxitoxin, specific blockers of voltage-dependent sodium channels. The [ 3H]DeCAF-labeled protein could not be identified as a known sodium channel subunit or as the 36-kDa subunit of the peripheral benzodiazepine receptor (another target of pyrethroids). [ 3H]DeCAF labeling was modified by addition of either GTPγS or pretreatment of membranes with cholera toxin. These results indicate that pyrethroids interact with a 36-kDa protein that is associated with voltage-sensitive sodium channels and is affected by modifiers of GTP-binding proteins.

Changes in membrane phospholipids, identified by Arrhenius plots of acetylcholinesterase and associated with pyrethroid resistance (kdr) in houseflies (Musca domestica)

AbstractMembrane‐bound acetylcholinesterase (AChE), extracted from the heads of susceptible and knockdown‐resistant (kdr) houseflies, was assayed at a range of temperatures between 5 and 35°C. Arrhenius plots using the results showed discontinuities commonly associated with membrane‐bound enzymes and generally attributed to an abrupt change in the viscosity of the lipids as they undergo a phase change at a temperature characteristic of their chemical composition. The enzyme from susceptible flies had a transition temperature of 14°C compared with 19°C and 21°C for the enzymes from kdr and super‐kdr strains, respectively. This variation was associated with a progressive decrease in activation energies, both above and below the transition temperature, with increasing resistance. The enzyme from a hybrid between susceptible and super‐kdr flies had the same properties as that from susceptible flies, corresponding with the genetically fully‐recessive behaviour of this resistance mechanism in toxicological studies. After digestion with phospholipase A2, the AChE from super‐kdr flies gave unchanged Arrhenius plots, whereas with the susceptible enzyme, both transition temperature and activation energies changed markedly to resemble more closely the enzyme from kdr flies. These results are discussed in relation to the likely changes in phospholipid composition and its effect on the conformation of the, as yet unidentified, target(s) of pyrethroids and DDT.

Nerve membrane as a target of pyrethroids

AbstractNerve membrane is one of the most important target sites of pyrethroids. Changes in excitability of nerve fibres caused by allethrin can be satisfactorily accounted for in terms of ionic permeabilities of the membrane. Temperature has a profound effect on the allethrin‐induced permeability changes.

Chemicals as tools in the study of excitable membranes.

Chemicals as tools in the study of excitable membranes.

Studies in asthma. XIX. The nose and throat in five hundred cases of asthma: Weille, F. L.: New England J. Med. 215: 235, 1936

<dm:abstracts xmlns:dm="http://www.elsevier.com/xml/dm/dtd"><ce:abstract xmlns:ce="http://www.elsevier.com/xml/common/dtd" view="all" class="author" id="aep-abstract-id1"><ce:section-title>Publisher Summary</ce:section-title><ce:abstract-sec view="all" id="aep-abstract-sec-id1"><ce:simple-para id="fsabs012" view="all">This chapter covers the neurophysiological mechanisms of action of various insecticides. Most insecticides are neuropoisons, but their target sites are rather limited. For example, voltage-gated sodium channels are the major target of pyrethroids and dichlorodiphenyltrichloroethane (DDT); gamma-aminobutyric acidA (GABA<ce:inf loc="post">A</ce:inf>) receptors are attacked by cyclodienes, hexachlorocyclohexane (HCH), and fipronil; neuronal nicotinic acetylcholine (nnACh) receptors are the target of nicotine, and nitromethylene and nitroimine heterocycles (for example, imidacloprid). Organophosphate and carbamate insecticides inhibit acetylcholinesterase. Despite apparent differences in chemical structure, pyrethroids and DDT exert similar actions on the nervous system through modulation of the function of voltage-gated sodium channels. Imidacloprid exhibits a unique mechanism of action on nicotinic acetylcholine (nACh) receptors. It binds to insect nACh receptors with a high affinity. Imidacloprid depolarized nerve membrane and caused spontaneous discharges in cockroaches. Fipronil has been found to block insect GABA receptors.</ce:simple-para></ce:abstract-sec></ce:abstract></dm:abstracts>