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PubMed1985

Interaction of DDT and pyrethroids with calmodulin and its significance in the expression of enzyme activities of phosphodiesterase.

To understand the significance of the inhibitory action of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and pyrethroid insecticides on calmodulin, a universal Ca2+ binding protein, a bovine heart phosphodiesterase-calmodulin system was studied. It was found that, at concentrations of less than 10(-5) M, the inhibitory action of DDT of the phosphodiesterase was due entirely to its action on calmodulin alone. Cypermethrin was less potent than DDT, but it also affected only calmodulin. Permethrin was the most potent inhibitor affecting calmodulin and, to a lesser extent, phosphodiesterase. The inhibitory action of these insecticides on calmodulin raises a possibility that many unsuspected Ca2+-related systems are being affected by these insecticidal chemicals, as calmodulin is known to play vital roles in many biological reactions dependent upon Ca2+. These include modulation of phosphodiesterase, neurotransmitter release, adenylate cyclase, Ca2+-dependent protein kinase, myosine light chain kinase and various membrane phosphorylation systems.

Animals↗
PubMed1988

Interactions of pyrethroids and octylguanidine with sodium channels of squid giant axons.

Kinetics of pyrethroid-modified sodium channels and the interaction of N-octylguanidine with the modified channels have been studied with internally perfused and voltage-clamped squid giant axons. The pyrethroids used were 1R-cis-phenothrin; 1R-cis-permethrin; 1R-cis-cyphenothrin; and 1R-cis-deltamethrin. Modification of sodium channels by pyrethroids resulted in marked slowing of opening and closing kinetics. The rate at which sodium channels arrived at the open pyrethroid-modified state during a depolarizing step was independent of the concentration of pyrethroids applied. The time of exposure to pyrethroids required for the pyrethroid-induced sodium tail current following a step depolarization to reach a steady-state amplitude was independent of the frequency of short (5 ms) depolarizing pulses, and in the pronase-treated axons was independent of the membrane potential (0 mV or -90 mV). We conclude that sodium channels are modified by pyrethroids primarily in the closed resting state. A small fraction of sodium channels is modified in the open state. The dose-response curve for N-octylguanidine block of sodium channels was not shifted by pyrethroids. The rate at which the pyrethroid-modified sodium channels were blocked by octylguanidine during a depolarizing step depended neither on the concentration of pyrethroids nor on the depolarizing potential, but depended on the concentration of octylguanidine. The time course of the pyrethroid-induced slow sodium tail current was not altered by octylguanidine. We conclude that the actions of pyrethroids and N-octylguanidine on sodium channels are independent of each other.

Animals↗
PubMed1989

Pyrethroids: involvement of sodium channels in effects on inositol phosphate formation in guinea pig synaptoneurosomes.

The effects of pyrethroids were studied on phosphoinositide breakdown in guinea pig synaptoneurosomes. Similar to other agents that activate voltage-dependent sodium channels, type I and type II pyrethroids stimulated phosphoinositide breakdown. Type II pyrethroids, like deltamethrin and fenvalerate, were more potent and, at least for deltamethrin, more efficacious than type I pyrethroids, like allethrin, resmethrin and permethrin. The effects of type II pyrethroids could be partially inhibited by the sodium channel blocker tetrodotoxin. The effects of allethrin and resmethrin were not affected by 5 microM tetrodotoxin. Stimulation of phosphoinositide breakdown by fenvalerate was additive to the stimulation elicited by the receptor agonists carbamylcholine and norepinephrine, but not to the stimulation elicited by sodium channel agents (batrachotoxin, scorpion venom and pumiliotoxin B). Stimulation by allethrin was not additive to the stimulation elicited either by receptor agonists or sodium channel agents. A submaximal concentration of allethrin, a type I pyrethroid, did not greatly affect the dose-dependent stimulation elicited by a type II pyrethroid, deltamethrin, while a higher concentration of allethrin prevented further stimulation by type II pyrethroids. A local anesthetic, dibucaine, which inhibits sodium channel activation, inhibited phosphoinositide breakdown induced by type II, but not by type I pyrethroids, except at higher concentrations. Thus, type II pyrethroids appear to stimulate phosphoinositide breakdown in synaptoneurosomes in a manner analogous to other sodium channel agents, while type I pyrethroids elicit phosphoinositide breakdown by a different mechanism, probably not involving sodium channels.

Animals↗
PubMed1995

Multi-residue matrix solid-phase dispersion method for the determination of six synthetic pyrethroids in vegetables followed by gas chromatography with electron capture detection.

An effective multi-residue matrix solid-phase dispersion (MSPD) extraction and gas chromatographic-electron-capture detection method for the determination of six synthetic pyrethroids (fenpropathrin, cyhalothrin, permethrin, cypermethrin, fenvalerate and deltamethrin) in 5 g of vegetables (West Indian gherkin, eggplant, pak-choi, cabbage and garden peas) is described. The method uses a Florisil-based MSPD column for direct in-line clean-up with n-hexane-acetone (9:1). Recoveries calculated at 0.1 and 0.5 micrograms/g fortification levels were between 92 and 113%. The method detection limits were between 5.1 and 91.5 ng/g. The method compared favourably with the traditional method in terms of the sample size, analysis time and overall cost. The method may serve as a screening protocol for the determination of pyrethroids in vegetables.

Chromatography, Gas↗
PubMed1994

Rapid method for the determination of multiple pyrethroid residues in fruits and vegetables by capillary column gas chromatography.

A rapid and economical simplified multi-residue method is described for the determination of multiple pyrethroid insecticides in fruits and vegetables. The residues are extracted from crops with methanol and the crop co-extractives are removed by toluene partitioning and Florisil-charcoal minicolumn chromatography. The final extract is analysed by capillary column gas chromatography with electron-capture detection. The recoveries were determined by fortifying six different crops (apples, oranges, cabbages, pears, peppers and tomatoes) with eleven pyrethroids (Py-115, allethrin, biphenthrin, fenpropathrin, cyhalothrin, permethrin, cyfluthrin, flucythrinate, fluvalinate, fenvalerate and deltamethrin) at three levels, 0.01-0.07, 0.10-0.70 and 1.0-7.0 mg/kg. Three determinations were made at each level for each crop. Recoveries of the eleven pyrethroids ranged from 70.4 to 110.0% at the three different levels. The practical determination limit of the method was in the range 3.0-30.0 micrograms/kg for all the pyrethroid insecticides. The proposed method had major advantages that simplified steps were achieved for the extraction and the clean-up, the solvent consumption was reduced and the analysis time was shortened.

Chromatography, Gas↗
PubMed1990

The binding properties of pyrethroids to human skin fibroblast androgen receptors and to sex hormone binding globulin.

The pyrethroids are a class of natural and synthetic pesticides which were associated with an epidemic of gynecomastia in Haitian men in 1981. In the present study we tested several pyrethroids for their ability to interact with androgen binding sites in dispersed, intact human genital skin fibroblasts and in human plasma to sex hormone binding globulin (SHBG). All the pyrethroids tested inhibited fibroblast binding of [3H]methyltrienolone (R1881) at 22 degrees C with the following rank order of potency:pyrethrins greater than bioallethrin greater than fenvalerate greater than fenothrin greater than fluvalinate greater than permethrin greater than resmethrin. 50% displacement of [3H]R1881 binding to fibroblast androgen receptors was achieved by 1.5-44 x 10(-5) M concentrations of the competitors, respectively. Previous studies with cimetidine, a known inhibitor of androgen receptor binding, showed 50% competition at a concentration of 1.4 x 10(-4) M in this system. Scatchard analysis of binding experiments performed with increasing concentrations of [3H]R1881 in the presence of the pyrethroids indicated that the binding inhibition was competitive. On the other hand, of the pyrethroids examined only the pyrethrins (50% inhibition) and bioallethrin (43% inhibition) were able to displace [3H]testosterone from SHBG when tested at a concentration of 10(-4) M. These data indicate that a novel class of non-steroidal compounds, the pyrethroids, can interact competitively with human androgen receptors and SHBG. These findings provide a mechanism by which chronic exposure of humans or animals to pesticides containing these compounds may result in disturbances in endocrine effects relating to androgen action.

Fibroblasts↗
PubMed1991

Pyrethroid insecticides indirectly inhibit GABA-dependent 36Cl- influx in synaptoneurosomes from the trout brain.

Rainbow trout (Oncorhynchus mykiss) are extremely sensitive to the neurotoxic activity of pyrethroid insecticides. One possible target for pyrethroids is the GABA(A) receptor of brain of the trout, the function of which can be tested by measurement of influx of 36Cl- into synaptoneurosomes, in response to the application of agonists. gamma-Aminobutyric acid produced a time- and concentration-dependent increase in influx of 36Cl- in synaptoneurosomes from the brain of the trout, which exhibited the pharmacology characteristic of a response mediated by activation of a GABAA receptor. Deltamethrin, (1R alpha S)-cis-cypermethrin and permethrin produced a dose-dependent increase in the basal uptake and a corresponding decrease in GABA-dependent influx, with a maximum inhibition of 70-82%. This effect of pyrethroid was stereospecific, of high potency and inhibited by tetrodotoxin (TTX) and t-butylbicyclophosphorothionate (TBPS). The sensitivity of the effect of the pyrethroid to TTX suggested an activation by pyrethroid of the voltage-dependent sodium channel. Veratridine, a sodium channel activator, elicited similar changes in the basal uptake of chloride, which were TTX-sensitive. Neither deltamethrin nor veratridine had a measurable effect on the efflux of 36Cl- from synaptoneurosomes. Thus, pyrethroid insecticides may interfere with the function of GABAA receptors indirectly through an interaction with the voltage-dependent sodium channel in the brain of the trout and consequently perturb chloride influx, possibly through a voltage-dependent chloride channel.

Animals↗
PubMedDate not supplied

The cost-effectiveness of chemoprophylaxis with Maloprim administered by primary health care workers in preventing death from malaria amongst rural Gambian children aged less than five years old.

In recent trials in The Gambia, mass chemoprophylaxis with Maloprim administered over several years by primary health care workers to children aged 3-59 months has reduced both mortality and morbidity without inducing impairment of natural immunity or significant development of drug resistance. Taking expenditure of both time and money, by both public authorities and village volunteers, into account, the costs and the cost effectiveness of such mass chemoprophylaxis are estimated here. The cost per child protected per season was (1990 US) $2.84; the cost per childhood death averted was $143. Both costs compare favourably with those of permethrin bed net impregnation. So in some circumstances where malaria is holoendemic, control of childhood malaria by chemoprophylaxis may be more economically efficient than provision of impregnated bed nets.

Antimalarials↗
PubMedDate not supplied

Alphamethrin-impregnated bed nets for malaria and mosquito control in China.

A community-based intervention trial was carried out to evaluate the effectiveness of alphamethrin-impregnated bed nets for control of Plasmodium vivax malaria and its vector in an area of moderate endemicity in southern Henan province, central China in 1990. Malaria incidence was significantly lower in the intervention group than in the comparison group (2.03 vs. 3.57 per 100 person-years at risk). The protective efficacy for malaria incidence was 43%. The prevalence of malaria parasitaemia among children under 10 years old in the intervention group was about one-quarter of that in the comparison group (0.93% vs. 3.25% and 0.71% vs. 1.96% after one and 4 months use of impregnated nets, respectively). Alphamethrin-impregnated bed nets had a mass killing effect on vector mosquitoes. The outdoor person-biting density of Anopheles anthropophagus and A. sinensis decreased by 70.3% and 29.3% respectively. The density of these 2 mosquito species found resting inside treated nets was close to zero. No side effect was found among users of impregnated bed nets. Impregnation with alphamethrin was more effective on polyester than on cotton netting and residual effects lasted at least one year. Use of alphamethrin is less expensive than permethrin and deltamethrin.

Animals↗
PubMed1984

Lack of mutagenicity of synthetic pyrethroids in Salmonella typhimurium strains and in V79 Chinese hamster cells.

Seven pyrethroids, i.e., cypermethrin, permethrin, deltamethrin, bioresmethrin, resmethrin, cismethrin and fenvalerate, were not found to be mutagenic in (a) Salmonella typhimurium strains TA100 or TA98 in the presence or absence of a rat liver activation system using the plate incorporation assay and fluctuation tests, or (b) V79 Chinese hamster cells in the presence or absence of hepatocytes.

Animals↗
PubMed1988

Mechanisms of resistance to pyrethroid insecticides.

In the 10 years or so since the photostable pyrethroid insecticides such as permethrin and fenvolerate were introduced, this family of compounds has become widely used to control agricultural pests, and finds increasing usage to control arthropods of medical and veterinary importance. The synthetic pyrethroids offer many advantages for veterinary and public health use, particularly their selectivity, high toxicity to insects, and relative lack of chronic effects. They are also inherently stable, and so have become widely used as residual sprays on house walls to control insects in the domestic environment. But as with other classes of insecticides such as organochlorines, organophosphotes and carbamates, resistance to pyrethroids is now increasingly reported. In this article, Tom Miller explains the principle mechanisms of resistance to pyrethroids, using the North American horn fly (Haematobia irritans) as an example now showing many common resistance traits.

Journal Article↗
PubMed1992

Demodicidosis in a child with leukemia.

A 2-year-old girl developed acute lymphoblastic leukemia at the age of 9 months. She was treated successfully with chemotherapy but developed a pruritic, papulopustular facial eruption that was caused by Demodex folliculorum. The eruption cleared after treatment with one overnight application of 5% permethrin cream. Demodicidosis should be included in the differential diagnosis of facial eruptions in children who undergo chemotherapy and in those with congenital or acquired immunodeficiency.

Child, Preschool↗
PubMed1985

Correlations between in vitro and in vivo mechanisms of pyrethroid insecticide action.

Classical neuropharmacological procedures have been used to elucidate insecticide mode of action in vitro. A good deal has thus been learned about pyrethroids but novel techniques have been necessary to explain the toxicology and symptomology. The free-walking, electrode-implanted cockroach technique, which was developed for this purpose, is described. It enabled correlations to be made between symptomology and effects on specific nerves. The negative temperature coefficient of toxicity of allethrin (the first pyrethroid) was explained in terms of repetitive firing in peripheral (sensory) nerves rather than by nerve blockage, which had been suggested from previous in vitro studies. The elucidation of target sites in vivo and the most useful parameter to study, i.e., repetitive firing in nerve axons, enabled the definition of a pyrethroid resistance mechanism in a major insect pest. It also showed two modes of action for permethrin and cypermethrin, its alpha-cyano analog. A structure-activity relationship for a range of pyrethroids, combining in vitro and in vivo approaches, confirmed two distinct types of pyrethroid action. Studies of poisoning signs and nerve disruptions in vivo in the mouse and cockroach, using diazepam in conjunction with pyrethroids, implicated the GABA-receptor complex as a target for alpha-CN-phenoxybenzyl pyrethroids. This was confirmed by making conductance measurements in crayfish claw opener muscle fibers in vitro.

Allethrins↗
PubMed1988

Effects of type I and type II pyrethroids on the startle response in rats.

The effects of type I and type II pyrethroids on the acoustic startle response of male Wistar rats were studied in three experiments. Pyrethroids were administered p.o. in 0.2 ml corn oil. In Expt. 1, techn. cis-permethrin (0, 30, 60, 90 mg/kg) and techn. cis, trans-cypermethrin (0, 60, 90, 120 mg/kg) increased startle in a dose-dependent way, whereas overt behavior and habituation of the startle response were not affected. In Expt 2, NAK 1901 (0, 1, 2.5, 4 mg/kg) enhanced startle amplitudes dose dependently and deltamethrin (0, 2, 4, 6 mg/kg) had no effect on startle. After both deltamethrin and NAK 1901 toxic signs increased dose dependently but an effect on potentiation of the startle reflex was not found. In Expt. 3, deltamethrin (0, 2, 4, 6 mg/kg) was administered and the highest dose attenuated startle amplitudes significantly, whereas toxic signs increased dose dependently. Deltamethrin had no effect on habituation of the startle response. It is concluded that type I pyrethroids increase the amplitude of the startle reflex; this effect does not depend on the presence of overt signs of toxicity. Type II pyrethroids have dissimilar effects on startle. Results are discussed suggesting that the effects of type II pyrethroids on startle amplitude are mediated by an indirect metabolic effect and a direct effect at the site of the muscle.

Animals↗
PubMed1991

Solid phase extraction method for rapid isolation and clean-up of some synthetic pyrethroid insecticides from human urine and plasma.

A simple and rapid method for the isolation of seven synthetic pyrethroid insecticides (methothrin, fenpropathrin, cyhalothrin, permethrin, cypermethrin, fenvalerate, deltamethrin) with a solid phase extraction (SPE), utilizing Sep-Pak C18 cartridges, from human urine and plasma is presented. The detection of the insecticides was performed using a wide bore capillary gas chromatograph (GC) with flame ionization detection (FID). The insecticide-containing samples mixed with 70% methanol were directly applied to the cartridges and eluted with 2 ml chloroform. The recoveries using the cartridges were between 90-102% for urine and 81-93% for plasma. Mixing samples with 70% methanol prior to extraction, seems very useful for the screening of synthetic pyrethroid insecticides.

Chromatography, Gas↗
PubMed2006

Characterization of pyrethroid hydrolysis by the human liver carboxylesterases hCE-1 and hCE-2.

Carboxylesterases hydrolyze a large array of endogenous and exogenous ester-containing compounds, including pyrethroid insecticides. Herein, we report the specific activities and kinetic parameters of human carboxylesterase (hCE)-1 and hCE-2 using authentic pyrethroids and pyrethroid-like, fluorescent surrogates. Both hCE-1 and hCE-2 hydrolyzed type I and II pyrethroids with strong stereoselectivity. For example, the trans-isomers of permethrin and cypermethrin were hydrolyzed much faster than corresponding cis-counterparts by both enzymes. Kinetic values of hCE-1 and hCE-2 were determined using cypermethrin and 11 stereoisomers of the pyrethroid-like, fluorescent surrogates. K(m) values for the authentic pyrethroids and fluorescent surrogates were in general lower than those for other ester-containing substrates of hCEs. The pyrethroid-like, fluorescent surrogates were hydrolyzed at rates similar to the authentic pyrethroids by both enzymes, suggesting the potential of these compounds as tools for high throughput screening of esterases that hydrolyze pyrethroids.

Carboxylic Ester Hydrolases↗
PubMed2005

Distribution of the molecular forms of Anopheles gambiae and pyrethroid knock down resistance gene in Nigeria.

We investigated the distribution of the molecular M and S forms of Anopheles gambiae and the knock down resistance (kdr) gene associated with pyrethroid and DDT resistance in A. gambiae s.s. at 13 localities across Nigeria. Two-three days old adult female mosquito reared from larval collections were tested using standard WHO procedures, diagnostic test kits and impregnated papers to assess their pyrethroid resistance status. Specimens were identified by PCR assays and characterized for the kdr gene. DNA from adult A. gambiae s.s. collected from human dwellings were also tested for the presence of the kdr gene. The overall collection was a mix of the molecular M and S forms across the mangrove (63:37%), forest (56:44%), and transitional (36:64%) ecotypes, but almost a pure collection of the S form in the Guinea and Sudan-savanna. Results of insecticide susceptibility tests showed that mosquitoes sampled at seven localities were susceptible to permethrin, deltamethrin, and DDT, but populations of A. gambiae resistant to these insecticides were recorded at six other localities mainly in the transitional and Guinea-savanna ecotypes. The kdr gene was found only in the molecular S forms, including areas where both forms were sympatric. The overall kdr frequency was low: <47% in forest, 37-48% in the transitional, and 45-53% in Guinea-savanna. The data suggest that pyrethroid resistance in A. gambiae in Nigeria is not as widespread when compared to neighbouring West African countries.

Animals↗
PubMed2005

Influence of container adsorption upon observed pyrethroid toxicity to Ceriodaphnia dubia and Hyalella azteca.

Pyrethroid insecticides are known for their potential toxicity to aquatic invertebrates and many fish species. A significant problem in the study of pyrethroid toxicity is their extreme hydrophobicity. They can adsorb to test container surfaces and many studies, therefore, report pyrethroid levels as nominal water concentrations. In this study, pyrethroid adsorption to sampling and test containers was measured and several container treatments were examined for their ability to decrease pyrethroid adsorption. None of the chemical treatments were successful at preventing pyrethroid loss from aqueous samples, but vortexing of containers served to resuspend pyrethroids. The effects of the observed adsorption on Ceriodaphnia dubia and Hyalella azteca permethrin toxicity were examined. Species-specific results showed a time-dependent decrease in toxicity following pyrethroid adsorption to test containers for C. dubia, but not for H. azteca. These results demonstrate that pyrethroid adsorption to containers can significantly affect the observed outcome in toxicity-testing and serves as a caution for researchers and testing laboratories.

Adsorption↗