The Efficacy of a Pyrethroid-impregnated Mattress Liner on Multiple International Strains of Cimex lectularius (Hemiptera: Cimicidae) and Cimex hemipterus (Hemiptera: Cimicidae)

Modern bed bugs are resistant to multiple insecticide classes, particularly the pyrethroids. The efficacy of pyrethroid-impregnated mattress liners marketed for bed bug management has been variable. This study evaluated the efficacy of a permethrin-impregnated mattress liner, ActiveGuard, against 24 bed bug strains, consisting of both Cimex hemipterus (F.) and Cimex lectularius L. A 'mat assay', employing an allethrin-impregnated mat, was used to establish the pyrethroid resistance profile of all strains. Three experiments were conducted to evaluate the effect of ActiveGuard exposure on bed bug knockdown: 1) exposing the bed bugs continuously on the liner for up to 24 d, 2) holding the bed bugs on the liner for either 4 or 6 h, and 3) placing a noninsecticide treated fabric above the liner with the bed bugs held continuously on top. Our results indicated that all modern strains (collected within the last 15 years during the current resurgence) were pyrethroid-resistant, although the magnitude of resistance was highly variable between strains. In the continuous exposure study, an incomplete knockdown was recorded for most modern bed bug strains, with some having no knockdown even up to 7 d of constant exposure. In the 4 or 6 h exposure study, the level of knockdown was reduced even further, and very few bed bugs were knocked down in the double fabric study. The results of this study indicate that pyrethroid-impregnated mattress liners are not likely to be effective in the management of most modern bed bug infestations involving either C. hemipterus or C. lectularius.

Identification of putative kdr mutations in the tropical bed bug, Cimex hemipterus (Hemiptera: Cimicidae)

BACKGROUND

Bed bugs [both Cimex hemipterus (F.) and Cimex lectularius L.] are highly resistant to pyrethroids worldwide. An important resistance mechanism known as 'knockdown resistance' (kdr) is caused by genetic point mutations on the voltage-gated sodium channel (VGSC) gene. Previous studies have identified two point mutations (V419L and L925I) on the VGSC gene in C. lectularius that are responsible for kdr-type resistance. However, the kdr mutations in C. hemipterus have not been investigated.

RESULTS

Four novel mutations, L899V (leucine to valine), M918I (methionine to isoleucine), D953G (aspartic acid to glycine) and L1014F (leucine to phenylalanine), were identified in the domain II region of the C. hemipterus VGSC gene. This region has been widely investigated for the study of kdr-type resistance to pyrethroids in other insect pests. The V419L and L925I kdr mutations as previously identified in C. lectularius were not detected in C. hemipterus.

CONCLUSION

M918I and L1014F are considered to be probable kdr mutations and may play essential roles in kdr-type resistance to pyrethroids in C. hemipterus. Further studies are under way in the authors' laboratory to determine the non-kdr-type resistance mechanisms in C. hemipterus.

Allethrin-Based Mosquito Control Device Causing Knockdown, Morbidity, and Mortality in Four Species of Field-Caught Mosquitoes (Diptera: Culicidae)

A mosquito control device marketed for spatial repellency, the ThermaCELL Mosquito Repellent Appliance, was evaluated in semifield trials against multiple field-caught species of mosquito. Using paper and mesh cages, mosquito test groups of at least 30 mosquitoes were suspended in a 2,337 cubic foot outdoor space while two ThermaCELL repellent devices were active. After 30 min of treatment, cages were moved to the laboratory to observe knockdown, morbidity, and mortality for 24 h. Species tested included Aedes atlanticus Dyar and Knab (98% average mortality), Psorophora ferox Humboldt (97% average mortality), Psorophora columbiae Dyar and Knab (96% average mortality), and Aedes taeniorhynchus Wiedemann (84% average mortality). The repellent devices showed effectiveness with high knockdown and mortality across all species tested. Mosquito control devices like the ThermaCELL Mosquito Repellent Appliance may have further practical applications to help combat viral exposures by limiting host mosquitoes. Such devices may provide a functional alternative to DEET dependence in the current state of mosquito management.

Laboratory evaluation of three commercial coil products for protection efficacy against Anopheles gambiae from southern Ghana: a preliminary study

Residents in irrigated urban agricultural sites face numerous mosquito problems such as increased mosquito populations and reduced insecticides susceptibility due to the creation of mosquito breeding sites and agricultural use of insecticides and hence require effective protective products against them. In this study, the protection effectiveness of three pyrethroid formulated mosquito coils of Malaysian origin against Anopheles gambiae sensu lato from an irrigated urban agricultural site in Ghana were evaluated for their potential use. Sucrose fed An. gambiae s.l. were exposed to insecticide-containing coils in a 70 cm x 70 cm x 70 cm glass chamber to assess the insecticidal effect of the coils. The 0.005% metofluthrin coil caused the most rapid knockdown of 50% of the test mosquitoes. The mean lethal effect of the coils on An. gambiae s.l. were as follows; 0.005% metofluthrin (86%), 0.3% d-allethrin (74.33%), 0.15% d-trans allethrin (72%) and the 0.25% d-allethrin reference coil (69%). The 0.005% metofluthrin coil achieved the highest insecticidal effect on An. gambiae s.l. compared to the other coils and hence performed better than the others as an anti-mosquito product. All the three test coils were effective against An. gambaie s.l. from the irrigated agricultural site compared to the reference coil.

Metofluthrin: A Potent New Synthetic Pyrethroid with High Vapor Activity against Mosquitoes

(1R)-trans-Norchrysanthemic acid fluorobenzyl esters are synthesized and their structure-activity relationships are discussed. These esters show outstanding insecticidal activity against mosquitoes. In particular, the 2,3,5,6-tetrafluoro-4-methoxymethylbenzyl analog (metofluthrin) exhibits the highest potency, being approximately forty times as potent as d-allethrin in a mosquito coil formulation when tested against southern house mosquitoes (Culex quinquefasciatus). Metofluthrin also exhibits a significant vapor action at room temperature.

Lack of insecticidal effect of mosquito coils containing either metofluthrin or esbiothrin on Anopheles gambiae sensu lato mosquitoes

Use of mosquito coils for personal protection against malaria and mosquito nuisance is advocated under mosquito and malaria control programmes. We performed field studies of mosquito coils containing either metofluthrin or esbiothrin in experimental huts situated in Kamhororo village, Gokwe district, Zimbabwe. All tests were performed on 3-5 day old reared female Anopheles gambiae sensu lato mosquitoes. The burning times were 9hr 20min for mosquito coils containing metofluthrin and 8 hr for those containing esbiothrin and the results were significantly different (p = <0.001). The mean knock down rate for mosquito coils containing metofluthrin was 90% and that for esbiothrin was 73.3% and the results were significantly different (p = 0.00). Mosquito coils containing metofluthrin had a mean repellence of 92.7% as compared to 85.4% for esbiothrin and the results were not significantly different (p=0.27). The protection time as required by EPA (1999) was 6 hr for mosquito coils containing metofluthrin and 5 hr for those containing esbiothrin. The mean insecticidal effect of mosquito coils containing metofluthrin was 84% as compared to 83% for those containing esbiothrin and the results were not significantly different (p = 0.56). Both mosquito formulations could not be classified as having insecticidal effect since none of them met the 95% mortality rate criteria.

Control of mosquito vectors of tropical infectious diseases: (2) pyrethroid susceptibility of Aedes aegypti ( l) collected from different sites in Thailand

Four strains (SS, BS, A and B) of Aedes aegypti collected from different sites in Bangkok and at different times were examined for their pyrethroid susceptibility. Mosquito coils containing dl, d-T80-allethrin, d, d-T-prallethrin and methoxymethyl-tetrafluorobenzyl tetramethyl-cyclopropanecarboxylate (K-3050) with or without a synergist were tested by the 25 m3 semi-field test method. One strain (SS) was the most susceptible with KT50 values of about < 30 minutes for all mosquito coils, while the other three strains (BS, A and B) were found to be around 10 to 20 times more tolerant to pyrethroids than the SS strain. A similar tendency for the pyrethroid susceptibility of the four strains was obtained with tests by topical application method. In field efficacy tests, mosquito coils with d, d-T-prallethrin 0.20% plus N-(2-ethylhexyl)bicycle-[2,2,1]- hept-5- ene-2,3-dicarboxyimide as a synergist exhibited a repellent effect of about 85%, while those with K-3050 0.10% plus the synergist exhibited a greater repellent effect of about 90%. In contrast, the repellent effect of commercial dl, d-T80-allethrin 0.20% coils was as low as about 50%. The d, d-T-prallethrin and K-3050 coils with the synergist were confirmed to be highly effective in repelling Ae. aegypti.

Influence of pyrethroids and piperonyl butoxide on histamine release from isolated rat mast cells

OBJECTIVE AND DESIGN

Pyrethroids are insecticides with low acute toxicity in mammals but their world-wide use for domestic and occupational purposes has caused concern about the risks of long-term exposure. The mammalian toxicity of pyrethroids is related to disturbances of membrane function in neuronal tissues whereas their influence on nonneuronal tissues is poorly understood. Recently, selected pyrethroids were shown to affect the function of rat synaptosomal and leukocyte membranes similarly. The present investigation explores to what extent their influence on the function of intact cells, i. e. isolated rat mast cells, correlates with these membrane interactions.

MATERIALS AND TREATMENT

Permethrin and the more water soluble esbiol (S-bioallethrin), both type I pyrethroids, and cyfluthrin, type II, used alone and together with the enhancing substance piperonyl butoxide (PBO) at concentration ratios of 1:5 and 1:10, were tested for influence on histamine release induced by compound 48/80 without and with calcium.

RESULTS

Permethrin (5-10 microM) caused a 10-25 % inhibition of the histamine release in the absence of calcium but did not affect the response with calcium present and had no interaction with PBO. Esbiol (10 microM) was an effective inhibitor on its own, with 70 and 45% inhibition in the absence and presence of calcium, respectively, and caused virtually complete inhibition in a synergistic interaction with PBO. The effect of esbiol could partly be ascribed to inhibition of oxidative energy production. Cyfluthrin was inactive at concentrations up to 10 microM. PBO alone (50 microM) caused some inhibition, in particular in the absence of calcium (ca. 25 %).

CONCLUSIONS

The results relating to mast cell histamine release reveal both similarities and differences with the influence of the pyrethroids on cell membrane activities. They indicate that not solely membrane interactions but also additional or alternative targets are involved in the effects of pyrethroids on mammalian tissues. Moreover, the pronounced effects of a brief cell exposure suggest that long-term exposure can be hazardous.

Vector control in leishmaniasis

Indoor residual spraying is a simple and cost effective method of controlling endophilic vectors and DDT remains the insecticide of choice for the control of leishmaniasis. However resistance to insecticide is likely to become more widespread in the population especially in those areas in which insecticide has been used for years. In this context use of slow release emulsified suspension (SRES) may be the best substitute. In this review spraying frequencies of DDT and new schedule of spray have been discussed. Role of biological control and environment management in the control of leishmaniasis has been emphasized. Allethrin (coil) 0.1 and 1.6 per cent prallethrin (liquid) have been found to be effective repellents against Phlebotomus argentipes, the vector of Indian kalaazar. Insecticide impregnated bednets is another area which requires further research on priority basis for the control of leishmaniasis. Role of satellite remote sensing for early prediction of disease by identifying the sandflygenic conditions cannot be undermined. In future synthetic pheromons can be exploited in the control of leishmaniasis.

[Effect of S-bioallethrin on human lymphocyte]

OBJECTIVE

To study the effect of the S-bioallethrin on human lymphocytes by microarray technique.

METHODS

The changes of normal human lymphocytes treated with S-bioallethrin were examined with light microscope, flow cytometry, electron microscope, DNA ladder and microarray techniques.

RESULTS

Morphological study showed that the lymphocytes underwent apoptosis after S-bioallethrin exposure, which as further confirmed by the expression changes of 346 genes.

CONCLUSION

S-bioallethrin can induce apoptosis of normal human lymphocytes and changes in their gene expression profiles.

Ultra low volume aerosol application of deltacide (deltamethrin 0.5% w/v, S-bioallethrin 0.71% w/v & piperonyl butoxide 8.9% w/v) against mosquitoes

BACKGROUND & OBJECTIVE

Insecticide in the form of space spray as an ultra low volume (ULV) aerosol are used during epidemics of vector borne diseases. Deltacide, a formulation comprising of three chemicals viz., deltamethrin 0.5 per cent w/v, S-bio-allethrin 0.71 per cent w/v and piperonyl butoxide 8.9 per cent w/v is suitable for ULV application. As this combination is found to be effective in preventing resistance development tackling the population, which had already developed resistance and cause immediate mortality, its synergistic effect was tested in Peet Grady chamber, against three species of mosquitoes, viz., Aedes aegypti, Anopheles stephensi and Culex quinquefasciatus.

METHODS

Blood fed females were exposed to ULV application of deltacide in a Peet Grady chamber at four dosages viz., 0.005, 0.01, 0.02 and 0.04 ml/m2 and examined for knockdown activity at 10 min interval for 60 min. Thereafter, the mosquitoes were removed from the chamber and maintained in another room having controlled temperature (28+/-2 degrees C) and humidity (60-75%) and observed for recovery, if any, and the per cent knockdown was calculated. Mortality rate after 24 h of holding period was also determined from moribund and dead adults.

RESULTS

Pairwise comparison showed that the effect of deltacide spray varied significantly (P<0.001) among the three species tested. The effectiveness was significantly higher in Ae. aegypti, when compared with that of Cx. quiquefasciatus (P<0.001) and An. stephensi (P<0.05). However, there was no significant difference in the efficacy of deltacide between Cx. quiquefasciatus and An. stephensi. All species of mosquitoes became inactive i.e., knocked down completely within 60 min of exposure at all the dosages tested and mortality observed was 100 per cent after 24 h of exposure.

INTERPRETATION & CONCLUSION

Deltacide when tested in the form of ULV cold aerosol, the dosage 0.01 ml/m2 was effective against both Ae. aegypti, and An. stephensi, and 0.02 ml/m2 against Cx. quiquefasciatus, causing 100 per cent mortality. The efficacy of ULV application of deltacide against vector mosquitoes needs to be assessed under field conditions.

Efficacy of thermal fog application of deltacide, a synergized mixture of pyrethroids, against Aedes aegypti, the vector of dengue

We evaluated the efficacy of indoor and peridomestic thermal fog applications of deltacide, a synergized mixture of pyrethroids (S-bioallethrin 0.7% w/v, deltamethrin 0.5% w/v and piperonyl butoxide 8.9% w/v) against adult populations of Aedes aegypti in Chennai, Tamil Nadu, India. We bioassayed adult caged mosquitoes, counted indoor resting and human landing adult mosquitoes and assessed the percentage of potential breeding sites with Aedes larvae. The bioassay mortalities indicated that the knockdown and killing effect was greater when fogging was applied inside houses rather than around them. Peridomestic thermal fogging reduced the resting and biting populations by 76% and 40%, respectively for the 3 days after treatment, whereas indoor fogging suppressed adult populations for 5 days.

Influence of pyrethroids and piperonyl butoxide on the Ca2+-ATPase activity of rat brain synaptosomes and leukocyte membranes

Pyrethroids are widely used insecticides of low acute toxicity in mammals but the consequences of long-term exposure are of concern. Their insecticidal action is related to neurotoxicity and, in addition, there are indications of mammalian immunotoxicity. In order to clarify structure-activity relationships of the membrane interactions of pyrethroids, the present study compared the influence of selected pyrethroids, i.e. permethrin and the more water soluble esbiol (S-bioallethrin), both type I, and cyfluthrin, type II, on the Ca(2+)-ATPase activity of rat brain synaptosomes and peritoneal leukocyte membranes. The pyrethroids were tested alone as well as mixed with the enhancing substance piperonyl butoxide (PBO) at concentration ratios of 1:5 and 1:10. At the highest concentration tested, permethrin (10 microM) alone inhibited the ATPase activity of leukocyte membranes by 20%, whereas the synaptosomes were affected less. Esbiol and cyfluthrin alone did not affect either membrane preparation significantly, whereas PBO (50 microM) alone caused 10-15% inhibition. Mixtures of either pyrethroid with PBO inhibited the ATPase activity of both types of membranes (up to 40% inhibition) in a synergistic manner, which always tended to be supra-additive. With esbiol a true potentiation took place. The synergistic interaction between pyrethroid and PBO was most apparent with mixtures of a concentration ratio of 1:5. The ATPase activity of leukocyte membranes tended to be more susceptible to inhibition than that of synaptosomes. The results are in accordance with the assumption that the mammalian toxicity of pyrethroids can be ascribed to a general disturbance of cell membrane function in neuronal tissue. The results indicate that it may also be the case in the immune apparatus.

Mammalian Voltage-Gated Calcium Channels Are Potently Blocked by the Pyrethroid Insecticide Allethrin

Pyrethroids are commonly used insecticides for both household and agricultural applications. It is generally reported that voltage-gated sodium channels are the primary target for toxicity of these chemicals to humans. The phylogenetic and structural relatedness between sodium channels and voltage-gated calcium (Ca) channels prompted us to examine the effects of the type 1 pyrethroid allethrin on the three major classes of mammalian calcium channels exogenously expressed in human embryonic kidney 293 cells. We report that all classes of mammalian calcium channels are targets for allethrin at concentrations very similar to those reported for interaction with sodium channels. Allethrin caused blockade with IC(50) values of 7.0 microM for T-type alpha(1G) (Ca(v)3.1), 6.8 microM for L-type alpha(1C) (Ca(v)1.2), and 6.7 microM for P/Q-type alpha(1A) (Ca(v)2.1) channels. Mechanistically, the blockade of calcium channels was found to be significantly different than the prolonged opening of mammalian sodium channels caused by pyrethroids. In all calcium channel subtypes tested, allethrin caused a significant acceleration of the inactivation kinetics and a hyperpolarizing shift in the voltage dependence of inactivation. The high-voltage-activated P/Q- and L-type channels showed a frequency of stimulation-dependent increase in block by allethrin, whereas the low-voltage-activated alpha(1G) subtype did not. Allethrin did not significantly modify the deactivation kinetics or current-voltage relationships of any of the calcium channel types. Our study indicates that calcium channels are another primary target for allethrin and suggests that blockade of different types of calcium channels may underlie some of the chronic effects of low-level pyrethroid poisoning.

Enhanced efficiency of electrostatically charged insecticide aerosols

The bioefficacy of a standard domestic aerosol insecticide has been compared with that of a similar spray in which the droplets were electrostatically charged. The aerosol was charged without the need for an external power supply, by enhancing natural charge separation processes that occur during atomisation. The charge-to-mass ratio achieved was 1.1 x 10(-4) C kg-1, compared with 2.2 x 10(-5) C kg-1 for the standard aerosol. Efficiency was assessed for insects in free flight. A direct space-spray application method was used to study the bioefficacy of these aerosols on houseflies, Musca domestica, and an indirect space-spray method on houseflies and mosquitoes, Culex quinquefasciatus. Two levels of concentration of active ingredients were compared. At low concentrations of 1.57 g kg-1 of bioallethrin and 0.29 g kg-1 of bioresmethrin, the charged aerosol achieved a significant reduction in KDT50 (time at which 50% of the flies were knocked down), compared with the standard aerosol. In the direct spray application to houseflies, the KDT50 was reduced by 50%, while in the indirect spray the KDT50 was reduced by 40%. In the indirect spray of mosquitoes, the KDT50 was reduced by 22%. With higher active ingredient concentrations of 2.09 g kg-1 for bioallethrin and 0.39 g kg-1 for bioresmethrin, the charged aerosol also demonstrated faster knockdown than the standard, but the improvement was less marked. In the direct spray application to houseflies, the KDT50 was reduced by 21% compared with the standard aerosol, while in the indirect spray the KDT50 was reduced by 16%. In the indirect spray of mosquitoes, the KDT50 was reduced by 24%. The percentage mortality after 24 h was also increased with the charged aerosol. Charge carried by the droplets results in increased interception of the insecticide, as the droplets are attracted to the insects in flight and space charge effects within the aerosol could cause improved dispersion in the test chamber.

Point mutations in domain III of a Drosophila neuronal Na channel confer resistance to allethrin

Voltage-gated sodium channels are the presumed site of action of pyrethroid insecticides and DDT. We screened several mutant sodium channel Drosophila lines for resistance to type I pyrethroids. In insecticidal bioassays the para(74) and para(DN7) fly lines showed greater than 4-fold resistance to allethrin relative to the allethrin sensitive Canton-S control line. The amino acid substitutions of both mutants are in domain III. The point mutation associated with para(74) lies within the S6 transmembrane region and the amino acid substitution associated with para(DN7) lies within the S4-S5 linker region. These sites are analogous to the mutations in domain II underlying knockdown resistance (kdr) and super-kdr, naturally occurring forms of pyrethroid resistance found in houseflies and other insects. Electrophysiological studies were performed on isolated Drosophila neurons from wild type and para(74) embryos placed in primary culture for three days to two weeks. The mutant para(74) sodium currents were kinetically similar to wild type currents, in activation, inactivation and time to peak. The only observed difference between para(74) and wild-type neurons was in the affinity of the type I pyrethroid, allethrin. Application of 500 nM allethrin caused removal of inactivation and prolonged tail currents in wild type sodium channels but had little or no effect on para(74) mutant sodium channels.

Time course and temperature dependence of allethrin modulation of sodium channels in rat dorsal root ganglion cells

Key effects of the pyrethroid insecticide allethrin, delivered to or washed out from cells at 10 or 100 microM in 0.1% DMSO, on neuronal Na(+) channel currents were studied in rat dorsal root ganglion (DRG) cells under whole-cell patch clamp. Tetrodotoxin-resistant (TTX-R) Na(+) channels were more responsive to allethrin than tetrodotoxin-sensitive (TTX-S) Na(+) channels. On application of 10 or 100 microM allethrin to cells with TTX-R Na(+) channels, the Na(+) tail current during repolarization developed a large slowly decaying component within 10 min. This slow tail developed multiphasically, suggesting that allethrin gains access to Na(+) channels by a multiorder process. On washout (with 0.1% DMSO present), the slow tail current disappeared monophasically (exponential tau=188+/-44 s). Development and washout rates did not depend systematically on temperature (12 degrees, 18 degrees, or 27 degrees C), but washout was slowed severely if DMSO was absent. As the duration of a depolarizing pulse was increased (range 0.32-10 ms), the amplitude of the slow component of the succeeding tail conductance first increased then decreased. Tail current amplitude had the same dependence on preceding pulse duration (at 18 degrees ) at 10 or 100 microM, consistent with allethrin modification of Na(+) channels at rest before opening. At 10 microM, slow tail conductance was at maximum 40% of the peak conductance during the previous depolarization, independent of temperature; evidently, the fraction of open modified channels did not change. However, at low temperature, the tail is more prolonged, bringing more Na(+) ions into a cell. In functioning neurons, this Na(+) influx would cause a larger depolarizing afterpotential, a condition favoring the repetitive discharges, which are signatory of pyrethroid intoxication.

In vitro effects of the pyrethroid S-bioallethrin on lymphocytes and basophils from atopic and nonatopic subjects

Synthetic pyrethroids are increasingly used as insecticides and marketed as having relatively low human toxicity. The aim of this study was to examine the in vitro effects of the synthetic pyrethroid S-bioallethrin on human blood lymphocytes and basophils in atopic individuals and nonatopic control subjects. S-bioallethrin caused inhibition of lymphocyte proliferation after a 72-h culture period in a concentration-dependent manner. The inhibition of the lymphocyte proliferation by S-bioallethrin at the concentration 6.5 microM correlated well with the total serum IgE values (r = -0.89, P < 0.001). Samples from atopic subjects were more sensitive to this inhibition than those from nonatopic volunteers. The regulatory interleukin-4/interferon-gamma (JL-4/IFN-gamma) balance showed a significant difference between atopic and nonatopic subjects after a short-term culture period (24 h) in the presence of the same concentration range of S-bioallethrin (P < 0.001). Additionally, IFN-gamma secretion was consistently lower in cells from the atopic donors. Furthermore, S-bioallethrin induced histamine release from human basophils in a concentration-dependent manner. Although the effect was small compared to histamine liberators such as N-formyl-Met-Leu-Phe and anti-IgE, the response to S-bioallethrin was significantly different in atopic donors from nonatopic (P = 0.0431). These findings are the first demonstration of the immunotoxicologic properties of the synthetic pyrethroid S-bioallethrin by this combined in vitro approach with human lymphocytes and basophils. Further studies will investigate the responses of lymphocytes from patients who are sensitive to these agents.

Effect of the pyrethroid insecticide allethrin on membrane fluidity

Allethrin is a widely used pyrethroid insecticide with an alkenylmethylcyclopentenolone group in its structure. We have analyzed its interaction with model and native membranes using DPH and its polar derivative TMA-DPH fluorescence polarization. Allethrin modified the bilayer order in the temperature range of the phase transition when incorporated into liposomes made with dimyristoyl-(DMPC), dipalmitoyl-(DPPC) and distearoyl-(DSPC) phosphatidylcholine. In DMPC: allethrin mixtures the pyrethroid decreased the bilayer order in the gel phase, without altering the liquid-crystalline one. In native membranes, DPH and TMA-DPH fluorescence polarization remained unchanged after incubation with allethrin. The release of hemoglobin was notably facilitated by the incorporation of allethrin into human erythrocytes. The results are discussed in terms of a possible aggregation of the insecticide in the lipid bilayer to create special domains with a consequent increase in membrane instability.

Effect of pyrethroid (allethrin and fenvalerate) on excitability changes following nerve impulse

Pyrethroid insecticides induce two different clinical symptoms. The difference has been reported to depend on the effect on the sodium channel opening time. We performed the present study to confirm this report by a double stimulation method. Allethrin (type I) 5 mg/kg and fenvalerate (type II) 1.5 kg/mg were injected into pentobarbital anesthetized rats. Tail nerve excitability was examined by a double stimulation method at from 4 msec to 40 msec intervals. The excitability was expressed as a percentage of the response to conditioned stimuli following supernormal stimuli to response to unconditioned stimuli. In control rats, the largest excitability was 94.6 +/- 19.2% at an 8 msec stimulus interval. After allethrin injection, we obtained two types of excitability changes. In some rats, supernormal excitability was present from 4 msec to 15 msec up to 120%. In other rats, the excitability was lower than that in the control from 4 msec to 15 msec. In fenvalerate treated rats, there was supernormal excitability from 4 msec to 40 msec. The peak of excitability was 122.4 +/- 35.3% at 10 msec. By double stimulation methods, we obtained characteristic nerve excitability changes in allethrin and fenvalerate treated rats after symptoms disappeared. These results showed that it should be possible to detect human nerve subclinical changes following lower doses or during chronic exposure.

Inhibition of phosphatase 2B prevents expression of hippocampal long-term potentiation

The induction of long-term potentiation (LTP) in the CA1 region of the hippocampus is mediated by N-methyl-D-aspartate (NMDA) receptor-coupled calcium influx. In addition, calcium/calmodulin (CaM) has been demonstrated to play an essential role in the induction process. In the present study, a possible role of CaM-dependent phosphatase (phosphatase 2B, PP-2B, calcineurin) in the LTP process was examined by intracellular recordings in apical dendrites of CA1 pyramidal cells of adult guinea-pigs. In dendrites in which cypermethrin, a potent and specific inhibitor of PP-2B (IC50 40 pM), was intracellularly applied, tetanization generated only short-term increases (15-30 min) of excitatory responses. In the intracellular presence of allethrin, a weak inhibitor of PP-2B, LTP expression was not affected. These findings demonstrate that activation of PP-2B is a necessary condition for the expression of LTP in CA1 pyramidal cell dendrites.

Interactions of the pyrethroid insecticide allethrin with liposomes

The action of allethrin, a pyrethroid with an alkenylmethylcyclopentenolone group, on the thermotropic properties of lipid vesicles has been investigated. Application of turbidimetry and differential scanning calorimetry to liposomes made with dimyristoyl- (DMPC), dipalmitoyl- (DPPC), and distearoyl- (DSPC) phosphatidycholine, containing variable concentrations of allethrin, showed that the pyrethroid lowers the temperature at which the phase transition of the phospholipid occurs. Furthermore, allethrin produces a broadening of the peak which marks the gel to liquid-crystalline phase transition. The appearance of a second peak as the allethrin concentration in the membranes rises indicates a limited miscibility of the pyrethroid in lipids. Incorporation of allethrin in carboxyfluorescein-trapped unilamellar liposomes, followed by incubation at several temperatures, enhances carboxyfluorescein release in allethrin-containing vesicles. The results are discussed in terms of a preferential localization of allethrin in an extended orientation in the bilayer with the carbonyl group of the alkenylmethylcyclopentenolone residue in the lipid water interface and the cyclopropanecarboxylate moiety between the hydrocarbon acyl chain of the phospholipids.

Neonatal exposure to a type-I pyrethroid (bioallethrin) induces dose-response changes in brain muscarinic receptors and behaviour in neonatal and adult mice

This study shows that neonatal exposure to the insecticide bioallethrin has a dose-dependent effect on muscarinic cholinergic receptors (MAChR) in the neonatal mouse, leading to permanent changes in MAChR and in spontaneous behaviour in adult mice. Neonatal NMRI mice, given oral doses of either bioallethrin or the vehicle, once daily between the 10th and 16th postnatal day, were killed at the age of 17 days or 1 week after the spontaneous motor behaviour tests at 4 months. The MAChR were assayed in the cerebral cortex by using the antagonist quinuclidinyl benzilate ([3H]QNB) and the agonist carbachol. In the 17-day-old mice bioallethrin exposure elicited a significant dose-dependent increase in the specific [3H]QNB binding. The competition study showed that the proportion of low-affinity binding was significantly increased in the 17-day-old mice compared with controls. In the adult mouse there was a significant dose-dependent decrease in specific [3H]QNB binding. In these adult mice the behavioural variables 'locomotion' and 'total activity' showed significant (P < or = 0.01) dose-dependent increases at all doses up to and including 0.70 mg/kg b.wt.

Differential sensitivity of tetrodotoxin-sensitive and tetrodotoxin-resistant sodium channels to the insecticide allethrin in rat dorsal root ganglion neurons

The pyrethroid insecticides are known to modify neuronal sodium channels to cause a prolongation of whole cell current. The sodium channels expressed in the dorsal root ganglion neurons of the rat are of two types, one highly sensitive to tetrodotoxin and the other highly resistant to tetrodotoxin. The pyrethroid allethrin exerted profound effects on tetrodotoxin-resistant sodium channels while causing minimal effects on tetrodotoxin-sensitive sodium channels. Currents derived from tetrodotoxin-resistant sodium channels were greatly prolonged during a step depolarization; the tail currents upon repolarization were also augmented and prolonged. In the tetrodotoxin-sensitive sodium channel currents, these changes caused by allethrin were much smaller or negligible. The activation and inactivation voltages of tetrodotoxin-resistant peak sodium currents were not significantly altered by allethrin. The differential action of allethrin on the two types of sodium channels would be important not only in identifying the target molecular structure but also in interpreting the symptoms of poisoning in mammals.

Mutagenic activity in synthetic pyrethroids in Salmonella typhimurium

Four pyrethroids, allethrin, resmethrin, permethrin and fenvalerate, were tested for mutagenicity in bacterial reversion assay systems with seven strains (TA1535, TA100, TA1538, TA98, TA1537, TA97 and TA104) of Salmonella typhimurium. Our results show that three pyrethroids, namely resmethrin, permethrin and fenvalerate, were not found to be mutagenic in S. typhimurium in the presence or absence of a rat liver activation system. Allethrin was found to be mutagenic with TA100, TA104 and TA97 strains and required metabolic activation (S9 mix) in order to show its activity, mainly with TA100 and TA104 strains.

Pyrethroids and the striatal dopaminergic system in vivo

1. Type I (permethrin and allethrin) or type II (cypermethrin and fenvalerate) pyrethroids caused 23-37% increases in the striatal content of the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC). 2. Toxicity symptoms and increases in DOPAC were associated with higher brain concentrations for type I (2.6-5.8 micrograms/gm) than type II pyrethroids (0.4-0.6 micrograms/gm). 3. No specific difference in the interaction between type I and II pyrethroids and the striatal dopaminergic system were recognized.

The effectiveness of mosquito coils containing esbiothrin under laboratory and field conditions

Tests were made to correlate the chemical content of mosquito coils with the knockdown and bite-inhibitory action of the smoke in the laboratory and with the protective effect in field use. Smoke from a blank coil, containing no pyrethroid, gave no knockdown, 10% inhibition of biting in the laboratory using Aedes aegypti, and 39% protection in field tests in village huts on the Kenyan coast with a mixed population of mosquitoes including 71% Anopheles gambiae. Coils containing low experimental contents of 0.044% and 0.099% Esbiothrin, an isomer blend rich in the D-allethrolone ester of D-trans-chrysanthemic acid, gave rapid knockdown in both small chamber and 25 m3 room tests, and 71% and 94% inhibition of biting respectively in the laboratory. In the field they gave 74% and 84% protection from mosquitoes alighting. Chemical content was therefore a good guide to knockdown and bite inhibition in the laboratory and also to the considerable protection found in the field.

Effects of pyrethroid insecticides on operant responding maintained by food

The pyrethroids are potent insecticides with low concomitant mammalian lethality when compared with other major insecticides. While high doses can lead to hyperactivity, tremors, convulsion and death, low doses have not been as well studied. Since operant behavior can be a sensitive measure of CNS function, male Holtzman rats were trained on a VR25 schedule maintained by 45 mg food pellets. Rats were injected IP with one of four different technical grade pyrethroids: permethrin, allethrin, deltamethrin and fenvalerate. All agents were effective in reducing operant responding and did so in a dose-dependent manner at levels 10 to 100 times below their LD50 values. Time course studies indicated a relatively short duration of action for the Type I agents of less than 60 min for permethrin and 15 min for allethrin. Type II agents were generally effective for greater than 60 min. Results of these studies indicate that operant responding maintained by food is a sensitive measure of the behaviorally disruptive effects of subconvulsive doses of pyrethroids.

Voltage-dependent gating of veratridine-modified Na channels

Na channels of frog muscle fibers treated with 100 microM veratridine became transiently modified after a train of repetitive depolarizations. They open and close reversibly with a gating process whose midpoint lies 93 mV more negative than the midpoint of normal activation gating and whose time course shows no appreciable delay in the opening or closing kinetics but still requires more than two kinetic states. Like normal activation, the voltage dependence of the modified gating can be shifted by changing the bathing Ca2+ concentration. The instantaneous current-voltage relation of veratridine-modified channels is curved at potentials negative to -90 mV, as if external Ca ions produced a voltage-dependent block but also permeated. Modified channels probably carry less current than normal ones. When the concentration of veratridine is varied between 5 and 100 microM, the initial rate of modification during a pulse train is directly proportional to the concentration, while the rate of recovery from modification after the train is unaffected. These are the properties expected if drug binding and modification of channels can be equated. Hyperpolarizations that close modified channels slow unbinding. Allethrin and DDT also modify channels. They bind and unbind far faster than veratridine does, and their binding requires open channels.

Effects of pyrethroids on lymphocyte mitogenic responsiveness

The in vitro effects of pyrethroids on the mitogenic responsiveness of murine splenic lymphocytes to concanavalin A (Con A) and lipopolysaccharide (LPS) have been determined. Mitogenic stimulation was measured by uptake of [6-3H]-thymidine. Permethrin and cypermethrin inhibited the mitogenic response to Con A over a concentration range of 1 X 10(-5) M to 5 X 10(-5) M. Relative to these pyrethroids, slightly lower concentrations of fenpropathrin were required to inhibit mitogenic responsiveness to Con A. Fluvalinate was least effective of the pyrethroids tested, and caused mitogenic inhibition at concentrations of 1.5 X 10(-5) M to 5 X 10(-5) M. Unlike the other pyrethroids, concentrations of fluvalinate as high as 1 X 10(-4) M did not result in complete inhibition of the mitogenic response to Con A. Allethrin, was the most potent inhibitor, with effective concentrations in the range of 1 X 10(-6) M to 1.5 X 10(-5) M. Permethrin (3 X 10(-5) M) inhibited the mitogenic response at each of several concentrations of Con A tested, and did not cause a shift in the lymphocyte mitogenic dose-response to Con A. The mitogenic responsiveness to LPS was found to be inhibited by allethrin and permethrin at the same concentrations which inhibited the mitogenesis induced by Con A. The results support the possibility of immune suppression by pyrethroid exposure.

Effects of pyrethroids on lymphocyte membrane lipid packing order

The effects of pyrethroids on the membrane lipid packing order of murine splenic lymphocytes have been investigated by utilizing the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene. Fluorescence anisotropy and lifetime measurements indicated alterations in the environment of the probe at pyrethroid concentrations near 1 microM. Decreased packing order of membrane lipids was detected for permethrin and cypermethrin by decreased anisotropy values. Permethrin and cypermethrin decreased fluorescence lifetime over a concentration range similar to that causing anisotropy changes. Anisotropy was predominantly increased in the presence of fluvalinate and fenpropathrin, indicating pronounced quenching of fluorescence by these compounds. However, the anisotropy changes in response to fluvalinate and fenpropathrin occurred at concentrations which were similar to effective concentrations of permethrin and cypermethrin. Compared to the other pyrethroids tested, allethrin required approximately 10 fold higher concentrations to alter anisotropy and lifetime values. Effects of pyrethroids on the phase transition of dipalmitoyl phosphatidylcholine liposomes were also studied to give further insight into the membrane interactions of these compounds. Results from the liposomal system indicate that the effects of pyrethroids on membrane order which were observed in the lymphocyte may be generalizable to other cell types.

Involvement of cholinergic mechanism in the action of allethrin in insect CNS

Allethrin had a stimulating action on spontaneous discharges in the cockroach sixth abdominal ganglion superfused with an insect saline solution. This action at a low concentration (5 X 10(-8) M) of allethrin was abolished by either of d-tubocurarine, hexamethonium or atropine at 5 X 10(-4) M. It was also abolished by the treatment of ganglia with hemicholinium-3 or by low-calcium-high magnesium insect saline solution. However, treatment of these blocked ganglia with allethrin at more than 5 X 10(-7) M overcame the block, producing increased spontaneous activity. Allethrin had no effect on insect cholinesterase activity. These results may suggest that the stimulating action at a low concentration of allethrin may be mediated by the release of ACh from cholinergic terminals in ganglia.

Allethrin interactions with the nicotinic acetylcholine receptor channel

Interactions of the synthetic pyrethroid allethrin with the nicotinic acetylcholine (ACh) receptor/channel were studied in membranes from Torpedo electric organ. Allethrin did not inhibit binding of [3H]ACh to the receptor sites, but inhibited noncompetitively binding of [3H]perhydrohistrionicotoxin ([3H]H12-HTX) to the ionic channel sites in a dose-dependent manner. The inhibition constant (Ki) of [3H]H12-HTX binding in absence of receptor agonist was 30 micro M, while in presence of 100 micro M carbamylcholine it was 4 micro M. This inhibitory effect of allethrin had a negative temperature coefficient. The high affinity binding of allethrin to the channel sites of the nicotinic ACh-receptor may be indicative of a postsynaptic site of action for pyrethroids, in addition to their known action on the sodium channel.

Modification of nerve membrane sodium channels by the insecticide pyrethroids

1. The synthetic pyrethroids exert potent and selective actions on nerve membrane sodium channels. (+)-trans tetramethrin and (+)-trans allethrin cause repetitive discharges to be produced in the isolated crayfish and squid giant axons in response to a single stimulus as a result of an increase in depolarizing after-potential. 2. The latter effect is due to slowing of the sodium channel kinetics which causes a prolonged sodium current following the normal peak sodium current. 3. A kinetic model is proposed to account for the action of the pyrethroids in which the pyrethroid molecule binds to the sodium channels at both closed and open states to produce a modified open state. 4. (-)-trans and (-)-cis isomers of tetramethrin are ineffective in causing the effects, but prevent the active (+)-trans and (+)-cis isomers from exerting the effects. This stereospecificity provides us with an excellent opportunity for the study of binding sites of pyrethroids and other sodium channel modulators.

Modulation of nerve membrane sodium channels by chemicals

1. Modulations of sodium channel kinetics by grayanotoxins and pyrethroids have been studied using voltage clamped, internally perfused giant axons from crayfish and squid. 2. Grayanotoxin I and alpha-dihydrograyanotoxin II greatly depolarize the nerve membrane through an increase in resting sodium channel permeability to sodium ions. 3. Grayanotoxins modify a fraction of sodium channel population to give rise to a slow conductance increase with little or no inactivation, and the slow conductance-membrane potential curve is shifted toward hyperpolarization. This accounts for the depolarization. 4. The tail current associated with step repolarization during the slow current in grayanotoxins decays with a dual exponential time course. 5. (+)-trans tetramethrin and (+)-trans allethrin also modify a fraction of sodium channel population in generating a slow current, which attains a maximum slowly and decays very slowly during a maintained depolarizing step. The membrane is depolarized only slightly. 6. The tail current associated with step repolarization during the slow current in the pyrethroids is very large in initial amplitude and decays very slowly. 7. The rate at which the sodium channel arrives at the modified open state in the presence of pyrethroids is expressed by a dual exponential function, and the slow phase disappears following removal of the sodium inactivation mechanism by internal perfusion of pronase. 8. A kinetic model is proposed to account for the actions of both grayanotoxins and pyrethroids on sodium channels. Both chemicals interact with the channel at both open and closed states to yield a modified open state which results in a slow sodium current.