Piperonyl Butoxide Treatment Research Articles

Resistance intensity status of Anopheles gambiae s.l. species at KOLOKOPE, eastern plateau Togo: A potential site to assess new vector control tools

According to WHO recommendations, the deployment of the next generation of Long-Lasting Insecticidal Nets (LLINs) for malaria vector control requires appropriate investigations on the insecticide resistance profile of the vector. Most of the next generation of LLINs are impregnated with a combination of pyrethroid insecticides and piperonyl butoxide (PBO), a synergist with an additional impact on the increase in the mortality rate of Anopheles gambiae s.l. (Diptera: Culicidae). Kolokopé is a cotton-growing area in the central region of Togo characterized by an intensive use of agricultural pesticides and insecticides where there is a phase II experimental hut station. For the characterization of the site, WHO susceptibility tests using diagnostic doses of ten insecticides, PBO synergist assays and intensity assays of three pyrethroids (5x and 10x) were conducted on adult female mosquitoes obtained from larvae collected around the site. Anopheles gambiae s.l. from Kolokopé showed high resistance to pyrethroids and DDT, but to a lesser extent to carbamates and organophosphates. Likewise, high intensity of resistance to pyrethroid was observed with less than 40% mortality at 10x deltamethrin, 52 and 29% mortality at 10x permethrin and 10x alphacypermethrin, respectively. Also, PBO treatment resulted in increased mortality which was higher than the mortality rate at 10x doses of pyrethroids. The high pyrethroid intensity resistance recorded at Kolokopé could be mainly due to the selection pressure on An. gambiae s.l. caused by the excessive use of insecticide in agriculture. These results can be used to assess the next generation of LLINs either in experimental hut or at a community trial.

Effects of piperonyl butoxide on exploratory behaviour in female mice.

Previous studies reported that piperonyl butoxide (PBO) induces adverse effects on exploratory behaviour in male mice. However, no consistent effects of PBO treatment were observed in female mice. This study aimed to evaluate PBO's neurobehavioral effects in female mice. Female mice were exposed to PBO through diet to provide levels of 0 (control), 0.025%, 0.1%, and 0.4% from 5 to 12 weeks of age, and selected behavioural parameters were measured. The average female body weight showed no significant effect from PBO treatment through the experimental periods. Regarding multiple-T water maze performance at 10 weeks of age, no significant effect caused by PBO treatment was observed. Exploratory behaviour examination of 8-week-old female mice indicated that the average speed declined in a significant dose-related manner, and the longitudinal pattern indicated a significant difference between the control and high-dose groups. For exploratory behaviour examination at 11 weeks of age, the total exploration distance shortened in a significant dose-related manner, and the average speed declined similarly. These longitudinal patterns showed significant differences between the control and high-dose groups. The PBO dose levels in this study produced several adverse effects on exploratory behaviour in female mice.

Contribution of non-target-site resistance in imidazolinone-resistant Imisun sunflower

ABSTRACT The first commercial herbicide-resistant trait in sunflower (Helianthus annuus L.) is known as ‘Imisun’. Imidazolinone resistance in Imisun cultivars has been reported to be genetically controlled by a major gene (known as Imr1 or Ahasl1-1) and modifier genes. Imr1 is an allelic variant of the Ahasl1 locus that codes for the acetohydroxyacid synthase, which is the target site of these herbicides. The mechanism of resistance endowed by modifier genes has not been characterized and it could be related to non-target-site resistance. The objective of this study was to evaluate the role of cytochrome P450 monooxygenases (P450s) in Imisun resistance. The response to imazapyr herbicide in combination with P450s inhibitor malathion was evaluated in 2 Imisun lines, IMI-1 and RHA426. Malathion reduced herbicide efficacy in both lines, but IMI-1 was affected in a greater extent. A significant reduction in plant growth in response to P450s inhibitors 1-aminobenzotriazole and piperonyl butoxide treatment was detected in the Imisun line HA425. The increased susceptibility to imazapyr after P450s-inhibitor treatment indicates that herbicide metabolism by P450s is a mechanism involved in Imisun resistance. These results also suggest the involvement of different P450s isozymes in endowing resistance to imazapyr in Imisun cultivars.

Reproductive and neurobehavioral effects of maternal exposure to piperonyl butoxide (PBO) in F1 -generation mice.

Female mice were exposed maternally to piperonyl butoxide (PBO) through diet to provide levels of 0 (control), 0.015, 0.03, and 0.06% during gestation and lactation periods, and selected reproductive and neurobehavioral parameters were measured in F1 generation. There was no adverse effect of PBO on litter size, litter weight, or sex ratio at birth. The average body weights of offspring showed no significant effects of PBO treatment through the lactation period in both sexes except for the low-dose group of females on PND 21. With respect to behavioral developmental parameters, swimming direction of female offspring on PND 7 was significantly accelerated in the low-dose group (p = 0.022). Exploratory behavior examination in male offspring indicated that total distance and movement time shortened significantly in dose-related manners (p = 0.0138 and 0.00231, respectively), average time of rearing lengthened significantly in a dose-related manner (p = 0.00814), and the frequencies of mice with urination was increased significantly in a dose-related manner (p < 0.05). For spontaneous behavior examination, the average time of movement in males and average time of rearing in females showed slightly dose-related effects in the F1 generation. The dose levels of PBO in the present study produced some adverse effects in neurobehavioral parameters in mice.

Effects of dietary quercetin on performance and cytochrome P450 expression of the cotton bollworm, Helicoverpa armigera.

Quercetin is ubiquitous in terrestrial plants. The cotton bollworm Helicoverpa armigera as a highly polyphagous insect has caused severe crop losses. Until now, interactions between this pest and quercetin are poorly understood at the biochemical and molecular levels. In this study, we investigated the in vivo effects of quercetin on performance of cotton bollworm and on cytochrome P450 (P450) expression. Deleterious effects of quercetin on the performance of the cotton bollworm, including growth, survival, pupation and adult emergence were observed after oral administration of 3 and 10 mg g(-1) quercetin to larvae since the third instar, whereas no significant toxic effect was found at 0.1 mg g(-1) quercetin treatment. Piperonyl butoxide treatment enhanced the toxicity of quercetin. In vitro metabolism studies showed that quercetin was rapidly transformed by gut enzymes of fifth instar larvae of the cotton bollworm. qRT-PCR results revealed that the effect of quercetin on P450 expression was tissue- and dose-specific. Quercetin regulated P450 expression in a mild manner, and it could serve as P450 inducer (CYP337B1, CYP6B6) or repressor (CYP337B1, CYP6B7, CYP6B27, CYP9A14, CYP6AE11, and CYP4M7). These findings are important for advancing our understanding of the biochemical and molecular response of insects to plant toxins and have implications for a smart pest control.

The Importance of Oxidases in the Tolerance of Deciduous Leaf Infusions by Aedes (Stegomyia) aegypti and Aedes (Stegomyia) albopictus (Diptera: Culicidae)

Aedes (Stegomyia) aegypti (L.) and Aedes (Stegomyia) albopictus (Skuse) larvae rely on oxidases to reduce toxicity of water soluble toxins from some senescent tree leaf infusions. The mortality of third instar Ae. aegypti larvae in live oak and pin oak leaf infusions increased significantly in the presence of piperonyl butoxide (PBO), a broad inhibitor of cytochrome P450s (CYPs). In contrast, PBO treatment did not increase mortality in water controls or infusions of northern red oak or sugar maple leaf infusions for Ae. aegypti larvae. A similar pattern was observed for Ae. albopictus larvae, that is, an increase in mortality when CYPs were inhibited in live oak leaf infusions and no increase in sugar maple leaf infusions or water controls. However, the fresh live oak leaf infusion (5 d old) was the most toxic infusion to Ae. aegypti, but appeared less toxic to Ae. albopictus than the older infusions. A direct comparison of survival between the two Aedes species revealed Ae. aegypti exhibited a greater mortality than Ae. albopictus in PBO-treated live oak leaf infusions. These findings suggest that toxic components of some leaf litter in larval habitats may impose cryptic energy costs (detoxification).

Effects of pyperonyl butoxide on the female reproductive tract in rats

This study was investigated the effects of piperonyl butoxide (PBO) on the female reproductive tract. Female Crj:Donryu rats were fed a basal diet containing 5,000, 10,000 or 20,000 ppm PBO for 28 days, and compared with food-restricted rats of comparable body weights to those in the PBO 10,000 or 20,000 ppm groups. Although treatment with 20,000 ppm PBO for 28 days depressed body weight gain, the abnormal estrous cyclicity, mainly prolonged diestrus, was also induced by the PBO treatment which was not correlated with body weight change. 20,000 ppm PBO treatment markedly decreased uterine weights and slightly decreased ovarian weights. 10,000 and 20,000 ppm PBO treatment increased liver weights. These cycle and organ weight changes were linked to atrophic uterus and increased atretic follicles in the ovary. In hormone assays, PBO at both doses reduced serum E2 levels, but did not affect corticosterone levels. An anti-uterotrophic assay showed a slight but significant decrease in absolute uterine weight and a reduction of endometrial epithelium height in the 20,000 ppm group. PBO was positive in an ER α antagonist reporter gene assay, although the activity was much weaker than that of 4-hydroxytamoxifen. These results indicate that high-dose PBO treatment directly induces atrophic changes in the female reproductive tract in rats, and these effects are likely the result of a hypoestrogenic state and the anti-estrogenic activity of PBO.

Oxidative and apoptotic effects of lambda-cyhalothrin modulated by piperonyl butoxide in the liver of Oreochromis niloticus

The aim of this study was to investigate the toxic effects of pyrethroid pesticide lambda-cyhalothrin in the presence of piperonyl butoxide as a modulator in the liver of juvenile Oreochromis niloticus. LC50 (96h) value of lambda-cyhalothrin was determined as 2.901μg/L for O. niloticus. The fish were exposed to 0.48μg/L (1/6 of the 96-h LC50) lambda-cyhalothrin and 10μg/L piperonyl butoxide for 96-h and 15-d. tGSH, GSH, GSSG, Hsp70 and TBARS contents, GPx, GR, GST and caspase-3 enzymes activities were determined. Lambda-cyhalothrin caused increases in tGSH, GSH, TBARS contents, and GST activity. Piperonyl butoxide treatment with lambda-cyhalothrin caused significant increases in tGSH GSH, Hsp70, TBARS contents, and GPx and GST activities while caspase-3 activity was decreased. The results of the present study revealed that lambda-cyhalothrin caused oxidative stress which upregulated GSH and GSH-related enzymes. Piperonyl butoxide increased the oxidative stress potential and apoptotic effects of lambda-cyhalothrin.

Insecticide detoxification indicator strains as tools for enhancing chemical discovery screens

Insecticide discovery screens carried out on whole organisms screen for potency resulting from chemical activity at the target site. However, many potentially insecticidal compounds are naturally detoxified in vivo and do not make it to the target site. It is hypothesised that insect strains with their xenobiotic detoxification machinery compromised could be used to identify such compounds that normally fail to show up in screens; these compounds could then be more rationally designed to increase their bioavailability. This strategy was tested with transgenic Drosophila lines with altered expression of Cyp6g1 and Dhr96. It was observed that Cyp6g1 knockdown transgenic lines have increased susceptibility to the test compound imidacloprid, while Dhr96 knockdown transgenic lines are resistant. Evidence was found for a systemic response to xenobiotic exposure, uncovered by piperonyl butoxide treatment and by gene expression profiling. Sex-specific gene expression regulated by DHR96 was also observed. The results confirm that this approach to chemical discovery could identify compounds that escape traditional screens. The complexity of the system means that a panel of single and multiple gene knockdown transgenic lines may be required.

Oxidative DNA damage and reporter gene mutation in the livers of gpt delta rats given non-genotoxic hepatocarcinogens with cytochrome P450-inducible potency

Previous reports have proposed that reactive oxygen species resulting from induction of cytochrome P450 (CYP) isozymes might be involved in the modes of action of hepatocarcinogens with CYP-inducible potency. In the present study, we investigated 8-hydroxydeoxyguanosine (8-OHdG) levels, in vivo mutagenicity and glutathione S-transferase placental form (GST-P)-positive foci in the livers of gpt delta rats treated with piperonyl butoxide (PBO) or phenobarbital (PhB) for 4 and 13 weeks. Significant elevations in Cyp 1A1 and Cyp 1A2 mRNA levels after PBO treatment, and in Cyp 2B1 mRNA levels after PBO or PhB treatment, appeared together with remarkable hepatomegaly through the experimental period. Time-dependent and statistically significant increases in 8-OHdG levels were observed in the PBO treatment group along with significant increases in proliferating cell nuclear antigen (PCNA)-positive hepatocytes at 4 weeks, while no increase in 8-OHdG levels was found in PhB-treated rats. No changes in mutant frequencies of gpt and red/gam (Spi(-)) genes in liver DNA from PBO- or PhB-treated rats were observed at 4 or 13 weeks. A 13-week exposure to either PBO or PhB did not affect the number and area of GST-P-positive hepatocytes. CYP 1A1 and 1A2 induction may be responsible for elevated levels of 8-OHdG in PBO-treated rats. However, neither GC:TA transversions nor deletion mutations, typically regarded as 8-OHdG-related mutations, were observed in any of the treated rats. We conclude that reactive oxygen species, possibly produced through CYP catalytic pathways, likely induced genomic DNA damage but did not give rise to permanent gene mutation.

Changes to oxfendazole chiral kinetics and anthelmintic efficacy induced by piperonyl butoxide in horses

The study of novel pharmacological strategies to control parasitism in horses is required since many parasite species have developed resistance to anthelmintic drugs. To evaluate the effects of piperonyl butoxide (PB) (a metabolic inhibitor) on the plasma availability and enantiomeric behaviour of oxfendazole (OFZ) given orally to horses, and to compare the clinical efficacy of OFZ given either alone or co-administered with PB in naturally parasitised horses. Fifteen naturally parasitised crossbred male ponies were allocated into 3 groups (n = 5) and treated orally as follows: Group I (control) received distilled water as placebo; Group II was dosed with OFZ (10 mg/kg bwt); and Group III was treated with OFZ (10 mg/kg bwt) co-administered with PB (63 mg/kg bwt). Jugular blood samples were obtained over 120 h post treatment. Three weeks after treatments, all experimental horses were subjected to euthanasia. The observed maximum plasma concentration (Cmax) and area under the concentration vs. time curve (AUC) values for OFZ increased 3- and 5-fold, respectively, in the presence of PB. The plasma concentration profiles of fenbendazole (FBZ), a metabolite generated from OFZ, were significantly lower after the treatment with OFZ alone (AUC = 0.8 microg x h/ml) compared to those obtained after the OFZ + PB treatment (AUC = 2.7 microg x h/ml). The enhanced pharmacokinetic profiles correlated with increased anthelmintic efficacy. The combination OFZ + PB showed 100% efficacy against mature nematode parasites. The efficacy against cyathostome L3 larvae increased from 94% (Group II) to 98.7% (Group III). Consistently, the number of L4 larvae recovered from OFZ + PB treated horses (Group III) (n = 146) was significantly lower (P<0.05) than that recovered from Group II (n = 1397). The use of PB as a metabolic inhibitor may be useful to enhance OFZ activity against mature and migrating larvae of different parasite species in horses. Metabolic inhibitors may be used to enhance the activity of benzimidazole anthelmintics and extend the effective lifespan of benzimidazole drugs in the face of increasing resistance.

Evaluation of Piperonyl Butoxide as a Deltamethrin Synergist for Pyrethroid-Resistant Bed Bugs

An understanding of the mechanisms of insecticide resistance in the bed bug, Cimex lectularius L., has the potential to lead to new approaches for the control of resistant populations. We used the cytochrome P450 monooxygenase (P450) inhibitor piperonyl butoxide (PBO) to assess the role of P450s in deltamethrin resistance in three field-collected bed bug strains, LA-1, CIN-1 and WOR-1. In addition, we exposed two highly resistant strains, CIN-1 and WOR-1 (resistance ratio [RR] >2,500-fold), to dry residues of piperonyl butoxide-synergized pyrethroid formulations to determine the utility of synergism by PBO. Piperonyl butoxide synergized deltamethrin in all three strains, but its impact was variable. The synergistic ratio varied from 40 in CIN-1 to 176 in WOR-1. Because the resistance ratio for each strain after piperonyl butoxide treatment was 174 and 39, respectively, our results suggest that P450s have some involvement in deltamethrin resistance, but other resistance mechanisms must be involved as well. No significant synergistic effect of formulated deltamethrin was observed with the addition of synergized pyrethrins or formulated piperonyl butoxide in the CIN-1 strain, but synergism occurred in the WOR-1 strain. Addition of PBO to pyrethroids is not a comprehensive solution to pyrethroid resistance because strains vary in both overall resistance level and the proportion of that resistance attributable to P450s.

Piperonyl butoxide activates c-Jun and ATF-2 in the hepatocytes of mice

In order to clarify the possible mechanism of hepatocarcinogenesis induced by piperonyl butoxide, we attempted to identify the transcription factor activated by piperonyl butoxide in the male ICR mouse liver. Administration of 0.6% piperonyl butoxide for 24 h elevated the level of liver nuclear proteins that bind to an AP-1 consensus oligonucleotide, and these proteins demonstrated a supershift with the anti-c-Jun antibody. Additionally, immunoblot analysis revealed that piperonyl butoxide induced c-Jun phosphorylation within 8 h of administration, and phosphorylated ATF-2 was detected after 24 h of piperonyl butoxide treatment. Immunohistochemical analysis also demonstrated the presence of phosphorylated ATF-2 in the hepatocyte nuclei of mice fed with 0.6% piperonyl butoxide for 24 h. Furthermore, piperonyl butoxide induced ATF-2 phosphorylation in TLR-3, a mouse immortalized hepatocyte cell line. These results indicated that piperonyl butoxide activated c-Jun and ATF-2 in mouse hepatocytes during the early stage of hepatocarcinogenesis.

Piperonyl butoxide induces the expression of cytochrome P450 and glutathione S‐transferase genes in Drosophila melanogaster

Piperonyl butoxide (PBO) is an insecticide synergist known to inhibit the activity of cytochrome P450 enzymes. PBO is currently used in some insecticide formulations, and has also been suggested as a pretreatment for some pesticide applications. Little is known about how insects respond to PBO exposure at the gene transcription level. The authors have characterised the transcriptional response of the Drosophila melanogaster genome after PBO treatment, using both a custom-designed 'detox' microarray, containing cytochrome P450 (P450), glutathione S-transferase (GST) and esterase genes, and a full genome microarray. A subset of P450 and GST genes is identified, along with additional metabolic genes, that are induced by PBO. The gene set is an extremely similar gene set to that induced by phenobarbital, a compound for which pretreatment is known to confer tolerance to a range of insecticide compounds. The implications of the induction of gene families known to metabolise insecticides and the use of PBO in pest management programs are discussed.

Phenobarbital induction of permethrin detoxification and phenobarbital metabolism in susceptible and resistant strains of the beet armyworm Spodoptera exigua (H�bner)

The permethrin resistant strain (TR-strain) of the beet armyworm, Spodoptera exigua (Hübner), has 92.5-fold resistance to permethrin (at LD50 level) compared to the permethrin susceptible strain (TS-strain). Bioassay involving permethrin mixed with piperonyl butoxide, an inhibitor of microsomal cytochrome P450s, significantly reduced the resistance ratio from 92.5- to 7.9-fold. However, S,S,S-tributylphosphorotrithioate and diethylmaleate which are inhibitors of esterases and glutathione S-transferase, respectively, did not affect the resistance level. These results indicate that the detoxification of permethrin in the TR-strain was primarily due to the cytochrome P450 monooxygenases. LD50 for permethrin was increased to 4.5-fold by the pre-treatment of phenobarbital in the TS-strain. The effect of induction by phenobarbital was almost completely overcome by the piperonyl butoxide treatment. However, it was observed that phenobarbital treatment did not cause any change in the toxicity of permethrin to TR strain. Since this result deviated from the expectation that the metabolism of phenobarbital in the TR-strain should be greater than that in the TS-strain, it was deemed necessary to compare the metabolism of phenobarbital between the TS- and TR-strains. Comparison was made based on the concentration of phenobarbital in the hemolymph and whole body. The results showed no significant difference in phenobarbital treatment between the two strains used in this study suggesting the possibility that the induction system in TS-strain is different from the TR-strain.

Phenobarbital induction of permethrin detoxification and phenobarbital metabolism in susceptible and resistant strains of the beet armyworm Spodoptera exigua (Hübner)

The permethrin resistant strain (TR-strain) of the beet armyworm, Spodoptera exigua (Hübner), has 92.5-fold resistance to permethrin (at LD 50 level) compared to the permethrin susceptible strain (TS-strain). Bioassay involving permethrin mixed with piperonyl butoxide, an inhibitor of microsomal cytochrome P450s, significantly reduced the resistance ratio from 92.5- to 7.9-fold. However, S, S, S-tributylphosphorotrithioate and diethylmaleate which are inhibitors of esterases and glutathione S-transferase, respectively, did not affect the resistance level. These results indicate that the detoxification of permethrin in the TR-strain was primarily due to the cytochrome P450 monooxygenases. LD 50 for permethrin was increased to 4.5-fold by the pre-treatment of phenobarbital in the TS-strain. The effect of induction by phenobarbital was almost completely overcome by the piperonyl butoxide treatment. However, it was observed that phenobarbital treatment did not cause any change in the toxicity of permethrin to TR strain. Since this result deviated from the expectation that the metabolism of phenobarbital in the TR-strain should be greater than that in the TS-strain, it was deemed necessary to compare the metabolism of phenobarbital between the TS- and TR-strains. Comparison was made based on the concentration of phenobarbital in the hemolymph and whole body. The results showed no significant difference in phenobarbital treatment between the two strains used in this study suggesting the possibility that the induction system in TS-strain is different from the TR-strain.

Studies on some enzymes involved in insecticide resistance in fenitrothion-resistant and -susceptible strains of Musca domestica L. (Dipt, Muscidae)

Abstract: The toxicity of fenitrothion and fenitrothion plus synergists was determined by topical application to adults of fenitrothion-resistant (571ab) and -susceptible (Cooper) strains of Musca domestica L. The strain 571ab was 232-fold resistant to fenitrothion when compared with the Cooper strain. Co-administration of fenitrothion with three synergists, namely piperonyl butoxide (PBO), tributylphosphorotrithioate (DEF) and diethyl maleate (DEM) was investigated, respectively, at 1 : 5, 1 : 5 and 1 : 10 ratio. This co-administration of fenitrothion with PBO, DEF and DEM caused a decrease in the doses which produced 50% lethality (LD50s) in 571ab but had no synergistic effect on fenitrothion toxicity was observed in the Cooper strain. The effect of topical application of fenitrothion alone and in combination with PBO, DEF and DEM at the LD50 level on some enzyme activities in 571ab and Cooper strains was examined. The application of fenitrothion alone and in combination with DEF and DEM at LD50 level caused a significant decrease in activities of total esterases, acetylcholinesterase (AChE) and glutathione S-transferase (GST) in the 571ab strain. The decrease in GST activity was not significant in treated flies of the Cooper strain when compared with GST activity of control flies. A non-significant effect on total cytochrome P450 level was observed with fenitrothion alone and the fenitrothion + PBO treatment. No increase in activity level of total esterases, AChE and GST was found, which might suggest that changes in activity level of these enzymes are not related to fenitrothion resistance in the 571ab strain.

Plasma achiral and chiral pharmacokinetic behaviour of intravenous oxfendazole co-administered with piperonyl butoxide in sheep.

Co-administration of piperonyl butoxide (PB) potentiates fenbendazole (FBZ) in small ruminants. The resultant increase in bioavailability of FBZ and its metabolite oxfendazole (OFZ) has important implications for the efficacy of these drugs against benzimidazole (BZD)-resistant strains of Teladorsagia circumcincta. This study evaluated the racemic (achiral) and enantiomeric (chiral) plasma disposition kinetics of OFZ and its metabolites after the co-administration of PB and OFZ in sheep. Six 6-8-month-old, parasite-free, female Dorset sheep (30-40 kg) were used in a two-phase crossover experiment. In phase I, three sheep received 30 mg/kg PB orally, followed by a single intravenous (i.v.) injection of OFZ at 5 mg/kg. The other three animals were treated similarly except that 5 mL of water replaced PB. In phase 2, treatments for the two groups were reversed and were given 14 days after the initiation of phase I. Three analytes OFZ, FBZ and fenbendazole sulphone (FBZSO(2)) were recovered in plasma up to 48 h post-treatment in both experimental groups. Achiral and chiral pharmacokinetic (PK) profiles for OFZ, after the co-administration of PB, were characterized by a significantly greater area under the concentration--time curve (AUC) and a longer mean residence time (MRT). Chiral OFZ distribution ratios were comparable in both treatment groups. Piperonyl butoxide treatment markedly influenced the plasma PK profiles for FBZ and FBZSO(2) following OFZ administration. Production of FBZ was enhanced as reflected by increased (> 60%) AUC, delayed T(max) and a significantly delayed (> 45%) elimination (t(1/2)(el)). Although AUC values for FBZSO(2) were not significantly different between groups, this metabolite was depleted more slowly from plasma (t(1/2)(el) > 60% and MRT > 42%) following PB treatment. This study demonstrated that PB co-administration is associated with an inhibition of OFZ biotransformation, as evidenced by the significantly higher plasma concentrations of OFZ and FBZ, and this could have important implications in terms of anti-parasite therapy against BZD-resistant parasite strains.

Pyrethroid resistance and cross-resistance in the German cockroach, Blattella germanica (L).

A German cockroach (Blatella germanica (L)) strain, Apyr-R, was collected from Opelika, Alabama after control failures with pyrethroid insecticides. Levels of resistance to permethrin and deltamethrin in Apyr-R (97- and 480-fold, respectively, compared with a susceptible strain, ACY) were partially or mostly suppressed by piperonyl butoxide (PBO) and S,S,S,-tributylphosphorotrithioate (DEF), suggesting that P450 monooxygenases and hydrolases are involved in resistance to these two pyrethroids in Apyr-R. However, incomplete suppression of pyrethroid resistance with PBO and DEF implies that one or more additional mechanisms are involved in resistance. Injection, compared with topical application, resulted in 43- and 48-fold increases in toxicity of permethrin in ACY and Apyr-R, respectively. Similarly, injection increased the toxicity of deltamethrin 27-fold in ACY and 28-fold in Apyr-R. These data indicate that cuticular penetration is one of the obstacles for the effectiveness of pyrethroids against German cockroaches. However, injection did not change the levels of resistance to either permethrin or deltamethrin, suggesting that a decrease in the rate of cuticular penetration may not play an important role in pyrethroid resistance in Apyr-R. Apyr-R showed cross-resistance to imidacloprid, with a resistance ratio of 10. PBO treatment resulted in no significant change in the toxicity of imidacloprid, implying that P450 monooxygenase-mediated detoxication is not the mechanism responsible for cross-resistance. Apyr-R showed no cross-resistance to spinosad, although spinosad had relatively low toxicity to German cockroaches compared with other insecticides tested in this study. This result further confirmed that the mode of action of spinosad to insects is unique. Fipronil, a relatively new insecticide, was highly toxic to German cockroaches, and the multi-resistance mechanisms in Apyr-R did not confer significant cross-resistance to this compound. Thus, we propose that fipronil could be a valuable tool in integrated resistance management of German cockroaches.

Regulation of hepatic CYP1A isozymes by piperonyl butoxide and acenaphthylene in the mouse

The regulation of CYP1A1 and CYP1A2 isozymes by piperonyl butoxide (PBO) and acenaphthylene (ACN) was studied in the liver of male C57BL/6 and DBA/2 mice. These two cytochrome P450 genes are known to be regulated by the aromatic hydrocarbon-responsive receptor (AHR); however, it has been suggested that CYP1A2 is also induced by an AHR-independent mechanism. In this study, PBO induced hepatic CYP1A1 considerably more in C57BL/6 ( Ahr b−1 ) than in DBA/2 ( Ahr d ) mice. In addition, the superinduction of CYP1A1 in wildtype hepa1c1c7 cells, which is AHR-dependent, resulted from PBO and cycloheximide treatment of the cells. In other studies in this laboratory using AHR knock-out (AHR −/−) mice, a hybrid of 129/SV and C57BL/6 strains, no induction of CYP1A1 occurred with PBO or ACN. [D.-Y. Ryu, P.E. Levi, P. Fernandez-Salguero, F.J. Gonzalez, E. Hodgson, Mol. Pharmacol., 50 (1996) 443–446.] ACN, however, did not induce CYP1A1 under the experimental conditions used. These results suggest that PBO, but not ACN, induces CYP1A1 through a weak activation of AHR. On the other hand, hepatic CYP1A2 mRNA and hnRNA were induced by PBO in both C57BL/6 and DBA/2 strains, but were not induced by ACN, a strong inducer of CYP1A2 in the B6C3F1 strain. However, both PBO and ACN induced CYP1A2 in AHR −/− mice. It is assumed, therefore, that the transcriptional induction of CYP1A2 by PBO and ACN is AHR-independent. In addition, the induction of CYP1A2 by ACN depends upon the strain of mice. Immunohistochemical studies for CYP1A1/CYP1A2 apoproteins showed that PBO induced CYP1A1/CYP1A2 around the central veins as did 3-methylcholanthrene (3-MC). The induction of CYP1A1/CYP1A2 by ACN, however, was not observed, consistent with the northern blot results.