Mixed Function Oxidase Activity Research Articles

Effects of Sub Chronic Dermal Exposure of Gasoline Blended with Varying Concentration of Benzene on Hepatic Mixed Function Oxidases in Rats

Interaction of chemicals in a mixture, their biotransformation and adverse impact, if any, on environment and workroom atmosphere needs to be evaluated to identify the nature of potential toxic effects elicited by constituent chemical(s) in a mixture. The nature of chemical interaction(s) through which an individual chemical in a mixture undergoes metabolism and/or biotransformation in the target tissue could be helpful in evaluation of its toxic potential. Gasoline is a unique example of such chemical mixture where interaction of aromatics viz., benzene, toluene, ethyl benzene and xylene (BTEX) traverses through a common metabolic pathway involving cytochrome P-450 dependent mixed function oxidases. Travis et al. [1] has quantitatively evaluated that gasoline vapor has an antagonistic effect on benzene metabolism and its biotransformation products. It was reported that 1000 ppm gasoline vapor had the same inhibitory effect as 500 ppm toluene on the metabolism of 290 ppm benzene, indicating that there may be many confounding factors in gasoline which might affect the metabolism of benzene in turn affecting its toxicity at the molecular level. It has been reported that benzene causes myelotoxicity through its bioactive metabolites. Such biotransformation mechanisms involve cytochrome P-450 dependent Phase-I enzymes and the products are further detoxified through Phase-II enzymes. It was therefore considered pertinent to study the impact of gasoline blended with 1, 3 and 5% benzene concentrations. Female albino rats weighing 200–250 gm were exposed by dermal route to gasoline blended with varying benzene concentrations, @ 2 g/kg body wt., six days a week over a period of 90 days. The activities of hepatic mixed function oxidases, viz., aniline hydroxylase and aminopyrene demethylase as a monitor of Phase-I enzymes and Glutathione-S-Transferase for Phase-II enzyme was estimated along with free glutathione levels. Serum creatine kinase was also estimated to assess the extent of muscular dystrophy. The results of this sub chronic study will be discussed in the context of interaction of gasoline with varying concentration of benzene in experimental animals. Keywords: mixed function oxidases, benzene, toxicology, gasoline

Azinphos-methyl and carbaryl resistance in adults of the codling moth (Cydia pomonella (L.), Lepidoptera: Tortricidae) from Northeastern Spain

The resistance of Cydia pomonella (L.) to organophosphates is widespread throughout the pome fruit growing areas. The lethal effects of two insecticides inhibitors of the acetylcholine esterase, azinphos-methyl and carbaryl, were evaluated in adults of five and four field populations of the codling moth, respectively. The lethal concentrations (LC50 and LC90) of these insecticides were determined in a susceptible strain from Spain (S_Spain). Topical bioassays using the approximate LC90 values (3000mg (a.i.)/L of carbaryl and 2000mg (a.i.)/L of azinphos-methyl) that were obtained in S_Spain were tested as diagnostic concentrations. The enzymatic activities of mixed-function oxidases (MFO), glutathione S-transferases (GST) and esterases (EST) were measured to investigate their potential role in the detoxification of these insecticides.Carbaryl and azinphos-methyl caused ⩽53% and ⩽39% corrected mortality, respectively, in field populations, although the diagnostic concentrations applied were twofold and fourfold higher than the maximum concentration registered in Spain, respectively. The activities of MFO and GST were 7.3- to 16.1-fold higher and 2.5- to 3.7-fold higher in all the field populations compared to those in S_Spain, respectively.

Detection of mutagens and BaPMO inducers in river water using the Blue Cotton adsorption technique

Induction of Mixed Function Oxidase (MFO) activity and bioactivation potential were measured in experimental carp and in native fish species from two rivers with different pollution level (Sava and Mrežnica). The experimental carp were intraperitoneally exposed to various water volume equivalents of Blue Cotton extracts from both rivers. The induction of MFO measured as a Benzo(a)pyrene monooxygenase (BaPMO) activity was increased up to 9.3-fold in experimental carp and up to 11.3-fold in native fish from Sava River, whereas the values from Mrežnica River showed only a slight increase when compared with the control (highest increase of 1.8-fold in nose carp). Accordingly, bioactivation potential using modified Ames test was higher in both experiments with Sava River. Both measured parameters in experimental carp increased in a dose-dependent manner in accordance to river volume equivalents. Different induction potential of native fish species comparable between two rivers confirmed the known possibility of their usage in biomonitoring studies. These results give qualitatively a new support to the idea of using Blue Cotton extraction technique combined with induction of MFO activity and Ames test in fish as a good biomarker for assessing risk of exposure to mutagens/carcinogens such as Polycyclic Aromatic Hydrocarbons (PAHs), especially due to the simplicity and cost-effectiveness of these methods.

Amniotic Mesenchymal Stem Cells: A New Source for Hepatocyte-Like Cells and Induction of CFTR Expression by Coculture with Cystic Fibrosis Airway Epithelial Cells

Cystic fibrosis (CF) is a monogenic disease caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, with lung and liver manifestations. Because of pitfalls of gene therapy, novel approaches for reconstitution of the airway epithelium and CFTR expression should be explored. In the present study, human amniotic mesenchymal stem cells (hAMSCs) were isolated from term placentas and characterized for expression of phenotypic and pluripotency markers, and for differentiation potential towards mesoderm (osteogenic and adipogenic) lineages. Moreover, hAMSCs were induced to differentiate into hepatocyte-like cells, as demonstrated by mixed function oxidase activity and expression of albumin, alpha1-antitrypsin, and CK19. We also investigated the CFTR expression in hAMSCs upon isolation and in coculture with CF airway epithelial cells. Freshly isolated hAMSCs displayed low levels of CFTR mRNA, which even decreased with culture passages. Following staining with the vital dye CM-DiI, hAMSCs were mixed with CFBE41o- respiratory epithelial cells and seeded onto permeable filters. Flow cytometry demonstrated that 33–50% of hAMSCs acquired a detectable CFTR expression on the apical membrane, a result confirmed by confocal microscopy. Our data show that amniotic MSCs have the potential to differentiate into epithelial cells of organs relevant in CF pathogenesis and may contribute to partial correction of the CF phenotype.

Metabolic mechanisms involved in the resistance of field populations of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) to spinosad

Tuta absoluta (Meyrick) resistance to insecticides has become a significant problem in many tomato production areas in South America. New insecticides are now available for the management of this pest (i.e. spinosad), however there is scarce information about their efficacy on field populations. With the aim of determining the susceptibility of T. absoluta to spinosad we evaluated the response of second instar larvae, from five field populations (Azapa 1, Azapa 2, Lluta, Colín and Valdivia) and a laboratory reference strain (S), to a diagnostic concentration of the insecticide. We also determined the activity of the detoxifying enzymes mixed-function oxidases (MFO), glutathione- S-transferases (GST) and esterases (EST) in the same larval stage. Larval mortality in field populations was significantly lower in Azapa 1 (50.0%), Azapa 2 (44.9%), Lluta (39.9%) and Colín (53.5%) when compared to the laboratory strain (91.7%). MFO activities in field populations were between 1.8 and 4.6 times higher than those observed in the S strain, while for EST, the ratio varied from 1.7 to 14.7. The lowest ratios were observed for the GST (0.5–2.7), however, significant differences were detected for the three enzyme systems. We conclude that the evaluated mechanisms would be involved in spinosad resistance of populations of T. absoluta, presenting an increased MFO activity in all populations.

Effects of cold stress and ether stress on aminopyrine demethylation kinetics in vivo

Abstract The effect of cold stress and ether stress on mixed function oxidase activity in vivo has been studied using the aminopyrine-−14CO2 exhalation rate (CER) method. Cold stress following both acute and chronic exposure resulted in enhanced rate of demethylation of both aminopyrine (CER α half-life) and its monomethyl metabolite (CER β half-life). However the time course of the response to cold stress differs for the two demethylations. The characteristics of the cold-induced enhancement of aminopyrine-CER would appear to differ in several aspects from that reported for phenobarbitone pretreatment. In contrast, ether exposure did not produce any consistent effect on drug metabolizing status of the rat.

The effect of adrenalectomy on hepatic mixed function oxidase activity in female rats.

The effect of adrenalectomy on hepatic mixed function oxidase activity in female rats.

The effect of some benzimidazoles on the disposition of antipyrine and tolbutamide from the rat isolated perfused liver.

The anthelmintic benzimidazoles, mebendazole, albendazole and flubendazole have been screened for any propensity to alter the disposition of antipyrine and tolbutamide in the rat isolated perfused liver preparation. The benzimidazoles were added as a 2.5 mg bolus dose into the perfusate reservoir 5 min before the administration of either antipyrine or tolbutamide. Neither mebendazole or albendazole produced any significant effect on the pharmacokinetics of either of the substrate drugs. In contrast, flubendazole significantly decreased the clearance of antipyrine (by 40%) indicating inhibition of mixed function oxidase activity. However, flubendazole did not alter the disposition of tolbutamide. The results suggest that not all benzimidazoles inhibit hepatic drug metabolizing enzymes and that different forms of cytochrome P-450 are involved in the metabolism of antipyrine and tolbutamide.

Tools for Resistance Monitoring in Oriental Fruit Moth (Lepidoptera: Tortricidae) and First Assessment in Brazilian Populations

In southern Brazilian apple (Malus spp.) orchards, predominantly organophosphates are used to control the oriental fruit moth, Cydia molesta (Busck) (Lepidoptera: Tortricidae), but control failures often occur. Therefore the susceptibility of three C. molesta Brazilian populations was investigated to five insecticides of different groups and modes of action, in comparison with a susceptible laboratory strain mass reared in southern France for >10 yr. At the same time, comparative biochemical and genetic analysis were performed, assessing the activities of the detoxification enzymatic systems and sequencing a gene of insecticide molecular target to find out markers associated with resistance. The three Brazilian populations were significantly resistant to chlorpyrifos ethyl compared with the reference strain. One of the field populations that had been frequently exposed to deltamethrin treatments showed significant decreasing susceptibility to this compound, whereas none of the three populations had loss of susceptibility to tebufenozide and thiacloprid compared with the reference strain. All three populations had slight but significant increases of glutathione transferase and carboxylesterases activities and significant decrease of specific acetylcholinesterase activities compared with the reference. Only the most resistant population to chlorpyriphos exhibited a significantly higher mixed function oxidase activity than the reference. The acetylcholinesterase of females was significantly less inhibited by carbaryl in the Brazilian populations than in the reference strain (1.7-2.5-fold), and this difference was not expressed in the male moth. However, no mutation in the MACE locus was detected. These biological and molecular characterizations of adaptive response to insecticides in C. molesta provide tools for early detection of insecticide resistance in field populations of this pest.

Assessment of insecticide resistance in eggs and neonate larvae of Cydia pomonella (Lepidoptera: Tortricidae)

Spanish Cydia pomonella (L.) field populations have developed resistance to several insecticide groups. Diagnostic concentrations were established as the LC 90 calculated on a susceptible strain (S_Spain) for five and seven insecticides and tested on eggs and neonate larvae field populations, respectively. The three most relevant enzymatic detoxification systems (mixed-function oxidases (MFO), glutathione S-tranferases (GST) and esterases (EST)) were studied for neonate larvae. In eggs, 96% of the field populations showed a significantly lower efficacy when compared with the susceptible strain (S_Spain) and the most effective insecticides were fenoxycarb and thiacloprid. In neonate larvae, a significant loss of susceptibility to the insecticides was detected. Flufenoxuron, azinphos-methyl and phosmet showed the lowest efficacy, while lambda-cyhalothrin, alpha-cypermethrin and chlorpyrifos-ethyl showed the highest. Biochemical assays showed that the most important enzymatic system involved in insecticide detoxification was MFO, with highest enzymatic activity ratios (5.1–16.6 for neonates from nine field populations). An enhanced GST and EST activities was detected in one field population, with enzymatic activity ratios of threefold and fivefold for GST and EST, respectively, when compared with the susceptible strain. The insecticide bioassays showed that the LC 90 used were effective as diagnostic concentrations. Measures of MFO activity alongside bioassays with insecticide diagnostic concentrations could be used as tools for monitoring insecticide resistance in neonate larvae of C. pomonella.

Resistance of Spanish codling moth (Cydia pomonella) populations to insecticides and activity of detoxifying enzymatic systems

Resistance of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) to insecticides has become a major problem in many apple and pear production areas. Our aim was to determine the level of insecticide resistance in Spanish field populations. Seven field populations collected from apple, Malus domestica Borkhausen (Rosaceae), orchards and three laboratory susceptible strains of codling moth were studied. Damage at harvest in all the conventional orchards from which codling moth populations were collected was higher than the economic threshold. The efficacy of eight insecticides, with five modes of action, was evaluated by topical application of the diagnostic concentrations on post-diapausing larvae. The enzymatic activity of mixed-function oxidases (MFOs), glutathione transferases (GSTs), and esterases (ESTs) was evaluated for each population. The susceptibility to insecticides and the biochemical activity of the three laboratory strains and one organic orchard population were not significantly different. Field populations were less susceptible to the tested insecticides than the susceptible strains, especially for azinphos-methyl, diflubenzuron, fenoxycarb, and phosalone. The efficacy of all insecticides was significantly dependent on the activity of MFOs. Only the toxicity of the three insecticides most used in Spain when the populations were collected (azinphos-methyl, fenoxycarb, and phosalone) was also dependent on the activity of ESTs and GSTs activity. According to our results, the control failures were due to the existence of populations resistant to the main insecticides used.

Combined detoxification mechanisms and target mutation fail to confer a high level of resistance to organophosphates in Cydia pomonella (L.) (Lepidoptera: Tortricidae)

Despite the frequent and widespread applications of organophosphates against Cydia pomonella this species has developed low levels of resistance to this chemical group. Investigations concerning the mechanisms involved in resistance are scarce, and usually consider only one of the potential mechanisms. With the aim of a better understanding the resistance mechanisms and their possible interaction, four of these mechanisms were investigated simultaneously in one sensitive (Sv) and two resistant strains (Raz and Rdfb) of this insect. Resistant strains displayed an increased mixed function oxidase activity, whereas carboxylesterase activity varied upon the substrate used. The three strains had similar β-naphtyl acetate activity, and the hydrolysis of α-naphthyl acetate and p-nitrophenyl valerate was higher in the Sv strain. The p-nitrophenyl acetate activity was highest in the resistant strains and was strongly inhibited by azinphos and DEF. The Raz strain has a modified acetylcholinesterase (AChE), which resulted in a 0.7-, 3.2- and 21.2-fold decrease in the susceptibility to chlorpyriphos-ethyl-oxon, azinphos-methyl-oxon, and paraoxon-methyl, respectively. These combined resistance mechanisms only conferred to Raz a 0.6-, 7.9- and 3.1-fold resistance to the related insecticides. Organophosphates resistance in C. pomonella results from a combination of mechanisms including modified affinities to carboxylesterase substrates, and increased metabolisation of the insecticide. The apparent antagonism between increased functionalisation and reduced sensitivity of the AChE target is discussed.

Susceptibility to Organophosphate Insecticides and Activity of Detoxifying Enzymes in Spanish Populations of <I>Cydia pomonella</I> (Lepidoptera: Tortricidae)

The mechanisms associated with resistance of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), to organophosphate insecticides in pome fruit orchards have been shown to depend on the area. Our objectives were to evaluate the susceptibility of Spanish codling moth populations to chlorpyrifos-ethyl, azinphos-methyl, and phosalone, and the activity of three enzymatic systems reported to be involved in resistance. Eleven field populations and a susceptible strain used as a reference were tested using a bioassay consisting in the topical application of a diagnostic concentration on postdiapausing larvae. The enzymatic activity of mixed function oxidases (MFO), glutathione transferases (GST), and esterases (EST) was measured in postdiapausing larvae and adults. A significant decrease in the efficacy of the organophosphates was observed for all field populations, although the decrease was smaller in the case of chlorpyrifos-ethyl. No differences between sexes were detected. In postdiapausing larvae, the activity of the three enzymatic systems was higher in all the field populations than in the susceptible population. The possible implication of EST in codling moth insecticide resistance is reported for the first time in European field populations. In adults, only MFO and GST were implicated. Codling moth resistance to organophosphates in Spanish populations must be taken into account in the implementation of antiresistance strategies.

Uptake and biochemical response to B[a]P in the sea anemone Anthopleura elegantissima

In order to evaluate the effects of benzo[a]pyrene (B[a]P), a polycyclic aromatic hydrocarbon (PAH) in the sea anemone Anthopleura elegantissima at the biochemical level. NADPH cytochrome P450 reductase and cytochrome P450 were assayed in A. elegantissima under toxicant. One toxicity test was performed with 75 organisms distributed in 5 groups. Animals in groups G1, G2 and G3 were given increasing B[a]P. Two groups named GC and GS were used as controls. GC was treated with seawater and GS was treated with acetone. After 72 h of exposure, enzymatic activities were determined. Microsomes were isolated from the columnar tissue and exposed in vitro to the toxicant in order to explore their ability to incorporate B[a]P. Basal activity for this enzyme was 1.69 ± 0.18 (Mean ± standard deviation) nmol cyt C red min−1 mg−1 and there was no significant effect in GS organisms compared to GC organisms. Significant increases were observed in NADPH cytochrome P450 reductase in G3 organisms. In this group, the enzyme activity was 3.53 ± 0.40 nmol cyt C red min−1 mg−1. For cytochrome P450 content, a gradual increase was observed in organisms in groups G1 to G3. Basal content was 10.25 ± 0.49 pmol mg−1 microsomal protein. For G3 animals, P450 content was 27.51 ± 0.32 pmol mg−1 microsomal. For the test in vitro, it was found that microsomes isolated from G2 and G3 had the capacity to incorporate this substance when exposed to B[a]P at a level of 4 μ M in the surrounding medium. Spectrum recorded from 350 to 450 nm after a 40-min exposure for these groups showed significant difference from spectra obtained for microsomes in GC, GS and G1. It was concluded that the capacity to increase NADPH cytochrome P450 reductase activity as well as to increase NADPH cytochrome P450 reductase activity as well as to increase P450 content shows the ability of A. elegantissima to induce a mixed function oxidase activity in the presence of B[a]P.

Effect of Nucleopolyhedrovirus andBacillus thuringiensisinfection on the activity of insecticide detoxification enzymes in cotton bollworm,Helicoverpa armigeraHbn.

Enzyme assays were carried out to study the influence of Nucleopolyhedrovirus (HearNPV) and Bacillus thuringiensis subsp. kurstaki (Btk) infection on the activity levels of pesticide detoxification enzymes, viz. carboxyl esterase (CE) and mixed function oxidase (MFO) in Helicoverpa armigera . HearNPV at LC 50 reduced the MFO activity by 12.0–13.5% and CE activity by 14.88–15.25% at 96 hours after treatment. Btk at LC 50 reduced the MFO activity by 4.17–4.27% and CE activity by 5.77–6.55%. The joint application of HearNPV and cypermethrin at LC 50 +LC 50 resulted in suppression of MFO activity by 15.08–17.35% and CE activity by 16.39–17.30%. Combined treatment of Btk and cypermethrin resulted in suppression of MFO by 4.24–6.72 and CE by 8.42–8.97%, respectively.

Characterisation of imidacloprid resistance mechanisms in the brown planthopper, Nilaparvata lugens Stål (Hemiptera: Delphacidae)

Effective control of the brown planthopper, Nilaparvata lugens Stål, across rice-growing regions of Asia has been seriously compromised over the last 2 years by the appearance of widespread resistance to the neonicotinoid insecticide, imidacloprid. Sequence analysis of the ligand-binding domain of the nicotinic acetylcholine receptor α1 subunit from two field-collected resistant strains (CHN-2 and IND-11) did not reveal the Y151S point mutation previously implicated in conferring target-site resistance in this species. This result was supported by ligand-binding studies with [ 3H]-imidacloprid that showed no significant change in insecticide binding to isolated membranes from susceptible and resistant strains. In contrast, there was an approximate 5-fold increase in the mixed function oxidase activity for the two resistant strains suggesting that imidacloprid metabolism by increased cytochrome P450 monooxygenase activity is the major mechanism of resistance in these strains.

Gender-related difference in the toxicity of 2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)benzotriazole in rats: Relationship to the plasma concentration, in vitro hepatic metabolism, and effects on hepatic metabolizing enzyme activity

Previously, we showed that the toxic susceptibility of male rats to an ultraviolet absorber, 2-(2′-hydroxy- 3′,5′-di-tert-butylphenyl)benzotriazole (HDBB), was nearly 25 times higher than that of females. The present study aimed to clarify the mechanism of gender-related differences in HDBB toxicity. Male and female rats were given HDBB by gavage at 0.5, 2.5, or 12.5 mg/kg/day for 28 days, and plasma HDBB levels were measured at various time points by using liquid chromatography–tandem mass spectrometry. HDBB was rapidly absorbed and eliminated from the plasma in both sexes, and no sexual variations were found in the plasma levels. In the plasma, HDBB metabolites were not detected at any dose by the liquid chromatography–photodiode array detector. In an in vitro metabolic study using hepatic microsomes from male and female rats, HDBB was slightly metabolized, but no sexual differences were found in the residual HDBB ratio after a 60-minute incubation with an NADPH-generation system. Following 28-day HDBB administration, sexually different changes were found in cytochrome P450–dependent microsomal mixed-function oxidase activities in the liver. In males, 7-ethoxyresorufin O-deethylase activity decreased and lauric acid 12-hydroxylase activity increased at all doses. Decreases in aminopyrine N-demethylase activity and testosterone 2α- and 16α-hydroxylase activity were also found at 2.5 mg/kg and above in males. In females, the only significant change was increased lauric acid 12-hydroxylase activity at 12.5 mg/kg. These findings indicate that HDBB would have hepatic peroxisome proliferative activity, and the difference in susceptibility of male and female rats to this effect might lead to marked gender-related differences in HDBB toxicity.

Intraoperative drugs: audit of prescribing practice

<h3></h3> Childhood cancers continue to be challenging clinical entities whose etiology, demographic characteristics, clinical progression, treatment efficacy, and outcomes remain incompletely understood. Research suggests that multiple environmental and genetic factors...

Metabolic Resistance Mechanisms of Different Pesticides in The Two-Spotted Spider Mite, Tetranychus urticae Koch (Tetranychidae:Acari)

An investigation was performed to determine the possible role of detoxification metabolism in resistant strains ofTetranychus urticea Koch.Adult females were subjected to selection pressure through 40 generations by LC50's andLC90's of Vertimec (Avermectines), Cypermethrin (Pyrethroids), Methomyl (Carbamates) and Malathion (O.P), were(41.308, 42.021, 44.881, and 49.265 folds) and (49.815 ,55.411 ,63.972 ,and 90.00 folds), respectively, whereas RRSslopes ranged from 0.884 to 1.395 folds. Comparative assay with esterases (EST) and mixed function oxidases(MFO)showed that LC50's of Mal-Resistant strains had higher EST. activiy (4.71) with lower MFO activity (3.80),while,LC50's of Vert-Rresistant strains had lower EST. activiy (2.70) with higher MFO activity (4.26). Synergist experimentsshowed low synergism by S,S,S tributylphosphorotrithioate (DEF) of EST activiy ranged from 4.81 to 2.99 folds,whilesynergism by Piperonyl Butoxide (PBO) of MFO activity ranged from 4.27 to 3.82folds to LC50's pesticides resistantstrains.

Worldwide variability of insecticide resistance mechanisms in the codling moth, Cydia pomonella L. (Lepidoptera: Tortricidae)

The activity of detoxifying enzymes (glutathione-S-transferases (GST), mixed-function oxidases (MFO), and esterases (EST)) and the presence of insensitive variants of target proteins (sodium channel and acetylcholinesterase) were examined in individual male and female codling moths. Twenty-nine populations from 11 countries and two laboratory strains were examined. Populations were classified as either unsprayed or sprayed. The ranges of enzyme activities across field populations varied 15-fold, 485-fold and fourfold for GST, MFO and EST, respectively. MFO was the only enzyme whose activity differed in a binomial classification of orchards based on their spray history. Few differences in enzyme activities were found due to sex among populations; and, in these cases, males had higher GST and lower MFO and EST activities than females. Activities of the three enzymatic systems across all populations were positively correlated. Populations from Greece, Argentina and Uruguay had significant percentages of moths with elevated GST and MFO activities. The co-occurrence of moths expressing both elevated MFO and low EST activities was found in conventional orchards from the Czech Republic and France. Chile was the only country where populations from treated orchards did not include a significant proportion of individuals with enhanced enzyme activity. The kdr mutation was found at significant levels in ten populations from five countries, including all French and Argentinean populations. The mutation in AChE was only detected in the Spanish population.