A pharmacokinetic model of cis- and trans-permethrin disposition in rats and humans with aggregate exposure application

Chlorpyrifos, permethrin and cyfluthrin effect on cell survival, permeability, and tight junction in an in-vitro model of the human blood-brain barrier (BBB)

The blood-brain barrier (BBB) is a structural and functional interface between the plasma and the human brain. Predictive BBB in-vitro models like immortalized human capillary microvascular endothelial cells (HCMEC/D3) can be used to explore the BBB disruption potential of daily exposed chemicals. The present study was focused on investigating the human BBB permeation potential of one organophosphate pesticide, chlorpyrifos (CPF), and two pyrethroids, permethrin (PMT) and cyfluthrin (CFT). HCMEC/D3 cells were exposed to the chemical and the time-dependent pass across BBB along with permeation coefficient (Papp) was calculated. Transendothelial electrical resistance (TEER) was measured for the cells to check the monolayer formation and later to check the reduction in integrity after chemical exposure. Real time PCR was conducted to investigate the effect of chemicals on the expression BBB´s tight and adherens junction proteins. Calculated Papp value for three chemicals was in the following order: CPF>CFT>PMT, where CPF showed the highest permeation coefficient. TEER calculation showed that the integrity decreased after CPF exposure which was in concordance with Papp value whereas for other chemicals, no change in TEER after exposure was observed. In addition, the transwell study showed a higher efflux ratio (ER) (>2) of CFT indicating that CFT could be a substrate for active transport. For CPF and PMT, ER was less than 2, so no active transport seems to be involved. The evaluation of the mRNA expression analysis revealed a statistically significant decrease in Occludin (OCLN) gene expression for CPF, VE-Cadherin (CDH5) for PMT and Zonula Occludens (ZO1) expression for CFT. Our study showed that CPF has the highest potential for inducing cell death, higher permeation, and capability to induce BBB dysfunction than among the above-mentioned chemicals. Additionally, the results of the permeation study could be useful to build a human PBPK model using in vitro-to-in vivo extrapolation approach.

Filling gaps between exposure modeling and the analysis of urinary biomarkers using personal air monitoring: An intervention study of permethrin used in home insecticide spray

Permethrin is one of the most widely used active ingredients in spray-type home insecticides. However, indoor permethrin exposure resulting from the use of home insecticides is not well-characterized, as measured permethrin concentrations in indoor environmental and biological media with a known application rate are scarce. We conducted an intervention study with four participants for seven days. We conducted personal air monitoring and collected 24-h urine samples in which we quantified time-weighted average (TWA) permethrin concentrations in indoor air (C_air ) and urinary concentrations of two permethrin metabolites, 3-phenoxybenzoic acid (3-PBA) and cis/trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylic acid (cis/trans-DCCA). We also estimated (1) TWA C_air using a simple indoor air model and (2) urinary excreted (UE) mass using a simple excretion model with both estimated and measured TWA C_air . Measurements of TWA C_air from personal air monitoring were lower than those estimated from the indoor model by a factor of 2.9 to 49.4. The ratio of estimated to measured UE mass ranged 3.5-18.2 when using estimated TWA C_air and 1.1-2.9 when using measured TWA C_air . Smaller ratios in estimating internal permethrin exposure from personal air monitoring suggest that personal air monitoring could reduce uncertainties in permethrin exposure assessment resulting from the use of spray-type insecticides.

Maternal and fetal tissue distribution of α-cypermethrin and permethrin in pregnant CD-1 mice

Pyrethroid insecticides are widely used throughout agriculture and household products. Recent studies suggest that prenatal exposure to these insecticides may adversely affect fetal development; however, little is known about the distribution of these chemicals in pregnant animals. The present study aimed to address this gap in knowledge by investigating the distribution of two commonly used pyrethroid insecticides, permethrin and α-cypermethrin, in maternal and fetal tissues of pregnant CD-1 mice. Dams were dosed from gestational days 6 to 16 via oral gavage with permethrin (1.5, 15, and 50 mg/kg), α-cypermethrin (0.3, 3, and 10 mg/kg), or corn oil vehicle. Pyrethroid levels were determined in gestational day 16 tissues collected 90 min after the final dose was administered. Across maternal tissues, levels of both pyrethroids were the highest in maternal ovaries, followed by liver and brain, respectively. In addition, levels of both pyrethroids in maternal tissues and placenta were significantly higher than those in the fetal body and amniotic fluid, suggesting that these compounds may exhibit low transfer across the mouse placenta. While additional toxicokinetic studies are needed to verify the time course of pyrethroids in the fetal compartment, these findings support investigation into indirect modes of action relevant to the effects of pyrethroids on mammalian fetal development.

Scabies: Epidemiology, Diagnosis, and Treatment

BACKGROUND

Scabies is a skin infestation whose incidence is apparently rising.

METHODS

This review is based on pertinent articles retrieved by a selective search of PubMed on diagnosis and treatment strategies.

RESULTS

Thread-like papules (burrows), new, intense pruritus, and dermatitis guide the suspected diagnosis which is confirmed by the microscopic or dermatoscopic demonstration of scabies mites. The first line therapy is topical application of permethrin, in accordance with the current recommendations for its use. Other treatment options include systemic ivermectin and topical crotamiton or benzyl benzoate. A combination of permethrin and ivermectin is used to treat otherwise intractable cases and is generally indicated for the treatment of crusted scabies. Known causes of treatment failure include improper application of the external agents, failure of repeated treatment with ivermectin, incomplete decontamination of furnishings and clothes, failure to simultaneously treat contact persons, absence of written documents explaining treatment modalities, and the patient's belonging to a risk group. Even though there has not yet been any direct proof of resistance of scabies mites to permethrin, there is a rising number of welldocumented cases of poor response to this agent. Moxidectin is a new substance now undergoing clinical testing.

CONCLUSION

Treatment of scabies according to the guidelines and the additional recommendations reported here should result in effective curing, even in cases that are thought to be intractable.

Development and Application of a Life-Stage Physiologically Based Pharmacokinetic (PBPK) Model to the Assessment of Internal Dose of Pyrethroids in Humans

To address concerns around age-related sensitivity to pyrethroids, a life-stage physiologically based pharmacokinetic (PBPK) model, supported by in vitro to in vivo extrapolation (IVIVE) was developed. The model was used to predict age-dependent changes in target tissue exposure of 8 pyrethroids; deltamethrin (DLM), cis-permethrin (CPM), trans-permethrin, esfenvalerate, cyphenothrin, cyhalothrin, cyfluthrin, and bifenthrin. A single model structure was used based on previous work in the rat. Intrinsic clearance (CLint) of each individual cytochrome P450 or carboxylesterase (CES) enzyme that are active for a given pyrethroid were measured in vitro, then biologically scaled to obtain in vivo age-specific total hepatic CLint. These IVIVE results indicate that, except for bifenthrin, CES enzymes are largely responsible for human hepatic metabolism (>50% contribution). Given the high efficiency and rapid maturation of CESs, clearance of the pyrethroids is very efficient across ages, leading to a blood flow-limited metabolism. Together with age-specific physiological parameters, in particular liver blood flow, the efficient metabolic clearance of pyrethroids across ages results in comparable to or even lower internal exposure in the target tissue (brain) in children than that in adults in response to the same level of exposure to a given pyrethroid (Cmax ratio in brain between 1- and 25-year old = 0.69, 0.93, and 0.94 for DLM, bifenthrin, and CPM, respectively). Our study demonstrated that a life-stage PBPK modeling approach, coupled with IVIVE, provides a robust framework for evaluating age-related differences in pharmacokinetics and internal target tissue exposure in humans for the pyrethroid class of chemicals.

Estimating human exposure to pyrethroids' mixtures from biomonitoring data using physiologically based pharmacokinetic modeling

Human biomonitoring data provide evidence to exposure of environmental chemicals. Physiologically based pharmacokinetic (PBPK) modelling together with an adequate exposure scenario allows to transpose measured concentrations of chemicals or their metabolites into exposure levels, as daily intakes. In France, high levels of urinary pyrethroids metabolites have been measured in populations. Our work aims at estimating the exposure of the French ENNS cohort to mixtures of four pyrethroids (deltamethrin, permethrin, cypermethrin, and cyfluthrin) from the urinary concentrations of five pyrethroids' metabolites commonly measured in biomonitoring studies. We developed a modelling approach based on a global toxicokinetic model that accounts for the cumulative exposure to pyrethroids as some of the metabolites can be shared by several parent compounds and for human inter-individual variability in metabolism. The median of the individual daily intakes was estimated to 8.1 ng/kg bw/day for permethrin, 17.7 ng/kg bw/day for cypermethrin, 20.4 ng/kg bw/day for cyfluthrin and 34.3 ng/kg bw/day for deltamethrin leading to similar weights for the pair permethrin and cypermethrin (36%), cyfluthrin (31%) and deltamethrin (33%) to the cumulative exposure. Accounting for human variability enabled to explain some of the variations in the metabolites' levels within the cohort. The cumulative exposure was then weighted by their toxicities towards three neurotoxic effects to calculate margins of exposure (MOE). Low MOE values were always associated with high measured concentrations of metabolites in urine and the lowest MOEs were observed for the autonomic division. No risks associated with reconstructed mixtures of pyrethroids were expected for the ENNS cohort. Our approach is an asset to analyse the biomarkers of exposure to pyrethroids simultaneously and could be easily adapted to any local or national specificities in pyrethroids' exposure or populations.

Evaluation of Placental Transfer and Tissue Distribution of cis- and Trans-Permethrin in Pregnant Rats and Fetuses Using a Physiological-Based Pharmacokinetic Model

Biomonitoring studies have highlighted the exposure of pregnant women to pyrethroids based on the measurement of their metabolites in urine. Pyrethroids can cross the placental barrier and be distributed in the fetus as some pyrethroids were also measured in the meconium of newborns. Prenatal exposure to pyrethroids is suspected to alter the neurodevelopment of children, and animal studies have shown that early life exposure to permethrin, one of the most commonly used pyrethroid in household applications, can alter the brain development. This study aimed to characterize the fetal permethrin exposure throughout gestation in rats. We developed a pregnancy physiologically based pharmacokinetic (pPBPK) model that describes the maternal and fetal kinetics of the cis- and trans- isomers of permethrin during the whole gestation period. Pregnant Sprague-Dawley rats were exposed daily to permethrin (50 mg/kg) by oral route from the start of gestation to day 20. Permethrin isomers were quantified in the feces, kidney, mammary gland, fat, and placenta in dams and in both maternal and fetal blood, brain, and liver. Cis- and trans-permethrin were quantified in fetal blood and tissues, with higher concentrations for the cis-isomer. The pPBPK model was fitted to the toxicokinetic maternal and fetal data in a Bayesian framework. Several parameters were adjusted, such as hepatic clearances, partition coefficients, and intestinal absorption. Our work allowed to estimate the prenatal exposure to permethrin in rats, especially in the fetal brain, and to quantitatively estimate the placental transfer. These transfers could be extrapolated to humans and be incorporated in a human pPBPK model to estimate the fetal exposure to permethrin from biomonitoring data.

Development of a Physiologically Based Pharmacokinetic Model of Mitragynine, Psychoactive Alkaloid in Kratom (Mitragyna Speciosa Korth.), In Rats and Humans

Mitragynine is a major psychoactive alkaloid in leaves of kratom (Mitragyna speciosa Korth.). To understand its disposition in organs, this study aimed to develop a physiologically based pharmacokinetic (PBPK) model that predicts mitragynine concentrations in plasma and organ of interests in rats and humans. The PBPK model consisted of six organ compartments (i.e. lung, brain, liver, fat, slowly perfused tissues, and rapidly perfused tissue). From systematic searching, three pharmacokinetic studies of mitragynine (two studies in rats and 1 study in humans) were retrieved from the literature. Berkeley Madonna Software (version 8.3.18) was used for model development and model simulation. The developed PBPK model consisted of biologically relevant features following involvement of (i) breast cancer-resistant protein (BCRP) in brain, (ii) a hepatic cytochrome P450 3A4 (CYP3A4)-mediated metabolism in the liver, and (iii) a diffusion-limited transport in fat. The simulations adequately describe simulated and observed data in the two species with different dosing regimens. PBPK models of mitragynine in rats and humans were successfully developed. The models may be used to guide optimal mitragynine dosing regimens.

Permethrin exposure affects neurobehavior and cellular characterization in rats' brain

This study investigated the neurotoxic effects of permethrin on the cerebellum, hippocampus and prefrontal cortex of Wistar rats and its effects on some behavioral patterns. Fifteen adult male Wistar rats were grouped into three categories: Group A received 0.1 mL normal saline (control), and Groups B and C received mixed feed with 500 mg/kg and 1,000 mg/kg of 0.6% permethrin, respectively, for 14 days. The animals were assessed for memory, anxiety and exploratory locomotion and thereafter anesthetized and transcardially perfused with normal saline and 4% paraformaldehyde (PFA). Cerebellum, hippocampus and prefrontal cortex were excised from the whole brain and processed for tissue histology, histochemistry and immunohistochemistry. Oxidative status and lipid peroxidation were also assessed using catalase, glutathione peroxidase, superoxide dismutase and malondialdehyde as biomarkers. Results revealed dosedependent decrease in body weights but increase in cerebellar and prefrontal weights, depletion of endogenous antioxidant markers, cognitive deficits, reduced locomotor activities, degenerative changes in the microarchitecture at high doses and presence of chromatolytic cells at both low and high doses of permethrin. Astrocytes were activated while synaptophysin expression was downregulated. Permethrin causes dose-dependent neurotoxicity on the morphology, neurochemistry and oxidative status of different brain regions, and these could affect behavioral performance and other neurologic functions.

Linear toxicokinetic of chlordecone in ewe's serum

Chlordecone (CLD) is an organochlorine pesticide used in banana fields of the French West Indies between 1972 and 1993. This use resulted in a long-term pollution of soils and the possible contamination of farm animals. Indeed, after involuntary ingestion of soil, CLD is absorbed and consequently leads to contaminated animals. The aim of this study was the determination of CLD half-life and the establishment of the linearity of CLD disappearance kinetics in non-lactating adult's ewes. Chlordecone diluted in cremophor was intravenously administrated to ewes at different doses: 0.04, 0.2, or 1 mg kg^-1 body weight (n = 5 for each dose). Blood samples were collected from time t = 0 to time t = 84 days. Serum samples were extracted with a solid-phase extraction and analyzed by electron capture detection gas chromatography. A two-compartmental model was applied to the serum CLD kinetics. An additional statistical analysis was applied to the observed elimination parameters in serum according to the administrated dose, and no significant differences were detected. The linear elimination of CLD between 0.04 and 1 mg kg^-1 body weight allowed the possibility of ewe's extrapolation half-life in this dose range. The estimated mean CLD half-life in ewes was 24 days. Overall, the results of this study will be useful to establish decontamination strategies in small ruminants reared in contaminated CLD areas. Graphical abstract Experimental design of the CLD toxicokinetic study in ewes.

Differential lymphatic versus portal vein uptake of the synthetic pyrethroids deltamethrin and cis-permethrin in rats

The objective of this study was to obtain data on pathways of absorption of the synthetic pyrethroids deltamethrin (DLM) and cis-permethrin (CPM) following oral administration to rats. Adult male Sprague-Dawley rats with cannulated mesenteric lymph ducts and hepatic portal veins were given single doses of either 5 mg/kg DLM or 60 mg/kg CPM via the duodenum and lymph and portal blood samples collected for up to 300 min. The pyrethroid dosing vehicles (5 mL/kg body weight) were either corn oil or glycerol formal. Levels of DLM and CPM in lymph and portal blood samples were determined by high-performance liquid chromatography-mass spectrometry-mass spectrometry. Over the time period studied, levels of both DLM and CPM following administration in either corn oil or glycerol formal were greater in lymph than in portal blood. Lymphatic uptake of both DLM and CPM was enhanced following dosing in glycerol formal than in corn oil. The results of this study suggest that after oral administration to rats, these two pyrethroids are predominantly absorbed via the lymphatic system rather than via portal blood. The data obtained in this study thus support a recently developed physiologically-based pharmacokinetic (PBPK) model to evaluate age-related differences in pyrethroid pharmacokinetics in the rat, where it was assumed that absorption of pyrethroids was predominantly via lymphatic uptake.

Physiologically Based Pharmacokinetic Modeling in Risk Assessment: Case Study With Pyrethroids

The assessment of potentially sensitive populations is an important application of risk assessment. To address the concern for age-related sensitivity to pyrethroid insecticides, life-stage physiologically based pharmacokinetic (PBPK) modeling supported by in vitro to in vivo extrapolation was conducted to predict age-dependent changes in target tissue exposure to 8 pyrethroids. The purpose of this age-dependent dosimetry was to calculate a Data-derived Extrapolation Factor (DDEF) to address age-related pharmacokinetic differences for pyrethroids in humans. We developed a generic human PBPK model for pyrethroids based on our previously published rat model that was developed with in vivo rat data. The results demonstrated that the age-related differences in internal exposure to pyrethroids in the brain are largely determined by the differences in metabolic capacity and in physiology for pyrethroids between children and adults. The most important conclusion from our research is that, given an identical external exposure, the internal (target tissue) concentration is equal or lower in children than in adults in response to the same level of exposure to a pyrethroid. Our results show that, based on the use of the life-stage PBPK models with 8 pyrethroids, DDEF values are essentially close to 1, resulting in a DDEF for age-related pharmacokinetic differences of 1. For risk assessment purposes, this indicates that no additional adjustment factor is necessary to account for age-related pharmacokinetic differences for these pyrethroids.

Aggregate and cumulative chronic risk assessment for pyrethroids in the French adult population

Pyrethroids are commonly used as insecticides in households, in agriculture or in veterinary and medicinal products. This study aimed to assess cumulative aggregate exposure to cyfluthrin, cypermethrin, deltamethrin and permethrin in adults in France and the associated health risk, and to identify major contributions of exposure sources and routes. External chronic exposures were estimated from dietary and several environmental sources for the oral, inhalation and dermal routes. Internal concentrations of five associated metabolites were simulated with a physiologically-based pharmacokinetic model. The predicted urinary concentrations were in same order of magnitude as those of the French ENNS biomonitoring survey. Dietary exposure, especially from cereals and animal products, was the major source of exposure. For the 1% of adults most highly exposed, dermal exposure to permethrin through medicinal and veterinary products was an important source of exposure. Considering alterations of motor, sensory and autonomic division, all individual margins of exposure were higher than 100, suggesting that no neurotoxic risk associated with the cumulative aggregate exposure to these four pyrethroids is expected for the French adult population.

Toxicokinetics of cis- and trans-Permethrin: Influence of Isomer, Maturation, and Sex

Permethrin exposure of children and adults is widespread in many populations, but knowledge of its relative toxicokinetics (TK) and health risks in immature age groups is lacking. Studies were conducted in rats to determine the influence of immaturity and sex (on plasma and target organ dosimetry of each of the insecticide’s 2 isomers, cis- and trans-permethrin [CIS and TRANS]). Postnatal day 15, 21, and 90 (adult), Sprague Dawley rats were orally administered a graduated series of doses of CIS and TRANS in corn oil. Serial sacrifices were conducted over 24 h to obtain plasma, brain, liver, skeletal muscle, and fat profiles of CIS and TRANS. Levels of TRANS decreased relatively rapidly, despite administration of relatively high doses. Concentrations of each isomer in plasma, brain, and other tissues monitored were inversely proportional to the animals’ age. The youngest pups exhibited 4-fold higher plasma and brain area under the curves than did adults. Little difference was observed in the TK of CIS or TRANS between adult male and female rats, other than higher initial plasma and liver CIS levels in females. Elevated exposure of the immature brain appears to be instrumental in increased susceptibility to the acute neurotoxicity of high-dose permethrin (Cantalamessa [1993]), but it remains to be established whether age-dependent TK is relevant to long-term, low-level risks.

Determination of maternal and foetal distribution of cis- and trans-permethrin isomers and their metabolites in pregnant rats by liquid chromatography tandem mass spectrometry (LC-MS/MS)

We developed a method to quantify cis-permethrin and trans-permethrin and their metabolites in several biological matrices in pregnant rats and foetuses using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The objective was to quantify cis-permethrin and trans-permethrin in faeces, kidney, mammary gland, fat and placenta in mothers and in both maternal and foetal blood, brain and liver. The metabolites cis-3-(2,2-dichlorovinyl)-2,2-dimethyl-(1-cyclopropane) carboxylic acid (cis-DCCA), trans-3-(2,2-dichlorovinyl)-2,2-dimethyl-(1-cyclopropane) carboxylic acid (trans-DCCA) and 3-phenoxybenzoic acid (3-PBA) were measured in blood, liver and urine. Sample preparation was performed by liquid-liquid extraction. A purification step was not carried out except for the more complex biological samples (fat, mammary glands and faeces). Validation parameters including specificity, linearity, matrix effect, limits of quantification (LOQs), accuracy and precision were evaluated. The recoveries of target compounds ranged from 47 to 136%. LOQs were in the range 4 to 80 ng/mL for permethrin isomers and 4 to 800 ng/mL for their respective metabolites. Intra- and inter-batch precision and accuracy in matrix were better than 15%. The validated method was applied in a preliminary toxicokinetic study in pregnant rats with oral dosing of 50 mg/kg permethrin. In pregnant rats, permethrin isomers and their metabolites were quantified in all requested matrices except maternal liver and blood for trans-permethrin and cis-DCCA respectively. In foetuses, cis- and trans-permethrin were also quantified, demonstrating that the method is suitable for the analysis of foetal distribution of permethrin in toxicokinetic studies.

Synthesis of molecularly imprinted nanoparticles for selective exposure assessment of permethrin: optimization by response surface methodology

BACKGROUND

Extensive use of high-efficiency pyrethroid pesticides as pest-control agents lead to remarkable adsorption and release of these materials in soil and aquatic environment which could have serious adverse effects on water and food chain quality as well as human health. In this study, a molecularly imprinted polymer was synthesized and used as a selective sorbent in the sample preparation procedure in order to facilitate sensitive and quantitative exposure assessment of insecticide permethrin.

METHODS

Molecular imprinted nanoparticles were prepared by precipitation polymerization technique using 1:4:20 mmol ratio of the template, functional monomer, and cross-linker, respectively, as well as 80 mL of chloroform as progen solvent. The obtained nanoparticles were characterized by field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectrometry (FT-IR). The optimization of critical variables in the MISPE process was done using the central composite design (CCD) of the response surface methodology.

RESULTS

Quadratic regressional models were developed to correlate the response and independent variables and the analysis of variance (ANOVA) verified the excellent fitting of proposed models for experimental data. Optimum conditions for the highest MISPE yield were selected as follow: sorbent mass of 7.71 mg, sample pH 5.58 and 5.68 for cis and trans-permethrin, respectively, sample flow rate of 0.6 mL/min, as well as 5 and 3.94 mL of methanol/acetic acid at the flow rate of 2 mL/min as elution solvents for cis and trans-permethrin, respectively. Under optimized conditions, the linear range was obtained 20-120 μg/L (R2 = 0.99) and the detection limits were 5.51 and 5.72 μg/L for cis and trans-permethrin, respectively. Analysis of real samples demonstrated the high extraction efficiency of designed protocol ranging from 93.01 to 97.14 with the relative standard deviation (RSD) less than 4.51%.

CONCLUSIONS

The satisfactory results confirmed the reliability and efficiency of the proposed method for trace analysis of permethrin isomers in biological and environmental samples.

Estimating the cumulative human exposures to pyrethroids by combined multi-route PBPK models: Application to the French population

Human biomarkers of exposure to pyrethroid insecticides are usually urinary concentrations of metabolites that can be specific to a pyrethroid or common to several compounds. We developed a global toxicokinetic model that links the external exposure to four widely-used pyrethroids and their isomers (deltamethrin and cis and trans isomers of permethrin, cypermethrin, and cyfluthrin) to the urinary concentrations of metabolites (cis- and trans-DCCA, 3-PBA, F-PBA and DBCA). This global model includes physiologically based pharmacokinetic models for each parent compound and one-compartment models for the metabolites. Existing in vivo, in vitro and in silico data were used for model calibration, and human toxicokinetic data for model evaluation. Overall, the global model reproduced the data accurately as about 90% of predictions were inside the 3-fold error interval. A sensitivity analysis showed that the most influent parameter for each urinary metabolite concentration was the fraction of parent compound that is transformed into that metabolite. The global model was then tested with realistic exposures for the French population: the predictions were consistent with biomonitoring data. The global model is a tool that will improve the interpretation of biomonitoring data for pyrethroids.

Toxicokinetics of Deltamethrin: Dosage Dependency, Vehicle Effects, and Low-Dose Age-Equivalent Dosimetry in Rats

There is increasing concern that infants and children may be at increased risk of neurological effects of pyrethroids, the most widely used class of insecticide. The objectives of this investigation were to (1) characterize the dose-dependent toxicokinetics (TK) of deltamethrin (DLM) for exposures ranging from environmentally relevant to acutely toxic; (2) determine the influence of an aqueous versus oil vehicle on oral absorption and bioavailability; and (3) determine whether DLM exhibits low-dose, age-equivalent internal dosimetry. Serial arterial plasma samples were obtained for 72 h from adult, male Sprague Dawley rats given 0.05-5.0 mg DLM/kg as an oral bolus in corn oil (CO). DLM exhibited linear, absorption rate-limited TK. Increases in maximum plasma concentration (Cmax) and AUC∘∞ were directly proportional to the dose. Oral bioavailability was quite limited. The vehicle and its volume had modest effect on the rate and extent of systemic absorption in adult rats. Postnatal day (PND) 15, 21, and 90 (adult) rats received 0.10, 0.25, or 0.50 mg DLM/kg orally in CO and were sacrificed periodically for plasma, brain, and liver collection. Age-dependent differences between PND 15 and 90 plasma Cmax and AUC∘24 values progressively diminished as the dose decreased, but there was a lack of low dose age equivalence in these brain and liver dosimeters. Other maturational factors may account for the lack of the low-dose age equivalence in brain and liver. This investigation provides support for the premise that the relatively low metabolic capacity of immature subjects may be adequate to effectively eliminate trace amounts of DLM and other pyrethroids from the plasma.

The pyrethroid insecticides permethrin and esfenvalerate do not disrupt testicular steroidogenesis in the rat fetus

The present study investigated the effects of maternal exposure to the widely used pyrethroid insecticides, permethrin and esfenvalerate, on fetal testicular steroidogenesis. Pregnant Sprague-Dawley rats were administered permethrin at doses of 1, 10, 50, or 100 mg/kg/day, or esfenvalerate at 0.1, 1, 7.5 or 15 mg/kg/day, by gavage, from gestation day (GD) 13 to 19. Testicular testosterone production and the expression of several key genes necessary for cholesterol and androgen synthesis and transport were assessed in GD 19 male fetuses. Dams treated with 100 mg/kg/day of permethrin or 15 mg/kg/day of esfenvalerate showed clinical signs of neurotoxicity. The highest dose of esfenvalerate also resulted in reduced maternal body weight gain throughout the treatment period. In the fetal testes, mRNA expressions of HMG-CoA synthase and reductase, SR-B1, StAR, P450scc, 3βHSD, P450 17A1, and 17βHSD were not affected by exposure to either pyrethroid. No significant change was observed in ex vivo testosterone production. In conclusion, in utero exposure to permethrin or esfenvalerate has no effect on the testosterone biosynthesis pathway in the fetal rat testis up to maternal toxic doses.

Kinetic time courses of lambda-cyhalothrin metabolites after dermal application of Matador EC 120 in volunteers

A controlled kinetic study was conducted in volunteers dermally exposed to the widely used lambda-cyhalothrin pyrethroid pesticide to document the time courses of relevant biomarkers of exposure, in order to better assess biomonitoring data in workers. Matador^® EC120 formulation (120 g/l) was applied on 40 cm² of the forearm at a 0.25 mg/kg dose of lambda-cyhalothrin and left without occlusion or washing for 6 h. The application site was then washed thoroughly with soap and water. The kinetic time courses of cis-3-(2-chloro-3,3,3-trifluoroprop-1-en-1-yl)-2,2-dimethylcyclopropane carboxylic acid (CFMP) and 3-phenoxybenzoic acid (3-PBA) metabolites were determined in plasma and urine up to 84 h post-application. Results show that the fraction of lambda-cyhalothrin absorbed in the body was rapidly cleared following dermal contact. According to CFMP and 3-PBA plasma profiles, calculated mean apparent absorption half-lives (t_1/2) were 3 and 7.3 h, respectively, and corresponding mean apparent elimination t_1/2 were 11.2 and 7.6 h. These differences suggest some metabolism at the site-of-entry and storage of metabolites by the dermal route. Toxicokinetic parameters calculated from urinary profiles confirm the values of absorption and elimination rates. Metabolites were almost completely excreted over the 84-h period post-application and, on average, 0.12 and 0.08% of the applied lambda-cyhalothrin dose was recovered in the urine as CFMP and 3-PBA, respectively, indicating a low dermal absorption fraction of this pyrethroid. This study showed the potential use of CFMP and 3-PBA biomarkers for the assessment of dermal exposure to lambda-cyhalothrin pyrethroid.

Environmental Exposure of the Adult French Population to Permethrin

This work aims to assess the exposure to permethrin of the adult French population from available contamination measurements of outdoor air, indoor air, and settled dust. Priority is given to the assessment of chronic exposure, given the potential of permethrin to induce cancers and/or endocrine disorders. A statistical method was devised to calculate exposure to permethrin by different pathways (inhalation, indirect dust ingestion, and dermal contact). This method considers anthropometric parameters, the population's space-time budget, and recent methods for calculating dermal exposure. Considering the media of interest, our results pointed to house dust as the main environmental source of permethrin exposure, followed by indoor and outdoor air. Dermal contact and indirect dust ingestion may be more important exposure pathways than inhalation. A sensitivity analysis indicated that exposure estimates were mainly affected by variability within contamination data. This study is the first step in aggregated exposure and risk assessment due to pyrethroid exposure. Outdoor air, indoor air, and settled dust may constitute significant exposure sources, in addition to diet, which could be important. The next step entails assessing internal doses and estimating the proportion of each exposure source and pathway relative to internal exposure.

Permethrin drastically affects the developmental cycle of the non-target slime mould Dictyostelium discoideum

The use of pyrethroids has increased throughout the world over the past few decades, as organophosphate, carbamate and organochlorine insecticides are being phased out. Permethrin is widely used in the USA for crops treatment, at concentrations around 750 × 10³ μg/L. In our study 3.6 μg/L permethrin decreases the fission-rate and the fruiting bodies formation of slime mould Dictyostelium discoideum. Whereas 3.6 × 10⁴ μg/L kills the 100% of amoebae, showing a 24 h-LC₅₀ = 96.6 μg/L. This concentration induces an increase in the pseudocholinesterase activity as well as in both butyrylcholinesterase and heat-shock-protein 70 presence. Our results highlight the high sensitivity of Dictyostelium to permethrin, at concentration of about 10⁵ lesser than what used for agricultural pest control. If we match our results on 6 days of exposure, with the permethrin relatively slow permanence (30 days) in the aerobic soil, as well as the higher effect of permethrin than organophosphate, carbamate and organochlorine pesticides on D. discoideum, the damage on the dictyostelids community, by use of permethrin, is clear. Our data suggest that, if the sustainable agriculture implementation is a topic of the modern "industrial" farming, the permethrin cannot represent a reliable alternative to organochlorine, organophosphate or carbamate pesticides, in implementing Integrated Pest Management programmes.

Evaluation and calibration of high-throughput predictions of chemical distribution to tissues

Toxicokinetics (TK) provides critical information for integrating chemical toxicity and exposure assessments in order to determine potential chemical risk (i.e., the margin between toxic doses and plausible exposures). For thousands of chemicals that are present in our environment, in vivo TK data are lacking. The publicly available R package "httk" (version 1.8, named for "high throughput TK") draws from a database of in vitro data and physico-chemical properties in order to run physiologically-based TK (PBTK) models for 553 compounds. The PBTK model parameters include tissue:plasma partition coefficients (Kp) which the httk software predicts using the model of Schmitt (Toxicol In Vitro 22 (2):457-467, 2008). In this paper we evaluated and modified httk predictions, and quantified confidence using in vivo literature data. We used 964 rat Kp measured by in vivo experiments for 143 compounds. Initially, predicted Kp were significantly larger than measured Kp for many lipophilic compounds (log10 octanol:water partition coefficient > 3). Hence the approach for predicting Kp was revised to account for possible deficiencies in the in vitro protein binding assay, and the method for predicting membrane affinity was revised. These changes yielded improvements ranging from a factor of 10 to nearly a factor of 10,000 for 83 Kp across 23 compounds with only 3 Kp worsening by more than a factor of 10. The vast majority (92%) of Kp were predicted within a factor of 10 of the measured value (overall root mean squared error of 0.59 on log10-transformed scale). After applying the adjustments, regressions were performed to calibrate and evaluate the predictions for 12 tissues. Predictions for some tissues (e.g., spleen, bone, gut, lung) were observed to be better than predictions for other tissues (e.g., skin, brain, fat), indicating that confidence in the application of in silico tools to predict chemical partitioning varies depending upon the tissues involved. Our calibrated model was then evaluated using a second data set of human in vivo measurements of volume of distribution (Vss) for 498 compounds reviewed by Obach et al. (Drug Metab Dispos 36(7):1385-1405, 2008). We found that calibration of the model improved performance: a regression of the measured values as a function of the predictions has a slope of 1.03, intercept of - 0.04, and R2 of 0.43. Through careful evaluation of predictive methods for chemical partitioning into tissues, we have improved and calibrated these methods and quantified confidence for TK predictions in humans and rats.

Permethrin alters glucose metabolism in conjunction with high fat diet by potentiating insulin resistance and decreases voluntary activities in female C57BL/6J mice

Permethrin, a type 1 pyrethroid insecticide, was previously reported to promote adipogenesis in 3T3-L1 adipocytes and insulin resistance in C2C12 muscle cells; however, the effects of permethrin exposure on glucose and lipid metabolisms in vivo remain unknown. The purpose of this study was to investigate the effects of permethrin exposure on glucose and lipid homeostasis as well as voluntary movement in female mice in response to dietary fat. We tested three doses of permethrin (50, 500, & 5000 μg/kg body weight/day) in low fat diet-fed (4% w/w of diet) and high fat diet-fed (20% w/w of diet) female C57BL/6 J mice for twelve weeks. Our results demonstrated that permethrin treatment potentiated high fat diet-induced insulin resistance as indicated by insulin tolerance tests, glucose tolerance tests, and homeostasis model assessment - insulin resistance (HOMA-IR) without altering weight or fat mass. Permethrin treatment significantly decreased voluntary movement and elevated blood glucose and insulin levels. Western blot results further showed that permethrin impaired insulin signaling via the Akt signaling pathway in the gastrocnemius muscle. Taken together, these results suggest that oral administration of permethrin potentiated high fat diet-induced insulin resistance, possibly increasing the risk of type 2 diabetes without altering weight gain in female C57BL/6 J mice.

The insect repellents: A silent environmental chemical toxicant to the health

In recent years, a large number of insect repellents have been developed with the idea of consumer benefits. In addition to already known advantageous application of insect repellents, there is increasing concern about the potential toxicity in environment leading to health caused by random use of these compounds. An increasing number of evidence suggests that insect repellents may trigger undesirable hazardous interactions with biological systems with a potential to generate harmful effects including intermediate metabolites. Biotransformation followed by bioaccumulation (vice e versa) may be an important phenomenon for toxic response of this chemicals. In this review, we have summarized the current state of knowledge on the insect repellent toxicity, including biochemical pathway alteration under in vitro and in vivo conditions considering different classes of organisms, from lower to higher vertebrate. Furthermore, we have tried to incorporate the effects of insect repellent in light of some clinical reports. We hope this review would provide useful information on potential side effects of uncontrolled use of insect repellents.

Computational Exposure Science: An Emerging Discipline to Support 21st-Century Risk Assessment

BACKGROUND

Computational exposure science represents a frontier of environmental science that is emerging and quickly evolving.

OBJECTIVES

In this commentary, we define this burgeoning discipline, describe a framework for implementation, and review some key ongoing research elements that are advancing the science with respect to exposure to chemicals in consumer products.

DISCUSSION

The fundamental elements of computational exposure science include the development of reliable, computationally efficient predictive exposure models; the identification, acquisition, and application of data to support and evaluate these models; and generation of improved methods for extrapolating across chemicals. We describe our efforts in each of these areas and provide examples that demonstrate both progress and potential.

CONCLUSIONS

Computational exposure science, linked with comparable efforts in toxicology, is ushering in a new era of risk assessment that greatly expands our ability to evaluate chemical safety and sustainability and to protect public health.

CITATION

Egeghy PP, Sheldon LS, Isaacs KK, Özkaynak H, Goldsmith M-R, Wambaugh JF, Judson RS, Buckley TJ. 2016. Computational exposure science: an emerging discipline to support 21st-century risk assessment. Environ Health Perspect 124:697-702; http://dx.doi.org/10.1289/ehp.1509748.

Completing the Link between Exposure Science and Toxicology for Improved Environmental Health Decision Making: The Aggregate Exposure Pathway Framework

Driven by major scientific advances in analytical methods, biomonitoring, computation, and a newly articulated vision for a greater impact in public health, the field of exposure science is undergoing a rapid transition from a field of observation to a field of prediction. Deployment of an organizational and predictive framework for exposure science analogous to the "systems approaches" used in the biological sciences is a necessary step in this evolution. Here we propose the aggregate exposure pathway (AEP) concept as the natural and complementary companion in the exposure sciences to the adverse outcome pathway (AOP) concept in the toxicological sciences. Aggregate exposure pathways offer an intuitive framework to organize exposure data within individual units of prediction common to the field, setting the stage for exposure forecasting. Looking farther ahead, we envision direct linkages between aggregate exposure pathways and adverse outcome pathways, completing the source to outcome continuum for more meaningful integration of exposure assessment and hazard identification. Together, the two frameworks form and inform a decision-making framework with the flexibility for risk-based, hazard-based, or exposure-based decision making.

Efficacy of naringenin against permethrin-induced testicular toxicity in rats

Permethrin (PM), a synthetic pyrethroid insecticide, has broad toxicity spectra. We aimed to investigate the effects of PM on the testes of adult albino rats, examine the recovery response and evaluate the efficacy of naringenin (NG) supplementation. Adult male albino rats were randomly assigned to five groups of six each: control, NG (50 mg/kg), PM (70 mg/kg), recovery (after subsequent withdrawal of PM) and NG-PM group. All treatments were given by oral gavage for 6 weeks and another 3 weeks for the recovery group. At the time of sacrifice, each testis was weighed. Biochemical analysis of epididymal sperm count and serum testosterone level was performed. Testes were processed for histological, ultrastructural and c-Kit immunohistochemical study. PM toxicity was evidenced by a highly significant decrease in testicular weight, epididymal sperm count and serum testosterone level compared to control. Furthermore, testicular structure abnormalities and reduced c-Kit immunoreactions were observed. Stoppage of PM in the recovery group partially reversed PM-induced changes. There was a mild decrease in testicular weight and biochemical parameters compared to control. The structure of seminiferous tubules was partially retained. The NG-PM group showed an overall improvement in testicular weight and biochemical alterations which were confirmed by light and electron microscopic examination. In conclusion, PM induced testicular toxicity, which was ameliorated by NG co-administration. However, stoppage of PM exposure was associated with partial recovery.

Developing a Physiologically-Based Pharmacokinetic Model Knowledgebase in Support of Provisional Model Construction

Developing physiologically-based pharmacokinetic (PBPK) models for chemicals can be resource-intensive, as neither chemical-specific parameters nor in vivo pharmacokinetic data are easily available for model construction. Previously developed, well-parameterized, and thoroughly-vetted models can be a great resource for the construction of models pertaining to new chemicals. A PBPK knowledgebase was compiled and developed from existing PBPK-related articles and used to develop new models. From 2,039 PBPK-related articles published between 1977 and 2013, 307 unique chemicals were identified for use as the basis of our knowledgebase. Keywords related to species, gender, developmental stages, and organs were analyzed from the articles within the PBPK knowledgebase. A correlation matrix of the 307 chemicals in the PBPK knowledgebase was calculated based on pharmacokinetic-relevant molecular descriptors. Chemicals in the PBPK knowledgebase were ranked based on their correlation toward ethylbenzene and gefitinib. Next, multiple chemicals were selected to represent exact matches, close analogues, or non-analogues of the target case study chemicals. Parameters, equations, or experimental data relevant to existing models for these chemicals and their analogues were used to construct new models, and model predictions were compared to observed values. This compiled knowledgebase provides a chemical structure-based approach for identifying PBPK models relevant to other chemical entities. Using suitable correlation metrics, we demonstrated that models of chemical analogues in the PBPK knowledgebase can guide the construction of PBPK models for other chemicals.

In vivo dermal absorption of pyrethroid pesticides in the rat

Exposure to pyrethroid pesticides is a potential cause for concern. The objective of this study was to examine the in vivo dermal absorption of bifenthrin, deltamethrin, and permethrin in the rat. Dorsal hair on adult male Long-Evans rats was removed. The next day, the skin was dosed with 1750 nmol (312.5 nmol/cm(2)) of radiolabeled (5 µCi) bifenthrin, deltamethrin, or permethrin in acetone. A nonoccluding plastic cover was glued over the dosing site. The animals were placed in metabolism cages to collect excreta. At 24 h postdosing, the skin was washed with soap and water, and rats in one group were euthanized and their tissues were collected. The skin was removed and tape stripped. The remaining animals were returned to the metabolism cages after the wash for 4 d. These rats were then euthanized and handled as already described. Excreta, wash, tape strips, tissues, and carcass were analyzed for pyrethroid-derived radioactivity. The wash and tape strips removed >50% of the dose and skin retained 9-24%. Cumulative radioactivity in excreta was 0.5-7% at 24 h and 3-26% at 120 h. Radioactivity in tissues was <0.3% of the dose, while carcass retained 2 to 5%. Assuming absorption equals cumulative recovery in skin (washed and tape stripped), excreta, tissues, and carcass, absorption was permethrin ~ bifenthrin > deltamethrin at 24 h and permethrin > deltamethrin > bifenthrin at 120 h. Using the parallelogram approach with published in vitro data, human dermal absorption of these pyrethroids was estimated to be <10% of the dose.

Time profiles and toxicokinetic parameters of key biomarkers of exposure to cypermethrin in orally exposed volunteers compared with previously available kinetic data following permethrin exposure

Biomonitoring of pyrethroid exposure is largely conducted but human toxicokinetics has not been fully documented. This is essential for a proper interpretation of biomonitoring data. Time profiles and toxicokinetic parameters of key biomarkers of exposure to cypermethrin in orally exposed volunteers have been documented and compared with previously available kinetic data following permethrin dosing. Six volunteers ingested 0.1 mg kg(-1) bodyweight of cypermethrin acutely. The same volunteers were exposed to permethrin earlier. Blood samples were taken over 72 h after treatment and complete timed urine voids were collected over 84 h postdosing. Cis- and trans-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane-1-carboxylic acids (trans- and cis-DCCA) and 3-phenoxybenzoic acid (3-PBA) metabolites, common to both cypermethrin and permethrin, were quantified. Blood and urinary time courses of all three metabolites were similar following cypermethrin and permethrin exposure. Plasma levels of metabolites reached peak values on average ≈ 5-7 h post-dosing; the elimination phase showed mean apparent half-lives (t½ ) for trans-DCCA, cis-DCCA and 3-PBA of 5.1, 6.9 and 9.2 h, respectively, following cypermethrin treatment as compared to 7.1, 6.2 and 6.5 h after permethrin dosing. Corresponding mean values obtained from urinary rate time courses were peak values at ≈ 9 h post-dosing and apparent elimination t½ of 6.3, 6.4 and 6.4 h for trans-DCCA, cis-DCCA and 3-PBA, respectively, following cypermethrin treatment as compared to 5.4, 4.5 and 5.7 h after permethrin dosing. These data confirm that the kinetics of cypermethrin is similar to that of permethrin in humans and that their common biomarkers of exposure may be used for an overall assessment of exposure.

A novel toxicokinetic modeling of cypermethrin and permethrin and their metabolites in humans for dose reconstruction from biomarker data

To assess exposure to pyrethroids in the general population, one of most widely used method nowadays consists of measuring urinary metabolites. Unfortunately, interpretation of data is limited by the unspecified relation between dose and levels in biological tissues and excreta. The objective of this study was to develop a common multi-compartment toxicokinetic model to predict the time courses of two mainly used pyrethroid pesticides, permethrin and cypermethrin, and their metabolites (cis-DCCA, trans-DCCA and 3-PBA) in the human body and in accessible biological matrices following different exposure scenarios. Toxicokinetics was described mathematically by systems of differential equations to yield the time courses of these pyrethroids and their metabolites in the different compartments. Unknown transfer rate values between compartments were determined from best fits to available human data on the urinary excretion time courses of metabolites following an oral and dermal exposure to cypermethrin in volunteers. Since values for these coefficients have not yet been determined, a mathematical routine was programmed in MathCad to establish the possible range of values on the basis of physiological and mathematical considerations. The best combination of parameter values was then selected using a statistic measure (reliability factor) along with a statistically acceptable range of values for each parameter. With this approach, simulations provided a close approximation to published time course data. This model allows to predict urinary time courses of trans-DCCA, cis-DCCA and 3-PBA, whatever the exposure route. It can also serve to reconstruct absorbed doses of permethrin or cypermethrin in the population using measured biomarker data.