Developmental Toxicity Studies Research Articles

Melengestrol Acetate (Veterinary Medicinal Products).

Food Safety Commission of Japan (FSCJ) conducted a risk assessment of melengestrol acetate (MGA, CAS No. 2919-66-6), a synthetic hormone, based on results from various studies. MGA was recognized to have no genotoxicity relevant to human health, and it enabled FSCJ to specify an acceptable daily intake (ADI) in the assessment. In vitro studies using various human hormone-receptors showed that MGA exerts biological action primarily as progestogens and secondarily as glucocorticoids. Major adverse effects of MGA observed were mammary gland hyperplasia, endometrial hyperplasia, and a lack of corpora lutea, accompanying the elevated level of serum prolactin. Increased incidence of mammary gland tumor was observed in C3Han/f mice at the dose of 1.5 mg/kg bw/day in a carcinogenicity study. The increase was presumably due to MGA-induced hyperprolactinemia, but not a direct effect of MGA from the experiment, using a prolactin inhibitor. Inhibitions of estrus and ovulation, in addition to dystocia, were observed in female animals in the reproductive and developmental toxicity studies. Malformations such as cleft palate, clubfoot, umbilical hernia, and defective skeletal ossification were observed in rabbits at doses of 0.8 and 1.6 mg/kg bw/day in a developmental toxicity study. However, these were likely due to the corticosteroidal (glucocorticoid) action of MGA. The no-observed-adverse-effect level (NOAEL) was obtained from a rhesus monkey study given orally 1.5 µg/kg bw/day of MGA over the one menstrual-cycle. The value was, however, the result of the study using the large common ratio of 10. In another study, the lowest-observed-adverse-effect level (LOAEL) of 5 µg/kg bw/day, obtained from a cynomolgus monkey given MGA over the three menstrual-cycles. The LOAEL value was estimated close to the biological threshold, because of no obvious hormonal disorders despite of minimal change of menstrual cycle. Therefore, FSCJ considered it appropriate to specify an ADI on the basis of the LOAEL obtained from a cynomolgus monkey study over the three menstrual-cycles, and to add an additional safety factor of 2. Consequently, FSCJ specified the ADI of 0.025 µg/kg bw/day by applying a safety factor of 200 to the LOAEL of 5 µg/kg bw/day in a cynomolgus monkey study over the three menstrual-cycles.

Folpet (Pesticides).

Food Safety Commission of Japan (FSCJ) conducted a risk assessment of folpet (CAS No. 133-07-3), a phthalimide fungicide, based on results from various studies. Major adverse effects of folpet were observed in hyper-keratosis in rats and in duodenal mucosal hyperplasia in mice. No neurotoxicity and adverse effect on fertility were detected. Increases in the incidence of duodenal adenoma and adenocarcinoma were identified in carcinogenicity studies in mice. FSCJ recognized no genotoxicity relevant to human health of folpet in spite of the positive results in vitro. Therefore, a genotoxic mechanism was unlikely involved in the tumor development, and it enabled us to establish a threshold in the assessment. In developmental toxicity studies, no adverse effects observed in fetus at the dose without maternal toxicity. No folpet-induced teratogenicity was detected in rats. Folpet (parent compound only) was identified as the residue definition for dietary risk assessment in agricultural products. The lowest no-observed-adverse-effect level (NOAEL) obtained in all the studies was 10 mg/kg bw/day in several studies in dogs, rats and rabbits. FSCJ specified an acceptable daily intake (ADI) of 0.1 mg/kg bw/day by applying a safety factor of 100 to the NOAEL. The lowest NOAEL for potential adverse effects of a single oral administration of folpet was 10 mg/kg bw/day in a developmental toxicity study in rabbits. FSCJ specified an acute reference dose (ARfD) of 0.1 mg/kg bw/day, for women who are or may be pregnant, by applying a safety factor of 100 to the NOAEL. FSCJ considered it unnecessary to specify ARfD for general population.

Flometoquin (Pesticides).

Food Safety Commission of Japan (FSCJ) conducted a risk assessment of flometoquin (CAS No. 875775-74-9), a quinoline insecticide, based on results from various studies. Major adverse effects of flometoquin observed were suppressed body weight and hepatocellular steatosis in rats, and ovarian atrophy with decreased numbers of small follicle in rats and mice. Neither teratogenicity nor genotoxicity relevant to human health was detected. Increased incidences of gonadal stromal tumor in female rats and of small intestine adenocarcinomas in male mice were identified in carcinogenicity studies. Genotoxic mechanisms were, however, unlikely involved in their tumor developments, and these enabled FSCJ to establish a threshold in the assessment. Mechanism and toxicity studies suggested that ovarian atrophy triggered the development of gonadal stromal tumor, through continuous stimulation of gonadotropin to the gonadal stroma, via negative feedback. A reproductive study showed the decreases in numbers of small follicle, implantation and also in litter size. Based on the results from various studies, flometoquin (parent compound only) was the residue definition for dietary risk assessment in agricultural products. The lowest no-observed-adverse-effect level (NOAEL) obtained from all the studies was 0.8 mg/kg bw/day in a developmental toxicity study in rabbits. FSCJ specified an acceptable daily intake (ADI) of 0.008 mg/kg bw/day by applying a safety factor of 100 to the NOAEL. FSCJ recognized that in considering the ambiguity of the underlying mechanism, the adverse effect on small follicle possibly occurred after single oral administration of flometoquin. Thus FSCJ specified an acute reference dose (ARfD) to be 0.044 mg/kg bw by applying a safety factor of 100 to the NOAEL of 4.45 mg/kg bw per day in a two-generation reproductive toxicity study in rats, based on a comprehensive evaluation of NOAEL for ovarian toxicity.

A Protocol for In Vitro High-Throughput Chemical Susceptibility Screening in Differentiating NT2 Stem Cells.

The incidence of neurological diseases including learning and developmental disorders has increased in recent years. Concurrently, the number and volume of worldwide registered and traded chemicals have also increased. There is a broad consensus that the developing brain is particularly sensitive to damage by chemicals and that evaluation of chemicals for developmental toxicity or neurotoxicity is critical to human health. Human pluripotent embryonal carcinoma (NTERA-2 or NT2) cells are increasingly considered as a suitable model for in vitro developmental toxicity and neurotoxicity (DT/DNT) studies as they undergo neuronal differentiation upon stimulation with retinoic acid (RA) and allow toxicity assessment at different stages of maturation. Here we describe a protocol for cell fitness screening in differentiating NT2 cells based on the analysis of intracellular ATP levels allowing for the identification of chemicals which are potentially harmful to the developing brain. The described method is suitable to be adapted to low-, medium-, and high-throughput screening and allows multiplexing with other cell fitness indicators. While the presented protocol focuses on cell fitness screening in human pluripotent stem cells it may also be applied to other in vitro models.

Prenatal Developmental Toxicity Study of Glycosides-based Standardized Fenugreek Seed Extract in Rats.

Context:Glycoside-based standardized fenugreek seed extract (SFSE-G) demonstrated promising efficacy in animal models of immune-inflammatory conditions.Aim:The present study was aimed at embryo-fetal development toxicity evaluation of SFSE-G in Wistar rats as per guideline No. 414 of the Organization for Economic Co-operation and Development (OECD).Material and Methods:Mated female rats were randomized into four groups of 30 each and received oral doses of either SFSE-G at 250, 500, and 1000 mg/kg or vehicle (water) during the period of gestation (postconception) from gestational day 5 (GD5, an implantation day) until 1 day before cesarean sections (GD19). Maternal food consumption, body weights, and clinical signs were monitored throughout gestation. Cesarean sections were performed on GD20 and fetal observations (gravid uterine weight, implantation sites, early and late resorptions, live and dead fetuses) were recorded. Live fetuses were weighed and examined for external, visceral, and skeletal variations and malformations.Results:None of the SFSE-G-treated groups showed maternal and embryo–fetal toxicity. Occasional and incidental skeletal and visceral malformations were observed and found to be spontaneous and unrelated to the treatment.Conclusion:Oral exposure of SFSE-G during the prenatal period did not show significant maternal and embryo-fetal toxicity up to a dose of 1000 mg/kg in rats. Therefore, the no-observed-adverse-effect level for SFSE-G for prenatal oral exposure was considered to be 1000 mg/kg.SUMMARY Prenatal toxicity of glycoside-based standardized fenugreek seed extract (SFSE-G) was evaluated.SFSE-G was orally gavaged to rats on gestational days 5-19 with a limit dose of 1000 mg/kg.SFSE-G did not show maternal or developmental toxicity.SFSE-G showed NOAEL of 1000 mg/kg for prenatal exposure in female rats. Abbreviations used: CPCSEA: Committee for the Purpose of Control and Supervision of Experiments on Animals; GD: Gestational day; GRAS: Generally recognized as safe; HED: Human equivalent dose; NOAEL: No-observed adverse effect levels; OECD: Organization for Economic Co-operation and Development; SFSE-G: glycoside-based standardized fenugreek seed extract.

Induced Developmental Toxicity Studies With Mercuric Chloride and Polychlorinated Biphenyls on Danio Rerio (Zebrafish) Embryo

Introduction: Fish population is generally considered very sensitive to all kinds of environmental changes to which it is exposed, as they are exclusively aquatic with an external mode of fertilization. The aim of this study is to highlight the effects of some of the most powerful environmental toxicants such as mercuric chloride (HgCl2) and polychlorinated biphenyls (PCBs), which alter the behavioral response, embryo survival rate, embryo hatching ratio, mortality rate, and heart rates of Danio rerio (zebrafish) embryo during its developmental stages. Materials and Methods: Zebrafish (D. rerio) were exposed to progressive concentrations of HgCl2 and PCBs. The water quality parameters were analyzed, and the acute toxicity test was conducted using eight fish for different concentrations; the results were compared with the control group. In addition, behavioral changes at each concentration were observed for the individual fish. Results and Discussion: The fish were exposed to various concentrations of 5, 10, 20, 30, 40, 50, and 60 μg/L of HgCl2 and PCB for a period of up to 2 weeks. The toxicity was concentration as well as time dependent. Toxicity tests revealed that the larvae of zebrafish were more sensitive to these toxicants as compared to the embryos.

Alternative Models of Developmental and Reproductive Toxicity in Pharmaceutical Risk Assessment and the 3Rs.

In the pharmaceutical industry, preclinical developmental and reproductive toxicity studies are conducted in laboratory animals in order to predict and prevent adverse effects of drugs on human reproductive health and development. However, these studies require a relatively large number of animals and are usually conducted late in the drug development process. Early, simple, and inexpensive screening assays could facilitate smarter decisions, reductions in animal use, and development of safe drugs. The current state and future needs for alternative models of developmental and reproductive toxicity are reviewed here. The most popular predictive developmental toxicity assays are embryonic stem cells, rodent whole embryo culture, and zebrafish, each of which involves fairly well-developed techniques with demonstrated utility in drug discovery and development. In vitro or ex vivo methods for male and female reproductive toxicity are less established, but there are promising assays available or being developed that may be useful in drug development, especially for elucidating mechanisms or screening backup compounds. While a number of challenges remain, much progress has been made in alternative developmental and reproductive toxicity models to date, and there is a strong collective enthusiasm in the industry to continue moving them forward. Therefore, it appears that these approaches may be widely used in the near future.

Developmental toxicity studies of lumefantrine and artemether in rats and rabbits.

The combination of artemether plus lumefantrine is a type of artemisinin-based combination therapy (ACT) recommended by the World Health Organization for uncomplicated falciparum malaria except in the first trimester of pregnancy. The first trimester restriction was based on the marked embryotoxicity in animals (including embryo death and cardiac and skeletal malformations) of artemisinins such as artesunate, dihydroartemisinin, and artemether. Before recommending ACTs for use in the first trimester, the World Health Organization has requested that all information relevant to the assessment of risk of ACTs to the embryo be made available to the public. This report describes the results of embryo-fetal development studies of artemether alone, lumefantrine alone, and the combination in rats and rabbits as well as toxicokinetic studies of lumefantrine in pregnant rabbits. The developmental no-effect levels for lumefantrine were 300 mg/kg/day in rats (based on a 25% decrease in litter size at 1000 mg/kg/day) and 1000 mg/kg/day in rabbits. The calculated safety margins based on human equivalent dose and plasma Cmax and AUC values were in the range of 2.5- to 17-fold. The developmental no-effect levels for artemether were 3 mg/kg/day in rats and 25 mg/kg/day in rabbits. Lumefantrine caused no teratogenicity and was not a potent embryotoxin in rats and rabbits. Expected artemisinin-like findings were seen with artemether alone and with artemether/lumefantrine combined except that no malformations were observed. There were no findings in pregnant rats and rabbits that would cause increased concern for the use of artemether-lumefantrine in the first trimester compared to other ACTs.

A Brief Overview of the STP 35th Annual Symposium on the Basis and Relevance of Variation in Toxicologic Responses.

The title of the 2016 Society of Toxicologic Pathology (STP) Symposium was the "Basis and Relevance of Variation in Toxicologic Responses." Many factors may contribute to variation in toxicologic responses and can confound results, complicate interpretation of data, interfere with reproducibility, and make extrapolation to humans problematic. This brief overview summarizes speaker presentations from each session which describes important factors that may impact the interpretation of nonclinical discovery and developmental toxicity studies. In addition, summaries of the Continuing Education (CE) courses and other educational events that occurred during the Symposium are highlighted.

Influence of Study Design on Developmental and Reproductive Toxicology Study Outcomes.

Regulatory studies of developmental and reproductive toxicity (DART) studies have remained largely unchanged for decades, with exposures occurring at various phases of the reproductive cycle and toxicity evaluations at different ages/times depending on the study purpose. The National Toxicology Program has conducted studies examining the power to detect adverse effects where there is a prenatal exposure, but evaluations occur postnatally. In these studies, examination is required of only 1 male and female pup from each litter beyond weaning. This provides poor resolving power to detect rare events (e.g., reproductive tract malformations). If an adverse effect is detected, there is little confidence in the shape of the dose-response curve (and the Benchmark Dose or No Observed Adverse Effect Level [NOAEL]). We have developed a new protocol to evaluate DART, the modified one generation study, with exposure commencing with pregnant animals and retention of 4 males and females from each litter beyond weaning to improve statistical power. These animals can be allocated to specific cohorts that examine subchronic toxicity, teratology, littering, and neurobehavioral toxicity in the same study. This approach also results in a reduction in animal numbers used, compared with individual stand-alone studies, and offers increased numbers of end points evaluated compared with recent Organization for Economic Cooperation and Development proposals.

The safety of nanostructured synthetic amorphous silica (SAS) as a food additive (E 551).

Key messages Particle sizes of E 551 products are in the micrometre range. The typical external diameters of the constituent particles (aggregates) are greater than 100 nm. E 551 does not break down under acidic conditions such as in the stomach, but may release dissolved silica in environments with higher pH such as the intestinal tract. E 551 is one of the toxicologically most intensively studied substances and has not shown any relevant systemic or local toxicity after oral exposure. Synthetic amorphous silica (SAS) meeting the specifications for use as a food additive (E 551) is and has always been produced by the same two production methods: the thermal and the wet processes, resulting in E 551 products consisting of particles typically in the micrometre size range. The constituent particles (aggregates) are typically larger than 100 nm and do not contain discernible primary particles. Particle sizes above 100 nm are necessary for E 551 to fulfil its technical function as spacer between food particles, thus avoiding the caking of food particles. Based on an in-depth review of the available toxicological information and intake data, it is concluded that the SAS products specified for use as food additive E 551 do not cause adverse effects in oral repeated-dose studies including doses that exceed current OECD guideline recommendations. In particular, there is no evidence for liver toxicity after oral intake. No adverse effects have been found in oral fertility and developmental toxicity studies, nor are there any indications from in vivo studies for an immunotoxic or neurotoxic effect. SAS is neither mutagenic nor genotoxic in vivo. In intact cells, a direct interaction of unlabelled and unmodified SAS with DNA was never found. Differences in the magnitude of biological responses between pyrogenic and precipitated silica described in some in vitro studies with murine macrophages at exaggerated exposure levels seem to be related to interactions with cell culture proteins and cell membranes. The in vivo studies do not indicate that there is a toxicologically relevant difference between SAS products after oral exposure. It is noted that any silicon dioxide product not meeting established specifications, and/or produced to provide new functionality in food, requires its own specific safety and risk assessment.

Embryo-fetal developmental toxicity study with kramecine in rat

Embryo-fetal developmental toxicity study with kramecine in rat

Optimizing neuronal differentiation of human pluripotent NT2 stem cells in monolayer cultures.

Human pluripotent embryonal carcinoma (NT2) cells are increasingly considered as a suitable model for invitro developmental toxicity and neurotoxicity (DT/DNT) studies as they undergo neuronal differentiation upon stimulation with retinoic acid (RA) and allow toxicity testing at different stages of maturation. However, differentiation of NT2 cells is not straightforward. There are different protocols available in the literature reporting varying results with regard to differentiation efficiency, expression of neuronal markers and morphological characteristics of differentiated cells. Yet, the efficiency of available protocols has not been systematically compared. To address this question, we quantified the number and size of cell cluster formed during differentiation using published and modified protocols and analyzed the abundance of neuronal and non-neuronal expression markers using immunocytochemistry. In the course of the experiments we observed that differentiation results strongly depend on the cell density at differentiation-initiation as well as on the type of used cell culture plastic ware. Based on those observations and the results from our comparative analysis, we created our own optimized and robust protocol that reproducibly reveals differentiated cells with high yield. We conclude that our method may be superior to differentiation of NT2 cells for systematic invitro-based primary screening for developmental toxicants and neurotoxicants at different stages of maturation over previous protocols used. Our approach will also contribute to reduce animal testing in the context of the 3Rs.

Dose-Response Modeling with Summary Data from Developmental Toxicity Studies.

Dose-response analysis of binary developmental data (e.g., implant loss, fetal abnormalities) is best done using individual fetus data (identified to litter) or litter-specific statistics such as number of offspring per litter and proportion abnormal. However, such data are not often available to risk assessors. Scientific articles usually present only dose-group summaries for the number or average proportion abnormal and the total number of fetuses. Without litter-specific data, it is not possible to estimate variances correctly (often characterized as a problem of overdispersion, intralitter correlation, or “litter effect”). However, it is possible to use group summary data when the design effect has been estimated for each dose group. Previous studies have demonstrated useful dose-response and trend test analyses based on design effect estimates using litter-specific data from the same study. This simplifies the analysis but does not help when litter-specific data are unavailable. In the present study, we show that summary data on fetal malformations can be adjusted satisfactorily using estimates of the design effect based on historical data. When adjusted data are then analyzed with models designed for binomial responses, the resulting benchmark doses are similar to those obtained from analyzing litter-level data with nested dichotomous models.

Dietary Route of Exposure for Rabbit Developmental Toxicity Studies.

Dietary administration is a relevant route of oral exposure for regulatory toxicity studies of agrochemicals as it mimics potential human intake of the chemical via treated crops and commodities. Moreover, dietary administration of test compounds during a developmental toxicity study can deliver a prolonged and stable systemic exposure to the embryo or fetus at all stages of development. In this study, strategies were employed to optimize rabbit test material consumption via diet. Comparative toxicokinetic profiles of gavage versus dietary administration were evaluated in pregnant or non-pregnant New Zealand White rabbits for 2 novel agrochemicals with different plasma half-lives of elimination (sulfoxaflor, t½ = 13.5 h and halauxifen, t½ = 1 h). Dietary administration of sulfoxaflor resulted in stable 24-h plasma concentrations, whereas gavage administration resulted in a 3-fold fluctuation in plasma levels between Cmax and Cmin Dietary administration of sulfoxaflor resulted in a 2-fold higher nominal and diurnal systemic dose when compared with gavage dosing due to Cmax-related maternal toxicity following gavage. Results with the shorter half-life molecule, halauxifen, were more striking with a 6-fold diurnal fluctuation by the dietary route compared with a 368-fold fluctuation between Cmax and Cmin by gavage. Furthermore, plasma halauxifen was detectable only up to 12 h following gavage but up to 24 h following dietary administration. Finally, the presence of these compounds in fetal blood samples was demonstrated, confirming that dietary exposure is appropriate for achieving fetal exposure. Collectively, the results of these studies support the use of dietary exposure in rabbit developmental toxicity studies.

Pregnancy Experience: Nonclinical Studies and Pregnancy Outcomes in the Daclizumab Clinical Study Program.

IntroductionMultiple sclerosis (MS) is more common in women and can occur during childbearing years; thus, information on outcomes following exposure to MS therapy during pregnancy is important. No formal studies of daclizumab have been conducted in pregnant women. Here, we report available nonclinical and clinical data on pregnancy outcomes from the daclizumab clinical study program.MethodsReproductive and developmental toxicity studies were conducted in cynomolgus monkeys. Reports of pregnancies that occurred during the daclizumab clinical study program through March 9, 2015 were collated and summarized. In the event of pregnancy, daclizumab was discontinued and safety monitoring continued.ResultsStudies in cynomolgus monkeys showed no daclizumab-related effects on maternal well-being, embryo–fetal development, indirect fertility end points, and pre- and postnatal development and growth. Across the clinical study program, 38 pregnancies were reported in 36 daclizumab-exposed women (on treatment ≤6 months from last dose); 20 resulted in live births and four (11%) in spontaneous abortions or miscarriages. One congenital heart defect (complex transposition of great vessels) occurred in one live birth (considered unrelated to daclizumab); daclizumab had been discontinued and intramuscular interferon beta-1a and lisinopril were used at conception. Eight women had an elective termination, two had an ectopic pregnancy, and two were lost to follow-up; two pregnancy outcomes are pending. Six additional pregnancies occurred in five women >6 months after their last daclizumab dose; in one additional pregnancy, exposure was unknown.ConclusionSpontaneous abortion rate in daclizumab-exposed women was consistent with early pregnancy loss in the general population (12%–26%). Data on pregnancies exposed to daclizumab do not suggest an increased risk of adverse fetal or maternal outcomes, although the numbers are too small for definitive conclusions.ClinicalTrials.gov identifiersNCT00390221, NCT01064401, NCT01462318, NCT00870740, NCT01051349, and NCT01797965.FundingBiogen and AbbVie Biotherapeutics Inc.

Scientific and Regulatory Policy Committee Points to Consider Review: Inclusion of Reproductive and Pathology End Points for Assessment of Reproductive and Developmental Toxicity in Pharmaceutical Drug Development.

Standard components of nonclinical toxicity testing for novel pharmaceuticals include clinical and anatomic pathology, as well as separate evaluation of effects on reproduction and development to inform clinical development and labeling. General study designs in regulatory guidances do not specifically mandate use of pathology or reproductive end points across all study types; thus, inclusion and use of these end points are variable. The Scientific and Regulatory Policy Committee of the Society of Toxicologic Pathology (STP) formed a Working Group to assess the current guidelines and practices on the use of reproductive, anatomic pathology, and clinical pathology end points in general, reproductive, and developmental toxicology studies. The Working Group constructed a survey sent to pathologists and reproductive toxicologists, and responses from participating organizations were collected through the STP for evaluation by the Working Group. The regulatory context, relevant survey results, and collective experience of the Working Group are discussed and provide the basis of each assessment by study type. Overall, the current practice of including specific end points on a case-by-case basis is considered appropriate. Points to consider are summarized for inclusion of reproductive end points in general toxicity studies and for the informed use of pathology end points in reproductive and developmental toxicity studies.

Tavaborole, a Novel Boron-Containing Small Molecule Pharmaceutical Agent for Topical Treatment of Onychomycosis: I. Reproductive and Developmental Toxicity Studies.

Tavaborole is a topical antifungal agent approved by the US Food and Drug Administration for the treatment of toenail onychomycosis. As part of the nonclinical development program, reproductive and developmental toxicity studies were conducted (rat oral fertility and early embryonic development, rat (oral) and rabbit (dermal) embryo-fetal development). There were no effects on fertility or reproductive performance at doses up to 300 mg/kg/d (107 times the maximum recommended human dose [MRHD] based on mean area under the plasma concentration-time curve comparisons). In the rat embryo-fetal development toxicity studies, teratogenicity was not observed at doses up to 100 mg/kg/d (29 times the MRHD). However, several treatment-related skeletal malformations and variations were observed at 300 mg/kg/d (570 times the MRHD). In rabbit embryo-fetal development toxicity studies dosed via oral or dermal administration, the no observable adverse effect level for maternal toxicity and embryo-fetal toxicity was 50 mg/kg/d (16 times the MRHD) and 5% (26 times the MRHD), respectively.

Human health risk assessment of chloroxylenol in liquid hand soap and dishwashing soap used by consumers and health-care professionals

A quantitative human risk assessment of chloroxylenol was conducted for liquid hand and dishwashing soap products used by consumers and health-care workers. The toxicological data for chloroxylenol indicate lack of genotoxicity, no evidence of carcinogenicity, and minimal systemic toxicity. No observed adverse effect levels (NOAEL) were established from chronic toxicity studies, specifically a carcinogenicity study that found no cancer excess (18 mg/kg-day) and studies of developmental and reproductive toxicity (100 mg/kg-day). Exposure to chloroxylenol for adults and children was estimated for two types of rinse-off cleaning products, one liquid hand soap, and two dishwashing products. The identified NOAELs were used together with exposure estimates to derive margin of exposure (MOE) estimates for chloroxylenol (i.e., estimates of exposure over NOAELs). These estimates were designed with conservative assumptions and likely overestimate exposure and risk (i.e., highest frequency, 100% dermal penetration). The resulting MOEs ranged from 178 to over 100, 000, 000 indicating negligibly small potential for harm related to consumer or health-care worker exposure to chloroxylenol in liquid soaps used in dish washing and hand washing.

Assessment of ABCG2-mediated transport of pesticides across the rabbit placenta barrier using a novel MDCKII in vitro model

In humans, the ATP-binding cassette efflux transporter ABCG2 contributes to the fetoprotective barrier function of the placenta, potentially limiting the toxicity of transporter substrates to the fetus. During testing of chemicals including pesticides, developmental toxicity studies are performed in rabbit. Despite its toxicological relevance, ABCG2-mediated transport of pesticides in rabbit placenta has not been yet elucidated. We therefore generated polarized MDCK II cells expressing the ABCG2 transporter from rabbit placenta (rbABCG2) and evaluated interaction of the efflux transporter with selected insecticides, fungicides, and herbicides. The Hoechst H33342 accumulation assay indicated that 13 widely used pesticidal active substances including azoxystrobin, carbendazim, chlorpyrifos, chlormequat, diflufenican, dimethoate, dimethomorph, dithianon, ioxynil, methiocarb, propamocarb, rimsulfuron and toclofos-methyl may be rbABCG2 inhibitors and/or substrates. No such evidence was obtained for chlorpyrifos-methyl, epoxiconazole, glyphosate, imazalil and thiacloprid. Moreover, chlorpyrifos (CPF), dimethomorph, tolclofos-methyl and rimsulfuron showed concentration-dependent inhibition of H33342 excretion in rbABCG2-transduced MDCKII cells. To further evaluate the role of rbABCG2 in pesticide transport across the placenta barrier, we generated polarized MDCKII-rbABCG2 monolayers. Confocal microscopy confirmed correct localization of rbABCG2 protein in the apical plasma membrane. In transepithelial flux studies, we showed the time-dependent preferential basolateral to apical (B>A) directed transport of [14C] CPF across polarized MDCKII-rbABCG2 monolayers which was significantly inhibited by the ABCG2 inhibitor fumitremorgin C (FTC). Using this novel in vitro cell culture model, we altogether showed functional secretory activity of the ABCG2 transporter from rabbit placenta and identified several pesticides like the insecticide CPF as potential rbABCG2 substrates.