Investigating open access new approach methods (NAM) to assess biological points of departure: A case study with 4 neurotoxic pesticides.

Open access new approach methods (NAM) in the US EPA ToxCast program and NTP Integrated Chemical Environment (ICE) were used to investigate activities of four neurotoxic pesticides: endosulfan, fipronil, propyzamide and carbaryl. Concordance of in vivo regulatory points of departure (POD) adjusted for interspecies extrapolation (AdjPOD) to modelled human Administered Equivalent Dose (AEDHuman) was assessed using 3-compartment or Adult/Fetal PBTK in vitro to in vivo extrapolation. Model inputs were from Tier 1 (High throughput transcriptomics: HTTr, high throughput phenotypic profiling: HTPP) and Tier 2 (single target: ToxCast) assays. HTTr identified gene expression signatures associated with potential neurotoxicity for endosulfan, propyzamide and carbaryl in non-neuronal MCF-7 and HepaRG cells. The HTPP assay in U-2 OS cells detected potent effects on DNA endpoints for endosulfan and carbaryl, and mitochondria with fipronil (propyzamide was inactive). The most potent ToxCast assays were concordant with specific components of each chemical mode of action (MOA). Predictive adult IVIVE models produced fold differences (FD) < 10 between the AEDHuman and the measured in vivo AdjPOD. The 3-compartment model was concordant (i.e., smallest FD) for endosulfan, fipronil and carbaryl, and PBTK was concordant for propyzamide. The most potent AEDHuman predictions for each chemical showed HTTr, HTPP and ToxCast were mainly concordant with in vivo AdjPODs but assays were less concordant with MOAs. This was likely due to the cell types used for testing and/or lack of metabolic capabilities and pathways available in vivo. The Fetal PBTK model had larger FDs than adult models and was less predictive overall.

Use of computational toxicology models to predict toxicological points of departure: A case study with triazine herbicides.

BACKGROUND: Atrazine simazine and propazine, widely used triazine herbicides on food crops and in residential areas, disrupt the neuroendocrine system raising human health concerns. USEPA developed a PBPK model based on triazine common Mode of Action (MOA)-suppression of luteinizing hormone surge in female rats-to generate human regulatory points of departure (POD: mg/kg/day). We compared triazine Human Administered Equivalent Dose (AEDHuman mg/kg/day) predictions from open access computational tools to the PBPK PODs to assess concordance. METHODS: Computational tools were the following: ToxCast/Tox21 in vitro assays; Toxicogenomic databases to assess concordance with ToxCast/Tox21 targets; integrated chemical environment (ICE) models with ToxCast/Tox21 inputs to predict AEDHuman PODs and population-based age-refined high throughput toxicokinetics (HTTK-Pop) to compare to age-related PBPK PODs. RESULTS: ToxCast/Tox21 assays identified critical targets in the triazine common MOA and gene databases; ICE AEDHuman predictions were mainly concordant with the USEPA PBPK PODs quantitatively. Low fold-differences between PBPK POD and ICE AEDHuman predictions indicated that the ICE models are health-protective. HTTK-Pop age-refinements were within 10-fold of the USEPA PBPK PODs. CONCLUSIONS: CompTox tools were used to identify assay targets in the MOA and identify potential molecular initiating targets in the adverse outcome pathway for potential use in risk assessment.

Use of computational toxicology tools to predict in vivo endpoints associated with Mode of Action and the endocannabinoid system: A case study with chlorpyrifos, chlorpyrifos-oxon and Δ9Tetrahydrocannabinol.

Currently, there is a lack of knowledge about the effects of co-exposures of cannabis, contaminated with pesticides like chlorpyrifos (CPF) and the toxic metabolite CPF-oxon (CPFO). CPF/CPFO residues, and Δ9Tetrahydrocannabinol (Δ9THC), the main component in cannabis, are known to disrupt the endocannabinoid system (eCBS) resulting in neurodevelopmental defects. Although there are in vivo data characterizing CPF/CPFO and Δ9THC, there are mechanistic data gaps and deficiencies. In this study, an investigation of open access CompTox tools and ToxCast/Tox21 data was performed to determine targets relating to the modes of action (MOA) for these compounds and, given the available biological targets, predict points of departure (POD). The main findings were as follows: 1) In vivo PODs for each chemical were from open literature, 2) Concordance between ToxCast/Tox21 assay targets and known targets in the metabolic and eCBS pathways was evaluated, 3) Human Equivalent Administered Dose (EADHuman) PODs showed the High throughput toxicokinetic (HTTK) 3 compartment model (3COMP) was more predictive of in vivo PODs than the PBTK model for CPF, CPFO and Δ9THC, 4) Age-adjusted 3COMP HTTK-Pop EADHuman, with CPF and CPFO ToxCast/Tox21 AC50 values as inputs were predictive for ages 0-4 when but not Δ9THC compared to in vivo PODs. 5) Age-related refinements for CPF/CPFO were primarily from ToxCast/Tox21 active hit-calls for nuclear receptors, CYP2B6 and AChE inhibition (CPFO only) associated with the metabolic pathway. Only one assay target (arylhydrocarbon hydroxylase receptor) was common between CPF/CPFO and Δ9THC. While computational refinements may select some sensitive events involved in the metabolic pathways; this is highly dependent on the cytotoxicity limits, availability of metabolic activity in the ToxCast/Tox21 assays and reliability of assay performance. Some uncertainties and data gaps for Δ9THC might be addressed with assays specific to the eCBS. For CPF, assays with appropriate metabolic activation could better represent the toxic pathway.

Chlorpyrifos and Δ9 Tetrahydrocannabinol exposure and effects on parameters associated with the endocannabinoid system and risk factors for obesity.

Marilyn Silva. Retired from a career in toxicology and risk assessment. Increased childhood and adult obesity are associated with chlorpyrifos (CPF), an organophosphate pesticide. Cannabis (Δ9Tetrahydrocannabinol: Δ9THC) use has increased globally with legalization. CPF applications on cannabis crops lacks federally regulated tolerances and may pose health risks through exposure during development and in adulthood. Both CPF and Δ9THC affect the endocannabinoid system (eCBS), a regulator of appetite, energy balance, and gut microbiota, which, if disrupted, increases risk for obesity and related diseases. CPF inhibits eCB metabolism and Δ9THC is a partial agonist/antagonist at the cannabinoid receptor (CB1R). Effects of each on obesogenic parameters were examined via literature search. Male rodents with CPF exposure showed increased body weights, dysbiosis, inflammation and oxidative stress, potentially associated with increased eCBs acting through the gut-microbiota-adipose-brain regulatory loop. Δ9THC generally decreased body weights via partial agonism at the CB1R, lowering levels of eCBs. Dysbiosis and/or oxidative stress associated inflammation occurred with CPF, but these parameters were not tested with Δ9THC. Database deficiencies included limited endpoints to compare between chemicals/age-groups, inter-study variables (dose ranges, dosing vehicle, rodent strain, treatment duration, etc.). CPF and Δ9THC were not tested together, but human co-chemical effects would depend on exposure ratio, subject age, exposure duration, and health status, among others. An overriding concern is that both chemicals are well-documented developmental neurotoxins in addition to their low dose effects on energy balance. A co-exposure risk assessment is warranted with increased use and lack of federal CPF regulation on cannabis.

Effects of low-dose chlorpyrifos on neurobehavior and potential mechanisms: A review of studies in rodents, zebrafish, and Caenorhabditis elegans.

OBJECTIVES: Exposure to chlorpyrifos (CPF), a neurotoxic insecticide, is implicated with adverse neurodevelopmental effects in children through noncholinergic mechanisms. METHODS: This review presents qualitative and quantitative evidence in three animal models (rodent, zebrafish, and Caenorhabditis elegans), for neurodevelopmental and behavioral effects occurring at CPF doses lower than those inhibiting acetylcholinesterase (AChE). RESULTS: CPF treatment in rodents at low noncholinergic doses during neurodevelopment showed behavioral effects, including locomotor activity, neuromotor function (NMF), cognition, anxiety, social behavior, and maternal care. Zebrafish and C. elegans, which are transparent during development, allow for detailed analysis of specific systems; further, they exhibit neurotoxic effects closely emulating those observed in mammalian pathways. Qualitative results showed concordance among rodents, zebrafish and C. elegans for adverse effects on locomotor activity, NMF, and AChE inhibition. Male rodents had greater sensitivity for effects on locomotor activity than females and exposure during the gestation day 10-14 window showed consistent increases in locomotor activity at low CPF doses (≤1.0 mg kg-1 day-1 ). Zebrafish had cognitive and anxiety deficits after CPF treatment at low doses and young adult C. elegans had reproductive dysfunction associated NMF and disruption of the serotonergic pathway. Quantitative data for all three species showed neurobehavioral effects after exposure to CPF doses approximately 2-10-fold below the threshold for AChE inhibition. CONCLUSIONS: Taken together, these findings provided a weight-of-evidence for low-dose CPF neurotoxicity and noncholinergic mechanisms. Variability in laboratories, exposure methods, tests, sex, and animal species/strain might have contributed to the inconsistent results. The detrimental CPF effects during early development are relevant to human populations.

Adverse outcome pathway of developmental neurotoxicity resulting from prenatal exposures to cannabis contaminated with organophosphate pesticide residues.

There is growing concern that increased use of medical and recreational cannabis may result in increased exposure to contaminants on the cannabis, such as pesticides. Several states are moving towards implementing robust regulation of the sales, cultivation, and manufacture of cannabis products. However, there are challenges with creating health-protective regulations in an industry that, to date, has been largely unregulated. The focus of this publication is a theoretical examination of what may happen when women are exposed pre-conceptually or during pregnancy to cannabis contaminated with pesticides. We propose an adverse outcome pathway of concomitant prenatal exposure to cannabinoids and the organophosphate pesticide chlorpyrifos by curating what we consider to be the key events at the molecular, cellular, and tissue levels that result in developmental neurotoxicity. The implications of this adverse outcome pathway underscore the need to elucidate the potential developmental neurotoxicity that may result from prenatal exposure to pesticide-contaminated cannabis.

Pregnancy recurrence in adolescents in Southern Brazil.

OBJECTIVE: To determine the pregnancy recurrence among adolescents and young people in a city located in the extreme south of Brazil and to identify associated factors. METHOD: One hundred and twelve (112) women participated, having delivered their children in 2010, while adolescents. The sample was stratified in two stages, being the first a census of the whole population of the city and the second a convenience sample. For statistical analysis, Pearson Chi-square test was used, with a significance level of 5%. RESULTS: The recurrence rate was 53.6%, with an average of 28.6 months. At the time of delivery, in 2010, recurrence was significantly associated with level of education (p=0.044) as well as not being in school (p=0.036). In 2014, the factors associated were level of education (p<0.001), transcript of grades (p=0.030) and income (p=0.030). CONCLUSION: Recurrence of teenage pregnancy represents a lack of importance given to formal education, a fact that mitigates the opportunities and hinders insertion in the labor market, creating a cycle of social inequality. Multidisciplinary efforts involving schools, health services and the youth in educational activities are thus vital, aiming at critical thinking to transform reality.

Pregnancy recurrence in adolescents in Southern Brazil / Recorrência de gestação em adolescentes do extremo sul do Brasil

Summary Objective: To determine the pregnancy recurrence among adolescents and young people in a city located in the extreme south of Brazil and to identify associated factors. Method: One hundred and twelve (112) women participated, having delivered their children in 2010, while adolescents. The sample was stratified in two stages, being the first a census of the whole population of the city and the second a convenience sample. For statistical analysis, Pearson Chi-square test was used, with a significance level of 5%. Results: The recurrence rate was 53.6%, with an average of 28.6 months. At the time of delivery, in 2010, recurrence was significantly associated with level of education (p=0.044) as well as not being in school (p=0.036). In 2014, the factors associated were level of education (p<0.001), transcript of grades (p=0.030) and income (p=0.030). Conclusion: Recurrence of teenage pregnancy represents a lack of importance given to formal education, a fact that mitigates the opportunities and hinders insertion in the labor market, creating a cycle of social inequality. Multidisciplinary efforts involving schools, health services and the youth in educational activities are thus vital, aiming at critical thinking to transform reality.

Resumo Objetivo: Determinar a recorrência de gravidez em adolescentes de um município no extremo sul do Brasil e identificar os fatores associados. Método: Participaram 112 mulheres que tiveram filho em 2010, quando eram adolescentes. A amostra foi estudada em dois estágios, sendo no primeiro por meio de um censo do município e no segundo por uma seleção de conveniência. Para análise estatística, foi utilizado o teste Qui-quadrado de Pearson com nível de significância de 5%. Resultados: A taxa de recorrência de gravidez encontrada foi de 53,6% com tempo médio de 28,6 meses. No momento do parto, em 2010, estiveram significativamente associados à recorrência a escolaridade (p=0,044) e o fato de não estar estudando (p=0,036). Em 2014, foram a escolaridade (p<0,001), o histórico escolar (p=0,030) e a renda (p=0,030). Conclusão: A recorrência de gravidez na adolescência representa a pouca valorização da educação formal, o que mitiga a vivência de oportunidades e dificulta a inserção no mercado de trabalho, criando um ciclo de desigualdade social. É imprescindível unir esforços multidisciplinares nas escolas e nos serviços de saúde, em conjunto com os jovens, em ações educativas que visem a uma relação crítica reflexiva transformadora da realidade.

Maternidade na adolescência: ressignificando a vida? / Teenage maternity: life's new meaning?

OBJECTIVE: To identify transformations arising from teen pregnancy from the perspective of young women. METHODS: Study of qualitative and descriptive approach with 34 young women of low socio-economic strata that gave birth in the year 2010 as teenagers. The data have been collected through semi-structured interviews with questions about life before and after maternity, explored through content analysis. RESULTS: The life of the teenagers before pregnancy is heterogeneous in social, work and schooling aspects. After maternity, the freedom of being is re-configured, bringing losses related to the abandonment of studies, to the reduction in social life and to the stigma of teenage maternity; the gains from resignification of lifestyle, the abandonment of illegal and criminal conduct, increased self-confidence the reduction of exposure to violence inside the family, accompanied by new responsibilities, from the reconciliation of study and work or the abandonment of one of these activities. CONCLUSION: Maternity generates a feeling of satisfaction brought about by the experience of being a mother, with a new social identity.

OBJETIVO: Identificar as transformações oriundas da maternidade na adolescência na perspectiva de jovens mulheres. MÉTODO: Estudo de abordagem qualitativa descritiva com 34 jovens de estrato socioeconômico baixo que tiveram parto no ano de 2010 enquanto adolescentes. Os dados foram coletados quatro anos após o parto por meio de entrevista semiestruturada com questões sobre a vida antes e após a maternidade e explorados por meio da Análise de Conteúdo. RESULTADOS: A vida das adolescentes antes da gravidez é heterogênea nos aspectos sociais, laborais e estudantis. Após a maternidade, reconfigura-se a liberdade de ser, trazendo perdas relacionadas ao abandono dos estudos, a privação da vida social e ao estigma da maternidade compreendida como precoce; e ganhos oriundos da ressignificação do modo de vida, abandono de condutas ilegais e criminosas, aquisição de autoconfiança e da redução da exposição à violência intrafamiliar, acompanhado de novas responsabilidades, da conciliação do estudo e trabalho ou do abandono de uma destas atividades. CONCLUSÃO: A maternidade acarreta um sentimento de plenitude trazido pela experiência de ser mãe, com uma nova identidade social.

Toxicity endpoint selections for a simazine risk assessment.

BACKGROUND: California uses simazine at one of the highest levels for states in the United States (approximately 2.5 million lbs 2006-2010). Simazine causes neuroendocrine disruption and mammary cancer in test animals. A risk assessment was prioritized by the California Department of Pesticide Regulation because of the nondietary concern for simazine exposure to occupational/nonoccupational simazine users, resident nonusers, and bystanders (especially children and children exhibiting pica) at greatest risk. METHODS: No observed effect levels (NOELs) from animal studies as well as human exposure data were used to determine nondietary values for the above populations. Registrant-submitted and open literature studies focusing on oral (major human route) effects for simazine and the major metabolites desisopropyl-s-atrazine and diaminochlorotriazine were reviewed as part of the hazard identification process. RESULTS: Developmental, reproduction, and chronic studies provided the lowest NOELs for the acute (5 mg/kg/day), subchronic (0.56 mg/kg/day), and chronic (0.52 mg/kg/day) exposure durations, respectively. A benchmark dose (95th percentile) was calculated for mammary tumorigenesis, assuming a threshold mechanism in rats (benchmark dose lower limit [95th percentile; BMDL05 ]: 2.9 mg/kg/day). Margins of exposure and uncertainty factors (100-300×, depending on exposure scenario) were used to characterize risk for designated population subgroups. CONCLUSIONS: Fetal developmental delays, endocrine disruption, and mammary tumors resulted from simazine treatment. Systemic and maternal/fetal effects determined the critical NOELs used in risk assessment. Margins of exposures for most scenarios were below acceptable levels, especially for children who may be bystanders where simazine is applied and children who exhibit pica. This risk characterization raises a concern for long-term effects in humans.

A review of developmental and reproductive toxicity of CS2 and H2 S generated by the pesticide sodium tetrathiocarbonate.

BACKGROUND: Sodium tetrathiocarbonate (STTC) is an example of a pesticide that when prepared for use in aqueous solution releases two toxic products carbon disulfide (CS2 ) (active ingredient) and hydrogen sulfide (H2 S) in ambient air in equimolar concentrations resulting in potential exposure to workers and bystanders. CS2 and H2 S are pollutants that are generated from several pesticides as well as in industrial settings. METHODS: Registrant submitted reports and open literature studies for STTC, CS2 and H2 S were reviewed. Previous reports suggest that CS2 was a concern as a developmental and reproductive toxicant. H2 S was also examined since it is a neurotoxicant and potentially harmful to developing fetuses. RESULTS: STTC did not induce developmental or reproductive effects in animal studies. CS2 was a developmental neurobehavioral toxin in rat pups (inhalation no observed effect level [NOEL]=0.01 ppm). Reproductive effects occurred in male and female factory workers after CS2 exposure (NOEL=1 ppm). H2 S had developmental effects in rats at doses at or above those observed for nasal pathology (NOEL=10 ppm) but was not a reproductive or developmental toxin in humans. CONCLUSIONS: The database for CS2 indicates a strong potential for developmental neurotoxicity in animals at low doses but it is lacking in acceptable, well-performed studies. There is also a lack of studies performed with CS2 and H2 S as a mixture.

Human health risk assessment of endosulfan: II. Dietary exposure assessment.

The California Department of Pesticide Regulation (CDPR) and the United States Environmental Protection Agency (USEPA) performed dietary exposure assessments for endosulfan in 1998 and 2002, respectively. Results of the USEPA assessment showed an increased risk for the population sub-group "Children 1-6 years" (>100% of the Population Adjusted Dose [PAD]). USEPA then required registrants to satisfy database uncertainties by performing subchronic neurotoxicity and developmental neurotoxicity studies and, based on the results, USEPA decreased the Food Quality Protection Act (FQPA, 1996) Safety Factor from 10x to 1x. Additionally, several tolerances on commodities consumed in quantity by children were cancelled in 2006. CDPR re-evaluated the dietary risk initially performed in 1998 after review of these same studies. Based on a review of the revised USEPA tolerances, decreased usage, decreased consumption, cancellations, and prior health protective margins of exposure (MOEs>100), CDPR determined that it was not necessary to redo the 1998 exposure assessment. In 2007, USEPA conducted a new human health risk assessment for endosulfan combining food+drinking water residues that characterized dietary risk as %PAD=([Exposure/PAD]x100). For all relevant USEPA population sub-groups, the %PADs were<100% (health protective benchmark).

Human health risk assessment of endosulfan. I: Toxicology and hazard identification.

Endosulfan is persistent in the environment and toxic to wildlife. Legal mandates necessitate that a risk assessments be performed for endosulfan by the California Department of Pesticide Regulation (CDPR) and the United States Environmental Protection Agency (USEPA). This hazard identification (hazard ID) compared critical no-observed effect levels (NOEL) for acute, subchronic and chronic exposure intervals between the agencies. NOELs were discussed in light of their application to numerous exposure scenarios (occupational, general population and dietary). Only the acute oral NOELs differed between CDPR (0.7 mg/kg/day) and USEPA (1.5 mg/kg/day). Pregnant rabbits were considered by CDPR to be more responsive to low gavage doses of endosulfan than non-pregnant female or male rats in the acute study selected by USEPA. NOELs for other exposure routes and durations were similar between agencies. CDPR and USEPA concurred that a Food Quality Protection Act (FQPA, 1996) Safety Factor is not needed after evaluating all studies including a Developmental Neurotoxicity study. The SF was reduced to 1x. NOELs generated from this hazard ID will be used to calculate the Margins of Exposure for all scenarios and subsequently the risk characterization for endosulfan.

An assessment of the developmental, reproductive, and neurotoxicity of endosulfan.

BACKGROUND: Endosulfan has been used for over 50 years. Although most analogs have been discontinued, endosulfan has less environmental persistence. Nevertheless, pressure groups are lobbying for a worldwide ban. The reasons are: possible rodent male reproductive toxicity, other endocrine effects and cancer; human epidemiology, and exposure studies; residues appearing in remote areas of the world, e.g., the Arctic. METHODS: The endosulfan toxicology database is described and risks of its use assessed. RESULTS: Endosulfan is an antagonist at the GABA(A) receptor Cl(-) ionophore in mammalian CNS. Rat acute toxicity is moderate, LD(50)=48 (M) or 10 mg/kg/d (F), oral gavage; 130 (M), 70 mg/kg/d (F) dermal; LC(50)=34.5 microg/L (M), 12.6 microg/L (F), inhalation. Critical NOELs for risk assessment: acute oral (gavage)=0.7 mg/kg/d (rabbit developmental); Subchronic oral (diet)=1.2 mg/kg/d (rat reproduction); Chronic oral (diet)=0.6 mg/kg/d. There were no acceptable dermal toxicity studies. The critical acute and subchronic inhalation NOELs=0.001 mg/L, chronic inhalation=0.0001 mg/L (estimated). Toxicity to rat sperm occurred at doses causing neurotoxicity. Endocrine effects, resulting from P450 oxygenase(s) induction, were reversible. Increased cancer, genotoxicity, or histopathology in rodents was not observed in any organ. Possible effects on brain biogenic amine levels were probably secondary. CONCLUSIONS: Epidemiology and rodent studies suggesting autism and male reproductive toxicity are open to other interpretations. Developmental/ reproductive toxicity or endocrine disruption occurs only at doses causing neurotoxicity. Toxicity to the fetus or young animals is not more severe than that shown by adults.