Evaluation of the effects of deltamethrin on the fetal rat testis

Dose addition in mixtures of compounds with dissimilar endocrine modes of action in in vitro receptor activation assays and the zebrafish sexual development test

BACKGROUND

Human exposure to pesticides is being associated with feminisation for which a decrease of the anogenital distance (AGD) is a sensitive endpoint. Dose addition for the cumulative risk assessment of pesticides in food is considered sufficiently conservative for combinations of compounds with both similar and dissimilar modes of action (MoA).

OBJECTIVE

The present study was designed to test the dose addition hypothesis in a binary mixture of endocrine active compounds with a dissimilar mode of action for the endpoint feminisation.

METHODS

Compounds were selected from a list of chemicals of which exposure is related to a decrease of the AGD in rats and completed with reference compounds. These chemicals were characterised using specific in vitro transcriptional activation (TA) assays for estrogenic and androgenic properties, leading to a final selection of dienestrol as an ER-agonist and flutamide, linuron, and deltamethrin as AR-antagonists. These compounds were then tested in an in vivo model, i.e. in zebrafish (Danio rerio), using sex ratio in the population as an endpoint in order to confirm their feminising effect and MoA. Ultimately, the fish model was used to test a binary mixture of flutamide and dienestrol.

RESULTS

Statistical analysis of the binary mixture of flutamide and dienestrol in the fish sexual development tests (FSDT) with zebrafish supported dose addition.

Effects of prenatal pesticide exposure on the fetal brain and placenta transcriptomes in a rodent model

Organophosphate and pyrethroid pesticides are among the most extensively used insecticides worldwide. Prenatal exposures to both classes of pesticides have been linked to a wide range of neurobehavioral deficits in the offspring. The placenta is a neuroendocrine organ and the crucial regulator of the intrauterine environment; early-life toxicant exposures could impact neurobehavior by disrupting placental processes. Female C57BL/6 J mice were exposed via oral gavage to an organophosphate, chlorpyrifos (CPF) at 5 mg/kg, a pyrethroid, deltamethrin (DM), at 3 mg/kg, or vehicle only control (CTL). Exposure began two weeks before breeding and continued every three days until euthanasia at gestational day 17. The transcriptomes of fetal brain (CTL n = 18, CPF n = 6, DM n = 8) and placenta (CTL n = 19, CPF n = 16, DM n = 12) were obtained through RNA sequencing, and resulting data was evaluated using weighted gene co-expression networks, differential expression, and pathway analyses. Fourteen brain gene co-expression modules were identified; CPF exposure disrupted the module related to ribosome and oxidative phosphorylation, whereas DM disrupted the modules related to extracellular matrix and calcium signaling. In the placenta, network analyses revealed 12 gene co-expression modules. While CPF exposure disrupted modules related to endocytosis, Notch and Mapk signaling, DM exposure dysregulated modules linked to spliceosome, lysosome and Mapk signaling pathways. Overall, in both tissues, CPF exposure impacted oxidative phosphorylation, while DM was linked to genes involved in spliceosome and cell cycle. The transcription factor Max involved in cell proliferation was overexpressed by both pesticides in both tissues. In summary, gestational exposure to two different classes of pesticide can induce similar pathway-level transcriptome changes in the placenta and the brain; further studies should investigate if these changes are linked to neurobehavioral impairments.

Prenatal Exposure to Insecticides and Weight Trajectories Among South African Children in the VHEMBE Birth Cohort

BACKGROUND

Dichlorodiphenyltrichloroethane (DDT) or pyrethroid insecticides are sprayed inside dwellings for malaria vector control, resulting in high exposure to millions of people, including pregnant women. These chemicals disrupt endocrine function and may affect child growth. To our knowledge, few studies have investigated the potential impact of prenatal exposure to DDT or pyrethroids on growth trajectories.

METHODS

We investigated associations between gestational insecticide exposure and child growth trajectories in the Venda Health Examination of Mothers, Babies and their Environment, a birth cohort of 751 children born between 2012 and 2013 in South Africa. Based on child weight measured at follow-up and abstracted from medical records, we modeled weight trajectories from birth to 5 years using SuperImposition, Translation and Rotation, which estimated two child-specific parameters: size (average weight) and tempo (age at peak weight velocity). We estimated associations between peripartum maternal concentrations of serum DDT, dichlorodiphenyldichloroethylene, or urinary pyrethroid metabolites and SuperImposition, Translation and Rotation parameters using marginal structural models.

RESULTS

We observed that a 10-fold increase in maternal concentrations of the pyrethroid metabolite trans-3-(2,2,-dicholorvinyl)-2,2-dimethyl-cyclopropane carboxylic acid was associated with a 21g (95% confidence interval = -40, -1.6) smaller size among boys but found no association among girls (Pinteraction = 0.07). Estimates suggested that pyrethroids may be associated with earlier tempo but were imprecise. We observed no association with serum DDT or dichlorodiphenyldichloroethylene.

CONCLUSIONS

Inverse associations between pyrethroids and weight trajectory parameters among boys are consistent with hypothesized disruption of androgen pathways and with our previous research in this population, and support the endocrine-disrupting potential of pyrethroids in humans.

Short-term intake of deltamethrin-contaminated fruit, even at low concentrations, induces testicular damage in fruit-eating bats (Artibeus lituratus)

Deltamethrin (DTM) is a pyrethroid insecticide widely used for agricultural purposes. Exposure to DTM has proven to be harmful to humans, but whether low, environmental concentrations of this pesticide also poses a threat to wild mammals is still unknown. In Neotropical areas, bats play important roles in contributing to forest regeneration. We investigated the effects of DTM exposure on the reproductive function of male Neotropical fruit-eating bats (Artibeus lituratus), known for contributing to reforestation through seed dispersal in Neotropical Forests. Bats were assigned to 3 groups: control (fed with papaya); DTM2 (fed with papaya treated with DTM at 0.02 mg/kg) and DTM4 (fed with papaya treated with DTM at 0.04 mg/kg) for seven days. Bats from DTM2 and DTM4 groups showed increased testicular levels of nitric oxide and superoxide dismutase and catalase activities. The germinal epithelium from DTM4 bats showed non-viable cells and cell desquamation, indicating microscopic lesions and Leydig cells atrophy. Our results demonstrate the onset of cell degeneration that may affect the reproductive function in DTM exposed bats.

Effect of long-term treatment with a mixture of pyrethroids on the expression of genes that govern male germ cell production in rats

Humans are exposed to pyrethroid-based pesticides through agricultural produce. In this study, male Wistar rats were orally treated for 9 to 12 months with a mixture of pyrethroids that is equivalent to one-fifth (high dose; HD) or one-twenty fifth (low dose; LD) of the amount of pyrethroids present in the cereals and rice consumed by an average Indian. In rats treated for 9 months, the spermatogenesis-associated genes Abp, Ar, Cd9, Dax1, Dazap1, Ddx3y, Gdnf, Gfra1, Grth, Inhb, Ovol1, P1, Plzf, Pygo2, Scf, Tgfb1, Tp1, Tp2, and Vim1 were downregulated in both LD and HD groups. In rats treated for 12 months Gdnf, Hsf2, Inhb, Tgfb1, Thy1, and Ybx2 expression was downregulated in both LD and HD groups. Steroidogenesis-associated genes 17-β-Hsd, Gata4, Hmgcr, Hmgcs1, Pde4b, and Tspo gene expression were reduced in both LD- and HD-treated groups treated for 9 months. In 12-month-treated rats, Creb1 expression decreased in both LD and HD groups. The epigenetic reprogramming-associated genes, Dnmt1, Dnmt3a, Dnmt3b, Hdac10, Hp1bp3, Kat3a Kat3b, Mch2ta, Ncoa7, and Sirt1 were downregulated in both HD and LD groups of 9-months-treated rats. In rats treated for 12 months, Hdac10, Mch2ta, Ncoa7, and Sirt1 messenger RNA levels decreased in both the HD and LD groups. Thus, we demonstrate that long-term exposure to a mixture of pyrethroids caused aberrations in the transcriptome of factors involved in sperm production and development.

A strategy to validate a selection of human effect biomarkers using adverse outcome pathways: Proof of concept for phthalates and reproductive effects

Human biomonitoring measures the concentrations of environmental chemicals or their metabolites in body fluids or tissues. Complementing exposure biomarkers with mechanistically based effect biomarkers may further elucidate causal pathways between chemical exposure and adverse health outcomes. We combined information on effect biomarkers previously implemented in human observational studies with mechanisms of action reported in experimental studies and with information from published Adverse Outcome Pathways (AOPs), focusing on adverse reproductive effects of phthalate exposure. Phthalates constitute a group of chemicals that are ubiquitous in consumer products and have been related to a wide range of adverse health effects. As a result of a comprehensive literature search, we present an overview of effect biomarkers for reproductive toxicity that are substantiated by mechanistic information. The activation of several receptors, such as PPARα, PPARγ, and GR, may initiate events leading to impaired male and female fertility as well as other adverse effects of phthalate exposure. Therefore, these receptors appear as promising targets for the development of novel effect biomarkers. The proposed strategy connects the fields of epidemiology and toxicology and may strengthen the weight of evidence in observational studies that link chemical exposures to health outcomes.

Non-target toxicity of novel insecticides

Humans have used insecticides since ancient times. The spectrum and potency of available insecticidal substances has greatly expanded since the industrial revolution, resulting in widespread use and unforeseen levels of synthetic chemicals in the environment. Concerns about the toxic effects of these new chemicals on non-target species became public soon after their appearance, which eventually led to the restrictions of use. At the same time, new, more environmentally-friendly insecticides have been developed, based on naturally occurring chemicals, such as pyrethroids (derivatives of pyrethrin), neonicotinoids (derivatives of nicotine), and insecticides based on the neem tree vegetable oil (Azadirachta indica), predominantly azadirachtin. Although these new substances are more selective toward pest insects, they can still target other organisms. Neonicotinoids, for example, have been implicated in the decline of the bee population worldwide. This review summarises recent literature published on non-target toxicity of neonicotinoids, pyrethroids, and neem-based insecticidal substances, with a special emphasis on neonicotinoid toxicity in honeybees. We also touch upon the effects of pesticide combinations and documented human exposure to these substances.

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.

Curcumin and Quercetin Ameliorated Cypermethrin and Deltamethrin-Induced Reproductive System Impairment in Male Wistar Rats by Upregulating The Activity of Pituitary-Gonadal Hormones and Steroidogenic Enzymes

Background

Dietary antioxidants protect tissues and organs against insecticides/xenobiotic-induced damage. In the present study, we evaluated the results of exposure to synthetic pyrethroid insecticides, cypermethrin (Cyp) and deltamethrin (Del) and possible protective effects of curcumin and quercetin on reproductive system in male Wistar rats.

Materials and Methods

In this controlled experimental study, 42 male Wistar rats were randomly divided into 7 groups of 6 animals. Group A served as control, group B was exposed to Cyp (2 mg/kg.bw), group C was exposed to Del (2 mg/kg.bw), group D was exposed to Cyp+Del (2 mg/kg.bw each), group E was exposed to Cyp+Del and treated with curcumin (100 mg/kg.bw), group F was exposed to Cyp+Del and treated with quercetin (100 mg/kg.bw) and group G was exposed to Cyp+Del and treated with quercetin+curcumin for 45 days.

Results

Exposure to Cyp and Del caused decreases in reproductive organs weight, sperm count, sperm motility, level of sex hormones viz. testosterone (T), follicle stimulating hormone (FSH) and luteinizing hormone (LH), steroidogenic enzymes viz. 3β-hydroxyl steroid dehydrogenase (3β-HSD) and 17β-HSD, non-enzymatic antioxi- dant glutathione (GSH) and enzymatic antioxidants viz. superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and glutathione reductase (GR) activity and increases in sperm abnormalities and lipid peroxidation (LPO). The exposure also adversely affected the histo-achitecture of testes. Single and combined treatment with curcumin and quercetin significantly ameliorated Cyp and Del-induced damage in reproductive system.

Conclusion

Curcumin and quercetin protected against Cyp and Del-induced reproductive system toxicity and oxidative damage in rats. The increases in activities of 3β-HSD and 17β-HSD with concomitant increases in testosterone were mainly responsible for ameliorating effects of curcumin and quercetin. Curcumin showed slightly better activity as compared to quercetin. The combination of both antioxidants offered more protection compared to each one alone.

Deltamethrin induced RIPK3-mediated caspase-independent non-apoptotic cell death in rat primary hepatocytes

Deltamethrin (DLM), a synthetic pyrethroid insecticide, is used all over the world for indoor and field pest management. In the present study, we investigated the elicited pathogenesis of DLM-induced hepatotoxicity in rat primary hepatocytes. DLM-induced cell death was accompanied with increased ROS generation, decreased mitochondrial membrane potential and G2/M arrest. Pre-treatment with N-acetyl cysteine/butylated hydroxyanisole/IM54 could partly rescue hepatocytes suggesting that ROS might play a role in DLM-induced toxicity. Interestingly, DLM treatment resulted in a caspase-independent but non-apoptotic cell death. Pre-treatment with pan-caspase inhibitor (ZVAD-FMK) could not rescue hepatocytes. Unaltered caspase-3 activity and absence of cleaved caspase-3 also corroborated our findings. Further, LDH release and Transmission electron microscopy (TEM) analysis demonstrated that DLM incites membrane disintegrity and necrotic damage. Immunochemical staining revealed an increased expression of inflammatory markers (TNFα, NFκB, iNOS, COX-2) following DLM treatment. Moreover, the enhanced RIPK3 expression in DLM treated groups and prominent rescue from cell death by GSK-872 indicated that DLM exposure could induce programmed necrosis in hepatocytes. The present study demonstrates that DLM could induce hepatotoxicity via non-apoptotic mode of cell death.