Effect on the H19 gene methylation of sperm and organs of offspring after chlorpyrifos-methyl exposure during organogenesis period

Endocrine-disrupting chemicals and male reproductive health

Modifiable factors, such as environmental exposures, can impact human fertility. The objective of this review is to summarize the potential effects of exposure to important endocrine-disrupting chemicals on male reproductive health. Most experimental and animal data demonstrate strong evidence for the negative effects of exposure to phenols, phthalates, pesticides, and perfluoroalkyl and polyfluoroalkyl substances on male reproductive health. Although evidence of negative associations in humans was overall strong for phthalates and pesticides, limited and inconclusive relationships were found for the other examined chemical biomarkers. Reasons for the discrepancies in results include but are not limited to, differences in study populations, exposure concentrations, number of samples collected, sample sizes, study design, and residual confounding. Additional studies are needed, particularly for newer phenols and perfluoroalkyl and polyfluoroalkyl substances, given the scarce literature on the topic and increasing exposures over time.

Prenatal exposure to organophosphate pesticides and risk-taking behaviors in early adulthood

INTRODUCTION

Previous studies show evidence for associations of prenatal exposure to organophosphate (OP) pesticides with poorer childhood neurodevelopment. As children grow older, poorer cognition, executive function, and school performance can give rise to risk-taking behaviors, including substance abuse, delinquency, and violent acts. We investigated whether prenatal OP exposure was associated with these risk-taking behaviors in adolescence and young adulthood in a Mexican American cohort.

METHODS

We measured urinary dialkyl phosphates (DAPs), non-specific metabolites of OPs, twice (13 and 26 weeks gestation) in pregnant women recruited in 1999-2000 in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) study, a birth cohort set in a primarily Latino agricultural community in the Salinas Valley, California. We followed up children throughout their childhood and adolescence; at the 18-year visit, adolescent youth (n = 315) completed a computer-based questionnaire which included questions about substance use, risky sexual activity, risky driving, and delinquency and police encounters. We used multivariable models to estimate associations of prenatal total DAPs with these risk-taking behaviors.

RESULTS

The prevalence of risk-taking behaviors in CHAMACOS youth ranged from 8.9% for smoking or vaping nicotine to 70.2% for committing a delinquent act. Associations of total prenatal DAPs (geometric mean = 132.4 nmol/L) with risk-taking behavior were generally null and imprecise. Isolated findings included a higher risk for smoking or vaping nicotine within the past 30 days (relative risk [RR] per 10-fold increase in prenatal DAPs = 1.89, 95% CI: 1.00, 3.56) and driving without a license (RR = 1.74, 95% CI: 1.25, 2.42). There were no consistent differences by sex or childhood adversity.

DISCUSSION

We did not find clear or consistent evidence for associations of prenatal OP exposure with risk-taking behaviors in adolescence/early adulthood in the CHAMACOS population. Our small sample size may have prevented us from detecting potentially subtle associations of early life OP exposure with these risk-taking behaviors.

Gestational Exposure to Organophosphate Pesticides and Longitudinally Assessed Behaviors Related to Attention-Deficit/Hyperactivity Disorder and Executive Function

The brain’s prefrontal cortex directs higher-order cognitive and behavioral processes that are important for attention, working memory, and inhibitory control. We investigated whether gestational exposure to organophosphate (OP) pesticides was associated with these abilities in childhood and early adolescence. Between 1999 and 2000, we enrolled pregnant women in a birth cohort drawn from an agricultural region of California. We measured dialkyl phosphate (DAP) metabolites of OP pesticides in maternal pregnancy urine samples (13 and 26 weeks) and estimated associations with behaviors related to attention-deficit/hyperactivity disorder and executive function, assessed longitudinally; 351 families provided neurodevelopmental outcome data at any point when the child was aged 7–12 years. We assessed function across multiple dimensions (e.g., working memory, attention), methods (e.g., behavior reports, child assessment), and reporters (e.g., mothers, teachers, child self-reports). Higher gestational DAP concentrations were consistently associated with behaviors related to attention-deficit/hyperactivity disorder and executive function. For example, a 10-fold increase in gestational DAP concentration was associated with poorer longitudinally assessed Behavior Rating Inventory of Executive Function scores, as reported by mothers (β = 4.0 (95% confidence interval: 2.1, 5.8); a higher score indicates more problems), and Weschler Intelligence Scale for Children—Fourth Edition Working Memory scores (a 3.8-point reduction; β = −3.8 (95% confidence interval: −6.2, −1.3)). Reducing gestational exposure to OP pesticides through public health policy is an important goal.

Environmental pollutants exposure and male reproductive toxicity: The role of epigenetic modifications

Male fertility rates have shown a progressive decrease in recent decades. There is a growing concern about the male reproductive dysfunction caused by environmental pollutants exposure, however the underlying molecular mechanisms are still not well understood. Epigenetic modifications play a key role in the biological responses to external stressors. Therefore, this review discusses the roles of epigenetic modifications in male reproductive toxicity induced by environmental pollutants, with a particular emphasis on DNA methylation, histone modifications and miRNAs. The available literature proposed that environmental pollutants can directly or cause oxidative stress and DNA damage to induce a variety of epigenetic changes, which lead to gene dysregulation, mitochondrial dysfunction and consequent male reproductive toxicity. However, future studies focusing on more kinds of epigenetic modifications and their crosstalk as well as epidemiological data are still required to fill in the current research gaps. In addition, the intrinsic links between pollutants-mediated epigenetic regulations and male reproduction-related physiological responses deserve to be further explored.

Gestational exposures to organophosphorus insecticides: From acute poisoning to developmental neurotoxicity

For over three-quarters of a century, organophosphorus (OP) insecticides have been ubiquitously used in agricultural, residential, and commercial settings and in public health programs to mitigate insect-borne diseases. Their broad-spectrum insecticidal effectiveness is accounted for by the irreversible inhibition of acetylcholinesterase (AChE), the enzyme that catalyzes acetylcholine (ACh) hydrolysis, in the nervous system of insects. However, because AChE is evolutionarily conserved, OP insecticides are also toxic to mammals, including humans, and acute OP intoxication remains a major public health concern in countries where OP insecticide usage is poorly regulated. Environmental exposures to OP levels that are generally too low to cause marked inhibition of AChE and to trigger acute signs of intoxication, on the other hand, represent an insidious public health issue worldwide. Gestational exposures to OP insecticides are particularly concerning because of the exquisite sensitivity of the developing brain to these insecticides. The present article overviews and discusses: (i) the health effects and therapeutic management of acute OP poisoning during pregnancy, (ii) epidemiological studies examining associations between environmental OP exposures during gestation and health outcomes of offspring, (iii) preclinical evidence that OP insecticides are developmental neurotoxicants, and (iv) potential mechanisms underlying the developmental neurotoxicity of OP insecticides. Understanding how gestational exposures to different levels of OP insecticides affect pregnancy and childhood development is critical to guiding implementation of preventive measures and direct research aimed at identifying effective therapeutic interventions that can limit the negative impact of these exposures on public health.

DNA methylation changes of apoptotic genes in organogenesis stage of mice embryos by maternal chlorpyrifos induction

The continued use of pesticides is one of the requirements of modern agriculture. Investigations have shown that pesticides can alter gene methylation and expression and subsequently may lead to abortion or birth of embryos with teratogenic disorders. In present study, 30 female NMRI mouse were divided in three experimental groups which in the CPF group, intraperitoneal chlorpyrifos was injected, in the sham group, DMSO was injected, and the control group without injection. The mice were mated and utinized 10 days' post gestation. The number of embryos in each fertilized female, maternal weight, and liver fibrosis was evaluated. The apoptosis pathway genes (caspase3, caspase9) and protein expressions (pro-caspase3, caspase3) of the embryos were evaluated with qRT-PCR and western blot, respectively. The DNA methylation of caspase3 and caspase9 were also assessed. The number of embryos and obtained maternal weight from the CPF group was significantly lower than other two groups. The mRNA expression of Caspase3 and Caspase9 were significantly higher in the CPF group. The protein expression evaluation confirmed the results achieved at the mRNA level. The percentage of Caspase9 DNA methylation in embryos collected from the CPF group was higher compared to the others. It can be considered that consumption of chlorpyrifos toxin can alter the DNA methylation and increase the expression of apoptotic genes. Therefore, continuous use of chlopyrifos may affect pregnancy by increasing the apoptosis pathway in the developing embryos which may lead to abortion or teratogenic disorders in newborn infants.

Prenatal organophosphate pesticide exposure and reproductive hormones in cord blood in Shandong, China

BACKGROUND

Organophosphate pesticides (OPs) have been found to be associated with endocrine disorders, but limited research has been conducted to evaluate the relationship between maternal OP exposure and fetal reproductive hormone levels. In this study, we investigated the association between prenatal OP exposure and fetal reproductive hormones.

METHODS

A total of 306 healthy pregnant women were enrolled between September 2010 and February 2012. Pesticide exposure was assessed via the analysis of maternal urinary nonspecific metabolites of OPs (dialkylphosphate, DAP), and four reproductive hormones were measured in cord blood. Linear regression models and generalized linear models were used to estimate the associations between DAP metabolites and reproductive hormones, and further stratified by infant sex.

RESULTS

We found that concentrations of diethylphosphate (DEP) (β = -0.03; 95% CI: -0.07, -0.00) were inversely associated with estradiol (E2). Dimethylphosphate (DMP) (β = -0.08; 95% CI: -0.13, -0.03), diethylthiophosphate (DETP) (β = -0.08; 95% CI: -0.14, -0.01), and DAPs (β = -0.10; 95% CI: -0.17, -0.03) were inversely associated with testosterone (T) levels. DMP was inversely associated with follicle-stimulating hormone (FSH) levels (β = -0.03; 95% CI: -0.05, -0.01). DMP (β = -0.06; 95% CI: -0.10, -0.01) and DETP (β = -0.07; 95% CI: -0.13, -0.01) showed inverse associations with the testosterone/estradiol (T/E2) ratio. Moreover, the magnitude of associations notably increased in higher quartiles of concentrations in a dose-response manner. After stratification by sex, these effects were mainly observed among female infants.

CONCLUSION

Our findings suggest the potential impacts of prenatal OP exposure on fetal reproductive hormones, and that sex-related differences may exist.

Updated statement on the available outcomes of the human health assessment in the context of the pesticides peer review of the active substance chlorpyrifos-methyl

In July 2019, the European Commission asked EFSA to provide a statement on the available outcomes of the human health assessment in the context of the pesticides peer review for the renewal of approval of the active substance chlorpyrifos-methyl conducted in accordance with Commission Implementing Regulation (EC) No 844/2012. Accordingly, EFSA delivered a statement to the Commission providing a summary of the main findings of the assessment related to human health following the pesticides peer review expert discussions in mammalian toxicology held between 1 and 5 April 2019, as well as EFSA's additional considerations, including whether the active substance can be expected to meet the approval criteria applicable to human health as laid down in Article 4 of Regulation (EC) No 1107/2009. A follow-up mandate was received to update the statement issued on 31 July 2019 with the outcome of the expert meeting in mammalian toxicology held on 5 September 2019 during which chlorpyrifos-methyl was rediscussed. The concerns identified in the previous statement are maintained.

In vitro exposure to CPF affects bovine sperm epigenetic gene methylation pattern and the ability of sperm to support fertilization and embryo development

Several studies have demonstrated that overexposure to pesticides can reduce mammalian sperm quality, impairing male fertility. Chlorpyrifos (CPF), a widely used organophosphate pesticide, was shown to impair spermatogenesis by inducing the formation of highly reactive toxic intermediates. To gain further insight into the mechanisms underlying the cytotoxicity and genotoxicity of CPF, bovine spermatozoa were exposed in vitro to environmental CPF concentrations and the motility, in vitro fertilization rates, DNA fragmentation, chromatin alterations, and methylation patterns were assessed. Motility and in vitro fertilization rates were significantly reduced in spermatozoa exposed to CPF, while DNA fragmentation and putative chromatin deconstruction appeared to increase at higher pesticide concentrations. In situ hybridization was carried out with X and Y probes on sperm samples exposed to different CPF concentrations, and subsequent analysis highlighted a significant percentage of spermatozoa with a peculiar morphological malformation, in which a narrowing occurred at the level of the hybridization. Analysis of potential abnormalities in the methylation pattern of NESP55-GNAS and XIST promoters displayed no differentially methylated regions in GNAS promoter relative to the control, whereas spermatozoa exposed to 10 μg/mL CPF had increased methylation variance in one region of imprinted XIST promoter. Our results provide support that CPF can induce a genotoxic effect on spermatozoa, impairig their ability to fertilize and support preimplantation embryo development in vitro. These observations are worrying since altered levels of sporadic methylation in genes of male gametes may affect the success of reproduction and contribute to infertility. Environ. Mol. Mutagen. 60:85-95, 2019. © 2018 Wiley Periodicals, Inc.

The link of organophosphorus pesticides with neurodegenerative and neurodevelopmental diseases based on evidence and mechanisms

Organophosphorus (OP) compounds have been known as the most widely used pesticides during the past half century and there have been a huge body of literature regarding their association with human chronic diseases. Neurodegenerative and neurodevelopmental disorders including Alzheimer, Parkinson, amyotrophic lateral sclerosis (ALS), attention deficit hyperactivity disorder (ADHD), and autism are among the afflicting neurological diseases which overshadow human life and their higher risk in relation to OP exposures have been uncovered by epidemiological studies. In addition, experimental studies exploring the underlying mechanisms have provided some evidence for involvement of cholinergic deficit, oxidative stress, neuro-inflammation, and epigenetic modifications as the processes which are common in the toxicity of the OP and pathophysiology of the mentioned diseases. In addition, genetic mutations and polymorphisms of different variants of some genes like paraoxonase have been shown to be implicated in both susceptibility to OPs toxicity and neurological diseases. In this article, we reviewed the epidemiological as well as experimental studies evidencing the association of exposure to OPs and incidence of neurodegenerative and neurodevelopmental diseases.

Developmental neurotoxicity of the organophosphorus insecticide chlorpyrifos: from clinical findings to preclinical models and potential mechanisms

Organophosphorus (OP) insecticides are pest-control agents heavily used worldwide. Unfortunately, they are also well known for the toxic effects that they can trigger in humans. Clinical manifestations of an acute exposure of humans to OP insecticides include a well-defined cholinergic crisis that develops as a result of the irreversible inhibition of acetylcholinesterase (AChE), the enzyme that hydrolyzes the neurotransmitter acetylcholine (ACh). Prolonged exposures to levels of OP insecticides that are insufficient to trigger signs of acute intoxication, which are hereafter referred to as subacute exposures, have also been associated with neurological deficits. In particular, epidemiological studies have reported statistically significant correlations between prenatal subacute exposures to OP insecticides, including chlorpyrifos, and neurological deficits that range from cognitive impairments to tremors in childhood. The primary objectives of this article are: (i) to address the short- and long-term neurological issues that have been associated with acute and subacute exposures of humans to OP insecticides, especially early in life (ii) to discuss the translational relevance of animal models of developmental exposure to OP insecticides, and (iii) to review mechanisms that are likely to contribute to the developmental neurotoxicity of OP insecticides. Most of the discussion will be focused on chlorpyrifos, the top-selling OP insecticide in the United States and throughout the world. These points are critical for the identification and development of safe and effective interventions to counter and/or prevent the neurotoxic effects of these chemicals in the developing brain. This is an article for the special issue XVth International Symposium on Cholinergic Mechanisms.

Sodium Fluoride Affects DNA Methylation of Imprinted Genes in Mouse Early Embryos

Fluorine is reported to affect embryonic development, but the underlining mechanism is unclear. The modification of DNA methylation of the H19 and Peg3 genes is important in embryonic development. Therefore, the effect of fluorine on methylation of H19 and Peg3 during early mouse embryos was studied. It was shown that the H19 gene was significantly downmethylated in E2.5, E3.5, and E4.5 embryos from pregnant mice treated with 120 mg/l NaF in drinking water for 48 h. But methylation of both H19 and Peg3 genes was disrupted when the parent male mice were treated with NaF for 35 days. H19 DNA methylation decreased significantly, while Peg3 was almost completely methylated. However, when pregnant mice, mated with NaF-treated male mice, were again treated with NaF for 48 h, either H19 or Peg3 methylation in the embryos decreased significantly. In addition, the mRNA level of H19 considerably increased in E3.5 and E4.5 embryos from NaF-treated pregnant mice. Further, the expression of DNMT1 decreased significantly after NaF treatment. Conclusively, we demonstrated that fluorine may adversely affect early embryonic development by disrupting the methylation of H19 and Peg3 through downregulation of DNMT1.