Long-term reproductive effects in male rats prenatally exposed to sodium arsenite

Arsenic is an environmental toxicant known to be a carcinogen and endocrine disruptor. Maternal exposure to arsenic has been associated with fetus malformation and reproductive disorders in male offspring. However, it is unclear the extent to which those effects remain during postnatal development and adulthood. Therefore, this study aimed to investigate the long-term effects of prenatal arsenic exposure on reproductive parameters of male offspring at peripubertal and adult periods. Pregnant female Wistar rats were exposed to 0 or 10 mg/L sodium arsenite in drinking water from gestational day 1 (GD 1) until GD 21 and male pups were analyzed at postnatal day 44 (PND 44) and PND 70. We observed that some reproductive parameters were affected differently by arsenic exposure at each age evaluated. The body and reproductive organs weights, as well as testicular and epididymal morphology were strongly affected in peripubertal animals and recovered at adult period. On the other hand, the antioxidant genes expression (SOD1, SOD2, CAT and GSTK1) and the endogenous antioxidant system were affected in the testes and epididymides from both peripubertal and adult rats. Finally, an impairment in daily sperm production and in sperm parameters was observed in adult animals. Taken together, our findings show that prenatal arsenic exposure affected reproductive parameters of peripubertal and adult male rats mainly due to oxidative stress. Collectively, those alterations may be affecting fertility potential of adult animals.

The imprinted gene Zac1 regulates steatosis in developmental cadmium-induced nonalcoholic fatty liver disease

Cadmium (Cd) exposure in adulthood is associated with nonalcoholic fatty liver disease (NAFLD), characterized by steatosis, inflammation, and fibrosis. The prevalence of NAFLD in children is increasing, suggesting a role for the developmental environment in programming susceptibility. However, the role of developmental Cd exposure in programming NAFLD and the underlying mechanisms remain unclear. We have proposed that imprinted genes are strong candidates for connecting the early life environment and later life disease. In support of this, we previously identified roles for the Imprinted Gene Network (IGN) and its regulator Zac1 in programming NAFLD in response to maternal metabolic dysfunction. Here, we test the hypothesis that developmental Cd exposure is sufficient to program NAFLD, and further, that this process is mediated by Zac1 and the IGN. Using mice, we show that developmental cadmium chloride (CdCl2) exposure leads to histological, biochemical, and molecular signatures of steatosis and fibrosis in juveniles. Transcriptomic analyses comparing livers of CdCl2-exposed and control mice show upregulation of Zac1 and the IGN coincident with disease presentation. Increased hepatic Zac1 expression is independent of promoter methylation and imprinting statuses. Finally, we show that over-expression of Zac1 in cultured hepatocytes is sufficient to induce lipid accumulation in a Pparγ-dependent manner and demonstrate direct binding of Zac1 to the Pparγ promoter. Our findings demonstrate that developmental Cd exposure is sufficient to program NAFLD in later life, and with our previous work, establish Zac1 and the IGN as key regulators of prosteatotic and profibrotic pathways, two of the major pathological hallmarks of NAFLD.

Discovering Novel Bioactivities of Controversial Food Additives by Means of Simple Zebrafish Embryotoxicity (ZET) Assays

The rising concerns about controversial food additives' potential hazardous properties require extensive yet animal-minimized testing strategies. Zebrafish embryos are the ideal in vivo model representing both human and environmental health. In this study, we exposed zebrafish embryos to eight controversial food additives. Our results indicate that Sodium Benzoate is a Cat.3 aquatic toxicant, while Quinoline Yellow is a strong teratogen. At high concentrations, non-toxic chemicals induced similar phenotypes, suggesting the impact of ionic strength and the applicability of the darkened yolk phenotype as an indicator of nephrotoxicity. Three food additives showed unpredicted bioactivities on the zebrafish embryos: Brilliant Blue could weaken the embryonic yolk, Quinoline Yellow may interfere with nutrient metabolism, and Azorubine induced precocious zebrafish hatching. In conclusion, the zebrafish embryo is ideal for high throughput chemical safety and toxicity screening, allowing systematic detection of biological effects-especially those unexpected by targeted in vitro and in silico models. Additionally, our data suggest the need to reconsider the safety status of food additives Quinoline Yellow, Brilliant Blue, Sodium Benzoate, and other controversial food additives in further studies, as well as pave the way to further applications based on the newly found properties of Brilliant Blue and Azorubine.

NRF2-Dependent Placental Effects Vary by Sex and Dose following Gestational Exposure to Ultrafine Particles

Exposure to ultrafine particles (UFPs, PM0.1) during pregnancy triggers placental oxidative stress and inflammation, similar to fine PM (PM2.5). The Nrf2 gene encodes a redox-sensitive transcription factor that is a major regulator of antioxidant and anti-inflammatory responses. Disruption of NRF2 is known to substantially enhance PM2.5-driven oxidant and inflammatory responses; however, specific responses to UFP exposure, especially during critical windows of susceptibility such as pregnancy, are not fully characterized; To investigate the role of NRF2 in regulating maternal antioxidant defenses and placental responses to UFP exposure, wildtype (WT) and Nrf2-/- pregnant mice were exposed to either low dose (LD, 100 µg/m3) or high dose (HD, 500 µg/m3) UFP mixture or filtered air (FA, control) throughout gestation; Nrf2-/- HD-exposed female offspring exhibited significantly reduced fetal and placental weights. Placental morphology changes appeared most pronounced in Nrf2-/- LD-exposed offspring of both sexes. Glutathione (GSH) redox analysis revealed significant increases in the GSH/GSSG ratio (reduced/oxidized) in WT female placental tissue exposed to HD in comparison with Nrf2-/- HD-exposed mice. The expression of inflammatory cytokine genes (Il1β, Tnfα) was significantly increased in Nrf2-/- placentas from male and female offspring across all exposure groups. Genes related to bile acid metabolism and transport were differentially altered in Nrf2-/- mice across sex and exposure groups. Notably, the group with the most marked phenotypic effects (Nrf2-/- HD-exposed females) corresponded to significantly higher placental Apoa1 and Apob expression suggesting a link between placental lipid transport and NRF2 in response to high dose UFP exposure; Disruption of NRF2 exacerbates adverse developmental outcomes in response to high dose UFP exposure in female offspring. Morphological effects in placenta from male and female offspring exposed to low dose UFPs also signify the importance of NRF2 in maternal-fetal response to UFPs.

Generative Adversarial Networks for Morphological-Temporal Classification of Stem Cell Images

Frequently, neural network training involving biological images suffers from a lack of data, resulting in inefficient network learning. This issue stems from limitations in terms of time, resources, and difficulty in cellular experimentation and data collection. For example, when performing experimental analysis, it may be necessary for the researcher to use most of their data for testing, as opposed to model training. Therefore, the goal of this paper is to perform dataset augmentation using generative adversarial networks (GAN) to increase the classification accuracy of deep convolutional neural networks (CNN) trained on induced pluripotent stem cell microscopy images. The main challenges are: 1. modeling complex data using GAN and 2. training neural networks on augmented datasets that contain generated data. To address these challenges, a temporally constrained, hierarchical classification scheme that exploits domain knowledge is employed for model learning. First, image patches of cell colonies from gray-scale microscopy images are generated using GAN, and then these images are added to the real dataset and used to address class imbalances at multiple stages of training. Overall, a 2% increase in both true positive rate and F1-score is observed using this method as compared to a straightforward, imbalanced classification network, with some greater improvements on a classwise basis. This work demonstrates that synergistic model design involving domain knowledge is key for biological image analysis and improves model learning in high-throughput scenarios.

Developmental Toxicity and Biotransformation of Two Anti-Epileptics in Zebrafish Embryos and Early Larvae

The zebrafish (Danio rerio) embryo is gaining interest as a bridging tool between in-vitro and in-vivo developmental toxicity studies. However, cytochrome P450 (CYP)-mediated drug metabolism in this model is still under debate. Therefore, we investigated the potential of zebrafish embryos and larvae to bioactivate two known anti-epileptics, carbamazepine (CBZ) and phenytoin (PHE), to carbamazepine-10,11-epoxide (E-CBZ) and 5-(4-hydroxyphenyl)-5-phenylhydantoin (HPPH), respectively. First, zebrafish were exposed to CBZ, PHE, E-CBZ and HPPH from 5¼- to 120-h post fertilization (hpf) and morphologically evaluated. Second, the formations of E-CBZ and HPPH were assessed in culture medium and in whole-embryo extracts at different time points by targeted LC-MS. Finally, E-CBZ and HPPH formation was also assessed in adult zebrafish liver microsomes and compared with those of human, rat, and rabbit. The present study showed teratogenic effects for CBZ and PHE, but not for E-CBZ and HPPH. No HPPH was detected during organogenesis and E-CBZ was only formed at the end of organogenesis. E-CBZ and HPPH formation was also very low-to-negligible in adult zebrafish compared with the mammalian species. As such, other metabolic pathways than those of mammals are involved in the bioactivation of CBZ and PHE, or, these anti-epileptics are teratogens and do not require bioactivation in the zebrafish.

Gestational exposure to Δ9-THC impacts ovarian follicular dynamics and angiogenesis in adulthood in Wistar rats

With the legalization of marijuana (Cannabis sativa) and increasing use during pregnancy, it is important to understand its impact on exposed offspring. Specifically, the effects of Δ-9-tetrahydrocannabinol (Δ9-THC), the major psychoactive component of cannabis, on fetal ovarian development and long-term reproductive health are not fully understood. The aim of this study was to assess the effect of prenatal exposure to Δ9-THC on ovarian health in adult rat offspring. At 6 months of age, Δ9-THC-exposed offspring had accelerated folliculogenesis with apparent follicular development arrest, but no persistent effects on circulating steroid levels. Ovaries from Δ9-THC-exposed offspring had reduced blood vessel density in association with decreased expression of the pro-angiogenic factor VEGF and its receptor VEGFR-2, as well as an increase in the anti-angiogenic factor thrombospondin 1 (TSP-1). Collectively, these data suggest that exposure to Δ9-THC during pregnancy alters follicular dynamics during postnatal life, which may have long-lasting detrimental effects on female reproductive health.

Translational Toxicology in Zebrafish

A major goal of translational toxicology is to identify adverse chemical effects and determine whether they are conserved or divergent across experimental systems. Translational toxicology encompasses assessment of chemical toxicity across multiple life stages, determination of toxic mode-of-action, computational prediction modeling, and identification of interventions that protect or restore health following toxic chemical exposures. The zebrafish is increasingly used in translational toxicology because it combines the genetic and physiological advantages of mammalian models with the higher-throughput capabilities and genetic manipulability of invertebrate models. Here, we review recent literature demonstrating the power of the zebrafish as a model for addressing all four activities of translational toxicology. Important data gaps and challenges associated with using zebrafish for translational toxicology are also discussed.

Maternal bisphenol A exposure disrupts spermatogenesis in adult rat offspring

Bisphenol A (BPA) is an endocrine-disrupting chemical (EDC) that is widely used in the manufacturing of plastics and inner linings of food cans. Previously, it was reported that BPA disturbed the sexual dimorphic nucleus of the hypothalamus and delaying the onset of puberty attributed to an estrogenic action. In addition, BPA during the perinatal period increased LH serum concentrations in male offspring of dams at doses below the reproductive NOAEL (No Observable Adverse Effect Level) based upon World Health Organization guidelines. Based upon these findings, the objective of this study was to (1) determine the effects of perinatal treatment with low doses of BPA on regulation of spermatogenesis in adult offspring and (2) elucidate molecular mechanisms involved in the pathogenesis of gonadal dysfunction. The expression of genes related to spermatogenesis was disrupted with adverse consequences on sperm production, reserves, and function. Both BPA treated groups exhibited reduction in sperm production and epithelial height of seminiferous tubules, accompanied by diminished integrity of the acrosome and plasma membrane, decreased mitochondrial activity and increased incidence of morphological abnormalities. The sperm transit time was also slower. However, only in the group receiving the higher BPA dose was transcript expression of genes affected (reduced Ar and increased Esr1). It is of interest that serum testosterone levels were elevated in the same group where Ar was decreased. Data suggest that exposure to low BPA doses during hypothalamic sexual differentiation period produces permanent deleterious effects on spermatogenesis in adulthood.

Pancreatic beta cells are a sensitive target of embryonic exposure to butylparaben in zebrafish (Danio rerio)

BACKGROUND

Butylparaben (butyl p-hydroxybenzoic acid) is a common cosmetic and pharmaceutical preservative reported to induce oxidative stress and endocrine disruption. Embryonic development is sensitive to oxidative stress, with redox potentials playing critical roles in progenitor cell fate decisions. Because pancreatic beta cells have been reported to have low antioxidant gene expression, they may be sensitive targets of oxidative stress. We tested the hypotheses that butylparaben causes oxidative stress in the developing embryo, and that pancreatic beta cells are a sensitive target of butylparaben embryotoxicity.

METHODS

Transgenic insulin:GFP zebrafish embryos (Danio rerio) were treated daily with 0, 250, 500, 1,000, and 3,000 nM butylparaben. Pancreatic islet and whole embryo development were examined though 7 days postfertilization, and gene expression was measured by quantitative real-time PCR. Glutathione (GSH) and cysteine redox content were measured at 28 hr postfertilization using HPLC.

RESULTS

Butylparaben exposure caused intestinal effusion, pericardial edema, and accelerated yolk utilization. At 250 nM, beta cell area increased by as much as 55%, and increased incidence of two aberrant morphologies were observed-fragmentation of the islet cluster and ectopic beta cells. Butylparaben concentrations of 500 and 1,000 nM increased GSH by 10 and 40%, respectively. Butylparaben exposure downregulated transcription factor pdx1, as well as genes involved in GSH synthesis, while upregulating GSH-disulfide reductase (gsr).

CONCLUSIONS

The endocrine pancreas is a sensitive target of embryonic exposure to butylparaben, which also causes developmental deformities and perturbs redox conditions in the embryo.

Editor's Highlight: In Utero Exposure to Gadolinium and Adverse Neonatal Outcomes in Premature Infants

Gadolinium is a toxic rare earth element that is used as a contrast enhancement agent for diagnostic medical imaging. However, because of safety concerns to the developing fetus derived from preclinical studies, gadolinium can only be used during pregnancy if the potential benefits justify the potential risks to a fetus. Because there are no previous well designed safety studies on the developing fetus, we aimed to evaluate the potential adverse effects of in utero gadolinium exposure in high-risk premature infants. We performed a prospective dose (cord blood gadolinium concentration) - response (outcomes) study involving 104, 24-33 weeks gestational age (GA) infants. The mean (range) cord blood gadolinium concentration of infants measured using Inductively Coupled Plasma Mass Spectrometry was 191 (3.4-3729.6) pg/ml. The association between cord blood gadolinium concentration and each neonatal outcome was evaluated using linear or logistic regression analysis. The GA, race, gender, and antenatal steroid exposure were considered priori confounders. Recent adult human studies have shown that gadolinium exposure may be associated with nephrotoxicity. However, we found no adverse effects on renal function or other common outcomes including degree of prematurity, small for GA, respiratory distress syndrome, hyperbilirubinemia, intraventricular hemorrhage, necrotizing enterocolitis, patent ductus arteriosus, chronic lung disease, retinopathy of prematurity, and osteopenia of prematurity during the neonatal period with an increase in cord blood gadolinium concentration. None of the infants had clinically evident congenital malformations. In conclusion, gadolinium use during pregnancy is unlikely to be associated with adverse effects in infants during the neonatal period.

Integration of Life-Stage Physiologically Based Pharmacokinetic Models with Adverse Outcome Pathways and Environmental Exposure Models to Screen for Environmental Hazards

A computational framework was developed to assist in screening and prioritizing chemicals based on their dosimetry, toxicity, and potential exposures. The overall strategy started with contextualizing chemical activity observed in high-throughput toxicity screening (HTS) by mapping these assays to biological events described in Adverse Outcome Pathways (AOPs). Next, in vitro to in vivo (IVIVE) extrapolation was used to convert an in vitro dose to an external exposure level, which was compared with potential exposure levels to derive an AOP-based margins of exposure (MOE). In this study, the framework was applied to estimate MOEs for chemicals that can potentially cause developmental toxicity following a putative AOP for fetal vasculogenesis/angiogenesis. A physiologically based pharmacokinetic (PBPK) model was developed to describe chemical disposition during pregnancy, fetal, neonatal, and infant to adulthood stages. Using this life-stage PBPK model, maternal exposures were estimated that would yield fetal blood levels equivalent to the chemical concentration that altered in vitro activity of selected HTS assays related to the most sensitive vasculogenesis/angiogenesis putative AOP. The resulting maternal exposure estimates were then compared with potential exposure levels using literature data or exposure models to derive AOP-based MOEs.

E-waste: a global hazard

BACKGROUND

Waste from end-of-life electrical and electronic equipment, known as e-waste, is a rapidly growing global problem. E-waste contains valuable materials that have an economic value when recycled. Unfortunately, the majority of e-waste is recycled in the unregulated informal sector and results in significant risk for toxic exposures to the recyclers, who are frequently women and children.

OBJECTIVES

The aim of this study was to document the extent of the problems associated with inappropriate e-waste recycling practices.

METHODS

This was a narrative review that highlighted where e-waste is generated, where it is recycled, the range of adverse environmental exposures, the range of adverse health consequences, and the policy frameworks that are intended to protect vulnerable populations from inappropriate e-waste recycling practices.

FINDINGS

The amount of e-waste being generated is increasing rapidly and is compounded by both illegal exportation and inappropriate donation of electronic equipment, especially computers, from developed to developing countries. As little as 25% of e-waste is recycled in formal recycling centers with adequate worker protection. The health consequences of both direct exposures during recycling and indirect exposures through environmental contamination are potentially severe but poorly studied. Policy frameworks aimed at protecting vulnerable populations exist but are not effectively applied.

CONCLUSIONS

E-waste recycling is necessary but it should be conducted in a safe and standardized manor. The acceptable risk thresholds for hazardous, secondary e-waste substances should not be different for developing and developed countries. However, the acceptable thresholds should be different for children and adults given the physical differences and pronounced vulnerabilities of children. Improving occupational conditions for all e-waste workers and striving for the eradication of child labor is non-negotiable.

Avian models in teratology and developmental toxicology

The avian embryo is a long-standing model for developmental biology research. It also has proven utility for toxicology research both in ovo and in explant culture. Like mammals, avian embryos have an allantois and their developmental pathways are highly conserved with those of mammals, thus avian models have biomedical relevance. Fertile eggs are inexpensive and the embryo develops rapidly, allowing for high-throughput. The chick genome is sequenced and significant molecular resources are available for study, including the ability for genetic manipulation. The absence of a placenta permits the direct study of an agent's embryotoxic effects. Here, we present protocols for using avian embryos in toxicology research, including egg husbandry and hatch, toxicant delivery, and assessment of proliferation, apoptosis, and cardiac structure and function.

Gene knockdown by morpholino-modified oligonucleotides in the zebrafish (Danio rerio) model: applications for developmental toxicology

The zebrafish (Danio rerio) has long been used as a model for developmental biology, making it an excellent model to use also in developmental toxicology. The many advantages of zebrafish include their small size, prolific spawning, rapid development, and transparent embryos. They can be easily manipulated genetically through the use of transgenic technology and gene knockdown via morpholino-modified antisense oligonucleotides (MOs). Knocking down specific genes to assess their role in the response to toxicant exposure provides a way to further our knowledge of how developmental toxicants work on a molecular and mechanistic level while establishing a relationship between these molecular events and morphological, behavioral, and/or physiological effects (i.e., phenotypic anchoring). In this chapter, we address important considerations for using MOs to study developmental toxicology in zebrafish embryos and provide a protocol for their use.

Developmental toxicology: new directions workshop: refining testing strategies and study designs

In April 2009, the International Life Sciences Institute (ILSI) Health and Environmental Sciences Institute's (HESI) Developmental and Reproductive Toxicology Technical Committee held a two-day workshop entitled "Developmental Toxicology-New Directions." The third session of the workshop focused on ways to refine animal studies to improve relevance and predictivity for human risk. The session included five presentations on: (1) considerations for refining developmental toxicology testing and data interpretation; (2) comparative embryology and considerations in study design and interpretation; (3) pharmacokinetic considerations in study design; (4) utility of genetically modified models for understanding mode-of-action; and (5) special considerations in reproductive testing for biologics. The presentations were followed by discussion by the presenters and attendees. Much of the discussion focused on aspects of refining current animal testing strategies, including use of toxicokinetic data, dose selection, tiered/triggered testing strategies, species selection, and use of alternative animal models. Another major area of discussion was use of non-animal-based testing paradigms, including how to define a "signal" or adverse effect, translating in vitro exposures to whole animal and human exposures, validation strategies, the need to bridge the existing gap between classical toxicology testing and risk assessment, and development of new technologies. Although there was general agreement among participants that the current testing strategy is effective, there was also consensus that traditional methods are resource-intensive and improved effectiveness of developmental toxicity testing to assess risks to human health is possible. This article provides a summary of the session's presentations and discussion and describes some key areas that warrant further consideration.

Impact of environmental chemicals on lung development

BACKGROUND

Disruption of fundamental biologic processes and associated signaling events may result in clinically significant alterations in lung development.

OBJECTIVES

We reviewed evidence on the impact of environmental chemicals on lung development and key signaling events in lung morphogenesis, and the relevance of potential outcomes to public health and regulatory science .

DATA SOURCES

We evaluated the peer-reviewed literature on developmental lung biology and toxicology, mechanistic studies, and supporting epidemiology.

DATA SYNTHESIS

Lung function in infancy predicts pulmonary function throughout life. In utero and early postnatal exposures influence both childhood and adult lung structure and function and may predispose individuals to chronic obstructive lung disease and other disorders. The nutritional and endogenous chemical environment affects development of the lung and can result in altered function in the adult. Studies now suggest that similar adverse impacts may occur in animals and humans after exposure to environmentally relevant doses of certain xenobiotics during critical windows in early life. Potential mechanisms include interference with highly conserved factors in developmental processes such as gene regulation, molecular signaling, and growth factors involved in branching morphogenesis and alveolarization.

CONCLUSIONS

Assessment of environmental chemical impacts on the lung requires studies that evaluate specific alterations in structure or function-end points not regularly assessed in standard toxicity tests. Identifying effects on important signaling events may inform protocols of developmental toxicology studies. Such knowledge may enable policies promoting true primary prevention of lung diseases. Evidence of relevant signaling disruption in the absence of adequate developmental toxicology data should influence the size of the uncertainty factors used in risk assessments.

Methods for quantification of exposure to cigarette smoking and environmental tobacco smoke: focus on developmental toxicology

Active and passive smoking have been associated with an array of adverse effects on health. The development of valid and accurate scales of measurement for exposures associated with health risks constitutes an active area of research. Tobacco smoke exposure still lacks an ideal method of measurement. A valid estimation of the risks associated with tobacco exposure depends on accurate measurement. However, some groups of people are more reluctant than others to disclose their smoking status and exposure to tobacco. This is particularly true for pregnant women and parents of young children, whose smoking is often regarded as socially unacceptable. For others, recall of tobacco exposure may also prove difficult. Because relying on self-report and the various biases it introduces may lead to inaccurate measures of nicotine exposure, more objective solutions have been suggested. Biomarkers constitute the most commonly used objective method of ascertaining nicotine exposure. Of those available, cotinine has gained supremacy as the biomarker of choice. Traditionally, cotinine has been measured in blood, saliva, and urine. Cotinine collection and analysis from these sources has posed some difficulties, which have motivated the search for a more consistent and reliable source of this biomarker. Hair analysis is a novel, noninvasive technique used to detect the presence of drugs and metabolites in the hair shaft. Because cotinine accumulates in hair during hair growth, it is a unique measure of long-term, cumulative exposure to tobacco smoke. Although hair analysis of cotinine holds great promise, a detailed evaluation of its potential as a biomarker of nicotine exposure, is needed. No studies have been published that address this issue. Because the levels of cotinine in the body are dependent on nicotine metabolism, which in turn is affected by factors such as age and pregnancy, the characterization of hair cotinine should be population specific. This review aims at defining the sensitivity, specificity, and clinical utilization of different methods used to estimate exposure to cigarette smoking and environmental tobacco smoke.