To improve the mechanistic screening of reproductive toxicants in  chemical-risk assessment and drug development, we have developed a three-dimensional (3D) heterogenous testicular co-culture model from neonatal mice. Di-n-butyl phthalate (DBP), an environmental contaminant that can affect reproductive health negatively, was used as a model compound to illustrate the utility of the in vitro model. The cells were treated with DBP (1 nM to 100 µM) for 7 days. Automated high-content imaging confirmed the presence of cell-specific markers of Leydig cells (CYP11A1 +), Sertoli cells (SOX9 +), and germ cells (DAZL +). Steroidogenic activity of Leydig cells was demonstrated by analyzing testosterone levels in the culture medium. DBP induced a concentration-dependent reduction in testosterone levels and decreased the number of Leydig cells compared to vehicle control. The levels of steroidogenic regulator StAR and the steroidogenic enzyme CYP11A1 were decreased already at the lowest DBP concentration (1 nM), demonstrating upstream effects in the testosterone biosynthesis pathway. Furthermore, exposure to 10 nM DBP decreased the levels of the germ cell-specific RNA binding protein DAZL, central for the spermatogenesis. The 3D model also captured the development of the Sertoli cell junction proteins, N-cadherin and Zonula occludens protein 1 (ZO-1), critical for the blood–testis barrier. However, DBP exposure did not significantly alter the cadherin and ZO-1 levels. Altogether, this 3D in vitro system models testicular cellular signaling and function, making it a powerful tool for mechanistic screening of developmental testicular toxicity. This can open a new avenue for high throughput screening of chemically-induced reproductive toxicity during sensitive developmental phases.

Di-n-butyl phthalate (DBP) is a ubiquitous environmental contaminant linked with various adverse health effects, including immune system dysfunction. Gut microbial dysbiosis can contribute to a wide range of pathogenesis, particularly immune disease. Here, we investigated the impact of DBP on the gut microbiome and examined correlations with immune system changes after five weeks oral exposure (10 or 100 mg/kg/day) in adult male mice. The fecal microbiome composition was characterized using 16S rRNA sequencing. DBP-treated mice displayed a significantly distinct microbial community composition, indicated by Bray-Curtis distance. Numerous amplicon sequence variants (ASVs) at the genus level were altered. Compared to the vehicle control group, the 10 mg/kg/day DBP group had 63 more abundant and 65 less abundant ASVs, while 60 ASVs were increased and 76 ASVs were decreased in the 100 mg/kg/day DBP group. Both DBP treatment groups showed higher abundances of ASVs assigned to Desulfovibrio (Proteobacteria phylum) and Enterorhabdus genera, while ASVs belonging to Parabacteroides, Lachnospiraceae UCG-006 and Lachnoclostridium were less common compared to the control group. Interestingly, an ASV belonging to Rumniniclostridium 6, which was less abundant in DBP-treated mice, demonstrated a negative correlation with the increased number of non-classical monocytes observed in the blood of DBP-treated animals. In addition, an ASV from Lachnospiraceae UCG-001, which was more abundant in the DBP-treated animals, showed a positive correlation with the non-classical monocyte increase. This study shows that DBP exposure greatly modifies the gut bacterial microbiome and indicates a potential contribution of microbial dysbiosis to DBP-induced immune system impairment, illustrating the importance of investigating how interactions between exposome components can affect health.

Nontarget mass spectrometry has great potential to reveal patterns of water contamination globally through community science, but few studies are conducted in low-income countries, nor with open-source workflows, and few datasets are FAIR (Findable, Accessible, Interoperable, Reusable). Water was collected from urban and rural rivers around Dhaka, Bangladesh, and analyzed by liquid chromatography high-resolution mass spectrometry in four ionization modes (electrospray ionization +/-, atmospheric pressure chemical ionization +/-) with data -independent MS2 acquisition. The acquisition strategy was complementary: 19,427 and 7365 features were unique to ESI and APCI, respectively. The complexity of water pollution was revealed by >26,000 unique molecular features resolved by MS-DIAL, among which >20,000 correlated with urban sources in Dhaka. A major wastewater treatment plant was not a dominant pollution source, consistent with major contributions from uncontrolled urban drainage, a result that encourages development of further wastewater infrastructures. Matching of deconvoluted MS2 spectra to public libraries resulted in 62 confident annotations (i.e., Level 1-2a) and allowed semiquantification of 42 analytes including pharmaceuticals, pesticides, and personal care products. In silico structure prediction for the top 100 unknown molecular features associated with an urban source allowed 15 additional chemicals of anthropogenic origin to be annotated (i.e., Level 3). The authentic MS2 spectra were uploaded to MassBank Europe, mass spectral data were openly shared on the MassIVE repository, a tool (i.e., MASST) that could be used for community science environmental surveillance was demonstrated, and current limitations were discussed.

This work presents a case study in applying a systematic review framework (SYRINA) to the identification of chemicals as endocrine disruptors. The suitability and performance of the framework is tested with regard to the widely accepted World Health Organization definition of an endocrine disruptor (ED). The endocrine disrupting potential of triphenyl phosphate (TPP), a well-studied flame retardant reported to exhibit various endocrine related effects was assessed. We followed the 7 steps of the SYRINA framework, articulating the research objective via Populations, Exposures, Comparators, Outcomes (PECO) statements, performed literature search and screening, conducted study evaluation, performed data extraction and summarized and integrated the evidence. Overall, 66 studies, consisting of in vivo, in vitro and epidemiological data, were included. We concluded that triphenyl phosphate could be identified as an ED based on metabolic disruption and reproductive function. We found that the tools used in this case study and the optimizations performed on the framework were suitable to assess properties of EDs. A number of challenges and areas for methodological development in systematic appraisal of evidence relating to endocrine disrupting potential were identified; significant time and effort were needed for the analysis of in vitro mechanistic data in this case study, thus increasing the workload and time needed to perform the systematic review process. Further research and development of this framework with regards to grey literature (non-peer-reviewed literature) search, harmonization of study evaluation methods, more consistent evidence integration approaches and a pre-defined method to assess links between adverse effect and endocrine activity are recommended. It would also be advantageous to conduct more case studies for a chemical with less data than TPP.

Concerns have been raised regarding the potential adverse health effects of the ubiquitous herbicide glyphosate. Here, we investigated long-term effects of developmental exposure to a glyphosate-based herbicide (GBH) by analyzing serum melatonin levels and cellular changes in the striatum of adult male rats (90 days old). Pregnant and lactating rats were exposed to 3% GBH (0.36% glyphosate) through drinking water from gestational day 5 to postnatal day 15. The offspring showed reduced serum melatonin levels (43%) at the adult age compared with the control group. The perinatal exposure to GBH also induced long-term oxidative stress-related changes in the striatum demonstrated by increased lipid peroxidation (45%) and DNA/RNA oxidation (39%) together with increased protein levels of the antioxidant enzymes, superoxide dismutase (SOD1, 24%), glutamate–cysteine ligase (GCLC, 58%), and glutathione peroxidase 1 (GPx1, 31%). Moreover, perinatal GBH exposure significantly increased the total number of neurons (20%) and tyrosine hydroxylase (TH)-positive neurons (38%) in the adult striatum. Mechanistic in vitro studies with primary rat pinealocytes exposed to 50 µM glyphosate demonstrated a decreased melatonin secretion partially through activation of metabotropic glutamate receptor 3 (mGluR3), while higher glyphosate levels (100 or 500 µM) also reduced the pinealocyte viability. Since decreased levels of the important antioxidant and neuroprotector melatonin have been associated with an increased risk of developing neurodegenerative disorders, this demonstrates the need to consider the melatonin hormone system as a central endocrine-related target of glyphosate and other environmental contaminants.

It is important to identify the factors that influence the prevalence of disinhibitory behaviors, as tobacco and alcohol use in adolescence is a strong predictor of continued use and substance abuse into adulthood. Organochlorine pesticides (OCPs) are persistent organic pollutants that pose a potential risk to the developing fetus and offspring long-term health. We examined associations between prenatal exposure OCPs and their metabolites (i. e., p,p'-DDT, p,p'-DDE, o,p'-DDT, oxychlordane, and hexachlombenzene (HCB)), both as a mixture and single compounds, and alcohol consumption and smoking at adolescence in a sample (n = 554) from the Child Health and Development Studies prospective birth cohort. Bayesian Kernel Machine Regression demonstrated a trend of higher risk of alcohol use and smoking with higher quartile mixture levels. Single-component analysis showed increased odds of smoking and drinking with increases in lipid-adjusted p,p'-DDE serum levels (aOR = 2.06, 95% CI 0.99-4.31, p = 0.05, per natural log unit increase). We found significant effect modification in these associations by sex with higher p,p '-DDT serum levels (aOR = 0.26, 95% CI 0.09-0.076, p = 0.01, per natural log unit increase) was associated with lower odds of smoking and drinking in female adolescents, while higher p,p'-DDE serum levels (aOR = 2.98, 95% CI 1.04-8.51, p = 0.04, per natural log unit increase) was associated with higher odds of the outcomes. Results of the mutually adjusted model were not significant for male adolescents. Further research to understand reasons for these sex-differences are warranted.

Polychlorinated biphenyls (PCBs) are chemicals used in a variety of products before they were widely banned due to toxic effects in humans and wildlife. Because of continued persistence and ubiquity of these contaminants, risk of exposure to people living in industrialized countries is still high. Experimental research show that developmental exposure to PCB may alter function of brain pleasure centers and potentially influence disinhibitory behaviors, including tobacco and alcohol use. Yet, the potential effects of developmental PCB exposure on adolescent substance use have not been studied in humans. We used the Child Health and Development Studies (CHDS), a prospective birth cohort study in the Oakland and East Bay areas of California, to investigate associations between prenatal exposure to PCB congeners (66, 74, 99, 118, 138, 153, 170, 180, 187, and 203) and later disinhibitory behaviors in adolescents, specifically alcohol consumption and smoking, in a randomly selected sample (n = 554). Total prenatal PCB exposure was not associated with disinhibitory behaviors, among adolescents. However, the adjusted odds ratio (aOR) for being a current smoker, was higher in subjects within the third quartile of maternal PCB 66 exposure compared to those below the median (aOR = 1.93; 95% CI 1.05, 3.55). The aOR for drinking > 2 alcoholic beverages per week, were also higher for adolescents within the third (aOR = 1.46; 95% CI 0.86, 2.47) and fourth quartile of PCB 66 exposure (aOR = 1.39; 95% CI 0.83, 2.35), but the differences did not reach statistical significance. These results suggest that this specific PCB congener may play a role inducing neurodevelopmental alterations that could potentially increase the risk of becoming a long-term user of tobacco and possibly alcohol. There were no notable differences between magnitude or direction of effect between boys and girls. Future replicate analyses with larger longitudinal samples and animal experimental studies of potential underlying mechanisms are warranted.

Air pollution and rapid chemical intensification are major threats to the environment and human health. Today, we have produced over 350,000 chemicals, and current testing strategies do not meet the de-mands. Therefore, it is important to develop new approach methodologies (NAMs) that can help fill current information gaps. Toxicology needs to evolve from hazard and risk assessments based on morphological endpoints in animal tests towards a mechanism-driven integrated approach that better includes computational modelling as well as molecular, human, and in vitro data. The application of new science and technology such as different types of imaging and omics methods can allow faster collection of high-quality toxicological data for hazard identification and better prediction of toxicological potential using advanced in silico approaches including machine learning. A shift toward active prevention of pollution through a safe and sustainable-by-design approach based on cutting-edge science could significantly help safeguard the population and planetary health. Moreover, it is necessary to improve the understanding of how interactions among chemical mixtures, climate change, infectious agents, and other stressors that constitute the exposome, may affect biota and human health. Individual responses to current exposures and susceptibility to disease are influenced by factors such as genetics, epigenetics, physiology, and health status, which involve changes in biological pathways caused by own previous exposures or even ancestral exposures. It is therefore important to better consider individual exposomes and susceptibility in future risk assessments and precision medicine. This review describes the central role of mechanistic toxicology in chemical safety and in the cross-disciplinary efforts needed to char-acterize the exposome and its complex interactions in detail.

In this interview, Oskar Karlsson speaks with Storm Johnson, commissioning editor for Epigenomics, on his work to date in the field of toxicological origins of disease and gene-environment interactions. Oskar Karlsson, is an associate professor at the Science for Life Laboratory (SciLifeLab), Department of Environmental Science, Stockholm University, Sweden. Dr. Karlsson earned a PhD in toxicology at the Department of Pharmaceutical Bioscience, Uppsala University, and has also worked at Centre of Molecular Medicine, Karolinska Institute, as well as Harvard University School of Public Health. His research combines experimental model systems, computational and omics tools, and epidemiological studies to investigate the influence of environmental exposures on wildlife and human health, and underlying molecular mechanisms. In particular, his research focuses on developmental origins of health and disease with an emphasis on environmental exposures and epigenetic mechanisms. The projects concern the effects of exposures such as endocrine disrupting chemicals, flame retardants, pesticides, metals and particulate air pollution, as well as drugs, psycho-social stressors and ethnical disparities. Ongoing efforts include studies of paternal epigenetic inheritance in the ERC-funded project PATER.

Underlying drivers of species extinctions need to be better understood for effective conservation of biodiversity. Nearly half of all amphibian species are at risk of extinction, and pollution may be a significant threat as seasonal high-level agrochemical use overlaps with critical windows of larval development. The potential of environmental chemicals to reduce the fitness of future generations may have profound ecological and evolutionary implications. This study characterized effects of male developmental exposure to environmentally relevant concentrations of the anti-androgenic pesticide linuron over two generations of offspring in Xenopus tropicalis frogs. The adult male offspring of pesticide-exposed fathers (F1) showed reduced body size, decreased fertility, and signs of endocrine system disruption. Impacts were further propagated to the grand-offspring (F2), providing evidence of transgenerational effects in amphibians. The adult F2 males demonstrated increased weight and fat body palmitoleic-to-palmitic acid ratio, and decreased plasma glucose levels. The study provides important cross-species evidence of paternal epigenetic inheritance and pollutant-induced transgenerational toxicity, supporting a causal and complex role of environmental contamination in the ongoing species extinctions, particularly of amphibians.

Interactions between environmental factors and genetics underlie the majority of chronic human diseases. Chemical exposures are likely an underestimated contributor, yet gene-environment (GxE) interaction studies rarely assess their modifying effects. Here, we describe a novel method to profile the human genome and identify regions associated with differential population susceptibility to chemical exposures. Single nucleotide polymorphisms (SNPs) implicated in enriched chemical-disease intersections were identified and validated for three chemical classes with expected GxE interaction potential (neuroactive, hepatoactive, and cardioactive compounds). The same approach was then used to characterize consumer product classes with unknown risk for GxE interactions (washing products, cosmetics, and adhesives). Additionally, high-risk variant sets that may confer differential population susceptibility were identified for these consumer product groups through frequent itemset mining and pathway analysis. A dataset of 2454 consumer product chemical-disease linkages, with risk values, SNPs, and pathways for each association was developed, describing the interplay between environmental factors and genetics in human disease progression. We found that genetic hotspots implicated in GxE interactions differ across chemical classes (e.g., washing products had high-risk SNPs implicated in nervous system disease) and illustrate how this approach can discover new associations (e.g., washing product n-butoxyethanol implicated SNPs in the PI3K-Akt signaling pathway for Alzheimer’s disease). Hence, our approach can predict high-risk genetic regions for differential population susceptibility to chemical exposures and characterize chemical modifying factors in specific diseases. These methods show promise for describing how chemical exposures can lead to varied health outcomes in a population and for incorporating inter-individual variability into chemical risk assessment.

Studies indicate that phthalates are endocrine disruptors affecting reproductive health. One of the most commonly used phthalates, di-n-butyl phthalate (DBP), has been linked with adverse reproductive health outcomes in men, but the mechanisms behind these effects are still poorly understood. Here, adult male mice were orally exposed to DBP (10 or 100 mg/kg/day) for five weeks, and the testis and adrenal glands were collected one week after the last dose, to examine more persistent effects. Quantification of testosterone, androstenedione, progesterone and corticosterone concentrations by liquid chromatography-mass spectrometry showed that testicular testosterone was significantly decreased in both DBP treatment groups, whereas the other steroids were not significantly altered. Western blot analysis of testis revealed that DBP exposure increased the levels of the steroidogenic enzymes CYP11A1, HSD3 beta 2, and CYP17A1, the oxidative stress marker nitrotyrosine, and the luteinizing hormone receptor (LHR). The analysis further demonstrated increased levels of the germ cell marker DAZL, the Sertoli cell markers vimentin and SOX9, and the Leydig cell marker SULT1E1. Overall, the present work provides more mechanistic understanding of how adult DBP exposure can induce effects on the male reproductive system by affecting several key cells and proteins important for testosterone biosynthesis and spermatogenesis, and for the first time shows that these effects persist at least one week after the last dose. It also demonstrates impairment of testosterone biosynthesis at a lower dose than previously reported.

The widespread environmental contaminant di-n-butyl phthalate (DBP) has been linked with reduced testosterone levels and adverse reproductive health outcomes in men. However, the underlying mechanisms of these anti-androgenic effects and the potential effects on other classes of steroid hormones remain to be elucidated. Here, we conducted mechanistic studies in human adrenocortical H295R cells exposed to 1–500 µM of DBP or its metabolite, mono-n-butyl phthalate (MBP), for 48 h. Quantification of steroid hormones in the cell medium by liquid chromatography-mass spectrometry revealed that both phthalates significantly decreased testosterone, androstenedione, corticosterone, and progesterone levels, in particular after dibutyryl-cyclic-AMP stimulation of steroidogenesis. Western blot analysis of key steroidogenic proteins showed that DBP induced a dose-dependent decrease of CYP11A1 and HSD3β2 levels, while MBP only significantly decreased CYP17A1 levels, indicating that the compounds affect early steps of the steroidogenesis differently. Both DBP and MBP exposure also lead to a dose-related decrease in HSD17β3, the enzyme which catalyzes the final step in the testosterone biosynthesis pathway, although these effects were not statistically significant. Interestingly, DBP increased the cortisol concentration, which may be due to the non-significant CYP11B1 increase in DBP-exposed cells. In contrast, MBP decreased cortisol concentration. Moreover, the analysis of superoxide generation and quantification of the protein oxidation marker nitrotyrosine demonstrated that DBP induced oxidative stress in H295R cells while MBP reduced protein nitrotyrosine levels. These findings confirm the anti-androgenic effects of DBP and MBP and reveal several differences in their toxicological mechanisms, with possible implications for future research on phthalate toxicity.

Developmental exposure to the environmental neurotoxin beta -N-methylamino-l-alanine (BMAA), a proposed risk factor for neurodegenerative disease, can induce long-term cognitive impairments and neurodegeneration in rats. While rodent studies have demonstrated a low transfer of BMAA to the adult brain, this toxin is capable to cross the placental barrier and accumulate in the fetal brain. Here, we investigated the differential susceptibility of primary neuronal cells and neural stem cells from fetal rat hippocampus to BMAA toxicity. Exposure to 250 mu M BMAA induced cell death in neural stem cells through caspase-independent apoptosis, while the proliferation of primary neurons was reduced only at 3mM BMAA. At the lowest concentrations tested (50 and 100 mu M), BMAA disrupted neural stem cell differentiation and impaired neurite development in neural stem cell-derived neurons (e.g., reduced neurite length, the number of processes and branches per cell). BMAA induced no alterations of the neurite outgrowth in primary neurons. This demonstrates that neural stem cells are more susceptible to BMAA exposure than primary neurons. Importantly, the changes induced by BMAA in neural stem cells were mitotically inherited to daughter cells. The persistent nature of the BMAA-induced effects may be related to epigenetic alterations that interfere with the neural stem cell programming, as BMAA exposure reduced the global DNA methylation in the cells. These findings provide mechanistic understanding of how early-life exposure to BMAA may lead to adverse long-term consequences, and potentially predispose for neurodevelopmental disorders or neurodegenerative disease later in life.

Gene-environment interactions are involved in the development of breast cancer, the tumor type that accounts for the majority of the cancer-related deaths among women. Here, we demonstrate that exposure to PFOS (10 mu M) and PFOA (100 mu M)-two contaminants ubiquitously found in human blood-for 72 h induced breast epithelial cell (MCF-10A cell line) proliferation and alteration of regulatory cell-cycle proteins (cyclin D1, CDK6, p21, p53, p27, ERK 1/2 and p38) that persisted after a multitude of cell divisions. The contaminants also promoted cell migration and invasion by reducing the levels of E-cadherin, occludin and beta-integrin in the unexposed daughter cells. The compounds further induced an increase in global DNA methylation and differentially altered histone modifications, epigenetic mechanisms implicated in tumorigenesis. This mechanistic evidence for PFOS- and PFOA-induced malignant transformation of human breast cells supports a role of these abundant contaminants in the development and progression of breast cancer. Increased knowledge of contaminant-induced effects and their contribution to breast tumorigenesis is important for a better understanding of gene-environment interactions in the etiology of breast cancer.

Environmental contaminants including long-chain per- and polyfluoroalkyl substances (PFAS) have been linked to cancer, which is a central cause of mortality in humans and many wildlife species. Today shorter-chain PFAS are extensively used as replacement compounds and commonly found in the environment. Mechanistic studies are important for a better understanding of their toxicological potential and possible role in cancer etiology. Here, we treated normal human breast epithelial cells (MCF-10A) with 500 pM to 500 μM of perfluorohexane sulfonate (PFHxS), undecafluorohexanoic acid (PFHxA), hexafluoropropylene oxide-dimer acid (GenX), perfluoro 3,6 dioxaoctanoic acid (PFO2OA), heptafluorobutyric acid (HFBA) and perfluorobutanesulfonic acid (PFBS) for 72 h to investigate potential effects on cell proliferation and neoplastic transformation. PFHxA, GenX, PFO2OA, HFBA and PFBS induced no alterations compared to controls at any of the concentrations tested. Exposure to 100 μM PFHxS on the other hand was shown to affect important regulatory cell-cycle proteins (cyclin D1, CDK6, p27, p53 and ERK) and induced cell proliferation, at least in part through activation of the constitutive androstane receptor (CAR) and the peroxisome proliferator-activated receptor alpha (PPARα). PFHxS also altered histone modifications and induced cell malignance by reducing the levels of adhesion proteins (E-cadherin and β-integrin) and promoting cell migration and invasion. These results demonstrate that five out of six alternative PFAS tested are clearly less harmful to MCF-10A cells than previously studied PFOS and PFOA, but raise concerns about PFHxS that also has been associated with breast cancer in epidemiological studies.

Per and polifluorinated substances (PFAS) are ubiquitous and persistent contaminants. Studies have indicated that fetuses and infants can be exposed to these chemicals in utero and through breastfeeding. Despite this, limited data about their effects on brain development are available. Here, we compared the effects of perfluoroctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) exposure in rat primary neurons and neural stem cells (NSC). Treatment with 1-250 mu M of either of these compounds caused no effects on cell viability or proliferation in primary neurons, while PFOS exposure increased the NSC proliferation already at the lowest concentration tested (1-100 mu M). Further analysis showed that both PFOS and PFOA caused morphological alterations of NSC-derived neurons. The neurons derived from NSC treated with either of the PFAS demonstrated a decrease in cell body area. Exposure to 1 and 10 mu M PFOA also affected the neurite network and caused an increase in the number of processes and branches per cell. None of the PFAS caused morphological alterations in primary neurons. These data suggest that NSC, mimicking the immature brain, is clearly more susceptible to PFOS and PFOA exposure than the primary neurons. The PFAS-induced alterations in NSC may be related to neurobehavioral alterations observed in rodents developmentally exposed to these compounds, and show the importance to consider the effects of these compounds on human brain development and disease.

The widespread environmental contaminant beta-methylamino-L-alanine (BMAA) is a developmental neurotoxicant that can induce long-term learning and memory deficits. Studies have shown high transplacental transfer of 3H-BMAA and a significant uptake in fetal brain. Therefore, more information on how BMAA may influence growth and differentiation of neural stem cells is required for assessment of the risk to the developing brain. The aim of this study was to investigate direct and mitotically inherited effects of BMAA exposure using primary striatal neurons and embryonic neural stem cells. The neural stem cells were shown to be clearly more susceptible to BMAA exposure than primary neurons. Exposure to 250 mu M BMAA reduced neural stem cell proliferation through apoptosis and G2/M arrest. At lower concentrations (50-100 mu M), not affecting cell proliferation, BMAA reduced the differentiation of neural stem cells into astrocytes, oligodendrocytes, and neurons through glutamatergic mechanisms. Neurons that were derived from the BMAA-treated neuronal stem cells demonstrated morphological alterations including reduced neurite length, and decreased number of processes and branches per cell. Interestingly, the BMAA-induced changes were mitotically heritable to daughter cells. The results suggest that early-life exposure to BMAA impairs neuronal stem cell programming, which is vital for development of the nervous system and may result in long-term consequences predisposing for both neurodevelopmental disorders and neurodegenerative disease later in life. More attention should be given to the potential adverse effects of BMAA exposure on brain development.

Perfluoroalkyl substances (PFAS) have been associated with cancer, but the potential underlying mechanisms need to be further elucidated and include studies of PFAS mixtures. This mechanistic study revealed that very low concentrations (500 pM) of the binary PFOS and PFOA mixture induced synergistic effects on human epithelial breast cell (MCF-10A) proliferation. The cell proliferation was mediated by pregnane X receptor (PXR) activation, an increase in cyclin D1 and CDK6/4 levels, decrease in p21 and p53 levels, and by regulation of phosphor-Akt and β-catenin. The PFAS mixture also altered histone modifications, epigenetic mechanisms implicated in tumorigenesis, and promoted cell migration and invasion by reducing the levels of occludin. High-content screening using the cell painting assay, revealed that hundreds of cell features were affected by the PFAS mixture even at the lowest concentration tested (100 pM). The detailed phenotype profiling further demonstrated that the PFAS mixture altered cell morphology, mostly in parameters related to intensity and texture associated with mitochondria, endoplasmic reticulum, and nucleoli. Exposure to higher concentrations (≥50 µM) of the PFOS and PFOA mixture caused cell death through synergistic interactions that induced oxidative stress, DNA/RNA damage, and lipid peroxidation, illustrating the complexity of mixture toxicology. Increased knowledge about mixture-induced effects is important for better understanding of PFAS’ possible role in cancer etiology, and may impact the risk assessment of these and other compounds. This study shows the potential of image-based multiplexed fluorescence assays and high-content screening for development of new approach methodologies in toxicology.

Increased exposure to manmade chemicals may be linked to an increase in immune-related diseases in humans and immune system dysfunction in wildlife. Phthalates are a group of endocrine-disrupting chemicals (EDCs) suspected to influence the immune system. The aim of this study was to characterize the persistent effects on leukocytes in the blood and spleen, as well as plasma cytokine and growth factor levels, one week after the end of five weeks of oral treatment with dibutyl phthalate (DBP; 10 or 100 mg/kg/d) in adult male mice. Flow cytometry analysis of the blood revealed that DBP exposure decreased the total leukocyte count, classical monocyte and T helper (Th) popula-tions, whereas it increased the non-classical monocyte population compared to the vehicle control (corn oil). Immuno-fluorescence analysis of the spleen showed increased CD11b+Ly6G+ (marker of polymorphonuclear myeloid-derived suppressor cells; PMN-MDSCs), and CD43+staining (marker of non-classical monocytes), whereas CD3+ (marker of total T cells) and CD4+ (marker of Th cells) staining decreased. To investigate the mechanisms of action, levels of plasma cytokines and chemokines were measured using multiplexed immunoassays and other key factors were ana-lyzed using western blotting. The observed increase in M-CSF levels and the activation of STAT3 may promote PMN-MDSC expansion and activity. Increased ARG1, NOX2 (gp91phox), and protein nitrotyrosine levels, as well as GCN2 and phosphor-eIRF alpha, suggest that oxidative stress and lymphocyte arrest drive the lymphocyte suppression caused by PMN-MDSCs. The plasma levels of IL-21 (promotes the differentiation of Th cells) and MCP-1 (regulates mi-gration and infiltration of monocytes/macrophages) also decreased. These findings show that adult DBP exposure can cause persistent immunosuppressive effects, which may increase susceptibility to infections, cancers, and immune dis-eases, and decrease vaccine efficacy.

Olfactory dysfunction is implicated in neurodegenerative disorders and typically manifests years before other symptoms. The cyanobacterial neurotoxin beta-N-methylamino-l-alanine (BMAA) is suggested as a risk factor for neurodegenerative disease. Detection of BMAA in air filters has increased the concern that aerosolization may lead to human BMAA exposure through the air. The aim of this study was to determine if BMAA targets the olfactory system. Autoradiographic imaging showed a distinct localization of radioactivity in the right olfactory mucosa and bulb following a unilateral intranasal instillation of H-3-BMAA (0.018 mu g) in mice, demonstrating a direct transfer of BMAA via the olfactory pathways to the brain circumventing the blood-brain barrier, which was confirmed by liquid scintillation. Treatment of mouse primary olfactory bulb cells with 100 mu M BMAA for 24 h caused a disruption of the neurite network, formation of dendritic varicosities and reduced cell viability. The NMDA receptor antagonist MK-801 and the metabotropic glutamate receptor antagonist MCPG protected against the BMAA-induced alterations, demonstrating the importance of glutamatergic mechanisms. The ionotropic non-NMDA receptor antagonist CNQX prevented the BMAA-induced decrease of cell viability in mixed cultures containing both neuronal and glial cells, but not in cultures with neurons only, suggesting a role of neuron-glial interactions and glial AMPA receptors in the BMAA-induced toxicity. The results show that the olfactory region may be a target for BMAA following inhalation exposure. Further studies on the relations between environmental olfactory toxicants and neurodegenerative disorders are warranted.

Early life exposure to endocrine disrupting chemicals (EDCs) has been suggested to adversely affect reproductive health in humans and wildlife. Here, we characterize endocrine and adverse effects on the reproductive system after juvenile exposure to propiconazole (PROP) or imazalil (IMZ), two common azole fungicides with complex endocrine modes of action. Using the frog Xenopus tropicalis, two short-term (2-weeks) studies were conducted. I: Juveniles (2 weeks post metamorphosis (PM)) were exposed to 0, 17 or 178 µg PROP/L. II: Juveniles (6 weeks PM) were exposed to 0, 1, 12 or 154 µg IMZ/L. Histological analysis of the gonads revealed an increase in the number of dark spermatogonial stem cells (SSCs)/testis area, and in the ratio secondary spermatogonia: dark SSCs were increased in all IMZ groups compared to control. Key genes in gametogenesis, retinoic acid and sex steroid pathways were also analysed in the gonads. Testicular levels of 3β-hsd, ddx4 were increased and cyp19 and id4 levels were decreased in the IMZ groups. In PROP exposed males, increased testicular aldh1a2 levels were detected, but no histological effects observed. Although no effects on ovarian histology were detected, ovarian levels of esr1, rsbn1 were increased in PROP groups, and esr1 levels were decreased in IMZ groups. In conclusion, juvenile azole exposure disrupted testicular expression of key genes in retinoic acid (PROP) and sex steroid pathways and in gametogenesis (IMZ). Our results further show that exposure to environmental concentrations of IMZ disrupted spermatogenesis in the juvenile testis, which is a cause for concern as it may lead to impaired fertility. Testicular levels of id4, ddx4 and the id4:ddx4 ratio were associated with the number of dark SSCs and secondary spermatogonia suggesting that they may serve as a molecular markers for disrupted spermatogenesis.

Peripubertal models to determine effects of anti-androgenic endocrine disrupting chemicals are needed. Using the toxicological model species Xenopus tropicalis, the aims of the study were to 1) provide data on sexual maturation and 2) characterise effects of short-term exposure to an anti-androgenic model substance. Juvenile (2.5 weeks post metamorphosis old) X. tropicalis were exposed to 0, 250, 500 or 1000 & mu;g flutamide/L (nominal) for 2.5 weeks. Upon exposure termination, histology of gonads and Mullerian ducts was characterised in detail. New sperm stages were identified: pale and dark spermatogonial stem cells (SSCs). The testes of control males contained spermatozoa, indicating pubertal onset. The ovaries were immature, and composed of non-follicular and pre-vitellogenic follicular oocytes. The Mullerian ducts were more mature in females than males indicating development/regression in the females and males, respectively. In the 500 & mu;g/L group, the number of dark SSCs per testis area was decreased and the number of secondary spermatogonia was increased. No treatment effects on ovaries or Mullerian ducts were detected. To conclude, our present data provide new knowledge on spermatogenesis, and pubertal onset in X. tropicalis. New endpoints for evaluating spermatogenesis are suggested to be added to existing assays used in endocrine and reproductive toxicology.