Early-life and chronic exposure to di(2-ethylhexyl) phthalate enhances amyloid-β toxicity associated with an autophagy-related gene in Caenorhabditis elegans Alzheimer's disease models

Role and mechanism of MiR-542-3p in regulating TLR4 in nonylphenol-induced neuronal cell pyroptosis

BACKGROUND

This study aimed to investigate the spatial learning/memory and motor abilities of rats and the alteration of miR-542-3p and pyroptosis in the midbrain nigrostriatal area in vivo after nonylphenol (NP) gavage and to explore the mechanism of miR-542-3p regulation of Toll-like receptor 4 (TLR4) in NP-induced pyroptosis in BV2 microglia in vitro.

METHODS

In vivo: Thirty-six specific-pathogen-free-grade Sprague-Dawley rats were divided into three equal groups: blank control group (treated with pure corn oil), NP group (treated with NP, 80 mg/kg body weight per day for 90 days), and positive control group [treated with lipopolysaccharide (LPS), 2 mg/kg body weight for 7 days]. In vitro: The first part of the experiment was divided into blank group (control, saline), LPS group [1 µg/ml + 1 mM adenosine triphosphate (ATP)], and NP group (40 µmol/L). The second part was divided into mimics NC (negative control) group, miR-542-3p mimics group, mimics NC + NP group, and miR-542-3p mimics + NP group.

RESULTS

In vivo: Behaviorally, the spatial learning/memory and motor abilities of rats after NP exposure declined, as detected via Y-maze, open field, and rotarod tests. Some microglia in the substantia nigra of the NP-treated rats were activated. The downregulation of miR-542-3p was observed in rat brain tissue after NP exposure. The mRNA/protein expression of pyroptosis-related indicators (TLR4), NOD-like receptor protein 3 (NLRP3), apoptosis-associated speck-like protein (ASC), gasdermin-D (GSDMD), cysteinyl aspartate-specific proteinase-1 (caspase-1), and interleukin-1β (IL-1β) in the substantia nigra of the midbrain increased after NP exposure. In vitro: ASC fluorescence intensity increased in BV2 cells after NP exposure. The mRNA and/or protein expression of pyroptosis-related indicators (TLR4, NLRP3, GSDMD, caspase-1, and IL-1β) in BV2 cells was upregulated after NP exposure. The transfection of miR-542-3p mimics inhibited NP-induced ASC expression in BV2 cells. The overexpression of miR-542-3p, followed by NP exposure, significantly reduced TLR4, NLRP3, ASC, caspase-1, and IL-1β gene and/or protein expression.

CONCLUSIONS

This study suggested that NP exposure caused a decline in spatial learning memory and whole-body motor ability in rats. Our study was novel in reporting that the upregulation of miR-542-3p targeting and regulating TLR4 could inhibit NLRP3 inflammatory activation and alleviate NP-induced microglia pyroptosis.

Subchronic exposure to di-(2-ethylhexyl) phthalate (DEHP) elicits blood-brain barrier dysfunction and neuroinflammation in male C57BL/6J mice

BACKGROUND

Exposure to di-(2-ethylhexyl) phthalate (DEHP) can cause neurotoxicity but the mechanism is not clear. Blood brain barrier (BBB) is one of the most important tissues to protect the brain. However, whether DEHP can disrupt the BBB or not remains unclear. The objective of this study is to investigate the potential effects of subchronic DEHP exposure on BBB integrity and discuss the role of BBB in DEHP inducible neurotoxicity with an emphasis on neuroinflammatory responses. Male adult C57BL/6J mice were orally administered with vehicle or 200 or 750 mg/kg/day DEHP for 90 days. Subchronic exposure to high-dose DEHP increased water intake but decreased body weight and brain weight. The concentrations of DEHP metabolites increased in serum from all DEHP-exposed groups while increased in brain only from the high-dose group. DEHP induced neurobehavioural alterations and damaged hippocampal neurons. DEHP increased BBB permeability by Evans blue (EB) extravasation and decreased tight junction proteins (ZO-1, occludin, and claudin-5) while presenting a neuroinflammatory feature characterized by the upregulated inflammatory mediators TNF-α and the NLRP3/caspase-1/IL-1β inflammasome pathway. Our data provide new insights into neurotoxicity caused by subchronic DEHP exposure, which is probably involved in BBB dysfunction and neuroinflammatory responses.

Monitoring long-term chemical exposome by characterizing the hair metabolome using a high-resolution mass spectrometry-based suspect screening approach

Hair has recently emerged as a biospecimen for characterizing the long-term chemical exposome in biomonitoring investigations spanning several months, as chemical compounds circulating in the bloodstream accumulate in hair. Although there has been interest in using human hair as a biospecimen for exposome studies, it has yet to be widely adopted compared to blood and urine. Here, we applied a high-resolution mass spectrometry (HRMS)-based suspect screening strategy to characterize the long-term chemical exposome in human hair. Hair samples were collected from 70 subjects and cut into 3 cm segments, which were then mixed to prepare pooled samples. The pooled hair samples underwent a sample preparation procedure, and the hair extracts were further analyzed using an HRMS-based suspect screening approach. An in-house chemical suspect list containing 1227 chemical entries from National Report on Human Exposure to Environmental Chemicals (Report) published by the U.S. CDC and the Exposome-Explorer 3.0 database developed by the WHO was subsequently used to screen and filter the suspect features against the HRMS dataset. Overall, we matched 587 suspect features in the HRMS dataset to 246 unique chemical formulas in the suspect list, and the structures of 167 chemicals were further identified through a fragmentation analysis. Among these, chemicals such as mono-2-ethylhexyl phthalate, methyl paraben, and 1-naphthol, which have been detected in the urine or blood for exposure assessment, were also identified in human hair. This suggests that hair reflects the accumulation of environmental compounds to which an individual is exposed. Exposure to exogenous chemicals may exert adverse effects on cognitive function, and we discovered 15 chemicals in human hair that may contribute to the pathogenesis of Alzheimer's disease. This finding suggests that human hair may be a promising biospecimen for monitoring long-term exposure to multiple environmental chemicals and perturbations in endogenous chemicals in biomonitoring investigations.

Prenatal DEHP exposure predicts neurological disorders via transgenerational epigenetics

Recent experimental and observational research has suggested that childhood allergic asthma and other conditions may be the result of prenatal exposure to environmental contaminants, such as di-(2-ethylhexyl) phthalate (DEHP). In a previous epidemiological study, we found that ancestral exposure (F0 generation) to endocrine disruptors or the common plasticizer DEHP promoted allergic airway inflammation via transgenerational transmission in mice from generation F1 to F4. In the current study, we employed a MethylationEPIC Beadchip microarray to examine global DNA methylation in the human placenta as a function of maternal exposure to DEHP during pregnancy. Interestingly, global DNA hypomethylation was observed in placental DNA following exposure to DEHP at high concentrations. Bioinformatic analysis confirmed that DNA methylation affected genes related to neurological disorders, such as autism and dementia. These results suggest that maternal exposure to DEHP may predispose offspring to neurological diseases. Given the small sample size in this study, the potential role of DNA methylation as a biomarker to assess the risk of these diseases deserves further investigation.

Long-term exposure to low-dose Di(2-ethylhexyl) phthalate aggravated high fat diet-induced obesity in female mice

The potential obesogenic roles of di(2-ethylhexyl) phthalate (DEHP) have attracted great attention. The current study aimed to evaluate the combined effects of chronic low-dose DEHP (0.05 mg/kg BW) and a high-fat diet (HFD) on obesity in female mice and explore the underlying mechanisms. We found that low-dose DEHP challenge for 29 weeks increased fat accumulation both in CD- and HFD-fed mice and significantly accelerated the weight gain without affecting food intake in HFD-fed mice. DEHP exposure reduced the energy metabolism, down-regulated the uncoupling protein 1 (UCP1) and total oxidative phosphorylation (OXPHOS) proteins expression in the brown adipose tissue, and up-regulated the PPARγ expression and its phosphorylation at Ser273 in white adipose tissue (WAT). Besides, the combination of DEHP and HFD drove the remodeling of gut microbiota of mice, characterized by the reduced richness and diversity and the elevated Firmicutes to Bacteroidetes (F/B) ratio. Short-chain fatty acids (SCFAs) analysis revealed that DEHP and HFD cotreatment led to a decrease in levels of acetic acid, butyric acid, and pentanoic acid. Interestingly, sodium butyrate (NaB) significantly inhibited the adipogenesis and lipid accumulation of NIH/3T3 mouse embryonic fibroblasts (PPARγ2 overexpression) and the PPARγ phosphorylation at Ser273 induced by DEHP or MEHP. These findings demonstrate that chronic low-dose DEHP challenge could prompt fat accumulation by increasing PPARγ phosphorylation at Ser273 and decreasing thermogenesis in BAT, which might be associated with the SCFAs reduction.

Chronic exposure to di(2-ethylhexyl) phthalate (DEHP) weakens innate immunity and leads to immunosenescence in C. elegans

Di(2-ethylhexyl) phthalate (DEHP), a widespread contaminant, has numerous adverse impacts on human health and ecosystems. Chronic DEHP exposure has been found to accelerate aging; however, its potential threat to age-dependent innate immune decline remains unknown. This study aims to evaluate the effects of chronic DEHP exposure on innate immunosenescence in Caenorhabditis elegans. We show that the length of the exposure period significantly impacts DEHP-induced age-related declines, which is linked to immunosenescence and oxidative stress. We found that the DEHP-caused immunosenescence is accompanied with downregulation of an antimicrobial gene lys-7 as well as an enhancement of the nuclear translocation of HLH-30, an orthologue of mammalian transcription factor EB (TFEB). Moreover, DEHP exposure increases the expression of riok-1, a human RIO kinase homolog, which is associated with DEHP-induced HLH-30/TFEB translocation. Our findings suggest that early-life and chronic exposure to DEHP, mostly due to parent compound rather than its metabolite mono(2-ethylhexyl) phthalate (MEHP), may weaken the innate immunity in C. elegans and may enhance susceptibility to infections or promote immunosenescence in aged populations.

Dietary Methylglyoxal Exposure Induces Alzheimer's Disease by Promoting Amyloid β Accumulation and Disrupting Autophagy in Caenorhabditis elegans

Methylglyoxal (MG) is a precursor of advanced glycation end products usually generated during cooking. The high level of MG in the brain is correlated to the pathogenesis of Alzheimer's disease (AD). However, it is not clear if MG consumed through the diet can cause AD-related toxicity. Herein, the Caenorhabditis elegans (C. elegans) AD model was used to investigate the neurotoxicity after long-term MG exposure at dietary levels. The results showed that C. elegans locomotive behaviors were significantly decreased after 0.1, 0.5, and 1 mM MG exposure (p < 0.001). In amyloid β (Aβ)-expressing transgenic C. elegans strains, 0.5 mM MG significantly promoted Aβ accumulation by around 50% in day-8 CL2006 (p < 0.001), enhanced paralysis in CL4176 (p < 0.001) and CL2006 (p < 0.01), and made CL2355 around 17% more vulnerable to 5-HT, indicating impaired serotonin reuptake (p < 0.05). Additionally, 0.5 mM MG significantly increased the reactive oxygen species level (p < 0.001) by inhibiting the expression of stress-response genes including sod-3, gst-4, and hsp-16.2 in day-8 aged worms. Moreover, the autophagic pathway was disrupted through lgg-1, vps-34, and bec-1 expression after MG exposure and Aβ accumulation. Treatment with the citrus flavonoid nobiletin reduced the MG-induced toxicity (p < 0.001). Overall, these findings imply that it is possible to exacerbate AD pathogenesis by MG exposure through the diet.

Chronic di(2-ethylhexyl) phthalate exposure leads to dopaminergic neuron degeneration through mitochondrial dysfunction in C. elegans

The plasticizer di(2-ethylhexyl) phthalate (DEHP) is frequently detected in the environment due to the abundance of its use. These levels might be hazardous to human health and ecosystems. Phthalates have been associated with neurological disorders, yet whether chronic DEHP exposure plays a role in Parkinson's disease (PD) or its underlying mechanisms is unknown. We investigated the effects of chronic DEHP exposure less than an environmentally-relevant dose on PD hallmarks, using Caenorhabditis elegans as a model. We show that developmental stage and exposure timing influence DEHP-induced dopaminergic neuron degeneration. In addition, in response to chronic DEHP exposure at 5 mg/L, mitochondrial fragmentation became significantly elevated, reactive oxygen species (ROS) levels increased, and ATP levels decreased, suggesting that mitochondrial dysfunction occurs. Furthermore, the data show that mitochondrial complex I (nuo-1 and gas-1) and complex II (mev-1) are involved in DEHP-induced dopaminergic neuron toxicity. These results suggest that chronic exposure to DEHP at levels less than an environmentally-relevant dose causes dopaminergic neuron degeneration through mitochondrial dysfunction involving mitochondrial complex I and II. Considering the high level of genetic conservation between C. elegans and mammals, chronic DEHP exposure might elevate the risk of developing PD in humans.

Chronic exposure to environmentally relevant levels of di(2-ethylhexyl) phthalate (DEHP) disrupts lipid metabolism associated with SBP-1/SREBP and ER stress in C. elegans

DEHP is commonly found in the environment, biota, food, and humans, raising significant health concerns. Whether developmental stage and exposure duration modify the obesogenic effects of DEHP is unclear, especially the underlying mechanisms by which chronic exposure to DEHP as well as its metabolites remain largely unknown. This study investigated the obesogenic effects of chronic DEHP exposure, with levels below environmentally-relevant amounts and provide the mechanism in Caenorhabditis elegans. We show that early-life DEHP exposure resulted in an increased lipid and triglyceride (TG) accumulation mainly attributed to DEHP itself, not its metabolite mono-2-ethylhexyl phthalate (MEHP). In addition, developmental stage and exposure timing influence DEHP-induced TG accumulation and chronic DEHP exposure resulted in the most significant effect. Analysis of fatty acid composition shows that chronic DEHP exposure altered fatty acid composition and TG, resulting in an increased ω-6/ω-3 ratio. The increased TG content by chronic DEHP exposure required lipogenic genes fat-6, fat-7, pod-2, fasn-1, and sbp-1. Moreover, chronic DEHP exposure induced XBP-1-mediated endoplasmic reticulum (ER) stress which might lead to up-regulation of sbp-1. This study suggests the possible involvement of ER stress and SBP-1/SREBP-mediated lipogenesis in chronic DEHP-induced obesogenic effects. Results from this study implies that chronic exposure to DEHP disrupts lipid metabolism, which is likely conserved across species due to evolutionary conservation of molecular mechanisms, raising concerns in ecological and human health.

Association between mixed exposure of phthalates and cognitive function among the U.S. elderly from NHANES 2011-2014: Three statistical models

BACKGROUND

Studies on the relationship between phthalate exposure and cognition in adults are sparse and inconsistent. These studies only assessed their association of single phthalates for one-time and the tools for assessing cognitive function were different.

OBJECTIVE

We aimed to examine the association between mixed phthalates and cognition in the U.S elderly using three statistical models.

METHODS

The generalized linear (GLM), weighted quantile sum (WQS), and Bayesian kernel machine regression (BKMR) models were used to evaluate the associations between mixed phthalates and the standardized z-scores of four cognitive tests [Immediate Recall test (IRT), Delayed Recall test (DRT), Animal Fluency test (AFT), and Digit Symbol Substitution test (DSST)] in participants aged over 60 years from NHANES 2011-2014.

RESULTS

835 individuals were included and the median raw scores of IRT, DRT, AFT, and DSST were 19 (IQR: 16-23), 6 (IQR: 5-8), 16 (IQR: 13-20), 46 (IQR: 35-59). In adjusted GLM, negative associations were observed between MECPP, MnBP, MCOP, MCPP, and the IRT z-scores; MCPP, MBzP, and the DRT z-scores. Positive relationships were found between MCOP, MCPP, and the AFT z-scores; MCPP and the DSST z-scores. The WQS index was associated with the IRT z-scores (β(95%CI): -0.069(-0.118, -0.020)), where MCPP weighted the highest. In the BKMR, negative overall trends between the mixture and the IRT, DRT z-scores were observed when the mixture was at 40th to 65th percentile, 65th percentile or above it, respectively, where MnBP and MBzP drove the main effect of the mixture.

CONCLUSION

This study is an academic exploration of the association between phthalates exposure and cognitive function, suggesting that exposure to phthalates might be associated with bad performance in IRT and DRT in the U.S. elderly.

UV-filter octyl methoxycinnamate causes reproductive toxicity associated with germline apoptosis and vitellogenin decrease in Caenorhabditis elegans

Octyl methoxycinnamate (OMC) is a common UV filter found in personal care products such as sunscreen and cosmetics. However, OMC's presence in wastewater has raised concerns that it could potentially pollute aquatic ecosystems because of its limited biodegradability and its estrogenic disrupting properties. In this study, we investigated the environmental toxicity of OMC and its potential biomarkers using the nematode Caenorhabditis elegans. Our results showed that body length, eggs in utero, and total brood size decreased with increasing dose (experimental concentrations = 0, 1, 5, 10, 100, 500 μM for body length and eggs in utero, and 0, 5, 10 μM for total brood size) in C. elegans after L1 larval stage (the first larval stage for 0 - 12 hours post-hatching) larval stage exposure to OMC. The minimum effective concentrations were 1, 5, and 10 μM, respectively. Modeling results demonstrated that the threshold concentration of OMC inducing 10% inhibited eggs in utero was 0.33 μM (95.11 μg/L). Furthermore, germline apoptosis was induced in 10 μM OMC-treated worms (experimental concentrations = 0, 5, 10 μM). Decreased mRNA levels of vitellogenin-related genes (vit-2 and vit-6) and increased mRNA levels of apoptosis-related genes (egl-1 and ced-3) were observed in 10 μM OMC-treated C. elegans (experimental concentrations = 0, 10 μM), suggesting that reproductive toxicity was associated with decreased vitellogenin levels and germline apoptosis. In summary, our study shows that OMC is reproductively toxic and leads to reduced egg formation and decreased brood size in C. elegans by reducing vitellogenin levels and promoting germline apoptosis.

Endoglin Modulates TGFβR2 Induced VEGF and Proinflammatory Cytokine Axis Mediated Angiogenesis in Prolonged DEHP-Exposed Breast Cancer Cells

Angiogenesis is the process of vascular network development and plays a crucial role in cancer growth, progression, and metastasis. Phthalates are a class of environmental pollutants that have detrimental effects on human health and are reported to increase cancer risk. However, the interplay between phthalate exposure and angiogenesis has not been investigated thoroughly. In this study, we investigated the effect of prolonged di (2-ethylhexyl) phthalate (DEHP) treatment on the angiogenic potential of triple-negative breast cancer. MDA-MB-231 cells were exposed to physiological concentrations of DEHP for more than three months. Prolonged DEHP exposure induced angiogenesis in breast cancer cells. Endoglin (ENG)/CD105 is a membrane glycoprotein and an auxiliary receptor of the TGFβ receptor complex. In endothelial cells, ENG is highly expressed and it is a prerequisite for developmental angiogenesis. A literature review highlights endoglin as a well-known mesenchymal stem cell marker responsible for vascular development and angiogenesis. NGS analysis showed that endoglin overexpression in DEHP-exposed MDA-MB-231 cells correlated with tumor development and growth. An in vivo zebrafish xenograft assay showed that VEGFA induced sprouting of the subintestinal vein (SIV) in embryos injected with DEHP-exposed cells. Endoglin knockdown reduced SIV sprouting and VEGFA expression in zebrafish embryos. An in vitro HUVEC tube formation assay showed that endoglin depletion reversed DEHP-induced VEGF-mediated HUVEC tube formation in coculture. DEHP-induced endoglin activated TGFβ/SMAD3/VEGF and MAPK/p38 signaling in MDA-MB-231 cells. A cytokine angiogenesis antibody array showed induced expression of the inflammatory cytokines IL1α, IL1β, IL6, and IL8, along with GMCSF and VEGF. Endoglin knockdown reversed DEHP-induced activation of the TGFβ/SMAD3/VEGF signaling axis, MAPK/p38 signaling, and cytokine regulation, limiting angiogenesis potential both in vivo and in vitro. Targeting endoglin might serve as a potential alternative treatment to control angiogenesis, leading to metastasis and limiting cancer progression.

Oxidative stress, intestinal damage, and cell apoptosis: Toxicity induced by fluopyram in Caenorhabditis elegans

Fluopyram, a succinate dehydrogenase inhibitor fungicide and nematicide, has been used extensively for agricultural pest control and toxicologically affects non-target organisms. In the present study, Caenorhabditis elegans, a well-established model organism, was used to evaluate the toxic effect of fluopyram and the possible molecular mechanisms. C. elegans was exposed to fluopyram for 24 h at three sublethal concentrations (0.01, 0.05 and 0.25 mg/L) and the physiological, biochemical, and molecular indicators were examined. The results showed that sublethal exposure to fluopyram could cause damage to growth, locomotion behavior, feeding, lifespan and reproduction of the nematodes. Fluopyram exposure induced oxidative stress as indicated by increase of ROS production, lipofuscin and lipid accumulation, and MDA level in the nematodes. In contrast, exposure to fluopyram significantly decreased the activities of target enzyme SDH and antioxidant enzymes including SOD, CAT and GST. Moreover, the expression of genes associated with oxidative stress (e.g., gst-4, sod-3, fat-7, mev-1 and daf-16), intestinal damage (e.g., mtm-6, nhx-2, opt-2, pkc-3, par-6, act-5 and egl-8), and cell apoptosis (e.g., ced-13, ced-3, egl-38, efl-2, cep-1 and lgg-1) was significantly influenced after exposure to fluopyram. According to Pearson correlation analyses, significant correlation existed between 190 pairs of parameters, which indicated that fluopyram induced multiple toxic related effects in C. elegans. These findings suggest that oxidative stress, intestinal damage, and cell apoptosis may play major roles in toxicity of fluopyram in the nematodes.

siRNA@superparamagnetic iron oxide nanoparticles attenuate physiological toxicity of DEHP by suppressing autophagy pathway activities in Caenorhabditis elegans

Bis(2-ethylhexyl)ortho-phthalate (DEHP) is a widely used plasticizer in polyvinyl chloride materials. Considering its widespread application, it has become a major environmental pollutant and can cause endocrine, reproductive system, and gastrointestinal disorders. Herein we aimed to elucidate the mechanisms via which DEHP causes cytotoxicity in Caenorhabditis elegans and assess whether siRNA@superparamagnetic iron oxide nanoparticles (SPIONs) can attenuate this effect. On exposing C. elegans to 10 μM DEHP, its physiological functions and gene expression levels were markedly affected. RNA-seq and Kyoto Encyclopedia of Genes and Genomes pathway analyses indicated that DEHP exposure significantly activated the autophagy-animal signal transduction pathway in the somatic cells of C. elegans. Subsequently, the surface of SPIONs was loaded with siRNAs and transfected into C. elegans. Transmission electron microscopy showed that SPIONs could smoothly enter the somatic cells of C. elegans. Further, qPCR showed that the expression levels of autophagy pathway-related genes, namely Atg-2, Epg-9, Atg-18, Bec-1, and Atg-16.2, in the siRNA@SPION intervention group were significantly lower than those in the control group. Biochemical and physiological test results suggested that siRNA@SPION complexes attenuated DEHP-induced physiological toxicity and oxidative stress damage in C. elegans. Collectively, our findings indicated that DEHP markedly affects the physiological activity of C. elegans, induces changes in gene expression levels, and activates the autophagy signal transduction pathway and that siRNA@SPION complexes suppress such toxic effects by silencing the expression of genes involved in the autophagy signal transduction pathway.