Neurotoxic effects of 2-ethylhexyl diphenyl phosphate exposure on zebrafish larvae: Insight into inflammation-driven changes in early motor behavior

New Psychoactive Substance Esketamine Causes Endocrine-Disrupting Effects and Developmental Toxicity

Esketamine (ESK), a new psychoactive substance known for its strong hallucinogenic effect, has been detected in surface water worldwide. The toxicity of ESK to fish at a certain environmental concentration remains unclear. In this study, zebrafish embryos and ZF4 cells were exposed to ESK (0, 0.12, 1.02, and 10.6 μg L-1, marked by SC, LC, MC, and HC, respectively) for 14 days post fertilization (dpf) and 24 h, respectively. Biphasic dose responses induced by ESK were observed after 24 h of exposure. ESK-LC and ESK-MC obviously increased embryo area and length, height, and volume of yolk sac, whereas ESK-HC had the opposite effect. ESK-LC and ESK-MC appreciably upregulated the transcription and expression levels of vtg, disrupting the cell cycle after 24 h of exposure. After 14 dpf exposure, KEGG analysis indicated that circadian rhythm, nucleotide excision repair, and estrogen signaling pathways were the top three impacted pathways, with ESK significantly enhancing gene transcription in these three pathways, except for cyp7a1 and bh1he41. Correspondingly, ESK notably increased the VTG level, aligning with the relatively high affinity of estrogen receptors, as analyzed through molecular docking. Our research demonstrated that ESK exhibits developmental toxicity and endocrine-disrupting effects in zebrafish, highlighting the need to address its ecological toxicity in fish.

Estrogenic and anti-estrogenic assessment of the flame retardant, 2-ethylhexyl diphenyl phosphate (EHDPP), and its metabolites: Evidence from in vitro, in silico, and transcriptome studies

2-Ethylhexyl diphenyl phosphate (EHDPP) is a replacement flame-retardant commonly found in several environmental matrices and human biospecimens. Although some adverse effects of EHDPP have been identified, the endocrine-disrupting effects of EHDPP and its key metabolites on the human estrogen receptor (ER) are largely unknown. Herein, we report for the first time that EHDPP, at concentrations found in the environment and humans, significantly promoted estrogenic activity and synergized with 17β-estradiol-induced ER transactivation. However, two major EHDPP metabolites 2-ethyl-3-hydroxyhexyl diphenyl phosphate (3-OH-EHDPP) and 2-ethyl-5-hydroxyhexyl diphenyl phosphate (5-OH-EHDPP), inhibited the ER through a non-competitive binding mechanism. Molecular docking showed that Pi-Pi stacking, hydrogen, and hydrophobic bonds primarily stabilize intermolecular interactions between EHDPP and the binding pockets of human ERα and ERβ. Moreover, transcriptome analysis confirmed the estrogenic effects of EHDPP, revealing notable enrichments in ER-mediated signaling and breast cancer pathways, consistent with the validated estrogenic gene expression profile. Intriguingly, EHDPP markedly promoted the clonogenic growth of two ER+ breast cancer cell lines, corroborating the expression levels of ERα protein. Our findings indicate that the common flame-retardant EHDPP activates the ER and downstream signaling, providing far-reaching implications for environmental and health risks associated with estrogen-related adversities such as the development of ER+ breast cancer.

3,3',5,5'-Tetrabromobiphenyl (BB-80) and Its Hydroxylation Product (OH-BB-80) Mediate Immunotoxicity and Inhibit Embryonic Development in Zebrafish (Danio rerio) via the TLR4/NF-κB Signaling Pathway

Polybrominated biphenyls (PBBs) are metabolically transformed into monohydroxylated PBBs (OH-PBBs) in the environment and living organisms. Although OH-PBBs pose a significant health threat to organisms, little is known about the immunotoxicity of OH-PBBs. Therefore, the objectives of this study were to validate BB-80 and OH-BB-80 induced immunotoxicity and to explore the associated pathway mechanisms. Early development of zebrafish (Danio rerio) larvae was inhibited by 10 μg/L BB-80 and OH-BB-80, as indicated by negative changes in developmental indices. BB-80 and OH-BB-80 induced oxidative stress, significantly up-regulated reactive oxygen species (ROS) and reactive nitrogen species (RNS), and activated the antioxidant enzyme system at 10 μg/L. The mRNA expression levels of inflammatory cytokines and inflammatory chemokines were up-regulated, indicative of the onset of inflammation in zebrafish after BB-80 and OH-BB-80 exposure. In addition, downregulation of toll-like receptor 4 (TLR4), MyD88, and NF-κB pathway-related genes was observed, suggesting that BB-80 and OH-BB-80 target the TLR/NF-κB signaling pathway. Molecular docking data showed that BB-80 and OH-BB-80 bound stably to TLR4. Taken together, BB-80 and OH-BB-80 mediate immunotoxicity and early developmental suppression associated with the TLR4/NF-κB signaling pathway. Our results further the understanding of BB-80- and OH-BB-80-induced immunotoxicity, highlighting the need for toxicological studies to examine the toxic effects of the transformation products of PBBs.

Tri-iso-butyl phosphate (TiBP) exposure induces neurotoxicity by triggering oxidative stress accompanied by neurotransmitter system disruptions and apoptosis in zebrafish larvae

The current research sheds light on the biological toxicity of organophosphate flame retardants (OPFRs), yet it overlooks the neurotoxicity and potential molecular mechanisms of tris(1,3-dichloro-2-propyl) phosphate (TiBP), a prominent constituent of the OPFRs. To address this, we utilized zebrafish larvae as a model to investigate TiBP's acute toxicity and neurotoxic effects, along with the associated molecular pathways. Our findings revealed that the 96 h and 120 h LC50 values for TiBP were 56.51 mg/L and 48.85 mg/L, respectively. Gradient exposure based on the 120 h LC50 demonstrated that TiBP induced developmental toxicity, characterized by elevated heart rate, reduced body length, and diminished eye distance. Additionally, a decrease in swimming activity was observed in the light test, along with the inhibition of the neuro crest cell development in Tg (HuC:eGFP) and Tg (sox10: eGFP) zebrafish larvae following TiBP exposure, as well as the alterations of neurogenesis and ACh-related genes. Expression of key neurodevelopment genes, including mbpa, gap43, nestin, ngfra, was significantly downregulated. Furthermore, heightened anxiety-like behaviors in open field and phototaxis tests were observed, concomitant with neurotransmitter imbalances. Specifically, there was an increase in DA levels, a decrease in GABA, and an upregulation of AChE activity. These disruptions were primarily mediated through transcriptional dysregulation of neurotransmitter synthesis, transport, and reception. Upon exposure to TiBP, zebrafish larvae exhibited a concentration-dependent increase in both ROS level and apoptosis. An upregulation of antioxidant enzymes and their transcription levels indicated the presence of oxidative stress in the larvae. The induction of ddit3 was congruent with the observed apoptosis, suggesting that it may be triggered by oxidative stress via the ERs-CHOP pathway. In summary, our study indicates that oxidative stress is a pivotal molecular event in the neurotoxicity induced by TiBP, implicating the disruption of the GABAergic, dopaminergic, and cholinergic systems, as well as triggering apoptosis.

2-Ethylhexyl diphenyl phosphate aggravates colitis-induced neuroinflammation and behavioral abnormalities by inhibiting the PI3K-AKT-NF-κB and Wnt/GSK3β signaling pathways

2-Ethylhexyl diphenyl phosphate (EHDPHP), a widely used organophosphorus flame retardant (OPFR), is ubiquitous in daily life because of its extensive application in plastic production. EHDPHPs, which are only superficially applied and not chemically bonded to products, are released into the environment, posing potential health risks. With increasing environmental concentrations, EHDPHP is a growing threat, particularly to individuals with preexisting health conditions who are more susceptible to environmental pollutants. This study examined the effects of EHDPHP exposure in a colitis model, reflecting a rising chronic health issue, by assessing changes in neuroinflammation and neurobehavioral abnormalities. Healthy and dextran sulfate sodium (DSS)-induced colitis C57BL/6 J mice were treated with either 0.2 % Tween or EHDPHP solution (10 mg/kg body weight/day) for 28 days. The study revealed significant increases in the serum and expression levels of TNFα and IL-1β, accompanied by depressive and anxiety-like behaviors. Coexposure to EHDPHP and DSS exacerbated these neurobehavioral impairments. RNA sequencing confirmed that EHDPHP triggered inflammation via the PI3K-Akt-NF-κB and Wnt/GSK3β signaling pathways, as confirmed by Western blot analysis. These findings suggest that EHDPHP aggravates colitis-induced neuroinflammation and neurobehavioral abnormalities, highlighting the harmful impact of EHDPHP, particularly in individuals with preexisting inflammatory conditions.

Long-Term Neurotoxic Effects and Alzheimer's Disease Risk of Early EHDPP Exposure in Zebrafish: Insights from Molecular Mechanisms to Adult Pathology

2-Ethylhexyl diphenyl phosphate (EHDPP), ubiquitously monitored in environmental media, is highly bioaccumulative and may pose long-term risks, even after short-term exposure. In this investigation, larval zebrafish were exposed to 0.05, 0.5, and 5.0 μg/L EHDPP from 4 to 120 h postfertilization (hpf) to examine the long-term neurotoxicity effects of early exposure. Exposure to 5.0 μg/L EHDPP yielded hyperactive locomotor behavior, which was characterized by increased swimming speed, larger turning angles, and heightened sensitivity to light-dark stimulation. The predicted targets of EHDPP (top 100 potential macromolecules) were primarily associated with brain diseases like Alzheimer's disease (AD). Comparisons of differentially expressed genes (DEGs) from AD patients (GSE48350) and RNA-seq data from EHDPP-exposed zebrafish confirmed consistently abnormal regulatory pathways. EHDPP's interaction with M1 and M5 muscarinic acetylcholine receptors likely disrupted calcium homeostasis, leading to mitochondrial dysfunction and neurotransmitter imbalance as well as abnormal locomotor behavior. Especially, 5.0 μg/L EHDPP exposure during early development (4-120 hpf) triggered early- and midstage AD-like symptoms in adulthood (180 dpf), characterized by cognitive confusion, aggression, blood-brain barrier disruption, and mitochondrial damage in brains. These findings provide deep insights into the long-term neurotoxicity effects and Alzheimer's disease risks of early EHDPP exposure at extremely low dosages.

Triphenyl Phosphate Alters Methyltransferase Expression and Induces Genome-Wide Aberrant DNA Methylation in Zebrafish Larvae

Emerging environmental contaminants, organophosphate flame retardants (OPFRs), pose significant threats to ecosystems and human health. Despite numerous studies reporting the toxic effects of OPFRs, research on their epigenetic alterations remains limited. In this study, we investigated the effects of exposure to 2-ethylhexyl diphenyl phosphate (EHDPP), tricresyl phosphate (TMPP), and triphenyl phosphate (TPHP) on DNA methylation patterns during zebrafish embryonic development. We assessed general toxicity and morphological changes, measured global DNA methylation and hydroxymethylation levels, and evaluated DNA methyltransferase (DNMT) enzyme activity, as well as mRNA expression of DNMTs and ten-eleven translocation (TET) methylcytosine dioxygenase genes. Additionally, we analyzed genome-wide methylation patterns in zebrafish larvae using reduced-representation bisulfite sequencing. Our morphological assessment revealed no general toxicity, but a statistically significant yet subtle decrease in body length following exposure to TMPP and EHDPP, along with a reduction in head height after TPHP exposure, was observed. Eye diameter and head width were unaffected by any of the OPFRs. There were no significant changes in global DNA methylation levels in any exposure group, and TMPP showed no clear effect on DNMT expression. However, EHDPP significantly decreased only DNMT1 expression, while TPHP exposure reduced the expression of several DNMT orthologues and TETs in zebrafish larvae, leading to genome-wide aberrant DNA methylation. Differential methylation occurred primarily in introns (43%) and intergenic regions (37%), with 9% and 10% occurring in exons and promoter regions, respectively. Pathway enrichment analysis of differentially methylated region-associated genes indicated that TPHP exposure enhanced several biological and molecular functions corresponding to metabolism and neurological development. KEGG enrichment analysis further revealed TPHP-mediated potential effects on several signaling pathways including TGFβ, cytokine, and insulin signaling. This study identifies specific changes in DNA methylation in zebrafish larvae after TPHP exposure and brings novel insights into the epigenetic mode of action of TPHP.

Melatonin improves mouse oocyte quality from 2-ethylhexyl diphenyl phosphate-induced toxicity by enhancing mitochondrial function

2-Ethylhexyl diphenyl phosphate (EHDPP) is a representative organophosphorus flame retardant (OPFR) that has garnered attention due to its widespread use and potential adverse effects. EHDPP exhibits cytotoxicity, genotoxicity, developmental toxicity, and endocrine disruption. However, the toxicity of EHDPP in mammalian oocytes and the underlying mechanisms remain poorly understood. Melatonin is a natural free radical scavenger that has demonstrated cytoprotective properties. In this study, we investigated the effect of EHDPP on mouse oocytes in vitro culture system and evaluated the rescue effect of melatonin on oocytes exposed to EHDPP. Our results indicated that EHDPP disrupted oocyte maturation, resulting in the majority of oocytes arrested at the metaphase I (MI) stage, accompanied by cytoskeletal damage and elevated levels of reactive oxygen species (ROS). Nevertheless, melatonin supplementation partially rescued EHDPP-induced mouse oocyte maturation impairment. Results of single-cell RNA sequencing (scRNA-seq) analysis elucidated potential mechanisms underlying these protective effects. According to the results of scRNA-seq, we conducted further tests and found that EHDPP primarily disrupts mitochondrial distribution and function, kinetochore-microtubule (K-MT) attachment, DNA damage, apoptosis, and histone modification, which were rescued upon the supplementation of melatonin. This study reveals the mechanisms of EHDPP on female reproduction and indicates the efficacy of melatonin as a therapeutic intervention for EHDPP-induced defects in mouse oocytes.

Prenatal organophosphate esters exposure and neurodevelopment trajectory in infancy: Evidence from the Shanghai Maternal-Child Pairs Cohort

BACKGROUND

Concerns remain about the neurotoxic properties of the ubiquitous organophosphate esters (OPEs), the replacement of the toxicant polybrominated diphenyl ethers.

OBJECTIVES

We examined the associations of prenatal exposure to OPEs and their mixtures with early-life neurodevelopment trajectories.

METHODS

Totally 1276 mother-child pairs were recruited from the Shanghai Maternal-Child Pairs Cohort. A high-performance liquid chromatography-triple quadrupole mass spectrometer was used to measure the levels of 7 OPEs in cord serum. Ages and Stages Questionnaires was used to examine children's neuropsychological development at 2, 6, 12, and 24 months of age. Group-based trajectory models were applied to derive the neurodevelopmental trajectories. Multiple linear regression and logistic regression model were performed to assess the relationships between OPEs exposure and neurodevelopment and trajectories. Mixtures for widely detected OPEs (n = 4) were investigated using quantile-based g-computation.

RESULTS

Tributyl phosphate (TBP), tris (2-butoxy ethyl) phosphate (TBEP), tris(1,3-dichloro-2-propyl) phosphate (TDCPP), and 2-ethylhexyl diphenyl phosphate (EHDPP), had detection rates >50 %. TDCPP had the highest median concentration (1.02 μg/L) in cord serum. EHDPP concentrations were negatively associated with scores in most domains at 12 months of age, with effect values (β) ranging from -1.89 to -0.57. EHDPP could negatively affect the total ASQ (OR = 1.07, 95 % CI: 1, 1.15) and gross-motor (OR = 1.09, 95 % CI: 1.02, 1.17) trajectory in infancy. Joint exposure to OPEs was associated with decreased scores in the total ASQ, gross-motor, fine-motor and problem-solving domain of 12-month-old infants, with β ranging from -5.93 to -1.25. In addition, the qgcomp models indicated significant positive associations between the concentrations of OPEs mixtures and risks of the persistently low group of the total ASQ, gross-motor and fine-motor development in early childhood. The impact of OPEs was more pronounced in boys.

DISCUSSION

Our findings suggested OPEs, especially EHDPP, had a persistently negative effect on neurodevelopment during the first 2 years.