Inhibition in growth and cardiotoxicity of tris (2-butoxyethyl) phosphate through down-regulating Wnt signaling pathway in early developmental stage of zebrafish (Danio rerio)

Degradation of organophosphate flame retardants by white-rot fungi: Degradation pathways and associated toxicity

The environmental persistence of organophosphate flame retardants (OPFRs) in water is becoming and environmental concern. White Rot Fungi (WRF) have proven its capability to degrade certain OPFRs such as tributyl phosphate (TBP), tris(2-butoxyethyl) phosphate (TBEP), tris(2-chloroethyl) phosphate (TCEP) and tris(2-chloroisopropyl) phosphate (TCPP). Despite this capability, there is limited knowledge about the specific pathways involved in the degradation. In this study, three different WRF were paired with individual OPFRs, and potential transformation products (TPs) were identified by UHPLC-HRMS. Some compounds structures were further validated by NMR. From these data degradation pathways were proposed. TBP was degraded by successive hydroxylation and hydrolysis reactions, with a novel dehydrogenation step suggested. Both TCEP and TCPP underwent oxidative dechlorination, with TCEP experiencing subsequent hydrolysis. Uncommon reductive dehalogenation was also observed. TCPP further underwent hydroxylation and environmentally relevant methylation. TBEP generated numerous TPs, mainly by successive dealkylations, along with hydroxylation. Notably, demethylation in TBEP degradation was proposed for the first time. Additional secondary products were formed through hydroxylation and oxidation of the initial metabolites. Finally, in vivo and in silico toxicity assessments were conducted, identifying certain TPs as potentially toxic.

Potential adverse outcome pathway of neurodevelopmental toxicity, inflammatory response, and oxidative stress induction mediated by three alkyl organophosphate flame retardants in zebrafish larvae

Following restrictions on polybrominated flame retardants, trimethyl phosphate (TMP), triethyl phosphate (TEP), and tris(2-butoxyethyl) phosphate (TBEP) have been frequently used as plasticizers for fire-resistant plastics. This study investigated the neurodevelopmental effects, inflammatory response, and oxidative stress induction of three alkyl organophosphate flame retardants using a zebrafish embryo/larvae model. After exposure of zebrafish embryos to TMP, TEP, and TBEP (0, 0.02, 0.2, 2, 20, and 200 μg L-1) for 96 h, survival, development, swimming behavior, changes in acetylcholinesterase (AChE) activity, dopamine, tumor necrosis factor-alpha (TNF-α), interleukin (IL), reactive oxygen species (ROS), and antioxidant enzyme activities were observed. Concentrations of TMP, TEP, and TBEP were also measured in the whole body of exposed larvae. Our results showed that exposure to 200 μg L-1 TEP and ≥20 μg L-1 TBEP significantly reduced larval body length; however, TMP had no significant effects on developmental parameters up to 200 μg L-1. After 96 h of exposure to TBEP, total distance moved, mean velocity, AChE, and dopamine concentrations were significantly decreased. Exposure to TEP and TBEP decreased the expression of genes that regulate central nervous system development (e.g. gap43 and mbpa), whereas ROS, antioxidant enzymes, TNF-α, and IL-1β concentrations were significantly increased. Notably, pretreatment with an antioxidant N-acetylcysteine reduced neurotoxicity and oxidative stress caused by TEP and TBEP. The results of this study demonstrated that exposure to TEP and TBEP causes oxidative stress and has adverse effects on the neurobehavioral and immune system of zebrafish, leading to hypoactivity and ultimately impairing development.

Levels of organophosphate flame retardants and their metabolites among 391 volunteers in Taiwan: difference between adults and children

Background

Organophosphate flame retardants (OPFRs) are ubiquitous in the environment. The compositions and concentrations of different OPFRs metabolites vary in different environments depending on different human activities. The objective of the present study was to evaluate the exposure of different age groups to OPFRs in Taiwan.

Methods

Volunteers provided urine samples and responded to questionnaires including demographic factors, underlying disease, lifestyle information, and occupation from October 2021 to January 2022. OPFR measurements were performed using a Waters Acquity Ultra-Performance Liquid Chromatography system coupled with a Waters Xevo TQ-XS mass spectrometer.

Results

A total of 391 volunteers (74 children and 317 adults) were enrolled in this study. The concentrations (presented as μg/g creatinine) of bis(1,3-dichloro-2-propyl) phosphate (BDCPP, p = 0.029) and tri-n-butyl phosphate (TNBP, p = 0.008) were higher in the adult group, while the concentrations of bis-2-chloroethyl phosphate (BCEP, p = 0.024), diphenyl phosphate (DPHP, p < 0.001), tris(1,3-dichloro-2-propyl) phosphate (TDCPP, p = 0.009), and Tris(2-butoxyethyl) phosphate (TBEP, p = 0.007) were higher in the child group. Compared with school age children (>6 years), the concentration of di(2-n-butoxyethyl) phthalate (DBEP, 1.14 vs. 0.20 μg/g creatinine, p = 0.001), DPHP (1.23 vs. 0.54 μg/g creatinine, p = 0.036), TBEP (1.63 vs. 0.29 μg/g creatinine, p < 0.001), and the sum of OPFR metabolites (ΣOPFRs, 6.58 vs. 2.04 μg/g creatinine, p < 0.001) were statistically higher in preschool-aged children. After adjusting for confounding factors, pre-school age [odds ratio (OR): 4.579, 95% confidence interval (CI): 1.389-13.115] and current smoker (OR: 5.328, 95%CI: 1.858-14.955) were independently associated with the risk of ΣOPFRs higher than 90 percentile.

Conclusion

This study revealed the distribution of different OPFRs metabolites in children and adults. DBEP, DPHP, TBEP, and ΣOPFR were higher in preschool-aged children. Pre-school age and current smoking status were independent risk factors for ΣOPFRs higher than 90 percentile.

Personal protective equipment and micro-nano plastics: A review of an unavoidable interrelation for a global well-being hazard

The usage and the demand for personal protective equipments (PPEs) for our day-to-day survival in this pandemic period of COVID-19 have seen a steep rise which has consequently led to improper disposal and littering. Fragmentation of these PPE units has eventually given way to micro-nano plastics (MNPs) emission in the various environmental matrices and exposure of living organisms to these MNPs has proven to be severely toxic. Numerous factors contribute to the toxicity imparted by these MNPs that mainly include their shape, size, functional groups and their chemical diversity. Even though multiple studies on the impacts of MNPs toxicity are available for other organisms, human cell line studies for various plastic polymers, other than the most common ones namely polyethylene (PE), polystyrene (PS) and polypropylene (PP), are still at their nascent stage and need to be explored more. In this article, we cover a concise review of the literature on the impact of these MNPs in biotic and human systems focusing on the constituents of the PPE units and the additives that are essentially used for their manufacturing. This review will subsequently identify the need to gather scientific evidence at the smaller level to help combat this microplastic pollution and induce a more in-depth understanding of its adverse effect on our existence.

Norgestrel causes digestive gland injury in the clam Mactra veneriformis: An integrated histological, transcriptomics, and metabolomics study

The potential adverse effects of progestins on aquatic organisms, especially non-target species, are of increasing concern worldwide. However, the effect and mechanism of progestin toxicity on aquatic invertebrates remain largely unexplored. In the present study, clams Mactra veneriformis were exposed to norgestrel (NGT, 0, 10, and 1000 ng/L), the dominant progestin detected in the aquatic environment, for 21 days. NGT accumulation, histology, transcriptome, and metabolome were assessed in the digestive gland. The bioconcentration factor (BCF) was 386 and 268 in the 10 ng/L NGT group and 1000 ng/L NGT group, respectively, indicating efficient accumulation of NGT in the clams. Histological analysis showed that NGT led to the swelling of epithelial cells and blurring of the basement membrane in the digestive gland. Differentially-expressed genes and KEGG pathway enrichment analysis using a transcriptomic approach suggested that NGT primarily disturbed the detoxification system, antioxidant defense, carbohydrate and amino acid metabolism, and steroid hormone metabolism, which was consistent with the metabolites analyzed using a metabolomic approach. Furthermore, we speculated that the oxidative stress caused by NGT resulted in histological damage to the digestive gland. This study showed that NGT caused adverse effects in the clams and sheds light on the mechanisms of progestin interference in aquatic invertebrates.

Insights into the circadian rhythm alterations of the novel PFOS substitutes F-53B and OBS on adult zebrafish

As alternatives to perfluorooctane sulfonate (PFOS), 6:2 Cl-PFESA (F-53B) and sodium p-perfluorous nonenoxybenzene sulfonate (OBS) are frequently detected in aquatic environments, but little is known about their neurotoxicity, especially in terms of circadian rhythms. In this study, adult zebrafish were chronically exposed to 1 μM PFOS, F-53B and OBS for 21 days taking circadian rhythm-dopamine (DA) regulatory network as an entry point to comparatively investigate their neurotoxicity and underlying mechanisms. The results showed that PFOS may affect the response to heat rather than circadian rhythms by reducing DA secretion due to disruption of calcium signaling pathway transduction caused by midbrain swelling. In contrast, F-53B and OBS altered the circadian rhythms of adult zebrafish, but their mechanisms of action were different. Specifically, F-53B might alter circadian rhythms by interfering with amino acid neurotransmitter metabolism and disrupting blood-brain barrier (BBB) formation, whereas OBS mainly inhibited canonical Wnt signaling transduction by reducing cilia formation in ependymal cells and induced midbrain ventriculomegaly, finally triggering imbalance in DA secretion and circadian rhythm changes. Our study highlights the need to focus on the environmental exposure risks of PFOS alternatives and the sequential and interactive mechanisms of their multiple toxicities.

Armour G, Horman BM, Rock KD, Witchey SK, Greenbaum A, Patisaul HB. Maternal organophosphate flame retardant exposure alters the developing mesencephalic dopamine system in fetal rat

Organophosphate flame retardants (OPFRs) have become the predominant substitution for legacy brominated flame retardants but there is concern about their potential developmental neurotoxicity (DNT). OPFRs readily dissociate from the fireproofed substrate to the environment, and they (or their metabolites) have been detected in diverse matrices including air, water, soil, and biota, including human urine and breastmilk. Given this ubiquitous contamination, it becomes increasingly important to understand the potential effects of OPFRs on the developing nervous system. We have previously shown that maternal exposure to OPFRs results in neuroendocrine disruption, alterations to developmental metabolism of serotonin (5-HT) and axonal extension in male fetal rats, and potentiates adult anxiety-like behaviors. The development of the serotonin and dopamine systems occur in parallel and interact, therefore, we first sought to enhance our prior 5-HT work by first examining the ascending 5-HT system on embryonic day 14 using whole mount clearing of fetal heads and 3-dimensional (3D) brain imaging. We also investigated the effects of maternal OPFR exposure on the development of the mesocortical dopamine system in the same animals through 2-dimensional and 3D analysis following immunohistochemistry for tyrosine hydroxylase (TH). Maternal OPFR exposure induced morphological changes to the putative ventral tegmental area and substantia nigra in both sexes and reduced the overall volume of this structure in males, whereas 5-HT nuclei were unchanged. Additionally, dopaminergic axogenesis was disrupted in OPFR exposed animals, as the dorsoventral spread of ventral telencephalic TH afferents were greater at embryonic day 14, while sparing 5-HT fibers. These results indicate maternal exposure to OPFRs alters the development trajectory of the embryonic dopaminergic system and adds to growing evidence of OPFR DNT.

Transcriptional responses of fluxapyroxad-induced dysfunctional heart in zebrafish (Danio rerio) embryos

Fluxapyroxad (FLU) is a succinate dehydrogenase inhibitor (SDHI) fungicide used in controlling crop diseases. Potential toxicity to aquatic organisms is not known. We exposed zebrafish to 1, 2, and 4 μM FLU for 3 days. The embryonic zebrafish showed developmental cardiac defects, including heart malformation, pericardial edema, and heart rate reduction. Compared with the controls, cardiac-specific transcription factors (nkx2.5, myh7, myl7, and myh6) exhibited dysregulated expression patterns after FLU treatment. We next used transcriptome and qRT-PCR analyses to explore the molecular mechanism of FLU cardiotoxicity. The transcriptome analysis and interaction network showed that the downregulated genes were enriched in calcium signaling pathways, adrenergic signaling in cardiomyocytes, and cardiac muscle contraction. FLU exposure repressed the cardio-related calcium signaling pathway, associated with apoptosis in the heart and other manifestations of cardiotoxicity. Thus, the findings provide valuable evidence that FLU exposure causes disruption of cardiac development in zebrafish embryos. Our findings will help to promote a better understanding of the toxicity mechanisms of FLU and act as a reference to explore the rational use and safety of FLU in agriculture.

Tris(2-butoxyethyl) phosphate (TBEP): A flame retardant in solid waste display hepatotoxic and carcinogenic risks for humans

Recent reports have confirmed that tris(2-butoxyethyl) phosphate (TBEP), an organophosphorous flame retardants (OPFRs), profoundly detected in the dust from solid waste (SW), e-waste dumping sites, landfills, and wastewater treatment facilities. Herein, we evaluated the hepatotoxic and carcinogenic potential of TBEP in human liver cells (HepG2). HepG2 cells exhibited cytotoxicity after 3 days of exposure, especially at greater concentrations (100-400 μM). TBEP induced severe DNA damage and cell cycle disturbances that trigger apoptosis in HepG2. TBEP treated cells showed an elevated level of esterase, nitric oxide (NO), reactive oxygen species (ROS), and influx of Ca²⁺ in exposed cells. Thereby, causing oxidative stress and proliferation inhibition. TBEP exposed HepG2 cells exhibited dysfunction in mitochondrial membrane potential (ΔΨm). Immunofluorescence analysis demonstrated cytoplasmic and nucleolar localization of DNA damage (P53) and apoptotic (caspase 3 and 9) proteins in HepG2 grown in the presence of TBEP for 3 days. Within the cohort of 84 genes of cancer pathway, 10 genes were upregulated and 3 genes were downregulated. The transcriptomic and toxicological data categorically emphasize that TBEP is hepatotoxic, and act as a putative carcinogenic agent. Thereby, direct or indirect ingestion of TBEP containing dusts by workers involved in handling and disposal of SW, as well as residents living nearby the disposal areas are prone to its adverse health risks.

Transcriptome Sequencing Analysis Reveals Dynamic Changes in Major Biological Functions during the Early Development of Clearhead Icefish, Protosalanx chinensis

Early development, when many important developmental events occur, is a critical period for fish. However, research on the early development of clearhead icefish is very limited, especially in molecular research. In this study, we aimed to explore the dynamic changes in the biological functions of five key periods in clearhead icefish early development, namely the YL (embryonic), PM (first day after hatching), KK (fourth day after hatching), LC (seventh day after hatching), and SL (tenth day after hatching) stages, through transcriptome sequencing and different analysis strategies. A trend expression analysis and an enrichment analysis revealed that the expression ofgenes encoding G protein-coupled receptors and their ligands, i.e., prss1_2_3, pomc, npy, npb, sst, rln3, crh, gh, and prl that are associated with digestion and feeding regulation gradually increased during early development. In addition, a weighted gene co-expression network analysis (WGCNA) showed that eleven modules were significantly associated with early development, among which nine modules were significantly positively correlated. Through the enrichment analysis and hub gene identification results of these nine modules, it was found that the pathways related to eye, bone, and heart development were significantly enriched in the YL stage, and the ccnd2, seh1l, kdm6a, arf4, and ankrd28 genes that are associated with cell proliferation and differentiation played important roles in these developmental processes; the pak3, dlx3, dgat2, and tas1r1 genes that are associated with jaw and tooth development, TG (triacylglycerol) synthesis, and umami amino acid receptors were identified as hub genes for the PM stage; the pathways associated with aerobic metabolism and unsaturated fatty acid synthesis were significantly enriched in the KK stage, with the foxk, slc13a2_3_5, ndufa5, and lsc2 genes playing important roles; the pathways related to visual perception were significantly enriched in the LC stage; and the bile acid biosynthetic and serine-type peptidase activity pathways were significantly enriched in the SL stage. These results provide a more detailed understanding of the processes of early development of clearhead icefish.

Thyroid Hormone Disruption by Organophosphate Esters Is Mediated by Nuclear/Membrane Thyroid Hormone Receptors: In Vitro, In Vivo, and In Silico Studies

Earlier mechanistic studies of many prohibited flame retardants (FRs) highlighted their thyroid hormone-disrupting activity through nuclear thyroid hormone receptors (nTRs), whereas some alternative FRs such as organophosphate esters (OPEs) exerted weak nTR-disrupting effects. However, an increasing number of studies have revealed that OPEs also exert thyroid hormone-disrupting effects, and the underlying mechanism is unclear. Herein, the thyroid hormone-disrupting effects and mechanisms of 8 typical OPEs were investigated using integrated in vitro, in vivo, and in silico assays. All tested chemicals competitively bound to the membrane thyroid hormone receptor (mTR) [the 20% relative inhibitory concentration (RIC20): (3.5 ± 0.2) × 10¹ to (4.9 ± 1.0) × 10⁷ nM], and Cl-OPEs and alkyl-OPEs had lower RIC20 values. In contrast, only 4 OPEs showed nTR antagonistic activities at higher concentrations [≥ (4.8 ± 0.8) × 10³ nM]. Cl-OPEs and alkyl-OPEs preferentially interacted with mTR. Molecular docking illustrated that OPEs docked into mTRs, consistent with the competitive binding assay. In vivo analyses of zebrafish embryonic development confirmed that tris(1,3-dichloro-2-propyl) phosphate induced inappropriate expression of proteins, and these protein interactions might be associated with mTR according to the quantitative proteomic analysis. Based on the results, mTR might play a critical role in mediating the thyroid hormone-disrupting effects of OPEs.

The enantioselective toxicity and oxidative stress of dinotefuran on zebrafish (Danio rerio)

Dinotefuran is a widely used neonicotinoid pesticides in agriculture and it has certain ecological toxicity to aquatic organisms. Studies on the potential toxicological effects of dinotefuran on fish are limited. In the present study, 96 h acute toxicity test indicated that enantiomers of R-(-)-dinotefuran had a greater toxic effect than Rac-dinotefuran on zebrafish, and S-(+)-dinotefuran was the least. In chronic assay, R-(-)-dinotefuran exerted more effects on the development of zebrafish than S-(+)-dinotefuran, and dinotefuran also had enantioselective effect on oxidative stress. Significant changes were observed in the superoxide dismutase (SOD), glutathione S-transferase (GST) and acetylcholinesterase (AChE) activities and malondialdehyde (MDA) contents, which demonstrated dinotefuran induced oxidative stress in zebrafish. Besides, through an ultra-performance liquid chromatography quadrupole-TOF mass spectrometry (UPLC-Q-TOF-MS)-based metabolomics method was used to evaluate the enantioselectivity of dinotefuran enantiomers in zebrafish. The results indicated that R-(-)-dinotefuran caused greater disturbances of endogenous metabolites. Phenylalanine metabolic pathways, glycine, serine and threonine metabolic pathways are only involved in zebrafish exposed to R-(-)-dinotefuran; whereas phenylalanine, tyrosine and tryptophan biosynthesis was only involved in zebrafish exposed to S-(+)-dinotefuran. This study provides a certain reference value for assessing the environmental risks of dinotefuran enantiomers to aquatic organisms, and has practical significance for guiding the ecologically and environmentally safety use of dinotefuran.

Current Insights into Potential Effects of Micro-Nanoplastics on Human Health by in-vitro Tests

Humans are exposed to micro and nanoplastics (MNPLs) through inhalation, ingestion and, to a lesser extent, dermal contact. In recent years, new insights indicate the potential of MNPLs to cause damages to human health. Particle toxicity can include oxidative stress, inflammatory lesions, and then increased internalization or translocation through tissues. On the other hand, plastic additives are used in plastic particles, once internalized, can release toxic substances. It is noteworthy that the potential effects of MNPLs encompass a wide range of polymers and chemical additives, showing various physicochemical and toxicological properties, and the size, shape and surface properties are other variables influencing their effects. In spite of the research carried out recently, MNPLs research is in its early stages, and further investigation is required. In this review article, the knowledge of human exposure routes and the recent results on the toxicological effects of MNPLs in human health are presented and discussed. Finally, the current limitations and the main gaps in the body of knowledge are summarised.