The developmental effects of pentachlorophenol on zebrafish embryos during segmentation: A systematic view

Aggravated visual toxicity in zebrafish larvae upon co-exposure to titanium dioxide nanoparticles and bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate

The bioavailability and toxicity of organic pollutants in aquatic organisms can be largely affected by the co-existed nanoparticles. However, the impacts of such combined exposure on the visual system remain largely unknown. Here, we systematically investigated the visual toxicity in zebrafish larvae after single or joint exposure to titanium dioxide nanoparticles (n-TiO2) and bis(2-ethylhexyl)-2,3,4,5-tetrabromophthalate (TBPH) at environmentally relevant levels. Molecular dynamics simulations revealed the enhanced transmembrane capability of the complex than the individual, which accounted for the increased bioavailability of both TBPH and n-TiO2 when combined exposure to zebrafish. Transcriptome analysis showed that co-exposure to n-TiO2 and TBPH interfered with molecular pathways related to eye lens structure and sensory perception of zebrafish. Particularly, n-TiO2 or TBPH significantly suppressed the expression of βB1-crystallin and rhodopsin in zebrafish retina and lens, which was further enhanced after co-exposure. Moreover, we detected disorganized retinal histology, stunted lens development and significant visual behavioral changes of zebrafish under co-exposure condition. The overall results suggest that combined exposure to water borne n-TiO2 and TBPH increased their bioavailability, resulted in severer damage to optic nerve development and ultimately abnormal visual behavior patterns, highlighting the higher potential health risks of co-exposure to aquatic vertebrates.

Development of a simplified human embryonic stem cell-based retinal pre-organoid model for toxicity evaluations of common pollutants

OBJECTIVE

To explore the retinal toxicity of pharmaceuticals and personal care products (PPCPs), flame retardants, bisphenols, phthalates, and polycyclic aromatic hydrocarbons (PAHs) on human retinal progenitor cells (RPCs) and retinal pigment epithelial (RPE) cells, which are the primary cell types at the early stages of retinal development, vital for subsequent functional cell type differentiation, and closely related to retinal diseases.

MATERIALS AND METHODS

After 23 days of differentiation, human embryonic stem cell (hESC)-based retinal pre-organoids, containing RPCs and RPE cells, were exposed to 10, 100, and 1000 nM pesticides (butachlor, terbutryn, imidacloprid, deltamethrin, pendimethalin, and carbaryl), flame retardants (PFOS, TBBPA, DBDPE, and TDCIPP), PPCPs (climbazole and BHT), and other typical pollutants (phenanthrene, DCHP, and BPA) for seven days. Then, mRNA expression changes were monitored and compared.

RESULTS

(1) The selected pollutants did not show strong effects at environmental and human-relevant concentrations, although the effects of flame retardants were more potent than those of other categories of chemicals. Surprisingly, some pollutants with distinct structures showed similar adverse effects. (2) Exposure to pollutants induced different degrees of cell detachment, probably due to alterations in extracellular matrix and/or cell adhesion.

CONCLUSIONS

In this study, we established a retinal pre-organoid model suitable for evaluating multiple pollutants' effects, and pointed out the potential retinal toxicity of flame retardants, among other pollutants. Nevertheless, the potential mechanisms of toxicity and the effects on cell detachment are still unclear and deserve further exploration. Additionally, this model holds promise for screening interventions aimed at mitigating the detrimental effects of these pollutants.

Probabilistic risk assessment of dietary exposure to pentachlorophenol in Guangzhou, China

Pentachlorophenol (PCP) is a ubiquitous environmental contaminant commonly existing as its sodium salt (NaPCP), which enters the human body primarily through long term but low-level dietary exposure. PCP contributes to chemical carcinogenesis and teratogenesis. In this study, the probabilistic risk of dietary exposure to PCP in Guangzhou citizens was investigated. In total, 923 food samples in the categories of pork, livestock (beef and lamb), poultry, offal, eggs, and freshwater fish (considered to be relatively susceptible to PCP contamination) were collected from various markets in Guangzhou and tested for PCP. Probabilistic risk assessment model calculations for PCP dietary exposure and margin of exposure (MOE) values were performed using @RISK software, based on a Monte Carlo simulation with 10,000 iterations. The overall detection rate of PCP (above 1 μg kg^-1, the detection limit) was 19.9% (184/923), with an average of 7.9 μg kg^-1. The highest rate of PCP detection, 28.2%, was in livestock (beef and lamb). The MOE value for dietary PCP exposure in general Guangzhou residents averaged 400, which was far below 5,000 (the borderline for judging a health risk). The lowest MOE value, 190, was observed in the 3- to-6-year old population and indicates a significant risk. In conclusion, this study suggests that PCP exposure in Guangzhou residents is of considerable health risk, especially for the pre-school young children.

Immunotoxicity of pentachlorophenol to a marine bivalve species and potential toxification mechanisms underpinning

The ubiquitous presence of pentachlorophenol (PCP) in ocean environments threatens marine organisms. However, its effects on immunity of marine invertebrates at environmentally realistic levels are still largely unknown. In this study, the immunotoxicity of PCP to a representative bivalve species was evaluated. In addition, its impacts on metabolism, energy supply, detoxification, and oxidative stress status were also analysed by physiological examination as well as comparative transcriptomic and metabolomic analyses to reveal potential mechanisms underpinning. Results illustrated that the immunity of blood clams was evidently hampered upon PCP exposure. Additionally, significant alterations in energy metabolism were detected in PCP-exposed clams. Meanwhile, the expressions of key detoxification genes and the in vivo contents (or activity) of key detoxification enzymes were markedly altered. Exposure to PCP also triggered significant elevations in intracellular ROS and MDA whereas evident suppression of haemocyte viability. The abovementioned findings were further supported by transcriptomic and metabolomic analyses. Our results suggest that PCP may hamper the immunity of the blood clam by (i) constraining the cellular energy supply through disrupting metabolism; and (ii) damaging haemocytes through inducing oxidative stress. Considering the high similarity of immunity among species, many marine invertebrates may be threatened by PCP, which deserves more attention.

Pentachlorophenol has significant adverse effects on hematopoietic and immune system development in zebrafish (Danio rerio)

In November 2018, the Camp Fire devastated the mountain community of Paradise, CA. The burning of plastic pipes, wiring, construction materials, paint, and car batteries released toxic chemicals into the environment, contaminating the air, soil, and local waterways. Examples of toxins that were identified in the creeks and waterways in and around Paradise included pentachlorophenol (PCP), chrysene, and polyaromatic hydrocarbons. The effects of some of these chemicals on embryonic development, hematopoiesis (blood formation), and the immune system have not been thoroughly studied. Defining safe levels and the long-term effects of exposure is imperative to understanding and mitigating potential negative future outcomes. To perform these studies, we utilized zebrafish (Danio rerio), a commonly used vertebrate model system to study development. We observed the adverse effects of PCP on the development of zebrafish by using fluorescence microscopy, and saw that increased concentrations of PCP decreased the numbers of normal red blood cells and myeloid cells. Additionally, we observed that animal survival decreased in response to increasing concentrations of PCP. Furthermore, the prevalence of characteristic physical deformities such as tail curvature were greater in the treatment groups. Lastly, runx1, cmyb, and cd41 expression was reduced in fish treated with PCP. These results suggest that PCP has a previously underappreciated effect on blood and immune cell development and future studies should be performed to determine the molecular mechanisms involved.

Visual system: An understudied target of aquatic toxicology

Visual system is increasingly recognized as a sensitive target of xenobiotics in aquatic ecosystems. Various environmental pollutants of distinct physicochemical properties are able to impair the retinal development and function of teleost fishes, including dioxin-like pollutants, flame retardants, pesticides, perfluoroalkyl acids, retinoic acids and metals. Considering the availability of developmental and functional database, zebrafish has been the most frequently used as the teleost model to study aquatic visual toxicology. A diversity of visual deficits has been displayed for fishes across multiple levels of biological organizations (e.g., molecule, cell, histology, physiology and behavior). Covering sensitive developmental windows of eyes during early embryogenesis, acute or chronic exposure to xenobiotics can disturb the expressions of visual gene and protein markers, which affect the retinal neurogenesis and induce degeneration of neurons. Morphological structures and physiological responses of retina and optic tectum are then disorganized, eventually compromising the performance of visually-mediated behaviors and recruitment of individuals. Environmental pollutants can cross the blood-retina barrier and accumulate in eyes, which might impact visual system directly. In addition, pollutants are very likely to interrupt retinal development and function indirectly by disturbing the signaling of retinoids and thyroid. However, exact mechanisms of visual toxicity are largely unknown currently. In this review, the development and structure of retina and available tools for studying visual science are described briefly. Advances in visual toxicology are summarized in detail and outlooks for future visual toxicity studies are discussed.

Investigation of finishing of leather for inside parts of the shoes with a natural biocide

The prevention of decrease of quality caused by microbial activity in footwear materials entails the use of biocides. However, these substances may pose a hazard to humans and to the natural environment. The paper presents the results of antimicrobial effect investigation for cowhide leather treated with oregano oil. In these studies oil was applied by spraying onto the finished leather surface and examined to determine its antimicrobial activity by using the Agar Diffusion Plate Test. These results were compared with those where a cowhide leather was treated with oil at the stage of fatliquoring. In addition, the oregano oil toxicity level was assessed and compared with biocides used in the tanning industry. Introducing oregano oil into the leather at the stage of fatliquoring provides a better antimicrobial effect than by spraying, however hygienic finishing of leather can be obtained by introducing oil into the raw material by these both methods. The oregano oil is characterised by the lowest number of hazards and toxicity as compared with commercial biocides. The use of essential oils as natural biocides in the tanning industry seems to be especially important and suitable solution considering the harmful effects of synthetic biocides to humans and the environment.

Developmental exposure to lead at environmentally relevant concentrations impaired neurobehavior and NMDAR-dependent BDNF signaling in zebrafish larvae

Lead (Pb) is one of the predominant heavy metals in e-waste recycling arears and recognized as a notorious environmental neurotoxic substance. However, whether Pb at environmentally relevant concentrations could cause neurobehavioral alteration and even what kind of signaling pathway Pb exposure would disrupt in zebrafish were not fully uncovered. In the present study, 6 h postfertilization (hpf) zebrafish embryos were exposed to Pb at the concentrations of 0, 5, 10, and 20 μg/L until 144 hpf. Then the neurobehavioral indicators including locomotor, turnings and social behaviors, and the expressions of selected genes concerning brain-derived neurotrophic factor (BDNF) signaling were investigated. The results showed that significant changes were obtained under 20 μg/L Pb exposure. The hypoactivity of zebrafish larvae in locomotor and turning behaviors was induced during the dark period, while hyperactivity was observed in a two-fish social assay during the light period. The significantly downregulation of genes encoding BDNF, its receptor TrkB, and N-methyl-D-aspartate glutamate receptor (NMDAR) suggested the involvement of NMDAR-dependent BDNF signaling pathway. Overall, our study demonstrated that developmental exposure to Pb at environmentally relevant concentrations caused obvious neurobehavioral impairment of zebrafish larvae by disrupting the NMDAR-dependent BDNF signaling, which could exert profound ecological consequences in the real environment.

Optical toxicity of triphenyl phosphate in zebrafish larvae

Triphenyl phosphate (TPhP) has been shown to cause developmental neurotoxicty. Considering the visual system is a sensitive target, in the present study, we investigated the potential toxicity of TPhP on the visual development and function in zebrafish larvae. Embryos were exposed to 0, 0.1, 1, 10, and 30 μg/L TPhP from 2 to 144 h post-fertilization (hpf). The transcription of photoreceptor opsin genes, and histopathological changes in the retina and visual behavior (optokinetic and phototactic responses) were evaluated. TPhP significantly downregulated the transcription of opsin genes (zfrho, opn1sw1, opn1sw2, opn1mw1, opn1mw2, opn1mw3, opn1mw4, opn1lw1 and opn1lw2) in all exposure groups. Histopathological analysis revealed that the areas of the outer nuclear layer (ONL), inner nuclear layer (INL), and inner plexiform layer (IPL) of the retina were significantly reduced in the 10 and 30 μg/L TPhP groups. The number of ganglion cells was reduced significantly in the 30 μg/L group. The optokinetic response (OKR) and phototactic response showed dose-dependent decreases caused by impaired visual function, which was confirmed by unchanged locomotor activity. The results indicated that exposure to environmentally relevant concentrations of TPhP could inhibit the transcription of genes related to visual function and impair retinal development, thus leading to visual impairment in zebrafish larvae.

Food components and environmental chemicals of inhibiting human placental aromatase

Human placental CYP19A1 catalyzes the estrogen synthesis from androgens. The enzyme is encoded by CYP19A1 gene located in chromosome 15q21. This enzyme is a monooxygenase in the smooth endoplasmic reticulum. The various promoters of the CYP19A1 gene determine its expression in different tissues and the distal promoter I.1 controls its expression in the placenta and retinoids can regulate the expression. Many food components and environmental chemicals inhibit CYP19A1 activity via different modes of action. These chemicals include gossypol, flavones, flavanones, chalconoids, resveratrol, and tobacco alkaloids derived from foods as well as phthalates, insecticides, fungicides, and biocides in the contaminated foods. The inhibition of placental CYP19A1 could impair pregnancy.

Accumulation of perfluorobutane sulfonate (PFBS) and impairment of visual function in the eyes of marine medaka after a life-cycle exposure

As an alternative to perfluorooctane sulfonate (PFOS), increasing usage of perfluorobutane sulfonate (PFBS) has led to ubiquitous presence in the environment. PFBS is also shown to potently disrupt the thyroid endocrine system. Considering the regulation of thyroid hormones in visual development, PFBS is likely to adversely affect the development and function of visual systems, which is a sensitive target of environmental pollutants. Therefore, the present study exposed marine medaka embryos to environmentally realistic concentrations of PFBS (0, 1.0, 2.9 and 9.5 μg/L) for an entire life-cycle. After exposure until sexual maturity, eyes of adult medaka were dissected to directly investigate the ocular accumulation and toxicity of PFBS. For the first time, substantial accumulation of an environmental pollutant (i.e., PFBS) was observed in the eye tissue. PFBS exposure was also found to impair the visual development and function in a sex-dependent manner. In female medaka, weight of eyes was significantly decreased, while content of water was increased, probably resulting in higher intraocular pressure. Multiple neural signaling processes were also disturbed by PFBS life-cycle exposure, including cholinergic, glutamatergic, GABAergic and monoaminergic systems. Increased levels of norepinephrine and epinephrine neurotransmitters may adaptively decrease the intraocular hypertension in female eyes. In addition, proteomic profiling identified the visual proteins of differential expressions (e.g., beta and gamma crystallins, arrestin and lumican), which were significantly associated with visual perception and motor activity of eyes. Overall, this study found that PFBS was able to accumulate in the eyes and induce ocular toxicities. The susceptibility and sex-specific responses of visual systems to environmental pollutants warrants more works for a comprehensive risk assessment.

Gestational exposure to ziram disrupts rat fetal Leydig cell development

Ziram is an endocrine disruptor and may cause birth abnormality of the male reproductive system. However, the effects of ziram on fetal Leydig cell (FLC) development are still unknown. The objective of the present study was to determine the endocrine-disrupting effect of ziram on rat FLC development after gestational exposure. Pregnant Sprague Dawley dams were randomly divided into 5 groups and were gavaged with 0 (corn oil, the control), 1, 2, 4, or 8 mg/kg ziram from gestational day 12 (GD12) to GD21. FLC development was evaluated by measuring serum testosterone, FLC number and distribution, and the expression levels of Leydig and Sertoli cell genes. Ziram significantly increased serum testosterone level at 1 mg/kg (1.350 ± 0.099 ng/ml vs. 0.989 ± 0.106 ng/ml in the control), while it remarkably lowered it at 8 mg/kg (0.598 ± 0.086 ng/ml). Quantitative immunohistochemical staining showed that ziram increased FLC number via stimulating cell proliferation at 1 mg/kg and lowered it via inhibiting its proliferation at 8 mg/kg without affecting Sertoli cell number. Further study demonstrated that the expression of Nr5a1, Lhcgr, Scarb1, Star, Cyp11a1, and Cyp17a1 genes and proteins in the testis was upregulated at 1 mg/kg and the expression of Leydig (Nr5a1, Lhcgr, Scarb1, Star, Cyp11a1, Cyp17a1, and Insl3) and Sertoli cell (Fshr, Hsd17b3, Dhh, Amh, and Sox9) genes and proteins was downregulated by ziram at 8 mg/kg. In conclusion, ziram had biphasic effects on FLC development with low dose to increase FLC number and function and high dose to decrease them.

Ketamine induction of p53-dependent apoptosis and oxidative stress in zebrafish (Danio rerio) embryos

Ketamine is a widely used pharmaceutical that has been detected in water sources worldwide. Zebrafish embryos were used in this study to investigate the oxidative stress and apoptotic signals following a 24h exposure to different ketamine concentrations (0, 50, 70 and 90 mg L^-1). Early blastula embryos (∼2 h post fertilisation-hpf) were exposed for 24 h and analysed at 8 and 26 hpf. Reactive oxygen species and apoptotic cells were identified in vivo, at 26 hpf. Enzymatic activities (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), lactate dehydrogenase (LDH) and acetylcholinesterase (AChE)), glutathione levels (oxidised (GSSG) and reduced (GSH)), oxidative damage (lipid peroxidation (LPO) and protein carbonyls (CO)) as well as oxidative stress (gclc, gstp1, sod1 and cat), apoptosis (casp3a, casp6, casp8, casp9, aifm1 and tp53) and cell proliferation (pcna) related-genes were evaluated at 8 and 26 hpf. Caspase (3 and 9) activity was also determined at both time-points by colorimetric methods. Superoxide dismutase (SOD), catalase (CAT), glutathione levels (GSSG), caspase-9 and reactive oxygen species (ROS) were shown to be affected by ketamine exposure while in vivo analysis showed no difference in ROS. A significant up-regulation of superoxide dismutase (sod1) and catalase (cat) genes expression was also perceived. Ketamine-induced apoptosis was observed in vivo and confirmed by the apoptotic-related genes up-regulation. The overall results suggest that ketamine induced oxidative stress and apoptosis through the involvement of p53-dependent pathways in zebrafish embryos which could be important for the evaluation of the overall risk of ketamine in aquatic environments.

Transcriptomic and phenotypic profiling in developing zebrafish exposed to thyroid hormone receptor agonists

There continues to be a need to develop in vivo high-throughput screening (HTS) and computational methods to screen chemicals for interaction with the estrogen, androgen, and thyroid pathways and as complements to in vitro HTS assays. This study explored the utility of an embryonic zebrafish HTS approach to identify and classify endocrine bioactivity using phenotypically-anchored transcriptome profiling. Transcriptome analysis was conducted on zebrafish embryos exposed to 25 estrogen-, androgen-, or thyroid-active chemicals at concentrations that elicited adverse malformations or mortality at 120 h post-fertilization in 80% of animals exposed. Analysis of the top 1000 significant differentially expressed transcripts and developmental toxicity profiles across all treatments identified a unique transcriptional and phenotypic signature for thyroid hormone receptor agonists. This unique signature has the potential to be used as a tiered in vivo HTS and may aid in identifying chemicals that interact with the thyroid hormone receptor.

Ziram inhibits aromatase activity in human placenta and JEG-3 cell line

Placenta produces progesterone and estradiol for maintaining pregnancy. Two critical enzymes are responsible for their production: 3β-hydroxysteroid dehydrogenase 1 (HSD3B1) that catalyzes the formation of progesterone from pregnenolone and aromatase that catalyzes the production of estradiol from testosterone. Fungicide ziram may disrupt the placental steroid production. In the present study, we investigated the effects of ziram on steroid formation in human placental cell line JEG-3 cells and on HSD3B1 and aromatase in the human placenta. Ziram did not inhibit progesterone production in JEG-3 cells and HSD3B1 activity at 100μM. Ziram was a potent aromatase inhibitor with the half maximal inhibitory concentration (IC₅₀) value of 333.8nM. When testosterone was used to determine the mode of action, ziram was found to be a competitive inhibitor. Docking study showed that ziram binds to the testosterone binding pocket of the aromatase. In conclusion, ziram is a potent inhibitor of human aromatase.

Early developmental exposure to pentachlorophenol causes alterations on mRNA expressions of caspase protease family in zebrafish embryos

Caspase proteases play an essential role in cell apoptosis and inflammation, thus matter greatly in animal development and other biological processes. As a ubiquitous environmental pollutant, pentachlorophenol (PCP) is considered to have adverse effects on animal apoptosis during embryonic development, yet the evidence that PCP interfere with caspase genes was seldom reported. To uncover the effects of PCP on caspases expression in early embryos of zebrafish, two concentrations of PCP (5 μg/L and 200 μg/L) were chosen and 14 types of caspase genes at two different developmental stages, 8 h post-fertilization (hpf) and 24 hpf were analyzed. Lower survival and hatching rates, distinct developmental delay and morphological deformities of head and tail were observed. PCP, especially in the high concentration, significantly altered the expressions of most caspase genes. At 8 hpf, PCP had the most significant inductive effects on gene casp8l2 with fold changes (FCs) of 6.87 at 5 μg/L and 4.48 at 200 μg/L, and casp6l1 (with FCs of 3.15/3.69), and inhibitory effects on caspa (with FCs of 0.93/0.53) and caspb (with FCs of 0.99/0.57). At 24 hpf, PCP had the most significant effects on casp6l2, casp9, and caspc. PCP exposure possibly disrupted intrinsic apoptosis pathway considering its effects on casp9 expression. In addition, most caspase genes exhibited higher levels at 24 hpf than 8 hpf except caspc. Our results suggested that PCP had different effects on varied caspase genes, which probably resulting in a profound impact on caspase proteins and apoptosis processes and, ultimately, developmental abnormality.