Acute Exposure to Tris(1,3-dichloro-2-propyl) Phosphate (TDCIPP) Causes Hepatic Inflammation and Leads to Hepatotoxicity in Zebrafish

TDMPP activation of estrogen receptor 2a regulates smc2 and p53 signaling to interfere with liver development in zebrafish (Danio rerio)

Tris (2,6-dimethylphenyl) phosphate (TDMPP), a novel organic phosphorus flame retardant (OPFR), has been found to have estrogenic activity. Estrogens are critical in regulating various biological responses during liver development. However, the effects of TDMPP on zebrafish liver development remain largely unexplored. Here, we utilized a chemical genetic screening approach to assess the estrogenic effects of TDMPP on liver development and to elucidate the underlying molecular mechanism. Our findings revealed that zebrafish larvae exposed to environmentally relevant concentrations of TDMPP (0.05 and 0.5 μM) exhibited concentration-dependent liver impairments, including reduced liver size, histopathological changes, and hepatocyte apoptosis. In addition, E2 caused similar adverse effects to TDMPP, but the pharmacological blockade of estrogen synthesis alleviated the effects on liver development. Chemical inhibitors and morpholino knockdown assays indicated that the reduction of esr2a blocked TDMPP-induced liver impairments, which was further confirmed in the esr2a-/- mutant line. Subsequently, transcriptomic analysis showed that the estrogen receptor activated by TDMPP inhibited the expression of smc2, which was linked to the suppression of liver development through p53 activation. Consistently, overexpression of smc2 and inhibition of p53 evidently rescued hepatic damages induced by TDMPP. Taken together, the above findings identified esr2a, downstream smc2, and p53 as important regulators for the estrogenic effects of TDMPP on liver development. Our work fills crucial gaps in the current knowledge of TDMPP's hepatotoxicity, providing new insights into the adverse effects of TDMPP and the molecular mechanisms of action. These findings underscore the need for further ecological risk assessment and regulatory considerations.

Exposure to tris (1,3-dichloro-2-propyl) phosphate affects the embryonic cardiac development of Oryzias melastigma

Tris (1,3-dichloro-2-propyl) phosphate (TDCPP) is a growing concern and may be a potential risk to marine environmental health due to its widespread usage and distribution. However, the toxic effects of TDCPP on cardiac development in marine fish have not been reported. In this study, Oryzias melastigma embryos were exposed to TDCPP at doses of 0, 0.04, 0.4, 4 and 40 μg/L from early embryogenesis to 10 days postfertilization (dpf). Then, the heart rate and sinus venosus-bulbus arteriosus (SV-BA) distance of the exposed embryos were measured at 5, 6, 8 and 10 dpf. Furthermore, alterations in the mRNA levels of the genes encoding cyclooxygenase-2 (COX-2), bone morphogenetic protein 4 (BMP4), fibroblast growth factor 8 (FGF8), and GATA-binding protein 4 (GATA4) were evaluated at 5, 6, 8 and 10 dpf. We found that the heart rate significantly increased in all TDCPP exposure groups at 10 dpf. The SV-BA distance significantly decreased in all TDCPP exposure groups at all developmental stages (except for the 0.4 μg/L group at 5 dpf and the 4 μg/L group at 10 dpf). The mRNA expression of COX-2 was downregulated at 5 dpf, BMP4 was downregulated at 5 and 6 dpf, FGF8 was downregulated at 5, 6 and 8 dpf, GATA4 was downregulated at 8 dpf, and GATA4 was upregulated at 10 dpf. These results indicate that the changes in heart rate and SV-BA distance might be accompanied by disturbances in the four genes involved in cardiac development. Our findings will help to illustrate the possible cardiac toxic effects of marine fish exposed to TDCPP.

Environmentally relevant concentrations of tris (2-chloroethyl) phosphate (TCEP) induce hepatotoxicity in zebrafish (Danio rerio): a whole life-cycle assessment

Tris (2-chloroethyl) phosphate (TCEP), a typical organophosphate flame retardant, is of increasingly great concern considering their ubiquitous presence in aquatic environments and potential ecotoxicity. The present work was aimed to investigate the potential growth inhibition and hepatic stress induced by whole life-cycle exposure to TCEP (0.8, 4, 20 and 100 μg/L) in zebrafish. The results revealed that the body length, body mass and hepatic-somatic index (HSI) of zebrafish were significantly declined after exposure to TCEP for 120 days. GPx activity and GSH content were increased in the liver of zebrafish treated with low concentrations (0.8 and 4 μg/L) of TCEP, while exposure to high concentrations (20 and 100 μg/L) of TCEP reduced antioxidative capacity and elevated lipid peroxidation (LPO) levels. Gene transcription analysis demonstrated that the mRNA levels of nrf2 were altered in a similar manner to the transcription of the downstream genes nqo1 and hmox1, suggesting that Nrf2-Keap1 pathway mediated TCEP-induced oxidative stress in zebrafish liver. In addition, TCEP exposure might alleviate inflammatory response through down-regulating transcription of inflammatory cytokines (il-1β, il-6 and inos), and induce apoptosis via activating the p53-Bax pathway. Moreover, whole life-cycle exposure to TCEP caused a series of histopathological anomalies in zebrafish liver. Overall, our results revealed that lifetime exposure to environmentally relevant concentrations of TCEP could result in growth retardation and induce significant hepatotoxicity in zebrafish.

Competition for H2A.Z underlies the developmental impacts of repetitive element de-repression

The histone variant H2A.Z is central to early embryonic development, determining transcriptional competency through chromatin regulation of gene promoters and enhancers. In addition to genic loci, we find that H2A.Z resides at a subset of evolutionarily young repetitive elements, including DNA transposons, long interspersed nuclear elements and long terminal repeats, during early zebrafish development. Moreover, increases in H2A.Z occur when repetitive elements become transcriptionally active. Acquisition of H2A.Z corresponds with a reduction in the levels of the repressive histone modification H3K9me3 and a moderate increase in chromatin accessibility. Notably, however, de-repression of repetitive elements also leads to a significant reduction in H2A.Z over non-repetitive genic loci. Genic loss of H2A.Z is accompanied by transcriptional silencing at adjacent coding sequences, but remarkably, these impacts are mitigated by augmentation of total H2A.Z protein via transgenic overexpression. Our study reveals that levels of H2A.Z protein determine embryonic sensitivity to de-repression of repetitive elements, that repetitive elements can function as a nuclear sink for epigenetic factors and that competition for H2A.Z greatly influences overall transcriptional output during development. These findings uncover general mechanisms in which counteractive biological processes underlie phenotypic outcomes.

Associations of urinary organophosphate esters metabolites and diet quality with nonalcoholic/metabolic dysfunction-associated fatty liver diseases in adults

Whether exposure to organophosphate esters (OPEs) is associated with metabolic dysfunction-associated fatty liver disease (MAFLD) and nonalcoholic fatty liver disease (NAFLD) remains unclear. A healthy diet is crucial to metabolic health and dietary intake is also an important route for OPEs exposure. However, the joint associations of OPEs, diet quality, and the effect modification by diet quality remain unknown. This study comprised 2618 adults with complete data on 6 urinary OPEs metabolites, 24 h dietary recalls, and definitions of NAFLD and MAFLD from the 2011-2018 National Health and Nutrition Examination Survey cycles. Multivariable binary logistic regression was applied to assess the associations of OPEs metabolites with NAFLD, MAFLD, and components of MAFLD. We also adopted the quantile g-Computation method to examine the associations of OPEs metabolites mixture. Our results revealed that OPEs metabolites mixture and three individual metabolites [i.e., bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), bis(2-chloroethyl) phosphate, and diphenyl phosphate] were significantly and positively associated with NAFLD and MAFLD (P-trend<0.001), with BDCIPP being identified as the dominant metabolite, whereas the 4 diet quality scores were monotonically and inversely associated with both MAFLD and NAFLD (P-trend<0.001). Of note, 4 diet quality scores were by and large negatively associated with BDCIPP, but not with other OPEs metabolites. Joint association analyses revealed that individuals with higher diet quality and lower BDCIPP concentration tend to have lower odds of having MAFLD and NAFLD in comparison with people in the low diet quality and high BDCIPP group, but the associations of BDCIPP were not modified by diet quality. Our findings suggest that certain OPEs metabolites and diet quality exhibited opposing associations with both MAFLD and NAFLD. Individuals adherent to a healthier diet may have a lower level of certain OPEs metabolites, and thus could have lower odds of having NAFLD and MAFLD.

Chlorinated Organophosphate Flame Retardants Impair the Lung Function via the IL-6/JAK/STAT Signaling Pathway

Toxicological studies have revealed the adverse impacts of organophosphate flame retardants (OPFRs) on the respiratory system, while there is a lack of epidemiological evidence, and information for risk assessment remains insufficient. Herein, we investigated the associations of urinary metabolites of OPFRs with the lung function in 987 adults participating in the U.S. National Health and Nutrition Examination Survey 2011-2012. The elevation of three primary metabolites of chlorinated OPFRs [bis(1,3-dichloro-2-propyl) phosphate (BDCIPP), bis(2-chloroethyl) phosphate (BCEP), and bis(1-chloro-2-propyl) phosphate (BCIPP)] was related to pulmonary dysfunction in a sample-weighted regression model. Each one-unit increase in the log-transformed levels of BDCIPP and BCEP was related to 91.52 and 79.34 mL reductions in the forced vital capacity (FVC). Each one-unit elevation in BCIPP was correlated with 130.86, 153.56, 302.26, and 148.24 mL reductions in forced expiratory volume 1st second (FEV₁), FVC, peak expiratory flow rate (PEF), and forced expiratory flow at 25-75% of FVC (FEF_25-75%), respectively. Then, an adverse outcome pathway (AOP) framework was constructed using the Comparative Toxicogenomics Database, the Toxicity Forecaster, and the GeneCards database. Based on the weight of the evidence, BDCIPP, BCEP, BCIPP, and their parent compounds (TDCIPP, TCEP, and TCIPP) may affect the IL-6/Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, induce airway remodeling, and impair the lung function. Additionally, tobacco smoke exposure may modify the effects of BDCIPP on the lung function (P_int < 0.05) and affect the IL-6-mediated AOP. These results suggested that chlorinated OPFRs were associated with pulmonary dysfunction via the IL-6/JAK/STAT pathway.

Tris(1,3-dichloro-2-propyl) phosphate disrupts the trajectory of cytosine methylation within developing zebrafish embryos

Tris (1,3-dichloro-2-propyl) phosphate (TDCIPP) is an organophosphate ester-based flame retardant widely used within the United States. Within zebrafish, initiation of TDCIPP exposure at 0.75 h post-fertilization (hpf) reliably disrupts cytosine methylation from cleavage (2 hpf) through early-gastrulation (6 hpf). Therefore, the objective of this study was to determine whether TDCIPP-induced effects on cytosine methylation persist beyond 6 hpf. First, we exposed embryos to vehicle or TDCIPP from 0.75 hpf to 6, 24, or 48 hpf, and then conducted bisulfite amplicon sequencing of a target locus (lmo7b) using genomic DNA derived from whole embryos. Within both vehicle- and TDCIPP-treated embryos, CpG methylation was similar at 6 hpf and CHG/CHH methylation were similar at 24 and 48 hpf (relative to 6 hpf). However, relative to 6 hpf within the same treatment, CpG methylation was lower within vehicle-treated embryos at 48 hpf and TDCIPP-treated embryos at 24 and 48 hpf - an effect that was driven by acceleration of CpG hypomethylation. Similar to our previous findings with DNA methyltransferase, we found that, even at high μM concentrations, TDCIPP had no effect on zebrafish and human thymine DNA glycosylase activity (a key enzyme that decreases CpG methylation), suggesting that TDCIPP-induced effects on CpG methylation are not driven by direct interaction with thymine DNA glycosylase. Finally, using 5-methylcytosine (5-mC)-specific whole-mount immunochemistry and automated imaging, we found that exposure to TDCIPP increased 5-mC abundance within the yolk of blastula-stage embryos, suggesting that TDCIPP may impact cytosine methylation of maternally loaded mRNAs during the maternal-to-zygotic transition. Overall, our findings suggest that TDCIPP disrupts the trajectory of cytosine methylation during zebrafish embryogenesis, effects which do not appear to be driven by direct interaction of TDCIPP with key enzymes that regulate cytosine methylation.

Insights into the mechanisms of tris(2-chloroethyl) phosphate-induced growth inhibition in juvenile yellow catfish Pelteobagrus fulvidraco

With the gradual elimination of brominated flame retardants (BFRs), the production and application of tris (2-chloroethyl) phosphate (TCEP), as a substitute of BFRs, has increased greatly. The objective of the present study was to comprehensively explore the potential adverse effects of TCEP on fish growth and the possible underlying mechanisms. To this end, juvenile yellow catfish (Pelteobagrus fulvidraco) were exposed to environmentally relevant concentrations of TCEP (0, 1, 10 and 100 µg/L) for 30 days. The results showed that exposure to high concentrations of TCEP (10 and 100 µg/L) significantly decreased body weight, body length and specific growth rate (SGR). Plasma IGF-I levels and hepatic mRNA levels of igf1 and igf1r were all reduced, while the transcriptional levels of IGFBPs (igfbp2, igfbp3, igfbp5) were significantly up-regulated in the liver of yellow catfish under exposure to 10 and 100 µg/L TCEP. TCEP-induced growth inhibition might be related to somatostatin (SS) signaling system, as evidenced by elevated mRNA transcriptions of ss in brain and its receptors (sstr2, sstr3, sstr5) in liver. In addition, fish exposed to high concentrations of TCEP displayed multiple histological alterations in liver. Taken together, these findings suggested that TCEP (>10 µg/L) might exert its inhibitory effect on fish growth through interfering with the GH/IGF axis and SS signaling system, and by impairing hepatic structures.

Bioaccumulation and potential risk of organophosphate flame retardants in coral reef fish from the Nansha Islands, South China Sea

Organophosphate flame retardant (OPFR) pollution in marine environment has attracted increasing attention in recent years. Coral reefs are regarded as significant marine ecosystems, however, research on OPFR contamination in coral reefs is limited. In the present work, 9 OPFR compounds were analyzed in fish samples collected from the Zhubi Reef and Yongshu Reef of the Nansha Islands, South China Sea, to evaluate the biomagnification and potential threats of OPFRs in the coral reef ecosystems. ∑OPFR concentrations in the coral reef fish ranged from 38.7 to 2090 ng/g lipid weight (lw), with an average of 420 ± 491 ng/g lw. Alkyl OPFRs were more abundant than chlorinated OPFRs and aryl OPFRs. Individually, TBEP and TCPP were the two most abundant OPFR compounds. Biomagnification potential was indicated for TCPP, TCEP, TBP, TBEP and TEHP along the marine food web, with trophic magnification factors being greater than one. The estimated dietary intakes of OPFRs via coral fish consumption were 0-1.11 ng/kg bw/d and 0.01-2.06 ng/kg bw/d, respectively, for rural and urban residents. Additionally, the hazard quotients of OPFR compounds ranged from 2 × 10^-7 to 7.41 × 10^-5 for rural residents and from 4 × 10^-7 to 1.37 × 10^-4 for urban residents. Although the risk to human health from exposure to OPFRs via consuming coral reef fish from the South China Sea was low, further investigation of these chemicals is still recommended.

Liver-Based Probabilistic Risk Assessment of Exposure to Organophosphate Esters via Dust Ingestion Using a Physiologically Based Toxicokinetic (PBTK) Model

Organophosphate esters (OPEs) are widely used and harmful to organisms and human health. Dust ingestion is an important exposure route for OPEs to humans. In this study, by integrating ToxCast high-throughput in vitro assays with in vitro to in vivo extrapolation (IVIVE) via physiologically based Toxicokinetic (PBTK) modeling, we assessed the hepatocyte-based health risk for humans around the world due to exposure to two typical OPEs (TPHP and TDCPP) through the dust ingestion exposure route. Results showed that the health guidance value of TPHP and TCDPP obtained in this study was lower than the value obtained through animal experiments. In addition, probabilistic risk assessment results indicate that populations worldwide are at low risk of exposure to TPHP and TDCPP through dust ingestion due to low estimated daily intakes (EDIs) which are much lower than the reference dose (RfDs) published by the US EPA, except in some regional cases. Most margin of exposure (MOE) ranges of TDCPP for children are less than 100, which indicates a moderately high risk. Researchers should be concerned about exposure to TDCPP in this area. The method proposed in this study is expected to be applied to the health risk assessment of other chemicals.

An adverse outcome pathway based in vitro characterization of novel flame retardants-induced hepatic steatosis

A wide range of novel replacement flame retardants (nFRs) is consistently detected in increasing concentrations in the environment and human matrices. Evidence suggests that nFRs exposure may be associated with disruption of the endocrine system, which has been linked with the etiology of various metabolic disorders, including nonalcoholic fatty liver disease (NAFLD). NAFLD is a multifactorial disease characterized by the uncontrolled accumulation of fats (lipids) in the hepatocytes and involves multiple-hit pathogenesis, including exposure to occupational and environmental chemicals such as organophosphate flame retardants (OPFRs). In the present study we aimed to investigate the potential mechanisms of the nFRs-induced hepatic steatosis in the human liver cells. In this study, we employed an in vitro bioassay toolbox to assess the key events (KEs) in the proposed adverse outcome pathways (AOP) (s) for hepatic steatosis. We examined nine nFRs using AOP- based in vitro assays measuring KEs such as lipid accumulation, mitochondrial dysfunction, gene expression, and in silico approach to identify the putative molecular initiating events (MIEs). Our findings suggest that several tested OPFRs induced lipid accumulation in human liver cell culture. Tricresyl phosphate (TMPP), triphenyl phosphate (TPHP), tris(1,3-dichloropropyl) phosphate (TDCIPP), and 2-ethylhexyl diphenyl phosphate (EHDPP) induced the highest lipid accumulation by altering the expression of genes encoding hepatic de novo lipogenesis and mitochondrial dysfunction depicted by decreased cellular ATP production. Available in vitro data from ToxCast and in silico molecular docking suggests that pregnane X receptor (PXR) and peroxisome proliferator-activated receptor gamma (PPARγ) could be the molecular targets for the tested nFRs. The study identifies several nFRs, such as TMPP and EHDPP, TPHP, and TDCIPP, as potential risk factor for NAFLD and advances our understanding of the mechanisms involved, demonstrating the utility of an AOP-based strategy for screening and prioritizing chemicals and elucidating the molecular mechanisms of toxicity.

A review on the occurrence of organophosphate flame retardants in the aquatic environment in China and implications for risk assessment

Organophosphate flame retardants (OPFRs), used extensively as substitutes for polybrominated diphenyl ethers, are ubiquitous environmental contaminants. OPFR pollution in aquatic environments, the main sink of pollutants, has been studied extensively over the past decade. Here, we review the current knowledge on the consumption and applications of OPFRs, and on their ecotoxicity in aquatic environments worldwide. We also synthesize the available evidence on the occurrence of OPFRs in aquatic environments in China (wastewater treatment plant influent and effluent, surface water, sediment, aquatic biota, and drinking water). Across China, the measured concentrations of OPFRs differ by more than three orders of magnitude. Risk assessments based on these measurements indicate a low level of ecological risk from OPFRs in most aquatic environments in China, and a low risk to human health from drinking water and aquatic products. Finally, we identify gaps in the current knowledge and directions for further research on OPFRs in aquatic environments.

Impact of dietary exposure to low-dose tris(1,3-dichloro-2-propyl)phosphate in allergic asthmatic mice

OBJECTIVE

Tris(1,3-dichloro-2-propyl)phosphate (TDCIPP) is an organophosphorus flame retardant that is an alternative to brominated flame retardants. Although TDCIPP can adversely affect human health, information about its effects on immune and allergic responses is scarce. We aimed to investigate the effects of dietary exposure to TDCIPP using less than the human tolerable daily intake (TDI) in allergic asthmatic mice.

METHODS

Male C3H/HeJSlc mice were fed a chow diet containing TDCIPP equivalent to 0.02 μg/kg/day (low; L), 0.2 μg/kg/day (medium; M), or 2 μg/kg/day (high; H) and were intratracheally administered ovalbumin (OVA, 1 μg/animal) every 2 weeks from 5 to 11 weeks of age.

RESULTS

In OVA-treated mice, TDCIPP-H exposure tended to enhance pulmonary inflammation compared with vehicle exposure. TDCIPP dose-dependently decreased mRNA level of G protein-coupled estrogen receptor (GPER) in the lungs with or without OVA. OVA + TDCIPP-H treatment tended to increase the total cell number and promoted CD4⁺ cell activation compared with OVA alone treatment in mediastinal lymph nodes. In splenocytes, an increase in the fraction of Breg cells, but not of total B and T cells, and an increase in IL-5 in cell culture supernatants following OVA re-stimulation in OVA + TDCIPP-H-treated mice was observed compared with OVA-alone-treated mice. Moreover, OVA + TDCIPP-H exposure decreased Gr-1 expression in bone marrow (BM) cells.

DISCUSSION

These results suggested that dietary exposure to TDCIPP at TDI level slightly enhances allergic diseases, such as allergic asthma, via GPER regulation at inflamed sites and secondary lymphoid tissue and BM cell alternations.

Lifetime bioaccumulation, gender difference, tissue distribution, and parental transfer of organophosphorus plastic additives in freshwater fish

Plastic pollution has been a growing global issue. Various plastic additives may enter the environment with plastic debris, which could also become contaminants. Lifetime bioaccumulation, gender difference, tissue distribution, and parental transfer potential of commonly applied organophosphorus plastic additives (OPPAs) were investigated in wildlife fish of the Pearl River system, China. The OPPAs were widely detected in 7 consumable fish species. Tris (2-chloropropyl) phosphate was the predominant compound, with a median concentration of 18.8 ng/g lipid weight. The total OPPA concentrations (ΣOPPAs) were higher in the livers and swimming bladders, suggesting important roles of lipophilicity on the OPPAs accumulation in the fish. Besides, the livers were more abundant in the non-chlorinated OPPAs relative to the other tissues, indicating potentially stronger metabolism of the chlorinated OPPAs in the livers. Redbelly tilapia contained obviously lower ΣOPPAs than the other species. On the other hand, proportions of the chlorinated OPPAs were obviously lower in barbel chub and Guangdong black bream. For an individual species, higher ΣOPPAs were usually detected in the female than in the male fish. Furthermore, the females contained higher proportions of the non-chlorinated OPPAs. These results suggested potentially more accumulation of the OPPAs, particularly the non-chlorinated OPPAs in the female than in the male fish. Body weight dependence of the OPPAs accumulation showed varied patterns depending on species, tissue, and compound. Species-specific characteristics affected by both ecology and organisms' physiology should be considered in combination in assessing bioaccumulation of the OPPAs. The OPPAs were slightly bioaccumulative with LogBAFs of 1.2-3.3. The OPPAs did not show obvious inclination to be partitioned to biota from sediment. Omnipresence of the OPPAs in both egg/ovary and testis of the fish suggested potential transgenerational transfer of these chemicals, which can be a serious ecological issue and warrants further research.

Flame Retardants-Mediated Interferon Signaling in the Pathogenesis of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is a growing concern worldwide, affecting 25% of the global population. NAFLD is a multifactorial disease with a broad spectrum of pathology includes steatosis, which gradually progresses to a more severe condition such as nonalcoholic steatohepatitis (NASH), fibrosis, cirrhosis, and eventually leads to hepatic cancer. Several risk factors, including exposure to environmental toxicants, are involved in the development and progression of NAFLD. Environmental factors may promote the development and progression of NAFLD by various biological alterations, including mitochondrial dysfunction, reactive oxygen species production, nuclear receptors dysregulation, and interference in inflammatory and immune-mediated signaling. Moreover, environmental contaminants can influence immune responses by impairing the immune system’s components and, ultimately, disease susceptibility. Flame retardants (FRs) are anthropogenic chemicals or mixtures that are being used to inhibit or delay the spread of fire. FRs have been employed in several household and outdoor products; therefore, human exposure is unavoidable. In this review, we summarized the potential mechanisms of FRs-associated immune and inflammatory signaling and their possible contribution to the development and progression of NAFLD, with an emphasis on FRs-mediated interferon signaling. Knowledge gaps are identified, and emerging pharmacotherapeutic molecules targeting the immune and inflammatory signaling for NAFLD are also discussed.

Dietary Inclusion of Black Soldier Fly (Hermetia Illucens) Larvae Meal and Paste Improved Gut Health but Had Minor Effects on Skin Mucus Proteome and Immune Response in Atlantic Salmon (Salmo Salar)

The present study investigated effects of dietary inclusion of black soldier fly larvae (BSFL) (Hermetia illucens) meal and paste on gut health, plasma biochemical parameters, immune response and skin mucus proteome in pre-smolt Atlantic salmon (Salmo salar). The seven-week experiment consisted of seven experimental diets: a control diet based on fishmeal and plant protein (Control-1); three BSFL meal diets, substituting 6.25% (6.25IM), 12.5% (12.5IM) and 25% (25IM) of protein; two BSFL paste diets, substituting 3.7% (3.7IP) and 6.7% (6.7IP) of protein and an extra control diet with 0.88% of formic acid (Control-2). The 6.25IM diet reduced enterocyte steatosis in pyloric caeca, improved distal intestine histology, and reduced IgM in distal intestine. The fish fed 12.5IM diet reduced enterocyte steatosis in pyloric caeca, improved distal intestine histology, had a higher plasma lysozyme content compared to 6.25IM, and tend to increase phagocytic activity in head-kidney macrophages-like cells. On the other hand, 25IM diet improved distal intestine histology, but showed mild-moderate enterocyte steatosis in pyloric caeca, increased IFNγ and reduced IgM in distal intestine. In the case of BSFL paste diets, 3.7IP diet caused mild inflammatory changes in distal intestine, although it reduced enterocyte steatosis in pyloric caeca. The 6.7IP diet reduced enterocyte steatosis in pyloric caeca and improved distal intestine histology. Increasing level of BSFL meal in the diet linearly decreased plasma C-reactive protein, whereas increasing level of BSFL paste linearly increased plasma antioxidant capacity. Dietary inclusion of BSFL meal and paste had minor effects on the expression profile of proteins in skin mucus and no effects on immune markers in splenocytes. BSFL meal showed no negative effect on liver and muscle health as indicated by plasma alanine aminotranseferase, asparate aminotransferase and creatine kinase. The present study showed that replacing conventional protein sources with low to moderate levels of BSFL meal (6.25% and 12.5%) or paste (3.7% and 6.7%) reduced enterocyte steatosis in pyloric caeca, while replacing up to 25% with BSFL meal or 6.7% with paste improved distal intestine histology. Further, dietary inclusion of BSFL meal and paste had minor effects on skin mucus proteome and immune response in Atlantic salmon.

Modified organophosphorus fire retardant with low toxicity/high flame retardancy using the pharmacophore model associated with Mamdani fuzzy inference approach

The bi-directional selective low toxicity/high flame retardancy organophosphorus fire retardants (OPFRs) derivatives were designed by a comprehensive effect 3D quantitative structure-activity relationship (QSAR) pharmacophore model, and the toxicity and flame retardancy mechanism of OPFR derivatives were explored. The 3D-QSAR comprehensive pharmacophore model was constructed using the toxicity/flame retardancy comprehensive evaluation values of OPFRs for molecular modifications, which were obtained by the Mamdani fuzzy inference approach. The environment-friendly OPFR derivatives (CDPP-F, CDPP-NO2, TPHP-F, TDCIPP-CH2CH3, and TDCIPP-Br) with high flame retardancy showed significantly reduced multi-toxicity effects (biotoxicity, reproductive toxicity, and neurotoxicity) in the comprehensive model. The spatial overlapping volumes of the toxicity/flame retardancy comprehensive effect model with the toxic effect and with flame retardant effect were 1 : 1. The trend (1 : 1) was similar to the degree of improvement of toxicity and flame retardancy of the OPFR derivatives. The toxicity and flame retardancy were decreased by more than 50%. This indicated that the spatial overlapping volumes in the comprehensive model with the toxic and flame retardant mono-models have significant effects. Based on the 2D-QSAR model, molecular docking, and density functional theory, it was found that, in molecular modification, the introduction of electronegative groups to improve the electronic parameters (q+) can reduce the toxicity of OPFRs. An increase in the bond length and bond angle of the molecular side chain increased the steric parameter (MR) that improved the molecular flame retardancy of OPFRs.

Roots and stems of Kadsura coccinea extract induced developmental toxicity in zebrafish embryos/larvae through apoptosis and oxidative stress

CONTEXT

Although the roots and stems of Kadsura coccinea (Lem.) A. C. Smith. [Schisandraceae] are herbs and traditional foods in Li nationality, its toxicity remains unclear.

OBJECTIVE

To study developmental toxicity of K. coccinea consumption and explain underlying mechanisms.

MATERIALS AND METHODS

Zebrafish were applied to assess LC₅₀ values of hydroethanol extract (KCH) and water extract (KCW) of Kadsura coccinea. In further study, three concentrations groups of KCH (3.75, 7.5 and 15 μg/mL for embryo, 7.5, 15 and 30 μg/mL for larvae) and control group (n = 30) were administered. At specific stages of zebrafish development, spontaneous movement, hatching rate, etc., were measured. Gene expressions related to developmental toxicity were examined.

RESULTS

The LC₅₀ value of KCH (24 or 45 μg/mL) was lower than KCW (1447 or 2011 μg/mL) in embryos or larvae. The inhibited spontaneous movement (20%), hatching rate (20%), body length (12%) and eye area (30%) were observed after KCH treatment. Moreover, the decreased liver areas (25%) and fluorescence intensity (33%), increased ALT (37%) and AST levels (42%) were found in larvae treated with KCH (30 μg/mL). The increased ROS (89%), MDA concentrations (30%), apoptosis generation (62%) and decreased T-SOD activity (16%) were also observed. The represented genes of developmental hepatotoxicity, oxidative stress and apoptosis in zebrafish were activated after KCH (15 or 30 μg/mL) treatment.

DISCUSSION AND CONCLUSIONS

These results demonstrate that KCH has developmental toxicity on zebrafish. Our study provides a scientific basis for further research on the toxicity of Kadsura coccinea.

Zebrafish as a model for inflammation and drug discovery

Zebrafish is a small teleost (bony) fish used in many areas of pharmacology and toxicology. This animal model has advantages for the discovery of anti-inflammatory drugs, such as the potential for real-time assessment of cell migration mechanisms. Additionally, zebrafish display a repertoire of inflammatory cells, mediators, and receptors that are similar to those in mammals, including humans. Inflammatory disease modeling in either larvae or adult zebrafish represents a promising tool for the screening of new anti-inflammatory compounds, contributing to our understanding of the mechanisms involved in chronic inflammatory conditions. In this review, we provide an overview of the characterization of inflammatory responses in zebrafish, emphasizing its relevance for drug discovery in this research area.

Cytotoxic Screening and Transcriptomics Reveal Insights into the Molecular Mechanisms of Trihexyl Phosphate-Triggered Hepatotoxicity

Mounting evidence shows that organophosphate flame retardants (OPFRs), especially aryl- and halogenated-OPFRs, exert various adverse health effects on living organisms. This study evaluated the hepatotoxic effect of trihexyl phosphate (THP) as a long-chain alkyl-OPFR on human hepatocyte cells (LO2) and mouse hepatocyte cells (AML12) by performing screening of cytotoxicity in vitro. In combination with transcriptomic analysis, toxicological mechanisms in vitro were further investigated. Results showed that THP triggered hepatotoxicity in vitro by altering four signaling pathways: endoplasmic reticulum (ER) stress, apoptosis, cell cycle, and the glycolysis signaling pathway. Exposure of LO2 and AML12 liver cells to THP (25 μg/mL) significantly induced ER stress-mediated apoptosis and cell cycle arrest. Meanwhile, downregulation of glycolysis caused the blockage of energy metabolism. Furthermore, the high performance liquid chromatography-quadrupole time-of-flight mass spectrometry (HPLC-Q-TOF-MS/MS) revealed that much of THP was absorbed into the cells and displayed stability in the two liver cell lines. In vivo assays using a mouse model demonstrated that exposure to THP at 400 mg/kg induced the ballooning degeneration of hepatocytes in liver tissue, whereas exposure to THP at 800 mg/kg caused acute liver injury with high alanine aminotransferase levels. This study provides novel insights into the impact of THP on hepatotoxicity in vitro and in vivo and uncovers the underlying toxicological mechanisms, which may serve as a guide for further ecological risk assessment and reasonable application of alkyl-OPFRs.

The toxicity effects and mechanisms of tris(1,3-dichloro-2-propyl) phosphate (TDCPP) and its ecological risk assessment for the protection of freshwater organisms

Tris (1,3-dichloro-2-propyl) phosphate (TDCPP) is a type halogenated organophosphate flame retardants (OPFRs), which has been identified as contaminants of emerging concern (CECs). The use and production of OPFRs began to increase gradually when brominated flame retardants (BFRs) were banned. Halogenated OPFRs, especially TDCPP have been considered to lead to mutagenicity and carcinogenesis and major concerns have been raised regarding their toxicity. In this study, the toxicity effects and mechanisms of TDCPP were summarized and ecological risk assessment was made regarding its potential impact on freshwater organisms. TDCPP has been widely detected in ecosystems throughout the world, with observed toxicity effects on both humans and freshwater organisms. Inhalation of the dust was found to be the main exposure for humans. TDCPP could be metabolized in the human body, and medium stability was achieved in human body with the main metabolite BDCPP. Aside from mutagenicity and carcinogenesis, TDCPP was also found to have the potential for endocrine disruption and impairing the human reproductive system. Furthermore, this study reviewed the results of previous toxicity experiments, including acute toxicity, growth and development toxicity, neurotoxicity, and hepatotoxicity in freshwater organisms. Risk assessment was made using the safety threshold method by comparing the toxicity data with the exposure data in freshwater. HC₅ (hazardous concentration for 5% of organisms) derived based on traditional endpoints of acute toxicity LC₅₀ (median lethal concentration) or EC₅₀ (concentration for 50% of maximal effect) was 877 μg/L. This value was much higher than the exposure concentration levels in the surface water with EXD₉₀ (exposure data with cumulative probability 90%) of 65.22 ng/L. However, based on the growth and development toxicity data, the derived HC₅ was 33.33 ng/L and the calculated MOS (margin of safety) was below 1. Therefore, the results validated the fact that the ecological risk of TDCPP could not be neglected for its growth and development toxicity.

Biochemical responses of a freshwater fish Cirrhinus mrigala exposed to tris(2-chloroethyl) phosphate (TCEP)

Freshwater fish Cirrhinus mrigala were exposed to tris(2-chloroethyl) phosphate (TCEP) with three different concentrations (0.04, 0.2, and 1 mg/L) for a period of 21 days. During the study period, thyroid-stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) levels were significantly (p < 0.05) inhibited. The superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and lipid peroxidation (LPO) levels were increased significantly (p < 0.05) in gills, liver, and kidney tissues, whereas glutathione (GSH) and glutathione peroxidase (GPx) (except liver tissue) activities were inhibited when compared to the control group. Likewise, exposure to TCEP significantly (p < 0.05) altered the biochemical (glucose and protein) and electrolyte (sodium, potassium, and chloride) levels of fish. Light microscopic studies exhibited series of histopathological anomalies in the gills, liver, and kidney tissues. The present study reveals that TCEP at tested concentrations causes adverse effects on fish and the studied biomarkers could be used for monitoring the ecotoxicity of organophosphate esters (OPEs).

Toxic effect and mechanism of tris (1,3-dichloro-2-propyl)phosphate (TDCPP) on the marine alga Phaeodactylum tricornutum

Tris (1,3-dichloro-2-propyl)phosphate (TDCPP) is an organophosphate-based plasticizer and flame retardant with a high production volume. The ubiquitous distribution and persistence of TDCPP in aquatic environment have led to concerns over its possible toxic effects on aquatic organism. However, data regarding the toxicity of TDCPP on algae are limited, and the molecular mechanism remains largely unknown. Therefore, we determined the growth characteristics, physiological changes and transcriptome profiles of Phaeodactylum tricornutum in response to 4 mg L^-1 TDCPP for 24 h. TDCPP caused morphological damage and growth inhibition with an EC₅₀ value of 3.71 mg L^-1 at 96 h. A decline in pigments and photosynthetic activity was observed, indicating the occurrence of photosynthesis inhibition. Although the activities of both glutathione peroxidase and glutathione reductase were stimulated, oxidative stress was not relieved in the algal cells, as evidenced by the elevated levels of reactive oxygen species and lipid peroxidation. Transcriptomic analyses revealed 3312 differentially expressed genes (DEGs), and photosynthesis was a key target, as genes related to this process were greatly altered under TDCPP stress. Moreover, some DEGs were also enriched in amino acid metabolism, nitrogen metabolism, nucleotide metabolism and lipid metabolism, implying that TDCPP-induced damage towards algae by various pathways. Additionally, several TFs related to stress signaling were differentially expressed, suggesting roles in the TDCPP stress response. The results will provide critical data to understand the ecological risks and toxic mechanism of OPFRs entering into marine habitat.

Elucidating mechanisms of immunotoxicity by benzotriazole ultraviolet stabilizers in zebrafish (Danio rerio): Implication of the AHR-IL17/IL22 immune pathway

Benzotriazole ultraviolet stabilizers (BUVSs) are widely used additives in industrial materials and personal care products that protect products from ultraviolet damage. Due to their high production volume and potential to bioaccumulate, BUVSs are an environmental pollutant of concern. In this study, juvenile zebrafish (Danio rerio) were exposed to 4 BUVSs (UV-234, UV-326, UV-329, and UV-P) at 10 and 100 μg/L for 28 d. BUVSs induced hepatic vacuolization and nuclei pyknosis in the liver following 100 μg/L UV-234 and UV-329 exposure. Transcriptomic analysis in the liver uncovered pathways related to inflammation that were affected by BUVSs. Based upon these data, we measured the expression levels of 9 genes involved in AHR-IL17/IL22 pathway in zebrafish larvae exposed to each BUVSs at one dose of either 10 or 100 μg/L for 6 days in a second set experiment. Transcript levels of interleukins il17a and il22 were decreased, while il6 mRNA was increased with exposure to UV-234, UV-329, and UV-P. No change to targeted transcripts was observed with UV-326 treatments. Moreover, cyp1a1 and ahr2 levels were increased in larvae treated with 100 μg/L UV-329 or UV-P. Consistent with expression data, protein abundance of IL22 was decreased by 29% with exposure to 100 μg/L UV-P. Taken together, these results demonstrate that exposure to different benzotriazole congeners may be associated with immunotoxicity in zebrafish through the AHR-IL17/IL22 pathway, and this may be associated with hepatic damage with prolonged exposures. This study provides new insight into unique pathways perturbed by specific BUVSs congeners.

Promotion effect of liver tumor progression in male kras transgenic zebrafish induced by tris (1, 3-dichloro-2-propyl) phosphate

A previous study reported that exposure to tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) could promote the progression of hepatocellular carcinoma (HCC) in female HCC model zebrafish. Due to the existence of gender disparity in the development of HCC between females and males, whether the promotion effect of TDCIPP still exists in male HCC model zebrafish remains unclear. In this study, Tg(fabp10:rtTA2s-M2; TRE2:EGFP-kras^G12V), referred as kras transgenic zebrafish which was shown to be an inducible liver tumor model, was applied as experimental model to assess the promotion potential of TDCIPP for HCC in males. In brief, kras males were exposed to 20 mg/L doxycycline (DOX), 0.3 mg/L TDCIPP and a binary mixture of 20 mg/L DOX with 0.3 mg/L TDCIPP, and after exposure liver size, histopathology and transcriptional profiles of liver from these treatments were examined. With the involvement of TDCIPP, the liver size was significantly increased and the lesion of hepatocyte became more aggressive. Furthermore, expressions of genes involved in DNA replication and inflammatory response were simultaneously up-regulated in the treatment of TDCIPP compared with the solvent control and in the treatment of the binary mixture of the two chemicals compared to the single DOX treatment. Overall, our results suggested that TDCIPP had promotion effect on the progression of liver tumor in kras males.

Longer commutes are associated with increased human exposure to tris(1,3-dichloro-2-propyl) phosphate

Organophosphate esters (OPEs) are a class of semi-volatile organic compounds (SVOCs) used as flame retardants, plasticizers, and anti-foaming agents. Due to stringent flammability standards in vehicles and the ability of OPEs to migrate out of end-use products, elevated concentrations of OPEs have been found in car dust samples around the world. As many residents of Southern California spend a significant amount of time in their vehicles, there is potential for increased exposure to OPEs associated with longer commute times. As approximately 70% of the University of California, Riverside's undergraduate population commutes, the objective of this study was to use silicone wristbands to monitor personal exposure to OPEs and determine if exposure was associated with commute time in a subset of these students. Participants were asked to wear wristbands for five continuous days and complete daily surveys about the amount of time spent commuting. Data were then used to calculate a participant-specific total commute score. Components of Firemaster 550 (triphenyl phosphate, or TPHP, and isopropylated triaryl phosphate isomers) and Firemaster 600 (TPHP and tert-butylated triaryl phosphate isomers) - both widely used commercial flame retardant formulations - were strongly correlated with other OPEs detected within participant wristbands. Moreover, the concentration of tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) was significantly correlated with the concentration of several Firemaster 500 components and tris(2-chloroisopropyl) phosphate (TCIPP). Finally, out of all OPEs measured, TDCIPP was significantly and positively correlated with total commute score, indicating that longer commutes are associated with increased human exposure to TDCIPP. Overall, our findings raise concerns about the potential for chronic TDCIPP exposure within vehicles and other forms of transportation, particularly within densely populated and traffic-congested areas such as Southern California.

Progression of liver tumor was promoted by tris(1,3-dichloro-2-propyl) phosphate through the induction of inflammatory responses in krasV12 transgenic zebrafish

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) has been detected in various environmental media and has been implicated as a weak mutagen or carcinogen, but whether TDCIPP can promote the progression of liver tumor remains unclear. In this study, krasV12 genetically modified zebrafish, Tg(fabp10:rtTA2s-M2; TRE2:EGFP-krasG12V), a model system in which liver tumors can be induced by doxycycline (DOX), was used to evaluate the liver tumor promotion potential of TDCIPP. Briefly, krasV12 transgenic females were exposed to 0.3 mg/L TDCIPP, 20 mg/L DOX or a binary mixture of 0.3 mg/L TDCIPP with 20 mg/L DOX, and liver size, histopathology, and transcriptional profiles of liver were determined. Treatment with TDCIPP resulted in increased liver size and caused more aggressive hepatocellular carcinoma (HCC). Compared with the exposure to DOX, TDCIPP in the presence of DOX up-regulated the expression of genes relevant with salmonella infection and the toll-like receptor signaling pathway. These results implied an occurrence of inflammatory reaction, which was sustained by the increase in the amount of infiltrated neutrophils in the liver of Tg(lyz:DsRed2) transgenic zebrafish larvae whose neutrophils were labelled by red fluorescent protein under the lysozyme C promoter. Furthermore, compared with the binary exposure of DOX and TDCIPP, treatment with a ternary mixture of TDCIPP, DOX and inflammatory response inhibitor (ketoprofen) significantly decrease the liver size and the amounts of neutrophils in the livers of kras and lyz double transgenic zebrafish larvae. Collectively, our results suggested that TDCIPP could promote the liver tumor progression by induction of hepatic inflammatory responses.

Sub-chronic exposure to Tris(1,3-dichloro-2-propyl) phosphate induces sex-dependent hepatotoxicity in rats

As the application and environmental release of tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) are being increased rapidly, serious concerns have been raised regarding its adverse effects on human health. Exposure to TDCIPP has been implicated in hepatotoxicity, but the molecular mechanisms remain unclear. Here, both male and female Sprague Dawley rats were administered TDCIPP with 125, 250, or 500 mg/kg/day for 12 weeks. Then the ultrastructure of liver, biochemical indicators in serum and liver, and hepatic gene expression were analyzed to reveal molecular mechanisms of hepatotoxicity induced by TDCIPP. Continuous TDCIPP exposure decreased body weight, particularly in 500 mg/kg/day TDCIPP-exposed males, and dose dependently increased the ratio of liver to body weight in both genders. The decreased levels of triglyceride, cholesterol, and transaminase in the serum and livers were observed in both genders after TDCIPP exposure, which indicated dysfunction in the hepatic metabolism. Liver histopathology revealed hepatocellular damages in males and females after TDCIPP exposure. The transcriptomic analysis indicated that TDCIPP exposure significantly changed pathways of bile acid metabolism, inflammatory response, oxidative phosphorylation and carcinogenicity in 250 and 500 mg/kg/day TDCIPP-exposed males and 500 mg/kg/day TDCIPP-exposed females, and there was no statistical significance in any other TDCIPP-exposed groups. The transcriptional analysis showed that TDCIPP exposure led to oxidative stress in the livers of rats, thereby increasing the inflammatory response and promoting mechanisms of carcinogenesis in both genders. Finally, TDCIPP led to more severe adverse phenotypic effects in male than female rats.

Hepatotoxicity evaluation of Euphorbia kansui on zebrafish larvae in vivo

BACKGROUND

Euphorbia kansui is effective in treating various diseases, such as ascites and edema, but its liver toxicity is a major obstacle in its wide use in the clinic. However, further investigations have suggested that Euphorbia kansui can cause liver injury.

HYPOTHESIS

The study aims to investigate the effect of Euphorbia kansui exposure on zebrafish, and explain the underlying toxicity mechanisms from a comprehensive perspective.

STUDY DESIGN

The 4dpf zebrafish larvae were exposed to Euphorbia kansui at a sub-lethal concentration.

METHODS

We evaluated the effect of Euphorbia kansui on the ultrastructure and function of the liver, apoptosis of liver cells by PCR and western blot, and metabolic profile by GC-MS based on sub-lethal concentrations.

RESULTS

Our results suggested Euphorbia kansui could lead to liver injury and significant alteration of the metabolomics of the zebrafish larvae in sub-lethal concentration conditions. It could also induce alterations in liver microstructure, hepatic function, gene expression and protein associated with the apoptosis process, as well as endogenous metabolism. KEGG pathway analysis identified some biological processes on the basis of different metabolisms and their associated processes especially for amino acid metabolism.

CONCLUSION

The results bring us closer to an in-depth understanding of the toxic effects of Euphorbia kansui on zebrafish liver, which will be significantly helpful in effectively guiding safer clinical application of this herb in the clinic. Furthermore, our results also showed the zebrafish model is reliable for evaluation of Euphorbia kansui extract hepatotoxicity and as a methodological reference for the evaluation of Traditional Chinese Medicine with underlying liver toxicity.

Identification of compounds that inhibit the binding of Keap1a/Keap1b Kelch DGR domain with Nrf2 ETGE/DLG motifs in zebrafish

The Keap1-Nrf2-ARE system serves as a premier defence mechanism to curb oxidative stress, which remains as one of the major causes of ageing and pathogenesis in various diseases. Nrf2 is the principal master regulator of the cellular defence system, and its activation remains the prospective therapeutic approach against chronic diseases. One of the recent strategies is to disrupt Keap1-Nrf2 protein-protein interaction (PPI) that alters the docking of Keap1 with Nrf2 by compounds occupying a position in the Keap1 blocking the interface with Nrf2. In this study, we made an attempt to identify the compounds with anticancer, antioxidant and anti-inflammatory properties to disrupt Keap1a/b-Nrf2 PPI through in silico molecular docking in zebrafish. The phylogenetic analysis of Keap1 proteins revealed the existence of orthologous Keap1-Nrf2-ARE system in lower vertebrates that includes zebrafish. The DGR domains of zebrafish Keap1a and Keap1b were modelled with Modeller 9.19 using Keap1 of Mus musculus (PDB ID:5CGJ) as template. Based on the docking calculations, top hit compounds were identified to disrupt both Keap1a and Keap1b interaction with Nrf2 which include quercetin 3,4'-diglucoside, flavin adenine dinucleotide disodium salt hydrate, salvianolic acid A, tunicamycin and esculin. The LC₅₀ of esculin in 3 dpf zebrafish larvae is 5 mmol/L, and the qRT-PCR results showed that esculin significantly increased the transcription of Nrf2 target genes-Gstpi, Nqo1, Hmox1a and Prdx1 in 3 dpf zebrafish larvae. These potential hits could serve as safer Nrf2 activators due to their non-covalent disruption of Keap1-Nrf2 PPI and be developed into efficacious preventive/therapeutic agents for various diseases.

Toxicity Evaluation and Biomarker Selection with Validated Reference Gene in Embryonic Zebrafish Exposed to Mitoxantrone

Notwithstanding the widespread use and promising clinical value of chemotherapy, the pharmacokinetics, toxicology, and mechanism of mitoxantrone remains unclear. To promote the clinical value in the treatment of human diseases and the exploration of potential subtle effects of mitoxantrone, zebrafish embryos were employed to evaluate toxicity with validated reference genes based on independent stability evaluation programs. The most stable and recommended reference gene was gapdh, followed by tubα1b, for the 48 h post fertilization (hpf) zebrafish embryo mitoxantrone test, while both eef1a1l1 and rpl13α were recommended as reference genes for the 96 hpf zebrafish embryo mitoxantrone test. With gapdh as an internal control, we analyzed the mRNA levels of representative hepatotoxicity biomarkers, including fabp10a, gclc, gsr, nqo1, cardiotoxicity biomarker erg, and neurotoxicity biomarker gfap in the 48 hpf embryo mitoxantrone test. The mRNA levels of gclc, gsr, and gfap increased significantly in 10 and 50 μg/L mitoxantrone-treated 48 hpf embryos, while the transcript levels of fabp10a decreased in a dose-dependent manner, indicating that mitoxantrone induced hepatotoxicity and neurotoxicity. Liver hematoxylin–eosin staining and the spontaneous movement of embryos confirmed the results. Thus, the present research suggests that mitoxantrone induces toxicity during the development of the liver and nervous system in zebrafish embryos and that fabp10a is recommended as a potential biomarker for hepatotoxicity in zebrafish embryos. Additionally, gapdh is proposed as a reference gene for the 48 hpf zebrafish embryo mitoxantrone toxicity test, while eef1a1l1 and rpl13α are proposed as that for the 96 hpf test.

Developing specific molecular biomarkers for thermal stress in salmonids

Background

Pacific salmon (Oncorhynchus spp.) serve as good biological indicators of the breadth of climate warming effects on fish because their anadromous life cycle exposes them to environmental challenges in both marine and freshwater environments. Our study sought to mine the extensive functional genomic studies in fishes to identify robust thermally-responsive biomarkers that could monitor molecular physiological signatures of chronic thermal stress in fish using non-lethal sampling of gill tissue.

Results

Candidate thermal stress biomarkers for gill tissue were identified using comparisons among microarray datasets produced in the Molecular Genetics Laboratory, Pacific Biological Station, Nanaimo, BC, six external, published microarray studies on chronic and acute temperature stress in salmon, and a comparison of significant genes across published studies in multiple fishes using deep literature mining. Eighty-two microarray features related to 39 unique gene IDs were selected as candidate chronic thermal stress biomarkers. Most of these genes were identified both in the meta-analysis of salmon microarray data and in the literature mining for thermal stress markers in salmonids and other fishes. Quantitative reverse transcription PCR (qRT-PCR) assays for 32 unique genes with good efficiencies across salmon species were developed, and their activity in response to thermally challenged sockeye salmon (O. nerka) and Chinook salmon (O. tshawytscha) (cool, 13–14 °C and warm temperatures 18–19 °C) over 5–7 days was assessed. Eight genes, including two transcripts of each SERPINH1 and HSP90AA1, FKBP10, MAP3K14, SFRS2, and EEF2 showed strong and robust chronic temperature stress response consistently in the discovery analysis and both sockeye and Chinook salmon validation studies.

Conclusions

The results of both discovery analysis and gene expression showed that a panel of genes involved in chaperoning and protein rescue, oxidative stress, and protein biosynthesis were differentially activated in gill tissue of Pacific salmon in response to elevated temperatures. While individually, some of these biomarkers may also respond to other stressors or biological processes, when expressed in concert, we argue that a biomarker panel comprised of some or all of these genes could provide a reliable means to specifically detect thermal stress in field-caught salmon.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5108-9) contains supplementary material, which is available to authorized users.

Toxicity profiling of flame retardants in zebrafish embryos using a battery of assays for developmental toxicity, neurotoxicity, cardiotoxicity and hepatotoxicity toward human relevance

Following the voluntary phase-out of brominated flame retardants (BFRs) due to their environmental persistence and toxicity, the organophosphorus flame retardants (OPFRs) are emerging replacements. However, there is limited information on the potential human health effects of the OPFRs. Zebrafish embryos are a viable vertebrate model organism with many advantages for high throughput testing toward human hazard assessment. We utilized zebrafish embryos to assess developmental toxicity, neurotoxicity, cardiotoxicity and hepatotoxicity, of eight replacement OPFRs: (triphenyl phosphate [TPHP], isopropylated phenyl phosphate [IPP], 2-ethylhexyl diphenyl phosphate [EHDP], tert-butylated phenyl diphenyl phosphate [BPDP], trimethyl phenyl phosphate [TMPP], isodecyl diphenyl phosphate [IDDP], tris(1,3-dichloroisopropyl) phosphate [TDCIPP], and tris(2-chloroethyl) phosphate [TCEP]) and two BFRs (3,3',5,5'- tetrabromobisphenol A [TBBPA] and 2,2'4,4'-brominated diphenyl ether [BDE-47]). To determine potential effects on teratogenicity, embryos were exposed to flame retardants (FRs) at 4 h post fertilization (hpf) to 4 days post fertilization (dpf) and morphological alterations and corresponding survival were evaluated at 2 and 4 dpf. Internal concentrations were measured in larvae used in this assay by liquid chromatography-mass spectrometry. Locomotor activity was assessed in larvae treated for 48 h (from 3 dpf to 5 dpf), followed by hepatotoxicity evaluation. Finally, alterations in heart rate and rhythmicity were assessed to determine cardiotoxicity in 48 hpf embryos exposed to compounds for 3 h. Results suggest that several OPFRs (BPDP, EHDP; IPP, TMPP; TPHP and TDCIPP) produced adverse effects in multiple target organs at concentrations comparable to the two BFRs. As these OPFRs have the capacity to disrupt an integrated vertebrate model, they potentially have the capacity to affect mammalian biology. Then, we compared the lowest effective levels (LEL) in zebrafish with estimated or measured human plasma concentrations using biomonitoring data (human plasma, breast milk, handwipe samples and house dust) and a high throughput toxicokinetic (HTTK) model. Results indicate that for some compounds, the nominal LELs were within the range of human exposures, while internal LELs in zebrafish are above internal exposures in humans. These findings demonstrate the value of the zebrafish model as a relevant screening tool and support the need for further hazard characterization of the OPFRs.

Investigation of the molecular mechanisms of hepatic injury upon naphthalene exposure in zebrafish (Danio rerio)

Naphthalene has been used worldwide as a commercial insecticide for decades, which when detected in the environment can have various negative effects on non-target organism, such as hepatotoxicity. However, the molecular mechanisms of how naphthalene acts to affect the liver in zebrafish (Danio rerio) remains unknown. In this study, we evaluated the potential toxic effects of naphthalene on livers in female adult zebrafish over a 21-day subacute exposure. Global hepatic gene expression was examined by microarrays and the results indicated the regulated genes were associated significantly with vital hepatic injury pathways and GO categories upon naphthalene exposure, such as disruptions in lipid metabolism, inflammatory response, and the carcinogenic processes. According to our observations of liver histology, nuclear enlargement as a potential indicator of cancers and hepatic lipometabolic disorder precisely were supported. The 96 h acute naphthalene tests on Tg(lysC:DsRed) and LiPan lines larvae revealed recruitment of neutrophils by the liver, as well as decreased liver size, which further confirmed hepatic inflammation response to naphthalene exposure. Thus, these findings advance the field of ecotoxicology by unveiling a new role of naphthalene as a leading cause of liver damage and provide potential biomarker-genes for environmental naphthalene monitoring.

Toxicity and Transcriptome Sequencing (RNA-seq) Analyses of Adult Zebrafish in Response to Exposure Carboxymethyl Cellulose Stabilized Iron Sulfide Nanoparticles

Increasing utilization of stabilized iron sulfides (FeS) nanoparticles implies an elevated release of the materials into the environment. To understand potential impacts and underlying mechanisms of nanoparticle-induced stress, we used the transcriptome sequencing (RNA-seq) technique to characterize the transcriptomes from adult zebrafish exposed to 10 mg/L carboxymethyl cellulose (CMC) stabilized FeS nanoparticles for 96 h, demonstrating striking differences in the gene expression profiles in liver. The exposure caused significant expression alterations in genes related to immune and inflammatory responses, detoxification, oxidative stress and DNA damage/repair. The complement and coagulation cascades Kyoto encyclopedia of genes and genomes (KEGG) pathway was found significantly up-regulated under nanoparticle exposure. The quantitative real-time polymerase chain reaction using twelve genes confirmed the RNA-seq results. We identified several candidate genes commonly regulated in liver, which may serve as gene indicators when exposed to the nanoparticles. Hepatic inflammation was further confirmed by histological observation of pyknotic nuclei, and vacuole formation upon exposure. Tissue accumulation tests showed a 2.2 times higher iron concentration in the fish tissue upon exposure. This study provides preliminary mechanistic insights into potential toxic effects of organic matter stabilized FeS nanoparticles, which will improve our understanding of the genotoxicity caused by stabilized nanoparticles.

Co-exposure to benzo[a]pyrene and ethanol induces a pathological progression of liver steatosis in vitro and in vivo

Hepatic steatosis (i.e. lipid accumulation) and steatohepatitis have been related to diverse etiologic factors, including alcohol, obesity, environmental pollutants. However, no study has so far analyzed how these different factors might interplay regarding the progression of liver diseases. The impact of the co-exposure to the environmental carcinogen benzo[a]pyrene (B[a]P) and the lifestyle-related hepatotoxicant ethanol, was thus tested on in vitro models of steatosis (human HepaRG cell line; hybrid human/rat WIF-B9 cell line), and on an in vivo model (obese zebrafish larvae). Steatosis was induced prior to chronic treatments (14, 5 or 7 days for HepaRG, WIF-B9 or zebrafish, respectively). Toxicity and inflammation were analyzed in all models; the impact of steatosis and ethanol towards B[a]P metabolism was studied in HepaRG cells. Cytotoxicity and expression of inflammation markers upon co-exposure were increased in all steatotic models, compared to non steatotic counterparts. A change of B[a]P metabolism with a decrease in detoxification was detected in HepaRG cells under these conditions. A prior steatosis therefore enhanced the toxicity of B[a]P/ethanol co-exposure in vitro and in vivo; such a co-exposure might favor the appearance of a steatohepatitis-like state, with the development of inflammation. These deleterious effects could be partly explained by B[a]P metabolism alterations.

A critical review of histopathological findings associated with endocrine and non-endocrine hepatic toxicity in fish models

Although frequently examined as a target organ for non-endocrine toxicity, histopathological evaluation of the liver is becoming a routine component of endocrine disruption studies that utilize various fish species as test subjects. However, the interpretation of microscopic liver findings can be challenging, especially when attempting to distinguish adverse changes associated with endocrine disrupting substances from those caused by systemic or direct hepatic toxicity. The purpose of this project was to conduct a critical assessment of the available peer-reviewed and grey literature concerning the histopathologic effects of reproductive endocrine active substances (EAS) and non-endocrine acting substances in the livers of fish models, and to determine if liver histopathology can be used to reliably distinguish endocrine from non-endocrine etiologies. The results of this review suggest that few compound-specific histopathologic liver effects have been identified, among which are estrogen agonist-induced increases in hepatocyte basophilia and proteinaceous intravascular fluid in adult male teleosts, and potentially, decreased hepatocyte basophilia in female fish exposed to substances that possess androgenic, anti-estrogenic, or aromatase inhibitory activity. This review also used published standardized methodology to assess the credibility of the histopathology data in each of the 117 articles that reported liver effects of treatment, and consequently it was determined that in only 37% of those papers were the data considered either highly credible or credible. The outcome of this work highlights the value of histopathologic liver evaluation as an investigative tool for EAS studies, and provides information that may have implications for EAS hazard assessment.

Effects of the bioconcentration and parental transfer of environmentally relevant concentrations of difenoconazole on endocrine disruption in zebrafish (Danio rerio)

Difenoconazole, a typical triazole fungicide, inhibits lanosterol-14R-demethylase (CYP51) to prevent fungal sterol synthesis and its residues are frequently detected in the environment due to its wide application. Previous studies have demonstrated that difenoconazole altered the triglyceride levels, and gene expression relevant to cholesterol biosynthesis in zebrafish. However, endocrine-disruption in the hypothalamus-pituitary-gonadal-liver (HPGL) axis, the effects of transferring to offspring, and the underlying mechanisms of difenoconazole in aquatic organisms are still unknown. In this study, we defined the effects of difenoconazole at environmental concentrations on endocrine disturbance using zebrafish as an experimental model. The results indicated that difenoconazole induced a significant change in the somatic index, and pathological variations in tissues, and steroid hormone levels. RT-PCR experiments further confirmed that difenoconazole significantly induced expression alteration of lhr, hsd3β, hsd11β, cyp19a in the ovary and star, cyp19a, cyp3c1 in the testis, and erα genes in livers. In addition, difenoconazole exposure in parental zebrafish affected the hatchability and length of its offspring. Moreover, the burdens of difenoconazole and difenoconazole alcohol in females were higher than in males. These findings highlighted that difenoconazole exposure at environmentally relevant concentrations elicited estrogenic endocrine-disruption effects via altering homeostasis of sex steroid hormones in the HPGL axis and the adverse effects can be transferred to the offspring.

Determination and prediction of octanol-air partition coefficients for organophosphate flame retardants

Organophosphate flame retardants (OPFRs) have attracted wide concerns due to their toxicities and ubiquitous occurrence in the environment. In this work, Octanol-air partition coefficient (K_OA) for 14 OPFRs including 4 halogenated alkyl-, 5 aryl- and 5 alkyl-OPFRs, were estimated as a function of temperature using a gas chromatographic retention time (GC-RT) method. Their log K_OA-GC values and internal energies of phase transfer (Δ_OAU/kJmol^-1) ranged from 8.03 to 13.0 and from 69.7 to 149, respectively. Substitution pattern and molar volume (V_M) were found to be capable of influencing log K_OA-GC values of OPFRs. The halogenated alkyl-OPFRs had higher log K_OA-GC values than aryl- or alkyl-OPFRs. The bigger the molar volume was, the greater the log K_OA-GC values increased. In addition, a predicted model of log K_OA-GC versus different relative retention times (RRTs) was developed with a high cross-validated value (Q²_(cum)) of 0.951, indicating a good predictive ability and stability. Therefore, the log K_OA-GC values of the remaining OPFRs can be predicted by using their RRTs on different GC columns.

Bioaccumulation mechanism of organophosphate esters in adult zebrafish (Danio rerio)

Although organophosphate esters (OPEs) have been detected with growing frequency in water ecosystems, the underlying accumulation mechanisms of these compounds in fish are still unknown. Here, we investigated the tissue-specific accumulation and depuration of seven OPEs in adult zebrafish at three levels (0, 1/150 LC₅₀ (environmentally relevant level), and 1/30 LC₅₀ per OPE congener) in laboratory after 19 days exposure and 3 days depuration. The bioaccumulation of OPEs varied among tissues. Muscle contained the lowest level of OPEs and liver had the highest level of two (TPP and TCEP) of the seven OPEs at steady state. The high levels and slow depuration rates of TDCIPP, TPHP, and TCP observed in roe indicated that the accumulated OPEs were potentially stored in roe and transferred to the next generation. After examination of the major metabolites (organophosphate diesters) in selected tissues, a physiologically based toxicokinetic (PBTK) model used in fish was adopted to explore the key factors affecting the bioaccumulation of OPEs in zebrafish. Biotransformation of OPEs with polychlorinated alkyl moieties (i.e. TDCIPP) and aryl moieties (i.e. TPHP and TCP) has more significant impacts on the accumulation than those of OPEs with alkyl or short chain chlorinated alkyl moieties. Furthermore, the partition process between tissues and blood was also investigated, and was demonstrated to be the dominant process for OPEs accumulation in zebrafish. This study provides critical information on the bioaccumulation, tissue distribution, and metabolization of OPEs in relation with OPE structures in fish, as well as the underlying bioaccumulation mechanisms/pathways of OPEs in aquatic life.

Editor's Highlight: Comparative Toxicity of Organophosphate Flame Retardants and Polybrominated Diphenyl Ethers to Caenorhabditis elegans

With the phasing-out of the polybrominated diphenyl ether (PBDE) flame retardants due to concerns regarding their potential developmental toxicity, the use of replacement compounds such as organophosphate flame retardants (OPFRs) has increased. Limited toxicity data are currently available to estimate the potential adverse health effects of the OPFRs. The toxicological effects of 4 brominated flame retardants, including 3 PBDEs and 3,3',5,5'-tetrabromobisphenol A, were compared with 6 aromatic OPFRs and 2 aliphatic OPFRs. The effects of these chemicals were determined using 3 biological endpoints in the nematode Caenorhabditis elegans (feeding, larval development, and reproduction). Because C. elegans development was previously reported to be sensitive to mitochondrial function, results were compared with those from an in vitro mitochondrial membrane permeabilization (MMP) assay. Overall 11 of the 12 flame retardants were active in 1 or more C. elegans biological endpoints, with only tris(2-chloroethyl) phosphate inactive across all endpoints including the in vitro MMP assay. For 2 of the C. elegans endpoints, at least 1 OPFR had similar toxicity to the PBDEs: triphenyl phosphate (TPHP) inhibited larval development at levels comparable to the 3 PBDEs; whereas TPHP and isopropylated phenol phosphate (IPP) affected C. elegans reproduction at levels similar to the PBDE commercial mixture, DE-71. The PBDEs reduced C. elegans feeding at lower concentrations than any OPFR. In addition, 9 of the 11 chemicals that inhibited C. elegans larval development also caused significant mitochondrial toxicity. These results suggest that some of the replacement aromatic OPFRs may have levels of toxicity comparable to PBDEs.