Parental exposure to microcystin-LR induced thyroid endocrine disruption in zebrafish offspring, a transgenerational toxicity

Parental (F0) exposure to Cadmium and Ketoprofen induces developmental deformities in offspring (F1): A transgenerational toxicity assessment in zebrafish model

In the aquatic environment, the primary pollutants of heavy metals and pharmaceuticals always occur in coexisting forms, and the research about combined impacts remains unclear, especially transgenerational effects. Cadmium (Cd) is a heavy metal that can damage the endocrine reproduction systems and cause thyroid dysfunction in fish. Meanwhile, ketoprofen (KPF) is a nonsteroidal anti-inflammatory drug (NSAID) that can cause neurobehavioral damage and physiological impairment. However, to our knowledge, the combined exposure of Cd and KPF in transgenerational studies has not been reported. In this investigation, sexually mature zebrafish were subjected to isolated exposure and combined exposure to Cd (10 μg/L) and KPF (10 and 100 μg/L) at environmentally relevant concentrations for 42 days. In this background, breeding capacity, chemical accumulation rate in gonads, and tissue morphologies are investigated in parental fish. This is followed by examining the malformation rate, inflammation rate, and gene transcription in the F1 offspring. Our results indicate that combined exposure of Cd and KPF to the parental fish could increase the chemical accumulation rate and tissue damage in the gonads of fish and significantly reduce the breeding ability. Furthermore, these negative impacts were transmitted to its produced F1 embryos, reflected by hatching rate, body deformities, and thyroid axis-related gene transcription. These findings provide further insights into the harm posed by Cd in the presence of KPF to the aquatic ecosystems.

Novel insights into DEHP-induced zebrafish spleen damage: Cellular apoptosis, mitochondrial dysfunction, and innate immunity

DEHP (Di(2-ethylhexyl) phthalate) is the most abundant phthalate component detected in environmental samples as it is widely used in the manufacturing of children's toys, medical devices and furniture. Due to its wide prevalence and propensity to accumulate in the food chain, significant concerns have risen about the safety profile of DEHP. Here, we used a zebrafish model to investigate the toxicity mechanisms of DEHP. Our results indicated that exposure to DEHP altered the ROS content in zebrafish spleen and inhibited the activities of antioxidant enzymes SOD and CAT, detoxification enzyme GSH-Px and induced histopathological damage. In addition, elucidated the mechanism of DEHP significantly promoted apoptosis and caused damage in spleen cells through the bax/bcl-2 pathway. Further genetic testing demonstrated significant alterations in mitochondrial biogenesis, fission, and fusion-related genes and suggested potential mechanistic pathways, including GM10532/m6A/FIS1 axis, the STAT3/POA1 axis, and the NFR1/TFAM axis. Serological and genomic analysis indicated that DEHP exposure activated the C3 complement cascade immune pathway and interfered with innate immune function. IBRv2 analysis proposes that innate immunity may serve as a signal indicator of early toxic responses to DEHP pollutants. This study provided comprehensive cellular and genetic data for DEHP toxicity studies and emphasized the need for future management and remediation of DEHP contamination. It also provides data to specifically support the health risk assessments of DEHP, as well as contributing to broader health and environmental research.

Long-term tralopyril exposure results in endocrinological and transgenerational toxicity: A two-generation study of marine medaka (Oryzias melastigma)

This study aims to investigate the impact of tralopyril, a newly developed marine antifouling agent, on the reproductive endocrine system and developmental toxicity of offspring in marine medaka. The results revealed that exposure to tralopyril (0, 1, 20 μg/L) for 42 days resulted in decreased reproductive capacity in marine medaka. Moreover, it disrupted the levels of sex hormones E2 and T, as well as the transcription levels of genes related to the HPG axis, such as cyp19b and star. Sex-dependent differences were observed, with females experiencing more pronounced effects. Furthermore, intergenerational toxicity was observed in F1 offspring, including increased heart rate, changes in retinal morphology and cartilage structure, decreased swimming activity, and downregulation of transcription levels of relevant genes (HPT axis, GH/IGF axis, cox, bmp4, bmp2, runx2, etc.). Notably, the disruption of the F1 endocrine system by tralopyril persisted into adulthood, indicating a transgenerational effect. Molecular docking analysis suggested that tralopyril's RA receptor activity might be one of the key factors contributing to the developmental toxicity observed in offspring. Overall, our study highlights the potential threat posed by tralopyril to the sustainability of fish populations, as it can disrupt the endocrine system and negatively impact aquatic organisms for multiple generations.

Effects of sub-chronic exposure to microcystin-LR on the endocrine system of male rats

Microcystins (MCs) can cause reproductive and developmental toxicity and disrupt endocrine homeostasis in mammals. In the present study, male, Sprague-Dawley (SD) rats were administrated 3 or 30 μg MC-LR/kg, body mass (bm) per day via intraperitoneal (i.p.) injections for 6 weeks. Effects of MC-LR on histology, hormone concentrations, gene transcriptional profiles and protein expressions along the hypothalamic-pituitary-adrenal (HPA), -gonad (HPG) and -thyroid (HPT) axes were assessed. Sub-chronic administration with MC-LR caused histological damage to hypothalamus, pituitary, adrenal, testes and thyroid and affected relative masses of pituitary, adrenal and testes. The HPA axis was activated and serum concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were significantly augmented. Along the HPG axis, serum concentrations of gonadotropin-releasing hormone (GnRH) and dihydrotestosterone (DHT) were diminished, while concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T) and estradiol (E2) were augmented. For the HPT axis, only concentrations of free tetra-iodothyronine (fT4) were significantly diminished, while concentrations of thyrotropin-releasing hormone (TRH), thyroid-stimulating hormone (TSH) or free tri-iodothyronine (fT3) were not significantly changed. Also, several genes and proteins related to synthesis of steroid hormones were significantly altered. Findings of the present study illustrate that MC-LR can cause endocrine-disrupting effects through the disruption of synthesis and secretion of hormones along the HPA, HPG and HPT axes and negative feedback regulation. Also, there could be crosstalk among HPA, HPG and HPT axes. These findings elucidate mechanisms of endocrine-disrupting effects of MCs.

Microcystin-LR immersion caused sequential endocrine disruption and growth inhibition in zebrafish (Danio rerio) from fertilization to sexual differentiation completion

Microcystin-LR (MC-LR) is a highly toxic congener and is also one of the most commonly found. Recent studies have demonstrated that MC-LR can disrupt growth and endocrine in fish, but how it works at the stage of the sex differentiation period had not been determined to date. In this study, zebrafish (Danio rerio) embryos were exposed to MC-LR (0 and 10μg/L), and sampled at 14, 28, and 42 days post fertilization (dpf), respectively. The results demonstrated that MC-LR caused the growth inhibition of zebrafish at 42 dpf. The expression levels of genes related to the growth hormone/insulin-like growth factor (GH/IGF) and hypothalamic-pituitary-thyroid (HPT) axes, as well as the levels of hormone 3,5,3'- Triiodothyronine (T3) and thyroxine (T4), were significantly decreased at all time points. A Significant decrease in the ratio of testosterone and estradiol (T/E2) were detected at 28 and 42 dpf in MC-LR group along with changes in genes related to the hypothalamic-pituitary-gonadal (HPG) axis. The result of sex ratio showed that the percentage of females was up to 61.84%, indicating a estrogenic effect induced by MC-LR. The significant changes on hormone levels and gene transcripts occurred mainly in the stage of sex differentiation. The correlation analysis further suggested that key cross-talks among three endocrine axes may be the growth hormone releasing hormone (GHRH), Transthyretin (TTR) and gonadotropin releasing hormone (GnRH) signaling molecules. Overall, our findings provide a new insight for understanding the mechanisms by which MC-LR affects fish growth and reproduction during gonadal development.

Microcystin-LR induced transgenerational effects of thyroid disruption in zebrafish offspring by endoplasmic reticulum stress-mediated thyroglobulin accumulation and apoptosis

MC-LR can interfere with thyroid function in fish, but the underlying mechanism is still unclear. Current study focuses to study the intergenerational inheritance of MC-LR-induced thyroid toxicity in zebrafish and in rat thyroid cells. In vivo experiments, adult female zebrafish (F0) were exposed to MC-LR (0, 5, and 25 μg/L) for 90 days and mated with male zebrafish without MC-LR exposure to generate F1 generation. F1 embryos were allowed to develop normally to 7 days post-fertilization (dpf) in clear water. In the F0 generation, MC-LR induced disturbance of the hypothalamic-pituitary-thyroid (HPT) axis, leading to a decrease in the production of thyroid hormones. Maternal MC-LR exposure also induced growth inhibition by altering thyroid hormones (THs) homeostasis and interfering with thyroid metabolism and development in F1 offspring. Mechanistically, MC-LR caused excessive accumulation of ROS and induced ER stress that further lead to activation of UPR in the F0 and F1 offspring of zebrafish. Interestingly, our findings suggested that MC-LR exposure hampered thyroglobulin turnover by triggering IRE1 and PERK pathway in zebrafish and FRTL-5 thyroid cells, thus disturbing the thyroid endocrine system and contributing to the thyroid toxicity from maternal to its F1 offspring of zebrafish. Particularly, inhibition of the IRE1 pathway by siRNA could alleviate thyroid development injury induced by MC-LR in FRTL-5 cells. In addition, MC-LR induced thyroid cell apoptosis by triggering ER stress. Taken together, our results demonstrated that maternal MC-LR exposure causes thyroid endocrine disruption by ER stress contributing to transgenerational effects in zebrafish offspring.

Acute exposure to microcystins affects hypothalamic-pituitary axes of male rats

Microcystins (MCs) produced by some cyanobacteria can cause toxicity in animals and humans. In recent years, growing evidence suggests that MCs can act as endocrine disruptors. This research systematically investigated effects of microcystin-LR (MC-LR) on endocrine organs, biosynthesis of hormones and positive/negative feedback of the endocrine system in rats. Male, Sprague-Dawley rats were acutely administrated MC-LR by a single intraperitoneal injection at doses of 45, 67.5 or 90 μg MC-LR/kg body mass (bm), and then euthanized 24 h after exposure. In exposed rats, histological damage of hypothalamus, pituitary, adrenal, testis and thyroid were observed. Serum concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and corticosterone (CORT), expressions of genes and proteins for biosynthesis of hormones were lesser, which indicated an overall suppression of the hypothalamus-pituitary-adrenal (HPA) axis. Along the hypothalamus-pituitary-gonadal (HPG) axis, lesser concentrations of gonadotropin-releasing hormone (GnRH) and testosterone (T), but greater concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and estradiol (E2) were observed. Except for greater transcription of cyp19a1 in testes, transcriptions of genes and proteins for T and E2 biosynthesis along the HPG axis were lesser. As for the hypothalamus-pituitary-thyroid (HPT) axis, after MCs treatment, greater concentrations of thyroid-stimulating hormone (TSH), but lesser concentrations of free tri-iodothyronine (fT3) were observed in serum. Concentrations of free tetra-iodothyronine (fT4) were greater in rats dosed with 45 μg MCs/kg, bm, but lesser in rats dosed with 67.5 or 90 μg MCs/kg, bm. Transcripts of genes for biosynthesis of hormones and receptors along the HPT axis and expressions of proteins for biosynthesis of tetra-iodothyronine (T4) and tri-iodothyronine (T3) in thyroid were significantly altered. Cross-talk among the HPA, HPG and HPT axes probably occurred. It was concluded that MCs caused an imbalance of positive and negative feedback of hormonal regulatory axes, blocked biosynthesis of key hormones and exhibited endocrine-disrupting effects.

Potential Endocrine Disruption of Cyanobacterial Toxins, Microcystins and Cylindrospermopsin: A Review

Microcystins (MCs) and cylindrospermopsin (CYN), although classified as hepatotoxins and cytotoxins, respectively, have been shown to also induce toxic effects in many other systems and organs. Among them, their potential endocrine disruption (ED) activity has been scarcely investigated. Considering the increasing relevance of ED on humans, mammals, and aquatic organisms, this work aimed to review the state-of-the-art regarding the toxic effects of MCs and CYN at this level. It has been evidenced that MCs have been more extensively investigated than CYN. Reported results are contradictory, with the presence or absence of effects, but experimental conditions also vary to a great extent. In general, both toxins have shown ED activity mediated by very different mechanisms, such as estrogenic responses via a binding estrogen receptor (ER), pathological changes in several organs and cells (testis, ovarian cells), and a decreased gonad-somatic index. Moreover, toxic effects mediated by reactive oxygen species (ROS), changes in transcriptional responses on several endocrine axes and steroidogenesis-related genes, and changes in hormone levels have also been reported. Further research is required in a risk assessment frame because official protocols for assessment of endocrine disrupters have not been used. Moreover, the use of advanced techniques would aid in deciphering cyanotoxins dose-response relationships in relation to their ED potential.

Parental whole life-cycle exposure to tris (2-chloroethyl) phosphate (TCEP) disrupts embryonic development and thyroid system in zebrafish offspring

Tris (2-chloroethyl) phosphate (TCEP), an emerging environmental pollutant, has been frequently detected in natural waters. The objective of this study was to investigate possible parental transfer of TCEP and transgenerational effects on the early development and thyroid hormone homeostasis in F1 larvae following parental whole life-cycle exposure to TCEP. To this end, zebrafish (Danio rerio) embryos were exposed to environmentally relevant concentrations (0.8, 4, 20 and 100 μg/L) of TCEP for 120 days until sexual maturation. Parental exposure to TCEP resulted in significant levels of TCEP, developmental toxicity including decreased survival and final hatching rates, accelerated heart rate and elevated malformation rate, as well as induction of oxidative stress and cell apoptosis in F1 offspring. In F1 eggs, declined thyroxin (T4) levels were observed, consistent with those in plasma of F0 adult females, indicating the maternal transfer of thyroid endocrine disruption to the offspring. In addition, mRNA levels of several genes along the hypothalamic-pituitary-thyroid (HPT) axis were significantly modified in F1 larvae, which could be linked to transgenerational developmental toxicity and thyroid hormone disruption. For the first time, we revealed that the parental exposure to environmentally relevant levels of TCEP could cause developmental toxicity and thyroid endocrine disruption in subsequent unexposed generation.

A new identity of microcystins: Environmental endocrine disruptors? An evidence-based review

Microcystins (MCs) are widely distributed cyanobacterial toxins in eutrophic waters. At present, the endocrine-disrupting effects of MCs have been extensively studied, but whether MCs can be classified as environmental endocrine disruptors (EDCs) is still unclear. This review is aimed to evaluate the rationality for MCs as to be classified as EDCs based on the available evidence. It has been identified that MCs meet eight of ten key characteristics of chemicals that can be classified as EDCs. MCs interfere with the six processes, including synthesis, release, circulation, metabolism, binding and action of natural hormones in the body. Also, they are fit two other characteristics of EDC: altering the fate of producing/responding cells and epigenetic modification. Further evidence indicates that the endocrine-disrupting effect of MCs may be an important cause of adverse health outcomes such as metabolic disorders, reproductive disorders and effects on the growth and development of offspring. Generally, MCs have endocrine-disrupting properties, suggesting that it is reasonable for them to be considered EDCs. This is of great importance in understanding and evaluating the harm done by MCs on humans.

Parental exposure to waterborne selenite induces transgenerational development toxicity in zebrafish offspring

Excessive selenium (Se), especially selenite form exerts great toxicity to fish. Most studies have attached considerable attention to the adverse effects of Se on parental fish. However, the transgenerational toxicity of Se on fish has been rarely reported. In the present study, zebrafish embryos were exposed to environmentally relevant concentrations of Na₂SeO₃ (0, 12.5, 25, 50, and 100 μg/L) for 120 days. And the exposed zebrafish (F0) were allowed to spawn with normal zebrafish after sexual maturity. Subsequently, the offspring (F1) were cultured in clean water for 5 days. In the F0 generation, exposure to 100 μg/L Na₂SeO₃ significantly increased the Se content in the tissues (liver, brain and gonad) and decreased the body length and weight. After parental exposure to 100 μg/L Na₂SeO₃, the increased mortality, elevated malformation rate and reduced body length were measured in F1 zebrafish. The Se content was only significantly increased in F1 larvae derived from exposed females in the 100 μg/L exposure group. The contents of thyroid hormones (THs), growth hormone (GH) and insulin-like growth factor (IGF) significantly decreased in F0 and F1 zebrafish. The transcriptional levels of genes along the hypothalamic-pituitary-thyroid (HPT) axis and growth hormone/insulin-like growth factor (GH/IGF) axis were detected to further explore the possible mechanisms of Se-induced thyroid and growth hormone disruption. The results suggest that the toxicity of Se in zebrafish can be markedly transmitted to offspring. And the transgenerational development toxicity might be different due to the differences in gender of exposed parents.

A review and assessment of cyanobacterial toxins as cardiovascular health hazards

Eutrophicated waters frequently support bloom-forming cyanobacteria, many of which produce potent cyanobacterial toxins (cyanotoxins). Cyanotoxins can cause adverse health effects in a wide range of organisms where the toxins may target the liver, other internal organs, mucous surfaces and the skin and nervous system. This review surveyed more than 100 studies concerning the cardiovascular toxicity of cyanotoxins and related topics. Over 60 studies have described various negative effects on the cardiovascular system by seven major types of cyanotoxins, i.e. the microcystin (MC), nodularin (NOD), cylindrospermopsin (CYN), anatoxin (ATX), guanitoxin (GNTX), saxitoxin (STX) and lyngbyatoxin (LTX) groups. Much of the research was done on rodents and fish using high, acutely toxin concentrations and unnatural exposure routes (such as intraperitoneal injection), and it is thus concluded that the emphasis in future studies should be on oral, chronic exposure of mammalian species at environmentally relevant concentrations. It is also suggested that future in vivo studies are conducted in parallel with studies on cells and tissues. In the light of the presented evidence, it is likely that cyanotoxins do not constitute a major risk to cardiovascular health under ordinary conditions met in everyday life. The risk of illnesses in other organs, in particular the liver, is higher under the same exposure conditions. However, adverse cardiovascular effects can be expected due to indirect effects arising from damage in other organs. In addition to risks related to extraordinary concentrations of the cyanotoxins and atypical exposure routes, chronic exposure together with co-existing diseases could make some of the cyanotoxins more dangerous to cardiovascular health.

Exposure to diclofenac alters thyroid hormone levels and transcription of genes involved in the hypothalamic-pituitary-thyroid axis in zebrafish embryos/larvae

Diclofenac (DCF), one of typical non-steroidal anti-inflammatory drugs (NSAIDs), has been frequently detected in various environmental media. Nevertheless，the potential endocrine disrupting effects of DCF on fish were poorly understood. In the present study, zebrafish embryos/larvae were used as a model to evaluate the adverse effects of DCF on development and thyroid system. The results demonstrated that DCF only significantly decreased the heart rate at 72 h post-fertilization (hpf), exhibiting limited influence on the embryonic development of zebrafish. Treatment with DCF significantly reduced whole-body thyroxine (T4) levels, and changed transcriptional levels of several genes related to the hypothalamic-pituitary-thyroid (HPT) axis. These findings provide important information regarding to the mechanisms of DCF-induced developmental toxicity and thyroid disruption in fish.

The presence of polystyrene nanoplastics enhances the MCLR uptake in zebrafish leading to the exacerbation of oxidative liver damage

The accumulation of diminutive plastic waste in the environment, including microplastics and nanoplastics, has threatened the health of multiple species. Nanoplastics can adsorb the pollutants from the immediate environment, and may be used as carriers for pollutants to enter organisms and bring serious ecological risk. To evaluate the toxic effects of microcystin-LR (MCLR) on the liver of adult zebrafish (Danio rerio) in the presence of 70 nm polystyrene nanoplastics (PSNPs), zebrafish were exposed to MCLR alone (0, 0.9, 4.5 and 22.5 μg/L) and a mixture of MCLR + PSNPs (100 μg/L) for three months. The results indicated that groups with combined exposure to MCLR and PSNPs further enhanced the accumulation of MCLR in the liver when compared to groups only exposed to MCLR. Cellular swelling, fat vacuolation, and cytoarchitectonic damage were observed in zebrafish livers after exposure to MCLR, and the presence of PSNPs exacerbated these adverse effects. The results of biochemical tests showed the combined effect of MCLR + PSNPs enhanced MCLR-induced hepatotoxicity, which could be attributed to the altered levels of reactive oxygen species, malondialdehyde and glutathione, and activities of catalase. The expression of genes related to antioxidant responses (p38a, p38b, ERK2, ERK3, Nrf2, HO-1, cat1, sod1, gax, JINK1, and gstr1) was further performed to study the mechanisms of MCLR combined with PSNPs aggravated oxidative stress of zebrafish. The results showed that PSNPs could improve the bioavailability of MCLR in the zebrafish liver by acting as a carrier and accelerate MCLR-induced oxidative stress by regulating the levels of corresponding enzymes and genes.

Fish tissue accumulation and proteomic response to microcystins is species-dependent

Cyanotoxins including microcystins are increasing globally, escalating health risks to humans and wildlife. Freshwater fish can accumulate and retain microcystins in tissues; however, uptake and depuration studies thus far have not exposed fish to microcystins in its intracellular state (i.e., cell-bound or conserved within cyanobacteria), which is a primary route of exposure in the field, nor have they investigated sublethal molecular-level effects in tissues, limiting our knowledge of proteins responsible for microcystin toxicity pathways in pre-to-postsenescent stages of a harmful algal bloom. We address these gaps with a 2-wk study (1 wk of 'uptake' exposure to intracellular microcystins (0-40 μg L^-1) produced by Microcystis aeruginosa followed by 1 wk of 'depuration' in clean water) using Rainbow Trout (Oncorhynchus mykiss) and Lake Trout (Salvelinus namaycush). Liver and muscle samples were collected throughout uptake and depuration phases for targeted microcystin quantification and nontargeted proteomics. For both species, microcystins accumulated at a higher concentration in the liver than muscle, and activated cellular responses related to oxidative stress, apoptosis, DNA repair, and carcinogenicity. However, intraspecific proteomic effects between Rainbow Trout and Lake Trout differed, and interspecific accumulation and retention of microcystins in tissues within each species also differed. We demonstrate that fish do not respond the same to cyanobacterial toxicity within and among species despite being reared in the same environment and diet.

Synthesis of ecotoxicological studies on cyanotoxins in freshwater habitats - Evaluating the basis for developing thresholds protective of aquatic life in the United States

In recent decades, cyanobacteria harmful algal blooms (cyanoHABs) have increased in magnitude, frequency, and duration in freshwater ecosystems. CyanoHABs can impact water quality by the production of potent toxins known as cyanotoxins. Environmental exposure to cyanotoxins has been associated with severe illnesses in humans, domestic animals, and wildlife. However, the effects of sustained exposure to cyanotoxins on aquatic life are poorly understood. In this study, over 150 peer-reviewed articles were critically evaluated to better understand the ecotoxicity of 5 cyanotoxin classes (microcystins, cylindrospermopsin, anatoxin-a, saxitoxins, nodularin) on fish, amphibians, aquatic invertebrates, and birds exclusively feeding in freshwater habitats. The systemic review demonstrated that microcystins, and more specifically microcystin-LR, were the most studied cyanotoxins. Ecotoxicological investigations were typically conducted using a fish or aquatic invertebrate model, with mortality, bioaccumulation, and biochemical responses as the most frequently measured endpoints. After excluding the studies that did not meet our acceptability criteria, remaining studies were examined to identify the no-observed and lowest observed effect concentrations (NOEC and LOEC) for microcystins; the limited amount of data for other cyanotoxins did not allow for analysis. The published ecotoxicity data suggests that the U.S. EPA recreational water quality criteria for microcystin (8 μg/L) may be protective of acute toxicity in aquatic organisms but does not appear to protect against chronic toxicity. Individual U.S. states have developed more stringent recreational health-based thresholds, such as 0.8 μg/L in California. Comparisons of this threshold to the chronic NOEC and LOEC data indicate that more restrictive microcystins thresholds may be required to be protective of aquatic life. Additional research is needed to evaluate the sublethal effects of a wider array of microcystin congeners and other cyanotoxins on organisms relevant to U.S. watersheds to better support nationwide thresholds protective of aquatic life.

Paternal exposure to microcystin-LR triggers developmental neurotoxicity in zebrafish offspring via an epigenetic mechanism involving MAPK pathway

Microcystin-LR (MCLR) induced impairment to male reproductive system and revealed the effects of transgenerational toxicity on offspring. But very little is known about the inheritance of these effects to offspring and the mechanisms involved. Here, we used methylated DNA immunoprecipitation sequencing (MeDIP-Seq) and microarray to characterize whole-genome DNA methylation and mRNA expression patterns in zebrafish testis after 6-week exposure to 5 and 20 μg/L MCLR. Accompanied with these analyses it revealed that MAPK pathway and ER pathway significantly enriched in zebrafish testes. Apoptosis and testicular damage were also observed in testis. Next, we test the transmission of effects to compare control-father and MCLR exposure-father progenies. DNA methylation analyses (via reduced representation bisulfite sequencing) reveal that the enrichment of differentially methylated regions on neurodevelopment after paternal MCLR exposure. Meanwhile, several genes associated with neurodevelopment were markedly downregulated in zebrafish larvae, and swimming speed was also reduced in the larvae. Interestingly, paternal MCLR exposure also triggered activation the phosphorylation of mitogen-activated protein kinase (MAPK) pathway which is also associated with neurodevelopmental disorders. These results demonstrated the significant effect that paternal MCLR exposure may have on gene-specific DNA methylation patterns in testis. Inherited epigenetic alterations through the germline may be the mechanism leading to developmental neurotoxicity in the offspring.

Immunotoxic Effects Induced by Microcystins and Cylindrospermopsin: A Review

Cyanotoxin occurrence is gaining importance due to anthropogenic activities, climate change and eutrophication. Among them, Microcystins (MCs) and Cylindrospermopsin (CYN) are the most frequently studied due to their ubiquity and toxicity. Although MCs are primary classified as hepatotoxins and CYN as a cytotoxin, they have been shown to induce deleterious effects in a wide range of organs. However, their effects on the immune system are as yet scarcely investigated. Thus, to know the impact of cyanotoxins on the immune system, due to its importance in organisms’ homeostasis, is considered of interest. A review of the scientific literature dealing with the immunotoxicity of MCs and CYN has been performed, and both in vitro and in vivo studies have been considered. Results have confirmed the scarcity of reports on the topic, particularly for CYN. Decreased cell viability, apoptosis or altered functions of immune cells, and changed levels and mRNA expression of cytokines are among the most common effects reported. Underlying mechanisms, however, are still not yet fully elucidated. Further research is needed in order to have a full picture of cyanotoxin immunotoxicity.

Early-life exposure to tris (1,3-dichloro-2-propyl) phosphate caused multigenerational neurodevelopmental toxicity in zebrafish via altering maternal thyroid hormones transfer and epigenetic modifications

Tris (1,3-dichloro-2-propyl) phosphate (TDCIPP), an alternative to brominated flame retardants, might pose an exposure risk to humans and wild animals during fetal development. Our recent study suggested that short-term TDCIPP exposure during early development caused sex-dependent behavioral alteration in adults. In the present study, multigenerational neurodevelopmental toxicity upon early-life exposure of parental zebrafish was evaluated, and the possible underlying mechanisms were further explored. Specifically, after embryonic exposure (0-10 days post-fertilization, dpf) to TDCIPP (0, 0.01, 0.10, and 1.00 μM), zebrafish larvae were cultured in clean water until the sexually matured to produce progeny (F1). The results confirmed neurodevelopmental toxicity in F1 larvae characterized by changes of developmental endpoints, reduced thigmotaxis, as well as altered transcription of genes including myelin basic protein a (mbpa), growth associated protein (gap43) and synapsin IIa (syn2a). Sex-specific changes in thyroid hormones (THs) indicated the relationship of abnormal THs levels with previously reported neurotoxicity in adult females after early-life exposure to TDCIPP. Similar changing profiles of TH levels (increased T3 and decreased T4) in adult females and F1 eggs, but not in F1 larvae, suggested that the TH disruptions were primarily inherited from the maternal fish. Further results demonstrated hypermethylation of global DNA and key genes related to TH transport including transthyretin (ttr) and solute carrier family 16 member 2 (slc16a2), which might affect the transport of THs to target tissues, thus at least partially contributing to the neurodevelopmental toxicity in F1 larvae. Overall, our results confirmed that early-life TDCIPP exposure of parental fish could affect the early neurodevelopment of F1 offspring. The underlying mechanism could involve altered TH levels inherited from maternal zebrafish and epigenetic modifications in F1 larvae.

Cyanotoxins within and Outside of Microcystis aeruginosa Cause Adverse Effects in Rainbow Trout (Oncorhynchus mykiss)

The global expansion of toxic Microcystis blooms, and production of cyanotoxins including microcystins, are an increasing risk to freshwater fish. Differentiating intracellular and extracellular microcystin toxicity pathways (i.e., within and outside of cyanobacterial cells) in fish is necessary to assess the severity of risks to populations that encounter harmful algal blooms in pre-to-postsenescent stages. To address this, adult and juvenile Rainbow Trout (Oncorhynchus mykiss) were, respectively, exposed for 96 h to intracellular and extracellular microcystins (0, 20, and 100 μg L^-1) produced by Microcystis aeruginosa. Fish were dissected at 24 h intervals for histopathology, targeted microcystin quantification, and nontargeted proteomics. Rainbow Trout accumulated intracellular and extracellular microcystins in all tissues within 24 h, with greater accumulation in the extracellular state. Proteomics revealed intracellular and extracellular microcystins caused sublethal toxicity by significantly dysregulating proteins linked to the cytoskeletal structure, stress responses, and DNA repair in all tissues. Pyruvate metabolism in livers, anion binding in kidneys, and myopathy in muscles were also significantly impacted. Histopathology corroborated these findings with evidence of necrosis, apoptosis, and hemorrhage at similar severity in both microcystin treatments. We demonstrate that sublethal concentrations of intracellular and extracellular microcystins cause adverse effects in Rainbow Trout after short-term exposure.

Effects of acute exposure to microcystins on hypothalamic-pituitary-adrenal (HPA), -gonad (HPG) and -thyroid (HPT) axes of female rats

Microcystins (MCs) are common, well-known cyanobacterial toxins that can affect health of humans. Recently, it has been reported that MCs affect endocrine functions. In the present study, for the first time, histopathology, concentrations of hormones and transcription of genes along the hypothalamic-pituitary-adrenal (HPA), hypothalamic-pituitary-gonad (HPG) and hypothalamic-pituitary-thyroid (HPT) axes were examined in rats exposed to microcystin-LR (MC-LR). Female, Sprague-Dawley (SD) rats were exposed acutely to MC-LR by a single intraperitoneal (i.p.) injection at doses of 0.5, 0.75, or 1 median lethal dose (LD₅₀), i.e. 36.5, 54.75, or 73 μg MC-LR/kg body mass (bm) then euthanized 24 hours after exposure. Acute exposure to MC-LR significantly increased relative mass of adrenal in a dose-dependent manner, but relative mass of hypothalamus, pituitary, ovary and thyroid were not significantly different from respective mass in controls. However, damage to all these tissues was observed by histology. Along the HPA axis, lesser concentrations of corticotropin-releasing hormone (CRH), adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were observed in blood serum of exposed individuals, relative to controls. For the HPG axis, concentrations of gonadotropin-releasing hormone (GnRH) and estradiol (E2) were significantly less in rats treated with MC-LR, but greater concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone (T) were observed. Along the HPT axis, MC-LR caused greater concentrations of thyroid-stimulating hormone (TSH), but lesser concentrations of thyrotropin-releasing hormone (TRH), free tetra-iodothyronine (fT4) and tri-iodothyronine (fT3). Significant positive/negative correlations of concentrations of hormones were observed among the HPA, HPG and HPT axes. In addition, profiles of transcription of genes for synthesis of hormones along the endocrine axes and nuclear hormone receptors in adrenal, ovary and thyroid were significantly altered. Therefore, these results suggested that MC-LR affected HPA, HPG and HPT axes and exerted endocrine-disrupting effects. Effects of MC-LR on crosstalk among these three axes need further studies.

Zebrafish Models for the Safety and Therapeutic Testing of Nanoparticles with a Focus on Macrophages

New nanoparticles and biomaterials are increasingly being used in biomedical research for drug delivery, diagnostic applications, or vaccines, and they are also present in numerous commercial products, in the environment and workplaces. Thus, the evaluation of the safety and possible therapeutic application of these nanomaterials has become of foremost importance for the proper progress of nanotechnology. Due to economical and ethical issues, in vitro and in vivo methods are encouraged for the testing of new compounds and/or nanoparticles, however in vivo models are still needed. In this scenario, zebrafish (Danio rerio) has demonstrated potential for toxicological and pharmacological screenings. Zebrafish presents an innate immune system, from early developmental stages, with conserved macrophage phenotypes and functions with respect to humans. This fact, combined with the transparency of zebrafish, the availability of models with fluorescently labelled macrophages, as well as a broad variety of disease models offers great possibilities for the testing of new nanoparticles. Thus, with a particular focus on macrophage-nanoparticle interaction in vivo, here, we review the studies using zebrafish for toxicological and biodistribution testing of nanoparticles, and also the possibilities for their preclinical evaluation in various diseases, including cancer and autoimmune, neuroinflammatory, and infectious diseases.

Mechanisms of parental co-exposure to polystyrene nanoplastics and microcystin-LR aggravated hatching inhibition of zebrafish offspring

The combined toxicity effects of microcystins-LR (MCLR) and polystyrene nanoplastics (PSNPs) on the hatching of F1 zebrafish (Danio rerio) embryos were investigated in this study due to the increasing concerns of both plastic pollution and eutrophication in aquatic environments. Three-month-old zebrafish were used to explore the molecular mechanisms underlying the combined effect of MCLR (0, 0.9, 4.5, and 22.5 μg/L) on egg hatching in the existence of PSNPs (100 μg/L). The results demonstrated the existence of PSNPs further increased the accumulation of MCLR in F1 embryos. The hatching rates of F1 embryos were inhibited after exposure to 22.5 μg/L MCLR, and the presence of PSNPs aggravated the hatching inhibition induced by MCLR. The decrease of hatching enzyme activity and the abnormality of spontaneous movement were observed. We examined the altered expression levels of the genes associated with the hatching enzyme (tox16, foxp1, ctslb, xpb1, klf4, cap1, bmp4, cd63, He1.2, zhe1, and prl), cholinergic system (ache and chrnα7), and muscle development (Wnt, MyoD, Myf5, Myogenin, and MRF4). The results suggested the existence of PSNPs exacerbated the hatching inhibition of F1 embryos through decreasing the activity of enzyme, interfering with the cholinergic system, and affecting the muscle development.

The joint effect of parental exposure to microcystin-LR and polystyrene nanoplastics on the growth of zebrafish offspring

The coexistence of nanoplastics (NPs) and various pollutants in the environment has become a problem that cannot be ignored. In order to identify the microcystin-LR (MCLR) bioaccumulation and the potential impacts on the early growth of F1 zebrafish (Danio rerio) offspring in the presence of polystyrene nanoplastics (PSNPs), PSNPs and MCLR were used to expose adult zebrafish for 21days. The exposure groups divided into MCLR (0, 0.9, 4.5 and 22.5μgL^-1) alone groups and PSNP (100μgL^-1) and MCLR co-exposure groups. F1 embryos were collected and developed to 120 h post-fertilization (hpf) in clear water. Compared with the exposure to MCLR only, the combined exposure increased the parental transfer of MCLR to the offspring and subsequently exacerbated the growth inhibition of F1 larvae. Further research clarified that combined exposure of PSNPs and MCLR could reduce the levels of thyroxine (T4) and 3, 5, 3'-triiodothyronine (T3) by altering the expression of hypothalamus-pituitary-thyroid (HPT) axis-related genes, eventually leading to growth inhibition of F1 larvae. Our results also exhibited combined exposure of PSNPs and MCLR could change the transcription of key genes of the GH/IGF axis compared with MCLR single exposure, suggesting the GH/IGF axis was a potential target for the growth inhibition of F1 larvae in PSNPs and MCLR co-exposure groups. The present study highlights the potential risks of coexistence of MCLR and PSNPs on development of fish offspring, and the environmental risks to aquatic ecosystems.

Effects of environmentally relevant concentrations of tris (2-chloroethyl) phosphate (TCEP) on early life stages of zebrafish (Danio rerio)

Tris (2-chloroethyl) phosphate (TCEP) has been received great concerns because of its increasing presence in various environmental compartments and toxicity. In the present study, zebrafish embryos were exposed to environmentally relevant concentrations of TCEP (0.2, 2, 20, 200 μg/L) from 3 to 120 h post-fertilization (hpf). The results showed that TCEP exposure (20, 200 μg/L) led to developmental toxicity including decreased body length and delay of hatching. Treatment with TCEP significantly decreased whole-body thyroxine (T4) levels and mRNA level of thyroglobulin (tg), and enhanced transcriptions of genes sodium/iodide symporter (nis), thyroid hormone receptor α (trα) and ugt1ab involved in thyroid synthesis and metabolism, respectively. Additionally, TCEP altered the transcription of α1-tubulin, gap43 and mbp related to nervous system development, even at relatively low concentrations. Overall, our results revealed that TCEP exposure can lead to developmental toxicity, thyroid endocrine disruption and neurotoxicity on early developmental stages of zebrafish.

Methodological Issues in Population-Based Studies of Multigenerational Associations

Laboratory-based animal research has revealed a number of exposures with multigenerational effects-ones that affect the children and grandchildren of those directly exposed. An important task for epidemiology is to investigate these relationships in human populations. Without the relative control achieved in laboratory settings, however, population-based studies of multigenerational associations have had to use a broader range of study designs. Current strategies to obtain multigenerational data include exploiting birth registries and existing cohort studies, ascertaining exposures within them, and measuring outcomes across multiple generations. In this paper, we describe the methodological challenges inherent to multigenerational studies in human populations. After outlining standard taxonomy to facilitate discussion of study designs and target exposure associations, we highlight the methodological issues, focusing on the interplay between study design, analysis strategy, and the fact that outcomes may be related to family size. In a simulation study, we show that different multigenerational designs lead to estimates of different exposure associations with distinct scientific interpretations. Nevertheless, target associations can be recovered by incorporating (possibly) auxiliary information, and we provide insights into choosing an appropriate target association. Finally, we identify areas requiring further methodological development.

Pollution Level and Ecological Risk Rssessment of Heavy Metals in Riverside Sediments of the Grand Canal (Beijing, Tianjin and Hebei section)

Pollution level and ecological risk assessment of heavy metals in riverside sediments of the Grand Canal (Beijing, Tianjin and Heibei sections) were studied. The concentrations of As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, V and Zn in shallow sediments were measured by ICP-MS. It was found that the concentrations of several heavy metals in shallow sediments were higher than the background values of soils in Beijing area. The results showed that the historical heavy metal discharge in the studied area still had some adverse effects on river sediments. The data of potential ecological risk assessment indicated that about 34.6% of the sampling sites reached medium ecological risk level. The main hazardous metal was Cd, and thus Cd should be managed in priority.

A review of the influences of microplastics on toxicity and transgenerational effects of pharmaceutical and personal care products in aquatic environment

PPCPs (pharmaceutical and personal care products) and microplastics (MPs) are two types of emerging pollutants that are ubiquitous and widely concerned in the environment. Both of them can accumulate in fish or aquatic invertebrates and transfer to offspring, thereby producing toxic effects on both parents and offspring, in which the characteristics of MPs also enable them to adsorb PPCPs thus producing carrier effects. In this study, we have conducted a comprehensive review of MPs and PPCPs and found that MPs can act as a carrier of PPCPs to influence the bioaccumulation of PPCPs. MPs and PPCPs have toxicity and transgenerational effects on both fish and aquatic invertebrates in many aspects, and MPs can also affect the toxicity and transgenerational effects of PPCPs due to their carrier effects. This paper revealed that MPs may have an important impact on the bioavailability of PPCPs and the interaction between MPs and PPCPs is a hot topic in future research. This study also puts forward the shortcomings of the current research and related suggestions, and relevant research should be carried out as soon as possible to provide the basis for the prevention and treatment of fresh water.

Parental exposure to cadmium chloride causes developmental toxicity and thyroid endocrine disruption in zebrafish offspring

Cadmium is a common heavy metal pollutant. Previous studies have found that long-term cadmium exposure can cause damage to multiple organs/systems in humans and experimental animals; however, there are few studies that elucidate its effects on offspring development, discuss whether it can be transmitted to offspring from the parent, and debate whether it affects the functional development of the thyroid hormone system in offsprings. In this study, sexually mature zebrafish were exposed to different concentrations of cadmium chloride (0.01 μmol/L, 0.1 μmol/L, and 1 μmol/L) to study reproductive toxicity. It was found that parental zebrafish exposed to 1 μmol/L of cadmium chloride produced offsprings with different degrees of malformation. At 5 days post-fertilization (dpf), the levels of 3,5,3'-triiododenosine (T3) and thyroxine (T4) in the zebrafish were decreased. At 10 dpf, the T4 and T3 levels in the zebrafish of the offspring were significantly reduced. At the same time, the expression of thyroid receptor (trα and trβ) genes in five dpf larvae was significantly up-regulated in the 1 μmol/L treatment group relative to the control group. The mRNAs of thyroid hormone synthesis and metabolism-related genes (tshβ, dio1, dio2, ugt1ab, and ttr) were significantly up-regulated in the 0.1 μmol/L and 1 μmol/L treatment groups. This study demonstrates that parental cadmium chloride exposure produces reproductive toxicity in zebrafish and that the effects can be transferred from the parent to the offspring, resulting in developmental toxicity in the thyroid endocrine system.

Transcriptome analysis of testis reveals the effects of developmental exposure to bisphenol a or 17α-ethinylestradiol in medaka (Oryzias latipes)

Endocrine disrupting chemicals (EDCs) can induce abnormalities in organisms via alteration of molecular pathways and subsequent disruption of endocrine functions. Bisphenol A (BPA) and 17α-ethinylestradiol (EE2) are ubiquitous EDCs in the environment. Many aquatic organisms, including fish, are often exposed to varying concentrations of BPA and EE2 throughout their lifespan. Both BPA and EE2 can activate estrogenic signaling pathways and cause adverse effects on reproduction via alteration of pathways associated with steroidogenesis. However, transcriptional pathways that are affected by chronic exposure to these two ubiquitous environmental estrogens during embryonic, larval, and juvenile stages are not clearly understood. In the present study, we examined transcriptional alterations in the testis of medaka fish (Oryzias latipes) chronically exposed to a low concentration of BPA or EE2. Medaka were exposed to BPA (10 μg/L) or EE2 (0.01 μg/L) from 8 h post-fertilization (as embryos) to adulthood 50 days post fertilization (dpf), and transcriptional alterations in the testis were examined by RNA sequencing (RNA-seq). Transcriptomic profiling revealed 651 differentially expressed genes (DEGs) between BPA-exposed and control testes, while 1475 DEGs were found between EE2-exposed and control testes. Gene ontology (GO) analysis showed a significant enrichment of "intracellular receptor signaling pathway", "response to steroid hormone" and "hormone-mediated signaling pathway" in the BPA-induced DEGs, and of "cilium organization", "microtubule-based process" and "organelle assembly" in the EE2-induced DEGs. Pathway analysis showed significant enrichment of "integrin signaling pathway" in both treatment groups, and of "cadherin signaling pathway", "Alzheimer disease-presenilin pathway" in EE2-induced DEGs. Single nucleotide polymorphism (SNP) and insertion-deletion (Indel) analysis found no significant differences in mutation rates with either BPA or EE2 treatments. Taken together, global gene expression differences in testes of medaka during early stages of gametogenesis were responsive to chronic BPA and EE2 exposure.

Intergenerational toxicity of nonylphenol ethoxylate (NP-9) in Caenorhabditis elegans

The ethoxylated isomers of nonylphenol (NPEs, NP-9) are one of the main active ingredients present in nonionic surfactants employed as herbicides, cosmetics, paints, plastics, disinfectants and detergents. These chemicals and their metabolites are commonly found in environmental matrices. The aim of this work was to evaluate the intergenerational toxicity of NP-9 in Caenorhabditis elegans. The lethality, length, width, locomotion and lifespan were investigated in the larval stage L4 of the wild strain N2. Transgenic green fluorescent protein (GFP) strains were employed to estimate changes in relative gene expression. RT-qPCR was utilized to measure mRNA expression for neurotoxicity-related genes (unc-30, unc-25, dop-3, dat-1, mgl-1, and eat-4). Data were obtained from parent worms (P0) and the first generation (F1). Lethality of the nematode was concentration-dependent, with 48 h-LC₅₀ values of 3215 and 1983 μM in P0 and F1, respectively. Non-lethal concentrations of NP-9 reduced locomotion. Lifespan was also decreased by the xenobiotic, but the negative effect was greater in P0 than in F1. Non-monotonic concentration-response curves were observed for body length and width in both generations. The gene expression profile in P0 was different from that registered in F1, although the expression of sod-4, hsp-70, gpx-6 and mtl-2 increased with the surfactant concentration in both generations. None of the tested genes followed a classical concentration-neurotoxicity relationship. In P0, dopamine presented an inverted-U curve, while GABA and glutamate displayed a bimodal type. However, in F1, inverted U-shaped curves were revealed for these genes. In summary, NP-9 induced intergenerational responses in C. elegans through mechanisms involving ROS, and alterations of the GABA, glutamate, and dopamine pathways.

Testing for thyroid hormone disruptors, a review of non-mammalian in vivo models

Thyroid hormones (THs) play critical roles in profound changes in many vertebrates, notably in mammalian neurodevelopment, although the precise molecular mechanisms of these fundamental biological processes are still being unravelled. Environmental and health concerns prompted the development of chemical safety testing and, in the context of endocrine disruption, identification of thyroid hormone axis disrupting chemicals (THADCs) remains particularly challenging. As various molecules are known to interfere with different levels of TH signalling, screening tests for THADCs may not rely solely on in vitro ligand/receptor binding to TH receptors. Therefore, alternatives to mammalian in vivo assays featuring TH-related endpoints that are more sensitive than circulatory THs and more rapid than thyroid histopathology are needed to fulfil the ambition of higher throughput screening of the myriad of environmental chemicals. After a detailed introduction of the context, we have listed current assays and parameters to assess thyroid disruption following a literature search of recent publications referring to non-mammalian models. Potential THADCs were mostly investigated in zebrafish and the frog Xenopus laevis, an amphibian model extensively used to study TH signalling.

Persistent Exposure to Environmental Levels of Microcystin-LR Disturbs Cortisol Production via Hypothalamic-Pituitary-Interrenal (HPI) Axis and Subsequently Liver Glucose Metabolism in Adult Male Zebrafish (Danio rerio)

There is growing evidence that microcystin-LR (MC-LR) is a new endocrine disruptor, whereas the impacts of persistent exposure to MC-LR on the hypothalamic-pituitary-interrenal (HPI) axis and health hazards thereafter have not been investigated. In this work, adult male zebrafish (Danio rerio) were immersed into MC-LR solutions at concentrations of 0, 1, 5 and 25 μg/L for 30 d, respectively. The results showed that persistent MC-LR exposure caused an extensive upregulation of HPI-axis genes but an inhibition of brain nuclear receptors (gr and mr), which finally increased serum cortisol levels. Furthermore, the decreased expression of hepatic gr might partly be responsible for the strong inhibition on the expression of downstream genes involved in glucose metabolic enzymes, including gluconeogenesis-related genes (pepck, fbp1a, g6pca), glycogenolysis-related gene (pyg), glycolysis-related genes (gk, pfk1b, pk) and glycogenesis-related gene (gys2). These findings are in accordance with the decline in serum glucose, indicating that long-term MC-LR exposure caused a lower production of glucose relative to glucose lysis. Our above results firstly establish the link between persistent MC-LR exposure and impaired glucose metabolism, suggesting that long-term MC-LR-mediated stress might threaten fish’s health.

Investigation of In Vitro Endocrine Activities of Microcystis and Planktothrix Cyanobacterial Strains

Cyanobacteria are cosmopolitan photosynthetic prokaryotes that can form dense accumulations in aquatic environments. They are able to produce many bioactive metabolites, some of which are potentially endocrine disrupting compounds, i.e., compounds that interfere with the hormonal systems of animals and humans. Endocrine disruptors represent potential risks to both environmental and human health, making them a global challenge. The aim of this study was to investigate the potential endocrine disrupting activities with emphasis on estrogenic effects of extracts from cultures of Microcystis or Planktothrix species. We also assessed the possible role of microcystins, some of the most studied cyanobacterial toxins, and thus included both microcystin-producing and non-producing strains. Extracts from 26 cyanobacterial cultures were initially screened in estrogen-, androgen-, and glucocorticoid-responsive reporter-gene assays (RGAs) in order to identify endocrine disruption at the level of nuclear receptor transcriptional activity. Extracts from selected strains were tested repeatedly in the estrogen-responsive RGAs, but the observed estrogen agonist and antagonist activity was minor and similar to that of the cyanobacteria growth medium control. We thus focused on another, non-receptor mediated mechanism of action, and studied the 17β-estradiol (natural estrogen hormone) biotransformation in human liver microsomes in the presence or absence of microcystin-LR (MC-LR), or an extract from the MC-LR producing M. aeruginosa PCC7806 strain. Our results show a modulating effect on the estradiol biotransformation. Thus, while 2-hydroxylation was significantly decreased following co-incubation of 17β-estradiol with MC-LR or M. aeruginosa PCC7806 extract, the relative concentration of estrone was increased.

Acute microcystin-LR exposure interfere thyroid hormones homeostasis in adult zebrafish (Danio rerio)

Microcystin-LR (MC-LR) in the aquatic environment may disturb thyroid hormone (TH) homeostasis. It is not clear how MC-LR affects downstream biological processes after TH disturbance. After exposure to 50, 100, 200 and 400 μg/L MC-LR for 24, 48, 72, or 96 h, alterations of the TH metabolism of adult zebrafish at thyroxine (T4), triiodothyronine (T3) levels, and iodothyronine deiodinase (Dio) activity, were observed. After exposure to MC-LR at 400 μg/L, T3 and T4 levels decreased significantly in females (p < 0.05) and returned to normal levels at 96 h. In males, T4 levels were not significantly different between groups. The expression of corticotropin releasing hormone, thyroid-stimulating hormone beta subunit, transthyretin, sodium/iodide cotransporter, thrombopoietin, thyroid hormone receptor alpha and beta changed, but not in a dose-dependent manner. Acute MC-LR exposure induced a negative feedback regulation of the hypothalamic-pituitary-thyroid axis in adult zebrafish, and females were more sensitive than males. In conclusion, acute MC-LR exposure disrupted the TH metabolism by altering Dio activity and gene expression of the HPT axis; these changes may affect the complement system through regulation of c9 mRNA synthesis.

Dysregulation of endocrine disruption, apoptosis and the transgenerational toxicity induced by spirotetramat

Spirotetramat (SPT) is a new tetronic acid derivative insecticide used to control scales and aphids; the potential for endocrine disruptor effects in fish could not be finalized with the available data. In this study, zebrafish were selected to assess the endocrine-disrupting effects. Significant decrease of plasma estradiol (E2), testosterone (T) and 11-ketotestosterone (11-KT) were observed in both male and female following the spirotetramat exposure; the vitellogenin (VTG) level in females significantly decreased. The expression of the hypothalamic-pituitary-gonad (HPG) axis genes fshr, lhr and esr1 showed significant increase in the gonads, which expression in males is higher than in females. In addition, the activities of capspase-3 and caspase-9 significantly decreased in both males and females liver, while the capspase-3 and caspase-9 were increased in male testis, the mRNA expression levels of genes expression related to the apoptosis pathway were also significantly altered after the spirotetramat exposure. Additionally, we found the parental zebrafish exposed to spirotetramat induced the development delay of its offspring. Above all, the adverse effects induced by spirotetramat suggesting that spirotetramat is a potential exogenous hazardous agent.

Parental exposure to triphenyltin inhibits growth and disrupts thyroid function in zebrafish larvae

Triphenyltin (TPT) is widely used and commonly found in a water environment, so its effects on aquatic systems are of great concern. This study aimed to reveal the effects of chronic parental exposure of TPT on thyroid disruption and growth inhibition in zebrafish. Adult zebrafish (F0 generation) were exposed to environmentally relevant concentrations (1, 10, and 100 ng/L) of TPT for 60 days, and the larvae (F1 generation) were tested without TPT treatment. Results demonstrated that parental exposure to TPT disrupts thyroid function in zebrafish offspring: serum thyroxine (T4) significantly decreased, while serum 3,5,3'-triiodothyronine (T3) increased, and several genes involved in the hypothalamic-pituitary-thyroid (HPT) axis were down-regulated. In addition, we observed developmental abnormalities in the larvae, demonstrated by a significantly altered hatching rate, malformation rate, body length, heart rate, and survival rate, as well as down-regulation of genes involved in the growth hormone/insulin-like growth factor (GH/IGF) axis. Therefore, parental exposure to TPT induces toxicity in fish offspring through perturbation of the HPT and GH/IGF axes.

Waterborne exposure to microcystin-LR alters thyroid hormone levels, iodothyronine deiodinase activities, and gene transcriptions in juvenile zebrafish (Danio rerio)

This study investigated the effects of microcystin (MC) on the regulation of thyroid hormone (TH) metabolism in juvenile zebrafish exposed to MC-LR. The results showed that acute MC-LR exposure at concentrations ranging from 50 μg/L to 400 μg/L led to significant reductions in thyroxine (T4) and triiodothyronine (T3) levels in juvenile zebrafish. The transcription levels of genes involved in TH synthesis, such as corticotropin-releasing hormone (crh), thyroid-stimulating hormone (tsh), thyroid peroxidase (tpo) and transthyretin (ttr), were significantly decreased followed by an increase after MC-LR exposure. Transcription of the TH nuclear receptors (tr-α and tr-β) was significantly reduced during the exposure period. Moreover, the activities of iodothyronine deiodinase type Ⅰ (ID1) and iodothyronine deiodinase type Ⅱ (ID2) showed initially decreased and then increased trend, while the activity of iodothyronine deiodinase type Ⅲ (ID3) significantly decreased during MC-LR exposure. In addition, the effect of MC-LR on deiodinase activities and T4 contents were important causes of the decreased T3 at the early exposure stage. These results indicated that acute MC-LR exposure significantly interfered with the transcription of genes related to TH synthesis, transport and metabolism, and affected normal function of the thyroid which leads to decrease of T4 and T3 in juvenile zebrafish. Therefore, the thyroid function is susceptible to interference by MC-LR, and it may cause adverse effects on the growth and development of juvenile zebrafish.

Parental Transfer of Microcystin-LR-Induced Innate Immune Dysfunction of Zebrafish: A Cross-Generational Study

Transgenerational effects of microcystin-LR (MC-LR) released by cyanobacterial blooms have become a hot topic. In the present study, adult zebrafish pairs were exposed to 0, 0.4, 2, and 10 μg/L MC-LR for 60 days and the embryos (F1 generation) were hatched without or with continued MC-LR exposures at the same concentrations until 5 days postfertilization (dpf). The results showed the existence of MC-LR both in F0 gonads and in F1 embryos and indicated that MC-LR could be transferred directly from the F0 adult fish to F1 offspring. The adverse effects on sex hormone levels, sexual development, and fecundity in F0 generation along with abnormal development in F1 offspring were observed. Furthermore, downregulation of antioxidant genes (cat, mn-sod, gpx1a) and upregulation of innate immune-related genes (tlr4a, myd88, tnfα, il1β) as well as increased proinflammation cytokine contents (TNF-α, IL-1β, IL-6) were noticed in F1 offspring without/with continued MC-LR exposures. In addition, significant differences between the two F1 embryo treatments demonstrated that continuous MC-LR exposure could result in a higher degree of inflammatory response compared to those without MC-LR exposure. Our findings revealed that MC-LR could exert cross-generational effects of immunotoxicity by inhibiting the antioxidant system and activating an inflammatory response.

Microcystin-LR exposure decreased the fetal weight of mice by disturbance of placental development and ROS-mediated endoplasmic reticulum stress in the placenta

The placenta is essential for sustaining the growth of the fetus. The aim of this study was to investigate the role of the placenta in MCLR-induced significant reduction in fetal weight, especially the changes in placental structure and function. Pregnant mice were intraperitoneally injected with MCLR (5 or 20 μg/kg) from gestational day (GD) 13 to GD17. The results showed MCLR reduced fetal weight and placenta weight. The histological specimens of the placentas were taken for light and electron microscopy studies. The internal space of blood vessels decreased obviously in the placental labyrinth layer of mice treated with MCLR. After the ultrastructural examination, the edema and intracytoplasmic vacuolization, dilation of the endoplasmic reticulum and corrugation of the nucleus were observed. In addition, maternal MCLR exposure caused a reduction of 11β-hydroxysteroid dehydrogenase type 2 (HSD11B2) expression in placentae, a critical regulator of fetal development. Several genes of placental growth factors, such as Vegfα and Pgf and several genes of nutrient transport pumps, such as Glut1 and Pcft were depressed in placentas of MCLR-treated mice, however nutrient transporters Fatp1 and Snat4 were promoted. Moreover, significant increases in malondialdehyde (MDA) revealed the occurrence of oxidative stress caused by MCLR, which was also verified by remarkable decrease in the glutathione levels, total antioxidant capacity (T-AOC) as well as the activity of antioxidant enzymes. Real-time PCR and western blot analysis revealed that GRP78, CHOP, XBP-1, peIF2α and pIRE1 were remarkable increased in placentas of MCLR-treated mice, indicating that endoplasmic reticulum (ER) stress pathway was activated by MCLR. Furthermore, oxidative stress and ER stress consequently triggered apoptosis which contributed to the impairment of placental development. Collectively, these results suggest maternal MCLR exposure results in reduced fetal body weight, which might be associated with ROS-mediated endoplasmic reticulum stress and impairment in placental structure and function.

Effects of low concentrations of triphenyltin on neurobehavior and the thyroid endocrine system in zebrafish

In the present study, to evaluate neurobehavioral toxicity and the thyroid-disrupting effects of environmental levels of triphenyltin (TPT), the zebrafish larvae were exposed to 1, 10 and 100 ng/l TPT. In the neurobehavioral assay, increased levels of dopamine and serotonin, decreased content of nitric oxide, inhibited activities of acetylcholinesterase and monoamine oxidase were observed in the whole body of zebrafish larvae after TPT treatment, as well as the serious abnormal non-reproductive behavior. Moreover, the whole-body the T4 levels were markedly decreased significantly, whereas T3 levels were not significantly changed under TPT stress. In addition, TPT exposure significantly changed the expression levels of genes related to thyroid system, including corticotropin-releasing hormone gene crh, thyroid-stimulating hormone gene tshβ, thyroglobulin gene tg, sodium/iodide symporter gene nis, thyroid hormone nuclear receptor trα, isoform trβ, types I deiodinase gene dio1and types II deiodinase gene dio2. The regulated responsiveness of thyroid hormone and related genes expression levels suggested that TPT could induce the thyroid disrupting effects in zebrafish larvae. Therefore, our results provide new aspects of TPT as an endocrine disrupting chemical.

Starvation stress affects the maternal development and larval fitness in zebrafish (Danio rerio)

The starvation is a common and severe stress for animal survival and development. In aquatic environment, many fish suffer starvation stress in different extent because of the natural migration or feed limitation. When subjected to starved conditions, organisms will employ various adaptive physiological, biochemical, and behavioral changes to regulate metabolism and maintain homeostasis. In the present study, adult female zebrafish were deprived of feed for 1 to 3 weeks to detect the starved effects on adults and larvae. The results showed that biological indexes, RNA/DNA ratios, and nutritional indexes significantly decreased in the female fish after starvation. The number of mature follicles reduced while the average spawning diameter of oocytes increased. For the larvae, the maternal starvation stress distinctly delayed embryonic hatching, decreased larval body length, disrupted larval swimming ability, and reduced survival rate at early-life stages. Furthermore, we found that DNA methylation might conduce to the downregulated mRNA expression of anti-Müllerian hormone and cytochrome P450 aromatase in retarded ovaries under starved conditions. Significant effects on autophagic transcription were shown in maternal ovary and larvae responded to starvation stress. Taken together, our study systematically revealed the reproductive impairments of starvation stress and would facilitate the investigation of environmental stress in teleost fish.

A new method based on diffusive gradients in thin films for in situ monitoring microcystin-LR in waters

The passive sampling method of diffusive gradients in thin-films (DGT) was developed to provide a quantitative and time-integrated measurement of microcystin-LR (MC-LR) in waters. The DGT method in this study used HLB (hydrophilic-lipophilic-balanced) material as a binding agent, and methanol as an eluent. The diffusion coefficient of MC-LR was 5.01 × 10⁻⁶ cm² s⁻¹ at 25 °C in 0.45 mm thick diffusion layer. This DGT method had a binding capacity of 4.24 μg per binding gel disk (3.14 cm²), ensuring sufficient capacity to measure MC-LR in most water matrices. The detection limit of HLB DGT was 0.48 ng L⁻¹. DGT coupled to analysis by HPLC appears to be an accurate method for MC-LR monitoring. Comparison of DGT measurements for MC-LR in water and a conventional active sampling method showed little difference. This study demonstrates that HLB-based DGT is a useful tool for in situ monitoring of MC-LR in fresh waters.

Co-exposure with titanium dioxide nanoparticles exacerbates MCLR-induced brain injury in zebrafish

Owing to the eutrophication in freshwater and industrial emissions, the detected concentrations of MCLR and nano-TiO₂ in nature water increase year by year. The purpose of this study was to evaluate the joint effect of microcystin-LR (MCLR) and titanium dioxide nanoparticles (nano-TiO₂) on the zebrafish brain and to investigate the underlying mechanisms. In this study, four-month old zebrafish were exposed to 0, 0.5, 4, and 32 μg/L MCLR and MCLR-co-nano-TiO₂ (100 μg/L) for 45 days. Obvious brain injury characterized by formation of glial scars and ventriculomegaly was observed in both MCLR groups and MCLR-co-nano-TiO₂ groups. In addition, our results showed the existence of nano-TiO₂ aggravated MCLR-induced abnormity of swimming behavior and social behavior of zebrafish. To clarify the mechanisms of nano-TiO₂ aggravated MCLR-induced brain injury, we firstly examined the reactive oxygen species (ROS) generation in the zebrafish brain. The results showed that co-exposure with nano-TiO₂ could further increase ROS content compared with MCLR only groups. We also detected a significant change of lipid peroxidation products (MDA, malondialdehyde) content, antioxidant enzyme (SOD, superoxide dismutase) activity, and non-enzymatic antioxidant (GSH, glutathione) content in MCLR-co-nano-TiO₂ groups. Transcriptional analysis indicated the expression of genes related to the antioxidant system was significantly altered in the zebrafish brain. Collectively, the observations in this study showed that the existence of nano-TiO₂ could exacerbate the damage of the zebrafish brain through the aggravation of MCLR-induced oxidative stress, ultimately leading to the abnormity of swimming behavior and social behavior.

Long-term exposure to the non-steroidal anti-inflammatory drug (NSAID) naproxen causes thyroid disruption in zebrafish at environmentally relevant concentrations

The presence of trace levels of pharmaceuticals is an emerging issue impacting the aquatic ecosystem. Naproxen (NPX) is a nonsteroidal anti-inflammatory drug (NSAID) that has been frequently detected in aquatic environments worldwide. Recently, concerns regarding endocrine disruption by NSAIDs have increased; however, their effects on the thyroid system have yet to be understood. In this study, zebrafish were utilized to evaluate the thyroid-disrupting effects of NPX. After a 60-day exposure to various concentrations of NPX (0.1, 1, 10 and 100 μg/L), the body length and weight of the zebrafish were significantly decreased. The decrease of cytochrome P450 gene expression and enzyme activity might inhibit the metabolism of NPX, which might result in the significant bioconcentration in zebrafish. Thyroid hormone (TH) analysis showed that both triiodothyronine (T3) and thyroxine (T4) levels were substantially decreased. Gene transcription expressions along the hypothalamic-pituitary-thyroid (HPT) axis were also markedly affected. Significant downregulation of dio1, dio2, nis, nkx2.1, pax8, tg, tpo, trβ and ttr levels, along with the stimulation of the tshβ gene, were also observed in exposed fish compared to controls. Western blot analysis indicated that expression of the TTR protein was significantly decreased, which coincides with the results of the gene expression analysis. Collectively, our observations show that NPX increases the risk of bioconcentration and thyroid disruption in zebrafish. Given the continued increasing consumption and emission of pharmaceuticals, thyroid disruption should be considered when assessing the aquatic risk of long-term exposure to environmentally relevant concentrations of pharmaceuticals.

Parental exposure to tebuconazole causes thyroid endocrine disruption in zebrafish and developmental toxicity in offspring

Azole fungicides are one class of the most extensively applied current-use pesticides. Tebuconazole is a common azole fungicide that has been frequently detected in aquatic ecosystems, thus raising concerns about its ecological safety. However, adverse effects of tebuconazole remain largely unknown, especially with regard to endocrine function in aquatic organisms. In the present study, sexually immature zebrafish were exposed to different concentrations of tebuconazole (0.05, 0.20 and 0.50 mg/L) for 60 days in order to test for transgenerational toxicity on the thyroid endocrine system. Thyroid hormone homeostasis, neuronal, and cardiovascular development were investigated in the F1 generation, which were reared in tebuconazole-free water. In the F0 generation, exposure to 0.20 and 0.50 mg/L tebuconazole reduced both thyroxine (T₄) and 3,5,3'-triiodothyronine (T₃) levels in females, while the T₃ levels were unchanged in males. Decreased heart rate was found in F1 larvae, as well as diminished T₄ levels in F1 eggs/larvae. We also observed significantly increased expression of ugt1ab mRNA in two generations of zebrafish. Moreover, expression of mRNA associated with neuronal development (e.g. α1-tubulin, mbp, gap43) and cardiovascular development (e.g. cacna1ab, tnncal) were significantly downregulated in F1 larvae at 5 and 10 dpf. In addition, tebuconazole was detected in F1 eggs following parental exposure, indicating maternal transfer. This study demonstrated that tebuconazole can be transferred to offspring from exposed parents, causing thyroid endocrine disruption and developmental toxicity.

Chronic exposure to microcystin-LR reduces thyroid hormone levels by activating p38/MAPK and MEK/ERK signal pathway

Microcystin-LR (MC-LR) is the most toxic and abundant microcystin that produced by cyanobacteria. Previous studies have shown MC-LR had acute toxic to thyroid, however, the mechanism is still unclear, and the effect of long-term, low-dose MC-LR on thyroid remains uncertain. In this study, we investigated the chronic, low-dose effect of MC-LR on mouse thyroid tissues and thyroid hormone metabolism. MC-LR was orally administered to mice at 0, 1, 10, 20 and 40 μg/L for 6 consecutive months for histopathological and immunoblot analysis. Nthy-ori 3-1 cells were cultured in various concentrations of MC-LR (0, 0.5, 5, 50, 500 nmol/L) for indicated time, meanwhile the cell viability and proteins change were tested. From our study, the chronic, low-dose MC-LR exposure can disturb thyroid hormone synthesis and metabolism through activating the p38/MAPK and MEK/ERK signaling pathways, then up-regulating the expression of type 3 deiodinase. These data support the potential toxic effects of MC-LR on thyroid tissue and thyroid hormone metabolism.

Parental exposure to tris(1,3-dichloro-2-propyl) phosphate results in thyroid endocrine disruption and inhibition of growth in zebrafish offspring

Tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) is a re-emerging environmental contaminant used as a suitable substitute for brominated flame retardants. The objective of this study was to evaluate the effects of TDCIPP on thyroid disruption and growth inhibition in zebrafish (Danio rerio) offspring after chronic parental exposure, and to examine the possible molecular mechanisms involved. When adult zebrafish (4 months old) were exposed to 5.66, 25.55, or 92.8 μg TDCIPP/L for 90 days, bioconcentration of TDCIPP and its metabolic product [bis(1,3-dichloro-2-propyl) phosphate, BDCIPP] was observed in 7-day postfertilization (dpf) F1 larvae, which suggests the transfer of this compound from adult fish to their offspring. Our results demonstrated that parental exposure to TDCIPP induced thyroid disruption in the offspring, demonstrated by significantly decreased thyroxine (T4) and increased 3,5,3'-triiodothyronine (T3) levels, and disruption of the transcription of several genes and expression of proteins involved in the hypothalamic-pituitary-thyroid (HPT) axis in F1 larvae. Parental exposure to TDCIPP resulted in developmental abnormalities in offspring; the smaller body length that was recorded might be partly the result of the perturbation of the HPT axis. In addition, the results revealed that growth inhibition also resulted from the downregulation of the transcription of genes and expression of proteins involved in the growth hormone/insulin-like growth factor (GH/IGF) axis. Our study provides a new set of evidence showing that parental exposure to TDCIPP can induce thyroid disruption and inhibition of growth in offspring, and that perturbation of the HPT axis and GH/IGF axis contribute to these adverse effects.

Maternal exposure to fipronil results in sulfone metabolite enrichment and transgenerational toxicity in zebrafish offspring: Indication for an overlooked risk in maternal transfer?

Ecotoxicological studies show the association between pesticide pollution and transgenerational toxicity in aquatic organisms. However, a less considered risk is that many pesticides can be metabolized and transferred to offspring as new toxicants. In this study, we used zebrafish to evaluate the maternal transfer risk of fipronil (FIP), which is a great threat to aquatic organisms with toxic metabolite formation. After 28-day exposure to environmentally relevant concentrations (1.0, 5.0 and 10.0 μg/L) of FIP in adult female zebrafish (F0), the toxicants off-loading and transgenerational toxicity in offspring were studied. High burdens of FIP and its sulfone metabolite were found in both F0 and the embryos (F1), resulting in increased CYP450 activity. The residual levels of the metabolite were higher than those of the parent compound. Chiral analysis further showed a preferential accumulation of S-enantiomer of FIP in both F0 and F1. Maternal exposure to FIP increased the malformation rate and decreased the swim speed in larvae. Additionally, after exposure, the levels of thyroid hormones (THs), including triiodothyronine (T3) and thyroxine (T4), decreased in both generations, particularly in the F1. Gene transcription expression along the hypothalamic-pituitary-thyroid (HPT) axis was also significantly affected. Maternal exposure to FIP increased sulfone metabolite enrichment and cause multiple toxic effects in F1. Findings from this study highlight the key role of biologically active product formation in the maternal transfer of pollutants and associated risk assessment.

Enantioselective thyroid disruption in zebrafish embryo-larvae via exposure to environmental concentrations of the chloroacetamide herbicide acetochlor

Acetochlor (ACT) is a chiral chloroacetamide pesticide that has been heavily used around the world, resulting in its residues being frequently found in surface waters. It has been reported that ACT is an endocrine disrupting chemical (EDC) with strong thyroid hormone-disrupting activity in aquatic organisms. However, the enantioselectivity underlying thyroid disruption has yet to be understood. In this study, using a zebrafish embryo-larvae model, the enantioselective thyroid disruption of ACT was investigated at a series of environmentally relevant concentrations (1, 2, 10 and 50 μg/L). Our results showed that both racemic ACT and its enantiomers significantly increased the malformation rates of embryos at 72 h postfertilization (hpf). Decreased thyroxine (T₄) contents and increased triiodothyronine (T₃) contents were found in larvae at 120 hpf, with (+)-S-ACT exhibiting a greater effect than (-)-R-enantiomer. Similarly, (+)-S-ACT also showed a stronger effect on the mRNA expressions of thyroid hormone receptors (TRα and TRβ), deiodinase2 (Dio2) and thyroid-stimulating hormone-β (TSHβ) genes. The observed enantioselectivity in TR expressions was consistent with that of in silico binding analysis, which suggested that (+)-S-enantiomer binds more potently to the TRs than (-)-R-enantiomer. In general, ACT enantiomers showed different influences on the secretion of THs, expression of TH-related key genes and binding affinity to TRs. Considering the different toxicity of different enantiomers, our study highlights the importance of enantioselectivity in understanding of thyroid disruption effects of chiral pesticides.