Teratogenic, bioenergetic, and behavioral effects of exposure to total particulate matter on early development of zebrafish (Danio rerio) are not mimicked by nicotine

Generalized additive modeling as a tool for the analysis of the time course of tail coiling behavior in zebrafish (Danio rerio) embryos - A proof-of-concept study with nicotine, a known developmental neurotoxicant

The early detectable tail coiling behavior of zebrafish (Danio rerio) embryos is receiving increasing attention in the context of (developmental) neurotoxicity testing and may be used as a rapid screening tool for compounds with unknown or suspected neurotoxic potential. The observation of this behavior over a longer period of time already offered advantages such as the possibility of detecting effects that only occur after a few hours of development. The two major parameters, duration and frequency of coiling, allow a detailed characterization of the movements. However, this approach usually leads to complex data sets, which are often heavily simplified to allow for simpler analysis of the effects on an hourly basis. In this study, the suitability of generalized additive modeling (GAM) for the analysis of coiling behavior was tested in order to obtain an integrated impression of the trends in movement patterns. To this end, nicotine, a known potent developmental neurotoxicant, was used in a proof-of-concept study. The main advantage of GAM for biological data lies in the relaxation of assumptions, such as effect monotony, data distribution and homogeneity of variances and is, therefore, more flexible in describing different trends over time. The possibility to consider replicates and individuals as additional sources of (biological) variance is a further benefit, as highly variable data are common in behavioral studies. Here, the modeling approach demonstrates a monotone reduction of movement duration as a direct consequence of nicotine exposure. Additional pathomorphological studies revealed structural damage in secondary motoneurons and skeletal muscles as potential underlying mechanisms of changes in movement patterns. The GAM proved well-suited to illustrate and analyze complex non-linear behavioral data with high natural variability. The model also allows to reliably extract no observed effect (NOEC) and lowest observed effect concentrations (LOEC) from complex data sets, which may be of relevance in a regulatory context.

Physiological and transcriptomic changes of zebrafish (Danio rerio) in response to Isopropylate Triphenyl Phosphate (IPPP) exposure

Isopropylate Triphenyl Phosphate (IPPP), a novel organophosphorus flame retardant, has become a widespread environmental pollutant. However, the toxic effects and mechanisms of IPPP remain unclear. In this study, we evaluated the neurodevelopmental toxicity effects of IPPP on zebrafish embryonic development, neurobehavior, and physiological and transcriptomic changes. The results showed that IPPP induced adverse developments such as low survival rates and hatching rates, decreased body length and eye distance, and also led to increased heart rates and embryonic malformation rates. The developmental defects mainly included typical pericardial edema, eye deformities, and a reduction in the number of newborn neurons. Mitochondrial energy metabolism disorders and apoptosis of cardiomyocytes may be responsible for heart malformation. Behavioral results showed that IPPP caused abnormal changes in swimming speed, total swimming distance and trajectory, and showed a low-dose effect. In addition, the decreased activity of neurotransmitters such as acetylcholinesterase (AchE) and dopamine (DA), and the changes in genes related to the central nervous system (CNS) and metabolism pathway may be the causes of neurodevelopmental toxicity of IPPP. Meanwhile, IPPP induced oxidative stress and apoptosis, and changed the ATPase activity of zebrafish larvae by altering nuclear factor erythroid2-related factor 2 (Nrf2) and mitochondrial signaling pathways, respectively. Transcriptome sequencing results indicated that Cytochrome P450 and drug metabolism, Energy metabolism-related pathways, Glutathione metabolism, Retinoid acid (RA) and REDOX signaling pathways were significantly enriched, and most of the genes in these pathways were up-regulated after IPPP treatment, which may be new targets for IPPP-induced neurodevelopment. In summary, the results of this study provide an important reference for a comprehensive assessment of the toxic effects and health risks of the new pollutant IPPP.

Reviewing the use of zebrafish for the detection of neurotoxicity induced by chemical mixtures through the analysis of behaviour

The knowledge and assessment of mixtures of chemical pollutants in the aquatic environment is a complex issue that is often challenging to address. In this review, we focused on the use of zebrafish (Danio rerio), a vertebrate widely used in biomedical research, as a model for detecting the effects of chemical mixtures with a focus on behaviour. Our aim was to summarize the current status of the ecotoxicological research in this sector. Specifically, we limited our research to the period between January 2012 and September 2023, including only those works aimed at detecting neurotoxicity through behavioural endpoints, utilizing zebrafish at one or more developmental stages, from egg to adult. Additionally, we gathered the findings for every group of chemicals involved and summarised data from all the works we included. At the end of the screening process 101 papers were considered eligible for inclusion. Results show a growing interest in zebrafish at all life stages for this kind of research in the last decade. Also, a wide variety of different assays, involving different senses, was used in the works we surveyed, with exposures ranging from acute to chronic. In conclusion, the results of this study show the versatility of zebrafish as a model for the detection of mixture toxicity although, for what concerns behavioural analysis, the lack of standardisation of methods and endpoints might still be limiting.

Integrated mRNA- and miRNA-sequencing analyses unveil the underlying mechanism of tobacco pollutant-induced developmental toxicity in zebrafish embryos

Tobacco pollutants are prevalent in the environment, leading to inadvertent exposure of pregnant females. Studies of these pollutants' toxic effects on embryonic development have not fully elucidated the potential underlying mechanisms. Therefore, in this study, we aimed to investigate the developmental toxicity induced by cigarette smoke extract (CSE) at concentrations of 0.25, 1, and 2.5% using a zebrafish embryo toxicity test and integrated transcriptomic analysis of microRNA (miRNA) and messenger RNA (mRNA). The findings revealed that CSE caused developmental toxicity, including increased mortality and decreased incubation rate, in a dose-dependent manner. Moreover, CSE induced malformations and apoptosis, specifically in the head and heart of zebrafish larvae. We used mRNA and miRNA sequencing analyses to compare changes in the expression of genes and miRNAs in zebrafish larvae. The bioinformatics analysis indicates that the mechanism underlying CSE-induced developmental toxicity was associated with compromised genetic material damage repair, deregulated apoptosis, and disturbed lipid metabolism. The enrichment analysis and RT-qPCR show that the ctsba gene plays a crucial function in embryo developmental apoptosis, and the fads2 gene mainly regulates lipid metabolic toxicity. The results of this study improve the understanding of CSE-induced developmental toxicity in zebrafish embryos and contribute insights into the formulation of novel preventive strategies against tobacco pollutants during early embryonic development.

N-nitrosodimethylamine exposure to zebrafish embryos/larvae causes cardiac and spinal developmental toxicity

N-nitrosodimethylamine (NDMA), one of the new nitrogen-containing disinfection by-products, is potentially cytotoxic, genotoxic, and carcinogenic. Its potential toxicological effects have attracted a wide range of attention, but the mechanism is still not sufficiently understood. To better understand the toxicological mechanisms of NDMA, zebrafish embryos were exposed to NDMA from 3 h post-fertilization (hpf) to 120hpf. Mortality and malformation were significantly increased, and hatching rate, heart rate, and swimming behavior were decreased in the exposure groups. The result indicated that NDMA exposure causes cardiac and spinal developmental toxicity. mRNA levels of genes involved in the apoptotic pathway, including p53, bax, and bcl-2 were significantly affected by NDMA exposure. Moreover, the genes associated with spinal and cardiac development (myh6, myh7, nkx2.5, eph, bmp2b, bmp4, bmp9, run2a, and run2b) were significantly downregulated after treatment with NDMA. Wnt and TGF-β signaling pathways, crucial for the development of diverse tissues and organs in the embryo and the establishment of the larval spine, were also significantly disturbed by NDMA treatment. In summary, the disinfection by-product, NDMA, exhibits spinal and cardiac developmental toxicity in zebrafish embryos, providing helpful information for comprehensive analyses and a better understanding the mechanism of its toxicity.

Systemic treatment with cigarette smoke extract affects zebrafish visual behaviour, intraocular vasculature morphology and outer segment phagocytosis

Introduction

Cigarette smoking adversely affects multiple aspects of human health including eye disorders such as age-related macular degeneration, cataracts and dry eye disease. However, there remains a knowledge gap in how constituents of cigarette smoke affect vision and retinal biology. We used zebrafish to assess effects of short-term acute exposure to cigarette smoke extract (CSE) on visual behaviour and retinal biology.

Methods

Zebrafish larvae with a developed visual system at three days post-fertilization (dpf) were exposed to CSE for 4, 24 or 48 hours. Visual behaviour, hyaloid vasculature morphology, retinal histology, oxidative stress gene expression and outer segment phagocytosis were investigated using visual behavioural optokinetic and visual motor response assays (OKR and VMR), microscopy (light, fluorescence and transmission electron microscopy), and real-time PCR.

Results

In zebrafish larvae, 48 hours of CSE treatment resulted in significantly reduced visual behaviour. Larvae treated with 10, 15 or 20 μg/mL CSE showed an average of 13.7, 10.7 or 9.4 saccades per minute, respectively, significantly lower compared with 0.05% DMSO controls (p=0.0093, p=0.0004 and p<0.0001, respectively) that exhibited 19.7 saccades per minute. The diameter of intraocular vessels increased from 4.833 μm in 0.05% DMSO controls to 5.885 μm in the 20 μg/mL CSE-treated larvae (p=0.0333). Biometry analysis highlighted a significant axial length elongation in 20 μg/mL CSE-treated larvae (216.9 μm, p<0.0001) compared to 0.05% dimethyl sulfoxide (DMSO) controls (205.1 μm). Larvae exposed to 20 μg/mL CSE had significantly (p=0.0002) higher numbers of RPE phagosomes compared to vehicle controls (0.1425 and 0.093 phagosomes/μm RPE, respectively).

Conclusions

Zebrafish larvae with a developed visual system display apparent defects in visual behaviour and retinal biology after acute exposure to CSE, establishing a valuable in vivo model to investigate ocular disorders related to cigarette smoke.

Mitochondrial dysfunction and oxidative stress contribute to cross-generational toxicity of benzo(a)pyrene in Danio rerio

The potential for polycyclic aromatic hydrocarbons (PAHs) to have adverse effects that persist across generations is an emerging concern for human and wildlife health. This study evaluated the role of mitochondria, which are maternally inherited, in the cross-generational toxicity of benzo(a)pyrene (BaP), a model PAH and known mitochondrial toxicant. Mature female zebrafish (F0) were fed diets containing 0, 12.5, 125, or 1250 μg BaP/g at a feed rate of 1% body weight twice/day for 21 days. These females were bred with unexposed males, and the embryos (F1) were collected for subsequent analyses. Maternally-exposed embryos exhibited altered mitochondrial function and metabolic partitioning (i.e. the portion of respiration attributable to different cellular processes), as evidenced by in vivo oxygen consumption rates (OCRs). F1 embryos had lower basal and mitochondrial respiration and ATP turnover-mediated OCR, and increased proton leak and reserve capacity. Reductions in mitochondrial DNA (mtDNA) copy number, increases in mtDNA damage, and alterations in biomarkers of oxidative stress were also found in maternally-exposed embryos. Notably, the mitochondrial effects in offspring occurred largely in the absence of effects in maternal ovaries, suggesting that PAH-induced mitochondrial dysfunction may manifest in subsequent generations. Maternally-exposed larvae also displayed swimming hypoactivity. The lowest observed effect level (LOEL) for maternal BaP exposure causing mitochondrial effects in offspring was 12.5 µg BaP/g diet (nominally equivalent to 250 ng BaP/g fish). It was concluded that maternal BaP exposure can cause significant mitochondrial impairments in offspring.

Mitigation of nicotine-induced developmental effects by 24-epibrassinolide in zebrafish

Nicotine is a highly addictive substance that can cause teratogenic impacts in the embryo through redox-dependent pathways. As antioxidants, naturally occurring chemicals can protect cells from redox imbalance. The purpose of this study was to evaluate the effectiveness of 24-epibrassinolide (24-EPI), a natural brassinosteroid with well-known antioxidant properties, in protecting zebrafish embryos against nicotine's teratogenic effects. For 96 h, embryos (2 h post-fertilization - hpf) were exposed to 100 μM nicotine, co-exposed with 24-EPI (0.01, 0.1, and 1 μM), and 24-EPI alone (1 μM). Lethal and sublethal developmental characteristics were evaluated during exposure. Biochemical tests were performed at the conclusion of the exposure, and distinct behavioural paradigms were analysed 24 h later. Nicotine exposure resulted in a higher proportion of larvae with deformities, which were decreased following co-exposure to 24-EPI. Nicotine exposure also caused an increase in oxidative stress as observed by the increased activity of superoxide dismutase and catalase accompanied by an increase in the malondialdehyde levels. Besides, metabolic changes were noticed as observed by the increased lactate dehydrogenase activity that were hypothesised to be associated to nicotine-induced hypoxia which may be responsible for the increased oxidative damage. In addition, locomotor deficits were observed as well as a decrease in the acetylcholinesterase activity denoting nicotine-induced cognitive dysfunction. However, co-exposure to 24-EPI alleviated behavioural deficits and improved nicotine-induced emotional states. Overall, and although further studies are required to clarify these effects, 24-EPI showed promising ameliorative properties against the teratogenic effects induced by nicotine.

Joint effects of micro-sized polystyrene and chlorpyrifos on zebrafish based on multiple endpoints and gut microbial effects

Microplastics often co-occur with a variety of organic contaminants in aquatic environment and pose combined risks to aquatic wildlife. Here, we investigated joint effects of micro-sized polystyrene (mPS, 5 µm) and an organophosphate pesticide chlorpyrifos on zebrafish, using multiple endpoints at both fish individual and gut microbiota levels. It was revealed that mPS ingested by zebrafish accumulated in gut and liver, and caused oxidative stress, hyperactive swimming performance and histological damages in fish, and induced disorders and diversity alterations of the gut microbial community. More importantly, mPS exhibited considerable adsorption capacity against chlorpyrifos, and those adsorbing chlorpyrifos presented greater effects on fish individuals but no different effects on gut microbiota compared to single mPS exposure. Together with body residues of chlorpyrifos in zebrafish, it was proposed that the joint effects between mPS and chlorpyrifos were attributed to the chlorpyrifos released from mPS within zebrafish. The present results provided a comprehensive understanding of joint effects of mPS and contaminants co-occurring in the environment and emphasized the importance of considering the adsorbed chemicals in toxicological studies of microplastics.

Embryonic exposure to benzo[a]pyrene causes age-dependent behavioral alterations and long-term metabolic dysfunction in zebrafish

Polycyclic aromatic hydrocarbons (PAH) are products of incomplete combustion which are ubiquitous pollutants and constituents of harmful mixtures such as tobacco smoke, petroleum and creosote. Animal studies have shown that these compounds exert developmental toxicity in multiple organ systems, including the nervous system. The relative persistence of or recovery from these effects across the lifespan remain poorly characterized. These studies tested for persistence of neurobehavioral effects in AB* zebrafish exposed 5-120 h post-fertilization to a typical PAH, benzo[a]pyrene (BAP). Study 1 evaluated the neurobehavioral effects of a wide concentration range of BAP (0.02-10 μM) exposures from 5 to 120 hpf during larval (6 days) and adult (6 months) stages of development, while study 2 evaluated neurobehavioral effects of BAP (0.3-3 μM) from 5 to 120 hpf across four stages of development: larval (6 days), adolescence (2.5 months), adulthood (8 months) and late adulthood (14 months). Embryonic BAP exposure caused minimal effects on larval motility, but did cause neurobehavioral changes at later points in life. Embryonic BAP exposure led to nonmonotonic effects on adolescent activity (0.3 μM hyperactive, Study 2), which attenuated with age, as well as startle responses (0.2 μM enhanced, Study 1) at 6 months of age. Similar startle changes were also detected in Study 2 (1.0 μM), though it was observed that the phenotype shifted from reduced pretap activity to enhanced posttap activity from 8 to 14 months of age. Changes in the avoidance (0.02-10 μM, Study 1) and approach (reduced, 0.3 μM, Study 2) of aversive/social cues were also detected, with the latter attenuating from 8 to 14 months of age. Fish from study 2 were maintained into aging (18 months) and evaluated for overall and tissue-specific oxygen consumption to determine whether metabolic processes in the brain and other target organs show altered function in late life based on embryonic PAH toxicity. BAP reduced whole animal oxygen consumption, and overall reductions in total basal, mitochondrial basal, and mitochondrial maximum respiration in target organs, including the brain, liver and heart. The present data show that embryonic BAP exposure can lead to neurobehavioral impairment across the life-span, but that these long-term risks differentially emerge or attenuate as development progresses.

Association between maternal exposure to PM10 and risk of anorectal atresia/stenosis in offspring: a population-based case-control study in Liaoning Province, China

The potential association between maternal exposure to PM₁₀ ranging from 3 months prior to conception to the end of the early trimester and the risk of anorectal atresia/stenosis in offspring has not been established. Thus, we determined the association between maternal exposure to PM₁₀ and risk of anorectal atresia/stenosis in offspring in this study. We recruited 713 patients including 480 male and 233 female with anorectal atresia/stenosis and 7950 randomly selected healthy offspring from the Maternal and Child Health Certificate Registry of Liaoning Province and delivered between 1 January 2010 and 31 December 2015. Monthly PM₁₀ concentrations were retrieved from the Environment Protection Bureau of each city in Liaoning Province. We established a multivariable logistic regression model to calculate the adjusted odds ratios (ORs) and 95% confidence intervals (CIs). Maternal exposure to PM₁₀ was associated with an increased risk for anorectal atresia/stenosis in offspring during the 3 months prior to conception (per 10 μg/m³ increment: OR = 1.15, 95% CI = 1.03-1.20; per SD [27 μg/m³] increment: OR = 1.33, 95% CI = 1.09-1.63) and the first trimester (per 10 μg/m³ increment: OR = 1.08, 95% CI = 1.00-1.17; per SD [28 μg/m³] increment: OR = 1.26, 95% CI = 1.01-1.57). Evaluation of the association with a shorter exposure window (1 month) revealed a positive association between anorectal atresia/stenosis and PM₁₀ from the 3rd month prior to pregnancy to each month of the 1st trimester. Maternal exposure to PM₁₀ 3 months prior to conception and during the 1st trimester was associated with an increased risk of anorectal atresia/stenosis in the offspring. Future perspective cohort studies are needed to confirm our findings.

Zebrafish as an experimental model for the simulation of neurological and craniofacial disorders

Zebrafish have gained momentum as a leading experimental model in recent years. At present, the zebrafish vertebrate model is increasingly used due to its multifactorial similarities to humans that include genetic, organ, and cellular factors. With the emergence of novel research techniques that are very expensive, it is necessary to develop affordable and valid experimental models. This review aimed to highlight some of the most important similarities between zebrafish and humans by emphasizing the relevance of the first in simulating neurological disorders and craniofacial deformity.

Physiological and transcriptomic changes of zebrafish (Danio rerio) embryos-larvae in response to 2-MIB exposure

2-Methylisoborneol (2-MIB), a natural odorous substance, is widely distributed in water environment, but there is a paucity of information concerning its systemic toxicity. Herein, we investigated the effects of 2-MIB exposure on developmental parameters, locomotive behavior, oxidative stress, apoptosis and transcriptome of zebrafish. Zebrafish embryos exposed to different concentrations (0, 0.5, 5 and 42.8 μg/L) of 2-MIB showed no changes in mortality, hatchability, and malformation rate, but the body length of zebrafish larvae was significantly increased in a dose-dependent manner, and accompanied by the changes of growth hormone/insulin-like growth factor (GH/IGF) axis and the hypothalamic-pituitary-thyroid (HPT) axis genes. Moreover, the swimming activity of zebrafish larvae increased, which may be due to the increase of acetylcholinesterase (AChE) activity. Meanwhile, 2-MIB caused oxidative stress and apoptosis in zebrafish larvae by altering the NF-E2-related factor 2 (Nrf2) and mitochondrial signaling pathways, respectively. Transcriptome sequencing assay showed that the phototransduction signaling pathway was significantly enriched, and most of the genes in this pathway exhibited enhanced expression after exposure to 2-MIB. These findings provide an important reference for risk assessment and early warning to 2-MIB exposure.

Zebrafish Models of Craniofacial Malformations: Interactions of Environmental Factors

The zebrafish is an appealing model organism for investigating the genetic (G) and environmental (E) factors, as well as their interactions (GxE), which contribute to craniofacial malformations. Here, we review zebrafish studies on environmental factors involved in the etiology of craniofacial malformations in humans including maternal smoking, alcohol consumption, nutrition and drug use. As an example, we focus on the (cleft) palate, for which the zebrafish ethmoid plate is a good model. This review highlights the importance of investigating ExE interactions and discusses the variable effects of exposure to environmental factors on craniofacial development depending on dosage, exposure time and developmental stage. Zebrafish also promise to be a good tool to study novel craniofacial teratogens and toxin mixtures. Lastly, we discuss the handful of studies on gene–alcohol interactions using mutant sensitivity screens and reverse genetic techniques. We expect that studies addressing complex interactions (ExE and GxE) in craniofacial malformations will increase in the coming years. These are likely to uncover currently unknown mechanisms with implications for the prevention of craniofacial malformations. The zebrafish appears to be an excellent complementary model with high translational value to study these complex interactions.

Developmental exposure of zebrafish to vitamin D receptor acting drugs and environmental toxicants disrupts behavioral function

Vitamin D receptor (VDR) signaling is important for optimal neurobehavioral development. Disruption of VDR signaling by environmental toxicants during early development might contribute to the etiology of behavioral dysfunction. In the current set of studies, we examined ten compounds known to affect VDR function in vitro for neurobehavioral effects in vivo in zebrafish. Zebrafish embryos were exposed to concentrations of the compounds in their water during the first 5 days post-fertilization. On day 5, the embryos were tested in an alternating light-dark locomotor assay using a computerized video tracking system. We found that most of the compounds produced significant changes in locomotor behavior in exposed zebrafish larvae, although the direction of the effect (i.e., hypo- or hyperactivity) and the sensitivity of the effect to changes in illumination condition varied across the compounds. The nature of the behavioral effects generally corresponded to the effects these compounds have been shown to exert on VDR. These studies lay a foundation for further investigation to determine whether behavioral dysfunction persists into adulthood and if so which behavioral functions are affected. Zebrafish can be useful for screening compounds identified in high throughput in vitro assays to provide an initial test for how those compounds would affect construction and behavioral function of a complex nervous system, helping to bridge the gap between in vitro neurotoxicity assays and mammalian models for risk assessment in humans.

Microplastics Lead to Hyperactive Swimming Behaviour in Adult Zebrafish

Microplastic pollution has drawn the attention of both scientists and the public regarding their potential ecotoxicological risks. In the present study, we carried out aqueous exposure experiments to adult zebrafish with polystyrene microplastics (5 μm) at a wide range of concentrations (0.001-20 mg/L, equals to 14.5∼2.9 × 10⁵ particles/mL). Our results showed the gastrointestinal tract (GIT) was the dominant microplastic accumulation site in zebrafish, followed by the gill, whereas no microplastics were detected in the brain or muscle. Microplastic accumulation in GIT did not cause obvious damages to intestinal villi in general. However, the thickness of muscularis layer in the foregut reduced by 32% after 1 mg/L (1.45 × 10⁴ particles/mL) microplastic exposure. As there were no signs of oxidative stress or other histological changes found in the fish, we further investigated the energy-supplying influential factors. We found that the zebrafish became hyperactive after microplastic exposure, whose swimming distance had increased to 1.3-2.4 folds than that of control, and also stayed at manic and active states much longer. The fish behavioural alteration is probably attributed to the particulate matter stimulation and the up-regulation of estrogen contents. Results also showed that the excessive movements of zebrafish also led to decreased glucose and acetaldehyde metabolite contents and increased amino acid amounts, which further proved the shortage of energy-supplying substances. Therefore, the present study suggests that micro-sized microplastics can induce obvious behavioural abnormality at concentrations that some other toxicological endpoints may not warn effects.

Particulate Matter 2.5 Induced Developmental Cardiotoxicity in Chicken Embryo and Hatchling

Particulate matter poses health risk to developing organisms. To investigate particulate matters with a diameter smaller than 2.5 um (PM2.5)-induced developmental cardiotoxicity, fertile chicken eggs were exposed to PM2.5 via air cell injection at doses of 0.05, 0.2, 0.5, 2, and 5 mg/egg kg. Morphological changes in the embryonic day four (ED4) and hatchling hearts were assessed with histological techniques. Heart rates of hatchling chickens were measured with electrocardiography. The protein expression levels of nuclear factor kappa-light-chain-enhancer of activated B cells p65 (NF-kb p65), inducible nitric oxide synthase (iNOS), and matrix metallopeptidase 9 (MMP9) were assessed with immunohistochemistry or western blotting in hatchling hearts. PM2.5 exposure elevated areas of heart in ED4 embryo, increased heart rate, and thickened right ventricular wall thickness in hatchling chickens. Immunohistochemistry revealed enhanced NF-kb p65 expression in hatchling hearts. Western blotting results indicated that both iNOS and MMP9 expression were enhanced by lower doses of PM2.5 exposure (0.2 and 0.5 mg/kg) but not 2 mg/kg. In summary, developmental exposure to PM2.5 induced developmental cardiotoxicity in chicken embryo and hatchling chickens, which is associated with NF-kb p65, iNOS, and MMP9.

In utero exposure to cigarette smoke and effects across generations: A conference of animals on asthma

BACKGROUND

The prevalence of asthma and chronic obstructive pulmonary disease (COPD) has risen markedly over the last decades and is reaching epidemic proportions. However, underlying molecular mechanisms are not fully understood, hampering the urgently needed development of approaches to prevent these diseases. It is well established from epidemiological studies that prenatal exposure to cigarette smoke is one of the main risk factors for aberrant lung function development or reduced fetal growth, but also for the development of asthma and possibly COPD later in life. Of note, recent evidence suggests that the disease risk can be transferred across generations, that is, from grandparents to their grandchildren. While initial studies in mouse models on in utero smoke exposure have provided important mechanistic insights, there are still knowledge gaps that need to be filled.

OBJECTIVE

Thus, in this review, we summarize current knowledge on this topic derived from mouse models, while also introducing two other relevant animal models: the fruit fly Drosophila melanogaster and the zebrafish Danio rerio.

METHODS

This review is based on an intensive review of PubMed-listed transgenerational animal studies from 1902 to 2018 and focuses in detail on selected literature due to space limitations.

RESULTS

This review gives a comprehensive overview of mechanistic insights obtained in studies with the three species, while highlighting the remaining knowledge gaps. We will further discuss potential (dis)advantages of all three animal models.

CONCLUSION/CLINICAL RELEVANCE

Many studies have already addressed transgenerational inheritance of disease risk in mouse, zebrafish or fly models. We here propose a novel strategy for how these three model organisms can be synergistically combined to achieve a more detailed understanding of in utero cigarette smoke-induced transgenerational inheritance of disease risk.

Nanoplastics Decrease the Toxicity of a Complex PAH Mixture but Impair Mitochondrial Energy Production in Developing Zebrafish

Plastics are recognized as a worldwide threat to the environment, possibly affecting human health and wildlife. Small forms of plastics such as micro- and nanoplastics can interact with other organic contaminants, potentially acting as chemical carriers and modulating their toxicity. In this study, we investigated the toxicity of polystyrene nanoparticles (Nano-PS) and a real-world environmental PAH mixture (Elizabeth River Sediment Extract, ERSE, comprised of 36 detected PAHs) to zebrafish embryos and larvae. Embryos were exposed to Nano-PS (0.1-10 ppm) or ERSE (0.1-5% v/v, equivalent to ΣPAH 5.07-25.36 ppb) or coexposed to a combination of both. Larvae exposed to Nano-PS did not exhibit developmental defects, while larvae exposed to ERSE (2-5%) showed classic signs of PAH toxicity such as heart malformation and deformities in the jaw, fin, and tail. ERSE (5%) also impaired vascular development in the brain. When coexposed, Nano-PS decreased the developmental deformities and impaired vascular development caused by ERSE. This was strongly correlated to the lower PAH bioaccumulation detected in the coexposed animals (whole larvae, as well as the yolk sac, brain, and heart). Our data suggest that PAHs are sorbing to the surface of the Nano-PS, decreasing the concentration, uptake, and toxicity of free PAHs during the exposure. Such sorption of PAHs increases the agglomeration rate of Nano-PS during the exposure time, potentially decreasing the uptake of Nano-PS and associated PAHs. Despite that, similar induction of EROD activity was detected in animals exposed to ERSE in the presence or not of Nano-PS, suggesting that enough PAHs were accumulated in the organisms to induce cellular defense mechanisms. Nano-PS exposure (single or combined with ERSE) decreased the mitochondrial coupling efficiency and increased NADH production, suggesting an impairment on ATP production accompanied by a compensatory mechanism. Our data indicate that nanoplastics can sorb contaminants and potentially decrease their uptake due to particle agglomeration. Nanoplastics also target and disrupt mitochondrial energy production and act as vectors for the mitochondrial uptake of sorbed contaminants during embryonic and larval stages. Such negative effects of nanoplastics on energy metabolism and efficiency could be detrimental under multiple-stressors exposures and energy-demanding scenarios, which remains to be validated.

Maternal transfer of nanoplastics to offspring in zebrafish (Danio rerio): A case study with nanopolystyrene

Plastics are ubiquitous anthropogenic contaminants that are a growing concern in aquatic environments. The ecological implications of macroplastics pollution are well documented, but less is known about nanoplastics. The current study investigates the potential adverse effects of nanoplastics, which likely contribute to the ecological burden of plastic pollution. To this end, we examined whether a dietary exposure of adult zebrafish (Danio rerio) to polystyrene nanoparticles (PS NPs) could lead to the transfer of nanoplastics to the offspring, and whether nanoplastics exposure affects zebrafish physiology. Specifically, adult female and male zebrafish (F0 generation) were exposed to PS NPs via diet for one week and bred to produce the F1 generation. Four F1 groups were generated: control (unexposed females and males), maternal (exposed females), paternal (exposed males), and co-parental (exposed males and females). Co-parental PS NP exposure did not significantly affect reproductive success. Assessment of tissues from F0 fish revealed that exposure to PS NPs significantly reduced glutathione reductase activity in brain, muscle, and testes, but did not affect mitochondrial function parameters in heart or gonads. Assessment of F1 embryos and larvae revealed that PS NPs were present in the yolk sac, gastrointestinal tract, liver, and pancreas of the maternally and co-parentally exposed F1 embryos/larvae. Bradycardia was also observed in embryos from maternal and co-parental exposure groups. In addition, the activity of glutathione reductase and the levels of thiols were reduced in F1 embryos/larvae from maternal and/or co-parental exposure groups. Mitochondrial function and locomotor activity were not affected in F1 larvae. This study demonstrates that (i) PS NPs are transferred from mothers to offspring, and (ii) exposure to PS NPs modifies the antioxidant system in adult tissues and F1 larvae. We conclude that PS NPs could bioaccumulate and be passed on to the offspring, but this does not lead to major physiological disturbances.

Suppression of Neutrophil Antimicrobial Functions by Total Particulate Matter From Cigarette Smoke

Chronic cigarette smoking is widely known to alter immune functions and compromise host defense against microbial infection. Neutrophils play an essential role in the immune defense against microbial pathogens and also participate in the development of the inflammatory responses. However, there is limited information about the effects of cigarette smoking on neutrophil response. In this study, cultured bone marrow neutrophils were exposed to total particulate matter (TPM) from cigarette smoke. We found that TPM not only reduced LPS-induced TNFα production, but also suppressed neutrophil bactericidal activity. We also observed that TPM priming reduced the expression of NADPH oxidase component gp91 and iNOS, molecules important for bacterial killing. Mechanistically, we documented that TPM-primed neutrophils have reduced STAT1 activation following subsequent LPS challenge. STAT1 is a key transcription factor responsible for the expression of inflammatory genes as well as gp91 and iNOS. Collectively, reduced STAT1 activation and reduced NADPH oxidase/iNOS may potentially explain the compromised anti-microbial function of TPM-programmed neutrophils. Taken together, our findings reveal that the key innate immune neutrophil is subject to reprogramming by smoking to adopt an immune-suppressed state, potentially responsible for chronic smoking-mediated immunosuppression.

A Novel In Vivo Model to Study Impaired Tissue Regeneration Mediated by Cigarette Smoke

Cigarette smoke is associated with several pathologies including chronic respiratory diseases and cancer. In addition, exposure to cigarette smoke is correlated with impaired wound healing, where a significant decrease in the regenerative capacity of smokers is well documented and broadly considered a negative risk factor after trauma or surgery. So far, some in vitro and in vivo models have been described to study how exposure to cigarette smoke diminishes the regenerative potential in different organisms. However, although useful, many of these models are difficult and expensive to implement and do not allow high-throughput screening approaches. In order to establish a reliable and accessible model, we have evaluated the effects of cigarette smoke extract (CSE) on zebrafish development and regeneration. In this work, zebrafish embryos and larvae were exposed to low doses of aqueous CSE showing severe developmental abnormalities in a dose-dependent manner. Furthermore, when adult zebrafish were subjected to caudal fin amputation, we observed a significant decrease in the regenerative capacity of animals exposed to CSE. The effect was exacerbated in male and aged fish compared to female or young organisms. The establishment of a zebrafish model to assess the consequences of cigarette smoke and its effects on animal physiology could provide a new tool to study the underlying mechanisms involved in impaired tissue regeneration, and aid the development of novel approaches to treat complications associated with cigarette smoke toxicity.

Toward an adverse outcome pathway for impaired growth: Mitochondrial dysfunction impairs growth in early life stages of the fathead minnow (Pimephales promelas)

Chemical contaminants present in the environment can affect mitochondrial bioenergetics in aquatic organisms and can have substantial effects on individual fitness. As early life stages of fish are particularly vulnerable to environmental contaminants, they are ideal models for examining the relationship between impaired mitochondrial bioenergetics (ATP-dependent respiration, basal oxidative respiration) and apical endpoints such as growth. Here, early life stages of the fathead minnow (Pimephales promelas), an ecologically relevant North American species, were used to investigate the relationship between mitochondrial bioenergetics and growth following perturbation with model mitochondrial toxicants 2,4-dinitrophenol and octylamine. Fathead minnows were exposed to 2,4-dinitrophenol and octylamine at 3 concentrations for 24 h and endpoints related to mitochondrial bioenergetics were measured with the Agilent Seahorse XFe24 Bioanalyzer. In order to link changes in mitochondrial bioenergetics to growth, fathead minnows were exposed to the same chemical contaminants for 7-14 days and growth was measured by measuring total length on a weekly basis. There was a significant correlation between decrease in average length at 14 days and basal respiration (r = 0.997, p = 0.050, n = 3), as well as maximal respiration (r = 0.998, p-value = 0.043, n = 3) for embryos exposed to 2,4 dinitrophenol. For octylamine, ATP production was highly correlated with average length at 7 days (p-value = 0.1) and spare respiratory capacity and average length at 14 days were highly correlated (p-value = 0.1). These data improve understanding of how mitochondrial toxicants impair growth in fish larvae and may be useful for developing an adverse outcome pathway for growth.

High-throughput assessment of oxidative respiration in fish embryos: Advancing adverse outcome pathways for mitochondrial dysfunction

Mitochondrial dysfunction is a prevalent molecular event that can result in multiple adverse outcomes. Recently, a novel high throughput method to assess metabolic capacity in fish embryos following exposure to chemicals has been adapted for environmental toxicology. Assessments of oxygen consumption rates using the Seahorse XF(e) 24/96 Extracellular Flux Analyzer (Agilent Technologies) can be used to garner insight into toxicant effects at early stages of development. Here we synthesize the current state of the science using high throughput metabolic profiling in zebrafish embryos, and present considerations for those wishing to adopt high throughput methods for mitochondrial bioenergetics into their research. Chemicals that have been investigated in zebrafish using this metabolic platform include herbicides (e.g. paraquat, diquat), industrial compounds (e.g. benzo-[a]-pyrene, tributyltin), natural products (e.g. quercetin), and anti-bacterial chemicals (i.e. triclosan). Some of these chemicals inhibit mitochondrial endpoints in the μM-mM range, and reduce basal respiration, maximum respiration, and spare capacity. We present a theoretical framework for how one can use mitochondrial performance data in zebrafish to categorize chemicals of concern and prioritize mitochondrial toxicants. Noteworthy is that our studies demonstrate that there can be considerable variation in basal respiration of untreated zebrafish embryos due to clutch-specific effects as well as individual variability, and basal oxygen consumption rates (OCR) can vary on average between 100 and 300 pmol/min/embryo. We also compare OCR between chorionated and dechorionated embryos, as both models are employed to test chemicals. After 24 h, dechorionated embryos remain responsive to mitochondrial toxicants, although they show a blunted response to the uncoupling agent carbonylcyanide-4-trifluoromethoxyphenylhydrazone (FCCP); dechorionated embryos are therefore a viable option for investigations into mitochondrial bioenergetics. We present an adverse outcome pathway framework that incorporates endpoints related to mitochondrial bioenergetics. High throughput bioenergetics assays conducted using whole embryos are expected to support adverse outcome pathways for mitochondrial dysfunction.

Uptake, tissue distribution, and toxicity of polystyrene nanoparticles in developing zebrafish (Danio rerio)

Plastic pollution is a critical environmental concern and comprises the majority of anthropogenic debris in the ocean, including macro, micro, and likely nanoscale (less than 100nm in at least one dimension) plastic particles. While the toxicity of macroplastics and microplastics is relatively well studied, the toxicity of nanoplastics is largely uncharacterized. Here, fluorescent polystyrene nanoparticles (PS NPs) were used to investigate the potential toxicity of nanoplastics in developing zebrafish (Danio rerio), as well as to characterize the uptake and distribution of the particles within embryos and larvae. Zebrafish embryos at 6h post-fertilization (hpf) were exposed to PS NPs (0.1, 1, or 10ppm) until 120 hpf. Our results demonstrate that PS NPs accumulated in the yolk sac as early as 24 hpf and migrated to the gastrointestinal tract, gallbladder, liver, pancreas, heart, and brain throughout development (48-120 hpf). Accumulation of PS NPs decreased during the depuration phase (120-168 hpf) in all organs, but at a slower rate in the pancreas and gastrointestinal tract. Notably, exposure to PS NPs did not induce significant mortality, deformities, or changes to mitochondrial bioenergetics, but did decrease the heart rate. Lastly, exposure to PS NPs altered larval behavior as evidenced by swimming hypoactivity in exposed larvae. Taken together, these data suggest that at least some nanoplastics can penetrate the chorion of developing zebrafish, accumulate in the tissues, and affect physiology and behavior, potentially affecting organismal fitness in contaminated aquatic ecosystems.

AKR1C1 as a Biomarker for Differentiating the Biological Effects of Combustible from Non-Combustible Tobacco Products

Smoking has been established as a major risk factor for developing oral squamous cell carcinoma (OSCC), but less attention has been paid to the effects of smokeless tobacco products. Our objective is to identify potential biomarkers to distinguish the biological effects of combustible tobacco products from those of non-combustible ones using oral cell lines. Normal human gingival epithelial cells (HGEC), non-metastatic (101A) and metastatic (101B) OSCC cell lines were exposed to different tobacco product preparations (TPPs) including cigarette smoke total particulate matter (TPM), whole-smoke conditioned media (WS-CM), smokeless tobacco extract in complete artificial saliva (STE), or nicotine (NIC) alone. We performed microarray-based gene expression profiling and found 3456 probe sets from 101A, 1432 probe sets from 101B, and 2717 probe sets from HGEC to be differentially expressed. Gene Set Enrichment Analysis (GSEA) revealed xenobiotic metabolism and steroid biosynthesis were the top two pathways that were upregulated by combustible but not by non-combustible TPPs. Notably, aldo-keto reductase genes, AKR1C1 and AKR1C2, were the core genes in the top enriched pathways and were statistically upregulated more than eight-fold by combustible TPPs. Quantitative real time polymerase chain reaction (qRT-PCR) results statistically support AKR1C1 as a potential biomarker for differentiating the biological effects of combustible from non-combustible tobacco products.

Resistance to polycyclic aromatic hydrocarbon toxicity and associated bioenergetic consequences in a population of Fundulus heteroclitus

Several locations in the Elizabeth River, VA, USA are highly contaminated with polycyclic aromatic hydrocarbons (PAHs) due to the release of creosote mixtures from wood treatment facilities. Interestingly, some populations of Atlantic killifish (Fundulus heteroclitus) inhabiting the Elizabeth River (ER) are resistant to PAH-induced teratogenesis. However, evolutionary resistance to PAHs due to chronic PAH exposure is associated with reduced fitness and increased susceptibility to other environmental stressors in at least one PAH-resistant ER killifish population. More specifically, wild-caught and first generation PAH-resistant juvenile killifish have altered metabolic demands when compared to non-resistant fish. Herein, we investigated this association further by examining a previously under-studied population captured from the creosote-contaminated site Republic Creosoting (Rep). We assessed PAH toxicity and effects on energy metabolism in Rep killifish in comparison with killifish from the reference site Kings Creek (KC). Following exposures to simple and complex PAH mixtures, Rep killifish exhibited several phenotypes associated with PAH resistance including decreased incidences of developmental cardiovascular deformities and recalcitrant cytochrome P450 1A (CYP1A) activity. We evaluated bioenergetics in killifish embryos throughout development and found elevated basal oxygen consumption rates in Rep embryos relative to KC embryos. Furthermore, juvenile F1 Rep fish had significantly lower maximal metabolic rates and aerobic scopes than KC juveniles. These results suggest that populations of killifish that have adapted or evolved to withstand the toxicity associated with PAHs consequently have altered energetic metabolism or demands. Such consequences could result in an enhanced vulnerability to other environmental and anthropogenic stressors in PAH-resistant killifish.

Exposure to 1,2-Propanediol Impacts Early Development of Zebrafish (Danio rerio) and Induces Hyperactivity

The use of electronic cigarettes (e-cigarettes) is increasing as an alternative to tobacco burning cigarettes; however, their safety remains to be fully determined. The long-term effects of e-cigarettes are unknown, including the effects of maternal e-cigarette use on pre- and postnatal development. Additional research on the safety of e-cigarettes is needed. Especially useful would be information from high- and moderate-throughput economic model systems. This study investigates the effects of 1,2-propanediol, which was identified as the main component of e-cigarette liquid, on early development of zebrafish (an in vivo high-throughput model system that was recently proposed for the study of tobacco cigarette and e-cigarette toxicity). Zebrafish embryos were exposed to 1.25% or 2.5% 1,2-propanediol from 6 to 72 h post-fertilization (hpf). We show that exposure to 1,2-propanediol did not significantly affect mortality. Hatching success was significantly lower in 2.5% 1,2-propanediol-exposed embryos at 48 hpf, but at 72 hpf no significant differences were noted. Moreover, exposure to 1,2-propanediol reduced growth and increased the incidence of string heart, pericardial edema, and yolk sac edema. Most importantly, developmental exposure to 1.25% 1,2-propanediol caused hyperactive swimming behavior in larvae. This study demonstrates that 1,2-propanediol has adverse impacts on early development in zebrafish.

Glutathione and zebrafish: Old assays to address a current issue

Several xenobiotic agents (e.g. metals, polycyclic aromatic hydrocarbons, nanoparticles, etc.) commonly involve the generation of reactive oxygen species (ROS) and oxidative stress as part of their toxic mode of action. Among piscine models, the zebrafish is a popular vertebrate model to study toxicity of various xenobiotic agents. Similarly to other vertebrates, zebrafish possess an extensive antioxidant system, including the reduced form of glutathione (GSH), which is an important antioxidant that acts alone or in conjunction with enzymes, such as glutathione peroxidase (GPx). Upon interaction with ROS, GSH is oxidized, resulting in the formation of glutathione disulfide (GSSG). GSSG is recycled by an auxiliary antioxidant enzyme glutathione reductase (GR). This article outlines detailed methods to measure the concentrations of GSH and GSSG, as well as the activities of GPx and GR in zebrafish larvae as robust and economical means to assess oxidative stress. The studies that have assessed these endpoints in zebrafish and alternative methods are also discussed. We conclude that the availability of these robust and economical methods support the use of zebrafish as a model organism in studies evaluating redox biology, as well as the induction of oxidative stress following exposure to toxic agents.

AHR2 morpholino knockdown reduces the toxicity of total particulate matter to zebrafish embryos

The zebrafish embryo has been proposed as a 'bridge model' to study the effects of cigarette smoke on early development. Previous studies showed that exposure to total particulate matter (TPM) led to adverse effects in developing zebrafish, and suggested that the antioxidant and aryl hydrocarbon receptor (AHR) pathways play important roles. This study investigated the roles of these two pathways in mediating TPM toxicity. The study consisted of four experiments. In experiment I, zebrafish embryos were exposed from 6h post fertilization (hpf) until 96hpf to TPM0.5 and TPM1.0 (corresponding to 0.5 and 1.0μg/mL equi-nicotine units) in the presence or absence of an antioxidant (N-acetyl cysteine/NAC) or a pro-oxidant (buthionine sulfoximine/BSO). In experiment II, TPM exposures were performed in embryos that were microinjected with nuclear factor erythroid 2-related factor 2 (Nrf2), AHR2, cytochrome P450 1A (CYP1A), or CYP1B1 morpholinos, and deformities were assessed. In experiment III, embryos were exposed to TPM, and embryos/larvae were collected at 24, 48, 72, and 96hpf to assess several genes associated with the antioxidant and AHR pathways. Lastly, experiment IV assessed the activity and protein levels of CYP1A and CYP1B1 after exposure to TPM. We demonstrate that the incidence of TPM-induced deformities was generally not affected by NAC/BSO treatments or Nrf2 knockdown. In contrast, AHR2 knockdown reduced, while CYP1A or CYP1B1 knockdowns elevated the incidence of some deformities. Moreover, as shown by gene expression the AHR pathway, but not the antioxidant pathway, was induced in response to TPM exposure, providing further evidence for its importance in mediating TPM toxicity.

Differences in cardiovascular toxicities associated with cigarette smoking and snuff use revealed using novel zebrafish models

Tobacco use is strongly associated with cardiovascular disease and the only avoidable risk factor associated with development of aortic aneurysm. While smoking is the most common form of tobacco use, snuff and other oral tobacco products are gaining popularity, but research on potentially toxic effects of oral tobacco use has not kept pace with the increase in its use. Here, we demonstrate that cigarette smoke and snuff extracts are highly toxic to developing zebrafish embryos. Exposure to such extracts led to a palette of toxic effects including early embryonic mortality, developmental delay, cerebral hemorrhages, defects in lymphatics development and ventricular function, and aneurysm development. Both cigarette smoke and snuff were more toxic than pure nicotine, indicating that other compounds in these products are also associated with toxicity. While some toxicities were found following exposure to both types of tobacco product, other toxicities, including developmental delay and aneurysm development, were specifically observed in the snuff extract group, whereas cerebral hemorrhages were only found in the group exposed to cigarette smoke extract. These findings deepen our understanding of the pathogenic effects of cigarette smoking and snuff use on the cardiovascular system and illustrate the benefits of using zebrafish to study mechanisms involved in aneurysm development.

Quantitation and prediction of sorptive losses during toxicity testing of polycyclic aromatic hydrocarbon (PAH) and nitrated PAH (NPAH) using polystyrene 96-well plates

Developing zebrafish are increasingly being used for rapid assessments of chemical toxicity, and these assays are frequently conducted in multi-well plastic plates. This study investigated the sorptive behavior of polycyclic aromatic hydrocarbons (PAHs) and nitrated PAHs (NPAHs) to uncoated 96-well polystyrene plates typically used for zebrafish (Danio rerio) testing. We measured the percent sorption in the presence and absence of zebrafish embryos, at two exposure concentrations, as well as using two different procedures (addition of embryos to polystyrene plates either before analyte addition, or allowing 24h of equilibrium between analyte addition and embryo addition to the polystyrene plates). Following exposure, the plates were extracted with hexane and analyzed using gas chromatography coupled with mass spectrometry (GC/MS). Allowing 24h of pre-incubation between the addition of analytes and embryos did not significantly impact the percent sorption. The percent sorption was higher for both PAHs and NPAHs at the lower exposure concentration, and sorption was lower in the presence of zebrafish embryos. A mass balance model was developed to predict the sorption to polystyrene plates, based on the PAH and NPAH mass distribution ratios between polystyrene and water. While PAH sorption was significantly correlated with subcooled liquid solubility, NPAH sorption did not correlate with any of the physical-chemical properties investigated. This indicates the need to better understand the sorptive behavior of hydrophobic analytes to plastics, and to better account for sorptive losses during toxicity testing in polystyrene plates.