Use of the zebrafish larvae as a model to study cigarette smoke condensate toxicity

The use of the model organism Caenorhabditis elegans in the investigation of the adverse effects of electronic cigarettes

The use of tobacco products is one of the most preventable risk factors for mortality from a variety of diseases, including cardiovascular, infectious, respiratory, and neoplastic conditions. The use of electronic cigarettes (ECIGs), also known as electronic nicotine delivery devices, has increased significantly in recent years. Nicotine, propylene glycol, and / or glycerine, water, alcohol, flavorings, and other substances are among the many chemicals found in ECIGs that are vaporized and inhaled. A review of the existing literature shows that research dedicated to ECIGs is a rapidly developing and growing field of study. The rationale for the use of ECIGs is that they represent a safer alternative to traditional tobacco products. However, vaping safety profiles are still under development, as this is a relatively recent phenomenon. Various model organisms can be employed to examine the cellular processes that may be altered by exposure to the electronic liquids utilized for vaping. For example, the translucent multicellular eukaryote Caenorhabditis elegans is widely used as a model organism to explain a broad range of biological processes, including aging, stress response, development, and many others. Due to its short lifespan and easy use, C. elegans is an ideal model organism for studying chronic exposure to drugs and environmental toxicology. This review presents a summary of the most recent findings on the impact of electronic cigarettes on the physiological health of this nematode. Preliminary observations made in C. elegans can provide insight into the consequences of exposure to fundamental cellular physiology, which can then be used for future research in humans and mammalian models.

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.

Assessment of toxicological validity using tobacco emission condensates: A comparative analysis of emissions and condensates from 3R4F reference cigarettes and heated tobacco products

The tobacco emission condensate, henceforth referred to as "tobacco condensate," plays a critical role in assessing the toxicity of tobacco products. This condensate, derived from tobacco emissions, provides an optimized liquid concentrate for storage and concentration control. Thus, the validation of its constituents is vital for toxicity assessments. This study used tobacco condensates from 3R4F cigarettes and three heated tobacco product (HTP) variants to quantify and contrast organic compounds (OCs) therein. The hazard index (HI) for tobacco emissions and condensates was determined to ascertain the assessment validity. The total particulate matter (TPM) for 3R4F registered at 17,667 μg cig-1, with its total OC (TOC) at 3777 μg cig-1. HTPs' TPM and TOC were 9342 ± 1918 μg cig-1 and 5258 ± 593 μg stick-1, respectively. 3R4F's heightened TPM likely arises from tar, while HTPs' OC concentrations are influenced by vegetable glycerin (2236-2688 μg stick-1) and propylene glycol (589-610 μg stick-1). During the condensation process, a substantial proportion of OCs in 3R4F smoke underwent significant concentration decreases, in contrast to HTPs, where fewer than half of the examined OCs exhibited notable concentration declines. The HI for tobacco emissions exhibited a marginally higher value compared to tobacco condensate, with variations ranging from 7.92% (HTPs) to 18.6% (3R4F), denoting a minimal differential. These observations emphasize the importance of accurate OC recovery techniques to maintain the validity and reliability of toxicity assessments based on tobacco condensates. This study not only deepens the comprehension of chemical behaviors in tobacco products but also establishes a novel benchmark for their toxicity evaluation, with profound implications for public health strategies and consumer protection.

Zebrafish (Danio rerio) as a Model for the Study of Developmental and Cardiovascular Toxicity of Electronic Cigarettes

The increasing popularity of electronic cigarettes (e-cigarettes) as an alternative to conventional tobacco products has raised concerns regarding their potential adverse effects. The cardiovascular system undergoes intricate processes forming the heart and blood vessels during fetal development. However, the precise impact of e-cigarette smoke and aerosols on these delicate developmental processes remains elusive. Previous studies have revealed changes in gene expression patterns, disruptions in cellular signaling pathways, and increased oxidative stress resulting from e-cigarette exposure. These findings indicate the potential for e-cigarettes to cause developmental and cardiovascular harm. This comprehensive review article discusses various aspects of electronic cigarette use, emphasizing the relevance of cardiovascular studies in Zebrafish for understanding the risks to human health. It also highlights novel experimental approaches and technologies while addressing their inherent challenges and limitations.

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.

Assessing the Morphological and Behavioral Toxicity of Catechol Using Larval Zebrafish

Catechol is a ubiquitous chemical used in the manufacturing of fragrances, pharmaceuticals and flavorants. Environmental exposure occurs in a variety of ways through industrial processes, during pyrolysis and in effluent, yet despite its prevalence, there is limited information regarding its toxicity. While the genotoxicity and gastric carcinogenicity of catechol have been described in depth, toxicological studies have potentially overlooked a number of other effects relevant to humans. Here, we have made use of a general and behavioral larval zebrafish toxicity assay to describe previously unknown catechol-based toxicological phenomena. Behavioral testing revealed catechol-induced hypoactivity at concentrations an order of magnitude lower than observable endpoints. Catechol exposure also resulted in punctate melanocytes with concomitant decreases in the expression of pigment production and regulation markers mitfa, mc1r and tyr. Because catechol is converted into a number of toxic metabolites by tyrosinase, an enzyme found almost exclusively in melanocytes, an evaluation of the effects of catechol on these cells is critical to evaluating the safety of this chemical. This work provides insights into the toxic nature of catechol and highlights the benefits of the zebrafish larval testing platform in being able to dissect multiple aspects of toxicity with one model.

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.

E-liquids and vanillin flavoring disrupts retinoic acid signaling and causes craniofacial defects in Xenopus embryos

Environmental teratogens such as smoking are known risk factors for developmental disorders such as cleft palate. While smoking rates have declined, a new type of smoking, called vaping is on the rise. Vaping is the use of e-cigarettes to vaporize and inhale an e-liquid containing nicotine and food-like flavors. There is the potential that, like smoking, vaping could also pose a danger to the developing human. Rather than waiting for epidemiological and mammalian studies, we have turned to an aquatic developmental model, Xenopus laevis, to more quickly assess whether e-liquids contain teratogens that could lead to craniofacial malformations. Xenopus, like zebrafish, has the benefit of being a well-established developmental model and has also been effective in predicting whether a chemical could be a teratogen. We have determined that embryonic exposure to dessert flavored e-liquids can cause craniofacial abnormalities, including an orofacial cleft in Xenopus. To better understand the underlying mechanisms contributing to these defects, transcriptomic analysis of the facial tissues of embryos exposed to a representative dessert flavored e-liquid vapor extract was performed. Analysis of differentially expressed genes in these embryos revealed several genes associated with retinoic acid metabolism or the signaling pathway. Consistently, retinoic acid receptor inhibition phenocopied the craniofacial defects as those embryos exposed to the vapor extract of the e-liquid. Such malformations also correlated with a group of common differentially expressed genes, two of which are associated with midface birth defects in humans. Further, e-liquid exposure sensitized embryos to forming craniofacial malformations when they already had depressed retinoic acid signaling. Moreover, 13-cis-retinoic acid treatment could significantly reduce the e-liquid induced malformation in the midface. Such results suggest the possibility of an interaction between retinoic acid signaling and e-liquid exposure. One of the most popular and concentrated flavoring chemicals in dessert flavored e-liquids is vanillin. Xenopus embryos exposed to this chemical closely resembled embryos exposed to dessert-like e-liquids and a retinoic acid receptor antagonist. In summary, we determined that e-liquid chemicals, in particular vanillin, can cause craniofacial defects potentially by dysregulating retinoic acid signaling. This work warrants the evaluation of vanillin and other such flavoring additives in e-liquids on mammalian development.

Effect of Water-Pipe Smoking on the Normal Development of Zebrafish

Background: Among all types of tobacco consumption, Water-Pipe Smoking (WPS) is the most widely used in the Middle East and second-most in several other countries. The effect of WPS on normal development is not yet fully understood, thus the aim of this study is to explore the acute toxicity effects of WPS extract on zebrafish larvae. Methods: In this study, we compared the effects of WPS smoke condensates at concentrations varying from 50 to 200 µg/mL on developmental, cardiac, and behavioural (neurotoxicity) functions. Gene expression patterns of cardiac biomarkers were also evaluated by RT-qPCR. Results: Exposing zebrafish embryos to 50, 100, 150 and 200 µg/mL WPS for three days did not affect the normal morphology of Zebrafish embryos, as the tail flicking, behavioural and locomotion assays did not show any change. However, WPS deregulated cardiac markers including atrial natriuretic peptide (ANP/NPPA) and brain natriuretic peptide (BNP/NPPB). Furthermore, it induced apoptosis in a dose-dependent manner. Conclusion: Our data demonstrate that WPS can significantly affect specific cardiac parameters during the normal development of zebrafish. Further investigations are necessary to elucidate the pathogenic outcome of WPS on different aspects of human life, including pregnancy.

Exploring Neurobehaviour in Zebrafish Embryos as a Screening Model for Addictiveness of Substances

Tobacco use is the leading cause of preventable death worldwide and is highly addictive. Nicotine is the main addictive compound in tobacco, but less is known about other components and additives that may contribute to tobacco addiction. The zebrafish embryo (ZFE) has been shown to be a good model to study the toxic effects of chemicals on the neurological system and thus may be a promising model to study behavioral markers of nicotine effects, which may be predictive for addictiveness. We aimed to develop a testing protocol to study nicotine tolerance in ZFE using a locomotion test with light-dark transitions as behavioral trigger. Behavioral experiments were conducted using three exposure paradigms: (1) Acute exposure to determine nicotine’s effect and potency. (2) Pre-treatment with nicotine dose range followed by a single dose of nicotine, to determine which pre-treatment dose is sufficient to affect the potency of acute nicotine. (3) Pre-treatment with a single dose combined with acute exposure to a dose range to confirm the hypothesized decreased potency of the acute nicotine exposure. These exposure paradigms showed that (1) acute nicotine exposure decreased ZFE activity in response to dark conditions in a dose-dependent fashion; (2) pre-treatment with increasing concentrations dose-dependently reversed the effect of acute nicotine exposure; and (3) a fixed pre-treatment dose of nicotine induced a decreased potency of the acute nicotine exposure. This effect supported the induction of tolerance to nicotine by the pre-treatment, likely through neuroadaptation. The interpretation of these effects, particularly in view of prediction of dependence and addictiveness, and suitability of the ZFE model to test for such effects of other compounds than nicotine, are discussed.

Identification of molecular toxicity pathways across early life-stages of zebrafish exposed to PCB126 using a whole transcriptomics approach

Although withdrawn from the market in the 1980s, polychlorinated biphenyls (PCBs) are still found ubiquitously in the aquatic environment and pose a serious risk to biota due to their teratogenic potential. In fish, early life-stages are often considered most sensitive with regard to their exposure to PCBs and other dioxin-like compounds. However, little is known about the molecular drivers of the frequently observed teratogenic effects. Therefore, the aims of our study were to: (1) characterize the baseline transcriptome profiles at different embryonic life-stages in zebrafish (Danio rerio); and (2) to identify the molecular response to PCB exposure and life-stage specific-effects of the chemical on associated processes. For both objectives, embryos were sampled at 12, 48, and 96 h post-fertilization (hpf) and subjected to Illumina sequence-by-synthesis and RNAseq analysis. Results revealed that with increasing age more genes and related pathways were upregulated both in terms of number and magnitude. Yet, other transcripts followed an opposite pattern with greater transcript abundance at the earlier time points. Additionally, embryos were exposed to PCB126, a potent agonist of the aryl hydrocarbon receptor (AHR). ClueGO network analysis revealed significant enrichment of genes associated with basic cell metabolism, communication, and homeostasis as well as eye development, muscle formation, and skeletal formation. We selected eight genes involved in the affected pathways for an in-depth characterization of their regulation throughout normal embryogenesis and after exposure to PCB126 by quantification of transcript abundances every 12 h until 118 hpf. Among these, fgf7 and c9 stood out because of their strong upregulation by PCB126 exposure at 48 and 96 hpf, respectively. Cyp2aa12 was upregulated from 84 hpf on. Fabp10ab, myhz1.1, col8a1a, sulf1, and opn1sw1 displayed specific regulation depending on the developmental stage. Overall, we demonstrate that (1) the developmental transcriptome of zebrafish is highly dynamic, and (2) dysregulation of gene expression by exposure to PCB126 was significant and in several cases not directly connected to AHR-signaling. Hence, this study improves the understanding of linkages between molecular events and apical outcomes that are of regulatory relevance.

Acute effects of acetaminophen on the developmental, swimming performance and cardiovascular activities of the African catfish embryos/larvae (Clarias gariepinus)

Acetaminophen is a widely used analgesic that has been detected in many water bodies with few reports concerning its potential toxicity to fish. This study sought to assess the developmental, swimming performance and cardiovascular activities of embryo/larvae catfish (Clarias gariepinus) exposed to acetaminophen. The Organization for Economic Development (OECD) Fish Embryo Acute Toxicity Test (OECD 236) was employed. Fertilized embryo were exposed to different concentrations of acetaminophen (0, 0.5, 1, 10 µg/L) for 96 h. Hatching rates of the embryo were observed to decrease with increasing concentrations of acetaminophen. Fish embryo exposed to acetaminophen displayed varying levels of teratogenic effects at different levels of development in a dose-dependent manner. The results also showed a significant (p < 0.05) dose-dependent increase in swimming speed and movement patterns in fish larvae exposed to acetaminophen, with distance travelled in larvae exposed to the highest concentration of acetaminophen (10 µg/L) about eight (8) times the distance travelled by the control larvae, indicating that acetaminophen-induced erratic swimming behaviour in the catfish species. Cardiotoxicity was evident, with a significant reduction in heartbeat rate with increasing concentrations of acetaminophen. The results showed that exposure to acetaminophen resulted in teratogenic, neurotoxic and cardiotoxic effects in embryo/larvae of Clarias gariepinus. The findings suggest that acetaminophen which has recently been detected in many water bodies could potentially impact on survival of aquatic life, especially catfish.

Adult and Developing Zebrafish as Suitable Models for Cardiac Electrophysiology and Pathology in Research and Industry

The electrophysiological behavior of the zebrafish heart is very similar to that of the human heart. In fact, most of the genes that codify the channels and regulatory proteins required for human cardiac function have their orthologs in the zebrafish. The high fecundity, small size, and easy handling make the zebrafish embryos/larvae an interesting candidate to perform whole animal experiments within a plate, offering a reliable and low-cost alternative to replace rodents and larger mammals for the study of cardiac physiology and pathology. The employment of zebrafish embryos/larvae has widened from basic science to industry, being of particular interest for pharmacology studies, since the zebrafish embryo/larva is able to recapitulate a complete and integrated view of cardiac physiology, missed in cell culture. As in the human heart, I_Kr is the dominant repolarizing current and it is functional as early as 48 h post fertilization. Finally, genome editing techniques such as CRISPR/Cas9 facilitate the humanization of zebrafish embryos/larvae. These techniques allow one to replace zebrafish genes by their human orthologs, making humanized zebrafish embryos/larvae the most promising in vitro model, since it allows the recreation of human-organ-like environment, which is especially necessary in cardiac studies due to the implication of dynamic factors, electrical communication, and the paracrine signals in cardiac function.

Exposure to the gut microbiota from cigarette smoke-exposed mice exacerbates cigarette smoke extract-induced inflammation in zebrafish larvae

Cigarette smoke (CS)-induced inflammation leads to a range of diseases including chronic obstructive pulmonary disease and cancer. The gut microbiota is a major modifying environmental factor that determine the severity of cigarette smoke-induced pathology. Microbiomes and metabolites from CS-exposed mice exacerbate lung inflammation via the gut-lung axis of shared mucosal immunity in mice but these systems are expensive to establish and analyse. Zebrafish embryos and larvae have been used to model the effects of cigarette smoking on a range of physiological processes and offer an amenable platform for screening modifiers of cigarette smoke-induced pathologies with key features of low cost and rapid visual readouts. Here we exposed zebrafish larvae to cigarette smoke extract (CSE) and characterised a CSE-induced leukocytic inflammatory phenotype with increased neutrophilic and macrophage inflammation in the gut. The CSE-induced phenotype was exacerbated by co-exposure to microbiota from the faeces of CS-exposed mice, but not control mice. Microbiota could be recovered from the gut of zebrafish and studied in isolation in a screening setting. This demonstrates the utility of the zebrafish-CSE exposure platform for identifying environmental modifiers of cigarette smoking-associated pathology and demonstrates that the CS-exposed mouse gut microbiota potentiates the inflammatory effects of CSE across host species.

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Zebrafish larvae develop gut inflammation in response to cigarette smoke exposure.

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The zebrafish larval cigarette smoke-induced inflammatory response is dose dependent.

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Microbiota from smoking mice potentiates smoke-induced inflammation in zebrafish.

Comparison of the Zebrafish Embryo Toxicity Assay and the General and Behavioral Embryo Toxicity Assay as New Approach Methods for Chemical Screening

The movement away from mammalian testing of potential toxicants and new chemical entities has primarily led to cell line testing and protein-based assays. However, these assays may not yet be sufficient to properly characterize the toxic potential of a chemical. The zebrafish embryo model is widely recognized as a potential new approach method for chemical testing that may provide a bridge between cell and protein-based assays and mammalian testing. The Zebrafish Embryo Toxicity (ZET) model is increasingly recognized as a valuable toxicity testing platform. The ZET assay focuses on the early stages of embryo development and is considered a more humane model compared to adult zebrafish testing. A complementary model has been developed that exposes larvae to toxicants at a later time point during development where body patterning has already been established. Here we compare the toxicity profiles of 20 compounds for this General and Behavioral Toxicity (GBT) assay to the ZET assay. The results show partially overlapping toxicity profiles along with unique information provided by each assay. It appears from this work that these two assays applied together can strengthen the use of zebrafish embryos/larvae as standard toxicity testing models.

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.

Melanogenic Inhibition and Toxicity Assessment of Flavokawain A and B on B16/F10 Melanoma Cells and Zebrafish (Danio rerio)

Excessive production of melanin implicates hyperpigmentation disorders. Flavokawain A (FLA) and flavokawain B (FLB) have been reported with anti-melanogenic activity, but their melanogenic inhibition and toxicity effects on the vertebrate model of zebrafish are still unknown. In the present study, cytotoxic as well as melanogenic effects of FLA and FLB on cellular melanin content and tyrosinase activity were evaluated in α-MSH-induced B16/F10 cells. Master regulator of microphthalmia-associated transcription factor (Mitf) and the other downstream melanogenic-related genes were verified via quantitative real time PCR (qPCR). Toxicity assessment and melanogenesis inhibition on zebrafish model was further observed. FLA and FLB significantly reduced the specific cellular melanin content by 4.3-fold and 9.6-fold decrement, respectively in α-MSH-induced B16/F10 cells. Concomitantly, FLA significantly reduced the specific cellular tyrosinase activity by 7-fold whilst FLB by 9-fold. The decrement of melanin production and tyrosinase activity were correlated with the mRNA suppression of Mitf which in turn down-regulate Tyr, Trp-1 and Trp-2. FLA and FLB exhibited non-toxic effects on the zebrafish model at 25 and 6.25 µM, respectively. Further experiments on the zebrafish model demonstrated successful phenotype-based depigmenting activity of FLA and FLB under induced melanogenesis. To sum up, our findings provide an important first key step for both of the chalcone derivatives to be further studied and developed as potent depigmenting agents.

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.

Possible involvement of Fas/FasL-dependent apoptotic pathway in α-bisabolol induced cardiotoxicity in zebrafish embryos

α-Bisabolol, an unsaturated monocyclic sesquiterpene alcohol, is a common ingredient in many pharmaceuticals and personal care products (PPCPs). Despite being widely used, little is known about its toxic effects on organisms and aquatic environment. In this study, we investigated the developmental toxicity of α-Bisabolol, especially its effects on the cardiac development using zebrafish embryos as a model. Embryos at 4 h post-fertilization (hpf) were exposed to 10, 30, 50, 70, 90, and 100 μM α-Bisabolol until 144 hpf. α-Bisabolol caused phenotypic defects and the most striking one is the heart malformation. Treatment of α-Bisabolol significantly increased the cardiac malformation rate, the SV-BA distance, as well as the pericardial edema area, and reduced heart rate in a concentration-dependent manner. Notably, considerable numbers of apoptotic cells were mainly observed in the heart region of zebrafish treated with α-Bisabolol. Further study on α-Bisabolol induced apoptosis in the zebrafsh heart suggested that an activation of Fas/FasL-dependent apoptotic pathway. Taken together, our study investigated the cardiotoxicity of α-Bisabolol on zebrafish embryonic development and its underlying molecular mechanism, shedding light on the full understanding of α-Bisabolol toxicity on living organisms and its environmental impact.

Using Zebrafish for Investigating the Molecular Mechanisms of Drug-Induced Cardiotoxicity

Over the last decade, the zebrafish (Danio rerio) has emerged as a model organism for cardiovascular research. Zebrafish have several advantages over mammalian models. For instance, the experimental cost of using zebrafish is comparatively low; the embryos are transparent, develop externally, and have high fecundity making them suitable for large-scale genetic screening. More recently, zebrafish embryos have been used for the screening of a variety of toxic agents, particularly for cardiotoxicity testing. Zebrafish has been shown to exhibit physiological responses that are similar to mammals after exposure to medicinal drugs including xenobiotics, hormones, cancer drugs, and also environmental pollutants, including pesticides and heavy metals. In this review, we provided a summary for recent studies that have used zebrafish to investigate the molecular mechanisms of drug-induced cardiotoxicity. More specifically, we focused on the techniques that were exploited by us and others for cardiovascular toxicity assessment and described several microscopic imaging and analysis protocols that are being used for the estimation of a variety of cardiac hemodynamic parameters.

In vitro and in vivo toxicity evaluation of halloysite nanotubes

Because of their outstanding properties, increasing numbers of research studies and emerging applications for manufacturing products are currently in progress for halloysite nanotubes (HNTs). Therefore, the impact of HNTs on the environment and human health should be taken into consideration. In order to clearly show the cell uptake of HNTs and the biodistribution of HNTs in zebrafish, HNTs are labeled with fluorescein isothiocyanate (FITC-HNTs). The cytotoxicity assays showed that the cell viabilities of human umbilical vein endothelial cells (HUVECs) and human breast adenocarcinoma (MCF-7) cells were above 60% after being treated with different concentrations of HNTs (2.5-200 μg mL^-1) for 72 h. Confocal laser scanning microscopy (CLSM) results showed the uptake of HNTs by HUVECs and MCF-7 cells. The in vivo toxicity of HNTs was then investigated in the early development of zebrafish embryos. The percent survival of zebrafish embryos and larvae showed no significant changes at different developmental stages (24, 48, 72, 96, and 120 hpf) when treated with various concentrations of HNTs (0.25-10 mg mL^-1). Besides, HNTs could promote the hatchability of zebrafish embryos and did not affect the morphological development of zebrafish at a concentration of ≤25 mg mL^-1. HNTs could also be ingested by zebrafish larvae and accumulated predominantly in the gastrointestinal tract. The fluorescence intensity of FITC-HNTs decreased gradually with time, which suggested that HNTs could be excreted by zebrafish larvae through the gastrointestinal metabolism. Therefore, it can be concluded that HNTs are relatively biocompatible nanomaterials, which can be utilized in many fields.

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.

Identification, growth and toxicity assessment of Coolia Meunier (Dinophyceae) from Nova Scotia, Canada

Benthic dinoflagellates of the toxigenic genus Coolia Meunier (Dinophyceae) are known to have a global distribution in both tropical and temperate waters. The type species, C. monotis, has been reported from the Mediterranean Sea, the NE Atlantic and from Rhode Island, USA in the NW Atlantic, whereas other species in the genus have been reported from tropical locations. Coolia cells were observed in algal drift samples collected at seven sites in Nova Scotia, Canada. Clonal isolates were established from four of these locations and identified with light and scanning electron microscopy, then confirmed with genetic sequencing to be C. monotis. This is the first record of this species in Nova Scotia. The isolates were established and incubated at 18 °C under a 14:10 L:D photoperiod with an approximate photon flux density of 50-60 μmol m^-2 s^-1. Growth experiments using an isolate from Johnston Harbour (CMJH) were carried out at temperatures ranging from 5 to 30 °C under the same photoperiod with an approximate photon flux density of 45-50 μmol m^-2 s^-1. Cells tolerated temperatures from 5 to 25 °C with optimum growth and mucilage aggregate production between 15 and 20 °C. Methanol extracts of this isolate examined by Liquid Chromatography-Mass Spectrometry (LC-MS) did not show the presence of the previously reported cooliatoxin. Toxic effects were assayed using two zebrafish bioassays, the Fish Embryo Toxicity (FET) assay and the General Behaviour and Toxicity (GBT) assay. The results of this study demonstrate a lack of toxicity in C. monotis from Nova Scotia, as has been reported for other genetically-confirmed isolates of this species. Conditions in which cell growth that could potentially degrade water quality and provide substrate and dispersal mechanisms for other harmful microorganisms via mucilage production are indicated.

Analysis of the Uptake, Metabolism, and Behavioral Effects of Cannabinoids on Zebrafish Larvae

The Cannabis sativa plant contains numerous phytocannabinoids and terpenes with known or potential biological activity. For decades, plant breeders have been breeding the Cannabis plant to control for a desired ratio of the major cannabinoids. A high-throughput in vivo model to understand the relationship between the chemical composition of different strains and their therapeutic potential then becomes of value. Measuring changes in the behavioral patterns of zebrafish larvae is an established model with which to test the biological activity of neuroactive compounds. However, there is currently little information regarding the uptake kinetics and metabolism of compounds by larvae. In this study, we chose to compare the uptake kinetics and metabolism of Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD) alone or in combination with their effects on larval behavior. We have shown that both compounds have distinct behavioral patterns and concentration response profiles. Additionally, the uptake kinetics observed for each compound appears to correlate with the change in behavior observed in the behavioral assays. When combinations of THC and CBD were tested there were shifts in both the behavioral activity and the uptake kinetics of each compound compared with when they were tested alone. Finally, the THC/CBD-derived metabolites detected in the larvae are similar to those found in mammalian systems. This study thus provides a model for further testing of additional cannabinoids and potentially plant extracts.

Adult zebrafish in CNS disease modeling: a tank that's half-full, not half-empty, and still filling

The zebrafish (Danio rerio) is increasingly used in a broad array of biomedical studies, from cancer research to drug screening. Zebrafish also represent an emerging model organism for studying complex brain diseases. The number of zebrafish neuroscience studies is exponentially growing, significantly outpacing those conducted with rodents or other model organisms. Yet, there is still a substantial amount of resistance in adopting zebrafish as a first-choice model system. Studies of the repertoire of zebrafish neural and behavioral functions continue to reveal new opportunities for understanding the pathobiology of various CNS deficits. Although some of these models are well established in zebrafish, including models for anxiety, depression, and addiction, others are less recognized, for example, models of autism and obsessive-compulsive states. However, mounting data indicate that a wide spectrum of CNS diseases can be modeled in adult zebrafish. Here, we summarize recent findings using zebrafish CNS assays, discuss model limitations and the existing challenges, as well as outline future directions of research in this field.

Impact of Nicotine Exposure on Hair Cell Toxicity and Embryotoxicity During Zebrafish Development

Objectives

Nicotine has various adverse effects including negative impacts associated with maternal exposure. In the current study, we examined nicotine-induced damage of hair cells and embryotoxicity during zebrafish development.

Methods

Zebrafish embryos were exposed to nicotine at several concentrations (5, 10, 20, and 40 μM) and embryotoxicity were evaluated at 72 hours, including hatching rate, mortality, teratogenicity rate, and heart rate. Hair cells within the supraorbital (SO1 and SO2), otic (O1), and occipital (OC1) neuromasts were identified at 120 hours. Apoptosis and mitochondrial damage of hair cells were analyzed using TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling) and DASPEI (2-[4-(dimethylamino)styryl]-N-ethylpyridinium iodide) assays, respectively, and changes of ultrastructure were observed by scanning electron microscopy.

Results

The control group without nicotine appeared normal with overall mortality and teratogenicity rate <5%. The hatching rate and mortality rate was not significantly different according to nicotine concentration (n=400 each). The abnormal morphology rate (n=400) increased and heart rate (n=150) decreased with increasing nicotine concentration (P<0.05). Nicotine-induced hair cell damage significantly increased as nicotine concentration increased. A significantly greater number of TUNEL-positive cells (P<0.01) and markedly smaller DASPEI area (P<0.01) were shown as nicotine concentration increased.

Conclusion

The current results suggest that nicotine induces dose-dependent hair cell toxicity in embryos by promoting apoptosis and mitochondrial and structural damage.

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.

Zebrafish as a Vertebrate Model System to Evaluate Effects of Environmental Toxicants on Cardiac Development and Function

Environmental pollution is a serious problem of the modern world that possesses a major threat to public health. Exposure to environmental pollutants during embryonic development is particularly risky. Although many pollutants have been verified as potential toxicants, there are new chemicals in the environment that need assessment. Heart development is an extremely sensitive process, which can be affected by environmentally toxic molecule exposure during embryonic development. Congenital heart defects are the most common life-threatening global health problems, and the etiology is mostly unknown. The zebrafish has emerged as an invaluable model to examine substance toxicity on vertebrate development, particularly on cardiac development. The zebrafish offers numerous advantages for toxicology research not found in other model systems. Many laboratories have used the zebrafish to study the effects of widespread chemicals in the environment on heart development, including pesticides, nanoparticles, and various organic pollutants. Here, we review the uses of the zebrafish in examining effects of exposure to external molecules during embryonic development in causing cardiac defects, including chemicals ubiquitous in the environment and illicit drugs. Known or potential mechanisms of toxicity and how zebrafish research can be used to provide mechanistic understanding of cardiac defects are discussed.

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.

Embryotoxicity and hair cell toxicity of silver nanoparticles in zebrafish embryos

OBJECTIVES

The purpose of the present study was to evaluate silver nanoparticles (AgNP)-induced embryotoxicity and hair cell toxicity during zebrafish development.

METHODS

We exposed zebrafish embryos to various AgNP concentrations (30, 60, 120, and 240nM) and evaluated embryotoxicity at 72h and ototoxicity at 120h. Embryotoxicity parameters including abnormal morphology, mortality, hatching rate, and heart rate were investigated. Hair cells within four neuromasts were evaluated. In the present study, the average number of hair cells of zebrafish exposed to AgNP was compared with that of an unexposed control group.

RESULTS

The hatching rate was not significantly different between groups (control: 90%; AgNP 240nM: 89%). The control group showed 2% mortality and 0% teratogenicity, while the AgNP 240nM group showed increased mortality (11%) and teratogenicity (15%) at 72h (n=100). The heart rate of AgNP-exposed embryos tended to be lower than that of the control group (n=38). Furthermore, AgNP induced apoptotic hair cell damage in the neuromasts (control: 50.7±7.4 cells; 240nM AgNP: 41.1±6.3 cells, n=23). TUNEL positive cell counts increased significantly as AgNP concentration increases (p<0.001, n=20 in each group).

CONCLUSIONS

The results of this study indicate that AgNP exposure causes embryotoxicity and hair cell toxicity in zebrafish embryos.

Mucosal inflammation at the respiratory interface: a zebrafish model

Inflammatory diseases of the respiratory system such as asthma and chronic obstructive pulmonary disease are increasing globally and remain poorly understood conditions. Although attention has long focused on the activation of type 1 and type 2 helper T cells of the adaptive immune system in these diseases, it is becoming increasingly apparent that there is also a need to understand the contributions and interactions between innate immune cells and the epithelial lining of the respiratory system. Cigarette smoke predisposes the respiratory tissue to a higher incidence of inflammatory disease, and here we have used zebrafish gills as a model to study the effect of cigarette smoke on the respiratory epithelium. Zebrafish gills fulfill the same gas-exchange function as the mammalian airways and have a similar structure. Exposure to cigarette smoke extracts resulted in an increase in transcripts of the proinflammatory cytokines TNF-α, IL-1β, and MMP9 in the gill tissue, which was at least in part mediated via NF-κB activation. Longer term exposure of fish for 6 wk to cigarette smoke extract resulted in marked structural changes to the gills with lamellar fusion and mucus cell formation, while signs of inflammation or fibrosis were absent. This shows, for the first time, that zebrafish gills are a relevant model for studying the effect of inflammatory stimuli on a respiratory epithelium, since they mimic the immunopathology involved in respiratory inflammatory diseases of humans.

Sodium selenite/selenium nanoparticles (SeNPs) protect cardiomyoblasts and zebrafish embryos against ethanol induced oxidative stress

Alcoholic cardiomyopathy is the damage caused to the heart muscles due to high level of alcohol consumption resulting in enlargement and inflammation of the heart. Selenium is an important trace element that is beneficial to human health. Selenium protects the cells by preventing the formation of free radicals in the body. In the present study, protein mediated synthesis of SeNPs was investigated. Two different sizes of SeNPs were synthesized using BSA and keratin. The synthesized SeNPs were characterized by scanning electron microscopy (SEM) with elemental composition analysis Energy Dispersive X-ray spectroscopy(EDX) and X-ray diffraction (XRD). This study demonstrates the in vitro and in vivo antioxidative effects of sodium selenite and SeNPs. Further selenium and SeNPs were evaluated for their ability to protect against 1% ethanol induced oxidative stress in H9C2 cell line. The selenium and SeNPs were found to reduce the 1% ethanol-induced oxidative damage through scavenging intracellular reactive oxygen species. The selenium and SeNPs could also prevent pericardial edema induced ethanol treatment and reduced apoptosis and cell death in zebrafish embryos. The results indicate that selenium and SeNPs could potentially be used as an additive in alcoholic beverage industry to control the cardiomyopathy.

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

Cigarette smoke has been associated with a number of pathologies; however, the mechanisms leading to developmental effects are yet to be fully understood. The zebrafish embryo is regarded as a 'bridge model'; however, not many studies examined its applicability to cigarette smoke toxicity. This study examined the effects of total particulate matter (TPM) from 3R4F reference cigarettes on the early development of zebrafish (Danio rerio). Zebrafish embryos were exposed to two concentrations of TPM (0.4 and 1.4 μg/mL equi-nicotine units) or nicotine at equivalent doses. The exposures began at 2h post-fertilization (hpf) and lasted until 96 hpf. Several physiological parameters were assessed during or after the exposure. We show that TPM increased mortality, delayed hatching, and increased the incidence of deformities in zebrafish. TPM exposure also increased the incidence of hemorrhage and disrupted the angiogenesis of the major vessels in the brain. Moreover, TPM exposure reduced the larval body length, decreased the heart rate, and reduced the metabolic rate. Biomarkers of xenobiotic metabolism and oxidative stress were also affected. TPM-exposed zebrafish also differed behaviorally: at 24 hpf the embryos had a higher frequency of spontaneous contractions and at 144 hpf the larvae displayed swimming hyperactivity. This study demonstrates that TPM disrupts several aspects of early development in zebrafish. The effects reported for TPM were not attributable to nicotine, since embryos treated with nicotine alone did not differ significantly from the control group. Collectively, our work illustrates the utility of zebrafish as an alternative model to evaluate the toxic effects of cigarette smoke constituents.

Characterizing Social Interaction in Tobacco-Oriented Social Networks: An Empirical Analysis

Social media is becoming a new battlefield for tobacco "wars". Evaluating the current situation is very crucial for the advocacy of tobacco control in the age of social media. To reveal the impact of tobacco-related user-generated content, this paper characterizes user interaction and social influence utilizing social network analysis and information theoretic approaches. Our empirical studies demonstrate that the exploding pro-tobacco content has long-lasting effects with more active users and broader influence, and reveal the shortage of social media resources in global tobacco control. It is found that the user interaction in the pro-tobacco group is more active, and user-generated content for tobacco promotion is more successful in obtaining user attention. Furthermore, we construct three tobacco-related social networks and investigate the topological patterns of these tobacco-related social networks. We find that the size of the pro-tobacco network overwhelms the others, which suggests a huge number of users are exposed to the pro-tobacco content. These results indicate that the gap between tobacco promotion and tobacco control is widening and tobacco control may be losing ground to tobacco promotion in social media.

Cardiac development in zebrafish and human embryonic stem cells is inhibited by exposure to tobacco cigarettes and e-cigarettes

Background

Maternal smoking is a risk factor for low birth weight and other adverse developmental outcomes.

Objective

We sought to determine the impact of standard tobacco cigarettes and e-cigarettes on heart development in vitro and in vivo.

Methods

Zebrafish (Danio rerio) were used to assess developmental effects in vivo and cardiac differentiation of human embryonic stem cells (hESCs) was used as a model for in vitro cardiac development.

Results

In zebrafish, exposure to both types of cigarettes results in broad, dose-dependent developmental defects coupled with severe heart malformation, pericardial edema and reduced heart function. Tobacco cigarettes are more toxic than e-cigarettes at comparable nicotine concentrations. During cardiac differentiation of hESCs, tobacco smoke exposure results in a delayed transition through mesoderm. Both types of cigarettes decrease expression of cardiac transcription factors in cardiac progenitor cells, suggesting a persistent delay in differentiation. In definitive human cardiomyocytes, both e-cigarette- and tobacco cigarette-treated samples showed reduced expression of sarcomeric genes such as MLC2v and MYL6. Furthermore, tobacco cigarette-treated samples had delayed onset of beating and showed low levels and aberrant localization of N-cadherin, reduced myofilament content with significantly reduced sarcomere length, and increased expression of the immature cardiac marker smooth muscle alpha-actin.

Conclusion

These data indicate a negative effect of both tobacco cigarettes and e-cigarettes on heart development in vitro and in vivo. Tobacco cigarettes are more toxic than E-cigarettes and exhibit a broader spectrum of cardiac developmental defects.