Nonlinear mixed-modelling discriminates the effect of chemicals and their mixtures on zebrafish behavior

Determining bad actors: A linear mixed effects model approach to elucidate behavioral toxicity of metal mixtures in drinking water

Mixtures of chemical contaminants can pose a significant health risk to humans and wildlife, even at levels considered safe for each individual chemical. There is a critical need to develop statistical methods to evaluate the drivers of toxic effects in chemical mixtures (i.e., bad actors) from exposure studies. Here, we develop a hierarchical modeling framework to disentangle the toxicity of complex metal mixtures from a screening study of 92 drinking well water samples containing multiple metal elements from Maine and New Hampshire, USA. In order to screen for neurodevelopmental impacts from exposure to these drinking water samples, we use a larval zebrafish (Danio rerio) behavioral assay. Zebrafish are an advantageous toxicological model organism due to combining the complexity of a vertebrate organism and higher-throughput exposure methods. We formulate a linear mixed modeling approach that captures intrinsic complexity in a common larval behavioral assay in order to improve its sensitivity and rigor and identify drivers of behavioral toxicity from the metal mixtures within the drinking water samples. Our analysis identifies lead (Pb), cadmium (Cd), nickel (Ni), copper (Cu), barium (Ba), and uranium (U) as metals that consistently impact larval locomotor activity, individually and across nine pairs of those metals. Our model also elucidates three distinct clusters of metal mixture components that drive behavioral effects: (Ba:Cu:U), (Ni:Pb:U), (Ba:Pb:U). Having identified a set of "bad-actor" metals from the water samples, we conduct exposure experiments for each individual metal (Pb, Cd, Ni, Cu, and Ba) at levels considered safe by the US Environmental Protection Agency drinking water regulatory limits and validate Pb, Ni, Cu, and Ba as behavioral toxicants at these concentrations. Collectively, our modeling approach estimates the impact of metal elements on a complex behavioral outcome in a statistically robust manner and establishes an approach to capture "bad actors" and key chemical interactions in a complex mixture.

Key HPI axis receptors facilitate light adaptive behavior in larval zebrafish

The vertebrate stress response (SR) is mediated by the hypothalamic-pituitary-adrenal (HPA) axis and contributes to generating context appropriate physiological and behavioral changes. Although the HPA axis plays vital roles both in stressful and basal conditions, research has focused on the response under stress. To understand broader roles of the HPA axis in a changing environment, we characterized an adaptive behavior of larval zebrafish during ambient illumination changes. Genetic abrogation of glucocorticoid receptor (nr3c1) decreased basal locomotor activity in light and darkness. Some key HPI axis receptors (mc2r [ACTH receptor], nr3c1), but not nr3c2 (mineralocorticoid receptor), were required to adapt to light more efficiently but became dispensable when longer illumination was provided. Such light adaptation was more efficient in dimmer light. Our findings show that the HPI axis contributes to the SR, facilitating the phasic response and maintaining an adapted basal state, and that certain adaptations occur without HPI axis activity.

Statistical methods for chemical mixtures: a roadmap for practitioners

Quantitative characterization of the health impacts associated with exposure to chemical mixtures has received considerable attention in current environmental and epidemiological studies. With many existing statistical methods and emerging approaches, it is important for practitioners to understand when each method is best suited for their inferential goals. In this study, we conduct a review and comparison of 11 analytical methods available for use in mixtures research, through extensive simulation studies for continuous and binary outcomes. These methods fall in three different classes: identifying important components of a mixture, identifying interactions and creating a summary score for risk stratification and prediction. We carry out an illustrative data analysis in the PROTECT birth cohort from Puerto Rico. Most importantly we develop an integrated package "CompMix" that provides a platform for mixtures analysis where the practitioner can implement a pipeline for several types of mixtures analysis. Our simulation results suggest that the choice of methods depends on the goal of analysis and there is no clear winner across the board. For selection of important toxicants in the mixture and for identifying interactions, Elastic net by Zou et al. (Enet), Lasso for Hierarchical Interactions by Bien et al (HierNet), Selection of nonlinear interactions by a forward stepwise algorithm by Narisetty et al. (SNIF) have the most stable performance across simulation settings. Additionally, the predictive performance of the Super Learner ensembling method by Van de Laan et al. and HierNet are found to be superior to the rest of the methods. For overall summary or a cumulative measure, we find that using the Super Learner to combine multiple Environmental Risk Scores can lead to improved risk stratification properties. We have developed an R package "CompMix: A comprehensive toolkit for environmental mixtures analysis", allowing users to implement a variety of tasks under different settings and compare the findings. In summary, our study offers guidelines for selecting appropriate statistical methods for addressing specific scientific questions related to mixtures research. We identify critical gaps where new and better methods are needed.

Development of a trace quantitative method to investigate caffeine distribution in the Yellow and Bohai Seas, China, and assessment of its potential neurotoxic effect on fish larvae

Caffeine is an emerging contaminant in aquatic environments. The study utilized a validated method to investigate the presence and distribution of caffeine in the surface water of the Yellow and Bohai Seas, urban rivers, and the Yantai estuary area. The analytical method conforms to EPA guidelines and exhibits a limit of quantification that is 200 times lower than that of prior investigations. The study revealed that the highest concentration of 1436.4 ng/L was found in convergence of ocean currents in the Yellow and Bohai Seas. The presence of larger populations and the process of urban industrialization have been observed to result in elevated levels of caffeine in offshore regions, confirming that caffeine can serve as a potential indicator of anthropogenic contamination. Fish larvae exhibited hypoactivity in response to caffeine exposure at environmentally relevant concentrations. The study revealed that caffeine pollution can have adverse effects on marine and offshore ecosystems. This emphasizes the importance of decreasing neurotoxic pollution in the aquatic environment.

The canonical HPA axis facilitates and maintains light adaptive behavior

The vertebrate stress response (SR) is mediated by the hypothalamic-pituitary-adrenal (HPA) axis and contributes to generating context appropriate physiological and behavioral changes. Although the HPA axis plays vital roles both in stressful and basal conditions, research has focused on the response under stress. To understand broader roles of the HPA axis in a changing environment, we characterized an adaptive behavior of larval zebrafish during ambient illumination changes. The glucocorticoid receptor (nr3c1) was necessary to maintain basal locomotor activity in light and darkness. The HPA axis was required to adapt to light more efficiently but became dispensable when longer illumination was provided. Light adaptation was more efficient in dimmer light and did not require the mineralocorticoid receptor (nr3c2). Our findings show that the HPA axis contributes to the SR at various stages, facilitating the phasic response and maintaining an adapted basal state, and that certain adaptations occur without HPA axis activity.

A comprehensive pharmacological analysis of fenoterol and its derivatives to unravel the role of β2-adrenergic receptor in zebrafish

β-adrenergic receptors (βARs) belong to a key molecular targets that regulate the most important processes occurring in the human organism. Although over the last decades a zebrafish model has been developed as a model complementary to rodents in biomedical research, the role of β₂AR in regulation of pathological and toxicological effects remains to elucidate. Therefore, the study aimed to clarify the role of β₂AR with a particular emphasis on the distinct role of subtypes A and B of zebrafish β₂AR. As model compounds selective β₂AR agonists - (R,R)-fenoterol ((R,R)-Fen) and its new derivatives: (R,R)-4'-methoxyfenoterol ((R,R)-MFen) and (R,R)-4'-methoxy-1-naphtylfenoterol ((R,R)-MNFen) - were tested. We described dose-dependent changes observed after fenoterols exposure in terms of general toxicity, cardiotoxicity and neurobehavioural responses. Subsequently, to better characterise the role of β₂-adrenergic stimulation in zebrafish, we have performed a series of molecular docking simulations. Our results indicate that (R,R)-Fen displays the highest affinity for subtype A of zebrafish β₂AR and β_2AAR might be involved in pigment depletion. (R,R)-MFen shows the lowest affinity for zebrafish β₂ARs out of the tested fenoterols and this might be associated with its cardiotoxic and anxiogenic effects. (R,R)-MNFen displays the highest affinity for subtype B of zebrafish β₂AR and modulation of this receptor might be associated with the development of malformations, increases locomotor activity and induces a negative chronotropic effect. Taken together, the presented data offer insights into the functional responses of the zebrafish β₂ARs confirming their intraspecies conservation, and support the translation of the zebrafish model in pharmacological and toxicological research.

Zebrafish Is a Powerful Tool for Precision Medicine Approaches to Neurological Disorders

Personalized medicine is currently one of the most promising tools which give hope to patients with no suitable or no available treatment. Patient-specific approaches are particularly needed for common diseases with a broad phenotypic spectrum as well as for rare and yet-undiagnosed disorders. In both cases, there is a need to understand the underlying mechanisms and how to counteract them. Even though, during recent years, we have been observing the blossom of novel therapeutic techniques, there is still a gap to fill between bench and bedside in a patient-specific fashion. In particular, the complexity of genotype-to-phenotype correlations in the context of neurological disorders has dampened the development of successful disease-modifying therapeutics. Animal modeling of human diseases is instrumental in the development of therapies. Currently, zebrafish has emerged as a powerful and convenient model organism for modeling and investigating various neurological disorders. This model has been broadly described as a valuable tool for understanding developmental processes and disease mechanisms, behavioral studies, toxicity, and drug screening. The translatability of findings obtained from zebrafish studies and the broad prospect of human disease modeling paves the way for developing tailored therapeutic strategies. In this review, we will discuss the predictive power of zebrafish in the discovery of novel, precise therapeutic approaches in neurosciences. We will shed light on the advantages and abilities of this in vivo model to develop tailored medicinal strategies. We will also investigate the newest accomplishments and current challenges in the field and future perspectives.

Getting more out of the zebrafish light dark transition test

In (eco-)toxicological studies the light/dark transition (LDT) test is one of the most frequently used behaviour assays with zebrafish eleutheroembryos. However, study results vary regarding data presentation and analysis and mostly focus on a limited amount of the recorded data. In this study, we investigated whether monitoring two behavioural outcomes (time and distance moved) together with analysing multiple parameters can improve test sensitivity and data interpretation. As a proof of principle 5-day old zebrafish (Danio rerio) eleutheroembryos exposed to either endocrine disruptors (EDs) or acetylcholine esterase (AChE) inhibitors were investigated. We analysed conventional parameters such as mean and sum and implemented additional endpoints such as minimum or maximum distance moved and new parameters assessing the bursting response of eleutheroembryos. Furthermore, changes in eleutheroembryonic behaviour during the moment of the light to dark transition were added. To improve data presentation control-normalised results were displayed in radar charts, enabling the simultaneous presentation of different parameters in relation to each other. This enabled us to identify parameters most relevant to a certain behavioural response. A cut off threshold using control data was applied to identify parameters that were altered in a biological relevant manner. Our approach was able to detect effects on different parameters that remained undetected when analysis was done using conventional bar graphs on - in most cases analysed - averaged, mean distance moved values. By combining the radar charts with additional parameters and by using control-based thresholds, we were able to increase the test sensitivity and promote a deeper understanding of the behaviour response of zebrafish eleutheroembryos in the LDT test and thereby increased its usability for behavioural toxicity studies.

Environmental levels of venlafaxine impact larval behavioural performance in fathead minnows

Venlafaxine, a selective serotonin and norepinephrine reuptake inhibitor, is one of the most abundant antidepressants in municipal wastewater effluents (MWWE). The early life stages are particularly sensitive to contaminant exposure, but few studies have examined whether persistent exposure to venlafaxine impart adverse developmental outcomes. The fathead minnow (Pimephales promelas) is a widely used model for ecotoxicological studies, and this fish is native to Alberta, Canada. We tested the hypothesis that environmental levels of venlafaxine compromises early developmental behavioural performances in fathead minnows. Embryos were exposed to waterborne venlafaxine at either 0, 0.06, 0.33, 0.66, 1.37 or 3 μg L^-1 concentration for 7 days. Environmental levels of venlafaxine did not impact the survival, hatch rate or heart rate of fathead minnow embryos and larvae but reduced the growth of larvae even at concentrations as low as 0.06 μg L^-1. We validated thigmotaxis as a screen for anxiolytic and anxiogenic behaviour in fathead minnow larvae by exposing them to concentrations of ethanol and caffeine, respectively. Behavioural analyses revealed that early developmental exposure to venlafaxine does not alter thigmotaxis but reduced the activity of fathead minnows. The larval behavioural assays reported here for fathead minnow have the potential to be used as screening tools for the risk assessment of neurotoxic contaminants in MWWE. Overall, we demonstrate for the first time that exposure to environmental levels of venlafaxine during the critical early developmental window does not elicit an anxiogenic response but may adversely affect the larval growth performance of fathead minnows.

Aconitine disrupts serotonin neurotransmission via 5-hydroxytryptamine receptor in zebrafish embryo

Medicinal plants of the genus Aconitum are one of the most commonly used herbs in traditional medicine in East Asia to treat conditions related to the heart, pain, or inflammation. However, these herbs are also dangerous as accidental poisoning due to misuse is a recurring issue. These plants contain a number of diester-diterpenoid alkaloid compounds and aconitine is the most abundant and active one. This study investigated neurotoxicity of aconitine to zebrafish embryos in early development in relation to serotonin regulation. Experimental results showed that aconitine exposure (1, 10, and 100 μM) increased frequency of coiling behavior in zebrafish embryos in a dose-dependent manner and this effect can be triggered by either exposure to 5-hydroxytryptamine 1A (5-HT1A) receptor agonist (±)-8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT) or overexpression of serotonin receptor 5-htr1ab. At the same time, coiling behavior caused by aconitine exposure could be rescued by co-exposure to 5-HT1A receptor antagonist WAY-100635 Maleate (WAY100635) and knockdown of 5-htr1ab using morpholino. Exposure to aconitine also significantly increased serotonin receptor 5-htr1ab and 5-htr1bd gene expression at 24 h post fertilization (hpf), but decreased their expression and protein expression of the serotonin receptor at 96 hpf with the high dose. These results suggest that neurotoxicity caused by aconitine is mediated through the 5-HT receptor.

Vape flavourants dull sensory perception and cause hyperactivity in developing zebrafish embryos

E-cigarette use (vaping) during pregnancy has been increasing, and the potential exists for the developing brain in utero to be exposed to chemical constituents in the vape. Vapes come in over 7000 unique flavours with and without nicotine, and while nicotine is a known neurotoxicant, the effects of vape flavouring alone, in the absence of nicotine, on brain function are not well understood. Here, we performed a screen of vape aerosol extracts (VAEs) to determine the potential for prenatal neurotoxicity using the zebrafish embryo photomotor response (PMR)-a translational biosensor of neurobehavioural effects. We screened three commonly used aerosolized vape liquids (flavoured and flavourless) either with or without nicotine. No neurobehavioural effects were detected in flavourless, nicotine-free VAEs, while the addition of nicotine to this VAE dulled sensory perception. Flavoured nicotine-free VAEs also dulled sensory perception and caused hyperactivity in zebrafish embryos. The combination of flavour and nicotine produced largely additive effects. Flavoured VAEs without nicotine had similar neuroactive potency to nicotine. Together, using zebrafish PMR as a high throughput translational behavioural model for prenatal exposure, our results demonstrate that e-cigarette flavourants that we screened elicit neurobehavioural effects worthy of further investigation for long-term neurotoxic potential and also have the potential to modulate nicotine impact on the developing brain.

Recycled low-density polyethylene composite to mitigate the environmental impacts generated from coal mining waste in Brazil

Waste materials from coal mining and consumer products can pose significant risks to the environment. Residual coal deposits lead to the formation of acid drainage and release of contaminants, causing negative changes in soil and aquatic systems. Low density polyethylene (LDPE) polymers are an environmental concern due to their high useage, and slow degradation in the environment. In this study both waste materials were used to develop a composite to mitigate the environmental impacts of coal mining waste (CMW). The composite material was produced in different formulations (0-80 % wt CMW), and samples were tested for formation of acid drainage and release of contaminants. Chemical characterisation of the CMW and leachate of the composite materials was performed by X-ray fluorescence and atomic absorption spectrometry. Ecotoxicological effects in soil and water were investigated using standard tests with the earthworm, Eisenia fetida, the collembolan, Folsomia candida and the bacterium, Aliivibrio fischeri. Composites with 20 % wt LDPE showed a 50% increase in the pH value of the leachate compared to the CMW leachate. Iron, aluminium and sulfate concentrations were lower in leachates of the composite materials, and a reduction in the ecotoxicological impact on the tested organisms was observed. The hydrophobic nature of the composite's polymeric matrix as well its physical properties contributed to a better coating of the coal residue particles, blocking the contact with water and reducing the environmental risks of CMW. These results show that the production of composite material is a viable alternative route for treating coal and LDPE waste.

Municipal wastewater effluent exposure disrupts early development, larval behavior, and stress response in zebrafish

While wastewater treatment standards have been progressively increasing, emerging contaminants such as pharmaceuticals can nonetheless pass through treatment and end up in our watersheds. Pharmaceuticals in the parts-per-billion range can impact fish behavior, survival, and recruitment in the wild. However, the ecological risk posed by whole municipal wastewater effluents (MWWE), a complex mixture, is not clear. This knowledge gap is particularly evident for early lifestages (ELS) of fish, and because effluent discharge events are typically short, the effects of short-term MWWE exposures to ELS fish are particularly important from an environmental perspective. Here we tested the effects of rapid 30-min exposures, and short-term 24- and 72-h exposures to MWWE on development, behaviors, and stress response in zebrafish (Danio rerio) embryos, larvae, and juveniles. We obtained 24-h composite samples of tertiary-treated MWWE that contained a mixture of chemicals with affinities for serotonergic, adrenergic, dopaminergic, and ion-channel receptors. Embryos exposed to 5%, 10%, and 50% MWWE experienced developmental delays in somitogenesis and hatching rate, although there was no effect on survival. Embryonic photomotor responses were affected following 30-min and 24-h exposures to 10% and 50% MWWE, and larval visual motor responses were reduced from 24-h exposure to 10% MWWE. Exposure to 10% MWWE dulled the juvenile cortisol and lactate response following an acute air-exposure. Compromised behavioral and stress performances demonstrate the capacity of MWWE to impact phenotypes critical to the survival of fish in the environment. Taken together, we found that zebrafish were sensitive to toxic effects of MWWE at multiple life-stages.

A rapid zebrafish embryo behavioral biosensor that is capable of detecting environmental β-blockers

β-Blockers (BB) are one of the most commonly prescribed pharmaceuticals used for treating cardiovascular and acute anxiety-related disorders. This class of drugs inhibit β-adrenoceptor signalling and given their growing, widespread use, BB are routinely detected in surface waters at nM concentrations. This is concerning as trace levels of BB impart developmental and reproductive dysfunction in non-target aquatic organisms, with potential for ecological risks. To date, environmental pharmaceutical risks to non-target animals are not part of the monitoring framework due to the lack of bioassays for assessing their biological effects. Behavioral endpoints have the advantage of a systems-level integration of multiple sensory signals and motor responses for toxicity screening; however, they are not currently used for risk assessment of environmental contaminants. The zebrafish (Danio rerio) embryo photomotor response (zfPMR) has been used in high-throughput behavioral screenings for neuroactive drug effects at high, therapeutic concentrations. Our objective here was to examine if we could utilize the zfPMR for screening environmental levels of BB. Embryos were placed into 96-well plates, exposed to chemicals and/or municipal wastewater effluent (MWWE), and their zfPMRs were measured with video-analysis. To specifically target BB, embryos were co-treated with isoproterenol, a β-adrenergic agonist that stimulates the zfPMR, and the inhibition of isoproterenol-induced response was used as a biomarker of BB exposure. Our results reveal that the inhibition of isoproterenol-stimulated zfPMRs can be used as a biosensor capable of detecting BB in the parts-per-billion to parts-per-trillion in water samples, including diluted MWWE. The method developed detects BB in spite of the presence of other neuroactive compounds in water samples. This systems level approach of rapid screening for BB effects provides the most promising evidence to date that behavioral neuromodulation can be potentially applied for environmental effects monitoring of pharmaceuticals.