Effects of Single and Combined Low Concentrations of Neuroactive Drugs on Daphnia magna Reproduction and Transcriptomic Responses

Environmental Risks of Pharmaceutical Mixtures in Aquatic Ecosystems: Reflections on a Decade of Research

Pharmaceuticals and personal care products (PPCPs) occur as variable mixtures in surface waters receiving discharges of human and animal wastes. A key question identified a decade ago is how to assess the effects of long-term exposures of these PPCP mixtures on nontarget organisms. We review the recent progress made on assessing the aquatic ecotoxicity of PPCP mixtures-with a focus on active pharmaceutical ingredients-and the challenges and research needs that remain. New knowledge has arisen from the use of whole-mixture testing combined with component-based approaches, and these studies show that mixtures often result in responses that meet the concentration addition model. However, such studies have mainly been done on individual species over shorter time periods, and longer-term, multispecies assessments remain limited. The recent use of targeted and nontargeted gene analyses has improved our understanding of the diverse pathways that are impacted, and there are promising new "read-across" methods that use mammalian data to predict toxicity in wildlife. Risk assessments remain challenging given the paucity of ecotoxicological and exposure data on PPCP mixtures. As such, the assessment of PPCP mixtures in aquatic environments should remain a priority given the potential for additive-as well as nontarget-effects in nontarget organisms. In addition, we need to improve our understanding of which species, life stages, and relevant endpoints are most sensitive to which types of PPCP mixtures and to expand our knowledge of environmental PPCP levels in regions of the globe that have been poorly studied to date. We recommend an increased use of new approach methodologies, in particular "omics," to advance our understanding of the molecular mechanics of mixture effects. Finally, we call for systematic research on the role of PPCP mixtures in the development of antimicrobial resistance. Environ Toxicol Chem 2024;43:549-558. © 2023 SETAC.

Systematic analysis of circadian disrupting substances with a high-throughput zebrafish circadian behavior screening approach

Circadian rhythm aligns numerous biological functions in majority of animals. Aside from well-known external factors such as the light-dark cycle and temperature, circadian rhythm can also be regulated by rarely explored factors such as synthetic substances. Here, we established a circadian behavior screening approach utilizing zebrafish larvae model, which integrated high-throughput capabilities with automated batch processing. With this approach, we systematically analyzed the circadian disruptive effects of >60 synthetic substances commonly detected in aquatic environment by assessing both the circadian period length and amplitude of circadian behavior, with an exposure concentration set at 100 μg/L. Among tested substances, a series of circadian disrupting compounds (circadian disruptors) were identified. Several categories of the hit compounds can be recognized, such as phthalate (diisopentyl phthalate (DIPP), with 10.1 % and 49.6 % increases for circadian period length and amplitude, respectively), neuroactive substance (mirtazapine, with 10.6 % and 63.1 % increases, respectively), and biocides (thiamethoxam, with 100.3 % increase for amplitude). Among these compounds, DIPP increased circadian period length and amplitude with a high degree. Aside from DIPP, we further examined eleven other phthalates and demonstrated that benzyl butyl phthalate, diisobutyl phthalate and diisohexyl phthalate could also significantly increase the zebrafish circadian period length by 7.9 %, 3.7 % and 8.5 %, respectively. Collectively, the present findings substantiated the feasibility of this high throughput screening strategy for circadian disruptor's discovery and provided novel insights into understanding of the potential risks of synthetic substances.

Freshwater crustacean exposed to active pharmaceutical ingredients: ecotoxicological effects and mechanisms

Concerns over the ecotoxicological effects of active pharmaceutical ingredients (APIs) on aquatic invertebrates have been raised in the last decade. While numerous studies have reported the toxicity of APIs in invertebrates, no attempt has been made to synthesize and interpret this dataset in terms of different exposure scenarios (acute, chronic, multigenerational), multiple crustacean species, and the toxic mechanisms. In this study, a thorough literature review was performed to summarize the ecotoxicological data of APIs tested on a range of invertebrates. Therapeutic classes including antidepressants, anti-infectives, antineoplastic agents, hormonal contraceptives, immunosuppressants, and neuro-active drugs exhibited higher toxicity to crustaceans than other API groups. The species sensitivity towards APIs exposure is compared in D. magna and other crustacean species. In the case of acute and chronic bioassays, ecotoxicological studies mainly focus on the apical endpoints including growth and reproduction, whereas sex ratio and molting frequency are commonly used for evaluating the substances with endocrine-disrupting properties. The multigenerational and "Omics" studies, primarily transcriptomics and metabolomics, were confined to a few API groups including beta-blocking agents, blood lipid-lowing agents, neuroactive agents, anticancer drugs, and synthetic hormones. We emphasize that in-depth studies on the multigenerational effects and the toxic mechanisms of APIs on the endocrine systems of freshwater crustacean are warranted.

Characterizing nutritional phenotypes using experimental nutrigenomics: Is there nutrient-specificity to different types of dietary stress?

The ability to directly measure and monitor poor nutrition in individual animals and ecological communities is hampered by methodological limitations. In this study, we use nutrigenomics to identify nutritional biomarkers in a freshwater zooplankter, Daphnia pulex, a ubiquitous primary consumer in lakes and a sentinel of environmental change. We grew animals in six ecologically relevant nutritional treatments: nutrient replete, low carbon (food), low phosphorus, low nitrogen, low calcium and high Cyanobacteria. We extracted RNA for transcriptome sequencing to identify genes that were nutrient responsive and capable of predicting nutritional status with a high degree of accuracy. We selected a list of 125 candidate genes, which were subsequently pruned to 13 predictive potential biomarkers. Using a nearest-neighbour classification algorithm, we demonstrate that these potential biomarkers are capable of classifying our samples into the correct nutritional group with 100% accuracy. The functional annotation of the selected biomarkers revealed some specific nutritional pathways and supported our hypothesis that animal responses to poor nutrition are nutrient specific and not simply different presentations of slow growth or energy limitation. This is a key step in uncovering the causes and consequences of nutritional limitation in animal consumers and their responses to small- and large-scale changes in biogeochemical cycles.

Transcriptomic responses to cytotoxic drug cisplatin in water flea Daphnia magna

Cytotoxic drugs have been recognized by the European Union as the potential threat in the aquatic environment. As a typical cytotoxic drug, effects of long-term exposure to cisplatin at the environmentally relevant concentrations on the crustacean health and its molecular mechanism remain undetermined. In this study, the growth and reproduction of Daphnia magna resulting from cisplatin exposure were initially assessed. While the phenotypes were not altered in 2 μg L^-1, 20 μg L^-1, and 200 μg L^-1 treatment groups, cisplatin at 500 µg L^-1 significantly reduced the offspring number to 8-13 neonates in each brood, which was lower than 13-27 neonates in the control group. In addition to the delay in the time of first pregnancy, the body length was decreased by approximate 12.13% at day 7. Meanwhile, all daphnids died after exposure to 500 µg L^-1 cisplatin for 17 days. Transcriptome profiling bioassays were performed for 10 days to explore the alternation at the molecular level. Briefly, 980 (257 up- and 723 down-regulated), 429 (182 up- and 247 down-regulated) and 1984 (616 up-regulated and 1368 down-regulated) genes were differentially expressed (adj p < 0.05) in low (2 μg L^-1), medium (200 μg L^-1) and high (500 μg L^-1) cisplatin treatment groups, respectively. Differentially expressed genes were primarily enriched in the digestion and absorption, nerve conduction, endocrine interference, and circulatory related pathways. Specifically, the down-regulated digestive secretion and nutrient absorption and neuronal conduction pathways may lead to insufficient energy supply involved in growth and reproduction, and hinder ovarian development and cell growth. Down-regulation of ovarian steroids and relaxin signaling pathways may be related to the reduction of offspring number and delayed pregnancy, and reduced body length of D. magna may attribute to the enrichment of insulin secretion pathway. In addition, the death of D. magna may result from the reduced expression of genes in cardiomyocyte contraction and apoptosome processes. Taken together, this study revealed the potential toxic mechanism of cisplatin in a model water flea.

Toxic Effects of Two Representative Rare Earth Elements (La and Gd) on Danio rerio Based on Transcriptome Analysis

The expanding applications of rare earth elements (REEs) in various fields have raised concerns about their biosafety. However, previous studies are insufficient to elucidate their toxic effects and mechanisms of action and whether there are uniform or predictable toxicity patterns among REEs. Herein, we investigated the toxic effects of two representative REEs (lanthanum (La) and gadolinium (Gd)) on zebrafish (Danio rerio) through toxicity experiments and transcriptome analysis. The results of the toxicity experiments showed that the two REEs have similar lethality, with half-lethal concentrations (LC50) at micromolar levels and mixed toxicity showing additive effects. Differential expression gene screening and functional group enrichment analysis showed that La and Gd might affect the growth and development of Danio rerio by interfering with some biological molecules. The two REEs showed significant effects on the metabolic pathways of exogenous or endogenous substances, including glutathione sulfotransferase and acetaldehyde dehydrogenase. Moreover, some basic biological processes, such as DNA replication, the insulin signaling pathway, and the p53 signaling pathway, were significantly enriched. Overall, the toxicity patterns of La and Gd may affect some biological processes with different intensities; however, there are many similarities in their toxicity mechanisms and modes of action. The concentrations investigated in this study were comparable to those of REE residues at highly contaminated sites, thus mimicking the ecotoxicological effects at environmentally relevant concentrations.

Investigating the toxically homogenous effects of three lanthanides on zebrafish

The adverse effects of rare earth elements (REEs) have been increasingly reported in the past decades and have raised concern about their environmental toxicities. However, the available data is insufficient to elucidate the toxic effects, mechanisms, and whether the toxicity across all REEs is uniform. In this study, zebrafish were exposed to 0, 0.8, 1.6, 3.2, 6.4, 12.8 and 25.6 mg/L Ln(NO₃)₃•6H₂O to test the acute toxicity of La(III), Ce(III), and Nd(III). LC₅₀ of the three lanthanides was compared to the extent of the impact on gene expression. We carried out the functionally grouped network-based transcriptome analysis using gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) to explore the molecular mechanisms. The acute toxicity test showed that LC₅₀ of La(III), Ce(III), and Nd(III) were 2.53, 2.03, and 2.76 mg/L, respectively. Consistent with acute toxicity, Ce(III) caused a little more DEGs than La(III) and Nd(III). Some biological processes such as metabolism of xenobiotics, oocyte meiosis, steroid biosynthesis, DNA replication, and p53 signaling pathway were affected following exposure of all the three lanthanides. Ce(III) also induced changes in the chemokine-mediated signaling pathway. The results indicated that the lethality is comparable, and the toxic patterns are similar across the three lanthanides. This study gives comparative research on the toxicities of three lanthanides to model organism zebrafish.

Effects of the anxiolytic benzodiazepine oxazepam on freshwater gastropod reproduction: a prospective study

Psychoactive drugs have emerged as contaminants over the last few decades. These drugs are frequently prescribed and poorly eliminated by wastewater treatment plants, and many are present at non-negligible concentrations in surface waters. Several studies have investigated the non-target organism toxicity of one such drug, oxazepam, a benzodiazepine anxiolytic frequently detected in rivers. However, very little is known about the impact of this drug on reproduction. We investigated the effects of environmentally relevant concentrations of oxazepam on Radix balthica, a freshwater gastropod widespread in Europe. We identified the reproductive organs of Radix balthica. We then exposed this gastropod to oxazepam for two months and assessed several reproductive parameters, from reproductive organ status to behavioral parameters. We found that adults exposed to 10 µg/L oxazepam display an increase in the density of spermatozoa, and that adults exposed to 0.8 µg/L oxazepam displayed a decrease in the number of eggs per egg mass over time. By contrast, oxazepam had no effect on shell length, the size of male reproductive organs or social interactions. Finally, a locomotor activity analysis showed the distance covered over time decreased in all conditions of exposure to oxazepam, potentially reflecting a disturbance of exploratory activity. These results shed light on the effects of oxazepam on the reproduction of a non-target freshwater mollusk.

Daphnia magna Gut-Specific Transcriptomic Responses to Feeding Inhibiting Chemicals and Food Limitation

Transcriptomic responses combined with apical adverse ecologically relevant outcomes have proven to be useful to unravel and anchor molecular mechanisms of action to adverse outcomes. This is the case for feeding inhibition responses in the model ecotoxicological species Daphnia magna. The aim of the present study was to assess the transcriptomic responses in guts dissected from D. magna individuals exposed to concentrations of selected compounds that inhibit feeding and compare them with the responses associated to 2 levels of food restriction (low food and starvation). Chemical treatments included cadmium, copper, fluoranthene, λ-cyhalothrin, and the cyanotoxin anatoxin-a. Although the initial hypothesis was that exposure to chemical feeding inhibitors should elicit similar molecular responses as food limitation, the corresponding gut transcriptomic responses differed significantly. In moderate food limitation conditions, D. magna individuals increased protein and carbohydrate catabolism, likely to be used as energetic sources, whereas under severe starving conditions most metabolism-related pathways appeared down-regulated. Treatment with chemical feeding inhibitors promoted cell turnover-related signaling pathways in the gut, probably to renew tissue damage caused by the reported oxidative stress effects of these compounds, and inhibited the transcription of gut digestive gene enzymes and energetic metabolic pathways. We conclude that chemical feeding inhibitors, rather than mimicking the physiological response to low- or no-food conditions, cause specific toxic effects, preventing Daphnia both from feeding and from adjusting its metabolism to the resulting low energy intake. Environ Toxicol Chem 2021;40:2510-2520. © 2021 SETAC.

Toxicogenomic differentiation of functional responses to fipronil and imidacloprid in Daphnia magna

Active substances of pesticides, biocides or pharmaceuticals can induce adverse side effects in the aquatic ecosystem, necessitating environmental hazard and risk assessment prior to substance registration. The freshwater crustacean Daphnia magna is a model organism for acute and chronic toxicity assessment representing aquatic invertebrates. However, standardized tests involving daphnia are restricted to the endpoints immobility and reproduction and thus provide only limited insights into the underlying modes-of-action. Here, we applied transcriptome profiling to a modified D. magna Acute Immobilization test to analyze and compare gene expression profiles induced by the GABA-gated chloride channel blocker fipronil and the nicotinic acetylcholine receptor (nAChR) agonist imidacloprid. Daphnids were expose to two low effect concentrations of each substance followed by RNA sequencing and functional classification of affected gene ontologies and pathways. For both insecticides, we observed a concentration-dependent increase in the number of differentially expressed genes, whose expression changes were highly significantly positively correlated when comparing both test concentrations. These gene expression fingerprints showed virtually no overlap between the test substances and they related well to previous data of diazepam and carbaryl, two substances targeting similar molecular key events. While, based on our results, fipronil predominantly interfered with molecular functions involved in ATPase-coupled transmembrane transport and transcription regulation, imidacloprid primarily affected oxidase and oxidoreductase activity. These findings provide evidence that systems biology approaches can be utilized to identify and differentiate modes-of-action of chemical stressors in D. magna as an invertebrate aquatic non-target organism. The mechanistic knowledge extracted from such data will in future contribute to the development of Adverse Outcome Pathways (AOPs) for read-across and prediction of population effects.

Effects of butyl benzyl phthalate exposure on Daphnia magna growth, reproduction, embryonic development and transcriptomic responses

Butyl benzyl phthalate (BBP) is widely used as a plasticizer to increase the plasticity and flexibility of plastic products. Although the potential health hazards of BBP have recently received extensive attention, its toxicological properties and mechanisms remain largely undefined. In the present work, growth, reproductive and developmental toxicity of BBP to Daphnia magna were evaluated, and the transcriptomic alteration of early embryos upon BBP exposure was analyzed. In a 21-day chronic toxicity test, reduced survival ratio, decreased body length, increased abnormal ratio, advanced time to first brood, and reduced offspring of D. magna were observed. BBP exposure inhibited expression of the vitellogenin gene. In addition, embryotoxicity of BBP was observed, which showed not only in the induction of abnormal neonates, but also in the shortened embryonic development cycle. RNA-Seq of early embryo treated with 0.1 mg/L BBP indicated that the pathways involved in signal transduction, cell communication, and embryonic development were significantly down-regulated, while those of biosynthesis, metabolism, cell homeostasis, redox homeostasis were remarkably up-regulated upon BBP exposure, which was consistent with the above phenotypic results. Taken together, our results highlight the toxic effects of BBP on the embryonic development and larval growth of D. magna.

Acute and chronic effects of diazepam on the polychaete Hediste diversicolor: Antioxidant, metabolic, pharmacologic, neurotoxic and behavioural mechanistic traits

Pharmaceutical drugs are widespread environmental contaminants, but data about their adverse effects are still limited to a few compounds. This study analyzed the acute (96 h) and chronic (28 days) impacts of environmentally realistic levels of diazepam (acute exposure: 0.001, 0.01, 0.1, 1, 10 μg/L; chronic exposure: 0.1, 1, 10, 100, 1000 ng/L), in the polychaete Hediste diversicolor, by measuring behavioral and biochemical (catalase [CAT], glutathione-S-transferases [GSTs], cholinesterases [ChEs], glutathione peroxidase [GPx], lipid peroxidation [TBARS]) parameters. Acute exposure to diazepam altered behavioral traits, decreasing burrowing times and causing hyperactivity, whilst burrowing time increased and hypoactivity resulted after chronic exposure. All biomarkers were affected after the chronic exposure, with the exception of lipid peroxidation. Our data demonstrate that realistic levels of diazepam may impair behavioral and biochemical traits in polychaetes, suggesting that diazepam exposure presents a significant challenge to the environment that supports these organisms.

Characterization of neurotransmitters and related metabolites in Daphnia magna juveniles deficient in serotonin and exposed to neuroactive chemicals that affect its behavior: A targeted LC-MS/MS method

Neurotransmitters are endogenous metabolites that play a crucial role within an organism, at the chemical synapses. There is a growing interest in their analytical determination for understanding the neurotoxic effect of contaminants. Daphnia magna represents an excellent aquatic model for these environmental studies, due to its similarities with vertebrates in several neurotransmitters and related gene pathways and because of its wide application in ecotoxicological studies. Within this study, an accurate and sensible method of analysis of 17 neurotransmitters and related precursors and metabolites was developed. The method was validated in terms of sensitivity, reproducibility, precision, and accuracy, and also matrix effect was evaluated. As an independent probe of method validation and applicability, the method was applied to two different scenarios. First, it was used for the study of neurotransmitter levels in genetically mutated tryptophan hydrolase D. magna clones, confirming the absence of serotonin and its metabolite 5-HIAA. Additionally, the method was applied for determining the effects of chemical compounds known to affect different neurotransmitter systems and to alter Daphnia behavior. Significant changes were observed in 13 of the analyzed neurotransmitters across treatments, which were related to the neurotransmitter systems described as being affected by these neurochemicals. These two studies, which provide results on the ways in which the neurotransmitter systems in D. magna are affected, have corroborated the applicability of the presented method, of great importance due to the suitability of this organism for environmental neurotoxicity studies.

Changes in lipid profiles in Daphnia magna individuals exposed to low environmental levels of neuroactive pharmaceuticals

Disruptive effects of chemicals on lipids in aquatic species are mostly limited to obesogens and vertebrates. Recent studies reported that antidepressants, anxiolytic, antiepileptic and β-adrenergic pharmaceuticals, with putative distinct mechanisms of action at low environmental relevant concentrations, up-regulated common neurological and lipid metabolic pathways and enhanced similarly reproduction in the crustacean Daphnia magna. Conversely CRISPR mutants for the tryptophan hydrolase enzyme gene (TRH) that lack serotonin had the opposed phenotype: the lipid metabolism down-regulated and impaired reproduction. Lipid metabolism is strongly linked to reproduction in D. magna. The aim of this study is to test if the above mentioned neuro-active chemicals disrupted common lipid groups and showed also the opposed lipidomic effects as those individuals lacking serotonin. This study used ultra-high performance liquid chromatography/time-of-flight mass spectrometry (UHPLC/TOFMS) to study how neuro-active chemicals (carbamazepine, diazepam, fluoxetine and propranolol) at low (0.1 μg/L) and higher concentrations (1 μg/L) and three CRISPR TRH mutant clones disrupt the dynamics of glycerophospholipids and glycerolipids in Daphnia adults. Lipidomic analysis identified 267 individual lipids corresponding to three classes of glycerolipids, eleven of glycerophospholipids, one of sterols and one of sphingolipids, of which 132 and 125 changed according to the chemical treatments or across clones, respectively. Most pharmaceutical treatments enhanced reproduction whereas mutated clones lacking serotonin reproduced to a lesser extent. Except for carbamazepine, most of the tested pharmaceuticals increased some triacylglycerol species and decreased monoacylglycerols, lysophospholipids, sphingomyelins and cholesterol esters in exposed females. Opposed lipidomic pattern was observed in mutated clones lacking serotonin. Lipidomic data, thus, indicate a close link between reported transcriptomic and lipidomic changes, which are likely related to serotonin and other neurological signalling pathways.

Ketoprofen affects swimming behavior and impairs physiological endpoints of Daphnia magna

Ketoprofen (KET) is a nonsteroidal anti-inflammatory and analgesic drug commonly used in human and veterinary medicine. This compound is detected in aquatic reservoirs however, little is known about its influence on cladocerans. Therefore, the aim of our study was to determine the influence of KET at concentrations of 0.005 mg/L, 0.05 mg/L, 0.5 mg/L, 5 mg/L and 50 mg/L on behavioral (swimming speed, hopping frequency) and physiological endpoints (heart rate, thoracic limb activity, mandible movements) of Daphnia magna after 24 h and 48 h exposure. The study showed that swimming speed frequency was decreased after 24 h and 48 h at all the concentrations used in the experiment. Hopping frequency was also inhibited, however the lowest amount of the drug induced transient increase of the parameter after 24 h and its subsequent decrease to the control level after 48 h. Although after 24 h of the exposure physiological parameters: heart rate, thoracic limb activity and mandible movements showed slightly lower sensitivity to KET than the behavioral endpoints: were found to be inhibited after 48 h. The results revealed that both behavioral and physiological endpoints of daphnids responded to KET also at the environmental level, therefore in natural conditions this drug should be considered as a hazardous toxicant to crustaceans.