Gene expression profiling in zebrafish embryos exposed to diclofenac, an environmental toxicant

Phenotypic and metabolic adaptations of Rhodococcus cerastii strain IEGM 1243 to separate and combined effects of diclofenac and ibuprofen

Introduction

The increasing use of non-steroidal anti-inflammatory drugs (NSAIDs) has raised concerns regarding their environmental impact. To address this, understanding the effects of NSAIDs on bacteria is crucial for bioremediation efforts in pharmaceutical-contaminated environments. The primary challenge in breaking down persistent compounds lies not in the biochemical pathways but in capacity of bacteria to surmount stressors.

Methods

In this study, we examined the biodegradative activity, morphological and physiological changes, and ultrastructural adaptations of Rhodococcus cerastii strain IEGM 1243 when exposed to ibuprofen, diclofenac, and their mixture.

Results and Discussion

Our findings revealed that R. cerastii IEGM 1243 exhibited moderate biodegradative activity towards the tested NSAIDs. Cellular respiration assay showed higher metabolic activity in the presence of NSAIDs, indicating their influence on bacterial metabolism. Furthermore, catalase activity in R. cerastii IEGM 1243 exposed to NSAIDs showed an initial decrease followed by fluctuations, with the most significant changes observed in the presence of DCF and the NSAID mixture, likely influenced by bacterial growth phases, active NSAID degradation, and the formation of multicellular aggregates, suggesting potential intercellular synergy and task distribution within the bacterial community. Morphometric analysis demonstrated alterations in size, shape, and surface roughness of cells exposed to NSAIDs, with a decrease in surface area and volume, and an increase in surface area-to-volume ratio (SA/V). Moreover, for the first time, transmission electron microscopy confirmed the presence of lipid inclusions, polyphosphates, and intracellular membrane-like structures in the ibuprofen-treated cells.

Conclusion

These results provide valuable insights into the adaptive responses of R. cerastii IEGM 1243 to NSAIDs, shedding light on the possible interaction between bacteria and pharmaceutical compounds in the environment.

Pharmaceuticals in the Aquatic Environment: A Review on Eco-Toxicology and the Remediation Potential of Algae

The pollution of the aquatic environment has become a worldwide problem. The widespread use of pesticides, heavy metals and pharmaceuticals through anthropogenic activities has increased the emission of such contaminants into wastewater. Pharmaceuticals constitute a significant class of aquatic contaminants and can seriously threaten the health of non-target organisms. No strict legal regulations on the consumption and release of pharmaceuticals into water bodies have been implemented on a global scale. Different conventional wastewater treatments are not well-designed to remove emerging contaminants from wastewater with high efficiency. Therefore, particular attention has been paid to the phycoremediation technique, which seems to be a promising choice as a low-cost and environment-friendly wastewater treatment. This technique uses macro- or micro-algae for the removal or biotransformation of pollutants and is constantly being developed to cope with the issue of wastewater contamination. The aims of this review are: (i) to examine the occurrence of pharmaceuticals in water, and their toxicity on non-target organisms and to describe the inefficient conventional wastewater treatments; (ii) present cost-efficient algal-based techniques of contamination removal; (iii) to characterize types of algae cultivation systems; and (iv) to describe the challenges and advantages of phycoremediation.

Thyroid disrupting effects of low-dose dibenzothiophene and cadmium in single or concurrent exposure: New evidence from a translational zebrafish model

Thyroid hormones (THs) are major regulators of biological processes essential for correct development and energy homeostasis. Although thyroid disruptors can deeply affect human health, the impact of exogenous chemicals and in particular mixture of chemicals on different aspects of thyroid development and metabolism is not yet fully understood. In this study we have used the highly versatile zebrafish model to assess the thyroid axis disrupting effects of cadmium (Cd) and dibenzothiophene (DBT), two environmental endocrine disruptors found to be significantly correlated in epidemiological co-exposure studies. Zebrafish embryos (5hpf) were exposed to low concentrations of Cd (from 0.05 to 2 μM) and DBT (from 0.05 to 1 μM) and to mixtures of them. A multilevel assessment of the pollutant effects has been obtained by combining in vivo morphological analyses allowed by the use of transgenic fluorescent lines with liquid chromatography mass spectrometry determination of TH levels and quantification of the expression levels of key genes involved in the Hypothalamic-Pituitary-Thyroid Axis (HPTA) and TH metabolism. Our results underscore for the first time an important synergistic toxic effect of these pollutants on embryonic development and thyroid morphology highlighting differences in the mechanisms through which they can adversely impact on multiple physiological processes of the HPTA and TH disposal influencing also heart geometry and function.

Feeding regimes modulate biomarkers responsiveness in mussels treated with diclofenac

This study investigated the role of the feeding regime on cellular (lysosomal membrane impairment), oxidative (superoxides and nitric oxides generation, as well as lipid peroxidation) and genotoxic (nuclear abnormalities) biomarkers measured in hemocytes of mussels Mytilus galloprovincialis treated with diclofenac (DCF). Specifically, unfed mussels, or mussels fed ad libitum with algal species Tisochrysis lutea or Tetraselmis suecica (Tiso/DCF- and Tetra/DCF- treated mussels, respectively) were exposed to DCF (20 μgL^-1) for 4 days. The results showed that biomarkers' responsiveness against DCF, were more pronounced in unfed and Tetra/DCF-, rather than Tiso/DCF- treated mussel hemocytes, thus revealing food deprivation, changes in mussel feeding/filtration rate and digestion processes, as potent factors of mussels' immune efficiency and response against DCF. Those findings could provide valuable data for the optimization of mussels' feeding regime during laboratory studies, in order to assess reliably the effects of emerging contaminants on non-target sentinel organisms, such as mussels.

Occurrence, interactive effects and ecological risk of diclofenac in environmental compartments and biota - a review

Diclofenac, a nonsteroidal anti-inflammatory drug has turned into a contaminant of emerging concern; hence, it was included in the previous Watch List of the EU Water Framework Directive. This review paper aims to highlight the metabolism of diclofenac at different trophic levels, its occurrence, ecological risks, and interactive effects in the water cycle and biota over the past two decades. Increased exposure to diclofenac not only raises health concerns for vultures, aquatic organisms, and higher plants but also causes serious threats to mammals. The ubiquitous nature of diclofenac in surface water (river, lake canal, estuary, and sea) is compared with drinking water, groundwater, and wastewater effluent in the environment. This comprehensive survey from previous studies suggests the fate of diclofenac in wastewater treatment plants (WWTPs) and may predict its persistence in the environment. This review offers evidence of fragmentary available data for the water environment, soil, sediment, and biota worldwide and supports the need for further data to address the risks associated with the presence of diclofenac in the environment. Finally, we suggest that the presence of diclofenac and its metabolites in the environment may represent a high risk because of their synergistic interactions with existing contaminants, leading to the development of drug-resistant strains and the formation of newly emerging pollutants.

Combined Ion-Trapping and Mass Balance Models To Describe the pH-Dependent Uptake and Toxicity of Acidic and Basic Pharmaceuticals in Zebrafish Embryos ( Danio rerio)

The aim of the current study was to understand and develop models to predict the pH-dependent toxicity of ionizable pharmaceuticals in embryos of the zebrafish Danio rerio. We found a higher uptake and toxicity with increasing neutral fraction of acids (diclofenac, genistein, naproxen, torasemide, and warfarin) and bases (metoprolol and propranolol). Simple mass balance models accounting for the partitioning to lipids and proteins in the zebrafish embryo were found to be suitable to predict the bioconcentration after 96 h of exposure if pH values did not differ much from the internal pH of 7.55. For other pH values, a kinetic ion-trap model for the zebrafish embryo explained the pH dependence of biouptake and toxicity. The total internal lethal concentrations killing 50% of the zebrafish embryos (ILC₅₀) were calculated from the measured BCF and LC₅₀. The resulting ILC₅₀ were independent of external pH. Critical membrane concentrations were deduced by an internal mass balance model, and apart from diclofenac, whose specific toxicity in fish had already been established, all pharmaceuticals were confirmed to act as baseline toxicants in zebrafish.

Determination and toxicity evaluation of the generated byproducts from sulfamethazine degradation during catalytic oxidation process

Sulfamethazine (SMZ), a kind of sulfonamide antibiotics, can exist for a long periods of time and has been widely detected in the environment, which could pose a potential health threat to human beings. In this study, sludge-derived carbon (SC) catalyst was modified and applied to degrade SMZ during catalytic oxidation process. Degradation products and possible transformation pathways were investigated based on data of GC-MS. The toxicity evolution of SMZ degradation after catalytic oxidation process was tested with zebrafish and microbial degradation respirometer. As a consequence, SC modified with nitric acid (SCHNO₃) exhibited highly catalytic efficiency reached 92.2% SMZ conversion and 75.2% total organic carbon (TOC) removal rate after 480 min. Ten kinds of possible products were identified by GC-MS during degradation process of SMZ, indicating two possible pathways. No pronounced malformation was observed in the toxicity experiments with zebrafish until 120 h post fertilization (hpf). However, further analysis showed that zebrafish incubated with SMZ solution had higher mortality, lower hatching rate, slower spontaneous movement and shorter body length, compared with the group used normal nutrient solution, while the water after treatment had lower toxicity effects on zebrafish. The toxicity experiments with microbial degradation respirometer showed that SMZ solution had lower value of oxygen uptake, which indicated that SMZ solution had higher values of toxicity and inhibition of pharmaceutical compounds. This study provides a catalyst with low cost and high catalytic efficiency for degradation process of SMZ and gives a deeper insight into the ecotoxicity of treated water.

High-Throughput Video Processing of Heart Rate Responses in Multiple Wild-type Embryonic Zebrafish per Imaging Field

Heart rate assays in wild-type zebrafish embryos have been limited to analysis of one embryo per video/imaging field. Here we present for the first time a platform for high-throughput derivation of heart rate from multiple zebrafish (Danio rerio) embryos per imaging field, which is capable of quickly processing thousands of videos and ideal for multi-well platforms with multiple fish/well. This approach relies on use of 2-day post fertilization wild-type embryos, and uses only bright-field imaging, circumventing requirement for anesthesia or restraint, costly software/hardware, or fluorescently-labeled animals. Our original scripts (1) locate the heart and record pixel intensity fluctuations generated by each cardiac cycle using a robust image processing routine, and (2) process intensity data to derive heart rate. To demonstrate assay utility, we exposed embryos to the drugs epinephrine and clonidine, which increased or decreased heart rate, respectively. Exposure to organic extracts of air pollution-derived particulate matter, including diesel or biodiesel exhausts, or wood smoke, all complex environmental mixtures, decreased heart rate to varying degrees. Comparison against an established lower-throughput method indicated robust assay fidelity. As all code and executable files are publicly available, this approach may expedite cardiotoxicity screening of compounds as diverse as small molecule drugs and complex chemical mixtures.

Effects of single exposure and binary mixtures of ultraviolet filters octocrylene and 2-ethylhexyl 4-(dimethylamino) benzoate on gene expression in the freshwater insect Chironomus riparius

Ultraviolet filters are used extensively in the production of many personal care and industrial products. These products can inadvertently pollute the environment through recreational activities. They have been associated with endocrine disruption in vertebrates but their effects in invertebrates are poorly understood. Chironomus riparius is a species of the dipteran order, with aquatic larvae that are frequently used in toxicity tests. Previously, we showed that octocrylene (OC) and 2-ethylhexyl 4-(dimethylamino) benzoate (OD-PABA) differentially affected the mRNA levels of the ecdysone receptor and Hsp70 genes. For a better understanding of their mode of action, transcriptional activity by real-time PCR was analyzed in fourth instar larvae exposed to OC, OD-PABA, or a binary mixture of both. We studied 16 genes related to the endocrine system, stress, the immune system, and biotransformation mechanisms to elucidate the putative interactions between these compounds. No response was observed for the genes involved in biotransformation, suggesting that enzymes other than cytochromes P450 and glutathione-S-transferases (GSTs) could get involved in transformation of these compounds. Similarly, no response was observed for endocrine-related genes while the stress gene HYOU1 was inhibited by OD-PABA, suggesting an effect in response to hypoxia. In addition, no significant interactions were observed following exposure to a binary mixture of these compounds. Overall, the results suggest a weak, acute response in different metabolic pathways and a lack of interaction between the compounds. Finally, new genes are identified in this organism, opening the possibility to analyze new cellular pathways as targets of toxicants.

Diclofenac exposure alter the expression of PXR and its downstream target genes in mosquito fish (Gambusia affinis)

As one of widely used drugs, Diclofenac (DCF) recently has been universally detected in aquatic environment and some negative effects derived from DCF exposure to mammals have been also reported. However, studies about its potential deleterious effects on non-target organisms like fish still require more investigation. In this study an ubiquitous small freshwater invader species in Southern of China, mosquito fish (Gambusia affinis), was employed as test organism. We firstly cloned the crucial partial sequences of nucleus transcriptional factor related genes pregnane X receptor (PXR) and its downstream genes, including P-glycoprotein (P-gp), cytochrome 3A (CYP3A), multidrug resistance protein 2 (MRP2), glutathione peroxidase (GPx) and thioredoxin reductase (TXR) in mosquito fish. The phylogenetic trees of PXR, CYP3A and MRP2 were constructed based on their deduced amino acids sequences, respectively. Phylogenetic trees and blast results showed a high similarity between G. affinis and other killifish species, such as Xiphophorus maculatus. The transcriptional expression of these genes mentioned above and partly related enzymes/proteins activities were then measured under the exposure of environmentally relevant concentrations of DCF (from 0.5μgL^-1 to 500μgL^-1) for 24h and 168h. Results showed that the mRNA expression of PXR, CYP3A, P-gp and TXR showed dramatic induction under DCF exposure, exhibiting an obvious time-effect relationship with the extend of exposure time. In terms of enzyme activity and protein content, no dramatic changes as in transcription were observed. Western blotting showed PXR protein increased at 24h but decreased at 168h with the increasing of DCF concentration, displaying a dose-effect relationship to some extent. GPX activity was continuously induced both at 24h and 168h, exhibiting a good consistency with the performance of GPX gene. GSSH/T-GSH increased in all treatments. Overall, DCF had traceable effects on the expression of PXR and its downstream target genes in mosquito fish.

Sensitive biomarkers identification for differentiating Cd and Pb induced toxicity on zebrafish embryos

Cadmium (Cd) and lead (Pb) are naturally existing heavy metals that pose significant health risks. The present study aims to identify sensitive biomarkers for differentiating the toxicities induced by Cd and Pb and for providing clues for the early prediction of toxicity and environmental risk assessment. Indicators related to oxidative stress and inflammatory responses in zebrafish treated with Cd and Pb over time (from 24hpf to 96hpf) were compared. Furthermore, endpoints such as embryo lethality and teratogenicity were detected. Then, several related genes involved in oxidative stress and inflammatory responses characterizing both Cd and Pb exposure, along with key molecules in the MAPKs pathway, were compared at the mRNA level, allowing the selection of the most sensitive and informative biomarkers. Significant increases in reactive oxygen species (ROS) production were observed in zebrafish exposed to Cd and Pb. Cd and Pb exposure induced developmental toxicity, influencing survival rate, hatching rate, larval growth, and heart rate and causing abnormal embryonic development. Similar trends in SOD1 and SOD2 gene expression were induced by Cd and Pb, while nuclear factor erythroid-2 related factor 2 (Nrf2) gene expression responded differently to each metal. In addition, Cd and Pb induced a delayed activation of the CAT and HO-1 genes, with no apparent change in the 24hpf and 48hpf groups. Genes related to immunotoxicity were activated significantly in a time-dependent manner, and these genes exhibited different sensitivities to Cd and Pb. MAPKs pathway genes were also activated in a time-dependent manner, and the expression of these genes showed different effects under Cd and Pb treatment. In summary, the present works have identified some potential sensitive biomarkers. The Nrf2 gene is a potential biomarker to differentiate Pb-induced toxicity from that of Cd, and the IFN-γ gene may be used as a sensitive biomarker for evaluating the risk of Pb contamination. We found that the timeline of MAPKs pathway activation helped to differentiate these two metals toxicities. Furthermore, Pb induced the early activation of ERK2/3 and JNK1, while p38 MAPKs showed delayed activation with no apparent change in the 24hpf group. Cd induced an early activation of ERK2 and a delayed activation of p38a, p38b, ERK3 and JNK1, indicating that the JNK1 pathway is sensitive to Pb exposure, while the p38 pathway may be susceptible to Cd. This work contributes to sensitive biomarker identification and early environmental risk evaluation for chemicals as well as toxicity prediction.

Effects of diclofenac on the expression of Nrf2 and its downstream target genes in mosquito fish (Gambusia affinis)

Diclofenac (DCF) is one of widely used non-steroidal anti-inflammatory drugs. Recently, this drug has been universally detected in aquatic environment. However, its potential adverse effects and oxidative stress toxic mechanisms on fish remain unclear. In the present study, we first cloned the crucial partial sequences of some key oxidative stress related genes, which include NF-E2-related factor 2 (Nrf2), NAD(P)H: quinoneoxidoreductase (NQO1), glutamate-cysteine ligase catalytic subunit (GCLC), Cu-Zn superoxide dismutase (SOD2), catalase (CAT), alpha-glutathione S-transferase (GSTA), and UDP-glucuronosyltransferases (UGT) in mosquito fish (Gambusia affinis). We also deduced amino acids of Nrf2 and then constructed the phylogenetic trees of Nrf2, NQO1 and GCLC, respectively. Results showed that a high identity percentage was founded between G. affinis and other bony fish species, such as Xiphophorus maculates and Poecilia reticulate. The transcriptional expression of these genes and partly related enzymes activities were then investigated under the included environmental relevant concentration DCF exposure (0μmolL^-1, 1.572×10^-3μmolL^-1, 1.572×10^-2μmolL^-1, 0.1572μmolL^-1 and 1.572μmolL^-1) for 24h and 168h. The expression of Nrf2 was inhibited at 24h but induced at 168h, exhibiting a significant time and/or dose-effect relationship under DCF exposure. Similar observation was found in its downstream target genes. However, Nrf2-mediated antioxidant enzymes activities displayed differently under the same concentration of DCF exposure for the same time. Under DCF exposure for 168h, the genes exhibited dramatic induction trend, but there were no significant changes in enzyme activities and MDA content. Overall, mRNA responses were more sensitive than enzyme changes in mosquito fish under DCF exposure.

Bioavailability and Kidney Responses to Diclofenac in the Fathead Minnow (Pimephales promelas)

Diclofenac is one of the most widely prescribed nonsteroidal anti-inflammatory drugs worldwide. It is frequently detected in surface waters; however, whether this pharmaceutical poses a risk to aquatic organisms is debated. Here we quantified the uptake of diclofenac by the fathead minnow (Pimephales promelas) following aqueous exposure (0.2-25.0 μg L^-1) for 21 days, and evaluated the tissue and biomolecular responses in the kidney. Diclofenac accumulated in a concentration- and time-dependent manner in the plasma of exposed fish. The highest plasma concentration observed (for fish exposed to 25 μg L^-1 diclofenac) was within the therapeutic range for humans. There was a strong positive correlation between exposure concentration and the number of developing nephrons observed in the posterior kidney. Diclofenac was not found to modulate the expression of genes in the kidney associated with its primary mode of action in mammals (prostaglandin-endoperoxide synthases) but modulated genes associated with kidney repair and regeneration. There were no significant adverse effects following 21 days exposure to concentrations typical of surface waters. The combination of diclofenac's uptake potential, effects on kidney nephrons and relatively small safety margin for some surface waters may warrant a longer term chronic health effects analysis for diclofenac in fish.

Zebrafish: A Model for the Study of Toxicants Affecting Muscle Development and Function

The rapid progress in medicine, agriculture, and allied sciences has enabled the development of a large amount of potentially useful bioactive compounds, such as drugs and pesticides. However, there is another side of this phenomenon, which includes side effects and environmental pollution. To avoid or minimize the uncontrollable consequences of using the newly developed compounds, researchers seek a quick and effective means of their evaluation. In achieving this goal, the zebrafish (Danio rerio) has proven to be a highly useful tool, mostly because of its fast growth and development, as well as the ability to absorb the molecules diluted in water through its skin and gills. In this review, we focus on the reports concerning the application of zebrafish as a model for assessing the impact of toxicants on skeletal muscles, which share many structural and functional similarities among vertebrates, including zebrafish and humans.

Balancing the health benefits and environmental risks of pharmaceuticals: Diclofenac as an example

Pharmaceuticals are designed to improve human and animal health, but even the most beneficial pharmaceuticals might raise some questions concerning the consequences of exposure to non-target organisms. To illustrate this situation and using diclofenac as a case-study, we analyze global consumption and occurrence data to identify hot spots of consumption without occurrence data, review the scientific literature on the harmful environmental effects to determine whether the observed concentrations in freshwater are of environmental concern, summarize the current pharmaceutical and environmental policies to highlight policy gaps, and suggest a series of research and policy recommendations, which can be summarized as follows: we need to improve the current knowledge on occurrence in freshwaters to properly implement environmental policies (i), diclofenac might pose a risk to non-target organisms in freshwater (ii); the harmful effects that some pharmaceuticals may have on the environment are not always addressed by environmental policies (iii).

Acute toxicological effects on the earthworm Eisenia fetida of 18 common pharmaceuticals in artificial soil

Following soil applications of recycled water and biosolids, pharmaceutical residues can eventually enter the terrestrial environment. In vitro and in vivo assays have largely focused on the acute ecotoxicity of these compounds in aquatic systems. However, studies on the ecotoxicological effects of pharmaceuticals in soil biota are especially scarce. The aim of this study was to investigate the acute toxicity of 18 pharmaceuticals (4 NSAIDs, 5 blood lipid-lowering agents, 6 β-blockers and 3 antibiotics) that are usually found in the environment by using an Eisenia fetida bioassay. In addition, the presence of these pharmaceuticals in artificial soil was verified at the end of the test. Our results indicate that seven of the studied drugs cause acute adverse effects in E. fetida, in particular, the NSAIDs and the blood lipid-lowering agents. Ibuprofen (LC50=64.80 mg/kg) caused the highest acute toxicity for all tested compounds, followed by diclofenac (LC50=90.49 mg/kg) and simvastatin (LC50=92.70 mg/kg). Other tested pharmaceuticals from NSAIDs and blood lipid-lowering families have toxicity effects, from a LC50=140.87 mg/kg for gemfibrozil to 795.07 mg/kg for lovastatin. Atorvastatin, bezafibrate, β-blockers and antibiotics showed no detectable lethality in E. fetida. The four NSAIDs showed evidence of modification of their original chemical structure after 14 days so the detected toxicity may be due to the original product as well as their degradation products. The three blood lipid-lowering agents seem to be more stable in soil. From an environmental perspective, the lethal concentrations of the tested drugs are much greater than those reported in wastewater and biosolids, therefore acute toxic effects may be improbable. However, little is known about the accumulation of these substances in soils after regular applications, so accumulative and chronic effects cannot be excluded. Moreover, more studies are needed to determine the role of the degradation products of these pharmaceuticals on terrestrial toxicity.

Identification of single-nucleotide polymorphism markers associated with cortisol response to crowding in rainbow trout

Understanding stress responses is essential for improving animal welfare and increasing agriculture production efficiency. Previously, we reported microsatellite markers associated with quantitative trait loci (QTL) affecting plasma cortisol response to crowding in rainbow trout. In this study, our main objectives were to identify single-nucleotide polymorphism (SNP) markers associated with cortisol response to crowding in rainbow trout using both GWAS (genome-wide association studies) and QTL mapping methods and to employ rapidly expanding genomic resources for rainbow trout toward the identification of candidate genes affecting this trait. A three-generation F2 mapping family (2008052) was genotyped using RAD-seq (restriction-site-associated DNA sequencing) to identify 4874 informative SNPs. GWAS identified 26 SNPs associated with cortisol response to crowding whereas QTL mapping revealed two significant QTL on chromosomes Omy8 and Omy12, respectively. Positional candidate genes were identified using marker sequences to search the draft genome assembly of rainbow trout. One of the genes in the QTL interval on Omy12 is a putative serine/threonine protein kinase gene that was differentially expressed in the liver in response to handling and confinement stress in our previous study. A homologue of this gene was differentially expressed in zebrafish embryos exposed to diclofenac, a nonsteroidal anti-inflammatory drug (NSAID) and an environmental toxicant. NSAIDs have been shown to affect the cortisol response in rainbow trout; therefore, this gene is a good candidate based on its physical position and expression. However, the reference genome resources currently available for rainbow trout require continued improvement as demonstrated by the unmapped SNPs and the putative assembly errors detected in this study.

Developmental toxicity of diclofenac and elucidation of gene regulation in zebrafish (Danio rerio)

Environmental pollution by emerging contaminants, e.g. pharmaceuticals, has become a matter of widespread concern in recent years. We investigated the membrane transport of diclofenac and its toxic effects on gene expression and the development of zebrafish embryos. The association of diclofenac with the embryos conformed to the general partition model at low concentration, the partition coefficient being 0.0033 ml per embryo. At high concentration, the interaction fitted the Freundlich model. Most of the diclofenac remained in the extracellular aqueous solution with less than 5% interacting with the embryo, about half of which was adsorbed on the membranes while the rest entered the cytoplasm. Concentrations of diclofenac over 10.13 μM were lethal to all the embryos, while 3.78 μM diclofenac was teratogenic. The development abnormalities at 4 day post treatment (dpt) include shorter body length, smaller eye, pericardial and body edema, lack of liver, intestine and circulation, muscle degeneration, and abnormal pigmentation. The portion of the diclofenac transferred into the embryo altered the expression of certain genes, e.g. down-regulation of Wnt3a and Gata4 and up-regulation of Wnt8a. The alteration of expression of such genes or the regulation of downstream genes could cause defects in the cardiovascular and nervous systems.

The read-across hypothesis and environmental risk assessment of pharmaceuticals

Pharmaceuticals in the environment have received increased attention over the past decade, as they are ubiquitous in rivers and waterways. Concentrations are in sub-ng to low μg/L, well below acute toxic levels, but there are uncertainties regarding the effects of chronic exposures and there is a need to prioritise which pharmaceuticals may be of concern. The read-across hypothesis stipulates that a drug will have an effect in non-target organisms only if the molecular targets such as receptors and enzymes have been conserved, resulting in a (specific) pharmacological effect only if plasma concentrations are similar to human therapeutic concentrations. If this holds true for different classes of pharmaceuticals, it should be possible to predict the potential environmental impact from information obtained during the drug development process. This paper critically reviews the evidence for read-across, and finds that few studies include plasma concentrations and mode of action based effects. Thus, despite a large number of apparently relevant papers and a general acceptance of the hypothesis, there is an absence of documented evidence. There is a need for large-scale studies to generate robust data for testing the read-across hypothesis and developing predictive models, the only feasible approach to protecting the environment.