Reducing the number of fish in bioconcentration studies with general chemicals by reducing the number of test concentrations

Evaluation of the EMA log kow trigger for fish BCF testing based on data for several human pharmaceuticals

In the European Medicines Agency (EMA) "Guideline for Environmental Risk Assessment of Medicinal Products for Human Use," a fish bioconcentration factor (BCF) study is triggered in Phase I for pharmaceuticals having log Kow >4.5, to support Persistence, Bioaccumulation and Toxicity (PBT) screening, and in Phase II to assess secondary poisoning and bioaccumulation ('B') potential when log Kow ≥3. The standard sampling schedule outlined in OECD Test Guideline 305 (TG305) may require assessment of approximately 200 fish following exposure to low- and high-test concentrations and a negative control. We report experimental log Kow and BCF values for 64 human pharmaceuticals that were used to evaluate the current BCF testing trigger of log Kow ≥3, and whether a single BCF exposure concentration allows accurate classification of bioaccumulation potential. Our data support raising the BCF testing trigger to log Kow ≥4, and use of a single test concentration. The resulting reduction in the use of fish is consistent with the 3 R s principle and did not adversely affect classification accuracy. An assessment of potential risk of secondary poisoning was also conducted for three drugs classified as either B or vB, and no risks were identified.

Uptake, tissue distribution, and biotransformation pattern of triclosan in tilapia exposed to environmentally-relevant concentrations

Although triclosan has been ubiquitously detected in aquatic environment and is known to have various adverse effects to fish, details on its uptake, bioconcentration, and elimination in fish tissues are still limited. This study investigated the uptake and elimination toxicokinetics, bioconcentration, and biotransformation potential of triclosan in Nile tilapia (Oreochromis niloticus) exposed to environmentally-relevant concentrations under semi-static regimes for 7 days. For toxicokinetics, triclosan reached a plateau concentration within 5-days of exposure, and decreased to stable concentration within 5 days of elimination. Approximately 50 % of triclosan was excreted by fish through feces, and up to 29 % of triclosan was excreted through the biliary excretion. For fish exposed to 200 ng·L-1, 2000 ng·L-1, and 20,000 ng·L-1, the bioconcentration factors (log BCFs) of triclosan in fish tissues obeyed similar order: bile ≈ intestine > gonad ≈ stomach > liver > kidney ≈ gill > skin ≈ plasma > brain > muscle. The log BCFs of triclosan in fish tissues are approximately maintained constants, no matter what triclosan concentrations in exposure water. Seven biotransformation products of triclosan, involved in both phase I and phase II metabolism, were identified in this study, which were produced through hydroxylation, bond cleavages, dichlorination, and sulfation pathways. Metabolite of triclosan-O-sulfate was detected in all tissues of tilapia, and more toxic product of 2,4-dichlorophenol was also found in intestine, gonad, and bile of tilapia. Meanwhile, two metabolites of 2,4-dichlorophenol-O-sulfate and monohydroxy-triclosan-O-sulfate were firstly discovered in the skin, liver, gill, intestine, gonad, and bile of tilapia in this study. These findings highlight the importance of considering triclosan biotransformation products in ecological assessment. They also provide a scientific basis for health risk evaluation of triclosan to humans, who are associated with dietary exposure through ingesting fish.

Are current regulatory log Kow cut-off values fit-for-purpose as a screening tool for bioaccumulation potential in aquatic organisms?

Persistent, Bioaccumulative and Toxic (PBT) and very Persistent and very Bioaccumulative (vPvB) are regulatory hazard categories that have been set to manage the possible risks to humans and the environment from these chemicals. In industrial chemicals regulations, their aquatic Bioaccumulation potential is usually assessed first with a screening based on the octanol/water partition coefficient (Kow). However, current log Kow cut-off values triggering classification, categorisation and/or further fish bioconcentration testing are not harmonised worldwide, and they have never been assessed for their regulatory relevance. In this study, the experimentally determined log Kow and fish bioconcentration factors (BCF) of 532 chemicals were compared. While the analysis underlined the robustness of using log Kow as a screening tool (5/532 were false negatives; log Kow: non-bioaccumulative, but BCF: bioaccumulative), it also demonstrated the conservatism of the cut-offs used worldwide. Indeed, many chemicals were deemed potentially Bioaccumulative based on log Kow when a fish bioaccumulation test showed no concern (false positives), therefore, leading to unnecessary use of vertebrate animals. Our analysis shows that the log Kow cut-off could be increased to 4.5 in all regions for all purposes without leading to a reduced protection of humans and the environment.

Accumulation and metabolization of the antidepressant venlafaxine and its main metabolite o-desmethylvenlafaxine in non-target marine organisms Holothuria tubulosa, Anemonia sulcata and Actinia equina

The assessment of exposure to the antidepressant venlafaxine and its major metabolite o-desmethylvenlafaxine in Holothuria tubulosa, Anemonia sulcata and Actinia equina is proposed. A 28-day exposure experiment (10 μg/L day) followed by a 52-day depuration period was conducted. The accumulation shows a first-order kinetic process reaching an average concentration of 49,125/54342 ng/g dw in H. tubulosa and 64,810/93007 ng/g dw in A. sulcata. Venlafaxine is considered cumulative (BCF > 2000 L/kg dw) in H. tubulosa, A. sulcata and A. equina respectively; and o-desmethylvenlafaxine in A. sulcata. Organism-specific BCF generally followed the order A. sulcata > A. equina > H. tubulosa. The study revealed differences between tissues in metabolizing abilities in H. tubulosa this effect increases significantly with time in the digestive tract while it was negligible in the body wall. The results provide a description of venlafaxine and o-desmethylvenlafaxine accumulation in common and non-target organisms in the marine environment.

Structure-Activity Relationship of Methyl 4-Aminobenzoate Derivatives as Being Drug Candidate Targeting Glutathione Related Enzymes: in Vitro and in Silico Approaches

A thiol compound, glutathione, is essential for healthy cell defence against xenobiotics and oxidative stress. Glutathione reductase (GR) and glutathione S-transferase (GST) are two glutathione-related enzymes that function in the antioxidant and the detoxification systems. In this study, potential inhibitory effects of methyl 4-aminobenzoate derivatives on GR and GST were examined in vitro. GR and GST were isolated from human erythrocytes with 7.63 EU/mg protein and 5.66 EU/mg protein specific activity, respectively. It was found that compound 1 (methyl 4-amino-3-bromo-5-fluorobenzoate with K_i value of 0.325±0.012 μM) and compound 5 (methyl 4-amino-2-nitrobenzoate with K_i value of 92.41±22.26 μM) inhibited GR and GST stronger than other derivatives. Furthermore, a computer-aided method was used to predict the binding affinities of derivatives, ADME characteristics, and toxicities. Derivatives 4 (methyl 4-amino-2-bromobenzoate) and 6 (methyl 4-amino-2-chlorobenzoate) were estimated to have the lowest binding energies into GR and GST receptors, respectively according to results of in silico studies.

Considerations for bioaccumulation studies in fish with nanomaterials

Nanomaterials (NMs) pose challenges in performing bioaccumulation studies in fish and in regulatory interpretation of results. Therefore, a clear guidance is needed to obtain reliable, reproducible and comparable results. By analysing all the available literature, we aim in this manuscript to identify the critical aspects that should be addressed in these type of studies. Seventy-eight studies from a total of 67 published articles were identified in which a variety of approaches were used: aqueous exposure (49 studies), dietary exposure (19), and pre-exposed animals for trophic transfer studies (10). The NMs tested included TiO₂, Zn, ZnO, Cu, CuO, Ag, Au, CeO₂, Fe₂O₃, Fe₃O₄, Se, CdS, CdSe/ZnS-QDs, CdTe/ZnS-QDs, graphene, fullerenol and MWCNTs. In general, there is a scarcity of bioaccumulation studies for the different NMs. In particular, studies that use the dietary exposure route are lacking. TiO₂ NMs are the most studied for bioaccumulation potential in fish (20%), whereas very few data were available for CuO, FeO and carbon-based NMs. Different information gaps were identified in these studies that hamper overall conclusions to be made on the bioaccumulation potential of NMs. The main critical issues related to NM testing for bioaccumulation include: maintenance of stable exposure concentrations, the influence of feeding regimen on uptake and elimination, the use of appropriate feed spiking methodologies, the potential need for testing different concentrations, and the reporting of bioaccumulation endpoints (BCF/BMF). Each of these issues needs further guidance to allow proper use and reporting of NM bioaccumulation data for regulatory purposes.

Current ecotoxicity testing needs among selected U.S. federal agencies

U.S. regulatory and research agencies use ecotoxicity test data to assess the hazards associated with substances that may be released into the environment, including but not limited to industrial chemicals, pharmaceuticals, pesticides, food additives, and color additives. These data are used to conduct hazard assessments and evaluate potential risks to aquatic life (e.g., invertebrates, fish), birds, wildlife species, or the environment. To identify opportunities for regulatory uses of non-animal replacements for ecotoxicity tests, the needs and uses for data from tests utilizing animals must first be clarified. Accordingly, the objective of this review was to identify the ecotoxicity test data relied upon by U.S. federal agencies. The standards, test guidelines, guidance documents, and/or endpoints that are used to address each of the agencies' regulatory and research needs regarding ecotoxicity testing are described in the context of their application to decision-making. Testing and information use, needs, and/or requirements relevant to the regulatory or programmatic mandates of the agencies taking part in the Interagency Coordinating Committee on the Validation of Alternative Methods Ecotoxicology Workgroup are captured. This information will be useful for coordinating efforts to develop and implement alternative test methods to reduce, refine, or replace animal use in chemical safety evaluations.

Design and Synthesis of Novel Dual Cholinesterase Inhibitors: In Vitro Inhibition Studies Supported with Molecular Docking

The major cholinesterase enzymes, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), are important in the therapy of Alzheimer's disease (AD) based on the cholinergic hypothesis. As a result, in recent years, the investigation of dual cholinesterase inhibition methods has become important among scientists. In this study, novel N-(4-chlorobenzyl)-3,4-dimethoxy-N-(m-substituted)benzamide derivatives were synthesized. Then, inhibitory properties of these derivatives were examined in human AChE and BuChE in vitro and possible interactions were determined by molecular docking studies. All benzamide derivatives were exhibited dual inhibitory character and high BBB permeability. The most effective inhibitor was found as N7 for both AChE and BuChE with IC₅₀ values of 1.57 and 2.85 μM, respectively. Besides the most potent inhibitor was predicted as N7 in terms of binding energies with -12.18 kcal/mol and -9.92 kcal/mol, respectively. The reason for these results is that bromine (N7) is the bulkiest molecule among the other substituted groups. These derivatives could be exploited to develop new medications for the treatment of central nervous system-related diseases as AD by acting as dual inhibitors of AChE and BChE.

Development of a method for assessing the accumulation and metabolization of antidepressant drugs in zebrafish (Danio rerio) eleutheroembryos

Antidepressant drugs are widely used for the treatment of common mental or other psychiatric disorders such as depression, which affect about 121 million people worldwide. This widespread use has contributed to the input of these pharmaceuticals and their metabolites into the environment. The aim of this work was to develop an analytical method to quantify the most widely used antidepressant drugs, selective serotonin reuptake inhibitors (SSRI), and their main metabolites in the environment. For this, a new and reliable miniaturized extraction method based on dispersive SPE cleanup procedure for extraction of SSRI followed by derivatization with n-heptafluorobutyrylimidazole, and detection by GC-MS was developed. The methodology, including a first-order one-compartment model, was then applied to a bioconcentration study in zebrafish (Danio rerio) eleutheroembryos. The results showed low bioaccumulation of these compounds; however, a biotransformation evidence of the parent compounds into their metabolites was observed after 6 h of exposure. These results indicate the need to integrate metabolic transformation rates to fully model and understand the bioaccumulation patterns of SSRI and their metabolites.

Stem cells of aquatic invertebrates as an advanced tool for assessing ecotoxicological impacts

Environmental stressors are assessed through methods that quantify their impacts on a wide range of metrics including species density, growth rates, reproduction, behaviour and physiology, as on host-pathogen interactions and immunocompetence. Environmental stress may induce additional sublethal effects, like mutations and epigenetic signatures affecting offspring via germline mediated transgenerational inheritance, shaping phenotypic plasticity, increasing disease susceptibility, tissue pathologies, changes in social behaviour and biological invasions. The growing diversity of pollutants released into aquatic environments requires the development of a reliable, standardised and 3R (replacement, reduction and refinement of animals in research) compliant in vitro toolbox. The tools have to be in line with REACH regulation 1907/2006/EC, aiming to improve strategies for potential ecotoxicological risks assessment and monitoring of chemicals threatening human health and aquatic environments. Aquatic invertebrates' adult stem cells (ASCs) are numerous and can be pluripotent, as illustrated by high regeneration ability documented in many of these taxa. This is of further importance as in many aquatic invertebrate taxa, ASCs are able to differentiate into germ cells. Here we propose that ASCs from key aquatic invertebrates may be harnessed for applicable and standardised new tests in ecotoxicology. As part of this approach, a battery of modern techniques and endpoints are proposed to be tested for their ability to correctly identify environmental stresses posed by emerging contaminants in aquatic environments. Consequently, we briefly describe the current status of the available toxicity testing and biota-based monitoring strategies in aquatic environmental ecotoxicology and highlight some of the associated open issues such as replicability, consistency and reliability in the outcomes, for understanding and assessing the impacts of various chemicals on organisms and on the entire aquatic environment. Following this, we describe the benefits of aquatic invertebrate ASC-based tools for better addressing ecotoxicological questions, along with the current obstacles and possible overhaul approaches.

Bioconcentration of cedarwood oil constituents in rainbow trout

Cedarwood oil is an essential oil used as a fragrance material and insect repellent. Its main constituents are sesquiterpenes which are potentially bioaccumulative according to the REACH screening criteria. Cedarwood oil is a complex mixture of hydrophobic and volatile organic chemicals. The volatility and limited water solubility of its constituents are a challenge for standard bioconcentration factor (BCF) test methods using aqueous exposure. We used an abbreviated dietary exposure in vivo testing protocol with internal benchmark substances as "internal standards" to derive the BCF of cedarwood oil constituents using rainbow trout (Oncorhynchus mykiss). Internal benchmarking proved to be a useful tool to control for inter-individual variability, enabling us to calculate the BCF for all major cedarwood oil constituents as a mixture. We found that the BCF of two out of six analysed cedarwood oil constituents exceed a BCF of 5000 and two others exceed a BCF of 2000 (90% confidence level) even though we found evidence for biotransformation for individual constituents. The results of this study indicate that more work is warranted to study the bioaccumulation of essential oils and highlights the utility of internal benchmarking in in vivo dietary exposure BCF tests to increase robustness and allow for the BCF measurement of complex mixtures.

Developing in vitro models to assess fish gill excretion of emerging contaminants

Advances in analytical methods have enabled the detection of emerging contaminants at ever lower concentrations in freshwaters. However, such measurements need to be linked to effect-based assays to identify risks. The bioconcentration factor (BCF) forms part of a chemical's environmental risk assessment (ERA), and current regulatory testing guidelines to calculate fish BCFs use hundreds of fish per chemical. Due to ethical concerns a reduction in the numbers of animals used is desired, and there is a need to identify in vitro or in silico alternatives which meet regulatory acceptance. This study describes the successful demonstration of a FIsh Gill Cell culture System (FIGCS) to assess an often overlooked parameter in pharmacokinetics: the excretion of drugs across the gill. The FIGCS tolerates the application of natural waters on its apical surface, mimicking the situation of the live fish, and thus in combination with advanced analytical methods, offers an opportunity to take lab-based testing used for ERA, such as compound uptake, biotransformation or excretion directly into field for validation with natural waters. Here we used the basic drug propranolol and the acidic ibuprofen as a demonstration of the FIGCS utility in three separate experiments. Excretion across the apical membrane showed saturation kinetics, suggesting the involvement of carrier-mediated processes. Both propranolol and ibuprofen were excreted across the epithelium from the media (internal blood equivalent) to the water, with ibuprofen excretion being considerably slower than propranolol excretion. Further studies indicate that ibuprofen may be complexing with fetal bovine serum (FBS) reducing bioavailability; in contrast propranolol efflux rate was unaffected, indicating that drugs behave differently in the presence of FBS and other plasma proteins. A key issue in future ERA is to better understand the effects of mixtures of different pollutant classes found in environmental samples, and this model offers an ethical path to do this.

Relationship among the acute toxicity, critical body residue, and bioconcentration of ortho-dinitrobenzene in zebrafish (Danio rerio) based on toxicokinetics

The internal critical concentration represented by the critical body residue (CBR) is an ideal indicator for reflecting the toxicity of a chemical. Although some authors have realized that the CBR₅₀ can be calculated from the LC₅₀ via the bioconcentration factor (BCF), the effects of exposure time and exposure concentration on the relationship between the LC₅₀ and CBR₅₀ have not been investigated to date. In this paper, the LC₅₀ and CBR₅₀ of ortho-dinitrobenzene in zebrafish were experimentally determined and their relationship was investigated. The results showed that ortho-dinitrobenzene exhibited excess toxicity and cannot completely be identified as a reactive compound based on toxic ratio. Comparison of the measured CBR₅₀ and the CBR₅₀ calculated from the LC₅₀ via the BCF showed that there was a 0.46 log unit difference. Investigation of the relationship between the concentration in fish calculated by the toxicokinetic model and exposure time showed that the bio-uptake of fish was fast and reached a steady state in the toxicity test, indicating that the difference in CBR₅₀ values could not be attributed to the different exposure times used in toxicity and BCF assays. On the other hand, investigation of the measured bioconcentration ratio (BCR) showed that the BCR (or BCF_app) decreased with increasing exposure concentration. Compared with the CBR₅₀ calculated from the LC₅₀ via the BCF, the CBR₅₀ calculated from the LC₅₀ via the BCF_app is close to the measured CBR₅₀, suggesting that the difference in CBR₅₀ values is attributed to the different exposure concentrations used in the BCF and toxicity assays.

Assessing the impact of benzo[a]pyrene with the in vitro fish gut model: An integrated approach for eco-genotoxicological studies

In vitro models are emerging tools for reducing reliance on traditional toxicity tests, especially in areas where information is sparse. For studies of fish, this is especially important for extrahepatic organs, such as the intestine, which, until recently, have been largely overlooked in favour of the liver or gill. Considering the importance of dietary uptake of contaminants, the rainbow trout (Oncorhynchus mykiss) intestine-derived cell line RTgutGC was cultured, to test its suitability as a high-throughput in vitro model. Benzo[a]pyrene (B[a]P) is an important contaminant and a model polycyclic aromatic hydrocarbon (PAH). Over 48 h exposure, a range of endpoints and xenobiotic metabolism rates were examined at three different pH levels indicative of the in vitro (pH 7.5) and in vivo mid-gut (pH 7.7) and hind-gut (pH 7.4) regions as a function of time. These endpoints included (i) cell viability: acid phosphatase (APH) and lactate dehydrogenase (LDH) assays; (ii) glucose uptake; (iii) cytochrome P450 enzyme activity: 7-ethoxyresoorufin-O-deethylase (EROD) assay; (iv) glutathione transferase (GST) activity; (v) genotoxic damage determined using the comet assay. Absence of cell viability loss, in parallel with decrease in the parent compound (B[a]P) in the medium and its subsequent increase in the cells suggested active sequestration, biotransformation, and removal of this representative PAH. With respect to genotoxic response, significant differences were observed at both the sampling times and the two highest concentrations of B[a]P. No significant differences were observed for the different pH conditions. Overall, this in vitro xenobiotic metabolism system appears to be a robust model, providing a basis for further development to evaluate metabolic and toxicological potential of contaminants without use of animals.

Application of the rainbow trout derived intestinal cell line (RTgutGC) for ecotoxicological studies: molecular and cellular responses following exposure to copper

There is an acknowledged need for in vitro fish intestinal model to help understand dietary exposure to chemicals in the aquatic environment. The presence and use of such models is however largely restrictive due to technical difficulties in the culturing of enterocytes in general and the availability of appropriate established cell lines in particular. In this study, the rainbow trout (Oncorhynchus mykiss) intestinal derived cell line (RTgutGC) was used as a surrogate for the "gut sac" method. To facilitate comparison, RTgutGC cells were grown as monolayers (double-seeded) on permeable Transwell supports leading to a two-compartment intestinal model consisting of polarised epithelium. This two-compartment model divides the system into an upper apical (lumen) and a lower basolateral (portal blood) compartment. In our studies, these cells stained weakly for mucosubstances, expressed the tight junction protein ZO-1 in addition to E-cadherin and revealed the presence of polarised epithelium in addition to microvilli protrusions. The cells also revealed a comparable transepithelial electrical resistance (TEER) to the in vivo situation. Importantly, the cell line tolerated apical saline (1:1 ratio) thus mimicking the intact organ to allow assessment of uptake of compounds across the intestine. Following an exposure over 72 h, our study demonstrated that the RTgutGC cell line under sub-lethal concentrations of copper sulphate (Cu) and modified saline solutions demonstrated uptake of the metal with saturation levels comparable to short term ex situ gut sac preparations. Gene expression analysis revealed no significant influence of pH or time on mRNA expression levels of key stress related genes (i.e. CYP3A, GST, mtA, Pgp and SOD) in the Transwell model. However, significant positive correlations were found between all genes investigated suggesting a co-operative relationship amongst the genes studied. When the outlined characteristics of the cell line are combined with the division of compartments, the RTgutGC double seeded model represents a potential animal replacement model for ecotoxicological studies. Overall, this model could be used to study the effects and predict aquatic gastrointestinal permeability of metals and other environmentally relevant contaminants in a cost effective and high throughput manner.

Stereoselective induction by 2,2',3,4',6-pentachlorobiphenyl in adult zebrafish (Danio rerio): Implication of chirality in oxidative stress and bioaccumulation

This study aimed to investigate the oxidative stress process and bioaccumulation the racemic/(-)-/(+)- 2,2',3,4',6-pentachlorobiphenyl were administered to adult zebrafish (Danio rerio) after prolonged exposure of 56-days uptake and 49-days depuration experiments. Stereoselective accumulation was observed in adult samples after racemic exposure as revealed by decreased enantiomer fractions. The two enantiomers of PCB91 accumulated at different rates with logBCFk values close to 3.7, suggesting that they were highly hazardous and persistent pollutants. Exposure to racemic/(-)-/(+)- PCB91 stereoselectively induced oxidative stress owing to changes in reactive oxygen species, malondialdehyde contents, antioxidant enzyme activities and gene expressions in brain and liver tissues. In addition, the stereoselective relationship between bioconcentration and oxidative stress were also presented in this study. Our findings might be helpful for elucidating the environmental risk of the two enantiomers of PCB91 that induce toxicity in aquatic organisms.

Advancing the 3Rs in regulatory ecotoxicology: A pragmatic cross-sector approach

The ecotoxicity testing of chemicals for prospective environmental safety assessment is an area in which a high number of vertebrates are used across a variety of industry sectors. Refining, reducing, and replacing the use of animals such as fish, birds, and amphibians for this purpose addresses the ethical concerns and the increasing legislative requirements to consider alternative test methods. Members of the UK-based National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs) Ecotoxicology Working Group, consisting of representatives from academia, government organizations, and industry, have worked together over the past 6 y to provide evidence bases to support and advance the application of the 3Rs in regulatory ecotoxicity testing. The group recently held a workshop to identify the areas of testing, demands, and drivers that will have an impact on the future of animal use in regulatory ecotoxicology. As a result of these discussions, we have developed a pragmatic approach to prioritize and realistically address key opportunity areas, to enable progress toward the vision of a reduced reliance on the use of animals in this area of testing. This paper summarizes the findings of this exercise and proposes a pragmatic strategy toward our key long-term goals-the incorporation of reliable alternatives to whole-organism testing into regulations and guidance, and a culture shift toward reduced reliance on vertebrate toxicity testing in routine environmental safety assessment. Integr Environ Assess Manag 2016;12:417-421. © 2015 SETAC.