Projects

Parabens have been used for decades as preservatives in food, drugs and cosmetics. The majority however, were banned in 2009 and 2014 leaving only methyl-, ethyl-, propyl-, and butyl-derivates available for subsequent use. Methyl- and propylparaben have been extensively tested in vivo, with no resulting evidence for developmental and reproductive toxicity (DART). In contrast, ethylparaben has not yet been tested for DART in animal experiments, and it is currently debated if additional animal studies are warranted. In order to perform a comparison of the four currently approved parabens, we used a previously established in vitro test based on human induced pluripotent stem cells (iPSC) that are exposed to test substances during their differentiation to neuroectodermal cells. EC50 values for cytotoxicity were 906 μM, 698 μM, 216 μM and 63 μM for methyl-, ethyl-, propyl- and butylparaben, respectively, demonstrating that cytotoxicity increases with increasing alkyl chain length. Genome-wide analysis demonstrated that FDR-adjusted significant gene expression changes occurred only at cytotoxic or close to cytotoxic concentrations, for example 1720 differentially expressed genes (DEG) at 1000 μM ethylparaben, 1 DEG at 316 μM, and no DEG at 100 μM or lower concentrations. The highest concentration of ethylparaben that did not induce any cytotoxicity nor DEG was 1670-fold above the highest published concentrations reported in biomonitoring studies (60 nM ethylparaben in cord blood). In conclusion, cytotoxicity and gene expression alterations of ethylparaben occurred at concentrations of approximately three orders of magnitude above human blood concentrations; moreover, the substance fitted well into a scenario where toxicity increases with the alkyl chain length, and gene expression changes only occur at cytotoxic or close to cytotoxic concentrations. Therefore, no evidence was obtained suggesting that in vivo DART with ethylparaben would lead to different results as the methyl- or propyl derivates.

The causes of nigrostriatal cell death in idiopathic Parkinson’s disease are unknown, but exposure to toxic chemicals may play some role. We followed up here on suggestions that bacterial secondary metabolites might be selectively cytotoxic to dopaminergic neurons. Extracts from Streptomyces venezuelae were found to kill human dopaminergic neurons (LUHMES cells). Utilizing this model system as a bioassay, we identified a bacterial metabolite known as aerugine (C₁₀H₁₁NO₂S; 2-[4-(hydroxymethyl)-4,5-dihydro-1,3-thiazol-2-yl]phenol) and confirmed this finding by chemical re-synthesis. This 2-hydroxyphenyl-thiazoline compound was previously shown to be a product of a wide-spread biosynthetic cluster also found in the human microbiome and in several pathogens. Aerugine triggered half-maximal dopaminergic neurotoxicity at 3-4 µM. It was less toxic for other neurons (10-20 µM), and non-toxic (at <100 µM) for common human cell lines. Neurotoxicity was completely prevented by several iron chelators, by distinct anti-oxidants and by a caspase inhibitor. In the Caenorhabditis elegans model organism, general survival was not affected by aerugine concentrations up to 100 µM. When transgenic worms, expressing green fluorescent protein only in their dopamine neurons, were exposed to aerugine, specific neurodegeneration was observed. The toxicant also exerted functional dopaminergic toxicity in nematodes as determined by the “basal slowing response” assay. Thus, our research has unveiled a bacterial metabolite with a remarkably selective toxicity toward human dopaminergic neurons in vitro and for the dopaminergic nervous system of Caenorhabditis elegans in vivo. These findings suggest that microbe-derived environmental chemicals should be further investigated for their role in the pathogenesis of Parkinson's disease.

Neonicotinoid pesticides were initially designed in order to achieve species selectivity on insect nicotinic acetylcholine receptors (nAChRs). However, concerns arose when agonistic effects were also detected in human cells expressing nAChRs. In the context of next-generation risk assessments (NGRAs), new approach methods (NAMs) should replace animal testing where appropriate. Herein, we present a combination of in silico and in vitro methodologies that are used to investigate the potentially toxic effects of neonicotinoids and nicotinoid metabolites on human neurons. First, an ensemble docking study was conducted on the nAChR isoforms α7 and α3β4 to assess potential crucial molecular initiating event (MIE) interactions. Representative docking poses were further refined using molecular dynamics (MD) simulations and binding energy calculations using implicit solvent models. Finally, calcium imaging on LUHMES neurons confirmed a key event (KE) downstream of the MIE. This method was also used to confirm the predicted agonistic effect of the metabolite descyano-thiacloprid (DCNT).

Human health is determined both by genetics (G) and environment (E). This is clearly illustrated in groups of individuals who are exposed to the same environmental factor showing differential responses. A quantitative measure of the gene–environment interactions (GxE) effects has not been developed and in some instances, a clear consensus on the concept has not even been reached; for example, whether cancer is predominantly emerging from “bad luck” or “bad lifestyle” is still debated. In this article, we provide a panel of examples of GxE interaction as drivers of pathogenesis. We highlight how epigenetic regulations can represent a common connecting aspect of the molecular bases. Our argument converges on the concept that the GxE is recorded in the cellular epigenome, which might represent the key to deconvolute these multidimensional intricated layers of regulation. Developing a key to decode this epigenetic information would provide quantitative measures of disease risk. Analogously to the epigenetic clock introduced to estimate biological age, we provocatively propose the theoretical concept of an “epigenetic score‐meter” to estimate disease risk.

To transfer toxicological findings from model systems, e.g. animals, to humans, standardized safety factors are applied to account for intra-species and inter-species variabilities. An alternative approach would be to measure and model the actual compound-specific uncertainties. This biological concept assumes that all observed toxicities depend not only on the exposure situation (environment = E), but also on the genetic (G) background of the model (G  ×  E). As a quantitative discipline, toxicology needs to move beyond merely qualitative G  ×  E concepts. Research programs are required that determine the major biological variabilities affecting toxicity and categorize their relative weights and contributions. In a complementary approach, detailed case studies need to explore the role of genetic backgrounds in the adverse effects of defined chemicals. In addition, current understanding of the selection and propagation of adverse outcome pathways (AOP) in different biological environments is very limited. To improve understanding, a particular focus is required on modulatory and counter-regulatory steps. For quantitative approaches to address uncertainties, the concept of “genetic” influence needs a more precise definition. What is usually meant by this term in the context of G  ×  E are the protein functions encoded by the genes. Besides the g ene sequence, the regulation of the gene expression and function should also be accounted for. The widened concept of past and present “ g ene expression” influences is summarized here as G e . Also, the concept of “environment” needs some re-consideration in situations where exposure timing (E t ) is pivotal: prolonged or repeated exposure to the insult (chemical, physical, life style) affects G e . This implies that it changes the model system. The interaction of G e with E t might be denoted as G e  ×  E t . We provide here general explanations and specific examples for this concept and show how it could be applied in the context of New Approach Methodologies (NAM).

The EU’s chemicals regulation, REACH, requires that most chemicals in the EU be evaluated for human health and ecosystem risks, with a mandate to minimize use of animal tests for these evaluations. The REACH process has been ongoing since about 2008, but a calculation of the resulting animal use is not publicly available. For this reason, we have undertaken a count of animals used for REACH. With EU legislators set to consider REACH revisions that could expand animal testing, we are releasing results for test categories counted to date: reproductive toxicity tests, developmental toxicity tests, and repeat­ed-dose toxicity tests for human health. The total animal count as of December 2022 for these categories is about 2.9 million. Additional tests involving about 1.3 million animals are currently required by a final proposal authorization or compliance check but not yet completed. The total, 4.2 million, for just these three test categories exceeds the original European Com­mission forecast of 2.6 million for all REACH tests. The difference is primarily because the European Commission estimate excluded offspring, which are most of the animals used for REACH. Other reasons for the difference are extra animals included in tests to ensure sufficient survive to meet the minimum test requirement; dose range-finding tests; extra test animal groups, e.g., for recovery analysis; and a high rejection rate of read-across studies. Given higher than forecast animal use, the upcoming debate on proposed REACH revisions is an opportunity to refocus on reducing animal numbers in keeping with the REACH mandate.

Metabolic glycoengineering (MGE) has been developed to visualize carbohydrates on live cells. The method allows the fluorescent labeling of sialic acid (Sia) sugar residues on neuronal plasma membranes. For instance, the efficiency of glycosylation along neurite membranes has been characterized as cell health measure in neurotoxicology. Using human dopaminergic neurons as model system, we asked here, whether it was possible to separately label diverse classes of biomolecules and to visualize them selectively on cells. Several approaches suggest that a large proportion of Sia rather incorporated in non-protein components of cell membranes than into glycoproteins. We made use here of deoxymannojirimycin (dMM), a non-toxic inhibitor of protein glycosylation, and of N-butyl-deoxynojirimycin (NBdNM) a well-tolerated inhibitor of lipid glycosylation, to develop a method of differential labeling of sialylated membrane lipids (lipid-Sia) or sialylated N-glycosylated proteins (protein-Sia) on live neurons. The time resolution at which Sia modification of lipids/proteins was observable was in the range of few hours. The approach was then extended to several other cell types. Using this technique of 'target-specific MGE', we found that in dopaminergic or sensory neurons > 60% of Sia is lipid bound, and thus polysialic acid-neural cell adhesion molecule (PSA-NCAM) cannot be considered the major sialylated membrane component. Different from neurons, most Sia was bound to protein in HepG2 hepatoma cells or in neural crest cells. Thus, our method allows visualization of cell-specific sialylation processes for separate classes of membrane constituents.

The EU’s REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) Regulation requires animal testing only as a last resort. However, our study (Knight et al., 2023) in this issue reveals that approximately 2.9 million animals have been used for REACH testing for reproductive toxicity, developmental toxicity, and repeated-dose toxicity alone as of December 2022. Currently, additional tests requiring about 1.3 million more animals are in the works. As compliance checks continue, more animal tests are anticipated. According to the European Chemicals Agency (ECHA), 75% of read-across methods have been rejected during compliance checks. Here, we estimate that 0.6 to 3.2 million animals have been used for other endpoints, likely at the lower end of this range. The ongoing discussion about the grouping of 4,500 regis­tered petrochemicals can still have a major impact on these numbers. The 2022 amendment of REACH is estimated to add 3.6 to 7.0 million animals. This information comes as the European Parliament is set to consider changes to REACH that could further increase animal testing. Two proposals currently under discussion would likely necessitate new animal testing: extending the requirement for a chemical safety assessment (CSA) to Annex VII substances could add 1.6 to 2.6 million animals, and the registration of polymers adds a challenge comparable to the petrochemical discussion. These findings high­light the importance of understanding the current state of REACH animal testing for the upcoming debate on REACH revisions as an opportunity to focus on reducing animal use.

The adoption of Directive 2010/63/EU on the protection of animals used for scientific purposes has given a major push to the formation of Three Rs initiatives in the form of centres and platforms. These centres and platforms are dedicated to the so-called Three Rs, which are the Replacement, Reduction and Refinement of animal use in experiments. ATLA's 50th Anniversary year has seen the publication of two articles on European Three Rs centres and platforms. The first of these was about the progressive rise in their numbers and about their founding history; this second part focuses on their current status and activities. This article takes a closer look at their financial and organisational structures, describes their Three Rs focus and core activities (dissemination, education, implementation, scientific quality/translatability, ethics), and presents their areas of responsibility and projects in detail. This overview of the work and diverse structures of the Three Rs centres and platforms is not only intended to bring them closer to the reader, but also to provide role models and show examples of how such Three Rs centres and platforms could be made sustainable. The Three Rs centres and platforms are very important focal points and play an immense role as facilitators of Directive 2010/63/EU 'on the ground' in their respective countries. They are also invaluable for the wide dissemination of information and for promoting the implementation of the Three Rs in general.

In vitro models of the peripheral nervous system would benefit from further refinements to better support studies on neuropathies. In particular, the assessment of pain-related signals is still difficult in human cell cultures. Here, we harnessed induced pluripotent stem cells (iPSCs) to generate peripheral sensory neurons enriched in nociceptors. The objective was to generate a culture system with signaling endpoints suitable for pharmacological and toxicological studies. Neurons generated by conventional differentiation protocols expressed moderate levels of P2X3 purinergic receptors and only low levels of TRPV1 capsaicin receptors, when maturation time was kept to the upper practically useful limit of 6 weeks. As alternative approach, we generated cells with an inducible NGN1 transgene. Ectopic expression of this transcription factor during a defined time window of differentiation resulted in highly enriched nociceptor cultures, as determined by functional (P2X3 and TRPV1 receptors) and immunocytochemical phenotyping, complemented by extensive transcriptome profiling. Single cell recordings of Ca2+-indicator fluorescence from >9000 cells were used to establish the "fraction of reactive cells" in a stimulated population as experimental endpoint, that appeared robust, transparent and quantifiable. To provide an example of application to biomedical studies, functional consequences of prolonged exposure to the chemotherapeutic drug oxaliplatin were examined at non-cytotoxic concentrations. We found (i) neuronal (allodynia-like) hypersensitivity to otherwise non-activating mechanical stimulation that could be blocked by modulators of voltage-gated sodium channels; (ii) hyper-responsiveness to TRPV1 receptor stimulation. These findings and several other measured functional alterations indicate that the model is suitable for pharmacological and toxicological studies related to peripheral neuropathies.

In many countries, animal experiments can only be performed when their necessity has been demonstrated in a legal document. As the usefulness of animals in research is also a significant societal and political issue, criteria to structure debates and evaluations are needed. Here, background information is given on laboratory animal studies. Moreover, parameters that may be considered in judging their usefulness are suggested. The discussion is strictly focused on animals used as tools/test systems/models to provide information on humans. In this context, general features and performance characteristics of models are discussed. Examples are given for well-recognized criteria (e.g., robustness, relevance, predictivity) to judge the usefulness of predictive models. The main hypothesis put forward here is that a benefits evaluation (usefulness metrics) is only possible within sharply circumscribed "use domains". Examples are given for the research fields of drug and vaccine research, toxicology, disease pathogenesis, and basic biological research. Efficacy, safety, and quality studies are highlighted as "use domains" within the field of drug discovery and production. A further separation into individual diseases, drug targets or symptoms is suggested for, e.g., efficacy studies or pathophysiology. Finally, an outlook is given on the evaluation of model advantages and disadvantages to arrive at their "net benefit". Moreover, the need to compare the net benefits of animal models versus that of their alternatives is highlighted.

In many industrial sectors, there is a need for reliable ways to evaluate the safety of chemicals with methods anchored to human biology and pathology. For this purpose, many animal-free new approach methods (NAMs) have been developed and implemented in various stages of risk assessment. Now it is time to assemble individual NAMs into a comprehensive next-generation risk assessment (NGRA) strategy. The European Horizon 2020 RISK-HUNT3R project ("Risk assessment of chemicals integrating human-centric next-generation testing strategies promoting the 3Rs") has been designed to promote a combination of computational toxicology, in vitro toxicology, and systems biology. It is assumed that this approach will lead to faster and more accurate risk assessment procedures. The RISK-HUNT3R NGRA strategy will be developed to address the implementation of a comprehensive NAM toolbox into the regulatory framework. Critical conceptual approaches of the project include i) the integration of human-relevant data on biotransformation and elimination, ii) the translation of high-content mode-of-action datasets into predictions of adverse outcomes, iii) development of quantitative adverse outcome pathways (qAOPs), and iv) quantification of uncertainties associated with the predictions based on NGRA strategies. Many of the project steps will be used iteratively to generate datasets with sufficient quality and certainty for NGRA. Scientists and regulators will work together on case studies to evaluate NAMs' practical applicability and the strategies to combine information therefrom. Here we delineate how the strategy will be deployed to establish an overall NGRA framework for chemicals, pesticides, food additives, and drugs.

Banning or reduction of the use of animals for laboratory experiments is a frequently-discussed societal and scientific issue. Moreover, the usefulness of animals needs to be considered in any decision process on the permission of specific animal studies. This complex issue is often simplified and generalized in the media around the question, "Are animals useful as a model?" To render an often emotional discussion about animal experimentation more rational, it is important to define "usefulness" in a structured and transparent way. To achieve such a goal, many sub-questions need to be asked, and the following aspects require clarification: (i) consistency of animal-derived data (robustness of the model system); (ii) scientific domain investigated (e.g., toxicology vs disease modelling vs therapy); (iii) measurement unit for "benefit" (inte-grating positive and negative aspects); (iv) benchmarking to alternatives; (v) definition of success criteria (how good is good enough); (vi) the procedure to assess benefit and necessity. This series of articles discusses the overall benchmarking process by specifying the six issues. The goal is to provide guidance on what needs to be clarified in scientific and political discussions. This framework should help in the future to structure available information, to identify and fill information gaps, and to arrive at rational decisions in various sub-fields of animal use. In part I of the series, we focus on the robustness of animal models. This describes the capacity of models to produce the same output/response when faced with the "same" input. Follow-up articles will cover the remaining usefulness aspects.