An in vitro assay for toxicity testing of Clostridium perfringens type C ß-toxin.

Introduction: Veterinary vaccines against Clostridium perfringens type C need to be tested for absence of toxicity, as mandated by pharmacopoeias worldwide. This toxicity testing is required at multiple manufacturing steps and relies on outdated mouse tests that involve severe animal suffering. Clostridium perfringens type C produces several toxins of which the ß-toxin is the primary component responsible for causing disease. Here, we describe the successful development of a new cell-based in vitro assay that can address the specific toxicity of the ß-toxin. Methods: Development of the cell-based assay followed the principle of in vitro testing developed for Cl. septicum vaccines, which is based on Vero cells. We screened four cell lines and selected the THP-1 cell line, which was shown to be the most specific and sensitive for ß-toxin activity, in combination with a commercially available method to determine cell viability (MTS assay) as a readout. Results: The current animal test is estimated to detect 100 - 1000-fold dilutions of the Cl. perfringens type C non-inactivated antigen. When tested with an active Cl. perfringens type C antigen preparation, derived from a commercial vaccine manufacturing process, our THP-1 cell-based assay was able to detect toxin activity from undiluted to over 10000-fold dilution, showing a linear range between approximately 1000- and 10000-fold dilutions. Assay specificity for the ß-toxin was confirmed with neutralizing antibodies and lack of reaction to Cl. perfringens culture medium. In addition, assay parameters demonstrated good repeatability. Conclusions: Here, we have shown proof of concept for a THP-1 cell-based assay for toxicity testing of veterinary Cl. perfringens type C vaccines that is suitable for all vaccine production steps. This result represents a significant step towards the replacement of animal-based toxicity testing of this veterinary clostridial antigen. As a next step, assessment of the assay's sensitivity and repeatability and validation of the method will have to be performed in a commercial manufacturing context in order to formally implement the assay in vaccine quality control.

Revolutionizing developmental neurotoxicity testing - a journey from animal models to advanced in vitro systems.

Developmental neurotoxicity (DNT) testing has seen enormous progress over the last two decades. Preceding even the publication of the animal-based OECD test guideline for DNT testing in 2007, a series of non-animal technology workshops and conferences (starting in 2005) shaped a community that has delivered a comprehensive battery of in vitro test methods (IVB). Its data interpretation is covered by a very recent OECD test guidance (No. 377). Here, we aim to overview the progress in the field, focusing on the evolution of testing strategies, the role of emerging technologies, and the impact of OECD test guidelines on DNT testing. In particular, this is an example of a targeted development of an animal-free testing approach for one of the most complex hazards of chemicals to human health. These developments started literally from a blank slate, with no proposed alternative methods available. Over two decades, cutting-edge science enabled the design of a testing approach that spares animals and enables throughput for this challenging hazard. While it is evident that the field needs guidance and regulation, the massive economic impact of decreased human cognitive capacity caused by chemical exposure should be prioritized more highly. Beyond this, the claim to fame of DNT in vitro testing is the enormous scientific progress it has brought for understanding the human brain, its development, and how it can be perturbed.

Developmental neurotoxicity (DNT) testing predicts the hazard of exposure to chemicals to human brain development. Comprehensive advanced non-animal testing strategies using cutting-edge technology can now replace animal-based approaches to assess this complex hazard. These strategies can assess large numbers of chemicals more accurately and efficiently than the animal-based approach. Recent OECD test guidance has formalized this battery of in vitro test methods for DNT, marking a pivotal achievement in the field. The shift towards non-animal testing reflects both a commitment to animal welfare and a growing recognition of the economic and public health impacts associated with impaired cognitive function caused by chemical exposures. These innovations ultimately contribute to safer chemical management and better protection of human health, especially during the vulnerable stages of brain development.

60 Years of the 3Rs symposium: Lessons learned and the road ahead.

When The Principles of Humane Experimental Technique was published in 1959, authors William Russell and Rex Burch had a modest goal: to make researchers think about what they were doing in the laboratory - and to do it more humanely. Sixty years later, their groundbreaking book was celebrated for inspiring a revolution in science and launching a new field: The 3Rs of alternatives to animal experimentation. On November 22, 2019, some pioneering and leading scientists and researchers in the field gathered at the Johns Hopkins Bloomberg School of Public Health in Bal-timore for the 60 Years of the 3Rs Symposium: Lessons Learned and the Road Ahead. The event was sponsored by the Johns Hopkins Center for Alternatives to Animal Testing (CAAT), the Foundation for Chemistry Research and Initiatives, the Alternative Research & Development Foundation (ARDF), the American Cleaning Institute (ACI), the International Fragrance Association (IFRA), the Institute for In Vitro Sciences (IIVS), John "Jack" R. Fowle III, and the Society of Toxicology (SoT). Fourteen pres-entations shared the history behind the groundbreaking publication, international efforts to achieve its aims, stumbling blocks to progress, as well as remarkable achievements. The day was a tribute to Russell and Burch, and a testament to what is possible when people from many walks of life - science, government, and industry - work toward a common goal.

William Russell and Rex Burch published their book The Principles of Humane Experimental Technique in 1959. The book encouraged researchers to replace animal experiments where it was possible, to refine experiments with animals in order to reduce their suffering, and to reduce the number of animals that had to be used for experiments to the minimum. Sixty years later, a group of pioneering and leading scientists and researchers in the field gathered to share how the publi­cation came about and how the vision inspired international collaborations and successes on many different levels including new laws. The paper includes an overview of important milestones in the history of alternatives to animal experimentation.

Ph. Eur. testing for histamine and depressor substances using guinea-pigs and cats: the end of an era. Strategy for removal of animal tests for histamine and depressor substances and their vestiges from the Ph. Eur.

For more than 50 years, in vivo assays have been used for testing pharmaceutical product safety due to their assumed ability to broadly detect potential unidentified contaminants. As part of these in vivo tests, the animal tests for depressor substances and histamine have been described in the European Pharmacopoeia since its first edition in 1977. Both tests measure the effect of histamine and histamine-like substances, using guinea-pigs and cats respectively. In 2024, the Histamine (2.6.10) general chapter is referenced in the Production section of four monographs and 10 monographs have variations of a sentence on designing the manufacturing process to eliminate or minimise substances lowering blood pressure in this same section, without referencing the chapter. The Depressor substances (2.6.11) chapter is referenced only in the Histamine (2.6.10) chapter as a next step if the histamine test is invalid. A historical search was performed and it has shown that the tests for histamine and for depressor substances were introduced by different groups of experts in an inconsistent way at different times, and for different reasons, leading to non-harmonised approaches across monographs. The control of histamine and other depressor substances has been the subject of numerous debates where their use was questioned. During these discussions, reports on positive cases or batches failing the test for histamine or depressor substances were anecdotal. In addition, in vivo tests can be considered non-specific, very variable, time-consuming, costly and ethically doubtful. More importantly, the majority of in vivo methods originate from a time when good manufacturing practice was not widely used and formal method validation requirements were not yet established. In view of the above, the removal of all references to animal tests for histamine or depressor substances from all texts still referring to them is proposed. Since the sentences in the Production section referring to the control of "substances lowering blood pressure", "vasoactive substances" or "hypotensive substances" appeared as remainders of the animal test without further guarantee of safety, it will also be proposed to remove all these sentences from the concerned monographs. Ultimately, the suppression of general chapters 2.6.10 and 2.6.11 from the Ph. Eur. is envisaged. Independently from the above, it is also envisaged to elaborate a new general chapter Histamine in active substances (2.5.47) to include physicochemical or immunochemical methods enabling the detection of histamine. This new text would aim at supporting manufacturers in their histamine control strategy following the inclusion of precaution statements in the general monograph on Products of fermentation (1468); these statements had been added in Ph. Eur. Supplements 9.6 and 10.4, following adverse events related to a GMP issue with gentamicin sulfate. This strategy has been endorsed by the European Pharmacopoeia Commission at its 177th Session in November 2023. The concerned monographs would be a subject of public consultation in Pharmeuropa 36.2 (April 2024).

Advancing ocular safety research: A comprehensive examination of benzocaine acute exposure without animal testing.

Benzocaine is a widely employed local anaesthetic; however, there is a notable dearth of preclinical and clinical evidence regarding its safety in ophthalmological products. To address this, a comprehensive strategy incorporating in silico and in vitro methodologies was proposed for assessing benzocaine's ocular toxicity without animal testing. To collect the in silico evidence, the QSAR Toolbox (v4.5) was used. A single exposure to two benzocaine concentrations (2% and 20%) was evaluated by in vitro methods. Hen's Egg Chorioallantoic Membrane Test (HET-CAM) was performed to evaluate the effects on the conjunctiva. To study corneal integrity, Short Time Exposure test (STE) and Bovine Corneal Opacity and Permeability (BCOP) assay, followed by histopathological analysis, were carried out. Results from both in silico and in vitro methodologies categorize benzocaine as non-irritating. The histopathological analysis further affirms the safety of using benzocaine in eye drops, as no alterations were observed in evaluated corneal strata. This research proposes a useful combined strategy to provide evidence on the safety of local anaesthetics and particularly show that 2% and 20% benzocaine solutions do not induce eye irritation or corneal damage, supporting the potential use of benzocaine in the development of ophthalmic anesthetic products.

Phase-out planning for animal experimentation.

Since the late 2010s, the idea of phase-out planning for animal experimentation (PPAE) has come to the foreground of political debates, but central notions and arguments are understood differently by different participants and stand in need of clarification. This article draws on public communications on ten political projects related to PPAE to propose a philosophical explication of PPAE and to articulate proponents' central moral argument. According to the argument, the phase-out of animal experimentation is morally desirable and planned interventions are both necessary and sufficient to achieve it. The normative and descriptive premises of the argument are stated and discussed, flagging questions that need answering for a more thorough assessment of the argument. This results in a series of seven action points for researchers and stakeholders of phase-out planning for animal experimentation. The overall goal is to enable an open and productive discussion about PPAE in public, political, and academic settings.

In recent years, a new demand has entered the political arena: that the phase-out of animal experimentation should be planned. But it is important to understand exactly what this means. This article draws on ten documents from governments, parliaments, and NGOs to tease out what they mean by "planning the phase-out of animal experimentation." It also discusses the main argument that is advanced in favor of phase-out planning and highlights seven gaps in our knowledge that we should try to fill in order to move the discussion forward. In sum, the article is the first to explicitly define phase-out planning for animal experimentation and to directly discuss its pros and cons from a philosophical point of view. This is helpful in avoiding misunderstandings and talking past each other, enabling an open and productive debate.

Rodent tests for psychiatric drugs get a rethink.

Under pressure to ditch a controversial swim test for depression, scientists look for more precise measures.

GARD™skin and GARD™potency: A proof-of-concept study investigating applicability domain for agrochemical formulations.

Several New Approach Methodologies (NAMs) for hazard assessment of skin sensitisers have been formally validated. However, data regarding their applicability on certain product classes are limited. The purpose of this project was to provide initial evidence on the applicability domain of GARD™skin and GARD™potency for the product class of agrochemical formulations. For this proof of concept, 30 liquid and 12 solid agrochemical formulations were tested in GARDskin for hazard predictions. Formulations predicted as sensitisers were further evaluated in the GARDpotency assay to determine GHS skin sensitisation category. The selected formulations were of product types, efficacy groups and sensitisation hazard classes representative of the industry's products. The performance of GARDskin was estimated by comparing results to existing in vivo animal data. The overall accuracy, sensitivity, and specificity were 76.2% (32/42), 85.0% (17/20), and 68.2% (15/22), respectively, with the predictivity for liquid formulations being slightly higher compared to the solid formulations. GARDpotency correctly subcategorized 14 out of the 17 correctly predicted sensitisers. Lack of concordance was justifiable by compositional or borderline response analysis. In conclusion, GARDskin and GARDpotency showed satisfactory performance in this initial proof-of-concept study, which supports consideration of agrochemical formulations being within the applicability domain of the test methods.

Impedance-based in vitro eye irritation testing enables the categorization of diluted chemicals.

Products containing chemicals with eye irritation potential need to be labeled with the respective hazard symbol. To avoid the testing of numerous dilutions of chemicals on animals, their labeling is directed by a theoretical approach. In this report, a previously described in vitro tissue model of the cornea based on human epithelial cells was used for eye irritation testing of dilutions. As a sensitive and non-destructive method to analyze the barrier function of the epithelium, impedance spectroscopy was applied. Moreover, the morphology and viability of the epithelial models were assessed. We tested four chemicals that, neatly, cause severe damage to the eye: tetrahydrofuran, acetic acid, diethylethanolamine, and benzalkonium chloride. With our test method, we were able to determine the concentrations of the chemicals which are critical for the integrity of the cornea. The threshold was < 0.1% for the most and > 5% for the least toxic substance. The described test system is not only an alternative for animal models but also for the theoretical examination of the hazard potential of diluted chemicals. By using the advantages of tissue engineering and non-destructive analysis tools, we can achieve more precise and safer labeling of the eye irritation potential of products.

The skin sensitization adverse outcome pathway: exploring the role of mechanistic understanding for higher tier risk assessment.

For over a decade, the skin sensitization Adverse Outcome Pathway (AOP) has served as a useful framework for development of novel in chemico and in vitro assays for use in skin sensitization hazard and risk assessment. Since its establishment, the AOP framework further fueled the existing efforts in new assay development and stimulated a plethora of activities with particular focus on validation, reproducibility and interpretation of individual assays and combination of assay outputs for use in hazard/risk assessment. In parallel, research efforts have also accelerated in pace, providing new molecular and dynamic insight into key events leading to sensitization. In light of novel hypotheses emerging from over a decade of focused research effort, mechanistic evidence relating to the key events in the skin sensitization AOP may complement the tools currently used in risk assessment. We reviewed the recent advances unraveling the complexity of molecular events in sensitization and signpost the most promising avenues for further exploration and development of useful assays.

Development of a hierarchical support vector regression-based in silico model for the prediction of the cysteine depletion in DPRA.

Topical and transdermal treatments have been dramatically growing recently and it is crucial to consider skin sensitization during the drug discovery and development process for these administration routes. Various tests, including animal and non-animal approaches, have been devised to assess the potential for skin sensitization. Furthermore, numerous in silico models have been created, providing swift and cost-effective alternatives to traditional methods such as in vivo, in vitro, and in chemico methods for categorizing compounds. In this study, a quantitative structure-activity relationship (QSAR) model was developed using the innovative hierarchical support vector regression (HSVR) scheme. The aim was to quantitatively predict the potential for skin sensitization by analyzing the percent of cysteine depletion in Direct Peptide Reactivity Assay (DPRA). The results demonstrated accurate, consistent, and robust predictions in the training set, test set, and outlier set. Consequently, this model can be employed to estimate skin sensitization potential of novel or virtual compounds.

A novel three-dimensional Nrf2 reporter epidermis model for skin sensitization assessment.

Skin sensitization assessment has progressed from the use of animal models towards the application of New Approach Methodologies (NAMs). Several skin sensitization NAMs are accepted for regulatory use, but a majority relies on submerged in vitro cell cultures that limit their applicability domain, posing challenges for testing hydrophobic chemicals and mixtures. A newly developed three-dimensional (3D) Nrf2 reporter epidermis model for skin sensitization assessment is reported. This NAM may help to overcome these limitations. The NAM combines the in vivo-like biology and exposure conditions of 3D epidermis models with the reliability, convenience, and cost-effectiveness of secreted reporter gene technology. The Keap1-Nrf2-ARE pathway was chosen as the reporter gene read-out, as it is induced by most skin sensitizers and already adopted in OECD Test guideline 442D. Immortalized human primary keratinocytes (Ker-CT) were stably transfected with the pIGB-Nrf2-SEAP vector to construct a Nrf2 reporter cell line. Ker-CT Nrf2 reporter cells showed negligible basal expression of the Secreted Embryonic Alkaline Phosphatase (SEAP) reporter, which was induced 13.5-fold by exposure to the skin sensitizer cinnamic aldehyde (CA). Co-exposure to CA and the Nrf2 inhibitor glucocorticoid clobetasol propionate significantly suppressed the CA-induced SEAP expression, confirming dependance of the SEAP expression on Nrf2 activation. Using air-liquid interface and animal constituent free culture conditions, the Ker-CT Nrf2 reporter cells differentiated to stratified 3D epidermis models with an in vivo-like skin architecture and functional skin barrier. Evaluation of a Ker-CT Nrf2 reporter cell-based 2D assay by testing 10 conventional reference chemicals showed a predictive accuracy for skin sensitization potential of 80% and 70% compared to LLNA and human data in two independent laboratories and a high intra- and interlaboratory reproducibility. Moreover, the 3D epidermis models predicted 3 sensitizing and 2 non-sensitizing reference chemicals correctly in a first proof-of-concept study. Further investigations foresee the testing of additional chemicals, including hydrophobic compounds and mixtures to confirm the potential of the 3D epidermis models to broaden the applicability domain for NAM-based skin sensitization assessment.

Examining animal testing for risk assessment: A WC-12 workshop report.

In toxicology and regulatory testing, the use of animal methods has been both a cornerstone and a subject of intense debate. To continue this discourse a panel and audience representing scientists from various sectors and countries convened at a workshop held during the 12th World Congress on Alternatives and Animal Use in the Life Sciences (WC-12). The ensuing discussion focused on the scientific and ethical considerations surrounding the necessity and responsibility of defending the creation of new animal data in regulatory testing. The primary aim was to foster an open dialogue between the panel members and the audience while encouraging diverse perspectives on the responsibilities and obligations of various stakeholders (including industry, regulatory bodies, technology developers, research scientists, and animal welfare NGOs) in defending the development and subsequent utilization of new animal data. This workshop summary report captures the key elements from this critical dialogue and collective introspection. It describes the intersection of scientific progress and ethical responsibility as all sectors seek to accelerate the pace of 21st century predictive toxicology and new approach methodologies (NAMs) for the protection of human health and the environment.

Computational application of internationally harmonized defined approaches to skin sensitization: DASS App.

BACKGROUND: Chemically induced skin sensitization, or allergic contact dermatitis, is a common occupational and public health issue. Regulatory authorities require an assessment of potential to cause skin sensitization for many chemical products. Defined approaches for skin sensitization (DASS) identify potential chemical skin sensitizers by integrating data from multiple non-animal tests based on human cells, molecular targets, and computational model predictions using standardized data interpretation procedures. While several DASS are internationally accepted by regulatory agencies, the data interpretation procedures vary in logical complexity, and manual application can be time-consuming or prone to error. RESULTS: We developed the DASS App, an open-source web application, to facilitate user application of three regulatory testing strategies for skin sensitization assessment: the Two-out-of-Three (2o3), the Integrated Testing Strategy (ITS), and the Key Event 3/1 Sequential Testing Strategy (KE 3/1 STS) without the need for software downloads or computational expertise. The application supports upload and analysis of user-provided data, includes steps to identify inconsistencies and formatting issues, and provides predictions in a downloadable format. CONCLUSION: This open-access web-based implementation of internationally harmonized regulatory guidelines for an important public health endpoint is designed to support broad user uptake and consistent, reproducible application. The DASS App is freely accessible via https://ntp.niehs.nih.gov/go/952311 and all scripts are available on GitHub ( https://github.com/NIEHS/DASS ).

Development of an in silico evaluation system that quantitatively predicts skin sensitization using OECD Guideline No. 497 ITSv2 defined approach for skin sensitization classification.

The Integrated Testing Strategy version 2 (ITSv2) Defined Approach, which is a reliable skin sensitization hazard and multi-step risk assessment method, does not support quantitative risk assessment such as local lymph node assay EC3 values. In this study, we developed a high-performance in silico evaluation system that quantitatively predicts the EC3 values of chemical substances by combining the ITSv2 Defined Approach for hazard identification (ITSv2 HI) with machine learning models. This system uses in chemico/in vitro test data, molecular descriptors, and distance information based on read-across concepts as explanatory variables. The system achieves an R2 value of 0.617 on external-validation data. Substances misclassified in ITSv2 HI are considered to have properties that do not match the correspondence between tests expressing the adverse outcome pathway assumed in the ITSv2 Defined Approach and skin sensitization. Therefore, ITSv2 HI is assumed to be correct within the applicability domains of this system. When using only substances within the applicability domains to reconstruct CatBoost models, the R2 value reached 0.824 on the external-validation data, representing an improvement in system performance. The results demonstrate the utility of explanatory variables that reflect the read-across concept and the advantages of integrating multiple prediction methods.