Engineering Sensory Ganglion Multicellular System to Model Tissue Nerve Ingrowth

Discogenic pain is associated with deep nerve ingrowth in annulus fibrosus tissue (AF) of intervertebral disc (IVD). To model AF nerve ingrowth, primary bovine dorsal root ganglion (DRG) micro-scale tissue units are spatially organised around an AF explant by mild hydrodynamic forces within a collagen matrix. This results in a densely packed multicellular system mimicking the native DRG tissue morphology and a controlled AF-neuron distance. Such a multicellular organisation is essential to evolve populational-level cellular functions and in vivo-like morphologies. Pro-inflammatory cytokine-primed AF demonstrates its neurotrophic and neurotropic effects on nociceptor axons. Both effects are dependent on the AF-neuron distance underpinning the role of recapitulating inter-tissue/organ anatomical proximity when investigating their crosstalk. This is the first in vitro model studying AF nerve ingrowth by engineering mature and large animal tissues in a morphologically and physiologically relevant environment. The new approach can be used to biofabricate multi-tissue/organ models for untangling pathophysiological conditions and develop novel therapies.

Proof of concept testing of a positive reference material for in vivo and in vitro sensitization testing of medical devices

In vivo skin sensitization tests are required to evaluate the biological safety of medical devices in contact with living organisms to provide safe medical care to patients. Negative and positive reference materials have been developed for biological tests of cytotoxicity, implantation, hemolysis, and in vitro skin irritation. However, skin sensitization tests are lacking. In this study, polyurethane sheets containing 1 wt/wt % 2,4-dinitrochlorobenzene (DNCB-PU) were developed and evaluated as a positive reference material for skin sensitization tests. DNCB-PU sheet extracts prepared with sesame oil elicited positive sensitization responses for in vivo sensitization potential in the guinea pig maximization test and the local lymph node assay. Furthermore, DNCB-PU sheet extracts prepared with water and acetonitrile, 10% fetal bovine serum-containing medium, or sesame oil elicited positive sensitization responses as alternatives to animal testing based on the amino acid derivative reactivity assay, human cell line activation test, and epidermal sensitization assay, respectively. These data suggest that the DNCB-PU sheet is an effective extractable positive reference material for in vivo and in vitro skin sensitization testing in medical devices. The formulation of this reference material will lead to the development of safer medical devices that contribute to patient safety.

Prediction of pharmacokinetics of an anaplastic lymphoma kinase inhibitor in rat and monkey: application of physiologically based pharmacokinetic model as an alternative tool to minimise animal studies

The pharmacokinetic (PK) and toxicokinetic profile of a drug from its preclinical evaluation helps the researcher determine whether the drug should be tested in humans based on its safety and toxicity.Preclinical studies require time and resources and are prone to error. Moreover, according to the United States Food and Drug Administration Modernisation Act 2, animal testing is no longer mandatory for new drug development, and an animal-free alternative, such as cell-based assay and computer models, can be used.Different physiologically based PK models were developed for an anaplastic lymphoma kinase inhibitor in rats and monkeys after intravenous and oral administration using its physicochemical properties and in vitro characterisation data.The developed model was validated against the in vivo data available in the literature, and the validation results were found within the acceptable limit. A parameter sensitivity analysis was performed to identify the properties of the compound influencing the PK profile.This work demonstrates the application of the physiologically based PK model to predict the PKs of a drug, which will eventually assist in reducing the number of animal studies and save time and cost of drug discovery and development.

Author Guide for Addressing Animal Methods Bias in Publishing

There is growing recognition that animal methods bias, a preference for animal-based methods where they are not necessary or where nonanimal-based methods may already be suitable, can impact the likelihood or timeliness of a manuscript being accepted for publication. Following April 2022 workshop about animal methods bias in scientific publishing, a coalition of scientists and advocates formed a Coalition to Illuminate and Address Animal Methods Bias (COLAAB). The COLAAB has developed this guide to be used by authors who use nonanimal methods to avoid and respond to animal methods bias from manuscript reviewers. It contains information that researchers may use during 1) study design, including how to find and select appropriate nonanimal methods and preregister a research plan, 2) manuscript preparation and submission, including tips for discussing methods and choosing journals and reviewers that may be more receptive to nonanimal methods, and 3) the peer review process, providing suggested language and literature to aid authors in responding to biased reviews. The author's guide for addressing animal methods bias in publishing is a living resource also available online at animalmethodsbias.org, which aims to help ensure fair dissemination of research that uses nonanimal methods and prevent unnecessary experiments on animals.

QSAR Models for the Prediction of Dietary Biomagnification Factor in Fish

Xenobiotics released in the environment can be taken up by aquatic and terrestrial organisms and can accumulate at higher concentrations through the trophic chain. Bioaccumulation is therefore one of the PBT properties that authorities require to assess for the evaluation of the risks that chemicals may pose to humans and the environment. The use of an integrated testing strategy (ITS) and the use of multiple sources of information are strongly encouraged by authorities in order to maximize the information available and reduce testing costs. Moreover, considering the increasing demand for development and the application of new approaches and alternatives to animal testing, the development of in silico cost-effective tools such as QSAR models becomes increasingly important. In this study, a large and curated literature database of fish laboratory-based values of dietary biomagnification factor (BMF) was used to create externally validated QSARs. The quality categories (high, medium, low) available in the database were used to extract reliable data to train and validate the models, and to further address the uncertainty in low-quality data. This procedure was useful for highlighting problematic compounds for which additional experimental effort would be required, such as siloxanes, highly brominated and chlorinated compounds. Two models were suggested as final outputs in this study, one based on good-quality data and the other developed on a larger dataset of consistent Log BMF_L values, which included lower-quality data. The models had similar predictive ability; however, the second model had a larger applicability domain. These QSARs were based on simple MLR equations that could easily be applied for the predictions of dietary BMF_L in fish, and support bioaccumulation assessment procedures at the regulatory level. To ease the application and dissemination of these QSARs, they were included with technical documentation (as QMRF Reports) in the QSAR-ME Profiler software for QSAR predictions available online.

Predicting the Bioconcentration Factor in Fish from Molecular Structures

The bioconcentration factor (BCF) is one of the metrics used to evaluate the potential of a substance to bioaccumulate into aquatic organisms. In this work, linear and non-linear regression QSARs were developed for the prediction of log BCF using different computational approaches, and starting from a large and structurally heterogeneous dataset. The new MLR-OLS and ANN regression models have good fitting with R2 values of 0.62 and 0.70, respectively, and comparable external predictivity with R2ext 0.64 and 0.65 (RMSEext of 0.78 and 0.76), respectively. Furthermore, linear and non-linear classification models were developed using the regulatory threshold BCF >2000. A class balanced subset was used to develop classification models which were applied to chemicals not used to create the QSARs. These classification models are characterized by external and internal accuracy up to 84% and 90%, respectively, and sensitivity and specificity up to 90% and 80%, respectively. QSARs presented in this work are validated according to regulatory requirements and their quality is in line with other tools available for the same endpoint and dataset, with the advantage of low complexity and easy application through the software QSAR-ME Profiler. These QSARs can be used as alternatives for, or in combination with, existing models to support bioaccumulation assessment procedures.

QSARINS-Chem standalone version: A new platform-independent software to profile chemicals for physico-chemical properties, fate, and toxicity

The new software QSARINS-Chem standalone version is a multiplatform tool, freely downloadable, for the in silico profiling of multiple properties and activities of organic chemicals. This software, which is based on the concept of the QSARINS-chem module embedded in the QSARINS software, has been fully redesigned and redeveloped in the Java™ language. In addition to a selection of models included in the old module, the new software predicts biotransformation rates and aquatic toxicities of pharmaceuticals and personal care products in multiple organisms, and offers a suite of tools for the analysis of predictions. Furthermore, a comprehensive and transparent database of molecular structures is provided. The new QSARINS-Chem standalone version is an informative and solid tool, which is useful to support the assessment of the potential hazard and risks related to organic chemicals and is dedicated to users which are interested in the application of QSARs to generate reliable predictions.

Development and Application of a Transcriptomic Signature of Bioactivation in an Advanced In Vitro Liver Model to Reduce Drug-induced Liver Injury Risk Early in the Pharmaceutical Pipeline

Early risk assessment of drug-induced liver injury (DILI) potential for drug candidates remains a major challenge for pharmaceutical development. We have previously developed a set of rat liver transcriptional biomarkers in short-term toxicity studies to inform the potential of drug candidates to generate a high burden of chemically reactive metabolites that presents higher risk for human DILI. Here, we describe translation of those NRF1-/NRF2-mediated liver tissue biomarkers to an in vitro assay using an advanced micropatterned coculture system (HEPATOPAC) with primary hepatocytes from male Wistar Han rats. A 9-day, resource-sparing and higher throughput approach designed to identify new chemical entities with lower reactive metabolite-forming potential was qualified for internal decision making using 93 DILI-positive and -negative drugs. This assay provides 81% sensitivity and 90% specificity in detecting hepatotoxicants when a positive test outcome is defined as the bioactivation signature score of a test drug exceeding the threshold value at an in vitro test concentration that falls within 3-fold of the estimated maximum drug concentration at the human liver inlet following highest recommended clinical dose administrations. Using paired examples of compounds from distinct chemical series and close structural analogs, we demonstrate that this assay can differentiate drugs with lower DILI risk. The utility of this in vitro transcriptomic approach was also examined using human HEPATOPAC from a single donor, yielding 68% sensitivity and 86% specificity when the aforementioned criteria are applied to the same 93-drug test set. Routine use of the rat model has been adopted with deployment of the human model as warranted on a case-by-case basis. This in vitro transcriptomic signature-based strategy can be used early in drug discovery to derisk DILI potential from chemically reactive metabolites by guiding structure-activity relationship hypotheses and candidate selection.

Blinded, Multicenter Evaluation of Drug-induced Changes in Contractility Using Human-induced Pluripotent Stem Cell-derived Cardiomyocytes

Animal models are 78% accurate in determining whether drugs will alter contractility of the human heart. To evaluate the suitability of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) for predictive safety pharmacology, we quantified changes in contractility, voltage, and/or Ca²⁺ handling in 2D monolayers or 3D engineered heart tissues (EHTs). Protocols were unified via a drug training set, allowing subsequent blinded multicenter evaluation of drugs with known positive, negative, or neutral inotropic effects. Accuracy ranged from 44% to 85% across the platform-cell configurations, indicating the need to refine test conditions. This was achieved by adopting approaches to reduce signal-to-noise ratio, reduce spontaneous beat rate to ≤ 1 Hz or enable chronic testing, improving accuracy to 85% for monolayers and 93% for EHTs. Contraction amplitude was a good predictor of negative inotropes across all the platform-cell configurations and of positive inotropes in the 3D EHTs. Although contraction- and relaxation-time provided confirmatory readouts forpositive inotropes in 3D EHTs, these parameters typically served as the primary source of predictivity in 2D. The reliance of these “secondary” parameters to inotropy in the 2D systems was not automatically intuitive and may be a quirk of hiPSC-CMs, hence require adaptations in interpreting the data from this model system. Of the platform-cell configurations, responses in EHTs aligned most closely to the free therapeutic plasma concentration. This study adds to the notion that hiPSC-CMs could add value to drug safety evaluation.

Applicability of hiPSC-Derived Neuronal Cocultures and Rodent Primary Cortical Cultures for In Vitro Seizure Liability Assessment

Seizures are life-threatening adverse drug reactions which are investigated late in drug development using rodent models. Consequently, if seizures are detected, a lot of time, money and animals have been used. Thus, there is a need for in vitro screening models using human cells to circumvent interspecies translation. We assessed the suitability of cocultures of human-induced pluripotent stem cell (hiPSC)-derived neurons and astrocytes compared with rodent primary cortical cultures for in vitro seizure liability assessment using microelectrode arrays. hiPSC-derived and rodent primary cortical neuronal cocultures were exposed to 9 known (non)seizurogenic compounds (pentylenetetrazole, amoxapine, enoxacin, amoxicillin, linopirdine, pilocarpine, chlorpromazine, phenytoin, and acetaminophen) to assess effects on neuronal network activity using microelectrode array recordings. All compounds affect activity in hiPSC-derived cocultures. In rodent primary cultures all compounds, except amoxicillin changed activity. Changes in activity patterns for both cell models differ for different classes of compounds. Both models had a comparable sensitivity for exposure to amoxapine (lowest observed effect concentration [LOEC] 0.03 µM), linopirdine (LOEC 1 µM), and pilocarpine (LOEC 0.3 µM). However, hiPSC-derived cultures were about 3 times more sensitive for exposure to pentylenetetrazole (LOEC 30 µM) than rodent primary cortical cultures (LOEC 100 µM). Sensitivity of hiPSC-derived cultures for chlorpromazine, phenytoin, and enoxacin was 10-30 times higher (LOECs 0.1, 0.3, and 0.1 µM, respectively) than in rodent cultures (LOECs 10, 3, and 3 µM, respectively). Our data indicate that hiPSC-derived neuronal cocultures may outperform rodent primary cortical cultures with respect to detecting seizures, thereby paving the way towards animal-free seizure assessment.

Atlantic Horseshoe Crabs and Endotoxin Testing: Perspectives on Alternatives, sustainable Methods, and the 3Rs (Replacement, Reduction, and Refinement)

Endotoxin testing is a vital part of quality and safety control in pharmaceutical production. The primary method for this testing in North America and Europe is the limulus amebocyte lysate (LAL) test, a critical component of which is the blood of Atlantic horseshoe crabs (Limuius poiyphemus). Procuring blood for LAL testing involves capturing and bleeding over 500,000 crabs from wild marine populations each year. Whilst efforts are made by manufacturers to return crabs to the sea following the collection of blood, there is a level of mortality and sub-lethal impact involved, prompting increasing discussions about welfare and ethics. The 3Rs - the ambition to where possible, replace, reduce, and refine the use of animals - are established and accepted worldwide as the best framework for governing animal-dependent science. However, the biomedical utilization of horseshoe crabs to produce the LAL test has rarely been viewed through a 3Rs framework. More recently, there has been a renewed attention on sustainable methods and alternatives to the LAL test. Drawing on in-depth qualitative interviews, this article examines stakeholder perspectives on opportunities for thinking with the 3Rs, considering current appetites to replace, refine, and reduce contemporary biomedical reliance on horseshoe crabs. The shape of conversations about the biomedical utilization of horseshoe crabs has shifted significantly in recent years, and the 3Rs are an important driver of change, offering the potential to advance the use of more sustainable methods, and realize the welfare considerations increasingly expected across science and society.

Identifying and Characterizing Stress Pathways of Concern for Consumer Safety in Next-Generation Risk Assessment

Many substances for which consumer safety risk assessments need to be conducted are not associated with specific toxicity modes of action, but rather exhibit nonspecific toxicity leading to cell stress. In this work, a cellular stress panel is described, consisting of 36 biomarkers representing mitochondrial toxicity, cell stress, and cell health, measured predominantly using high content imaging. To evaluate the panel, data were generated for 13 substances at exposures consistent with typical use-case scenarios. These included some that have been shown to cause adverse effects in a proportion of exposed humans and have a toxicological mode-of-action associated with cellular stress (eg, doxorubicin, troglitazone, and diclofenac), and some that are not associated with adverse effects due to cellular stress at human-relevant exposures (eg, caffeine, niacinamide, and phenoxyethanol). For each substance, concentration response data were generated for each biomarker at 3 timepoints. A Bayesian model was then developed to quantify the evidence for a biological response, and if present, a credibility range for the estimated point of departure (PoD) was determined. PoDs were compared with the plasma Cmax associated with the typical substance exposures, and indicated a clear differentiation between "low" risk and "high" risk chemical exposure scenarios. Developing robust methods to characterize the in vitro bioactivity of xenobiotics is an important part of non-animal safety assessment. The results presented in this work show that the cellular stress panel can be used, together with other new approach methodologies, to identify chemical exposures that are protective of consumer health.

Improvement of a Three-Layered in vitro Skin Model for Topical Application of Irritating Substances

In the field of skin tissue engineering, the development of physiologically relevant in vitro skin models comprising all skin layers, namely epidermis, dermis, and subcutis, is a great challenge. Increasing regulatory requirements and the ban on animal experiments for substance testing demand the development of reliable and in vivo-like test systems, which enable high-throughput screening of substances. However, the reproducibility and applicability of in vitro testing has so far been insufficient due to fibroblast-mediated contraction. To overcome this pitfall, an advanced 3-layered skin model was developed. While the epidermis of standard skin models showed an 80% contraction, the initial epidermal area of our advanced skin models was maintained. The improved barrier function of the advanced models was quantified by an indirect barrier function test and a permeability assay. Histochemical and immunofluorescence staining of the advanced model showed well-defined epidermal layers, a dermal part with distributed human dermal fibroblasts and a subcutis with round-shaped adipocytes. The successful response of these advanced 3-layered models for skin irritation testing demonstrated the suitability as an in vitro model for these clinical tests: only the advanced model classified irritative and non-irritative substances correctly. These results indicate that the advanced set up of the 3-layered in vitro skin model maintains skin barrier function and therefore makes them more suitable for irritation testing.

The Overt and Hidden Use of Animal-Derived Products in Alternative Methods for Skin Sensitisation: A Systematic Review

In vitro methods that can replace animal testing in the identification of skin sensitisers are now a reality. However, as cell culture and related techniques usually rely on animal-derived products, these methods may be failing to address the complete replacement of animals in safety assessment. The objective of this study was to identify the animal-derived products that are used as part of in vitro methods for skin sensitisation testing. Thus, a systematic review of 156 articles featuring 83 different in vitro methods was carried out and, from this review, the use of several animal-derived products from different species was identified, with the use of fetal bovine serum being cited in most of the methods (78%). The use of sera from other animals, monoclonal antibodies and animal proteins were also variously mentioned. While non-animal alternatives are available and methods free of animal-derived products are emerging, most of the current methods reported used at least one animal-derived product, which raises ethical and technical concerns. Therefore, to deliver technically and ethically better in vitro methods for the safety assessment of chemicals, more effort should be made to replace products of animal origin in existing methods and to avoid their use in the development of new method protocols.

Towards animal-free neurotoxicity screening: Applicability of hiPSC-derived neuronal models for in vitro seizure liability assessment

A sizeable proportion of drug attrition is due to drug-induced seizures. Current available animal models frequently fail to predict human seizure liability. Therefore, there is a need for in vitro alternatives, preferably based on human-derived neurons to circumvent interspecies translation. The increasing number of commercially available human induced pluripotent stem cell (hiPSC)-derived neuronal models holds great promise for replacing rodent primary cultures. We therefore tested three different hiPSC-derived neuronal models for their applicability for in vitro seizure liability assessment. Using immunofluorescent staining and multi-well micro-electrode arrays we show that all models develop functional neuronal networks that exhibit spontaneous activity and (network) bursting behavior. Developmental patterns differ between the models, probably due to differences in model composition and seeding density. Nevertheless, neuronal activity and (network) bursting can be reproducibly modulated with the seizurogenic compounds strychnine, picrotoxin (PTX) and 4-aminopyridine (4-AP). However, the sensitivity and degree of chemical-induced effects differs between the models, which can likely be explained by differences in seeding density, maturation and different ratios of inhibitory and excitatory cell types. Importantly, compared to rat primary cortical neurons, the hiPSC-derived neuronal models were equally, or even better in the case of 4-AP, suited to detect seizurogenicity. Overall, our data indicate that hiPSC-derived neuronal models may in the future be used as a first screening tool for in vitro seizure liability assessment. However, before hiPSC-derived neuronal models can fully replace animal experiments, more compounds should be tested and the available models must be further characterized to fully understand their applicability.

Predicting toxicity of chemicals: software beats animal testing

We created earlier a large machine-readable database of 10,000 chemicals and 800,000 associated studies by natural language processing of the public parts of Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) registrations until December 2014. This database was used to assess the reproducibility of the six most frequently used Organisation for Economic Co-operation and Development (OECD) guideline tests. These tests consume 55% of all animals in safety testing in Europe, i.e. about 600,000 animals. With 350-750 chemicals with multiple results per test, reproducibility (balanced accuracy) was 81% and 69% of toxic substances were found again in a repeat experiment (sensitivity 69%). Inspired by the increasingly used read-across approach, we created a new type of QSAR, which is based on similarity of chemicals and not on chemical descriptors. A landscape of the chemical universe using 10 million structures was calculated, when based on Tanimoto indices similar chemicals are close and dissimilar chemicals far from each other. This allows placing any chemical of interest into the map and evaluating the information available for surrounding chemicals. In a data fusion approach, in which 74 different properties were taken into consideration, machine learning (random forest) allowed a fivefold cross-validation for 190,000 (non-) hazard labels of chemicals for which nine hazards were predicted. The balanced accuracy of this approach was 87% with a sensitivity of 89%. Each prediction comes with a certainty measure based on the homogeneity of data and distance of neighbours. Ongoing developments and future opportunities are discussed.

Toward Good In Vitro Reporting Standards

A good experiment reported badly is worthless. Meaningful contributions to the body of science are made by sharing the full methodology and results so that they can be evaluated and reproduced by peers. Erroneous and incomplete reporting does not do justice to the resources spent on conducting the experiment and the time peers spend reading the article. In theory peer-review should ensure adequate reporting - in practice it does not. Many areas have developed reporting standards and checklists to support the adequate reporting of scientific efforts, but in vitro research still has no generally accepted criteria. It is characterized by a "Wild West" or "anything goes" attitude. Such a culture may undermine trust in the reproducibility of animal-free methods, and thus parallel the "reproducibility crisis" discussed for other life science fields. The increasing data retrieval needs of computational approaches (in extreme as "big data" and artificial intelligence) makes reporting quality even more important so that the scientific community can take full advantage of the results. The first priority of reporting standards is to ensure the completeness and transparency of information provided (data focus). The second tier is a quality of data display that makes information digestible and easy to grasp, compare and further analyze (information focus). This article summarizes a series of initiatives geared towards improving the quality of in vitro work and its reporting. This shall ultimately lead to Good In Vitro Reporting Standards (GIVReSt).

The Impact of Novel Assessment Methodologies in Toxicology on Green Chemistry and Chemical Alternatives

The field of experimental toxicology is rapidly advancing by incorporating novel techniques and methods that provide a much more granular view into the mechanisms of potential adverse effects of chemical exposures on human health. The data from various in vitro assays and computational models are useful not only for increasing confidence in hazard and risk decisions, but also are enabling better, faster and cheaper assessment of a greater number of compounds, mixtures, and complex products. This is of special value to the field of green chemistry where design of new materials or alternative uses of existing ones is driven, at least in part, by considerations of safety. This article reviews the state of the science and decision-making in scenarios when little to no data may be available to draw conclusions about which choice in green chemistry is "safer." It is clear that there is no "one size fits all" solution and multiple data streams need to be weighed in making a decision. Moreover, the overall level of familiarity of the decision-makers and scientists alike with new assessment methodologies, their validity, value and limitations is evolving. Thus, while the "impact" of the new developments in toxicology on the field of green chemistry is great already, it is premature to conclude that the data from new assessment methodologies have been widely accepted yet.

Zebrafish embryo and acute fish toxicity test show similar sensitivity for narcotic compounds

The zebrafish embryo test has been discussed as an alternative test system to provide data on acute fish toxicity required by diverse regulations. A meta-analysis of zebrafish embryo acute toxicity (ZFET) data has revealed conflicting evidence that narcotic compounds (i.e. compounds with baseline toxicity) may exhibit weaker sensitivity in the ZFET if compared to the acute (adult) fish toxicity test (AFT). Therefore, six compounds with presumably narcotic or unknown mode of action, and for which a previous meta-analysis has indicated weaker sensitivity were experimentally analysed for their fish embryo acute toxicity and exposure concentrations were monitored. The data indicated that ZFET and AFT for the selected compounds revealed similar sensitivity and differences were in the range of species differences of the AFT.

Cross-linked Collagen Hydrogel Matrix Resisting Contraction To Facilitate Full-Thickness Skin Equivalents

Full-thickness skin equivalents are gathering increased interest as skin grafts for the treatment of large skin defects or chronic wounds or as nonanimal test platforms. However, their fibroblast-mediated contraction and poor mechanical stability lead to disadvantages toward their reproducibility and applicability in vitro and in vivo. To overcome these pitfalls, we aimed to chemically cross-link the dermal layer of a full-thickness skin model composed of a collagen type I hydrogel. Using a noncytotoxic four-arm succinimidyl glutarate polyethylene glycol (PEG-SG), cross-linking could be achieved in cell seeded collagen hydrogels. A concentration of 0.5 mg of PEG-SG/mg of collagen led to a viability comparable to non-cross-linked collagen hydrogels and no increased release of intracellular lactate dehydrogenase. Cross-linked collagen hydrogels were more mechanically stable and less prone to enzymatic degradation via collagenase when compared with non-cross-linked collagen hydrogels. Remarkably, during 21 days, cross-linked collagen hydrogels maintain their initial surface area, whereas standard dermal models contracted up to 50%. Finally, full-thickness skin equivalents were generated by seeding human epidermal keratinocytes on the surface of the equivalents and culturing these equivalents at an air-liquid interface. Immunohistochemical stainings of the cross-linked model revealed well-defined epidermal layers including an intact stratum corneum and a dermal part with homogeneously distributed human dermal fibroblasts. These results indicate that cross-linking of collagen with PEG-SG reduces contraction of collagen hydrogels and thus increases the applicability of these models as an additional tool for efficacy and safety assessment or a new generation of skin grafts.

Predicting Transport of 3,5,6-Trichloro-2-Pyridinol Into Saliva Using a Combination Experimental and Computational Approach

A combination experimental and computational approach was developed to predict chemical transport into saliva. A serous-acinar chemical transport assay was established to measure chemical transport with nonphysiological (standard cell culture medium) and physiological (using surrogate plasma and saliva medium) conditions using 3,5,6-trichloro-2-pyridinol (TCPy) a metabolite of the pesticide chlorpyrifos. High levels of TCPy protein binding were observed in cell culture medium and rat plasma resulting in different TCPy transport behaviors in the 2 experimental conditions. In the nonphysiological transport experiment, TCPy reached equilibrium at equivalent concentrations in apical and basolateral chambers. At higher TCPy doses, increased unbound TCPy was observed, and TCPy concentrations in apical and basolateral chambers reached equilibrium faster than lower doses, suggesting only unbound TCPy is able to cross the cellular monolayer. In the physiological experiment, TCPy transport was slower than nonphysiological conditions, and equilibrium was achieved at different concentrations in apical and basolateral chambers at a comparable ratio (0.034) to what was previously measured in rats dosed with TCPy (saliva:blood ratio: 0.049). A cellular transport computational model was developed based on TCPy protein binding kinetics and simulated all transport experiments reasonably well using different permeability coefficients for the 2 experimental conditions (1.14 vs 0.4 cm/h for nonphysiological and physiological experiments, respectively). The computational model was integrated into a physiologically based pharmacokinetic model and accurately predicted TCPy concentrations in saliva of rats dosed with TCPy. Overall, this study demonstrates an approach to predict chemical transport in saliva, potentially increasing the utility of salivary biomonitoring in the future.

Adaptation of the KeratinoSens™ skin sensitization test to animal-product-free cell culture

Skin sensitization is the process by which a substance induces an allergic reaction following skin contact. The process has been described as an adverse outcome pathway (AOP), including several key events, from skin penetration and covalent protein binding, to keratinocyte activation, dendritic cell activation and T-lymphocyte proliferation. The in vitro assay KeratinoSens™ measures the activation of keratinocytes. It is fully accepted at a regulatory level (OECD TG 442d) and complies with a range of legislation including the EU Cosmetics Regulation, REACH, and the CLP Regulation. Currently, many in vitro methods use animal-derived components in their cell culture systems. Many stakeholders in the cosmetics industry have both scientific and ethical concerns relating to this issue and have stated a strong preference for fully human in vitro test systems. We have adapted the KeratinoSens™ method to animal product-free condi­tions, and carried out an in-house validation with 21 reference substances, including those listed in the Performance Standards associated with OECD TG442d. The modified method was shown to be equivalent to the Validated Ref­erence Method (VRM), with comparable values for accuracy (85.7%), sensitivity (84.6%) and specificity (87.5%), and all acceptance criteria being met. In Europe, data generated by the adapted method may be used in REACH submissions, and we are now seeking approval to list the adaptation in OECD TG 442d, enabling formal compliance with a range of global regulations.

Non-animal approaches for toxicokinetics in risk evaluations of food chemicals

The objective of the present work was to review the availability and predictive value of non-animal toxicokinetic approaches and to evaluate their current use in European risk evaluations of food contaminants, additives and food contact materials, as well as pesticides and medicines. Results revealed little use of quantitative animal or human kinetic data in risk evaluations of food chemicals, compared with pesticides and medicines. Risk evaluations of medicines provided sufficient in vivo kinetic data from different species to evaluate the predictive value of animal kinetic data for humans. These data showed a relatively poor correlation between the in vivo bioavailability in rats and dogs versus that in humans. In contrast, in vitro (human) kinetic data have been demonstrated to provide adequate predictions of the fate of compounds in humans, using appropriate in vitro-in vivo scalers and by integration of in vitro kinetic data with in silico kinetic modelling. Even though in vitro kinetic data were found to be occasionally included within risk evaluations of food chemicals, particularly results from Caco-2 absorption experiments and in vitro data on gut-microbial conversions, only minor use of in vitro methods for metabolism and quantitative in vitro-in vivo extrapolation methods was identified. Yet, such quantitative predictions are essential in the development of alternatives to animal testing as well as to increase human relevance of toxicological risk evaluations. Future research should aim at further improving and validating quantitative alternative methods for kinetics, thereby increasing regulatory acceptance of non-animal kinetic data.

Editor's Highlight: Evaluation of a Microelectrode Array-Based Assay for Neural Network Ontogeny Using Training Set Chemicals

Thousands of compounds in the environment have not been characterized for developmental neurotoxicity (DNT) hazard. To address this issue, methods to screen compounds rapidly for DNT hazard evaluation are necessary and are being developed for key neurodevelopmental processes. In order to develop an assay for network formation, this study evaluated effects of a training set of chemicals on network ontogeny by measuring spontaneous electrical activity in neural networks grown on microelectrode arrays (MEAs). Rat (0-24 h old) primary cortical cells were plated in 48 well-MEA plates and exposed to 6 compounds: acetaminophen, bisindolylmaleimide-1 (Bis-1), domoic acid, mevastatin, sodium orthovanadate, and loperamide for a period of 12 days. Spontaneous network activity was recorded on days 2, 5, 7, 9, and 12 and viability was assessed using the Cell Titer Blue assay on day 12. Network activity (e.g. mean firing rate [MFR], burst rate [BR], etc), increased between days 5 and 12. Random Forest analysis indicated that across all compounds and times, temporal correlation of firing patterns (r), MFR, BR, number of active electrodes and % of spikes in a burst were the most influential parameters in separating control from treated wells. All compounds except acetaminophen (≤ 30 µM) caused concentration-related effects on one or more of these parameters. Domoic acid and sodium orthovanadate altered several of these parameters in the absence of cytotoxicity. Although cytotoxicity was observed with Bis1, mevastatin, and loperamide, some parameters were affected by these compounds at concentrations below those resulting in cytotoxicity. These results demonstrate that this assay may be suitable for screening of compounds for DNT hazard identification.

Can the Direct Peptide Reactivity Assay Be Used for the Identification of Respiratory Sensitization Potential of Chemicals?

Prospective identification of low molecular weight respiratory sensitizers is difficult due to the current lack of adequate test methods. The direct peptide reactivity assay (DPRA) seems to be a promising method to determine the sensitization potential of chemicals because it determines the intrinsic characteristic of sensitizers to bind to proteins. It is already applied in the field of skin sensitization, and adaptation to respiratory sensitization has started recently. This article further evaluates the ability of the DPRA to predict the respiratory sensitization potential of chemicals. In addition, the added value of applying High Performance Liquid Chromatography (HPLC)-MS and measurements after 20 minutes and 24 hours of incubation was evaluated. Eighteen respiratory sensitizers (10 haptens, 3 prehaptens, and 5 prohaptens) and 14 nonsensitizers were tested with 2-model peptides. Based on peptide depletion, a prediction model was proposed for the identification of (respiratory) sensitizers. Application of mass spectrometry and measurements at 2 time-points increased prediction accuracy of the assay by resolving discordant results. The prediction model correctly identified all haptens and prehaptens as sensitizers. The 5 prohaptens were not identified as sensitizers, most likely due to lack of metabolic activity in the DPRA. All but 1 nonsensitizer was correctly predicted. The model, therefore, shows an accuracy of 78% for the tested dataset. Unfortunately, this assay cannot be used to distinguish respiratory from skin sensitizers. To make this distinction, the DPRA needs to be combined with other test methods that are able to identify respiratory sensitizers.

Is the time right for in vitro neurotoxicity testing using human iPSC-derived neurons?

Current neurotoxicity testing heavily relies on expensive, time consuming and ethically debated in vivo animal experiments that are unsuitable for screening large number of chemicals. Consequently, there is a clear need for (high-throughput) in vitro test strategies, preferably using human cells as this increases relevance and eliminates the need for interspecies translation. However, human stem cell-derived neurons used to date are not well characterised, require prolonged differentiation and are potentially subject to batch-to-batch variation, ethical concerns and country-specific legislations. Recently, a number of human induced pluripotent stem cell (iPSC)-derived neurons became commercially available that may circumvent these concerns. We therefore used immunofluorescent stainings to demonstrate that human iPSC-derived neurons from various suppliers form mixed neuronal cultures, consisting of different types of (excitatory and inhibitory) neurons. Using multi-well microelectrode array (mwMEA) recordings, we demonstrate that these human iPSC-derived cultures develop spontaneous neuronal activity over time, which can be modulated by different physiological, toxicological and pharmacological compounds. Additional single cell calcium imaging illustrates the presence of functional GABA, glutamate, and acetylcholine receptors as well as voltage-gated calcium channels. While human iPSC-derived neuronal cultures appear not yet suitable to fully replace the rat primary cortical model, our data indicate that these rapidly differentiating, commercially available human iPSC-derived neuronal cultures are already suitable for in vitro prioritisation and effect screening studies. Further characterisation and toxicological validation is now required to facilitate acceptance and large-scale implementation of these animal-free, physiologically-relevant human iPSC-based modelsfor future neurotoxicity testing.

Simple and rapid in vitro assay for detecting human thyroid peroxidase disruption

A simple and rapid luminometric assay for the detection of chemical inhibitors of human thyroid peroxidase (hTPO) activity was developed and validated with 10 model compounds. hTPO was derived from the human thyroid follicular cell line Nthy-ori 3-1 and its activity was quantified by measuring the oxidation of luminol in the presence of hydrogen peroxide (H2O2), which results in the emission of light at 428 nm. In this assay,hTPO activity was shown to be inhibited by 5 known TPO inhibitors and not inhibited by 5 non-inhibitors. Similar results were obtained with porcine TPO (pTPO).The inhibition of hTPO by the model compounds was also tested with guaiacol and Ampliflu Red as alternative indicator substrates. While all substrates allowed the detection of pTPO activity and its inhibition, only the Ampliflu Red and luminol-based methods were sensitive enough to allow the quantification of hTPO activity from Nthy-ori 3-1 cell lysates. Moreover, luminol gave results with a narrower 95% confidence interval and therefore more reliable data.Whole extracts of fast-growing Nthy-ori 3-1 cells circumvent the need for animal-derived thyroid organs,thereby reducing costs, eliminating potential contamination and providing the possibility to study human instead of porcine TPO. Overall, the application of luminol and Nthy-ori 3-1 cell lysate for the detection of the disruption of hTPO activity was found to represent a valuable in vitro alternative and a possible candidate for inclusion within a high throughput integrated testing strategy for the detection of compounds that potentially interfere with normal thyroid function in vivo.

Evaluation of in silico models for the identification of respiratory sensitizers

Low molecular weight (LMW) respiratory sensitizers can cause occupational asthma but due to a lack of adequate test methods, prospective identification of respiratory sensitizers is currently not possible. This article presents the evaluation of structure-activity relationship (SAR) models as potential methods to prospectively conclude on the sensitization potential of LMW chemicals. The predictive performance of the SARs calculated from their training sets was compared to their performance on a dataset of newly identified respiratory sensitizers and nonsensitizers, derived from literature. The predictivity of the available SARs for new substances was markedly lower than their published predictive performance. For that reason, no single SAR model can be considered sufficiently reliable to conclude on potential LMW respiratory sensitization properties of a substance. The individual applicability domains (ADs) of the models were analyzed for adequacies and deficiencies. Based on these findings, a tiered prediction approach is subsequently proposed. This approach combines the two SARs with the highest positive and negative predictivity taking into account model specific chemical AD issues. The tiered approach provided reliable predictions for one-third of the respiratory sensitizers and nonsensitizers of the external validation set compiled by us. For these chemicals, a positive predictive value of 96% and a negative predictive value of 89% were obtained. The tiered approach was not able to predict the other two-thirds of the chemicals, meaning that additional information is required and that there is an urgent need for other test methods, e.g., in chemico or in vitro, to reach a reliable conclusion.

Early identification of clinically relevant drug interactions with the human bile salt export pump (BSEP/ABCB11)

A comprehensive analysis was performed to investigate how inhibition of the human bile salt export pump (BSEP/ABCB11) relates to clinically observed drug-induced liver injury (DILI). Inhibition of taurocholate (TA) transport was investigated in BSEP membrane vesicles for a data set of 250 compounds, and 86 BSEP inhibitors were identified. Structure-activity modeling identified BSEP inhibition to correlate strongly with compound lipophilicity, whereas positive molecular charge was associated with a lack of inhibition. All approved drugs in the data set (n = 182) were categorized according to DILI warnings in drug labels issued by the Food and Drug Administration, and a strong correlation between BSEP inhibition and DILI was identified. As many as 38 of the 61 identified BSEP inhibitors were associated with severe DILI, including 9 drugs not previously linked to BSEP inhibition. Further, among the tested compounds, every second drug associated with severe DILI was a BSEP inhibitor. Finally, sandwich-cultured human hepatocytes (SCHH) were used to investigate the relationship between BSEP inhibition, TA transport, and clinically observed DILI in detail. BSEP inhibitors associated with severe DILI greatly reduced the TA canalicular efflux, whereas BSEP inhibitors with less severe or no DILI resulted in weak or no reduction of TA efflux in SCHH. This distinction illustrates the usefulness of SCHH in refined analysis of BSEP inhibition. In conclusion, BSEP inhibition in membrane vesicles was found to correlate to DILI severity, and altered disposition of TA in SCHH was shown to separate BSEP inhibitors associated with severe DILI from those with no or mild DILI.