The Use of Chemical Reactivity Assays in Toxicity Prediction

The use of so-called “in chemico” methodology - abiotic assays that measure chemical reactivity - is gaining ground as relevant and reliable means of toxicity prediction. In this report we explain the basis of the in chemico approach to toxicity prediction and we review the studies that have developed the concept and its practical application since the 1930s, with special attention being paid to studies aimed at the development of Quantitative Structure-Activity Relationship (QSAR) models and read-across approaches. The studies covered in this review are limited to non-enzymatic experiments and to nucleophiles up to 50 amino acids. The main applications identified are related to the assessment of skin sensitisation, aquatic toxicity and hepatotoxicity. Various experimental measures of nucleophile depletion or adduct formation have been proposed as chemical reactivity descriptors, but no single protocol has emerged as the most generally useful. It is concluded that in chemico approaches provide a promising means of toxicity prediction within their applicability domains and should be further developed and investigated as alternative methods to animal testing, especially when used in the context of integrated testing strategies based on the use of multiple non-animal methods.JRC.DG.I.6-Systems toxicolog

Dissecting the hindered rotation of ethane

The existence of a rotational barrier of ca. 3 kcal mol À1 around the CÀC single bond in ethane has been known The steric repulsion still remains the most popular explanation of the hindered rotation of ethane. This effect is often understood as the increase in energy that accompanies the antisymmetrization of a wave function originally formed by strictly localized descriptions of two methyl groups brought up to the final ethane geometry where they overlap. This so-called Pauli repulsion is considered to be more important for the eclipsed conformation, The hyperconjugation [21] The electron delocalization effect can easily be assessed in valence bond (VB) theory calculations Previous energy decomposition analyses relied, in one way or another, on the definition of two methyl fragments. However, in the last years there have been a growing interest in other kinds of energy partitioning schemes, The diatomic terms naturally reflect the attractive or repulsive interactions between the atoms in the molecule. The onecenter terms correspond to the effective energy of each atom in the molecule; its value relative to that of the corresponding free atom accounts for the promotion that occurs upon bond formation. In this sense, it is important to recall that the oneand two-center contributions are static parameters. [26] They measure to which extent the energy of a given atom or atomic pair contributes to the total molecular energy at that geometry and with the wave function used at that point. Thus, the diatomic values cannot be put into direct correspondence with the dissociation energies, as dissociation involves changes in both geometry and wave function. The main advantage of this methodology for the present case is that one can decompose all energetic interactions within the molecule on the basis of a single ab initio calculation, without recurring to an arbitrar

Evaluation of the availability and applicability of computational approaches in the safety assessment of nanomaterials: Final report of the Nanocomput project

This is the final report of the Nanocomput project, the main aims of which were to review the current status of computational methods that are potentially useful for predicting the properties of engineered nanomaterials, and to assess their applicability in order to provide advice on the use of these approaches for the purposes of the REACH regulation. Since computational methods cover a broad range of models and tools, emphasis was placed on Quantitative Structure-Property Relationship (QSPR) and Quantitative Structure-Activity Relationship (QSAR) models, and their potential role in predicting NM properties. In addition, the status of a diverse array of compartment-based mathematical models was assessed. These models comprised toxicokinetic (TK), toxicodynamic (TD), in vitro and in vivo dosimetry, and environmental fate models. Finally, based on systematic reviews of the scientific literature, as well as the outputs of the EU-funded research projects, recommendations for further research and development were also made. The Nanocomput project was carried out by the European Commission’s Joint Research Centre (JRC) for the Directorate-General (DG) for Internal Market, Industry, Entrepreneurship and SMEs (DG GROW) under the terms of an Administrative Arrangement between JRC and DG GROW. The project lasted 39 months, from January 2014 to March 2017, and was supported by a steering group with representatives from DG GROW, DG Environment and the European Chemicals Agency (ECHA).JRC.F.3-Chemicals Safety and Alternative Method

Ability of non-animal methods for skin sensitisation to detect pre- and pro-haptens: Report and recommendations of an EURL ECVAM expert meeting

Significant progress has been made in the development, validation and regulatory acceptance of in chemico and in vitro test methods for skin sensitisation. Although these methods have been shown to perform relatively well (about 80% accuracy in predicting Local Lymph Node Assay (LLNA) classifications) a concern was raised on the regulatory acceptability of negative results since it was questioned whether these methods are able to predict chemicals that need to be activated to act as sensitisers. In order to inform ongoing discussions at the regulatory level in the EU, EURL ECVAM held an expert meeting on 10-11 November 2015 to analyse the extent to which in chemical and in vitro methods are able to correctly identify chemicals that need to be activated either through abiotic activation (pre-haptens) and/or through biotic (enzyme-mediated) mechanisms (pro-haptens) to acquire skin sensitisation potential. The expert group analysed a list of 127 chemicals, with available LLNA and in vitro data, 22% of which were considered to be pre- and/or pro-haptens. The pre-haptens, constituting the vast majority of chemicals requiring activation, where mostly correctly identified by both the in chemico and in vitro assays whereas the pro-haptens which represent a small subset of sensitising chemicals, were generally identified correctly by one of the cell-based assays. As a result, the expert group recommended that negative in vitro data should be accepted unless there is a compelling scientific argument that a substance is likely to be an exclusively metabolically activated pro-hapten.JRC.I.5-Systems Toxicolog

Grouping of nanomaterials to read-across hazard endpoints: a review

The use of non-testing strategies like read-across in the hazard assessment of chemicals and nanomaterials (NMs) is deemed essential to perform the safety assessment of all NMs in due time and at lower costs. The identification of physicochemical (PC) properties affecting the hazard potential of NMs is crucial, as it could enable to predict impacts from similar NMs and outcomes of similar assays, reducing the need for experimental (and in particular animal) testing. This manuscript presents a review of approaches and available case studies on the grouping of NMs to read-across hazard endpoints. We include in this review grouping frameworks aimed at identifying hazard classes depending on PC properties, hazard classification modules in control banding (CB) approaches, and computational methods that can be used for grouping for read-across. The existing frameworks and case studies are systematically reported. Relevant nanospecific PC properties taken into account in the reviewed frameworks to support grouping are shape and surface properties (surface chemistry or reactivity) and hazard classes are identified on the basis of biopersistence, morphology, reactivity, and solubility.JRC.F.3-Chemicals Safety and Alternative Method

SpheraCosmolife: a new tool for the risk assessment of cosmetic products.

A new, freely available software for cosmetic products has been designed that considers the regulatory framework for cosmetics. The software allows an overall toxicological evaluation of cosmetic ingredients without the need for additional testing and, depending on the product type, it applies defined exposure scenarios to derive risk for consumers. It takes regulatory thresholds into account and uses either experimental values, if available, or predictions. Based on the exper­imental or predicted no observed adverse effect level (NOAEL), the software can define a point of departure (POD), which is used to calculate the margin of safety (MoS) of the query chemicals. The software also provides other toxico­logical properties, such as mutagenicity, skin sensitization, and the threshold of toxicological concern (TTC) to provide an overall evaluation of the potential chemical hazard. Predictions are calculated using in silico models implemented within the VEGA software. The full list of ingredients of a cosmetic product can be processed at the same time, at the effective concentrations in the product as given by the user. SpheraCosmolife is designed as a support tool for safety assessors of cosmetic products and can be used to prioritize the cosmetic ingredients or formulations according to their potential risk to consumers. The major novelty of the tool is that it wraps a series of models (some of them new) into a single, user-friendly software system

EURL ECVAM Status Report on the Development, Validation and Regulatory Acceptance of Alternative Methods and Approaches (2016)

Replacement, Reduction and Refinement of animal testing is anchored in EU legislation. Alternative non-animal approaches facilitate a shift away from animal testing. Cell-based methods and computational technologies are integrated to translate molecular mechanistic understanding of toxicity into safety testing strategies.JRC.F.3-Chemicals Safety and Alternative Method

Grouping of nanomaterials to read-across hazard endpoints: from data collection to assessment of the grouping hypothesis by application of chemoinformatic techniques

An increasing number of manufactured nanomaterials (NMs) are being used in industrial products and need to be registered under the REACH legislation. The hazard characterisation of all these forms is not only technically challenging but resource and time demanding. The use of non-testing strategies like read-across is deemed essential to assure the assessment of all NMs in due time and at lower cost. The fact that read-across is based on the structural similarity of substances represents an additional difficulty for NMs as in general their structure is not unequivocally defined. In such a scenario, the identification of physicochemical properties affecting the hazard potential of NMs is crucial to define a grouping hypothesis and predict the toxicological hazards of similar NMs. In order to promote the read-across of NMs, ECHA has recently published “Recommendations for nanomaterials applicable to the guidance on QSARs and Grouping”, but no practical examples were provided in the document. Due to the lack of publicly available data and the inherent difficulties of reading-across NMs, only a few examples of read-across of NMs can be found in the literature. This manuscript presents the first case study of the practical process of grouping and read-across of NMs following the workflow proposed by ECHA. The workflow proposed by ECHA was used and slightly modified to present the read-across case study. The Read-Across Assessment Framework (RAAF) was used to evaluate the uncertainties of a read-across within NMs. Chemoinformatic techniques were used to support the grouping hypothesis and identify key physicochemical properties. A dataset of 6 nanoforms of TiO2 with more than 100 physicochemical properties each was collected. In vitro comet assay result was selected as the endpoint to read-across due to data availability. A correlation between the presence of coating or large amounts of impurities and negative comet assay results was observed. The workflow proposed by ECHA to read-across NMs was applied successfully. Chemoinformatic techniques were shown to provide key evidence for the assessment of the grouping hypothesis and the definition of similar NMs. The RAAF was found to be applicable to NMs