The dimer effect: A refinement approach towards skin sensitization assessment in-chemico using Amino acid Derivative Reactivity Assay.

Skin sensitization is a key endpoint for safety assessment, especially for cosmetics and personal care products. The adverse outcome pathway for skin sensitization and the chemical and biological events driving the induction of human skin sensitization are now well understood. Several non-animal test methods have been developed to predict sensitizer potential by measuring the impact of chemical sensitizers on these key events. In this work, we have focused on Key Event 1 (the molecular initiating step), which is based on formation of a covalent adduct between skin sensitizers and endogenous proteins and/or peptides in the skin. There exists three in-chemico assays approved by the Organization for Economic Co-operation and Development-(1) Direct Peptide Reactivity Assay (DPRA), (2) Amino Acid Derivative Reactivity Assay (ADRA), and (3) Kinetic Direct Peptide Reactivity Assay (kDPRA) to quantify peptide/amino acid derivative depletion after incubation with test chemicals. However, overestimated depletion of the cysteine-based peptide/amino acid derivatives is known in such assays because of the dimerization of the thiol group. In this present work, we report the synthesis and structural confirmation of the dimer of N-(2-[1-naphthyl]acetyl)-L-cysteine (NAC) from the ADRA assay to allow simultaneous determination of (a) peptide depletion by quantifying NAC monomer and (b) peptide dimerization by quantifying NAC dimer thereby eliminating the overestimation. We present a case study with three chemicals to demonstrate the importance of this approach. Thus, this simultaneous assay gives a more informed view of the peptide reactivity of chemicals to better identify skin sensitizers.

Skin sensitisation prediction using read-across, an illustrative next generation risk assessment (NGRA) case study for vanillin.

Skin sensitisation is a key adverse human health effect to be addressed in the safety assessment of cosmetic ingredients. Regulatory demands and scientific progress have led to the development of a Next Generation Risk Assessment (NGRA) framework, relying on the use of New Approach Methodologies (NAM) Defined Approaches (DA) and read-across instead of generating animal data. This case study illustrates the application of read-across for the prediction of the skin sensitisation potential of vanillin at the hypothetical use concentration of 0.5% in a shower gel and face cream. A three-step process was applied to select the most suitable analogues based on their protein reactivity, structural characteristics, physicochemical properties, skin metabolism profile and availability of skin sensitisation data. The applied read-across approach predicted a weak skin sensitiser potential for vanillin corresponding with a Local Lymph Node Assay EC3 value of 10%. Based on this EC3 value a point of departure of 2500 µg/cm2 was derived, resulting in an acceptable exposure level (AEL) of 25 µg/cm2. Because the consumer exposure levels (CEL) for the face cream (13.5 µg/cm2) and shower gel (0.05 µg/cm2) scenarios were lower than the AEL, the NGRA concluded both uses as safe.

Transferability and reproducibility of the EpiSkin™ Micronucleus Assay.

A novel in vitro 3D micronucleus assay was developed in China using the EpiSkin™ 3D human skin model. This EpiSkin™ Micronucleus Assay showed good predictivity and reproducibility during internal validation and is expected to contribute to in vitro genotoxicity testing as a follow-up for positive results from 2D micronucleus assay. Having developed the assay in one laboratory, further work focused on the transferability and inter-laboratory reproducibility in two additional Chinese authority laboratories (Guangdong Provincial Center for Disease Control and Prevention and Zhejiang Institute for Food and Drug Control). Formal training was provided for both laboratories, which resulted in good transferability based on the results of two positive compounds, such as mitomycin C and vinblastine. Independent experiments were then performed, and inter-laboratory reproducibility was checked using 2-acetylaminofluorene, 5-fluorouracil, 2,4-dichlorophenol, and d-limonene. The dose-responses of the positive control chemical, mitomycin C, were similar to those of the developing laboratory, and all test chemicals were correctly classified by all laboratories. Overall, there was a good transferability as well as intra- and inter-laboratory reproducibility of the EpiSkin™ Micronucleus Assay. This study further confirmed the assay's robustness and provided confidence to enter following validation stages for scientific acceptance.

Expansion of the Cosmetics Europe skin sensitisation database with new substances and PPRA data.

The assessment of skin sensitisation is a key requirement in all regulated sectors, with the European Union's regulation of cosmetic ingredients being most challenging, since it requires quantitative skin sensitisation assessment based on new approach methodologies (NAMs). To address this challenge, an in-depth and harmonised understanding of NAMs is fundamental to inform the assessment. Therefore, we compiled a database of NAMs, and in vivo (human and local lymph node assay) reference data. Here, we expanded this database with 41 substances highly relevant for cosmetic industry. These structurally different substances were tested in six NAMs (Direct Peptide Reactivity Assay, KeratinoSens™, human Cell Line Activation Test, U-SENS™, SENS-IS, Peroxidase Peptide Reactivity Assay). Our analysis revealed that the substances could be tested without technical limitations, but were generally overpredicted when compared to reference results. Reasons for this reduced predictivity were explored through pairwise NAM comparisons and association of overprediction with hydrophobicity. We conclude that more detailed understanding of how NAMs apply to a wider range of substances is needed. This would support a flexible and informed choice of NAMs to be optimally applied in the context of a next generation risk assessment framework, ultimately contributing to the characterisation and reduction of uncertainty.

A new 3D model for genotoxicity assessment: EpiSkin™ Micronucleus Assay.

The European Regulation on Cosmetics (no. 1223/2009) has prohibited the use of animals in safety testing since March 2009 for ingredients used in cosmetics. Irreversible events at the chromosome level (clastogenesis and aneugenesis) are commonly evaluated by scoring either micronuclei or chromosome aberrations using cell-based genotoxicity assays. Like most in vitro genotoxicity assays, the 2D in vitro micronucleus assay exhibits a poor specificity and does not mimic the dermal route. To address these limitations, the current project aims to develop and validate a 3D micronucleus assay using the EpiSkin™ model. This project is scientifically supported by the Cosmetics Europe Genotoxicity Task Force. In a first step, two key criteria for the development of micronucleus assay, namely, the sufficient yield of cells from the EpiSkin™ model and an acceptable proliferation rate of the basal layer, were assessed and demonstrated. Subsequently, six chemicals (vinblastine, n-ethylnitrosourea, ß-butyrolactone, 2-acetylaminofluorene, 2,4-dichlorophenoland d-limonene) were evaluated in the EpiSkin™ Micronucleus Assay. At least two independent experiments using 48- and 72-h incubations were performed for each chemical. Results showed good inter-experimental reproducibility, as well as the correct identification of all six tested chemicals. The metabolism of 2-acetylaminofluorene on the EpiSkin™ model was also investigated and confirmed by the formation of an intermediate metabolite (2-aminofluorene). These preliminary results from the EpiSkin™ Micronucleus Assay indicate that it is a promising in vitro assay for assessing genotoxicity. The availability and suitability of this test method contribute significantly to the development of non-animal testing methods in China and its impact on the worldwide field.

Next generation risk assessment for skin sensitisation: A case study with propyl paraben.

Skin sensitisation is a key adverse health effect to be addressed in the safety assessment of cosmetic ingredients. Regulatory demands have urged the development of Next Generation Risk Assessment (NGRA) using New Approach Methodologies (NAM) and Defined Approaches (DA) instead of animal models. An illustrative NGRA case study shall demonstrate if the use of propyl paraben at 0.2% in a face cream was safe for consumers. A sequential stacking tier testing DA based on NAM data predicted propyl paraben to be a non-sensitiser, while some NAM input data showed positive results. To increase confidence, structurally related parabens were considered, which revealed NAM and DA hazard predictions similar to those of propyl paraben, non-sensitiser classifications in animal models and very rare cases of human skin allergy. Based on a weight of evidence it was decided that propyl paraben should be considered a non-sensitiser leading to a favourable NGRA conclusion, in line with traditional risk assessment. Examination of an ab initio NGRA based on NAM and metabolism data resulted in a more conservative weak sensitiser consideration as point of departure, which still led to a favourable conclusion.

Read-across can increase confidence in the Next Generation Risk Assessment for skin sensitisation: A case study with resorcinol.

Historically skin sensitisation risk assessment for cosmetic ingredients was based on animal models, however regulatory demands have led to Next Generation Risk Assessment (NGRA), using data from New Approach Methodologies (NAM) and Defined Approaches (DA). This case study was meant to investigate if the use of resorcinol at 0.2% in a face cream was safe and a maximum use concentration could be defined. The NAM data and DA predictions could not provide sufficient confidence to determine a point of departure (POD). Therefore, the application of read-across was explored to increase the level of confidence. Analogue searches in various tools and databases using "mode of action" and "chemical structural features" retrieved 535 analogues. After refinement by excluding analogues without a defined structure, similar reactivity profile and skin sensitisation data, 39 analogues remained. A final selection was made based on three approaches: expert judgment, chemical similarity or Local Lymph Node Assay data (LLNA). All read-across approaches supported a moderate potency. A POD derived from the LLNA EC3 of 3.6% was determined leading to a favourable NGRA conclusion and a maximum use concentration of 0.36%. This was supported by a traditional risk assessment based on the available animal data for resorcinol.

Development of a next generation risk assessment framework for the evaluation of skin sensitisation of cosmetic ingredients.

All cosmetic products placed onto the market must undergo a risk assessment for human health to ensure they are safe for consumers, including an assessment of skin sensitisation risk. Historically, in vivo animal test methods were used to identify and characterise skin sensitisation hazard, however non-animal and other new approach methodologies (NAMs) are now the preferred and mandated choice for use in risk assessment for cosmetic ingredients. The experience gained over the last three decades on how to conduct risk assessments based upon NAMs has allowed us to develop a non-animal, next generation risk assessment (NGRA) framework for the assessment of skin sensitisers. The framework presented here is based upon the principles published by the International Cooperation on Cosmetic Regulation (ICCR) and is human relevant, exposure led, hypothesis driven and designed to prevent harm. It is structured in three tiers and integrates all relevant information using a weight of evidence (WoE) approach that can be iterated when new information becomes available. The initial tier (TIER 0) involves a thorough review of the existing information including; identification of the use scenario/consumer exposure; characterisation of the chemical purity and structure; in silico predictions; existing data pertaining to skin sensitisation hazard (historical or non-animal); the identification of suitable read-across candidates with supporting hazard identification/characterisation information and application of exposure-based waiving. Considering all information identified in TIER 0, the next step is the generation of a hypothesis (TIER 1). All data are considered in an exposure-led WoE approach, taking into account an initial view on whether a chemical is likely to be a skin sensitiser or not, choice of defined approach (DA) and availability of read-across candidates. If existing information is insufficient for concluding the risk assessment, the generation of additional information may be required to proceed (TIER 2). Such targeted testing could involve refinement of the exposure estimation or generation of data from in vitro or in chemico NAMs. Once sufficient information is available, the final stage of the NGRA framework is the determination of a point of departure (POD), characterising uncertainty and comparing to the consumer exposure in a WoE. Thorough evaluation of the sources of uncertainty is essential to ensure transparency and build trust in new risk assessment approaches. Although significant progress has been made, industry must continue to share its experience in skin sensitisation NGRA via case studies to demonstrate that this new risk assessment approach is protective for consumers. Dialogue and collaboration between key stakeholders, i.e. risk assessors, clinicians and regulators are important to gain mutual understanding and grow confidence in new approaches.

Non-animal methods to predict skin sensitization (II): an assessment of defined approaches *.

Skin sensitization is a toxicity endpoint of widespread concern, for which the mechanistic understanding and concurrent necessity for non-animal testing approaches have evolved to a critical juncture, with many available options for predicting sensitization without using animals. Cosmetics Europe and the National Toxicology Program Interagency Center for the Evaluation of Alternative Toxicological Methods collaborated to analyze the performance of multiple non-animal data integration approaches for the skin sensitization safety assessment of cosmetics ingredients. The Cosmetics Europe Skin Tolerance Task Force (STTF) collected and generated data on 128 substances in multiple in vitro and in chemico skin sensitization assays selected based on a systematic assessment by the STTF. These assays, together with certain in silico predictions, are key components of various non-animal testing strategies that have been submitted to the Organization for Economic Cooperation and Development as case studies for skin sensitization. Curated murine local lymph node assay (LLNA) and human skin sensitization data were used to evaluate the performance of six defined approaches, comprising eight non-animal testing strategies, for both hazard and potency characterization. Defined approaches examined included consensus methods, artificial neural networks, support vector machine models, Bayesian networks, and decision trees, most of which were reproduced using open source software tools. Multiple non-animal testing strategies incorporating in vitro, in chemico, and in silico inputs demonstrated equivalent or superior performance to the LLNA when compared to both animal and human data for skin sensitization.

Non-animal methods to predict skin sensitization (I): the Cosmetics Europe database.

Cosmetics Europe, the European Trade Association for the cosmetics and personal care industry, is conducting a multi-phase program to develop regulatory accepted, animal-free testing strategies enabling the cosmetics industry to conduct safety assessments. Based on a systematic evaluation of test methods for skin sensitization, five non-animal test methods (DPRA (Direct Peptide Reactivity Assay), KeratinoSensTM, h-CLAT (human cell line activation test), U-SENSTM, SENS-IS) were selected for inclusion in a comprehensive database of 128 substances. Existing data were compiled and completed with newly generated data, the latter amounting to one-third of all data. The database was complemented with human and local lymph node assay (LLNA) reference data, physicochemical properties and use categories, and thoroughly curated. Focused on the availability of human data, the substance selection resulted nevertheless resulted in a high diversity of chemistries in terms of physico-chemical property ranges and use categories. Predictivities of skin sensitization potential and potency, where applicable, were calculated for the LLNA as compared to human data and for the individual test methods compared to both human and LLNA reference data. In addition, various aspects of applicability of the test methods were analyzed. Due to its high level of curation, comprehensiveness, and completeness, we propose our database as a point of reference for the evaluation and development of testing strategies, as done for example in the associated work of Kleinstreuer et al. We encourage the community to use it to meet the challenge of conducting skin sensitization safety assessment without generating new animal data.

Cosmetics Europe compilation of historical serious eye damage/eye irritation in vivo data analysed by drivers of classification to support the selection of chemicals for development and evaluation of alternative methods/strategies: the Draize eye test Reference Database (DRD).

A thorough understanding of which of the effects assessed in the in vivo Draize eye test are responsible for driving UN GHS/EU CLP classification is critical for an adequate selection of chemicals to be used in the development and/or evaluation of alternative methods/strategies and for properly assessing their predictive capacity and limitations. For this reason, Cosmetics Europe has compiled a database of Draize data (Draize eye test Reference Database, DRD) from external lists that were created to support past validation activities. This database contains 681 independent in vivo studies on 634 individual chemicals representing a wide range of chemical classes. A description of all the ocular effects observed in vivo, i.e. degree of severity and persistence of corneal opacity (CO), iritis, and/or conjunctiva effects, was added for each individual study in the database, and the studies were categorised according to their UN GHS/EU CLP classification and the main effect driving the classification. An evaluation of the various in vivo drivers of classification compiled in the database was performed to establish which of these are most important from a regulatory point of view. These analyses established that the most important drivers for Cat 1 Classification are (1) CO mean ≥ 3 (days 1-3) (severity) and (2) CO persistence on day 21 in the absence of severity, and those for Cat 2 classification are (3) CO mean ≥ 1 and (4) conjunctival redness mean ≥ 2. Moreover, it is shown that all classifiable effects (including persistence and CO = 4) should be present in ≥60 % of the animals to drive a classification. As a consequence, our analyses suggest the need for a critical revision of the UN GHS/EU CLP decision criteria for the Cat 1 classification of chemicals. Finally, a number of key criteria are identified that should be taken into consideration when selecting reference chemicals for the development, evaluation and/or validation of alternative methods and/or strategies for serious eye damage/eye irritation testing. Most important, the DRD is an invaluable tool for any future activity involving the selection of reference chemicals.

Retrospective analysis of the Draize test for serious eye damage/eye irritation: importance of understanding the in vivo endpoints under UN GHS/EU CLP for the development and evaluation of in vitro test methods.

For more than two decades, scientists have been trying to replace the regulatory in vivo Draize eye test by in vitro methods, but so far only partial replacement has been achieved. In order to better understand the reasons for this, historical in vivo rabbit data were analysed in detail and resampled with the purpose of (1) revealing which of the in vivo endpoints are most important in driving United Nations Globally Harmonized System/European Union Regulation on Classification, Labelling and Packaging (UN GHS/EU CLP) classification for serious eye damage/eye irritation and (2) evaluating the method's within-test variability for proposing acceptable and justifiable target values of sensitivity and specificity for alternative methods and their combinations in testing strategies. Among the Cat 1 chemicals evaluated, 36-65 % (depending on the database) were classified based only on persistence of effects, with the remaining being classified mostly based on severe corneal effects. Iritis was found to rarely drive the classification (<4 % of both Cat 1 and Cat 2 chemicals). The two most important endpoints driving Cat 2 classification are conjunctiva redness (75-81 %) and corneal opacity (54-75 %). The resampling analyses demonstrated an overall probability of at least 11 % that chemicals classified as Cat 1 by the Draize eye test could be equally identified as Cat 2 and of about 12 % for Cat 2 chemicals to be equally identified as No Cat. On the other hand, the over-classification error for No Cat and Cat 2 was negligible (<1 %), which strongly suggests a high over-predictive power of the Draize eye test. Moreover, our analyses of the classification drivers suggest a critical revision of the UN GHS/EU CLP decision criteria for the classification of chemicals based on Draize eye test data, in particular Cat 1 based only on persistence of conjunctiva effects or corneal opacity scores of 4. In order to successfully replace the regulatory in vivo Draize eye test, it will be important to recognise these uncertainties and to have in vitro tools to address the most important in vivo endpoints identified in this paper.

Development of a defined approach for eye hazard identification of solid chemicals according to the three UN GHS categories.

Currently there are two OECD-adopted defined approaches (DA) for eye hazard identification of non-surfactant liquids (OECD TG 467). The current study aimed to develop a DA for eye hazard identification of solid chemicals according to the three UN GHS categories (Cat.1, Cat. 2, No Cat.): the DAS. The DAS combines two test methods described in OECD TG 437 and TG 492. The DAS was developed based on in-depth statistical analysis of a database on solids containing in vitro and historically curated in vivo Draize eye test data. The performance of the DAS was assessed by comparing the predictions with the classification based on in vivo Draize eye test data, on the one hand, and with the performance criteria established by the OECD expert group, on the other hand. In a first tier of the DAS, the SkinEthic™ HCE EIT method (TG 492) is used to distinguish No Cat. from classified substances. For classified substances, the BCOP LLBO method (TG 437) is used to identify Cat. 1, and the remaining solids are predicted Cat. 2. In summary, 77.4% Cat. 1 (N=31), 52.3% Cat. 2 (N=18), and 70.0% of No Cat. (N=60) solids were correctly identified compared to the classification based on the Draize eye test. The percentage of correct predictions met the minimum OECD performance values of 75% Cat. 1, 50% Cat. 2, and 70% No Cat., and the percentage of mispredictions was below the established maximum values. Therefore, inclusion of the DAS in OECD TG 467 has been achieved.

Defined approaches combine information from different non-animal testing methods in a specific way and interpret the results according to a fixed procedure. Such defined approaches are already available as full replacements of animal testing to assess the eye hazard of liquid chemicals (OECD Test Guideline 467). This study used two OECD-adopted in vitro methods, based on human cells and corneas from cattle, to create a defined approach that can be used for solid chemicals. The performance of the procedure was assessed against data from previous animal tests for 109 solid chemicals. The results have already led to this defined approach being adopted by the OECD TGs programme for inclusion in TG 467. With the adoption of the new defined approach, non-animal human relevant strategies are now available for eye hazard assessment of liquids and solids, reducing the need for animal testing.

Deriving a Continuous Point of Departure for Skin Sensitization Risk Assessment Using a Bayesian Network Model.

Regulations of cosmetic ingredients and products have been the most advanced in embracing new approach methodologies (NAMs). Consequently, the cosmetic industry has assumed a forerunner role in the development and implementation of animal-free next-generation risk assessment (NGRA) that incorporates defined approaches (DAs) to assess the skin sensitization potency of ingredients. A Bayesian network DA predicting four potency categories (SkinSens-BN) was constructed against reference Local Lymph Node Assay data for a total of 297 substances, achieving a predictive performance similar to that of other DAs. With the aim of optimally informing risk assessment with a continuous point of departure (PoD), a weighted sum of the SkinSens-BN probabilities for four potency classes (non-, weak, moderate, and strong/extreme sensitizer) was calculated, using fixed weights based on associated LLNA EC3-values. The approach was promising, e.g., the derived PoDs for substances classified as non-sensitizers did not overlap with any others and 77% of PoDs were similar or more conservative than LLNA EC3. In addition, the predictions were assigned a level of confidence based on the probabilities to inform the evaluation of uncertainty in an NGRA context. In conclusion, the PoD derivation approach can substantially contribute to reliable skin sensitization NGRAs.

Skin sensitisation--moving forward with non-animal testing strategies for regulatory purposes in the EU.

In a previous EPAA-Cefic LRI workshop in 2011, issues surrounding the use and interpretation of results from the local lymph node assay were addressed. At the beginning of 2013 a second joint workshop focused greater attention on the opportunities to make use of non-animal test data, not least since a number of in vitro assays have progressed to an advanced position in terms of their formal validation. It is already recognised that information produced from non-animal assays can be used in regulatory decision-making, notably in terms of classifying a substance as a skin sensitiser. The evolution into a full replacement for hazard identification, where the decision is not to classify, requires the generation of confidence in the in vitro alternative, e.g. via formal validation, the existence of peer reviewed publications and the knowledge that the assay(s) are founded on key elements of the Adverse Outcome Pathway for skin sensitisation. It is foreseen that the validated in vitro assays and relevant QSAR models can be organised into formal testing strategies to be applied for regulatory purposes by the industry. To facilitate progress, the European Partnership for Alternative Approaches to animal testing (EPAA) provided the platform for cross-industry and regulatory dialogue, enabling an essential and open debate on the acceptability of an in vitro based integrated strategy. Based on these considerations, a follow up activity was agreed upon to explore an example of an Integrated Testing Strategy for skin sensitisation hazard identification purposes in the context of REACH submissions.

How to facilitate the implementation of 3D models in China by applying good in vitro method practice for regulatory use.

The Organization for Economic Co-operation and Development (OECD) Guidance Document No. 34 and No. 286 on Good In Vitro Method Practices (GIVIMPs) for the development and implementation of in vitro methods for regulatory use in human safety assessment have been endorsed. Considering that China is accelerating the development of alternative approaches in both research and acceptance, early application of these principles is beneficial to the implementation and acceptance of in vitro alternative methods in China. To promote the replacement of animal testing for regulatory use, L'Oréal initiated the EpiSkin™ skin irritation test (SIT) implementation program in China. More than 50 external scientists participated, and the method has been established in 34 organizations including authorities, industries, and testing service laboratories. Taking two collaborations with Guangdong CDC and Shanghai SGS for in vitro SIT as examples, we demonstrated a method implementation process in good alignment with the OECD principles. The current study illustrated the practical way in which both OECD Guidance documents assisted in the transfer and establishment of in vitro approaches and further promoted the future scientific recognition and acceptance of new OECD-accepted alternative testing methodologies in China.

Off to a good start? Review of the predictivity of reactivity methods modelling the molecular initiating event of skin sensitization.

The assessment of skin sensitizing properties of chemicals has moved away from animal methods to new approach methodologies (NAM), guided by qualitative mechanistic understanding operationalized in an adverse outcome pathway (AOP). As with any AOP, the molecular initiating event (MIE) of covalent binding of a chemical to skin proteins is particularly important. This MIE has been modelled by several test methods by measuring the reaction of a test chemical with model peptides in chemico. To better understand the similarities and differences, a data repository with publicly available data for the direct peptide reactivity assay (DPRA), amino acid derivative reactivity assay (ADRA) and kinetic DPRA (kDPRA), as well as the peroxidase peptide reactivity assay (PPRA) was assembled. The repository comprises 260 chemicals with animal and human reference data, data on four relevant physicochemical properties, and between 161 to 242 test chemical results per test method. First, an overview of the experimental conditions of the four test methods was compiled allowing to readily compare them. Second, data analyses demonstrated that the test methods' predictivity was consistently reduced for poorly watersoluble chemicals and that the DPRA and ADRA can be used interchangeably. It also revealed new categorization thresholds for the DPRA and ADRA that are potentially relevant for strategic uses. In summary, a detailed assessment of reactivity test methods is provided, highlighting their potential and limitations. The results presented are intended to stimulate scientific discussion around test methods modelling the MIE of the skin sensitization AOP.

Applying a next generation risk assessment framework for skin sensitisation to inconsistent new approach methodology information.

Cosmetic products must be safe for their intended use. Regulatory bans on animal testing for new ingredients have resulted in a shift towards the use of new approach methodologies (NAMs) such as in silico predictions and in chemico / in vitro data. Defined approaches (DAs) have been developed to interpret combinations of NAMs to provide information on skin sensitization hazard and potency, three having been adopted within OECD Test Guideline 497. However, the challenge remains as to how DAs can be used to derive a quantitative point of departure for use in next generation risk assessment (NGRA). Here we provide an update to our previously published NGRA framework and present two hypothetical consumer risk assessment scenarios (rinse-off and leave-on) on one case study ingredient. Diethanolamine (DEA) was selected as the case study ingredient based on the existing NAM information demonstrating differences with respect to the outcomes from in silico predictions and in chemico / in vitro data. Seven DAs were applied, and these differences resulted in divergent DA outcomes and reduced confidence with respect to the hazard potential and potency predictions. Risk assessment conclusion for the rinse-off exposure led to an overall decision of safe for all applied DAs. Risk assessment conclusion for the higher leave-on exposure was safe when based on some DAs but unsafe based on others. The reasons for this were evaluated as well as the inherent uncertainty from the use of each NAM and DA in the risk assessment, enabling further refinement of our NGRA framework.

Guiding principles for the implementation of non-animal safety assessment approaches for cosmetics: skin sensitisation.

Characterisation of skin sensitisation potential is a key endpoint for the safety assessment of cosmetic ingredients especially when significant dermal exposure to an ingredient is expected. At present the mouse local lymph node assay (LLNA) remains the 'gold standard' test method for this purpose however non-animal test methods are under development that aim to replace the need for new animal test data. COLIPA (the European Cosmetics Association) funds an extensive programme of skin sensitisation research, method development and method evaluation and helped coordinate the early evaluation of the three test methods currently undergoing pre-validation. In May 2010, a COLIPA scientific meeting was held to analyse to what extent skin sensitisation safety assessments for cosmetic ingredients can be made in the absence of animal data. In order to propose guiding principles for the application and further development of non-animal safety assessment strategies it was evaluated how and when non-animal test methods, predictions based on physico-chemical properties (including in silico tools), threshold concepts and weight-of-evidence based hazard characterisation could be used to enable safety decisions. Generation and assessment of potency information from alternative tools which at present is predominantly derived from the LLNA is considered the future key research area.

Regulatory assessment of in vitro skin corrosion and irritation data within the European framework: Workshop recommendations.

Validated in vitro methods for skin corrosion and irritation were adopted by the OECD and by the European Union during the last decade. In the EU, Switzerland and countries adopting the EU legislation, these assays may allow the full replacement of animal testing for identifying and classifying compounds as skin corrosives, skin irritants, and non irritants. In order to develop harmonised recommendations on the use of in vitro data for regulatory assessment purposes within the European framework, a workshop was organized by the Swiss Federal Office of Public Health together with ECVAM and the BfR. It comprised stakeholders from various European countries involved in the process from in vitro testing to the regulatory assessment of in vitro data. Discussions addressed the following questions: (1) the information requirements considered useful for regulatory assessment; (2) the applicability of in vitro skin corrosion data to assign the corrosive subcategories as implemented by the EU Classification, Labelling and Packaging Regulation; (3) the applicability of testing strategies for determining skin corrosion and irritation hazards; and (4) the applicability of the adopted in vitro assays to test mixtures, preparations and dilutions. Overall, a number of agreements and recommendations were achieved in order to clarify and facilitate the assessment and use of in vitro data from regulatory accepted methods, and ultimately help regulators and scientists facing with the new in vitro approaches to evaluate skin irritation and corrosion hazards and risks without animal data.