Evaluation of in vitro testing strategies for hazard assessment of the skin sensitization potential of “real‐life” mixtures: the case of henna‐based hair coloring products containing p‐phenylenediamine

Wiley Online Library, First published: 21 April 2019,  https://doi.org/10.1111/cod.13294.

Renato I. de Ávila Danillo F. M. C. Veloso Gabriel C. Teixeira Thaisângela L. Rodrigues Tim Lindberg Malin Lindstedt Simone G. Fonseca Eliana M. Lima Marize C. Valadares

Abstract

Background
Allergic contact dermatitis reported to henna‐based hair coloring products (HPs) has been associated with adulteration of henna with p‐phenylenediamine (PPD).

Objectives
To develop a testing approach based on in vitro techniques that address key events within the skin sensitization adverse outcome pathway to evaluate allergenic potential of HPs.

Methods
The following in vitro assays were used to test the sensitizing capacity of hair dye ingredients: micro‐direct peptide reactivity assay (mDPRA); HaCaT keratinocytes‐associated IL‐18 assay; U937 cell line activation test (USENS)/IL‐8 levels; blood monocyte‐derived dendritic cell test; genomic allergen rapid detection (GARD skin). Those techniques with better human concordance were selected to evaluate the allergenic potential of ten HPs.

Results
Contrasting to the label’s information, chromatographic analyses identified PPD in all products. The main henna biomarker, lawsone, was not detected in one of 10 the products. Among the techniques evaluated by testing HDIs, mDPRA, IL‐18 assay, GARD skin and U‐SENS correlated better with human classification (concordances 91.7 to 100%) and were superior to the animal testing (concordance 78.5%). Thus, these assays were used to evaluate HPs, which were classified as skin sensitizers using different two‐out‐of‐three approaches.

Conclusions
Our findings highlight toxicological consequences and risks associated of the undisclosed use of PPD in henna‐based “natural” “real‐life” products.

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Skin Sensitization Testing—What’s Next?

Int. J. Mol. Sci. 2019, 20(3), 666; https://doi.org/10.3390/ijms20030666  

Gunilla Grundström and Carl A.K. Borrebaeck

Abstract

There is an increasing demand for alternative in vitro methods to replace animal testing, and, to succeed, new methods are required to be at least as accurate as existing in vivo tests. However, skin sensitization is a complex process requiring coordinated and tightly regulated interactions between a variety of cells and molecules. Consequently, there is considerable difficulty in reproducing this level of biological complexity in vitro, and as a result the development of non-animal methods has posed a major challenge. However, with the use of a relevant biological system, the high information content of whole genome expression, and comprehensive bioinformatics, assays for most complex biological processes can be achieved. We propose that the Genomic Allergen Rapid Detection (GARD™) assay, developed to create a holistic data-driven in vitro model with high informational content, could be such an example. Based on the genomic expression of a mature human dendritic cell line and state-of-the-art machine learning techniques, GARD™ can today accurately predict skin sensitizers and correctly categorize skin sensitizing potency. Consequently, by utilizing advanced processing tools in combination with high information genomic or proteomic data, we can take the next step toward alternative methods with the same predictive accuracy as today’s in vivo methods—and beyond.

Keywords

genomics; machine learning; skin sensitization; adverse outcome pathways; next generation in vitro tests

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The use of Genomic Allergen Rapid Detection (GARD) assays to predict the respiratory and skin sensitising potential of e-liquids

Regulatory Toxicology and Pharmacology. Volume 103, April 2019, Pages 158-165 https://doi.org/10.1016/j.yrtph.2019.01.001

Matthew Stevenson, Lukasz Czekala, Liam Simms, Nicole Tschierske, Olivia Larne, Tanvir Walele

Abstract
Electronic cigarettes (e-cigarettes) are an increasingly popular alternative to combustible tobacco cigarettes among smokers worldwide. A growing body of research indicates that flavours play a critical role in attracting and retaining smokers into the e-cigarette category, directly contributing to declining smoking rates and tobacco harm reduction. The responsible selection and inclusion levels of flavourings in e-liquids must be guided by toxicological principles. Some flavour ingredients, whether natural extracts or synthetic, are known allergens. In this study, we used the Genomic Allergen Rapid Detection (GARD) testing strategy to predict and compare the respiratory and skin sensitising potential of three experimental and two commercial e-liquids. These novel, myeloid cell-based assays use changes in the transcriptional profiles of genomic biomarkers that are collectively relevant for respiratory and skin sensitisation. Our initial results indicate that the GARD assays were able to differentiate and broadly classify e-liquids based on their sensitisation potential, which are defined mixtures. Further studies need to be conducted to assess whether and how these assays could be used for the screening and toxicological assessment of e-liquids to support product development and commercialisation.

Keywords
Electronic cigarettesSkin sensitisationRespiratory sensitisationIn vitroAlternative methods

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Is a combination of assays really needed for non-animal prediction of skin sensitization potential? Performance of the GARD™ (Genomic Allergen Rapid Detection) assay in comparison with OECD guideline assays alone and in combination

Regulatory Toxicology and Pharmacology, Volume 98, October 2018, Pages 155-160, https://doi.org/10.1016/j.yrtph.2018.07.014.

David W.Roberts

Highlights

  • Prediction of skin sensitization potential does not need multiple assays representing Key Events of the AOP.
  • This has been argued on theoretical grounds and is now tested against published data.
  • A single assay, GARD™, can outperform combinations of OECD test guideline assays.

Abstract
To meet regulatory requirements, and avoid or minimize animal testing, there is a need for non-animal methods to assess the potential of chemicals to cause skin sensitization. It is widely assumed that no one test will be sufficient and that combined data from several assays spanning key events from the adverse outcome pathway will be required. This paper challenges that assumption. The predictive performance of a single assay, the Genomic Allergen Rapid Detection (GARD™) assay, was compared with the performance, singly and in combination, of three formally validated non-animal approaches that appear as OECD test guidelines: the direct peptide reactivity assay (DPRA), the ARE-Nrf2 luciferase test method, and the human cell line activation test (h-CLAT).

It is shown here that GARD™ alone outperforms each of DPRA, ARE-Nrf2 luciferase or h-CLAT, alone or in any combination as a 2 out of 3 strategy, in terms of sensitivity, specificity and accuracy.

Based on the datasets analysed here, the sensitivity and specificity of GARD™ alone are 90–92% and 79–84% (“2 out of 3”, 86% and 76%). Thus, in any situation where the 2 out of 3 strategy is considered adequate, GARD™ alone could be used with equal or better performance.

Keywords
Skin sensitization potential, Non-animal assays, Integrated testing strategies, GARD™

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Predicting skin sensitizers with confidence – Using conformal prediction to determine applicability domain of GARD

Toxicol In Vitro.  Jan 30 2018,  [Epub ahead of print];48:179-187. doi: 10.1016/j.tiv.2018.01.021.

Andy Forreryd, Ulf Norinder, Tim Lindberg, Malin Lindstedt.

Abstract

GARD – Genomic Allergen Rapid Detection is a cell based alternative to animal testing for identification of skin sensitizers. The assay is based on a biomarker signature comprising 200 genes measured in an in vitro model of dendritic cells following chemical stimulations, and consistently reports predictive performances ~90% for classification of external test sets. Within the field of in vitro skin sensitization testing, definition of applicability domain is often neglected by test developers, and assays are often considered applicable across the entire chemical space. This study complements previous assessments of model performance with an estimate of confidence in individual classifications, as well as a statistically valid determination of the applicability domain for the GARD assay. Conformal prediction was implemented into current GARD protocols, and a large external test dataset (n = 70) was classified at a confidence level of 85%, to generate a valid model with a balanced accuracy of 88%, with none of the tested chemical reactivity domains identified as outside the applicability domain of the assay. In conclusion, results presented in this study complement previously reported predictive performances of GARD with a statistically valid assessment of uncertainty in each individual prediction, thus allowing for classification of skin sensitizers with confidence.

KEYWORDS:
Applicability domain; Conformal prediction; GARD; In vitro assay; Skin sensitization

PMID: 29374571     DOI: 10.1016/j.tiv.2018.01.021

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An alternative biomarker-based approach for the prediction of proteins known to sensitize the respiratory tract.

Toxicol In Vitro. 2017 Oct 7;46:155-162. doi: 10.1016/j.tiv.2017.09.029.

Zeller KS, Johansson H, Lund TØ, Kristensen NN, Roggen EL, Lindstedt M.

 

Abstract

Many natural and industrial proteins are known to have properties that can result in type I hypersensitivity, however, to date, no validated test system exists that can predict the sensitizing potential of these allergens. Thus, the objective of this study was to develop a protocol based on the myeloid cell-based Genomic Allergen Rapid Detection (GARD) assay that can be used to assess and predict the capacity of protein allergens known to induce sensitization in the respiratory tract. Cellular responses induced by eight selected proteins were assessed using transcriptional profiling, flow cytometry and multiplex cytokine analysis. 391 potential biomarkers were identified as a predictive signature and a series of cross-validations supported the validity of the model. These results together with biological pathway analysis of the transcriptomic data indicate that the investigated cell system is able to capture relevant events linked to type I hypersensitization.

Copyright © 2017. Published by Elsevier Ltd.

KEYWORDS:
Biomarker; Cell-based assay; Dendritic cells; Protein allergens; Respiratory sensitization

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Skin Sensitization: Challenging the Conventional Thinking – A Case Against 2 Out of 3 as Integrated Testing Strategy

Toxicological Sciences, Volume 159, Issue 1, 1 September 2017, Pages 3–5, https://doi.org/10.1093/toxsci/kfx115
Published: 27 June 2017

Henrik Johansson,  Robin Gradin

Background

Recent years have seen a surge in development of alternative methods for assessment of skin sensitizers. This has been in order to meet the regulatory and industrial demand for accurate safety assessment without the use of animal experimentation, and to address societal expectations. Today, 3 such assays are formally validated and have achieved OECD Guideline status (EC, 2013, 2014, 2015). However, partly due to insufficient predictive capacity, none of the validated assays have received a recommendation for use as a stand-alone method. In addition, there is a view that accurate hazard identification must be based upon an assessment of several key events in the relevant Adverse Outcome Pathway (AOP).

For these reasons it is proposed that tests are used in combinations, forming so-called Integrated Testing Strategies (ITSs), to address deficiencies in the performance of individual methods and to incorporate end points that reflect several key events in the AOP (Hartung etal., 2013; Jaworska and Hoffmann, 2010; Rovida etal., 2015). Although such ITSs may be configured in a number of ways, one heavily advocated approach relies on the majority vote of individual assays, often referred to as a 2 out of 3 ITS. That is, the identification of hazard is dependent upon the chemical eliciting a positive response in at least 2 of 3 test methods. This approach is based on the view that this will provide an increased weight of evidence and thereby greater confidence in hazard characterization and risk assessment.

Here, we present arguments opposing the claimed benefits of 2 out of 3 ITSs by examining the theoretical probability propagation of combined outcomes, simulated predictions generated by hypothetical assays, and actual data obtained from recently published literature. We argue that the added value of combining the top-performing assay with other assays with less predictive accuracy is overestimated, if present, and may actually be detrimental.

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The GARD platform for potency assessment of skin sensitizing chemicals

ALTEX Online first published April 12, 2017, version 2 https://doi.org/10.14573/altex.1701101

Kathrin S. Zeller, Andy Forreryd, Tim Lindberg, Robin Gradin, Aakash Chawade and Malin Lindstedt,

Summary

Contact allergy induced by certain chemicals is a common health concern, and several alternative methods have been developed to fulfill the requirements of European legislation with regard to hazard assessment of potential skin sensitizers. However, validated methods, which provide information about the potency of skin sensitizers, are still lacking. The cell-based assay Genomic Allergen Rapid Detection (GARD), targeting key event 3, dendritic cell activation, of the skin sensitizer AOP, uses gene expression profiling and a machine learning approach for the prediction of chemicals as sensitizers or non-sensitizers. Based on the GARD platform, we here expanded the assay to predict three sensitizer potency classes according to the European Classification, Labelling and Packaging (CLP) Regulation, targeting categories 1A (strong), 1B (weak) and no cat (non-sensitizer). Using a random forest approach and 70 training samples, a potential biomarker signature of 52 transcripts was identified. The resulting model could predict an independent test set consisting of 18 chemicals, six from each CLP category and all previously unseen to the model, with an overall accuracy of 78%. Importantly, the model was shown to be conservative and only underestimated the class label of one chemical. Furthermore, an association of defined chemical protein reactivity with distinct biological pathways illustrates that our transcriptional approach can reveal information contributing to the understanding of underlying mechanisms in sensitization.

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Evaluation of the GARD assay in a blind Cosmetics Europe study

ALTEX Online first published February 17, 2017 https://doi.org/10.14573/altex.1701121

Johansson H., Gradin R., Forreryd A., Agemark M., Zeller K., Johansson A., Larne O., van Vliet E.,  Borrebaeck C., Lindstedt M.,

Summary

Chemical hypersensitivity is an immunological response towards foreign substances, commonly referred to as sensitizers, which gives rise primarily to the clinical symptoms known as allergic contact dermatitis. For the purpose of mitigating risks associated with consumer products, chemicals are screened for sensitizing effects. Historically, such predictive screenings have been performed using animal models. However, due to industrial and regulatory demand, animal models for the purpose of sensitization assessment are being replaced by animalfree testing methods, a global trend that is spreading across industries and market segments. To meet this demand, the Genomic Allergen Rapid Detection (GARD) assay was developed. GARD is a novel, cell-based assay that utilizes the innate recognition of xenobiotic substances by dendritic cells, as measured by a multivariate readout of genomic biomarkers. Following cellular stimulation, chemicals are classified as sensitizers or non-sensitizers based on induced transcriptional profiles. Recently, a number of animal-free methods were comparatively evaluated by Cosmetic Europe, using a coherent and blinded test panel of reference chemicals with human and local lymph node assay data, comprising a wide range of sensitizers and non-sensitizers. In this paper, the outcome of the GARD assay is presented. It was demonstrated that GARD is a highly functional assay with a predictive performance of 83% in this Cosmetics Europe dataset. The average accumulated predictive accuracy of GARD across independent datasets was 86%, for skin sensitization hazard. Keywords: GARD, sensitization, in vitro, predictive accuracy, alternative methods

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Testing Human Skin and Respiratory Sensitizers—What Is Good Enough?

Int. J. Mol. Sci. 2017, 18(2), 241; doi:10.3390/ijms18020241

Malmborg A., Borrebaeck C. A.K.

Abstract

Alternative methods for accurate in vitro assessment of skin and respiratory sensitizers are urgently needed. Sensitization is a complex biological process that cannot be evaluated accurately using single events or biomarkers, since the information content is too restricted in these measurements. On the contrary, if the tremendous information content harbored in DNA/mRNA could be mined, most complex biological processes could be elucidated. Genomic technologies available today, including transcriptional profiling and next generation sequencing, have the power to decipher sensitization, when used in the right context. Thus, a genomic test platform has been developed, denoted the Genomic Allergen Rapid Detection (GARD) assay. Due to the high informational content of the GARD test, accurate predictions of both the skin and respiratory sensitizing capacity of chemicals, have been demonstrated. Based on a matured dendritic cell line, acting as a human-like reporter system, information about potency has also been acquired. Consequently, multiparametric diagnostic technologies are disruptive test principles that can change the way in which the next generation of alternative methods are designed.
Keywords:

genomics; skin sensitization; adverse outcome pathways; next generation in vitro tests

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