Tag Archive for: hydrophobic substances

New scientific publication by ExxonMobil: Challenges integrating skin sensitization data for assessment of difficult to test substances

New scientific publication by ExxonMobil.

Check out this newly published article by ExxonMobil focusing on the challenges of determining skin sensitization hazard in the case of difficult-to-test substances with conflicting or low-confidence data, where GARDskin data on UVCBs and hydrophobic substances provides valuable input for the integrated hazard assessment.

The article provides new peer-reviewed evidence for the applicability domain of GARDskin on UVCBs, hydrophobic and highly complex substances.

Greminger A, Frasca J, Goyak K, North C. 
Challenges integrating skin sensitization data for assessment of difficult to test substances. 
ALTEX - Alternatives to animal experimentation, published Oct 12, 2023
doi: 10.14573/altex.2201122. Epub ahead of print. PMID: 37843019.


LLNA; ToxPi; new approach methodologies; skin sensitization; weight of evidence.


Difficult to test substances including poorly soluble, mildly irritating, or Unknown or Variable Composition Complex reaction products or Biological Materials (UVCBs), producing weak or borderline in vivo results, face additional challenges in in vitro assays that often necessitates data integration in a weight of evidence (WOE) approach to inform skin sensitization potential. Here we present several case studies on difficult to test substances and highlight the utility of Toxicological Prioritization Index (ToxPi) as a data visualization tool to compare skin sensitization biological activity. The case study test substances represent two poorly soluble substances, tetrakis (2-ethylbutyl) orthosilicate and decyl palmitate, and two UVCB substances, alkylated anisole and hydrazinecarboximidamide, 2-[(2-hydroxyphenyl)methylene]-, reaction products with 2 undecanone. Data from key events within the skin sensitization adverse outcome pathway were gathered from publicly available sources or specifically generated. Incorporating the data for these case study test substances as well as on chemicals of a known sensitization class (sensitizer, irritating non-sensitizer, and non-sensitizer) into ToxPi produced biological activity profiles which were grouped using unsupervised hierarchical clustering. Three of the case study test substances concluded to lack skin sensitization potential by traditional WOE produced biological activity profiles most consistent with non-sensitizing substances, whereas the prediction was less definitive for a substance considered positive by traditional WOE. Visualizing the data using bioactivity profiles can provide further support for WOE conclusions in certain circumstances but is unlikely to replace WOE as a stand-alone prediction due to limitations of the method including the impact of missing data points.


The GARDskin assay: Investigation of the applicability domain for metals

Joint publication with Johnson Matthey

ALTEX – Alternatives to animal experimentation, published Nov 03, 2022, accepted manuscript

DOI: https://doi.org/10.14573/altex.2203021

Forreryd, A., Gradin, R., Larne, O., Rajapakse, N., Deag, E. and Johansson, H.


New approach methods (NAMs) for hazard identification of skin sensitizing chemicals have been adopted as test guidelines by the OECD during the last decade as alternatives to animal models. These models align to individual key events (KE) in the adverse outcome pathway (AOP) for skin sensitization for which the molecular initiating event (MIE) is covalent binding to proteins. As it currently stands, the AOP does not include mechanistic events of sensitization by metals, and limited information is available on whether NAMs accurately the predict sensitization potential of such molecules, which have been proposed to act via alternative mechanisms to organic chemicals.

Methods for assessing the sensitization potential of metals would comprise valuable tools to support risk management within e.g., occupational settings during production of new metal salts or within the medical device industry to evaluate leachables from metal alloys.

This paper describes a systematic evaluation of the applicability domain of the GARD™skin assay for assessment of metals. Hazard classifications were supplemented with an extended analysis of gene expression profiles induced by metal sensitizers to compare the induction of toxicity pathways between metals and organic sensitizers. Based on the results of this study, the accuracy, sensitivity, and specificity of GARD™skin for prediction of skin sensitizing hazard were 92% (12/13), 100% (7/7) and 83% (5/6), respectively.

Thus, the performance of GARD™skin for assessment of metals was found to be similar to what is observed on conventional organic substances, providing support for inclusion of metals within the applicability domain of the test method.


skin sensitization, metals, regulatory testing, medical devices

Full article on line with open access

Exploration of the GARDskin applicability domain: Indirectly acting haptens, hydrophobic substances and UVCBs

Joint publication with the Lubrizol Corporation

ALTEX – Alternatives to animal experimentation, published April 21, 2022, accepted manuscript, https://doi.org/10.14573/altex.2201281

Forreryd, A., Gradin, R., Humfrey, C., Sweet, L. and Johansson, H.


Hazard assessments of skin sensitizers are increasingly being performed using new approach methodologies (NAMs), with several in chemico, in vitro and most recently also defined approaches (DAs) being accepted for regulatory use. However, keeping track of potential limitations of each method in order to define applicability domains remains a crucial component to ensure adequate predictivity as well as facilitating the appropriate selection of method(s) for each hazard assessment task. The objective of this report is to share test results generated with the GARD™skin assay on chemicals that have traditionally been considered as difficult to test in some of the conventional in vitro and in chemico OECD Test Guidelines for skin sensitization. Such compounds may include, for example, indirectly acting haptens, hydrophobic substances, and substances of unknown variable composition or biological substances (UVCBs). Based on the results of this study, the sensitivity for prediction of skin sensitizing hazard of indirectly acting haptenswas92.4%and 87.5%, when compared with LLNA(n=25)and human data(n=8), respectively. Similarly, the sensitivity for prediction of skin sensitizing hazard of hydrophobic substances was 85.1% and 100%, when compared with LLNA(n=24)and human data(n=9), respectively. Lastly, a case study involving the assessment of a set of hydrophobic UVCBs(n=7) resulted in a sensitivity of 100, as compared to available reference data. Thus, it was concluded that these data provide support for the inclusion of such chemistries in the GARD™skin applicability domain, without an increased risk of false negative classifications.

Key words: GARD, GARDskin, skin sensitization, applicability domain, difficult to test substances, Indirectly acting haptens, hydrophobic substances, UVCBs


Full article
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