A growing number of people are reporting skin reactions to substances. Currently, around 15-20% of the population suffers from a contact allergy, and the number of people reporting some form of skin reaction to chemical contact is increasing.
Chemical products, including personal care products and cosmetics, agrochemicals, and many others, have relied on animal testing to predict the likelihood of human reaction or sensitivity to the product. Animal testing involves exposing them to chemicals and testing for reactivity. Skin sensitisation testing is a critical factor in determining the toxicology risk of chemicals.
A kinder way to test
However, the ban on animal testing for cosmetics has led to a ban on using live animals for testing in many cases, and non-animal-based testing methods have taken over. Gentronix, experts in predictive toxicology screening, are one such company offering in vitro skin toxicology assays to assess the dermal toxicology, corrosion, irritation and skin sensitisation potential of a substance. The assays available provide an alternative by testing components of the complex interactions between the immune system and the sensitising chemical. Below, we describe the tests such experts use and what they can achieve.
OECD proficient in vitro testing for skin sensitisation and dermal toxicity
There are various methods for testing when it comes to skin sensitisation and dermal toxicity. These include:
- OECD 431 Skin Corrosion – this test identifies the corrosive or non-corrosive potential of substances and mixtures, offering a partial sub-categorisation of corrosives with a reconstructed human epidermis.
- OECD 439 Skin Irritation – a reconstructed human epidermal test that addresses human health endpoint skin irritation through topical application of small quantities of the test substance. The non-transformed reconstructed human epidermis model provides a representative cytoarchitecture and histology platform to assess skin irritation.
- OECD 432 Phototoxicity – this test assesses whether a chemical will be photoactivated on UV exposure. Where a chemical is applied topically, understanding the risk of photoactivation is essential. Chemicals exposed to the environment and topical human tissue are likely to lead to come into contact with UV.
The below specifically look at skin sensitisation
- OECD 442C DPRA – a test that identifies the molecular initiating event to assess peptide reactivity via a test substance’s depletion of lysine and cysteine. This determines the first step considered a risk in skin allergenicity by detecting a substance’s covalent binding to skin proteins.
- OECD 442D KeratinoSensTM – this assay assesses the second key event to be considered in the adverse outcome pathway. Luciferase gene reporter responses are evaluated in response to activating this inflammatory pathway as a precursor to T-cell proliferation and dendritic cell activation that could indicate an allergic reaction.
- OECD 442E h-CLAT: Flow cytometry testing is used to identify the activation of dendritic cells. This assay investigates the adverse outcome pathway’s third key event of skin sensitisation. Cell surface expression markers are assessed, and positive activation of dendritic cells is a precursor for skin allergenicity with T-cell proliferation.
These offer fully validated in vitro testing methods for measuring biomarkers using human cells with small test item quantities. To provide results that, when combined with other structural alerts and read-across chemical analogues based on the weight of evidence and expert judgement, these non-animal test methods for skin sensitisation prediction can support hazard identification and discriminate between skin sensitisers and non-skin sensitisers.
The current test assays are designed to be used in combination to provide an overall assessment of the test substance’s skin toxicity and give the necessary reliable hazard and potency information required to assess potential skin sensitisation.
A great choice
The growing need to reduce the number of animals used in testing has led to the development of a multitude of non-animal mechanistic testing strategies to understand the chemical and biological events that lead to skin sensitisation through test methods that are aligned to early key reaction events, which experts in their development can help navigate.