Skin sensitisation is an adverse reaction to a substance that leads to any form of allergic skin reaction, such as inflammation or contact dermatitis.
Skin sensitisation testing allows chemical regulators to assess the potential of a chemical to cause skin morbidities and thus be harmful to workers or consumers. The process identifies the elements likely to cause a reaction. This is an integral part of developing a product, and a critical part of the risk assessment for cosmetic, pesticide and industrial chemicals. Therefore, skin sensitisation testing forms part of the classification and labelling requirements for many regulatory purposes.
An immune response can be triggered by the body when it comes into contact with one of the many hundreds of chemicals identified as having the potential to cause skin sensitisation.
How is skin sensitisation tested?
Skin sensitisation testing has traditionally seen the in vivo use of animals. However, the demand to reduce the number of animals used in testing formed part of the UK Government replace, refine and reduce programme announced in mid-2011. There has since been an increasing demand to develop new skin sensitisation testing assessments, which removes the need for widespread animal testing.
In vitro skin sensitisation testing methods
Gentronix is one such company leading the way in predictive skin toxicology through skin sensitisation assays that overcome or reduce animal testing requirements. Intensive studies into the biology of skin sensitisation have enabled the development of several in vitro ethically acceptable testing assays.
Testing assays address three of the four key events identified in the ‘adverse outcome pathway’. From the molecular initiating event, intermediate steps through to assessing adverse outcomes of allergic sensitisation. Together, the assays provide a means to address most of the key events with their associated OECD test guideline and provide a fully validated alternative to traditional in vivo animal testing to help with the demand to reduce animal use in testing.
KE1:DPRA – direct peptide reactivity assay
OECD 442C investigates the initiating molecular event of haptenation. HPLC is used to determine the reactivity potential to cysteine and lysine peptides of the test substance. Peptide depletion via reactivity of the test substance supports discrimination between skin sensitisers and non-sensitisers. Incubation test times of 22-24 hours see fast, accurate results.
KE2: KeratinoSensTM
OECD 442D, the second key event of the adverse outcome pathway is the activation of keratinocytes. This assay measures the expression of luciferase gene reporters for the ARE-dependent pathway to assess covalent binding to skin proteins recognised as a key step in skin allergenicity. Incubation test times of 48 hours conducted to GLP is achievable.
KE3: h-CLAT
OECD 442E, dendritic cell activation, utilising monocytic THP-1 cell lines, investigates key event three. Flow cytometry assesses the test substance’s ability to increase expression of CD54 and CD86 cell surface markers associated with dendritic cell activation leading to the stimulation of immune responses. Incubation test time is 24 hours and the study requires at least two independent test runs.
Where positive results are obtained from the testing processes, expert advice can assist you in interpreting the results and identifying suitable pathways to move forward.
Conclusion
There is clearly an ethical and moral drive to reduce the number of animals used in testing, which can now be met by In vitro predictive toxicology solutions. Chemical industries producing pharmaceutical, industrial and cosmetic products can reliably screen small quantities of test substance using predictive genotoxicity assays to identify skin toxicity and chemical allergenic properties and meet regulatory requirements without using animals or animal derivatives.
The use of in vitro assay based testing provides several additional benefits. They provide accurate, reliable and more readily reproducible testing facilities for all companies previously reliant on animal testing. Scientific experience and expert judgement support data to assist clients in interpreting results, identifying mechanisms, and navigating regulatory landscapes by managing adverse toxicology findings.