The EpiSkin Skin Corrosion Test (SCT) can be used to identify whether a chemical has the potential to corrode skin.
Skin corrosion is generally defined as full thickness destruction of skin tissue but can also include any irreversible alterations to skin.
The method uses a 3D human skin model and involves topical application of a test substance and subsequent assessment of cell viability and cytotoxicity.
The results of the validation study, the ESAC statement and our recommendation will be soon available on TSAR, the Tracking System for Alternative methods towards Regulatory acceptance.
[collapsed]Skin corrosion usually refers to chemically-induced full thickness destruction of skin tissue. In certain circumstances it also refers to any irreversible alterations to the skin. This sets skin corrosion apart from skin irritation where effects are usually judged to be reversible.
The potential of a chemical to cause skin corrosion is an important consideration from the perspective of safe-handling, packaging and transport of chemicals.[/collapse]
EpiSkin Skin Corrosion Test (SCT)
[collapsed]The method is based on the EpiSkin standard model, which is a three-dimensional human skin model comprised of a reconstructed epidermis and a functional stratum corneum (i.e. the outer layer of skin).
For the purposes of testing for skin corrosion potential, substances are applied topically to the surface of the model and then cell viability is assessed.
Specifically, cytotoxicity is assessed through the MTT assay, which is a colorimetric assay for assessing cell metabolic activity.[/collapse]
Animal testing replacement
[collapsed]The method has previously been validated and has received regulatory approval as a replacement for the in vivo skin corrosively test, specifically the Draize rabbit skin test.[/collapse]
[collapsed]The EpiSkin Skin Corrosion Test (SCT) was first evaluated in-house by EURL ECVAM and then subsequently in a pre-validation study of the protocol. This happened between 1994 and 1996. The outcomes are available below.
Following this prevalidation study, the method was included in the EURL ECVAM International Validation Study on In Vitro Tests for Skin Corrosivity. The objective of this study was to identify tests that could distinguish corrosives from non-corrosives for selected groups of chemicals.
The four tests included in the study were evaluated in three independent laboratories, with prediction models pre-specified in test protocols. In total 60 chemicals were used in the validation study.[/collapse]
Validation study outcomes
[collapsed]On the basis of comparisons between in vitro and in vivo classification, the sensitivity, specificity, predictivity and accuracy were all between 77 and 83%.[/collapse]
EURL ECVAM recommendations
[collapsed]On the basis of the data obtained, the EURL ECVAM Scientific Advisory Committee (ESAC) peer reviewed the study and concluded that the method was reproducible, both within and between laboratories.
The method was applicable to a wide range of chemicals and concordance between skin corrosivity in vitro and in vivo was very good.
On that basis ESAC concluded that the method is scientifically validated as a replacement for the Draize skin corrosivity test and that it was ready for consideration in terms of regulatory acceptance.
Subsequently, the method did receive regulatory acceptance and was developed into an OECD test guideline.
Later re-evaluation of validation data from four skin corrosivity methods (including the EpiSkin skin corrosion test) revealed unacceptably high variability in relation to the classification of a small number of reference chemicals.
ESAC reviewed this data and concluded that in these cases the mis-classification was likely due to their specific physicochemical properties. ESAC also concluded that this issue did not signify unacceptable performance standards of these methods. Instead, it illustrated the likely difficulty of testing certain substances with these specific properties both in vitro and in vivo.
The OECD test guideline no 431 has been updated numerous times to reflect these changes.[/collapse]