Validated Non-animal Alternatives
Skin Corrosion
The reconstructed human skin models, EpiDerm, EpiSkin, and SkinEthic, consist of cells cultured on membranes at the air-liquid interface where they differentiate and form an epithelial barrier. All of these commercial models come prepackaged as multiwell cultures ready for use in testing assays. The endpoint evaluated for skin corrosion was cytotoxicity (MTT assay). The specifications and limitations on the uses of these in vitro methods are described in documents on the ECVAM and ICCVAM websites.
The rat skin Transcutaneous Electrical Resistance (TER) assay evaluates two endpoints following the exposure of isolated rat skin for 2-24 hours to a test chemical: changes in the transcutaneous electrical resistance and the binding of a dye, sulforhodamine B.
The Corrositex assay is based on the time it takes for a chemical to penetrate an artificial biobarrier. If penetration occurs, a dye reaction takes place to indicate a positive response; the shorter the time, the more corrosive the chemical.
EpiSkin, EpiDerm and the rat TER tests were validated by ECVAM and endorsed by ESAC in 1998 as "scientifically validated for use as a replacement for the animal test, and … ready to be considered for regulatory acceptance." These tests underwent a subsequent validation review by ICCVAM, which in 2002 recommended their use as part of a tiered testing strategy. They achieved formal EU acceptance for regulatory purposes in 2000, followed by international acceptance as OECD TGs 430 and 431 in 2004. A Draft Revised TG 431 is currently under consideration, which includes a technical update on performance standards to OECD TG 431 and recommends substitution of two reference chemicals of TG 431.
In 1999, an ICCVAM review of Corrositex recommended its use as a stand-alone assay for evaluating acids, bases, and acid derivatives for DOT, and otherwise, as part of a tiered testing strategy. A reciprocal statement of validity was issued by ESAC in 2000. That same year, Corrositex achieved formal acceptance by US regulators, and in 2006, the method achieved international acceptance as OECD TG 435.
In June 2009, the ESAC endorsed the EST-1000 RHE method for predicting skin corrosion potential based on its meeting performance standards in OECD TG 431; this method is also considered compliant with EU Test Method B.40.
Skin Irritation
Variants of EpiSkin and EpiDerm corrosivity tests were evaluated for their ability to predict milder forms of skin irritation (Spielmann, et al., 2007). On the basis of this validation study, ESAC (2007) concluded that the EpiSkin Skin Irritation Test (SIT) "showed evidence of being a reliable and relevant stand-alone test for predicting rabbit skin irritation...and for being used as a replacement...for the Draize Skin Irritation Test...for the purposes of distinguishing between R38 skin irritating and no-label (non-skin irritating) test substances."
The following year, ESAC (2008) endorsed two additional skin models for skin irritation testing: the EpiDerm SIT and SkinEthic Reconstructed Human Epidermis (RHE) models. Both showed results similar to the validated reference method, EpiSkin, and are considered as valid replacement methods.
The in vitro skin irritation test methods have achieved regulatory acceptance in the EU. In 2009, the ESAC endorsed three ECVAM-validated Reconstructed Human Epidermis (RHE) methods (EpiSkin; Modified EpiDerm SIT; SkinEthic RHE) for testing under the United Nations Globally Harmonized System (UN GHS). The ESAC also endorsed revised ECVAM Performance Standards for validating skin irritation testing methods based on RHE methods; this update was necessary due to adoption of the UN GHS system by the EU in December 2008. Method B.46 was included into Annex to 440/2008/EC in July 2009 during its 1st adaptation to technical progress (761/2009/EC): EpiDerm SIT, SkinEthic RHE assay, and EPISKIN as stand-alone tests for replacement of Draize Skin Irritation Test; EpiDerm as screening method or as part of a sequential testing strategy.
Additional information on in vitro methods for skin irritation/corrosion toxicity testing can be found on AltTox at: Toxicity Endpoints & Tests: Skin Irritation/Corrosion.
Additional Resources
MatTek Skin Irritation
MatTek Dermal Corrosion
1 On December 11, 2009, the Draft Test Guideline, In Vitro Skin Irritation: Reconstructed Human Epidermis (RhE) Test Method, was posted on the OECD website for comment. On March 25, 2010 the OECD National Coordinators Meeting WNT22 approved this draft Test Guideline. The TG will be submitted to the Joint Meeting and then Council for final adoption.
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