Validated Non-animal Alternatives
The Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) recommendation for in vitro skin irritation and skin corrosion test methods is as follows: "In 1999, Corrositex® recommended as a stand-alone assay for evaluating acids, bases, and acid derivatives for DOT; otherwise, recommended as part of a tiered testing strategy; in 2000, accepted by U.S. agencies; in 2006, adopted by OECD as TG 435. In 2002, TER and human skin models (EPISKINTM, EpiDermTM) recommended as part of a tiered testing strategy; in 2004, adopted by OECD as TG 430/431."
The specific limitations on the uses of these in vitro methods are described in the documents on the ECVAM and ICCVAM websites.
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 endpoints evaluated in validation studies using these tissues were cytotoxicity (MTT assay) and IL-1α (a cytokine) for skin irritation and cytotoxicity (MTT assay) for skin corrosion.
The OECD TG 431 described the skin corrosion assays using human skin models as follows: "The test material (solid or liquid) is applied uniformly and topically to a three-dimensional human skin model, comprising at least a reconstructed epidermis with a functional stratum corneum....Corrosive materials are identified by their ability to produce a decrease in cell viability below defined threshold levels at specified exposure periods. The principle of the human skin model assay is based on the hypothesis that corrosive chemicals are able to penetrate the stratum corneum by diffusion or erosion, and are cytotoxic to the underlying cell layers."
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. The endpoints evaluated in the exposed rat skin are 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.
Additional information on in vitro methods being developed for skin irritation/corrosion toxicity testing can be found in Toxicity Endpoints & Tests: Skin Irritation/Corrosion.
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