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Special Feature: REACH and In Vitro Alternatives—Corrosive Potential Testing

Posted: November 28, 2007

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As the new REACH regulations go into effect and new testing methods are being introduced, a period of confusion has settled on the chemical industry as to which are acceptable testing methods. Thus, this article begins a series that will provide an overview of some of the currently validated in vitro methods that are alternatives to animal testing, or alternative methods to animal testing that are being considered for validation.

Alternative Methods to Assess Skin Corrosion Potential

The corrosive potential of a chemical is an important concern when determining how chemicals will be packaged, transported and handled. Since the skin is the prime site for exposure to corrosive chemicals, the traditional animal based model to assess the corrosive potential of a chemical has been a Draize rabbit test (see the "Draize rabbit skin test" sidebar at the end of this article). However, in 2004 the Organization for Economic Co-Operation and Development (OECD) set out some guidelines for in vitro epidermal models of corrosive potential testing to replace animal based models.3

The guidelines for the construction of the model require that the epidermal model should be made using human keratinocytes and the keratinocytes should be cultured so that they form a three dimensional, multilayered structure of viable cells similar to the human epidermis. The epidermal model should have a functional stratum corneum with chemical and structural properties that provide the culture with a barrier function that is similar to human skin, and the epidermal model also should be grown in a manner where materials that are applied topically to the stratum corneum can only access the viable lower layers of the tissues by penetrating through the stratum corneum and not flowing around the edges of the epidermal model. In addition, the epidermal model should be prepared in such a way that it is free from contaminating microorganisms.

In addition to the construction guidelines, guidelines regarding how the model should function also were given. These functional guidelines state that the metabolic activity of the tissue should be measured using a vital dye, such as 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and there should be sufficient difference in the optical density of the dye extracted from negative control tissues and the extraction solvent alone. Also, the barrier function of the stratum corneum should distinguish between chemicals of differing corrosive potential and resist the immediate penetration of cytotoxic chemicals. The results obtained from the epidermal model should be consistent and reproducible with respect to the same chemical over time.