A number of in vitro tests have recently been accepted as alternatives to animal models by the European Centre for the Validation of Alternative Methods (ECVAM).
The models are based on human keratinocytes which are then cultured to produce a reconstructed human epidermis to which the chemical under investigation is applied.
If the application of the chemical significantly increases the expression of cytokine interleukin-1 alpha(IL-1 alpha), a signalling molecule that is known to play an important role in the skin’s irritation response, the chemical is deemed to be an irritant.
According to the Japanese scientists, other than a few cytokines, such as IL-1 alpha, the marker genes for irritation in the reconstructed human epidermis are not yet fully identified.
Widening number of genes involved
They claim that a newly developed microarray called Genoplan, which includes over 200 genes associated with inflammation, immunity, stress and cell housekeeping, could be a useful tool in evaluating mild skin irritation by widening the number of genes tested.
The team, led by Masuko Kobori, tested sodium dodecyl sulphate (SDS) with the Genoplan microarray, and found that it upregulated the expression of 10 out of the 205 genes included.
According to the team, this is the first time the upregulation of these genes has been shown with the application of SDS onto the reconstructed epidermis.
Both IL-1 alpha and IL-1 beta were upregulated, as were a number of genes known to be upregulated by environmental and physiological stress such as HSPA1, FOSL1 and JUNB.
The scientists conclude that: “It is imperative that a sensitive human epidermis model is developed that can replace the use of animals…Our results show that the DNA microarray is a useful and efficient tool to evaluate mild skin irritation using a reconstructed human epidermal model.”
Source: Biological and Pharmacological BulletinFebruary 2009, 32 (2) pages 203-208Evaluation of the skin irritation using a DNA microarray on a reconstructed human epidermal modelMakoto Niwa, Kanji Nagao, Hideaki Oike, Masuko Kobori