Dermal Irritation
By using the in vitro skin irritation testing services CeeTox offers, clients can practice the 3Rs (reduce, refine, or replace animal testing) and achieve Amendment 7 and REACH directives by reducing or eliminating the need for in vivo testing. These in vitro assays produce reliable outcomes that supplement or replace in vivo data at reasonable cost.
Download Dermal Irritation PDF
Dermal Irritation refers to the production of reversible damage to the skin following the application of a test substance for up to 4 hours. The principle of the in vitro skin model irritation assay is based on the premise that irritant chemicals are able to penetrate the stratum corneum by diffusion and are cytotoxic to the cells in the underlying layers. Moreover, if the cytotoxic effect is absent or weak, a quantifiable amount of inflammatory mediators is released by the epidermis and may be used in a tiered approach to increase the sensitivity of the test.
CeeTox uses validated 3D skin models to test for dermal irritation. Either liquids or solids can be tested with the models. The in vitro models have undergone extensive in-house validation at CeeTox and have a high concordance with in vivo findings.
The dermal model irritation assay is based on the premise that irritant chemicals are able to penetrate the stratum corneum (see above) by diffusion and are cytotoxic to the cells in the underlying layers. The viability of these cells is determined by the MTT assay, which measures total activity of a cell population e.g., as ability of cellular mitochondrial dehydrogenases to reduce the vital dye MTT ([3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, Thiazolyl blue), which correlates with the total number and/or vitality of living cells.
If the cytotoxic effect measured by the MTT assay is absent or weak, a tiered approach may be used to increase the sensitivity of the test by measuring inflammatory mediators that are released by the epidermis. Testing is done for release of Interleukin 1 alpha, a vertebrate cytokine that is especially important in inducing inflammatory responses. Human keratinocytes express and release large amounts of IL-1α.
In addition, histology can be performed to visualize the morphological changes to the models caused by the test compounds. The histological evaluation improves interpretations and reduces false negatives.