Discrimination of the Irritancy Potential of Surfactants in Vitro by Two Cytotoxicity Assays Using Normal Human Keratinocytes, HaCaT Cells and 3T3 Mouse Fibroblasts: Correlation with in Vivo Data from a Soap Chamber Assay

Cell cultures have been proposed as a promising model for local tolerance testing. This study evaluated the cytotoxic effects of surfactants on early passage normal human keratinocytes, transformed human keratinocytes (HaCaT cells) and Swiss 3T3 embryonic mouse fibroblasts. Cell membrane integrity, as assessed by the release of the vital dye neutral red, and cell proliferation, as assessed by measurement of the total protein content, were both affected in a dose-dependent manner in response to surfactant exposure. There was a close correlation between the dose-response characteristics for the three cell types. Two surfactants exhibited differential effects on membrane integrity and proliferation, and thus no significant correlation was found between the two endpoints. The irritation potential of the surfactants to human forearm skin in vivo was assessed in a soap chamber test using transepidermal water loss and skin redness as quantitative endpoints. A comparison between the responses in vivo and in vitro yielded the highest correlation for the neutral red release test on normal keratinocytes. The total protein test did not significantly correlate with the soap chamber assay for keratinocytes and HaCaT cells. These results suggest that cultured normal human keratinocytes may be predictive for the irritancy of various surfactants in man. Definite judgement, however, has still to be based on confirmation in human volunteers of larger groups of compounds with diverse physico-chemical properties.