Keratinocyte ATP release assay for testing skin-irritating potentials of structurally diverse chemicals

Irritant dermatitis represents innate inflammatory responses to toxic chemicals. We have reported recently that ATP released from chemically injured keratinocytes may serve as a causative mediator for irritant dermatitis. In this study, we examined whether ATP release from keratinocytes would serve as a reliable readout for predicting skin irritating potentials of structurally diverse compounds. A vast majority (19/20) of the tested compounds, i.e., strong and weak irritant chemicals selected from the literature, induced rapid (<10 min) and significant (P<0.05) ATP release from Pam 212 keratinocytes. Two compounds caused no detectable skin inflammation in our standard mouse model, documenting relatively high sensitivity (false negative rate of 0/18) and specificity (false positive rate of 1/20) of our ATP release assay. Selected compounds, primarily those containing phenol residues or hydrophobic hydrocarbon chains, triggered rapid (<10 min) and robust leakage of a fluorescence probe from liposomes, suggesting that lipid bilayers serve as one, but not the only, target moiety on keratinocytes. Not only do our data support the pathogenic role for keratinocyte-derived ATP in irritant dermatitis, they also form the basis for a formal validation study to evaluate the utility of the keratinocyte-based in vitro assay in screening environmental and industrial chemicals.