In vitro differentiation of skin sensitizers by cell signaling pathways

Animal testing causes ethical problems and in view of EU regulations (e.g. EU-Guideline (76/768/EEC, February 2003)) or REACH the development of reliable in vitro assays has become even more important. Up to now, we use the modified local lymph node assay (IMDS) for toxicological hazard identification of sensitizing and irritant properties of chemicals in accordance with OECD Guideline 429. In this study, we investigated whether analyses of cell signaling pathways can provide a methodology for the detection of sensitizing compounds in vitro. Murine and human skin explants as well as reconstituted skin models (epidermal model EST-1000 and full-thickness model AST-2000) were exposed to sensitizing (oxazolone and DNFB) or irritant compounds (SDS and TritonX-100). Phosphorylation of MAP-kinases (p38, ERK1/2 and JNK1/2), STAT1 and PLCγ were determined by cytometric bead array (CBA). In skin explants, all three MAP-kinases were exclusively activated after exposure to sensitizing compounds. For the reconstituted skin models phosphorylations of p38 and JNK1/2 were obtained after stimulation with allergens, whereas treatments with irritant compounds led to ERK1/2 activation. Activation of PLCγ and STAT1 were never detected. In conclusion, MAP-kinase activation provides a promising in vitro tool for the discrimination between sensitizers and irritants.