A potential in vitro epidermal equivalent assay to determine sensitizer potency

Most in vitro assays aim to distinguish sensitizers from non-sensitizers. Few aim to classify sensitizers according to potency. Here, we describe a potential method for classifying sensitizers according to their irritant potency with the aid of in house epidermal equivalents (EE). Sixteen sensitizers were applied topically in a dose response to EE for 24 h. The EE-EC50 value (effective chemical concentration required to reduce cell viability by 50%) and the EE-IL-1α10× value (chemical concentration which increases IL-1α secretion by 10-fold) were calculated. From 16 sensitizers, EE-EC50 and/or EE-IL-1α10× values were obtained from 12 skin sensitizers. EE-EC50 and IL-1α10× values decreased in proportion to increasing sensitizer potency. The in vitro assay correlated with existing in vivo mouse and human sensitization data (LLNA, HRIPT), and showed low intra- and inter-experimental variability. Additionally DNCB and resorcinol were correctly assessed as extreme and moderate sensitizers using commercial EE (EST1000™ and RHE™). In conclusion, our data supports the view that irritancy may in part be a factor determining sensitizer potency. Since this assay does not distinguish sensitizers from non-sensitizers, its potential application is in a tiered strategy, where Tier 1 identifies sensitizers which may then tested in Tier 2, this assay, which determines sensitizer potency.