Borderline Range Determined Using Data From Validation Study of Alternative Methods for Skin Sensitization: ADRA, IL-8 Luc Assay, and EpiSensA.

Most predictive models that use alternatives to animal experiments divide judgements into two classes with a cutoff value for each model. However, if the results of alternative methods are close to the cutoff values, the true result may be ambiguous because of variability in the data. Therefore, the OECD GL497 uses a judgement method that establishes a borderline range (BR) around a cutoff value using a statistical method. However, because there is no detailed description of how the BR is calculated, we clarified two specific points. The scale-constant correction method was used to calculate the median absolute deviation (MAD) around the median. In addition, the bottom-raised transformation method was used when the data were "0" because calculation of the BR requires that all data are logarithmic. Indeed, the BRs for the amino acid derivative reactivity assay (ADRA), interleukin-8 reporter gene assay (IL-8 Luc), and epidermal sensitization assay (EpiSensA) were calculated using data from each validation study. The results showed that the BR for ADRA and IL-8 Luc ranged from 4.1 to 5.9 and 1.25 to 1.57, respectively. Furthermore, the BRs of four genes (ATF3, GCLM, DNAJB4, and IL-8) evaluated using EpiSensA ranged from 10.71 to 21.02, 1.64 to 2.45, 1.61 to 2.52, and 3.11 to 5.16, respectively. The difference (deviation) between the lower and upper BR limits and cutoff value for each alternative method were comparable to those of the alternative methods listed in the guidelines (DPRA, KerarinoSens, and h-CLAT) and thus were considered as adequate.