Perkins, M.A., Osborne, R., Johnson, G.R. Procter & Gamble Company.

The United States Department of Transportation recently granted an exemption for use of the in vitro Skin2 Model ZK1350 Corrosivity Assay as a replacement to rabbit skin corrosion testing for 6 chemical classes. The in vitro skin corrosion test is based on methods scientists at Procter & Gamble Co. previously developed in which test substances are applied topically to the stratum corneum surface of human skin cultures and damage is assessed using cell viability assay (MTT metabolism). The DOT exemption specifies that if chemicals are found to be corrosive in the in vitro test using the MTT endpoint, they may be labeled as corrosive. However, a non-corrosive classification requires confirmatory histopathologic analysis. If standard histopathology using Hematoxylin and Eosin (H & E) is not used or indicates a material causes alterations, then a standard rabbit skin test must be performed. P&G scientists established histopathologic criteria to evaluate human skin equivalent cultures in order to distinguish corrosive chemicals from non-corrosives. Treated and control Skin2 and EpiDerm human skin cultures were graded for epithelial degeneration and necrosis. The grades ranged from 0, which was considered normal skin culture epithelium, to a grade of 5, which represented severe degeneration/necrosis of epithelium. The histologic appearance (grade) of skin cultures treated with non-corrosive chemicals was statistically indistinguishable from control Skin2 and EpiDerm cultures. However, Skin2 and EpiDerm cultures treated with corrosives showed severe histologic changes with grades that were significantly different from controls (p < 0.003). Standardized histopathologic grading criteria will provide for definitive analysis of degenerative changes in human skin cultures, and aid in interpretation of in vitro data for regulatory classification.


Chemicals, Chemicals, irritants/irritancy assessment, Corrosion, Corrosivity, Corrosivity testing, Dermal corrosion, Endpoints, MTT, EpiDerm, Histopathologic criteria, MTT, MTT ET-50 tissue viability assay, MTT assay, Necrosis, Skin corrosion, Skin corrosivity, U.S. Department of Transportation (DOT), Viability

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