Use of human and rat keratinocyte cultures to assess skin irritation potential

An in vitro cell culture approach was evaluated for its ability to provide data pertinent to the assessment of skin irritation potential. The hypothesis of this approach is that a direct toxic insult to the epidermal keratinocyte in vivo may lead to release of inflammatory mediators, which are responsible for initiation of a local primary skin irritant reaction. This paper presents data on the cytotoxic potential of a number of structurally unrelated chemicals (chloroform, 2-methoxyethanol, 2-butoxyethylacetate, toluene, 1-butanol, acetaldehyde, n-hexane, sodium dodecyl sulfate, benzalkonium chloride, silver nitrate, dibutyltin dichloride and tributyltin chloride). Cytotoxicity (neutral red uptake and intracellular acid phosphatase activity) of a number of structurally unrelated chemicals, representative of a wide range of skin irritation potential, was evaluated in cultures of rat and human epidermal keratinocytes. The sensitivity of human and rat keratinocytes to the test chemicals was very similar, irrespective of the endpoint of cytotoxicity. The neutral red uptake assay appeared more generally applicable to the diverse range of chemical structures represented in this study, since not all test chemicals elicited an early increase in intracellular acid phosphatase activity. The results were very encouraging, as a good correlation was evident between cytotoxicity in rat keratinocytes and the degree of erythema and oedema associated with an in vivo skin irritant response in rabbits. Keratinocyte cytotoxicity data may provide an indication of the potential of a chemical to induce a severe skin irritant reaction, or if a chemical is more likely to be a marginal or non-irritant. However, the data illustrate that such assays appear unable to discriminate correctly between more subtle classes of irritancy, such as non-irritant, mild, moderate or severe. Available human in vivo skin irritation data were insufficient to conclude which cell type is preferable for evaluation of human skin irritation potential.