In vitro skin irritation testing with human skin cell cultures

Cultured human skin cells are a potentially useful model for skin irritancy testing. We have evaluated the effects of chemical irritants on human epidermal keratinocytes (NHEK) and on keratinocyte-dermal fibroblast (NHEK/DF) co-cultures. Cell viability in NHEK cultures, measured as incorporation of the vital dye neutral red (NR), was reduced in a dose-dependent manner in response to the chemical irritants tested. The half-maximal effective concentration (NR(50)) values correlated with irritation scores in human patch tests with these materials. Certain materials were found to be incompatible with this test system. NHEK/DF cultures were treated with ten prototype surfactants, and were evaluated for cell viability (MTT incorporation), cytotoxicity (release of the enzymes lactate dehydrogenase and N-acetyl glucosaminidase), metabolism (glucose utilization), and inflammatory mediator (prostaglandin E(2)) release. There was a close correlation of the dose-response characteristics for all the endpoints tested, and between the in vitro responses and human patch test scores for the surfactants tested. These results demonstrate the usefulness of human skin cell cultures and of cell viability, cytotoxicity, and inflammatory mediator release as endpoints, for the in vitro assessment of skin irritancy.