The effects of nickel and chromium on human keratinocytes: Differences in viability, cell associated metal and IL-1α release

This study was carried out to assess the effects of chromium and nickel upon isolated keratinocytes as an in vitro model of human skin. Keratinocytes were isolated from healthy volunteer skin samples of unknown metal sensitivity (n = 10) and were compared with cells from patient biopsies of known metal sensitivity (n = 7). Cells were dosed with a concentration range of nickel and chromium (0-10,000 μM) and cellular mitochondrial activity, viability, metal uptake and cytokine release were measured. Responses of primary versus passaged keratinocytes were also compared. Toxicity data from primary and passaged keratinocytes was statistically analysed by the non-linear Hill Plot model. Results showed that hexavalent chromium was significantly more cytotoxic, associated more with keratinocytes and induced a dose dependant release of IL-1α compared to nickel. Significant differences were observed between primary and passaged keratinocytes with regard to the toxicity of chromium and nickel and variation of response. No differences were observed in the cytotoxicity or cytokine release induced by chromium or nickel for the known sensitised biopsy patient samples (n = 4) compared to patch test negative controls (n = 3). The results from this study suggest human keratinocytes in vitro respond very differently to chromium and nickel.