Nickel, cobalt and chromium-induced cytotoxicity and intracellular accumulation in human hacat keratinocytes

Nickel, cobalt and chromium can induce allergic contact dermatitis (ACD) and may provoke irritant reactions in the skin. This study aimed at investigating cytotoxicity and cell viability along with intracellular metal accumulation in HaCaT human keratinocytes exposed to soluble forms of nickel, cobalt or chromium. The EC50 (24 h) values as detected by MTT test were 30 muM for sodium chromate (Na2CrO4), 475 muM for cobalt chloride (CoCl2) and 600 muM for nickel chloride (NiCl2). Chromium chloride (CrCl3) was not toxic up to 1 mM. No clear effects were observed after 4 h, but 24-h treatments with 1 mM CoCl2 or 10 muM Na2CrO4 were found to almost completely abolish the ability of the cells to form colonies, whilst 1 mM NiCl2 reduced cellular survival to only 70% of control cultures. Intracellular accumulation of metals was evaluated by the use of radioisotopes at the EC50 Value and at 1/10-1/5 of this concentration. Accumulation of (Na2CrO4)-Cr-51 was linear with increasing dose. This was not the case for (NiCl2)-Ni-63 and (CoCl2)-Co-58. All metals were accumulated preferentially in the cytosols; 96% or more for (NiCl2)-Ni-63, approximately 90% for (CoCl2)-Co-58 and 60-70% for (Na2CrO4)-Cr-51. Finally, it was observed that HaCaT human keratinocytes can concentrate the metals present in the media up to 3.9 and 12.5 times for NiCl2 and CoCl2, respectively, and up to 167 for Na2CrO4. These striking metal intracellular accumulation patterns, which have not been earlier described in keratinocytes, highlight the relevance of searching for specific biomarkers of early cellular toxic effects, such as cytosolic proteins that bind the metals. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.