Binding of nickel to human epidermis in vitro

Human epidermis was homogenized, dried and incubated with nickel chloride solutions in the concentration range 0.008-3.4 mM/50 mg epidermis. Nickel uptake was found to occur according to the Freundlich adsorption isotherm, giving a slope of 0.55, indicating that nickel is associatively bound to constituents of the epidermis. The binding characteristics of cobalt were very similar to those of nickel, but the two metals were not found to compete significantly for binding sites in the epidermis. The metal-chelating agents, ethylenediamine tetra-acetic acid disodium, (Na-EDTA) L-histidine and D-penicillamine were tested for ability to remove nickel from its binding sites. Na-EDTA was found to be the most efficient, removing 70-90% of the nickel bound to the tissue. The possible clinical significance of these in vitro observations are discussed in relation to percutaneous absorption and allergic contact dermatitis.