The regulation of ionic nickel uptake and cytotoxicity by specific amino acids and serum components

The effects of serum components and amino acids on the uptake and cytotoxicity of NiCl2 were examined in cultured Chinese hamster ovary (CHO) cells. CHO cells maintained in a minimal salts/glucose medium accumulated 10-fold more(63)Ni than did cells maintained in complete medium supplemented with 10% fetal bovine serum. Cell-surface binding of(63)Ni appeared to account for the majority of this increased accumulation of cell-associated nickel observed in the simple maintenance medium since such increases were reduced 70% by trypsin treatment. The addition of the Ni(2+)-binding amino acids cysteine or histidine to the salts/glucose medium markedly decreased(63)Ni accumulations, an effect not observed following addition of any of several amino acids that do not bind Ni(2+). Supplementation of the salts/glucose medium with fetal bovine serum decreased in a concentration dependent fashion both the(63)Ni(2+) uptake and cell detachment caused by Ni(2+), while dialyzed (amino acid-free) serum was 3-5-fold less effective than undialyzed serum at reducing(63)Ni(2+) uptake and similarly exhibited only a slight protective effect against nickel-induced cytotoxicity. Supplementation of dialyzed serum with cysteine at levels approximating those in whole serum partially restored its inhibitory activity toward nickel uptake by cells and restored completely its inhibition of nickel's cytotoxicity, indicating the predominant role of specific amino acids over serum proteins in regulating the uptake and subsequent cytotoxicity of Ni(2+). Addition of cysteine to the salts/glucose medium during a 2 h exposure of cells to either 100 μM HgCl2 or 1 mM NiCl2 masked the cytotoxic effects of these metal ions. These results demonstrate the importance of extracellular small molecular weight metal ion chelators in altering the biological effects of metal ions at the level of metal uptake.