Cobalt and chromium ions induce nitration of proteins in human U937 macrophages in vitro

The in situ localization of nitrotyrosine, a product of the nitration of tyrosine residues by peroxynitrite, in the interface membranes from Co-Cr-Mo and Ti-Al-V prostheses provided evidence of nitric oxide-induced oxidative damage in the periprosthetic environment. In the present study, we compared the effects of different wear products from hip prostheses on the nitration of proteins in macrophages in vitro. Nitration of proteins was measured by Western blot using a polyclonal antibody directed against nitrotyrosines. Results showed that Co2+ and Cr3+ ions induced the nitration of a 79 +/- 4 kDa protein in a time- and dose-dependent manner. Indeed, the stimulation was significant (p < 0.05) after 24 h with 10 ppm Co2+ and reached a plateau level between 48 and 72 h. With Cr3+, the stimulation was significant (p < 0.05) only after 48 and 72 h. The effect of both Co2+ and Cr3+ ions was inhibited by glutathione monoethyl-ester that provides protection against oxidative stress. However, ultrahigh-molecular-weight-polyethylene and alumina ceramic particles had no significant effect on the nitration of proteins. Finally, the results showed that nitrated proteins are mainly found in the cytoplasmic fraction of cells and are absent from the nucleus. In conclusion, our results show that Co2+ and Cr3+ ions induce the nitration of cytoplasmic proteins in human U937 macrophages, suggesting that metal ions from MM prostheses have the potential to modify protein function in the periprosthetic environment and in circulating cells. (c) 2006 Wiley Periodicals, Inc.