Cobalt and chromium ions reduce human osteoblast-like cell activity in vitro, reduce the OPG to RANKL ratio, and induce oxidative stress

Abstract

Metal-on-metal hip arthroplasty is associated with elevated levels of cobalt and chromium ions. The effects of cobalt and chromium ions on cell number, activity, expression of osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) and oxidative stress on human osteoblast-like cells were addressed. Saos-2 cells were supplemented with Co 2+, Cr 3+, or Co 2+ + Cr 3+ (1:2) at 0, 1, 10, and 100 μg/L and incubated for 24, 48, 72, and 96 h. Cell activity was assessed by MTT-assay and cell number by Crystal Violet staining. RNA levels of OPG and RANKL were evaluated using real-time quantitative polymerase chain reaction (qPCR). Compared to controls Co 2+ reduced cell numbers: at 10 μg/L by 17 ± 8% after 48 h and at 100 μg/L after 24 h by 35 ± 8%. Cr 3+ decreased cell numbers at 10 μg/L after 48 and 72 h. Co 2+ + Cr 3+ combined at 1 μg/L lowered cell numbers after 24 and 96 h (17 ± 13, resp. 13 ± 4%). The 10 and 100 μg/L concentrations reduced cell numbers significantly after 24, 48, and 96 h. Cr 3+ reduced osteoblast activity at 1, 10, and 100 μg/L at all incubation times. The strongest reduction (11 ± 1%) was seen at 100 μg/L after 96 h. The OPG/RANKL ratio was reduced after 72 h with almost all Co 2+ and Cr 3+ concentrations. After 96 h, glutathione, superoxide dismutase, and catalase levels were indicative for an oxidative stress response in all samples. In conclusion, cobalt and chromium ions reduce human osteoblast activity, reduce OPG/RANKL ratio and lead to oxidative stress. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc.