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

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.

Surface modifications created by using engineered hydrophobins.

Hydrophobins are small (ca. 100 amino acids) secreted fungal proteins that are characterized by the presence of eight conserved cysteine residues and by a typical hydropathy pattern. Class I hydrophobins self-assemble at hydrophilic-hydrophobic interfaces into highly insoluble amphipathic membranes, thereby changing the nature of surfaces. Hydrophobic surfaces become hydrophilic, while hydrophilic surfaces become hydrophobic. To see whether surface properties of assembled hydrophobins can be changed, 25 N-terminal residues of the mature SC3 hydrophobin were deleted (TrSC3). In addition, the cell-binding domain of fibronectin (RGD) was fused to the N terminus of mature SC3 (RGD-SC3) and TrSC3 (RGD-TrSC3). Self-assembly and surface activity were not affected by these modifications. However, physiochemical properties at the hydrophilic side of the assembled hydrophobin did change. This was demonstrated by a change in wettability and by enhanced growth of fibroblasts on Teflon-coated with RGD-SC3, TrSC3, or RGD-TrSC3 compared to bare Teflon or Teflon coated with SC3. Thus, engineered hydrophobins can be used to functionalize surfaces.