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Total joint replacement is one of the most effective treatments for osteoarthritis, while the aseptic loosening of artificial joint is a major complication leading to the joint replacement failure. There are very limited studies about the effects of titanium-alloy particles on the osteogenic differentiation of mesenchymal stem cells. In this study, human bone marrow-derived mesenchymal stem cells (BM-hMSCs) were treated with different concentrations of TiAl6V4 particles. The cell viability was detected by MTT assay, and the cell proliferation was assessed by CKK-8 assay. The early and late stages of osteogenic differentiation were determined by alkaline phosphatase (ALP) and Alizarin Red S (ARS) staining assays. The expression of osteogenic genes and proteins was analyzed by RT-PCR and Western blot. TiAl6V4 particles at high concentration 100 μg/ml inhibited the cell viability of BM-hMSCs. However, TiAl6V4 in the range of 5–50 μg/ml did not show effects neither on the cell viability nor on the cell proliferation of BM-hMSCs. TiAl6V4 particles showed concentration-dependent bidirectional regulations on BM-hMSC osteogenesis. Specifically, TiAl6V4 at 5 μg/ml promoted the osteogenesis of BM-hMSCs, which was suppressed by TiAl6V4 at 50 μg/ml. Further, mechanism study revealed that the regulation of TiAl6V4 on BM-hMSCs was related to Wnt signaling pathway. Given the potential of mesenchymal cells, our study suggested that the minimization of metal use would be an attractive strategy to reduce the joint replacement failure.

Currently, tissue damage induced by cobalt nanoparticles (CoNPs) and cobalt ions (Co2+) are the most serious syndrome in the patients with metal-on-metal hip prostheses. Therefore, an urgent need exists for the identification of the mechanisms and the development of therapeutic strategies to limit it. The purpose of this study was to explore the mechanism of this damage and to demonstrate if L-ascorbic acid (L-AA) could protect against the cell toxicities induced by CoNPs and Co2+ in vitro. With CoNPs and Co2+ treatment, cell viability was significantly decreased; the ROS (reactive oxygen species) level in mitochondria was dramatically increased in CoNPs treated cells, but cobalt ions could barely induce the ROS. Consistently, the level of cell apoptosis was increased with the upregulation of pro-apoptotic factors (caspases 8, 9, and 3, and Bax) and the downregulation of anti-apoptotic factor Bcl-2. Besides that, the levels of cytochrome c and AIF were increased and released from mitochondria into the cytoplasm. After the cells were pretreated with L-AA, the cell viability decreased by CoNPs was reversed and the ROS induced by CoNPs was suppressed. The level of cell apoptosis induced by CoNPs was decreased as well. But it could not reverse the effects induced by Co2+. These studies demonstrated that CoNPs induce extrinsic and intrinsic apoptotic pathways via generation of ROS, and L-AA could prevent the cytotoxicity by reducing the level of ROS. While Co2+ may induce cytotoxicity through other signals, it could not be protected by L-AA treatment.