Homocysteine enhances apoptosis in human bone marrow stromal cells

Introduction: High plasma homocysteine (Hey) levels have been associated with increased risk of fracture. Since Hey has been shown to induce apoptosis in many cell types, including vascular endothelial cells, we hypothesized that Hcy would have a similar apoptotic effect on osteoblasts, leading to osteoporosis by reducing bone formation. Materials and methods: Using primary human bone marrow stromal cells (hBMSC) and HS-5 cell line (human bone mar-row stromal cell line), we investigated the effects of Hey on these cells by cell viability assay and analysis of cytoplasmic histone-associated DNA fragments. Caspase activity assay, Western blots, and electrophoresis mobility shift assay (EMSA) were performed to find the mechanism of apoptosis. Intracellular reactive oxygen species (ROS) were measured by spectrometry using dichlorofluorescein diacetate, and cellular total glutathione level was determined by a commercially available kit. N-acetylcysteine (NAC) and pyrrolidine dithiocarbarnate (PDTQ were used as tools for investigating the role of ROS and nuclear factor-kappa B (NF-kappa B), respectively. Results: Hey induced apoptosis in primary human bone marrow stromal cells and the HS-5 cell line, and this apoptotic effect was caspase-dependent. In addition, Hcy increased cytochrome c release into the cytosol, and activated caspase-9 and caspase-3, but not caspase-8, indicating that Hey induces apoptosis via the mitochondria pathway. Hey increased ROS, and NAC inhibited the apoptotic effect of Hey. Western blot and EMSA showed that Hey activated the NF-kappa B pathway. PDTC blocked Hcy-induced caspase-3 activation and apoptosis. Conclusion: These results suggest that Hcy induces apoptosis via the ROS-mediated mitochondrial pathway and NF-kappa B activation in hBMSCs, and that Hey may contribute to the development of osteoporosis by reducing bone formation. Antioxidants may have a role in preventing bone loss in individuals with hyperhomocysteinemia. (c) 2006 Elsevier Inc. All rights reserved.