The Effect of Different Extracellular Magnesium Concentrations on the Growth and Differentiation of Osteosarcoma Cell Line (SaOS-2): in vitro Study
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Introduction: Magnesium is the second most abundant intracellular cation and an indispensable cofactor in more than 300 enzymes that are involved in regulation of a variety of cellular functions. It is also an important modulator of the intracellular pH and free calcium concentration, which are crucial for cell motility and proliferation. Therefore, the effects of low and high Mg2+ concentrations on the proliferation and differentiation of normal osteoblasts and neoplastic cells have been studied. Moreover, bone growth factors, mainly Bone morphogenetic proteins (BMPs), Transforming growth factor-ß (TGF-B), and Platelet-derived growth factor (PDGF) appear to have an essential role in the differentiation and proliferation of osteoblasts and have an important proliferative effect on many types of neoplastic cells. PDGF is expressed by different cells including osteoblasts and also is one of major components of the platelet rich plasma involved in bone fracture healing. It is also known for the promotion of bone formation and remodeling by stimulating proliferation and migration of osteoblasts. Because of the previous work on normal human osteoblastic cells as well as other osteosarcoma cell lines, in this present study, the activity, differentiation, and mineralization ability of the osteosarcoma cell line (SaOS-2) was evaluated in physiological and low Mg2+ extracellular concentrations with and without PDGF. The overall goal of our work is to develop better therapeutic approaches for the regulation of abnormal and normal osteoblastic cell function. Aim: To evaluate the growth, differentiation, and mineralization ability of the osteosarcoma cell line (SaOS-2) in physiological and low Mg2+ extracellular concentrations with and without PDGF. Materials and Methods: The cell metabolic activity of SaOS-2 cells was evaluated in different Mg2+ concentrations (0.01 mM, 0.8 mM) and in Mg-free medium with and without PDGF using the MTT assay. The differentiation and mineralization capabilities of the cells were assessed using an alkaline phosphatase and alizarin red assay, respectively. Results: The absence of extracellular Mg2+ had an inhibitory effect on the metabolic activity of SaOS-2 cells. The effect of extracellularly added PDGF on the metabolic activity was not significant despite the Mg2+ presence. In addition, the mineralization ability of SaOS-2 cells appeared to be independent of the extracellular Mg2+ concentration. The differentiation potential of SaOS-2 cells, assessed by alkaline phosphatase activity, was not significant when cells were incubated for 1 to 3 days. However, when the cells were incubated for 4 or 5 days, the osteoblastic differentiation was dependent on the physiological Mg2 concentration. Conclusion: Metabolic activity and osteoblastic differentiation of SaOS-2 cells are decreased in the absence of extracellular Mg2. However, the presence of extracellular Mg2 does not appear to be essential for the mineralization capability of SaOS-2 cells. The growth factor, PDGF, does not appear to have a significant role in the regulation of the activity of the SaOS-2 cells in the presence or absence of extracellular Mg2.