Transition metal ions including Se2+, Cd2+, Hg2+ or Mn2+ have been thought to disturb the bone metabolism directly. However, the mechanism for the bone lesion is unknown. In this study, we demonstrated that MC3T3E1 osteoblasts, exposed to various transition metal ions; selenium, cadmium, mercury or manganese, generated massive amounts of reactive oxygen species (ROS). The released ROS were completely quenched by free radical scavengers-N-acetyl cysteine (NAC), reduced glutathione (GSH), or superoxide dismutase (SOD). First, we have observed that selenium (10 micrometer), cadmium (100 micrometer), mercury (100 micrometer) or manganese (1 mM) treatment induced apoptotic phenomena like DNA fragmentation, chromatin condensation and caspase-3-like cysteine protease activation in MC3T3E1 osteoblasts. Concomitant treatment of antioxidant; N-acetyl-L-cysteine (NAC), reduced-form glutathione (GSH), or superoxide dismutase (SOD), prevented apoptosis induced by each of the transition metal ions. Catalase or dimethylsulfoxide (DMSO) has less potent inhibitory effect on the apoptosis, compared with NAC, GSH or SOD. In line with the results, nitroblue tetrazolium (NBT) stain shows that each of the transition metals is a potent source of free radicals in MC3T3E1 osteoblast. Our data show that oxidative damage is associated with the induction of apoptosis in MC3T3E1 osteoblasts following Se2+, Cd2+, Hg2+ or Mn2+ treatment.
Acetylcysteine ; Apoptosis* ; Cadmium ; Catalase ; Chromatin ; Cysteine ; Cysteine Proteases ; Dimethyl Sulfoxide ; DNA Fragmentation ; Free Radicals ; Glutathione ; Ions ; Manganese ; Metabolism ; Metals ; Nitroblue Tetrazolium ; Osteoblasts* ; Reactive Oxygen Species ; Selenium ; Superoxide Dismutase

Bone is a complex tissue in which resorption and formation continue throughout life. The bone tissue contains various types of cells, of which the bone forming osteoblasts and bone resorbing osteoclasts are mainly responsible for bone remodeling. Periodontal disease represents example of abnormal bone remodeling. Osteoclasts are multinucleated cells present only in bone. It is believed that osteoclast progenitors are hematopoietic origin, and they are recruited from hematopoietic tissues such as bone marrow and circulating blood to bone. Cells present in the osteoclast microenvironment include marrow stromal cells, osteoblasts, macrophages, T-lymphocytes, and marrow cells. These cells produce cytokines that can affect osteoclast formation. In vitro model systems using bone marrow cultures have demonstrated that IL-1 beta, IL-3, TNF-alpha, bFGF can stimulate the formation of osteoclasts. In contrast, IL-4 inhibits osteoclast formation. Knowledge of cytokines and bFGF that affect osteoclast formation and their capacity to modulate the bone-resorbing process should provide critical insights into normal calcium homeostasis and disorders of bone turnover such as periodontal disease, osteoporosis and Paget's disease.
Bone and Bones ; Bone Marrow* ; Bone Remodeling ; Calcium ; Cytokines* ; Fibroblast Growth Factor 2 ; Homeostasis ; Interleukin-1beta ; Interleukin-3 ; Interleukin-4 ; Macrophages ; Osteoblasts ; Osteoclasts* ; Osteoporosis ; Periodontal Diseases ; Stromal Cells ; T-Lymphocytes ; Tumor Necrosis Factor-alpha