metallothionein and Osteoporosis

Metallothionein (MT), a cysteine-rich, metal-binding protein, is involved in homeostatic regulation of essential metals and protection of cells against oxidative injury. It has been shown that oxidative stress is associated with pathogenesis of osteoporosis and is capable of inhibiting osteoblastic differentiation of bone cells by nuclear factor-kappaB (NF-kappaB). In this study, the effect of MT on oxidative stress-induced inhibition of osteoblast differentiation was examined. 50-200 microM hydrogen peroxide-induced oxidative stress suppressed the osteoblastic differentiation process of primary mouse bone marrow stromal cells (BMSCs), manifested by a reduction in the differentiation marker alkaline phosphatase (ALP). The presence of exogenous MT (20-500 microM) or induction of endogenous MT by ZnCl2 (50-200 microM) could protect BMSCs against H2O2-induced inhibition of osteoblastic differentiation, manifested by a resumption of H2O2-inhibited ALP activity and ALP positive cells. Furthermore, adding exogenous MT or inducing endogenous MT expression impaired H2O2-stimulated NF-kappaB signaling. These data indicate the ability of MT to protect BMSCs against oxidative stress-induced inhibition of osteoblastic differentiation.

Topics: Alkaline Phosphatase; Animals; Biomarkers; Bone Marrow Cells; Cell Differentiation; Cells, Cultured; Chlorides; Hydrogen Peroxide; Metallothionein; Mice; NF-kappa B; Osteoblasts; Osteogenesis; Osteoporosis; Oxidants; Oxidative Stress; Signal Transduction; Stromal Cells; Zinc Compounds

Clone MC3T3-E1 cells at various differentiation stages were exposed to 0.44-13.3 microM Cd or 50-175 microM Zn in culture medium. After a 2-h culture period, the amount of Zn accumulated in the cells was shown to be larger than that for Cd, but the production of Zn-thionein was much less compared with that of Cd-thionein. After a 24-h incubation period, the synthesis of Zn-thionein increased markedly at levels of 150 microM Zn or greater, Cd induced metallothionein (MT) synthesis in a dose-dependent manner at 0.44 microM Cd or greater. Since calcified cells differentiated into osteoblastic cells also produced MT, osteoblasts were confirmed to have an ability to induce MT synthesis. Initiation of production of Cd-or Zn-thionein in the cells occurred at an accumulation of about 0.4 nmol Cd and 2.5 nmol Zn/mg cytosol protein. The ratios of thionein-binding Cd/Cd accumulated in the cytosol and thionein-binding Zn/Zn accumulated in the cytosol were 0.11 mol/mol and 0.067 mol/mol, respectively. These results show that the concentration of accumulated Zn necessary for initiating production of MT is about six times that of Cd and one molecule of Cd induces thionein about 1.6 times as effectively as one molecule of Zn does.

Topics: Cadmium; Cell Differentiation; Cells, Cultured; Dose-Response Relationship, Drug; Humans; Metallothionein; Osteoblasts; Osteoporosis; Zinc