Participation of oxidative stress in the process of osteoclast differentiation.

In the present paper, the involvement of active oxygen species in bone resorption has been studied. In order to compare the production of active oxygen by mouse marrow culture cells, fluorescence due to peroxides reacted with 2,7-dichlorofluorescin was measured. After marrow cells were cultured with 1,25-(OH)2D3 for 8 days, there were tartrate resistant acid phosphatase positive multinucleated cells (TRACP(+)MNCs), TRACP positive mononucleated cells, macrophage-like cells and marrow derived stromal cells. Among these cells, TRACP(+) cells could produce almost the equivalent amount of peroxides as could the macrophage-like cells. In order to examine the role of active oxygen in bone metabolism, the amount of oxidative stress was altered during the culture period in the same marrow culture system. Catalase, a catabolic enzyme of hydrogen peroxide (H2O2), significantly suppressed the formation of TRACP(+)MNCs in a dose dependent manner. This suppression was limited in the early stage of the culture period and was reduced by the addition of exogenous H2O2 to culture. Moreover, when superoxide dismutase, a converting enzyme from superoxide anion to H2O2, was added in this system, the formation of TRACP(+)MNCs was significantly increased. These results strongly suggest that active oxygen species, especially H2O2, may be involved in the regulation of osteoclast formation.