Effects of Estrogen and Cytokine on Nitric Oxide Production and Alkaline Phosphatase Activity of Osteoblastic Cells

다국어 초록 (Multilingual Abstract)

Nitric oxide (NO) is a mediator of bone metabolism with effects on bone resorption and formation. Its production by both the constitutive and inducible isoforms of nitric oxide synthase (NOS) is affected by estrogen in several types of cell and in tissues other than bone cells. Many systemic and local factors regulate bone remodeling under normal and pathological conditions through their effects on the recruitment, differentiation, and function of osteoblast and osteoclast. Estrogen deficiency is one of the most important factors in the pathogenesis of osteoporosis, although the mechanisms by which estrogen prevents bone loss are poorly understood. Recently, the multifunctional signal molecule, NO, has been shown to serve as an important intercellular signal modulator in bone. Moreover, other reports showed that the protective effect of estrogen on ovariectomy-induced bone loss in rats was inhibited by the NOS inhibitor. Cytokines are important in the modulation of bone metabolism. Estrogen alters the production of cytokines or changes the responsivenss of cells to estrogen, or both. Thus, this study performed to know whether cytokine-induced NO production by MC3T3/E1 cells ans rat calvarial cells was affected by estrogen. This studies investigated the effect of 17-β estradiol (10^-1-, 10^-8 and 10^-6M), IL-1β (0.1 and 1ng/ml), TNF-α (2 and 20ng/ml) or IFN-γ(50 and 500U/ml) on NO production and ALP activity by MC2T3/E1 cells and RCCs, to determine potential role of estrogen and cytokine in the regulation of osteoblast function. At 10^-10M, 17β -estradiol slightly increased NO production, whereas, at 10^-8 and 10^-6M 17β -estradiol decreased it in the culture medium of the MC3T3/E1 cells. Pretreatment for 24 hours with 17β -estradiol and stimulation for additional 48 hours with a IL-1β or TNF-α -estradiol decreased NO production in the culture medium of the MC3T3/E1 cells. NAME induced a significant decrease of NO production without alteration of patterns of stimulation and/or inhibition. At 10^-8 and 10^-6M, 17β -estradiol slightly increased NO release in the culture medium of the RCCs. Pretreatment for 24 hours with 17 -estradiol and stimulation for additional 48 hours with cytokines had no effect on the ALP activity of MC3T3/E1 cells. However, pretreatment with 10^-8M 17β -estradiol and stimulation with cytokines increased ALP activity of RCCs. Pretreatment for 24 hours with 10^-8M 17β -estradiol and stimulation for additional 48 hours with cytokines had effect on the cell viability of MC3T3/E1 and RCCs. These results showed that estrogen had biphasic effect on the production of NO by osteoblasts. Estrogen showed an increase in ALP activity. Thus, these study suggested that estrogen might prevent bone loss trough regulated osteoblastic activity.