Oestrogenic compounds modulate cytokine-induced nitric oxide production inmouse osteoblast-like cells

Nitric oxide (NO) is a mediator of bone metabolism with effects on both bon e resorption and formation. Its production by both the constitutive and ind ucible isoforms of nitric oxide synthase (NOS) is affected by oestrogen in several types of cell and in tissues other than bone cells. Recently, oestr ogens were found to increase basal NO production by osteoblasts via enhance d activity or expression, or both, of NOS-3. Inflammatory cytokines, howeve r, increase NO by increasing the expression of NOS-2. In this study we have examined whether cytokine-induced NO production by os teoblastic cells was affected by oestrogenic compounds by studying the effe ct of 17 beta-oestradiol and the anti-oestrogens ICI164,384 and 4-hydroxyta moxifen on cytokine-induced NO production in oestrogen receptor positive MC 3T3-E1 osteoblast-like cells. Combinations of the inflammatory cytokines in terleukin-1 beta, tumour necrosis factor-alpha, and interferon-gamma with l ipopolysaccharide stimulated NO production up to Ii-fold. This cytokine-ind uced NO production was further increased dose-dependently by the anti-oestr ogens ICI163,384 and 4-hydroxytamoxifen (133.3 +/- 3.2% and 146.0 +/- 13.2% , respectively). 17 beta-Oestradiol either had no effect on or slightly inh ibited cytokine-induced NO production. It did, however, dose-dependently co unteract the stimulatory effect of the anti-oestrogens. Concentrations of 1 7 beta-oestradiol needed to prevent the stimulatory effect of 4-hydroxytamo xifen were ca tenfold that of ICI164,384. These findings show that, in addition to the stimulatory effect of oestroge n on basal NO production by NOS-3, cytokine-induced NO production is also a ffected by oestrogenic compounds in osteoblasts.