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Oestrogenic compounds modulate cytokine-induced nitric oxide production in mouse osteoblast-like cells
R L van Bezooijen1, C Van der Bent, S E Papapoulos
1Department of Endocrinology and Metabolic Diseases, Leiden University Medical Centre, The Netherlands.
Abstract:
Nitric oxide (NO) is a mediator of bone metabolism with effects on both bone resorption and formation. Its production by both the constitutive and inducible isoforms of nitric oxide synthase (NOS) is affected by oestrogen in several types of cell and in tissues other than bone cells. Recently, oestrogens were found to increase basal NO production by osteoblasts via enhanced activity or expression, or both, of NOS-3. Inflammatory cytokines, however, increase NO by increasing the expression of NOS-2. In this study we have examined whether cytokine-induced NO production by osteoblastic cells was affected by oestrogenic compounds by studying the effect of 17beta-oestradiol and the anti-oestrogens ICI164,384 and 4-hydroxytamoxifen on cytokine-induced NO production in oestrogen receptor positive MC3T3-E1 osteoblast-like cells. Combinations of the inflammatory cytokines interleukin-1beta, tumour necrosis factor-alpha, and interferon-gamma with lipopolysaccharide stimulated NO production up to 11-fold. This cytokine-induced NO production was further increased dose-dependently by the anti-oestrogens ICI164,384 and 4-hydroxytamoxifen (133.3 +/- 3.2% and 146.0 +/- 13.2%, respectively). 17Beta-oestradiol either had no effect on or slightly inhibited cytokine-induced NO production. It did, however, dose-dependently counteract the stimulatory effect of the anti-oestrogens. Concentrations of 17beta-oestradiol needed to prevent the stimulatory effect of 4-hydroxytamoxifen were ca tenfold that of ICI164,384. These findings show that, in addition to the stimulatory effect of oestrogen on basal NO production by NOS-3, cytokine-induced NO production is also affected by oestrogenic compounds in osteoblasts.
Insights
Oestrogenic compounds, particularly anti-oestrogens, can increase nitric oxide (NO) production in osteoblasts stimulated by inflammatory cytokines. However, 17beta-oestradiol counteracts this effect, influencing NO mediation in bone metabolism.
Area of Science:
- Bone biology and endocrinology
- Nitric oxide signaling pathways
- Osteoblast cellular mechanisms
Background:
- Nitric oxide (NO) plays a crucial role in regulating bone metabolism, affecting both resorption and formation.
- Oestrogen influences NO production by nitric oxide synthase (NOS) isoforms in various cell types, including bone cells.
- While oestrogens enhance basal NO production via NOS-3 in osteoblasts, inflammatory cytokines increase NO through NOS-2 expression.
Purpose of the Study:
- To investigate the effect of oestrogenic compounds on cytokine-induced NO production in osteoblast-like cells.
- To determine how 17beta-oestradiol and anti-oestrogens (ICI164,384, 4-hydroxytamoxifen) modulate NO production stimulated by inflammatory cytokines in MC3T3-E1 cells.
Main Methods:
- Utilized MC3T3-E1 osteoblast-like cells, which are oestrogen receptor-positive.
- Administered combinations of inflammatory cytokines (interleukin-1beta, tumour necrosis factor-alpha, interferon-gamma) with lipopolysaccharide to stimulate NO production.
- Assessed the impact of 17beta-oestradiol, ICI164,384, and 4-hydroxytamoxifen on cytokine-induced NO levels.
Main Results:
- Cytokine and lipopolysaccharide stimulation increased NO production up to 11-fold.
- Anti-oestrogens ICI164,384 and 4-hydroxytamoxifen dose-dependently enhanced this cytokine-induced NO production.
- 17beta-oestradiol showed minimal effect or slight inhibition on cytokine-induced NO and dose-dependently counteracted the stimulatory effects of anti-oestrogens.
Conclusions:
- Cytokine-induced NO production in osteoblasts is modulated by oestrogenic compounds, in addition to oestrogen's effect on basal NO via NOS-3.
- Anti-oestrogens can amplify NO production stimulated by inflammatory cytokines in osteoblasts.
- The interplay between oestrogen, anti-oestrogens, and inflammatory cytokines influences NO signaling in osteoblasts, impacting bone metabolism.