On Osteoprotegerin Research Articles

The effect of risedronate treatment on serum osteoprotegerin and bone marker levels in postmenopausal women with osteoporosis

Background. To evaluate the effect of risedronate treatment on osteoprotegerin (OPG), C-terminal cross-linking telopeptide of type 1 collagen (CTX), osteocalcin (OC), and deoxypyridinoline (DPD).Methods. Eighty postmenopausal osteoporotic patients were randomized into two groups. In first group, patients received 35 mg of risedronate once a week and calcium with vitamin D per day. In second group, patients received only calcium with vitamin D per day. Bone turnover markers were measured at baseline, 1st, 3rd and 6th month.Results. OPG levels were significantly reduced at 1st and 6th month of treatment in both groups, but no statistically significant difference was detected between groups. In the group treated with risedronate, difference in CTX level was observed at 3rd month of treatment, while a difference in DPD and OC levels were observed at 6th month of treatment. The baseline OPG levels correlated with age, menopause duration, and CTX levels. There was no correlation between OPG levels and the levels of the other markers during treatment.Conclusion. The present study showed that using risedronate in treatment of postmenopausal osteoporosis causes no specific changes in OPG levels; therefore, in contrast to some of the studies in the literature OPG may not be useful marker in monitoring of bisphosphonate.

Effect of icariside II on the expression of osteoprotegerin in mouse osteoblasts

To explore the effect of icariside ? on osteoprotegerin(OPG) expression in osteoblasts, primary osteoblasts were cultured with different concentration of icariside ? and 17?estradiol. As a major metabolite of icarrin in vivo, icariside ? exerted a better effect on OPG expression which plays a key role in osteoporosis. 20 ng/dl icariside ? also exerted better effect on OPG secretion than that of positive control group. Consequently, icariside ?could be a candidate for osteoporosis treatment. Key words: Icariside Ⅱ; Obsteoblasts; Osteoprotegerin

Enamel matrix derivative neutralized the effect of lipopolysaccharide on osteoprotegerin and receptor activator of nuclear factor kappa B ligand expression of osteoblasts

Objective In this study, we investigated the effects of enamel matrix derivative (EMD) on osteoprotegerin (OPG) and receptor activator of nuclear factor kappa B ligand (RANKL) expression of osteoblasts in the presence of lipopolysaccharide (LPS). Study design OPG and RANKL gene expression and protein synthesis of MC3T3-E1 osteoblastic cells were examined by reverse transcription-polymerase chain reaction and enzyme-linked immunosorbent assay. Results LPS inhibited OPG gene expression and protein synthesis, and stimulated RANKL gene expression and soluble RANKL synthesis. EMD enhanced OPG gene expression and protein synthesis, and inhibited RANKL gene expression and soluble RANKL synthesis. Furthermore, EMD neutralized the effects of LPS on OPG and RANKL expression in osteoblasts. Conclusions EMD might regulate the function of osteoblasts by elevating the ratio of OPG/RANKL gene expression, which is downregulated by LPS, and suppress the induction of osteoclastogenesis. Thereby, EMD might contribute to periodontal tissue regeneration.

The effect of exercise and estrogen on osteoprotegerin in premenopausal women

Background The benefits of exercise are widely recognized, however physically active women can develop exercise associated menstrual cycle disturbances such as amenorrhea (i.e., estrogen deficiency) secondary to a chronic energy deficiency. Objective To assess the effects of exercise status and estrogen deficiency on osteoprotegerin (OPG) and its relationship to bone resorption in premenopausal exercising women. Design Cross-sectional study of serum OPG, urinary c-telopeptides (uCTX), urinary estrone 3-glucuronide (E1G), urinary pregnanediol 3-glucuronide (PdG) and bone mineral density (BMD) measured on multiple occasions in 67 women. Volunteers were retrospectively grouped: 1) sedentary menstruating group (SedMen n = 8), 2) exercising menstruating group (ExMen, n = 36), and 3) exercising amenorrheic group (ExAmen, n = 23). One-way ANOVAs were performed, and LSD post-hoc tests were performed when differences were detected. Results Subjects were similar with respect to age (24.2 ± 1.0 years), weight (57.8 ± 1.7 kg), and height (164.3 ± 1.3 cm) ( p > 0.05). ExMen and ExAmen groups were more aerobically fit ( p = 0.003) and had less body fat ( p = 0.002) than the SedMen group. Resting energy expenditure/fat free mass was lowest ( p = 0.001) in the ExAmen groups. Mean E1G across the measurement period ( p < 0.001) and overall E1G exposure as assessed by E1G area under the curve (AUC) ( p < 0.001) were lower in the ExAmen group vs. the SedMen and ExMen groups. U-CTX-I was elevated ( p = 0.033) in the ExAmen group (281.8 ± 40.3 μg/L/mmCr), compared with the SedMen and ExMen groups (184.5 ± 22.4, 197.2 ± 14.7 μg/L/mmCr, respectively). OPG was suppressed ( p = 0.005) in the ExAmen group (4.6 ± 0.2 pmol/L) vs. ExMen group (5.2 ± 0.2 pmol/L), and OPG was lower in the SedMen group (4.1 ± 0.3 pmol/L) compared with the ExMen group. Findings were translated to BMD; the ExAmen group had suppressed total body BMD ( p = 0.014) and L2–L4 BMD ( p = 0.015) vs. the ExMen group. Conclusions Our results suggest that OPG responds to the bone loading effect of exercise, and that suppressed OPG may play a role in the etiology of increased bone resorption observed in exercising women with chronic estrogen deficiency secondary to hypothalamic amenorrhea.

T Cells: Unexpected Players in the Bone Loss Induced by Estrogen Deficiency and in Basal Bone Homeostasis

The bone-immune interface has become a subject of intense interest in recent years. It has long been recognized that infection, inflammation, and autoimmune disorders are associated with systemic and local bone loss. Yet, it is only recently that T lymphocytes and their products have been recognized as key regulators of osteoclast formation, life span, and activity. Similarly, sex steroids and aging have been known to regulate the immune system and T cells for decades. In spite of the abundance of clinical and physiological clues, it is only in the last few years that investigators have linked immune cells to the etiology of postmenopausal and senile osteoporosis, as well as to the bone loss caused by a variety of endocrine conditions. As surprising is new evidence showing that in contrast to their bone destructive effects under certain pathological conditions, T cells are highly protective of basal bone homeostasis, through complex regulatory effects on osteoprotegerin (OPG) production by B cells, involving CD40 to CD40 Ligand (CD40L) costimulation. This article examines the experimental evidence suggesting that estrogen prevents bone loss by regulating T cell function, and that T cell costimulation with B cells is critical for OPG production and maintenance of basal bone homeostasis.

Recombinant human thyroid stimulating hormone does not acutely change serum osteoprotegerin and soluble receptor activator of nuclear factor-?? ligand in patients under evaluation for differentiated thyroid carcinoma*

Some extra-thyroid actions of thyroid stimulating hormone (TSH), such as an in vitro action on bone, have been described. Our aim was to evaluate in vivo the acute effect of a recombinant human TSH (rhTSH)-induced TSH surge on Osteoprotegerin (OPG) and receptor activator of the nuclear factor-kappaBeta (RANK-L) levels in patients under levo-thyroxine (L-T4) therapy. 24 patients with differentiated thyroid carcinoma (DTC) were studied. Standard rhTSH testing was performed. OPG, RANK-L, TSH, thyroid hormones, thyroglobulin and several parameters of bone metabolism were evaluated. Baseline OPG and RANK-L levels were in the range of our reference population. An inverse correlation between OPG and spinal Z-score (p=0.029) and between RANK-L and age (p=0.018) or urinary calcium/creatinine ratio (p=0.011) was detected. After rhTSH administration, a significant (p<0.001) increase in TSH was found. No significant increase in OPG or RANK-L levels after rhTSH was observed. No correlation was detected between TSH peak value after rhTSH and maximal percentage change in OPG or RANK-L. A slight increase in urinary cross-links after rhTSH was found. In a small group of subjects with a history of DTC on L-T4 regimen, our study did not support an acute direct effect of TSH on OPG and RANK-L.

Effects of dissociated glucocorticoids on OPG and RANKL in osteoblastic cells

Glucocorticoids are effective anti-inflammatory and immunosuppressive agents, but their use is often associated with debilitating side effects such as glucocorticoid-induced osteoporosis. Newly developed glucocorticoid analogues such as the so-called dissociated glucocorticoids are potent immunosuppressants and have the potential for fewer side effects. The effects of these new analogues on osteoprotegerin (OPG) and receptor activator of NF-κB ligand (RANKL) in osteoblastic cells have not been studied. OPG and RANKL are osteoblast-derived proteins pivotal to the regulation of bone mass. RANKL stimulates bone resorption by increasing osteoclast differentiation, activation and survival. OPG is the decoy receptor for RANKL and thus inhibits bone resorption. Here, we show that dexamethasone, prednisolone, deflazacort and the dissociated glucocorticoids, RU24858, RU40066, RU24782, AL438-F1 and ZK216348 significantly inhibit OPG production in two human osteoblastic cell lines (MG63 and hFOB). The potency for OPG inhibition was ligand and cell-type specific. In both cell types, dexamethasone and prednisolone were the most potent ligands inhibiting OPG production with IC 50s of ∼0.1 nM and 10 nM respectively. In MG63 cells, deflazacort and the RU compounds were the next most potent ligands followed by AL438-F1 and ZK216348. In hFOB cells, however, the RU compounds were the least potent ligands with an IC 50 74 times higher than in MG63 cells. In contrast, the level of maximum inhibition or effectiveness of OPG inhibition did not vary between cell types but did vary according to the ligand. Dexamethasone, prednisolone, deflazacort and the RU compounds all inhibited OPG production by a maximum of ∼70–80%, whereas AL438-F1 and ZK 216348 inhibited OPG production by a maximum of only 40–50% at 1 μM. All of the dissociated glucocorticoids and deflazacort were poor stimulators of RANKL gene expression stimulating by only ∼1–3-fold compared to 7-fold by prednisolone. These data demonstrate that deflazacort and the dissociated glucocorticoids are weak stimulators of the RANKL:OPG ratio compared to prednisolone. Therefore, these compounds have the potential to cause less bone loss than that seen with prednisolone, though this was not investigated here.

α-Lipoic acid suppresses osteoclastogenesis despite increasing the receptor activator of nuclear factor κB ligand/osteoprotegerin ratio in human bone marrow stromal cells

Growing evidence has shown a biochemical link between increased oxidative stress and reduced bone density. Although alpha-lipoic acid (alpha-LA) has been shown to act as a thiol antioxidant, its effect on bone cells has not been determined. Using proteomic analysis, we identified six differentially expressed proteins in the conditioned media of alpha-LA-treated human bone marrow stromal cell line (HS-5). One of these proteins, receptor activator of nuclear factor kappaB ligand (RANKL), was significantly up-regulated, as confirmed by immunoblotting with anti-RANKL antibody. ELISA showed that alpha-LA stimulated RANKL production in cellular extracts (membranous RANKL) about 5-fold and in conditioned medium (soluble RANKL) about 23-fold, but had no effect on osteoprotegerin (OPG) secretion. Despite increasing the RANKL/OPG ratio, alpha-LA showed a dose-dependent suppression of osteoclastogenesis, both in a coculture system of mouse bone marrow cells and osteoblasts and in a mouse bone marrow cell culture system, and reduced bone resorption in a dose-dependent manner. In addition, alpha-LA-induced soluble RANKL was not inhibited by matrix metalloprotease inhibitors, indicating that soluble RANKL is produced by alpha-LA without any posttranslational processing. In contrast, alpha-LA had no significant effect on the proliferation and differentiation of HS-5 cells. These results suggest that alpha-LA suppresses osteoclastogenesis by directly inhibiting RANKL-RANK mediated signals, not by mediating cellular RANKL production. In addition, our findings indicate that alpha-LA-induced soluble RANKL is not produced by shedding of membranous RANKL.

Production of Prostaglandin D2 by Human Osteoblasts and Modulation of Osteoprotegerin, RANKL, and Cellular Migration by DP and CRTH2 Receptors

Human osteoblasts produce PGD(2), which acts on the DP receptor to decrease osteoprotegerin production and on the CRTH2 receptor to decrease RANKL expression and to induce osteoblast chemotaxis. These results indicate that activation of CRTH2 may lead to an anabolic response in bone. Whereas the actions of prostaglandin (PG)E(2) as a modulator of bone and osteoblast function are relatively well characterized, little is known about PGD(2) and bone metabolism. The objectives of this study were to determine if human osteoblasts can produce PGD(2), which prostaglandin D(2) synthases are implicated in this synthesis, to identify the PGD(2) receptors (DP and CRTH2) on these cells and to characterize the biological effects resulting from their activation. RT-PCR analysis and immunohistochemistry were used to detect PGD(2) receptor and synthases in cultured human osteoblasts. Immunohistochemistry was used to identify the synthases and receptors in human bone tissue. Intracellular cAMP and calcium levels were determined to verify receptor activation. The cells were stimulated with PGD(2) or the specific agonists BW 245C (DP) and DK-PGD(2) (CRTH2), and the resulting effects on osteoprotegerin (OPG) secretion, RANKL expression, and chemotaxis were determined. Osteoblast production of PGD(2) was evaluated by measuring PGD(2) in the culture supernatants after stimulation with interleukin (IL)-1, TNF-alpha, PTH, vascular endothelial growth factor (VEGF), and insulin-like growth factor I (IGF-I). Human osteoblasts in culture generated PGD(2) when stimulated. Both osteoblasts in culture and in situ present the lipocalin-type PGD(2) synthase only. Both DP and CRTH2 receptors were present in human osteoblasts in culture and in situ. Stimulation of DP resulted in an increase in cAMP, whereas CRTH2 increased the intracellular calcium level. OPG production was reduced by 60% after DP receptor stimulation, whereas CRTH2 receptor stimulation decreased RANKL expression on human osteoblasts. As reported for other cell types, CRTH2 was a potent inducer of chemotaxis for human osteoblasts in culture. Human osteoblasts in culture produce PGD(2) under biologically relevant stimuli through the lipocalin-type PGD(2) synthase (L-PGDS) pathway. As an autacoid, PGD(2) can act on DP and CRTH2 receptors, both present on these cells. Specific activation of CRTH2 could lead directly and indirectly to an anabolic response in bone.

Vitamin A differentially regulates RANKL and OPG expression in human osteoblasts

All- trans-retinoic acid (ATRA) induces bone resorption, but the molecular mechanisms are unknown. We have studied the effect of ATRA on osteoprotegerin (OPG) and receptor activator of NF-κB ligand (RANKL) expression in human MG-63 osteosarcoma cells and primary osteoblast-like cultures. ATRA dose-dependently down-regulated protein levels of OPG in MG-63 cells, with a maximum (−56%) observed at a dose of 10 −6 M. This effect was confirmed with quantitative real-time PCR, where OPG mRNA was decreased after 4 h (−68%) in primary cultures and after 8 h (−87%) in MG-63 cells. The reduction in OPG expression was inhibited by a retinoic acid receptor (RAR)-antagonist and was mimicked by a RARβ,γ-agonist, indicating that the ATRA effect is mediated by these receptors. In primary cultures we found a threefold induction of RANKL mRNA expression. Thus, the RANKL/OPG ratio was markedly increased, suggesting a potential mechanism of ATRA-induced bone resorption.

NF-κB-dependent induction of osteoprotegerin by Porphyromonas gingivalis in endothelial cells

Porphyromonas gingivalis is a major etiological pathogen of adult periodontitis characterized by alveolar bone resorption. Vascular endothelial cells supply many inflammatory cytokines into periodontal tissue. However, whether the cells contribute to bone metabolism in periodontitis remains unknown. In this study, we investigated the effect of P. gingivalis on osteoprotegerin (OPG) and receptor activator of NF-κB ligand (RANKL) production, both of which are key regulators of bone metabolism, in human microvascular endothelial cells (HMVECs). We showed that P. gingivalis upregulated expression of OPG but not RANKL mRNA in HMVEC. P. gingivalis induced NF-κB activation, and the induction of OPG in HMVEC by the pathogen was blocked by the inhibitors of NF-κB. In addition, incubation of OPG with P. gingivalis supernatant resulted in loss of the protein. These results indicate that P. gingivalis-stimulated HMVEC secrete OPG via a NF-κB-dependent pathway, while the OPG is partly degraded by the bacteria. Thus, microvascular endothelial cells can act as a source of OPG and thereby may play an important role in regulating bone metabolism in periodontitis.