Immunological study on circulating murine osteoprotegerin/osteoclastogenesis inhibitory factor (OPG/OCIF): possible role of OPG/OCIF in the prevention of osteoporosis in pregnancy

Roles of osteoprotegerin in endocrine and metabolic disorders through receptor activator of nuclear factor kappa-B ligand/receptor activator of nuclear factor kappa-B signaling

Endocrine and metabolic diseases show increasing incidence and high treatment costs worldwide. Due to the complexity of their etiology and mechanism, therapeutic strategies are still lacking. Osteoprotegerin (OPG), a member of the tumor necrosis factor receptor superfamily, appears to be a potential candidate for the treatment of these diseases. Studies based on clinical analysis and rodent animal models reveal the roles of OPG in various endocrine and metabolic processes or disorders, such as bone remodeling, vascular calcification, and β-cell proliferation, through the receptor activator of nuclear factor kappa-B ligand (RANKL) and the receptor activator of NF-κB (RANK). Thus, in this review, we mainly focus on relevant diseases, including osteoporosis, cardiovascular disease (CVD), diabetes, and gestational diabetes mellitus (GDM), to summarize the effects of the RANKL/RANK/OPG system in endocrine and metabolic tissues and diseases, thereby providing a comprehensive insight into OPG as a potential drug for endocrine and metabolic diseases.

Rank-Rankl-Opg Axis in Multiple Sclerosis: The Contribution of Placenta

Women with multiple sclerosis (MS) can safely become pregnant and give birth, with no side effects or impediments. Pregnancy is generally accepted as a period of well-being in which relapses have a softer evolution, particularly in the third trimester. Herein, we hypothesized that the placenta, via its “secretome”, could contribute to the recognized beneficial effects of pregnancy on MS activity. We focused on a well-known receptor/ligand/decoy receptor system, such as the one composed by the receptor activator of nuclear factor-kB (RANK), its ligand (RANKL), and the decoy receptor osteoprotegerin (OPG), which have never been investigated in an integrated way in MS, pregnancy, and placenta. We reported that pregnancy at the term of gestation influences the balance between circulating RANKL and its endogenous inhibitor OPG in MS women. We demonstrated that the placenta at term is an invaluable source of homodimeric OPG. By functional studies on astrocytes, we showed that placental OPG suppresses the mRNA expression of the CCL20, a chemokine responsible for Th17 cell recruitment. We propose placental OPG as a crucial molecule for the recognized beneficial effect of late pregnancy on MS and its potential utility for the development of new and more effective therapeutic approaches.

Prepartum measurement of serum biomarkers reflecting osteoclastic and osteoblastic bone metabolism for predicting the risk of milk fever in dairy cows

We investigated whether prepartum levels of serum bone biomarkers are related to the degree of parturient hypocalcaemia and risk of milk fever (MF) in dairy cows with advancing parity. A total of 58 late-pregnant cattle were assigned to four groups: nulliparous, primiparous, multiparous in the 2nd lactation and multiparous in the 3rd-5th lactation. The multiparous cows were further assigned to MF and non-MF groups according to the onset of MF. Serum samples were obtained from the cows during the 3 weeks prepartum to 5 d postpartum period for the measurement of serum calcium (Ca) and three bone biomarkers: tartrate-resistant acid phosphatase isoform 5b (TRAP5b), osteoprotegerin (OPG) and bone isoenzyme of alkaline phosphatase (ALP3). The ratios of OPG to TRAP5b (O/T ratio) and ALP3 to TRAP5b (A/T ratio) were calculated. The data from all cattle showed that the severity of hypocalcaemia at parturition increased with advancing parity/age. The MF cows had elevated serum TRAP5b activity and a decreased O/T ratio after parturition, suggesting an increased number of osteoclasts due to osteoclastogenesis, in response to severe hypocalcaemia. The MF cows showed lower serum ALP3 activity during the 3 weeks prepartum than the non-MF cows, therefore, prepartum osteoblast function was likely weak in the MF cows. During the 2-3 weeks prepartum, serum ALP3 activity and the A/T ratio had moderate associations with the serum Ca concentration at day 0 (day of calving) in the multiparous cows, and receiver operating characteristic curve analysis revealed that ALP3 activity had excellent ability to predict MF. In conclusion, prepartum serum ALP3 activity is a promising biomarker to predict MF in multiparous cows.

Placenta-Derived Osteoprotegerin Is Required for Glucose Homeostasis in Gestational Diabetes Mellitus

Osteoprotegerin (OPG) is involved in various biological processes, including bone remodeling, vascular calcification and pancreatic β-cell function. Although some clinical studies have shown an increase in serum OPG level during pregnancy, the role of OPG in gestational diabetes mellitus (GDM) is largely unknown. Therefore, we explored the effect of OPG in metabolic homeostasis during pregnancy. We initially evaluated serum OPG levels using ELISA and western blotting techniques on samples from GDM patients. We also assessed OPG expression levels in maternal mice. We then used blastocysts transduced with lentiviruses capable of trophoblast-specific transgene expression to establish placenta-specific OPG knockdown or overexpression mouse models for functional and mechanistic investigation after embryo transplantation. We found that OPG expression was positively associated with GDM in clinical samples, and OPG levels were significantly increased in GDM patient sera and term placenta. Serum OPG was significantly increased in maternal compared to non-pregnant mice, and expression levels of OPG were the highest in placenta compared with other organs, including bone, liver and pancreas. OPG was also significantly increased in pregnant mice fed a high-fat diet (HFD). Placenta-specific OPG knockdown induced glucose intolerance, decreased β-cell proliferation and decreased serum insulin levels, whereas placenta-specific OPG overexpression promoted glucose tolerance and enhanced β-cell proliferation, which increased serum insulin production and decreased fetal weight in HFD-feeding pregnant mice. Placenta-derived OPG (pl-OPG) regulated glucose homeostasis during pregnancy via enhancement of β-cell proliferation, which suggests a potential therapeutic application of OPG for GDM.

Bone Regeneration Induced by Strontium Folate Loaded Biohybrid Scaffolds

Nowadays, regenerative medicine has paid special attention to research (in vitro and in vivo) related to bone regeneration, specifically in the treatment of bone fractures or skeletal defects, which is rising worldwide and is continually demanding new developments in the use of stem cells, growth factors, membranes and scaffolds based on novel nanomaterials, and their applications in patients by using advanced tools from molecular biology and tissue engineering. Strontium (Sr) is an element that has been investigated in recent years for its participation in the process of remodeling and bone formation. Based on these antecedents, this is a review about the Strontium Folate (SrFO), a recently developed non-protein based bone-promoting agent with interest in medical and pharmaceutical fields due to its improved features in comparison to current therapies for bone diseases.

Evaluation of biochemical parameters and local and systemic levels of osteoactive and B-cell stimulatory factors in gestational diabetes in the presence or absence of gingivitis

BACKGROUND

Gestational diabetes mellitus (GDM) is defined as varying glucose intolerance, with first onset or recognition in pregnancy. This study evaluates clinical and biochemical parameters in a possible association between GDM and gingivitis.

METHODS

A total of 167 pregnant females was included in the study. There were 101 females with GDM and 66 females without GDM. Subgroups were created according to the presence or absence of gingival inflammation. Plaque index, bleeding on probing, and probing depth were recorded at four sites per tooth. Serum, saliva, and gingival crevicular fluid (GCF) levels of interleukin (IL)-6, IL-8, soluble receptor activator of nuclear factor-kappa B ligand (sRANKL), osteoprotegerin (OPG), B-cell activating factor (BAFF), and a proliferation-inducing ligand (APRIL) were determined by enzyme-linked immunosorbent assay. Data were analyzed by Kruskal-Wallis and Mann-Whitney U tests and Spearman correlation analysis.

RESULTS

Age and anthropometric indices were higher in the GDM than non-GDM group (P <0.0001). Clinical periodontal recordings, serum BAFF, IL-8, and saliva sRANKL levels were higher in the GDM group (P <0.05). Saliva IL-6 level was higher in the GDM with gingivitis group than non-GDM with gingivitis group (P = 0.044). Serum and GCF BAFF (P <0.0001), serum, saliva, and GCF APRIL (P <0.0001; P <0.0001; P = 0.032, respectively), GCF OPG (P = 0.036), and serum and saliva sRANKL (P <0.0001) were higher in the GDM with gingivitis group than GDM without gingivitis group.

CONCLUSIONS

The inflammatory response seems to be more pronounced in females with GDM. The observed increase in both local and systemic levels of inflammatory cytokines may suggest an interaction between gingivitis and GDM.

Calcium economy in human pregnancy and lactation

Pregnancy and lactation are times of additional demand for Ca. Ca is transferred across the placenta for fetal skeletal mineralisation, and supplied to the mammary gland for secretion into breast milk. In theory, these additional maternal requirements could be met through mobilisation of Ca from the skeleton, increased intestinal Ca absorption efficiency, enhanced renal Ca retention or greater dietary Ca intake. The extent to which any or all of these apply, the underpinning biological mechanisms and the possible consequences for maternal and infant bone health in the short and long term are the focus of the present review. The complexities in the methodological aspects of interpreting the literature in this area are highlighted and the inter-individual variation in the response to pregnancy and lactation is reviewed. In summary, human pregnancy and lactation are associated with changes in Ca and bone metabolism that support the transfer of Ca between mother and child. The changes generally appear to be independent of maternal Ca supply in populations where Ca intakes are close to current recommendations. Evidence suggests that the processes are physiological in humans and that they provide sufficient Ca for fetal growth and breast-milk production, without relying on an increase in dietary Ca intake or compromising long-term maternal bone health. Further research is needed to determine the limitations of the maternal response to the Ca demands of pregnancy and lactation, especially among mothers with marginal and low dietary Ca intake, and to define vitamin D adequacy for reproductive women.

Effects of relaxin and estrogens on bone remodeling markers, receptor activator of NF-kB ligand (RANKL) and osteoprotegerin (OPG), in rat adjuvant-induced arthritis

Rheumatoid arthritis (RA) is characterized by joint inflammation and bone destruction. The receptor activator of nuclear factor-kappa B ligand (RANKL)-osteoprotegerin (OPG) system is important for maintaining the balance between bone resorption and formation. Both serum RANKL/OPG protein and synovial tissue RANKL/OPG mRNA ratios are elevated in patients with RA. Studies indicate that hormones of pregnancy, estrogens and relaxin, administered in combination, reduce circulating (TNF)-α and joint inflammation in a rat adjuvant-induced arthritis (AIA) model of RA. The purpose of this study was to investigate whether relaxin (RLX), alone or in combination with estrogens, regulates the bone remodeling markers RANKL and OPG in vivo and in vitro. Results show that in AIA rats, treatment with relaxin, estradiol valerate (EV) or EV in combination with relaxin had no effect on circulating RANKL. However, EV increased systemic OPG and combined treatment with EV and relaxin further increased circulating OPG in comparison to EV alone. Importantly, the RANKL/OPG protein ratio was lower in rats treated with EV or EV+RLX when compared to arthritic controls. Relaxin in combination with EV decreased local RANKL transcripts, increased OPG mRNA and decreased the RANKL/OPG mRNA ratio in joints of arthritic rats when compared to controls. RLX family peptide receptor 1 (RXFP1) gene expression in joints of AIA rats increased in response to EV and EV+RLX. In parathyroid hormone-pretreated murine UMR 106-01 osteoblast cells, 17-β-estradiol (E) and E+RLX increased RXFP1 transcripts, while RLX reduced RANKL mRNA and protein expression. However, in vitamin D-treated primary rat osteoblast cells E+RLX increased OPG protein and reduced the RANKL/OPG protein ratio. These results suggest that modulation of the RANKL-OPG system by estrogens and RLX may contribute to their antiarthritic effects on bone during pregnancy.

The influence of folic acid supplementation on maternal and fetal bone turnover

The aim of our study was to investigate the relationship between maternal and fetal bone turnover markers and folic acid supplementation during pregnancy. In an observational study performed in Tehran University of Medical Sciences related hospitals, 113 healthy pregnant women with gestational age between 8 and 12 weeks and aged between 15 and 42 years were recruited and followed until delivery time. The participants were divided into two groups; women who took 1 mg of folic acid daily supplement from the beginning of the pregnancy until the end of the second trimester entered into group I and women who choose to continue their daily intake of folic acid until the delivery time entered into group II. The two groups were matched based on the maternal anthropometric data, energy, calcium and vitamin D intake. Following the delivery, venous blood samples were collected from mothers and umbilical cords of the neonates. Maternal and fetal serum concentrations of 25-hydroxy vitamin D3, PTH, osteocalcin (OC), crosslaps and maternal serum level of homocysteine, folate, soluble receptor activator of NF-kappaB ligand (sRANKL), osteoprotegerin (OPG), calcium, and phosphate were measured. Measured birth outcome parameters included weight, length, head circumference, appearance, and respiration. With regard to maternal assessment, the serum levels of OC and OPG and folate were significantly higher in group II compared to group I, while the serum levels of RANKL and homocysteine were significantly higher in group I. We did not find significant differences in serum levels of 25-OH vitamin D, PTH, crosslaps, calcium, or phosphate between the two groups. The neonates from mothers recruited in group II had higher (but not significantly) serum level of OC. We observed that the neonates born from mothers in group II had overall better birth outcome parameters and apgar scores compare to the neonates born from mothers in group I. Our results show that daily supplementation of folic acid during pregnancy could have a positive impact on the bone turnover markers in mothers and their newborns. This may suggest that both pregnant mothers and their fetuses could benefit from positive effects of folic acid taken during the whole period of pregnancy.

CLINICAL Review #: the role of receptor activator of nuclear factor-kappaB (RANK)/RANK ligand/osteoprotegerin: clinical implications

CONTEXT

Receptor activator of nuclear factor-kappaB ligand (RANKL), receptor activator of nuclear factor-kappaB (RANK), and osteoprotegerin (OPG) play a central role in bone remodeling and disorders of mineral metabolism.

EVIDENCE ACQUISITION

A PubMed search was conducted from January 1992 until 2007 for basic, observational, and clinical studies in subjects with disorders related to imbalances in the RANK/RANKL/OPG system.

EVIDENCE SYNTHESIS

RANK, RANKL, and OPG are members of the TNF receptor superfamily. The pathways involving them in conjunction with various cytokines and calciotropic hormones play a pivotal role in bone remodeling. Several studies involving mutations in the genes encoding RANK and OPG concluded in the discovery of a number of inherited skeletal disorders. In addition, basic and clinical studies established a consistent relationship between the RANK/RANKL/OPG pathway and skeletal lesions related to disorders of mineral metabolism. These studies were a stepping stone in further defining the role of the RANK/RANKL/OPG pathway in osteoporosis, rheumatoid arthritis, bone loss associated with malignancy-related skeletal diseases, and its relationship to vascular calcifications. Subsequently, the further understanding of this pathway led to the development of new therapeutic modalities including the human monoclonal antibody to RANKL and recombinant OPG as a target for treatment of postmenopausal osteoporosis and multiple myeloma.

CONCLUSIONS

The RANK/RANKL/OPG system mediates the effects of calciotropic hormones and, consequently, alterations in their ratio are key in the development of several clinical conditions. New agents with the potential to block effects of RANKL have emerged for treatment of postmenopausal osteoporosis and malignancy-related skeletal disease.

Vitamin D: the secosteroid hormone and human reproduction

Vitamin D is a secosteroid with an endocrine mechanism of action which is sequentially synthesized in humans in the skin, liver and kidneys. The active hormone, 1alpha,25-dihydrocholecalciferol [1,25(OH)2D3], is often considered only in terms of its role in controlling calcium and phosphorus homeostasis. However, cumulative evidence points to the presence of vitamin D receptors in many tissues. The present article summarizes key points regarding the participation of vitamin D in pregnancy and breastfeeding. During pregnancy, sufficient vitamin D concentrations are needed not only to address the growing demand for calcium on the part of the fetus, but also to participate in fetal growth, development of the nervous system, lung maturation and fetal immune system function. Hypovitaminosis D has been related to the development of diabetes, pre-eclampsia and fetal neurological disorders. During pregnancy and lactation, calcium from the maternal skeleton is mobilized, with a rise in bone turnover and a reduction in bone mass. It is advisable for pregnant and nursing women to maintain adequate levels of vitamin D, through small doses of solar exposure to facilitate natural formation of the hormone or by ingesting appropriate vitamin supplements. Further studies are needed to clarify the many gaps in knowledge and elucidate the role of vitamin D in the context of reproduction. Confirmation of experimental observations relating to the risks of hypovitaminosis D would have important public health implications.

Functional Dissection of Osteoprotegerin and Its Interaction with Receptor Activator of NF-κB Ligand

The receptor activator of NF-kappaB (RANK) belongs to the neuregulin/tumor necrosis factor (TNF) receptor superfamily and is activated by RANK ligand (RANK-L), a homotrimeric, TNF-like cytokine. RANK is present on the surface of osteoclast cell precursors, where its interaction with RANK-L induces their terminal differentiation into osteoclasts, thus increasing bone breakdown. The secreted, soluble receptor osteoprotegerin (OPG) interrupts this activation by binding directly to RANK-L. Therefore, osteoclast maturation (and bone homeostasis) is regulated in vivo by OPG levels of expression. We have studied the assembly state and affinity of OPG for RANK-L by sedimentation analyses and surface plasmon resonance (Biacore). Full-length, homodimeric OPG binds to RANK-L with a KD of 10 nM. OPG is also a member of the TNF receptor superfamily and contains four disulfide-rich ligand-binding domains, yet lacks a transmembrane region separating the ligand-binding region from the two death domains, as observed for other receptor family members. We showed that dimerization of OPG results from noncovalent interactions mediated by the death domains and to a lesser extent by a C-terminal heparin-binding region. In contrast, a C-terminal intermolecular disulfide bond does not contribute to the formation or stability of OPG dimers. A truncate of osteoprotegerin, containing the ligand-binding domains but lacking the dimerization domains, bound RANK-L with a KD of approximately 3 microM, indicating that monomer oligomerization for the OPG provides an increase of 3 orders of magnitude in the affinity for RANK-L. Therefore, OPG dimer formation is required for the mechanism of inhibition of the RANK-L/RANK receptor interaction.

[Osteoprotegerin--a neutralizing receptor, protector of bones and a potential antiresorptive agent]

INTRODUCTION

The receptor activator of NF-B ligand (RANKL), expressed on the surface of osteoblasts and stromal cells in the bone marrow, plays an essential role in the formation and differentiation of osteoclasts and bone resorption. RANKL binds to its functional receptor, receptor activator of NF-B (RANK), expressed as a transmembrane heterotrimer on the surface of hematopoietic osteoclasts progenitors and mature osteoclasts. RANKL-RANK interaction is inhibited by soluble receptor-osteoprotegerin.

OSTEOPROTEGERIN

Osteoprotegerin (OPG), a member of the tumor necrosis factor receptor superfamily, acts as a natural decoy receptor that blocks the interaction between RANKL and RANK. The balance between RANKL and osteoprotegerin is of major importance in bone homeostasis. Osteoprotegerin inhibits differentiation and formation of osteoclasts and induces apoptosis of osteoclasts. OPG knock-out mice develop severe osteoporosis. In contrast, overexpression of OPG in transgenic mice causes osteopetrosis.

OSTEOPROTEGERIN AS A THERAPEUTIC AGENT

Antiresorptive activity of osteoprotegerin is proved in numerous experimental models. Osteoprotective effect of osteoprotegerin has recently been proved in postmenopausal women with osteoporosis as well as in patients with multiple myeloma and osteolytic metastases of breast cancer.

CONCLUSION

Osteoprotegerin is a potent antiosteoclast agent that may prove useful in the treatment of bone disorders with net bone loss, such as postmenopausal osteoporosis and cancer metastases.

Changes in receptor activator of nuclear factor-kappaB, and its ligand, osteoprotegerin, bone-type alkaline phosphatase, and tartrate-resistant acid phosphatase in ovariectomized rats

We investigated time-course changes in the expression of receptor activator of nuclear factor-kappaB (RANK), its ligand (RANKL), osteoprotegerin (OPG), bone-type alkaline phosphatase (BAP), and tartrate-resistant acid phosphatase (TRAP) in ovariectomized (OVX) rats. Samples of sera and coccyges were used for analysis of the enzyme activities and expression levels of proteins and mRNAs, and an immunohistochemical analysis was also performed. Serum BAP activity increased to 158.6% of the pre-operation value at 1 week after OVX, and then decreased to 38.7% at 8 weeks after OVX. On the other hand, the serum TRAP activity increased to 130.9% of the pre-operation level at 1 week after OVX, and was maintained at a high level, compared with the pre-operation level. The patterns of BAP and TRAP activity in the coccyges specimens were similar to those seen in the sera. The expression profiles of TRAP, RANK, and RANKL proteins in the coccyx specimens were similar to the pattern of serum TRAP activity, while the profiles of the BAP and OPG proteins were similar to the pattern of serum BAP activity in OVX rats. The changes in the mRNA expression levels of the osteogenic proteins were similar to those for protein expression. These biochemical changes in OVX rats were confirmed by immunohistochemical studies. Our results suggest that not only osteoclastogenesis accelerated but also osteoblastogenesis transiently increased during the early phase of osteoporosis.

Relationships between the changes of serum levels of OPG and RANKL with age, menopause, bone biochemical markers and bone mineral density in Chinese women aged 20-75

The correlations between the serum levels of OPG, RANKL with age, menopause, bone markers, and bone mineral densities (BMDs) at the lumbar spine and proximal femur were studied in 504 pre- and postmenopausal Chinese women aged 20-75 years. We found that age was positively and negatively correlated with serum concentrations of OPG (r = 0.442, P < 0.001) and RANKL (r = -0.263, P < 0.001), respectively. Compared with premenopausal women, postmenopausal women showed higher serum OPG levels (107.6 +/- 3.0 vs 72.0 +/- 1.8 pg/ml, P < 0.001), lower serum RANKL concentrations (4.7 +/- 0.4 vs. 5.8 +/- 0.3 pg/ml, P < 0.001) and RANKL/OPG ratios (0.045 +/- 0. 004 vs. 0.099 +/- 0.008, P < 0.001). Neither serum levels of OPG nor RANKL or RANKL/OPG ratio correlated with BMDs after adjustment of age and menopause. They also showed no differences among normal, osteopenic and osteoporotic postmenopausal women. Serum levels of OPG were positively correlated with urinary excretion of NTx (r = 0.1453, P = 0.006). Serum levels of RANKL (r = -0.1928, P < 0.001) and RANKL/OPG ratio (r = -0.1303, P = 0.013) were inversely correlated with serum concentrations of OC. In multiple regression analysis, up to 20% variance (R(2) = 0.106-0.224) of the OPG-RANKL system in peripheral circulation can be explained by age, menopause and bone markers. These results suggest that although serum OPG and RANKL concentrations were unrelated with BMDs, the age- and menopause- dependent changes of serum OPG and RANKL might be a protective mechanism against the accelerated bone loss in postmenopausal women.

Osteoprotegerin in human milk: a potential role in the regulation of bone metabolism and immune development

Osteoprotegerin (OPG) is a member of the tumor necrosis factor superfamily. It is a soluble "decoy" receptor for tumor necrosis factor-related apoptosis-inducing ligand and ligand of the receptor activator of NF-kappaB. As such, OPG inhibits osteoclast activity and regulates the immune system. Human milk is a complex biologic fluid that supplies nutritional and protective factors to the breast-fed infant. In the present study, human milk samples at various times postpartum were assessed for the presence of OPG. Using biochemical as well as immunologic and biologic techniques we showed that human milk contains OPG at a level that is 1000-fold higher than that found in normal human serum. We observed that human breast milk cells and the human mammary epithelial cell line MCF-7 express OPG, indicating that both cell types are possible sources of milk OPG in vivo. In vitro studies demonstrated that milk OPG is biologically active and suggested that it may contribute to the antiresorptive activity of milk on bone, as well as tumor necrosis factor-related apoptosis-inducing ligand-induced inhibition of T cell proliferation. OPG-like activity was also observed in bovine colostrum and milk. Furthermore, we were able to detect human OPG in the sera of rats gavaged with human milk. We discuss the relevance of our findings for the breast-fed infant and for the prevention of immune and bone disorders.

Serum osteoprotegerin as a determinant of bone metabolism in a longitudinal study of human pregnancy and lactation

Osteoprotegerin (OPG) is a soluble decoy receptor that inhibits bone resorption by binding to receptor activator of nuclear factor kappa B ligand. Murine studies suggest that OPG is elevated in pregnancy, but its role in human pregnancy is unknown. We evaluated the relationship among OPG, bone turnover, and bone density in a longitudinal study of planned human pregnancy and lactation (n = 17; age, 20-36 yr). Samples were collected before conception; at 16, 26, and 36 wk gestation; and at 2 and 12 wk postpartum. Indexes of bone resorption included serum beta C-terminal and urinary N-terminal (uNTX) telopeptides of type I collagen. OPG increased by 110 +/- 16% (mean +/- SEM) at 36 wk (P < 0.001), followed by a rapid postpartum decline in both lactating and nonlactating women. Bone resorption was elevated at 36 wk (serum beta C-terminal telopeptides by 76 +/- 17%; urinary N-terminal telopeptides by 219 +/- 41%; P < 0.001). The tissue source of OPG in pregnancy is unknown. Human breast milk contains large amounts of OPG (162 +/- 58 ng/ml in milk vs. 0.42 +/- 0.03 ng/ml in nonpregnant serum). However, the rapid postpartum decline in serum OPG and the low serum OPG in neonates suggest a placental source. There was no correlation between change in OPG and bone turnover or bone mineral density (P > 0.05), and the physiological importance of elevated OPG in human pregnancy remains uncertain.

Osteoprotegerin, RANK, RANKL

Osteoprotegerin, RANK (Receptor Activator of Nuclear factor kappa B) and RANKL (Receptor Activator of Nuclear faktor kappa B ligand) became the aim of intensive research. RANK is considered as a hematopoietic surface receptor controlling osteoclastogenesis and calcium metabolism. RANKL may promote osteoresorption by induction of cathepsin K gene expression. The present paper summarizes the most significant data in osteoprotegerin, RANK and RANKL problems obtained.

Osteoprotegerin and bone density

Aim of study was determine if a correlation exists between bone mass density and concentration of osteoprotegerin. We examined the group of 199 patients of mean age of 63 years. Of the group under study, 31 patients had normal bone density (T score > -1 and < 1) and 168 probands had osteopenia or osteoporosis (T < -1). Persons with normal BMD values had median values of OPG 60.8 ng/l, while patients with reduced bone density had median values of 73 ng/l OPG. Cut-off for reduction of bone density was 128 ng/l OPG. We demonstrated that OPG concentrations vary inversely with bone density values (correlation coefficient -0.31). These results suggest that determination of OPG could allow discrimination of individuals with normal bone density and those with reduced bone density.