Increased Osteoprotegerin Levels Research Articles

Increased Osteoprotegerin Levels in Response to Increased Bone Resorption in AL Amyloidosis: Comparisons with Bone Remodeling of Multiple Myeloma.

Primary systemic amyloidosis (AL) and multiple myeloma (MM) are both clonal plasma cell disorders with distinct clinical characteristics. Bone disease is a hallmark of symptomatic MM in contrast to AL where lytic bone lesions are not found. Myeloma bone disease is characterized by an imbalance between osteoblastic and osteolytic activity induced by plasma cell-stroma interaction resulting in deregulation of numerous cytokines involved in bone remodeling. There are no data about bone metabolism in AL and the similarities or differences with MM. Levels of bone remodeling indices were measured in stored serum samples, collected from 62 previously untreated patients with AL amyloidosis. These included:i.bone resorption markers [C- and N- telopeptide of type-I collagen (CTX and NTX, respectively), and tartrate resistant acid phosphatase type-5b (TRACP-5b)],ii.bone formation markers [bone-alkaline phosphatase (bALP), and osteocalcin (OC)], andiii.osteoclast regulators [soluble receptor activator of nuclear factor-kB ligand (sRANKL), osteoprotegerin (OPG), macrophage inflammatory protein-1 alpha (MIP-1a), interleukin-6 (IL-6) and osteopontin (OPN)], as previously described.These markers were also measured in serum collected from 35 age-matched healthy controls and 35 newly diagnosed, untreated, symptomatic myeloma patients. Median age of AL patients at diagnosis was 61 years (range 39–80 years); heart was involved in 60% and kidneys in 66% of patients, while in 64% ≥2 organs were involved. In 16% of AL patients creatinine was ≥2 mg/dl. Median b2-microglobulin was 1.8 mg/l (range 0.5–28 mg/l); 64% of patients had >10% bone marrow infiltration by plasma cells. None of AL patients had lytic bone lesions in plain radiography or other features suggestive of myeloma such as hypercalcemia, significant anemia unrelated to renal impairment or predominant Bence-Jones proteinuria. The levels of sRANKL and OPG were both increased in AL patients compared to controls (p=0.07 and p<0.001). OPG was significantly higher in AL than in MM patients (p<0.001), but not sRANKL; thus sRANKL/OPG ratio was not different between AL and controls but it was significantly lower than in MM patients (p=0.009). Other osteoclast stimulators (MIP-1a, OPN, IL-6) were also increased in AL compared to controls (p<0.02). Bone resorption markers (CTX, NTX, TRACP-5b) were elevated in both AL and MM (p=0.008, p<0.001 and p<0.001 for AL vs. controls, respectively, and p=0.006, p<0.001 and p<0.001 for MM vs. controls). On the contrary, bone formation markers were not different between AL patients and controls, while in MM both bALP and OC had lower values compared to controls. Renal involvement did not affect bone markers but in AL patients with a creatinine level of >2 mg/dl CTX and NTX were higher than in patients with a creatinine level of <2mg/dl (p<0.001 and p=0.016, respectively). Involvement of other organs or the number of involved organs did not appear to influence bone remodeling. This study suggests that bone metabolism in AL is characterized by increased bone resorption with a pattern similar to that found in MM. Increased OPG levels in AL indicate more effective compensation of osteoclast activation compared to MM, probably explaining the lack of lytic disease in AL and possibly reflecting differences in the pathophysiology of plasma cell-stroma interaction between AL and MM.

Increased Osteoprotegerin Levels in Cushing’s Syndrome Are Associated with an Adverse Cardiovascular Risk Profile

Patients with Cushing's syndrome (CS) have a mortality rate four times higher than age- and sex-matched subjects, mainly due to cardiovascular events. Serum osteoprotegerin (OPG) levels are increased in patients with cardiovascular disease and/or excess bone resorption. The aim of the study was to assess serum OPG and soluble receptor activator of nuclear factor-kappaB ligand (sRANKL) levels in CS and their possible relationship with coronary risk profile. We conducted a cross-sectional study at a tertiary referral center. We studied 48 adult patients with CS and 48 age- and sex-matched controls. Twenty-six patients had pituitary-dependent CS; five patients had CS caused by ectopic ACTH secretion; and 17 patients had adrenal-dependent CS, accounted for by cortisol-secreting adenoma (n = 9), ACTH-independent macronodular bilateral adrenal hyperplasia (n = 4), or World Health Organization stage II cortisol-secreting carcinoma (n = 4). Patients underwent assessment of the absolute coronary risk and measurement of bone mineral density by dual-energy x-ray absorptiometry. Serum OPG and total sRANKL were measured by ELISA. Serum OPG (but not sRANKL) levels were significantly higher in CS patients than in controls (P < 0.01). In patients, serum OPG showed a positive correlation with age (r = 0.36; P = 0.01). OPG levels were higher in patients with the metabolic syndrome [median, 1262 (range, 199-2306) pg/ml vs. 867 (412-2479) pg/ml; P = 0.03], and showed a positive correlation with the absolute coronary risk (r = 0.36; P = 0.01). Serum OPG levels were higher in patients with pituitary-dependent CS in comparison with adrenal-dependent CS. In patients with CS, serum OPG levels are increased and appear to be associated with coronary risk.

Serum OPG and RANKL levels before and after intravenous bisphosphonate treatment in Paget's disease of bone

Paget's disease of bone (PDB) is a focal disorder of bone remodeling characterized by increased osteoclast-mediated bone resorption. Even though increasing evidence indicates enhanced nuclear factor-kB (NF-kB) signaling as a common mechanism involved in PDB and other related disorders, few studies investigated circulating osteoprotegerin (OPG) and receptor of activator of NF-kB-ligand (RANKL) levels in PDB patients. In this study we explored the relationships between OPG or RANKL levels and bone turnover markers in a group of patients with PDB, before and after intravenous bisphosphonate treatment (pamidronate 60 mg). Both OPG and RANKL were markedly elevated in PDB patients with respect to control groups (healthy or osteoporotic postmenopausal women and elderly men) and were positively associated with bone turnover markers. Higher levels of these cytokines were observed in polyostotic than monostotic PDB cases. The ratio between RANKL and OPG was more than 3-fold higher in PDB patients than in controls. Interestingly, in the group of patients treated with pamidronate, we found an increase in OPG levels that become statistically significant after 3 and 6 months from treatment. A trend toward a decrease in RANKL levels after treatment was also observed. The RANKL/OPG ratio was significantly reduced after 3 and 6 months of therapy. In contrast, in patients classified as non-responders, OPG and RANKL levels after pamidronate infusion did not significantly differ with respect to pre-treatment values. Thus, the positive effect of amino bisphosphonates in the treatment of PDB may be due to either direct or indirect suppression of RANKL-induced bone resorption through decreased RANKL and increased OPG production.

Serum Levels of Osteoprotegerin and Receptor Activator of Nuclear Factor-κB Ligand as Markers of Periprosthetic Osteolysis

Previous studies have suggested that the balance between receptor activator of nuclear factor-kappaB ligand (RANKL) and its decoy-receptor osteoprotegerin (OPG) in local tissue seems to play a crucial role in the loosening of the total hip replacement. The aim of this study was to evaluate whether the circulating levels of OPG and RANKL, as well as their ratio, could be different in patients with aseptic loosening compared with patients with stable implants. One hundred and twenty-eight subjects were recruited. They included thirty-nine patients with osteoarthritis who had not yet undergone total hip arthroplasty, thirty-three patients who had undergone total hip arthroplasty and had clinically and radiographically stable implants, thirty-six patients with aseptic loosening of total hip arthroplasty components, and twenty healthy volunteers. Serum levels of OPG and RANKL were measured with use of an immunoenzymatic method, and in each individual the OPG-to-RANKL ratio was calculated. In every group, a significant correlation was detected between OPG concentration and age (r = 0.58, p < 0.0001), especially in individuals older than fifty years, while gender and underlying disease were not found to influence serum levels of the tested parameters. In comparison with the levels in healthy donors and patients with a stable total hip replacement, the serum levels of OPG were increased in the patients who had not yet had an arthroplasty, those with aseptic loosening of a total hip replacement, and those with a cemented total hip replacement. Moreover, the OPG serum level provided good diagnostic accuracy in detecting the implant failure. A correlation was found between the sum of the osteolytic areas seen radiographically around the femoral stem and the RANKL level (r = 0.38, p = 0.02) and the OPG-to-RANKL ratio (r = -0.29, p = 0.04). An increase in OPG levels may reflect a protective mechanism of the skeleton to compensate for the osteolytic activity that occurs in severe osteoarthritis and in aseptic loosening. Prospective studies are needed to determine whether serum OPG levels could be used as markers for monitoring the stability of the implant, as well as for predicting aseptic loosening. Diagnostic study, Level III. See Instructions to Authors for a complete description of levels of evidence.

SERUM LEVELS OF OSTEOPROTEGERIN AND RECEPTOR ACTIVATOR OF NUCLEAR FACTOR-κB LIGAND AS MARKERS OF PERIPROSTHETIC OSTEOLYSIS

Background: Previous studies have suggested that the balance between receptor activator of nuclear factor-κB ligand (RANKL) and its decoy-receptor osteoprotegerin (OPG) in local tissue seems to play a crucial role in the loosening of the total hip replacement. The aim of this study was to evaluate whether the circulating levels of OPG and RANKL, as well as their ratio, could be different in patients with aseptic loosening compared with patients with stable implants. Methods: One hundred and twenty-eight subjects were recruited. They included thirty-nine patients with osteoarthritis who had not yet undergone total hip arthroplasty, thirty-three patients who had undergone total hip arthroplasty and had clinically and radiographically stable implants, thirty-six patients with aseptic loosening of total hip arthroplasty components, and twenty healthy volunteers. Serum levels of OPG and RANKL were measured with use of an immunoenzymatic method, and in each individual the OPG-to-RANKL ratio was calculated. Results: In every group, a significant correlation was detected between OPG concentration and age (r = 0.58, p < 0.0001), especially in individuals older than fifty years, while gender and underlying disease were not found to influence serum levels of the tested parameters. In comparison with the levels in healthy donors and patients with a stable total hip replacement, the serum levels of OPG were increased in the patients who had not yet had an arthroplasty, those with aseptic loosening of a total hip replacement, and those with a cemented total hip replacement. Moreover, the OPG serum level provided good diagnostic accuracy in detecting the implant failure. A correlation was found between the sum of the osteolytic areas seen radiographically around the femoral stem and the RANKL level (r = 0.38, p = 0.02) and the OPG-to-RANKL ratio (r = –0.29, p = 0.04). Conclusions: An increase in OPG levels may reflect a protective mechanism of the skeleton to compensate for the osteolytic activity that occurs in severe osteoarthritis and in aseptic loosening. Prospective studies are needed to determine whether serum OPG levels could be used as markers for monitoring the stability of the implant, as well as for predicting aseptic loosening. Level of Evidence: Diagnostic study, Level III. See Instructions to Authors for a complete description of levels of evidence.

Osteoprotegerin and receptor activator of nuclear factor‐κB ligand system in the early post‐operative period of liver transplantation

The precise mechanism that leads to accelerated bone resorption in the early post-transplant period remains unclear. Recent data suggest that osteoprotegerin (OPG) and its ligand receptor activator of nuclear factor-kappaB ligand (RANKL) constitute a novel cytokine system that can influence the function of both bone and immune cells. The aim of our study was to assess OPG and RANKL concentrations in the early post-operative period of liver transplantation. Serum OPG and RANKL levels were measured in 30 patients who underwent liver transplantation at 1, 7 and 14 d post-operatively. These values were compared with 22 age- and sex-matched healthy controls. Plasma sodium, creatinine, aspartate-aminotransferase, alanine-amino transferase, gamma-glutamyl transferase, alkaline phosphatase, bilirubin, albumin, prothrombin time, tacrolimus and cyclosporine levels were measured in each patient. We found a significant increase in OPG levels in the early post-operative period compared with the control group: day 1 (10.42 pmol/L, range 3.80-17.50 vs. 3.91 pmol/L, range 1.20-6.60; p = 0.0001), day 7 (6.90 pmol/L, range 3.00-15.30 vs. 3.91 pmol/L, range 1.20-6.60; p = 0.0001) and day 14 (5.76 pmol/L, range 2.60-10.70 vs. 3.91 pmol/L, range 1.20-6.60; p = 0.001). Similarly, serum RANKL levels were significantly higher than in the control group in this period, day 1 (0.123 pmol/L, range 0.010-0.420 vs. 0.054 pmol/L, range 0.010-0.300; p = 0.02), day 7 (0.236 pmol/L, range 0.010-0.720 vs. 0.054 pmol/L, range 0.010-0.300; p = 0.0004) and day 14 (0.137 pmol/L, range 0.010-0.520 vs. 0.054 pmol/L, range 0.010-0.300; p = 0.007). No correlation was found between OPG levels and RANKL, ischemic times, liver function tests, albumin, sodium or creatinine concentrations and tacrolimus or cyclosporine levels. A significant amount of OPG and RANKL is released in the early post-transplant period of liver transplantation. This might be explained by an activation of the immune system caused by the allograft. Therefore, the RANKL/OPG system may be involved in the pathophysiological evolution of transplantation osteoporosis.

Hepatic osteodystrophy: Does the osteoprotegerin/receptor activator of nuclear factor-kB ligand systemplay a role?

Multiple factors can contribute to the development of osteodystrophy in patients with chronic liver disease (CLD). Recently, two new cytokines, osteoprotegerin (OPG) and the receptor activator of nuclear factor-kB ligand (RANKL), have been implicated in the pathogenesis of postmenopausal osteoporosis and other metabolic bone diseases. Therefore, the aim of our study was to evaluate bone metabolism, bone mineral density (BMD) and OPG/RANKL system in 65 male patients with CLD and in 65 healthy controls. Our patients showed lower BMD values than controls both at lumbar and femoral levels. Moreover, they had an unbalanced bone turnover with an increased resorption phase, as shown by high levels of urinary deoxypyridinoline and a decreased formation phase, as shown by the slightly, but significant, low levels of bone-alkaline phosphatase. Patients showed lower plasma levels of free-testosterone than controls and higher - although not significantly so - plasma levels of 17 beta-estradiol. Furthermore, patients with CLD had higher levels of sex hormone-binding globulin and OPG, and lower levels of 25-hydroxyvitamin D (25-HOD) and IGF-I than the control group, while RANKL levels were similar in the two groups. In conclusion, our data do not confirm the hypothesis that the OPG/RANKL system could exert a key role in the pathogenesis of hepatic osteodystrophy, but rather that the observed increase in OPG levels may represent either the result of the inflammatory process per se or a compensation for the observed enhanced bone resorption.

Serum levels of osteoprotegerin and RANKL in patients with ST elevation acute myocardial infarction

OPG (osteoprotegerin) has been suggested to have an important role in atherogenesis and vascular calcification. In the present study, we have investigated serum OPG and RANKL (receptor activator of nuclear factor kappaB ligand) concentrations in patients with ST elevation AMI (acute myocardial infarction) and established CAD (coronary artery disease). OPG and RANKL were measured in 58 male patients hospitalized in the coronary care unit with ST elevation AMI, in 52 asymptomatic male patients with an established diagnosis of CAD and in 52 healthy male controls. These last two groups were matched with the AMI patients for age and body mass index. OPG was significantly (P<0.05) higher in patients with AMI at 1 h after AMI (8.04+/-4.86 pmol/l) than in both patients with established CAD (4.92+/-1.65 pmol/l) and healthy subjects (3.15+/-1.01 pmol/l). Subjects with established CAD had significantly (P<0.05) increased OPG levels compared with controls. RANKL levels in patients with established CAD (0.02+/-0.05 pmol/l) and with AMI (0.11+/-0.4 pmol/l) were significantly (P<0.05) lower compared with controls (0.32+/-0.35 pmol/l). In the AMI group, OPG decreased significantly (P<0.05) at 1 and 4 weeks after infarction (8.04+/-4.86 compared with 6.38+/-3.87 and 6.55+/-2.6 pmol/l respectively), but OPG levels, either at 1 h or 1-4 weeks after AMI, remained significantly (P<0.05) higher compared with established CAD (4.92+/-1.65 pmol/l) and controls (3.15+/-1.01 pmol/l). Our data show for the first time that OPG levels are increased in ST elevation AMI within 1 h of infarction. Whether the increase in OPG is a consequence or a causal factor of plaque destabilization deserves further investigation.

Osteoprotegerin and Bone Mineral Density in Hemodiafiltration Patients

A newly identified cytokine, osteoprotegerin (OPG) appears to be involved in the regulation of bone remodeling. In vitro studies suggest that OPG, a soluble member of the TNF receptor family of proteins, inhibits osteoclastogenesis by interrupting the intercellular signaling between osteoblastic stromal cells and osteoclast progenitors. As patients with chronic renal failure (CRF) often have renal osteodystrophy (ROD), we investigated the role of osteoprotegerin (OPG) in ROD, and investigated whether there was any relationship between serum OPG, intact parathyroid (PTH) (iPTH), vitamin D, and trabecular bone. Serum OPG combined with iPTH might be a useful tool in the noninvasive diagnosis of ROD, at least in cases in which the range of PTH values compromises reliable diagnosis. Thirty-six patients on maintenance hemodiafiltration (HDF) and a control group of 36 age and sex matched healthy subjects with no known metabolic bone disease were studied. The following assays were made on serum: iPTH, osteocalcin (BGP), bone alkaline phosphatase, 25(OH)-cholecalciferol, calcium, phosphate, OPG, IGF-1, estradiol, and free testosterone. Serum Ca+ +, P, B-ALP, BGP, IGF-1, iPTH, and OPG levels were significantly higher in HDF patients than in controls, while DXA measurements and quantitative ultrasound (QUS) parameters were significantly lower. On grouping patients according to their mean OPG levels, we observed significantly lower serum IGF-1, vitamin D3 concentrations, and lumbar spine and hip bone mineral density in the high OPG groups. No correlation was found between OPG and bone turnover markers, whereas a negative correlation was found between serum OPG and IGF-1 levels (r= − 0.64, p = 0.032). Serum iPTH concentrations were positively correlated with bone alkaline phosphatase (B-ALP) (r = 0.69, p = 0.038) and BGP (r = 0.92, p < 0.001). The findings made suggest that an increase in OPG levels may be a compensatory response to elevated bone loss. The low bone mineral density (BMD) levels found in the high OPG group might have been due to the significant decrease in serum IGF-1 and vitamin D3 observed. In conclusion, the findings made in the present study demonstrate that increased OPG in hemodiafiltration patients is only partly due to decreased renal clearance. As it may partly reflect a compensatory response to increased bone loss, this parameter might be helpful in the identification of patients with a marked reduction in trabecular BMD.

Cementoblast gene expression is regulated by Porphyromonas gingivalis lipopolysaccharide partially via toll-like receptor-4/MD-2.

Lipopolysaccharides are potent inflammatory mediators considered to contribute to destruction of periodontal tissues. Here, we hypothesized that Porphyromonas gingivalis lipopolysaccharide (P-LPS) treatment would regulate gene expression in murine cementoblasts through Toll-like receptor 4. Real-time (RT)-PCR and Northern blot analysis indicated that P-LPS decreased expression of transcripts for osteocalcin (OCN) and receptor activator of nuclear factor kappaB ligand (RANKL). In contrast, a dose-dependent up-regulation in mRNA levels for osteopontin (OPN) and osteoprotegerin (OPG) was observed. Similarly, ELISA demonstrated decreased RANKL and increased OPG levels. A monoclonal antibody specific for mouse TLR-4/MD-2 partially neutralized the P-LPS effect on cementoblasts. These results indicate that exposure of cementoblasts to P-LPS can alter cell function by regulating markers of osteoclastic activity (e.g., RANKL/OPG), thereby potentially affecting the inflammation-associated resorption of mineralized tissues.

Stimulation of osteoprotegerin production is responsible for osteosclerosis in mice overexpressing TPO

AbstractMyelofibrosis and osteosclerosis are prominent features arising in mice overexpressing thrombopoietin (TPO). The pivotal role of transforming growth factor β1 (TGF-β1) in the pathogenesis of myelofibrosis has been documented, but the mechanisms mediating osteosclerosis remain unclear. Here, we used mice deficient in osteoprotegerin (OPG), a secreted inhibitor of bone resorption, to determine whether osteosclerosis occurs through a deregulation of osteoclastogenesis. Marrow cells fromopg-deficient mice (opg−/−) or wild-type (WT) littermates were infected with a retrovirus encoding TPO and engrafted into anopg−/−or WT background for long-term reconstitution. The 4 combinations of graft/host (WT/WT,opg−/−/opg−/−,opg−/−/WT, and WT/opg−/−) were studied. Elevation of TPO and TGF-β1 levels in plasma was similar in the 4 experimental groups and all the mice developed a similar myeloproliferative syndrome associated with severe myelofibrosis. Osteosclerosis developed in WT hosts engrafted with WT oropg−/−hematopoietic cells and was associated with increased OPG levels in plasma and decreased osteoclastogenesis. In contrast,opg−/−hosts exhibited an osteoporotic phenotype and a growth of bone trabeculae was rarely seen. These findings suggest that osteosclerosis in mice with TPO overexpression occurs predominantly via an up-regulation of OPG in host stromal cells leading to disruption of osteoclastogenesis.

Osteoprotegerin levels increased by interleukin-1beta in human periodontal ligament cells are suppressed through prostaglandin E(2) synthesized de novo.

Osteoprotegerin (OPG) is a novel tumor necrosis factor receptor superfamily that inhibits osteoclast differentiation, activity, and survival. Interleukin-1beta (IL-1beta) increases OPG expression. IL-1beta also increases prostaglandin E(2) (PGE(2)) production and stimulates bone resorption. In the present study, we examined the involvement of PGE(2) in IL-1beta-induced increases in OPG levels in human periodontal ligament cells (HPL cells) in an effort to clarify apparently conflicting IL-1beta actions on bone resorption and understand IL-1beta-induced increases in secretion of OPG and PGE(2) in HPL cells. 5,6-dichloro-1-beta-D-ribofuranosyl-benzimidazole, a mRNA synthesis inhibitor, partly inhibited the increase in OPG mRNA levels induced by IL-1beta. Cycloheximide, a protein synthesis inhibitor, enhanced the stimulatory effect of IL-1beta. Etodolac, a selective cyclooxygenase-2 inhibitor, suppressed the increase in PGE(2) levels. Furthermore, etodolac reinforced the promotion of OPG expression by IL-1beta at the mRNA and protein levels. PGE(2) added to cultures of HPL cells decreased OPG mRNA levels in a dose- and time- dependent manner. These findings suggest that the increase in OPG levels induced by IL-1beta in HPL cells is suppressed through PGE(2) synthesized de novo.