RANK ligand and osteoprotegerin: paracrine regulators of bone metabolism and vascular function

Low serum osteoprotegerin levels in normoalbuminuric type 1 diabetes mellitus

The aim of this study is to establish whether abnormal mineral metabolism is present in patients with type 1 DM with normal renal function and in the absence of microalbuminuria. Serum levels of 1,25-dihydroxyvitamin D, osteoprotegerin (OPG) and receptor activator for nuclear factor kappa β ligand (RANKL) and other determinants of bone metabolism were measured in 35 patients with type 1 DM and in 25 age-, sex- and ethnicity-matched healthy controls. Serum OPG (1.98 vs. 2.98 pmol/l: P = 0.001), 1,25-dihydroxyvitamin D (41.1 vs. 48.2 pmol/l: P = 0.035) and magnesium (0.84 vs. 0.89 mmol/l P = 0.029) levels were significantly lower in patients with type 1 DM compared to normal controls. RANKL levels were similar in both groups. The groups did not differ with respect to calcium, phosphate, PTH, 25-hydroxyvitamin D, tubular reabsorption of phosphate and cross-linked N-telopeptides of type 1-collagen levels. Abnormalities of mineral metabolism including low serum OPG and 1,25-dihydroxyvitamin D levels occur in patients with type 1 DM with normal renal function and in the absence of microalbuminuria. These abnormalities may promote altered bone metabolism and vascular pathology.

The relationship between coronary artery calcification score, plasma osteoprotegerin level and arterial stiffness in asymptomatic type 2 DM

Because T2DM increases the risk of coronary atherosclerosis and CAD and new noninvasive techniques to assess CVD risk have gained considerable popularity, it is important to know how these tools relate to each other. The aim of this study was to evaluate the relationship between the extent of coronary artery calcification measured by MDCT, plasma OPG levels, baPWV and the established cardiovascular risk factors in Korean patients with T2DM. From November 2006 to December 2007, 110 asymptomatic Korean patients with T2DM without prior evidence of CAD were assessed (mean age 57.2 years). CAC imaging was performed using a 40-slice MDCT. Serum OPG levels were measured by an enzyme-linked immunosorbent assay (Oscotec, Korea) from the serum samples of each subject. We measured the baPWV as an index of arterial stiffness. In addition, we measured fasting glucose, HbA(1)C, hsCRP and lipid profiles. A total of 74 patients (67.3%) had minimal or insignificant CAC (<10). The CACS, OPG and baPWV showed significant positive correlations with each other. The CACS was significantly associated with the baPWV, smoking and use of a statin. The baPWV was significantly associated with age, duration of DM, total cholesterol and CACS by multiple linear regression models of the dependent variables of CACS or baPWV. CAC and baPWV were significant predictors of each other (r = 0.359, P = 0.014 and r = 0.361, P = 0.004). The results of this study showed that CAC, baPWV and serum OPG levels were significantly correlated with each other in asymptomatic Korean patients with T2DM. Furthermore, our results suggest that arterial stiffness, as determined by baPWV, may predict the extent of coronary calcification by MDCT.

Receptor activator of nuclear factor kappa B ligand/osteoprotegerin pathway is a promising target to reduce atherosclerotic plaque calcification

Atherosclerotic plaque calcification represents a common pathophysiologic process in the advanced phases of the disease. Both inflammatory and vascular cells (such as osteoblast-like cells, osteoclast-like cells, dendritic cells, macrophages, smooth muscle cells, and endothelial cells) are active players in the balance between intraplaque bone deposition and resorption. Inflammatory processes underlying plaque calcification are regulated by soluble mediators that also contribute to plaque destabilization and increased vulnerability. Among different mediators, the receptor activator of nuclear factor-kappa B (NF-kappa B) ligand (RANKL)/osteoprogerin (OPG) system is a major determinant in inflammatory cell differentiation toward osteoclast-like cells. Thus, this system might be a promising parameter to be investigated as a marker of calcification-related cardiovascular risk and a therapeutic target. Despite some promising results, several limitations have been shown in the potential clinical use of serum RANKL/OPG to better assess the cardiovascular risk. At present, the potential relationship between RANKL/OPG and the content of calcium within the intima of the coronary arteries (CAC score, assessed by computed tomography) needs to be explored in large clinical studies. On the other hand, the antiatherosclerotic relevance of treatments antagonizing RANKL is still under investigation. Despite that clinical evidence is needed, this therapeutic approach might be of particular benefit in selective populations (such as rheumatoid arthritis patients) with an increased cardiovascular risk.

Receptor activator of nuclear factor-κB ligand and osteoprotegerin: maintaining the balance to prevent bone loss

Bone remodeling requires a precise balance between resorption and formation. It is a complex process that involves numerous factors: hormones, growth factors, vitamins, and cytokines, and notably osteoprotegerin (OPG) and receptor activator for nuclear factor-κB (RANK) ligand. The signaling pathway OPG/RANK/RANKL is key to regulation for maintaining the balance between the activity of osteoblasts and osteoclasts in order to prevent bone loss and ensure a normal bone turnover. In this review, the RANK/RANKL/OPG pathway is described. The multiple interactions of various factors (hormones, cytokines, growth factors, and vitamins) with the OPG/RANK/RANKL pathway are also commented on. Finally, the effects of denosumab, a human monoclonal antibody that binds to RANKL and thereby inhibits the activation of osteoclasts, and of strontium ranelate are also described. Indeed, these two new drugs afford appreciable assistance in daily care practice, helping to prevent bone loss in patients with osteoporosis.

Maternal circulating osteoprotegerin and soluble RANKL in pre-eclamptic women

OBJECTIVE

To evaluate alterations in the concentrations of osteoprotegerin (OPG), RANKL and the OPG/RANKL ratio in pre-eclamptic women during the puerperium.

STUDY DESIGN

This cross-sectional study was performed in the maternity ward of Aretaieio Hospital in Athens, Greece. Fifteen pregnant women with severe pre-eclampsia and 15 matched controls with premature rupture of the membranes were recruited. Fasting blood samples were obtained antepartum, immediately after diagnosing pre-eclampsia (median: 32nd gestational week), and during the 3rd-6th day postpartum, to estimate levels of circulating OPG and RANKL as well as the OPG/RANKL ratio. The anthropometric parameters evaluated included body mass index and blood pressure.

RESULTS

Mean circulating OPG levels decreased significantly in both groups in the postpartum period (controls: 43.7 ± 19.1 ng/ml vs 22.9 ± 9.1 ng/ml, p = 0.008; pre-eclamptic group: 72.3 ± 49.9 vs 49.7 ± 40.9 ng/ml, p = 0.002). The antepartum OPG/RANKL ratio was elevated in hypertensive pregnancies (2.41 ± 1.72) compared to normotensive pregnancies (1.45 ± 0.63), but the difference did not reach statistical significance (p = 0.1). The OPG/RANKL ratio decreased in the control group (0.76 ± 0.30, NS) following delivery, while it remained unchanged in the pre-eclamptic women (1.63 ± 1.40, p = 0.13). Consequently, the postpartum OPG/RANKL ratio was significantly higher in the pre-eclamptic women compared to control women (1.63 ± 1.40 vs 0.76 ± 0.30, p = 0.01). Levels of RANKL demonstrated no significant alterations during puerperium in both cases.

CONCLUSION

Pregnancies complicated with pre-eclampsia exhibit higher OPG levels and OPG/RANKL ratios, compared to control pregnancies, which might be compatible with lower bone turnover. The significance of this finding with respect to bone metabolism remains to be elucidated in larger studies.

Lovastatin raises serum osteoprotegerin level in people with type 2 diabetic nephropathy

OBJECTIVES

Osteoprotegerin (OPG), a glycoprotein, is a member of the tumor necrotizing factor alpha receptor super-family. By considering the possible role of OPG in cardiovascular disease (CVD), higher incidence of CVD in people with type 2 diabetic nephropathy (T2DN), and anti-atherosclerotic effects of statins, the present study aimed to investigate the effects of lovastatin on serum levels of OPG and soluble receptor activator of nuclear factor-κB ligand (sRANKL) in people with T2DN.

DESIGN AND METHODS

Thirty patients completed the study course, out of 38 adult male patients with T2DN who were initially enrolled. Lovastatin, 20mg/d, was administered for 90 days. Afterwards, lovastatin was withdrawn for the next 30 days. Serum levels of OPG and sRANKL were measured using commercial ELISA kits at baseline, after 90 days of intervention, and after 30 days of withdrawal of lovastatin.

RESULTS

Serum level of OPG was significantly increased (10.76 ± 16.44) and decreased (-7.38 ± 11.98) during 90 days of intervention and 30 days of withdrawal periods, respectively, while, sRANKL level was significantly decreased (-1192.08 ± 578.20) and increased (4418.67 ± 2124.66) during the same periods, respectively.

CONCLUSIONS

Lovastatin therapy increased serum OPG level and decreased sRANKL level in people with T2DN. The withdrawal of lovastatin decreased serum OPG level, while sRANKL level was extensively increased.

Coronary artery calcification and cardiovascular risk: the role of RANKL/OPG signalling

BACKGROUND

Coronary artery disease (CAD) represents the most relevant cause of death and morbidity in the adult population of developed and developing countries. During the last decades, a strong research effort has been performed to identify more selective markers and better assess the cardiovascular risk in both primary and secondary prevention.

MATERIALS AND METHODS

This review updates current knowledge regarding the pathophysiological relevance as possible markers of coronary calcification of the receptor activator of nuclear factor-kappa ligand (RANKL)/osteoprotegerin (OPG) system. Furthermore, the potential clinical use of both RANKL/OPG and coronary calcium score (CAC) to assess cardiovascular vulnerability has been discussed.

RESULTS

Emerging evidence indicates that atherosclerotic plaque calcification is positively correlated with vulnerability. Several inflammatory mediators have been shown to modulate arterial calcification, thus increasing the risk of plaque rupture. Among these factors, RANKL/OPG axis might be of particular interest as a promising biomarker of plaque vulnerability in subjects with diffuse coronary calcification.

CONCLUSION

Together with clinical parameters of coronary calcification (such as CAC), circulating RANKL/OPG levels could contribute to better assess and predict cardiac events.

Association of serum osteoprotegerin with left ventricular mass in African American adults with hypertension

BACKGROUND

African-Americans with hypertension are susceptible to left ventricular hypertrophy (LVH). Serum osteoprotegerin level has been reported to be associated with LVH. We investigated the association of osteoprotegerin with LV mass (LVM) in 898 African-Americans with hypertension (mean age 65 years, 71% women).

METHODS

Osteoprotegerin levels were measured in serum by an immunoassay and log-transformed for analyses. LVM index (LVMi; LVM/height(2.7)) was estimated using M-mode echocardiography. Linear regression analyses using generalized estimating equations were used to assess the association of osteoprotegerin with LVMi.

RESULTS

Serum osteoprotegerin was correlated with LVMi (r = 0.21; P < 0.0001), an estimated increase in LVMi of 5.05 (95% confidence interval 2.93, 7.17) g/m(2.7) in the highest compared to the lowest osteoprotegerin quartile. This association remained statistically significant after adjustment for conventional cardiovascular risk factors (age, sex, body mass index (BMI), history of smoking, diabetes, systolic blood pressure (BP), total and high-density lipoprotein cholesterol), estimated renal function, history of myocardial infarction and stroke, lifestyle factors (physical activity score, years of education, amount of alcohol consumption), medications (aspirin, antihypertensives, statins, estrogens), and C-reactive protein (CRP) (P = 0.02). Additionally, osteoprotegerin was correlated with early/atrial (E/A) ratio (r = -0.16; P < 0.0001), LV mean wall thickness (r = 0.17; P < 0.0001) and relative wall thickness (r = 0.14; P < 0.0001) but not ejection fraction (r = 0.04; P = 0.24) or internal end-diastolic dimension (r = 0.02; P = 0.60).

CONCLUSION

In African-Americans with hypertension, a higher serum osteoprotegerin level is weakly but independently associated with a higher LVM.

Association of osteoprotegerin with aortic stiffness in patients with symptomatic peripheral artery disease and in healthy subjects

BACKGROUND

Arterial stiffening is an independent predictor for cardiovascular mortality. Preliminary studies have shown that arterial calcification may have an impact on increased vascular stiffness. However, there are limited data about the role of calcification inhibitor osteoprotegerin (OPG) as an independent predictor for arterial stiffness in patients with peripheral arterial disease (PAD) and in healthy subjects. The aim of this study was to evaluate the association between OPG and arterial stiffness parameters in patients with PAD and in healthy subjects.

METHODS

We studied 69 men with PAD (age 63 + or - 7 years) and 68 healthy subjects (age 54 + or - 8 years). Serum OPG and oxidized low-density lipoprotein (oxLDL) were measured using the enzyme-linked immunosorbent assay method. Radial and aortic pulse wave velocity (aPWV) and augmentation index (AIx) were determined by applanation tonometry.

RESULTS

The OPG (5.4 + or - 1.7 vs. 4.4 + or - 1.1 pmol/l; P < 0.001) and aPWV (10.1 + or - 2.5 vs. 7.6 + or - 1.6 m/s; P < 0.001) were different for the patients and for the controls. There was a linear relationship between OPG and aPWV in patients with PAD (R = 0.37; P = 0.003) and in healthy individuals (R = 0.40; P = 0.001). In multiple regression models after adjustment for potential confounders, OPG was independently associated with aPWV in the patients (R(2) = 0.47; P < 0.0001) and in the controls (R(2) = 0.44; P < 0.0001). The AIx or radial PWV was not correlated with OPG for either group.

CONCLUSION

The independent association between OPG and aPWV in patients with PAD and in controls suggests that the calcification inhibitor OPG may influence aortic stiffening in atherosclerosis and in clinically healthy subjects.

A polymorphism near osteoprotegerin gene confer risk of obesity in Uyghurs

To investigate the association of single nucleotide polymorphism (SNP) rs4355801 near osteoprotegerin (OPG) gene and rs3736228 in low-density lipoprotein receptor-related protein 5 (LRP5) gene with metabolic phenotypes [body mass index (BMI), waist-hip ratio, glucose, total cholesterol (CHO), and triglyceride], we carried out a population-based association study in Uyghur population living in Xinjiang Uyghur Autonomous Region of China. We observed a significant higher level of BMI in AG/AA carriers than in GG carriers (P = 0.022) for rs4355801. Subjects with the AG/GG genotype significantly increased the risk of BMI related obesity than subjects with the AA genotype, with an odds ratio of 1.31 (95% CI 1.09-1.56, P = 0.005). The association remained significant after controlling for covariates of age and gender. In addition, we observed a significant higher level of CHO in CT/TT carriers than in CC carriers (P = 0.021) for rs3736228. Our observations provide the first evidence that rs4355801 near OPG gene may confer susceptibility to obesity. In addition, SNP rs3736228 in LPR5 gene may affects the level of CHO in Uyghur population.

Possible Role of Osteoprotegerin and Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand as Markers of Plaque Instability in Coronary Artery Disease

Osteoprotegerin (OPG) produced by cardiovascular system raising the possibility that alterations of OPG serum levels may be associated with coronary artery disease (CAD). Our aim is to assess the possible role of serum OPG and soluble tumor necrosis factor-related apoptosis-inducing ligand (s-TRAIL) in the pathology of CAD and their uses as markers of plaque stability. A total of 80 male participants were categorized into 3 groups: 28 patients with acute myocardial infarction (AMI), 32 established stable CAD, and 20 healthy controls were enrolled in this study. Acute myocardial infarction and CAD groups exhibited significantly higher OPG levels and lower s-TRAIL levels compared to the stable CAD and control participants. These results are aggravated as the number of affected coronary vessels increase in AMI and stable CAD groups. Conclusion: There is an association between raised serum OPG and reduced s-TRAIL in patients with CAD. Elevation of circulating OPG levels may represent a crucial compensatory mechanism to limit further vascular damage.

Osteoprotegerin in relation to type 2 diabetes mellitus and the metabolic syndrome in postmenopausal women

Osteoprotegerin (OPG) is an inhibitor of bone resorption. Circulating levels of OPG seem to be elevated in patients with cardiovascular disorders and diabetes. The relationship between OPG and the metabolic syndrome has never been studied in postmenopausal women. In a population-based study, 382 Iranian postmenopausal women were randomly selected. Cardiovascular risk factors, high-sensitivity C-reactive protein, and OPG were measured. The diabetes classification and the metabolic syndrome definition were based on the criteria of the American Diabetes Association and the National Cholesterol Education Program-Adult Treatment Panel III, respectively. The mean serum OPG level was higher in those with type 2 diabetes mellitus than those without diabetes (4.33 +/- 1.70 vs 3.84 +/- 1.76 pmol/L, P = .016). In multiple logistic regression analysis, type 2 diabetes mellitus showed a significant association with serum OPG levels when adjustments were made for age, high-sensitivity C-reactive protein, and cardiovascular risk factors (odds ratio = 2.21; confidence interval, 1.34-3.66; P = .002). No significant difference was found between the mean serum OPG levels of those with the metabolic syndrome and those without the metabolic syndrome. Mean OPG levels did not differ significantly between subjects with and without hypertension, dyslipidemia, glucose intolerance, or abdominal obesity according to the National Cholesterol Education Program-Adult Treatment Panel III criteria. In conclusion, circulating OPG levels are significantly associated with diabetes, independent of cardiovascular risk factors in postmenopausal women. However, OPG levels have no correlation with the metabolic syndrome or its components. Further studies are warranted to determine the pathophysiologic origin of elevated OPG in type 2 diabetes mellitus.

Review: Endothelial cell dysfunction, medial arterial calcification and osteoprotegerin in diabetes

Macrovascular complications such as cardiovascular disease and peripheral vascular disease are the leading cause of increased mortality and morbidity, respectively, in patients with diabetes mellitus. The aetiopathogenesis of macrovasculopathy in diabetes is multifactorial and differs in types 1 and 2 diabetes. Endothelial cell dysfunction is an early feature of diabetic vasculopathy and is associated with poor glycaemic control. Chronic hyperglycaemia may promote an adverse vascular milieu leading to early endothelial cell apoptosis, in the long run. The presence of apoptotic cells in the vascular lumen may trigger a cascade of reactions between the promoters and inhibitors of arterial calcification. Medial arterial calcification, a characteristic feature of diabetes, is an important predictor of cardiovascular disease and occurs independently of atherosclerosis. Medial arterial calcification may occur in the presence of normal serum calcium and phosphate levels. Osteoprotegerin is an important modulator of mineral metabolism and manifests its effects in the bone and arteries. It is hypothesised that osteoprotegerin is a key inhibitor of arterial calcification which is released by endothelial cells as a protective measure for survival in adverse conditions. It is a potential risk marker for early identification and monitoring of disturbed mineral metabolism and vasculopathy in diabetes.

Elevated osteoprotegerin is associated with abnormal ankle brachial indices in patients infected with HIV: a cross-sectional study

Background

Patients infected with HIV have an increased risk for accelerated atherosclerosis. Elevated levels of osteoprotegerin, an inflammatory cytokine receptor, have been associated with a high incidence of cardiovascular disease (including peripheral arterial disease, or PAD), acute coronary syndrome, and cardiovascular mortality. The objective of this study was to determine whether PAD is prevalent in an HIV-infected population, and to identify an association with HIV-specific and traditional cardiovascular risk factors, as well as levels of osteoprotegerin.

Methods

One hundred and two patients infected with HIV were recruited in a cross-sectional study. To identify the prevalence of PAD, ankle-brachial indices (ABIs) were measured. Four standard ABI categories were utilized: ≤ 0.90 (definite PAD); 0.91-0.99 (borderline); 1.00-1.30 (normal); and >1.30 (high). Medical history and laboratory measurements were obtained to determine possible risk factors associated with PAD in HIV-infected patients.

Results

The prevalence of PAD (ABI ≤ 0.90) in a young HIV-infected population (mean age: 48 years) was 11%. Traditional cardiovascular risk factors, including advanced age and previous cardiovascular history, as well as elevated C-reactive protein levels, were associated with PAD. Compared with patients with normal ABIs, patients with high ABIs had significantly elevated levels of osteoprotegerin [1428.9 (713.1) pg/ml vs. 3088.6 (3565.9) pg/ml, respectively, p = 0.03].

Conclusions

There is a high prevalence of PAD in young HIV-infected patients. A number of traditional cardiovascular risk factors and increased osteoprotegerin concentrations are associated with abnormal ABIs. Thus, early screening and aggressive medical management for PAD may be warranted in HIV-infected patients.

RANK/RANKL/OPG role in distraction osteogenesis

Distraction osteogenesis is a fundamental pillar for craniomaxillofacial reconstruction processes. Nonetheless, although the clinical, biomechanical, and histologic changes associated with distraction osteogenesis have been widely described, this is not the case with the molecular mechanisms that regulate bone synthesis in the interfragmentary gap resulting from the gradual separation of bone segments. Recent studies have attributed a decisive role to the RANK/RANKL/OPG system in regulating bone metabolism and osteoclastogenesis. Receptor activator of nuclear factor kappa beta (RANK), belonging to the tumor necrosis factor superfamily, is present in the osteoclasts. It promotes osteoclastogenesis when it binds to RANK ligand (RANKL), which is produced by the osteoblasts and other stromal cells. Osteoprotegerin (OPG) acts as a decoy receptor by binding to RANKL and preventing RANK signaling. Osteoclast activation is thus blocked and apoptosis induced. The aim of this review is to analyze the influence of the RANK/RANKL/OPG system on the bone healing and remodeling processes that occur in distraction osteogenesis, with a view to possibly developing molecular mechanisms that stimulate bone regeneration and inhibit resorption, thereby improving the clinical outcome for distraction osteogenesis.

Evaluation of effects on bone tissue of different osteotomy techniques

The aim of this study is to evaluate and compare the response of bone tissue after osteotomy carried out with either rotating cutters or with piezoelectric terminals.Bioptic samples of bone tissue were taken during operations with rotating burs and piezoelectric terminals to increase bone volume before implantology. Samples first underwent histomorphometric analysis. Subsequently, osteoblastic cells, obtained from different samples, were placed in culture and allowed to proliferate to in vitro evaluate the time to initiate growth and to reach confluence. Finally, a molecular biologic study by reverse transcription polymerase chain reaction was performed to evaluate the expression of typical osteoblastic molecular markers, such as osteoprotegerin and osteopontin.Histomorphometric analysis showed that the width of necrotic line on the osteotomic margins from samples taken using different techniques did not vary significantly. Moreover, the times of initial growth and of confluence in cells from the 2 groups did not show any statistically significant differences. However, a highly significant correlation was revealed between the age of the patient and the initial growth time and the confluence. Similarly, reverse transcription polymerase chain reaction showed that the osteoprotegerin and osteopontin expression levels did not change significantly according to the surgical technique used.In conclusion, osteotomies carried out with either instrument do not seem to substantially influence the vitality of the bone tissue. The variability of the expression levels of typical osteoblastic markers seems to be linked more to other factors than to the surgical technique used.

A cohort study of the effects of serum osteoprotegerin and osteoprotegerin gene polymorphisms on cardiovascular mortality in elderly women

OBJECTIVE

To investigate the role of serum osteoprotegerin (OPG) and OPG gene polymorphisms in relation to cardiovascular (CV) and all-cause mortality in elderly women.

BACKGROUND

The OPG/RANK/RANKL plays a vital role in bone cell biology. It has also been detected in myocardial tissue and atherosclerotic plaques. In some population studies, OPG and OPG gene polymorphisms have been associated with CV disease risk.

DESIGN, MEASUREMENTS AND RESULTS

In an 8.5-year cohort population study of 1333 postmenopausal women mean age 75.2 ± 2.7 years, serum OPG concentrations above the median were associated with an increased risk of all-cause [odds ratio (OR) 1.39 (1.04-1.85)], and in particular CV mortality [OR 1.83 (1.10-3.05)], before and after adjusting for age, BMI, treated hypertension, diabetes, hypercholesterolemia, previous HRT use, calcium supplementation and smoking. Genotyping the OPG gene did not provide further information on the association between OPG and CV risk or mortality events.

CONCLUSIONS

Raised osteoprotegerin appears to be an independent risk factor for total and CV death and thus has potential as a useful biomarker of risk as well as a potential target for therapeutic intervention.

Evolution of coronary artery calcifications following kidney transplantation: relationship with osteoprotegerin levels

We prospectively assessed the evolution of coronary artery calcification (CAC) and osteoprotegerin (OPG) levels after renal transplantation (RT). Eighty-three recipients were followed-up prospectively during 1 year. Blood was collected before (baseline) and after RT for determination of mineral metabolism parameters including OPG. CAC was measured by multidetector computed tomography at transplantation (baseline) and 1 year later. Progression of CAC was defined as a difference between the follow-up square-root transformed volume (SRV) and the baseline SRV >or= 2.5. By multivariate analysis, baseline OPG level, age and low LDL levels were significantly associated with baseline CAC. RT was accompanied by mineral metabolism improvement with a decrease of OPG from 955 [395-5652] to 527 [217-1818] pg/mL and parathyroid hormone from 94 [1-550] to 62 [16-410] pg/mL. Thirty-one percent of patients did not exhibit CAC at baseline. CAC diminished in 14.5%, stabilized in 59.2% and progressed in 26.3% of patients. Baseline CAC was associated with progression (OR 2.92 [1.02-8.36]). No significant association was found between OPG and CAC progression despite a higher baseline OPG level in progressors (1046 [456-3285]) vs. non-progressors (899 [396-5952] pg/mL). CAC at baseline, but not 1 year after RT, is independently associated with baseline OPG; posttransplant CAC progression is predicted by baseline CAC score.

Therapeutic implications of osteoprotegerin

Osteoprotegerin (OPG), a member of the tumor necrosis factor (TNF) receptor superfamily, contributes determinatively to the bone remodeling as well as to the pathogenetic mechanism of bone malignancies and disorders of mineral metabolism. There is additional evidence that OPG can promote cell survival by inhibiting TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis. A number of recent in vitro, in vivo and clinical studies have defined the role of the RANK/RANKL/OPG pathway in skeletal and vascular diseases. These works were the milestone of the deep understanding of the mechanism of OPG. This review provides an overview of the potential innovative therapeutic strategies of OPG in metastatic breast and prostate carcinoma, multiple myeloma, postmenopausal osteoporosis, glucocorticoid-induced osteoporosis and rheumatoid arthritis. Special reference is given to the increasing evidence that RANKL and OPG may link the skeletal with the vascular system.

Root resorption and the OPG/RANKL/RANK system: a mini review

Odontoclastic root resorption is a significant clinical issue in relation to orthodontic tooth movement, and resorption of the roots of primary teeth is an intriguing biological phenomenon. The functional coordination of the OPG/RANKL/RANK system seems to contribute not only to alveolar remodeling, but also to resorption during orthodontic tooth movement and physiological root resorption. Serum OPG and s-RANKL are related to regulation of bone homeostasis by the OPG/RANKL/RANK system, and determination of their concentrations might be useful for predicting the rate of bone remodeling during orthodontic tooth movement, the net effect between bone remodeling and root resorption, and the degree of root resorption. It is therefore rational to speculate that a study of the levels of OPG and s-RANKL in blood and GCF, in relation to the degree of root resorption during orthodontic tooth movement, using healthy experimental animals and a carefully planned and organized experimental design, may be able to answer this intriguing question.

Association of serum osteoprotegerin with ankle-brachial index and urine albumin: creatinine ratio in African-Americans and non-Hispanic whites

Osteoprotegerin (OPG), a member of tumor necrosis factor receptor superfamily, has been implicated in vascular disease. We investigated the association of serum OPG with the ankle-brachial index (ABI) and urine albumin:creatinine ratio (UACR), in a bi-ethnic cohort of 1324 African-Americans (mean age 64 years, 71% women) and 1237 non-Hispanic whites (mean age 59 years, 57% women) belonging to hypertensive sibships. Serum levels of OPG were measured by solid phase sandwich immunoassay. ABI was measured using a standard protocol and peripheral arterial disease (PAD) defined as ABI<0.90. UACR was expressed as mg albumin/gm creatinine. Multivariable regression analysis using generalized estimating equations (GEE) were performed to assess whether serum OPG levels were associated with ABI and UACR. After adjustment for conventional risk factors (age, sex, diabetes, waist circumference, history of smoking, total and HDL cholesterol, hypertension), prior history of myocardial infarction or stroke, and medication (renin-angiotensin-aldosterone system inhibitors, statins, aspirin, estrogen) use, higher OPG levels were significantly associated with lower ABI and higher UACR in African-Americans (P=0.001 and P<0.0001, respectively) and non-Hispanic whites (P=0.017 and P=0.002, respectively); the association remained significant after further adjustment for plasma C-reactive protein (CRP) in both ethnic groups. In multivariable logistic regression analysis, higher OPG levels were associated with PAD in African-Americans, independent of the covariates listed above (P=0.026); the association remained significant after additional adjustment for plasma CRP (P=0.047). In non-Hispanic whites, the association of higher OPG levels with PAD was of borderline significance after adjustment for the relevant covariates (P=0.106). We conclude that higher OPG levels are associated with lower ABI and higher UACR, independent of conventional risk factors and plasma CRP.

RANKL increases vascular smooth muscle cell calcification through a RANK-BMP4-dependent pathway

Vascular calcification commonly associated with several pathologies and it has been suggested to be similar to bone mineralization. The axis RANKL-OPG (receptor activator of nuclear factor kappaB ligand-osteoprotegerin) finely controls bone turnover. RANKL has been suggested to increase vascular calcification, but direct evidence is missing. Thus, in the present work, we assess the effect of RANKL in vascular smooth muscle cell (VSMC) calcification. VSMCs incubated with RANKL showed a dose-dependent increase in calcification, which was abolished by coincubation with OPG. To test whether the effect was mediated by signaling to its receptor, knockdown of RANK was accomplished by short hairpin (sh)RNA. Indeed, cells lacking RANK showed no increases in vascular calcification when incubated with RANKL. To further elucidate the mechanism by which RANK activation increases calcification, we blocked both nuclear factor (NF)-kappaB activation pathways. Only IKKalpha inactivation inhibited calcification, pointing to an involvement of the alternative NF-kappaB activation pathway. Furthermore, RANKL addition increased bone morphogenetic protein (BMP)4 expression in VSMCs, and that increase disappeared in cells lacking RANK or IKKalpha. The increase in calcification was also blunted by Noggin, pointing to a mediation of BMP4 in the calcification induced by RANKL. Furthermore, in an in vivo model, the increase in vascular calcium content was parallel to an increase in RANKL and BMP4 expression, which was localized in calcified areas. However, blood levels of the ratio RANKL/OPG did not change. We conclude that RANKL increases vascular smooth muscle cell calcification by binding to RANK and increasing BMP4 production through activation of the alternative NF-kappaB pathway.

Mechanism of bone metastasis: the role of osteoprotegerin and of the host-tissue microenvironment-related survival factors

Osteoprotegerin (OPG), member of tumor necrosis factor (TNF) receptor superfamily, has various biological functions including bone remodeling. OPG binds to receptor activator of nuclear factor-kB ligand (RANKL) and prevents osteoclastic bone resorption. Recently, OPG has gained more clinical interest as its role in cancer-mediated bone destruction and the potential of RANKL inhibition could act as a novel treatment in tumor-induced bone disease. OPG protects prostate cancer cells from apoptotic effects of TRAIL and therefore provides tumor cells producing OPG with survival advantages. Additionally, the increased RANKL/OPG ratio in metastatic breast cancer results in severe osteolysis. Thus, bone formation and resorption are the crux of cancer metastasis, resulting in bone pain and pathological fractures. This review provides an overview of the role of OPG in cancer-induced bone disease.

Circulating osteoprotegerin levels are elevated and correlated with antiphospholipid antibodies in patients with systemic lupus erythematosus

Patients with antiphospholipid syndrome (APS) have an increased risk for the development of thrombotic complications. Recent studies indicate that osteoprotegerin (OPG) acts as an important molecule in the development of vascular diseases. The aim of the present study was to examine the association between serum OPG levels and APS manifestations in patients with SLE. Seventy-nine patients with SLE and ninety-two healthy controls, matched for age and sex, were included in this study. Serum levels of OPG, monocyte chemoattractant protein(MCP)-1 and soluble E-selectin were determined by ELISA. At the time of serum sampling, various clinical and laboratory parameters were assessed. We found that serum levels of OPG were significantly higher in patients with SLE than in healthy controls (1236 ± 82 vs 967 ± 37 pg/mL, P = 0.003). Particularly, serum OPG levels were significantly higher in SLE patients with APS than those without (1615 ± 191 vs 1171 ± 91 pg/mL, P = 0.006). Serum OPG levels correlated with titres of IgG anti-cardiolipin antibody ( P = 0.026) and anti-β2-glycoprotein I antibody ( P < 0.001). Moreover, serum OPG also correlated with serum levels of sE-selectin ( P = 0.002), which is an endothelial cell activation marker, and MCP-1 ( P = 0.003), a well known chemokine implicated in thrombogenesis. Collectively, serum OPG levels were increased in SLE patients with APS and correlated with titres of antiphospholipid antibodies, suggesting that OPG might be linked to the development of APS.

Large-scale association study for structural soundness and leg locomotion traits in the pig

BACKGROUND

Identification and culling of replacement gilts with poor skeletal conformation and feet and leg (FL) unsoundness is an approach used to reduce sow culling and mortality rates in breeding stock. Few candidate genes related to soundness traits have been identified in the pig.

METHODS

In this study, 2066 commercial females were scored for 17 traits describing body conformation and FL structure, and were used for association analyses. Genotyping of 121 SNPs derived from 95 genes was implemented using Sequenom's MassARRAY system.

RESULTS

Based on the association results from single trait and principal components using mixed linear model analyses and false discovery rate testing, it was observed that APOE, BMP8, CALCR, COL1A2, COL9A1, DKFZ, FBN1 and VDBP were very highly significantly (P < 0.001) associated with body conformation traits. The genes ALOX5, BMP8, CALCR, OPG, OXTR and WNT16 were very highly significantly (P < 0.001) associated with FL structures, and APOE, CALCR, COL1A2, GNRHR, IHH, MTHFR and WNT16 were highly significantly (P < 0.01) associated with overall leg action. Strong linkage disequilibrium between CALCR and COL1A2 on SSC9 was detected, and haplotype -ACGACC- was highly significantly (P < 0.01) associated with overall leg action and several important FL soundness traits.

CONCLUSION

The present findings provide a comprehensive list of candidate genes for further use in fine mapping and biological functional analyses.

Parathyroid hormone decreases endothelial osteoprotegerin secretion: role of protein kinase A and C

Parathyroid hormone (PTH), which is elevated in patients with chronic renal failure, has been shown to participate in the development of vascular calcification. Previous studies have demonstrated that PTH may promote endothelial expressions of proinflammatory parameters. On the basis of these data, we evaluated whether PTH may have an impact on endothelial osteoprotegerin (OPG), a vascular-protective factor which may control vascular calcification. Endothelial cells were stimulated with 10−12to 10−10mol/l PTH. PKC and PKA are the main cellular pathways of PTH. Inhibitors and activators of PKC or PKA were used to determine whether these signaling pathways are involved in the control of endothelial OPG. PTH induced a decrease in OPG secretion and mRNA expression. Treatment of PTH-stimulated cells by calphostin C (PKC inhibitor) induced a further decrease in OPG secretion, while Rp-cAMP (PKA inhibitor) had no additional effect. In nonstimulated cells, a PKC activator significantly stimulated OPG secretion, while a PKA activator was associated with a decline. These effects were blunted in the presence of calphostin C and Rp-cAMP, respectively. An increase in OPG secretion induced by a PKC activator indicates that the basal OPG secretion is mediated through PKC. The decrease induced by a PKA activator, which is similar to the decrease observed with PTH, suggests that the action of PTH on OPG secretion and mRNA expression may be due to the PKA pathway.

Plasma osteoprotegerin levels predict cardiovascular and all-cause mortality and deterioration of kidney function in type 1 diabetic patients with nephropathy

AIMS/HYPOTHESIS

The bone-related peptide osteoprotegerin is produced by vascular cells and is involved in the process of vascular calcification. The aim of this study was to investigate the predictive value of plasma levels of osteoprotegerin in relation to mortality, cardiovascular events and deterioration in kidney function in patients with type 1 diabetes.

METHODS

This prospective observational follow-up study included 397 type 1 diabetic patients with overt diabetic nephropathy (243 men; age [mean+/-SD] 42.1 +/- 10.6 years, duration of diabetes 28.3 +/- 9.9 years, GFR 67 +/- 28 ml min(-1) 1.73 m(2)) and a group of 176 patients with longstanding type 1 diabetes and persistent normoalbuminuria (105 men; age 42.6 +/- 9.7 years, duration of diabetes 27.6 +/- 8.3 years).

RESULTS

The median (range) follow-up period was 11.3 (0.0-12.9) years. Among patients with diabetic nephropathy, individuals with high osteoprotegerin levels (fourth quartile) had significantly higher all-cause mortality than patients with low levels (first quartile) (covariate-adjusted hazard ratio [HR] 3.00 [1.24-7.27]). High osteoprotegerin levels also predicted cardiovascular mortality (covariate-adjusted HR 4.88 [1.57-15.14]). Furthermore, patients with high osteoprotegerin levels had significantly higher risk of progression to end-stage renal disease than patients with low levels (covariate-adjusted HR 4.32 [1.45-12.87]). In addition, patients with high levels of plasma osteoprotegerin had an elevated rate of decline in GFR.

CONCLUSIONS/INTERPRETATION

High levels of osteoprotegerin predict all-cause and cardiovascular mortality in patients with diabetic nephropathy. Furthermore, high levels of osteoprotegerin predict deterioration of kidney function towards end-stage renal disease.

Osteoprotegerin, vascular calcification and atherosclerosis

The association of bone pathologies with atherosclerosis has stimulated the search for common mediators linking the skeletal and the vascular system. Since its initial discovery as a key regulator in bone metabolism, osteoprotegerin (OPG) has become the subject of intense interest for its role in vascular disease and calcification. Studies in vitro and in animal models suggest that OPG inhibits vascular calcification. Paradoxically however, clinical studies suggest that serum OPG levels increase in association with vascular calcification, coronary artery disease, stroke and future cardiovascular events. This has led to an extensive debate on the potential of OPG as a biomarker of vascular disease. However the exact significance and mechanisms by which this bone-regulatory protein influences cardiovascular pathophysiology is still unclear. The need for a more complete picture is being addressed in increasing valuable research indicating OPG as not only a marker but also a mediator of vascular pathology modulating osteogenic, inflammatory and apoptotic responses. By integrating the results of recent experimental research, animal models and clinical studies, this review summarises the present understanding of the role of OPG in vascular disease and calcification.

Abdominal aortic calcification, BMD, and bone microstructure: a population-based study

To better define the relationship between vascular calcification and bone mass/structure, we assessed abdominal aortic calcification (AAC), BMD, and bone microstructure in an age-stratified, random sample of 693 Rochester, MN, residents. Participants underwent QCT of the spine and hip and high-resolution pQCT (HRpQCT) of the radius to define volumetric BMD (vBMD) and microstructural parameters. AAC was quantified with the Agatston scoring method. In men, AAC correlated with lower vertebral trabecular and femoral neck vBMD (p < 0.001), but not after age or multivariable (age, body mass index, smoking status) adjustment. Separation into <50 and >or=50 yr showed this pattern only in the older men. BV/TV and Tb.Th inversely correlated with AAC in all men (p < 0.001), and Tb.Th remained significantly correlated after age adjustment (p < 0.05). Tb.N positively correlated with AAC in younger men (p < 0.001) but negatively correlated in older men (p < 0.001). The opposite was true with Tb.Sp (p = 0.01 and p < 0.001, respectively). Lower Tb.N and higher Tb.Sp correlated with AAC in older men even after multivariable adjustment. Among all women and postmenopausal women, AAC correlated with lower vertebral and femoral neck vBMD (p < 0.001) but not after adjustment. Lower BV/TV and Tb.Th correlated with AAC (p = 0.03 and p = 0.04, respectively) in women, but not after adjustment. Our findings support an age-dependent association between AAC and vBMD. We also found that AAC correlates with specific bone microstructural parameters in older men, suggesting a possible common pathogenesis for vascular calcification and deterioration in bone structure. However, sex-specific differences exist.

Sex hormone levels and subclinical atherosclerosis in postmenopausal women: the Multi-Ethnic Study of Atherosclerosis

We examined cross-sectional associations between sex hormones and carotid artery intimal-medial thickness (cIMT) and coronary artery calcium in women in the Multi-Ethnic Study of Atherosclerosis. Serum testosterone, estradiol, sex hormone binding globulin (SHBG), and dehydroepiandrosterone levels were measured in 1947 postmenopausal women aged 45-84 years (30% White, 14% Chinese-American, 31% Black, and 25% Hispanic) and not on hormone therapy. Using multiple linear regression we evaluated associations between log(sex hormone) levels and log(cIMT) adjusted for age, ethnicity, body mass index (BMI) and cardiac risk factors. Associations between sex hormone levels and the presence and extent of coronary calcium were evaluated. Total and bioavailable testosterone were positively associated with common cIMT independent of age, BMI, hypertension, smoking, HDL-cholesterol, LDL-cholesterol and insulin sensitivity (p=0.009 and p=0.002, respectively). SHBG was negatively associated with common cIMT (p=0.001) but further adjustment for BMI, cardiovascular risk factors, and LDL- and HDL-cholesterol removed significance. Estradiol and dehydroepiandrosterone were not associated with common cIMT. Sex hormones were not associated with presence of coronary calcium. Among women with measurable coronary calcium, higher SHBG (p=0.012) and lower bioavailable testosterone (p=0.007) were associated with greater coronary calcium score. No heterogeneity by ethnicity was found. In postmenopausal women, testosterone is independently associated with greater common cIMT. SHBG is negatively associated and this may be mediated by LDL- and HDL-cholesterol. In contrast, SHBG and testosterone were associated with extent of coronary calcium but in the opposite direction compared to carotid intimal-medial thickness. These differences warrant further evaluation.

Bone mineral density, bone remodeling and osteoprotegerin in patients with acute coronary syndrome

The objective of this study was to evaluate the relationship between coronary disease and osteoporosis and determine the effect of osteoprotegerin (OPG) on bone remodeling and bone mineral density (BMD) in a group of patients with acute coronary syndrome. Eighty-three patients (52 males and 31 women) with acute coronary syndrome (75 patients with acute myocardial infarction and 8 with unstable angina) with an average age of 61+/-10 years were studied. Levels of osteocalcin, urinarydeoxypyridinoline, OPG and the receptor activator of nuclear factor-kappaB ligand (RANKL) were determined during the hospital stay. Femoral neck, trochanter and lumbar spine densitometry was carried out using a DXA densitometer. Thirty percent of patients presented osteoporosis (39% of females and 26% of males). Osteoporotic patients were older and had a lower weight and height and elevated serum levels of osteocalcin (3.6+/-2.25 2.63 versus +/-1.55, p=0.05). Levels of OPG and RANKL were similar in both groups and showed no relationship with BMD. In conclusion, no relationship was observed between the OPG/RANKL system and BMD in these patients.

Relationship of calcification of atherosclerotic plaque and arterial stiffness to bone mineral density and osteoprotegerin in postmenopausal women referred for osteoporosis screening

Arterial calcification leading to increased arterial stiffness, a powerful risk factor for cardiovascular disease, may underlie the association of osteoporosis with cardiovascular disease in postmenopausal women. Osteoprotegerin (OPG), an indirect inhibitor of osteoclastogenesis, may be involved in arterial calcification. We examined relationships between calcification of subclinical atherosclerotic plaque and arterial stiffness with bone mineral density (BMD) and OPG in a group of 54 postmenopausal women referred for routine osteoporosis screening by dual-energy X-ray absorptiometric scanning of the lumbar spine and hip. Presence of calcified and noncalcified plaque in carotid and femoral arteries was examined using ultrasonography. Pulse wave velocity (PWV), a measure of arterial stiffness, was determined by sequential tonometry over the carotid and femoral region. Fifty-nine percent of osteoporotic women had calcified (echogenic) plaque at one or more sites compared with 42% and 20% for women with osteopenia and normal BMD, respectively (P = 0.04). There was a significant negative correlation between PWV and hip BMD (r = -0.35, P = 0.01), which remained significant when age, mean arterial pressure, and serum lipids were taken into account (P = 0.05). No significant relationships were observed between serum concentrations of OPG and lumbar spine or total hip BMD or with the number of arterial sites with calcified or noncalcified plaque. However, there was a strong correlation between OPG and PWV (r = 0.44, P = 0.001), which remained significant when adjusted for age (P = 0.01). These findings suggest that decreased BMD is associated with arterial calcification and stiffening and raise the possibility that OPG is a marker of arterial stiffening, independent of any association with BMD.

Effect of long-term treatment with risedronate on arterial compliance in osteoporotic patients with cardiovascular risk factors

Accumulating evidence suggests that osteoporosis and coronary artery disease have epidemiologic similarities. Moreover, the anti-atherogenic effects of bisphosphonates have been observed in vitro and in animal models. The present study investigated the effect of risedronate on indices of arterial compliance, serum osteoprotegerin (OPG) level, inflammatory and metabolic parameters in osteoporotic women with cardiovascular risk factors. In an open label, prospective study 68 postmenopausal osteoporotic women were evaluated for the study. Patients received risedronate orally in a dose of 35 mg per week, daily supplements of calcium and cholecalciferol during 6month treatment period. Patients were evaluated for lipid profile, HbA1C, insulin, C-peptide, fibrinogen, hs-CRP and plasma osreoprotegerin. Arterial elasticity was evaluated using pulse wave contour analysis (HDI CR 2000, Eagan, Minnesota). Large artery elasticity index (LAEI) increased from 9.86+/-3.66 to 11.54+/-">+/-3.16 ml/mm HgX10 (p<0.0001) during treatment period. Small artery elasticity index (SAEI) increased from 2.64+/-1.10 to 3.28+/-1.16 ml/mm HgX100 (p<0.0001). Systemic vascular resistance (SVR) decreased from 1876.12+/-457.72 to 1646.12+/-260.17 dyn/s/cm(- 5) (p<0.013). Metabolic parameters did not change during the treatment period. Plasma osteoprotegerin was significantly, positively correlated to SVR at baseline (r=0.36, p=0.045). At the final visit, OPG was marginally inversely associated with LAE (r=- 0.312, p=0.09), and significantly, positively associated with total vascular impedance (r=0.43, p=0.015). In conclusion, prolonged treatment with risedronate improved arterial elasticity of small and large arteries, and decreased SVR. These beneficial vascular effects were not related to changes in cardiovascular risk factors and may be attributed to direct effects of risedronate on the vascular wall.

Serum levels of the osteoprotegerin, receptor activator of nuclear factor kappa-B ligand, metalloproteinase-1 (MMP-1) and tissue inhibitors of MMP-1 levels are increased in men 6 months after acute myocardial infarction

BACKGROUND

Osteoprotegerin (OPG) and receptor activator of nuclear factor kappa-B ligand (RANKL) are critical regulators of bone remodeling and RANKL/RANK signaling could also play an important role in the remodeling process of several tissues, such as myocardium. Therefore, we investigated whether the serum concentrations of OPG and RANKL correlate with the serum levels of metalloproteinase-1 (MMP-1), MMP-9 and tissue inhibitors of MMP-1 (TIMP-1), which are known regulators of myocardial healing in acute myocardial infarction (AMI) patients.

METHODS

We analyzed blood samples from 51 consecutively hospitalized men with AMI, 12 men with established ischemic heart failure (New York Heart Association category II, NYHA-II) and 12 healthy men age-matched to the NYHA-II patients. Serum levels of MMP-1, MMP-9, TIMP-1, OPG and RANKL were quantified using commercially available ELISA kits. AMI patients were sampled 4 days and 6 months after MI.

RESULTS

Our data revealed increased serum levels of OPG, RANKL, MMP-1 and TIMP-1 levels and significant correlations between increased RANKL levels and MMP-1 and TIMP-1 serum levels 6 months after MI. In addition, the ratio OPG/RANKL was very low 6 months after MI, suggesting that the nuclear factor kappa-B signaling is possibly more active 6 months post-MI than it is on day 4 post-MI.

CONCLUSIONS

Our data suggest that OPG, RANKL, MMP-1 and TIMP-1 serum levels can be potential mediators of myocardial healing after MI. However, further large studies are needed to confirm the utility of OPG and RANKL as markers of healing after ST elevation in MI.

Interleukin-4 and interleukin-13 stimulate the osteoclast inhibitor osteoprotegerin by human endothelial cells through the STAT6 pathway

INTRODUCTION

Endothelial cells of the bone vasculature modulate development, remodeling, and repair of bone by secreting osteotropic cytokines and hormones, which can act on osteoblastic and osteoclastic lineage cells. RANKL is the essential factor for differentiation, activation, and survival of osteoclasts, whereas osteoprotegerin (OPG) is a soluble decoy receptor and inhibitor for RANKL.

MATERIALS AND METHODS

In this study, we analyzed the regulation of OPG by T helper 2 (Th2) cytokines interleukin (IL)-4 and the closely related IL-13 in human umbilical vein endothelial cells (HUVECs), the underlying signaling pathway, and its functional relevance on osteoclastic resorption.

RESULTS

IL-4 and IL-13 induced OPG mRNA levels and protein secretion in HUVEC by up to 4-fold in a dose- and time-dependent fashion (maximum effect after 48 h and at 10 ng/ml). Activation of the transcription factor STAT6 preceded IL-4-induced OPG expression, and blockade of IL-4-induced STAT6 activation by the phospholipase C-specific inhibitor D609 decreased OPG expression. Soluble IL-4 receptor (sIL-4R) dose-dependently abolished both IL-4-induced STAT6 phosphorylation and OPG expression. RANKL stimulated the activity of osteoclasts, which was antagonized by HUVEC-derived supernatant containing OPG. The inhibitory effect on osteoclastogenesis was completely and specifically abrogated by a neutralizing OPG antibody in unstimulated HUVEC supernatant and partially in IL-4-stimulated HUVEC supernatant.

CONCLUSIONS

In summary, IL-4 and IL-13 induced OPG expression through activation of STAT6 in endothelial cells, and HUVEC-derived OPG is an IL-4/IL-13-induced inhibitor of osteoclastic resorption. These data underline the impact of Th2 cytokines on bone resorption through modulation of endothelial cell-derived cytokines.

Does osteoprotegerin or receptor activator of nuclear factor-kappaB ligand mediate the association between bone and coronary artery calcification?

CONTEXT

Accumulating evidence indicates that vascular and bone mineralization may be related, although the exact mechanism remains unknown.

OBJECTIVE

Our objective was to investigate whether an observed inverse association between bone mineral density (BMD) and coronary artery calcification (CAC) in postmenopausal women currently taking estrogen therapy is mediated by osteoprotegerin (OPG) or receptor activator of nuclear factor-kappaB ligand (RANKL).

DESIGN

Participants were 92 postmenopausal women (aged 58-81 yr) taking estrogen therapy who had hip and spine BMD assessed by dual-energy x-ray absorptiometry and CAC measured by electron-beam computed tomography in 1998-2002 and serum RANKL and OPG levels measured in samples collected in 1997-1999. Total CAC score was dichotomized as none/minimal (</=10) vs. some (>10).

RESULTS

OPG serum levels were higher in women who had some CAC compared with those who had none/minimal (126.8 +/- 1.08 vs. 102.9 +/- 1.07 pg/ml, respectively, P = 0.03); these differences became nonsignificant after adjustment for age and other risk factors (P = 0.51). A 1 sd increase in hip BMD was associated with significantly lower odds of having CAC > 10 (odds ratio = 0.52; 95% confidence interval = 0.29-0.93) independent of age, fat-free mass, high-density lipoprotein cholesterol, current smoking, and use of cholesterol-lowering medications. Other skeletal sites demonstrated a similar pattern. Addition of RANKL and/or OPG to the model had minimal effect on the magnitude or statistical significance of the BMD-CAC association. Additionally, a test of interaction indicated that RANKL and OPG are not significant effect modifiers.

CONCLUSIONS

Serum OPG and RANKL do not account for the observed association between bone and coronary artery calcification among postmenopausal women using hormone therapy.