Human full-length osteoprotegerin induces the proliferation of rodent vascular smooth muscle cells both in vitro and in vivo

Association of Serum Osteoprotegerin With Vascular Calcification, and Cardiovascular and Graft Outcomes in Kidney Transplant Patients: Results From the KNOW-KT

BACKGROUND

Vascular calcification and stiffness contribute to increased cardiovascular morbidity in patients with chronic kidney disease. This study investigated associations between serum osteoprotegerin (OPG) levels and vascular calcification or stiffness to assess cardiovascular and graft outcomes in kidney transplant patients.

METHODS

The KoreaN cohort study for Outcome in patients With Kidney Transplantation was a prospective multicenter cohort study. Serum OPG levels were measured at baseline and 3 y after transplantation in 1018 patients. Patients were classified into high and low OPG groups according to median serum OPG levels. The median follow-up duration was 93.5 mo.

RESULTS

The mean age was 45.8 ± 11.7 y and 62.9% were men. Patients with high OPG had significantly higher coronary artery calcium scores, abdominal aortic calcification scores, and brachial-ankle pulse wave velocities than those with lower OPG; these parameters remained significant for 5 y after transplantation. The 3-y OPG levels were lower than baseline values ( P  < 0.001) and were positively correlated ( r  = 0.42, P  < 0.001). Multivariate Cox regression analysis showed that high OPG levels were significantly associated with posttransplant cardiovascular events ( P  = 0.008) and death-censored graft loss ( P  = 0.004). Similar findings regarding posttransplant cardiovascular events ( P  = 0.012) and death-censored graft loss ( P  = 0.037) were noted in patients with high OPG at the 3-y follow-up. Mediation analyses revealed that coronary artery calcium scores, abdominal aortic calcification scores, and brachial-ankle pulse wave velocities could act as mediators between serum OPG levels and posttransplant cardiovascular events.

CONCLUSIONS

Serum OPG concentration is associated with vascular calcification and stiffness and could be a significant risk factor for cardiovascular outcomes and graft loss in patients undergoing kidney transplantation.

Angiotensin II Induces Aortic Rupture and Dissection in Osteoprotegerin-Deficient Mice

Background

The biological mechanism of action for osteoprotegerin, a soluble decoy receptor for the receptor activator of nuclear factor‐kappa B ligand in the vascular structure, has not been elucidated. The study aim was to determine if osteoprotegerin affects aortic structural integrity in angiotensin II (Ang II)‐induced hypertension.

Methods and Results

Mortality was higher (P<0.0001 by log‐rank test) in 8‐week‐old male homozygotes of osteoprotegerin gene‐knockout mice given subcutaneous administration of Ang II for 28 days, with an incidence of 21% fatal aortic rupture and 23% aortic dissection, than in age‐matched wild‐type mice. Ang II‐infused aorta of wild‐type mice showed that osteoprotegerin immunoreactivity was present with proteoglycan. The absence of osteoprotegerin was associated with decreased medial and adventitial thickness and increased numbers of elastin breaks as well as with increased periostin expression and soluble receptor activator of nuclear factor‐kappa B ligand concentrations. PEGylated human recombinant osteoprotegerin administration decreased all‐cause mortality (P<0.001 by log‐rank test), the incidence of fatal aortic rupture (P=0.08), and aortic dissection (P<0.001) with decreasing numbers of elastin breaks, periostin expressions, and soluble receptor activator of nuclear factor‐kappa B ligand concentrations in Ang II‐infused osteoprotegerin gene‐knockout mice.

Conclusions

These data suggest that osteoprotegerin protects against aortic rupture and dissection in Ang II‐induced hypertension by inhibiting receptor activator of nuclear factor‐kappa B ligand activity and periostin expression.

Radial BMD and serum CTX-I can predict the progression of carotid plaque in rheumatoid arthritis: a 3-year prospective cohort study

OBJECTIVE

Patients with rheumatoid arthritis (RA) are almost twice as likely to develop cardiovascular disease (CVD) as those without. However, traditional CVD risks have been shown to underperform in RA patients; thus, we aimed to identify new surrogate risk factors to better reflect their atherosclerotic burden.

METHODS

A total of 380 RA patients with carotid atherosclerosis data were analyzed in this prospective cohort study. The primary outcome was carotid plaque progression over the 3-year follow-up period. Risk parameters assessed for the progression of carotid plaque were categorized as demographics, traditional CVD risks, RA-related risks, and bone parameters.

RESULTS

The progression of carotid plaque was associated with the level of rheumatoid factor (p = 0.025), serum C-terminal telopeptide of type-I collagen (CTX-I) (p = 0.014), and femur and distal radius bone mass density (BMD) (p = 0.007 and 0.004, respectively), as well as traditional CVD risk factors. In multivariable analyses, the bone parameters of serum CTX-I and distal radius BMD proved to be independent predictors of the progression of carotid plaque along with hyperlipidemia, smoking, and baseline carotid plaque (all, p < 0.05). Adding both serum CTX-I and distal radius BMD increased the carotid plaque progression prediction model's percentage of explained variance from 24 to 30%.

CONCLUSION

High serum CTX-I and lower radius BMD, reflecting high bone turnover, were independent risk factors for the progression of carotid plaque in RA patients, implicating the direct or indirect role of bone metabolism on the atherosclerotic burden.

The role of osteoprotegerin in the development, progression and management of abdominal aortic aneurysms

Osteoprotegerin (OPG) appears to be a very promising marker both in the diagnosis of abdominal aortic aneurysms (AAAs) and as a potential target in its treatment. This article presents an overview of the current literature that discusses the role of OPG in the pathogenesis of atherosclerosis and its potential value as a prognostic factor in AAA. Pharmacological modulation of OPG expression has been considered. In conclusion, it seems that further research designed to assess the relationship between OPG and AAA is needed as this may contribute to improved AAA monitoring and more effective treatment of patients with AAA.

Increased osteoprotegerin level is associated with impaired cardiovagal modulation in type-2 diabetic patients treated with oral antidiabetic drugs

Background

An increased osteoprotegerin (OPG) level has been reported in both type-2 diabetes mellitus (T2DM) and cardiovascular diease (CVD) that are linked to sympathovagal imbalance (SVI). We explored the link of osteoprotegerin with cardiovagal modulation in T2DM.

Methods

We assessed fasting serum OPG, high-sensitive C-reactive protein (hsCRP), glucose, insulin and lipid profile in patients having T2DM receiving oral antidiabetic drugs (OAD) (n = 42) compared with age, gender and body composition-matched healthy participants without diabetes (n = 42). Rate pressure product (RPP), spectral indices of heart rate variability (HRV) and body composition were recorded in both the groups. Association of HOMA-IR and OPG with various parameters were assessed.

Results

Osteoprotegerin, HOMA-IR, hsCRP, coronary lipid risk factor were significantly increased, markers of cardiovagal modulation (TP, SDNN, RMSSD) were considerably decreased, ratio of low-frequency to high-frequency (LH-HF ratio), the indicator of SVI, and RPP, the marker of myocardial work stress were significantly higher in patients with diabetes, suggesting an overall elevated CVD risks in them. HOMA-IR was correlated with RMSSD, lipid risk factors and OPG. Rise in OPG was correlated with decreased cardiovagal modulation in patients with diabetes. There was significant contribution of OPG in decreasing TP, suggesting impaired cardiovagal modulation.

Conclusion

T2DM patients receiving OAD had higher cardiometabolic risks compared to age, gender and body composition-matched healthy individuals. Increased level of OPG is linked to decreased cardiovagal modulation in T2DM patients.

Osteoprotegerin Prevents Intracranial Aneurysm Progression by Promoting Collagen Biosynthesis and Vascular Smooth Muscle Cell Proliferation

Background Decreased extracellular matrix formation and few vascular smooth muscle cells (VSMCs) in cerebral vascular walls are the main characteristics of intracranial aneurysm (IA) pathogenesis. Recently, osteoprotegerin was reported to activate collagen biosynthesis and VSMC proliferation via the TGF-β1 (transforming growth factor-β1) signaling. This study aimed to investigate whether osteoprotegerin can prevent IA progression in rats through enhanced collagen expression and VSMC proliferation. Methods and Results IAs were surgically induced in 7-week-old male Sprague-Dawley rats; at 1-week post-operation, recombinant mouse osteoprotegerin or vehicle control was continuously infused for 4 weeks into the lateral ventricle using an osmotic pump. In the osteoprotegerin-treatment group, the aneurysmal size was significantly smaller (37.5 μm versus 60.0 μm; P<0.01) and the media of IA walls was thicker (57.1% versus 36.0%; P<0.01) than in the vehicle-control group. Type-I and type-III collagen, TGF-β1, phosphorylated Smad2/3, and proliferating cell nuclear antigen were significantly upregulated in the IA walls of the osteoprotegerin group than that in the control group. No significant difference was found in the expression of proinflammatory genes between the groups. In mouse VSMC cultures, osteoprotegerin treatment upregulated the expression of collagen and TGF-β1 genes, and activated VSMC proliferation; the inhibition of TGF-β1 signaling nullified this effect. Conclusions Osteoprotegerin suppressed the IA progression by a unique mechanism whereby collagen biosynthesis and VSMC proliferation were activated via TGF-β1 without altering proinflammatory gene expression. Osteoprotegerin may represent a novel therapeutic target for IAs.

Elevated serum osteoprotegerin is associated with increased left ventricular mass index and myocardial stiffness

AIM

Osteoprotegerin (OPG) is associated with a poor prognosis in patients with heart failure with preserved ejection fraction (HFpEF). OPG has also been associated with fibrosis and collagen cross-linking, which increase arterial and left ventricle (LV) myocardial stiffness. Little is known about the relation of OPG and LV structure and function in African-Americans who are disproportionately affected by HFpEF.

METHODS AND RESULTS

Our analysis included 1172 participants with preserved LV ejection fraction (>50%) from the African-American cohort in the Genetic Epidemiology Network of Arteriopathy Study (mean age 63 years, 72% female). We used diastolic wall strain indicator measured by echocardiography to assess LV myocardial stiffness. Diastolic wall strain was calculated as (LV posterior thickness at end-systole - LV posterior thickness at end-diastole)/LV posterior thickness at end-systole. Associations between OPG levels and indices of arterial and LV structure and function were evaluated by using generalized linear mixed models and adjusted for possible confounders. OPG levels were correlated with age, female sex, presence of hypertension and diabetes, and lower estimated glomerular filtration rate (P < 0.05 for all). Multivariable analysis revealed that higher OPG levels were associated with greater LV mass index, increased LV myocardial stiffness, and higher N-terminal prohormone brain natriuretic peptide levels (P < 0.05 for all).

CONCLUSION

In African-Americans, higher OPG levels were associated with characteristics common in patients with HFpEF and were significantly associated with known precursors to HFpEF. These findings indicate a potential role for OPG in the pathophysiology of HFpEF in African-Americans.

Effects of osteoprotegerin/TNFRSF11B in two models of abdominal aortic aneurysms

Osteoprotegerin (OPG), additionally termed tumor necrosis factor receptor superfamily member 11B, is produced by vascular smooth muscle cells (VSMCs) and endothelial cells in the vasculature, and its release may be modulated by pro-inflammatory cytokines, including interleukin-1β and tumor necrosis factor-α. The present study investigated the effects of treatment with low-dose human recombinant OPG on abdominal aortic aneurysm (AAA) development in mice. Mice were treated with 1 µg human recombinant OPG four times (or vehicle) for 2 weeks prior to inducing AAA. A total of two different models for inducing AAA were used to investigate the hypothesis as to whether OPG is involved in key events of AAA development, using osmotic mini-pumps with angiotensin II in apolipoprotein-E (ApoE^−/−) mice for 28 days or using periaortic application of CaCl₂ on the aorta in C57Bl/6J mice for 14 days. OPG was continuously administered during the experimental period. Histological staining using Masson's trichrome, Verhoeff's van-Gieson and picro-sirius red, in addition to reverse transcription-quantitative polymerase chain reaction analysis of various markers, were used to analyze phenotypic alterations. Treatment with OPG had no inhibitory effect on AAA development in the angiotensin II model in ApoE^−/− mice, which developed suprarenal aneurysms, although it increased vessel wall thickness of the aorta and total collagen in C57Bl/6J mice using the CaCl₂ model that induced infrarenal dilation of the aorta. Treatment with OPG did not inhibit aneurysm development and key events, including inflammation, extracellular matrix or VSMC remodeling, in aortas from OPG-treated mice with periaortic treatment with CaCl₂. The results indicated that mice treated with low levels of human recombinant OPG may have a more stable aneurysmal phenotype due to compensatory production of collagen and increased vessel wall thickness of the aorta, potentially protecting the aneurysm from rupture. Further studies investigating rupture models of AAA in addition to using higher levels of OPG are require to verify this speculation. Furthermore, treatment with low levels of OPG in patients with AAA may represent a novel therapeutic strategy for the treatment of AAA as well as attenuate the adverse effects associated with the administration of normal and high dosages of OPG.

Circulating osteoprotegerin is associated with chronic kidney disease in hypertensive patients

Background

Osteoprotegerin (OPG) is a glycoprotein that plays an important regulatory role in the skeletal, vascular, and immune system. It has been shown that OPG predicts chronic kidney disease (CKD) in diabetic patients. We hypothesized that OPG could be a risk marker of CKD development also in non-diabetic hypertensive patients.

Methods

A case-control study was carried out to measure circulating OPG levels in 42 hypertensive patients with CKD and in 141 hypertensive patients without CKD. A potential relationship between OPG and the presence of CKD was investigated and a receiver-operating characteristic (ROC) curve was designed thereafter to identify a cut-off value of OPG that best explained the presence of CKD. Secondly, to evaluate whether OPG increase could affect the kidney, 18 C57BL/6J mice were randomized to be treated with saline or recombinant OPG every 3 weeks for 12 weeks.

Results

Circulating OPG levels were significantly higher in hypertensive patients with CKD, and there was a significant inverse association between OPG and renal function, that was independent from other variables. ROC analysis showed that OPG levels had a high statistically predictive value on CKD in hypertensive patients, which was greater than that of hypertension. The OPG best cut-off value associated with CKD was 1109.19 ng/L. In the experimental study, OPG delivery significantly increased the gene expression of pro-inflammatory and pro-fibrotic mediators, as well as the glomerular nitrosylation of proteins.

Conclusions

This study shows that OPG is associated with CKD in hypertensive patients, where it might have a higher predictive value than that of hypertension for CKD development. Secondly, we found that OPG delivery significantly increased the expression of molecular pathways involved in kidney damage. Further longitudinal studies are needed not only to evaluate whether OPG predicts CKD development but also to clarify whether OPG should be considered a risk factor for CKD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12882-017-0625-3) contains supplementary material, which is available to authorized users.

Dyslipidemia and Diabetes Increase the OPG/TRAIL Ratio in the Cardiovascular System

Background. Dyslipidemia and diabetes are two of the most well established risk factors for the development of cardiovascular disease (CVD). Both of them usually activate a complex range of pathogenic pathways leading to organ damage. Here we hypothesized that dyslipidemia and diabetes could affect osteoprotegerin (OPG) and TNF-related apoptosis-inducing ligand (TRAIL) expression in the vessels and the heart. Materials and Methods. Gene and protein expression of OPG, TRAIL, and OPG/TRAIL ratio were quantified in the aorta and the hearts of control mice, dyslipidemic mice, and diabetic mice. Results. Diabetes significantly increased OPG and the OPG/TRAIL ratio expression in the aorta, while dyslipidemia was the major determinant of the changes observed in the heart, where it significantly increased OPG and reduced TRAIL expression, thus increasing cardiac OPG/TRAIL ratio. Conclusions. This work shows that both dyslipidemia and diabetes affect OPG/TRAIL ratio in the cardiovascular system. This could contribute to the changes in circulating OPG/TRAIL which are observed in patients with diabetes and CVD. Most importantly, these changes could mediate/contribute to atherosclerosis development and cardiac remodeling.

RANKL promotes osteoblastic activity in vascular smooth muscle cells by upregulating endothelial BMP-2 release

INTRODUCTION

Receptor activator of nuclear factor kappa beta-ligand (RANKL) is thought to promote vascular calcification (VC) by inducing osteoblastic behaviour in vascular smooth muscle cells (VSMC) in an ill-defined process. The present study assessed whether RANKL affects pro-osteoblastic paracrine signalling between human aortic endothelial cells (HAEC) and human aortic smooth muscle cells (HASMC) using both conditioned media transfer and cell co-culture experimental approaches.

METHODS AND RESULTS

For initial experiments (6-well format), HAEC-conditioned media was harvested following 72h exposure to RANKL, and transferred to reporter HASMCs with/without noggin, an inhibitor of pro-osteoblastic bone morphogenetic protein (BMP) paracrine signalling. In further experiments, HAECs and HASMCs were co-cultured within the CellMax(®) Duo, a perfusing bioreactor unit that mimics the flow-mediated co-interaction of these cells within the arterial wall, and RANKL was added to the perfusing media for 72h. At the conclusion of each experiment markers of osteoblastic activity were measured in HASMCs, including alkaline phosphatase (ALP) activity, mRNA levels of ALP and Runx2, as well as BMP-2 and BMP-4 concentrations. RANKL increased BMP-2 release from HAECs, while exposure of HASMCs to RANKL-treated HAEC-conditioned media induced osteoblastic behaviour in HASMCs, an effect prevented by noggin. Within the CellMax(®) Duo bioreactor, the addition of RANKL to the intraluminal HAECs also produced an increase in BMP-2 and increased osteoblastic behaviour within the co-cultured HASMC population.

CONCLUSIONS

RANKL promotes VC by inducing BMP-2 release from HAECs, which in turn appears to act in a paracrine fashion on the adjacent HASMC population to increase osteoblastic activity.

Mitral valve endothelial cells secrete osteoprotegerin during endothelial mesenchymal transition

AIMS

Mitral valve prolapse (MVP) has a prevalence of 3% in the general population, affecting >176 million people worldwide. Despite this, little is known about the molecular and cellular mechanisms involved in the progression of MVP and surgical intervention is the only available option. In this study we investigated the role of osteoprotegerin (OPG) during endothelial to mesenchymal transition (EndMT) in MVP.

METHODS AND RESULTS

VECs and VICs were isolated from posterior mitral valve leaflets of patients undergoing mitral valve repair (n=25). Plasma was collected from 57 subjects (29 controls and 28 MVP patients). Overexpression of OPG during EndMT followed by autocrine effects characterised by reactive oxygen species increment and accelerated migration was documented. In addition, OPG increased VIC proliferation. Finally, OPG plasma levels were significantly higher in MVP patients compared to control subjects and the area under the ROC curve was 0.92.

CONCLUSION

EndMT has been recognised as a possible pathological mechanism for MVP. For the first time, we report the involvement of OPG in cellular and molecular changes in MVP isolated cells. In addition, we detected elevated circulating OPG levels in MVP patients when compared to controls, which supports the hypothesis that OPG is involved in MVP development and progression.

Roles and Clinical Applications of OPG and TRAIL as Biomarkers in Cardiovascular Disease

Cardiovascular diseases (CVD) remain the major cause of death and premature disability in Western societies. Assessing the risk of CVD is an important aspect in clinical decision-making. Among the growing number of molecules that are studied for their potential utility as CVD biomarkers, a lot of attention has been focused on osteoprotegerin (OPG) and its ligands, which are receptor activator of nuclear factor κB ligand (RANKL) and TNF-related apoptosis-inducing ligand. Based on the existing literature and on our experience in this field, here we review what the possible roles of OPG and TRAIL in CVD are and their potential utility as CVD biomarkers.

Long Term Effect of High Glucose and Phosphate Levels on the OPG/RANK/RANKL/TRAIL System in the Progression of Vascular Calcification in rat Aortic Smooth Muscle Cells

Osteoprotegerin (OPG), receptor activator of NF-κB ligand (RANKL)/receptor activator of NF-κB (RANK) axis, and TNF-related apoptosis-inducing ligand (TRAIL) participate in vascular calcification process including atherosclerosis, but their contributions under high glucose (HG) and phosphate (HP) condition for a long-term period (more than 2 weeks) have not been fully determined. In this study, we evaluated the effects of HG and HP levels over 2 or 4 weeks on the progression of vascular calcification in rat vascular smooth muscle cells (VSMCs). Calcium deposition in VSMCs was increased in medium containing HG (30 mmol/L D-glucose) with β-glycerophosphate (β-GP, 12 mmol/L) after 2 weeks and increased further after 4 weeks. OPG mRNA and protein expressions were unchanged in HG group with or without β-GP after 2 weeks. However, after 4 weeks, OPG mRNA and protein expressions were significantly lower in HG group with β-GP. No significant expression changes were observed in RANKL, RANK, or TRAIL during the experiment. After 4 weeks of treatment in HG group containing β-GP and rhBMP-7, an inhibitor of vascular calcification, OPG expressions were maintained. Furthermore, mRNA expression of alkaline phosphatase (ALP), a marker of vascular mineralization, was lower in the presence of rhBMP-7. These results suggest that low OPG levels after long term HG and phosphate stimulation might reduce the binding of OPG to RANKL and TRAIL, and these changes could increase osteo-inductive VSMC differentiation, especially vascular mineralization reflected by increased ALP activity during vascular calcification.

The influence of the telomere-telomerase system on diabetes mellitus and its vascular complications

INTRODUCTION

The telomere-telomerase system plays an important role in the pathogenesis and disease progression of diabetes mellitus as well as in its vascular complications. Recent studies suggest that telomere shortening and abnormal telomerase activity occur in patients with diabetes mellitus, and targeting the telomere-telomerase system has become a prospective treatment for diabetes mellitus and its vascular complications. This review highlights the significance of the telomere-telomerase system and supports its role as a possible therapeutic target for patients with diabetes mellitus and its vascular complications Areas covered: This review covers the advances in understanding the telomere-telomerase system over the last 30 years and its significance in diabetes mellitus. In addition, it provides knowledge regarding the significance of the telomere-telomerase system in diabetes mellitus and its vascular complications as well as its role and mechanisms in oxidative stress, cell therapy and antioxidant activity Expert opinion: The telomere-telomerase system may be a potential therapeutic target that can protect against DNA damage and apoptosis in patients with diabetes mellitus and its vascular complications. DNA damage and apoptosis are associated with oxidative stress and are involved in the dysfunction of pancreatic β cells, insulin resistance, and its vascular complications. Abnormalities in the telomere-telomerase system may be associated with diabetes mellitus and its vascular complications. Therapies targeting telomere-telomerase system, telomerase reverse transcriptase transfection and alterative telomere lengthening must be identified before gene therapy can commence.

Osteoprotegerin in Cardiometabolic Disorders

Osteoprotegerin (OPG), a glycoprotein traditionally implicated in bone remodelling, has been recently related to cardiovascular disease (CVD). Human studies show a positive relationship between circulating OPG, vascular damage, and CVD, and as such OPG has emerged as a potential biomarker for CVD. This review focuses on the relationship between circulating OPG and different endocrine cardiometabolic alterations such as type 1 and 2 diabetes. The association of OPG with diabetic complications (neuropathy, nephropathy, or retinopathy) as well as with atherosclerosis, coronary artery calcification, morbidity, and mortality is pointed out. Moreover, OPG modulation by different treatments is also established. Besides, other associated diseases such as obesity, hypertension, and metabolic syndrome, which are known cardiovascular risk factors, are also considered.

Role of osteoprotegerin and its gene polymorphisms in the occurrence of left ventricular hypertrophy in essential hypertensive patients

The aim of the study was to investigate the role of osteoprotegerin (OPG) in left ventricular hypertrophy (LVH) development in patients with essential hypertension (EH). A total of 1092 patients diagnosed with EH were recruited. The LVHs were determined and OPG gene polymorphisms were genotyped. Patients with LVH had a significantly higher mean serum OPG level than those without LVH. The 1181CC genotype carriers had significantly lower risk for LVH compared with GC and GG genotype carriers. The serum OPG level and OPG 1181 G>C polymorphism were found to be independent risk factors for the occurrence of LVH in hypertensive patients. In vitro study shows that OPG overexpression upregulates cell surface size, protein synthesis per cell, and hypertrophy- and fibrosis-related proteins in both cardiomyocytes and cardiac fibroblasts, whereas OPG inhibition can abolish the above-mentioned changes. Consistent with the in vitro data, our in vivo study revealed that the OPG administration induced the LVH in hypertensive rats. This study is the first to report the close association between OPG and LVH development in EH patients and the regulatory effect of OPG on cardiomyocytes and cardiac fibroblasts.

TNFRSF11B gene polymorphisms increased risk of peripheral arterial occlusive disease and critical limb ischemia in patients with type 2 diabetes

AIMS

Osteoprotegerin (OPG) is a secretory glycoprotein that belongs to the tumor necrosis factor receptor family and plays a role in atherosclerosis. OPG has been hypothesized to modulate vascular functions; however, its role in mediating atherosclerosis is controversial. Epidemiological data in patients with cardiovascular disease (CVD) indicate that OPG serum levels are associated with several inflammatory markers, myocardial infarction events, and calcium scores, suggesting that OPG may be causative for CVD.

METHODS

The present study aimed to evaluate whether the OPG gene (TNFRSF11B) polymorphisms are involved in the development of peripheral arterial occlusive disease (PAOD) and critical limb ischemia (CLI) in patients with type 2 diabetes. This genetic association study included 402 diabetic patients (139 males and 263 females) with peripheral arterial occlusive disease and 567 diabetic subjects without peripheral arterial occlusive disease (208 males and 359 females). The T245G, T950C, and G1181C polymorphisms of the OPG gene were analyzed by polymerase chain reaction and restriction fragment length polymorphism.

RESULTS

We found that the T245G, T950C, and G1181C gene polymorphisms of the OPG gene were significantly (27.9 vs. 12.2 %, P < 0.01; 33.6 vs. 10.4 %, P < 0.01 and 24.4 vs. 12.7 %, P < 0.01, respectively) and independently (adjusted OR 4.97 (3.12-6.91), OR 7.02 (4.96-11.67), and OR 2.85 (1.95-4.02), respectively) associated with PAOD. We also found that these three polymorphisms act synergistically in patients with PAOD and are associated with different levels of risk for PAOD and CLI, depending on the number of high-risk genotypes carried concomitantly by a given individual.

CONCLUSION

The TNFRSF11B gene polymorphisms under study are associated with PAOD, and synergistic effects between these genotypes might be potential markers for the presence and severity of atherosclerotic disorders.

No relationship between osteoprotegerin concentrations and endothelial dysfunction in non-obese women with and without polycystic ovary syndrome

PURPOSE

To investigate the relationships of osteoprotegerin (OPG) concentrations to brachial artery flow-mediated vasodilation (FMD) and the carotid artery intima media thickness (CIMT) in polycystic ovary syndrome (PCOS).

METHODS

Thirty-seven women with PCOS and 41 controls matched for body mass index (BMI) and age were included in study. The serum OPG concentrations, hormonal and metabolic profiles were measured in women with PCOS and in control group. The CIMT and brachial artery FMD were evaluated in both groups.

RESULTS

The mean serum concentrations of all hormones were comparable, except LH, which was higher in women with PCOS. Lipid parameters were similar between groups. There were no differences between groups with respect to fasting glucose, 2-h glucose, fasting insulin, HbA1c and HOMA-IR. The mean osteoprotogerin concentrations were higher in PCOS group (11.39 ± 2.29 vs. 10.22 ± 2.25 pmol/L, P = 0.026). The mean CIMT was higher in PCOS group than control group (0.52 ± 0.058 vs. 0.45 ± 0.059 mm, P < 0.01). The mean brachial artery FMD was lower in PCOS group (0.068 ± 0.022 vs. 0.055 ± 0.029, P = 0.017).

CONCLUSIONS

We found high osteoprotogerin concentrations, increased CIMT and decreased FMD, in women with PCOS. However, there was no correlation between osteoprotegerin and cardiovascular risk markers.

Osteoprotegerin increases in metabolic syndrome and promotes adipose tissue proinflammatory changes

BACKGROUND

Inflammation is believed to link obesity to insulin resistance, as in the setting of metabolic syndrome (MetS). Osteoprotegerin (OPG) is a soluble protein that seems to exert proatherogenic and prodiabetogenic effects. This study aims at determining OPG levels in MetS and whether OPG might contribute to MetS development and progression.

METHODOLOGY/PRINCIPAL FINDINGS

Circulating OPG was measured in 46 patients with MetS and 63 controls, and was found significantly elevated in those with MetS. In addition, circulating and tissue OPG was significantly increased in high-fat diet (HFD) fed C57BL6 mice, which is one of the animal models for the study of MetS. To evaluate the consequences of OPG elevation, we delivered this protein to C57BL6 mice, finding that it promoted systemic and adipose tissue proinflammatory changes in association with metabolic abnormalities.

CONCLUSIONS/SIGNIFICANCE

These data suggest that OPG may trigger adipose tissue proinflammatory changes in MetS/HFD-induced obesity.

The osteoprotegerin/tumor necrosis factor related apoptosis-inducing ligand axis in the kidney

PURPOSE OF REVIEW

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a cytokine belonging to the TNF superfamily. TRAIL may modulate cell survival and proliferation through interaction with two different receptors, TRAIL-R1 and TRAIL-R2. The actions of TRAIL are regulated by three decoy receptors, TRAIL-R3, TRAIL-R4 and osteoprotegerin (OPG). There is evidence that both TRAIL and OPG are expressed by renal cells. The OPG/TRAIL axis has been recently linked to the pathogenesis of renal damage and, in particular, diabetic nephropathy.

RECENT FINDINGS

In patients with kidney diseases, serum TRAIL and OPG levels are increased in parallel and are significantly associated with each other. In diabetic nephropathy, the renal expression of TRAIL and OPG is elevated, and in tubular cells proinflammatory cytokines enhance TRAIL expression. Additionally, a high-glucose microenvironment sensitizes tubular cells to apoptosis induced by TRAIL, whereas OPG counteracts the actions of TRAIL in cultured cells.

SUMMARY

It seems that the expression and levels of TRAIL and OPG at serum and kidney levels are crucial for the pathogenesis of kidney diseases, and in particular diabetic nephropathy. Although further studies are necessary to clarify the exact role of the OPG/TRAIL axis in the kidney, this system seems to hold promise to provide therapeutic approaches for the management of renal damage.

VIDEO ABSTRACT AVAILABLE

See the Video Supplementary Digital Content 1 (http://links.lww.com/CONH/A5).

Prediction of subclinical atherosclerosis by serum osteoprotegerin in premenopausal women with systemic lupus erythematous: correlation of osteoprotegerin with monocyte chemotactic protein-1

Objective

Patients with systemic lupus erythematosus (SLE) have increased risk for cardiovascular disease. Previous studies disclosed the association of serum osteoprotegerin (OPG) with the presence of symptomatic atherosclerosis in the general population and several disease conditions. We thus investigated the association between serum OPG levels and subclinical atherosclerosis in premenopausal SLE patients.

Methods

Serum OPG levels and carotid artery intima-media thickness (IMT) were measured in 181 premenopausal SLE patients and age-matched 85 control subjects. Traditional cardiovascular risk factors and SLE-related factors were analyzed.

Results

Patients with SLE had significantly increased serum OPG levels (1086 versus 517 pg/ml, p < 0.001) and carotid IMT (0.63 versus 0.45 mm, p < 0.001) compared with control subjects. Carotid IMT significantly increased across the quartiles of OPG. Logistic regression analysis revealed that compared to the lowest OPG quartile, the odds ratio (OR, 95% confidence interval) for increased carotid IMT in quartile 2, 3, and 4 was 1.126 (1.013–1.801), 1.562 (1.268–2.799), and 4.460 (1.126–7.128), respectively, after multiple adjustments ( p for trend across quartiles < 0.001). These associations remained significant after further adjustment for inflammatory parameters. Interestingly, serum monocyte chemotactic protein-1 (MCP-1) levels were positively correlated with serum OPG levels (γ = 0.332, p < 0.001). Parallel analysis showed that serum MCP-1 was also an independent predictor of carotid IMT incrassation, but this association was lost when serum OPG was included in the model.

Conclusion

Serum OPG levels were increased and correlated with serum MCP-1 levels in premenopausal SLE patients. Increased serum OPG was independently associated with subclinical atherosclerosis in these patients.

The worrisome liaison between left ventricular systolic dysfunction and mitral annulus calcification in type 2 diabetes without coronary artery disease: data from the SHORTWAVE study

BACKGROUND AND AIM

Mitral annulus calcification (MAC) is a marker for coronary artery disease (CAD) and predicts poor outcome in the general population. No data are available on MAC in patients with type 2 diabetes. In these patients we assessed prevalence of MAC and the relation between MAC and left ventricular (LV) systolic function.

METHODS AND RESULTS

As many as 386 patients with type 2 diabetes without CAD were studied with Doppler echocardiography. LV systolic dysfunction was defined by analyzing 120 healthy subjects. Stress-corrected midwall shortening (sc-MS) and mitral annular peak systolic velocity (peak S') were considered as indexes of LV circumferential and longitudinal shortening and classified low if <89% and <8.5 cm/s, respectively (10th percentiles of controls). Patients who had MAC (107 = 28%) were older with longer duration of DM and were receiving more anti-hypertension medications than those who had not. At echocardiographic evaluation patients with MAC showed higher LV mass, larger left atrial volume (LAV), reduced sc-MS (88.4 ± 14.9 vs 92.6 ± 14.3%; p = 0.01) and peak S' (8.9 ± 2.2 vs 10.0 ± 2.0 cm/s; p < 0.001) than patients without MAC. Multiple logistic regression demonstrated older age (OR 1.03 [IC 1.01-1.06], p = 0.009), larger LAV (OR 1.19 [IC 1.11-1.28], p < 0.001) and combined reduction in sc-MS and peak S' (OR 3.00 [IC 1.57-5.72], p = 0.001) as independent factors associated with MAC.

CONCLUSIONS

MAC is detectable in one fourth of patients with type 2 diabetes without CAD and is mostly related to LV systolic dysfunction expressed as combined impairment of LV circumferential and longitudinal fibers, independent of age and LAV.

Osteoprotegerin promotes the proliferation of chondrocytes and affects the expression of ADAMTS-5 and TIMP-4 through MEK/ERK signaling

The involvement of osteoprotegerin (OPG) in bone metabolism has previously been established; however, whether OPG regulates chondrocytes directly and exerts precise cellular and molecular effects on chondrocytes remains to be determined. Thus, the present study aimed to investigate the direct effect of OPG on the viability, proliferation and functional consequences of chondrocytes. Primary chondrocytes were isolated from the knee of Sprague-Dawley rats. Passage 1 chondrocytes were identified by toluidine blue staining and used in the experiments. The cell proliferation induced by OPG at various concentrations was measured by a Cell Counting kit-8 (CCK-8) assay. Following pretreatment with mitogen-activated/extracellular signal-regulated kinase kinase (MEK) inhibitor U0126, extracellular signal-regulated kinase (ERK) inhibitor PD098059, and P38 mitogen-activated protein kinase (P38MAPK) inhibitor SB203580 for 30 min, chondrocytes were treated with OPG, and CCK-8 was performed. The cellular signals of MAPKs, including ERK, P38MAPK and c-Jun N-terminal protein kinase (JNK), were investigated by western blot analysis following treatment with OPG. The functional consequences following treatment with soluble OPG were analyzed by qPCR and western blot analysis. OPG increased chondrocyte proliferation with maximal effect at 10 ng/ml, and induced the phosphorylation of MEK and ERK but not P38MAPK or JNK. Suppression of ERK activity via PD098095 inhibited OPG-induced chondrocyte proliferation. Administration of OPG significantly downregulated ADAMTS‑5 and upregulated tissue inhibitor of metalloproteinase (TIMP)-4 production, but had no effect on the expression of TIMP-1, -2 and -3, insulin-like growth factor I, transforming growth factor-β, basic fibroblast growth factor, bone morphogenetic protein-2, collagen II, aggrecan and ADAMTS-4. Suppression of ERK activity via PD098095 inhibited the alteration of ADAMTS-5 and TIMP-4 expression induced by OPG. OPG therefore regulated the proliferation of chondrocytes via MEK/ERK signaling, and directly affected chondrocytes by influencing the expression profile of ADAMTS-5 and TIMP-4.

Osteoprotegerin causes apoptosis of endothelial progenitor cells by induction of oxidative stress

OBJECTIVE

Elevated serum osteoprotegerin (OPG) levels represent an independent risk factor for atherosclerotic disease, although the underlying mechanism is not clear. The aim of this study was to investigate the association of serum OPG levels and circulating endothelial progenitor cell (EPC) numbers, and to explore the effect of OPG on EPC apoptosis and its underlying mechanisms.

METHODS

Flow cytometry was used to enumerate EPCs in the peripheral blood of 91 patients with systemic lupus erythematosus (SLE). Cultured EPCs, isolated from peripheral blood, were challenged with OPG, and apoptosis was evaluated by TUNEL staining. Expression of apoptosis-related proteins was measured by real-time quantitative polymerase chain reaction (qPCR) and Western blotting. Reactive oxygen species (ROS) were detected by flow cytometry, and the expression of NADPH oxidase (NOX) and MAP kinases (MAPK) was measured by qPCR and Western blotting.

RESULTS

The serum OPG level was independently associated with reduced numbers of EPCs in patients with SLE. In vitro treatment with OPG significantly induced apoptosis of EPCs; this effect was mediated by syndecan 4. OPG-induced apoptosis was abolished by the ROS scavenger N-acetylcysteine and the NOX inhibitor diphenyleniodonium. OPG increased ROS production through activation of NOX-2 and NOX-4 and triggered phosphorylation of ERK-1/2 and p38 MAPK. Quenching of ROS by knockdown of NOX-2 or NOX-4 transcripts inhibited phosphorylation of ERK-1/2 and p38 MAPK. Moreover, inhibitors of ERK-1/2 and p38 MAPK decreased ROS production and subsequent EPC apoptosis, indicating a feed-forward loop between NOX and MAPK to amplify ROS production related to apoptosis.

CONCLUSION

Elevated OPG levels increase apoptosis of EPCs by induction of oxidative stress.

Proper design of silica nanoparticles combines high brightness, lack of cytotoxicity and efficient cell endocytosis

Silica-based luminescent nanoparticles (SiNPs) show promising prospects in nanomedicine in light of their chemical properties and versatility. In this study, we have characterized silica core-PEG shell SiNPs derivatized with PEG moieties (NP-PEG), with external amino- (NP-PEG-amino) or carboxy-groups (NP-PEG-carbo), both in cell cultures as well as in animal models. By using different techniques, we could demonstrate that these SiNPs were safe and did not exhibit appreciable cytotoxicity in different relevant cell models, of normal or cancer cell types, growing either in suspension (JVM-2 leukemic cell line and primary normal peripheral blood mononuclear cells) or in adherence (human hepatocarcinoma Huh7 and umbilical vein endothelial cells). Moreover, by multiparametric flow cytometry, we could demonstrate that the highest efficiency of cell uptake and entry was observed with NP-PEG-amino, with a stable persistence of the fluorescence signal associated with SiNPs in the loaded cell populations both in vitro and in vivo settings suggesting this as an innovative method for cell traceability and detection in whole organisms. Finally, experiments performed with the endocytosis inhibitor Genistein clearly suggested the involvement of a caveolae-mediated pathway in SiNP endocytosis. Overall, these data support the safe use of these SiNPs for diagnostic and therapeutic applications.

Osteoprotegerin is an independent predictor of vascular events in Finnish adults with type 1 diabetes

OBJECTIVE

Osteoprotegerin (OPG) is involved in the process of vascular calcification. We investigated whether OPG is associated with the development and progression of diabetes complications in adults with type 1 diabetes (T1D).

RESEARCH DESIGN AND METHODS

Serum OPG was measured in 1,939 adults with T1D participating in the Finnish Diabetic Nephropathy (FinnDiane) Study. Patients with end-stage renal disease (dialysis or transplantation) at baseline were excluded from analysis. Data on cardiovascular (CV) events and mortality during follow-up were verified from hospital discharge registries (ICD codes) and the Finnish National Death Registry, respectively. The follow-up time was 10.4 ± 2.0 (mean ± SD) years.

RESULTS

Only patients with macroalbuminuria and/or renal impairment had elevated OPG concentrations, when compared with participants without overt kidney disease. Patients with retinopathy or CV disease also had higher OPG concentrations, but this was attributable to their higher frequency of chronic kidney disease. OPG predicted an incident CV event (hazard ratio 1.21 [95% CI 1.01-1.45]; P = 0.035) and peripheral vascular disease/amputation events (1.46 [1.13-1.88]; P = 0.004) during follow-up.

CONCLUSIONS

We showed that serum OPG is an independent predictor of CV complications. OPG may be directly involved in extraosseous calcification, resulting in stiffening of the arteries and subsequent vascular insufficiency in patients with T1D.

Plasma osteoprotegerin levels increase with the severity of cerebral artery atherosclerosis

OBJECTIVES

Osteoprotegerin (OPG) is a member of the tumor necrosis factor receptor superfamily and suggested as a marker of atherosclerosis. We investigated whether plasma OPG levels were associated with the presence and severity of cerebral atherosclerosis.

DESIGN AND METHODS

We used an enzyme-linked immunosorbent assay to measure the plasma OPG levels of 107 patients with acute cerebral infarction. We compared the plasma OPG levels according to the presence and number of arteries with cerebral atherosclerosis (≥ 50% stenosis).

RESULTS

Of 107 patients, 73 (68.2%) had cerebral atherosclerosis. OPG levels were increased in patients with cerebral atherosclerosis (374.69 ± 206.48 vs 261.17 ± 166.91 pg/mL, p=0.006). OPG levels showed positive correlation with the number of cerebral arteries with atherosclerosis (Spearman's rho=0.342, p<0.001). After adjustment for vascular risk factors, OPG>229.9 pg/mL was independently associated with the presence [OR 4.61, 95% CI 1.57-13.55, p=0.005, binary logistic regression] of cerebral atherosclerosis and number [OR 3.20, 95% CI 1.26-8.12, p=0.014, ordinal logistic regression] of arteries with cerebral atherosclerosis.

CONCLUSIONS

Plasma OPG levels were significantly associated with the presence and severity of cerebral atherosclerosis. This finding suggests that plasma OPG might have a role in cerebral atherosclerosis.

Multimarker Risk Assessment Including Osteoprotegerin and CXCL16 in Acute Coronary Syndromes

Objective—

CXCL16 and osteoprotegerin (OPG) both predict mortality in acute coronary syndromes. We hypothesized that a combination of CXCL16 and OPG concentrations would add prognostic information to the Global Registry of Acute Coronary Events (GRACE) score in patients hospitalized for acute coronary syndromes.

Methods and Results—

We assessed the associations between circulating OPG and soluble CXCL16 levels, obtained within 24 hours of admission (day 1) and after 3 months, and mortality, heart failure and reinfarction in 1322 patients admitted with acute coronary syndromes. After adjustment for the GRACE score, medication, diabetes mellitus and sex, the combination of high values (fourth quartile) for OPG and CXCL16 at baseline was associated with increased short-term (3 months) cardiovascular mortality (hazard ratio, 3.28; 95% CI, 1.84–5.82; P <0.0001). The combined high values were also significantly associated with the long-term (median 91 months) prognosis after adjustment, with hazard ratios 2.18 for cardiovascular mortality (95% CI, 1.62–2.92; P <0.0001), and 2.22 for heart failure (95% CI, 1.67–2.96; P <0.0001). These long-term associations remained significant after further adjustment for left ventricular ejection fraction, C-reactive protein, and pro B-type natriuretic peptide. For 635 patients with blood samples within 24 hours and at 3 months, the combination of high CXCL16 and OPG values (fourth quartile) in the early or stable phase was of a similar order associated with mortality and morbidity beyond 3 months.

Conclusion—

Circulating CXCL16 and OPG are independent predictors of long-term mortality and heart failure development in acute coronary syndromes patients, even after extensive adjustments. Their combination gives more information than either marker alone.

[Update on diabetic macroangiopathy]

Current findings from the literature on the multifactorial genesis of macroangiopathy of diabetes mellitus (DM) were compiled using the PubMed database. The primary aim was to find an explanation for the morphological, immunohistochemical and molecular characteristics of this form of atherosclerosis. The roles of advanced glycation end products (AGE), defective signal transduction and imbalance of matrix metalloproteinases in the increased progression of atherosclerosis in coronary and cerebral arteries as well as peripheral vascular disease are discussed. The restricted formation of collateral arteries (arteriogenesis) in diabetic patients with postischemic lesions is also a focus of attention. The increased level of prothrombotic factors and the role of diabetic neuropathy in DM are also taken into account. Therapeutic influences of AGE-RAGE (receptor of AGE) interactions on the vascular wall and the effects of endothelial progenitor cells in the repair of diabetic vascular lesions are additionally highlighted.

No influence of OPG and its ligands, RANKL and TRAIL, on proliferation and regulation of the calcification process in primary human vascular smooth muscle cells

The aim of this study was to examine the effects of the OPG-RANKL-TRAIL system on proliferation, regulation of calcification-associated genes and calcification of human vascular smooth muscle cells (HVSMCs). Small interfering (si)RNA-mediated knockdown of OPG was followed by treatment of HVSMCs with recombinant RANKL or TRAIL. Regulation of a calcification-associated gene set was assayed by pathway analysis of microarray results. The lack of OPG in HVSMCs or treatment with RANKL or TRAIL did not affect proliferation of HVSMCs. In addition, OPG, RANKL or TRAIL did not modify the regulation of a calcification-associated gene set. Finally, in the long term calcification assay, we found that cells isolated from seven different human donors showed a great variability in the response to RANKL and insulin. However, overall RANKL and/or insulin did not affect the development of calcification of HVSMCs. These studies indicate that OPG knockdown does not alter the calcification process in HVSMCs.

Cell-based therapies for diabetic complications

In recent years, accumulating experimental evidence supports the notion that diabetic patients may greatly benefit from cell-based therapies, which include the use of adult stem and/or progenitor cells. In particular, mesenchymal stem cells and the circulating pool of endothelial progenitor cells have so far been the most studied populations of cells proposed for the treatment of vascular complications affecting diabetic patients. We review the evidence supporting their use in this setting, the therapeutic benefits that these cells have shown so far as well as the challenges that cell-based therapies in diabetic complications put out.

Osteoprotegerin promotes vascular fibrosis via a TGF-β1 autocrine loop

BACKGROUND

This study was designed to evaluate the potential role of osteoprotegerin (OPG) in arterial fibrosis.

METHODS

Aortic samples were analyzed after in vivo treatment of ApoE(-/-) mice with recombinant human OPG. Mouse vascular smooth muscle cells (VSMC) were exposed in vitro to recombinant OPG and analyzed for markers of inflammation and fibrosis, such as fibronectin, collagen I, III, IV and transforming growth factor-β1 (TGF-β1). Conversely, the potential modulation of endogenous OPG expression and release by VSMC was analyzed in response to different pro-atherosclerotic cytokines, TGF-β1, platelet derived growth factor (PDGF) and angiogensin II (Ang II).

RESULTS

In vivo treatment with human OPG induced signs of fibrosis and up-regulated the arterial expression of TGF-β1. Consistently, in vitro treatment of VSMC with human OPG induced the expression of fibronectin, collagen type I, III, IV, metalloprotein-2 (MMP-2) and MMP-9, as well as of TGF-β1. On the other hand, exposure to recombinant TGF-β1 promoted the expression/release of endogenous OPG and mediated the increase of OPG release induced by PDGF and Ang II in VSMC.

CONCLUSIONS

Taken together, these data support a pathogenic role for OPG in the development and progression of atherosclerotic lesions and suggest the existence of a vicious circle between TGF-β1 and OPG.

Crystallizing nanoparticles derived from vascular smooth muscle cells contain the calcification inhibitor osteoprotegerin

Osteoprotegerin (OPG), a member of the TNF receptor superfamily, was initially found to modulate bone mass by blocking osteoclast maturation and function. Rodent models have also revealed a role for OPG as an inhibitor of vascular calcification. However, the precise mode of how OPG blocks mineralization is unclear. In this study, OPG was found in an in vitro assay to significantly inhibit calcification of vascular smooth muscle cells (VSMC) induced by high calcium/phosphate (Ca/P) treatment (p=0.0063), although this effect was blunted at high OPG concentrations. By confocal microscopy, OPG was detected in VSMC in the Golgi, the same localization seen in osteoblasts, which express OPG in bone. Treatment of VSMC by minerals (Ca, P, or both) induced OPG mRNA expression as assessed by real-time quantitative PCR, and VSMC derived from atherosclerotic plaque material also exhibited higher OPG expression as compared to control cells (p<0.05). Furthermore, OPG was detected by Western blotting in matrix vesicles (MV), nanoparticles that are released by VSMC with the capacity to nucleate mineral. In atherosclerotic arteries, OPG colocalized immunohistochemically with annexin VI, a calcium-dependent membrane and phospholipid binding protein found in MV. Thus, the calcification inhibitor OPG is contained in crystallizing MV and has a biphasic effect on VSMC: physiologic concentrations inhibit calcification, whereas high concentrations commonly seen in patients with vascular disease have no effect. Like other calcification inhibitors, OPG may be specifically loaded into these nanoparticles to be deposited at remote sites, where it acts to inhibit calcification.

Circulating osteoprotegerin and soluble receptor activator of nuclear factor κB ligand in polycystic ovary syndrome: relationships to insulin resistance and endothelial dysfunction

OBJECTIVE

There is plenty of evidence that osteoprotegerin (OPG) is linked to subclinical vascular damage and predicts cardiovascular disease in high-risk populations. Our aim is to investigate the relationships of OPG/free soluble receptor activator of nuclear factor κB ligand (sRANKL) to insulin resistance, brachial artery flow-mediated vasodilation (FMD), and the carotid artery intima-media thickness (CIMT) in polycystic ovary syndrome (PCOS), a disorder characterized by hyperandrogenism, impaired glucose control, and endothelial injury.

DESIGN

A cross-sectional, observational study.

METHODS

Hormonal and metabolic profiles, FMD, CIMT, serum OPG, and ampli-sRANKL were assessed in 64 young PCOS patients and 20 controls of similar age. Body composition was measured by dual energy X-ray absorptiometry.

RESULTS

OPG was significantly lower in PCOS and related negatively to free testosterone and positively to estradiol (E(2)) levels. In multivariate analysis, OPG but not ampli-sRANKL correlated positively to fasting insulin, insulin sensitivity indices, and FMD. Neither OPG nor ampli-sRANKL was associated with CIMT. Significantly lower adjusted FMD values were demonstrated in women in the upper OPG quartile group (>2.65 pmol/l) compared with all other quartile groups together (P=0.012). In PCOS, multiple regression analysis retained E(2)/sex hormone-binding globulin ratio, fat mass, and homeostasis model assessment of insulin resistance as independent predictors of OPG.

CONCLUSIONS

In PCOS, circulating OPG is related to both endothelial dysfunction and insulin resistance, independent of obesity and androgen excess, suggesting OPG as a useful biomarker of these effects. Further studies are needed to evaluate OPG in relation to cardiovascular events and cardiovascular mortality in PCOS.