Role of osteoprotegerin and its ligands and competing receptors in atherosclerotic calcification

Efficacy and safety of denosumab treatment for Korean patients with Stage 3b-4 chronic kidney disease and osteoporosis

BACKGROUND/AIMS

We evaluated the efficacy and safety of denosumab treatment in severe chronic kidney disease (CKD) patients with osteoporosis. We also investigated whether the treatment affects the coronary artery calcifications.

METHODS

Twenty-seven postmenopausal women with Stage 3b-4 CKD and osteoporosis were enrolled. Twenty patients received denosumab plus calcium carbonate and vitamin D, and seven controls received calcium carbonate and vitamin D for 1 year. Dual-energy X-ray absorptiometry and coronary artery calcium (CAC) scoring computed tomography were performed before and after treatment. Hypocalcemic symptoms and serum calcium levels were evaluated.

RESULTS

After 1 year of treatment, the percent changes of femur neck (3.6 ± 3.2% vs. -0.7 ± 4.4%, p = 0.033) and total hip (3.4 ± 3.8% vs. -1.9 ± 2.1%, p = 0.001) bone mineral density (BMD) were significantly increased in the denosumab treated group compared to the control group. However, the percent change of lumbar spine BMD did not differ between two groups (5.6 ± 5.9% vs. 2.7 ± 3.9%, p = 0.273). The percent change of bone alkaline phosphatase was significantly different in the denosumab-treated group and control group (-31.1 ± 30.0% vs. 0.5 ± 32.0%, p = 0.027). CAC scores did not differ between groups. No hypocalcemic events occurred in both groups.

CONCLUSION

If carefully monitored and supplemented with calcium and vitamin D, denosumab treatment for 1 year provides significant benefits in patients with Stage 3b-4 CKD and osteoporosis. However, denosumab treatment did not affect coronary artery calcifications in these patients.

Cellular Senescence, Aging and Non-Aging Processes in Calcified Aortic Valve Stenosis: From Bench-Side to Bedside

Aortic valve stenosis (AS) is the most common valvular heart disease. The incidence of AS increases with age, however, a significant proportion of elderly people have no significant AS, indicating that both aging and nonaging pathways are involved in the pathomechanism of AS. Age-related and stress-induced cellular senescence accompanied by further active processes represent the key elements of AS pathomechanism. The early stage of aortic valve degeneration involves dysfunction and disruption of the valvular endothelium due to cellular senescence and mechanical stress on blood flow. These cells are replaced by circulating progenitor cells, but in an age-dependent decelerating manner. When endothelial denudation is no longer replaced by progenitor cells, the path opens for focal lipid deposition, initiating subsequent oxidation, inflammation and micromineralisation. Later stages of AS feature a complex active process with extracellular matrix remodeling, fibrosis and calcification. Echocardiography is the gold standard method for diagnosing aortic valve disease, although computed tomography and cardiac magnetic resonance are useful additional imaging methods. To date, no medical treatment has been proven to halt the progression of AS. Elucidation of differences and similarities between vascular and valvular calcification pathomechanisms may help to find effective medical therapy and reduce the increasing health burden of the disease.

The Novel gem-Dihydroperoxide 12AC3O Suppresses High Phosphate-Induced Calcification via Antioxidant Effects in p53LMAco1 Smooth Muscle Cells

The excessive intake of phosphate (Pi), or chronic kidney disease (CKD), can cause hyperphosphatemia and eventually lead to ectopic calcification, resulting in cerebrovascular diseases. It has been reported that reactive oxygen species (ROS), induced by high concentrations of Pi loading, play a key role in vascular calcification. Therefore, ROS suppression may be a useful treatment strategy for vascular calcification. 12AC3O is a newly synthesized gem-dihydroperoxide (DHP) that has potent antioxidant effects. In the present study, we investigated whether 12AC3O inhibited vascular calcification via its antioxidative capacity. To examine whether 12AC3O prevents vascular calcification under high Pi conditions, we performed Alizarin red and von Kossa staining, using the mouse aortic smooth muscle cell line p53LMAco1. Additionally, the effect of 12AC3O against oxidative stress, induced by high concentrations of Pi loading, was investigated using redox- sensitive dyes. Further, the direct trapping effect of 12AC3O on reactive oxygen species (ROS) was investigated by ESR analysis. Although high concentrations of Pi loading exacerbated vascular smooth muscle calcification, calcium deposition was suppressed by the treatment of both antioxidants and 12AC3O, suggesting that the suppression of ROS may be a candidate therapeutic approach for treating vascular calcification induced by high concentrations of Pi loading. Importantly, 12AC3O also attenuated oxidative stress. Furthermore, 12AC3O directly trapped superoxide anion and hydroxyl radical. These results suggest that ROS are closely involved in high concentrations of Pi-induced vascular calcification and that 12AC3O inhibits vascular calcification by directly trapping ROS.

Nϵ-Carboxymethyl-Lysine Deteriorates Vascular Calcification in Diabetic Atherosclerosis Induced by Vascular Smooth Muscle Cell-Derived Foam Cells

Nϵ-carboxymethyl-lysine (CML), an advanced glycation end product, is involved in vascular calcification (VC) in diabetic atherosclerosis. This study aimed to investigate the effects of CML on VC in diabetic atherosclerosis induced by vascular smooth muscle cell (VSMC)–derived foam cells. Human studies, animal studies and cell studies were performed. The human study results from 100 patients revealed a poor blood glucose and lipid status and more severe coronary lesions and stenosis in patients with coronary artery disease and diabetes mellitus. Intraperitoneal injection of streptozotocin combined with a high-fat diet was used to build a diabetic atherosclerosis model in ApoE^−/− mice. The animal study results indicated that CML accelerated VC progression in diabetic atherosclerosis by accelerating the accumulation of VSMC-derived foam cells in ApoE^−/− mice. The cell study results illustrated that CML induced VSMC-derived foam cells apoptosis and aggravated foam cells calcification. Consistent with this finding, calcium content and the expression levels of alkaline phosphatase, bone morphogenetic protein 2 and runt-related transcription factor 2 were significantly elevated in A7r5 cells treated with oxidation-low-density lipoprotein and CML. Thus, we concluded that CML promoted VSMC-derived foam cells calcification to aggravate VC in diabetic atherosclerosis, providing evidence for the contribution of foam cells to diabetic VC.

Aortic Valve Stenosis: From Basic Mechanisms to Novel Therapeutic Targets

Aortic valve stenosis is the most prevalent heart valve disease worldwide. Although interventional treatment options have rapidly improved in recent years, symptomatic aortic valve stenosis is still associated with high morbidity and mortality. Calcific aortic valve stenosis is characterized by a progressive fibro-calcific remodeling and thickening of the aortic valve cusps, which subsequently leads to valve obstruction. The underlying pathophysiology is complex and involves endothelial dysfunction, immune cell infiltration, myofibroblastic and osteoblastic differentiation, and, subsequently, calcification. To date, no pharmacotherapy has been established to prevent aortic valve calcification. However, novel promising therapeutic targets have been recently identified. This review summarizes the current knowledge of pathomechanisms involved in aortic valve calcification and points out novel treatment strategies.

A GTPase-activating protein-binding protein (G3BP1)/antiviral protein relay conveys arteriosclerotic Wnt signals in aortic smooth muscle cells

In aortic vascular smooth muscle (VSM), the canonical Wnt receptor LRP6 inhibits protein arginine (Arg) methylation, a new component of noncanonical Wnt signaling that stimulates nuclear factor of activated T cells (viz NFATc4). To better understand how methylation mediates these actions, MS was performed on VSM cell extracts from control and LRP6-deficient mice. LRP6-dependent Arg methylation was regulated on >500 proteins; only 21 exhibited increased monomethylation (MMA) with concomitant reductions in dimethylation. G3BP1, a known regulator of arteriosclerosis, exhibited a >30-fold increase in MMA in its C-terminal domain. Co-transfection studies confirm that G3BP1 (G3BP is Ras-GAP SH3 domain-binding protein) methylation is inhibited by LRP6 and that G3BP1 stimulates NFATc4 transcription. NFATc4 association with VSM osteopontin (OPN) and alkaline phosphatase (TNAP) chromatin was increased with LRP6 deficiency and reduced with G3BP1 deficiency. G3BP1 activation of NFATc4 mapped to G3BP1 domains supporting interactions with RIG-I (retinoic acid inducible gene I), a stimulus for mitochondrial antiviral signaling (MAVS) that drives cardiovascular calcification in humans when mutated in Singleton-Merten syndrome (SGMRT2). Gain-of-function SGMRT2/RIG-I mutants increased G3BP1 methylation and synergized with osteogenic transcription factors (Runx2 and NFATc4). A chemical antagonist of G3BP, C108 (C108 is 2-hydroxybenzoic acid, 2-[1-(2-hydroxyphenyl)ethylidene]hydrazide CAS 15533-09-2), down-regulated RIG-I-stimulated G3BP1 methylation, Wnt/NFAT signaling, VSM TNAP activity, and calcification. G3BP1 deficiency reduced RIG-I protein levels and VSM osteogenic programs. Like G3BP1 and RIG-I deficiency, MAVS deficiency reduced VSM osteogenic signals, including TNAP activity and Wnt5-dependent nuclear NFATc4 levels. Aortic calcium accumulation is decreased in MAVS-deficient LDLR^-/- mice fed arteriosclerotic diets. The G3BP1/RIG-I/MAVS relay is a component of Wnt signaling. Targeting this relay may help mitigate arteriosclerosis.

Deletion of a Distal RANKL Gene Enhancer Delays Progression of Atherosclerotic Plaque Calcification in Hypercholesterolemic Mice

Receptor activator of NF-κB ligand (RANKL) is a TNF-like cytokine which mediates diverse physiological functions including bone remodeling and immune regulation. RANKL has been identified in atherosclerotic lesions; however, its role in atherosclerotic plaque development remains elusive. An enhancer located 75 kb upstream of the murine Rankl gene's transcription start site designated D5 is important for its calciotropic hormone- and cytokine-mediated expression. Here, we determined the impact of RANKL levels in atherosclerotic plaque development in the D5 enhancer-null (D5^-/- ) mice in an atherogenic Apoe^-/- background fed a high-fat diet (HFD). Rankl mRNA transcripts were increased in aortic arches and thoracic aortae of Apoe^-/- mice; however, this increase was blunted in Apoe^-/- ;D5^-/- mice. Similarly, higher Rankl transcripts were identified in splenic T lymphocytes in Apoe^-/- mice, and their levels were reduced in Apoe^-/- ;D5^-/- mice. When analyzed by micro-computed tomography (µCT), atherosclerotic plaque calcification was identified in six out of eight Apoe^-/- mice, whereas only one out of eight Apoe^-/- ;D5^-/- mice developed plaque calcification after 12 weeks of HFD. However, following 18 weeks of HFD challenge, all of Apoe^-/- and Apoe^-/- ;D5^-/- animals developed atherosclerotic plaque calcification. Likewise, atherosclerotic lesion sizes were site-specifically reduced in the aortic arch of Apoe^-/- ;D5^-/- mice at initial stage of atherosclerosis and this effect was diminished as atherosclerosis proceeded to a more advanced stage. Our data suggest that deletion of the RANKL D5 enhancer delays the progression of atherosclerotic plaque development and plaque calcification in hypercholesterolemic mice. This work provides important insight into RANKL's regulatory role in atherosclerosis. J. Cell. Biochem. 118: 4240-4253, 2017. © 2017 Wiley Periodicals, Inc.

Understanding the structural features of symptomatic calcific aortic valve stenosis: A broad-spectrum clinico-pathologic study in 236 consecutive surgical cases

BACKGROUND

With age, aortic valve cusps undergo varying degrees of sclerosis which, sometimes, can progress to calcific aortic valve stenosis (AVS). To perform a retrospective clinico-pathologic investigation in patients with calcific AVS.

METHODS

We characterized and graded the structural remodeling in 236 aortic valves (200 tricuspid and 36 bicuspid) from patients with calcific AVS (148 males; average 72years); possible relationships between general/clinical/echocardiographic characteristics and the histopathologic changes were explored. Twenty autopsy aortic valves served as controls. In 40 cases, we also tested the immunohistochemical expression of metalloproteinases and cytokines, and characterized the inflammatory infiltrate. In 5 cases, we cultured cusp stem cells and explored their potential to differentiate into osteoblasts/adipocytes.

RESULTS

AVS cusps showed structural remodeling as severe fibrosis (100%), calcific nodules (100%), neoangiogenesis (81%), inflammation (71%), bone metaplasia with or without hematopoiesis (6% and 53%, respectively), adipose metaplasia (16%), and cartilaginous metaplasia (7%). At multivariate analysis, AVS degree and interventricular septum thickness were the only predictors of remodeling (barring inflammation). All the tested metalloproteinases (except MMP-13) and cytokines were expressed in AVS cusps. Inflammation mainly consisted of B and T lymphocytes (CD4+/CD8+ cell ratio 3:1) and plasma cells. AVS changes were mostly different from typical atherosclerosis. Cultured mesenchymal cusp stem cells could differentiate into osteoblasts/adipocytes.

CONCLUSIONS

Structural remodeling in AVS is peculiar and considerable, and is related to the severity of the disease. However, the different newly formed tissues-where "valvular interstitial cells" play a key role-and their well-known slow turnover suggest a reverse structural remodeling improbable.

The effects of insulin and liraglutide on osteoprotegerin and vascular calcification in vitro and in patients with type 2 diabetes

OBJECTIVE

Vascular calcification (VC) is inhibited by the glycoprotein osteoprotegerin (OPG). It is unclear whether treatments for type 2 diabetes are capable of promoting or inhibiting VC. The present study examined the effects of insulin and liraglutide on i) the production of OPG and ii) the emergence of VC, both in vitro in human aortic smooth muscle cells (HASMCs) and in vivo in type 2 diabetes.

DESIGN/METHODS

HASMCs were exposed to insulin glargine or liraglutide, after which OPG production, alkaline phosphatase (ALP) activity and levels of Runx2, ALP and bone sialoprotein (BSP) mRNA were measured. A prospective, nonrandomised human subject study was also conducted, in which OPG levels and coronary artery calcification (CAC) were measured in a type 2 diabetes population before and 16 months after the commencement of either insulin or liraglutide treatment and in a control group that took oral hypoglycemics only.

RESULTS

Exposure to insulin glargine, but not liraglutide, was associated with significantly decreased OPG production (11 913±1409 pg/10(4) cells vs 282±13 pg/10(4) cells, control vs 10 nmol/l insulin, P<0.0001), increased ALP activity (0.82±0.06 IU/10(4) cells vs 2.40±0.16 IU/10(4) cells, control vs 10 nmol/l insulin, P<0.0001) and increased osteogenic gene expression by HASMCs. In the clinical study (n=101), insulin treatment was associated with a significant reduction in OPG levels and, despite not achieving full statistical significance, a trend towards increased CAC in patients.

CONCLUSION

Exogenous insulin down-regulated OPG in vitro and in vivo and promoted VC in vitro. Although neither insulin nor liraglutide significantly affected CAC in the present pilot study, these data support the establishment of randomised trials to investigate medications and VC in diabetes.

Carotid atherosclerosis is not associated with lower bone mineral density and vertebral fractures in patients with systemic lupus erythematosus

Background

Low bone mineral density (BMD) and vertebral fractures (VF) have been associated with atherosclerosis in the general population. We sought to investigate the relationship between BMD and VF and carotid atherosclerosis in women with systemic lupus erythematosus (SLE).

Methods

We studied 122 women with SLE. All patients had BMD, carotid intima-media thickness (IMT), and carotid artery atherosclerotic plaque assessment by ultrasound.

Results

Mean age at study entry was 44 years and mean disease duration was 11 years. Carotid plaque was found in 13 (11%) patients (9 postmenopausal and 4 premenopausal). Patients in the highest IMT quartile were more likely to be older ( p = 0.001), have a higher body mass index ( p = 0.008), and exhibit dyslipidemia at study entry ( p = 0.041), compared with the lower three quartiles. BMD at the lumbar spine was lower in patients in the highest IMT quartile compared with the lower quartiles in the multivariate logistic analysis, however, there was no association between lumbar or total hip BMD and IMT ( p = 0.91 and p = 0.6, respectively). IMT measurements did not differ according to the presence or absence of VF (0.08 ± 0.12 vs. 0.06 ± 0.03 mm, p = 0.11). A trend towards higher incidence of VF was found in patients with carotid plaque compared with those without (33% vs. 21%; p = 0.2).

Conclusions

In patients with SLE, the presence of carotid atherosclerosis is not associated with low BMD or VF.

TWEAK/Fn14 Axis: A Promising Target for the Treatment of Cardiovascular Diseases

Cardiovascular diseases (CVD) are the first cause of mortality in Western countries. CVD include several pathologies such as coronary heart disease, stroke or cerebrovascular accident, congestive heart failure, peripheral arterial disease, and aortic aneurysm, among others. Interaction between members of the tumor necrosis factor (TNF) superfamily and their receptors elicits several biological actions that could participate in CVD. TNF-like weak inducer of apoptosis (TWEAK) and its functional receptor and fibroblast growth factor-inducible molecule 14 (Fn14) are two proteins belonging to the TNF superfamily that activate NF-κB by both canonical and non-canonical pathways and regulate several cell functions such as proliferation, migration, differentiation, cell death, inflammation, and angiogenesis. TWEAK/Fn14 axis plays a beneficial role in tissue repair after acute injury. However, persistent TWEAK/Fn14 activation mediated by blocking experiments or overexpression experiments in animal models has shown an important role of this axis in the pathological remodeling underlying CVD. In this review, we summarize the role of TWEAK/Fn14 pathway in the development of CVD, focusing on atherosclerosis and stroke and the molecular mechanisms by which TWEAK/Fn14 interaction participates in these pathologies. We also review the role of the soluble form of TWEAK as a biomarker for the diagnosis and prognosis of CVD. Finally, we highlight the results obtained with other members of the TNF superfamily that also activate canonical and non-canonical NF-κB pathway.

Oxidized low density lipoprotein increases RANKL level in human vascular cells. Involvement of oxidative stress

Receptor Activator of NFκB Ligand (RANKL) and its decoy receptor osteoprotegerin (OPG) have been shown to play a role not only in bone remodeling but also in inflammation, arterial calcification and atherosclerotic plaque rupture. In human smooth muscle cells, Cu(2+)-oxidized LDL (CuLDL) 10-50 μg/ml increased reactive oxygen species (ROS) and RANKL level in a dose-dependent manner, whereas OPG level was not affected. The lipid extract of CuLDL reproduced the effects of the whole particle. Vivit, an inhibitor of the transcription factor NFAT, reduced the CuLDL-induced increase in RANKL, whereas PKA and NFκB inhibitors were ineffective. LDL oxidized by myeloperoxidase (MPO-LDL), or other pro-oxidant conditions such as ultraviolet A (UVA) irradiation, incubation with H2O2 or with buthionine sulfoximine (BSO), an inhibitor of glutathione synthesis, also induced an oxidative stress and enhanced RANKL level. The increase in RANKL in pro-oxidant conditions was also observed in fibroblasts and endothelial cells. Since RANKL is involved in myocardial inflammation, vascular calcification and plaque rupture, this study highlights a new mechanism whereby OxLDL might, by generation of an oxidative stress, exert a deleterious effect on different cell types of the arterial wall.

Osteoprotegerin inhibits aortic valve calcification and preserves valve function in hypercholesterolemic mice

BACKGROUND

There are no rigorously confirmed effective medical therapies for calcific aortic stenosis. Hypercholesterolemic Ldlr (-/-) Apob (100/100) mice develop calcific aortic stenosis and valvular cardiomyopathy in old age. Osteoprotegerin (OPG) modulates calcification in bone and blood vessels, but its effect on valve calcification and valve function is not known.

OBJECTIVES

To determine the impact of pharmacologic treatment with OPG upon aortic valve calcification and valve function in aortic stenosis-prone hypercholesterolemic Ldlr (-/-) Apob (100/100) mice.

METHODS

Young Ldlr (-/-) Apob (100/100) mice (age 2 months) were fed a Western diet and received exogenous OPG or vehicle (N = 12 each) 3 times per week, until age 8 months. After echocardiographic evaluation of valve function, the aortic valve was evaluated histologically. Older Ldlr (-/-) Apob (100/100) mice were fed a Western diet beginning at age 2 months. OPG or vehicle (N = 12 each) was administered from 6 to 12 months of age, followed by echocardiographic evaluation of valve function, followed by histologic evaluation.

RESULTS

In Young Ldlr (-/-) Apob (100/100) mice, OPG significantly attenuated osteogenic transformation in the aortic valve, but did not affect lipid accumulation. In Older Ldlr (-/-) Apob (100/100) mice, OPG attenuated accumulation of the osteoblast-specific matrix protein osteocalcin by ∼80%, and attenuated aortic valve calcification by ∼ 70%. OPG also attenuated impairment of aortic valve function.

CONCLUSIONS

OPG attenuates pro-calcific processes in the aortic valve, and protects against impairment of aortic valve function in hypercholesterolemic aortic stenosis-prone Ldlr (-/-) Apob (100/100) mice.

The role of osteoprotegerin in cardiovascular disease

Osteoprotegerin (OPG) is a 401 amino acid N-glycosylated protein, which is highly expressed in a large number of tissues. OPG mainly binds to two ligands, i.e. RANKL (receptor activator of nuclear factor κB ligand) and TRAIL (tumor necrosis factor- related apoptosis-inducing ligand). Upon binding to the former ligand, OPG inhibits the activation of osteoclasts and promotes apoptosis of osteoclasts, whereas the binding of OPG with TRAIL prevents apoptosis of tumor cells. There is now emerging evidence that OPG participates in the pathogenesis of atherosclerosis and cardiovascular diseases by amplifying the adverse effects of inflammation and several traditional risk factors such as hyperlipidemia, endothelial dysfunction, diabetes mellitus, and hypertension. Some epidemiological studies also showed a positive association between OPG levels and cardiovascular morbidity and mortality. The aim of this article is to provide an overview of the main biochemical, physiological, and pathological aspects of OPG biology in cardiovascular disease.

Cardiovascular diseases in older patients with osteoporotic hip fracture: prevalence, disturbances in mineral and bone metabolism, and bidirectional links

BACKGROUND

Considerable controversy exists regarding the contribution of mineral/bone metabolism abnormalities to the association between cardiovascular diseases (CVDs) and osteoporotic fractures.

AIMS AND METHODS

To determine the relationships between mineral/bone metabolism biomarkers and CVD in 746 older patients with hip fracture, clinical data were recorded and serum concentrations of parathyroid hormone (PTH), 25-hydroxyvitamin D, calcium, phosphate, magnesium, troponin I, parameters of bone turnover, and renal, liver, and thyroid functions were measured.

RESULTS

CVDs were diagnosed in 472 (63.3%) patients. Vitamin D deficiency was similarly prevalent in patients with (78.0%) and without (82.1%) CVD. The CVD group had significantly higher mean PTH concentrations (7.6 vs 6.0 pmol/L, P < 0.001), a higher prevalence of secondary hyperparathyroidism (SPTH) (PTH > 6.8 pmol/L, 43.0% vs 23.3%, P < 0.001), and excess bone resorption (urinary deoxypyridinoline corrected by creatinine [DPD/Cr] > 7.5 nmol/μmol, 87.9% vs 74.8%, P < 0.001). In multivariate regression analysis, SHPT (odds ratio [OR] 2.6, P = 0.007) and high DPD/Cr (OR 2.8, P = 0.016) were independent indictors of CVD. Compared to those with both PTH and DPD/Cr in the normal range, multivariate-adjusted ORs for the presence of CVD were 17.3 (P = 0.004) in subjects with SHPT and 9.7 (P < 0.001) in patients with high DPD/Cr. CVD was an independent predicator of SHPT (OR 2.8, P = 0.007) and excess DPD/Cr (OR 2.5, P = 0.031). CVD was predictive of postoperative myocardial injury, while SHPT was also an independent predictor of prolonged hospital stay and in-hospital death.

CONCLUSION

SHPT and excess bone resorption are independent pathophysiological mediators underlying the bidirectional associations between CVD and hip fracture, and therefore are important diagnostic and therapeutic targets.

TNFRSF11B gene polymorphisms 1181G > C and 245T > G as well as haplotype CT influence bone mineral density in postmenopausal women

OBJECTIVES

Osteoprotegerin (OPG) inhibits osteoclast function by acting as a decoy receptor for receptor activator of nuclear factor-κB ligand (RANKL), thus being an important candidate gene for osteoporosis. Three recent genome-wide association studies also identified the TNFRSF11B gene, coding for OPG, as playing a key role in bone mineral density (BMD) regulation. As variations in the TNFRSF11B gene could alter the susceptibility to osteoporosis, the aim of study was to investigate association of two TNFRSF11B gene polymorphisms with BMD and serum OPG concentration in postmenopausal women.

STUDY DESIGN

478 postmenopausal women were genotyped for the presence of TNFRSF11B gene polymorphisms 245T > G (rs3134069) and 1181G > C (rs2073618). BMDs and serum OPG concentrations were measured.

RESULTS

Two common haplotypes GT and CT occurred in 41.2% and 52.4% of subjects. In osteoporotic postmenopausal women, lumbar spine BMD was associated with polymorphisms 245T > G and 1181G > C, as well as with CT haplotype (p values 0.013, 0.006 and 0.006, respectively). Additionally, femoral neck BMD showed the association with 245T > G (p = 0.047). No other statistically significant associations with BMD were found for the studied SNPs and haplotypes. No association with serum OPG concentration was shown in any of the studied groups.

CONCLUSIONS

Our results suggest that, in postmenopausal osteoporosis, polymorphisms 245T > G and 1181G > C, as well as haplotype CT in TNFRSF11B gene influence BMD.

The bone-vascular axis in chronic kidney disease

PURPOSE

This review highlights the most recent publications addressing the relationship between bone and vascular calcification in patients with chronic and end-stage kidney disease.

RECENT FINDINGS

The relatively new term 'chronic kidney disease-mineral bone disorder' reflects the growing reach of chronic kidney disease research into the realm of systems physiology, involving a triad of renal, skeletal, and vascular tissues. Recent studies address underlying mechanisms of the bone and vascular complications of chronic kidney disease and point to a variety of biochemical factors, including phosphatonins (fibroblast growth factor-23, matrix extracellular phosphoglycoprotein), bone morphogenetic protein 7, osteoprotegerin, matrix GLA protein, ectonucleotide pyrophosphatase/phosphodiesterase 1, alkaline phosphatase, and lipid oxidation products. Studies also demonstrate that agents used for treatment of one component of the triad often act on the other components of the triad - beneficially or adversely. These findings emphasize the importance of avoiding the subspecialty, single organ viewpoint when treating individual components of chronic kidney disease-mineral bone disorder.

SUMMARY

The consistent synchrony among chronic kidney disease, aortic calcification, and bone loss offers clues to underlying mechanisms for the systemic abnormalities.

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.

Vascular calcification and bone disease: the calcification paradox

Vascular calcification or ectopic mineralization in blood vessels is an active, cell-regulated process, increasingly recognized as a general cardiovascular risk factor. Remarkably, ectopic artery mineralization is frequently accompanied by decreased bone mineral density or disturbed bone turnover. This contradictory association, observed mainly in osteoporosis and chronic kidney disease, is called the 'calcification paradox'. Here, we review recent advances in our understanding of the calcification paradox, including protein expression patterns governing both normal and ectopic mineralization, the conversion of vascular smooth muscle cells to bone-like cells, and the regulatory pathways involved in both bone and vessel mineralization. Further elucidation of the mechanisms underlying the calcification paradox is crucial in order to develop preventive and therapeutic strategies to deal with vascular calcification and reduce the associated cardiovascular risk.

Hemodynamic forces, vascular oxidative stress, and regulation of BMP-2/4 expression

Changes in the hemodynamic environment (e.g., hypertension, disturbed-flow conditions) are known to promote atherogenesis by inducing proinflammatory phenotypic alterations in endothelial and smooth muscle cells; however, the mechanisms underlying mechanosensitive induction of inflammatory gene expression are not completely understood. Bone morphogenetic protein-2 and -4 (BMP-2/4) are TGF-beta superfamily cytokines that are expressed by both endothelial and smooth muscle cells and regulate a number of cellular processes involved in atherogenesis, including vascular calcification and endothelial activation. This review considers how hemodynamic forces regulate BMP-2/4 expression and explores the role of mechanosensitive generation of reactive oxygen species by NAD(P)H oxidases in the control of BMP signaling.

Immunomodulatory and anti-inflammatory effects of chondroitin sulphate

Chondroitin sulphate (CS) is a natural glycosaminoglycan present in the extracellular matrix and is formed by the 1–3 linkage of D-glucuronic acid to N-acetylgalactosamine. In chondrocytes, CS diminishes interleukin-1 p (IL-1p)-induced increases in p38 mitogen-activated protein kinase (p38MAPK) and signal-regulated kinase 1/2 (Erk1/2) phosphorylation, and decreases nuclear factor-KB (NF-kB) nuclear translocation and as a consequence, reduces the formation of pro-inflammatory cytokines, IL-1 p and TNF-a, and pro-inflammatory enzymes, such as phospholipase A2 (PLA2), cyclooxygenase 2 (COX-2) and nitric oxide synthase-2 (NOS-2). The mechanism of action of CS explains its beneficial effect on the cartilage, synovial membrane and subchondral bone. On the other hand, in vivo, CS given orally prevents hepatic NF-κB nuclear translocation, suggesting that systemic CS may elicit an anti-inflammatory effect in many tissues besides the articulation. There is preliminary evidence showing that in human beings, CS may be of benefit in other diseases where inflammation is an essential marker, such as psoriasis and atherosclerosis. The review of the literature suggest that CS might also be of interest for the treatment of other diseases with an inflammatory and/or autoimmune character, such as inflammatory bowel disease, degenerative diseases of the central nervous system and stroke, multiple sclerosis and other autoimmune diseases.

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.

The immune response is involved in atherosclerotic plaque calcification: could the RANKL/RANK/OPG system be a marker of plaque instability?

Atherogenesis is characterized by an intense inflammatory process, involving immune and vascular cells. These cells play a crucial role in all phases of atherosclerotic plaque formation and complication through cytokine, protease, and prothrombotic factor secretion. The accumulation of inflammatory cells and thus high amounts of soluble mediators are responsible for the evolution of some plaques to instable phenotype which may lead to rupture. One condition strongly associated with plaque rupture is calcification, a physiopathological process orchestrated by several soluble factors, including the receptor activator of nuclear factor (NF)κB ligand (RANKL)/receptor activator of nuclear factor (NF)κB (RANK)/osteoprotegerin (OPG) system. Although some studies showed some interesting correlations with acute ischemic events, at present, more evidences are needed to evaluate the predictive and diagnostic value of serum sRANKL and OPG levels for clinical use. The major limitation is probably the poor specificity of these factors for cardiovascular disease. The identification of tissue-specific isoforms could increase the importance of sRANKL and OPG in predicting calcified plaque rupture and the dramatic ischemic consequences in the brain and the heart.

Osteoprotegerin Lys3Asn polymorphism and the risk of fracture in older women

CONTEXT

Osteoprotegerin (OPG) is a soluble decoy receptor for receptor activator nuclear factor kappa-beta that blocks osteoclastic bone resorption.

OBJECTIVE

We investigated the association between a Lys3Asn polymorphism in the OPG gene and bone mineral density (BMD), and the risk of fracture in 6695 women aged 65 yr and older participating in the Study of Osteoporotic Fractures.

DESIGN

BMD was measured using either single-photon absorptiometry (Osteon Osteoanalyzer; Dove Medical Group, Los Angeles, CA) or dual-energy x-ray absorptiometry (Hologic QDR 1000; Hologic, Inc., Bedford, MA). Incident fractures were confirmed by physician adjudication of radiology reports. Genotyping was performed using an immobilized probe-based assay.

RESULTS

Women who were homozygous for the minor G (Lys) allele had significantly lower BMD at the intertrochanter, distal radius, lumbar spine, and calcaneus than those with the C (Asn) allele. There were 701 incident hip fractures during 13.6-yr follow-up (91,249 person-years), including 362 femoral neck and 333 intertrochanteric hip fractures. Women with the C/C (Asn-Asn) genotype had a 51% higher risk of femoral neck fracture (95% confidence interval, 1.13-2.02) and 26% higher risk of hip fracture (95% confidence interval, 1.02-1.54) than those with the G/G (Lys-Lys) genotype. These associations were independent of BMD. Intertrochanteric fractures were not associated with the Lys3Asn polymorphism.

CONCLUSION

These results require confirmation but suggest a role for the OPG Lys3Asn polymorphism in the genetic susceptibility to hip fractures among older white women.

An enhancer 20 kilobases upstream of the human receptor activator of nuclear factor-kappaB ligand gene mediates dominant activation by 1,25-dihydroxyvitamin D3

Receptor activator of nuclear factor-kappaB ligand (RANKL) is a TNF-like factor that is both produced by osteoblasts, mesenchymal cells, and activated T cells and required for osteoclast maturation and survival. The gene is up-regulated by the two primary calcemic hormones, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and PTH. Previous studies have indicated that five enhancer regions located significantly upstream of the mouse Rankl transcriptional start site mediate up-regulation by 1,25(OH)2D3 and PTH. The most distal of these, termed mRLD5, is highly conserved in the human gene at -96 kb where it was also shown to be functionally active. Four additional mouse Rankl upstream enhancers are also highly conserved in the human gene at -20, -25, -75, and -87 kb. In the present studies, we characterized the activity of these regions, explored their capacity to mediate the actions of 1,25(OH)2D3, and identified the vitamin D response elements contained within the two most proximal segments. Interestingly, whereas the most distal of the five enhancers is the dominant mediator of 1,25(OH)2D3 activity in the mouse Rankl gene, that role in the human gene is manifested by the most proximal element at -20 kb. Importantly, activity at this region in response to 1,25(OH)2D3 was associated with a significant increase in histone acetylation as well as the enhanced recruitment of RNA polymerase II. Both likely reflect the primary role of this enhancer in human RANKL gene expression. Our studies confirm the complex nature of RANKL regulation and indicate that although the five enhancers are evolutionarily conserved across several species, their relative contributions to RANKL expression in response to 1,25(OH)2D3 may be different.

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

CONTEXT

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

EVIDENCE ACQUISITION

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

EVIDENCE SYNTHESIS

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

CONCLUSIONS

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

Basic Science for the Clinician 44

There has been a sea change in our understanding of atherosclerosis. We have come a long way from the days where eating too much fat and not getting enough exercise and having the wrong genetic background was thought to be the entire story. A few years ago, the cardiologists began to embrace inflammation as a possible pathogenetic mechanism and from that came high-sensitivity C-reactive protein testing for just about everyone. Chronic systemic inflammation became an area of interest. We have learned that it is more than just corticosteroid use that causes accelerated atherosclerosis in our rheumatoid and lupus patients. Even C-reactive protein may be a pathogenetic player, not only a diagnostic clue. Oxidized phospholipids and the cells that recognize them may be crucial in the evolution of the atherosclerotic plaque. Statins may be useful in suppressing inflammation, not only in suppressing cholesterol levels. And now even cardiologists are thinking about immune mechanisms! A strange world, but the beneficiaries of going through this looking glass will be our patients. A true understanding of this seems to have required a most circuitous route-sometimes you have to leave for a long journey before you can return and really see home for the first time.

Differential expression of TRAIL and its receptors relative to calcification in AAA

Abdominal aortic aneurysm (AAA) is commonly associated with atherosclerosis. Human AAA tissue displays cells undergoing all stages of apoptosis. Tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induces apoptosis in tumour cells but not in normal cells. It has death receptors and decoy receptors. An inhibitor of TRAIL, osteoprotegerin (OPG), is involved in osteogenesis and vascular calcification. We investigated TRAIL and its receptors in AAA compared within normal aorta (NA). Both qualitative and quantitative analyses of calcification in AAA walls were determined using Von Kossa staining and pre-operation computer tomography (CT) scans. There was a significant difference in calcification level at different locations in the AAA wall (p <0.05). Apoptosis was confirmed in AAA by TUNEL assay. A significant difference in TRAIL and its receptor expression was observed between normal aortae and AAA (p<0.05). Significant differences were also observed between tissues displaying different extents of calcification for TRAIL mRNA (p<0.05) by RT-PCR examination and OPG protein (p<0.01) by protein blotting examination. We propose that this pattern of expression of TRAIL and its receptors may contribute to AAA formation and calcification in the AAA wall.