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

Osteoprotegerin (OPG) as a biomarker for diabetic cardiovascular complications

Osteoprotegerin (OPG) is a glycoprotein involved in bone metabolisms and with a regulatory role in immune, skeletal and vascular systems. Recently, circulating OPG levels have emerged as independent biomarkers of cardiovascular disease (CVD) in patients with acute or chronic heart disease, as well as in the healthy population. Furthermore, OPG has been implicated in various inflammations and linked to diabetes and poor glycaemic control. This review focuses on the relations between circulating OPG levels and cardiovascular complications, with special emphasis on diabetic patients. OPG levels were observed to increase concurrently with the severity of diabetic complications, that is, with the highest circulating OPG levels observed in diabetic patients dying from CVD. Although the clinical prognostic use of OPG may seem far away, OPG does look promising as a biomarker in order to help the cardiologist to a better risk-stratification of the patients.

Optimizing bone health and minimizing skeletal morbidity in men with prostate cancer

Maintaining bone health is important in the management of men with prostate cancer. Patients receiving androgen deprivation therapy are at increased risk for treatment-related osteoporosis, and patients with bone metastases are at increased risk for skeletal morbidity related to debilitating skeletal-related events (SREs). Optimizing bone health in these patients includes lifestyle modifications, calcium/vitamin D supplementation, and osteoclast-targeted agents in select high-risk patients. No agent is approved for the prevention of bone metastases. Novel systemic agents have shown a beneficial effect bone by directly affecting tumor growth. Integration of these anticancer agents with osteoclast-targeted agents warrants further investigation.

TRAIL-deficiency accelerates vascular calcification in atherosclerosis via modulation of RANKL

The osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL) cytokine system, not only controls bone homeostasis, but has been implicated in regulating vascular calcification. TNF–related apoptosis-inducing ligand (TRAIL) is a second ligand for OPG, and although its effect in vascular calcification in vitro is controversial, its role in vivo is not yet established. This study aimed to investigate the role of TRAIL in vascular calcification in vitro using vascular smooth muscle cells (VSMCs) isolated from TRAIL^−/− and wild-type mice, as well as in vivo, in advanced atherosclerotic lesions of TRAIL^−/−ApoE^−/− mice. The involvement of OPG and RANKL in this process was also examined. TRAIL dose-dependently inhibited calcium-induced calcification of human VSMCs, while TRAIL^−/− VSMCs demonstrated accelerated calcification induced by multiple concentrations of calcium compared to wild-type cells. Consistent with this, RANKL mRNA was significantly elevated with 24 h calcium treatment, while OPG and TRAIL expression in human VSMCs was inhibited. Brachiocephalic arteries from TRAIL^−/−ApoE^−/− and ApoE^−/− mice fed a high fat diet for 12 w demonstrated increased chondrocyte-like cells in atherosclerotic plaque, as well as increased aortic collagen II mRNA expression in TRAIL^−/−ApoE^−/− mice, with significant increases in calcification observed at 20 w. TRAIL^−/−ApoE^−/− aortas also had significantly elevated RANKL, BMP-2, IL-1β, and PPAR-γ expression at 12 w. Our data provides the first evidence that TRAIL deficiency results in accelerated cartilaginous metaplasia and calcification in atherosclerosis, and that TRAIL plays an important role in the regulation of RANKL and inflammatory markers mediating bone turn over in the vasculature.

Shaping development through mechanical strain: the transcriptional basis of diet-induced phenotypic plasticity in a cichlid fish

Adaptive phenotypic plasticity, the ability of an organism to change its phenotype to match local environments, is increasingly recognized for its contribution to evolution. However, few empirical studies have explored the molecular basis of plastic traits. The East African cichlid fish Astatoreochromis alluaudi displays adaptive phenotypic plasticity in its pharyngeal jaw apparatus, a structure that is widely seen as an evolutionary key innovation that has contributed to the remarkable diversity of cichlid fishes. It has previously been shown that in response to different diets, the pharyngeal jaws change their size, shape and dentition: hard diets induce an adaptive robust molariform tooth phenotype with short jaws and strong internal bone structures, while soft diets induce a gracile papilliform tooth phenotype with elongated jaws and slender internal bone structures. To gain insight into the molecular underpinnings of these adaptations and enable future investigations of the role that phenotypic plasticity plays during the formation of adaptive radiations, the transcriptomes of the two divergent jaw phenotypes were examined. Our study identified a total of 187 genes whose expression differs in response to hard and soft diets, including immediate early genes, extracellular matrix genes and inflammatory factors. Transcriptome results are interpreted in light of expression of candidate genes-markers for tooth size and shape, bone cells and mechanically sensitive pathways. This study opens up new avenues of research at new levels of biological organization into the roles of phenotypic plasticity during speciation and radiation of cichlid fishes.

Intima-media thickness of the carotid arteries is related to serum osteoprotegerin levels in healthy postmenopausal women

Osteoprotegerin (OPG) regulates bone mass by inhibiting osteoclast differentiation and activation, and also plays a role in vascular calcification. The objective of this study was to evaluate the relationship between serum OPG levels, and carotid artery intima-media thickness (IMT) and carotid plaque formation in healthy postmenopausal women. We recruited 68 healthy postmenopausal women for the study. Carotid plaque presence and IMT were evaluated by high resolution B-mode ultrasound. IMT was positively correlated with presence of plaque, age, menopause age and OPG, and inversely correlated with Apolipoprotein A1 (Apo A1). Serum OPG level was positively correlated with IMT (r = 0.366; p < 0.003) and age (r = 0.324; p < 0.008), and negatively correlated with Apo A1 (r = -0.481; p < 0.0001). We did not observe any significant relation between plaque occurrence and levels of serum OPG. In regression analysis OPG (p < 0.02) and menopause age (p < 0.05) were independent risk factors for IMT, and age (p < 0.05) and IMT (p < 0.05) were independent risk factors for plaque formation. Although the role of OPG in the vascular biology is poorly understood, our results suggest that elevated levels of serum OPG is associated with IMT and may play a role in the pathogenesis of atherosclerotic disease.

Osteoprotegerin contributes to the metastatic potential of cells with a dysfunctional TSC2 tumor-suppressor gene

In addition to its effects on bone metabolism, osteoprotegerin (OPG), a soluble member of the tumor necrosis factor family of receptors, promotes smooth muscle cell proliferation and migration and may act as a survival factor for tumor cells. We hypothesized that these cellular mechanisms of OPG may be involved in the growth and proliferation of lymphangioleiomyomatosis (LAM) cells, abnormal smooth muscle-like cells with mutations in one of the tuberous sclerosis complex tumor-suppressor genes (TSC1/TSC2) that cause LAM, a multisystem disease characterized by cystic lung destruction, lymphatic infiltration, and abdominal tumors. Herein, we show that OPG stimulated proliferation of cells cultured from explanted LAM lungs, and selectively induced migration of LAM cells identified by the loss of heterozygosity for TSC2. Consistent with these observations, cells with TSC2 loss of heterozygosity expressed the OPG receptors, receptor activator of NF-κB ligand, syndecan-1, and syndecan-2. LAM lung nodules showed reactivities to antibodies to tumor necrosis factor-related apoptosis-inducing ligand, receptor activator of NF-κB ligand, syndecan-1, and syndecan-2. LAM lung nodules also produced OPG, as shown by expression of OPG mRNA and colocalization of reactivities to anti-OPG and anti-gp100 (HMB45) antibodies in LAM lung nodules. Serum OPG was significantly higher in LAM patients than in normal volunteers. Based on these data, it appears that OPG may have tumor-promoting roles in the pathogenesis of lymphangioleiomyomatosis, perhaps acting as both autocrine and paracrine factors.

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.

The association of insulin resistance with serum osteoprotegerin in obese adolescents

Some data indicate a potential relationship between insulin resistance level and the concentration of osteoprotegerin (OPG) in the body. There have been few studies concerning OPG level and its relationship with insulin resistance and body composition in young people. The aim of this study was to assess serum osteoprotegerin concentration in obese adolescents, and to evaluate its potential association with insulin resistance. Seventy-eight obese adolescents and 20 healthy volunteers aged 12-18 years were recruited in the study. Selected anthropometrical measurements and blood biochemical analyses were performed. Insulin resistance in the participants was evaluated according to the homeostasis model assessment-insulin resistance (HOMA-IR) protocol. Level of OPG was assessed in serum. Obese subjects had significantly higher HOMA-IR indices and OPG levels in serum than the control group. A significant positive correlation between OPG and insulin resistance was found. It was observed that high concentrations of osteoprotegerin are associated with insulin resistance in obese adolescents.

Effect of compressive force on human osteoblast-like cells and bone remodelling: an in vitro study

OBJECTIVE

The aim of this study was to determine the effect of continuous compressive force (CF) on expression by human alveolar bone-derived osteoblasts (HOBs) of some specific molecules involved in bone remodelling.

DESIGN

HOBs were cultured with or without CF (control, 2.0, 4.0gcm(-2)) for 1, 3 and 7 days. Expression of alkaline phosphatase (ALP), type I collagen (Col I), osteopontin (OPN), osteocalcin (OCN), transcription factor Runx2, receptor activator of nuclear factor κB ligand (RANKL), osteoprotegerin (OPG) and prostaglandin E2 (PGE2) was analysed by real-time-polymerase chain reaction (RT-PCR), enzyme-linked immunosorbent assay (ELISA) and/or immunostaining.

RESULTS

The results revealed that CF upregulated ALP and Col I expression at both messenger RNA (mRNA) and protein levels but did not affect expression of OPN and OCN mRNA. Runx2 mRNA was inhibited by CF, which also altered the expression of molecules involved in osteoclastogenesis, by enhancing RANKL expression and suppressing OPG expression. At 4.0gcm(-2) of CF, the expression of RANKL and PGE2 was significantly upregulated.

CONCLUSION

The results suggest that initial application of CF on HOBs can simultaneously affect expression of markers related to both osteogenesis and osteoclastogenesis.

Association of salivary levels of the bone remodelling regulators sRANKL and OPG with periodontal clinical status

AIM

To determine the variations in salivary concentrations of sRANKL, osteoprotegerin (OPG) and its ratio, regarding the periodontal status.

MATERIALS AND METHODS

Ninety-seven chronic periodontitis (CP) subjects and 43 healthy controls were selected. Periodontal status was assessed based on full-mouth clinical periodontal measurements. sRANKL and OPG salivary levels were analysed by ELISA. The association between these analytes and its ratio with CP was analysed individually and adjusted for confounding using a binary logistic regression model.

RESULTS

sRANKL and sRANKL/OPG ratio were increased, whereas OPG was decreased in CP compared with healthy controls subjects. Although univariate analysis revealed a positive association of sRANKL salivary levels ≥6 pg/ml, OPG salivary levels ≤131 pg/ml and sRANKL/OPG ratio ≥0.062 with CP, after logistic regression analysis only the latter parameter was strongly and independently associated with disease status. Confounding and interaction effects of ageing and smoking habit on sRANKL and OPG levels could be noted.

CONCLUSION

Although salivary concentrations of sRANKL, OPG and its ratio may act as indicators of the amount/extent of periodontal breakdown, the mutual confounding and synergistic biological interactive effects related to ageing and smoking habit of the susceptible host may also promote the tissue destruction in CP.

Osteoclast migration, differentiation and function: novel therapeutic targets for rheumatic diseases

RA is a chronic autoimmune disease characterized by joint synovial inflammation and progressive cartilage/bone destruction. Although various kinds of RA drug have been developed worldwide, there are currently no established methods for preventing RA-associated bone destruction, the most severe outcome of this disease. One of the major pathogenic factors in arthritic bone destruction is the enhanced activity of osteoclasts at inflammatory sites. Osteoclasts are bone-resorbing giant polykaryons that differentiate from mononuclear macrophage/monocyte-lineage haematopoietic precursors. Upon stimulation by cytokines, such as M-CSF and RANK ligand, osteoclast precursor monocytes migrate and attach onto the bone surface (migration). They then fuse with each other to form giant cells (differentiation) and mediate bone resorption (function). In this review, we summarize the current understanding regarding the mechanisms underlying these three dynamic steps of osteoclastic activity and discuss novel lines of osteoclast-targeted therapies that will impact future treatment of RA.

Effect of gender, season, and vitamin D status on bone biochemical markers in Saudi diabetes patients

Biochemical bone turnover markers (BTMs) provide important information on the diagnosis, therapy and monitoring of metabolic bone diseases. They are evident before measurable changes in bone mineral density (BMD) take place. A total of 35 adult Saudi patients (23 males; 12 females) with type 2 diabetes and diagnosed to be vitamin D deficient were recruited in this prospective study. Here we investigated the effects of gender, season, and vitamin D status on bone biochemical markers of bone remodeling. Anthropometry and blood samples were collected at different intervals. Metabolic parameters and bone biomarkers were measured routinely and by ELISA. Both males and females had a significant increase in their vitamin D status over time, but no significant changes in the bone biomarkers were observed in females. In males there was a significant increase in circulating levels of corrected calcium and OPN (p = 0.004 and 0.01 respectively) and a significant decrease in crosslaps (p = 0.005). In all subjects there was a modest but significant positive relationship between vitamin D status and OC (R = 0.34; p = 0.04). In conclusion, our study demonstrates that changes in bone remodeling markers are affected by season, gender, and possibly vitamin D status. This gender difference may well reflect the physiologic pathway responsible for the higher peak bone mass achieved in males compared to females.

Amelogenesis imperfecta and other biomineralization defects in Fam20a and Fam20c null mice

The FAM20 family of secreted proteins consists of three members (FAM20A, FAM20B, and FAM20C) recently linked to developmental disorders suggesting roles for FAM20 proteins in modulating biomineralization processes. The authors report here findings in knockout mice having null mutations affecting each of the three FAM20 proteins. Both Fam20a and Fam20c null mice survived to adulthood and showed biomineralization defects. Fam20b (-/-) embryos showed severe stunting and increased mortality at E13.5, although early lethality precluded detailed investigations. Physiologic calcification or biomineralization of extracellular matrices is a normal process in the development and functioning of various tissues (eg, bones and teeth). The lesions that developed in teeth, bones, or blood vessels after functional deletion of either Fam20a or Fam20c support a significant role for their encoded proteins in modulating biomineralization processes. Severe amelogenesis imperfecta (AI) was present in both Fam20a and Fam20c null mice. In addition, Fam20a (-/-) mice developed disseminated calcifications of muscular arteries and intrapulmonary calcifications, similar to those of fetuin-A deficient mice, although they were normocalcemic and normophosphatemic, with normal dentin and bone. Fam20a gene expression was detected in ameloblasts, odontoblasts, and the parathyroid gland, with local and systemic effects suggesting both local and/or systemic effects for FAM20A. In contrast, Fam20c (-/-) mice lacked ectopic calcifications but were severely hypophosphatemic and developed notable lesions in both dentin and bone to accompany the AI. The bone and dentin lesions, plus the marked hypophosphatemia and elevated serum alkaline phosphatase and FGF23 levels, are indicative of autosomal recessive hypophosphatemic rickets/osteomalacia in Fam20c (-/-) mice.

Osteoprotegerin Is Associated With Aneurysm Diameter and Proteolysis in Abdominal Aortic Aneurysm Disease

Objective—

Serum osteoprotegerin (OPG) concentrations have previously been associated with growth of abdominal aortic aneurysms (AAAs). In vitro experiments showed that OPG promotes matrix metalloprotease (MMP) release from monocytes and vascular smooth muscle cells. We hypothesized that OPG expression is increased in human AAAs and is associated with proteolysis.

Methods and Results—

AAA biopsies were collected from 329 patients. We assessed the concentrations of OPG, cathepsins A, B, and S as well as the activity of MMP-2 and MMP-9. The AAA wall infiltration by macrophages, lymphocytes, and plasma cells was estimated by immunohistochemistry. The concentration of OPG correlated positively with aortic diameter (<55 mm: 16.1 [5.8–28.7], 55–70 mm: 21.9 [10.2–36.0], >70 mm: 24.0 [13.5–52.9] ng OPG/mg total amount of protein, P =0.020), cathepsin A ( r =0.221, P =0.005), B ( r =0.384, P <0.001), and S ( r =0.467, P<0.001), MMP-2 ( r =0.180, P <0.001), MMP-9 ( r =0.178, P<0.001), and the number of lymphocytes ( P <0.001) and plasma cells ( P =0.001). OPG immunostaining was predominantly demonstrated in plasma cells.

Conclusion—

The concentration of aortic wall OPG is positively associated with established markers of AAA severity and pathogenesis. OPG appeared to be associated with lymphocytes and plasma cells. These human data support previous experimental data suggesting a role for OPG in AAA pathogenesis.

Osteoprotegerin as a marker of atherosclerosis: a systematic update

OBJECTIVE

Osteoprotegerin (OPG) may be involved in development of atherosclerosis. To evaluate plasma concentrations of OPG in individuals with stable coronary artery disease (CAD), acute coronary syndrome (ACS), peripheral artery disease (PAD), and cerebrovascular disease (CBVD) a systematic literature review was performed.

DESIGN AND METHODS

Studies investigating OPG concentrations in stable CAD, ACS, PAD, and CBVD were extracted from PubMed and the Cochrane Library, retrieving 280 articles. Nonrelevant articles were excluded and after thorough evaluation, and only 14 studies with clearly defined cohorts qualified for this review.

RESULTS

In 11 studies, OPG concentrations were elevated. Severity of atherosclerosis was significantly associated with higher OPG concentrations compared to healthy controls. No association between PAD and OPG concentrations was observed.

CONCLUSION

OPG concentrations are associated with the presence and severity of stable CAD, ACS, and CBVD. Larger studies are needed to reach conclusions concerning OPG concentrations in PAD. Studies addressing a putative role for OPG in suspected CAD and CBVD are warranted.

Osteoprotegerin is associated with cardiovascular risk in hypertension and/or diabetes

BACKGROUND

Osteoprotegerin (OPG), a secreted member of the tumour necrosis factor receptor superfamily of cytokines, has been associated with endothelial dysfunction. We studied in type 2 diabetic and/or hypertensive patients the relationship between serum OPG and vascular alterations associated with these pathologies.

MATERIALS AND METHODS

We analysed 191 consecutive patients (52 with type 2 diabetes and 139 hypertensive nondiabetic patients) and 54 healthy controls. We assessed the relationship of OPG serum levels measured by ELISA with basal glycaemia, glycosylated haemoglobin, blood pressure, endothelial dysfunction (assessed by pulse wave velocity), retinopathy (by Keith-Wagener classification), left ventricular hypertrophy (by Cornell index), cardiovascular risk and target organs (heart, vascular, kidney) damage.

RESULTS

Serum OPG levels were higher in either hypertensive or diabetic patients and in patients with non-dipper and riser circadian blood pressure patterns. We found significant correlations between OPG levels and age, height, glycaemia, systolic, diastolic and pulse blood pressure, pulse wave velocity and left ventricular hypertrophy in both hypertensive and diabetic patients. OPG levels were also higher in hypertensive patients with retinopathy, patients with high probability of 10-year cardiovascular risk, patients with three or more damaged target organs (heart, vessels, kidneys) and patients with previous episodes of ischaemic cardiopathy or hypercholesterolaemia.

CONCLUSIONS

Osteoprotegerin is an indicator of diabetes- and hypertension-associated vascular pathologies as endothelial dysfunction and cardiovascular risk.

Role of the OPG/RANK/RANKL triad in calcifications of the atheromatous plaques: comparison between carotid and femoral beds

Recent works demonstrated the difference of calcification genesis between carotid and femoral plaques, femoral plaques being more calcified. It has been clearly demonstrated that the molecular triad osteoprotegerin (OPG)/Receptor Activator of NFkB (RANK)/RANK Ligand (RANKL) exerts its activities in the osteoimmunology and vascular system. The aim of this study was to determine their expression and their potential role in calcifications of the atheromatous plaques located in two different peripheral arterial beds, carotid and femoral. The expression of OPG, RANK and RANKL was analyzed by immunochemistry in 40 carotid and femoral samples. Blood OPG and RANKL were quantified using specific ELISA assays. OPG staining was more frequently observed in carotid than in femoral plaques, especially in lipid core. Its expression correlated with macrophage infiltration more abundantly observed in carotid specimens. Surprisingly, serum OPG concentration was significantly lower in carotid population compared to femoral population while RANK and RANKL were equally expressed in both arterial beds. Carotid plaques that are less rich in calcium than femoral specimens, express more frequently OPG, this expression being correlated with the abundance of macrophages in the lesions. These data strengthen the key role played by OPG in the differential calcification in carotid and femoral plaques.

Effect of Ultra-marathon (308 km) Race on Bone Metabolism and Cartilage Damage Biomarkers

Objective

To evaluate the potential effects of a 308-km ultra-marathon on bone and cartilage biomarkers.

Method

Venous blood samples were collected at pre-race, 100 km, 200 km, and 308 km checkpoints. The following markers of cartilage damage and bone metabolism were studied: osteocalcin (OC), osteoprotegerin (OPG), and calcium, phosphorous, and cartilage oligomeric matrix protein (COMP).

Results

Blood samples were taken from 20 male runners at four different checkpoints. Serum COMP was increased by 194.1% (130.7% at 100 km and 160.4% at 200 km). Serum OPG was significantly increased by 158.57% at 100 km and 114.1% at 200 km compared to the pre-race measures. OC was transiently suppressed at 200 km. Serum calcium and phosphorous concentrations decreased compared to the pre-race measures.

Conclusion

This study showed that the 308-km ultra-marathon induced several changes, including transient uncoupling of bone metabolism, increased bone resorption, suppressed bone formation, and bone turnover and had a major impact on cartilage structure.

RANKL-mediated osteoclast formation from murine RAW 264.7 cells

Extensive research efforts over the years have provided us with great insights into how bone-resorbing osteoclasts (OCs) develop and function and, based on such work, valuable antiresorptive therapies have been developed to help combat the excessive bone loss that occurs in numerous skeletal disorders. The RAW 264.7 murine cell line has proven to be an important tool for in vitro studies of OC formation and function, having particular advantages over the use of OCs generated from primary bone marrow cell populations or directly isolated from murine bones. These include their ready access and availability, simple culture for this pure macrophage/pre-OC population, sensitive and rapid development into highly bone-resorptive OCs expressing hallmark OC characteristics following their RANKL stimulation, abundance of RAW cell-derived OCs that can be generated to provide large amounts of study material, relative ease of transfection for genetic and regulatory manipulation, and close correlation in characteristics, gene expression, signaling, and developmental or functional processes between RAW cell-derived OCs and OCs either directly isolated from murine bones or formed in vitro from primary bone marrow precursor cells. Here, we describe methods for the culture and RANKL-mediated differentiation of RAW cells into bone-resorptive OCs as well as procedures for their enrichment, characterization, and general use in diverse analytical assays.

Leptin is an independent determinant of bone mineral density in men with type 2 diabetes mellitus

To investigate the possible relationship of leptin to bone mineral density (BMD) in men with type 2 diabetes mellitus (T2DM), we screened 168 Belarusian men aged 45-65 years. Plasma total cholesterol (TC), high-density lipoprotein cholesterol, and triglyceride concentrations were assessed, and low-density lipoprotein cholesterol and very low-density lipoprotein cholesterol (LDL-C) were calculated. Hemoglobin A(1c), immune-reactive insulin (IRI), serum total testosterone, and sex hormone-binding globulin were also evaluated. BMD was evaluated using dual-energy X-ray absorptiometry. By univariate linear regression analysis, BMD was significantly correlated with body mass index (r = 0.23, P = 0.002) and leptin (r = 0.21, P = 0.006). By multivariate regression analysis adjusting for confounding factors, log leptin was independently correlated with BMD (β = 0.058, P = 0.001). Our study revealed that leptin is an independent determinant of BMD in patients with T2DM. Further research is necessary to confirm this association and to develop ways to correct abnormalities of bone metabolism in patients with T2DM.

The foot in type 2 diabetes: is there a link between vascular calcification and bone mineral density?

AIMS

To examine the relationship between vascular calcification in the foot (FVC) and bone mineral density (BMD) in the heel of type 2 diabetes mellitus (DM) subjects.

METHODS

65 subjects with type 2 DM and serum creatinine<125 μmol/l underwent CT scanning of the foot to assess FVC and dual energy X ray absorptiometry (DEXA) scan to assess heel BMD. Routine biochemistry including osteoprotegerin (OPG) and Receptor activator of nuclear factor kappa-B ligand (RANKL) was also carried out.

RESULTS

The proportion of subjects with FVC was 43%, whilst 40% had low BMD (T score<-1.0). Age, neuropathy and 25 hydroxyvitamin D were independent predictors of FVC. Body-weight, eGFR, 25 hydroxyvitamin D, OPG, and total cholesterol were independent predictors of low heel BMD. There was no correlation between albuminuria and BMD or FVC. There was no difference in heel BMD between those with FVC and those without, but those with frank osteoporosis were significantly more likely to have FVC than those with higher BMD.

CONCLUSIONS

There is no clear-cut association between FVC and low BMD in type 2 DM with relatively well-preserved renal function. Age, neuropathy, eGFR, hyperlipidemia, body-weight, 25 hydroxyvitamin D and OPG play a complex role in their pathogenesis.

Lipoic acid increases the expression of genes involved in bone formation in mice fed a high-fat diet

Antioxidant lipoic acid (LA) has been reported to have a potential prophylactic effect on bone loss induced by high-fat diet (HFD). The aim of this work was to examine the hypothesis that LA decreases bone resorption-related gene expression and increases bone formation-related gene expression in HFD-fed mice, preventing a shift in the bone metabolism balance toward resorption. Male C57BL/6 mice were fed a normal diet, HFD, or HFD plus 0.1% LA for 12 weeks. The bone metabolism-related genes differentially expressed between mice fed HFD and those fed HFD supplemented with LA were identified through complementary DNA microarray. The supplemental LA significantly increased bone mineral density and bone antioxidant capacity in mice fed HFD (P < .05). Compared with the HFD-fed mice, LA induced the decreased expression of genes associated with bone resorption, such as Mmp9 (1.9-fold) and Ctsk (2.3-fold), and increased those genes associated with bone formation, such as Col1a1 (1.3-fold) and Alp1 (1.5-fold). Furthermore, LA upregulated many genes involved in the Igf signaling pathway, such as Igf-1 (increased 1.7-fold), and downregulated genes involved in the p53 apoptotic pathway, such as p53 (decreased 2.3-fold), thus attenuating the HFD-induced inhibition of bone formation. Lipoic acid induced upregulation of Il12a (2.1-fold) and downregulation of Tgfbr1 (4.3-fold) and Il17a (11.3-fold), which may reduce bone resorption. In summary, LA supplementation during HFD could affect bone density, altering gene expression.

The RANKL/RANK/OPG signaling pathway mediates medial arterial calcification in diabetic Charcot neuroarthropathy

OBJECTIVE

The receptor activator of nuclear factor-κB (RANK), RANK ligand (RANKL), and osteoprotegerin (OPG) signaling pathway (RANKL/RANK/OPG signaling) is implicated in the osteolysis associated with diabetic Charcot neuroarthropathy (CN); however, the links with medial arterial calcification (MAC) seen in people with CN are unclear. This study aimed to investigate the role of RANKL/OPG in MAC in patients with CN.

RESEARCH DESIGN AND METHODS

Enzyme-linked immunosorbent assay and Bio-plex multiarray technology were used to quantify a range of cytokines, including RANKL and OPG in sera from 10 patients with diabetes, 12 patients with CN, and 5 healthy volunteers. Human tibial artery segments were immunohistochemically stained with Alizarin red and human RANKL antibody. Human vascular smooth muscle cells (VSMCs) were also explanted from arterial segments for in vitro studies.

RESULTS

We demonstrate colocalization and upregulation of RANKL expression in areas displaying MAC. Systemic levels of RANKL, OPG, and inflammatory cytokines (interleukin-8, granulocyte colony-stimulating factor) were elevated in those with CN compared with diabetic patients and healthy control subjects. Human VSMCs cultured in CN serum showed accelerated osteoblastic differentiation (alkaline phosphatase activity) and mineralization (alizarin red staining) compared with cells treated with diabetic or control serum (P < 0.05). Coincubation with OPG, the decoy receptor for RANKL, attenuated osteogenic differentiation of VSMCs and was independent of a high calcium-phosphate milieu. The accelerated mineralization induced by RANKL and CN serum correlated with nuclear translocation of nuclear factor-κB, a process abrogated by OPG.

CONCLUSIONS

Our data provide direct evidence that RANKL/RANK/OPG signaling is modulated in patients with CN and plays a role in vascular calcification. This study highlights this pathway as a potential target for intervention.

Association of plasma osteoprotegerin and adiponectin with arterial function, cardiac function and metabolism in asymptomatic type 2 diabetic men

BACKGROUND

Osteoprotegerin (OPG), a soluble member of the tumor necrosis factor receptor superfamily, is linked to cardiovascular disease. Negative associations exist between circulating OPG and cardiac function. The adipocytokine adiponectin (ADPN) is downregulated in type 2 diabetes mellitus (T2DM) and coronary artery disease and shows an inverse correlation with insulin sensitivity and cardiovascular disease risk. We assessed the relationship of plasma OPG and ADPN and arterial function, cardiac function and myocardial glucose metabolism in T2DM.

METHODS

We included 78 asymptomatic men with uncomplicated, well-controlled T2DM, without inducible ischemia, assessed by dobutamine-stress echocardiography, and 14 age-matched controls. Cardiac function was measured by magnetic resonance imaging, myocardial glucose metabolism (MMRglu) by 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography. OPG and ADPN levels were measured in plasma.

RESULTS

T2DM patients vs. controls showed lower aortic distensibility, left ventricular (LV) volumes, impaired LV diastolic function and MMRglu (all P < 0.05). In T2DM men vs. controls, OPG levels were higher (P = 0.02), whereas ADPN concentrations were decreased (P = 0.04). OPG correlated inversely with aortic distensibility, LV volumes and E/A ratio (diastolic function), and positively with LV mass/volume ratio (all P < 0.05). Regression analyses showed the associations with aortic distensibility and LV mass/volume ratio to be independent of age-, blood pressure- and glycated hemoglobin (HbA1c). However, the associations with LV volumes and E/A ratio were dependent of these parameters. ADPN correlated positively with MMRglu (P < 0.05), which, in multiple regression analysis, was dependent of whole-body insulin sensitivity, HbA1c and waist.

CONCLUSIONS

OPG was inversely associated with aortic distensibility, LV volumes and LV diastolic function, while ADPN was positively associated with MMRglu. These findings indicate that in asymptomatic men with uncomplicated T2DM, OPG and ADPN may be markers of underlying mechanisms linking the diabetic state to cardiac abnormalities.

TRIAL REGISTRATION

Current Controlled Trials ISRCTN53177482.

Future of anticathepsin K drugs: dual therapy for skeletal disease and atherosclerosis?

BACKGROUND

Until fairly recently, cathepsin K was recognized solely as a bone-resorbing enzyme expressed selectively in the osteoclast. Evidence of its requirement for normal bone remodeling has resulted in this protease receiving considerable attention from the pharmaceutical industry. In the last decade, intense research efforts were aimed at development of cathepsin K inhibitors for treatment of osteoporosis and other skeletal disorders associated with pathological bone loss. Emerging new evidence suggests that in addition to bone resorption, cathepsin K is involved in the turnover of extracellular matrix proteins in organs, such as the lung, thyroid and skin, and plays important roles in cardiovascular disease, inflammation and obesity.

DISCUSSION

This review highlights the physiological and pathophysiological implications of this potent protease, with a focus on recent developments in the design and use of cathepsin K inhibitors to target skeletal pathologies. Therapeutic implications of anticathepsin K drugs in the context of common links between bone disease and atherosclerosis are also discussed.

CONCLUSION

The association of cathepsin K with skeletal and cardiovascular disorders offers intriguing future applications for inhibitors of this potent protease.

Increased levels of bone remodeling biomarkers (osteoprotegerin and osteopontin) in hypertensive individuals

OBJECTIVES

Osteoprotegerin (OPG) and osteopontin (OPN) are bone metabolism biomarkers which are involved in the regulation of vascular calcification processes and prediction of future adverse cardiac events.

DESIGN AND METHODS

OPG, OPN levels and classic risk factors were determined in 130 asymptomatic and hypertensive subjects. Receiver operator characteristic (ROC) analysis was performed and the area under the curve (AUC) was calculated.

RESULTS

The hypertensive subjects had elevated OPG, OPN, fibrinogen, CRP and fasting glucose levels in comparison to the normotensive ones. There were significant correlations between age, CRP and OPG. Multiple regression analysis showed that as well as inflammation (CRP), age and hypertension were predictors of increased OPG levels. OPN increase was correlated with CRP and glucose levels. The AUCs were similar for OPG and OPG biomarkers.

CONCLUSIONS

Plasma OPG and OPN levels were significantly associated with inflammation and arterial hypertension. They might be useful as additional biomarkers for monitoring endothelial dysfunction and prognosis of cardiovascular diseases.

Relationship between serum osteoprotegerin, glycemic control, renal function and markers of atherosclerosis in type 2 diabetes

We aimed to investigate the relationship between serum osteoprotegerin (OPG) level and glycemic control, lipids, renal function, microalbuminuria, insulin resistance and markers of atherosclerosis including C-reactive protein (CRP), fibrinogen and erythrocyte sedimentation rate (ESR) in patients with type 2 diabetes mellitus (DM). A total of 166 patients (99 women and 67 men) with type 2 DM were recruited in the study. Serum OPG level was higher in poorly controlled diabetic patients (HbA(1c) ≥ 7%) than in well-controlled diabetic patients (HbA(1c) < 7%) [4.0 (3.6-5.0) and 3.5 (2.9-4.4) pmol/L, p = 0.02]. There was no difference between the patients with and without microalbuminuria with respect to OPG levels (p > 0.05). LogOPG was correlated with age (r = 0.47, p = 0.0001). After adjustment for age, sex and BMI, logOPG correlated positively with fasting blood glucose (FBG) (r = 0.28, p = 0.001), prandial blood glucose (PBG) (r = 0.22, p = 0.009), glycated hemoglobin (HbA(1c)) (r = 0.26, p = 0.002), logHOMA-IR (r = 0.30, p = 0.006), fibrinogen (r = 0.17, p = 0.04), mean albumin excretion rate (MAER) (r = 0.20, p = 0.01) and negatively with creatinine clearance (r = - 0.20, p = 0.01). Regression analysis revealed that logOPG was independently associated with age (p = 0.0001), HbA(1c) (p = 0.01) and MAER (p = 0.02) (r(2) = 0.25). In conclusion; we found that serum OPG levels are increased in poorly controlled type 2 DM and associated with age, glycemic control and microalbuminuria.

The role of low-grade inflammation in the polycystic ovary syndrome

PCOS is not only the most frequent cause of oligomenorrhea in young women, but also a metabolic disorder characterized by insulin resistance, glucose intolerance, dyslipidemia, and obesity, especially the visceral phenotype. PCOS represents a broad spectrum of endocrine and metabolic alterations which change with age and with increasing adiposity. In fact, during adolescence and youth the predominant clinical manifestations of PCOS are menstrual abnormalities, hirsutism and acne, whereas in peri-menopausal and post-menopausal periods metabolic disorders and an increased risk for cardiovascular diseases prevail. The pathogenetic links between PCOS and metabolic or cardiovascular complications are still debated. However, recent evidence has been focused on a condition of low-grade chronic inflammation as a potential cause of the long-term consequence of the syndrome. In this review we describe the state of low-grade inflammation observed in PCOS. In addition, we hypothesize the potential mechanisms responsible for the generation of this inflammatory state and the role played by low-grade inflammation in linking hyperandrogenism and insulin resistance with the metabolic and cardiovascular long-term complications of the syndrome.

Arterial calcifications

Arterial calcifications as found with various imaging techniques, like plain X-ray, computed tomography or ultrasound are associated with increased cardiovascular risk. The prevalence of arterial calcification increases with age and is stimulated by several common cardiovascular risk factors. In this review, the clinical importance of arterial calcification and the currently known proteins involved are discussed. Arterial calcification is the result of a complex interplay between stimulating (bone morphogenetic protein type 2 [BMP-2], RANKL) and inhibitory (matrix Gla protein, BMP-7, osteoprotegerin, fetuin-A, osteopontin) proteins. Vascular calcification is especially prevalent and related to adverse outcome in patients with renal insufficiency and diabetes mellitus. We address the special circumstances and mechanisms in these patient groups. Treatment and prevention of arterial calcification is possible by the use of specific drugs. However, it remains to be proven that reduction of vascular calcification in itself leads to a reduced cardiovascular risk.

The effect of polyunsaturated fatty acids on bone health

The essential polyunsaturated fatty acids (PUFAs) are divided into two classes, n-3 (ω-3) and n-6 (ω-6) and their dietary precursors are α-linolenic (ALA) and linoleic acid (LA), respectively. PUFAs are precursors of a wide range of metabolites, for example eicosanoids like prostaglandins and leukotrienes, which play critical roles in the regulation of a variety of biological processes, including bone metabolism.

A large body of evidence supports an effect of PUFA on bone metabolism which may be mediated by regulation of osteoblastogenesis and osteoclast activity, change of membrane function, decrease in inflammatory cytokines, such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumour necrosis factor alpha (TNF-α), modulation of peroxisome proliferators-activated receptor γ (PPARγ) and influence in NO secretion and NO synthase.

Animal studies have shown that a higher dietary omega-3/omega-6 fatty acids ratio is associated with beneficial effects on bone health. Human studies conducted in elderly subjects suggest that omega-3 instead of omega-6 has a positive effect on bone metabolism. In spite of increasing evidence, studies conducted in humans do not allow us to draw a definitive conclusion on the usefulness of PUFAs in clinical practice.

Treated Hypertension has No Influence on the Efficacy of Alendronate in the Therapy of Postmenopausal Osteoporosis: A Non-Randomized, Non-Blind, Controlled Prospective Study

Changes in hormone metabolism during menopause are involved in the development of osteoporosis and arterial hypertension. A mutual influence of these two clinical pictures is evident on the basis of pathophysiological factors.In this study, we investigated whether a drug therapy of hypertension influences the efficacy of a bisphosphonate (alendronate) in the treatment of postmenopausal osteoporosis. For this purpose, 60 female patients were enrolled in the study, 30 of them on drug treatment for hypertension in addition to requiring treatment for osteoporosis, while the control group was only suffering from osteoporosis.Bone density was measured at the start of the study and 6 months after therapy (QCT).A significant increase in bone density was demonstrated in both groups, while a difference between the groups could not be seen.Treated arterial hypertension does not have a negative influence on the treatment of postmenopausal osteoporosis with alendronate. Rather, the concomitant treatment of these two clinical pictures would appear to make sense, in order to reduce morbidity and mortality.

Low serum osteoprotegerin levels in normoalbuminuric type 1 diabetes mellitus

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