Age-related changes in cortical bone content of insulin-like growth factor binding protein (IGFBP)-3, IGFBP-5, osteoprotegerin, and calcium in postmenopausal osteoporosis: a cross-sectional study

Therapeutic Treatments for Osteoporosis-Which Combination of Pills Is the Best among the Bad?

Osteoporosis is a chronical, systemic skeletal disorder characterized by an increase in bone resorption, which leads to reduced bone density. The reduction in bone mineral density and therefore low bone mass results in an increased risk of fractures. Osteoporosis is caused by an imbalance in the normally strictly regulated bone homeostasis. This imbalance is caused by overactive bone-resorbing osteoclasts, while bone-synthesizing osteoblasts do not compensate for this. In this review, the mechanism is presented, underlined by in vitro and animal models to investigate this imbalance as well as the current status of clinical trials. Furthermore, new therapeutic strategies for osteoporosis are presented, such as anabolic treatments and catabolic treatments and treatments using biomaterials and biomolecules. Another focus is on new combination therapies with multiple drugs which are currently considered more beneficial for the treatment of osteoporosis than monotherapies. Taken together, this review starts with an overview and ends with the newest approaches for osteoporosis therapies and a future perspective not presented so far.

Association of RANKL and OPG Gene Polymorphism in Arab Women with and without Osteoporosis

Receptor activator of the nuclear factor-κB ligand (RANKL) and osteoprotegerin genes (OPG) were identified as susceptible loci for postmenopausal osteoporosis (PMO) in various ethnicities, but neither have been studied in an Arabian population. Hence, the current study aimed to fill this gap. A total of 372 postmenopausal women (174 osteoporosis (OP) and 198 control group (CTRs)) were genotyped for four SNPs: rs2277438A/G and rs9533156T/C (RANKL), and rs2073618C/G and rs3102735T/C (OPG). Anthropometrics, bone mineral density, 25(OH)D and several other bone markers were measured. The frequency distribution of the heterozygous CG genotype of rs2073618 (OPG) was lower in the OP (36.8%) than in CTRs (47%) (OR: 0.6, 95% CI: 0.3–0.97; p = 0.041). No differences in the allelic/genotypic frequencies were detected between the two groups for all other studied SNPs. However, the heterozygous TC genotype of rs3102735 (OPG) was associated significantly with lower BMD at the femoral neck in OP subjects (p = 0.04). The homozygous rare CC genotype of rs9533156 (RANKL) was associated with lower 25(OH)D levels in CTRs (p = 0.032). In contrast, heterozygous AG genotype of rs2277438 (RANKL) is associated with lower 25(OH)D in the OP group (p = 0.02). Our results suggest that RANKL SNPs may impact 25(OH)D levels and that OPG SNP rs2073618A/G is a significant genetic risk factor for PMO Saudi Arabian women.

The impact of forced swimming on expression of RANKL and OPG in a type 2 diabetes mellitus rat model

OBJECTIVE

The importance of swimming in bone metabolism during type 2 diabetes (T2DM) is not well known. Receptor activator of nuclear factor-kB ligand (RANKL)/ osteoprotegerin (OPG) system as a critical pathway in bone remodeling may play a role in pathogenesis of T2DM. Hence, we tested this pathway and the possible beneficial effects of swim training on T2DM.

MATERIALS AND METHODS

Forty male rats were assigned to groups (n = 10): control(C), diabetic (D), exercised control (E), and diabetic exercised (DE). One week after the induction of diabetes, animals were subjected to swim. At the end of training, fasting blood sugar, insulin, bone and serum OPG and RANKL levels were measured.

RESULTS

Diabetes significantly increased OPG and decreased RANKL mRNAs and proteins in bone and serum and swim training could reverse these changes to control.

CONCLUSION

Swim training could partially compensate T2DM associated changes of bone and serum OPG/RANKL in rats.

Bone Matrix Levels of Dickkopf and Sclerostin are Positively Correlated with Bone Mass and Strength in Postmenopausal Osteoporosis

Wnt signaling plays a pivotal role in maintaining bone mass. Secreted pathway modulators such as sclerostin (SOST) and Dickkopfs (DKKs) may influence bone mass inhibiting the canonical Wnt pathway. We evaluated whether bone protein content of secreted Wnt antagonists is related to age, bone mass, and strength in postmenopausal osteoporosis. We measured cortical and trabecular bone contents of SOST and Dickkopf-1 (DKK1) in combined extracts obtained after ethylenediaminetetraacetic acid and guanidine hydrochloride extraction in 56 postmenopausal women aged 47–74 (mean, 63) yr with a previous distal forearm fracture and a hip or spine Z-score less than 0. Our findings were (i) SOST and DKK1 protein levels were higher in trabecular bone, (ii) cortical and trabecular DKK1 and trabecular SOST correlated positively with bone matrix levels of osteocalcin (r between 0.28 and 0.45, p < 0.05), (iii) cortical DKK1 correlated with lumbar spine bone mineral density (BMD) (r = 0.32, p < 0.05) and femoral neck BMD (r = 0.41, p < 0.01), and (iv) cortical DKK1 and SOST correlated with apparent bone volumetric density and compressive strength (r between 0.34 and 0.51, p < 0.01). In conclusion, cortical bone matrix levels of DKK1 and SOST were positively correlated with bone mass and bone strength in postmenopausal osteoporotic women.

Associations of insulin-like growth factor-I and insulin-like growth factor binding protein-3 with bone quality in the general adult population

OBJECTIVE

Growth hormone (GH) and its main mediator, insulin-like growth factor-I (IGF-I), play a significant role in bone metabolism. The relations between IGF-I and bone mineral density (BMD) or osteoporosis have been assessed in previous studies but whether the associations are sex-specific remains uncertain. Moreover, only a few studies examined bone quality assessed by quantitative ultrasound (QUS). We aimed to investigate these associations in the general population of north-east Germany.

DESIGN AND MEASUREMENTS

Data from 1759 men and 1784 women who participated in the baseline examination of the Study of Health in Pomerania (SHIP)-Trend were used. IGF-I and IGF-binding protein-3 (IGFBP-3) concentrations were measured on the IDS-iSYS multidiscipline automated analyser (Immunodiagnostic Systems Limited). QUS measurements were performed at the heel (Achilles InSight, GE Healthcare). Sex-specific linear and multinomial logistic regression models adjusted for potential confounders were calculated.

RESULTS

Linear regression analyses revealed significant positive associations between IGF-I and IGF-I/IGFBP-3 ratio, a marker for free IGF-I, with all QUS parameters in men. Among women, we found an inverse association between IGF-I and the QUS-based fracture risk but no association with any other QUS parameter. There was no association between IGFBP-3 and the QUS-based fracture risk.

CONCLUSIONS

Our data suggest an important role of IGF-I on bone quality in men. The observed association of IGF-I with the QUS-based stiffness index and QUS-based fracture risk in this study might animate clinicians to refer patients with low IGF-I levels, particularly men, to a further evaluation of risk factors for osteoporosis and a detailed examination of the skeletal system.

Insulin- like Growth Factor-Binding Protein Action in Bone Tissue: A Key Role for Pregnancy- Associated Plasma Protein-A

The insulin-like growth factor (IGF) axis is required for the differentiation, development, and maintenance of bone tissue. Accordingly, dysregulation of this axis is associated with various skeletal pathologies including growth abnormalities and compromised bone structure. It is becoming increasingly apparent that the action of the IGF axis must be viewed holistically taking into account not just the actions of the growth factors and receptors, but also the influence of soluble high affinity IGF binding proteins (IGFBPs).There is a recognition that IGFBPs exert IGF-dependent and IGF-independent effects in bone and other tissues and that an understanding of the mechanisms of action of IGFBPs and their regulation in the pericellular environment impact critically on tissue physiology. In this respect, a group of IGFBP proteinases (which may be considered as ancillary members of the IGF axis) play a crucial role in regulating IGFBP function. In this model, cleavage of IGFBPs by specific proteinases into fragments with lower affinity for growth factor(s) regulates the partition of IGFs between IGFBPs and cell surface IGF receptors. In this review, we examine the importance of IGFBP function in bone tissue with special emphasis on the role of pregnancy associated plasma protein-A (PAPP-A). We examine the function of PAPP-A primarily as an IGFBP-4 proteinase and present evidence that PAPP-A induced cleavage of IGFBP-4 is potentially a key regulatory step in bone metabolism. We also highlight some recent findings with regard to IGFBP-2 and IGFBP-5 (also PAPP-A substrates) function in bone tissue and briefly discuss the actions of the other three IGFBPs (-1, -3, and -6) in this tissue. Although our main focus will be in bone we will allude to IGFBP activity in other cells and tissues where appropriate.

Human decellularized bone scaffolds from aged donors show improved osteoinductive capacity compared to young donor bone

To improve the safe use of allograft bone, decellularization techniques may be utilized to produce acellular scaffolds. Such scaffolds should retain their innate biological and biomechanical capacity and support mesenchymal stem cell (MSC) osteogenic differentiation. However, as allograft bone is derived from a wide age-range, this study aimed to determine whether donor age impacts on the ability an osteoinductive, acellular scaffold produced from human bone to promote the osteogenic differentiation of bone marrow MSCs (BM-MSC). BM-MSCs from young and old donors were seeded on acellular bone cubes from young and old donors undergoing osteoarthritis related hip surgery. All combinations resulted in increased osteogenic gene expression, and alkaline phosphatase (ALP) enzyme activity, however BM-MSCs cultured on old donor bone displayed the largest increases. BM-MSCs cultured in old donor bone conditioned media also displayed higher osteogenic gene expression and ALP activity than those exposed to young donor bone conditioned media. ELISA and Luminex analysis of conditioned media demonstrated similar levels of bioactive factors between age groups; however, IGF binding protein 1 (IGFBP1) concentration was significantly higher in young donor samples. Additionally, structural analysis of old donor bone indicated an increased porosity compared to young donor bone. These results demonstrate the ability of a decellularized scaffold produced from young and old donors to support osteogenic differentiation of cells from young and old donors. Significantly, the older donor bone produced greater osteogenic differentiation which may be related to reduced IGFBP1 bioavailability and increased porosity, potentially explaining the excellent clinical results seen with the use of allograft from aged donors.

Influence of pre-analytical and analytical factors on osteoprotegerin measurements

INTRODUCTION

Osteoprotegerin (OPG), an osteoclastogenesis inhibitor implicated in bone remodelling, has emerged as a potential biomarker for cardiovascular disease. In order to implement OPG determination in the clinical laboratory, it is crucial to identify the most appropriate specimen type, preparation and measurement conditions. The present study focuses on identifying the pre-analytical variables that may influence OPG measurements.

METHODS

Serum and plasma (in EDTA, heparin and citrate) were collected from 45 healthy volunteers (men (n=21, 46.7%), women (n=24, 53.3%)). OPG was analysed by ELISA. The influence of the centrifugation speed, the number of freeze-thaw cycles, delay in sample processing, thermo-stability and endogenous interfering agents (haemolysis, triglycerides, bilirubin, cholesterol and RANKL) were studied.

RESULTS

OPG concentrations were significantly lower (p<0.0001) in serum (1015±357 pg/mL) than in all plasma samples (1314±448 pg/mL in EDTA, 1209±417 pg/mL in heparin and 1260±498 pg/mL in citrate). Increasing centrifugation speed (200 g to 3000 g) did not change serum OPG concentration (p=0.88). However, OPG concentration significantly increased when centrifuged serum samples were stored at 48 h at room temperature (p<0.0001). Repeated freeze-thaw cycles did not modify OPG levels until 4 cycles (p<0.0001). Increasing time before processing the samples (2 h and 6 h) raised OPG concentrations both at room temperature (p<0.0001) or 4°C (p<0.001). Positive concentration-dependent interference of triglycerides was found in the analysed pooled samples; however, OPG concentrations were falsely diminished with haemoglobin interference. Bilirubin, cholesterol and RANKL did not interfere with OPG measurements.

Age-related changes in serum levels of insulin-like growth factor-II and its binding proteins correlate with calcaneal bone mineral density among post-menopausal South-Indian women

BACKGROUND

Insulin-like growth factor (IGF) system components are important regulators of bone metabolism, which have a predominant role in determining bone mineral density (BMD). While the serum levels of IGF-I are regulated by various systemic hormones and growth factors, IGF-II levels reflect the skeletal production relative to physical activity, mechanical loading, aging, race etc. Though various studies have been carried out among women of different ethnic groups to understand the relationship between serum levels of IGF-II and BMD, the results seem to be quite inconclusive.

METHODS

We evaluated the same, recruiting South-Indian women who engage themselves in a wide variety of physical activities pertaining to their profession and life style.

RESULTS

Serum levels of IGF-II and IGF binding protein (IGFBP)-3 showed positive correlation with calcaneal BMD, whereas IGFBP-4 showed negative correlation. These IGF system components exhibited similar correlations with serum bone formation markers and opposite trend with bone resorption marker. While both IGF-II and IGFBP-3 levels were observed to be decreased with aging and menopause, IGFBP-4 levels increased.

CONCLUSIONS

The alterations in serum levels of IGF-II and its binding proteins due to aging and menopause could be some of the major contributors of decreased calcaneal BMD observed among elderly women.

Female recruits sustaining stress fractures during military basic training demonstrate differential concentrations of circulating IGF-I system components: a preliminary study

OBJECTIVE

Stress fracture injuries sustained during military basic combat training (BT) are a significant problem and occur at a higher rate in female recruits than male recruits. Insulin-like growth factor-I (IGF-I) is an easily measured biomarker that is involved in bone formation and positively correlated with bone mineral density, especially in women. This study examined the response of the IGF-I system between female soldiers that sustained a stress fracture (SFX, n=13) during BT and female soldiers who did not (NSFX, n=49).

DESIGN

Female soldiers (n=62, 18.8 ± 0.6 yr) from 2 companies of a gender-integrated combat battalion in the Israeli Defense Forces participated in this study. Height, weight and blood draws were taken upon entry to BT (preBT) and after a four-month BT program (postBT). Stress fractures were diagnosed by bone scan. Serum was analyzed for total IGF-I, free IGF-I, IGF binding proteins (IGFBP)1-6, BAP, calcium, CTx, IL1β, IL6, PINP, PTH, TNFα, TRAP, and 25(OH)D. Statistical differences between SFX and NSFX groups and time points were assessed by RM ANOVA with Fisher post-hoc (p≤0.05).

RESULTS

The SFX group was significantly taller and had lower BMI than NSFX (p≤0.05). Serum concentrations of total IGF-I, bioavailable IGF-I, other bone biomarkers, and cytokines were not significantly different between SFX and NSFX preBT. Serum IGFBP-2 and IGFBP-5 were significantly higher in the SFX compared to the NSFX preBT (p≤0.05). In both groups, total IGF-I increased pre to postBT (p≤0.05). Additionally, a significant difference was observed in the bioavailable IGF-I response pre to postBT for both groups. The SFX group demonstrated a significant decrease in bioavailable IGF-I pre to postBT (preBT: 0.58 ± 0.58 ng/mL; postBT 0.39 ± 0.48; p≤0.05) whereas the NSFX group demonstrated a significant increase in bioavailable IGF-I pre to postBT (preBT: 0.53 ± 0.37 ng/mL; postBT: 0.63 ± 0.45; p≤0.05).

CONCLUSIONS

Our study demonstrated that serum IGF-I changes during basic training and that women sustaining stress fractures during BT significantly decreased bioavailable IGF-I, whereas their uninjured counter parts increased bioavailable IGF-I. These results suggest that stress fracture susceptibility may be related to differential IGF-I system concentrations and response to physical training.

Differential effects of raloxifene and estrogen on body composition in growth hormone-replaced hypopituitary women

CONTEXT

GH deficiency causes reduction in muscle and bone mass and an increase in fat mass (FM), the changes reversed by GH replacement. The beneficial effects of GH on fat oxidation and protein anabolism are attenuated more markedly by raloxifene, a selective estrogen receptor modulator, compared with 17β-estradiol. Whether this translates to a long-term detrimental effect on body composition is unknown.

OBJECTIVE

Our objective was to compare the effects of 17β-estradiol and raloxifene on FM, lean body mass (LBM), and bone mineral density (BMD) during GH replacement.

DESIGN

This was an open-label randomized crossover study.

PATIENTS AND INTERVENTION

Sixteen hypopituitary women received GH (0.5 mg/d) replacement for 24 months. One group received 17β-estradiol (2 mg/d) for the first 6 months before crossover to raloxifene (60 mg/d) for the remaining 18 months; the other received the reversed sequence.

MAIN OUTCOME MEASURES

Serum IGF-I and IGF-binding protein-3 concentrations, and FM, LBM, lumbar spine and femoral neck BMD were analyzed at baseline and at 6, 12, and 24 months within and between subjects.

RESULTS

GH therapy significantly increased mean IGF-I during 17β-estradiol and raloxifene cotreatments equally, but elevated IGF-binding protein-3 to a greater extent during raloxifene cotreatment. GH cotreatment with 17β-estradiol increased LBM and lumbar spine and femoral neck BMD and reduced FM to a greater extent than with raloxifene.

CONCLUSIONS

In hypopituitary women, raloxifene at therapeutic doses significantly attenuated the beneficial effects of GH on body composition compared with 17β-estradiol. Raloxifene has no metabolic advantage over 17β-estradiol during GH replacement.

Similar to adiponectin, serum levels of osteoprotegerin are associated with obesity in healthy subjects

An increase in serum osteoprotegerin (OPG) is associated with type 2 diabetes mellitus, the severity of vascular calcification, and coronary artery disease. Obesity is a risk factor for diabetes and cardiovascular disease, but little is known about the relationship between OPG and obesity. The purpose of this study was to determine if changes in body mass index (BMI) and insulin sensitivity influence circulating OPG in healthy subjects. A total of 100 subjects (36 lean, 41 overweight, and 23 obese) with normal glucose tolerance, blood pressure, and electrocardiogram stress test result volunteered for this study. Insulin sensitivity was estimated using a 2-hour oral glucose tolerance test with oral glucose insulin sensitivity analysis. Osteoprotegerin, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL),soluble receptor activator of nuclear factor-κβ ligand (sRANKL), and adiponectin were analyzed using commercially available enzyme-linked immunosorbent assays. Osteoprotegerin (P < .01) and adiponectin (P < .001) were significantly decreased in the obese compared with lean subjects. There was no significant difference between BMI categories for TRAIL or sRANKL. Controlling for age and sex, there was a significant correlation between OPG and adiponectin (r = 0.391, P < .001), BMI (r = -0.331, P < .001), waist circumference (r = -0.268, P < .01), homeostasis model assessment of insulin resistance (r = -0.222, P < .05), and oral glucose insulin sensitivity (r = 0.221, P < .05). Both OPG and adiponectin were negatively correlated with body weight, BMI, waist circumference, and fasting plasma insulin while being positively correlated with insulin sensitivity (P < .05). Controlling for age, sex, and BMI, TRAIL was positively related to fat mass (r = 0.373, P < .001) and waist circumference (r = 0.257, P < .05). In contrast to patients with type 2 diabetes mellitus, circulating OPG is lower in obese, but otherwise healthy subjects and is positively correlated with indices of insulin sensitivity.

Reduced osteoclastogenesis and RANKL expression in marrow from women taking alendronate

Alendronate (AL) is commonly used for the prevention and treatment of osteoporotic fractures. Little is known about the effects of AL administration on osteoclast differentiation from human marrow progenitor cells. We used marrow discarded during orthopedic surgery to test the hypothesis that cultures of bone marrow-derived stem cells (BMCs) from subjects receiving AL (+AL) may differ from control subjects with respect to in vitro osteoclast differentiation and regulatory factors. The number of osteoclasts generated in BMC cultures from control subjects was 4.7-fold greater than that from +AL subjects (P = 0.015). RANKL expression in +AL BMCs was 57% of that in controls (P = 0.001), and OPG expression in +AL BMCs was greater than in controls (153%, P = 0.01). The mean RANKL/OPG ratio in BMCs was 0.65 ± 0.35 for +AL specimens and 1.28 ± 0.53 for controls (P = 0.031). In addition, we assessed the direct effect of AL on expression of RANKL and OPG in marrow stromal cells isolated from nine control women. Treatment with AL downregulated RANKL expression and upregulated OPG expression, with an average 50% decrease in RANKL/OPG ratio at 10(-7) M (P = 0.004). These results show that osteoclast differentiation is dysregulated in marrow isolated from +AL subjects. Furthermore, AL may inhibit human osteoclastogenesis by affecting the key regulatory genes in marrow cells.

Bone loss in relation to serum levels of osteoprotegerin and nuclear factor-kappaB ligand: the Tromsø Study

SUMMARY

In this longitudinal study of 4,137 persons, bone mineral density was negatively associated with osteoprotegerin at baseline in both genders. In postmenopausal women not using hormone replacement therapy (HRT), bone-loss increased with increasing osteoprotegerin levels, whereas no relationship was found in men, premenopausal women, or postmenopausal women taking HRT.

INTRODUCTION

In a population-based study of 2,003 men and 2,134 women, the relationship between the osteoprotegerin (OPG)/factor-kappaB ligand (RANKL) system and bone mineral density (BMD) and changes in BMD was examined.

METHODS

Baseline measurements included height, weight, BMD of the forearm, OPG, RANKL, vitamin D, and serum parathyroid hormone (PTH) and information about lifestyle, prevalent diseases, and use of medication. BMD was remeasured at follow-up 6 years later.

RESULTS

BMD was negatively associated with OPG at baseline in both men and women (p trend over OPG levels = 0.01 and 0.007, respectively, after adjustments for age, and other confounders). In postmenopausal women not on hormone replacement therapy, bone loss increased with increasing OPG (p = 0.005), whereas no relationship was found in men, premenopausal women, or postmenopausal women on HRT (p >or= 0.28). BMD at baseline and BMD changes were not related to RANKL levels in any of the groups (p >or= 0.14).

CONCLUSIONS

In postmenopausal women not using HRT, bone loss associated positively with OPG. The results indicate that in women deficient in sex steroids, the OPG/RANKL system may play an important counter regulatory role in order to avoid bone loss and maintain BMD. In men and women replete in sex steroids, the OPG/RANKL system was not associated with BMD.

The potential role of insulin-like growth factor 1, insulin-like growth factor binding protein 3 and bone mineral density in patients with chronic hepatitis C virus in Cairo, Egypt

Insulin-like growth factor 1 (IGF-1) levels have been found to correlate with measurements of bone mineral density (BMD) in liver diseases. This study investigated the relationship between IGF-1, insulin-like growth factor binding protein 3 (IGFBP-3) and BMD in patients with chronic hepatitis C virus. This study was conducted for 30 patients with chronic hepatitis C virus infection (16 patients without and 14 patients with cirrhosis) and 11 healthy controls. Serum levels of IGF-1 and IGFBP-3 and BMD of the proximal femur and lumbar spine were measured in all subjects. Osteoporosis of the proximal femur and lumbar spine was found in 42.9% and 21.4%, respectively, of the patients with cirrhosis. Patients with liver cirrhosis and osteoporosis of the proximal femur and lumbar spine had lower IGF-1 (P<0.001, P=0.04, P=0.04 respectively). BMD of the proximal femur was lower in cirrhotic patients compared with controls (P<0.01). Patients with liver cirrhosis had lower IGFBP-3 than patients without cirrhosis and controls (P<0.001). Patients with osteoporosis of the proximal femur had lower IGFBP-3 than those without osteoporosis (P<0.01). IGF-1 and IGFBP-3 levels were lower in patients with liver cirrhosis. IGF-1 and IGFBP-3 may play a role in hepatic osteoporosis.

Lack of Observed Association between High Plasma Osteoprotegerin Concentrations and Ischemic Stroke Risk in a Healthy Population

Background: Several studies suggest that osteoprotegerin (OPG) concentrations may be associated with the risk of ischemic stroke, but no large prospective studies have been conducted. We conducted a nested case-control study within a large cohort to elucidate a possible relation.

Methods: The study was done within a follow-up study including 57 053 men and women. Baseline data included OPG concentrations, lifestyle factors, and medical history. Median length of follow-up was 3.1 years. We assessed the relationship between OPG and stroke risk using conditional logistic regression to adjust for known risk factors (smoking, blood pressure, cholesterol, diabetes, body mass index, alcohol use, polyunsaturated fatty acids, and education).

Results: We identified 254 cases with verified incident acute ischemic stroke and 254 age- and sex-matched controls. Median plasma OPG concentration among cases was 1.84 μg/L (25th–75th percentile 1.45–2.30 μg/L) compared with 1.87 μg/L (1.49–2.27 μg/L) in the control group. The adjusted odds ratio was 0.87 (95% CI 0.46–1.63) comparing participants in the highest quartile of OPG concentrations with those in the lowest quartile.

Conclusions: These findings provide no support for the hypothesis that plasma OPG concentrations are associated with an increased risk of ischemic stroke. This result could indicate a different pathogenic process in stroke development from that in ischemic heart disease, where OPG is a strong predictor.

Interleukin-6 inhibits receptor activator of nuclear factor kappaB ligand-induced osteoclastogenesis by diverting cells into the macrophage lineage: key role of Serine727 phosphorylation of signal transducer and activator of transcription 3

Osteoclasts are bone-resorptive cells that differentiate from hematopoietic precursors upon receptor activator of nuclear factor kappaB ligand (RANKL) activation. Previous studies demonstrated that IL-6 indirectly stimulates osteoclastogenesis through the production of RANKL by osteoblasts. However, few data described the direct effect of IL-6 on osteoclasts. To investigate this effect, we used several models: murine RAW264.7 cells, mouse bone marrow, and human blood monocytes. In the three models used, the addition of IL-6 inhibited RANKL-induced osteoclastogenesis. Furthermore, IL-6 decreased the expression of osteoclast markers and up-modulated macrophage markers. To elucidate this inhibition, signal transducer and activator of transcription (STAT) 3, the main signaling molecule activated by IL-6, was analyzed. Addition of two STAT3 inhibitors completely abolished RANKL-induced osteoclastogenesis, revealing a key role of STAT3. We demonstrated that a basal level of phosphorylated-STAT3 on Serine(727) associated with an absence of phosphorylation on Tyrosine(705) is essential for osteoclastogenesis. Furthermore, a decrease of Serine(727) phosphorylation led to an inhibition of osteoclast differentiation, whereas an increase of Tyrosine(705) phosphorylation upon IL-6 stimulation led to the formation of macrophages instead of osteoclasts. In conclusion, we showed for the first time that IL-6 inhibits RANKL-induced osteoclastogenesis by diverting cells into the macrophage lineage, and demonstrated the functional role of activated-STAT3 and its form of phosphorylation in the control of osteoclastogenesis.

OPG, RANK and RANK ligand expression in thyroid lesions

Receptor activator of NF-kappaB (RANK), RANK ligand (RANKL) and osteoprotegerin (OPG) play essential roles in bone metabolism. RANKL binds to RANK, which is expressed by osteoclasts whereas OPG acts as its decoy receptor blocking the RANK-RANKL interaction. OPG/RANK/RANKL are produced by variety of tissues including epithelial and mesenchymal cells. However, the role of RANKL/OPG in thyroid pathophysiology remains unclear. The aim of this study was to determine the expression pattern of RANK/RANKL/OPG in primary neoplastic thyroid lesions and in lymph node metastases. 27 specimens from total thyroidectomy were studied by immunohistochemistry: 9 papillary carcinomas (PC), 9 medullary carcinomas (MC), 9 macrovesicular adenomas (MA). Immunohistochemical evidence of RANKL was found in 30 % of MC, 22% of PC while RANKL has never been detected in PC. The expression of RANK is closely related to RANKL. OPG was restricted to the cytoplasm of epithelial in 1 MA and 1 MC. In contrast to pathological tissues, any expression of OPG/RANK/RANKL was detected in healthy thyroid tissue. This work reveals for the first time that OPG/RANK/RANKL are expressed in the pathological thyroid gland by follicular cells, by malignant parafollicular cells as well as in metastatic lymph node microenvironment. Thus OPG/RANK/RANKL molecular triad might play a role during pathogenesis of follicular and parafollicular tumors.

Osteoclasts prefer aged bone

We investigated whether the age of the bones endogenously exerts control over the bone resorption ability of the osteoclasts, and found that osteoclasts preferentially develop and resorb bone on aged bone. These findings indicate that the bone matrix itself plays a role in targeted remodeling of aged bones.

INTRODUCTION

Osteoclasts resorb aging bone in order to repair damage and maintain the quality of bone. The mechanism behind the targeting of aged bone for remodeling is not clear. We investigated whether bones endogenously possess the ability to control osteoclastic resorption.

METHODS

To biochemically distinguish aged and young bones; we measured the ratio between the age-isomerized betaCTX fragment and the non-isomerized alphaCTX fragment. By measurement of TRACP activity, CTX release, number of TRACP positive cells and pit area/pit number, we evaluated osteoclastogenesis as well as osteoclast resorption on aged and young bones.

RESULTS

We found that the alphaCTX/betaCTX ratio is 3:1 in young compared to aged bones, and we found that both alpha and betaCTX are released by osteoclasts during resorption. Osteoclastogenesis was augmented on aged compared to young bones, and the difference was enhanced under low serum conditions. We found that mature osteoclasts resorb more on aged than on young bone, despite unchanged adhesion and morphology.

CONCLUSIONS

These data indicate that the age of the bone plays an important role in controlling osteoclast-mediated resorption, with significantly higher levels of osteoclast differentiation and resorption on aged bones when compared to young bones.

Effects of insulin-like growth factor binding proteins in bone -- a matter of cell and site

The actions of the insulin-like growth factor (IGF)-system are controlled by six IGF-binding proteins (IGFBPs). The IGFBPs are thought to affect local effects of IGF-I and IGF-II due to higher affinity if compared to IGF-I receptors and due to cell-type specific IGFBP expression patterns. It was found in IGFBP knockout models that the IGFBP family is functionally redundant. Thus, functional analysis of potential effects of IGFBPs is dependent on descriptive studies and models of IGFBP overexposure in vitro and in vivo. In the literature, the role of the IGFBPs for bone growth is highly controversial and, to date, no systematic look has been taken at IGFBPs resolving functional aspects of IGFBPs at levels of cell types and specific locations within bones. Since IGFBPs are thought to represent local modulators of the IGF actions and also exert IGF-independent effects, this approach is particularly reasonable on a physiological level. By sorting the huge number of in part controversial results on IGFBP effects in bone present in the literature for distinct cell types and bone sites it is possible to generate a focused, more specific and a less controversial picture of IGFBP functions in bone.

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

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

No associations between OPG gene polymorphisms or serum levels and measures of osteoporosis in elderly Australian women

Bone mass is the single most important risk factor for osteoporotic fractures in the elderly and is mainly influenced by genetic factors accounting for 40-75% of the inter-individual variation. Critical for the bone remodeling process is the balance between the newly discovered members of the tumor necrosis factor ligand and receptor superfamilies, osteoprotegerin (OPG) and receptor activator of nuclear factor-kappaB ligand, which mediate the effects of many upstream regulators of bone metabolism. In the present study, we evaluated the impact of sequence variations in the OPG gene on bone mass, bone-related biochemistry including serum OPG and fracture frequency in elderly Australian women. A total of 1101 women were genotyped for 3 different single nucleotide polymorphisms (SNP) within the OPG gene (G1181C, T950C and A163G). The effects of these SNPs and serum OPG on calcaneal quantitative ultrasound measurements, osteodensitometry of the hip and bone-related biochemistry were examined. We found no significant relationship between sequence variations in the OPG gene or serum OPG and bone mass, bone-related biochemistry or fracture frequency. Our findings confirm some recent publications investigating the same SNPs but diverge from others, indicating that generalization of the relationships found in this type of study must be done with caution and signify the importance of determining associations between polymorphisms and osteoporosis in different ethnic groups.

Resorption of auditory ossicles and hearing loss in mice lacking osteoprotegerin

Bones conduct sound in the middle ear. The three ossicles-the malleus, incus, and stapes-form a chain that transmits vibrations from the tympanic membrane to the oval window of the inner ear. Little is known about bone remodeling events in these ossicles and about potential effects of osteoporosis on hearing loss. Osteoclastic bone resorption is enhanced in Opg(-/-) mice lacking osteoprotegerin, which is a soluble decoy receptor for the osteoclastogenic cytokine RANKL. We asked whether auditory ossicles are resorbed in Opg(-/-) mice, and whether these mice suffer from impaired auditory function. All three ossicles in Opg(-/-) mice showed thinning, especially at the malleal manubrium and incus body. Most notably, unlike in the case in wild-type mice, the junction between the stapes and the otic capsule was fixed in Opg(-/-) mice, and the stapedial footplate was thinner and broader. Radiological analyses revealed that malleal cortical thickness was positively correlated with tibial bone mineral density in Opg(-/-) and control littermate mice. Furthermore, progressive hearing loss was detected in Opg(-/-) mice starting at 6 to 15 weeks of age. These data suggest that osteoprotegerin plays a crucial role in hearing by protecting the auditory ossicles and otic capsule from osteoclastic bone resorption.

Serum markers of bone turnover in dialyzed patients separated according to age

BACKGROUND

Bone metabolism changes with aging in healthy population. Our aim was to determine serum markers of bone turnover in dialysis patients separated according to age.

METHODS

Peritoneal dialysis (PD) or hemodialysis (HD) patients were divided into two groups. Group I (n = 30) consisted of patients older than 65 years. Patients at the age less or equal 65 years were included in group II (n = 37). In all patients we determined serum concentration of intact parathyroid hormone (iPTH), cyclase activating parathyroid hormone (CAP), osteoprotegrin (OPG) and osteoprotegrin ligand (OPGL). Cyclase inactive parathyroid hormone (CIP) was calculated. Healthy volunteers (n = 13) at the age of 42.1 years (range 23.5-70.9 years) served as controls.

RESULTS

When results of dialysis patients were adjusted to gender, dialysis modality and duration, group I revealed significantly lower iPTH (113.0, 10.3-606.3 pg/ml), CAP (70.0, 6.5-442.6 pg/ml) and CIP (53.3, 3.3-214.4 pg/ml) than group II (310.6, 13.7-1266.9 pg/ml for iPTH; 205.0, 9.3-887.9 pg/ml for CAP; 76.0, 2.4-399.0 pg/ml for CIP), but this group showed significantly higher serum OPG (7.39, 1.52-15.84 pg/ml) than group II (5.45, 0.95-16.47 pg/ml) and controls (2.17, 1.05-3.95 pg/ml). Only patients of group II showed significantly higher iPTH, CAP and CIP than controls (34.9, 18.9-76.9 pg/ml; 24.3, 11.2-42.6 pg/ml, 12.0, 1.0-34.2 pg/ml, respectively for iPTH, CAP and CIP).

CONCLUSION

Our results suggest that age over 65 years is a risk factor for low bone turnover in dialyzed patients. An increase in serum OPG probably reflects a paracrine mechanism of bone cells to compensate for age dependent bone loss.

IGF-I and IGF-II stimulate directed cell migration of bone-marrow-derived human mesenchymal progenitor cells

Insulin-like growth factors (IGFs) are known to be key regulators of bone growth, remodeling, and repair. Since all these processes depend on the recruitment of cells with the potential to be committed to the osteoblastic lineage, we studied possible effects of IGF-I and -II on migration of human mesenchymal progenitor cells (MPC) using a modified Boyden chamber assay. The results were compared to those of primary osteoblasts and in vitro-osteogenic-differentiated MPC. IGF-I and -II stimulated cell migration of all these cell populations in a dose-dependent manner from 1 to 100ng/mL. The maximal chemotactic index (CI) was 4-5 for MPC and primary osteoblasts and about 3 for in vitro-differentiated MPC. Checkerboard analysis revealed that IGFs stimulated true directed cell migration (chemotaxis) and not simply chemokinesis. Addition of an antibody against the type I IGF receptor (alphaIR3) completely abolished (MPC) or markedly reduced (primary osteoblasts) the chemotactic effects of each of the IGFs. IGFBP-3 itself had no direct effect, while IGFBP-5 stimulated MPC migration at concentrations of 80 and 160ng/mL. Parallel application of IGFBP-3 had borderline inhibitory effects while the addition of 40ng/mL of IGFBP-5 enhanced the chemotactic effect of IGF-I on MPC. In conclusion, our results show that IGF-I and -II are chemotactic factors for MPC and indicate that IGFBP-5 both modulates the IGF-I effect and directly stimulates migration of human mesenchymal progenitor cells.

Early posttransplant serum osteoprotegerin levels predict long-term (8-year) patient survival and cardiovascular death in renal transplant patients

The primary objectives of this analysis were to examine the effects of early posttransplantation (10 wk) serum levels of osteoprotegerin (OPG), mannose-binding lectin (MBL), and MBL-associated serine proteases (MASP; MASP-2 and MASP-3) on long-term (8-yr) patient survival, graft survival, and cardiovascular (CV) death. During a period of 16 mo (1995 to 1996), a total of 173 consecutive renal transplant recipients without diabetes before transplantation were included in a prospective study that was designed to address the impact of metabolic CV risk factors on survival and CV end points. Baseline sera from 172 patients were available for analysis. Follow-up data until January 1, 2004, were obtained from a national renal registry. Patients with high (fourth quartile) serum levels of OPG had significantly higher all-cause mortality (hazard ratio [HR] 6.3; 95% confidence interval [CI] 3.3 to 11.8; P<0.001) and CV death (HR 10.8; 95% CI 3.8 to 30.4; P<0.001) than patients with lower OPG concentrations. After multiple Cox regression analysis, high serum levels of OPG remained an independent predictor of all-cause mortality (HR 6.0; 95% CI 3.1 to 11.6, P<0.001) and CV death (HR 8.2; 95% CI 2.5 to 26.4; P<0.001). Multiple linear regression analysis revealed that age, creatinine clearance, and high-sensitivity C-reactive protein all were independently associated with OPG (R2=0.42). No significant association between OPG and death-censored graft loss was revealed. Serum levels of MBL, MASP-2, and MASP-3 were not significantly associated with patient survival, CV death, or graft loss. Early measured posttransplantation serum OPG is a highly significant independent predictor of death from any cause or CV death in white renal transplant recipients.

Effects of GH and/or sex steroids on circulating IGF-I and IGFBPs in healthy, aged women and men

Circulating GH, IGF-I, IGFBP-3, and sex steroid concentrations decrease with age. GH or sex steroid treatment increases IGFBP-3, but little is known regarding the effects of these hormones on other IGFBPs. We assessed the effects of 26 wk of administration of GH, sex steroids, or GH + sex steroids on AM levels of IGF-I, IGFBPs 1-5, insulin, glucose, and osteocalcin and 2-h urinary excretion of deoxypyridinolline (DPD) cross-links in 53 women and 71 men aged 65-88 yr. Before treatment, in women and men, IGF-I was directly related to IGFBP-3 (P < 0.001 and P < 0.0001) and IGFBP-1 to IGFBP-2 (P = 0.0001). In women, IGFBP-1 was inversely related to insulin (P < 0.0005) and glucose (P < 0.005) and IGFBP-4 to osteocalcin (P < 0.01). IGFBP-4 and IGFBP-5 were not significantly related to DPD cross-links. GH and/or sex steroid increased IGF-I levels in both sexes, with higher concentrations in men (P < 0.001). In women, the IGF-I increment after GH was attenuated by hormone replacement therapy (HRT) coadministration (P < 0.05). Hormone administration also increased IGFBP-3. IGFBP-1 was unaffected by GH + sex steroids, whereas GH decreased IGFBP-2 by 15% in men (P < 0.05). Hormone administration did not change IGFBP-4, whereas in men IGFBP-5 increased by 20% after GH (P < 0.05) and 56% after GH + testosterone (P = 0.0003). These data demonstrate sexually dimorphic IGFBP responses to GH. Additionally, HRT attenuated or prevented GH-mediated increases in IGF-I and IGFBP-3. Whether GH and/or sex steroid administration alters local tissue production of IGFBPs and whether the latter influence autocrine or paracrine actions of IGF-I remain to be determined.

Insulin-like growth factor-I and mineral metabolism markers in children with idiopathic decrease in bone mass

OBJECTIVE

The aim of the study was to determine whether the serum concentration of insulin-like growth factor-I (IGF-I) and its binding protein-3 (IGFBP-3) correlates with the mineral metabolism markers in children with idiopathic decrease in bone mass.

PATIENTS AND METHODS

The study comprised 62 patients aged 6-18 years, including 42 with idiopathic decrease in bone mineral density (20 with osteoporosis and 22 with osteopenia) and 20 control children. Osteoporosis and osteopenia were diagnosed on the basis of complex clinical, densitometric and biochemical examinations (in all patients secondary causes of the decreased bone mass were excluded). Serum concentration of IGF-I was determined with radioimmunoassay and IGFBP-3 using immunoradiometry.

RESULTS

The children with osteoporosis and osteopenia were found to have mean IGF-I concentration statistically significantly lower than the controls (548 and 645 v. 819 ng/ml, respectively; p<0.05). Moreover, IGF-I correlated positively with total and spinal bone mineral density. In children with osteoporosis there was also a significant relationship between IGF-I and pyridinoline and deoxypyridinoline in urine.

CONCLUSIONS

Lower serum IGF-I concentration together with higher bone resorption and low bone mineral density reveal involvement of this growth factor in the development of idiopathic decrease of bone mass in children.

Correlations between leptin, body composition, bone mineral density, and bone metabolism in kidney transplant recipients

INTRODUCTION

In kidney transplant recipients leptin levels are often elevated and bone mineral density (BMD) decreased. However, to date there are no about correlations between leptin and BMD in this population. It has been suggested that leptin is a predictor of BMD in postmenopausal women. Moreover, leptin acts as a marker of fat stores. We examined the relationships between leptinemia, some markers of nutritional status, BMD, and bone metabolism in kidney transplant recipients. We also assessed whether leptin was a significant and independent predictor of BMD in this population.

METHODS

BMD and fat content (global, percentage, trunk) were measured using dual-energy X-ray absorptiometry in 27 kidney allograft recipients. Markers of bone turnover and leptin were studied using commercially available kits.

RESULTS

Leptin correlated with the percentage of body fat, trunk fat, lean body mass, serum creatinine, and urea. Insulin growth factor binding protein 1 was negatively related to waist-hip ratio and global and trunk fat, whereas BMD of the lumbar spine was correlated with the daily dose of prednisone, azathioprine, cyclosporine trough levels, serum calcium, as well as osteoprotegerin level.

CONCLUSIONS

Leptin levels are associated with graft function and body fat in kidney allograft recipients. Leptin is not related to nutritional status, BMD, or bone metabolism in kidney allograft recipients, but is associated with the current dosage of immunosuppressants and the serum calcium.

Circulating amounts of osteoprotegerin and RANK ligand: genetic influence and relationship with BMD assessed in female twins

Osteoprotegerin (OPG) is a circulating receptor that inhibits osteoclastogenesis by binding to RANK ligand (RANKL). OPG knock-out animals develop severe osteoporosis. Treatment with OPG lowers bone resorption and increases BMD. OPG production is influenced by a wide range of hormones and cytokines. The influence of genetic factors on circulating amounts of OPG and RANKL is not known. BMD has been demonstrated to have a high heritability and there is evidence also that bone turnover and bone loss rates are controlled at least in part by genetic factors.

OBJECTIVE

Assessing the genetic impact on serum OPG and RANKL in women and estimation of the relative contribution of this inheritance to the total heritability of BMD.

METHODS

188 female twins (52 DZ and 42 MZ pairs) from the Danish Twin Registry were included in the study. Mean age was 35 years (range 19-64 years), average spine BMD was 1.04 +/- 0.11 g/cm2. Serum levels of OPG and RANKL were measured by ELISA (Biomedica, Vienna, Austria). This register covers twins born in Denmark since 1870. Heritability and environmental influence was assessed using a maximum-likelihood model for genetic pleiotropy.

RESULTS

RANKL levels showed a negative correlation with age and lower values in smokers. OPG levels were higher in postmenopausal women. Heritability (h(2)) was 85% for spine BMD and 52% for serum RANKL after adjustment for age, smoking and BMI. By contrast, there was no significant genetic influence on OPG levels (h(2) = 0, 95% CI: 0 to 0.31). Serum OPG was determined almost exclusively by individual environment (e(2) = 0.79), with a small, non-significant contribution from shared environment (c(2) = 0.21). Restricting analyses to the 158 premenopausal twins did not alter the findings.

CONCLUSIONS

Serum OPG and RANKL levels have only a weak relation to BMD in healthy women. Phenotype correlations indicate that the genes that contribute to twin similarity for BMD are not genes regulating serum levels of RANKL or OPG. The weak correlation with BMD appears to consist in shared environmental factors.

GH/IGF-I and bone resorption in vivo and in vitro

IGF-I may act as one of several coupling agents by activating bone formation and bone resorption. In vivo studies in normal subjects, postmenopausal women and patients with excess or diminished GH production (acromegaly and GHD) indicate that both GH and IGF-I activate osteoclasts, but that GH has a more pronounced effect, independently of IGF-I. In vitro, GH and IGF receptors have been demonstrated on osteoclasts and both GH and IGF-I may directly modify osteoclast function and activity. In addition to direct effects on osteoclasts, GH and IGF-I may affect bone resorption indirectly by stimulating release of paracrine mediators that regulate osteoclastic resorption (cytokines). Critical for the bone resorptive process is the balance between OPG and RANKL, which is regulated by many systemic factors. In vivo and in vitro, GH/IGF-I may modulate this balance but these studies are difficult to interpret, reflecting the complexity of this system. Increased OPG expression may possibly protect against GH/IGF-I-induced bone resorption and potentially be important for the long-term beneficial effects of GH replacement. Further studies investigating the OPG/RANKL ratio and system in experimental and transgenic GH/IGF models may clarify these issues.

Arterial osteoprotegerin: increased amounts in diabetes and modifiable synthesis from vascular smooth muscle cells by insulin and TNF-alpha

AIMS/HYPOTHESIS

Extracellular matrix modifications and linear medial calcifications are elements of diabetic macroangiopathy. We hypothesised that the bone-related protein osteoprotegerin (OPG) may occur in altered amounts in the arterial wall in diabetes, putatively associated with altered synthesis from vascular cells.

METHODS

The amount of OPG in the thoracic aorta, obtained at autopsy from 21 diabetic and 42 sex- and age-matched controls, was measured in tissue extracts by an ELISA. The production of OPG was estimated in conditioned media by an ELISA, and OPG mRNA was estimated by RT-PCR in vascular cells grown in vitro.

RESULTS

The content of OPG was increased in tunica media samples from diabetic individuals. No differences between diabetic and non-diabetic subjects were observed in tunica intima. Human vascular smooth muscle cells (HVSMCs) produced approximately 30 times more OPG than human umbilical vein endothelial cells. The OPG production into the medium decreased dose- and time-dependently after insulin treatment (maximal effect approximately 60% of control) in HVSMCs, whereas TNF-alpha supplement gave rise to increased OPG synthesis in a time- and dose-dependent manner (maximal effect approximately 200% of control). Similar effects on OPG mRNA expression were observed. Addition of growth hormone (10 ng/ml) or extra glucose (25 mmol/l) to the growth medium had no effect.

CONCLUSIONS/INTERPRETATION

Increased OPG concentrations in the arterial wall in diabetes may be part of generalised matrix alterations, putatively related to the development of vascular calcifications. Altered arterial OPG content may be a consequence of the effects of hormones and cytokines, like insulin and TNF-alpha.

Bone metabolism in relation to alterations in systemic growth hormone

Growth hormone (GH) has a major role in the maintenance of bone mass in adults by regulating bone remodeling through a complex interaction of circulating GH, insulin-like growth factors (IGFs), IGF binding protein (IGFBPs), and locally produced IGFs and IGFBPs, acting in an autocrine and paracrine way. In vitro data has greatly increased our understanding of GH and IGFs effects and regulation in bone cells under controlled conditions, and especially the molecular pathways involved. However, the GH-and type I IGF-receptor are present in many tissues and various systemic factors may potentially regulate local expression of IGFs and IGFBPs in the intact organism. The use of genetically altered mice has changed this and had a major impact on defining the role of IGFs in skeletal homeostasis, and especially the role of systemic IGF-I in the development and maintenance of the adult skeleton. The focus of this review is to describe recent work on the effect of GH/IGF on remodeling in the adult skeleton emphasizing on data obtained in patient populations (i.e. acromegaly, GH deficiency, postmenopausal osteoporosis) and experimental models (i.e. animals with genetically altered expression of different GH and IGF family members) characterized by different systemic levels of these proteins. The role of IGF-I as a coupling agent between resorption and bone formation through effects on osteoprotegerin (OPG) and receptor activator of NFkappaB ligand (RANKL) are also discussed.

IL-6, RANKL, TNF-alpha/IL-1: interrelations in bone resorption pathophysiology

All osteogenic cells (osteoclasts, osteoblasts) contribute individually to bone remodeling. Their cellular interactions control their cellular activities and the bone remodeling intensity. These interactions can be established either through a cell-cell contact, involving molecules of the integrin family, or by the release of many polypeptidic factors and/or their soluble receptor chains. These factors can act directly on osteogenic cells and their precursors to control differentiation, formation and functions (matrix formation, mineralization, resorption...). Here, we present the involvement of three groups of cytokines which seem to be of particular importance in bone physiology: interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-alpha) (TNF-alpha)/IL-1, and the more recently known triad osteoprotegerin (OPG)/receptor activator of NF-kappaB (RANK)/RANK ligand (RANKL). The interactions between these three groups are presented within the framework of bone resorption pathophysiology such as tumor associated osteolysis. The central role of the OPG/RANK/RANKL triad is pointed out.

The relationship between circulating osteoprotegerin levels and bone mineral metabolism in healthy women

OBJECTIVE

Osteoprotegerin (OPG) is a recently identified cytokine that acts as a decoy receptor for the RANK ligand. Moreover, OPG has been shown to be an important inhibitor of osteoclastogenesis in animal models. However, the relationship between circulating OPG levels and female bone status in human populations is unclear. In this study we undertook to investigate the relationship between circulating OPG levels and bone mineral metabolism in healthy women.

PATIENTS AND MEASUREMENTS

Our subjects were 287 women aged 37-73 years (mean age 51.5 years). The serum concentrations of OPG were determined by enzyme-linked immunosorbent assay (ELISA). The biochemical markers of bone turnover and FSH were measured using standard methods. Bone mineral densities at the lumbar spine and femoral neck were measured by dual-energy X-ray absorptiometry.

RESULTS

Postmenopausal women had a significantly higher mean value of serum OPG than premenopausal women (1358.5 +/- 32.5 pg/ml vs. 1228.8 +/- 33.3 pg/ml, P < 0.01). Serum OPG levels were positively correlated with age (r = 0.169, P < 0.01), as were urine deoxypyridinoline levels (r = 0.133, P < 0.05) and serum FSH levels (r = 0.187, P < 0.01) in a bivariate correlation analyses. In a multiple regression analysis, only urine calcium excretion was identified as a significant predictor for serum OPG levels.

CONCLUSIONS

Circulating OPG levels were found to be associated with urine calcium excretion and menopause in healthy women. Our observations suggest that circulating OPG levels reflect an antiresorptive activity in bone, and they are related to endogenous oestrogen levels.

Effects of oral contraceptives on circulating osteoprotegerin and soluble RANK ligand serum levels in healthy young women

OBJECTIVE

Osteoprotegerin (OPG) represents a secreted cytokine which regulates bone mass by blocking receptor activator of nuclear factor-kappaB ligand (RANKL), the principal regulator of osteoclast function. In vitro, OPG production is upregulated by oestrogens in osteoblastic lineage cells, a mechanism that has been discussed as a protective paracrine mechanism of oestrogens on the skeleton. To define the effects of oestrogens on the RANKL/OPG system in vivo, we evaluated OPG and both free and total soluble RANKL (sRANKL) serum levels in healthy young women with or without oral contraceptives.

DESIGN AND PATIENTS

Serum levels of OPG and sRANKL were prospectively assessed in a cohort of healthy young women with (n = 30) or without (n = 25) combined oestrogen-progestin-based oral contraceptives.

MEASUREMENTS

OPG, total and free sRANKL serum levels were determined by enzyme-linked immunosorbent assays (ELISA).

RESULTS

In women using oral contraceptives, OPG serum levels were significantly higher (2.71 +/- 1.42 pmol/l) compared to nonusers (1.35 +/- 1.02 pmol/l; P = 0.0003), whereas free (P = 0.55) and total (P = 0.24) sRANKL serum levels did not differ between both groups. This resulted in an increased OPG/free sRANKL ratio (P = 0.02) in women on oral contraceptives. During the ovarian cycle, OPG (P = 0.22) and free sRANKL (P = 0.99) serum levels remained unchanged in women without oral contraceptives (n = 19), while total sRANKL levels were higher in the follicular than in the luteal phase (P = 0.02).

CONCLUSIONS

Intake of oral contraceptives is associated with increased OPG serum levels, but not sRANKL levels, resulting in a higher OPG/sRANKL ratio. This may contribute to the positive effects of oral contraceptives on the skeleton.

Receptor activator of nuclear factor kappaB ligand (RANKL)/osteoprotegerin (OPG) ratio is increased in severe osteolysis

Pathological osteolyses are considered a consequence of a disturbance in the mechanisms that govern the bone remodeling, mainly the communication between osteoclasts and osteoblasts. Osteoprotegerin (OPG) and receptor activator of NF-kappaB ligand (RANKL) are newly discovered molecules that play a key role in these communications. RANKL is essential for osteoclast differentiation via its receptor RANK located on the osteoclast membrane. OPG is a soluble decoy receptor that inhibits osteoclast differentiation through its binding to RANKL. The aim of this study is the analysis of the RANKL/OPG balance by complementary methods (semiquantitative reverse transcription-polymerase chain reaction, immunohistochemistry, and enzyme-linked immunosorbent assay) in human osteolysis associated to various bone etiologies (n = 60), tumoral (primitive, secondary) or not, compared to healthy tissues (n = 16). Results demonstrated that RANKL/OPG ratio was significantly increased in patients suffering from severe osteolysis compared to the control group and that this imbalance is involved in bone resorption mechanisms. In this study, OPG expression appears to reflect a protective mechanism of the skeleton to compensate increased bone resorption by inhibiting osteoclast formation and bone resorbing activity. Moreover, as revealed by immunohistochemistry, RANKL and OPG were colocalized in all of the tissues analyzed. To define the veracity of RANKL/OPG index in assessing and managing patients with severe osteolysis, an extended population of patients suffering from severe osteolysis must be now monitored.

Biglycan deficiency interferes with ovariectomy-induced bone loss

Biglycan is a matrix proteoglycan with a possible role in bone turnover. In a 4-week study with sham-operated or OVX biglycan-deficient or wildtype mice, we show that biglycan-deficient mice are resistant to OVX-induced trabecular bone loss and that there is a gender difference in the response to biglycan deficiency.

INTRODUCTION

Biglycan (bgn) is a small extracellular matrix proteoglycan enriched in skeletal tissues, and biglycan-deficient male mice have decreased trabecular bone mass and bone strength. The purpose of this study was to investigate the bone phenotype of the biglycan-deficient female mice and to investigate the effect of estrogen depletion by ovariectomy (OVX).

MATERIALS AND METHODS

OVX or sham operations were performed on 21-week-old mice that were divided into four groups: wt sham (n = 7), wt OVX (n = 9), bgn-deficient sham (n = 10) and bgn-deficient OVX (n = 10). The mice were killed 4 weeks after surgery. Bone mass and bone turnover were analyzed by peripheral quantitative computed tomography (pQCT), biochemical markers, and histomorphometry.

RESULTS AND CONCLUSIONS

In contrast to the male mice, there were only few effects of bgn deficiency on bone metabolism in female mice, showing a clear gender difference. However, when stressed by OVX, the female bgn knockout (KO) mice were resistant to the OVX-induced trabecular bone loss. The wt mice showed a decrease in trabecular bone mineral density by pQCT measurements, a decrease in trabecular bone volume (BV/TV), and an increase in mineral apposition rate. In contrast, no significant changes were detected in bgn KO mice after OVX. In addition, analysis of the bone resorption marker deoxypyridinoline showed no significant increase in the bgn KO OVX mice compared with bgn KO sham mice. Measurements of serum osteoprotegerin (OPG) and RANKL revealed increased levels of OPG and decreased levels of RANKL in the bgn KO mice compared with wt mice. In conclusion, the bgn deficiency protects against increased trabecular bone turnover and bone loss in response to estrogen depletion, supporting the concept that bgn has dual roles in bone, where it may modulate both formation and resorption ultimately influencing the bone turnover process.

Growth hormone substitution increases gene expression of members of the IGF family in cortical bone from women with adult onset growth hormone deficiency--relationship with bone turn-over

OBJECTIVE

To investigate the effects of growth hormone (GH) replacement therapy on bone matrix gene expression of insulin-like growth factors (IGFs) and markers of bone metabolism in women with adult-onset GH deficiency (GHD).

DESIGN AND METHODS

Nineteen women, mean age 45 (range 24-56) years, were included in a double-blind, placebo-controlled parallel group study for 12 months. Biochemical markers were measured at baseline, 6 and 12 months. Bone biopsies were obtained and BMD was measured at baseline and after 12 months.

RESULTS

Maximum responses were observed after 6 and 12 months, for bone resorptive and bone formative markers respectively. GH therapy enhanced gene expression in cortical bone of IGFs, GH-and calcitonin-receptor (CR) and osteoprotegerin (OPG), however with the most pronounced effects on CR and IGF-I. Changes in IGF-I gene expression during longitudinal follow-up were significantly correlated with changes in both circulating IGF-I (r = 0.82, p < 0.05), changes in markers of enhanced osteoclastic activity, measured both locally in bone (CR, r = 0.87, p < 0.01) and in serum (CTX-I, r = 0.86, p < 0.05), as well as serum bone ALP (r = 0.96, p < 0.01).

CONCLUSIONS

This study indicates that both liver- and bone-derived IGF-I may be significant in mediating the effects of GH on bone metabolism in humans.

Osteoprotegerin and its correlations with new markers of bone formation and bone resorption in kidney transplant recipients

Osteoprotegerin (OPG), a natural decoy receptor for osteoclast differentiation factor, is produced by osteoblasts in response to PTH. OPG and its ligand RANKL constitute a complex mediator system involved in the regulation of bone resorption, probably playing an important role in the homeostasis of bone turnover. At present, little is known about the effects of OPG on uremic bone. Successful kidney transplantation reverses many abnormalities of bone metabolism; however, the improvement is often incomplete. The aim of the study was to assess OPG and RANKL concentrations in long-term kidney allograft recipients and their correlations with biochemical markers of bone resorption and formation. The present studies on 48 kidney transplant recipients and 25 healthy volunteers included concentrations of parathormone, osteocalcin, bone-specific alkaline phosphatase, serum CrossLaps, calcidiol, calcitriol, ICTP, PICP, tartrate-resistant acid phosphatase, beta2 microglobulin, IGF-1, IFGBP-1, IGFBP-3, OPG, and RANKL using commercially available kits for measurements. Among kidney transplant recipients OPG and RANKL did not differ between transplant patients and healthy volunteers, whereas other markers of bone formation and resorption were significantly higher in the former group. OPD was related to age, time on dialysis prior transplantation, urea, platelet count, CSA dose, azathioprine dose, 25(OH)D(3), TRAP, IGF-1, IGFBP-3, whereas RANKL was related to leukocyte count, CSA concentration and dose, urine DPD, and beta2 microglobulin content. In healthy volunteers OPG correlated only with CrossLaps, whereas RANKL correlated only with osteocalcin and TRAP. Correlations between OPG, IGF system components, and some markers of bone metabolism may indicate the role of OPG/RANKL system in the pathogenesis of bone metabolism disturbances following renal transplantation.