Estrogen via the estrogen receptor blocks cAMP-mediated parathyroid hormone (PTH)-stimulated osteoclast formation

The Diverse Roles of 17β-Estradiol in Non-Gonadal Tissues and Its Consequential Impact on Reproduction in Laying and Broiler Breeder Hens

Estradiol-17β (E2) has long been studied as the primary estrogen involved in sexual maturation of hens. Due to the oviparous nature of avian species, ovarian production of E2 has been indicated as the key steroid responsible for activating the formation of the eggshell and internal egg components in hens. This involves the integration and coordination between ovarian follicular development, liver metabolism and bone physiology to produce the follicle, yolk and albumen, and shell, respectively. However, the ability of E2 to be synthesized by non-gonadal tissues such as the skin, heart, muscle, liver, brain, adipose tissue, pancreas, and adrenal glands demonstrates the capability of this hormone to influence a variety of physiological processes. Thus, in this review, we intend to re-establish the role of E2 within these tissues and identify direct and indirect integration between the control of reproduction, metabolism, and bone physiology. Specifically, the sources of E2 and its activity in these tissues via the estrogen receptors (ERα, ERβ, GPR30) is described. This is followed by an update on the role of E2 during sexual differentiation of the embryo and maturation of the hen. We then also consider the implications of the recent discovery of additional E2 elevations during an extended laying cycle. Next, the specific roles of E2 in yolk formation and skeletal development are outlined. Finally, the consequences of altered E2 production in mature hens and the associated disorders are discussed. While these areas of study have been previously independently considered, this comprehensive review intends to highlight the critical roles played by E2 to alter and coordinate physiological processes in preparation for the laying cycle.

Paracrine Kynurenic Pathway Activation in the Bone of Young Uremic Rats Can Antagonize Anabolic Effects of PTH on Bone Turnover and Strength through the Disruption of PTH-Dependent Molecular Signaling

Secondary hyperparathyroidism and abnormalities in tryptophan (TRP) metabolism are commonly observed in chronic kidney disease (CKD). The present study aimed to establish potential interactions between endogenous parathyroid hormone (PTH) and activation of the bone kynurenine (KYN) pathway in relation to bone turnover and strength in young rats after one month (CKD-1) and three months (CKD-3) of experimental CKD. TRP, KYN, KYN/TRP ratio and bone turnover markers (BTMs) were measured in trabecular and cortical bone tissue. Expression of aryl hydrocarbon receptor (AhR) and the genes involved in osteogenesis was determined in femoral bone. Biomechanical testing of femoral diaphysis and femoral neck was also performed. Activation of the KYN pathway in trabecular bone during CKD development intensified the expression of genes related to osteogenesis, which led to a decrease in cyclic adenosine monophosphate (cAMP) and BTMs levels, resulting in a stiffer and mechanically weaker femoral neck. In contrast, reduction of the KYN pathway in cortical bone allowed to unblock the PTH-dependent anabolic activating transcription factor 4/parathyroid hormone 1 receptor (PTH1R/ATF4) axis, led to cAMP accumulation, better bone turnover and strength in the course of CKD development. In summary, the paracrine KYN pathway in bone can interfere with the anabolic effects of PTH on bone through disrupting PTH-dependent molecular signaling.

Effect of Age on Bone Structure Parameters in Laying Hens

Changes in medullary and cortical bone structure with age remain unclear. Twenty Hy-Line W36 hens, 25 or 52 weeks of age, were euthanized, and both tibiae were collected when an egg was present in the magnum. Serial cross sections of the tibiae were stained with Alcian blue. The bones were scanned using micro-computed tomography. Trabecular width (Tb.Wi) was significantly higher (p < 0.05) in 25-week-old hens, whereas medullary bone tissue volume (TV) was significantly higher (p < 0.01) in 52-week-old hens. 25-week-old hens had significantly higher (p < 0.01) bone volume fraction (BVF = calcified tissue / TV). Moreover, the cortical bone parameters were significantly higher (TV and bone mineral content (BMC) at p < 0.05, and bone volume (BV) and BVF at p < 0.01) in younger hens. Open porosity and total porosity, which indicate less density, were significantly higher (p < 0.01) in older hens. Older hens showed significantly higher (p < 0.01) tibial diaphysis TV than younger hens. Younger hens had significantly higher (p < 0.01) BV, BVF and bone mineral density (BMD) of the tibial diaphysis. These findings reveal that reductions in medullary bone quality might be associated with age-related low estrogen levels and stimulation of osteoclastic bone resorption by parathyroid hormone. Cortical bone quality decreased with enlargement of the Haversian canals and loss of volume, with a longer egg-laying period leading to osteoporosis.

Estrogen and estrogen receptors in kidney diseases

Acute kidney injury (AKI) and chronic kidney disease (CKD) are posing great threats to global health within this century. Studies have suggested that estrogen and estrogen receptors (ERs) play important roles in many physiological processes in the kidney. For instance, they are crucial in maintaining mitochondrial homeostasis and modulating endothelin-1 (ET-1) system in the kidney. Estrogen takes part in the kidney repair and regeneration via its receptors. Estrogen also participates in the regulation of phosphorus homeostasis via its receptors in the proximal tubule. The ERα polymorphisms have been associated with the susceptibilities and outcomes of several renal diseases. As a consequence, the altered or dysregulated estrogen/ERs signaling pathways may contribute to a variety of kidney diseases, including various causes-induced AKI, diabetic kidney disease (DKD), lupus nephritis (LN), IgA nephropathy (IgAN), CKD complications, etc. Experimental and clinical studies have shown that targeting estrogen/ERs signaling pathways might have protective effects against certain renal disorders. However, many unsolved problems still exist in knowledge regarding the roles of estrogen and ERs in distinct kidney diseases. Further research is needed to shed light on this area and to enable the discovery of pathway-specific therapies for kidney diseases.

Role of APD-Ribosylation in Bone Health and Disease

The transfer of adenosine diphosphate (ADP)-ribose unit(s) from nicotinamide adenine dinucleotide (NAD⁺) to acceptor proteins is known as ADP-ribosylation. This post-translational modification (PTM) unavoidably alters protein functions and signaling networks, thereby impacting cell behaviors and tissue outcomes. As a ubiquitous mechanism, ADP-ribosylation affects multiple tissues, including bones, as abnormal ADP-ribosylation compromises bone development and remodeling. In this review, we describe the effects of ADP-ribosylation in bone development and maintenance, and highlight the underlying mechanisms.

Letrozole induced changes in bone mineral properties and mechanical functions of laying hens

Bone volumes and quality are related to their hormone levels in laying hens. In this study, we investigated letrozole (LZ) induced effects on the physicochemical properties of cortical bone in laying hens. After 9-wk LZ treatment, we observed that LZ could decrease estrogen level in laying hens. As a result, both the plasma tartrate-resistant acid phosphatase and bone Gla protein activities were suppressed significantly. In addition, carbonate substitution was inhibited significantly in humerus and femur confirmed by Raman spectroscopy. Meanwhile, the mineral density and yield load capacities of humerus and femur were improved. This study demonstrated that the high crystallinity and low carbonate substitution were tightly correlated with the relatively enhanced mechanical properties. Moreover, it elucidated biochemical mechanisms of estrogen in regulating mineralogical and mechanical properties of bones in laying hens.

Caffeic Acid Inhibits NFkappaB Activation of Osteoclastogenesis Signaling Pathway

BACKGROUND: Caffeic acid (3,4-dihydroxycinnamic acids) is involved in various green plants. Based on our previous report, a major component of sweet potato extracts, possibly caffeic acid, was shown as a promising inhibitor of osteoclastogenesis. However, the effect of caffeic acid in inhibiting osteoclastogenesis needs to be confirmed. The underlying mechanism needs to be disclosed as well.METHODS: Caffeic acid in various concentrations was added to in vitro osteoclastogenesis of receptor activator nuclear factor kB ligand (RANKL)-tumor necrosis factor alpha (TNF-α)-macrophage colony stimulating factor (M-CSF)-induced bone marrow-derived monocyte/macrophage precursor cells (BMMs) and RANKL-TNF-α-induced RAW264 cells D-Clone (RAW-D cells). Tartrate resistant acid phosphatase (TRAP) staining was performed and TRAP-positive polynucleated cells (PNCs) were counted. For apoptosis analysis, caffeic acid-treated BMMs, RAW-D cells and osteoclast-like PNCs were subjected to Sub-G1 Apoptosis and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assays. To measure NFkB activity, RAW-D cells were transfected with pNFkB-TA-Luc and subjected to Dual Luciferase Reporter Assay System.RESULTS: Caffeic acid inhibited osteoclastogenesis of RANKL-TNF-α-M-CSF-induced BMMs as well as RANKL-TNF-α-induced RAW-D cells in a dose dependent manner. Caffeic acid did not induce apoptosis in BMMs, RAW-D cells and osteoclast-like PNCs. RANKL-TNF-α-induced NFkB activity in RAW-D was diminished by caffeic acid in a dose dependent manner. Significant NFkB activity inhibtion was observed starting from 1 µg/mL caffeic acid. CONCLUSIONS: Caffeic acid could be a potent osteoclastogenesis inhibitor through inhibition of NFkB activity. Our present study should be further followed up to disclose caffeic acid's possible overlying signaling pathways in inhibiting osteoclastogenesis.KEYWORDS: caffeic acid, osteoclastogenesis, NFkB, RANKL, TNF-α

Differential effects of 17beta-estradiol and raloxifene on bone and lipid metabolism in rats with chronic kidney disease and estrogen insufficiency

OBJECTIVE

The aim of this study was to evaluate the effect of 17beta-estradiol, raloxifene, and 1-alpha,25-dihydroxycholecalciferol or calcitriol on bone and lipid metabolism in chronic kidney disease and estrogen insufficiency.

METHODS

Six-month-old female Sprague-Dawley rats (n = 48) were ovariectomized and nephrectomized (seven eighths). One week after surgery, the rats were divided into six groups and treated with (1) placebo, (2) 17beta-estradiol 10 microg kg day, (3) raloxifene 1 mg kg day, (4) calcitriol 10 ng kg day, (5) 17beta-estradiol + calcitriol, and (6) raloxifene + calcitriol. A group of untreated animals with chronic kidney disease and normal ovarian function was used as a control group (n = 5). The rats were killed after 8 weeks of treatment. Blood samples were drawn for serum analyses; the right tibia was removed to perform histomorphometric analyses, uteri were used as tissue markers of estrogen replacement, and paraffin-embedded sections of the uterus and the fourth breast were used for histopathologic evaluation.

RESULTS

Raloxifene, alone or combined with calcitriol, and 17beta-estradiol combined with calcitriol significantly diminished total cholesterol level compared with placebo. Qualitative histological and histomorphometric analyses showed that both the single treatments and their combinations were able to increase the trabecular connectivity compared with placebo. The less beneficial results were obtained with 17beta-estradiol alone, whereas the more beneficial results were obtained with the combined treatments, particularly with raloxifene and calcitriol.

CONCLUSIONS

In summary, this experimental study demonstrates the advantages of replacing both hormonal deficiencies together. The combination of calcitriol and raloxifene, a selective estrogen receptor modulator, showed a better lipid, uterus, and bone profile.

Letrozole inhibits the osteogenesis of medullary bone in prelay pullets

This study was performed to investigate the effect of letrozole, an aromatase inhibitor, on osteogenesis of medullary bone in prelay pullets. Three hundred fifteen 95-d-old ISA prelay pullets were used. After 10 d of adaptation in the cages, 15 pullets were selected randomly to collect the serum and bone samples and the rest were randomly assigned to 2 groups with 3 replicates each. One group was control and the other was letrozole-treated, fed 0.5 mg of letrozole per prelay pullet per day for 18 d. The serum and bone samples from these birds were collected during the experiment. Estradiol and testosterone in serum were assayed using commercial RIA kits. The serum alkaline phosphatase (ALP), tartrate-resistant acid phosphatase (TRAP), Ca, and inorganic P were measured by an automatic biochemistry analyzer with commercial kits. The periosteum perimeter, endosteum perimeter, cortical bone index, cortical width, cortical bone area, and cortical area ratios of tibia were measured by transmitted scanner and a computer-assisted image analyzer. Our results showed that relative to the control-fed pullet, letrozole-fed pullets had reduced serum estrogen (57.5%), Ca (33.2%), ALP (33.6%), and TRAP (24.2%) and that values of serum estrogen, Ca, estrogen receptor expression, tibia radiographic density, serum ALP, and TRAP were all reduced (P < 0.05) and the serum P had a degressive trend in letrozole-treated groups. By contrast, the serum androgen and the tibia cortical bone index values were higher in the letrozole-treated group (P < 0.05). No differences were observed in the periosteum perimeter, endosteum perimeter, cortical width, and cortical area ratios of tibia between the 2 groups. The results showed that letrozole can inhibit the development of bone and medullary osteogenesis by inhibiting the synthesis of estrogen and its receptor in prelay pullets.

The impact of sex hormone changes on bone mineral deficit in chronic renal failure

In chronic renal failure several factors affect bone homeostasis leading to the development of renal osteodystrophy. Common calcitropic hormone derangements in renal failure play a central role in bone structure and mineral defects, which in turn accompany osteodystrophy frequently resulting in low bone mineral density (BMD) values. However, patients with end-stage renal disease (ESRD) suffer from several comorbidities, which may partly account for renal bone disease lesions. Hypogonadism in particular accompanies chronic renal failure frequently and exerts an additive effect on bone loss potential. Sex hormones contribute to the equilibrium of osteotropic hormones and cytokines, exerting a protective action on bone tissue. Estrogens have a regulatory effect on bone metabolism in women with renal failure as well. Hypogonadal ESRD women experience a higher bone turnover and more significant bone mass decrements than ESRD women with relatively normal hormone profile and menstrual habits. Female hemodialysis patients have lower BMD values than male patients on average, probably because of menstrual cycle irregularities. However, hypogonadal ESRD men may also experience bone mineral deficits and the severity of hypogonadism may correlate to their bone mineral status. Hormone replacement therapy (HRT) appears to reverse bone mineral loss to some extent in both sexes. In conclusion hypogonadism in renal failure contributes to the bone structure and mineral defects as well as the low-energy fracture risk, reflected in BMD measurements. HRT in ESRD patients should therefore not be overlooked in these patients in the face of their significant comorbidities.

Effect of high molecular weight water-soluble chitosan on the trabecular bone and thickness in ovariectomized rats

High molecular weight water-soluble chitosan(WSC), having an average molecular weight of 300,000 Da and a degree of deacethylation over 90%, can be produced using a simple multi-step membrane separation process. In this study, the trabecular bone area and thickness in ovariectomized(OVX) rats decreased by almost 50% from those in sham-operated rats. WSC was evaluated for inhibition of the progress of bone loss induced by OVX rats. We measured bone histomorphometry in sham, OVX or WSC-administered OVX rats. From light microscopic analyses, a porous or erosive appearances were observed on the surface of trabecular bone of tibia in OVX rats, whereas those of the same bone in sham-operated rats were composed of fine particles. The trabecular bone area and trabecular thickness in OVX rats decreased by 50% from those in sham rats, these decreases were completely inhibited by administration of WSC at a concentration of 15 mg/kg/daily for 7 weeks. In this study, the mechanical strength in femur neck was significantly enhanced by the treatment of WSC for 7 weeks. In OVX rats, free T(3) was normal in all cases, whereas free T(4) was significantly increased. Although there was no difference between OVX and WSC-administered rats in T(3) level, we have found significant difference between them in T(4) level. These results strongly suggest that WSC is effective in preventing the development of bone loss induced by OVX in rats.

The effect of matrix bound parathyroid hormone on bone regeneration

INTRODUCTION

Autogenous bone is the most successful bone-grafting material; however, multiple disadvantages continue to drive developments of improved methods for bone regeneration.

AIM

The aim of the present study was to test the hypothesis that an arginine-glycine-aspartic acid (RGD) modified polyethylene glycol-based matrix (PEG) containing covalently bound peptides of the parathyroid hormone (PTH(1-34)) enhances bone regeneration to a degree similar to autogenous bone.

MATERIAL AND METHODS

Six American foxhounds received a total of 48 cylindrical titanium implants placed in the mandible between the first premolar and the second molar. Five, respectively, 7 months following tooth extraction, implants were placed into the center of surgically created defects. This resulted in a circumferential bone defect simulating an alveolar defect with a circular gap of 1.5 mm. Four treatment modalities were randomly allocated to the four defects per side: (1) PEG-matrix containing 20 microg/ml of PTH(1-34), and 350 microg/ml cys-RGD peptide, (2) PEG alone, (3) autogenous bone and (4) empty defects. Histomorphometric analysis was performed 4 and 12 weeks after implantation. The area fraction of newly formed bone was determined within the former defect and the degree of bone-to-implant contact (BIC) was evaluated both in the defect region and in the apical region of the implant. For statistical analysis ANOVA and subsequent pairwise Student's t-test were applied.

RESULTS

Healing was uneventful and all implants were histologically integrated. Histomorphometric analysis after 4 weeks showed an average area fraction of newly formed bone of 41.7+/-1.8% for matrix-PTH, 26.6+/-4.1% for PEG alone, 43.9+/-4.5% for autogenous bone, and 28.9+/-1.5% for empty defects. After 12 weeks, the respective values were 49.4+/-7.0% for matrix-PTH, 39.3+/-5.7% for PEG alone, 50.5+/-3.4% for autogenous bone and 38.7+/-1.9% for empty defects. Statistical analysis after 4 and 12 weeks revealed significantly more newly formed bone in the PTH(1-34) group compared with PEG alone or empty defects, whereas no difference could be detected against autogenous bone. Regarding BIC no significant difference was observed between the four treatment groups neither at 4 nor at 12 weeks.

CONCLUSION

It is concluded that an RGD-modified PEG hydrogel containing PTH(1-34) is an effective matrix system to obtain bone regeneration.

Influence of the parathyroid glands on bone metabolism

Bone is a classic target tissue for parathyroid hormone (PTH), whose calciotropic effect is mediated largely via catabolic actions on this tissue. Paradoxically, PTH also exerts anabolic actions, with intermittent injections of PTH or its amino-terminal fragments causing an increase in bone formation and bone mass, actions that form the basis for the use of PTH in the treatment of osteoporosis. Besides vitamin D, PTH is the only other known bone anabolic agent. High-affinity PTH receptors (PTH-1R) have been detected on osteoblasts and osteoclasts (albeit in lower numbers). Bone turnover, which includes activation of osteoclasts and osteoblasts, appears to be best reflected not by absolute concentrations of PTH (which can vary based on the assay and antibody used) but by a balance of circulating full-length PTH-(1-84) and amino-terminally truncated C-PTH fragments. When PTH-(1-84) is predominant, bone turnover is promoted. Among PTH fragments, PTH-(7-84) appears to be the most potent antagonist of PTH-(1-84). The mechanisms involved in these effects are unclear although mediation via unique C-terminal receptors has been suggested. We propose that, within the range of total PTH (100-1000 pg mL(-1)), the ratio of PTH-(1-84)/C-PTH fragment is a valuable tool for diagnosis of bone turnover. Data indicate that at PTH levels < 100-150 pg mL(-1) and > 1000 pg mL(-1), the ratio looses its predictive power. Assay type, patient characteristics (race, underlying renal disease) and treatment attributes (vitamin D, corticosteroids, phosphate binders) have an impact on the PTH ratio, and care should be used in interpreting assay results and making subsequent treatment decisions.

Effects of age, grip strength and smoking on forearm volumetric bone mineral density and bone geometry by peripheral quantitative computed tomography: comparisons between female and male

Peripheral quantitative computed tomography (pQCT) is useful to measure volumetric bone mineral density (vBMD) distinguishing trabecular from cortical bones as well as quantity of bone geometry. In the present study, we examined the effects of age, grip strength and smoking on vBMD, bone geometry and bone strength index (polar strength strain index (SSIp)), and then compared with the differences between female and male by employing pQCT in Japanese 252 female and 230 male subjects. Age was negatively correlated with vBMD, cortical area (Ct.Ar) and cortical thickness (Ct.Th) as well as SSIp in both sexes, and the correlation coefficients were higher in female, compared with those in male. Although age was correlated with endocortical circumferences (En.Le) in both sexes, periosteal circumferences (Ex.Le) were correlated with age only in male. Volumetric BMD, Ct.Ar, Ct.Th and SSIp were significantly lower in the group with vertebral fractures, although En.Le and Ex.Le were similar between subjects with and without vertebral fractures. Grip strength was positively correlated with vBMD, Ct.Ar, Ct.Th as well as SSIp. The extent of correlation was much higher in female, compared with that in male. Ct.vBMD, Ct.Ar, Ct.Th and SSIp, but not trabecular vBMD, were significantly lower in the group with high Brinkman index (number of cigarettes smoked per day) x (duration of smoking (years)) in female. These parameters were not significantly different between groups with high and low Brinkman index in male. In conclusion, the present study demonstrated that age, grip strength and smoking affected forearm vBMD, bone geometry and bone strength index by pQCT. These effects were greater in female, compared with those in male.

Effect of raloxifene and its interaction with human PTH on bone formation

We studied the of effects raloxifene alone or in combination with human PTH (hPTH) 1-34 in mineralizing cultures of SaOS-2 cells. Raloxifene (10(-8)-10(-6) M) increased bone nodule formation in cultures of SaOS-2 cells when added intermittently from day 8 to day 17. A single 24-h treatment with 10(-8) M hPTH (1-34) at day 8 reduced the nodule area by 75.6% at day 17, and raloxifene added concomitantly with hPTH (1-34) reduced this inhibitory effect in a dose-dependent manner. Raloxifene also reduced the hPTH (1-34)-induced inhibition of alkaline phosphatase (ALP) activity. The 10-fold stimulation of c-fos mRNA expression by hPTH (1-34) was not influenced by raloxifene co-treatment. The protein kinase A (PKA) inhibitor 6-22 amide (1.7 nM) and the protein kinase C (PKC) inhibitor-bisindolylmaleimide 1 (10 nM) did not influence the separate effects of PTH and raloxifene on mineralized bone nodule formation. This is the first report on the interaction of PTH and raloxifene in an osteoblast culture system.

Role of estrogen in avian osteoporosis

One of the difficulties associated with commercial layer production is the development of osteoporosis in hens late in the production cycle. In light of this fact and because of hens' unique requirements for Ca, many studies have focused on the regulation of Ca and the role of estrogen in this process. The time course of estrogen synthesis over the productive life of hens has been well documented; increased circulating estrogen accompanies the onset of sexual maturity while decreases signal a decline in egg production prior to a molt. Numbers of estrogen receptors decrease with age in numerous tissues. The parallel changes in calcium-regulating proteins, primarily Calbindin D28K, and in the ability of duodenal cells to transport Ca, are thought to occur as a result of the changes in estrogen, and are also reversible by the molt process. In addition to the traditional model of estrogen action, evidence now exists for a possible nongenomic action of estrogen via membrane-bound receptors, demonstrated by extremely rapid surges of ionized Ca in chicken granulosa cells in response to 17beta-estradiol. Estrogen receptors have also been discovered in duodenal tissue, and tamoxifen, which binds to the estrogen receptor, has been shown to cause a rapid increase in Ca transport in the duodenum. In addition, recent evidence also suggests that mineralization of bone per se may not explain entirely the etiology of osteoporosis in the hen but that changes in the collagen matrix may contribute through decreases in bone elasticity. Taken together, these studies suggest that changes in estrogen synthesis and estrogen receptor populations may underlie the age-related changes in avian bone. As with postmenopausal women, dietary Ca and vitamin D are of limited benefit as remedies for osteoporosis in the hen.

Thyroid hormone stimulates osteoclast differentiation by a mechanism independent of RANKL-RANK interaction

It is well known that thyroid hormone excess causes bone loss. However, the precise mechanism of bone loss by thyroid hormone still remains unclear. When T(3) was added to unfractionated bone cells after degeneration of pre-existent osteoclasts, T(3) (1 pM-100 nM) dose-dependently stimulated osteoclast-like cell formation, irrespective of the presence of indomethacin and IL-6 Ab. T(3) increased the expression of osteoprotegerin (OPG) messenger RNA (mRNA), but not of receptor activator of nuclear factor kappaB ligand (RANKL) in unfractionated bone cells, suggesting that the stimulatory effect of T(3) on osteoclast formation was not mediated by the RANKL/OPG system. We next examined the direct effect of T(3) on osteoclast precursors in the absence of osteoblasts, using hemopoietic blast cells derived from spleen cells. T(3) (1 pM-100 nM) dose-dependently stimulated osteoclast-like cell formation from osteoclast precursors. OPG did not inhibit T(3)-induced osteoclast formation from osteoclast precursor cells. The polymerase chain reaction (PCR) product corresponding in size to the mouse T(3) receptor alpha1 cDNA was detected in osteoclast precursors from mouse hemopoietic blast cells as well as mouse heart and mouse osteoblastic cell line MC3T3-E1 cells, suggesting that T(3) directly stimulated osteoclast-like cell formation from osteoclast precursors in the absence of osteoblasts. Further, T(3) increased the expression of c-Fos mRNA at 15 min and 24 h and Fra-1 mRNA at 2 and 6 h in osteoclast precursors. Consistent with the increased expression of c-Fos mRNA observed by RT-PCR, the activation of c-Fos occurred in osteoclast precursor cells stimulated by T(3), while the activation of neither NF-kappaB nor MAPKs was observed by immunoblot analysis. Antisense oligodeoxynucleotides (as-ODN) complementary to c-Fos mRNA at 1 microM significantly inhibited T(3)-induced osteoclast-like cell formation from osteoclast precursors in the absence of stromal cells while sense-ODN did not affect T(3)-induced osteoclast-like cell formation. These results indicate that T(3) directly stimulates osteoclast differentiation at least in part by up-regulation of c-fos protein in osteoclast precursor cells.

Effect of high phosphate concentration on osteoclast differentiation as well as bone-resorbing activity

Although high inorganic phosphate (Pi) concentration in culture media directly inhibits generation of new osteoclasts and also inhibits bone resorption by mature osteoclasts, its precise mechanism and the physiological role have not been elucidated. The present study was performed to investigate these issues. Increase in extracellular Pi concentration ([Pi](e)) (2.5-4 mM) concentration dependently inhibited 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] or parathyroid hormone (PTH)-(1-34)-induced osteoclast-like cell formation from unfractionated bone cells in the presence of stromal cells. Increase in [Pi](e) (2.5-4 mM) concentration dependently inhibited 1,25(OH)(2)D(3)-, PTH-(1-34)-, or receptor activator of NF-kappaB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF)-induced osteoclast-like cell formation from hemopoietic blast cells in the absence of stromal cells. Increase in [Pi](e) (2.5-4 mM) dose dependently stimulated the expression of osteoprotegerin (OPG) mRNA and increased the expression of OPG mRNA suppressed by PTH-(1-34) or 1,25(OH)(2)D(3) in unfractionated bone cells, while it did not affect RANKL mRNA. Increase in [Pi](e) (2.5-4 mM) concentration dependently inhibited the bone-resorbing activity of isolated rabbit osteoclasts. Increase in [Pi](e) (4 mM) induced the apoptosis of isolated rabbit osteoclasts while it did not affect the apoptosis of osteoclast precursor cells and mouse macrophage-like cell line C7 cells that can differentiate into osteoclasts in the presence of RANKL and M-CSF. These results indicate that increase in [Pi](e) inhibits osteoclast differentiation both by up-regulating OPG expression and by direct action on osteoclast precursor cells. It is also indicated that increase in [Pi](e) inhibits osteoclastic activity at least in part by the direct induction of apoptosis of osteoclasts.

Postmenopausal osteoporosis in the dialysis patient

PURPOSE OF REVIEW

Osteoporosis is the most prevalent bone disorder in the general population, particularly in the middle and older age groups. Although more than half of the prevalent dialysis population is within these age groups, little concern has been given to the possible role of estrogen deficiency in the pathogenesis of bone disease in end-stage renal disease. The purpose of this review is to summarize the recent published evidence that supports a potential role of the postmenopausal state in the pathogenesis of bone disease in end-stage renal disease and their implications for treatment.

RECENT FINDINGS

Recent studies have shown that although the risk factors for fracture in end-stage renal disease are similar to the general population, the incidence is three to fourfold higher. The high prevalence of older population, the frequently observed premature amenorrhea and early menopause in dialysis patients may play a role. Similarly, the proportion of end-stage renal disease women receiving hormone replacement therapy is at least three times lower than the general population. Recent evidence on the risk of hormone replacement therapy should caution about its use in end-stage renal disease patients. New evidence suggests that selective estrogen receptor modulators may increase bone mass without significant secondary effects. Other alternatives, such as the use of bisphosphonates, should be considered with caution due to the risk of excessive suppression of bone turnover, worsening or favoring the development of adynamic bone disease.

SUMMARY

Osteoporosis should be recognized as an important entity that may modify the current conception of renal osteodystrophy in postmenopausal patients with end-stage renal disease. Further clinical studies are needed in order to propose strategies that may reduce the impact of postmenopausal osteoporosis in the dialysis population.

Changes in vasoactive factors associated with altered vessel morphology in the tibial metaphysis during ovariectomy-induced bone loss in rats

We hypothesized that estrogen deficiency induces changes in bone vascularization which might be involved in bone loss mechanisms. First, we studied gene expression of angiogenic (vascular endothelial growth factor (VEGF), fibroblast growth factor-2 (FGF-2)) and vasodilator (endothelial nitric oxide synthase (ecNOS), neuronal NOS (nNOS), inducible NOS (iNOS), PTH-related protein (PTHrP), and its receptor PTH/PTHrP) factors in proximal tibial metaphysis of ovariectomized (OVX) rats and OVX 17beta-estradiol-treated rats at 3, 7, and 14 days. We then evaluated bone and vessel histomorphometry in secondary spongiosae by infusing vessels with a mixture of India ink/barium sulfate after 7 and 14 days of OVX. After 7 days expression of angiogenic and vasodilator factors decreased, concomitant with a decrease in the bone vessel number and possibly area. After 14 days all factors except FGF-2 exhibited either increased or normalized expression, which was associated with the stimulation of both bone formation and resorption. 17beta-Estradiol administration for 7 or 14 days prevented not only the OVX-induced changes in bone remodeling but also the morphological alterations observed in bone vessels. It also prevented the alterations in the expression of genes modified by OVX, except for that of FGF-2 whose transcription was similarly down-regulated in OVX rats with or without estrogen treatment.

Effects of raloxifene on bone metabolism and serum lipids in postmenopausal women on chronic hemodialysis

BACKGROUND

Premature amenorrhea and hypoestrogenism and lack of hormone replacement therapy after menopause have been frequently reported in uremic women on dialysis. Therefore, in addition to renal osteodystrophy, postmenopausal women on dialysis could be at risk of osteoporosis. In addition, these patients are at higher risk for hyperlipidemia, arteriosclerosis, and subsequent coronary heart disease and stroke. Recent evidence has suggested that hormone replacement therapy (HRT) in postmenopausal women could have several beneficial effects as well as potentially serious risks. Great efforts have been made to identify therapeutic alternatives that would have the benefits of estrogen on brain and bone without its adverse effects on breast and endometrium. In the present study, we evaluated the effect of raloxifene, a selective estrogen receptor modulator (SERM), on bone metabolism and serum lipids in postmenopausal women on chronic hemodialysis.

METHODS

We performed a prospective, blind, placebo-controlled, and randomized study. Fifty postmenopausal women on chronic hemodialysis with proven severe osteopenia or osteoporosis by bone densitometry were selected. After a written informed consent, patients were randomized into two groups: 25 women on placebo and 25 women on the study drug, raloxifene hydrochloride, at a dose of 60 mg/day. In all patients, we performed a baseline bone mineral density (BMD) analysis and simultaneously evaluated different biochemical parameters, serum lipids (total low-density lipoprotein [LDL] and high-density lipoprotein [HDL] cholesterol and triglycerides) and serum markers of bone resorption (pyridinoline crosslinks). BMD was reassessed after 1 year of therapy. Bone resorption markers were determined every 3 months for 1 year.

RESULTS

After 1 year on raloxifene therapy, lumbar spine BMD (trabecular bone) significantly improved, whereas femoral neck BMD (cortical bone) did not change significantly. No changes in BMD were observed at trabecular or cortical sites in the placebo group. Serum pyridinoline levels showed a significant decrease after 6 months on raloxifene that persisted thereafter. Low-density lipoprotein (LDL)-cholesterol decreased significantly in the raloxifene group with no changes in serum triglycerides, total cholesterol, or HDL cholesterol. No significant side effects were observed in the raloxifene group.

CONCLUSION

The study demonstrates that after one year on raloxifene, postmenopausal women on hemodialysis have a significant increase in trabecular BMD, decrease in bone resorption markers and LDL-cholesterol values, suggesting that SERMs could constitute a therapeutic alternative to improve bone metabolism and control of hyperlipidemia in these patients. The possible long-term effects of raloxifene remain to be determined.

Bone growth stimulators. New tools for treating bone loss and mending fractures

In the new millennium, humans will be traveling to Mars and eventually beyond with skeletons that respond to microgravity by self-destructing. Meanwhile in Earth's aging populations growing numbers of men and many more women are suffering from crippling bone loss. During the first decade after menopause all women suffer an accelerating loss of bone, which in some of them is severe enough to result in "spontaneous" crushing of vertebrae and fracturing of hips by ordinary body movements. This is osteoporosis, which all too often requires prolonged and expensive care, the physical and mental stress of which may even kill the patient. Osteoporosis in postmenopausal women is caused by the loss of estrogen. The slower development of osteoporosis in aging men is also due at least in part to a loss of the estrogen made in ever smaller amounts in bone cells from the declining level of circulating testosterone and is needed for bone maintenance as it is in women. The loss of estrogen increases the generation, longevity, and activity of bone-resorbing osteoclasts. The destructive osteoclast surge can be blocked by estrogens and selective estrogen receptor modulators (SERMs) as well as antiosteoclast agents such as bisphosphonates and calcitonin. But these agents stimulate only a limited amount of bone growth as the unaffected osteoblasts fill in the holes that were dug by the now suppressed osteoclasts. They do not stimulate osteoblasts to make bone--they are antiresorptives not bone anabolic agents. (However, certain estrogen analogs and bisphosphates may stimulate bone growth to some extent by lengthening osteoblast working lives.) To grow new bone and restore bone strength lost in space and on Earth we must know what controls bone growth and destruction. Here we discuss the newest bone controllers and how they might operate. These include leptin from adipocytes and osteoblasts and the statins that are widely used to reduce blood cholesterol and cardiovascular damage. But the main focus of this article is necessarily the currently most promising of the anabolic agents, the potent parathyroid hormone (PTH) and certain of its 31- to 38-aminoacid fragments, which are either in or about to be in clinical trial or in the case of Lilly's Forteo [hPTH-(1-34)] tentatively approved by the Food and Drug Administration for treating osteoporosis and mending fractures.

Humoral hypercalcemia of malignancy in female F344 rats implanted with a transplantable rat pulmonary carcinoma line (IP)

A transplantable rat pulmonary carcinoma line (IP) in F344 rats is a useful animal model for humoral hypercalcemia of malignancy (HHM). The present study analyzed the degree of HHM by implanting IP into F344 female rats aged 6, 20 or 45 weeks. IP-bearing females developed elevated plasma parathyroid hormone-related protein levels, hypercalcemia and increased osteoclastic activity as well as calcification in various organs. The severity of such HHM differed depending on age; particularly, calcification showed age-dependent reduction. HHM development in IP-bearing females may be influenced by age-related factors.

Hormone replacement therapy in postmenopausal women with end-stage renal disease: a review of the issues

Hormone replacement is an integral part of therapies to prevent osteoporosis in postmenopausal women and may be considered a component in the treatment of dyslipidemia, cardiovascular disease, and possibly cognitive function. The indications for, and efficacy and prescription of, hormone replacement therapy in postmenopausal women with ESRD have been infrequently studied and less than 10% of postmenopausal women on dialysis are receiving hormone replacement. Small studies suggest that hormone replacement therapy is valuable in treating the dyslipidemia of women on dialysis, but indicate that a reduction in the dosage of hormone replacement may be needed. A potential role for hormone replacement therapy in the treatment and/or prevention of osteoporosis and sexual dysfunction in postmenopausal women on dialysis exists as well.

Effects of the selective oestrogen receptor modulator-raloxifene-on calcium and PTH secretory dynamics in women with osteoporosis

OBJECTIVES

A possible mechanism for the maintenance of bone mass by oestrogens and the selective oestrogen receptor modulator (SERM)-raloxifene-is an interaction with calciotropic hormones. We studied the effects of raloxifene on calcium-PTH homeostasis.

PATIENTS AND MEASUREMENTS

Calcium and EDTA infusions were performed in 32 post-menopausal women with osteoporosis (BMD T score < - 2.5). This cross-sectional study was performed in the third year of the MORE (Multiple Outcomes of Raloxifene Evaluation) trial, a double-blind, placebo-controlled study. After an overnight fast, calcium glubionate (5 mg/kg BW*h), and after 2.5 h of test-free interval, Na3EDTA (40 mg/kg BW*h) were given intravenously. The duration of infusions was based on individual plasma total calcium before the calcium infusion (t = 0), the target calcium (2.60 and 1.95 mmol/l, respectively), and desired mean calcium change (0.010 mmol/L*min). Blood samples were taken at 0 and every 5 minutes of both infusions. Plasma PTH levels were fitted into an inversed sigmoidal relation with plasma calcium. The effect of raloxifene on calcium-PTH homeostasis was tested in linear regression models adjusted for age and BMI. Nine patients used placebo, 13 raloxifene 60 mg/day and 10 raloxifene 120 mg/day.

RESULTS

Raloxifene use was associated with lower plasma albumin (40.7 +/- 1.8 vs. 38.0 +/- 2.0 and 38.5 +/- 2.3 g/l, for placebo, raloxifene 60 mg/day and raloxifene 120 mg/day, respectively, P = 0.01), lower plasma total calcium at t = 0 (2.28 vs. 2.24 and 2.21; +/- 0.07 mmol/L; P = 0.03), lower plasma total calcium at 50% of maximal PTH secretion (PTH set-point: 2.23 +/- 0.06 vs. 2.18 +/- 0.07 and 2.16 +/- 0.08 mmol/l, P = 0.06), and lower plasma non-suppressible PTH (0.84 +/- 0.19 vs. 0.75 +/- 0.10 and 0.73 +/- 0.05 pmol/l, P = 0.02). After correction for plasma albumin, the differences for plasma calcium at t = 0 and at PTH set-point were no longer significant. In contrast, the difference in PTH suppression during calcium load was not explained either by differences in plasma albumin or calcium.

CONCLUSION

Raloxifene did not have any detectable effect on the PTH set-point. An effect on non-suppressible PTH secretion cannot be excluded.

Parathyroid hormone/parathyroid hormone-related peptide type 1 receptor in human bone

The parathyroid hormone/parathyroid hormone-related peptide (PTH/PTHrP) receptor (denoted as PTH-1R) is a key signaling factor through which calcium-regulating hormones PTH and PTHrP exert their effects on bone. There are contradictory reports regarding the capability of osteoclasts to express PTH-1R. To address this issue in humans, bone biopsy specimen samples from 9 normal controls and 16 patients with moderate to severe secondary renal hyperparathyroid bone disease (2 degrees HPT) with elevated PTH levels were studied to determine whether osteoclasts in the bone microenvironment express PTH-1R messenger RNA (mRNA) and protein. We report that osteoclasts express the PTH-1R mRNA but the protein is detected only in patients with 2 degrees HPT. The PTH-1R mRNA and protein also were found in osteoblasts, osteocytes, and bone marrow cells. Receptor expression was higher in osteoclasts and osteoblasts of patients with 2 degrees HPT than normal controls (98.0 +/- 1.1% vs. 65.7 +/- 14.3% and 65.8 +/- 3.4% vs. 39.1 +/- 6.2%; p < 0.01, respectively). Approximately half of osteoclasts found in bone of patients with 2 degrees HPT have the PTH-1R protein. In patients with 2 degrees HPT, a positive relationship exists between erosion depth, a parameter of osteoclastic activity, and the percentage of osteoclasts with PTH-1R protein (r = 0.58; p < 0.05). In normal controls, an inverse relationship exists between the percentage of osteoblasts with receptor mRNA, mRNA signals/cell, and serum PTH levels (r = -0.82 and p < 0.05 and r = -0.78 and p < 0.01, respectively). The results provide the novel evidence of PTH-1R in human osteoclasts and suggest a functional role for the receptors in 2 degrees HPT.

Maintenance of cortical bone in human parathyroid hormone(1-84)-treated ovariectomized rats

The purpose of this cross-sectional study was to evaluate the effects of human parathyroid hormone(1-84) (hPTH) followed by maintenance treatment with 17beta-estradiol (E(2)), risedronate (Ris), or a reduced dose of hPTH (LowPTH) on cortical bone in the ovariectomized (ovx) rat. Eight groups of ovx and one group of intact female rats (3.5 months) were left untreated for 11 weeks. For the following 12 weeks, four groups received subcutaneous injections of hPTH (75 microg/kg per day on 3 days/week) and four groups received vehicle. Treatments were then changed to E(2) (10 microg/kg per day on 2 days/week), Ris (3 microg/kg per day on 3 days/week), LowPTH (25 microg/kg per day on 3 days/week), or vehicle. Bone tissue was collected at weeks -11 (baseline), 0 (ovx effect), 12 (hPTH effect), 24, 36, and 48 (maintenance effect). Bone mineral density (BMD) and bone mineral content (BMC) of the diaphyseal femur and total cross-sectional area (Tt.Ar), marrow area (Ma.Ar), cortical area (Ct.Ar), and periosteal and endocortical bone formation of the tibia were measured. Ovariectomy resulted in lower BMD (weeks 0-48), unaffected BMC, and greater Tt.Ar (weeks 12 and 36), Ma.Ar (week 48), and Ct.Ar (weeks 0 and 12) compared with intact rats. Endocortical and periosteal bone formation were greater in the ovx than in the intact rats up to 23 weeks postovariectomy. Treatment of ovx rats with hPTH for 12 weeks resulted in greater cortical BMD, BMC, and endocortical bone formation than in intact or ovx controls. In ovx rats pretreated with hPTH and then treated with Ris for 36 weeks, BMD and BMC were greater and Ma.Ar was smaller than in ovx controls. In ovx rats pretreated with hPTH and then treated with LowPTH, BMD, BMC, Ct.Ar, and endocortical bone formation were greater and Ma.Ar was smaller than in ovx controls. Treatment of hPTH-pretreated rats with E(2) for 36 weeks did not affect cortical BMD, BMC, and Ct.Ar, although periosteal bone formation was lower in the E(2) group compared with the ovx group. Thus, in ovariectomized rats, cortical bone gained by 12 weeks of hPTH treatment was maintained for up to 36 weeks by treatment with risedronate or low-dose hPTH, but not with 17beta-estradiol.

Cells in regenerating deer antler cartilage provide a microenvironment that supports osteoclast differentiation

Deer antlers are a rare example of mammalian epimorphic regeneration. Each year, the antlers re-grow by a modified endochondral ossification process that involves extensive remodelling of cartilage by osteoclasts. This study identified regenerating antler cartilage as a site of osteoclastogenesis in vivo. An in vitro model was then developed to study antler osteoclast differentiation. Cultured as a high-density micromass, cells from non-mineralised cartilage supported the differentiation of large numbers of osteoclast-like multinucleated cells (MNCs) in the absence of factors normally required for osteoclastogenesis. After 48 h of culture, tartrate-resistant acid phosphatase (TRAP)-positive mononuclear cells (osteoclast precursors) were visible, and by day 14 a large number of TRAP-positive MNCs had formed (783+/−200 per well, mean +/− s.e.m., N=4). Reverse transcriptase/polymerase chain reaction (RT-PCR) showed that receptor activator of NF κ B ligand (RANKL) and macrophage colony stimulating factor (M-CSF) mRNAs were expressed in micromass cultures. Antler MNCs have the phenotype of osteoclasts from mammalian bone; they expressed TRAP, vitronectin and calcitonin receptors and, when cultured on dentine, formed F-actin rings and large resorption pits. When cultured on glass, antler MNCs appeared to digest the matrix of the micromass and endocytose type I collagen. Matrix metalloproteinase-9 (MMP-9) may play a role in the resorption of this non-mineralised matrix since it is highly expressed in 100 % of MNCs. In contrast, cathepsin K, another enzyme expressed in osteoclasts from bone, is only highly expressed in resorbing MNCs cultured on dentine. This study identifies the deer antler as a valuable model that can be used to study the differentiation and function of osteoclasts in adult regenerating mineralised tissues.

Role of persistent amenorrhea in bone mineral metabolism of young hemodialyzed women

BACKGROUND

Chronic renal failure in women is frequently associated with endocrine disturbances leading to menstrual disorders. However, most studies on renal osteodystrophy have not taken into account the possible role of these hormonal disturbances on the pathogenesis of bone alterations seen in these patients. In the present study, we evaluated bone mineral metabolism in a group of young hemodialyzed women with persistent amenorrhea and compared them with similar women with regular menstruation.

METHODS

We studied 74 women who were further subdivided into 43 women with regular menstrual periods and 31 women with persistent amenorrhea, defined as the absence of menstrual bleeding for more than six months. In all patients, we performed a bone mineral density (BMD) analysis and simultaneously evaluated different biochemical parameters, intact parathyroid hormone (iPTH), sexual hormone determinations that included total estradiol, follicle-stimulating (FSH), and luteinizing hormone and markers of bone resorption such as the procollagen type 1 cross-linked carboxy-terminal telopeptide (ICTP).

RESULTS

Serum calcium, phosphorus, and iPTH were similar in both groups. Serum alkaline phosphatase was higher in amenorrheic women. Although the total serum estradiol concentration was normal in the amenorrheic women when compared with nonuremic women, the values were significantly lower than those in regularly menstruating women. Serum FSH and ICTP values were significantly higher in the amenorrheic women. Trabecular BMD in the lumbar spine was also significantly lower in the amenorrheic women compared with regularly menstruating dialysis patients. Lumbar spine BMD and total estradiol levels correlated significantly in the amenorrheic group.

CONCLUSIONS

These studies show that persistent amenorrheic young women on dialysis have lower trabecular BMD and evidence of increased bone resorption when compared with normal menstruating women on dialysis. The possible impact of these results in the natural history of the uremic osteodystrophy remains to be determined.

The parathyroid hormone, its fragments and analogues--potent bone-builders for treating osteoporosis

As populations age a rising number of men and women, but especially women during the first decade after menopause, become victims of a severe, accelerated loss of bone with crippling fractures known as osteoporosis. This often results in costly, prolonged hospitalisation and perhaps indirectly, death. Osteoporosis in women is caused by the menopausal oestrogen decline, which removes several key restraints on the generation, longevity and activity of bone-resorbing osteoclasts. Although there are many antiresorptive drugs on or coming onto the market (calcitonin, bisphosphonates, oestrogen and SERMS) that can slow or stop further bone loss, there are none that can restore lost bone mechanical strength by directly stimulating osteoblast activity and bone growth. However, there is a family of potent bone-building peptides, namely the 84 amino acid parathyroid hormone (PTH). Its 31 to 38 amino acid N-terminal fragments are currently in or about to enter clinical trials. We can predict that these peptides will be effective therapeutics for osteoporosis especially when supplemented with bisphosphonates or SERMs to protect the new bone from osteoclasts. These peptides should also accelerate the healing of fractures in persons of all ages and restore lost bone mass and mechanical strength to astronauts following their return to earth after long voyages in space.

Stimulatory effect of insulin-like growth factor binding protein-5 on mouse osteoclast formation and osteoclastic bone-resorbing activity

Insulin-like growth factor binding protein-5 (IGFBP-5) stimulates osteoblast proliferation directly or indirectly through IGF-I action, but its effects on osteoclast formation and osteoclastic activity are unknown. We tested the effects of IGFBP-5 on osteoclastic activity and osteoclast formation. IGFBP-5 significantly stimulated pit formation by pre-existent osteoclasts in mouse bone cell cultures and its stimulatory effect was completely blocked by IGF-I antibody (Ab). However, IGFBP-5 did not affect the bone-resorbing activity of isolated rabbit osteoclasts. When IGFBP-5 was added to unfractionated bone cells after degeneration of pre-existent osteoclasts, IGFBP-5 (77 pM-7.7 nM) dose-dependently stimulated osteoclast-like cell formation, irrespective of the presence of IGF-I Ab. Moreover, osteoclast-like cells newly formed by IGFBP-5 from unfractionated bone cells possessed the ability to form pits on dentine slices. We next examined the direct effect of IGFBP-5 on osteoclast precursors in the absence of stromal cells, using hemopoietic blast cells derived from spleen cells. IGFBP-5 dose-dependently stimulated osteoclast-like cell formation from osteoclast precursors, irrespective of the presence of IGF-I Ab. Growth hormone (GH) as well as IGF-I significantly stimulated bone resorption by pre-existent osteoclasts in mouse bone cell cultures and these stimulatory effects were completely blocked by IGF-I Ab. GH as well as IGF-I stimulated osteoclast-like cell formation from unfractionated bone cells and this stimulatory effect of GH was significantly but partially blocked by IGF-I Ab. The direct stimulatory effect of GH on osteoclast-like cell formation from hemopoietic blast cells was not affected by IGF-I Ab. The present data indicate that IGFBP-5 stimulates bone resorption both by stimulation of osteoclast formation in an IGF-I-independent fashion and by IGF-I-dependent activation of mature osteoclasts, possibly via osteoblasts, in vitro.

Relationship between the ability to support differentiation of osteoclast-like cells and adipogenesis in murine stromal cells derived from bone marrow

In vitro osteoclast differentiation is supported by stromal cells. In order to isolate a stromal cell line that can support osteoclast differentiation, 22 cell lines were cloned from mouse bone marrow. One of these clones, TMS-14, is a line of preadipocytes that supports osteoclast-like cell formation without any bone resorbing factors; and another, TMS-12, is a line of preosteoblasts that supports osteoclast-like cell formation with bone resorbing factors such as prostaglandin E(2)(PGE(2)). The difference of these two lines for osteoclast formation was not related with their abilities of PGE(2)production, but with the expression of osteoclast differentiation factor (ODF, also called OPGL, RANKL, and TRANCE), which detected with RT-PCR, in both cell lines. In TMS-14 cells, ODF mRNA was detected with or without PGE(2). In TMS-12 cells, ODF expression was detected in the PGE(2)-treated cells alone. When TMS-14 cells were induced to undergo adipogenic differentiation in response to treatment with thiazolidinedione, a ligand and activator of peroxisome proliferator-activated receptor gamma (PPARgamma), the ability of TMS-14 cells to support osteoclast-like cell formation was prevented in the presence or absence of 1,25(OH)(2)D(3). The gene expression of ODF in TMS-14 cells was also inhibited by treatment with thiazolidinedione. These results suggest that adipogenesis in bone marrow cells is related to the ability to support osteoclast differentiation. This is the first report of a cloned stromal cell line that can support osteoclastogenesis without the treatment with any osteotropic factors. Furthermore, this murine clonal preadipose cell line may be useful for studying senescence-dependent osteoporosis.

High extracellular calcium inhibits osteoclast-like cell formation by directly acting on the calcium-sensing receptor existing in osteoclast precursor cells

Although it has recently been suggested that high extracellular calcium ([Ca(2+)](e)) inhibits osteoclast function via a calcium-sensing receptor (CaSR) in mature osteoclasts, the role of CaSR in the regulation of osteoclast formation remains unknown. The present study was performed to investigate whether osteoclast precursor cells possess CaSR and to clarify the possible role of CaSR in the regulation of osteoclast formation. Immunocytochemistry detected CaSR in osteoclast precursor cells derived from spleen cells as well as in osteoblastic MC3T3-E1 cells. The use of reverse-transcription polymerase chain reaction (RT-PCR) with CaSR-specific primers, followed by nucleotide sequencing of the amplified products, also identified CaSR transcripts in osteoclast precursor cells derived from spleen cells as well as in MC3T3-E1 cells. High [Ca(2+)](e) (3 to 5 mM) concentration dependently inhibited 1,25(OH)2D3- or human parathyroid hormone (hPTH) (1-34)-induced osteoclast-like cell (Ocl) formation from osteoclast precursor cells derived from spleen cells. Further, the CaSR agonist neomycin also concentration dependently inhibited 1,25(OH)2D3- or hPTH(1-34)-induced Ocl formation. Moreover, a calcimimetic which mimics or potentiates the effects of [Ca(2+)](e) at the CaSR NPS R-467 (1-100 microM) concentration dependently inhibited Ocl formation stimulated by 1,25(OH)2D3 or hPTH(1-34). These findings first demonstrated that osteoclast precursor cells possess CaSR very similar, if not identical, to those in the parathyroid and kidney. Furthermore, the CaSR in osteoclast precursor cells could play a key role in regulating Ocl formation by sensing local changes in [Ca(2+)](e) at the resorptive sites.