Human giant cell tumors of the bone (osteoclastomas) are estrogen target cells

Arterial stiffness and risk of new-onset fragility fracture in Chinese men and women: The Kailuan cohort study

BACKGROUND

Previous studies have shown an association between increased arterial stiffness and reduced bone mineral density. However, the relationship between arterial stiffness and fragility fracture remains unclear. In this study, we explored the impact of arterial stiffness on the risk of new-onset fragility fracture.

METHODS

The study included 53,107 participants in the Kailuan Study in whom brachial-ankle pulse wave velocity (baPWV) measurements were obtained between 2010 and 2021. All participants were free of fragility fractures at baseline. A Cox proportional hazard regression model was used to estimate the hazard ratio (HR) and 95 % confidence interval (CI) for incident fragility fracture on the baseline baPWV groups: <1400 cm/s (reference), 1400 ≤ baPWV < 1800 cm/s, and ≥1800 cm/s.

RESULTS

In total, 327 incident fragility fractures were recorded during an average follow-up of 4.99 ± 3.02 years. After adjustment for potential confounders, the HR for the risk of new-onset fragility fracture was 1.66 (95 % CI 1.14-2.42) for the arterial stiffness group in comparison with the normal baPWV group. The risk of fragility fracture was higher in men (HR 1.64, 95 % CI 1.05-2.57). There was a linear association between higher baPWV and fragility fracture.

CONCLUSIONS

Arterial stiffness as measured by baPWV was associated with the risk of fragility fracture.

Osteoimmunology: The Crosstalk between T Cells, B Cells, and Osteoclasts in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an ongoing inflammatory condition that affects the joints and can lead to severe damage to cartilage and bones, resulting in significant disability. This condition occurs when the immune system becomes overactive, causing osteoclasts, cells responsible for breaking down bone, to become more active than necessary, leading to bone breakdown. RA disrupts the equilibrium between osteoclasts and osteoblasts, resulting in serious complications such as localized bone erosion, weakened bones surrounding the joints, and even widespread osteoporosis. Antibodies against the receptor activator of nuclear factor-κB ligand (RANKL), a crucial stimulator of osteoclast differentiation, have shown great effectiveness both in laboratory settings and actual patient cases. Researchers are increasingly focusing on osteoclasts as significant contributors to bone erosion in RA. Given that RA involves an overactive immune system, T cells and B cells play a pivotal role by intensifying the immune response. The imbalance between Th17 cells and Treg cells, premature aging of T cells, and excessive production of antibodies by B cells not only exacerbate inflammation but also accelerate bone destruction. Understanding the connection between the immune system and osteoclasts is crucial for comprehending the impact of RA on bone health. By delving into the immune mechanisms that lead to joint damage, exploring the interactions between the immune system and osteoclasts, and investigating new biomarkers for RA, we can significantly improve early diagnosis, treatment, and prognosis of this condition.

Menstrual Cycle Related Fluctuations in Circulating Markers of Bone Metabolism at Rest and in Response to Running in Eumenorrheic Females

This study examined potential fluctuations in bone metabolic markers across the menstrual cycle both at rest and after a 30-min bout of continuous running at 80% of V̇O_2max. Resting and post-exercise (0, 30, 90 min) sclerostin, parathyroid hormone (PTH), carboxy-terminal cross-linking telopeptide of type I collagen (β-CTXI), and procollagen type 1 N propeptide (PINP) were assessed in 10 eumenorrheic women (age: 21 ± 3 y, BMI: 23.2 ± 3.0 kg^.m²) during the mid- to late-follicular (FP: day 8.0 ± 1.4) and mid-luteal (LP: day 22.0 ± 2.5) phases of the menstrual cycle. Ovulation was determined using ovulation kits and daily measurement of oral body temperature upon awakening. Menstrual cycle phase was subsequently confirmed by measurement of plasma estradiol and progesterone. On average, resting estradiol concentrations increased from 46.3 ± 8.9 pg·mL^-1 in the FP to 67.3 ± 23.4 pg·mL^-1 in the LP (p = 0.015), and resting progesterone increased from 4.12 ± 2.36 ng·mL^-1 in the FP to 11.86 ± 4.49 ng·mL^-1 in the LP (p < 0.001). At rest, there were no differences between menstrual cycle phases in sclerostin (FP: 260.1 ± 135.0 pg·mL^-1; LP: 303.5 ± 99.9 pg·mL^-1; p = 0.765), PTH (FP: 0.96 ± 0.64 pmol·L^-1; LP: 0.79 ± 0.44 pmol·L^-1; p = 0.568), β-CTXI (FP: 243.1 ± 158.0 ng·L^-1; LP: 202.4 ± 92.3 ng·L^-1; p = 0.198), and PINP (FP: 53.6 ± 8.9 μg·L^-1; LP: 66.2 ± 20.2 μg·L^-1; p = 0.093). Main effects for time (p < 0.05) were shown in sclerostin, PTH, β-CTXI and PINP, without phase or interaction effects. Sclerostin increased from pre- to immediately post-exercise (45%; p = 0.007), and so did PTH (43%; p = 0.011), both returning to resting concentrations 30 min post-exercise. β-CTXI decreased from pre- to post-exercise (20%; p = 0.027) and was still below its pre-exercise concentrations at 90 min post-exercise (17%; p = 0.013). PINP increased immediately post-exercise (29%; p < 0.001), returning to resting concentrations at 30 min post-exercise. These results demonstrate no effect of menstrual cycle phase on resting bone marker concentrations or on the bone metabolic marker response to intense exercise.

Aggressive giant cell tumour (GCT) of the distal humerus in a young pregnant woman

A 25-year-old pregnant woman reported suffering from an aggressive giant cell tumour of the distal humerus extending into the elbow joint. The successful management required a careful evaluation of the various treatment options due to her pregnancy. Surgical excision of the mass was performed. The residual bone defect was reconstructed with an elbow mega-prosthesis. The patient made a pain-free recovery with a good range of motion and delivered the baby at term with no complications.

An insight into the implications of estrogen deficiency and transforming growth factor β in antiepileptic drugs-induced bone loss

There have been a number of reports that chronic antiepileptic drug (AEDs) therapy is associated with abnormal bone and calcium metabolism, osteoporosis/osteomalacia, and increased risk of fractures. Bony adverse effects of long term antiepileptic drug therapy have been reported for more than four decades but the exact molecular mechanism is still lacking. Several mechanisms have been proposed regarding AEDs induced bone loss; Hypovitaminosis D, hyperparathyroidism, estrogen deficiency, calcitonin deficiency. Transforming growth factor-β (TGF- β) is abundant in bone matrix and has been shown to regulate the activity of osteoblasts and osteoclasts in vitro. All isoforms of TGF- β are expressed in bone and intricately play role in bone homeostasis by modulating estrogen level. Ovariectomised animal have shown down regulation of TGF- β in bone that could also be a probable target of AEDs therapy associated bone loss. One of the widely accepted hypotheses regarding the conventional drugs induced bone loss is hypovitaminosis D which is by virtue of their microsomal enzyme inducing effect. However, despite of the lack of enzyme inducing effect of certain newer antiepileptic drugs, reduced bone mineral density with these drugs have also been reported. Thus an understanding of bone biology, pathophysiology of AEDs induced bone loss at molecular level can aid in the better management of bone loss in patients on chronic AEDs therapy. This review focuses mainly on certain new molecular targets of AEDs induced bone loss.

Unraveling the Links Underlying Arterial Stiffness, Bone Demineralization, and Muscle Loss

The effects of elevated arterial stiffness on cardiovascular outcomes are widely studied, whereas the relation to noncardiovascular outcomes relevant to older persons, such as the effect on bones and muscles, is less well established. Arterial stiffness, bone demineralization, and muscle loss are all age-related processes with common risk factors, however, whether these are just parallel age-related alterations or whether these processes share common pathways is not yet understood. In this review, we outline previous literature using different assessments of arterial stiffness in various populations across the world to produce a comprehensive overview. Although there are many studies showing an association between arterial stiffness and loss of bone and muscle, the majority are cross-sectional and there is limited longitudinal evidence to justify causal conclusions. We also give an in-depth review of hypotheses and possible mechanisms which may underlie these associations including hormone dysregulation, impaired glucose metabolism, and inflammation. This narrative review highlights the associations between vessels, bones, and muscles with aging, offering insights into possible shared pathways.

Gonadal Hormones and Bone

In both sexes, estrogen is one of the most essential hormones for maintaining bone integrity. Also, especially in men, androgen has beneficial effects on bone independent of estrogen. However, estrogen replacement therapy for postmenopausal women increases the risk of developing breast cancer and endometrial cancer, and androgen replacement therapy for partial androgen deficiency of the aging male increases the risk of developing prostate cancer. Various mechanisms have been proposed on the effects of gonadal hormones on bone, such as effects through cytokines including IL-6 and effects on the OPG/RANKL ratio. In addition, large amounts of new information deriving from high-throughput gene expression analysis raise the possibility of multiple other effects on bone cells. Both estrogen and androgen exert their effects via the estrogen receptor (ER) or the androgen receptor (AR), which belongs to the nuclear receptor superfamily. Compounds such as selective estrogen receptor modulators (SERMs) and selective androgen receptor modulators (SARMs) also bind ER and AR, respectively. However, SERMs and SARMs alter the ER or AR structure differently from estrogen or androgen, resulting in other downstream gene responses. As a result they can exert favorable effects on bone while suppressing the undesirable actions of estrogen and androgen. Elucidation of ER and AR ligand-specific and tissue-specific gene regulation mechanisms will also provide information on the signal transduction mechanisms of other nuclear receptors and will be valuable for the development of new therapeutic agents.

Regulation of Bone Metabolism by Sex Steroids

Osteoporosis is a significant public health problem, and a major cause of the disease is estrogen deficiency following menopause in women. In addition, considerable evidence now shows that estrogen is also a major regulator of bone metabolism in men. Since the original description of the effects of estrogen deficiency on bone by Fuller Albright more than 70 years ago, there has been enormous progress in understanding the mechanisms of estrogen and testosterone action on bone using human and mouse models. Although we understand more about the effects of estrogen on bone as compared with testosterone, both sex steroids do play important roles, perhaps in a somewhat compartment-specific (i.e., cancellous vs. cortical bone) manner. This review summarizes our current knowledge of sex steroid action on bone based on human and mouse studies, identifies both agreements and potential discrepancies between these studies, and suggests directions for future research in this important area.

Coronary Calcification Is Reversely Related with Bone and Hair Calcium: The Relationship among Different Calcium Pools in Body

Background

With aging, calcium efflux from bone is increased with age-related bone loss, and it can reduce bone mineral density (BMD). On the contrary, age-related calcium adoption into arterial wall progressively stiffens blood vessels. Theses process insinuates shift of calcium among different pools in body. However, their relationships have not been elucidated yet. So we investigated the correlation among calcium contents in different body pools, such as hair, bone, and blood vessels in women.

Methods

We analyzed 50 females retrospectively who measured Agatston coronary artery calcium score (CACS), BMD, and hair calcium concentration at a regular health check-up in a university hospital. CACS was achieved by coronary multidetector computed tomography, BMD was measured by dual energy X-ray absorptiometry in the lumbar spine and femur, and hair calcium level was checked by hair tissue mineral analysis.

Results

CACS inversely correlated with BMD (r=-0.280, P=0.049 with lumbar vertebrae 1-4, r=-0.310, P=0.028 with femur neck, r=-0.333, P=0.018 with femur total) and hair calcium concentration (r=-0.352, P=0.012).

Conclusions

CACS has negative correlation with BMD and hair calcium level in women. Different body calcium pools such as bone, hair and blood vessel significantly correlated each other.

Review : Gonadal Steroids and Affective Illness

Gonadal steroids seem to regulate affective state in some people (but not all), despite the absence of abnormal steroid hormone levels or dysfunction of the reproductive endocrine axis. In this article, we attempt to explain this paradox 1) by describing the molecular mechanisms by which gonadal steroids can regulate neuronal function; 2) by describing the specific regulatory impact of gonadal steroids on two systems im plicated in the pathophysiology of mood disorders; and 3) by defining the role of gonadal steroids in several mood disorders linked to periods of reproductive change. We suggest that the context in which the neuro- regulatory actions of gonadal steroids occur determines the impact of steroid signaling on the regulation of affective state. NEUROSCIENTIST 5:227-237, 1999

Exophytic giant-cell tumor of the tibial tubercle

A 23-year-old pregnant woman presented to the orthopedic tumor clinic with gradual onset of left anteriomedial tibial pain for one month and a lytic lesion of the proximal tibia on radiography. MRI showed an exophytic mass of the left tibial tubercle with fluid-fluid levels. The patient underwent surgical excision, and pathology was consistent with giant-cell tumor. This lesion is notable for its exophytic growth pattern and its location at the tibial tubercle. Giant-cell tumors are almost always epiphyseal in location in skeletally mature patients. Although the tibial tubercle is sometimes thought of as metaphyseal, it is an epiphyseal equivalent for bone tumor growth. The role of the patient's pregnancy in the pathophysiology of her tumor is unclear.

Metachronous multicentric giant cell tumour in a young woman

Multicentric giant cell tumours (GCTs) are very rare and account for less than 1% of all GCTs of bone. We report a case of a young woman with metachronous multicentric GCTs with 5 documented lesions in the same lower limb. The initial lesion started during the first trimester of pregnancy around her right pelvis, which rapidly progressed as a painful swelling with gradually restricted mobility of her right hip joint. The radiological appearance of this tumour was that of a GCT and biopsy confirmed the diagnosis. The role of positron emission tomography (PET) has been highlighted to detect occult lesions. A possible hormonal correlation for these tumours has been discussed. The patient was managed successfully by an aggressive surgical approach for knee and talar lesions, whereas repeated embolisation and denosumab injections were given to treat her pelvic lesion.

Interaction between bone and muscle in older persons with mobility limitations

Aging is associated with a progressive loss of bone-muscle mass and strength. When the decline in mass and strength reaches critical thresholds associated with adverse health outcomes, they are operationally considered geriatric conditions and named, respectively, osteoporosis and sarcopenia. Osteoporosis and sarcopenia share many of the same risk factors and both directly or indirectly cause higher risk of mobility limitations, falls, fractures and disability in activities of daily living. This is not surprising since bones adapt their morphology and strength to the long-term loads exerted by muscle during anti-gravitational and physical activities. Non-mechanical systemic and local factors also modulate the mechanostat effect of muscle on bone by affecting the bidirectional osteocyte-muscle crosstalk, but the specific pathways that regulate these homeostatic mechanisms are not fully understood. More research is required to reach a consensus on cut points in bone and muscle parameters that identify individuals at high risk for adverse health outcomes, including falls, fractures and disability. A better understanding of the muscle-bone physiological interaction may help to develop preventive strategies that reduce the burden of musculoskeletal diseases, the consequent disability in older persons and to limit the financial burden associated with such conditions. In this review, we summarize age-related bone-muscle changes focusing on the biomechanical and homeostatic mechanisms that explain bone-muscle interaction and we speculate about possible pathological events that occur when these mechanisms become impaired. We also report some recent definitions of osteoporosis and sarcopenia that have emerged in the literature and their implications in clinical practice. Finally, we outline the current evidence for the efficacy of available anti-osteoporotic and proposed antisarcopenic interventions in older persons.

Increased bone remodelling around titanium implants coated with chondroitin sulfate in ovariectomized rats

Coating titanium implants with artificial extracellular matrices based on collagen and chondroitin sulfate (CS) has been shown to enhance bone remodelling and de novo bone formation in vivo. The aim of this study was to evaluate the effect of estrogen deficiency and hormone replacement therapy (HRT) on the osseointegration of CS-modified Ti implants. 30 adult female, ovariectomized Wistar rats were fed either with an ethinyl-estradiol-rich diet (E) to simulate a clinical relevant HRT or with a genistein-rich diet (G) to test an alternative therapy based on nutritionally relevant phytoestrogens. Controls (C) received an estrogen-free diet. Uncoated titanium pins (Ti) or pins coated with type-I collagen and CS (Ti/CS) were inserted 8weeks after ovarectomy into the tibia. Specimens were retrieved 28days after implantation. Both the amount of newly formed bone and the affinity index (P<0.05) were moderately higher around Ti/CS implants as compared to uncoated Ti. The highest values were measured in the G-Ti/CS and E-Ti/CS groups, the lowest values for the E-Ti and G-Ti controls. Quantitative synchrotron radiation micro-computed tomography (SRμCT) revealed the highest increase in total bone formation around G-Ti/CS as compared to C-Ti (P<0.01). The effects with respect to direct bone apposition were less pronounced with SRμCT. Using scanning nanoindentation, both the indentation modulus and the hardness of the newly formed bone were highest in the E-Ti/CS, G-Ti/CS and G-Ti groups as compared to C-Ti (P<0.05). Coatings with collagen and CS appear to improve both the quantity and quality of bone formed around Ti implants in ovarectomized rats. A simultaneous ethinyl estradiol- and genistein-rich diet seems to enhance these effects.

Glucocorticoids and estrogens modulate the NF-κB pathway differently in the micro- and macrovasculature

Estrogens and glucocorticoids have synergistic effects in the micro and macrovasculature of endothelial cells (ECs), having pro-inflammatory effects in the former and inhibiting the expression of adhesion molecules in the latter. The molecular basis of these effects in the endothelium has not yet been clarified. We postulate that the ECs of the micro- and macrovasculature have different non-genomic mechanisms that regulate levels of preexisting complexes of glucocorticoids and estrogens with their respective receptors. Since these receptors are regulated by NF-κB, their expression could be critical to the activation of a pro- or anti-inflammatory response. In the macrovasculature the synergistic effects of estrogens and glucocorticoids on ECs may be through the inhibition of NF-κB, leading to the inhibition of the expression of inflammatory molecules. It seems likely that glucocorticoid-receptor and estrogen-receptor complexes directly bind to NF-κB proteins in the macrovasculature, resulting in the inhibition of an excessive proinflammatory response. Further insights into these processes may help clarify the role of the endothelial cells of different vascular beds during the inflammatory response and chronic inflammation, and thus contribute to the design of more effective therapeutic strategies for the prevention of diseases related to inflammation, including atherosclerosis, systemic lupus erythematosus and rheumatoid arthritis.

Pulse Wave Velocity in Postmenopausal Women

Cardiovascular disease (CVD) and osteoporosis are major causes of morbidity and mortality in postmenopausal women. The relationship between atherosclerosis and osteoporosis has been established by studies of the underlying pathophysiological mechanisms and biochemical pathways that seem to overlap in many places. Pulse wave velocity (PWV) is one of the known predictors of cardiovascular and all-cause mortality. Studies indicate that PWV in hypertensive postmenopausal women is increased, and hormone replacement therapy (HRT) attenuates this increase. In addition, recently, many studies have suggested a role for arterial stiffness in the association between CVD and osteoporosis. From these findings, it appears that estrogen deficiency combined with production of inflammatory cytokines plays a role in increased PWV closely associated with CVD and osteoporosis, although the mechanisms of arterial stiffness in postmenopausal women may be more complex. Accordingly, a possible role for PWV as a surrogate marker of CVD as well as osteoporosis in postmenopausal women is discussed in this review. First, menopause leads to increased arterial stiffness with aging in females. Further, epidemiological data evaluating arterial stiffness assessed by PWV provided evidence that most of the established CVD risk factors are determinants of PWV, and these risk factors are increased in patients with CVD. In turn, contrary to expectation, HRT did not always contribute to a lower incidence of CVD in postmenopausal women. By reviewing the current data available, it becomes clear that, at present, the effects of menopause including HRT on PWV remain controversial, and further studies are needed to clarify these associations.

Giant cell tumor of bone: a basic science perspective

Comprehending the pathogenesis of giant cell tumor of bone (GCT) is of critical importance for developing novel targeted treatments for this locally-aggressive primary bone tumor. GCT is characterized by the presence of large multinucleated osteoclast-like giant cells distributed amongst mononuclear spindle-like stromal cells and other monocytes. The giant cells are principally responsible for the extensive bone resorption by the tumor. However, the spindle-like stromal cells chiefly direct the pathology of the tumor by recruiting monocytes and promoting their fusion into giant cells. The stromal cells also enhance the resorptive ability of the giant cells. This review encompasses many of the attributes of GCT, including the process of giant cell formation and the mechanisms of bone resorption. The significance of the receptor activator of nuclear factor-κB ligand (RANKL) in the development of GCT and the importance of proteases, including numerous matrix metalloproteinases, are highlighted. The mesenchymal lineage of the stromal cells and the origin of the hematopoietic monocytes are also discussed. Several aspects of GCT that require further understanding, including the etiology of the tumor, the mechanisms of metastases, and the development of an appropriate animal model, are also considered. By exploring the current status of GCT research, this review accentuates the significant progress made in understanding the biology of the tumor, and discusses important areas for future investigation.

The pathogenesis of osteoarthritis involves bone, cartilage and synovial inflammation: may estrogen be a magic bullet?

The female predominance of polyarticular osteoarthritis (OA), and in particular the marked increase of OA in women after the menopause points to a likely involvement of female sex hormones in the maintenance of cartilage homeostasis. This perception has inspired many research groups to investigate the role of estrogens in the modulation of cartilage homeostasis with the ultimate aim to clarify whether estrogen replacement therapy (ERT) could provide benefits in preventing the rapid rise in the prevalence of OA in postmenopausal women. The effects of ERT and selective estrogen-receptor modulators on the joint in various experimental models have been investigated. Clinically, the effects of estrogens have been evaluated by post hoc analysis in clinical trials using biochemical markers of cartilage and bone degradation. Lastly, the Women's Health Initiative trial (WHI) investigated the effects of estrogens on the joint and joint replacements. Even though the exact mode of action still needs to be elucidated, the effect involves both direct and indirect mechanisms on the whole joint pathophysiology. Several animal models have demonstrated structural benefits of estrogens, as well as significant effects on joint inflammation. This is in complete alignment with clinical data using biochemical markers of joint degradation which demonstrated approximately 50% inhibition of cartilage destruction. These finding were recently validated in WHI, where women taking estrogens had significantly less joint replacement. In conclusion, the pleiotropic effect of estrogens on several different tissues may match the complicated aetiology of OA in some important aspects.

Aging and bone loss: new insights for the clinician

It is well known that the underlying mechanisms of osteoporosis in older adults are different than those associated with estrogen deprivation. Age-related bone loss involves a gradual and progressive decline, which is also seen in men. Markedly increased bone resorption leads to the initial fall in bone mineral density. With increasing age, there is also a significant reduction in bone formation. This is mostly due to a shift from osteoblastogenesis to predominant adipogenesis in the bone marrow, which also has a lipotoxic effect that affects matrix formation and mineralization. We review new evidence on the pathophysiology of age-related bone loss with emphasis upon the mechanism of action of current osteoporosis treatments. New potential treatments are also considered, including therapeutic approaches to osteoporosis in the elderly that focus on the pathophysiology and potential reversal of adipogenic shift in bone.

Expression pattern of SVEP1 alternatively-spliced forms

SVEP1 is a multi-domain protein recognized as a cell adhesion molecule (CAM). In this study, we focused on the activity regulation of an alternative promoter (AP) and the expression of alternative splice forms of mRNA from SVEP1 gene. The expression of SVEP1 isoforms was analyzed on RNA isolated from pre-osteoblastic MBA-15 and mammary adenocarcinoma DA3 cells grown alone or following co-culture between these cells. The co-culture system aimed to mimic the cellular cross talk that exists in the bone microenvironment once the mammary cells invade the bone. We demonstrated that SVEP1 isoforms were differentially expressed between these cells. The various isoforms levels were affected by co-culturing or in cells treated with TNFα or estrogen. Both cell lines exhibited an increase of message levels of a and e isoforms following the co-culture conditions. A novel aspect presented here is related to existence of an alternative promoter (AP) in SVEP1 gene. The AP was in silico predicted and analyzed for binding by specific transcription factors (TFIIB, ERα, NF-κB, Sp1 and pcJUN) using Chromatin immunoprecipitation (ChIP) assay. The binding of these TFs results in a non uniform binding pattern when comparing between the DA3 and MBA-15 cells. Using the demethylation agent, 5'-aza-deoxycitidine and histone deacetylase inhibitor, Trichostatin-A allowed to study the methylation level of the AP and the message expression. This study provides insights into alternative splice forms of SVEP1 and their regulation that may play a role within the bone niche with invading carcinoma cells.

Regulation of SVEP1 gene expression by 17β-estradiol and TNFα in pre-osteoblastic and mammary adenocarcinoma cells

Breast cancer is one of several tumors, including prostate, thyroid and kidney, which display a remarkable predilection for metastasis to bone. The preference to metastasize to bone by tumor cells relies on specific interactions among tumor cells, bone marrow microenvironment and bone cells. Osteomimicry is postulated to enable the survival of tumor cells in the bone tissue. Using gene profiling array and RT-PCR we demonstrated the message expression of few bone matrix proteins in mammary adenocarcinoma cells as well as that of cell adhesion molecules (CAMs). A CAM molecule, named SVEP1, was previously shown to be expressed in osteoblastic cells both in vivo and in vitro mediating cell adhesion in the bone-marrow niches. Both estradiol (17βE(2)) and TNFα regulate the expression of adhesion molecules and act in bone-cancer-crosstalk. We focused on differential regulation of SVEP1 gene comparing pre-osteoblastic MBA-15 and mammary adenocarcinoma DA3 cells. 17βE(2) and TNFα activated SVEP1 promoter, increased its message and protein levels in both cell types. Using chromatin immunoprecipitation assay, we quantified SVEP1 promoter occupancy by transcription factors; TFIIB, ERα, NF-κB, Sp1 and their binding was also regulated by both factors. By comparing pre-osteoblastic with mammary adenocarcinoma cells, the study expands our understanding of SVEP1 gene expression regulation and it sheds light on its involvement in bone-cancer-microenvironment interactions.

TGF-β mediates suppression of adipogenesis by estradiol through connective tissue growth factor induction

In the bone marrow cavity, adipocyte numbers increase, whereas osteoblast progenitor numbers decrease with aging. Because adipocytes and osteoblasts share a common progenitor, it is possible that this shift is due to an increase in adipocyte-lineage cells at the expense of osteoblast-lineage commitment. Estrogens inhibit adipocyte differentiation, and in both men and women, circulating estrogens correlate with bone loss with aging. In bone cells, estrogens stimulate expression of TGF-β and suppress mesenchymal cell adipogenesis. Using a tripotential mesenchymal cell line, we have examined whether estradiol suppression of adipocyte differentiation is due to stimulation of TGF-β and the mechanism by which TGF-β suppresses adipogenesis. We observed that estradiol-mediated suppression of adipogenic gene expression required at least 48 h treatment. TGF-β expression increased within 24 h of estradiol treatment, and TGF-β inhibition reversed estradiol influences on adipogenesis and adipocyte gene expression. Connective tissue growth factor (CTGF) mediates TGF-β suppression of adipogenesis in mouse 3T3-L1 cells. CTGF expression was induced within 24 h of TGF-β treatment, whereas estradiol-mediated induction required 48 h treatment. Moreover, estradiol-mediated induction of CTGF was abrogated by TGF-β inhibition. These data support that estradiol effects on adipogenesis involves TGF-β induction, which then induces CTGF to suppress adipogenesis.

Giant cell bone tumor of the thoracic spine presenting in late pregnancy

BACKGROUND

We report a case of a large giant cell tumor of the thoracic spine presenting with spinal cord compression during pregnancy.

CASE

A 24-year-old woman presented at term with lower back pain, bilateral lower extremity weakness, numbness, and bowel and bladder incontinence. Magnetic resonance imaging revealed a spinal soft tissue mass compressing the spinal cord. The patient delivered a healthy girl by cesarean then underwent a T8-T9 laminectomy, posterior spinal decompression, and instrument fusion. Two days later, she had a thoracotomy, corpectomy of the vertebral body, and anterior tumor debulking. Ultimately, the patient was discharged to inpatient rehabilitation with improved lower extremity strength and returned bowel and bladder function.

CONCLUSION

Obstetricians should be vigilant regarding progressive neurologic symptoms during pregnancy.

Osteoclast activity and subtypes as a function of physiology and pathology--implications for future treatments of osteoporosis

Osteoclasts have traditionally been associated exclusively with catabolic functions that are a prerequisite for bone resorption. However, emerging data suggest that osteoclasts also carry out functions that are important for optimal bone formation and bone quality. Moreover, recent findings indicate that osteoclasts have different subtypes depending on their location, genotype, and possibly in response to drug intervention. The aim of the current review is to describe the subtypes of osteoclasts in four different settings: 1) physiological, in relation to turnover of different bone types; 2) pathological, as exemplified by monogenomic disorders; 3) pathological, as identified by different disorders; and 4) in drug-induced situations. The profiles of these subtypes strongly suggest that these osteoclasts belong to a heterogeneous cell population, namely, a diverse macrophage-associated cell type with bone catabolic and anabolic functions that are dependent on both local and systemic parameters. Further insight into these osteoclast subtypes may be important for understanding cell-cell communication in the bone microenvironment, treatment effects, and ultimately bone quality.

Effects of chronic estrogen treatment on modulating age-related bone loss in female mice

While female mice do not have the equivalent of a menopause, they do undergo reproductive senescence. Thus, to dissociate the effects of aging versus estrogen deficiency on age-related bone loss, we sham-operated, ovariectomized, or ovariectomized and estrogen-replaced female C57/BL6 mice at 6 months of age and followed them to age 18 to 22 months. Lumbar spines and femurs were excised for analysis, and bone marrow hematopoietic lineage negative (lin-) cells (enriched for osteoprogenitor cells) were isolated for gene expression studies. Six-month-old intact control mice were euthanized to define baseline parameters. Compared with young mice, aged/sham-operated mice had a 42% reduction in lumbar spine bone volume/total volume (BV/TV), and maintaining constant estrogen levels over life in ovariectomized/estrogen-treated mice did not prevent age-related trabecular bone loss at this site. By contrast, lifelong estrogen treatment of ovariectomized mice completely prevented the age-related reduction in cortical volumetric bone mineral density (vBMD) and thickness at the tibial diaphysis present in the aged/sham-operated mice. As compared with cells from young mice, lin- cells from aged/sham-operated mice expressed significantly higher mRNA levels for osteoblast differentiation and proliferation marker genes. These data thus demonstrate that, in mice, age-related loss of cortical bone in the appendicular skeleton, but not loss of trabecular bone in the spine, can be prevented by maintaining constant estrogen levels over life. The observed increase in osteoblastic differentiation and proliferation marker gene expression in progenitor bone marrow cells from aged versus young mice may represent a compensatory mechanism in response to ongoing bone loss.

Steroid hormone metabolizing enzymes in benign and malignant human bone tumors

IMPORTANCE IN THE FIELD: Primary bone tumors are considered as (sex steroid) hormone-dependent tumors. Osteosarcoma, osteoblastoma and bone cysts are preferentially found in males, while giant cell tumors are more common in females. Indeed, bone tumor development and progression are influenced by sex steroid hormones derived from in situ synthesis in bone cells.

AREAS COVERED IN THIS REVIEW

This review describes intracrine mechanisms for local formation of the biologically most active estrogen, 17beta-estradiol (E2), from circulating steroid precursors through the 'aromatase' (aromatization of androgens) and the 'sulfatase' (conversion of inactive estrone-sulfate) pathway.

WHAT THE READER WILL GAIN

The reader gains knowledge on both pathways and the enzymes, which contribute to the in situ availability of active hormones, namely 3beta-hydroxysteroid dehydrogenases, 17beta-hydroxysteroid dehydrogenases, aromatase, steroid sulfatases and sulfotransferases. An overview is given and the expression and function of these enzymes in bone tumors are discussed.

TAKE HOME MESSAGE

Knowledge on pathways for the in situ formation of E2 in bone cells may allow the identification of potential targets for i) novel endocrine therapeutic options in primary bone tumors and ii) future preventive interventions.

Physiology of bone loss

The physiology of bone loss in aging women and men is largely explained by the effects of gonadal sex steroid deficiency on the skeleton. In women, estrogen deficiency is the main cause of early rapid postmenopausal bone loss, whereas hyperparathyroidism and vitamin D deficiency are thought to explain age-related bone loss later in life. Surprisingly, estrogen deficiency also plays a dominant role in the physiology of bone loss in aging men. Many other factors contribute to bone loss in aging women and men, including defective bone formation by aging osteoblasts, impairment of the growth hormone/insulin-like growth factor axis, reduced peak bone mass, age-associated sarcopenia, leptin secreted by adipocytes, serotonin secreted by the intestine, and a long list of sporadic secondary causes. Further elucidation of the relative importance of each of these factors will lead to improved preventive and therapeutic approaches for osteoporosis.

Female reproductive system and bone

The female reproductive system plays a major role in regulating the acquisition and loss of bone by the skeleton from menarche through senescence. Onset of gonadal sex steroid secretion at puberty is the major factor responsible for skeletal longitudinal and radial growth, as well as significant gain in bone density, until peak bone density is achieved in third decade of life. Gonadal sex steroids then help maintain peak bone density until menopause, including during the transient changes in skeletal mineral content associated with pregnancy and lactation. At menopause, decreased gonadal sex steroid production normally leads to rapid bone loss. The most rapid bone loss associated with decreased estrogen levels occurs in the first 8-10 years after menopause, with slower age-related bone loss occurring during later life. Age-related bone loss in women after the early menopausal phase of bone loss is caused by ongoing gonadal sex steroid deficiency, vitamin D deficiency, and secondary hyperparathyroidism. Other factors also contribute to age-related bone loss, including intrinsic defects in osteoblast function, impairment of the GH/IGF axis, reduced peak bone mass, age-associated sarcopenia, and various sporadic secondary causes. Further understanding of the relative contributions of the female reproductive system and each of the other factors to development and maintenance of the female skeleton, bone loss, and fracture risk will lead to improved approaches for prevention and treatment of osteoporosis.

Neuropeptide Y and sex hormone interactions in humoral and neuronal regulation of bone and fat

The hypothalamus regulates the skeleton and adipose tissue via endocrine mechanisms. Changes in sex steroid levels in menopause and aging are central to the associated changes in bone mass and adiposity. Whereas many of these effects occur via direct actions on osteoblasts or adipocytes, sex hormones can also mediate effects on bone and adipose tissue via interaction with neuronal pathways. A key hypothalamic regulator of bone and adipose tissue is neuropeptide Y (NPY), which coordinately influences these tissues via effects on neuroendocrine and sympathetic nervous output. Better understanding of the interaction between NPY and sex steroids in regulating skeletal and energy homeostasis could lead to more effective treatments for osteoporosis and obesity.

Bone mineral density, arterial stiffness, and coronary atherosclerosis in healthy postmenopausal women

OBJECTIVE

The aim of this study was to assess the correlation between bone mineral density (BMD), arterial stiffness, and coronary atherosclerosis in healthy postmenopausal women.

METHODS

We performed a retrospective review of 152 postmenopausal women who visited the health promotion center for a routine checkup, after excluding participants who had factors affecting BMD and coronary artery disease. BMD was evaluated by dual-energy x-ray absorptiometry in the lumbar spine and femur. Arterial stiffness was measured by brachial-ankle pulse wave velocity (baPWV), and coronary atherosclerosis was assessed by 64-row multidetector computed tomography.

RESULTS

Women with osteoporosis had a significantly higher baPWV than those in the osteopenia and normal BMD groups. Higher baPWV was also associated with the presence of atherosclerosis. The baPWV was significantly positively correlated with age, systolic blood pressure, diastolic blood pressure, and neutrophil to lymphocyte ratio and negatively correlated with femur BMD. The optimum predictive value of baPWV in coronary atherosclerosis was estimated using the receiver operating characteristic curve. A cutoff of 1,506 cm/second would give a sensitivity of 83.3% and specificity of 82.9%. A higher overall risk for coronary atherosclerosis emerges with higher baPWV levels (>1,500 cm/s) after controlling for age and cardiovascular risk factors.

CONCLUSIONS

Arterial stiffness by measuring baPWV can be a useful independent predictor for coronary atherosclerosis. In addition, our results suggest that postmenopausal women with osteoporosis should be considered for further evaluation of coronary atherosclerosis.

Estrous Cycle‐Dependent Expression of Estrogen Receptor α in Periodontal Tissue

Estrogen receptor alpha (ERalpha) may play important roles in many estrogen physiological effects, but little is known about the fluctuation of ERalpha during the estrous cycle. In this study, the dynamic expression of ERalpha mRNA and protein in periodontal tissue during the estrous cycle were examined. Forty 12-week-old female rats were divided into four groups, based on the estrous cycle stage, and sacrificed. Immunohistochemistry and in situ hybridization were used to detect dynamic changes in ERalpha protein and mRNA in periodontal tissue during the estrous cycle, and data were analyzed by one-way ANOVA and cosinor analysis for temporal patterns. Significant differences (p<0.05) were found in the expression of ERalpha protein and mRNA among the four groups. The expression of ERalpha protein and mRNA exhibited an infradian rhythm with a period of about 120 h (five days). The phase and amplitude differences between ERalpha protein and mRNA were not significant (p>0.05). The results suggest the expression of ERalpha is dynamic during the estrous cycle and that in the future chronobiologic methods should be used to study the mechanism of estrogen effect on periodontal tissue.

Estrogen action on bone marrow osteoclast lineage cells of postmenopausal women in vivo

In bone marrow aspirates from postmenopausal women, systemic estrogen treatment decreased differentiation of mononuclear progenitor cells toward a more mature osteoclast phenotype. This was not associated with changes in surface receptor for proresorptive cytokines.

INTRODUCTION

Although mechanisms by which estrogen (E) decreases bone resorption have been extensively studied in rodents, little information is available in humans.

METHODS

In bone marrow aspirates from 34 early postmenopausal women randomly assigned to receive 4 weeks of treatment (100 microg/day of transdermal 17beta-estradiol) or no treatment, we assessed osteoclast differentiation and surface receptors using flow cytometry with fluorescent-labeled specific antibodies.

RESULTS

E treatment decreased (P < 0.05) the proportion of bone marrow mononuclear cells (BMMNCs) expressing the calcitonin receptor (CTR), a late osteoclast phenotype marker. There was an increase in c-Fms concentration in osteoclast lineage cells (P < 0.05) and in the proportion of BMMNCs expressing TNFR2 (P < 0.05), but there were no significant effects on other surface receptors for proresorptive factors (RANK, TNFR1, TREM2, or OSCAR). Changes in serum CTx and TRAP 5b, markers for bone resorption, correlated directly (P < 0.05) with the proportion of BMMNCs expressing CTR and, for TRAP 5b only, TNFR2 and inversely with c-Fms concentration (all P < 0.05).

CONCLUSION

E reduces bone resorption, in part, by decreasing differentiation of BMMNCs into mature osteoclasts. This action cannot be explained by decreased concentrations of surface receptors for proresorptive factors. The roles of increases in c-Fms concentration and the proportion of TNFR2((+)) cells are unclear.

Relationship between carotid atherosclerosis and lumbar spine bone mineral density in postmenopausal women

Osteoporosis and increased carotid intima-media thickness (IMT) have been associated with atherosclerosis. We investigated the correlation between carotid IMT and lumbar spine bone mineral density (BMD) in postmenopausal women. We studied the carotid IMT in 175 postmenopausal women, including 43 women (control) with normal spinal BMD, 73 women with osteopenia, and 59 women with osteoporosis. Carotid IMT was assessed by ultrasonography. BMD at the lumbar spine (lumbar 2 to 4 vertebrae) was measured by dual-energy X-ray absorptiometry. Age, years since menopause, and carotid IMT were significantly greater in the osteoporosis group than in the control (all p<0.01) and osteopenia groups (all p<0.01). Estradiol was significantly lower in the osteoporosis group than in the control group (p<0.05). BMD was significantly lower in the osteoporosis group than in the osteopenia or control group (both p<0.01) and in the osteopenia group than in the control group (p<0.01). After adjusting for age, years since menopause, and estradiol, women with osteoporosis had significantly greater carotid IMT than controls (p<0.05). The univariate linear regression analysis revealed that carotid IMT was significantly positively correlated with age, years since menopause, and low-density lipoprotein (LDL) cholesterol (all p<0.05) and was significantly negatively correlated with estradiol and BMD (all p<0.05), but showed no significant association with other clinical variables. In multivariate regression analysis, the carotid IMT was significantly positively correlated with LDL cholesterol (p<0.01) and negatively correlated with BMD (p<0.01), but not with other variables. Carotid atherosclerosis might be associated with lumbar spine bone mass in postmenopausal women, suggesting that postmenopausal women with osteoporosis may have more advanced carotid atherosclerosis than those with a normal bone mass.

The effect of sexual hormone abnormalities on proximal femur bone mineral density in hemodialysis patients and the possible role of RANKL

Sexual hormone concentrations are commonly affected in chronic renal failure. The contribution of sex steroids to bone turnover regulation implies that sex steroid's dysfunction may be implicated in the emergence of renal osteodystrophy. This study was conducted to evaluate sex steroids and gonadotrophins in hemodialysis (HD) patients and to investigate their role in bone homeostasis in concert with other hormones and cytokines. Bone mineral density (BMD) at the proximal femur and intact parathyroid hormone (iPTH), osteoprotegerin, soluble receptor activator of NF-kappaB ligand (sRANKL), prolactin, total testosterone, estradiol, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were measured in serum samples in 42 patients, 21 men and 21 women, on maintenance HD therapy. Possible associations between clinical characteristics, biochemical parameters, and BMD values were investigated. In male HD patients, the testosterone concentration declined significantly with aging, whereas the estradiol level increased with longer duration of HD. Concurrently, testosterone correlated negatively with sRANKL concentrations (r=-0.520, p=0.016). Luteinizing hormone levels in male patients demonstrated statistically significant negative correlations with BMD values of the proximal femur. In the entire cohort of patients, FSH and LH were negatively associated with absolute values of proximal femur BMD. Gonadotrophin and sexual hormone concentrations in HD patients are associated with bone mineral status and consequently their derangements appear to contribute to the development of bone composition abnormalities in different types of renal osteodystrophy. Furthermore, testosterone's association with sRANKL levels in male HD patients suggests that RANKL may mediate the effect of testosterone on bone metabolism in these patients.

Estrogen-TGFbeta cross-talk in bone and other cell types: role of TIEG, Runx2, and other transcription factors

It is well established that E(2) and TGFbeta have major biological effects in multiple tissues, including bone. The signaling pathways through which these two factors elicit their effects are well documented. However, the interaction between these two pathways and the potential consequences of cross-talk between E(2) and TGFbeta continue to be elucidated. In this prospectus, we present known and potential roles of TIEG, Runx2, and other transcription factors as important mediators of signaling between these two pathways.

The effect of combined androgen blockade on bone turnover and bone mineral density in men with prostate cancer

Our study and previous reports suggest that castration results in increased bone turnover and lowered BMD and that these changes might be attenuated by anti-androgens, such as BL and EMP.

INTRODUCTION

Recent studies have shown that castration for PC decreases bone mineral density (BMD), while estrogen therapy or bicalutamide (BL) monotherapy maintains BMD. However, the effect of combined androgen blockade (CAB) on bone turnover is not well studied.

METHODS

A total of 204 men were evaluated in the study (control group: n = 56, castration group: n = 102, 'CAB with BL' group: n = 22, 'CAB with estramustine phosphate (EMP)' group: n = 24). We measured steroid hormone levels, BMD (measured at one-third distal radius), bone turnover markers (levels of urinary N-telopeptide cross links of type 1 collagen (u-NTx) and deoxypyridinoline (u-DPD), serum concentrations of osteocalcin (OC)) in order to assess differences between groups.

RESULTS

The BMD % Z score of the castration group was significantly lower than that of the control group or the 'CAB with EMP' group (90.6% vs. 95.5%, 98.6%; p < 0.042, p < 0.044, respectively). Levels of u-NTx, u-DPD, OC of the castration group were the highest followed by the control group, then the 'CAB with BL' group and the 'CAB with EMP' group.

CONCLUSIONS

Our study and previous reports suggests that castration results in increased bone turnover and lowered BMD and that these changes might be attenuated by anti-androgens, such as BL and EMP.

Androgen deprivation therapy for prostate cancer: new concepts and concerns

PURPOSE OF REVIEW

The aim of this review is to summarize new concepts and concerns regarding treatment-related osteoporosis, diabetes, and cardiovascular disease in men receiving androgen deprivation therapy for prostate cancer.

RECENT FINDINGS

Gonadotropin-releasing hormone agonists increase bone turnover, decrease bone mineral density, and increase fracture risk. Bisphosphonates, selective and estrogen receptor modulators significantly increase bone mineral density during androgen deprivation therapy. Ongoing randomized controlled trials will assess efficacy of denosumab, toremifene, and zoledronic acid to prevent fractures in this setting. Gonadotropin-releasing hormone agonists also increase fat mass, decrease insulin sensitivity, and increase serum lipoproteins. In contrast to the classical metabolic syndrome, however, the phenotype of men during androgen deprivation therapy is characterized by increased high-density lipoprotein cholesterol and preferential accumulation of subcutaneous fat. Gonadotropin-releasing hormone agonists are associated with greater risk of incident diabetes and cardiovascular disease in men with prostate cancer.

SUMMARY

Androgen therapy increases risk of fractures, diabetes mellitus, and cardiovascular disease in men with prostate cancer. Current and planned studies will evaluate strategies to prevent these treatment-related adverse effects.

Relationship Between Brachial Arterial Endothelial Function and Lumbar Spine Bone Mineral Density in Postmenopausal Women

BACKGROUND

Osteoporosis and endothelial dysfunction have been associated with atherosclerosis. The correlation between brachial arterial endothelial function and lumbar spine bone mineral density (BMD) in postmenopausal women will be investigated.

METHODS AND RESULTS

The endothelial function in 85 postmenopausal women, including 28 women with normal spinal BMD, 27 women with osteopenia, and 30 women with osteoporosis were studied. Brachial arterial flow-mediated vasodilatation (FMD) after reactive hyperemia was assessed by ultrasonography. The BMD at the lumbar spine (lumbar 2 to 4 vertebrae) was measured by dual-energy X-ray absorptiometry. Age, years since menopause, and FMD were significantly greater in the osteoporosis group than in the normal BMD group (p<0.01, p<0.05, and p<0.05, respectively). The BMD was significantly lower in the osteoporosis group than in the osteoporosis or normal BMD group (both p<0.01). After adjusting for age and years since menopause, women with osteoporosis had significantly lesser FMD than those with normal BMD (p<0.05). The univariate linear regression analysis revealed that brachial arterial FMD was significantly positively correlated with BMD (r=0.31, p<0.01), but showed no significant association with other clinical variables. In multivariate regression analysis, the FMD was significantly positively correlated with BMD (p<0.01), but not with other variables.

CONCLUSIONS

Postmenopausal women with osteoporosis might have impaired brachial arterial endothelial function, suggesting that brachial artery endothelial function might be associated with lumbar spine bone mass in postmenopausal women.

Treatment-related osteoporosis in men with prostate cancer

The intended therapeutic effect of gonadotropin-releasing hormone (GnRH) agonists is hypogonadism, a major cause of acquired osteoporosis in men. Consistent with this observation, GnRH agonists increase bone turnover and decrease bone mineral density, a surrogate for fracture risk. Large claims-based analyses and other retrospective studies provide compelling evidence that GnRH agonists increase risk of clinical fractures. Estrogens play a central role in homeostasis of the normal male skeleton, and estrogen deficiency rather than testosterone deficiency seems to be primarily responsible for the adverse skeletal effects of GnRH agonists. In randomized controlled trials, bisphosphonates (pamidronate and zoledronic acid) and selective estrogen receptor modulators (raloxifene and toremifene) increased bone mineral density in GnRH agonist-treated men. Two ongoing large randomized placebo-controlled studies will prospectively define fracture outcomes in men with prostate cancer and assess the efficacy of novel pharmacologic interventions (AMG162, toremifene) during GnRH agonist treatment.

Elevated arterial stiffness in postmenopausal women with osteoporosis

OBJECTIVES

Osteoporosis and increased pulse wave velocity (PWV) are cardiovascular risk factors. We investigated the relationship between PWV and bone mass in the lumbar spine in postmenopausal women.

METHODS

We studied the PWV in 95 women; 38 postmenopausal women with normal spinal bone mineral density (BMD), 32 osteopenic postmenopausal women, and 25 osteoporotic postmenopausal women. The brachial-ankle PWV (baPWV) was measured using an automated device. The BMD of the lumbar spine (L2-L4) was measured using dual-energy X-ray absorptiometry.

RESULTS

After adjusting for age and years since menopause, women with osteoporosis had a significantly higher baPWV than those with normal BMD (1500 +/- 220 cm/s versus 1340 +/- 215 cm/s; P < 0.05), but no significant differences in baPWV were seen between the osteoporotic and osteopenic groups or between the osteopenic and normal BMD groups. In univariate regression analysis, the baPWV was significantly negatively correlated with BMD (r = -0.450, P < 0.01), and significantly positively correlated with age (r = 0.601, P < 0.01), years since menopause (r = 0.577, P < 0.01), systolic blood pressure (r = 0.295, P < 0.01), and diastolic blood pressure (r = 0.264, P < 0.05), but was not with other variables. In multivariate regression analysis, the baPWV was significantly correlated with BMD (P < 0.05), but not with other variables.

CONCLUSIONS

Postmenopausal women with osteoporosis may have elevated arterial stiffness, suggesting that osteoporotic postmenopausal women may have a higher risk of cardiovascular disease.

Estrogen Directly Attenuates Human Osteoclastogenesis, But Has No Effect on Resorption by Mature Osteoclasts

Estrogen deficiency arising with the menopause promotes marked acceleration of bone resorption, which can be restored by hormone replacement therapy. The inhibitory effects of estrogen seem to involve indirect cytokine- mediated effects via supporting bone marrow cells, but direct estrogen-receptor mediated effects on the bone-resorbing osteoclasts have also been proposed. Little information is available on whether estrogens modulate human osteoclastogenesis or merely inhibit the functional activity of osteoclasts. To clarify whether estrogens directly modulate osteoclastic activities human CD14+ monocytes were cultured in the presence of M-CSF and RANKL to induce osteoclast differentiation. Addition of 0.1-10 nM 17beta-estradiol to differentiating osteoclasts resulted in a dose-dependent reduction in tartrate resistant acid phosphatase (TRACP) activity reaching 60% at 0.1 nM. In addition, 17beta-estradiol inhibited bone resorption, as measured by the release of the C-terminal crosslinked telopeptide (CTX), by 60% at 0.1 nM, but had no effect on the overall cell viability. In contrast to the results obtained with differentiating osteoclasts, addition of 17beta-estradiol (0.001-10 nM) to mature osteoclasts did not affect bone resorption or TRACP activity. We investigated expression of the estrogen receptors, using immunocytochemistry and Western blotting. We found that ER-alpha is expressed in osteoclast precursors, whereas ER- beta is expressed at all stages, indicating that the inhibitory effect of estrogen on osteoclastogenesis is mediated by ER-alpha for the major part. In conclusion, these results suggest that the in vivo effects of estrogen are mediated by reduction of osteoclastogenesis rather than direct inhibition of the resorptive activity of mature osteoclasts.

Interleukin-7 influences osteoclast function in vivo but is not a critical factor in ovariectomy-induced bone loss

IL-7 is produced by stromal cells in bone marrow and is a major regulator of B and T lymphopoiesis. It is also a direct inhibitor of osteoclastogenesis in vitro. In this study we show that IL-7-deficient mice have increased OC and decreased trabecular bone volume compared with WT mice but mimic WT mice in the amount of trabecular but not cortical bone lost after ovariectomy.

INTRODUCTION

Interleukin (IL)-7 is a potent regulator of lymphocyte development, which has significant effects on bone. Bone marrow cell cultures from IL-7 deficient (IL-7KO) mice produced significantly more TRACP(+) osteoclasts (OCs) than did cells from wildtype (WT) mice. A previous study found that treatment of mice with a neutralizing antibody to IL-7 blocked ovariectomy (OVX)-induced bone loss. We examined if differences exist between the bones of WT and IL-7KO mice and if OVX altered bone mass in IL-7KO mice.

MATERIALS AND METHODS

Studies were in 2-month-old sham-operated (SHAM) and OVX female mice that were killed 4 weeks after surgery. IL-7KO mice and WT controls were in a C57BL/6 background. Both vertebrae (L(1)) and femora were evaluated by DXA, muCT, and histomorphometry. IL-7KO mice were confirmed as IL-7 deficient by their almost total lack of mature B cells in their bone marrow.

RESULTS

There was significantly less trabecular bone volume in the vertebrae of IL-7KO mice than in WT mice. In addition, IL-7KO mice had significantly decreased (p < 0.05) trabecular number (13%) and increased trabecular spacing (15%). OVX decreased vertebral trabecular bone volume (TBV) by 21% (p < 0.05) in WT mice and by 22% (p < 0.05) in IL-7KO mice compared with SHAM. IL-7KO SHAM mice also had significantly less (30%) TBV (TA/TTA) in their femurs, as measured histomorphometrically, than did WT SHAM mice. Femurs from IL-7KO SHAM mice had significantly increased percent OC surface (23%) compared with WT SHAM. As in the vertebrae, OVX significantly decreased femoral TBV in both WT and IL-7KO mice by similar amounts (47% and 48%, respectively, p < 0.05 for both) compared with SHAM. However, OVX decreased cortical bone mass in WT but not in IL-7KO bones. We also examined bone marrow cells from WT and IL-7KO mice. Bone marrow cells from IL-7KO animals showed a significant increase in the number of TRACP(+) osteoclast-like cells (OCLs), which formed in cultures that were stimulated with macrophage-colony stimulating factor (M-CSF) and RANKL (both at 30 ng/ml). However, there was no significant difference in the number of OCLs that formed in B lymphocyte-depleted (B220(-)) bone marrow cell cultures from WT and IL-7KO mice.

CONCLUSIONS

IL-7 deficiency in mice caused increased OC number in bone and decreased bone mass. OVX-induced bone loss in IL-7-deficient mice was selective and occurred in trabecular but not cortical bone.

Therapy Insight: osteoporosis during hormone therapy for prostate cancer

The intended therapeutic effect of gonadotropin-releasing-hormone (GnRH) agonists is hypogonadism, which is a leading cause of osteoporosis in men. Observations are consistent with this effect: GnRH agonists decrease bone mineral density and increase fracture risk in men with prostate cancer. Estrogens play a central role in homeostasis of the normal male skeleton and evidence suggests that estrogen deficiency is primarily responsible for the adverse skeletal effects of GnRH agonists. The mechanism of treatment-related bone loss involves acceleration of physiologic bone turnover. In small, randomized, controlled trials, bisphosphonates (pamidronate, zoledronic acid) and selective estrogen-receptor modulators (raloxifene, toremifene) increased bone mineral density in GnRH-agonist-treated men. Two ongoing large, randomized, placebo-controlled studies will prospectively define fracture outcomes in men with prostate cancer and assess the efficacy of novel pharmacologic interventions (AMG 162, toremifene) in GnRH-agonist-treated men.