Estrogen modulation of osteoclast lysosomal enzyme secretion

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.

Effect of Growth Hormone and Estrogen Replacement Therapy on Bone Mineral Density in Women with Turner Syndrome: A Meta-Analysis and Systematic Review

Osteoporosis is a serious implication of Turner syndrome (TS). Common methods for the treatment of TS are growth hormone (GHT) and estrogen replacement therapy (ERT). We examined the relationship between the treatment of TS and bone mineral density (BMD) of the lumbar spine. The purpose of our study was to show the currency of BMD states among patients with TS for treatment with GHT and ERT. We searched databases for studies published from inception to April 2023. The articles were related to TS, osteoporosis, ERT, GHT, BMD and treatment patients with TS. We applied the selection criteria: lumbar spine values at L1-L4; dual-energy X-ray absorptiometry (DXA); treatment which was applied: one group of articles: ERT and two group of articles: GHT; results performed as means ± SD. In total, 79 articles were analyzed, of which 20 studies were included and 5 were considered for meta-analysis. The total number of women in the articles selected was 71. Based on the results of the meta-analysis, the effect of ERT on BMD demonstrated a significant increase in BMD (the standardized mean difference in the random model was 0.593 g/cm2, 95% CI: 0.0705 to 1.116; p = 0.026), which showed that treatment with estrogen particularly increases bone mass during treatment, which contributes to reducing the risk of fractures. The effect of GHT on BMD demonstrated a non-significant decrease in BMD in patients with TS. The results for growth hormone show that this therapy does not improve bone density. However, our review emphasizes the beneficial effect of supplementing growth hormone (GH) on the clinical presentation of TS.

The Promise of Nanotechnology in Personalized Medicine

Both personalized medicine and nanomedicine are new to medical practice. Nanomedicine is an application of the advances of nanotechnology in medicine and is being integrated into diagnostic and therapeutic tools to manage an array of medical conditions. On the other hand, personalized medicine, which is also referred to as precision medicine, is a novel concept that aims to individualize/customize therapeutic management based on the personal attributes of the patient to overcome blanket treatment that is only efficient in a subset of patients, leaving others with either ineffective treatment or treatment that results in significant toxicity. Novel nanomedicines have been employed in the treatment of several diseases, which can be adapted to each patient-specific case according to their genetic profiles. In this review, we discuss both areas and the intersection between the two emerging scientific domains. The review focuses on the current situation in personalized medicine, the advantages that can be offered by nanomedicine to personalized medicine, and the application of nanoconstructs in the diagnosis of genetic variability that can identify the right drug for the right patient. Finally, we touch upon the challenges in both fields towards the translation of nano-personalized medicine.

Ovarian Aging and Osteoporosis

Osteoporosis is the most common bone metabolic disease with a very high morbidity, and women usually got a higher risk of osteoporosis than men. The high incidence rate of osteoporosis in women was mainly caused by (1) women having fewer skeletons and bone mass, (2) pregnancy consuming a large amount of calcium and other nutrients, and most importantly (3) the cease of estrogen secretion by ovaries after menopause. Along with ovarian aging, the follicle pool gradually declines and the oocyte quality reduced, accompanied with decline in serum estrogen. Estrogen deficiency plays an important role in the pathogenesis of postmenopausal osteoporosis; it is mainly a result of the recognition that estrogen regulates bone remodeling by modulating the production of cytokines and growth factors from bone marrow and bone cells. This review will summarize current knowledge concerning ovarian aging and postmenopause osteoporosis and also discuss clinical treatment and new ideas of drug development for osteoporosis.

A hindsight reflection on the clinical studies of poly(l-glutamic acid)-paclitaxel

Chemotherapy for cancer treatment is limited by the excessive toxicity to normal tissues. The design of chemodrug-loaded nanoformulations provides a unique approach to improve the treatment efficacy while minimizing toxicity. Despite the numerous publications of nanomedicine for the last several decades, however, only a small fraction of the developed nanoformulations have entered clinical trials, with even fewer being approved for clinical application. Poly(l-glutamic acid)-paclitaxel (PG-TXL) belongs to the few formulations that reached phase III clinical trials. Unfortunately, the development of PG-TXL stopped in 2016 due to the inability to show significant improvement over current standard care. This review will provide an overview of the preclinical and clinical evaluations of PG-TXL, and discuss lessons to be learned from this ordeal. The precise identification of suitable patients for clinical trial studies, deep understanding of the mechanisms of action, and an effective academic-industry partnership throughout all phases of drug development are important for the successful bench-to-bedside translation of new nanoformulations. This article is categorized under: Implantable Materials and Surgical Technologies > Nanomaterials and Implants Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Biology-Inspired Nanomaterials > Peptide-Based Structures.

Estrogens and Androgens in Skeletal Physiology and Pathophysiology

Estrogens and androgens influence the growth and maintenance of the mammalian skeleton and are responsible for its sexual dimorphism. Estrogen deficiency at menopause or loss of both estrogens and androgens in elderly men contribute to the development of osteoporosis, one of the most common and impactful metabolic diseases of old age. In the last 20 years, basic and clinical research advances, genetic insights from humans and rodents, and newer imaging technologies have changed considerably the landscape of our understanding of bone biology as well as the relationship between sex steroids and the physiology and pathophysiology of bone metabolism. Together with the appreciation of the side effects of estrogen-related therapies on breast cancer and cardiovascular diseases, these advances have also drastically altered the treatment of osteoporosis. In this article, we provide a comprehensive review of the molecular and cellular mechanisms of action of estrogens and androgens on bone, their influences on skeletal homeostasis during growth and adulthood, the pathogenetic mechanisms of the adverse effects of their deficiency on the female and male skeleton, as well as the role of natural and synthetic estrogenic or androgenic compounds in the pharmacotherapy of osteoporosis. We highlight latest advances on the crosstalk between hormonal and mechanical signals, the relevance of the antioxidant properties of estrogens and androgens, the difference of their cellular targets in different bone envelopes, the role of estrogen deficiency in male osteoporosis, and the contribution of estrogen or androgen deficiency to the monomorphic effects of aging on skeletal involution.

A Modified Glycosaminoglycan, GM-0111, Inhibits Molecular Signaling Involved in Periodontitis

Background

Periodontitis is characterized by microbial infection, inflammation, tissue breakdown, and accelerated loss of alveolar bone matrix. Treatment targeting these multiple stages of the disease provides ways to treat or prevent periodontitis. Certain glycosaminoglycans (GAGs) block multiple inflammatory mediators as well as suppress bacterial growth, suggesting that these GAGs may be exploited as a therapeutic for periodontitis.

Methods

We investigated the effects of a synthetic GAG, GM-0111, on various molecular events associated with periodontitis: growth of Porphyromonas gingivalis (P. gingivalis) and Aggregatibacter actinomycetemcomitans (A. actinomycetemcomitans) pathogenic bacteria associated with periodontitis; activation of pro-inflammatory signaling through TLR2 and TLR4 in mouse macrophage RAW 264.7 cells and heterologously expressed HEK 293 cells; osteoclast formation and bone matrix resorption in cultured mouse pre-osteoclasts.

Results

(1) GM-0111 suppressed the growth of P. gingivalis and A. actinomycetemcomitans even at 1% (w/v) solution. The antibacterial effects of GM-0111 were stronger than hyaluronic acid (HA) or xylitol in P. gingivalis at all concentrations and comparable to xylitol in A. actinomycetemcomitans at ≥2% (w/v) solution. We also observed that GM-0111 suppressed biofilm formation of P. gingivalis and these effects were much stronger than HA. (2) GM-0111 inhibited TLR-mediated pro-inflammatory cellular signaling both in macrophage and HEK 293 cells with higher selectivity for TLR2 than TLR4 (IC₅₀ of 1–10 ng/mL vs. > 100 μg/mL, respectively). (3) GM-0111 blocked RANKL-induced osteoclast formation (as low as 300 ng/mL) and bone matrix resorption. While GM-0111 showed high affinity binding to RANKL, it did not interfere with RANKL/RANK/NF-κB signaling, suggesting that GM-0111 inhibits osteoclast formation by a RANKL-RANK-independent mechanism.

Conclusions

We report that GM-0111 inhibits multiple molecular events involved in periodontitis, spanning from the early pro-inflammatory TLR signaling, to pathways activated at the later stage component of bone loss.

Management of central giant cell granuloma of the jaws with intralesional steroid injection and review of the literature

PURPOSE

We report the results of the intralesional steroid injections for the management of central giant cell granuloma (CGCG) of the jaws.

METHODS

Seven CGCGs were treated with intralesional injection of corticosteroids. To accomplish this, 3.5 mL of triamcinolone and 3.5 mL of 0.5 % marcaine with 1/200,000 epinephrine (total 7 mL) were mixed. An adequate amount of steroid was injected into different areas of the lesion. This procedure was repeated on a weekly basis for 6 weeks.

RESULTS

Clinical and radiological examination showed complete resolution and ossification of the lesions in four patients. Partial recovery was achieved in two patients. One patient did not respond to the treatment and underwent surgical curettage.

CONCLUSIONS

We suggest that intralesional steroid injection is safe and effective for the treatment of CGCG, especially in non-aggressive lesions.

Treatment of mouth and jaw diseases with intralesional steroid injection

Many lesions of the oral region are treated with surgical methods such as curettage and resection. Chemotherapy and radiation therapy with or without surgical intervention can be used as an adjunct in some cases. Intralesional steroid injection is a conservative procedure which is already used in various regions of the body and joints. This technique is used also for a number of mouth and jaw lesions. Localized langerhans cell histiocytosis, central giant cell granuloma, oral submucous fibrosis, oral lichen planus, lichen sclerosus of the oral mucosa, lymphatic malformations and orofacial granulomatosis can be considered among these diseases. The purpose of this review is to investigate the effects of intralesional steroid injections in the treatment of oral diseases.

Interactions of nanomaterials and biological systems: Implications to personalized nanomedicine

The application of nanotechnology to personalized medicine provides an unprecedented opportunity to improve the treatment of many diseases. Nanomaterials offer several advantages as therapeutic and diagnostic tools due to design flexibility, small sizes, large surface-to-volume ratio, and ease of surface modification with multivalent ligands to increase avidity for target molecules. Nanomaterials can be engineered to interact with specific biological components, allowing them to benefit from the insights provided by personalized medicine techniques. To tailor these interactions, a comprehensive knowledge of how nanomaterials interact with biological systems is critical. Herein, we discuss how the interactions of nanomaterials with biological systems can guide their design for diagnostic, imaging and drug delivery purposes. A general overview of nanomaterials under investigation is provided with an emphasis on systems that have reached clinical trials. Finally, considerations for the development of personalized nanomedicines are summarized such as the potential toxicity, scientific and technical challenges in fabricating them, and regulatory and ethical issues raised by the utilization of nanomaterials.

Tissue-Specific Effects of Loss of Estrogen during Menopause and Aging

The roles of estrogens have been best studied in the breast, breast cancers, and in the female reproductive tract. However, estrogens have important functions in almost every tissue in the body. Recent clinical trials such as the Women's Health Initiative have highlighted both the importance of estrogens and how little we know about the molecular mechanism of estrogens in these other tissues. In this review, we illustrate the diverse functions of estrogens in the bone, adipose tissue, skin, hair, brain, skeletal muscle and cardiovascular system, and how the loss of estrogens during aging affects these tissues. Early transcriptional targets of estrogen are reviewed in each tissue. We also describe the tissue-specific effects of selective estrogen receptor modulators (SERMs) used for the treatment of breast cancers and postmenopausal symptoms.

Combined treatment of aggressive central giant cell granuloma in the lower jaw

BACKGROUND

The aggressive type lesions of central giant cell granuloma (CGCG) require wide resection that leads to major defects in the jaws. This form of surgical treatment can be particularly disfiguring. A number of alternative non-surgical therapies have been advocated in recent years for the management of the central giant cell granuloma (CGCG). These include calcitonin injections and nasal spray, intralesional steroid injections and subcutaneous interferon injections.

MATERIALS AND METHODS

A large central giant cell granuloma aggressive type lesion in the mandible of a 24-year-old patient was treated successfully by intralesional injection of corticosteroid and nasal spray calcitonin that was followed by curettage with peripheral ostectomy with preservation of the continuity of the mandible and the teeth. At the 5-year clinical and radiological follow up there was no sign of recurrence.

CONCLUSIONS

This combined medical and surgical treatment is advantageous for large aggressive lesions in order to reduce the size of the lesion and thus minimize the need for extensive bone resection and loss of teeth that can result in functional and aesthetic defects.

Direct transcriptional targets of sex steroid hormones in bone

The sex steroid hormones, androgens and estrogens, via their respective nuclear receptors, regulate bone mineral density in humans and mice. Very little is known about the direct targets of the androgen and estrogen receptors in bone cells. First, models of hormone and receptor deficiency in mouse and human bone are discussed. This review then focuses on the direct targets of the receptors in osteoblasts and osteoclasts. A direct target of a NR is defined here as a gene that is regulated by NR binding to the DNA (either through DNA binding or association with a DNA binding protein) at an enhancer or promoter of that gene. The experimental evidence that illustrates androgen and estrogen gene regulation in osteoblasts and osteoclasts will be summarized and compared with the phenotype of the hormones in vivo.

Estrogens in rheumatoid arthritis; the immune system and bone

Rheumatoid arthritis (RA) is an autoimmune disease that is more common in women than in men. The peak incidence in females coincides with menopause when the ovarian production of sex hormones drops markedly. RA is characterized by skeletal manifestations where production of pro-inflammatory mediators, connected to the inflammation in the joint, leads to bone loss. Animal studies have revealed distinct beneficial effects of estrogens on arthritis, and a positive effect of hormone replacement therapy has been reported in women with postmenopausal RA. This review will focus on the influence of female sex hormones in the pathogenesis and progression of RA.

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.

Dietary and demographic correlates of serum beta-glucuronidase activity

beta-glucuronidase, an acid hydrolase that deconjugates glucuronides, may increase cancer risk; however, little is known about factors associated with human beta -glucuronidase. Our objective was to examine whether dietary and demographic factors were associated with serum beta -glucuronidase activity. We conducted a cross-sectional study among 279 healthy men and women aged 20 to 40 yr. Diet, categorized by botanical families and nutrient intakes, was assessed from 3-day food records and a validated semiquantitative food frequency questionnaire. Demographic factors were directly measured or self-reported. Adjusted mean beta -glucuronidase activity across categories of exposure variables were calculated by multiple linear regression. Higher beta -glucuronidase activity was significantly associated with being male, older age (> or = 30 yr), non-Caucasian, overweight (> or = 25 kg/m(2)), and higher intakes of gamma-tocopherol. Conversely, lower beta -glucuronidase activity was significantly associated with higher intakes of calcium, iron, and magnesium. A suggestive decrease in beta -glucuronidase activity was observed for the botanical families Cruciferae, Rutaceae, Compositae, Roseaceae, and Umbelliferae, but tests for trend were not statistically significant. In conclusion, several dietary and nondietary factors were associated with beta -glucuronidase activity; however, confirmation of these associations are needed.

Central giant cell granuloma of the jaw: a review of the literature with emphasis on therapy options

Central giant cell granuloma (CGCG) is a benign lesion of the jaws with an unknown etiology. Clinically and radiologically, a differentiation between aggressive and non-aggressive lesions can be made. The incidence in the general population is very low and patients are generally younger than 30 years. Histologically identical lesions occur in patients with known genetic defects such as cherubism, Noonan syndrome, or neurofibromatosis type 1. Surgical curettage or, in aggressive lesions, resection, is the most common therapy. However, when using surgical curettage, undesirable damage to the jaw or teeth and tooth germs is often unavoidable and recurrences are frequent. Therefore, alternative therapies such as injection of corticosteroids in the lesion or subcutaneous administration of calcitonin or interferon alpha are described in several case reports with variable success. Unfortunately, randomized clinical trials are very rare or nonexistent. In the future, new and theoretically promising therapy options, such as imatinib and OPG/AMG 162, will be available for these patients.

Paclitaxel poliglumex (PPX, CT-2103): macromolecular medicine for advanced non-small-cell lung cancer

Taxanes, including paclitaxel and docetaxel, are widely used cytotoxic agents for the treatment of solid tumors. Paclitaxel, a small, hydrophobic agent, binds extensively to plasma proteins, and its pharmacokinetic profile is characterized by a short plasma elimination half-life with a broad tissue distribution. These unfavorable pharmacokinetic characteristics are associated with limited tumor exposure and high systemic exposure, reducing the therapeutic index of paclitaxel. Paclitaxel poliglumex (PPX, CT-2103), a polymer-drug conjugate of paclitaxel and poly-L-glutamic acid, was designed to enhance the therapeutic index of paclitaxel by improving its pharmacokinetic profile, and to provide a water-soluble alternative to the standard paclitaxel formulation. Potential advantages of polymer-drug conjugates include delivery of a higher concentration of active drug to tumor tissue and limited exposure of normal tissues. In addition, the slow release of drug from the polymer carrier lowers peak plasma concentrations of the active drug.

Polymer conjugates as anticancer nanomedicines

The transfer of polymer-protein conjugates into routine clinical use, and the clinical development of polymer-anticancer-drug conjugates, both as single agents and as components of combination therapy, is establishing polymer therapeutics as one of the first classes of anticancer nanomedicines. There is growing optimism that ever more sophisticated polymer-based vectors will be a significant addition to the armoury currently used for cancer therapy.

In vitro and in vivo metabolism of paclitaxel poliglumex: identification of metabolites and active proteases

BACKGROUND

The efficacy and tolerability of paclitaxel is limited by its low solubility, high systemic exposure, and a lack of selective tumor uptake. Paclitaxel poliglumex (PPX; XYOTAX) is a macromolecular drug conjugate that was developed to overcome these limitations; the 2' hydroxyl group of paclitaxel is linked to a biodegradable polymer, poly-L: -glutamic acid, to form an inactive polymeric conjugate. PPX was previously shown to accumulate in tumor tissue, presumably by taking advantage of the hyperpermeable tumor vasculature and suppressed lymphatic clearance in tumor tissue.

METHODS

Because anti-tumor activity requires the release of paclitaxel from the polymer-drug conjugate, the current report characterizes PPX biodegradation and release of paclitaxel as determined by quantitative HPLC/mass spectral analysis.

RESULTS

The identification of monoglutamyl-paclitaxel metabolites in tumor tissue confirmed the in vivo metabolism of PPX in a panel of mouse tumor models. In vitro characterization of the metabolic pathway suggests that PPX can enter tumor cells, and is metabolized to form both mono- and diglutamyl-paclitaxel cleavage products. The intracellular formation of these intermediate metabolites is at least partially dependent on the proteolytic activity of the lysosomal enzyme cathepsin B; PPX metabolism is inhibited by a highly selective inhibitor of cathepsin B, CA-074. Reduced metabolism of PPX in livers and spleens from cathepsin B deficient mice confirms that cathepsin B is an important mediator of PPX metabolism in vivo; however, other proteolytic enzymes may contribute as well.

CONCLUSIONS

The cathepsin B-mediated release of paclitaxel may have therapeutic implications as cathepsin B is upregulated in malignant cells, particularly during tumor progression.

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.

Molecular mechanisms underlying osteoclast formation and activation

Osteoporosis is one of the leading causes of morbidity in the elderly and is characterized by a progressive loss of total bone mass and bone density. Bone loss in osteoporosis is due to the persistent excess of osteoclastic bone resorption over osteoblastic bone formation. Receptor activator of NFkappaB ligand (RANKL) critically regulates both osteoclast differentiation and activation. TRAFs appear to be central coupling molecules in the signal transduction pathways that regulate osteoclastogenesis, cathepsin K is the major mediator of osteoclastic bone resorption, and sex steroids and aging also affect osteoclastogenesis and osteoclast activity. However, bone homeostasis depends upon the intimate coupling of bone formation and bone resorption, wherein both osteoclasts and osteoblasts exert vital stimulatory and inhibitory effects upon each other via molecules such as RANKL, TGFbeta, PDGF, BMP2, and Mim-1. This review will highlight some of the major features of the complex circuit of cytokines, growth factors, and hormones that underlies the formation and function of osteoclasts and the dynamic equilibrium that marks the interaction between osteoclasts and osteoblasts.

Use of a phage display technique to identify potential osteoblast binding sites within osteoclast lacunae

There is a temporal coupling between the processes of bone resorption and bone formation in normal skeletal remodeling. That is, osteoblastic activity usually follows episodes of osteoclastic activity. However, what has not been universally appreciated is that there also is a spatial coupling between these processes. Bone formation only occurs in the immediate vicinity of the resorptive event. In this study, we describe a phage display technique that has been used to identify the mechanisms by which osteoblasts recognize components of the prior resorbed lacunar surface. Using a type V tartrate-resistant acid phosphatase (TRAP) as the bait and a random peptide M13 phage display library as the probe, we have identified specific sequences that show a very high affinity for TRAP. One of these peptides, designated clone 5, has a subnanomolar Kd for TRAP, interacts with TRAP in a Far-Western assay, binds exclusively to TRAP within osteoclast lacunae, is present in osteoblasts, and can effectively block osteoblast binding to resorption surfaces. The clone 5 peptide shows a high homology to glypican 4 (GPC4), a proteoglycan attachment receptor found in a number of cell types.

Intralesional corticosteroids as an alternative treatment for central giant cell granuloma

Four cases of central giant cell granuloma were treated with intralesional infiltration of a solution of Kenacort-A (10 mg/mL, triamcinolone aqueous suspension SQUIBB) and either (1) Lidocaine 2% with epinephrine 1:200,000 Marcaine or (2) Bupivacaine, 50% mixture by volume. These cases were originally diagnosed by radiographic and histologic studies in 3 Guatemalan males--ages 31, 34, and 6 years old--and a 21/2-year-old Guatemalan girl. The average dosage of the aforementioned solution was 6 mL (equivalent to 30 mg of triamcinolone) for the adults and 5 mL (equivalent to 25 mg of triamcinolone) for the pediatric patients. Before treatment, an endocrinologist evaluated all of the patients to rule out hyperparathyroidism. Also before treatment, an incisional biopsy of the lesion was obtained from each patient for microscopic examination. Follow-up radiographs for all the cases showed progressive improvement and eventual resolution of the lesions.

Estrogen receptor expression in giant cell tumors of the bone

Giant cell tumors (GCTs) of the bone are primary skeletal neoplasms that behave intermediately between a true benign and an overtly malignant neoplasm. For two decades, controversial reports have found estrogen receptor (ER) expression in isolated cells or small numbers of samples from these tumors. In this report, we studied by immunohistochemistry 88 cases of GCTs and found that 51% of the samples expressed ER. Furthermore, we found that a subset of seven samples analyzed for ER expression by western blot was positive. To address whether the ER expressed in these samples could be functional, isolated cells were exposed to beta-estradiol and growth curves were generated. Exposure of cells to beta-estradiol induced a small but significant growth in the cells. These results strongly support that GCTs of the bone express functional ERs.

Macrophage colony-stimulating factor suppresses osteoblast formation

We provide the first evidence that the bone marrow-derived cytokine, macrophage colony-stimulating factor (M-CSF), inhibits the formation of bone-forming osteoblasts. We examined both osteoclast and osteoblast formation in primary rat bone marrow cultures. As expected, M-CSF together with osteoprotegerin ligand (OPGL) markedly accelerated osteoclastogenesis. In contrast, treatment with M-CSF alone yielded no osteoclasts at any time. The most striking and novel observation was that M-CSF with or without OPGL dramatically suppressed osteoblast formation. In separate experiments, estradiol markedly suppressed osteoclast formation in the M-CSF/OPGL-treated cultures independently of osteoblasts. Consistent with this was the expression of estrogen receptor-alpha (ERalpha) and ERbeta mRNA in osteoclast precursors. We therefore conclude that in addition to the well-known action of M-CSF to modulate osteoclastogenesis, this cytokine may also regulate osteoblast formation.

The Src signaling pathway regulates osteoclast lysosomal enzyme secretion and is rapidly modulated by estrogen

To investigate the role of the pp60src signaling pathway in osteoclast activity, we have used dominant negative pp60src, c-ras, and c-raf expression vectors to individually disrupt their functions in osteoclasts. Osteoclasts were transiently transfected and secretions of cathepsin B/K and tartrate-resistant acid phosphatase (TRAP) were monitored. Expression of these constructs increased secretion of lysosomal enzymes. In contrast, constitutively active pp60src expression caused decreased lysosomal enzyme secretion. Osteoclasts respond to 17-beta estradiol (17betaE2) treatment with decreased lysosomal enzyme secretion. Therefore, we investigated the effects of E2 on pp60src kinase activity and observed an E2 time- and dose-dependent decrease in cytoskeletal membrane-associated pp60src tyrosine kinase activity. We have shown that estrogen decreases lysosomal enzyme gene expression and secretion; so we have examined the effects of the expression constructs on estrogen regulation of enzyme secretion. Constitutively active pp60src blocked E2 effects on secretion whereas expression of dominant negative pp60src, c-Ras, or c-Raf enhanced E2 effects. These data support that the kinase domain of cytoskeletal-associated pp60src is likely to be involved in the regulation of lysosomal enzyme secretion.

Sex steroids and bone

Sex steroids are essential for skeletal development and the maintenance of bone health throughout adult life, and estrogen deficiency at menopause is a major pathogenetic factor in the development of osteoporosis in postmenopausal women. The mechanisms by which the skeletal effects of sex steroids are mediated remain incompletely understood, but in recent years there have been considerable advances in our knowledge of how estrogens and, to a lesser extent androgens, influence bone modeling and remodeling in health and disease. New insights into estrogen receptor structure and function, recent discoveries about the development and activity of osteoclasts, and lessons learned from human and animal genetic mutations have all contributed to increased understanding of the skeletal effects of estrogen, both in males and females. Studies of untreated and treated osteoporosis in postmenopausal women have also contributed to this knowledge and have provided unequivocal evidence for the potential of high-dose estrogen therapy to have anabolic skeletal effects. The development of selective estrogen receptor modulators has provided a new approach to the prevention of osteoporosis and other major diseases of menopause and has implications for the therapeutic use of other steroid hormones, including androgens. Further elucidation of the mechanisms by which sex steroids affect bone thus has the potential to improve the clinical management not only of osteoporosis, both in men and women, but also of a number of other diseases related to sex hormone status.

Regulation of collagenolytic protease secretion through c-Src in osteoclasts

The role of pp60c-src activity in the synthesis and secretion of the collagenolytic cysteine proteases (CCPs), cathepsin K (CAK), cathepsin L (CAL), and cathepsin B (CAB), by osteoclasts was investigated. Synthesis and secretion of CAL were up-regulated by 1alpha,25-(OH)2D3, but neither those of CAK, dominant relative to CAL, nor CAB, barely detectable, levels changed in the experiments. Though PP1, a pp60c-src inhibitor, had no effect on CCPs synthesis, suppressed the CAK and CAL secretion. Wortmannin, a phosphatidylinositol 3-kinase (PI3-kinase) inhibitor that works as a second messenger for pp60c-src, and cytochalasin B, an inhibitor of actin polymerization, suppressed the secretion of both CAK and CAL without suppressing synthesis. Hydroxyproline release, an indicator of degradation of type-I collagen, and F-actin ring formation, a structure linked to osteoclastic bone resorption, were suppressed by PP1, cytochalasin B or wortmannin. These results suggested inhibition of pp60c-src activity affected the osteoclastic cytoskeleton, which in turn reflected the suppression of bone resorption.

Depolarization of osteoclast plasma membrane potential by 17beta-estradiol

The effect of estrogen on plasma membrane potential of isolated avian osteoclasts was examined through the use of a fluorescent potential-sensitive dye, bis-(1,3-dibutylbarbiturate) trimethine oxonol, also known as bis-oxonol. A decrease in potential was observed within seconds of addition of 17beta-estradiol. Ouabain, a specific Na+K+-ATPase inhibitor, and BaCl2, an inhibitor of the inwardly rectifying K+ channel, blocked the estrogen response. Verapamil and lanthanum chloride (LaCl3), inhibitors of inward Ca2+ channels, and 4'4-diisothiocyanatostilbene-2'2-disulfonic acid (DIDS), an inhibitor of Cl- channels, did not affect the depolarization. Herbimycin A, a tyrosine kinase inhibitor, also had no effect on the decreased membrane potential. These data provide evidence which suggests that estrogen regulates osteoclasts through ion channel activities. The change in K+ channel activity was observed within seconds of addition of 17beta-estradiol, indicating an action at the level of the plasma membrane.

Estrogen's bone-protective effects may involve differential IL-1 receptor regulation in human osteoclast-like cells

Declining estrogen levels during the first postmenopausal decade lead to rapid bone loss and increased fracture risk that can be reversed by estrogen replacement therapy. The bone-protective effects of estrogen may involve suppression of inflammatory cytokines that promote osteoclastogenesis and bone resorption, such as IL-1, TNF-alpha, and IL-6. We investigated whether estrogen modulates IL-1 actions on human osteoclasts (OCs) and other bone cell types. Isolated human OCs and primary bone marrow-derived OC-like cells expressed both the signaling (IL-1RI) and decoy (IL-1RII) IL-1 receptors, whereas only IL-1RI was detected in osteoblasts. IL-1RII/IL-1RI mRNA ratios and release of soluble IL-1RII (sIL-1RII) were lower in OC-like cells derived from women in the late postmenopausal period compared with younger women, but were unrelated to male donor age, suggesting that estrogen might play a role in regulating IL-1 receptor levels in vivo. Estrogen directly reduced in vitro OC-like cell IL-1RI mRNA levels while increasing IL-1RII mRNA levels and sIL-1RII release. These estrogenic events were associated with inhibited IL-1-mediated cytokine (IL-8) mRNA induction and cell survival, i.e., increased apoptosis. In contrast, estrogen did not alter IL-1R levels or IL-1 responsiveness in primary human osteoblasts or bone marrow stromal cells. We conclude that one novel mechanism by which estrogen exerts bone-protective effects may include a selective modulation of IL-1R isoform levels in OC or OC-like cells, thereby reducing their IL-1 responsiveness and cell survival. Conversely, this restraint on IL-1 actions may be lost as estrogen levels decline in aging women, contributing to an enhanced OC-mediated postmenopausal bone loss.

Evidence of a correlation of estrogen receptor level and avian osteoclast estrogen responsiveness

Isolated osteoclasts from 5-week-old chickens respond to estradiol treatment in vitro with decreased resorption activity, increased nuclear proto-oncogene expression, and decreased lysosomal enzyme secretion. This study examines osteoclasts from embryonic chickens and egg-laying hens for evidence of estrogen responsiveness. Although osteoclasts from both of these sources express estrogen receptor mRNA and protein, estradiol treatment had no effect on resorption activity. In contrast to the lack of effect on resorption, estradiol treatment for 30 minutes resulted in steady-state mRNA levels of c-fos and c-jun increasing in osteoclasts from embryonic chickens and decreasing in osteoclasts from egg-laying hens. These data suggest that a nuclear proto-oncogene response may not be involved in estradiol-mediated decreased osteoclast resorption activity. To examine the influence of circulating estrogen on osteoclast estrogen responsiveness, 5-week-old chickens were injected with estrogen for 4 days prior to sacrifice. Estradiol treatment of osteoclasts from these chickens did not decrease resorption activity in vitro. Transfection of an estrogen receptor expression vector into osteoclasts from the estradiol-injected chickens and egg-laying hens restored estrogen responsiveness. Osteoclasts from 5-week-old chickens and estradiol treated 5-week-old chickens transfected with the estrogen receptor expression vector contained significantly higher levels of estrogen receptor protein and responded to estradiol treatment by decreasing secretion of cathepsins B and L and tartrate-resistant acid phosphatase. In contrast, osteoclasts from embryonic chickens, egg-laying hens, and estradiol-treated 5-week-old chickens either untransfected or transfected with an empty expression vector did not respond similarly. These data suggest that modulation of osteoclast estrogen responsiveness may be controlled by changes in the osteoclast estrogen receptor levels.

Cathepsin K, but not cathepsins B, L, or S, is abundantly expressed in human osteoclasts

Random high throughput sequencing of a human osteoclast cDNA library was employed to identify novel osteoclast-expressed genes. Of the 5475 ESTs obtained, approximately 4% encoded cathepsin K, a novel cysteine protease homologous to cathepsins S and L; ESTs for other cathepsins were rare. In addition, ESTs for cathepsin K were absent or at low frequency in cDNA libraries from numerous other tissues and cells. In situ hybridization in osteoclastoma and osteophyte confirmed that cathepsin K mRNA was highly expressed selecively in osteoclasts; cathepsins S, L, and B were not detectable. Cathepsin K was not detected by in situ hybridization in a panel of other tissues. Western blot of human osteoclastoma or fetal rat humerus demonstrated bands of 38 and 27 kDa, consistent with sizes predicted for pro- and mature cathepsin K. Immunolocalization in osteoclastoma and osteophyte showed intense punctate staining of cathepsin K exclusively in osteoclasts, with a polar distribution that was more intense at the bone surface. The abundant expression of cathepsin K selectively in osteoclasts strongly suggests that it plays a specialized role in bone resorption. Furthermore, the data suggest that random sequencing of ESTs from cDNA libraries is a valuable approach for identifying novel cell-selective genes.