Treatment Of Metabolic Bone Diseases Research Articles

Nitrogen-Containing Biphosphonates Inhibit the Mevalonate Pathway and Prevent Post-Translational Prenylation of GTP-Binding Proteins, Including Ras

Abstract Bisphosphonates are currently the most important class of antiresorptive drugs used for the treatment of metabolic bone diseases. Although the molecular targets of bisphosphonates have not been identified, these compounds inhibit bone resorption by mechanisms that can lead to osteoclast apoptosis. Bisphosphonates also induce apoptosis in mouse J774 macrophages in vitro, probably by the same mechanisms that lead to osteoclast apoptosis. We have found that, in J774 macrophages, nitrogen-containing bisphosphonates (such as alendronate, ibandronate, and risedronate) inhibit post-translational modification (prenylation) of proteins, including the GTP-binding protein Ras, with farnesyl or geranylgeranyl isoprenoid groups. Clodronate did not inhibit protein prenylation. Mevastatin, an inhibitor of 3-hydroxy-3-methylglutatyl (HMG)-CoA reductase and hence the bio-synthetic pathway required for the production of farnesyl pyrophosphate and geranylgeranyl pyrophosphate, also caused apoptosis in J774 macrophages and murine osteoclasts in vitro. Furthermore, alendronate-induced apoptosis, like mevastatin-induced apoptosis, could be suppressed in J774 cells by the addition of farnesyl pyrophosphate or geranylgeranyl pyrophosphate, while the effect of alendronate on osteoclast number and bone resorption in murine calvariae in vitro could be overcome by the addition of mevalonic acid. These observations suggest that nitrogen-containing bisphosphonate drugs cause apoptosis following inhibition of post-translational prenylation of proteins such as Ras. It is likely that these potent antiresorptive bisphosphonates also inhibit bone resorption by preventing protein prenylation in osteoclasts and that enzymes of the mevalonate pathway or prenyl protein transferases are the molecular targets of the nitrogen-containing bisphosphonates. Furthermore, the data support the view that clodronate acts by a different mechanism.

Treatment of metabolic bone disease in patients with chronic renal disease: A perspective for rheumatologists

As glomerular filtration rate (GFR) declines from age-related bone loss or disease that specifically induces a decline in GFR, there are a number of metabolic bone conditions that may accompany the decline in GFR. These metabolic bone conditions span a spectrum from mild-to-severe secondary hyperparathyroidism in early stages of chronic kidney disease (CKD) to the development of additional heterogeneous forms of bone diseases each with distinctly quantitative bone histomorphometric characteristics. Osteoporosis can also develop in patients with CKD and end-stage renal disease (ESRD) for many reasons beyond age-related bone loss and postmenopausal (PMO) bone loss. Diagnosing osteoporosis in patients with severe CKD or ESRD is not as easy to do as it is in patients with PMO. The diagnosis of osteoporosis in patients with CKD/ESRD must be done by first excluding other forms of renal osteodystrophy, through biochemical profiling or by double tetracycline-labeled bone biopsy and the finding of low trabecular bone volume. In such patients oral bisphosphonates seem to be safe and effective down to GFR levels of 15 mL/min. In patients with stage 5 CKD, who are fracturing because of osteoporosis or who are on chronic glucocorticoids, reducing the oral bisphosphonate dosage to half of its usual prescribed dosing for PMO seems reasonable from known bisphosphonate pharmacokinetics. However, we need better scientific data to fully understand bisphosphonate usage in this population. This paper deals with the evidence available to understand management of patients with CKD and opinions on what might be a reasonable clinical approach where evidence is currently lacking.

Transient Versus Sustained Phosphorylation and Nuclear Accumulation of ERKs Underlie Anti-Versus Pro-apoptotic Effects of Estrogens

Sex steroids exert anti-apoptotic effects on osteoblasts/osteocytes but exert pro-apoptotic effects on osteoclasts, in both cases requiring activation of the extracellular signal-regulated kinases (ERKs). To explain the mechanistic basis of this divergence, we searched for differences in the kinetics of phosphorylation and/or in the subcellular localization of ERKs in response to 17beta-estradiol in the two cell types. In contrast to its transient effect on ERK phosphorylation in osteocytic cells (return to base line by 30 min), 17beta-estradiol-induced ERK phosphorylation in osteoclasts was sustained for at least 24 h following exposure to the hormone. Conversion of sustained ERK phosphorylation to transient, by means of cholera toxin-induced activation of the adenylate cyclase/cAMP/protein kinase A pathway, abrogated the pro-apoptotic effect of 17beta-estradiol on osteoclasts. Conversely, prolongation of ERK activation in osteocytes, by means of leptomycin B-induced inhibition of ERK export from the nucleus or overexpression of a green fluorescent protein-ERK2 mutant that resides permanently in the nucleus, converted the anti-apoptotic effect of 17beta-estradiol to a pro-apoptotic one. These findings indicate that the kinetics of ERK phosphorylation and the length of time that phospho-ERKs are retained in the nucleus are responsible for pro-versus anti-apoptotic effects of estrogen on different cell types of bone and perhaps their many other target tissues.

Statins prevent bisphosphonate-induced gamma,delta-T-cell proliferation and activation in vitro.

The acute phase response is the major adverse effect of intravenously administered N-BPs. In this study we show that N-BPs cause gamma,delta-T-cell activation and proliferation in vitro by an indirect mechanism through inhibition of FPP synthase, an effect that can be overcome by inhibiting HMG-CoA reductase with a statin. These studies clarify the probable initial cause of the acute phase response to N-BP drugs and suggest a possible way of preventing this phenomenon. The acute phase response is the major adverse effect of intravenously administered nitrogen-containing bisphosphonate drugs (N-BPs), used in the treatment of metabolic bone diseases. This effect has recently been attributed to their action as non-peptide antigens and direct stimulation of gamma,delta-T-cells. However, because N-BPs are potent inhibitors of farnesyl diphosphate (FPP) synthase, they could cause indirect activation of gamma,delta-T-cells owing to the accumulation of intermediates upstream of FPP synthase in the mevalonate pathway, such as isopentenyl diphosphate/dimethylallyl diphosphate, which are known gamma,delta-T-cell agonists. Peripheral blood mononuclear cells (PBMCs) were isolated from healthy volunteers and treated with N-BP, statin, or intermediates/inhibitors of the mevalonate pathway for 7 days in the presence of interleukin (IL)-2. Flow cytometric analysis of the T-cell-gated population was used to quantify the proportion of gamma,delta-T-cells in the CD3+ population. The ability of N-BPs to stimulate proliferation of CD3+ gamma,delta-T-cells in human PBMC cultures matched the ability to inhibit FPP synthase. Gamma,delta-T-cell proliferation and activation (interferon gamma [IFNgamma] and TNFalpha release) was prevented by mevastatin or lovastatin, which inhibit HMG-CoA reductase upstream of FPP synthase and prevent the synthesis of isopentenyl diphosphate/dimethylallyl diphosphate. Desoxolovastatin, an analog of lovastatin incapable of inhibiting HMG-CoA reductase, did not overcome the stimulatory effect of N-BP. Furthermore, statins did not prevent the activation of gamma,delta-T-cells by a synthetic gamma,delta-T-cell agonist or by anti-CD3 antibody. Together, these observations show that N-BPs indirectly stimulate the proliferation and activation of gamma,delta-T-cells caused by inhibition of FPP synthase and intracellular accumulation of isopentenyl diphosphate/ dimethylallyl diphosphate in PBMCs. Because activation of gamma,delta-T-cells could be the initiating event in the acute phase response to bisphosphonate therapy, co-administration of a statin could be an effective approach to prevent this adverse effect.

Chemically modified tetracyclines selectively inhibit IL-6 expression in osteoblasts by decreasing mRNA stability

In bone biology, interleukin (IL)-6 is an autocrine/paracrine cytokine which can induce osteoclasts formation and activation to help mediate inflammatory bone destruction. Previous studies have shown that tetracycline and its derivatives have potentially beneficial therapeutic effects in the prevention and treatment of metabolic bone diseases by modulating osteoblast and osteoclast activities. Our previous studies indicated that non-antimicrobial chemically modified tetracyclines (CMTs) can dose-dependently inhibit IL-1β-induced IL-6 secretion in osteoblastic cells. In the present study, we explored the molecular mechanisms underlying the ability of doxycycline analogs CMT-8 and its non-chelating pyrazole derivative, CMT-5 to affect IL-6 gene expression in murine osteoblasts. Steady-state IL-6 mRNA was decreased with CMT-8 (ca. 50%) but not by CMT-5 when stimulated by IL-1β. CMT-8 regulation of IL-1β-induced IL-6 gene expression was further explored. CMT-8 did not affect IL-6 promoter activity in reporter gene assays. However, the IL-6 mRNA stability was decreased in the presence of CMT-8. These effects require de novo protein synthesis as they were inhibited by cycloheximide. Western blot analysis indicated that CMT-8 did not affect p38 mitogen-activated protein kinase, c- jun NH 2-terminal kinases, or extracellular signal-regulated kinases (1 and 2) phosphorylation in response to IL-1β. These data suggest that CMT-8 can modulate inhibit IL-1β-induced IL-6 expression in MC3T3-E1 cells at the post-transcriptional level affecting IL-6 mRNA stability. These observations may offer a novel molecular basis for this treatment of metabolic bone diseases that are mediated by IL-6.

Inhibition of mevalonate pathway is involved in alendronate-induced cell growth inhibition, but not in cytokine secretion from macrophages in vitro.

Bisphosphonates are antiresorptive drugs used for the treatment of metabolic bone diseases. They can be divided into two different pharmacological classes: nitrogen-containing and non-nitrogen-containing bisphosphonates. Non-nitrogen-containing bisphosphonates, like clodronate, are metabolised to a toxic ATP-analogue preventing osteoclast mediated bone resorption. Nitrogen-containing bisphosphonates, including alendronate, prevent osteoclast function by inhibiting the mevalonate pathway. Clodronate is known to have anti-inflammatory properties while alendronate induces cytokine secretion from lipopolysaccharide- (LPS) induced macrophages. This study investigates whether the cytotoxicity and cytokine production induced by alendronate and LPS could be counteracted by clodronate or products of mevalonate pathway: oxidized low density lipoprotein (ox-LDL), farnesol and geranylgeraniol. Treatment with alendronate increased LPS-induced secretion of IL-1beta, IL-6 and TNF-alpha from RAW 264 macrophages 2.4-, 1.4- and 1.8-fold, respectively. This treatment was cytotoxic for macrophages as indicated by lowered cell viability. Clodronate and ox-LDL both counteracted the cytokine secretion and cytotoxicity of alendronate. Farnesol and geranylgeraniol did neither reverse the cytokine secretion nor reduce the cytotoxicity of alendronate. Clodronate and ox-LDL were able to counteract the effects of alendronate on macrophages in vitro, probably by their known ability to inhibit DNA binding activity of transcription factors, nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1). These findings suggest that inhibition of mevalonate pathway is not the mechanism responsible for the proinflammatory response caused by alendronate, as it is in alendronate-induced apoptosis and prevention of osteoclast function.

Effects of receptor activator of NFκB (RANK) signaling blockade on fracture healing

As dominant regulators of osteoclastogenesis and bone resorption, receptor activator of NFκB (RANK), receptor activator of NFκB ligand, and OPG have been identified as ideal drug targets for the treatment of metabolic bone disease. One concern regarding the therapeutic use of RANK signaling inhibitors is their effect on fracture healing. Therefore we tested if uncoupling and osteoclast depletion via RANK blockade affects callus formation, maturation and matrix remodeling, as well as union rates in a mouse tibia fracture model. Low dose (1 mg/kg i.p.) RANK:Fc therapy had no effect on callus formation, matrix maturation and remodeling, and resulted in 100% bony union by day 28. High dose RANK:Fc treatment (10 mg/kg i.p.) effectively eliminated osteoclasts at the fracture site on day 14, with no significant effects on fracture healing. When therapy was discontinued, normal numbers of osteoclasts were observed at the fracture site by day 28. However, continuous therapy resulted in a large osteopetrotic callus consisting of both mineralized and unmineralized matrix that was void of osteoclasts, but bony union was unaffected at day 28. We also evaluated this process in the complete absence of RANK signaling using RANK −/− mice. These animals exhibited significant radiographic and histologic evidence of callus formation, indicating that RANK signaling is not required for fracture callus formation. However, only 33% of RANK −/− animals formed bony unions compared to 100% of the osteopetrotic control mice. This defect was most likely a result of decreased blood flow, as evidenced by fewer blood vessels in the RANK −/− animals. Together, these data imply that osteoclast depletion via inhibition of RANK signaling is a viable option for the treatment of pathological bone loss since no adverse effects on fracture healing are observed when therapy is discontinued.

Pharmacological actions and pharmacokinetics of bisphosphonates

Bisphosphonates are potent inhibitors of osteoclastic bone resorption and have been used for the treatment of various metabolic bone diseases such as osteoporosis and hypercalcemia of malignancy. However, the pharmacological action, the mechanism of action, and even side effects vary depending on the chemical structure of the side chain attached to the carbon atom of P-C-P bond. This review discussed about the pharmacological characteristics and possible application of different classes of bisphosphonates with different side chains.

Mediators of periodontal osseous destruction and remodeling: principles and implications for diagnosis and therapy.

Osteoclastic bone resorption is a prominent feature of periodontal disease. Bone resorption via osteoclasts and bone formation via osteoblasts are coupled, and their dysregulation is associated with numerous diseases of the skeletal system. Recent developments in the area of mediators of osteoclastic differentiation have expanded our knowledge of the process of resorption and set the stage for new diagnostic and therapeutic modalities to treat situations of localized bone loss as in periodontal disease. This review describes the current state of knowledge of osteoclast differentiation and activity, mediators, and biochemical markers of bone resorption and their use and potential use in clinical periodontics. Finally, therapeutic strategies based on knowledge gained in the treatment of metabolic bone diseases and in periodontal clinical trials are discussed, and the potential for future strategies is proposed relative to their biologic basis. The intent is to update the field of periodontics on the current state of pathophysiology of the osteoclastic lesion and outline diagnostic and therapeutic strategies with a rational basis in the underlying biology.

Rapid inhibition of thyroxine-induced bone resorption in the rat by an orally active vitronectin receptor antagonist.

An excess of thyroid hormone results in increased bone turnover and loss of bone mass in humans. Exogenous administration of thyroid hormone to rats has served as a model of human hyperthyroidism in which antiresorptive therapies have been tested. We have further refined this model of thyroxine (T4)-induced turnover in the rat. Daily administration of T4 to aged rats for as short as 1 week resulted in elevated bone resorption determined by significantly higher urinary deoxypyridinoline (Dpd) compared with vehicle controls or animals receiving T4 plus estradiol. Three weeks of daily administration of T4 led to significantly lower bone mineral density compared with untreated controls or animals receiving T4 plus estradiol. In a follow-up study, a depot formulation of T4 caused an increase in Dpd identical to that achieved with a bolus dose. SB-273005 [(4S)-2,3,4,5-tetrahydro-8-[2-[6-(methylamino)-2-pyridinyl] ethoxy]-3-oxo-2-(2,2,2-trifluoroethyl)-1H-2-benzazepine-4- acetic acid] a potent antagonist of the integrins alpha(v)beta(3) and alpha(v)beta(5), has been shown previously to inhibit bone resorption in cultures of human osteoclasts and to protect bone in ovariectomized rats. The effect of SB-273005 by oral administration was evaluated in this thyroxine-induced turnover model. Dose-dependent inhibition of resorption was seen with SB-273005 after 7 days of dosing using Dpd as a measure of bone resorption. In summary, it has been demonstrated that the antiresorptive activity of a vitronectin receptor antagonist can be measured after only 7 days of treatment in this refined rat model of thyroxine-induced bone turnover. These data suggest that SB-273005 may be useful for the treatment of metabolic bone diseases, including those resulting from hyperthyroidism.

Osteoclastic acidification pathways during bone resorption

Osteoclasts resorb bone by attaching to the surface and then secreting protons into an extracellular compartment formed between osteoclast and bone surface. This secretion is necessary for bone mineral solubilization and the digestion of organic bone matrix by acid proteases. This study summarizes the characterization and role of each type of ion transport and defines the main biochemical mechanisms involved in the dissolution of bone mineral during bone resorption. The primary mechanism responsible for acidification of the osteoclast-bone interface is vacuolar H +-adenosine triphosphatase (ATPase) coupled with Cl − conductance localized to the ruffled membrane. Carbonic anhydrase II (CAII) provides the proton source for extracellular acidification by H +-ATPase and the HCO 3 − source for the HCO 3 −/Cl − exchanger. Whereas some transporters are responsible for the bone resorption process, others are essential for pH regulation in the osteoclast. The HCO 3 −/Cl − exchanger, in association with CAII, is the major transporter for maintenance of normal intracellular pH. An Na +/H + antiporter may also contribute to the recovery of intracellular pH during early osteoclast activation. Once this mechanism has been rendered inoperative, another conductive pathway translocates the protons and modulates cytoplasmic pH. Inward-rectifying K + channels may also be involved by compensating for the external acidification due to H + transport. These different effects of transport processes, either on bone resorption or pH homeostasis, increase the number of possible sites for pharmacological intervention in the treatment of metabolic bone diseases.

Bisphosphonates Pamidronate and Zoledronic Acid Stimulate Osteoprotegerin Production by Primary Human Osteoblasts

Bisphosphonates are potent antiresorptive drugs commonly employed in the treatment of metabolic bone diseases. Despite their frequent use, the mechanisms of bisphosphonates on bone cells have largely remained unclear. Receptor activator of nuclear factor-κB ligand (RANKL) is essential for osteoclast formation and activation, whereas osteoprotegerin (OPG) neutralizes RANKL. Various osteotropic drugs have been demonstrated to modulate osteoblastic production of RANKL and OPG. In this study, we assessed the effects of the bisphosphonates pamidronate (PAM) and zoledronic acid (ZOL) on OPG mRNA steady-state levels (by semiquantitative RT-PCR) and protein production (by ELISA) in primary human osteoblasts (hOB). PAM increased OPG mRNA levels and protein secretion by hOB by up to 2- to 3-fold in a dose-dependent fashion with a maximum effect at 10−6 M (P < 0.001) after 72 h. Similarly, ZOL enhanced OPG gene expression and protein secretion by hOB in a dose-dependent fashion with a maximum effect at 10−8 M after 72 h, consistent with the higher biological potency of ZOL. Time course experiments indicated a stimulatory effect of PAM and ZOL on osteoblastic OPG protein secretion by 6-fold, respectively (P < 0.001). Pretreatment with PAM and ZOL prevented the inhibitory effects of the glucocorticoid dexamethasone on OPG mRNA and protein production. Analysis of cellular markers of osteoblastic differentiation revealed that PAM and ZOL induced type I collagen secretion and alkaline phosphatase activity by 2- and 4-fold, respectively (P < 0.0001 by ANOVA). In conclusion, our data suggest that bisphosphonates modulate OPG production by normal human osteoblasts, which may contribute to the inhibition of osteoclastic bone resorption. Since, OPG production increases with osteoblastic cell maturation, enhancement of OPG by bisphosphonates could be related to their stimulatory effects on osteoblastic differentiation.

Treatment of Metabolic Bone Disease

Treatment of Metabolic Bone Disease

Immuno-PCR Assay for Homodimeric Osteoprotegerin

Osteoprotegerin (OPG)/osteoclastogenesis inhibitory factor is a recently cloned cytokine that specifically inhibits differentiation and maturation of osteoclasts (1)(2)(3)(4). OPG is present as a monomer (60 kDa) and a homodimer (120 kDa) in conditioned media from human fibroblasts and from CHO cells producing human OPG (3)(5). Notably, the homodimeric form of recombinant OPG exerted more potent biologic activity than the monomeric form in vivo (5)(6)(7). Which form of OPG predominates in human serum has not been definitively determined. Determining the amount of each form of OPG in patient serum may be useful in the diagnosis and treatment of metabolic bone diseases associated with abnormal osteoclast recruitment and function, such as osteopetrosis, osteoporosis, metastatic bone disease, Paget disease, rheumatoid arthritis, and periodontal disease. Yano et al. (8) have described ELISAs with tetramethylbenzidine for total OPG and the homodimeric form of OPG (detection range for both ELISAs, 65–500 ng/L). The homodimeric form of OPG, however, cannot be detected in human serum by conventional ELISAs because the concentrations are below the detection limit. Additionally, the monomeric form of OPG cannot be measured directly at the present time because no specific antibody for the monomeric form is available. We therefore devised a highly sensitive immuno-PCR assay to measure the homodimeric form of OPG in sera from healthy individuals and patients with osteoporosis. Blood samples were obtained from 11 healthy volunteers and 22 patients with osteoporosis. The immuno-PCR assay consisted of the following steps: an ELISA for antigen detection, followed by PCR for signal amplification. The ELISA for human OPG (hOPG) was performed according to a method described previously (8). Monomeric …

Treatment of metabolic bone disease.

Treatment of metabolic bone disease.

Ulcerative esophagitis caused by etidronate

Bisphosphonates are emerging as an important component in the treatment of established osteoporosis. Other possible clinical uses of bisphosphonates are currently being explored, such as prevention of perimenopausal bone loss, treatment of corticosteroid-induced osteopenia, and treatment of skeletal manifestations of malignancy. 1 Meunier PJ Confravreux E Tuninon I Hardouin C. Cyclic alendronate therapy prevents bone loss in the early postmenopausal period. J Bone Miner Res. 1995; 10 ([abstract]): S357 Google Scholar , 2 Mulder H Struys A. Intermittent cyclical etidronate in the prevention of corticosteroid-induced bone loss. Br J Rheumatol. 1994; 33: 348-350 Crossref PubMed Scopus (155) Google Scholar , 3 Berenson J Lichtenstein A Porter L. Efficacy of pamidronate in reducing skeletal events in patients with advanced multiple myeloma. New Engl J Med. 1996; 334: 488-493 Crossref PubMed Scopus (992) Google Scholar Among the bisphosphonates, etidronate has been the most extensively studied in the treatment of metabolic bone diseases and is currently the most widely available of all bisphosphonates for the treatment of postmenopausal osteoporosis. The efficacy, clinical tolerance, and safety of etidronate have been well established in many controlled clinical trials. 4 Harris ST Watts NB Jackson RD. Four-year study of intermittent cyclic etidronate treatment of postmenopausal osteoporosis: three years of blinded therapy followed by one year of open therapy. Am J Med. 1993; 95: 557-567 Abstract Full Text PDF PubMed Scopus (382) Google Scholar , 5 Silberstein EB Schnur W. Cyclic oral phosphate and etidronate increase femoral and lumbar bone mineral density and reduce lumbar spine fracture rate over three years. J Nucl Med. 1992; 33: 1-5 PubMed Google Scholar

Lesión hepatocelular inducida por alendronato

Bisphosphonates are widely used in the treatment of metabolic bone disease. Bisphosphonate-induced hepatotoxicity is extremely infrequent. We present the case of a 76-year-old female patient with osteoporosis who was prescribed alendronate. A routine laboratory investigation carried out three months later revealed markedly elevated transaminase concentrations. Six weeks after withdrawal of treatment, laboratory parameters had returned to normal levels. We analyze this adverse reaction to alendronate as well as its possible pathogenic mechanisms.

Breakthrough in bone: the molecular mechanism of osteoclast/osteoblast coupling revealed

Control of osteoclastogenesis and osteoclast activity is critical for the treatment of metabolic bone diseases. The long sought after molecules that directly control the function and fate of these specialized bone-resorbing cells have recently been identified. Here we review the discovery of these molecules (receptor activator of nuclear factor κB/osteoclast differentiation and activation receptor; osteoclast differentiation factor/osteoprotegerin ligand/tumor necrosis factor–related activation-induced cytokine; and osteoprotegerin/osteoclast inhibitory factor) and the in vivo preclinical and clinical data supporting their role as dominant regulators of osteoclasts. These molecules are all members of the tumor necrosis factor receptor superfamily, which has been shown to regulate programmed cell death by either suppressing apoptosis via inducing the expression of survival genes, or initiating apoptosis through activation of the caspase cascade. In an attempt to explain the teleology of this signaling pathway and how it controls the osteoclast lifespan, we propose a model in which a loose analogy is drawn between this pathway and that of tumor necrosis factor signaling in T lymphocytes. Future experimentation to test this model will provide a better understanding of this pathway and information as to the best way to manipulate this system to treat patients with musculoskeletal disease.

Protein geranylgeranylation is required for osteoclast formation, function, and survival: inhibition by bisphosphonates and GGTI-298.

Bisphosphonates are the important class of antiresorptive drugs used in the treatment of metabolic bone diseases. Although their molecular mechanism of action has not been fully elucidated, recent studies have shown that the nitrogen-containing bisphosphonates can inhibit protein prenylation in macrophages in vitro. In this study, we show that the nitrogen-containing bisphosphonates risedronate, zoledronate, ibandronate, alendronate, and pamidronate (but not the non nitrogen-containing bisphosphonates clodronate, etidronate, and tiludronate) prevent the incorporation of [14C]mevalonate into prenylated (farnesylated and geranylgeranylated) proteins in purified rabbit osteoclasts. The inhibitory effect of nitrogen-containing bisphosphonates on bone resorption is likely to result largely from the loss of geranylgeranylated proteins rather than loss of farnesylated proteins in osteoclasts, because concentrations of GGTI-298 (a specific inhibitor of geranylgeranyl transferase I) that inhibited protein geranylgeranylation in purified rabbit osteoclasts prevented osteoclast formation in murine bone marrow cultures, disrupted the osteoclast cytoskeleton, inhibited bone resorption, and induced apoptosis in isolated chick and rabbit osteoclasts in vitro. By contrast, concentrations of FTI-277 (a specific inhibitor of farnesyl transferase) that prevented protein farnesylation in purified rabbit osteoclasts had little effect on osteoclast morphology or apoptosis and did not inhibit bone resorption. These results therefore show the molecular mechanism of action of nitrogen-containing bisphosphonate drugs in osteoclasts and highlight the fundamental importance of geranylgeranylated proteins in osteoclast formation and function.

The Role of Receptor Activator of Nuclear Factor- B Ligand and Osteoprotegerin in the Pathogenesis and Treatment of Metabolic Bone Diseases

The Role of Receptor Activator of Nuclear Factor- B Ligand and Osteoprotegerin in the Pathogenesis and Treatment of Metabolic Bone Diseases