Effects of two novel bisphosphonates on bone cells in vitro

The Role of Matrix Metalloproteinases in Periodontal Disease

This review provides a detailed description of matrix metalloproteinases (MMPs), focusing on those that are known to have critical roles in bone and periodontal disease. Periodontal disease is an inflammatory process initiated by anaerobic bacteria, which promote the host immune response in the form of a complex network of molecular pathways involving proinflammatory mediators such as cytokines, growth factors, and MMPs. MMPs are a family of 23 endopeptidases, collectively capable of degrading virtually all extracellular matrix (ECM) components. This study critically discusses the available research concerning the involvement of the MMPs in periodontal disease development and progression and presents possible therapeutic strategies. MMPs participate in morphogenesis, physiological tissue turnover, and pathological tissue destruction. Alterations in the regulation of MMP activity are implicated in the manifestation of oral diseases, and MMPs comprise the most important pathway in tissue destruction associated with periodontal disease. MMPs can be considered a risk factor for periodontal disease, and measurements of MMP levels may be useful markers for early detection of periodontitis and as a tool to assess prognostic follow-ups. Detection and inhibition of MMPs could, therefore, be useful in periodontal disease prevention or be an essential part of periodontal disease therapy, which, considering the huge incidence of the disease, may greatly improve oral health globally.

Zoledronic acid and bone cellular respiration

Phosphorescence O₂ analyzer was used to measure calvarial bone cellular respiration (cellular mitochondrial O₂ consumption) in Taylor Outbred mice in the presence and absence of zoledronic acid. This potent bisphosphonate inhibits osteoclast-mediated calcium resorption, and its effects on bone respiration have not been previously investigated. The change of O₂ concentration with time was measured in closed vials containing phosphate-buffered saline (PBS), 5 mM glucose and 5-25 mg calvarial bone fragments, and it was complex for t = 0-30 h. Cyanide (specific inhibitor of cytochrome oxidase) halted O₂ consumption, confirming the oxidation occurred in the respiratory chain. Initial rate of respiration was estimated from the zero-order plots d[O₂]/dt for t = 0-4 h. For untreated specimens, the rate (mean ± SD) was 2.0 ± 1.2 µM O₂ h^-1 mg^-1 (n = 6). This value was 7-10 times lower than that of other murine organs, but similar to that reported for rat and Guinea pig calvaria (averaging, 2.7 nmol O₂ h^-1 mg^-1). The corresponding rate in the presence of 10-100 µM zoledronic acid was 2.7 ± 0.7 µM O₂ h^-1 mg^-1 (n = 11), p = 0.216. The first-order plots ln ([O₂] _t  ÷ [O₂] _t=0) versus time for t = 0-30 h were also used to compare treated and untreated specimens. The rate (h^-1 mg^-1 10³) for specimens incubated in PBS without glucose was 1.3 ± 0.6 (n = 3, p = 0.007), in PBS + glucose it was 10.7 ± 6.9 (n = 10), in PBS + glucose + 10 µM zoledronic acid it was 12.1 ± 6.7 (n = 10, p = 0.579), in PBS + glucose + 20 µM zoledronic acid it was 12.9 ± 3.3 (n = 9, p = 0.356), and in PBS + glucose + 100 µM zoledronic acid it was 13.7 ± 7.7 (n = 9, p = 0.447). Thus, exposure to high-doses of zoledronic acid over several hours imposed a statistically insignificant increase in calvarial bone cellular respiration.

Osteoblast as a target of anti-osteoporotic treatment

Osteoblasts are mesenchymal cells that play a key role in maintaining bone homeostasis; they are responsible for the production of extracellular matrix proteins, regulation of matrix mineralization, control of bone remodeling and regulate osteoclast differentiation. Osteoblasts have an essential role in the pathogenesis of many bone diseases, particularly osteoporosis. For many decades, the main current available treatments for osteoporosis have been represented by anti-resorptive drugs, such as bisphosphonates, which act mainly by inhibiting osteoclasts maturation, proliferation and activity; nevertheless, in recent years much attention has been paid on anabolic aspects of osteoporosis treatment. Many experimental evidences support the hypothesis of direct effects of the classical anti-resorptive drugs also on osteoblasts, and recent progress in understanding bone physiology have led to the development of new pharmacological agents such as anti-sclerostin antibodies and teriparatide which directly target osteoblasts, inducing anabolic effects and promoting bone formation.

Everolimus and zoledronic acid--a potential synergistic treatment for lung adenocarcinoma bone metastasis

Non-small-cell lung cancer (NSCLC) frequently metastasizes to bone. It is known that zoledronic acid is cytostatic to tumors, and everolimus, the inhibitor for mammalian target of the rapamycin, could inhibit many types of cancer. Herein, we evaluated the effect of zoledronic acid alone and in combination with everolimus on treating lung adenocarcinoma bone metastasis in vitro and in vivo. Mice treated with zoledronic acid in combination with everolimus had more apoptotic lung cancer cells and more cells were arrested in the G1/G0 phase. The phosphorylation of p70S6K was inhibited in the combination treatment group. Lung cancer cell invasion was also significantly inhibited in the group with combination treatment in vitro. Bone nuclear scans revealed more metastatic lesions in controls compared with those in the combination treatment group. Bone scans and radiographic images indicated that combination therapy significantly reduced bone metastasis. The moderate survival rate suggested that the drug combination was synergistic, which can delay NSCLC bone metastasis and prolong survival in vivo.

The effects of zoledronic acid and hyperbaric oxygen on posterior lumbar fusion in a rabbit model

We studied the effects of hyperbaric oxygen (HBO) and zoledronic acid (ZA) on posterior lumbar fusion using a validated animal model. A total of 40 New Zealand white rabbits underwent posterior lumbar fusion at L5-6 with autogenous iliac bone grafting. They were divided randomly into four groups as follows: group 1, control; group 2, HBO (2.4 atm for two hours daily); group 3, local ZA (20 μg of ZA mixed with bone graft); and group 4, combined HBO and local ZA. All the animals were killed six weeks after surgery and the fusion segments were subjected to radiological analysis, manual palpation, biomechanical testing and histological examination. Five rabbits died within two weeks of operation. Thus, 35 rabbits (eight in group 1 and nine in groups 2, 3 and 4) completed the study. The rates of fusion in groups 3 and 4 (p = 0.015) were higher than in group 1 (p < 0.001) in terms of radiological analysis and in group 4 was higher than in group 1 with regard to manual palpation (p = 0.015). We found a statistically significant difference in the biomechanical analysis between groups 1 and 4 (p = 0.024). Histological examination also showed a statistically significant difference between groups 1 and 4 (p = 0.036). Our results suggest that local ZA combined with HBO may improve the success rate in posterior lumbar spinal fusion.

Alendronate enhances osteogenic differentiation of bone marrow stromal cells: a preliminary study

Alendronate inhibits osteoclastic activity. However, some studies suggest alendronate also has effects on osteoblast activity. We hypothesized alendronate would enhance osteoblastic differentiation without causing cytotoxicity of the osteoblasts. We evaluated the effect of alendronate on the osteogenic differentiation of mouse mesenchymal stem cells. D1 cells (multipotent mouse mesenchymal stem cells) were cultured in osteogenic differentiation medium for 7 days and then treated with alendronate for 2 days before being subjected to various tests using MTT assays, Alizarin Red, enzyme-linked immunosorbent assay, energy-dispersive xray spectrophotometry, reverse transcriptase-polymerase chain reaction, confocal microscopy, and flow cytometric analysis. D1 cells differentiated into osteoblasts in the presence of osteogenic differentiation medium as confirmed by positive Alizarin Red S staining, increased alkaline phosphatase activity and osteocalcin mRNA expression, a calcium peak by energy-dispersive xray spectrophotometry, and by positive immunofluorescence staining against CD44. Osteogenic differentiation was enhanced after treatment with alendronate as confirmed by Alizarin Red S staining, elevated alkaline phosphatase activity and osteocalcin mRNA expression, a greater calcium peak by energy-dispersive xray spectrophotometry, and by immunofluorescence staining against CD44 by flow cytometric analysis. These data suggest alendronate enhances osteogenic differentiation when treated with mouse mesenchymal stem cells in osteogenic differentiation medium.

Experimental evaluation of the effects of zoledronic acid on regenerate bone formation and osteoporosis in mandibular distraction osteogenesis

PURPOSE

The aim of this study was to evaluate the effects of systemically administered zoledronic acid (ZA) on the bone mineral density (BMD) and bone mineral content (BMC) at mandibular distraction sites in rabbits.

MATERIALS AND METHODS

Eighteen New Zealand white rabbits were randomly divided into 2 groups. Bone lengthening was performed in the left portion of the mandible through distraction osteogenesis at a rate of 0.5 mm every 12 hours for 5 days. While the experimental group rabbits were administered intravenous 0.1 mg/kg ZA, control group rabbits were given only saline infusion during operation. All animals were sacrificed at the end of the consolidation period of 28 days. The mandibles of all animals were removed and both the anterior and posterior pin regions of the regenerate and regenerate region were evaluated by dual energy x-ray absorptiometry (DEXA). BMD and BMC data were statistically analyzed.

RESULTS

Except for 1 rabbit from the experimental group that had an infection at the external pin region, all animals showed complete clinical healing. When the values in the group receiving ZA were compared with those of the control group, it was observed that the BMD values of the anterior pin region of regenerate, regenerate region, and posterior pin region increased by 23%, 20%, and 31%, respectively; and BMC values increased by 22%, 24%, and 32%, respectively. When data of these regions were compared, both BMD and BMC were found statistically different in all regions (P < .05).

CONCLUSION

Results of this study showed that ZA had positive effects on new bone formation at and around the distraction gaps of the lengthened rabbit mandibles by distraction osteogenesis.

Osteoblast proliferation and maturation by bisphosphonates

Aseptic loosening and osteolysis are currently the most common causes of failure of total joint replacements. Osteolysis is initiated by a macrophage response to wear debris, resulting in localized, osteoclastic peri-implant bone loss. We have previously inhibited osteoclast-mediated bone resorption in a canine total hip arthroplasty model using oral bisphosphonate therapy. Based on serendipitous observations from our canine study, we hypothesized that bisphosphonates have an anabolic effect on osteoblasts, in a manner distinct from their inhibitory effect on osteoclastic bone resorption. We studied the anabolic effects of two FDA-approved bisphosphonates (alendronate and risedronate) on two in vitro models: a primary human trabecular bone cell culture and the MG-63 osteoblast-like cell line. Following treatment with bisphosphonates at varying concentrations and time periods, cells were assayed for proliferation effects and results were quantified using the methods of direct cell count, and the colorimetric MTT (3-dimethylthiazol-2,5-diphenyltetrazolium bromide) assay at 24, 48, and 72 h. The effect of bisphosphonates on the maturation of osteoblasts were tested with alkaline phosphatase bioassay and reverse transcription-polymerase chain reaction for markers of osteoblast differentiation. Results from both the primary human trabecular bone cell culture and the MG-63 osteoblast-like cell line showed that both bisphosphonates significantly increased the cell number over controls, attaining peak levels at a concentration of 10(-8)M. Alkaline phosphatase activity was also increased, representing earlier commitment of osteoprogenitor cells towards the osteoblastic phenotype. Bisphosphonates also enhanced gene expression of BMP-2, Type I collagen and osteocalcin. In summary, bisphosphonates, aside from their role as inhibitors of osteoclastic bone resorption, are promoters of osteoblast proliferation and maturation.

Bisphosphonates may reduce recurrence in giant cell tumor by inducing apoptosis

Giant cell tumor of bone is an aggressive tumor characterized by extensive bone destruction and high recurrence rates. This tumor consists of stromal cells and hematopoietic cells that interact in an autocrine manner to produce tumoral osteoclastogenesis and bone resorption. This autocrine regulation may be disrupted by novel therapeutic agents. Nonspecific local adjuvant therapies such as phenol or liquid nitrogen have been used in the treatment of giant cell tumor, but specific adjuvant therapies have not been described. The bisphosphonates pamidronate and Zoledronate can induce apoptosis in giant cell tumor culture in a dose-dependent manner. We established giant cell tumor cultures from patients with extensive destruction of bone. One of the four cultures formed osteoclastlike giant cells in vitro after more than six passages without exogenous receptor activator of NF-kappaB ligand or macrophage colony stimulating factor. Annexin V staining, presence of active cleaved form of caspase-3, and disappearance of poly (ADP-ribose) polymerase on Western blotting indicated activation of apoptosis by bisphosphonates in giant cell tumor. These results indicate that topical or systemic use of pamidronate or zoledronate can be a novel adjuvant therapy for giant cell tumor by targeting osteoclastlike giant cells, mononuclear giant cell precursor cells, and the autocrine loop of tumor osteoclastogenesis.

Zoledronic Acid

Zoledronic acid (Zometa), a parenteral bisphosphonate, is an inhibitor of osteoclast-mediated bone resorption and is used in the management of patients with cancer. Zoledronic acid 4 mg is administered as an intravenous infusion over 15 minutes. In the treatment of bone metastases, zoledronic acid is the first and only bisphosphonate to demonstrate efficacy in patients with a broad range of tumour types and in multiple myeloma. In well-designed trials, a single 4 mg dose of zoledronic acid showed good efficacy in the treatment of patients with hypercalcaemia of malignancy. Zoledronic acid 4 mg was superior to pamidronic acid 90 mg, administered as a 2-hour infusion, as assessed by normalised serum calcium concentrations 10 days after administration. In conjunction with antineoplastic therapy, zoledronic acid was an effective long-term (up to 25 months) treatment for skeletal-related events in patients with bone metastases associated with multiple myeloma or solid tumours. In patients with bone metastases secondary to breast cancer or bone lesions from myeloma, zoledronic acid was at least as effective as pamidronic acid, based on assessments of skeletal-related events 25 months after the start of treatment. In addition, compared with pamidronic acid, the overall risk of developing skeletal complications, including hypercalcaemia of malignancy, was significantly reduced in recipients of zoledronic acid. Compared with pamidronic acid, zoledronic acid reduced the risk of patients with breast cancer developing a skeletal-related event by an additional 20%. Zoledronic acid was significantly more effective than placebo on most efficacy measures in patients with bone metastases secondary to other solid tumours (e.g. lung, prostate) and showed sustained efficacy for up to 15 months. Preliminary data indicate that its efficacy in these patients is sustained for up to 24 months. Estimates of the cost effectiveness of zoledronic acid in the treatment of prostate cancer were consistent with those of other bisphosphonates, and cost-effectiveness ratios were within limits considered acceptable economic value. Zoledronic acid was generally well tolerated, with a tolerability profile similar to that of pamidronic acid and placebo. As with other bisphosphonates, deterioration of renal function has occasionally been reported in patients receiving zoledronic acid and monitoring of serum creatinine is recommended during treatment. The efficacy of zoledronic acid is therefore well established in patients with hypercalcaemia of malignancy and, for up to 25 months, in the treatment of complications arising from metastatic bone disease in patients with multiple myeloma or solid tumours. The clinical profile of zoledronic acid compares favourably with that of pamidronic acid in patients with cancer and zoledronic acid has a more convenient administration schedule with the potential for better compliance. Thus, zoledronic acid is an effective bisphosphonate and is positioned to play an important role in the management of advanced cancer patients with bone metastases.

Breakthroughs in the management of multiple myeloma

Although multiple myeloma remains a terminal illness, the past four decades have seen a dramatic change in the outlook for a newly diagnosed patient in terms of therapies available, supportive care and insight into the pathogenesis of this disease. Among the newer agents available for treatment, thalidomide has been resurrected and discovered to be a valuable therapy for myeloma. Thalidomide appears to work, at least in part, through its anti-angiogenic properties, but much remains to be learned about its mechanism of action as well as optimal administration regimens. With the development of increasingly more potent bisphosphonates it has become possible to diminish the painful skeletal complications of myeloma, one of the most devastating problems of this disease. The most recent generation of bisphosphonates, pamidronic acid and zoledronic acid, have provided a statistically significant decrease in the skeletal complications of myeloma when used in a prophylactic manner. These agents appear to work by inhibiting osteoclast function. Progressive improvement in cytogenetic techniques has now demonstrated that almost all patients with myeloma have chromosomal abnormalities, some of which appear to confer varying degrees of prognostic significance. In particular, the changes in chromosome 13 are associated with an unusually poor outcome. These findings are serving as a guide toward learning more about the pathogenesis of myeloma as well as in identifying potential targets for therapy. Stem cell transplantation has emerged as the standard treatment for the large majority of patients with myeloma following the demonstration of superior complete remission and survival, both disease-free and overall, in a French randomised trial. Unfortunately, virtually all patients will eventually relapse following autologous stem cell transplantation, prompting continuing efforts such as tandem transplants, CD34+ selection, as well as modifications in the conditioning regimen to improve outcomes. Allogeneic bone marrow transplants appear to offer a better chance for a possible cure of myeloma but have been associated with an unusually high mortality. However, this approach is being revived with the advent of the less toxic non-myeloablative transplant that has provided an 81% short-term survival in a trial combining this approach with an initial conventional autologous bone marrow transplant. Immunotherapy with dendritic cells appears now to be a feasible way to enhance innate or acquired immunity to help eliminate minimal residual disease following autologous bone marrow transplant. Unfortunately, a cure for myeloma remains elusive but the continuing advances in management may significantly prolong survival in affected patients.

Zoledronic acid: a review of its use in the management of bone metastases and hypercalcaemia of malignancy

Zoledronic acid (Zometa) is an effective inhibitor of osteoclast-mediated bone resorption. Zoledronic acid demonstrated efficacy in the reduction of skeletalrelated events (SREs) in patients with multiple myeloma or bone metastases secondary to breast cancer, prostate cancer or other solid tumours, or hypercalcaemia of malignancy. Zoledronic acid was effective in patients with multiple myeloma or metastatic breast cancer with osteolytic or mixed bone lesions. The proportion of patients who experienced an SRE was similar during 12 months of treatment with zoledronic acid 4mg or pamidronic acid 90mg, but significantly fewer patients receiving zoledronic acid required radiotherapy to bone. Furthermore, in patients with breast cancer and osteolytic lesions, median time to a first SRE was more than 4 months longer with zoledronic acid than with pamidronic acid. In the multiple event analysis in a 12-month extension study (total study duration was 25 months) in patients with breast cancer, zoledronic acid was superior to pamidronic acid, with an 18% reduction in the risk of experiencing an SRE. Both drugs were associated with a slight reduction in pain. Zoledronic acid 4mg, compared with placebo, significantly reduced the proportion of patients with prostate cancer bone metastases experiencing an SRE, particularly pathological fractures after 15 months' treatment. The drug also significantly delayed the onset of skeletal complications compared with placebo in patients with prostate cancer and other solid tumours including non-small cell lung cancer. When administered as a single 15-minute intravenous infusion, zoledronic acid 4mg was significantly more effective than pamidronic acid administered as a 2-hour infusion in the treatment of severe hypercalcaemia of malignancy, as assessed by complete responses measuring normalised serum calcium concentrations at day 10 after a single dose. Furthermore, zoledronic acid normalised serum calcium concentrations significantly faster than pamidronic acid, and the duration of response and median time to relapse were approximately twice as long in zoledronic acid recipients than in pamidronic acid recipients. Zoledronic acid is well tolerated and has a similar tolerability profile to pamidronic acid. The most commonly reported adverse events included flu-like symptoms (fever, arthralgias, myalgias and bone pain), fatigue, gastrointestinal reactions, anaemia, weakness, dyspnoea and oedema.

CONCLUSION

In conjunction with antitumour therapy, zoledronic acid should be considered for routine use to reduce skeletal complications in patients with advanced malignancies involving bone. In patients with hypercalcaemia of malignancy, zoledronic acid is expected to become the treatment of choice.

Zoledronic acid (Zometa) use in bone disease

Zoledronic acid (Zometa) is the most recent addition to the clinically available bisphosphonates. Clinical benefits in metabolic, as well as cancer-related bone disease have been observed. In addition to its profound antiosteoclast effects, it has demonstrated anticancer effects in preclinical models. Zoledronic acid has been evaluated in randomized, double-blind clinical trials of osteoporosis, Paget's disease of bone, and metastatic, osteolytic and osteoblastic bone disease. Antiosteoclast activity has been demonstrated by reductions in the bone breakdown products N-telopeptide, C-telopeptide and deoxypyridinoline. Bone mineral density, measured by dual energy x-ray absorptometry, is increased with administration of zoledronic acid in postmenopausal osteoporosis. Clinical benefit in cancer includes improvement in bone pain, reductions in skeletal events and delay in time-to-first-skeletal-events. These zoledronic acid treatment benefits have been demonstrated in patients with multiple myeloma, breast, prostate and lung cancer, and other solid tumors.

Bisphosphonates influence the proliferation and the maturation of normal human osteoblasts

The key pharmacological action for the clinical use of bisphosphonates lies in the inhibition of osteoclast-mediated bone resorption. Osteoblasts could be other target cells for bisphosphonates. We studied the effects of bisphosphonates on the proliferation and the differentiation of normal human bone trabecular osteoblastic cells (hOB). We tested 4 different compounds: clodronate, pamidronate and 2 newer compounds: ibandronate, a nitrogen-containing bisphosphonate and zoledronate, which is a heterocyclic imidazole compound. Ibandronate and zoledronate stimulated hOB cell proliferation by up to 30% (p<0.05) after 72 h for concentrations ranging from 10(-8) M to 10(-5) M. Clodronate transiently enhanced hOB cell survival after only 24 h (+60%, p<0.001) whereas pamidronate had no effect. Longer time course studies, in presence of fetal calf serum, revealed that cell growth was finally reduced by all 4 bisphosphonates (40% after 7 days). Type I collagen synthesis was transiently increased by all 4 bisphosphonates after only 48 h incubation (+17% to +67%, p<0.05). Clodronate increased ALP activity by up to 1.7-fold after 4 days of culture (p<0.05) whereas ibandronate or zoledronate exhibited lesser stimulatory effects (+17 to +30%), and pamidronate had no significant effect. In conclusion, we found that different bisphosphonates, currently used or tested in various clinical conditions, transiently stimulated the growth of preosteoblastic cells and thereafter increased their differentiation according to sequential events (type I collagen synthesis first, then ALP activity to a lesser extent). Our data suggest that the beneficial effects of bisphosphonate treatment on bone mass and integrity could be partly mediated through a direct action on osteoblasts.

Effects of topical administration of clodronate on alveolar bone resorption in rats with experimental periodontitis

BACKGROUND

We examined whether topical administration of a bisphosphonate clodronate could prevent alveolar bone loss in rats with experimental periodontitis.

METHODS

On day 0, elastic rings were placed around the cervix of the right and left maxillary first molars (M1) to induce inflammatory periodontitis. Fifty microl of clodronate solution at a concentration of either 0 (0.9% NaCl), 20, 40, or 60 mM was injected into the subperiosteal palatal area adjacent to the interdental area between M1 and M2 on either the left or right (experimental) side on days 0, 2, 4, and 6. The contralateral side served as a control and received 0.9% NaCl solution without clodronate. The animals were sacrificed on day 7.

RESULTS

Histological examination and determination of bone mineral density in the interdental alveolar bone area between M1 and M2 revealed that placement of an elastic ring caused severe vertical and horizontal bone resorption on the control side, while the topical administration of clodronate significantly prevented such alveolar bone loss. The number of osteoclasts on the experimental side was decreased compared with the control side. Furthermore, many of the osteoclasts on the experimental side were detached from the surface of the alveolar bone and had degenerated appearances, such as rounded shapes and a loss of polarity.

CONCLUSIONS

These results suggest that topical administration of clodronate may be effective in preventing osteoclastic bone resorption in periodontitis.

Distinct mechanisms of bisphosphonate action between osteoblasts and breast cancer cells: identity of a potent new bisphosphonate analogue

While the effects of bisphosphonates on bone-resorbing osteoclasts have been well documented, the effects of bisphosphonates on other cell types are not as well studied. Recently, we reported that bisphosphonates have direct effects on bone-forming human fetal osteoblast cells (hFOB). In this report, the role of the mevalonate pathway in the actions of bisphosphonates on hFOB, and MDA-MB-231 human breast cancer cells was examined. These studies included a novel bisphosphonate analog, the anhydride formed between arabinocytidine 5' phosphate and etidronate (Ara-CBP). Ara-CBP was the most potent inhibitor of hFOB and MDA-MB-231 cell proliferation, and stimulator of hFOB cell mineralization compared to etidronate, the anhydride formed between AMP and etidronate (ABP), pamidronate, and zoledronate. Inhibition of hFOB cell proliferation by Ara-CBP and zoledronate was partially reversed by mevalonate pathway intermediates, and stimulation of hFOB cell mineralization was completely reversed by mevalonate pathway intermediates. These results suggest that zoledronate and Ara-CBP act, at least in part, via inhibition of the mevalonate pathway in hFOB cells. In contrast, none of the mevalonate pathway intermediates reversed the inhibition of MDA-MB-231 cell proliferation by the bisphosphonates, or the effects of pamidronate on hFOB cells. As a positive control, the effects of mevastatin on hFOB and MDA-MB-231 cells were completely reversed by mevalonate. In summary, these data suggest that zoledronate and Ara-CBP induce human osteoblast differentiation via inhibition of the mevalonate pathway. In contrast, the inhibition of MDA-MB-231 cell proliferation by the bisphosphonates appears to be through mechanisms other than inhibition of the mevalonate pathway.

Recovery of proximal tibia bone mineral density and strength, but not cancellous bone architecture, after long-term bisphosphonate or selective estrogen receptor modulator therapy in aged rats

Various bisphosphonates and the selective estrogen receptor modulator (SERM) raloxifene are approved treatments of postmenopausal osteoporosis. They increase bone mineral density (BMD), decrease bone turnover, and reduce vertebral fracture incidence through different cellular mechanisms. We investigated the bone cellular activities, architecture, mineral content/density, and strength of ovariectomized (ovx) rats on a long-term bisphosphonate or SERM treatment, at doses of either agent correcting bone strength. Eleven weeks postovariectomy, 6-month-old rats were treated with the SERM MDL 103,323 or with the bisphosphonate pamidronate for 5 months. Doses of pamidronate and MDL 103,323 were selected from previous studies showing correction of the ovx-induced decrease of ultimate strength of proximal tibia. Ultimate and yield strengths, BMD, and histomorphometric parameters were all quantified at the same site, i.e., the proximal tibia metaphysis. Long-term pamidronate decreases bone turnover and bone formation activity, leading to trabecular thinning. MDL 103,323 decreases bone turnover to a lesser extent, and slightly protects trabecular architecture by uncoupling bone resorption and formation activities. The yield strength is corrected by pamidronate, but not by MDL 103,323 treatment. However, neither compound restores the ovariectomy-induced cancellous bone loss. Total tissue area and cortical thickness are unchanged with pamidronate or MDL 103,323 treatment, indicating that cortical bone mass, thickness, and cross-sectional area are not modified. The discrepancy between proximal tibia BMD and mechanical resistance to fracture modifications, on the one hand, and cancellous bone volume, on the other hand, could be due to changes in the degree of mineralization of bone matrix and/or of the intrinsic properties of the bone matrix.

The effects of MMP inhibitors on human salivary MMP activity and caries progression in rats

Previous studies suggest that salivary and pulp-derived host enzymes, matrix metalloproteinases (MMPs), may be involved in dentin caries pathogenesis. To study the inhibition of acid-activated human salivary MMPs by non-antimicrobial chemically modified tetracyclines (CMTs), we used a functional activity assay with 125I-labeled gelatin as a substrate. To address the role of MMPs in the progression of fissure caries in vivo, we administered the MMP inhibitors CMT-3 and zoledronate to young rats per os for 7 weeks, 5 days a week. Caries lesions were visualized by Schiff reagent in sagittally sectioned mandibular molars. Marked reduction in gelatinolytic activity of human salivary MMPs was observed with CMT-3. CMT-3 and zoledronate, both alone and in combination, also reduced dentin caries progression in the rats. These results suggest that MMPs have an important role in dentin caries pathogenesis, and that MMP inhibitors may prove to be useful in the prevention of caries progression.

Bisphosphonates regulate cell growth and gene expression in the UMR 106-01 clonal rat osteosarcoma cell line

Local growth of osteosarcoma involves destruction of host bone by proteolytic mechanisms and/or host osteoclast activation. Osteoclast formation and activity are regulated by osteoblast-derived factors such as the osteoclast differentiating factor, receptor activator of NF-kappaB ligand (RANKL) and the inhibitor osteoprotegerin (OPG). We have investigated the in vitro effects of bisphosphonates on a clonal rat osteosarcoma cell line. The aminobisphosphonate pamidronate was added to UMR 106-01 cell cultures (10(-8)M to 10(-4)M up to 5 days). The non-aminobisphosphonate clodronate was administered for the same time periods (10(-6)M to 10(-2)M). Cell proliferation, apoptosis and mRNA expression was assessed. Both agents inhibited cell proliferation in a time- and dose-dependent manner. ELISA analysis demonstrated an increase in DNA fragmentation although there was no significant dose-related difference between the doses studied. Bisphosphonate-treated cultures had a greater subpopulation of cells exhibiting morphological changes of apoptosis. Expression of mRNA for osteopontin and RANKL was down-regulated by both agents, while the expression of mRNA for alkaline phosphatase, pro-alpha1(I) collagen and OPG was not altered. Out in vitro work suggests the bisphosphonates not only have direct effects on osteosarcoma cell growth and apoptosis, but also, by altering the relative expression of osteoclast-regulating factors, they may inhibit the activity of osteoclasts and their recruitment.

Intermittent and continuous administration of the bisphosphonate ibandronate in ovariohysterectomized beagle dogs: effects on bone morphometry and mineral properties

Bisphosphonates have emerged as a valuable treatment for postmenopausal osteoporosis. Bisphosphonate treatment is usually accompanied by a 3-6% gain in bone mineral density (BMD) during the first year of treatment and by a decrease in bone turnover. Despite low bone turnover, BMD continues to increase slowly beyond the first year of treatment. There is evidence that bisphosphonates not only increase bone volume but also enhance secondary mineralization. The present study was conducted to address this issue and to compare the effects of continuous and intermittent bisphosphonate therapy on static and dynamic parameters of bone structure, formation, and resorption and on mineral properties of bone. Sixty dogs were ovariohysterectomized (OHX) and 10 animals were sham-operated (Sham). Four months after surgery, OHX dogs were divided in six groups (n = 10 each). They received for 1 year ibandronate daily (5 out of 7 days) at a dose of 0, 0.8, 1.2, 4.1, and 14 microg/kg/day or intermittently (65 microg/kg/day, 2 weeks on, 11 weeks off). Sham dogs received vehicle daily. At month 4, there was a significant decrease in bone volume in OHX animals (p < 0.05). Doses of ibandronate >/= 4.1 microg/kg/day stopped or completely reversed bone loss. Bone turnover (activation frequency) was significantly depressed in OHX dogs given ibandronate at the dose of 14 microg/kg/day. This was accompanied by significantly higher crystal size, a higher mineral-to-matrix ratio, and a more uniformly mineralized bone matrix than in control dogs. This finding lends support to the hypothesis that an increase in secondary mineralization plays a role in gain in BMD associated with bisphosphonate treatment. Moreover, intermittent and continuous therapies had a similar effect on bone volume. However, intermittent therapy was more sparing on bone turnover and bone mineral properties. Intermittent therapy could therefore represent an attractive alternative approach to continuous therapy.

A third-generation bisphosphonate, YM175, inhibits osteoclast formation in murine cocultures by inhibiting proliferation of precursor cells via supporting cell-dependent mechanisms

The theory that bisphosphonates inhibit osteoclast formation through their effects on osteoblastic cells remains controversial. To confirm the inhibitory effect of bisphosphonates on osteoclast formation and gain some insights into the underlying mechanisms, we examined the effect of disodium dihydrogen (cycloheptylamino)-methylene-bisphosphonate monohydrate (YM175) on osteoclast-like multinucleated cell (OCL) formation in various mouse coculture systems. When different origins of osteoclast precursors (bone marrow, spleen, or nonspecific esterase-positive cells) were cocultured with the same supporting cells (calvarial osteoblasts), YM175 inhibited OCL formation similarly in all cultures. When the same osteoclast precursors (spleen cells) were cocultured with supporting cells of different origin, the results were variable. YM175 inhibited OCL formation almost completely in cocultures with calvarial osteoblasts or osteoblastic cell line KS4, while it did not, or only slightly, inhibit OCL formation in cocultures with stromal cell lines, ST2 or MC3T3-G2/PA6. Temporal addition of YM175 in cocultures of spleen cells with osteoblastic cells revealed that YM175 was effective when it was present at an early phase of the culture period. Consistent with this observation, YM175 in the presence of osteoblastic cells inhibited proliferation of preosteoclastic cells, but did not inhibit the fusion of mononuclear prefusion osteoclasts. In conclusion, the inhibitory effect of YM175 on OCL formation was confirmed in various murine coculture systems, but the effect was dependent on the types of bone-derived cells supporting osteoclastogenesis. The findings suggest that YM175 inhibits osteoclastogenesis by inhibiting the proliferation of osteoclast precursors through its action on supporting cells of osteoblast lineage rather than acting directly on osteoclast precursors.

Bisphosphonates act on osteoblastic cells and inhibit osteoclast formation in mouse marrow cultures

We examined the mode of action of bisphosphonates on osteoclastic cell recruitment using mouse marrow cultures with or without osteoblastic cells. Tartrate-resistant acid phosphatase-positive multinucleated cells [TRAP(+)MNC] formed in cultures were determined to be osteoclastic cells. In marrow cultures, TRAP(+) MNC formation in the presence of 10(-8) mol/L 1,25(OH)2D3 was not affected by the addition of 10(-6) mol/L dihydrogen (cycloheptylamino)-methylenebisphosphonate monohydrate (YM175). However, it was inhibited in cocultures of marrow cells with osteoblastic cells. The inhibitory effect was evident throughout the entire culture period. YM175 dose dependently inhibited TRAP(+) MNC formation, and other bisphosphonates--pamidronate and alendronate--also inhibited TRAP(+) MNC formation in the coculture. Similar observations were also made in the coculture of spleen cells with osteoblastic cells. The conditioned media of osteoblastic cells treated with 10(-6) mol/L YM175 inhibited TRAP(+) MNC formation in marrow cultures. The presence of YM175 in methylcellulose cultures affected neither the colony formation of monocyte-macrophage lineage, nor TRAP(+) MNC formation in the succeeding cocultures of recovered cells with osteoblastic cells. These results indicate that YM175 and probably other bisphosphonates as well preferentially inhibit the later stage of osteoclastogenesis through its action on osteoblastic cells. Our findings suggest that part of the inhibitory action by osteoblastic cells in the presence of bisphosphonates is mediated through soluble factor(s).