Alendronate modulates osteogenesis of human osteoblastic cells in vitro

Histological evaluation of pulp response to alendronate and Biodentine as pulp capping agents: an animal study

Objectives

This study aimed to comparatively assess the histological response of the pulp toward alendronate and Biodentine in a direct pulp capping procedure.

Materials and Methods

Twenty-four anterior teeth from 6 New Zealand rabbits were used in this study. Firstly, all rabbits were anesthetized according to their weight. Class V cavities were prepared on the buccal surfaces of anterior teeth. A pin-point exposure of the pulp was then made using a small, sterile round carbide bur and bleeding was arrested with a saline-soaked, sterile cotton pellet. The teeth under study were divided into 2 groups (n = 12). The intentionally exposed pulp was capped with alendronate (Group 1) and Biodentine (Group 2), correspondingly. After 30 days, all rabbits were euthanized; the teeth under study were extracted and taken up for histological analysis.

Results

Biodentine showed an intact, very dense dentin bridge formation with a uniform odontoblast (OD) layer pattern and mild or absent inflammatory response whereas specimens capped with alendronate demonstrated a dense dentin bridge formation with non-uniform OD layer pattern and mild to moderate inflammatory response.

Conclusions

Biodentine showed more biocompatibility than alendronate. However, alendronate can initiate reparative dentin formation and may be used as an alternative pulp capping agent.

Multiple Porous Synthetic Bone Graft Comprising EngineeredMicro-Channel for Drug Carrier and Bone Regeneration

Due to high demand but limited supply, there has been an increase in the need to replace autologous bone grafts with alternatives that fulfill osteogenic requirements. In this study, two different types of bone grafts were tested for their drug carrying abilities along with their osteogenic properties. Two different types of alendronate-loaded bone grafts, Bio-Oss (bovine bone graft) and InRoad (biphasic synthetic bone graft) were observed to see how different concentrations of alendronate would affect the sustained release to enhance osteogenesis. In this study, defected ovariectomize-induced osteoporotic rat calvarias were observed for 28 days with three different concentrations of alendronate (0 mg, 1 mg, 5 mg) for both Bio-Oss and InRoad. A higher concentration (5 mg) allowed for a more controlled and sustained release throughout the 28-day comparison to those of lower concentrations (0 mg, 1 mg). When comparing Bio-Oss and InRoad through histology and Micro-CT, InRoad showed higher enhancement in osteogenesis. Through this study, it was observed that alendronate not only brings out robust osteogenesis with InRoad bone grafts, but also enhances bone regeneration in an alendronate-concentration-dependent manner. The combination of higher concentration of alendronate and multiple porous bone graft containing internal micro-channel structure of InRoad resulted in higher osteogenesis with a sustained release of alendronate.

Histopathological Examination of the Effects of Local and Systemic Bisphosphonate Usage in Bone Graft Applications on Bone Healing

Background

The effect of bisphosphonates on the resorption process of normal bone tissue has been clearly mentioned in the literature, while their effect on the grafting material is a new research area. Limited former study is not sufficient to determine the strength, reliability and dosage of bisphosphonates. In this study, our aim is to examine the effects of local and systemic use of bisphosphonates in bone graft applications on bone healing, histopathologically.

Methods

Therefore, 32 Sprague-Dawley rats are separated into four groups. In the first group, only an empty bone defect is made on tibia and the tissue is sutured primarily without any other application. In the second group, bone defect is filled with allograft material and closed without any other application. In the third group (LA), alendronate solution is locally added to the graft material before its application to the site of bone defect. In the fourth group, alendronate is applied systemically after the site of bone defect is grafted and primarily closed. After 6 weeks, all rats are killed and the obtained samples are examined histopathologically.

Results

Local and systemic application of alendronate increases new bone formation in a statistically significant degree. In LA group, newly formed bone was observed more mature and well developed. Alendronate application does not cause an increase in inflammation, fibrosis and necrosis. There is no increased necrosis with alendronate application.

Conclusion

Local and systemic application of alendronate in bone grafting increases bone formation without any other complication. But we believe that further research should be made on dosage, usage and possible side effects.

Effects of Local Low-Dose Alendronate Injections Into the Distraction Gap on New Bone Formation and Distraction Rate on Distraction Osteogenesis

Bisphosphonates that constrain bone resorption have a direct effect on osteoclast function. In this experimental study, the effects of low-dose local alendronate injections on the distraction gap (DG) in rabbit mandible at 2 different rates were evaluated.The experimental study was conducted on 20 male, New Zealand white rabbits. The animals were divided into 3 experimental groups and 1 control group. Group 1 consisted of animals with distraction at the rate of 1 mm/day, receiving postoperative local low-dose alendronate local injections into the DG. Group 2 consisted of animals with distraction at the rate of 2 mm/day, receiving postoperative 0.75 μg/kg of alendronate local injections into the DG. Group 3 consisted of animals with distraction at the rate of 2 mm/day, receiving postoperative 0.2 mL local saline injections into the DG. Group 4 consisted of animals with distraction at the rate of 1 mm/day, receiving postoperative 0.2 mL local saline injections into the DG. All the injections were performed immediately postoperatively and for all groups at 1, 2, 3, and 4 weeks following surgery. The distraction zones were evaluated using dual-energy X-ray absorptiometry and histological analysis.Histologically, bone healing was found to be significantly accelerated in Groups 1 and 4 compared with Groups 2 and 3 (P < 0.05). Bone healing was superior in Group 1 and the difference was statistically significant compared with Group 4. There was a significant increase in mean bone mineral density in the 1 mm daily rate groups (Groups 1 and 4) compared with the 2 mm daily rate groups (Groups 2 and 3) (P < 0.05).Local low-dose alendronate injections could be an effective way for improving bone formation in distraction osteogenesis. Furthermore, the results of this study did not support the hypothesis that injections of local low-dose alendronate may allow 2 mm/day instead of 1 mm/day of elongation in the rabbit mandible.

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.

Alendronate Can Improve Bone Alterations in Experimental Diabetes by Preventing Antiosteogenic, Antichondrogenic, and Proadipocytic Effects of AGEs on Bone Marrow Progenitor Cells

Bisphosphonates such as alendronate are antiosteoporotic drugs that inhibit the activity of bone-resorbing osteoclasts and secondarily promote osteoblastic function. Diabetes increases bone-matrix-associated advanced glycation end products (AGEs) that impair bone marrow progenitor cell (BMPC) osteogenic potential and decrease bone quality. Here we investigated the in vitro effect of alendronate and/or AGEs on the osteoblastogenic, adipogenic, and chondrogenic potential of BMPC isolated from nondiabetic untreated rats. We also evaluated the in vivo effect of alendronate (administered orally to rats with insulin-deficient Diabetes) on long-bone microarchitecture and BMPC multilineage potential. In vitro, the osteogenesis (Runx2, alkaline phosphatase, type 1 collagen, and mineralization) and chondrogenesis (glycosaminoglycan production) of BMPC were both decreased by AGEs, while coincubation with alendronate prevented these effects. The adipogenesis of BMPC (PPARγ, intracellular triglycerides, and lipase) was increased by AGEs, and this was prevented by coincubation with alendronate. In vivo, experimental Diabetes (a) decreased femoral trabecular bone area, osteocyte density, and osteoclastic TRAP activity; (b) increased bone marrow adiposity; and (c) deregulated BMPC phenotypic potential (increasing adipogenesis and decreasing osteogenesis and chondrogenesis). Orally administered alendronate prevented all these Diabetes-induced effects on bone. Thus, alendronate could improve bone alterations in diabetic rats by preventing the antiosteogenic, antichondrogenic, and proadipocytic effects of AGEs on BMPC.

PLGA-linked alendronate enhances bone repair in diaphysis defect model

Alendronate (ALN) is known as an anti-resorptive drug for the treatment of osteoporosis. Recently, ALN was found to stimulate osteogenic differentiation in mesenchymal stem cells and enhance new bone formation in calvarial bone defects. Previous in vitro and in vivo studies found that the effective concentration of ALN was approximately 1-10   μm. In the present study, a poly (lactic-co-glycolic acid) (PLGA) cross-linked ALN (PLGA-ALN) with a short-term controlled-release property for local application to enhance bone repair was developed. An in vitro drug-release kinetic test showed that PLGA-ALN microspheres released an effective concentration (50-100 nm) of ALN for 9 days. The effect of PLGA-ALN on bone repair was tested in a rat femoral bone defect model. The biomechanical study results showed that the maximal strength, stiffness and energy absorption were significantly increased in the PLGA-ALN group compared with the PLGA group. The microstructure of the newly formed bone at the defect site was analysed using microcomputed tomography. The PLGA-ALN group significantly improved the trabecular bone volume at the defect site compared with the PLGA group. The fibril collagen and immunolocalized bone morphogenetic protein 2 were evident in the newly formed trabecular bone in the PLGA-ALN group. Local use of newly developed PLGA-ALN-enhanced bone repair was attributable to increasing bone matrix formation, which improved the ultrastructure of the newly formed bone and thus increased the biomechanical properties of the repaired bone. It is suggested that PLGA-ALN may be a potential bone graft substitute to enhance bone repair. Copyright © 2016 John Wiley & Sons, Ltd.

Zoledronic acid at subtoxic dose extends osteoblastic stage span of primary human osteoblasts

OBJECTIVE

This study aimed to check the effect of zoledronic acid (ZA) at subtoxic dose on human osteoblasts (HOs) in terms of cell viability, apoptosis occurrence, and differentiation induction. ZA belongs to the family of bisphosphonates (BPs), largely used in the clinical practice for the treatment of bone diseases, often associated with jaw osteonecrosis onset. Their pharmacological action consists in the direct block of the osteoclast-mediated bone resorption along with indirect action on osteoblasts.

MATERIALS AND METHODS

HOs were treated choosing the highest limit concentration (10(-5) M) which does not induce toxic effects. Live/dead staining, flow cytometry, mitochondrial membrane potential assay, osteocalcin western blotting, gp38 RT-PCR, collagen type I, PGE2, and IL-6 ELISA assays were performed.

RESULTS

Similar viability level between control and ZA-treated samples is found along with no significant increase of apoptotic and necrotic cells in ZA-treated sample. To establish if an early apoptotic pathway was triggered, Bax expression and mitochondrial membrane potential were evaluated finding a higher protein expression in control sample and a good integrity of mitochondrial membrane in both experimental points. Type I collagen secretion and alkaline phosphatase (ALP) activity appear increased in ZA-treated sample, osteocalcin expression level is reduced in ZA-treated cells, whereas no modifications of gp38 mRNA level are evidenced. No statistical differences are identified in PGE2 secretion level whereas IL-6 secretion is lower in ZA-treated HOs with respect to control ones.

CONCLUSIONS

These results highlight that ZA, delaying the osteoblastic differentiation process versus the osteocytic lineage, strengthens its pharmacological activity enhancing bone density.

CLINICAL RELEVANCE

The knowledge of ZA effects on osteoblasts at subtoxic dose allows to improve therapeutic protocols in order to strengthen drug pharmacological activity through a combined action on both osteoclastic and osteoblastic cells.

Advanced glycation end products play adverse proinflammatory activities in osteoporosis

Osteoporosis is a major public health burden that is expected to further increase as the global population ages. In the last twenty years, advanced glycation end products (AGEs) have been shown to be critical mediators both in the pathogenesis and development of osteoporosis and other chronic degenerative diseases related to aging. The accumulation of AGEs within the bone induces the formation of covalent cross-links with collagen and other bone proteins which affects the mechanical properties of tissue and disturbs bone remodelling and deterioration, underlying osteoporosis. On the other hand, the gradual deterioration of the immune system during aging (defined as immunosenescence) is also characterized by the generation of a high level of oxidants and AGEs. The synthesis and accumulation of AGEs (both localized within the bone or in the systemic circulation) might trigger a vicious circle (in which inflammation and aging merged in the word "Inflammaging") which can establish and sustain the development of osteoporosis. This narrative review will update the molecular mechanisms/pathways by which AGEs induce the functional and structural bone impairment typical of osteoporosis.

Fourier transform infrared imaging as a tool to chemically and spatially characterize matrix-mineral deposition in osteoblasts

Mineralizing osteoblasts are regularly used to study osteogenesis and model in vivo bone formation. Thus, it is important to verify that the mineral and matrix being formed in situ are comparable to those found in vivo. However, it has been shown that histochemical techniques alone are not sufficient for identifying calcium phosphate-containing mineral. The goal of the present study was to demonstrate the use of Fourier transform infrared imaging (FTIRI) as a tool for characterizing the spatial distribution and colocalization of the collagen matrix and the mineral phase during the mineralization process of osteoblasts in situ. MC3T3-E1 mouse osteoblasts were mineralized in culture for 28 days and FTIRI was used to evaluate the collagen content, collagen cross-linking, mineralization level and speciation, and mineral crystallinity in a spatially resolved fashion as a function of time. To test whether FTIRI could detect subtle changes in the mineralization process, cells were treated with risedronate (RIS). Results showed that collagen deposition and mineralization progressed over time and that the apatite mineral was associated with a collagenous matrix rather than ectopic mineral. The process was temporarily slowed by RIS, where the inhibition of osteoblast function caused slowed collagen production and cross-linking, leading to decreased mineralization. This study demonstrates that FTIRI is a complementary tool to histochemistry for spatially correlating the collagen matrix distribution and the nature of the resultant mineral during the process of osteoblast mineralization. It can further be used to detect small perturbations in the osteoid and mineral deposition process.

Thermodynamic dissociation constants of risedronate using spectrophotometric and potentiometric pH-titration

Risedronate inhibits bone resorption in diseases like osteoporosis, Paget’s disease, tumor bone diseases or the malfunction of phosphocalcium metabolism. The acid-base properties of risedronate in an aqueous solution have been studied in a pH range from 2 to 12 and can be described in terms of four dissociation steps: pK a,2, pK a,4, pK a,5 (related to the dissociation of POH groups) and pK a,3 related to the dissociation of protonated amino group NH3+. The mixed dissociation constants were determined at different ionic strengths I = 0.02 to 0.20 mol dm−3 KCl and of 25°C and 37°C using pH-spectrophotometric and pH-potentiometric titration methods. Determination of group parameters L 0, H T might lead to false estimates of common parameters p K a;therefore, the computational strategy employed is important. A comparison between the two programs ESAB and HYPERQUAD demonstrated that the ESAB program provides a better fit of potentiometric titration curve. The thermodynamic dissociation constants pK aT were estimated by a nonlinear regression of (pK a, I) data and a Debye-Hückel equation at 25°C and 37°C, pK a,2T = 2.37(1) and 2.44(1), pK a,3T = 6.29(3) and 6.26(1), pK a,4T = 7.48(1) and 7.46(2) and pK a,5T = 9.31(7) and 8.70(3) at 25°C and 37°C using pH-spectroscopic data and pK a,2T = 2.48(3) and 2.43(1), pK a,3T= 6.12(2) and 6.10(2), pK a,4T = 7.25(2) and 7.23(1) and pK a,5T = 12.04(5) and 11.81(2) at 25°C and 37°C. The ascertained estimates of three dissociation constants pK a,3, pK a,4, pK a,5 are in agreement with the predicted values obtained using PALLAS

Bisphosphonates: effects on osteoblast

PURPOSE

Bisphosphonates are synthetic analogues of pyrophosphate usually used in treating bone disorders such as osteoporosis, Paget's disease, fibrous dysplasia, hypercalcemia of malignancy, and inflammation-related bone loss. Though therapeutic effects of bisphosphonates depend primarily on their inhibitory effect on osteoclasts, increasing attention is being given to other effector cells, such as osteoblasts. This review focuses on the presumed effect of bisphosphonates on osteoblasts.

METHODS

A review of the literature was conducted to evaluate the pharmacodynamic effects of bisphosphonates including inhibition of osteoclasts and apoptosis of osteocytes and osteoblasts as well as their potential stimulatory effects on the proliferation of osteoblasts.

RESULTS

Studies have demonstrated that bisphosphonates may stimulate proliferation of osteoblasts and inhibit apoptosis of osteocytes and osteoblasts.

CONCLUSION

Considering that osteoblasts may be involved in bone disorders, such as osteoporosis, osteopetrosis, osteogenesis imperfecta, and Paget's disease, and that bisphosphonates may stimulate proliferation of osteoblasts and inhibit apoptosis of osteocytes and osteoblasts, it is conceivable that a role for bisphosphonates exists in these diseases beyond merely the osteoclast influence.

Comparison of local and systemic alendronate on distraction osteogenesis

This study compared the effect of systemic and local administration of alendronate on distraction osteogenesis in rabbit mandibles. Thirty New Zealand white rabbits were allocated to 3 groups: 10 rabbits for systemic alendronate; 9 for local alendronate; and 11 as controls. After a 5 day latency period, distraction was performed at a rate of 0.8mm/day for 9 days via a custom-made distractor. Animals were killed at the end of the consolidation period of 28 days. The distracted mandibles were harvested and evaluated by plain radiography, computed tomography (CT), dual energy X-ray absorptiometry (DEXA), and histomorphometry. Histologically, comparing the systemic and local alendronate groups, there were no statistically significant differences in the bone healing parameters, but each group showed a statistically superior effect over the control group (p<0.05). Quantitative CT evaluation showed a significant difference mean in the density of the regeneration between experimental and control groups. There was a significant increase in mean bone mineral density in the experimental groups compared with the control group. Histologic, CT, and DEXA analysis demonstrated that using systemic and local alendronate may be effective in accelerating new bone formation in the distraction gap in rabbit mandibles.

Novel actions of bisphosphonates in bone: preservation of osteoblast and osteocyte viability

Bisphosphonates stop bone loss by inhibiting the activity of bone-resorbing osteoclasts. However, the effect of bisphosphonates on bone mass cannot completely explain the reduction in fracture incidence observed in patients treated with these agents. Recent research efforts provided an explanation to this dichotomy by demonstrating that part of the beneficial effect of bisphosphonates on the skeleton is due to prevention of osteoblast and osteocyte apoptosis. Work of our group, independently confirmed by other investigators, demonstrated that bisphosphonates are able to prevent osteoblast and osteocyte apoptosis in vitro and in vivo. This prosurvival effect is strictly dependent on the expression of connexin (Cx) 43, as demonstrated in vitro using cells lacking Cx43 or expressing dominant-negative mutants of the protein as well as in vivo using Cx43 osteoblast/osteocyte-specific conditional knock-out mice. Remarkably, this Cx43-dependent survival effect of bisphosphonates is independent of gap junctions and results from opening of Cx43 hemichannels. Hemichannel opening leads to activation of the kinases Src and extracellular signal-regulated kinases (ERKs), followed by phosphorylation of the ERK cytoplasmic target p90(RSK) kinase and its substrates BAD and C/EBPβ, resulting in inhibition of apoptosis. The antiapoptotic effect of bisphosphonates is separate from the effect of the drugs on osteoclasts, as analogs that lack antiresorptive activity are still able to inhibit osteoblast and osteocyte apoptosis in vitro. Furthermore, a bisphosphonate analog that does not inhibit osteoclast activity prevented osteoblast and osteocyte apoptosis and the loss of bone mass and strength induced by glucocorticoids in mice. Preservation of the bone-forming function of mature osteoblasts and maintenance of the osteocytic network, in combination with lack anticatabolic actions, open new therapeutic possibilities for bisphosphonates in the treatment of osteopenic conditions in which decreased bone resorption is not desired.

Opposing effects of bisphosphonates and advanced glycation end-products on osteoblastic cells

Patients with long-standing Diabetes mellitus can develop osteopenia and osteoporosis. We have previously shown that advanced glycation endproducts reduce the bone-forming activity of osteoblasts. Bisphosphonates are used for the treatment of various bone disorders, since they reduce osteoclastic function and survival, and stimulate osteoblastic bone-forming capacity. In this work we have investigated whether bisphosphonates are able to revert advanced glycation endproducts-induced deleterious effects in osteoblasts. MC3T3E1 and UMR106 osteoblastic cells were incubated with control or advanced glycation endproducts-modified bovine serum albumin, in the presence or absence of different doses of the bisphosphonates Alendronate, Pamidronate or Zoledronate. After 24-72 h of culture, we evaluated their effects on cell proliferation and apoptosis, type-1 collagen production, alkaline and neutral phosphatase activity, and intracellular reactive oxygen species production. Advanced glycation endproducts significantly decreased osteoblast proliferation, alkaline phosphatase activity and type 1 collagen production, while increasing osteoblastic apoptosis and reactive oxygen species production. These effects were completely reverted by low doses (10(-8) M) of bisphosphonates. High doses of bisphosphonates (10(-4)-10(-5) M) were toxic for osteoblasts. Nifedipine (L-type calcium channel blocker) did not affect the advanced glycation endproducts-induced decrease in osteoblastic proliferation, although it blocked the reversion of this effect by 10(-8) M Alendronate. Both advanced glycation endproducts and Alendronate inhibited the activity of intracellular neutral phosphatases. In conclusion, we show that bisphosphonates revert the deleterious actions of advanced glycation endproducts on osteoblastic cells, and that these effects of bisphosphonates depend on: (a) Ca(2+) influx through L-type voltage-sensitive channels, and (b) blockage of advanced glycation endproducts-induced reactive oxygen species generation.

Use of bisphosphonates to improve the durability of total joint replacements

Total joint arthroplasty is very effective for improving the quality of life of patients with end-stage arthritis. Despite advances in materials, surgical technique, and rehabilitation regimens, joint replacements are still fraught with complications leading to their premature failure. Aseptic loosening and osteolysis are the primary causes of implant failure. Other reasons include early migration of components leading to instability, lack of ingrowth into implant porosities, and bone loss caused by stress shielding. Pharmaceutical agents used for preventing and managing postmenopausal osteoporosis (eg, bisphosphonates) may in the future play an important role in improving the long-term duration of joint arthroplasties. Early findings indicate that bisphosphonates upregulate bone morphogenetic protein-2 production and stimulate new bone formation. Because of their anabolic effect on osteoblasts, bisphosphonates have the potential to enhance bone ingrowth into implant porosities, prevent bone resorption under adverse conditions, and dramatically extend the long-term durability of joint arthroplasties. The long-term effects of bisphosphonate use on the mechanical properties of bone have not been adequately investigated. Along with improvements in implant design and material properties, bisphosphonates and other pharmaceutical agents may, in the near future, be part of the growing armamentarium that provides more durable joint arthroplasties.

Histological comparison of alendronate, calcium hydroxide and formocresol in amputated rat molar

The purpose of this study was to evaluate the potential of alendronate sodium (ALN), a biphosohonate to stimulate hard tissue formation in pulpotomized (amputated) rat molars. Two commonly used pulpotomy materials, calcium hydroxide (CH) and formocresol (FC) were utilized for comparisons. Histological evaluations were performed by observers blinded to treatment allocation on days 7, 15, 30 and 60, followed by statistical analysis of selected histological criteria. In all evaluation periods, hard tissue deposition was evident along the radicular dentin in ALN and CH groups. In days 30 and 60, the latter two groups showed no differences in inflammatory cell response and hard tissue deposition scores (P > 0.05). ALN appears to be capable of maintaining pulpal vitality, while promoting hard tissue formation, similar to CH.

Neridronate and human osteoblasts in normal, osteoporotic and osteoarthritic subjects

The objective of this study was to evaluate the metabolic in vitro effect of the bisphosphonate neridronate on normal and pathological human osteoblasts. Primary human osteoblast cultures were obtained from cancellous bone of osteoarthritic (OA) and osteoporotic (OP) patients and a corresponding healthy control group. Osteocalcin production was evaluated by cultured cells in neridronate 10(-4) M and 10(-6) M, both under basal conditions and after vitamin D3 stimulation. In the absence of neridronate, vitamin D3 increased osteocalcin production in all cell cultures; under the same conditions, and in the absence of vitamin D3, OA osteoblasts showed a significantly higher osteocalcin production whereas OP osteoblasts showed a significantly lower osteocalcin production compared to the normal osteoblasts, respectively. In all cellular populations neridronate at a higher concentration (10(-4) M) induced a reduction in osteocalcin synthesis, but in normal and osteoarthritic osteoblasts did not reduce the stimulatory effect of vitamin D3, whereas it inhibited the vitamin D3-induced increase of osteocalcin synthesis in the osteoporotic cells. In normal and osteoporotic osteoblasts stimulation with the lower neridronate concentration (10(-6) M) significantly increased osteocalcin production, which was further enhanced by vitamin D3 as an additional effect of the combined treatment. In OA osteoblasts, neridronate 10(-6) M did not induce an increase in osteocalcin synthesis and the additional effect of combined treatment with vitamin D3 was not observed. Neridronate can modify the metabolic activity of human osteoblasts by enhancing or decreasing their biosynthetic activity, both in normal and in pathological conditions, depending on compound concentration and on different cell types. These results confirm the validity of using neridronate at doses usually administered in treating osteoporosis, and they suggest using it to treat other diseases which show an altered osteoblast metabolism, such as osteoarthritis.

The bisphosphonate pamidronate on the surface of titanium stimulates bone formation around tibial implants in rats

Many materials with differing surfaces have been developed for clinical implant therapy in dentistry and orthopedics. We analyzed the quantity of new bone formed in vivo around calcium-immobilized titanium implants with surfaces modified using pamidronate (PAM), a nitrogen-containing bisphosphonate (N-BP), implants of pure titanium, and titanium implants immobilized with calcium ions. New bone formation was visualized using fluorescent labeling (calcein blue and alizarin complexone) with intravenous injection at 1 and 3 weeks after implantation. After 4 weeks, undecalcified sections were prepared, and new bone formation around the implants was examined by morphometry using confocal laser scanning microscopy images. After 1 week, more new bone formed around the PAM-immobilized implant than around the calcium-immobilized and pure titanium implants. This was also seen with the new bone formation after 3 weeks. After 4 weeks, significantly more new bones were formed around the BP-immobilized implant than around the calcium ion-implanted and pure titanium implants. The new N-BP-modified titanium surface stimulates new bone formation around the implant, which might contribute to the success of implant therapy.

Optimizing Administration of Bisphosphonates in Women with Postmenopausal Osteoporosis

Bisphosphonates have been approved in the US as oral medication for the treatment of osteoporosis for about 10 years. Efficacy data exists for fracture reduction for the commonly used oral bisphosphonates but not for intravenous formulations. Based on the mechanism of action that appears to allow for longer intervals between doses, it has been possible to extend the treatment choices from the original more demanding daily oral dose to an array of options including oral weekly and more recently monthly treatment (so-called cyclical therapy) and intravenous treatment with various administration regimens. The possibility of treatment with an annual (or less frequent) intravenous administration with zoledronic acid exists. Compliance, adverse effects, and efficacy vary with each administration regimen.

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.

Long-term effects of neridronate on human osteoblastic cell cultures

Bisphosphonates (BPs) are widely used in the treatment of a variety of bone-related diseases, particularly where the bone turnover is skewed in favor of osteolysis. The mechanisms by which BPs reduce bone resorption directly acting on osteoclasts are now largely clarified even at molecular level. Researches concerning the BP's effects on osteoblast have instead shown variable results. Many in vitro studies have reported positive effects on osteoblasts proliferation and mineralization for several BPs; however, the observed effects differ, depending on the variety of different model system that has been used.

OBJECTIVES

We have investigated if neridronate, an aminobisphosphonate suitable for pulsatory parenteral administration, could have an effect on human osteoblastic proliferation and differentiation in vitro.

METHODS

We have investigated whether prolonged addition of neridronate (from 10(-3) to 10(-11) M) to different human osteoblasts cultures, obtained from 14 different bone specimens, could affect the cells number, the endogenous cellular alkaline phosphatase (ALKP) activity, and the formation of mineralized nodules.

RESULTS

Our results show that neridronate does not negatively affect in vitro the viability, proliferation, and cellular activity of normal human osteoblasts even after a long period addition of the drug (20 days) at concentrations equal or lower than 10(-5) mol/l (therapeutic dose). In addition, neridronate seems to enhance the differentiation of cultured osteoblasts in mature bone-forming cells. A maximum increase of alkaline phosphatase activity (+50% after 10 days; P < 0.01) and mineralized nodules (+48% after 20 days; P < 0.05) was observed in cultures treated with neridronate 10(-8) M.

CONCLUSIONS

These results encourage the use of neridronate in long-term therapy of demineralizing metabolic bone disorders.

The effect of alendronate sodium on spinal fusion: a rabbit model

BACKGROUND CONTEXT

Bisphosphonates affect bone remodeling and increase bone mass through the inhibition of osteoclasts. Their effect on osteoblasts, and the balance between osteoblastic and osteoclastic activity on bone turnover and healing, is not completely understood. Specifically, the effect of bisphosphonates on spinal fusion has yet to be determined. With the increasing use of bisphosphonates in the elderly population, this effect needs to be delineated.

PURPOSE

To evaluate the effect of alendronate sodium after an intertransverse process spinal fusion in a rabbit model.

STUDY DESIGN/SETTING

Randomized double-blinded in vivo study of the effect of alendronate sodium in a spinal fusion model.

METHODS

Fifty New Zealand white rabbits underwent a posterolateral L5-L6 intertransverse process arthrodesis with autogenous iliac crest bone graft. The rabbits were then randomly divided into two groups. Group I received 3 cc of saline placebo per oral gavage, and Group II received 200 micrograms (approximately 0.05 mg/kg/day) of alendronate sodium dissolved in 3 cc of saline per day for 8 weeks. Upon completion, the rabbits were sacrificed and the lumbar spines harvested, radiographed and graded for motion across the fusion site with manual palpation. Two independent pathologists then prepared and sectioned each left and right fusion mass. Three random x10 fields were examined and graded for both the cephalad and caudad ends of each section (516 fields). Fusion quality was graded using an established histological scoring scale (score 0 to 7 based on fibrous and bone content of the fusion mass).

RESULTS

Two rabbits died on the day of operation, and 48 rabbits survived the operation. Five additional rabbits died within the first 2 postoperative weeks. Thus, 43 rabbits (21 in Group I, 22 in Group II) completed the 8-week course of treatment. Grading each side separately, 26 of 42 fusion masses (62%) in Group I and 24 of 44 fusion masses (55%) in Group II had radiographic evidence of fusion (p=.76). With gross palpation, 11 of 21 motion segments (52%) in Group I versus 13 of 22 motion segments (59%) in Group II were determined to have a solid fusion (p=.76). Histologically, Group I had a higher median score (6.0; range, 0 to 7 vs. 1.0; range, 0 to 7; p<.0001) and a higher fusion rate (76% vs. 45%; p=.004) than Group II.

CONCLUSIONS

Alendronate sodium appears to inhibit or delay bone fusion in a rabbit model. Presumably, this occurs as a result of uncoupling the balanced osteoclastic and osteoblastic activity inherent to bone healing. These findings suggest that a discontinuance of alendronate sodium postoperatively during the acute fusion period may be warranted.

The nitrogen-containing bisphosphonate, zoledronic acid, increases mineralisation of human bone-derived cells in vitro

Previous studies have attributed the increase in bone mass observed following bisphophonate (BP) therapy to their effects on bone-resorbing osteoclasts (OCs). However, recent evidence suggests that BPs can also act directly on bone forming osteoblasts (OBs) to increase their anabolic activity. Using an established model of in vitro OB differentiation, we found that the potent nitrogen-containing BP, zoledronic acid (ZOL), may enhance the bone forming potential of human adult OB-like cells in vitro by inducing their differentiation. ZOL dose dependently induced both cytostasis and cell death in OB-like cells at concentrations of 0.5 microM or greater. Cells expressing high levels of the osteoprogenitor antigen, STRO-1, exhibited a greater proliferative potential than STRO-1negative/dim cells, and were more susceptible to the cytostatic and apoptotic effects of ZOL. ZOL was also found to promote bone cell differentiation, as evidenced by an increase in the number of cells exhibiting a more differentiated (STRO-1(-)/AP+ and STRO-1(-)/AP-) phenotype. Analysis of gene expression, using semi-quantitative RT-PCR, demonstrated that ZOL treatment resulted in a significant upregulation of osteocalcin (OCN) and bone morphogenetic protein-2 (BMP-2) gene expression. Furthermore, in vitro mineralisation studies revealed that ZOL enhanced mineralised matrix formation at concentrations between 5 and 25 microM. These results show that, in addition to its direct effects on OCs, ZOL also directly affects the proliferation and differentiation of human OB-like cells in vitro and may enhance bone formation in vivo.

Clodronate stimulates osteoblast differentiation in ST2 and MC3T3-E1 cells and rat organ cultures

We investigated the direct effects of various bisphosphonates on osteoblasts. At 10(-5) M, clodronate increased alkaline phosphatase activity in cultured MC3T3-E1 (osteoblast-like line) and ST2 (pluripotent mesenchymal line) cells. Etidronate significantly increased alkaline phosphatase activity at 10(-5) M only in MC3T3-E1 cells. These effects were due to an increase in alkaline phosphatase-positive cell numbers, and the differentiation-enhanced cells were capable of mineralization (von Kossa stain). Other bisphosphonates (pamidronate, alendronate, and incadronate) did not increase alkaline phosphatase activity in either cell line. In cultured rat calvariae, clodronate stimulated the expression of genes for alkaline phosphatase and osteocalcin (osteoblast-differentiation markers), but decreased the expression of the gene for tartrate-resistant acid phosphatase (osteoclast marker). Clodronate, etidronate, and incadronate inhibited protein Tyr phosphatase and Ser/Thr phosphatase activities in MC3T3-E1 cells. These data suggest that clodronate acts directly on mesenchymal cells to enhance osteoblast differentiation, and this effect may be partly expressed through inhibition of protein Tyr phosphatase and/or Ser/Thr phosphatase activity.

Alendronate interacts with the inhibitory effect of 1,25(OH)2D3 on parathyroid hormone-related protein expression in human osteoblastic cells

The bisphosphonate alendronate is a potent inhibitor of bone resorption by its direct action on osteoclasts. In addition, there is some data suggesting that alendronate could also inhibit bone resorption indirectly by interacting with osteoblasts. Parathyroid hormone-related protein (PTHrP) produced by osteoblasts and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] are regulators of bone remodeling, which have interrelated actions in these cells. In this study, we assessed whether alendronate can affect PTHrP expression in the presence or absence of 1,25(OH)2D3 in human primary osteoblastic (hOB) cells from trabecular bone. Cell total RNA was isolated, and semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) was carried out using human PTHrP-specific primers. PTHrP in the hOB cell-conditioned medium was analyzed by a specific immunoradiometric assay. We found that PTHrP mRNA and secreted PTHrP were maximally inhibited by 10(-8) - 10(-6) M of 1,25(OH)2D3 treatment within 8-72 h in hOB cells. Alendronate (10(-14) - 10(-8) M) modified neither PTHrP mRNA nor PTHrP secretion, although it consistently abrogated the decrease in PTHrP production induced by 1,25(OH)2D3 in these cells. On the other hand, alendronate within the same dose range did not affect either the vitamin D receptor (VDR) mRNA or osteocalcin secretion, with or without 1,25(OH)2D3, in hOB cells. The inhibitory effect of alendronate on the 1,25(OH)2D3-induced decrease in PTHrP in these cells was mimicked by the calcium ionophore A23187 (5 x 10-6 M), while it was eliminated by 5 x 10(-5) M of nifedipine. Furthermore, although alendronate alone failed to affect [Ca2+]i in these cells, it stimulated [Ca2+]i after pretreatment of hOB cells with 10(-8) M of 1,25(OH)2D3, an effect that was abolished by 5 x 10(-5) M of nifedipine. These results show that alendronate disrupts the modulatory effect of 1,25(OH)2D3 on PTHrP production in hOB cells. Our findings indicate that an increase in calcium influx appears to be involved in the mechanism mediating this effect of alendronate.

[Pharmacological and clinical properties of alendronate sodium hydrate]

Alendronate (alendronate sodium hydrate; Bonalon Tablet, 5 mg) is a nitrogen-containing bisphosphonate, which combines with the bone surface and reduces osteoclast-mediated bone resorption. It is a third-generation bisphosphonate compound, specifically distributed on the surface of bone resorption and taken into osteoclasts. Under the closed circumstances which is formed with osteoclast and the bone surface, alendronate becomes detached from the bone surface and taken into osteoclast since acid released from osteoclast leads to pH decrease (acidified). The uptaken alendronate blocks the pathway of mevalonic acid synthesis, which is cholesteric synthesis, inhibits the prenylation of GTP binding protein, and decreases the osteoclast's function by influencing the cytoskeleton. This restraint of alendronate in bone resorption against osteoclasts is reversible, showing no cytotoxicity at more than hundredfold concentration level at which action occurs. Alendronate is an agent for the treatment of osteoporosis that has established safety with regards to bone quality since it neither inhibits bone calcification nor influences fracture healing in chronic administration. The most serious morbidity in osteoporosis is developing fractures. The efficacy of alendronate on restraining fracture, as well as on increase in BMD, is evidenced in Japan. Recently, in addition to senile or postmenopausal osteoporosis, drug-induced osteoporosis, such as steroid-induced osteoporosis, has attracted attention. In this regard, alendronate has been found to be an effective agent for the treatment of osteoporosis overseas, being approved in over 90 countries and used by more than 4.5 million patients. This review will give an outline of alendronate, the preparation to have introduced a concept of Evidence Based Medicine earlier, from pharmacodynamic action to clinical efficacy.

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.

Alendronate does not inhibit early bone apposition to hydroxyapatite-coated total joint implants: a preliminary study

BACKGROUND

Alendronate is a pyrophosphate analogue of bisphosphonate that has been shown to inhibit osteoclastic bone resorption. Bone formation and remodeling are necessary to establish initial fixation of uncemented implants, especially those coated with a bioactive surface such as hydroxyapatite. Because the process of bone-remodeling that culminates in new-bone formation is thought to be initiated by osteoclastic bone resorption, it is appropriate to test the influence of osteoclast-inhibiting medications on bone apposition to hydroxyapatite-coated implants.

METHODS

Twelve dogs underwent staged bilateral total hip arthroplasty, with twenty weeks between the first and second operations, with use of a titanium-alloy femoral stem that had a proximal macrotextured surface and a plasma-sprayed hydroxyapatite coating. Six of the dogs received oral alendronate therapy from the time of the surgery until they were killed; the other six dogs were untreated controls. The animals were killed four weeks after the second operation. Sections from matched implant sites (proximal, middle, and distal) were histologically analyzed. The linear extent of bone apposition, the linear extent and the thickness of the hydroxyapatite coating, and the total amount of cortical and trabecular bone were measured with the use of an interactive image analysis system.

RESULTS

There were no significant differences in radiographic or histologic findings between the two groups at either four or twenty-four weeks. Although the extent of the hydroxyapatite coating decreased significantly with time in both groups (p < 0.01), we identified no significant influence of alendronate on the extent of bone apposition, the extent or thickness of the hydroxyapatite coating, or the cortical or trabecular bone area around the implants.

CONCLUSIONS

Many patients who are receiving alendronate for osteoporosis or other disorders may also be candidates for cementless total joint arthroplasty. Although bone formation is generally thought to be initiated by and coupled with bone resorption, our results suggest that alendronate has no discernible effect on the initial fixation of or the short-term bone-remodeling around hydroxyapatite-coated femoral total joint implants.

Incadronate and etidronate accelerate phosphate-primed mineralization of MC4 cells via ERK1/2-Cbfa1 signaling pathway in a Ras-independent manner: further involvement of mevalonate-pathway blockade for incadronate

Two types of bisphosphonates (BPs), incadronate (INC) and etidronate (ETI) accelerated phosphate (Pi)-primed mineralization of MC4 cells in a subnanomolar dose range. Intracellular signaling pathways involved were examined. 1) The effect of INC but not ETI was partially suppressed by two mevalonate (MVA) pathway metabolites, farnesylpyrophosphate (FPP) and geranylgeranylpyrophosphate (GGPP). 2) The BP-like accelerating effect was produced by statins and also by Toxin B, a Rho GTPases-specific inhibitor. 3) INC induced Cbfa1-nuclear localization within hours; and in an in vivo experiment using ovariectomized mice, its 3 weeks dosing exhibited the same effect in tibial extracts. 4) BPs promoted luciferase expression in murine p1.3-osteocalcin gene 2-luc and p6-osteoblast specific element 2-luc transfected cells, just as MVA, FPP and GGPP did independently and additively to INC. 5) BPs activated extracellular signal-regulated kinase (ERK1/2) in a Ras-independent manner within 5 min, and Pi was found to sensitize MC4 cells to BPs. MVA and its metabolites also activated ERKs but in a Ras-dependent manner and additively to INC. Ras dependency was determined using N17Ras-transfected cells. A MEK (MAP kinase-ERK kinase)-specific inhibitor PD98059 alone partly and with FPP completely blocked INC-induced mineralization. The results suggest that BPs act on Pi-sensitized MC4 cells to accelerate mineralization via nonRas-MEK-ERK1/2-Cbfa1 transactivation pathway and INC additionally acts by inhibiting the MVA pathway.

Alendronate administration and skeletal response during chronic alcohol intake in the adolescent male rat

Alendronate is an aminobisphosphonate that inhibits bone resorption in osteoporotic humans and rats but does not induce osteomalacia. Several bisphosphonates, including alendronate, also have direct positive actions on osteoblasts, bone formation, and mineralization. We studied the effects of alendronate on skeletal development in adolescent male rats during chronic alcohol intake. Four groups of age- and weight-matched male Sprague-Dawley rats (35 days of age) were fed the Lieber-DeCarli diet containing 36% of calories as EtOH (E), the EtOH diet plus 60 mg/kg alendronate (EA) every other day intraperitoneally (ip), an isocaloric diet (I), or the isocaloric diet plus 60 mg/kg alendronate (IA) every other day ip. Body weight, femur length, serum levels of osteocalcin (OC), insulin-like growth factor 1 (IGF-1), testosterone, and luteinizing hormone (LH); femur distal metaphyseal and middiaphyseal bone mineral density (BMD) and tibial metaphyseal gene expression for alpha-1-type I collagen (Col I), OC, and bone alkaline phosphatase (AP); and femur strength by four-point bending to failure were measured after 28 days of feeding and alendronate injections. Serum alcohol levels at death were 156 +/- 13 mg/dl (E) and 203 +/- 40 mg/dl (EA). Alendronate given to alcohol-fed rats increased metaphyseal BMD by more than 3-fold over rats fed alcohol alone. Alendronate given to isocaloric pair-fed rats increased metaphyseal BMD by more than 2.5-fold over rats fed the isocaloric diet alone. Cortical BMD was reduced by alcohol but was increased by alendronate. Alcohol consumption reduced serum IGF-1 levels, and alendronate increased IGF-1 levels in alcohol-fed rats. Serum OC, testosterone, and LH were unaffected by alcohol and alendronate. Quantitative dot blot hybridization using rat complementary DNA (cDNA) probes and normalization against 18S subunit ribosomal RNA (rRNA) levels revealed no changes in tibial metaphyseal gene expression for type I collagen, osteocalcin, or alkaline phosphatase. Alcohol significantly reduced the biomechanical properties of the femurs that were partially compensated by alendronate. Chronic alcohol consumption uncouples formation from ongoing resorption, and resorption is inhibited by alendronate. However, alendronate's positive effects on osteoblast-mediated mineralization during chronic alcohol consumption point to the potential use of bisphosphonates in the treatment of decreased bone formation secondary to alcohol-induced diminished osteoblast function.

Qualitative analysis of peripheral peri-implant bone and influence of alendronate sodium on early bone regeneration

BACKGROUND

Alendronate sodium increases alveolar bone density with systemic use. It inhibits osteoclast activity and is thought to result in a net increase in osteoblastic activity. However, little is known about local in vivo use. The purpose of this study was to evaluate the effect of local delivery of alendronate on bone regeneration within peri-implant defects. Peri-implant bone was examined histomorphometrically to evaluate the amount of supporting bone peripheral to the bone-implant interface.

METHODS

Six adult hound dogs were evenly divided into 2 groups, with one group receiving alendronate-coated dental implants and the other group serving as controls. Dental implants were placed immediately after extraction of right and left second, third, and fourth mandibular premolars. Forty-eight dental implants were placed (2 types in each dog: 24 hydroxyapatite [HA]-coated and 24 titanium machine-polished [TMP]), for a total of 4 variables. A bioabsorbable collagen membrane was secured over the implants and defects, and the flaps closed primarily. The dogs were sacrificed on day 28. Specimens were sectioned, mounted, and stained with Stevenel's blue and van Gieson's picric fuchsin. The amount of bone adjacent and 1 mm peripheral to the implant surface was recorded with a computerized microscopic digitizer.

RESULTS

Locally applied alendronate resulted in significantly increased amounts of bone (P<0.0002, ANOVA) in the peripheral area with both HA and TMP implants. However, the most influential factor in the amount of peripheral bone was the type of implant surface (P<0.0001).

CONCLUSIONS

Local application of alendronate is useful in increasing the amount of peripheral peri-implant bone. Also, the amount of supporting bone was not related to the bone-to-implant contact but to the surface characteristics of the implant. The findings of the present study indicate that the evaluation of dental implant-supporting bone should include peripheral bone as well as bone-to-implant interface.

Use of alendronate in peri-implant defect regeneration

BACKGROUND

Previous studies have demonstrated an increase in bone mass and density with use of systemic alendronate sodium. This agent acts as an inhibitor of osteoclast activity, and is thought to result in more net osteoblastic activity. The objective of this study was to determine the effects of locally applied alendronate sodium on guided bone regeneration around dental implants.

METHODS

Six adult mongrel dogs were divided into 2 groups: one group received alendronate-coated dental implants, and the other group served as control. Two types of dental implants were used in each dog: hydroxyapatite (HA)-coated and titanium machine-polished (TMP), for a total of 4 groups. Dental implants were placed immediately after extraction of the right and left second, third, and fourth mandibular premolars; a resorbable collagen membrane was secured over the implants and defects; and the flaps were closed primarily. Fluorescent labels were administered intravenously on days 0, 6, 12, and 22 to measure bone formation rate. Dogs were sacrificed on day 28. The specimens were sectioned and mounted, and bone formation rate was recorded with a computerized microscopic digitizer. Specimens were stained with Stevenel's blue and van Gieson's picric fuchsin. Bone-to-implant contact was recorded with a computerized microscopic digitizer.

RESULTS

The results indicated a significant effect of locally applied alendronate (P < 0.0001) with both types of implants (HA and TMP), as well as the HA coating (P< 0.02) on increased bone formation rate. Additionally, alendronate had a significant effect on bone-to-implant contact, with an increase in the TMP model (P < 0.0001) and a decrease in the HA model (P < 0.0001 ). HA coating also had a significant effect on increasing bone-to-implant contact (P < 0.04).

CONCLUSIONS

The results indicate that alendronate increases early bone formation rate around dental implants. Additionally, the local application as described resulted in greater bone-to-implant contact with TMP implants.

Bisphosphonates stimulate formation of osteoblast precursors and mineralized nodules in murine and human bone marrow cultures in vitro and promote early osteoblastogenesis in young and aged mice in vivo

Recent in vitro findings suggest that bisphosphonates, potent inhibitors of osteoclastic bone resorption, may also have a direct action on osteoblasts. The purpose of this study was to search for potential effects of etidronate and alendronate on the formation of early and late osteoblastic cell precursors by measuring the number of colony-forming units for fibroblasts (CFU-F) and colony-forming units for osteoblasts (CFU-OB) in murine and human bone marrow cultures. In murine marrow cultures, etidronate (10(-5) to 10(-9) mol/L) significantly stimulated the formation of CFU-F with a maximal effect at 10(-5) mol/L (mean increase over control values+/-SD: 106+/-17%;p < 0.001), whereas alendronate had a biphasic effect, being stimulatory at concentrations below 10(-7) mol/L (78+/-5%; p < 0.001), and inhibitory at higher doses. The formation of CFU-OB was also inhibited by both bisphosphonates at the highest concentrations (10(-5) mol/L and 10(-6) mol/L), but it was significantly stimulated at lower concentrations (from 10(-7) to 10(-9) mol/L for etidronate and 10(-7) to 10(-10) mol/I, for alendronate; p < 0.001). In human bone marrow cultures, alendronate (10(-8) to 10-(12) mol/L) increased CFU-F formation with a maximal effect at 10(-10) mol/L (161+/-12 %; p < 0.01). CFU-OB formation, observed only in the presence of dexamethasone (10(-8) mol/L), was markedly stimulated by alendronate at the above concentrations with a maximal increase at 10(-10) mol/L (133+/-34%; p < 0.001). The in vivo short-term effects of bisphosphonates on the formation of early osteoblast precursors were also studied in bone marrow cultures from young female mice treated with weekly subcutaneous injections of etidronate (0.3, 3, and 30 mg/kg) or alendronate (0.3, 3, and 30 microg/kg) and from aging female mice treated with the two lowest doses of both drugs. After 1 month of treatment, etidronate (0.3 and 3 mg/kg) and alendronate (0.3 and 3 microg/kg) significantly increased the number of CFU-F colonies in the bone marrow from young and old animals, whereas the highest dose of both drugs had no effect in young mice. Our results, together with previously reported observations of bone-forming effects in osteoporosis, suggest that bisphosphonates may have, in vivo, a potentially relevant influence on cells of the osteoblastic lineage, distinct from their inhibitory action on osteoclasts.

Effect of alendronate on cultured normal human osteoblasts

Alendronate is an aminobisphosphonate with a potent anti-reabsorptive action that does not appear to interfere with bone mineralization, and is even able to increase bone mineral density in osteoporotic postmenopausal women through a still not fully understood mechanism. This study was conducted to assess the direct effect of alendronate on diverse aspects of normal human osteoblast physiology. For that purpose, the in vitro effect of a wide range of concentrations [from 10(-1) to 10(-12) mol/L] of alendronate on cell viability, proliferation, collagen synthesis, and the mineral-depositing capacity of normal human osteoblasts was tested. Alendronate effects were examined at 48 and 96 h of culture in the presence or absence of fetal calf serum. In vitro alendronate affected osteoblast viability at concentrations equal to or higher than 10(-4) mol/L. At concentrations equal to or higher than 10(-3) mol/L, no viable cells were observed in cultures. In vitro alendronate at concentrations between 10(-5) and 10(-12) mol/L did not have any effect on the proliferative capacity of normal human osteoblasts determined by two different techniques: (1) tritiated thymidine incorporation to DNA and (2) cell counting. Collagen synthesis by normal human osteoblasts showed a tendency to decrease following incubation with alendronate supplemented with fetal calf serum. This decrease was only statistically significant after 96 h of culture; however, a dose-response effect could not be documented. Finally, no effect of alendronate was observed on calcium deposition in vitro by normal human osteoblasts at concentrations equal to or lower than 10(-5) mol/L. In conclusion, the present study shows that alendronate in vitro does not affect viability, proliferation, and mineral deposit capacity of normal human osteoblasts at the concentration at which it inhibits by 50% the resorptive capacity of osteoclasts that for this drug has been reported as 2 x 10(-9) mol/L.

Alendronate inhibition of protein-tyrosine-phosphatase-meg1

Alendronate (4-amino-1-hydroxybutylidene-1,1-bisphosphonate) is a potent bisphosphonate that inhibits osteoclastic bone resorption and has proven effective for the treatment of osteoporosis. Its molecular mechanism of action, however, has not been defined precisely. Here we report that alendronate is a potent inhibitor of the protein-tyrosine-phosphatase-meg1 (PTPmeg1). Two substrates were employed in this study: fluorescein diphosphate and the phosphotyrosyl peptide src-pY527. With either substrate, alendronate was a slow binding inhibitor of PTPmeg1. Among the other bisphosphonates studied, alendronate was more potent and selective for PTPmeg1. The hydrolysis of fluorescein diphosphate by PTP epsilon and PTPmeg1 was sensitive to alendronate, with IC50 values of less than 1 microM; PTPsigma, however, under the same conditions, was inhibited by only 50% with 141 microM alendronate. Similarly, with the src-pY527 substrate, alendronate inhibition was also PTP dependent. Alendronate inhibited PTPmeg1 with an IC50 value of 23 microM, PTPsigma with an IC50 value of 2 microM, and did not inhibit PTP epsilon at concentrations up to 1 mM. The alendronate inhibition of these three PTPs and two substrates is consistent with the formation of a ternary complex comprised of enzyme, substrate, and inhibitor. PTP inhibition by hisphosphonates or vanadate was diminished by the metal chelating agent EDTA, or by the reducing agent dithiothreitol, suggesting that a metal ion and the oxidation of a cysteine residue are required for full inhibition. These observations show substrate- and enzyme-specific PTP inhibition by alendronate and support the possibility that a certain PTP(s) may be the molecular target for alendronate action.

Effects of bisphosphonates on alkaline phosphatase activity, mineralization, and prostaglandin E2 synthesis in the clonal osteoblast-like cell line MC3T3-E1

The effects of 3 bisphosphonates, AHBuBP, AHPrBP, and Cl2MBP on cell growth, alkaline phosphatase (ALP) activity, mineralization, and prostaglandin E2 (PGE2) synthesis in the clonal osteoblast-like cell line MC3T3-E1 were studied. These bisphosphonates had essentially similar effects on growth and the osteoblastic functions of the cells, i.e., they had no inhibitory effects on cell growth except at higher concentrations, they increased ALP activity, and inhibited PGE2 production. In the presence of AHBuBP, ALP activity was higher than that in the control after day 6 of culture. Lower concentrations of AHBuBP slightly facilitated mineralization by the cells. It is probable that bisphosphonates enhance the functions of osteoblasts in certain concentration and that the inhibition of endogenous PGE2 production may be involved in the mechanism of action of bisphosphonates.

Bone sialoprotein in serum of patients with malignant bone diseases

Bone sialoprotein (BS), a protein synthesized by osteoblasts and osteoclasts and highly modified posttranslationally, constitutes a predominant fraction of the noncollagenous organic matrix in human bone. We report an assessment of serum concentrations of BS in patients with malignant bone diseases. In patients with bone metastases (according to scintigraphic criteria), serum BS concentrations were greater than in patients without bone metastases (P &lt;0.05). However, ROC curve analysis revealed that serum BS was inferior to serum bone alkaline phosphatase in discriminating between patients with and without bone metastases. Patients with bone metastases showed a weak correlation between serum BS concentrations and bone formation markers. Only “traditional” markers of bone formation—but not BS—were correlated with urinary deoxypyridinoline (P &lt;0.01). Liver and kidney dysfunction had no significant influence on BS values in these patients (as assessed by analysis of variance; P &gt;0.05). In multiple myeloma patients treated with corticosteroids and bisphosphonates, BS concentrations were lower than in tumor patients without bone metastases (P &lt;0.001), and the correlation between BS concentrations and the number of bisphosphonate courses applied was significant (r = −0.578; P &lt;0.05). In postmenopausal women, serum BS concentrations averaged 142% greater than in premenopausal women. Further studies should be done, therefore, to elucidate whether serum BS is able to predict high bone turnover after menopause.