Recovery of trabecular and cortical bone turnover after discontinuation of risedronate and alendronate therapy in ovariectomized rats

Ångstrom-scale gold particles loaded with alendronate via alpha-lipoic acid alleviate bone loss in osteoporotic mice

Osteoporosis is a highly prevalent metabolic disease characterized by low systemic bone mass and deterioration of bone microarchitecture, resulting in reduced bone strength and increased fracture risk. Current treatment options for osteoporosis are limited by factors such as efficacy, cost, availability, side effects, and acceptability to patients. Gold nanoparticles show promise as an emerging osteoporosis therapy due to their osteogenic effects and ability to allow therapeutic delivery but have inherent constraints, such as low specificity and the potential for heavy metal accumulation in the body. This study reports the synthesis of ultrasmall gold particles almost reaching the Ångstrom (Ång) dimension. The antioxidant alpha-lipoic acid (LA) is used as a dispersant and stabilizer to coat Ångstrom-scale gold particles (AuÅPs). Alendronate (AL), an amino-bisphosphonate commonly used in drug therapy for osteoporosis, is conjugated through LA to the surface of AuÅPs, allowing targeted delivery to bone and enhancing antiresorptive therapeutic effects. In this study, alendronate-loaded Ångstrom-scale gold particles (AuÅPs-AL) were used for the first time to promote osteogenesis and alleviate bone loss through regulation of the WNT signaling pathway, as shown through in vitro tests. The in vivo therapeutic effects of AuÅPs-AL were demonstrated in an established osteoporosis mouse model. The results of Micro-computed Tomography, histology, and tartrate-resistant acid phosphatase staining indicated that AuÅPs-AL significantly improved bone density and prevented bone loss, with no evidence of nanoparticle-associated toxicity. These findings suggest the possible future application of AuÅPs-AL in osteoporosis therapy and point to the potential of developing new approaches for treating metabolic bone diseases using Ångstrom-scale gold particles.

An unusual case of bone regeneration of a necrotic mandible with pathologic fracture in an elderly hemodialysis patient with medication-related osteonecrosis of the jaw: a case report and review of the literature

Background

Bisphosphonates are frequently used for osteoporosis. Medication-related osteonecrosis of the jaw, a complication of bone-modifying agents, including bisphosphonates or angiogenic inhibitors, can be challenging to treat in elderly patients with numerous preexisting conditions. Achieving good treatment outcomes is especially difficult in patients with pathological fractures accompanied with extraoral fistulae.

Case presentation

We report an unusual case of prominent bone regeneration following palliative surgical treatment in a 72-year-old Japanese female patient undergoing hemodialysis. She previously had severe osteoporosis due to renal osteodystrophy and was receiving antiresorptive intravenous bisphosphonate. Computed tomography revealed a discontinuous left lower mandibular margin with a pathologic fracture and extensive, morphologically irregular sequestrum formation (80 × 35 × 20 mm). The patient was diagnosed with stage III medication-related osteonecrosis of the jaw and pathologic mandibular fracture. Immediately before the surgery, the anticoagulant used for dialysis was changed from heparin to nafamostat mesylate to reduce the risk of intraoperative bleeding. Sequestrectomy was performed under general anesthesia. Postoperative infection was not observed, the intraoral and submandibular fistula disappeared, and, surprisingly, prominent spontaneous bone regeneration was observed postoperatively at 6 months. Despite the severe systemic condition of the patient, the conservative surgical approach with sequestrectomy has yielded desirable results for more than 6 years since the surgery.

Conclusions

This rare report of spontaneous bone regeneration in a patient of advanced age and poor general condition is the oldest case of mandibular regeneration ever reported.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13256-021-03206-5.

Correlation of the quantitative methods for the measurement of bone uptake and plasma clearance of 18F-NaF using positron emission tomography. Systematic review and meta-analysis

PURPOSE

¹⁸F-NaF PET is valuable for detecting bone metabolism through osteoblastic activity in the assessment of bone disease. Hawkins, Patlak, and standardised uptake value (SUV) are the most common quantitative measurements used to evaluate bone metabolism. This systematic review evaluates the correlation between quantitative positron emission tomography (PET) methods and to compare their precision.

METHODS

A systematic search in Medline, PubMed, SCOPUS, and Web of Science was undertaken to find relevant papers published from 2000. All studies with human adults undergoing ¹⁸F-NaF PET, PET/CT, or PET/MRI were included except for subjects diagnosed with non-diffuse metabolic bone disease or malignancy. Quality Assessment Tool for Studies of Diverse Designs (QATSDD) was used to assess risk of bias. A qualitative review and meta-analysis using Hedges random-effect model was used producing summary size effects of the correlation between methods in healthy and unhealthy bone sites and assessing study heterogeneity.

RESULTS

228 healthy and unhealthy participants were included across 12 studies resulted from the systematic search. One-third of studies had a moderate quality percentage while the rest had relatively high quality. The pooled correlation coefficient in meta-analysis showed a high correlation of more than 0.88 (0.71-1.05. 95 %CI) between SUV and Hawkins and more than 0.96 (0.88-1.03. 95 %CI) between Patlak and Hawkins within all subgroups, suggesting all methods yield similar results in healthy and unhealthy bone sites. SUV has the lowest precision error followed by Patlak while Hawkins method showed the highest precision error.

CONCLUSION

Patlak is the best within research and SUV is better within clinical practice.

A Bisphosphonate With a Low Hydroxyapatite Binding Affinity Prevents Bone Loss in Mice After Ovariectomy and Reverses Rapidly With Treatment Cessation

Bisphosphonates (BPs) are a mainstay of osteoporosis treatment; however, concerns about bone health based on oversuppression of remodeling remain. Long‐term bone remodeling suppression adversely affects bone material properties with microdamage accumulation and reduced fracture toughness in animals and increases in matrix mineralization and atypical femur fractures in patients. Although a “drug holiday” from BPs to restore remodeling and improve bone quality seems reasonable, clinical BPs have long functional half‐lives because of their high hydroxyapatite (HAP) binding affinities. This places a practical limit on the reversibility and effectiveness of a drug holiday. BPs with low HAP affinity and strong osteoclast inhibition potentially offer an alternative approach; their antiresorptive effect should reverse rapidly when dosing is discontinued. This study tested this concept using NE‐58025, a BP with low HAP affinity and moderate osteoclast inhibition potential. Young adult female C57Bl/6 mice were ovariectomized (OVX) and treated with NE‐58025, risedronate, or PBS vehicle for 3 months to test effectiveness in preventing long‐term bone loss. Bone microarchitecture, histomorphometry, and whole‐bone mechanical properties were assessed. To test reversibility, OVX mice were similarly treated for 3 months, treatment was stopped, and bone was assessed up to 3 months post‐treatment. NE‐58025 and RIS inhibited long‐term OVX‐induced bone loss, but NE‐58025 antiresorptive effects were more pronounced. Withdrawing NE‐58025 treatment led to the rapid onset of trabecular resorption with a 200% increase in osteoclast surface and bone loss within 1 month. Cessation of risedronate treatment did not lead to increases in resorption indices or bone loss. These results show that NE‐58025 prevents OVX‐induced bone loss, and its effects reverse quickly following cessation treatment in vivo. Low‐HAP affinity BPs may have use as reversible, antiresorptive agents with a rapid on/off profile, which may be useful for maintaining bone health with long‐term BP treatment. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Sustained anti-osteoporotic action of risedronate compared to anti-RANKL antibody following discontinuation in ovariectomized mice

Bisphosphonates and the anti-receptor activator of nuclear factor-kappa B ligand (RANKL) antibody denosumab are effective anti-resorptive drugs commonly prescribed for osteoporosis. Both drugs may, however, have intolerable side effects; so, it is critical to examine their residual efficacy such as maintenance of bone mass following cessation. Therefore, we compared the changes in bone histology following discontinuation of the aminobisphosphonate risedronate and anti-RANKL antibody in ovariectomized (OVX) mice. Twelve-week-old female C57BL/6 N mice were OVX or sham operated. Four weeks after surgery, mice were treated with vehicle, a single injection of anti-RANKL antibody (5 mg/kg), or risedronate (5 μg/kg/day, s.c.) for 4 weeks (the treatment period), followed by vehicle treatment for an additional 4 weeks (discontinuation period). The lumbar spine and proximal tibia were evaluated by micro-computed tomography. In addition, the lumbar spine, proximal tibia, and the femoral shaft were examined by bone histomorphometry. After 4 weeks of discontinuation, OVX mice initially treated with the anti-RANKL antibody exhibited a trend of bone loss associated with increased turnover in both trabecular and cortical bones, although the difference was not significant. By contrast, OVX mice treated with risedronate exhibited maintained or even increased bone mass and suppressed bone turnover. Patients discontinuing denosumab should be carefully monitored for recurrent osteoporosis symptoms, and a replacement drug should be considered.

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Bone mass and suppression of turnover were maintained after stopping bisphophonates.

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Bone turnover was rapidly increased after discontinuation of anti-RANKL antibody.

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Periosteal bone formation was maintained after administration of antiresorptive drugs.

ATRAID regulates the action of nitrogen-containing bisphosphonates on bone

Nitrogen-containing bisphosphonates (N-BPs), such as alendronate, are the most widely prescribed medications for diseases involving bone, with nearly 200 million prescriptions written annually. Recently, widespread use of N-BPs has been challenged due to the risk of rare but traumatic side effects such as atypical femoral fracture (AFF) and osteonecrosis of the jaw (ONJ). N-BPs bind to and inhibit farnesyl diphosphate synthase, resulting in defects in protein prenylation. Yet, it remains poorly understood what other cellular factors might allow N-BPs to exert their pharmacological effects. Here, we performed genome-wide studies in cells and patients to identify the poorly characterized gene, ATRAID Loss of ATRAID function results in selective resistance to N-BP-mediated loss of cell viability and the prevention of alendronate-mediated inhibition of prenylation. ATRAID is required for alendronate inhibition of osteoclast function, and ATRAID-deficient mice have impaired therapeutic responses to alendronate in both postmenopausal and senile (old age) osteoporosis models. Last, we performed exome sequencing on patients taking N-BPs that suffered ONJ or an AFF. ATRAID is one of three genes that contain rare nonsynonymous coding variants in patients with ONJ or an AFF that is also differentially expressed in poor outcome groups of patients treated with N-BPs. We functionally validated this patient variation in ATRAID as conferring cellular hypersensitivity to N-BPs. Our work adds key insight into the mechanistic action of N-BPs and the processes that might underlie differential responsiveness to N-BPs in people.

[Risedronate inhibits rat bone marrow adipogenesis and reduces RANKL expression in adipocytes]

OBJECTIVE

To investigate the effects of risedronate on bone marrow adipogenesis and the expression of the receptor activator of nuclear factor κB ligand (RANKL) in adipocytes in the bone marrow micro-environment.

METHODS

Primary cultured rat mesenchymal stem cells (BMSCs) with or without adipogenic induction for 14 days were treated with 1, 5, 10, and 25 μmol/L risedronate. The droplets of the differentiated adipocytes were analyzed, and Western blotting was performed to detect the expression level of RANKL. Female SD rats (24-week-old) were randomly divided into sham-operated group and ovariectomy (OVX) group, and 12 weeks after the operation, the OVX rats were further divided into control group and risedronate group (2.4 μg/kg, injected subcutaneously for 3 times a week). Eight weeks later, the bone mineral density (BMD) of the rats and bone marrow histopathology of the femurs was examined to evaluate the effect of risedronate on the fat fraction in the bone marrow.

RESULTS

Risdronate significantly inhibited adipogenic differentiation of rat BMSCs and suppressed RANKL expression in the adipocytes derived from the BMSCs in a concentration-dependent manner. In OVX rats, risdronate treatment significantly increased the BMD and decreased the fat content in the bone marrow.

CONCLUSIONS

Risdronate can effectively inhibit the adipogenic differentiation of rat BMSCs, decrease fat content in the bone marrow, and suppress the generation and function of osteoclasts by down-regulating the expression of RANKL, which can be an important mechanism underlying the therapeutic effect of risedronate against osteoporosis.

The effect of alendronate sodium on trabecular bone structure in an osteoporotic rat model

Objectives

TObjectives: This study aims to investigate the effect of alendronate sodium on trabecular bone structure in an osteoporotic rat model.

Materials and methods

Between May 2006 and July 2006, 60 female Wistar Albino rats aged three months were randomly allocated to three groups: sham operated receiving no treatment (Shm); ovariectomized-alendronate receiving 1 mg/kg/day alendronate sodium (Ovx-A), and ovariectomized-vehicle receiving 1 mL/kg/day physiological saline (Ovx-PS). Both Ovx groups received treatment through gastric gavage for 56 days.

Results

Densitometric measurements showed that bone mineral density decreased in the Ovx-PS and increased in Ovx-A groups (p<0.05). Biomechanical measurements showed a decrease in the breaking force in the Ovx-PS group and an increase in the Ovx-A group (p<0.05). Histomorphometric measurements showed that the Shm group had normal trabecular structure, while the Ovx-PS group had a less well- formed trabecular structure with a loss in the trabecular number and thickness and a corresponding increase in the trabecular spacing (p<0.05). In the Ovx-A group, there was an improvement in the trabecular structure with an increase in the trabecular number and thickness and a loss in the trabecular space (p<0.05).

Conclusion

Our study results suggest that alendronate sodium is a valuable treatment agent for osteoporosis in postmenopausal women.

What Animal Models Have Taught Us About the Safety and Efficacy of Bisphosphonates in Chronic Kidney Disease

PURPOSE OF REVIEW

Bisphosphonates (BPs) have long been the gold-standard anti-remodeling treatment for numerous metabolic bone diseases. Since these drugs are excreted unmetabolized through the kidney, they are not recommended for individuals with compromised kidney function due to concerns of kidney and bone toxicity. The goal of this paper is to summarize the preclinical BP work in models of kidney disease with particular focus on the bone, kidney, and vasculature.

RECENT FINDINGS

Summative data exists showing positive effects on bone and vascular calcifications with minimal evidence for bone or kidney toxicity in animal models. Preclinical data suggest it may be worthwhile to take a step back and reconsider the use of bisphosphonates to lessen skeletal/vascular complications associated with compromised kidney function.

Bisphosphonate Withdrawal: Effects on Bone Formation and Bone Resorption in Maturing Male Mice

Bisphosphonates are being increasingly used to treat pediatric patients with skeletal disorders. However, the effects of long-term bisphosphonate therapy and cessation of therapy during growth are unclear. Thus, studies were undertaken to determine the effects of alendronate discontinuation after treatment of C57Bl/6 mice during the period of rapid skeletal growth. Compared with vehicle-treated mice, 16 weeks of alendronate treatment starting at age 18 days resulted in a 3.7-fold increase in trabecular bone in the setting of suppressed bone formation. Alendronate therapy for 8 weeks followed by 8 weeks of vehicle treatment resulted in a more pronounced increase in trabecular bone compared with mice treated with alendronate for 16 weeks (1.7-fold) and to vehicle-treated controls (6.5-fold). Mice that received alendronate for 8 weeks followed by 8 weeks of vehicle exhibited increased osteoblast surface (2.5-fold), mineralizing surface (5.7-fold), and bone formation rate (5.1-fold) compared with mice treated continuously with alendronate. However, these parameters were not restored to the levels observed in the vehicle-treated mice. Thus, partial resumption of bone formation upon cessation of bisphosphonate therapy leads to a greater increase in trabecular bone than that found when bisphosphonates are administered continuously to growing mice. These data suggest that intermittent administration of bisphosphonates may optimize their beneficial effects on the growing skeleton. © 2017 American Society for Bone and Mineral Research.

Effects of drug discontinuation after short-term daily alendronate administration on osteoblasts and osteocytes in mice

In order to determine whether osteoclastic bone resorption is restarted after withdrawn of bisphosphonates, we conducted histological examinations on murine osteoclasts, osteoblasts and osteocytes after discontinuation of a daily regimen of alendronate (ALN) with a dosage of 1 mg/kg/day for 10 days. After drug discontinuation, metaphyseal trabecular number and bone volume remained unaltered for the first 4 days. Osteoclast number did not increase, while the number of apoptotic osteoclasts was elevated. On the other hand, tissue non-specific alkaline phosphatase-immunoreactive area was markedly reduced after ALN discontinuation. In addition, osteocytes showed an atrophic profile with empty lacunar areas during and after ALN treatment. Interestingly, as early as 36 h after a single ALN injection, osteocytes show signs of atrophy despite the presence of active osteoblasts. Structured illumination microscopy system showed shortening of osteocytic cytoplasmic processes after drug cessation, suggesting a possible morphological and functional disconnection between osteocytes and osteoblasts. Taken together, it appears that osteoclastic bone resorption is not resumed after ALN discontinuation; also, osteoblasts and osteocytes hardly seem to recover once they are inactivated and atrophied by ALN. In summary, it seems that one must pay more attention to the responses of osteoblasts and osteocytes, rather focusing on the resuming of osteoclastic bone resorption after the ALN discontinuation.

Attenuation of Antiresorptive Action in Withdrawal of Minodronic Acid for Three Months After Treatment for Twelve Months in Ovariectomized Rats

The purpose of this study was to evaluate the effects of withdrawal of minodronic acid (MIN) for 3 months after 12 months of treatment in ovariectomized (OVX) rat. OVX rats were orally treated with MIN (6, 30, and 150 µg/kg/day) for 12 months and necropsied on the day after the last dosing or following 3 months of withdrawal. Lumbar and femoral BMD were decreased in OVX controls. MIN dose-dependently increased BMD. Withdrawal eliminated the effect of MIN on BMD loss after treatment at 6 µg/kg, but not after treatment at 30 and 150 µg/kg. In MIN-treated rats, trabecular thinning occurred during withdrawal after treatment at 6 µg/kg, but the trabecular microstructure was maintained at 30 and 150 µg/kg. In a mechanical test of the femoral diaphysis, stiffness of in OVX controls was decreased but ultimate load was similar to that in sham after withdrawal. MIN increased ultimate load and stiffness, but endosteal length decreased after withdrawal. Suppression of bone turnover by MIN based on bone turnover markers and histomorphometric indices was attenuated by withdrawal after treatment at 6 and 30 µg/kg and partially at 150 µg/kg. The MIN concentration in the humerus decreased during withdrawal, and half-life at 30 µg/kg was shorter than that at 150 µg/kg. These results show that the antiresorptive action of MIN was dose-dependently attenuated by 3-month withdrawal in a rat OVX model. An absence of BMD increase was only observed at a low dose but decreases in antiresorptive activity occurred over a wide dose range.

Compromised vertebral structural and mechanical properties associated with progressive kidney disease and the effects of traditional pharmacological interventions

BACKGROUND/AIMS

Patients with chronic kidney disease mineral and bone disorder (CKD-MBD) have a significantly higher vertebral and non-vertebral fracture risk than the general population. Several preclinical models have documented altered skeletal properties in long bones, but few data exist for vertebral bone. The goal of this study was to examine the effects of progressive CKD on vertebral bone structure and mechanics and to determine the effects of treatment with either bisphosphonates or anti-sclerostin antibody in groups of animals with high or low PTH.

METHODS

Animals with progressive kidney disease were left untreated, treated with calcium to lower PTH, zoledronic acid to lower remodeling without affecting PTH, anti-sclerostin antibody, or anti-sclerostin antibody plus calcium. Non-diseased, untreated littermates served as controls. Vertebral bone morphology (trabecular and cortical) and mechanical properties (structural and material-level) were assessed at 35 weeks of age by microCT and mechanical testing, respectively.

RESULTS

CKD with high PTH resulted in 6-fold higher bone formation rate, significant reductions in the amount of trabecular and cortical bone, and compromised whole bone mechanical properties in the vertebra compared to normal animals. Treatments that reduced bone remodeling were effective in normalizing vertebral structure and mechanical properties only if the treatment reduced serum PTH. Similarly, treatment with anti-sclerostin antibody was effective in enhancing bone mass and mechanical properties but only if combined with PTH-suppressive treatment.

CONCLUSIONS

CKD significantly altered both cortical and trabecular bone properties in the vertebra resulting in compromised mechanical properties and these changes can be normalized by interventions that involve reductions in PTH levels.

Inhibited osteoclastic bone resorption through alendronate treatment in rats reduces severe osteoarthritis progression

Osteoarthritis (OA) is a non-rheumatoid joint disease characterized by progressive degeneration of extra-cellular cartilage matrix (ECM), enhanced subchondral bone remodeling, osteophyte formation and synovial thickening. Alendronate (ALN) is a potent inhibitor of osteoclastic bone resorption and results in reduced bone remodeling. This study investigated the effects of pre-emptive use of ALN on OA related osteoclastic subchondral bone resorption in an in vivo rat model for severe OA. Using multi-modality imaging we measured effects of ALN treatment within cartilage and synovium. Severe osteoarthritis was induced in left rat knees using papain injections in combination with a moderate running protocol. Twenty rats were treated with subcutaneous ALN injections and compared to twenty untreated controls. Animals were longitudinally monitored for 12weeks with in vivo μCT to measure subchondral bone changes and SPECT/CT to determine synovial macrophage activation using a folate-based radiotracer. Articular cartilage was analyzed at 6 and 12weeks with ex vivo contrast enhanced μCT and histology to measure sulfated-glycosaminoglycan (sGAG) content and cartilage thickness. ALN treatment successfully inhibited subchondral bone remodeling. As a result we found less subchondral plate porosity and reduced osteophytosis. ALN treatment did not reduce subchondral sclerosis. However, after the OA induction phase, ALN treatment protected cartilage ECM from degradation and reduced synovial macrophage activation. Surprisingly, ALN treatment also improved sGAG content of tibia cartilage in healthy joints. Our data was consistent with the hypothesis that osteoclastic bone resorption might play an important role in OA and may be a driving force for progression of the disease. However, our study suggest that this effect might not solely be effects on osteoclastic activity, since ALN treatment also influenced macrophage functioning. Additionally, ALN treatment and physical activity exercised a positive effect in healthy control joints, which increased cartilage sGAG content. More research on this topic might lead to novel insights as to improve cartilage quality.

Bisphosphonates and bone quality

Bisphosphonates (BPs) are bone-avid compounds used as first-line medications for the prevention and treatment of osteoporosis. They are also used in other skeletal pathologies such as Paget's and metastatic bone disease. They effectively reduce osteoclast viability and also activity in the resorptive phase of bone remodelling and help preserve bone micro-architecture, both major determinants of bone strength and ultimately of the susceptibility to fractures. The chemically distinctive structure of each BP used in the clinic determines their unique affinity, distribution/penetration throughout the bone and their individual effects on bone geometry, micro-architecture and composition or what we call 'bone quality'. BPs have no clinically significant anabolic effects. This review will touch upon some of the components of bone quality that could be affected by the administration of BPs.

Unfocused extracorporeal shock waves induce anabolic effects in osteoporotic rats

Unfocused extracorporeal shock waves (UESW) have been shown to have an anabolic effect on bone mass. Therefore we investigated the effects of UESW on bone in osteoporotic rats with and without anti-resorptive treatment. Twenty-week-old rats were ovariectomized (n = 27). One group was treated with saline and another group with Alendronate (ALN) 2.4 µg/kg, 3×/week. UESW were applied 2 weeks after ovariectomy. Thousand UESW were applied to one hind leg, the contra-lateral hind leg was not treated and served as control. With the use of in vivo micro-CT scanning it was shown that in saline treated rats trabecular bone volume fraction (BV/TV) was higher at 2 weeks follow-up in UESW treated legs compared to control legs. However, at 4 and 10 weeks no difference was found. In ALN treated animals UESW led to a pronounced anabolic response resulting in an increase in BV/TV at all time-points. Furthermore, UESW resulted in increased cortical volume (CtV), higher trabecular connectivity and, more plate-like and thicker trabeculae. Biomechanical testing showed that UESW lead to a higher maximum force before failure and higher stiffness in all treatment groups. With histology abundant areas of intramembranous bone formation along the periosteal cortex and within the bone marrow were observed. In conclusion this study shows promising results for the use of UESW in the treatment of osteoporosis, especially when this treatment is combined with an anti-resorptive treatment.

No effect of risedronate on articular cartilage damage in the Dunkin Hartley guinea pig model of osteoarthritis

OBJECTIVES

To investigate whether treatment with a bisphosphonate would influence the subchondral bone plate stiffness and the development of cartilage damage in Dunkin Hartley guinea pigs, which develop osteoarthritis (OA) spontaneously.

METHOD

Fifty-six 3-month-old male Dunkin Hartley guinea pigs were randomized into a baseline group and six groups receiving either the bisphosphonate risedronate (30 µg/kg) or vehicle five times a week for 6, 12, or 24 weeks. The medial condyle of the right stifle joint was investigated by histology, using the Osteoarthritis Research Society International (OARSI) score, along with static and dynamic histomorphometry. The subchondral bone plate of the left tibia was tested mechanically with indentation testing. Degradation products of C-terminal telopeptides of type II collagen (CTX-II) were measured in serum.

RESULTS

The OARSI score did not differ between risedronate-treated and control animals at any time point. The fraction of bone surfaces covered with osteoclasts (Oc.S/BS) was significantly suppressed in risedronate-treated animals at all time points, as were the fractions of mineralizing surfaces (MS/BS) and osteoid-covered surfaces (OS/BS), and also serum CTX-II. This was accompanied by a significant increase in the epiphyseal content of calcified tissue and in the thickness of the subchondral bone plate. However, this did not result in a stiffer subchondral bone at any time point.

DISCUSSION

The risedronate treatment inhibited osteoclastic resorption of calcified cartilage in the primary spongiosa under the epiphyseal growth plate, explaining the risedronate-mediated decrease in CTX-II. Moreover, the serum CTX-II level was not related to the OA-induced articular cartilage degradation seen in this model.

CONCLUSIONS

Risedronate did not influence the OARSI score and subchondral plate stiffness, but decreased serum CTX-II in Dunkin Hartley guinea pigs.

Bisphosphonates improve trabecular bone mass and normalize cortical thickness in ovariectomized, osteoblast connexin43 deficient mice

The gap junction protein, connexin43 (Cx43) controls both bone formation and osteoclastogenesis via osteoblasts and/or osteocytes. Cx43 has also been proposed to mediate an anti-apoptotic effect of bisphosphonates, potent inhibitors of bone resorption. We studied whether bisphosphonates are effective in protecting mice with a conditional Cx43 gene deletion in osteoblasts and osteocytes (cKO) from the consequences of ovariectomy on bone mass and strength. Ovariectomy resulted in rapid loss of trabecular bone followed by a slight recovery in wild type (WT) mice, and a similar degree of trabecular bone loss, albeit slightly delayed, occurred in cKO mice. Treatment with either risedronate (20 μg/kg) or alendronate (40 μg/kg) prevented ovariectomy-induced bone loss in both genotypes. In basal conditions, bones of cKO mice have larger marrow area, higher endocortical osteoclast number, and lower cortical thickness and strength relative to WT. Ovariectomy increased endocortical osteoclast number in WT but not in cKO mice. Both bisphosphonates prevented these increases in WT mice, and normalized endocortical osteoclast number, cortical thickness and bone strength in cKO mice. Thus, lack of osteoblast/osteocyte Cx43 does not alter bisphosphonate action on bone mass and strength in estrogen deficiency. These results support the notion that one of the main functions of Cx43 in cortical bone is to restrain osteoblast and/or osteocytes from inducing osteoclastogenesis at the endocortical surface.

Regional bone metabolism at the lumbar spine and hip following discontinuation of alendronate and risedronate treatment in postmenopausal women

The aim of this study was to examine the effects of bisphosphonate discontinuation on bone metabolism at the spine and hip measured using (18) F-fluoride PET. Bone metabolism at the spine remained stable following discontinuation of alendronate and risedronate at 1 year but increased in the hip in the alendronate group only.

INTRODUCTION

Bisphosphonates such as alendronate (ALN) or risedronate (RIS) have persistent effects on spine BMD following discontinuation.

METHODS

Positron emission tomography (PET) was used to examine regional bone metabolism in 20 postmenopausal women treated with ALN (n = 11) or RIS (n = 9) for a minimum of 3 years at screening (range 3-9 years, mean 5 years for both groups). Subjects underwent a dynamic scan of the lumbar spine and a static scan of both hips at baseline and 6 and 12 months following treatment discontinuation. (18) F-fluoride plasma clearance (K(i)) at the spine was calculated using a three-compartment model. Standardised uptake values (SUV) were calculated for the spine, total hip, femoral neck and femoral shaft. Measurements of BMD and biochemical markers of bone turnover were also performed.

RESULTS

With the exception of a significant decrease in spine BMD in the ALN group, BMD remained stable. Bone turnover markers increased significantly from baseline by 12 months for both study groups. Measurements of K(i) and SUV at the spine and femoral neck did not change significantly in either group. SUV at the femoral shaft and total hip increased significantly but in the ALN group only, increasing by 33.8% (p = 0.028) and 24.0% (p = 0.013), respectively.

CONCLUSIONS

Bone metabolism at the spine remained suppressed following treatment discontinuation. A significant increase in SUV at the femoral shaft and total hip after 12 months was observed but for the ALN group only. This study was small, and further clinical studies are required to fully evaluate the persistence of BP treatment.

A model for the change of cancellous bone volume and structure over time

A model is presented for characterizing the process by which cancellous bone changes in volume and structure over time. The model comprises simulations of local changes resulting from individual remodelling events, known as bone multicellular units (BMU), and an ordinary differential equation for connecting the number of remodelling events to real time. The model is validated on micro-CT scans of tibiae of normal rats, estrogen deprived rats and estrogen deprived rats treated with bisphosphonates. The model explains the asymptotic trends seen in changes of bone volume over time resulting from estrogen deprivation as well as trends seen subsequent to treatment. The model demonstrates that both bone volume and structure changes can be explained in terms of resetting remodelling parameters. The model also shows that either current understanding of the effects of bisphosphonates is not correct or that the simplest description of remodelling does not suffice to explain both the change in bone volume and structure of rats treated with bisphosphonates.

Combined treatment with a traditional Chinese medicine, Hachimi-jio-gan (Ba-Wei-Di-Huang-Wan) and alendronate improves bone microstructure in ovariectomized rats

ETHNOPHARMACOLOGICAL RELEVANCE

Hachimi-jio-gan is one of the most common recipes in traditional Chinese, Japanese and Korean medicines and has been used for preventing and treating various diseases associated with aging, including osteoporosis.

AIM OF THE STUDY

The present study was performed to examine the combined effects of a traditional Chinese medicine, Hachimi-jio-gan (HJG) and antiresorptive agent, alendronate (ALN) on ovariectomy-induced bone loss in rats.

MATERIALS AND METHODS

Six-month-old female Sprague-Dawley rats were underwent ovariectomy (OVX) or sham operation. Eight weeks later, the OVX rats were treated either with HJG or ALN alone or in combination of both. The skeletal response was evaluated using micro-computed tomography (micro-CT), image analysis software, and biochemical markers.

RESULTS

This study demonstrated that treatment with HJG or ALN alone increased trabecular bone volume and bone mineral density (BMD), and partially improved bone microstructure of the proximal tibia and vertebra in OVX rats. Treatment with ALN to OVX rats resulted in significant reduction in both bone resorption and bone formation. Treatment with HJG to OVX rats inhibited bone resorption, with no marked effects on bone formation. Combined treatment of HJG and ALN significantly improved trabecular bone mass and bone microstructure, compared with either agent alone.

CONCLUSIONS

We conclude that the combined treatment with HJG and ALN has beneficial effects on trabecular bone mass, improving the structural properties of both tibia and vertebra in OVX rats.

Bisphosphonates do not alter the rate of secondary mineralization

Bisphosphonates function to reduce bone turnover, which consequently increases the mean degree of tissue mineralization at an organ level. However, it is not clear if bisphosphonates alter the length of time required for an individual bone-modeling unit (BMU) to fully mineralize. We have recently demonstrated that it takes ~350 days (d) for normal, untreated cortical bone to fully mineralize. The aim of this study was to determine the rate at which newly formed trabecular BMUs become fully mineralized in rabbits treated for up to 414 d with clinical doses of either risedronate (RIS) or alendronate (ALN). Thirty-six, 4-month old virgin female New Zealand white rabbits were allocated to RIS (n=12; 2.4 μg/kg body weight), ALN (n=12; 2.4 μg/kg body weight), or volume-matched saline controls (CON; n=12). Fluorochrome labels were administered at specific time intervals to quantify the rate and level of mineralization of trabecular bone from the femoral neck (FN) by Fourier transform infrared microspectroscopy (FTIRM). The organic (collagen) and inorganic (phosphate and carbonate) IR spectral characteristics of trabecular bone from undecalcified 4 micron thick tissue sections were quantified from fluorescently labels regions that had mineralized for 1, 8, 18, 35, 70, 105, 140, 210, 280, and 385 d (4 rabbits per time point and treatment group). All groups exhibited a rapid increase in mineralization over the first 18 days, the period of primary mineralization, with no significant differences between treatments. Mineralization continued to increase, at a slower rate up, to 385 days (secondary mineralization), and was not different among treatments. There were no significant differences between treatments for the rate of mineralization within an individual BMU; however, ALN and RIS both increased global tissue mineralization as demonstrated by areal bone mineral density from DXA. We conclude that increases in tissue mineralization that occur following a period of bisphosphonate treatment is a function of the suppressed rate of remodeling that allows for a greater number of BMUs to obtain a greater degree of mineralization.

Teriparatide in bisphosphonate-resistant osteoporosis: microarchitectural changes and clinical results after 6 and 18 months

A number of osteoporotic patients under bisphosphonate treatment present persistent fragility fractures and bone loss despite good compliance. The objective of this 18-month prospective study was to investigate the effect of teriparatide [rhPTH(1-34)] in 25 female osteoporotics who were inadequate responders to oral bisphosphonates and to correlate microarchitectural changes in three consecutive iliac crest biopsies measured by micro-computed tomography (μCT) with bone mineral density (BMD) and bone serum markers. Scanned biopsies at baseline (M0), 6 months (M6), and 18 months (M18) demonstrated early significant (P < 0.01) increases in bone volume per tissue volume (+34%) and trabecular number (+14%) at M6 with only moderate changes in most μCT structural parameters between M6 and M18. μCT-measured bone tissue density was significantly decreased at M18, expressing an overall lower degree of tissue mineralization characteristic for new bone formation despite unchanged trabecular thickness due to increased intratrabecular tunneling at M18. μCT results were consistent with serum bone turnover markers, reaching maximal levels of bone alkaline phosphatase and serum β-crosslaps at M6, with subsequent decline until M18. BMD assessed by DXA demonstrated persistent increases at the lumbar spine until M12, whereas no significant change was observed at the hip. Type (alendronate/risedronate) and duration (3.5 ± 4 years) of prior bisphosphonate treatment did not influence outcome on μCT, BMD, or bone marker results. The overall results indicate a positive ceiling effect of teriparatide on bone microarchitecture and bone markers after 6 and 12 months for lumbar spine BMD, with no additional gain until M18 in bisphosphonate nonresponders.

Greater magnitude of turnover suppression occurs earlier after treatment initiation with risedronate than alendronate

Clinical data suggest that reductions in fractures associated with osteoporosis may occur sooner in patients treated with risedronate (RIS) compared to those treated with alendronate (ALN). This could be explained by differences in the time course of turnover suppression between these two bisphosphonates. To determine if differences in the onset of turnover suppression exist between RIS and ALN, female New Zealand white rabbits (total n=32) were treated with clinically relevant doses of RIS or ALN and then administered different fluorochrome labels weekly for four weeks in order to allow histological assessment of the time-course of turnover suppression. By the third week of treatment vertebral trabecular bone formation rate (BFR/BS) was significantly suppressed with RIS-treatment compared to both VEH and ALN. By the 4th week of treatment, turnover rates in RIS-treated animals remained significantly lower than in VEH-treated animals and were also lower than ALN; at this time-point ALN was significantly lower than VEH. There was no significant reduction in intra-cortical remodeling in the tibial mid-diaphysis at any time point for either RIS or ALN. This greater effect on turnover suppression with RIS early in treatment compared to ALN is likely the result of both risedronate's greater potency on osteoclast inhibition and its lower binding affinity. Together with studies showing more rapid return toward baseline turnover following withdrawal of RIS compared to ALN, this pre-clinical study provides evidence of the differences between bisphosphonates with respect to onset and recovery of bone turnover suppression.

Risedronate does not reduce mechanical loading-related increases in cortical and trabecular bone mass in mice

To establish whether the combination of anti-resorptive therapy with mechanical loading has a negative, additive or synergistic effect on bone structure, we assessed the separate and combined effects of risedronate and non-invasive dynamic loading on trabecular and cortical bone. Seventeen-week-old female C57BL/6 mice were given daily subcutaneous injections of vehicle (n=20) or risedronate at a dose of 0.15, 1.5, 15 or 150 μg/kg/day (n=10 in each) for 17 days. From the fourth day of treatment, the right tibiae were subjected to a single period of axial loading (40 cycles/day) for three alternate days per week for two weeks. The left tibiae were used as internal controls. Trabecular and cortical sites in the tibiae were analyzed by high-resolution micro-computed tomography and imaging of fluorochrome labels. In the non-loaded tibiae, treatment with the higher doses of risedronate at 15 or 150 μg/kg/day resulted in higher trabecular bone volume and trabecular number than in vehicle-treated controls, whereas such treatment was associated with no differences in cortical bone volume at any dose. In the loaded tibiae, loading induced increases in trabecular and cortical bone volume compared with contra-lateral controls primarily through increased trabecular thickness and periosteal expansion, respectively, independently of risedronate treatment. In conclusion, the response to mechanical loading in both trabecular and cortical bone in mice is therefore not impaired by short-term treatment with risedronate, even over a 1000-fold dose range. In considering the optimization of treatments for osteoporosis, it is reassuring that anti-resorptive therapy and mechanical loading can exert independent beneficial effects.

Bisphosphonate effects on bone turnover, microdamage, and mechanical properties: what we think we know and what we know that we don't know

The bisphosphonates (BPs) have been useful tools in our understanding of the role that bone remodeling plays in skeletal health. The purpose of this paper is to outline what we know, and what is still unknown, about the role that BPs play in modulating bone turnover, how this affects microdamage accumulation, and ultimately what the effects of these changes elicited by BPs are to the structural and the material biomechanical properties of the skeleton. We know that BPs suppress remodeling site-specifically, probably do not have a direct effect on formation, and that the individual BPs vary with respect to speed of onset, duration of effect and magnitude of suppression. However, we do not know if these differences are meaningful in a clinical sense, how much remodeling is sufficient, the optimal duration of treatment, or how long it takes to restore remodeling to pre-treatment levels following withdrawal. We also know that suppression is intimately tied to microdamage accumulation, which is also site-specific, that BPs impair targeted repair of damage, and that they can reduce the energy absorption capacity of bone at the tissue level. However, the BPs are clearly effective at preventing fracture, and generally increase bone mineral density and whole bone strength, so we do not know whether these changes in damage accumulation and repair, or the mechanical effects at the tissue level, are clinically meaningful. The mechanical effects of BPs on the fatigue life of bone, or BP effects on bone subject to an impact, are entirely unknown. This paper reviews the literature on these topics, and identifies gaps in knowledge that can be addressed with further research.

Differential maintenance of cortical and cancellous bone strength following discontinuation of bone-active agents

Osteoporotic patients treated with antiresorptive or anabolic agents experience an increase in bone mass and a reduction in incident fractures. However, the effects of these medications on bone quality and strength after a prolonged discontinuation of treatment are not known. We evaluated these effects in an osteoporotic rat model. Six-month-old ovariectomized (OVX) rats were treated with placebo, alendronate (ALN, 2 µg/kg), parathyroid hormone [PTH(1-34); 20 µg/kg], or raloxifene (RAL, 2 mg/kg) three times a week for 4 months and withdrawn from the treatments for 8 months. Treatment with ALN, PTH, and RAL increased the vertebral trabecular bone volume (BV/TV) by 47%, 53%, and 31%, with corresponding increases in vertebral compression load by 27%, 51%, and 31%, respectively (p < .001). The resulting bone strength was similar to that of the sham-OVX control group with ALN and RAL and higher (p < .001) with PTH treatment. After 4 months of withdrawal, bone turnover (BFR/BS) remained suppressed in the ALN group versus the OVX controls (p < .001). The vertebral strength was higher than in the OVX group only in ALN-treated group (p < .05), whereas only the PTH-treated animals showed a higher maximum load in tibial bending versus the OVX controls (p < .05). The vertebral BV/TV returned to the OVX group level in both the PTH and RAL groups 4 months after withdrawal but remained 25% higher than the OVX controls up to 8 months after withdrawal of ALN (p < .05). Interestingly, cortical bone mineral density increased only with PTH treatment (p < .05) but was not different among the experimental groups after withdrawal. At 8 months after treatment withdrawal, none of the treatment groups was different from the OVX control group for cortical or cancellous bone strength. In summary, both ALN and PTH maintained bone strength (maximum load) 4 months after discontinuation of treatment despite changes in bone mass and bone turnover; however, PTH maintained cortical bone strength, whereas ALN maintained cancellous bone strength. Additional studies on the long-term effects on bone strength after discontinuation and with combination of osteoporosis medications are needed to improve our treatment of osteoporosis.

Effects of the combination treatment of raloxifene and alendronate on the biomechanical properties of vertebral bone

Raloxifene (RAL) and alendronate (ALN) improve the biomechanical properties of bone by different mechanisms. The goal here was to investigate the effects of combination treatment of RAL and ALN on the biomechanical properties of vertebral bone. Six-month-old Sprague-Dawley rats (n = 80) were randomized into five experimental groups (sham, OVX, OVX + RAL, OVX + ALN, and OVX + RAL + ALN; n = 16/group). Following euthanization, structural and derived material biomechanical properties of vertebral bodies were assessed. Density and dynamic histomorphometric measurements were made on cancellous bone. The results demonstrate that the structural biomechanical properties of vertebral bone are improved with the combination treatment. Stiffness and ultimate load of the OVX + RAL and OVX + ALN groups were significantly lower than those of sham animals, but the combination treatment with RAL + ALN was not significantly different from sham. Furthermore, the OVX + RAL + ALN group was the only agent-treated group in which the ultimate load was significantly higher than that in OVX animals (p < .05). Cancellous bone fractional volume (BV/TV(canc)) and bone mineral density (aBMD) also were improved with the combination treatment. BV/TV(canc) of the OVX + RAL + ALN group was 6.7% and 8.7% greater than that of the OVX + RAL (p < .05) and OVX + ALN (p < .05) groups, respectively. Areal BMD of the OVX + RAL or OVX + ALN groups was not significantly different from that in OVX animals, but the value in animals undergoing combination treatment was significantly higher than that in OVX or OVX + RAL animals alone and not significantly different from that in sham-operated animals. Turnover rates of both the RAL + ALN and ALN alone groups were lower than in the RAL-treated alone group (p < .05). We conclude that the combination treatment of raloxifene and alendronate has beneficial effects on bone volume, resulting in improvement in the structural properties of vertebral bone.

Development of a new ELISA for serum periostin: evaluation of growth-related changes and bisphosphonate treatment in mice

Periostin is a gamma-carboxyglutamic acid protein preferentially expressed in periosteum and bone mesenchymal stem cells. Lack of a precise assay for measuring circulating levels impairs the investigation of its biological significance. We developed a new ELISA and studied changes of periostin levels both locally at the bone site and systemically in circulating blood during growth and after bisphosphonate-induced inhibition of bone remodeling in the mouse. The ELISA we developed is based on an affinity-purified polyclonal antibody that was raised against the C-terminal sequence of mouse periostin. Reproducibility, repeatability, precision, and accuracy tests met standards of acceptance. Serum periostin and levels of the bone turnover markers osteocalcin, PINP, CTX-I, and TRAP5b were measured in (1) 4-, 6-, 8-, 10-, and 12-week-old wild-type female Balb/c mice and (2) adult ovariectomized female Balb/c mice treated with zoledronic acid or vehicle. Serum periostin decreased during growth and stabilized from 8 weeks and older, its levels correlating with bone turnover markers. Immunohistochemistry in bones from different growth stages showed that periostin localized specifically at the sites of endochondral and intramembranous ossification, especially at the periosteal envelopes. Zoledronic acid induced a marked decrease in bone remodeling markers but did not alter serum periostin levels or periostin immunostaining pattern. The novel ELISA is highly specific and allows accurate and precise measurements of serum periostin levels in mice.

Higher doses of bisphosphonates further improve bone mass, architecture, and strength but not the tissue material properties in aged rats

We report the results of a series of experiments designed to determine the effects of ibandronate (Ibn) and risedronate (Ris) on a number of bone quality parameters in aged osteopenic rats to explain how bone material and bone mass may be affected by the dose of bisphosphonates (BP) and contribute to their anti-fracture efficacy. Eighteen-month old female rats underwent either ovariectomy or sham surgery. The ovariectomized (OVX) groups were left untreated for 2 months to develop osteopenia. Treatments started at 20 months of age as follows: sham and OVX control (treated with saline), OVX + risedronate 30 and 90 (30 or 90 microg/kg/dose), and OVX + ibandronate 30 and 90 (30 or 90 microg/kg/dose). The treatments were given monthly for 4 months by subcutaneous injection. At sacrifice at 24 months of age the 4th lumbar vertebra was used for microCT scans (bone mass, architecture, and degree of mineralization of bone, DMB) and histomorphometry, and the 6th lumbar vertebra, tibia, and femur were collected for biomechanical testing to determine bone structural and material strength, cortical fracture toughness, and tissue elastic modulus. The compression testing of the vertebral bodies (LVB6) was simulated using finite-element analysis (FEA) to also estimate the bone structural stiffness. Both Ibn and Ris dose-dependently increased bone mass and improved vertebral bone microarchitecture and mechanical properties compared to OVX control. Estimates of vertebral maximum stress from FEA were correlated with vertebral maximum load (r=0.5, p<0.001) and maximum stress (r=0.4, p<0.005) measured experimentally. Tibial bone bending modulus and cortical strength increased compared to OVX with both BP but no dose-dependent effect was observed. DMB and elastic modulus of trabecular bone were improved with Ibn 30 compared to OVX but were not affected in other BP-treated groups. DMB of tibial cortical bone showed no change with BP treatments. The fracture toughness examined in midshaft femurs did not change with BP even with the higher doses. In summary, the anti-fracture efficacy of BP is largely due to their preservation of bone mass and while the higher doses further improve the bone structural properties do not improve the localized bone material characteristics such as tissue strength, elastic modulus, and cortical toughness.

Osteocyte apoptosis and control of bone resorption following ovariectomy in mice

INTRODUCTION

Osteocyte apoptosis has been linked to bone resorption resulting from estrogen depletion and other resorptive stimuli; however, precise spatial and temporal relationships between the two events have not been clearly established. The purpose of this study was to characterize the patterns of osteocyte apoptosis in relation to bone resorption following ovariectomy to test whether osteocyte apoptosis occurs preferentially in areas known to activate resorption. Moreover, we report that osteocyte apoptosis is necessary to initiate endocortical remodeling in response to estrogen withdrawal.

MATERIALS AND METHODS

Adult female C57BL/6J mice (17 weeks old) underwent either bilateral ovariectomy (OVX), or sham surgery (SHAM) and were euthanized on days 3, 7, 14, or 21 days after OVX. Diaphyseal cross-sections were stained by immunohistochemistry for activated caspase-3 as a marker of apoptosis. The percentages of caspase-positive stained osteocytes (Casp+Ot.) were measured along major and minor anatomical axes around the femoral diaphysis to evaluate the distribution of osteocyte apoptosis after estrogen loss; resorption surface was measured at the adjacent endocortical regions. In a second study to test whether osteocyte apoptosis plays a regulatory role in the initiation of bone resorption, a group of OVX mice received the pan-caspase inhibitor, QVDOPh, to inhibit osteocyte apoptosis. Remaining experimental and sham groups received either QVD or Vehicle.

RESULTS

OVX increased osteocyte apoptosis in a non-uniform distribution throughout the femoral diaphyses. Increases in Casp+osteocytes were predominantly located in the posterior diaphyseal cortex. Here, the number of apoptotic osteocytes 4- to 7-fold higher than sham controls (p<0.005) by day 3 post-OVX and remained elevated. Increases in resorption post-OVX also occurred along the posterior endocortical surface overlying the region of osteocyte apoptosis, but these increases occurred only at 14 and 21 days post-OVX (p<0.002) well after the increases in osteocyte apoptosis. Treatment with QVD in OVX animals suppressed osteocyte apoptosis, with levels in QVD-treated samples equivalent to baseline. Moreover, the increases in osteoclastic resorption normally observed after estrogen loss did not occur in OVX mice treated with QVD.

CONCLUSIONS

The results of this study demonstrate that osteocyte apoptosis following estrogen loss occur regionally, rather than uniformly throughout the cortex. We also showed that estrogen loss increased osteocyte apoptosis. Apoptotic osteocytes were overwhelmingly localized within the posterior cortical region, the location where endocortical resorption was subsequently activated in ovariectomized mice. Finally, the increases in osteoclastic resorption normally observed after estrogen withdrawal did not occur in the absence of osteocyte apoptosis indicating that this apoptosis is necessary to activate endocortical remodeling following estrogen loss.

Bisphosphonates do not inhibit periosteal bone formation in estrogen deficient animals and allow enhanced bone modeling in response to mechanical loading

The suppressive effects of bisphosphonates (BPs) on bone remodeling are clear yet there is conflicting data concerning the effects of BPs on modeling (specifically formation modeling on the periosteal surface). The normal periosteal expansion that occurs during aging has significant benefits to maintaining/improving the bones' mechanical properties and thus it is important to understand whether BPs affect this bone surface. Therefore, the purpose of this study was to determine the effects of BPs on periosteal bone formation modeling induced by ovariectomy (OVX) and mechanical loading. Six-month-old Sprague-Dawley OVX rats (n=60; 12/group) were administered vehicle, risedronate, alendronate, or zoledronate at doses used clinically for treatment of post-menopausal osteoporosis. Three weeks after initiating BP treatment, all animals underwent in vivo ulnar loading of the right limb every other day for 1 week (3 total sessions). Periosteal surface mineral apposition rate, mineralizing surface, and bone formation rate were determined at the mid-diaphysis of both loaded (right) and non-loaded (left) ulnae. There was no significant effect of any of the BPs on periosteal bone formation parameters compared to VEH-treated animals in the non-loaded limb, suggesting that BP treatment does not compromise the normal periosteal expansion associated with estrogen loss. Mechanical loading significantly increased BFR in the loaded limb compared to the non-loaded limb in all BP-treated groups, with no difference in the magnitude of this effect among the various BPs. Collectively, these data show that BP treatment, at doses comparable to those used for treatment of post-menopausal osteoporosis, (1) does not alter the periosteal formation activity that occurs in the absence of estrogen and (2) allows normal stimulation of periosteal bone formation in response to the anabolic stimulation of mechanical loading.

To stop or not to stop, that is the question

Treatment aimed at preventing fractures should be stopped if evidence of continued antifracture efficacy is lacking, if continued treatment increases bone fragility by adversely affecting matrix properties, and if stopping does not increased bone fragility. Credible evidence of antifracture efficacy beyond 5 years is lacking because of attrition of the cohort originally allocated to treatment or placebo and lack of controls. Prolonged suppression of remodeling is associated with accumulation of microdamage, advanced glycation products and increased tissue mineral density in animal studies but the structural benefits appear to out weight these adverse effects. Atypical minimal trauma subtrochanteric fractures are associated with prolonged treatment in human subjects but these are exceedingly rare. Stopping treatment does result in the reemergence of remodeling, rapidly with some drugs, more slowly with others while fracture rates are increased in poor compliers to treatment. Thus, within the constraints of limited evidence, I infer that stopping therapy is more likely to do net harm than continuing therapy - treatment should be continued in the majority of individuals.

Skeletal accumulation of bisphosphonates: implications for osteoporosis treatment

BACKGROUND

Bisphosphonates (BPs), the gold-standard pharmacological treatment for osteoporosis, are unique in that they become physically bound to the bone matrix and therefore accumulate over time. This skeletal accumulation has important physiological implications that are not completely understood.

OBJECTIVE

To review concepts related to the biological effects of BP accumulation in the skeleton.

METHODS

Articles concerning skeletal accumulation of BP treatment were identified.

RESULTS/CONCLUSIONS

Skeletal accumulation of BP, dictated by both chemical and biological factors, is dose-dependent, differs among skeletal sites and likely differs among the various BPs. Bisphosphonate embedded within the skeletal matrix has lasting biological effects, the results of which have both positive and negative implications for bone remodeling. As alternative anti-remodeling agents gain approval for treatment of osteoporosis, the property of skeletal accumulation will likely be unique to BPs and therefore may be the property that determines the future use of this drug class.