Positive effects of bisphosphonates on bone and muscle in a mouse model of Duchenne muscular dystrophy

Bisphosphonates attenuate age-related muscle decline in Caenorhabditis elegans

BACKGROUND

Age-related muscle decline (sarcopenia) associates with numerous health risk factors and poor quality of life. Drugs that counter sarcopenia without harmful side effects are lacking, and repurposing existing pharmaceuticals could expedite realistic clinical options. Recent studies suggest bisphosphonates promote muscle health; however, the efficacy of bisphosphonates as an anti-sarcopenic therapy is currently unclear.

METHODS

Using Caenorhabditis elegans as a sarcopenia model, we treated animals with 100 nM, 1, 10, 100 and 500 μM zoledronic acid (ZA) and assessed lifespan and healthspan (movement rates) using a microfluidic chip device. The effects of ZA on sarcopenia were examined using GFP-tagged myofibres or mitochondria at days 0, 4 and 6 post-adulthood. Mechanisms of ZA-mediated healthspan extension were determined using combined ZA and targeted RNAi gene knockdown across the life-course.

RESULTS

We found 100 nM and 1 μM ZA increased lifespan (P < 0.001) and healthspan [954 ± 53 (100 nM) and 963 ± 48 (1 μM) vs. 834 ± 59% (untreated) population activity AUC, P < 0.05]. 10 μM ZA shortened lifespan (P < 0.0001) but not healthspan (758.9 ± 37 vs. 834 ± 59, P > 0.05), whereas 100 and 500 μM ZA were larval lethal. ZA (1 μM) significantly improved myofibrillar structure on days 4 and 6 post-adulthood (83 and 71% well-organized myofibres, respectively, vs. 56 and 34% controls, P < 0.0001) and increased well-networked mitochondria at day 6 (47 vs. 16% in controls, P < 0.01). Genes required for ZA-mediated healthspan extension included fdps-1/FDPS-1 (278 ± 9 vs. 894 ± 17% population activity AUC in knockdown + 1 μM ZA vs. untreated controls, respectively, P < 0.0001), daf-16/FOXO (680 ± 16 vs. 894 ± 17%, P < 0.01) and agxt-2/BAIBA (531 ± 23 vs. 552 ± 8%, P > 0.05). Life/healthspan was extended through knockdown of igdb-1/FNDC5 (635 ± 10 vs. 523 ± 10% population activity AUC in gene knockdown vs. untreated controls, P < 0.01) and sir-2.3/SIRT-4 (586 ± 10 vs. 523 ± 10%, P < 0.05), with no synergistic improvements in ZA co-treatment vs. knockdown alone [651 ± 12 vs. 635 ± 10% (igdb-1/FNDC5) and 583 ± 9 vs. 586 ± 10% (sir-2.3/SIRT-4), both P > 0.05]. Conversely, let-756/FGF21 and sir-2.2/SIRT-4 were dispensable for ZA-induced healthspan [630 ± 6 vs. 523 ± 10% population activity AUC in knockdown + 1 μM ZA vs. untreated controls, P < 0.01 (let-756/FGF21) and 568 ± 9 vs. 523 ± 10%, P < 0.05 (sir-2.2/SIRT-4)].

CONCLUSIONS

Despite lacking an endoskeleton, ZA delays Caenorhabditis elegans sarcopenia, which translates to improved neuromuscular function across the life course. Bisphosphonates might, therefore, be an immediately exploitable anti-sarcopenia therapy.

Strategies to reduce the onset of sleeve gastrectomy associated bone loss (STRONG BONES): Trial design and methods

Background

Despite recognized improvements in obesity-related comorbidities, mounting evidence implicates surgical weight loss in the onset of skeletal fragility. Sleeve gastrectomy (SG) is the most commonly performed bariatric procedure and is associated with 3-7% axial bone loss in the year following surgery. Bisphosphonates are FDA-approved medications for the prevention and treatment of age-related bone loss and may represent a strategy to reduce bone loss following SG surgery.

Methods

The Strategies to Reduce the Onset of Sleeve Gastrectomy Associated Bone Loss (STRONG BONES) trial (NCT04922333) is designed to definitively test whether monthly administration of the bisphosphonate, risedronate, for six months can effectively counter SG-associated bone loss. Approximately 120 middle-aged and older (≥40 years) SG patients will be randomized to six months of risedronate or placebo treatment, with skeletal outcomes assessed at baseline, six, and 12-months post-surgery. The primary outcome of the trial is 12-month change in total hip areal bone mineral density (aBMD), measured by dual energy x-ray absorptiometry (DXA). This will be complemented by DXA-acquired aBMD assessment at other skeletal sites and quantitative computed tomography (QCT) derived changes in bone quality. Change in muscle mass and function will also be assessed, as well as biomarkers of bone health, turnover, and crosstalk, providing mechanistic insight into intervention-related changes to the bone-muscle unit.

Discussion

Results from the STRONG BONES trial have the potential to influence current clinical practice by determining the ability of bisphosphonate use to mitigate bone loss and concomitant fracture risk in middle-aged and older SG patients.

Sarcopenia, osteoporosis and frailty

Muscles and bones are intricately connected tissues displaying marked co-variation during development, growth, aging, and in many diseases. While the diagnosis and treatment of osteoporosis are well established in clinical practice, sarcopenia has only been classified internationally as a disease in 2016. Both conditions are associated with an increased risk of adverse health outcomes such as fractures, dysmobility and mortality. Rather than focusing on one dimension of bone or muscle mass or weakness, the concept of musculoskeletal frailty captures the overall loss of physiological reserves in the locomotor system with age. The term osteosarcopenia in particular refers to the double jeopardy of osteoporosis and sarcopenia. Muscle-bone interactions at the biomechanical, cellular, paracrine, endocrine, neuronal or nutritional level may contribute to the pathophysiology of osteosarcopenia. The paradigm wherein muscle force controls bone strength is increasingly facing competition from a model centering on the exchange of myokines, osteokines and adipokines. The most promising results have been obtained in preclinical models where common drug targets have been identified to treat these conditions simultaneously. In this narrative review, we critically summarize the current understanding of the definitions, epidemiology, pathophysiology, and treatment of osteosarcopenia as part of an integrative approach to musculoskeletal frailty.

Risedronate use may blunt appendicular lean mass loss secondary to sleeve gastrectomy: Results from a pilot randomized controlled trial

Background

Despite robust weight loss and cardiometabolic benefit, lean mass loss following sleeve gastrectomy (SG) confers health risk. Bisphosphonates are a potential therapeutic agent for lean mass maintenance. Thus, our objective was to explore the effect of six months of risedronate (vs placebo) on change in dual energy x-ray absorptiometry (DXA) and computed tomography (CT) derived lean mass metrics in the year following SG.

Methods

24 SG patients were randomized to six months of 150 mg oral risedronate or placebo capsules (NCT03411902). Body composition was assessed at baseline and six months with optional 12-month follow-up using whole-body DXA and CT at the lumbar spine and mid-thigh. Group treatment effects and 95% CIs were generated from a mixed model using contrast statements at six and 12 months, adjusted for baseline values.

Results

Of 24 participants enrolled [55.7±6.7 years (mean±SD), 79% Caucasian, 83% women, body mass index (BMI) 44.7±6.3kg/m2], 21 returned for six-month testing, and 14 returned for 12-month testing. Six-month weight loss was -16.3 kg (-20.0, -12.5) and -20.9 kg (-23.7, -18.1) in the risedronate and placebo groups, respectively (p=.057). Primary analysis at six-months revealed a non-significant sparing of appendicular lean mass in the risedronate group compared to placebo [-1.2 kg (-2.3, -0.1) vs -2.1 kg (-3.0, -1.2)]; p=.20. By 12-months, the risedronate group displayed no change in appendicular lean mass from baseline [-0.5 kg (-1.5, 0.6)]; however, the placebo group experienced significantly augmented loss [-2.9 kg (-3.6, -2.1)].

Conclusion

Pilot data indicate risedronate treatment may mitigate appendicular lean mass loss following SG. Further study is warranted.

Risedronate or Exercise for Lean Mass Preservation During Menopause: Secondary Analysis of a Randomized Controlled Trial

BACKGROUND

The menopause transition is marked by hormonal shifts leading to body composition changes, such as fat mass gain and lean mass loss. Weight-bearing and resistance exercise can help maintain lean mass during the menopause transition; however, uptake is low. Pre-clinical research points to bisphosphonates as also being effective in preventing loss of lean mass. Thus, we sought to investigate whether bisphosphonate therapy can mitigate loss of lean mass and outperform weight-bearing exercise in the years immediately following menopause.

METHODS

Data come from the Heartland Osteoporosis Prevention Study (NCT02186600), where osteopenic, postmenopausal women were randomized to bisphosphonate (n=91), weight-bearing/resistance exercise (n=92), or control (n=93) conditions over a one-year period. Dual energy X-ray absorptiometry (DXA)-derived body composition measures (including total lean mass, total fat mass, lean mass index, and lean mass-to-fat mass ratio) were ascertained at baseline, six, and 12-months. Adherence to risedronate and weight-bearing exercise was defined as the percentage of dosages taken and exercise sessions attended. Intent-to-treat analysis using linear modeling was used to generate treatment effects on body composition. Secondary analysis utilized per-protocol analysis and included adjustment for weight change.

RESULTS

276 women (age: 54.5 years; 83.3% Caucasian; BMI: 25.7 kg/m²) were included in the analyses. 12-month adherence to the risedronate and exercise interventions was 89% and 64%, respectively. Group-by-time interactions were observed for lean mass, revealing exercise (0.43±1.49kg) and risedronate groups (0.31±1.68 kg) gained significantly more lean mass than control (-0.15±1.27 kg) over 12-months. However, after controlling for weight change in secondary analysis, the difference in lean mass change between control and risedronate became non-significant (p=0.059).

CONCLUSIONS

Results suggest both 12 months of oral risedronate and 12 months of weight-bearing exercise may diminish lean mass loss experienced during the menopause transition as compared to control. The lean mass sparing effect for risedronate may be driven by overall weight change.

Retrospective Study of the Effects of Zoledronic Acid on Muscle Mass in Osteoporosis Patients

Purpose

Several osteoporosis drugs can continuously improve bone mass, but the impact on muscle mass is still unknown. This study aims to investigate how zoledronic acid monotherapy affected muscle mass in osteoporosis patients.

Patients and Methods

Patients from an osteoporosis database were divided into two groups in this retrospective cohort, case–control study: zoledronic acid-treated patients (n = 113) and a control group without osteoporosis treatment (n = 118). At four years, appendicular skeletal muscle mass (ASM) and appendicular skeletal muscle mass index (ASMI) were calculated using dual-energy X-ray absorptiometry. The differences in muscle mass between the groups were compared.

Results

At baseline, there was no difference in sex, ASM, ASMI, and bone mineral density between the zoledronic acid treatment group and the control group. The treatment group’s skeletal muscle mass increased by 841 g in ASM and 0.35 kg/m² in ASMI after three years, while decreased in the control group.

Conclusion

This study for the first time demonstrated that that zoledronic acid is beneficial not only to the bone but also to muscle.

Effects of Bisphosphonates on Osteoporosis Induced by Duchenne Muscular Dystrophy: A Prospective Study

OBJECTIVE

Duchenne muscular dystrophy (DMD) is a severe X-linked progressive neuromuscular disease that brings a significantly increased risk of osteoporosis and bone fractures. We prospectively evaluated the effects of oral and intravenous bisphosphonates on the bones of children with DMD.

METHODS

This study included a total of 52 children with DMD. They were divided into zoledronic acid (ZOL), alendronate (ALN), and control groups according to bone mineral density (BMD) and history of fragility fractures. For 2 years, all patients took calcium, vitamin D, and calcitriol. Meanwhile, 17 patients received infusions of ZOL, and 18 patients received ALN. BMD, serum levels of alkaline phosphatase (ALP) and the cross-linked C-telopeptide of type I collagen (β-CTX) were evaluated.

RESULTS

After 24 months of treatment, the percentage changes in lumbar spine BMD were 23.2 ± 9.7% and 23.6 ± 8.8% in the ZOL and ALN groups (all P<.01 vs. baseline). The increases did not differ between the ZOL and ALN groups, but were significantly larger than those of the control group (P<.01). Serum β-CTX and ALP levels, respectively, were decreased by 44.4 ± 18.0% and 31.9 ± 26.7% in the ZOL group and by 36.0 ± 20.3% and 25.8 ± 14.4% in the ALN group (all P<.01 vs. baseline).

CONCLUSION

Zoledronic acid and alendronate had similar protective effects to increase bone mineral density and reduce bone resorption in children with DMD, which were superior to treatment of calcium, vitamin D, and calcitriol.

ABBREVIATIONS

25OHD = 25 hydroxyvitamin D; ALN = alendro-nate; ALP = alkaline phosphatase; ALT = alanine aminotransferase; BMD = bone mineral density; BP = bisphosphonate; Ca = calcium; β-CTX = cross-linked C-telopeptide of type I collagen; DMD = Duchenne muscular dystrophy; FN = femoral neck; GC = glucocorticoid; LS = lumbar spine; ZOL = zoledronic acid.

Burn injury and restoration of muscle function

Burn injury in children results in a systemic inflammatory reaction as well as a stress response. Consequences of these non-specific adaptive responses include resorptive bone loss and muscle catabolism. These adverse events can result in a post-burn fracture rate of approximately 15% and long-term muscle weakness that prolongs recovery. A randomized controlled trial of a single dose of the bisphosphonate pamidronate within the first ten days of burn injury resulted in the prevention of resorptive bone loss and continuous bone accrual. Examining the muscle protein kinetics in pediatric burn patients enrolled in that randomized controlled trial revealed that those who had been given the single dose bisphosphonate experienced preservation of muscle mass and strength. An in vitro study of mouse myoblasts incubated with serum from patients who participated in the randomized controlled study demonstrated that mouse myoblasts exposed to serum from patients given the single dose bisphosphonate exhibited greater myotube diameter than those from burned children given placebo. Moreover, the serum from bisphosphonate treated patients stimulated the protein anabolic pathways and suppressed protein catabolic pathways in these cells. Inasmuch as incubation of the myotubes with an antibody to transforming growth factor beta (TGFβ) rescued myotube size in the cultures with serum from patients who received the placebo to the same magnitude as cultures with serum from patients treated with single dose bisphosphonate, we postulate that post-burn bone resorption liberates muscle catabolic factors which cause muscle wasting. Future uses of bisphosphonates could include studies designed to prevent short-term acute bone resorption in conditions that may result in muscle wasting as well as in short-term interventions in chronic inflammatory conditions which may flare and cause acute bone and muscle loss.

Systemic investigation of bone and muscle abnormalities in dystrophin/utrophin double knockout mice during postnatal development and the mechanisms

The dystrophin-/-/utrophin-/-/ double knockout (dKO-Hom) mouse is a murine model of human Duchenne muscular dystrophy. This study investigated the bone and muscle abnormalities of dKO-Hom mouse and mechanisms. We collected bone and skeletal muscle samples from control mice and three muscular dystrophic mouse models at different ages and performed micro-computer tomography and histological analyses of both bone and skeletal muscle tissues. Serum receptor activator of nuclear factor kappa-Β ligand (RANKL) and sclerostin (SOST) levels, osteoclastogenesis and serum proteomics were also analyzed. Our results indicated that dKO-Hom mice developed skeletal muscle histopathologies by 5 days of age, whereas bone abnormalities developed at 4 weeks of age. Furthermore, our results indicated that the numbers of osteoblasts and osteoclasts were decreased in the proximal tibia and spine trabecular bone of dKO-Hom mice compared to wild-type (WT) mice, which correlated with a significant reduction in serum RANKL levels. The number of tibia cortical osteocytes also decreased, whereas serum SOST levels increased significantly in dKO-Hom mice than WT mice. Osteoblastic number was significantly lower, but osteoclast number increased, in the spine L6 of dKO-Hom mice than WT mice at 6 weeks of age, resulting in a decrease in bone formation and an increase in bone resorption. Serum proteomics results revealed abnormal proteome profiles in dKO-Hom mice compared to control mice. In conclusion, our study elucidated the timing of development of bone and muscle abnormalities. The bone abnormalities in dKO-Hom mice are correlated with lower serum RANKL and higher SOST levels that resulted in dysregulation of osteogenesis and osteoclastogenesis and bone loss.

The role of the musculoskeletal system in post-burn hypermetabolism

Burn injury results in a triad of inter-related adaptive responses: a systemic inflammatory response, a stress response, and a consequent hypermetabolic state which supports the former two. Details of what precisely triggers these responses as well as the sequence of events leading up to these responses are not clear. We review the musculoskeletal effects of burn injury to determine the precise contributions of this system in the generation and sustenance of this post-burn triad as well as the possible effects of pharmacologic intervention in the musculoskeletal response to burns on the resulting hypermetabolism. Inflammation-associated bone resorption liberates calcium, which may either prolong or intensify the systemic inflammatory response. Phosphate and magnesium liberated from bone could contribute to sustaining the increased ATP turnover in skeletal muscle that accompanies burn hypermetabolism. Reduced bone formation resulting from both pro-inflammatory cytokines and elevated endogenous glucocorticoid production results in reduced bone mass and therefore reduced osteocalcin production, which may contribute to reduced glucose uptake by skeletal muscle. Moreover, bone resorption liberates muscle catabolic factors such as transforming growth factor β, which contribute to the muscle wasting of burn hypermetabolism. Pharmacologic intervention with anti-resorptive agents early in the process preserve bone and muscle mass post-burn and future research should address the consequences for the hypermetabolic triad duration and intensity accompanying burn injury.

Pre-treatment with Pamidronate Improves Bone Mechanical Properties in Mdx Mice Treated with Glucocorticoids

Duchenne muscular dystrophy (DMD) is an X-linked disease of progressive muscle deterioration and weakness. Patients with DMD have poor bone health which is partly due to treatment with glucocorticoids, a standard therapy to prolong muscle function that also induces bone loss. Bisphosphonates are used to treat adults at risk of glucocorticoid-induced osteoporosis but are not currently used in DMD patients until after they sustain fractures. In this study, C57BL/10ScSn-mdx mice, a commonly used DMD animal model, received continuous glucocorticoid, prednisone treatment (0.083 mg/day) from 5 to 10 weeks of age. Pre-treatment with the bisphosphonate pamidronate started at 4 weeks of age over a period of 2 weeks or 6 weeks (cumulative dose 8 mg/kg for both) to assess the effectiveness of the two dosing regimens in ameliorating glucocorticoid-induced bone loss. Mdx mice treated with prednisone had improved muscle function that was not changed by pamidronate treatment. Glucocorticoid treatment caused cortical bone loss and decreased cortical bone strength. Both 2 and 6 week pamidronate treatment increased cortical thickness and bone area compared to prednisone-treated Mdx mice, however, only 2 week pamidronate treatment improved the strength of cortical bone compared to that of glucocorticoid-treated Mdx mice. In the trabecular bone, both pamidronate treatments significantly increased the amount of bone, and increased the ultimate load but not the energy to fail. These results highlight the importance of when and how much bisphosphonate is administered prior to glucocorticoid exposure.

Bisphosphonate Treatment Ameliorates Chemotherapy-Induced Bone and Muscle Abnormalities in Young Mice

Chemotherapy is frequently accompanied by several side effects, including nausea, diarrhea, anorexia and fatigue. Evidence from ours and other groups suggests that chemotherapy can also play a major role in causing not only cachexia, but also bone loss. This complicates prognosis and survival among cancer patients, affects quality of life, and can increase morbidity and mortality rates. Recent findings suggest that soluble factors released from resorbing bone directly contribute to loss of muscle mass and function secondary to metastatic cancer. However, it remains unknown whether similar mechanisms also take place following treatments with anticancer drugs. In this study, we found that young male CD2F1 mice (8-week old) treated with the chemotherapeutic agent cisplatin (2.5 mg/kg) presented marked loss of muscle and bone mass. Myotubes exposed to bone conditioned medium from cisplatin-treated mice showed severe atrophy (-33%) suggesting a bone to muscle crosstalk. To test this hypothesis, mice were administered cisplatin in combination with an antiresorptive drug to determine if preservation of bone mass has an effect on muscle mass and strength following chemotherapy treatment. Mice received cisplatin alone or combined with zoledronic acid (ZA; 5 μg/kg), a bisphosphonate routinely used for the treatment of osteoporosis. We found that cisplatin resulted in progressive loss of body weight (-25%), in line with reduced fat (-58%) and lean (-17%) mass. As expected, microCT bone histomorphometry analysis revealed significant reduction in bone mass following administration of chemotherapy, in line with reduced trabecular bone volume (BV/TV) and number (Tb.N), as well as increased trabecular separation (Tb.Sp) in the distal femur. Conversely, trabecular bone was protected when cisplatin was administered in combination with ZA. Interestingly, while the animals exposed to chemotherapy presented significant muscle wasting (~-20% vs. vehicle-treated mice), the administration of ZA in combination with cisplatin resulted in preservation of muscle mass (+12%) and strength (+42%). Altogether, these observations support our hypothesis of bone factors targeting muscle and suggest that pharmacological preservation of bone mass can benefit muscle mass and function following chemotherapy.

Targeting the Muscle-Bone Unit: Filling Two Needs with One Deed in the Treatment of Duchenne Muscular Dystrophy

PURPOSE OF REVIEW

In Duchenne muscular dystrophy (DMD), the progressive skeletal and cardiac muscle dysfunction and degeneration is accompanied by low bone mineral density and bone fragility. Glucocorticoids, which remain the standard of care for patients with DMD, increase the risk of developing osteoporosis. The scope of this review emphasizes the mutual cohesion and common signaling pathways between bone and skeletal muscle in DMD.

RECENT FINDINGS

The muscle-bone interactions involve bone-derived osteokines, muscle-derived myokines, and dual-origin cytokines that trigger common signaling pathways leading to fibrosis, inflammation, or protein synthesis/degradation. In particular, the triad RANK/RANKL/OPG including receptor activator of NF-kB (RANK), its ligand (RANKL), along with osteoprotegerin (OPG), regulates bone matrix modeling and remodeling pathways and contributes to muscle pathophysiology in DMD. This review discusses the importance of the muscle-bone unit in DMD and covers recent research aimed at determining the muscle-bone interactions that may eventually lead to the development of multifunctional and effective drugs for treating muscle and bone disorders regardless of the underlying genetic mutations in DMD.

Effect of 25-HydroxyVitamin D Deficiency and Its Interaction with Prednisone Treatment on Musculoskeletal Health in Growing Mdx Mice

Duchenne muscular dystrophy (DMD) results from genetic mutations of the gene encoding dystrophin, leading to muscle inflammation and degeneration that is typically treated with glucocorticoids. DMD and its treatment with glucocorticoids result in poor bone health and high risk of fractures. Insufficient levels of 25-hydroxyvitamin D (25-hydroxy D) that may contribute to weakened bone are routinely found in DMD patients. To determine the effect of 25-hydroxy D deficiency, this study examined the effects of low vitamin D dietary intake with and without glucocorticoids on the musculoskeletal system of the Mdx mouse model of DMD. At 10 weeks of age, Mdx mice on control diet had low trabecular bone mineral density of distal femurs and lumbar vertebrae with increased osteoclast numbers compared to wild-type mice. Low vitamin D intake resulted in 25-hydroxy D deficiency but had no effect on trabecular or cortical bone. Cortical bone loss and bone weakness were induced by glucocorticoids while they improved muscle grip strength in Mdx mice. 25-hydroxy D deficiency did not result in any significant effects on growing bone or muscle in the Mdx mice. In combination with glucocorticoid treatment, low 25-hydroxy D resulted in no change in cortical bone mineral density but bone ductility was significantly increased suggesting lower bone mineralization.

Preventing muscle wasting by osteoporosis drug alendronate in vitro and in myopathy models via sirtuin-3 down-regulation

BACKGROUND

A global consensus on the loss of skeletal muscle mass and function in humans refers as sarcopenia and cachexia including diabetes, obesity, renal failure, and osteoporosis. Despite a current improvement of sarcopenia or cachexia with exercise training and supportive therapies, alternative and specific managements are needed to discover for whom are unable or unwilling to embark on these treatments. Alendronate is a widely used drug for osteoporosis in the elderly and postmenopausal women. Osteopenic menopausal women with 6 months of alendronate therapy have been observed to improve not only lumbar bone mineral density but also handgrip strength. However, the effect and mechanism of alendronate on muscle strength still remain unclear. Here, we investigated the therapeutic potential and the molecular mechanism of alendronate on the loss of muscle mass and strength in vitro and in vivo.

METHODS

Mouse myoblasts and primary human skeletal muscle-derived progenitor cells were used to assess the effects of low-dose alendronate (0.1-1 μM) combined with or without dexamethasone on myotube hypertrophy and myogenic differentiation. Moreover, we also evaluated the effects of low-dose alendronate (0.5 and 1 mg/kg) by oral administration on the limb muscle function and morphology of mice with denervation-induced muscle atrophy and glycerol-induced muscle injury.

RESULTS

Alendronate inhibited dexamethasone-induced myotube atrophy and myogenic differentiation inhibition in mouse myoblasts and primary human skeletal muscle-derived progenitor cells. Alendronate significantly abrogated dexamethasone-up-regulated sirtuin-3 (SIRT3), but not SIRT1, protein expression in myotubes. Both SIRT3 inhibitor AKG7 and SIRT3-siRNA transfection could also reverse dexamethasone-up-regulated atrogin-1 and SIRT3 protein expressions. Animal studies showed that low-dose alendronate by oral administration ameliorated the muscular malfunction in mouse models of denervation-induced muscle atrophy and glycerol-induced muscle injury with a negative regulation of SIRT3 expression.

CONCLUSIONS

The putative mechanism by which muscle atrophy was improved with alendronate might be through the SIRT3 down-regulation. These findings suggest that alendronate can be a promising therapeutic strategy for management of muscle wasting-related diseases and sarcopenia.

The Role of Bone Secreted Factors in Burn-Induced Muscle Cachexia

PURPOSE OF REVIEW

Burn injury results in resorptive bone loss, failure to make new bone, and muscle protein breakdown resulting in cachexia. The purpose of this review is to examine the relationship between bone loss and muscle atrophy in burn injury with a view to understanding the process at work and how it may apply to other conditions that have similar features.

RECENT FINDINGS

We present data suggesting that the use of bisphosphonates in the first 10 days following the burn prevents not only the resorptive bone loss but also the muscle wasting. While an extra-osseous effect of bisphosphonates remains possible, existing evidence points to a paracrine effect of bone on maintenance of muscle mass and strength. Proposed paracrine factors produced by bone include prostaglandin E2 and components of the Wnt signaling pathway. TGFβ may be a bone paracrine factor that causes oxidative damage to muscle. In the light of the pattern of evidence, burn patients suffer acute resorptive bone loss and muscle wasting. This is likely due to the effects of inflammatory cytokines and endogenous glucocorticoid production in exacerbating oxidative stress. Early use of bisphosphonates can maintain bone mass leading to a paracrine effect of bone in the maintenance of muscle mass, although one cannot completely discount a direct effect of bisphosphonate on muscle. Because investigators report this relationship in a variety of conditions in addition to burns, physicians should seriously consider the early use of bisphosphonates to maintain bone and muscle mass in a variety of neuromuscular and skeletal diseases.

Zoledronic acid in pediatric metabolic bone disorders

Zoledronic acid (ZA), a highly potent intravenous bisphosphonate (BP), has been increasingly used in children with primary and secondary osteoporosis due to its convenience of shorter infusion time and less frequent dosing compared to pamidronate. Many studies have also demonstrated beneficial effects of ZA in other conditions such as hypercalcemia of malignancy, fibrous dysplasia (FD), chemotherapy-related osteonecrosis (ON) and metastatic bone disease. This review summarizes pharmacologic properties, mechanism of action, dosing regimen, and therapeutic outcomes of ZA in a variety of metabolic bone disorders in children. Several potential novel uses of ZA are also discussed. Safety concerns and adverse effects are also highlighted.

Enhanced Energetic State and Protection from Oxidative Stress in Human Myoblasts Overexpressing BMI1

The Polycomb group gene BMI1 is essential for efficient muscle regeneration in a mouse model of Duchenne muscular dystrophy, and its enhanced expression in adult skeletal muscle satellite cells ameliorates the muscle strength in this model. Here, we show that the impact of mild BMI1 overexpression observed in mouse models is translatable to human cells. In human myoblasts, BMI1 overexpression increases mitochondrial activity, leading to an enhanced energetic state with increased ATP production and concomitant protection against DNA damage both in vitro and upon xenografting in a severe dystrophic mouse model. These preclinical data in mouse models and human cells provide a strong rationale for the development of pharmacological approaches to target BMI1-mediated mitochondrial regulation and protection from DNA damage to sustain the regenerative potential of the skeletal muscle in conditions of chronic muscle wasting.

Prophylactic pamidronate partially protects from glucocorticoid-induced bone loss in the mdx mouse model of Duchenne muscular dystrophy

Glucocorticoids are extensively used to treat patients with Duchenne muscular dystrophy because of their ability to delay muscle damage, prolong ambulation and extend life. However, use of glucocorticoids significantly increases bone loss, fragility and fractures. To determine if antiresorptive bisphosphonates could prevent the effects of glucocorticoids on bone quality, we used dystrophic mdx mice treated with the glucocorticoid prednisone during 8weeks of rapid bone growth from 5 to 13weeks of age and treated some mice with the bisphosphonate pamidronate during the first two weeks of prednisone administration. Prednisone reduced long bone growth, decreased cortical bone thickness and area and decreased the strength of the femurs. Pamidronate treatment protected mice from cortical bone loss but did not increase bone strength. The combination of prednisone and pamidronate inhibited remodeling of metaphyseal trabecular bone with large numbers of trabeculae containing remnants of calcified cartilage. Prednisone improved muscle strength in the mdx mice and decreased serum creatine kinase with evidence of improved muscle histology and these effects were maintained in mice treated with pamidronate.

Elevated Gα11 expression in osteoblast lineage cells promotes osteoclastogenesis and leads to enhanced trabecular bone accrual in response to pamidronate

Osteoblastic cells indirectly induce osteoclastogenesis in the bone microenvironment by expressing paracrine factors such as RANKL and M-CSF, leading to increased bone resorption. These cytokines can be regulated by a variety of intracellular pathways, which include G protein-coupled receptor signaling. To explore how enhanced signaling of the Gαq/11 pathway in osteoblast lineage cells may mediate osteoclast formation, we cocultured wild-type (WT) preosteoclasts with BMSCs derived from either WT or transgenic mice with osteoblast-specific overexpression of Gα11 (G11-Tg). G11-Tg cocultures had elevated osteoclast numbers with greater resorptive capacity and increased expression of Rankl, Rankl:Opg (osteoprotegerin), and M-csf compared with cocultures with WT BMSCs. As well, cocultures with G11-Tg BMSCs required a higher concentration of OPG to inhibit osteoclast formation and less angiotensin II to increase osteoclast size. These indicate that G11-Tg osteoblasts drive the increased osteoclast formation and osteopenia seen in G11-Tg mice. Pamidronate treatment of G11-Tg mice restored the trabecular bone loss phenotype, as bone mineral density, bone volume, trabecular number, separation, and expressions of osteoblastic and osteoclastic genes were comparable with WT parameters. These changes were characterized by enhanced accumulation of calcified cartilage in trabecular bone, demonstrating that resorption of the cartilaginous intermediate by osteoclasts is more affected by bisphosphonate treatment in G11-Tg mice. In conclusion, overexpression of Gα11 in osteoblastic cells promotes osteoclastogenesis by upregulation of Rankl and M-csf and bone loss by increased osteoclast resorption of the trabecular bone and cartilaginous matrix.