Changes in bone remodeling rate influence the degree of mineralization of bone which is a determinant of bone strength: therapeutic implications

Deciphering the Relevance of Bone ECM Signaling

Bone mineral density, a bone matrix parameter frequently used to predict fracture risk, is not the only one to affect bone fragility. Other factors, including the extracellular matrix (ECM) composition and microarchitecture, are of paramount relevance in this process. The bone ECM is a noncellular three-dimensional structure secreted by cells into the extracellular space, which comprises inorganic and organic compounds. The main inorganic components of the ECM are calcium-deficient apatite and trace elements, while the organic ECM consists of collagen type I and noncollagenous proteins. Bone ECM dynamically interacts with osteoblasts and osteoclasts to regulate the formation of new bone during regeneration. Thus, the composition and structure of inorganic and organic bone matrix may directly affect bone quality. Moreover, proteins that compose ECM, beyond their structural role have other crucial biological functions, thanks to their ability to bind multiple interacting partners like other ECM proteins, growth factors, signal receptors and adhesion molecules. Thus, ECM proteins provide a complex network of biochemical and physiological signals. Herein, we summarize different ECM factors that are essential to bone strength besides, discussing how these parameters are altered in pathological conditions related with bone fragility.

Spirulina Enhances Bone Modeling in Growing Male Rats by Regulating Growth-Related Hormones

In recent years, growth hormone deficiency in children has been treated with hormone therapy despite the possible significant side effects. Therefore, it was deemed beneficial to develop functional foods or dietary supplements for safely improving children's growth. Spirulina platensis is known for its high antioxidant, anti-aging, anti-cancer, and immunity-enhancing properties, as well as its high digestibility and high protein content, but little has been reported about its influence on bone development in children with a normal supply of protein. In this study, we evaluated the effects of spirulina on the bone metabolism and antioxidant profiles of three-week-old growing male rats. The animals were divided into four groups (n = 17 per group) and were fed AIN93G diets with 0% (control), 30% (SP30), 50% (SP50), and 70% (SP70) of casein protein replaced by spirulina, respectively, for seven weeks. We observed that spirulina enhanced bone growth and bone strength by stimulating parathyroid hormone and growth hormone activities, as well its increased antioxidant activity. These results indicate that spirulina provides a suitable dietary supplement and alternative protein source with antioxidant benefits for growth improvement in early developmental stages.

Caveats of bisphosphonate abuse

BACKGROUND

Bisphosphonates (BPs) are the common drugs used for the treatment of postmenopausal osteoporosis. Short term benefits of the BPs are well known. However, there are concerns regarding their long term use. The aim of the study was to analyze the association between atypical femoral fractures and BP misuse/abuse as well as study the outcome of management of these fractures.

MATERIALS AND METHODS

A retrospective study of a prospectively studied patients who presented with atypical femoral fractures between January 2010 and August 2012 and were followed up upto June 2014. The cohort consisted of nine female patients (12 fractures) with an average age of 71 years (range 58-85 years). Analysis was done for the indications, duration of BP use, configuration of associated fractures and method of treatment.

RESULTS

The mean duration of BP use was 6.6 years (range 4-10 years). BP treatment was initiated without sufficient indication and continued without proper review and followup in most cases. Most patients did not followup and continued to consume BPs without any review by the doctors. All patients had prodromal thigh pain of various duration, which was inadequately investigated and managed before the presentation. Two cases with an incomplete fracture and no thigh pain were managed successfully with conservative treatment. The rest were treated by surgery with intramedullary nailing. The average union time was longer and two fractures went into nonunion which required further surgical intervention.

CONCLUSION

Atypical femoral fractures appear to be strongly related to abuse of BPs. Great care is to be exercised at initiation as well as the continuation of BP therapy, and regular review is required. There is a need for improved awareness among physicians about the possibility of such fractures, and interpretation of thigh pain and radiological findings, especially if the patient has been on BPs therapy. Internal fixation for complete fractures and for incomplete fractures with thigh pain is needed. Delayed union is common.

Ulnar fractures with bisphosphonate therapy: a systematic review of published case reports

SUMMARY

A systematic review of eight ulnar fractures in seven patients with bisphosphonate therapy was performed to describe the characteristics and predisposing factors. The proximal ulna is likely to be fractured, especially in the dominant limb of elderly female patients using walking aids after 7 to 15 years of bisphosphonate use.

INTRODUCTION

Long-term bisphosphonate use has been suggested to result in decreased bone remodelling and increased risk of atypical fractures. While the relationship between bisphosphonate use and atypical femoral fractures has been extensively studied, there is relative rarity and unawareness of these fractures in the forearm. We conducted a systematic review of existing case reports to better describe the characteristics and predisposing factors for fractures occurring in patients with bisphosphonate therapy.

METHODS

The systematic review was conducted according to PRISMA guidelines. All studies with ulnar fractures in individuals with history of bisphosphonate use were included, with data extracted and analysed in totality.

RESULTS

Seven patients with eight fractures are included. Predisposing factors include elderly females requiring walking aids. There is a propensity for the proximal ulna to be fractured, especially in the dominant limb used for ambulation or transfer. All patients were on bisphosphonate for 7 to 15 years. All fractures were atraumatic, non-comminuted, transverse in configuration, had localised periosteal or endosteal thickening at the fracture site and generalised cortical thickening of the diaphysis.

CONCLUSION

Ulnar fractures in patients with bisphosphonate therapy demonstrate features similar to those described for atypical femoral fractures, suggesting that these fractures could also possibly be due to bisphosphonate use. However, the ulna appears to be able to tolerate longer periods of alendronate use prior to fracture development. The mechanism and characteristics of these fractures additionally suggest the presence of repetitive stress that accumulates over time due to suppressed bone remodelling in patients on bisphosphonates, eventually resulting in these fractures.

Bone quality: the determinants of bone strength and fragility

Bone fragility is a major health concern, as the increased risk of bone fractures has devastating outcomes in terms of mortality, decreased autonomy, and healthcare costs. Efforts made to address this problem have considerably increased our knowledge about the mechanisms that regulate bone formation and resorption. In particular, we now have a much better understanding of the cellular events that are triggered when bones are mechanically stimulated and how these events can lead to improvements in bone mass. Despite these findings at the molecular level, most exercise intervention studies reveal either no effects or only minor benefits of exercise programs in improving bone mineral density (BMD) in osteoporotic patients. Nevertheless, and despite that BMD is the gold standard for diagnosing osteoporosis, this measure is only able to provide insights regarding the quantity of bone tissue. In this article, we review the complex structure of bone tissue and highlight the concept that its mechanical strength stems from the interaction of several different features. We revisited the available data showing that bone mineralization degree, hydroxyapatite crystal size and heterogeneity, collagen properties, osteocyte density, trabecular and cortical microarchitecture, as well as whole bone geometry, are determinants of bone strength and that each one of these properties may independently contribute to the increased or decreased risk of fracture, even without meaningful changes in aBMD. Based on these findings, we emphasize that while osteoporosis (almost) always causes bone fragility, bone fragility is not always caused just by osteoporosis, as other important variables also play a major role in this etiology. Furthermore, the results of several studies showing compelling data that physical exercise has the potential to improve bone quality and to decrease fracture risk by influencing each one of these determinants are also reviewed. These findings have meaningful clinical repercussions as they emphasize the fact that, even without leading to improvements in BMD, exercise interventions in patients with osteoporosis may be beneficial by improving other determinants of bone strength.

Bisphosphonates and nonhealing femoral fractures: analysis of the FDA Adverse Event Reporting System (FAERS) and international safety efforts: a systematic review from the Research on Adverse Drug Events And Reports (RADAR) project

BACKGROUND

In the United States, hip fracture rates have declined by 30% coincident with bisphosphonate use. However, bisphosphonates are associated with sporadic cases of atypical femoral fracture. Atypical femoral fractures are usually atraumatic, may be bilateral, are occasionally preceded by prodromal thigh pain, and may have delayed fracture-healing. This study assessed the occurrence of bisphosphonate-associated nonhealing femoral fractures through a review of data from the U.S. FDA (Food and Drug Administration) Adverse Event Reporting System (FAERS) (1996 to 2011), published case reports, and international safety efforts.

METHODS

We analyzed the FAERS database with use of the proportional reporting ratio (PRR) and empiric Bayesian geometric mean (EBGM) techniques to assess whether a safety signal existed. Additionally, we conducted a systematic literature review (1990 to February 2012).

RESULTS

The analysis of the FAERS database indicated a PRR of 4.51 (95% confidence interval [CI], 3.44 to 5.92) for bisphosphonate use and nonhealing femoral fractures. Most cases (n = 317) were attributed to use of alendronate (PRR = 3.32; 95% CI, 2.71 to 4.17). In 2008, international safety agencies issued warnings and required label changes. In 2010, the FDA issued a safety notification, and the American Society for Bone and Mineral Research (ASBMR) issued recommendations about bisphosphonate-associated atypical femoral fractures.

CONCLUSIONS

Nonhealing femoral fractures are unusual adverse drug reactions associated with bisphosphonate use, as up to 26% of published cases of atypical femoral fractures exhibited delayed healing or nonhealing.

Pamidronate prevents bone loss and decreased bone strength in adult female and male rats fed an isocaloric low-protein diet

Isocaloric dietary protein deficiency is associated with decreased BMD and bone strength as well as depressed somatotroph and gonadotroph axis. Inhibition of increased bone resorption by the bisphosphonate pamidronate in rats fed an isocaloric low-protein diet fully prevents bone loss and alteration of bone strength.

INTRODUCTION

Isocaloric dietary protein deficiency is associated with decreased BMD and bone strength as well as depressed somatotroph and gonadotroph axis. This negative bone balance is the consequence of increased bone resorption and decreased bone formation. Whether inhibition of bone resorption could prevent low-protein diet-induced bone loss and alteration of biomechanics is not known.

MATERIALS AND METHODS

The effect of the bisphosphonate pamidronate was studied in 5.5-month-old female or 6-month-old male rats pair-fed a control (15% casein) or an isocaloric low-protein (2.5% casein) diet for 19 and 26 weeks, respectively. Pamidronate (0.6 mg/kg) was given subcutaneously 5 days/month for 4 months in female rats or for 5 months in male rats. BMD, microarchitecture, and bone strength were measured at the level of the proximal and midshaft tibia. Urinary deoxypyridinoline excretion, serum osteocalcin, and IGF-I were also measured.

RESULTS

The increase in bone resorption in female rats (+100%) and in male rats (+33%) fed a low-protein diet was prevented by pamidronate treatment. The reduced osteocalcin levels observed in rats fed a low-protein diet were further decreased in both female (-34%) and male (-30%) rats treated with pamidronate. The bone turnover decrease induced by pamidronate prevented bone strength reduction, trabecular bone loss, microarchitecture, and BMD alterations induced by the isocaloric low-protein diet. Similar effects were observed at the level of the midshaft tibia. Significant decrease of plasma IGF-I was observed in rats fed a low-protein diet independently of the pamidronate treatment.

CONCLUSION

In conclusion, inhibition of increased bone resorption in rats fed an isocaloric low-protein diet fully prevents bone loss and alteration of bone strength.

The relations among upper-extremity loading characteristics and bone mineral density changes in young women

The relations among the reaction forces engendered during an upper-extremity dynamic impact-loading exercise (DILE) program and bone mineral density adaptations (DeltaBMD) in the radius were investigated in 24 healthy premenopausal women (mean age = 29 +/- 6 years). Subjects performed DILE 36 cycles/day, 3 days/week for 24 weeks. The exercised arm was allocated randomly to either the dominant or the nondominant limb. In addition, subjects were assigned randomly into either damped or nondamped treatment arms to examine the effects of both higher- and lower-magnitude loading prescriptions. Measurements including anthropometrics, self-reported physical activity levels, hand-grip strength, radial BMD (DEXA, Hologic QDR1500, MA) at the ultradistal radius (UD), distal 1/3 radius (DR), and total distal radius (TOTAL), and exercise-related loading characteristics (impact load, loading rate, and impulse) were recorded at baseline and at 6 months. Simple linear regression models were used to fit the regional BMD changes to the reaction force, changes in hand-grip strength (DeltaGRIP), and changes in body weight (DeltaBW). Findings demonstrated that the damping condition utilized during DILE influenced the relations between loading events and BMD changes. Specifically, none of the reaction-force characteristics significantly predicted changes in BMD in participants performing DILE using the damped condition, whereas, in the nondamped condition, impact load accounted for 58% of the variance in BMD change at DR and 66% of the variance in BMD change at TOTAL. Thresholds of 345 and 285 N of impact force to promote BMD increases at DR and TOTAL, respectively, were obtained from the regression models in the nondamped group. Impulse was also an independent predictor of BMD changes at TOTAL, accounting for 56% of the variance. Neither DeltaGRIP nor DeltaBW significantly predicted DeltaBMD at any radial site. These findings, in young adult women, parallel previous reports identifying significant, regionally specific relations among external loading events and BMD changes in both animal and human models.

Relationship between changes in biochemical markers of bone turnover and BMD to predict vertebral fracture risk

The change in BMD is a poor predictor of vertebral fracture risk after raloxifene treatment. One-year percent change in bone turnover and BMD was used to predict vertebral fracture risk. The percent change in osteocalcin was determined to be a better predictor of vertebral fracture risk than BMD.

INTRODUCTION

The association between baseline BMD and fracture risk is well understood. However, the relationship between changes in BMD and fracture risk is not well defined. It has previously been demonstrated that BMD change was a poor predictor of vertebral fracture risk in raloxifene-treated women, whereas bone turnover markers were significantly associated with fracture risk. In the current analysis, we explore the prediction of vertebral fracture risk using changes in both BMD and bone turnover.

MATERIALS AND METHODS

The Multiple Outcomes of Raloxifene Evaluation (MORE) trial was a randomized, placebo-controlled trial of 7705 women with osteoporosis treated with raloxifene 60 or 120 mg/day for 3 years. Markers of bone turnover were measured in one-third of the study population (n = 2503), and the present analyses include these women. Logistic regression models were constructed using one-year percent changes in BMD and bone turnover and relevant baseline demographics to predict the risk of vertebral fracture with pooled raloxifene therapy at 3 years. All covariates were standardized before modeling to facilitate direct comparisons between changes in BMD and bone turnover.

RESULTS AND CONCLUSION

Prevalent vertebral fracture status (p < 0.0001), baseline lumbar spine BMD (p < 0.0001), and number of years postmenopausal (p = 0.0005) were independent predictors of fracture risk in raloxifene-treated patients. Therapy-by-change in femoral neck BMD (p = 0.02) and therapy-by-change in osteocalcin (OC; p = 0.01) were also significant for all treatment groups, indicating that changes in BMD and OC have different effects on fracture risk for the placebo and pooled raloxifene groups. The final model included significant baseline variables and change in OC (p = 0.01), whereas change in femoral neck BMD was not significant. After adjustment of each significant baseline variable, the percent change in OC was better able to predict the reduction in vertebral fracture risk than the percent change in femoral neck BMD in patients treated with raloxifene.

Response to alendronate in osteoporotic women previously treated with pamidronate

INTRODUCTION

Different bisphosphonates have been shown to increase bone mineral density (BMD) and reduce the risk of fracture in osteoporotic patients. It is unclear how shifting from a treatment with one bisphosphonate to another will influence the evolution of BMD and bone turnover.

METHODS

In the present study, we followed BMD (DXA, Hologic QDR1000) of the lumbar spine (BMDL) and of the total hip (BMDH), bone alkaline phosphatase (Ostase, Hibritech), and urinary collagen cross links (pyridinoline, deoxypyridinoline, Biorad) in 39 patients treated with IV pamidronate (60 mg/3 months) since at least 2 years and who were shifted to oral alendronate (10 mg/day, n=18) or left to IV pamidronate (n=21) for 2 more years.

RESULTS

BMD increased similarly and significantly in both groups after 2 additional years of treatment as compared to baseline (P<0.05, sign test). BMDL: +3.8% in the alendronate group vs +4.1% in the pamidronate group; BMDH: +4.3% in alendronate group vs +3.6% in pamidronate group, There was no significant change in the biological parameters of bone turnover in any group.

CONCLUSION

The increase of BMD with both bisphosphonates in these previously treated patients was as expected after a 2 more years of treatment. Alendronate administration did not induce a larger gain in BMD as compared to cyclic pamidronate. Bone turnover was no longer affected by switching the bisphosphonate treatment.