Beta-blocker use, bone mineral density, and fracture risk in older women: results from the Epidemiologie de l'Osteoporose prospective study

Hypertension and Dental Implants: A Systematic Review and Meta-Analysis

PURPOSE

The aim of the present systematic review was to investigate the influence of hypertension on the dental implant failure rate.

METHODS

An electronic search was undertaken in four databases, plus a manual search of journals. The I2 statistic was used to check heterogeneity and the inverse-variance method was used for the meta-analysis. The estimate of relative effect for dichotomous outcome was expressed as an odds ratio (OR).

RESULTS

The review included 24 publications. There were 4874 implants (257 failures) placed in hypertensive patients and 16,192 implants (809 failures) placed in normotensive patients. A pairwise meta-analysis showed that implants in hypertensive patients did not have a higher risk of failure than implants placed in normotensive patients (OR 1.100, p = 0.671). The log OR of implant failure between hypertensive and normotensive patients did not significantly change with the follow-up time (p = 0.824).

CONCLUSIONS

This review suggests that implants in hypertensive patients do not present higher odds of failure in comparison to normotensive patients. However, further research on this topic, with the use of more rigorous criteria to diagnose patients as being hypertensive, as well as clearer information about the pharmacological management of the condition in the patients, is recommended.

The effects of intraperitoneal metoprolol administration on healing of bone defects in rat tibia: a pilot study

OBJECTIVES

Metoprolol is a cardioselective competitive beta-1 adrenergic receptor antagonist with antihypertensive properties, devoid of intrinsic sympathomimetic activity. Various studies have suggested the effect of beta-blockers on bone remodeling. We aimed to investigate whether metoprolol affects bone remodeling by altering anti-inflammatory and pro-inflammatory cytokines.

MATERIALS AND METHODS

Surgical defects of 3 mm diameter were created in tibiae of 72 Sprague-Dawley rats. Rats were randomly assigned to a control group without metoprolol treatment (n = 36), and a test group treated with 0.1 mg/kg/day metoprolol (n = 36). Six rats from each group were sacrificed at days 0, 1, 3, 5, 7, and 14. The percentages of cells, which showed positive immunohistochemical staining for IL-1β, IL-6, IL-10, and RANKL, were assessed in the defect area. Differences in percentages of stained cells within each of the test and control groups over various time intervals were tested using one-way ANOVA test. A P value of < 0.05 was considered statistically significant.

RESULTS

No significant differences in IL-1β, IL-10, IL-6, and RANKL expressions were found between test and control groups at the same interval. Significant reduction was observed at different time intervals in the same group (P < 0.05).

CONCLUSION

Metoprolol did not reduce bone-active cytokine: IL-1β, IL-6, and RANKL. It also did not elevate IL-10 expression levels. Thus, it does not appear to decrease osteoclastogenesis.

CLINICAL RELEVANCE

Results from this animal model help us understand any effect of metoprolol on bone healing by potential contribution to different real-world clinical research.

Atherosclerosis and Osteoporosis. Common Targets for the Effects of Cardiovascular and Anti-osteoporotic Drugs (Part I). The Effect of Cardiovascular Drugs on Bone Strength

Daily use of antihypertensive and lipid-lowering drugs in clinical practice dictates the need for knowledge of their pleiotropic effects. The article presents the results of studies of the effect of cardiovascular drugs, such as statins, beta-blockers, ACE inhibitors, diuretics, calcium antagonists and nitrates on bone mineral density and fractures associated with osteoporosis. The mechanisms of action of drugs on bone mass, markers of bone metabolism, the frequency of fractures in osteoporosis are discussed. Most studies show that the use of cardiac drugs along with a positive effect on the vascular wall, slow bone resorption and increase bone mass. Knowledge of the additional effect on bone metabolism of drugs used in cardiovascular diseases allows to choose an adequate therapy and improve the prognosis of both diseases.

Impact of the Autonomic Nervous System on the Skeleton

It is from the discovery of leptin and the central nervous system as a regulator of bone remodeling that the presence of autonomic nerves within the skeleton transitioned from a mere histological observation to the mechanism whereby neurons of the central nervous system communicate with cells of the bone microenvironment and regulate bone homeostasis. This shift in paradigm sparked new preclinical and clinical investigations aimed at defining the contribution of sympathetic, parasympathetic, and sensory nerves to the process of bone development, bone mass accrual, bone remodeling, and cancer metastasis. The aim of this article is to review the data that led to the current understanding of the interactions between the autonomic and skeletal systems and to present a critical appraisal of the literature, bringing forth a schema that can put into physiological and clinical context the main genetic and pharmacological observations pointing to the existence of an autonomic control of skeletal homeostasis. The different types of nerves found in the skeleton, their functional interactions with bone cells, their impact on bone development, bone mass accrual and remodeling, and the possible clinical or pathophysiological relevance of these findings are discussed.

Effects of Leptin on the Skeleton

Leptin originates in adipocytes, including those in bone marrow, and circulates in concentrations 20 to 90 times higher than those in the cerebrospinal fluid. It has direct anabolic effects on osteoblasts and chondrocytes, but it also influences bone indirectly, via the hypothalamus and sympathetic nervous system, via changes in body weight, and via effects on the production of other hormones (e.g., pituitary). Leptin's role in bone physiology is determined by the balance of these conflicting effects. Reflecting this inconsistency, the leptin-deficient mouse has reduced length and bone mineral content of long bones but increased vertebral trabecular bone. A consistent bone phenotype in human leptin deficiency has not been established. Systemic leptin administration in animals and humans usually exerts a positive effect on bone mass, and leptin administration into the cerebral ventricles usually normalizes the bone phenotype in leptin-deficient mice. Reflecting the role of the sympathetic nervous system in mediating the central catabolic effects of leptin on the skeleton, β-adrenergic agonists and antagonists have major effects on bone in mice, but this is not consistently seen in humans. The balance of the central and peripheral effects of leptin on bone remains an area of substantial controversy and might vary between species and according to other factors such as body weight, baseline circulating leptin levels, and the presence of specific pathologies. In humans, leptin is likely to contribute to the positive relationship observed between adiposity and bone density, which allows the skeleton to respond appropriately to changes in soft tissue mass.

The Time Point-Specific Effect of Beta-Adrenergic Blockade in Attenuating High Fat Diet-Induced Obesity and Bone Loss

We aimed to clarify the key factor determining the effect of beta blocker attenuating high fat diet- induced obesity and bone loss. Six-week-old C57BL/6 male mice were assigned to groups reflecting different relative onset of obesity and beta blocker administration, different diet (control vs. high fat), and treatment (vehicle vs. beta blocker: propranolol). Mice in Group 1 were fed a control diet (CON) or high fat diet (HIGH) with vehicle or propranolol for 12 weeks. Mice in Group 2 were fed a CON or HIGH without pharmaceutical treatment for the first 12 weeks, followed by another 12 weeks of treatment with vehicle or propranolol. Mice in Group 3 were fed a CON without pharmaceutical treatment for the first 12 weeks, followed by stratification into diet-based subgroups and another 12 weeks of treatment with vehicle or propranolol. Propranolol attenuated the HIGH-induced increase in body weight/fat mass in Group 1 mice and in Group 3 mice, but not in Group 2 mice. Propranolol mitigated HIGH-induced reduction in femoral trabecular bone mineral density and bone architecture deterioration in Group 1 mice but not in Group 2 mice. HIGH feeding in Group 3 did not compromise skeletal integrity. Taken together, propranolol attenuates HIGH-induced body weight increases while weight gain is in progress but not once obesity has already been established. HIGH feeding during the growth period results in compromised bone mass/architecture; which can be attenuated by propranolol administration during the growth period, but not by propranolol administration after obesity has already been established.

The Impact of Antihypertensive Medications on Bone Mineral Density and Fracture Risk

PURPOSE OF REVIEW

This review summarizes the impact of thiazide diuretics on fracture risk in older hypertensive individuals.

RECENT FINDINGS

We performed a post hoc evaluation of the Antihypertensive and Lipid-Lowering Treatment to Prevent Heart Attack Trial, a randomized, prospective, double blind hypertension study comparing a thiazide-like diuretic, a calcium channel blocker (CCB), and an angiotensin converting enzyme inhibitor (ACEi). We examined the risk of hip and pelvic fractures during the in-trial period (n = 22,180 participants; mean 4.9-year follow-up) and during the post-trial period using national data bases (n = 16,622 participants) (mean total follow-up 7.8 years). During the trial, participants randomized to the thiazide diuretic versus the CCB or the ACEi had a lower risk of fracture on adjusted analyses (HR 0.79 [95% CI, 0.63, 0.98], p = 0.04). Risk of fracture was significantly lower in participants randomized to the diuretic as compared to those randomized to the ACEi (HR 0.75 [95% CI, 0.58, 0.98]; p = 0.04), but not significantly different compared to the CCB (HR 0.87 [95% CI, 0.71, 1.09]; p = 0.17). Over the entire trial and post-trial period of follow-up, the cumulative incidence of fractures was non-significantly lower in participants assigned to the diuretic vs assignment to the ACEi or the CCB (HR 0.87 [0.74-1.03], p = 0.10) and versus each medication separately. These findings establish a benefit for thiazide diuretic treatment for the prevention of fractures versus other commonly used antihypertensive medications using prospective, randomized data. The effects of the thiazide diuretic on bone appear to be long lasting.

Long-term Effects of Antihypertensive Drug Use and New-onset Osteoporotic Fracture in Elderly Patients: A Population-based Longitudinal Cohort Study

Background:

Antihypertensive drugs have been linked to new-onset osteoporotic fracture (NOF), and different classes of antihypertensive drugs may alter the risk for the development of NOF; however, the classic effect of different antihypertensive drugs on the development of NOF in the elderly has not been well studied during long-term follow-up.

Methods:

In this study, we investigated the association between different classic antihypertensives and the development of NOF in the elderly. This was a longitudinal cohort study performed using data from claim forms submitted to the Taiwan Bureau of National Health Insurance in Central Taiwan, China including case patients with NOF aged 65–80 years from January 2002 to December 2012 and non-NOF controls. Prescriptions for antihypertensives before the index date were retrieved from a prescription database. We estimated the hazard ratios (HRs) of NOF associated with antihypertensive use. Non-NOF controls served as the reference group.

Results:

A total of 128 patients with NOF were identified from among 1144 patients with hypertension during the study period. The risk of NOF after adjusting age, sex, comorbidities, and concurrent medications was higher among the users of angiotensin-converting enzyme (ACE) inhibitors (HR, 1.64; 95% confidence interval [CI], 1.01–2.66) than among nonusers. Patients who took calcium channel blockers (CCBs) (HR, 0.70; 95% CI, 0.49–0.99) were at a lower risk of developing NOF than nonusers. Loop diuretics, thiazide diuretics, angiotensin receptor blocker, beta-blocker, and alpha-blocker were not associated with the risk of NOF.

Conclusions:

Elderly with hypertension who take CCBs are at a lower risk of NOF and that the use of ACE inhibitors was associated with a significantly increased risk of developing NOF during the 11-year follow-up.

Body mass index and the risk of low bone mass-related fractures in women compared with men: A PRISMA-compliant meta-analysis of prospective cohort studies

BACKGROUND

Body mass index (BMI) is inconsistently associated with the progression of low bone mass-related fractures. We conducted a systematic review and meta-analysis to summarize the evidence regarding the relationship between BMI and the risk of fracture in men and women separately. Furthermore, we analyzed the association between BMI and fracture risk in women compared with men.

METHODS

PubMed, EmBase, and the Cochrane Library were searched up to November 2015 to identify prospective cohort studies of low bone mass-related fractures. Prospective cohort studies that reported effect estimates of fracture risk for different BMI categories compared to normal weight were included. Relative risk (RR) and the ratio of relative risk (RRR) were calculated using a random-effect model to measure the relationship between BMI and fracture risk.

RESULTS

We analyzed 37 cohorts (32 articles), which included a total of 506,004 women and 118,372 men; overall, 38,200 incident cases were reported. Overall, a lower BMI was not associated with fracture risk in men (RR: 1.50, 95% confidence interval [CI]: 1.00-2.26; P = 0.051) or women (RR: 1.25, 95% CI: 0.97-1.62; P = 0.083). Although a higher BMI might play a beneficial impact in men (RR: 0.80, 95% CI: 0.69-0.93; P = 0.003), it has little effect in women (RR: 0.91, 95% CI: 0.74-1.11; P = 0.343). In addition, an increase in BMI by 5 kg/m decreased the risk of fractures in men (RR: 0.90, 95% CI: 0.83-0.98; P = 0.017) and women (RR: 0.85, 95% CI: 0.81-0.89; P < 0.001). Finally, there was no evidence of a sex difference in the RR for fractures between participants with different BMI categories compared with those with normal BMI. Finally, gender did not affect the risk of fracture for any category of BMI values.

CONCLUSION

Higher BMI may affect the risk of fractures regardless of the sex. This association may be due to the interaction between the participants' BMI and their bone mass density.

Clonidine increases bone resorption in humans

SUMMARY

Inhibition of sympathetic signaling to bone reduces bone resorption in rodents. In contrast, we show that pharmacological reduction of the sympathetic tone increases bone resorption in humans in vivo. This effect does not appear to be mediated via a direct pharmacological effect on the osteoclast.

INTRODUCTION

Inhibition of sympathetic signaling to bone reduces bone resorption in rodents. It is uncertain whether a similar role for the sympathetic nervous system exists in humans. The sympathetic tone can be reduced by clonidine, which acts via alpha-2-adrenergic receptors in the brainstem. Our objective was to determine the effect of clonidine on bone turnover in humans.

METHODS

The acute effect of a single oral dose of 0.3 mg clonidine on serum bone turnover markers (C-terminal cross-linking telopeptides of collagen type I (CTx), a marker for bone resorption, and procollagen type 1 N propeptide (P1NP), a marker for bone formation) was determined in a randomized crossover design in 12 healthy volunteers, aged 18-70 years. In addition, we assessed the effect of clonidine on the number of tartrate-resistant acid phosphatase-positive multinucleated cells (TRAcP(+) MNCs) and bone resorption.

RESULTS

CTx concentrations increased after clonidine treatment compared to the control condition (p = 0.035). P1NP concentrations were not affected by clonidine (p = 0.520). In vitro, clonidine had no effect on the number of TRAcP(+) MNCs (p = 0.513) or on bone resorption (p = 0.996).

CONCLUSIONS

We demonstrated that clonidine increases bone resorption in humans in vivo. This effect does not appear to be mediated via a direct effect on the osteoclast.

Endocrinology of bone/brain crosstalk

Bone metabolism is regulated by the action of two skeletal cells: osteoblasts and osteoclasts. This process is controlled by many genetic, hormonal and lifestyle factors, but today more and more studies have allowed us to identify a neuronal regulation system termed 'bone-brain crosstalk', which highlights a direct relationship between bone tissue and the nervous system. The first documentation of an anatomic relationship between nerves and bone was made via a wood cut by Charles Estienne in Paris in 1545. His diagram demonstrated nerves entering and leaving the bones of a skeleton. Later, several studies were conducted on bone innervation and, as of today, many observations on the regulation of bone remodeling by neurons and neuropeptides that reside in the CNS have created a new research field, that is, neuroskeletal research.

Intensive blood pressure control, falls, and fractures in patients with type 2 diabetes: the ACCORD trial

BACKGROUND

There are few rigorous studies to confirm or refute the commonly cited concern that control of blood pressure to lower thresholds may result in an increased risk of falls and fractures.

OBJECTIVE

To compare falls and fractures in participants with type 2 diabetes in the intensive (targeting a systolic blood pressure of < 120 mmHg) and standard (targeting a systolic blood pressure of < 140 mmHg) blood pressure control arms of the Action to Control Cardiovascular Risk in Diabetes (ACCORD) randomized trial (N = 4,733).

PARTICIPANTS

A subset of 3,099 participants self-reported annually on the occurrence of falls and non-spine fractures. Fractures were centrally adjudicated.

MAIN MEASURES

The incidence of falls in the two treatment groups was compared using a random-effects negative binomial model, and fracture risk was compared using Cox proportional hazards models.

KEY RESULTS

At enrollment in both groups, the mean age was 62 years, 44% were women, 25% were Black, and mean blood pressure was 138/75 mmHg. During follow-up, all classes of medications, particularly thiazide diuretics, were more commonly prescribed in the intensive group. After 1 year of follow-up, the mean systolic blood pressure was 133 ± 15 mmHg in the standard group and 119 ± 14 mmHg in the intensive group. The adjusted rate of falls did not differ in the intensive and standard groups (62.2/100 person-years vs. 74.1/100 person-years, RR = 0.84, 95% CI 0.54-1.29, p = 0.43). The risk of non-spine fractures was nonsignificantly lower in the intensive than in the standard blood pressure group (HR 0.79, 95% CI 0.62-1.01, p = 0.06).

CONCLUSIONS

We conclude that intensive antihypertensive treatment that lowered mean systolic blood pressure to below 120 mmHg was not associated with an increased risk of falls or non-spine fractures in patients age 40 to 79 years with type 2 diabetes.

Relationship between autonomic nervous system activity and bone mineral density in non-medicated perimenopausal women

The autonomic nervous system (ANS) has attracted attention as a regulator of bone remodeling and the effects of beta-blockers on the prevention of osteoporosis have been studied. However, results are as yet inconclusive and the physiological role of the ANS in bone metabolism has not been clarified. Thus, we investigated the relationship between bone mineral density (BMD) and ANS activity in non-medicated perimenopausal women. ANS activity was evaluated by power spectral analysis of heart rate variability, and overall ANS activity and the balance between sympathetic and parasympathetic nervous activities (SNS and PNS) were quantified. Pre- and postmenopausal subjects were divided into higher or lower overall ANS activity groups, and were also divided into SNS- and PNS-dominant groups. BMD (percentage of young adult mean) was significantly higher in the higher overall ANS group than in the lower group (112.2 ± 16.2 % vs 99.7 ± 14.8 %, p < 0.05) of premenopausal subjects, but not in postmenopausal subjects (91.5 ± 15.9 % vs 91.0 ± 14.9 %). BMD was significantly higher in the SNS-dominant group than in the PNS-dominant group (94.1 ± 16.3 % vs 88.4 ± 18.8 %, p < 0.05) of postmenopausal subjects, but not in the premenopausal subjects (103.5 ± 18.4 % vs. 107.2 ± 14.6 %). Our study revealed that ANS influences bone metabolism under physiological conditions. Thus, it appears to be worthwhile to introduce ANS activity evaluation into the management of bone health in perimenopausal women.

Long-term effects of antihypertensive medications on bone mineral density in men older than 55 years

Introduction

In this study, we investigated the effects of long-term antihypertensive treatment with calcium channel blockers or beta blockers on the bone mineral density of maxilla, as determined by cone-beam computed tomography (CBCT).

Material and methods

This retrospective study was conducted on CBCT images of men older than 55 years who had received different dental indications. Data were grouped into three categories according to the antihypertensive medication history of the patients: group A included patients who had been taking beta-blocker treatment for more than 5 years, group B included patients who had been taking calcium channel blocker treatment for more than 5 years, and the control group included patients who had never used any hypertensive medications before.

Results

Statistically significant differences were observed between the beta blocker and calcium channel blocker groups.

Conclusion

In hypertension treatment, beta blockers may be preferred to calcium channel blockers in patients at high risk for osteoporosis and bone resorption.

β-Adrenergic receptor antagonists and fracture risk: a meta-analysis of selectivity, gender, and site-specific effects

By meta-analysis, the risk of fracture was 15% lower in patients treated with β-adrenergic blockers compared to controls independent of gender, fracture site, and dose. This might be attributable to β1-selective blockers.

INTRODUCTION

The aim of this study is to determine by meta-analysis whether β-adrenergic blockers (BBs) reduce fracture risk and whether the effect, if demonstrable, is dependent upon selectivity, dose, gender, or fracture site.

METHODS

A literature search was performed in electronic databases MEDLINE, EMBASE, and reference sections of relevant articles to identify eligible studies. Adjusted estimates of fracture risk effect size (ES) were pooled across studies using fixed or random-effects (RE) meta-analysis as appropriate. Dose-related effects were evaluated using meta-regression. To explore the relative efficacy of β1-selective blockers in comparison to nonselective BBs, adjusted indirect comparison was performed.

RESULTS

A total of 16 studies (7 cohort and 9 case-control studies), involving 1,644,570 subjects, were identified. The risk of any fracture was found to be significantly reduced in subjects receiving BBs as compared to control subjects (16 studies, RE pooled ES = 0.86, 95% CI 0.78-0.93; I(2) = 87 %). In a sensitivity analysis limited to those studies deemed to be most robust, the BB effect to reduce fracture risk was sustained (four studies, pooled ES = 0.79, 95% CI 0.67-0.94; I(2) = 96%). The risk of a hip fracture was lower in both women and men receiving BBs (women: pooled ES = 0.86, 95% CI 0.80-0.91; I(2) = 1% and men: pooled ES = 0.80, 95% CI 0.71-0.90; I(2) = 0%). Similar risk reductions were found for clinical vertebral and forearm fractures, although statistical significance was not reached. The reduction in risk did not appear to be dose-related (test for a linear trend p value 0.150). Using adjusted indirect comparisons, it was estimated that β1-selective agents were significantly more effective than nonselective BBs in reducing the risk of any fracture (six studies, β1-selective blockers vs. nonselective BBs: RE pooled ES = 0.82, 95% CI = 0.69-0.97).

CONCLUSIONS

The findings suggest that the risk of fracture is approximately 15% lower in patients treated with BBs compared to controls independent of gender, fracture site, and dose. This risk reduction might be associated with the effects of β1-selective blockers.

β1 selectivity of β-blockers and reduced risk of fractures in elderly hypertension patients

INTRODUCTION

Hypertension and osteoporosis are prevalent in the elderly population. Treatments beneficial to both conditions would be helpful. We examined the protective effect of β-blockers (BBs) and their receptor selectivity against fractures compared to other antihypertensives.

MATERIALS AND METHODS

A retrospective cohort was assembled using the Korean Health Insurance Review and Assessment Service database from January 2005 to June 2006. The cohort consisted of 501,924 patients (ages 65 and older) on single-drug therapy for hypertension. Participants were followed to either the date of the first fracture, date of death or end of the study period (30 June 2006), whichever came first. Cox's proportional hazard model was used to calculate the adjusted hazard ratio (aHR) and 95% confidence interval (CI) by sex, adjusting for confounders. Risk of fractures by BBs according to β1 selectivity was compared to non BBs measured in aHR.

RESULTS

Among 501,924 (65% female), the incidence density of fractures in non BB users was 29.3 and 48.2 per 1000 person-years for men and women, respectively, which was higher than in BB users (17.2 for men and 30.5 for women). Compared to BB users, non BB users showed an increased risk of all fracture [aHR 1.56 (95% CI, 1.42-1.72) in men and 1.44 (95% CI, 1.36-1.51) in women] and hip fracture [aHR 2.17 (95% CI 1.45-3.24) in men and 1.61 (95% CI 1.31-1.98) in women] after adjusting for confounding variables. Compared to BBs, the risks of all fractures in α-blockers, calcium channel blockers, diuretics, and renin-angiotensin-aldosterone system blockers were significantly higher (1.72, 1.77, 1.58, 1.29 in men; 2.11, 1.50, 1.46, 1.22 in women, respectively). Compared to non BBs, β1 selective BBs showed a lower risk of fracture (39% for men and 33% for women) after adjusting for confounding factors. On the contrary, non-selective BBs were not protective against fracture.

CONCLUSION

Our results suggested that β1 selective BBs reduce the risk of fractures compared to other classes of antihypertensives in an elderly population, which could have practical applications for strategies to control and prevent adverse outcomes from both hypertension and osteoporosis in this population.

Association between beta-blockers and fracture risk: a Bayesian meta-analysis

BACKGROUND

The association between beta-blockers (BB) and fracture risk is controversial, due largely to conflicting findings from previous studies. The present study sought to evaluate the effect of BB on fracture risk by using a Bayesian meta-analysis approach.

METHODS AND RESULTS

We systematically retrieved 13 observational studies on the association between BB use and fracture risk. This meta-analysis involved more than 907,000 men and women with mean/median age of individual studies ranging from 43 to 81 years. We used a hierarchical Bayesian random effects model to synthesize the results. BB use was associated with an average 17% reduction in the risk of any fracture (risk ratio [RR] 0.83; 95% credible interval [CrI]: 0.71-0.93), hip fracture (RR 0.83; 95% CrI: 0.70-0.92) and vertebral fracture (RR 0.81; 95% CrI: 0.61-0.99). The probability that BB use reduces fracture risk by at least 10% was 0.91.

CONCLUSIONS

Beta-blockers are associated with reduced risk of fracture in older adults, but the effect size is likely to be modest.

Relationship of sympathetic activity to bone microstructure, turnover, and plasma osteopontin levels in women

CONTEXT

Studies in rodents have demonstrated that sympathetic activity reduces bone formation and bone mass; these effects are mediated by the noncollagenous matrix protein, osteopontin.

OBJECTIVE

The objective of the study was to relate sympathetic activity (measured using microneurography at the peroneal nerve) to bone microstructure (assessed by high resolution peripheral quantitative computed tomography), bone turnover, and plasma osteopontin levels.

DESIGN, SETTING, AND PATIENTS

Twenty-three women aged 20-72 yr (10 premenopausal and 13 postmenopausal) were studied in the Clinical Research Unit.

RESULTS

Sympathetic activity (bursts per 100 heart beats) was 2.4-fold higher in postmenopausal as compared with premenopausal women (P < 0.001). In the two groups combined and after age adjustment, sympathetic activity was inversely correlated with trabecular bone volume fraction (r = -0.55, P < 0.01) and thickness (r = -0.59, P < 0.01) and positively correlated with trabecular separation (r = 0.45, P < 0.05). Sympathetic activity was negatively correlated with serum amino-terminal propeptide of type I collagen in postmenopausal women (r = -0.65, P = 0.015), with a similar trend in premenopausal women (r = -0.58, P = 0.082). Sympathetic activity was also negatively correlated with plasma osteopontin levels (r = -0.43, P = 0.045), driven mainly by the correlation in postmenopausal women (r = -0.76, P = 0.002).

CONCLUSION

These findings represent the first demonstration in humans of a relationship between sympathetic activity and bone microstructure and circulating levels of amino-terminal propeptide of type I collagen and osteopontin. Given the critical role of osteopontin in mediating the effects of β-adrenergic signaling on bone, the inverse association between sympathetic activity and plasma osteopontin levels may reflect a negative feedback loop to limit the deleterious effects of sympathetic activity on bone metabolism. Based on the higher sympathetic activity observed in postmenopausal women, additional human studies are needed to define the role of increased sympathetic activity in mediating postmenopausal bone loss.

Heart drugs that affect bone

There have been important developments in our understanding of the mechanisms underlying the development of osteoporosis, and several of these mechanisms also underlie atherosclerosis. Drugs given to treat cardiovascular disease may impact on bone health in either a beneficial or a harmful way. There is evidence that nitrates are beneficial to bone, but evidence for the benefit of statins, thiazide diuretics, and β-blockers is weaker. By contrast, it is likely to be that some drugs such as loop-acting diuretics are harmful to bone, whereas evidence for harm caused by drugs such as warfarin is weaker. These observations point towards opportunities for new drug development for bone diseases, and possibly the development of treatments that will benefit more than one disease.

[Effect of different propranolol doses on skeletal structural and mechanic efficiency in an animal model of growth retardation]

OBJECTIVE

To assess in a growth retardation (GR) model the impact of different propranolol (P) doses on anthropomorphometric and biomechanical variables of the appendicular skeleton.

MATERIALS AND METHODS

Twenty-one day-old male Wistar rats were divided into the following groups: control (C), C+P3.5 (CP3.5); C+P7 (CP7); C+P10.5 (CP10.5); C+P14 (CP14); ED, ED+P3.5 (EDP3.5); ED+P7 (EDP7); ED+P10.5 (EDP10.5), and ED+P14 (EDP14). Control animals with/without P were fed a rodent diet ad libitum. GR rats with/without P were given 80% of the same diet per 100g body weight for 4 weeks (T4). Propranolol 3.5, 7, 10.5, and 14 mg/kg/day was intraperitoneally injected 5 days/week for 4 weeks to the CP3.5 and EDP3.5; CP7 and EDP7; CP10.5 and EDP10.5, and CP14 and EDP14 groups respectively.

RESULTS

At T4, energy restriction had negative effects upon overall growth, femur, and its mechanical competence. Propranolol improved bone rigidity in GR animals at doses of 7 and 10.5mg/kg/day, with a maximum response at 7 mg/kg/day.

CONCLUSIONS

Propranolol 7 mg/kg/day would be the most effective dose for modeling incorporation of bone, as shown by the increased skeletal structural and mechanic efficiency in this animal model of growth retardation. Such effect may result from maintenance of mechanosensor viability, changes in its sensitivity, the biomechanical reference point and/or effector response in GR rats.

Risk of fractures in older adults using antihypertensive medications

Many medications used to control blood pressure have been associated with bone metabolism. In addition, hypertension itself may be associated with reduced bone mineral density. We examined the relative risk of fracture among subjects with hypertension initiating single-drug therapy for antihypertension treatment. We assembled a large cohort of Medicare beneficiaries with a diagnosis of hypertension who had not filled a prescription for an antihypertensive medication in the prior 365 days. All subsequently began treatment with a single antihypertensive drug. These subjects were followed forward using health care utilization data to determine the risk of a typical osteoporotic fracture. Adjusted Cox proportional hazards regression models were constructed to assess the relative risk of fracture across types of antihypertensive medications. We identified 376,061 eligible subjects. Fracture rate in the total cohort was 35.2 per 1000 person-years [95% confidence interval (CI) 34.4-36.1]. Rates varied significantly across type of antihypertensive, with thiazide diuretics having the lowest rate (28.5, 95% CI 25.4-31.9) and loop diuretics the highest rate (49.0, 95% CI 46.1-52.1). In models adjusting for relevant comorbidities and comedications accessible in health care utilization data, the risk of fracture was reduced in users of angiotensin receptor blockers [hazard ratio (HR) = 0.76, 95% CI 0.68-0.86) and thiazide diuretics (HR = 0.85, 95% CI 0.76-0.97) compared with calcium channel blockers. The adjusted fracture risk was not significantly different from the reference for loop diuretics, beta blockers, and angiotensin-converting enzyme (ACE) inhibitors. It is concluded that the risk of fracture differs across users of different antihypertensive medications.

The roles of the sympathetic nervous system in osteoporotic diseases: A review of experimental and clinical studies

With the rapid aging of the world population, the issue of skeletal health is becoming more prominent and urgent. The bone remodeling mechanism has sparked great interest among bone research societies. At the same time, increasing clinical and experimental evidence has driven attention towards the pivotal role of the sympathetic nervous system (SNS) in bone remodeling. Bone remodeling is thought to be partially controlled by the hypothalamus, a process which is mediated by the adrenergic nerves and neurotransmitters. Currently, new knowledge about the role of the SNS in the development and pathophysiology of osteoporosis is being generated. The aim of this review is to summarize the evidence that proves the involvement of the SNS in bone metabolism and to outline some common osteoporotic diseases that occur under different circumstances. The adrenergic signaling pathway and its neurotransmitters are involved to various degrees of importance in the development of osteoporosis in postmenopause, as well as in spinal cord injury, depression, unloading and the complex regional pain syndrome. In addition, clinical and pharmacological studies have helped to increase the comprehension of the adrenergic signaling pathway. We try to individually examine the contributions of the SNS in osteoporotic diseases from a different perspective. It is our hope that a further understanding of the adrenergic signaling by the SNS will pave the way for conceptualizing optimal treatment regimens for osteoporosis in the near future.

Evolution of β-blockers: from anti-anginal drugs to ligand-directed signalling

Sir James Black developed β-blockers, one of the most useful groups of drugs in use today. Not only are they being used for their original purpose to treat angina and cardiac arrhythmias, but they are also effective therapeutics for hypertension, cardiac failure, glaucoma, migraine and anxiety. Recent studies suggest that they might also prove useful in diseases as diverse as osteoporosis, cancer and malaria. They have also provided some of the most useful tools for pharmacological research that have underpinned the development of concepts such as receptor subtype selectivity, agonism and inverse agonism, and ligand-directed signalling bias. This article examines how β-blockers have evolved and indicates how they might be used in the future.

Association of menopausal vasomotor symptoms with increased bone turnover during the menopausal transition

The purpose of this study was to determine the longitudinal association between menopausal vasomotor symptoms (VMS) and urinary N-telopeptide level (NTX) according to menopausal stage. We analyzed data from 2283 participants of the Study of Women's Health Across the Nation, a longitudinal community-based cohort study of women aged 42 to 52 years at baseline. At baseline and annually through follow-up visit 8, participants provided questionnaire data, urine samples, serum samples, and anthropometric measurements. Using multivariable repeated-measures mixed models, we examined associations between annually assessed VMS frequency and annual NTX measurements. Our results show that mean adjusted NTX was 1.94 nM of bone collagen equivalents (BCE)/mM of creatinine higher among early perimenopausal women with any VMS than among early perimenopausal women with no VMS (p < .0001). Mean adjusted NTX was 2.44 nM BCE/mM of creatinine higher among late perimenopausal women with any VMS than among late perimenopausal women with no VMS (p = .03). Among premenopausal women, VMS frequency was not significantly associated with NTX level. When NTX values among women with frequent VMS (≥6 days in past 2 weeks) were expressed as percentages of NTX values among women without frequent VMS, the differences were 3% for premenopausal women, 9% for early perimenopausal women, 7% for late perimenopausal women, and 4% for postmenopausal women. Adjustment for serum follicle-stimulating hormone (FSH) level greatly reduced the magnitudes of associations between VMS and NTX level. We conclude that among early perimenopausal and late perimenopausal women, those with VMS had higher bone turnover than those without VMS. Prior to the final menstrual period, VMS may be a marker for risk of adverse bone health.

Sympathetic neural influence on bone metabolism in microgravity (Review)

Bone loss is one of the most important complications for astronauts who are exposed to long-term microgravity in space and also for bedridden elderly people. Recent studies have indicated that the sympathetic nervous system plays a role in bone metabolism. This paper reviews findings concerning with sympathetic influences on bone metabolism to hypothesize the mechanism how sympathetic neural functions are related to bone loss in microgravity. Animal studies have suggested that leptin stimulates hypothalamus increasing sympathetic outflow to bone and enhances bone resorption through noradrenaline and β-adrenoreceptors in bone. In humans, even though there have been some controversial findings, use of β-adrenoblockers has been reported to be beneficial for prevention of osteoporosis and bone fracture. On the other hand, microneurographically-recorded sympathetic nerve activity was enhanced by exposure to microgravity in space as well as dry immersion or long-term bed rest to simulate microgravity. The same sympathetic activity became higher in elderly people whose bone mass becomes generally reduced. Our recent findings indicated a significant correlation between muscle sympathetic nerve activity and urinary deoxypyridinoline as a specific marker measuring bone resorption. Based on these findings we would like to propose a following hypothesis concerning the sympathetic involvement in the mechanism of bone loss in microgravity: An exposure to prolonged microgravity may enhance sympathetic neural traffic not only to muscle but also to bone. This sympathetic enhancement increases plasma noradrenaline level and inhibits osteogenesis and facilitates bone resorption through β-adrenoreceptors in bone to facilitate bone resorption to reduce bone mass. The use of β-adrenoblockers to prevent bone loss in microgravity may be reasonable.

Association between beta-blocker use and fracture risk: the Dubbo Osteoporosis Epidemiology Study

INTRODUCTION

In animal model, mice treated with beta-blockers (BB) had increased bone mass. In humans, high bone mass is associated with reduce fracture risk. The present study sought to test the hypothesis that BB use is associated with reduced fracture risk.

MATERIALS AND METHODS

Data from 3488 participants (1285 men) aged 50 years and above in the Dubbo Osteoporosis Epidemiology Study (DOES) were analyzed. Baseline characteristics of participants were obtained at the initial visit which had taken place between 1989 and 1993. Bone mineral density (BMD) at the lumbar spine and femoral neck was measured by dual energy X-ray absorptiometry (GE-LUNAR Corp, Madison, WI). Two hundred and sixty two (20%) men and 411 (19%) women had been on BB, as ascertained by direct interview and verification with medication history. The incidence of fragility fractures was ascertained during the follow-up period (1989-2008).

RESULTS

In men, BB use was associated with higher BMD at the femoral neck (0.96 versus 0.92 g/cm², P < 0.01), higher lumbar spine (1.32 versus 1.25 g/cm², P < 0.01), and lower fracture risk than those not on BB (odds ratio [OR]: 0.49; 95% CI: 0.32-0.75). In women, BB users also had higher femoral neck BMD (0.83 versus 0.81 g/cm², P < 0.01), higher lumbar spine BMD (1.11 versus 1.06 g/cm², P < 0.01), and lower risk of fracture than non-users (OR 0.68, 95% CI: 0.53-0.87). The associations between BB use and fracture risk were independent of age, BMD, and clinical risk factors. Subgroup analysis suggested that the association was mainly found in selective BB, not in non-selective BB.

CONCLUSION

Beta-blockers use, particularly selective BB, was associated with reduced fracture risk in both men and women, and the association was independent of BMD.

Double disruption of α2A- and α2C-adrenoceptors results in sympathetic hyperactivity and high-bone-mass phenotype

Evidence demonstrates that sympathetic nervous system (SNS) activation causes osteopenia via β(2)-adrenoceptor (β2-AR) signaling. Here we show that female mice with chronic sympathetic hyperactivity owing to double knockout of adrenoceptors that negatively regulate norepinephrine release, α(2A)-AR and α(2C)-AR (α(2A) /α(2C)-ARKO), present an unexpected and generalized phenotype of high bone mass with decreased bone resorption and increased formation. In α(2A) /α(2C)-ARKO versus wild-type (WT) mice, micro-computed tomographic (µCT) analysis showed increased, better connected, and more plate-shaped trabeculae in the femur and vertebra and increased cortical thickness in the vertebra, whereas biomechanical analysis showed increased tibial and femoral strength. Tibial mRNA expression of tartrate-resistant acid phosphatase (TRACP) and receptor activator of NF-κB (RANK), which are osteoclast-related factors, was lower in knockout (KO) mice. Plasma leptin and brain mRNA levels of cocaine amphetamine-regulated transcript (CART), which are factors that centrally affect bone turnover, and serum levels of estradiol were similar between mice strains. Tibial β(2)-AR mRNA expression also was similar in KO and WT littermates, whereas α(2A)-, α(2B)- and α(2C)-AR mRNAs were detected in the tibia of WT mice and in osteoblast-like MC3T3-E1 cells. By immunohistochemistry, we detected α(2A)-, α(2B)-, α(2C)- and β(2)-ARs in osteoblasts, osteoclasts, and chondrocytes of 18.5-day-old mouse fetuses and 35-day-old mice. Finally, we showed that isolated osteoclasts in culture are responsive to the selective α(2)-AR agonist clonidine and to the nonspecific α-AR antagonist phentolamine. These findings suggest that β(2)-AR is not the single adrenoceptor involved in bone turnover regulation and show that α(2)-AR signaling also may mediate the SNS actions in the skeleton.

A systems approach to bone pathophysiology

With evolving interest in multiscalar biological systems one could assume that reductionist approaches may not fully describe biological complexity. Instead, tools such as mathematical modeling, network analysis, and other multiplexed clinical- and research-oriented tests enable rapid analyses of high-throughput data parsed at the genomic, proteomic, metabolomic, and physiomic levels. A physiomic-level approach allows for recursive horizontal and vertical integration of subsystem coupling across and within spatiotemporal scales. Additionally, this methodology recognizes previously ignored subsystems and the strong, nonintuitively obvious and indirect connections among physiological events that potentially account for the uncertainties in medicine. In this review, we flip the reductionist research paradigm and review the concept of systems biology and its applications to bone pathophysiology. Specifically, a bone-centric physiome model is presented that incorporates systemic-level processes with their respective therapeutic implications.

A paradigm of integrative physiology, the crosstalk between bone and energy metabolisms

Thanks to integrative physiology, new relationships between organs and homeostatic functions have emerged. This approach to physiology based on a whole organism approach has allowed the bone field to make fundamental progress. In the last decade, clinical observations and scientific evidences in vivo have uncovered that fat with leptin controls bone mass through brain including a hypothalamic relay and sympathetic nervous system. The finding that energy metabolism affects bone remodelling suggested that in an endocrine perspective, a feedback loop should exist. Beside its classical functions, bone can now be considered as a true endocrine organ secreting osteocalcin, a hormone pharmacologically active on glucose and fat metabolism. Indeed osteocalcin stimulates insulin secretion and beta-cell proliferation. Simultaneously, osteocalcin acts on adipocytes to induce Adiponectin which secondarily reduce insulin resistance. This cross regulation between bone and energy metabolism offers novel therapeutic targets in type 2 diabetes and osteoporosis.

Mice lacking beta-adrenergic receptors have increased bone mass but are not protected from deleterious skeletal effects of ovariectomy

Activation of beta2-adrenergic receptors inhibits osteoblastic bone formation and enhances osteoclastic bone resorption. Whether beta-blockers inhibit ovariectomy-induced bone loss and decrease fracture risk remains controversial. To further explore the role of beta-adrenergic signaling in skeletal acquisition and response to estrogen deficiency, we evaluated mice lacking the three known beta-adrenergic receptors (beta-less). Body weight, percent fat, and bone mineral density were significantly higher in male beta-less than wild-type (WT) mice, more so with increasing age. Consistent with their greater fat mass, serum leptin was significantly higher in beta-less than WT mice. Mid-femoral cross-sectional area and cortical thickness were significantly higher in adult beta-less than WT mice, as were femoral biomechanical properties (+28 to +49%, P < 0.01). Young male beta-less had higher vertebral (1.3-fold) and distal femoral (3.5-fold) trabecular bone volume than WT (P < 0.001 for both) and lower osteoclast surface. With aging, these differences lessened, with histological evidence of increased osteoclast surface and decreased bone formation rate at the distal femur in beta-less vs. WT mice. Serum tartrate-resistance alkaline phosphatase-5B was elevated in beta-less compared with WT mice from 8-16 wk of age (P < 0.01). Ovariectomy inhibited bone mass gain and decreased trabecular bone volume/total volume similarly in beta-less and WT mice. Altogether, these data indicate that absence of beta-adrenergic signaling results in obesity and increased cortical bone mass in males but does not prevent deleterious effects of estrogen deficiency on trabecular bone microarchitecture. Our findings also suggest direct positive effects of weight and/or leptin on bone turnover and cortical bone structure, independent of adrenergic signaling.

Pharmacological topics of bone metabolism: the physiological function of the sympathetic nervous system in modulating bone resorption

The vertebrate skeleton is richly innervated with adrenergic and peptidergic nerve terminals, and these play important roles in bone remodeling. Recent studies have generally shown that increased sympathetic nervous activity causes bone loss via an increase in bone resorption and a decrease in bone formation. Increased bone resorption is based on the stimulation of both osteoclast formation and osteoclast activity. These effects are associated with beta(2)-adrenergic activity toward both osteoblastic and osteoclastic cells. Such findings indicate that beta-blockers may be effective against osteoporosis, in which case there is increased sympathetic activity. This review summarizes evidence obtained both in vitro and in vivo implicating sympathetic neuron action in bone resorption.

Leptin and the sympathetic connection of fat to bone

Loss of body weight is associated with bone loss, and body weight gain is associated with increased bone formation. The molecular mechanisms linking body weight, body composition, and bone density are now better understood. Lean mass is likely to have a significant, local effect on bone modeling and remodeling through mechanotransduction pathways. In contrast to the local regulation of bone formation and resorption by muscle-derived stimuli, peripheral body fat appears to influence bone mass via secretion of systemic, endocrine factors that link body weight to bone density even in non-weight bearing regions (e.g., the forearm). The cytokine-like hormone leptin, which is secreted by fat cells, is an important candidate molecule linking changes in body composition with bone formation and bone resorption. Increases in body fat increase leptin levels and stimulate periosteal bone formation through its direct anabolic effects on osteoblasts, and through central (CNS) effects including the stimulation of the GH-IGF-1 axis and suppression of neuropeptide Y, a powerful inhibitor of bone formation. Stimulation of beta2-adrenergic receptors through central (hypothalamic) leptin receptors does, however, increase remodeling of trabecular bone, resulting in a lower cancellous bone volume that may be better adapted to a concomitantly larger cortical bone compartment. These findings suggest that body weight and body fat can regulate bone mass and structure through molecular pathways that are independent of load-bearing. Furthermore, pharmacological manipulation of the signaling pathways activated by leptin may have significant potential for the treatment and prevention of bone loss.

Regulation of bone remodeling by the central and peripheral nervous system

The homeostatic nature of bone remodeling has become a notion further supported lately by the demonstration that neuropeptides and their receptors regulate osteoblast and osteoclast function in vivo. Following initial studies reporting the presence of nerves and nerve-derived products within the bone microenvironment and the expression of receptors for these neuropeptides in bone cells, new experimental and mechanistic evidence based on in vivo murine genetic and pharmacologic models recently demonstrated that inputs from the central and peripheral nervous system feed into the already complex regulatory machinery controlling bone remodeling. The function of a number of "osteo-neuromediators" has been characterized, including norepinephrine and the beta2-adrenergic receptor, Neuropeptide Y and the Y1 and Y2 receptors, endocannabinoids and the CB1 and CB2 receptors, as well as dopamine, serotonin and their receptors and transporters, Calcitonin gene-related peptide, and neuronal NOS. This new body of evidence suggests that neurons in the central nervous system integrate clues from the internal and external milieux, such as energy homeostasis, glycemia or reproductive signals, with the regulation of bone remodeling. The next major tasks in this new area of bone biology will be to understand, at the molecular level, the mechanisms by which common central neural systems regulate and integrate these major physiological functions, the relative importance of the central and peripheral actions of neuropeptides present in both compartments and their relationship, and how bone cells signal back to central centers, because the definition of a homeostatic function implies the existence of feedback signals. Together, these findings shed a new light on the complexity of the mechanisms regulating bone remodeling and uncovered new potential therapeutic strategies for the design of bone anabolic treatments. This review summarizes the latest advances in this area, focusing on investigations based on in vivo animal studies.

Beta-blocker use and risk of fractures in men and women from the general population: the MONICA/KORA Augsburg cohort study

Use of beta-blockers is associated with a reduced risk of fractures in middle-aged and older subjects from the general population.

INTRODUCTION

The present prospective population-based study investigated the association between use of beta-blockers and incidence of any fracture.

METHODS

The study was based on 1,793 persons 55 to 74 years of age who participated in one of the three MONICA Augsburg surveys between 1984 and 1995. Subjects were without any fracture at baseline. Incident fractures were assessed using a health questionnaire. Hazard ratios (HRs) were estimated from Cox proportional hazard models.

RESULTS

During a mean follow-up of 10.7 years, there occurred 263 incident fractures. beta-blocker users were older, were significantly more likely to be obese, to drink no alcohol, to have hypertension or diabetes, to use thiazides and statins, and to be physically inactive. The use of beta-blockers was associated with a lower risk of any fracture (HR 0.57; 95% CI = 0.36-0.90) after adjustment for age, sex and survey. Further adjustment for body mass index and education years only slightly attenuated the relationship (HR 0.60; 95% CI = 0.38-0.95) and additional adjustment for a variety of further risk factors did not attenuate the association (HR 0.60; 95% CI = 0.37-0.96).

CONCLUSION

Use of beta-blockers was associated with a reduced risk of fractures in middle-aged and older subjects from the general population.

Use of beta-2 agonists and risk of hip/femur fracture: a population-based case-control study

INTRODUCTION

Administration of beta-2 agonists decreased bone mineral density in rats. But the association between bronchodilators and fracture risk has not been studied in humans.

OBJECTIVES

To examine the association between use of beta-2 agonists and risk of hip/femur fracture.

METHODS

We conducted a population-based case-control study (6763 cases) in the Dutch PHARMO database. Current beta-2 agonist use was compared to never use. We adjusted for severity of the underlying respiratory disease and disease and drug history.

RESULTS

A hospitalisation for asthma/COPD in the year before index date increased risk of hip/femur fracture: crude OR 2.17 (95% CI, 1.41-3.34). Patients using higher doses of beta-2 agonists had increased risk of hip/femur fracture: crude OR 1.94 (95% CI, 1.41-2.66) for daily dosages of >or=1600 microg albuterol equivalent. The excess fracture risk reduced after adjustment for disease severity (1.46; 95% CI, 1.02-2.08) and after exclusion of oral glucocorticoid users (1.31; 95% CI, 0.80-2.15). Risk of hip/femur fracture was similar between users of beta-2 agonists, inhaled glucocorticoids and anticholinergics.

CONCLUSION

We found increases in the risk of hip/femur fracture in patients using higher doses of beta-2 agonists. However, the excess risk of hip/femur fracture substantially reduced after exclusion of oral glucocorticoid users and after adjustment for the underlying disease. Risk of hip/femur fracture was similar between users of beta-2 agonists, inhaled glucocorticoids and anticholinergics. The severity of the underlying disease, rather than the use of beta-2 agonists, may play an important role in the aetiology of hip/femur fractures in patients using beta-2 agonists.

Blockade of beta-adrenergic signaling does not influence the bone mechano-adaptive response in mice

The involvement of the sympathetic nervous system (SNS) in the modulation of bone adaptation to its load-bearing demand remains controversial. This study tested the involvement of SNS in the adaptive response of trabecular and cortical bone to either external loading or disuse. External loading consisted of cyclic strain (40 cycles, peak 1500 microstrain) applied for 7 min, 3 days/week, while disuse was induced by unilateral sciatic neurectomy (SN). C57Bl/J6 mice, female, 9 weeks old, were subjected to loading or disuse for 2 weeks. Half of the loaded and SN mice were injected with the beta-adrenergic antagonist, propranolol (PRO, 20 mug/g) 1 week before the start of loading or disuse and during all the duration of the experiment. MicroCT analysis of the tibiae showed that the applied load induced significant changes on both trabecular architecture and cortical geometry compared to the contralateral controls, indicating increased bone mass. In contrast, disuse markedly reduced trabecular and cortical indexes. However, these adaptive responses were not altered by PRO treatment. We further tested whether the lack of protective effect of PRO against disuse-induced bone loss was due to the very short duration of treatment by blocking SNS signaling for 8 weeks with either PRO (0.5 mg/ml in drinking water) or guanethidine sulfate (GS, 40 mug/g, injected). At the end of fourth week of treatment, mice underwent SN surgery so that disuse was induced for the remaining 4 weeks. Again, neither PRO nor GS treatments altered the disuse-induced bone loss in the neurectomized tibia. In addition, blockade of SNS signaling for either 3 or 8 weeks did not affect the basal trabecular bone architecture in control tibiae and in L4 vertebrae. This study shows that the mechano-adaptive response occurring in trabecular and cortical bone upon loading or disuse is not altered by inactivation of beta-adrenergic signaling. Furthermore, sympathectomy had no effect on trabecular bone at different skeletal sites. This suggests that the osteo-regulatory action of beta-adrenergic signaling is not involved in the bone mechano-adaptive response and must therefore affect other bone regulatory pathways.

Endogenous PKI gamma limits the duration of the anti-apoptotic effects of PTH and beta-adrenergic agonists in osteoblasts

PKI gamma knockdown substantially extended the anti-apoptotic effects of PTH and beta-adrenergic agonists, whereas PKI gamma overexpression decreased these effects. Therefore, inhibition of PKI gamma activity may provide a useful co-therapy in combination with intermittent PTH or beta-adrenergic agonists for bone loss in conditions such as osteoporosis.

INTRODUCTION

PTH has both catabolic and anabolic effects on bone, which are primarily caused by cAMP/protein kinase A (PKA) signaling and regulation of gene expression. We previously showed that protein kinase inhibitor-gamma (PKI gamma) is required for efficient termination of cAMP/PKA signaling and gene expression after stimulation with PTH or beta-adrenergic agonists. Inhibition of osteoblast apoptosis is thought to be an important, but transient, mechanism partly responsible for the anabolic effects of intermittent PTH. Therefore, we hypothesized that endogenous PKI gamma also terminates the anti-apoptotic effect of PTH.

MATERIALS AND METHODS

PKI gamma knockdown by antisense transfection or siRNA was used to examine the ability of endogenous PKI gamma to modulate the anti-apoptotic effects of PTH and beta-adrenergic agonists in ROS 17/2.8 cells.

RESULTS

Knockdown of PKI gamma substantially extended the anti-apoptotic effects of PTH, whether apoptosis was induced by etoposide or dexamethasone. In contrast, overexpression of PKI gamma decreased the anti-apoptotic effect of PTH pretreatment. This study is also the first demonstration that beta-adrenergic agonists mimic the anti-apoptotic effects of PTH in osteoblasts. Moreover, PKI gamma knockdown also substantially extended this anti-apoptotic effect of beta-adrenergic agonists. Taken together, these results show that endogenous PKI gamma limits the duration of the anti-apoptotic effects of cAMP/PKA signaling in osteoblasts.

CONCLUSIONS

Because significant individual variability exists in the anabolic responses to PTH therapy in current clinical treatment of osteoporosis, inhibition of PKI gamma activity may provide a useful co-therapy in combination with intermittent PTH or beta-adrenergic agonists for bone loss in conditions such as osteoporosis. However, the potential use of such a co-therapy would depend on it not adversely affecting bone formation or other organ systems.

The new field of neuroskeletal biology

The fields of neuroscience and bone biology have recently converged following the discovery that bone remodeling is directly regulated by the brain. This work has defined bone remodeling as one of the cardinal physiological functions of the body, subject to homeostatic regulation and integrated with the other major physiological functions by the hypothalamus. Central to this discovery was the definition of the adipocyte-derived hormone leptin as a regulator of both arms of bone remodeling, formation and resorption, through its action on the ventromedial hypothalamus and subsequently via the sympathetic nervous system to osteoblasts. The characterization of the sympathetic nervous system as a regulator of bone remodeling has led to several large clinical studies demonstrating a substantial protective effect of beta-blockers, particularly beta1-blockers, on fracture risk. Studies in model organisms have reinforced the role of the central nervous system in the regulation of bone remodeling in vivo by the identification of several additional genes, namely cocaine and amphetamine regulated transcript (Cart), melanocortin 4 receptor (Mc4R), neuropeptide Y (NPY), Y2 receptor, cannabinoid receptor CB1 (Cnbr1), and the genes of the circadian clock. These genes have several common features, including high levels of expression in the hypothalamus and the ability to regulate other major physiological functions in addition to bone remodeling including energy homeostasis, body weight, and reproduction. We review the major pathways that define the new field of neuroskeletal biology and identify further avenues of inquiry.

Effect of beta-blockers on bone mass and biomechanical parameters of the femoral neck in males with acute myocardial infarction

OBJECTIVES

Evaluate the effect of cardioselective beta-blockers on bone mass and biomechanical properties of the femoral neck in males with acute myocardial infarction.

METHODS

Forty males with acute myocardial infarction were studied during one year. Seventy-five percent of the patients (30 patients) were treated with cardioselective beta-blockers and 10 were not similarly treated. A hip densitometry was performed upon release and one year later. The BMD was measured in the femoral neck and in biomechanical elements obtained by DXA.

RESULTS

Both groups had similar clinical conditions at the beginning of the study and after a one-year follow-up. No differences in the BMD (0.934+/-0.12 vs. 0.921+/-0.14) were observed in the group without beta-blockers or in the group with beta-blockers (0.980+/-0.12 vs. 0.977+/-0.12). No differences were observed in the measured structural parameters.

CONCLUSION

The cardioselective beta-blockers do not modify bone mass or the structural bone parameters in males with acute myocardial infarction.

Use of beta-blockers and the risk of hip/femur fracture in the United Kingdom and The Netherlands

Data from in vivo studies have indicated a role for beta-blockers in the prevention of bone loss. Some epidemiological studies have found protective effects of beta-blockers on fracture risk. However, there is limited information on the association with cumulative dose and type of beta-blockers used. We conducted two case-control studies using data from the UK General Practice Research Database (GPRD) and the Dutch PHARMO Record Linkage System (RLS). Cases were patients with a first hip or femur fracture; controls were individually matched on practice/region, gender, year of birth, and calendar time. Current use of beta-blockers was defined as a prescription in 90 days before the index date. We adjusted for medical conditions and drugs associated with falling or bone mineral density. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using conditional logistic regression analysis. The study population included 22,247 cases and controls in the GPRD and 6,763 cases and 26,341 controls in the PHARMO RLS. Current use of beta-blockers was associated with a reduced risk of hip/femur fracture in both the GPRD (adjusted OR = 0.82, 95% CI 0.74-0.91) and PHARMO RLS (adjusted OR = 0.87, 95% CI 0.80-0.95) study populations. However, this reduction of risk was not associated with cumulative dose, lipophilicity, or receptor selectivity of beta-blockers. The protective effect of beta-blockers was only present among patients with a history of use of other antihypertensive agents (GPRD adjusted OR = 0.72, 95% CI 0.64-0.83; PHARMO RLS adjusted OR = 0.76, 95% CI 0.67-0.86) but not in patients using beta-blockers only (GPRD adjusted OR = 0.97, 95% CI 0.82-1.14; PHARMO RLS adjusted OR = 1.01, 95% CI 0.90-1.14). Also, in patients with a history of use of other antihypertensive agents, no dose-response relationship with beta-blocker use was found. The effect was constant with cumulative dose and the OR was below 1.0 even among patients who just started treatment with beta-blockers. As the mechanism by which beta-blockers could influence bone mineral density is likely to need some time to exert a clinically relevant effect, all these finding suggests that the association between beta-blockers and fracture risk is not causal.

Angiotensin converting enzyme inhibitor use is associated with higher bone mineral density in elderly Chinese

Hypertension and osteoporosis are two major chronic diseases affecting the elderly. A cross-sectional study of 3887 Chinese men (n = 1958) and women (n = 1929) was used to explore the association between angiotensin converting enzyme inhibitor (ACEI) use and bone mineral density (BMD). The participants were aged 65 years and above, and were recruited using a combination of private solicitation and public advertising from community centers, housing estates, and the general community in Hong Kong. Demographic, medical, and lifestyle information was obtained from face to face interviews using standardized questionnaire, and physical examination measurements included anthropometry, tibial, and brachial systolic blood pressures, femoral neck, total hip, and lumbar spine BMD. In multiple regression analyses, after adjusting for age, weight, height, thiazide, beta-blocker, calcium channel blocker, statin, corticosteroid, and calcium supplement use, history of diabetes, heart disease, peripheral vascular disease, cigarette smoking, alcohol intake, and physical activity level, ACEI use was associated with higher femoral neck BMD (+0.015 g/cm2, P = 0.035) in women, and higher femoral neck (+0.015 g/cm2, P = 0.017), total hip (+0.016 g/cm2, P = 0.021), and lumbar spine (+0.043 g/cm2, P < 0.001) BMD in men. Thiazide use was associated with higher BMD at all three sites in general, although associations with BMD increase at the total hip (P = 0.07) and femoral neck (P = 0.09) were weak in men. Calcium channel blocker use was only significantly associated with BMD increase at the lumbar spine (P = 0.03) in women, and beta-blocker use did not have significant associations with BMD at any site. This study suggests that in addition to thiazide diuretics ACEI may have possible benefits in treating not only hypertension but also osteoporosis among older Chinese.