Fracture risk in perimenopausal women treated with beta-blockers

Evaluation of antihypertensive drug-induced changes in mandibular bone using fractal analysis

OBJECTIVE

The aim was to evaluate changes in trabecular and cortical mandibular bone caused by antihypertensive (AHT) drugs through fractal analysis.

STUDY DESIGN

This retrospective study included 230 patients who were taking AHT medication and had no conditions affecting bone metabolism other than hypertension. A control group of 230 healthy, sex-matched individuals was also included. Patients were divided into subgroups according to AHT drugs: thiazide diuretics (TDs), beta-blockers (BBs), angiotensin converting enzyme inhibitors (ACEIs), angiotensin receptor blockers (ARBs), calcium channel blockers (CCBs), and a combination of drugs. The fractal dimension (FD) was calculated bilaterally in 5 regions of interest (ROI 1 - ROI 5) including 4 trabecular regions and 1 cortical region using Image J software.

RESULTS

Mean FD values were significantly higher in all ROIs for the study group compared to the control group (P < .001). FDs were significantlty higher for BB, ACEI, ARB, CCB, and combined subgroups compared to controls in ROIs 1, 2, and 4; for ACEI and CCB subgroups compared to controls in ROI 3; and for TD, BB, ACEI, ARB, CCB, and combined subgroups compared to controls in ROI 5 (P < .001).

CONCLUSIONS

AHTs may increase FD values of the trabecular and cortical structures. Assessment of the effects of AHT drugs is essential for predicting the prognosis for bone healing after tooth extraction, osseointegration after implant surgery, or other surgical procedures.

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 Association of Beta-Blocker Use and Bone Mineral Density Level in Hemodialysis Patients: A Cross-Sectional Study

Background and Objectives: Osteoporosis results in increasing morbidity and mortality in hemodialysis patients. The medication for treatment has been limited. There is evidence that beta-blockers could increase bone mineral density (BMD) and reduce the risk of fracture in non-dialysis patients, however, a study in hemodialysis patients has not been conducted. This study aims to determine the association between beta-blocker use and bone mineral density level in hemodialysis patients. Materials and Methods: We conducted a cross-sectional study in hemodialysis patients at Thammasat University Hospital from January 2018 to December 2020. A patient receiving a beta-blocker ≥ 20 weeks was defined as a beta-blocker user. The association between beta-blocker use and BMD levels was determined by univariate and multivariate linear regression analysis. Results: Of the 128 patients receiving hemodialysis, 71 were beta-blocker users and 57 were non-beta-blocker users (control group). The incidence of osteoporosis in hemodialysis patients was 50%. There was no significant difference in the median BMD between the control and the beta-blocker groups of the lumbar spine (0.93 vs. 0.91, p = 0.88), femoral neck (0.59 vs. 0.57, p = 0.21), total hip (0.73 vs. 0.70, p = 0.38), and 1/3 radius (0.68 vs. 0.64, p = 0.40). The univariate and multivariate linear regression analyses showed that the beta-blocker used was not associated with BMD. In the subgroup analysis, the beta-1 selective blocker used was associated with lower BMD of the femoral neck but not within the total spine, total hip, and 1/3 radius. The multivariate logistic regression showed that the factors of age ≥ 65 years (aOR 3.31 (1.25−8.80), p = 0.02), female sex (aOR 4.13 (1.68−10.14), p = 0.002), lower BMI (aOR 0.89 (0.81−0.98), p = 0.02), and ALP > 120 U/L (aOR 3.88 (1.33−11.32), p = 0.01) were independently associated with osteoporosis in hemodialysis patients. Conclusions: In hemodialysis patients, beta-blocker use was not associated with BMD levels, however a beta-1 selective blocker used was associated with lower BMD in the femoral neck.

Pharmacogenomic Effects of β-Blocker Use on Femoral Neck Bone Mineral Density

CONTEXT

Recent studies have shown that β-blocker (BB) users have a decreased risk of fracture and higher bone mineral density (BMD) compared to nonusers, likely due to the suppression of adrenergic signaling in osteoblasts, leading to increased BMD. There is also variability in the effect size of BB use on BMD in humans, which may be due to pharmacogenomic effects.

OBJECTIVE

To investigate potential single-nucleotide variations (SNVs) associated with the effect of BB use on femoral neck BMD, we performed a cross-sectional analysis using clinical data, dual-energy x-ray absorptiometry, and genetic data from the Framingham Heart Study's (FHS) Offspring Cohort. We then sought to validate our top 4 genetic findings using data from the Rotterdam Study, the BPROOF Study, the Malta Osteoporosis Fracture Study (MOFS), and the Hertfordshire Cohort Study.

METHODS

We used sex-stratified linear mixed models to determine SNVs that had a significant interaction effect with BB use on femoral neck (FN) BMD across 11 gene regions. We also evaluated the association of our top SNVs from the FHS with microRNA (miRNA) expression in blood and identified potential miRNA-mediated mechanisms by which these SNVs may affect FN BMD.

RESULTS

One variation (rs11124190 in HDAC4) was validated in females using data from the Rotterdam Study, while another (rs12414657 in ADRB1) was validated in females using data from the MOFS. We performed an exploratory meta-analysis of all 5 studies for these variations, which further validated our findings.

CONCLUSION

This analysis provides a starting point for investigating the pharmacogenomic effects of BB use on BMD measures.

Neurogenic Obesity and Skeletal Pathology in Spinal Cord Injury

Spinal cord injury (SCI) results in dramatic changes in body composition, with lean mass decreasing and fat mass increasing in specific regions that have important cardiometabolic implications. Accordingly, the recent Consortium for Spinal Cord Medicine (CSCM) released clinical practice guidelines for cardiometabolic disease (CMD) in SCI recommending the use of compartmental modeling of body composition to determine obesity in adults with SCI. This recommendation is guided by the fact that fat depots impact metabolic health differently, and in SCI adiposity increases around the viscera, skeletal muscle, and bone marrow. The contribution of skeletal muscle atrophy to decreased lean mass is self-evident, but the profound loss of bone is often less appreciated due to methodological considerations. General-population protocols for dual-energy x-ray absorptiometry (DXA) disregard assessment of the sites of greatest bone loss in SCI, but the International Society for Clinical Densitometry (ISCD) recently released an official position on the use of DXA to diagnose skeletal pathology in SCI. In this review, we discuss the recent guidelines regarding the evaluation and monitoring of obesity and bone loss in SCI. Then we consider the possible interactions of obesity and bone, including emerging evidence suggesting the possible influence of metabolic, autonomic, and endocrine function on bone health in SCI.

miRNA Mechanisms Underlying the Association of Beta Blocker Use and Bone Mineral Density

Osteoporosis is a debilitating and costly disease that causes fractures in 33% of women and 20% of men over the age of 50 years. Recent studies have shown that beta blocker (BB) users have higher bone mineral density (BMD) and decreased risk of fracture compared with non-users. The mechanism underlying this association is thought to be due to suppression of adrenergic signaling in osteoblasts, which leads to increased BMD in rodent models; however, the mechanism in humans is unknown. Also, several miRNAs are associated with adrenergic signaling and BMD in separate studies. To investigate potential miRNA mechanisms, we performed a cross-sectional analysis using clinical data, dual-energy X-ray absorptiometry (DXA) scans, and miRNA and mRNA profiling of whole blood from the Framingham Study's Offspring Cohort. We found nine miRNAs associated with BB use and increased BMD. In parallel network analyses, we discovered a subnetwork associated with BMD and BB use containing two of these nine miRNAs, miR-19a-3p and miR-186-5p. To strengthen this finding, we showed that these two miRNAs had significantly higher expression in individuals without incident fracture compared with those with fracture in an external data set. We also noted a similar trend in association between these miRNA and Z-score as calculated from heel ultrasound measures in two external cohorts (SOS-Hip and SHIP-TREND). Because miR-19a directly targets the ADRB1 mRNA transcript, we propose BB use may downregulate ADRB1 expression in osteoblasts through increased miR-19a-3p expression. We used enrichment analysis of miRNA targets to find potential indirect effects through insulin and parathyroid hormone signaling. This analysis provides a starting point for delineating the role of miRNA on the association between BB use and BMD. © 2020 American Society for Bone and Mineral Research (ASBMR).

Association of Beta Blocker Use With Bone Mineral Density in the Framingham Osteoporosis Study: A Cross-Sectional Study

Some, but not all, prior observational studies have shown that beta blocker (BB) use is associated with lower fracture risk and higher bone mineral density (BMD). Rodent studies show the mechanism to involve the reduction in the effects of beta‐adrenergic signaling on bone remodeling. Because previous studies did not have detailed information on dose, duration, and beta‐1 selectivity, we examined these in a cross‐sectional analysis of the association between BB use and hip and spine BMD using DXA with the Offspring Cohort of the Framingham Heart Study. The sample size was n = 1520, and 397 individuals used BBs. We used propensity score modeling to balance a comprehensive set of covariates using inverse probability of treatment weighting (IPTW) to minimize bias due to treatment indication. We found significant differences in BMD between BB users and non‐users for three of four BMD measurements (femoral neck: 3.1%, 95% CI, 1.1% to 5.0%; total femur: 2.9%, 95% CI, 0.9% to 4.9%; femoral trochanter: 2.4%, 95% CI, −0.1% to 5.0%; and lumbar spine: 2.7%, 95% CI, 0.2% to 5.0%). Results were found to be similar between sexes although the magnitude of association was larger for women. Similar differences were estimated for beta‐1 selective and nonselective BBs compared with no BB use. We modeled dose in categories (no BB use, low‐dose, high‐dose) and as a continuous variable and found an increasing dose response that levels off at higher doses. Finally, associations were similar for short‐term versus long‐term (≤4 years versus >4 years) use. In summary, this large comprehensive study shows that BB use is associated with higher BMD in a dose‐related manner regardless of beta‐1 specificity and duration of use, which supports the conduct of a randomized clinical trial of BBs for achieving improvements in BMD for individuals at risk of bone loss with aging. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Predictors and Outcome of Fragility Hip Fracture: A Prospective Study from North India

INTRODUCTION

Fragility hip fracture is a useful surrogate marker of the burden of osteoporosis. With improving life expectancy and progressive ageing of population, the global burden of osteoporotic fracture is increasing. Despite this, there is paucity of data regarding epidemiology, predictors, and outcomes of fragility hip fractures in the Indian population.

METHODS

In this multicenter, prospective observational study, 264 patients of fragility hip fracture were followed up for 12 months.

RESULTS

Men (46.2%) and women (53.8%) had a nearly equal distribution of fragility hip fracture. Mean (±SD) age of study population was 65.9 ± 12.6 years and men had earlier age (64.7 ± 12.6 years) of fracture as compared to women (66.9 ± 12.6 years). Out of these, 89.7% patients had osteoporosis, 7.6% had osteopenia, and 2.7% patients had normal bone mineral density (BMD). Fractures predominantly occurred inside the home (229, 86.7%) as compared to outside (35, 13.3%). Female gender, hypertension, diabetes, anemia, smoking, and alcohol were associated with lower BMD, but not a predictor of morbidity. Aging (P = 0.000), osteoporosis (P = 0.012), and diabetes (P = 0.008) were predictors of increased mortality. A total of 243 (92%) patients underwent surgery with a mean hospital stay of 13.5 ± 2.9 days and 34 (12.9%) patients died. Maximum death (73.5%) occurred in first 3 months and the commonest cause of death was cardiovascular (44.1%) related.

CONCLUSION

The majority of fragility hip fractures occurred inside the home. Distribution of fractures in either gender is comparable. Aging, osteoporosis, and diabetes are predictors of poor outcome. We recommend development of newer strategies that target male as well as female patients with osteoporosis with particular attention to prevent in-house falls and fractures.

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.

Cortical bone is an extraneuronal site of norepinephrine uptake in adult mice

The sympathetic nervous system is a major efferent pathway through which the central nervous system controls the function of peripheral organs. Genetic and pharmacologic evidence in mice indicated that stimulation of the β2 adrenergic receptor (β2AR) in osteoblasts promotes bone loss, leading to the paradigm that high sympathetic nervous activity is deleterious to bone mass. However, considerably less data exist to understand the putative impact of endogenous norepinephrine (NE), released by sympathetic nerves, on bone homeostasis. In this study, we investigated the in vivo expression and activity of the norepinephrine transporter (NET), a membrane pump known to actively uptake NE from the extracellular space in presynaptic neurons. Consistent with previously published in vitro data showing NET uptake activity in differentiated osteoblasts, we were able to detect active NET-specific NE uptake in the mouse cortical bone compartment in vivo. This uptake was the highest in young mice and accordingly with an age-related reduction in NET uptake, NE bone content increased whereas Net RNA and protein expression decreased with age. Histologically, NET expression in adult mouse bones was detected in osteocytes via immunofluorescence. Lastly, taking advantage of tissue-specific fluorescent reporter mice, we used CLARITY imaging and light sheet microscopy to visualize the 3D distribution of sympathetic fibers in whole mount preparations of bone tissues. These analyses allowed us to detect tyrosine hydroxylase (TH)-positive sympathetic nerve fibers penetrating the cortical bone, where NET+ osteocytes reside. Together, these in vitro results support the existence of an age-dependent extraneuronal and osteocytic function of NET with potential to buffer the bone catabolic action of endogenous NE released by sympathetic nerves in vivo.

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.

Heart Rate and Bone Mineral Density in Older Women with Hypertension: Results from the Korea National Health and Nutritional Examination Survey

OBJECTIVES

To determine whether high heart rate is associated with low bone mineral density (BMD) in older women with hypertension.

DESIGN

Retrospective cohort study.

SETTING

Population-based study conducted in Korea (Korea National Health and Nutritional Examination Survey 2009-10).

PARTICIPANTS

Postmenopausal women aged 60 and older with hypertension (N=981) divided into 2 groups according to resting heart rate, with a cut-off value of 80 bpm, which has been found to be associated with osteoporosis.

MEASUREMENTS

BMD profiles and clinical and laboratory data were collected. Osteoporosis was defined as a T-score of -2.5 or less, according to World Health Organization criteria.

RESULTS

BMD was significantly lower in participants with a high heart rate, even after adjustment for age, diabetes mellitus, white blood cell count, and fasting glucose and triglyceride levels. The prevalence of osteoporosis was also significantly higher in those participants. In multivariate logistic regression analysis, the group with high heart rate was 1.7 times as likely (95% confidence interval=1.2-2.3) to have osteoporosis as those with a lower heart rate, independent of age, body mass index, comorbidities, and laboratory findings.

CONCLUSION

High heart rate is independently associated with lower BMD in older women with hypertension; proactive surveillance of BMD could be helpful when managing older women with hypertension and a high heart rate.

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.

Neuronal Control of Bone Remodeling

Although the brain is well established as a master regulator of homeostasis in peripheral tissues, central regulation of bone mass represents a novel and rapidly expanding field of study. This review examines the current understanding of central regulation of the skeleton, exploring several of the key pathways connecting brain to bone and their implications both in mice and the clinical setting. Our understanding of central bone regulation has largely progressed through examination of skeletal responses downstream of nutrient regulatory pathways in the hypothalamus. Mutations and modulation of these pathways, in cases such as leptin deficiency, induce marked bone phenotypes, which have provided vital insights into central bone regulation. These studies have identified several central neuropeptide pathways that stimulate well-defined changes in bone cell activity in response to changes in energy homeostasis. In addition, this work has highlighted the endocrine nature of the skeleton, revealing a complex cross talk that directly regulates other organ systems. Our laboratory has studied bone-active neuropeptide pathways and defined osteoblast-based actions that recapitulate central pathways linking bone, fat, and glucose homeostasis. Studies of neural control of bone have produced paradigm-shifting changes in our understanding of the skeleton and its relationship with the wider array of organ systems.

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.

The Vestibular System: A Newly Identified Regulator of Bone Homeostasis Acting Through the Sympathetic Nervous System

The vestibular system is a small bilateral structure located in the inner ear, known as the organ of balance and spatial orientation. It senses head orientation and motion, as well as body motion in the three dimensions of our environment. It is also involved in non-motor functions such as postural control of blood pressure. These regulations are mediated via anatomical projections from vestibular nuclei to brainstem autonomic centers and are involved in the maintenance of cardiovascular function via sympathetic nerves. Age-associated dysfunction of the vestibular organ contributes to an increased incidence of falls, whereas muscle atrophy, reduced physical activity, cellular aging, and gonadal deficiency contribute to bone loss. Recent studies in rodents suggest that vestibular dysfunction might also alter bone remodeling and mass more directly, by affecting the outflow of sympathetic nervous signals to the skeleton and other tissues. This review will summarize the findings supporting the influence of vestibular signals on bone homeostasis, and the potential clinical relevance of these findings.

Lipid metabolism disorders and bone dysfunction--interrelated and mutually regulated (review)

The association between lipid and bone metabolism has become an increasing focus of interest in recent years, and accumulating evidence has shown that atherosclerosis (AS) and osteoporosis (OP), a disorder of bone metabolism, frequently co-exist. Fat and bone are known to share a common progenitor cell: Multipotent mesenchymal stem cells (MSC) in the bone marrow (BM), which are able to differentiate into various cell phenotypes, including osteoblasts, adipocytes and chondrocytes. Laboratory-based and clinical trials have shown that increasing adipocytes are accompanied by a decrease in bone mineral density (BMD) and bone mass. Statins, lipid-lowering drugs used to treat hyperlipidemia, also provide benefit in the treatment of OP. There is thus evidence that the metabolism of lipids is correlated with that of bone, and that the two are mutually regulated. The present review primarily focuses on the potential association between lipid metabolism disturbance and OP, based on biological metabolism, pathophysiological processes, results from clinical and experimental animal studies, processes involved in the differentiation of adipocytes and osteoblasts, as well as pharmacological treatments of these diseases.

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.

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.

The role of catecholamines in mesenchymal stem cell fate

Mesenchymal stem cells (MSCs) are multipotent stem cells found in many adult tissues, especially bone marrow (BM) and are capable of differentiation into various lineage cells such as osteoblasts, adipocytes, chondrocytes and myocytes. Moreover, MSCs can be mobilized from connective tissue into circulation and from there to damaged sites to contribute to regeneration processes. MSCs commitment and differentiation are controlled by complex activities involving signal transduction through cytokines and catecholamines. There has been an increasing interest in recent years in the neural system, functioning in the support of stem cells like MSCs. Recent efforts have indicated that the catecholamine released from neural and not neural cells could be affected characteristics of MSCs. However, there have not been review studies of most aspects involved in catecholamines-mediated functions of MSCs. Thus, in this review paper, we will try to describe the current state of catecholamines in MSCs destination and discuss strategies being used for catecholamines for migration of these cells to damaged tissues. Then, the role of the nervous system in the induction of osteogenesis, adipogenesis, chondrogenesis and myogenesis from MSCs is discussed. Recent progress in studies of signaling transduction of catecholamines in determination of the final fate of MSCs is highlighted. Hence, the knowledge of interaction between MSCs with the neural system could be applied towards the development of new diagnostic and treatment alternatives for human diseases.

Do effects of propranolol on the skeletal system depend on the estrogen status?

BACKGROUND

Propranolol, a nonselective β-adrenergic receptor antagonist, was reported to favorably affect the skeletal system in different animal models. The aim of the study was to investigate whether the effects of propranolol on the skeletal system depend on the estrogen status.

METHODS

The in vivo experiments were carried out on the following groups of mature female Wistar rats: sham-operated control rats, sham-operated rats receiving propranolol, ovariectomized (OVX) control rats, OVX rats receiving propranolol, OVX rats receiving estradiol, OVX rats receiving estradiol and propranolol. Propranolol hydrochloride (10 mg/kg po) and/or estradiol (0.1 mg/kg po) were administered daily for 4 weeks. Bone mass, mineral and calcium content, macrometric and histomorphometric parameters, and mechanical properties were examined. In vitro, effects of estradiol and propranolol on the formation of mouse osteoclasts and on the mRNA expression of genes related to osteoclastogenesis, bone formation and mineralization, as well as adrenergic and estrogen signalling in mouse osteoblasts were investigated.

RESULTS AND CONCLUSION

Propranolol exerted some favorable effects on the rat skeletal system in vivo, independently of the estrogen status. However, in vitro studies indicated a possibility of some antagonistic relations between the estradiol and propranolol effects.

Control of bone remodeling by the peripheral sympathetic nervous system

The skeleton is no longer seen as a static, isolated, and mostly structural organ. Over the last two decades, a more complete picture of the multiple functions of the skeleton has emerged, and its interactions with a growing number of apparently unrelated organs have become evident. The skeleton not only reacts to mechanical loading and inflammatory, hormonal, and mineral challenges, but also acts of its own accord by secreting factors controlling the function of other tissues, including the kidney and possibly the pancreas and gonads. It is thus becoming widely recognized that it is by nature an endocrine organ, in addition to a structural organ and site of mineral storage and hematopoiesis. Consequently and by definition, bone homeostasis must be tightly regulated and integrated with the biology of other organs to maintain whole body homeostasis, and data uncovering the involvement of the central nervous system (CNS) in the control of bone remodeling support this concept. The sympathetic nervous system (SNS) represents one of the main links between the CNS and the skeleton, based on a number of anatomic, pharmacologic, and genetic studies focused on β-adrenergic receptor (βAR) signaling in bone cells. The goal of this report was to review the data supporting the role of the SNS and βAR signaling in the regulation of skeletal homeostasis.

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.

The effects of antihypertensive drugs on bone mineral density in ovariectomized mice

The effects of several antihypertensive drugs on bone mineral density (BMD) and micro-architectural changes in ovariectomized (OVX) mice were investigated. Eight-week-old female C57/BL6 mice were used for this study. Three days after ovariectomy, mice were treated intraperitoneally with nifedipine (15 mg/kg), telmisartan (5 mg/kg), enalapril (20 mg/kg), propranolol (1 mg/kg) or hydrochlorothiazide (12.5 mg/kg) for 35 consecutive days. Uterine atrophy of all mice was confirmed to evaluate estrogen deficiency state. BMD and micro-architectural analyses were performed on tibial proximal ends by micro-computed tomography (micro-CT). When OVX mice with uterine atrophy were compared with mice without atrophy, BMD decreased (P < 0.001). There were significant differences in BMD loss between different antihypertensive drugs (P = 0.005). Enalapril and propranolol increased BMD loss in mice with atrophied uteri compared with control mice. By contrast, thiazide increased BMD in mice with uterine atrophy compared with vehicle-treated mice (P = 0.048). Thiazide (P = 0.032) and telmisartan (P = 0.051) reduced bone loss and bone fraction in mice with uterine atrophy compared with the control. Thiazide affects BMD in OVX mice positively. The reduction in bone loss by thiazide and telmisartan suggest that these drugs may benefit menopausal women with hypertension and osteoporosis.

The relationship among hypertension, antihypertensive medications, and osteoporosis: a narrative review

Osteoporosis and hypertension are two frequent diseases among the aging population that share a similar etiopathology and often coexist. Moreover, treatment of hypertension affects bone mineral density and, therefore, can worsen osteoporosis. This narrative review considers the influence of the main etiologic factors that contribute to the development of hypertension and osteoporosis and examines the effect of the most often used antihypertensives on bones. A computerized literature search of relevant English publications regarding the etiology of hypertension and osteoporosis as well as the impact of antihypertensives on osteoporosis from 1996 to 2011 was completed in October 2011. The latest update in the search was performed from May to June 2012. The most relevant nongenetic factors in the etiology of osteoporosis and hypertension are low calcium intake, vitamin D and vitamin K deficiency, high consumption of sodium salt, and the effects of different forms of nitric oxide. Thiazide diuretics are the only antihypertensives that have a positive influence on bone mineral density. For other antihypertensive drugs, the data are conflicting, indicating that they may have a potentially negative or positive influence on bone mineral density and fracture risk reduction. Some studies did not find a correlation between the use of antihypertensives and bone mineral density. Due to the frequent coexistence of hypertension and osteoporosis, when selecting long-term antihypertensive therapy the potential effects of antihypertensive drugs on development, worsening, or improvement of osteoporosis should also be considered.

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.

Assessment of bone mineral status in children with Marfan syndrome

Marfan syndrome (MFS) is an autosomal dominant connective tissue disorder with skeletal involvement. It is caused by mutations in fibrillin1 (FBN1) gene resulting in activation of TGF-β, which developmentally regulates bone mass and matrix properties. There is no consensus regarding bone mineralization in children with MFS. Using dual-energy X-ray absorptiometry (DXA), we evaluated bone mineralization in 20 children with MFS unselected for bone problems. z-Scores were calculated based on age, gender, height, and ethnicity matched controls. Mean whole body bone mineral content (BMC) z-score was 0.26 ± 1.42 (P = 0.41). Mean bone mineral density (BMD) z-score for whole body was −0.34 ± 1.4 (P = 0.29) and lumbar spine was reduced at −0.55 ± 1.34 (P = 0.017). On further adjusting for stature, which is usually higher in MFS, mean BMC z-score was reduced at −0.677 ± 1.37 (P = 0.04), mean BMD z-score for whole body was −0.82 ± 1.55 (P = 0.002) and for lumbar spine was −0.83 ± 1.32 (P = 0.001). An increased risk of osteoporosis in MFS is controversial. DXA has limitations in large skeletons because it tends to overestimate BMD and BMC. By adjusting results for height, age, gender, and ethnicity, we found that MFS patients have significantly lower BMC and BMD in whole body and lumbar spine. Evaluation of diet, exercise, vitamin D status, and bone turnover markers will help gain insight into pathogenesis of the reduced bone mass. Further, larger longitudinal studies are required to evaluate the natural history, incidence of fractures, and effects of pharmacological therapy. © 2012 Wiley Periodicals, Inc.

Deletion of β-adrenergic receptor 1, 2, or both leads to different bone phenotypes and response to mechanical stimulation

As they age, mice deficient for the β2-adrenergic receptor (Adrb2(-/-) ) maintain greater trabecular bone microarchitecture, as a result of lower bone resorption and increased bone formation. The role of β1-adrenergic receptor signaling and its interaction with β2-adrenergic receptor on bone mass regulation, however, remains poorly understood. We first investigated the skeletal response to mechanical stimulation in mice deficient for β1-adrenergic receptors and/or β2-adrenergic receptors. Upon axial compression loading of the tibia, bone density, cancellous and cortical microarchitecture, as well as histomorphometric bone forming indices, were increased in both Adrb2(-/-) and wild-type (WT) mice, but not in Adrb1(-/-) nor in Adrb1b2(-/-) mice. Moreover, in the unstimulated femur and vertebra, bone mass and microarchitecture were increased in Adrb2(-/-) mice, whereas in Adrb1(-/-) and Adrb1b2(-/-) double knockout mice, femur bone mineral density (BMD), cancellous bone volume/total volume (BV/TV), cortical size, and cortical thickness were lower compared to WT. Bone histomorphometry and biochemical markers showed markedly decreased bone formation in Adrb1b2(-/-) mice during growth, which paralleled a significant decline in circulating insulin-like growth factor 1 (IGF-1) and IGF-binding protein 3 (IGF-BP3). Finally, administration of the β-adrenergic agonist isoproterenol increased bone resorption and receptor activator of NF-κB ligand (RANKL) and decreased bone mass and microarchitecture in WT but not in Adrb1b2(-/-) mice. Altogether, these results demonstrate that β1- and β2-adrenergic signaling exert opposite effects on bone, with β1 exerting a predominant anabolic stimulus in response to mechanical stimulation and during growth, whereas β2-adrenergic receptor signaling mainly regulates bone resorption during aging.

Osteoblastogenesis regulation signals in bone remodeling

Bone remodeling is essential for adult bone homeostasis. The failure of this process often leads to the development of osteoporosis, a present major global health concern. The most important factor that affects normal bone remodeling is the tightly controlled and orchestrated regulation of osteoblasts and osteoclasts. The present review summarized the recent discoveries related to osteoblast regulation from several signals, including transforming growth factor-β, bone morphogenetic proteins, Wnt signal, Notch, Eph-Ephrin interaction, parathyroid hormone/parathyroid hormone-related peptide, and the leptin-serotonin-sympathetic nervous systemic pathway. The awareness of these mechanisms will facilitate further research that explores bone remodeling and osteoporosis. Future investigations on the endogenous regulation of osteoblastogenesis will increase the current knowledge required for the development of potential drug targets in the treatment of osteoporosis.

β-Blocker and Other Analogous Treatments that Affect Bone Mass and Sympathetic Nerve Activity in Ovariectomized Rats

We investigated whether treatments with beta-blockers or other administrations that have similar actions to β-blockers, such as Chinese herbs or needling, were effective in treating osteoporosis induced by ovariectomy (OVX). Female Wister rats were divided into five groups: a sham-operated control group treated with vehicle (Sham, n = 8), an ovariectomized (OVX) group treated with vehicle (Model, n = 8), an OVX group administered with propranolol (Pro, n = 10), an OVX group administered an ethanol extract of Fructus Citri Sarcodactylis (Fcs, n = 9), and an OVX punctured at Sanyinjiao (SP-6) and Neiguan (PC-6) (Needling, n = 8). The treatment started when rats were 12 weeks old and continued for 24 weeks. Serum osteocalcin and urinary deoxypyridinoline (Dpd) levels were upregulated in rats in response to OVX, together with a significantly decreased BMD and trabecular bone area. The Pro, Fcs and Needling treatment improved the decreased BMD and the trabecular area, increased the trabecular number, lowered the trabecular separation to some extent as well as significantly depressed the urinary Dpd levels ( p < 0.05). The bone formation markers, such as the mineralizing surface, mineral apposition rate and bone formation rate were not significantly changed, along with a slightly higher trend of osteocalcin levels when compared with the Model rats. The slower heart rate and lower plasma NE levels in these therapeutic groups were also found. Our results suggested that propranolol, Fcs and needling on Sanyinjiao (SP-6) and Neiguan (PC-6) may improve the bone mass of OVX rats, and it provides an alternative and potential therapy for the prevention of postmenopausal osteoporosis.

Effects of propranolol on the development of glucocorticoid-induced osteoporosis in male rats

Glucocorticoid-induced osteoporosis is the most frequently occurring type of secondary osteoporosis. Antagonists of β-adrenergic receptors are now considered to be potential drugs under investigation for osteoporosis. The aim of the present study was to investigate the effects of propranolol, a nonselective β-receptor antagonist, on the skeletal system of mature male rats and on the development of bone changes induced by glucocorticoid (prednisolone) administration. The experiments were performed on 24-week-old male Wistar rats. The effects of prednisolone 21-hemisuccinate sodium salt (7 mg/kg, sc daily) or/and propranolol hydrochloride (10 mg/kg, ip daily) administered for 4 weeks on the skeletal system were studied. Bone and bone mineral mass in the tibia, femur and L-4 vertebra, length and diameter of the long bones, mechanical properties of tibial metaphysis, femoral diaphysis and femoral neck, bone histomorphometric parameters and turnover markers in serum were determined. Prednisolone-induced unfavorable skeletal changes led to disorders in bone mechanical properties. Propranolol not only did not improve bone parameters, but even caused deleterious effects on the skeletal system. Concurrent administration of propranolol with prednisolone did not counteract the changes induced by prednisolone. The results of this study may help to understand the equivocal results of human studies on the effects of β-blockers on the skeletal system. It is possible that the drugs exert biphasic effects on the skeletal system, both favorable and deleterious, depending on the dose or individual susceptibility.

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.

β2-Adrenergic receptor signaling in osteoblasts contributes to the catabolic effect of glucocorticoids on bone

The sympathetic nervous system is a physiological regulator of bone homeostasis. Autonomic nerves are indeed present in bone, bone cells express the β2-adrenergic receptors (β2AR), and pharmacological or genetic disruption of sympathetic outflow to bone induces bone gain in rodents. These recent findings implied that conditions that affect β2AR signaling in osteoblasts and/or sympathetic drive to bone may contribute to bone diseases. In this study, we show that dexamethasone stimulates the expression of the β2AR in differentiated primary calvarial osteoblasts, as measured by an increase in Adrβ2 mRNA and β2AR protein level after short-term dexamethasone treatment. Isoproterenol-induced cAMP accumulation and the expression of the β2AR target gene Rankl were also significantly increased after dexamethasone pretreatment, indicating that dexamethasone promotes the responsiveness of differentiated osteoblasts to adrenergic stimulation. These in vitro results led to the hypothesis that glucocorticoid-induced bone loss, provoked by increased endogenous or high-dose exogenous glucocorticoids given for the treatment of inflammatory diseases, might, at least in part, be mediated by increased sensitivity of bone-forming cells to the tonic inhibitory effect of sympathetic nerves on bone formation or their stimulatory effect on bone resorption. Supporting this hypothesis, both pharmacological and genetic β2AR blockade in mice significantly reduced the bone catabolic effect of high-dose prednisolone in vivo. This study emphasizes the importance of sympathetic nerves in the regulation of bone homeostasis and indicates that this neuroskeletal signaling axis can be modulated by hormones or drugs and contribute to enhance pathological bone loss.

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.