The effects of beta-2 adrenergic agonist and antagonist on human bone metabolism: a randomized controlled trial

The Role of Neuromodulation and Potential Mechanism in Regulating Heterotopic Ossification

Heterotopic ossification (HO) is a pathological process characterized by the aberrant formation of bone in muscles and soft tissues. It is commonly triggered by traumatic brain injury, spinal cord injury, and burns. Despite a wide range of evidence underscoring the significance of neurogenic signals in proper bone remodeling, a clear understanding of HO induced by nerve injury remains rudimentary. Recent studies suggest that injury to the nervous system can activate various signaling pathways, such as TGF-β, leading to neurogenic HO through the release of neurotrophins. These pathophysiological changes lay a robust groundwork for the prevention and treatment of HO. In this review, we collected evidence to elucidate the mechanisms underlying the pathogenesis of HO related to nerve injury, aiming to enhance our understanding of how neurological repair processes can culminate in HO.

Deteriorated bone microarchitecture caused by sympathetic overstimulation in pheochromocytoma and paraganglioma

PURPOSE

Despite the potentially destructive effect of sympathetic activity on bone metabolism, its impact on bone microarchitecture, a key determinant of bone quality, has not been thoroughly investigated. This study aims to evaluate the impact of sympathetic activity on bone microarchitecture and bone strength in patients with pheochromocytoma and paraganglioma (PPGL).

METHODS

A cross-sectional study was conducted in 38 PPGL patients (15 males and 23 females). Bone turnover markers serum procollagen type 1 N-terminal propeptide (P1NP) and β-carboxy-terminal crosslinked telopeptide of type 1 collagen (β-CTX) were measured. 24-h urinary adrenaline (24hUE) and 24-h urinary norepinephrine levels (24hUNE) were measured to indicate sympathetic activity. High-resolution peripheral quantitative computed tomography (HR-pQCT) was conducted to evaluate bone microarchitecture in PPGL patients and 76 age-, sex-matched healthy controls (30 males and 46 females). Areal bone mineral density (aBMD) was measured by dual-energy X-ray absorptiometry (DXA) simultaneously.

RESULTS

PPGL patients had a higher level of β-CTX. HR-pQCT assessment revealed that PPGL patients had notably thinner and more sparse trabecular bone (decreased trabecular number and thickness with increased trabecular separation), significantly decreased volume BMD (vBMD), and bone strength at both the radius and tibia compared with healthy controls. The deterioration of Tt.vBMD, Tb.Sp, and Tb.1/N.SD was more pronounced in postmenopausal patients compared with the premenopausal subjects. Moreover, subjects in the highest 24hUNE quartile (Q4) showed markedly lower Tb.N and higher Tb.Sp and Tb.1/N.SD at the tibia than those in the lowest quartile (Q1). Age-related bone loss was also exacerbated in PPGL patients to a certain extent.

CONCLUSIONS

PPGL patients had significantly deteriorated bone microarchitecture and strength, especially in the trabecular bone, with an increased bone resorption rate. Our findings provide clinical evidence that sympathetic overstimulation may serve as a secondary cause of osteoporosis, especially in subjects with increased sympathetic activity.

Bone mass loss in chronic heart failure is associated with sympathetic nerve activation

PURPOSE

Chronic heart failure causes osteoporosis, but the mechanism remains unclear. The sympathetic nerve plays an important role in both bone metabolism and cardiovascular function.

METHODS

Thirty-six adult male SD rats were randomly divided into the following four groups: sham surgery (Sham) group, guanethidine (GD) group, abdominal transverse aorta coarctation-induced heart failure + normal saline (TAC) group, and TAC + guanethidine (TAC + GD) group. Normal saline (0.9 % NaCl) or guanethidine (40 mg/kg/ml) was intraperitoneally injected daily for 5 weeks. Then, DXA, micro-CT, ELISA and RT-PCR analyses were performed 12 weeks after treatment.

RESULTS

The bone loss in rats subjected to TAC-induced chronic heart failure and chemical sympathectomy with guanethidine was increased. Serum norepinephrine levels were increased in rats with TAC-induced heart failure but were decreased in TAC-induced heart failure rats treated with guanethidine. The expression of α2A adrenergic receptor, α2C adrenergic receptor, osteoprotegerin (OPG), and osteocalcin in the tibia decreased in the TAC-induced heart failure group, and the expression of β1 adrenergic receptor, β2 adrenergic receptor, receptor activator of nuclear factor-κ B ligand (RANKL), and RANKL/OPG in the tibia increased in the heart failure group. In addition, these changes in gene expression levels were rescued by chemical sympathectomy with guanethidine.

CONCLUSIONS

TAC-induced chronic heart failure is associated with bone mass loss, and the sympathetic nerve plays a significant role in heart failure-related bone mass loss.

MINI ABSTRACT

The present study supports the hypothesis that heart failure is related to bone loss, and the excessive activation of sympathetic nerves participates in this pathophysiological process. The present study suggests a potential pathological mechanism of osteoporosis associated with heart failure and new perspectives for developing strategies for heart failure-related bone loss.

Mechanical loading alleviated the inhibition of β2-adrenergic receptor agonist terbutaline on bone regeneration

The long-term use of adrenergic medication in treating various conditions, such as asthma, increases the chances of bone fracture. Dynamic mechanical loading at a specific time is a method for improving bone quality and promoting healing. Therefore, we hypothesized that precisely controlling the mechanical environment can contribute to the alleviation of the negative effects of chronic treatment with the common asthma drug terbutaline, which is a β2-adrenergic receptor agonist that facilitates bone homeostasis and defect repair through its anabolic effect on osteogenic cells. Our in vitro results showed that terbutaline can directly inhibit osteogenesis by impairing osteogenic differentiation and mineralization. Chronic treatment in vivo was simulated by administering terbutaline to C57BL/6J mice for 4 weeks before bone defect surgery and mechanical loading. We utilized a stabilized tibial defect model, which allowed the application of anabolic mechanical loading. During homeostasis, chronic terbutaline treatment reduced the bone formation rate, the fracture toughness of long bones, and the concentrations of bone formation markers in the sera. During defect repair, terbutaline decreased the bone volume, type H vessel, and total blood vessel volume. Terbutaline treatment reduced the number of osteogenic cells. Periostin, which was secreted mainly by Prrx1+ osteoprogenitors and F4/80+ macrophages, was inhibited by treating the bone defect with terbutaline. Interestingly, controlled mechanical loading facilitated the recovery of bone volume and periostin expression and the number of osteogenic cells within the defect. In conclusion, mechanical loading can rescue negative effects on new bone accrual and repair induced by chronic terbutaline treatment.

Regulation of bone metabolism mediated by β-adrenergic receptor and its clinical application

Recent studies have confirmed that β-adrenergic receptors (β-ARs) are expressed on the surface of osteoblasts and osteoclasts, and that the sympathetic nervous system can regulate bone metabolism by activating them. β-AR blockers (BBs) are commonly used in the treatment of cardiovascular diseases in the elderly. It is important to investigate whether BBs have a beneficial effect on bone metabolism in the treatment of cardiovascular diseases, so as to expand their clinical application. This article reviews the effects of BB on bone metabolism and the progress of clinical research.

Biomechanical and Biochemical Analyses of the Effects of Propranolol on the Osseointegration of Implants

This study aimed to investigate the effects of systemic propranolol on the osseointegration of titanium implants. After the surgical insertion of titanium implants into the metaphyseal part of the tibiae of rats, the rats were randomly divided into three equal groups: the control (n = 8), propranolol dosage-1 (PRP-1) (n = 8), and propranolol dosage-2 (PRP-2) (n = 8) groups. In the control group, the rats received no further treatment during the 4-week experimental period after the surgery. After the surgical insertion of the implants, the rats in the PRP-1 and PRP-2 groups were given 5 mg/kg and 10 mg/kg propranolol, respectively, every 3 days for the 4-week experimental period. After the experimental period, the rats were euthanized. Blood sera were collected for biochemical analysis, and the implants and surrounding bone tissues were used for the biomechanical reverse torque analysis. One-way ANOVA and Tukey's honest significant difference test were used for statistical analysis. The student t-test was used to analyze the data obtained from the tests and the controls. There were no significant differences in the reverse torque analysis results and the biochemical parameters (alkaline phosphatase, calcium, and phosphorus) of the groups (P > 0.05). Alkaline phosphatase was, however, found to be higher in test animals compared to the controls (P < 0.05). Also, propranolol did not biomechanically affect the osseointegration of titanium implants, while alkaline phosphatase activity was higher in the test animals.

The Role of Nerves in Skeletal Development, Adaptation, and Aging

The skeleton is well-innervated, but only recently have the functions of this complex network in bone started to become known. Although our knowledge of skeletal sensory and sympathetic innervation is incomplete, including the specific locations and subtypes of nerves in bone, we are now able to reconcile early studies utilizing denervation models with recent work dissecting the molecular signaling between bone and nerve. In total, sensory innervation functions in bone much as it does elsewhere in the body-to sense and respond to stimuli, including mechanical loading. Similarly, sympathetic nerves regulate autonomic functions related to bone, including homeostatic remodeling and vascular tone. However, more study is required to translate our current knowledge of bone-nerve crosstalk to novel therapeutic strategies that can be effectively utilized to combat skeletal diseases, disorders of low bone mass, and age-related decreases in bone quality.

Evaluation of bone health in patients with adrenal tumors

PURPOSE OF REVIEW

Adrenal tumors occur in 5% of population with higher prevalence in elderly. Patients with adrenal tumors present with overt hormonal excess in up to 15% of cases, and mild autonomous cortisol secretion in 30-40% of cases. Overt Cushing syndrome, mild autonomous cortisol secretion, pheochromocytoma, and primary aldosteronism have been associated with higher cardiovascular morbidity and mortality. Increasing experimental and clinical evidence also suggests that adrenal hormone excess is detrimental to bone health. This review aims to discuss the effect of cortisol, aldosterone, and catecholamine excess on bone metabolism, secondary osteoporosis, and fragility fractures.

RECENT FINDINGS

Several studies have reported that patients with hormonally active adrenal tumors demonstrate increased prevalence of fragility fractures incongruous to bone density scan findings. The utility of dual absorptiometry X-ray (DXA) in diagnosing secondary osteoporosis is unclear in patients with cortisol, aldosterone, and catecholamine excess. Trabecular bone score and bone turn over markers could serve as potential diagnostic tools in assessment of severity of bone disease in patients with hormonally active adrenal tumors.

SUMMARY

Adrenalectomy is the mainstay of therapy in patients with overt hormone production. Appropriate case detection strategies to identify patients at risk of fragility fractures are needed in patients not treated with adrenalectomy, such as bilateral primary aldosteronism and mild autonomous cortisol secretion.

Long-term use of inhaled glucocorticoids in patients with stable chronic obstructive pulmonary disease and risk of bone fractures: a narrative review of the literature

Patients with chronic obstructive pulmonary disease (COPD) demonstrate a greater osteoporosis prevalence than the general population. This osteoporosis risk may be enhanced by treatment with inhaled corticosteroids (ICSs), which are recommended for COPD management when combined with long-acting bronchodilators, but may also be associated with reduced bone mineral density (BMD). We conducted a narrative literature review reporting results of randomized controlled trials (RCTs) of an ICS versus placebo over a treatment period of at least 12 months, with the aim of providing further insight into the link between bone fractures and ICS therapy. As of 16 October 2017, we identified 17 RCTs for inclusion. The ICSs studied were budesonide (six studies), fluticasone propionate (five studies), mometasone furoate (three studies), beclomethasone dipropionate, triamcinolone acetonide, and fluticasone furoate (one each). We found no difference in the number of bone fractures among patients receiving ICSs versus placebo across the six identified RCTs reporting fracture data. BMD data were available for subsets of patients in few studies, and baseline BMD data were rare; where these data were given, they were reported for treatment groups without stratification for factors known to affect BMD. Risk factors for reduced BMD and fractures, such as smoking and physical activity, were also often not reported. Furthermore, a standardized definition of the term "fracture" was not employed across these studies. The exact relationship between long-term ICS use and bone fracture incidence in patients with stable COPD remains unclear in light of our review. We have, however, identified several limiting factors in existing studies that may form the basis of future RCTs designed specifically to explore this relationship.

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.

Higher sympathetic activity as a risk factor for skeletal deterioration in pheochromocytoma

Despite the potential biological importance of sympathetic activity in human bone metabolism, its effects on bone microarchitecture, a key determinant of bone quality, has not been thoroughly studied. In the present study, we investigated the lumbar spine trabecular bone score (TBS) as an indicator of skeletal deterioration in pheochromocytoma. Among 620 consecutive patients with newly diagnosed adrenal incidentaloma, 29 with histologically confirmed pheochromocytoma (a catecholamine-secreting neuroendocrine tumor) and 266 with nonfunctional adrenal incidentaloma were defined as cases and controls, respectively. After adjustment for confounders, subjects with pheochromocytoma had 2.9% lower lumbar spine TBS than those without pheochromocytoma (P = 0.038). Moreover, urinary normetanephrine level, but not urinary metanephrine level, was inversely correlated with lumbar spine TBS (P = 0.009). Subjects in the highest urinary normetanephrine quartile showed markedly lower lumbar spine TBS than those in the lowest quartile (P = 0.018), in a dose-response manner across increasing urinary normetanephrine quartile categories (P for trend = 0.021). Consistent with the results of previous studies, subjects with pheochromocytoma had significantly lower bone mass at the lumbar spine and higher serum level of C-terminal telopeptide of type I collagen than controls (P = 0.013 and 0.002, respectively). These findings provide clinical evidence that catecholamine excess and the resultant sympathetic overstimulation in pheochromocytoma may contribute to bone fragility, especially in the trabecular bone, through a weak microarchitecture in addition to a lower bone mass and increased bone resorption, and support the possibility of pheochromocytoma as a secondary cause of osteoporosis.

Sympathetic β1-adrenergic signaling contributes to regulation of human bone metabolism

BACKGROUND

Evidence from rodent studies indicates that the sympathetic nervous system (SNS) regulates bone metabolism, principally via β2-adrenergic receptors (β2-ARs). Given the conflicting human data, we used multiple approaches to evaluate the role of the SNS in regulating human bone metabolism.

METHODS

Bone biopsies were obtained from 19 young and 19 elderly women for assessment of ADRB1, ADRB2, and ADRB3 mRNA expression. We examined the relationship of β-blocker use to bone microarchitecture by high-resolution peripheral quantitative CT in a population sample of 248 subjects. A total of 155 postmenopausal women were randomized to 1 of 5 treatment groups for 20 weeks: placebo; propranolol, 20 mg b.i.d.; propranolol, 40 mg b.i.d.; atenolol, 50 mg/day; or nebivolol, 5 mg/day. We took advantage of the β1-AR selectivity gradient of these drugs (propranolol [nonselective] << atenolol [relatively β1-AR selective] < nebivolol [highly β1-AR selective]) to define the β-AR selectivity for SNS effects on bone.

RESULTS

ADRB1 and ADRB2, but not ADRB3, were expressed in human bone; patients treated clinically with β1-AR-selective blockers had better bone microarchitecture than did nonusers, and relative to placebo, atenolol and nebivolol, but not propranolol, reduced the bone resorption marker serum C-telopeptide of type I collagen (by 19.5% and 20.6%, respectively; P < 0.01) and increased bone mineral density of the ultradistal radius (by 3.6% and 2.9%; P < 0.01 and P < 0.05, respectively).

CONCLUSIONS

These 3 independent lines of evidence strongly support a role for adrenergic signaling in the regulation of bone metabolism in humans, principally via β1-ARs.

TRIAL REGISTRATION

ClinicalTrials.gov NCT02467400.

FUNDING

This research was supported by the NIH (AG004875 and AR027065) and a Mayo Clinic Clinical and Translational Science Award (CTSA) (UL1 TR002377).

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.

Neuronal hypothalamic regulation of body metabolism and bone density is galanin dependent

In the brain, the ventral hypothalamus (VHT) regulates energy and bone metabolism. Whether this regulation uses the same or different neuronal circuits is unknown. Alteration of AP1 signaling in the VHT increases energy expenditure, glucose utilization, and bone density, yet the specific neurons responsible for each or all of these phenotypes are not identified. Using neuron-specific, genetically targeted AP1 alterations as a tool in adult mice, we found that agouti-related peptide-expressing (AgRP-expressing) or proopiomelanocortin-expressing (POMC-expressing) neurons, predominantly present in the arcuate nucleus (ARC) within the VHT, stimulate whole-body energy expenditure, glucose utilization, and bone formation and density, although their effects on bone resorption differed. In contrast, AP1 alterations in steroidogenic factor 1-expressing (SF1-expressing) neurons, present in the ventromedial hypothalamus (VMH), increase energy but decrease bone density, suggesting that these effects are independent. Altered AP1 signaling also increased the level of the neuromediator galanin in the hypothalamus. Global galanin deletion (VHT galanin silencing using shRNA) or pharmacological galanin receptor blockade counteracted the observed effects on energy and bone. Thus, AP1 antagonism reveals that AgRP- and POMC-expressing neurons can stimulate body metabolism and increase bone density, with galanin acting as a central downstream effector. The results obtained with SF1-expressing neurons, however, indicate that bone homeostasis is not always dictated by the global energy status, and vice versa.

Bone Health in Adrenal Disorders

Secondary osteoporosis resulting from specific clinical disorders may be potentially reversible, and thus continuous efforts to find and adequately treat the secondary causes of skeletal fragility are critical to ameliorate fracture risk and to avoid unnecessary treatment with anti-osteoporotic drugs. Among the hyperfunctional adrenal masses, Cushing's syndrome, pheochromocytoma, and primary aldosteronism are receiving particularly great attention due to their high morbidity and mortality mainly by increasing cardiovascular risk. Interestingly, there is accumulating experimental and clinical evidence that adrenal hormones may have direct detrimental effects on bone metabolism as well. Thus, the present review discusses the possibility of adrenal disorders, especially focusing on pheochromocytoma and primary aldosteronism, as secondary causes of osteoporosis.

Lower Bone Mass and Higher Bone Resorption in Pheochromocytoma: Importance of Sympathetic Activity on Human Bone

CONTEXT

Despite the apparent biological importance of sympathetic activity on bone metabolism in rodents, its role in humans remains questionable.

OBJECTIVE

To clarify the link between the sympathetic nervous system and the skeleton in humans.

DESIGN, SETTING, AND PATIENTS

Among 620 consecutive subjects with newly diagnosed adrenal incidentaloma, 31 patients with histologically confirmed pheochromocytoma (a catecholamine-secreting neuroendocrine tumor) and 280 patients with nonfunctional adrenal incidentaloma were defined as cases and controls, respectively.

RESULTS

After adjustment for confounders, subjects with pheochromocytoma had 7.2% lower bone mass at the lumbar spine and 33.5% higher serum C-terminal telopeptide of type 1 collagen (CTX) than those without pheochromocytoma (P = 0.016 and 0.001, respectively), whereas there were no statistical differences between groups in bone mineral density (BMD) at the femur neck and total hip and in serum bone-specific alkaline phosphatase (BSALP) level. The odds ratio (OR) for lower BMD at the lumbar spine in the presence of pheochromocytoma was 3.31 (95% confidence interval, 1.23 to 8.56). However, the ORs for lower BMD at the femur neck and total hip did not differ according to the presence of pheochromocytoma. Serum CTX level decreased by 35.2% after adrenalectomy in patients with pheochromocytoma, whereas serum BSALP level did not change significantly.

CONCLUSIONS

This study provides clinical evidence showing that sympathetic overstimulation in pheochromocytoma can contribute to adverse effects on human bone through the increase of bone loss (especially in trabecular bone), as well as bone resorption.

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.