Characterization of beta-adrenergic receptors on rat and human osteoblast-like cells and demonstration that beta-receptor agonists can stimulate bone resorption in organ culture

Systemic Factors Affecting Prognosis of Dental Implants

Clinicians who place and restore implants are always concerned about the success and longevity of the same. There are several local and systemic factors that affect osseointegration and the health of the peri-implant tissues. In this study, we review the systemic factors that can affect implant survival, osseointegration, and long-term success. The study highlights the importance of delineating, and taking into consideration these systemic factors from the planning phase to the restorative phase of dental implants. A thorough medical history, including prescription and over-the-counter medications, is vital, as there may be numerous factors that could directly or indirectly influence the prognosis of dental implants.

Neuronal regulation of bone and tendon injury repair: a focused review

Beyond the sensation of pain, peripheral nerves have been shown to play crucial roles in tissue regeneration and repair. As a highly innervated organ, bone can recover from injury without scar formation, making it an interesting model in which to study the role of nerves in tissue regeneration. As a comparison, tendon is a musculoskeletal tissue that is hypo-innervated, with repair often resulting in scar formation. Here, we reviewed the significance of innervation in 3 stages of injury repair (inflammatory, reparative, and remodeling) in 2 commonly injured musculoskeletal tissues: bone and tendon. Based on this focused review, we conclude that peripheral innervation is essential for phases of proper bone and tendon repair, and that nerves may dynamically regulate the repair process through interactions with the injury microenvironment via a variety of neuropeptides or neurotransmitters. A deeper understanding of neuronal regulation of musculoskeletal repair, and the crosstalk between nerves and the musculoskeletal system, will enable the development of future therapies for tissue healing.

Systemic administration of propranolol reduces bone resorption and inflammation in apical periodontitis of chronically stressed rats

AIM

To evaluate the effect of systemic administration of propranolol on the severity of apical periodontitis (AP) in chronically stressed rats.

METHODOLOGY

Twenty-four 70-day-old male Wistar rats (Rattus norvegicus, albinus) were distributed into three groups (n = 8): rats with AP without stressful conditions (AP-Control), rats with AP and submitted to a chronic unpredictable stress (CUS) protocol (AP + S) and rats with AP and submitted to a CUS protocol treated with propranolol (AP + S + PRO). Stress procedures were applied daily until the end of the experiment. After 3 weeks of CUS, AP was induced in all groups by exposing the pulpal tissue of mandibular and maxillary first molars to the oral environment. Propranolol treatment was administered orally once a day for the entire period of the experiment. Rats were sacrificed at 42 days, and the blood was collected for stress biomarkers serum dosage by multiplex assay. Mandibles were removed and submitted to microtomography and histopathological analyses. Periapical tissue surrounding the upper first molar was homogenized and subjected to RT-PCR analysis to evaluate the mRNA expression of RANKL, TRAP and OPG. Parametric data were assessed using one-way ANOVA followed by Tukey's test while the nonparametric data were analysed by the Kruskal-Wallis followed by Dunn's test. Significance level was set at 5% (p < .05) for all assessed parameters.

RESULTS

Micro-CT revealed statistically significant differences in bone resorption which was greater in the AP + S group (p < .05), but no differences were observed between the Control and AP + S + PRO groups (p > .05). The AP + S + PRO group had a lower intensity and extent of inflammatory infiltrate compared to the AP + S group with smaller areas of bone loss (p < 0.05). The gene expression of RANKL and TRAP was significantly higher in the stressed group AP + S compared to the control group (p < .05), and a significantly higher OPG expression was observed in AP + S + PRO compared to the AP + S group (p < .05).

CONCLUSIONS

Oral administration of propranolol had a significant effect on the AP severity in stressed rats, suggesting an anti-inflammatory effect and a protective role on bone resorption of AP in stressed animals. Further research is necessary to fully comprehend the underlying mechanisms.

Protective Effects of β-Blockers on Bone in Older Adults with Dementia

Increased β-adrenergic receptor activity has been hypothesized to cause bone loss in those with dementia. We investigated the effect of long-term β-blocker use on rate of bone loss in older adults with dementia. We used a linear mixed-effects model to estimate the relationship between long-term β-blocker use and rate of bone loss in participants from the Health Aging and Body Composition study. Records of 1198 participants were analyzed, 44.7% were men. Among the men, 25.2% had dementia and 20.2% were on β-blockers, while in the women, 22.5% had dementia and 16.6% received β-blockers. In the 135 men with dementia, 23 were taking β-blockers, while 15 of 149 women with dementia were using β-blockers. In men with dementia, β-blocker users had 0.00491 g/cm2 less bone mineral density (BMD) loss per year at the femoral neck (i.e., 0.63% less loss per year) than non-users (p < 0.05). No differences were detected in women with or without dementia and men without dementia. β-blockers may be protective by slowing down bone loss in older men with dementia.

Autonomic neural regulation in mediating the brain-bone axis: mechanisms and implications for regeneration under psychological stress

Efficient regeneration of bone defects caused by disease or significant trauma is a major challenge in current medicine, which is particularly difficult yet significant under the emerging psychological stress in the modern society. Notably, the brain-bone axis has been proposed as a prominent new concept in recent years, among which autonomic nerves act as an essential and emerging skeletal pathophysiological factor related to psychological stress. Studies have established that sympathetic cues lead to impairment of bone homeostasis mainly through acting on mesenchymal stem cells (MSCs) and their derivatives with also affecting the hematopoietic stem cell (HSC)-lineage osteoclasts, and the autonomic neural regulation of stem cell lineages in bone is increasingly recognized to contribute to the bone degenerative disease, osteoporosis. This review summarizes the distribution characteristics of autonomic nerves in bone, introduces the regulatory effects and mechanisms of autonomic nerves on MSC and HSC lineages, and expounds the crucial role of autonomic neural regulation on bone physiology and pathology, which acts as a bridge between the brain and the bone. With the translational perspective, we further highlight the autonomic neural basis of psychological stress-induced bone loss and a series of pharmaceutical therapeutic strategies and implications toward bone regeneration. The summary of research progress in this field will add knowledge to the current landscape of inter-organ crosstalk and provide a medicinal basis for the achievement of clinical bone regeneration in the future.

Brown adipose tissue but not tibia exhibits a dramatic response to acute reduction in environmental temperature in growing male mice

Mice are typically housed at room temperature (∼22 °C), which is well below their thermoneutral zone and results in cold stress. Chronic cold stress leads to increased adaptive thermogenesis and reductions in cancellous bone volume and bone marrow adipose tissue mass in long bones of growing mice. There is strong evidence that increased neuronal activity initiates the metabolic response of intrascapular brown adipose tissue (BAT) to cold stress, but it is less clear whether bone is regulated through a similar mechanism. Therefore, we compared the short-term response of BAT and whole tibia to a reduction in environmental temperature. To accomplish this, we transferred a group of 6-week-old male mice from 32 °C to 22 °C housing and sacrificed the mice 24 h later. Age-matched controls were maintained at 32 °C. We then evaluated expression levels of a panel of genes related to adipocyte differentiation and fat metabolism in BAT and tibia, and a panel of genes related to bone metabolism in tibia. The decrease in housing temperature resulted in changes in expression levels for 47/86 genes related to adipocyte differentiation and fat metabolism in BAT, including 9-fold and 17-fold increases in Ucp1 and Dio2, respectively. In contrast, only 1/86 genes related to adipocyte differentiation and fat metabolism and 4/84 genes related to bone metabolism were differentially expressed in tibia. These findings suggest that bone, although innervated with sensory and sympathetic neurons, does not respond as rapidly as BAT to changes in environmental temperature.

Interoceptive regulation of skeletal tissue homeostasis and repair

Recent studies have determined that the nervous system can sense and respond to signals from skeletal tissue, a process known as skeletal interoception, which is crucial for maintaining bone homeostasis. The hypothalamus, located in the central nervous system (CNS), plays a key role in processing interoceptive signals and regulating bone homeostasis through the autonomic nervous system, neuropeptide release, and neuroendocrine mechanisms. These mechanisms control the differentiation of mesenchymal stem cells into osteoblasts (OBs), the activation of osteoclasts (OCs), and the functional activities of bone cells. Sensory nerves extensively innervate skeletal tissues, facilitating the transmission of interoceptive signals to the CNS. This review provides a comprehensive overview of current research on the generation and coordination of skeletal interoceptive signals by the CNS to maintain bone homeostasis and their potential role in pathological conditions. The findings expand our understanding of intersystem communication in bone biology and may have implications for developing novel therapeutic strategies for bone diseases.

The Sympathetic Nervous System in Dental Implantology

The sympathetic nervous system plays a vital role in various regulatory mechanisms. These include the well-known fight-or-flight response but also, for example, the processing of external stressors. In addition to many other tissues, the sympathetic nervous system influences bone metabolism. This effect could be highly relevant concerning osseointegration, which is responsible for the long-term success of dental implants. Accordingly, this review aims to summarize the current literature on this topic and to reveal future research perspectives. One in vitro study showed differences in mRNA expression of adrenoceptors cultured on implant surfaces. In vivo, sympathectomy impaired osseointegration in mice, while electrical stimulation of the sympathetic nerves promoted it. As expected, the beta-blocker propranolol improves histological implant parameters and micro-CT measurements. Overall, the present data are considered heterogeneous. However, the available publications reveal the potential for future research and development in dental implantology, which helps to introduce new therapeutic strategies and identify risk factors for dental implant failure.

Bone Regeneration in Rat using Polycaprolactone/Gelatin/Epinephrine Scaffold

Solid supports like the extracellular matrix network are necessary for bone cell attachment and start healing in the damaged bone. Scaffolds which are made of different materials are widely used as a supportive structure in bone tissue engineering. In the current study, a 3-D Polycaprolactone/Gelatin bone scaffold was developed by blending electrospinning and freeze-drying techniques for bone tissue engineering. To improve the efficiency of the scaffold, different concentrations of epinephrine due to its effect on bone healing were loaded. Fabricated scaffolds were characterized by different tests such as surface morphology, FTIR, porosity, compressive strength, water contact angle, degradation rate. The interaction between prepared scaffolds and blood and cells was evaluated by hemolysis, and MTT test, respectively, and bone healing was evaluated by a rat calvaria defect model. Based on the results, the porosity of scaffolds was about 75% and by adding epinephrine, mechanical strength decreased while due to the hydrophilic properties of it, degradation rate increased. In vivo and in vitro studies showed the best cell proliferation and bone healing were in PCL/Gelatin/Epinephrine1%-treated group. These results showed the positive effect of fabricated scaffold on osteogenesis and bone healing and the possibility of using it in clinical trials.

Prostate Cancer Cell Extracellular Vesicles Increase Mineralisation of Bone Osteoblast Precursor Cells in an In Vitro Model

Simple Summary

Prostate cancer frequently metastasizes to the bone, where it forms primarily osteoblastic lesions. Currently there is no real therapeutic option for this late stage of disease, and understanding prostate cancer-bone interaction and communication is vital. Using a simple in vitro model of os-teoblast differentiation and mineralization, we studied this interaction and observed that prostate cancer cells secreted large quantities of extracellular vesicles containing microRNAs. When ex-posed to the extracellular vesicles, increased osteoblast differentiation and mineralization could be observed, and upon RNA-seq several of these microRNAs were implicated as upstream regulators of the mineralization process. These microRNAs also correlated with poor survival in online analysis of patient datasets. We characterized and validated four genes known to be targeted by microRNA-16, and found that extracellular vesicles could deliver miR-16, and increase minerali-zation.

Abstract

Skeletal metastases are the most common form of secondary tumour associated with prostate cancer (PCa). The aberrant function of bone cells neighbouring these tumours leads to the devel-opment of osteoblastic lesions. Communication between PCa cells and bone cells in bone envi-ronments governs both the formation/development of the associated lesion, and growth of the secondary tumour. Using osteoblasts as a model system, we observed that PCa cells and their conditioned medium could stimulate and increase mineralisation and osteoblasts’ differentiation. Secreted factors within PCa-conditioned medium responsible for osteoblastic changes included small extracellular vesicles (sEVs), which were sufficient to drive osteoblastogenesis. Using MiR-seq, we profiled the miRNA content of PCa sEVs, showing that miR-16-5p was highly ex-pressed. MiR-16 was subsequently higher in EV-treated 7F2 cells and a miR-16 mimic could also stimulate mineralisation. Next, using RNA-seq of extracellular vesicle (EV)-treated 7F2 cells, we observed a large degree of gene downregulation and an increased mineralisation. Ingenuity® Pathway Analysis (IPA^®) revealed that miR-16-5p (and other miRs) was a likely upstream effec-tor. MiR-16-5p targets in 7F2 cells, possibly involved in osteoblastogenesis, were included for val-idation, namely AXIN2, PLSCR4, ADRB2 and DLL1. We then confirmed the targeting and dow-regulation of these genes by sEV miR-16-5p using luciferase UTR (untranslated region) reporters. Conversely, the overexpression of PLSCR4, ADRB2 and DLL1 lead to decreased osteoblastogene-sis. These results indicate that miR-16 is an inducer of osteoblastogenesis and is transmitted through prostate cancer-derived sEVs. The mechanism is a likely contributor towards the for-mation of osteoblastic lesions in metastatic PCa.

Systemic bone loss following myocardial infarction in mice

Myocardial infarction (MI) and osteoporotic fracture are leading causes of morbidity and mortality, and epidemiological evidence linking their incidence suggests possible crosstalk. MI can exacerbate atherosclerosis through the sympathetic nervous system (SNS) activation and β₃ adrenoreceptor-mediated release of hematopoietic stem cells, leading to monocytosis. We hypothesized that this same pathway initiates systemic bone loss following MI, since osteoclasts differentiate from monocytes. In this study, MI was created with left anterior descending artery ligation in 12-week-old male mice (n = 24) randomized to β₃ -adrenergic receptor (AR) antagonist (SR 59230A) treatment or no treatment for 10 days postoperatively. Additional mice (n = 21, treated and untreated) served as unoperated controls. Bone mineral density (BMD), bone mineral content (BMC), and body composition were quantified at baseline and 10 days post-MI using dual-energy x-ray absorptiometry; circulating monocyte levels were quantified and the L5 vertebral body and femur were analyzed with microcomputed tomography 10 days post-MI. We found that MI led to circulating monocyte levels increases, BMD and BMC decreases at the femur and lumbar spine in MI mice (-6.9% femur BMD, -3.5% lumbar BMD), and trabecular bone volume decreases in MI mice compared with control mice. β₃ -AR antagonist treatment appeared to diminish the bone loss response (-5.3% femur BMD, -1.2% lumbar BMD), though these results were somewhat inconsistent. Clinical significance: These results suggest that MI leads to systemic bone loss, but that the SNS may not be a primary modulator of this response; bone loss and increased fracture risk may be important clinical comorbidities following MI or other ischemic injuries.

Crosstalk between Bone and Nerves within Bone

For the past two decades, the function of intrabony nerves on bone has been a subject of intense research, while the function of bone on intrabony nerves is still hidden in the corner. In the present review, the possible crosstalk between bone and intrabony peripheral nerves will be comprehensively analyzed. Peripheral nerves participate in bone development and repair via a host of signals generated through the secretion of neurotransmitters, neuropeptides, axon guidance factors and neurotrophins, with additional contribution from nerve-resident cells. In return, bone contributes to this microenvironmental rendezvous by housing the nerves within its internal milieu to provide mechanical support and a protective shelf. A large ensemble of chemical, mechanical, and electrical cues works in harmony with bone marrow stromal cells in the regulation of intrabony nerves. The crosstalk between bone and nerves is not limited to the physiological state, but also involved in various bone diseases including osteoporosis, osteoarthritis, heterotopic ossification, psychological stress-related bone abnormalities, and bone related tumors. This crosstalk may be harnessed in the design of tissue engineering scaffolds for repair of bone defects or be targeted for treatment of diseases related to bone and peripheral nerves.

Sympathetic activity in breast cancer and metastasis: partners in crime

The vast majority of patients with advanced breast cancer present skeletal complications that severely compromise their quality of life. Breast cancer cells are characterized by a strong tropism to the bone niche. After engraftment and colonization of bone, breast cancer cells interact with native bone cells to hinder the normal bone remodeling process and establish an osteolytic "metastatic vicious cycle". The sympathetic nervous system has emerged in recent years as an important modulator of breast cancer progression and metastasis, potentiating and accelerating the onset of the vicious cycle and leading to extensive bone degradation. Furthermore, sympathetic neurotransmitters and their cognate receptors have been shown to promote several hallmarks of breast cancer, such as proliferation, angiogenesis, immune escape, and invasion of the extracellular matrix. In this review, we assembled the current knowledge concerning the complex interactions that take place in the tumor microenvironment, with a special emphasis on sympathetic modulation of breast cancer cells and stromal cells. Notably, the differential action of epinephrine and norepinephrine, through either α- or β-adrenergic receptors, on breast cancer progression prompts careful consideration when designing new therapeutic options. In addition, the contribution of sympathetic innervation to the formation of bone metastatic foci is highlighted. In particular, we address the remarkable ability of adrenergic signaling to condition the native bone remodeling process and modulate the bone vasculature, driving breast cancer cell engraftment in the bone niche. Finally, clinical perspectives and developments on the use of β-adrenergic receptor inhibitors for breast cancer management and treatment are discussed.

Bone Marrow Microvasculature

The skeleton is highly vascularized due to the various roles blood vessels play in the homeostasis of bone and marrow. For example, blood vessels provide nutrients, remove metabolic by-products, deliver systemic hormones, and circulate precursor cells to bone and marrow. In addition to these roles, bone blood vessels participate in a variety of other functions. This article provides an overview of the afferent, exchange and efferent vessels in bone and marrow and presents the morphological layout of these blood vessels regarding blood flow dynamics. In addition, this article discusses how bone blood vessels participate in bone development, maintenance, and repair. Further, mechanical loading-induced bone adaptation is presented regarding interstitial fluid flow and pressure, as regulated by the vascular system. The role of the sympathetic nervous system is discussed in relation to blood vessels and bone. Finally, vascular participation in bone accrual with intermittent parathyroid hormone administration, a medication prescribed to combat age-related bone loss, is described and age- and disease-related impairments in blood vessels are discussed in relation to bone and marrow dysfunction. © 2020 American Physiological Society. Compr Physiol 10:1009-1046, 2020.

The neural system regulates bone homeostasis via mesenchymal stem cells: a translational approach

Large bone reconstruction is a major clinical issue associated with several challenges, and autograft is the main method for reconstructing large defects of maxillofacial bone. However, postoperative osteoporosis of the bone graft, even with sufficient vascularization, remains a primary problem. Therefore, better understanding of the mechanisms and clinical translation of bone homeostasis is required. Neuronal innervation of the bone is an emerging research topic, especially with regards to the role of peripheral nerves in regulating bone homeostasis. Moreover, sensory and autonomic nerves regulate this process via different types of neurotransmitters, but the specific mechanism is still elusive. In this review article, the current understanding of the interaction between the peripheral nerve and the skeleton system is summarized, with a particular focus on bone marrow mesenchymal stem cells (BMMSCs), except for osteoblasts and osteoclasts. The novel application of nerve-based bone regeneration via BMMSCs may provide a new strategy in tissue engineering and clinical treatment of osteoporosis and bone disorders.

The influence of adrenergic blockade in rats with apical periodontitis under chronic stress conditions

OBJECTIVE

To investigate the influence of chronic stress and adrenergic blockade in a rat model of apical periodontitis.

METHODS

Thirty-two Wistar rats were submitted to an animal model of periapical lesion and randomly divided into 4 groups (n = 8): no stress (NS); stress + saline solution (SS); stress + β-adrenergic blocker (Sβ); stress + α-adrenergic blocker (Sα). The SS, Sβ and Sα groups were submitted to an animal model of chronic stress for 28 days and received daily injections of saline solution, propranolol (β adrenergic blocker) and phentolamine (α adrenergic blocker), respectively. After 28 days the animals were euthanized and the following analyses were carried out: a) serum corticosterone levels through Radioimmunoassay; b) measurement of serum levels of IL-1B, IL-6, IL-10 and IL-17 by enzyme-linked immunosorbent assay (ELISA); c) volume of periapical bone resorption by micro-computed tomography; d) histomorphometric analysis by staining with hematoxylin and eosin; e) expression of β-AR, α-AR, receptor activator of nuclear factor kappa-B ligand (RANKL) and osteoprotegerin (OPG) by immunohistochemistry; f) tartrate-resistant acid phosphatase (TRAP) staining; g) ex-vivo cytokine release followed by the stimulation with LPS in superfusion system, by ELISA.

RESULTS

SS group displayed significantly higher corticosterone levels than NS group (non-stressed). Higher IL-1β serum level was observed in the NS group (p < .05); compared to all stressed groups. Other cytokines were present in similar amounts in the serum of all groups. All groups presented similar periapical lesions. All groups presented moderate inflammatory infiltrate, without statistically significant differences between them. No differences were observed regarding β-AR, α-AR, Rank-L and OPG expression. The number of TRAP-positive cells was significantly decreased in the groups that received daily injections of adrenergic blockers. The IL-1β release followed LPS stimulation was significantly suppressed when the superfusion media contained propranolol (p < .05). Perfusion containing phentolamine induced a greater release of IL-10. TGF-β was significantly suppressed by phentolamine perfusion in the NS group (p < .05).

CONCLUSIONS

Chronic stress can significantly change the inflammatory cytokines release. Rank-L/OPG system and periapical lesion volume were not affected following the current method applied. The administration of adrenergic blockers was not able to modulate the inflammatory response but presented effectivity in reducing the number of osteoclasts in the periapical region.

Biomarkers of Osteoporosis: An Update

Background:

Osteoporosis, characterized by compromised bone quality and strength is associated with bone fragility and fracture risk. Biomarkers are crucial for the diagnosis or prognosis of a disease as well as elucidating the mechanism of drug action and improve decision making.

Objective:

An exhaustive description of traditional markers including bone mineral density, vitamin D, alkaline phosphatase, along with potential markers such as microarchitectural determination, trabecular bone score, osteocalcin, etc. is provided in the current piece of work. This review provides insight into novel pathways such as the Wnt signaling pathway, neuro-osseous control, adipogenic hormonal imbalance, gut-bone axis, genetic markers and the role of inflammation that has been recently implicated in osteoporosis.

Methods:

We extensively reviewed articles from the following databases: PubMed, Medline and Science direct. The primary search was conducted using a combination of the following keywords: osteoporosis, bone, biomarkers, bone turnover markers, diagnosis, density, architecture, genetics, inflammation.

Conclusion:

Early diagnosis and intervention delay the development of disease and improve treatment outcome. Therefore, probing for novel biomarkers that are able to recognize people at high risk for developing osteoporosis is an effective way to improve the quality of life of patients and to understand the pathomechanism of the disease in a better way.

Oral dosing of pentoxifylline, a pan-phosphodiesterase inhibitor restores bone mass and quality in osteopenic rabbits by an osteogenic mechanism: A comparative study with human parathyroid hormone

The non-selective phosphodiesterase inhibitor pentoxifylline (PTX) is used for the treatment of intermittent claudication due to artery occlusion. Previous studies in rodents have reported salutary effects of the intraperitoneal administration of PTX in segmental bone defect and fracture healing, as well as stimulation of bone formation. We determined the effect of orally dosed PTX in skeletally mature ovariectomized (OVX) rabbits with osteopenia. The half-maximal effective concentration (EC₅₀) of PTX in rabbit bone marrow stromal cells was 3.07 ± 1.37 nM. The plasma PTX level was 2.05 ± 0.522 nM after a single oral dose of 12.5mg/kg, which was one-sixth of the adult human dose of PTX. Four months of daily oral dosing of PTX at 12.5 mg/kg to osteopenic rabbits completely restored bone mineral density, bone mineral content (BMC), microarchitecture and bone strength to the level of the sham-operated (ovary intact) group. The bone strength to BMC relationship between PTX and sham was similar. The bone restorative effect of PTX was observed in both axial and appendicular bones. In osteopenic rabbits, PTX increased serum amino-terminal propeptide, mineralized nodule formation by stromal cells and osteogenic gene expression in bone. PTX reversed decreased calcium weight percentage and poor crystal packing found in osteopenic rabbits. Furthermore, similar to parathyroid hormone (PTH), PTX had no effect on bone resorption. Taken together, our data show that PTX completely restored bone mass, bone strength and bone mineral properties by an anabolic mechanism. PTX has the potential to become an oral osteogenic drug for the treatment of post-menopausal osteoporosis.

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.

Cardiovascular autonomic neuropathy and bone metabolism in Type 1 diabetes

AIM

To investigate the association between cardiovascular autonomic neuropathy and bone metabolism in people with Type 1 diabetes.

METHODS

We assessed cardiovascular autonomic neuropathy in 329 people with Type 1 diabetes according to heart rate response to deep breathing, to standing and to the Valsalva manoeuvre, and 2-min resting heart rate. More than one pathological non-resting test was defined as cardiovascular autonomic neuropathy. Bone mineral density of the femoral neck (BMDfn) was assessed by dual energy X-ray absorptiometry. Serum parathyroid hormone levels and other bone markers were measured.

RESULTS

The mean (sd) age of the participants was 55.6 (9.4) years, 52% were men, and the mean (sd) diabetes duration was 40 (8.9) years, HbA_1c 62 (9) mmol/mol and estimated GFR 78 (26) ml/min/1.73m² . In all, 36% had cardiovascular autonomic neuropathy. Participants with cardiovascular autonomic neuropathy had 4.2% (95% CI -8.0 to -0.2; P=0.038) lower BMDfn and 33.6% (95% CI 14.3 to 53.8; P=0.0002) higher parathyroid hormone levels compared with participants without cardiovascular autonomic neuropathy in adjusted models. Higher resting heart rate remained associated with higher parathyroid hormone level and lower BMDfn after additional adjustment for eGFR (P<0.0001 and P = 0.042, respectively).

CONCLUSIONS

The presence of cardiovascular autonomic neuropathy was associated with reduced BMDfn and increased levels of parathyroid hormone. Kidney function may either confound or mediate these findings. Cardiovascular autonomic neuropathy could be associated with increased risk of osteoporosis in Type 1 diabetes. Whether cardiovascular autonomic neuropathy directly affects bone metabolism detrimentally or if this association is mediated via decreased kidney function should be investigated further.

Engineering vascularized and innervated bone biomaterials for improved skeletal tissue regeneration

Blood vessels and nerve fibers are distributed throughout the entirety of skeletal tissue, and play important roles during bone development and fracture healing by supplying oxygen, nutrients, and cells. However, despite the successful development of bone mimetic materials that can replace damaged bone from a structural point of view, most of the available bone biomaterials often do not induce sufficient formation of blood vessels and nerves. In part, this is due to the difficulty of integrating and regulating multiple tissue types within artificial materials, which causes a gap between native skeletal tissue. Therefore, understanding the anatomy and underlying interaction mechanisms of blood vessels and nerve fibers in skeletal tissue is important to develop biomaterials that can recapitulate its complex microenvironment. In this perspective, we highlight the structure and osteogenic functions of the vascular and nervous system in bone, in a coupled manner. In addition, we discuss important design criteria for engineering vascularized, innervated, and neurovascularized bone implant materials, as well as recent advances in the development of such biomaterials. We expect that bone implant materials with neurovascularized networks can more accurately mimic native skeletal tissue and improve the regeneration of bone tissue.

Osteogenic actions of metoprolol in an ovariectomized rat model of menopause

OBJECTIVE

Osteoporosis and hypertension are age-related chronic diseases with increased morbidity rates among postmenopausal women. Clinical epidemiological investigations have demonstrated that hypertensive patients treated with β1-selective β-blockers have a higher bone mineral density (BMD) and lower fracture risk. Nevertheless, no fundamental studies have examined the relationships between β1-selective β-blockers and these effects. The present study explored the effects and mechanisms of metoprolol in the in vitro treatment of osteoblasts and the in vivo treatment of ovariectomy-induced osteoporosis in rats.

METHODS

Primary osteoblasts were obtained by digestion of the cranial bones of 24-hour-old Sprague-Dawley rats. After metoprolol treatment, cell proliferation and differentiation capacities were assessed at the corresponding time points. In addition, 3-month-old female Sprague-Dawley rats (200-220 g) were divided into a sham-operated group (n = 8) and three ovariectomized (OVX) (bilateral removal of ovaries) groups as follows: vehicle (OVX; n = 8), low-dose metoprolol (L-M, oral, 120 mg/kg/d; n = 8), and high-dose metoprolol (H-M, oral, 240 mg/kg/d; n = 8). After 12 weeks of metoprolol treatment, BMD, microarchitecture, and biomechanical properties were evaluated.

RESULTS

The results indicated that the treatments with 0.01 to 0.1 μM metoprolol increased osteoblast proliferation, alkaline phosphatase activity, and calcium mineralization, and promoted the expression of osteogenic genes. The in vivo study indicated that administration of metoprolol to OVX rats resulted in maintenance of the BMDs of the L4 vertebrae. Moreover, amelioration of trabecular microarchitecture deterioration and preservation of bone biomechanical properties were detected in the trabecular bones of the OVX rats.

CONCLUSIONS

Our findings indicate that metoprolol prevents estrogen deficiency-induced bone loss by increasing the number and enhancing the biological functions of osteoblasts, implying its potential use as an alternative treatment for postmenopausal osteoporosis in hypertensive patients.

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.

Sympathetic Signaling Reactivates Quiescent Disseminated Prostate Cancer Cells in the Bone Marrow

Clinical observations have identified an association between psychologic stress and cancer relapse, suggesting that the sympathetic nervous system/norepinephrine (NE) plays a role in reactivation of dormant disseminated tumor cells (DTC) in the bone marrow niche. Here, the mechanism by which NE regulates prostate cancer DTCs in the marrow is explored. NE directly stimulated prostate cancer cell proliferation through β2-adrenergic receptors (ADRB2). NE also altered prostate cancer proliferation in the marrow niche by indirectly downregulating the secretion of the dormancy inducing molecule growth arrest specific-6 (GAS6) expressed by osteoblasts. These observations were confirmed in cocultures of prostate cancer cells expressing the fluorescent ubiquitination-based cell-cycle reporters (FUCCI) and osteoblasts isolated from GAS6-deficient (GAS6^-/-) animals. A novel ex vivo model system, using femurs harvested from GAS6^+/+ or GAS6^-/- mice, was used to confirm these results. As in coculture, when prostate cancer cells were injected into the marrow cavities of GAS6^+/+ femurs, NE altered the prostate cancer cell cycle. However, NE had less of an impact on prostate cancer cells in femur explants isolated from GAS6^-/- mice. Together, this study demonstrates that NE reactivates prostate cancer cell cycling through both a direct action on prostate cancer cells and indirectly on adjacent niche cells.Implications: Identification of mechanisms that target DTCs may provide novel therapeutic approaches to prevent or treat cancer metastases more effectively. Mol Cancer Res; 15(12); 1644-55. ©2017 AACR.

Repurposing of approved cardiovascular drugs

Research and development of new drugs requires both long time and high costs, whereas safety and tolerability profiles make the success rate of approval very low. Drug repurposing, applying known drugs and compounds to new indications, has been noted recently as a cost-effective and time-unconsuming way in developing new drugs, because they have already been proven safe in humans. In this review, we discuss drug repurposing of approved cardiovascular drugs, such as aspirin, beta-blockers, angiotensin converting enzyme inhibitors, angiotensin II receptor blockers, cardiac glycosides and statins. Regarding anti-tumor activities of these agents, a number of experimental studies have demonstrated promising pleiotropic properties, whereas all clinical trials have not shown expected results. In pathological conditions other than cancer, repurposing of cardiovascular drugs is also expanding. Numerous experimental studies have reported possibilities of drug repurposing in this field and some of them have been tried for new indications ('bench to bedside'), while unexpected results of clinical studies have given hints for drug repurposing and some unknown mechanisms of action have been demonstrated by experimental studies ('bedside to bench'). The future perspective of experimental and clinical studies using cardiovascular drugs are also discussed.

Norepinephrine inhibits mesenchymal stem cell chemotaxis migration by increasing stromal cell-derived factor-1 secretion by vascular endothelial cells via NE/abrd3/JNK pathway

Mesenchymal stem cells (MSCs), which are physiologically maintained in vascular endothelial cell (VEC)-based niches, play a critical role in tissue regeneration. Our previous studies demonstrated that sympathetic denervation could promote MSC mobilization, thereby enhancing bone formation in distraction osteogenesis (DO), a self-tissue engineering for craniofacial and orthopeadic surgeries. However, the mechanisms on how sympathetic neurotransmitter norepinephrine (NE) regulates MSC migration are not well understood. Here we showed that deprivation of NE by transection of cervical sympathetic trunk (TCST) inhibited stromal cell-derived factor-1 (SDF-1) expression in the perivascular regions in rat mandibular DO. In vitro studies showed that NE treatment markedly upregulated p-JNK and therefore stimulated higher SDF-1 expression in VECs than control groups, and siRNA knockdown of the abrd3 gene abolished the NE-induced p-JNK activation. On the other hand, osteoblasts differentiated from MSCs showed an increase in SDF-1 secretion with lack of NE. Importantly, NE-treated VECs inhibited the MSC chemotaxis migration along the SDF-1 concentration gradient as demonstrated in a novel 3-chamber Transwell assay. Collectively, our study suggested that NE may increase the SDF-1 secretion by VECs via NE/abrd3/JNK pathway, thereby inhibiting the MSC chemotaxis migration from perivascular regions toward bone trabecular frontlines along the SDF-1 concentration gradient in bone regeneration.

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.

Expression of neuropeptide receptor mRNA during osteoblastic differentiation of mouse iPS cells

Various studies have shown a relationship between nerves and bones. Recent evidence suggests that both sensory and sympathetic nerves affect bone metabolism; however, little is known about how neuropeptides are involved in the differentiation of pluripotent stem cells into osteoblastic (OB) cells. To evaluate the putative effects of neuropeptides during the differentiation of mouse induced pluripotent stem (iPS) cells into calcified tissue-forming OB cells, we investigated the expression patterns of neuropeptide receptors at each differentiation stage. Mouse iPS cells were seeded onto feeder cells and then transferred to low-attachment culture dishes to form embryoid bodies (EBs). EBs were cultured for 4 weeks in osteoblastic differentiation medium. The expression of α1-adrenergic receptor (AR), α2-AR, β2-AR, neuropeptide Y1 receptor (NPY1-R), neuropeptide Y2 receptor (NPY2-R), calcitonin gene-related protein receptor (CGRP-R), and neurokinin 1-R (NK1-R) was assessed by reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR. Among these neuropeptide receptors, CGRP-R and β2-AR were expressed at all stages of cell differentiation, including the iPS cell stage, with peak expression occurring at the early osteoblastic differentiation stage. Another sensory nervous system receptor, NK1-R, was expressed mainly in the late osteoblastic differentiation stage. Furthermore, CGRP-R mRNA showed an additional small peak corresponding to EBs cultured for 3 days, suggesting that EBs may be affected by serum CGRP. These data suggest that the sensory nervous system receptor CGRP-R and the sympathetic nervous system receptor β2-AR may be involved in the differentiation of iPS cells into the osteoblastic lineage. It follows from these findings that CGRP and β2-AR may regulate cell differentiation in the iPS and EB stages, and that each neuropeptide has an optimal period of influence during the differentiation process.

Adrenaline facilitates calcium channel currents in osteoblasts

Adrenaline (Adr) is known to directly or indirectly modulate bone cell activity under physiological and pathological conditions. Osteoblasts play a major role in bone formation, employing intracellular Ca(2+) as a second messenger to modulate hormonal responses and as a cofactor for mineralization. Voltage-dependent Ca(2+) channels (VDCCs) mediate the influx of Ca(2+) in response to membrane depolarization. The purpose of this study was to investigate the effects of Adr on VDCC currents in osteoblasts using a patch-clamp recording method. Application of 1 mM Adr facilitated VDCC currents in a concentration-dependent manner. Pre-treatment with b receptor antagonist propranolol blocked Adr-induced facilitation of VDCC currents carried by Ba(2+) (IBa). These results indicate that Adr-induced facilitation of IBa was mediated by b receptors in MC3T3-E1 osteoblast-like cells. To our knowledge, the data presented here demonstrate for the first time that Adr facilitates VDCCs in MC3T3-E1 osteoblast-like cells.

Beta-1 adrenergic agonist treatment mitigates negative changes in cancellous bone microarchitecture and inhibits osteocyte apoptosis during disuse

The sympathetic nervous system (SNS) plays an important role in mediating bone remodeling. However, the exact role that beta-1 adrenergic receptors (beta1AR) have in this process has not been elucidated. We have previously demonstrated the ability of dobutamine (DOB), primarily a beta1AR agonist, to inhibit reductions in cancellous bone formation and mitigate disuse-induced loss of bone mass. The purpose of this study was to characterize the independent and combined effects of DOB and hindlimb unloading (HU) on cancellous bone microarchitecture, tissue-level bone cell activity, and osteocyte apoptosis. Male Sprague-Dawley rats, aged 6-mos, were assigned to either normal cage activity (CC) or HU (n = 18/group) for 28 days. Animals were administered either daily DOB (4 mg/kg BW/d) or an equal volume of saline (VEH) (n = 9/gp). Unloading resulted in significantly lower distal femur cancellous BV/TV (−33%), Tb.Th (−11%), and Tb.N (−25%) compared to ambulatory controls (CC-VEH). DOB treatment during HU attenuated these changes in cancellous bone microarchitecture, resulting in greater BV/TV (+29%), Tb.Th (+7%), and Tb.N (+21%) vs. HU-VEH. Distal femur cancellous vBMD (+11%) and total BMC (+8%) were significantly greater in DOB- vs. VEH-treated unloaded rats. Administration of DOB during HU resulted in significantly greater osteoid surface (+158%) and osteoblast surface (+110%) vs. HU-VEH group. Furthermore, Oc.S/BS was significantly greater in HU-DOB (+55%) vs. CC-DOB group. DOB treatment during unloading fully restored bone formation, resulting in significantly greater bone formation rate (+200%) than in HU-VEH rats. HU resulted in an increased percentage of apoptotic cancellous osteocytes (+85%), reduced osteocyte number (−16%), lower percentage of occupied osteocytic lacunae (−30%) as compared to CC-VEH, these parameters were all normalized with DOB treatment. Altogether, these data indicate that beta1AR agonist treatment during disuse mitigates negative changes in cancellous bone microarchitecture and inhibits increases in osteocyte apoptosis.

Sympathetic denervation-induced MSC mobilization in distraction osteogenesis associates with inhibition of MSC migration and osteogenesis by norepinephrine/adrb3

The sympathetic nervous system regulates bone formation and resorption under physiological conditions. However, it is still unclear how the sympathetic nerves affect stem cell migration and differentiation in bone regeneration. Distraction osteogenesis is an ideal model of bone regeneration due to its special nature as a self-engineering tissue. In this study, a rat model of mandibular distraction osteogenesis with transection of cervical sympathetic trunk was used to demonstrate that sympathetic denervation can deplete norepinephrine (NE) in distraction-induced bone callus, down-regulate β3-adrenergic receptor (adrb3) in bone marrow mesenchymal stem cells (MSCs), and promote MSC migration from perivascular regions to bone-forming units. An invitro Transwell assay was here used to demonstrate that NE can inhibit stroma-derived factor-1 (SDF-1)-induced MSC migration and expression of the migration-related gene matrix metalloproteinase-2 (MMP-2) and downregulate that of the anti-migration gene tissue inhibitor of metalloproteinase-3 (TIMP-3). Knockdown of adrb3 using siRNA abolishes inhibition of MSC migration. An in vitro osteogenic assay was used to show that NE can inhibit the formation of MSC bone nodules and expression of the osteogenic marker genes alkaline phosphatase (ALP), osteocalcin (OCN), and runt-related transcription factor-2 (RUNX2), but knockdown of adrb3 by siRNA can abolish such inhibition of the osteogenic differentiation of MSCs. It is here concluded that sympathetic denervation-induced MSC mobilization in rat mandibular distraction osteogenesis is associated with inhibition of MSC migration and osteogenic differentiation by NE/adrb3 in vitro. These findings may facilitate understanding of the relationship of MSC mobilization and sympathetic nervous system across a wide spectrum of tissue regeneration processes.

Antihypertensive medications, bone mineral density, and fractures: a review of old cardiac drugs that provides new insights into osteoporosis

Osteoporosis is increasing in prevalence and importance as society's age, with the clinical consequence of fractures of the hip, spine, and upper extremity, leading to impaired quality of life, loss of function and independence, and increased morbidity and mortality. A major risk factor for osteoporosis is older age, and cardiovascular diseases also share this risk factor; therefore, osteoporosis and cardiovascular disease often coexist and share risk factors. Medications used for the treatment of cardiovascular diseases, in particular antihypertensive drugs, have been shown in a variety of studies of varying designs to modulate bone health in both a positive or negative manner. In this article, we reviewed the pharmacology, potential mechanisms, and possible effects on bone mineral density and fracture risk of commonly prescribed antihypertensive medications, including thiazide and non-thiazide diuretics, beta-blockers, calcium channel blockers, renin-angiotensin-aldosterone system agents, and nitrates.

ADDITIONAL BENEFITS OF ANTIHYPERTENSIVE MOXONIDINE THERAPY IN POSTMENOPAUSAL WOMEN WITH ARTERIAL HYPERTENSION

Aim. To assess the effects of moxonidine in terms of target blood pressure (BP) achievement; to identify potential additional benefits of moxonidine and its effects on bone metabolism and bone mineral density (BMD) in postmenopausal women with arterial hypertension (AH).

Material and methods. The study included 48 postmenopausal women with Stage 1-2 AH, aged 57-71 years.

Results. All participants were divided into two groups by the type of antihypertensive therapy: those receiving moxonidine and those receiving angiotensin-converting enzyme inhibitors / angiotensin receptor antagonists (ACEI/ARA). All women also received calcium and vitamin D. All participants had AH and osteopenia (both in the lumbar spine and proximal femur, according to the X-ray absorptiometry results). In the moxonidine group, BP levels remained within the target range 48 weeks later. There was a significant reduction in the levels of a bone resorption marker (p=0,041), while the dynamics of an osteopoetic marker was statistically non-significant (p=0,31). A tendency towards increasing BMD in lumbar spine and proximal femur was also observed (p=0,059 and p=0,068, respectively). In the ACEI/ARA group, BP levels also remained within the target range 48 weeks later. However, no significant changes in the levels of bone metabolism markers were registered. There was a tendency towards decreasing BMD in lumbar spine and proximal femur (p=0,052 and p=0,054, respectively).

Conclusion. Moxonidine therapy was associated with a significant reduction in bone resorption activity, as demonstrated by the decrease in the concentration of a bone resorption marker, as well as with a tendency towards increasing BMD.

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.

Association between polymorphisms in leptin, leptin receptor, and β-adrenergic receptor genes and bone mineral density in postmenopausal Korean women

OBJECTIVE

The purpose of this study was to investigate the association between single nucleotide polymorphisms in leptin (LEP), leptin receptor (LEPR), and β-adrenergic receptor (ADRB) genes and bone mineral density (BMD) in postmenopausal Korean women.

METHODS

LEP c.280G>A, LEPR c.326A>G, LEPR c.668A>G, LEPR c.1968G>C, LEPR c.2096C>T, ADRB2 c.46A>G, ADRB2 c.79C>G, ADRB2 c.718T>C, ADRB2 c.741G>T, ADRB2 c.769G>A, and ADRB3 c.190T>C polymorphisms were analyzed in 592 postmenopausal Korean women. Serum levels of leptin, soluble leptin receptor, osteoprotegerin, soluble receptor activator of the nuclear factor-κB ligand, bone alkaline phosphatase, and carboxy-terminal telopeptide of type I collagen were measured, and BMDs at the lumbar spine and femoral neck were also examined.

RESULTS

Among the polymorphisms measured, only the LEPR c.1968G>C polymorphism was found to be associated with BMD at the femoral neck, and higher BMD was observed with increasing number of G alleles (P = 0.04). Osteoporosis at the femoral neck was 3.27 and 3.89 times more frequently observed in the AG and GG genotypes than in the AA genotype in the ADRB2 c.46A>G polymorphism (P = 0.024 and P = 0.015, respectively). However, no significant differences in serum levels of leptin, soluble leptin receptor, free leptin index, osteoprotegerin, soluble receptor activator of the nuclear factor-κB ligand, and bone turnover markers were detected among single and haplotype genotypes.

CONCLUSIONS

These results suggest that the LEPR c.1968G>C polymorphism may be one of the genetic factors affecting femoral neck BMD in postmenopausal Korean women and that an analysis of the ADRB2 c.46A>G polymorphism may be useful in identifying women at risk for osteoporosis at the femoral neck.

Outcome of enamel matrix derivative treatment in the presence of chronic stress: histometric study in rats

BACKGROUND

Psychologic stress and clinical hypercortisolism have been related to direct effects on bone metabolism. However, there is a lack of information regarding the outcomes of regenerative approaches under the influence of chronic stress (CS). Enamel matrix derivative (EMD) has been used in periodontal regenerative procedures, resulting in improvement of clinical parameters. Thus, the aim of this histomorphometric study is to evaluate the healing of periodontal defects after treatment with EMD under the influence of CS in the rat model.

METHODS

Twenty Wistar rats were randomly assigned to two groups; G1: CS (restraint stress for 12 hours/day) (n = 10), and G2: not exposed to CS (n = 10). Fifteen days after initiation of CS, fenestration defects were created at the buccal aspect of the first mandibular molar of all animals from both groups. After the surgeries, the defects of each animal were randomly assigned to two subgroups: non-treated control and treated with EMD. The animals were euthanized 21 days later.

RESULTS

G1 showed less bone density (BD) compared to G2. EMD provided an increased defect fill (DF) in G1 and higher BD and new cementum formation (NCF) in both groups. The number of tartrate-resistant acid phosphatase-positive osteoclasts was significantly higher in G1 when compared to G2 and in EMD-treated sites of both groups.

CONCLUSIONS

CS may produce a significant detrimental effect on BD. EMD may provide greater DF compared to non-treated control in the presence of CS and increased BD and NCF in the presence or absence of CS.

β-Adrenergic signaling stimulates osteoclastogenesis via reactive oxygen species

Sympathetic signaling regulates bone resorption through receptor activator of nuclear factor-κB ligand (RANKL) expression via the β-adrenergic receptor (β-AR) on osteoblasts. Reactive oxygen species (ROS) are known as one type of osteoclast regulatory molecule. Here we show that an antioxidant, α-lipoic acid (α-LA), treatment prevent the β-adrenergic signaling-induced bone loss by suppressing osteoclastogenesis, and sympathetic signaling directly regulates osteoclastogenesis through β2-AR expressed on osteoclasts via intracellular ROS generation. In an in vitro study, the β-AR agonist isoprenaline increased intracellular ROS generation in osteoclasts prepared from bone marrow macrophages (BBMs) and RAW 264.7 cells. Isoprenaline enhanced osteoclastogenesis through β2-AR expressed on BMMs and RAW 264.7 cells. The antioxidant α-LA inhibited isoprenaline-enhanced osteoclastogenesis. Isoprenaline increased the expression of osteoclast-related genes such as nuclear factor of activated T cells, cytoplasmic, calcineurin-dependent 1, tartrate-resistant acid phosphatase, and cathepsin K on osteoclasts. α-LA also inhibited isoprenaline-induced increases of these gene expressions. These in vitro results led to the hypothesis that β-adrenergic signaling directly stimulates osteoclastogenesis via ROS generation. In an in vivo study, isoprenaline treatment alone caused oxidative damage in local bone and reduced bone mass because of an increase in bone resorption, and, in α-LA-treated mice, isoprenaline did not increase tibial osteoclast number even though the RANKL-to-osteoprotegerin ratio increased. These in vitro and in vivo results indicate that β-adrenergic signaling, at least in part, directly stimulates osteoclastogenesis through β2-AR on osteoclasts via ROS generation.

Dose effects of butoxamine, a selective β2-adrenoceptor antagonist, on bone metabolism in spontaneously hypertensive rat

Recent studies have shown that osteoblasts and osteoclasts express β2-adrenoceptor, and increased sympathetic nervous activity causes bone loss via an increase in osteoclastic bone resorption and a decrease in osteoblastic bone formation. We previously demonstrated that non-selective β-adrenoceptor antagonist propranolol at low doses (0.1 and 1mg/kg), but not at a higher dose (10mg/kg), prevented a decrease in bone mass and an increase in bone fragility in spontaneously hypertensive rat (SHR), an animal model of osteoporosis with hyperactivity of the sympathetic nervous system, without affecting blood pressure. In the present study, the dose effects of butoxamine, a selective β2-adrenoceptor antagonist, on bone metabolism were examined in SHR by analysis of microcomputed tomography, bone histomorphometry, biomechanical testing and plasma biochemistry. Treatment of SHR with butoxamine at 0.1, 1 and 10mg/kg (per os) for 12 weeks increased bone mass indices and biomechanical parameters of strength and toughness of the lumbar vertebrae, suggesting antiosteoporotic activity. Butoxamine dose-dependently decreased osteoclast number and surface per bone surface with decreases in plasma tartrate-resistant acid phosphatase-5b level, a biochemical index of osteoclastic activity. On the other hand, histomorphometry indices of bone formation and plasma osteocalcin concentration reflecting osteoblastic activity were increased in SHR treated with butoxamine at 0.1 and 1mg/kg, but not at 10mg/kg. These results suggest that β-adrenoceptor antagonists at a low dose may improve osteoporosis with hyperactivity of the sympathetic nervous system via β2-adrenoceptor blocking action, while they may have a somewhat inhibitory effect on osteoblastic activity at a high dose.

Heart failure as a risk factor for osteoporosis and fractures

Although heart failure (HF) and osteoporosis are common diseases, particularly in elderly populations, patients with HF have an increased risk for osteoporosis. The relationship of HF with osteoporosis is modified by gender and the severity of HF. In addition, shared risk factors, medication use, and common pathogenic mechanisms affect both HF and osteoporosis. Shared risk factors for these 2 conditions include advanced age, hypovitaminosis D, renal disease, and diabetes mellitus. Medications used to treat HF, including spironolactone, thiazide diuretics, nitric oxide donors, and aspirin, may protect against osteoporosis. In contrast, loop diuretics may make osteoporosis worse. HF and osteoporosis appear to share common pathogenic mechanisms, including activation of the renin-angiotensin-aldosterone system, increased parathyroid hormone levels, and/or oxidative/nitrosative stress. HF is a major risk factor for mortality following fractures. Thus, in HF patients, it is important to carefully assess osteoporosis and take measures to reduce the risk of osteoporotic fractures.

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

CONTEXT

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

OBJECTIVE

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

DESIGN, SETTING, AND PATIENTS

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

RESULTS

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

CONCLUSION

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

Stimulation of host bone marrow stromal cells by sympathetic nerves promotes breast cancer bone metastasis in mice

The activation of sympathetic nerves by psychosocial stress creates a favorable environment in bone for the establishment of cancer cells in a mouse model of breast cancer.

Bone and lung metastases are responsible for the majority of deaths in patients with breast cancer. Following treatment of the primary cancer, emotional and psychosocial factors within this population precipitate time to recurrence and death, however the underlying mechanism(s) remain unclear. Using a mouse model of bone metastasis, we provide experimental evidence that activation of the sympathetic nervous system, which is one of many pathophysiological consequences of severe stress and depression, promotes MDA-231 breast cancer cell colonization of bone via a neurohormonal effect on the host bone marrow stroma. We demonstrate that induction of RANKL expression in bone marrow osteoblasts, following β2AR stimulation, increases the migration of metastatic MDA-231 cells in vitro, independently of SDF1-CXCR4 signaling. We also show that the stimulatory effect of endogenous (chronic stress) or pharmacologic sympathetic activation on breast cancer bone metastasis in vivo can be blocked with the β-blocker propranolol, and by knockdown of RANK expression in MDA-231 cells. These findings indicate that RANKL promotes breast cancer cell metastasis to bone via its pro-migratory effect on breast cancer cells, independently of its effect on bone turnover. The emerging clinical implication, supported by recent epidemiological studies, is that βAR-blockers and drugs interfering with RANKL signaling, such as Denosumab, could increase patient survival if used as adjuvant therapy to inhibit both the early colonization of bone by metastatic breast cancer cells and the initiation of the “vicious cycle” of bone destruction induced by these cells.

Improved detection programs and better drugs to eradicate breast tumors have increased survival in women with breast cancer. However, pain and metastasis to distant organs, including bone, remain significant clinical problems. Understanding why and how metastatic cancer cells colonize specific organs is therefore critical if we are to further improve morbidity and mortality for these patients. Using a mouse model of breast cancer bone metastasis, we present evidence that activation of sympathetic nerves, which is typical in chronic stress or depression, promotes the colonization and establishment of metastatic cancer cells within the bone marrow, leading to an increase in bone osteolytic lesions. We show that this effect is mediated via a β-adrenergic receptor-dependent response of the host bone marrow stroma to catecholamines, that are released upon sympathetic activation, and via the pro-migratory activity of RANKL, a cytokine that is well known to promote bone resorption. Of importance clinically, blocking sympathetic activation with a β-blocker, or blocking RANKL signaling in cancer cells, inhibited the stimulatory effect of sympathetic activation on bone metastasis in this mouse model. Stress-induced sympathetic activation may thus explain, at least in part, the reduced survival rate of breast cancer patients experiencing severe depression. The data also support the use of β-blockers or RANKL blockade as possible adjuvant therapy for women with breast cancer.

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.