Neuronal regulation of bone metabolism and anabolism: calcitonin gene-related peptide-, substance P-, and tyrosine hydroxylase-containing nerves and the bone

Local injection of substance P increases bony formation during mandibular distraction osteogenesis in rats

Substance P is a neuropeptide that is distributed in those sensory nerve fibres that innervate the medullary tissues of bone. It is a potent accelerator of proliferation and differentiation of osteoblasts in vitro. However, its capacity for promoting repair of mandibular defects is not known. We have investigated the osteogenic effects of local injections of substance P during mandibular distraction osteogenesis in rats. Twenty Sprague-Dawley rats were randomly assigned to 2 groups (n = 10 in each): substance P 10(-7) mmol/l in normal saline 0.2ml was injected into the experimental group, and saline alone into the controls. The mandibular distraction rate was 0.2mm every 12hours for 10 days. Daily injections of substance P or saline were given during the distraction period. Regeneration of bone was assessed quantitatively on days 15 and 29 using microcomputed tomography (microCT), and histological analysis. The rate of bony union in the group treated with substance P was significantly higher than that in the saline alone group on day 29 (p=0.001) The microCT images and quantitation showed more callus and more mature cortical bone when substance P was given than with control. Histological examination showed that cartilaginous tissues had formed in the middle of the distraction gaps in both groups. Bony bridges were seen only in the substance P group at the final time point (day 29). Injection of substance P into the gap of a rat mandible during mandibular distraction improved formation of good-quality bone and accelerated bony union.

Absence of substance P and the sympathetic nervous system impact on bone structure and chondrocyte differentiation in an adult model of endochondral ossification

OBJECTIVE

Sensory and sympathetic nerve fibers (SNF) innervate bone and epiphyseal growth plate. The role of neuronal signals for proper endochondral ossification during skeletal growth is mostly unknown. Here, we investigated the impact of the absence of sensory neurotransmitter substance P (SP) and the removal of SNF on callus differentiation, a model for endochondral ossification in adult animals, and on bone formation.

METHODS

In order to generate callus, tibia fractures were set in the left hind leg of wild type (WT), tachykinin 1-deficient (Tac1-/-) mice (no SP) and animals without SNF. Locomotion was tested in healthy animals and touch sensibility was determined early after fracture. Callus tissue was prepared for immunofluorescence staining for SP, neurokinin1-receptor (NK1R), tyrosine-hydroxylase (TH) and adrenergic receptors α1, α2 and β2. At the fracture site, osteoclasts were stained for TRAP, osteoblasts were stained for RUNX2, and histomorphometric analysis of callus tissue composition was performed. Primary murine bone marrow derived macrophages (BMM), osteoclasts, and osteoblasts were tested for differentiation, activity, proliferation and apoptosis in vitro. Femoral fractures were set in the left hind leg of all the three groups for mechanical testing and μCT-analysis.

RESULTS

Callus cells stained positive for SP, NK1R, α1d- and α2b adrenoceptors and remained β2-adrenoceptor and TH-negative. Absence of SP and SNF did not change the general locomotion but reduces touch sensitivity after fracture. In mice without SNF, we detected more mesenchymal callus tissue and less cartilaginous tissue 5 days after fracture. At day 13 past fracture, we observed a decrease of the area covered by hypertrophic chondrocytes in Tac1-/- mice and mice without SNF, a lower number of osteoblasts in Tac1-/- mice and an increase of osteoclasts in mineralized callus tissue in mice without SNF. Apoptosis rate and activity of osteoclasts and osteoblasts isolated from Tac1-/- and sympathectomized mice were partly altered in vitro. Mechanical testing of fractured- and contralateral legs 21 days after fracture, revealed an overall reduced mechanical bone quality in Tac1-/- mice and mice without SNF. μCT-analysis revealed clear structural alteration in contralateral and fractured legs proximal of the fracture site with respect to trabecular parameters, bone mass and connectivity density. Notably, structural parameters are altered in fractured legs when related to unfractured legs in WT but not in mice without SP and SNF.

CONCLUSION

The absence of SP and SNF reduces pain sensitivity and mechanical stability of the bone in general. The micro-architecture of the bone is profoundly impaired in the absence of intact SNF with a less drastic effect in SP-deficient mice. Both sympathetic and sensory neurotransmitters are indispensable for proper callus differentiation. Importantly, the absence of SP reduces bone formation rate whereas the absence of SNF induces bone resorption rate. Notably, fracture chondrocytes produce SP and its receptor NK1 and are positive for α-adrenoceptors indicating an endogenous callus signaling loop. We propose that sensory and sympathetic neurotransmitters have crucial trophic effects which are essential for proper bone formation in addition to their classical neurological actions.

Acetylcholine affects osteocytic MLO-Y4 cells via acetylcholine receptors

The identification of the neuronal control of bone remodeling has become one of the many significant recent advances in bone biology. Cholinergic activity has recently been shown to favor bone mass accrual by complex cellular regulatory networks. Here, we identified the gene expression of the muscarinic and nicotinic acetylcholine receptors (m- and nAChRs) in mice tibia tissue and in osteocytic MLO-Y4 cells. Acetylcholine, which is a classical neurotransmitter and an osteo-neuromediator, not only influences the mRNA expression of the AChR subunits but also significantly induces the proliferation and viability of osteocytes. Moreover, acetylcholine treatment caused the reciprocal regulation of RANKL and OPG mRNA expression, which resulted in a significant increase in the mRNA ratio of RANKL:OPG in osteocytes via acetylcholine receptors. The expression of neuropeptide Y and reelin, which are two neurogenic markers, was also modulated by acetylcholine via m- and nAChRs in MLO-Y4 cells. These results indicated that osteocytic acetylcholine receptors might be a new valuable mediator for cell functions and even for bone remodeling.

The effect of combined regulation of the expression of peroxisome proliferator-activated receptor-γ and calcitonin gene-related peptide on alcohol-induced adipogenic differentiation of bone marrow mesenchymal stem cells

Studies have shown that alcohol can upregulate the expression of peroxisome proliferator-activated receptor-γ (PPARγ) gene in bone marrow mesenchymal stem cells (BMSCs). High expression of PPARγ can promote adipogenic differentiation of BMSCs, and reduce their osteogenic differentiation. Abnormal proliferation of adipocytes and fatty accumulation in osteocytes can result in high intraosseous pressure and disturbance of blood circulation in the femoral head, which induces osteonecrosis of the femoral head (ONFH). Downregulation of PPARγ is efficient in inhibiting adipogenesis and maintaining osteogenesis of BMSCs, which might potentially reduce the incidence of ONFH. Calcitonin gene-related peptide (CGRP) is a neuropeptide gene which has been closely associated with bone regeneration. In this study, we aimed to observe the effect of combined regulation of the expression of PPARγ and CGRP genes on alcohol-induced adipogenic differentiation of BMSCs. Our results demonstrated that simultaneous downregulation of PPARγ and upregulation of CGRP was efficient in suppressing adipogenic differentiation of BMSCs and promoting their osteogenic differentiation. These findings might enlighten a novel approach for the prevention of ONFH.

Neuropeptide SP activates the WNT signal transduction pathway and enhances the proliferation of bone marrow stromal stem cells

Substance P (SP) mediates multiple activities in various cell types, such as proliferation, anti-apoptotic response, and inflammation. We have investigated the effects of SP, NK1 antagonist and DKK1 on proliferation of bone marrow stromal stem cells (BMSCs), as well as the underlying mechanism. Isolated BMSCs were exposed to SP (10(-8)  M) (group A), SP + NK1 antagonist (1 µM) (group B), SP + DKK1 (0.2 µg/mL) (group C), or the same amount of PBS (group D). Expression of gene and protein of Wnt/β-catenin signalling was detected using quantitative PCR and western blotting. SP (10(-8)  M) significantly enhanced the proliferation of BMSCs and the number of viable cells was reduced by treatment with NK1 antagonist (1 µM) or DKK1 (0.2 µg/mL). SP also significantly increased the expression of C-myc mRNA, Lef1, β-catenin protein and C-myc protein, but decreased the expression of Tcf7 and p-β-catenin protein compared to group D. These roles of SP were inhibited by the NK1 antagonist and DKK1. Expression of CyclinD1 and β-catenin mRNAs, however, was not significantly influenced by SP, NK1 antagonist and DKK1. These findings suggest that SP enhances BMSC proliferation via regulation of the Wnt/β-catenin signalling pathway.

An overview of the Charcot foot pathophysiology

Charcot arthropathy of the foot is a rare but devastating complication of diabetes that remains to be a challenging issue for the foot and ankle surgeons. Charcot foot fails to be an obvious diagnostic option that comes to mind, even in a pathognomonic clinical appearance. The rarity of the disorder, more common pathologies that mimic the condition, and the self-limiting prognosis deviate the clinician from the right diagnosis. The clinical challenges in the diagnosis of Charcot foot require in-depth investigations of its enigmatic nature to establish useful guidelines. Yet, this goal seems to be beyond reach, without a holistic view of the immense literature concerning the pathophysiology of the disorder. The primary objective of this article is to put together and review the recent advancements about the etiology and intrinsic mechanisms of diabetic Charcot foot.

Neuropeptides stimulate human osteoblast activity and promote gap junctional intercellular communication

Neuropeptides released from the skeletal nerve fibers have neurotransmitter and immunoregulatory roles; they exert paracrine biological effects on bone cells present close to the nerve endings expressing these signaling molecules. The aims of this study were a systematic investigation of the effects of the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), Neuropeptide Y (NPY) and tyrosine hydroxylase (TH) on the cell viability and function of the human osteoblasts, and comparing their difference in the role of regulating bone formation. Cultures of normal human osteoblasts were treated with SP, CGRP, VIP, NPY or TH at three concentrations. We found that each of the five neuropeptides induced increases in cell viability of human osteoblasts. The stimulatory action of NPY was the highest, followed by VIP, SP and TH, while CGRP had the lowest stimulatory effect. The viability index of osteoblasts was inversely associated with the concentration of neuropeptides, and positively with the time of exposure. Moreover, the five neuropeptides increased the ALP activity and osteocalcin to different extents in a dose-dependent manner. The GJIC of osteoblasts was significantly promoted by neuropeptides. The results demonstrated that neuropeptides released from skeletal nerve endings after a stimulus appeared to be able to induce the proliferation and activity of osteoblasts via enhancing GJIC between cells, and further influence the bone formation. These findings may contribute toward a better understanding of the neural influence on bone remodeling and improving treatments related to bone diseases.

Exercise induced mechano-sensing and substance P mediated bone modeling in Atlantic salmon

Mechanical stress plays a vital role in maintaining bone architecture. The process by which osteogenic cells convert the mechanical signal into a biochemical response governing bone modeling is not clear, however. In this study, we investigated how Atlantic salmon (Salmo salar) vertebra responds to exercise-induced mechanical loading. Bone formation in the vertebrae was favored through increased expression of genes involved in osteoid production. Fourier transform infrared spectroscopy (FT-IR) showed that bone matrix secreted both before and during sustained swimming had different properties after increased load compared to control, suggesting that both new and old bones are affected. Concomitantly, both osteoblasts and osteocytes in exercised salmon showed increased expression of the receptor nk-1 and its ligand substance P (SP), both known to be involved in osteogenesis. Moreover, in situ hybridization disclosed SP mRNA in osteoblasts and osteocytes, supporting an autocrine function. The functional role of SP was investigated in vitro using osteoblasts depleted for SP. The cells showed severely reduced transcription of genes involved in mineralization, demonstrating a regulatory role for SP in salmon osteoblasts. Investigation of α-tubulin stained osteocytes revealed cilia-like structures. Together with SP, cilia may link mechanical responses to osteogenic processes in the absence of a canaliculi network. Our results imply that salmon vertebral bone responds to mechanical load through a highly interconnected and complex signal and detection system, with SP as a key factor for initializing mechanically-induced bone formation in bone lacking the canaliculi system.

Captopril improves osteopenia in ovariectomized rats and promotes bone formation in osteoblasts

The present study was designed to investigate the effects of captopril, an angiotensin-converting enzyme inhibitor (ACEI), on bone loss in aged ovariectomized (OVX) rats and its impact on the differentiation of cultured primary osteoblasts. Ten-month-old female Sprague-Dawley rats were used for the study. After 2 months post ovariectomy (OVX), the rats were treated with captopril (1 or 5 mg/kg/day, respectively) for another 2 months. At endpoint, trabecular bone of the fourth lumbar vertebrae (L4) was undecalcified and examined by bone histomorphometry; the fifth lumbar vertebrae (L5) were examined by compression test. Primary osteoblasts were isolated from the calvaria of newborn rats and treated with different concentrations of captopril in a different durations. The content of secreted alkaline phosphatase (ALP) and mRNA expression of collagen I in osteoblasts were determined to demonstrate osteoblast bone formation. In aged rats with estrogen deficiency-induced osteopenia, captopril increased the trabecular area (%BV/TV) of L4 up to 33% and improved biomechanical properties by increasing L5 break stress and elastic modulus when compared to those in the OVX group (P < 0.01). Captopril showed dose-dependent effects on promoting the secretion of ALP and increased mRNA expression of collagen I in the cultured rat osteoblasts. In summary, captopril, one of the most widely used ACEIs, has the potential effects of improving lumbar vertebral bone strength in aged OVX rats and promoting osteoblast bone formation in vitro.

Down-regulation of the Wnt, estrogen receptor, insulin-like growth factor-I, and bone morphogenetic protein pathways in osteoblasts from rats with chronic spinal cord injury

OBJECTIVES

To investigate the anabolic response of osteoblasts to chronic spinal cord injury and to identify potential signaling pathways that are associated with the osteogenic response after spinal cord injury by using in-house microarray analyses in osteoblasts.

METHODS

Ten young male Sprague-Dawley rats were randomized into spinal cord injury (SCI) and SHAM groups. The tibiae were assessed for DXA and bone histomorphometry, and osteoblasts from femora were used for microarray analysis.

RESULTS

SCI rats showed lower BMD and deteriorated microstructure in the proximal tibiae as compared with SHAM rats. The Wnt, BMP/TGF, estrogen receptor (ER), and IGF-I pathways were down-regulated in osteoblasts from spinal cord-injured rats.

CONCLUSION

Down-regulation of the Wnt, BMP/TGF, ER, and growth hormone/IGF-I pathways is associated with decreased bone formation after spinal cord injury.

Role of substance P (SP) and calcitonin gene-related peptide (CGRP) in gibbon-ape-leukemia virus (GALV) transduction of CD34+ cells

AIMS

Optimization of transduction condition is an important goal to improve gene transduction. Therefore, we aimed to assess the effect of SP and/or CGRP as novel growth/transducing factors on the efficacy of CD34(+) transduction.

METHODS

CD34(+) cells were transduced with Gibbon-Ape-Leukemia virus (GALV), containing Neomycin gene. CD34(+) cells were transduced with GALV presence of SP and/or CGRP. Real Time PCR and colony formation assay (CFU-C) was performed.

RESULTS

Viral vectors titration on Hela cells indicated transduction efficiency of 1×10(6)CFU/ml. Real Time PCR of Neo and CFU-C showed stimulatory role of SP on gene transfer 5.9% and 14.84% compared to 3.6% and 12.58% in control group, while opposite role observed for CGRP 0.89% and 7.86%. Both SP and CGRP showed no significant effect in these assays.

DISCUSSION

This study showed including of SP in growth factor cocktail is beneficial for CD34(+) transduction, which could be applied to genetic modification procedures.

Effects of capsaicin-induced sensory denervation on bone metabolism in adult rats

Bone metabolism has recently been revealed to be under nerve regulation. In this study, the integrity of the sensory innervation contributing to bone metabolism was examined by capsaicin-induced sensory neuron lesions. Eight-week-old male Wistar strain rats in a modeling phase of skeletal growth were divided into four groups (8 rats per group) and treated with capsaicin at one of three different doses (37.5, 75, 150 mg/kg) or vehicle, subcutaneously. Five weeks later, high-dose (150 mg/kg) capsaicin treatment had reduced trabecular bone volume (BV/TV) due to increased trabecular separation (Tb.Sp) in the proximal tibia and the modification of mechanical properties such as strength, ductility, and toughness toward increasing bone fragility in the trunk of the sixth lumbar vertebrae (L6). Moderate-dose (75 mg/kg) capsaicin treatment had no significant effect on trabecular BV/TV or bone mechanical properties but increased Tb.Sp as seen high-dose capsaicin treatment. Bone histomorphometry showed osteoclast number (Oc.N/BS) and surface (Oc.S/BS) were increased in both the moderate-dose and high-dose capsaicin treatment groups. High-dose capsaicin significantly increased the level of tartrate-resistant acid phosphatase form 5b (TRAP 5b) in plasma, a systemic bone resorption marker, but had no influence on plasma osteocalcin concentration, a bone formation marker, suggesting that capsaicin-induced sensory nerve denervation increased bone resorption but had no influence on bone formation. Low-dose (37.5mg/kg) capsaicin had no influence on bone remodeling. These results suggest that sensory nerve innervation contributes to the maintenance of trabecular bone mass and its mechanical properties by inhibiting bone resorption.

Structural and cellular features in metaphyseal and diaphyseal periosteum of osteoporotic rats

Despite the important physiological role of periosteum in the pathogenesis and treatment of osteoporosis, little is known about the structural and cellular characteristics of periosteum in osteoporosis. To study the structural and cellular differences in both diaphyseal and metaphyseal periosteum of osteoporotic rats, samples from the right femur of osteoporotic and normal female Lewis rats were collected and tissue sections were stained with hematoxylin and eosin, antibodies or staining kit against tartrate resistant acid phosphatase (TRAP), alkaline phosphatase (ALP), vascular endothelial growth factor (VEGF), von Willebrand (vWF), tyrosine hydroxylase (TH) and calcitonin gene-related peptide (CGRP). The results showed that the osteoporotic rats had much thicker and more cellular cambial layer of metaphyseal periosteum compared with other periosteal areas and normal rats (P < 0.001). The number of TRAP⁺ osteoclasts in bone resorption pits, VEGF⁺ cells and the degree of vascularization were found to be greater in the cambial layer of metaphyseal periosteum of osteoporotic rats (P < 0.05), while no significant difference was detected in the number of ALP⁺ cells between the two groups. Sympathetic nerve fibers identified by TH staining were predominantly located in the cambial layer of metaphyseal periosteum of osteoporotic rats. No obvious difference in the expression of CGRP between the two groups was found. In conclusion, periosteum may play an important role in the cortical bone resorption in osteoporotic rats and this pathological process may be regulated by the sympathetic nervous system.

NPY revealed as a critical modulator of osteoblast function in vitro: new insights into the role of Y1 and Y2 receptors

Neuropeptide Y (NPY) has recently emerged as a potential regulator of bone homeostasis. However, the relevance of NPY's role in osteoblast activity and the biological functions involving NPY receptors in bone homeostasis remain to be clarified. Here we report that chronically elevated NPY levels leaded to a modulation of the level of Y2 receptor expression marked with a transient down and upregulation according to the stage of osteoblast differentiation. We also show that NPY is a negative regulator of Y1 receptor expression. The pharmacological activation of Y2 receptor with its agonist resulted in similar effect. Functional analysis also revealed the osteogenic potential of NPY with osteoblast phenotype markers being significantly enhanced in osteoprogenitor cells stimulated by NPY, probably due to the down-regulation of Y1 receptor. In contrasts, these cells exhibit a reduction in calcium deposition in extracellular matrix most likely mediated via Y2 receptor signalling. Furthermore, we show that NPY modulates receptor activator of nuclear factor kB (NF-kB) (RANK) ligand and osteoprotegerin, two key factors regulating bone remodelling. Specifically, NPY inhibits the transcriptional activity of RANKL promoter in osteoprogenitor cells and enhances OPG expression in osteoblasts at early stages of differentiation. However, NPY effect on OPG seemed to be unrelated to Y2 receptor activation. Taken together the present data supported the contribution of NPY pathway in bone homeostasis via a direct action on osteoblasts cells.

Major depression is a risk factor for low bone mineral density: a meta-analysis

BACKGROUND

The role of depression as a risk factor for low bone mineral density (BMD) and osteoporosis is not fully acknowledged, mainly because the relevant literature is inconsistent and because information on the mechanisms mediating brain-to-bone signals is rather scanty.

METHODS

Searching databases and reviewing citations in relevant articles, we identified 23 studies that quantitatively address the relationship between depression and skeletal status, comparing 2327 depressed with 21,141 nondepressed individuals. We subjected these studies to meta-analysis, assessing the association between depression and BMD as well as between depression and bone turnover markers.

RESULTS

Overall, depressed individuals displayed lower BMD than nondepressed subjects, with a composite weighted mean effect size (d) of -.23 (95% confidence interval: -.33 to -.13; p < .001). The association between depression and BMD was similar in the spine, hip, and forearm. It was stronger in women (d = -.24) than men (d = -.12) and in premenopausal (d = -.31) than postmenopausal (d = -.12) women. Only women individually diagnosed for major depression by a psychiatrist with DSM criteria displayed significantly low BMD (d = -.36); women diagnosed by self-rating questionnaires did not (d = -.06). Depressed subjects had increased urinary levels of bone resorption markers (d = .52).

CONCLUSIONS

The present findings portray depression as a significant risk factor for low BMD. Premenopausal women who are psychiatrically diagnosed with major depression are particularly at high-risk for depression-associated low BMD. Hence, periodic BMD measurements and antiosteoporotic prophylactic and curative measures are strongly advocated for these patients.

Effects of neuropeptides and vasoactive substances on microcirculation of the callus after tibial osteotomy in rabbits

Previous studies have demonstrated a dynamic ingrowth of vessels into the developing callus. In this study, maturation and development of the regulation of microcirculation were followed in the callus of rabbits. In the first series, the effects of vasoactive substances on blood flow velocity, perfusion pressure, duration of effects and peripheral vascular resistance of the bone marrow in the femur and tibia were compared. In the second series, the same parameters were measured in the femur and in the developing callus 10 and 15 days following gap osteotomy of the tibia. There were no significant differences between the microcirculatory reactions of the intact femur and tibia. Basal blood flow could be verified in the callus on the 10th postoperative day. No vascular reactions could be elicited. Basal blood flow velocity was higher on the 15th day, when compared to the measurements on the 10th day. The substances elicited statistically significant differences in flow velocity, resistance and 50% recovery time in the callus on the 15th day. Blood flow reactions of the ipsilateral femoral and tibial bone marrow are identical, thus the femur can serve as a reference site for blood flow measurements in the callus. Regulation and maturation of callus microcirculation develop rapidly between the 10th and 15th days.

Substance P stimulates bone marrow stromal cell osteogenic activity, osteoclast differentiation, and resorption activity in vitro

INTRODUCTION

SP is a neuropeptide distributed in the sensory nerve fibers that innervate the medullar tissues of bone, as well as the periosteum. Previously we demonstrated that inhibition of neuropeptide signaling after capsaicin treatment resulted in a loss of bone mass and we hypothesized that SP contributes to bone integrity by stimulating osteogenesis.

MATERIALS AND METHODS

Osteoblast precursors (bone marrow stromal cells, BMSCs) and osteoclast precursors (bone marrow macrophages, BMMs) derived from C57BL/6 mice were cultured. Expression of the SP receptor (NK1) was detected by using immunocytochemical staining and PCR. Effects of SP on proliferation and differentiation of BMSCs were studied by measuring BrdU incorporation, gene expression, alkaline phosphatase activity, and osteocalcin and Runx2 protein levels with EIA and western blot assays, respectively. Effects of SP on BMMs were determined using a BrdU assay, counting multinucleated cells staining positive for tartrate-resistant acid phosphatase (TRAP(+)), measuring pit erosion area, and evaluating RANKL protein production and NF-kappaB activity with ELISA and western blot.

RESULTS

The NK1 receptor was expressed in both BMSCs and BMMs. SP stimulated the proliferation of BMSCs in a concentration-dependent manner. Low concentrations (10(-12) M) of SP stimulated alkaline phosphatase and osteocalcin expression, increased alkaline phosphatase activity, and up-regulated Runx2 protein levels, and higher concentrations of SP (10(-8) M) enhanced mineralization in differentiated BMSCs. SP also stimulated BMSCs to produce RANKL, but at concentrations too low to evoke osteoclastogenesis in co-culture with macrophages in the presence of SP. SP also activated NF-kappaB in BMMs and directly facilitate RANKL-induced macrophage osteoclastogenesis and bone resorption activity.

CONCLUSIONS

NK1 receptors are expressed by osteoblast and osteoclast precursors and SP stimulates osteoblast and osteoclast differentiation and function in vitro. SP neurotransmitter release from sensory neurons could potentially regulate local bone turnover in vivo.

Ethanol and stress activate catecholamine synthesis in the adrenal: effects on bone

Ethanol consumption and mental stress activate the sympathetic nervous system, which can adversely affect bone. We compared six groups of 10 young adult rats, three with and three without 2 h daily restraint stress. Two groups consumed food and water ad libitum, two received food and 6% (w/v) ethanol as drinking water, and two received the amount of food consumed by ethanol rats the previous day plus water ad libitum (pairfed). After 6 weeks, rats were killed. Plasma, femurs, lumbar vertebrae, and adrenals were harvested. Femoral dimensions were measured and biomechanical properties were tested by three-point bending. Plasma osteocalcin, vertebral osteocalcin mRNA levels, and adrenomedullary tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyl transferase (PNMT) mRNA levels were quantified. Daily restraint decreased weight gain and femoral length compared to dietary controls, and appeared to partially preserve bone strength, especially in calorie-restricted pairfed rats. Femoral strength was significantly affected by treatment in that bones of pairfed controls were weakest, ethanol drinkers were intermediate, and ad libitum restrained were strongest. Femoral yield load, displacement, and work at yield load were negatively correlated with TH and DBH mRNA levels, but not PNMT, suggesting a negative influence of norepinephrine. Plasma osteocalcin and dry weight of lumbar 3-5 vertebrae were unaffected; however, osteocalcin mRNA in second lumbar vertebrae was positively correlated with TH, DBH, and PNMT levels. Ethanol consumption at this level had little effect on femur morphology or strength. In contrast, the data suggested possible stimulation rather than inhibition of vertebral bone formation.

Peripheral nerve may regulate the jaw bone resorption after tooth extraction

A various amount of alveolar ridge resorption is likely to occur after tooth extraction, making it difficult to restore the missing teeth with either endosseous dental implants or prosthodontics approaches. It is commonly thought that the bone resorption is due to the absence of the mechanical stimulation from the occlusal force. However, regulation of the bone mass is a complex homeostatic system involved in hormonal, paracrine/autocrine, mechanical and neuronal nature. Studies have shown that the central and peripheral nervous system play an important role in bone remodeling. The hypothalamus integrates peripheral and central signals, and sends efferent hormonal and neuronal signals in response to stimulation. Numerous neuropeptides detected in the bone marrow have effect on the osteoblast and osteoclast. After tooth extraction, great loss of the axons is observed in the edentulous bone. So we speculate that innervation in the alveolar bone regulates the bone resorption in edentulous area. Methods to promote the nerve regeneration are expected to prevent the jaw bone resorption. The hypothesis also implies that after the placement of the oral implant the abundant nerves in the alveolar bone can increase the bone healing ability and long term survival rate of the implant.

Regulation of bone remodeling by the central and peripheral nervous system

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

Dose estimation and surveillance of mechanical loading interventions for bone loss after spinal cord injury

BACKGROUND AND PURPOSE

The interpretation of the results of previous anti-osteoporosis interventions after spinal cord injury (SCI) is undermined by incomplete information about the intervention dose or patient adherence to dose requirements. Rehabilitation research as a whole traditionally has struggled with these same issues. The purpose of this case report is to offer proof of the concepts that careful dose selection and surveillance of patient adherence should be integral components in rehabilitation interventions.

CASE DESCRIPTION

A 21-year-old man with T4 complete paraplegia (7 weeks) enrolled in a unilateral soleus muscle electrical stimulation protocol. Compressive loads applied to the tibia approximated 1.4 times body weight. Over 4.8 years of home-based training, data logging software provided surveillance of adherence. Soleus muscle torque and fatigue index adaptations to training as well as bone mineral density (BMD) adaptations in the distal tibia were measured.

OUTCOMES

The patient performed nearly 8,000 soleus muscle contractions per month, with occasional fluctuations. Adherence tracking permitted intervention when adherence fell below acceptable values. The soleus muscle torque and fatigue index increased rapidly in response to training. The BMD of the untrained tibia declined approximately 14% per year. The BMD of the trained tibia declined only approximately 7% per year. The BMD was preferentially preserved in the posterior half of the tibia; this region experienced only a 2.6% annual decline.

DISCUSSION

Early administration of a load intervention, careful estimation of the loading dose, and detailed surveillance of patient adherence aided in the interpretation of a patient's adaptations to a mechanical load protocol. These concepts possess wider applicability to rehabilitation research and should be emphasized in future physical therapy investigations.

The role of calcitonin and alpha-calcitonin gene-related peptide in bone formation

The Calca gene encodes two polypeptides, calcitonin (CT) and alpha-calcitonin gene-related peptide (alpha-CGRP), generated through alternative splicing. While CT, a hormone mainly produced by thyroidal C cells, has been described as a major regulator of bone resorption, alpha-CGRP, a neuropeptide expressed in the cells of the central and peripheral nervous system, is mostly known as a regulator of vascular tone. Surprisingly, the generation and skeletal analyses of two mouse deficiency models has recently uncovered a physiological function for both peptides in the regulation of bone formation. In the first model, where the replacement of exons 2-5 of the Calca gene resulted in the combined deficiency of CT and alpha-CGRP, an increased bone formation rate (BFR) was observed, whereas decreased BFR was found in the second model, where the introduction of a translational termination codon into exon 5 of the Calca gene resulted in the specific absence of alpha-CGRP.

The causes of the Charcot syndrome

The Charcot syndrome is a rare complication of neuropathy in diabetes and is characterized by an acute inflammatory episode of the foot that is associated with variable degrees of dislocation, fracture, and deformity. It has no single cause but represents the final common pathway in people who are predisposed to its development by the varying overlap of several different factors. The association of the active phase of the disease with inflammation, increasing osteopenia, and increasing calcification of the arterial walls strongly suggests, however, the involvement of the receptor activator of nuclear factor-kappaB ligand (RANKL)/osteoprotegerin (OPG) cytokine pathway, which is closely involved in all three processes. The evidence for increased expression of RANKL and OPG in diabetes and neuropathy as well as its potential significance is reviewed.

The antiproliferative role of ERG K+ channels in rat osteoblastic cells

We report on the role of K+ currents in the mechanisms regulating the proliferation of UMR 106-01 osteoblastic osteosarcoma cells. Electrophysiological analysis showed that UMR 106-01 cells produce robust K+ currents that can be pharmacologically separated into two major components: a E-4031-susceptible current, I E-4031, and a tetraethylammonium (TEA)-susceptible component, I TEA. Western blot and RT-PCR analysis showed that I E-4031 is produced by ether a go-go (eag)-related channels (ERG). Incubation of the cells with E-4031 enhanced their proliferation by 80%. Application of E-4031 in the bath solution did not induce instantaneous changes in the membrane resting potential or in the level of cytosolic calcium; however, the cells were slightly depolarized and the calcium content was significantly increased upon prolonged incubation with the compound. Taken together these findings indicate that ERG channels can impair cell proliferation. This is a novel finding that underscores new modes of regulation of mitosis by voltage-gated K+ channels and provides an unexpected insight into the current view of the mechanisms governing bone tissue proliferation.

Site-specific CGRP innervation coincides with bone formation during fracture healing and modeling: A study in rat angulated tibia

Sensory neuropeptide involved in local bone turnover is known, but poorly understood. In the present study, we analyze the occurrence of neuronal CGRP during healing and modeling of straight and angular tibial fractures in 74 rats. Bone healing and modeling was assessed by radiography and reinnervation by semi-quantitative immunohistochemistry method at fracture site between 1-12 weeks postfracture. The regenerating nerve fibers containing CGRP were observed in fracture callus as well as in close proximity to chondrocytes, with woven bone in both fractures already at week 1. Notably, it located predominantly on the concave side of angulated fracture in the manner of sprouting into bone from weeks 3 to 5 postfracture. In both fractures, fracture calluses peaked radiographically at week 3 postfracture. In angulated fracture, a reduction of 11% in callus thickness on convex side and an increase of 365% on concave side were noted from weeks 3 to 12. A 27-fold increase in total neuronal CGRP in straight fracture and 38-fold increases in angular fracture compared to intact bone was observed at week 3. In both types of fracture, neuronal CGRP was greater on the concave side than the convex; this difference was more pronounced in the angulated fracture. CGRP immunoreactivity clearly coincides with amount of new bone formation especially on the concave side of angulated fracture. The combined results suggest that fracture evokes an intense, localized in-growth of new nerve fibers containing CGRP, which may prove to be a prerequisite of fracture healing and modeling.

Polyethylene particle-induced bone resorption in alpha-calcitonin gene-related peptide-deficient mice

This study investigates the impact of alpha-CGRP on bone metabolism after implantation of polyethylene particles. alpha-CGRP knockout mice showed less osteolysis compared with wildtype mice. The local neurogenic microenvironment might be a crucial factor in particle-induced osteolysis.

INTRODUCTION

Periprosthetic osteolysis is the major reason for aseptic loosening in joint arthroplasty. This study aimed to investigate the potential impact of alpha-calcitonin gene-related peptide (alpha-CGRP) deficiency on bone metabolism under conditions of polyethylene particle-induced osteolysis.

MATERIALS AND METHODS

We used the murine calvarial osteolysis model based on polyethylene particles in 14 C57BL 6 mice and 14 alpha-CGRP-deficient mice divided into four groups of 7 mice each. Groups 1 (C57BL/J 6) and 3 (alpha-CGRP knockout) received sham surgery, and groups 2 (C57BL/J 6) and 4 (alpha-CGRP knockout) were treated with polyethylene particles. Qualitative and quantitative 3D analyses were performed using microCT. In addition, bone resorption was measured within the midline suture by histological examination. The number of osteoclasts was determined by counting the TRACP(+) cells. Calvarial bone was tested for RANKL expression by RT-PCR and immunocytochemistry.

RESULTS

Bone resorption was significantly reduced in alpha-CGRP-deficient mice compared with their corresponding wildtype C57BL 6 mice as confirmed by histomorphometric data (p < 0.001) and microCT (p < 0.01). Osteoclast numbers were significantly reduced in group 3 and the particle subgroup compared with group 1 (p < 0.001). We observed a >3-fold increase of basal RANKL mRNA levels within group 1 compared with group 3. Additional low RANKL immunochemistry staining was noted in groups 3 and 4.

CONCLUSIONS

In conclusion, alpha-CGRP knockout mice did not show the expected extended osteolysis compared with wildtype mice expressing alpha-CGRP. One of the most reasonable explanations for the observed decrease in osteolysis could be linked to the osteoprotegerin (OPG)/RANK/RANKL system in alpha-CGRP-deficient animals. As a consequence, the fine tuning of osteoclasts mediating resorption in alpha-CGRP-null mice may be deregulated.

Musculoskeletal plasticity after acute spinal cord injury: effects of long-term neuromuscular electrical stimulation training

Maintaining the physiologic integrity of paralyzed limbs may be critical for those with spinal cord injury (SCI) to be viable candidates for a future cure. No long-term intervention has been tested to attempt to prevent the severe musculoskeletal deterioration that occurs after SCI. The purposes of this study were to determine whether a long-term neuromuscular electrical stimulation training program can preserve the physiological properties of the plantar flexor muscles (peak torque, fatigue index, torque-time integral, and contractile speed) as well as influence distal tibia trabecular bone mineral density (BMD). Subjects began unilateral plantar flexion electrical stimulation training within 6 wk after SCI while the untrained leg served as a control. Mean compliance for the 2-yr training program was 83%. Mean estimated compressive loads delivered to the tibia were approximately 1-1.5 times body weight. The training protocol yielded significant trained versus untrained limb differences for torque (+24%), torque-time integral (+27%), fatigue index (+50%), torque rise time (+45%), and between-twitch fusion (+15%). These between-limb differences were even greater when measured at the end of a repetitive stimulation protocol (125 contractions). Peripheral quantitative computed tomography revealed 31% higher distal tibia trabecular BMD in trained limbs than in untrained limbs. The intervention used in this study was sufficient to limit many of the deleterious muscular and skeletal adaptations that normally occur after SCI. Importantly, this method of load delivery was feasible and may serve as the basis for an intervention to preserve the musculoskeletal properties of individuals with SCI.

Bone challenges for the hand surgeon: from basic bone biology to future clinical applications

Bone is a complex tissue composed of a calcified extracellular matrix with specialized cells that produce, maintain, and resorb the bone. Bone also has a rich vascular and neural supply. Bone has a great capability of regeneration, healing, and remodelling that is influenced by external factors, such as stress forces, and internal regulators that include hormones, vitamins, and growth factors. These factors dictate bone biology, and variations result in pathophysiologic conditions that have clinical implications in hand surgery. Solutions to the challenges in hand surgery rely on a thorough understanding of the biology of bone.

Neural regulation of bone and the skeletal effects of serotonin (5-hydroxytryptamine)

There is increasing evidence for a contribution of the neural system to the regulation of bone metabolism. The skeleton is richly innervated by both sympathetic and sensory neurons. While these nerves serve sensory and vascular functions, they are also being found to influence bone cell activities. The most convincing evidence for this has been provided by studies into the skeletal effects of the hormone leptin, which has been shown to centrally regulate bone mass, and through studies into the skeletal effects of hypothalamic neuropeptide Y2 and Y4 receptors. This paper discusses recent evidence for the neural regulation of bone metabolism and, in particular, the potential role of the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). Recent studies have demonstrated the presence of functional pathways in bone for both responding to and regulating the uptake of 5-HT. This is of high clinical relevance given the role of the serotonergic system in affective disorders, and the wide use of pharmacological agents that target the 5-HT system to manage these disorders. Initial data suggest that exposure to these agents at different stages during the lifespan may have significant effects on the skeleton.

Abnormalities of vasomotor regulation in the pathogenesis of the acute charcot foot of diabetes mellitus

The acute Charcot foot complicates distal symmetrical neuropathy but is remarkably rare. This article reviews the multiple processes that may complicate both diabetes and neuropathy and might, in turn, explain the association of features that are typical of this disorder: osteolysis, vascular calcification in association with intact lower limb blood flow, and uncontrolled inflammation. Specifically, it is suggested that the disorder arises because of abnormal expression of the nuclear transcription factor, NFkappaB, in diabetic neuropathy and that this is further enhanced at the onset of the acute arthropathy as a result of the release of proinflammatory cytokines, such as tumor necrosis factor-alpha and interleukin-1. These proinflammatory cytokines and RANKL may then enter a cycle of mutual augmentation, and this is a factor that underlies the continuing inflammation that characterizes the disorder. If this hypothesis is confirmed, it would suggest the option of new effective treatments for this sometimes devastating disorder.

Effects of alpha-ketoglutarate on bone homeostasis and plasma amino acids in turkeys

The objective of the study was to evaluate the effect of denervation and alpha-ketoglutarate (AKG) administration on the development of osteopenia in the turkey radius. At 22 d of age, all turkeys were subjected to neurectomy of the right radius. Control turkeys were given a saline solution into the crop each day for 97 d. Experimental turkeys were given 0.4 g of AKG/kg of BW into the crop each day. After 98 d, BW was not affected by the AKG treatment. Volumetric bone mineral density of the radius was measured by quantitative computed tomography. Mechanical properties were tested using a 3-point bending test. Cross-sectional area, second moment of inertia, and mean relative wall thickness were measured as well. Amino acid concentrations were assessed with the use of ion-exchange chromatography. Denervation had a negative effect on all bone characteristics that were measured except bone length. The AKG had a positive effect on all bone characteristics except bone length. Plasma concentrations of proline and leucine were increased by AKG, whereas concentrations of taurine and glutamine were decreased. The turkey radius appears to be a good model for studying osteopenia because its development can be affected by treatments such as denervation and AKG administration.

Long-term denervation of the humerus in turkeys as an experimental model for osteopenia

The aim of this study was to evaluate the influence of long-term denervation on volumetric bone mineral density, and geometrical and mechanical properties of the humerus in turkeys. The experiment was conducted from d 22 after hatching until wk 17 of life. All experimental birds (male turkeys) were randomly divided into 2 weight-matched groups. The first group of turkeys served as the control group and underwent a sham operation on the right wing, and the second group was subjected to surgical denervation of the right humerus. The denervation was performed by neurectomy of the radialis and the mediano-ulnaris nerves in the region of the proximal epiphysis of the humerus. All the left wings within both groups were surgically untouched. The left humerus served as the control bone to the right humerus in both investigated groups. Effect of denervation of humerus was determined in terms of geometrical and mechanical properties and quantitative computed tomography. The denervation of the humerus in turkeys significantly decreased volumetric bone mineral density, and geometrical and mechanical properties of this bone, when compared with the results obtained in humerus from the sham-operated or surgically untouched wings. However, no significant differences between right and left humerus were observed when analyzing all of the investigated parameters in the sham-operated group of turkeys. It is concluded that long-term denervation of humerus in turkeys induces osteopenia and may serve as a new experimental model for investigating factors that affect skeletal homeostasis in poultry and other vertebrates.

Capsaicin-sensitive sensory neurons contribute to the maintenance of trabecular bone integrity

This investigation used capsaicin to selectively lesion unmyelinated sensory neurons in rats. Neuronal lesioning induced a loss of trabecular integrity, reduced bone mass and strength, and depleted neuropeptides in nerve and bone. These data suggest that capsaicin-sensitive sensory nerves contribute to trabecular bone integrity.

INTRODUCTION

Familial dysautomia is an autosomal recessive disease in which patients suffer from unmyelinated sensory neuron loss, reduced BMD, and frequent fractures. It has been proposed that the loss of neurotransmitters synthesized by unmyelinated neurons adversely affects bone integrity in this hereditary syndrome. The purpose of this study was to determine whether small sensory neurons are required for the maintenance of bone integrity in rats.

MATERIALS AND METHODS

Ten-month-old male Sprague-Dawley rats were treated with either capsaicin or vehicle. In vivo DXA scanning and micro CT scanning, and histomorphometry were used to evaluate BMD, structure, and cellular activity. Bone strength was measured in distal femoral sections. Body weight and gastrocnemius/soleus weights were measured and spontaneous locomotor activity was monitored. Peroneal nerve morphometry was evaluated using light and electron microscopy. Substance P and calcitonin gene-related peptide (CGRP) content in the sciatic nerve and proximal tibia were determined by enzyme immunoassay (EIA). Substance P signaling was measured using a sciatic nerve stimulation extravasation assay.

RESULTS

Four weeks after capsaicin treatment, there was a loss of BMD in the metaphyses of the tibia and femur. In the proximal tibia, the osteoclast number and surface increased, osteoblast activity and bone formation were impaired, and trabecular bone volume and connectivity were diminished. There was also a loss of bone strength in the distal femur. No changes occurred in body weight, 24-h grid-crossing activity, weight bearing, or muscle mass after capsaicin treatment, indicating that skeletal unloading did not contribute to the loss of bone integrity. Capsaicin treatment destroyed 57% of the unmyelinated sensory axons, reduced the substance P and CGRP content in the sciatic nerve and proximal tibia, and inhibited neurogenic extravasation.

CONCLUSION

These results support the hypothesis that capsaicin-sensitive sensory neurons contribute to the maintenance of trabecular bone integrity. Capsaicin-sensitive neurons have efferent functions in the tissues they innervate, effects mediated by transmitters released from the peripheral nerve terminals. We postulate that the deleterious effects of capsaicin treatment on trabecular bone are mediated by reductions in local neurotransmitter content and release.

Decreased bone formation and osteopenia in mice lacking alpha-calcitonin gene-related peptide

We recently described an unexpected high bone mass phenotype in mice lacking the Calca gene that encodes CT and alphaCGRP. Here we show that mice specifically lacking alphaCGRP expression display an osteopenia caused by a decreased bone formation. These results show that alphaCGRP is a physiological activator of bone formation and that the high bone mass phenotype of the Calca-deficient mice is caused by the absence of CT.

INTRODUCTION

Calcitonin (CT) and alpha-calcitonin gene-related peptide (alphaCGRP) are two polypeptides without completely defined physiologic functions that are both derived from the Calca gene by alternative splicing. We have recently described an unexpected high bone mass phenotype in mice carrying a targeted deletion of the Calca gene. To uncover whether this phenotype is caused by the absence of CT or by the absence of alphaCGRP, we analyzed a mouse model, where the production of alphaCGRP is selectively abolished.

MATERIALS AND METHODS

Bones from Calca(-/-) mice, alphaCGRP(-/-) mice, and their corresponding wildtype controls were analyzed using radiography, muCT imaging, and undecalcified histology. Cellular activities were assessed using dynamic histomorphometry and by measuring the urinary collagen degradation products. CT expression was determined using radioimmunoassay and RT-PCR. Immunohistochemistry was performed using an anti-CGRP antibody on decalcified bone sections.

RESULTS

Unlike the Calca-deficient mice, the alphaCGRP-deficient mice do not display a high bone mass phenotype. In contrast, they develop an osteopenia that is caused by a reduced bone formation rate. Serum levels and thyroid expression of CT are not elevated in alphaCGRP-deficient mice. While CGRP expression is detectable in neuronal cell close to trabecular bone structures, the components of the CGRP receptor are expressed in differentiated osteoblast cultures.

CONCLUSION

The discrepancy between the bone phenotypes of Calca(-/-) mice and alphaCGRP(-/-) mice show that the high bone mass phenotype of the Calca(-/-) mice is caused by the absence of CT. The osteopenia observed in the alphaCGRP(-/-) mice that have normal levels of CT further show that alphaCGRP is a physiologic activator of bone formation.

Genetic determinants of bone mass

PURPOSE OF REVIEW

This review examines recent advances in the analysis of genetic determinants of bone mass. It addresses both human and animal linkage studies as well as genetic manipulations in animals, inbred mouse models, and candidate gene analyses.

RECENT FINDINGS

Recent studies have implicated novel regulatory pathways in bone biology including both the neuroendocrine system and metabolic pathways linked to lipid metabolism. Variations in the lipoprotein receptor-related protein 5 (LRP5), part of the Wnt-frizzled pathway, were independently identified by linkage in high and low bone mass families. Subsequently, other high bone mass syndromes have been shown to have mutations in this gene. Neural studies have shown the skeletal regulatory activity of leptin and neuropeptide Y receptors via the hypothalamus. Subsequently, the beta-adrenergic pathway has been implicated, with important changes in bone mass. The lipoxygenase 12/15 pathway, identified through inbred mouse models and through pharmacologic studies with specific inhibitors, has also been shown to have important effects on bone mass. These studies exemplify the value of genetic models both to identify and then confirm pathways by mutational study and pharmacologic interventions. Continuing candidate gene studies often performed with multiple loci complement such discoveries. However, these studies have not focused on the clinical endpoint of fracture and few have included large enough groups to engender confidence in the associations reported, as such studies may require thousands of individuals. Interestingly, results often differ by ethnicity, age, or gender. A small proportion have examined whether relevant genes influence response to treatment.

SUMMARY

The combinations of human and animal genetic linkage studies have advanced understanding of the regulation of bone mass. Studies ranging from linkage to pharmacology provide optimism for new targets and treatments for osteoporosis.

Vascular calcification and osteolysis in diabetic neuropathy-is RANK-L the missing link?

Diabetic neuropathy is associated with osteopenia and calcification of vascular smooth muscle cells. These changes are most marked in patients with acute neuropathic osteoarthropathy (Charcot foot), in which osteopenia is universal and the prevalence of vascular calcification exceeds 90%. While it has been thought that both osteopenia and vascular calcification may be linked to sympathetic denervation with increased peripheral limb perfusion, the cellular mechanism was not clear. However, the recent recognition that the receptor activator of nuclear factor kappa B ligand (RANK-L)/osteoprotegerin (OPG) signalling pathway is central to the processes regulating bone turnover in a wide variety of medical conditions has raised the possibility that the same cytokines may be involved in the osteolysis which accompanies diabetic neuropathy. This is made more likely by the realisation that the RANK-L/OPG pathway is also thought to mediate the calcification of vascular smooth muscle cells in coronary and peripheral vascular disease. The circumstantial evidence underpinning this hypothesis is reviewed here, and it is suggested that the unregulated activation of RANK-L-mediated effects on bone and arteries may be triggered by the loss of nerve-derived peptides, e.g. calcitonin gene-related peptide, which normally exert a moderating influence on the pathway.

Depletion of mucosal substance P in acute otitis media

OBJECTIVE

The neuropeptide substance P (SP) is an inducer of neurogenic inflammation and bone resorption in the middle ear. Resorption of the bone tissue structures surrounding the middle ear cavity is a distinct feature of the initial stage of acute otitis media (AOM), which may be due to nerve fiber release of SP.

MATERIAL AND METHODS

To investigate possible release of SP in the middle ear mucosa during AOM, we used a well-established rat model of AOM caused by Streptococcus pneumoniae. Following tissue extraction on Days 1, 3 and 6 post-inoculation, the mucosal concentration of SP was measured using a radioimmunoassay.

RESULTS

Compared to sham-inoculated control ears, the concentration of SP was significantly reduced on Day 1 and even further reduced on Day 3, whereas partial replenishment was found on Day 6.

CONCLUSION

SP seems to be depleted in the rat middle ear mucosa in the hyperacute phase of AOM. This depletion is followed by replenishment and the concentration of SP approaches its normal level 6 days post-inoculation. The release of SP may be the trigger of the concurrent bone resorption and may further augment the inflammatory response to the bacterial colonization.

Calcitonin gene-related peptide elevates calcium and polarizes membrane potential in MG-63 cells by both cAMP-independent and -dependent mechanisms

Published data suggest that the neuropeptide calcitonin gene-related peptide (CGRP) can stimulate osteoblastic bone formation; however, interest has focused on activation of cAMP-dependent signaling pathways in osteogenic cells without full consideration of the importance of cAMP-independent signaling. We have now examined the effects of CGRP on intracellular Ca(2+) concentration ([Ca(2+)](int)) and membrane potential (E(m)) in preosteoblastic human MG-63 cells by single-cell fluorescent confocal analysis using fluo 4-AM-fura red-AM and bis(1,3-dibarbituric acid)-trimethine oxanol [DiBAC(4)(3)] bis-oxonol assays. CGRP produced a two-stage change in [Ca(2+)](int): a rapid transient peak and a secondary sustained increase. Both responses were dose dependent with an EC(50) of approximately 0.30 nM, and the maximal effect (initially approximately 3-fold over basal levels) was observed at 20 nM. The initial phase was sensitive to inhibition of Ca(2+) mobilization with thapsigargin, whereas the secondary phase was eliminated only by blocking transmembrane Ca(2+) influx with verapamil or inhibiting cAMP-dependent signaling with the Rp isomer of adenosine 3',5'-cyclic monophosphorothioate (Rp-cAMPS). These data suggest that CGRP initially stimulates Ca(2+) discharge from intracellular stores by a cAMP-independent mechanism and subsequently stimulates Ca(2+) influx through L-type voltage-dependent Ca(2+) channels by a cAMP-dependent mechanism. In addition, CGRP dose-dependently polarized cellular E(m), with maximal effect at 20 nM and an EC(50) of 0.30 nM. This effect was attenuated with charybdotoxin (-20%) or glyburide (glibenclamide; -80%), suggesting that E(m) hyperpolarization is induced by both Ca(2+)-activated and ATP-sensitive K(+) channels. Thus CGRP signals strongly by both cAMP-dependent and cAMP-independent signaling pathways in preosteoblastic human MG-63 cells.

Alpha-ketoglutarate treatment early in postnatal life improves bone density in lambs at slaughter

This study has investigated the long-term effect on skeletal development of a short postnatal period of oral alpha-ketoglutarate (AKG) administration, a compound known to regulate the synthesis of proline, which in turn is important for collagen production. Male lambs born to Shropshire ewes were used in this study. Lambs were randomly assigned to either an AKG-treated group or a control group receiving an equal volume of distilled water. AKG-treated lambs received 0.1 g/kg body weight orally from the first 14 days of postnatal life. Lambs were slaughtered at approximately 130 day of life and a body weight of 43-49 kg. Plasma samples, collected from lambs at days 14 and 130, were analyzed for IGF-1 concentration using sheep-specific RIA kits. Bone development was determined on the femur in terms of geometrical and mechanical properties and quantitative computed tomography (QCT). Trabecular bone density, cortical bone density, and the mechanical properties of the bones were significantly higher for AKG-treated compared with control lambs. However, neither plasma IGF-1 concentration nor the geometrical properties of the bones were significantly influenced by AKG treatment. It is concluded that early postnatal treatment of lambs with AKG positively affects bone strength, an effect that does not appear to be mediated by an increased plasma IGF-1 concentration.

NEUROPEPTIDES AND NEUROGENIC MECHANISMS IN ORAL AND PERIODONTAL INFLAMMATION

It is generally accepted that the nervous system contributes to the pathophysiology of peripheral inflammation, and a neurogenic component has been implicated in many inflammatory diseases, including periodontitis. Neurogenic inflammation should be regarded as a protective mechanism, which forms the first line of defense and protects tissue integrity. However, severe or prolonged noxious stimulation may result in the inflammatory response mediating injury rather than facilitating repair. This review focuses on the accumulating evidence suggesting that neuropeptides have a pivotal role in the complex cascade of chemical activity associated with periodontal inflammation. An overview of neuropeptide synthesis and release introduces the role of neuropeptides and their interactions with other inflammatory factors, which ultimately lead to neurogenic inflammation. The biological effects of the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), and neuropeptide Y (NPY) are summarized, and evidence for their involvement in the localized inflammatory lesions which characterize periodontitis is presented. In this context, the role of CGRP in bone metabolism is described in more detail. Recent research highlighting the role of the nervous system in suppressing pain and inflammation is also discussed.

Beta-adrenergic blockers reduce the risk of fracture partly by increasing bone mineral density: Geelong Osteoporosis Study

This population-based study documented beta-blocker use in 59/569 cases with incident fracture and 112/775 controls. OR for fracture associated with beta-blocker use was 0.68 (95%CI, 0.49-0.96). Beta-blockers were associated with higher BMD at the total hip (2.5%) and UD forearm (3.6%) after adjusting for age, anthropometry, and thiazide use. Beta-blocker use is associated with reduced fracture risk and higher BMD.

INTRODUCTION

Animal data suggests that bone formation is under beta-adrenergic control and that beta-blockers stimulate bone formation and/or inhibit bone resorption.

MATERIALS AND METHODS

We evaluated the association between beta-blocker use, bone mineral density (BMD), and fracture risk in a population-based study in Geelong, a southeastern Australian city with a single teaching hospital and two radiological centers providing complete fracture ascertainment for the region. Beta-blocker use was documented for 569 women with radiologically confirmed incident fractures and 775 controls without incident fracture. Medication use and lifestyle factors were documented by questionnaire.

RESULTS

Odds ratio for fracture associated with beta-blocker use was 0.68 (95% CI, 0.49-0.96) for any fracture. Adjusting for age, weight, medications, and lifestyle factors had little effect on the odds ratio. Beta-blocker use was associated with a higher BMD at the total hip (2.5%, p = 0.03) and ultradistal forearm (3.6%, p = 0.04) after adjustment for age, anthropometry, and thiazide use.

CONCLUSION

Beta-blockers are associated with a reduction in fracture risk and higher BMD.