Neuropeptide substance P stimulates the formation of osteoclasts via synovial fibroblastic cells

Nervous System-Driven Osseointegration

Implants are essential therapeutic tools for treating bone fractures and joint replacements. Despite the in-depth study of osseointegration for more than fifty years, poor osseointegration caused by aseptic loosening remains one of the leading causes of late implant failures. Osseointegration is a highly sophisticated and spatiotemporal process in vivo involving the immune response, angiogenesis, and osteogenesis. It has been unraveled that the nervous system plays a pivotal role in skeletal health via manipulating neurotrophins, neuropeptides, and nerve cells. Herein, the research related to nervous system-driven osseointegration was systematically analyzed and reviewed, aiming to demonstrate the prominent role of neuromodulation in osseointegration. Additionally, it is indicated that the implant design considering the role of neuromodulation might be a promising way to prevent aseptic loosening.

Performance of Schwann cell transplantation into extracted socket after inferior alveolar nerve injury in a novel rat model

An inferior alveolar nerve (IAN) injury is a common clinical problem that can affect a patients' quality of life. Cellular therapy has been proposed as a promising treatment for this injury. However, the current experimental models for IAN injury require surgery to create bone windows that expose the nerve, and these models do not accurately mimic human IAN injuries. Therefore, in this study, a novel experimental model for IAN injury has been established in rats. Using this model, the effects of Schwann cells and their role in the recovery from IAN injuries were investigated. Schwann cells were isolated from rat sciatic nerves and cultured. The first molar in the mandible was extracted and the IAN was immediately injured for 30 min by inserting an insect pin. Then, the Schwann cells or culture medium were transplanted into the extracted sockets of the cell and injury groups, respectively. After the surgery, the cell group displayed significantly increased sensory reflexes in response to mechanical stimulation, regenerated IAN width, and myelin basic protein-positive myelin sheaths when compared with the injury group. In conclusion, a novel animal experimental model for IAN injury has been developed that does not require the creation of a bone window to evaluate the impacts of cell transplantation and demonstrates that Schwann cell transplantation facilitates the regeneration of injured IANs.

Effects of Early Life Stress on Bone Homeostasis in Mice and Humans

Bone pathology is frequent in stressed individuals. A comprehensive examination of mechanisms linking life stress, depression and disturbed bone homeostasis is missing. In this translational study, mice exposed to early life stress (MSUS) were examined for bone microarchitecture (μCT), metabolism (qPCR/ELISA), and neuronal stress mediator expression (qPCR) and compared with a sample of depressive patients with or without early life stress by analyzing bone mineral density (BMD) (DXA) and metabolic changes in serum (osteocalcin, PINP, CTX-I). MSUS mice showed a significant decrease in NGF, NPYR1, VIPR1 and TACR1 expression, higher innervation density in bone, and increased serum levels of CTX-I, suggesting a milieu in favor of catabolic bone turnover. MSUS mice had a significantly lower body weight compared to control mice, and this caused minor effects on bone microarchitecture. Depressive patients with experiences of childhood neglect also showed a catabolic pattern. A significant reduction in BMD was observed in depressive patients with childhood abuse and stressful life events during childhood. Therefore, future studies on prevention and treatment strategies for both mental and bone disease should consider early life stress as a risk factor for bone pathologies.

The Role of Substance P in the Regulation of Bone and Cartilage Metabolic Activity

Substance P (SP) is a neuropeptide that is released from sensory nerve endings and is widely present in nerve fibers. It acts on bones and related tissues by binding to receptors, thereby regulating bone metabolism, cartilage metabolism, and fracture healing. SP has attracted widespread attention as a signaling substance that can be recognized by both the immune system and the nervous system. Previous studies have shown that bone and chondrocytes can synthesize and secrete sensory neuropeptides and express their receptors, and can promote proliferation, differentiation, apoptosis, matrix synthesis, and the degradation of target cells through autocrine/paracrine modes. In this paper, we review the research progress made in this field in recent years in order to provide a reference for further understanding the regulatory mechanism of bone and cartilage physiology and pathological metabolism.

Contribution of Infrapatellar Fat Pad and Synovial Membrane to Knee Osteoarthritis Pain

Osteoarthritis (OA) is the most common form of joint disease and a major cause of pain and disability in the adult population. Interestingly, there are patients with symptomatic OA displaying pain, while patients with asymptomatic OA that do not experience pain but show radiographic signs of joint damage. Pain is a complex experience integrating sensory, affective, and cognitive processes related to several peripheral and central nociceptive factors besides inflammation. During the last years, the role of infrapatellar fat pad (IFP), other than the synovial membrane, has been investigated as a potential source of pain in OA. Interestingly, new findings suggest that IFP and synovial membrane might act as a functional unit in OA pathogenesis and pain. The present review discuss the role of IFP and synovial membrane in the development of OA, with a particular focus on pain onset and the possible involved mediators that may play a role in OA pathology and pain mechanisms. Inflammation of IFP and synovial membrane may drive peripheral and central sensitization in KOA. Since sensitization is associated with pain severity in knee OA and may potentially contribute to the transition from acute to chronic, persistent pain in knee OA, preventing sensitization would be a potentially effective and novel means of preventing worsening of pain in knee OA.

Innervation is higher above Bone Remodeling Surfaces and in Cortical Pores in Human Bone: Lessons from patients with primary hyperparathyroidism

Mounting evidence from animal studies suggests a role of the nervous system in bone physiology. However, little is known about the nerve fiber localization to human bone compartments and bone surface events. This study reveals the density and distribution of nerves in human bone and the association of nerve profiles to bone remodeling events and vascular structures in iliac crest biopsies isolated from patients diagnosed with primary hyperparathyroidism (PHPT). Bone sections were sequentially double-immunostained for tyrosine hydroxylase (TH), a marker for sympathetic nerves, followed by protein gene product 9.5 (PGP9.5), a pan-neuronal marker, or double-immunostained for either PGP9.5 or TH in combination with CD34, an endothelial marker. In the bone marrow, the nerve profile density was significantly higher above remodeling surfaces as compared to quiescent bone surfaces. Ninety-five percentages of all nerve profiles were associated with vascular structures with the highest association to capillaries and arterioles. Moreover, vasculature with innervation was denser above bone remodeling surfaces. Finally, the nerve profiles density was 5-fold higher in the intracortical pores compared to bone marrow and periosteum. In conclusion, the study shows an anatomical link between innervation and bone remodeling in human bone.

Effects of medical ozone upon healthy equine joints: Clinical and laboratorial aspects

OBJECTIVE

The aim of this study was to verify whether transient inflammatory reactions induced by intra-articular medicinal ozone administration affect joint components, by in vivo evaluation of inflammatory (prostaglandin E2, Substance P, Interleukin-6, Interleukine-1, Tumor Necrosis Factor), anti-inflammatory (Interleukin-10) and oxidative (superoxide dismutase activity and oxidative burst) biomarkers and extracellular matrix degradation products (chondroitin sulphate and hyaluronic acid) in synovial fluid.

METHODS

The effects of medicinal ozone were analyzed at two ozone concentrations (groups A and B, 20 and 40 μg/ml, respectively), using oxygen-injected joints as controls (group C); each group received ten treatments (15 ml gas per treatment). Physical evaluation, evaluation of lameness, ultrasonography, and synovial fluid analysis were performed.

RESULTS

All joints presented mild and transient effusion throughout the study. Group B exhibited the highest lameness score on day 14 (P<0.05), detected by the lameness measurement system, probably because of the higher ozone concentration. All groups exhibited increased ultrasonography scores on day 14 (P < 0.05). Groups A and B exhibited increased proteins concentrations on day 21 (P<0.05). There was no change in hyaluronic acid concentration or the percentage of high-molecular weight hyaluronic acid throughout the experiment. Chondroitin sulfate concentrations decreased in group B, and did not change in group A and C, indicating that neither treatment provoked extracellular matrix catabolism. Cytokine and eicosanoid concentrations were not significantly changed.

CONCLUSIONS

The ozonetherapy did not cause significant inflammation process or cartilage degradation, therefore, ozonetherapy is safe at both evaluated doses.

Synovial membrane receptors as therapeutic targets: A review of receptor localization, structure, and function

Joint pathology and degeneration is a significant cause of pain. The synovial membrane plays an important role in maintenance of the joint, contributes to the pathology of many arthropathies and may be adversely affected in joint disease. Improving knowledge of the receptors present within the synovium will aid in a better understanding of joint pathology and the development of new treatments for diseases such as osteoarthritis and rheumatoid arthritis. Knowledge of the location and function of synovial membrane receptors (both in healthy and diseased synovium) may provide important targets in the treatment of various arthropathies. Classic pain receptors such as opioid receptors in the synovium are a mainstay in local and systemic management of chronic pain in many species. In addition to these, many other receptors such as bradykinin, neurokinin, transient receptor potential vanilloid, and inflammatory receptors, such as prostanoid and interleukin receptors have been discovered within the synovial membrane. These receptors are important in pain, inflammation, and in maintenance of normal joint function and may serve as targets for pharmacologic intervention in pathologic states. The goal of this review is to outline synovial membrane receptor localization and local therapeutic modulation of these receptors, in order to stimulate further research into pharmacological management of arthropathies at the local level. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1589-1605, 2017.

Peripheral Nerve Fibers and Their Neurotransmitters in Osteoarthritis Pathology

The importance of the nociceptive nervous system for maintaining tissue homeostasis has been known for some time, and it has also been suggested that organogenesis and tissue repair are under neuronal control. Changes in peripheral joint innervation are supposed to be partly responsible for degenerative alterations in joint tissues which contribute to development of osteoarthritis. Various resident cell types of the musculoskeletal system express receptors for sensory and sympathetic neurotransmitters, allowing response to peripheral neuronal stimuli. Among them are mesenchymal stem cells, synovial fibroblasts, bone cells and chondrocytes of different origin, which express distinct subtypes of adrenoceptors (AR), receptors for vasoactive intestinal peptide (VIP), substance P (SP) and calcitonin gene-related peptide (CGRP). Some of these cell types synthesize and secrete neuropeptides such as SP, and they are positive for tyrosine-hydroxylase (TH), the rate limiting enzyme for biosynthesis of catecholamines. Sensory and sympathetic neurotransmitters are involved in the pathology of inflammatory diseases such as rheumatoid arthritis (RA) which manifests mainly in the joints. In addition, they seem to play a role in pathogenesis of priori degenerative joint disorders such as osteoarthritis (OA). Altogether it is evident that sensory and sympathetic neurotransmitters have crucial trophic effects which are critical for joint tissue and bone homeostasis. They modulate articular cartilage, subchondral bone and synovial tissue properties in physiological and pathophysiological conditions, in addition to their classical neurological features.

Bone health nutraceuticals alter microarray mRNA gene expression: A randomized, parallel, open-label clinical study

BACKGROUND AND OBJECTIVE

Dietary intake of fruits and vegetables has been suggested to have a role in promoting bone health. More specifically, the polyphenols they contain have been linked to physiological effects related to bone mineral density and bone metabolism. In this research, we use standard microarray analyses of peripheral whole blood from post-menopausal women treated with two fixed combinations of plant extracts standardized to polyphenol content to identify differentially expressed genes relevant to bone health.

METHODS

In this 28-day open-label study, healthy post-menopausal women were randomized into three groups, each receiving one of three investigational fixed combinations of plant extracts: an anti-resorptive (AR) combination of pomegranate fruit (Punica granatum L.) and grape seed (Vitis vinifera L.) extracts; a bone formation (BF) combination of quercetin (Dimorphandra mollis Benth) and licorice (Glycyrrhiza glabra L.) extracts; and a fixed combination of all four plant extracts (AR plus BF). Standard microarray analysis was performed on peripheral whole blood samples taken before and after each treatment. Annotated genes were analyzed for their association to bone health by comparison to a gene library.

RESULTS

The AR combination down-regulated a number of genes involved in reduction of bone resorption including cathepsin G (CTSG) and tachykinin receptor 1 (TACR1). The AR combination also up-regulated genes associated with formation of extracellular matrix including heparan sulfate proteoglycan 2 (HSPG2) and hyaluronoglucosaminidase 1 (HYAL1). In contrast, treatment with the BF combination resulted in up-regulation of bone morphogenetic protein 2 (BMP-2) and COL1A1 (collagen type I α1) genes which are linked to bone and collagen formation while down-regulating genes linked to osteoclastogenesis. Treatment with a combination of all four plant extracts had a distinctly different effect on gene expression than the results of the AR and BF combinations individually. These results could be due to multiple feedback systems balancing activities of osteoblasts and osteoclasts.

CONCLUSION

In summary, this ex-vivo microarray study indicated that the pomegranate, grape seed, quercetin and licorice combinations of plant extracts modulated gene expression for both osteoclastic and osteogenic processes.

Endocrinology of bone/brain crosstalk

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

Changes in peptidergic fiber density in the synovium of mice with collagenase-induced acute arthritis

The effect of acute osteoarthritis (OA) on peripheral nerve fibers (NFs) in synovial tissue, and their association with histological changes were investigated in collagenase-induced OA mice. Collagenase (10 U in 5 μL saline) was injected into the right knee, and the same volume of saline was injected into the left knee as the control. Mice were sacrificed 1, 2, 3, and 4 weeks after the collagenase injection. Histopathological changes in the knee joints were evaluated. The numbers of protein gene product (PGP) 9.5-, calcitonin-gene-related peptide (CGRP)-, and substance P (SP)-positive NFs in the synovial tissue were determined, and their densities in the tissue were calculated. The densities of PGP 9.5- and CGRP-positive NFs in the synovium were drastically decreased 1 week after the collagenase injection. However, by week 4, the density of PGP 9.5- and CGRP-positive NFs had recovered to 84% and 79% of their normal levels, respectively. Despite the poor correlation between the synovitis score and the density of CGRP- or SP-positive NFs in the synovium, the ossification rate of chondrophytes in chondro/osteophyte lesions correlated strongly with the density of CGRP-positive NFs (R = 0.855). These results suggest that the ossification of chondrophytes occurred in parallel with the increase in CGRP-positive fiber density in the synovium during the acute phase of collagenase-induced OA.

Substance P enhanced titanium particles-induced RANKL expression in fibroblasts from periprosthetic membrane

Aseptic loosening remains the primary cause of failure in total joint arthroplasty. Implant-derived particles are thought to be a main cause of osteolysis that leads to the failure. Substance P (SP) immunoreactive nerve fibers have been detected in the periprosthetic membrane of aseptic loose hip prostheses. We isolated fibroblasts from periprosthetic membrane. Fibroblasts were examined by real-time RT-PCR and enzyme-linked immunosorbent assay for expression of the receptor activator of nuclear factor kappa B ligand (RANKL), osteoprotegerin (OPG), cyclooxygenase (COX)-1, and COX-2. Experiments were performed in the presence and absence of titanium particles, SP and NS-398 (a selective COX-2 inhibitor). Titanium particles or SP stimulated RANKL and COX-2 expression in fibroblasts, whereas NS-398 inhibited RANKL production, suggesting a COX-2-mediated event. Moreover, SP enhanced COX-2 and RANKL expression by titanium particles-stimulated fibroblasts. Thus, SP and titanium particles acted synergistically to increase RANKL expression.

Occurrence of substance P in bone repair under different load comparison of straight and angulated fracture in rat tibia

Substance P (SP) has been shown in vitro to stimulate both formation and resorption of bone. This seemingly contradictory observation could be explained by in vivo variations in skeletal loading and rate of bone turnover, features which may be explored during different phases of fracture healing. In 50 SD rats, the right tibia was fractured and fixed with an intramedullary pin in straight alignment and in anterior angulation resulting in a convex and concave side under different load. Fracture repair was assessed by radiography, histology, and semi-quantitative immunohistochemistry of SP nerve fiber occurrence at days 7, 21, 35, 56, and 84 post-fracture. During regeneration, days 7-35, abundant SP-nerve ingrowth was observed in the fracture callus reaching a side-symmetrical peak at day 21 in straight fractures. In angulated fractures, the SP peak was also observed at day 21 on the concave loaded side, but not until day 35 on the convex unloaded side. Each SP-peak coincided with cortical bridging. During remodeling, days 35-84, a side-symmetrical disappearance of SP-positive fibers was seen in straight fractures. The same pattern was seen on the concave loaded side of angulated fractures. However, on the convex unloaded side, where resorption now took place, SP-fibers remained until the end of the experiment. Our study suggests that neuronal SP during bone regeneration has a stimulatory role on bone formation, while during remodeling increased SP fiber density in unloaded areas may be related to bone resorption.

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.

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.

The contribution of the synovium, synovial derived inflammatory cytokines and neuropeptides to the pathogenesis of osteoarthritis

Osteoarthritis (OA) is one of the most common and disabling chronic joint disorders affecting horses, dogs and humans. Synovial inflammation or synovitis is a frequently observed phenomenon in osteoarthritic joints and contributes to the pathogenesis of OA through formation of various catabolic and pro-inflammatory mediators altering the balance of cartilage matrix degradation and repair. Catabolic mediators produced by the inflamed synovium include pro-inflammatory cytokines, nitric oxide, prostaglandin E(2) and several neuropeptides, which further contribute to the pathogenesis of OA by increasing cartilage degradation. Recent studies suggest that substance P, corticotropin-releasing factor, urocortin and vasoactive intestinal peptide may also be involved in OA development, but the precise role of these neuropeptides in the pathogenesis of OA is not known. Since increased production of matrix metalloproteinases by the synovium is stimulated by pro-inflammatory cytokines, future anti-inflammatory therapies should focus on the synovium as a means of controlling subsequent inflammatory damage.

High levels of substance P and CGRP in pseudosynovial fluid from patients with aseptic loosening of their hip prosthesis

BACKGROUND

Aseptic loosening is the most important complication after total hip arthroplasty (THA). The nervous system has been implicated in the etiology and pathogenesis of joint diseases.

METHODS

We compared levels of substance P (SP) and calcitonin gene-related peptide (CGRP) in pseudosynovial fluid from patients with aseptic loosening after THA with those in synovial fluid from patients undergoing primary THA for osteoarthritis, who served as controls. Levels of SP and CGRP were measured using an enzyme immunoassay.

RESULTS

We found that SP and CGRP levels were significantly higher in the pseudosynovial fluid of loose artificial joints than in the synovial fluid of controls.

INTERPRETATION

SP and CGRP may have a role in aseptic loosening.

Observations favouring the occurrence of local production and marked effects of bombesin/gastrin-releasing peptide in the synovial tissue of the human knee joint--comparisons with substance P and the NK-1 receptor

We have previously shown that levels of the neuropeptides substance P (SP) and bombesin/gastrin-releasing peptide (BN/GRP) in blood and synovial fluid correlate with levels of pro-inflammatory cytokines in patients with rheumatoid arthritis (RA). It is well-established that SP is present in nerve endings in the synovium whilst the source of BN/GRP in human joints is completely unknown. Nor is it known whether GRP-receptors (GRP-R) are present in human synovial tissue. This study aimed to investigate the expression pattern of SP, BN/GRP and their receptors (NK-1R and GRP-R) in synovial tissue. Synovial tissue specimens from patients with RA or osteoarthritis (OA) were processed for immunohistochemistry, in situ hybridisation and ELISA. The results show the presence of BN/GRP, but not SP, in cells in the synovial tissue at both the protein and mRNA level. We did not find immunoreactive BN/GRP in nerve structures. NK-1R and GRP-R were also expressed at both protein and mRNA levels in cells associated with blood vessels and cells in the interstitial tissue. ELISA analyses revealed both SP and BN/GRP to be present in synovial tissue extracts and that synovial levels of SP were higher in RA patients than those with OA. Our results indicate that BN/GRP is produced by non-neuronal cells in the synovial tissue. Furthermore, both BN/GRP and SP may exert their effects on the synovial tissue through the respective receptors. These results suggest that BN/GRP and SP may modulate inflammation and vascular events, and possibly healing processes in the synovium. Finally, nerves should not be considered as the source of BN/GRP in synovial tissue although this peptide is presumably intimately involved functionally in synovial tissue, a previously unrecognised fact.

Presence of substance P and the neurokinin-1 receptor in tenocytes of the human Achilles tendon

Nerve signal substances, such as the tachykinin substance P (SP), may be involved in the changes that occur in response to tendinopathy (tendinosis). It is previously known that the level of SP innervation within tendon tissue is limited, but results of experimental studies have suggested that SP may have stimulatory, angiogenetic and healing effects in injured tendons. Therefore, it would be of interest to know if there is a local SP-supply in tendon tissue. In the present study, the patterns of expression of SP and its preferred receptor, the neurokinin-1 receptor (NK-1 R), in normal and tendinosis human Achilles tendons were analyzed by use of both immunohistochemistry and in situ hybridization. We found that there was expression of SP mRNA in tenocytes, and that tenocytes showed expression of NK-1 R at protein as well as mRNA levels. The observations concerning both SP and NK-1 R were most evident for tenocytes in tendinosis tendons. Our findings suggest that SP is produced in tendinosis tendons, and furthermore that SP has marked effects on the tenocytes via the NK-1 R. It cannot be excluded that the SP effects are of importance concerning the processes of reorganization and healing that occur for tendon tissue in tendinosis. In conclusion, it appears as if SPergic autocrine/paracrine effects occur in tendon tissue during the processes of tendinosis, hitherto unknown effects for human tendons.

The impact of substance P signalling on the development of experimental staphylococcal sepsis and arthritis

Substance P (SP), acting on the neurokinin-1 receptor (NK-1R), is a neuropeptide, involved in the inflammatory processes. It promotes vasodilatation and increases vasopermeability, thus ensuing extravasation and accumulation of leucocytes at sites of injury. The aim of this study was to assess the impact of SP signalling on the responses during staphylococcal infection and the accompanying arthritis. Three experiments were performed where NK-1R-/- mice and controls were intravenously infected with different doses of Staphylococcus aureus. Clinical assessment of arthritis was performed as well as histological analysis of bone and cartilage destruction in the joints. In addition, the impact of NK-1R mutation on bacterial load in the kidneys as well as the phagocytic capacity of blood leucocytes were studied. Mice lacking the NK-1R displayed significantly higher bacterial load in the kidneys and significantly more severe synovitis and cartilage/bone destruction than the controls when inoculated with 1.4 x 10(7) staphylococci. Infection with 3.5 x 10(8) CFU/mouse induced sepsis. Thus, 11 days after bacterial inoculation 15 of 19 mice in the NK-1R-/- group had died versus 8 of 15 in the control group. Phagocytosis test revealed that significantly fewer macrophages from NK-1R-/- mice were able to phagocytose S. aureus when compared with macrophages from congenic control mice. Blocking the biological responses to substance P via its receptor NK-1R results in a less efficient clearance of bacteria leading to more severe arthritic lesions in mice.

Substance P and its receptors in bone metabolism

Accumulating evidence on bone physiopathology has indicated that the skeleton contains numerous nerve fibers and its metabolism is regulated by the nervous system. Until now, more than 10 neuropeptides have been identified in bone. Substance P (SP) is a neuropeptide released from axons of sensory neurons, belongs to the tachykinin family and plays important roles in many physiological and pathological processes by acting as a neurotransmitter, neuromodulator, or trophic factor. It activates signal transduction cascades by acting on the neurokinin-1 receptor (NK(1)-R). Previous studies have confirmed that the SP-immunoreactive (IR) axons innervate bone and adjacent tissues, and that their density varies depending on the regions and physiological or pathological conditions. Over the past few decades, it has been found that SP takes part in the stimulation of bone resorption, and its receptors have been demonstrated to be located in osteoclasts. Notably, in studies of skeletal ontogeny, SP-IR axons have been shown to appear at an early stage, mostly coinciding with the sequence of long bone mineralization. These findings, together with data obtained from chemically or surgically targeted nerve deletions, strongly suggest that SP is a potent regulator of skeletal physiology. The specific distribution of SP-IR nerve fibers, the different amount of SP within regions, and the various levels of expression of NK(1)-R in targeted cells presumably related to and participate in bone metabolism. It can be predicted that the indirect roles of SP through other cytokines are as important as its direct roles in bone metabolism. This new regulating pathway of bone metabolism would have enormous implications in skeletal physiology and the relevant research might present curative potentials to a spectrum of bone diseases.

The Effects of Substance P on the Biomechanic Properties of Ruptured Rat Achilles’ Tendon

OBJECTIVE

To determine whether injection of substance P into the paratendinous region of a ruptured and subsequently sutured rat Achilles' tendon alters the biomechanic properties of the tendon.

DESIGN

Interventional animal study.

SETTING

Animal laboratory at a university hospital.

ANIMALS

Ninety-six 2-month-old, male Sprague-Dawley rats.

INTERVENTION

Injection of saline, substance P (10(-6)micromol/kg of body weight [BW] or 10(-8)micromol/kg BW) associated with neutral endopeptidase inhibitors, or neutral endopeptidase inhibitors alone into the paratendinous region of ruptured and subsequently sutured rat Achilles' tendons from the second until the sixth day postoperatively.

MAIN OUTCOME MEASURES

Stress at maximal load and work to maximal load and stiffness.

RESULTS

Stress at maximal load was higher in the groups injected with substance P than in the saline group in the first, second, and sixth weeks. Work to maximal load was higher from the second until the sixth weeks in the substance P-treated groups than in the saline group. Stiffness did not differ between the 4 groups in any of the weeks.

CONCLUSIONS

Injection of substance P into the paratendinous region of ruptured and subsequently sutured rat Achilles' tendons improved tendon healing by enhancing stress at maximal load and work to maximal load. However, stiffness was not significantly affected.

Exogenously administered substance P and neutral endopeptidase inhibitors stimulate fibroblast proliferation, angiogenesis and collagen organization during Achilles tendon healing

BACKGROUND

In the last few years much research has been conducted in methods to promote tendon healing. The aim of this study was to determine if the healing process after operative repair of rat Achilles tendons could be stimulated by the paratendinous injection of a sensory peptide, substance P (SP).

METHODS

Ninety-six male Sprague-Dawley rats were randomly allocated to four groups: (I) control buffer injections, (II) injections of SP 10(-6) mol/kg body weight combined with a carrier, (III) injections of SP 10(-8) mol/kg BW with the carrier, and (IV) injections with the carrier only (thiorphan 1 micromol/kg BW and captopril 30 micromol/kg BW, both neutral endopeptidase inhibitors). The influence on tissue repair was determined from the histologic measurement of fibroblast proliferation, angiogenesis, and collagen organization. On days 7, 14, 28 and 42, animals were sacrificed and histologic evaluations were performed on the injured Achilles tendon constructs.

RESULTS

The two groups subjected to SP injections showed a significant initial fibroblast proliferation on day 7 (p < 0.05), which rapidly declined by day 14 to the level of cellular proliferation observed with the use of thiorphan and captopril. Capillary proliferation showed a similar evolution, except that in the second week angiogenesis in the treated groups was below the level of the control group. Strikingly, collagen orientation increased faster in the groups injected with SP. This was obvious from the second week already and the difference remained until the completion of the study.

CONCLUSION

This is the first study to demonstrate that paratendinous injections of SP after operative repair of the Achilles tendon in rats appears to provide a boost to the initial stages of healing and significantly accelerate the reparative phase of the healing process.