Substance P and arthritis: analysis of plasma and synovial fluid levels

A comprehensive review of the literature on CD10: its function, clinical application, and prospects

CD10, a zinc-dependent metalloprotease found on the cell surface, plays a pivotal role in an array of physiological and pathological processes including cardiovascular regulation, immune function, fetal development, pain response, oncogenesis, and aging. Recognized as a biomarker for hematopoietic and tissue stem cells, CD10 has garnered attention for its prognostic potential in the progression of leukemia and various solid tumors. Recent studies underscore its regulatory significance and therapeutic promise in combating Alzheimer's disease (AD), and it is noted for its protective role in preventing heart failure (HF), obesity, and type-2 diabetes. Furthermore, CD10/substance P interaction has also been shown to contribute to the pain signaling regulation and immunomodulation in diseases such as complex regional pain syndrome (CRPS) and osteoarthritis (OA). The emergence of COVID-19 has sparked interest in CD10's involvement in the disease's pathogenesis. Given its association with multiple disease states, CD10 is a prime therapeutic target; inhibitors targeting CD10 are now being advanced as therapeutic agents. This review compiles recent and earlier literature on CD10, elucidating its physicochemical attributes, tissue-specific expression, and molecular functions. Furthermore, it details the association of CD10 with various diseases and the clinical advancements of its inhibitors, providing a comprehensive overview of its growing significance in medical research.

Stroke risk in rheumatoid arthritis patients: exploring connections and implications for patient care

Rheumatoid arthritis (RA) can independently increase the risk of stroke, affecting both young and adult RA patients. Recent attention has been drawn to the association between stroke and RA, supported by mounting evidence. Given that stroke is a significant and an urgent public health concern, this review aims to highlight the relationship between stroke and RA, covering mechanisms, underlying risk factors, early detection tools, and treatment implications. By uncovering the connection that links RA to stroke, we can pave the way for targeted healthcare practices and the development of preventive strategies for individuals with RA. Therefore, further research is imperative to deepen our understanding of this association and, ideally, guide treatment decisions for individuals at risk of both RA and stroke.

Subchondral bone microenvironment in osteoarthritis and pain

Osteoarthritis comprises several joint disorders characterized by articular cartilage degeneration and persistent pain, causing disability and economic burden. The incidence of osteoarthritis is rapidly increasing worldwide due to aging and obesity trends. Basic and clinical research on osteoarthritis has been carried out for decades, but many questions remain unanswered. The exact role of subchondral bone during the initiation and progression osteoarthritis remains unclear. Accumulating evidence shows that subchondral bone lesions, including bone marrow edema and angiogenesis, develop earlier than cartilage degeneration. Clinical interventions targeting subchondral bone have shown therapeutic potential, while others targeting cartilage have yielded disappointing results. Abnormal subchondral bone remodeling, angiogenesis and sensory nerve innervation contribute directly or indirectly to cartilage destruction and pain. This review is about bone-cartilage crosstalk, the subchondral microenvironment and the critical role of both in osteoarthritis progression. It also provides an update on the pathogenesis of and interventions for osteoarthritis and future research targeting subchondral bone.

Profiling of inflammatory mediators in the synovial fluid related to pain in knee osteoarthritis

Background

Inflammatory mediators in the synovial fluid (SF) play critical roles in the initiation and development of pain in knee osteoarthritis (KOA). However, data for inflammatory marker expression are conflicting, and the role of SF inflammatory mediators in neuropathic pain is not clear. Therefore, the aim of this study was to identify SF inflammatory mediators associated with nociceptive and neuropathic pain in KOA.

Methods

Levels of IL-1β, IL-6, TNF-α, macrophage colony-stimulating factor, MMP-3, MMP-13, metalloproteinase with thrombospondin motifs 5, calcitonin gene-related peptide, neuropeptide Y, substance P and bradykinin were measured using enzyme-linked immunosorbent assays in 86 patients. Nociceptive pain was assessed using the numeric rating scale (NRS), visual analog scale (VAS) and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain score. Neuropathic pain was determined using the PainDETECT questionnaire. Moreover, knee function was evaluated by the WOMAC score and range of motion (ROM) assessments. Radiological grade was defined using the Kellgren-Lawrence (K-L) grading scale.

Results

Pain scores measured using different methods correlated highly with each other. A worse K-L grade and knee function were associated with worse pain. Expression of IL-1β and IL-6 was increased in the early stage compared with the late stage. The NRS score correlated positively with age, K-L grade, and the WOMAC score and negatively with ROM and TNF-α expression. The VAS correlated positively with age, K-L grade, and the WOMAC score but negatively with ROM and levels of IL-1β, IL-6 and TNF-α. The WOMAC pain score did not correlate with any of the inflammatory mediators measured; it correlated only with ROM. The PainDETECT score correlated only with the WOMAC score. Expression of other inflammatory mediators did not correlate with any of the pain scores.

Conclusions

IL-1β, IL-6 and TNF-α play critical roles in pain in the early stage of KOA and correlate with pain. The catabolic enzymes and neuropeptides measured do not correlate with nociceptive and neuropathic pain. New biomarkers related to pain in the late stage need to be further investigated.

Neuropeptides: important regulators of joint homeostasis

PURPOSE

This review explores the mechanisms of joint pain with a special focus on the role of neuropeptides in pain transmission and their potential role in the progression of joint degeneration as seen in osteoarthritis.

METHODS

A literature search was performed on papers published between January 1990 and September 2017 using the Web of Science Core Collection, MEDLINE and Scopus databases.

RESULTS

What is seen in the subchondral bone and synovia is mirrored in the central nervous system (CNS). Substance P, calcitonin gene-related peptide, vasoactive intestinal peptide and neuropeptide Y are the major peptides involved both in the generation of pain as well as reducing pain post-joint trauma. The interplay between them and other neuropeptides and cytokines influence how noxious stimuli are transduced, transmitted and modulated for a final pain perception as part of a complex cascade of events. There is a close interaction between the different components in the joint that together cross-talk to adapt to load and catabolic factors during injury and inflammation.

CONCLUSION

The articular joint should be seen as an organ where local joint pain development and maintenance is influenced by interplay between the local transmitters in the joints as well as their dependence on the CNS. A slow-release cocktail of mixed antibodies targeted against neuropeptides and receptor blockers/stimulators involved in the events of early joint pain or any inflammatory joint disease is a future treatment target.

LEVEL OF EVIDENCE

V.

Changes in biomarkers in equine synovial fluid two weeks after intra-articular hyaluronan treatment: a randomised double-blind clinical trial

BACKGROUND

Inflammatory and degenerative activity inside the joint can be studied in vivo via analysis of synovial fluid (SF) biomarkers, which are molecular markers of inflammatory processes and tissue turnover. The aim of this study was to investigate the response of selected biomarkers in the SF after an intra-articular (IA) high-molecular-weight non-animal stabilized hyaluronic acid (NASHA) treatment. Our hypothesis was that prostaglandin E₂ (PGE₂), substance P, aggrecan chondroitin sulfate 846 epitope (CS846), and carboxypeptide of type II collagen (CPII) concentrations in SF would decrease more in the NASHA than in the placebo group. Twenty-eight clinically lame horses with positive responses to diagnostic IA anaesthesia of the metacarpophalangeal or metatarsophalangeal joints were randomized into treatment (n = 15) and control (n = 13) groups. After collection of baseline SF samples followed by IA diagnostic anaesthesia, horses in the treatment group received 3 ml of a NASHA product IA. Those in the placebo group received an equivalent volume of sterile 0.9% saline solution. The horses were re-evaluated and a second SF sample was obtained after a 2-week period.

RESULTS

CS846 concentration decreased in the NASHA group only (P = 0.010). Both PGE₂ and CPII concentrations decreased within the groups (PGE₂, P = 0.010 for the NASHA group; P = 0.027 for the placebo group; CPII, P < 0.001 for NASHA group; P = 0.009 for placebo group). No significant treatment effect for any biomarker was found between groups. NASHA induced an increase in white blood cell count; this was significant compared with baseline (P = 0.021) and the placebo group (P = 0.045).

CONCLUSIONS

Although the SF concentration of the cartilage-derived biomarker CS846 decreased in the NASHA group, no statistically significant treatment effect of any of the biomarkers were observed between treatment groups. The significant increase in SF white blood cell count after IA NASHA may indicate a mild inflammatory response. However, as no clinical adverse effects were observed, we conclude that IA NASHA was well tolerated.

Pain in knee osteoarthritis is associated with variation in the neurokinin 1/substance P receptor (TACR1) gene

BACKGROUND

Substance P (SP) is a pain- and inflammation-related neuropeptide which preferentially binds to the neurokinin receptor 1 (NK₁ ). SP and NK₁ receptors have been implicated in joint pain, inflammation and damage in animal models and human studies of osteoarthritis (OA). The aim of this study was to test if genetic variation at the neurokinin 1 receptor gene (TACR1) is associated with pain in individuals with radiographic knee OA.

METHODS

Participants from the Genetics of OA and Lifestyle study were used for the discovery group (n = 1615). Genotype data for six SNPs selected to cover most variation in the TACR1 gene were used to test for an association with symptomatic OA. Replication analysis was performed using data from the Chingford 1000 Women Study, Hertfordshire Cohort Study, Tasmanian Older Adult Cohort Study and the Clearwater OA Study. In total, n = 1715 symptomatic OA and n = 735 asymptomatic OA individuals were analysed.

RESULTS

Out of six SNPs tested in the TACR1 gene, one (rs11688000) showed a nominally significant association with a decreased risk of symptomatic OA in the discovery cohort. This was then replicated in four additional cohorts. After adjusting for age, gender, body mass index and radiographic severity, the G (minor) allele at rs11688000 was associated with a decreased risk of symptomatic OA compared to asymptomatic OA cases (p = 9.90 × 10^-4 , OR = 0.79 95% 0.68-0.90 after meta-analysis).

CONCLUSIONS

This study supports a contribution from the TACR1 gene in human OA pain, supporting further investigation of this gene's function in OA.

SIGNIFICANCE

This study contributes to the knowledge of the genetics of painful osteoarthritis, a condition which affects millions of individuals worldwide. Specifically, a contribution from the TACR1 gene to modulating pain sensitivity in osteoarthritis is suggested.

Substance P and Chronic Pain in Patients with Chronic Inflammation of Connective Tissue

Objective

Evidence suggests that substance P (SP) is involved in chronic joint inflammation, such as the pathogenesis of rheumatoid arthritis and osteoarthritis. The goal of the research was to evaluate the correlation between chronic pain and changes in the SP level in patients with chronic inflammation of the connective tissue.

Methods

Patients with osteoarthritis and rheumatoid arthritis were enrolled in this study. The relationship between chronic pain intensity and the serum SP concentration was evaluated in these groups of patients with osteoarthritis and rheumatoid arthritis.

Results

The results showed a positive correlation between the serum SP concentrations and chronic pain intensity.

Conclusions

1. The SP serum concentration was significantly different between the groups of patients with OA and RA. 2. There was a positive correlation between the serum SP concentration and chronic pain intensity in OA and RA patients.

Neuroinflammatory Mechanisms of Connective Tissue Fibrosis: Targeting Neurogenic and Mast Cell Contributions

Significance: The pathogenesis of fibrogenic wound and connective tissue healing is complex and incompletely understood. Common observations across a vast array of human and animal models of fibroproliferative conditions suggest neuroinflammatory mechanisms are important upstream fibrogenic events. Recent Advances: As detailed in this review, mast cell hyperplasia is a common observation in fibrotic tissue. Recent investigations in human and preclinical models of hypertrophic wound healing and post-traumatic joint fibrosis provides evidence that fibrogenesis is governed by a maladaptive neuropeptide-mast cell-myofibroblast signaling pathway. Critical Issues: The blockade and manipulation of these factors is providing promising evidence that if timed correctly, the fibrogenic process can be appropriately regulated. Clinically, abnormal fibrogenic healing responses are not ubiquitous to all patients and the identification of those at-risk remains an area of priority. Future Directions: Ultimately, an integrated appreciation of the common pathobiology shared by many fibrogenic connective tissue conditions may provide a scientific framework to facilitate the development of novel antifibrotic prevention and treatment strategies.

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.

Hypomagnesemia and inflammation: clinical and basic aspects

In recent years, increasing awareness of hypomagnesemia has resulted in clinical trials that associate this mineral deficiency with diabetes, metabolic syndrome, and drug therapies for cancer and cardiovascular diseases. However, diagnostic testing for tissue deficiency of magnesium still presents a challenge. Investigations of animal and cellular responses to magnesium deficiency have found evidence of complex proinflammatory pathways that may lead to greater understanding of mediators of the pathobiology in neuronal, cardiovascular, intestinal, renal, and hematological tissues. The roles of free radicals, cytokines, neuropeptides, endotoxin, endogenous antioxidants, and vascular permeability, and interventions to limit the inflammatory response associated with these parameters, are outlined in basic studies of magnesium deficiency. It is hoped that this limited review of inflammation associated with some diseases complicated by magnesium deficiency will prompt greater awareness by clinicians and other health providers and in turn increase efforts to prevent and treat this disorder.

Immunohistochemical analysis of the effects of estrogen on intraarticular neurogenic inflammation in a rat anterior cruciate ligament transection model of osteoarthritis

Synovitis is considered as one of the factors associated with the pathogenesis of osteoarthritis (OA). There is currently a significant amount of research linking estrogen deficiencies with the development of OA in estrogen-deficient women, including postmenopausal women; however, the exact etiology remains unclear. Various neuropeptides, such as substance P (SP) and calcitonin gene-related peptide (CGRP), have been shown to contribute to synovitis in OA joints, and the influence of estrogen on the expressions of SP and CGRP in the synovium of OA joints has been noted. After ovariectomy (OVX) followed by estradiol (E2) replacement, 24 female rats were divided into three groups: OVX group, OVX + E2 replacement group (E2 group), and a sham group. All rats underwent transection of the anterior cruciate ligament at the same time. After 30 days, the histological findings of knee joints by hematoxylin-eosin staining and immunofluorescence staining of protein gene product 9.5 (pan-neuronal marker), SP, and CGRP were compared among experimental groups. The degree of synovitis in the OVX group was higher than in the E2 and sham groups. No significant differences in the density of protein gene product 9.5-immunoreactive nerve fibers were observed among the three experimental groups, but the density of SP- or CGRP-immunoreactive nerve fibers in the OVX group was significantly higher than in the E2 and sham groups. These findings suggest that estrogen partly regulates intraarticular neurogenic inflammation in OA joints by modulating the expressions of neuropeptides in the synovium.

Normative values of substance P and neurokinin A in neonates

BACKGROUND

Substance P (SP) and neurokinin A (NKA) are neuropeptides that have been researched as pain markers in adults, as they are involved in transmission and modulation of pain signals. There is a potential role for them as neurochemical markers of pain in neonates, but this has never previously been investigated.

AIM

To establish normative values of SP and NKA in neonates.

METHODS

Longitudinal once-daily morning blood samples were collected over two weeks from 142 neonates, gestation 23-40 weeks. Peptides were extracted, and then quantified using an in-house radioimmunoassay. Infants with presumed painful conditions were excluded.

RESULTS

SP concentrations ranged from <0.98 to 11.2 pmol/L (median 1.7 pmol/L) and NKA concentrations from <1.95 to 74.6 pmol/L (median 6.0 pmol/L). Gestation and birth weight had no significant correlation with peptide concentrations. Postnatally, there was a gradual rise in median SP during the first three days, which decreased again by day 14. Median NKA showed a similar rise, but was not statistically significant. This postnatal rise and fall were more apparent in preterm infants < or = 32 weeks gestation.

CONCLUSIONS

This is the first description of normative values of SP and NKA in neonates. SP and NKA show changes with postnatal age, which are more marked in preterm infants.

Diclofenac: an update on its mechanism of action and safety profile

BACKGROUND

Diclofenac is a proven, commonly prescribed nonsteroidal anti-inflammatory drug (NSAID) that has analgesic, anti-inflammatory, and antipyretic properties, and has been shown to be effective in treating a variety of acute and chronic pain and inflammatory conditions. As with all NSAIDs, diclofenac exerts its action via inhibition of prostaglandin synthesis by inhibiting cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) with relative equipotency. However, extensive research shows the pharmacologic activity of diclofenac goes beyond COX inhibition, and includes multimodal and, in some instances, novel mechanisms of action (MOA).

DATA SOURCES

Literature retrieval was performed through PubMed/MEDLINE (through May 2009) using combinations of the terms diclofenac, NSAID, mechanism of action, COX-1, COX-2, and pharmacology. Reference citations resulting from publications identified in the literature search were reviewed when appropriate.

METHODS

This article reviews the established, putative, and emerging MOAs of diclofenac; compares the drug's pharmacologic and pharmacodynamic properties with other NSAIDs to delineate its potentially unique qualities; hypothesizes why it has been chosen for further recent formulation enhancement; and evaluates the potential effect of its MOA characteristics on safety.

DISCUSSION

Research suggests diclofenac can inhibit the thromboxane-prostanoid receptor, affect arachidonic acid release and uptake, inhibit lipoxygenase enzymes, and activate the nitric oxide-cGMP antinociceptive pathway. Other novel MOAs may include the inhibition of substrate P, inhibition of peroxisome proliferator activated receptor gamma (PPARgamma), blockage of acid-sensing ion channels, alteration of interleukin-6 production, and inhibition of N-methyl-D-aspartate (NMDA) receptor hyperalgesia. The review was not designed to compare MOAs of diclofenac with other NSAIDs. Additionally, as the highlighted putative and emerging MOAs do not have clinical data to demonstrate that these models are correct, further research is necessary to ascertain if the proposed pathways will translate into clinical benefits. The diversity in diclofenac's MOA may suggest the potential for a relatively more favorable profile compared with other NSAIDs.

Open access chemical and clinical probes to support drug discovery

Drug discovery resources in academia and industry are not used efficiently, to the detriment of industry and society. Duplication could be reduced, and productivity could be increased, by performing basic biology and clinical proofs of concept within open access industry-academia partnerships. Chemical biologists could play a central role in this effort.

Novel method for determination of substance P levels in unextracted human plasma by using acidification

Substance P (SP) is a member of the tachykinin family and has an important role in immune responses. SP is detectable in plasma in a free and bound state. Simple modification of a commercially available SP enzyme-linked immunosorbent assay allows the dissociation and capture of plasma SP without solid-phase extraction.

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.

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.

Predicting outcome of TENS in chronic pain: a prospective, randomized, placebo controlled trial

Transcutaneous electrical nerve stimulation (TENS) is an easy to use non-invasive analgesic intervention applied for diverse pain states. However, effects in man are still inconclusive, especially for chronic pain. Therefore, to explore the factors predicting result of TENS treatment in chronic pain we conducted a prospective, randomized, placebo-controlled trial (n=163), comparing high frequency TENS (n=81) with sham TENS (n=82). Patients' satisfaction (willingness to continue treatment; yes or no) and pain intensity (VAS) were used as outcome measures. The origin of pain and cognitive coping strategies were evaluated as possible predictors for result of TENS treatment.

RESULTS

Fifty-eight percent of the patients in the TENS group and 42.7% of the sham-TENS group were satisfied with treatment result (chi square=3.8, p=0.05). No differences were found for pain intensity. Patients diagnosed with osteoarthritis and related disorders (especially of the vertebral column) or peripheral neuropathic pain were less satisfied with high frequency TENS (OR=0.12 (95% CI 0.04-0.43) and 0.06 (95% CI 0.006-0.67), respectively). Injury of bone and soft tissue (especially postsurgical pain disorder) provided the best results. Treatment modality or interactions with treatment modality did not predict intensity of pain as a result of treatment. We conclude, that predicting the effect of high frequency TENS in chronic pain depends on the choice of outcome measure. Predicting patients' satisfaction with treatment result is related to the origin of pain. Predicting pain intensity reflects mechanisms of pain behavior and perceived control of pain, independent of treatment modality. Pain catastrophizing did not predict TENS treatment outcome.

Neuropeptides regulate expression of matrix molecule, growth factor and inflammatory mediator mRNA in explants of normal and healing medial collateral ligament

Denervation degrades normal ligament properties and impairs ligament healing. This suggests that secreted neuromediators, such as neuropeptides, could be modulating cell metabolism in ligament and scar tissue. To test this hypothesis we investigated the effect of exogenous substance P (SP), neuropeptide Y (NPY) or calcitonin gene-related peptide (CGRP) on the mRNA levels for proteins associated with inflammation, angiogenesis, and matrix production in tissue-cultured specimens of normal and injured medial collateral ligament. SP and NPY induced increased mRNA levels for several inflammatory mediators in the 2-week post-injury specimens. All three neuropeptides induced decreases in mRNA levels for healing-associated growth factors and matrix molecules, including basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF) and collagen types I and III. The results indicate that neuropeptides strongly influence the metabolic activity of cells in healing ligament, particularly at early time points after injury.

Polyethylene particle-induced bone resorption in substance P-deficient mice

Aseptic loosening is the major cause of total joint replacement failure. Substance P (SP) is a neurotransmitter richly distributed in sensory nerve fibers, bone, and bone-related tissue. The purpose of this study was to investigate the potential impact of SP on bone metabolism in polyethylene particle-induced osteolysis. We utilized the murine calvarial osteolysis model based on ultrahigh molecular weight polyethylene (UHMWPE) particles in 14 wild-type mice (C57BL/J6) and 14 SP-deficient mice. Group 1 (C57BL/J 6) and group 3 (SP-knockout) received sham surgery, and group 2 (C57BL/J6) and group 4 (SP-knockout) were treated with polyethylene particles. Analytical methods included three-dimensional micro-computed tomographic (micro-CT) analysis and histomorphometry. Bone resorption was measured within the midline suture. The number of osteoclasts was determined by counting the tartrate-resistant acid phosphatase-positive cells. UHMWPE-particle treated SP-deficient mice showed significantly reduced osteolysis compared to wild-type mice, as confirmed by histomorphometry (P < 0.001) and micro-CT (P = 0.035). Osteoclast numbers were significantly reduced in groups 3 and 4 compared to groups 1 and 2 (P < 0.001). Unexpectedly, SP-deficient mice (group 3) showed a significantly increased absolute bone mass compared to wild-type mice (group 1) (P = 0.02). The findings of our murine calvaria model lead to the assumption that SP is a promoter in particle-induced osteolysis. The pathophysiology of aseptic loosening is complex, and neuropeptides are not solely responsible for the progress of implant loosening; however, we conclude that there could be coherence between neurotransmitters and particle-induced osteolysis in patients with aseptic loosening.

Measurement of plasma-derived substance P: biological, methodological, and statistical considerations

The undecapeptide substance P (SP) is a member of the tachykinin family of neurotransmitters, which has a pivotal role in the regulation of inflammatory and immune responses. One of the major barriers to the study of the in vivo role of SP in a number of immune disorders is the accurate measurement of SP in fluids. This is reflected in the variability of reported SP levels in serum and plasma of humans in both healthy and diseased states. This study was initiated in order to identify sources of variability by the comparative evaluation of the influences of sample preparation and analytical detection methods on the measurement of SP in plasma. The results indicate that sample preparation (peptide extraction versus no extraction) and the choice of analytical method for SP quantitation may yield significantly different values and may contribute to the variability in SP values reported in the literature. These results further emphasize the need for careful consideration in the selection of methods for SP quantitation, as well as caution in the interpretation and comparison of data reported in the literature.

Localization of SP- and CGRP-immunopositive nerve fibers in the hip joint of patients with painful osteoarthritis and of patients with painless failed total hip arthroplasties

Using immunohistochemical methods we determined the presence of SP- and CGRP-immunopositive nerve fibers in the hip joint of patients with femoral neck fracture (controls, group 1), painful osteoarthritis (group 2), and painless failed total hip arthroplasties (group 3). Immunoreactive nerve fibers were found in the soft tissue of the fossa acetabuli as well as in the subintimal part of the synovial layer in the hip joint capsule of groups 1 and 2. In the capsule of controls the innervation density had a median of 5.7fibers/cm(2) for CGRP-ir and 3.2fibers/cm(2) for SP-ir afferents. In the osteoarthritic group, the density significantly increased to a median of 15.6fibers/cm(2) for CGRP-ir and 8.2fibers/cm(2) for SP-ir neurons (p=0.05). Patients with failed hip arthroplasties completely lacked these neuropeptide containing afferents. Innervation density in the fossa acetabuli of osteoarthritc patients showed a median of 14.1fibers/cm(2) for CGRP-ir and 5.9fibers/cm(2) for SP-ir afferents. From these data we assume that the hip joint capsule and the soft tissue of the fossa acetabuli are important triggers of nociception. This is supported by the fact, that patients with loosened total hip arthroplasties, where we failed to detect SP- and CGRP-immunoreactive fibers, did not feel pain. The upregulation of SP- and CGRP-positive neurons in response to arthritic stages suggests a mechanism involving neuropeptides in the maintenance of a painful degenerative joint disease and in mediating noxious stimuli from the periphery. Furthermore, these findings help to explain clinical observations, such as effectiveness of local therapy to control hip pain with intraarticular injection, synovectomy and denervation procedures.

Levels of gastrin-releasing peptide and substance P in synovial fluid and serum correlate with levels of cytokines in rheumatoid arthritis

It is well known that cytokines are highly involved in the disease process of rheumatoid arthritis (RA). Recently, targeting of neuropeptides has been suggested to have potential therapeutic effects in RA. The aim of this study was to investigate possible interrelations between five neuropeptides (bombesin/gastrin-releasing peptide (BN/GRP), substance P (SP), vasoactive intestinal peptide, calcitonin-gene-related peptide, and neuropeptide Y) and the three cytokines tumour necrosis factor (TNF)-α, IL-6, and monocyte chemoattractant protein-1 in synovial fluid of patients with RA. We also investigated possible interrelations between these neuropeptides and soluble TNF receptor 1 in serum from RA patients. Synovial fluid and sera were collected and assayed with ELISA or RIA. The most interesting findings were correlations between BN/GRP and SP and the cytokines. Thus, in synovial fluid, the concentrations of BN/GRP and SP grouped together with IL-6, and SP also grouped together with TNF-α and monocyte chemoattractant protein-1. BN/GRP and SP concentrations in synovial fluid also grouped together with the erythrocyte sedimentation rate. In the sera, BN/GRP concentrations and soluble TNF receptor 1 concentrations were correlated. These results are of interest because blocking of SP effects has long been discussed in relation to RA treatment and because BN/GRP is known to have trophic and growth-promoting effects and to play a role in inflammation and wound healing. Furthermore, the observations strengthen a suggestion that combination treatment with agents interfering with neuropeptides and cytokines would be efficacious in the treatment of RA. In conclusion, BN/GRP and SP are involved together with cytokines in the neuroimmunomodulation that occurs in the arthritic joint.

The role of substance P in inflammatory disease

The diffuse neuroendocrine system consists of specialised endocrine cells and peptidergic nerves and is present in all organs of the body. Substance P (SP) is secreted by nerves and inflammatory cells such as macrophages, eosinophils, lymphocytes, and dendritic cells and acts by binding to the neurokinin-1 receptor (NK-1R). SP has proinflammatory effects in immune and epithelial cells and participates in inflammatory diseases of the respiratory, gastrointestinal, and musculoskeletal systems. Many substances induce neuropeptide release from sensory nerves in the lung, including allergen, histamine, prostaglandins, and leukotrienes. Patients with asthma are hyperresponsive to SP and NK-1R expression is increased in their bronchi. Neurogenic inflammation also participates in virus-associated respiratory infection, non-productive cough, allergic rhinitis, and sarcoidosis. SP regulates smooth muscle contractility, epithelial ion transport, vascular permeability, and immune function in the gastrointestinal tract. Elevated levels of SP and upregulated NK-1R expression have been reported in the rectum and colon of patients with inflammatory bowel disease (IBD), and correlate with disease activity. Increased levels of SP are found in the synovial fluid and serum of patients with rheumatoid arthritis (RA) and NK-1R mRNA is upregulated in RA synoviocytes. Glucocorticoids may attenuate neurogenic inflammation by decreasing NK-1R expression in epithelial and inflammatory cells and increasing production of neutral endopeptidase (NEP), an enzyme that degrades SP. Preventing the proinflammatory effects of SP using tachykinin receptor antagonists may have therapeutic potential in inflammatory diseases such as asthma, sarcoidosis, chronic bronchitis, IBD, and RA. In this paper, we review the role that SP plays in inflammatory disease.

Correlation of prostaglandin E2 concentrations in synovial fluid with ground reaction forces and clinical variables for pain or inflammation in dogs with osteoarthritis induced by transection of the cranial cruciate ligament

OBJECTIVE

To evaluate the temporal pattern of prostaglandin (PG) E2 concentrations in synovial fluid after transection of the cranial cruciate ligament (CCL) in dogs and to correlate PGE2 concentrations with ground reaction forces and subjective clinical variables for lameness or pain.

ANIMALS

19 purpose-bred adult male Walker Hounds.

PROCEDURE

Force plate measurements, subjective clinical analysis of pain or lameness, and samples of synovial fluid were obtained before (baseline) and at various time points after arthroscopic transection of the right CCL. Concentrations of PGE2 were measured in synovial fluid samples, and the PGE2 concentrations were correlated with ground reaction forces and clinical variables.

RESULTS

The PGE2 concentration increased significantly above the baseline value throughout the entire study, peaking 14 days after transection. Peak vertical force and vertical impulse significantly decreased by day 14 after transection, followed by an increase over time without returning to baseline values. All clinical variables (eg, lameness, degree of weight bearing, joint extension, cumulative pain score, effusion score, and total protein content of synovial fluid, except for WBC count in synovial fluid) increased significantly above baseline values. Significant negative correlations were detected between PGE2 concentrations and peak vertical force (r, -0.5720) and vertical impulse (r, -0.4618), and significant positive correlations were detected between PGE2 concentrations and the subjective lameness score (r, 0.5016) and effusion score (r, 0.6817).

CONCLUSIONS AND CLINICAL RELEVANCE

Assessment of the acute inflammatory process by measurement of PGE2 concentrations in synovial fluid may be correlated with the amount of pain or lameness in dogs.

Excitatory amino acids, TNF-alpha, and chemokine levels in synovial fluids of patients with active arthropathies

The aim of this study was to assess the synovial fluid (SF) neurotransmitter excitatory amino acid (EAA) levels, including glutamate (Glu) and aspartate (Asp), in the context of SF levels of other amino acids, TNF-alpha and chemokines from patients with active arthropathies. The SF was collected from patients with active rheumatoid arthritis (RA), gout, or osteoarthritis (OA). The SF samples were analysed for levels of neurotransmitters glutamate and aspartate, tumour necrosis factor-alpha (TNF-alpha), Regulated upon Activation Normally T-cell Expressed and Secreted (RANTES), macrophage inhibitory factor-1 alpha (MIP-1alpha) and interleukin 8 (IL-8). SF WBC counts were also determined. Correlations between SF EAA, TNF-alpha and chemokines were determined by the Pearson product-moment correlation. Primary cultures derived from SF from active RA and gout patients were incubated with added l-glutamate, to assess if exposure to Glu could increase TNF-alpha levels. There were significant elevations in SF EAA, SF TNF-alpha and SF RANTES in RA patients compared to gout or OA patients. Significant correlations between SF EAA and SF RANTES, MIP-1alpha and IL-8 levels were seen, and SF EAA and SF TNF-alpha or SF WBC levels approached significance. Addition of exogenous neurotransmitter glutamate significantly increased TNF-alpha levels in primary cell cultures derived from RA and gout patients. The SF neurotransmitter EAA levels significantly correlated to selected SF chemokine levels, in clinically active RA, gout and OA patients, independent of disease. Added Glu resulted in significantly increased TNF-alpha levels in primary synovial cell cultures. These data expand the relationship of SF neurotransmitter EAA levels to SF cytokines and chemokines in patients with clinically active arthritis, and suggest that neurotransmitters Glu and Asp contribute to peripheral inflammatory processes.

Tachykinins and tachykinin receptors in bone

Tachykinins are neuropeptides that are widely distributed in the body and function as neurotransmitters and neuromodulators. Five tachykinin subtypes: substance P (SP), neurokinin A, neurokinin B, neuropeptide K, and neuropeptide gamma; and three receptor subtypes: neurokinin-1, -2, and -3 receptors, have been identified. SP was the first peptide of the tachykinin family to be identified. It is considered to be an important neuropeptide, and to function in the nervous system and intestine. However, recent advances in the analysis of SP receptors, particularly neurokinin-1 receptors (NK(1)-Rs) that have high affinity for SP, have demonstrated that NK(1)-Rs are distributed not only in neurons and immune cells, but also in other peripheral cells, including bone cells. This article reviews the current understanding of the distribution of SP and other tachykinins in bone, and the function of tachykinins, through neurokinin receptors. The distribution of tachykinin-immunoreactive axons and neurokinin receptors suggests that tachykinins may directly modulate bone metabolism through neurokinin receptors.

Clinical effects of betamethasone and hyaluronan, and of defocalized carbon dioxide laser treatment on traumatic arthritis in the fetlock joints of horses

The clinical effects of intra-articular betamethasone together with hyaluronan (betaM/HA) and treatment with a defocalized carbon dioxide laser on acute traumatic arthritis of the fetlock joint were assessed. The horses in these studies were selected using a thorough lameness examination, including intra-articular anaesthesia abolishing the lameness. This investigation comprised an observer-blind study, including 10 sport horses (10 joints), and a prospective study, including 180 sport horses (333 joints). In both studies, the material was divided into two groups treated with either betaM/HA or a carbon dioxide laser. The treatment doses were 12 mg of betaM, 20 mg of HA or 60 J/cm2 of treated area. Convalescence before training was 21 days for both groups in the observer-blind study. In the prospective study, convalescence in the betaM/HA group was 21 days but was only 7 days for the laser-treated group. In the observer-blind study, three of five treated joints recovered in both cohorts. In the prospective study, the groups had significantly different recovery rates--68% of the betaM/HA-treated joints and 80% of the carbon dioxide laser-treated joints. These results indicate that the defocalized carbon dioxide laser should be an applicable mode of treatment of acute traumatic synovitis in horses. However, the biochemical functions related to carbon dioxide laser treatment require further elucidation.

Local neurokinin-1 receptor in the knee joint contributes to the induction, but not maintenance, of arthritic pain in the rat

Substance P is known to exert various pro-inflammatory effects that are mediated by neurokinin-1 (NK-1) receptor in peripheral tissues. This study examined the effect of the NK-1 receptor antagonist cis-2-[diphenylmethyl]-N-[(2-iodophenyl)-1-azabicyclo[2.2.2]octan-3-amine] (L-703,606) on nociceptive response following carrageenan injection (2%, 50 microl) into the knee joint cavity of the right hind leg. L-703,606 injection (0.1 or 1 mM, 50 microl) into the same joint cavity immediately before the carrageenan injection significantly reduced the nociceptive response. However, antagonist treatment at 5 h after carrageenan injection was ineffective in alleviating nociception. Neither intraperitoneal injection of the antagonist (1 mM, 50 microl) immediately before the carrageenan injection was effective. These results suggest that local NK-1 receptor contributes to the induction, but not maintenance, of arthritic pain.

The neurokinin-1 receptor antagonist RP 67580 reduces the sensitization of primary afferents by substance P in the rat

The inflammatory mediator substance P (SP) produces a variety of biological effects in several tissues by binding to the tachykinin receptor neurokinin 1 (NK1) and, to a lesser extent, by binding to the neurokinin 2 receptor (NK2). To assess the sensitizing effect of SP on articular afferent fibres the NK1receptor antagonist RP 67580 was applied in normal and acutely inflamed rat knee joints. Altogether 38 fine afferent nerve fibres from the rat knee with conduction velocities of 0.71-13.5 m/s were recorded as single units, during non-noxious and noxious joint rotations. SP, injected i.a. as a bolus close to the knee joint, was able to sensitize 45.5% (10 of 22) of the units recorded from normal joints and 33.3% (five of 15) of afferents from inflamed joints. The following i.a. application of RP 67580 in a range of 20-200 nmol antagonized in a dose-dependent manner the sensitizing effect of SP in a large proportion of slowly conducting articular afferents from normal (66.7%) and inflamed (46.2%) knee joints. Subsequent SP application enhanced the afferent sensitivity further. The electrophysiological results presented here further support the suggestion that the sensitization of afferents by SP in the rat knee joint is mediated mainly by the NK1 receptor, which is probably located on the primary afferents.

Perturbations of arginine vasopressin secretion during inflammatory stress. Pathophysiologic implications

Pro-inflammatory cytokines, such as interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF alpha), released from inflammatory foci, can activate the hypothalamus to produce corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP). These hypothalamic peptides in synergy increase ACTH production by the pituitary gland and hence corticosteroid (CS) secretion by the adrenal cortices. CS dampens inflammation. The pituitary also produces prolactin (PRL), which is pro-inflammatory, and macrophage inhibitory factor (MIF), which by counteracting the anti-inflammatory and immunosuppressive effects of CS, is pro-inflammatory. Lewis rats develop a variety of induced-autoimmune inflammatory conditions, such as streptococcal cell wall arthritis, whereas the histocompatible F344 Fisher rats are resistant to this condition. Lewis rats have a defective hypothalamic-pituitary adrenal (HPA) response to a variety of hypothalamic stimuli, but have augmented systemic secretion of AVP. Patients with rheumatoid arthritis (RA) have deficient CS with exaggerated PRL responses to inflammatory stimuli. Within inflammatory foci, CRH is pro-inflammatory. AVP, which augments autologous mixed lymphocyte reactions, can replace the IL-2 requirement for gamma IFN production by T cells via V1a receptors, and potentiates primary antibody responses, is also pro-inflammatory. Lewis rats have significantly high plasma levels, hypothalamic content, and in vitro release of AVP in comparison to the inflammatory disease-resistant Fischer rats. Immunoneutralization of AVP attenuates inflammatory responses. In Sprague-Dawley rats, AVP potentiates PRL secretion. Preliminary studies in patients with RA have shown that the circulating levels of AVP are significantly increased, which might be a compensatory response to low CS levels or a result of elevated levels of IL-6 in these patients but could nevertheless contribute to rheumatoid inflammation. A similar observation has been made in patients with ankylosing spondylitis.

Assessment and management of chronic pain in elderly people

The ageing process can bring with it an increased incidence of conditions which give rise to chronic pain. Persistent musculoskeletal and/or neuropathic pain due to conditions such as back pain, arthritis, osteoporosis and diabetes in elderly people can lead to a marked deterioration in their quality of life. Pain assessment can be complicated by concomitant disorientation, confusion and communication deficits, leading to the undertreatment of pain in this client group. Pain management can be difficult due to the existence of multiple medical problems and the increased incidence of side-effects related to the treatment. This article aims to update nurses on the assessment and management of pain in the older adult, and will provide a broad overview of pain management strategies suitable for elderly patients.

Abnormalities of somatosensory perception in patients with painful osteoarthritis normalize following successful treatment

To investigate the effect of chronic nociceptive pain on somatosensory perception, quantitative sensibility testing was performed in the most painful area and the homologous contralateral side in 14 patients with painful osteoarthritis of the hip. Twelve patients were reassessed in a painfree state 6-14 months following surgery. Von Frey filaments were used to test low-threshold mechanoreceptive function. Pressure pain sensitivity was assessed with a pressure algometer and thermal sensitivity with a Thermotest. Sex- and age-matched controls were examined in the corresponding areas at similar time intervals. There was no statistically significant difference between groups in the sensitivity to light touch and innocuous cold in either session. Compared to controls, patients had increased sensitivity to pressure pain in the most painful area (p < 0.002), bilaterally increased sensitivity to innocuous warmth (p < 0.03), cold pain (p< 0.05) and a tendency toward bilaterally increased sensitivity to heat pain (p = 0.054) before surgery. In the painful area, patients' sensitivity to pressure pain decreased (p < 0.04) and, remaining within normal limits, sensitivity to light touch increased (p < 0.006) compared to values prior to surgery. No statistically significant differences between the groups were seen following surgery, indicating that the sensibility changes had been maintained by chronic nociceptive pain.

Reciprocal interactions between the neuroendocrine and immune systems during inflammation

The neuroendocrine and immune responses to inflammatory stress represent important integrated physiologic circuits for the regulation of inflammation whose basis has been reviewed. Proinflammatory cytokines such as IL-1 beta, TNF alpha, and IL-6 released from inflammatory foci initiate a local inflammatory response and travel by way of the blood-stream to the central nervous system, where they trigger a variety of neuroendocrine counterregulatory mechanisms. There is an important NEI loop. Stimulatory signals are received by the neural systems from inflammatory foci and are transduced by the hypothalamus, thereby initiating a complex hormonal and cytokine cascade of reactions aimed at modulating inflammation and returning the organism to normal physiologic homeostasis once the trigger has been neutralized. Conversely, a number of mechanisms that modulate the anti-inflammatory activity of the neuroendocrine responses to inflammation are also activated. Defects in the neuroendocrine-immune interactions can profoundly affect the susceptibility to developing chronic inflammatory disease and influencing survival after bacterial infections. The NEI loop has important pathophysiologic implications for disease processes.

Lack of pressure pain modulation by heterotopic noxious conditioning stimulation in patients with painful osteoarthritis before, but not following, surgical pain relief

To investigate the influence of chronic nociceptive pain on endogenous pain modulation, the effect of heterotopic noxious conditioning stimulation (HNCS) on perception of various somatosensory modalities was assessed in 15 patients with painful osteoarthritis of the hip. Thirteen patients were re-assessed when pain-free 6-14 months following surgery. Sex- and age matched healthy subjects assessed at similar time intervals served as controls. The effects of HNCS were tested using the upper extremity submaximal effort tourniquet test. Subjects rated tourniquet-induced pain intensity on a visual analogue scale (VAS). Quantitative sensory testing (QST) was performed contralaterally to the maximally painful area in 13 patients and contralaterally to the second most painful area in two patients (i.e. lateral thigh n = 12, frontal thigh n = 1, lateral calf n = 2). Sensibility was assessed before, during and 45 min following the tourniquet test. Perception thresholds to light touch were assessed using von Frey filaments and pressure pain thresholds by pressure algometry. Perception thresholds to non-painful and painful warmth and cold were determined using a Thermotest. In both sessions, patients rated the tourniquet-induced pain higher than controls at the start (P < 0.003 and P < 0.006, respectively), but not at the end of the tourniquet test. Decreased sensitivity to light touch (P < 0.001) and innocuous cold (P < 0.002) was seen during the tourniquet in patients and controls alike, on both occasions, while perception thresholds to innocuous warmth and heat pain remained unaffected. In the first session, pressure pain thresholds increased during the tourniquet test in controls (P < 0.002), but not in patients. In the second session, pressure pain thresholds increased during the tourniquet test in controls (P < 0.001) and in patients (P < 0.02). In conclusion, no pressure pain modulation was induced by HNCS in patients before surgery, as opposed to controls, suggesting a dysfunction in systems subserving 'diffuse noxious inhibitory controls' (DNIC). Normal pressure pain modulation induced by HNCS was seen when patients were re-assessed in a pain-free state following surgery, indicating that the dysfunction of DNIC had been maintained by chronic nociceptive pain.

Concentrations of substance P and prostaglandin E2 in synovial fluid of normal and abnormal joints of horses

OBJECTIVE

To correlate substance P content of synovial fluid with prostaglandin E2 content, radiographic evidence of joint abnormality, and anatomic location of the joint for normal and osteoarthritic joints of horses.

SAMPLE POPULATION

Synovial fluid from 46 normal joints in 21 horses and 16 osteoarthritic joints in 10 horses.

PROCEDURE

Normal and osteoarthritic joints were identified by clinical and radiographic examination, by response to nerve blocks, during scintigraphy or surgery, or by clinicopathologic evaluation. Substance P and prostaglandin E2 contents of synovial fluid were determined by radioimmunoassay. Radio-graphs of joints were assigned a numeric score reflecting severity of lesions. Joints were assigned a numeric score reflecting anatomic location.

RESULTS

Median concentrations of substance P and prostaglandin E2 were significantly increased in osteoarthritic joints, compared with normal joints. A significant correlation was found between concentrations of substance P and prostaglandin E2 in synovial fluid, but a correlation was not detected between substance P concentration in synovial fluid and anatomic location of the joint or between radiographic scores of osteoarthritic joints and concentrations of substance P or prostaglandin E2.

CONCLUSIONS AND CLINICAL RELEVANCE

A correlation existed between concentrations of substance P and prostaglandin E2 in synovial fluid obtained from normal and osteoarthritic joints. However, content of substance P in synovial fluid cannot be predicted by the radiographic appearance of the joint or its anatomic location. Substance P and prostaglandin E2 may share an important and related role in the etiopathogenesis of osteoarthritis, lending credence to the importance of neurogenic inflammation in horses.

Tachykinin receptor modulators: novel therapeutics for rheumatoid arthritis

The activation of a cellular immune response in a genetically susceptible individual is widely recognised as a main step in triggering rheumatoid arthritis (RA). The tachykinins, substance P (SP) and neurokinin A (NKA), can play a major role in different immune diseases. In patients with inflammatory joint disease, elevated levels of SP have been demonstrated in the synovial fluid of affected joints. It is well known that SP and, to a lesser extent, NKA are deeply involved in the processing of nociceptive signals and exert many pro-inflammatory actions, which may be elicited by an increased neuronal neurokinin release in arthritis; the mechanism behind this increase remains to be fully elucidated. Different observations suggest that one approach to the treatment of RA might be to inhibit the local effects of neurokinins in the affected joints. This review will summarise the more relevant aspects of this topic.