Contribution of interleukin-1 beta to the inflammation-induced increase in nerve growth factor levels and inflammatory hyperalgesia

Peripheral mechanisms underlying the essential role of P2X7 receptors in the development of inflammatory hyperalgesia

Activation of P2X7 receptors by endogenous ATP contributes to the development of inflammatory hyperalgesia. Given the clinical importance of mechanical hyperalgesia in inflammatory states, we hypothesized that the activation of the P2X7 receptor by endogenous ATP contributes to carrageenan-induced mechanical hyperalgesia, and that this contribution is mediated by an indirect sensitization of the primary afferent nociceptors. Co-administration of the selective P2X7 receptor antagonist, A-438079, or the P2X7 receptor antagonist, oATP, with carrageenan blocked the mechanical hyperalgesia induced by carrageenan and significantly reduced the increased concentration of TNF-alpha, IL-6 and CINC-1, but not of IL-1beta induced by carrageenan in the subcutaneous tissue of the rat's hind paw. We concluded that the activation of P2X7 receptors by endogenous ATP is essential to the development of the mechanical hyperalgesia induced by carrageenan in the subcutaneous tissue. It is suggested that this essential role of P2X7 receptors in the development of carrageenan-induced mechanical hyperalgesia is mediated by an indirect sensitization of the primary afferent nociceptors dependent on the previous release of TNF-alpha, IL-6 and CINC-1, but not of IL-1beta.

Electroacupuncture increases CB2 receptor expression on keratinocytes and infiltrating inflammatory cells in inflamed skin tissues of rats

Endogenous cannabinoids and peripheral cannabinoid CB2 receptors (CB2Rs) are involved in the antinociceptive effect of electroacupuncture (EA) on inflammatory pain. However, it remains unclear about how EA affects the expression and distribution patterns of peripheral CB2Rs in inflamed skin tissues. To study this, inflammatory pain was induced by local injection of complete Freund's adjuvant into the hindpaw of rats. The mRNA and protein levels of CB2Rs were quantified by using RTPCR and Western blotting, respectively. The distribution of CB2Rs on keratinocytes and immune cells recruited to the inflamed skin tissues was determined by using double-immunofluorescence labeling. Induction of tissue inflammation significantly increased the mRNA and protein levels of CB2Rs in the skin tissue. Also, both 2 Hz and 100 Hz EA, applied to GB30 and GB34, significantly increased the mRNA and protein levels of CB2Rs in inflamed tissues compared to the sham EA group. CB2Rimmunoreactivities were mainly distributed in keratinocytes, macrophages, and T-lymphocytes in the epidermis and dermis of the inflamed skin tissue. Inflammation caused a significant increase in the number of CB2R-immunoreactive keratinocytes, macrophages, and T-lymphocytes. Furthermore, compared to the sham EA group, EA at 2 or 100 Hz significantly increased the number of keratinocytes, macrophages, and T-lymphocytes with CB2R-immunoreactivity in the inflamed skin tissue. Therefore, our findings suggest that EA is associated with upregulation of local CB2Rs in the inflamed skin tissue. EA primarily potentiates the expression of CB2Rs on keratinocytes and infiltrating inflammatory cells at the site of inflammation.

PERSPECTIVE

This study shows that electroacupuncture increases the CB2 receptor expression on keratinocytes and infiltrating inflammatory cells in inflammatory skin tissues. This finding provides new evidence showing the potential role of CB2 receptors in the analgesic effect of acupuncture on inflammatory pain.

Intervertebral disc, sensory nerves and neurotrophins: who is who in discogenic pain?

The normal intervertebral disc (IVD) is a poorly innervated organ supplied only by sensory (mainly nociceptive) and postganglionic sympathetic (vasomotor efferents) nerve fibers. Interestingly, upon degeneration, the IVD becomes densely innervated even in regions that in normal conditions lack innervation. This increased innervation has been associated with pain of IVD origin. The mechanisms responsible for nerve growth and hyperinnervation of pathological IVDs have not been fully elucidated. Among the molecules that are presumably involved in this process are some members of the family of neurotrophins (NTs), which are known to have both neurotrophic and neurotropic properties and regulate the density and distribution of nerve fibers in peripheral tissues. NTs and their receptors are expressed in healthy IVDs but much higher levels have been observed in pathological IVDs, thus suggesting a correlation between levels of expression of NTs and density of innervation in IVDs. In addition, NTs also play a role in inflammatory responses and pain transmission by increasing the expression of pain-related peptides and modulating synapses of nociceptive neurons at the spinal cord. This article reviews current knowledge about the innervation of IVDs, NTs and NT receptors, expression of NTs and their receptors in IVDs as well as in the sensory neurons innervating the IVDs, the proinflammatory role of NTs, NTs as nociception regulators, and the potential network of discogenic pain involving NTs.

Intra-arterial tert-Butyl-hydroperoxide infusion induces an exacerbated sensory response in the rat hind limb and is associated with an impaired tissue oxygen uptake

The objective of this study was to investigate oxidative stress and oxygen extraction mechanisms in an animal model of continuous intra-arterial infusion of a free radical donor and in an in vitro model using isolated mitochondria. tert-Butyl-hydroperoxide (tert-BuOOH, 25 mM) was infused for 24 h in the left hind limb of rats to induce soft tissue damage (n = 8). After 7 days, we assessed local sensory response, tissue oxygen consumption, oxygen radicals, and antioxidant levels. In vitro mitochondrial function was measured after stimulation of isolated mitochondria of skeletal muscle cells with increasing doses of tert-BuOOH. tert-BuOOH infusion resulted in an increased skin temperature (p = 0.04), impaired function, and a significantly increased pain sensation (p = 0.03). Venous oxygen saturation levels (p = 0.01) and the antioxidant ceruloplasmin (p = 0.04) were increased. tert-BuOOH inhibited mitochondrial function in vitro. Induction of free radical formation in the rat hind limb results in an exacerbated sensory response and is associated with impaired oxygen extraction, which likely results from mitochondrial dysfunction caused by free radicals.

Anti-NGF treatment reduces bone resorption in periodontitis

Periodontitis is characterized by periodontal tissue destruction, including the alveolar bone. One of its critical components is the release of pro-inflammatory neuropeptides from sensory nerve endings innervating the periodontium. Since nerve growth factor (NGF) has been reported to up-regulate neuropeptides in sensory neurons, we hypothesized that it would be increased in ligature-induced periodontitis in rats, and that systemic NGF neutralization would reduce the periodontitis-associated alveolar bone resorption. Real-time PCR analysis disclosed a statistically significant time-dependent up-regulation of NGF mRNA in gingiva during 2 weeks of periodontitis. Interestingly, NGF up-regulation was also detected in the contralateral gingiva. In addition, immunohistochemistry of trigeminal ganglion neurons innervating the gingivomucosa demonstrated increased expression of TrkA receptor for NGF. Systemic anti-NGF treatment during periodontitis significantly reduced interleukin-1beta expression in gingiva and bilateral alveolar bone resorption. This suggests that NGF promotes periodontal inflammation and implicates a possible use of anti-NGF treatment in periodontitis.

Nitric oxide synthase modulates CFA-induced thermal hyperalgesia through cytokine regulation in mice

Background

Although it has been largely demonstrated that nitric oxide synthase (NOS), a key enzyme for nitric oxide (NO) production, modulates inflammatory pain, the molecular mechanisms underlying these effects remain to be clarified. Here we asked whether cytokines, which have well-described roles in inflammatory pain, are downstream targets of NO in inflammatory pain and which of the isoforms of NOS are involved in this process.

Results

Intraperitoneal (i.p.) pretreatment with 7-nitroindazole sodium salt (7-NINA, a selective neuronal NOS inhibitor), aminoguanidine hydrochloride (AG, a selective inducible NOS inhibitor), L-N(G)-nitroarginine methyl ester (L-NAME, a non-selective NOS inhibitor), but not L-N(5)-(1-iminoethyl)-ornithine (L-NIO, a selective endothelial NOS inhibitor), significantly attenuated thermal hyperalgesia induced by intraplantar (i.pl.) injection of complete Freund's adjuvant (CFA). Real-time reverse transcription-polymerase chain reaction (RT-PCR) revealed a significant increase of nNOS, iNOS, and eNOS gene expression, as well as tumor necrosis factor-alpha (TNF), interleukin-1 beta (IL-1β), and interleukin-10 (IL-10) gene expression in plantar skin, following CFA. Pretreatment with the NOS inhibitors prevented the CFA-induced increase of the pro-inflammatory cytokines TNF and IL-1β. The increase of the anti-inflammatory cytokine IL-10 was augmented in mice pretreated with 7-NINA or L-NAME, but reduced in mice receiving AG or L-NIO. NNOS-, iNOS- or eNOS-knockout (KO) mice had lower gene expression of TNF, IL-1β, and IL-10 following CFA, overall corroborating the inhibitor data.

Conclusion

These findings lead us to propose that inhibition of NOS modulates inflammatory thermal hyperalgesia by regulating cytokine expression.

Prenatal endotoxin exposure alters behavioural pain responses to lipopolysaccharide in adult offspring

Evidence suggests that exposure to bacterial endotoxin in early life can alter the production of pro-inflammatory cytokines in later life. This phenomenon may have significant consequences for pain and pain related behaviours as pro-inflammatory cytokines heighten pain sensitivity. This association has yet to be examined. As such, the aim of the present study was to characterize pain behaviours in adult rat offspring following prenatal endotoxin (PE) exposure. Pregnant F344 rats received endotoxin (200microg/kg, s.c.) or saline on gestational days 16, 18 and 20. Pain thresholds were assessed in the adult PE offspring (n=23) and control offspring (n=24) prior to and 4h following administration of lipopolysaccharide (LPS; 100microg/kg, s.c.). Three assays of pain were employed - the hot plate, tail immersion and von Frey tests. Results demonstrated sex-specific effects of prenatal endotoxin on the offspring, with PE males displaying unaltered pain thresholds on the von Frey test post-LPS administration (p<0.01), while male control offspring (n=24) displayed the expected hyperalgesia. Male PE offspring also displayed increased pain thresholds on the tail immersion test (p<0.01), while no change in pain sensitivity was observed in control males following LPS exposure. No difference in response was observed between the female PE and control offspring on the von Frey test, however PE female offspring displayed increased thresholds on the tail immersion test compared to baseline - an effect not observed in the control female offspring. Pain sensitivity on the hot plate test was unaffected by prenatal exposure to endotoxin. These data suggest that prenatal exposure to products associated with bacterial infection have the capacity to alter pain responses, which are evident in the adult offspring.

OA clinical trials: current targets and trials for OA. Choosing molecular targets: what have we learned and where we are headed?

OBJECTIVE

The purpose of this article is to review the current status of drug development as it relates to both molecular targets and clinical trials for osteoarthritis (OA).

METHODS

A review of the literature in the context of currently what is known of the pathophysiology of OA and the learnings from past clinical trials is provided. Also discussed is the challenge of demonstrating efficacy and clinical benefit for pharmacologic interventions for OA in the context of current regulatory guidance documents for therapies for the treatment of OA.

RESULTS

There is a large unmet medical need for pharmacologic therapeutic interventions that modify the progression of OA and treat the symptoms associated with OA. The development of Disease Modifying OA Drugs (DMOADs) should take into account the current status of therapeutic interventions, as well as the various tissues that constitute the joint and contribute to joint mechanics, and the symptoms associated with structural changes. There is much to be learned about the pathophysiology of the joint that is currently poorly understood particularly as it relates to tissues other than hyaline articular cartilage. Improving our understanding that these tissues play in OA pathophysiology will likely yield treatment breakthroughs. Recently, tremendous progress has been made in the understanding of pain pathways with an emerging diversity of pain mechanisms and biology suggesting heterogeneity in pain etiology in OA. A multitude of new targets have been identified at the level of neuronal transduction/excitability, conduction, sensitization and transmission with multiple emerging compounds in development.

CONCLUSIONS

The development of symptom modifying OA drug is exploding with a plethora of pain pathways being pursued and multiple candidates in advanced stages of clinical development. Structure modification in OA remains complex with significant development challenges.

The NALP1 inflammasome controls cytokine production and nociception in a rat fracture model of complex regional pain syndrome

Tibia fracture followed by limb immobilization in rats evokes nociceptive and vascular changes resembling complex regional pain syndrome type I (CRPS I). Previously we observed that substance P (SP) and interleukin-1beta (IL-1beta) signaling contribute to chronic regional nociceptive sensitization in this model. It is known that inflammasome multi-protein complexes containing caspase-1 and NALP1 are involved in the activation of the IL-1beta family of pro-nociceptive cytokines expressed in skin and other tissues. Therefore, we hypothesized that SP activated inflammasomes might contribute to mechanical allodynia after fracture. Using this model we observed that: (1) inflammasome components and products NALP1, caspase-1, IL-1beta and IL-18 were present in low levels in normal skin, but expression of all these was strongly up-regulated after fracture, (2) NALP1, caspase-1 and IL-1beta were co-expressed in keratinocytes, and the number of NALP1, caspase-1, and IL-1beta positive cells dramatically increased at 4 weeks post-fracture, (3) LY303870, an NK1 receptor antagonist, effectively blocked fracture-induced up-regulation of activated inflammasome components and cytokines, (4) IL-1beta and IL-18 intraplantar injection induced mechanical allodynia in normal rats, and (5) both a selective caspase-1 inhibitor and an IL-1 receptor antagonist attenuated fracture-induced hindpaw mechanical allodynia. Collectively, these data suggest that NALP1 containing inflammasomes activated by NK1 receptors are expressed in keratinocytes and contribute to post-traumatic regional nociceptive sensitization. These findings highlight the possible importance of neuro-cutaneous signaling and innate immunity mechanisms in the development of CRPS.

Nerve growth factor as a signaling molecule for nerve cells and also for the neuroendocrine-immune systems

Nerve growth factor (NGF) is a signaling molecule, originally discovered for its role on differentiation and survival of peripheral sensory and sympathetic neurons. It has also been associated with functional activities of cells of the immune and endocrine systems. NGF biological activity is mediated by two classes of receptors: (i) p75 neurotrophin receptor (p75(NTR)), a 75 kDa glycoprotein, belonging to a superfamily of cytokine receptors including TNF receptors, and (ii) TrkA, a transmembrane tyrosine kinase of 140 kDa. Both TrkA and p75(NTR) are known to play a marked action in neurodegenerative disorders, immune-related deficits, and neuroendocrine (including adipoendocrine) mechanisms. This review focuses on these cellular events and presents a working model which attempts to explain the close interrelationships of the neuro-endocrine-immune triad via a modulatory action of NGF.

The P2X7 purinergic receptor: from physiology to neurological disorders

Purine nucleotides are well established as extracellular signaling molecules. P2X receptors are ATP-gated cation channels that mediate fast excitatory transmission in diverse regions of the brain and spinal cord. Several P2X receptor subtypes, including P2X(7), have the unusual property of changing their ion selectivity during prolonged exposure to ATP, which results in progressive dilation of the channel pore and the development of permeability to molecules as large as 900 Da. The P2X(7) receptor was originally described in cells of hematopoietic origin, including macrophages, microglia, and certain lymphocytes, and mediates the influx of Ca(2+) and Na(+) ions, as well as the release of proinflammatory cytokines. P2X(7) receptors may affect neuronal cell death through their ability to regulate the processing and release of interleukin-1beta, a key mediator in neurodegeneration, chronic inflammation, and chronic pain. Activation of P2X(7) receptors provides an inflammatory stimulus, and P2X(7) receptor-deficient mice have substantially attenuated inflammatory responses, including models of neuropathic and chronic inflammatory pain. Moreover, P2X(7) receptor activity, by regulating the release of proinflammatory cytokines, may be involved in the pathophysiology of depression. The P2X(7) receptor may thus represent a critical communication link between the nervous and immune systems, while providing a target for therapeutic exploitation. This review discusses the current biology and cellular signaling pathways of P2X(7) receptor function, as well as insights into the role for this receptor in neurological/psychiatric diseases, outstanding questions, and the therapeutic potential of P2X(7) receptor antagonism.

Molecular Roles of Cdk5 in Pain Signaling

Injury and inflammation trigger activation of several critical cellular pathways in nociceptive signaling in the peripheral nervous system, but their precise molecular mechanisms have not been clearly defined. Cyclin-dependent kinase 5 (Cdk5), a serine/threonine kinase, is mainly expressed in the post-mitotic neurons, and has many important roles in the development, functions and pathophysiology of diseases of the nervous system. Although many functional roles of Cdk5 have been identified in neurons, its precise role in pain signaling has not been well determined. Experimental inflammation in the hind paws of mice resulted in increased mRNA and protein levels of Cdk5 and its activator p35, as well as the Cdk5 activity in nociceptive neurons (Pareek et al., 2006). Furthermore, we also identified that Cdk5 phosphorylates transient receptor potential vanilloid 1 (TRPV1), a key receptor that modulates agonist-induced calcium influx in the neurons (Pareek et al., 2007). We subsequently demonstrated that inflammation triggers increase in Cdk5 activity through activation of early growth response 1 (Egr-1) and p35 expression by tumor necrosis factor alpha (TNF-α) (Utreras et al., 2009). These findings suggest that Cdk5 plays an important role in pain signaling and therefore Cdk5 and its activators are potentially important drug targets for development of novel analgesics to treat neuropathic pain.

Sensory pulpal nerve fibres and trigeminal ganglion neurons express IL-1RI: a potential mechanism for development of inflammatory hyperalgesia

AIM

To localize interleukin-1 receptor type I (IL-1RI) in rat dental pulp and trigeminal ganglion (TG) and to test the hypothesis that pulpal inflammation increases neuronal expression of IL-1RI.

METHODOLOGY

Female Wistar rats were subjected to unilateral pulp exposures in the maxillary and mandibular first molars, whereas the contralateral jaws served as untreated controls. Seven days later the animals were transcardiacally perfused and the jaws and the TGs were removed and prepared for immunohistochemistry. Immunoreactivity for IL-1RI was examined alone (DAB) and together with calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), CD31 or CD34 by multiple-labelling immunofluorescence. Quantification of IL-1RI-immunoreactive (-IR) cells in the maxillary and mandibular division of the ganglion was performed in parasagittal immunoreacted sections of the right and left TGs. Data were analysed with Mann-Whitney Rank Sum test (P < 0.05).

RESULTS

Interleukin-1 receptor type I was found on sensory (CGRP-IR) and sympathetic (NPY-IR) nerve fibres and on blood vessels (CD31- and CD34-IR) in the dental pulp. It was also localized on sensory neurons and axons in the TG. Pulpal inflammation significantly increased the expression of IL-1RI in the TG (P < 0.001).

CONCLUSIONS

The localization of IL-1RI on sensory nerve fibres and its up-regulation in TG neurons during pulpal inflammation may imply a direct effect of IL-1 in pulpal nociception. The presence of IL-1RI on sympathetic nerve fibres and on blood vessels may indicate a vasoactive role of the same cytokine in the pulp.

P2X(7) Receptors in Neurological and Cardiovascular Disorders

P2X receptors are ATP-gated cation channels that mediate fast excitatory transmission in diverse regions of the brain and spinal cord. Several P2X receptor subtypes, including P2X(7), have the unusual property of changing their ion selectivity during prolonged exposure to ATP, which results in a channel pore permeable to molecules as large as 900 daltons. The P2X(7) receptor was originally described in cells of hematopoietic origin, and mediates the influx of Ca(2+) and Na(+) and Ca(2+) and Na(+) ions as well as the release of proinflammatory cytokines. P2X(7) receptors may affect neuronal cell death through their ability to regulate the processing and release of interleukin-1beta, a key mediator in neurodegeneration, chronic inflammation, and chronic pain. Activation of P2X(7), a key mediator in neurodegeneration, chronic inflammation, and chronic pain. Activation of P2X(7) receptors provides an inflammatory stimulus, and P2X(7) receptor-deficient mice have substantially attenuated inflammatory responses, including models of neuropathic and chronic inflammatory pain. Moreover, P2X(7) receptor activity, by regulating the release of proinflammatory cytokines, may be involved in the pathophysiology of depression. Apoptotic cell death occurs in a number of vascular diseases, including atherosclerosis, restenosis, and hypertension, and may be linked to the release of ATP from endothelial cells, P2X(7) receptor activation, proinflammatory cytokine production, and endothelial cell apoptosis. In this context, the P2X(7) receptor may be viewed as a gateway of communication between the nervous, immune, and cardiovascular systems.

Presence of NGF and its receptor TrkA in degenerative lumbar facet joint specimens

In a preliminary study, the recurrent presence of nervous terminations was demonstrated with optical microscopy in several slides of degenerative lumbar facet joints and surrounding soft tissues. The purpose of this study was to prove the presence of NGF (nerve growth factor) and its receptor TrkA (tyrosine kinase receptor) with immunofluorescence. The peri/articular tissues were harvested from the lumbar facet joints of ten patients surgically treated for degenerative diseases. There were seven females (one bilateral) and two males whose mean age at surgery was 72 years (range, 67-80 years). The affected levels were L3-L4 in two cases and L4-L5 in seven cases (one bilateral). All specimens were fixed in formalin, dehydrated and enclosed in paraffin. From each specimen, four slides were obtained. Two slides were employed for the search of NGF: one was treated with specific antibodies and marked with FITC (fluorescein isothiocyanate conjugated), and the second slide was for control purposes. It was exposed to FITC, but without prior exposure to the specific antibody. The same procedure was repeated to obtain on two more slides, to repeat the search for Trka with specific antibodies. All the slides were finally studied on a fluoromicroscope. The analysis of these specimens revealed the presence of the neurotrophin (NGF) and its own receptor (TrkA) in all cases: the immunohistochemical reaction between the specimens and the specific antibodies marked with FITC was seen under fluoromicroscopy, but in none of the control cases treated with FITC only. NGF is released by mastocytes, fibroblasts and other cell types involved in the inflammatory processes. The level of peripheral NGF is increased in inflammatory processes, while the administration of exogenous NGF has a hyperalgesic effect on rats and produces muscular pain in humans. Furthermore, NGF produces hypersensitization to heat stimulation in humans and mammals in general. There is considerable evidence showing that the system constituted by the NGF and its high-affinity receptor TrkA plays a fundamental role in the molecular processes underlying the main forms of "persistent" pain. This indicates a possible therapeutic area for the antibodies that could block the NGF/TrkA system, in order to modulate the frequency and the duration of the action potential of nociceptive neurons during chronic inflammation. This study demonstrated the presence of NGF and TrkA in specimens collected from degenerative facet joints, suggesting that specific molecules could be used in order to modulate chronic pain in patients with degenerative lumbar spine.

The role of enhanced cutaneous IL-1beta signaling in a rat tibia fracture model of complex regional pain syndrome

Tibia fracture in rats initiates a syndrome resembling the complex regional pain syndrome type I. Accumulating evidence indicates that IL-1beta is involved in the modulation of nociceptive information and it acts as an intermediate inflammatory mediator via up-regulation of NGF. We hypothesized that IL-1beta signaling might mediate the development of the CRPS-like changes after tibial fracture, either directly or by stimulating NGF expression. Rats underwent distal tibia fracture and casting for 4 weeks and were chronically treated with an IL-1 receptor antagonist (IL-1ra). Nociceptive testing and assessment of edema and hindpaw warmth were performed at baseline and after cast removal. Bone microarchitecture was evaluated by micro-computed tomography. Confocal immunofluorescence and in situ hybridization techniques were used to evaluate changes in the cutaneous expression of IL-1beta at 4 weeks post-fracture. The nociceptive and vascular effects of intraplantar IL-1beta injections were evaluated in intact rats at different time points after injection. We found that: (1) IL-1ra reduced fracture-induced nociceptive sensitization, but did not decrease hindpaw edema or warmth, (2) fracture chronically up-regulated IL-1beta mRNA and protein expression in hindpaw skin keratinocytes, (3) IL-1beta intraplantar injection induced mechanical allodynia in a dose-dependent manner and stimulated keratinocyte NGF expression in the hindpaw skin, and (4) intraplantar injection of NGF-induced nociceptive sensitization. Collectively, these results indicate that cutaneous IL-1beta signaling can contribute to chronic regional nociceptive sensitization after fracture, possibly by stimulating NGF over-expression in keratinocytes. Our data also highlight the importance of the keratinocyte as the primary source of post-traumatic IL-1beta over-expression.

The antihyperalgesic activity of a selective P2X7 receptor antagonist, A-839977, is lost in IL-1alphabeta knockout mice

The pro-inflammatory cytokine interleukin-1beta (IL-1beta) has been implicated in both inflammatory processes and nociceptive neurotransmission. Activation of P2X7 receptors is the mechanism by which ATP stimulates the rapid maturation and release of IL-1beta from macrophages and microglial cells. Recently, selective P2X7 receptor antagonists have been shown to reduce inflammatory and neuropathic pain in animal models. However, the mechanisms underlying these analgesic effects are unknown. The present studies characterize the pharmacology and antinociceptive effects of a structurally novel P2X7 antagonist. A-839977 potently (IC50=20-150 nM) blocked BzATP-evoked calcium influx at recombinant human, rat and mouse P2X7 receptors. A-839977 also potently blocked agonist-evoked YO-PRO uptake and IL-1beta release from differentiated human THP-1 cells. Systemic administration of A-839977 dose-dependently reduced thermal hyperalgesia produced by intraplantar administration of complete Freund's adjuvant (CFA) (ED50=100 micromol/kg, i.p.) in rats. A-839977 also produced robust antihyperalgesia in the CFA model of inflammatory pain in wild-type mice (ED50=40 micromol/kg, i.p.), but the antihyperalgesic effects of A-839977 were completely absent in IL-1alphabeta knockout mice. These data demonstrate that selective blockade of P2X7 receptors in vivo produces significant antinociception in animal models of inflammatory pain and suggest that the antihyperalgesic effects of P2X7 receptor blockade in an inflammatory pain model in mice are mediated by blocking the release of IL-1beta.

Hyperalgesia induced by oral stavudine administration to rats does not depend on spinal neuronal cell death, or on spinal or systemic inflammatory cytokine secretion, or metabolic dysregulation

To investigate possible mechanisms of the hyperalgesia induced by the nucleoside reverse transcriptase inhibitor (NRTI) stavudine in rats, we examined neuronal death and inflammatory cytokine secretion in the spinal cord, and cytokine and lactate secretion in the plasma. Stavudine (50 mg kg(-1)) or placebo was administered orally to Sprague-Dawley rats once daily for three or six weeks. In one group, rats' responses to a blunt noxious mechanical stimulus applied to their tails were recorded before and at the end of the period of stavudine or placebo administration. Spinal cords excised from these rats after three and six weeks of stavudine or placebo administration were examined for neuronal necrosis and apoptosis. In a second group of rats, plasma and spinal cord samples collected after three and six weeks of placebo or stavudine administration were examined for changes in CINC-1, IL-6, adiponectin (plasma only) and lactate (plasma only) concentration. Daily stavudine administration induced mechanical hyperalgesia within three weeks, which was sustained until week six, but the hyperalgesia was not associated with neuronal apoptosis or necrosis, or elevated IL-6 concentrations in the spinal cord. The spinal cord concentration of CINC-1 increased, but only after six weeks of stavudine administration, when the hyperalgesia had been established for over three weeks. Stavudine administration did not affect the plasma concentration of IL-6, CINC-1, adiponectin or lactate. Thus, neither peripheral nor central inflammatory cytokine secretion, or neuronal death, or metabolic dysregulation contributed to the development of hyperalgesia in our model of stavudine-induced hyperalgesia in rats.

The role of IL-6 and IL-1beta in painful perineural inflammatory neuritis

Inflammation along a nerve trunk (perineural inflammation), without detectable axonal damage, has been shown to induce transient pain in the organ supplied by the nerve. The aims of the present study were to study the role IL-6 and IL-1beta, in pain induced by perineural inflammation.

METHODS

IL-6 and IL-1beta secretion from rat's sciatic nerves, L-5 Dorsal Root Ganglia (DRG), and the hind paw skin, 3 and 8 days following exposure of the nerve to Complete Freund's Adjuvant (CFA), were measured using ELISA method. Hind paw tactile-allodynia, mechano-hyperalgesia, heat-allodynia and electrical detection thresholds were tested up to 8 days following the application of CFA, IL-6 or IL-1beta adjacent to the sciatic nerve trunk. Employing electrophysiological recording, saphenous nerve spontaneous activity, nerve trunk mechano-sensitivity and paw tactile detection threshold (determined by recording action potential induced by the lowest mechanical stimulus) were assessed 3 and 8 days following exposure of the nerve trunk to CFA, IL-6, or IL-1beta.

RESULTS

IL-6 and IL-1beta secretion from the nerve was significantly elevated on the 3rd day post-operation (DPO). On the 8th DPO, IL-6 levels returned to baseline while IL-1beta levels remained significantly elevated. The DRG cytokine's level was increased on the 3rd and 8th DPOs, contralateral cytokine's level was increased on the 3rd DPO. The skin IL-6 level was increased bilaterally on the 3rd DPO and returned to baseline on the 8th DPO. IL-1beta levels increased in the affected side on the 3rd and bilaterally on the 8th DPO. Direct application of IL-6 or CFA on the sciatic nerve induced significant hind paw tactile-allodynia from the 1st to 5th DPOs, reduced electrical detection threshold from the 1st to 3rd DPOs, mechano-hyperalgesia from 3rd to 5th DPOs and heat-allodynia on the 3rd DPO. Direct application of IL-1beta induced paw tactile and heat-allodynia on the 7-8th DPOs and mechano-hyperalgesia on the 5-8th DPOs. Perineural inflammation significantly increased spontaneous activity myelinated fibres 3 and 8 days following the application. Direct application of IL-6 induced elevation of spontaneous activity on the 3rd while IL-1beta on the 8th DPO. Nerve mechano-sensitivity was significantly increased on the 3rd day following exposure to CFA and IL-6 and on the 8th following CFA application. The rat's paw lowest mechanical force necessary for induction of action potential, was significantly reduced 3 days following CFA application.

CONCLUSION

IL-6 and IL-1beta play an important role in pain induced by perineural inflammation. IL-6 activity is more prominent immediately following application (2-5th DPOs), while IL-1beta, activity is more significant in a later stage (5-8th DPOs).

Up-regulation of TNF-alpha in neurons of dorsal root ganglia and spinal cord during coronary artery occlusion in rats

Knowledge about the physiologic and pathophysiologic roles of tumor necrosis factor-alpha (TNF-alpha) in acute myocardial ischemia/infarction is still very limited. Evidence implies that TNF-alpha is involved in neural activity including nociception in peripheral and central nervous system. Current study was designed to examine the association of change in TNF-alpha and its mRNA in upper thoracic dorsal root ganglia and spinal cord (T1-T5) during acute myocardial ischemia/infarction induced by coronary artery occlusion (CAO) in rats. The experiment was performed using immunohistochemistry, enzyme immunoassay, in situ hybridization and real time reverse transcription-polymerase chain reaction techniques. At 0.5h, 1h, 3h and 6h of acute myocardial ischemia/infarction, TNF-alpha was mainly up-regulated in a sub-population of small and medium neurons and satellite cells in the dorsal root ganglia (DRG) and spinal neurons, mainly in laminae I, II and V, VI of the spinal dorsal horn of upper thoracic segments. The up-regulation of TNF-alpha mRNA was observed at 30min of CAO, which was statistically significant, compared with the control and the sham surgery groups (P<0.01). The TNF-alpha mRNA was located in the satellite cells and afferent neurons of the DRG and spinal neurons, located mainly in laminae II-VI. The findings indicate an association of up-regulation of TNF-alpha in DRG and spinal cord with acute myocardial ischemia/infarction, suggesting that TNF-alpha may be associated with the nociception initiated by acute myocardial ischemia/infarction, while the pathophysiological role needs to be studied.

Nociceptors are interleukin-1beta sensors

A cardinal feature of inflammation is heightened pain sensitivity at the site of the inflamed tissue. This results from the local release by immune and injured cells of nociceptor sensitizers, including prostaglandin E(2), bradykinin, and nerve growth factor, that reduce the threshold and increase the excitability of the peripheral terminals of nociceptors so that they now respond to innocuous stimuli: the phenomenon of peripheral sensitization. We show here that the proinflammatory cytokine interleukin-1beta (IL-1beta), in addition to producing inflammation and inducing synthesis of several nociceptor sensitizers, also rapidly and directly activates nociceptors to generate action potentials and induce pain hypersensitivity. IL-1beta acts in a p38 mitogen-activated protein kinase (p38 MAP kinase)-dependent manner, to increase the excitability of nociceptors by relieving resting slow inactivation of tetrodotoxin-resistant voltage-gated sodium channels and also enhances persistent TTX-resistant current near threshold. By acting as an IL-1beta sensor, nociceptors can directly signal the presence of ongoing tissue inflammation.

The roles of nerve growth factor and cholecystokinin in the enhancement of morphine analgesia in a rodent model of central nervous system inflammation

Animal models of inflammatory pain are characterized by the release of inflammatory mediators such as cytokines and neurotrophic factors, and enhanced analgesic sensitivity to opioids. In this study, we examine the mechanisms underlying this effect, in particular the roles of cholecystokinin (CCK) and nerve growth factor (NGF), in an animal model of central nervous system (CNS) inflammation induced by spinal administration of lipopolysaccharide (LPS). Although spinal administration of LY-225910 (25 ng), a CCK-B antagonist, enhanced morphine analgesia in naïve rats, it was unable to do so in LPS-treated animals. Conversely, spinal CCK-8S administration (1 ng) decreased morphine analgesia in LPS-treated rats, but not in naïve animals. Further, spinal anti-NGF (3 microg) was able to reduce morphine analgesia in LPS-treated rats, but not in naïve animals, an effect that was reversed by spinal administration of LY-225910. While CCK-8S concentration was increased in spinal cord extracts of LPS animals as compared to controls, morphine-induced spinal CCK release in the extracellular space, as measured by in-vivo spinal cord microdialysis was inhibited in LPS animals as compared to controls, and this was reversed by anti-NGF pretreatment. Finally, chronic spinal administration of beta-NGF (7 microg/day) for 7 days enhanced spinal morphine analgesia, possibly by mimicking a CNS inflammatory state. We suggest that in intrathecally LPS-treated rats, spinal CCK release is altered resulting in enhanced morphine analgesia, and that this mechanism may be regulated to an important extent by NGF.

Central nervous action of interleukin-1 mediates activation of limbic structures and behavioural depression in response to peripheral administration of bacterial lipopolysaccharide

Although receptors for the pro-inflammatory cytokine interleukin-1 have long been known to be expressed in the brain, their role in fever and behavioural depression observed during the acute phase response (APR) to tissue infection remains unclear. This may in part be due to the fact that interleukin-1 in the brain is bioactive only several hours after peripheral administration of bacterial lipopolysaccharide (LPS). To study the role of cerebral interleukin-1 action in temperature and behavioural changes, and activation of brain structures during the APR, interleukin-1 receptor antagonist (IL-1ra; 100 microg) was infused into the lateral brain ventricle 4 h after intraperitoneal (i.p.) LPS injection (250 microg/kg) in rats. I.p. LPS administration induced interleukin-1beta (IL-1beta) production in systemic circulation as well as in brain circumventricular organs and the choroid plexus. Intracerebroventricular (i.c.v.) infusion of IL-1ra 4 h after i.p. LPS injection attenuated the reduction in social interaction, a cardinal sign of behavioural depression during sickness, and c-Fos expression in the amygdala and bed nucleus of the stria terminalis. However, LPS-induced fever, rises in plasma corticosterone, body weight loss and c-Fos expression in the hypothalamus and caudal brainstem were not altered by i.c.v. infusion of IL-1ra. These findings, together with our previous observations showing that i.c.v. infused IL-1ra diffuses throughout perivascular spaces, where macrophages express interleukin-1 receptors, can be interpreted to suggest that circulating or locally produced brain IL-1beta acts on these cells to bring about behavioural depression and activation of limbic structures during the APR after peripheral LPS administration.

Lectin extracted from Canavalia grandiflora seeds presents potential anti-inflammatory and analgesic effects

Neutrophil migration is responsible for tissue damage observed in inflammatory diseases and is also implicated in inflammatory nociception. The use of lectins has been demonstrated to be effective in different activities including anti-inflammatory, antimicrobial, and in cancer therapy. In this study, we addressed the potential use of a lectin from Canavalia grandiflora seeds (ConGF) to control neutrophil migration and inflammatory hypernociception. Pretreatment of the animals intravenously (15 min before) with ConGF inhibited neutrophil migration to the peritoneal cavity in a dose-dependent fashion confirmed by an inhibition of rolling and adhesion of leukocytes by intravital microscopy. Another set of experiments showed that pretreatment of the animals with ConGF inhibited the mechanical hypernociception in mice induced by the i.pl. injection of carrageenan or formalin. This anti-nociceptive effect correlated with an effective blockade of neutrophil influx, as assessed by the hind paw tissue myeloperoxidase levels. Furthermore, ConGF had important inhibitory effects on the mouse carrageenan-induced paw edema. In addition, animals treated with ConGF showed inhibition of cytokines release. In conclusion, we demonstrated that the lectin ConGF inhibits neutrophil migration and mechanical inflammatory hypernociception.

Interleukin-1 (IL-1): a central regulator of stress responses

Ample evidence demonstrates that the pro-inflammatory cytokine interleukin-1 (IL-1), produced following exposure to immunological and psychological challenges, plays an important role in the neuroendocrine and behavioral stress responses. Specifically, production of brain IL-1 is an important link in stress-induced activation of the hypothalamus-pituitary-adrenal axis and secretion of glucocorticoids, which mediate the effects of stress on memory functioning and neural plasticity, exerting beneficial effects at low levels and detrimental effects at high levels. Furthermore, IL-1 signaling and the resultant glucocorticoid secretion mediate the development of depressive symptoms associated with exposure to acute and chronic stressors, at least partly via suppression of hippocampal neurogenesis. These findings indicate that whereas under some physiological conditions low levels of IL-1 promote the adaptive stress responses necessary for efficient coping, under severe and chronic stress conditions blockade of IL-1 signaling can be used as a preventive and therapeutic procedure for alleviating stress-associated neuropathology and psychopathology.

How close are we to having structure-modifying drugs available?

This review describes the potential of disease-modifying osteoarthritis drugs (DMOADs), distinguishing between preventing, retarding, stopping, and reversing disease and what might be clinically meaningful. The authors also describe whether there is any evidence to suggest that one can modify disease, and whether the current tissue that is predominantly focused on, namely, cartilage, is an appropriate target. The methodologic approaches and other obstacles to demonstrating efficacy of these agents in clinical trials are considered. This discussion is a narrative review in a field that is rapidly evolving. It is hoped the reader appreciates the complexity of the field and the likely road ahead to DMOAD development.

Role of interleukin-1beta during pain and inflammation

The cytokine cascade in pain and inflammatory processes is a tremendously complex system, involving glial, immune, and neuronal cell interactions. IL-1beta is a pro-inflammatory cytokine that has been implicated in pain, inflammation and autoimmune conditions. This review will focus on studies that shed light on the critical role of IL-1beta in various pain states, including the role of the intracellular complex, the inflammasome, which regulates IL-1beta production. Evidence will be presented demonstrating the importance of IL-1beta in both the induction of pain and in the maintenance of pain in chronic states, such as after nerve injury. Additionally, the involvement of IL-1beta as a key mediator in the interaction between glia and neurons in pain states will be discussed. Taken together, the evidence presented in the current review showing the importance of IL-1beta in animal and human pain states, suggests that blockade of IL-1beta be considered as a therapeutic opportunity.

Peripheral mechanisms underlying the essential role of P2X3,2/3 receptors in the development of inflammatory hyperalgesia

Activation of P2X3,2/3 receptors by endogenous ATP contributes to the development of inflammatory hyperalgesia. Given the clinical importance of mechanical hyperalgesia in inflammatory states, we hypothesized that the activation of P2X3,2/3 receptors by endogenous ATP contributes to carrageenan-induced mechanical hyperalgesia and that this contribution is mediated by an indirect and/or a direct sensitization of the primary afferent nociceptors. Co-administration of the selective P2X3,2/3 receptors antagonist A-317491, or the non-selective P2X3 receptor antagonist, TNP-ATP, with carrageenan blocked the mechanical hyperalgesia induced by carrageenan, and significantly reduced the increased concentration of tumor necrosis factor alpha (TNF-alpha) and chemokine-induced chemoattractant-1 (CINC-1) but not of interleukin-1 beta (IL-1 beta) induced by carrageenan. Co-administration of the selective P2X3,2/3 receptors antagonist A-317491 with carrageenan did not affect the neutrophil migration induced by carrageenan. Intrathecal administration of oligonucleotides antisense against P2X3 receptors for seven days significantly reduced the expression of P2X3 receptors in the saphenous nerve and significantly reduced the mechanical hyperalgesia induced by carrageenan. We concluded that the activation of P2X3,2/3 receptors by endogenous ATP is essential to the development of the mechanical hyperalgesia induced by carrageenan. Furthermore, we showed that this essential role of P2X3,2/3 receptors in the development of carrageenan-induced mechanical hyperalgesia is mediated by an indirect sensitization of the primary afferent nociceptors dependent on the previous release of TNF-alpha and by a direct sensitization of the primary afferent nociceptors.

Tumor necrosis factor-alpha regulates cyclin-dependent kinase 5 activity during pain signaling through transcriptional activation of p35

Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine/threonine kinase. We have previously reported that Cdk5 participates in the regulation of nociceptive signaling, and the expression of Cdk5 and its activator, p35, are up-regulated in nociceptive neurons during peripheral inflammation. The aim of our current study was to identify the proinflammatory molecules that regulate Cdk5/p35 activity in response to inflammation. We constructed a vector that contains the mouse p35 promoter driving luciferase expression. We transiently transfected this vector in PC12 cells to test the effect of several cytokines on p35 transcriptional activity and Cdk5 activity. Our results indicate that tumor necrosis factor-alpha (TNF-alpha) activates p35 promoter activity in a dose- and time-dependent manner and concomitantly up-regulates Cdk5 activity. Because TNF-alpha is known to activate ERK1/2, p38 MAPK, JNK, and NF-kappaB signaling pathways, we examined their involvement in the activation of p35 promoter activity. MEK inhibitor, which inhibits ERK activation, decreased p35 promoter activity, whereas the inhibitors of p38 MAPK, JNK, and NF-kappaB increased p35 promoter activity, indicating that these pathways regulate p35 expression differently. The mRNA and protein levels of Egr-1, a transcription factor, were increased by TNF-alpha treatment, and this increase was dependent on ERK signaling. In a mouse model of inflammation-induced pain in which carrageenan injection into the hind paw causes hypersensitivity to heat stimuli, TNF-alpha mRNA was increased at the site of injection. These findings suggest that TNF-alpha-mediated regulation of Cdk5 activity plays an important role in inflammation-induced pain signaling.

Cerebral microdialysis of interleukin (IL)-1beta and IL-6: extraction efficiency and production in the acute phase after severe traumatic brain injury in rats

BACKGROUND

As a research tool, cerebral microdialysis might be a useful technique in monitoring the release of cytokines into the extracellular fluid (ECF) following traumatic brain injury (TBI). We established extraction efficiency of Interleukin(IL)-1ss and Interleukin(IL)-6 by an in vitro microdialysis-perfusion system, followed by in vivo determination of the temporal profile of extracellular fluid cytokines after severe TBI in rats.

MATERIALS AND METHODS

In vitro experiments using a polyether sulfon (PES) microdialysis probe especially developed for recovery of macromolecules such as cytokines, were carried out to establish the extraction efficiency of IL-1ss and IL-6 from artificial cerebrospinal fluid (CSF) with defined IL-1ss and IL-6 concentrations. In vivo experiments in which rats were subjected to TBI or sham and microdialysis samples were collected from the parietal lobe for measurement of cytokines.

FINDINGS

The extraction efficiency was maximal 6.05% (range, 5.97-6.13%) at 0.5 microl/min(-1) and decreased at higher flow rates. Both cytokines were detectable in the dialysates. Highest IL-1ss levels were found within 200 min, highest IL-6 concentrations were detected at later intervals (200-400 min). No differences were found between the TBI and control groups.

CONCLUSIONS

Cerebral microdialysis allows measurement of cytokine secretion in the ECF of brain tissue in rats.

How close are we to having structure-modifying drugs available?

This article describes what structure modification is, explains the distinctions among preventing, retarding, stopping, and reversing disease, and suggests approaches that might be clinically meaningful. It discusses whether any evidence suggests it is possible to modify disease and whether the current focus on cartilage is appropriate. It considers the methodologic approaches and the obstacles to demonstrating efficacy of these agents in clinical trials. The authors hope that at the end of this narrative review the reader will appreciate the complexities of this rapidly evolving field and of the development of disease-modifying drugs for osteoarthritis drugs.

Contribution of activated interleukin receptors in trigeminal ganglion neurons to hyperalgesia via satellite glial interleukin-1beta paracrine mechanism

The present study investigated whether under in vivo conditions, inflammation alters the excitability of nociceptive Adelta-trigeminal ganglion (TRG) neurons innervating the facial skin via a cytokine paracrine mechanism. We used extracellular electrophysiological recording with multibarrel-electrodes in this study, and complete Freund's adjuvant (CFA) was injected into the rat facial skin. The threshold for escape from mechanical stimulation applied to the whisker pad area in inflamed rats (2 days after CFA injection) was significantly lower than that in control rats. A total of 45 Adelta-nociceptive-TRG neurons responding to electrical stimulation of the whisker pad were recorded in pentobarbital-anesthetized rats. The number of Adelta-TRG neurons with spontaneous firings and their firing rate in inflamed rats were significantly larger than those in control rats. The firing rates of the Adelta-TRG neuronal spontaneous activity were current-dependently decreased by local iontophoretic application of an interleukin I receptor type I antagonist (IL-1ra) in inflamed rats, but not in controls, and current-dependently increased by iontophoretic application of interleukin 1beta (IL-1beta) in both control and inflamed rats. IL-1ra also inhibited Adelta-TRG neuron activity evoked by mechanical stimulation in the inflamed rats. The mechanical threshold of nociceptive-TRG neurons in inflamed rats was significantly lower than that in control rats, but was not significantly different between control and inflamed rats after application of an IL-1ra. These results suggested that inflammation modulates the excitability of nociceptive Adelta-TRG neurons innervating the facial skin via IL-1beta paracrine action within trigeminal ganglia. Such an IL-1beta release could be important in determining trigeminal inflammatory hyperalgesia.

Differences in innervation and innervated neurons between hip and inguinal skin

Pain originating from the hip may be referred to the groin and anterior thigh. We investigated sensory dorsal root ganglion neurons innervating the hip and the inguinal skin in rats using retrograde neurotransport and immunohistochemistry. A retrograde neurotracer Fluoro-Gold was injected into the left hip or inguinal skin of rats. Seven days later, we harvested bilateral dorsal root ganglions and counted the number of Fluoro-Gold-labeled neurons positive for calcitonin gene-related peptide, a marker of nerve growth factor-dependent neurons, or isolectin B4, a marker of glial cell line-derived neurotrophic factor-dependent neurons. In the hip group, Fluoro-Gold-labeled neurons were distributed throughout the left dorsal root ganglions from T13 to L5, primarily at L1, L2, L3, and L4, and the percentage of calcitonin gene-related peptide-positive neurons was higher than that of isolectin B4-binding neurons. In the inguinal skin group, Fluoro-Gold-labeled neurons were distributed throughout the left dorsal root ganglions from T13 to L3, primarily at L1, L2, and L3, and the percentage of isolectin B4-binding neurons was higher than that of calcitonin gene-related peptide-positive neurons. These data suggest the sensory innervation pattern and characteristics of the sensory nerve of the rat hip are different from those of inguinal skin.

Antinociceptive effect of amygdalin isolated from Prunus armeniaca on formalin-induced pain in rats

Amygdalin is a plant glucoside isolated from the stones of rosaceous fruits, such as apricots, peaches, almond, cherries, and plums. To investigate the pain-relieving activity of amygdalin, we induced pain in rats through intraplantar injection of formalin, and evaluated the antinociceptive effect of amygdalin at doses of 0.1, 0.5, 1.0, and 10.0 mg/kg-body weight by observing nociceptive behavior such as licking, biting and shaking, the number of Fos-immunoreactive neurons in the spinal cord, and the mRNA expression of inflammatory cytokines in the plantar skin. The intramuscular injection of amygdalin significantly reduced the formalin-induced tonic pain in both early (the initial 10 min after formalin injection) and late phases (10-30 min following the initial formalin injection). During the late phase, amygdalin did reduce the formalin-induced pain in a dose-dependent manner in a dose range less than 1 mg/kg. Molecular analysis targeting c-Fos and inflammatory cytokines such as tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1beta) also showed a significant effect of amygdalin, which matched the results of the behavioral pain analysis. These results suggest that amygdalin is effective at alleviating inflammatory pain and that it can be used as an analgesic with anti-nociceptive and anti-inflammatory activities.

Are there promising biologic therapies for osteoarthritis?

A large unmet need exists for desirable pharmacologic therapeutic interventions for osteoarthritis (OA). Developers of these interventions should be mindful of the current status of therapeutic interventions and focus on the mechanics of the joint and tissues of symptom origin. Much of the pathophysiology of the joint is still poorly understood, particularly as it relates to tissues other than hyaline articular cartilage. Improved knowledge of the role of these tissues (especially bone, fat, and synovium) in OA pathophysiology will likely yield treatment breakthroughs. This review discusses promising biologic therapies for the treatment of OA. Investigators are developing promising therapies, but we need to pay heed to the lessons learned thus far if new therapies are to be effective.

Inflammatory mediators in the frontal lobe of patients with mixed and vascular dementia

Vascular dementia (VaD) accounts for about 20% of all dementias, and vascular risk is a key factor in more than 40% of people with Alzheimer's disease (AD). Little is known about inflammatory processes in the brains of these individuals. We have examined inflammatory mediators (interleukin (IL)-1beta, IL-1alpha, IL-6 and tumour necrosis factor alpha) and chemokines (macrophage inflammatory protein 1, monocyte chemo-attractant protein (MCP)-1 and granulocyte macrophage colony-stimulating factor) in brain homogenates from grey and white matter of the frontal cortex (Brodmann area 9) from patients with VaD (n = 11), those with concurrent VaD and AD (mixed dementia; n = 8) and from age-matched controls (n = 13) using ELISA assays. We found a dramatic reduction of MCP-1 levels in the grey matter in VaD and mixed dementia in comparison to controls (55 and 66%, respectively). IL-6 decreases were also observed in the grey matter of VaD and mixed dementia (72 and 71%, respectively), with a more modest decrease (30%) in the white matter of patients with VaD or mixed dementia. In the first study to examine the status of inflammatory mediators in a brain region severely affected by white-matter lesions, our findings highlight - in contrast to previous reports in AD - that patients at the later stage of VaD or mixed dementia have a significantly attenuated neuro-inflammatory response.

Acute myocardial ischemia up-regulates nociceptin/orphanin FQ in dorsal root ganglion and spinal cord of rats

Nociceptin/orphanin FQ (N/OFQ) possesses modulatory effects on somatic noxious signals in spinal cord, while the potential role in visceral nociception remains elusive. We designed this study to investigate the hypothesis that cardiac nociceptive signals from acute ischemic myocardium to the spinal cord are transmitted or modulated by mechanisms including N/OFQ. We examined the changes of N/OFQ and its mRNA in the dorsal root ganglia and spinal cord of upper thoracic segments innervating the heart of rats. Thoracic epidural anesthesia was performed to confirm neural mechanism underlying the changes. We observed that selective coronary artery occlusion significantly up-regulated N/OFQ and ppN/OFQ mRNA in the dorsal root ganglia and spinal cord. Thoracic epidural anesthesia abolished the changes in the expression of N/OFQ and its mRNA. The observations indicate that cardiac noxious neural afferent drive is responsible for the up-regulation of N/OFQ in the primary afferent neurons and intrinsic spinal neurons.

Leukocytes as mediators of pain and analgesia

In inflammation, resident cells and infiltrating leukocytes produce proalgesic mediators. Although these mediators induce pain, the role of specific cell populations is still controversial. In addition, resident cells and leukocytes also generate analgesic mediators that counteract inflammatory pain, including anti-inflammatory cytokines, endocannabinoids, and opioid peptides. Chemokines and adhesion molecules orchestrate the migration of opioid peptide-containing leukocytes to inflamed tissue. Leukocytes secrete opioid peptides under stressful conditions or in response to releasing agents (eg, corticotropin-releasing factor and chemokines). Secretion requires intracellular calcium mobilization and activation of phosphinositol-3 kinase and p38 mitogen activated kinase. Following release, opioid peptides bind to receptors on peripheral sensory neurons and produce analgesia in animal models and humans. This review presents recent findings on the role of leukocytes in the generation and inhibition of inflammatory pain.

Anticytokine therapy in neuropathic pain management

Cytokine activation or dysregulation is implied in a variety of painful disease states. Numerous experimental studies provide evidence that proinflammatory cytokines induce or facilitate neuropathic pain. Cytokine levels are rapidly and markedly upregulated in the peripheral nerves, dorsal root ganglia, spinal cord and in particular regions of the brain, after peripheral nerve injuries. Direct receptor-mediated actions on afferent nerve fibers as well as cytokine effects involving further mediators have been reported. Whereas direct application of exogenous proinflammatory cytokines induces pain, blockade of these cytokines or application of anti-inflammatory cytokines reduces pain behavior in most experimental paradigms. Cytokine measurements may identify patients at risk of developing chronic pain associated with their neuropathic conditions, as in the examples of peripheral neuropathies and postherpetic neuralgia. Anticytokine agents currently on the market are effective for the treatment of mostly inflammatory pain conditions, and are starting to be introduced for neuropathic pain states; however, their use is limited by potential life-threatening complications. Owing to the pleiotropy and redundancy of the cytokine system, the successful approach may not be inhibition of one particular cytokine but strategies shifting the balance between pro- and anti-inflammatory cytokines in properly selected patients. Agents that specifically target downstream signaling molecules may provide hope for safer and more specific therapies.

Role of complement C5a in mechanical inflammatory hypernociception: potential use of C5a receptor antagonists to control inflammatory pain

BACKGROUND AND PURPOSE

C5a, a complement activation product, exhibits a broad spectrum of inflammatory activities particularly neutrophil chemoattraction. Herein, the role of C5a in the genesis of inflammatory hypernociception was investigated in rats and mice using the specific C5a receptor antagonist PMX53 (AcF-[OP(D-Cha)WR]).

EXPERIMENTAL APPROACH

Mechanical hypernociception was evaluated with a modification of the Randall-Selitto test in rats and electronic pressure meter paw test in mice. Cytokines were measured by ELISA and neutrophil migration was determined by myeloperoxidase activity.

KEY RESULTS

Local pretreatment of rats with PMX53 (60-180 microg per paw) inhibited zymosan-, carrageenan-, lipopolysaccharide (LPS)- and antigen-induced hypernociception. These effects were associated with C5a receptor blockade since PMX53 also inhibited the hypernociception induced by zymosan-activated serum and C5a but not by the direct-acting hypernociceptive mediators, prostaglandin E(2) and dopamine. Underlying the C5a hypernociceptive mechanisms, PMX53 did not alter the cytokine release induced by inflammatory stimuli. However, PMX53 inhibited cytokine-induced hypernociception. PMX53 also inhibited the recruitment of neutrophils induced by zymosan but not by carrageenan or LPS, indicating an involvement of neutrophils in the hypernociceptive effect of C5a. Furthermore, the C5a-induced hypernociception was reduced in neutrophil-depleted rats. Extending these findings in rats, blocking C5a receptors also reduced zymosan-induced joint hypernociception in mice.

CONCLUSIONS AND IMPLICATIONS

These results suggest that C5a is an important inflammatory hypernociceptive mediator, acting by a mechanism independent of hypernociceptive cytokine release, but dependent on the presence of neutrophils. Therefore, we suggest that inhibiting the action of C5a has therapeutic potential in the control of inflammatory pain.

Behavioural, histological and cytokine responses during hyperalgesia induced by carrageenan injection in the rat tail

We produced experimental inflammatory hyperalgesia by injecting carrageenan into the tail of Sprague-Dawley rats. We compared the rats' voluntary running wheel activity following carrageenan injection into the tail to that after carrageenan injection into the hind paw, the conventional site of inflammation, to identify whether the site of inflammatory-induced hyperalgesia altered voluntary activity. We also measured voluntary running before and after injection of carrageenan or saline into the tail or hind paw, and in separate groups of rats we measured the nociceptive response and the associated pro-inflammatory cytokine profiles following a carrageenan injection into the tail. Female rats were injected intradermally with either 2 mg carrageenan or saline into the dorsal surface of the tail. Withdrawal responses to noxious heat (49 degrees C water), and punctate mechanical (electronic anaesthesiometer) challenges were recorded in 12 rats for 3 days before and 1 h to 48 h after injection. In a separate group of rats, interleukin (IL)-1beta, IL-6, tumour necrosis factor-alpha (TNF-alpha) and cytokine-induced neutrophil chemoattractant (CINC-1) concentrations were measured in plasma and tail tissue samples taken at the site of injection, 3 h, 6 h and 24 h after injections. Voluntary wheel running was reduced significantly following carrageenan injection into the hind paw compared to that after saline injection into the hind paw. Carrageenan injection into the tail did not result in significant reduction in wheel running compared to that after saline injection into the tail. Both thermal and mechanical hyperalgesia were present after carrageenan injection into the tail (P<0.01, ANOVA). The hyperalgesia at the site coincided with significant increases in TNF-alpha, IL-1beta, IL-6 and CINC-1 tissue concentrations, peaking 6 h after carrageenan injection (P<0.01, ANOVA). We conclude that carrageenan injection into the tail produces inflammatory hyperalgesia with underlying pro-inflammatory cytokine release, but does not affect voluntary running wheel activity in rats.

Pharmacological modulation of wound healing in experimental burns

Factors involved in wound healing and their interdependence are not yet fully understood; nevertheless, new prospects for therapy to favor speedy and optimal healing are emerging. Reports about wound healing modulation by local application of simple and natural agents abound even in the recent literature, however, most are anecdotal and lack solid scientific evidence. We describe the effect of silver sulfadiazine and moist exposed burn ointment (MEBO), a recently described burn ointment of herbal origin, on mast cells and several wound healing cytokines (bFGF, IL-1, TGF-beta, and NGF) in the rabbit experimental burn model. The results demonstrate that various inflammatory cells, growth factors and cytokines present in the wound bed may be modulated by application of local agents with drastic effects on their expression dynamics with characteristic temporal and spatial regulation and changes in the expression pattern. Such data are likely to be important for the development of novel strategies for wound healing since they shed some light on the potential formulations of temporally and combinatory optimized therapeutic regimens.