Involvement of interleukin-1 beta, nerve growth factor and prostaglandin E2 in endotoxin-induced localized inflammatory hyperalgesia

Targeting inflammatory components in neuropathic pain: The analgesic effect of thymulin related peptide

Neuropathic pain is considered to be pathological in nature and has been shown to involve, at least partially, dysregulated inflammatory processes. It is a severe chronic disease that can develop following lesions to the central nervous system or to peripheral nerves. The peripheral nerve damage can be caused by either diseases such as diabetes, or by trauma. A common underlying mechanism of neuropathic pain is the presence of inflammation at the site of the damaged or affected nerve(s). This inflammatory response, especially when unresolved, initiates and maintains a cascade of events resulting in the activation of innate immune cells at the site of tissue injury. The release of inflammatory mediators such as cytokines, neurotrophic factors, and chemokines initiates local actions and can result in a more generalized immune response. The resultant neuroinflammatory environment can cause activation of glial cells, which can release, in an uncontrolled manner, more of these mediators and exasperate the situation, thus having a prominent role in nociception. The neuropathic pain pathophysiology is complex and includes peripheral and central neuronal alterations as well as neuro-immune interactions, which become more prominent during inflammatory reactions. This report focuses on how targeting inflammatory mediators may result in novel therapeutic approaches to neuropathic pain management.

Anti-Hyperuricemic, Anti-Inflammatory and Analgesic Effects of Siegesbeckia orientalis L. Resulting from the Fraction with High Phenolic Content

Background

The medicinal plant Siegesbeckia orientalis L. has been commonly used for the treatment of acute arthritis, rheumatism, and gout in Vietnam. However, pharmacological research of this plant associated with gout has not been reported. Anti-hyperuricemic and anti-inflammatory effects were evaluated and observed for the crude ethanol extract (CEE) of S. orientalis. Retention of these biological properties was found in a n-butanol-soluble fraction (BuOH fr.) of the extract, and therefore further biological and chemical investigations were undertaken on the BuOH fr. to support the medical relevance of this plant.

Methods

The aerial part of S. orientalis was obtained in the mountainous region of Vietnam. The crude ethanol extract (CEE) and its BuOH fr. were prepared from the plant materials. Anti-hyperuricemic activities of the CEE and BuOH fr. were tested in vivo using the model oxonate-induced hyperuricemia rats through determination of serum uric acid levels and inhibitory effects on xanthine oxidase (XO) in the rat liver. Anti-inflammatory activities of the BuOH fr. were also evaluated in vivo using carrageenan-induced paw edema and urate-induced synovitis in rats. Active components of the BuOH fr. were characterized by comparison of HPLC retention time (t_R) and spectroscopic data (UV, ¹H–NMR) with those of reference compounds.

Results

The CEE of S. orientalis displayed anti-hyperuricemic activity, and the BuOH fr. was found to be the most active portion of the extract. Further in vivo studies on this fraction showed 31.4% decrease of serum uric acid levels, 32.7% inhibition of xanthine oxidase (XO), 30.4% reduction of paw edema volume, symptomatic relief in urate-induced synovitis and significant analgesic effect at the dose of 120 mg/kg, as compared to the corresponding values of the control groups. Chemical analysis of the BuOH fr. revealed high phenolic content, identified as caffeic acid analogues and flavonones.

Conclusions

This study suggested that anti-hyperuricemic and anti-inflammatory mechanism of S. orientalis is related to XO inhibitory effect of the phenolic components. Our findings support the use of this plant as the treatment of gout and other inflammatory diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12906-017-1698-z) contains supplementary material, which is available to authorized users.

The role of slow and persistent TTX-resistant sodium currents in acute tumor necrosis factor-α-mediated increase in nociceptors excitability

Tetrodotoxin-resistant (TTX-r) sodium channels are key players in determining the input-output properties of peripheral nociceptive neurons. Changes in gating kinetics or in expression levels of these channels by proinflammatory mediators are likely to cause the hyperexcitability of nociceptive neurons and pain hypersensitivity observed during inflammation. Proinflammatory mediator, tumor necrosis factor-α (TNF-α), is secreted during inflammation and is associated with the early onset, as well as long-lasting, inflammation-mediated increase in excitability of peripheral nociceptive neurons. Here we studied the underlying mechanisms of the rapid component of TNF-α-mediated nociceptive hyperexcitability and acute pain hypersensitivity. We showed that TNF-α leads to rapid onset, cyclooxygenase-independent pain hypersensitivity in adult rats. Furthermore, TNF-α rapidly and substantially increases nociceptive excitability in vitro, by decreasing action potential threshold, increasing neuronal gain and decreasing accommodation. We extended on previous studies entailing p38 MAPK-dependent increase in TTX-r sodium currents by showing that TNF-α via p38 MAPK leads to increased availability of TTX-r sodium channels by partial relief of voltage dependence of their slow inactivation, thereby contributing to increase in neuronal gain. Moreover, we showed that TNF-α also in a p38 MAPK-dependent manner increases persistent TTX-r current by shifting the voltage dependence of activation to a hyperpolarized direction, thus producing an increase in inward current at functionally critical subthreshold voltages. Our results suggest that rapid modulation of the gating of TTX-r sodium channels plays a major role in the mediated nociceptive hyperexcitability of TNF-α during acute inflammation and may lead to development of effective treatments for inflammatory pain, without modulating the inflammation-induced healing processes.

The immunomodulation of a novel tumor necrosis factor (CgTNF-1) in oyster Crassostrea gigas

Tumor necrosis factor (TNF) is one of the most important cytokines involved in many processes in both vertebrate and invertebrate. In the present study, a new tumor necrosis factor with a typical TNF domain was identified in oyster Crassostrea gigas (designated CgTNF-1). CgTNF-1 shared low sequence identity and similarity with the TNF superfamily members from other vertebrate and invertebrate. After LPS stimulation, the mRNA expression of CgTNF-1 in haemocytes increased significantly and peaked at 12h (1.39±0.12, P<0.05) post treatment, and the expression of CgTNF-1 protein in haemolymph also increased obviously during 6-12h. When the oyster haemocytes were incubated with rCgTNF-1, its apoptosis and phagocytosis rate were both effectively induced and peaked at 12h post the treatment of rCgTNF-1 with the concentration of 100ngmL(-1) (23.3±3%, P<0.01), 50ngmL(-1) (5.3±0.6%, P<0.05) and 10ngmL(-1) (6.7±1.2%, P<0.05), respectively. After the co-stimulation of LPS and rCgTNF-1, the apoptosis and phagocytosis rate of oyster haemocytes, and the activities of PO and lysozyme in the haemolymph all increased significantly, and reached the peak at 12h (apoptosis rate 26.7±1.5%, P<0.01), 12h (phagocytosis rate 8.3±0.6%, P<0.01), 6h (PO 1.11±0.01Umg prot(-1), P<0.01) and 12h (lysozyme 168.9±8.3Umg prot(-1), P<0.05), respectively, which were significantly higher than that in the LPS group. Furthermore, the anti-bacteria activity in the LPS+TNF group was significantly higher than that in the LPS group during 6-12h. All the results collectively indicated that CgTNF-1 was involved in the oyster immunity and played a crucial role in the modulation of immune response including apoptosis and phagocytosis of haemocytes, and regulation of anti-bacterial activity as well as the activation of immune relevant enzymes.

Low rather than high dose lipopolysaccharide 'priming' of muscle provides an animal model of persistent elevated mechanical sensitivity for the study of chronic pain

Experimental animal pain models involving peripheral nerve lesions have expanded the understanding of the pathological changes caused by nerve damage. However models for the pathogenesis of chronic pain patients lacking obvious nerve injuries have not been developed to the same extent. Guided by clinical observations, we focused on the initiating noxious event, the context when applying nociceptive stimulation targeting long-lasting pain elicited by muscle insult. The administration of a nociceptive agent (6% hypertonic saline: HS; 5-time repeated-injection: HS5) after pretreatment with an immuno-inflammatory agent (lipopolysaccharide: LPS, 2 μg/kg) into one gastrocnemius muscle produced markedly long-persisting biphasic sustained mechanical hypersensitivity on the plantar surface of both hindpaws. In the acute phase, the blockade of afferent inputs from the injected-site was effective in returning the contralateral enhanced-responses to baseline levels. In contrast, similar blockade during the chronic phase did not affect the contralateral enhanced-responses, indicating that the hypersensitivity in the two phases was probably induced by different mechanisms. However, increasing the dose of LPS (20 μg/kg) before applying HS5 eliminated the development of mechanical hypersensitivity in the chronic phase, while the hypersensitivity in the acute phase was significantly more severe than with low-dose LPS-pretreatment. In this model, the development of hypersensitivity could be modulated by manipulating LPS-doses prior to noxious stimulation. This novel chronic pain model based on a preceding 'priming' myalgic stimulus provides an intriguing means for studying the pathogenesis of chronic pain.

On the mechanisms and putative pathways involving neuroimmune interactions

Bidirectional interdependence between the immune system and the CNS involves the intervention of common cofactors. Cytokines are endogenous to the brain, endocrine and immune systems. These shared ligands are used as a chemical language for communication. Such interaction suggests an immunoregulatory role for the brain, and a sensory function for the immune system. Interplay between the immune, nervous and endocrine systems is associated with effects of stress on immunity. Cytokines are thus capable of modulating responses in the CNS, while neuropeptides can exert their effects over cellular groups in the immune system. One way is controlled by the HPA axis, a coordinator of neuroimmune interactions that is essential to unravel in order to elucidate vital communications in a manner that this crosstalk remains a cornerstone in perpetuating a stance of homeostasis.

Evaluation of the effects of the herbal product Catuama in inflammatory and neuropathic models of nociception in rats

Here we evaluated the antinociceptive effects of the herbal drug Catuama in rat inflammatory and neuropathic models of pain, in order to assess some of the mechanisms involved in its actions. Catuama given orally, in both acute and chronic schedules of treatment, consistently inhibited the mechanical allodynia induced by the intraplantar (i.pl.) injection of complete Freund's adjuvant (CFA). The same treatment with Catuama failed to significantly affect CFA-caused thermal hyperalgesia. In addition, Catuama did not significantly modify the mechanical allodynia or hyperalgesia observed following the partial ligation of the sciatic nerve or the diabetic polyneuropathy, respectively. In another series of experiments, Catuama caused a striking reduction of the mechanical allodynia induced by LPS. Oral treatment with Catuama was not, however, effective in altering the production of the pro-inflammatory mediators IL-1beta, TNFalpha, PGE(2) or LTB(4) following i.pl. administration of LPS in the rat paw. Of high interest, the antinociceptive effects of Catuama in the LPS model were reversed significantly by the non-selective dopamine antagonist haloperidol, but not by serotonin methysergide or adrenergic yohimbine receptor antagonists. Our results indicate that the herbal drug Catuama diminishes inflammatory, but not neuropathic, nociceptive responses in rats, by mechanisms involving an interference with dopaminergic pathways. Catuama might represent a potential therapeutic tool for the management of persistent inflammatory pain.

Pronociceptive response elicited by TRPA1 receptor activation in mice

Ankyrin-repeat transient receptor potential 1 (TRPA1) is a member of the transient receptor potential (TRP) channel family and it is found in sensory neurons. In the present study, we found that TRPA1 receptor activation with allyl isothiocyanate or cinnamaldehyde caused dose-dependent spontaneous nociception when injected into the mouse hind paw. Very similar results were obtained when stimulating transient receptor potential vanilloid 1 (TRPV1) receptors with capsaicin. Pretreatment with the TRP receptor antagonist Ruthenium Red (1 nmol/paw) inhibited capsaicin-(0.1 nmol/paw) and allyl isothiocyanate-(1 nmol/paw) induced nociceptive responses. However, the nonselective TRPV1 receptor antagonist capsazepine (1 nmol/paw) and the selective TRPV1 receptor antagonist SB 366791 (1 nmol/paw) only attenuated capsaicin-induced nociception. In contrast, the intrathecal treatment with TRPA1 antisense oligodeoxynucleotide (2.5 nmol/site) and the degeneration of the subset of primary afferent fibers sensitive to capsaicin significantly reduced allyl isothiocyanate-induced nociception. Consequently to TRPA1 antisense oligodeoxynucleotide treatment there was a marked decrease of the expression of TRPA1 receptor in both sciatic nervous and spinal cord segments. Moreover, capsaicin and allyl isothiocyanate-induced nociception were not significantly changed by chemical sympathectomy produced by guanethidine. The previous degranulation of mast cells by compound 48/80 and treatment with antagonist H(1) receptor antagonist pyrilamine (400 microg/paw) both significantly inhibited the capsaicin- and allyl isothiocyanate-induced nociception. The selective NK(1) receptor antagonist N(2)-[(4R)-4-hydroxy-1-(1-methyl-1H-indol-3-yl) carbony-1-L-prolyl]-N-methyl-N-phenylmethyl-3-2-(2-naphtyl)-L-alaninamide (10 nmol/paw) reduced either capsaicin- or allyl isothiocyanate-induced nociception. Collectively, the present findings demonstrate that the TRPA1 agonist allyl isothiocyanate produces a consistent nociceptive response when injected into the mouse paw, an effect that seems to be mediated via activation of TRPA1 receptor and dependent on the capsaicin-sensitive fibers, release of histamine by mast cells and participation of tachykinins. Thus, the TRPA1 receptor has an apparently relevant role in nociceptive processes and the selective TRPA1 antagonist might possess a potential antinociceptive property.

Movement-evoked hyperalgesia induced by lipopolysaccharides is not suppressed by glucocorticoids

Systemic exposure to lipopolysaccharides (LPS) produces a variety of effects, including movement-evoked hyperalgesia that can be measured using the grip force assay in mice. Because both lethality and enhanced sensitivity to cutaneous pain following exposure to endotoxins have each been attributed to inflammatory mediators, we explored the possibility that LPS-induced movement-evoked hyperalgesia is also sensitive to manipulations of glucocorticoids that regulate these other LPS responses. We found that the hyperalgesic effect of LPS (5mg/kg s.c.) in mice that were adrenalectomized did not differ from that in control mice that were sham operated, even though mortality after LPS was potentiated by adrenalectomy. The development of tolerance to the movement-evoked hyperalgesic effect of LPS also did not differ between adrenalectomized and sham-operated control mice. In addition, mifepristone (25mg/kg s.c.), a glucocorticoid antagonist, did not attenuate the hyperalgesic effect of LPS (2mg/kg s.c.), yet this dose of mifepristone was sufficient to enhance the incidence of lethality induced by LPS. Enhancement of glucocorticoid activity by two injections of dexamethasone (1mg/kg s.c.) had no effect on the degree of hyperalgesia in mice injected with LPS (5mg/kg s.c.), yet this dose of dexamethasone was sufficient to attenuate the incidence of mortality induced by LPS in adrenalectomized mice. Finally, morphine (10mg/kg i.p.) reversed the decrease in grip force caused by LPS (5mg/kg i.p.), supporting the interpretation that decreases in grip force produced by LPS reflect muscle hyperalgesia that is not sensitive to glucocorticoids.

Antihyperalgesic effects induced by the IL-1 receptor antagonist anakinra and increased IL-1β levels in inflamed and osteosarcoma-bearing mice

Based on the well established involvement of IL-1beta in inflammatory hyperalgesia, we have assessed the possible role played by IL-1beta in a murine model of bone cancer-induced pain. With this aim, we measured IL-1beta levels at the region of the tibia and the spinal cord in mice bearing a tibial osteosarcoma induced by the inoculation of NCTC 2472 cells, and we tested whether the IL-1 receptor antagonist, anakinra, inhibits some hypernociceptive reactions evoked by the neoplastic injury. Parallel experiments were performed in mice with a chronic inflammatory process (intraplantar injection of complete Freund's adjuvant, CFA). IL-1beta levels were increased in the tibial region of osteosarcoma-bearing mice and in the paws of inflamed mice. To a lesser extent, the content of IL-1beta in the spinal cord was also augmented in both situations. Osteosarcoma-induced thermal hyperalgesia was inhibited by 30 and 100 mg/kg of systemic anakinra, but only 300 mg/kg prevented inflammatory thermal hyperalgesia. Mechanical hyperalgesia induced by the osteosarcoma was blocked by 100 and 300 mg/kg of anakinra, whereas a partial reversion of inflammatory mechanical hyperalgesia was induced by 300 mg/kg. Anakinra, intrathecally administered (1 and 10 microg) did not modify hyperalgesia of either origin. Besides, both tumoral and inflammatory mechanical allodynia remained unaltered after the administration of anakinra. In conclusion, some hyperalgesic symptoms observed in this model of bone cancer are mediated by the peripheral release of IL-1beta and may be inhibited by antagonists of type I IL-1 receptors with a similar or greater potency than symptoms produced by inflammation.

Up-regulation of nerve growth factor and interleukin-10 in inflamed and non-inflamed intestinal segments in rats with experimental colitis

Inflammatory bowel diseases are characterized by dysregulated immune response to the normal microflora and structural and functional changes of the enteric nervous system which occur in inflamed as well as non-inflamed areas of the bowel. This study describes the changes in the expression of nerve growth factor (NGF) and interleukin-10 (IL-10) in the colon and in various segments of the small intestine in two rat models of experimental colitis induced by iodoacetamide or 2,4,6-trinitrobenzene sulfonic acid (TNBS). Levels of NGF and IL-10 were measured by ELISA in tissue homogenate sampled from duodenum, jejunum, ileum and colon at different time intervals. NGF and IL-10 increased significantly in homogenates of strips isolated from all small intestinal segments, 3-6h after iodoacetamide or TNBS administration and remained elevated until the colonic inflammation subsided. Similar but more pronounced increase occurred in areas of the colon adjacent to the ulcer. Histologic examinations revealed inflammatory changes in the colon; however, examination of sections from the small intestines did not reveal significant differences between controls and rats with colitis. The marked up-regulation of nerve growth factor and interleukin-10 in colitis suggests that they play a role in limiting or resolving inflammation and in preventing it from becoming uncontrolled. It also suggests that experimental colitis may be associated with latent inflammation in the small bowel.

Role of Thymulin or Its Analogue as a New Analgesic Molecule

The thymic peptide thymulin is known for its immunomodulatory role. However, several recent reports have indicated that thymulin is capable of interacting directly and/or indirectly with the nervous system. One of the first lines of evidence of this interaction was obtained in a series of experiments showing the hyperalgesic actions of this peptide. We demonstrated that, at low doses (ng), local (intraplantar) or systemic (intraperitoneal) injections of thymulin resulted in hyperalgesia with an increase in proinflammatory mediators, and that this peptide could act directly on the afferent nerve terminals through prostaglandin-E2 (PGE2)-dependent mechanisms, thus forming a neuroimmune loop involving capsaicin-sensitive primary afferent fibers. In further experiments, systemic injections of relatively high doses (1-25 microg) of thymulin or of an analogue peptide (PAT) deprived of hyperalgesic effect, have been shown to reduce the inflammatory pain and the upregulated levels of cytokines induced by endotoxin (ET) injection. In addition, PAT treatment appeared to alleviate the sickness behavior (motor behavior and fever) induced by systemic inflammation. These effects could be attributed, at least partly, to the downregulation of proinflammatory mediators. Furthermore, when compared with the effects of other anti-inflammatory drugs, PAT exerted equal or even stronger analgesic effects, and at much lower concentrations. Subsequent experiments were designed to examine the effects of intracerebroventricular (i.c.v.) injections of thymulin on cerebral inflammation induced by i.c.v. injection of ET. Pretreatment with thymulin reduced, in a dose-dependent manner, the ET-induced hyperalgesia, and exerted differential effects on the upregulated levels of cytokines in different areas of the brain, suggesting a neuroprotective role for thymulin in the central nervous system (CNS). Preliminary results demonstrate that thymulin inhibits in the hippocampus the ET-induced nuclear activation of NF-kappaB, the transcription factor required for the expression of proinflammatory cytokines genes. Although the mechanism of action of these molecules is not totally elucidated, our results indicate a possible therapeutic use of thymulin or PAT as analgesic and anti-inflammatory drugs.

Localized colonic inflammation increases cytokine levels in distant small intestinal segments in the rat

Local inflammation in the colon has been associated with nutrient malabsorption and altered motility in the small bowel. These remote effects suggest the release of mediators which can act (or alter) the function of intestinal segments located far from the primary area of inflammation. This study describes the changes in the expression of pro-inflammatory cytokines in the colon and in various segments of the small intestine in two rat models of experimental colitis. Colitis was induced by the intracolonic administration of 100 microL of 6% iodoacetamide or 250 microL of 2, 4, 6-trinitrobenzene sulfonic acid. Levels of interleukin one beta, interleukin 6, and tumor necrosis factor alpha were measured by ELISA in tissue homogenate sampled from duodenum, jejunum, ileum and colon at different time intervals. In homogenates of strips isolated from duodenum, jejunum and ileum, tumor necrosis alpha and interleukin-6, increased significantly 3-6 h after iodoacetamide or TNBS administration and remained elevated until the colonic inflammation subsided. Interleukin one beta showed comparable but delayed increase. Similar, but more pronounced increase of the three cytokines was noticed in areas of the colon adjacent to the ulcer. Histologic examinations revealed important inflammatory changes in the colon; however, examination of sections from the small intestines did not reveal significant differences between controls and rats with colitis. In conclusion, expression of pro-inflammatory cytokines is increased in remote segments of the small intestines during colitis. The findings may provide a partial explanation or a molecular substrate for the associated small bowel dysfunction.

Effects of intravesical instillation of cyclooxygenase-2 inhibitor on the expression of inducible nitric oxide synthase and nerve growth factor in cyclophosphamide-induced overactive bladder

OBJECTIVE

To examine the effects of intravesical cyclooxygenase-2 (COX-2) inhibitors on the expression of inducible nitric oxide synthase (iNOS) and nerve growth factor (NGF) in cyclophosphamide (CYP)-induced overactive bladder (OAB).

MATERIALS AND METHODS

In all, 40 Sprague-Dawley rats were divided into control, OAB, and COX-2 inhibitor-treated groups. OAB was induced by an intraperitoneal injection with CYP. Cystometry was performed in all rats and, in half of the OAB rats, a COX-2 inhibitor was administered intravesically. The bladders of all rats were stained immunohistochemically for iNOS and NGF.

RESULTS

In the OAB rats, the contraction interval and intercontraction interval were significantly shorter than in control rats, and the contraction time and pressure were significantly greater. In the COX-2 inhibitor-treated rats, the contraction interval and intercontraction interval were significantly longer than in the OAB rats, and the contraction time was significantly shorter. On immunohistochemical staining, there was no iNOS activity and NGF activity was minimally localized in the mucosa and submucosa in the control group. In the OAB rats, NGF activity in the mucosa and submucosa were increased, and there was greater expression of iNOS in all layers and of NGF in detrusor; in the COX-2 inhibitor-treated rats, their expression was less in all layers.

CONCLUSIONS

Intravesical instillation with COX-2 inhibitors can reduce CYP-induced bladder hyperactivity and expression of iNOS and NGF. Intravesical instillation with COX-2 inhibitors can be considered as a possible treatment for OAB.

Nociceptive Effect of Subcutaneously Injected Interleukin-12 Is Mediated by Endothelin (ET) Acting on ETB Receptors in Rats

Interleukin-12 (IL-12) is an inflammatory Th1-driving cytokine that has been clinically used as immune therapy and vaccine adjuvant. Recently, it was reported that patients receiving IL-12 presented hyperalgesia. In the present study, we investigated the mechanical hyperalgesic effect of IL-12 in rats using two tests: 1) paw constant pressure and 2) electronic pressure-meter. In both tests, intraplantar administration of IL-12 (3-30 ng paw(-1)) caused a dose- and time-dependent mechanical hyperalgesia, which peaked between 3 to 5 h, remaining significantly different from control levels until 7 h and resolved 24 h postinjection. However, the same doses of IL-12 did not induce thermal hyperalgesia, determined using the Hargreaves test. Pretreatments with effective doses of indomethacin (2.5 mg kg(-1)), atenolol (1 mg kg(-1)), 3-[1-(p-chlorobenzyl)-5-(isopropyl)-3-t-butylthioindol-2-yl]-2,2-dimethylpropanoic acid, sodium (MK886) (5-lipoxygenase activating protein inhibitor; 1 mg kg(-1)), or cyclo[(D)Trp-(D)Asp-Pro-(D)Val-Leu] (BQ123) [endothelin (ET)(A) receptor antagonist; 30 nmol paw(-1)] did not inhibit IL-12-evoked mechanical hyperalgesia (10 ng paw(-1)). However, dexamethasone (2 mg kg(-1)), morphine (3-12 microg paw(-1)), and N-cys-2,6 dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarboyl-d-norleucine (BQ788) (ET(B) receptor antagonist; 3-30 nmol paw(-1)) did inhibit IL-12 hyperalgesia. Furthermore, neither pretreatment with effective doses of antiserum against rat-TNF-alpha (50 microl paw(-1)) nor against IL-18 (10 microg paw(-1)) inhibited the IL-12-induced hyperalgesia. Likewise, antiserum against IL-12 (10 ng paw(-1)) did not alter IL-18-induced hyperalgesia. In conclusion, we demonstrated for the first time that IL-12 is a prohyperalgesic cytokine that induces mechanical hyperalgesia mediated by endothelin action on the ET(B) receptor. Therefore, endothelin receptor antagonism could be beneficial in controlling IL-12 therapy-induced pain or hyperalgesia.

Anti-inflammatory and antinociceptive activities of an acid fraction of the seeds of Carpotroche brasiliensis (Raddi) (Flacourtiaceae)

Carpotroche brasiliensis is a native Brazilian tree belonging to the Oncobeae tribe of Flacourtiaceae. The oil extracted from its seeds contains as major constituents the same cyclopentenyl fatty acids hydnocarpic (40.5%), chaulmoogric (14.0%) and gorlic (16.1%) acids found in the better known chaulmoogra oil prepared from the seeds of various species of Hydnocarpus (Flacourtiaceae). These acids are known to be related to the pharmacological activities of these plants and to their use as anti-leprotic agents. Although C. brasiliensis oil has been used in the treatment of leprosy, a disease that elicits inflammatory responses, the anti-inflammatory and analgesic activities of the oil and its constituents have never been characterized. We describe the anti-inflammatory and antinociceptive activities of C. brasiliensis seed oil in acute and chronic models of inflammation and in peripheral and central nociception. The mixture of acids from C. brasiliensis administered orally by gavage showed dose-dependent (10-500 mg/kg) anti-inflammatory activity in carrageenan-induced rat paw edema, inhibiting both the edema by 30-40% and the associated hyperalgesia. The acid fraction (200 mg/kg) also showed significant antinociceptive activity in acetic acid-induced constrictions (57% inhibition) and formalin-induced pain (55% inhibition of the second phase) in Swiss mice. No effects were observed in the hot-plate (100 mg/kg; N = 10), rota-road (200 mg/kg; N = 9) or adjuvant-induced arthritis (50 mg/kg daily for 7 days; N = 5) tests, the latter a chronic model of inflammation. The acid fraction of the seeds of C. brasiliensis which contains cyclopentenyl fatty acids is now shown to have significant oral anti-inflammatory and peripheral antinociceptive effects.

Pharmacological investigation of the nociceptive response and edema induced by venom of the scorpion Tityus serrulatus

In this study we characterized the nociceptive response and edema induced by the venom of the scorpion Tityus serrulatus in rats and mice and carried out a preliminary pharmacological investigation of the mechanisms involved in these responses. Intraplantar injection of the venom (1 or 10mug) induced edema and a marked ipsilateral nociceptive response, characterized by thermal and mechanical allodynia and paw licking behaviour. The nociceptive response was inhibited by previous intraperitoneal administration of indomethacin (4mg/kg), dipyrone (200mg/kg), cyproheptadine (10mg/kg) or morphine (5 or 10mg/kg), but not by dexamethasone (1 or 4mg/kg) or promethazine (1 or 5mg/kg). The edema was inhibited by previous treatment with promethazine (5 or 10mg/kg) or cyproheptadine (5 or 10mg/kg), but not by indomethacin (2 or 4mg/kg), dexamethasone (1 or 4mg/kg) or cromolyn (40 or 80mg/kg). Some bioactive amines, including histamine and 5-hydroxytryptamine, were found in the venom in low concentrations. In conclusion, the nociceptive response and edema induced by the venom of T. serrulatus may result from the action of multiple mediators including eicosanoids, histamine and 5-hydroxytryptamine. These results may lead to a better understanding of the host response to potent animal toxins and also give insights into a more rational pharmacological approach to alleviate the intense pain associated with the scorpion envenomation.

Sensitization of mesenteric afferents to chemical and mechanical stimuli following systemic bacterial lipopolysaccharide

BACKGROUNDS AND AIMS

The mechanisms underlying endotoxin-induced hyperalgesia remain unknown. We aimed to study the mechanisms underlying the sensitizing action of lipopolysaccharide (LPS) on intestinal afferent responses to mechanical and chemical stimuli.

METHODS

Extracellular recordings of jejunal afferent nerve discharge were obtained from pentobarbitone-anaesthetized rats.

RESULTS

Lipopolysaccharide (6 mg kg(-1), i.v.) stimulated a short-term, transient (<30 min) increase in chemosensitivity to systemic 5-HT (6 microg kg(-1)) and responses to mechanical distension and a delayed but maintained (>30 min) increase in spontaneous afferent discharge. Naproxen (10 mg kg(-1)) and the prostaglandin receptor antagonist AH6809 (1 mg kg(-1)) significantly attenuated both the short-term sensitization to mechanical distension and 5-HT and the long-term increase in baseline afferent firing following LPS. In contrast, the iNOS inhibitor aminoguanidine (15 mg kg(-1)) and the L-type calcium channel antagonist nifedipine (1 mg kg(-1)) both prolonged the period of afferent sensitization to distension and 5-HT without influencing the augmented baseline-firing rate. omega-Conotoxin GVIA attenuated the increase in afferent discharge to LPS, without any change in mechano- and chemosensitivity.

CONCLUSIONS

The long-term (>30 min) increase in afferent firing following systemic LPS involves neurogenic release of prostanoids. The short-term (<30 min) sensitization also appears to depend on prostanoid release, while nitric oxide production may serve to down-regulate LPS-induced afferent hypersensitivity.

Tolerance develops to the effect of lipopolysaccharides on movement-evoked hyperalgesia when administered chronically by a systemic but not an intrathecal route

Single exposures to lipopolysaccharides (LPS) produce deep tissue pain in humans and cutaneous hyperalgesia in rodents. While tolerance develops to many effects of LPS, sensitization to hyperalgesia is documented after a single injection. To determine the effect of long-term exposure to LPS, we explored the chronic effect of LPS on movement-evoked pain using a new assay based on grip force in mice. We found that a single systemic injection of LPS (i.p. or s.c.) induced a dose-related decrease in forelimb grip force responses beginning 6-8 h after injection and peaking between 9 and 24 h. The consequence of LPS is likely hyperalgesia rather than weakness as these decreases were rapidly attenuated by either 10 mg/kg of morphine i.p. or 10 microg of morphine injected intrathecally (i.t.). Complete tolerance to this hyperalgesia developed after repeated injections of LPS at doses of 0.9 mg/kg i.p. or 5 mg/kg s.c. Tolerance began after a single injection and was fully developed after as few as four injections of 5 mg/kg of LPS delivered s.c. The concentration of circulating LPS 5 h after a single parenteral injection was less in LPS-tolerant mice than naïve controls, suggesting that tolerance may result from a more efficient clearance of LPS from the circulation. Injected i.t., LPS also induced hyperalgesia, however, tolerance did not develop to multiple injections by this route. There was no cross-tolerance between s.c. and i.t. injections of LPS. These data indicate that decreases in grip force are a sensitive measure of LPS-induced movement-evoked hyperalgesia and that tolerance develops to parenteral but not central hyperalgesic effects of LPS.

Involvement of substance P, CGRP and histamine in the hyperalgesia and cytokine upregulation induced by intraplantar injection of capsaicin in rats

Intraplantar (i.pl.) injection of small doses of capsaicin has been shown to produce hyperalgesia and upregulation of the levels of proinflammatory cytokines. The present work aimed at investigating the possible mediation of these effects by sensory neuropeptides and mast cells. Various groups of rats received i.pl. injection of capsaicin alone or preceded by the injection of antagonists to substance P (SP), calcitonin gene-related protein (CGRP) and histamine (H1, H2) or the mast cell blocker ketotifen. All pretreatments prevented, in a dose-related manner, the capsaicin-induced hyperalgesia. The SP, H2 antagonists and ketotifen prevented the upregulation of all cytokines and nerve growth factor (NGF) levels, while the CGRP and H1 antagonists showed only attenuation of the NGF level.

Growth hormone releasing hormone reverses endotoxin-induced localized inflammatory hyperalgesia without reducing the upregulated cytokines, nerve growth factor and gelatinase activity

During inflammatory processes, the hypothalamic-pituitary axis is activated which can subsequently result in analgesia. For example, hypothalamic corticotrophin-releasing hormone (CRH) that is released during such activation has been attributed with analgesic actions. It is believed that the somatotrophic axis is also activated during inflammation. The aim of this study was to determine the analgesic actions of growth hormone-releasing hormone (GHRH), in a rat model of localized inflammatory hyperalgesia, induced by intraplantar (i.pl.) endotoxin (ET) injections. Pretreatment with intraperitoneal (i.p.) injections of GHRH (2, 5, 10 microg kg(-1)) 30 min before i.pl. ET injection (1.25 microg in 50 microl saline) prevented, in a dose-dependent manner, both mechanical hyperalgesia determined by the paw pressure (PP) test and thermal hyperalgesia determined by the hot plate (HP) and paw immersion (PI) tests. Pretreatment with GHRH had no significant effect on the elevated levels of the inflammatory mediators, interleukin (IL)-1beta, tumor necrosis factor (TNF)-alpha, IL-6 and nerve growth factor (NGF) due to i.pl. ET injection. No significant effect was obtained by pretreatment with GHRH, on the increased expression of gelatinase B due to ET injection. In conclusion, GHRH reverses inflammatory hyperalgesia in the rat without affecting the upregulated inflammatory mediators and these actions may be clinically important.

The effect of endotoxin on functional parameters of mammary CID-9 cells

The effect of endotoxin on mammary CID-9 cells, which differentiate in culture and express beta-casein, was investigated. Cells in culture supplemented with lactogenic hormones and dripped with EMS-Matrix (EMS-drip), were treated daily with endotoxin (0.5-500 microg/ml). Endotoxin at concentrations of less or equal to 10 microg/ml did not affect cell growth and viability up to 5 days post endotoxin treatment. Endotoxin (0.01-10 microg/ml) was added to the culture medium, upon confluence, and functional parameters were examined within 48 h post endotoxin treatment. Nuclear factor-kappaB (NF-kappaB) (p52) increased in nuclear extracts from endotoxin-stimulated cells within 1 h of treatment, while beta-casein mRNA and protein expression decreased in a concentration-dependent manner at 24 and 48 h post treatment. Zymography showed that the 72 and 92 kDa gelatinase activity increased in cells at 24 and 48 h post endotoxin treatment at 10 and 50 microg/ml. At the latter concentration, the active form of 72 kDa gelatinase was induced at 48 h. Interleukin-6 and tumor necrosis factor-alpha levels increased at 1-3 h post endotoxin treatment and peaked at 6 h in cells on plastic and EHS-drip. Nerve growth factor (NGF) levels increased in control and endotoxin-treated cells in a time-dependent manner, and endotoxin increased NGF levels in culture at 6 and 9 h post endotoxin treatment. This study shows that endotoxin activated NF-kappaB, suppressed beta-casein expression and upregulated gelatinases, cytokines and NGF. This model could be used to investigate the role of mammary cells in initiating and propagating inflammation and to test candidate molecules for potential anti-inflammatory properties.

Thymulin reverses inflammatory hyperalgesia and modulates the increased concentration of proinflammatory cytokines induced by i.c.v. endotoxin injection

The immunomodulatory thymic hormone thymulin has been shown previously to possess anti-inflammatory actions in the periphery. In this study, we have examined the effect of i.c.v. injections of either endotoxin (ET) or thymulin, in separate groups of conscious rats, on pain-related behavior and cytokine levels in different areas of the brain. Furthermore, we investigated the effect of pretreatment with either i.c.v. or i.p. injections of thymulin on endotoxin-induced hyperalgesia and the effect of pretreatment with i.c.v. thymulin on endotoxin-induced up-regulation of cytokine levels. Our results demonstrate that i.c.v. injection of endotoxin (1 microg in 5 microl saline) resulted in a significant decrease in the nociceptive thresholds as assessed by different pain tests, with peak hyperalgesia at 3 h. However, thymulin at different doses, when injected (i.c.v.), had no significant effect on pain related behavior. Pretreatment (i.c.v.) with thymulin (0.1, 0.5 and 1 microg in 5 microl saline) 20 min before endotoxin (i.c.v.) injection (1 microg in 5 microl saline) reduced, in a dose dependent manner, the endotoxin-induced hyperalgesia and exerted differential effects on the up-regulated levels of cytokines in different areas of the brain. The results provide behavioral and immunochemical characterization of a rat model for intracerebral inflammation and indicates a neuroprotective role for thymulin in the CNS.

A comparison of the pharmacological modulation of hyperalgesia and bronchial hyperresponsiveness

It has been proposed that there may be similarities in the mechanisms contributing toward hyperalgesia/allodynia observed in various clinical pain syndromes and bronchial hyperresponsiveness (BHR) in asthma. Both features are characterized by an increase in responsivity to various stimuli. In the case of pain, these include increase in responsiveness to mechanical and thermal stimuli whilst asthmatics bronchoconstrict in response to substances that are otherwise innocuous. A variety of mediators can induce hyperalgesia and pain when injected into the skin and these same mediators are also released during an inflammatory insult in the airways and in many cases can induce hyperresponsiveness experimentally. In this review, a comparison of the pharmacological modulation of afferent activity in hyperalgesia and in BHR will be made to ascertain whether any commonality exists between the treatment of these two disease states.

Interleukin-10 and the regulation of mitogen-activated protein kinases: are these signalling modules targets for the anti-inflammatory action of this cytokine?

The many specific, yet overlapping and redundant activities of individual cytokines have been the basis for current concepts of therapeutical intervention. Cytokines are powerful two-edged weapons that can trigger a cascade of reactions and may show activities that often go beyond the single highly specific property that it is hoped they possess. Nevertheless, it can be stated that our new, though burgeoning, understanding of the biological mechanisms governing cytokine actions is an important contribution to medical knowledge. The crucial role of the anti-inflammatory cytokine, interleukin (IL)-10, in regulating potential molecular pathway mediating injury and cell death has attracted paramount attention in recent years. In this respect, the mitogen-activated protein kinase (MAPK) components have emerged as potential signalling cascades that regulate a plethora of cell functions, including inflammation and cell death. The biochemistry and molecular biology of cytokine actions, particularly IL-10, explain some well known and sometimes also some of the more obscure clinical aspects of the evolution of diseases.

Cytokines and neuro-immune-endocrine interactions: a role for the hypothalamic-pituitary-adrenal revolving axis

Cytokines, peptide hormones and neurotransmitters, as well as their receptors/ligands, are endogenous to the brain, endocrine and immune systems. These shared ligands and receptors are used as a common chemical language for communication within and between the immune and neuroendocrine systems. Such communication suggests an immunoregulatory role for the brain and a sensory function for the immune system. Interplay between the immune, nervous and endocrine systems is most commonly associated with the pronounced effects of stress on immunity. The hypothalamic-pituitary-adrenal (HPA) axis is the key player in stress responses; it is well established that both external and internal stressors activate the HPA axis. Cytokines are chemical messengers that stimulate the HPA axis when the body is under stress or experiencing an infection. This review discusses current knowledge of cytokine signaling pathways in neuro-immune-endocrine interactions as viewed through the triplet HPA axis. In addition, we elaborate on HPA/cytokine interactions in oxidative stress within the context of nuclear factor-kappaB transcriptional regulation and the role of oxidative markers and related gaseous transmitters.

Upregulation of proinflammatory cytokines and nerve growth factor by intraplantar injection of capsaicin in rats

Capsaicin-sensitive primary afferents (CSPA) are known to be involved in nociception and neurogenic inflammation. Extensive research has been devoted to the sensory role of these fibres but less attention has been paid to their local effector function. This study aimed at gaining more insight into the molecular mechanisms underlying the neurogenic inflammation induced by this special group of afferent fibres. Different groups of rats (n = 5 in each group), either naive or subjected to selective ablation of their CSPA, received individual intraplantar injections of saline, capsaicin, its vehicle or capsaicin preceded by its antagonist, capsazepine. Acute tests for nociception were used to assess the variations of the nociceptive thresholds. Variations of the levels of proinflammatory cytokines and nerve growth factor (NGF) were measured by enzyme-linked immunosorbent assay (ELISA). Intraplantar injection of capsaicin (10 microg in 50 microl) produced a sustained thermal and mechanical hyperalgesia that peaked at 3-6 h and disappeared 24 h following the injection. Similar capsaicin injection in further groups of rats produced an early upregulation of the proinflammatory cytokines and NGF, which peaked at 30-60 min and returned to control levels within 2-5 h. Similar effects were observed following the application of either capsaicin or intense electrical stimulation on the cut end of the distal portion of the sciatic nerve. The effects of capsaicin were abolished in rats subjected to selective ablation of their CSPA. These results demonstrate that CSPA can simultaneously challenge the immune system through the release of proinflammatory mediators and the central nervous system through nociceptive signalling and can therefore serve as a common afferent pathway to both immune and nervous systems.

Potent analgesic and anti-inflammatory actions of a novel thymulin-related peptide in the rat

1. The present study examines the effect of PAT (peptide analogue of thymulin) in two rat models of inflammatory hyperalgesia induced by either i.pl. (1.25 microg in 50 microl saline) or i.p. (50 microg in 100 microl) injections of endotoxin ET. 2. Pretreatment with PAT (1, 5 or 25 microg in 100 microl saline, i.p.) decreased, in a dose dependent manner, both mechanical hyperalgesia, determined by the paw pressure (PP) test and thermal hyperalgesia determined by the hot plate (HP), the paw immersion (PI) and the tail flick (TF) tests. 3. Compared to the tripeptides K(D)PT and K(D)PV, known to antagonize interleukin (IL)-1beta or IL-1beta and PGE(2) mechanisms, PAT, at lower dosages, exerted stronger anti-hyperalgesic effects. 4. When compared with the effect of a steroidal (dexamethasone) and a non-steroidal (indomethacin) anti-inflammatory drugs (NSAID), PAT demonstrated equal analgesic actions. 5. Pretreatment with PAT, reduced significantly the increased concentration of IL-1beta, IL-6, TNF-alpha and NGF due to i.pl. injection of ET. 6. Injection of i.p. ET produced sickness behaviour characterized by hyperalgesia and fever. Pretreatment with PAT prevented the hyperalgesia and maintained the body temperature within the normal range and was accompanied by a down-regulation of the levels of pro-inflammatory cytokines and PGE(2) in the liver. 7. PAT, in all doses used, did not result in any evident changes in the physiological parameters or in the normal behaviour of the rats. 8. The anti-hyperalgesic and anti-inflammatory effects of PAT can be attributed, at least partially, to the down-regulation of pro-inflammatory mediators.

The role of the sympathetic efferents in endotoxin-induced localized inflammatory hyperalgesia and cytokine upregulation

The sympathetic system (SNS) is considered to be a major component of the neurogenic contribution to inflammation and hyperalgesia. We have investigated the role of the SNS in the local inflammatory pain induced by intraplantar (i.pl) injections of bacterial endotoxin (ET). Treatment of rats with an alpha-adrenoceptor antagonist (phentolamine, 0.25-1 mg/kg, i.p.), a beta-adrenoceptor antagonist (propranolol, 1-10 mg/kg, p.o.) or a sympathetic neuron-blocking agent (guanethedine, 30 mg/kg, s.c.) resulted in a dose-dependent reduction of the thermal hyperalgesia induced by ET. Mechanical hyperalgesia, however, was less sensitive to inhibition by propranolol and guanethedine but significantly inhibited by phentolamine. ET injection produced significant upregulation of tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), IL-6, and nerve growth factor (NGF). Treatment with any one of the three sympatholytics abolished the upregulation of NGF and IL-6, while phentolamine and guanethedine also reversed the upregulation of TNF-alpha. IL-1 beta was resistant to all of the sympatholytic treatments. We conclude that the SNS can contribute to the local inflammation and hyperalgesia following injection of ET. The resistance to sympatholytics shown by IL-1 beta, known to play a key role in the inflammatory cascade, suggests that ET can initiate inflammation and hyperalgesia independently of peripheral and central sympathetic mechanisms.

The involvement of L-gamma-glutamyl-L-cysteinyl-glycine (glutathione/GSH) in the mechanism of redox signaling mediating MAPK(p38)-dependent regulation of pro-inflammatory cytokine production

Redox regulation of mitogen-activated protein kinase (MAPK(p38))-mediated pro-inflammatory cytokine production is not well characterized in the alveolar epithelium. It was hypothesized that the involvement of the MAPK(p38) pathway in regulating lipopolysaccharide (LPS)-induced tumor necrosis factor (TNF)-alpha and interleukin-6 secretion is redox-sensitive and affected by NAC, an antioxidant and a precursor of glutathione, and L-buthionine-(S,R)-sulfoximine, an irreversible inhibitor of gamma-glutamylcysteine synthetase, the rate-limiting enzyme in GSH biosynthesis. Exposure of fetal alveolar type II epithelial cells to Escherichia coli-derived LPS induced, in a time-dependent manner, the phosphorylation/activation of MAPK(p38) (peak at 15min). In addition, LPS up-regulated the phosphorylation of MAPK(p38) in a dose-dependent manner. The effect of LPS on the MAPK(p38) pathway was associated with the activation of MAPK-activated protein kinase, which phosphorylated the small 27kDa heat-shock protein (Hsp27). LPS induced the phosphorylation of Hsp27 in a time- and dose-dependent manner. Selective blockage of the MAPK(p38) pathway by a pyridinyl-imidazole (SB-203580) abrogated LPS-induced release of TNF-alpha and IL-6. Pre-treatment with NAC reduced LPS-mediated secretion of TNF-alpha and IL-6. Incubation of cells with NAC induced intracellular accumulation of GSH, but reduced the concentration of GSSG. On the other hand, pre-treatment with BSO augmented LPS-mediated secretion of TNF-alpha and IL-6. In addition, BSO induced intracellular accumulation of GSSG, but reduced the concentration of GSH. Whereas NAC blocked the phosphorylation/activation of MAPK(p38), BSO amplified the LPS-mediated effect on MAPK(p38). These results indicated that intracellular redox signaling plays an important role in regulating LPS-induced activation of the MAPK(p38) pathway and MAPK(p38)-mediated regulation of LPS-dependent inflammatory cytokine production in the alveolar epithelium.

Redox/ROS regulation of lipopolysaccharide-induced mitogen-activated protein kinase (MAPK) activation and MAPK-mediated TNF-alpha biosynthesis

Redox and ROS regulation of MAPK-mediated TNF-alpha biosynthesis is not well characterized. It was hypothesized that the involvement of the MAPK pathway in regulating LPS-mediated TNF-alpha secretion is redox-dependent, NF-kappaB-sensitive and attenuated by N-acetyl-L-cysteine (NAC) and other antioxidants. In alveolar epithelial cells, LPS induced a time- and dose-dependent phosphorylation of MAPK(p38). This was associated with the activation of MAPK-activated protein kinase, which phosphorylated the small heat-shock protein, Hsp27. MAPK(p38) inhibition (SB-203580) abrogated LPS-induced TNF-alpha production. MAPK(ERK) blockade (PD-98059) attenuated TNF-alpha secretion, an effect synergistically amplified in the presence of SB-203580. Regulation of NF-kappaB by selective inhibitors revealed that this pathway is partially involved in regulating LPS-mediated TNF-alpha secretion. Whereas the proteasome inhibitor, MG-132, had no effect on LPS-mediated TNF-alpha production, CAPE, sulfasalazine and SN-50, a cell-permeant NF-kappaB inhibitor, attenuated but did not abrogate TNF-alpha biosynthesis. LPS up-regulated ROS, an effect abrogated by 4'-hydroxy-3'-methoxy-acetophenone and NAC, which reduced TNF-alpha secretion, induced the accumulation of GSH, reduced the concentration of GSSG, and blockaded the phosphorylation/activation of MAPK(p38) pathway. ROS induced MAPK(p38) phosphorylation and selective antioxidants, including the permeant GSH precursor, gamma-GCE, reduced ROS-dependent MAPK(p38) phosphorylation. These results indicate that the MAPK pathway and MAPK-mediated regulation of TNF-alpha production is redox-dependent, GSH-mediated and requires, at least in part, a NF-kappaB/ROS-sensitive mechanism.

Nociceptor sensitization by extracellular signal-regulated kinases

Inflammatory pain, characterized by a decrease in mechanical nociceptive threshold (hyperalgesia), arises through actions of inflammatory mediators, many of which sensitize primary afferent nociceptors via G-protein-coupled receptors. Two signaling pathways, one involving protein kinase A (PKA) and one involving the epsilon isozyme of protein kinase C (PKCepsilon), have been implicated in primary afferent nociceptor sensitization. Here we describe a third, independent pathway that involves activation of extracellular signal-regulated kinases (ERKs) 1 and 2. Epinephrine, which induces hyperalgesia by direct action at beta(2)-adrenergic receptors on primary afferent nociceptors, stimulated phosphorylation of ERK1/2 in cultured rat dorsal root ganglion cells. This was inhibited by a beta(2)-adrenergic receptor blocker and by an inhibitor of mitogen and extracellular signal-regulated kinase kinase (MEK), which phosphorylates and activates ERK1/2. Inhibitors of G(i/o)-proteins, Ras farnesyltransferases, and MEK decreased epinephrine-induced hyper-algesia. In a similar manner, phosphorylation of ERK1/2 was also decreased by these inhibitors. Local injection of dominant active MEK produced hyperalgesia that was unaffected by PKA or PKCepsilon inhibitors. Conversely, hyperalgesia produced by agents that activate PKA or PKCepsilon was unaffected by MEK inhibitors. We conclude that a Ras-MEK-ERK1/2 cascade acts independent of PKA or PKCepsilon as a novel signaling pathway for the production of inflammatory pain. This pathway may present a target for a new class of analgesic agents.

Nociceptor sensitization by extracellular signal-regulated kinases

Inflammatory pain, characterized by a decrease in mechanical nociceptive threshold (hyperalgesia), arises through actions of inflammatory mediators, many of which sensitize primary afferent nociceptors via G-protein-coupled receptors. Two signaling pathways, one involving protein kinase A (PKA) and one involving the epsilon isozyme of protein kinase C (PKCepsilon), have been implicated in primary afferent nociceptor sensitization. Here we describe a third, independent pathway that involves activation of extracellular signal-regulated kinases (ERKs) 1 and 2. Epinephrine, which induces hyperalgesia by direct action at beta(2)-adrenergic receptors on primary afferent nociceptors, stimulated phosphorylation of ERK1/2 in cultured rat dorsal root ganglion cells. This was inhibited by a beta(2)-adrenergic receptor blocker and by an inhibitor of mitogen and extracellular signal-regulated kinase kinase (MEK), which phosphorylates and activates ERK1/2. Inhibitors of G(i/o)-proteins, Ras farnesyltransferases, and MEK decreased epinephrine-induced hyper-algesia. In a similar manner, phosphorylation of ERK1/2 was also decreased by these inhibitors. Local injection of dominant active MEK produced hyperalgesia that was unaffected by PKA or PKCepsilon inhibitors. Conversely, hyperalgesia produced by agents that activate PKA or PKCepsilon was unaffected by MEK inhibitors. We conclude that a Ras-MEK-ERK1/2 cascade acts independent of PKA or PKCepsilon as a novel signaling pathway for the production of inflammatory pain. This pathway may present a target for a new class of analgesic agents.

The biphasic immunoregulation of pyrimidylpiperazine (Y-40138) is IL-10 sensitive and requires NF-kappa B targeting in the alveolar epithelium

1. Pyrimidylpiperazine (Y-40138), a synthetic derivative of N-[1-(4-([4-(pyrimidin-2-yl)piperazin-1-yl]methyl)phenyl)cyclopropyl] acetamide, is a novel dual regulator of pro- and anti-inflammatory cytokines in vivo. The aim of the present study was to determine the signal transduction mechanisms implicated in vitro. 2. In alveolar epithelial cells, pre-treatment (30 min) with Y-40138 reduced LPS-induced biosynthesis of IL-1 beta, IL-6 and TNF-alpha, an effect paralleled by up-regulating an anti-inflammatory counter-loop mediated through IL-10. 3. This differential regulation of pro- and anti-inflammatory signals was accompanied by an inhibition of the nuclear localization of selective NF-kappa B subunits, particularly NF-kappa B(1) (p50), RelA (p65), the major transactivating member of the Rel family, RelB (p68) and c-Rel (p75). In addition, Y-40138 blockaded, in a dose-dependent manner, the LPS-induced nuclear activation of NF-kappa B. 4. Analysis of the upstream pathway involved in Y-40138-dependent retardation of LPS-induced NF-kappa B translocation/activation revealed the involvement of an I kappa B-alpha sensitive pathway. Pre-treatment with Y-40138 ameliorated LPS-induced degradation of I kappa B-alpha in the cytosolic compartment and retarded its phosphorylation, suggesting the involvement of an upstream kinase. 5. Recombinant IL-10 (0 -- 10 ng ml(-1)) blockaded, in a dose-dependent manner, LPS-induced biosynthesis of IL-1 beta, IL-6 and TNF-alpha. Furthermore, rhIL-10 reduced the DNA binding activity of NF-kappa B. Immunoneutralization of endogenous IL-10 by a polyclonal alpha IL-10 (5 microg ml(-1)) reversed the inhibitory effect of Y-40138 on pro-inflammatory cytokines and partially restored the DNA binding activity of NF-kappa B. 6. These results indicate that Y-40138 mediated dual immunoregulation of pro- and anti-inflammatory cytokines is IL-10 sensitive and mediated through the I kappa B-alpha/NF-kappa B signal transduction pathway.

Alpha-melanocyte-related tripeptide, Lys-d-Pro-Val, ameliorates endotoxin-induced nuclear factor kappaB translocation and activation: evidence for involvement of an interleukin-1beta193-195 receptor antagonism in the alveolar epithelium

The potential anti-inflammatory role of alpha-melanocyte-stimulating hormone (alpha-MSH)-related tripeptide, lysine(11)-D-proline-valine(13) (KDPV), an analogue of interleukin (IL)-1beta(193-195) and an antagonist of IL-1beta/prostaglandin E(2), is not well characterized in the alveolar epithelium. In a model of foetal alveolar type II epithelial cells in vitro, we showed that lipopolysaccharide endotoxin (LPS) differentially, but selectively, induced the nuclear subunit composition of nuclear factor kappaB(1) (NF-kappaB(1)) (p50), RelA (p65) and c-Rel (p75), in parallel to up-regulating the DNA-binding activity (supershift indicating the presence of the p50-p65 complex). LPS accelerated the degradation of inhibitory kappaB-alpha (IkappaB-alpha), accompanied by enhancing its phosphorylation in the cytosolic compartment but not in the nucleus. KDPV suppressed, in a dose-dependent manner, the nuclear localization of p50, p65 and p75, an effect that led to the subsequent inhibition of NF-kappaB activation. Interleukin-1 receptor antagonist (IL-1ra) decreased the nuclear abundance of p50, p65 and p75, and subsequently depressed the DNA-binding activity induced by LPS. Analysis of the mechanism involved in the KDPV- and IL-1ra-mediated inhibition of NF-kappaB nuclear localization revealed a reversal in IkappaB-alpha phosphorylation and degradation, followed by cytosolic accumulation. LPS induced endogenous IL-1beta biosynthesis in a time-dependent manner; the administration of exogenous recombinant human interleukin 1 (rhIL-1) resulted in a dose-dependent activation of NF-kappaB. KDPV and IL-1ra abrogated the effect of rhIL-1. Pretreatment with the non-steroidal anti-inflammatory drug (NSAID) indomethacin, an inhibitor of cyclo-oxygenase, blocked the LPS-induced activation of NF-kappaB. These results indicate the involvement of prostanoid-dependent (NSAID-sensitive) and IL-1-dependent (IL-1ra-sensitive) mechanisms mediating LPS-induced NF-kappaB translocation and activation, a pathway that is regulated, in part, by a negative feedback mechanism transduced through IkappaB-alpha, the major cytosolic inhibitor of NF-kappaB.

Chemioxyexcitation (delta pO2/ROS)-dependent release of IL-1 beta, IL-6 and TNF-alpha: evidence of cytokines as oxygen-sensitive mediators in the alveolar epithelium

The signalling mechanisms in oxidative stress mediated by cytokines in the perinatal alveolar epithelium are not well known. In an in vitro model of fetal alveolar type II epithelial cells, we investigated the profile of cytokines in response to ascending Deltap O(2)regimen (oxyexcitation). The peak of TNF-alpha (4 h) preceded IL-1beta and IL-6 (6-9 h), indicating a positive feedback autocrine loop confirmed by exogenous rmTNF-alpha. Reactive oxygen species (ROS) induced a dose-dependent release of cytokines, an effect specifically obliterated by selective antioxidants of the hydroxyl radical (*OH) and superoxide anion (O(2)-). Actinomycin and cycloheximide blocked the induced production of cytokines, implicating transcriptional and translational control. Whilst the dismutating enzymes superoxide dismutase (SOD) and catalase were ineffective in reducing ROS-induced cytokines, MnP, a cell-permeating SOD mimetic, abrogated xanthine/xanthine oxidase-dependent cytokine release. Desferrioxamine mesylate, which inhibits the iron-catalysed generation of *OH via the Fenton reaction, exhibited a mild effect on the release of cytokines. Dynamic variation in alveolar p O(2)constitutes a potential signalling mechanism within the perinatal lung allowing upregulation of cytokines in an ROS-dependent manner.

Modulation of ultraviolet-induced hyperalgesia and cytokine upregulation by interleukins 10 and 13

1. Exposure to midrange ultraviolet radiation (UVB) is known to produce skin inflammation similar to sunburn. The aim of this study was to characterize the hyperalgesia and cytokine upregulation induced by UVB and their modulation by antiinflammatory cytokines. 2. Acute exposure of the dorsal skin of mice to UVB (200, 250 and 300 mJ cm(2)) resulted in a dose-dependent decrease in the latencies of the hot plate and tail flick tests, without evident signs of skin lesions. 3. The observed hyperalgesia displayed a biphasic temporal evolution with an acute phase (3 - 6 h) and a late (48 - 96 h) phase. 4. Exposure to UVB (300 mJ cm(2)) elicited significant upregulation of interleukin (IL)-1 beta, tumour necrosis factor (TNF)-alpha and nerve growth factor (NGF), determined by ELISA in the exposed skin. This upregulation was more important during the acute phase of hyperalgesia. 5. Daily treatment of mice, with i.p. injections of either IL-10 or IL-13 (1.5, 7.5 and 15 ng in 100 microl saline) produced a dose-dependent attenuation of the UVB-induced hyperalgesia. 6. Treatment with the highest doses of either IL-10 or IL-13, produced significant attenuation of the levels of the cytokines and NGF by UVB, with relatively more pronounced effects by IL-13. 7. Acute exposure to moderate amounts of UVB results in a systemic hyperalgesia related to the upregulation of cytokine and NGF levels, since both were prevented by treatment with antiinflammatory cytokines.

Systemic lipopolysaccharide influences rectal sensitivity in rats: role of mast cells, cytokines, and vagus nerve

Intraperitoneal lipopolysaccharide (LPS) produces somatic hyperalgesia, releases interleukin (IL)-1beta and tumor necrosis factor-alpha (TNF-alpha), and activates vagal afferents. The aim of this study was to evaluate the effect of peripheral LPS on rectal sensitivity and to specify the mechanisms involved. Abdominal muscle contractions were recorded in conscious rats equipped with intramuscular electrodes. Rectal distension (RD) was performed at various times after LPS or experimental treatments. In controls, RD significantly increased the number of abdominal contractions from a threshold volume of distension of 0.8 ml. At the lowest volume (0.4 ml), this number was increased after administration of LPS (3, 9, and 12 h later), recombinant human IL-1beta (from 3 to 9 h), recombinant bovine TNF-alpha (from 6 to 9 h), and BrX-537A (from 6 to 12 h), a mast cell degranulator. The effect of LPS was reduced by doxantrazole, Lys-D-Pro-Thr, and soluble recombinant TNF receptor. Vagotomy selectively amplified the response to LPS. We conclude that, in vivo, intraperitoneal LPS lowers visceral pain threshold (allodynia) through a mechanism involving mast cell degranulation and IL-1beta and TNF-alpha release and that the vagus nerve may exert a tonic protective role against LPS-induced rectal allodynia.

The role of cytokines and prostaglandin-E(2) in thymulin induced hyperalgesia

We have recently reported that intraperitoneal (i.p.) injection of thymulin at low doses (50 ng) resulted in thermal and mechanical hyperalgesia and upregulation of the level of interleukin-1beta in the liver. In this study, we demonstrate that such injections of thymulin result in a significant elevation in the levels of TNF-alpha (P<0.01), NGF (P<0.01) and PGE(2) (P<0.01) in the liver of the treated rats, in addition to the increase in the levels of IL-1beta. Pretreatment with specific antagonists to each of these factors (polyclonal anti-TNF-alpha, anti-NGF antiserum and IL-1 receptor antagonist) did not result in the abolition of the hyperalgesia as assessed by the paw pressure, hot plate, paw immersion and tail flick tests. However, pretreatment with a combination of the above antagonist and antisera almost completely prevented thymulin-induced hyperalgesia. The cyclooxygenase inhibitor, meloxicam, reversed in a dose dependent manner (0.2, 0.4 and 2 mg/kg) thymulin effects as assessed by the different pain tests. It also abolished the thymulin-induced increase in the level of cytokines and NGF in the liver. Our results indicate that PGE(2) could be the key mediator of the hyperalgesic action of thymulin and the observed upregulation of proinflammatory cytokines and NGF.

Functional interplay between gelatinases and hyperalgesia in endotoxin-induced localized inflammatory pain

The role of ECM-degrading proteinases in normal developmental processes and in pathological conditions is extensively studied. However, few reports describe the role ECM-degrading proteinases play in modulating hyperalgesia. The goal of this study is to describe the regulation of gelatinases during endotoxin mediated local inflammation, induced by intra plantar endotoxin (ET; 1.25 microg/50 microl) injection in Balb/c mice, and to correlate that with hyperalgesia. ET injections induced hyperalgesia, as determined by hot plate and paw pressure tests, which peaked by 24 h and recovered by 48 h post-injection. Contralateral paw of ET injected mice and saline injected paws in control mice elicited no hyperalgesia. Zymography showed that ET and saline injected paws elicited increased gelatinase activity by 9 h after injection. However, only the former maintained high levels of expression of a 90 kD gelatinase up to at least 96 h post ET injection, while in the latter gelatinase expression was down regulated by 24 h. Interestingly, the 90-kD gelatinase was upregulated in the contralateral paw of the ET-injected mice beyond 48 h post injection. Saline injection in that paw, during a time when gelatinases are upregulated, induced hyperalgesia. Intraperitoneal injection of either ZnCl(2) (100 microM), thymulin (5 microg/100 microl), or morphine (2 mg/kg/100 microl) reversed the ET-induced hyperalgesia and suppressed gelatinase activity. Furthermore, intraperitoneal injection of MPI, an ECM-degrading proteinase inhibitor, reversed ET induced hyperalgesia. Taken together, the above suggests that a functional interplay exists between gelatinase upregulation triggered by ET injections and hyperalgesia. The exact mechanism underlying such correlation remains to be determined.

The induction of pain: an integrative review

The highly disagreeable sensation of pain results from an extraordinarily complex and interactive series of mechanisms integrated at all levels of the neuroaxis, from the periphery, via the dorsal horn to higher cerebral structures. Pain is usually elicited by the activation of specific nociceptors ('nociceptive pain'). However, it may also result from injury to sensory fibres, or from damage to the CNS itself ('neuropathic pain'). Although acute and subchronic, nociceptive pain fulfils a warning role, chronic and/or severe nociceptive and neuropathic pain is maladaptive. Recent years have seen a progressive unravelling of the neuroanatomical circuits and cellular mechanisms underlying the induction of pain. In addition to familiar inflammatory mediators, such as prostaglandins and bradykinin, potentially-important, pronociceptive roles have been proposed for a variety of 'exotic' species, including protons, ATP, cytokines, neurotrophins (growth factors) and nitric oxide. Further, both in the periphery and in the CNS, non-neuronal glial and immunecompetent cells have been shown to play a modulatory role in the response to inflammation and injury, and in processes modifying nociception. In the dorsal horn of the spinal cord, wherein the primary processing of nociceptive information occurs, N-methyl-D-aspartate receptors are activated by glutamate released from nocisponsive afferent fibres. Their activation plays a key role in the induction of neuronal sensitization, a process underlying prolonged painful states. In addition, upon peripheral nerve injury, a reduction of inhibitory interneurone tone in the dorsal horn exacerbates sensitized states and further enhance nociception. As concerns the transfer of nociceptive information to the brain, several pathways other than the classical spinothalamic tract are of importance: for example, the postsynaptic dorsal column pathway. In discussing the roles of supraspinal structures in pain sensation, differences between its 'discriminative-sensory' and 'affective-cognitive' dimensions should be emphasized. The purpose of the present article is to provide a global account of mechanisms involved in the induction of pain. Particular attention is focused on cellular aspects and on the consequences of peripheral nerve injury. In the first part of the review, neuronal pathways for the transmission of nociceptive information from peripheral nerve terminals to the dorsal horn, and therefrom to higher centres, are outlined. This neuronal framework is then exploited for a consideration of peripheral, spinal and supraspinal mechanisms involved in the induction of pain by stimulation of peripheral nociceptors, by peripheral nerve injury and by damage to the CNS itself. Finally, a hypothesis is forwarded that neurotrophins may play an important role in central, adaptive mechanisms modulating nociception. An improved understanding of the origins of pain should facilitate the development of novel strategies for its more effective treatment.

Interleukin-1 and nociception in the rat

It has recently become accepted that several cytokines may affect peripheral and central nervous system functions. Consistently with these findings, accumulating evidence points toward an important role for interleukin- in the modulation of nociceptive information. Here we review the observations collected after the administration of this cytokine by intracerebroventricular, intrathecal or peripheral route in rats. Taken together, these data suggest that IL-1 can differently affect pain responsivity depending on the dose and the site of action, and clearly demonstrate that this immune factor is deeply involved in the modulation of neuronal functions.

Interleukin-10 reduces the endotoxin-induced hyperalgesia in mice

In the endotoxin-induced inflammation, interleukin-10 reduced significantly, and in a dose-dependent manner, the inflammatory pain as assessed by mechanical and thermal tests. The levels of Tumour Necrosis Factor (TNF)alpha and NGF were upregulated at 1.5 h whereas those of IL-1beta at 6 h after ET injection. IL-10 downregulated the levels of TNFalpha (from 4974.75 +/- 875.78 to 1008 +/- 350 pg/hind paw), NGF (from 352.9 +/- 46.7 to 33.9 +/- 2.4 pg/hind paw) and IL-1beta (from 2773.88 +/- 423.96 to 1108 +/- 399.56 pg/hind paw). These data suggest that IL-10 inhibits ET-induced hyperalgesia by downregulation of TNFalpha, IL-1beta and NGF production.