Antinociceptive effects of tumor necrosis factor alpha neutralization in a rat model of antigen-induced arthritis: evidence of a neuronal target

Surgical synovectomy decreases density of sensory nerve fibers in synovial tissue of non-inflamed controls and rheumatoid arthritis patients

Surgical synovectomy is a technique to treat synovitis and pain in patients with rheumatoid arthritis (RA) resistant to DMARDs or therapy with biologics. Indication to synovectomy is subject to tight cooperation of orthopaedic surgeons and rheumatologists. It was thought that synovectomy leads to a reduction of sensory nerve fibers, called sensory denervation. Since sensory denervation after synovectomy has never been histologically tested, we aimed to investigate sensory and sympathetic innervation in synovial tissue before and after synovectomy. Eight non-inflamed control subjects and eight patients with RA were included in this study with a two-stage synovectomy approach (interval 40–50 days). Nerve fibers and cells in synovial tissue were detected and counted using immunofluorescence. Density of sympathetic nerve fibers did not change after synovectomy, whereas density of sensory nerve fibers decreased in all control subjects and seven of eight patients with RA. In parallel, the density of synovial cells increased after synovectomy in all control subjects and six of eight RA patients, which is indicative of a wound healing response. In one female RA patient, density of sensory nerve fibers increased and a very marked rise of cellular density was observed, too. This indicates that probably not all patients profit from surgical synovectomy. The majority of patients (94%) demonstrated sensory denervation after surgical synovectomy accompanied by a wound healing cell response. This study can help to explain the positive effects of surgical synovectomy which usually leads to pain reduction and improved mobility.

Blockade of TNF-α rapidly inhibits pain responses in the central nervous system

There has been a consistent gap in understanding how TNF-α neutralization affects the disease state of arthritis patients so rapidly, considering that joint inflammation in rheumatoid arthritis is a chronic condition with structural changes. We thus hypothesized that neutralization of TNF-α acts through the CNS before directly affecting joint inflammation. Through use of functional MRI (fMRI), we demonstrate that within 24 h after neutralization of TNF-α, nociceptive CNS activity in the thalamus and somatosensoric cortex, but also the activation of the limbic system, is blocked. Brain areas showing blood-oxygen level-dependent signals, a validated method to assess neuronal activity elicited by pain, were significantly reduced as early as 24 h after an infusion of a monoclonal antibody to TNF-α. In contrast, clinical and laboratory markers of inflammation, such as joint swelling and acute phase reactants, were not affected by anti-TNF-α at these early time points. Moreover, arthritic mice overexpressing human TNF-α showed an altered pain behavior and a more intensive, widespread, and prolonged brain activity upon nociceptive stimuli compared with wild-type mice. Similar to humans, these changes, as well as the rewiring of CNS activity resulting in tight clustering in the thalamus, were rapidly reversed after neutralization of TNF-α. These results suggest that neutralization of TNF-α affects nociceptive brain activity in the context of arthritis, long before it achieves anti-inflammatory effects in the joints.

In vivo molecular imaging of experimental joint inflammation by combined (18)F-FDG positron emission tomography and computed tomography

Introduction

The purpose of this work was to establish and validate combined small animal positron emission tomography - computed tomography (PET/CT) as a new in vivo imaging method for visualisation and quantification of joint inflammation.

Methods

Signalling of radioisotope ¹⁸F labelled Fluorodeoxyglucose (¹⁸F-FDG) injected in mice with glucose-6-phosphate isomerase (G6PI)-induced arthritis was analysed by PET/CT. Accumulation of ¹⁸F-FDG in tissue was quantified by PET measurement, whereas high definition CT delivered anatomical information. The fusion of both images revealed in detail spatial and temporal distribution and metabolism of ¹⁸F-FDG.

Results

A distinct ¹⁸F-FDG signal could be measured by PET in carpal and tarsal joints, from mice with early or established arthritis. In contrast, no accumulation of ¹⁸F-FDG was detectable before arthritis onset. Comparison of ¹⁸F-FDG joint uptake with histopathological evaluation revealed a significant correlation of both methods.

Conclusions

Small animal PET/CT using ¹⁸F-FDG is a feasible method for monitoring and, more importantly, quantitative assessment of inflammation in G6PI-arthritis. Since it is possible to perform repeated non-invasive measurements in vivo, not only numbers of animals in preclinical studies can markedly be reduced by this method, but also longitudinal studies come into reach, e. g. for individual flare-up reactions or monitoring therapy response in progressive arthritis.

Characterization of the acute and persistent pain state present in K/BxN serum transfer arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune arthritis that affects approximately 1% of the population. Synovial inflammation cannot fully explain the level of pain reported by patients and facilitation of pain processing at the spinal level has been implicated. We characterized the K/BxN serum transfer arthritis model as a model of joint inflammation-induced pain and examined pharmacologic responsiveness and spinal glia activation. Mechanical allodynia developed congruently with joint swelling. Surprisingly, allodynia persisted after resolution of inflammation. At the peak of joint inflammation (days 4-10), hypersensitivity was attenuated with i.p. etanercept, gabapentin, and ketorolac. Following resolution of synovial inflammation (days 19-23), only gabapentin relieved allodynia. The superficial dorsal horn of arthritic mice displayed increased staining of microglia at early and late time points, but astrocyte staining increased only during the inflammatory phase. ATF3, a marker of nerve injury, was significantly increased in the lumbar dorsal root ganglia during the late phase (day 28). Hence, serum transfer in the K/BxN serum transfer arthritis model produces a persistent pain state, where the allodynia during the inflammatory state is attenuated by TNF and prostaglandin inhibitors, and the pharmacology and histochemistry data suggest a transition from an inflammatory state to a state that resembles a neuropathic condition over time. Therefore, the K/BxN serum transfer model represents a multifaceted model for studies exploring pain mechanisms in conditions of joint inflammation and may serve as a platform for exploring novel treatment strategies for pain in human arthritic conditions.

[The role of TNF-alpha as pain mediator]

Tumor necrosis factor (TNF)-alpha is not only a proinflammatory mediator but also a pain mediator. Numerous nociceptors express the TNF receptors 1 and 2. By a direct action at the nociceptor TNF-alpha is involved in the generation and maintenance of inflammation-related pain.

Local metabolism of glucocorticoids and its role in rat adjuvant arthritis

11beta-Hydroxysteroid dehydrogenase 1 (11HSD1) regulates local glucocorticoid activity and plays an important role in various diseases. Here, we studied whether arthritis modulates 11HSD1, what is the role of pro-inflammatory cytokines in this process and whether altered local metabolism of glucocorticoids may contribute to the feedback regulation of inflammation. Adjuvant arthritis increased synovial 11HSD1 mRNA and 11-reductase activity but treatments with tumor necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta) antagonists etanercept and anakinra reduced 11HSD1 upregulation. Treatment with carbenoxolone, an 11HSD inhibitor, increased expression of TNF-alpha, cyclooxygenase 2, and osteopontin mRNA without any changes in the plasma levels of corticosterone. Similar changes were observed when arthritic rats were treated with RU486, an antagonist of GR. This study suggests that arthritis upregulates synovial 11HSD1, this upregulation is controlled by TNF-alpha and IL-1beta and that the increased supply of local corticosterone might contribute to feedback regulation of inflammation.

Differential effects of locally and systemically administered soluble glycoprotein 130 on pain and inflammation in experimental arthritis

INTRODUCTION

Interleukin-6 (IL-6) is a key player in systemic arthritis, involved in inflammation and joint destruction. IL-6 signalling has also been revealed in nerve cells. Recently, IL-6 and in particular IL-6 together with its soluble IL-6 receptor (sIL-6R) were shown to induce a long-lasting robust sensitization of joint nociceptors for mechanical stimuli which was difficult to reverse, suggesting that IL-6 signalling plays a significant role in the generation and maintenance of arthritic pain. Here we tested in a preclinical model of arthritis, antigen-induced arthritis (AIA) in the rat, whether systemic or local neutralization of IL-6/sIL-6R complexes with soluble glycoprotein 130 (sgp130) alters arthritic pain and how sgp130 influences the inflammatory process in AIA.

METHODS

Rats with AIA were either treated with sgp130 or saline intra-peritoneally or intra-articularly (each group n = 9). Then, pain-related and locomotor behaviour, as well as joint swelling, were measured during an observation period of 21 days, followed by histopathological end-point analysis for inflammatory and destructive changes.

RESULTS

A single intra-articular application of sgp130 at the time of AIA induction barely reduced the development of AIA, but significantly attenuated pain-related behaviour, that is, primary mechanical hyperalgesia in the acute phase of AIA. By contrast, repeated systemic application of sgp130 after onset of AIA only slightly attenuated pain at a late stage of AIA. None of the treatments reduced secondary hyperalgesia. Furthermore, in the present study joint destruction at 21 days was significantly attenuated after intra-articular sgp130 treatment, but not after systemic sgp130.

CONCLUSIONS

In addition to its role in chronic inflammation, IL-6 in the joint plays a significant role in the generation and maintenance of arthritic joint pain at acute and chronic stages of AIA. The particular effectiveness of intra-articular injection of sgp130 indicates, first, that IL-6/sIL-6R in the inflamed joint, rather than circulating IL-6/sIL-6R, is responsible for the generation of hyperalgesia, and, second, that early neutralization of IL-6/sIL-6R is particularly successful in producing antinociception. Furthermore, neutralization of IL-6/sIL-6R (and possibly other cytokines which use the transmembrane signal-transducing subunit gp130) directly at the site of joint inflammation seems to be effective in the prevention of joint destruction.

Spinal tumor necrosis factor alpha neutralization reduces peripheral inflammation and hyperalgesia and suppresses autonomic responses in experimental arthritis: a role for spinal tumor necrosis factor alpha during induction and maintenance of peripheral inflammation

OBJECTIVE

In addition to the sensitization of pain fibers in inflamed tissues, the increased excitability of the spinal cord is an important mechanism of inflammatory pain. Furthermore, spinal neuronal excitability has been suggested to play a role in modulating peripheral inflammation. This study was undertaken to test the hypothesis that spinal actions of the proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) add significantly to both hyperalgesia and maintenance of peripheral inflammation.

METHODS

Rats with antigen-induced arthritis (AIA) were treated intrathecally with the TNFalpha-neutralizing compound etanercept continuously during the complete time course of AIA, which was 3 days for the acute phase and 21 days for the chronic phase. During this time, inflammation and pain-related behavior were monitored. Since a role for autonomic control of inflammation was proposed, measures from heart rate time series were obtained in the acute phase. Findings were compared with those in vehicle-treated animals and in animals receiving etanercept intraperitoneally.

RESULTS

Spinally administered etanercept acutely reduced pain-related behavior, attenuated both the development and the maintenance of inflammation, and was superior to systemic administration. Parameters indicating autonomic modulation showed a shift toward a sympathetically dominated state in vehicle-treated animals, which was prevented by intrathecal etanercept.

CONCLUSION

Our findings indicate that spinal TNFalpha plays an important role in both pain signaling and modulation of peripheral inflammation. Thus, neutralizing this cytokine at the spinal site not only represents a putative therapeutic option for different pain syndromes, but may be directly used to attenuate peripheral inflammation.

Spinally applied ketamine or morphine attenuate peripheral inflammation and hyperalgesia in acute and chronic phases of experimental arthritis

Inflammation causes sensitization of peripheral and central nociceptive neurons. Pharmacological modulation of the latter has successfully been used for clinical pain relief. In particular, inhibitors of the NMDA glutamate receptor such as ketamine and agonists at the mu-opioid receptor such as morphine are broadly used. Besides driving the propagation of pain signals, spinal mechanisms are also discussed to modulate inflammation in the periphery. Here, we tested the hypothesis that intrathecally applied ketamine or morphine not only reduce pain-related behavior, but also attenuate induction and maintenance of the inflammatory response in a model of chronic antigen-induced arthritis (AIA). Ketamine, morphine or vehicle was applied to the spinal cords of anesthesized animals with AIA. Swelling and histopathological changes were assessed after 6h (acute phase). Intrathecal catheters were implanted in another set of animals with AIA and substances were applied continuously. During the observation period of 21 days, inflammation and pain-related behavior were assessed. Ketamine and morphine significantly reduced arthritis severity as indicated by reduced joint swelling, but even more intriguingly by reduced infiltration with inflammatory cells and joint destruction in the acute and the chronic phase of arthritis. Morphine showed strong antinociceptive effects in the acute phase only, while the newly established effective dose for ketamine in a continuous application design reduced hyperalgesia in the acute and the chronic stage. In conclusion, both compounds exhibit anti-inflammatory effects during induction and maintenance of arthritis when applied intrathecally. These data thus propose a role of spinal NMDA- and opioid-receptors in the neuronal control of immune-mediated inflammation.

Involvement of the Toll-like receptor 4 pathway and use of TNF-alpha antagonists for treatment of the mucopolysaccharidoses

Enzyme replacement therapy is currently available for three of the mucopolysaccharidoses (MPSs) but has limited effects on the skeletal lesions. We investigated the involvement of the Toll-like receptor 4 (TLR4) signaling pathway in the pathogenesis of MPS bone and joint disease, and the use of the anti-TNF-alpha drug, Remicade (Centocor, Inc.), for treatment. TLR4 KO (TLR4(lps-/-)) mice were interbred with MPS VII mice to produce double-KO (DKO) animals. The DKO mice had longer and thinner faces and longer femora as revealed by micro-computed tomography analysis compared with MPS VII mice. Histological analyses also revealed more organized and thinner growth plates. The serum levels of TNF-alpha were normalized in the DKO animals, and the levels of phosphorylated STAT1 and STAT3 in articular chondrocytes were corrected. These findings led us to evaluate the effects of Remicade in MPS VI rats. When initiated at 1 month of age, i.v. treatment prevented the elevation of TNF-alpha, receptor activator of NF-kappaB, and other inflammatory molecules not only in the blood but in articular chondrocytes and fibroblast-like synoviocytes (FLSs). Treatment of 6-month-old animals also reduced the levels of these molecules to normal. The number of apoptotic articular chondrocytes in MPS VI rats was similarly reduced, with less infiltration of synovial tissue into the underlying bone. These studies revealed the important role of TLR4 signaling in MPS bone and joint disease and suggest that targeting TNF-alpha may have positive therapeutic effects.

IL-17 mediates articular hypernociception in antigen-induced arthritis in mice

IL-17 is an important cytokine in the physiopathology of rheumatoid arthritis (RA). However, its participation in the genesis of nociception during RA remains undetermined. In this study, we evaluated the role of IL-17 in the genesis of articular nociception in a model of antigen (mBSA)-induced arthritis. We found that mBSA challenge in the femur-tibial joint of immunized mice induced a dose- and time-dependent mechanical hypernociception. The local IL-17 concentration within the mBSA-injected joints increased significantly over time. Moreover, co-treatment of mBSA challenged mice with an antibody against IL-17 inhibited hypernociception and neutrophil recruitment. In agreement, intraarticular injection of IL-17 induced hypernociception and neutrophil migration, which were reduced by the pre-treatment with fucoidin, a leukocyte adhesion inhibitor. The hypernociceptive effect of IL-17 was also reduced in TNFR1(-/-) mice and by pre-treatment with infliximab (anti-TNF antibody), a CXCR1/2 antagonist or by an IL-1 receptor antagonist. Consistent with these findings, we found that IL-17 injection into joints increased the production of TNF-alpha, IL-1beta and CXCL1/KC. Treatment with doxycycline (non-specific MMPs inhibitor), bosentan (ET(A)/ET(B) antagonist), indomethacin (COX inhibitor) or guanethidine (sympathetic blocker) inhibited IL-17-induced hypernociception. IL-17 injection also increased PGE(2) production, MMP-9 activity and COX-2, MMP-9 and PPET-1 mRNA expression in synovial membrane. These results suggest that IL-17 is a novel pro-nociceptive cytokine in mBSA-induced arthritis, whose effect depends on both neutrophil migration and various pro-inflammatory mediators, as TNF-alpha, IL-1beta, CXCR1/2 chemokines ligands, MMPs, endothelins, prostaglandins and sympathetic amines. Therefore, it is reasonable to propose IL-17 targeting therapies to control this important RA symptom.

The tumour necrosis factor as a mediator of vessel inflammation: importance of exposed receptor residues for its neutralization

BACKGROUND

The analysis of the macromolecular tumour necrosis factor (TNF)-receptor interface helps to understand the antigenicity of this inflammatory protein.

METHOD

The calculations are based on structural data from the protein database. The residues of the macromolecular interface are identified in the interface contact matrix, a plot of pair-wise interactions between adjacent residues in the TNF-receptor complex. Starting from the matrix elements, the most exposed residues of the receptor, together with their relative contribution to the interface, are determined. This is done by Voronoi tessellation, a unique and well defined partition of the protein into polyhedral cells defining the proprietary space of the associated amino acid and its contact faces with neighboured residue cells.

RESULTS

Several interfacial receptor residues, contributing with a total amount of 63% to the macromolecular interface, could be identified.

CONCLUSION

Based on the assumption that residues with higher interfacial exposure values are playing the most important role in TNF-receptor complex, they will be the original material for further developments in engineering more efficient TNF blockers.

Spinal antinociceptive effects of cyclooxygenase inhibition during inflammation: Involvement of prostaglandins and endocannabinoids

Both cyclooxygenase-1 and -2 are expressed in the spinal cord, and the spinal COX product prostaglandin E(2) (PGE(2)) contributes to the generation of central sensitization upon peripheral inflammation. Vice versa spinal COX inhibition is considered an important mechanism of antihyperalgesic pain treatment. Recently, however, COX-2 was shown to be also involved in the metabolism of endocannabinoids. Because endocannabinoids can have analgesic actions it is conceivable that inhibition of spinal COX produces analgesia not only by inhibition of PG synthesis but also by inhibition of endocannabinoid breakdown. In the present study, we recorded from spinal cord neurons with input from the inflamed knee joint and we measured the spinal release of PGE(2) and the endocannabinoid 2-arachidonoyl glycerol (2-AG) in vivo, using the same stimulation procedures. COX inhibitors were applied spinally. Selective COX-1, selective COX-2 and non-selective COX inhibitors attenuated the generation of spinal hyperexcitability when applied before and during development of inflammation but, when inflammation and spinal hyperexcitability were established, only selective COX-2 inhibitors reversed spinal hyperexcitability. During established inflammation all COX inhibitors reduced release of spinal PGE(2) almost equally but only the COX-2 inhibitor prevented breakdown of 2-AG. The reversal of spinal hyperexcitability by COX-2 inhibitors was prevented or partially reversed by AM-251, an antagonist at the cannabinoid-1 receptor. We conclude that inhibition of spinal COX-2 not only reduces PG production but also endocannabinoid breakdown and provide evidence that reversal of inflammation-evoked spinal hyperexcitability by COX-2 inhibitors is more related to endocannabinoidergic mechanisms than to inhibition of spinal PG synthesis.

Incidence and nature of infectious disease in patients treated with anti-TNF agents

Tumor necrosis factor alpha (TNF-alpha) inhibitors offer a targeted therapeutic strategy that contrasts with the nonspecific immunosuppressive agents traditionally used to treat most inflammatory diseases. These biologic agents have had a significant impact in ameliorating the signs and symptoms of inflammatory rheumatoid disease and improving patient function. From the onset of clinical trials, a central concern of cytokine blockade has been a potential increase in susceptibility to infections. Not surprisingly, a variety of infections have been reported in association with the use of TNF-alpha inhibitor agents. In particular, there is evidence suggesting an increased rate of granulomatous infections in patients treated with monoclonal TNF-alpha inhibitors. This review provides the incidence and nature of infections in patients treated with TNF-alpha inhibitor agents and reminds the clinician of the required vigilance in monitoring patients.

Gait abnormalities differentially indicate pain or structural joint damage in monoarticular antigen-induced arthritis

Gait abnormalities have been suggested to provide an objective measure for joint pain in animal models. Here, we aimed to assess whether parameters of gait analysis correlate with measures of pain-related behavior in experimental monoarthritis. For this purpose, antigen-induced arthritis was induced in the left knee joints of 68 female Lewis rats, of which 30 were treated with tumor necrosis factor-alpha(TNF)-neutralizing compounds. During the course of arthritis, paw print analysis parameters and measures for mechanical and thermal hyperalgesia were obtained. Knee joints harvested on either day 3 or day 21 were scored histologically for signs of inflammation and cartilage and bone destructions. Data were compared to those obtained from 33 immunized control rats and correlated for days 3 and 21. Arthritic rats showed distinct asymmetric gait abnormalities. In the acute stage of antigen-induced arthritis, but not in the chronic phase, there was a significant correlation between the gait parameter 'left-right distance' and measures of primary and secondary hyperalgesia. Both in the acute and chronic phases, however, the gait parameter 'angle between paws' indicating outward rotation of paws mainly correlated with joint destruction as assessed using histology. Etanercept treatment exhibited pronounced anti-nociceptive and pro-locomotional effects, but the described correlations remained. In conclusion, some parameters of gait analysis may represent a good measure for arthritis pain, mainly in acute inflammation, while others are increasingly influenced by mechanical joint deformation as indicated by cartilage and bone destructions. Thus, gait abnormalities may not unequivocally be suitable for objective pain assessment in all stages of experimental arthritis.

TNFalpha mechanically sensitizes masseter muscle afferent fibers of male rats

Behavioral evidence in rats indicates that injection of tumor necrosis factor alpha (TNFalpha) into skeletal muscle results in a prolonged mechanical sensitization without gross inflammation. To investigate whether a peripheral mechanism could underlie this effect, in the present study, TNFalpha (1 or 0.1 microg) was injected into the rat masseter muscle to assess its effect on the excitability and mechanical threshold (MT) of muscle nociceptors as well as on inflammation. Expression of TNFR1 (P55 receptors) and TNFR2 (P75 receptors) by the masseter muscle and trigeminal ganglion neurons that innervate that muscle was determined by Western blot and immunohistochemistry, respectively. The Evans blue dye technique was used at the end of the TNFalpha experiments to assess for plasma protein extravasation. In subsequent experiments to confirm the involvement of receptor activation in TNFalpha-induced effects, P55 or P75 receptor antibody was co-injected with TNFalpha. Intramuscular injection of 1 microg TNFalpha did not excite nociceptors but did significantly decrease MT compared with vehicle control. There was no evidence of gross inflammation 3 h after injection of TNFalpha. Co-injection of TNFalpha with P55 or P75 receptor antibodies attenuated TNFalpha-induced mechanical sensitization. P55 and P75 receptors were expressed by 29 and 62% of masseter nociceptors, respectively. These findings indicate that TNFalpha induces mechanical sensitization of masseter nociceptors that is mediated through activation of peripheral P55 and P75 receptors. These results support the hypothesis that a peripheral receptor mechanism could contribute to TNFalpha-induced noninflammatory mechanical sensitization of skeletal muscle previously reported in behaving rats.

Joint pain

Both inflammatory and degenerative diseases of joints are major causes of chronic pain. This overview addresses the clinical problem of joint pain, the nociceptive system of the joint, the mechanisms of peripheral and central sensitization during joint inflammation and long term changes during chronic joint inflammation. While the nature of inflammatory pain is obvious the nature and site of origin of osteoarthritic pain is less clear. However, in both pathological conditions mechanical hyperalgesia is the major pain problem, and indeed, both joint nociceptors and spinal nociceptive neurons with joint input show pronounced sensitization for mechanical stimulation. Molecular mechanisms of mechanical sensitization of joint nociceptors are addressed with an emphasis on cytokines, and molecular mechanisms of central sensitization include data on the role of excitatory amino acids, neuropeptides and spinal prostaglandins. The overview will also address long-term changes of pain-related behavior, response properties of neurons and receptor expression in chronic animal models of arthritis.

Nociceptive and inflammatory responses induced by formalin in the orofacial region of rats: effect of anti-TNFalpha strategies

This study evaluated the effects of different anti-TNFalpha strategies on the nociceptive and inflammatory responses triggered by formalin in the rat orofacial region. Formalin injection (2.5%) into the right upper lip caused a nociceptive response that was biphasic, with the first phase observed between 0 and 3 min and the second phase between 12 and 30 min. Plasma extravasation induced by formalin was time-related and reached the peak at 360 min. The monoclonal antibody anti-TNFalpha (25 and 50 pg/lip) significantly inhibited the second phase of formalin-induced nociceptive behavior, while the first phase remained unaltered. The systemic treatment with the chimeric anti-TNFalpha antibody infliximab also caused a significant inhibition of the second phase. Interestingly, the local administration of infliximab (50 pg/lip) produced a significant reduction of both phases of formalin-induced nociception. In addition, the systemic pretreatment with the preferential inhibitor of TNFalpha synthesis thalidomide (25 and 50 mg/kg, p.o) promoted a marked reduction of the first and second phases of formalin-evoked nociception. The local administration of the monoclonal antibody anti-TNFalpha (25 and 50 pg/lip) or infliximab (50 pg/lip) markedly reduced the plasma extravasation induced by formalin. Otherwise, formalin-elicited plasma extravasation was not significantly affected by the systemic administration of either infliximab (1 mg/kg; s.c) or thalidomide (50 mg/kg, p.o). Present data suggest that blocking TNFalpha effects, through different pharmacological tools, could represent a good alternative to control orofacial inflammatory pain that is refractory to other drugs.