Distribution and tumor necrosis factor-alpha isoform binding specificity of locally administered etanercept into injured and uninjured rat sciatic nerve

An Autocrine Regulator Loop Involving Tumor Necrosis Factor and Chemokine (C-C motif) Ligand-2 Is Activated by Transforming Growth Factor-β in Rat Basophilic Leukemia-2H3 Mast Cells

TGF-β is a pleiotropic cytokine with both stimulatory and inhibitory effects on immune cells, depending on the microenvironmental context. It targets mast cells (MCs) in different physio-pathological conditions, such as inflammation and cancer. Besides acting as a potent chemoattractant for MCs, TGF-β regulates many other aspects of MCs' physiology, including the secretion of many regulatory molecules. MCs secrete a variety of mediators, either pre-formed or newly synthesized, upon appropriate stimulation. CCL-2 chemokine and TNF cytokine act as potent chemoattractants for several immune cells and participate in the initiation of inflammatory responses by recruiting them to injured tissues. TGF-β regulates CCL-2 and TNF secretion in different cell types and under distinct cellular contexts. Here, we report that the treatment with TGF-β alone induces the secretion of both pre-formed and newly synthesized CCL-2 in the rat RBL-2H3 mast cells but not in mouse bone marrow-derived mast cells (BMMCs). TGF-β-induced CCL-2 secretion depends on rapid rearrangements of the actin cytoskeleton and, remarkably, on the early secretion of soluble TNF that triggers an autocrine TNF signaling. In conclusion, we found cooperation between TGF-β and TNF signaling pathways to promote the secretion of CCL-2 chemokine by MCs in a cell-context specific manner.

Platelet-rich plasma and cytokines in neuropathic pain: A narrative review and a clinical perspective

BACKGROUND AND OBJECTIVE

Neuropathic pain arises as a direct consequence of a lesion or disease affecting the somatosensory system. A number of preclinical studies have provided evidence for the involvement of cytokines, predominantly secreted by a variety of immune cells and by glial cells from the nervous system, in neuropathic pain conditions. Clinical trials and the use of anti-cytokine drugs in different neuropathic aetiologies support the relevance of cytokines as treatment targets. However, the use of such drugs, in particularly biotherapies, can provoke notable adverse effects. Moreover, it is challenging to select one given cytokine as a target, among the various neuropathic pain conditions. It could thus be of interest to target other proteins, such as growth factors, in order to act more widely on the neuroinflammation network. Thus, platelet-rich plasma (PRP), an autologous blood concentrate, is known to contain a natural concentration of growth factors and immune system messengers and is widely used in the clinical setting for tissue regeneration and repair.

DATABASE AND DATA TREATMENT

In the present review, we critically assess the current knowledge on cytokines in neuropathic pain by taking into consideration both human studies and animal models.

RESULTS

This analysis of the literature highlights the pathophysiological importance of cytokines. We particularly highlight the concept of time- and tissue-dependent cytokine activation during neuropathic pain conditions.

RESULTS

Conclusion: Thus, direct or indirect cytokines modulation with biotherapies or growth factors appears relevant. In addition, we discuss the therapeutic potential of localized injection of PRP as neuropathic pain treatment by pointing out the possible link between cytokines and the action of PRP.

SIGNIFICANCE

Preclinical and clinical studies highlight the idea of a cytokine imbalance in the development and maintenance of neuropathic pain. Clinical trials with anticytokine drugs are encouraging but are limited by a 'cytokine candidate approach' and adverse effect of biotherapies. PRP, containing various growth factors, is a new therapeutic used in regenerative medicine. Growth factors can be also considered as modulators of cytokine balance. Here, we emphasize a potential therapeutic effect of PRP on cytokine imbalance in neuropathic pain. We also underline the clinical interest of the use of PRP, not only for its therapeutic effect but also for its safety of use.

Peripheral-to-central immune communication at the area postrema glial-barrier following bleomycin-induced sterile lung injury in adult rats

The pathways for peripheral-to-central immune communication (P → C I-comm) following sterile lung injury (SLI) are unknown. SLI evokes systemic and central inflammation, which alters central respiratory control and viscerosensory transmission in the nucleus tractus solitarii (nTS). These functional changes coincide with increased interleukin-1 beta (IL-1β) in the area postrema, a sensory circumventricular organ that connects P → C I-comm to brainstem circuits that control homeostasis. We hypothesize that IL-1β and its downstream transcriptional target, cyclooxygenase-2 (COX-2), mediate P → C I-comm in the nTS. In a rodent model of SLI induced by intratracheal bleomycin (Bleo), the sigh frequency and duration of post-sigh apnea increased in Bleo- compared to saline- treated rats one week after injury. This SLI-dependent change in respiratory control occurred concurrently with augmented IL-1β and COX-2 immunoreactivity (IR) in the funiculus separans (FS), a barrier between the AP and the brainstem. At this barrier, increases in IL-1β and COX-2 IR were confined to processes that stained for glial fibrillary acidic protein (GFAP) and that projected basolaterally to the nTS. Further, FS radial-glia did not express TNF-α or IL-6 following SLI. To test our hypothesis, we blocked central COX-1/2 activity by intracerebroventricular (ICV) infusion of Indomethacin (Ind). Continuous ICV Ind treatment prevented Bleo-dependent increases in GFAP + and IL-1β + IR, and restored characteristics of sighs that reset the rhythm. These data indicate that changes in sighs following SLI depend partially on activation of a central COX-dependent P → C I-comm via radial-glia of the FS.

Acetaminophen combined with tramadol is more effective than acetaminophen or tramadol to reduce neuropathic root pain: an experimental study with application of nucleus pulposus in a rat model

INTRODUCTION

Various drugs are used to treat patients with neuropathic pain; however, optimal treatment using acetaminophen (A) and/or tramadol (T) remains unclear. The evidence supporting the drug choice and the timing of administration is insufficient. Therefore, the objective of the present study was to investigate the effect of T and/or A on pain-related behavior in a nucleus pulposus (NP) rat model.

MATERIALS AND METHODS

Sprague-Dawley rats (n = 180) were divided into NP-A (52 mg/kg), NP-T (6 mg/kg), NP-AT (combined A and T), NP-S (saline), and sham groups (n = 36 per group). The rats received 0.2 mL of treatment solution orally once daily for 7 days after application of NP on the left L5 dorsal root ganglion (DRG). Behavioral testing and immunohistochemistry analysis for some markers' expressions in DRGs and the spinal cord were performed.

RESULTS

Pain thresholds in the NP-AT group did not significantly differ from the sham at all time points, while those were significantly lower in the NP-A and in the NP-T groups at D7 and/or D14 (p < 0.05). Tumor necrosis factor-α in the NP-S group was significantly higher at D2 and D7 (p < 0.05). Among the three treatment groups, activating transcriptional factor 3 and growth-associated protein 43 showed a tendency toward an increase at D7-D21.

CONCLUSION

Combined administration of acetaminophen and tramadol maintained in the pain threshold in the rat NP model. These findings suggest that the combination of acetaminophen and tramadol might be a potential therapeutic modality for patients with lumbar disc herniation. These slides can be retrieved under Electronic Supplementary Material.

The kinin B1 and B2 receptors and TNFR1/p55 axis on neuropathic pain in the mouse brachial plexus

Tumour necrosis factor (TNF) and kinins have been associated with neuropathic pain-like behaviour in numerous animal models. However, the way that they interact to cause neuron sensitisation remains unclear. This study assessed the interaction of kinin receptors and TNF receptor TNFR1/p55 in mechanical hypersensitivity induced by an intraneural (i.n.) injection of rm-TNF into the lower trunk of brachial plexus in mice. The i.n. injection of rm-TNF reduced the mechanical withdrawal threshold of the right forepaw from the 3rd to the 10th day after the injection, indicating that TNF1/p55 displays a critical role in the onset of TNF-elicited neuropathic pain. The connection between TNF1/p55 and kinin B₁ and B₂ receptors (B₁R and B₂R) was confirmed using both knockout mice and mRNAs quantification in the injected nerve, DRG and spinal cord. The treatment with the B₂R antagonist HOE 140 or with B₁R antagonist des-Arg⁹-Leu⁸-BK reduced both BK- and DABK-induced hypersensitivity. The experiments using kinin receptor antagonists and CPM inhibitor (thiorphan) suggest that BK does not only activate B₂R as an orthosteric agonist, but also seems to be converted into DABK that consequently activates B₁R. These results indicate a connection between TNF and the kinin system, suggesting a relevant role for B₁R and B₂R in the process of sensitisation of the central nervous systems by the cross talk between the receptor and CPM after i.n. injection of rm-TNF.

Intrinsic Inflammation Is a Potential Anti-Epileptogenic Target in the Organotypic Hippocampal Slice Model

Understanding the mechanisms of epileptogenesis is essential to develop novel drugs that could prevent or modify the disease. Neuroinflammation has been proposed as a promising target for therapeutic interventions to inhibit the epileptogenic process that evolves from traumatic brain injury. However, it remains unclear whether cytokine-related pathways, particularly TNFα signaling, have a critical role in the development of epilepsy. In this study, we investigated the role of innate inflammation in an in vitro model of post-traumatic epileptogenesis. We combined organotypic hippocampal slice cultures, representing an in vitro model of post-traumatic epilepsy, with multi-electrode array recordings to directly monitor the development of epileptiform activity and to examine the concomitant changes in cytokine release, cell death, and glial cell activation. We report that synchronized ictal- and interictal-like activities spontaneously evolve in this culture. Dynamic changes in the release of the pro-inflammatory cytokines IL-1β, TNFα, and IL-6 were observed throughout the culture period (3 to 21 days in vitro) with persistent activation of microglia and astrocytes. We found that neutralizing TNFα with a polyclonal antibody significantly reduced ictal discharges, and this effect lasted for 1 week after antibody washout. Neither phenytoin nor an anti-IL-6 polyclonal antibody was efficacious in inhibiting the development of epileptiform activity. Our data show a sustained effect of the anti-TNFα antibody on the ictal progression in organotypic hippocampal slice cultures supporting the critical role of inflammatory mediators in epilepsy and establishing a proof-of-principle evidence for the utility of this preparation to test the therapeutic effects of anti-inflammatory treatments.

Intrinsic Inflammation Is a Potential Anti-Epileptogenic Target in the Organotypic Hippocampal Slice Model

Understanding the mechanisms of epileptogenesis is essential to develop novel drugs that could prevent or modify the disease. Neuroinflammation has been proposed as a promising target for therapeutic interventions to inhibit the epileptogenic process that evolves from traumatic brain injury. However, it remains unclear whether cytokine-related pathways, particularly TNFα signaling, have a critical role in the development of epilepsy. In this study, we investigated the role of innate inflammation in an in vitro model of post-traumatic epileptogenesis. We combined organotypic hippocampal slice cultures, representing an in vitro model of post-traumatic epilepsy, with multi-electrode array recordings to directly monitor the development of epileptiform activity and to examine the concomitant changes in cytokine release, cell death, and glial cell activation. We report that synchronized ictal- and interictal-like activities spontaneously evolve in this culture. Dynamic changes in the release of the pro-inflammatory cytokines IL-1β, TNFα, and IL-6 were observed throughout the culture period (3 to 21 days in vitro) with persistent activation of microglia and astrocytes. We found that neutralizing TNFα with a polyclonal antibody significantly reduced ictal discharges, and this effect lasted for 1 week after antibody washout. Neither phenytoin nor an anti-IL-6 polyclonal antibody was efficacious in inhibiting the development of epileptiform activity. Our data show a sustained effect of the anti-TNFα antibody on the ictal progression in organotypic hippocampal slice cultures supporting the critical role of inflammatory mediators in epilepsy and establishing a proof-of-principle evidence for the utility of this preparation to test the therapeutic effects of anti-inflammatory treatments.

Nuclear factor erythroid 2-related factor 2 antibody attenuates thermal hyperalgesia in the dorsal root ganglion: Neurochemical changes and behavioral studies after sciatic nerve-pinch injury

Oxidative stress is generated in several peripheral nerve injury models.Nuclear factor erythroid 2-related factor 2 (Nrf2) is activated to have a role in antioxidant effect. After nerve injury, the severely painful behavior is also performed. However, little has been explored regarding the function of Nrf2 in this painful process. Therefore, in this study, we compared the effects of Nrf2 antibody administration following sciatic nerve-pinch injury on painful behavior induced in young mice and neurochemical changes in dorsal root ganglion neurons. After pinch nerve injury, we found that the magnitude of the thermal allodynia was significantly decreased after application of Nrf2 antibody (5ul, 1mg/ml) in such injured animals and phosphorylated ERK(p-ERK) as well as the apoptotic protein (i.e., Bcl-6) in DRG neurons were also down-regulated in the anti-Nrf2-treated injured groups compared to the saline-treated groups. Taken collectively, these data suggested that the Nrf2 antibody reduced thermal hyperalgesia via ERK pathway and the down regulation of Bcl-6 protein from the apoptosis pathway might be protecting against the protein deletions caused by anti-Nrf2 effect and suggested the new therapeutic strategy with Nrf2 inhibitor following nerve injury.

The effect of etanercept and methylprednisolone on functional recovery of the facial nerve after crush injury

OBJECTIVE

To establish whether etanercept, a TNF-α antagonist, is an alternative and effective treatment on facial nerve after crush injury.

METHOD

Fifty-four rats underwent exposure of the left main trunk of the facial nerve followed by a standard crush injury. Animals were randomly divided into 3 groups: control group, methylprednisolone-treated group, and etanercept-treated group. All these groups were divided into 2 subgroups; animals were sacrificed on the 4th day after facial crush injury in the first subgroup and on the 28th day in the second subgroup. Functional recovery of vibrissae movement, eye blink reflex, and vibrissae orientation was measured on a 3-point scale (1 = no recovery, 2 = partial recovery, and 3 = complete recovery) during the recovery process. Facial nerve, from the main trunk at the stylomastoid foramen to the zygomatic, buccal, and marginal branches, were dissected and postfixed in the same fixative. The paraffin sections were studied with macrophage marker, GAP-43 and T Cell Marker.

RESULTS

Animals receiving etanercept demonstrated significantly better functional recovery compared with control and methylprednisolone-treated animals. The etanercept-treated group showed highest GAP-43 immunoreactivity in the nerves. After the macrophage marker and T cell marker staining, the etanercept and methylprednisolone groups demonstrated statistically significant difference compared with the control group (p < 0.001).

CONCLUSION

The present study demonstrates accelerated functional recovery associated with etanercept treatment after facial nerve crush injury in rats.

Perispinal etanercept for post-stroke neurological and cognitive dysfunction: scientific rationale and current evidence

There is increasing recognition of the involvement of the immune signaling molecule, tumor necrosis factor (TNF), in the pathophysiology of stroke and chronic brain dysfunction. TNF plays an important role both in modulating synaptic function and in the pathogenesis of neuropathic pain. Etanercept is a recombinant therapeutic that neutralizes pathologic levels of TNF. Brain imaging has demonstrated chronic intracerebral microglial activation and neuroinflammation following stroke and other forms of acute brain injury. Activated microglia release TNF, which mediates neurotoxicity in the stroke penumbra. Recent observational studies have reported rapid and sustained improvement in chronic post-stroke neurological and cognitive dysfunction following perispinal administration of etanercept. The biological plausibility of these results is supported by independent evidence demonstrating reduction in cognitive dysfunction, neuropathic pain, and microglial activation following the use of etanercept, as well as multiple studies reporting improvement in stroke outcome and cognitive impairment following therapeutic strategies designed to inhibit TNF. The causal association between etanercept treatment and reduction in post-stroke disability satisfy all of the Bradford Hill Criteria: strength of the association; consistency; specificity; temporality; biological gradient; biological plausibility; coherence; experimental evidence; and analogy. Recognition that chronic microglial activation and pathologic TNF concentration are targets that may be therapeutically addressed for years following stroke and other forms of acute brain injury provides an exciting new direction for research and treatment.

Targeting anti-inflammatory treatment can ameliorate injury-induced neuropathic pain

Tumor necrosis factor-α plays important roles in immune system development, immune response regulation, and T-cell-mediated tissue injury. The present study assessed the net value of anti-tumor necrosis factor-α treatment in terms of functional recovery and inhibition of hypersensitivity after peripheral nerve crush injury. We created a right sciatic nerve crush injury model using a Sugita aneurysm clip. Animals were separated into 3 groups: the first group received only a skin incision; the second group received nerve crush injury and intraperitoneal vehicle injection; and the third group received nerve crush injury and intraperitoneal etanercept (6 mg/kg). Etanercept treatment improved recovery of motor nerve conduction velocity, muscle weight loss, and sciatic functional index. Plantar thermal and von Frey mechanical withdrawal thresholds recovered faster in the etanercept group than in the control group. On day 7 after crush injury, the numbers of ED-1-positive cells in crushed nerves of the control and etanercept groups were increased compared to that in the sham-treated group. After 21 days, ED-1-positive cells had nearly disappeared from the etanercept group. Etanercept reduced expression of interleukin-6 and monocyte chemotactic and activating factor-1 at the crushed sciatic nerve. These findings demonstrate the utility of etanercept, in terms of both enhancing functional recovery and suppressing hypersensitivity after nerve crush. Etanercept does not impede the onset or progression of Wallerian degeneration, but optimizes the involvement of macrophages and the secretion of inflammatory mediators.

Selective TNF inhibition for chronic stroke and traumatic brain injury: an observational study involving 629 consecutive patients treated with perispinal etanercept

BACKGROUND

Brain injury from stroke and traumatic brain injury (TBI) may result in a persistent neuroinflammatory response in the injury penumbra. This response may include microglial activation and excess levels of tumour necrosis factor (TNF). Previous experimental data suggest that etanercept, a selective TNF inhibitor, has the ability to ameliorate microglial activation and modulate the adverse synaptic effects of excess TNF. Perispinal administration may enhance etanercept delivery across the blood-CSF barrier.

OBJECTIVE

The objective of this study was to systematically examine the clinical response following perispinal administration of etanercept in a cohort of patients with chronic neurological dysfunction after stroke and TBI.

METHODS

After approval by an independent external institutional review board (IRB), a chart review of all patients with chronic neurological dysfunction following stroke or TBI who were treated open-label with perispinal etanercept (PSE) from November 1, 2010 to July 14, 2012 at a group medical practice was performed.

RESULTS

The treated cohort included 629 consecutive patients. Charts of 617 patients following stroke and 12 patients following TBI were reviewed. The mean age of the stroke patients was 65.8 years ± 13.15 (range 13-97). The mean interval between treatment with PSE and stroke was 42.0 ± 57.84 months (range 0.5-419); for TBI the mean interval was 115.2 ± 160.22 months (range 4-537). Statistically significant improvements in motor impairment, spasticity, sensory impairment, cognition, psychological/behavioural function, aphasia and pain were noted in the stroke group, with a wide variety of additional clinical improvements noted in individuals, such as reductions in pseudobulbar affect and urinary incontinence. Improvements in multiple domains were typical. Significant improvement was noted irrespective of the length of time before treatment was initiated; there was evidence of a strong treatment effect even in the subgroup of patients treated more than 10 years after stroke and TBI. In the TBI cohort, motor impairment and spasticity were statistically significantly reduced.

DISCUSSION

Irrespective of the methodological limitations, the present results provide clinical evidence that stroke and TBI may lead to a persistent and ongoing neuroinflammatory response in the brain that is amenable to therapeutic intervention by selective inhibition of TNF, even years after the acute injury.

CONCLUSION

Excess TNF contributes to chronic neurological, neuropsychiatric and clinical impairment after stroke and TBI. Perispinal administration of etanercept produces clinical improvement in patients with chronic neurological dysfunction following stroke and TBI. The therapeutic window extends beyond a decade after stroke and TBI. Randomized clinical trials will be necessary to further quantify and characterize the clinical response.

Study of the genetic factors predisposing to the development of psoriasis

Many findings confirm the influence of neuropsychic factors on the manifestation and exacerbation of the atopic dermatitis and psoriasis. Nowadays it is assumed that by means of neurotransmitters’ secretion the nervous system can influence different processes, including the immune mediated inflammation, which has the key role in the pathogenesis of such dermatosis. The article hereunder contains comprehensive data on prospective trends of following studies of the nervous regulation participation in the pathogenesis of such dermatosis.

The ology of neuropathy: an integrative review of the role of neuroinflammation and TNF-α axonal transport in neuropathic pain

This 2011 Peripheral Nerve Society plenary lecture reviews the role of axonal transport in neuroimmune communication following peripheral nerve injury, linking focal changes in Schwann cell activation and release of the proinflammatory cytokine tumor necrosis factor-alpha (TNF-α) with subsequent activation and sensitization of ascending sensory neurons and glia which culminate in the neuropathic pain state. New data demonstrate that axonally transported (biotinylated) TNF-α activates and localizes with dorsal horn astrocytes within 96 h after injection into sciatic nerve, and that glial fibrillary acidic protein (GFAP) activation in these glial cells is diminished in TNF receptor 1 knockout mice. The pathophysiology, neuropathology and molecular biology of Wallerian degeneration are also reviewed from a perspective that links it to upregulation of proinflammatory cytokines and the development of neuropathic pain states. Finally, insights into neuroimmune communication provide rationale for new therapy based on interference with the processes of Wallerian degeneration, cytokine signaling and TNF-α protein sequestration.

Kinematic and dynamic gait compensations in a rat model of lumbar radiculopathy and the effects of tumor necrosis factor-alpha antagonism

Introduction

Tumor necrosis factor-α (TNFα) has received significant attention as a mediator of lumbar radiculopathy, with interest in TNF antagonism to treat radiculopathy. Prior studies have demonstrated that TNF antagonists can attenuate heightened nociception resulting from lumbar radiculopathy in the preclinical model. Less is known about the potential impact of TNF antagonism on gait compensations, despite being of clinical relevance. In this study, we expand on previous descriptions of gait compensations resulting from lumbar radiculopathy in the rat and describe the ability of local TNF antagonism to prevent the development of gait compensations, altered weight bearing, and heightened nociception.

Methods

Eighteen male Sprague-Dawley rats were investigated for mechanical sensitivity, weight-bearing, and gait pre- and post-operatively. For surgery, tail nucleus pulposus (NP) tissue was collected and the right L5 dorsal root ganglion (DRG) was exposed (Day 0). In sham animals, NP tissue was discarded (n = 6); for experimental animals, autologous NP was placed on the DRG with or without 20 μg of soluble TNF receptor type II (sTNFRII, n = 6 per group). Spatiotemporal gait characteristics (open arena) and mechanical sensitivity (von Frey filaments) were assessed on post-operative Day 5; gait dynamics (force plate arena) and weight-bearing (incapacitance meter) were assessed on post-operative Day 6.

Results

High-speed gait characterization revealed animals with NP alone had a 5% decrease in stance time on their affected limbs on Day 5 (P ≤0.032). Ground reaction force analysis on Day 6 aligned with temporal changes observed on Day 5, with vertical impulse reduced in the affected limb of animals with NP alone (area under the vertical force-time curve, P <0.02). Concordant with gait, animals with NP alone also had some evidence of affected limb mechanical allodynia on Day 5 (P = 0.08) and reduced weight-bearing on the affected limb on Day 6 (P <0.05). Delivery of sTNFRII at the time of NP placement ameliorated signs of mechanical hypersensitivity, imbalanced weight distribution, and gait compensations (P <0.1).

Conclusions

Our data indicate gait characterization has value for describing early limb dysfunctions in pre-clinical models of lumbar radiculopathy. Furthermore, TNF antagonism prevented the development of gait compensations subsequent to lumbar radiculopathy in our model.

Systemic and spinal administration of etanercept, a tumor necrosis factor alpha inhibitor, blocks tactile allodynia in diabetic mice

Painful diabetic neuropathy is one of the most common forms of neuropathic pain syndromes. Tumor necrosis factor alpha (TNF-alpha) is a proinflammatory cytokine that has been implicated as a key pain mediator in the development and maintenance of neuropathic pain conditions. Recent studies showed that endogenous TNF-alpha production was also accelerated in neural tissues and spinal cord under chronic hyperglycemia. Thus, in this study, we investigated whether pharmacological inhibition of TNF-alpha by etanercept, a TNF-alpha antagonist, could block behavioral sign of diabetic neuropathic pain. Diabetes was induced by streptozotocin (STZ) (200 mg/kg, i.p.) in Balb-c mice and behavioral tests were performed between 45 and 60 days after STZ administration. Mechanical and thermal sensitivities were measured by a series of calibrated Von Frey filaments and hot plate test, respectively. Etanercept was given by either intravenous (i.v.), intrathecal (i.th.) or intraplantar (i.pl.) routes to the diabetic mice. Tactile allodynia, but not thermal hyperalgesia, developed in diabetic mice. Both i.v. (1, 10 and 20 mg/kg) or i.th. (1, 5 and 10 μg/mouse) treatments with etanercept produced dose dependent reversal of tactile allodynia in diabetic mice. However, etanercept was found to be inactive against allodynia when given i.pl. (1, 5 and 10 μg/mouse). Our results suggest that etanercept has promising effects on diabetic neuropathic pain with antiallodynic effects when given systemically or intrathecally.

Role of TNF-alpha during central sensitization in preclinical studies

Tumor necrosis factor-alpha (TNF-α) is a principal mediator in pro-inflammatory processes that involve necrosis, apoptosis and proliferation. Experimental and clinical evidence demonstrate that peripheral nerve injury results in activation and morphological changes of microglial cells in the spinal cord. These adjustments occur in order to initiate an inflammatory cascade in response to the damage. Between the agents involved in this reaction, TNF-α is recognized as a key player in this process as it not only modulates lesion formation, but also because it is suggested to induce nociceptive signals. Nowadays, even though the function of TNF-α in inflammation and pain production seems to be generally accepted, diverse sources of literature point to different pathways and outcomes. In this review, we systematically searched and reviewed original articles from the past 10 years on animal models of peripheral nervous injury describing TNF-α expression in neural tissue and pain behavior.

Cellular and molecular insights into neuropathy-induced pain hypersensitivity for mechanism-based treatment approaches

Neuropathic pain is currently being treated by a range of therapeutic interventions that above all act to lower neuronal activity in the somatosensory system (e.g. using local anesthetics, calcium channel blockers, and opioids). The present review highlights novel and often still largely experimental treatment approaches based on insights into pathological mechanisms, which impact on the spinal nociceptive network, thereby opening the 'gate' to higher brain centers involved in the perception of pain. Cellular and molecular mechanisms such as ectopia, sensitization of nociceptors, phenotypic switching, structural plasticity, disinhibition, and neuroinflammation are discussed in relation to their involvement in pain hypersensitivity following either peripheral neuropathies or spinal cord injury. A mechanism-based treatment approach may prove to be successful in effective treatment of neuropathic pain, but requires more detailed insights into the persistence of cellular and molecular pain mechanisms which renders neuropathic pain unremitting. Subsequently, identification of the therapeutic window-of-opportunities for each specific intervention in the particular peripheral and/or central neuropathy is essential for successful clinical trials. Most of the cellular and molecular pain mechanisms described in the present review suggest pharmacological interference for neuropathic pain management. However, also more invasive treatment approaches belong to current and/or future options such as neuromodulatory interventions (including spinal cord stimulation) and cell or gene therapies, respectively.

Effects of asialo-erythropoietin on pain-related behavior and expression of phosphorylated-p38 map kinase and tumor necrosis factor-alpha induced by application of autologous nucleus pulposus on nerve root in rat

STUDY DESIGN

this study was designed to examine the neuroprotective effects of asialo-erythropoietin (A-EPO) in a rat model of lumbar disc herniation.

OBJECTIVE

to investigate the effects of A-EPO on pain-related behavior, the expression of phosphorylated-p38 (p-p38) mitogen activated kinase, and the expression of tumor necrosis factor alpha (TNF-α) induced by nucleus pulposus (NP) application on the nerve root.

SUMMARY OF BACKGROUND DATA

erythropoietin (EPO) has neuroprotective effects in a variety of models of central and peripheral nerve injuries. However, EPO is a hematopoietic growth factor and can therefore cause significant side effects such as thicker blood and promotion of blood clotting. A-EPO is a neuroprotective derivative of EPO that is not hematopoietic.

METHODS

female Sprague-Dawley rats (n = 149) were used in this study. NP harvested from the tail was applied to the left L5 nerve root and the rats were then divided into four groups: NP + nontreatment group, no further treatment; NP + A-EPO group, 13.4 microg/kg A-EPO; NP + EPO group, 13.4 microg/kg EPO; and NP + vehicle group, received vehicle. The substances were administered subcutaneously 1 day before surgery and daily for 2 weeks. In the sham group of animals, the L5 nerve root was exposed and NP was not applied. Withdrawal thresholds were determined by the von-Frey test 28 days after surgery. The expressions of p-p38 and TNF-α were assessed by immunohistochemical and immunoblotting analysis. Data were analyzed by unpaired Student t test and Dunnett t test (significance level, P < 0.05).

RESULTS

in the NP + nontreatment and NP + vehicle groups, withdrawal thresholds were decreased significantly for 28 days compared with the sham group (P < 0.05). In the NP + A-EPO group, the thresholds were significantly increased on day 28, and in the NP + EPO group, the thresholds were significantly increased on days 21 and 28 (P < 0.05) compared with the NP + nontreatment and NP + vehicle groups. The expression of p-p38 in the NP + A-EPO group was significantly lower than that in the NP + vehicle group on day 1 (P < 0.05). The expression of TNF in the NP + A-EPO and NP + EPO groups was significantly lower than that in the NP + vehicle group on days 1 and 7 (P < 0.05).

CONCLUSIONS

A-EPO improved pain-related behavior and reduced the expression of p-p38 and TNF-α. The effect of A-EPO may be related to the inhibitory action of p-p38 and TNF-α in the dorsal root ganglion.

Evaluation of behavior and neuropeptide markers of pain in a simple, sciatic nerve-pinch pain model in rats

Pathomechanisms of injured-nerve pain have not been fully elucidated. Radicular pain and chronic constriction injury models have been established; however, producing these models is complicated. A sciatic nerve-pinch injury is easy to produce but the reliability of this model for evaluating pain behavior has not been examined. The current study evaluated pain-related behavior and change in pain markers in the dorsal root ganglion (DRG) of rats in a simple, sciatic nerve-pinch injury model. In the model, the sciatic nerve was pinched for 2 s using forceps (n = 20), but not injured in sham-operated animals (n = 20). Mechanical and thermal hyperalgesia were measured every second day for 2 weeks using von Frey filaments and a Hargreaves device. Calcitonin gene-related peptide (CGRP), activating transcription factor-3 (ATF-3), phosphorylated p38 mitogen activated protein (Map) kinase (p-p38), and nuclear factor-kappa B (NF-κB; p65) expression in L5 DRGs were examined at 4 and 7 days after surgery using immunohistochemistry. The proportion of neurons immunoreactive for these markers was compared between the two groups. Mechanical (during 8 days) and thermal hyperalgesia (during 6 days) were found in the pinch group rats, but not in the sham-operated animals (p < 0.05); however, hyperalgesia was not significant from days 10 to 14. CGRP, ATF-3, p-p38, and NF-κB expression in L5 DRGs was upregulated in the nerve-injured rats compared with the sham-operated rats (p < 0.01). Our results indicate that a simple sciatic nerve pinch produced pain-related behavior. Upregulation of the pain-marker expression in the nerve-injury model suggested it could be used as a model of pain. However, it was not considered as suitable for long-term studies.

Immediate anti-tumor necrosis factor-alpha (etanercept) therapy enhances axonal regeneration after sciatic nerve crush

Peripheral nerve regeneration begins immediately after injury. Understanding the mechanisms by which early modulators of axonal degeneration regulate neurite outgrowth may affect the development of new strategies to promote nerve repair. Tumor necrosis factor-alpha (TNF-alpha) plays a crucial role in the initiation of degenerative cascades after peripheral nerve injury. Here we demonstrate using real-time Taqman quantitative RT-PCR that, during the time course (days 1-60) of sciatic nerve crush, TNF-alpha mRNA expression is induced at 1 day and returned to baseline at 5 days after injury in nerve and the corresponding dorsal root ganglia (DRG). Immediate therapy with the TNF-alpha antagonist etanercept (fusion protein of TNFRII and human IgG), administered systemically (i.p.) and locally (epineurially) after nerve crush injury, enhanced the rate of axonal regeneration, as determined by nerve pinch test and increased number of characteristic clusters of regenerating nerve fibers distal to nerve crush segments. These fibers were immunoreactive for growth associated protein-43 (GAP-43) and etanercept, detected by anti-human IgG immunofluorescence. Increased GAP-43 expression was found in the injured nerve and in the corresponding DRG and ventral spinal cord after systemic etanercept compared with vehicle treatments. This study established that immediate therapy with TNF-alpha antagonist supports axonal regeneration after peripheral nerve injury.