The effects of epidural application of allografted nucleus pulposus in rats on cytokine expression, limb withdrawal and nerve root discharge

High frequency alternating current neurostimulation decreases nocifensive behavior in a disc herniation model of lumbar radiculopathy

BACKGROUND

The purpose of this study was to evaluate if kilohertz frequency alternating current (KHFAC) stimulation of peripheral nerve could serve as a treatment for lumbar radiculopathy. Prior work shows that KHFAC stimulation can treat sciatica resulting from chronic sciatic nerve constriction. Here, we evaluate if KHFAC stimulation is also beneficial in a more physiologic model of low back pain which mimics nucleus pulposus (NP) impingement of a lumbar dorsal root ganglion (DRG).

METHODS

To mimic a lumbar radiculopathy, autologous tail NP was harvested and placed upon the right L5 nerve root and DRG. During the same surgery, a cuff electrode was implanted around the sciatic nerve with wires routed to a headcap for delivery of KHFAC stimulation. Male Lewis rats (3 mo., n = 18) were separated into 3 groups: NP injury + KHFAC stimulation (n = 7), NP injury + sham cuff (n = 6), and sham injury + sham cuff (n = 5). Prior to surgery and for 2 weeks following surgery, animal tactile sensitivity, gait, and static weight bearing were evaluated.

RESULTS

KHFAC stimulation of the sciatic nerve decreased behavioral evidence of pain and disability. Without KHFAC stimulation, injured animals had heightened tactile sensitivity compared to baseline (p < 0.05), with tactile allodynia reversed during KHFAC stimulation (p < 0.01). Midfoot flexion during locomotion was decreased after injury but improved with KHFAC stimulation (p < 0.05). Animals also placed more weight on their injured limb when KHFAC stimulation was applied (p < 0.05). Electrophysiology measurements at end point showed decreased, but not blocked, compound nerve action potentials with KHFAC stimulation (p < 0.05).

CONCLUSIONS

KHFAC stimulation decreases hypersensitivity but does not cause additional gait compensations. This supports the idea that KHFAC stimulation applied to a peripheral nerve may be able to treat chronic pain resulting from sciatic nerve root inflammation.

Bone mesenchymal stem cells attenuate radicular pain by inhibiting microglial activation in a rat noncompressive disk herniation model

Spinal disk herniation can induce radicular pain through chemical irritation caused by proinflammatory and immune responses. Bone marrow mesenchymal stem cells (BMSCs) are a unique type of adult stem cell with the functions of suppressing inflammation and modulating immune responses. This study was undertaken to observe the effect of intrathecal BMSCs on the treatment of mechanical allodynia and the suppression of microglial activation in a rat noncompressive disk herniation model. The model was induced by the application of nucleus pulposus (NP) to the L5 dorsal root ganglion (DRG). The study found that the use of NP in the DRG can induce abnormal mechanical pain, increase the contents of the proinflammatory factors TNF-α and IL-1β, decrease the content of the anti-inflammatory cytokine TGF-β1 and activate microglia in the spinal dorsal horns (L5) (P < 0.05). BMSC administration could increase the mechanical withdrawal thresholds dramatically, decrease the contents of IL-1β and TNF-α, increase the content of TGF-β1 significantly (P < 0.05) and inhibit microglial activation in the bilateral spinal dorsal horn. Our results indicate that BMSC administration can reduce mechanical allodynia and downregulate the expression of proinflammatory cytokines by inhibiting microglial activation in the spinal dorsal horn in a rat noncompressive disk herniation model.

Animal models for disc degeneration-an update

Intervertebral disc degeneration is considered a major cause of back pain that places a heavy burden on society, both because of its effect on the physiology of individuals and its consequences on the world economy. During the past few decades, research findings in the pre-clinical setting have led to a significant increase in the understanding of intervertebral disc degeneration, although many aspects of the disease remain unclear. The goal of this review is to summarize existing animal models for disc degeneration studies and the difficulties that are associated with the use of such models. A firm understanding of the cellular and molecular events that ensue as a result of injuries, as well as environmental factors, could be instrumental in the development of targeted therapies for the treatment of intervertebral disc degeneration.

The Effect of GCSB-5 a New Herbal Medicine on Changes in Pain Behavior and Neuroglial Activation in a Rat Model of Lumbar Disc Herniation

Objective

Lumbar disc herniation can induce sciatica by mechanical compression and/or chemical irritation. The aim of this study was to compare the effects of GCSB-5 (Shinbaro®) and NSAIDs on pain-related behavior and on the expressions of microglia, astrocytes, CGRP, TRPV1, IL-6, and CX3CL1 in a rat model of lumbar disc herniation.

Methods

112 male Sprague-Dawley rats underwent implantation of nucleus pulposus to a dorsal root ganglion (DRG). Rats were divided into five groups as follows; a saline group (the vehicle control group) (n=27), a 10 mg/kg aceclofenac group (the aceclofenac group) (n=22), and 100, 300 or 600 mg/kg GCSB-5 groups (the GCSB-5 100, 300, or 600 groups) (n=21 for each group). Rats were tested for mechanical allodynia at 3 days after surgery and at 1 day, 3 days, 7 days, 14 days, 21 days, 28 days, 35 days, 42 days, 49 days, and 56 days after treatment commencement. Immunohistochemical staining of microglia (Iba1), astrocytes (GFAP), CGRP, and TRPV1, and PCR for IL-6 and CX3CL1 were performed on spinal dorsal horns and DRGs at 56 days after medication commencement.

Results

After 56 days of GCSB-5 300 administration, mechanical withdrawal thresholds were significantly increased (p<0.05), and immunohisto-chemical expressions of Iba1, GFAP, CGRP, and TRPV1 were reduced than other groups, but this difference was not statistically significant.

Conclusion

These results indicate GCSB-5 reduces mechanical allodynia and downregulates neuroglial activity and the expressions of CGRP and TRPV1 in the spinal segments of a rat model of lumbar disc herniation.

Interleukin-23 may contribute to the pathogenesis of lumbar disc herniation through the IL-23/IL-17 pathway

BACKGROUND

Studies have indicated that interleukin 23 (IL-23) plays an important role in many inflammatory- and autoimmune-related diseases. However, there is little knowledge about IL-23 in lumbar disc herniation (LDH). Thus, in this study, we aimed to find out whether IL-23 is expressed in intervertebral discs (IVDs) and what roles it may play.

METHODS

Human IVD tissues were collected from 29 LDH patients and 8 vertebral fracture patients (normal control, NC group). According to the integrity of annulus fibrosus, LDH patients were divided into two groups: R group (ruptured group, n = 16) and NR group (non-ruptured group, n = 13). Morphological changes of IVDs were assessed by hematoxylin and eosin (HE staining), and expression of IL-23 in IVD tissues was detected by immunohistochemical staining. Besides gene expression of IL-23, IL-17, IL-6, IL-1β, and TNF-α was also evaluated by reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

The results showed that the R group was more degenerated than the other two groups and NC group showed the least degenerated performance; stronger positive IL-23 expression was observed in herniated IVDs, especially in the R group. Meanwhile, higher gene expression of IL-23, IL-17, IL-6, IL-1β, and TNF-α was found in the tissues from LDH patients and a positive correlation between IL-17 and IL-23 gene expression was also observed.

CONCLUSIONS

Taken all above results together, it may be deduced that higher expression of IL-23 may contribute to the deterioration of IVDs through the IL-23/IL-17 pathway.

Changes in the Expressions of Iba1 and Calcitonin Gene-Related Peptide in Adjacent Lumbar Spinal Segments after Lumbar Disc Herniation in a Rat Model

Lumbar disc herniation is commonly encountered in clinical practice and can induce sciatica due to mechanical and/or chemical irritation and the release of proinflammatory cytokines. However, symptoms are not confined to the affected spinal cord segment. The purpose of this study was to determine whether multisegmental molecular changes exist between adjacent lumbar spinal segments using a rat model of lumbar disc herniation. Twenty-nine male Sprague-Dawley rats were randomly assigned to either a sham-operated group (n=10) or a nucleus pulposus (NP)-exposed group (n=19). Rats in the NP-exposed group were further subdivided into a significant pain subgroup (n=12) and a no significant pain subgroup (n=7) using mechanical pain thresholds determined von Frey filaments. Immunohistochemical stainings of microglia (ionized calcium-binding adapter molecule 1; Iba1), astrocytes (glial fibrillary acidic protein; GFAP), calcitonin gene-related peptide (CGRP), and transient receptor potential vanilloid 1 (TRPV1) was performed in spinal dorsal horns and dorsal root ganglions (DRGs) at 10 days after surgery. It was found immunoreactivity for Iba1-positive microglia was higher in the L5 (P=0.004) dorsal horn and in the ipsilateral L4 (P=0.009), L6 (P=0.002), and S1 (P=0.002) dorsal horns in the NP-exposed group than in the sham-operated group. The expression of CGRP was also significantly higher in ipsilateral L3, L4, L6, and S1 segments and in L5 DRGs at 10 days after surgery in the NP-exposed group than in the sham-operated group (P<0.001). Our results indicate that lumbar disc herniation upregulates microglial activity and CGRP expression in many adjacent and ipsilateral lumbar spinal segments.

Lipoxin A4 attenuates radicular pain possibly by inhibiting spinal ERK, JNK and NF-κB/p65 and cytokine signals, but not p38, in a rat model of non-compressive lumbar disc herniation

Inflammatory response induced by protrused nucleus pulposus (NP) has been shown to play a crucial role in the process of radicular pain. Lipoxins represent a unique class of lipid mediators that have anti-inflammatory and pro-resolving action. The present study was undertaken to investigate if intrathecal lipoxin A4 (LXA4) could alleviate mechanical allodynia in the rat models of application of NP to the L5 dorsal root ganglion (DRG). Non-compressive models of application of NP to L5 DRG were established and intrathecal catheterization for drug administration was performed in rats. Daily intrathecal injection of vehicle or LXA4 (10ng or 100ng) was performed for three successive days post-operation. Mechanical thresholds were tested and the ipsilateral lumbar (L4-L6) segment of spinal dorsal horns were removed for the determination of tumor necrosis factor-α (TNF-α), IL-1β, transforming growth factor-β1 (TGF-β1) and IL-10 expression and NF-κB/p65, extracellular signal-regulated kinase (ERK), C-Jun N-terminal kinase (JNK) and P38 expression. Application of NP to DRG in rats induced mechanical allodynia, increased the expression of pro-inflammatory factors (TNF-α and IL-1β), NF-κB/p65, the phosphorylated-ERK (p-ERK), -JNK (p-JNK) and -P38 (p-p38) and decreased the expression of anti-inflammatory cytokines (TGF-β1 and IL-10) in the ipsilateral lumbar (L4-L6) segment of spinal dorsal horns. Intrathecal injection of LXA4 alleviated the development of neuropathic pain, inhibited the upregulation of pro-inflammatory cytokines (TNF-α and IL-1β), upregulated the expression of anti-inflammatory cytokines (TGF-β1 and IL-10) and attenuated the activation of NF-κB/p65, p-ERK, p-JNK, but not p-p38, in a dose-dependent manner. In this study, we have demonstrated that LXA4 potently alleviate radicular pain in a rat model of non-compressive lumbar disc herniation. The anti-inflammatory and pro-resolution properties of LXA4 have shown a great promise for the management of radicular pain caused by intervertebral disc herniation.

Role of interleukin-17 in chondrocytes of herniated intervertebral lumbar discs

Lumbar disc herniation (LDH) is a common cause of lumbosacral radiculopathy. An autoimmune response to a herniated nucleus pulposus (NP) has been suggested to play an important role in the initiation of radiculopathy. Interleukin-17 (IL-17) is a cytokine associated with inflammation and autoimmunity. The presence of IL-17 has been studied in patients with LDH; however, extensive investigation into the expression of IL-17 in different disc pathologies of LDH has not yet been conducted. The aim of the present study was to investigate the role of neovascularization and hypertrophic chondrocytes in herniated intervertebral lumbar discs. Fifty-two intervertebral lumbar disc specimens were extracted from 46 patients with LDH and were subsequently classified as either contained or non-contained disc herniation (CDH and NCDH, respectively). The specimens were stained with hematoxylin and eosin or toluidine blue, or were immunostained with polyclonal antibodies to IL-17 using the streptavidin-peroxidase method. The neovascular tissue and staining results were graded to establish the histological differences between the two herniation types. The intervertebral discs (IVDs) obtained from patients with NCDH showed significantly more neovascularization and granulation tissue than the discs obtained from patients with CDH (P<0.05). Furthermore, hypertrophic chondrocytes were more abundant in the NCDH specimens than in the CDH specimens (P<0.05). Similarly, the number of IL-17-immunoreactive cells was significantly higher in the NCDH specimens than that in the CDH specimens (P<0.01). In conclusion, local inflammation and autoreactive immune activation may play an important role in the pathogenesis of LDH. These results also suggest a role of chondrocytes in the repair of herniated IVDs.

Sciatica: detection and confirmation by new method

We need to overcome limitations of present assessment and also integrate newer research in our work about sciatica. Inflammation induces changes in the DRG and nerve root. It sensitizes the axons. Nociceptor is a unique axon. It is pseudo unipolar: both its ends, central and peripheral, behave in similar fashion. The nerve in periphery which carries these axons may selectively become sensitive to mechanical pressure--"mechanosensitized," as we coin the phrase. Many pain questionnaires are used and are effective in identifying neuropathic pain solely on basis of descriptors but they do not directly physically correlate nerve root and pain. A thorough neurological evaluation is always needed. Physical examination is not direct pain assessment but testing mobility of nerve root and its effect on pain generation. There is a dogmatic dominance of dermatomes in assessment of leg pain. They are unreliable. Images may not correlate with symptoms and pathology in about 28% of cases. Electrophysiology may be normal in purely inflamed nerve root. Palpation may help in such inflammatory setting to refine our assessment further. Confirmation of sciatica is done by selective nerve root block (SNRB) today but it is fraught with several complications and needs elaborate inpatient and operating room set up. We have used the unique property of the pseudo unipolar axon that both its ends have similar functional properties and so inject along its peripheral end sodium channel blockers to block the basic cause of the mechanosensitization namely upregulated sodium channels in the root or DRG. Thus using palpation we may be able to detect symptomatic nerve in stage of inflammation and with distal end injection, along same inflamed nerve we may be able to abolish and so confirm sciatica. Discussions of sciatica pain diagnosis tend to immediately shift and centre on the affected disc rather than the nerve. Theoretically it may be possible to detect the affected nerve by palpating the nerve and relieve pain moment we desensitize the nerve.

A rat model for chronic spinal nerve root compression

OBJECTIVES

The pathophysiology of radiculopathy associated with lumbar spinal stenosis and lumbar disc herniation is incompletely understood. The goal of the present study was to establish a chronic spinal nerve root compression model that can mimic lumbar disc herniation or spinal stenosis using silicone tube compression. We also try to link the pathology changes of damaged nerve root with the reaction of microglia in spinal cord in same rat at different time points.

METHODS

Thirty rats were used in this study. The L5 nerve roots (dorsal and ventral) were exposed by hemilaminectomy; the diameter of the L5 nerve root was measured at the 2 mm proximal from the dorsal root ganglia. The dorsal and ventral nerve roots of L5 were compressed using a silicone tube, and the sham group was only exposed dorsal and ventral roots of L5. Five rats from the sham group were perfused at 8 days after surgery, and 25 rats from the model groups were perfused at 3, 8, 12, 45 days, and 5 months after surgery, each model group was composed of 5 rats according to the time point. The L5 spinal cord segments and nerve root that compressed by silicone tube were harvested from the same rat. Microglia and neuron in the spinal cord were stained by immunohistochemistry, and the nerve root was shown by electron microscope.

RESULTS

In sham-operated rat, the arrangement of axon and myelin sheath is normal, the ventral root is mainly composed of large axon (>6 μm) and it is composed of 46.3 % of all the axons of the ventral root; the average myelin thickness of large axon is 1.86 μm; the dorsal root is mainly composed of medium (2-3.9 or 4-5.9 μm) axons and they are composed of 79.1 % of all the axons of the dorsal root; the average myelin thickness of this category is 0.94 or 1.55 μm. The average myelin thickness of large axon in ventral root reduced to 0.97 and 1.19 μm from more than 1.86 μm after compression for 3 and 8 days separately. Most of myelin sheath disappeared after 12 days of compression; the myelin sheath was partly restored at 45 days after compression which the myelin sheath thickness of large axons in ventral root was 0.47 μm. The medium category in dorsal root reduced to 0.59 or 0.72 μm from 0.94 μm, and 1.55 μm after compression for 3 days (p < 0.05 to p < 0.0001). The medium category axon in dorsal root is also 0.47 μm after compression for 45 days (p ≤ 0.0001). The myelin sheath was almost totally restored at the 5 months of compression; the myelin sheath thickness returned to normal and the axons were intact in structure under EM. The number of Iba1-positive microglia increased by 18.69, 40.44, and 18.49 % after compression for 3, 8, and 12 days separately in the ipsilateral dorsal horn and 21.26, 32.15, 22.87 % in ventral horns, and the activation of microglia was also prominent in contralateral sides of the dorsal and ventral horn at 8 days time point. The microglia cell reconverted to resting status after compression for 45 days or 5 months.

CONCLUSION

The chronic spinal nerve root compression with silicone tube produces a recoverable damage to nerve root, which produces recoverable microglial activation in the spinal cord. These results demonstrated that the chronic spinal nerve root compression with silicone tube could mimic the pathological changes of lumbar spinal stenosis or lumbar disc herniation.

Mechanical compression and nucleus pulposus application on dorsal root Ganglia differentially modify evoked neuronal activity in the thalamus

A combination of mechanical compression caused by a protruding disc and leakage of nucleus pulposus (NP) from the disc core is presumed to contribute to intervertebral disc hernia-related pain. Experimental models of disc hernia including both components have resulted in changes in neuronal activity at the level of the dorsal root ganglion (DRG) and spinal cord, but changes within the brain have been less well studied. However, acute application of NP to a DRG without mechanical compression rapidly increases neuronal activity in the thalamus, a major brain relay nucleus processing information from sensory pathways including ascending nociceptive tracts. The combination of mechanical compression and NP might therefore result in further increases in central neuronal activity. Using an experimental disc herniation rat model including both mechanical compression and NP the present study aimed to investigate changes in neuronal activity in the contralateral thalamic ventral posterior lateral nucleus in vivo. Measurements were obtained while electrically stimulating the ipsilateral sciatic nerve at Aδ fiber intensities. The L4 DRG was subjected to light mechanical compression and NP exposure, and acute changes in evoked thalamic responses were recorded for up to 40 min. In order to compare effects in naïve animals with effects following a longer period of NP exposure, animals that were either disc-punctured or sham-operated 24 h previously were also included. In all animals, light mechanical compression of the DRG depressed the number of evoked neuronal responses. Prior NP exposure resulted in less potent changes following mechanical compression (80% of baseline) than that observed in naïve animals (50%). During the subsequent NP application, the number of evoked responses compared to baseline increased in pre-exposed animals (to 87%) as well as in naïve animals (72%) in which the removal of the mechanical compression resulted in a further increase (106%). The contribution of acute DRG compression and disc material leakage to changes in transmission in central neuronal networks is likely to be complex and to involve both short-term and long-term effects. Since a light mechanical compression may reduce transmission in nociceptive pathways, it is possible that the presence or absence of NP is crucial for pain development in the acute phase of disc herniation.

Changes in pain behavior and glial activation in the spinal dorsal horn after pulsed radiofrequency current administration to the dorsal root ganglion in a rat model of lumbar disc herniation: laboratory investigation

OBJECT

Herniated discs can induce sciatica by mechanical compression and/or chemical irritation caused by proinflammatory cytokines. Using immunohistochemistry methods in the dorsal horn of a rat model of lumbar disc herniation, the authors investigated the effects of pulsed radiofrequency (PRF) current administration to the dorsal root ganglion (DRG) on pain-related behavior and activation of microglia, astrocytes, and mitogen-activated protein kinase.

METHODS

A total of 33 Sprague-Dawley rats were randomly assigned to either a sham-operated group (n = 10) or a nucleus pulposus (NP)-exposed group (n = 23). Rats in the NP-exposed group were further subdivided into NP exposed with sham stimulation (NP+sham stimulation, n = 10), NP exposed with PRF (NP+PRF, n = 10), or euthanasia 10 days after NP exposure (n = 3). The DRGs in the NP+PRF rats were exposed to PRF waves (2 Hz) for 120 seconds at 45 V on postoperative Day 10. Rats were tested for mechanical allodynia 10 days after surgery and at 8 hours, 1 day, 3 days, 10 days, 20 days, and 40 days after PRF administration. Immunohistochemical staining of astrocytes (glial fibrillary acidic protein), microglia (OX-42), and phosphorylated extracellular signal-regulated kinases (pERKs) in the spinal dorsal horn was performed at 41 days after PRF administration.

RESULTS

Starting at 8 hours after PRF administration, mechanical withdrawal thresholds dramatically increased; this response persisted for 40 days (p < 0.05). After PRF administration, immunohistochemical expressions of OX-42 and pERK in the spinal dorsal horn were quantitatively reduced (p < 0.05).

CONCLUSIONS

Pulsed radiofrequency administration to the DRG reduced mechanical allodynia and downregulated microglia activity and pERK expression in the spinal dorsal horn of a rat model of lumbar disc herniation.

Changes in midbrain pain receptor expression, gait and behavioral sensitivity in a rat model of radiculopathy

Intervertebral disc herniation may contribute to inflammatory processes that associate with radicular pain and motor deficits. Molecular changes at the affected dorsal root ganglion (DRG), spinal cord, and even midbrain, have been documented in rat models of radiculopathy or nerve injury. The objective of this study was to evaluate gait and the expression of key pain receptors in the midbrain in a rodent model of radiculopathy. Radiculopathy was induced by harvesting tail nucleus pulposus (NP) and placing upon the right L5 DRG in rats (NP-treated, n=12). Tail NP was discarded in sham-operated animals (n=12). Mechanical allodynia, weight-bearing, and gait were evaluated in all animals over time. At 1 and 4 weeks after surgery, astrocyte and microglial activation was tested in DRG sections. Midbrain sections were similarly evaluated for immunoreactivity to serotonin (5HT_2B), mu-opioid (µ-OR), and metabotropic glutamate (mGluR4 and 5) receptor antibodies. NP-treated animals placed less weight on the affected limb 1 week after surgery and experienced mechanical hypersensitivity over the duration of the study. Astroctye activation was observed at DRGs only at 4 weeks after surgery. Findings for pain receptors in the midbrain of NP-treated rats included an increased expression of 5HT_2B at 1, but not 4 weeks; increased expression of µ-OR and mGluR5 at 1 and 4 weeks (periaqueductal gray region only); and no changes in expression of mGluR4 at any point in this study. These observations provide support for the hypothesis that the midbrain responds to DRG injury with a transient change in receptors regulating pain responses.

The effect of hyaluronidase in interlaminar lumbar epidural injection for failed back surgery syndrome

Objective

To evaluate the effect of hyaluronidase in patients with failed back surgery syndrome (FBSS) treated with interlaminar lumbar epidural injection (ILEI).

Method

Sixty patients suffering from severe low back pain and sciatica were randomly allocated into three groups. Group T received ILEI with 2 ml triamcinolone 40 mg/ml and 5 ml bupivacaine 0.25%. Group H received ILEI with 1500 IU hyaluronidase and 5 ml bupivacaine 0.25%. Group TH received interlaminar lumbar epidural injection (ILEI) with 1500 IU hyaluronidase, 2 ml triamcinolone 40 mg/ml and 5 ml bupivacaine 0.25%. The effect was evaluated using Visual Analogue Scale (VAS) and Oswestry Disability Index (ODI) at pre-injection, 2 weeks, 6 weeks and 12 weeks after ILEI.

Results

After 2 weeks and after 6 weeks, patients in both Group T and Group TH had significant effectiveness more than Group H in decrease of VAS and ODI. After 12 weeks, only patients in Group TH had significant effectiveness in decrease of VAS and ODI (p<0.05). In every period, Group TH had the most effectivess in decrease of VAS and ODI after ILEI.

Conclusion

ILEI for FBSS with triamcinolone and hyaluronidase is considered to have more long term effectiveness to reduce pain and improve function after ILEI than injection with triamcinolone alone or hyaluronidase alone.

Changes in expression of mRNA for interleukin-8 and effects of interleukin-8 receptor inhibitor in the spinal dorsal horn in a rat model of lumbar disc herniation

STUDY DESIGN

Autologous nucleus pulposus obtained from coccygeal intervertebral discs was grafted on the proximal of L5 dorsal root ganglion. Pain behavior, mRNA expression of Interleukin-8 (IL-8), and immunohistochemical changes were assessed.

OBJECTIVE

The purpose of this study is to investigate temporal changes of IL-8 expression in the spinal cord and dorsal root ganglion and the pain-related behaviors with time course and to elucidate whether repertaxin (IL-8 receptor inhibitor) attenuates pain-related behaviors in a rat model of lumbar disc herniation.

SUMMARY OF BACKGROUND DATA

Inflammatory mediators like cytokines and chemokines have been implicated in radicular pain because of disc herniation. IL-8, known as CXCL8, is a chemokine, which has been reported to be associated with painful degenerative disc disorders and chronic inflammatory pain states.

METHODS

Lumbar disc herniated rat model was made by implantation of the autologous nucleus pulposus, harvested from the coccygeal vertebra of each tail, on the left L5 nerve root just proximal to the dorsal root ganglion. Rats were tested for mechanical allodynia and thermal hyperalgesia at 2 days before surgery, and on days 1, 5, 10, 20, 30, 40, 50, and 60 postoperatively. Experimental group was intrathecally injected with the IL-8 receptor inhibitor at L5 level on postoperative day 10. Mechanical allodynia of the plantar surface of both hindpaw was tested on 30 minutes, 1, 3 hours, 1, 3, 5, and 10 days after administration. For the staining of astrocytes and microglia, immunohistochemical study was done 20 days after surgery.

RESULTS

Mechanical allodynia in ipsilateral hindpaw developed 1 day after surgery and lasted until 60 days and thermal withdrawal latency decreased significantly on the ipsilateral side 10 days after surgery and gradually increased through day 60. The IL-8 receptor inhibitor attenuated the mechanical allodynia caused by nucleus pulposus when it was administered on postoperative day 10 and reduced microglial activation and phosphorylated form of mitogen-activated protein kinase (pERK) expression in the spinal dorsal horn.

CONCLUSION

IL-8 might be a potential therapeutic target in chronic radicular neuropathic pain because of disc herniation, CXCL8 inhibitor could be one of its promising therapeutic agents.

The red wine polyphenol resveratrol shows promising potential for the treatment of nucleus pulposus-mediated pain in vitro and in vivo

STUDY DESIGN

Descriptive and mechanistic investigation of the anti-inflammatory and anticatabolic effect of resveratrol in intervertebral discs (IVDs) in vitro and of the analgetic effect in vivo.

OBJECTIVE

To determine whether resveratrol may be useful in treating nucleus pulposus (NP)-mediated pain.

SUMMARY OF BACKGROUND DATA

Proinflammatory cytokines seem to be key mediators in the development of NP-mediated pain. Patients with discogenic or radiculopathic pain may substantially benefit from anti-inflammatory substances that could be used in a minimal-invasive treatment approach. Resveratrol, a polyphenolic phytoalexin found in red wine exhibits anti-inflammatory effects in various cell types and tissues, but no data exists so far with regards to the IVD in the context of low back and leg pain.

METHODS

In part 1, the anti-inflammatory and anticatabolic effect of resveratrol was investigated in a cell culture model on interleukin 1β (IL-1β) prestimulated human IVD cells on the gene and protein expression level. In part 2, the molecular mechanisms underlying the effects observed upon resveratrol treatment were investigated (toll-like receptors, nuclear factor κB, sirtuin 1 (SIRT1), mitogen-activated protein (MAP) kinases p38/ERK/JNK). In part 3, the analgetic effects of resveratrol were investigated in vivo using a rodent model of radiculopathy and von Frey filament testing. All quantitative data were statistically evaluated either by Mann-Whitney U test or by one-way analysis of variance and Bonferroni post hoc testing (P < 0.05).

RESULTS

In vitro, resveratrol exhibited an anti-inflammatory and anticatabolic effect on the messenger RNA and protein level for IL-6, IL-8, MMP1, MMP3 and MMP13. This effect does not seem to be mediated via the MAP kinase pathways (p38, ERK, JNK) or via the NF-κB/SIRT1 pathway, although toll-like receptor 2 was regulated to a minor extent. In vivo, resveratrol significantly reduced pain behavior triggered by application of NP tissue on the dorsal root ganglion for up to 14 days.

CONCLUSION

Resveratrol was able to reduce levels of proinflammatory cytokines in vitro and showed analgetic potential in vivo. A decrease in proinflammatory cytokines may possibly be the underlying mechanism of pain reduction observed in vivo. Resveratrol seems to have considerable potential for the treatment of NP-mediated pain and may thus be an alternative to other currently discussed (biological) treatment options.

Triptolide exhibits anti-inflammatory, anti-catabolic as well as anabolic effects and suppresses TLR expression and MAPK activity in IL-1β treated human intervertebral disc cells

INTRODUCTION

Increased levels of proinflammatory cytokines seem to play a pivotal role in the development of back pain in a subpopulation of patients with degenerative intervertebral disc (IVD) disease. As current treatment options are mostly limited to surgical interventions or conservative treatment, anti-inflammatory substances might offer a novel, more target-orientated therapeutic approach. Triptolide (TPL), a natural substance found in the Chinese medicinal herb Tripterygium wilfordii Hook, has been demonstrated to possess anti-inflammatory effects in various cells, but no studies exist so far for the IVD. Therefore, the aim of this study was to determine the effects of TPL on human IVD cells by analyzing changes in gene expression and underlying molecular mechanisms.

MATERIALS AND METHODS

In order to investigate the anti-inflammatory, anabolic and anti-catabolic effect of TPL, dose-dependency experiments (n = 5) and time course experiments (n = 5) were performed on IL-1β prestimulated human IVD cells and changes in gene expression of IL-6/-8, TNF-α, PGE2S, MMP1/2/3/13, aggrecan and collagen-I/-II were analyzed by real-time RT-PCR. The molecular mechanisms underlying the effects observed upon TPL treatment were investigated by analyzing involvement of Toll-like receptors TLR2/4 (real-time RT-PCR, n = 5), NF-κB, MAP kinases p38, ERK and JNK (immunoblotting and immunocytochemistry, n = 4) as well as RNA polymerase II (immunoblotting, n = 3).

RESULTS

Results showed that 50 nM TPL exhibited an anti-inflammatory, anti-catabolic and anabolic effect on the mRNA level for IL-6/-8, PGE2S, MMP1/2/3/13, aggrecan, collagen-II and TLR2/4, with most pronounced changes after 18 h for proinflammatory cytokines and MMPs or 30 h for TLRs and matrix proteins. However, we also observed an up-regulation of TNF-α at higher concentrations. The effects of TPL did not seem to be mediated via an inhibition of NF-κB or a decrease of RNA polymerase II levels, but TPL influenced activity of MAP kinases p38 and ERK (but not JNK) and expression of TLR2/4.

CONCLUSIONS

In conclusion, TPL may possess promising potential for the treatment of inflammation-related discogenic back pain in vitro, but its analgetic effect will need to be confirmed in an appropriate in vivo animal model.

Changes in spinal cord expression of fractalkine and its receptor in a rat model of disc herniation by autologous nucleus pulposus

STUDY DESIGN

Behavior, mRNA and immunohistochemical assessment of the expression of fractalkine (CX3CL1) and its receptor (CX3CR1) in a rat model of disc herniation by autologous nucleus pulposus (NP) implantation.

OBJECTIVE

To evaluate the changes in expression of fractalkine and its receptor in the spinal cord and their association with pain behavior in a rat model of disc herniation.

SUMMARY OF BACKGROUND DATA

Chemokines have recently been implicated in the pathophysiology of neuropathic pain. They mediate astrocytic migration and microglial proliferation, which are involved in the regulation of nociceptive transmission. Fractalkine is a chemokine, which participates in the mechanisms of neuropathic pain as a mediator of neuron-glia interactions.

METHODS

Sixty-six rats (NP-treated = 47, sham = 19) were implanted with autologous NP (approximately 3 mg) on the left L5 nerve root, just proximal to the dorsal root ganglion and tested for thermal hyperalgesia and mechanical allodynia before surgery and on days 1, 5, 10, 20, and 30 after surgery. The changes of expression of fractalkine and its receptor in the spinal cord were studied using real time PCR and immunohistochemistry.

RESULTS

Rats developed ipsilateral mechanical allodynia at day 1 and bilateral thermal hyperalgesia at day 5 after surgery, and these changes in sensitivity persisted throughout the observation period. The expression of mRNA for fractalkine in the spinal cord was increased by day 5 and remained upregulated for the duration of the experiment. The immunostaining for fractalkine increased in neurons and astrocytes and that for the fractalkine receptor increased in microglia in the dorsal horn ipsilateral to the disc herniation.

CONCLUSION

Our results indicate that autologous implantation of NP induces thermal hyperalgesia and mechanical allodynia, and leads to an upregulation of fractalkine and its receptor in spinal neurons and glia, implicating fractalkine in association with radicular pain.

Gait abnormalities and inflammatory cytokines in an autologous nucleus pulposus model of radiculopathy

STUDY DESIGN

The authors investigated gait abnormalities and mechanical hypersensitivity associated with invertebral disc herniation in a rat model of radiculopathy. Further evaluation involved assessing how nucleus pulposus (NP) injury affected systemic cytokine expression and molecular changes at the dorsal root ganglion (DRG).

OBJECTIVE

The objective of this work was to describe the gait and behavioral changes in an animal model of disc-herniation induced radiculopathy. A second objective included examining how these functional changes correlated with neuroinflammation and autoreactive lymphocyte immune activation.

SUMMARY OF BACKGROUND DATA

Animal models of radiculopathy describe demyelination, slowed nerve conduction, and heightened pain sensitivity after application of autologous NP to the DRG. The quantitative impact of disc herniation on animal locomotion has not been investigated. Further, while local inflammation occurs at the injury site, the role of autoimmune cytokines reactive against previously immune-sequestered NP requires investigation.

METHODS

NP-treated animals (n = 16) received autologous tail NP placed onto the L5 DRG exposed by unilateral facetectomy, and control animals (n = 16) underwent exposure only. At weekly time points, animals were evaluated for mechanical allodynia, thermal hyperalgesia, and gait characteristics through digitized video analysis. Serum cytokine content was measured after animal sacrifice, and immunohistochemistry tested DRG tissue for mediators of inflammation and immune activation.

RESULTS

Sensory testing revealed mechanical allodynia in the affected limb of NP-treated rats compared with sham animals (P < 0.01) at all time points. Gait analysis reflected functional locomotive consequences of marked asymmetry (P = 0.048) and preference to bear weight on the contralateral limb (duty factor imbalance, P < 0.01) at early time points. Equivalent serum cytokine expression occurred in both groups, confirming the local inflammatory nature of this disease model. Immunohistochemistry of the sectioned DRGs revealed equivalent postsurgical inflammatory activation (interleukin 23, P = 0.47) but substantial early immune activation in the NP-treated group (interleukin 17, P = 0.01).

CONCLUSION

This model of radiculopathy provides evidence of altered gait in a model of noncompressive disc herniation. Systemic inflammation was absent, but mechanical allodynia, local inflammation, and autoreactive immune activation were observed. Future work will involve therapeutic interventions to rescue animals from the phenotype of inflammatory radiculopathy.

Chemical and mechanical nerve root insults induce differential behavioral sensitivity and glial activation that are enhanced in combination

Both chemical irritation and mechanical compression affect radicular pain from disc herniation. However, relative effects of these insults on pain symptoms are unclear. This study investigated chemical and mechanical contributions for painful cervical nerve root injury. Accordingly, the C7 nerve root separately underwent chromic gut exposure, 10gf compression, or their combination. Mechanical allodynia was assessed, and glial reactivity in the C7 spinal cord tissue was assayed at days 1 and 7 by immunohistochemistry using GFAP and OX-42 as markers of astrocytes and microglia, respectively. Both chromic gut irritation and 10gf compression produced ipsilateral increases in allodynia over sham (p<0.048); combining the two insults significantly (p<0.027) increased ipsilateral allodynia compared to either insult alone. Behavioral hypersensitivity was also produced in the contralateral forepaw for all injuries, but only the combined insult was significantly increased over sham (p<0.031). Astrocytic activation was significantly increased over normal (p<0.001) in the ipsilateral dorsal horn at 1 day after either compression or the combined injury. By day 7, GFAP-reactivity was further increased for the combined injury compared to day 1 (p<0.001). In contrast, spinal OX-42 staining was generally variable, with only mild activation at day 1. By day 7 after the combined injury, there were significant (p<0.003) bilateral increases in OX-42 staining over normal. Spinal astrocytic and microglial reactivity follow different patterns after chemical root irritation, compression, and a combined insult. The combination of transient compression and chemical irritation produces sustained bilateral hypersensitivity, sustained ipsilateral spinal astrocytic activation and late onset bilateral spinal microglial activation.

Anti-TNF-alpha antibody reduces pain-behavioral changes induced by epidural application of nucleus pulposus in a rat model depending on the timing of administration

STUDY DESIGN

An experimental animal study.

OBJECTIVE

To study if antitumor necrosis factor-alpha (TNF-alpha) antibody, which is administered at different times, reduces the pain behavior induced by application of nucleus pulposus (NP) to the nerve root.

SUMMARY OF BACKGROUND DATA

Treatment with TNF-alpha inhibitor reduces the pain-related behavior induced by epidural application of NP in rats.

METHODS

Left L5 partial laminectomy was performed and NP was applied to the L5 nerve root in 24 rats. The rats were divided into 4 groups. In 3 groups, anti-rat TNF-alpha antibody was intravenously administered immediately after, or 6 or 20 days after NP application. The fourth group was not treated with anti-rat TNF-alpha antibody (untreated rats). The withdrawal threshold of the plantar surface was determined 1 day before up through 28 days after NP application.

RESULTS

The withdrawal threshold of rats that had been treated with anti-rat TNF-alpha antibody immediately after or 6 days after, but not 20 days after, NP application, was significantly higher than that of the untreated rats.

CONCLUSIONS

Anti-TNF-alpha antibody reduced allodynia only when it was administered soon after the onset of allodynia. Late administration of anti-TNF-alpha antibody did not have an antiallodynic effect.

Effects of interleukin-1 beta, interleukin-6, and tumor necrosis factor on sensitivity of dorsal root ganglion and peripheral receptive fields in rats

This study was designed to characterize the effects of low doses (0.5-5 ng) of pro-inflammatory cytokines, interleukin-1 beta (IL-1beta), interleukin-6 (IL-6), and tumor necrosis factor (TNF), on the neural activity of dorsal root ganglion (DRG) in rats. The purpose of this study was to examine the effects of cytokines (IL-1beta, IL-6, and TNF) on the somatosensory neural response of DRG. The release of inflammatory cytokines by an injured disc may play a critical role in pain production at nerve endings, axons, and nerve cell bodies. Herniated disc tissue has been shown to release IL-1beta, IL-6, TNF, and other algesic chemicals. Their effects on nerve endings in disc and adjacent tissue may lead to low back pain and their effects on dorsal root axons and ganglia may lead to sciatica. Exposed lumbar DRGs were investigated by electrophysiologic techniques. Sham (mineral oil), control (carrier solution), or IL-1beta, IL-6, or TNF at doses of 0.5, 1, and 5 ng were applied over the DRG. Baseline discharge rates as well as mechanosensitivity of the DRG and peripheral receptive fields were evaluated over 30 min. Applications of IL-1beta at 1 ng resulted in an increase in the discharge rate, 5 ng resulted in an increased mechanosensitivity of the DRG in group II units. Similarly, after 1 ng TNF applications, group II units also showed an increase in mechanosensitivity of DRG and peripheral receptive fields. At low doses IL-1beta and TNF sensitization of receptive fields were observed. The responses observed in the group II units indicate that a sub-population of afferent units might have long-term effects modifying the sensory input to the central nervous system. This study provides added evidence to the role of cytokines in modulating afferent activity following inflammation.