Effects of selective tumor necrosis factor-alpha inhibition to pain-behavioral changes caused by nucleus pulposus-induced damage to the spinal nerve in rats

Pulsed Electromagnetic Fields Accelerate Sensorimotor Recovery Following Experimental Disc Herniation

STUDY DESIGN

An experimental animal study.

OBJECTIVE

The aim of this study was to investigate the effect of pulsed electromagnetic fields (PEMF) on recovery of sensorimotor function in a rodent model of disc herniation (DH).

SUMMARY OF BACKGROUND DATA

Radiculopathy associated with DH is mediated by proinflammatory cytokines. Although we have demonstrated the anti-inflammatory effects of PEMF on various tissues, we have not investigated the potential therapeutic effect of PEMF on radiculopathy resulting from DH.

METHODS

Nineteen rats were divided into three groups: positive control (PC; left L4 nerve ligation) (n = 6), DH alone (DH; exposure of left L4 dorsal root ganglion [DRG] to harvested nucleus pulposus and DRG displacement) (n = 6), and DH + PEMF (n = 7). Rodents from the DH + PEMF group were exposed to PEMF immediately postoperatively and for 3 hours/day until the end of the study. Sensory function was assessed via paw withdrawal thresholds to non-noxious stimuli preoperatively and 1 and 3 days postoperatively, and every 7 days thereafter until 7 weeks after surgery. Motor function was assessed via DigiGait treadmill analysis preoperatively and weekly starting 7 days following surgery until 7 weeks following surgery.

RESULTS

All groups demonstrated marked increases in the left hindlimb response threshold postoperatively. However, 1 week following surgery, there was a significant effect of condition on left hindlimb withdrawal thresholds (one-way analysis of variance: F = 3.82, df = 2, P = 0.044) where a more rapid recovery to baseline threshold was evident for DH + PEMF compared to PC and DH alone. All groups demonstrated gait disturbance postoperatively. However, DH + PEMF rodents were able to regain baseline gait speeds before DH and PC rodents. When comparing gait parameters, DH + PEMF showed consistently less impairment postoperatively suggesting that PEMF treatment was associated with less severe gait disturbance.

CONCLUSION

These data demonstrate that PEMF accelerates sensorimotor recovery in a rodent model of DH, suggesting that PEMF may be reasonable to evaluate for the clinical management of patients with herniation-associated radiculopathy.Level of Evidence: N/A.

Biologic Drugs as Analgesics for the Management of Low Back Pain and Sciatica

Objective

To discuss the current knowledge on the impact of commonly used biologic agents (i.e., anti–tumor necrosis factor–alpha [anti-TNF-α] and anti–nerve growth factor [anti-NGF]) in the management of low back pain with or without sciatica.

Methods

A narrative literature review of studies investigating the use of biologic agents for the management of low back pain and sciatica was conducted. We searched MEDLINE and EMBASE for English language publications. A hand-search of reference lists of relevant studies was also performed.

Results

Although some observational studies showed that inhibition of TNF-α reduced pain and improved function, randomized controlled trials and a meta-analysis failed to demonstrate the superiority of anti-TNF-α over placebo in this regard. Anti-TNF-α, however, reduced the risk of having invasive procedures such as discectomy and radicular block in cases of sciatica. Conversely, controlled studies showed moderate pain reduction and mild functional improvement with anti-NGF administration, but the side effect profile of anti-NGF was unfavorable compared with placebo.

Conclusions

Overall, anticytokine treatments have limited efficacy in patients with chronic low back pain with or without sciatica. However, larger and better-designed studies may need to be performed in specific patient subpopulations. Low back pain is particularly disabling in younger patients. This group therefore represents a potential target population for investigating the effectiveness of anticytokine therapies, especially where other pharmacological and nonpharmacological management strategies have failed.

Effectiveness of conservative interventions for sickness and pain behaviors induced by a high repetition high force upper extremity task

Background

Systemic inflammation is known to induce sickness behaviors, including decreased social interaction and pain. We have reported increased serum inflammatory cytokines in a rat model of repetitive strain injury (rats perform an upper extremity reaching task for prolonged periods). Here, we sought to determine if sickness behaviors are induced in this model and the effectiveness of conservative treatments.

Methods

Experimental rats underwent initial training to learn a high force reaching task (10 min/day, 5 days/week for 6 weeks), with or without ibuprofen treatment (TRHF vs. TRHF + IBU rats). Subsets of trained animals went on to perform a high repetition high force (HRHF) task for 6 or 12 weeks (2 h/day, 3 days/week) without treatment, or received two secondary interventions: ibuprofen (HRHF + IBU) or a move to a lower demand low repetition low force task (HRHF-to-LRLF), beginning in task week 5. Mixed-effects models with repeated measures assays were used to assay duration of social interaction, aggression, forepaw withdrawal thresholds and reach performance abilities. One-way and two-way ANOVAs were used to assay tissue responses. Corrections for multiple comparisons were made.

Results

TRHF + IBU rats did not develop behavioral declines or systemic increases in IL-1beta and IL-6, observed in untreated TRHF rats. Untreated HRHF rats showed social interaction declines, difficulties performing the operant task and forepaw mechanical allodynia. Untreated HRHF rats also had increased serum levels of several inflammatory cytokines and chemokines, neuroinflammatory responses (e.g., increased TNFalpha) in the brain, median nerve and spinal cord, and Substance P and neurokinin 1 immunoexpression in the spinal cord. HRHF + IBU and HRHF-to-LRLF rats showed improved social interaction and reduced inflammatory serum, nerve and brain changes. However, neither secondary treatment rescued HRHF-task induced forepaw allodynia, or completely attenuated task performance declines or spinal cord responses.

Conclusions

These results suggest that inflammatory mechanisms induced by prolonged performance of high physical demand tasks mediate the development of social interaction declines and aggression. However, persistent spinal cord sensitization was associated with persistent behavioral indices of discomfort, despite use of conservative secondary interventions indicating the need for prevention or more effective interventions.

Electronic supplementary material

The online version of this article (doi:10.1186/s12868-017-0354-3) contains supplementary material, which is available to authorized users.

Etanercept attenuates thermal and mechanical hyperalgesia induced by bone cancer

Bone cancer pain commonly occurs when tumors originating in the breast, prostate or lung metastasize to long bones, spinal vertebrae and/or the pelvis. However, the underlying mechanisms of bone cancer pain remain largely unknown. The present study aimed to determine the role of spinal tumor necrosis factor-α (TNF-α) in the development of bone cancer pain. Osteosarcoma NCTC 2472 cells were implanted into the femoral intramedullary space of C3H/HeJ mice to establish a bone cancer model. Resulting pain-related behaviors, namely spontaneous foot lifting, paw withdrawal mechanical threshold and paw withdrawal thermal latency were observed prior to inoculation and on days 3, 5, 7, 10 and 14 thereafter. Reverse transcription-quantitative polymerase chain reaction was also performed to assess the levels of TNF-α mRNA within the spinal cord. In addition, the effects of the TNF-α antagonist etanercept on TNF-α levels and pain behaviors were evaluated. It was observed that the levels of TNF-α mRNA in the spinal cord were significantly higher in tumor-bearing mice 10 days post-inoculation, which was accompanied by increases in spontaneous flinching, mechanical hyperalgesia and thermal hyperalgesia, relative to control mice. Etanercept attenuated the bone cancer-induced increase in TNF-α and pain-related behaviors. These results suggest that etanercept may be a potential therapeutic for the treatment of bone cancer pain.

Comparison of the Intravenous and Epidural Administration of Tumor Necrosis Factor-alpha Antagonists in an Experimental Rat Pain Model

Introduction

Inflammatory cytokines secreted from the nucleus pulposus are thought to lead to lumbar nerve root compression-like symptoms. Tumor necrosis factor-alpha (TNF-α), an inflammatory cytokine, likely plays an important role in lumbar disc hernia-related leg pain. In this experimental study, we compared the effectiveness of TNF-α antagonists administered through the intravenous or epidural route in lumbar spine pathologies.

Materials and Methods

After ethics committee approval had been obtained, 24 Sprague Dawley male rats aged 70-90 days and weighing 250-300 g each were allocated to four groups. In Group I, only the surgical procedure was performed; in Group II, 1 ml of saline solution was administered into the epidural field; in Group III, 10 mg/kg of infliximab was administered into the coccygeal vein; and in Group IV (epidural group), 25 mg of etanercept was administered into the epidural region.

Results

When the left leg pull values were analyzed on day 14, whereas there was not a significant difference among the three groups, a decreasing difference was observed in Group IV (P < 0.05). When the 21^st and 28^th day left leg pull values were compared between groups, the values from Groups II, III, and IV were significantly lower than those of Group I (P < 0.05).

Conclusion

The absence of a difference between the baseline values and left leg pull values on days 14, 21, and 28 in Group IV indicates that recovery began on day 21 with the epidural administration of etanercept. There was no difference between intravenous saline administration and intravenous infliximab administration with regard to the start of the recovery. In the present study of rats with discopathy, TNF-α antagonists administered epidurally led to earlier recovery from radiculopathy-related allodynia compared to intravenous administration.

Protective effects of resveratrol on autologous nucleus pulposus model of radiculopathy

Nucleus pulposus (NP) has been suggested to trigger an autoimmune response if exposed to the immune system, which plays a key role in neuropathic pain. Therefore, appropriate suppression of inflammation is a key factor for treating the radiculopathy caused by intervertebral disk (IVD) degeneration. Resveratrol, a key component of red wine, has been suggested to exhibit anti-inflammatory properties in vitro and in vivo. However, the effects of resveratrol on NP-mediated pain in vivo have not been studied. The aim of the present study was to investigate whether resveratrol may be useful in treating NP-mediated pain in an autologous NP model of radiculopathy. A total of 36 adult male Sprague-Dawley rats were allocated randomly into sham (group I), saline-treated (group II) and resveratrol-treated (group III) groups. Animal behavior in response to non-noxious mechanical stimulation with von Frey filaments was compared at days 0 (baseline), 3, 7, 14 and 21 following surgery. The expression of proinflammatory cytokines such as tumor necrosis factor α (TNF-α) and interleukin-1 (IL-1) were assessed at days 7 and 14. The data showed that resveratrol exhibited an anti-inflammatory effect on the expression of proinflammatory cytokines. Compared with group II, the expression of TNF-α and IL-1 was significantly decreased at each time point in group III. In addition, resveratrol significantly reduced pain behavior triggered by the application of NP tissue on the dorsal root ganglion for up to 14 days. These data suggest that resveratrol has potential for the treatment of NP-mediated pain, indicating a potential clinical application.

Sickness behaviors (reduced social interaction and pain behaviors) are linked to inflammatory mechanisms in a rat model of work-related musculoskeletal disorders

We sought to determine if sickness behaviors (decreased social interaction and pain) are induced in a rat model of work-related overuse and effectiveness of anti-inflammatory treatments. Rats first trained to learn a high force reaching task (15 min/week day for 6 wks), with subsets treated prophylactically with ibuprofen or anti-TNFalpha. Others performed a high repetition high force (HRHF) task for 6 or 12 weeks (2 hrs/day, 3 days/wk) untreated, or with ibuprofen, anti-TNFalpha or rest treatments beginning task week 5. Untreated HRHF rats had increased IL-1beta, IL-6 and TNFalpha in serum and brain, increased Substance P in spinal cord, decreased social interaction and increased forepaw allodynia. Secondary anti-inflammatory treatments attenuated social interaction and brain changes, but not allodynia or spinal cord changes; rest provided partial attenuation. Prophylactic treatments prevented all changes. Thus, inflammatory mechanisms mediate the development of sickness behaviors induced by work-related overuse, but not maintenance of allodynia.

Current trends in biologics delivery to restore intervertebral disc anabolism

Low back pain is generally attributed to intervertebral disc (IVD) degeneration. This is a multifactorial disease induced by genetic and environmental factors and that progresses with aging. Disc degeneration is characterized by a limited ability of IVD cells to produce functional matrix while producing abnormal amounts of matrix-degrading enzymes. The prolonged imbalance between anabolism and catabolism in degenerative discs alters their composition and hydration. In turn, this results in increased angiogenesis and the loss of the disc's ability to maintain its aneural condition. Inflammation in the IVD, in particular the presence of pro-inflammatory cytokines, was found to favor innervation and also sensitization of the nociceptive pathways, thereby exacerbating degenerative symptoms. In this review, we discuss anti-inflammatory approaches to encounter disc catabolism, potential treatments to lower discogenic pain and pro-anabolic approaches in the form of protein delivery, gene therapy and cell delivery, to trigger regeneration in the IVD.

Tumor necrosis factor-α inhibitors alleviation of experimentally induced neuropathic pain is associated with modulation of TNF receptor expression

Inflammation plays a key role in the development of sensitization after peripheral nerve damage. We recently demonstrated that tumor necrosis factor-α receptor (TNFR) levels in the spinal cord correlate with pain sensation in herniated disc patients in a rat chronic constriction injury (CCI) model. By using the sciatic nerve CCI model, we studied the effect of anti-TNF-α treatment on recovery from hypersensitivity and TNFR expression in the dorsal root ganglion (DRG) and dorsal horn (DH). Experimental groups consisted of sham-operated and CCI-operated rats that received two s.c. injections (one immediately after surgery, the other 5 days later), both containing saline, etanercept (3 mg/kg body weight), or infliximab (10 mg/kg body weight). Mechanical allodynia (with von Frey filaments) and thermal hyperalgesia (Hargreaves test) were assessed preoperatively and weekly during the first 4 postoperative weeks. DRG and DH samples were collected 2 and 4 weeks after surgery and analyzed for TNFR1 and TNFR2 protein levels by Western blotting and analyzed for mRNA levels by quantitative real-time polymerase chain reaction. Anti-TNF-α treatment resulted in a significant alleviation of pain. TNFR levels were increased five- to sixfold in CCI rats compared with sham controls. Both treatments significantly diminished these increased levels. Treated animals that showed a ≥50% alleviation of pain exhibited a significantly reduced TNF R1/R2 mRNA ratio compared with treated animals that recovered less well. These results demonstrate that attenuation of TNFR expression is associated with recovery from nerve injury and suggest that this may be one of the working mechanisms of anti-TNF therapies.

Tumor necrosis factor-α-dependent infiltration of macrophages into the dorsal root ganglion in a rat disc herniation model

STUDY DESIGN

A prospective molecular mechanism of macrophages infiltration in experimental disc herniation.

OBJECTIVE

To investigate the mechanisms of macrophages infiltration into the dorsal root ganglion (DRG) in a rat model of disc herniation.

SUMMARY OF BACKGROUND DATA

Macrophages infiltrate the DRG after application of nucleus pulposus (NP) on the DRG, and may play an important role in radiculopathy. However, the mechanisms of macrophages infiltration after NP application remain poorly understood.

METHODS

After experimental disc herniation in this study, we investigated changes in the expression of ED1 (a marker of macrophages) and vascular cell adhesion molecule-1 (VCAM-1) in DRG using immunofluorescence. We also investigated the expression of ED1 and VCAM-1 in DRG by treatment with tumor necrosis factor-α (TNF-α) inhibitor at the time of surgery.

RESULTS

We found a massive ED1-positive macrophages infiltrated the DRG, and VCAM-1-like immunoreactivity vessels became evident after NP application. Furthermore, both macrophage infiltration and VCAM-1 expression were prevented by treatment with TNF-α inhibitor at the time of surgery.

CONCLUSION

These findings indicated that macrophages infiltration into the DRG was TNF-α-dependent, and might be partly mediated by VCAM-1 in the early stage of experimental lumbar disc herination. Taken together, this study provides important preliminary data suggesting that TNF-α plays an important role in the macrophage infiltration.

LEVEL OF EVIDENCE

N/A.

Effects of epidural TNF-α inhibitor injection: analysis of the pathological changes in a rat model of chronic compression of the dorsal root ganglion

OBJECTIVES

To evaluate the efficacy of a single direct epidural injection of tumor necrosis factor (TNF)-α inhibitor to reduce the pathological changes in nerve fiber injuries in a rat model of chronic compression of the dorsal root ganglion (CCD).

MATERIALS AND METHODS

A surgical procedure for CCD was performed in 17 adult male F-344 rats. The effects of the epidural TNF-α inhibitors on CCD-induced pathological changes were investigated. Three groups of rats (n = 17) were used: (1) CCD + saline (n = 4), (2) CCD + triamcinolone (n = 5), and (3) CCD + TNF-α inhibitors (n = 8). Their dorsal root ganglia and nerve roots were removed on postoperative day 14. The intraneural edema, demyelination, and Wallerian degeneration of all 17 rats were scored pathologically.

RESULTS

The pathology scores of the rats in the TNF-α inhibitor treatment group (1.38 ± 0.74) indicated a mild degree of intraneural edema compared to the saline treatment group (2.25 ± 0.50, p = 0.041). In addition, rats in the TNF-α inhibitor treatment group (2.13 ± 0.35) had a mild degree of demyelination compared to the saline treatment group (2.75 ± 0.50, p = 0.038) and the triamcinolone treatment group (2.80 ± 0.45, p = 0.019). The differences in the pathology scores for Wallerian degeneration were not statistically significant in all three study groups (p = 0.658).

CONCLUSION

The epidural injection of a TNF-α inhibitor was more effective than a placebo and comparable to triamcinolone in reducing pathological nerve injury progression.

Measurements in the Blood of BDNF for RA Patients and in Response to Anti-TNF Treatment Help Us to Clarify the Magnitude of Centrally Related Pain and to Explain the Relief of This Pain upon Treatment

Brain-derived neurotrophic factor (BDNF) is a neurotrophin with functions related to neuronal survival/proliferation processes and inflammation. BDNF is also an important central pain mediator. The levels of BDNF have been found to be high for RA patients with severe disease and to become lowered in response to anti-TNF treatment. New information says that the levels of BDNF in the blood parallel the BDNF concentrations in the brain and that BDNF can pass the blood-brain barrier. Furthermore, most of the circulating BDNF is produced in the brain. Habitual and regular exercise, in contrast to temporary exercise, does also lead to a lowering of BDNF blood levels. Both anti-TNF treatment and habitual and regular exercise do have pain-relieving effects. It might be that the pain-relieving effect of anti-TNF treatment is related to an affection of central neuronal regions, hereby influencing BDNF production. Measurements of BDNF in the blood help us to clarify the magnitude of centrally related pain for RA patients and help us to explain the relief of this pain in response to anti-TNF treatment.

Changes in intramuscular cytokine levels during masseter inflammation in male and female rats

The present study was conducted to examine cytokine profiles in the masseter muscle before and after complete Freund's adjuvant (CFA)-induced inflammation and possible sex differences in the cytokine levels. Age matched male and female Sprague Dawley rats were injected with CFA in the mid-region of the masseter muscle. Muscle tissue surrounding the injection site was extracted 6h, 1, 3 and 7 days after the injection to measure TNF-α, IL-1β, IL-6 and IL-4 levels with Luminex multi-analyte profiling (xMAP) technology. The cytokine levels were compared to those obtained from naïve rats. CFA injection into the masseter muscle led to a significant time effect in the level of TNF-α compared to that of naïve rats. The pattern of changes in TNF-α level after CFA injection was significantly different between the male and female rats owing to the differences in basal levels. CFA injection induced significant time-dependent increases in the levels of IL-1β and IL-6 in the masseter muscle in both male and female rats. The level of IL-4 was slightly, but significantly, reduced in both sexes at 6h and 3 days after CFA-induced inflammation. No significant sex differences were observed in the levels of IL-1β, IL-6 or IL-4. The results provided novel information about distinct cytokine profiles during CFA-induced muscle inflammation, and the basis for further pursuing contributions of each cytokine in pain processing and analgesic responses in both sexes.

Role of TNF alpha and PLF in bone remodeling in a rat model of repetitive reaching and grasping

We have previously developed a voluntary rat model of highly repetitive reaching that provides an opportunity to study effects of non-weight bearing muscular loads on bone and mechanisms of naturally occurring inflammation on upper limb tissues in vivo. In this study, we investigated the relationship between inflammatory cytokines and matricellular proteins (Periostin-like-factor, PLF, and connective tissue growth factor, CTGF) using our model. We also examined the relationship between inflammatory cytokines, PLF and bone formation processes. Rats underwent initial training for 5 weeks, and then performed a high repetition high force (HRHF) task (12 reaches/min, 60% maximum grip force, 2 h/day, 3 days/week) for 6 weeks. We then examined the effect of training or task performance with or without treatment with a rat specific TNFalpha antibody on inflammatory cytokines, osteocalcin (a bone formation marker), PLF, CTGF, and behavioral indicators of pain or discomfort. The HRHF task decreased grip strength and induced forepaw mechanical hypersensitivity in both trained control and 6-week HRHF animals. Two weeks of anti-TNFalpha treatment improved grip strength in both groups, but did not ameliorate forepaw hypersensitivity. Moreover, anti-TNFalpha treatment attenuated task-induced increases in inflammatory cytokines (TNFalpha, IL-1alpha, and MIP2 in serum; TNFalpha in forelimb bone and muscles) and serum osteocalcin in 6-week HRHF animals. PLF levels in forelimb bones and flexor digitorum muscles increased significantly in 6-week HRHF animals, increases attenuated by anti-TNFalpha treatment. CTGF levels were unaffected by task performance or anti-TNFalpha treatment in 6-week HRHF muscles. In primary osteoblast cultures, TNFalpha, MIP2 and MIP3a treatment increased PLF levels in a dose dependent manner. Also in primary osteoblast cultures, increased PLF promoted proliferation and differentiation, the latter assessed by measuring Runx2, alkaline phosphatase (ALP) and osteocalcin mRNA levels; ALP activity; as well as calcium deposition and mineralization. Increased PLF also promoted cell adhesion in MC3T3-E1 osteoblast-like cell cultures. Thus, tissue loading in vivo resulted in increased TNFalpha, which increased PLF, which then induced anabolic bone formation, the latter results confirmed in vitro.

Anti-nociceptive effect of bovine milk-derived lactoferrin in a rat lumbar disc herniation model

STUDY DESIGN

An experimental animal study.

OBJECTIVE

We evaluated the efficacy of lactoferrin (LF) compared with diclofenac to reduce the pain, using a rat lumbar disc herniation model.

SUMMARY OF BACKGROUND DATA

LF is a multifunctional protein that is found in milk. Recent studies have reported that LF reduces nociception in various experimental models.

METHODS

Rats were operated on the left L5 vertebral arch. The left L5 nerve root and dorsal root ganglion (DRG) were exposed by a L5 partial laminectomy. An L-shaped stainless steel rod was inserted from the laminectomy toward the intervertebral foramen to compress the nerve root. In addition, nucleus pulposus from coccygeal discs was applied on the nerve root. At 1 day before operation, all rats were tested regarding the withdrawal threshold of the left plantar surface using von Frey filaments to determine baseline values. Additional von Frey tests were performed on postoperative days 3, 7, 14, and 21. Thirty minutes before each test except for baseline, the rats received LF (100 mg/kg), diclofenac (10 mg/kg), or saline by intraperitoneal injection (n = 6).

RESULTS

As compared with the control group, thresholds of rats in the diclofenac group were significantly higher on postoperative days 3 and 7. However, on postoperative days 14 and 21, there were no significant differences. Thresholds of rats in the LF group were significantly higher on all postoperative days compared with the control group.

CONCLUSION

Analgesic effect of diclofenac reduced with time. However, the effect of LF continued during the whole experimental period. LF might become useful as pain-killer.

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.

BDNF in RA: downregulated in plasma following anti-TNF treatment but no correlation with inflammatory parameters

The involvement of brain-derived neurotrophic factor (BDNF) in rheumatoid arthritis (RA) is largely unknown. The distribution of BDNF and its associated receptors, TrkB and p75, in the synovial tissue of patients with RA was examined and contrasted with that in patients with osteoarthritis (OA). Additionally, levels of BDNF in both synovial tissue and synovial fluid were measured. Furthermore, the effects of anti-tumour necrosis factor (anti-TNF; infliximab) treatment on BDNF levels in the plasma of RA patients were analysed. Cells in the synovium showed immunoreactivity for BDNF and BDNF-, p75- and TrkB-receptor immunoreactions were seen in nerve fibres of nerve fascicles and in association with sensory corpuscles. The levels of BDNF in synovial tissue were not correlated with the number of inflammatory cells observed microscopically or with levels of TNFalpha. Nor did the BDNF levels in synovial fluid correlate with erythrocyte sedimentation rate (ESR) or white blood cell counts. Anti-TNF treatment lead to a decrease in plasma levels of BDNF 14 weeks after the initiation of anti-TNF therapy, i.e., 8 weeks after the last infusion. Higher levels of BDNF were observed in RA patients at baseline compared with those for healthy individuals. However, the levels of BDNF in plasma of patients treated with anti-TNF did not correlate with the changes in ESR or a disease activity score. The clinical significance of this study is that anti-TNF treatment influences plasma levels of BDNF although there was no evidence that BDNF levels correlate with inflammatory parameters in either infliximab-treated or non-infliximab-treated patients with RA. Instead it is likely that sources other than inflammatory cells, including nerve structures, are important sources of BDNF and that the effects of anti-TNF treatment on BDNF levels may be related to effects on circulating and various local cells and/or BDNF-containing neurons.

An injectable and in situ-gelling biopolymer for sustained drug release following perineural administration

STUDY DESIGN

This study evaluated whether the aggregation behavior of a thermally responsive elastin-like polypeptide (ELP) prolongs protein residence time at the dorsal root ganglion (DRG). This work involves development of a sustained-release drug delivery vehicle to provide high and sustained levels of biologic therapeutics to the dorsal root ganglion while minimizing systemic exposure.

OBJECTIVE

To study the potential of the ELP biopolymer to sustain release and lower systemic exposure of bioactive peptides following perineural administration.

SUMMARY OF BACKGROUND DATA

Anticytokine treatment for lumbar radiculopathy may offer clinical improvement, but exposes patients to systemic toxicities of immunosuppression. ELPs are environmentally responsive polypeptides that undergo a phase transition on heating to form an insoluble aggregate. Drug conjugates with ELP exhibit both temperature-sensitivity and in vitro bioactivity. Monomer resolubilization yields solution-phase molecules, and this reversible aggregation behavior may create a perineural drug depot to sustain drug delivery to an inflamed nerve.

METHODS

This experiment involved 48 rats in which radiolabeled ELPs (aggregating or soluble) were injected overlying the L5 dorsal root ganglion. Animals were killed at 6 different time points, and radioactivity associated with the injected segment, serum, and other tissues was evaluated.

RESULTS

The aggregating ELP demonstrated a 7-fold longer perineural half-life compared with the soluble ELP. This supports the hypothesis that the aggregating ELP forms a depot from which slow resolubilization and clearance provides sustained, local protein release. Furthermore, serum radioactivity reached a lower peak for the aggregating group, demonstrating slower absorption of the aggregating protein into the systemic circulation.

CONCLUSION

These results suggest that ELP aggregation confer the benefit of perineural compartment longevity for bioactive therapeutics delivered fused with this carrier. This may sustain release of potent immunomodulator therapeutics to treat local neuroinflammation. Desirable features include delivery of high local doses and protection against systemic exposure and associated toxicity.

Anticytokine therapy in neuropathic pain management

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

Dorsal horn neurons having input from low back structures in rats

The mechanisms of nociception in the low back are poorly understood, partly because systematic recordings from dorsal horn neurons with input from the low back are largely missing. The purpose of this investigation was to (1) identify spinal segments and dorsal horn neurons receiving input from the low back, (2) test the effect of nerve growth factor (NGF) injected into the multifidus muscle (MF) on the neurons' responsiveness, and (3) study the influence of a chronic MF inflammation on the responses. In rats, microelectrode recordings were made in the segments L2, L3, and L5 to find dorsal horn neurons having input from the low back (LB neurons). In control animals, the proportion of LB neurons in L2 was larger than in L3 and L5. Most LB neurons had a convergent input from several tissues. Injections of NGF into MF increased the proportion of LB neurons significantly. A chronic MF inflammation likewise increased the proportion of LB neurons and the input convergence. The centers of the neurons' receptive fields (RFs) were consistently located 2-3 segments caudally relative to their recording site. The results show that (1) input convergence from various tissues is common for LB neurons, (2) the input from structures of the low back is processed 2-3 segments cranially relative to the vertebral level of the RFs, and (3) the responsiveness of LB neurons is increased during a pathologic alteration of the MF. The above findings may be relevant for some cases of chronic low back pain in patients.

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.

Axonal growth potential of lumbar dorsal root ganglion neurons in an organ culture system: response of nerve growth factor-sensitive neurons to neuronal injury and an inflammatory cytokine

STUDY DESIGN

The axonal growth potential of dorsal root ganglion (DRG) neurons in an organ culture system was investigated.

OBJECTIVE

To examine the effects of neuronal injury and tumor necrosis factor-alpha (TNF-alpha) on the axonal growth potential of 2 types of nociceptive DRG neurons: nerve growth factor (NGF)-sensitive and glial cell line-derived neurotrophic factor (GDNF)-sensitive neurons.

SUMMARY OF BACKGROUND DATA

Nerve ingrowth into the disc is recognized to be one of the causes of discogenic pain. Almost all of these disc-innervating neurons are NGF-sensitive. The axonal growth potential of NGF-sensitive neurons has not been investigated.

METHODS

Adult Sprague-Dawley rats were used for immunohistochemistry (n = 7) and cell viability studies (n = 6). Bilateral L3-L5 DRGs, which were successfully removed without damage, were noncultured or cultured in serum-free medium containing TNF-alpha at 0, 0.01, 0.1, and 1 ng/mL for 48 hours (n = 5, each treatment). The DRGs were then immunostained for activating transcription factor 3 (ATF3, a marker for injured neurons) or double-stained for growth-associated protein 43 (GAP-43, a marker for axonal growth) with calcitonin gene-related peptide (CGRP, a marker for NGF-sensitive neurons) or isolectin B4 (IB4, a marker for GDNF-sensitive neurons). Cell viability was assessed by a lactate dehydrogenase (LDH) assay and an MTS assay (n = 6, each treatment).

RESULTS

Immunoreactive evidence of injured neurons (ATF3 positive) was frequently observed in cultured DRGs, but never in noncultured DRGs. The percentage of neurons exhibiting axonal growth potential (GAP-43 immunoreactive) was significantly higher for NGF-sensitive neurons than for GDNF-sensitive neurons at any concentration of TNF-alpha. More than 95% of the cultured neurons were viable.

CONCLUSIONS

The results suggest that the cultured DRG neurons exhibit pathologic changes similar to those found in injured neurons. NGF-sensitive neurons, which include disc-innervating neurons, may have a greater potential to extend their axons in response to neuronal injury under pathologic conditions in the presence of TNF-alpha than GDNF-sensitive neurons.

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.

Cytokine profiles during carrageenan-induced inflammatory hyperalgesia in rat muscle and hind paw

It is not known if a cytokine cascade develops during muscle inflammation and whether cytokines contribute to muscle inflammatory pain. We measured plasma and tissue cytokine concentrations, and behavioral responses to noxious mechanical stimuli, after inducing inflammation in the gastrocnemius muscle and the hind paw of rats. Tissue and plasma samples were taken 3, 6, or 24 h after carrageenan or saline injection into one of the 2 sites. Tumor necrosis factor alpha (TNF-alpha), interleukin (IL)-1beta, IL-6, and cytokine-induced neutrophil chemoattractant 1 (CINC-1) concentrations were measured. Hyperalgesia was present 3 h after carrageenan injection into the hind paw and muscle. The TNF-alpha was elevated significantly in the inflamed hind paw tissue (P < .001) but not in inflamed muscle tissue. IL-1beta was elevated 6 h after carrageenan injection in the hind paw tissue but only 24 h in the muscle tissue (P < .001). The IL-6 was elevated 3 h after injection in the hind paw tissue but only after 6 h in the muscle tissue (P < .01). The CINC-1 in plasma, muscle, and hind paw was elevated from 3 h to 24 h after carrageenan injection (P < .01). The release of IL-1beta and IL-6, known to mediate hyperalgesia elsewhere, is delayed in muscle inflammation compared with cutaneous inflammation, whereas TNF-alpha is not elevated during muscle inflammation.

PERSPECTIVE

The quality and mechanisms of muscle pain are different from that of cutaneous pain. So too is the pattern of cytokine release during inflammation. Inhibiting TNF-alpha is unlikely to be effective in managing inflammatory muscle pain, but other cytokines, notably IL-1beta and CINC-1, may prove useful therapeutic targets.