The degenerated lumbar intervertebral disc is innervated primarily by peptide-containing sensory nerve fibers in humans

Expression of Glial-Cell-Line-Derived Neurotrophic Factor Family Ligands in Human Intervertebral Discs

Glial-cell-line-derived neurotrophic factor (GDNF) family ligands (GFLs) contribute to the sensitization of primary afferents and are involved in the pathogenesis of inflammatory pain. The purpose of this preliminary study was to examine the expression of other GFLs (neurturin (NRTN), artemin (ARTN), persephin (PSPN)) and receptors in human IVD cells and tissues exhibiting early and advanced stages of degeneration. Human IVD cells were cultured as a monolayer after isolation from the nucleus pulposus (NP) and anulus fibrosus (AF) tissues. The mRNA expression of NRTN, ARTN, PSPN, and their receptors (GFRA2-GFRA4) was quantified using real-time PCR. Protein expression was evaluated using immunohistochemistry and Western blotting. The expression of NRTN, ARTN, PSPN, and their co-receptors (GFRA2-GFRA4) was identified in human IVD cells at both mRNA and protein levels. A trend was noted wherein the mRNA expression of ARTN, PSPN, and GFRA2 was upregulated by IL-1β treatment in a dose-dependent manner. The percentages of immunopositive cells in the advanced degenerate stage of ARTN, PSPN, and GFRA2 were significantly higher than those in the early degenerate stage. Their expression was enhanced in advanced tissue degeneration, which suggests that GFLs (ARTN and PSPN) may be involved in the pathogenesis of discogenic pain.

An update on animal models of intervertebral disc degeneration and low back pain: Exploring the potential of artificial intelligence to improve research analysis and development of prospective therapeutics

Animal models have been invaluable in the identification of molecular events occurring in and contributing to intervertebral disc (IVD) degeneration and important therapeutic targets have been identified. Some outstanding animal models (murine, ovine, chondrodystrophoid canine) have been identified with their own strengths and weaknesses. The llama/alpaca, horse and kangaroo have emerged as new large species for IVD studies, and only time will tell if they will surpass the utility of existing models. The complexity of IVD degeneration poses difficulties in the selection of the most appropriate molecular target of many potential candidates, to focus on in the formulation of strategies to effect disc repair and regeneration. It may well be that many therapeutic objectives should be targeted simultaneously to effect a favorable outcome in human IVD degeneration. Use of animal models in isolation will not allow resolution of this complex issue and a paradigm shift and adoption of new methodologies is required to provide the next step forward in the determination of an effective repairative strategy for the IVD. AI has improved the accuracy and assessment of spinal imaging supporting clinical diagnostics and research efforts to better understand IVD degeneration and its treatment. Implementation of AI in the evaluation of histology data has improved the usefulness of a popular murine IVD model and could also be used in an ovine histopathological grading scheme that has been used to quantify degenerative IVD changes and stem cell mediated regeneration. These models are also attractive candidates for the evaluation of novel anti-oxidant compounds that counter inflammatory conditions in degenerate IVDs and promote IVD regeneration. Some of these compounds also have pain-relieving properties. AI has facilitated development of facial recognition pain assessment in animal IVD models offering the possibility of correlating the potential pain alleviating properties of some of these compounds with IVD regeneration.

Injectable bioorthogonal hydrogel (BIOGEL) accelerates tissue regeneration in degenerated intervertebral discs

Intervertebral disc (IVD) degeneration is a leading cause of back pain and precursor to more severe conditions, including disc herniation and spinal stenosis. While traditional growth factor therapies (e.g., TGFβ) are effective at transiently reversing degenerated disc by stimulation of matrix synthesis, it is increasingly accepted that bioscaffolds are required for sustained, complete IVD regeneration. Current scaffolds (e.g., metal/polymer composites, non-mammalian biopolymers) can be improved in one or more IVD regeneration demands: biodegradability, noninvasive injection, recapitulated healthy IVD biomechanics, predictable crosslinking, and matrix repair induction. To meet these demands, tetrazine-norbornene bioorthogonal ligation was combined with gelatin to create an injectable bioorthogonal hydrogel (BIOGEL). The liquid hydrogel precursors remain free-flowing across a wide range of temperatures and crosslink into a robust hydrogel after 5-10 min, allowing a human operator to easily inject the therapeutic constructs into degenerated IVD. Moreover, BIOGEL encapsulation of TGFβ potentiated histological repair (e.g., tissue architecture and matrix synthesis) and functional recovery (e.g., high water retention by promoting the matrix synthesis and reduced pain) in an in vivo rat IVD degeneration/nucleotomy model. This BIOGEL procedure readily integrates into existing nucleotomy procedures, indicating that clinical adoption should proceed with minimal difficulty. Since bioorthogonal crosslinking is essentially non-reactive towards biomolecules, our developed material platform can be extended to other payloads and degenerative injuries.

The role of nerve fibers and their neurotransmitters in regulating intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) has been the major contributor to chronic lower back pain (LBP). Abnormal apoptosis, senescence, and pyroptosis of IVD cells, extracellular matrix (ECM) degradation, and infiltration of immune cells are the major molecular alternations during IVDD. Changes at tissue level frequently occur at advanced IVD tissue. Ectopic ingrowth of nerves within inner annulus fibrosus (AF) and nucleus pulposus (NP) tissue has been considered as the primary cause for LBP. Innervation at IVD tissue mainly included sensory and sympathetic nerves, and many markers for these two types of nerves have been detected since 1940. In fact, in osteoarthritis (OA), beyond pain transmission, the direct regulation of neuropeptides on functions of chondrocytes have attracted researchers' great attention recently. Many physical and pathological similarities between joint and IVD have shed us the light on the neurogenic mechanism involved in IVDD. Here, an overview of the advances in the nervous system within IVD tissue will be performed, with a discussion on in the role of nerve fibers and their neurotransmitters in regulating IVDD. We hope this review can attract more research interest to address neuromodulation and IVDD itself, which will enhance our understanding of the contribution of neuromodulation to the structural changes within IVD tissue and inflammatory responses and will help identify novel therapeutic targets and enable the effective treatment of IVDD disease.

DUSP-1 Induced by PGE2 and PGE1 Attenuates IL-1β-Activated MAPK Signaling, Leading to Suppression of NGF Expression in Human Intervertebral Disc Cells

The molecular mechanism of discogenic low back pain (LBP) involves nonphysiological nerve invasion into a degenerated intervertebral disc (IVD), induced by nerve growth factor (NGF). Selective cyclooxygenase (COX)-2 inhibitors are mainly used in the treatment of LBP, and act by suppressing the inflammatory mediator prostaglandin E₂ (PGE₂), which is induced by inflammatory stimuli, such as interleukin-1β (IL-1β). However, in our previous in vitro study using cultured human IVD cells, we demonstrated that the induction of NGF by IL-1β is augmented by a selective COX-2 inhibitor, and that PGE₂ and PGE₁ suppress NGF expression. Therefore, in this study, to elucidate the mechanism of NGF suppression by PGE₂ and PGE₁, we focused on mitogen-activated protein kinases (MAPKs) and its phosphatase, dual-specificity phosphatase (DUSP)-1. IL-1β-induced NGF expression was altered in human IVD cells by MAPK pathway inhibitors. PGE₂ and PGE₁ enhanced IL-1β-induced DUSP-1 expression, and suppressed the phosphorylation of MAPKs in human IVD cells. In DUSP-1 knockdown cells established using small interfering RNA, IL-1β-induced phosphorylation of MAPKs was enhanced and prolonged, and NGF expression was significantly enhanced. These results suggest that PGE₂ and PGE₁ suppress IL-1β-induced NGF expression by suppression of the MAPK signaling pathway, accompanied by increased DUSP-1 expression.

Innervation of the Human Intervertebral Disc: A Scoping Review

OBJECTIVE

Back pain is an elusive symptom complicated by a variety of possible causes, precipitating and maintaining factors, and consequences. Notably, the underlying pathology remains unknown in a significant number of cases. Changes to the intervertebral disc (IVD) have been associated with back pain, leading many to postulate that the IVD may be a direct source of pain, typically referred to as discogenic back pain. Yet despite decades of research into the neuroanatomy of the IVD, there is a lack of consensus in the literature as to the distribution and function of neural elements within the tissue. The current scoping review provides a comprehensive systematic overview of studies that document the topography, morphology, and immunoreactivity of neural elements within the IVD in humans.

METHOD

Articles were retrieved from six separate databases in a three-step systematic search and were independently evaluated by two reviewers.

RESULTS

Three categories of neural elements were described within the IVD: perivascular nerves, sensory nerves independent of blood vessels, and mechanoreceptors. Nerves were consistently localized within the outer layers of the annulus fibrosus. Neural ingrowth into the inner annulus fibrosus and nucleus pulposus was found to occur only in degenerative and disease states.

CONCLUSION

While the pattern of innervation within the IVD is clear, the specific topographic arrangement and function of neural elements in the context of back pain remains unclear.

Long-term histological analysis of innervation and macrophage infiltration in a mouse model of intervertebral disc injury-induced low back pain

Low back pain (LBP) is a leading cause of global disability. Multiple anatomical, cellular, and molecular factors are implicated in LBP, including the degeneration of lumbar intervertebral discs (IVDs). We previously described a mouse model that displays behavioral symptoms of chronic LBP. Here, we investigated the development of pathological innervation and macrophage infiltration into injured IVDs following a puncture injury in mice over 12 months. 2-month old CD1 female mice underwent a single puncture of the ventral L4/5 IVD using a 30G needle, and were sacrificed 4 days and 0.5-, 3-, 6- and 12-months post-injury. Severity of disc degeneration was assessed using colorimetric staining. IVD innervation was measured by PGP9.5-immunoreactivity (-ir) and calcitonin gene-related peptide-ir (CGRP-ir). Macrophage accumulation into IVDs was detected by F4/80-ir. Mechanical IVD injury resulted in severe degeneration and increased PGP9.5-ir nerve fiber density starting at 4 days that persisted for up to 12 months and dorsal herniations began to occur at 3 months. CGRP-ir was also upregulated in injured IVDs, with the largest increase at 12 months after injury. Infiltration of F4/80-ir macrophages was observed in injured IVDs by day 4 both dorsally and ventrally, with the latter diminishing in the later stage. Persistent LBP is a complex disease with multiple underlying pathologies. By highlighting pathological changes in IVD innervation and inflammation, our study suggests that strategies targeting these mechanisms might be useful therapeutically.

Development of an in vitro intervertebral disc innervation model to screen neuroinhibitory biomaterials

Pain originating from an intervertebral disc (discogenic pain) is a major source of chronic low back pain. Pathological innervation of the disc by pain-sensing nerve fibers is thought to be a key component of discogenic pain, so treatment with biomaterials that have the ability to inhibit neurite growth will greatly benefit novel disc therapeutics. Currently, disc therapeutic biomaterials are rarely screened for their ability to modulate nerve growth, mainly due to a lack of models to screen neuromodulation. To address this deficit, our lab has engineered a three dimensional in vitro disc innervation model that mimics the interface between primary sensory nerves and the intervertebral disc. Further, herein we have demonstrated the utility of this model to screen the efficacy of chondroitin sulfate biomaterials to inhibit nerve fiber invasion into the model disc. Biomaterials containing chondroitin-4-sulfate (CS-A) decrease neurite growth in a uniform gel and at an interface between a growth-permissive and a growth-inhibitory gel, while chondroitin-6-sulfate (CS-C) is less neuroinhibitory. This in vitro model holds great potential for screening inhibitors of nerve fiber growth to further improve intervertebral disc replacements and therapeutics. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:1016-1026, 2020.

The association between headache and low back pain: a systematic review

Background

To systematically review studies quantifying the association between primary chronic headaches and persistent low back pain (LBP).

Main text

We searched five electronic databases. We included case-control, cross-sectional and cohort studies that included a headache and back pain free group, reporting on any association between persistent LBP and primary headache disorders. Methodological quality was assessed using Newcastle-Ottawa Scale. Our primary outcome was the association between primary headache disorders and persistent LBP. Our secondary outcomes were any associations between severity of LBP and severity of headache, and the relationship between specific headache sub-types classified as per International Classification of Headache Disorders (ICHD) criteria and persistent LBP.

We included 14 studies. The sizes of the studies ranged from 88 participants to a large international study with 404, 206 participants. Odds ratios for the association were between 1.55 (95% confidence interval (CI) 1.13–2.11) and 8.00 (95% CI 5.3–12.1). Study heterogeneity meant statistical pooling was not possible. Only two studies presented data investigating persistent LBP and chronic headache disorders in accordance with ICDH criteria.

Conclusions

We identified a positive association between persistent LBP and primary headache disorders. The quality of the review findings is limited by diversity of populations, study designs and uncertainly about headache and LBP definitions.

Trial registration

PROSPERO 2018 CRD42018086557.

Electronic supplementary material

The online version of this article (10.1186/s10194-019-1031-y) contains supplementary material, which is available to authorized users.

Chronic low back pain: a mini-review on pharmacological management and pathophysiological insights from clinical and pre-clinical data

Globally, low back pain (LBP) is one of the most common health problems affecting humans. The lifetime prevalence of non-specific LBP is approximately 84%, with the chronic prevalence at about 23%. Chronic LBP in humans is defined as LBP that persists for more than 12 weeks without a significant pain improvement. Although there are numerous evidence-based guidelines on the management of acute LBP, this is not the case for chronic LBP, which is regarded as particularly difficult to treat. Research aimed at discovering new drug treatments for alleviation of chronic mechanical LBP is lacking due to the paucity of knowledge on the pathobiology of this condition, despite its high morbidity in the affected adult population. For a debilitating condition such as chronic LBP, it is necessary to assess the sustained effects of pharmacotherapy of various agents spanning months to years. Although many rodent models of mechanical LBP have been developed to mimic the human condition, some of the major shortcomings of many of these models are (1) the presence of a concurrent neuropathic component that develops secondary to posterior intervertebral disc puncture, (2) severe model phenotype, and/or (3) use of behavioural endpoints that have yet to be validated for pain. Hence, there is a great, unmet need for research aimed at discovering new biological targets in rodent models of chronic mechanical LBP for use in drug discovery programs as a means to potentially produce new highly effective and well-tolerated analgesic agents to improve relief of chronic LBP. On a cautionary note, it must be borne in mind that because humans and rats display orthograde and pronograde postures, respectively, the different mechanical forces on their spines add to the difficulty in translation of promising rodent data to humans.

Calcitonin gene-related peptide and pain: a systematic review

BACKGROUND

Calcitonin gene-related peptide (CGRP) is widely distributed in nociceptive pathways in human peripheral and central nervous system and its receptors are also expressed in pain pathways. CGRP is involved in migraine pathophysiology but its role in non-headache pain has not been clarified.

METHODS

We performed a systematic literature search on PubMed, Embase and ClinicalTrials.gov for articles on CGRP and non-headache pain covering human studies including experimental studies and randomized clinical trials.

RESULTS

The literature search identified 375 citations of which 50 contained relevant original data. An association between measured CGRP levels and somatic, visceral, neuropathic and inflammatory pain was found. In 13 out of 20 studies in somatic pain conditions, CGRP levels had a positive correlation with pain. Increased CGRP levels were reported in plasma, synovial and cerebrospinal fluid in subjects with musculoskeletal pain. A randomized clinical trial on monoclonal antibody, which selectively binds to and inhibits the activity of CGRP (galcanezumab) in patients with osteoarthritis knee pain, failed to demonstrate improvement of pain compared with placebo. No studies to date have investigated the efficacy of monoclonal antibodies against CGRP receptor in non-headache pain conditions.

CONCLUSION

The present review revealed the association between measured CGRP levels and somatic, visceral, neuropathic and inflammatory pain. These data suggest that CGRP may act as a neuromodulator in non-headache pain conditions. However, more studies are needed to fully understand the role of CGRP in nociceptive processing and therapy of chronic pain.

Creation of an injectable in situ gelling native extracellular matrix for nucleus pulposus tissue engineering

BACKGROUND CONTEXT

Disc degeneration is the leading cause of low back pain and is often characterized by a loss of disc height, resulting from cleavage of chondroitin sulfate proteoglycans (CSPGs) present in the nucleus pulposus. Intact CSPGs are critical to water retention and maintenance of the nucleus osmotic pressure. Decellularization of healthy nucleus pulposus tissue has the potential to serve as an ideal matrix for tissue engineering of the disc because of the presence of native disc proteins and CSPGs. Injectable in situ gelling matrices are the most viable therapeutic option to prevent damage to the anulus fibrosus and future disc degeneration.

PURPOSE

The purpose of this research was to create a gentle decellularization method for use on healthy nucleus pulposus tissue explants and to develop an injectable formulation of this matrix to enable therapeutic use without substantial tissue disruption.

STUDY DESIGN

Porcine nuclei pulposi were isolated, decellularized, and solubilized. Samples were assessed to determine the degree of cell removal, matrix maintenance, gelation ability, cytotoxic residuals, and native cell viability.

METHODS

Nuclei pulposi were decellularized using serial detergent, buffer, and enzyme treatments. Decellularized nuclei pulposi were solubilized, neutralized, and buffered. The efficacy of decellularization was assessed by quantifying DNA removal and matrix preservation. An elution study was performed to confirm removal of cytotoxic residuals. Gelation kinetics and injectability were quantified. Long-term in vitro experiments were performed with nucleus pulposus cells to ensure cell viability and native matrix production within the injectable decellularized nucleus pulposus matrices.

RESULTS

This work resulted in the creation of a robust acellular matrix (>96% DNA removal) with highly preserved sulfated glycosaminoglycans (>47%), and collagen content and microstructure similar to native nucleus pulposus, indicating preservation of disc components. Furthermore, it was possible to create an injectable formulation that gelled in situ within 45 minutes and formed fibrillar collagen with similar diameters to native nucleus pulposus. The processing did not result in any remaining cytotoxic residuals. Solubilized decellularized nucleus pulposus samples seeded with nucleus pulposus cells maintained robust viability (>89%) up to 21 days of culture in vitro, with morphology similar to native nucleus pulposus cells, and exhibited significantly enhanced sulfated glycosaminoglycans production over 21 days.

CONCLUSIONS

A gentle decellularization of porcine nucleus pulposus followed by solubilization enabled the creation of an injectable tissue-specific matrix that is well tolerated in vitro by nucleus pulposus cells. These matrices have the potential to be used as a minimally invasive nucleus pulposus therapeutic to restore disc height.

Operative Management of Lumbar Degenerative Disc Disease

Lumbar degenerative disc disease is extremely common. Current evidence supports surgery in carefully selected patients who have failed non-operative treatment and do not exhibit any substantial psychosocial overlay. Fusion surgery employing the correct grafting and stabilization techniques has long-term results demonstrating successful clinical outcomes. However, the best approach for fusion remains debatable. There is some evidence supporting the more complex, technically demanding and higher risk interbody fusion techniques for the younger, active patients or patients with a higher risk of non-union. Lumbar disc arthroplasty and hybrid techniques are still relatively novel procedures despite promising short-term and mid-term outcomes. Long-term studies demonstrating superiority over fusion are required before these techniques may be recommended to replace fusion as the gold standard. Novel stem cell approaches combined with tissue engineering therapies continue to be developed in expectation of improving clinical outcomes. Results with appropriate follow-up are not yet available to indicate if such techniques are safe, cost-effective and reliable in the long-term.

Nerves are more abundant than blood vessels in the degenerate human intervertebral disc

BACKGROUND

Chronic low back pain (LBP) is the most common cause of disability worldwide. New ideas surrounding LBP are emerging that are based on interactions between mechanical, biological and chemical influences on the human IVD. The degenerate IVD is proposed to be innervated by sensory nerve fibres and vascularised by blood vessels, and it is speculated to contribute to pain sensation. However, the incidence of nerve and blood vessel ingrowth, as well as whether these features are always associated, is unknown. We investigated the presence of nerves and blood vessels in the nucleus pulposus (NP) of the IVD in a large population of human discs.

METHODS

Immunohistochemistry was performed with 61 human IVD samples, to identify and localise nerves (neurofilament 200 [NF200]/protein gene product 9.5) and blood vessels (CD31) within different regions of the IVD.

RESULTS

Immunopositivity for NF200 was identified within all regions of the IVD within post-mortem tissues. Nerves were seen to protrude across lamellar ridges and through matrix towards NP cells. Nerves were identified deep within the NP and were in many cases, but not always, seen in close proximity to fissures or in areas where decreased matrix was seen. Fifteen percent of samples were degenerate and negative for nerves and blood vessels, whilst 16 % of all samples were degenerate with nerves and blood vessels. We identified 52% of samples that were degenerate with nerves but no blood vessels. Interestingly, only 4% of all samples were degenerate with no nerves but positive for blood vessels. Of the 85 samples investigated, only 6 % of samples were non-degenerate without nerves and blood vessels and 7% had nerves but no blood vessels.

CONCLUSIONS

This study addresses the controversial topic of nerve and blood vessel ingrowth into the IVD in a large number of human samples. Our findings demonstrate that nerves are present within a large proportion of NP samples from degenerate IVDs. This study shows a possible link between nerve ingrowth and degeneration of the IVD and suggests that nerves can migrate in the absence of blood vessels.

Interleukin-6 and interleukin-6 receptor expression, localization, and involvement in pain-sensing neuron activation in a mouse intervertebral disc injury model

The pathological mechanism of intractable low back pain is unclear. However, intervertebral disc (IVD) degeneration is a primary cause of low back pain, and pain-related mediators, such as interleukin-6 (IL-6), have been correlated with discogenic pain. The objective of this study is to elucidate the mechanism of local IL-6 and IL-6 receptor (IL-6R) expression after IVD injury as well as determine the involvement of IL-6/IL-6 signaling in discogenic pain. To do this, quantitative and immunohistological analyses in a mouse model of IVD injury were performed. Firstly, we measured the local expression levels of IL-6 and IL-6R in IVDs by enzyme-linked immunosorbent assay (ELISA). Secondly, we immunohistochemically confirmed their localization in injured IVDs. Lastly, we evaluated the effects of intradiscal injection of an IL-6 inhibitor by evaluating pain-related protein, calcitonin gene-related peptide (CGRP), expression in dorsal root ganglia (DRG) neurons that innervate IVDs. Injured IVDs showed increased production of IL-6 and IL-6R. IL-6 and IL-6R expression in the injured IVD were predominantly localized in the annulus fibrosus and endplate, and intradiscal injection of the IL-6 inhibitor suppressed CGRP expression in the DRG neurons. These results show that IL-6 and IL-6R expression levels are responsive to IVD injury and that inhibition of IL-6/IL-6R signaling may be a promising analgesic treatment for degenerative disc diseases.

Prevalence and Characteristics of Discogenic Pain in Tertiary Practice: 223 Consecutive Cases Utilizing Lumbar Discography

BACKGROUND

Between 26% and 42% of chronic low back pain is attributed to internal disc disruption of lumbar intervertebral discs. These prevalence estimates and data characterizing discogenic pain originate largely from research at elite practices, conducted 20 years ago. With few studies since, their concordance with rates in community practice has rarely been addressed.

OBJECTIVE

To assess the prevalence and key features of discogenic pain within community-based tertiary practice, and to evaluate the accuracy and clinical utility of discography.

DESIGN

This prospective, three-year study of 223 consecutive cases of chronic low back pain used image-guided lumbar discography to identify symptomatic and flanking asymptomatic discs. A subset of patients (n = 195) had previously undergone posterior column blocks to investigate spinal facet and/or sacroiliac joints as contributing pain sources.

RESULTS

A total of 644 discs were tested without infection or complication. Positive discograms were recorded in 74% of patients, with 22.9% negative and 3.1% assessed as indeterminate. Among patients receiving both discography and diagnostic blocks, 63% had proven discogenic pain, 18% had pain of mixed etiology and 14% remained undiagnosed. Taking into account all low back pain cases during this study (n = 756), discogenic pain prevalence was 21.8% (95% CI: 17-26%).

CONCLUSION

The prevalence of discogenic pain in this community practice is below the range, but within confidence intervals, previously reported. Prevalence is considerably elevated, however, among well-selected patients and discography enabled a firm diagnosis in most such cases. These findings are broadly in keeping with those reached in key publications and support the clinical utility of discography.

Anti-RANKL antibodies decrease CGRP expression in dorsal root ganglion neurons innervating injured lumbar intervertebral discs in rats

PURPOSE

Nuclear factor-κB (NF-κB), receptor activator of NF-κB (RANK), and RANK ligand (RANKL) are transcriptional regulators of inflammatory cytokines. RANKL expression in dorsal root ganglion (DRG) neurons is elevated in animal models of pain or intervertebral disc herniation. We sought to evaluate the effect of anti-RANKL antibodies on sensory nerves innervating injured intervertebral discs.

METHOD

We labeled DRG neurons innervating L5-6 discs with FluoroGold (FG). The L5-6 discs of 36 rats were punctured using a 23-gage needle and 18 rats underwent sham surgery without disc puncture. The puncture group was evenly subdivided into a group in which 10 μl saline was administered to the injured disc and a group in which 10 μl of anti-RANKL antibody was administered. Seven and 14 days postsurgery, DRGs at L2 level were harvested, sectioned, and immunostained for calcitonin gene-related peptide (CGRP). The proportion of CGRP-immunoreactive (IR) DRG neurons of all FG-positive neurons was determined. Amount of tumor necrosis factor (TNF)-α and interleukin(IL)-6 was measured within the intervertebral discs in each group at 7 and 14 days after surgery using an enzyme-linked immunosorbent assay (ELISA).

RESULTS

The proportion of CGRP-IR DRG neurons to total FG-labeled neurons innervating injured intervertebral discs and amount of TNF-α and IL-6 in the injured discs in the saline control group was significantly increased compared with that found in rats from the sham surgery group (P < 0.05). However, application of anti-RANKL antibody to the injured discs significantly decreased the proportion of CGRP-IR DRG neurons to total FG-labeled neurons and amount of TNF-α and IL-6 in the injured discs (P < 0.05).

CONCLUSIONS

TNF-α and IL-6 in the injured discs increased and CGRP expression increased in DRG neurons innervating injured discs, and antibodies to RANKL could suppress this increased TNF-α, IL-6, and CGRP expression. RANKL may be a therapeutic target for pain control in patients with lumbar disc degeneration.

Pathomechanisms of discogenic low back pain in humans and animal models

BACKGROUND CONTEXT

Although explored in humans and animal models, the pathomechanisms of discogenic low back pain (LBP) remain unknown.

PURPOSE

The aim of this study was to review the literature about the pathomechanisms of discogenic LBP.

METHODS

Animal models of discogenic pain and specimens from degenerated human intervertebral discs (IVDs) have provided clues about the pathomechanisms of discogenic LBP. Painful discs are characterized by a confluence of innervation, inflammation, and mechanical hypermobility. These three possible mechanisms are discussed in this review.

RESULTS

Animal models and specimens from humans have revealed sensory innervation of lumbar IVDs and sensory nerve ingrowth into the inner layer of IVDs. Cytokines such as tumor necrosis factor-α and interleukins induce this ingrowth. Nerve growth factor has also been recently identified as an inducer of ingrowth. Finally, disc degeneration induces several collagenases; their action results in hypermobility and pain.

CONCLUSIONS

To treat discogenic LBP, it is important to prevent sensitization of sensory nerve fibers innervating the IVD, to suppress pathogenic increases of cytokines, and to decrease disc hypermobility.

Differential gene expression in anterior and posterior annulus fibrosus

STUDY DESIGN

Laboratory study.

OBJECTIVE

To evaluate the differential gene expression of cytokines and growth factors in anterior versus posterior annulus fibrosus (AF) intervertebral disc (IVD) specimens.

SUMMARY OF BACKGROUND DATA

Histological analysis has demonstrated regional differences in vascular and neural ingrowth in the IVD, and similar differences may exist for cytokine and growth factor expression in patients with degenerative disc disease (DDD). Regional expression of these cytokines may also be related to the pain experienced in DDD.

METHODS

IVD tissue was obtained from patients undergoing anterior lumbar interbody fusion surgery for back pain with radiological evidence of disc degeneration. For a control group, the discs of patients undergoing anterior lumbar discectomy for degenerative scoliosis were obtained as well. The tissue was carefully removed and separated into anterior and posterior AF. After tissue processing, an antibody array was completed to determine expression levels of 42 cytokines and growth factors.

RESULTS

Nine discs from 7 patients with DDD and 5 discs from 2 patients with scoliosis were analyzed. In the DDD group, there were 10 cytokines and growth factors with significantly increased expression in the posterior AF versus the anterior AF ([interleukin] IL-4, IL-5, IL-6, M-CSF, MDC, tumor necrosis factor β, EGF, IGF-1, angiogenin, leptin). In the scoliosis group, only angiogenin and PDGF-BB demonstrated increased expression in the posterior AF. No cytokines or growth factors had increased expression in the anterior AF compared with posterior AF.

CONCLUSION

The posterior AF expresses increased levels of cytokines and growth factors compared with the anterior AF in patients with DDD. This differential expression may be important for targeting treatment of painful IVDs.

LEVEL OF EVIDENCE

N/A.

Increase of nerve growth factor levels in the human herniated intervertebral disc: can annular rupture trigger discogenic back pain?

INTRODUCTION

Nerve growth factor (NGF) has an important role in the generation of discogenic pain. We hypothesized that annular rupture is a trigger for discogenic pain through the action of NGF. In this study, the protein levels of NGF in discs from patients with disc herniation were examined and compared with those from discs of patients with other lumbar degenerative disc diseases.

METHODS

Patients (n = 55) with lumbar degenerative disc disease treated by surgery were included. Nucleus pulposus tissue (or herniated disc tissue) was surgically removed and homogenized; protein levels were quantified using an enzyme-linked immunosorbent assay (ELISA) for NGF. Levels of NGF in the discs were compared between 1) patients with herniated discs (herniated group) and those with other lumbar degenerative disc diseases (non-herniated group), and 2) low-grade and high-grade degenerated discs. Patient's symptoms were assessed using a visual analog scale (VAS) and the Oswestry disability index (ODI); the influence of NGF levels on pre- and post-operative symptoms was examined.

RESULTS

Mean levels of NGF in discs of patients were significantly higher in herniated discs (83.4 pg/mg total protein) than those in non-herniated discs (68.4 pg/mg).

CONCLUSIONS

This study reports that NGF increased in herniated discs, and may play an important role in the generation of discogenic pain. Analysis of patient symptoms revealed that pre-operative NGF levels were related to post-operative residual lower extremity pain and LBP in motion. The results suggest that NGF in the disc is related to pain generation, however, the impact of NGF on generation of LBP varies in individual patients.

Efficacy of anti-nerve growth factor therapy for discogenic neck pain in rats

STUDY DESIGN

Immunohistological analysis of the cervical dorsal root ganglia (DRG).

OBJECTIVE

To investigate immunohistologically in rats whether intradiscal administration of anti-nerve growth factor (NGF) antibody in injured cervical intervertebral discs (IVDs) suppresses pain-related peptide expression in DRG neurons.

SUMMARY OF BACKGROUND DATA

Neck pain can involve the entire neck and become chronic and intractable. Cervical disc degeneration is a primary cause of neck pain, and pain-related mediators, such as NGF, have been correlated with discogenic pain.

METHODS

We examined Sprague-Dawley rats that received 10 punctures in the C5-C6 IVD, and were treated with saline (puncture group) or an anti-NGF antibody (anti-NGF group). The retrograde neurotracer Fluoro-Gold (FG) was then injected into the C5-C6 IVD. In addition, we examined a sham group that did not receive punctures (disc nonpuncture). The C2-C7 DRG were harvested 1 week after surgery and immunostained for calcitonin gene-related peptide (CGRP), a marker for peptide-containing neurons. We determined for each group the percentages of FG-labeled DRG neurons that were CGRP-immunoreactive (CGRP-ir).

RESULTS

FG-labeled neurons innervating the C5-C6 IVD were found in all C2-C7 DRG examined. The percentage of FG-labeled CGRP-ir DRG neurons in the puncture group was significantly higher than that observed in the sham (P < 0.001) and anti-NGF groups (P < 0.001), but there was no significant difference between the sham and anti-NGF groups (P > 0.05). Therefore, intradiscal administration of anti-NGF antibody suppressed CGRP expression the cervical DRG.

CONCLUSION

Neurons located in the C2-C7 DRG innervated the C5-C6 IVD. These findings indicate that neck pain may be derived from degenerated IVDs. Furthermore, intradiscal administration of anti-NGF antibody suppressed CGRP expression in the cervical DRG innervating the injured IVD. Therefore, inhibiting NGF upregulation in the cervical IVD may be an efficient treatment for discogenic neck pain.

LEVEL OF EVIDENCE

N/A.

Painful, degenerating intervertebral discs up-regulate neurite sprouting and CGRP through nociceptive factors

Intervertebral disc degeneration (IVD) can result in chronic low back pain, a common cause of morbidity and disability. Inflammation has been associated with IVD degeneration, however the relationship between inflammatory factors and chronic low back pain remains unclear. Furthermore, increased levels of nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) are both associated with inflammation and chronic low back pain, but whether degenerating discs release sufficient concentrations of factors that induce nociceptor plasticity remains unclear. Degenerating IVDs from low back pain patients and healthy, painless IVDs from human organ donors were cultured ex vivo. Inflammatory and nociceptive factors released by IVDs into culture media were quantified by enzyme-linked immunosorbent assays and protein arrays. The ability of factors released to induce neurite growth and nociceptive neuropeptide production was investigated. Degenerating discs release increased levels of tumour necrosis factor-α, interleukin-1β, NGF and BDNF. Factors released by degenerating IVDs increased neurite growth and calcitonin gene-related peptide expression, both of which were blocked by anti-NGF treatment. Furthermore, protein arrays found increased levels of 20 inflammatory factors, many of which have nociceptive effects. Our results demonstrate that degenerating and painful human IVDs release increased levels of NGF, inflammatory and nociceptive factors ex vivo that induce neuronal plasticity and may actively diffuse to induce neo-innervation and pain in vivo.

The neurobiology of skeletal pain

Disorders of the skeleton are one of the most common causes of chronic pain and long-term physical disability in the world. Chronic skeletal pain is caused by a remarkably diverse group of conditions including trauma-induced fracture, osteoarthritis, osteoporosis, low back pain, orthopedic procedures, celiac disease, sickle cell disease and bone cancer. While these disorders are diverse, what they share in common is that when chronic skeletal pain occurs in these disorders, there are currently few therapies that can fully control the pain without significant unwanted side effects. In this review we focus on recent advances in our knowledge concerning the unique population of primary afferent sensory nerve fibers that innervate the skeleton, the nociceptive and neuropathic mechanisms that are involved in driving skeletal pain, and the neurochemical and structural changes that can occur in sensory and sympathetic nerve fibers and the CNS in chronic skeletal pain. We also discuss therapies targeting nerve growth factor or sclerostin for treating skeletal pain. These therapies have provided unique insight into the factors that drive skeletal pain and the structural decline that occurs in the aging skeleton. We conclude by discussing how these advances have changed our understanding and potentially the therapeutic options for treating and/or preventing chronic pain in the injured, diseased and aged skeleton.

Regulation of nerve growth factor by anti-inflammatory drugs, a steroid, and a selective cyclooxygenase 2 inhibitor in human intervertebral disc cells stimulated with interleukin-1

STUDY DESIGN

Regulation of nerve growth factor (NGF) by 2 different anti-inflammatory drugs was investigated in vitro using isolated human intervertebral disc (IVD) cells stimulated with the proinflammatory cytokine interleukin-1 (IL-1).

OBJECTIVE

To investigate the regulation of NGF by a synthetic steroid and a selective cyclooxygenase-2 (COX-2) inhibitor and to clarify the biological role of prostaglandin E2 (PGE2) in this process.

SUMMARY OF BACKGROUND DATA

NGF is known to play an important role in pain, including low back pain, and to be induced by proinflammatory cytokines in IVD cells. However, the effect of clinically used drugs for managing low back pain on the regulation of NGF is unclear.

METHODS

Isolated human IVD cells were stimulated with interleukin-1 (IL-1) in the presence or absence of dexamethasone or a selective COX-2 inhibitor (NS-398). NGF expression and release were determined by real-time polymerase chain reaction and enzyme-linked immuno sorbent assay, respectively. Inhibition of PGE2 release was determined by enzyme-linked immuno sorbent assay. The effects of exogenous PGE2 and its receptor (E-series prostanoid receptors [EPs] 1-4) agonists were also tested for NGF regulation.

RESULTS

IL-1 transiently induced, in a dose-dependent manner, the induction of NGF in human IVD cells. Pretreatment with dexamethasone strongly inhibited the NGF expression, whereas NS-398 significantly enhanced it at the concentration at which PGE2 release was substantially inhibited. Exogenous PGE2 inhibited IL-1 induction of NGF and this effect was mimicked when EP2 and EP4, but not EP1 and EP3, agonists were supplemented to the culture.

CONCLUSION

Although selective COX-2 inhibitors have been shown to be effective for acute low back pain by inhibiting PGE2 release, our findings suggest that it may have a limited efficacy because it exaggerated NGF expression, whereas dexamethasone inhibited it. On the other hand, PGE2 had an inhibitory function for NGF induction by mediating EP2/4 in human IVD cells. Further studies are needed to clarify whether these observations could take place in vivo.

LEVEL OF EVIDENCE

N/A.

Assessment of pain behavior in a rat model of intervertebral disc injury using the CatWalk gait analysis system

STUDY DESIGN

Pain behavior and immunohistological analysis in intervertebral disc (IVD) injury model.

OBJECTIVE

To investigate pain behavior in a rat model of IVD injury using the CatWalk system.

SUMMARY OF BACKGROUND DATA

There are few reports examining low back pain behavior in animal models. The CatWalk is a computer-assisted gait analysis system that provides an automated way to assess gait function and pain-related alterations of this behavior.

METHODS

In the IVD injury group, L5-L6 IVDs were injured with a 24-gauge needle. Simultaneously, the neurotracer Fluoro-Gold (FG; Fluorochrome, Denver, CO) was injected into the L5-L6 IVDs. In the sham group, FG was injected into the L5-L6 IVDs only. Animals in the control group received no operation. One, 2, 3, and 4 weeks after surgery, the gait of rats in the 3 groups was investigated using the CatWalk system. One, 2, and 4 weeks after surgery, in IVD injury and sham groups, dorsal root ganglions from the L1 to L6 levels were resected. Dorsal root ganglions were immunostained for calcitonin gene-related peptide.

RESULTS

In the IVD injury group, the mean stands of hind paws and the mean duty cycle of front paws at some time points were significantly higher than those in the sham group. Furthermore, the mean stride length of the front and hind paws and the mean swing speed of the front and hind paws at some time points were significantly shorter than those in the sham group. The proportion of calcitonin gene-related peptide-immunoreactive, FG-labeled neurons among all FG-labeled dorsal root ganglion neurons in the IVD injury group was significantly higher than the corresponding proportion in the sham group.

CONCLUSION

These results suggest that IVD injury produced significant changes in rat gait, including longer stance phases and shorter strides. In the future, we may be able to apply the CatWalk system to the evaluation of behavior associated with pain in models of low back pain.

LEVEL OF EVIDENCE

N/A.

New hypothesis of chronic back pain: low pH promotes nerve ingrowth into damaged intervertebral disks

The pathogenesis of low back pain is still elusive. Here, we proposed a new hypothesis that low pH is a possible cause of the development and progression of low back pain. We propose that low pH promotes the production of the inflammatory mediators and the depletion of proteoglycan in the damaged intervertebral disk. The inflammation response, evoked by the dorsal root ganglia, changes the delicate nutrient balance in the nucleus, resulting in a vicious cycle and leading to choronic back pain. Our hypothesis may explain many of the available clinical and experimental data on low back pain, thus it may help elucidate the pathogenesis of low back pain and improve clinical management.

The relationship between low pH in intervertebral discs and low back pain: a systematic review

INTRODUCTION

To systematically review the relationship between low pH in intervertebral discs and low back pain.

MATERIAL AND METHODS

Electronic database (PubMed, ISI Web of Science, Cochrane Library, CINAHL, AMED, and China National Knowledge Infrastructure) searches and hand searching of conference proceedings were conducted. Two authors independently evaluated the methodological quality and abstracted relevant data according to standard criteria. Then the experimental methods and samples employed in the finally retrieved articles were assessed.

RESULTS

We first retrieved 136 articles regarding pain and pH, and only 16 of them were mainly about low back pain and pH. Finally, 7 articles met our expectation to focus on the pathogenesis of low back pain caused by pH. In these 7 studies the authors held three opinions to explain the pathogenesis of low back pain in relation to low pH. First, low pH caused by lactate stimulates the muscle and increases the muscle tension, which causes low back pain. Second, low pH stimulates the nerve roots and produces the feeling of pain. Third, low pH changes the matrix metabolism, leading to neuronal death and low back pain.

CONCLUSIONS

In this systematic review we propose a new hypothesis that low back pain may be caused by low pH based on the previous literature. Further experimental studies are necessary to verify our hypothesis. This hypothesis will promote our understanding of the pathogenesis of low back pain and the development of novel diagnostic and therapeutic approaches for low back pain.

ISSLS prize winner: disc dynamic compression in rats produces long-lasting increases in inflammatory mediators in discs and induces long-lasting nerve injury and regeneration of the afferent fibers innervating discs: a pathomechanism for chronic discogenic low back pain

STUDY DESIGN

Animal model of intravertebral disc (IVD) degeneration.

OBJECTIVE

To examine production of inflammatory mediators in IVDs and neuropeptides in dorsal root ganglia (DRGs) in rat models of IVD compression and injury.

SUMMARY OF BACKGROUND DATA

Sensory nerve fibers in IVDs and inflammatory mediator responses have been verified in animal models of IVD injury. However, the IVD injury in animals incompletely models degenerated human IVDs causing discogenic low back pain, because human IVDs are also subject to compression.

METHODS

Experimental groups (controls, IVD injury, IVD compression, and their combination) of Sprague Dawley rats were prepared. Fluoro-Gold (FG; Fluorochrome, Denver, CO) was applied into coccygeal IVDs. Inflammatory mediators in IVDs, including nerve growth factor, tumor necrosis factor α, interleukin 1β, and interleukin 6, were quantified using enzyme-linked immunosorbent assays. DRGs were immunostained for calcitonin gene-related peptide, activating transcription factor 3, and growth-associated phosphoprotein 43.

RESULTS

The upregulation of inflammatory mediators was transient in the IVD injury group but delayed and long-lasting in the IVD compression group. When the IVD injury and compression were combined, the upregulation of inflammatory mediators was long-lasting through 8 weeks. The proportion of calcitonin gene-related peptide-immunoreactive neurons among Fluoro-Gold-labeled neurons remained significantly higher in the IVD injury, compression, and combination groups than in the controls. In contrast, increases in the proportions of activating transcription factor 3-immunoreactive or growth-associated phosphoprotein 43-immunoreactive neurons in the IVD injury group animals were transient but long-lasting in the compression and combination groups compared with controls.

CONCLUSION

Disc injury in rats produces persistent increases in neuropeptides in DRGs but only transient increases in inflammatory mediators in IVDs. On the contrary, disc compression in rats produces a long-lasting increase in inflammatory mediators in IVDs and neuropeptides in DRGs. Moreover, disc compression induces persistent nerve injury and regeneration of the afferent fibers innervating IVDs.

Platelet-rich plasma combined with hydroxyapatite for lumbar interbody fusion promoted bone formation and decreased an inflammatory pain neuropeptide in rats

STUDY DESIGN

A prospective interventional trial, using a rat model of lumbar interbody fusion.

OBJECTIVE

To examine the potential efficacy of platelet-rich plasma (PRP) for lumbar interbody fusion, using hydroxyapatite (HA).

SUMMARY OF BACKGROUND DATA

PRP is an autologous product containing a high concentration of platelets in a small volume of plasma and has osteoinductive effects. HA has osteoconductive ability and has been used in combination with autogenous bone for spine fusion. However, reports using PRP with HA for spine fusion are very few. The purpose of this study was to examine the efficacy of PRP with HA for spinal interbody fusion and at the same time to estimate the change in immunoreactivity of the inflammatory neuropeptide, calcitonin gene-related peptide (CGRP), in dorsal root ganglion (DRG) neurons innervating spinal discs.

METHODS

A total of 35 Sprague-Dawley rats were used in this study. Twenty-one rats were used for conducting interbody fusion experiments, 7 rats were used as immunostaining controls, and 7 other rats were used as blood donors for making PRP. L5-L6 interbody fusion was performed on 21 rats using HA + PRP (n = 7), HA + platelet-poor plasma (n = 7), or HA + saline (n = 7). Simultaneously, Fluoro-Gold neurotracer was applied to the intervertebral space to detect DRG neurons innervating the discs. L5-L6 lumbar radiographs were obtained and lumbar DRGs were immunostained for CGRP. The rate of bone union and the change in CGRP immunoreactive DRG neurons innervating the discs were evaluated and compared among groups.

RESULTS

All L5-L6 lumbar discs were fused in the PRP + HA group (fused 7/total 7), whereas only 1 case was fused in the platelet-poor plasma group (1 of 7) and no cases in the HA-only group (0 of 7), which was a significant difference. Upon immunohistochemical analysis, CGRP-positive neurons innervated L5-L6 intervertebral discs in nonunion cases, and these were significantly increased compared with those in union cases.

CONCLUSION

Our study suggests that using PRP with HA was beneficial for spine fusion. This combination may promote bone union and also decrease inflammatory neuropeptide in sensory neurons innervating the discs.

Fluoroscopic lumbar interlaminar epidural injections in managing chronic lumbar axial or discogenic pain

Among the multiple causes of chronic low back pain, axial and discogenic pain are common. Various modalities of treatments are utilized in managing discogenic and axial low back pain including epidural injections. However, there is a paucity of evidence regarding the effectiveness, indications, and medical necessity of any treatment modality utilized for managing axial or discogenic pain, including epidural injections. In an interventional pain management practice in the US, a randomized, double-blind, active control trial was conducted. The objective was to assess the effectiveness of lumbar interlaminar epidural injections of local anesthetic with or without steroids for managing chronic low back pain of discogenic origin. However, disc herniation, radiculitis, facet joint pain, or sacroiliac joint pain were excluded. Two groups of patients were studied, with 60 patients in each group receiving either local anesthetic only or local anesthetic mixed with non-particulate betamethasone. Primary outcome measures included the pain relief-assessed by numeric rating scale of pain and functional status assessed by the, Oswestry Disability Index, Secondary outcome measurements included employment status, and opioid intake. Significant improvement or success was defined as at least a 50% decrease in pain and disability. Significant improvement was seen in 77% of the patients in Group I and 67% of the patients in Group II. In the successful groups (those with at least 3 weeks of relief with the first two procedures), the improvement was 84% in Group I and 71% in Group II. For those with chronic function-limiting low back pain refractory to conservative management, it is concluded that lumbar interlaminar epidural injections of local anesthetic with or without steroids may be an effective modality for managing chronic axial or discogenic pain. This treatment appears to be effective for those who have had facet joints as well as sacroiliac joints eliminated as the pain source.

Degenerative joint disease of the spine

Degenerative changes are the manifestations of metabolic disturbances in the matrix of intervertebral disks and zygapophysial joints. Genetic factors and physical loading contribute, but the strongest correlation is with age. Degenerative changes lack any significant correlation with spinal pain. Therefore, they do not constitute a diagnosis. Internal disk disruption is a distinctive condition that is independent of degeneration and age. Its biophysical and morphologic features correlate with back pain, as do its manifestations on magnetic resonance imaging.

Peripheral disc margin shape and internal disc derangement: imaging correlation in significantly painful discs identified at provocation lumbar discography

Annular margin shape is used to characterize lumbar disc abnormality on CT/MR imaging studies. Abnormal discs also have internal derangement including annular degeneration and radial defects. The purpose of this study was to evaluate potential correlation between disc-margin shape and annular internal derangement on post-discogram CT in significantly painful discs encountered at provocation lumbar discography (PLD). Significantly painful discs were encountered at 126 levels in 86 patients (47 male, 39 female) studied by PLD where no prior surgery had been performed and response to intradiscal lidocaine after provocation resulted in either substantial/total relief or no improvement after lidocaine administration. Post-discogram CT and discogram imaging was evaluated for disc-margin characteristics (bulge/protrusion), features of disc internal derangement (radial annular defect [RD: radial tear/fissure/annular gap], annular degeneration) and presence/absence of discographic contrast leakage. In discs with focal protrusion, 50 of 63 (79%) demonstrated Grade 3 RD with 13 (21%) demonstrating severe degenerative change only. In discs with generalized-bulge-only, 48 of 63 (76%) demonstrated degenerative change only (primarily Dallas Grade 3) with 15 of 63 (24%) demonstrating a RD (Dallas Grade 3). Differences were highly statistically significant (p<0.001). Pain elimination with intra-discal lidocaine correlated with discographic contrast leakage (p<0.001). Disc-margin shape correlates with features of internal derangement in significantly painful discs encountered at PLD. Discs with focal protrusion typically demonstrate RD while generalized bulging discs typically demonstrated degenerative changes only (p<0.001). Disc-margin shape may provide an important imaging clue to the cause of chronic discogenic low back pain.

Lateral interbody fusion for treatment of discogenic low back pain: minimally invasive surgical techniques

Low back pain is one of the most common ailments in the general population, which tends to increase in severity along with aging. While few patients have severe enough symptoms or underlying pathology to warrant surgical intervention, in those select cases treatment choices remain controversial and reimbursement is a substancial barrier to surgery. The object of this study was to examine outcomes of discogenic back pain without radiculopathy following minimally-invasive lateral interbody fusion. Twenty-two patients were treated at either one or two levels (28 total) between L2 and 5. Discectomy and interbody fusion were performed using a minimallyinvasive retroperitoneal lateral transpsoas approach. Clinical and radiographic parameters were analyzed at standard pre- and postoperative intervals up to 24 months. Mean surgical duration was 72.1 minutes. Three patients underwent supplemental percutaneous pedicle screw instrumentation. Four (14.3%) stand-alone levels experienced cage subsidence. Pain (VAS) and disability (ODI) improved markedly postoperatively and were maintained through 24 months. Segmental lordosis increased significantly and fusion was achieved in 93% of levels. In this series, isolated axial low back pain arising from degenerative disc disease was treated with minimally-invasive lateral interbody fusion in significant radiographic and clinical improvements, which were maintained through 24 months.

Disk injury in rats produces persistent increases in pain-related neuropeptides in dorsal root ganglia and spinal cord glia but only transient increases in inflammatory mediators: pathomechanism of chronic diskogenic low back pain

STUDY DESIGN

Immunohistological analysis in an injured intervertebral disk (IVD) model.

OBJECTIVE

To elucidate and compare in rats the behavior of the sensory nervous system and inflammatory mediators in experimentally injured IVDs.

SUMMARY OF BACKGROUND DATA

Multiple human and animal studies have verified the presence of sensory nerve fibers in IVDs or investigated the behavior of inflammatory mediators in injured IVDs, but no in vivo study to date has examined the relationship between the 2.

METHODS

Eight-week-old female rats were used. In the disk-injured group, L5/L6 disks were injured with a 24-gauge needle; simultaneously, the neurotracer Fluoro-gold was injected into the L5/L6 IVD. The L5/L6 IVD dorsal root ganglia (DRGs) from the L1 to L6 levels, and the spinal cord was resected at several time points after surgery. Nerve growth factor, tumor necrosis factor (TNF)-α and interleukin (IL)-6 production in the IVDs were quantified using enzyme-linked immunosorbent assay. DRGs were immunostained for calcitonin gene-related peptide, and spinal cord sections were immunostained for ionized calcium-binding adaptor molecule-1 and glial fibrillary acidic protein.

RESULTS

Nerve growth factor, and TNF-α levels (through 1 week) and IL-6 levels (through 4 days) were significantly higher in the disk-injured group than in the noninjured group (P < 0.05). However, starting at 2 weeks (nerve growth factor and TNF-α) or 1 week (IL-6), the differences in inflammatory mediator levels between the 2 groups no longer were significant. In contrast, the percentage of calcitonin gene-related peptide-immunoreactive neurons among Fluoro-gold-labeled DRG neurons, and the numbers of ionized calcium-binding adaptor molecule-1-immunoreactive microglia and glial fibrillary acidic protein-immunoreactive astrocytes in the spinal dorsal horn remained significantly higher in the injured group than in the noninjured group at all-time points (P < 0.05).

CONCLUSION

Disk injury in rats produces persistent increases in neuropeptides in DRGs and glia in the spinal cord, but only transient increases in inflammatory mediators in IVDs.

Pharmacological inhibition of tumor necrosis factor may reduce pain behavior changes induced by experimental disc puncture in the rat: an experimental study in rats

STUDY DESIGN

Pain behavior assessment in rats following disc puncture (DP) and simultaneous tumor necrosis factor (TNF) inhibition.

OBJECTIVE

To assess if treatment with TNF inhibition could reduce the pain behavior changes induced by DP in the rat.

SUMMARY OF BACKGROUND DATA

Anular tears with leakage of nucleus pulposus have been suggested to be one possible cause of low back pain (LBP). In an experimental model, it was recently shown that DP might induce specific pain behavior changes. The aim of the present study was to a study if inhibition of TNF might reduce such pain behavior changes.

METHODS

Sixty rats underwent facetectomy and puncture of the fourth lumbar disc. The rats were simultaneously treated with doxycycline locally at 0.3 and 3.0 mg/kg and systemically at 3.0 mg/kg, or infliximab locally at 0.5 and 5.0 mg/kg, and systemically at 5.0 mg/kg, (n ∇ 10 for each subseries). The rats were videotaped at 1, 3, 7, 14, and 21 days after surgery. The videos were analyzed regarding presence of wet-dog shakes (WDS). Data from a previous study with sham surgery and DP without treatment were included for comparison.

RESULTS

All groups treated with doxycycline resulted in a statistically significant reduction of WDS compared to the group without treatment (DP). In infliximab treated animals, WDS decreased with statistically significance compared to the nontreated DP group at all analyzed days except for the group with high dose local treatment where a statistically significant reduction was obtained only at days 14 and 21.

CONCLUSION

The present study showed that TNF inhibition induced a marked reduction of wet dog shakes. It is not fully understood if wet-dog shakes may relate to LBP, but in view of recent clinical findings one may consider clinical studies of TNF inhibition for the treatment of LBP.

Sustained blockade of neurotrophin receptors TrkA, TrkB and TrkC reduces non-malignant skeletal pain but not the maintenance of sensory and sympathetic nerve fibers

Current therapies for treating skeletal pain have significant limitations as available drugs (non-steroidal anti-inflammatory drugs and opiates) have significant unwanted side effects. Targeting nerve growth factor (NGF) or its cognate receptor tropomysin receptor kinase A (TrkA) has recently become an attractive target for inhibition of adult skeletal pain. Here we explore whether sustained administration of a selective small molecule Trk inhibitor that blocks TrkA, TrkB and TrkC kinase activity with nanomolar affinity reduces skeletal pain while allowing the maintenance of sensory and sympathetic neurons in the adult mouse. Twice-daily administration of a Trk inhibitor was begun 1 day post fracture and within 8 h of acute administration fracture pain-related behaviors were reduced by 50% without significant sedation, weight gain or inhibition of fracture healing. Following administration of the Trk inhibitor for 7 weeks, there was no significant decline in the density of unmyelinated or myelinated sensory nerve fibers, sympathetic nerve fibers, measures of acute thermal pain, acute mechanical pain, or general neuromuscular function. The present results suggest that sustained administration of a peripherally selective TrkA, B and C inhibitor significantly reduces skeletal pain without having any obvious detrimental effects on adult sensory and sympathetic nerve fibers or early fracture healing. As with any potential therapeutic advance, understanding whether the benefits of Trk blockade are associated with any risks or unexpected effects will be required to fully appreciate the patient populations that may benefit from this therapeutic approach.

The majority of myelinated and unmyelinated sensory nerve fibers that innervate bone express the tropomyosin receptor kinase A

Although skeletal pain is a leading cause of chronic pain and disability, relatively little is known about the specific populations of nerve fibers that innervate the skeleton. Recent studies have reported that therapies blocking nerve growth factor (NGF) or its cognate receptor, tropomyosin receptor kinase A (TrkA) are efficacious in attenuating skeletal pain. A potential factor to consider when assessing the analgesic efficacy of targeting NGF-TrkA signaling in a pain state is the fraction of NGF-responsive TrkA+ nociceptors that innervate the tissue from which the pain is arising, as this innervation and the analgesic efficacy of targeting NGF-TrkA signaling may vary considerably from tissue to tissue. To explore this in the skeleton, tissue slices and whole mount preparations of the normal, adult mouse femur were analyzed using immunohistochemistry and confocal microscopy. Analysis of these preparations revealed that 80% of the unmyelinated/thinly myelinated sensory nerve fibers that express calcitonin gene-related peptide (CGRP) and innervate the periosteum, mineralized bone and bone marrow also express TrkA. Similarly, the majority of myelinated sensory nerve fibers that express neurofilament 200 kDa (NF200) which innervate the periosteum, mineralized bone and bone marrow also co-express TrkA. In the normal femur, the relative density of CGRP+, NF200+ and TrkA+ sensory nerve fibers per unit volume is: periosteum>bone marrow>mineralized bone>cartilage with the respective relative densities being 100:2:0.1:0. The observation that the majority of sensory nerve fibers innervating the skeleton express TrkA+, may in part explain why therapies that block NGF/TrkA pathway are highly efficacious in attenuating skeletal pain.

Direct application of the tumor necrosis factor-α inhibitor, etanercept, into a punctured intervertebral disc decreases calcitonin gene-related peptide expression in rat dorsal root ganglion neurons

STUDY DESIGN

retrograde neurotracing and immunohistochemistry were used to investigate the effect of the tumor necrosis factor (TNF)-α inhibitor, etanercept, on calcitonin gene-related peptide (CGRP) expression in dorsal root ganglion (DRG) neurons innervating intervertebral discs in rats.

OBJECTIVE

to clarify the action of a TNF-α inhibitor on a sensory neuropeptide in DRG neurons innervating intervertebral discs.

SUMMARY OF BACKGROUND DATA

degeneration of lumbar intervertebral discs is a cause of low back pain. TNF-α in the intervertebral disc is a major contributor to discogenie pain. Effects of TNF-α inhibition on CGRP expression in DRG neurons were evaluated.

METHODS

the neurotracer FluoroGold was applied to the surfaces of L4/5 discs to label their innervating DRG neurons (n = 30). Of 30 rats, 10 were in a nonpunctured disc sham surgery control group, whereas the other 20 were in experimental groups in which intervertebral discs were punctured with a 23-gauge needle. Etanercept or saline was applied into the punctured discs (n = 10 each treatment). After 14 days of surgery, DRGs from L1 to L6 were harvested, sectioned, and immunostained for CGRP. The proportion of FluoroGold-labeled CGRP-immunoreactive DRG neurons was evaluated in all groups.

RESULTS

FluoroGold-labeled neurons innervating the L4/5 disc were distributed throughout L1-L6 DRGs in all groups. Of the FluoroGold-labeled neurons, the proportion of CGRP-immunoreactive neurons was 21% ± 4% in the sham surgery control group, 32% ± 7% in the puncture + saline group, and 23% ± 4% in the puncture + etanercept group. The proportion of CGRP-immunoreactive neurons was significantly greater in the puncture + saline group compared with the sham control and puncture + etanercept groups (P < 0.01).

CONCLUSION

in this model, CGRP was upregulated in DRG neurons innervating damaged discs. However, direct intradiscal application of etanercept immediately after disc puncture suppressed CGRP expression in DRG neurons innervating injured discs. This finding may further elucidate the mechanism for the effectiveness of etanercept in upregulation of neuropeptide in DRG neurons innervating intervertebral discs.

Administration of a tropomyosin receptor kinase inhibitor attenuates sarcoma-induced nerve sprouting, neuroma formation and bone cancer pain

Pain often accompanies cancer and most current therapies for treating cancer pain have significant unwanted side effects. Targeting nerve growth factor (NGF) or its cognate receptor tropomyosin receptor kinase A (TrkA) has become an attractive target for attenuating chronic pain.

In the present report, we use a mouse model of bone cancer pain and examine whether oral administration of a selective small molecule Trk inhibitor (ARRY-470, which blocks TrkA, TrkB and TrkC kinase activity at low nm concentrations) has a significant effect on cancer-induced pain behaviors, tumor-induced remodeling of sensory nerve fibers, tumor growth and tumor-induced bone remodeling. Early/sustained (initiated day 6 post cancer cell injection), but not late/acute (initiated day 18 post cancer cell injection) administration of ARRY-470 markedly attenuated bone cancer pain and significantly blocked the ectopic sprouting of sensory nerve fibers and the formation of neuroma-like structures in the tumor bearing bone, but did not have a significant effect on tumor growth or bone remodeling.

These data suggest that, like therapies that target the cancer itself, the earlier that the blockade of TrkA occurs, the more effective the control of cancer pain and the tumor-induced remodeling of sensory nerve fibers. Developing targeted therapies that relieve cancer pain without the side effects of current analgesics has the potential to significantly improve the quality of life and functional status of cancer patients.

Healing of a painful intervertebral disc should not be confused with reversing disc degeneration: implications for physical therapies for discogenic back pain

BACKGROUND

Much is known about intervertebral disc degeneration, but little effort has been made to relate this information to the clinical problem of discogenic back pain, and how it might be treated.

METHODS

We re-interpret the scientific literature in order to provide a rationale for physical therapy treatments for discogenic back pain.

INTERPRETATION

Intervertebral discs deteriorate over many years, from the nucleus outwards, to an extent that is influenced by genetic inheritance and metabolite transport. Age-related deterioration can be accelerated by physical disruption, which leads to disc "degeneration" or prolapse. Degeneration most often affects the lower lumbar discs, which are loaded most severely, and it is often painful because nerves in the peripheral anulus or vertebral endplate can be sensitised by inflammatory-like changes arising from contact with blood or displaced nucleus pulposus. Surgically-removed human discs show an active inflammatory process proceeding from the outside-in, and animal studies confirm that effective healing occurs only in the outer anulus and endplate, where cell density and metabolite transport are greatest. Healing of the disc periphery has the potential to relieve discogenic pain, by re-establishing a physical barrier between nucleus pulposus and nerves, and reducing inflammation.

CONCLUSION

Physical therapies should aim to promote healing in the disc periphery, by stimulating cells, boosting metabolite transport, and preventing adhesions and re-injury. Such an approach has the potential to accelerate pain relief in the disc periphery, even if it fails to reverse age-related degenerative changes in the nucleus.

Use of Temporary Implantable Biomaterials to Reduce Leg Pain and Back Pain in Patients with Sciatica and Lumbar Disc Herniation

The principle etiology of leg pain (sciatica) from lumbar disc herniation is mechanical compression of the nerve root. Sciatica is reduced by decompression of the herniated disc, i.e., removing mechanical compression of the nerve root. Decompression surgery typically reduces sciatica more than lumbar back pain (LBP). Decompression surgery reduces mechanical compression of the nerve root. However, decompression surgery does not directly reduce sensitization of the sensory nerves in the epidural space and disc. In addition, sensory nerves in the annulus fibrosus and epidural space are not protected from topical interaction with pain mediators induced by decompression surgery. The secondary etiology of sciatica from lumbar disc herniation is sensitization of the nerve root. Sensitization of the nerve root results from a) mechanical compression, b) exposure to cellular pain mediators, and/or c) exposure to biochemical pain mediators. Although decompression surgery reduces nerve root compression, sensory nerve sensitization often persists. These observations are consistent with continued exposure of tissue in the epidural space, including the nerve root, to increased cellular and biochemical pain mediators following surgery. A potential contributor to lumbar back pain (LBP) is stimulation of sensory nerves in the annulus fibrosus by a) cellular pain mediators and/or b) biochemical pain mediators that accompany annular tears or disruption. Sensory fibers located in the outer one-third of the annulus fibrosus increase in number and depth as a result of disc herniation. The nucleus pulposus is comprised of material that can produce an autoimmune stimulation of the sensory nerves located in the annulus and epidural space leading to LBP. The sensory nerves of the annulus fibrosus and epidural space may be sensitized by topical exposure to cellular and biochemical pain mediators induced by lumbar surgery. Annulotomy or annular rupture allows the nucleus pulposus topical access to sensory nerve fibers, thereby leading to LBP. Coverage of the annulus and adjacent structures in the epidural space by absorbable viscoelastic gels appears to reduce LBP following surgery by protecting sensory fibers from cellular and biochemical pain mediators.

Effect of applying p75NTR saporin to a punctured intervertebral disc on calcitonin gene-related peptide expression in rat dorsal root ganglion neurons

BACKGROUND

Recent studies have revealed that the low-affinity nerve growth factor receptor, p75 neurotrophin receptor (p75NTR), is important in inflammatory pain. Moreover, p75NTR immunoreactive sensory nerve and dorsal root ganglion (DRG) neurons have been found to innervate lumbar intervertebral discs. The purpose of the current study was to investigate the effect of p75NTR saporin, a toxin used to destroy p75NTR, on calcitonin gene-related peptide (CGRP), an inflammatory neuropeptide associated with pain, in DRG neurons innervating punctured intervertebral discs in rats.

METHODS

The neurotracer fluorogold (FG) was applied to the surfaces of L5/6 discs to label their innervating DRG neurons (n = 30). Of 30 rats, 10 were in a nonpunctured disc sham surgery control group (nonpuncture group), and the other 20 were in experimental groups in which intervertebral discs were punctured with a 23-gauge needle. p75NTR saporin was applied to the discs of 10 rats (puncture + p75NTR saporin group) and the other 10 received the same volume of saline (puncture + saline group). At 14 days after surgery, DRGs from L1 to L6 were harvested, sectioned, and immunostained for CGRP, and the proportions of CGRP-immunoreactive DRG neurons was evaluated.

RESULTS

Of the FG-labeled neurons innervating the L5/6 disc, the proportion of CGRP-immunoreactive neurons was 32% +/- 6% (mean +/- SE) in the nonpuncture group, 47.2% +/- 8% in the puncture + saline group, and 34.6% +/- 9% in the puncture + p75NTR saporin group. The proportion of CGRP-immunoreactive neurons was significantly greater in the puncture + saline group compared with the nonpuncture and puncture + p75NTR saporin groups (P < 0.01).

CONCLUSIONS

Half of the DRG neurons innervating the discs were positive for CGRP in the puncture + saline group. CGRP is important for mediating inflammatory and nerve-injured pain and may be important in discogenic pain. However, p75NTR saporin suppressed CGRP expression in DRG neurons. Therefore, p75NTR may be an important receptor for mediating discogenic pain via CGRP expression.

A phenotypically restricted set of primary afferent nerve fibers innervate the bone versus skin: therapeutic opportunity for treating skeletal pain

Although musculoskeletal pain is one of the most common causes of chronic pain and physical disability in both developing and developed countries, relatively little is known about the nerve fibers and mechanisms that drive skeletal pain. Small diameter sensory nerve fibers, most of which are C-fiber nociceptors, can be separated into two broad populations: the peptide-rich and peptide-poor nerve fibers. Peptide-rich nerve fibers express substance P (SP) and calcitonin gene-related peptide (CGRP). In contrast, the peptide-poor nerve fibers bind to isolectin B4 (IB(4)) and express the purinergic receptor P(2)X(3) and Mas-related G protein-coupled receptor member d (Mrgprd). In the present report, we used mice in which the Mrgprd(+) nerve fibers express genetically encoded axonal tracers to determine the peptide-rich and peptide-poor sensory nerve fibers that innervate the glabrous skin of the hindpaw as compared to the bone marrow, mineralized bone and periosteum of the femur. Whereas the skin is richly innervated by CGRP(+), SP(+), P(2)X(3)(+) and Mrgprd(+) sensory nerve fibers, the bone marrow, mineralized bone and periosteum receive a significant innervation by SP(+) and CGRP(+), but not Mrgprd(+) and P(2)X(3)(+) nerve fibers. This lack of redundancy in the populations of C-fibers that innervate the bone may present a unique therapeutic opportunity for targeting skeletal pain as the peptide-rich and peptide-poor sensory nerve fibers generally express a different repertoire of receptors and channels to detect noxious stimuli. Thus, therapies that target the specific types of C-nerve fibers that innervate the bone may be uniquely effective in attenuating skeletal pain as compared to skin pain.

Expression of semaphorin 3A and its receptors in the human intervertebral disc: potential role in regulating neural ingrowth in the degenerate intervertebral disc

Introduction

Intervertebral disc (IVD) degeneration is considered a major underlying factor in the pathogenesis of chronic low back pain. Although the healthy IVD is both avascular and aneural, during degeneration there is ingrowth of nociceptive nerve fibres and blood vessels into proximal regions of the IVD, which may contribute to the pain. The mechanisms underlying neural ingrowth are, however, not fully understood. Semaphorin 3A (sema3A) is an axonal guidance molecule with the ability to repel nerves seeking their synaptic target. This study aimed to identify whether members of the Class 3 semaphorins were expressed by chondrocyte-like cells of the IVD addressing the hypothesis that they may play a role in repelling axons surrounding the healthy disc, thus maintaining its aneural condition.

Methods

Human IVD samples were investigated using reverse transcription polymerase chain reaction (RT-PCR) to identify gene expression of sema3A, 3F and their receptors: neuropilins (1 and 2) and plexins (A1-4). Sema3A protein was also localised within sections of normal and degenerate human IVD and immunopositivity quantified. Serial sections were stained using PGP9.5 and CD31 to correlate semaphorin 3A expression with nerve and blood vessel ingrowth, respectively.

Results

Sema3A protein was expressed highly in the healthy disc, primarily localised to the outer annulus fibrosus. In degenerate samples, sema3A expression decreased significantly in this region, although cell clusters within the degenerate nucleus pulposus exhibited strong immunopositivity. mRNA for sema3A receptors was also identified in healthy and degenerate tissues. CD31 and PGP9.5 were expressed most highly in degenerate tissues correlating with low expression of sema3A.

Conclusions

This study is the first to establish the expression of semaphorins and their receptors in the human IVD with a decrease seen in the degenerate painful IVD. Sema3A may therefore, amongst other roles, act as a barrier to neuronal ingrowth within the healthy disc.