Annulus fissures are mechanically and chemically conducive to the ingrowth of nerves and blood vessels

Mast Cell/Proteinase Activated Receptor 2 (PAR2) Mediated Interactions in the Pathogenesis of Discogenic Back Pain

Mast cells (MCs) are present in the painful degenerate human intervertebral disc (IVD) and are associated with disease pathogenesis. MCs release granules containing enzymatic and inflammatory factors in response to stimulants or allergens. The serine protease, tryptase, is unique to MCs and its activation of the G-protein coupled receptor, Protease Activated Receptor 2 (PAR2), induces inflammation and degradation in osteoarthritic cartilage. Our previously published work has demonstrated increased levels of MC marker tryptase in IVD samples from discogenic back pain patients compared to healthy control IVD samples including expression of chemotactic agents that may facilitate MC migration into the IVD. To further elucidate MCs’ role in the IVD and mechanisms underlying its effects, we investigated whether (1) human IVD cells can promote MC migration, (2) MC tryptase can mediate up-regulation of inflammatory/catabolic process in human IVD cells and tissue, and (3) the potential of PAR2 antagonist to function as a therapeutic drug in in vitro human and ex vivo bovine pilot models of disease. MC migration was quantitatively assessed using conditioned media from primary human IVD cells and MC migration examined through Matrigel. Exposure to soluble IVD factors significantly enhanced MC migration, suggesting IVD cells can recruit MCs. We also demonstrated significant upregulation of MC chemokine SCF and angiogenic factor VEGFA gene expression in human IVD cells in vitro in response to recombinant human tryptase, suggesting tryptase can enhance recruitment of MCs and promotion of angiogenesis into the usually avascular IVD. Furthermore, tryptase can degrade proteoglycans in IVD tissue as demonstrated by significant increases in glycosaminoglycans released into surrounding media. This can create a catabolic microenvironment compromising structural integrity and facilitating vascular migration usually inhibited by the anti-angiogenic IVD matrix. Finally, as a “proof of concept” study, we examined the therapeutic potential of PAR2 antagonist (PAR2A) on human IVD cells and bovine organ culture IVD model. While preliminary data shows promise and points toward structural restoration of the bovine IVD including down-regulation of VEGFA, effects of PAR2 antagonist on human IVD cells differ between gender and donors suggesting that further validation is required with larger cohorts of human specimens.

SDF1/CXCR4 axis plays a role in angiogenesis during the degeneration of intervertebral discs

Low back pain (LBP) is a ubiquitous disease affecting quality of life. The ingrowth of new blood vessels is an important pathological feature of LBP, but its underlying mechanisms are poorly understood. The present study aimed to investigate the influence and relative mechanism of stromal cell derived factor 1 (SDF1) on the angiogenesis of degenerated intervertebral discs. The expression of SDF1 in nucleus pulposus cells (NPCs) was upregulated and downregulated by virus transfection, and the NPCs were allocated to either the downregulation (Down), degeneration (D) or upregulation (Up) group according to the expression of SDF1. The different groups of NPCs or NPC conditioned media were co-cultured with vascular endothelial cells (VECs) under different conditions. A Cell Counting Kit-8 (CCK-8) assay, a Transwell migration assay and a tube formation assay were conducted to evaluate the influence on angiogenesis. The results showed that SDF1 was significantly up- and downregulated in the Up and Down groups, respectively. Each group of NPCs or their conditioned medium was co-cultured with VECs; the CCK-8, Transwell migration and tube formation assays showed that cell viability, chemotactic migration and the tube formation ability of VECs increased with the rise in SDF1. The aforementioned results were significantly different between each group. After adding the CXCR4 inhibitor, AMD3100, the viability, migration and tube formation of VECs were suppressed in the D and Up groups, and there was a significant difference compared with the prior to the addition of the inhibitor, while there was a declining tendency in the Down group and no significant difference following addition of the inhibitor. The results demonstrated that SDF1 is expressed in human NPCs, and the SDF1/CXCR4 axis can influence the viability, migration and tube formation of VECs and may play an important role in the angiogenesis of human degenerated discs.

Could Hyperbaric Oxygen Be a Solution in the Treatment of Spinal Infections?

Background and Objective: Pyogenic spinal infections are rare and potentially devastating, requiring prompt recognition and management. Parallel to the ever-increasing number of invasive spinal procedures, its incidence is on a steady rise, particularly in an expanding elderly population. The aim of this study was to evaluate the efficacy of hyperbaric oxygen (HBO₂) therapy in the treatment of this heterogeneous group of disorders. Materials and Methods: Nineteen patients who were referred to our center for HBO₂ with a clinical diagnosis of spinal infections (vertebral osteomyelitis, pyogenic spondylitis, spondylodiscitis, surgical site infection following spine surgery, epidural abscess) were retrospectively reviewed. Results: Infection resolution was adequately achieved in 12 of 13 patients (92.3%) on magnetic resonance imaging at the end of HBO₂ treatment or during the first month of follow-up. The mean follow-up period was 11 months (range 1 month to 3 years). Conclusions: This study suggests that HBO₂ therapy is efficacious in patients with pyogenic spinal infections complicated by primary therapy failure or by medical comorbidities that may impede the eradication of microbial infection and delay wound healing. HBO₂ therapy may be useful for reducing long hospital stays, repeated surgeries, and morbidities.

SDF1/CXCR7 Signaling Axis Participates in Angiogenesis in Degenerated Discs via the PI3K/AKT Pathway

Degenerative disc disease (DDD) is the main cause of low back pain, and the ingrowth of new blood vessels is one of its pathological features. The stromal cell-derived factor 1 (SDF1)/CXCR7 signaling axis plays a role in these physiological and pathological activities. The aims of this study were to explore whether this signaling axis participates in the angiogenesis of degenerated intervertebral discs (IVDs) and to define its underlying mechanism. In this study, we cocultured human nucleus pulposus cells (NPCs) and vascular endothelial cells (VECs) and regulated the expression of SDF1/CXCR7 to investigate the effect of VEC angiogenesis by NPCs. The results revealed that angiogenesis was enhanced with increased SDF1 and that angiogenesis was weakened with the inhibition of CXCR7. We found that PI3K/AKT was involved in the downstream pathway in the coculture. VEC angiogenesis induction by NPCs was enhanced with an increase in pAKT or a decrease in PTEN. We conclude that the SDF1/CXCR7 signaling axis plays a role in the angiogenesis of degenerated IVD through the PI3K/AKT pathway.

Notochordal cell matrix: An inhibitor of neurite and blood vessel growth?

Blood vessel and neurite ingrowth into the degenerating intervertebral disc (IVD) are related to pain. In reported studies, notochordal cell (NC)-conditioned medium (NCCM) induced a regenerative response of nucleus pulposus (NP) cells, but also inhibition of neurite and vessel formation. NC matrix (NCM) derived from NC-rich NP tissue, induced even stronger anabolic effects than NCCM. Thus, the aim was to investigate whether NCM has similar anti-neurogenic and -angiogenic properties as NCCM. NCM and NCCM where produced from porcine NC-rich NP tissue. Human umbilical vein endothelial cells (HUVECs) were cultured in base medium (BM, 300 mOsm), NCCM (produced at 300 and 400 mOsm), NCM, or with chondroitin sulfate (CS, positive control) in angiogenesis-inducing medium, after which vessel length was measured. Although CS alone inhibited vessel growth, NCCM (both osmolarities) stimulated vessel formation by HUVECs. NCM did not affect vessel growth relative to BM. SH-SY5Y cells were cultured in BM, NCCM, and NCM on poly-D-lysine coated and polystyrene surfaces, and analyzed for neurite length and percentage of neurite expressing cells. On coated surfaces, neither NCCM nor NCM affected neurite growth. On a polystyrene surface, NCCM and NCM induced a higher number of neurite-expressing cells. NCCM's previously reported anti-angiogenic and -neurogenic effects were not observed in this study. Although addition of CS inhibited HUVEC vessel formation, other factors may be present in NCCM and NCM that affect neurite and vessel growth. Therefore, future studies testing an NC-based regenerative strategy should carefully assess the risk of such adverse effects in an in vivo setting. © 2018 The Authors. Journal of Orthopaedic Research® Published by Wiley Periodicals, Inc. J Orthop Res 36:3188-3195, 2018.

Annulus fibrosus cell phenotypes in homeostasis and injury: implications for regenerative strategies

Despite considerable efforts to develop cellular, molecular, and structural repair strategies and restore intervertebral disk function after injury, the basic biology underlying intervertebral disk healing remains poorly understood. Remarkably, little is known about the origins of cell populations residing within the annulus fibrosus, or their phenotypes, heterogeneity, and roles during healing. This review focuses on recent literature highlighting the intrinsic and extrinsic cell types of the annulus fibrosus in the context of the injury and healing environment. Spatial, morphological, functional, and transcriptional signatures of annulus fibrosus cells are reviewed, including inner and outer annulus fibrosus cells, which we propose to be referred to as annulocytes. The annulus also contains peripheral cells, interlamellar cells, and potential resident stem/progenitor cells, as well as macrophages, T lymphocytes, and mast cells following injury. Phases of annulus fibrosus healing include inflammation and recruitment of immune cells, cell proliferation, granulation tissue formation, and matrix remodeling. However, annulus fibrosus healing commonly involves limited remodeling, with granulation tissues remaining, and the development of chronic inflammatory states. Identifying annulus fibrosus cell phenotypes during health, injury, and degeneration will inform reparative regeneration strategies aimed at improving annulus fibrosus healing.

VEGF vascularization pathway in human intervertebral disc does not change during the disc degeneration process

Objective

During degeneration of the intervertebral disc ingrowth of blood vessels and nerves into the disc are associated with back pain. Vascular endothelial growth factors promote vasculogenesis by binding to the membrane vascular endothelial growth factor receptor 1, while shorter soluble forms of this receptor can inhibit vascularization. We hypothesized that membrane and soluble receptor forms might change between stages of intervertebral disc degeneration.

Results

Expression of soluble and membrane forms of vascular endothelial growth factor receptor 1 in human degenerated intervertebral discs and healthy bovine caudal discs was assessed by qRT-PCR and immunoblot. Comparative microarray meta-analysis across disc degeneration grades showed that membrane and soluble forms of this receptor, together with other components of classic vascularization pathways, are constitutively expressed across human disc degeneration stages. Contrary to our hypothesis, we observed that expression of the classic vascularization pathway is stable across degeneration stages and we assume that soluble vascular endothelial growth factor receptor 1 does not contribute to prevent disc degeneration. However, we observed increased expression levels of genes involved in alternative vascularization signalling pathways in severely degenerated discs, suggesting that abnormal vascularization is part of the pathological progression of disc degeneration.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-3441-3) contains supplementary material, which is available to authorized users.

A Mouse Intervertebral Disc Degeneration Model by Surgically Induced Instability

STUDY DESIGN

An experimental study to develop a mouse model of lumbar intervertebral disc degeneration (IDD).

OBJECTIVE

The aim of this study was to develop a mouse lumbar IDD model using surgically induced instability and to compare the findings of this model to those in human IDD.

SUMMARY OF BACKGROUND DATA

Previously, various kinds of inducers have been used to reproduce IDD in experimental animals; however, there is yet no standard mouse lumbar IDD model without direct injury to intervertebral disc.

METHODS

A total number of 59 C57BL/6J male mice at 8 weeks old were used. Instability of lumbar spine was induced by surgical resection of posterior elements, including facet joints, supra- and interspinous ligaments. We then analyzed time course changes in radiographical (n = 17) and histological analyses (n = 42), and compared these findings with those in human IDD.

RESULTS

Radiographical analyses showed that the disc height began to decrease in the first 2 weeks after the surgery, and the decrease continued throughout 12 weeks. Bone spurs at the vertebral rims were observed in the late stage of 8 and 12 weeks after the surgery. Histological analyses showed that the disorder of the anterior anulus fibrosus (AF) was initially obvious, followed by posterior shift and degeneration of the nucleus pulposus (NP). Proteoglycan detected in inner layer of AF and periphery of NP was decreased after 8 weeks. Immunohistochemistry displayed the increase of type I and X collagen, and matrix metalloproteinase 13 in the anterior AF.

CONCLUSION

Surgical resection of posterior elements of mouse lumbar spine resulted in reproducible IDD. Because the present procedure does not employ direct injury to intervertebral disc and the radiological and histological findings are compatible with those in human IDD, it may contribute to further understanding of the native pathophysiology of IDD in future.

LEVEL OF EVIDENCE

N/A.

Nerves and blood vessels in degenerated intervertebral discs are confined to physically disrupted tissue

Nerves and blood vessels are found in the peripheral annulus and endplates of healthy adult intervertebral discs. Degenerative changes can allow these vessels to grow inwards and become associated with discogenic pain, but it is not yet clear how far, and why, they grow in. Previously we have shown that physical disruption of the disc matrix, which is a defining feature of disc degeneration, creates free surfaces which lose proteoglycans and water, and so become physically and chemically conducive to cell migration. We now hypothesise that blood vessels and nerves in degenerated discs are confined to such disrupted tissue. Whole lumbar discs were obtained from 40 patients (aged 37-75 years) undergoing surgery for disc herniation, disc degeneration with spondylolisthesis or adolescent scoliosis ('non-degenerated' controls). Thin (5-μm) sections were stained with H&E and toluidine blue for semi-quantitative assessment of blood vessels, fissures and proteoglycan loss. Ten thick (30-μm) frozen sections from each disc were immunostained for CD31 (an endothelial cell marker), PGP 9.5 and Substance P (general and nociceptive nerve markers, respectively) and examined by confocal microscopy. Volocity image analysis software was used to calculate the cross-sectional area of each labelled structure, and its distance from the nearest free surface (disc periphery or internal fissure). Results showed that nerves and blood vessels were confined to proteoglycan-depleted regions of disrupted annulus. The maximum distance of any blood vessel or nerve from the nearest free surface was 888 and 247 μm, respectively. Blood vessels were greater in number, grew deeper, and occupied more area than nerves. The density of labelled blood vessels and nerves increased significantly with Pfirrmann grade of disc degeneration and with local proteoglycan loss. Analysing multiple thick sections with fluorescent markers on a confocal microscope allows reliable detection of thin filamentous structures, even within a dense matrix. We conclude that, in degenerated and herniated discs, blood vessels and nerves are confined to proteoglycan-depleted regions of disrupted tissue, especially within annulus fissures.

Proinflammatory Cytokines IL-1β and TNF-α Influence Human Annulus Cell Signaling Cues for Neurite Growth: In Vitro Coculture Studies

STUDY DESIGN

Institutional review board-approved research using human annulus cells cocultured with F11 nerve cells.

OBJECTIVE

To perform functional, kinetic assays of neurite dynamics and media neurotrophin measurements to test whether proinflammatory cytokines influence annulus cells' signaling cues for neurite growth/repulsion.

SUMMARY OF BACKGROUND DATA

Nerves grow in response to signaling molecules called neurotrophins, which disc cells produce (e.g., brain-derived neurotrophic factor [BDNF], glial cell line-derived neurotrophic factor [GDNF], and neurotrophin 3 [NT3]) and which influence neuron survival, differentiation, and migration. How proinflammatory cytokines influence disc signaling cues for neurite growth/repulsion is poorly understood.

METHODS

Studies used our previous model of 4-day human annulus cell-F11 nerve cell coculture to assess effects of added proinflammatory cytokines interleukin 1 beta (IL-1β; 10 pmol/L) or tumor necrosis factor alpha (TNF-α) (10 pmol/L). Annulus cells were cultured from 6 Thompson grade I, 9 grade II, 8 grade III, 11 grade IV, and 7 grade V discs. Neurite lengths were measured following control conditions or with added IL-1β or TNF-α, and conditioned media assayed with RayBiotech Growth Factor Arrays. Standard statistical methods used analysis of variance and Spearman correlation coefficient testing associations of neurite length with neurotrophin levels.

RESULTS

IL-1-β or TNF-α significantly increased neurite lengths (P < 0.001) and BDNF, NT3, and GDNF media levels (P ≤ 0.01) versus controls. Significant positive correlations were present between media neurotrophin levels for BDNF, NT3, and GDNF and neurite lengths under control conditions, following addition of IL-1β, and following addition of TNF-α. Novel data showed production of the neurotrophin amphiregulin.

CONCLUSION

In vitro data supported the hypothesis that nerve-disc cell interactions may be influenced by the heightened proinflammatory milieu present in degenerating discs, leading to increased nerve migration. Data may have direct clinical relevance/implications for nerve ingrowth and pain in the outer annulus (where disc cell numbers are high), and in regions where nerves penetrate into the disc via annular tears.

LEVEL OF EVIDENCE

N/A.

Morphologic features of spontaneous annular tears and disc degeneration in the aging sand rat (Psammomys obesus obesus)

The sand rat, a member of the gerbil family, is a valuable small animal model in which intervertebral disc degeneration occurs spontaneously as the animal ages. Radiographic features of cervical and lumbar degeneration resemble those in human spines. We conducted a retrospective analysis of spines of 140 animals 3-41 months old focusing specifically on the presence of annular tears that are not visible by radiography and have not been described previously in the sand rat disc. During degeneration of the nucleus pulposus, notochordal cell death occurs and granular material, which stains with Alcian blue for proteoglycans, accumulates. Lamellar architecture also deteriorates and annular tears occur that are morphologically similar to the concentric, radiating and transdiscal annular tears in human discs. These tears contain granular material that provides a "marker" that can be used to distinguish the annular tears from artefactual separations during sectioning. We observed lamellar degeneration and separation in the annulus fibrosus at 4 months with associated tears that contained granular material in the nucleus. Tears that contained granular material and displacement of the degenerating nucleus were common in cervical and lumbar discs of animals older than 9 months; some specimens showed tears at 4 and 5 months. With advanced degeneration, granular globules were displaced dorsally adjacent to and into the spinal cord area and also ventrally into regions where osteophytes formed. We present morphologic data that expand the utility of this rodent model of spontaneous age-related disc degeneration and provide novel information on annular tears and disc degeneration.

Looking beyond the intervertebral disc: the need for behavioral assays in models of discogenic pain

Orthopedic research into chronic discogenic back pain has commonly focused on aging- and degeneration-related changes in intervertebral disc structure, biomechanics, and biology. However, the primary spine-related reason for physician office visits is pain. The ambiguous nature of the human condition of discogenic low back pain motivates the use of animal models to better understand the pathophysiology. Discogenic back pain models must consider both emergent behavioral changes following pain induction and changes in the nervous system that mediate such behavior. Looking beyond the intervertebral disc, we describe the different ways to classify pain in human patients and animal models. We describe several behavioral assays that can be used in rodent models to augment disc degeneration measurements and characterize different types of pain. We review rodent models of discogenic pain that employed behavioral pain assays and highlight a need to better integrate neuroscience and orthopedic science methods to extend current understanding of the complex and multifactorial pathophysiology of discogenic back pain.

Effects of annulus defects and implantation of poly(lactic-co-glycolic acid) (PLGA)/fibrin gel scaffolds on nerves ingrowth in a rabbit model of annular injury disc degeneration

Background

Growth of nerve fibers has been shown to occur in a rabbit model of intravertebral disc degeneration (IVD) induced by needle puncture. As nerve growth may underlie the process of chronic pain in humans affected by disc degeneration, we sought to investigate the factors underlying nerve ingrowth in a minimally invasive annulotomy rabbit model of IVD by comparing the effects of empty disc defects with those of defects filled with poly(lactic-co-glycolic acid)/fibrin gel (PLGA) plugs.

Methods

New Zealand white rabbits (n = 24) received annular injuries at three lumbar levels (L3/4, L4/5, and L5/6). The discs were randomly assigned to four groups: (a) annular defect (1.8-mm diameter; 4-mm depth) by mini-trephine, (b) annular defect implanted with a PLGA scaffold containing a fibrin gel, (c) annular puncture by a 16G needle (5-mm depth), and (d) uninjured L2/3 disc (control). Disc degeneration was evaluated by radiography, MRI, histology, real-time PCR, and analysis of proteoglycan (PG) content. Nerve ingrowth into the discs was assessed by immunostaining with the nerve marker protein gene product 9.5.

Results

Injured discs showed a progressive disc space narrowing with significant disc degeneration and proteoglycan loss, as confirmed by imaging results, molecular and compositional analysis, and histological examinations. In 16G punctured discs, nerve ingrowth was observed on the surface of scar tissue. In annular defects, nerve fibers were found to be distributed along small fissures within the fibrocartilaginous-like tissue that filled the AF. In discs filled with PLGA/ fibrin gel, more nerve fibers were observed growing deeper into the inner AF along the open annular track.  In addition, innervations scores showed significantly higher than those of punctured discs and empty defects. A limited vascular proliferation was found in the injured sites and regenerated tissues.

Conclusions

Nerve ingrowth was significantly higher in PLGA/fibrin-filled discs than in empty defects. Possible explanations include (i) annular fissures along the defect and early loss of proteoglycan may facilitate the ingrowth process and (ii) biodegradable PLGA/fibrin gel may promote adverse growth of nerves and blood vessels into deeper parts of injured disc. The rabbit annular defect model of disc degeneration appears suitable to investigate the effects of nerve ingrowth in relation to pain generation.

Annulus fibrosus cells express and utilize C-C chemokine receptor 5 (CCR5) for migration

BACKGROUND CONTEXT

Disc degeneration is associated with the progressive loss of the proteoglycan content of the intervertebral disc, decreased matrix synthesis, higher concentrations of proteolytic enzymes, and increased levels of proinflammatory cytokines. In previous studies, we have shown that C-C chemokine ligand (CCL)2, CCL3, and CCL5 are highly expressed by cultured nucleus pulposus (NP) and annulus fibrosus (AF) cells that have been treated by interleukin-1. The major function of these chemokines is to recruit immune cells into the disc. It is unclear if disc cells can respond to these chemokines. Recent studies by Phillips et al. (2015) showed that NP cells express a number of cytokines and chemokine receptors.

PURPOSE

The purpose of this study is to determine the gene and protein expression of C-C chemokine receptor (CCR)1, CCR2, and CCR5 in NP and AF cells, and to test if these receptors can respond to their ligands in these cells by cell signaling and migration.

STUDY DESIGN/SETTING

This is an in vitro study.

METHODS

For RNA, surface expression, and cell signaling studies, human cells were isolated from the NP and AF tissues collected after spine surgery or from donated spine segments (Gift of Hope Human Donor & Tissue Network of Illinois) and cultured in monolayer. The gene expression of human CCR1, CCR2, and CCR5 was analyzed using real-time polymerase chain reaction. The surface expression of CCR1, CCR2, and CCR5 was analyzed using flow cytometry and fluorescently tagged antibodies specific for these proteins. Extracellular signal-regulated kinase (ERK) phosphorylation was analyzed from the cell lysates of NP and AF cells treated with CCL2 and CCL5 for 1 hour using enzyme-linked immunosorbent assay. Migration of primary rabbit AF cells was assayed using 8-µm Corning Transwell inserts in the presence or absence of CCL5. This study was partially funded by a North American Spine Society 2014 Basic Research Grant Award ($50,000).

RESULTS

RNA analysis showed that gene expression of CCR1, CCR2, and CCR5 was evident in human NP and AF cells (n=6). Only a small population of NP and AF cells expressed CCR1 (1.9% and 1.2%, respectively) and CCR2 (0.8% and 1.4%, respectively) on the cell surface, whereas a larger percentage expressed CCR5 (12.7% and 11.6%, respectively). Significantly higher levels of ERK phosphorylation were detected in AF cells after treatment with CCL5 and not CCL2. Treatment with either chemokine did not cause significantly higher ERK phosphorylation in NP cells. There was an increase in average AF cell migration in the presence of CCL5. The increase was significant when the migration was induced with CCL5 (500 ng/mL) at both 2- and 6-hour time points.

CONCLUSIONS

CCR5 is expressed at the RNA level and on the cell surface of NP and AF cells. In the presence of CCL5, we detected increased levels of ERK phosphorylation and AF cell migration, suggesting that the CCR5 receptors in AF cells are functional. These data suggest that AF cells may have the ability to migrate in response to disc damage or inflammation.

Contaminants in commercial preparations of 'purified' small leucine-rich proteoglycans may distort mechanistic studies

The present study reports the perplexing results that came about because of seriously impure commercially available reagents. Commercial reagents and chemicals are routinely ordered by scientists and expected to have been rigorously assessed for their purity. Unfortunately, we found this assumption to be risky. Extensive work was carried out within our laboratory using commercially sourced preparations of the small leucine-rich proteoglycans (SLRPs), decorin and biglycan, to investigate their influence on nerve cell growth. Unusual results compelled us to analyse the composition and purity of both preparations of these proteoglycans (PGs) using both mass spectrometry (MS) and Western blotting, with and without various enzymatic deglycosylations. Commercial ‘decorin’ and ‘biglycan’ were found to contain a mixture of PGs including not only both decorin and biglycan but also fibromodulin and aggrecan. The unexpected effects of ‘decorin’ and ‘biglycan’ on nerve cell growth could be explained by these impurities. Decorin and biglycan contain either chondroitin or dermatan sulfate glycosaminoglycan (GAG) chains whereas fibromodulin only contains keratan sulfate and the large (>2500 kDa), highly glycosylated aggrecan contains both keratan and chondroitin sulfate. The different structure, molecular weight and composition of these impurities significantly affected our work and any conclusions that could be made. These findings beg the question as to whether scientists need to verify the purity of each commercially obtained reagent used in their experiments. The implications of these findings are vast, since the effects of these impurities may already have led to inaccurate conclusions and reports in the literature with concomitant loss of researchers’ funds and time.

The Contribution of Biomechanical-Biological Interactions of the Spine to Low Back Pain

OBJECTIVE

The objective of this mini-review is to examine a subset of literature that demonstrates multiple interactions between mechanics and biology within the spine and propose how incorporation of these mechano-biologic interactions can be applied to improve the conceptual understanding of tissue tolerances.

BACKGROUND

Low back pain represents a major musculoskeletal problem in the workplace. Traditional biomechanical assessments have employed tissue tolerances as an approach for reducing workplace injuries; however, development of more universal biologically sensitive tolerances requires incorporation of mechano-biologic interactions.

METHODS

A focused literature review addressing the interactions between mechanical loading and biology in the spine.

RESULTS

Mechanical loads applied to the body are distributed across all spatial scales from the body to the tissues to the cells. These mechanical loads regulate cellular metabolism and over time can lead to tissue strengthening or weakening. Mechanical loading also interacts with the biologic environment (e.g., tissue inflammation, nerve sensitization) to influence the perception of pain, thereby changing the risk of experiencing pain. Biologic tissues also exhibit time-dependent changes in mechanical behaviors that occur throughout the day and with disease, suggesting tissue tolerances are time dependent.

CONCLUSION

Incorporating mechano-biologic interactions into the traditional tissue tolerance paradigm through describing tissue tolerances as a function of multiple factors (e.g., preexisting risk factors, underlying pathology, and time) may lead to the development of tissue tolerances that are more representative of the in vivo situation.

APPLICATION

Efforts must work toward incorporating biological concepts into tissue tolerances in order to improve risk assessment tools.

Clinical outcome following DIAM implantation for symptomatic lumbar internal disk disruption: a 3-year retrospective analysis

BACKGROUND/OBJECTIVE

Internal disk disruption (IDD), an early event of lumbar disk degeneration, is the most common cause of low back pain. Since increased intradiskal pressure (IDP) is associated with symptoms and progression of disk degeneration, unloading a painful disk with an interspinous process device (IPD) is a rational treatment option. The goal of this study was to evaluate the effectiveness of dynamic stabilization with an IPD in the treatment of symptomatic IDD of the lumbar spine.

PATIENTS AND METHODS

Patients with symptomatic IDD were treated with implantation of an IPD, the device for intervertebral assisted motion (DIAM). Diagnosis of IDD was based on typical MRI finding of posterior annular high-intensity zone and positive provocative test on discography. IDP was analyzed intraoperatively. Axial back and leg pain was evaluated with visual analog scale, functional status with Oswestry Disability Index, and final clinical outcomes with Odom criteria. Data from 34 patients followed up for at least 3 years were collected.

RESULTS

DIAM implantation significantly reduced IDP (n=11, P<0.0001). All 34 patients reported symptom relief. Thirty-one patients (91%) remained symptom free until the last followups. Three patients (9%) experienced recurrence of pain, of which the causes were unrelated to the IDD or surgery. Disk status at the DIAM-implanted segments remained stable. Segmental flexion/extension mobility was preserved in 27 of 30 patients with preoperative mobility. No proximal or distal adjacent segment degeneration was observed. The final clinical outcomes were excellent/good in 31 and fair/poor in three patients.

CONCLUSION

For patients with symptomatic IDD, dynamic stabilization with DIAM provides pain relief and functional improvement. The implantation maintains disk status and prevents progression of disk degeneration, without compromising segmental flexion/extension mobility or causing adjacent segment degeneration.

Evaluating the low back biomechanics of three different office workstations: Seated, standing, and perching

The objective of this study was to evaluate how different workstations may influence physical behavior in office work through motion and how that may affect spinal loads and discomfort. Twenty subjects performed a typing task in three different workstations (seated, standing, and perching) for one hour each. Measures of postural transitions, spinal loads, discomfort, and task performance were assessed in order to understand the effects of workstation interaction over time. Results indicated that standing had the most amount of motion (6-8 shifts/min), followed by perching (3-7 shifts/min), and then seating (<1 shift/min). Standing had the highest reports of discomfort and seating the least. However, spinal loads were highest in A/P shear during standing (190N posterior shear, 407N anterior shear) compared to perching (65N posterior shear, 288N anterior shear) and seating (106N posterior shear, 287 anterior shear). These loads are below the risk threshold for shear, but may still elicit a cumulative response. Perching may induce motion through supported mobility in the perching stool, whereas standing motion may be due to postural discomfort. Office workstation designs incorporating supported movement may represent a reasonable trade-off in the costs-benefits between seating and standing.

Catabolic effects of endothelial cell-derived microparticles on disc cells: Implications in intervertebral disc neovascularization and degeneration

Neovascularization of intervertebral discs, a phenomenon considered pathological since normal discs are primarily avascular structures, occurs most frequently in annulus fibrosus (AF) of degenerated discs. Endothelial cells (ECs) are involved in this process, but the mechanism of the interaction between AF and endothelial cells is unclear. In this study, we evaluated the effects on matrix catabolic activity of AF cells by the extracellular endothelial microparticles (EMPs) and soluble protein factors (SUP fraction) produced from ECs. Passage 1 human AF cells grown in monolayer cultures were treated for 72 h with 250 µg of EMPs or SUP fraction isolated from culture of the microvascular endothelial cell line, HEMC-I. Live-cell imaging revealed uptake of EMPs by AF cells. RT-PCR analysis demonstrated increased mRNA expression of MMP-1 (50.3-fold), MMP-3 (4.5-fold) and MMP-13 (5.5-fold) in AF cell cultures treated with EMPs compared to untreated control. Western analysis also demonstrated increased MMP protein expression in EMP-treated AF cells. AF cells treated with the SUP fraction also exhibited a dramatic increase in MMP mRNA and protein expression. Increased MMP expression is primarily due to EMP or SUP stimulation of AF cells since EMPs or SUP fraction alone contained negligible amount of MMPs. Interestingly, MMP activity was elevated in AF cell cultures treated with EMPs but not with SUP. This study revealed enhanced matrix catabolism as a molecular consequence of action of ECs on AF cells via EMPs, which might be expected during neo-angiogenesis of degenerating disc. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1466-1474, 2016.

Human annulus signaling cues for nerve outgrowth: In vitro studies

The relationship between neurotrophins produced by human annulus cells, such as neurotrophin-4 (NT4) and brain-derived neurotrophic factor (BDNF) which function in neurite survival and outgrowth, and nerve ingrowth into the disc remains poorly understood. In this work, we tested F11 neurite growth during exposure to control media, media with added nerve growth factor (NGF), conditioned media (CM) harvested from previous human annulus culture, or co-culture with annulus cells. Co-culture of F11 cells with annulus cells significantly increased media levels of amphiregulin, BDNF, glial-derived neurotrophic factor, and vascular endothelial growth factor compared to levels from in culture of F11 cells alone (p ≤ 0.04). Cell-based assays of neurite growth revealed that BDNF levels present in CM bore a significant (p = 0.01) positive relationship to neurite length and accounted for 38.5% of the change in neurite length. NT4 levels produced during co-culture with annulus cells bore a significant (p = 0.04) positive relationship to neurite length and accounted for 40.9% of the change in length. Statement of clinical significance: In vitro findings point to a potential role of annulus cells related to nerve ingrowth in vivo, and may have relevance in the outer annulus (where cell numbers are high) or in regions where nerves penetrate into annular tears or fissures. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1456-1465, 2016.

Optical Coherence Tomographic Elastography Reveals Mesoscale Shear Strain Inhomogeneities in the Annulus Fibrosus

STUDY DESIGN

Basic science study using in vitro tissue testing and imaging to characterize local strains in annulus fibrosus (AF) tissue.

OBJECTIVE

To characterize mesoscale strain inhomogeneities between lamellar and inter-/translamellar (ITL) matrix compartments during tissue shear loading.

SUMMARY OF BACKGROUND DATA

The intervertebral disc is characterized by significant heterogeneities in tissue structure and plays a critical role in load distribution and force transmission in the spine. In particular, the AF possesses a lamellar architecture interdigitated by a complex network of extracellular matrix components that form a distinct ITL compartment. Currently, there is not a firm understanding of how the lamellar and ITL matrix coordinately support tissue loading.

METHODS

AF tissue samples were prepared from frozen porcine lumbar spines and mounted onto custom fixtures of a materials testing system that incorporates optical coherence tomography (OCT) imaging to perform tissue elastography. Tissues were subjected to 20 and 40% nominal shear strain, and OCT images were captured and segmented to identify regions of interest corresponding to lamellar and ITL compartments. Images were analyzed using an optical flow algorithm to quantify local shear strains within each compartment.

RESULTS

Using histology and OCT, we first verified our ability to visualize and discriminate the ITL matrix from the lamellar matrix in porcine AF tissues. Local AF strains in the ITL compartment (22.0 ± 13.8, 31.1 ± 16.9 at 20% and 40% applied shear, respectively) were significantly higher than corresponding strains in the surrounding lamellar compartment (12.1 ± 5.6, 15.3 ± 5.2) for all tissue samples (P < 0.05).

CONCLUSION

Results from this study demonstrate that the lamellar and ITL compartments of the AF distribute strain unevenly during tissue loading. Specifically, shear strain is significantly higher in the ITL matrix, suggesting that these regions may be more susceptible to tissue damage and more mechanobiologically active.

LEVEL OF EVIDENCE

N/A.

Class 3 semaphorins expression and association with innervation and angiogenesis within the degenerate human intervertebral disc

Nerve and blood vessel ingrowth during intervertebral disc degeneration, is thought to be a major cause of low back pain, however the regulation of this process is poorly understood. Here, we investigated the expression and regulation of a subclass of axonal guidance molecules known as the class 3 semaphorins, and their receptors; plexins and neuropilins within human NP tissue and their regulation by pro-inflammatory cytokines. Importantly this determined whether semaphorin expression was associated with the presence of nerves and blood vessels in tissues from human intervertebral discs. The study demonstrated that semaphorin3A, 3C, 3D, 3E and 3F and their receptors were expressed by native NP cells and further demonstrated their expression was regulated by IL-1β but to a lesser extent by IL-6 and TNFα. This is the first study to identify sema3C, sema3D and their receptors within the nucleus pulposus of intervertebral discs. Immunopositivity shows significant increases in semaphorin3C, 3D and their receptor neuropilin-2 in degenerate samples which were shown to contain nerves and blood vessels, compared to non-degenerate samples without nerves and blood vessels. Therefore data presented here suggests that semaphorin3C may have a role in promoting innervation and vascularisation during degeneration, which may go on to cause low back pain.

Annular puncture with tumor necrosis factor-alpha injection enhances painful behavior with disc degeneration in vivo

BACKGROUND CONTEXT

Painfulintervertebral disc degeneration is extremely common and costly. Effective treatments are lacking because the nature of discogenic pain is complex with limited capacity to distinguish painful conditions from age-related changes in the spine. Hypothesized sources of discogenic pain include chronic inflammation, neurovascular ingrowth, and structural disruption.

PURPOSE

This study aimed to investigate inflammation, pro-neurovascular growth factors, and structural disruption as sources of painful disc degeneration

STUDY DESIGN/SETTING

This study used an in vivo study to address these hypothesized mechanisms with anterior intradiscal injections of tumor necrosis factor-alpha (TNFα), pro-neurovascular growth factors: nerve growth factor and vascular endothelial growth factor (NGF and VEGF), and saline with additional sham surgery and naïve controls. Depth of annular puncture was also evaluated for its effects on structural and painful degeneration.

METHODS

Rat lumbar discs were punctured (shallow or deeper puncture) and intradiscally injected with saline, TNFα, or NGF and VEGF. Structural disc degeneration was assessed using X-ray, magnetic resonance imaging (MRI), and histology. The rat painful condition was evaluated using Von Frey hyperalgesia measurements, and substance P immunostaining in dorsal root ganglion (DRG) was performed to determine the source of pain.

RESULTS

Saline injection increased painful responses with degenerative changes in disc height, MRI intensity, and morphologies of disc structure and cell. TNFα and NGF/VEGF accelerated painful behavior, and TNFα-injected animals had increased substance P in DRGs. Deeper punctures led to more severe disc degeneration. Multiple regression analysis showed that the painful behavior was correlated with disc height loss.

CONCLUSIONS

We concluded that rate and severity of structural disc degeneration was associated with the amount of annular disruption and puncture depth. The painful behavior was associated with disc height loss and discal inflammatory state, whereas pro-inflammatory cytokines might play a more important role in the level of pain, which might have resulted from enhanced DRG sensitization. These in vivo painful disc degeneration models with different severities of structural changes may be useful for investigating discogenic pain mechanisms and for screening therapies, although interpretations must note the differences between all surgically induced animal models and the human condition.

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.

Fibrin-genipin annulus fibrosus sealant as a delivery system for anti-TNFα drug

BACKGROUND CONTEXT

Intervertebral discs (IVDs) are attractive targets for local drug delivery because they are avascular structures with limited transport. Painful IVDs are in a chronic inflammatory state. Although anti-inflammatories show poor performance in clinical trials, their efficacy treating IVD cells suggests that sustained, local drug delivery directly to painful IVDs may be beneficial.

PURPOSE

The purpose of this study was to determine if genipin cross-linked fibrin (FibGen) with collagen Type I hollow spheres (CHS) can serve as a drug-delivery carrier for infliximab, the anti-tumor necrosis factor α (TNFα) drug. Infliximab was chosen as a model drug because of the known role of TNFα in increasing downstream production of several pro-inflammatory cytokines and pain mediators. Genipin cross-linked fibrin was used as drug carrier because it is adhesive, injectable, and slowly degrading hydrogel with the potential to seal annulus fibrosus (AF) defects. CHS allow simple and nondamaging drug loading and could act as a drug reservoir to improve sustained delivery.

STUDY DESIGN/SETTING

This is a study of biomaterials and human AF cell culture to determine drug release kinetics and efficacy.

METHODS

Infliximab was delivered at low and high concentrations using FibGen with and without CHS. Gels were analyzed for structure, drug release kinetics, and efficacy treating human AF cells after release.

RESULTS

Fibrin showed rapid infliximab drug release but degraded quickly. CHS alone showed a sustained release profile, but the small spheres may not remain in a degenerated IVD with fissures. Genipin cross-linked fibrin showed steady and low levels of infliximab release that was increased when loaded with higher drug concentrations. Infliximab was bound in CHS when delivered within FibGen and was only released after enzymatic degradation. The infliximab released over 20 days retained its bioactivity as confirmed by the sustained reduction of interleukin (IL)-1β, IL-6, IL-8, and TNFα concentrations produced by AF cells.

CONCLUSIONS

Direct mixing of infliximab into FibGen was the simplest drug-loading protocol capable of sustained release. Results show feasibility of using drug-loaded FibGen for delivery of infliximab and, in the context with the literature, show potential to seal AF defects and partially restore IVD biomechanics. Future investigations are required to determine if drug-loaded FibGen can effectively deliver drugs, seal AF defects, and promote IVD repair or prevent further IVD degeneration in vivo.

Effects of proinflammatory cytokines on axonal outgrowth from adult rat lumbar dorsal root ganglia using a novel three-dimensional culture system

BACKGROUND CONTEXT

Degeneration of the intervertebral disc is often associated with low back pain and increased infiltration of nerve fibers originating from dorsal root ganglia (DRG). The degenerated disc is also characterized by the presence of proinflammatory cytokines, which may influence axonal outgrowth. Toward an improved understanding of the growth of DRG neurons into compliant extracellular matrices, we developed a novel experimental system to measure axonal outgrowth of adult rat lumbar DRG neurons within three-dimensional (3D) collagen hydrogels and used this system to examine the effects of interleukin 1β (IL-1β) and tumor necrosis factor (TNF)-α treatment.

PURPOSE

The aim was to investigate the effects of proinflammatory cytokines on 3D neuronal growth into collagen matrices.

STUDY DESIGN

This was an in vitro study of neurite outgrowth from adult rat lumbar DRG into collagen gels in response to IL-1β and TNF-α.

METHODS

Lumbar DRG were obtained from adult Sprague Dawley rats, bisected to expose cell bodies and placed onto collagen gel constructs prepared in 24-well Transwell inserts. Dorsal root ganglia were then treated with nerve growth factor (NGF)-free Neurobasal media (negative control) or NGF-supplemented media containing 0, 1, and 10 ng/mL of IL-1β and TNF-α. After 7 days, collagen gel-DRG constructs were immunostained for phosphorylated neurofilament, an axonal marker. Simple Neurite Tracer (Fiji/ImageJ) was used to quantify 3D axonal outgrowth from confocal image stacks. Data were analyzed using one-way analysis of variance, with Tukey HSD post hoc correction at a level of p<.05.

RESULTS

Immunostaining showed robust axonal outgrowth into collagen gels from all NGF-treated DRG. The negative control demonstrated very few and short neurites. Tumor necrosis factor-α (1 and 10 ng/mL) significantly inhibited axonal outgrowth compared with NGF-only media (p<.026 and p<.02, respectively). After IL-1β treatment, average axon length was 10% lower at 1 ng/mL and 7.5% higher at 10 ng/mL, but these differences were not statistically significant. Among cytokine treatments, however, average axon length in the IL-1β (10 ng/mL) group was significantly higher than that in the other groups (p<.05).

CONCLUSIONS

A novel 3D collagen gel culture system was used to investigate factors modulating neuronal ingrowth. Our results showed that NGF was necessary to promote neurite growth into collagen gels. In the presence of proinflammatory cytokines, high concentrations of IL-1β induced significantly higher axonal outgrowth than TNF-α and low levels of IL-1β.

Expression of matrix factors in the process of neovascularization of intervertebral disc

<sec><title>OBJECTIVE:</title><p> To investigate the effects of proteins products of endothelial cells (ECs) on the annulus fibrosus (AF) cell metabolism in an in vitro culture.</p></sec><sec><title>METHODS:</title><p>Human AF cells were expanded in monolayer cultures and treated with proteins from the medium of cell line HMEC-1 (Human Microvascular Endothelial Cells) (125µg/ml). After 72h of treatment RNA was isolated from AF cells for analysis of gene expression and the culture medium was collected for protein expression analysis.</p></sec><sec><title>RESULTS:</title><p> The qRT-PCR analysis demonstrated increased gene expression of matrix metalloproteinases (MMPs) in AF cells treated with protein products of endothelial cells compared with cells from control group of AF cells: MMP-1 243.10 times (p<0.05), MMP-2 1.37 time (p<0.05), MMP-3 39.83 times (p<0.05) and MMP-13 5.70 times (p<0.05). In contrast, tissue inhibitors of metalloproteinases (TIMPs) were suppressed; TIMP-2 (0.55 time) (p<0.05) and TIMP-3 (0.60 time) (p<0.05) in the exposed groups. The expression of aggrecan gene (0.83 time) (p<0.05), an important extracellular matrix component, was also reduced. MMP-1 and MMP-3 detection was performed, confirming the results of PCR by Western Blot technique.</p></sec><sec><title>CONCLUSIONS:</title><p> In this study, we observed that the proteins produced by ECs induced the MMPs expression and suppressed the TIMPs as well as the aggrecan in primary cells of the human intervertebral disc, targeting the development of potential treatments for intervertebral disc degeneration and associated discogenic pain.</p></sec>

Assessment of functional and behavioral changes sensitive to painful disc degeneration

The development of an in vivo rodent discogenic pain model can provide insight into mechanisms for painful disc degeneration. Painful disc degeneration in rodents can be inferred by examining responses to external stimuli, observing pain-related behaviors, and measuring functional performance. This study compared the sensitivity of multiple pain and functional assessment methods to disc disruption for identifying the parameters sensitive to painful disc degeneration in rats. Disc degeneration was induced in rats by annular injury with saline injection. The severity of disc degeneration, pain sensitivity, and functional performance were compared to sham and naïve control rats. Saline injection induced disc degeneration with decreased disc height and MRI signal intensity as well as more fibrous nucleus pulposus, disorganized annular lamellae and decreased proteoglycan. Rats also demonstrated increased painful behaviors including decreased hindpaw mechanical and thermal sensitivities, increased grooming, and altered gait patterns with hindpaw mechanical hyperalgesia and duration of grooming tests being most sensitive. This is the first study to compare sensitivities of different pain assessment methods in an in vivo rat model of disc degeneration. Hindpaw mechanical sensitivity and duration of grooming were the most sensitive parameters to surgically induced degenerative changes and overall results were suggestive of disc degeneration associated pain.

Intact glycosaminoglycans from intervertebral disc-derived notochordal cell-conditioned media inhibit neurite growth while maintaining neuronal cell viability

BACKGROUND CONTEXT

Painful human intervertebral discs (IVDs) exhibit nerve growth deep into the IVD. Current treatments for discogenic back pain do not address the underlying mechanisms propagating pain and are often highly invasive or only offer temporary symptom relief. The notochord produces factors during development that pattern the spine and inhibit the growth of dorsal root ganglion (DRG) axons into the IVD. We hypothesize that notochordal cell (NC)-conditioned medium (NCCM) includes soluble factors capable of inhibiting neurite growth and may represent a future therapeutic target.

PURPOSE

To test if NCCM can inhibit neurite growth and determine if NC-derived glycosaminoglycans (GAGs) are necessary candidates for this inhibition.

STUDY DESIGN

Human neuroblastoma (SH-SY5Y) cells and rat DRG cells were treated with NCCM in two-dimensional culture in vitro, and digestion and mechanistic studies determined if specific GAGs were responsible for inhibitory effects.

METHODS

Notochordal cell-conditioned medium was generated from porcine nucleus pulposus tissue that was cultured in Dulbecco's modified eagle's medium for 4 days. A dose study was performed using SH-SY5Y cells that were seeded in basal medium for 24 hours and neurite outgrowth and cell viability were assessed after treatment with basal media or NCCM (10% and 100%) for 48 hours. Glycosaminoglycans from NCCM were characterized using multiple digestions and liquid chromatography mass spectroscopy (LC-MS). Neurite growth was assessed on both SH-SY5Y and DRG cells after treatment with NCCM with and without GAG digestion.

RESULTS

Notochordal cell-conditioned medium significantly inhibited the neurite outgrowth from SH-SY5Y cells compared with basal controls without dose or cytotoxic effects; % of neurite expressing cells were 39.0±2.9%, 27.3±3.6%, and 30.2±2.7% and mean neurite length was 60.3±3.5, 50.8±2.4, 53.2±3.7 μm for basal, 10% NCCM, and 100% NCCM, respectively. Digestions and LC-MS determined that chondroitin-6-sulfate was the major GAG chain in NCCM. Neurite growth from SH-SY5Y and DRG cells was not inhibited when cells were treated with NCCM with digested chondroitin sulfate (CS).

CONCLUSIONS

Soluble factors derived from NCCM were capable of inhibiting neurite outgrowth in multiple neural cell types without any negative effects on cell viability. Cleavage of GAGs via digestion was necessary to reverse the neurite inhibition capacity of NCCM. We conclude that intact GAGs such as CS secreted from NCs are potential candidates that could be useful to reduce neurite growth in painful IVDs.

Three dimensional mesoscale analysis of translamellar cross-bridge morphologies in the annulus fibrosus using optical coherence tomography

The defining characteristic of the annulus fibrosus (AF) of the intervertebral disc (IVD) has long been the lamellar structures that consist of highly ordered collagen fibers arranged in alternating oblique angles from one layer to the next. However, a series of recent histologic studies have demonstrated that AF lamellae contain elastin- and type VI collagen-rich secondary "cross-bridge" structures across lamellae. In this study, we use optical coherence tomography (OCT) to elucidate the three-dimensional (3-D) morphologies of these translamellar cross-bridges in AF tissues. Mesoscale volumetric images by OCT revealed a 3-D network of heterogeneously distributed cross-bridges. The results of this study confirm the translamellar cross-bridge is identifiable as a distinguishable structure, which lies in the interbundle space of adjacent lamellae and crisscrosses multiple lamellae in the radial direction. In contrast to previously proposed models extrapolated from 2-D sections, results from this current study show that translamellar cross-bridges exist as a complex, interconnected network. We also found much greater variation in lengths of cross-bridges within the interbundle space of lamellae (0.8-1.4 mm from the current study versus 0.3-0.6 mm from 2-D sections). OCT-based 3-D morphology of translamellar cross-bridge provides novel insight into the AF structure.

Form and function of the intervertebral disc in health and disease: a morphological and stain comparison study

Multiple histologic measurements are commonly used to assess degenerative changes in intervertebral disc (IVD) structure; however, there is no consensus on which stains offer the clearest visualization of specific areas within the IVD. The objective of this study was to compare multiple tinctorial stains, evaluate their ability to highlight structural features within the IVD, and investigate how they influence the capacity to implement a degeneration scoring system. Lumbar IVDs from seven human autopsy specimens were stained using six commonly used stains (Hematoxylin/Eosin, Toluidine Blue, Safranin-O/Fast Green, Extended FAST, modified Gomori's Trichrome, and Picrosirius Red Alcian Blue). All IVDs were evaluated by three separate graders to independently determine which stains (i) were most effective at discerning different structural features within different regions of the IVDs and (ii) allowed for the most reproducible assessment of degeneration grade, as assessed via the Rutges histological scoring system (Rutges et al. A validated new histological classification for intervertebral disc degeneration. Osteoarthritis Cartilage, 21, 2039-47). Although Trichrome, XFAST and PR/AB stains were all effective at highlighting different regions of whole IVDs, we recommend the use of PR/AB because it had the highest degree of rater agreement on assigned degeneration grade, allowed greater resolution of degeneration grade, has an inferential relationship between color and composition, and allowed clear differentiation of the different regions and structural disruptions within the IVD. The use of a standard set of stains together with a histological grading scheme can aid in the characterization of structural changes in different regions of the IVD and may simplify comparisons across the field. This collection of human IVD histological images highlights how IVD degeneration is not a single disease but a composite of multiple processes such as aging, injury, repair, and disease, each of which are unique to the individual.

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.

Expression and regulation of neurotrophic and angiogenic factors during human intervertebral disc degeneration

Introduction

The degenerate intervertebral disc (IVD) becomes innervated by sensory nerve fibres, and vascularised by blood vessels. This study aimed to identify neurotrophins, neuropeptides and angiogenic factors within native IVD tissue and to further investigate whether pro-inflammatory cytokines are involved in the regulation of expression levels within nucleus pulposus (NP) cells, nerve and endothelial cells.

Methods

Quantitative real-time PCR (qRT-PCR) was performed on 53 human IVDs from 52 individuals to investigate native gene expression of neurotrophic factors and their receptors, neuropeptides and angiogenic factors. The regulation of these factors by cytokines was investigated in NP cells in alginate culture, and nerve and endothelial cells in monolayer using RT-PCR and substance P (SP) protein expression in interleukin-1 (IL-1β) stimulated NP cells.

Results

Initial investigation on uncultured NP cells identified expression of all neurotrophins by native NP cells, whilst the nerve growth factor (NGF) receptor was only identified in severely degenerate and infiltrated discs, and brain derived neurotrophic factor (BDNF) receptor expressed by more degenerate discs. BDNF expression was significantly increased in infiltrated and degenerate samples. SP and vascular endothelial growth factor (VEGF) were higher in infiltrated samples. In vitro stimulation by IL-1β induced NGF in NP cells. Neurotropin-3 was induced by tumour necrosis factor alpha in human dermal microvascular endothelial cells (HDMECs). SP gene and protein expression was increased in NP cells by IL-1β. Calcitonin gene related peptide was increased in SH-SY5Y cells upon cytokine stimulation. VEGF was induced by IL-1β and interleukin-6 in NP cells, whilst pleiotrophin was decreased by IL-1β. VEGF and pleiotrophin were expressed by SH-SY5Y cells, and VEGF by HDMECs, but were not modulated by cytokines.

Conclusions

The release of cytokines, in particular IL-1β during IVD degeneration, induced significant increases in NGF and VEGF which could promote neuronal and vascular ingrowth. SP which is released into the matrix could potentially up regulate the production of matrix degrading enzymes and also sensitise nerves, resulting in nociceptive transmission and chronic low back pain. This suggests that IL-1β is a key regulatory cytokine, involved in the up regulation of factors involved in innervation and vascularisation of tissues.

ISSLS Prize winner: Mechanical influences in progressive intervertebral disc degeneration

STUDY DESIGN

Mechanical study on cadaver motion segments.

OBJECTIVE

To determine whether high gradients of compressive stress within the intervertebral disc are associated with progressive disc degeneration.

SUMMARY OF BACKGROUND DATA

Mechanical loading can initiate disc degeneration but may be unimportant in disease progression, because degenerative changes cause the disc to be increasingly "stress-shielded" by the neural arch. However, the most typical feature of advanced disc degeneration (delamination and collapse of the annulus) may not depend on absolute values of compressive stress but on gradients of compressive stress that act to shear annulus lamellae.

METHODS

A total of 191 motion segments (T7-T8 to L5-S1) were dissected from 42 cadavers aged 19 to 92 years. Each was subjected to approximately 1 kN compression, while intradiscal stresses were measured by pulling a pressure transducer along the disc's midsagittal diameter. "Stress gradients" in the annulus were quantified as the average rate of increase in compressive stress (MPa/mm) between the nucleus and the region of maximum stress in the anterior or posterior annulus. Measurements were repeated before and after creep loading and in simulated flexed and erect postures. Disc degeneration was assessed macroscopically on a scale of 1 to 4.

RESULTS

As grade of disc degeneration increased from 2 to 4, nucleus pressure decreased by an average 68%, and maximum compressive stress in the annulus decreased by 48% to 64%, depending on location and posture. In contrast, stress gradients in the annulus increased by an average 75% in the anterior annulus (in flexed posture) and by 108% in the posterior annulus (in erect posture). Spearman rank correlation showed that these increases were statistically significant.

CONCLUSION

Despite stress-shielding by the neural arch, gradients of compressive stress increase with increasing grade of disc degeneration. Stress gradients act to shear adjacent lamellae and can explain progressive annulus delamination and collapse.

LEVEL OF EVIDENCE

N/A.

Why do some intervertebral discs degenerate, when others (in the same spine) do not?

This review suggests why some discs degenerate rather than age normally. Intervertebral discs are avascular pads of fibrocartilage that allow movement between vertebral bodies. Human discs have a low cell density and a limited ability to adapt to mechanical demands. With increasing age, the matrix becomes yellowed, fibrous, and brittle, but if disc structure remains intact, there is little impairment in function, and minimal ingrowth of blood vessels or nerves. Approximately half of old lumbar discs degenerate in the sense of becoming physically disrupted. The posterior annulus and lower lumbar discs are most affected, presumably because they are most heavily loaded. Age and genetic inheritance can weaken discs to such an extent that they are physically disrupted during everyday activities. Damage to the endplate or annulus typically decompresses the nucleus, concentrates stress within the annulus, and allows ingrowth of nerves and blood vessels. Matrix disruption progresses by mechanical and biological means. The site of initial damage leads to two disc degeneration "phenotypes": endplate-driven degeneration is common in the upper lumbar and thoracic spine, and annulus-driven degeneration is common at L4-S1. Discogenic back pain can be initiated by tissue disruption, and amplified by inflammation and infection. Healing is possible in the outer annulus only, where cell density is highest. We conclude that some discs degenerate because they are disrupted by excessive mechanical loading. This can occur without trauma if tissues are weakened by age and genetic inheritance. Moderate mechanical loading, in contrast, strengthens all spinal tissues, including discs.

Innervation of pathologies in the lumbar vertebral end plate and intervertebral disc

BACKGROUND CONTEXT

Magnetic resonance imaging (MRI) has limited diagnostic value for chronic low back pain because of the unclear relationship between any anatomic abnormalities on MRI and pain reported by the patient. Assessing the innervation of end plate and disc pathologies-and determining the relationship between these pathologies and any abnormalities seen on MRI-could clarify the sources of back pain and help identify abnormalities with enhanced diagnostic value.

PURPOSE

To quantify innervation in the vertebral end plate and intervertebral disc and to relate variation in innervation to the presence of pathologic features observed by histology and conventional MRI.

STUDY DESIGN/SETTING

A cross-sectional histology and imaging study of vertebral end plates and intervertebral discs harvested from human cadaver spines.

METHODS

We collected 92 end plates and 46 intervertebral discs from seven cadaver spines (ages 51-67 years). Before dissection, the spines were scanned with MRI to grade for Modic changes and high-intensity zones (HIZ). Standard immunohistochemical techniques were used to localize the general nerve marker protein gene product 9.5. We quantified innervation in the following pathologies: fibrovascular end-plate marrow, fatty end-plate marrow, end-plate defects, and annular tears.

RESULTS

Nerves were present in the majority of end plates with fibrovascular marrow, fatty marrow, and defects. Nerve density was significantly higher in fibrovascular end-plate marrow than in normal end-plate marrow (p<.001). Of the end plates with fibrovascular and fatty marrow, less than 40% were Modic on MRI. Innervated marrow pathologies collocated with more than 75% of the end plate defects; hence, innervation was significantly higher in end plate defects than in normal end plates (p<.0001). In the disc, nerves were observed in only 35% of the annular tears; in particular, innervation in radial tears tended to be higher than in normal discs (p=.07). Of the discs with radial tears, less than 13% had HIZ on T2 MRI. Innervation was significantly less in radial tears than in fibrovascular end-plate marrow (p=.05) and end-plate defects (p=.02).

CONCLUSIONS

These findings indicate that vertebral end-plate pathologies are more innervated than intervertebral disc pathologies and that many innervated end-plate pathologies are not detectable on MRI. Taken together, these findings suggest that improved visualization of end-plate pathologies could enhance the diagnostic value of MRI for chronic low back pain.

Do intervertebral discs degenerate before they herniate, or after?

The belief that an intervertebral disc must degenerate before it can herniate has clinical and medicolegal significance, but lacks scientific validity. We hypothesised that tissue changes in herniated discs differ from those in discs that degenerate without herniation. Tissues were obtained at surgery from 21 herniated discs and 11 non-herniated discs of similar degeneration as assessed by the Pfirrmann grade. Thin sections were graded histologically, and certain features were quantified using immunofluorescence combined with confocal microscopy and image analysis. Herniated and degenerated tissues were compared separately for each tissue type: nucleus, inner annulus and outer annulus.

Herniated tissues showed significantly greater proteoglycan loss (outer annulus), neovascularisation (annulus), innervation (annulus), cellularity/inflammation (annulus) and expression of matrix-degrading enzymes (inner annulus) than degenerated discs. No significant differences were seen in the nucleus tissue from herniated and degenerated discs. Degenerative changes start in the nucleus, so it seems unlikely that advanced degeneration caused herniation in 21 of these 32 discs. On the contrary, specific changes in the annulus can be interpreted as the consequences of herniation, when disruption allows local swelling, proteoglycan loss, and the ingrowth of blood vessels, nerves and inflammatory cells.

In conclusion, it should not be assumed that degenerative changes always precede disc herniation.

Cite this article: Bone Joint J 2013;95-B:1127–33.

Inflammatory mediators in intervertebral disk degeneration and discogenic pain

Although degeneration of the intervertebral disk has historically been described as a misbalance between anabolic and catabolic factors, the role of inflammatory mediators has long been neglected. However, past research clearly indicates that inflammatory mediators such as interleukin (IL)-1β, IL-6, IL-8 and tumor necrosis factor-α are expressed at higher levels in "diseased" intervertebral disks. Both disk cells as well as invading macrophages can be the source of the detected cytokines. Importantly, occurrence of inflammatory mediators in the disk can worsen the progress of degeneration by inducing the expression of matrix degrading enzymes as well as by inhibiting extracellular matrix synthesis. In addition, inflammatory mediators play a crucial role in pain development during intervertebral disk herniation (i.e., sciatica) and disk degeneration (i.e., discogenic pain). This review provides information on the most relevant inflammatory mediators during different types of disk diseases and explains how these factors can induce disk degeneration and the development of discogenic and sciatic/radiculopathic pain.

Intervertebral disc degeneration: evidence for two distinct phenotypes

We review the evidence that there are two types of disc degeneration. 'Endplate-driven' disc degeneration involves endplate defects and inwards collapse of the annulus, has a high heritability, mostly affects discs in the upper lumbar and thoracic spine, often starts to develop before age 30 years, usually leads to moderate back pain, and is associated with compressive injuries such as a fall on the buttocks. 'Annulus-driven' disc degeneration involves a radial fissure and/or a disc prolapse, has a low heritability, mostly affects discs in the lower lumbar spine, develops progressively after age 30 years, usually leads to severe back pain and sciatica, and is associated with repetitive bending and lifting. The structural defects which initiate the two processes both act to decompress the disc nucleus, making it less likely that the other defect could occur subsequently, and in this sense the two disc degeneration phenotypes can be viewed as distinct.