Nitric oxide mediates the change of proteoglycan synthesis in the human lumbar intervertebral disc in response to hydrostatic pressure

Mechanical Factors Regulate Annulus Fibrosus (AF) Injury Repair and Remodeling: A Review

Low back pain is a common chronic disease that can severely affect the patient's work and daily life. The breakdown of spinal mechanical homeostasis caused by intervertebral disc (IVD) degeneration is a leading cause of low back pain. Annulus fibrosus (AF), as the outer layer structure of the IVD, is often the first affected part. AF injury caused by consistent stress overload will further accelerate IVD degeneration. Therefore, regulating AF injury repair and remodeling should be the primary goal of the IVD repair strategy. Mechanical stimulation has been shown to promote AF regeneration and repair, but most studies only focus on the effect of single stress on AF, and lack realistic models and methods that can mimic the actual mechanical environment of AF. In this article, we review the effects of different types of stress stimulation on AF injury repair and remodeling, suggest possible beneficial load combinations, and explore the underlying molecular mechanisms. It will provide the theoretical basis for designing better tissue engineering therapy using mechanical factors to regulate AF injury repair and remodeling in the future.

Contribution of immune cells to intervertebral disc degeneration and the potential of immunotherapy

Substantial evidence supports that chronic low back pain is associated with intervertebral disc degeneration (IDD), which is accompanied by decreased cell activity and matrix degradation. The role of immune cells, especially macrophages, in a variety of diseases has been extensively studied; therefore, their role in IDD has naturally attracted widespread scholarly interest. The IVD is considered to be an immunologically-privileged site given the presence of physical and biological barriers that include an avascular microenvironment, a high proteoglycan concentration, high physical pressure, the presence of apoptosis inducers such as Fas ligand, and the presence of notochordal cells. However, during IDD, immune cells with distinct characteristics appear in the IVD. Some of these immune cells release factors that promote the inflammatory response and angiogenesis in the disc and are, therefore, important drivers of IDD. Although some studies have elucidated the role of immune cells, no specific strategies related to systemic immunotherapy have been proposed. Herein, we summarize current knowledge of the presence and role of immune cells in IDD and consider that immunotherapy targeting immune cells may be a novel strategy for alleviating IDD symptoms.

Role of the mechanosensitive piezo1 channel in intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a multifactorial skeletal disease involving mechanical, genetic, systemic, and biological factors, and it is characterized by apoptosis of the nucleus pulposus cells and breakdown of the extracellular matrix (ECM), which will impair the structure and function of the intervertebral disc (IVD), and cause low back pain. Recently, the piezo1 is recognized as a critical mechanically activated ion channel of IDD. Numerous studies have reported that the piezo1 ion channel was aberrantly activated in the degenerated disc tissues and deeply participated in the pathogenesis of IDD. Inactivating or interfering with the piezo1 channel could effectively prevent the progression of IDD under the experimental conditions. It may be a promising target for the prevention and treatment of the disabling disease. Therefore, we have to make a comprehensive investigation and understanding of the mechanisms and functions of the piezo1 in the biomechanics of the spine. This study mainly elucidates the role of the piezo1 channel in IDD, which may facilitate the development of therapeutic targets for this disease.

Immuno-Modulatory Effects of Intervertebral Disc Cells

Low back pain is a highly prevalent, chronic, and costly medical condition predominantly triggered by intervertebral disc degeneration (IDD). IDD is often caused by structural and biochemical changes in intervertebral discs (IVD) that prompt a pathologic shift from an anabolic to catabolic state, affecting extracellular matrix (ECM) production, enzyme generation, cytokine and chemokine production, neurotrophic and angiogenic factor production. The IVD is an immune-privileged organ. However, during degeneration immune cells and inflammatory factors can infiltrate through defects in the cartilage endplate and annulus fibrosus fissures, further accelerating the catabolic environment. Remarkably, though, catabolic ECM disruption also occurs in the absence of immune cell infiltration, largely due to native disc cell production of catabolic enzymes and cytokines. An unbalanced metabolism could be induced by many different factors, including a harsh microenvironment, biomechanical cues, genetics, and infection. The complex, multifactorial nature of IDD brings the challenge of identifying key factors which initiate the degenerative cascade, eventually leading to back pain. These factors are often investigated through methods including animal models, 3D cell culture, bioreactors, and computational models. However, the crosstalk between the IVD, immune system, and shifted metabolism is frequently misconstrued, often with the assumption that the presence of cytokines and chemokines is synonymous to inflammation or an immune response, which is not true for the intact disc. Therefore, this review will tackle immunomodulatory and IVD cell roles in IDD, clarifying the differences between cellular involvements and implications for therapeutic development and assessing models used to explore inflammatory or catabolic IVD environments.

Sa12b-Modified Functional Self-Assembling Peptide Hydrogel Enhances the Biological Activity of Nucleus Pulposus Mesenchymal Stem Cells by Inhibiting Acid-Sensing Ion Channels

Various hydrogels have been studied for nucleus pulposus regeneration. However, they failed to overcome the changes in the acidic environment during intervertebral disc degeneration. Therefore, a new functionalized peptide RAD/SA1 was designed by conjugating Sa12b, an inhibitor of acid-sensing ion channels, onto the C-terminus of RADA16-I. Then, the material characteristics and biocompatibility of RAD/SA1, and the bioactivities and mechanisms of degenerated human nucleus pulposus mesenchymal stem cells (hNPMSCs) were evaluated. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) confirmed that RAD/SA1 self-assembling into three-dimensional (3D) nanofiber hydrogel scaffolds under acidic conditions. Analysis of the hNPMSCs cultured in the 3D scaffolds revealed that both RADA16-I and RAD/SA1 exhibited reliable attachment and extremely low cytotoxicity, which were verified by SEM and cytotoxicity assays, respectively. The results also showed that RAD/SA1 increased the proliferation of hNPMSCs compared to that in culture plates and pure RADA16-I. Quantitative reverse transcription polymerase chain reaction, enzyme-linked immunosorbent assay, and western blotting demonstrated that the expression of collagen I was downregulated, while collagen II, aggrecan, and SOX-9 were upregulated. Furthermore, Ca²⁺ concentration measurement and western blotting showed that RAD/SA1 inhibited the expression of p-ERK through Ca²⁺-dependent p-ERK signaling pathways. Therefore, the functional self-assembling peptide nanofiber hydrogel designed with the short motif of Sa12b could be used as an excellent scaffold for nucleus pulposus tissue engineering. Moreover, RAD/SA1 exhibits great potential applications in the regeneration of mildly degenerated nucleus pulposus.

Single Impact Injury of Vertebral Endplates Without Structural Disruption, Initiates Disc Degeneration Through Piezo1 Mediated Inflammation and Metabolism Dysfunction

STUDY DESIGN

In vitro experimental study.

OBJECTIVE

To establish an axial impact injury model of intervertebral disc (IVD) and to investigate if a single impact injury without endplate structural disruption could initiate intervertebral disc degeneration (IDD), and what is the roles of Piezo1 in this process.

SUMMARY OF BACKGROUND DATA

Although IDD process has been confirmed to be associated with structural failures such as endplate fractures, whether a single impact injury of the endplates without structural disruption could initiate IDD remains controversial. Previous studies reported that Piezo1 mediated inflammation participated in the progression of IDD induced by mechanical stretch; however, the roles of Piezo1 in IVD impact injury remain unknown.

METHODS

Rats spinal segments were randomly assigned into Control, Low, and High Impact groups, which were subjected to pure axial impact loading using a custom-made apparatus, and cultured for 14 days. The degenerative process was investigated by using histomorphology, real-time Polymerase Chain Reaction(PCR), western-blot, immunofluorescence, and energy metabolism of IVD cell. The effects of Piezo1 were investigated by using siRNA transfection, real-time PCR, western-blot, and immunofluorescence.

RESULTS

The discs in both of the impact groups presented degenerative changes after 14 days, which showed significant up-regulation of Piezo1, NLRP3 inflammasome, the catabolic (MMP-9, MMP-13), and pro-inflammatory gene (IL-1β) expression than that of the control group (P < 0.05), accompanied by significantly increased release of ATP, lactate, nitric oxide (NO), and glucose consumption of IVD cells at first 7 days. Silencing Piezo1 reduced the activation of NLRP3 inflammasome and IL-1β expression in the nucleus pulposus induced by impact injury.

CONCLUSION

It demonstrated that not only fracture of the endplate but also a single impact injury without structural impairment could also initiate IDD, which might be mediated by activation of Piezo1 induced inflammation and abnormal energy metabolism of IVD cells.Level of Evidence: N/A.

In Situ Cell Signalling of the Hippo-YAP/TAZ Pathway in Reaction to Complex Dynamic Loading in an Intervertebral Disc Organ Culture

Recently, a dysregulation of the Hippo-YAP/TAZ pathway has been correlated with intervertebral disc (IVD) degeneration (IDD), as it plays a key role in cell survival, tissue regeneration, and mechanical stress. We aimed to investigate the influence of different mechanical loading regimes, i.e., under compression and torsion, on the induction and progression of IDD and its association with the Hippo-YAP/TAZ pathway. Therefore, bovine IVDs were assigned to one of four different static or complex dynamic loading regimes: (i) static, (ii) "low-stress", (iii) "intermediate-stress", and (iv) "high-stress" regime using a bioreactor. After one week of loading, a significant loss of relative IVD height was observed in the intermediate- and high-stress regimes. Furthermore, the high-stress regime showed a significantly lower cell viability and a significant decrease in glycosaminoglycan content in the tissue. Finally, the mechanosensitive gene CILP was significantly downregulated overall, and the Hippo-pathway gene MST1 was significantly upregulated in the high-stress regime. This study demonstrates that excessive torsion combined with compression leads to key features of IDD. However, the results indicated no clear correlation between the degree of IDD and a subsequent inactivation of the Hippo-YAP/TAZ pathway as a means of regenerating the IVD.

Suramin attenuates intervertebral disc degeneration by inhibiting NF-κB signalling pathway

Aims

Interleukin (IL)-1β is one of the major pathogenic regulators during the pathological development of intervertebral disc degeneration (IDD). However, effective treatment options for IDD are limited. Suramin is used to treat African sleeping sickness. This study aimed to investigate the pharmacological effects of suramin on mitigating IDD and to characterize the underlying mechanism.

Methods

Porcine nucleus pulposus (NP) cells were treated with vehicle, 10 ng/ml IL-1β, 10 μM suramin, or 10 μM suramin plus IL-1β. The expression levels of catabolic and anabolic proteins, proinflammatory cytokines, mitogen-activated protein kinase (MAPK), and nuclear factor (NF)-κB-related signalling molecules were assessed by Western blotting, quantitative real-time polymerase chain reaction (qRT-PCR), and immunofluorescence analysis. Flow cytometry was applied to detect apoptotic cells. The ex vivo effects of suramin were examined using IDD organ culture and differentiation was analyzed by Safranin O-Fast green and Alcian blue staining.

Results

Suramin inhibited IL-1β-induced apoptosis, downregulated matrix metalloproteinase (MMP)-3, MMP-13, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)-4, and ADAMTS-5, and upregulated collagen 2A (Col2a1) and aggrecan in IL-1β-treated NP cells. IL-1β-induced inflammation, assessed by IL-1β, IL-8, and tumour necrosis factor α (TNF-α) upregulation, was alleviated by suramin treatment. Suramin suppressed IL-1β-mediated proteoglycan depletion and the induction of MMP-3, ADAMTS-4, and pro-inflammatory gene expression in ex vivo experiments.

Conclusion

Suramin administration represents a novel and effectively therapeutic approach, which could potentially alleviate IDD by reducing extracellular matrix (ECM) deposition and inhibiting apoptosis and inflammatory responses in the NP cells.

Cite this article: Bone Joint Res 2021;10(8):498–513.

Intervertebral Disk Degeneration: The Microenvironment and Tissue Engineering Strategies

Intervertebral disk degeneration (IVDD) is a leading cause of disability. The degeneration is inevitable, and the mechanisms are complex. Current therapeutic strategies mainly focus on the relief of symptoms, not the intrinsic regeneration of the intervertebral disk (IVD). Tissue engineering is a promising strategy for IVDD due to its ability to restore a healthy microenvironment and promote IVD regeneration. This review briefly summarizes the IVD anatomy and composition and then sets out elements of the microenvironment and the interactions. We rationalized different scaffolds based on tissue engineering strategies used recently. To fulfill the complete restoration of a healthy IVD microenvironment, we propose that various tissue engineering strategies should be combined and customized to create personalized therapeutic strategies for each individual.

NF-κB signalling pathways in nucleus pulposus cell function and intervertebral disc degeneration

Intervertebral disc degeneration (IDD) is a common clinical degenerative disease of the spine. A series of factors, such as inflammation, oxidative stress and mechanical stress, promote degradation of the extracellular matrix (ECM) of the intervertebral discs (IVD), leading to dysfunction and structural destruction of the IVD. Nuclear factor-κB (NF-κB) transcription factor has long been regarded as a pathogenic factor of IDD. Therefore, NF-κB may be an ideal therapeutic target for IDD. As NF-κB is a multifunctional functional transcription factor with roles in a variety of biological processes, a comprehensive understanding of the function and regulatory mechanism of NF-κB in IDD pathology will be useful for the development of targeted therapeutic strategies for IDD, which can prevent the progression of IDD and reduce potential risks. This review discusses the role of the NF-κB signalling pathway in the nucleus pulposus (NP) in the process of IDD to understand pathological NP degeneration further and provide potential therapeutic targets that may interfere with NF-κB signalling for IDD therapy.

Inhibition of toll-like receptor 4 protects against inflammation-induced mechanobiological alterations to intervertebral disc cells

Intervertebral disc (IVD) degeneration is associated with elevated levels of inflammatory cytokines implicated in disease aetiology and matrix degradation. Toll-like receptor-4 (TLR4) has been shown to participate in the inflammatory responses of the nucleus pulposus (NP) and its levels are upregulated in disc degeneration. Activation of TLR4 in NP cells leads to significant, persistent changes in cell biophysical properties, including hydraulic permeability and osmotically active water content, as well as alterations to the actin cytoskeleton. The study hypothesis was that inflammation-induced changes to cellular biomechanical properties and actin cytoskeleton of NP cells could be prevented by inhibiting TLR4 signalling. Isolated NP cells from bovine discs were treated with lipopolysaccharide (LPS), the best studied TLR4 agonist, with or without treatment with the TLR4 inhibitor TAK-242. Cellular volume regulation responses to step osmotic loading were measured and the transient volume-response was captured by time-lapse microscopy. Volume-responses were analysed using mixture theory framework to investigate hydraulic permeability and osmotically active intracellular water content. Hydraulic permeability and cell radius were significantly increased with LPS treatment and these changes were blocked in cells treated with TAK-242. LPS-induced remodelling of cortical actin and IL-6 upregulation were also mitigated by TAK-242 treatment. These findings indicated that TLR4 signalling participated in NP cell biophysical regulation and may be an important target for mitigating altered cell responses observed in IVD inflammation and degeneration.

Prospects for the Personalized Multimodal Therapy Approach to Pain Management via Action on NO and NOS

Chronic pain syndromes are an important medical problem generated by various molecular, genetic, and pathophysiologic mechanisms. Back pain, neuropathic pain, and posttraumatic pain are the most important pathological processes associated with chronic pain in adults. Standard approaches to the treatment of them do not solve the problem of pain chronicity. This is the reason for the search for new personalized strategies for the prevention and treatment of chronic pain. The nitric oxide (NO) system can play one of the key roles in the development of peripheral pain and its chronicity. The purpose of the study is to review publications devoted to changes in the NO system in patients with peripheral chronical pain syndromes. We have carried out a search for the articles published in e-Library, PubMed, Oxford Press, Clinical Case, Springer, Elsevier, and Google Scholar databases. The search was carried out using keywords and their combinations. The role of NO and NO synthases (NOS) isoforms in peripheral pain development and chronicity was demonstrated primarily from animal models to humans. The most studied is the neuronal NOS (nNOS). The role of inducible NOS (iNOS) and endothelial NOS (eNOS) is still under investigation. Associative genetic studies have shown that single nucleotide variants (SNVs) of NOS1, NOS2, and NOS3 genes encoding nNOS, iNOS, and eNOS may be associated with acute and chronic peripheral pain. Prospects for the use of NOS inhibitors to modulate the effect of drugs used to treat peripheral pain syndrome are discussed. Associative genetic studies of SNVs NOS1, NOS2, and NOS3 genes are important for understanding genetic predictors of peripheral pain chronicity and development of new personalized pharmacotherapy strategies.

Bioactive lipids in intervertebral disc degeneration and its therapeutic implications

Intervertebral disc (IVD) degeneration is not uncommon. It is estimated that approximately >60% of individuals above the age of 40 years suffer from IVD degeneration. Shan et al. showed that hyperglycemia can enhance apoptosis of anulus fibrosis cells in a JNK pathway and p38 mitogen-activated protein kinase (MAPK) pathway dependent fashion. Recent studies showed that IVD degeneration could be an inflammatory condition characterized by increased production of matrix metalloproteinases, TNF-α, nitric oxide, IL-6, IL-17, IL-9, and prostaglandin E2, and decreased formation of anti-inflammatory molecules such as lipoxin A4. This imbalance between pro- and anti-inflammatory molecules seem to activate JNK pathway and p38 MAPK pathway to induce apoptosis of anulus fibrosis and nucleus pulposus cells. The activation of production of PGE2 (due to activation of COX-2 pathway) seems to be dependent on p38/c-Fos and JNK/c-Jun activation in an AP-1-dependent manner. These results imply that suppressing pro-inflammatory events in the disc by either augmenting anti-inflammatory events or suppressing production of pro-inflammatory molecules or both may form a logical step in the prevention and management of IVD degeneration.

Mechanical Aspects of Intervertebral Disc Injury and Implications on Biomechanics

STUDY DESIGN

This article comprises a review of the literature.

OBJECTIVE

The purpose of this study was to elucidate the different types of structural failures exhibited in intervertebral discs (IVDs), summarize their potential causes with respect to mechanical loading conditions and the consequences on cell homeostasis and biomechanics.

SUMMARY OF BACKGROUND DATA

Many studies have been performed to gain insight into how discogenic back pain progresses in humans both in vitro and in vivo as well as in animal disc models. However, there is a major need to summarize the common factors which initiate the structural failures observed in IVDs and the typical biomechanical changes. This work could help in developing mechanisms aiming to restore the biochemical and biomechanical balance of IVDs.

METHODS

The different types of structural failures encountered in IVDs were reviewed from published literature. The types of mechanical loading causing these injuries and their physiological and biomechanical consequences were then summarized and linked to ongoing research in this area.

RESULTS

The most prominent structural failures associated with IVDs are annulus tears, disc prolapse, endplate damage, disc narrowing, radial bulging, and osteophyte formation in the vertebrae. IVDs were found to be vulnerable to compression, flexion, axial rotation, and complex loading mechanisms through single impact, cyclical, and continuous loading. However, chronic loadings had a more damaging impact on the spine. Significant consequences include imbalance of metabolic enzymes and growth factors, alteration in stress profiles of IVDs and a decrease in mechanical stiffness resulting in impaired biomechanics of the spine.

CONCLUSION

The mode of loading has an important impact on the severity and nature of failures seen in IVDs and the resulting consequences to biomechanics. However, further research is necessary to better understand to the mechanisms that link injury to degeneration and regeneration of IVD tissues.

LEVEL OF EVIDENCE

3.

The Evaluation of Proteoglycan Levels and the Possible Role of ACAN Gene (c.6423T>C) Variant in Patients with Lumbar Disc Degeneration Disease

BACKGROUND/AIM

The present study aimed to investigate the role of an aggrecan (ACAN) gene variant and proteoglycan levels in the risk of lumbar degenerative disc disease (LDDD).

MATERIALS AND METHODS

A total of 108 patients with LDDD and 103 healthy controls were enrolled. Molecular assessment of the ACAN gene (c.6423T>C) variant was determined by real time-polymerase chain reaction. Proteoglycan levels in serum were measured with enzyme-linked immunosorbent assay.

RESULTS

The frequency of all alleles and genotypes in all study groups were distributed according to the Hardy-Weinberg equilibrium. In addition, no association between the ACAN gene (c.6423T>C) variant and presence of risk factors for LDDD was detected. However, proteoglycan levels were significantly lower in patients with LDDD compared to the control group (p<0.00001).

CONCLUSION

Our findings suggest that proteoglycan has emerged as a potential novel biomarker which might be used for prediction of LDDD risk.

Upregulation of miR-107 expression following hyperbaric oxygen treatment suppresses HMGB1/RAGE signaling in degenerated human nucleus pulposus cells

Background

The expression of both high-mobility group box 1 (HMGB1) and receptor for advanced glycation end-products (RAGE) is upregulated in degenerated discs. HMGB1 is known to function as a coupling factor between hypoxia and inflammation in arthritis, and this inflammatory response is modulated by microRNAs (miRNAs), with miR-107 expression downregulated during hypoxia. In this study, we investigated the regulation of the miR-107/HMGB1/RAGE pathway in degenerated nucleus pulposus cells (NPCs) after hyperbaric oxygen (HBO) treatment.

Methods

NPCs were separated from human degenerated intervertebral disc tissues. The control cells were maintained in 5% CO₂/95% air, and the hyperoxic cells were exposed to 100% O₂ at 2.5 atmospheres absolute. MiRNA expression profiling was performed via microarray and confirmed by real-time PCR, and miRNA target genes were identified using bioinformatics and luciferase reporter assays. The cellular protein and mRNA levels of HMGB1, RAGE, and inducible nitric oxide synthase (iNOS) were assessed, and the phosphorylation of MAPK (p38MAPK, ERK, and JNK) was evaluated. Additionally, cytosolic and nuclear fractions of the IκBα and NF-κB p65 proteins were analyzed, and secreted HMGB1 and metalloprotease (MMP) levels in the conditioned media were quantified.

Results

Using microarray analyses, 96 miRNAs were identified as upregulated and 66 downregulated following HBO treatment. Based on these results, miR-107 was selected for further investigation. Bioinformatics analyses indicated that the 3′ untranslated region of the HMGB1 mRNA contained the “seed-matched-sequence” for hsa-miR-107, which was validated via dual-luciferase reporter assays. MiR-107 was markedly induced by HBO, and simultaneous suppression of HMGB1 was observed in NPCs. Knockdown of miR-107 resulted in upregulation of HMGB1 expression in HBO-treated cells, and HBO treatment downregulated the mRNA and protein levels of HMGB1, RAGE, and iNOS and the secretion of HMGB1. In addition, HBO treatment upregulated the protein levels of cytosolic IκBα and decreased the nuclear translocation of NF-κB in NPCs. Moreover, HBO treatment downregulated the phosphorylation of p38MAPK, ERK, and JNK and significantly decreased the secretion of MMP-3, MMP-9, and MMP-13.

Conclusions

HBO inhibits pathways related to HMGB1/RAGE signaling via upregulation of miR-107 expression in degenerated human NPCs.

Leptin and the intervertebral disc: a biochemical link exists between obesity, intervertebral disc degeneration and low back pain-an in vitro study in a bovine model

PURPOSE

The aim of this study was to identify the effects of leptin upon the intervertebral disc (IVD) and to determine whether these responses are potentiated within an environment of existing degeneration. Obesity is a significant risk factor for low back pain (LBP) and IVD degeneration. Adipokines, such as leptin, are novel cytokines produced primarily by adipose tissue and have been implicated in degradative and inflammatory processes. Obese individuals are known to have higher concentrations of serum leptin, and IVD cells express leptin receptors. We hypothesise that adipokines, such as leptin, mediate a biochemical link between obesity, IVD degeneration and LBP.

METHODS

The bovine intervertebral disc was used as a model system to investigate the biochemical effects of obesity, mediated by leptin, upon the intervertebral disc. Freshly isolated cells, embedded in 3D alginate beads, were subsequently cultured under varying concentrations of leptin, alone or together with the pro-inflammatory cytokines TNF-α, IL-1β or IL-6. Responses in relation to production of nitric oxide, lactate, glycosaminoglycans and expression of anabolic and catabolic genes were analysed.

RESULTS

Leptin influenced the cellular metabolism leading particularly to greater production of proteases and NO. Addition of leptin to an inflammatory environment demonstrated a marked deleterious synergistic effect with greater production of NO, MMPs and potentiation of pro-inflammatory cytokine production.

CONCLUSIONS

Leptin can initiate processes involved in IVD degeneration. This effect is potentiated in an environment of existing degeneration and inflammation. Hence, a biochemical mechanism may underlie the link between obesity, intervertebral disc degeneration and low back pain. These slides can be retrieved under Electronic Supplementary Material.

Propionibacterium acnes Induces Intervertebral Disc Degeneration by Promoting iNOS/NO and COX-2/PGE2 Activation via the ROS-Dependent NF-κB Pathway

Accumulating evidence suggests that Propionibacterium acnes (P. acnes) is a novel pathogenic factor promoting intervertebral disc degeneration (IVDD). However, the underlying mechanisms by which P. acnes induces IVDD have been unclear. In this study, we quantified the severity of IVDD, as well as the expressions of inducible nitric oxide synthase (iNOS)/nitric oxide (NO) and cyclooxygenase (COX-2)/prostaglandin (PGE₂) in human intervertebral discs (IVDs) infected with P. acnes. Compared with P. acnes-negative IVDs, P. acnes-positive IVDs showed increased iNOS/NO and COX-2/PGE₂ activity concomitant with more severe IVDD. In order to detect the potential correlation between iNOS/NO expression, COX-2/PGE₂ expression, and IVDD, we developed a P. acnes-induced IVDD rat model and found that the upregulation of iNOS/NO and COX-2/PGE₂ was essential to the occurrence of P. acnes-induced IVDD. This finding was supported by the fact that the inhibition of iNOS/NO and COX-2/PGE₂ activity ameliorated IVDD significantly, as evidenced by restored aggrecan and collagen II expression both in vivo and in vitro. Mechanistically, we found that P. acnes induced iNOS/NO and COX-2/PGE₂ expressions via a reactive oxygen species- (ROS-) dependent NF-κB cascade. Furthermore, NADPH oxidase participated in P. acnes-induced ROS, iNOS/NO, and COX-2/PGE₂ expressions. Overall, these findings further validated the involvement of P. acnes in the pathology of IVDD and provided evidence that P. acnes-induced iNOS/NO and COX-2/PGE₂ activation via the ROS-dependent NF-κB pathway is likely responsible for the pathology of IVDD.

Strategies for Annulus Fibrosus Regeneration: From Biological Therapies to Tissue Engineering

Intervertebral disc (IVD) is an avascular tissue which contributes to the weight bearing, motion, and flexibility of spine. However, IVD is susceptible to damage and even failure due to injury, pathology, and aging. Annulus fibrosus (AF), the structural and functional integrity of which is critically essential to confine nucleus pulpous (NP) and maintain physiological intradiscal pressure under mechanical loading, plays a critical role in the biomechanical properties of IVD. AF degeneration commonly results in substantial deterioration of IVD. During this process, the biomechanical properties of AF and the balance between anabolism and catabolism in IVD are progressively disrupted, leading to chronic back pain, and even disability of individuals. Therefore, repairing and regenerating AF are effective treatments to degeneration-associated pains. However, they remain highly challenging due to the complexity of natural AF tissue in the aspects of cell phenotype, biochemical composition, microstructure, and mechanical properties. Tissue engineering (TE), by combining biological science and materials engineering, shed lights on AF regeneration. In this article, we review recent advances in the pro-anabolic approaches in the form of cell delivery, bioactive factors delivery, gene therapy, and TE strategies for achieving AF regeneration.

Link protein N-terminal peptide and fullerol promote matrix production and decrease degradation enzymes in rabbit annulus cells

PURPOSE

Intervertebral disc degeneration is a major cause of back pain. Novel therapies for prevention or reversal of disc degeneration are needed. It is desirable for potential therapies to target both inflammation and matrix degeneration.

MATERIALS AND METHODS

The combined regenerative potential of link protein N-terminal peptide (LN) and fullerol on annulus fibrosus (AF) cells was evaluated in a 3D culture model.

RESULTS

Interleukin-1α (IL-1α)-induced AF cell degeneration was counteracted by fullerol, LN, and fullerol + LN, with the latter having the greatest effect on matrix production as evaluated by real-time polymerase chain reaction and glycosaminoglycan assay. IL-1α-induced increases in pro-inflammatory mediators (interleukin-6 and cyclooxygenase-2) and matrix metalloproteinases (MMP-1, -2, -9, and -13) were also counteracted by fullerol and LN.

CONCLUSION

Our data demonstrate that LN and fullerol individually, and in combination, promote matrix production and have anti-inflammatory and anti-catabolic effects on AF cells.

Biomechanics in Annulus Fibrosus Degeneration and Regeneration

Degenerative disc degeneration (DDD) is the major cause of low back pain, which seriously affects the life of patients. Current surgical and conservative treatments only relieve the pain temporarily, yet fail to restore the normal biomechanics and functions of healthy spine. Indeed, high recurrence of disc herniation commonly happens after discectomy. Degenerative changes in biomechanical and structural properties of the intervertebral disc (IVD), including fissures in annulus fibrosus (AF) and volume loss of nucleus pulposus (NP), mainly contribute to DDD development. AF plays a critical role in the biomechanical properties of IVD as it structural integrity is essential to confine NP and maintain physiological intradiscal pressure under loading. Maintaining the homeostasis of AF and NP, and thereby IVD, requires regulation of their biomechanics, which is also involved in the onset and subsequent development of AF degeneration. Therefore, it is essential to understand the biomechanical changes of AF during degeneration, which can also provide valuable insights into the repair and regeneration of AF. In this review, we focus on the biomechanical properties of AF tissue associated with its homeostasis and degeneration, and discuss the biomechanical stimulus required for regeneration of AF. We also provide an overview of recent strategies to target and modulate cell mechanics toward AF regeneration.

The Presence of the Neuronal Nitric Oxide Synthase Isoform in the Intervertebral Disk

Intervertebral disk degeneration is a progressive and debilitating disease with multifactorial causes. Nitric oxide (NO) might contribute to the cell death pathway. We evaluated the presence of the constitutive form of the neuronal NOS (nNOS) in both health and degenerated intervertebral disk through qPCR and immunohistochemistry. We also analyzed the potential role of nNOS modulation in the tail needle puncture model of intervertebral disk degeneration. Male Wistar rats were submitted to percutaneous disk puncture with a 21-gauge needle of coccygeal vertebras. The selective nNOS pharmacological inhibitor N ^(ω)-propyl-L-arginine (NPLA) or a nNOS-target siRNA (siRNAnNOShum_4400) was injected immediately after the intervertebral disk puncture with a 30-gauge needle. Signs of disk degeneration were analyzed by in vivo magnetic resonance imaging and histological score. We found that intact intervertebral disks express low levels of nNOS mRNA. Disk injury caused a 4 fold increase in nNOS mRNA content at 5 h post disk lesion. However, NPLA or nNOS-target siRNA slight mitigate the intervertebral disk degenerative progress. Our data show evidence of the nNOS presence in the intervertebral disk and its upregulation during degeneration. Further studies would disclose the nNOS role and its potential therapeutical value in the intervertebral disk degeneration.

Cyclic tensile stress of human annulus fibrosus cells induces MAPK activation: involvement in proinflammatory gene expression

OBJECTIVE

To study the role of mitogen-activated protein kinases (MAPKs) in human annulus fibrosus (AF) cells subjected to cyclic tensile stress (CTS).

DESIGN

An in vitro system for CTS studies was established using AF cultures on fibronectin-coated silicone dishes. MAPK phosphorylation was studied by western analysis, while gene expression was followed by qRT-PCR. DNA synthesis was assessed by both tritiated thymidine incorporation and flow cytometry, and collagen synthesis using tritiated proline incorporation and the protease-free collagenase method.

RESULTS

All three MAPKs studied, i.e., ERK, SAPK/JNK, and p38 were found to be phosphorylated immediately after CTS application within physiological range. A second wave of phosphorylation appeared at later time points. MAPK activation was elevated at higher CTS magnitudes, but independent of the frequency. CTS did not stimulate DNA synthesis neither extracellular matrix turnover, but it stimulated the proinflammatory genes, COX-2, IL-6, and IL-8. This stimulation was more intense at the highest magnitude (8%) tested and at the median frequency (1 Hz) and time interval (12 h). Blocking of ERK, SAPK/JNK, and p38 MAPK inhibited the CTS-induced stimulation of COX-2 and IL-8, while IL-6 expression was mediated only by SAPK/JNK and p38 MAPK.

CONCLUSIONS

We have described for the first time the activation of MAPKs in human AF cells in response to CTS and showed that it drives an inflammatory reaction. These observations shed light on the mechanisms of intervertebral disc (IVD) cell responses to mechanical stress, contributing to the understanding of disc pathophysiology and possibly to the design of novel therapeutic interventions.

Leukocytes Enhance Inflammatory and Catabolic Degenerative Changes in the Intervertebral Disc After Endplate Fracture In Vitro Without Infiltrating the Disc

STUDY DESIGN

An established rabbit intervertebral disc (IVD)/endplate explant fracture model was extended with physiologic post-traumatic dynamic loading (PTDL) and coculturing of peripheral blood mononuclear cells (PBMCs).

OBJECTIVE

The aim of this study was to quantify the effects of PTDL and of cocultured PBMCs on post-traumatic disc degeneration (DD) and to determine whether PTDL facilitates homing of PBMC to fractured IVD/endplates.

SUMMARY OF BACKGROUND DATA

DD is associated with endplate fracture. In vivo studies suggest a key role of immune cells in the pathogenesis of DD. However, the complexity of in vivo systems impedes the investigation of single factors governing the pathogenesis.

METHODS

Seventy-two IVD/endplate specimens were divided into 4 groups. In group A, endplate fractures were induced with a high-velocity axial load and exposed to PTDL in coculture with PBMCs for 14 days. Group A was compared with 3 control groups, with single-factor removal, in order to assess the relative contribution of PTDL (group B), PBMCs (group C), and endplate fracture (group D) to the biological response of the IVD. Disc gene transcription and serum nitric oxide (NO) serum concentration were measured to investigate differences in anabolism, catabolism, and inflammatory response between the groups. Changes in matrix composition and disc structure were assessed histologically.

RESULTS

PBMCs did not home to fractured IVDs, with or without PTDL. Group A compared with group D showed an enhanced transcription of anabolic, catabolic, and pro-inflammatory genes during the entire experiment, and an increased NO concentration for the first 3 days. Changes typical for DD were also found in histological sections. Group A compared with group C showed significant increases in catabolic and pro-inflammatory gene transcription after at least 7 days. No differences were found between groups A and B.

CONCLUSION

Trauma induces degenerative changes; PTDL neither aggravates nor ameliorates this response. Although PBMCs do not infiltrate the disc, they aggravate the degenerative changes.

LEVEL OF EVIDENCE

N/A.

Mechanics and biology in intervertebral disc degeneration: a vicious circle

Intervertebral disc degeneration is a major cause of low back pain. Despite its long history and large socio-economical impact in western societies, the initiation and progress of disc degeneration is not well understood and a generic disease model is lacking. In literature, mechanics and biology have both been implicated as the predominant inductive cause; here we argue that they are interconnected and amplify each other. This view is supported by the growing awareness that cellular physiology is strongly affected by mechanical loading. We propose a vicious circle of mechanical overloading, catabolic cell response, and degeneration of the water-binding extracellular matrix. Rather than simplifying the disease, the model illustrates the complexity of disc degeneration, because all factors are interrelated. It may however solve some of the controversy in the field, because the vicious circle can be entered at any point, eventually leading to the same pathology. The proposed disease model explains the comparable efficacy of very different animal models of disc degeneration, but also helps to consider the consequences of therapeutic interventions, either at the cellular, material or mechanical level.

Efficacy, Safety, and Predictors of Intradiscal Methylene Blue Injection for Discogenic Low Back Pain: Results of a Multicenter Prospective Clinical Series

STUDY DESIGN

Prospective clinical study of intradiscal methylene blue injection for the treatment of lumbar discogenic pain.

OBJECTIVE

The objective of this study was to collect information about efficacy, safety, and acceptability of the intervention, gain and burden of outcome measures, and sample size assumptions for a potential following randomized controlled trial (RCT). If the pilot study demonstrates that this treatment is potentially effective and safe, and the methods and procedures used in this study are feasible, a RCT follows.

SUMMARY OF BACKGROUND DATA

Low back pain (LBP) is a highly common problem with a lifetime prevalence of more than 70%. A substantial part of chronic LBP is attributable to degenerative changes in the intervertebral disc. A recently published RCT assessing the treatment intradiscal injection of methylene blue for chronic discogenic LBP, showed exceptionally good results.

METHODS

Patients were selected on clinical criteria, magnetic resonance imaging, and a positive provocative discogram. The primary outcome measure was mean pain reduction at 6 months.

RESULTS

Fifteen consecutive patients with chronic lumbar discogenic pain enrolled in a multicenter prospective case series in two interventional pain treatment centers in the Netherlands. Six months after the intervention, 40% of the patients claimed at least 30% pain relief. In patients who responded, physical function improved and medication use diminished. We observed no procedural complications or adverse events. Predictors for success were Pfirrmann grading of 2 or less and higher quality of life mental component scores.

CONCLUSIONS

Our findings of 40% positive respondents, and no complications, give reason to set up a randomized, double-blind, placebo-controlled, trial.

Dose-dependent response of tissue-engineered intervertebral discs to dynamic unconfined compressive loading

Because of the limitations of current surgical methods in the treatment of degenerative disc disease, tissue-engineered intervertebral discs (TE-IVDs) have become an important target. This study investigated the biochemical and mechanical responses of composite TE-IVDs to dynamic unconfined compression. TE-IVDs were manufactured by floating an injection molded alginate nucleus pulposus (NP) in a type I collagen annulus fibrosus (AF) that was allowed to contract for 2 weeks before loading. The discs were mechanically stimulated at a range of strain amplitude (1-10%) for 2 weeks with a duty cycle of 1 h on-1 h off-1 h on before being evaluated for their biochemical and mechanical properties. Mechanical loading increased all properties in a dose-dependent manner. Glycosaminoglycans (GAGs) increased between 2.8 and 2.2 fold in the AF and NP regions, respectively, whereas the hydroxyproline content increased between 1.2 and 1.8 fold. The discs also experienced a 2-fold increase in the equilibrium modulus and a 4.3-fold increase in the instantaneous modulus. Full effects for all properties were seen by 5% strain amplitude. These data suggest that dynamic loading increases the functionality of our TE-IVDs with region-dependent responses using a method that may be scaled up to larger disc models to expedite maturation for implantation.

Adipose-derived stromal cells protect intervertebral disc cells in compression: implications for stem cell regenerative disc therapy

Introduction: Abnormal biomechanics plays a role in intervertebral disc degeneration. Adipose-derived stromal cells (ADSCs) have been implicated in disc integrity; however, their role in the setting of mechanical stimuli upon the disc's nucleus pulposus (NP) remains unknown. As such, the present study aimed to evaluate the influence of ADSCs upon NP cells in compressive load culture.

Methods: Human NP cells were cultured in compressive load at 3.0MPa for 48 hours with or without ADSCs co-culture (the ratio was 50:50). We used flow cytometry, live/dead staining and scanning electron microscopy (SEM) to evaluate cell death, and determined the expression of specific apoptotic pathways by characterizing the expression of activated caspases-3, -8 and -9. We further used real-time (RT-) PCR and immunostaining to determine the expression of the extracellular matrix (ECM), mediators of matrix degradation (e.g. MMPs, TIMPs and ADAMTSs), pro-inflammatory factors and NP cell phenotype markers.

Results: ADSCs inhibited human NP cell apoptosis via suppression of activated caspase-9 and caspase-3. Furthermore, ADSCs protected NP cells from the degradative effects of compressive load by significantly up-regulating the expression of ECM genes (SOX9, COL2A1 and ACAN), tissue inhibitors of metalloproteinases (TIMPs) genes (TIMP-1 and TIMP-2) and cytokeratin 8 (CK8) protein expression. Alternatively, ADSCs showed protective effect by inhibiting compressive load mediated increase of matrix metalloproteinases (MMPs; MMP-3 and MMP-13), disintegrin and metalloproteinase with thrombospondin motifs (ADAMTSs; ADAMTS-1 and 5), and pro-inflammatory factors (IL-1beta, IL-6, TGF-beta1 and TNF-alpha).

Conclusions: Our study is the first in vitro study assessing the impact of ADSCs on NP cells in an un-physiological mechanical stimulation culture environment. Our study noted that ADSCs protect compressive load induced NP cell death and degradation by inhibition of activated caspase-9 and -3 activity; regulating ECM and modulator genes, suppressing pro-inflammatory factors and preserving CK8. Consequently, the protective impact of ADSCs found in this study provides an essential understanding and expands our knowledge as to the utility of ADSCs therapy for intervertebral disc regeneration.

Antioxidative nanofullerol prevents intervertebral disk degeneration

Compelling evidence suggests that reactive oxygen species (ROS) play a pivotal role in disk degeneration. Fullerol nanoparticles prepared in aqueous solution have been demonstrated to have outstanding ability to scavenge ROS. In this report, in vitro and in vivo models were used to study the efficacy of fullerol in preventing disk degeneration. For in vitro experiments, a pro-oxidant H₂O₂ or an inflammatory cytokine interleukin (IL)-1β was employed to induce degenerated phenotypes in human nucleus pulposus cells encapsulated in alginate beads, and fullerol was added in the culture medium. For the animal study, an annulus-puncture model with rabbit was created, and fullerol was injected into disks. It was shown that cytotoxicity and cellular ROS level induced by H₂O₂ were significantly diminished by fullerol. IL-1β-induced nitric oxide generation in culture medium was suppressed by fullerol as well. Gene-profile and biochemical assays showed that fullerol effectively reversed the matrix degradation caused by either H₂O₂ or IL-1β. The animal study delineated that intradiskal injection of fullerol prevented disk degeneration, increasing water and proteoglycan content and inhibiting ectopic bone formation. These results suggest that antioxidative fullerol may have a potential therapeutic application for disk degeneration.

Glutathione protects human nucleus pulposus cells from cell apoptosis and inhibition of matrix synthesis

Abstract Cell death (apoptosis and necrosis) and extracellular matrix destruction induced by oxidative stress have been suggested to be closely involved in the process of disc degeneration. Glutathione, a natural peptide as a powerful antioxidant in human cytoplasm, plays an important role in protecting living cells. This study is to investigate whether glutathione could retard degenerated phenotypes in cultured disc cells. Human nucleus pulposus cells were isolated and cultured in alginate beads and subsequently treated with a pro-oxidant H2O2 alone or a pro-inflammatory cytokine IL-1β alone or either of them together with glutathione. It was shown that H2O2 dose-dependently promoted nucleus pulposus cell apoptosis detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining and decreased mRNA levels of matrix proteins aggrecan and type II collagen determined by quantitative reverse transcription-polymerase chain reaction (RT-PCR). IL-1β could induce production of nitric oxide and decrease of proteoglycan, detected by the Griess reagent and the dimethyl methylene blue, respectively. The deleterious effects of either H2O2 or IL-1β could be efficiently prevented by glutathione. These results indicated that glutathione might be considered as an option for intervention of disc degeneration.

CK8 phosphorylation induced by compressive loads underlies the downregulation of CK8 in human disc degeneration by activating protein kinase C

Cytokeratin 8 (CK8) is a member of the cytokeratins family with multiple functions on the basis of its unique structural hallmark. The aberrant expression of CK8 and its phosphorylation are pertinent with various diseases. We have previously shown that CK8 exists in normal human nucleus pulposus (NP) cells and decreases as the intervertebral disc degenerates. However, the underlying molecular regulatory machinery of CK8 in intervertebral disc degeneration (IDD) has not been clarified. Here, we collected NP samples from patients with idiopathic scoliosis as control and IDD as degenerate groups. We found that CK8 expression decreased in IDD with an increased phosphorylation in degenerate NP cells. Moreover, NP cells were cultured under different compressive load schemes for diverse time duration. We found that compressive loads resulted in phosphorylation and disassembly of CK8 in a time-dependent and degree-dependent manner in vitro. The activation of protein kinase C was a significant molecular factor contributing to this phenomenon. Taken together, this study is the first to address the molecular mechanisms of CK8 downregulation in NP cells. Importantly, our findings provide clues regarding a molecular link between compressive loads and CK8 alterations, which shed a novel light on the etiology of IDD.

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.

Sodium-coupled vitamin C transporter (SVCT2): expression, function, and regulation in intervertebral disc cells

BACKGROUND CONTEXT

Vitamin C (ascorbic acid [AA]) is essential for the synthesis of collagen and also acts as an antioxidant in the intervertebral disc (IVD). However, there is very little information currently available on the identity of the transporter that facilitates AA entry into IVD cells and the factors that mediate the transport process.

PURPOSE

To investigate the expression of the two known isoforms of Na+ -coupled vitamin C transporter, SVCT1 and SVCT2, in IVD cells and its regulation by insulin-like growth factor 1 (IGF-1) and the steroid hormone dexamethasone.

STUDY DESIGN

To identify the expression and functional activity of the sodium-dependent vitamin C transporter (SVCT) in the IVD.

METHODS

Uptake studies were carried out with rabbit annulus fibrosis and nucleus pulposus cells in 24-well plates using [14C]-AA. To characterize SVCT transporter, uptake was done in the presence and absence of Na+ in the uptake buffer. Time dependency, Na+ activation kinetics, saturation kinetics, and substrate selectivity studies were performed. Regulatory studies were performed in the presence of IGF-1 and the steroid hormone dexamethasone. Gene expression was analyzed by quantitative polymerase chain reaction.

RESULTS

Our real-time polymerase chain reaction results showed the presence of SVCT2 but not SVCT1 in IVD cells. Uptake of vitamin C in IVD cells is Na+ dependent and saturable. The Michaelis constant for the process is 96±11 μM. The activation of vitamin C uptake by Na+ exhibits a sigmoidal relationship, indicating involvement of more than one Na+ in the activation process. The uptake system does not recognize any other water-soluble vitamin as a substrate. Immunocytochemical analysis shows robust expression of SVCT2 protein in IVD cells. The growth factors IGF-1 and the steroid hormone dexamethasone upregulate the expression of SVCT2 in IVD cells.

CONCLUSIONS

Our studies demonstrate that the active SVCT2 is expressed in IVD cells and that the expression of this transporter is regulated by growth factors IGF-1 and dexamethasone.

Association of endothelin-1 expression and cartilaginous endplate degeneration in humans

Background

Inflammatory cytokines are involved in intervertebral disc (IVD) degeneration. Endothelin-1 (ET-1), a 21-amino-acid cytokine implicated with cartilage degradation, is secreted by vascular endothelial cells and also by many other cell types. The expression of ET-1 in human IVD cartilage endplate (CEP) and its role in disc degeneration have not been explored.

Methods and Findings

The expression of ET-1 in degenerated CEP was analyzed by immunohistochemical staining and Western blotting; ET-1 was demonstrated in cartilaginous endplate cells (CECs) by immunofluorescent staining. The ET-1 mRNA expression and protein production by CECs stimulated by tumor necrosis factor alpha (TNF-α), a pro-inflammatory cytokine, were determined by real-time PCR analysis and Western blotting, respectively. The matrix metalloprotease-1 (MMP-1), MMP-13 and tissue inhibitor of metalloproteases-1 (TIMP-1) levels in the supernatant of cultured CECs treated with ET-1 were determined using enzyme-linked immunosorbent assays. Nitric oxide (NO) release and nitric oxide synthase (NOS) activity were measured using a spectrophotometric assay. The apoptosis of CECs by ET-1 was measured by an Annexin V-FITC detection assay. The production of ET-1 in degenerated cartilage endplate was significantly higher than normal CEP. The results showed that ET-1 was expressed by CECs and modulated by TNF-α in a dose-dependent manner. ET-1 increased production of MMP-1 and MMP-13, decreased TIMP-1 production, and induced NO and NOS release by cultured CECs. The direct stimulation of CECs by ET-1 did not promote cell apoptosis.

Conclusion

The study results suggest that ET-1 played a pivotal role in human CEP degeneration, and may be a new target for development of therapies for this condition.

Hyperbaric oxygen treatment suppresses MAPK signaling and mitochondrial apoptotic pathway in degenerated human intervertebral disc cells

Nucleus pulposus cells (NPCs) from degenerating discs produce catabolic and inflammatory factors, including interleukin (IL)-1 and nitric oxide (NO). Enhanced production of NO has been implicated in the apoptosis of degenerating disc cells. This study evaluates the effects of hyperbaric oxygen (HBO) on degenerated human NPCs. All hyperoxic cells were exposed to 100% O(2) at 2.5 atmospheres absolute (ATA). Phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK) in NPCs was detected using the phosphor-kinase array kit. RNA was isolated for real-time polymerase chain reaction (PCR) analysis of aggrecan and type II collagen gene expression. The levels of IL- 1β and NO were quantified by enzyme-linked immunosorbent assay (ELISA). To identify the HBO-induced anti-apoptotic pathways, expression of Bcl-2 and Bax proteins as well as activation of cysteine-containing aspartate-specific proteases (caspases) 3, 8, and 9 was evaluated using Western blotting after HBO treatment. Our data showed that HBO treatment decreased the expression of IL-1β, suppressed phosphorylation of ERK1/2, JNK, and p38 MAPK, decreased synthesis of NO, and increased the gene expression of aggrecan and type II collagen in NPCs as compared with the atmospheric treatment. HBO up-regulated the ratio of Bcl-2 to Bax expression and reduced the activity of caspases 9 and 3 but not of caspase 8, indicating a selective effect over the mitochondrial apoptosis pathway in degenerated NPCs. These results support our hypothesis that HBO treatment suppresses MAPK signaling and mitochondrial apoptotic pathway in degenerated human intervertebral disc cells.

Effect of hyperbaric oxygenation on intervertebral disc degeneration: an in vivo study with sprague-dawley rats

STUDY DESIGN

An in vivo study was conducted to test the effect of hyperbaric oxygenation (HBO) on intervertebral disc degeneration in Sprague-Dawley rats.

OBJECTIVE

To observe the changes in intervertebral disc height and levels of glycosaminoglycan, collagen, interleukin-1β (IL-1β), prostaglandin E2 (PGE2), and inducible nitric oxide synthase (iNOS) in degenerated intervertebral discs after HBO therapy.

SUMMARY OF BACKGROUND DATA

Although the involvement of IL-1β, PGE-2, NO, and low O2 concentration has been demonstrated in intervertebral disc degeneration, the actual mechanism is not clear. It has been reported that HBO influences changes in IL-1β, PGE-2, NO, and O2 concentration. Previously, a study demonstrated an in vitro positive effect of HBO on the human nucleus pulposus. Thus, an in vivo study in animals was necessary.

METHODS

Twelve Sprague-Dawley rats were each injected with chondroitinase ABC in 2 proximal intervertebral discs of the tail. After treating with 100% oxygen at 2.5 atmospheres 2 hours per days for 10 days, the change in disc height was determined by radiography. The amounts of PGE-2, iNOS, glycosaminoglycan, and total collagen in the intervertebral disc were quantified by enzyme-linked immunosorbent assay. Tissue morphology and the distribution of glycosaminoglycan, IL-1β, and iNOS in the intervertebral disc were assessed by histology and immunohistochemistry. The area of IL-1β in the intervertebral discs was quantified using image analysis software.

RESULTS

HBO therapy stopped the decrease in intervertebral disc height, caused an increase in the amount of glycosaminoglycan, and inhibited IL-1β, PGE-2, and iNOS production.

CONCLUSION

HBO provides a potential treatment modality for intervertebral disc degeneration.

Effect of Intradiscal Methylene Blue Injection for the Chronic Discogenic Low Back Pain: One Year Prospective Follow-up Study

Objective

To evaluate the efficacy of intradiscal methylene blue (MB) injection in patients with chronic discogenic low back pain.

Method

Twenty patients with discogenic low back pain (4 males, 16 females; mean age 45.6 years) refractory to conservative management were recruited. All subjects underwent MB injection in target lumbar intervertebral discs confirmed by provocative discography. The clinical outcome was assessed by visual analog scale (VAS) and Oswestry disability index (ODI) at baseline and 1, 3, 6 and 12 months after treatment. Successful outcome was described as minimum of 2 points reduction in pain intensity compared with the baseline.

Results

VAS and ODI significantly decreased after one injection. The average VAS and ODI were reduced significantly from 5.1 and 38.0 at baseline to 3.2 and 27.4 at 3 months after injection (p<0.05). However, the mean score of VAS at 12 month follow-up was 4.5 and we could not observe any difference between 12 months after injection and pretreatment. Eleven of twenty patients (55%) reported successful outcomes after intradiscal MB injection at 3 month follow up and the average VAS was reduced by 3.3±1.1 (p<0.05). At the time of 12 month follow up, pain had relapsed in 6 patients who have had satisfactory effect at 3 month follow up. Successful outcome was maintained in only 5 patients (20%) for 1 year.

Conclusion

The intradiscal MB injection is a short-term effective minimally invasive treatment indicated for discogenic back pain but it may lose its effectiveness long-term.

Nucleus pulposus replacement and regeneration/repair technologies: present status and future prospects

Degenerative disc disease is implicated in the pathogenesis of many painful conditions of the back, chief among which is low back pain. Acute and/or chronic low back pain (A/CLBP) afflicts a large number of people, thus making it a major healthcare issue with concomitant cost ramifications. When conservative treatments for A/CLBP, such as bed rest, anti-inflammatory medications, and physical therapy, prove to be ineffectual, surgical options are recommended. The most popular of these is discectomy followed by fusion. Although there are many reports of good to excellent outcomes with this method, there are concerns, such as long-term adverse biomechanical consequences to adjacent functional spinal unit(s). A surgical option that has been attracting much attention recently is replacement or regeneration/repair of the nucleus pulposus, an approach that holds the prospect of not compromising either mobility or function and causing no adjacent-level injury. There is a sizeable body of literature highlighting this option, comprising in vitro biomechanical studies, finite element analyses, animal-model studies, and limited clinical evaluations. This work is a review of this body of literature and is organized into four parts, with the focus being on replacement technologies, regeneration/repair technologies, and detailed expositions on 14 areas for future study. This review ends with a summary of the salient points made.

Interactions of environmental conditions and mechanical loads have influence on matrix turnover by nucleus pulposus cells

Disc degeneration is associated with several changes in the physicochemical environment of intervertebral disc cells. Nucleus pulposus (NP) cells in the center of degenerated discs are exposed to decreased glucose supply, osmolarity, pH, and oxygen levels. To understand the complexity of these interactions on a cellular level, we designed standardized experiments in which we compared responses to these environmental factors under normal levels with those seen under two different degrees of disc degeneration. We hypothesized that these changes in environmental stimuli influence gene expression of matrix proteins and matrix degrading enzymes and alter their responses to cyclic hydrostatic pressure (HP). Our results suggest that a simulation of degenerative conditions influences the degradation of disc matrix through impairing matrix formation and accelerating matrix resorption via up- or down-regulation of the respective target genes. The greatest effects were seen for decreases in glucose concentration and pH. Low oxygen had little influence. HP had little direct effect but appeared to counteract matrix degradation by reducing or inverting some of the adverse effects of other stimuli. For ongoing in vitro studies, interactions between mechanical stimuli and factors in the physicochemical environment should not be ignored as these could markedly influence results.

Effect of hyperbaric oxygenation on intervertebral disc degeneration: an in vitro study with human lumbar nucleus pulposus

STUDY DESIGN

An in vitro study with degenerated human lumbar intervertebral disc specimens cultured under hyperbaric oxygenation (HBO).

OBJECTIVE

To observe the changes in interleukin (IL)-1β, prostaglandin (PG)-E2, nitric oxide (NO), cell growth, and apoptosis of the human nucleus pulposus cell (NPC) after HBO.

SUMMARY OF BACKGROUND DATA

Intervertebral disc degeneration has been demonstrated as related to IL-1β, PG-E2, NO, and O2 concentration but the actual mechanism is not clear. HBO also has also been reported in the literature to influence changes in IL-1β, prostaglandin E2, NO, and O2 concentration. However, the direct effect of HBO on the disc cells has not been previously reported.

METHODS

We collected 12 human lumbar degenerated disc specimens and evaluated the effects of HBO on the cultured NPCs. The amounts of IL-1β, PG-E2, and NO in the conditioned medium were quantified by enzyme-linked immunosorbent assay and high performance liquid chromatography. Cell growth was measured by increase in cell number. Cell viability and proteoglycan content were evaluated by histologic study using safranin O staining. In situ analysis of apoptosis was performed using Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining.

RESULTS

Our data indicated that HBO treatment inhibited IL-1β, PG-E2, and NO production but increased cell number and matrix synthesis of cultured NPCs. TUNEL staining showed that HBO treatment suppressed the apoptosis of cultured NPCs.

CONCLUSION

HBO provides a potential treatment modality for disc degeneration.

The IL-1β (+3953 T/C) gene polymorphism associates to symptomatic lumbar disc herniation

PURPOSE

To determine whether polymorphisms (SNPs) in the genes encoding cytokines and nitric oxide synthase (NOS) might play some role in lumbar disc herniation (LDH).

PATIENTS AND METHODS

Case-control study in which 179 patients were retrospectively reviewed. The case group was made of 50 patients with symptomatic LDH diagnosed by MRI while the control group was made of 129 individuals undergoing routine hip or knee arthroplasty with a lifetime lack of low back pain. SNPs in the cytokine genes of IL-1 [IL-1α (-889 C/T), IL-1β (+3953 T/C)], TNF-α (-308 G/A and -238 G/A) and NOS genes [eNOS (r 27 bp, intron 4 and -786 T/C) and iNOS (22 G/A)].

RESULTS

The CC genotype and C allele of the IL-1β (+3953 T/C) SNP were significantly more frequent among LDH patients compared to controls. On the other hand, eNOS (-768 T/C) and iNOS (22 G/A) SNPs were significantly more common in the control group.

CONCLUSIONS

Carriers of the CC genotype of the IL-1β (+3953 T/C) SNP were more frequent among LDH patients suggesting some potential role of the IL-1β SNP on LDH pathogenesis. The eNOS (-786 T/C) and iNOS (22 G/A) SNPs were more frequent among the control subjects, suggesting their possible protective role against LDH. Genotyping these SNPs could be useful to identify persons with an increased lifetime risk of disc herniation in whom measures to avoid LDH could be implemented.

The efficacy of Link N as a mediator of repair in a rabbit model of intervertebral disc degeneration

INTRODUCTION

Intervertebral disc (IVD) degeneration is associated with proteolytic degradation of the extracellular matrix, and its repair requires both the production of extracellular matrix and the downregulation of proteinase activity. These properties are associated with several growth factors. However, the use of growth factors in clinical practice is limited by their high cost. This cost can be circumvented using synthetic peptides, such as Link N, which can stimulate the synthesis of proteoglycan and collagen by IVD cells in vitro. The purpose of the present study was to evaluate the effect of Link N in vivo in a rabbit model of IVD degeneration.

METHODS

New Zealand white rabbits received annular puncture in two lumbar discs. Two weeks after puncture, both punctured discs of each rabbit were injected with either Link N or saline. After 2 weeks, nine rabbits were euthanized and the annulus fibrosus (AF) and nucleus pulposus (NP) of Link N-injected and saline-injected IVDs were removed and used to prepare total RNA. Following reverse transcription, quantitative PCR was performed for aggrecan, COL2A1, COL1A1, ADAMTS-4, ADAMTS-5 and MMP-3. After 12 weeks, 19 rabbits were euthanized and the injected IVDs were removed for biochemical and histological analysis. Proteinase K digests were analyzed for DNA and sulfated glycosaminoglycan content. Disc height was monitored radiographically biweekly.

RESULTS

Following needle puncture, disc height decreased by about 25% over 2 weeks, and was partially restored by Link N injection. Puncture of the IVD resulted in a trend towards decreased proteoglycan content in both the NP and AF, and a trend towards partial restoration following Link N injection, although under the time course used this did not achieve statistical significance. Link N did not alter the DNA content of the discs. Link N injection led to a significant increase in aggrecan gene expression and a significant decrease in proteinase gene expression in both the NP and AF, when compared with saline alone.

CONCLUSIONS

When administered to the degenerate disc in vivo, Link N stimulated aggrecan gene expression and downregulated metalloproteinase expression, and there was a trend towards increased proteoglycan content of the disc, in both the NP and AF. These are features needed for any agent designed to stimulate disc repair. In principle, therefore, Link N supplementation could be an option for treating disc degeneration.

Attenuation of inflammatory events in human intervertebral disc cells with a tumor necrosis factor antagonist

STUDY DESIGN

The inflammatory responses of primary human intervertebral disc (IVD) cells to tumor necrosis factor α (TNF-α) and an antagonist were evaluated in vitro.

OBJECTIVE

To investigate an ability for soluble TNF receptor type II (sTNFRII) to antagonize TNF-α-induced inflammatory events in primary human IVD cells in vitro.

SUMMARY OF BACKGROUND DATA

TNF-α is a known mediator of inflammation and pain associated with radiculopathy and IVD degeneration. sTNFRs and their analogues are of interest for the clinical treatment of these IVD pathologies, although information on the effects of sTNFR on human IVD cells remains unknown.

METHODS

IVD cells were isolated from surgical tissues procured from 15 patients and cultured with or without 1.4 nmol/L TNF-α (25 ng/mL). Treatment groups were coincubated with varying doses of sTNFRII (12.5-100 nmol/L). Nitric oxide (NO), prostaglandin E₂ (PGE₂), and interleukin-6 (IL6) levels in media were quantified to characterize the inflammatory phenotype of the IVD cells.

RESULTS

Across all patients, TNF-α induced large, statistically significant increases in NO, PGE₂, and IL6 secretion from IVD cells compared with controls (60-, 112-, and 4-fold increases, respectively; P < 0.0001). Coincubation of TNF-α with nanomolar doses of sTNFRII significantly attenuated the secretion of NO and PGE₂ in a dose-dependent manner, whereas IL6 levels were unchanged. Mean IC₅₀ values for NO and PGE₂ were found to be 35.1 and 20.5 nmol/L, respectively.

CONCLUSION

Nanomolar concentrations of sTNFRII were able to significantly attenuate the effects of TNF-α on primary human IVD cells in vitro. These results suggest this sTNFR to be a potent TNF antagonist with potential to attenuate inflammation in IVD pathology.

The effects of dynamic loading on the intervertebral disc

Loading is important to maintain the balance of matrix turnover in the intervertebral disc (IVD). Daily cyclic diurnal assists in the transport of large soluble factors across the IVD and its surrounding circulation and applies direct and indirect stimulus to disc cells. Acute mechanical injury and accumulated overloading, however, could induce disc degeneration. Recently, there is more information available on how cyclic loading, especially axial compression and hydrostatic pressure, affects IVD cell biology. This review summarises recent studies on the response of the IVD and stem cells to applied cyclic compression and hydrostatic pressure. These studies investigate the possible role of loading in the initiation and progression of disc degeneration as well as quantifying a physiological loading condition for the study of disc degeneration biological therapy. Subsequently, a possible physiological/beneficial loading range is proposed. This physiological/beneficial loading could provide insight into how to design loading regimes in specific system for the testing of various biological therapies such as cell therapy, chemical therapy or tissue engineering constructs to achieve a better final outcome. In addition, the parameter space of 'physiological' loading may also be an important factor for the differentiation of stem cells towards most ideally 'discogenic' cells for tissue engineering purpose.