Efficacy of intradiscal hepatocyte growth factor injection for the treatment of intervertebral disc degeneration

Modulating the Thermoresponsive Characteristics of PLGA-PEG-PLGA Hydrogels via Manipulation of PLGA Monomer Sequences

Hydrogels are promising materials for biomedical applications, particularly in drug delivery and tissue engineering. This study highlights thermoresponsive hydrogels, specifically poly(lactic-co-glycolic acid) (PLGA)-poly(ethylene glycol) (PEG)-PLGA triblock copolymers, and introduces a feed rate-controlled polymerization (FRCP) method. By utilizing an organic catalyst and regulating the monomer feed rate, the sequence distribution of PLGA within the triblock copolymer is controlled. Various analyses, including 13C NMR and rheological measurements, were conducted to investigate the impact of sequence distribution. Results show that altering sequence distribution significantly influences the sol-gel transition, hydrophobicity-hydrophilicity balance, and drug release profile. Increased sequence uniformity lowers the glass transition temperature, raises the sol-gel transition temperature due to enhanced hydrophilicity, and promotes a more uniform drug (curcumin) distribution within the PLGA domain, resulting in a slower release rate. This study emphasizes the importance of PLGA sequence distribution in biomedical applications and the potential of FRCP to tailor thermoresponsive hydrogels for biomedical advancements.

Reviving Intervertebral Discs: Treating Degeneration Using Advanced Delivery Systems

Intervertebral disc degeneration (IVDD) is commonly associated with many spinal problems, such as low back pain, and significantly impacts a patient's quality of life. However, current treatments for IVDD, which include conservative and surgical methods, are limited in their ability to fully address degeneration. To combat IVDD, delivery-system-based therapy has received extensive attention from researchers. These delivery systems can effectively deliver therapeutic agents for IVDD, overcoming the limitations of these agents, reducing leakage and increasing local concentration to inhibit IVDD or promote intervertebral disc (IVD) regeneration. This review first briefly introduces the structure and function of the IVD, and the related pathophysiology of IVDD. Subsequently, the roles of drug-based and bioactive-substance-based delivery systems in IVDD are highlighted. The former includes natural source drugs, nonsteroidal anti-inflammatory drugs, steroid medications, and other small molecular drugs. The latter includes chemokines, growth factors, interleukin, and platelet-rich plasma. Additionally, gene-based and cell-based delivery systems are briefly involved. Finally, the limitations and future development of the combination of therapeutic agents and delivery systems in the treatment of IVDD are discussed, providing insights for future research.

Precision medicine strategies for spinal degenerative diseases: Injectable biomaterials with in situ repair and regeneration

As the population ages, spinal degeneration seriously affects quality of life in middle-aged and elderly patients, and prevention and treatment remain challenging for clinical surgeons. In recent years, biomaterials-based injectable therapeutics have attracted much attention for spinal degeneration treatment due to their minimally invasive features and ability to perform precise repair of irregular defects. However, the precise design and functional control of bioactive injectable biomaterials for efficient spinal degeneration treatment remains a challenge. Although many injectable biomaterials have been reported for the treatment of spinal degeneration, there are few reviews on the advances and effects of injectable biomaterials for spinal degeneration treatment. This work reviews the current status of the design and fabrication of injectable biomaterials, including hydrogels, bone cements and scaffolds, microspheres and nanomaterials, and the current progress in applications for treating spinal degeneration. Additionally, registered clinical trials were also summarized and key challenges and clinical translational prospects for injectable materials for the treatment of spinal degenerative diseases are discussed.

Treatment outcomes of injectable thermosensitive hydrogel containing bevacizumab in intervertebral disc degeneration

Intervertebral disc (IVD) degeneration (IDD) is a common musculoskeletal disease and its treatment remains a clinical challenge. It is characterised by reduced cell numbers and degeneration of the extracellular matrix (ECM). Nucleus pulposus (NP) cells play a crucial role in this process. The purpose of this study is to explore the role of bevacizumab, a vascular endothelial growth factor (VEGF) inhibitor, in the treatment of IDD through local drug delivery. High expression of VEGF was observed in degenerating human and rat IVDs. We demonstrated that MMP3 expression was decreased and COL II synthesis was promoted, when VEGF expression was inhibited by bevacizumab, thereby improving the degree of disc degeneration. Thus, these findings provide strong evidence that inhibition of VEGF expression by local delivery of bevacizumab is safe and effective in ameliorating disc degeneration in rats. The injectable thermosensitive PLGA-PEG-PLGA hydrogels loaded with bevacizumab is a potential therapeutic option for disc degeneration.

Glucagon-like peptide-1 receptor activation maintains extracellular matrix integrity by inhibiting the activity of mitogen-activated protein kinases and activator protein-1

Disruption of the intervertebral disc extracellular matrix (ECM) is a hallmark of intervertebral disc degeneration (IDD), which is largely attributed to excessive oxidative stress. However, there is a lack of clinically feasible approaches to promote the reconstruction of the disc ECM. Glucagon-like peptide-1 (GLP-1), a safe polypeptide hormone adopted to treat type 2 diabetes mellitus, has shown great potential for relieving oxidative stress-related damage. To our knowledge, this is the first study to reveal that exenatide, a GLP-1 receptor (GLP-1R) agonist, can upregulate disc ECM synthesis and attenuate oxidative stress-induced ECM degradation and IDD. Mechanistically, we found that exenatide inhibited the activation of mitogen-activated protein kinases (MAPK) signaling pathway and the formation of BATF/JUNs heterodimers (an index of activator protein-1 (AP-1) activity). The restoration of MAPK signaling activation reversed the protective effects of exenatide and enhanced downstream BATF/JUNs binding. BATF overexpression was also found to aggravate disc ECM damage, even in the presence of exenatide. In summary, exenatide is an effective agent that regulates ECM anabolic balance and restores disc degeneration by inhibiting MAPK activation and its downstream AP-1 activity. The present study provides a therapeutic rationale for activating the GLP-1 receptor against IDD and establishes the important role of AP-1 activity in the pathogenesis of IDD.

Activation of Hypoxia-Inducible Factor-1α Signaling Pathway Has the Protective Effect of Intervertebral Disc Degeneration

Intervertebral discs (IVDs) have poor nutrient diffusion, because the nucleus pulposus (NP) lacks direct vascular supply and likely generates adenosine triphosphate by anaerobic glycolysis. Regulation of glycolysis is mediated by hypoxia-inducible factor-1α (HIF-1α), a transcription factor that responds to local oxygen tension. Constitutively active HIF-1α (CA HIF-1α) was created by point mutation and determined the protective role of HIF-1α in IVD degeneration. Under fluoroscopy, rat caudal IVD segments were stabbed by a needle puncture, and pcDNA3- HIF-1α wild-type (WT) or pcDNA3-CA HIF-1α was transfected into NP cell lines. The constitutive activity of CA HIF-1α was analyzed using a luciferase assay after cell lysis. Next, IVD tissue samples were retrieved from five patients with degenerative lumbar spinal stenosis at the time of surgery, and NP cells were cultured. NP cells were transfected with CA HIF-1α, and relevant gene expression was measured. HIF-1α protein levels in the nucleus were significantly higher, and transcriptional activity was 10.3-fold higher in NP cells with CA HIF-1α than in those with HIF-1α WT. Gene transfer of CA HIF-1α into NP cells enhanced the expression of Glut-1, Glut-3, aggrecan, type II collagen, and Sox9. Moreover, CA HIF-1α reduced the apoptosis of NP cells induced by the Fas ligand. The HIF-1α and collagen 2 expression levels were notably increased in the NP cells of the CA HIF-1α transfected segments in histology and immunohistochemistry study. Collectively, these results suggest that activation of HIF-1α signaling pathway may play a protective role against IVD degeneration and could be used as a future therapeutic agent.

Platelet-Derived Biomaterials Inhibit Nicotine-Induced Intervertebral Disc Degeneration Through Regulating IGF-1/AKT/IRS-1 Signaling Axis

Apart from aging process, adult intervertebral disc (IVD) undergoes various degenerative processes. However, the nicotine has not been well identified as a contributing etiology. According to a few studies, nicotine ingestion through smoking, air or clothing may significantly accumulate in active as well as passive smokers. Since nicotine has been demonstrated to adversely impact various physiological processes, such as sympathetic nervous system, leading to impaired vasculature and cellular apoptosis, we aimed to investigate whether nicotine could induce IVD degeneration. In particular, we evaluated dose-dependent impact of nicotine in vitro to simulate its chronic accumulation, which was later treated by platelet-derived biomaterials (PDB). Further, during in vivo studies, mice were subcutaneously administered with nicotine to examine IVD-associated pathologic changes. The results revealed that nicotine could significantly reduce chondrocytes and chondrogenic indicators (Sox, Col II and aggrecan). Mice with nicotine treatment also exhibited malformed IVD structure with decreased Col II as well as proteoglycans, which was significantly increased after PDB administration for 4 weeks. Mechanistically, PDB significantly restored the levels of IGF-1 signaling proteins, particularly pIGF-1 R, pAKT, and IRS-1, modulating ECM synthesis by chondrocytes. Conclusively, the PDB impart reparative and tissue regenerative processes by inhibiting nicotine-initiated IVD degeneration, through regulating IGF-1/AKT/IRS-1 signaling axis.

The Potential Role of Hepatocyte Growth Factor in Degenerative Disorders of the Synovial Joint and Spine

This paper aims to provide a comprehensive review of the changing role of hepatocyte growth factor (HGF) signaling in the healthy and diseased synovial joint and spine. HGF is a multifunctional growth factor that, like its specific receptor c-Met, is widely expressed in several bone and joint tissues. HGF has profound effects on cell survival and proliferation, matrix metabolism, inflammatory response, and neurotrophic action. HGF plays an important role in normal bone and cartilage turnover. Changes in HGF/c-Met have also been linked to pathophysiological changes in degenerative joint diseases, such as osteoarthritis (OA) and intervertebral disc degeneration (IDD). A therapeutic role of HGF has been proposed in the regeneration of osteoarticular tissues. HGF also influences bone remodeling and peripheral nerve activity. Studies aimed at elucidating the changing role of HGF/c-Met signaling in OA and IDD at different pathophysiological stages, and their specific molecular mechanisms are needed. Such studies will contribute to safe and effective HGF/c-Met signaling-based treatments for OA and IDD.

Intervertebral Disc Regeneration Using Stem Cell/Growth Factor-Loaded Porous Particles with a Leaf-Stacked Structure

Although biological therapies based on growth factors and transplanted cells have demonstrated some positive outcomes for intervertebral disc (IVD) regeneration, repeated injection of growth factors and cell leakage from the injection site remain considerable challenges for human therapeutic use. Herein, we prepare human bone marrow-derived mesenchymal stem cells (hBMSCs) and transforming growth factor-β3 (TGF-β3)-loaded porous particles with a unique leaf-stack structural morphology (LSS particles) as a combination bioactive delivery matrix for degenerated IVD. The LSS particles are fabricated with clinically acceptable biomaterials (polycaprolactone and tetraglycol) and procedures (simple heating and cooling). The LSS particles allow sustained release of TGF-β3 for 18 days and stable cell adhesiveness without additional modifications of the particles. On the basis of in vitro and in vivo studies, it was observed that the hBMSCs/TGF-β3-loaded LSS particles can provide a suitable milieu for chondrogenic differentiation of hBMSCs and effectively induce IVD regeneration in a beagle dog model. Thus, therapeutically loaded LSS particles offer the promise of an effective bioactive delivery system for regeneration of various tissues including IVD.

Inhibiting Heat Shock Protein 90 Protects Nucleus Pulposus-Derived Stem/Progenitor Cells From Compression-Induced Necroptosis and Apoptosis

Nucleus pulposus-derived stem/progenitor cells (NPSCs) provide novel prospects for the regeneration of degenerated intervertebral disc (IVD). Nevertheless, with aging and degeneration of IVD, the frequency of NPSCs markedly decreases. Excessive cell death could be the main reason for declined frequency of NPSCs, however, the exact mechanisms remain elusive. Thus, the present study was undertaken to explore the mechanisms of compression-induced NPSCs death, and the effects of heat shock protein 90 (HSP90) on NPSCs survival. Here, we found that compression could trigger receptor-interacting protein kinase 1 (RIPK1)/receptor-interacting protein kinase 3 (RIPK3)/mixed lineage kinase domain-like protein (MLKL)-mediated necroptosis of NPSCs. Furthermore, we found that elevated expression of HSP90 was involved in compression-induced NPSCs death, and inhibiting HSP90 could dramatically attenuate compression-induced necroptosis of NPSCs via regulating the expression and activity of RIPK1/RIPK3/MLKL, and alleviating the mitochondrial dysfunction (mitochondrial membrane potential loss and ATP depletion) and oxidative stress [production of mitochondrial reactive oxygen species (ROS), cellular total ROS and malondialdehyde, and downregulation of superoxide dismutase 2]. Besides necroptosis, compression-induced apoptosis of NPSCs was also attenuated by HSP90 inhibition. In addition, we found that enhanced expression of HSP70 contributed to the cytoprotective effects of inhibiting HSP90. More encouragingly, our results demonstrated that inhibiting HSP90 could also mitigate the exhaustion of NPSCs in vivo. In conclusion, RIPK1/RIPK3/MLKL-mediated necroptosis participates in compression-induced NPSCs death. Furthermore, targeting HSP90 to simultaneously inhibit necroptosis and apoptosis of NPSCs might be an efficient strategy for preventing the death of NPSCs, thus rescuing the endogenous repair capacity of NP tissue.

Overexpressed IGFBP5 promotes cell proliferation and inhibits apoptosis of nucleus pulposus derived from rats with disc degeneration through inactivating the ERK/MAPK axis

It is previously suggested that insulin-like growth factor binding proteins (IGFBPs) potentially share an association with disc degeneration (DD) that causes back pain. This study aimed at exploring the functional relevance of IGFBP5 in DD by establishing a rat model of DD. The nucleus pulposus (NP) cells were transduced with IGFBP5-shRNA or IGFBP5 overexpression to determine the cellular processes (proliferation, apoptosis, as well as colony formation). The protein levels of apoptosis-related proteins were evaluated. Furthermore, NP cells were treated with the extracellular signal-regulated kinases/mitogen-activated protein kinase (ERK/MAPK) pathway inhibitor (PD98059) followed by measurement of ERK protein level and ERK phosphorylation content. The NP cells showed suppressed proliferation and colony formation ability, yet promoted apoptosis after transfection with IGFBP5-shRNA. It was found that silencing of IGFBP5 could lead to the ERK/MAPK axis activation, as indicated by an elevated ERK protein level and ERK phosphorylation content. However, overexpression of IGFBP5 could reverse all the reaction induced by silenced IGFBP5. These key findings demonstrate that overexpressed IGFBP5 inactivates the ERK/MAPK axis to stimulate the proliferation and inhibit apoptosis of NP cells in a rat model of DD.

Intradiscal Injection of Induced Pluripotent Stem Cell-Derived Nucleus Pulposus-Like Cell-Seeded Polymeric Microspheres Promotes Rat Disc Regeneration

Background

Cell replacement therapy is an attractive alternative for treating degenerated intervertebral discs (IVDs), which are related to the reduction of nucleus pulposus-like cells (NP-lCs) and the loss of the extracellular matrix. Induced pluripotent stem cells (iPSCs) which resemble embryonic stem cells are considered to be a potential resource for restoring NP-lCs and disc homeostasis. Here, we proposed an efficient two-step differentiation protocol of human iPSCs into NP-lCs and continuously tested their in vivo ability to regenerate IVDs.

Methods

A polymeric gelatin microsphere (GM) was generated for sustained release of growth and differentiation factor-5 (GDF-5) and as a cell delivery vehicle of NP-lCs. By injecting NP-lC-seeded GDF-5-loaded GMs into the rat coccygeal intervertebral discs, the disc height and water content were examined with the molybdenum target radiographic imaging test and magnetic resonance imaging examination. Histology and immunohistochemistry results were shown with H&E, S-O-Fast Green, and immunohistochemistry staining.

Results

We demonstrated that the injection of NP-lC-seeded GDF-5-loaded GMs could reverse IDD in a rat model. The imaging examination indicated that disc height recovered and water content increased. Histology and immunohistochemistry results indicated that the NP cells as well as their extracellular matrix were partially restored.

Conclusions

The results suggest that NP-lC-seeded GDF-5-loaded GMs could partially regenerate degenerated intervertebral discs after transplantation into rat coccygeal intervertebral discs. Our study will help develop a promising method of stem cell-based therapy for IDD.

Therapeutic potential of growth differentiation factors in the treatment of degenerative disc diseases

Intervertebral disc (IVD) degeneration is a major contributing factor to chronic low back pain and disability, leading to imbalance between anabolic and catabolic processes, altered extracellular matrix composition, loss of tissue hydration, inflammation, and impaired mechanical functionality. Current treatments aim to manage symptoms rather than treat underlying pathology. Therefore, IVD degeneration is a target for regenerative medicine strategies. Research has focused on understanding the molecular process of degeneration and the identification of various factors that may have the ability to halt and even reverse the degenerative process. One such family of growth factors, the growth differentiation factor (GDF) family, have shown particular promise for disc regeneration in in vitro and in vivo models of IVD degeneration. This review outlines our current understanding of IVD degeneration, and in this context, aims to discuss recent advancements in the use of GDF family members as anabolic factors for disc regeneration. An increasing body of evidence indicates that GDF family members are central to IVD homeostatic processes and are able to upregulate healthy nucleus pulposus cell marker genes in degenerative cells, induce mesenchymal stem cells to differentiate into nucleus pulposus cells and even act as chemotactic signals mobilizing resident cell populations during disc injury repair. The understanding of GDF signaling and its interplay with inflammatory and catabolic processes may be critical for the future development of effective IVD regeneration therapies.

Optimization of puncture injury to rat caudal disc for mimicking early degeneration of intervertebral disc

The caudal discs of rats have been proposed as a puncture model in which intervertebral disc (IVD) degeneration can be induced and novel therapies can be tested. For biological repair, treatments for ongoing IVD degeneration are ideally administered during the earlier stages. The purpose of this study was to elucidate the optimal puncture needle size for creating a model that mimicked the earlier stages of IVD degeneration. According to the disc height index, histologic score, and MRI grading, a puncture needle sized 21G or larger induced rapid degenerative processes in rat caudal discs during the initial 2-4 weeks. The degenerative changes were severe and continued deteriorating after 4 weeks. Conversely, puncture injury induced by needles sized 25G or smaller also produced degenerative changes in rat caudal discs during initial 2-4 weeks; however, the changes were less severe. Furthermore, the degenerative process became stabilized and showed no further deterioration or spontaneous recovery after 4 weeks. In the discs punctured by 25G needles, the expression of collagen I was increased at 2-4 weeks with a gradually fibrotic transformation thereafter. The expressions of collagen II and SOX9 were enhanced initially but returned to pre-injury levels at 4-8 weeks. The above-mentioned findings were more compatible with earlier degeneration in discs punctured by needles sized 25G or smaller than by needles sized 21G or larger, and the appropriate timing for intradiscal administration of proposed therapeutic agents would be 4 weeks or longer after puncture. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:202-211, 2018.

Synthesis, characterisation and preliminary investigation of the haemocompatibility of poly(d,l-lactide-co-glycolide)–poly(ethyleneglycol)–poly(d,l-lactide-co-glycolide) copolymer for simvastatin delivery

The development of nanomedicine has provided advanced treatment opportunities for many diseases. Simvastatin, a widely used anti-lipidaemic drug, has potential for the treatment of orthopaedic diseases. However, the clinical application of simvastatin is limited because of its hydrophobicity and lack of distribution in osseous tissue. In this study, an amphiphilic nanoparticle, poly(d,l-lactide- co-glycolide)–poly(ethyleneglycol)–poly(d,l-lactide- co-glycolide), was synthesised to improve the biocompatibility of simvastatin. The haemocompatibility of the poly(d,l-lactide- co-glycolide)–poly(ethyleneglycol)–poly(d,l-lactide- co-glycolide) copolymer was investigated through its aggregation, morphology and lysis of human red blood cells, along with its impact on the clotting function according to the activated partial thromboplastin time, prothrombin time and thromboelastographic assays. The results demonstrated that the poly(d,l-lactide- co-glycolide)–poly(ethyleneglycol)–poly(d,l-lactide- co-glycolide) copolymer with a concentration lower than 10 mg/mL had little impact on the aggregation, morphology or lysis of red blood cells, or on blood coagulation. Therefore, the copolymer may be a strong alternative candidate as an effective and safe drug carrier.

Modified PLGA–PEG–PLGA thermosensitive hydrogels with suitable thermosensitivity and properties for use in a drug delivery system

PLGA–PEG–PLGA (PPP) triblock copolymer is the most widely studied thermosensitive hydrogel owing to its non-toxic, biocompatible, biodegradable, and thermosensitive properties.

Expression levels of IL-17 and TNF-α in degenerated lumbar intervertebral discs and their correlation

The present study aimed to investigate the expression and roles of interleukin (IL)-17 and tumor necrosis factor (TNF)-α in intervertebral disc degeneration (IDD) and to identify the association between the effects of IL-17 and TNF-α in IDD. This may increase understanding of the pathogenic mechanism underlying IDD, and aid the development of alternative therapies. The experimental group consisted of 40 samples of nucleus pulposus tissue obtained from the intervertebral discs (IVDs) of patients with IDD by surgical intervention, and was further divided into an annulus fibrosus disrupted group, comprising 18 patients in which the external annulus was ruptured, and an annulus fibrosus intact group comprising 22 patients. The control group consisted of 20 samples of nucleus pulposus tissue from the IVDs of patients with traumatic lumbar disc fractures. The mRNA and protein expression levels of IL-17 and TNF-α in the 50 tissue samples were detected by semi-quantitative reverse transcription polymerase chain reaction and immunohistochemical staining, respectively, and the results were statistically analyzed. The IL-17 and TNF-α protein and mRNA expression levels in the annulus fibrosus disrupted and annulus fibrosus intact groups were both higher compared with those in the control group. In addition, the expression levels of IL-17 and TNF-α in the annulus fibrosus disrupted group were significantly higher compared with those in the annulus fibrosus intact group (P<0.01). A positive correlation was identified between the mRNA and protein expression levels of IL-17 and TNF-α in the experimental group (r=0.957, P<0.01). IL-17 and TNF-α may therefore be involved in the progression of human IDD, and may have synergistic effects in the development of IDD.

Exploratory study for identifying systemic biomarkers that correlate with pain response in patients with intervertebral disc disorders

Molecular events that drive disc damage and low back pain (LBP) may precede clinical manifestation of disease onset and can cause detrimental long-term effects such as disability. Biomarkers serve as objective molecular indicators of pathological processes. The goal of this study is to identify systemic biochemical factors as predictors of response to treatment of LBP with epidural steroid injection (ESI). Since inflammation plays a pivotal role in LBP, this pilot study investigates the effect of ESI on systemic levels of 48 inflammatory biochemical factors (cytokines, chemokines, and growth factors) and examines the relationship between biochemical factor levels and pain or disability in patients with disc herniation (DH), or other diagnoses (Other Dx) leading to low back pain, which included spinal stenosis (SS) and degenerative disc disease (DDD). Study participants (n = 16) were recruited from a back pain management practice. Pain numerical rating score (NRS), Oswestry Disability Index (ODI), and blood samples were collected pre- and at 7 to 10 days post-treatment. Blood samples were assayed for inflammatory mediators using commercial multiplex assays. Mediator levels were compared pre- and post-treatment to investigate the potential correlations between clinical and biochemical outcomes. Our results indicate that a single ESI significantly decreased systemic levels of SCGF-β and IL-2. Improvement in pain in all subjects was correlated with changes in chemokines (MCP-1, MIG), hematopoietic progenitor factors (SCGF-β), and factors that participate in angiogenesis/fibrosis (HGF), nociception (SCF, IFN-α2), and inflammation (IL-6, IL-10, IL-18, TRAIL). Levels of biochemical mediators varied based on diagnosis of LBP, and changes in pain responses and systemic mediators from pre- to post-treatment were dependent on the diagnosis cohort. In the DH cohort, levels of IL-17 and VEGF significantly decreased post-treatment. In the Other Dx cohort, levels of IL-2Rα, IL-3, and SCGF-β significantly decreased post-treatment. In order to determine whether mediator changes were related to pain, correlations between change in pain scores and change in mediator levels were performed. Subjects with DH demonstrated a profile signature that implicated hematopoiesis factors (SCGF-β, GM-CSF) in pain response, while subjects with Other Dx demonstrated a biomarker profile that implicated chemokines (MCP-1, MIG) and angiogenic factors (HGF, VEGF) in pain response. Our findings provide evidence that systemic biochemical factors in patients with LBP vary by diagnosis, and pain response to treatment is associated with a unique profile of biochemical responses in each diagnosis group. Future hypothesis-based studies with larger subject cohorts are warranted to confirm the findings of this pilot exploratory study.

Annular repair using high-density collagen gel: a rat-tail in vivo model

STUDY DESIGN

Animal in vivo study.

OBJECTIVE

To test the capability of high-density collagen gel to repair annular defects.

SUMMARY OF BACKGROUND DATA

Annular defects are associated with spontaneous disc herniations and disc degeneration, which can lead to significant morbidity. Persistent annular defects after surgical discectomies can increase reherniation rates. Several synthetic and biological materials have been developed for annular repair. This is the first study to test an injectable biomaterial in vivo.

METHODS

We punctured caudal intervertebral discs in 42 athymic rats, using an 18-gauge needle to create an annular defect. High-density collagen (HDC), either alone or cross-linked with riboflavin (RF), was injected into the defect. There were 4 separate study groups: HDC, HDC cross-linked with either 0.25 mM RF or 0.50 mM RF, and a negative control that was punctured and not treated. The animals were followed for 5 weeks; radiographs were used to assess disc heights and magnetic resonance images were used to evaluate degenerative changes. We developed an algorithm on the basis of T2-relaxation time measurements to assess the size of the nucleus pulposus. Tails were collected for histological analysis to evaluate disc degeneration and measure the cross-sectional area of the nucleus pulposus.

RESULTS

After 5 weeks, the control and the uncross-linked HDC groups both showed signs of progressive degenerative changes with minimal or no residual nucleus pulposus tissue in the disc space. Cross-linking significantly improved the ability of HDC gels to repair annular defects. The 0.50 mM RF cross-linked group showed only a slight decrease in nuclear tissue when compared with healthy discs, with no signs of intervertebral disc (IVD) degeneration. The annulus fibrosus was partially repaired by a fibrous cap that bridged the defect. Host fibroblasts infiltrated and remodeled the injected collagen.

CONCLUSION

HDC is capable of repairing annular defects induced by needle puncture. The stiffness of HDC can be modified by riboflavin cross-linking and seems to positively affect the repair mechanism. These results need to be replicated in a larger animal model.

LEVEL OF EVIDENCE

N/A.