Intradiscal application of rhBMP-7 does not induce regeneration in a canine model of spontaneous intervertebral disc degeneration

Innovative design of minimal invasive biodegradable poly(glycerol-dodecanoate) nucleus pulposus scaffold with function regeneration

Minimally invasive biodegradable implants with regeneration have been a frontier trend in clinic. Degeneration of nucleus pulposus (NP) is irreversible in most of spine diseases, and traditional spinal fusion or discectomy usually injure adjacent segments. Here, an innovative minimally invasive biodegradable NP scaffold with function regeneration inspired by cucumber tendril is developed using shape memory polymer poly(glycerol-dodecanoate) (PGD), whose mechanical property is controlled to the similar with human NP by adjusting synthetic parameters. The chemokine stromal cell-derived factor-1α (SDF-1α) is immobilized to the scaffold recruiting autologous stem cells from peripheral tissue, which has better ability of maintaining disc height, recruiting autologous stem cells, and inducing regeneration of NP in vivo compared to PGD without chemokine group and hydrogel groups significantly. It provides an innovative way to design minimally invasive implants with biodegradation and functional recovery, especially for irreversible tissue injury, including NP, cartilage and so on.

Intradiscal injection of human recombinant BMP-4 does not reverse intervertebral disc degeneration induced by nuclectomy in sheep

Background

Methods

Results

Conclusion

The Translational Potential of This Article

Lumbar spine intervertebral disc gene delivery of BMPs induces anterior spine fusion in lewis rats

Minimally invasive techniques and biological autograft alternatives such as the bone morphogenetic proteins (BMPs) can reduce morbidity associated with spinal fusions. This study was a proof-of-concept for gene-therapy-mediated anterior spine fusion that could be adapted to percutaneous technique for clinical use. Isogeneic bone marrow stromal cells genetically programmed to express b-galactosidase (LACZ, a marker gene), BMP2, BMP7, a mixture of BMP2 and BMP7 infected cells (homodimers, HM), or BMP2/7 heterodimers (HT) were implanted into the discs between lumbar vertebrae 4 and 5 (L4/5) and L5/6 of male Lewis rats. Spine stiffening was monitored at 4, 8 and 12 weeks using noninvasive-induced angular displacement (NIAD) testing. At 12 weeks isolated spines were assessed for fusion and bone formation by palpation, biomechanical testing [four-point bending stiffness, moment to failure in extension, and in vitro angular displacement (IVAD)], faxitron x-rays, microCT, and histology. Progressive loss of NIAD occurred in only the HT group (p < 0.001), and biomechanical tests correlated with the NIAD results. Significant fusion occurred only in the HT group (94% of animals with one or both levels) as assessed by palpation (p < 0.001), which predicted HT bone production assessed by faxitron (p ≤ 0.001) or microCT (p < 0.023). Intervertebral bridging bone was consistently observed only in HT-treated specimens. Induced bone was located anterior and lateral to the disc space, with no bone formation noted within the disc. Percutaneous anterior spine fusions may be possible clinically, but induction of bone inside the disc space remains a challenge.

Anatomic description of the basivertebral nerve and meningeal branch of the spinal nerve in the dog

PURPOSE

The existence of the basivertebral nerve and meningeal branch of the spinal nerve has not been proven in dogs to date. The objectives of this study are to 1) determine whether dogs have a meningeal branch of the spinal nerve (MBSN) and a basivertebral nerve (BVN) and to (2) describe anatomical characteristics of these two nerves. Authors also put forward a discussion on the possible clinical relevance of these findings.

MATERIAL AND METHODS

Dissections were performed on six embalmed dogs at the Veterinary Faculty of Barcelona with the use of stereomicroscopy and microsurgery equipment.

RESULTS

The MBSN (grossly) and BVN (grossly and histologically) were identified in the cervical, thoracic, and lumbar region in all dog specimens. In addition, other small fibers (suspected nerves) entering the vertebral body through small foramina close to the end plates were identified. Histological examination of the tissues confirmed the presence of nerve fibers (myelinated and unmyelinated) in suspected BVN samples. Results of the present study indicated that dogs have BVNs. Also, suspected nerve fibers were identified among the epidural fat, running from the intervertebral foramina, that likely represent the MBSN.

CONCLUSION

These findings open up the discussion on extrapolation of treatment options employed in human medicine for "low back pain", such as BVN ablation, which is discussed in this article. Further anatomic and clinical studies of the innervation for the vertebral body, periosteum, vasculature, dorsal longitudinal ligament and anulus fibrosus are necessary to elucidate possible anatomical variants and breed differences as well as potential clinical (e.g., therapeutic) relevance.

Stem Cells and Exosomes: New Therapies for Intervertebral Disc Degeneration

Intervertebral disc degeneration (IVDD) occurs as a result of an imbalance of the anabolic and catabolic processes in the intervertebral disc, leading to an alteration in the composition of the extracellular matrix (ECM), loss of nucleus pulposus (NP) cells, excessive oxidative stress and inflammation. Degeneration of the IVD occurs naturally with age, but mechanical trauma, lifestyle factors and certain genetic abnormalities can increase the likelihood of symptomatic disease progression. IVDD, often referred to as degenerative disc disease (DDD), poses an increasingly substantial financial burden due to the aging population and increasing incidence of obesity in the United States. Current treatments for IVDD include pharmacological and surgical interventions, but these lack the ability to stop the progression of disease and restore the functionality of the IVD. Biological therapies have been evaluated but show varying degrees of efficacy in reversing disc degeneration long-term. Stem cell-based therapies have shown promising results in the regeneration of the IVD, but face both biological and ethical limitations. Exosomes play an important role in intercellular communication, and stem cell-derived exosomes have been shown to maintain the therapeutic benefit of their origin cells without the associated risks. This review highlights the current state of research on the use of stem-cell derived exosomes in the treatment of IVDD.

A comprehensive tool box for large animal studies of intervertebral disc degeneration

Preclinical studies involving large animal models aim to recapitulate the clinical situation as much as possible and bridge the gap from benchtop to bedside. To date, studies investigating intervertebral disc (IVD) degeneration and regeneration in large animal models have utilized a wide spectrum of methodologies for outcome evaluation. This paper aims to consolidate available knowledge, expertise, and experience in large animal preclinical models of IVD degeneration to create a comprehensive tool box of anatomical and functional outcomes. Herein, we present a Large Animal IVD Scoring Algorithm based on three scales: macroscopic (gross morphology, imaging, and biomechanics), microscopic (histological, biochemical, and biomolecular analyses), and clinical (neurologic state, mobility, and pain). The proposed algorithm encompasses a stepwise evaluation on all three scales, including spinal pain assessment, and relevant structural and functional components of IVD health and disease. This comprehensive tool box was designed for four commonly used preclinical large animal models (dog, pig, goat, and sheep) in order to facilitate standardization and applicability. Furthermore, it is intended to facilitate comparison across studies while discerning relevant differences between species within the context of outcomes with the goal to enhance veterinary clinical relevance as well. Current major challenges in pre-clinical large animal models for IVD regeneration are highlighted and insights into future directions that may improve the understanding of the underlying pathologies are discussed. As such, the IVD research community can deepen its exploration of the molecular, cellular, structural, and biomechanical changes that occur with IVD degeneration and regeneration, paving the path for clinically relevant therapeutic strategies.

Biomechanical effects of a titanium intervertebral cage as a stand-alone device, and in combination with locking plates in the canine caudal cervical spine

Objective

To evaluate the change in ex vivo biomechanical properties of the canine cervical spine, due to an intervertebral cage, both as a stand‐alone device and in combination with plates.

Study Design

Experimental ex vivo study.

Animals

Cervical spinal segments (C5‐C7) from eight canine cadavers.

Methods

The range of motion (ROM) and elastic zone stiffness (EZS) of the spines were determined with a four‐point bending device in flexion/extension, lateral bending, and axial rotation for four conditions: native, discectomy, cage (at C6‐C7), and cage with plates (at C6‐C7). The disc height index (DHI) for each condition was determined using radiography.

Results

Discectomy resulted in overall increased ROM (p < .01) and EZS (p < .05) and decreased DHI (p < .005) when compared to the native condition. Placement of the cage increased DHI (p < .001) and restored total ROM during flexion/extension, lateral bending and axial rotation, and EZS during flexion/extension to the level of the native spine. Application of the plates further reduced the total ROM during flexion/extension (p < .001) and lateral bending (p < .001), but restored ROM in extension and EZS during lateral bending. No implant failure, subsidence, or significant cage migration occurred during loading.

Conclusion

An anchorless intervertebral cage used as a stand‐alone device was able to restore the disc height and spinal stability to the level of the native cervical spine, whereas the addition of plates further reduced the spinal unit mobility.

Clinical Significance

This study implies that the intervertebral cage may be used as a stand‐alone device in the spinal unit fixation in the canine cervical spine.

Multiscale Regulation of the Intervertebral Disc: Achievements in Experimental, In Silico, and Regenerative Research

Intervertebral disc (IVD) degeneration is a major risk factor of low back pain. It is defined by a progressive loss of the IVD structure and functionality, leading to severe impairments with restricted treatment options due to the highly demanding mechanical exposure of the IVD. Degenerative changes in the IVD usually increase with age but at an accelerated rate in some individuals. To understand the initiation and progression of this disease, it is crucial to identify key top-down and bottom-up regulations' processes, across the cell, tissue, and organ levels, in health and disease. Owing to unremitting investigation of experimental research, the comprehension of detailed cell signaling pathways and their effect on matrix turnover significantly rose. Likewise, in silico research substantially contributed to a holistic understanding of spatiotemporal effects and complex, multifactorial interactions within the IVD. Together with important achievements in the research of biomaterials, manifold promising approaches for regenerative treatment options were presented over the last years. This review provides an integrative analysis of the current knowledge about (1) the multiscale function and regulation of the IVD in health and disease, (2) the possible regenerative strategies, and (3) the in silico models that shall eventually support the development of advanced therapies.

Animal models of regenerative medicine for biological treatment approaches of degenerative disc diseases

Degenerative disc disease (DDD) is a painful, chronic and progressive disease, which is characterized by inflammation, structural and biological deterioration of the intervertebral disc (IVD) tissues. DDD is specified as cell-, age-, and genetic-dependent degenerative process that can be accelerated by environmental factors. It is one of the major causes of chronic back pain and disability affecting millions of people globally. Current treatment options, such as physical rehabilitation, pain management, and surgical intervention, can provide only temporary pain relief. Different animal models have been used to study the process of IVD degeneration and develop therapeutic options that may restore the structure and function of degenerative discs. Several research works have depicted considerable progress in understanding the biological basis of disc degeneration and the therapeutic potentials of cell transplantation, gene therapy, applications of supporting biomaterials and bioactive factors, or a combination thereof. Since animal models play increasingly significant roles in treatment approaches of DDD, we conducted an electronic database search on Medline through June 2020 to identify, compare, and discuss publications regarding biological therapeutic approaches of DDD that based on intradiscal treatment strategies. We provide an up-to-date overview of biological treatment strategies in animal models including mouse, rat, rabbit, porcine, bovine, ovine, caprine, canine, and primate models. Although no animal model could profoundly reproduce the clinical conditions in humans; animal models have played important roles in specifying our knowledge about the pathophysiology of DDD. They are crucial for developing new therapy approaches for clinical applications.

"Old Drugs, New Tricks" - Local controlled drug release systems for treatment of degenerative joint disease

Osteoarthritis (OA) and chronic low back pain (CLBP) caused by intervertebral disc (IVD) degeneration are joint diseases that have become major causes for loss of quality of life worldwide. Despite the unmet need, effective treatments other than invasive, and often ineffective, surgery are lacking. Systemic administration of drugs entails suboptimal local drug exposure in the articular joint and IVD. This review provides an overview of the potency of biomaterial-based drug delivery systems as novel treatment modality, with a focus on the biological effects of drug release systems that have reached translation at the level of in vivo models and relevant ex vivo models. These studies have shown encouraging results of biomaterial-based local delivery of several types of drugs, mostly inhibitors of inflammatory cytokines or other degenerative factors. Prevention of inflammation and degeneration and pain relief was achieved, although mainly in small animal models, with interventions applied at an early disease stage. Less convincing data were obtained with the delivery of regenerative factors. Multidisciplinary efforts towards tackling the discord between in vitro and in vivo release, combined with adaptations in the regulatory landscape may be needed to enhance safe and expeditious introduction of more and more effective controlled release-based treatments with the OA and CLBP patients.

Characterization of biomaterials intended for use in the nucleus pulposus of degenerated intervertebral discs

Biomaterials for regeneration of the intervertebral disc must meet complex requirements conforming to biological, mechanical and clinical demands. Currently no consensus on their characterization exists. It is crucial to identify parameters and their method of characterization for accurate assessment of their potential efficacy, keeping in mind the translation towards clinical application. This review systematically analyses the characterization techniques of biomaterial systems that have been used for nucleus pulposus (NP) restoration and regeneration. Substantial differences in the approach towards assessment became evident, hindering comparisons between different materials with respect to their suitability for NP restoration and regeneration. We have analysed the current approaches and identified parameters necessary for adequate biomaterial characterization, with the clinical goal of functional restoration and biological regeneration of the NP in mind. Further, we provide guidelines and goals for their measurement. STATEMENT OF SIGNIFICANCE: Biomaterials intended for restoration of regeneration of the nucleus pulposus within the intervertebral disc must meet biological, biomechanical and clinical demands. Many materials have been investigated, but a lack of consensus on which parameters to evaluate leads to difficulties in comparing materials as well as mostly partial characterization of the materials in question. A gap between current methodology and clinically relevant and meaningful characterization is prevalent. In this article, we identify necessary methods and their implementation for complete biomaterial characterization in the context of clinical applicability. This will allow for a more unified approach to NP-biomaterials research within the field as a whole and enable comparative analysis of novel materials yet to be developed.

Injectable Biologics for the Treatment of Degenerative Disc Disease

Purpose of Review

Spinal pain and associated disability is a leading cause of morbidity worldwide that has a strong association with degenerative disc disease (DDD). Biologically based therapies to treat DDD face significant challenges posed by the unique milieu of the environment within the intervertebral disc, and many promising therapies are in the early stages of development. Patient selection, reasonable therapeutic goals, approach, and timing will need to be discerned to successfully translate potential therapeutics. This review provides a brief overview of the status of intradiscal biologic therapies.

Recent Findings

Proposed systemic delivery of therapeutic agents has not progressed very much in large part due to the risk of adverse events in remote tissues plus the very limited vascular supply and therefore questionable delivery to the intervertebral disc nucleus pulposus. Intradiscal delivery of therapeutic proteins shows good potential for clinical trials and translation with encouraging results from large animal pre-clinical studies plus an enhanced understanding of the biology of DDD. There are a few cell-based therapies currently under pre-clinical and clinical trial investigation; however, these attempts continue to be hampered by unknown if any, mechanism of action, no downstream detection of transplanted cells, mixed results concerning efficacy, small sample numbers, and a lack of objective evidence of pain mediation.

Summary

Treatment of DDD using biologically based therapeutics is a widely sought-after goal; however, potential therapies need to address pain and disability in larger, well-controlled studies.

Bone Morphogenetic Proteins for Nucleus Pulposus Regeneration

Matrix production by nucleus pulposus (NP) cells, the cells residing in the center of the intervertebral disc, can be stimulated by growth factors. Bone morphogenetic proteins (BMPs) hold great promise. Although BMP2 and BMP7 have been used most frequently, other BMPs have also shown potential for NP regeneration. Heterodimers may be more potent than single homodimers, but it is not known whether combinations of homodimers would perform equally well. In this study, we compared BMP2, BMP4, BMP6, and BMP7, their combinations and heterodimers, for regeneration by human NP cells. The BMPs investigated induced variable matrix deposition by NP cells. BMP4 was the most potent, both in the final neotissue glysosaminoglycan content and incorporation efficiency. Heterodimers BMP2/6H and BMP2/7H were more potent than their respective homodimer combinations, but not the BMP4/7H heterodimer. The current results indicate that BMP4 might have a high potential for regeneration of the intervertebral disc. Moreover, the added value of BMP heterodimers over their respective homodimer BMP combinations depends on the BMP combination applied.

Application of Cytokines of the Bone Morphogenetic Protein (BMP) Family in Spinal Fusion - Effects on the Bone, Intervertebral Disc and Mesenchymal Stromal Cells

Low back pain is a prevalent socio-economic burden and is often associated with damaged or degenerated intervertebral discs (IVDs). When conservative therapy fails, removal of the IVD (discectomy), followed by intersomatic spinal fusion, is currently the standard practice in clinics. The remaining space is filled with an intersomatic device (cage) and with bone substitutes to achieve disc height compensation and bone fusion. As a complication, in up to 30% of cases, spinal non-fusions result in a painful pseudoarthrosis. Bone morphogenetic proteins (BMPs) have been clinically applied with varied outcomes. Several members of the BMP family, such as BMP2, BMP4, BMP6, BMP7, and BMP9, are known to induce osteogenesis. Questions remain on why hyper-physiological doses of BMPs do not show beneficial effects in certain patients. In this respect, BMP antagonists secreted by mesenchymal cells, which might interfere with or block the action of BMPs, have drawn research attention as possible targets for the enhancement of spinal fusion or the prevention of non-unions. Examples of these antagonists are noggin, gremlin1 and 2, chordin, follistatin, BMP3, and twisted gastrulation. In this review, we discuss current evidence of the osteogenic effects of several members of the BMP family on osteoblasts, IVD cells, and mesenchymal stromal cells. We consider in vitro and in vivo studies performed in human, mouse, rat, and rabbit related to BMP and BMP antagonists in the last two decades. We give insights into the effects that BMP have on the ossification of the spine. Furthermore, the benefits, pitfalls, and possible safety concerns using these cytokines for the improvement of spinal fusion are discussed.

Is Osteogenic Differentiation of Human Nucleus Pulposus Cells a Possibility for Biological Spinal Fusion?

OBJECTIVE

The purpose of this study was to investigate whether a simple, biologically robust method for inducing calcification of degenerate intervertebral discs (IVD) could be developed to provide an alternative treatment for patients requiring spinal fusion.

DESIGN

Nucleus pulposus (NP) cells isolated from 14 human IVDs were cultured in monolayer and exposed to osteogenic medium, 1,25-dihydroxyvitamin D₃ (VitD₃), parathyroid hormone (PTH), and bone morphogenic proteins (BMPs) 2/7 to determine if they could become osteogenic. Similarly explant cultures of IVDs from 11 patients were cultured in osteogenic media with and without prior exposure to VitD₃ and BMP-2. Osteogenic differentiation was assessed by alkaline phosphatase activity and areas of calcification identified by alizarin red or von Kossa staining. Expression of osteogenic genes during monolayer culture was determined using polymerase chain reaction and explant tissues assessed for BMP inhibitors. Human bone marrow-derived mesenchymal stromal cells (MSCs) were used for comparison.

RESULTS

Standard osteogenic media was optimum for promoting mineralization by human NP cells in monolayer. Some osteogenic differentiation was observed with 10 nM VitD₃, but none following application of PTH or BMPs. Regions of calcification were detected in 2 of the eleven IVD tissue explants, one cultured in osteogenic media and one with the addition of VitD₃ and BMP-2.

CONCLUSIONS

Human NP cells can become osteogenic in monolayer and calcification of the extracellular matrix can also occur, although not consistently. Inhibitory factors within either the cells or the extracellular matrix may hinder osteogenesis, indicating that a robust biological fusion at this time requires further optimization.

Hedgehog proteins and parathyroid hormone-related protein are involved in intervertebral disc maturation, degeneration, and calcification

Parathyroid hormone-related protein (PTHrP) and hedgehog signaling play an important role in chondrocyte development, (hypertrophic) differentiation, and/or calcification, but their role in intervertebral disc (IVD) degeneration is unknown. Better understanding their involvement may provide therapeutic clues for low back pain due to IVD degeneration. Therefore, this study aimed to explore the role of PTHrP and hedgehog proteins in postnatal canine and human IVDs during the aging/degenerative process. The expression of PTHrP, hedgehog proteins and related receptors was studied during the natural loss of the notochordal cell (NC) phenotype during IVD maturation using tissue samples and de-differentiation in vitro and degeneration by real-time quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry. Correlations between their expression and calcification levels (Alizarin Red S staining) were determined. In addition, the effect of PTHrP and hedgehog proteins on canine and human chondrocyte-like cells (CLCs) was determined in vitro focusing on the propensity to induce calcification. The expression of PTHrP, its receptor (PTHR1) and hedgehog receptors decreased during loss of the NC phenotype. N-terminal (active) hedgehog (Indian hedgehog/Sonic hedgehog) protein expression did not change during maturation or degeneration, whereas expression of PTHrP, PTHR1 and hedgehog receptors increased during IVD degeneration. Hedgehog and PTHR1 immunopositivity were increased in nucleus pulposus tissue with abundant vs no/low calcification. In vitro, hedgehog proteins facilitated calcification in CLCs, whereas PTHrP did not affect calcification levels. In conclusion, hedgehog and PTHrP expression is present in healthy and degenerated IVDs. Hedgehog proteins had the propensity to induce calcification in CLCs from degenerated IVDs, indicating that in the future, inhibiting hedgehog signaling could be an approach to inhibit calcification during IVD degeneration.

Lessons learned from intervertebral disc pathophysiology to guide rational design of sequential delivery systems for therapeutic biological factors

Intervertebral disc (IVD) degeneration has been associated with low back pain, which is a major musculoskeletal disorder and socio-economic problem that affects as many as 600 million patients worldwide. Here, we first review the current knowledge of IVD physiology and physiopathological processes in terms of homeostasis regulation and consecutive events that lead to tissue degeneration. Recent progress with IVD restoration by anti-catabolic or pro-anabolic approaches are then analyzed, as are the design of macro-, micro-, and nano-platforms to control the delivery of such therapeutic agents. Finally, we hypothesize that a sequential delivery strategy that i) firstly targets the inflammatory, pro-catabolic microenvironment with release of anti-inflammatory or anti-catabolic cytokines; ii) secondly increases cell density in the less hostile microenvironment by endogenous cell recruitment or exogenous cell injection, and finally iii) enhances cellular synthesis of extracellular matrix with release of pro-anabolic factors, would constitute an innovative yet challenging approach to IVD regeneration.

Intervertebral Disc Nucleus Repair: Hype or Hope?

Chronic back pain is a common disability, which is often accredited to intervertebral disc degeneration. Gold standard interventions such as spinal fusion, which are mainly designed to mechanically seal the defect, frequently fail to restore the native biomechanics. Moreover, artificial implants have limited success as a repair strategy, as they do not alter the underlying disease and fail to promote tissue integration and subsequent native biomechanics. The reported high rates of spinal fusion and artificial disc implant failure have pushed intervertebral disc degeneration research in recent years towards repair strategies. Intervertebral disc repair utilizing principles of tissue engineering should theoretically be successful, overcoming the inadequacies of artificial implants. For instance, advances in the development of scaffolds aided with cells and growth factors have opened up new possibilities for repair strategies. However, none has reached the stage of clinical trials in humans. In this review, we describe the hitches encountered in the musculoskeletal field and summarize recent advances in designing tissue-engineered constructs for promoting nucleus pulposus repair. Additionally, the review focuses on the effect of biomaterial aided with cells and growth factors on achieving effective functional reparative potency, highlighting the ways to enhance the efficacy of these treatments.

Intervertebral disc regeneration: From cell therapy to the development of novel bioinspired endogenous repair strategies

Low back pain (LBP), frequently associated with intervertebral disc (IVD) degeneration, is a major public health concern. LBP is currently managed by pharmacological treatments and, if unsuccessful, by invasive surgical procedures, which do not counteract the degenerative process. Considering that IVD cell depletion is critical in the degenerative process, the supplementation of IVD with reparative cells, associated or not with biomaterials, has been contemplated. Recently, the discovery of reparative stem/progenitor cells in the IVD has led to increased interest in the potential of endogenous repair strategies. Recruitment of these cells by specific signals might constitute an alternative strategy to cell transplantation. Here, we review the status of cell-based therapies for treating IVD degeneration and emphasize the current concept of endogenous repair as well as future perspectives. This review also highlights the challenges of the mobilization/differentiation of reparative progenitor cells through the delivery of biologics factors to stimulate IVD regeneration.

Safety of intradiscal delivery of triamcinolone acetonide by a poly(esteramide) microsphere platform in a large animal model of intervertebral disc degeneration

BACKGROUND CONTEXT

Local corticosteroids have been used to relieve symptoms of chronic low back pain, although treatment effects have been shown to wear off relatively fast. Prolonging corticosteroid presence by controlled release from biomaterials may allow for longer pain relief while circumventing adverse effects such as high bolus dosages.

PURPOSE

The purpose of this study was to evaluate the safety and efficacy of intradiscal controlled release of triamcinolone acetonide (TAA) by poly(esteramide) microspheres in a canine degenerated intervertebral disc (IVD) model.

STUDY DESIGN

In a preclinical experimental large animal model, the effect of prolonged glucocorticoid exposure on disc degeneration was evaluated.

METHODS

Degeneration was accelerated by nucleotomy of lumbar IVDs of Beagle dogs. After 4 weeks, microspheres loaded with 8.4 µg TAA, and 0.84mg TAA were administered to the degenerated IVDs by intradiscal injection (n=6 per group). Empty microspheres (n=6) and all adjacent non-nucleotomized noninjected IVDs were included as controls (n=24). Immediately prior to TAA administration and after 12 weeks, magnetic resonance imaging was performed. Degenerative changes were evaluated by disc height index, Pfirrmann grading, T1ρ and T2 mapping values, postmortem CT scans, macroscopic and microscopic grading, and biochemical/immunohistochemical analysis of inflammation and extracellular matrix content. In addition, nerve growth factor (NGF) protein expression, a biomarker for pain, was scored in nucleus pulposus (NP) tissues. The study was funded by a research grant from Health Holland (1.3million euros = 1.5million US dollars).

RESULTS

Macroscopic evaluation and CT images postmortem were consistent with mild disc degeneration. Other abnormalities were not observed. Nucleotomy-induced degeneration and inflammation was mild, reflected by moderate Pfirrmann grades and PGE₂ levels. Regardless of TAA dosage, local sustained delivery did not affect disc height index nor Pfirrmann grading, T1ρ and T2 mapping values, PGE₂ tissue levels, collagen, GAG, and DNA content. However, the low dosage of TAA microspheres significantly reduced NGF immunopositivity in degenerated NP tissue.

CONCLUSIONS

This is the first in vivo application in a preclinical large animal model of a controlled release formulation of corticosteroids in mild IVD degeneration. Sustained release of TAA locally in the IVD appeared safe and reduced NGF expression, suggesting its potential applicability for pain relief, although beneficial effects were absent on tissue degeneration.

CLINICAL SIGNIFICANCE

The present platform seems to be promising in extending the local controlled delivery of TAA with the potency to provide long-standing analgesia in the subset of LBP patients suffering from discogenic pain.

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.

The future of disc surgery and regeneration

Low back and neck pain are among the top contributors for years lived with disability, causing patients to seek substantial non-operative and operative care. Intervertebral disc herniation is one of the most common spinal pathologies leading to low back pain. Patient comorbidities and other risk factors contribute to the onset and magnitude of disc herniation. Spine fusions have been the treatment of choice for disc herniation, due to the conflicting evidence on conservative treatments. However, re-operation and costs have been among the main challenges. Novel technologies including cage surface modifications, biologics, and 3D printing hold a great promise. Artificial disc replacement has demonstrated reduced rates of adjacent segment degeneration, need for additional surgery, and better outcomes. Non-invasive biological approaches are focused on cell-based therapies, with data primarily from preclinical settings. High-quality comparative studies are needed to evaluate the efficacy and safety of novel technologies and biological therapies.

Biomaterials for intervertebral disc regeneration: Current status and looming challenges

A biomaterial-based strategy is employed to regenerate the degenerated intervertebral disc, which is considered a major generator of neck and back pain. Although encouraging enhancements in the anatomy and kinematics of the degenerative disc have been gained by biomaterials with various formulations in animals, the number of biomaterials tested in humans is rare. At present, most studies that involve the use of newly developed biomaterials focus on regeneration of the degenerative disc, but not pain relief. In this review, we summarise the current state of the art in the field of biomaterial-based regeneration or repair for the nucleus pulposus, annulus fibrosus, and total disc transplantation in animals and humans, and we then provide essential suggestions for the development and clinical translation of biomaterials for disc regeneration. It is important for researchers to consider the commonly neglected issues instead of concentrating solely on biomaterial development and fabrication.

Leaping the hurdles in developing regenerative treatments for the intervertebral disc from preclinical to clinical

Chronic back and neck pain is a prevalent disability, often caused by degeneration of the intervertebral disc. Because current treatments for this condition are less than satisfactory, a great deal of effort is being applied to develop new solutions, including regenerative strategies. However, the path from initial promising idea to clinical use is fraught with many hurdles to overcome. Many of the keys to success are not necessarily linked to science or innovation. Successful translation to clinic will also rely on planning and awareness of the hurdles. It will be essential to plan your entire path to clinic from the outset and to do this with a multidisciplinary team. Take advice early on regulatory aspects and focus on generating the proof required to satisfy regulatory approval. Scientific demonstration and societal benefits are important, but translation cannot occur without involving commercial parties, which are instrumental to support expensive clinical trials. This will only be possible when intellectual property can be protected sufficiently to support a business model. In this manner, commercial, societal, medical, and scientific partners can work together to ultimately improve patient health. Based on literature surveys and experiences of the co-authors, this opinion paper presents this pathway, highlights the most prominent issues and hopefully will aid in your own translational endeavors.

Short Link N promotes disc repair in a rabbit model of disc degeneration

Background

The degeneration of the intervertebral disc (IVD) is characterized by proteolytic degradation of the extracellular matrix, and its repair requires the production of an extracellular matrix with a high proteoglycan-to-collagen ratio characteristic of a nucleus pulposus (NP)-like phenotype in vivo. At the moment, there is no medical treatment to reverse or even retard disc degeneration. The purpose of the present study was to determine if a low dose of short link N (sLN), a recently discovered fragment of the link N peptide, could behave in a manner similar to that of link N in restoring the proteoglycan content and proteoglycan-to-collagen ratio of the disc in a rabbit model of IVD degeneration, as an indication of its potential therapeutic benefit in reversing disc degeneration.

Methods

Adolescent New Zealand white rabbits received an annular puncture with an 18-gauge needle into two noncontiguous discs to induce disc degeneration. Two weeks later, either saline (10 μL) or sLN (25 μg in 10 μL saline) was injected into the center of the NP. The sLN concentration was empirically chosen at a lower molar concentration equivalent to half that of link N (100 μg in 10 μL). The effect on radiographic, biochemical and histologic changes were evaluated.

Results

Following needle puncture, disc height decreased by about 25–30% within 2 weeks and maintained this loss for the duration of the 12-week study; a single 25-μg sLN injection at 2 weeks partially restored this loss in disc height. sLN injection led to an increase in glycosaminoglycans (GAG) content 12 weeks post-injection in both the NP and annulus fibrosus (AF). There was a trend towards maintaining control disc collagen-content with sLN supplementation and the GAG-to-collagen ratio in the NP was increased when compared to the saline group.

Conclusions

When administered to the degenerative disc in vivo, sLN injection leads to an increase in proteoglycan content and a trend towards maintaining control disc collagen content in both the NP and AF. This is similar to link N when it is administered to the degenerative disc. Thus, pharmacologically, sLN supplementation could be a novel therapeutic approach for treating disc degeneration.

Intradiscal delivery of celecoxib-loaded microspheres restores intervertebral disc integrity in a preclinical canine model

Low back pain, related to degeneration of the intervertebral disc (IVD), affects millions of people worldwide. Clinical studies using oral cyclooxygenase-2 (COX-2) inhibitors have shown beneficial effects, although side-effects were reported. Therefore, intradiscal delivery of nonsteroidal anti-inflammatory drugs can be an alternative treatment strategy to halt degeneration and address IVD-related pain. In the present study, the controlled release and biologic potency of celecoxib, a selective COX-2 inhibitor, from polyesteramide microspheres was investigated in vitro. In addition, safety and efficacy of injection of celecoxib-loaded microspheres were evaluated in vivo in a canine IVD degeneration model. In vitro, a sustained release of celecoxib was noted for over 28 days resulting in sustained inhibition of inflammation, as indicated by decreased prostaglandin E₂ (PGE₂) production, and anti-catabolic effects in nucleus pulposus (NP) cells from degenerated IVDs on qPCR. In vivo, there was no evidence of adverse effects on computed tomography and magnetic resonance imaging or macroscopic evaluation of IVDs. Local and sustained delivery of celecoxib prevented progression of IVD degeneration corroborated by MRI, histology, and measurement of NP proteoglycan content. Furthermore, it seemed to harness inflammation as indicated by decreased PGE₂ tissue levels and decreased neuronal growth factor immunopositivity, providing indirect evidence that local delivery of a COX-2 inhibitor could also address pain related to IVD degeneration. In conclusion, intradiscal controlled release of celecoxib from polyesteramide microspheres prevented progression of IVD degeneration both in vitro and in vivo. Follow-up studies are warranted to determine the clinical efficacy of celecoxib-loaded PEAMs in chronic back pain.

Biologic canine and human intervertebral disc repair by notochordal cell-derived matrix: from bench towards bedside

The socioeconomic burden of chronic back pain related to intervertebral disc (IVD) disease is high and current treatments are only symptomatic. Minimally invasive strategies that promote biological IVD repair should address this unmet need. Notochordal cells (NCs) are replaced by chondrocyte-like cells (CLCs) during IVD maturation and degeneration. The regenerative potential of NC-secreted substances on CLCs and mesenchymal stromal cells (MSCs) has already been demonstrated. However, identification of these substances remains elusive. Innovatively, this study exploits the regenerative NC potential by using healthy porcine NC-derived matrix (NCM) and employs the dog as a clinically relevant translational model. NCM increased the glycosaminoglycan and DNA content of human and canine CLC aggregates and facilitated chondrogenic differentiation of canine MSCs in vitro. Based on these results, NCM, MSCs and NCM+MSCs were injected in mildly (spontaneously) and moderately (induced) degenerated canine IVDs in vivo and, after six months of treatment, were analyzed. NCM injected in moderately (induced) degenerated canine IVDs exerted beneficial effects at the macroscopic and MRI level, induced collagen type II-rich extracellular matrix production, improved the disc height, and ameliorated local inflammation. MSCs exerted no (additive) effects. In conclusion, NCM induced in vivo regenerative effects on degenerated canine IVDs. NCM may, comparable to demineralized bone matrix in bone regeneration, serve as ‘instructive matrix’, by locally releasing growth factors and facilitating tissue repair. Therefore, intradiscal NCM injection could be a promising regenerative treatment for IVD disease, circumventing the cumbersome identification of bioactive NC-secreted substances.

The chondrodystrophic dog: A clinically relevant intermediate-sized animal model for the study of intervertebral disc-associated spinal pain

Low back pain (LBP) is the leading cause of disability worldwide, with an estimated 80% of the American population suffering from a painful back condition at some point during their lives. The most common cause of LBP is intervertebral disc (IVD) degeneration (IVDD), a condition that can be difficult to treat, either surgically or medically, with current available therapies. Thus, understanding the pathological mechanisms of IVDD and developing novel treatments are critical for improving outcome and quality of life in people living with LBP. While experimental animal models provide valuable mechanistic insight, each model has limitations that complicate translation to the clinical setting. This review focuses on the chondrodystrophic canine clinical model of IVDD as a promising model to assess IVD-associated spinal pain and translational therapeutic strategies for LBP. The canine IVD, while smaller in size than human, goat, ovine, and bovine IVDs, is larger than most other small animal IVDD models and undergoes maturational changes similar to those of the human IVD. Furthermore, both dogs and humans develop painful IVDD as a spontaneous process, resulting in similar characteristic pathologies and clinical signs. Future exploration of the canine model as a model of IVD-associated spinal pain and biological treatments using the canine clinical model will further demonstrate its translational capabilities with the added ethical benefit of treating an existing veterinary patient population with IVDD.

Intradiscal application of a PCLA-PEG-PCLA hydrogel loaded with celecoxib for the treatment of back pain in canines: What's in it for humans?

Chronic low back pain is a common clinical problem in both the human and canine population. Current pharmaceutical treatment often consists of oral anti-inflammatory drugs to alleviate pain. Novel treatments for degenerative disc disease focus on local application of sustained released drug formulations. The aim of this study was to determine safety and feasibility of intradiscal application of a poly(ε-caprolactone-co-lactide)-b-poly(ethylene glycol)-bpoly(ε-caprolactone-co-lactide) PCLA-PEG-PCLA hydrogel releasing celecoxib, a COX-2 inhibitor. Biocompatibility was evaluated after subcutaneous injection in mice, and safety of intradiscal injection of the hydrogel was evaluated in experimental dogs with early spontaneous intervertebral disc (IVD) degeneration. COX-2 expression was increased in IVD samples surgically obtained from canine patients, indicating a role of COX-2 in clinical IVD disease. Ten client-owned dogs with chronic low back pain related to IVD degeneration received an intradiscal injection with the celecoxib-loaded hydrogel. None of the dogs showed adverse reactions after intradiscal injection. The hydrogel did not influence magnetic resonance imaging signal at long-term follow-up. Clinical improvement was achieved by reduction of back pain in 9 of 10 dogs, as was shown by clinical examination and owner questionnaires. In 3 of 10 dogs, back pain recurred after 3 months. This study showed the safety and effectiveness of intradiscal injections in vivo with a thermoresponsive PCLA-PEG-PCLA hydrogel loaded with celecoxib. In this set-up, the dog can be used as a model for the development of novel treatment modalities in both canine and human patients with chronic low back pain.

Link-N: The missing link towards intervertebral disc repair is species-specific

Introduction

Degeneration of the intervertebral disc (IVD) is a frequent cause for back pain in humans and dogs. Link-N stabilizes proteoglycan aggregates in cartilaginous tissues and exerts growth factor-like effects. The human variant of Link-N facilitates IVD regeneration in several species in vitro by inducing Smad1 signaling, but it is not clear whether this is species specific. Dogs with IVD disease could possibly benefit from Link-N treatment, but Link-N has not been tested on canine IVD cells. If Link-N appears to be effective in canines, this would facilitate translation of Link-N into the clinic using the dog as an in vivo large animal model for human IVD degeneration.

Materials and methods

This study’s objective was to determine the effect of the human and canine variant of Link-N and short (s) Link-N on canine chondrocyte-like cells (CLCs) and compare this to those on already studied species, i.e. human and bovine CLCs. Extracellular matrix (ECM) production was determined by measuring glycosaminoglycan (GAG) content and histological evaluation. Additionally, the micro-aggregates’ DNA content was measured. Phosphorylated (p) Smad1 and -2 levels were determined using ELISA.

Results

Human (s)Link-N induced GAG deposition in human and bovine CLCs, as expected. In contrast, canine (s)Link-N did not affect ECM production in human CLCs, while it mainly induced collagen type I and II deposition in bovine CLCs. In canine CLCs, both canine and human (s)Link-N induced negligible GAG deposition. Surprisingly, human and canine (s)Link-N did not induce Smad signaling in human and bovine CLCs. Human and canine (s)Link-N only mildly increased pSmad1 and Smad2 levels in canine CLCs.

Conclusions

Human and canine (s)Link-N exerted species-specific effects on CLCs from early degenerated IVDs. Both variants, however, lacked the potency as canine IVD regeneration agent. While these studies demonstrate the challenges of translational studies in large animal models, (s)Link-N still holds a regenerative potential for humans.

Bedside to bench and back to bedside: Translational implications of targeted intervertebral disc therapeutics

Spinal pain and associated disability is a leading cause of morbidity worldwide that has a strong association with degenerative disc disease (DDD). DDD can begin in early–late adolescence and has a variable course. Biologically based therapies to treat DDD face significant challenges posed by the unique milieu of the environment within the intervertebral discs. Many potential promising therapies are still in the early stages of development with a hostile microenvironment within the disc presenting unique challenges.

The translational potential of this article: Patient selection, reasonable therapeutic goals, approach, and timing will need to be discerned in order to successfully translate potential therapeutics.

Molecular Therapy for Degenerative Disc Disease: Clues from Secretome Analysis of the Notochordal Cell-Rich Nucleus Pulposus

Degenerative disc disease (DDD) is associated with spinal pain often leading to long-term disability. However, the non-chondrodystrophic canine intervertebral disc is protected from the development of DDD, ostensibly due to its retention of notochordal cells (NC) in the nucleus pulposus (NP). In this study, we hypothesized that secretome analysis of the NC-rich NP will lead to the identification of key proteins that delay the onset of DDD. Using mass-spectrometry, we identified 303 proteins including components of TGFβ- and Wnt-signaling, anti-angiogeneic factors and proteins that inhibit axonal ingrowth in the bioactive fractions of serum free, notochordal cell derived conditioned medium (NCCM). Ingenuity Pathway Analysis revealed TGFβ1 and CTGF as major hubs in protein interaction networks. In vitro treatment with TGFβ1 and CTGF promoted the synthesis of healthy extra-cellular matrix proteins, increased cell proliferation and reduced cell death in human degenerative disc NP cells. A single intra-discal injection of recombinant TGFβ1 and CTGF proteins in a pre-clinical rat-tail disc injury model restored the NC and stem cell rich NP. In conclusion, we demonstrate the potential of TGFβ1 and CTGF to mitigate the progression of disc degeneration and the potential use of these molecules in a molecular therapy to treat the degenerative disc.

Inorganic polyphosphates enhances nucleus pulposus tissue formation in vitro

Disc degeneration is associated with low back pain for which currently there is no optimal therapy so there is a great need to identify new treatment approaches. Inorganic polyphosphates (polyP) are linear polymers of orthophosphate units varying in chain length and present in many cell types. As polyP has anabolic effects on chondrocytes, we hypothesized that polyP treatment would enhance matrix accumulation by nucleus pulposus (NP) cells. NP cells isolated from bovine caudal discs were grown in 3D culture under normoxic or in select experiments under hypoxic conditions, in the presence or absence of various concentrations and sizes of polyP. Gene expression was determined using RT-PCR. Matrix accumulation was quantified by measuring proteoglycan and collagen contents. DAPI fluorescence shift was used to stain for polyP in tissue. DAPI staining showed polyP present predominantly in the pericellular region of in vitro formed tissue. PolyP treatment enhanced matrix accumulation in a concentration and chain length dependant manner. NP cells exposed to polyP-22 (22 phosphate units length) showed an increase in gene expression of aggrecan, Collagen II, Sox 9, and MMP-13 which was maintained for the 14 days of culture. This suggests that polyP may enhance NP tissue formation in vitro by upregulating the expression of matrix genes. As polyP enhances proteoglycan accumulation even under hypoxic conditions, this raises the possibility that polyP may be a novel treatment to induce NP regeneration. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:41-50, 2017.

Increased caveolin-1 in intervertebral disc degeneration facilitates repair

Background

Preceding intervertebral disc (IVD) degeneration, the cell phenotype in the nucleus pulposus (NP) shifts from notochordal cells (NCs) to chondrocyte-like cells (CLCs). Microarray analysis showed a correlation between caveolin-1 expression and the phenotypic transition of NCs to CLCs. With a clinical directive in mind, the aim of this study was to determine the role of caveolin-1 in IVD degeneration. As a scaffolding protein, caveolin-1 influences several signaling pathways, and transforming growth factor (TGF)-β receptors have been demonstrated to colocalize with caveolin-1. Therefore, the hypothesis of this study was that caveolin-1 facilitates repair by enhancing TGF-β signaling in the IVD.

Methods

Protein expression (caveolin-1, apoptosis, progenitor cell markers, extracellular matrix, and phosphorylated Smad2 [pSmad2]) was determined in IVDs of wild-type (WT) and caveolin-1-null mice and canine IVDs of different degeneration grades (immunofluorescence, immunohistochemistry, and TUNEL assay). Canine/human CLC microaggregates were treated with chondrogenic medium alone or in combination with caveolin-1 scaffolding domain (CSD) peptide and/or caveolin-1 silencing RNA. After 28 days, gene and protein expression profiles were determined.

Results

The NP of WT mice was rich in viable NCs, whereas the NP of caveolin-1-null mice contained more collagen-rich extracellular matrix and fewer cells, together with increased progenitor cell marker expression, pSmad2 TGF-β signaling, and high apoptotic activity. During canine IVD degeneration, caveolin-1 expression and apoptotic activity increased. In vitro caveolin-1 silencing decreased the CLC microaggregate glycosaminoglycan (GAG) content, which could be rescued by CSD treatment. Furthermore, CSD increased TGF-β/pSmad2 signaling at gene and protein expression levels and enhanced the anabolic effects of TGF-β₁, reflected in increased extracellular matrix deposition by the CLCs.

Conclusions

Caveolin-1 plays a role in preservation of the NC phenotype. Additionally, it may be related to CLC apoptosis, given its increased expression in degenerated IVDs. Nevertheless, CSD enhanced CLC GAG deposition in vitro, and hence the increased caveolin-1 expression during IVD degeneration may also facilitate an ultimate attempt at repair. Further studies are needed to investigate how caveolin-1 modifies other signaling pathways and facilitates IVD repair.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-0960-y) contains supplementary material, which is available to authorized users.

Safety of intradiscal injection and biocompatibility of polyester amide microspheres in a canine model predisposed to intervertebral disc degeneration

Repair of degenerated intervertebral discs (IVD) might be established via intradiscal delivery of biologic therapies. Polyester amide polymers (PEA) were evaluated for in vitro cytotoxicity and in vivo biocompatibility, and thereafter intradiscal application of PEA microspheres (PEAMs) in a canine model predisposed to IVD degeneration at long-term (6 months) follow-up. PEA extracts did not induce cytotoxicity in mouse fibroblast cells (microscopy and XTT assay), while a slight foreign body reaction was demonstrated by histopathology after intramuscular implantation in rabbits. Intradiscal injection of a volume of 40 µL through 26 and 27G needles induced no degenerative changes in acanine model susceptible to IVD disease. Although sham-injected IVDs showed increased CAV1 expression compared with noninjected IVDs, which may indicate increased cell senescence, these findings were not supported by immunohistochemistry, biomolecular analysis of genes related to apoptosis, biochemical and histopathological results. PEAM-injected IVDs showed significantly higher BAX/BCL2 ratio vs sham-injected IVDs suggestive of an anti-apoptotic effect of the PEAMs. These findings were not supported by other analyses (clinical signs, disc height index, T2 values, biomolecular and biochemical analyses, and IVD histopathology). PEAs showed a good cytocompatibility and biocompatibility. PEAMs are considered safe sustained release systems for intradiscal delivery of biological treatments. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 707-714, 2017.

Osteogenic protein 1 does not stimulate a regenerative effect in cultured human degenerated nucleus pulposus tissue

Low back pain is a major cause of disability and is heavily associated with intervertebral disc degeneration. Osteogenic protein 1 (OP-1) is a growth factor that has shown potential to regenerate the intervertebral disc in human cells and animal models. However, high doses are required, presumably due to clearance from the tissue; controlled release may be a solution to this problem. In this study, we developed a preclinical, pathophysiological human tissue explant culture model of degenerated nucleus pulposus (NP). The NP explants were cultured for 28 days and injected with 100 µg OP-1 as a bolus, or with sustained-release biodegradable microspheres loaded with 16 or 1.6 µg OP-1. After culture, the tissue explants were analysed for biochemical content [water, sulphated glycosaminoglycans (GAGs), hydroxyproline and DNA], histology, cell viability and gene expression (disc matrix anabolic and catabolic markers). Untreated degenerated NP explants lost some of their GAG content when cultured for 4 weeks, but maintained other tissue constituents. Gene expression levels were close to native values. A bolus injection of OP-1 partially restored GAG content to the native level in half of the donors, while the sustained release of OP-1 did not affect the NP explants. No effect of treatment was observed on anabolic or catabolic gene expression at day 28. These results demonstrated that the regenerative potential of OP-1 is donor dependent, and only at very high doses. This questions the clinical use of OP-1 as a regenerative agent, as these high doses may increase the incidence of complications. Copyright © 2015 John Wiley & Sons, Ltd.

The Stimulatory Effect of Notochordal Cell-Conditioned Medium in a Nucleus Pulposus Explant Culture

OBJECTIVES

Notochordal cell-conditioned medium (NCCM) has previously shown to have a stimulatory effect on nucleus pulposus cells (NPCs) and bone marrow stromal cells (BMSCs) in alginate and pellet cultures. These culture methods provide a different environment than the nucleus pulposus (NP) tissue, in which the NCCM ultimately should exert its effect. The objective of this study is to test whether NCCM stimulates NPCs within their native environment, and whether combined stimulation with NCCM and addition of BMSCs has a synergistic effect on extracellular matrix production.

METHODS

Bovine NP tissue was cultured in an artificial annulus in base medium (BM), porcine NCCM, or BM supplemented with 1 μg/mL Link N. Furthermore, BM and NCCM samples were injected with 10(6) BMSCs per NP sample. Samples were cultured for 4 weeks, and analyzed for biochemical contents (water, glycosaminoglycan [GAG], hydroxyproline, and DNA), gene expression (COL1A1, COL2A1, ACAN, and SOX9), and histology by Safranin O/Fast Green staining.

RESULTS

Culture in NCCM resulted in increased proteoglycan content compared to day 0 and BM, similar to Link N. However, only minor differences in gene expression compared to day 0 were observed. Addition of BMSCs did not result in increased GAG content, and surprisingly, DNA content in BMSC-injected groups was not higher than in the other groups after 4 weeks of culture.

DISCUSSION

This study shows that, indeed, NCCM is capable of stimulating NPC matrix production within the NP environment. The lack of increased DNA content in the BMSC-injected groups indicates that BMSCs have died over time. Identification of the bioactive factors in NCCM is crucial for further development of an NCCM-based treatment for intervertebral disc regeneration.

BMP-2 and BMP-2/7 Heterodimers Conjugated to a Fibrin/Hyaluronic Acid Hydrogel in a Large Animal Model of Mild Intervertebral Disc Degeneration

Intervertebral disc (IVD) degeneration is etiologically associated with low back pain and is currently only treated in severe cases with spinal fusion. Regenerative medicine attempts to restore degenerated tissue by means of cells, hydrogels, and/or growth factors and can therefore be used to slow, halt, or reverse the degeneration of the IVD in a minimally invasive manner. Previously, the growth factors bone morphogenetic proteins 2 and 7 (BMP-2, -7) were shown to enhance disc regeneration, in vitro and in vivo. Since BMPs have only a short in vivo half-life, and to prevent heterotopic ossification, we evaluated the use of a slow release system for BMP-2 homodimers and BMP-2/7 heterodimers for IVD regeneration. BMP growth factors were conjugated to a fibrin/hyaluronic acid (FB/HA) hydrogel and intradiscally injected in a goat model of mild IVD degeneration to study safety and efficacy. Mild degeneration was induced in five lumbar discs of seven adult Dutch milk goats, by injections with the enzyme chondroitinase ABC. After 12 weeks, discs were treated with either FB/HA-hydrogel only or supplemented with 1 or 5 μg/mL of BMP-2 or BMP-2/7. BMPs were linked to the FB/HA hydrogels using a transglutaminase moiety, to be released through an incorporated plasmin cleavage site. After another 12 weeks, goats were sacrificed and discs were assessed using radiography, MRI T2* mapping, and biochemical and histological analyses. All animals maintained weight throughout the study and no heterotopic bone formation or other adverse effects were noted during follow-up. Radiographs showed significant disc height loss upon induction of mild degeneration. MRI T2* mapping showed strong and significant correlations with biochemistry and histology as shown before. Surprisingly, no differences could be demonstrated in any parameter between intervention groups. To our knowledge, this is the first large animal study evaluating BMPs conjugated to an FB/HA-hydrogel for the treatment of mild IVD degeneration. The conjugated BMP-2 and BMP-2/7 appeared safe, but no disc regeneration was observed. Possible explanations include too low dosages, short follow-up time, and/or insufficient release of the conjugated BMPs. These aspects should be addressed in future studies.

Biocompatibility and intradiscal application of a thermoreversible celecoxib-loaded poly-N-isopropylacrylamide MgFe-layered double hydroxide hydrogel in a canine model

Introduction

Chronic low back pain due to intervertebral disc (IVD) degeneration is associated with increased levels of inflammatory mediators. Current medical treatment consists of oral anti-inflammatory drugs to alleviate pain. In this study, the efficacy and safety of a novel thermoreversible poly-N-isopropylacrylamide MgFe-layered double hydroxide (pNIPAAM MgFe-LDH) hydrogel was evaluated for intradiscal controlled delivery of the selective cyclooxygenase (COX) 2 inhibitor and anti-inflammatory drug celecoxib (CXB).

Methods

Degradation, release behavior, and the ability of a CXB-loaded pNIPAAM MgFe-LDH hydrogel to suppress prostaglandin E₂ (PGE₂) levels in a controlled manner in the presence of a proinflammatory stimulus (TNF-α) were evaluated in vitro. Biocompatibility was evaluated histologically after subcutaneous injection in mice. Safety of intradiscal application of the loaded and unloaded hydrogels was studied in a canine model of spontaneous mild IVD degeneration by histological, biomolecular, and biochemical evaluation. After the hydrogel was shown to be biocompatible and safe, an in vivo dose–response study was performed in order to determine safety and efficacy of the pNIPAAM MgFe-LDH hydrogel for intradiscal controlled delivery of CXB.

Results

CXB release correlated to hydrogel degradation in vitro. Furthermore, controlled release from CXB-loaded hydrogels was demonstrated to suppress PGE₂ levels in the presence of TNF-α. The hydrogel was shown to exhibit a good biocompatibility upon subcutaneous injection in mice. Upon intradiscal injection in a canine model, the hydrogel exhibited excellent biocompatibility based on histological evaluation of the treated IVDs. Gene expression and biochemical analyses supported the finding that no substantial negative effects of the hydrogel were observed. Safety of application was further confirmed by the absence of clinical symptoms, IVD herniation or progression of degeneration. Controlled release of CXB resulted in a nonsignificant maximal inhibition (approximately 35 %) of PGE₂ levels in the mildly degenerated canine IVDs.

Conclusions

In conclusion, this study showed biocompatibility and safe intradiscal application of an MgFe LDH-pNIPAAM hydrogel. Controlled release of CXB resulted in only limited inhibition of PGE₂ in this model with mild IVD degeneration, and further studies should concentrate on application of controlled release from this type of hydrogel in animal models with more severe IVD degeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0727-x) contains supplementary material, which is available to authorized users.