Safety assessment of intradiscal gene therapy II: effect of dosing and vector choice

Application of single and cooperative different delivery systems for the treatment of intervertebral disc degeneration

Intervertebral disc (IVD) degeneration (IDD) is the most universal pathogenesis of low back pain (LBP), a prevalent and costly medical problem across the world. Persistent low back pain can seriously affect a patient's quality of life and even lead to disability. Furthermore, the corresponding medical expenses create a serious economic burden to both individuals and society. Intervertebral disc degeneration is commonly thought to be related to age, injury, obesity, genetic susceptibility, and other risk factors. Nonetheless, its specific pathological process has not been completely elucidated; the current mainstream view considers that this condition arises from the interaction of multiple mechanisms. With the development of medical concepts and technology, clinicians and scientists tend to intervene in the early or middle stages of intervertebral disc degeneration to avoid further aggravation. However, with the aid of modern delivery systems, it is now possible to intervene in the process of intervertebral disc at the cellular and molecular levels. This review aims to provide an overview of the main mechanisms associated with intervertebral disc degeneration and the delivery systems that can help us to improve the efficacy of intervertebral disc degeneration treatment.

Gene Therapy in Orthopaedics: Progress and Challenges in Pre-Clinical Development and Translation

In orthopaedics, gene-based treatment approaches are being investigated for an array of common -yet medically challenging- pathologic conditions of the skeletal connective tissues and structures (bone, cartilage, ligament, tendon, joints, intervertebral discs etc.). As the skeletal system protects the vital organs and provides weight-bearing structural support, the various tissues are principally composed of dense extracellular matrix (ECM), often with minimal cellularity and vasculature. Due to their functional roles, composition, and distribution throughout the body the skeletal tissues are prone to traumatic injury, and/or structural failure from chronic inflammation and matrix degradation. Due to a mixture of environment and endogenous factors repair processes are often slow and fail to restore the native quality of the ECM and its function. In other cases, large-scale lesions from severe trauma or tumor surgery, exceed the body’s healing and regenerative capacity. Although a wide range of exogenous gene products (proteins and RNAs) have the potential to enhance tissue repair/regeneration and inhibit degenerative disease their clinical use is hindered by the absence of practical methods for safe, effective delivery. Cumulatively, a large body of evidence demonstrates the capacity to transfer coding sequences for biologic agents to cells in the skeletal tissues to achieve prolonged delivery at functional levels to augment local repair or inhibit pathologic processes. With an eye toward clinical translation, we discuss the research progress in the primary injury and disease targets in orthopaedic gene therapy. Technical considerations important to the exploration and pre-clinical development are presented, with an emphasis on vector technologies and delivery strategies whose capacity to generate and sustain functional transgene expression in vivo is well-established.

A Review of Gene Therapy Delivery Systems for Intervertebral Disc Degeneration

Background: :

Intervertebral Disc (IVD) degeneration is a major public health concern, and gene therapy seems a promising approach to delay or even reverse IVD degeneration. However, the delivery system used to transfer exogenous genes into intervertebral disc cells remains a challenge.

Methods::

The MEDLINE, Web of Science, and Scopus databases were searched for English-language articles related to gene therapy for IVD degeneration articles from 1999 to May 2019. The keywords included “gene therapy” AND “intervertebral disc”. The history of the development of different delivery systems was analysed, and the latest developments in viral and non-viral vectors for IVD degeneration treatment were reviewed.

Results: :

Gene therapy delivery systems for IVD degeneration are divided into two broad categories: viral and non-viral vectors. The most commonly used viral vectors are adenovirus, adeno-associated virus (AAV), and lentivirus. Enthusiasm for the use of adenovirus vectors has gradually declined and has been replaced by a preference for lentivirus and AAV vectors. New technologies, such as RNAi and CRISPR, have further enhanced the advantage of viral vectors. Liposomes are the classic non-viral vector, and their successors, polyplex micelles and exosomes, have more potential for use in gene therapy for IVD degeneration.

Conclusion::

Lentivirus and AAV are the conventional viral vectors used in gene therapy for IVD degeneration, and the new technologies RNAi and CRISPR have further enhanced their advantages. Nonviral vectors, such as polyplex micelles and exosomes, are promising gene therapy vectors for IVD degeneration.

Photopolymerizable biogel scaffold seeded with mesenchymal stem cells: safety and efficacy evaluation of novel treatment for intervertebral disc degeneration

Tissue engineering approaches to treatment of intervertebral disc degeneration (IDD) represent a novel avenue of addressing the biologic basis of this disease. However, such approaches remain limited by their invasive nature and disruption to the annular fibrosis (AF). This study sought to explore a new minimally-invasive tissue-engineering approach utilizing an injection of a photopolymerizable biogel scaffold seeded with mesenchymal stem cells (MSCs) directly into the nucleus pulposus (NP). This study was performed using rabbit specimens for both in vivo and in vitro outcome measures. The treatment in this study was performed by injecting 25 μl of 10% (w/v) methacrylated gelatin biogel with 0.15% (w/v) lithium phenyl 2,4,6-trimethylbenzoylphosphinate (LAP) and rabbit MSCs (1 × 10⁶ ) cells/ml into the NP. Samples were then photopolymerized in situ using non-ultraviolet light irradiation via a fiberoptic wire. For the in vitro arm of this study, gene expression analysis demonstrated increased anabolic activity in irradiated MSCs with and without biogel scaffolds. For the in vivo arm of this study, while GAG analysis did not demonstrate significant differences between groups, MRI analysis exhibited a trend toward improved NP matrix. Histological analysis was consistent with increased cellularity and less severe disc degeneration in the MSC + Gel group. However, osteophyte formation was noted in both Stab and MSC + Gel groups after the study period. Increased matrix gene expression of irradiated groups within in vitro studies indicates a photobiologic effect of 405 nm light. Despite promising anabolic actions, osteophyte formation and AF defects could not be avoided with implementation of this minimally-invasive tissue-engineering approach. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1451-1459, 2019.

Injectable nanofibrous spongy microspheres for NR4A1 plasmid DNA transfection to reverse fibrotic degeneration and support disc regeneration

Safe and efficient gene therapy is highly desired for controlling pathogenic fibrosis of nucleus pulposus (NP) tissue, which would result in intervertebral disc (IVD) degeneration and disability if left untreated. In this work, a hyperbranched polymer (HP) with high plasmid DNA (pDNA) binding affinity and negligible cytotoxicity is synthesized, which can self-assemble into nano-sized polyplexes with a "double shell" structure that can transfect pDNA into NP cells with very high efficiency. These polyplexes are then encapsulated in biodegradable nanospheres (NS) to enable two-stage delivery: 1) temporally-controlled release of pDNA-carrying polyplexes and 2) highly efficient delivery of pDNA into cells by the released polyplexes. These biodegradable NS are co-injected with nanofibrous spongy microspheres (NF-SMS) to localize the cellular transfection of the pDNA encoding orphan nuclear receptor 4A1 (NR4A1), which was recently reported as a therapeutic agent to delay pathogenic fibrosis. It is shown that HP can transfect human NP cells efficiently in vitro with low cytotoxicity. The two-stage delivery system is able to present the polyplexes over a sustained time period (more than 30 days) in the tail of a rat. The NR4A1 pDNA carried by the HP polyplexes is found to therapeutically reduce the pathogenic fibrosis of NP tissue in a rat-tail degeneration model. In conclusion, the combination of the two-stage NR4A1 pDNA delivery NS and NF-SMS is able to repress fibrosis and to support IVD regeneration.

Identification and characterization of human nucleus pulposus cell specific serotypes of adeno-associated virus for gene therapeutic approaches of intervertebral disc disorders

Background

Intervertebral disc (IVD) disorders are often accompanied by painful inflammatory and immunopathological processes. Nucleus pulposus (NP) cells play a pivotal role in maintenance of IVD by organizing the expression of anabolic, catabolic, anti-catabolic and inflammatory cytokines. Human NP cells have been targeted by gene therapeutic approaches using lentiviral or adenoviral systems that could be critical due to genome incorporation or immunological side effects. Adeno-associated viruses (AAVs), which do not express any viral gene and are not linked with any known disease in humans, are attractive gene delivery vectors. However, their lack of specific tissue tropism and preexisting immune response are main problems for therapeutic applications. Heretofore, AAVs have not been studied in human IVD research. Therefore, we attempted to identify NP cell specific AAV serotype by targeting human NP cells with different self-complementary AAV (scAAV) serotypes.

Identification and characterization of the proper serotype is crucial to establish less immunogenic and safer gene therapeutic approaches of IVD disorders.

Methods

Preoperative magnetic resonance imaging (MRI) was used for grading of IVD degeneration. NP cells were isolated, cultured with low-glucose and transduced with green fluorescent protein (GFP) packing scAAV serotypes (scAAV1-8) in a dose-dependent manner. scAAV titers were determined by quantitative polymerase chain reaction (qPCR). Transduction efficiencies were determined by fluorescence microscopy and fluorescence-activated cell sorting within 48 days of post-transduction. The 3-(4, 5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay was used to determine NP cell viability. Three-dimensional (3D) cell culture and enzyme-linked immunosorbant assay (ELISA) were performed to examine the expression levels of inflammatory, catabolic and matrix proteins in NP cells.

Results

scAAV6, scAAV2 and scAAV3 showed high and prolonged transgene GFP expressions with transdution efficiencies of 98.6 %, 91.5 % and 89.6 % respectively (p ≤ 0.002). Unlike scAAV6, the serotypes scAAV2 and scAAV3 declined the viability of NP cells by about 25 % and 10 % respectively (p ≤ 0.001). Moreover, scAAV6 did not affect the expression of the inflammatory, catabolic and matrix proteins.

Conclusions

As original primary research evaluating AAVs in degenerative human IVDs, this study identified scAAV6 as a proper serotype for high, stable and non-immunogenic target gene expression in human NP cells. The data could be very important to design efficient and safer gene therapeutic approaches of IVD disorders.

Biological approaches to treating intervertebral disk degeneration: devising stem cell therapies

Intervertebral disk (IVD) degeneration is a common, chronic, and complex degeneration process that frequently leads to back pain and disability, resulting in a major public health issue. In this review we describe biological therapies under preclinical or clinical development with an emphasis on stem cell-based multimodal approaches that target prevention and treatment of IVD degeneration. Systematical review of the basic science and clinical literature was performed to summarize the current status of devising biological approaches to treating IVD degeneration. Since the exact mechanisms underlying IVD degeneration have not yet been fully elucidated and conservative managements appear to be mostly ineffective, current surgical treatment focuses on removal of the pathological disk tissues combined with spinal fusion. The treatment options, however, often produce insufficient efficacy and even serious complications. Therefore, there have been growing demands and endeavors for developing novel regenerative biology-guided strategies for repairing the IVD via delivery of exogenous growth factors, introduction of therapeutic genes, and transplantation of stem cells, or combinatorial therapies. Overall, the data suggest that when applied under a recovery neurobiology principle, multimodal regimens comprising ex vivo engineered stem cell-based disks hold a high potential promise for efficacious clinical translations.

Gene therapy for nucleus pulposus regeneration by heme oxygenase-1 plasmid DNA carried by mixed polyplex micelles with thermo-responsive heterogeneous coronas

Safe and high-efficiency gene therapy for nucleus pulposus (NP) regeneration was urgently desired to treat disc degeneration-associated diseases. In this work, an efficient nonviral cationic block copolymer gene delivery system was used to deliver therapeutic plasmid DNA (pDNA), which was prepared via complexation between the mixed cationic block copolymers, poly(ethylene glycol)-block-poly{N-[N-(2-aminoethyl)-2-aminoehtyl]aspartamide} [PEG-b-PAsp(DET)] and poly(N-isopropylacrylamide)-block-PAsp(DET) [PNIPAM-b-PAsp(DET)], and pDNA at 25 °C. The mixed polyplex micelles (MPMs) containing heterogeneous coronas with hydrophobic and hydrophilic microdomains coexisting could be obtained upon heating from 25 to 37 °C, which showed high tolerability against nuclease and strong resistance towards protein adsorption. The gene transfection efficiency of MPMs in NP cells was significantly higher than that of regular polyplex micelles prepared from sole block copolymer of PEG-b-PAsp(DET) (SPMs) in in vitro and in vivo evaluation due to the synergistic effect of improved colloidal stability and low cytotoxicity. High expression of heme oxygenase-1 (HO-1) in NP cells transfected by MPMs loading HO-1 pDNA significantly decreased the expression activity of matrix metalloproteinases 3 (MMP-3) and cyclo-oxygenase-2 (COX-2) induced by interleukin-1β (IL-1β), and simultaneously increased the NP phenotype-associated genes such as aggrecan, type II collagen, and SOX-9. Moreover, the therapeutic effects of MPMs loading pDNA were tested to treat disc degeneration induced by stab injury. The results demonstrated that administration of HO-1 pDNA carried by MPMs in rat tail discs apparently reduced inflammatory responses induced by need stab and increased glycosaminoglycan (GAG) content, finally achieving better therapeutic efficacy as compared with SPMs. Consequently, MPMs loading HO-1 pDNA were demonstrated to be potential as a safe and high-efficiency nonviral gene delivery system for retarding or regenerating the degenerative discs.

MMP-2 mediates local degradation and remodeling of collagen by annulus fibrosus cells of the intervertebral disc

INTRODUCTION

Degeneration of the intervertebral disc (IVD) is characterized by marked degradation and restructuring of the annulus fibrosus (AF). Although several matrix metalloproteinases (MMPs) have been found to be more prevalent in degenerate discs, their coordination and function within the context of the disease process are still not well understood. In this study, we sought to determine whether MMP-2 is associated with degenerative changes in the AF and to identify the manner by which AF cells use MMP-2.

METHODS

Two established animal models of disc degeneration, static compression and transannular needle puncture of rodent caudal discs, were examined for MMP-2 immunopositivity. With lentiviral transduction of an shRNA expression cassette, we screened and identified an effective shRNA sequence for generating stable RNA interference to silence MMP-2 expression in primary rat AF cells. Gelatin films were used to compare gelatinase activity and spatial patterns of degradation between transduced cells, and both noninfected and nonsense shRNA controls. The functional significance of MMP-2 was determined by assessing the ability for cells to remodel collagen gels.

RESULTS

Both static compression and 18-g annular puncture of rodent caudal discs stimulated an increase in MMP-2 activity with concurrent lamellar disorganization in the AF, whereas 22-g and 26-g needle injuries did not. To investigate the functional role of MMP-2, we established lentivirus-mediated RNAi to induce stable knockdown of transcript levels by as much as 88%, and protein levels by as much as 95% over a 10-day period. Culturing transduced cells on gelatin films confirmed that MMP-2 is the primary functional gelatinase in AF cells, and that MMP-2 is used locally in regions immediately around AF cells. In collagen gels, transduced cells demonstrated an inability to remodel collagen matrices.

CONCLUSIONS

Our study indicates that increases in MMP-2 observed in human degenerate discs are mirrored in experimentally induced degenerative changes in rodent animal models. AF cells appear to use MMP-2 in a very directed fashion for local matrix degradation and collagen remodeling. This suggests that MMP-2 may have a functionally significant role in the etiology of degenerative disc disease and could be a potential therapeutic target.

Intervertebral disc regeneration: from the degenerative cascade to molecular therapy and tissue engineering

Low back pain is one of the major health problems in industrialized countries, as a leading source of disability in the working population. Intervertebral disc degeneration has been identified as its main cause, being a progressive process mainly characterized by alteration of extracellular matrix composition and water content. Many factors are involved in the degenerative cascade, such as anabolism/catabolism imbalance, reduction of nutrition supply and progressive cell loss. Currently available treatments are symptomatic, and surgical procedures consisting of disc removal are often necessary. Recent advances in our understanding of intervertebral disc biology led to an increased interest in the development of novel biological treatments aimed at disc regeneration. Growth factors, gene therapy, stem cell transplantation and biomaterials-based tissue engineering might support intervertebral disc regeneration by overcoming the limitation of the self-renewal mechanism. The aim of this paper is to overview the literature discussing the current status of our knowledge from the degenerative cascade of the intervertebral disc to the latest molecular, cell-based therapies and tissue-engineering strategies for disc regeneration.

Retroperitoneal approach to the intervertebral disc for the annular puncture model of intervertebral disc degeneration in the rabbit

BACKGROUND CONTEXT

The rabbit annular puncture model of degeneration is among the most widely used models of intervertebral disc (IVD) degeneration. There are no published reports of the specific surgical technique used to produce this model.

PURPOSE

To describe the model in detail in an effort to reduce center-to-center variability and hopefully improve the reproducibility of future experimental results.

STUDY DESIGN

Technical report of surgical approach and experience.

PATIENT SAMPLE

New Zealand White Rabbits.

METHODS

A detailed report of the annular puncture technique in rabbits is provided including preparation of the animals, instrumentation, a description of retroperitoneal approach to the lumbar area, and the technique for IVD injury. Common pitfalls and complications of the procedure are described.

CONCLUSIONS

The methods described can serve to standardize the implementation of this important preclinical model of disc degeneration.

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

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

Injection of AAV2-BMP2 and AAV2-TIMP1 into the nucleus pulposus slows the course of intervertebral disc degeneration in an in vivo rabbit model

BACKGROUND CONTEXT

Intervertebral disc degeneration (IDD) is a common cause of back pain. Patients who fail conservative management may face the morbidity of surgery. Alternative treatment modalities could have a significant impact on disease progression and patients' quality of life.

PURPOSE

To determine if the injection of a virus vector carrying a therapeutic gene directly into the nucleus pulposus improves the course of IDD.

STUDY DESIGN

Prospective randomized controlled animal study.

METHODS

Thirty-four skeletally mature New Zealand white rabbits were used. In the treatment group, L2-L3, L3-L4, and L4-L5 discs were punctured in accordance with a previously validated rabbit annulotomy model for IDD and then subsequently treated with adeno-associated virus serotype 2 (AAV2) vector carrying genes for either bone morphogenetic protein 2 (BMP2) or tissue inhibitor of metalloproteinase 1 (TIMP1). A nonoperative control group, nonpunctured sham surgical group, and punctured control group were also evaluated. Serial magnetic resonance imaging (MRI) studies at 0, 6, and 12 weeks were obtained, and a validated MRI analysis program was used to quantify degeneration. The rabbits were sacrificed at 12 weeks, and L4-L5 discs were analyzed histologically. Viscoelastic properties of the L3-L4 discs were analyzed using uniaxial load-normalized displacement testing. Creep curves were mathematically modeled according to a previously validated two-phase exponential model. Serum samples obtained at 0, 6, and 12 weeks were assayed for biochemical evidence of degeneration.

RESULTS

The punctured group demonstrated MRI and histologic evidence of degeneration as expected. The treatment groups demonstrated less MRI and histologic evidence of degeneration than the punctured group. The serum biochemical marker C-telopeptide of collagen type II increased rapidly in the punctured group, but the treated groups returned to control values by 12 weeks. The treatment groups demonstrated several viscoelastic properties that were distinct from control and punctured values.

CONCLUSIONS

Treatment of punctured rabbit intervertebral discs with AAV2-BMP2 or AAV2-TIMP1 helps delay degenerative changes, as seen on MRI, histologic sampling, serum biochemical analysis, and biomechanical testing. Although data from animal models should be extrapolated to the human condition with caution, this study supports the potential use of gene therapy for the treatment of IDD.

In vitro and in vivo testing of a novel regulatory system for gene therapy for intervertebral disc degeneration

STUDY DESIGN

In vitro and in vivo testing of a gene expression control system.

OBJECTIVE

The purpose of this study is to establish the ability of controlling gene expression using an adeno-associated viral vector containing a novel control system (AAV-RheoSwitch GFP [Intrexon Corp., Blacksburg, VA]) in intervertebral disc cells for potential use in gene therapy trials.

SUMMARY OF BACKGROUND DATA

Gene therapy for disc degeneration shows promise; however, concern remains regarding safety. Careful control of gene expression is needed to facilitate translation into clinical trials.

METHODS

Rabbit nucleus pulposus cells were treated in vitro with increasing multiplicities of infection of AAV-RheoSwitch GFP, followed by increasing concentrations of Intrexon's activator ligand, and examined for fluorescence during and after removal of ligand. New Zealand white rabbits were injected with AAV-RheoSwitch GFP and killed either before or after 5 days of daily ligand injection. Tissues were analyzed for the presence of green fluorescent protein (GFP) with fluorescence microscopy and immunohistochemical staining.

RESULTS

In vitro, GFP expression was noted to be dose and time dependent, decreased 24 hours after removal of ligand, and was minimally detectable in cells after 48 hours. In vivo, increasing GFP expression was seen in animals treated with viral vector and ligand. No GFP expression was evident in tissues from rabbits that received only virus, or activator ligand alone. In addition, no GFP expression was evident in the adjacent discs, spinal cord, dura, bone, liver, or brain of any animals.

CONCLUSION

These data demonstrate that in vitro ligand-induced gene expression can be stimulated and effectively turned off by removal of the ligand. In addition, we demonstrated the in vivo utility of this system through showing up-regulation of GFP without nonspecific gene expression or expression in adjacent tissues. This system, therefore, has the potential to increase the safety of gene therapy in the treatment of intervertebral disc degeneration.

Teriparatide therapy and beta-tricalcium phosphate enhance scaffold reconstruction of mouse femoral defects

To investigate the efficacy of endocrine parathyroid hormone treatment on tissue-engineered bone regeneration, massive femoral defects in C57Bl/6 mice were reconstructed with either 100:0 or 85:15 poly-lactic acid (PLA)/beta-tricalcium phosphate (β-TCP) scaffolds (hereafter PLA or PLA/βTCP, respectively), which were fabricated with low porosity (<30%) to improve their structural rigidity. Experimental mice were treated starting at 1 week postop with daily subcutaneous injections of 40 μg/kg teriparatide until sacrifice at 9 weeks, whereas control mice underwent the same procedure but were injected with sterile saline. Bone regeneration was assessed longitudinally using planar X-ray and quantitative microcomputed tomography, and the reconstructed femurs were evaluated at 9 weeks either histologically or biomechanically to determine their torsional strength and rigidity. Teriparatide treatment increased bone volume and bone mineral content significantly at 6 weeks and led to enhanced trabeculated bone callus formation that appeared to surround and integrate with the scaffold, thereby establishing union by bridging bone regeneration across the segmental defect in 30% of the reconstructed femurs, regardless of the scaffold type. However, the bone volume and mineral content in the PLA reconstructed femurs treated with teriparatide was reduced at 9 weeks to control levels, but remained significantly increased in the PLA/βTCP scaffolds. Further, bridged teriparatide-treated femurs demonstrated a prototypical brittle bone torsion behavior, and were significantly stronger and stiffer than control specimens or treated specimens that failed to form bridging bone union. Taken together, these observations suggest that intermittent, systemic parathyroid hormone treatment can enhance bone regeneration in scaffold-reconstructed femoral defects, which can be further enhanced by mineralized (βTCP) particles within the scaffold.

Monitoring of the effect of intervertebral disc nucleus pulposus ablation by MRI

In order to investigate intervertebral disc (IVD) degeneration and repair, a quantitative non-invasive tool is needed. Various MRI methods including qCPMG, which yields dipolar echo relaxation time (T(DE)), magnetization transfer contrast (MTC), and (1)H and (2)H double quantum filtered (DQF) MRI were used in the present work to monitor changes in rat IVD after ablation of the nucleus pulposus (NP), serving as a model of severe IVD degeneration. In the intact IVD, a clear distinction between the annulus fibrosus (AF) and the NP is obtained on T(2) and T(DE) weighted images as well as on MTC maps, reflecting the high concentration of ordered collagen fibers in the AF. After ablation of the NP, the distinction between the compartments is lost. T(2) and T(DE) relaxation times are short throughout the disc and MTC is high. (1)H and (2)H DQF signal, which in intact discs is obtained only for the AF, is now observable throughout the tissue. These results indicate that after ablation, there is an ingression of collagen fibers from the AF into the area that was previously occupied by the NP, as was confirmed by histology.

Emerging technologies for degenerative disk disease: potential synergy between biochemical signaling and spinal biomechanics

Interventional spinal procedures are performed with increasing frequency, and they remain an important tool for physiatrists treating patients with spine pain. As the potential treatment options expand with novel technologies on the horizon, such as gene- and cell-based therapies, the physiatrist will be uniquely poised to deliver such treatments in conjunction with exercise-based therapies. Therefore, the development of novel technologies requires particular attention to the potential synergy between biochemical signaling and spinal biomechanics. It is hoped that such insight will result in improved treatment options for patients with pain related to degenerative disk disease, leading to improved nonoperative outcomes. This article reviews the current knowledge of precipitants of disk degeneration, the effects of beneficial and traumatic levels of disk loading, and how each of these can be impacted by novel treatment options.

Localized Intervertebral Disc Injury Leads to Organ Level Changes in Structure, Cellularity, and Biosynthesis

A literature review and new data are presented to evaluate the influence of intervertebral disc (IVD) injury on biomechanics, cellularity, inflammation, and biosynthesis. Literature and new experimental evidence support the hypothesis that localized injury in the disc can lead to immediate and long-term organ level changes in biomechanics and biology of the IVD. Biomechanical properties defining motion segment bending behaviors sensitive to injuries that affect anulus fibrosus (AF) integrity and nucleus pulposus (NP) pressurization. Axial mechanics and IVD height measurements show sensitivity to puncture and other injuries that reduce NP pressurization. Torsional biomechanics are strongly affected by the extent and location of AF lesions but are less sensitive to reduced NP pressurization. IVD injuries such as puncture and stab incisions may also lead to a cascade of biological changes consistent with degeneration, including loss of cellularity, altered biosynthesis and inflammation. New results on effects of 25G needle injection of saline into a bovine IVD organ culture model demonstrated a loss of cellularity and down-regulation of matrix gene expression, providing a specific example of how a minor injury affects the IVD organ response. We conclude that localized injuries in the IVD can induce an organ level degenerative cascade through biomechanical and biological mechanisms, and their interactions. Attempts at IVD repair should target the dual biomechanical roles of the anulus of maintaining nucleus pressurization and transmitting loads across the vertebrae. Biologically, it remains important to maintain IVD cellularity and biosynthesis rates following injury to prevent downstream degenerative changes.

The cellular pathobiology of the degenerate intervertebral disc and discogenic back pain

In 2007, three times as many peer reviewed publications covering the biology and biotherapeutics of intervertebral disc (IVD) disease appeared in the literature than in 1997. This is testimony to the upsurge in interest in the IVD, mainly driven by the openings that modern molecular pathology has generated to investigate mechanisms of human disease and the potential offered by novel therapeutic technologies to use data coming from these studies to positively influence chronic discogenic back pain and sciatica. Molecular pathology has shown IVD degeneration, a major cause of low back pain, to be a complex, active disorder in which disturbed cytokine biology, cellular dysfunction and altered load responses play key roles. This has translated into a search for target molecules and disease processes that might be the focus of future, evidence-based therapies for back pain. It is not possible to describe the totality of advances that have been made in understanding the biology of the IVD in recent years, but in this review those areas of biology that are currently influencing, or could conceivably soon impinge on, clinical thinking or practice around IVD degeneration and discogenic back pain are described and discussed.

Safety of adeno-associated viral vectors

Vectors based on recombinant adeno-associated viruses (AAVs) are being extensively explored for gene therapy owing to some of their distinguishing characteristicss such as lack of pathogenicity, wide range of infectivity and ability to provide long-term transgene expression. For many of the same reasons, recombinant AAV (rAAV) vectors have also been used as vaccine carriers to elicit immune responses against their transgene products. Extensive studies of rAAV vectors in animal models and in the clinic have revealed some safety concerns relating to their construction and production, adverse events following delivery, potential integration of the vector’s genome into host cell genomes, and the impairment of rAAV-induced CD8+ T-cell responses, which could have dire consequences for rAAV-treated individuals. Further studies to advance our knowledge of the biology of AAV and rAAV vectors are deemed necessary to allow for their more successful application in the clinic.