Slow depressurization following intradiscal injection leads to injectate leakage in a large animal model

Single-Cell Microgel Encapsulation Improves the Therapeutic Efficacy of Mesenchymal Stem Cells in Treating Intervertebral Disc Degeneration via Inhibiting Pyroptosis

While mesenchymal stem cell (MSC) shows great potentials in treating intervertebral disc degeneration, most MSC die soon after intradiscal transplantation, resulting in inferior therapeutic efficacy. Currently, bulk hydrogels are the common solution to improve MSC survival in tissues, although hydrogel encapsulation impairs MSC migration and disrupts extracellular microenvironment. Cell hydrogel encapsulation has been proposed to overcome the limitation of traditional bulk hydrogels, yet this technique has not been used in treating disc degeneration. Using a layer-by-layer self-assembly technique, we fabricated alginate and gelatin microgel to encapsulate individual MSC for treating disc degeneration. The small size of microgel allowed intradiscal injection of coated MSC. We demonstrated that pyroptosis was involved in MSC death under oxidative stress stimulation, and microgel coating suppressed pyroptosis activation by maintaining mitochondria homeostasis. Microgel coating protected MSC in the harsh disc microenvironment, while retaining vital cellular functions such as migration, proliferation, and differentiation. In a rat model of disc degeneration, coated MSC exhibits prolonged retention in the disc and better efficacy of attenuating disc degeneration, as compared with bare MSC treatment alone. Further, microgel-coated MSC exhibited improved therapeutic effects in treating disc degeneration via suppressing the activation of pyroptosis in the disc. For the first time, microgel-encapsulated MSC was used to treat disc degeneration and obtain encouraging outcomes. The developed biocompatible single-cell hydrogel is an effective strategy to protect MSC and maintain cellular functions and may be an efficacious approach to improving the efficacy of MSC therapy in treating disc degeneration. The objective of this study is to improve the efficacy of cell therapy for treating disc degeneration using single-cell hydrogel encapsulation and further to understand related cytoprotective mechanisms.

Intervertebral disc degeneration-Current therapeutic options and challenges

Degeneration of the intervertebral disc (IVD) is a normal part of aging. Due to the spine's declining function and the development of pain, it may affect one's physical health, mental health, and socioeconomic status. Most of the intervertebral disc degeneration (IVDD) therapies today focus on the symptoms of low back pain rather than the underlying etiology or mechanical function of the disc. The deteriorated disc is typically not restored by conservative or surgical therapies that largely focus on correcting symptoms and structural abnormalities. To enhance the clinical outcome and the quality of life of a patient, several therapeutic modalities have been created. In this review, we discuss genetic and environmental causes of IVDD and describe promising modern endogenous and exogenous therapeutic approaches including their applicability and relevance to the degeneration process.

Hydrogel-Embedded Poly(Lactic-co-Glycolic Acid) Microspheres for the Delivery of hMSC-Derived Exosomes to Promote Bioactive Annulus Fibrosus Repair

OBJECTIVE

Intervertebral disk degeneration is a prevalent postoperative complication after discectomy, underscoring the need to develop preventative and bioactive treatment strategies that decelerate degeneration and seal annulus fibrosus (AF) defects. Human mesenchymal stem cell-derived exosomes (MSC-Exos) hold promise for cell-free bioactive repair; however, their ability to promote AF repair is poorly understood. The objective of this study was to evaluate the ability of MSC-Exos to promote endogenous AF repair processes and integrate MSC-Exos within a biomaterial delivery system.

DESIGN

We characterize biophysical and biochemical properties of normoxic (Nx) and hypoxic (Hx) preconditioned MSC-Exos from young, healthy donors and examine their effects on AF cell proliferation, migration, and gene expression. We then integrate a poly(lactic-co-glycolic acid) microsphere (PLGA µSphere) delivery platform within an interpenetrating network hydrogel to facilitate sustained MSC-Exo delivery.

RESULTS

Hx MSC-Exos led to a more robust response in AF cell proliferation and migration than Nx MSC-Exos and was selected for a downstream protection experiment. Hx MSC-Exos maintained a healthy AF cell phenotype under a TNFα challenge in vitro and attenuated catabolic responses. In all functional assays, AF cell responses were more sensitive to Hx MSC-Exos than Nx MSC-Exos. PLGA µSpheres released MSC-Exos over a clinically relevant timescale without affecting hydrogel modulus or pH upon initial embedment and µSphere degradation.

CONCLUSIONS

This MSC-Exo treatment strategy may offer benefits of stem cell therapy without the need for exogenous stem cell transplantation by stimulating cell proliferation, promoting cell migration, and protecting cells from the degenerative proinflammatory microenvironment.

In-vitro models of disc degeneration - A review of methods and clinical relevance

The intervertebral disc (IVD) provides flexibility, acts as a shock absorber, and transmits load. Degeneration of the IVD includes alterations in the biomechanics, extracellular matrix (ECM), and cellular activity. These changes are not always perceived, however, IVD degeneration can lead to severe health problems including long-term disability. To understand the pathogenesis of IVD degeneration and suitable testing methods for emerging treatments and therapies, this review documents in-vitro models of IVD degeneration including physical disruption, hyperphysiological loading, ECM degradation by enzyme digestion, or a combination of these methods. This paper reviews and critically analyses the models of degeneration published since the year 2000 in either in human or animal specimens. The results are categorised in terms of the IVD biomechanics, physical attributes, ECM composition, tissue damage and cellularity to evaluate the models with respect to natural human degeneration, and to provide recommendations for clinically relevant models for the various stages of degeneration. There is no one model that replicates the wide range of degenerative changes that occur as part of normal degeneration. However, cyclic overloading replicates many aspects of degeneration, with the advantage of a dose-response allowing the tuning of damage initiated. Models of severe degeneration are currently lacking, but there is potential that combining cyclic overloading and enzymatic digestion will provide model that closely resembles human IVD degeneration. This will provide an effective way to investigate the effects of severe degeneration, and the evaluation of treatments for the IVD, which would generally be indicated at this advanced stage of degeneration.

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.

Establishing a through-puncture model for assessing post-injection leakage in the intervertebral disc

PURPOSE

Needle injection through the outer annulus fibrosus of the intervertebral disc (IVD) is the most practical approach for delivery of therapeutic agents, which have been shown to potentially leak following needle retraction. The goal of this work was to establish a protocol for quantifying post-injection leakage and test its sensitivity to factors believed to affect needle track geometry.

METHODS

A through-puncture defect procedure, followed by controlled injection, was performed on bovine caudal IVDs. Sensitivity to needle size was tested by injection of saline into unconstrained discs with either a 30G, 26G, or 21G hypodermic needle. Sensitivity to axial load was tested by repeated injection via a 26G needle with either no constraint, fixed height, or 10% axial compressive strain. Sensitivity to flexion was tested by applying combined 0.2 MPa compression and 15° of flexion following injection of 5% of disc volume.

RESULTS

Needle diameter significantly affected maximum volume prior to leakage, ranging from 34.6 ± 31.9 µL when using 21G to 115.6 ± 23.6 µL when using 30G. While all unloaded discs leaked, axial compression decreased the incidence of leakage events by 50-100% depending on load history. Forward flexion resulted in a 22% incidence of leakage.

CONCLUSION

Fluid injected into IVDs is at significant risk of leakage following needle retraction. This risk depends on factors which alter the geometry of the needle track, including needle size, pinching due to axial compression, and stretching as a result of forward flexion.

Extracellular Vesicles as an Emerging Treatment Option for Intervertebral Disc Degeneration: Therapeutic Potential, Translational Pathways, and Regulatory Considerations

Emergent approaches in regenerative medicine look toward the use of extracellular vesicles (EVs) as a next-generation treatment strategy for intervertebral disc (IVD) degeneration (IVDD) because of their ability to attenuate chronic inflammation, reduce apoptosis, and stimulate proliferation in a number of tissue systems. Yet, there are no Food and Drug Administration (FDA)-approved EV therapeutics in the market with an indication for IVDD, which motivates this article to review the current state of the field and provide an IVD-specific framework to assess its efficacy. In this systematic review, 29 preclinical studies that investigate EVs in relation to the IVD are identified, and additionally, the regulatory approval process is reviewed in an effort to accelerate emerging EV-based therapeutics toward FDA submission and timeline-to-market. The majority of studies focus on nucleus pulposus responses to EV treatment, where the main findings show that stem cell-derived EVs can decelerate the progression of IVDD on the molecular, cellular, and organ level. The findings also highlight the importance of the EV parent cell's pathophysiological and differentiation state, which affects downstream treatment responses and therapeutic outcomes. This systematic review substantiates the use of EVs as a promising cell-free strategy to treat IVDD and enhance endogenous repair.

Laser-Assisted Fabrication of Injectable Nanofibrous Cell Carriers

The use of injectable biomaterials for cell delivery is a rapidly expanding field which may revolutionize the medical treatments by making them less invasive. However, creating desirable cell carriers poses significant challenges to the clinical implementation of cell-based therapeutics. At the same time, no method has been developed to produce injectable microscaffolds (MSs) from electrospun materials. Here the fabrication of injectable electrospun nanofibers is reported on, which retain their fibrous structure to mimic the extracellular matrix. The laser-assisted micro-scaffold fabrication has produced tens of thousands of MSs in a short time. An efficient attachment of cells to the surface and their proliferation is observed, creating cell-populated MSs. The cytocompatibility assays proved their biocompatibility, safety, and potential as cell carriers. Ex vivo results with the use of bone and cartilage tissues proved that NaOH hydrolyzed and chitosan functionalized MSs are compatible with living tissues and readily populated with cells. Injectability studies of MSs showed a high injectability rate, while at the same time, the force needed to eject the load is no higher than 25 N. In the future, the produced MSs may be studied more in-depth as cell carriers in minimally invasive cell therapies and 3D bioprinting applications.

Proteoglycan-depleted regions of annular injury promote nerve ingrowth in a rabbit disc degeneration model

Background

To assess the effects of proteoglycan-depleted regions of annular disruptions on nerve ingrowth in the injury site in vivo.

Methods

New Zealand white rabbits (n = 18) received annular injuries at L3/4, L4/5, and L5/6. The experimental discs were randomly assigned to four groups: (a) an annular defect was created; (b) an annular defect implanted with a poly lactic-co-glycolic acid (PLGA)/fibrin/PBS plug; (c) an annular defect implanted with a PLGA/fibrin/chondroitinase ABC (chABC) plug; and (d) an uninjured L2/3 disc (control). Disc degeneration was evaluated by radiography, MRI, histology, and analysis of the proteoglycan (PG) content. Immunohistochemical detection of nerve fibers and chondroitin sulfate (CS) was performed.

Results

The injured discs produced progressive and reliable disc degeneration. In the defective discs, the lamellated appearance of AF (Annulus fibrosus) was replaced by extensive fibrocartilaginous-like tissue formation outside the injured sites. In contrast, newly formed tissue was distributed along small fissures, and small blood vessels appeared in the outer part of the disrupted area in the PLGA/fibrin/PBS discs. More sprouting nerve fibers grew further into the depleted annulus regions in the PLGA/fibrin/chABC discs than in the control discs and those receiving PLGA/fibrin/PBS. In addition, the innervation scores of the PLGA/fibrin/chABC discs were significantly increased compared with those of the PLGA/fibrin/PBS discs and defected discs.

Conclusion

ChABC-based PLGA/fibrin gel showed promising results by achieving biointegration with native annulus tissue and providing a local source for the sustained release of active chABC. Disc-derived PG-mediated inhibition of nerve and blood vessel ingrowth was abrogated by chABC enzymatic deglycosylation in an annular-injured rabbit disc degeneration model.