The fate of transplanted xenogeneic bone marrow-derived stem cells in rat intervertebral discs

Current Trends in Orthobiologics: An 11-Year Review of the Orthopaedic Literature

BACKGROUND

The use of "orthobiologics" or regenerative therapies in orthopaedic surgery has grown in recent years. Particular interest has been raised with regard to platelet-rich plasma, bone marrow aspirate, adipose-derived cells, and amniotic cells. Although studies have analyzed outcomes after orthobiologic treatment, no study has analyzed how the literature as a whole has evolved.

PURPOSE

To evaluate trends in platelet-rich plasma, bone marrow aspirate, adipose-derived cells, and amniotic cell publications and to assess how these might inform efforts to establish minimum reporting standards and forecast future use.

STUDY DESIGN

Systematic review; Level of evidence, 4.

METHODS

A database was compiled systematically using PubMed to identify articles published between 2009 and 2019 within 9 prominent orthopaedic journals and pertaining to the use of platelet-rich plasma, bone marrow aspirate, adipose-derived cells, and amniotic cells in the treatment of musculoskeletal conditions. Included articles were classified as clinical, nonclinical (translational or basic science), or review, and a variety of study parameters were recorded for each. Additional queries were performed to identify articles that utilized minimum reporting standards.

RESULTS

A total of 474 articles (132 clinical, 271 nonclinical, 71 review) were included, consisting of 244 (51.5%) platelet-rich plasma, 146 (30.8%) bone marrow aspirate, 72 (15.2%) adipose-derived cells, and 12 (2.5%) amniotic cells. The greatest annual increase in publications for each orthobiologic topic was from 2018 to 2019. The American Journal of Sports Medicine demonstrated the highest number of overall (34.2%) and clinical (50.0%) publications, and accounted for 44.3% of all platelet-rich plasma publications. The Journal of Orthopaedic Research accounted for the second highest overall number of publications (24.9%) and highest nonclinical publications (41.0%). Platelet-rich plasma accounted for 91.5% of all level 1 clinical studies, while much greater than half of bone marrow aspirate, adipose-derived cells, and amniotic cell publications were level 3 or lower. Out of the 207 articles that used some form of reporting protocol, 59 (28.5%) used an established algorithm and 125 (60.4%) used their own.

CONCLUSION

Interest in orthobiologics continues to grow, as evidenced by an increasing trend in publications over an 11-year period. However, current reporting on orthobiologic formulations is largely heterogeneous, emphasizing the need for minimum reporting standards and higher-quality studies.

Biomaterials and Cell-Based Regenerative Therapies for Intervertebral Disc Degeneration with a Focus on Biological and Biomechanical Functional Repair: Targeting Treatments for Disc Herniation

Intervertebral disc (IVD) degeneration is a common cause of low back pain and most spinal disorders. As IVD degeneration is a major obstacle to the healthy life of so many individuals, it is a major issue that needs to be overcome. Currently, there is no clinical treatment for the regeneration of degenerated IVDs. However, recent advances in regenerative medicine and tissue engineering suggest the potential of cell-based and/or biomaterial-based IVD regeneration therapies. These treatments may be indicated for patients with IVDs in the intermediate degenerative stage, a point where the number of viable cells decreases, and the structural integrity of the disc begins to collapse. However, there are many biological, biomechanical, and clinical challenges that must be overcome before the clinical application of these IVD regeneration therapies can be realized. This review summarizes the basic research and clinical trials literature on cell-based and biomaterial-based IVD regenerative therapies and outlines the important role of these strategies in regenerative treatment for IVD degenerative diseases, especially disc herniation.

Cell sources proposed for nucleus pulposus regeneration

Lower back pain (LBP) occurs in 80% of adults in their lifetime; resulting in LBP being one of the biggest causes of disability worldwide. Chronic LBP has been linked to the degeneration of the intervertebral disc (IVD). The current treatments for chronic back pain only provide alleviation of symptoms through pain relief, tissue removal, or spinal fusion; none of which target regenerating the degenerate IVD. As nucleus pulposus (NP) degeneration is thought to represent a key initiation site of IVD degeneration, cell therapy that specifically targets the restoration of the NP has been reviewed here. A literature search to quantitatively assess all cell types used in NP regeneration was undertaken. With key cell sources: NP cells; annulus fibrosus cells; notochordal cells; chondrocytes; bone marrow mesenchymal stromal cells; adipose-derived stromal cells; and induced pluripotent stem cells extensively analyzed for their regenerative potential of the NP. This review highlights: accessibility; expansion capability in vitro; cell survival in an IVD environment; regenerative potential; and safety for these key potential cell sources. In conclusion, while several potential cell sources have been proposed, iPSC may provide the most promising regenerative potential.

Directed Differentiation of Notochord-like and Nucleus Pulposus-like Cells Using Human Pluripotent Stem Cells

Intervertebral disc degeneration might be amenable to stem cell therapy, but the required cells are scarce. Here, we report the development of a protocol for directed in vitro differentiation of human pluripotent stem cells (hPSCs) into notochord-like and nucleus pulposus (NP)-like cells of the disc. The first step combines enhancement of ACTIVIN/NODAL and WNT and inhibition of BMP pathways. By day 5 of differentiation, hPSC-derived cells express notochordal cell characteristic genes. After activating the TGF-β pathway for an additional 15 days, qPCR, immunostaining, and transcriptome data show that a wide array of NP markers are expressed. Transcriptomically, the in vitro-derived cells become more like in vivo adolescent human NP cells, driven by a set of influential genes enriched with motifs bound by BRACHYURY and FOXA2, consistent with an NP cell-like identity. Transplantation of these NP-like cells attenuates fibrotic changes in a rat disc injury model of disc degeneration.

Granulocyte-colony stimulating factor improves intervertebral disc degeneration in experimental adult male rats: A microscopic and radiological study

Intervertebral disc degeneration (IVDD) is a major contributor to low back pain (LBP). Granulocyte-colony stimulating factor (GCSF) is known to mobilize hematopoietic stem cells (HSCs) that may be implicated in intervertebral disc (IVD) regeneration. Rats were divided into the following three groups: (i) control group; (ii) IVDD group-the rats underwent Co5/Co6 and Co7/Co8 IVDD operation; and (iii) GCSF-treated group-the rats received daily GCSF subcutaneous injections starting 6 weeks after the IVDD operation and continued for 5 days. All of the rats were euthanized after 8 weeks, and IVDs were assessed by tail X-ray and histopathological, immunohistochemical, and transmission electron microscopy (TEM) analyses. The X-rays showed disc narrowing in the IVDD group that was significantly widened in the GCSF-treated rats. Histologically, the IVDD group showed disarrangement of the annulus fibrosis lamellae, complete degeneration of the nucleus pulposus, and loss of proteoglycan content. These changes were improved after GCSF treatment. Vertebral endplate thickness and cellularity were significantly decreased with IVDD and significantly increased after GCSF treatment. Stromal cell-derived factor-1α (SDF-1α) immune expression was significantly increased in the IVDD group but decreased in the GCSF-treated group. However, the caspase-3 expression percentage showed no significant difference among the studied groups. TEM showed excessive collagen deposits around the notochordal cells in the IVDD group, which were attenuated in the GCSF-treated group. These results indicate that GCSF improves IVDD and promotes its recovery based on radiological, histological and TEM findings.

Stem Cell Senescence: the Obstacle of the Treatment of Degenerative Disk Disease

Intervertebral disc (IVD) has a pivotal role in the maintenance of flexible motion. IVD degeneration is one of the primary causes of low back pain and disability, which seriously influences patients' health, and increases the family and social economic burden. Recently, stem cell therapy has been proven to be more effective on IVD degeneration disease. However, stem cell senescence is the limiting factor in the IVD degeneration treatment. Senescent stem cells have a negative effect on the self-repair on IVD degeneration. In this review, we delineate that the factors such as telomerase shortening, DNA damage, oxidative stress, microenvironment and exosomes will induce stem cell aging. Recent studies tried to delay the aging of stem cells by regulating the expression of aging-related genes and proteins, changing the activity of telomerase, improving the survival microenvironment of stem cells and drug treatment. Understanding the mechanism of stem cell aging and exploring new approaches to delay or reverse stem cell aging asks for research on the repair of the degenerated disc.

Evaluation of Percutaneous Intradiscal Amniotic Suspension Allograft in a Rabbit Model of Intervertebral Disc Degeneration

STUDY DESIGN

A laboratory study using a rabbit annular puncture model of intervertebral disc degeneration (IDD).

OBJECTIVE

The aims of this study were to assess whether an amniotic suspension allograft (ASA) containing particulated human amnion and amniotic fluid derived cells regains intervertebral disc height and morphology and improves histologic scoring in a rabbit model of IDD.

SUMMARY OF BACKGROUND DATA

In contrast to current surgical interventions for IDD, in which the primary goal is to relieve symptomatic pain, one novel strategy involves the direct injection of anabolic cytokines. Current therapies for IDD are limited by both the short half-life of therapeutic proteins and general decline in anabolic cell populations.

METHODS

Intervertebral discs in New Zealand white rabbits were punctured using 18-gauge needle under fluoroscopic guidance. Four weeks post-puncture, two groups of rabbits were injected with either ASA or a vehicle/sham control, while a third group was untreated. Weekly radiographs were obtained for 12 weeks to assess disc height index (DHI). Magnetic resonance imaging (MRI) T2 relaxation time was evaluated at weeks 4 and 12 to assess morphological changes. Histologic sections were evaluated on a semi-quantitative grading scale.

RESULTS

Before treatment at week 4, DHIs and normalized T2 relaxation times between the three groups were not significantly different. At week 12, ASA-treated rabbits exhibited significantly greater DHIs and MRI T2 relaxation times than vehicle and untreated control groups. The ASA group had higher mean histologic score than the vehicle group, which demonstrated extensive fiber disorganization and delamination with reduced proteoglycan staining on histology.

CONCLUSION

Minimally invasive intervention with intradiscal injection of ASA was successful in reducing IDD in a reproducible rabbit model, with significant improvement in disc height and morphology when compared with vehicle and untreated control groups on radiographic and MRI analyses.

LEVEL OF EVIDENCE

N/A.

Human Bone Marrow Mesenchymal Stromal Cells Promote Bone Regeneration in a Xenogeneic Rabbit Model: A Preclinical Study

Significant research efforts have been undertaken during the last decades to treat musculoskeletal disorders and improve patient's mobility and quality of life. The goal is the return of function as quickly and completely as possible. Cellular therapy has been increasingly employed in this setting. The design of this study was focused on cell-based alternatives. The present study aimed at investigating the bone regeneration capacity of xenogeneic human bone marrow-derived mesenchymal stromal cell (hMSC) implantation with tricalcium phosphate (TCP) granules in an immunocompetent rabbit model of critical-size bone defects at the femoral condyles. Two experimental groups, TCP and hMSC + TCP, were compared. Combination of TCP and hMSC did not affect cell viability or osteogenic differentiation. We also observed significantly higher bone regeneration in vivo in the hMSC + TCP group, which also displayed better TCP osteointegration. Also, evidence of hMSC contribution to a better TCP osteointegration was noticed. Finally, no inflammatory reaction was detected, besides the xenotransplantation of human cells into an immunocompetent recipient. In summary, hMSC combined with TCP granules is a potential combination for bone regeneration purposes that provides better preclinical results compared to TCP alone.

Human umbilical cord derivatives regenerate intervertebral disc

Intervertebral disc (IVD) degeneration is characterized by the loss of nucleus pulposus (NP), which is a common cause for lower back pain. Although, currently, there is no cure for the degenerative disc disease, stem cell therapy is increasingly being considered for its treatment. In this study, we investigated the feasibility and efficacy of human umbilical cord mesenchymal stem cells (MSCs) and chondroprogenitor cells (CPCs) derived from those cells to regenerate damaged IVD in a rabbit model. Transplanted cells survived, engrafted and dispersed into NP in situ. Significant improvement in the histology, cellularity, extracellular matrix proteins, and water and glycosaminoglycan contents in IVD recipients of CPCs was observed compared to MSCs. In addition, IVDs receiving CPCs exhibited higher expression of NP-specific human markers, SOX9, aggrecan, collagen 2, FOXF1 and KRT19. The novelty of the study is that in vitro differentiated CPCs derived from umbilical cord MSCs, demonstrated far greater capacity to regenerate damaged IVDs, which provides basis and impetus for stem cell based clinical studies to treat degenerative disc disease. Copyright © 2016 John Wiley & Sons, Ltd.

Comparison of biological characteristics of nucleus pulposus mesenchymal stem cells derived from non-degenerative and degenerative human nucleus pulposus

Cell therapy using mesenchymal stem cells provides a promising approach for the treatment of intervertebral disc degeneration (IDD). In recent years, human nucleus pulposus mesenchymal stem cells (NPMSCs) have been identified in nucleus pulposus tissue and displayed great potential for the regeneration of IDD. However, biological differences between non-degenerative and degenerative nucleus pulposus-derived NPMSCs have remained to be defined. The aim of the present study was to compare the biological characteristics of human NPMSCs derived from non-degenerative and degenerative nucleus pulposus. NPMSCs were isolated from non-degenerative and degenerative nucleus pulposus, which were assessed using the Pfirrmann grading system. The biological characteristics of the NPMSCs, including the expression of surface markers, multipotent differentiation, colony formation, chemotactic cell migration, cell activity and stemness gene expression were compared. It was found that NPMSCs could be obtained from non-degenerative and degenerative human nucleus pulposus. However, degenerative nucleus pulposus-derived NPMSCs displayed decreased ability of colony formation, chemotactic migration, cell activity and expression of stemness genes compared with non-degenerative nucleus pulposus-derived NPMSCs. Therefore, NPMSCs derived from non-degenerative and degenerative nucleus pulposus show different biological behaviors. The degenerative status of nucleus pulposus tissue should be considered when selecting NPMSCs as a source for clinical application.

Cell therapy for the degenerating intervertebral disc

Spinal conditions related to intervertebral disc (IVD) degeneration cost billions of dollars in the US annually. Despite the prevalence and soaring cost, there is no specific treatment that restores the physiological function of the diseased IVD. Thus, it is vital to develop new treatment strategies to repair the degenerating IVD. Persons with IVD degeneration without back pain or radicular leg pain often do not require any intervention. Only patients with severe back pain related to the IVD degeneration or biomechanical instability are likely candidates for cell therapy. The IVD progressively degenerates with age in humans, and strategies to repair the IVD depend on the stage of degeneration. Cell therapy and cell-based gene therapy aim to address moderate disc degeneration; advanced stage disease may require surgery. Studies involving autologous, allogeneic, and xenogeneic cells have all shown good survival of these cells in the IVD, confirming that the disc niche is an immunologically privileged site, permitting long-term survival of transplanted cells. All of the animal studies reviewed here reported some improvement in disc structure, and 2 studies showed attenuation of local inflammation. Among the 50 studies reviewed, 25 used some type of scaffold, and cell leakage is a consistently noted problem, though some studies showed reduced cell leakage. Hydrogel scaffolds may prevent cell leakage and provide biomechanical support until cells can become established matrix producers. However, these gels need to be optimized to prevent this leakage. Many animal models have been leveraged in this research space. Rabbit is the most frequently used model (28 of 50), followed by rat, pig, and dog. Sheep and goat IVDs resemble those of humans in size and in the absence of notochordal cells. Despite this advantage, there were only 2 sheep and 1 goat studies of 50 studies in this cohort. It is also unclear if a study in large animals is needed before clinical trials since some of the clinical trials proceeded without a study in large animals. No animal studies or clinical trials completely restored IVD structure. However, results suggest cause for optimism. In light of the fact that patients primarily seek medical care for back pain, attenuating local inflammation should be a priority in benchmarks for success. Clinicians generally agree that short-term back pain should be treated conservatively. When interventions are considered, the ideal therapy should also be minimally invasive and concurrent with other procedures such as discography or discectomy. Restoration of tissue structure and preservation of spinal motion are desirable.

Strategies to Optimize Adult Stem Cell Therapy for Tissue Regeneration

Stem cell therapy aims to replace damaged or aged cells with healthy functioning cells in congenital defects, tissue injuries, autoimmune disorders, and neurogenic degenerative diseases. Among various types of stem cells, adult stem cells (i.e., tissue-specific stem cells) commit to becoming the functional cells from their tissue of origin. These cells are the most commonly used in cell-based therapy since they do not confer risk of teratomas, do not require fetal stem cell maneuvers and thus are free of ethical concerns, and they confer low immunogenicity (even if allogenous). The goal of this review is to summarize the current state of the art and advances in using stem cell therapy for tissue repair in solid organs. Here we address key factors in cell preparation, such as the source of adult stem cells, optimal cell types for implantation (universal mesenchymal stem cells vs. tissue-specific stem cells, or induced vs. non-induced stem cells), early or late passages of stem cells, stem cells with endogenous or exogenous growth factors, preconditioning of stem cells (hypoxia, growth factors, or conditioned medium), using various controlled release systems to deliver growth factors with hydrogels or microspheres to provide apposite interactions of stem cells and their niche. We also review several approaches of cell delivery that affect the outcomes of cell therapy, including the appropriate routes of cell administration (systemic, intravenous, or intraperitoneal vs. local administration), timing for cell therapy (immediate vs. a few days after injury), single injection of a large number of cells vs. multiple smaller injections, a single site for injection vs. multiple sites and use of rodents vs. larger animal models. Future directions of stem cell-based therapies are also discussed to guide potential clinical applications.

Stem cells sources for intervertebral disc regeneration

Intervertebral disc regeneration field is rapidly growing since disc disorders represent a major health problem in industrialized countries with very few possible treatments. Indeed, current available therapies are symptomatic, and surgical procedures consist in disc removal and spinal fusion, which is not immune to regardable concerns about possible comorbidities, cost-effectiveness, secondary risks and long-lasting outcomes. This review paper aims to share recent advances in stem cell therapy for the treatment of intervertebral disc degeneration. In literature the potential use of different adult stem cells for intervertebral disc regeneration has already been reported. Bone marrow mesenchymal stromal/stem cells, adipose tissue derived stem cells, synovial stem cells, muscle-derived stem cells, olfactory neural stem cells, induced pluripotent stem cells, hematopoietic stem cells, disc stem cells, and embryonic stem cells have been studied for this purpose either in vitro or in vivo. Moreover, several engineered carriers (e.g., hydrogels), characterized by full biocompatibility and prompt biodegradation, have been designed and combined with different stem cell types in order to optimize the local and controlled delivery of cellular substrates in situ. The paper overviews the literature discussing the current status of our knowledge of the different stem cells types used as a cell-based therapy for disc regeneration.

Systemic human CD34(+) cells populate the brain and activate host mechanisms to counteract nigrostriatal degeneration

AIM

Here we investigated the neuroprotective potential of systemic CD34(+) human cord blood cells (hCBCs) in a 6-hydroxydopamine rat model of Parkinson's disease.

METHODS

Purified CD34(+) hCBCs were intravenously administered to rats subjected to 6-hydroxydopamine 24 h earlier, and behavioral and immunohistological analysis performed.

RESULTS

CD34(+) hCBC administration significantly prevented host nigrostriatal degeneration inducing behavioral recovery in treated rats. Although donor hCBCs did not differentiate into neural phenotypes, they stimulated the production of new neuroblasts and angiogenesis, and reduced gliosis in recipient animals. Importantly, surviving donor hCBCs were identified, and their tissue distribution pattern correlated with the observed therapeutic effects.

CONCLUSION

Peripherally applied CD34(+) hCBCs can migrate into brain tissues and elicit host-based protective mechanisms to support the survival of midbrain dopamine neurons.

A comparison between nucleus pulposus-derived stem cell transplantation and nucleus pulposus cell transplantation for the treatment of intervertebral disc degeneration in a rabbit model

INTRODUCTION

In recent years, nucleus pulposus cell (NPC) transplantation has been used to treat intervertebral disc degeneration (IDD); however, the degenerative nature of NPCs influences its effectiveness. Nucleus pulposus-derived stem cells (NPSCs), which are self-renewing, have high expansion potential and can adapt to the intervertebral disc (IVD) microenvironment and may have a better regenerative capacity, which is favourable for treating IDD. The aim of this study was to compare the effectiveness of transplantation with NPSCs and NPCs on the regeneration of the IVD in rabbit models.

METHODS

NPSCs and NPCs were isolated from human degenerate nucleus pulposus tissue by differential adhesion method, and stem cell surface markers were detected by flow cytometry. Degenerative discs in rabbits were randomly distributed into three groups: NPSCs, NPCs and vehicle control group; the normal discs served as the normal control group. Cells of the P3 generation were prepared for transplantation. About 20 μl of cell suspension (NPSCs or NPCs) or DMEM was injected into corresponding discs, while the normal discs were left untreated. After 8 weeks, disc height was evaluated using X-ray, water content was evaluated by MRI, and gene and protein expression levels of collagen II and aggrecan in the nucleus were determined by real-time PCR and ELISA.

RESULTS

NPCs and NPSCs from the P3 generation were polygonal and spindle-shaped, respectively. Both NPSCs and NPCs strongly expressed surface markers CD73, CD90, and CD105 and weakly expressed CD34 and CD45. The relative rates of expression of CD73, CD90, and CD105 were higher in NPSCs than in NPCs. After 8 weeks, X-ray results showed no significant difference in disc height index among the groups (p > 0.05). MRI revealed that the intensity of the nucleus pulposus signal was increased in NPSCs (p < 0.05). The results from PCR and ELISA demonstrated that NPSCs promoted gene and protein expression of aggrecan instead of collagen II (p < 0.05).

CONCLUSION

Compared to NPCs, NPSCs harvested by differential adhesion method displayed a higher positive rate of stem cell surface markers and showed superior regenerative effectiveness for treating IDD in rabbit models. Therefore, NPSCs are potential candidates for cell therapy for the regeneration of the IVD.

Cell Therapy Using Bone Marrow-Derived Stem Cell Overexpressing BMP-7 for Degenerative Discs in a Rat Tail Disc Model

Degenerative discs can cause low back pain. Cell-based transplantation or growth factors therapy have been suggested as a strategy to stimulate disc regeneration. Bone marrow-derived mesenchymal stem cells (BMDMSC) containing bone morphogenetic protein-7 (BMP-7) gene were constructed. We evaluated the effectiveness of these BMP-7 overexpressing cells on degenerative discs in rat tails. In vitro and in vivo studies were designed. In the first stage, the rats were divided into two group according to discs punctured by different needle gauges (18 gauge and 22 gauge). In the second stage, the ideal size of needle was used to induce rat tail disc degeneration. These animals are divided into three groups according to timing of treatment (zero-week, two-week, four-week). Each group was divided into three treating subgroups: control group, BMDMSC group, and Baculo-BMP-7-BMDMSC group. Each rat undergoes radiography examination every two weeks. After eight weeks, the discs were histologically examined with hematoxylin and eosin stain and Alcian blue stain. The 18-gauge group exhibited significant decrease in disc height index (%) than 22-gauge group at eight weeks at both Co6-7 (58.1% ± 2.8% vs. 63.7% ± 1.0%, p = 0.020) and Co8-9 discs (62.7% ± 2.8% vs. 62.8% ± 1.5%, p = 0.010). Baculo-BMP-7-BMDMSCs group showed significant difference in disc height index compared to the BMDMSCs group at both Co6-7 (93.7% ± 1.5% vs. 84.8% ± 1.0%, p = 0.011) and Co8-9 (86.0% ± 2.1% vs. 81.8% ± 1.7%, p = 0.012). In Baculo-BMP-7-BMDMSCs group, the zero-week treatment subgroup showed significant better in disc height index compared to two-week treatment group (p = 0.044), and four-week treatment group (p = 0.011). The zero-week treatment subgroup in Baculo-BMP-7-BMDMSCs group also had significant lower histology score than two-week treatment (4.3 vs. 5.7, p = 0.045) and four-week treatment (4.3 vs. 6.0, p = 0.031). In conclusion, Baculo-BMP-7-BMDMSC can slow down the progression of disc degeneration, but could not provide evidence of regeneration. Early treatment might obtain more distinct results.

[The Use of Stem Cells in the Treatment of Intervertebral Disc Degeneration]

The paper presents a review of current data on the use of stem cells in the treatment of intervertebral disc degeneration. Acute spinal pain is often a consequence of the pathology affecting the intervertebral disc. Many applied therapeutic techniques do not provide effective results as expected because most of them address symptoms, but do not treat the underlying disease. We have outlined current findings on the molecular mechanisms of intervertebral disc degeneration, analyzed international experimental studies demonstrating the feasibility of a stem cell therapy for intervertebral disc degeneration. The conducted studies reported on the clinical application of mesenchymal stem cells or stem cells derived from adipose, synovium, and bone marrow tissue. The most pressing and undetermined issues that require further experimental and clinical studies are indicated and defined in the article.

Transplantation of human Wharton's jelly-derived mesenchymal stem cells highly expressing TGFβ receptors in a rabbit model of disc degeneration

Introduction

Mesenchymal stem cells (MSCs) are widely considered to hold promise for the treatment of intervertebral disc (IVD) degeneration. However, variation in the therapeutic efficacy of MSCs is a major problem and the derivation of MSCs for use in IVD regeneration has not been optimized. Additionally, no data are available on the efficacy of Wharton’s Jelly-derived MSC (WJ-MSC) transplantation in an animal model of IVD degeneration.

Methods

This study evaluated the effectiveness of a cross-linked hyaluronic acid (XHA) scaffold loaded with human WJ-MSCs, according to their expression levels of transforming growth factor-β receptor I/activin-like kinase receptor 5 (TβRI/ALK5) and TβRII, for IVD regeneration in a rabbit model. We compared the degree of IVD regeneration between rabbits transplanted with a XHA scaffold loaded with WJ-MSCs highly and lowly expressing TβRI/ALK5 and TβRII (MSC-highTR and MSC-lowTR, respectively) using magnetic resonance imaging (MRI) and histological analysis.

Results

At 12 weeks after transplantation, T2-weighted MRI analysis showed significant restoration of the disc water content in rabbits treated with a MSC-highTR-loaded XHA scaffold in comparison to rabbits treated with the scaffold alone or a MSC-lowTR-loaded XHA scaffold. In addition, morphological and histological analyses revealed that IVD regeneration was highest in rabbits transplanted with a MSC-highTR-loaded XHA scaffold.

Conclusion

Taken together, our results suggest that a MSC-highTR-loaded XHA scaffold supports IVD regeneration more effectively than a MSC-lowTR-loaded XHA scaffold. This study supports the potential clinical use of MSC-highTR-loaded XHA scaffolds to halt IVD degeneration or to enhance IVD regeneration.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-015-0183-1) contains supplementary material, which is available to authorized users.

Stem Cell Approaches to Intervertebral Disc Regeneration: Obstacles from the Disc Microenvironment

Intervertebral disc (IVD) degeneration results in segmental instability and irritates neural compressive symptoms, such as low back pain and motor deficiency. The transplanting of stem cell into degenerative discs has attracted increasing clinical attention, as a new and proven approach to alleviating disc degeneration and to relieving discogenic pains. Aside from supplementation with stem cells, the IVD itself already contains a pool of stem and progenitor cells. Since the resident disc stem cells are incapable of reversing the pathologic changes that occur during aging and disc degeneration, it has been debated as to whether transplanted stem cells are capable of providing an efficient and durable therapeutic effect, even though there have been positive outcomes in both animal models and in clinical trials. This review aims to decipher the interactions between the stem cell and the disc microenvironment. Within their new niches in the IVD, the exogenous stem cell shows metabolic adaptation to the low-glucose supply, hypoxia, and compressive loadings, but demonstrates little tolerance to the disc-like acidity and hypertonicity. Similarly, the survival of endogenous stem cells is threatened as well by the harsh disc microenvironment, which may exhaust the stem cell resources and restrict the self-repair capacity of a degenerating IVD. To eliminate the intrinsic obstacles within the stressful disc niches, stem cells should be delivered with an injectable scaffold that provides both survival and mechanical support. Quick healing or concretion of the injection injuries, which minimizes stem cell leakage and disturbance to disc homeostasis, is of equal importance toward achieving efficient stem cell-based disc regeneration.

The effects of human Wharton's jelly cell transplantation on the intervertebral disc in a canine disc degeneration model

Introduction

Cell-based therapy was a promising treatment method for disc degenerative diseases. Wharton’s jelly cell (WJC) has been explored to cure various human diseases, while it still remains unknown about this MSC for disc repair. In our prior work, WJCs could differentiate into nucleus pulposus (NP)-like cells by co-culturing with NP cells in vitro. Thence, the aim of this study was further to investigate the survival and function of WJCs in vivo after transplantation into degenerated canine discs.

Method

WJCs were isolated from human umbilical cords and labeled with EGFP. The degeneration of L4-5, L5-6, and L6-7 discs of beagles was induced by aspirating the NP tissues. Four weeks after the operation, the injured discs were left to be no treatment at L4-5 (DS group), injected with 0.9 % saline at L5-6 (FS group), and transplanted with EGFP-labeled WJCs at L6-7 (TS group). In all animals, the intact disc L3-4 served as a control (CS group). The animals were followed up for 24 weeks after initial operation. Spine imaging was evaluated at 4, 8, 12, and 24 weeks, respectively. Histologic, biomechanics and gene expression analyses were performed at 24 weeks. Immunohistochemistry for aggrecan, types II collagen, SOX-9 was employed to investigate the matrix formation in the NP.

Results

The TS group showed a significantly smaller reduction in the disc height and T2-weighted signal intensity, and a better spinal segmental stability than DS and FS groups. Histologic assay demonstrated that WJCs were specifically detected in TS group at 24 weeks and the discs of TS group maintained a relatively well preserved structure as compared to the discs of DS and FS groups. Furthermore, real-time PCR and immunohistochemistry demonstrated that expressions of disc matrix genes, aggrecan, type II collagen, and SOX-9, were up-regulated in TS group compared to DS and FS groups.

Conclusion

WJCs could not only survive in the degenerate IVDs, but also promote the disc matrix formation of aggrecan and type II collagen in the degenerate IVDs. It may have value in cell-based therapy for degenerative disc disease.

Allogeneic Articular Chondrocyte Transplantation Downregulates Interleukin 8 Gene Expression in the Degenerating Rabbit Intervertebral Disk In Vivo

OBJECTIVE

The aim of this study was to investigate whether repopulating the degenerating intervertebral disk (IVD) with articular chondrocytes will decrease inflammation in the degenerating rabbit IVD.

DESIGN

This was a biologic study in a rabbit IVD-injury model in vivo. Dual cell tracking methods (infrared dye labeling and adenovirus transduction) were used to demonstrate the viability of allogeneic articular chondrocytes injected into degenerating rabbit IVDs. Interleukin 8 gene expression was determined via real-time polymerase chain reaction. Infiltrating inflammatory cells (macrophages, T cells, or neutrophils) were examined with immunohistochemistry. The IVDs were also examined by routine histology.

RESULTS

Articular chondrocytes labeled with infrared dye were detected in the degenerating IVDs at both 2 and 8 wks after injection. At the 2-wk time point, interleukin 8 gene expression was comparable in IVDs injected with chondrocytes and in intact disks as control (P = 0.647), whereas its expression in IVDs injected with saline increased 50-fold (P = 0.028). Transgene expression of red fluorescent protein, β-galactosidase, and human bone morphogenetic protein 7 diminished at 8 wks after injection. IVDs injected with chondrocytes overexpressing human bone morphogenetic protein 7 did not show lower interleukin 8 gene expression or improved histology. Macrophages were consistently detected by immunohistochemistry in the cartilage formed around the needle insertion sites in both the saline and chondrocyte groups, whereas neither T cells nor neutrophils were detected.

CONCLUSIONS

Allogeneic rabbit articular chondrocyte survived in the degenerating rabbit IVDs for at least 8 wks. Cell treatment resulted in reduced IVD inflammation but did not significantly improve IVD structure.

Efficacy and Safety of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells in Anterior Cruciate Ligament Reconstruction of a Rabbit Model: New Strategy to Enhance Tendon Graft Healing

PURPOSE

To investigate whether non-autologous transplantation of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) could be integrated safely at the bone-tendon junction without immune rejection and could enhance bone-tendon healing effectively during anterior cruciate ligament (ACL) reconstruction in an animal model.

METHODS

ACL reconstructions using hamstring tendons were performed in 30 adult rabbits. The bone tunnels were treated with hUCB-MSCs or were untreated. The specimens were harvested at 4, 8, and 12 weeks. We performed a gross examination of the knee joint; a histologic assessment using H&E staining, as well as immunohistochemical staining, for type II collagen; and an evaluation of bone tunnel widening using micro-computed tomography.

RESULTS

No evidence of immune rejection was detected. Tendon-bone healing through Sharpey-like fibers was noticed around tendon grafts at 12 weeks in the control group. A smooth transition from bone to tendon through broad fibrocartilage formation was identified in the treatment group, and the interface zone showed abundant type II collagen production on immunohistochemical staining. Histologic scores for bone-tendon healing were significantly higher in the treatment group at all time points (P < .001). Micro-computed tomography at 12 weeks showed a significantly smaller tibial (P = .029) and femoral (P = .033) bone tunnel enlargement in the treated group than in the control group.

CONCLUSIONS

Non-autologous transplantation of hUCB-MSCs was applied in ACL reconstruction without early immune rejection. There was enhanced tendon-bone healing through broad fibrocartilage formation with higher histologic scores and decreased femoral and tibial tunnel widening compared with the control group (79.2% and 80%, respectively, of the control group tunnel area at 12 weeks).

CLINICAL RELEVANCE

Non-autologous transplantation of hUCB-MSCs has therapeutic potential in promoting tendon-to-bone healing after ACL reconstruction. Further study in the human model is warranted.

Cell-Based Therapies Used to Treat Lumbar Degenerative Disc Disease: A Systematic Review of Animal Studies and Human Clinical Trials

Low back pain and degenerative disc disease are a significant cause of pain and disability worldwide. Advances in regenerative medicine and cell-based therapies, particularly the transplantation of mesenchymal stem cells and intervertebral disc chondrocytes, have led to the publication of numerous studies and clinical trials utilising these biological therapies to treat degenerative spinal conditions, often reporting favourable outcomes. Stem cell mediated disc regeneration may bridge the gap between the two current alternatives for patients with low back pain, often inadequate pain management at one end and invasive surgery at the other. Through cartilage formation and disc regeneration or via modification of pain pathways stem cells are well suited to enhance spinal surgery practice. This paper will systematically review the current status of basic science studies, preclinical and clinical trials utilising cell-based therapies to repair the degenerate intervertebral disc. The mechanism of action of transplanted cells, as well as the limitations of published studies, will be discussed.

Advancing the cellular and molecular therapy for intervertebral disc disease

The healthy intervertebral disc (IVD) fulfils the essential function of load absorption, while maintaining multi-axial flexibility of the spine. The interrelated tissues of the IVD, the annulus fibrosus, the nucleus pulposus, and the cartilaginous endplate, are characterised by their specific niche, implying avascularity, hypoxia, acidic environment, low nutrition, and low cellularity. Anabolic and catabolic factors balance a slow physiological turnover of extracellular matrix synthesis and breakdown. Deviations in mechanical load, nutrient supply, cellular activity, matrix composition and metabolism may initiate a cascade ultimately leading to tissue dehydration, fibrosis, nerve and vessel ingrowth, disc height loss and disc herniation. Spinal instability, inflammation and neural sensitisation are sources of back pain, a worldwide leading burden that is challenging to cure. In this review, advances in cell and molecular therapy, including mobilisation and activation of endogenous progenitor cells, progenitor cell homing, and targeted delivery of cells, genes, or bioactive factors are discussed.

The role of stem cell therapies in degenerative lumbar spine disease: a review

Degenerative conditions of the lumbar spine are extremely common. Ninety percent of people over the age of 60 years have degenerative change on imaging; however, only a small minority of people will require spine surgery (Hicks et al. Spine (Phila Pa 1976) 34(12):1301-1306, 2009). This minority, however, constitutes a core element of spinal surgery practice. Whilst the patient outcomes from spinal surgeries have improved in recent years, some patients will remain with pain and disability despite technically successful surgery. Advances in regenerative medicine and stem cell therapies, particularly the use of mesenchymal stem cells and allogeneic mesenchymal precursor cells, have led to numerous clinical trials utilising these cell-based therapies to treat degenerative spinal conditions. Through cartilage formation and disc regeneration, fusion enhancement or via modification of pain pathways, stem cells are well suited to enhance spinal surgery practice. This review will focus on the outcomes of lumbar spinal procedures and the role of stem cells in the treatment of degenerative lumbar conditions to enhance clinical practice. The current status of clinical trials utilising stem cell therapies will be discussed, providing clinicians with an overview of the various cell-based treatments likely to be available to patients in the near future.

Stem cell therapy for intervertebral disc regeneration: obstacles and solutions

Intervertebral disc (IVD) degeneration is frequently associated with low back and neck pain, which accounts for disability worldwide. Despite the known outcomes of the IVD degeneration cascade, the treatment of IVD degeneration is limited in that available conservative and surgical treatments do not reverse the pathology or restore the IVD tissue. Regenerative medicine for IVD degeneration, by injection of IVD cells, chondrocytes or stem cells, has been extensively studied in the past decade in various animal models of induced IVD degeneration, and has progressed to clinical trials in the treatment of various spinal conditions. Despite preliminary results showing positive effects of cell-injection strategies for IVD regeneration, detailed basic research on IVD cells and their niche indicates that transplanted cells are unable to survive and adapt in the avascular niche of the IVD. For this therapeutic strategy to succeed, the indications for its use and the patients who would benefit need to be better defined. To surmount these obstacles, the solution will be identified only by focused research, both in the laboratory and in the clinic.

3D-Printed Drug/Cell Carrier Enabling Effective Release of Cyclosporin A for Xenogeneic Cell-Based Therapy

Systemic administration of the immunosuppressive drug cyclosporin A (CsA) is frequently associated with a number of side effects; therefore, sometimes it cannot be applied in sufficient dosage after allogeneic or xenogeneic cell transplantation. Local delivery is a possible solution to this problem. We used 3D printing to develop a CsA-loaded 3D drug carrier for the purpose of local and sustained delivery of CsA. The carrier is a hybrid of CsA-poly(lactic-co-glycolic acid) (PLGA) microsphere-loaded hydrogel and a polymeric framework so that external force can be endured under physiological conditions. The expression of cytokines, which are secreted by spleen cells activated by Con A, and which are related to immune rejection, was significantly decreased in vitro by the released CsA from the drug carrier. Drug carriers seeded with xenogeneic cells (human lung fibroblast) were subcutaneously implanted into the BALB/c mouse. As a result, T-cell-mediated rejection was also significantly suppressed for 4 weeks. These results show that the developed 3D drug carrier can be used as an effective xenogeneic cell delivery system with controllable immunosuppressive drugs for cell-based therapy.

Intra-articular administration of xenogeneic neonatal Mesenchymal Stromal Cells early after meniscal injury down-regulates metalloproteinase gene expression in synovium and prevents cartilage degradation in a rabbit model of osteoarthritis

OBJECTIVE

The anti-inflammatory and anti-catabolic effects of neonatal Mesenchymal Stromal Cell (MSC) were investigated in a xenogeneic model of mild osteoarthritis (OA). The paracrine properties of MSC on synoviocytes were further investigated in vitro.

STUDY DESIGN

OA was induced by medial meniscal release (MMR) in 30 rabbit knees. A single early (day 3) or delayed (day 15) intra-articular (IA) injection of MSC isolated from equine Umbilical Cord Wharton's jelly (UC-MSC) was performed. Rabbits were euthanized on days 15 or 56. OA grading was performed and gene expression of inflammatory cytokines and metalloproteinases was measured in synovial tissue. Paracrine effects of UC-MSC were investigated using UC-conditioned vs control medium on rabbit primary synoviocytes stimulated with interleukin 1 beta in vitro.

RESULTS

No adverse local or systemic responses were observed clinically after xenogeneic UC-MSC injection. At study end point, cartilage fibrillation was lower in early treatment than in delayed treatment group. Cellular infiltrate was observed in the synovium of both UC-MSC groups. OA synovium exhibited a reduced expression of metalloproteinases-1, -3, -13 in the early cell-treated group at d56. In vitro, UC-conditioned medium exerted anti-inflammatory and anti-catabolic effects on synoviocytes exposed to pro-inflammatory stimulus.

CONCLUSIONS

Early IA injection of equine UC-MSC was effective in preventing OA signs in rabbit knees following MMR. UC-MSC target the synovium and modulate the gene expression pattern of synoviocytes to promote an anti-catabolic environment. This confirms the synovium is a major target and mediator of MSC therapy, modulating the expression of matrix-degrading enzymes.

A systematic review of the safety and efficacy of mesenchymal stem cells for disc degeneration: insights and future directions for regenerative therapeutics

Intervertebral disc degeneration is associated with low-back pain. Mesenchymal stem cells (MSCs) have been used to "regenerate" the disc. The aim of this study was to perform a systematic review of comparative controlled studies that have assessed the safety and efficacy of using MSCs for disc regeneration. Literature databases were extensively searched. Trial design, subject-type, MSC sources, injection method, disc assessment, outcome intervals, and complication events were assessed. Validity of each study was performed. Twenty-four animal studies were included with 20.8% of the studies reporting randomization of groups. Trials in humans fulfilling inclusion criteria were not noted. The studies represented 862 discs that were injected with MSCs and 1,603 discs as controls. All three types of MSCs (ie, bone marrow, synovial, and adipose tissues) showed successful inhibition of disc degeneration. Bone-marrow-derived MSCs demonstrated superior quality of repair compared with other non-MSC treatments. A 2.7% overall complication rate was noted, whereby complications were noted only in rabbits. Overall, evidence suggested that MSCs increased disc space height in the majority of animal models. This is the first systematic review to assess the safety and efficacy of MSCs for the treatment of disc degeneration. Short-term MSC transplantation is safe and effective; however, additional, larger, and higher-quality studies are needed to assess the long-term safety and efficacy. Inconsistencies in methodological design and outcome parameters prevent any robust conclusions. Human-based clinical trials are needed. Recommendations are further made to improve efficacy, reduce potential complications, and standardize techniques for future studies.

Mesenchymal progenitor cells combined with pentosan polysulfate mediating disc regeneration at the time of microdiscectomy: a preliminary study in an ovine model

OBJECT

Following microdiscectomy, discs generally fail to undergo spontaneous regeneration and patients may experience chronic low-back pain and recurrent disc prolapse. In published studies, formulations of mesenchymal progenitor cells combined with pentosan polysulfate (MPCs+PPS) have been shown to regenerate disc tissue in animal models, suggesting that this approach may provide a useful adjunct to microdiscectomy. The goal of this preclinical laboratory study was to determine if the transplantation of MPCs+PPS, embedded in a gelatin/fibrin scaffold (SCAF), and transplanted into a defect created by microdiscectomy, could promote disc regeneration.

METHODS

A standardized microdiscectomy procedure was performed in 18 ovine lumbar discs. The subsequent disc defects were randomized to receive either no treatment (NIL), SCAF only, or the MPC+PPS formulation added to SCAF (MPCs+PPS+SCAF). Necropsies were undertaken 6 months postoperatively and the spines analyzed radiologically (radiography and MRI), biochemically, and histologically.

RESULTS

No adverse events occurred throughout the duration of the study. The MPC+PPS+SCAF group had significantly less reduction in disc height compared with SCAF-only and NIL groups (p < 0.05 and p < 0.01, respectively). Magnetic resonance imaging Pfirrmann scores in the MPC+PPS+SCAF group were significantly lower than those in the SCAF group (p = 0.0213). The chaotropic solvent extractability of proteoglycans from the nucleus pulposus of MPC+PPS+SCAF-treated discs was significantly higher than that from the SCAF-only discs (p = 0.0312), and using gel exclusion chromatography, extracts from MPC+PPS+SCAF-treated discs also contained a higher percentage of proteoglycan aggregates than the extracts from both other groups. Analysis of the histological sections showed that 66% (p > 0.05) of the MPC+PPS+SCAF-treated discs exhibited less degeneration than the NIL or SCAF discs.

CONCLUSIONS

These findings demonstrate the capacity of MPCs in combination with PPS, when embedded in a gelatin sponge and sealed with fibrin glue in a microdiscectomy defect, to restore disc height, disc morphology, and nucleus pulposus proteoglycan content.

Mesenchymal stem cells: potential application in intervertebral disc regeneration

Chronic low back pain is one of the leading public health problems in developed countries. Degeneration of the intervertebral disc (IVD) is a major pathological process implicated in low back pain, which is characterized by cellular apoptosis and senescence with reduced synthesis of extracellular matrix (ECM). Currently, there is no clinical therapy targeting the reversal of disc degeneration. Recent advances in cellular and molecular biology have provided an exciting approach to disc regeneration that focuses on the delivery of viable cells to the degenerative disc. Adult mesenchymal stem cells (MSCs) are multipotent stem cells with self-renewal capacities and are able to differentiate into diverse specialized cell types, including chondrocyte lineages. The potential of stem cell therapy in disc degeneration is to repopulate the disc with viable cells capable of producing the ECM and restoring damaged tissue. The present literature review summarizes recent advances in basic research and clinical trials of MSCs to provide an outline of the key roles of MSCs therapies in disc repair. The review also discusses the controversies, challenges and therapeutic concepts for the future.

Delivering mesenchymal stem cells in collagen microsphere carriers to rabbit degenerative disc: reduced risk of osteophyte formation

Mesenchymal stem cells (MSCs) have the potential to treat early intervertebral disc (IVD) degeneration. However, during intradiscal injection, the vast majority of cells leaked out even in the presence of hydrogel carrier. Recent evidence suggests that annulus puncture is associated with cell leakage and contributes to osteophyte formation, an undesirable side effect. This suggests the significance of developing appropriate carriers for intradiscal delivery of MSCs. We previously developed a collagen microencapsulation platform, which entraps MSCs in a solid microsphere consisting of collagen nanofiber meshwork. These solid yet porous microspheres support MSC attachment, survival, proliferation, migration, differentiation, and matrix remodeling. Here we hypothesize that intradiscal injection of MSCs in collagen microspheres will outperform that of MSCs in saline in terms of better functional outcomes and reduced side effects. Specifically, we induced disc degeneration in rabbits and then intradiscally injected autologous MSCs, either packaged within collagen microspheres or directly suspended in saline, into different disc levels. Functional outcomes including hydration index and disc height were monitored regularly until 6 months. Upon sacrifice, the involved discs were harvested for histological, biochemical, and biomechanical evaluations. MSCs in collagen microspheres showed advantage over MSCs in saline in better maintaining the dynamic mechanical behavior but similar performance in hydration and disc height maintenance and matrix composition. More importantly, upon examination of gross appearance, radiograph, and histology of IVD, delivering MSCs in collagen microspheres significantly reduced the risk of osteophyte formation as compared to that in saline. This work demonstrates the significance of using cell carriers during intradiscal injection of MSCs in treating disc degeneration.

Thermoreversible hyaluronan-based hydrogel supports in vitro and ex vivo disc-like differentiation of human mesenchymal stem cells

BACKGROUND CONTEXT

The fate of human mesenchymal stem cells (hMSCs) supplied to the degenerating intervertebral disc (IVD) is still not fully understood and can be negatively affected by low oxygen, pH, and glucose concentration of the IVD environment. The hMSC survival and yield upon injection of compromised IVD could be improved by the use of an appropriate carrier and/or by predifferentiation of hMSCs before injection.

PURPOSE

To optimize hMSC culture conditions in thermoreversible hyaluronan-based hydrogel, hyaluronan-poly(N-isopropylacrylamide) (HA-pNIPAM), to achieve differentiation toward the disc phenotype in vitro, and evaluate whether preconditioning contributes to a better hMSC response ex vivo.

STUDY DESIGN

In vitro and ex vivo whole-organ culture of hMSCs.

METHODS

In vitro cultures of hMSCs were conducted in HA-pNIPAM and alginate for 1 week under hypoxia in chondropermissive medium alone and with the supplementation of transforming growth factor β1 or growth and differentiation factor 5 (GDF-5). Ex vivo, hMSCs were either suspended in HA-pNIPAM and directly supplied to the IVDs or predifferentiated with GDF-5 for 1 week in HA-pNIPAM and then supplied to the IVDs. Cell viability was evaluated by Live-Dead assay, and DNA, glycosaminoglycan (GAG), and gene expression profiles were used to assess hMSC differentiation toward the disc phenotype.

RESULTS

The HA-pNIPAM induced hMSC differentiation toward the disc phenotype more effectively than alginate: in vitro, higher GAG/DNA ratio and higher collagen type II, SOX9, cytokeratin-19, cluster of differentiation 24, and forkhead box protein F1 expressions were found for hMSCs cultured in HA-pNIPAM compared with those cultured in alginate, regardless of the addition of growth factors. Ex vivo, direct combination of HA-pNIPAM with the disc environment induced a stronger disc-like differentiation of hMSCs than predifferentiation of hMSCs followed by their delivery to the discs.

CONCLUSIONS

Hyaluronan-based thermoreversible hydrogel supports hMSC differentiation toward the disc phenotype without the need for growth factor supplementation in vitro and ex vivo. Further in vivo studies are required to confirm the suitability of this hydrogel as an effective stem cell carrier for the treatment of IVD degeneration.

Bone marrow stromal cells inhibit caspase-12 expression in rats with spinal cord injury

The mechanisms underlying the potentially beneficial effect of bone marrow stem cells (BMSCs) on spinal cord injury (SCI) are unknown. Therefore, the aim of the present study was to explore the protective effect of BMSCs in rats with SCI. A total of 45 adult male Sprague-Dawley rats were randomly divided into three groups; the SCI group (n=15), the BMSC group (n=15) and the sham-operation group (n=15). In the SCI and BMSC treatment groups, a modified Allen’s weight-drop technique was used to induce SCI. The BMSC treatment group received an injection of BMSCs using a microneedle into the epicenter of the spinal cord 24 h after injury. Rats in the sham-operation group were not subjected to SCI; however, the corresponding vertebral laminae were removed. Seven days after transplantation, a rapid recovery was observed in the Basso, Beattie and Bresnahan (BBB) scores of the BMSC treatment group, whereas the BBB scores in the SCI group remained low (P<0.05). Caspase-12 expression in the SCI group was increased compared with that in the sham-operation group, whereas caspase-12 expression was attenuated 24 h after transplantation in the BMSC treatment group (P<0.05). In conclusion, the transplantation of BMSCs may improve locomotor function and attenuate caspase-12 expression following SCI. Therefore, it is likely to be an effective strategy for preventing severe injury of the spinal cord.

Effects of nucleus pulposus cell-derived acellular matrix on the differentiation of mesenchymal stem cells

Recent attempts to treat disc degeneration with mesenchymal stem cells (MSCs) showed encouraging results. Differentiating MSCs towards nucleus pulposus cell (NPC)-like lineages represents a speculative mechanism. Niche factors including hypoxia, growth factors and cell-cell interactions have been suggested but the matrix niche factor has not been studied. Our collagen microencapsulation provides a 3D model to study matrix niche as it enables the encapsulated cells to remodel the template matrix. We previously demonstrated the chondro-inductive role of of chondrocytes-derived matrix in MSCs and showed that NPCs maintained their phenotype and remodeled the template matrix of collagen microspheres into a glycosaminoglycan (GAG)-rich one. Here we aim to study the effects of NPC-derived matrix on MSC differentiation towards NPC-like lineages by firstly producing an NPC-derived matrix in collagen microspheres, secondly optimizing a decellularization protocol to discard NPCs yet retaining the matrix, thirdly repopulating the acellular NPC-derived matrix with MSCs and fourthly evaluating their phenotype. Finally, we injected these microspheres in a pilot rabbit disc degeneration model. Results showed that NPCs survived, maintained their phenotypic markers and produced GAGs. A decellularization protocol with maximal removal of the NPCs, minimal loss in major matrix components and partial retention of NPC-specific markers was identified. The resulting acellular matrix supported MSC survival and matrix production, and up-regulated the gene expression of NPC markers including type II collagen and glypican 3. Finally, injection of MSC in these microspheres in rabbit degenerative disc better maintained hydration level with more pronounced staining of GAGs and type II collagen than controls.

The effects of microenvironment in mesenchymal stem cell-based regeneration of intervertebral disc

BACKGROUND CONTEXT

Recent studies have demonstrated new therapeutic strategy using transplantation of mesenchymal stem cells (MSCs), especially bone marrow-derived MSCs (BM-MSCs), to preserve intervertebral disc (IVD) structure and functions. It is important to understand whether and how the MSCs survive and thrive in the hostile microenvironment of the degenerated IVD. Therefore, this review majorly examines how resident disc cells, hypoxia, low nutrition, acidic pH, mechanical loading, endogenous proteinases, and cytokines regulate the behavior of the exogenous MSCs.

PURPOSE

To review and summarize the effect of the microenvironment in biological characteristics of BM-MSCs for IVD regeneration; the presence of endogenous stem cells and the state of the art in the use of BM-MSCs to regenerate the IVD in vivo were also discussed.

STUDY DESIGN

Literature review.

METHODS

MEDLINE electronic database was used to search for articles concerning stem/progenitor cell isolation from the IVD, regulation of the components of microenvironment for MSCs, and MSC-based therapy for IVD degeneration. The search was limited to English language.

RESULTS

Stem cells are probably resident in the disc, but exogenous stem cells, especially BM-MSCs, are currently the most popular graft cells for IVD regeneration. The endogenous disc cells and the biochemical and biophysical components in the degenerating disc present a complicated microenvironment to regulate the transplanted BM-MSCs. Although MSCs regenerate the mildly degenerative disc effectively in the experimental and clinical trials, many underlying questions are in need of further investigation.

CONCLUSIONS

There has been a dramatic improvement in the understanding of potential MSC-based therapy for IVD regeneration. The use of MSCs for IVD degeneration is still at the stage of preclinical and Phase 1 studies. The effects of the disc microenvironment in MSCs survival and function should be closely studied for transferring MSC transplantation from bench to bedside successfully.

Challenges and strategies in the repair of ruptured annulus fibrosus

Lumbar discectomy is the surgical procedure most frequently performed for patients suffering from low back pain and sciatica. Disc herniation as a consequence of degenerative or traumatic processes is commonly encountered as the underlying cause for the painful condition. While discectomy provides favourable outcome in a majority of cases, there are conditions where unmet requirements exist in terms of treatment, such as large disc protrusions with minimal disc degeneration; in these cases, the high rate of recurrent disc herniation after discectomy is a prevalent problem. An effective biological annular repair could improve the surgical outcome in patients with contained disc herniations but otherwise minor degenerative changes. An attractive approach is a tissue-engineered implant that will enable/stimulate the repair of the ruptured annulus. The strategy is to develop three-dimensional scaffolds and activate them by seeding cells or by incorporating molecular signals that enable new matrix synthesis at the defect site, while the biomaterial provides immediate closure of the defect and maintains the mechanical properties of the disc. This review is structured into (1) introduction, (2) clinical problems, current treatment options and needs, (3) biomechanical demands, (4) cellular and extracellular components, (5) biomaterials for delivery, scaffolding and support, (6) pre-clinical models for evaluation of newly developed cell- and material-based therapies, and (7) conclusions. This article highlights that an interdisciplinary approach is necessary for successful development of new clinical methods for annulus fibrosus repair. This will benefit from a close collaboration between research groups with expertise in all areas addressed in this review.

Stem cell therapy for degenerative disc disease

Low back pain is widely recognized as one of the most prevalent pathologies in the developed world. In the United States, low back pain is the most common health problem for adults under the age of 50, resulting in significant societal and personal costs. While the causes of low back pain are myriad, it has been significantly associated with intervertebral disc (IVD) degeneration. Current first-line therapies for IVD degeneration such as physical therapy and spinal fusion address symptoms, but do not treat the underlying degeneration. The use of tissue engineering to treat IVD degeneration provides an opportunity to correct the pathological process. Novel techniques are currently being investigated and have shown mixed results. One major avenue of investigation has been stem cell injections. Mesenchymal stem cells (MSCs) have shown promise in small animal models, but results in larger vertebrates have been mixed.

Bi-directional exchange of membrane components occurs during co-culture of mesenchymal stem cells and nucleus pulposus cells

Mesenchymal stem cell (MSC)-based therapies have been proposed as novel treatments for intervertebral disc (IVD) degeneration. We have previously demonstrated that when MSCs are co-cultured with nucleus pulposus (NP) cells with direct cell-cell contact, they differentiate along the NP lineage and simultaneously stimulate the degenerate NP cell population to regain a normal (non-degenerate) phenotype, an effect which requires cell-cell communication. However, the mechanisms by which NP cells and MSCs interact in this system are currently unclear. Thus, in this study we investigated a range of potential mechanisms for exchange of cellular components or information that may direct these changes, including cell fusion, gap-junctional communication and exchange of membrane components by direct transfer or via microvesicle formation. Flow cytometry of fluorescently labeled MSCs and NP cells revealed evidence of some cell fusion and formation of gapjunctions, although at the three timepoints studied these phenomena were detectable only in a small proportion of cells. While these mechanisms may play a role in cell-cell communication, the data suggests they are not the predominant mechanism of interaction. However, flow cytometry of fluorescently dual-labeled cells showed that extensive bi-directional transfer of membrane components is operational during direct co-culture of MSCs and NP cells. Furthermore, there was also evidence for secretion and internalization of membrane-bound microvesicles by both cell types. Thus, this study highlights bi-directional intercellular transfer of membrane components as a possible mechanism of cellular communication between MSC and NP cells.

Mesenchymal cell populations: development of the induction systems for Schwann cells and neuronal cells and finding the unique stem cell population

Mesenchymal cell populations, referred to as mesenchymal stem cells or multipotent stromal cells (MSCs), which include bone marrow stromal cells (BMSCs), umbilical cord stromal cells and adipose stromal cells (ASCs), participate in tissue repair when transplanted into damaged or degenerating tissues. The trophic support and immunomodulation provided by MSCs can protect against tissue damage, and the differentiation potential of these cells may help to replace lost cells. MSCs are easily accessible and can be expanded on a large scale. In addition, BMSCs and ASCs can be harvested from the patient himself. Thus, MSCs are considered promising candidates for cell therapy. In this review, I will discuss recently discovered high-efficiency induction systems for deriving Schwann cells and neurons from MSCs. Other features of MSCs that are important for tissue repair include the self-renewing property of stem cells and their potential for differentiation. Thus, I will also discuss the stemness of MSCs and describe the discovery of a certain stem cell type among adult MSCs that can self-renew and differentiate into cells of all three germ layers. Furthermore, I will explore the prospects of using this cell population for cell therapy.

Investigation of different cell types and gel carriers for cell-based intervertebral disc therapy, in vitro and in vivo studies

Biological treatment options for the repair of intervertebral disc damage have been suggested for patients with chronic low back pain. The aim of this study was to investigate possible cell types and gel carriers for use in the regenerative treatment of degenerative intervertebral discs (IVD). In vitro: human mesenchymal cells (hMSCs), IVD cells (hDCs), and chondrocytes (hCs) were cultivated in three gel types: hyaluronan gel (Durolane®), hydrogel (Puramatrix®), and tissue-glue gel (TISSEEL®) in chondrogenic differentiation media for 9 days. Cell proliferation and proteoglycan accumulation were evaluated with microscopy and histology. In vivo: hMSCs or hCs and hyaluronan gel were co-injected into injured IVDs of six minipigs. Animals were sacrificed at 3 or 6 months. Transplanted cells were traced with anti-human antibodies. IVD appearance was visualized by MRI, immunohistochemistry, and histology. Hyaluronan gel induced the highest cell proliferation in vitro for all cell types. Xenotransplanted hMSCs and hCs survived in porcine IVDs for 6 months and produced collagen II in all six animals. Six months after transplantation of cell/gel, pronounced endplate changes indicating severe IVD degeneration were observed at MRI in 1/3 hC/gel, 1/3 hMSCs/gel and 1/3 gel only injected IVDs at MRI and 1/3 hMSC/gel, 3/3 hC/gel, 2/3 gel and 1/3 injured IVDs showed positive staining for bone mineralization. In 1 of 3 discs receiving hC/gel, in 1 of 3 receiving hMSCs/gel, and in 1 of 3 discs receiving gel alone. Injected IVDs on MRI results in 1 of 3 hMSC/gel, in 3 of 3 hC/gel, in 2 of 3 gel, and in 1 of 3 injured IVDs animals showed positive staining for bone mineralization. The investigated hyaluronan gel carrier is not suitable for use in cell therapy of injured/degenerated IVDs. The high cell proliferation observed in vitro in the hyaluronan could have been a negative factor in vivo, since most cell/gel transplanted IVDs showed degenerative changes at MRI and positive bone mineralization staining. However, this xenotransplantation model is valuable for evaluating possible cell therapy strategies for human degenerated IVDs.

Stem cell regeneration of the intervertebral disk

The use of stem cell applications has been explored and aimed at regenerating the intervertebral disk. The microenvironment in which cells of the intervertebral disk reside is harsh; however, researchers have reported on many applications for stem cells, including research aimed at defining and stimulating endogenous stem cell populations, methods to induce stem cell differentiation toward intervertebral disk cell phenotype in vivo, and direct transplantation of stem cells into damaged intervertebral disk to promote transplanted site-dependant differentiation. Successful results have been reported, although limitations remain. This article reviews the current status of stem cell research as applied to the intervertebral disk.

Differential response of human bone marrow stromal cells to either TGF-β(1) or rhGDF-5

Cell therapy along with growth factor injection is currently widely investigated to restore the intervertebral disc. However, there is increasing evidence that transplanted unconditioned bone marrow-derived stromal cells (BMSCs) cannot thrive in the intervertebral disc "niche". Moreover, uncertainty exists with respect to the cell phenotype that would be suitable to inject. The intervertebral disc cell phenotype only recently has been started to be characterised using transcriptomics profiling. Recent findings suggest that cytokeratin 19 (KRT-19) could be used as a potential candidate marker for the intervertebral disc, or more specifically the nucleus pulposus cell (NPC) phenotype. We present in vitro cell culture data using alginate bead culture of primary human BMSCs exposed to the standard chondrogenic stimulus, transforming growth factor beta-1 (TGF-β), the growth and differentiation factor 5 and/or bovine NPCs to induce a potential "discogenic" pathway. Chondrogenic induction via TGF-β pathway provoked down-regulation of KRT-19 gene expression in four out of five donors after 18 days of culture, whereas KRT-19 expression remained unchanged in the "discogenic" groups. In addition, the ratio of aggrecan/collagen II gene expression showed a remarkable difference (of at least 3 magnitudes) between the chondrogenic stimulus (low ratio) and the discogenic stimulus (high ratio). Therefore, KRT-19 and aggrecan/collagen II ratio may be potential markers to distinguish chondrogenic from "discogenic" differentiation.

The effect of needle size inducing degeneration in the rat caudal disc: evaluation using radiograph, magnetic resonance imaging, histology, and immunohistochemistry

BACKGROUND CONTEXT

The rat caudal disc has been increasingly used in studying of disc degeneration because of its simplicity, low cost, and efficiency. However, the reproducibility and standardization are essential to facilitate the investigations of biologic therapeutics at different stages of degeneration.

PURPOSE

To identify the effect of different needle gauges to the degenerative response in rat caudal discs and to examine its pathogenesis by looking at the cellular and matrix changes.

STUDY DESIGN

In vivo study of injury-induced rat caudal disc degeneration using needle puncture.

PATIENT SAMPLE

Thirty-six Lewis rats aged 12-14 weeks.

OUTCOME MEASURES

The induced degenerative discs were analyzed by plain radiograph, magnetic resonance imaging (MRI) and histological examination. Proteoglycan content was assessed by alcian blue stain. Immunohistochemistry using aggrecan, collagen II, and Sox-9 was also evaluated to investigate cell differentiation and matrix changes.

METHODS

All rats were divided into three groups according to different needle gauges (18G, 20G, and 22G). Caudal discs were punctured percutaneously under image guidance. Radiographs and MRI were obtained at 2 weeks interval until 8 weeks. At each time point, three rats from each group were sacrificed for histological analysis and immunohistochemistry.

RESULTS

Larger needle gauges, especially 18G, produced more deterioration of the disc when compared with smaller sizes, particularly with time. Significant differences were identified in almost all parameters compared between 18G and 22G at the 8-week time point. For the effect of time in the same needle size, the differences occurred between 2- or 4-week and 8-week time point in the 18G and 20G groups. The proteoglycan and aggrecan stain gradually decreased over time. Chondrogenic differentiation was identified within the degenerative disc by detecting Sox-9 positive cells and collagen II accumulation increased as degeneration progressed.

CONCLUSIONS

The puncture-induced degenerative changes in rat caudal discs can imitate the human degenerative cascade as observed in plain radiograph, MRI, histology, and immunohistochemistry. We suggest that needle size affects the occurrence of progression of degeneration; thus, the large needle size was required to accelerate the deterioration. The size of needle and time point after injury should be considered when investigating the effect of therapeutic materials to retard degeneration or regenerate the intervertebral disc.

Regeneration potential and mechanism of bone marrow mesenchymal stem cell transplantation for treating intervertebral disc degeneration

Intervertebral disc degeneration is a primary cause of low back pain and has a high societal cost. The pathological mechanism by which the intervertebral disc degenerates is largely unknown. Cell-based therapy especially using bone marrow mesenchymal stem cells as seeds for transplantation, although still in its infancy, is proving to be a promising, realistic approach to intervertebral disc regeneration. This article reviews current advances regarding regeneration potential in both the in vivo and vitro studies of bone marrow mesenchymal stem cell-based therapy and discusses the up-to-date regeneration mechanisms of stem cell transplantation for treating intervertebral disc degeneration.