The effect of hyaluronan-based delivery of stromal cell-derived factor-1 on the recruitment of MSCs in degenerating intervertebral discs

The effect of SDF-1α on low dose BMP-2 mediated bone regeneration by release from heparinized mineralized collagen type I matrix scaffolds in a murine critical size bone defect model

The treatment of critical size bone defects represents a challenge. The growth factor bone morphogenetic protein 2 (BMP-2) is clinically established but has potentially adverse effects when used at high doses. The aim of this study was to evaluate if stromal derived factor-1 alpha (SDF-1α) and BMP-2 released from heparinized mineralized collagen type I matrix (MCM) scaffolds have a cumulative effect on bone regeneration. MCM scaffolds were functionalized with heparin, loaded with BMP-2 and/or SDF-1α and implanted into a murine critical size femoral bone defect (control group, low dose BMP-2 group, low dose BMP-2 + SDF-1α group, and high dose BMP-2 group). After 6 weeks, both the low dose BMP-2 + SDF-1α group (5.8 ± 0.6 mm³, p = 0.0479) and the high dose BMP-2 group (6.5 ± 0.7 mm³, p = 0.008) had a significantly increased regenerated bone volume compared to the control group (4.2 ± 0.5 mm³). There was a higher healing score in the low dose BMP-2 + SDF-1α group (median grade 8; Q1-Q3 7-9; p = 0.0357) than in the low dose BMP-2 group (7; Q1-Q3 5-9) histologically. This study showed that release of BMP-2 and SDF-1α from heparinized MCM scaffolds allows for the reduction of the applied BMP-2 concentration since SDF-1α seems to enhance the osteoinductive potential of BMP-2. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2126-2134, 2016.

Organ culture bioreactors--platforms to study human intervertebral disc degeneration and regenerative therapy

In recent decades the application of bioreactors has revolutionized the concept of culturing tissues and organs that require mechanical loading. In intervertebral disc (IVD) research, collaborative efforts of biomedical engineering, biology and mechatronics have led to the innovation of new loading devices that can maintain viable IVD organ explants from large animals and human cadavers in precisely defined nutritional and mechanical environments over extended culture periods. Particularly in spine and IVD research, these organ culture models offer appealing alternatives, as large bipedal animal models with naturally occurring IVD degeneration and a genetic background similar to the human condition do not exist. Latest research has demonstrated important concepts including the potential of homing of mesenchymal stem cells to nutritionally or mechanically stressed IVDs, and the regenerative potential of "smart" biomaterials for nucleus pulposus or annulus fibrosus repair. In this review, we summarize the current knowledge about cell therapy, injection of cytokines and short peptides to rescue the degenerating IVD. We further stress that most bioreactor systems simplify the real in vivo conditions providing a useful proof of concept. Limitations are that certain aspects of the immune host response and pain assessments cannot be addressed with ex vivo systems. Coccygeal animal disc models are commonly used because of their availability and similarity to human IVDs. Although in vitro loading environments are not identical to the human in vivo situation, 3D ex vivo organ culture models of large animal coccygeal and human lumbar IVDs should be seen as valid alternatives for screening and feasibility testing to augment existing small animal, large animal, and human clinical trial experiments.

A Degenerative/Proinflammatory Intervertebral Disc Organ Culture: An Ex Vivo Model for Anti-inflammatory Drug and Cell Therapy

Resolution of intervertebral disc (IVD) degeneration-associated inflammation is a prerequisite for tissue regeneration and could possibly be achieved by strategies ranging from pharmacological to cell-based therapies. In this study, a proinflammatory disc organ culture model was established. Bovine caudal disc punches were needle punctured and additionally stimulated with lipopolysaccharide (10 μg/mL) or interleukin-1β (IL-1β, 10-100 ng/mL) for 48 h. Two intradiscal therapeutic approaches were tested: (i) a nonsteroidal anti-inflammatory drug, diclofenac (Df) and (ii) human mesenchymal stem/stromal cells (MSCs) embedded in an albumin/hyaluronan hydrogel. IL-1β-treated disc organ cultures showed a statistically significant upregulation of proinflammatory markers (IL-6, IL-8, prostaglandin E2 [PGE2]) and metalloproteases (MMP1, MMP3) expression, while extracellular matrix (ECM) proteins (collagen II, aggrecan) were significantly downregulated. The injection of the anti-inflammatory drug, Df, was able to reduce the levels of proinflammatory cytokines and MMPs and surprisingly increase ECM protein levels. These results point the intradiscal application of anti-inflammatory drugs as promising therapeutics for disc degeneration. In parallel, the immunomodulatory role of MSCs on this model was also evaluated. Although a slight downregulation of IL-6 and IL-8 expression could be found, the variability among the five donors tested was high, suggesting that the beneficial effect of these cells on disc degeneration needs to be further evaluated. The proinflammatory/degenerative IVD organ culture model established can be considered a suitable approach for testing novel therapeutic drugs, thus reducing the number of animals in in vivo experimentation. Moreover, this model can be used to address the cellular and molecular mechanisms that regulate inflammation in the IVD and their implications in tissue degeneration.

Inflammation in intervertebral disc degeneration and regeneration

Intervertebral disc (IVD) degeneration is one of the major causes of low back pain, a problem with a heavy economic burden, which has been increasing in prevalence as populations age. Deeper knowledge of the complex spatial and temporal orchestration of cellular interactions and extracellular matrix remodelling is critical to improve current IVD therapies, which have so far proved unsatisfactory. Inflammation has been correlated with degenerative disc disease but its role in discogenic pain and hernia regression remains controversial. The inflammatory response may be involved in the onset of disease, but it is also crucial in maintaining tissue homeostasis. Furthermore, if properly balanced it may contribute to tissue repair/regeneration as has already been demonstrated in other tissues. In this review, we focus on how inflammation has been associated with IVD degeneration by describing observational and in vitro studies as well as in vivo animal models. Finally, we provide an overview of IVD regenerative therapies that target key inflammatory players.

Mesenchymal stem cells in regenerative medicine: Focus on articular cartilage and intervertebral disc regeneration

Musculoskeletal disorders represent a major cause of disability and morbidity globally and result in enormous costs for health and social care systems. Development of cell-based therapies is rapidly proliferating in a number of disease areas, including musculoskeletal disorders. Novel biological therapies that can effectively treat joint and spine degeneration are high priorities in regenerative medicine. Mesenchymal stem cells (MSCs) isolated from bone marrow (BM-MSCs), adipose tissue (AD-MSCs) and umbilical cord (UC-MSCs) show considerable promise for use in cartilage and intervertebral disc (IVD) repair. This review article focuses on stem cell-based therapeutics for cartilage and IVD repair in the context of the rising global burden of musculoskeletal disorders. We discuss the biology MSCs and chondroprogenitor cells and specifically focus on umbilical cord/Wharton's jelly derived MSCs and examine their potential for regenerative applications. We also summarize key components of the molecular machinery and signaling pathways responsible for the control of chondrogenesis and explore biomimetic scaffolds and biomaterials for articular cartilage and IVD regeneration. This review explores the exciting opportunities afforded by MSCs and discusses the challenges associated with cartilage and IVD repair and regeneration. There are still many technical challenges associated with isolating, expanding, differentiating, and pre-conditioning MSCs for subsequent implantation into degenerate joints and the spine. However, the prospect of combining biomaterials and cell-based therapies that incorporate chondrocytes, chondroprogenitors and MSCs leads to the optimistic view that interdisciplinary approaches will lead to significant breakthroughs in regenerating musculoskeletal tissues, such as the joint and the spine in the near future.

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.

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

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