David Oehme

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.

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.

A Review of Animal Models of Intervertebral Disc Degeneration: Pathophysiology, Regeneration, and Translation to the Clinic

Lower back pain is the leading cause of disability worldwide. Discogenic pain secondary to intervertebral disc degeneration is a significant cause of low back pain. Disc degeneration is a complex multifactorial process. Animal models are essential to furthering understanding of the degenerative process and testing potential therapies. The adult human lumbar intervertebral disc is characterized by the loss of notochordal cells, relatively large size, essentially avascular nature, and exposure to biomechanical stresses influenced by bipedalism. Animal models are compared with regard to the above characteristics. Numerous methods of inducing disc degeneration are reported. Broadly these can be considered under the categories of spontaneous degeneration, mechanical and structural models. The purpose of such animal models is to further our understanding and, ultimately, improve treatment of disc degeneration. The role of animal models of disc degeneration in translational research leading to clinical trials of novel cellular therapies is explored.

Lateral Surgical Approach to Lumbar Intervertebral Discs in an Ovine Model

The sheep is becoming increasingly used as a large animal model for preclinical spine surgery studies. Access to the ovine lumbar intervertebral discs has traditionally been via an anterior or anterolateral approach, which requires larger wound incisions and, at times, significant abdominal retraction. We present a new minimally invasive operative technique for a far-lateral approach to the ovine lumbar spine that allows for smaller incisions, excellent visualisation of intervertebral discs, and minimal abdominal retraction and is well tolerated by animals with minimal morbidity.

Current and Future Applications for Stem Cell Therapies in Spine Surgery

Spinal surgery involves the bone-cartilage-neural interface. It is a field of surgery that is rapidly changing and evolving; not only through the development of novel techniques, approaches and devices but also through evidence from large clinical trials assessing indications, efficacy and outcomes. The use of biologics in spine surgery has now become widespread. Biologics in the form of autologous or allogeneic stem cells or progenitor cells are not yet in routine clinical use in spine surgery. However it is likely that they will have a significant role in the future, since increasing numbers of preclinical and clinical studies have demonstrated the safety and efficacy of progenitor cells to treat a variety of spinal conditions. Such studies have paved the way to larger clinical trials. Cell therapies encompass a wide range of stem cell and progenitor cell types. Stem cells subtypes differ in their lineage potential often being described as pluripotent or multipotent, some of which have potential application in therapies to treat diseases of the spine having the ability to differentiate into tissues including bone and cartilage and to secrete factors that promote matrix repair and regeneration. Furthermore, studies have shown that some cells, particularly mesenchymal stromal cells, modulate oxidative stress and secrete cytokines and growth factors that have immunomodulatory, antiinflammatory, angiogenic and antiapoptotic effects. It is these combined characteristics that make cell based therapies prime candidates for advancing current techniques in spine surgery and for providing new strategies directed at targeting the underlying causes of spinal diseases and disorders to promote repair and regeneration. This review will explore the characteristics of various stem cells and other progenitor cells derived from different sources. The authors are not suggesting that all these cells are necessarily suitable clinically. The review will thus focus on their application to both current and potentially future areas of spine surgery based on results of the available evidence and clinical trials. This review will not address spinal cord injury.

Reconstitution of degenerated ovine lumbar discs by STRO-3–positive allogeneic mesenchymal precursor cells combined with pentosan polysulfate

OBJECTIVE Disc degeneration and associated low-back pain are major causes of suffering and disability. The authors examined the potential of mesenchymal precursor cells (MPCs), when formulated with pentosan polysulfate (PPS), to ameliorate disc degeneration in an ovine model. METHODS Twenty-four sheep had annular incisions made at L2-3, L3-4, and L4-5 to induce degeneration. Twelve weeks after injury, the nucleus pulposus of a degenerated disc in each animal was injected with ProFreeze and PPS formulated with either a low dose (0.1 million MPCs) or a high dose (0.5 million MPCs) of cells. The 2 adjacent injured discs in each spine were either injected with PPS and ProFreeze (PPS control) or not injected (nil-injected control). The adjacent noninjured L1-2 and L5-6 discs served as noninjured control discs. Disc height indices (DHIs) were obtained at baseline, before injection, and at planned death. After necropsy, 24 weeks after injection, the spines were subjected to MRI and morphological, histological, and biochemical analyses. RESULTS Twelve weeks after the annular injury, all the injured discs exhibited a significant reduction in mean DHI (low-dose group 17.19%; high-dose group 18.01% [p < 0.01]). Twenty-four weeks after injections, the discs injected with the low-dose MPC+PPS formulation recovered disc height, and their mean DHI was significantly greater than the DHI of PPS- and nil-injected discs (p < 0.001). Although the mean Pfirrmann MRI disc degeneration score for the low-dose MPC+PPS-injected discs was lower than that for the nil- and PPS-injected discs, the differences were not significant. The disc morphology scores for the nil- and PPS-injected discs were significantly higher than the normal control disc scores (p < 0.005), whereas the low-dose MPC+PPS-injected disc scores were not significantly different from those of the normal controls. The mean glycosaminoglycan content of the nuclei pulposus of the low-dose MPC+PPS-injected discs was significantly higher than that of the PPS-injected controls (p < 0.05) but was not significantly different from the normal control disc glycosaminoglycan levels. Histopathology degeneration frequency scores for the low-dose MPC+PPS-injected discs were lower than those for the PPS- and Nil-injected discs. The corresponding high-dose MPC+PPS-injected discs failed to show significant improvements in any outcome measure relative to the controls. CONCLUSIONS Intradiscal injections of a formulation composed of 0.1 million MPCs combined with PPS resulted in positive effects in reducing the progression of disc degeneration in an ovine model, as assessed by improvements in DHI and morphological, biochemical, and histopathological scores.

Evaluation of the safety and tolerability of a high-dose intravenous infusion of allogeneic mesenchymal precursor cells

BACKGROUND AIMS Over the past decade, mounting evidence has shown that mesenchymal stromal cells have the potential to exert protective and reparative effects in a variety of disease settings. Clinical trials are being increasingly established to investigate the therapeutic potential of these cells; however, several safety concerns remain to be addressed, of which dosage safety for intravenous administration is paramount. Published safety studies thus far have predominantly been carried out in small-animal models, whereas data for high-dose allogeneic intravenous administration in large-animal models are limited. This study investigates the safety and tolerability of a single high-dose intravenous infusion of 450 million allogeneic ovine mesenchymal precursor cells (oMPCs) in adult sheep. METHODS Allogeneic oMPCs (n = 450 million) were intravenously administered to 2-year-old castrated male sheep through the use of three different infusion rates. Sheep were intensively monitored for 7 days by means of vital physiological observations (temperature, blood pressure, heart rate, respiratory rate and oxygen saturation) as well as venous and arterial blood analysis. In addition, full post mortem examination was performed in all animals. RESULTS A single high dose of intravenously administered cells was well tolerated, with no serious adverse effects reported. No physiologically significant changes in vital signs, oxygen saturation, blood gas analysis or clinical pathology were observed over the duration of the study. CONCLUSIONS Intravenous delivery of a single high-dose infusion of oMPCs is well tolerated in a large animal model. This study provides additional safety evidence for their intravenous use in future human clinical trials.

Mesenchymal stem cell tracking in the intervertebral disc

Low back pain is a common clinical problem, which leads to significant social, economic and public health costs. Intervertebral disc (IVD) degeneration is accepted as a common cause of low back pain. Initially, this is characterized by a loss of proteoglycans from the nucleus pulposus resulting in loss of tissue hydration and hydrostatic pressure. Conservative management, including analgesia and physiotherapy often fails and surgical treatment, such as spinal fusion, is required. Stem cells offer an exciting possible regenerative approach to IVD disease. Preclinical research has demonstrated promising biochemical, histological and radiological results in restoring degenerate IVDs. Cell tracking provides an opportunity to develop an in-depth understanding of stem cell survival, differentiation and migration, enabling optimization of stem cell treatment. Magnetic Resonance Imaging (MRI) is a non-invasive, non-ionizing imaging modality with high spatial resolution, ideally suited for stem cell tracking. Furthermore, novel MRI sequences have the potential to quantitatively assess IVD disease, providing an improved method to review response to biological treatment. Superparamagnetic iron oxide nanoparticles have been extensively researched for the purpose of cell tracking. These particles are biocompatible, non-toxic and act as excellent MRI contrast agents. This review will explore recent advances and issues in stem cell tracking and molecular imaging in relation to the IVD.

Ovine lumbar intervertebral disc degeneration model utilizing a lateral retroperitoneal drill bit injury

Intervertebral disc degeneration is a significant contributor to the development of back pain and the leading cause of disability worldwide. Numerous animal models of intervertebral disc degeneration have been developed. The ideal animal model should closely mimic the human intervertebral disc with regard to morphology, biomechanical properties and the absence of notochordal cells. The sheep lumbar intervertebral disc model fulfils these criteria. We present an ovine model of intervertebral disc degeneration utilizing a drill bit injury through a lateral retroperitoneal approach. The lateral approach significantly reduces the incision and potential morbidity associated with the traditional anterior approach to the ovine spine. Utilization of a drill-bit method of injury affords the ability to produce a consistent and reproducible injury, of precise dimensions, that initiates a consistent degree of intervertebral disc degeneration. The focal nature of the annular and nucleus pulposus defect more closely mimics the clinical condition of focal intervertebral disc herniation. Sheep recover rapidly following this procedure and are typically mobile and eating within the hour. Intervertebral disc degeneration ensues and sheep undergo necropsy and subsequent analysis at periods from eight weeks. We believe that the drill bit injury model of intervertebral disc degeneration offers advantages over more conventional annular injury models.

Radiological, Morphological, Histological and Biochemical Changes of Lumbar Discs in an Animal Model of Disc Degeneration Suitable for Evaluating the Potential Regenerative Capacity of Novel Biological Agents

Circumferential tears of the Annulus Fibrosus (AF) are frequently observed pathological features of degenerate lumbar discs and have been associated with vascular propagation and the generation of low back pain. In order to evaluate the potential of novel biological agents to repair annular defects and arrest disc degeneration we required an animal model that would permit injection of cells or their cryoprotectant into adjacent lumbar discs of the same animal. Three lumbar discs (L2/3, L3/4 and L4/5) of 6 sheep were subjected to a peripheral lateral annular surgical incision. The adjacent uninjured lumbar L1/2 and L5/6 discs served as uninjured controls. After three months the spines were radiographed and disc height indices (DHI) calculated and Pfirrmann disc degeneration scores determined from MRI spinal images. Isolated lumbar discs were analysed morphologically, histologically and biochemically using published procedures. Disc height index measurements of injured discs revealed an average decrease of 23.67% relative to baseline values (p<0.0001). The corresponding MRI Pfirrmann degeneration scores were significantly higher than non-injured control discs (p<0.05), as were their morphology scores (p<0.005). The sulphated - glycosaminoglycan content, of the Nucleus Pulposus (NP) and injured side of the AF of lumbar discs, were significantly lower than control discs (p<0.05 and p<0.0005) respectively. Conversely, the DNA levels of the injured side of the AF were higher than the uninjured side (p<0.05). The histological scores showed higher degenerative changes in injured than in control discs (p<0.005). For all parameters monitored in this study no statistical differences were observed between the three injured lumbar discs confirming their uniform response to injury. This study therefore confirmed the suitability of this large animal model for evaluating the potential of biologicals to reconstitute degenerate ovine lumbar discs relative to their carriers/cryoprotectant.