Spinal cord clinical trials and the role for bioengineering

Characterization of microglia/macrophage phenotypes in the spinal cord following intervertebral disc herniation

Dogs frequently suffer from traumatic spinal cord injury (SCI). Most cases of SCI have a favorable prognosis but 40-50% of dogs with paraplegia and absence of nociception do not regain ambulatory abilities, eventually leading to euthanasia. Microglia and infiltrating macrophages play a crucial role in inflammatory process after SCI. However, little is known about microglia/macrophage phenotypes representing a potential target for future therapeutic strategies. In the present study, the microglia/macrophage phenotype was characterized by immunohistochemistry in the morphologically unaltered canine spinal cord (10 control dogs) and during acute and subacute SCI (1-4 and 5-10 days post injury, 9 and 8 dogs, respectively) using antibodies directed against IBA1, MAC387, MHC-II, lysozyme, EGR2, myeloperoxidase, CD18, CD204 and lectin from Griffonia simplicifolia (BS-1). The expression of these markers was also analyzed in the spleen as reference for the phenotype of histiocytic cells. Histological lesions were absent in controls. In acute SCI, 4 dogs showed mild to moderate hemorrhages, 2 dogs bilateral gray matter necrosis and 6 dogs mild multifocal axonal swellings and myelin sheath dilation. One dog with acute SCI did not show histological alterations except for few dilated myelin sheaths. In subacute SCI, variable numbers of gitter cells, axonal changes and dilated myelin sheaths were present in all dogs and large areas of tissue necrosis in 2 dogs. Neuronal chromatolysis was found in 3 dogs with acute and subacute SCI, respectively. In control dogs, microglia/macrophage constitutively expressed IBA1 and rarely other markers. In acute SCI, a similar marker expression was found except for an increase in MAC387-positive cells in the spinal cord white matter due to an infiltration of few blood-borne macrophages. In subacute SCI, increased numbers of microglia/macrophages expressed CD18, CD204 and MHC-II in the gray matter SCI indicating enhanced antigen recognition, processing and presentation as well as cell migration and phagocytosis during this stage. Interestingly, only CD204-positive cells were upregulated in the white matter, which might be related to gray-white matter heterogeneity of microglia as previously described in humans. The present findings contribute to the understanding of the immunological processes during SCI in a large animal model for human SCI.

Thermosensitive collagen/fibrinogen gels loaded with decorin suppress lesion site cavitation and promote functional recovery after spinal cord injury

The treatment of spinal cord injury (SCI) is a complex challenge in regenerative medicine, complicated by the low intrinsic capacity of CNS neurons to regenerate their axons and the heterogeneity in size, shape and extent of human injuries. For example, some contusion injuries do not compromise the dura mater and in such cases implantation of preformed scaffolds or drug delivery systems may cause further damage. Injectable in situ thermosensitive scaffolds are therefore a less invasive alternative. In this study, we report the development of a novel, flowable, thermosensitive, injectable drug delivery system comprising bovine collagen (BC) and fibrinogen (FB) that forms a solid BC/FB gel (Gel) immediately upon exposure to physiological conditions and can be used to deliver reparative drugs, such as the naturally occurring anti-inflammatory, anti-scarring agent Decorin, into adult rat spinal cord lesion sites. In dorsal column lesions of adult rats treated with the Gel + Decorin, cavitation was completely suppressed and instead lesion sites became filled with injury-responsive cells and extracellular matrix materials, including collagen and laminin. Decorin increased the intrinsic potential of dorsal root ganglion neurons (DRGN) by increasing their expression of regeneration associated genes (RAGs), enhanced local axon regeneration/sprouting, as evidenced both histologically and by improved electrophysiological, locomotor and sensory function recovery. These results suggest that this drug formulated, injectable hydrogel has the potential to be further studied and translated into the clinic.

Injectable Scaffold-Systems for the Regeneration of Spinal Cord: Advances of the Past Decade

Nowadays, whenever is possible and as an alternative to open spine surgery, minimally invasive procedures are preferred to treat spinal cord injuries (SCI), with percutaneous injections or small incisions, that are faster, less traumatic, and require less recovery time. Injectable repair systems are based on materials that can be injected in the lesion site, can eventually be loaded with drugs or even cells, and act as scaffolds for the lesion repair. The review analyzes papers written from 2010 onward on injectable materials/systems used/proposed for the regenerative and combinatorial therapies of SCI and discusses the in vivo models that have been used to validate them.

Co-delivery of minocycline and paclitaxel from injectable hydrogel for treatment of spinal cord injury

Spinal cord injury (SCI) induces pathological and inflammatory responses that create an inhibitory environment at the site of trauma, resulting in axonal degeneration and functional disability. Combination therapies targeting multiple aspects of the injury, will likely be more effective than single therapies to facilitate tissue regeneration after SCI. In this study, we designed a dual-delivery system consisting of a neuroprotective drug, minocycline hydrochloride (MH), and a neuroregenerative drug, paclitaxel (PTX), to enhance tissue regeneration in a rat hemisection model of SCI. For this purpose, PTX-encapsulated poly (lactic-co-glycolic acid) PLGA microspheres along with MH were incorporated into the alginate hydrogel. A prolonged and sustained release of MH and PTX from the alginate hydrogel was obtained over eight weeks. The obtained hydrogels loaded with a combination of both drugs or each of them alone, along with the blank hydrogel (devoid of any drugs) were injected into the lesion site after SCI (at the acute phase). Histological assessments showed that the dual-drug treatment reduced inflammation after seven days. Moreover, a decrease in the scar tissue, as well as an increase in neuronal regeneration was observed after 28 days in rats treated with dual-drug delivery system. Over time, a fast and sustained functional improvement was achieved in animals that received dual-drug treatment compared with other experimental groups. This study provides a novel dual-drug delivery system that can be developed to test for a variety of SCI models or neurological disorders.

Synthetic Polymers Provide a Robust Substrate for Functional Neuron Culture

Substrates for neuron culture and implantation are required to be both biocompatible and display surface compositions that support cell attachment, growth, differentiation, and neural activity. Laminin, a naturally occurring extracellular matrix protein is the most widely used substrate for neuron culture and fulfills some of these requirements, however, it is expensive, unstable (compared to synthetic materials), and prone to batch-to-batch variation. This study uses a high-throughput polymer screening approach to identify synthetic polymers that supports the in vitro culture of primary mouse cerebellar neurons. This allows the identification of materials that enable primary cell attachment with high viability even under "serum-free" conditions, with materials that support both primary cells and neural progenitor cell attachment with high levels of neuronal biomarker expression, while promoting progenitor cell maturation to neurons.

Generating level-dependent models of cervical and thoracic spinal cord injury: Exploring the interplay of neuroanatomy, physiology, and function

The majority of spinal cord injuries (SCI) occur at the cervical level, which results in significant impairment. Neurologic level and severity of injury are primary endpoints in clinical trials; however, how level-specific damages relate to behavioural performance in cervical injury is incompletely understood. We hypothesized that ascending level of injury leads to worsening forelimb performance, and correlates with loss of neural tissue and muscle-specific neuron pools. A direct comparison of multiple models was made with injury realized at the C5, C6, C7 and T7 vertebral levels using clip compression with sham-operated controls. Animals were assessed for 10weeks post-injury with numerous (40) outcome measures, including: classic behavioural tests, CatWalk, non-invasive MRI, electrophysiology, histologic lesion morphometry, neuron counts, and motor compartment quantification, and multivariate statistics on the total dataset. Histologic staining and T1-weighted MR imaging revealed similar structural changes and distinct tissue loss with cystic cavitation across all injuries. Forelimb tests, including grip strength, F-WARP motor scale, Inclined Plane, and forelimb ladder walk, exhibited stratification between all groups and marked impairment with C5 and C6 injuries. Classic hindlimb tests including BBB, hindlimb ladder walk, bladder recovery, and mortality were not different between cervical and thoracic injuries. CatWalk multivariate gait analysis showed reciprocal and progressive changes forelimb and hindlimb function with ascending level of injury. Electrophysiology revealed poor forelimb axonal conduction in cervical C5 and C6 groups alone. The cervical enlargement (C5-T2) showed progressive ventral horn atrophy and loss of specific motor neuron populations with ascending injury. Multivariate statistics revealed a robust dataset, rank-order contribution of outcomes, and allowed prediction of injury level with single-level discrimination using forelimb performance and neuron counts. Level-dependent models were generated using clip-compression SCI, with marked and reliable differences in forelimb performance and specific neuron pool loss.

Effect of oscillating electrical field stimulation on motor function recovery and myelin regeneration after spinal cord injury in rats

[Purpose] The aim of this study was to evaluate the effect of oscillating electrical field stimulation on motor function recovery and myelin regeneration in rats with spinal cord injury. [Subjects and Methods] A rat model of spinal cord injury was constructed by using the Allen weight-drop method. These rats were randomly divided into normal, spinal cord injury, and spinal cord injury + oscillating electrical field stimulation groups. The experimental group received the intervention with oscillating electrical field stimulation, and the control group received the intervention with an electrical field stimulator without oscillating electrical field stimulation. Each group was then randomly divided into seven subgroups according to observation time (1, 2, 4, 6, 8, 10, and 12 weeks). Basso-Beattie-Bresnahan score and inclined plate test score evaluation, motor evoked potential detection, and histological observation were performed. [Results] In the first 2 weeks of oscillating electrical field stimulation, the oscillating electrical field stimulation and inclined plate test scores of spinal cord injury group and spinal cord injury + oscillating electrical field stimulation group were not significantly different. In the fourth week, the scores of the spinal cord injury group were significantly lower than those of the spinal cord injury + oscillating electrical field stimulation group. The motor evoked potential incubation period in the spinal cord injury + oscillating electrical field stimulation group at the various time points was shorter than that in the spinal cord injury group. In the sixth week, the relative area of myelin in the spinal cord injury + oscillating electrical field stimulation group was evidently larger than that in the spinal cord injury group. [Conclusion] Oscillating electrical field stimulation could effectively improve spinal cord conduction function and promote motor function recovery in rats with spinal cord injury, as well as promote myelin regeneration.

Bridging the lesion-engineering a permissive substrate for nerve regeneration

Biomaterial-based strategies to restore connectivity after lesion at the spinal cord are focused on bridging the lesion and providing an favourable substrate and a path for axonal re-growth. Following spinal cord injury (SCI) a hostile environment for neuronal cell growth is established by the activation of multiple inhibitory mechanisms that hamper regeneration to occur. Implantable scaffolds can provide mechanical support and physical guidance for axon re-growth and, at the same time, contribute to alleviate the hostile environment by the in situ delivery of therapeutic molecules and/or relevant cells. Basic research on SCI has been contributing with the description of inhibitory mechanisms for regeneration as well as identifying drugs/molecules that can target inhibition. This knowledge is the background for the development of combined strategies with biomaterials. Additionally, scaffold design is significantly evolving. From the early simple hollow conduits, scaffolds with complex architectures that can modulate cell fate are currently being tested. A number of promising pre-clinical studies combining scaffolds, cells, drugs and/or nucleic acids are reported in the open literature. Overall, it is considered that to address the multi-factorial inhibitory environment of a SCI, a multifaceted therapeutic approach is imperative. The progress in the identification of molecules that target inhibition after SCI and its combination with scaffolds and/or cells are described and discussed in this review.

Advances in regenerative therapies for spinal cord injury: a biomaterials approach

Spinal cord injury results in the permanent loss of function, causing enormous personal, social and economic problems. Even though neural regeneration has been proven to be a natural mechanism, central nervous system repair mechanisms are ineffective due to the imbalance of the inhibitory and excitatory factors implicated in neuroregeneration. Therefore, there is growing research interest on discovering a novel therapeutic strategy for effective spinal cord injury repair. To this direction, cell-based delivery strategies, biomolecule delivery strategies as well as scaffold-based therapeutic strategies have been developed with a tendency to seek for the answer to a combinatorial approach of all the above. Here we review the recent advances on regenerative/neural engineering therapies for spinal cord injury, aiming at providing an insight to the most promising repair strategies, in order to facilitate future research conduction.

Translating mechanisms of neuroprotection, regeneration, and repair to treatment of spinal cord injury

One of the big challenges in neuroscience that remains to be understood is why the central nervous system is not able to regenerate to the extent that the peripheral nervous system does. This is especially problematic after traumatic injuries, like spinal cord injury (SCI), since the lack of regeneration leads to lifelong deficits and paralysis. Treatment of SCI has improved during the last several decades due to standardized protocols for emergency medical response teams and improved medical, surgical, and rehabilitative treatments. However, SCI continues to result in profound impairments for the individual. There are many processes that lead to the pathophysiology of SCI, such as ischemia, vascular disruption, neuroinflammation, oxidative stress, excitotoxicity, demyelination, and cell death. Current treatments include surgical decompression, hemodynamic control, and methylprednisolone. However, these early treatments are associated with modest functional recovery. Some treatments currently being investigated for use in SCI target neuroprotective (riluzole, minocycline, G-CSF, FGF-2, and polyethylene glycol) or neuroregenerative (chondroitinase ABC, self-assembling peptides, and rho inhibition) strategies, while many cell therapies (embryonic stem cells, neural stem cells, induced pluripotent stem cells, mesenchymal stromal cells, Schwann cells, olfactory ensheathing cells, and macrophages) have also shown promise. However, since SCI has multiple factors that determine the progress of the injury, a combinatorial therapeutic approach will most likely be required for the most effective treatment of SCI.

New trends in spinal cord tissue engineering

ABSTRACT 

Restoration of lost neuronal function after spinal cord injury still remains a considerable challenge for current medicine. Over the last decade, regenerative medicine has recorded rapid and promising advancements in stem cell research, genetic engineering and the progression of new sophisticated biomaterials as well as nanotechnology. This advancement has also been reflected in neural tissue engineering, where, along with the development of a new generation of well-designed biopolymer scaffolds, multifactorial therapeutic strategies are being validated in order to determine the greatest possible repair efficacy of the complex CNS pathophysiology. Much attention is currently focused on the designing of multifunctional polymer scaffolds as systems for targeted drug or gene delivery, electrical stimulation or as substrates creating a special micro-environment, promoting the growth and desired differentiation of various cell lines. In this review, the latest advances in biomaterial technology together with various combinatorial strategies designed to treat spinal cord injury treatment are summarized and discussed.

The Potential for iPS-Derived Stem Cells as a Therapeutic Strategy for Spinal Cord Injury: Opportunities and Challenges

Spinal cord injury (SCI) is a devastating trauma causing long-lasting disability. Although advances have occurred in the last decade in the medical, surgical and rehabilitative treatments of SCI, the therapeutic approaches are still not ideal. The use of cell transplantation as a therapeutic strategy for the treatment of SCI is promising, particularly since it can target cell replacement, neuroprotection and regeneration. Cell therapies for treating SCI are limited due to several translational roadblocks, including ethical and practical concerns regarding cell sources. The use of iPSCs has been particularly attractive, since they avoid the ethical and moral concerns that surround other stem cells. Furthermore, various cell types with potential for application in the treatment of SCI can be created from autologous sources using iPSCs. For applications in SCI, the iPSCs can be differentiated into neural precursor cells, neurons, oligodendrocytes, astrocytes, neural crest cells and mesenchymal stromal cells that can act by replacing lost cells or providing environmental support. Some methods, such as direct reprogramming, are being investigated to reduce tumorigenicity and improve reprogramming efficiencies, which have been some of the issues surrounding the use of iPSCs clinically to date. Recently, iPSCs have entered clinical trials for use in age-related macular degeneration, further supporting their promise for translation in other conditions, including SCI.

Neural precursor cell transplantation enhances functional recovery and reduces astrogliosis in bilateral compressive/contusive cervical spinal cord injury

Spinal cord injury has a significant societal and personal impact. Although the majority of injuries involve the cervical spinal cord, few studies of cell transplantation have used clinically relevant models of cervical spinal cord injury, limiting translation into clinical trials. Given this knowledge gap, we sought to examine the effects of neural stem/precursor cell (NPC) transplants in a rodent model of bilateral cervical contusion-compression spinal cord injury. Bilateral C6-level clip contusion-compression injuries were performed in rats, which were then blindly randomized at 2 weeks after injury into groups receiving adult brain-derived NPCs, vehicle, or sham operation. Long-term survival of NPCs was evident at 10 weeks after transplant. Cell grafts were localized rostrocaudally surrounding the lesion, throughout white and gray matter. Graft-derived cells were found within regions of gliotic scar and motor tracts and deposited myelin around endogenous axons. The majority of NPCs developed an oligodendroglial phenotype with greater neuronal profiles in rostral grafts. Following NPC transplantation, white matter was significantly increased compared with control. Astrogliosis and glial scar deposition, measured by GFAP-positive and chondroitin sulfate proteoglycan-positive volume, was significantly reduced. Forelimb grip strength, fine motor control during locomotion, and axonal conduction (by in vivo electrophysiology) was greater in cell-treated animals compared with vehicle controls. Transplantation of NPCs in the bilaterally injured cervical spinal cord results in significantly improved spinal cord tissue and forelimb function, warranting further study in preclinical cervical models to improve this treatment paradigm for clinical translation.

Fibroblast engraftment in the decellularized mouse lung occurs via a β1-integrin-dependent, FAK-dependent pathway that is mediated by ERK and opposed by AKT

Creation of bioartificial organs has been enhanced by the development of strategies involving decellularized mammalian lung. Because fibroblasts critically support lung function through a number of mechanisms, study of these cells in the context of the decellularized lung has the potential to improve the structure and function of tissue-engineered lungs. We characterized the engraftment and survival of a mouse fibroblast cell line in decellularized rat lung slices and found a time-dependent increase in cell numbers assessed by hematoxylin and eosin staining, cell proliferation assessed by Ki67 staining, and minimal cell death assessed by TUNEL staining. We developed a repopulation index to allow quantification of cell survival that accounts for variation in cell density throughout the seeded scaffold. We then applied this method to the study of mouse lung scaffolds and found that decellularization of presliced mouse lungs produced matrices with preserved alveolar architecture and proteinaceous components including fibronectin, collagens I and IV, laminin, and elastin. Treatment with a β1-integrin-neutralizing antibody significantly reduced the repopulation index after 24 h of culture. Treatment with focal adhesion kinase (FAK) inhibitor and extracellular signal-regulated kinase (ERK) inhibitor further reduced initial repopulation scores while treatment with AKT inhibitor increased initial scores. Rho-associated kinase inhibitor had no discernible effect. These data indicate that initial adhesion and survival of mouse fibroblasts in the decellularized mouse lung occur in a β1-integrin-dependent, FAK/ERK-dependent manner that is opposed by AKT.

Intraspinal transplantation of mouse and human neural precursor cells

This unit describes the preparation and transplantation of human neural precursor cells (hNPCs) and mouse neural precursor cells (mNPCs) into the thoracic region of the mouse spinal cord. The techniques in this unit also describe how to prepare the mouse for surgery by performing a laminectomy to expose the spinal cord for transplantation. NPCs genetically labeled with eGFP transplanted into the spinal cord of a mouse following viral-mediated demyelination can efficiently be detected via eGFP expression. Transplantation of these cells into the spinal cord is an efficacious way to determine their effects in neurological disorders such as multiple sclerosis, Alzheimer's disease, and spinal cord injury.

Methacrylate-endcapped caprolactone and FM19G11 provide a proper niche for spinal cord-derived neural cells

Spinal cord injury (SCI) is a cause of paralysis. Although some strategies have been proposed to palliate the severity of this condition, so far no effective therapies have been found to reverse it. Recently, we have shown that acute transplantation of ependymal stem/progenitor cells (epSPCs), which are spinal cord-derived neural precursors, rescue lost neurological function after SCI in rodents. However, in a chronic scenario with axon repulsive reactive scar, cell transplantation alone is not sufficient to bridge a spinal cord lesion, therefore a combinatorial approach is necessary to fill cavities in the damaged tissue with biomaterial that supports stem cells and ensures that better neural integration and survival occur. Caprolactone 2-(methacryloyloxy) ethyl ester (CLMA) is a monomer [obtained as a result of ε-caprolactone and 2-hydroxyethyl methacrylate (HEMA) ring opening/esterification reaction], which can be processed to obtain a porous non-toxic 3D scaffold that shows good biocompatibility with epSPC cultures. epSPCs adhere to the scaffolds and maintain the ability to expand the culture through the biomaterial. However, a significant reduction of cell viability of epSPCs after 6 days in vitro was detected. FM19G11, which has been shown to enhance self-renewal properties, rescues cell viability at 6 days. Moreover, addition of FM19G11 enhances the survival rates of mature neurons from the dorsal root ganglia when cultured with epSPCs on 3D CLMA scaffolds. Overall, CLMA porous scaffolds constitute a good niche to support neural cells for cell transplantation approaches that, in combination with FM19G11, offer a new framework for further trials in spinal cord regeneration.