Cationic liposome-mediated GDNF gene transfer after spinal cord injury

Recent advances in nanomaterials for the treatment of spinal cord injury

Spinal cord injuries (SCIs) are devastating. In SCIs, a powerful traumatic force impacting the spinal cord results in the permanent loss of nerve function below the injury level, leaving the patient paralyzed and wheelchair-bound for the remainder of his/her life. Unfortunately, clinical treatment that depends on surgical decompression appears to be unable to handle damaged nerves, and high-dose methylprednisolone-based therapy is also associated with problems, such as infection, gastrointestinal bleeding, femoral head necrosis, obesity, and hyperglycemia. Nanomaterials have opened new avenues for SCI treatment. Among them, performance-based nanomaterials derived from a variety of materials facilitate improvements in the microenvironment of traumatic injury and, in some cases, promote neuron regeneration. Nanoparticulate drug delivery systems enable the optimization of drug effects and drug bioavailability, thus contributing to the development of novel treatments. The improved efficiency and accuracy of gene delivery will also benefit the exploration of SCI mechanisms and the understanding of key genes and signaling pathways. Herein, we reviewed different types of nanomaterials applied to the treatment of SCI and summarized their functions and advantages to provide new perspectives for future clinical therapies.

Biomaterials and stem cells as drug/gene-delivery vehicles for Parkinson's treatment: an update

By introducing biomaterials and stem cells into Parkinson's disease (PD), therapeutic approaches have led to promising results due to facilitating brain targeting and blood-brain barrier permeation of the drugs and genes. Here, after reviewing the most recent drug- and gene-delivery vehicles including liposomes, exosomes, natural/synthetic polymeric particles/fibers, metallic/ceramic nanoparticles and microbubbles, used for Parkinson's disease treatment, the effect of stem cells as a reservoir of neurotrophic factors and exosomes is provided.

Investigation of the Molecular Role of Brain-Derived Neurotrophic Factor in Alzheimer's Disease

Brain-derived neurotrophic factor (BDNF), or abrineurin, is a member of the neurotrophin family of growth factors that acts on both the central and peripheral nervous systems. BDNF is also well known for its cardinal role in normal neural maturation. It binds to at least two receptors at the cell surface known as tyrosine kinase B (TrkB) and p75^NTR. Additional neurotrophins that are anatomically linked with BDNF include neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), and nerve growth factor (NGF). It is evident that BDNF levels in patients with Alzheimer's disease (AD) are altered. AD is a progressive disorder and a form of dementia, where the mental function of an elderly person is disrupted. It is associated with a progressive decline in cognitive function, which mainly targets the thinking, memory, and behavior of the person. The degeneration of neurons occurs in the cerebral cortex region of brain. The two major sources responsible for neuronal degeneration are protein fragment amyloid-beta (Aβ), which builds up in the spaces between the nerve cells, known as plaques, disrupting the neuron signaling pathway and leading to dementia, and neurofibrillary tangles (NFTs), which are the twisted fibers of proteins that build up inside the cells. AD is highly prevalent, with recent data indicating nearly 5.8 million Americans aged 65 and older with AD in 2020, and with 80% of patients 75 and older. AD is recognized as the sixth leading cause of death in the USA, and its prevalence is predicted to increase exponentially in the coming years. As AD worsens over time, it becomes increasingly important to understand the exact pathophysiology, biomarkers, and treatment. In this article, we focus primarily on the controversial aspect of BDNF in AD, including its influence on various other proteins and enzymes and the current treatments associated with BDNF, along with future perspectives.

Localised non-viral delivery of nucleic acids for nerve regeneration in injured nervous systems

Axons damaged by traumatic injuries are often unable to spontaneously regenerate in the adult central nervous system (CNS). Although the peripheral nervous system (PNS) has some regenerative capacity, its ability to regrow remains limited across large lesion gaps due to scar tissue formation. Nucleic acid therapy holds the potential of improving regeneration by enhancing the intrinsic growth ability of neurons and overcoming the inhibitory environment that prevents neurite outgrowth. Nucleic acids modulate gene expression by over-expression of neuronal growth factor or silencing growth-inhibitory molecules. Although in vitro outcomes appear promising, the lack of efficient non-viral nucleic acid delivery methods to the nervous system has limited the application of nucleic acid therapeutics to patients. Here, we review the recent development of efficient non-viral nucleic acid delivery platforms, as applied to the nervous system, including the transfection vectors and carriers used, as well as matrices and scaffolds that are currently used. Additionally, we will discuss possible improvements for localised nucleic acid delivery.

Multifarious Biologic Loaded Liposomes that Stimulate the Mammalian Target of Rapamycin Signaling Pathway Show Retina Neuroprotection after Retina Damage

A common event in optic neuropathies is the loss of axons and death of retinal ganglion cells (RGCs) resulting in irreversible blindness. Mammalian target of rapamycin (mTOR) signaling pathway agonists have been shown to foster axon regeneration and RGC survival in animal models of optic nerve damage. However, many challenges remain in developing therapies that exploit cell growth and tissue remodeling including (i) activating/inhibiting cell pathways synergistically, (ii) avoiding tumorigenesis, and (iii) ensuring appropriate physiological tissue function. These challenges are further exacerbated by the need to overcome ocular physiological barriers and clearance mechanisms. Here we present liposomes loaded with multiple mTOR pathway stimulating biologics designed to enhance neuroprotection after retina damage. Liposomes were loaded with ciliary neurotrophic factor, insulin-like growth factor 1, a lipopeptide N-fragment osteopontin mimic, and lipopeptide phosphatase tension homologue inhibitors for either the ATP domain or the c-terminal tail. In a mouse model of N-methyl-d-aspartic acid induced RGC death, a single intravitreal administration of liposomes reduced both RGC death and loss of retina electrophysiological function. Furthermore, combining liposomes with transplantation of induced pluripotent stem cell derived RGCs led to an improved electrophysiological outcome in mice. The results presented here show that liposomes carrying multiple signaling pathway modulators can facilitate neuroprotection and transplant electrophysiological outcome.

Nanomaterials in Neural-Stem-Cell-Mediated Regenerative Medicine: Imaging and Treatment of Neurological Diseases

Patients are increasingly being diagnosed with neuropathic diseases, but are rarely cured because of the loss of neurons in damaged tissues. This situation creates an urgent clinical need to develop alternative treatment strategies for effective repair and regeneration of injured or diseased tissues. Neural stem cells (NSCs), highly pluripotent cells with the ability of self-renewal and potential for multidirectional differentiation, provide a promising solution to meet this demand. However, some serious challenges remaining to be addressed are the regulation of implanted NSCs, tracking their fate, monitoring their interaction with and responsiveness to the tissue environment, and evaluating their treatment efficacy. Nanomaterials have been envisioned as innovative components to further empower the field of NSC-based regenerative medicine, because their unique physicochemical characteristics provide unparalleled solutions to the imaging and treatment of diseases. By building on the advantages of nanomaterials, tremendous efforts have been devoted to facilitate research into the clinical translation of NSC-based therapy. Here, recent work on emerging nanomaterials is highlighted and their performance in the imaging and treatment of neurological diseases is evaluated, comparing the strengths and weaknesses of various imaging modalities currently used. The underlying mechanisms of therapeutic efficacy are discussed, and future research directions are suggested.

Physicochemical stability and transfection efficiency of cationic amphiphilic copolymer/pDNA polyplexes for spinal cord injury repair

Multiple age-related and injury-induced characteristics of the adult central nervous system (CNS) pose barriers to axonal regeneration and functional recovery following injury. In situ gene therapy is a promising approach to address the limited availability of growth-promoting biomolecules at CNS injury sites. The ultimate goal of our work is to develop, a cationic amphiphilic copolymer for simultaneous delivery of drug and therapeutic nucleic acids to promote axonal regeneration and plasticity after spinal cord injury. Previously, we reported the synthesis and characterization of a cationic amphiphilic copolymer, poly (lactide-co-glycolide)-graft-polyethylenimine (PgP) and its ability to efficiently transfect cells with pDNA in the presence of serum. We also demonstrated the efficacy of PgP as a therapeutic siRhoA carrier in a rat compression spinal cord injury model. In this work, we show that PgP/pDNA polyplexes provide improved stability in the presence of competing polyanions and nuclease protection in serum relative to conventional branched polyethylenimine control. PgP/pDNA polyplexes maintain bioactivity for transfection after lyophilization/reconstitution and during storage at 4 °C for up to 5 months, important features for commercial and clinical application. We also demonstrate that PgP/pDNA polyplexes loaded with a hydrophobic fluorescent dye are retained in local neural tissue for up to 5 days and that PgP can efficiently deliver pβ-Gal in a rat compression SCI model.

The nanomaterial toolkit for neuroengineering

There is a growing interest in developing effective tools to better probe the central nervous system (CNS), to understand how it works and to treat neural diseases, injuries and cancer. The intrinsic complexity of the CNS has made this a challenging task for decades. Yet, with the extraordinary recent advances in nanotechnology and nanoscience, there is a general consensus on the immense value and potential of nanoscale tools for engineering neural systems. In this review, an overview of specialized nanomaterials which have proven to be the most effective tools in neuroscience is provided. After a brief background on the prominent challenges in the field, a variety of organic and inorganic-based nanomaterials are described, with particular emphasis on the distinctive properties that make them versatile and highly suitable in the context of the CNS. Building on this robust nano-inspired foundation, the rational design and application of nanomaterials can enable the generation of new methodologies to greatly advance the neuroscience frontier.

Adenoviral vector carrying glial cell-derived neurotrophic factor for direct gene therapy in comparison with human umbilical cord blood cell-mediated therapy of spinal cord injury in rat

STUDY DESIGN

Experimental study.

OBJECTIVE

To evaluate the treatment of spinal cord injury with glial cell-derived neurotrophic factor (GDNF) delivered using an adenoviral vector (AdV-GDNF group) in comparison with treatment performed using human umbilical cord blood mononuclear cells (UCB-MCs)-transduced with an adenoviral vector carrying the GDNF gene (UCB-MCs+AdV-GDNF group) in rat.

SETTING

Kazan, Russian Federation.

METHODS

We examined the efficacy of AdV-GDNF and UCB-MCs+AdV-GDNF therapy by conducting behavioral tests on the animals and morphometric studies on the spinal cord, performing immunofluorescence analyses on glial cells, investigating the survival and migration potential of UCB-MCs, and evaluating the expression of the recombinant GDNF gene.

RESULTS

At the 30th postoperative day, equal positive locomotor recovery was observed after both direct and cell-based GDNF therapy. However, after UCB-MCs-mediated GDNF therapy, the area of preserved tissue and the number of spared myelinated fibers were higher than those measured after direct GDNF gene therapy. Moreover, we observed distinct changes in the populations of glial cells; expression patterns of the specific markers for astrocytes (GFAP, S100B and AQP4), oligodendrocytes (PDGFαR and Cx47) and Schwann cells (P0) differed in various areas of the spinal cord of rats treated with AdV-GDNF and UCB-MCs+AdV-GDNF.

CONCLUSION

The differences detected in the AdV-GDNF and UCB-MCs+AdV-GDNF groups could be partially explained by the action of UCB-MCs. We discuss the insufficiency and the advantages of these two methods of GDNF gene delivery into the spinal cord after traumatic injury.

Neural plasticity after spinal cord injury

Plasticity changes of uninjured nerves can result in a novel neural circuit after spinal cord injury, which can restore sensory and motor functions to different degrees. Although processes of neural plasticity have been studied, the mechanism and treatment to effectively improve neural plasticity changes remain controversial. The present study reviewed studies regarding plasticity of the central nervous system and methods for promoting plasticity to improve repair of injured central nerves. The results showed that synaptic reorganization, axonal sprouting, and neurogenesis are critical factors for neural circuit reconstruction. Directed functional exercise, neurotrophic factor and transplantation of nerve-derived and non-nerve-derived tissues and cells can effectively ameliorate functional disturbances caused by spinal cord injury and improve quality of life for patients.

Neurotrophin delivery using nanotechnology

Deficits or overexpression of neurotrophins cause neurodegenerative diseases and psychiatric disorders. These proteins are required for the maintenance of the function, plasticity and survival of neurons in the central (CNS) and peripheral nervous systems. Significant efforts have been devoted to developing therapeutic delivery systems that enable control of neurotrophin dosage in the brain. Here, we suggest that nanoparticulate carriers favoring targeted delivery in specific brain areas and minimizing biodistribution to the systemic circulation should be developed toward clinical benefits of neuroregeneration. We also provide examples of improved targeted neurotrophin delivery to localized areas in the CNS.

From molecular to nanotechnology strategies for delivery of neurotrophins: emphasis on brain-derived neurotrophic factor (BDNF)

Neurodegenerative diseases represent a major public health problem, but beneficial clinical treatment with neurotrophic factors has not been established yet. The therapeutic use of neurotrophins has been restrained by their instability and rapid degradation in biological medium. A variety of strategies has been proposed for the administration of these leading therapeutic candidates, which are essential for the development, survival and function of human neurons. In this review, we describe the existing approaches for delivery of brain-derived neurotrophic factor (BDNF), which is the most abundant neurotrophin in the mammalian central nervous system (CNS). Biomimetic peptides of BDNF have emerged as a promising therapy against neurodegenerative disorders. Polymer-based carriers have provided sustained neurotrophin delivery, whereas lipid-based particles have contributed also to potentiation of the BDNF action. Nanotechnology offers new possibilities for the design of vehicles for neuroprotection and neuroregeneration. Recent developments in nanoscale carriers for encapsulation and transport of BDNF are highlighted.

Non-viral gene therapy for spinal cord regeneration

Spinal cord injury (SCI) normally results in life-long disabilities and a broad range of secondary complications. Advances in therapeutic delivery during the past few decades offer hope for such victims. However, the limited functional improvement shown in in vivo studies hinders effective therapeutic application in clinical practice. Recent studies showed that gene vectors can transfect cells present in the lesion of an injured spinal cord (endogenous cells) and thereby produce therapeutic molecules with long-lasting biological effects that promote neural tissue regeneration. In this article we review recent advances in non-viral gene delivery into neural cells and their use for gene therapy in SCI.

Enhanced regenerative axon growth of multiple fibre populations in traumatic spinal cord injury following scar-suppressing treatment

We analysed the effect of scar-suppressing treatment (anti-scarring treatment; AST) on augmenting axonal regeneration of various neuronal populations following spinal cord injury (SCI) in adult rat. AST included local iron chelator (2,2'-dipyridine-5,5'-dicarboxylic acid) injection and 8-bromo-cyclic adenosine monophosphate application to the lesion core. In previous studies, this treatment promoted long-distance regeneration of cut corticospinal tract axons, neuroprotection of projecting cortical neurons and functional improvement of treated rats [N. Klapka et al. (2005)Eur. J. Neurosci., 22, 3047-3058]. Treatment yielded significantly enhanced regrowth of descending serotonergic (5-HT), catecholaminergic (tyrosine hydroxylase; TH), corticospinal and rubrospinal axons into the lesion zone, as assessed by anterograde tracing and immunohistochemistry followed by quantification of axon profiles at 5 and 12 weeks post-injury. In addition, the determination of axons crossing the proximal borderline from uninjured tissue into fibrous scar area revealed a significant AST-promoted increase of intersecting fibres for 5-HT, TH and calcitonin gene-related peptide containing ascending sensory fibres. For a prolonged time period after lesion, the delayed (secondary) scar developing in treated rats is significantly more permeable for all analysed axon tracts than the initial (primary) scar forming in injured control animals lacking treatment. Furthermore, enhanced outgrowth of descending axons from fibrous scar into distal healthy spinal tissue was achieved in treated animals, and is in line with previous functional studies [S. Hermanns et al. (2001) Restor. Neurol. Neurosci., 19,139-148; N. Klapka et al. (2005)Eur. J. Neurosci., 22, 3047-3058]. Our findings indicate that AST exerts a prolonged beneficial effect on fibrous scarring allowing enhanced axonal regrowth of different fibre tracts in SCI regardless of their distinct regenerative demands.

Mature adipocyte-derived cells, dedifferentiated fat cells (DFAT), promoted functional recovery from spinal cord injury-induced motor dysfunction in rats

Transplantation of mature adipocyte-derived cells (dedifferentiated fat cells) led to marked functional recovery from spinal cord injury (SCI)-induced motor dysfunction in rats. When mature adipocytes were isolated from rat adipose tissue and grown in ceiling culture, transformation into fibroblast-like cells without lipid droplets occurred. These fibroblast-like cells, termed dedifferentiated fat cells (DFAT), could proliferate and could also differentiate back into adipocytes. DFAT expressed neural markers such as nestin, betaIII tubulin, and GFAP. Allografting of DFAT into SCI-induced rats led to significant recovery from hindlimb dysfunction. Grafted cells were detected at the injection site, and some of these cells expressed betaIII tubulin. DFAT expressed neurotrophic factors such as BDNF and GDNF prior to transplantation, and grafted cells were also positive for these factors. Therefore, these neurotrophic factors derived from grafted DFAT might have contributed to the promotion of functional recovery. These findings also suggest that mature adipocytes could become a new source for cell replacement therapy to treat central nervous system disorders.

GDNF isoform affects intracellular trafficking and secretion of GDNF in neuronal cells

Glial cell line derived neurotrophic factor (GDNF) plays a critical role in central and peripheral neuron survival and function. In human and rodents, GDNF exists in an alternative spliced isoform (GDNF Delta 78), which has a 78 bp deletion in the pro-region of the GDNF encoding sequence. Whether the GDNF isoform affects GDNF function is unknown. Here, we investigated the secretion and intracellular localization of the GDNF Delta 78 isoform in neuronal cell populations. Our data indicate that a decreased secretion and an abnormal intracellular distribution of GDNF Delta 78 occurred in neuronal cells. The colocalization studies revealed much more localization of GDNF Delta 78 with Golgi marker-TGN38, which indicates that the accumulation of GDNF Delta 78 in the Golgi apparatus might in part account for its intracellular trafficking and secretion deficit. To our knowledge, it is reported for the first time that the GDNF Delta 78 isoform has a deficit in GDNF intracellular trafficking and secretion.

Changes in Glial cell line-derived neurotrophic factor expression in the rostral and caudal stumps of the transected adult rat spinal cord

Limited information is available regarding the role of endogenous Glial cell line-derived neurotrophic factor (GDNF) in the spinal cord following transection injury. The present study investigated the possible role of GDNF in injured spinal cords following transection injury (T(9)-T(10)) in adult rats. The locomotor function recovery of animals by the BBB (Basso, Beattie, Bresnahan) scale score showed that hindlimb support and stepping function increased gradually from 7 days post operation (dpo) to 21 dpo. However, the locomotion function in the hindlimbs decreased effectively in GDNF-antibody treated rats. GDNF immunoreactivty in neurons in the ventral horn of the rostral stump was stained strongly at 3 and 7 dpo, and in the caudal stump at 14 dpo, while immunostaining in astrocytes was also seen at all time-points after transection injury. Western blot showed that the level of GDNF protein underwent a rapid decrease at 7 dpo in both stumps, and was followed by a partial recovery at a later time-point, when compared with the sham-operated group. GDNF mRNA-positive signals were detected in neurons of the ventral horn, especially in lamina IX. No regenerative fibers from corticospinal tract can be seen in the caudal segment near the injury site using BDA tracing technique. No somatosensory evoked potentials (SEP) could be recorded throughout the experimental period as well. These findings suggested that intrinsic GDNF in the spinal cord could play an essential role in neuroplasticity. The mechanism may be that GDNF is involved in the regulation of local circuitry in transected spinal cords of adult rats.

Advances in the treatment of Parkinson's disease

Parkinson's disease (PD) affects one in every 100 persons above the age of 65 years, making it the second most common neurodegenerative disease after Alzheimer's disease. PD is a disease of the central nervous system that leads to severe difficulties with body motions. The currently available therapies aim to improve the functional capacity of the patient for as long as possible; however they do not modify the progression of the neurodegenerative process. The need for newer and more effective agents is consequently receiving a great deal of attention and consequently being subjected to extensive research. This review concisely compiles the limitations of currently available therapies and the most recent research regarding neuroprotective agents, antioxidants, stem cell research, vaccines and various surgical techniques available and being developed for the management of PD.

Designing cell- and gene-based regeneration strategies to repair the injured spinal cord

There is an array of new and promising strategies being developed to improve function after spinal cord injury (SCI). The targeting of a diversity of deleterious processes within the tissue after SCI will necessitate a multi-factorial intervention, such as the combination of cell- and gene-based approaches. To ensure proper development and design of these experiments, many issues need to be addressed. It is the purpose of this review to consider the strategies involved in testing the efficacy of these new combinations to improve axonal regeneration. For cell-based therapy, issues are choosing a SCI model, the time of cell implantation, placement of cells and their subsequent migration, fluid versus solid grafts, use of agents to prevent immune rejection, and tracking of implanted cells. Grafting is also discussed in view of improving function, reducing secondary damage, bridging the injured spinal cord, supporting axonal regrowth, replacing lost neurons, facilitating myelination, and promoting axonal growth from the implant into the cord. The choice of a gene delivery system, gene-based therapies in vivo to provide chemoattractant and guidance cues, altering the intrinsic regenerative capacity of neurons, enhancing endogenous non-neuronal cell functions, and targeting the synthesis of growth inhibitory molecules are also discussed, as well as combining ex vivo gene and cell therapies.

Regeneration of descending axon tracts after spinal cord injury

Axons within the adult mammalian central nervous system do not regenerate spontaneously after injury. Upon injury, the balance between growth promoting and growth inhibitory factors in the central nervous system dramatically changes resulting in the absence of regeneration. Axonal responses to injury vary considerably. In central nervous system regeneration studies, the spinal cord has received a lot of attention because of its relatively easy accessibility and its clinical relevance. The present review discusses the axon-tract-specific requirements for regeneration in the rat. This knowledge is very important for the development and optimalization of therapies to repair the injured spinal cord.

Why study transport of peptides and proteins at the neurovascular interface

The blood-brain barrier (BBB) is an immense neurovascular interface. In neurodegenerative, ischemic, and traumatic disorders of the central nervous system (CNS), the BBB may hinder the delivery of many therapeutic peptides and proteins to the brain and spinal cord. Fortunately, the mistaken dogma that peptides and proteins do not cross the BBB has been corrected during the past two decades by the accumulating evidence that peptides and proteins in the periphery exert potent effects in the CNS. Not only can peptides and proteins serve as carriers for selective therapeutic agents, but they themselves may directly cross the BBB after delivery into the bloodstream. Their passage may be mediated by simple diffusion or specific transport, both of which can be affected by interactions in the blood compartment (outside the BBB) and within the endothelial cells (at the BBB level). Although the majority of current delivery strategies focuses on modification of the molecule to be delivered, understanding the mechanisms of transport will eventually facilitate regulation of the BBB directly. We review the different aspects of interactions and discuss recent advances in the cell biology of peptide/protein transport across the BBB. Better understanding of the nature and regulation of the transport systems at the BBB will provide a new direction to enhance the interactions of peripheral peptides and proteins with the CNS.

Neurotrophic factors expressed in both cortex and spinal cord induce axonal plasticity after spinal cord injury

We reported recently that overexpression of neurotrophin-3 (NT-3) by motoneurons in the spinal cord of rats will induce sprouting of corticospinal tract (CST) axons (Zhou et al. [2003] J. Neurosci. 23:1424-1431). We now report that overexpression of brain-derived neurotrophic factor (BDNF) or glial cell-derived neurotrophic factor (GDNF) in the rat sensorimotor cortex near the CST neuronal cell bodies together with overexpression of NT-3 in the lumbar spinal cord significantly increases axonal sprouting compared to that induced by NT-3 alone. Two weeks after unilaterally lesioning the CST at the level of the pyramids, we injected rats with saline or adenoviral vectors (Adv) carrying genes coding for BDNF (Adv.BDNF), GDNF (Adv.GDNF) or enhanced green fluorescent protein (Adv.EGFP) at six sites in the sensorimotor cortex, while delivering Adv.NT3 to motoneurons in each of these four groups on the lesioned side of the spinal cord by retrograde transport from the sciatic nerve. Four days later, biotinylated dextran amine (BDA) was injected into the sensorimotor cortex on the unlesioned side to mark CST axons in the spinal cord. Morphometric analysis of axonal sprouting 3 weeks after BDA injection showed that the number of CST axons crossing the midline in rats treated with Adv.BDNF or Adv.GDNF were 46% and 52% greater, respectively, than in rats treated with Adv.EGFP or PBS (P < 0.05). These data demonstrate that sustained local expression of neurotrophic factors in the sensorimotor cortex and spinal cord will promote increased axonal sprouting after spinal cord injury, providing a basis for continued development of neurotrophic factor therapy for central nervous system damage.