Repair of spinal cord injury by inhibition of astrocyte growth and inflammatory factor synthesis through local delivery of flavopiridol in PLGA nanoparticles

Cell cycle inhibition limits development and maintenance of neuropathic pain following spinal cord injury

Chronic pain after spinal cord injury (SCI) may present as hyperalgesia, allodynia, and/or spontaneous pain and is often resistant to conventional pain medications. Identifying more effective interventions to manage SCI pain requires improved understanding of the pathophysiological mechanisms involved. Cell cycle activation (CCA) has been implicated as a key pathophysiological event following SCI. We have shown that early central or systemic administration of a cell cycle inhibitor reduces CCA, prevents glial changes, and limits SCI-induced hyperesthesia. Here, we compared the effects of early vs late treatment with the pan-cyclin-dependent kinase inhibitor flavopiridol on allodynia as well as spontaneous pain. Adult C57BL/6 male mice subjected to moderate SCI were treated with intraperitoneal injections of flavopiridol (1 mg/kg), daily for 7 days beginning either 3 hours or 5 weeks after injury. Mechanical/thermal allodynia was evaluated, as well as spontaneous pain using the mouse grimace scale (MGS). We show that sensitivity to mechanical and thermal stimulation, and locomotor dysfunction were significantly reduced by early flavopiridol treatment compared with vehicle-treated controls. Spinal cord injury caused robust and extended increases of MGS up to 3 weeks after trauma. Early administration of flavopiridol significantly shortened duration of MGS changes. Late flavopiridol intervention significantly limited hyperesthesia at 7 days after treatment, associated with reduced glial changes, but without effect on locomotion. Thus, our data suggest that cell cycle modulation may provide an effective therapeutic strategy to reduce hyperesthesia after SCI, with a prolonged therapeutic window.

Ablation of the transcription factors E2F1-2 limits neuroinflammation and associated neurological deficits after contusive spinal cord injury

Traumatic spinal cord injury (SCI) induces cell cycle activation (CCA) that contributes to secondary injury and related functional impairments such as motor deficits and hyperpathia. E2F1 and E2F2 are members of the activator sub-family of E2F transcription factors that play an important role in proliferating cells and in cell cycle-related neuronal death, but no comprehensive study have been performed in SCI to determine the relative importance of these factors. Here we examined the temporal distribution and cell-type specificity of E2F1 and E2F2 expression following mouse SCI, as well as the effects of genetic deletion of E2F1-2 on neuronal cell death, neuroinflammation and associated neurological dysfunction. SCI significantly increased E2F1 and E2F2 expression in active caspase-3(+) neurons/oligodendrocytes as well as in activated microglia/astrocytes. Injury-induced up-regulation of cell cycle-related genes and protein was significantly reduced by intrathecal injection of high specificity E2F decoy oligodeoxynucleotides against the E2F-binding site or in E2F1-2 null mice. Combined E2F1+2 siRNA treatment show greater neuroprotection in vivo than E2F1 or E2F2 single siRNA treatment. Knockout of both E2F1 and E2F2 genes (E2Fdko) significantly reduced neuronal death, neuroinflammation, and tissue damage, as well as limiting motor dysfunction and hyperpathia after SCI. Both CCA reduction and functional improvement in E2Fdko mice were greater than those in E2F2ko model. These studies demonstrate that SCI-induced activation of E2F1-2 mediates CCA, contributing to gliopathy and neuronal/tissue loss associated with motor impairments and post-traumatic hyperesthesia. Thus, E2F1-2 provide a therapeutic target for decreasing secondary tissue damage and promoting recovery of function after SCI.

Nanoparticle Technologies in the Spinal Cord

Nanoparticles are increasingly being studied within experimental models of spinal cord injury (SCI). They are used to image cells and tissue, move cells to specific regions of the spinal cord, and deliver therapeutic agents locally. The focus of this article is to provide a brief overview of the different types of nanoparticles being studied for spinal cord applications and present data showing the capability of nanoparticles to deliver the chondroitinase ABC (chABC) enzyme locally following acute SCI in rats. Nanoparticles releasing chABC helped promote axonal regeneration following injury, and the nanoparticles also protected the enzyme from rapid degradation. In summary, nanoparticles are viable materials for diagnostic or therapeutic applications within experimental models of SCI and have potential for future clinical use.

Nanotherapeutics of PTEN Inhibitor with Mesoporous Silica Nanocarrier Effective for Axonal Outgrowth of Adult Neurons

Development of therapeutic strategies such as effective drug delivery is an urgent and yet unmet need for repair of damaged nervous systems. Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) regulates axonal regrowth of central and peripheral nervous systems; its inhibition, meanwhile, facilitates axonal outgrowth of injured neurons. Here we show that nanotherapeutics based on mesoporous silica nanoparticles loading PTEN-inhibitor bisperoxovanadium (BpV) are effective for delivery of drug molecules and consequent improvement of axonal outgrowth. Mesoporous nanocarriers loaded BpV drug at large amount (27 μg per 1 mg of carrier), and released sustainably over 10 d. Nanocarrier-BpV treatment of primary neurons from the dorsal root ganglions (DRGs) of rats and mice at various concentrations induced them to actively take up the nanocomplexes with an uptake efficiency as high as 85%. The nanocomplex-administered neurons exhibited significantly enhanced axonal outgrowth compared with those treated with free-BpV drug. The expression of a series of proteins involved in PTEN inhibition and downstream signaling was substantially up-/down-regulated by the nanocarrier-BpV system. Injection of the nanocarriers into neural tissues (DRG, brain cortex, and spinal cord), moreover, demonstrated successful integration into neurons, glial cells, oligodendrocytes, and macrophages, suggesting the possible nanotherapeutics applications in vivo. Together, PTEN-inhibitor delivery via mesoporous nanocarriers can be considered a promising strategy for stimulating axonal regeneration in central and peripheral nervous systems.

Combination of a peptide-modified gellan gum hydrogel with cell therapy in a lumbar spinal cord injury animal model

Spinal Cord Injury (SCI) is a highly incapacitating condition for which there is still no cure. Current clinical approaches are mainly based on palliative care, so there is a need to find possible treatments to SCI. Cellular transplantation is regarded with great expectation due to the therapeutic potential of cells such as Adipose tissue-derived Stromal/Stem Cells (ASCs) or Olfactory Ensheathing Cells (OECs). Both are accessible sources and present positive paracrine and cell-to-cell interactions, previously reported by our group. Additionally, biomaterials such as hydrogels have been applied in SCI repair with promising results. We propose to combine a GRGDS-modified gellan gum hydrogel with ASCs and OECs in order to promote SCI regeneration. In vitro, ASCs and OECs could be co-cultured within GG-GRGDS hydrogels inducing a more robust neurite outgrowth when compared to controls. In vivo experiments in a hemisection SCI rat model revealed that the administration of ASCs and OECs encapsulated in a GG-GRGDS hydrogel led to significant motor improvements when compared to both control (SCI) and hydrogel alone (GG-GRGDS) groups. This was accompanied by a decreased infiltration of inflammatory cells and astrocytes, and by an increased intensity of neurofilament. These results suggest evident gains induced by the encapsulation of ASCs and OECs in GG-GRGDS based hydrogels.

MRI-Guided Stereotactic System for Delivery of Intraspinal Microstimulation

STUDY DESIGN

Laboratory/animal-based proof of principle study.

OBJECTIVE

To validate the accuracy of a magnetic resonance imaging (MRI)-guided stereotactic system for intraspinal electrode targeting and demonstrate the feasibility of such a system for controlling implantation of intraspinal electrodes.

SUMMARY OF BACKGROUND DATA

Intraspinal microstimulation (ISMS) is an emerging preclinical therapy, which has shown promise for the restoration of motor function following spinal cord injury. However, targeting inaccuracy associated with existing electrode implantation techniques remains a major barrier preventing clinical translation of ISMS.

METHODS

System accuracy was evaluated using a test phantom comprised of nine target locations. Targeting accuracy was determined by calculating the root mean square error between MRI-generated coordinates and actual frame coordinates required to reach the target positions. System performance was further validated in an anesthetized pig model by performing MRI-guided intraspinal electrode implantation and stimulation followed by computed tomography of electrode location. Finally, system compatibility with a commercially available microelectrode array was demonstrated by implanting the array and applying a selection of stimulation amplitudes that evoked hind limb responses.

RESULTS

The root mean square error between actual frame coordinates and software coordinates, both acquired using the test phantom, was 1.09 ± 0.20 mm. Postoperative computed tomography in the anesthetized pig confirmed spatially accurate electrode placement relative to preoperative MRI. Additionally, MRI-guided delivery of a microwire electrode followed by ISMS evoked repeatable electromyography responses in the biceps femoris muscle. Finally, delivery of a microelectrode array produced repeatable and graded hind limb evoked movements.

CONCLUSION

We present a novel frame-based stereotactic system for targeting and delivery of intraspinal instrumentation. This system utilizes MRI guidance to account for variations in anatomy between subjects, thereby improving upon existing ISMS electrode implantation techniques.

LEVEL OF EVIDENCE

N/A.

Therapeutic Use of 3β-[N-(N',N'-Dimethylaminoethane) Carbamoyl] Cholesterol-Modified PLGA Nanospheres as Gene Delivery Vehicles for Spinal Cord Injury

Gene delivery holds therapeutic promise for the treatment of neurological diseases and spinal cord injury. Although several studies have investigated the use of non-viral vectors, such as polyethylenimine (PEI), their clinical value is limited by their cytotoxicity. Recently, biodegradable poly (lactide-co-glycolide) (PLGA) nanospheres have been explored as non-viral vectors. Here, we show that modification of PLGA nanospheres with 3β-[N-(N′,N′-dimethylaminoethane) carbamoyl] cholesterol (DC-Chol) enhances gene transfection efficiency. PLGA/DC-Chol nanospheres encapsulating DNA were prepared using a double emulsion-solvent evaporation method. PLGA/DC-Chol nanospheres were less cytotoxic than PEI both in vitro and in vivo. DC-Chol modification improved the uptake of nanospheres, thereby increasing their transfection efficiency in mouse neural stem cells in vitro and rat spinal cord in vivo. Also, transgene expression induced by PLGA nanospheres was higher and longer-lasting than that induced by PEI. In a rat model of spinal cord injury, PLGA/DC-Chol nanospheres loaded with vascular endothelial growth factor gene increased angiogenesis at the injury site, improved tissue regeneration, and resulted in better recovery of locomotor function. These results suggest that DC-Chol-modified PLGA nanospheres could serve as therapeutic gene delivery vehicles for spinal cord injury.

Intraspinal Delivery of Polyethylene Glycol-coated Gold Nanoparticles Promotes Functional Recovery After Spinal Cord Injury

Failure of the mammalian central nervous system (CNS) to regenerate effectively after injury leads to mostly irreversible functional impairment. Gold nanoparticles (AuNPs) are promising candidates for drug delivery in combination with tissue-compatible reagents, such as polyethylene glycol (PEG). PEG administration in CNS injury models has received interest for potential therapy, but toxicity and low bioavailability prevents clinical application. Here we show that intraspinal delivery of PEG-functionalized 40-nm-AuNPs at early stages after mouse spinal cord injury is beneficial for recovery. Positive outcome of hind limb motor function was accompanied by attenuated inflammatory response, enhanced motor neuron survival, and increased myelination of spared or regrown/sprouted axons. No adverse effects, such as body weight loss, ill health, or increased mortality were observed. We propose that PEG-AuNPs represent a favorable drug-delivery platform with therapeutic potential that could be further enhanced if PEG-AuNPs are used as carriers of regeneration-promoting molecules.

Posttraumatic inflammation as a key to neuroregeneration after traumatic spinal cord injury

Pro- and anti-inflammatory cytokines might have a large impact on the secondary phase and on the neurological outcome of patients with acute spinal cord injury (SCI). We measured the serum levels of different cytokines (Interferon-γ, Tumor Necrosis Factor-α, Interleukin-1β, IL-6, IL-8, IL-10, and Vascular Endothelial Growth Factor) over a 12-week period in 40 acute traumatic SCI patients: at admission on average one hour after initial trauma; at four, nine, 12, and 24 h; Three, and seven days after admission; and two, four, eight, and twelve weeks after admission. This was done using a Luminex Performance Human High Sensitivity Cytokine Panel. SCI was classified using the American Spinal Injury Association (ASIA) Impairment Scale (AIS) at time of admission and after 12 weeks. TNFα, IL-1β, IL-6, IL-8, and IL-10 concentrations were significantly higher in patients without neurological remission and in patients with an initial AIS A (p < 0.05). This study shows significant differences in cytokine concentrations shown in traumatic SCI patients with different neurological impairments and within a 12-week period. IL-8 and IL-10 are potential peripheral markers for neurological remission and rehabilitation after traumatic SCI. Furthermore our cytokine expression pattern of the acute, subacute, and intermediate phase of SCI establishes a possible basis for future studies to develop standardized monitoring, prognostic, and tracking techniques.

Optical stimulation for restoration of motor function after spinal cord injury

Spinal cord injury can be defined as a loss of communication between the brain and the body due to disrupted pathways within the spinal cord. Although many promising molecular strategies have emerged to reduce secondary injury and promote axonal regrowth, there is still no effective cure, and recovery of function remains limited. Functional electrical stimulation (FES) represents a strategy developed to restore motor function without the need for regenerating severed spinal pathways. Despite its technological success, however, FES has not been widely integrated into the lives of spinal cord injury survivors. In this review, we briefly discuss the limitations of existing FES technologies. Additionally, we discuss how optogenetics, a rapidly evolving technique used primarily to investigate select neuronal populations within the brain, may eventually be used to replace FES as a form of therapy for functional restoration after spinal cord injury.