Affinity for, and localization of, PEG-functionalized silica nanoparticles to sites of damage in an ex vivo spinal cord injury model

On the therapeutic targets and pharmacological treatments for pain relief following spinal cord injury: A mechanistic review

Spinal cord injury (SCI) is globally considered as one of the most debilitating disorders, which interferes with daily activities and life of the affected patients. Despite many developments in related recognizing and treating procedures, post-SCI neuropathic pain (NP) is still a clinical challenge for clinicians with no distinct treatments. Accordingly, a comprehensive search was conducted in PubMed, Medline, Scopus, Web of Science, and national database (SID and Irandoc). The relevant articles regarding signaling pathways, therapeutic targets and pharmacotherapy of post-SCI pain were also reviewed. Data were collected with no time limitation until November 2020. The present study provides the findings on molecular mechanisms and therapeutic targets, as well as developing the critical signaling pathways to introduce novel neuroprotective treatments of post-SCI pain. From the pathophysiological mechanistic point of view, post-SCI inflammation activates the innate immune system, in which the immune cells elicit secondary injuries. So, targeting the critical signaling pathways for pain management in the SCI population has significant importance in providing new treatments. Indeed, several receptors, ion channels, excitatory neurotransmitters, enzymes, and key signaling pathways could be used as therapeutic targets, with a pivotal role of n-methyl-D-aspartate, gamma-aminobutyric acid, and inflammatory mediators. The current review focuses on conventional therapies, as well as crucial signaling pathways and promising therapeutic targets for post-SCI pain to provide new insights into the clinical treatment of post-SCI pain. The need to develop innovative delivery systems to treat SCI is also considered.

Recent advances in nanotherapeutic strategies for spinal cord injury repair

Spinal cord injury (SCI) is a devastating and complicated condition with no cure available. The initial mechanical trauma is followed by a secondary injury characterized by inflammatory cell infiltration and inhibitory glial scar formation. Due to the limitations posed by the blood-spinal cord barrier, systemic delivery of therapeutics is challenging. Recent development of various nanoscale strategies provides exciting and promising new means of treating SCI by crossing the blood-spinal cord barrier and delivering therapeutics. As such, we discuss different nanomaterial fabrication methods and provide an overview of recent studies where nanomaterials were developed to modulate inflammatory signals, target inhibitory factors in the lesion, and promote axonal regeneration after SCI. We also review emerging areas of research such as optogenetics, immunotherapy and CRISPR-mediated genome editing where nanomaterials can provide synergistic effects in developing novel SCI therapy regimens, as well as current efforts and barriers to clinical translation of nanomaterials.

Neuroprotection by chitosan nanoparticles in oxidative stress-mediated injury

Objective

Oxidative stress is a critical component of nervous system secondary injury. Oxidative stress produces toxic chemical byproducts including reactive aldehydes that traverse intact membranes and attack neighboring healthy cells. This secondary damage often leads to further patho-biochemical cascades that exacerbate the original insult. In this work, we investigate the therapeutic effects of chitosan nanoparticles on cell cultures exposed to oxidative stress.

Results

We found chitosan nanoparticles can rescue BV-2 glial cells from death, but only for cells undergoing necrosis. Necrosis occurred when cultures were challenged with high concentrations of H₂O₂ (> 110 μM) whereas a slow and progressive loss of cultures was observed in more dilute (50–100 μM) peroxide applications. In the latter case, the primary mode of cell death was apoptosis. These studies revealed that while rescue of H₂O₂ challenged cultures was achieved for necrotic cell death, no such sparing was observed in apoptotic cells. Based on the current and cumulative data regarding the membrane fusogenic properties of chitosan, we conclude that chitosan neuroprotection arises from its membrane sealing effects. Consistent with this hypothesis is the observation that apoptotic cells did not exhibit early stage membrane damage. These in vitro results elucidate mechanisms by which membrane fusogens may provide therapeutic benefit.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-3162-7) contains supplementary material, which is available to authorized users.

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.

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.

From demyelination to remyelination: the road toward therapies for spinal cord injury

Myelin integrity is crucial for central nervous system (CNS) physiology while its preservation and regeneration after spinal cord injury (SCI) is key to functional restoration. Disturbance of nodal organization acutely after SCI exposes the axon and triggers conduction block in the absence of overt demyelination. Oligodendrocyte (OL) loss and myelin degradation follow as a consequence of secondary damage. Here, we provide an overview of the major biological events and underlying mechanisms leading to OL death and demyelination and discuss strategies to restrain these processes. Another aspect which is critical for SCI repair is the enhancement of endogenously occurring spontaneous remyelination. Recent findings have unveiled the complex roles of innate and adaptive immune responses in remyelination and the immunoregulatory potential of the glial scar. Moreover, the intimate crosstalk between neuronal activity, oligodendrogenesis and myelination emphasizes the contribution of rehabilitation to functional recovery. With a view toward clinical applications, several therapeutic strategies have been devised to target SCI pathology, including genetic manipulation, administration of small therapeutic molecules, immunomodulation, manipulation of the glial scar and cell transplantation. The implementation of new tools such as cellular reprogramming for conversion of one somatic cell type to another or the use of nanotechnology and tissue engineering products provides additional opportunities for SCI repair. Given the complexity of the spinal cord tissue after injury, it is becoming apparent that combinatorial strategies are needed to rescue OLs and myelin at early stages after SCI and support remyelination, paving the way toward clinical translation.

Nanoparticles carrying neurotrophin-3-modified Schwann cells promote repair of sciatic nerve defects

Schwann cells and neurotrophin-3 play an important role in neural regeneration, but the secretion of neurotrophin-3 from Schwann cells is limited, and exogenous neurotrophin-3 is inactived easily in vivo. In this study, we have transfected neurotrophin-3 into Schwann cells cultured in vitro using nanoparticle liposomes. Results showed that neurotrophin-3 was successfully transfected into Schwann cells, where it was expressed effectively and steadily. A composite of Schwann cells transfected with neurotrophin-3 and poly(lactic-co-glycolic acid) biodegradable conduits was transplanted into rats to repair 10-mm sciatic nerve defects. Transplantation of the composite scaffold could restore the myoelectricity and wave amplitude of the sciatic nerve by electrophysiological examination, promote nerve axonal and myelin regeneration, and delay apoptosis of spinal motor neurons. Experimental findings indicate that neurotrophin-3 transfected Schwann cells combined with bridge grafting can promote neural regeneration and functional recovery after nerve injury.

Nanoparticulate strategies for the five R’s of traumatic spinal cord injury intervention: restriction, repair, regeneration, restoration and reorganization

Nanomedicinal approaches for spinal cord injury (SCI) intervention encompasses the use of nanoscale materials and devices that prevent primary to secondary injury transition and improvement in the anatomical, physiological and functional outcomes of SCI. This review provides an incursion into the advances in nanoparticle-based neurotherapeutics for SCI and focuses on neuroactive-loaded nanoparticles for localized delivery of therapeutic factors to the severed spinal cord, targeted or nontargeted systemic drug delivery and nanoenclatherated neuroscaffolds. Special emphasis has been placed on the use of metal nanoparticles and functionalized structures as ‘drug-free’ interventions in SCI. Despite the immense advancements in nanoscience, nanointerventions still pose key challenges that need to be resolved in SCI. Several combinatorial strategies are proposed for the reconstruction of spinal architecture via restriction of the secondary injury cascade, reparation of the tethered neural architecture, regeneration of axons, restoration of biochemical functions and reorganization of the topographical and cortical networks of the spinal cord.

Electrical stimulation modulates injury potentials in rats after spinal cord injury

An injury potential is the direct current potential difference between the site of spinal cord injury and the healthy nerves. Its initial amplitude is a significant indicator of the severity of spinal cord injury, and many cations, such as sodium and calcium, account for the major portion of injury potentials. This injury potential, as well as injury current, can be modulated by direct current field stimulation; however, the appropriate parameters of the electrical field are hard to define. In this paper, injury potential is used as a parameter to adjust the intensity of electrical stimulation. Injury potential could be modulated to slightly above 0 mV (as the anode-centered group) by placing the anodes at the site of the injured spinal cord and the cathodes at the rostral and caudal sections, or around -70 mV, which is resting membrane potential (as the cathode-centered group) by reversing the polarity of electrodes in the anode-centered group. In addition, rats receiving no electrical stimulation were used as the control group. Results showed that the absolute value of the injury potentials acquired after 30 minutes of electrical stimulation was higher than the control group rats and much lower than the initial absolute value, whether the anodes or the cathodes were placed at the site of injury. This phenomenon illustrates that by changing the polarity of the electrical field, electrical stimulation can effectively modulate the injury potentials in rats after spinal cord injury. This is also beneficial for the spontaneous repair of the cell membrane and the reduction of cation influx.

Intravenous magnetic nanoparticle cancer hyperthermia

Magnetic nanoparticles heated by an alternating magnetic field could be used to treat cancers, either alone or in combination with radiotherapy or chemotherapy. However, direct intratumoral injections suffer from tumor incongruence and invasiveness, typically leaving undertreated regions, which lead to cancer regrowth. Intravenous injection more faithfully loads tumors, but, so far, it has been difficult achieving the necessary concentration in tumors before systemic toxicity occurs. Here, we describe use of a magnetic nanoparticle that, with a well-tolerated intravenous dose, achieved a tumor concentration of 1.9 mg Fe/g tumor in a subcutaneous squamous cell carcinoma mouse model, with a tumor to non-tumor ratio > 16. With an applied field of 38 kA/m at 980 kHz, tumors could be heated to 60°C in 2 minutes, durably ablating them with millimeter (mm) precision, leaving surrounding tissue intact.

Pushing the science forward: chitosan nanoparticles and functional repair of CNS tissue after spinal cord injury

BACKGROUND

We continue our exploration of the large polysaccharide polymer Chitosan as an acute therapy for severe damage to the nervous system. We tested the action of subcutaneously injected nanoparticles (~ 100 - 200 nanometers in diameter; 1 mg per ml) against control injections (silica particle of the same size and concentration) in a standardized in vivo spinal cord injury model. These functional tests used standardized physiological measurements of evoked potentials arriving at the sensorimotor cortex subsequent to stimulation of the tibial nerve of the contralateral hindlimb. We further explored the degree of acetylation and molecular weight of chitosan on the success of sealing cell damage using specific probes of membrane integrity.

RESULTS

Not one of the control group showed restored conduction of evoked potentials stimulated from the tibial nerve of the hindleg - through the lesion - and recorded at the sensorimotor cortex of the brain. Investigation if the degree of acetylation and molecular weight impacted "membrane sealing" properties of Chitosan were unsuccessful. Dye - exchange membrane probes failed to show a difference between the comparators in the function of Chitosan in ex vivo injured spinal cord tests.

CONCLUSIONS

We found that Chitosan nanoparticles effectively restore nerve impulse transmission through the crushed adult guinea pig spinal cord in vivo after severe crush/compression injury. The tests of the molecular weight (MW) and degree of acetylation did not produce any improvement in Chitosan's membrane sealing properties.