Local Polyethylene Glycol in Combination with Chitosan Based Hybrid Nanofiber Conduit Accelerates Transected Peripheral Nerve Regeneration

Gold and Cobalt Oxide Nanoparticles Modified Poly-Propylene Poly-Ethylene Glycol Membranes in Poly (ε-Caprolactone) Conduits Enhance Nerve Regeneration in the Sciatic Nerve of Healthy Rats

Reconstruction of nerve defects is a clinical challenge. Autologous nerve grafts as the gold standard treatment may result in an incomplete restoration of extremity function. Biosynthetic nerve conduits are studied widely, but still have limitations. Here, we reconstructed a 10 mm sciatic nerve defect in healthy rats and analyzed nerve regeneration in poly (ε-caprolactone) (PCL) conduits longitudinally divided by gold (Au) and gold-cobalt oxide (AuCoO) nanoparticles embedded in poly-propylene poly-ethylene glycol (PPEG) membranes (AuPPEG or AuCoOPPEG) and compared it with unmodified PPEG-membrane and hollow PCL conduits. After 21 days, we detected significantly better axonal outgrowth, together with higher numbers of activated Schwann cells (ATF3-labelled) and higher HSP27 expression, in reconstructed sciatic nerve and in corresponding dorsal root ganglia (DRG) in the AuPPEG and AuCoOPPEG groups; whereas the number of apoptotic Schwann cells (cleaved caspase 3-labelled) was significantly lower. Furthermore, numbers of activated and apoptotic Schwann cells in the regenerative matrix correlated with axonal outgrowth, whereas HSP27 expression in the regenerative matrix and in DRGs did not show any correlation with axonal outgrowth. We conclude that gold and cobalt-oxide nanoparticle modified membranes in conduits improve axonal outgrowth and increase the regenerative performance of conduits after nerve reconstruction.

Relevance and Recent Developments of Chitosan in Peripheral Nerve Surgery

Developments in tissue engineering yield biomaterials with different supporting strategies to promote nerve regeneration. One promising material is the naturally occurring chitin derivate chitosan. Chitosan has become increasingly important in various tissue engineering approaches for peripheral nerve reconstruction, as it has demonstrated its potential to interact with regeneration associated cells and the neural microenvironment, leading to improved axonal regeneration and less neuroma formation. Moreover, the physiological properties of its polysaccharide structure provide safe biodegradation behavior in the absence of negative side effects or toxic metabolites. Beneficial interactions with Schwann cells (SC), inducing differentiation of mesenchymal stromal cells to SC-like cells or creating supportive conditions during axonal recovery are only a small part of the effects of chitosan. As a result, an extensive body of literature addresses a variety of experimental strategies for the different types of nerve lesions. The different concepts include chitosan nanofibers, hydrogels, hollow nerve tubes, nerve conduits with an inner chitosan layer as well as hybrid architectures containing collagen or polyglycolic acid nerve conduits. Furthermore, various cell seeding concepts have been introduced in the preclinical setting. First translational concepts with hollow tubes following nerve surgery already transferred the promising experimental approach into clinical practice. However, conclusive analyses of the available data and the proposed impact on the recovery process following nerve surgery are currently lacking. This review aims to give an overview on the physiologic properties of chitosan, to evaluate its effect on peripheral nerve regeneration and discuss the future translation into clinical practice.

Polyethylene Glycol: The Future of Posttraumatic Nerve Repair? Systemic Review

Peripheral nerve injury is a common posttraumatic complication. The precise surgical repair of nerve lesion does not always guarantee satisfactory motor and sensory function recovery. Therefore, enhancement of the regeneration process is a subject of many research strategies. It is believed that polyethylene glycol (PEG) mediates axolemmal fusion, thus enabling the direct restoration of axon continuity. It also inhibits Wallerian degeneration and recovers nerve conduction. This systemic review, performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, describes and summarizes published studies on PEG treatment efficiency in various nerve injury types and repair techniques. Sixteen original experimental studies in animal models and one in humans were analyzed. PEG treatment superiority was reported in almost all experiments (based on favorable electrophysiological, histological, or behavioral results). To date, only one study attempted to transfer the procedure into the clinical phase. However, some technical aspects, e.g., the maximal delay between trauma and successful treatment, await determination. PEG therapy is a promising prospect that may improve the surgical treatment of peripheral nerve injuries in the clinical practice.

Effect of exogenous spastin combined with polyethylene glycol on sciatic nerve injury

Polyethylene glycol can connect the distal and proximal ends of an injured nerve at the cellular level through axonal fusion to avoid Wallerian degeneration of the injured distal nerve and promote peripheral nerve regeneration. However, this method can only prevent Wallerian degeneration in 10% of axons because the cytoskeleton is not repaired in a timely fashion. Reconstruction of the cytoskeletal trunk and microtubule network has been suggested to be the key for improving the efficiency of axonal fusion. As a microtubule-severing protein, spastin has been used to enhance cytoskeletal reconstruction. Therefore, we hypothesized that spastin combined with polyethylene glycol can more effectively promote peripheral nerve regeneration. A total of 120 male Sprague-Dawley rats were randomly divided into sham, suture, polyethylene glycol, and polyethylene glycol + spastin groups. In suture group rats, only traditional nerve anastomosis of the end-to-end suture was performed after transection of the sciatic nerve. In polyethylene glycol and polyethylene glycol + spastin groups, 50 μL of polyethylene glycol or 25 μL of polyethylene glycol + 25 μL of spastin, respectively, were injected immediately under the epineurium of the distal suture. Sensory fiber regeneration distance, which was used to assess early nerve regeneration at 1 week after surgery, was shortest in the suture group, followed by polyethylene glycol group and greatest in the polyethylene glycol + spastin group. Behavioral assessment of motor function recovery in rats showed that limb function was restored in polyethylene glycol and polyethylene glycol + spastin groups at 8 weeks after surgery. At 1, 2, 4 and 8 weeks after surgery, sciatic functional index values and percentages of gastrocnemius muscle wet weight were highest in the sham group, followed by polyethylene glycol + spastin and polyethylene glycol groups, and lowest in the suture group. Masson staining was utilized to assess the morphology of muscle tissue. Morphological changes in skeletal muscle were detectable in suture, polyethylene glycol, and polyethylene glycol + spastin groups at 1, 2, 4, and 8 weeks after surgery. Among them, muscular atrophy of the suture group was most serious, followed by polyethylene glycol and polyethylene glycol + spastin groups. Ultrastructure of distal sciatic nerve tissue, as detected by transmission electron microscopy, showed a pattern of initial destruction, subsequent disintegration, and gradual repair in suture, polyethylene glycol, and polyethylene glycol + spastin groups at 1, 2, 4, and 8 weeks after surgery. As time proceeded, axonal ultrastructure gradually recovered. Indeed, the polyethylene glycol + spastin group was similar to the sham group at 8 weeks after surgery. Our findings indicate that the combination of polyethylene glycol and spastin can promote peripheral nerve regeneration. Moreover, the effect of this combination was better than that of polyethylene glycol alone, and both were superior to the traditional neurorrhaphy. This study was approved by the Animal Ethics Committee of the Second Military Medical University, China (approval No. CZ20170216) on March 16, 2017.

Local Xenotransplantation of Bone Marrow Derived Mast Cells (BMMCs) Improves Functional Recovery of Transected Sciatic Nerve in Cat: A Novel Approach in Cell Therapy

Objective

To determine the effects of bone marrow derived mast cells (BMMCs) on functional recovery of transected sciatic nerve in animal model of cat.

Method

A 20-mm sciatic nerve defect was bridged using a silicone nerve guide filled with BMMCs in BMMC group. In Sham-surgery group (SHAM), the sciatic nerve was only exposed and manipulated. In control group (SILOCONE) the gap was repaired with a silicone nerve guide and both ends were sealed using sterile Vaseline to avoid leakage and the nerve guide was filled with 100 μL of phosphate-buffered saline alone. In cell treated group ([SILOCONE/BMMC) the nerve guide was filled with 100 μL BMMCs (2× 106 cells/100 μL). The regenerated nerve fibers were studied, biomechanically, histologically and immunohiscochemically 6 months later.

Results

Biomechanical studies confirmed faster recovery of regenerated axons in BMMCs transplanted animals compared to control group (p<0.05). Morphometric indices of the regenerated fibers showed that the number and diameter of the myelinated fibers were significantly higher in BMMCs transplanted animals than in control group (p<0.05). In immunohistochemistry, location of reactions to S-100 in BMMCs transplanted animals was clearly more positive than that in control group.

Conclusion

BMMCs xenotransplantation could be considered as a readily accessible source of cells that could improve recovery of transected sciatic nerve.

Local Administration of Methylprednisolone Laden Hydrogel Enhances Functional Recovery of Transected Sciatic Nerve in Rat

Objective

To determine the effects of methylprednisolone-laden hydrogel loaded into a chitosan conduit on the functional recovery of peripheral nerve using a rat sciatic nerve regeneration model was assessed.

Methods

10-mm sciatic nerve defect was bridged using a chitosan conduit (CHIT/CGP-Hydrogel) filled with CGP-hydrogel. In authograft group (AUTO) a segment of sciatic nerve was transected and reimplanted reversely. In methylprednisolone treated group (CHIT/MP) the conduit was filled with methylprednisolone-laden CGP-hydrogel. The regenerated fibers were studied within 16 weeks after surgery.

Results

The behavioral, functional and electrophysiological studies confirmed faster recovery of the regenerated axons in methylprednisolone treated group compared to CHIT/Hydrogel group (p<0.05). The mean ratios of gastrocnemius muscles weight were measured. There was statistically significant difference between the muscle weight ratios of CHIT/MP and CHIT/Hydrogel groups (p<0.05). Morphometric indices of regenerated fibers showed number and diameter of the myelinated fibers were significantly higher in CHIT/MP than in CHIT/Hydrogel group.

Conclusion

Methylprednisolone-laden hydrogel when loaded in a chitosan conduit resulted in improvement of functional recovery and quantitative morphometric indices of sciatic nerve.

Mast cells improve functional recovery of transected peripheral nerve: A novel preliminary study

BACKGROUND

Employment of regenerative properties of cells at the service of nerve repair has been initiated during recent decades. Effects of local transplantation of bone marrow-derived mast cells on peripheral nerve regeneration were studied using a rat sciatic nerve transection model.

MATERIALS AND METHODS

A 10-mm sciatic nerve defect was bridged using a conduit chitosan-based hybrid conduit filled with BMMCs in BMMC group. In positive control group (Pos), the conduit was filled with phosphate-buffered saline alone. The regenerated nerve fibers were studied within 12 weeks after surgery. In sham-operated group, the sciatic nerve was only exposed and manipulated. In negative control (Neg) a 10-mm sciatic nerve defect was created and the nerve stumps were sutured to the adjacent muscles. The regenerated nerve fibers were studied functionally, biomechanically, histologically and immunohiscochemically.

RESULTS

Functional and biomechanical studies confirmed faster recovery of regenerated axons in BMMCs transplanted animals compared to Pos group (p<0.05). Morphometric indices of the regenerated fibers showed that the number and diameter of the myelinated fibers were significantly higher in BMMCs transplanted animals than in Pos group (p<0.05). In immunohistochemistry, location of reactions to S-100 in BMMCs transplanted animals was clearly more positive than that in Pos group.

CONCLUSIONS

BMMCs transplantation could be considered as a readily accessible source of cells that could improve functional recovery of transected sciatic nerve.